Condensation Reactions of 3-Oxo-2-arylhydrazonopropanals with Active Methylene Reagents: Formation of 2-Hydroxy- and 2-Amino-6-substituted-5-arylazonicotinates and Pyrido[3,2-c]cinnolines via 6π-Electrocyclization Reactions

3-Oxo-3-phenyl-2-(p-tolylhydrazono)propanal (1a) undergoes condensation with ethyl cyanoacetate in acetic acid in the presence of ammonium acetate to yield either 2-hydroxy-6-phenyl-5-p-tolylazonicotinic acid ethyl ester (6a) or 2-amino-6-phenyl-5-p-tolyl-azonicotinic acid ethyl ester (8), depending on the reaction conditions. Similarly, other 3-oxo-3-aryl-2-arylhydrazonopropanals 1a,b condense with active methylene nitriles 2c,d to yield arylazonicotinates 6b,c. In contrast, 2-[(4-nitrophenyl)-hydrazono]-3-oxo-3-phenyl-propanal (1c) reacts with ethyl cyanoacetate to yield ethyl 6-(4-nitrophenyl)-2-oxo-2,6-dihydropyrido[3,2–c]cinnoline-3-carboxylate (11), via a novel 6π-electrocyclization pathway. Finally, 3-oxo-2-(phenylhydrazono)-3-p-tolylpropanal (1d) condenses with 2a–c to yield pyridazinones 13a–c.