The Outcome of the Oxidations of Unusual Enediamide Motifs Is Governed by the Stabilities of the Intermediate Iminium Ions

We compare the results from the oxidation of two unusual enediamide'' motifs (3,4-dihydropyrazin-2(1H)-ones), where a double bond is flanked by two amides. In one case the oxidation led to a ring-opened product arising from the cleavage of the double bond, and in the other a rare cis-dioxygenated compound was obtained. Both products have been characterized by X-ray crystallography. The outcomes of the key reactions are rationalized based on calculated free energies of intermediates.