Organophotoredox-Catalyzed Alkene Functionalization Reactions Using α-Bromocarbonyl Compounds

The first example of visible-light organophotoredox-catalyzed carbolactonization reactions of alkenoic acids with α-bromocarbonyl compounds is reported. The excited state of a phosphonium ylide reduces the number of α-bromocarbonyl compounds to generate the corresponding carbon-centered radicals that add to the C═C bond of alkenoic acids. This protocol can be applied to C-H functionalization reactions of 1,1-diphenylethylene or 3-methylindole. Mechanistic studies on the basis of radical and fluorescence quenching experiments support a proposed catalytic cycle for the transformation.