A redox-neutral cobalt(III)-catalyzed synthetic approach for the direct synthesis of unprotected indoles showcasing an N−N bond cleavage is reported. The herein newly introduced Boc-protected hydrazines establish a beneficial addition to the limited portfolio of oxidizing directing groups for cobalt(III) catalysis. Moreover, the developed catalytic methodology tolerates a good variety of functional groups.

A novel asymmetric hydrogenation of vinylthioethers was developed using a ruthenium(II) NHC complex. This method provides an efficient approach to optically active 1,5-benzothiazepines featuring stereocenters with C−S bonds. Excellent enantioselectivities (up to 95 % ee) and high yields (up to 99 %) were obtained for a variety of substrates bearing a range of useful functional groups. Moreover, this methodology could be directly applied to the synthesis of the antidepressant drug R-(−)-thiazesim.

Herein, we report a conceptually novel mechanism-based screening approach to accelerate discovery in photocatalysis. In contrast to most screening methods, which consider reactions as discrete entities, this approach instead focuses on a single constituent mechanistic step of a catalytic reaction. Using luminescence spectroscopy to investigate the key quenching step in photocatalytic reactions, an initial screen of 100 compounds led to the discovery of two promising substrate classes. Moreover, a second, more focused screen provided mechanistic insights useful in developing proof-of-concept reactions. Overall, this fast and straightforward approach both facilitated the discovery and aided the development of new light-promoted reactions and suggests that mechanism-based screening strategies could become useful tools in the hunt for new reactivity.

A facile route toward the synthesis of isoquinolin-3-ones through a cooperative B(C₆F₅)₃- and Cp*Co^III-catalyzed C−H bond activation of imines with diazo compounds is presented. The inclusion of a catalytic amount of B(C₆F₅)₃ results in a highly efficient reaction, thus enabling unstable NH imines to serve as substrates.

Herein is reported the catalytic, visible light-promoted, decarboxylative halogenation (bromination, chlorination, and iodination) of aliphatic carboxylic acids. This operationally-simple reaction tolerates a range of functional groups, proceeds at room temperature, and is redox neutral. By employing an iridium photocatalyst in concert with a halogen atom source, the use of stoichiometric metals such as silver, mercury, thallium, and lead can be circumvented. This reaction grants access to valuable synthetic building blocks from the large pool of cheap, readily available carboxylic acids.

The first trichloromethylthiolation of a broad range of indoles and pyrroles is reported employing bench-stable N-trichloromethylthiosaccharin as reagent. This methodology is highly regioselective, exhibits high functional group tolerance, and provides access to two previously unknown classes of potentially bioactive compounds.

Herein, we report a new visible-light-promoted strategy to access radical trifluoromethylthiolation reactions by combining halide and photoredox catalysis. This approach allows for the synthesis of vinyl–SCF₃ compounds of relevance in pharmaceutical chemistry directly from alkenes under mild conditions with irradiation from household light sources. Furthermore, alkyl–SCF₃-containing cyclic ketone and oxindole derivatives can be accessed by radical-polar crossover semi-pinacol and cyclization processes. Inexpensive halide salts play a crucial role in activating the trifluoromethylthiolating reagent towards photoredox catalysis and aid the formation of the SCF₃ radical.

Described herein is a new and straightforward decarboxylative di- and trifluoromethylthiolation of alkyl carboxylic acids promoted by visible light. This approach enables the synthesis of biologically relevant alkyl SCF₂H and SCF₃ compounds from cheap and abundant carboxylic acids. The method is operationally simple, using irradiation from household light sources, and its mild reaction conditions make it tolerant of a range of functional groups. The strategy employs electrophilic phthalimide-derived di- and trifluoromethylthiolation reagents and exploits the ability of the imidyl radical to carry a radical chain.

