Photoredox-catalyzed synthesis of trifluoromethylated benzimidazo-fused heterocycles

Abstract

A photoredox-catalyzed trifluoromethylation/cyclization of N-allylbenzimidazoles using eosin Y-Na₂ under visible light affords trifluoromethylated benzimidazo-fused heterocycles. Two complementary protocols are established: Method A employs Togni's II under nitrogen—the first example of this catalyst–reagent combination; Method B utilizes the more economical Langlois reagent under air. The reaction features broad substrate scope and enables unprecedented seven-membered ring formation.