Chiral Amine‐Catalyzed Enantioselective Cascade Aza–Ene‐Type Cyclization Reactions

A new asymmetric cascade aza–ene-type cyclization process has been developed. The cascade reaction of α,β-unsaturated aldehydes with enamides is efficiently catalyzed by simple chiral diphenylprolinol–TMS ether with high enantioselectivity to afford synthetically useful enantioenriched six-membered ring enamide hemiaminals (see scheme, DNBA=2,4-dinitrobenzoic acid). A multistep imminium/enamine transformation involved in the cascade sequence is described for the first time.