Synthesis of beta-aminonitrones by regioselective oxidation of 4H-imidazoles

A new regioselective synthesis for aminonitrones of type 4 via oxidative mo dification of 4H-imidazoles 1 has been developed. An X-ray structural analy sis revealed an unexpected tautomeric fixation of the hydrogen atom in 4. N MR investigations of the N-15-labelled derivative 4b showed that this fixat ion is also present in solution. All new synthesized aminonitrones reported here are unusually stable which can be explained by contribution of anioni c as well as cationic delocalized mesomeric structures. Treatment of 4 with acetic anhydride leads to formation of the O-acylated hydroxylamine deriva tives 5.