To a solution of methyl 4-bromo-1H-indole-7-carboxylate (6 g, 23 mmol, Preparation 1 Step B) in tetrahydrofuran (THF, 300 mL) was added water (60 mL), methanol (MeOH, 60 mL) and lithium hydroxide (2.83 g, 118 mmol). The reaction mixture was heated to reflux and stirred overnight. After completion of the reaction, it was cooled to room temperature and concentrated under reduced pressure to remove the solvent. To the remaining aqueous layer 4N hydrochloric acid (HCl) was slowly added to adjust the pH to about 6. The precipitate precipitated was collected by filtration and the solid was dried to give 4-bromo-1H-indole-7-carboxylic acid (5.5 g, 97% yield). The structure of the product was confirmed by 1H NMR (DMSO-d6): δ 11.39 (br, 1H), 7.65-7.63 (d, J = 8.0 Hz, 1H), 7.46-7.44 (m, 1H), 7.33-7.31 (d, J = 8.0 Hz, 1H), 6.49-6.48 (m, 1H).
