6-Methyl-3(2H)-pyridazinone (18 g, 163.44 mmol) was mixed with phosphorus tribromide oxide (93.8 g, 327.6 mmol) and the reaction was stirred at 70 °C overnight. Upon completion of the reaction, the reaction mixture was cooled to 40 °C and quenched by slowly pouring it into ice water. Subsequently, the reaction mixture was neutralized with saturated sodium bicarbonate solution (20 mL) and extracted with dichloromethane (100 mL x 3). The organic phases were combined, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford the target product 3-bromo-6-methylpyridazine (8 g, 31% yield). The product was detected by LCMS (ESI), m/z: 173 [M + 1]+. 1H NMR (chloroform-d, Bruker Avance 400MHz) data were as follows: δ 7.86-7.88 (d, 1H, J = 8Hz), 7.52-7.54 (d, 1H, J = 8Hz), 2.55 (s, 3H).
