Ethyl 5-amino-3,4-diphenyl-7H-pyrrolo[2,3-c]pyridazine-6-carboxylate (1), ethyl 5-aminofuro[ 2,3-c]pyridazine-6-carboxylate (2) and 5-aminofuro[2,3-c]pyridazine-6-carboxamide (3), are obtained from 4-cyano-5,6-diphenyl-3(2H)-pyridazinone. 5-Acetamido and 5-chloroacetamido derivatives prepared from 1, undergo cyclization on heating to form 2-substituted pyridazino[4',3':4,5]pyrrolo[3,2-d]oxazin-4(5H)-one (5a, b). The reaction of 1 and 2 with hydrazine gave 6-carbohydrazide derivatives (7 a, b). Compound 3 undergoes condensation with acetyl chloride, chloroacetyl chloride, benzoyl chloride, formamide and carbon disulphide to furnish the corresponding pyrimido[4',5' :4,5]furo[2,3-c]pyridazin-4(3 H)-one derivatives. The reaction of 1 with o-aminophenol gave 3,4-diphenyl-11-oxo-10,11-dihydro-12H -pyridazino[ 4',3' :4,5]pyrrolo[3,2-b][1,5]benzoxazepine.