Highly Regioselective Dichalcogenation of Alkenyl Sulfonium Salts to Access 1,1-Dichalcogenalkenes.

An unprecedented geminal olefinic dichalcogenation of alkenyl sulfonium salts with dichalcogenides ArYYAr (Y = S, Se, Te) is reported, providing various trisubstituted 1,1-dichalcogenalkenes [Ar 1 CH = C(YAr 2 ) 2 ] in a highly selective manner under mild and catalyst-free conditions. The key process involves the formation of two geminal olefinic C-Y bonds via sequential C-Y cross-coupling and C-H chalcogenation. A mechanistic rationale is further supported by control experiments and density functional theory calculations.