[C:1](Cl)(=O)[C:2]([Cl:4])=[O:3].[CH2:7]([C:11]1[O:12][C:13]2[CH:22]=[CH:21][CH:20]=[CH:19][C:14]=2C=1C(O)=O)[CH2:8][CH2:9][CH3:10].CN(C=O)C>C(Cl)Cl.C1C=CC=CC=1>[CH2:7]([C:11]1[O:12][C:13]2[CH:22]=[CH:21][CH:20]=[CH:19][C:14]=2[C:1]=1[C:2]([Cl:4])=[O:3])[CH2:8][CH2:9][CH3:10]Oxalyl Chloride (10.0 mL, 114.6 mmol) was added under nitrogen at room temperature to a solution of 2-butyl-benzofuran-3-carboxylic acid (5.00 g, 22.9 mmol), prepared in the previous step, in 200 mL of methylene chloride. After the addition a catalytic amount of DMF (100 μL) was added and the reaction stirred at room temperature for 1.5 h. The solvent was removed under reduced pressure to give a brown oil. The oil was dissolved in benzene and the solvent removed under reduced pressure to give 2-butyl-benzofuran-3-carbonyl chloride (5.46 g, 100%) as a brown oil. The material was immediately used in subsequent reactions with out additional purification.
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