Conversion of α,β-Unsaturated Aldehydes into Saturated Esters: An Umpolung Reaction Catalyzed by Nucleophilic Carbenes
journal contributionposted on 03.03.2005, 00:00 by Audrey Chan, Karl A. Scheidt
N-Heterocyclic carbenes derived from benzimidazolium salts are effective catalysts for generating homoenolate species from α,β-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 α,β-unsaturated aldehyde into a saturated ester. A kinetic resolution of secondary alcohols can be achieved using chiral imidazoylidene catalysts.