FC(F)(F)C(OC(=O)C(F)(F)F)=O.[N:14]([N:16]1[CH2:21][CH2:20][CH2:19][CH2:18][CH:17]1[C:22]([OH:24])=[O:23])=O>C1COCC1>[NH:14]1[N:16]2[CH2:21][CH2:20][CH2:19][CH2:18][CH:17]2[C:22](=[O:23])[O:24]1Trifluoroacetic anhydride (1.93 g) was added to the THF (92 mL) solution of crude (2RS)-1-nitrosopiperidine-2-carboxylic acid under a nitrogen atmosphere at 0° C. and stirred for 5 h at 0° C. and for 2 h at room temperature. The solution was concentrated under a reduced pressure. The residue was applied to silica gel column chromatography, then the column was eluted with n-hexane-AcOEt (1/1-0/1). The titled compound was obtained as colorless crystals (1.10 g, 33%).
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