Trimethyl borate → 2-(Benzyloxy)-4-methoxyphenylboronic acid

Participants

Reaction Conditions

Reaction Steps

A 2 L three-necked flask equipped with thermometer, reflux condenser and mechanical stirrer was charged with 1-bromo4-methoxy-2-(phenylmethoxy)benzene (43.0 g, 0.147 mol), anhydrous THF (600 mL) under nitrogen. Magnesium turnings (4.2 g, 0.17 mol) and 1,2-dibromoethane (0.5 mL, 6 mmol) was then added and the mixture heated to reflux. After 1.5 h, the reaction was cooled to −78° C. and B(OMe)3 (33.4 mL, 0.294 mol) added dropwise while maintaining an internal temperature below −60° C. Upon complete addition, the reaction was quenched with 5% HCl (15 mL) to pH=3.0, partioned with EtOAc (100 mL), the organic phase separated, washed with brine (100 mL), dried (MgSO4) and concentrated in vacuo giving a pale yellow solid. The solid was triturated with hexane (90 mL), filtered and dried to afford [4-methoxy-2(phenylmethoxy)phenyl]boronic acid as a pale white solid (32 g, 85%): mp 127.0-129.0° C.; 1H NMR δ7.8 (d, 3=8.2 Hz, 1H), 7.5-7.3 (m, 5H), 6.6 (dd, J=8.2, 2.7 Hz, 1H), 6.55 (d, J=5 Hz, 1H), 5.65 (s, 2H), 5.15 (s, 2H), 3.85 (s, 3H).

Provenance & Evidence