Photoinduced Alcoholic α‐C−H Bond Anti‐Markovnikov Addition to Vinylphosphonium Bromides Followed by Wittig Olefination: Two‐Step Protocol for α‐C−H Allylic Alkylation of Alcohols

Abstract Herein reported is a two‐step protocol for the α‐allylic alkylation of alcohols consisting of photocatalytic anti‐Markovnikov addition of the α‐C−H bond of alcohols to vinylphosphonium bromides and subsequent Wittig olefination with aldehydes. The protocol is marked by simplicity of the photoreaction system with a single catalyst and broad scope of alcohols, ranging from readily available chemical feedstocks to functionalized molecules, and is attractive as a synthetic tool. Both primary and secondary alcohols can be functionalized at the α‐C−H bond to produce the corresponding α‐tertiary and quaternary ( E )‐homoallylic alcohols. The mechanistic studies suggest that α‐C−H activation of alcohols occurs through hydrogen atom transfer by a bromine radical, which is photocatalytically generated from a vinylphosphonium bromide.