[C:1]1([S:7]([NH:10][C:11]2[CH:15]=[CH:14][S:13][C:12]=2[C:16]([OH:18])=O)(=[O:9])=[O:8])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.C(Cl)(=O)C([Cl:22])=O>ClCCl.CN(C)C=O>[C:1]1([S:7]([NH:10][C:11]2[CH:15]=[CH:14][S:13][C:12]=2[C:16]([Cl:22])=[O:18])(=[O:9])=[O:8])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=13-Benzenesulfonylaminothiophene-2-carboxylic acid (0.61 g, 2.15 mmol) was suspended in dichloromethane (8.6 mL). The resulting mixture was sequentially treated with N,N-dimethylformamide (1 drop), and, in two portions, oxalyl chloride (0.42 mL, 4.8 mmol). After stirring briefly at room temperature, the foaming subsided and the solution was refluxed until the reaction was complete. The mixture was concentrated to dryness, re-dissolved in dichloromethane, and filtered through very small pad of course silica gel, eluting with dichloromethane. Upon concentration of the eluent, the desired 3-benzenesulfonylaminothiophene-2-carboxylic acid chloride was obtained as a yellow solid (0.32 g, 49%), which was used without further purification.
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