A mixture of tert-butyl (R)-4-[4-(2-methyl-6-nitro-2,3-dihydroimidazo[2,1-b]oxazol-2-ylmethoxy)-phenyl]piperazine-1-carboxylate prepared in Example 148 (800 mg, 1.74 mmol) and trifluoroacetic acid (3 ml) was stirred at room temperature for 7 hours. The reaction mixture was concentrated under reduced pressure, and the residue was dissolved in methylene chloride (10 ml). To the solution, triethylamine (3 ml, 21.52 mmol) was added followed by stirring at room temperature for 5 minutes. The mixture was concentrated under reduced pressure, and the residue was dissolved in methanol (10 ml). To the solution, 4-trifluoromethylbenzaldehyde (910 mg, 5.23 mmol), sodium cyanotrihydroborate (328 mg, 5.23 mmol) and acetic acid (0.33 ml, 5.23 mmol) were added followed by stirring at room temperature overnight. To the reaction mixture, a saturated sodium hydrogencarbonate solution and methylene chloride were added, and the solution was stirred and then extracted with methylene chloride. The organic phase was dried over magnesium sulfate and filtered. The resulting filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (methylene chloride/methanol=200/1) to afford (R)-2-methyl-6-nitro-2-{4-[4-(4-trifluoromethylbenzyl)piperazin-1-yl]phenoxymethyl}-2,3-dihydroimidazo[2,1-b]oxazole (667 mg, yield 74%) as a light yellow powder.
