FC(F)(F)C(OC(=O)C(F)(F)F)=[O:4].[CH:14]1([C:17]2[CH:22]=[N+:21]([O-])[C:20]([C:24]([O:26][CH2:27][CH3:28])=[O:25])=[CH:19][CH:18]=2)[CH2:16][CH2:15]1.O>CN(C)C=O>[CH:14]1([C:17]2[CH:18]=[CH:19][C:20]([C:24]([O:26][CH2:27][CH3:28])=[O:25])=[N:21][C:22]=2[OH:4])[CH2:16][CH2:15]1Trifluoroacetic anhydride (23 mL) was added to a solution of ethyl 5-cyclopropylpyridine-2-carboxylate 1-oxide (15.4 g) in N,N-dimethylformamide (45 mL), and the mixture was stirred at 50° C. for two hours. The reaction solution was poured into water, followed by extraction with ethyl acetate. The organic layer was washed with saturated aqueous sodium bicarbonate and brine, dried over anhydrous magnesium sulfate and filtered. The solvent was then evaporated under reduced pressure. The residue was purified by silica gel column chromatography (chloroform:methanol=10:0→9:1) to give ethyl 5-cyclopropyl-6-hydroxypyridine-2-carboxylate (12.4 g, 78%) as a colorless powder.
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