C(O[C:6]([N:8]1[CH2:13][CH2:12][CH:11]([O:14][C:15]2[CH:20]=[CH:19][C:18]([N+:21]([O-:23])=[O:22])=[CH:17][C:16]=2[C:24]([F:27])([F:26])[F:25])[CH2:10][CH2:9]1)=O)(C)(C)C.C=O.C(=O)([O-])O.[Na+]>C(O)=O>[CH3:6][N:8]1[CH2:13][CH2:12][CH:11]([O:14][C:15]2[CH:20]=[CH:19][C:18]([N+:21]([O-:23])=[O:22])=[CH:17][C:16]=2[C:24]([F:25])([F:26])[F:27])[CH2:10][CH2:9]1To a suspension of 4-(1-t-butoxycarbonylpiperidin-4-yloxy)-3-trifluoromethylnitrobenzene (2.45 g) obtained in reference example 100 in 90% formic acid (8.80 g) was added 37% formaldehyde (5.50 g), and the resulting mixture was stirred at 100° C. for 6 hours. After cooling to room temperature, the reaction mixture was neutralized with an aqueous sodium hydrogencarbonate solution and extracted with ethyl acetate. The extract was washed with a saturated aqueous sodium chloride solution, dried over anhydrous magnesium sulfate and evaporated in vacuo. The residue obtained was purified by chromatography on a silica gel column using a mixed solvent of dichloromethane and methanol (10:1) as the eluent to afford the title compound (1.82 g, yield: 95%) as a yellow oil.
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