Dean Toste

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Organization: University of California
Department: Department of Chemistry
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Co-reporter:Zachary L. Niemeyer, Suresh Pindi, Dimitri A. Khrakovsky, Christian N. Kuzniewski, Cynthia M. Hong, Leo A. Joyce, Matthew S. Sigman, and F. Dean Toste
Journal of the American Chemical Society September 20, 2017 Volume 139(Issue 37) pp:12943-12943
Publication Date(Web):September 8, 2017
DOI:10.1021/jacs.7b08791
Computed descriptors for acyclic diaminocarbene ligands are developed in the context of a gold catalyzed enantioselective tandem [3,3]-sigmatropic rearrangement-[2+2]-cyclization. Surrogate structures enable the rapid identification of parameters that reveal mechanistic characteristics. The observed selectivity trends are validated in a robust multivariate analysis facilitating the development of a highly enantioselective process.
Co-reporter:Manuel Orlandi, Jaime A. S. Coelho, Margaret J. Hilton, F. Dean Toste, and Matthew S. Sigman
Journal of the American Chemical Society May 24, 2017 Volume 139(Issue 20) pp:6803-6803
Publication Date(Web):May 5, 2017
DOI:10.1021/jacs.7b02311
The use of computed interaction energies and distances as parameters in multivariate correlations is introduced for postulating non-covalent interactions. This new class of descriptors affords multivariate correlations for two diverse catalytic systems with unique non-covalent interactions at the heart of each process. The presented methodology is validated by directly connecting the non-covalent interactions defined through empirical data set analyses to the computationally derived transition states.
Co-reporter:Cynthia M. Hong, David M. Kaphan, Robert G. Bergman, Kenneth N. Raymond, and F. Dean Toste
Journal of the American Chemical Society June 14, 2017 Volume 139(Issue 23) pp:8013-8013
Publication Date(Web):June 5, 2017
DOI:10.1021/jacs.7b03812
This study offers a detailed mechanistic investigation of host–guest encapsulation behavior in a new enzyme–mimetic metal–ligand host and provides the first observation of a conformational selection mechanism (as opposed to induced fit) in a supramolecular system. The Ga4L4 host described features a C3-symmetric ligand motif with meta-substituted phenyl spacers, which enables the host to initially self-assemble into an S4-symmetric structure and then subsequently isomerize to a T-symmetric tetrahedron for better accommodation of a sufficiently large guest. Selective inversion recovery 1H NMR studies provide structural insights into the self-exchange behaviors of the host and the guest individually in this dynamic system. Kinetic analysis of the encapsulation–isomerization event revealed that increasing the concentration of guest inhibits the rate of host–guest relaxation, a key distinguishing feature of conformational selection. A comprehensive study of this simple enzyme mimic provides insight into analogous behavior in biophysics and enzymology and aims to inform the design of efficient self-assembled microenvironment catalysts.
Co-reporter:Jie Zhao;Bing Yuan;Rong Ye;Wen-Chi Liu;Matthew Chang;Franco F. Faucher;Joyce Rodrigues De Araujo;Christophe V. Deraedt;F. Dean Toste;Gabor A. Somorjai
Nano Letters January 11, 2017 Volume 17(Issue 1) pp:584-589
Publication Date(Web):December 14, 2016
DOI:10.1021/acs.nanolett.6b04827
The Hayashi–Ito aldol reaction of methyl isocyanoacetate (MI) and benzaldehydes, a classic homogeneous Au(I)-catalyzed reaction, was studied with heterogenized homogeneous catalysts. Among dendrimer encapsulated nanoparticles (NPs) of Au, Pd, Rh, or Pt loaded in mesoporous supports and the homogeneous analogues, the Au NPs led to the highest yield and highest diastereoselectivity of products in toluene at room temperature. The Au catalyst was stable and was recycled for at least six runs without substantial deactivation. Moreover, larger pore sizes of the support and the use of a hydrophobic solvent led to a high selectivity for the trans diastereomer of the product. The activation energy is sensitive to neither the size of Au NPs nor the support. A linear Hammett plot was obtained with a positive slope, suggesting an increased electron density on the carbonyl carbon atom in the rate-limiting step. IR studies revealed a strong interaction between MI and the gold catalyst, supporting the proposed mechanism, in which rate-limiting step involves an electrophilic attack of the aldehyde on the enolate formed from the deprotonated MI.Keywords: aldol reaction; gold catalyst; Heterogenized homogeneous catalyst; mechanism; selectivity; support effect;
Co-reporter:Patrick T. Bohan and F. Dean Toste
Journal of the American Chemical Society August 16, 2017 Volume 139(Issue 32) pp:11016-11016
Publication Date(Web):August 3, 2017
DOI:10.1021/jacs.7b06025
The development of a gold(III) catalyzed direct enantioconvergent 1,5-enyne cycloisomerization and kinetic resolution reaction is described. The transformation results in highly enantioenriched bicyclo[3.1.0]hexenes at all levels of conversion, with no racemization or symmetrization taking place during the course of the reaction, and simultaneously affords optically enriched 1,5-enynes. This report marks the first highly enantioselective transformation catalyzed by a well-defined cationic gold(III) catalyst and demonstrates the unique potential of gold(III) complexes in enantioselective catalysis.
Co-reporter:Dr. Carolina M. Avila;Dr. Jigar S. Patel;Yernaidu Reddi;Masato Saito;Dr. Hosea M. Nelson;Dr. Hunter P. Shunatona; Dr. Matthew S. Sigman; Dr. Raghavan B. Sunoj; Dr. F. Dean Toste
Angewandte Chemie 2017 Volume 129(Issue 21) pp:5900-5905
Publication Date(Web):2017/05/15
DOI:10.1002/ange.201702107
AbstractA mild, asymmetric Heck–Matsuda reaction of five-, six- and seven-membered ring alkenes and aryl diazonium salts is presented. High yields and enantioselectivities were achieved using Pd0 and chiral anion co-catalysts, the latter functioning as a chiral anion phase-transfer (CAPT) reagent. For certain substrate classes, the chiral anion catalysts were modulated to minimize the formation of undesired by-products. More specifically, BINAM-derived phosphoric acid catalysts were shown to prevent alkene isomerization in cyclopentene and cycloheptene starting materials. DFT(B3LYP-D3) computations revealed that increased product selectivity resulted from a chiral anion dependent lowering of the activation barrier for the desired pathway.
Co-reporter:Dr. Carolina M. Avila;Dr. Jigar S. Patel;Yernaidu Reddi;Masato Saito;Dr. Hosea M. Nelson;Dr. Hunter P. Shunatona; Dr. Matthew S. Sigman; Dr. Raghavan B. Sunoj; Dr. F. Dean Toste
Angewandte Chemie International Edition 2017 Volume 56(Issue 21) pp:5806-5811
Publication Date(Web):2017/05/15
DOI:10.1002/anie.201702107
AbstractA mild, asymmetric Heck–Matsuda reaction of five-, six- and seven-membered ring alkenes and aryl diazonium salts is presented. High yields and enantioselectivities were achieved using Pd0 and chiral anion co-catalysts, the latter functioning as a chiral anion phase-transfer (CAPT) reagent. For certain substrate classes, the chiral anion catalysts were modulated to minimize the formation of undesired by-products. More specifically, BINAM-derived phosphoric acid catalysts were shown to prevent alkene isomerization in cyclopentene and cycloheptene starting materials. DFT(B3LYP-D3) computations revealed that increased product selectivity resulted from a chiral anion dependent lowering of the activation barrier for the desired pathway.
Co-reporter:Xiaoyu Yang;Shixian Lin;Peter S. Lee;Rita V. Nichiporuk;Shang Jia;Amy M. Weeks;Anthony T. Iavarone;James A. Wells;Michael Hornsby;F. Dean Toste;Christopher J. Chang
Science 2017 Volume 355(Issue 6325) pp:597-602
Publication Date(Web):10 Feb 2017
DOI:10.1126/science.aal3316

Targeting proteins at the other sulfur

As the only amino acid with a thiol (SH) group, cysteine is easily targeted for site-selective protein modifications. Hydrophobic methionine also has sulfur in its side chain, but its capping methyl group has hindered analogous targeting efforts. Lin et al. introduce a complementary protocol to tether new substituents exclusively to methionine, even in the presence of cysteine. They used an oxaziridine group as an oxidant to form sulfimide (S=N) linkages. The approach allowed antibody-drug conjugation and chemoproteomic screening for reactive methionine surface residues.

Science, this issue p. 597

Co-reporter:Richard T. Thornbury;Vaneet Saini;Talita de A. Fernandes;Celine B. Santiago;Eric P. A. Talbot;Matthew S. Sigman;Jeffrey M. McKenna;F. Dean Toste
Chemical Science (2010-Present) 2017 vol. 8(Issue 4) pp:2890-2897
Publication Date(Web):2017/03/28
DOI:10.1039/C6SC05102B
A mild palladium-catalyzed ligand-controlled regioselective 1,3-arylfluorination of 2[H]-chromenes has been developed. The products with a syn-1,3 substitution pattern were obtained with high enantiomeric excess using a PyrOx ligand, wherein the utility of these pyranyl-fluorides was further demonstrated through their participation in a diastereoselective C–C bond forming reaction. Ligand dependent divergent formation of both the 1,3- and 1,2- alkene difunctionalization products was observed. The nature of this bifurcation was investigated through experimental studies in combination with computational and statistical analysis tools. Ultimately, the site selectivity was found to rely on ligand denticity and metal electrophilicity, the electronics of the boronic acid, and the donor ability of the directing group in the substrate.
Co-reporter:Mark D. Levin;Tiffany Q. Chen;Megan E. Neubig;Cynthia M. Hong;Cyril A. Theulier;Ilia J. Kobylianskii;Mustafa Janabi;F. Dean Toste;James P. O’Neil
Science 2017 Volume 356(Issue 6344) pp:
Publication Date(Web):
DOI:10.1126/science.aan1411

Trifluoromethylation via broken C-F bonds

Trifluoromethyl substituents are widely used in pharmaceutical research to tune the properties of drug candidates. Generally, they are introduced intact through the formation of carbon-carbon bonds. Levin et al. discovered an unusual alternative mechanism, in which borane abstracts fluoride from the CF3 group in a gold complex. The activated CF2 fragment can then bond to a wide variety of other carbon substituents added to the same gold center. Return of the fluoride liberates a trifluoromethylated compound from the metal. This mechanism could be useful for the introduction of radioactive fluoride substituents for positron emission tomography applications.

