In a light-protected flask, at 0°C and under an argon atmosphere, KH (62 mg, 1.53 mmol) was suspended in anhydrous THF (0.4 mL). 7-Bromoindole (300 mg, 1.53 mmol) in anhydrous THF (2.6 mL) was added, and the mixture was stirred for 15 minutes. After cooling to -78°C, a solution of tert-butyllithium in pentane (3.1 mmol), pre-cooled to -78°C, was added dropwise. The mixture was allowed to reach room temperature, stirred for 15 minutes, and then cooled again to -78°C.
Add B(OMe)
3 (341 μl, 1.53 mmol) and continue stirring at room temperature for 3 hours. Add H
2O (5 ml) and extract the mixture with EtAcO (2 x 10 ml). Acidify the aqueous phase to pH 1 with 10% HCl and extract again with EtAcO (3 x 10 ml). Dry the combined organic extracts on anhydrous MgSO
4 and filter. Evaporate the solvent, leaving crude indole-7-boronic acid in the form of a light brown oil.
