[N+]([O-])(O)=O.[Mn]([O-])(=O)(=O)=O.[K+].[O-2:11].[Mg+2].[CH2:13]([C:15]1[CH:16]=[CH:17][C:18]2[O:27][C:22]3=[N:23][CH:24]=[CH:25][CH:26]=[C:21]3[C:20](=[O:28])[C:19]=2[CH:29]=1)[CH3:14]>O>[C:13]([C:15]1[CH:16]=[CH:17][C:18]2[O:27][C:22]3=[N:23][CH:24]=[CH:25][CH:26]=[C:21]3[C:20](=[O:28])[C:19]=2[CH:29]=1)(=[O:11])[CH3:14]7.6 ml of nitric acid (specific gravity 1.38) and 7.9 g of potassium permanganate are added to a suspension of 2 g of magnesium oxide in 50 ml of water, and the mixture is heated to 60°C. To the mixture is added 4.5 g of 7-ethyl-5-oxo-5H-[1]benzopyrano[2,3-b]pyridine over a period of 30 minutes with stirring, keeping the temperature at 60°-70°C. After the addition the mixture is stirred at 60°-70°C for 4.5 hours. After cooling, the reaction mixture is filtered under reduced pressure, and the residue containing manganese dioxide is extracted several times with chloroform. The chloroform layer is washed with water, dried, and the chloroform is distilled off. The residue is recrystallized from toluene to give 3.2 g of 7-acetyl-5-oxo-5H-[1]benzopyrano[2,3-b]pyridine melting at 195°-196°C.
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