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