Hydrochloric Acid → (3,5-Difluorophenyl)boronic acid

Participants

Reaction Conditions

Reaction Steps

In a separate reaction vessel, 40 mL of tetrahydrofuran was cooled to -78 ° C., and the Grignard reagent of 3,5-difluorophenyl bromide and a solution of 11.3 grams (0.109 mole) of trimethyl borate in 15 mL of tetrahydrofuran were added simultaneously dropwise in an effort to provide an equimolar addition of each. An additional 115 mL of tetrahydrofuran was added during the additions to dilute the thickening reaction mixture. The completion of additions required about 15 minutes. After this time the reaction mixture was allowed to warm to ambient temperature as it stirred for about 18 hours. The reaction mixture was then poured into 300 mL of an aqueous dilute solution of hydrochloric acid. The resultant mixture was extracted with two 150 mL portions of ethyl acetate. The combined extracts were dried with magnesium sulfate and filtered. The filtrate was concentrated under reduced pressure, yielding 13.6 grams of 3,5-difluoro-phenylboronic acid. The NMR spectrum was consistent with the proposed structure.

Provenance & Evidence