4-Methylpyrazole → 1-Ethylpyrazole-5-boronic acid, pinacol ester

Participants

Reaction Steps

At 0° C., to above solution of 4-methylpyrazole (˜50 mmol) was added n-BuLi (2.5M in hexane, 22 mL, 55 mmol). 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 (10.2 g, 55 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 a tan solid (9.8 g, 89%) which was used without further purification. LCMS (ES) m/z 141 (M+H)+for [RB(OH)2]; 1H NMR (CDCl3, 400 MHz) δ ppm 7.52 (d, J=2 Hz, 1H), 6.36 (d, J=2 Hz, 1H), 4.48 (q, J=7.2 Hz, 2H), 1.44 (t, J=7.2 Hz, 3H), 1.36 (s, 12H)

Provenance & Evidence