3-Bromo-1H-pyrazole

Uses

3-Bromopyrazole is a useful synthetic intermediate in the synthesis of Rynaxypyr (C325380); an insecticidal anthranilic diamide that acts as a potent and selective ryanodine receptor activator.

Synthesis

General procedure for the synthesis of 3-bromopyrazole from 1-(dimethylaminosulfonyl)-3-bromopyrazole: 3-bromo-N,N-dimethyl-1H-pyrazole-1-sulfonamide (5.83 g) obtained in step B was mixed with trifluoroacetic acid (9.0 mL) and the reaction was stirred for 2 hours at room temperature. Upon completion of the reaction, ethyl acetate was added to the mixture, followed by neutralization of the reaction solution with saturated aqueous sodium bicarbonate and washing with saturated aqueous sodium chloride. The organic layer was separated, dried with anhydrous sodium sulfate and concentrated under reduced pressure to remove the solvent. The resulting crude product was purified by silica gel column chromatography (eluent: ethyl acetate/hexane) to give the final target compound 3-bromopyrazole (2.92 g). The product was characterized by 1H NMR (400 MHz, CDCl3): δ 6.37 (1H, d, J=2.4 Hz), 7.57 (1H, d, J=2.4 Hz).

References

[1] Patent: WO2006/68669, 2006, A1. Location in patent: Page/Page column 19; 24
[2] Patent: WO2003/106427, 2003, A2. Location in patent: Page 18
[3] Patent: WO2004/11447, 2004, A2. Location in patent: Page 42-43
[4] Patent: EP2818473, 2014, A1. Location in patent: Paragraph 0583
[5] Patent: US9113630, 2015, B2. Location in patent: Page/Page column 41; 42