Hydrochloric Acid → 4-(2-Hydroxyethyl)phenylboronic acid

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Reaction Steps

To a suspension of magnesium (0.264 g, 11 mmol) in dry tetrahydrofuran (10 ml) under nitrogen gas was added dropwise over 1/2 hour the t-butyl dimethyl silyl ether of 4-bromophenyl ethyl alcohol (a, 3.45 g, 10.9 mmol) in tetrahydrofuran (10 ml). Magnesium was then activated by the addition of dibromoethane (0.1 g). The metal went into solution slowly over a period of 8 hours. The Grignard reagent was then cooled to -78° C. and treated with freshly distilled trimethyl borate (1.15 g, 11 mmol) added dropwise with stirring. The reaction mixture was then warmed to room temperature and stirred overnight. It was then treated with 2N hydrochloric acid till acidic and the tetrahydrofuran layer was separated from the aqueous layer. The aqueous portion was thoroughly extracted with ethyl acetate (5×50 ml) and the combined organic layer was washed with water and finally with saturated sodium chloride. The organic phase was then dried, concentrated and the residue was purified by chromatography (silica gel). Elution with ethyl acetate/methanol (95:5) provided the boronic acid, which was recrystallized from ethyl acetate/hexane. Yield: 0.69 g (38%), m.p. 218°-220° C., M.S. 184 (M+NH4), 156, 140, 1H NMR (DMSO-d6): δ2.7 (t, 2H), 4.6 (t, 2H), 7.1 and 7.7 (2d, 4H) and 7.9 (s, 2H).

Provenance & Evidence