4-BROMO-3-CHLORO-5-METHYL-1H-PYRAZOLE synthesis

Yield: 93.03%

Reaction Conditions:

with N-Bromosuccinimide in dichloromethane at 20;

Steps:

3.A Step A, 4-Bromo-3-chloro-5-methyl-1H-pyrazole
3 -Chloro-5 -methyl- 1H-pyrazole (2.5 g, 21.45 mmol) was dissolved in DCM (50 mL), and then NBS (3.8 g, 21.45 mmol) was added. The reaction mixture was stirred at room temperature overnight. The reaction mixture was diluted with DCM (100 mL), washed with sat. aq. Na₂S₂O₃ (100 mL) and brine (100 mL). The organic layer was separated, dried over Na₂SO₄, filtered, and concentrated under reduced pressure. Purification by flash column chromatography (SiO₂, petroleum ether/DCM=1/0 to 0/1, then DCM/MeOH=1/0 to 20/1) afforded the title compound (3.9 g, 19.95 mmol, 93.03% yield) as a white solid. MS (ESI): mass calcd. for C₄H₄BrClN₂, 193.9; m/z found, 196.8 [M+H]⁺. ¹H NMR (400MHz. CDCl₃) δ = 11.49 (br s, 1H), 2.35 (s, 3H).

References:

JANSSEN BIOTECH, INC. WO2021/84500, 2021, A1 Location in patent:Page/Page column 66