A convenient synthesis of 2-amino-4H-1,3,4-oxadiazino[5,6-b]quinoxaline derivatives

The reaction of 6-chloro-2-(1-methylhydrazino)quinoxaline-4-oxide 5 with a 2-fold molar amount of ethyl chloroglyoxalate gave ethyl 8-chloro-4-methyl-4H-1,3,4-oxadiazino[5,6-b]quinoxaline-2-carboxylate 6, whose reaction with hydrazine hydrate afforded the C-2-hydrazinocarbonyl derivative 7. The reaction of compound 7 with nitrous acid provided the C-2-acylazide derivative 8, which was converted into the C-2-amino 9, C-2-carbamate 11a-c, 12a,b, and C-2-ureido 13a-c, 14 derivatives. The mass spectral fragmentation patterns were examined for compounds 10-14, wherein the molecular ion peak did not appear in the mass spectra of compounds 10c, 11a-c, 12a,b, 13c, and 14.