An improved synthesis of 1-methyl-1H-pyrazole-4-boronic acid pinacol ester and its corresponding lithium hydroxy ate complex: application in Suzuki couplings

An improved synthesis of 1-methyl-1H-pyrazole-4-boronic acid pinacol ester via isolation of the corresponding lithium hydroxy ate complex is described. The hydroxy ate complex is available in one pot from 4-bromo-1-methyl-1H-pyrazole and triisopropyl borate, and is isolated by filtration in high yield. Furthermore, the resulting lithium hydroxy ate complex has long-term bench stability and can be employed directly in Suzuki couplings without the need for added base.