Phenylhydrazine → 5-Methoxy-3-(1-Phenyl-1h-Pyrazol-5-Yl)-1-[3-(Trifluoromethyl)phenyl]pyridazin-4(1h)-One

A solution of 3-[3-(dimethylamino)prop-2-enoyl]-5-methoxy-1-[3-(trifluoromethyl)phenyl]pyridazin-4(1H)-one (3.41 g, 9.29 mmol) and phenylhydrazine (1.83 mL, 18.6 mmol) in AcOH (25 mL) was refluxed for 2 h. After cooling to room temperature, the reaction mixture was concentrated under reduced pressure. The residue was diluted with AcOEt, washed successively with 1 M HCl aqueous solution, 1 M NaOH aqueous solution, and brine, dried over MgSO4, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography eluting with AcOEt and crystallized from hexane/AcOEt to give the title compound (2.70 g, 71% yield) as colorless crystals: mp 139-141° C.; 1H NMR (300 MHz, CDCl3): δ ppm 3.98 (3H, s), 7.05 (1H, dd, J=1.9, 7.9 Hz), 7.19 (1H, s), 7.34-7.47 (7H, m), 7.56 (1H, d, J=7.9 Hz), 7.80 (1H, d, J=1.9 Hz), 7.92 (1H, s). LC-MS (ESI) m/z 413 [M+H]+. Anal. Calcd for C21H15F3N4O2: C, 61.17; H, 3.67; N, 13.59. Found: C, 61.15; H, 3.65; N, 13.57.