1-Bromo-4-fluorobenzene → (5-Bromo-2-fluorophenyl)boronic acid

Participants

Reaction Conditions

Reaction Steps

A cooled (−20° C.) solution of 2,2,6,6-tetramethylpiperidine (28 ml, 165 mmol) in tetrahydrofuran (400 ml) was treated with m-butyllithium (63 ml of a 2.5M solution in hexanes, 157.5 mmol). This mixture was then cooled to −78° C. 1-Bromo-4-fluorobenzene (16.5 ml, 150 mmol) was then added neat and dropwise over 10 min and stirring at −78° C. was continued for 3 h. Triisopropyl borate (40 ml, 172.5 mmol) was then added and stirring at −78° C. continued for 30 min before removing the cooling bath. When the internal temperature of the reaction reached −4° C., 5N hydrochloric acid (75 ml) was added and the mixture was stirred to ambient temperature. After stirring at ambient temp for 1 h the majority of the tetrahydrofuran was removed and the mixture partitioned between ether (500 ml) and 1N hydrochloric acid (500 ml). The organics were then extracted with 2N sodium hydroxide (400 ml) and the organics were discarded. The aqueous was cooled in an ice-water bath and 5N hydrochloric acid (150 ml) was added dropwise over 15 min. The resulting white solid was collected and dried under vacuum to afford 5-bromo-2-fluorobenzeneboronic acid (25 g, 76%).

Provenance & Evidence