Bromomethylcyclopropane → 1-(cyclopropylmethyl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole

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Reaction Steps

To a stirred solution of pyrazole-4-boronic acid pinacol ester (0.25 g, 1.29 mmol) in THF (5 mL) was added a solution of sodium bis(trimethylsilyl)amide (0.71 mL, 2M in THF, 1.42 mmol), followed by (bromomethyl)cyclopropane (0.19 mL, 1.93 mmol). The reaction mixture was stirred at r.t. in a sealed tube for 16 h, then at 80° C. for 4 h. Additional (bromomethyl)cyclopropane (0.06 mL, 0.65 mmol) was added. The reaction mixture was stirred at 80° C. for 16 h, then concentrated in vacuo. EtOAc (30 mL) and aqueous sat. NH4Cl (15 mL) were added. The organic fraction was separated, washed with H2O (15 mL), then brine (15 mL), dried (MgSO4), filtered and concentrated in vacuo to give the title compound (0.27 g, 84%) as a clear yellow oil that was used without further purification. δH (CDCl3) 7.82 (1H, s), 7.80 (1H, s), 3.99 (2H, d, J 7.2 Hz), 1.32 (12H, s), 1.32-1.19 (1H, m), 0.70-0.59 (2H, m), 0.42-0.33 (2H, m). LCMS (ES+) 249.0 (M+H)+, RT 3.42 minutes (Method 1).

Provenance & Evidence