Investigations on pyrazine derivatives IX: On the effect of hydrogen peroxide on 5,6‐diphenyl‐2,3‐dihydropyrazine

The effect of hydrogen peroxide on 5,6‐diphenyl‐2,3‐dihydropyrazine has been studied. Several reactions take place which might be considered as models for some of the spontaneous conversions shown by partially reduced pyrazines on exposure to air. In no case was 5,6‐diphenyl‐2,3‐dihydropyrazine 1,4‐di‐N‐oxide formed, but products of ring‐opening: N/N′‐dibenzoylethylenediamine, and N‐benzoylethylenediamine, and a product of a most interesting ring‐contraction: 2‐phenyl‐2‐imidazoline. In addition some 2,3‐diphenylpyrazine could be isolated. Reaction mechanisms have been postulated; the primary product of oxidation has been formulated as 5,6‐diphenyl‐1,2,3,6‐tetrahydro‐pyrazine 6‐hydroperoxide. Tetrahydropyrazine hydroperoxides may also be formed spontaneously, for example, after catalytical hydrogenation, if tetrahydropyrazines are exposed to air. The results described in this paper seem also to be of some importance in the fields of condensed pyrazines like quinoxalines, pteridines, iso‐alloxazines and, moreover, they contain principles for new syntheses of 2‐imidazolines.