Br[C:2]1[CH:3]=[C:4]([CH3:11])[CH:5]=[C:6]2[C:10]=1[NH:9][CH:8]=[CH:7]2.[Li]CCCC.[C:17](=[O:19])=[O:18].O>C1COCC1.CCCCCC>[CH3:11][C:4]1[CH:5]=[C:6]2[C:10](=[C:2]([C:17]([OH:19])=[O:18])[CH:3]=1)[NH:9][CH:8]=[CH:7]2
1.68 g of 7-bromo-5-methyl-indole (8 mmol) were dissolved in 30 ml THF and 15 ml of a 1.6 molar solution of n-BuLi in hexane were added at −78° C. The reaction mixture was then allowed to warm to 0-5° C. and was stirred at this temperature for 30 min. Then it was cooled again to −78° C., dry ice was added and the mixture was allowed to warm to rt. After 15 min at rt it was poured into water and extracted twice with ether. The aqueous phase was then acidified with 1 N HCl solution and extracted several times with DCM. The combined DCM extracts were then washed with brine, dried with magnesium sulfate, filtered and the solvent was evaporated. The remaining residue was triturated with n-hexane. Final filtration yielded 0.78 g (56%) of 5-methyl-1H-indole-7-carboxylic acid as light brown solid. 1H NMR (DMSO-d, 300 MHz): δ 2.41 (s, 3H), 6.44 (m, 1H), 7.31 (m, 1H), 7.58 (s, 1H), 7.61 (s, 1H), 10.91 (br s, 1H), 12.92 (br s, 1H).
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