[CH:1]([C:4]1[CH:9]=[CH:8][C:7]([C:10]2[S:11][CH:12]=[C:13]([CH2:15][C:16]([OH:18])=[O:17])[N:14]=2)=[CH:6][CH:5]=1)([CH3:3])[CH3:2].O.[C:20]1(C)C=CC(S(O)(=O)=O)=CC=1>CO.C(OC)(OC)OC>[CH3:20][O:17][C:16](=[O:18])[CH2:15][C:13]1[N:14]=[C:10]([C:7]2[CH:6]=[CH:5][C:4]([CH:1]([CH3:3])[CH3:2])=[CH:9][CH:8]=2)[S:11][CH:12]=1A solution of 6.9 g (26.4 mmol) of [2-(4-isopropyl-phenyl)-thiazol-4-yl]-acetic acid and 0.5 g of p-toluenesulfonic acid mono-hydrate (catalyst) in 70 ml of methanol and 5 ml of trimethyl orthoformate was heated at reflux for 5 hours. After neutralization with aqueous sodium bicarbonate solution, evaporation of the solvents, extraction of the residue with tert-butyl methyl ether, drying over anhydrous sodium sulfate and evaporation of the solvent, 6.4 g (88% of theory) of [2-(4-isopropyl-phenyl)-thiazol-4-yl]-acetic acid methyl ester were obtained as light brown oil.
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