Protonation of Homoenolate Equivalents Generated by N-Heterocyclic Carbenes

Abstract

Homoenolate equivalents are generated by Lewis basic N-heterocyclic carbene catalysts and then protonated to generate efficiently saturated esters from unsaturated aldehydes. This reactivity is extended to the generation of β-acylvinyl anions from alkynyl aldehydes. The asymmetric protonation of a homoenolate equivalent generated from a β,β-disubstituted aldehyde can be accomplished with a chiral N-heterocyclic carbene.

Figure 1

Chiral NHC precursors

Scheme 1

Homoenolate generation and protonation with NHC catalysis

Scheme 2

Reaction pathway for homoenolate protonation

Scheme 3

Kinetic resolution of 1-phenylethanol

Scheme 4

Generation of oxidized side product 23