[O:1]1[C:9]2[C:4](=[N:5][CH:6]=[CH:7][CH:8]=2)[CH2:3][CH2:2]1.[N+:10]([O-])([OH:12])=[O:11].[OH-].[Na+]>S(=O)(=O)(O)O.O>[N+:10]([C:6]1[N:5]=[C:4]2[CH2:3][CH2:2][O:1][C:9]2=[CH:8][CH:7]=1)([O-:12])=[O:11]To a solution of 2,3-dihydrofuro[3,2-b]pyridine (32.9 g, 271 mmol) in sulfuric acid (50 mL) was added dropwise a mixed solution of fuming nitric acid (20 mL) and sulfuric acid (20 mL) under ice-cooling, and the mixture was stirred at room temperature for 1 hr. The reaction solution was neutralized with 8M aqueous sodium hydroxide solution and diluted with water. The resulting crystals were collected by filtration to give the title compound (37.5 g, yield 83%).
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