[C:1]1(=O)[CH2:6][CH2:5][CH2:4][CH2:3][CH2:2]1.C[C:9]1[NH:10][C:11]2[C:16]([CH:17]=1)=[CH:15][CH:14]=[C:13]([C:18]([OH:20])=[O:19])[CH:12]=2.C[O-].[Na+]>CO>[C:1]1([C:17]2[C:16]3[C:11](=[CH:12][C:13]([C:18]([OH:20])=[O:19])=[CH:14][CH:15]=3)[NH:10][CH:9]=2)[CH2:6][CH2:5][CH2:4][CH2:3][CH:2]=1Cyclohexanone (96 mL, 0.926 mol) was added to a stirred solution of methyl indole-6-carboxylic acid (50.0 g, 0.335 mol) in methanol (920 mL) at 22° C. Methanolic sodium methoxide (416 mL of 25% w/w, 1.82 mol) was added in portions over 10 minutes. The mixture was stirred at reflux for 18 hours, cooled to room temperature, concentrated, diluted with cold water, and acidified with 36% HCl solution. The resulting precipitate was collected by filtration, washed with cold water, and dried over phosphorous pentoxide (0.1 mm) to provide the title compound as a tan colored solid (80.9 g, 97.5% yield).
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