CuI/L-Proline-Catalyzed Synthesis of Vinyl Sulfides in 95% Alcohol

A method for the synthesis of vinyl sulfides using the simple CuI/L-proline as a catalyst system is reported. The best yields were obtained in the 95% ethanol with 10 mol% CuI, 20 mol% L-proline, and 1.2 equiv of K₂CO₃. The amino acids act as base and excellent promoter for the copper-catalyzed coupling reactions, and this protocol tolerates both aromatic and heterocyclic thiols and avoids using other expensive additives.