P(Cl)(Cl)(Cl)=O.[CH3:6][O:7][C:8]1[CH:9]=[C:10]2[C:14](=[CH:15][CH:16]=1)[NH:13][C:12]([CH3:17])=[CH:11]2.[OH-].[Na+].[CH3:20][C:21](N(C)C)=[O:22]>O>[CH3:6][O:7][C:8]1[CH:9]=[C:10]2[C:14](=[CH:15][CH:16]=1)[NH:13][C:12]([CH3:17])=[C:11]2[C:21](=[O:22])[CH3:20]
Dimethylacetamide (17.5 ml, 188.4 mmol) is added dropwise with stirring to phosphorous oxychloride (12.9 ml, 138.2 mmol) at 0° C. Stirring is maintained for 45 minutes, at which time the bath is removed and 5-methoxy-2-methylindole (20.25 g, 125.6 mmol) in 15 ml of dimethylacetamide is added dropwise over a period of 75 minutes. The resulting mixture is warmed to 40°-45° C. for 4 hours. The reaction mixture is cooled to 0° C., and 100 g of ice water is added followed by dropwise addition of a solution of sodium hydroxide (50 g) in water (75 ml). The first 1/3 of this sodium hydroxide solution is added slowly and the remainder is added quickly. The exothermic reaction is quickly warmed to boiling for 15 minutes, cooled to room temperature and refrigerated overnight. The resulting crystals are collected by filtration and rinsed four times with water. Recrystallization from ethanol/water gives 17.2 g (67.2%) of pure 1-(5-methoxy-2-methyl-1H-indol-3-yl)ethanone; mp 229.0°-230.5° C.
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