Sodium triacetoxyborohydride (0.32 g) and acetic acid (1 ml) were added to a 1,2-dichloroethane solution (8 ml) of 1-[4-((R)-2-nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazin-7-ylmethoxy)phenyl]piperidin-4-one (0.40 g) and 4-(4-trifluoromethoxybenzyloxy)phenylamine (0.33 g), and the mixture was stirred at room temperature for 5 days. The reaction mixture was diluted with methylene chloride. The result was washed with a potassium carbonate aqueous solution and water in this order, and then dried over magnesium sulfate. After filtering, the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (methylene chloride:methanol=1:0→methylene chloride:methanol=9:1) to afford the title compound as a yellow powder (0.46 g).
