Recent advances in studying the mechanism of phospha-Michael addition of tertiary phosphines to electron-deficient alkenes on the basis of kinetic isotope effects

Abstract

The previously proposed mechanism for phospha-Michael addition of tertiary phosphines to electron-deficient alkenes has been amended according to the secondary kinetic isotope effects provided by α-deuterated activated alkenes. The data obtained have shown that rate-determining protonation of intermediate phosphonium zwitterion proceeds not directly at its carbanionic center but first at a heteroatom of the attached electron-withdrawing group, with subsequent isomerization of the enolic/eniminic intermediate to stable keto-/cyanophosphonium product.