[C:1]([C:4]1[S:5][C:6]([Br:9])=[CH:7][CH:8]=1)(=[O:3])[CH3:2].[C:10](OC)(=[O:15])[C:11]([O:13][CH3:14])=[O:12].C[O-].[Na+].Cl>CO>[CH3:14][O:13][C:11](=[O:12])[C:10](=[O:15])[CH2:2][C:1]([C:4]1[S:5][C:6]([Br:9])=[CH:7][CH:8]=1)=[O:3]To a solution of 2-acetyl-5-bromothiophene (25 g, 122 mmol) and dimethyl oxalate (23 g, 194 mmol) in dry methanol (800 mL) was added a solution of NaOMe in MeOH (25%, 51 mL, 224 mmol) at ambient temperature. The reaction mixture was stirred at 20° C. for 4 h and then acidified to pH 1 with 6 N aqueous HCl. The yellow solid was collected by filtration, washed with H2O, and dried under high vacuum to afford 4-(5-bromo-thiophen-2-yl)-2,4-dioxo-butyric acid methyl ester (31.3 g, 88%). 1H-NMR (DMSO-d6): δ 8.14 (s, 1H), 7.46 (d, 1H), 7.05 (s, 1H), 3.85 (s, 3H).
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