Functionally substituted arylhydrazones as building blocks in heterocyclic synthesis: routes to pyridazines and pyridazinoquinazolines

The arylhydrazones 2a-c were prepared via coupling acetoacetic acid with aromatic diazonium salts. These arylhydrazones condensed with ethyl cyanoacetate and malononitrile to yield the acyclic product 4 which cyclised only after long reflux into the pyridazines 5 or 6,11dihydropyridazino[1,6-a]quinazoline-4-carbonitrile 6 depending on the nature of substituent on the aryl moiety. Compound 2b and 2c reacted with ,-unsaturatednitriles 7 to yield the pyridazinoquinazoline 13 and 16 respectively.