An unexpected N-heterocyclic carbene-catalyzed esterification of α,β-unsaturated aldehydes including aromatic aldehydes with reactive cinnamyl bromides in the presence of air oxygen or MnO(2) as an oxidant is described. In the presence of oxygen, halogenated and electron-deficient aldehydes react smoothly to furnish esters in good yields. Great efforts have been made on mechanistic studies to deduce a plausible mechanism, based on the experimental results and isotopic labeling experiment.

N-Heterocyclic Carbene Mediated Oxidative Esterification of Aldehydes: Ester Formation and Mechanistic Studies. -The carbene generated from BIM efficiently promotes the esterification of aromatic and conjugated aldehydes with cinnamyl and benzyl bromides. The mechanism is discussed. -(MAJI, B.; VEDACHALAN, S.; GE, X.; CAI, S.; LIU*, X.-W.; J. Org. Chem. 76 (2011) 9, 3016-3023, http://dx.