GENERAL PROCEDURE: To a tetrahydrofuran (THF, 4 mL) solution of diisopropylaminoborane (DIPAB, 863 mg, 7.5 mmol) and magnesium (Mg, 182 mg, 7.5 mmol) was added a 1 M solution of phenylmagnesium bromide (PhMgBr) THF (375 μL, 375 μmol) at room temperature. After 10 min of reaction, 30 mL of anhydrous THF was added, followed by 4-bromo-2-chlorotoluene (5 mmol). The reaction mixture was cooled to 0 °C and quenched by slowly adding 7 mL of methanol (MeOH). After 1 h of reaction, the volatiles were removed under reduced pressure and the resulting solid was dissolved in a 1 N hydrochloric acid/methanol (7:3, v/v) mixture. After 1 h of reaction at room temperature, 100 mL of ethyl acetate (AcOEt) was added, and 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 a solid product, which was finally purified by recrystallization from water (H2O) to give 3-chloro-4-methylphenylboronic acid.
