General procedure for the synthesis of 3-methoxypyridazine from 6-methoxy-3-chloropyridazine: 3-chloro-6-methoxypyridazine (3.60 g, 24.90 mmol), 10% Pd/C (1.590 g, 1.49 mmol), and ammonium formate (3.14 g, 49.81 mmol) were dissolved in methanol (20 mL) at room temperature and the reaction was stirred for 30 minutes. Upon completion of the reaction, the mixture was filtered through diatomaceous earth to remove the Pd/C catalyst. Subsequently, the filtrate was concentrated to dryness under reduced pressure. The resulting residue was dissolved in dichloromethane, washed once with water, dried over anhydrous magnesium sulfate, filtered and concentrated again under reduced pressure to give the title compound 3-methoxypyridazine in brown liquid form (2.41 g, 88% yield, 95% purity). The crude product could be directly used in the subsequent reaction without further purification. The product was confirmed by 1H NMR (300 MHz, chloroform-d): δ 8.83 (dd, J = 4.4, 1.3 Hz, 1H), 7.35 (dd, J = 8.9, 4.4 Hz, 1H), 6.97 (dd, J = 8.9, 1.3 Hz, 1H), 4.14 (s, 3H). Mass spectra (APCI) showed m/z = 152 (M + ACN + H). HPLC analysis showed a retention time of 0.43 min.
