8-(5-Fluoro-2-methylphenoxymethyl)-7-(2-methoxy-5-methoxycarbonylphenyl)-1,3,3-trimethyl-3,4-dihydro-1H-quinoxalin-2-one (Compound No. 6-37, 50.2 mg, 0.102 mmol) was dissolved in anhydrous tetrahydrofuran (0.5 ml), and lithium aluminum hydride (6.8 mg, 0.18 mmol) was added thereto at 0° C. After the reaction mixture was stirred at same temperature for 30 minutes, ethyl acetate (1 mL) and water (1 mL) were added thereto successively. Moreover ethyl acetate (10 mL) and water (10 mL) were added and partitioned. The organic layer was washed with saturated brine (10 mL), dried over anhydrous magnesium sulfate, and then the solvent was removed under reduced pressure. The obtained residue was purified by silica gel column chromatography (hexane-ethyl acetate) to give the titled compound (29.8 mg) as a pale yellow solid. (Yield 47%)
