Thermal Decomposition of N-Acyloxy-N-alkoxyamides - a New HERON Reaction

The HERON reaction has been observed in the thermal decompositions of N-acyloxy-N-alkoxyamides 1b, members of the class of anomeric amides. The N,N-bisoxo-substitution results in reduced amide resonance and this, combined with an n(O)-sigma(NOAcyl)* anomeric destabilization of the N-OAcyl bond, results in their intramolecular rearrangement to anhydrides 42 and alkoxynitrenes 43 in competition with homolysis of the N-OAcyl bond to alkoxyamidyls 51. The primary HERON product alkoxynitrenes are scavenged by oxygen, giving a nitrate ester, in competition with a rearrangement to nitriles and dimerization to hyponitrites, leading, under the conditions, to alcohols and aldehydes. Persistent alkoxyamidyls most likely form a 1,3-diradical in a solvent-cage reaction, which cyclizes to 3,5-disubstituted-(5H)-1,4,2-dioxazoles 47. Substituent effects support this competition reaction.