General procedure for the synthesis of 6-methyl-3(2H)-pyridazinone from 4,5-dihydro-6-methylpyridazin-3(2H)-one: bromine (7.68 g, 48.05 mmol) was added slowly and dropwise to a solution of 6-methyl-4,5-dihydropyridazin-3(2H)-one (9.0 g, 80.26 mmol) in acetic acid (90 mL) at 90 °C. The reaction mixture was stirred continuously at 90 °C for 5-6 hours. Upon completion of the reaction, the excess acetic acid was removed by distillation under reduced pressure. The resulting residue was neutralized with aqueous sodium bicarbonate solution, followed by filtration to collect the solid product. The filter cake was dried to give the title compound 6-methyl-3(2H)-pyridazinone (6.0 g, 68% yield). The structure of the product was confirmed by 1H NMR (300 MHz, DMSO-d6): δ 12.73 (s, 1H), 7.30 (d, J = 9.6 Hz, 1H), 6.80 (d, J = 9.9 Hz, 1H), 2.14 (s, 3H).
