To a stirred solution of N-(5-benzyloxy-6-formyl-4-oxo-4H-pyran-2-ylmethyl)-benzene sulfonamide (11-01) (700.0 mg, 1.75 mmol) in acetone (10 mL) and water (15 mL) were added sulfamic acid (240.45 mg, 2.45 mmol) and sodium chlorite (166.6 mg, 1.84 mmol) and the reaction mixture was allowed to stir for 16 h at room temperature. After completion of the reaction, the solvent and the volatile substances were removed and extracted with dichloromethane. The combined organic layer was washed with saturated ammonium chloride solution, water and then brine, dried over Na2SO4 and concentrated under reduced pressure to get 6-(benzene sulfonyl amino-methyl)-3-benzyloxy-4-oxo-4H-pyran-2-carboxylic acid (12-01) (640.0 mg, 87.82%) as a white solid.
