[N:1]1[CH:6]=[CH:5][CH:4]=[C:3]2[CH2:7][C:8]3[CH:14]=[C:13]([CH:15](C#N)[C:16]([CH3:18])=[O:17])[CH:12]=[CH:11][C:9]=3[O:10][C:2]=12.N1C=CC=C2CC3C=C(CC#N)C=CC=3OC=12.S(=O)(=O)(O)O.[OH-].[Na+]>O.C(OCC)(=O)C>[N:1]1[CH:6]=[CH:5][CH:4]=[C:3]2[CH2:7][C:8]3[CH:14]=[C:13]([CH2:15][C:16](=[O:17])[CH3:18])[CH:12]=[CH:11][C:9]=3[O:10][C:2]=121-(5H-[1]benzopyrano[2,3-b]pyridin-7-yl)-1-cyano-acetone prepared from 33 g of 5H-[1]benzopyrano[2,3-b]pyridin-7-yl-acetonitrile and 75 ml of ethyl acetate is added in small portions to 75 ml of concentrated sulfuric acid with stirring, while the temperature is maintained at below 20°C by cooling with ice. 225 ml of water is added at a stretch to the mixture, and the whole mixture is stirred under reflux for 5 hours. The reaction mixture is ice-cooled and strongly alkalified by adding 30% sodium hydroxide with stirring. The crystalline precipitate is extracted with chloroform, and the extract is washed with water and dried over anhydrous sodium sulfate. The chloroform is distilled off, and the residue is recrystallized from isopropyl alcohol to give 25 g of 5H-[1]benzopyrano[2,3-b]pyridin-7-yl-acetone as white needles melting at 124°-125°C.
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