GENERAL PROCEDURE: A 1 M THF solution (375 μL, 375 μmol) of phenylmagnesium bromide (PhMgBr) was added dropwise to a tetrahydrofuran (THF, 4 mL) solution of diisopropylaminoborane (DIPAB, 863 mg, 7.5 mmol) and magnesium scrapings (Mg, 182 mg, 7.5 mmol) at room temperature. After 10 min of reaction, 30 mL of anhydrous THF was added, followed by 3,5-dimethylbromobenzene (5 mmol). The reaction mixture was cooled to 0 °C and quenched by slow addition of methanol (MeOH, 7 mL). After 1 h of reaction, the volatiles were removed under reduced pressure and the resulting solid was dissolved in a 1N hydrochloric acid/methanol (7:3, v/v) mixture. The reaction was continued for 1 h at room temperature, followed by the addition of ethyl acetate (AcOEt, 100 mL) for extraction. The organic phase was washed sequentially with 1N hydrochloric acid (30 mL) and saturated saline (3 x 30 mL). The organic phase was concentrated under reduced pressure to give the crude product, which was finally purified by recrystallization from water (H2O) to give 3,5-dimethylphenylboronic acid.
