4-hydroxypyrazole synthesis

Yield:-

Reaction Conditions:

Stage #1:pyrazole-4-boronic acid pinacol ester with sodium hydroxide;dihydrogen peroxide in tetrahydrofuran;water at 0 - 20; for 0.883333 h;
Stage #2: with hydrogenchloride in tetrahydrofuran;water

Steps:

733.A
At 0 °C Hydrogen peroxide (30% in H₂O. 379 μL. 3.71 mmol) and NaOH (2M in H₂O.1.86 mL. 3.71 mmol) were added to a stirred solution of 4-(4.4.5.5-tetramethyl- [1.3.2]dioxaborolan-2-yl)-lH-pyrazole in THF (5 mL). After stirring for 3 min at 0 °C the reaction was warmed to room temperature and stirred for further 50 min. The reaction was diluted with H₂O (20 mL). acidified with HCl (2 N) and extracted four times with DCM (50 mL) and four times with DCM/isopropanol (4:1. 50 mL). The combined organic layers were dried over Na₂SO₄. filtered, and concentrated in vacuo. The resulting title compound was used for the next reaction without purification. MS (m/z): 85.0 [MH-H⁺].

References:

JERINI AG WO2008/116620, 2008, A1 Location in patent:Page/Page column 171