S(Cl)([Cl:3])=O.[O:5]=[C:6]1[C:15]2[C:10](=[N:11][CH:12]=[CH:13][CH:14]=2)[O:9][C:8]2[CH:16]=[CH:17][C:18]([C:20]([O-:22])=O)=[CH:19][C:7]1=2.[Na+]>C(Cl)(Cl)(Cl)Cl>[O:5]=[C:6]1[C:15]2[C:10](=[N:11][CH:12]=[CH:13][CH:14]=2)[O:9][C:8]2[CH:16]=[CH:17][C:18]([C:20]([Cl:3])=[O:22])=[CH:19][C:7]1=22.5 g of thionyl chloride is added to a suspension of 4.5 g of sodium 5-oxo-5H-[1]benzopyrano[2,3-b]pyridine-7-carboxylate in 35 ml of carbon tetrachloride with stirring, and the mixture is stirred under reflux for 3 hours. After cooling, the crystals are filtered off, washed with cool water and then with acetone, and dried to give 5-oxo-5H-[1]benzopyrano[2,3-b]pyridine-7-carboxylic acid chloride melting at 234°-235°C.
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