Triisopropyl borate → 1-(Tetrahydropyran-2-yl)pyrazole-5-boronic acid

Participants

Reaction Steps

To a solution of 1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazole (2.10 g, 13.8 mmol) in anhydrous THF (30.0 mL) was added n-BuLi (2.5 M in hexane, 14.0 mL) at −78° C. The mixture was kept at this temperature for 30 min. Triisopropyl borate (2.85 g, 15.2 mmol) was added over 10 min at −78° C. and held for 1 hr. The resulting mixture was allowed to reach room temperature over 4 hr. After being quenched by aq. HCl (2.00 M, 55.0 mL) with intensive stirring, the aqueous phase was added NaCl (s) and extracted with THF/EtOAc. The combined organic layer was washed with brine, sat NaHCO3, dried over MgSO4, filtered and evaporated to afford 1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazol-5-ylboronic acid (3.6 g, 52% yield) as yellow oil. LCMS (ESI) m/z: 197.0 [M+H+].

Provenance & Evidence