Allylic Substitution by Carbon Nucleophiles on 4-Bromo-4-methyl-2-pentenoate: Anti-Michael Regioselectivity.

Abstract The reaction of carbanions α-to nitriles with tertiary bromoester 1 does not give cyclopropanes, whatever the reaction conditions, while Li enolate of methyl phenylacetate does, in THF or THF-Et2O. From lithiated aminonitriles 5, in THF-HMPA, the reaction leads to a mixture of SN and SN' products in equal amounts via a radical process. From arylaceto- and propionitriles 4 whatever the conditions, and from methyl phenylacetate enolate 16, either associated to Li in THF-HMPA or to K in THF, SN' anti-Michael products are predominantly formed via a concerted inner sphere process, showing thus the possibility of a polar-SET mechanistic spectrum from a single electrophilic reagent.