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

Abstract

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.

Advances in photoinduced radical–polar crossover cyclization (RPCC) of bifunctional alkenes

“…Finally, the lactone 169 is delivered through an intramolecular nucleophilic substitution under base conditions (Scheme 19). 23 In 2014, Koike, Akita, and co-workers discovered a strategy for the highly regio-and diastereoselective synthesis of CF 3substituted lactones from both terminal and internal alkenoic acids by a photoredox catalysis RPCC process. The reaction of alkenoic acids, CF 3 reagents and K 2 CO 3 in MeCN using 5 mol% of [Ru(bpy) 3 ](PF 6 ) 2 as a photoredox catalyst under visible-light irradiation from 425 nm blue LEDs at room temperature could deliver the highly regio-and diastereoselective CF 3 -substituted lactones bearing various functional groups smoothly in moderate-to-excellent yields.…”

“…Finally, the lactone 169 is delivered through an intramolecular nucleophilic substitution under base conditions (Scheme 19). 23…”