Highly selective tandem nucleophilic addition/cross-coupling reactions of alkynes have been developed using visible-light-promoted dual gold/photoredox catalysis. The simultaneous oxidation of Au^I and coordination of the coupling partner by photo-generated aryl radicals, and the use of catalytically inactive gold precatalysts allows for high levels of selectivity for the cross-coupled products without competing hydrofunctionalization or homocoupling. As demonstrated in representative arylative Meyer–Schuster and hydration reactions, this work expands the scope of dual gold/photoredox catalysis to the largest class of substrates for gold catalysts and benefits from the mild and environmentally attractive nature of visible-light activation.

Herein, we report the oxidative addition of aryldiazonium salts to ligand-supported gold(I) complexes under visible light photoredox conditions. This method provides experimental evidence for the involvement of such a process in dual gold/photoredox-catalyzed reactions and delivers well-defined (C,N)-cyclometalated gold(III) species. The remarkably mild reaction conditions and the ability to widely vary the ancillary ligand make this method a potentially powerful synthetic tool to access diverse gold(III) complexes for systematic studies into their properties and reactivity. Initial studies show that these species can undergo chloride abstraction to afford Lewis acidic dicationic gold(III) species.

Eine redoxneutrale Cobalt(III)-katalysierte direkte Synthese von freien Indolen wird durch eine N-N-Bindungsspaltung ermöglicht. Die neu eingeführten Boc-geschützten Hydrazine eröffnen eine nützliche Erweiterung der begrenzten Auswahl an internen oxidierenden dirigierenden Gruppen in der Cobalt(III)-Katalyse. Der Ansatz ist gut mit funktionellen Gruppen verträglich.

Eine neuartige asymmetrische Hydrierung von Vinylthioethern unter Verwendung eines Ruthenium(II)-NHC-Komplexes ermöglicht die effiziente Herstellung optisch aktiver 1,5-Benzothiazepine mit C-S-Bindungen am Stereozentrum. Exzellente Enantioselektivitäten (bis zu 95 % ee) und hohe Ausbeuten (bis zu 99 %) wurden für eine Vielzahl von Substraten mit nützlichen funktionellen Gruppen erhalten. Außerdem konnte diese Methode bei der Synthese des Antidepressivums R-(−)-Thiazesim angewendet werden.

Ein konzeptionell neuartiger mechanismusbasierter Screeningansatz zur schnellen Entdeckung photokatalytischer Reaktionen wird beschrieben. Im Unterschied zu herkömmlichen Screeningmethoden, in denen die gesamte Reaktion betrachtet wird, wird bei diesem Ansatz nur ein einzelner mechanistischer Schritt einer katalytischen Reaktion analysiert. Durch Verwendung von Lumineszenzspektroskopie zur Identifizierung des Quenching-Schlüsselschritts in photokatalytischen Reaktionen wurden in einem initialen Screening von 100 Komponenten zwei vielversprechende Substratklassen identifiziert. Ein zweites, fokussierteres Screening lieferte mechanistische Einblicke, die zur Entwicklung von Proof-of-Concept-Reaktionen verwendet wurden. Zusammenfassend erleichtert diese schnelle und intuitive Herangehensweise die Entdeckung und Entwicklung neuer photokatalytischer Reaktionen.

Eine einfache Route zur Synthese von Isochinolin-3-onen durch Kooperation von B(C₆F₅)₃- und Cp*Co^III-katalysierter C-H-Bindungsaktivierung von Iminen mit Diazoverbindungen wird beschrieben. Der Einsatz von katalytischen Mengen an B(C₆F₅)₃ ermöglicht eine hocheffiziente Reaktion, sodass selbst labile NH-Imine als Substrate eingesetzt werden können.

The first Cp*Rh^III-catalyzed arylation of unactivated C(sp³)H bonds is presented. The unactivated primary C(sp³)H bond of 2-alkylpyridines can be activated by Rh^III and further reacts with triarylboroxines to efficiently build new C(sp³)aryl bonds. The methodology also provides a facile and efficient synthesis of unsymmetrical triarylmethanes by Rh^III-catalyzed C(sp³)H arylation of diarylmethanes.

