Highly stereoselective Michael addition of azlactones to electron-deficient triple bonds under P-spiro chiral iminophosphorane catalysis: importance of protonation pathway

A catalyst-controlled, geometrically divergent asymmetric Michael addition of azlactones to methyl propiolate has been achieved under the catalysis of P-spiro chiral triaminoiminophosphoranes. An uncommon O-protonation of the intermediary allenic enolate is proposed to rationalize geometric control and its validity is proven by the development of highly Z- and enantioselective Michael addition of azlactones to cyanoacetylene with broad substrate scope.