Divergent functionalization of alkenes enabled by photoredox activation of CDFA and α-halo carboxylic acids

Abstract

Herein we present our studies on the solvent-controlled difunctionalization of alkenes utilizing chlorodifluoroacetic acid (CDFA) and α-halo carboxylic acids for the synthesis of γ-lactones, γ-lactams and α,α-difluoroesters. Mechanistic insights revealed that photocatalytic reductive mesolytic cleavage of the C–X bond delivers elusive α-carboxyl alkyl radicals. In the presence of an olefin molecule, this species acts as a unique bifunctional intermediate allowing for stipulated formation of C–O, C–N and C–H bonds on Giese-type adducts via single electron transfer (SET) or hydrogen atom transfer (HAT) events. These protocols exhibit great efficiency across a broad spectrum of readily available α-halo carboxylic acids and are amenable to scalability in both batch and flow. To demonstrate the versatility of this concept, the synthesis of (±)-boivinianin A, its fluorinated analog and eupomatilone-6 natural products was successfully accomplished.