Unsymmetric di(heteroaryl) sulfides were synthesized by a rhodium-catalyzed heteroarylthio exchange reaction of heteroaryl aryl ethers and S-(heteroaryl) thioesters. The reaction has broad applicability, giving diverse unsymmetric di(heteroaryl) sulfides containing five- and six-membered heteroarenes. No base is required in this reaction, which has been developed by the judicious design of organic substrates.

A rhodium complex derived from RhH(PPh3)4, dppe, and 4-ethynyltoluene catalyzes the addition reaction of sulfur to norbornenes giving the corresponding thiiranes under acetone reflux conditions. The rhodium complex effectively transfers a sulfur atom to the double bond from sulfur, and exo-adducts are obtained. The reaction is also applicable to (E)-cyclooctene and cyclic allenes. The ring-opening reaction of the thiiranes with lithium aluminium hydride gives the corresponding thiols.

A palladium complex derived from Pd2(dba)3 and tris(2,4,6-trimethoxyphenyl)phosphine catalyzes the addition reaction of thioesters to norbornenes, giving trans-2-acyl -3-organothionorbornanes. The trans-adducts are predominantly obtained with the acyl group at the endo-position and the organothio group at the exo-position. Aroyl and heteroaroyl thioesters as well as alkanoyl thioesters were reacted, including S-(4-tolyl) phenylthioglyoxylate and methyl 2-(4-tolylthio)-2-oxo-acetate.

RhH(PPh3)4 and 1,2-bis(diphenylphosphino)benzene catalyze the reaction of aryl/heteroarylmethyl ketones and aryl heteroaryl ethers giving unsymmetrical diarylmethanes containing one or two heteroarenes in high yields. The reaction does not use alkali metal bases, and therefore does not form large amounts of metal waste.

A palladium complex derived from Pd2(dba)3 and dppp catalyzes the addition reaction of aroyl/heteroaroyl acid anhydrides to norbornenes, giving 2-aroyl/heteroaroyl-3-aroyloxy/heteroaroyloxy-bicyclo[2,2,1]heptanes. The C–O bond of acid anhydride is cleaved, and the aroyl/heteroaroyl and aroyloxy/heteroaroyloxy groups are added to alkenes. trans-Adducts are selectively obtained with the endo-benzoyl group and exo-benzoyloxy group.

A catalyst changes the course of a reaction without affecting the relative thermodynamic stability of substrates and products, and a catalytic reaction must be exergonic in order to obtain high yields of the product and to attain reasonable reaction rates. In the case that the desired reaction is in equilibrium or is endergonic, devices for making products thermodynamically more stable than substrates are needed. In this review, the transition-metal-catalyzed synthesis of organosulfides using a substitution reaction is summarized, where metal inorganic and organic co-substrate/co-product methods are used in developing exergonic reactions.Figure optionsDownload full-size imageDownload as PowerPoint slide

RhH(PPh3)4 and 1,2-bis(diphenylphosphino)benzene (dppBz) catalyze the aryl exchange reaction of polyfluorinated diaryl sulfides. By employing these catalysts, unsymmetrical polyfluorinated diaryl sulfides are synthesized by the reaction of symmetrical polyfluorinated diaryl sulfides and substituted pentafluorobenzenes in the presence of triisopropylsilane.

RhH(PPh3)4 and 1,2-bis(diphenylphosphino)benzene (dppBz) catalyzed the oxidative coupling reaction of aryl benzyl ketones giving 2,3-diaryl-1,4-diketones in high yields. 3,3-Dimethyl-1-methylthio-2-butanone was used as the oxidizing reagent, which was converted to 3,3-dimethyl-2-butanone and dimethyl disulfide. Rhodium enolates were catalytically formed from ketones, which underwent oxidative coupling using an organosulfur reagent.

A rhodium complex catalyzed the reaction of aryl methyl ethers and thioesters giving the corresponding aryl esters and methyl sulfides. S-(p-Chlorophenyl) p-(dimethylamino)benzothioate was used for the reaction of methyl aryl ethers with electron-withdrawing groups, and an S-(p-tolyl) derivative was used for those with electron-donating groups. Polymethoxybenzenes were converted to the esters in a regioselective manner.

In the presence of catalytic amounts of RhH(CO)(PPh3)3 and 1,2-bis(diphenylphosphino)benzene (dppBz), acyl groups were transferred between benzyl ketones and thioesters/aryl esters. The rhodium complex catalyzed the cleavage of ketone CO–C bonds and intermolecular rearrangement giving unsymmetric ketones. The acyl-transfer reaction also occurred with 1-(p-chlorophenyl)-3-(p-cyanophenyl)propane-2-one giving unsymmetric ketones.

Substituted pentafluorobenzenes react with sulfur to give bis(4-substituted 2,3,5,6-tetrafluorophenyl) sulfides in the presence of RhH(PPh3)4, 1,2-bis(diphenylphosphino)benzene (dppBz), and tributylsilane. The reaction proceeds efficiently between room temperature and 80 °C. A comparative study of the reactivities of an organic trisulfide and a tetrasulfide showed notable substrate specificity. Di-tert-butyl tetrasulfide reacted with reactive aryl monofluorides and substituted pentafluorobenzenes. Di-tert-butyl trisulfide reacted with aryl monofluorides. The reactivity was explained on the basis of the difference in S–S bond energy.

In the presence of catalytic amounts of RhH(PPh3)4 and 1,2-bis(diphenylphosphino)ethane (dppe), 1-nitroalkanes reacted with a diaryl disulfide giving 1-arylthio-1-nitroalkanes in air. The equilibrium to form thermodynamically disfavored products was shifted by the rhodium-catalyzed oxidation of thiols to disulfides and water. The thiolation reaction of cyclic nitroalkanes proceeded in high yields provided that suitable diaryl disulfides were employed depending on the substrate: di(p-chlorophenyl) disulfide was used for the thiolation reaction of 1-nitroalkanes, 1-nitrocyclopentane and 1-nitrocycloheptane with acidic α-protons (pKa 16 and 17); di(p-methoxyphenyl) disulfide for 1-nitrocyclobutane and 1-nitrocyclohexane with less acidic α-protons (pKa ca. 18). Related reactivities were observed in the thiolation reactions of malonate and 1,2-diphenylethanone.

A palladium complex derived from Pd2(dba)3 and dppp catalyzes the addition reaction of aroyl/heteroaroyl acid anhydrides to norbornenes, giving 2-aroyl/heteroaroyl-3-aroyloxy/heteroaroyloxy-bicyclo[2,2,1]heptanes. The C–O bond of acid anhydride is cleaved, and the aroyl/heteroaroyl and aroyloxy/heteroaroyloxy groups are added to alkenes. trans-Adducts are selectively obtained with the endo-benzoyl group and exo-benzoyloxy group.

A rhodium complex derived from RhH(PPh3)4, dppe, and 4-ethynyltoluene catalyzes the addition reaction of sulfur to norbornenes giving the corresponding thiiranes under acetone reflux conditions. The rhodium complex effectively transfers a sulfur atom to the double bond from sulfur, and exo-adducts are obtained. The reaction is also applicable to (E)-cyclooctene and cyclic allenes. The ring-opening reaction of the thiiranes with lithium aluminium hydride gives the corresponding thiols.

RhH(PPh3)4 and 1,2-bis(diphenylphosphino)benzene catalyze the reaction of aryl/heteroarylmethyl ketones and aryl heteroaryl ethers giving unsymmetrical diarylmethanes containing one or two heteroarenes in high yields. The reaction does not use alkali metal bases, and therefore does not form large amounts of metal waste.