P(Cl)(Cl)(O[Cl:4])=O.[NH:7]1[C:15]2[CH:14]=[CH:13][CH:12]=[C:11]([C:16]([O:18][CH3:19])=[O:17])[C:10]=2[CH:9]=[CH:8]1.[C:20](=O)(O)[O-:21].[Na+].[CH3:25][N:26]([CH3:29])[CH:27]=O>O>[CH3:25][N+:26]([CH3:29])=[CH:27][Cl:4].[Cl-:4].[CH:20]([C:9]1[C:10]2[C:11]([C:16]([O:18][CH3:19])=[O:17])=[CH:12][CH:13]=[CH:14][C:15]=2[NH:7][CH:8]=1)=[O:21]The Vilsmeier reagent was prepared by the dropwise addition of phosphoryl oxychloride (0.75 mg) to cooled N,N-dimethylformamide (20.0 ml) under constant stirring. A solution of methyl indole-4-carboxylate in N,N-dimethylformamide (12.0 ml) was added to the above solution at 0° C. and the solution was stirred for 30 minutes. The mixture was diluted with water (40 ml) and the solution was neutralized with saturated sodium bicarbonate aqueous solution and extracted with ethyl acetate (60 ml). The organic layer was washed successively with water and brine, dried over magnesium sulfate and concentrated invacuo. The solid was triturated with diethyl ether (7 ml) to give methyl 3-formylindole-4-carboxylate (792 mg).
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