Dihydropyridine-based multicomponent reactions. Efficient entry into new tetrahydroquinoline systems through Lewis acid-catalyzed formal [4 + 2] cycloadditions.

The three-component reaction of dihydropyridines, aldehydes, and p-methylaniline efficiently forms highly substituted tetrahydroquinolines in a stereoselective manner through a Lewis acid-catalyzed formal [4 + 2] cycloaddition. InCl(3) and Sc(OTf)(3) are the catalysts of choice for this process. The in situ generation of a reactive 1,4-dihydropyridine through the regioselective nucleophilic addition of cyanide to pyridinium salts allows a one-pot four-component transformation.