[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), N,N-dimethylformamide (0.1 ml) and benzene (300 ml) was refluxed for 1.5 hours. After the addition of thionyl chloride (2.6 ml) and N,N-dimethylformamide (0.1 ml), the mixture was refluxed for a further hour and evaporated to dryness. The residue was triturated with n-hexane to afford the desired compound (9.3 g, 92.6%).
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