[C:1]([O:4][C:5]1[C:14]([O:15][C:16](=[O:18])[CH3:17])=[C:13]2[C:8]([C:9](=[O:22])[C:10]([C:19](O)=[O:20])=[CH:11][O:12]2)=[CH:7][CH:6]=1)(=[O:3])[CH3:2].S(Cl)([Cl:25])=O.C1C=CC=CC=1>CN(C)C=O>[C:1]([O:4][C:5]1[C:14]([O:15][C:16](=[O:18])[CH3:17])=[C:13]2[C:8]([C:9](=[O:22])[C:10]([C:19]([Cl:25])=[O:20])=[CH:11][O:12]2)=[CH:7][CH:6]=1)(=[O:3])[CH3:2]A mixture of 7,8-diacetoxychromone-3-carboxylic acid (9.5 g, 31 mmol), thionyl chloride (2.6 ml), dimethylformamide (0.1 ml) and benzene (300 ml) was refluxed for 1.5 hours. After the addition of thionyl chloride (2.6 ml) was dimethylformamide (0.1 ml), the mixture was refluxed for a further one hour and evaporated to dryness. The residue was triturated with n-hexane to give the desired compound (9.3 g).
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