General procedure for the synthesis of 4-methoxypyridazine from 4-methoxy-3,6-dichloropyridazine: 10% palladium carbon (3 g) catalyst was added to a solution of methanol (500 mL) containing 3,6-dichloro-4-methoxypyridazine (30 g, 167.59 mmol, 1.00 equiv) and ammonium formate (31 g, 491.63 mmol, 2.93 equiv). The reaction mixture was stirred at room temperature and 1 atm overnight. Upon completion of the reaction, the catalyst was removed by filtration and the filtrate was concentrated under vacuum. The concentrated residue was ground in a solvent mixture of dichloromethane and methanol (500 mL, 10:1 v/v) and subsequently filtered to collect the solid. The filtrate was again concentrated under vacuum and the residue was purified by silica gel column chromatography with the eluent being a solvent mixture of ethyl acetate and petroleum ether (the ratio was tapered from 2:1 to 1:1), resulting in 15 g (81% yield) of 4-methoxypyridazine as a brown oil. Thin-layer chromatography (TLC) conditions: the ratio of petroleum ether to ethyl acetate was 2:1, and the Rf value was 0.1.
