Highly diastereoselective multicomponent synthesis of 2-piperidone-sub- stituted pyridinium salts with three and four stereogenic centers

A novel four-component (five-molecular) diastereoselective synthesis of pyridinium salts of 2-piperidinones is reported. The Knoevenagel-Michael-Mannich cascade of reactions of aromatic aldehydes (2 eq.), nitriles, pyridinium ylides and ammonium acetate in ethanol provides convenient access to 1-((3R*,4S*,6R*)-5,5-dicyano-2-oxo-4,6-diarylpiperidin-3-yl)pyridin-1-ium halogenides with three stereocenters (55-85 % yields) or 1(3R*,4S*,5S*,6R*)-(5-cyano-5-(alkoxycarbonyl)-2-oxo-4,6-diarylpiperidin-3-yl)pyridin-1-ium halogenides with four stereocenters (56-84 % yields).