A suspension of 5-methoxy-3-(1-phenyl-1H-pyrazol-5-yl)pyridazin-4-ol (60 mg), 2-fluoropyridine (65 mg) and cesium carbonate (364 mg) in NMP (2 mL) was stirred at 100° C. for 3 days, 1M hydrochloric acid was added thereto, and the mixture was extracted with ethyl acetate. The extract was dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The residue was purified by basic silica gel column chromatography (ethyl acetate/methanol) to give the title compound (20 mg).
