MECHANISM AND PRODUCTS OF ELECTROCHEMICAL REDUCTION OF 4-(NITROPHENYL) SUBSTITUTED 1,4-DIHYDROPYRIDINES

Electrochemical reduction of isomeric 4-(nitrophenyl)-1,4-dihydropyridines (I) on mercury and solid electrodes leads to free radicals of the nitro- and nitrosobenzene type as evidenced by ESR spectroscopy. The dihydropyridine cycle undergoes reduction only in cases of N-substituted para- and meta-nitrophenyl derivatives of 1,4-dihydropyridine. 1,6-Dimethyl-3,5-dicyano-4-(para-, meta-nitrophenyl)-2-pyridonemethide (VIa, b) was identified as intermediate. The primary and secondary chemical reactions occurring during electrochemical reduction of the title compounds are discussed. The electroreduction does not involve the occurrence of an intramolecular redox system between the 1,4-dihydropyridine and nitrophenyl moieties in the molecule.