Synthesis
Example 29A Synthesis of 4-bromo-1-phenyl-1H-pyrazole: 1-phenylpyrazole (Aldrich, 1 g, 6.94 mmol) was dissolved in 10 mL of acetic acid, followed by the addition of 1.1 g of bromine (Fisher, 6.94 mmol) to a 10 mL solution of acetic acid. The reaction mixture was transferred to a pressure tube and the reaction was heated at 100 °C for 8 hours. After the reaction was completed, it was cooled to room temperature and the reaction solution was slowly poured into a 500 mL beaker containing ice and water and saturated aqueous NaHCO3 solution was added dropwise until the acetic acid was completely neutralized. The organic layer was separated by adding 50 mL of ethyl acetate (EtOAc) for extraction. The aqueous layer was then extracted with 2 x 15 mL of ethyl acetate, the organic phases were combined and dried with anhydrous Na2SO4. The organic phase was concentrated under reduced pressure to obtain the crude product. Purification by fast column chromatography (silica gel, 5:0 to 5:5 gradient elution of hexane-ethyl acetate) afforded 1.5 g of the target compound 4-bromo-1-phenyl-1H-pyrazole (6.72 mmol, 97% yield). Mass spectrum (DCI/NH3) m/z 223,225 (M+H)+.
References
[1] Chemistry - A European Journal, 2015, vol. 21, # 34, p. 11976 - 11979
[2] Patent: US2005/65178, 2005, A1. Location in patent: Page/Page column 31
[3] Patent: US2005/101602, 2005, A1. Location in patent: Page/Page column 68
[4] RSC Advances, 2016, vol. 6, # 93, p. 90031 - 90034
[5] Tetrahedron Letters, 2007, vol. 48, # 26, p. 4595 - 4599
