Synthesis of [1,2,4]triazolo[4,3:1′,6′]pyrimido[4′,5′:3,4]pyridazino[1,6-d] [1,2,4]triazine; a novel tetracyclic system

The condensation reaction of 6-acetyl-3-amino-5-aryl-2-phenyl-2,5-dihydropyridazine-4-carbonitrile with triethyl orthoformate and then with hydrazine hydrate to obtain the new fused bicyclic 4-aryl-5-hydrazinyl-3-(1-hydrazonoethyl)-1-phenyl-1,4-dihydropyrimido[4,5-c]pyridazines via the Dimroth rearrangement is reported. Further cyclisation was achieved by the treatment of latter compounds with triethyl orthoformate to afford several derivatives of a novel tetracyclic fused system [1,2,4]triazolo[4 '',3 '':1',6']pyrimido[4',5':3,4]pyridazino[1,6-d][1,2,4]triazine.