Computational and ¹³C investigations of the diazadienes and oxazadienes formed via the rearrangement of methylenecyclopropyl hydrazones and oximes

Computational and further experimental investigations of the previously reported diazadienes, obtained via the rearrangement of methylenecyclopropyl hydrazone 1 are reported. Calculations at the CCSD(T)/cc-pVTZ//B3LYP/6-31G(d) level of theory indicate that the initially reported product 3 would, if formed, undergo rapid electrocyclic ring opening and, hence, would be unstable under the reaction conditions. Based on this computational prediction, further analysis of the ¹³C NMR spectrum, previously attributed to 3, led to the revision of structure 3 to that of its N-tosylaminopyrrole constitutional isomer 11. Similarly, structure 8, formed in the rearrangement of oxime 6, was revised to that of N-hydroxypyrrole 12.