[BH4-].[Na+].[Br:3][C:4]1[CH:8]=[C:7]([Br:9])[S:6][C:5]=1[C:10](=[O:16])[C:11]([O:13][CH2:14][CH3:15])=[O:12]>O1CCCC1.Cl>[Br:3][C:4]1[CH:8]=[C:7]([Br:9])[S:6][C:5]=1[CH:10]([OH:16])[C:11]([O:13][CH2:14][CH3:15])=[O:12]Under a nitrogen atmosphere, sodium borohydride (0.14 g, 3.7 mmol) was added portionwise to a solution of ethyl 2-(3,5-dibromothiophen-2-yl)-2-oxoacetate (7a) (0.42 g, 1.24 mmol) in anhydrous tetrahydrofuran (10 mL), previously cooled to −10° C. After 30 minutes stirring, a few drops of 1 M hydrochloric acid were added and the resulting precipitate was filtered. The filtrate was concentrated in vavuo. The residue was dissolved in brine, and extracted with ethyl acetate (2×20 mL). The organic layer was dried over sodium sulfate, filtered, and evaporated to dryness. The residue was purified by flash chromatography on silica gel (cyclohexane/ethyl acetate: 80/20) to provide ethyl 2-(3,5-dibromothiophen-2-yl)-2-hydroxyacetate (0.32 g, 0.93 mmol, 75%).
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