Saccharin-catalyzed multicomponent cascade reactions for the synthesis of 1,2,3,4,6-pentasubstituted piperidines

A convenient and efficient method is developed for the synthesis of 1,2,3,4,6-pentasubstituted piperidines via a three-component, one-pot domino reaction of beta-ketoesters, aromatic aldehydes, and aromatic amines in the presence of a catalytic amount of saccharin in methanol at 40 degrees C. The desired piperidines could be easily collected through simple filtration with excellent diastereoselectivities.