Semicarbazones from N-hydroxyureas and amines: a novel entry in the reactivity of the acyl nitroso group.

The condensation of carbamoyl nitroso compounds, obtained by oxidation of N-hydroxyureas, with amines unexpectedly afforded semicarbazones (aka carbamoyl hydrazones). Although the substitution of the nitrosyl moiety might compete to afford the corresponding urea, an excess of amine led to the semicarbazone as the major product, which is presumably formed via isomerization of an initially generated acyl azo compound.