O[C:2]1[C:10]2[C:9]([C:11]([O:13][CH3:14])=[O:12])=[C:8]([CH2:15][CH2:16][C:17]([O:19][CH3:20])=[O:18])[N:7]=[CH:6][C:5]=2[O:4][C:3]=1C(OC)=O.Cl.C[Si](C=[N+]=[N-])(C)C.C(OCC)C>C(=O)([O-])O.[Na+]>[CH3:20][O:19][C:17](=[O:18])[CH2:16][CH2:15][C:8]1[N:7]=[CH:6][C:5]2[O:4][CH2:3][CH2:2][C:10]=2[C:9]=1[C:11]([O:13][CH3:14])=[O:12]A mixture of dimethyl 3-hydroxy-5-(3-methoxy-3-oxopropyl)furo[2,3-c]pyridine-2,4-dicarboxylate (3.10 g, 9.19 mmol) and 12M hydrochloric acid (31 mL) was stirred at 150° C. for 1 hr and concentrated under reduced pressure. The residue was dissolved in methanol (60 mL), palladium-carbon powder (600 mg) was added, and the mixture was stirred at room temperature for 3 hr under a hydrogen atmosphere. The catalyst was filtered off, and the filtrate was evaporated under reduced pressure. The residue was dissolved in methanol (60 mL) again, palladium-carbon powder (1.00 g) was added, and the mixture was stirred at 50° C. for 4 hr under a hydrogen atmosphere. The catalyst was filtered off, and the filtrate was evaporated under reduced pressure. The residue was dissolved in methanol (60 mL), 2M trimethylsilyldiazomethane/diethyl ether solution (9.2 mL, 18 mmol) was added under ice-cooling, and the mixture was stirred for 30 min. The reaction solution was diluted with saturated aqueous sodium hydrogen carbonate solution, and the mixture was extracted with ethyl acetate. The extract was dried over anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure to give the title compound (1.98 g, yield 81%).
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