Evidence for an enolate mechanism in the asymmetric Michael reaction of α,β-unsaturated aldehydes and ketones <i>via</i> a hybrid system of two secondary amine catalysts
Nariyoshi Umekubo, Takahiro Terunuma, Eunsang Kwon, Yujiro Hayashi
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.
Topics & Concepts
PyrrolidineChemistryEnamineCatalysisNucleophileAmine gas treatingMichael reactionSilyl enol etherEnolOrganic chemistrySilylationMedicinal chemistryAsymmetric Synthesis and CatalysisOrganic Chemistry Cycloaddition ReactionsSynthetic Organic Chemistry Methods