General procedure for the synthesis of 3-chloro-4-hydroxyphenylboronic acid from 4-bromo-2-chlorophenol:
1. n-BuLi (12 mL of 2.44 M solution, 29 mmol) was added slowly and dropwise to a stirring solution of 4-bromo-2-chlorophenol (5 g, 24 mmol) in anhydrous THF (75 mL) at -78°C and stirring was continued for 2 hours at -78°C.
2. trimethyl borate (3.3 mL, 29 mmol) was added to the reaction mixture, followed by allowing the reaction mixture to slowly warm to room temperature and stirring for 19 hours.
3. The reaction was quenched using 2M HCl aqueous solution followed by organic phase extraction with EtOAc (2 x 60mL).
4. The organic extracts were combined and concentrated under reduced pressure to give an oily substance containing a white precipitate.
5. Hexane was added to the oily substance, and the white powder was collected by filtration and washed with hexane.
Yield: 15%.
1H NMR (270 MHz, DMSO-d6) δ: 6.49 (bs), 6.91 (1H, d, J = 7.9 Hz), 7.54 (1H, dd, J = 8.2, 1.5 Hz), 7.72 (1H, d, J = 1.5 Hz), 8.02 (bs), 10.32 (1H, s).
HPLC retention time: 3.36 min (>91% purity, aqueous solution of 90% MeCN).
LC/MS (APCI) m/z: 171.16 (M-H)-.
