Potassium Hydroxide → 1-(2-Methoxyethyl)-1H-pyrazole-4-boronic acid, pinacol ester

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Reaction Conditions

Reaction Steps

A solution of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (10 g, 51.5 mmol) in ethanol (50 mL) was treated with KOH (3.47 g, 61.8 mmol) and 1-bromo-2-(methyloxy)ethane (5.81 mL, 61.8 mmol) at room temperature and the resulting mixture was stirred at 50° C. under nitrogen for 16 h then cooled to room temperature. 1-Bromo-2-(methyloxy)ethane (2 mL, 21.3 mmol) was added and the resulting mixture was stirred at 50° C. for 60 h then cooled to room temperature. The mixture was filtered through celite and the insoluble were washed with ethanol. The combined filtrate and washings were concentrated in vacuo. Purification of the residue on SP4 using a 100 G silica cartridge (gradient: 0 to 100% AcOEt in Hexanes) gave 1-[2-(methyloxy)ethyl]-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (2.72 g, 10.25 mmol, 20%) as a yellow oil. LCMS (method G): Retention time 0.87 min, [M+H]+=252.9

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