Die erste Cp*Rh^III-katalysierte Arylierung nichtaktivierter C(sp³)-H-Bindungen wird vorgestellt. Nichtaktivierte primäre C(sp³)-H-Bindungen von 2-Alkylpyridinen können mit Rh^III aktiviert und mit Triarylboroxinen umgesetzt werden, um neue C(sp³)-Aryl-Bindungen zu knüpfen. Die entwickelte Methode erlaubt auch die einfache Synthese unsymmetrischer Triarylmethane durch Rh^III-katalysierte C(sp³)-H-Arylierung von Diarylmethanen.

Wir stellen eine Rh^III-katalysierte C-H-Aktivierung/Abfangcyclisierung vor, an der eine nukleophile Addition einer C(sp³)-Rh-Spezies an polarisierte Doppelbindungen beteiligt ist. Dies ist die erste intermolekulare katalytische Methode zur direkten Synthese von 1-Aminoindolinen mit großer Substratbreite und unter milden Reaktionsbedingungen.

Die erste generelle Methode zur direkten Thiolierung elektronenreicher Heteroarene wird vorgestellt. Sie nutzt den kommerziell erhältlichen Heterogenkatalysator Pd/Al₂O₃ und CuCl₂. Die Methode eröffnet einen einfachen Zugang zu solchen wertvollen Verbindungen. Mechanistische Experimente deuten auf ein heterogenkatalytisches System hin, in dem beide Metalle eine komplementäre Rolle bei der Bildung der thiolierten Produkte spielen.

Eine neuartige durch sichtbares Licht vermittelte Photoredox-katalysierte Semipinakol-Umlagerung wurde entwickelt, die über eine 1,2-Alkylverschiebung verläuft. In dieser Transformation schließt sich der Trifluormethylierung einer CC-Bindung von α-(1-Hydroxycycloalkyl)-substituierten Styrolderivaten eine Ringerweiterung der 1-Hydroxycycloalkylgruppe an, um neue Cycloalkanone mit quartären, ausschließlich C-substituierten Stereozentren aufzubauen. Die Reaktion verläuft über einen radikalisch-polaren Crossover-Mechanismus mit Trifluormethylierung (radikalisch) und Ringerweiterung (ionisch) in einer Transformation.

Eine enantioselektive intramolekulare Hydroacylierung mit einem N-heterocyclischen Carben (NHC) als Katalysator ermöglicht die Bildung von cyclischen Ketonen aus nichtaktivierten Olefin-substituierten Aldehyden (bis zu 99 % ee). Darüber hinaus wurden zum ersten Mal aliphatische Aldehyde in einer effizienten NHC-katalysierten Hydroacylierung eingesetzt.

Eine durch sichtbares Licht vermittelte Synthese von wertvollen, polycyclischen Indolizin-Heterocyclen aus leicht zugänglichen bromierten Pyridinen und Enolcarbamaten wurde entwickelt. Dieser Prozess, welcher bei Raumtemperatur unter Bestrahlung mit sichtbarem Licht stattfindet, läuft auch ohne die Zugabe eines externen Photokatalysators ab. Mechanistische Experimente deuten darauf hin, dass die Indolizinprodukte ihre eigene Bildung beschleunigen können. Zudem sind sie in der Lage, andere durch sichtbares Licht vermittelte Reaktionen zu beschleunigen.

A Rh^III-catalyzed C–H activation/cyclative capture approach, involving a nucleophilic addition of C(sp³)–Rh species to polarized double bonds is reported. This constitutes the first intermolecular catalytic method to directly access 1-aminoindolines with a broad substituent scope under mild conditions.

A visible-light-mediated photoredox-catalyzed semipinacol-type rearrangement proceeding via 1,2 alkyl migration was developed. In this transformation, trifluoromethylation of the CC bond of α-(1-hydroxycycloalkyl)-substituted styrene derivatives is followed by ring expansion of the 1-hydroxycycloalkyl group to deliver novel cycloalkanones with all-carbon quaternary centers. The reaction proceeds via a radical–polar mechanism, with trifluoromethylation (radical) and ring expansion (ionic) occurring in the same transformation.

