[CH3:1][S:2][C:3]1[O:7][C:6]2[C:8](=[O:17])[C:9]3[C:14]([C:15](=[O:16])[C:5]=2[CH:4]=1)=[CH:13][CH:12]=[CH:11][CH:10]=3.I(O)(=O)(=O)=[O:19].O>C(#N)C>[CH3:1][S:2]([C:3]1[O:7][C:6]2[C:8](=[O:17])[C:9]3[C:14]([C:15](=[O:16])[C:5]=2[CH:4]=1)=[CH:13][CH:12]=[CH:11][CH:10]=3)=[O:19]To a solution of 0.5 gram (2.05 mmoles) of 2-methylthio-naphtho[2,3-b]furan-4,9-dione (prepared in example 7) in 20 mL of acetonitrile at room temperature, 0.49 grams (2.15 mmoles) of periodic acid followed by 2 mg of ferric chloride was added. The mixture was stirred for 10 minutes at room temperature, then 50 mL of water was added, and the resulting mixture was evaporated to remove acetonitrile. The remaining aqueous suspension was filtered, and the obtained solid was washed with water and dried under vacuum. The crude solid product was purified with silica gel chromatograph using dichloromethane/ethyl acetate (9:1) as elution solvent. 0.43 grams of product (yield 80%) was obtained and characterized by 1H NMR and mass spectrum. 1H NMR (in DMSO) δ 3.14 (s, 3H), 7.81 (s, 1H), 7.92-7.94 (m, 2H), 8.12-8.17 (m, 2H). Mass (M+H) is 261.
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