Science, this issue p. 1272

Co-reporter:Weiwei Zi and F. Dean Toste  
Chemical Society Reviews 2016 vol. 45(Issue 16) pp:4567-4589
Publication Date(Web):18 Feb 2016
DOI:10.1039/C5CS00929D
Interest in homogeneous gold catalysis has undergone a marked increase. As strong yet air- and moisture-tolerant π-acids, cationic gold(I) complexes have been shown to catalyze diverse transformations of alkenes, alkynes and allenes, opening new opportunities for chemical synthesis. The development of efficient asymmetric variants is required in order to take full advantage of the preparative potential of these transformations. During the last few years, the chemical community has achieved tremendous success in the area. This review highlights the updated progress (2011–2015) in enantioselective gold catalysis. The discussion is classified according to the π-bonds activated by gold(I), in an order of alkynes, allenes and alkenes. Other gold activation modes, such as σ-Lewis acid catalyzed reactions and transformations of diazo compounds are also discussed.
Co-reporter:Zhenyu Yang, Ying He, and F. Dean Toste
Journal of the American Chemical Society 2016 Volume 138(Issue 31) pp:9775-9778
Publication Date(Web):July 29, 2016
DOI:10.1021/jacs.6b05939
Herein is reported the direct asymmetric addition of phenol nucleophiles to benzopyrylium salts as a means to produce enantioenriched flavonoid-like compounds. This enantioselective C–C bond construction was achieved through a chiral anion phase-transfer strategy that mimics the proposed biosynthesis of this structurally diverse set of natural products. The utility of this methodology was demonstrated in enantioselective synthesis of a 2,8-dioxabicyclo[3.3.1]nonane and a 2,4-diarylbenzopyran.
Co-reporter:Mark D. Levin; David M. Kaphan; Cynthia M. Hong; Robert G. Bergman; Kenneth N. Raymond;F. Dean Toste
Journal of the American Chemical Society 2016 Volume 138(Issue 30) pp:9682-9693
Publication Date(Web):July 26, 2016
DOI:10.1021/jacs.6b05442
The scope and mechanism of the microenvironment-catalyzed C(sp3)−C(sp3) reductive elimination from transition metal complexes [Au(III), Pt(IV)] is explored. Experiments detailing the effect of structural perturbation of neutral and anionic spectator ligands, reactive alkyl ligands, solvent, and catalyst structure are disclosed. Indirect evidence for a coordinatively unsaturated encapsulated cationic intermediate is garnered via observation of several inactive donor-arrested inclusion complexes, including a crystallographically characterized encapsulated Au(III) cation. Finally, based on stoichiometric experiments under catalytically relevant conditions, a detailed mechanism is outlined for the dual supramolecular and platinum-catalyzed C–C coupling between methyl iodide and tetramethyltin. Determination of major platinum species present under catalytic conditions and subsequent investigation of their chemistry reveals an unexpected interplay between cis–trans isomerism and the supramolecular catalyst in a Pt(II)/Pt(IV) cycle, as well as several off-cycle reactions.
Co-reporter:Andrew J. Neel; Anat Milo; Matthew S. Sigman;F. Dean Toste
Journal of the American Chemical Society 2016 Volume 138(Issue 11) pp:3863-3875
Publication Date(Web):March 11, 2016
DOI:10.1021/jacs.6b00356
Enantioselectivity values represent relative rate measurements that are sensitive to the structural features of the substrates and catalysts interacting to produce them. Therefore, well-designed enantioselectivity data sets are information rich and can provide key insights regarding specific molecular interactions. However, if the mechanism for enantioselection varies throughout a data set, these values cannot be easily compared. This premise, which is the crux of free energy relationships, exposes a challenging issue of identifying mechanistic breaks within multivariate correlations. Herein, we describe an approach to addressing this problem in the context of a chiral phosphoric acid catalyzed fluorination of allylic alcohols using aryl boronic acids as transient directing groups. By designing a data set in which both the phosphoric and boronic acid structures were systematically varied, key enantioselectivity outliers were identified and analyzed. A mechanistic study was executed to reveal the structural origins of these outliers, which was consistent with the presence of several mechanistic regimes within the data set. While 2- and 4-substituted aryl boronic acids favored the (R)-enantiomer with most of the studied catalysts, meta-alkoxy substituted aryl boronic acids resulted in the (S)-enantiomer when used in combination with certain (R)-phosphoric acids. We propose that this selectivity reversal is the result of a lone pair-π interaction between the substrate ligated boronic acid and the phosphate. On the basis of this proposal, a catalyst system was identified, capable of producing either enantiomer in high enantioselectivity (77% (R)-2 to 92% (S)-2) using the same chiral catalyst by subtly changing the structure of the achiral boronic acid.
Co-reporter:Hiroyuki Kawai; William J. Wolf; Antonio G. DiPasquale; Matthew S. Winston;F. Dean Toste
Journal of the American Chemical Society 2016 Volume 138(Issue 2) pp:587-593
Publication Date(Web):January 8, 2016
DOI:10.1021/jacs.5b10720
A recent trend in homogeneous gold catalysis has been the development of oxidative transformations relying on Au(I)/Au(III) redox cycling. Typically, phosphine-supported Au(I) precatalysts are used in the presence of strong oxidants to presumably generate phosphine Au(III) intermediates. Herein, we disclose that such Au(III) complexes can undergo facile Caryl–P reductive elimination to afford phosphonium salts, which have been spectroscopically and crystallographically characterized. Mechanistic studies indicate that this process occurs from cationic species at temperatures as low as −20 °C but can be accelerated in the presence of nucleophiles, such as acetonitrile and phosphines, via a five-coordinate intermediate. Importantly, this study highlights that irreversible Caryl–P reductive elimination is a feasible decomposition or activation pathway for phosphine-supported Au(III) catalysts and should not be ignored in future reaction development.
Co-reporter:Konstantinos A. Goulas; Sanil Sreekumar; Yuying Song; Purnima Kharidehal; Gorkem Gunbas; Paul J. Dietrich; Gregory R. Johnson; Y. C. Wang; Adam M. Grippo; Lars C. Grabow; Amit A. Gokhale;F. Dean Toste
Journal of the American Chemical Society 2016 Volume 138(Issue 21) pp:6805-6812
Publication Date(Web):May 19, 2016
DOI:10.1021/jacs.6b02247
Condensation reactions such as Guerbet and aldol are important since they allow for C–C bond formation and give higher molecular weight oxygenates. An initial study identified Pd-supported on hydrotalcite as an active catalyst for the transformation, although this catalyst showed extensive undesirable decarbonylation. A catalyst containing Pd and Cu in a 3:1 ratio dramatically decreased decarbonylation, while preserving the high catalytic rates seen with Pd-based catalysts. A combination of XRD, EXAFS, TEM, and CO chemisorption and TPD revealed the formation of CuPd bimetallic nanoparticles with a Cu-enriched surface. Finally, density functional theory studies suggest that the surface segregation of Cu atoms in the bimetallic alloy catalyst produces Cu sites with increased reactivity, while the Pd sites responsible for unselective decarbonylation pathways are selectively poisoned by CO.
Co-reporter:Rong Ye; Bing Yuan; Jie Zhao; Walter T. Ralston; Chung-Yeh Wu; Ebru Unel Barin; F. Dean Toste;Gabor A. Somorjai
Journal of the American Chemical Society 2016 Volume 138(Issue 27) pp:8533-8537
Publication Date(Web):June 20, 2016
DOI:10.1021/jacs.6b03977
Understanding the C–C bond activation mechanism is essential for developing the selective production of hydrocarbons in the petroleum industry and for selective polymer decomposition. In this work, ring-opening reactions of cyclopropane derivatives under hydrogen catalyzed by metal nanoparticles (NPs) in the liquid phase were studied. 40-atom rhodium (Rh) NPs, encapsulated by dendrimer molecules and supported in mesoporous silica, catalyzed the ring opening of cyclopropylbenzene at room temperature under hydrogen in benzene, and the turnover frequency (TOF) was higher than other metals or the Rh homogeneous catalyst counterparts. Comparison of reactants with various substitution groups showed that electron donation on the three-membered ring boosted the TOF of ring opening. The linear products formed with 100% selectivity for ring opening of all reactants catalyzed by the Rh NP. Surface Rh(0) acted as the active site in the NP. The capping agent played an important role in the ring-opening reaction kinetics. Larger particle size tended to show higher TOF and smaller reaction activation energy for Rh NPs encapsulated in either dendrimer or poly(vinylpyrrolidone). The generation/size of dendrimer and surface group also affected the reaction rate and activation energy.
Co-reporter:Kenichi Hiramatsu, Takashi Honjo, Vivek Rauniyar, and F. Dean Toste
ACS Catalysis 2016 Volume 6(Issue 1) pp:151
Publication Date(Web):December 4, 2015
DOI:10.1021/acscatal.5b02182
Stereoselective synthesis of two fluorine-bearing drug-like scaffolds, dihydroquinazolone and benzooxazinone, has been accomplished through asymmetric fluorocyclization reactions initiated by the fluorination process. The reaction employs double axially chiral anionic phase-transfer catalysts to achieve high diastereo- and enantioselectivities, and a wide range of fluorine-containing dihydroquinazolones were obtained (>20:1 dr, up to 98% ee).Keywords: asymmetric synthesis; chiral anion; cyclization; fluorination; phase-transfer catalyst
Co-reporter:Xiaoyu Yang and F. Dean Toste  
Chemical Science 2016 vol. 7(Issue 4) pp:2653-2656
Publication Date(Web):19 Jan 2016
DOI:10.1039/C5SC04202J
We describe the asymmetric addition of unactivated α-branched cyclic ketones to allenamides catalyzed by a chiral phosphoric acid, generating an all-carbon quaternary stereocenter with broad substrate scope and high enantioselectivity. The products are easily transformed into their corresponding 1,5- and 1,4-ketoaldehyde derivatives, which are both important building blocks in organic synthesis.
Co-reporter:Suhong Kim, Jaime Rojas-Martin and F. Dean Toste  
Chemical Science 2016 vol. 7(Issue 1) pp:85-88
Publication Date(Web):10 Nov 2015
DOI:10.1039/C5SC03025K
A dual photoredox and gold-catalysed cross-coupling reaction of alkynyltrimethylsilanes and aryldiazonium tetrafluoroborates is described. The reaction proceeds through visible-light mediated oxidative addition of aryldiazoniums, transmetalation of alkynyltrimethylsilanes and aryl–alkynyl reductive elimination. Exclusive selectivity for silyl-substituted alkynes is observed, with no reactivity observed for terminal alkynes.
Co-reporter:Dimitri A. Khrakovsky;Dr. Chuanzhou Tao;Miles W. Johnson;Richard T. Thornbury;Sophia L. Shevick;Dr. F. Dean Toste
Angewandte Chemie 2016 Volume 128( Issue 20) pp:6183-6187
Publication Date(Web):
DOI:10.1002/ange.201601550

Abstract

The gold-catalyzed enantioselective hydroazidation and hydroamination reactions of allenes are presented herein. ADC gold(I) catalysts derived from BINAM were critical for achieving high levels of enantioselectivity in both transformations. The sense of enantioinduction is reversed for the two different nucleophiles, allowing access to both enantiomers of the corresponding allylic amines using the same catalyst enantiomer.

Co-reporter:Mark D. Levin, Suhong Kim, and F. Dean Toste
ACS Central Science 2016 Volume 2(Issue 5) pp:293
Publication Date(Web):May 3, 2016
DOI:10.1021/acscentsci.6b00090
Since initial reports, cross-coupling technologies employing photoredox catalysts to access novel reactivity have developed with increasing pace. In this Outlook, prominent examples from the recent literature are organized on the basis of the elementary transformation enabled by photoredox catalysis and are discussed in the context of relevant historical precedent in stoichiometric organometallic chemistry. This treatment allows mechanistic similarities inherent to odd-electron transition metal reactivity to be generalized to a set of lessons for future reaction development.
Co-reporter:Dimitri A. Khrakovsky;Dr. Chuanzhou Tao;Miles W. Johnson;Richard T. Thornbury;Sophia L. Shevick;Dr. F. Dean Toste
Angewandte Chemie International Edition 2016 Volume 55( Issue 20) pp:6079-6083
Publication Date(Web):
DOI:10.1002/anie.201601550

Abstract

The gold-catalyzed enantioselective hydroazidation and hydroamination reactions of allenes are presented herein. ADC gold(I) catalysts derived from BINAM were critical for achieving high levels of enantioselectivity in both transformations. The sense of enantioinduction is reversed for the two different nucleophiles, allowing access to both enantiomers of the corresponding allylic amines using the same catalyst enantiomer.

Co-reporter:Johnathan N. Brantley, Andrew V. Samant, and F. Dean Toste
ACS Central Science 2016 Volume 2(Issue 5) pp:341
Publication Date(Web):May 13, 2016
DOI:10.1021/acscentsci.6b00119
The strategic incorporation of the trifluoromethyl (CF3) functionality within therapeutic or agrochemical agents is a proven strategy for altering their associated physicochemical properties (e.g., metabolic stability, lipophilicity, and bioavailability). Electrophilic trifluoromethylation has emerged as an important methodology for installing the CF3 moiety onto an array of molecular architectures, and, in particular, CF3 λ3-iodanes have garnered significant interest because of their unique reactivity and ease of handling. Trifluoromethylations mediated by these hypervalent iodine reagents often require activation through an exogenous Lewis or Brønsted acid; thus, putative intermediates invoked in these transformations are cationic CF3 iodoniums. These iodoniums have, thus far, eluded isolation and investigation of their innate reactivity (which has encouraged speculation that such species cannot be accessed). A more complete understanding of the mechanistic relevance of CF3 iodoniums is paramount for the development of new trifluoromethylative strategies involving λ3-iodanes. Here, we demonstrate that CF3 iodonium salts are readily prepared from common λ3-iodane precursors and exhibit remarkable persistence under ambient conditions. These reagents are competent electrophiles for a variety of trifluoromethylation reactions, and their reactivity is reminiscent of that observed when CF3 iodanes are activated using Lewis acids. As such, our results suggest the mechanistic relevance of CF3 iodonium intermediates in trifluoromethylative processes mediated by λ3-iodanes. The isolation of CF3 iodonium salts also presents the unique opportunity to employ them more generally as mechanistic probes.
Co-reporter:Xiaoyu Yang, Tao Wu, Robert J. Phipps, and F. Dean Toste
Chemical Reviews 2015 Volume 115(Issue 2) pp:826
Publication Date(Web):October 22, 2014
DOI:10.1021/cr500277b
Co-reporter:Casey J. Brown, F. Dean Toste, Robert G. Bergman, and Kenneth N. Raymond
Chemical Reviews 2015 Volume 115(Issue 9) pp:3012
Publication Date(Web):April 21, 2015
DOI:10.1021/cr4001226
Co-reporter:Ying He; Zhenyu Yang; Richard T. Thornbury;F. Dean Toste
Journal of the American Chemical Society 2015 Volume 137(Issue 38) pp:12207-12210
Publication Date(Web):September 17, 2015
DOI:10.1021/jacs.5b07795
The development of an enantioselective palladium-catalyzed 1,1-fluoroarylation of unactivated aminoalkenes is described. The reaction uses arylboronic acids as the arene source and Selectfluor as the fluorine source to generate benzylic fluorides in good yields with excellent enantioselectivities. This transformation, likely proceeding through an oxidative Heck mechanism, affords 1,1-difunctionalized alkene products.
Co-reporter:Weiwei Zi; Hongmiao Wu;F. Dean Toste
Journal of the American Chemical Society 2015 Volume 137(Issue 9) pp:3225-3228
Publication Date(Web):February 24, 2015
DOI:10.1021/jacs.5b00613
A highly enantioselective dearomative Rautenstrauch rearrangement catalyzed by cationic (S)-DTBM-Segphosgold(I) is reported. This reaction provides a straightforward method to prepare enantioenriched cyclopenta[b]indoles. These studies show vast difference in enantioselectivity in the reactions of propargyl acetates and propargyl acetals in the chiral ligand-controlled Rautenstrauch reaction.
Co-reporter:Hosea M. Nelson; Brett D. Williams; Javier Miró;F. Dean Toste
Journal of the American Chemical Society 2015 Volume 137(Issue 9) pp:3213-3216
Publication Date(Web):February 27, 2015
DOI:10.1021/jacs.5b00344
A palladium-catalyzed three-component coupling of α-olefins, aryldiazonium salts, and bis(pinacolato)diboron affords direct access to chiral benzylic boronic esters. This process is rendered highly enantioselective using an unprecedented example of cooperative chiral anion phase transfer and transition-metal catalysis.
Co-reporter:Xiaoyu Yang;F. Dean Toste
Journal of the American Chemical Society 2015 Volume 137(Issue 9) pp:3205-3208
Publication Date(Web):February 26, 2015
DOI:10.1021/jacs.5b00229
Here we report the direct asymmetric amination of α-substituted cyclic ketones catalyzed by a chiral phosphoric acid, yielding products with a N-containing quaternary stereocenter in high yields and excellent enantioselectivities. Kinetic resolution of the starting ketone was also found to occur on some of the substrates under milder conditions, providing enantioenriched α-branched ketones, another important building block in organic synthesis. The utility of this methodology was demonstrated in the short synthesis of (S)-ketamine, the more active enantiomer of this versatile pharmaceutical.
Co-reporter:Xing-Zhong Shu; Son C. Nguyen; Ying He; Fadekemi Oba; Qiao Zhang; Christian Canlas; Gabor A. Somorjai; A. Paul Alivisatos;F. Dean Toste
Journal of the American Chemical Society 2015 Volume 137(Issue 22) pp:7083-7086
Publication Date(Web):May 29, 2015
DOI:10.1021/jacs.5b04294
An efficient method for the synthesis of heterogeneous gold catalysts has been developed. These catalysts were easily assembled from readily available silica materials and gold complexes. The heterogeneous catalysts exhibited superior reactivity in various reactions where protodeauration is the rate-limiting step. Dramatic enhancement in regio- and enantioselectivity was observed when compared to the homogeneous unsupported gold catalyst. The catalysts are easily recovered and recycled up to 11 times without loss of enantioselectivity.
Co-reporter:Matthew S. Winston; William J. Wolf;F. Dean Toste
Journal of the American Chemical Society 2015 Volume 137(Issue 24) pp:7921-7928
Publication Date(Web):June 11, 2015
DOI:10.1021/jacs.5b04613
Two unique organometallic halide series (Ph3P)Au(4-Me-C6H4)(CF3)(X) and (Cy3P)Au(4-F-C6H4)(CF3)(X) (X = I, Br, Cl, F) have been synthesized. The PPh3-supported complexes can undergo both Caryl–X and Caryl–CF3 reductive elimination. Mechanistic studies of thermolysis at 122 °C reveal a dramatic reactivity and kinetic selectivity dependence on halide ligand. For X = I or F, zero-order kinetic behavior is observed, while for X = Cl or Br, kinetic studies implicate product catalysis. The selectivity for Caryl–CF3 bond formation increases in the order X = I < Br < Cl < F, with exclusively Caryl–I bond formation when X = I, and exclusively Caryl–CF3 bond formation when X = F. Thermodynamic measurements show that Au(III)–X bond dissociation energies increase in the order X = I < Br < Cl, and that ground state Au(III)–X bond strength ultimately dictates selectivities for Caryl–X and Caryl–CF3 reductive elimination.
Co-reporter:Dillon H. Miles; Joan Guasch;F. Dean Toste
Journal of the American Chemical Society 2015 Volume 137(Issue 24) pp:7632-7635
Publication Date(Web):June 12, 2015
DOI:10.1021/jacs.5b04518
The enantioselective addition of anilines to azoalkenes was accomplished through the use of a chiral phosphoric acid catalyst. The resulting α-arylamino hydrazones were obtained in good yields and excellent enantioselectivities and provide access to enantioenriched α-arylamino ketones. A serendipitous kinetic resolution of racemic α-arylamino hydrazones is also described.
Co-reporter:David M. Kaphan; F. Dean Toste; Robert G. Bergman;Kenneth N. Raymond
Journal of the American Chemical Society 2015 Volume 137(Issue 29) pp:9202-9205
Publication Date(Web):July 15, 2015
DOI:10.1021/jacs.5b01261
Supramolecular assembly 1 catalyzes a bimolecular aza-Prins cyclization featuring an unexpected transannular 1,5-hydride transfer. This reaction pathway, which is promoted by constrictive binding within the supramolecular cavity of 1, is kinetically disfavored in the absence of 1, as evidenced by the orthogonal reactivity observed in bulk solution. Mechanistic investigation through kinetic analysis and isotopic labeling studies indicates that the rate-limiting step of the transformation is the encapsulation of a transient iminium ion and supports the proposed 1,5-hydride transfer mechanism. This represents a rare example of such an extreme divergence of product selectivity observed within a catalytic metal–ligand supramolecular enzyme mimic.
Co-reporter:Derek M. Dalton; Scott R. Ellis; Eva M. Nichols; Richard A. Mathies; F. Dean Toste; Robert G. Bergman;Kenneth N. Raymond
Journal of the American Chemical Society 2015 Volume 137(Issue 32) pp:10128-10131
Publication Date(Web):August 10, 2015
DOI:10.1021/jacs.5b06317
The K12Ga4L6 supramolecular cage is photoactive and enables an unprecedented photoreaction not observed in bulk solution. Ga4L612– cages photosensitize the 1,3-rearrangement of encapsulated cinnamylammonium cation guests from the linear isomer to the higher energy branched isomer when irradiated with UVA light. The rearrangement requires light and guest encapsulation to occur. The Ga4L612– cage-mediated reaction mechanism was investigated by UV/vis absorption, fluorescence, ultrafast transient absorption, and electrochemical experiments. The results support a photoinduced electron transfer mechanism for the 1,3-rearrangement, in which the Ga4L612– cage absorbs photons and transfers an electron to the encapsulated cinnamylammonium ion, which undergoes C–N bond cleavage, followed by back electron transfer to the cage and recombination of the guest fragments to form the higher energy isomer.
Co-reporter:Ying He, Hongmiao Wu and F. Dean Toste  
Chemical Science 2015 vol. 6(Issue 2) pp:1194-1198
Publication Date(Web):25 Nov 2014
DOI:10.1039/C4SC03092C
A new method for the P-arylation of aryldiazonium salts with H-phosphonates via dual gold and photoredox catalysis is described. The reaction proceeds smoothly at room temperature in the absence of base and/or additives, and offers an efficient approach to arylphosphonates. The reaction is proposed to proceed through a photoredox-promoted generation of an electrophilic arylgold(III) intermediate that undergoes coupling with the H-phosphonate nucleophile.
Co-reporter:William M. Hart-Cooper, Chen Zhao, Rebecca M. Triano, Parastou Yaghoubi, Haxel Lionel Ozores, Kristen N. Burford, F. Dean Toste, Robert G. Bergman and Kenneth N. Raymond  
Chemical Science 2015 vol. 6(Issue 2) pp:1383-1393
Publication Date(Web):28 Nov 2014
DOI:10.1039/C4SC02735C
The effect of host structure on the selectivity and mechanism of intramolecular Prins reactions is evaluated using K12Ga4L6 tetrahedral catalysts. The host structure was varied by modifying the structure of the chelating moieties and the size of the aromatic spacers. While variation in chelator substituents was generally observed to affect changes in rate but not selectivity, changing the host spacer afforded differences in efficiency and product diastereoselectivity. An extremely high number of turnovers (up to 840) was observed. Maximum rate accelerations were measured to be on the order of 105, which numbers among the largest magnitudes of transition state stabilization measured with a synthetic host-catalyst. Host/guest size effects were observed to play an important role in host-mediated enantioselectivity.
Co-reporter:H. M. Nelson, J. S. Patel, H. P. Shunatona and F. D. Toste  
Chemical Science 2015 vol. 6(Issue 1) pp:170-173
Publication Date(Web):02 Oct 2014
DOI:10.1039/C4SC02494J
Chiral anion phase-transfer of aryldiazonium cations was utilized to achieve highly enantioselective α-amination of carbonyl compounds. A broad scope of indanone- and benzosuberone-derived substrates was amenable to this strategy. Critical to obtaining high levels of enantioselectivity was the use of BINAM-derived phosphoric acids. The utility of this transformation was demonstrated through facile conversion of diazene products to valuable α-amino acid derivatives.
Co-reporter:Robert M. Rioux and F. Dean Toste  
Catalysis Science & Technology 2015 vol. 5(Issue 3) pp:1357-1359
Publication Date(Web):22 Jan 2015
DOI:10.1039/C5CY90005K
A graphical abstract is available for this content
Co-reporter:Cristina Navarro, Nathan D. Shapiro, Maurizio Bernasconi, Takahiro Horibe, F. Dean Toste
Tetrahedron 2015 Volume 71(Issue 35) pp:5800-5805
Publication Date(Web):2 September 2015
DOI:10.1016/j.tet.2015.04.109
An asymmetric gold(I)-catalyzed [3+2] cycloaddition of propargyl acetals/ketals and aldehydes is reported, which proceeds via stepwise migration-fragmentation of acetals/ketals and cycloaddition of the in situ generated gold-carbenoid intermediate. Various functionalized 2,5-dihydrofurans were obtained in good yields and high enantioselectivities. Furthermore, an example of the first gold(I) catalyzed [3+3] cycloaddition of secondary propargyl ketals and nitrones is presented.
Co-reporter:David M. Kaphan;Mark D. Levin;Robert G. Bergman;Kenneth N. Raymond;F. Dean Toste
Science 2015 Vol 350(6265) pp:1235-1238
Publication Date(Web):04 Dec 2015
DOI:10.1126/science.aad3087