A highly enantioselective intramolecular N-heterocyclic carbene (NHC)-catalyzed hydroacylation reaction gives access to a range of cyclic ketones from unactivated olefin-substituted aldehydes (up to 99 % ee). Remarkably, aliphatic aldehydes were also transformed efficiently in an NHC-catalyzed hydroacylation reaction for the first time.

A visible-light-mediated synthesis of valuable polycyclic indolizine heterocycles from easily accessed brominated pyridine and enol carbamate derivatives has been developed. This process, which operates at room temperature under irradiation from readily available light sources, does not require the addition of an external photocatalyst. Instead, an investigation into the reaction mechanism indicates that the indolizine products themselves may be in some way involved in mediating and accelerating their own formation. Preliminary studies also show that these simple heterocyclic compounds may be capable of facilitating other visible-light-mediated transformations.

The first general methodology for the direct thiolation of electron-rich heteroarenes was developed by employing Pd/Al₂O₃, a recoverable and commercially available heterogeneous catalyst, and CuCl₂. This method represents an operationally simple approach for the synthesis of these valuable compounds. Preliminary mechanistic studies indicate a heterogeneous catalytic system, in which both metals play a complementary role in the formation of the thiolated products.

Gold nanoparticles (Au NPs) with tailor-made structures and properties are highly desirable for applications in catalysis and sensing. In this context, surface modifications of Au NPs are of particular relevance. Herein, we present a sequential surface modification of Au NPs with Ag^I coordination complexes, which can be converted into Ag⁰-doped Au NPs by simple ligand-exchange reaction. The key innovative element of this surface modification is a multifunctional bioxazoline-based ligand that brings coordinated Ag^I into close proximity to the particle surface.

A general and efficient methodology for the direct transition metal free trifluoromethylthiolation of a broad range of biologically relevant N-heteroarenes is reported employing abundant sodium chloride as the catalyst. This method is operationally simple, exhibits high functional group tolerance, and does not require protecting groups.

A combination of an N-heterocyclic carbene (NHC) ligand and a structurally simple surfactant has been realized, the hybrid surfactant–NHC. The related gold complex was synthesized, fully characterized, and applied in catalysis. This remarkably simple strategy allows, in combination with a co-surfactant, the application of gold catalysis in water.

A series of imidazolium salts bearing two alkyl chains in the backbone of the imidazolium core were synthesized, resembling the structure of lipids. Their antibacterial activity and cytotoxicity were evaluated using Gram-positive and Gram-negative bacteria and eukaryotic cell lines including tumor cells. It is shown that the length of alkyl chains in the backbone is vital for the antibiofilm activities of these lipid-mimicking components. In addition to their biological activity, their surface activity and their membrane interactions are shown by film balance and quartz crystal microbalance (QCM) measurements. The structure–activity relationship indicates that the distinctive chemical structure contributes considerably to the biological activities of this novel class of lipids.

Ein sterisch gehindertes Homoenolat wurde durch NHC-katalysierte, konjugierte Umpolung von β,β-disubstituierten Enalen generiert und in einer direkten, stereoselektiven Anellierung mit Isatinen eingesetzt. Diese Strategie bietet einen effizienten Zugang zu spirocyclischen Oxindolen, die zwei hochsubstituierte, benachbarte, quartäre Stereozentren enthalten. Die Verwendung einer Brønsted-Säure als Cokatalysator erwies sich als entscheidend für sowohl ausgezeichnete Reaktivität als auch hohe Stereoselektivität.

Die vollständig C3-selektive Arylierung von Thiophenen und Benzo[b]thiophenen wurde unter Verwendung von Pd/C als Heterogenkatalysator ohne Ligand und Additive unter milden Reaktionsbedingungen erreicht. Die Praktikabilität dieser Transformation beruht auf ihrer bemerkenswerten Toleranz für funktionelle Gruppen und der Unempfindlichkeit gegen H₂O und Luft. Die Methode ist ebenso anwendbar auf Benzofuran, 1H-Indol und 2-n-Butylfuran und führt zu den entsprechenden C2-arylierten Produkten. Drei-Phasen-, Hg-Vergiftungs- und Filtrationstests deuten in hohem Maße auf eine heterogene katalytisch aktive Spezies hin.

