N-Heterocyclic Carbene/Lewis Acid Catalyzed Enantioselective Aerobic Annulation of α,β-Unsaturated Aldehydes with 1,3-Dicarbonyl Compounds.

A novel and efficient aerobic asymmetric cyclization reaction of cinnamaldehydes and 1,3-dicarbonyl compounds through oxidative NHC-catalysis has been developed, and it allows the synthesis of a wide range of enantiomeric enriched dihydropyranone derivatives in good yields with good to excellent enantioselectivities. Various α,β-unsaturated aldehydes with aliphatic and aromatic substitution groups and 1,3-dicarbonyl compounds were well tolerated. The air was directly used as the oxidant, which made this asymmetric cyclization reaction in a highly efficient, cheap, and green manner.