Hydrochloric Acid → 1-(4-Fluorophenyl)-1H-pyrazol-5-ylboronic acid

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Reaction Conditions

Reaction Steps

To a stirred solution of commercially available 1-(4-fluorophenyl)-1H-pyrazole [CAS No 81329-32-0] (1.6 g, 9.87 mmol) in THF (39.5 ml) was added drop wise at −78° C. under nitrogen atmosphere N-butyllithium (1.6 N in hexane, 6.47 ml, 10.4 mmol). After the mixture was allowed to stir at −78° C. for 1 h triisopropyl borate (7.65 g, 9.35 ml, 39.5 mmol) was added at −78° C. The mixture was allowed to stir at −78° C. for 1 h, gradually warmed to room temperature, and the pH of the mixture was adjusted to 5 with 1 M HCl solution. The mixture was evaporated and the remaining water layer extracted with ethyl acetate (2×30 ml). The combined organic layers were washed with brine (30 ml), dried over MgSO4 and evaporated. The raw product was purified by column chromatography on silica gel (dichloromethane/MeOH) and trituration (diethyl ether/hexane) to yield the title compound as a white solid (479 mg, 24%), MS (ISN) m/z=205.0 [(M−H)−], mp 115° C.

Provenance & Evidence