Addition of 1 to two moles of phenylhydrazine gives 1,2,4,6-tetraphenyl-(2,3-d)-pyrazolo-5,6-pyridazine-7-one 4 isomer compound 1,2,3,5-tetraphenyl-(2,3-d) pyrazolo-5,6-pyridazine-7-one 5 of 4 was synthesized by the reaction of 2 with phenylhydrazine. 3,4-Diphenyl-(2,3-d)-pyrazolo-(1H,6H)-pyridazine-7-one 6 was also obtained in two different ways. Reaction of 1 and 4-benzoyl-5 phenyl-furan-2,3-dione 3 with hydrazinium hydrate furnished compound 6. The structures of 4,5 and 6 were determined by the (13) C-NMR, IR spectra and elemental analysis. These new isomer and condensed compounds synthesized in this study are important for heterocyclic chemistry.