Cycloaddition of a 1,2-diaza-1,3-butadiene to phenylpropiolic acid: an efficient route to pyridazinoquinolone derivatives

Diazocoupling of dihydroquinolin-4-ones with aryldiazonium nitrates gave the corresponding diazo derivatives, which undergo facile (4+2) cycloaddition reactions with phenylpropiolic acid to afford 2-aryl-4a-methyl-10-oxo-4-phenyl-2,4a,5,10-tetrahydropyridazino[4,3-b]quinoline-3-carboxylic acid derivatives 3. However, with β-nitrostyrene a mixture of three isomeric products 4a–c was obtained.