2-methylphenyl boronic acid

The first microwave-promoted Suzuki couplings were published in 1996 (Scheme 44). Phenyl boronic acid was coupled with 4-methylphenyl bromide... 

To a dichloromethane solution (5 ml) containing triphenylbismuth difluoride (239 mg, 0.50 mmol) and 4-methylphenylboronic acid (68 mg, 0.50 mmol) was added boron trifluoride diethyl etherate (65 p.1, 0.50 mmol) at 0°C, and the resulting mixture was stirred at room temperature for 2 h. An aqueous solution (20 M) of sodium fluoroborate (500 mg, 4.55 mmol) was then added and the two-phase mixture was vigorously stirred for 30 min. The water phase was extracted with dichloromethane (5 ml X 2), and the combined extracts were dried over MgS04, and passed through a short silica gel column. Evaporation of the solvent under reduced pressure left an oily residue, which was crystallized from ether-dichloromethane (10 1) to yield (4-methylphenyl)triphenylbismuthonium tetrafluoroborate (300 mg, 97%) as a colorless solid [980M4332]. 

Also obtained by hydrolysis of 2-difluoroboryloxy-4-methylphenyl benzyl ketone (SM) (m.p. 125-126°) with refluxing dilute ethanol for 15-20 min. SM was prepared by action of phenylacetic acid with m-cresol in the presence of boron trifluoride etherate for 30 min at 125-130° (50%) [5309],... 

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