O=[C:2]([CH2:6][CH3:7])[C:3]([OH:5])=[O:4].BrBr.[Br:10][C:11]1[CH:12]=[C:13]([C:21](=[S:23])[NH2:22])[CH:14]=[C:15]([C:17]([F:20])([F:19])[F:18])[CH:16]=1.C(=O)([O-])O.[Na+].[CH2:29](OCC)[CH3:30]>C(O)C>[Br:10][C:11]1[CH:12]=[C:13]([C:21]2[S:23][C:6]([CH3:7])=[C:2]([C:3]([O:5][CH2:29][CH3:30])=[O:4])[N:22]=2)[CH:14]=[C:15]([C:17]([F:19])([F:20])[F:18])[CH:16]=1Under a nitrogen atmosphere at 0° C., to a solution (30 mL) of 2-oxobutyric acid (3.0 g, 29 mmol) in diethyl ether was slowly added dropwise a solution (20 mL) of bromine (2.6 g, 33 mmol) in diethyl ether over 30 min, and the mixture was stirred at the same temperature for 3 hr. The solvent was evaporated under reduced pressure, and to a solution (50 mL) of the residue in ethanol was added the compound (3.2 g, 11 mmol) obtained in Example 77b, and the mixture was stirred at 80° C. overnight. Saturated aqueous sodium hydrogen carbonate was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The obtained organic layer was washed with saturated brine, and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure. The resulting crude title compound was purified by column chromatography (hexane-hexane/ethyl acetate=90/10) to give a crude title compound (5.9 g) as a pale-yellow solid.
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