Faster elimination inside a cavity

Metals are adept at shuffling molecular bonds. They pry apart two atoms and then pair each one with a different partner. Sometimes the atoms get stuck on the metal, though, and the newly partnered products aren't released. Kaphan et al. designed a strategy for accelerating this elimination process (see the Perspective by Yan and Fujita). A hollow supramolecular capsule captured a gold or platinum complex and induced rapid bond formation between the carbon atoms in methyl groups bound to the metal. Generalization of this strategy could open the door to a wide range of chemical transformations that are currently held up by slow eliminations.

Science, this issue p. 1235; see also p. 1165

Co-reporter:Anat Milo;Andrew J. Neel;F. Dean Toste;Matthew S. Sigman
Science 2015 Vol 347(6223) pp:737-743
Publication Date(Web):13 Feb 2015
DOI:10.1126/science.1261043

Optimizing a catalyst many ways at once

Optimization strategies are often likened to hikes in a hilly landscape. If your goal is to get to the top of the highest hill, and you only take steps toward higher ground, you might never find a peak on a route that requires a preliminary descent. So it is in chemistry, where optimizing each structural feature of a catalyst consecutively might gloss over subtle tradeoffs that in combination offer the best performance. Milo et al. use multidimensional analysis techniques to generate a predictive model of how selectivity depends on multiple characteristics of the catalyst and substrate in a C-N bond-forming reaction (see the Perspective by Lu). They then apply this model to improve the catalyst globally.

Science, this issue p. 737; see also p. 719

Co-reporter:Dr. Weiwei Zi ;Dr. F. Dean Toste
Angewandte Chemie International Edition 2015 Volume 54( Issue 48) pp:14447-14451
Publication Date(Web):
DOI:10.1002/anie.201508331

Abstract

A gold(I)-catalyzed enantioselective desymmetrization of 1,3-diols was achieved by intramolecular hydroalkoxylation of allenes. The catalyst system 3-F-dppe(AuCl)2 /(R)-C8-TRIPAg proved to be specifically efficient to promote the desymmetrizing cyclization of 2-aryl-1,3-diols, which have proven challenging substrates in previous reports. Multisubstituted tetrahydrofurans were prepared in good yield with good enantioselectivity and diastereoselectivity by this method.

Co-reporter:Dr. Weiwei Zi ;Dr. F. Dean Toste
Angewandte Chemie 2015 Volume 127( Issue 48) pp:14655-14659
Publication Date(Web):
DOI:10.1002/ange.201508331

Abstract

A gold(I)-catalyzed enantioselective desymmetrization of 1,3-diols was achieved by intramolecular hydroalkoxylation of allenes. The catalyst system 3-F-dppe(AuCl)2 /(R)-C8-TRIPAg proved to be specifically efficient to promote the desymmetrizing cyclization of 2-aryl-1,3-diols, which have proven challenging substrates in previous reports. Multisubstituted tetrahydrofurans were prepared in good yield with good enantioselectivity and diastereoselectivity by this method.

