Synthesis
General procedure for the synthesis of 1-phenyl-3-aminopyrazole from 1-phenyl-4,5-dihydro-1H-pyrazol-3-amine: to a solution of 1-phenyl-4,5-dihydro-1H-pyrazol-3-amine (7.4 g, 46 mmol) in dioxane (200 mL) was added 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (11.54 g, 50 mmol ). After addition, the reaction mixture was stirred at room temperature for 1 h. The resulting dark-colored solution was then filtered through a pad of diatomaceous earth. The filtrate was acidified with 1N HCl aqueous solution (100 mL) and extracted with dichloromethane (50 mL). The organic layer was extracted again with 1N HCl aqueous solution (50 mL). The combined aqueous layers were washed with dichloromethane (2 x 50 mL) and then adjusted to pH 12 with NaOH, followed by extraction with dichloromethane (3 x 100 mL). The combined dichloromethane extracts were washed with saturated aqueous NaCl (100 mL), dried (MgSO4), and concentrated under reduced pressure to give 1-phenyl-3-aminopyrazole as a light orange solid (3.0 g, 41% yield).LC/MS (Method A): retention time = 1.43 min, (M+H)+ =160.
References
[1] Bioorganic and medicinal chemistry, 2002, vol. 10, # 3, p. 817 - 827
[2] Patent: US4149005, 1979, A
[3] Farmaco, Edizione Scientifica, 1985, vol. 40, # 11, p. 808 - 817
[4] Patent: US2006/154956, 2006, A1. Location in patent: Page/Page column 9
[5] Zhurnal Obshchei Khimii, 1959, vol. 29, p. 658,659; engl. Ausg. S. 650, 651
