[CH2:1]([O:3][C:4]1[C:5]([OH:16])=[CH:6][C:7]2[S:11][C:10]([C:12]([OH:14])=[O:13])=[CH:9][C:8]=2[CH:15]=1)[CH3:2].[CH3:17]O.S(=O)(=O)(O)O>C(Cl)Cl.C(OCC)(=O)C>[CH2:1]([O:3][C:4]1[C:5]([OH:16])=[CH:6][C:7]2[S:11][C:10]([C:12]([O:14][CH3:17])=[O:13])=[CH:9][C:8]=2[CH:15]=1)[CH3:2]A solution of 0.71 g. of 5 -ethoxy-6-hydroxybenzothiophene-2-carboxylic acid, 0.29 g. of methanol, and a catalytic amount of sulfuric acid in methylene chloride was heated to reflux for 48 hours. The solution was diluted with ethyl acetate and was washed first with a 10% aqueous sodium bicarbonate solution and then with water. The organic solution was dried over sodium sulfate and evaporated to dryness providing the desired ester intermediate which was used without further purification.
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