[CH2:1]([N:5]1C2C(=CC(C)=CC=2)[CH:7]=[C:6]1[C:15]([O:17][CH2:18][CH3:19])=[O:16])[CH:2]([CH3:4])[CH3:3].[Br:20]N1C(=O)CCC1=O.N(C(C)(C)C#N)=NC(C)(C)C#N.[C:40]([O-:43])(=O)C.[K+].[CH:45]1[CH:50]=[CH:49][CH:48]=[CH:47][CH:46]=1>CN(C)C=O.O.C(OCC)(=O)C>[Br:20][C:7]1[C:50]2[C:45](=[CH:46][CH:47]=[C:48]([CH:40]=[O:43])[CH:49]=2)[N:5]([CH2:1][CH:2]([CH3:4])[CH3:3])[C:6]=1[C:15]([O:17][CH2:18][CH3:19])=[O:16]In 10 ml of benzene are suspended 1.00 g of ethyl 1-isobutyl-5-methyl-1H-indole-2-carboxylate, 0.76 g of N-bromosuccinimide and 0.07 g of 2,2′-azobisisobutyronitrile. The suspension is heated under reflux for two hours. The reaction mixture is concentrated under reduced pressure, and the residue thus obtained is dissolved in 10 ml of N,N-dimethylformamide. After adding 0.57 g of potassium acetate, the mixture is stirred at 40° C. for 30 minutes. The reaction mixture is added to a mixture of ethyl acetate and water, and the organic layer is separated. The organic layer thus obtained is washed with water and saturated aqueous solution of sodium chloride successively and dried over anhydrous magnesium sulfate, and then the solvent is distilled off under reduced pressure. The residue thus obtained is purified by silica gel column chromatography (eluent; hexane:ethyl acetate=6:1) to obtain 0.68 g of ethyl 3-bromo-5-formyl-1-isobutyl-1H-indole-2-carboxylate as a yellow oily product.
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