To a solution of 6-(5-methyl-3-phenyl-isoxazol-4-ylmethoxy)-pyridazin-3-ylamine (280 mg, 1 mmol) and p-N,N-dimethylaminopyridine (61 mg, 0.5 mmol) in pyridine (5 mL) was added ethyl chloroformate (0.11 mL, 1.2 mmol) at room temperature. The resulting mixture was stirred at room temperature for 5 h. After evaporation the residue was extracted with ethyl acetate/water and the organic phase was dried over sodium sulfate and concentrated. Chromatography (SiO2, heptane/ethyl acetate=100:0 to 70:30) afforded the title compound (260 mg, 73%) as a white solid. MS: m/e=355.0 [M+H]+.
