Three.0 g (8.85 mmol) of potassium phosphate heptahydrate, 1.50 g (5.90 mmol) of bis(boronic acid) pinacol ester B2(pin)2, 12 mg
(0.015 mmol) Xphos-Pd-G2 and 4 mg (0.008 mmol)
Xphos were added sequentially to the reaction vial, 6 mL of ethanol was added and stirred well, then 0.36 mL (2.95 mmol)
4-methoxy-2-(trifluoromethyl)chlorobenzene and reacted for 1 hour at room temperature. The reaction solution was diluted by adding 5mL of ethyl acetate, filtered through diatomaceous earth, washed by ethyl acetate, the filtrates were combined and concentrated under reduced pressure to obtain the crude product, which was separated by silica gel column chromatography, eluting with petroleum ether-ethyl acetate to obtain 4-methoxy-2-(trifluoromethyl)phenylboronic acid pinacol ester.
4-Methoxy-2-(trifluoromethyl)phenylboronic acid pinacol ester was added to the reaction flask and hydrolyzed dropwise with dilute HCl. The solution first produced a precipitate, with the precipitate gradually disappeared, adjust the system pH to 1. To the solution was added NaOH solution with a mass fraction of 25% dropwise to pH 13, stirring 1.
h. The solution was partitioned and the organic phase was extracted with 15 .
mL of NaOH with a mass fraction of 10%, the aqueous phases were combined, and the base solution was extracted twice with 15 mL of THF, respectively. The pH of the obtained alkaline solution was adjusted with dilute HCl, turbidity was produced at the beginning and flocculent appeared slowly, the pH was adjusted to 5.0. 70 was used to
mL THF extraction of the aqueous phase, the organic phase spin-dried and purified to obtain 4-methoxy-2-(trifluoromethyl)phenylboronic acid.
