NMR spectra of cyclic nitrones. 4. Synthesis and 13C NMR spectra of 4H-imidazole N-oxides and N,N-dioxides

4H-Imidazole 1,3-dioxides and 4H-imidazole 3-oxides were obtained by oxidation of 1-hydroxy-3-imidazoline 3-oxides and 1-hydroxy-3-imidazolines with lead and manganese dioxides or the stable nitroxyl radical, while 4H-imidazole 1-oxides were obtained by thermal decomposition of 1-acetoxy-3-imidazoline 3-oxides. Facile oxidation of the ethyl group in 5-ethyl-4H-imidazole 1,3-dioxide and the formation of 5-acetyl-4H-imidazole 1,3-dioxide and 5-acetyl-4H-imidazole 3-oxide were observed. It is shown that a strictly determined region of chemical shifts of the C(₂), C(₅), and C(₄) atoms is characteristic for each group of 4H-imidazole N-oxides in the ¹³C NMR spectra; this makes it possible to clearly establish the position of the N-oxide oxygen atom.See 1] for Communication 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1640–1648, December, 1988.