The general procedure for the synthesis of 1-isopropylpyrazole-5-boronic acid from 1-isopropylpyrazole was as follows: n-BuLi (17.46 g, 110 ml, 273 mM in hexane) was slowly added to a THF solution of 1-isopropyl-1H-pyrazole over a period of 30 min at -78 °C. The reaction mixture was stirred at -78 °C for 2 hours. Subsequently, a cooled solution of triisopropoxyborate (170.0 g, 909 mmol) was slowly added through a cannula over 45 minutes. The reaction mixture was slowly warmed from -50 °C to room temperature and stirred overnight. The pH of the reaction mixture was adjusted to 6-7 with 1 M HCl (170 mL). the solvent was evaporated to dryness and the resulting residue was ground with a 1:1 mixture of ethyl acetate:dichloromethane. The suspension was filtered and the solvent was evaporated in vacuo to give 1-isopropylpyrazole-5-boronic acid as a colorless solid (20.0 g, 58% yield).LCMS m/z (%) = 154 [M+H]+ (100).1H NMR (400 MHz, DMSO-d6) δ: 8.14 (s, 2H), 7.2 (s, 1H), 6.5 (s, 1H). 5.05 (m, 1H), 1.2 (d, J = 9.0Hz, 6H).
