Theoretical investigation of the reaction of dialkylzincs with α-alkoxycarbonyl radicals. Evaluation of α-bromoacrylates as radical acceptors in radical-polar crossover processes. Issue 47 (25th November 2015)

• Record Type: Journal Article
• Authors: Vibert, François; Maury, Julien; Lingua, Hugo; Besson, Eric; Siri, Didier; Bertrand, Michèle P.; Feray, Laurence
• Is Part Of: Tetrahedron. Volume 71:Issue 47(2015)
• Page Start: 8991
• Page End: 9002
• Publication Date: 2015-11-25
• Subjects: Dialkylzinc -- Homolytic substitution -- α-Alkoxy carbonyl radical -- Radical-polar crossover reaction -- Theoretical calculations; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2015.09.045
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: The evaluation of ethyl α-bromoacrylate as radical acceptor in dialkylzinc radical-polar cascades addresses the question of the parameters controlling homolytic substitution at zinc by α-alcoxycarbonyl radicals. Under non-degassed medium ethyl α-bromoacrylate reacts with diethylzinc to give a bromocyclopropane. The reaction involves successively radical addition, SH 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 SH 2 step. Additional experiments performed in the presence of other electrophiles–aldehydes and acylsilanes–are discussed. Graphical abstract: