Electrophotocatalytic tri- or difluoromethylative cyclization of alkenes

We describe an electrophotocatalytic tri- or difluoromethylation/cyclization cascade of alkenes with fluoromethanesulfinate salts. This external-oxidant-free oxidative cyclization proceeds under mild electrode potentials yet is robust, and it is applicable to a broad range of alkenes, either activated or unactivated, affording a diverse array of fluoromethylated heterocycles with good functional-group tolerance using the inexpensive photocatalyst eosin Y. Of note is that an unactivated olefin is generally not accommodated by previous oxidative cyclization of alkenes unless a strong chemical oxidant is present. The protocol is amenable to the late-stage diversification of complex molecular architectures as well as a gram-scale synthesis, and sunlight could serve as the light source. Preliminary mechanistic studies suggest the merger of electrolysis with the reductive quenching photocatalytic cycle of eosin Y.