α-Halogenierte und pseudohalogenierte Ketone werden zum ersten Mal als sp³-Kohlenstoff-Elektrophile in der Übergangsmetall-katalysierten C-H-Aktivierung sowie als oxidierte Alkin-Äquivalente in der Rh^III-katalysierten redoxneutralen Anellierung zur Herstellung verschiedener N-Heterocyclen eingesetzt. Die vorgestellte Methode ist effizient und skalierbar. Durch die milden Reaktionsbedindungen wird eine weite Zahl an funktionellen Gruppen toleriert.

Eine enantioselektive Hydrierung disubstituierter Furane in Gegenwart eines chiralen Rutheniumkatalysators mit N-heterocyclischem Carbenliganden überführt Furane in wertvolle enantiomerenangereicherte, disubstituierte Tetrahydrofurane.

Die Reaktivität und Selektivität von 1,3-Diinen in der übergangsmetallkatalysierten C-H-Aktivierung wurden genutzt, um zügig vielfältige polysubstituierte Bisheterocyclen aufzubauen, die bedeutend, aber schwer zugänglich sind. Mit der C-H-Aktivierungs/1,3-Diin-Strategie überwanden wir die Hürden hinsichtlich der Selektivität (Chemo- und Regioselektivität sowie Mono-/Dianellierung) und erhielten sieben Arten von benachbarten Bisheterocyclen durch Knüpfung von vier strategischen Bindungen mit hoher Effizienz und Selektivität.

An experimentally simple method has been developed to rapidly establish the stability of widely utilized silyl, acetal, and carbamate protecting groups to a given set of reaction conditions. Assessment of up to twelve protecting groups in a single experiment has been demonstrated. Evaluation of this protocol in two unrelated synthetic transformations suggests that this method can be used to select appropriate protecting groups in the design of synthetic routes.

The photoredox activation of organic substrates with visible light is a powerful methodology that generates reactive radical species under very mild conditions. When combined with another catalytic process in a dual catalytic system, novel, visible-light-promoted transformations have been realized that do not proceed using either catalyst in isolation. In this minireview, the state of the art in organic reactions mediated by dual catalytic systems merging photoredox activation with organo-, acid or metal catalysis is discussed.

A sterically hindered homoenolate has been generated by the NHC-catalyzed conjugate umpolung of β,β-disubstituted enals and successfully employed in a facile stereoselective annulation with isatins. The strategy provides efficient access to spirocyclic oxindoles bearing two highly congested contiguous quaternary carbon centers. The use of a Brønsted acid cocatalyst was found to be crucial for guaranteeing both excellent reactivity and high stereoselectivity.

Eine hoch enantioselektive, durch N-heterocyclische Carbene (NHC) katalysierte formale [3+2]-Anellierung von α,β-ungesättigten Aldehyden mit Azaauronen oder Auron wurde entwickelt, die Spiroheterocyclen liefert. Dieses Protokoll stellt einen einzigartigen Zugang zu Spiroheterocyclen mit quartärem Stereozentrum dar.

The completely C3-selective arylation of thiophenes and benzo[b]thiophenes was achieved by using Pd/C as a heterogeneous catalyst without ligands or additives under mild reaction conditions. The practicability of this transformation is demonstrated by notable functional group tolerance and the insensitivity of the reaction to H₂O and air. This method is also applicable to nitrogen- and oxygen-containing heterocycles, yielding the corresponding C2-arylated products. Three-phase tests along with Hg-poisoning and hot-filtration tests suggest that the catalytically active species is heterogeneous in nature.

α-Halo and pseudohalo ketones are used for the first time as C(sp³)-based electrophiles in transition-metal-catalyzed CH activation and as oxidized alkyne equivalents in Rh^III-catalyzed redox-neutral annulations to generate diverse N-heterocycles. This transformation is efficient and scalable. Due to the mild reaction conditions, a variety of functional groups could be tolerated.

