Copper-mediated C-H activation/C-S cross-coupling of heterocycles with thiols.

We report the synthesis of a series of aryl- or alkyl-substituted 2-mercaptobenzothiazoles by direct thiolation of benzothiazoles with aryl or alkyl thiols via copper-mediated aerobic C-H bond activation in the presence of stoichiometric CuI, 2,2'-bipyridine and Na(2)CO(3). We also show that the approach can be extended to thiazole, benzimidazole, and indole substrates. In addition, we present detailed mechanistic investigations on the Cu(I)-mediated direct thiolation reactions. Both computational studies and experimental results reveal that the copper-thiolate complex [(L)Cu(SR)] (L: nitrogen-based bidentate ligand such as 2,2'-bipyridine; R: aryl or alkyl group) is the first reactive intermediate responsible for the observed organic transformation. Furthermore, our computational studies suggest a stepwise reaction mechanism based on a hydrogen atom abstraction pathway, which is more energetically feasible than many other possible pathways including ß-hydride elimination, single electron transfer, hydrogen atom transfer, oxidative addition/reductive elimination, and σ-bond metathesis.

Synthesis of aryl sulfides by decarboxylative C-S cross-couplings.

Without the need for organohalide precursors, the convenient and general synthesis of aryl (or diaryl) sulfides can be achieved by using aryl carboxylic acids and thiols or disulfides for decarboxylative C-S cross-coupling catalyzed by a bimetallic system (see scheme).

One-pot synthesis of amine-substituted aryl sulfides and benzo[b]thiophene derivatives.

A series of amine-substituted aryl sulfides have been synthesized from nitroaryl halides via a simple one-pot procedure involving metal-free C-S cross-coupling and in situ nitro group reduction. Various nitroaryl halides were reacted with thiols in recyclable poly(ethylene glycol) to afford the amine-substituted aryl sulfides in high yield. Additionally, the cross-coupling reactions of nitro- and aldehyde-substituted aryl halides with benzyl thiols under the same reaction conditions were demonstrated to afford benzothiazole and phenylbenzo[b]thiophene derivatives.

Synthesis of vinyl sulfides by copper-catalyzed decarboxylative C-S cross-coupling.

A novel method for the synthesis of vinyl sulfides by the decarboxylative cross-coupling of arylpropiolic acids with thiols using copper(I) salts as catalysts has been developed. In the presence of CuI and Cs(2)CO(3), a variety of thiols reacted with arylpropiolic acids to afford the corresponding vinyl sulfides in good to excellent yields with high stereoselectivity for Z-isomers.

Nanocontact-induced catalytic activation in palladium nanoparticles.

We report the synthesis and catalytic studies of novel palladium nanostructures assembled from small nanoparticles by a surfactant-templated method. These one-dimensional nanomaterials comprise high-density nanocontacts of approximately 1 nm in contact length at the particle-particle interface. In contrast to dispersed Pd nanoparticles ( approximately 5 nm), the polycrystalline palladium nanowires exhibit enhanced ( approximately 200 times) catalytic reactivity towards carbon-carbon cross-couplings under mild conditions. Theoretical modeling studies suggest that the presence of nanocontacts triggers electron transfer and localized charge redistribution in the contact region. The charge redistribution causes the nanocontacts to become highly attractive to charged organic molecules, resulting in the facilitation of organic transformations.