[F:1][C:2]([F:19])([F:18])[C:3]1[CH:8]=[CH:7][C:6]([C:9]2[S:10][CH:11]=[C:12]([CH2:14][C:15]([OH:17])=[O:16])[N:13]=2)=[CH:5][CH:4]=1.O.[C:21]1(C)C=CC(S(O)(=O)=O)=CC=1>CO.C(OC)(OC)OC>[CH3:21][O:16][C:15](=[O:17])[CH2:14][C:12]1[N:13]=[C:9]([C:6]2[CH:7]=[CH:8][C:3]([C:2]([F:1])([F:18])[F:19])=[CH:4][CH:5]=2)[S:10][CH:11]=1A solution of [2-(4-trifluoromethyl-phenyl)-thiazol-4-yl]-acetic acid (3 g, 10.4 mmol) and p-toluenesulfonic acid mono-hydrate (0.5 g, 2.6 mmol) in methanol (30 ml) and trimethyl orthoformate (2 ml) was heated under reflux for 5 hours. After neutralization with aqueous sodium bicarbonate solution and evaporation of the solvents under reduced pressure, the residue was redissolved in tert-butyl methyl ether and dried over anhydrous sodium sulfate. Evaporation of the solvent gave 2.65 g (8.8 mmol, 84%) of [2-(4-trifluoromethyl-phenyl)-thiazol-4-yl]-acetic acid methyl ester as light brown solid.
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