[CH3:1][O:2][C:3]1[CH:4]=[C:5]([CH:9]=[CH:10][C:11]=1[C:12]([O:14][CH3:15])=[O:13])[C:6](O)=[O:7].C(Cl)(=O)C([Cl:19])=O>ClCCl.CN(C)C=O>[CH3:1][O:2][C:3]1[CH:4]=[C:5]([CH:9]=[CH:10][C:11]=1[C:12]([O:14][CH3:15])=[O:13])[C:6]([Cl:19])=[O:7]To a stirred suspension of 3-methoxy-4-methoxycarbonylbenzoic acid (4.1 g, 19.5 mmol) and oxalyl chloride (2.4 ml, 27.3 mmol) in dry dichloromethane (100 ml) was added 2 drops of dimethylformamide. After 3 h at room temperature the clear solution was evaporated to an oil. The oil was redissolved in dry dichloromethane and evaporated, this procedure was repeated to give 3-methoxy-4-methoxycarbonylbenzoyl chloride as an oil (100%) which was used immediately in the next step.
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