To a solution of N-{[6-cyano-2-oxo-4-(trifluoromethyl)-1,4-dihydro-2H-3,1-benzoxazin-4-yl]methyl}-4-fluorobenzamide (50 mg, 0.127 mmol) synthesized in Example 159 in ethanol (0.5 mL), hydroxylamine (50% aqueous solution, 40 μL) was added, and the solution was stirred overnight at room temperature. The solution was diluted with ethyl acetate, which was washed sequentially with water and saturated brine and then dried over magnesium sulfate. The residue was dissolved in dioxane (1 mL), and under stirring the solution at room temperature, CDI (41 mg, 0.25 mmol) was added thereto. After the reaction solution was stirred at 90° C. for 3 hours, the temperature of the solution was brought to room temperature. Then, the solution was diluted with ethyl acetate, which was washed sequentially with water, 1 N hydrochloric acid and saturated brine and then dried over magnesium sulfate. After the drying agent was removed by filtration, the residue was crystallized with ethanol and water, whereby the objective compound (18 mg, 31%) was obtained as a white solid.
