Sodium Hydroxide → (2-(1-methyl-1H-pyrazol-5-yl)-4-(trifluoromethyl)phenyl)boronic acid

Participants

Reaction Conditions

Reaction Steps

An 250 mL round-bottom flask was charged with 5-(2-bromo-5-(trifluoromethyl)phenyl)-1-methyl-1H-pyrazole (Intermediate F) (2.956 g, 9.69 mmol), diethyl ether (74.5 mL), and triisopropyl borate (2.70 mL, 11.63 mmol). The flask was cooled to −78° C. for 10 min, after which butyllithium (2.5M in hexanes) (4.65 mL, 11.63 mmol) was added dropwise. The mixture was stirred for 30 min, and then warmed to room temperature. A 2N aq. NaOH solution (100 mL) was added, and the resulting biphasic mixture was stirred vigorously for 1 h. The mixture was diluted with water, and the layers separated. The ethereal layer was extracted with water (twice) and the water layers were combined and washed with diethyl ether. The ether layers were back-extracted once more, and all aqueous layers combined and acidified to a pH of about 2 with 6N aq. HCl to give a clear solution. The aqueous layer was extracted with ethyl acetate (twice), and the combined organics were dried over sodium sulfate, filtered and concentrated. The residue was concentrated from DCM to give (2-(1-methyl-1H-pyrazol-5-yl)-4-(trifluoromethyl)phenyl)boronic acid (2.36 g, 8.74 mmol) as a yellow solid. m/z (ESI) 271.2 (M+H)+.

Provenance & Evidence