A Sn(OTf)₂-Mediated Diastereoselective Vinylogous Mannich-Type Reaction of Chiral Imines

Yang et al. have reported a stereoselective synthesis of chiral 6-substituted piperidinones and 2-substituted piperidines via Sn(OTf)₂-mediated diastereoselective vinylogous Mannich-type reaction. The reaction began with the condensation of chiral 1-(1-naphthyl)ethylamine with aldehydes. The in situ-generated chiral imines were then treated with the silyl ketene acetal in the presence of Sn(OTf)₂ to give the chiral adducts. Using aldehydes bearing steric bulky residues gave good diastereoselectivities as high as 9:1. The chiral adducts provided the chiral piperidinones and piperidines. Furthermore, they have applied the strategy to a synthesis of (S)-anabasine, which is a tobacco alkaloid.