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We disclose a catalytic photoredox carbobromination of unactivated alkenes with α-bromocarbonyl compounds under blue-light-emitting diode (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 the 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+).
Singh et al. (Fri,) studied this question.