Asymmetric N‑Heterocyclic Carbene (NHC)-Catalyzed Annulation of Modified Enals with Enolizable Aldehydes

N-Heterocyclic carbene (NHC)-catalyzed highly enantioselective lactonization of modified enals with enolizable aldehydes, proceeding via the α,β-unsaturated acylazolium intermediates, is reported. The reaction results in the asymmetric synthesis of synthetically important 4,5-disubstituted dihydropyranones