Co-reporter:William M. Hart-Cooper;Charles L. Perrin;Carmelo Sgarlata;F. Dean Toste;Kenneth N. Raymond;Robert G. Bergman
PNAS 2015 Volume 112 (Issue 50 ) pp:15303-15307
Publication Date(Web):2015-12-15
DOI:10.1073/pnas.1515639112
The mechanism of proton exchange in a metal–ligand enzyme active site mimic (compound 1) is described through amide hydrogen–deuterium exchange kinetics. The type and ratio of cationic guest to host in solution affect the rate of isotope exchange, suggesting that the rate of exchange is driven by a host whose cavity is occupied by water. Rate constants for acid-, base-, and water-mediated proton exchange vary by orders of magnitude depending on the guest, and differ by up to 200 million-fold relative to an alanine polypeptide. These results suggest that the unusual microenvironment of the cavity of 1 can dramatically alter the reactivity of associated water by magnitudes comparable to that of enzymes.
Co-reporter:Madhesan Balakrishnan;Eric R. Sacia;Sanil Sreekumar;Amit A. Gokhale;Gorkem Gunbas;F. Dean Toste;Alexis T. Bell;Corinne D. Scown
PNAS 2015 Volume 112 (Issue 25 ) pp:7645-7649
Publication Date(Web):2015-06-23
DOI:10.1073/pnas.1508274112
Decarbonizing the transportation sector is critical to achieving global climate change mitigation. Although biofuels will play an important role in conventional gasoline and diesel applications, bioderived solutions are particularly important in jet fuels and lubricants, for which no other viable renewable alternatives exist. Producing compounds for jet fuel and lubricant base oil applications often requires upgrading fermentation products, such as alcohols and ketones, to reach the appropriate molecular-weight range. Ketones possess both electrophilic and nucleophilic functionality, which allows them to be used as building blocks similar to alkenes and aromatics in a petroleum refining complex. Here, we develop a method for selectively upgrading biomass-derived alkyl methyl ketones with >95% yields into trimer condensates, which can then be hydrodeoxygenated in near-quantitative yields to give a new class of cycloalkane compounds. The basic chemistry developed here can be tailored for aviation fuels as well as lubricants by changing the production strategy. We also demonstrate that a sugarcane biorefinery could use natural synergies between various routes to produce a mixture of lubricant base oils and jet fuels that achieve net life-cycle greenhouse gas savings of up to 80%.
Co-reporter:Chen Zhao, Mark R. Crimmin, F. Dean Toste, and Robert G. Bergman
Accounts of Chemical Research 2014 Volume 47(Issue 2) pp:517
Publication Date(Web):December 23, 2013
DOI:10.1021/ar400176x
Over the past few decades, researchers have made substantial progress in the development of transition metal complexes that activate and functionalize C–H bonds. For the most part, chemists have focused on aliphatic and aromatic C–H bonds and have put less effort into complexes that activate and functionalize vinylic C–H bonds. Our groups have recently developed a novel method to functionalize vinylic C–H bonds that takes advantage of the unique ligand-based reactivity of a rare class of metal dinitrosyl complexes. In this Account, we compare and discuss the chemistry of cobalt and ruthenium dinitrosyl complexes, emphasizing alkene binding, C–H functionalization, and catalysis.Initially discovered in the early 1970s by Brunner and studied more extensively in the 1980s by the Bergman group, the cyclopentadienylcobalt dinitrosyl complex CpCo(NO)2 reacts reversibly with alkenes to give, in many cases, stable and isolable cobalt dinitrosoalkane complexes. More recently, we found that treatment with strong bases, such as lithium hexamethyldisilazide, Verkade’s base, and phosphazene bases, deprotonates these complexes and renders them nucleophilic at the carbon α to the nitroso group. This conjugate anion of metal dinitrosoalkanes can participate in conjugate addition to Michael acceptors to form new carbon–carbon bonds. These functionalized cobalt complexes can further react through alkene exchange to furnish the overall vinylic C–H functionalized organic product. This stepwise sequence of alkene binding, functionalization, and retrocycloaddition represents an overall vinylic C–H functionalization reaction of simple alkenes and does not require directing groups. We have also developed an asymmetric variant of this reaction sequence and have used this method to synthesize C1- and C2-symmetric diene ligands with high enantioinduction. Building upon these stepwise reactions, we eventually developed a simple one-pot procedure that uses stoichiometric amounts of a cobalt dinitrosoalkane complex for both inter- and intramolecular C–H functionalization. We can achieve catalysis in one-pot intramolecular reactions with a limited range of substrates.Our groups have also reported an analogous ruthenium dinitrosyl complex. In analogy to the cobalt complex, this ruthenium complex reacts with alkenes in the presence of neutral bidentate ligands, such as TMEDA, to give octahedral dinitrosoalkane complexes. Intramolecular functionalization or cyclization of numerous ruthenium dinitrosoalkane complexes proceeds under mild reaction conditions to give the functionalized organic products in excellent yields. However, despite extensive efforts, so far we have not been able to carry out intermolecular reactions of these complexes with a variety of electrophiles or C–H functionalization reactions.Although additional work is necessary to further boost the catalytic capabilities of both cobalt and ruthenium dinitrosyl complexes for vinylic C–H functionalization of simple alkenes, we believe this ligand-based vinylic C–H functionalization reaction has provided chemists with a useful set of tools for organic synthesis.
Co-reporter:Yi-Ming Wang, Aaron D. Lackner, and F. Dean Toste
Accounts of Chemical Research 2014 Volume 47(Issue 3) pp:889
Publication Date(Web):November 14, 2013
DOI:10.1021/ar400188g
During the past decade, the use of Au(I) complexes for the catalytic activation of C–C π-bonds has been investigated intensely. Over this time period, the development of homogeneous gold catalysis has been extraordinarily rapid and has yielded a host of mild and selective methods for the formation of carbon–carbon and carbon–heteroatom bonds. The facile formation of new bonds facilitated by gold naturally led to efforts toward rendering these transformations enantioselective.In this Account, we survey the development of catalysts and ligands for enantioselective gold catalysis by our research group as well as related work by others. We also discuss some of our strategies to address the challenges of enantioselective gold(I) catalysis. Early on, our work with enantioselective gold-catalyzed transformations focused on bis(phosphinegold) complexes derived from axially chiral scaffolds. Although these complexes were highly successful in some reactions like cyclopropanation, the careful choice of the weakly coordinating ligand (or counterion) was necessary to obtain high levels of enantioselectivity for the case of allene hydroamination. These counterion effects led us to use the anion itself as a source of chirality, which was successful in the case of allene hydroalkoxylation. In general, these tactics enhance the steric influence around the reactive gold center beyond the two-coordinate ligand environment. The use of binuclear complexes allowed us to use the second gold center and its associated ligand (or counterion) to exert a further steric influence. In a similar vein, we employed a chiral anion (in place of or in addition to a chiral ligand) to move the chiral information closer to the reactive center.In order to expand the scope of reactions amenable to enantioselective gold catalysis to cycloadditions and other carbocyclization processes, we also developed a new class of mononuclear phosphite and phosphoramidite ligands to supplement the previously widely utilized phosphines. However, we needed to judiciously design the steric environment to create “walls” that enclose the gold center. We also successfully applied these same considerations to the development of binuclear carbene ligands for gold. Finally, we describe the design of bifunctional urea–monophosphine ligands used in a gold-catalyzed three-component coupling.
Co-reporter:Qiao Zhang, Xing-Zhong Shu, J. Matthew Lucas, F. Dean Toste, Gabor A. Somorjai, and A. Paul Alivisatos
Nano Letters 2014 Volume 14(Issue 1) pp:379-383
Publication Date(Web):December 8, 2013
DOI:10.1021/nl4045372
An “inorganic micelle” structure that has a hydrophilic cavity and hydrophobic surface has been synthesized. The inorganic micelles possess large surface area and controllable hydrophobic/hydrophilic interface. It shows high catalytic efficiency and great recyclability in the bromination of alcohols. This work suggests that inorganic micelles may be suitable for selective organic syntheses as well as industrial applications and demonstrates the value of translating nanostructure design from organic to inorganic.
Co-reporter:Elad Gross ; Xing-Zhong Shu ; Selim Alayoglu ; Hans A. Bechtel ; Michael C. Martin ; F. Dean Toste ;Gabor A. Somorjai
Journal of the American Chemical Society 2014 Volume 136(Issue 9) pp:3624-3629
Publication Date(Web):February 5, 2014
DOI:10.1021/ja412740p
Analysis of catalytic organic transformations in flow reactors and detection of short-lived intermediates are essential for optimization of these complex reactions. In this study, spectral mapping of a multistep catalytic reaction in a flow microreactor was performed with a spatial resolution of 15 μm, employing micrometer-sized synchrotron-based IR and X-ray beams. Two nanometer sized Au nanoclusters were supported on mesoporous SiO2, packed in a flow microreactor, and activated toward the cascade reaction of pyran formation. High catalytic conversion and tunable products selectivity were achieved under continuous flow conditions. In situ synchrotron-sourced IR microspectroscopy detected the evolution of the reactant, vinyl ether, into the primary product, allenic aldehyde, which then catalytically transformed into acetal, the secondary product. By tuning the residence time of the reactants in a flow microreactor a detailed analysis of the reaction kinetics was performed. An in situ micrometer X-ray absorption spectroscopy scan along the flow reactor correlated locally enhanced catalytic conversion, as detected by IR microspectroscopy, to areas with high concentration of Au(III), the catalytically active species. These results demonstrate the fundamental understanding of the mechanism of catalytic reactions which can be achieved by the detailed mapping of organic transformations in flow reactors .
Co-reporter:Eric P. A. Talbot ; Talita de A. Fernandes ; Jeffrey M. McKenna ;F. Dean Toste
Journal of the American Chemical Society 2014 Volume 136(Issue 11) pp:4101-4104
Publication Date(Web):March 11, 2014
DOI:10.1021/ja412881j
A mild catalytic asymmetric direct fluoro-arylation of styrenes has been developed. The palladium-catalyzed three-component coupling of Selectfluor, a styrene and a boronic acid, provides chiral monofluorinated compounds in good yield and in high enantiomeric excess. A mechanism proceeding through a Pd(IV)-fluoride intermediate is proposed for the transformation and synthesis of an sp3 C–F bond.
Co-reporter:Xiaoyu Yang ; Robert J. Phipps ;F. Dean Toste
Journal of the American Chemical Society 2014 Volume 136(Issue 14) pp:5225-5228
Publication Date(Web):March 31, 2014
DOI:10.1021/ja500882x
We report a study involving the successful merger of two separate chiral catalytic cycles: a chiral anion phase-transfer catalysis cycle to activate Selectfluor and an enamine activation cycle, using a protected amino acid as organocatalyst. We have demonstrated the viability of this approach with the direct asymmetric fluorination of α-substituted cyclohexanones to generate quaternary fluorine-containing stereocenters. With these two chiral catalytic cycles operating together in a matched sense, high enantioselectivites can be achieved, and we envisage that this dual catalysis method has the potential to be more broadly applicable, given the breadth of enamine catalysis. It also represents a rare example of chiral enamine catalysis operating successfully on α-branched ketones, substrates commonly inert to this activation mode.
Co-reporter:Xing-zhong Shu ; Miao Zhang ; Ying He ; Heinz Frei ;F. Dean Toste
Journal of the American Chemical Society 2014 Volume 136(Issue 16) pp:5844-5847
Publication Date(Web):April 14, 2014
DOI:10.1021/ja500716j
A combination of visible light photocatalysis and gold catalysis is applied to a ring expansion–oxidative arylation reaction. The reaction provides an entry into functionalized cyclic ketones from the coupling reaction of alkenyl and allenyl cycloalkanols with aryl diazonium salts. A mechanism involving generation of an electrophilic gold(III)–aryl intermediate is proposed on the basis of mechanistic studies, including time-resolved FT-IR spectroscopy.
Co-reporter:Matthew S. Winston ; William J. Wolf ;F. Dean Toste
Journal of the American Chemical Society 2014 Volume 136(Issue 21) pp:7777-7782
Publication Date(Web):May 16, 2014
DOI:10.1021/ja503974x
Herein we report the mechanism of oxidative addition of CF3I to Au(I), and remarkably fast Caryl–CF3 bond reductive elimination from Au(III) cations. CF3I undergoes a fast, formal oxidative addition to R3PAuR′ (R = Cy, R′ = 3,5-F2-C6H4, 4-F-C6H4, C6H5, 4-Me-C6H4, 4-MeO-C6H4, Me; R = Ph, R′ = 4-F-C6H4, 4-Me-C6H4). When R′ = aryl, complexes of the type R3PAu(aryl)(CF3)I can be isolated and characterized. Mechanistic studies suggest that near-ultraviolet light (λmax = 313 nm) photoinitiates a radical chain reaction by exciting CF3I. Complexes supported by PPh3 undergo reversible phosphine dissociation at 110 °C to generate a three-coordinate intermediate that undergoes slow reductive elimination. These processes are quantitative and heavily favor Caryl–I reductive elimination over Caryl–CF3 reductive elimination. Silver-mediated halide abstraction from all complexes of the type R3PAu(aryl)(CF3)I results in quantitative formation of Ar–CF3 in less than 1 min at temperatures as low as −10 °C.
Co-reporter:Chen Zhao ; F. Dean Toste ; Kenneth N. Raymond ;Robert G. Bergman
Journal of the American Chemical Society 2014 Volume 136(Issue 41) pp:14409-14412
Publication Date(Web):September 29, 2014
DOI:10.1021/ja508799p
While the reactive pocket of many enzymes has been shown to modify reactions of substrates by changing their chemical properties, examples of reactions whose stereochemical course is completely reversed are exceedingly rare. We report herein a class of water-soluble host assemblies that is capable of catalyzing the substitution reaction at a secondary benzylic carbon center to give products with overall stereochemical retention, while reaction of the same substrates in bulk solution gives products with stereochemical inversion. Such ability of a biomimetic synthetic host assembly to reverse the stereochemical outcome of a nucleophilic substitution reaction is unprecedented in the field of supramolecular host–guest catalysis.
Co-reporter:Weiwei Zi, Yi-Ming Wang, and F. Dean Toste
Journal of the American Chemical Society 2014 Volume 136(Issue 37) pp:12864-12867
Publication Date(Web):September 9, 2014
DOI:10.1021/ja507468u
An enantioselective fluorination of allylic alcohols under chiral anion phase-transfer conditions is reported. The in situ generation of a directing group proved crucial for achieving effective enantiocontrol. In the presence of such a directing group, a range of acyclic substrates underwent fluorination to afford highly enantioenriched α-fluoro homoallylic alcohols. Mechanistic studies suggest that this transformation proceeds through a concerted enantiodetermining transition state involving both C–F bond formation and C–H bond cleavage.
Co-reporter:Mark D. Levin ;Dr. F. Dean Toste
Angewandte Chemie 2014 Volume 126( Issue 24) pp:6325-6329
Publication Date(Web):
DOI:10.1002/ange.201402924

Abstract

A sp3–sp2 CC cross-coupling reaction catalyzed by gold in the absence of a sacrificial oxidant is described. Vital to the success of this method is the implementation of a bimetallic catalyst bearing a bis(phosphino)amine ligand. A mechanistic hypothesis is presented, and observable transmetalation, CBr oxidative addition, and CC reductive elimination in a model gold complex are shown. We expect that this method will serve as a platform for the development of novel transformations involving redox-active gold catalysts.

Co-reporter:Dr. Hosea M. Nelson;Solomon H. Reisberg;Hunter P. Shunatona;Jigar S. Patel ;Dr. F. Dean Toste
Angewandte Chemie 2014 Volume 126( Issue 22) pp:5706-5709
Publication Date(Web):
DOI:10.1002/ange.201310905

Abstract

Herein is reported the first asymmetric utilization of aryldiazonium cations as a source of electrophilic nitrogen. This is achieved through a chiral anion phase-transfer pyrroloindolinization reaction that forms C3-diazenated pyrroloindolines from simple tryptamines and aryldiazonium tetrafluoroborates. The title compounds are obtained in up to 99 % yield and 96 % ee. The air- and water-tolerant reaction allows electronic and steric diversity of the aryldiazonium electrophile and the tryptamine core.

Co-reporter:Miles W. Johnson, Antonio G. DiPasquale, Robert G. Bergman, and F. Dean Toste
Organometallics 2014 Volume 33(Issue 16) pp:4169-4172
Publication Date(Web):August 12, 2014
DOI:10.1021/om500663m
A series of gold(III) complexes supported by pyridine-based bis(amidate), bis(carboxylate), and bis(iminothiolate) substituents is reported. These compounds represent rare examples of pincer-ligated gold(III) centers with multiple anionic heteroaom donors. Reactivity and electrochemical studies demonstrate the stability of these compounds and the marked difference in reduction potentials with varying ligand scaffolds.
Co-reporter:Dr. Sanil Sreekumar;Zachary C. Baer;Dr. Elad Gross;Dr. Sasisanker Padmanaban;Konstantinos Goulas;Gorkem Gunbas;Dr. Selim Alayoglu; Harvey W. Blanch; Douglas S. Clark; F. Dean Toste
ChemSusChem 2014 Volume 7( Issue 9) pp:2445-2448
Publication Date(Web):
DOI:10.1002/cssc.201402244

Abstract

Biological and chemocatalytic processes are tailored in order to maximize the production of sustainable biodiesel from lignocellulosic sugar. Thus, the combination of hydrotalcite-supported copper(II) and palladium(0) catalysts with a modification of the fermentation from acetone–butanol–ethanol to isopropanol–butanol–ethanol predictably produces higher concentrations of diesel-range components in the alkylation reaction.

Co-reporter:Mark D. Levin ;Dr. F. Dean Toste
Angewandte Chemie International Edition 2014 Volume 53( Issue 24) pp:6211-6215
Publication Date(Web):
DOI:10.1002/anie.201402924

Abstract

A sp3–sp2 CC cross-coupling reaction catalyzed by gold in the absence of a sacrificial oxidant is described. Vital to the success of this method is the implementation of a bimetallic catalyst bearing a bis(phosphino)amine ligand. A mechanistic hypothesis is presented, and observable transmetalation, CBr oxidative addition, and CC reductive elimination in a model gold complex are shown. We expect that this method will serve as a platform for the development of novel transformations involving redox-active gold catalysts.

Co-reporter:Miles W. Johnson;Scott W. Bagley; Neal P. Mankad; Robert G. Bergman;Dr. Vincent Mascitti; F. Dean Toste
Angewandte Chemie International Edition 2014 Volume 53( Issue 17) pp:4404-4407
Publication Date(Web):
DOI:10.1002/anie.201400037

Abstract

The development of a gold(I)-catalyzed sulfination of aryl boronic acids is described. This transformation proceeds through an unprecedented mechanism which exploits the reactivity of gold(I)–heteroatom bonds to form sulfinate anions. Further in situ elaboration of the sulfinate intermediates leads to the corresponding sulfones and sulfonamides, two pharmacophores routinely encountered in drug discovery.

Co-reporter:Dr. Hosea M. Nelson;Solomon H. Reisberg;Hunter P. Shunatona;Jigar S. Patel ;Dr. F. Dean Toste
Angewandte Chemie International Edition 2014 Volume 53( Issue 22) pp:5600-5603
Publication Date(Web):
DOI:10.1002/anie.201310905

Abstract

Herein is reported the first asymmetric utilization of aryldiazonium cations as a source of electrophilic nitrogen. This is achieved through a chiral anion phase-transfer pyrroloindolinization reaction that forms C3-diazenated pyrroloindolines from simple tryptamines and aryldiazonium tetrafluoroborates. The title compounds are obtained in up to 99 % yield and 96 % ee. The air- and water-tolerant reaction allows electronic and steric diversity of the aryldiazonium electrophile and the tryptamine core.

