Phosphoric Acid → 1H-Indol-6-ylboronic acid

Participants

Reaction Steps

A solution of 6-bromoindole (200 mg, 1.02 mmol) in anhydrous ether (4 mL), at −78° C., is treated dropwise with tert-butyllithium (1.7 M solution in pentane, 2 mL, 3.4 mmol). After stirring for 30 minutes the mixture is treated dropwise with tributyl borate (0.822 mL, 3.06 mmol) and allowed to warm up to room temperature. After stirring overnight the reaction mixture is diluted with ether, and this mixture is added in portions to phosphoric acid (15 mL, 1M), stirred for 30 minutes and extracted three times with ether (20 mL). The combined extracts are extracted three times with sodium hydroxide solution (20 mL, 1N). The combined sodium hydroxide extracts are acidified with phosphoric acid (1 M) to pH=2, extracted with ether. The combined ether extracts are washed with brine, dried over sodium sulfate and concentrated to obtain 1H-indol-6-yl-boronic acid [Intermediate (77)] as a solid, which is used for the next step without further purification.

Provenance & Evidence