Mechanism of substitution reaction on sp²-carbon center with lithium organocuprate

Theory and experiments suggest that the substitution reaction of a lithium dialkylcuprate(I) with an alkenyl bromide takes place through a π-complex (cuprio(III)cyclopropane) that directly breaks down to the alkenylated product rather than via a conventional three-centered transition state. This mechanism is consistent with the broader mechanistic picture of the organocuprate reactions and accounts for the retentive stereochemistry and the kinetic isotope effect observed in the experiments.