Iminium ion-mediated cyclizations of 4-aryl-1,4-dihydropyridines. Alternate cyclization pathways

Acid-catalyzed cyclization of dimethyl 2,6-dimethyl-4-[(2-ethenyl-5-methoxy)phenyl]-1,4-dihydropyridine-3,5-dicarboxy-late affords novel products via competing intramolecular processes. The present mechanistic pathways differ from previous iminium ion-mediated cycloadditions, to afford conformationally constrained dihydropyridine analogs for study as calcium antagonists. These results illustrate the ability of the dihydropyridine nucleus to function as either a nucleophile or an electrophile, depending upon substituents in the aryl ring.