C([O:3][C:4](=[O:18])[C:5]([C:7]1[CH:12]=[CH:11][C:10]([S:13][CH:14]2[CH2:16][CH2:15]2)=[C:9]([Br:17])[CH:8]=1)=[O:6])C.[OH-].[Na+].O.Cl>C1(C)C=CC=CC=1.C(OCC)(=O)C>[Br:17][C:9]1[CH:8]=[C:7]([C:5](=[O:6])[C:4]([OH:18])=[O:3])[CH:12]=[CH:11][C:10]=1[S:13][CH:14]1[CH2:15][CH2:16]1
A solution of ethyl[3-bromo-4-(cyclopropylsulfanyl)phenyl](oxo)acetate (30 g) in toluene (60 mL) was heated to 50° C., and a 3 M aqueous sodium hydroxide solution (36 mL) was added thereto at an internal temperature of 60° C. or lower, followed by stirring at 50° C. for 1 hour. After leaving it to be cooled at room temperature, water (150 mL) and ethyl acetate (100 mL) were added to the reaction mixture. To the aqueous layer was added concentrated hydrochloric acid (12 mL) under ice-cooling, followed by extraction with ethyl acetate (100 mL×3). The organic layer was washed with saturated brine (100 mL) and dried over anhydrous magnesium sulfate, and the solvent was then evaporated under reduced pressure. The residue was sequentially washed with hexane/ethyl acetate (19/1, 200 mL) and diethyl ether/hexane (1/2, 200 mL) to obtain [3-bromo-4-(cyclopropylsulfanyl)phenyl](oxo)acetic acid (14.7 g) as a pale yellow solid.
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