[CH2:1]([O:3][C:4]1[CH:5]=[C:6]([C:13]2[S:14][CH:15]=[C:16]([CH2:18][CH2:19][C:20]([OH:22])=[O:21])[N:17]=2)[CH:7]=[CH:8][C:9]=1[O:10][CH2:11][CH3:12])[CH3:2].S(Cl)(Cl)=O.[CH3:27]O>>[CH2:1]([O:3][C:4]1[CH:5]=[C:6]([C:13]2[S:14][CH:15]=[C:16]([CH2:18][CH2:19][C:20]([O:22][CH3:27])=[O:21])[N:17]=2)[CH:7]=[CH:8][C:9]=1[O:10][CH2:11][CH3:12])[CH3:2]A solution (2.3 l) of 3-[2-(3,4-diethoxyphenyl)thiazole-4-yl]propionic acid (254.5 g) in methanol was ice-cooled, and 58 ml of thionyl chloride was added dropwise. After completion of the addition, the resulting mixture was heated under reflux for 2 hours and cooled to room temperature. The solvent was distilled off under reduced pressure, and the residue was subjected to extraction with ethyl acetate. The organic layer was washed with a saturated aqueous sodium hydrogencarbonate solution, and dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography (eluent: ethyl acetate/n-hexane=1/3). The solvent was distilled off under reduced pressure, and the residue was recrystallized from an ethyl acetate/n-hexane mixed solvent, to thereby obtain 219.35 g (yield: 68%) of methyl 3-[2-(3,4-diethoxyphenyl)thiazole-4-yl]propionate as a white powder.
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