[OH:1][C:2]1[CH:3]=[C:4]2[C:8](=[CH:9][CH:10]=1)[N:7]([CH3:11])[C:6]([CH2:12][O:13][CH3:14])=[C:5]2[C:15]([O:17][CH3:18])=[O:16].[H-].[Na+].[CH3:21]I.O>CN(C)C=O>[CH3:21][O:1][C:2]1[CH:3]=[C:4]2[C:8](=[CH:9][CH:10]=1)[N:7]([CH3:11])[C:6]([CH2:12][O:13][CH3:14])=[C:5]2[C:15]([O:17][CH3:18])=[O:16]14.9 g of 5-hydroxy-3-methoxycarbonyl-2-methoxymethyl-1-methylindole (59.8 mmol) obtained in Example 1 was dissolved in 150 ml of anhydrous dimethylformamide, and the solution was stirred in a stream of nitrogen under ice cooling. To this were added 2.63 g (65.8 mmol) of sodium hydride (60% oil dispersion) and 4.1 ml (65.9 mmol) of methyl iodide in that order. After 2 hours of heating at 50° C., the resulting reaction mixture was cooled down, mixed with water and then extracted with ethyl acetate. The ethyl acetate layer was washed with water and saturated sodium chloride aqueous solution and then dried over anhydrous magnesium sulfate. After anhydrous magnesium sulfate was filtered off and the solvent was distilled off under reduced pressure, the resulting residue was purified by a silica gel column chromatography (eluent: hexane-ethyl acetate, 3:1) to obtain 14.1 g of the title compound with a yield of 89%.
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