Abstract The mechanism of Lewis acid catalysed hetero-Michael addition reactions of weakly basic nucleophiles to α, β-unsaturated ketones was investigated. Protons, rather than metal ions, were identified as the active catalysts. Other mechanisms have been ruled out by analyses of side products and of stoichiometric enone–catalyst mixtures and by the use of radical inhibitors. No evidence for the involvement of π-olefin–metal complexes or ...
