Reactivity of the Enamine Tautomer of a Cyclic 1,4-Diazadiene with a Diketone

This is the authors' abstract. We don't add key points for this paper.

Cyclic 1,4-diazadiene (2,3-dihydro-5-methyl-6-phenylpyrazine) and diketone (1-phenyl-1,2-propanedione) yielded two products via dehydrationcondensation of the diamine and diketone moieties when a mixture of H2O and MeOH was used as the solvent.The structures of the new products were established by 2D NMR analysis.Single-crystal X-ray structural characterization and density functional theory calculations allowed us to determine that this reaction took place via reaction of the enamine tautomer.N-Heterocycles are widely present in bioactive organic compounds such as pharmaceuticals. 1 Among heterocyclic compounds, pyrazines, which can be isolated from foods, 2 exhibit various properties. 3Dihydropyrazines (DHPs), which are pyrazine precursors for the Maillard reaction, can generate radicals 4 and have a high chemical reactivity. 5,6Particularly, we are interested in the reactivity of cyclic 1,4-diazadienes as DHPs and have made them our research focus.In a previous paper, 5 we reported the reaction between the lone pair on the nitrogen of cyclic 1,4-diazadienes and ketenes.Herein, we report that the enamine tautomer of a cyclic 1,4-diazadiene shows different reactivity from that previously reported.This change in reactivity is not unprecedented, as when the dimerization of DHPs occurs, 6 they tautomerize during the early stages of cyclization, resulting in an ene reaction between the -NH-C=C moiety of enamine-type DHPs and the C=N moiety of imine-type DHPs.