[CH3:1][O:2][C:3]([C:5]1[CH:10]=[CH:9][C:8]([OH:11])=[CH:7][N:6]=1)=[O:4].[H-].[Na+].[F:14][C:15]([F:26])([F:25])[CH2:16]OS(C(F)(F)F)(=O)=O.C(=O)([O-])[O-].[Na+].[Na+]>CN(C)C=O>[CH3:1][O:2][C:3]([C:5]1[CH:10]=[CH:9][C:8]([O:11][CH2:16][C:15]([F:26])([F:25])[F:14])=[CH:7][N:6]=1)=[O:4]
Under an atmosphere of nitrogen a solution of 5-hydroxy-pyridine-2-carboxylic acid methyl ester (200 mg, 1.31 mmol) in N,N-dimethylformamide (2 ml) was treated at room temperature with sodium hydride (55% dispersion in oil, 64 mg). After the gas formation had ceased, the suspension was cooled to 0° C. and trifluoro-methanesulphonic acid 2,2,2-trifluoro-ethyl ester (364 mg, 1.57 mmol) was added. After stirring at room temperature for 2 hours about 50% of the starting material was left. Another 364 mg of trifluoro-methanesulphonic acid 2,2,2-trifluoro-ethyl ester were added and after 30 minutes the reaction was complete. For the workup, the reaction mixture was treated with a saturated solution of sodium carbonate, then extracted with ethyl acetate (3×). The combined organic layers were washed with brine, dried over sodium sulphate, and evaporated at reduced pressure. The crude product was purified by chromatography on silica gel using a 3:1-mixture of heptane and ethyl acetate as the eluent. The 5-(2,2,2-trifluoro-ethoxy)-pyridine-2-carboxylic acid methyl ester was obtained as a white solid (216 mg, 70% of theory). MS (ISP): m/z=236.3 [M+H]+.
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