3.0 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) of Xphos-Pd-G2, and 4 mg (0.008 mmol) of Xphos were added sequentially to a reaction vial with 6 mL of ethanol stirred to mix well, and then 0.36 mL (2.95 mmol) 3-(N-methylformylamino)chlorobenzene was added and the reaction was carried out at room temperature for 1 hour. The reaction solution was diluted by adding 5 mL of ethyl acetate, filtered through diatomaceous earth, washed with ethyl acetate, the filtrates were combined and concentrated under reduced pressure to obtain the crude product, which was separated by silica gel column chromatography, eluted with petroleum ether-ethyl acetate, to obtain 3-(N-methylformylammonio)phenylboronic acid pinacol ester.
3-(N-Methylformylammonio)phenylboronic acid pinacol ester was added to a reaction vial and hydrolyzed dropwise with dilute HCl. The solution first produced a precipitate, and as the precipitate gradually disappeared, the pH of the system was adjusted to 1. NaOH solution with a mass fraction of 25% was added dropwise to the solution to pH 13, and stirred for 1 h. The solution was partitioned, and the organic phase was extracted with 15 mL of NaOH with a mass fraction of 10%, and the aqueous phases were combined, and the bases were extracted with 15 mL of THF for 2 times, respectively. The pH of the obtained base solution was adjusted with dilute HCl, turbidity was produced at the beginning, flocculent appeared slowly, and the pH was adjusted to 5.0. The aqueous phase was extracted with 70 mL of THF, and the organic phase was spin-dried and purified to obtain 3-(N-methylformylamino)phenylboronic acid.
