H. Gutknecht, Ber. 12, 2290 (1879); 13, 1116 (1880).

Cyclization of α-amino ketones, produced by reduction of isonitroso ketones to yield the dihydropyrazines which are dehydrogenated with mercury(I) oxide or copper(II) sulfate, or sometimes with atmospheric oxygen:

I. J. Krems, P. E. Spoerri, Chem. Rev. 40, 291 (1947); Y. T. Pratt, Heterocyclic Compounds 6, 379, 385 (1957).