We disclose a catalytic photoredox carbobromination of unactivated alkenes with α-bromocarbonyl compounds under a blue LED light. The reaction proceeds with α-bromoesters, α-bromonitriles and α-bromo-γ-lactones along with terminal and 1,2-disubstituted internal alkenes. Reactions with indenes and 1,1-disubstituted alkenes generate alkylated alkenes. Mechanistic studies by product selectivity and three-way competitive crossover experiments suggest that the reaction operates by a radical-addition radical-pairing (RARP) mechanism. The catalytic turnover is achieved by a single electron reduction of PC•+ by Br- (or Br3 -), rather than by alkyl radical (R•), and the product is generated by the pairing of Br• (or Br2•-) and R•, instead of the combination of Br- and a carbocation (R+).
Keywords: Carbobromination; Carbohalogenation; Competition; Crossover; Photoredox; Unactivated alkene; α-Bromocarbonyl.