Condensation of thiophenols with aryl halides using metallic copper as a reactant. Intermediation of cuprous thiophenolates

Abstract

The reaction of thiophenol (PhSH) with metallic copper affords CuSPh and H2 through Cu-catalyzed dehydrogenative coupling of PhSH to PhSSPh and ensuing addition of PhSSPh to Cu. Condensation between thiophenols (ArSH) and aryl iodides or bromides (Ar′X) in the presence of Cu affords diaryl sulfides (ArSAr′) in good or moderate yields (ArSH + Ar′X + Cu → ArSAr′ + CuX + 1/2H2). Use of alkyl iodides (RI), instead of Ar′X, affords alkyl aryl sulfides (ArSR) in good yields. These condensations are considered to proceed mainly through (1) copper-catalyzed dehydrogenative coupling of ArSH to ArSSAr with evolution of H2, (2) addition of ArSSAr to Cu giving CuSAr, and (3) coupling of CuSAr with Ar′X giving ArSAr′ and CuX; temperature dependence of products, time course of the reaction, the reaction of PhSSPh with Cu, and the reaction of Ar′X with CuSPh support this view. Use of copper oxides (Cu2O and CuO), instead of Cu, also affords diaryl sulfides in good or moderate yields.