To a solution of 3-ethynyl-1-[3-(trifluoromethyl)phenyl]pyridazin-4(1H)-one (104 mg, 0.391 mmol) and N-hydroxybenzenecarboximidoyl chloride (122 mg, 0.782 mmol) in THF (5 mL) was added Et3N (0.108 mL, 0.782 mmol) at 0° C. The suspension was stirred at room temperature for 14 h. The reaction was quenched with water. The mixture was extracted with AcOEt, washed with brine, dried over Na2SO4, filtered, concentrated in vacuo, purified by column chromatography on silica gel (hexane/AcOEt=50/50 to 0/100) and on basic silica gel (hexane/AcOEt=50/50 to 43/57) and crystallized with AcOEt/heptane to yield the title compound (82.4 mg, 55% yield) as a white solid: mp 217-219° C. 1H NMR (DMSO-d6, 300 MHz): δ ppm 6.87 (1H, d, J=8.0 Hz), 7.50-7.59 (3H, m), 7.86-7.92 (2H, m), 7.94-8.02 (3H, m), 8.15-8.26 (2H, m), 9.09 (1H, d, J=8.2 Hz). Anal. Calcd for C20H12F3N3O2: C, 62.67; H, 3.16; N, 10.96. Found: C, 62.60; H, 3.19; N, 10.95.
