Reactions with β‐ketodianilides. I. New synthesis of Pyrido[3,4‐c]pyridine Derivatives

Acetonedicarboxylic acid dianiline reacted with malononitrile, ethyl cyanoacetate or benzoylacetonitrile to give (6-amino-5-cyano-1,2-dihydro-2-oxo-1-phenylpyrid-4-yl)-acetanilide (3), (3-cyano-2,6-dioxo-1-phenyl-1,2,5,6-tetrahydropyrid-4-yl)acetanilide (8) or (3-cyano-1,6-dihydro-1,2-diphenyl-6-oxopyrid-4-yl)acetanilide (9). Compounds 3 and 8 could be cyclised into 8-amino-1,6-diphenyl-1,2,4,5,6,7-hexahydro-7-iminopyrido[3,4-c]pyridine-2,5-dione (4) and 7-amino-1,2,3,5,6,8-hexahydro-1,6-diphenylpyrido[3,4-c]pyridine-2,5,8-trione (10) respectively by heating their solutions in dimethylformamide in the presence of triethylamine. Each of 3 and 4 coupled with arenediazonium chlorides to give the corresponding arylhydrazone derivatives (5a–d) and (6a–c), respectively. Condensation of 4 with p-nitrosodimethylaniline yielded 8-amino-4- (p-dimethylaminophenylimino)-1,6-diphenyl-1,2,4,5,6,7-hexahydro-7-iminopyrido[3,4-c]pyridine2,5-dione (7).