Intramolecular Aza-Michael Reaction

Significance

The highly enantioselective intra­molecular aza-Michael reaction of carbamates 1 bearing pendant α,α-unsaturated aldehydes is reported. α,α-Diaryl prolinol silyl ether 2 in combination with benzoic acid activates the α,β-unsaturated aldehydes via iminium catalysis. After reduction to the alcohol various five- and six-membered heterocycles 3 are obtained in good to excellent enantioselectivities and in moderate to good yields. The method has been applied to the synthesis of three piperidine alkaloids, (+)-Sed­amine, (+)-Allosedamine, and (+)-Coniine, in only three steps from the respective carbamates 1.