Stereochemical effects in the nitrosation of some α,β‐unsaturated ketoximes. Formation of 1‐hydroxypyrazole 2‐oxides and 4‐oximino‐4,5‐dihydroisoxazoles

Several α,β‐unsaturated ketoximes R 1 CH=CHC(=NOH)R 2 were nitrosated using butyl nitrite in aqueous ethanol in the presence of copper(II) sulfate and pyridine. The product distribution varied depending on whether the oxime hydroxyl group was syn or anti with respect to the carboncarbon double bond. The anti ‐oximes gave the copper complexes of 1‐hydroxypyrazole 2‐oxides in high yields. The isomeric syn ‐oximes gave lower yields of the pyrazole complexes along with 4‐oximino‐4,5‐dihydroisoxazole derivatives. For the syn ‐oximes where R 1 is phenyl and R 2 is either methyl or ethyl, conversion of the oximes to the parent ketones was also observed. The results may be explained by processes involving N ‐nitrosonitrone intermediates.