Potassium carbonate (135 mg) and sodium iodide (146 mg) were added to an N-methylpyrrolidone solution (6 ml) of (R)-7-[4-((2S,5R)-2,5-dimethyl-piperazin-1-yl)phenoxymethyl]-2-nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine trifluoroacetate (343 mg) and 1-(chloromethyl)-4-[4-(trifluoromethoxy)phenoxy]benzene (269 mg), and the mixture was stirred at 60° C. for 3 hours. Sodium tert-butoxide (112 mg) was added to the mixture and stirred at room temperature for 3 hours. Water was added thereto, followed by extraction with ethyl acetate. The organic layer was washed with a saturated sodium chloride aqueous solution and then dried over sodium sulfate. After filtering, the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate:n-hexane=1:1→ethyl acetate:n-hexane=3:1) to afford the title compound as a pale brown amorphous compound (200 mg).
