Synthesis of β‐Aminonitrones by Regioselective Oxidation of 4H‐Imidazoles

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