Co-reporter:Robert J. Phipps ;F. Dean Toste
Journal of the American Chemical Society 2013 Volume 135(Issue 4) pp:1268-1271
Publication Date(Web):January 18, 2013
DOI:10.1021/ja311798q
Chiral anion phase-transfer catalysis has enabled the direct and highly enantioselective fluorinative dearomatization of phenols catalyzed by a BINOL-derived phosphate. The process efficiently transforms simple, readily available phenols into fluorinated chiral small molecules bearing reactive functionality under ambient reaction conditions with high enantioselectivity. The close relationship of the products with well-studied o-quinols provides numerous avenues for synthetic elaboration and exciting opportunities for bioisosteric replacement of hydroxyl with fluorine in natural products.
Co-reporter:Elad Gross ; Jack H. Liu ; Selim Alayoglu ; Matthew A. Marcus ; Sirine C. Fakra ; F. Dean Toste ;Gabor A. Somorjai
Journal of the American Chemical Society 2013 Volume 135(Issue 10) pp:3881-3886
Publication Date(Web):February 13, 2013
DOI:10.1021/ja310640b
Research to develop highly versatile, chiral, heterogeneous catalysts for asymmetric organic transformations, without quenching the catalytic reactivity, has met with limited success. While chiral supramolecular structures, connected by weak bonds, are highly active for homogeneous asymmetric catalysis, their application in heterogeneous catalysis is rare. In this work, asymmetric catalyst was prepared by encapsulating metallic nanoclusters in chiral self-assembled monolayer (SAM), immobilized on mesoporous SiO2 support. Using olefin cyclopropanation as an example, it was demonstrated that by controlling the SAM properties, asymmetric reactions can be catalyzed by Au clusters embedded in chiral SAM. Up to 50% enantioselectivity with high diastereoselectivity were obtained while employing Au nanoclusters coated with SAM peptides as heterogeneous catalyst for the formation of cyclopropane-containing products. Spectroscopic measurements correlated the improved enantioselectivity with the formation of a hydrogen-bonding network in the chiral SAM. These results demonstrate the synergetic effect of the catalytically active metallic sites and the surrounding chiral SAM for the formation of a mesoscale enantioselective catalyst.
Co-reporter:Weiwei Zi ;F. Dean Toste
Journal of the American Chemical Society 2013 Volume 135(Issue 34) pp:12600-12603
Publication Date(Web):August 19, 2013
DOI:10.1021/ja407150h
A highly enantioselective carboalkoxylation of alkynes catalyzed by cationic (DTBM-MeO-Biphep)gold(I) complexes is reported. Various optically active β-alkoxyindanone derivatives were obtained in good yields with high enantioselectivities. Furthermore, this methodology was extended to the enantioselective synthesis of 3-methoxycyclopentenones. The reaction is proposed to proceed through an enantioselective cyclization of intermediates containing vinylgold(I) and prochiral oxocarbenium moieties.
Co-reporter:Aaron D. Lackner ; Andrew V. Samant ;F. Dean Toste
Journal of the American Chemical Society 2013 Volume 135(Issue 38) pp:14090-14093
Publication Date(Web):September 11, 2013
DOI:10.1021/ja4082827
The single-operation deracemization of 3H indolines and tetrahydroquinolines is described. An asymmetric redox approach was employed, in which a phosphoric acid catalyst, oxidant, and reductant are present in the reaction mixture. The simultaneous presence of both oxidant and reductant was enabled by phase separation and resulted in the isolation of highly enantioenriched starting materials in high yields.
Co-reporter:Andrew J. Neel ; Jörg P. Hehn ; Pascal F. Tripet ;F. Dean Toste
Journal of the American Chemical Society 2013 Volume 135(Issue 38) pp:14044-14047
Publication Date(Web):September 11, 2013
DOI:10.1021/ja407410b
This report describes the development of an enantioselective C–N bond-forming reaction to produce 1,2,3,4-tetrahydroisoquinoline-derived cyclic aminals catalyzed by chiral phosphate anions. Central to the success of this goal was the design of a library of 3,3′-triazolyl BINOL-derived phosphoric acids capable of forming attractive hydrogen-bonding interactions with the peptide-like substrate. We envision this work will offer an alternative to the conventional strategy of increasing catalyst steric bulk to improve enantioselectivity with BINOL-derived phosphoric acids.
Co-reporter:Chen Zhao ; Qing-Fu Sun ; William M. Hart-Cooper ; Antonio G. DiPasquale ; F. Dean Toste ; Robert G. Bergman ;Kenneth N. Raymond
Journal of the American Chemical Society 2013 Volume 135(Issue 50) pp:18802-18805
Publication Date(Web):November 27, 2013
DOI:10.1021/ja411631v
The synthesis of a novel supramolecular tetrahedral assembly of K12Ga4L6 stoichiometry is reported. The newly designed chiral ligand exhibits high diastereoselective control during cluster formation, leading exclusively to a single diastereomer of the desired host. This new assembly also exhibits high stability toward oxidation or a low pH environment and is a more robust and efficient catalyst for asymmetric organic transformations of neutral substrates.
Co-reporter:Julian M. W. Chan, Stefan Bauer, Hagit Sorek, Sanil Sreekumar, Kun Wang, and F. Dean Toste
ACS Catalysis 2013 Volume 3(Issue 6) pp:1369
Publication Date(Web):May 21, 2013
DOI:10.1021/cs400333q
Lignin samples isolated from Miscanthus giganteus using organosolv processes were treated with vanadium catalysts that were previously developed in our group. We demonstrate that the catalyst with high β-O-4′ bond-cleaving activity in dimeric lignin models was also effective in depolymerizing actual lignin. Molecular weight-lowering was evidenced by gel permeation chromatography (GPC), whereas 2D NMR experiments showed that β-O-4′ linkages were selectively cleaved in the degradation process, just as in the case of lignin models. Monophenolic degradation products were also formed, and the individual molecules were identified and quantified by GC/MS.Keywords: biofuels; depolymerization; lignin; lignocellulose; vanadium
Co-reporter:Dillon H. Miles, Marcos Veguillas and F. Dean Toste  
Chemical Science 2013 vol. 4(Issue 9) pp:3427-3431
Publication Date(Web):05 Jul 2013
DOI:10.1039/C3SC50811K
The enantioselective bromocyclization of allenes is accomplished through the use of a chiral dinuclear gold complex and/or chiral phosphate anions in the presence of an N-bromolactam as an electrophilic bromine source. This method provides access to heterocyclic vinyl bromides with an allylic stereocenter in excellent yield and enantioselectivity. These enantioenriched vinyl bromides may serve as a handle for further derivatization via cross-coupling reactions.
Co-reporter:Miles W. Johnson, Sophia L. Shevick, F. Dean Toste and Robert G. Bergman  
Chemical Science 2013 vol. 4(Issue 3) pp:1023-1027
Publication Date(Web):18 Dec 2012
DOI:10.1039/C2SC21519E
Nucleophilic terminal gold(I) amides have been prepared and their reactivity toward a variety of electrophiles has been explored. For the first time these frequently proposed intermediates were isolated and shown to be unreactive in the amination of π-bonds. The first crystallographically determined terminal group 11 metal phosphide was also synthesized. Preliminary DFT studies have been conducted to understand the structure and reactivity of these complexes.
Co-reporter:Henry S. La Pierre, Stefan G. Minasian, Mark Abubekerov, Stosh A. Kozimor, David K. Shuh, Tolek Tyliszczak, John Arnold, Robert G. Bergman, and F. Dean Toste
Inorganic Chemistry 2013 Volume 52(Issue 19) pp:11650-11660
Publication Date(Web):September 11, 2013
DOI:10.1021/ic4020543
Syntheses of neutral halide and aryl vanadium bisimides are described. Treatment of VCl2(NtBu)[NTMS(NtBu)], 2, with PMe3, PEt3, PMe2Ph, or pyridine gave vanadium bisimides via TMSCl elimination in good yield: VCl(PMe3)2(NtBu)2 3, VCl(PEt3)2(NtBu)2 4, VCl(PMe2Ph)2(NtBu)2 5, and VCl(Py)2(NtBu)2 6. The halide series (Cl–I) was synthesized by use of TMSBr and TMSI to give VBr(PMe3)2(NtBu)2 7 and VI(PMe3)2(NtBu)2 8. The phenyl derivative was obtained by reaction of 3 with MgPh2 to give VPh(PMe3)2(NtBu)2 9. These neutral complexes are compared to the previously reported cationic bisimides [V(PMe3)3(NtBu)2][Al(PFTB)4] 10, [V(PEt3)2(NtBu)2][Al(PFTB)4] 11, and [V(DMAP)(PEt3)2(NtBu)2][Al(PFTB)4] 12 (DMAP = dimethylaminopyridine, PFTB = perfluoro-tert-butoxide). Characterization of the complexes by X-ray diffraction, 13C NMR, 51V NMR, and V L3,2-edge X-ray absorption near-edge structure (XANES) spectroscopy provides a description of the electronic structure in comparison to group 6 bisimides and the bent metallocene analogues. The electronic structure is dominated by π bonding to the imides, and localization of electron density at the nitrogen atoms of the imides is dictated by the cone angle and donating ability of the axial neutral supporting ligands. This phenomenon is clearly seen in the sensitivity of 51V NMR shift, 13C NMR Δδαβ, and L3-edge energy to the nature of the supporting phosphine ligand, which defines the parameters for designing cationic group 5 bisimides that would be capable of breaking stronger σ bonds. Conversely, all three methods show little dependence on the variable equatorial halide ligand. Furthermore, this analysis allows for quantification of the electronic differences between vanadium bisimides and the structurally analogous mixed Cp/imide system CpV(NtBu)X2 (Cp = C5H51–).
Co-reporter:Mika Shiramizu ; F. Dean Toste
Angewandte Chemie International Edition 2013 Volume 52( Issue 49) pp:12905-12909
Publication Date(Web):
DOI:10.1002/anie.201307564
Co-reporter:Hunter P. Shunatona;Natalja Früh;Yi-Ming Wang;Dr. Vivek Rauniyar ;Dr. F. Dean Toste
Angewandte Chemie International Edition 2013 Volume 52( Issue 30) pp:7724-7727
Publication Date(Web):
DOI:10.1002/anie.201302002
Co-reporter:Mika Shiramizu ; F. Dean Toste
Angewandte Chemie 2013 Volume 125( Issue 49) pp:13143-13147
Publication Date(Web):
DOI:10.1002/ange.201307564
Co-reporter:Jeffrey Wu;Vivek Rauniyar;Yi-Ming Wang;Amela Drljevic;F. Dean Toste;Robert J. Phipps
PNAS 2013 Volume 110 (Issue 34 ) pp:13729-13733
Publication Date(Web):2013-08-20
DOI:10.1073/pnas.1304346110
We report a catalytic enantioselective electrophilic fluorination of alkenes to form tertiary and quaternary C(sp3)-F bonds and generate β-amino- and β-aryl-allylic fluorides. The reaction takes advantage of the ability of chiral phosphate anions to serve as solid–liquid phase transfer catalysts and hydrogen bond with directing groups on the substrate. A variety of heterocyclic, carbocyclic, and acyclic alkenes react with good to excellent yields and high enantioselectivities. Further, we demonstrate a one-pot, tandem dihalogenation–cyclization reaction, using the same catalytic system twice in series, with an analogous electrophilic brominating reagent in the second step.
Co-reporter:Hunter P. Shunatona;Natalja Früh;Yi-Ming Wang;Dr. Vivek Rauniyar ;Dr. F. Dean Toste
Angewandte Chemie 2013 Volume 125( Issue 30) pp:7878-7881
Publication Date(Web):
DOI:10.1002/ange.201302002
Co-reporter:Britton K. Corkey, Stephen T. Heller, Yi-Ming Wang, F. Dean Toste
Tetrahedron 2013 69(27–28) pp: 5640-5646
Publication Date(Web):
DOI:10.1016/j.tet.2013.02.091
Co-reporter:Yi-Ming Wang ; Jeffrey Wu ; Christina Hoong ; Vivek Rauniyar ;F. Dean Toste
Journal of the American Chemical Society 2012 Volume 134(Issue 31) pp:12928-12931
Publication Date(Web):July 25, 2012
DOI:10.1021/ja305795x
A chiral anion phase-transfer system for enantioselective halogenation is described. Highly insoluble, ionic reagents were developed as electrophilic bromine and iodine sources, and application of this system to o-anilidostyrenes afforded halogenated 4H-3,1-benzoxazines with excellent yield and enantioselectivity.
Co-reporter:Robert J. Phipps, Kenichi Hiramatsu, and F. Dean Toste
Journal of the American Chemical Society 2012 Volume 134(Issue 20) pp:8376-8379
Publication Date(Web):May 11, 2012
DOI:10.1021/ja303959p
The use of a BINOL-derived phosphate as a chiral anionic phase-transfer catalyst in a nonpolar solvent allows the enantioselective fluorination of enamides using Selectfluor as the fluorinating reagent. We demonstrate that a wide range of stable and synthetically versatile α-(fluoro)benzoylimines can be readily accessed with high enantioselectivity. These compounds have the potential to be readily elaborated into a range of highly stereodefined β-fluoroamines, compounds that constitute highly valuable building blocks of particular importance in the synthesis of pharmaceuticals.
Co-reporter:Jean-François Brazeau ; Suyan Zhang ; Ignacio Colomer ; Britton K. Corkey ;F. Dean Toste
Journal of the American Chemical Society 2012 Volume 134(Issue 5) pp:2742-2749
Publication Date(Web):January 31, 2012
DOI:10.1021/ja210388g
The discovery of complementary methods for enantioselective transition metal-catalyzed cyclization with silyloxyenynes has been accomplished using chiral phosphine ligands. Under palladium catalysis, 1,6-silyloxyenynes bearing a terminal alkyne led to the desired five-membered ring with high enantioselectivities (up to 91% ee). As for reactions under cationic gold catalysis, 1,6- and 1,5-silyloxyenynes bearing an internal alkyne furnished the chiral cyclopentane derivatives with excellent enantiomeric excess (up to 94% ee). Modification of the substrate by incorporating an α,β-unsaturation led to the discovery of a tandem cyclization. Remarkably, using silyloxy-1,3-dien-7-ynes under gold catalysis conditions provided the bicyclic derivatives with excellent diastereo- and enantioselectivities (up to >20:1 dr and 99% ee).
Co-reporter:William M. Hart-Cooper ; Kristen N. Clary ; F. Dean Toste ; Robert G. Bergman ;Kenneth N. Raymond
Journal of the American Chemical Society 2012 Volume 134(Issue 43) pp:17873-17876
Publication Date(Web):October 15, 2012
DOI:10.1021/ja308254k
A polyanionic supramolecular assembly (1) is shown to catalytically cyclize the monoterpene citronellal and two homologues. In contrast to cyclization in acidic aqueous solution, the hydrophobic interior of 1 prevents the capture of reactive intermediates by water. This effect was also observed in the gold-catalyzed cycloisomerization of an enyne. Due to the steric confinement of the catalyst’s interior, Prins cyclizations in 1 proceed cleanly both for substrates containing and lacking gem-dimethyl substitution. Encapsulation in 1 consequently imposes a degree of mechanistic control that, similar to enzyme catalysis, is not observed in bulk aqueous solution.
Co-reporter:Iain D. G. Watson and F. Dean Toste  
Chemical Science 2012 vol. 3(Issue 10) pp:2899-2919
Publication Date(Web):26 Jun 2012
DOI:10.1039/C2SC20542D
This review describes important recent advancements in asymmetric cycloisomerization reactions. A wide variety of catalytic and asymmetric strategies have been applied to these reactions over the past twenty years. Cycloisomerization reactions have the ability to produce diverse polycyclic compounds in excellent yields and selectivity. They constitute a powerful and efficient strategy for asymmetric carbon-carbon bond formation in cyclic compounds. Enyne and related olefin cyclizations comprise the majority of reactions of this type and important advances have recently occurred in this area. However, significant changes have also occurred in the area of classical cyclization as well as intramolecular hydroacylation and C–H activation initiated cyclization and these will also be described.
Co-reporter:Neal P. Mankad and F. Dean Toste  
Chemical Science 2012 vol. 3(Issue 1) pp:72-76
Publication Date(Web):13 Oct 2011
DOI:10.1039/C1SC00515D
Rare examples of C(sp3)–F reductive elimination were observed from several cis-F2Au(R)(IPr) intermediates generated by oxidation of (IPr)AuR complexes with XeF2. For R groups bearing β-hydrogens, β-hydride elimination was competitive with C(sp3)–F reductive elimination. For strained cyclic R groups and most acyclic R groups lacking β-hydrogens, carbocation-like rearrangements occurred prior to C(sp3)–F reductive elimination. Kinetics of the decay of one cis-F2Au(R)(IPr) species, stereochemical analysis of reductive elimination with a chiral R group, and DFT analysis collectively suggest C(sp3)–F reductive elimination proceeding through transient cationic [(IPr)Au(F)(R)]+ intermediates with significant ionization of the Au–alkyl bonds.
