Photocatalytic Aldehyde C−H Bond Phosphonioethylation with Vinylphosphonium Bromide

Abstract Photocatalytic C−H bond phosphonioethylation of aldehydes with vinylphosphonium bromide has been developed. Various β‐phosphonioalkylketones are synthesized from readily available aldehydes under neutral conditions. Mechanistic studies suggest that C−H activation of aldehydes occurs through hydrogen‐atom transfer by a bromine radical and that an alcoholic additive, which showed marked effects in increasing the efficiency of the reaction, is involved in the reaction as a proton source.