Visible-Light Photoredox-Catalyzed Acyl Lactonization of Alkenes with Acyl Chlorides

A photocatalytic acyl lactonization of unsaturated carboxylic acids using simple and inexpensive acyl chlorides has been developed for a modular synthesis of acyl lactones. Significantly, the simple protocol could allow an efficient construction of biologically important phthalide framework. The transformation could be extended to a wide variety of unsaturated carboxylic acids, including substituted 2-vinyl benzoic acids and different types of alkenoic acids. Moreover, a series of aroyl, heteroaroyl chlorides could serve as coupling partners. Notably, functional groups including MeO, F, Cl and Br could survive. It is believed that acyl radicals generated from acyl chlorides under photoredox catalysis reacted with alkenes via atom-transfer radical addition (ATRA) and triggered subsequent lactonization in the process. Preliminary mechanistic investigations revealed that the transformation probably proceeded through a free radical pathway.