Electrochemically Induced Ring-Opening/Friedel-Crafts Arylation of Chalcone Epoxides Catalyzed by a Triarylimidazole Redox Mediator

The indirect anodic oxidation of chalcone epoxides in the presence of electron-rich heteroarenes mediated by a triarylimidazole (Med) was investigated by cyclic voltammetry (CV) and controlled potential electrolysis. The CV results indicate that a homogeneous electron transfer between Med(center dot+) and chalcone epoxides is facilitated by an electron-rich heteroarene that serves as an arylation reagent. The preparative scale electrolysis generated epoxide-ring-opened/Friedel-Crafts arylation products in moderate to good yields. The fact that only a catalytic amount of charge was required suggests that Med(center dot+) initiates a chain reaction. In addition, overoxidation of the products is avoided even though their oxidation potential is less than that of the starting chalcone epoxides.