(1-Methyl-1H-pyrazol-5-yl)-boronic acid

930-36-9

720702-41-0

General procedure for the synthesis of 1-methyl-1H-pyrazole-5-boronic acid from 1-methylpyrazole: 1-methylpyrazole (25 mL, 0.3 mol) was dissolved in 500 mL of tetrahydrofuran (THF). The solution was then cooled to -78°C in a dry ice/isopropanol bath. After the solution temperature stabilized at -78 °C, n-butyllithium (n-BuLi, 140 mL, 0.40 mol) was slowly added dropwise through the cannula. After the dropwise addition, the reaction mixture was stirred continuously at -78 °C for 1.5 hours. Next, triisopropyl borate (280 mL, 1.2 mol) was added to the reaction system via cannula and the reaction mixture was allowed to slowly warm from -78 °C to 0 °C while stirring overnight. Upon completion of the reaction, the pH of the mixture was adjusted to 6 with 1 N hydrochloric acid (HCl).Subsequently, THF was evaporated under reduced pressure and the remaining aqueous phase was extracted with ethyl acetate (EtOAc, 2 × 100 mL). Finally, the solid was collected by filtration to afford 108 g (100% yield) of 1-methyl-1H-pyrazole-5-boronic acid as a yellow solid.