C(OC([N:8]1[C:16]2[C:11](=[CH:12][C:13]([F:17])=[CH:14][CH:15]=2)[C:10]([C:18]([C:21]([O:23][CH3:24])=[O:22])([CH3:20])[CH3:19])=[CH:9]1)=O)(C)(C)C.C([O-])([O-])=O.[K+].[K+]>CO.[Cl-].[Na+].O>[CH3:24][O:23][C:21](=[O:22])[C:18]([C:10]1[C:11]2[C:16](=[CH:15][CH:14]=[C:13]([F:17])[CH:12]=2)[NH:8][CH:9]=1)([CH3:20])[CH3:19]A solution of 5-fluoro-3-(1-methoxycarbonyl-1-methyl-ethyl)-indole-1-carboxylic acid tert-butyl ester (5.2 mmol) in MeOH (25 mL) is treated with K2CO3 (720 mg, 5.2 mmol) and heated at reflux for 2 h. The mixture is diluted with brine (50 mL) and extracted with EtOAc (3×50 mL). The combined organic layer is dried (Na2SO4), filtered and concentrated in vacuo to afford 2-(5-fluoro-1H-indol-3-yl)-2-methyl-propionic acid methyl ester (650 mg, 53%, 2 steps), which is used in the next step without further purification. MS: 236 (M+H); 1H NMR (300 MHz, DMSO-d6): δ 7.35 (m, 1H), 7.30 (m, 1H), 7.14 (m, 1H), 6.91 (m, 1H), 3.54 (s, 3H), 1.57 (s, 6H).
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