An enantioselective hydrogenation of disubstituted furans has been developed by using a chiral ruthenium catalyst with N-heterocyclic carbene ligands. This reaction converts furans into valuable enantioenriched disubstituted tetrahydrofurans.

The reactivity and selectivity of 1,3-diynes in transition-metal-catalyzed CH activation is exploited to quickly assemble diverse polysubstituted bisheterocycles, which are highly important but difficult to access. By using the CH activation/1,3-diyne strategy, we overcame the challenges of selectivity (chemo-, regio-, and mono-/diannulation) and constructed seven kinds of adjacent bisheterocycles through the formation of four strategic bonds with high efficiency and high selectivity.

A highly enantioselective N-heterocyclic carbene (NHC) catalyzed formal [3+2] annulation of α,β-unsaturated aldehydes with azaaurones or aurone generating spiro-heterocycles has been developed. The protocol represents a unique NHC-activation-based approach to access spiro-heterocyclic derivatives bearing a quaternary stereogenic center with high optical purity (up to 95 % ee).

A palladium/Cinchona alkaloid-catalyzed α-arylation between cyclic ketones and aryl halides under phosphine-free conditions is presented. The use of a simple, unmodified Cinchona alkaloid results in high levels of activity and selectivity with up to 93% ee. These enantioinduction levels are comparable or even higher than the ones reported using palladium/BINAP complexes. To the best of our knowledge, this represents the first use of unmodified Cinchona alkaloids as ligands/catalysts in asymmetric transition metal complex-catalyzed cross-coupling reactions.

The rhodium(III)-catalyzed oxidative olefination of 2-aryloxazolines is described and has been employed for the synthesis of olefin-oxazoline ligands (OlefOx). The highly modular synthesis starting from readily available 2-aryloxazolines can be performed under an atmosphere of air as the terminal oxidant with catalytic amounts of copper(II)-acetate.

Based on our recent finding that 2,6-dimethoxyphenyl-substituted NHCs show superior reactivity in the hydroacylation reactions of electron-neutral olefins compared with known NHCs, we now report the syntheses and crystal structures of four highly electron-rich 2,6-dimethoxyphenyl-substituted NHCs and show the increase in efficiency caused by the electron-rich aryl substituent in hydroacylation reactions.

The use of coordinating moieties as directing groups for the functionalization of aromatic CH bonds has become an established tool to enhance reactivity and induce regioselectivity. Nevertheless, with regard to the synthetic applicability of CH activation, there is a growing interest in transformations in which the directing group can be fully abandoned, thus allowing the direct functionalization of simple benzene derivatives. However, this approach requires the disclosure of new strategies to achieve reactivity and to control selectivity. In this review, recent advances in the emerging field of non-chelate-assisted CH activation are discussed, highlighting some of the most intriguing and inspiring examples of induction of reactivity and selectivity.

Der Einsatz von koordinierenden Gruppen als dirigierende Gruppen ist eine zuverlässige Methode zur Kontrolle von Reaktivität und Selektivität bei der Aktivierung von Aryl-C-H-Bindungen. Im Hinblick auf die Anwendbarkeit von C-H-Aktivierungen in der Synthese besteht derzeit ein großes Interesse daran, Reaktionen zu entwickeln, in denen völlig auf dirigierende Gruppen verzichtet werden kann und somit die Funktionalisierung einfacher Benzolderivate möglich wird. Dieser Ansatz erfordert jedoch neue Strategien zur Reaktivitäts- und Selektivitätskontrolle. In diesem Kurzaufsatz werden aktuelle Fortschritte in dem noch jungen Gebiet der nicht-chelatvermittelten C-H-Aktivierung diskutiert, wobei einige inspirierende Beispiele zur Reaktivitäts- und Selektivitätsinduktion hervorgehoben werden.

A family of thiazolium salt derived N-heterocyclic carbenes (NHCs) bearing sterically demanding aryl substituents on the nitrogen and with varying backbone substitution patterns have been synthesized. Investigation of the catalytic activity of these NHCs in a number of benzoin-type coupling reactions revealed markedly different levels of reactivity and selectivity. To elucidate the underlying factors leading to differences in reactivity, a study of the electronic and steric properties of these NHC catalysts was conducted. By using the best catalyst in this study, the intermolecular cross-benzoin condensation reaction was explored in more detail.

