A mechanistic investigation into the zinc carbenoid-mediated homologation reaction by DFT methods: is a classical donor-acceptor cyclopropane intermediate involved?

Density functional theory (DFT) is used for examining the zinc carbenoid-mediated homologation reaction of [beta]-keto esters. Pathway B has explained the proposed, but spectroscopically unobservable donor-acceptor cyclopropane intermediate, while the second pathway A has disclosed an alternative to the classical intermediate in that a cyclopropane transition state leads to product.