Co-reporter:Henry S. La Pierre, John Arnold, Robert G. Bergman, and F. Dean Toste
Inorganic Chemistry 2012 Volume 51(Issue 24) pp:13334-13344
Publication Date(Web):November 26, 2012
DOI:10.1021/ic302044q
A series of carbon monoxide, isocyanide, and nitrile complexes of [V(PR3)2(NtBu)2][Al(PFTB)4], (R = Me, Et) were prepared. [V(PMe3)3(NtBu)2][Al(PFTB)4], (PFTB = perfluoro-tert-butoxide) reacts with 2,6-xylylisocyanide (CNXyl) or acetonitrile to afford complexes [V(PMe)2(NtBu)2(CNXyl)][Al(PFTB)4] (2) and [V(PMe)2(NtBu)2(MeCN)][Al(PFTB)4] (3). Complex 2 was crystallographically characterized, revealing a C–N bond length of (1.152(4) Å); the C–N stretching frequency occurs at 2164 cm–1 in the IR. To access the analogous carbon monoxide complex, the larger cone angle phosphine, triethylphosphine, was employed, starting from the chloride VCl(PEt3)2(NtBu)2, 4, then to the lower coordinate C2v symmetrical complex, [V(PEt3)2(NtBu)2][Al(PFTB)4], 5. Derivatization of 5 with DMAP (4-dimethylaminopyridine) afforded complex 6, [V(DMAP)(PEt3)2(NtBu)2][Al(PFTB)4]. Treatment of 5 with CNXyl yielded [V(CNXyl)(PEt3)2(NtBu)2][Al(PFTB)4] (7) in 60% yield (υC–N = 2156 cm–1). The d0 vanadium bisimido, carbonyl complex, [V(η1-CO)(PEt3)2(NtBu)2][Al(PFTB)4] (8), was prepared via the exposure of 5 to 1 atm of CO. Complex 8 has a C–O stretching frequency of 2015 cm–1. Isotopic labeling with 99% 13CO reveals a stretching frequency of 1970 cm–1, which confirms the assignment of the complex as a terminal η1-CO complex. This is also implied by its NMR data in comparison to the other crystallographically characterized compounds presented here. The 13C{31P}{1H} NMR spectrum of 8-13C reveals a broad singlet at 228.36 ppm implying deshielding of the carbonyl carbon. This datum, in conjunction with the shielded vanadium NMR shift of −843.71 ppm, suggests π back-bonding is operative in the bond between carbon monoxide and the d0 vanadium center in 8. This model was further confirmed by density functional theory (DFT) analysis of the model complex [V(η1-CO)(PMe3)2(NtBu)2]+, 9, which reveals that the basis of the reduced stretching frequency in 8 is π back-bonding from the 2b1 and 1b2 orbitals of 8.
Co-reporter:Mika Shiramizu ; F. Dean Toste
Angewandte Chemie International Edition 2012 Volume 51( Issue 32) pp:8082-8086
Publication Date(Web):
DOI:10.1002/anie.201203877
Co-reporter:Dr. Takashi Honjo;Dr. Robert J. Phipps;Dr. Vivek Rauniyar ; F. Dean Toste
Angewandte Chemie 2012 Volume 124( Issue 38) pp:9822-9826
Publication Date(Web):
DOI:10.1002/ange.201205383
Co-reporter:Mika Shiramizu ; F. Dean Toste
Angewandte Chemie 2012 Volume 124( Issue 32) pp:8206-8210
Publication Date(Web):
DOI:10.1002/ange.201203877
Co-reporter:Dr. Takashi Honjo;Dr. Robert J. Phipps;Dr. Vivek Rauniyar ; F. Dean Toste
Angewandte Chemie International Edition 2012 Volume 51( Issue 38) pp:9684-9688
Publication Date(Web):
DOI:10.1002/anie.201205383
Co-reporter:Cheol Hong Cheon ; Osamu Kanno ;F. Dean Toste
Journal of the American Chemical Society 2011 Volume 133(Issue 34) pp:13248-13251
Publication Date(Web):August 4, 2011
DOI:10.1021/ja204331w
A chiral Brønsted acid has been developed from a cationic gold(I) disphosphine complex in the presence of alcoholic solvent and applied to the enantioselective protonation reaction of silyl enol ethers of ketones. Various optically active cyclic ketones were obtained in excellent yields and high enantioselectivities, including cyclic ketones bearing aliphatic substrates at the α-position. Furthermore, the application of this Brønsted acid was extended to the first Brønsted acid-catalyzed enantioselective protonation reaction of silyl enol ethers of acyclic substrates, regardless of their E/Z ratio.
Co-reporter:Yimin Li ; Jack Hung-Chang Liu ; Cole A. Witham ; Wenyu Huang ; Matthew A. Marcus ; Sirine C. Fakra ; Pinar Alayoglu ; Zhongwei Zhu ; Christopher M. Thompson ; Arpana Arjun ; Kihong Lee ; Elad Gross ; F. Dean Toste ;Gabor A. Somorjai
Journal of the American Chemical Society 2011 Volume 133(Issue 34) pp:13527-13533
Publication Date(Web):July 1, 2011
DOI:10.1021/ja204191t
The design and development of metal-cluster-based heterogeneous catalysts with high activity, selectivity, and stability under solution-phase reaction conditions will enable their applications as recyclable catalysts in large-scale fine chemicals production. To achieve these required catalytic properties, a heterogeneous catalyst must contain specific catalytically active species in high concentration, and the active species must be stabilized on a solid catalyst support under solution-phase reaction conditions. These requirements pose a great challenge for catalysis research to design metal-cluster-based catalysts for solution-phase catalytic processes. Here, we focus on a silica-supported, polymer-encapsulated Pt catalyst for an electrophilic hydroalkoxylation reaction in toluene, which exhibits superior selectivity and stability against leaching under mild reaction conditions. We unveil the key factors leading to the observed superior catalytic performance by combining X-ray absorption spectroscopy (XAS) and reaction kinetic studies. On the basis of the mechanistic understandings obtained in this work, we also provide useful guidelines for designing metal-cluster-based catalyst for a broader range of reactions in the solution phase.
Co-reporter:Yi-Ming Wang ; Christian N. Kuzniewski ; Vivek Rauniyar ; Christina Hoong ;F. Dean Toste
Journal of the American Chemical Society 2011 Volume 133(Issue 33) pp:12972-12975
Publication Date(Web):July 28, 2011
DOI:10.1021/ja205068j
A highly enantioselective transformation catalyzed by chiral (acyclic diaminocarbene)gold(I) complexes is reported. The enantioselective synthesis of 2-substituted chromenyl pivalates from racemic phenol-substituted propargyl pivalates was developed. Rearrangement of the substrates in the presence of cationic gold gave allene intermediates, whose cyclization resulted in formation of enantioenriched product through a dynamic kinetic asymmetric transformation.
Co-reporter:Neil C. Tomson ; Mark R. Crimmin ; Taras Petrenko ; Lauren E. Rosebrugh ; Stephen Sproules ; W. Christopher Boyd ; Robert G. Bergman ; Serena DeBeer ; F. Dean Toste ;Karl Wieghardt
Journal of the American Chemical Society 2011 Volume 133(Issue 46) pp:18785-18801
Publication Date(Web):November 2, 2011
DOI:10.1021/ja206042k
Multiple spectroscopic and computational methods were used to characterize the ground-state electronic structure of the novel {CoNO}9 species Tp*Co(NO) (Tp* = hydro-tris(3,5-Me2-pyrazolyl)borate). The metric parameters about the metal center and the pre-edge region of the Co K-edge X-ray absorption spectrum were reproduced by density functional theory (DFT), providing a qualitative description of the Co–NO bonding interaction as a Co(II) (SCo = 3/2) metal center, antiferromagnetically coupled to a triplet NO– anion (SNO = 1), an interpretation of the electronic structure that was validated by ab initio multireference methods (CASSCF/MRCI). Electron paramagnetic resonance (EPR) spectroscopy revealed significant g-anisotropy in the S = 1/2 ground state, but the linear-response DFT performed poorly at calculating the g-values. Instead, CASSCF/MRCI computational studies in conjunction with quasi-degenerate perturbation theory with respect to spin–orbit coupling were required for obtaining accurate modeling of the molecular g-tensor. The computational portion of this work was extended to the diamagnetic Ni analogue of the Co complex, Tp*Ni(NO), which was found to consist of a Ni(II) (SNi = 1) metal center antiferromagnetically coupled to an SNO = 1 NO–. The similarity between the Co and Ni complexes contrasts with the previously studied Cu analogues, for which a Cu(I) bound to NO0 formulation has been described. This discrepancy will be discussed along with a comparison of the DFT and ab initio computational methods for their ability to predict various spectroscopic and molecular features.
Co-reporter:Asa D. Melhado ; Giovanni W. Amarante ; Z. Jane Wang ; Marco Luparia ;F. Dean Toste
Journal of the American Chemical Society 2011 Volume 133(Issue 10) pp:3517-3527
Publication Date(Web):February 22, 2011
DOI:10.1021/ja1095045
Azlactones participate in stereoselective reactions with electron-deficient alkenes and N-sulfonyl aldimines to give products of 1,3-dipolar cycloaddition and Mannich addition reactions, respectively. Both of these reactions proceed with good to excellent diastereo- and enantioselectivity using a single class of gold catalysts, namely C2-symmetric bis(phosphinegold(I) carboxylate) complexes. The development of the azlactone Mannich reaction to provide fully protected anti-α,β-diamino acid derivatives is described. 1,3-Dipolar cycloaddition reactions of several acyclic 1,2-disubstituted alkenes and the chemistry of the resultant cycloadducts are examined to probe the stereochemical course of this reaction. Reaction kinetics and tandem mass spectrometry studies of both the cycloaddition and Mannich reactions are reported. These studies support a mechanism in which the gold complexes catalyze addition reactions through nucleophile activation rather than the more typical activation of the electrophilic reaction component.
Co-reporter:Ana Z. González ; Diego Benitez ; Ekaterina Tkatchouk ; William A. Goddard ; III;F. Dean Toste
Journal of the American Chemical Society 2011 Volume 133(Issue 14) pp:5500-5507
Publication Date(Web):March 23, 2011
DOI:10.1021/ja200084a
In this article the utility of phosphoramidite ligands in enantioselective AuI catalysis was explored in the development of highly diastereo- and enantioselective AuI-catalyzed cycloadditions of allenenes. A AuI-catalyzed synthesis of 3,4-disubstituted pyrrolidines and γ-lactams is described. This reaction proceeds through the enantioselective AuI-catalyzed cyclization of allenenes to form a carbocationic intermediate that is trapped by an exogenous nucleophile, resulting in the highly diastereoselective construction of three contiguous stereogenic centers. A computational study (DFT) was also performed to gain some insight into the underlying mechanisms of these cycloadditions. The utility of this new methodology was demonstrated through the formal synthesis of (−)-isocynometrine.
Co-reporter:Z. Jane Wang ; Casey J. Brown ; Robert G. Bergman ; Kenneth N. Raymond ;F. Dean Toste
Journal of the American Chemical Society 2011 Volume 133(Issue 19) pp:7358-7360
Publication Date(Web):April 25, 2011
DOI:10.1021/ja202055v
Gold(I)–phosphine complexes are readily encapsulated by a tetrahedral supramolecular host (Ga4L6). We have investigated the catalytic activity of the resulting complexes for the intramolecular hydroalkoxylation of allenes. The catalytic activity of Me3PAuBr was increased 8-fold by encapsulation, as determined by initial rate kinetics, and we observed up to 67 catalytic turnovers by Me3PAu+ encapsulated in Ga4L6.
Co-reporter:Vivek Rauniyar ; Z. Jane Wang ; Heather E. Burks ;F. Dean Toste
Journal of the American Chemical Society 2011 Volume 133(Issue 22) pp:8486-8489
Publication Date(Web):May 11, 2011
DOI:10.1021/ja202959n
A catalytic enantioselective reaction based on a copper(II) catalyst strictly containing chiral anionic ligands is described. In the present work, copper(II)–phosphate catalyst promotes the intramolecular heterocyclization of 2-(1-alkynyl)-2-alkene-1-ones and facilitates high levels of enantioselectivity in the subsequent nucleophile attack. Mechanistic studies suggest that formation of a copper(II)–indole species is important for catalysis.
Co-reporter:Chen Zhao ; F. Dean Toste ;Robert G. Bergman
Journal of the American Chemical Society 2011 Volume 133(Issue 28) pp:10787-10789
Publication Date(Web):June 23, 2011
DOI:10.1021/ja204564z
We report a one-pot, direct C–H functionalization reaction of alkenes mediated by [CpCo(NO)2]. All intermediates in the proposed reaction sequence have been characterized. A variety of Michael acceptors can be utilized with the one-pot procedure to give the desired cyclic tetra-alkyl-substituted, γ,δ-unsaturated compounds in good yields. We also provide a preliminary result for catalytic turnover in both base and [CpCo(NO)2].
Co-reporter:Ekaterina Tkatchouk ; Neal P. Mankad ; Diego Benitez ; William A. Goddard ; III;F. Dean Toste
Journal of the American Chemical Society 2011 Volume 133(Issue 36) pp:14293-14300
Publication Date(Web):August 23, 2011
DOI:10.1021/ja2012627
We present a detailed study of the mechanism for oxidative heteroarylation, based on DFT calculations and experimental observations. We propose binuclear Au(II)–Au(II) complexes to be key intermediates in the mechanism for gold catalyzed oxidative heteroarylation. The reaction is thought to proceed via a gold redox cycle involving initial oxidation of Au(I) to binuclear Au(II)–Au(II) complexes by Selectfluor, followed by heteroauration and reductive elimination. While it is tempting to invoke a transmetalation/reductive elimination mechanism similar to that proposed for other transition metal complexes, experimental and DFT studies suggest that the key C–C bond forming reaction occurs via a bimolecular reductive elimination process (devoid of transmetalation). In addition, the stereochemistry of the elimination step was determined experimentally to proceed with complete retention. Ligand and halide effects played an important role in the development and optimization of the catalyst; our data provides an explanation for the ligand effects observed experimentally, useful for future catalyst development. Cyclic voltammetry data is presented that supports redox synergy of the Au···Au aurophilic interaction. The monometallic reductive elimination from mononuclear Au(III) complexes is also studied from which we can predict a ∼15 kcal/mol advantage for bimetallic reductive elimination.
Co-reporter:Rachel M. Zeldin and F. Dean Toste  
Chemical Science 2011 vol. 2(Issue 9) pp:1706-1709
Publication Date(Web):24 Jun 2011
DOI:10.1039/C1SC00290B
The recent development of new gold(I) catalysis methodologies has opened the door to new disconnections for the total synthesis of bioactive complex molecules. Below is described the application of a gold(I)-catalyzed hydroarylation of an allene with indole toward the total synthesis of flinderoles B–C, members of a new class of antimalarial bisindole alkaloids isolated from plants of the Flindersia genus. The key gold(I) step establishes both the pyrrolidine and isobutenyl functionalities unique to these compounds. Other important steps of the synthesis include a convergent Horner–Wadsworth–Emmons olefination to construct the bridging alkene and a new strategy for α-indole enolate alkylations.
Co-reporter:Matthew J. Campbell and F. Dean Toste  
Chemical Science 2011 vol. 2(Issue 7) pp:1369-1378
Publication Date(Web):12 May 2011
DOI:10.1039/C1SC00160D
A racemic Au(I)-catalyzed three-component reaction has been developed to prepare cyclic carbamimidates from imines, terminal alkynes, and sulfonylisocyanates. This reaction exploits the carbophilic π-acidity of gold catalysts to first activate an alkyne toward deprotonation and secondly, to activate the internal alkyne generated toward intramolecular O-cyclization. Unlike similar previously reported multicomponent gold-catalyzed reactions, the stereocenter generated during the alkynylation is preserved in the product. This trait was exploited by developing an enantioselective variant, using an unusual trans-1-diphenylphosphino-2-arylsulfamidocyclohexane ligand. Moderate to excellent levels of enantioselectivity were obtained using a variety of N-arylbenzylidene anilines (41–95% ee, 18 examples).
Co-reporter:Dr. Osamu Kanno;Dr. Wataru Kuriyama;Z. Jane Wang ; F. Dean Toste
Angewandte Chemie 2011 Volume 123( Issue 42) pp:10093-10096
Publication Date(Web):
DOI:10.1002/ange.201104076
Co-reporter:Julian M.W. Chan, Giovanni W. Amarante, F. Dean Toste
Tetrahedron 2011 67(24) pp: 4306-4312
Publication Date(Web):
DOI:10.1016/j.tet.2011.04.011
Co-reporter:Vivek Rauniyar;Aaron D. Lackner;Gregory L. Hamilton;F. Dean Toste
Science 2011 Vol 334(6063) pp:1681-1684
Publication Date(Web):23 Dec 2011
DOI:10.1126/science.1213918

