N-{1-[4-((R)-2-Nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazin-7-ylmethoxy)phenyl]piperidin-4-yl}-N-[4-(4-trifluoromethoxybenzyloxy)phenyl]amine (0.47 g) was suspended in 1,2-dichloroethane (5 ml). Acetaldehyde (0.41 ml) and sodium triacetoxyborohydride (0.46 g) were added to the suspension, and the mixture was stirred at room temperature for 3 days. A potassium carbonate aqueous solution was added to the reaction mixture, followed by extraction with methylene chloride. The organic layer was washed with a saturated sodium chloride aqueous solution, dried over sodium sulfate, and then concentrated under reduced pressure. The residue was purified by medium pressure silica gel column chromatography (methylene chloride:methanol=10:0→methylene chloride:methanol=9:1) and recrystallized from methanol to afford the title compound as a yellow powder (0.25 g).
