To 1 ml of N,N-dimethylformamide containing 193 mg (0.352 mmol) of 3-cyclobutoxymethyl-2-(3-cyclopropoxy-4-difluoromethoxyphenyl)-5-(2-trimethylsilylethoxymethyl)-1,5-dihydropyrrolo[2,3-d]pyridazin-4-one obtained in Example 13-(b) were added 38.2 mg (0.440 mmol) of lithium bromide, 10 μl of ethylenediamine and 3 ml of tetrahydrofuran solution containing 1M tetrabutylammonium fluoride, and the mixture was stirred at 100° C. for 8 hours while removing tetrahydrofuran. After completion of the reaction, water was added to the reaction mixture, and the precipitated solid was collected by filtration. The obtained crude solid was applied to silica gel column chromatography (Eluent; chloroform:ethyl acetate=1:0→0:1 (V/V)), the fractions containing the desired compound were concentrated under reduced pressure, and recrystallized from a mixed solvent of ethanol and water to obtain 70 mg of the title compound as a white solid. (Yield: 47%)
