Jf. Hansen et al., PREPARATION OF 4-BROMO-1-HYDROXYPYRAZOLE 2-OXIDES BY NITROSATION OF ALPHA-BROMO-ALPHA-BETA-UNSATURATED KETOXIMES, Journal of heterocyclic chemistry, 31(2), 1994, pp. 281-286
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 ni
trite in acetic acid gave low yields of 4-pyrazolone 1,2-dioxides. Nit
rosation 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-hy
droxypyrazole 2-oxides could be liberated by treatment with dilute pot
assium hydroxide, filtration, and acidification of the filtrate. High
yields were obtained with the first two oximes, but, presumably due to
unfavorable stereochemistry of the oxime, the diphenyl derivative gav
e 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.