[CH:1]([C:3]1[CH:12]=[CH:11][C:6]([C:7]([O:9][CH3:10])=[O:8])=[C:5]([O:13][CH3:14])[CH:4]=1)=[O:2].S(=O)(=O)([OH:17])N.Cl([O-])=O.[Na+]>CC(C)=O>[CH3:14][O:13][C:5]1[CH:4]=[C:3]([CH:12]=[CH:11][C:6]=1[C:7]([O:9][CH3:10])=[O:8])[C:1]([OH:17])=[O:2]To a cold solution of methyl 4-formyl-2-methoxybenzoate (6.0 g, 7.73 mmol) in acetone (50 mL) was added aqueous sulphamic acid solution (4.5 g, 11.59 mmol) and aqueous sodium chlorite solution (4.04 g, 11.59 mmol) at 0-5° C. The reaction mixture was stirred at RT for 3-4 h. Excess of solvent was removed under vacuum. The obtained residue was diluted with water and basified with saturated sodium bicarbonate solution. The aqueous layer was washed with diethyl ether to remove organic impurities and the obtained aqueous layer was again acidified with conc. HCl. The solid obtained was filtered and suck dried to afford 2.00 g of desired product. 1H NMR (300 MHz, DMSO d6): δ 3.80 (s, 3H), 3.87 (s, 3H), 7.55-7.59 (m, 2H), 7.70 (d, J=7.8 Hz, 1H), 13.37 (s, 1H); MS (m/z): 210.97 (M+H)+.
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