Novel Regioselectivity: Three-Component Cascade Synthesis of Unsymmetrical 1,4- and 1,2-Dihydropyridines

The three-component sequential reaction of α,β-unsaturated aldehydes, amines, and enaminones proceeded smoothly to give 1,3,4-trisubstituted 1,4-dihydropyridines in aqueous DMF. Moreover, the unexpected regioselective formation of 1,2-dihydropyridines has been observed for the first time in such an approach. On the basis of a systematic study, the novel regioselectivity could be assigned both to steric and electronic effects originating from the amine partner.