A chiral phosphate ion plays a dual role, coaxing a fluorinating agent into solution and then catalyzing its reaction there.

Co-reporter:Mika Shiramizu ; F. Dean Toste
Chemistry - A European Journal 2011 Volume 17( Issue 44) pp:12452-12457
Publication Date(Web):
DOI:10.1002/chem.201101580

Abstract

Polyethylene terephthalate (PET) is a polymeric material with high global demand. Conventionally, PET is produced from fossil-fuel-based materials. Herein, we explored the feasibility of a sustainable method for PET production by using solely bio-renewable resources. Specifically, 2,5-dimethylfuran (derived from lignocellulosic biomass through 5-(hydroxymethyl)furfural) and acrolein (produced from glycerol, a side product of biodiesel production) were converted into the key intermediate p-xylene (a precursor of terephthalic acid). This synthesis consists of a sequential Diels–Alder reaction, oxidation, dehydration, and decarboxylation. In particular, the pivotal first step, the Diels–Alder reaction, was studied in detail to provide useful kinetic and thermodynamic data. Although it was found that this reaction requires low temperature to proceed efficiently, which presents a limitation on economic feasibility on an industrial scale, the concept was realized and bio-derived p-xylene was obtained in 34 % overall yield over four steps.

Co-reporter:Dr. Mark R. Crimmin; Robert G. Bergman; F. Dean Toste
Angewandte Chemie International Edition 2011 Volume 50( Issue 19) pp:4484-4487
Publication Date(Web):
DOI:10.1002/anie.201100816
Co-reporter:Henry S. LaPierre;Dr. John Arnold;Dr. F. Dean Toste
Angewandte Chemie International Edition 2011 Volume 50( Issue 17) pp:3900-3903
Publication Date(Web):
DOI:10.1002/anie.201007876
Co-reporter:Dr. Osamu Kanno;Dr. Wataru Kuriyama;Z. Jane Wang ; F. Dean Toste
Angewandte Chemie International Edition 2011 Volume 50( Issue 42) pp:9919-9922
Publication Date(Web):
DOI:10.1002/anie.201104076
Co-reporter:Steven G. Sethofer ; Timo Mayer ;F. Dean Toste
Journal of the American Chemical Society 2010 Volume 132(Issue 24) pp:8276-8277
Publication Date(Web):June 2, 2010
DOI:10.1021/ja103544p
A series of enantioselective polycyclization reactions, catalyzed by a cationic bisphosphine gold complexes, are described. The polycyclization reactions, which employ an alkyne as an initiating group, begin with a gold-promoted 6-exo-dig cyclization and can be terminated with a variety of nucleophiles including carboxylic acids, phenols, sulfonamides, and electron-rich aryl groups. This method allows for the preparation of up to four bonds in a single operation with excellent diastereo- and enantioselectivity.
Co-reporter:Z. Jane Wang ; Diego Benitez ; Ekaterina Tkatchouk ; William A. Goddard III ;F. Dean Toste
Journal of the American Chemical Society 2010 Volume 132(Issue 37) pp:13064-13071
Publication Date(Web):August 25, 2010
DOI:10.1021/ja105530q
The intermolecular hydroamination of allenes occurs readily with hydrazide nucleophiles, in the presence of 3−12% Ph3PAuNTf2. Mechanistic studies have been conducted to establish the resting state of the gold catalyst, the kinetic order of the reaction, the effect of ligand electronics on the overall rate, and the reversibility of the last steps in the catalytic cycle. We have found the overall reaction to be first order in gold and allene and zero order in nucleophile. Our studies suggest that the rate-limiting transition state for the reaction does not involve the nucleophile and that the active catalyst is monomeric in gold(I). Computational studies support an “outersphere” mechanism and predict that a two-step, no intermediate mechanism may be operative. In accord with this mechanistic proposal, the reaction can be accelerated with the use of more electron-deficient phosphine ligands on the gold(I) catalyst.
Co-reporter:Neal P. Mankad ;F. Dean Toste
Journal of the American Chemical Society 2010 Volume 132(Issue 37) pp:12859-12861
Publication Date(Web):August 20, 2010
DOI:10.1021/ja106257n
Previously, alkylgold(III) fluorides have been proposed as catalytic intermediates that undergo C−C coupling with reagents such as arylboronic acids in Au(I)/Au(III) cross-coupling reactions. Here is reported the first experimental evidence for this elementary mechanistic step. Complexes of the type (NHC)AuMe (NHC = N-heterocyclic carbene) were oxidized with XeF2 to yield cis-(NHC)AuMeF2 products, which were found to be in equilibrium with their fluoride-dissociated, dimeric [(NHC)AuMe(μ-F)]2[F]2 forms. In one case, a monomeric cis-(NHC)AuMeF2 complex was favored exclusively in solution, and it was found to react with a variety of ArB(OH)2 reagents to yield Ar−CH3 products.
Co-reporter:W. Christopher Boyd ; Mark R. Crimmin ; Lauren E. Rosebrugh ; Jennifer M. Schomaker ; Robert G. Bergman ;F. Dean Toste
Journal of the American Chemical Society 2010 Volume 132(Issue 46) pp:16365-16367
Publication Date(Web):October 29, 2010
DOI:10.1021/ja107968c
The asymmetric C−H functionalization of norbornene and norbornadiene with five-, six-, and seven-membered cyclic enones mediated by the reactive intermediate [{η5-(tBuMe2Si)C5H4}Co(NO)2] is reported. A novel base mixture derived from enantiopure ammonium salts and NaHMDS was used as a source of chirality, and this enantioselective desymmetrization of Cs alkenes has been applied to the asymmetric synthesis of C2- and C1-symmetric diene ligands in high regioselectivity (3.7−20:1 anti/syn), near perfect diastereoselectivity (>99:1 dr), and high enantioselectivity (90−96% ee).
Co-reporter:Wenyu Huang ; Jack Hung-Chang Liu ; Pinar Alayoglu ; Yimin Li ; Cole A. Witham ; Chia-Kuang Tsung ; F. Dean Toste ;Gabor A. Somorjai
Journal of the American Chemical Society 2010 Volume 132(Issue 47) pp:16771-16773
Publication Date(Web):November 9, 2010
DOI:10.1021/ja108898t
A highly active heterogeneous Pd-nanoparticle catalyst for the intramolecular addition of phenols to alkynes was developed and employed in a continuous flow reaction system. Running the reaction in flow mode revealed reaction kinetics, such as the activation energy and catalyst deactivation, and provides many potential practical advantages.
Co-reporter:Asa D. Melhado ; William E. Brenzovich ; Jr.; Aaron D. Lackner ;F. Dean Toste
Journal of the American Chemical Society 2010 Volume 132(Issue 26) pp:8885-8887
Publication Date(Web):June 17, 2010
DOI:10.1021/ja1034123
The three-component coupling of terminal alkenes with arylboronic acids and oxygen nucleophiles is described. The reaction employs a binuclear gold(I) bromide as a catalyst and Selectfluor reagent as the stoichiometric oxidant. Alcohols, carboxylic acids, and water can be employed as oxygen nucleophiles, thus providing an efficient entry into β-aryl ethers, esters, and alcohols from alkenes.
Co-reporter:Rebecca L. LaLonde, William E. Brenzovich, Jr., Diego Benitez, Ekaterina Tkatchouk, Kotaro Kelley, William A. Goddard, III and F. Dean Toste  
Chemical Science 2010 vol. 1(Issue 2) pp:226-233
Publication Date(Web):10 Jun 2010
DOI:10.1039/C0SC00255K
Alkylgold(I) complexes were formed from the gold(I)-promoted intramolecular addition of various amine nucleophiles to alkenes. These experiments provide the first direct experimental evidence for the elementary step of gold-promoted nucleophilic addition to an alkene. Deuterium-labeling studies and X-ray crystal structures provide support for a mechanism involving anti-addition of the nucleophile to a gold-activated alkene, which is verified by DFT analysis of the mechanism. Ligand studies indicate that the rate of aminoauration can be drastically increased by use of electron-poor arylphosphines, which are also shown to be favored in ligand exchange experiments. Attempts at protodeauration lead only to recovery of the starting olefins, though the gold can be removed under reducing conditions to provide the purported hydroamination products.
Co-reporter:Ana Z. González and F. Dean Toste
Organic Letters 2010 Volume 12(Issue 1) pp:200-203
Publication Date(Web):December 4, 2009
DOI:10.1021/ol902622b
An enantioselective gold(I)-catalyzed intramolecular [4 + 2]-cycloaddition of allenes and dienes is reported. The reactions allow for the asymmetric synthesis of trans-hexahydroindenes and pyrrolidine products using C3-symmetric phosphitegold(I) and ortho-arylphosphoramiditegold(I) complexes as catalysts, respectively.
Co-reporter:William E. Brenzovich Jr., Jean-François Brazeau, and F. Dean Toste
Organic Letters 2010 Volume 12(Issue 21) pp:4728-4731
Publication Date(Web):September 29, 2010
DOI:10.1021/ol102194c
During continuing studies with a novel oxidative gold oxyarylation reaction, arylsilanes were found to be competent coupling partners, providing further evidence for an intramolecular electrophilic aromatic substitution mechanism. While providing yields complementary to those of the previously described boronic acid methods, the use of trimethylsilanes reduces the observation of homocoupling byproducts and allows for facile intramolecular coupling reactions.
Co-reporter:R.L. LaLonde;Z.J. Wang;M. Mba Dr.;A.D. Lackner ;F.&x2005
Angewandte Chemie International Edition 2010 Volume 49( Issue 3) pp:598-601
Publication Date(Web):
DOI:10.1002/anie.200905000
Co-reporter:William E. Brenzovich Jr. Dr.;Diego Benitez Dr.;Aaron D. Lackner;Hunter P. Shunatona;Ekaterina Tkatchouk Dr.;William A. Goddard III ;F.&x2005
Angewandte Chemie International Edition 2010 Volume 49( Issue 32) pp:5519-5522
Publication Date(Web):
DOI:10.1002/anie.201002739
Co-reporter:Sunghee Son Dr. ;F.&x2005
Angewandte Chemie International Edition 2010 Volume 49( Issue 22) pp:3791-3794
Publication Date(Web):
DOI:10.1002/anie.201001293
Co-reporter:KristineA. Nolin Dr.;RichardW. Ahn;Yusuke Kobayashi Dr.;JoshuaJ. Kennedy-Smith Dr. ;F.&x2005
Chemistry - A European Journal 2010 Volume 16( Issue 31) pp:9555-9562
Publication Date(Web):
DOI:10.1002/chem.201001164

Abstract

The development and application of chiral, non-racemic ReV–oxo complexes to the enantioselective reduction of prochiral ketones is described. In addition to the enantioselective reduction of prochiral ketones, we report the application of these complexes to 1) a tandem Meyer–Schuster rearrangement/reduction to access enantioenriched allylic alcohols and 2) the enantioselective reduction of imines.

Co-reporter:R.L. LaLonde;Z.J. Wang;M. Mba Dr.;A.D. Lackner ;F.&x2005
Angewandte Chemie 2010 Volume 122( Issue 3) pp:608-611
Publication Date(Web):
DOI:10.1002/ange.200905000
Co-reporter:William E. Brenzovich Jr. Dr.;Diego Benitez Dr.;Aaron D. Lackner;Hunter P. Shunatona;Ekaterina Tkatchouk Dr.;William A. Goddard III ;F.&x2005
Angewandte Chemie 2010 Volume 122( Issue 32) pp:5651-5654
Publication Date(Web):
DOI:10.1002/ange.201002739
Co-reporter:Sunghee Son Dr. ;F.&x2005
Angewandte Chemie 2010 Volume 122( Issue 22) pp:3879-3882
Publication Date(Web):
DOI:10.1002/ange.201001293
Co-reporter:Florian Kleinbeck and F. Dean Toste
Journal of the American Chemical Society 2009 Volume 131(Issue 26) pp:9178-9179
Publication Date(Web):June 16, 2009
DOI:10.1021/ja904055z
The asymmetric gold(I)-catalyzed ring expansion of 1-allenylcyclopropanols is described. The method provides synthetically valuable cyclobutanones with a vinyl-substituted quaternary stereogenic center in high enantioselectivities and yields. The method shows a broad substrate scope, tolerating protected alcohols and amines, alkenes, unsaturated esters, and acetals. The reaction is easily adjustable to large-scale synthesis, leading to product formation without significant loss of selectivity or yield with only 0.5 mol% catalyst loading.
Co-reporter:Pablo Mauleón ; Rachel M. Zeldin ; Ana Z. González ;F. Dean Toste
Journal of the American Chemical Society 2009 Volume 131(Issue 18) pp:6348-6349
Publication Date(Web):April 20, 2009
DOI:10.1021/ja901649s
By adjustment of the electronic properties of the ancilliary ligands, high selectivity can be achieved for either [4 + 2] or [4 + 3] cycloaddition reactions of allene-dienes catalyzed by gold(I). Triarylphosphitegold(I) complexes are employed as catalysts for a [4 + 2] cycloaddition reaction leading to alkylidenecyclohexenes. Conversely, di-tert-butylbiphenylphosphinegold(I)-catalyzed reactions afford cycloheptadienes via [4 + 3] cycloaddition reactions.
Co-reporter:Diego Benitez, Ekaterina Tkatchouk, Ana Z. Gonzalez, William A. Goddard III and F. Dean Toste
Organic Letters 2009 Volume 11(Issue 21) pp:4798-4801
Publication Date(Web):September 25, 2009
DOI:10.1021/ol9018002
It is shown that [4 + 3] and [4 + 2] cycloaddition pathways are accessible in the Au(I) catalysis of allene−dienes. Seven-membered ring gold-stabilized carbenes, originating from the [4 + 3] cycloaddition process, are unstable and can rearrange via a 1,2-H or a 1,2-alkyl shift to yield six- and seven-membered products. Both steric and electronic properties of the AuL+ catalyst affect the electronic structure of the intermediate gold-stabilized carbene and its subsequent reactivity.
Co-reporter:David J. Gorin, Benjamin D. Sherry and F. Dean Toste
Chemical Reviews 2008 Volume 108(Issue 8) pp:3351
Publication Date(Web):July 25, 2008
DOI:10.1021/cr068430g
Co-reporter:Nathan D. Shapiro;F. Dean Toste
PNAS 2008 Volume 105 (Issue 8 ) pp:2779-2782
Publication Date(Web):2008-02-26
DOI:10.1073/pnas.0710500105
The chemical community has recently witnessed a dramatic increase in the application of cationic gold(I)-phosphine complexes as homogeneous catalysts for organic synthesis. The majority of gold(I)-catalyzed reactions rely on nucleophilic additions to carbon–carbon multiple bonds, which have been activated by coordination to a cationic gold(I) catalyst. However, structural evidence for coordination of cationic gold(I) complexes to alkynes has been limited. Here, we report the crystal structure of a gold(I)-phosphine η2-coordinated alkyne. Related Ag(I) and Cu(I) complexes have been synthesized for comparison. The crystallization of these complexes was enabled by tethering a labile alkyne ligand to a strongly coordinating triarylphosphine. This approach also proved applicable to crystallization of the first gold(I)-phosphine η2-coordinated alkene.
Co-reporter:AlexerT. Radosevich;VincentS. Chan;Hui-Wen Shih ;F.&x2005
Angewandte Chemie International Edition 2008 Volume 47( Issue 20) pp:3755-3758
Publication Date(Web):
DOI:10.1002/anie.200800554
Co-reporter:AlexerT. Radosevich;VincentS. Chan;Hui-Wen Shih ;F.&x2005
Angewandte Chemie 2008 Volume 120( Issue 20) pp:3815-3818
Publication Date(Web):
DOI:10.1002/ange.200800554
Co-reporter:Xin Linghu Dr.;Joshua J. Kennedy-Smith Dr.;F. Dean Toste
Angewandte Chemie 2007 Volume 119(Issue 40) pp:
Publication Date(Web):29 AUG 2007
DOI:10.1002/ange.200702695

Eine effektive Kombination: Die erste asymmetrische Totalsynthese von Fawcettimin (1) beweist, dass die Kombination aus organokatalytischer Anellierung und Gold(I)-katalysierter Cyclisierung eine effektive Synthese komplexer Verbindungen ermöglicht. Die absolute Konfiguration von 1 wurde anhand einer Röntgenstrukturanalyse des Hydrobromids ermittelt.

