1-[4-((R)-2-Nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazin-7-ylmethoxy)phenyl]piperidin-4-one (700 mg) and 4-(4-trifluoromethoxyphenoxy)phenylamine (557 mg) were suspended in 1,2-dichloroethane (20 ml) and tetrahydrofuran (20 ml). Sodium triacetoxyborohydride (558 mg) and acetic acid (0.13 ml) were added to the suspension, and stirred at room temperature for 20 hours. The reaction mixture was concentrated under reduced pressure and the remaining water layer was ice-cooled. A 20% sodium carbonate aqueous solution was added thereto, followed by extraction with methylene chloride. The organic layer was washed with a saturated sodium chloride aqueous solution and dried over sodium sulfate. After filtering, the filtrate was concentrated under reduced pressure. The residue was then purified by silica gel column chromatography (methylene chloride:methanol=100:1→methylene chloride:methanol=40:1) and recrystallized from isopropyl alcohol-isopropyl ether to afford the title compound as a yellow solid (226 mg).
