Diethyl Ether → 1-ethyl-4-methyl-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole

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Reaction Steps

At 0° C., to the above ether solution of 4-methylpyrazole was added n-BuLi (36.4 mL, 2.5 M in Hexane, 91 mmol) dropwise. The reaction solution was stirred for 1 hour at RT and then cooled to −78° C. [J. Heterocyclic Chem. 41, 931 (2004)]. To the reaction solution was added 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (18.49 g, 99 mmol). After 15 min at −78° C., the reaction was allowed to warm to 0° C. over 1 hour. The reaction was diluted with saturated NH4Cl solution and extracted with DCM. The organics were dried over Na2SO4 and concentrated under vacuum to afford 1-ethyl-4-methyl-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (16 g, 80% purity) as a syrup which was used without further purification: LC-MS (ES) m/z 155 (M+H)+for [RB(OH)2].

Provenance & Evidence