A novel fused tricyclic heterocycles, 1-(5-amino-1,4-diphenyl-1,4-dihydrobenzo[b]pyridazino[4,3f][1,4]thiazepin-3-yl)ethanone was synthesized. The reaction of 1-(2-phenylhydrazono) propan-2- one(1) with substituted 2-benzylidenemalonitriles2(a-e) under reflux condition in EtOH gave the compounds 3(a-e) which on treatment with HCl/HOACafforded the 6-acetyl-5-aryl-3-oxo-2-phenyl2,3,4,5-tetrahydropyridazine-4-carbonitrile4(a-e). Reaction of 4(a-e) with N,N-diethyl aniline and POCl 3 under reflux conditions gave the 6-acetyl-5-aryl-3-chloro-2-phenyl-2,5-dihydropyridazine-4carbonitrile 5(a-e). The reaction of 5(a-e)with 2-aminothiophenol gave 6(a-e). These later products were subsequently cyclized in boiling ethanol and Et N to give the new fused tricyclic heterocyclic compounds 7(a-e). 3

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