1-[2-Fluoro-4-(1H-pyrazol-1-yl)phenyl]-N,5-dimethoxy-N-methyl-4-oxo-1,4-dihydropyridazine-3-carboxamide → 3-Acetyl-1-(2-fluoro-4-(1H-pyrazol-1-yl)phenyl)-5-methoxypyridazin-4(1H)-one

MeMgBr (1 M solution in THF, 2.8 mL, 2.8 mmol) was added dropwise at −78° C. to a solution of 1-[2-fluoro-4-(1H-pyrazol-1-yl)phenyl]-N,5-dimethoxy-N-methyl-4-oxo-1,4-dihydropyridazine-3-carboxamide (351 mg, 0.94 mmol) in THF (100 mL). After stirring for 1 h, the reaction mixture was quenched with 1 M HCl aqueous solution and extracted with AcOEt. The extract was washed with brine, dried over MgSO4, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography eluting with AcOEt and recrystallized from MeOH/H2O to give the title compound (223 mg, 72% yield) as a pale yellow solid: mp 159-161° C.; 1H NMR (300 MHz, CDCl3): δ ppm 2.69 (3H, s), 3.93 (3H, s), 6.56 (1H, dd, J=1.5, 2.3 Hz), 7.64 (1H, ddd, J=1.1, 2.3, 9.0 Hz), 7.71-7.79 (4H, m), 7.99 (1H, d, J=2.6 Hz). Anal. Calcd for C16H13FN4O3: C, 58.54; H, 3.99; N, 17.07. Found: C, 58.42; H, 4.01; N, 16.98.