[Cl:1][C:2]1[S:6][C:5]([C:7](=[O:17])[CH2:8][CH2:9][CH2:10][CH2:11][C:12]([O:14][CH2:15][CH3:16])=[O:13])=[CH:4][CH:3]=1.[Br:18]Br.S([O-])([O-])=O.[Na+].[Na+]>C(Cl)Cl>[Br:18][CH:8]([C:7]([C:5]1[S:6][C:2]([Cl:1])=[CH:3][CH:4]=1)=[O:17])[CH2:9][CH2:10][CH2:11][C:12]([O:14][CH2:15][CH3:16])=[O:13]Ethyl 6-(5-chloro-2-thienyl)-6-oxohexanoate (50.0 g) was dissolved in methylene chloride (150 ml), to which was added dropwise bromine (24.5 g) with stirring at room temperature. The mixture was stirred at room temperature for 1 hour, a 10% aqueous solution of sodium sulfite was then carefully added until disappearance of the red color of bromine, which was extracted with diethyl ether (200 ml×2). The organic layer was washed with a 10% aqueous solution of sodium hydrogen carbonate (100 ml), dried over anhydrous magnesium sulfate, and concentrated to give ethyl 5-bromo-6-(5-chloro-2-thienyl)-6-oxohexanoate as an oil (64.4 g, >99%).
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