[NH:1]1[C:9]2[C:8]([C:10]([O:12]C)=[O:11])=[CH:7][CH:6]=[C:5]([C:14]([O:16][C:17]([CH3:20])([CH3:19])[CH3:18])=[O:15])[C:4]=2[CH:3]=[CH:2]1.O1CCCC1.O.[OH-].[Li+]>CO>[C:17]([O:16][C:14]([C:5]1[CH:6]=[CH:7][C:8]([C:10]([OH:12])=[O:11])=[C:9]2[C:4]=1[CH:3]=[CH:2][NH:1]2)=[O:15])([CH3:20])([CH3:18])[CH3:19]To a solution of 4-tert-butyl 7-methyl 1H-indole-4,7-dicarboxylate (0.58 g, 2.10 mmol) in a mixture of methanol (20 mL), terahydrofuran (10 mL) and water (10 mL) was added a 2M aqueous solution of lithium hydroxide (2.1 mL, 4.20 mmol), and the reaction mixture was stirred at 40° C. until full consumption of starting material. The organic portion of the solvent was evaporated and the pH of the aqueous solution was adjusted to 3-4 by the addition of 1 M aqueous hydrochloric acid. The acidic aqueous phase was partitioned with ethyl acetate (150 mL), and the organic layer was separated and washed with brine, dried over sodium sulfate, filtered and concentrated to give 4-(tert-butoxycarbonyl)-1H-indole-7-carboxylic acid (0.36 g, 67%). MS (EI) for C14H15NO4: 260 (M−H).
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