Trimethyl borate (94 mL, 840 mmol) and tetrahydrofuran (600 mL) were added to a 3L three-necked round-bottomed flask equipped with a stir bar. The solution was cooled to -78°C. Vinyl magnesium bromide (1.0 M solution in tetrahydrofuran, 800 mL, 800 mmol) was added dropwise through a cannula over 2 hr 45 min. The resulting solution was stirred at -78°C for 15 minutes and then at 23°C for 2 hours and 30 minutes. Dry N-methyliminodiacetic acid (235.0 g, 1.6 mol) and dimethyl sulfoxide (600 mL) were added to a separate 2L three-necked round-bottomed flask fitted with a stir bar, internal thermometer, and distillation apparatus. The solution was heated to an internal temperature of 110-115°C using an oil bath. The borate suspension was added dropwise to the hot N-methyliminodiacetic acid solution through a polytetrafluoroethylene cannula over a period of 2 hours and 10 minutes, maintaining the internal temperature between 105 and 115°C. After complete addition of the borate solution, the reaction solution was cooled to 23°C. The resulting solution was transferred to a split funnel containing water (1 L), brine (1 L), ethyl acetate (1.5 L) and acetone (1 L). The mixture was shaken to remove the aqueous layer and extracted with ethyl acetate/acetone (2:1, 260mL). The combined organic layers were washed with water (2500 mL). The combined aqueous washings were back-extracted with ethyl acetate/acetone (2:1, 2300mL). The combined organic phases were dried over magnesium sulfate, filtered, and concentrated in vacuum. The resulting solid was suspended in 300 mL of acetone and 4 L of ether was added to precipitate the product. The resulting solid was collected by vacuum filtration to give vinylboronic acid methyliminodiacetate as a white solid (81.2 g, 55%). The spectral data of the product were in agreement with those previously reported by our laboratory.
