Carbon Dioxide Mediated Stereoselective Copper-Catalyzed Reductive Coupling of Alkynes and Thiols

A simple protocol for the stereoselective copper-catalyzed hydrothiolation of alkynes under a CO2 atmosphere has been developed. The stereoselectivity is determined by the presence/absence of a CO2 atmosphere. The reaction system is robust and utilizes inexpensive, readily available substrates. A cyclic alkene/carboxylate copper complex intermediate is proposed as the key step in determining the stereoselectivity, and an equivalent amount of water is found to play an active role as a proton donor.