Conversion of alpha,beta-unsaturated aldehydes into saturated esters: an Umpolung reaction catalyzed by nucleophilic carbenes.
N-Heterocyclic carbenes derived from benzimidazolium salts are effective catalysts for generating homoenolate species from alpha,beta-unsaturated aldehydes. These nucleophilic intermediates can be protonated, and the resulting activated carbonyl unit is trapped with an alcohol nucleophile, thereby promoting a highly efficient conversion of an alpha,beta-unsaturated aldehyde into a saturated ester. A kinetic resolution of secondary alcohols can be achieved using chiral imidazoylidene catalysts. [reaction: see text]
Chan
Audrey
A
Department of Chemistry, Northwestern University, Evanston, IL 60208, USA.
Scheidt
Karl A
KA