N-Heterocyclic Carbene CatalyzedCross Coupling of Aromatic Aldehydes with Baylis-HillmanBromides: An Easy Access to α-Arylidene-γ-ketoEsters

N-Heterocyclic carbene catalyzed carbonyl umpolung reaction of aldehydes with Baylis―Hillman (BH) bromides as activated halides were realized for the first time. This intermolecular cross-coupling reaction features the easily available catalyst and mild reaction conditions to provide α-arylidene- γ-keto esters in excellent yields for a wide range of substrates. Thus, the present work opens up a new aspect of the synthetic utility ofBH adducts via the reactivity umpolung of aldehydes.