[O:1]([C:8]1[CH:15]=[C:12]([CH:13]=O)[C:11]([OH:16])=[CH:10][CH:9]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[CH:17](=[O:21])/[CH:18]=[CH:19]/[CH3:20].C(=O)([O-])[O-].[K+].[K+]>O1CCOCC1.O>[O:1]([C:8]1[CH:9]=[CH:10][C:11]2[O:16][CH:19]([CH3:20])[C:18]([CH:17]=[O:21])=[CH:13][C:12]=2[CH:15]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1The starting material is prepared as follows: A mixture of 5-phenoxysalicylaldehyde (6.52 g, 30.4 mmol), crotonaldehyde (3.2 g, 45.7 mmol) and potassium carbonate (8.41 g, 60.9 mmol) in 100 ml of 1,4-dioxane is heated at reflux for 2 hours. The mixture is cooled, diluted with water, and extracted three times with dichloromethane. The combined organic layers are dried (MgSO4) and evaporated. Purification by flash chromatography (silica gel, 7% ethyl acetate/hexane) yields 6-phenoxy-2-methyl-2H-1-benzopyran-3-carboxaldehyde which is converted to 6-phenoxy-2-methyl-3-(N-hydroxyaminomethyl)-2H-1-benzopyran as described above.
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