Dioxygen oxidation of a stable 1,4-dihydropyrazine

The stable 1,4-dihydropyrazine 4a,8a-diaza-2,6-dioxa-3,4,7,8-tetrahydro-4,4,8,8-tetramethylanthracene-1,5-dione (DDTTA) is oxidized by dioxygen in various organic solvents to give mixtures of 5,6-dihydro-5,5-dimethyl-3-formyl-1,4-oxazine-2-one (1) and a second product that was previously ascribed a dioxetane structure. The latter is now fully characterized by X-ray crystallography and found to be the diol 4a,8a-diaza-9,9a-dihydroxy-2,6-dioxa-3,4,7,8,9,9a-hexahydro-4,4,8,8-tetramethylanthracene-1,5-dione (4). The oxidation rate and product ratio are highly solvent dependent, Trapping experiments, reaction stoichiometry, and kinetic measurements are all consistent with a hydroperoxide intermediate that reacts with DDTTA to give the diol 4 or undergoes intramolecular fragmentation to give aldehyde 1. Both DDTTA and the intermediate hydroperoxide are significantly less reactive than their biologically active 1,4-dihydropyrazine counterparts.