Theoretical investigation of the reaction of dialkylzincs with alpha-alkoxycarbonyl radicals. Evaluation of alpha-bromoacrylates as radical acceptors in radical-polar crossover processes

摘要

The evaluation of ethyl alpha-bromoacrylate as radical acceptor in dialkylzinc radical-polar cascades addresses the question of the parameters controlling homolytic substitution at zinc by alpha-alcoxycarbonyl radicals. Under non-degassed medium ethyl alpha-bromoacrylate reacts with diethylzinc to give a bromo-cydopropane. The reaction involves successively radical addition, S(H)2 at zinc, conjugate addition of the resulting enolate to the electrophilic substrate and ring closure. Theoretical calculations were performed to get a better insight into the detailed mechanism. They highlight the impact of zinc(II) chelation on the formal SH2 step. Additional experiments performed in the presence of other electrophiles aldehydes and acylsilanes are discussed. (C) 2015 Elsevier Ltd. All rights reserved.