2-Isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane → 3-cyclopropyl-1-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyrazole

Participants

Reaction Steps

To a stirred solution of 4-bromo-3-cyclopropyl-1-methyl-1H-pyrazole (500 mg, 2.5 mmol) in THF (10 mL) was added dropwise a 2.5 M solution of n-BuLi (1.4 mL, 3.5 mmol) at −78° C., and the resulting light yellow solution was stirred for 30 min. To the mixture was added a solution of 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (1.1 mL, 5.5 mmol) in THF (1 mL), and the mixture was warmed to room temperature over 30 min. The reaction was quenched with saturated aqueous NH4Cl solution. The mixture was extracted with EtOAc (50 mL), washed with brine, dried over MgSO4, filtered and concentrated under reduced pressure. The residue was purified by normal phase flash chromatography on silica gel (5% MeOH—CH2Cl2, Rf=0.35) to provide 3-cyclopropyl-1-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (294 mg, 48%) as a yellow oil.

Provenance & Evidence