Evidence for an enolate mechanism in the asymmetric Michael reaction of α,β-unsaturated aldehydes and ketones via a hybrid system of two secondary amine catalysts†
Nariyoshi Umekubo,Takahiro Terunuma,Eunsang Kwon,Yujiro Hayashi
Chemical Science Pub Date : 09/21/2020 00:00:00 , DOI:10.1039/D0SC03359F
Abstract

The key nucleophile was found to be neither an enamine nor an enol, but an enolate in the direct Michael reaction of α,β-unsaturated aldehydes and non-activated ketones catalyzed by two amine catalysts namely diphenylprolinol silyl ether and pyrrolidine. This is a rare example of an enolate from a ketone serving as a key intermediate in the asymmetric organocatalytic reaction involving secondary amine catalysts because the ketone enolates are generally generated using a strong base, and the enamine is a common nucleophile in this type of reaction.

Graphical abstract: Evidence for an enolate mechanism in the asymmetric Michael reaction of α,β-unsaturated aldehydes and ketones via a hybrid system of two secondary amine catalysts