Co-reporter:Gregory L. Hamilton;Eun Joo Kang;Miriam Mba;F. Dean Toste
Science 2007 Volume 317(Issue 5837) pp:496-499
Publication Date(Web):27 Jul 2007
DOI:10.1126/science.1145229

Abstract

Traditionally, transition metal–catalyzed enantioselective transformations rely on chiral ligands tightly bound to the metal to induce asymmetric product distributions. Here we report high enantioselectivities conferred by a chiral counterion in a metal-catalyzed reaction. Two different transformations catalyzed by cationic gold(I) complexes generated products in 90 to 99% enantiomeric excess with the use of chiral binaphthol–derived phosphate anions. Furthermore, we show that the chiral counterion can be combined additively with chiral ligands to enable an asymmetric transformation that cannot be achieved by either method alone. This concept of relaying chiral information via an ion pair should be applicable to a vast number of metal-mediated processes.

Co-reporter:Xin Linghu Dr.;Joshua J. Kennedy-Smith Dr.;F. Dean Toste
Angewandte Chemie International Edition 2007 Volume 46(Issue 40) pp:
Publication Date(Web):29 AUG 2007
DOI:10.1002/anie.200702695

An effective combination: With the first asymmetric total synthesis of fawcettimine (1) it has been shown that the use of organocatalytic annulation and gold(I)-catalyzed cyclization reactions provides an effective combination for the synthesis of complex molecules. The absolute configuration of 1 was established through an X-ray structure analysis of its hydrobromide.

Co-reporter:Aurélien Blanc,F. Dean Toste
Angewandte Chemie International Edition 2006 45(13) pp:2096-2099
Publication Date(Web):
DOI:10.1002/anie.200503852
Co-reporter:Aurélien Blanc Dr.;F. Dean Toste Dr.
Angewandte Chemie 2006 Volume 118(Issue 13) pp:
Publication Date(Web):27 FEB 2006
DOI:10.1002/ange.200503852

Zwei Stufen, ein Katalysator: Ein Vanadium(V)-Oxo-Komplex mit einer dreizähnigen Schiff-Base als weiterem Ligand katalysiert die Titelreaktion, die racemische (Bis)homoallyl-α-hydroxyester in trans-Tetrahydropyrane (THPs) oder cis-Tetrahydrofurane (THFs) überführt. Auf diese Art lassen sich cyclische Ether effizient asymmetrisch synthetisieren, wie mit der ersten enantioselektiven Synthese von (−)-Pantofuranoid E belegt wird.

Co-reporter:Rebecca L. LaLonde, William E. Brenzovich, Jr., Diego Benitez, Ekaterina Tkatchouk, Kotaro Kelley, William A. Goddard, III and F. Dean Toste
Chemical Science (2010-Present) 2010 - vol. 1(Issue 2) pp:NaN233-233
Publication Date(Web):2010/06/10
DOI:10.1039/C0SC00255K
Alkylgold(I) complexes were formed from the gold(I)-promoted intramolecular addition of various amine nucleophiles to alkenes. These experiments provide the first direct experimental evidence for the elementary step of gold-promoted nucleophilic addition to an alkene. Deuterium-labeling studies and X-ray crystal structures provide support for a mechanism involving anti-addition of the nucleophile to a gold-activated alkene, which is verified by DFT analysis of the mechanism. Ligand studies indicate that the rate of aminoauration can be drastically increased by use of electron-poor arylphosphines, which are also shown to be favored in ligand exchange experiments. Attempts at protodeauration lead only to recovery of the starting olefins, though the gold can be removed under reducing conditions to provide the purported hydroamination products.
Co-reporter:Matthew J. Campbell and F. Dean Toste
Chemical Science (2010-Present) 2011 - vol. 2(Issue 7) pp:NaN1378-1378
Publication Date(Web):2011/05/12
DOI:10.1039/C1SC00160D
A racemic Au(I)-catalyzed three-component reaction has been developed to prepare cyclic carbamimidates from imines, terminal alkynes, and sulfonylisocyanates. This reaction exploits the carbophilic π-acidity of gold catalysts to first activate an alkyne toward deprotonation and secondly, to activate the internal alkyne generated toward intramolecular O-cyclization. Unlike similar previously reported multicomponent gold-catalyzed reactions, the stereocenter generated during the alkynylation is preserved in the product. This trait was exploited by developing an enantioselective variant, using an unusual trans-1-diphenylphosphino-2-arylsulfamidocyclohexane ligand. Moderate to excellent levels of enantioselectivity were obtained using a variety of N-arylbenzylidene anilines (41–95% ee, 18 examples).
Co-reporter:Rachel M. Zeldin and F. Dean Toste
Chemical Science (2010-Present) 2011 - vol. 2(Issue 9) pp:NaN1709-1709
Publication Date(Web):2011/06/24
DOI:10.1039/C1SC00290B
The recent development of new gold(I) catalysis methodologies has opened the door to new disconnections for the total synthesis of bioactive complex molecules. Below is described the application of a gold(I)-catalyzed hydroarylation of an allene with indole toward the total synthesis of flinderoles B–C, members of a new class of antimalarial bisindole alkaloids isolated from plants of the Flindersia genus. The key gold(I) step establishes both the pyrrolidine and isobutenyl functionalities unique to these compounds. Other important steps of the synthesis include a convergent Horner–Wadsworth–Emmons olefination to construct the bridging alkene and a new strategy for α-indole enolate alkylations.
Co-reporter:Iain D. G. Watson and F. Dean Toste
Chemical Science (2010-Present) 2012 - vol. 3(Issue 10) pp:NaN2919-2919
Publication Date(Web):2012/06/26
DOI:10.1039/C2SC20542D
This review describes important recent advancements in asymmetric cycloisomerization reactions. A wide variety of catalytic and asymmetric strategies have been applied to these reactions over the past twenty years. Cycloisomerization reactions have the ability to produce diverse polycyclic compounds in excellent yields and selectivity. They constitute a powerful and efficient strategy for asymmetric carbon-carbon bond formation in cyclic compounds. Enyne and related olefin cyclizations comprise the majority of reactions of this type and important advances have recently occurred in this area. However, significant changes have also occurred in the area of classical cyclization as well as intramolecular hydroacylation and C–H activation initiated cyclization and these will also be described.
Co-reporter:Miles W. Johnson, Sophia L. Shevick, F. Dean Toste and Robert G. Bergman
Chemical Science (2010-Present) 2013 - vol. 4(Issue 3) pp:NaN1027-1027
Publication Date(Web):2012/12/18
DOI:10.1039/C2SC21519E
Nucleophilic terminal gold(I) amides have been prepared and their reactivity toward a variety of electrophiles has been explored. For the first time these frequently proposed intermediates were isolated and shown to be unreactive in the amination of π-bonds. The first crystallographically determined terminal group 11 metal phosphide was also synthesized. Preliminary DFT studies have been conducted to understand the structure and reactivity of these complexes.
Co-reporter:Dillon H. Miles, Marcos Veguillas and F. Dean Toste
Chemical Science (2010-Present) 2013 - vol. 4(Issue 9) pp:NaN3431-3431
Publication Date(Web):2013/07/05
DOI:10.1039/C3SC50811K
The enantioselective bromocyclization of allenes is accomplished through the use of a chiral dinuclear gold complex and/or chiral phosphate anions in the presence of an N-bromolactam as an electrophilic bromine source. This method provides access to heterocyclic vinyl bromides with an allylic stereocenter in excellent yield and enantioselectivity. These enantioenriched vinyl bromides may serve as a handle for further derivatization via cross-coupling reactions.
Co-reporter:Ying He, Hongmiao Wu and F. Dean Toste
Chemical Science (2010-Present) 2015 - vol. 6(Issue 2) pp:NaN1198-1198
Publication Date(Web):2014/11/25
DOI:10.1039/C4SC03092C
A new method for the P-arylation of aryldiazonium salts with H-phosphonates via dual gold and photoredox catalysis is described. The reaction proceeds smoothly at room temperature in the absence of base and/or additives, and offers an efficient approach to arylphosphonates. The reaction is proposed to proceed through a photoredox-promoted generation of an electrophilic arylgold(III) intermediate that undergoes coupling with the H-phosphonate nucleophile.
Co-reporter:H. M. Nelson, J. S. Patel, H. P. Shunatona and F. D. Toste
Chemical Science (2010-Present) 2015 - vol. 6(Issue 1) pp:NaN173-173
Publication Date(Web):2014/10/02
DOI:10.1039/C4SC02494J
Chiral anion phase-transfer of aryldiazonium cations was utilized to achieve highly enantioselective α-amination of carbonyl compounds. A broad scope of indanone- and benzosuberone-derived substrates was amenable to this strategy. Critical to obtaining high levels of enantioselectivity was the use of BINAM-derived phosphoric acids. The utility of this transformation was demonstrated through facile conversion of diazene products to valuable α-amino acid derivatives.
Co-reporter:William M. Hart-Cooper, Chen Zhao, Rebecca M. Triano, Parastou Yaghoubi, Haxel Lionel Ozores, Kristen N. Burford, F. Dean Toste, Robert G. Bergman and Kenneth N. Raymond
Chemical Science (2010-Present) 2015 - vol. 6(Issue 2) pp:NaN1393-1393
Publication Date(Web):2014/11/28
DOI:10.1039/C4SC02735C
The effect of host structure on the selectivity and mechanism of intramolecular Prins reactions is evaluated using K12Ga4L6 tetrahedral catalysts. The host structure was varied by modifying the structure of the chelating moieties and the size of the aromatic spacers. While variation in chelator substituents was generally observed to affect changes in rate but not selectivity, changing the host spacer afforded differences in efficiency and product diastereoselectivity. An extremely high number of turnovers (up to 840) was observed. Maximum rate accelerations were measured to be on the order of 105, which numbers among the largest magnitudes of transition state stabilization measured with a synthetic host-catalyst. Host/guest size effects were observed to play an important role in host-mediated enantioselectivity.
Co-reporter:Weiwei Zi and F. Dean Toste
Chemical Society Reviews 2016 - vol. 45(Issue 16) pp:NaN4589-4589
Publication Date(Web):2016/02/18
DOI:10.1039/C5CS00929D
Interest in homogeneous gold catalysis has undergone a marked increase. As strong yet air- and moisture-tolerant π-acids, cationic gold(I) complexes have been shown to catalyze diverse transformations of alkenes, alkynes and allenes, opening new opportunities for chemical synthesis. The development of efficient asymmetric variants is required in order to take full advantage of the preparative potential of these transformations. During the last few years, the chemical community has achieved tremendous success in the area. This review highlights the updated progress (2011–2015) in enantioselective gold catalysis. The discussion is classified according to the π-bonds activated by gold(I), in an order of alkynes, allenes and alkenes. Other gold activation modes, such as σ-Lewis acid catalyzed reactions and transformations of diazo compounds are also discussed.
Co-reporter:Robert M. Rioux and F. Dean Toste
Catalysis Science & Technology (2011-Present) 2015 - vol. 5(Issue 3) pp:NaN1359-1359
Publication Date(Web):2015/01/22
DOI:10.1039/C5CY90005K
A graphical abstract is available for this content
Co-reporter:Suhong Kim, Jaime Rojas-Martin and F. Dean Toste
Chemical Science (2010-Present) 2016 - vol. 7(Issue 1) pp:NaN88-88
Publication Date(Web):2015/11/10
DOI:10.1039/C5SC03025K
A dual photoredox and gold-catalysed cross-coupling reaction of alkynyltrimethylsilanes and aryldiazonium tetrafluoroborates is described. The reaction proceeds through visible-light mediated oxidative addition of aryldiazoniums, transmetalation of alkynyltrimethylsilanes and aryl–alkynyl reductive elimination. Exclusive selectivity for silyl-substituted alkynes is observed, with no reactivity observed for terminal alkynes.
Co-reporter:Richard T. Thornbury, Vaneet Saini, Talita de A. Fernandes, Celine B. Santiago, Eric P. A. Talbot, Matthew S. Sigman, Jeffrey M. McKenna and F. Dean Toste
Chemical Science (2010-Present) 2017 - vol. 8(Issue 4) pp:NaN2897-2897
Publication Date(Web):2017/02/09
DOI:10.1039/C6SC05102B
A mild palladium-catalyzed ligand-controlled regioselective 1,3-arylfluorination of 2[H]-chromenes has been developed. The products with a syn-1,3 substitution pattern were obtained with high enantiomeric excess using a PyrOx ligand, wherein the utility of these pyranyl-fluorides was further demonstrated through their participation in a diastereoselective C–C bond forming reaction. Ligand dependent divergent formation of both the 1,3- and 1,2- alkene difunctionalization products was observed. The nature of this bifurcation was investigated through experimental studies in combination with computational and statistical analysis tools. Ultimately, the site selectivity was found to rely on ligand denticity and metal electrophilicity, the electronics of the boronic acid, and the donor ability of the directing group in the substrate.
Co-reporter:Xiaoyu Yang and F. Dean Toste
Chemical Science (2010-Present) 2016 - vol. 7(Issue 4) pp:NaN2656-2656
Publication Date(Web):2016/01/19
DOI:10.1039/C5SC04202J
We describe the asymmetric addition of unactivated α-branched cyclic ketones to allenamides catalyzed by a chiral phosphoric acid, generating an all-carbon quaternary stereocenter with broad substrate scope and high enantioselectivity. The products are easily transformed into their corresponding 1,5- and 1,4-ketoaldehyde derivatives, which are both important building blocks in organic synthesis.
Co-reporter:Neal P. Mankad and F. Dean Toste
Chemical Science (2010-Present) 2012 - vol. 3(Issue 1) pp:NaN76-76
Publication Date(Web):2011/10/13
DOI:10.1039/C1SC00515D
Rare examples of C(sp3)–F reductive elimination were observed from several cis-F2Au(R)(IPr) intermediates generated by oxidation of (IPr)AuR complexes with XeF2. For R groups bearing β-hydrogens, β-hydride elimination was competitive with C(sp3)–F reductive elimination. For strained cyclic R groups and most acyclic R groups lacking β-hydrogens, carbocation-like rearrangements occurred prior to C(sp3)–F reductive elimination. Kinetics of the decay of one cis-F2Au(R)(IPr) species, stereochemical analysis of reductive elimination with a chiral R group, and DFT analysis collectively suggest C(sp3)–F reductive elimination proceeding through transient cationic [(IPr)Au(F)(R)]+ intermediates with significant ionization of the Au–alkyl bonds.
prolylproline