Diphenylprolinol Silyl Ether as a Catalyst in an Enantioselective, Catalytic, Formal Aza 3+3 Cycloaddition Reaction for the Formation of Enantioenriched Piperidines

Aza-ene reaction: Diphenylprolinol silyl ether was found to be an effective organocatalyst for the formal aza 3+3 cycloaddition reaction of α,β-unsaturated aldehydes and enecarbamates (see scheme). The reaction proceeds through an asymmetric catalytic ene reaction, isomerization, hydrolysis, and cyclization to afford piperidine derivatives in good yields and excellent enantioselectivities.