Pyrazine ketones isomerization

Meyer (17) in the following year then expressed the view that the products of the action of nitrous acid on the ketones were not true nitroso compounds (4) but isomeric oximes (5), and he considered their reduction to be analogous to the conversion of a nitro to amino group, rather than that of ketone to pinacol. Thereafter the Treadwell formulation of pyrazines was abandoned. 

This method is well suited to the formation of symmetrical pyrazines, " but if both diketone and diamine are unsymmetrical, two isomeric pyrazines are formed. The dihydro-pyrazines can be dehydrogenated and they will also react with aldehydes and ketones, with introduction of another alkyl group at the same time as achieving the aromatic oxidation level. ... 

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