[Cl:1][C:2]1[S:6][C:5]([C:7]([OH:9])=O)=[CH:4][CH:3]=1.C(Cl)(=O)C([Cl:13])=O>CCOC(C)=O.CN(C=O)C>[Cl:1][C:2]1[S:6][C:5]([C:7]([Cl:13])=[O:9])=[CH:4][CH:3]=1To a chilled solution of 5-chlorothiophene-2-carboxylic acid (0.16 g, 1.0 mmol) in EtOAc (3 mL) and DMF (1 drop) was added neat oxalyl chloride (92 μL, 1.05 mmol). The reaction mixture was stirred cold for 2 hr and concentrated in vacuo to give crude 5-chlorothiophene-2-carbonyl chloride.
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