71989-66-7Relevant articles and documents
Preparation of 4-Bromo-1-hydroxypyrazole 2-Oxides by Nitrosation of α-Bromo-α,β-unsaturated Ketoximes
Hansen, John F.,Easter, John A.,Eckert, David A.,Hunt, Karen J.,Little, David A.
, p. 281 - 286 (2007/10/02)
Nitrosation of the oximes of 3-bromo-3-penten-2-one, 3-bromo-4-phenyl-3-buten-2-one, and 2-bromo-1,3-diphenyl-2-propen-1-one using sodium nitrite in acetic acid gave low yields of 4-pyrazolone 1,2-dioxides.Nitrosation using butyl nitrite in the presence of copper(II) sulfate and pyridine in aqueous ethanol produced insoluble copper complexes from which 3,5-dimethyl-, 3-methyl-5-phenyl-, and 3,5-diphenyl-4-bromo-1-hydroxypyrazole 2-oxides could be liberated by treatment with dilute potassium hydroxide, filtration, and acidification of the filtrate.High yields wereobtained with the first two oximes, but, presumably due to unfavorable stereochemistry of the oxime, the diphenyl derivative gave a lower yield of the complex, accompanied by 4-bromo- and 4-nitro-3,5-diphenylisoxazole and 4-oximino-3,5-diphenyl-4,5-dihydroisoxazole.
Halogenation of N-Oxygenated Pyrazoles. Preparation of N-Oxygenated 4-Halopyrazole and 4,4-Dihalo-4H-pyrazole Derivatives
Hansen, John F.,Kim, Yong In,Griswold, Linus J.,Hoelle, Gary W.,Taylor, Deborah L.,Vietti, David E.
, p. 76 - 80 (2007/10/02)
Reaction of some 1-hydroxypyrazoles and 1-hydroxypyrazole 2-oxides with iodine or with 1 equiv of N-chloro- or N-bromosuccinamide (NCS or NBS) gives high yields of the 4-halo derivatives.With 2 equiv of NBS or NCS or with tert-butyl hypochlorite the products are 4,4-dihalo-4H-pyrazole 1-oxides or 1,2-dioxides.Reaction of 3,5-diphenylpyrazole with 2 equiv of tert-butyl hypochlorite gives 1,4-dichloro-3,5-diphenylpyrazole, which rearranges to 4,4-dichloro-3,5-diphenyl-4H-pyrazole.Silver ion assisted solvolysis of the gem-dihalides to form 4-chloro-3H-pyrazole derivatives is described.
