Some reactions with 6-(biphenyl)-4-(5-oxo-1,3-diphenyl-2-pyrazolin-4-yl)-4,5-dihydropyridazin-3-(2H) ones

4-biphenyl-4-oxo-2-butenoic acid (1) reacted with 1,3-diphenyl-2-pyrazolin-5-one (2) to give 4-biphenyl-4-oxo-2-(5-oxo-1,3-diphenyl-2-pyrazolin-4-yl) butanoic acid (3) The condensation of (3) with hydrazines affords the corresponding pyridazinones (4, 5). Reaction of pyridazinone (4) with POCl 3 gave the chloropyridazine derivative (7) which was subjected to further studies with hydrazine hydrate, aromatic amines, anthranilic acid, thiourea and sulfa drugs to give compounds (8-15). Reaction of pyridazinone (4) with phosphorus pentasulfide gave the corresponding thiopyridazine derivative (16). The in-vitro antibacterial screening revealed that some of the new compounds possess activity against Gram-positive, Gram-negative bacteria and fungi.