The direct Pd-catalyzed oxidative coupling of two CH-bonds within N-aryl-enamines 1 allows the efficient formation of differently substituted indoles 2. In this cross-dehydrogenative coupling, many different functional groups are tolerated and the starting material N-aryl-enamines 1 can be easily prepared in one step from commercially available anilines. In addition, the whole sequence can also be run in a one-pot fashion. Optimization data, mechanistic insight, substrate scope, and applications are reported in this full paper.

Chiral metal–organic frameworks with a three-dimensional network structure and wide-open pores (>30 Å) were obtained by using chiral trifunctional linkers and multinuclear zinc clusters. The linkers, H₃ChirBTB-n, consist of a 4,4′,4′′-benzene-1,3,5-triyltribenzoate (BTB) backbone decorated with chiral oxazolidinone substituents. The size and polarity of these substituents determines the network topology formed under solvothermal synthesis conditions. The resulting chiral MOFs adsorb even large molecules from solution. Moreover, they are highly active Lewis acid catalysts in the Mukaiyama aldol reaction. Due to their chiral functionalization, they show significant levels of enantioselectivity, thereby proving the validity of the modular design concept employed.

The stereoselective hydrogenation of auxiliary-substituted quinolines was used to build up saturated and partially saturated heterocycles. In a first step, the formation and diastereoselective hydrogenation of 2-oxazolidinone-substituted quinolines to 5,6,7,8-tetrahydroquinolines is reported. In this unprecedented process, stereocenters on the carbocyclic quinoline ring were formed with a dr of up to 89:11. Platinum oxide as a catalyst and trifluoroacetic acid as a solvent were found to be optimal for high levels of chemo- and stereoselectivity in this step. In a second hydrogenation step, the completely saturated decahydroquinolines with 4 newly formed stereocenters were obtained with enantioselectivities of up to 99%. Rhodium on carbon as a catalyst and acetic acid as a solvent gave the best results for this hydrogenation and allowed a traceless cleavage of the chiral auxiliary. Thus, this new method allows an efficient stereoselective synthesis of valuable 5,6,7,8-tetrahydro- and decahydroquinoline products.

Die Quantifizierung und Variation der charakteristischen Eigenschaften von Ligandenklassen ist ein spannendes und lohnenswertes Forschungsgebiet. N-heterocyclische Carbene (NHCs) sind dabei wegen ihres Elektronenreichtums und ihrer Struktur von besonderem Interesse. Deshalb haben NHCs weite Verbreitung als Liganden in der Übergangsmetallkatalyse und der Organometallchemie sowie auch direkt in der Organokatalyse gefunden. Hier wird ein Überblick über die physikochemischen Daten (Elektronik, Sterik, Bindung) von NHCs gegeben, die für das Design, die Anwendung und das mechanistische Verständnis dieser Verbindungen in der Katalyse nützlich sind.

Quantification and variation of characteristic properties of different ligand classes is an exciting and rewarding research field. N-Heterocyclic carbenes (NHCs) are of special interest since their electron richness and structure provide a unique class of ligands and organocatalysts. Consequently, they have found widespread application as ligands in transition-metal catalysis and organometallic chemistry, and as organocatalysts in their own right. Herein we provide an overview on physicochemical data (electronics, sterics, bond strength) of NHCs that are essential for the design, application, and mechanistic understanding of NHCs in catalysis.

The N-heterocyclic carbene-catalyzed conjugate umpolung of differently substituted α,β-unsaturated aldehydes is described. Coupling of these compounds with a variety of trifluoromethylated ketones results in the selective formation of fluorinated γ-butyrolactones. Using thiazolium-derived N-heterocyclic carbenes, the unlike stereoisomers are formed predominantly, whereas the imidazol-2-ylidene IMes results in lower selectivities and the preferred formation of the like isomer.