Formation of thioesters by dehydrogenative coupling of thiols and alcohols with H(2)evolution

Thioesters play important roles in chemistry and biology, but their synthesis generally exhibits a poor atom economy and generates copious waste. We report here the dehydrogenative coupling of alcohols and thiols to yield thioesters and evolve H-2. This waste-free reaction is catalysed by an acridine-based ruthenium pincer complex in hexamethyldisiloxane as the optimal solvent without any additives. Various thioesters were formed in good-to-excellent yields using equivalent amounts of alcohols and thiols in excellent selectivity with hydrogen gas as the only by-product. A plausible mechanism, which involves an outer-sphere dehydrogenation process in which the thiol not only serves as a reactant, but also as an assisting ligand, is proposed based on mechanistic studies and the isolation of intermediates. This system provides a facile, efficient and waste-free synthesis of thioesters.