SYNTHESIS OF 4H-1,3,4-OXADIAZINO[5,6-B]QUINOXALINES FROM 2-SUBSTITUTED QUINOXALINE 4-OXIDES

The reaction of 6-chloro-2-(1-methylhydrazino)quinoxaline 4-oxide 8 wi th acetic anhydride resulted in the intramolecular cyclization to give 2,4-dimethyl-4H-1,3,4-oxadiazino[5,6-b]quinoxaline 7a, while the reac tion of compound 8 with acetic anhydride/pyridine or acetic anhydride/ acetic acid afforded ylhydrazino)-7-chloro-2-oxo-1,2-dihydroquinoxalin e 9, effecting no intramolecular cyclization. The reaction of 2-(2-ace tyl-1-methylhydrazino)-6-chloroquinoxaline 4-oxide 10a or -2(1-methyl- 2-trifluoroacetylhydrazino)quinoxaline 4-oxide 10b with phosphoryl chl oride provided compound 7a or ethyl-2-trifluoromethyl-4H-1,3,4-oxadiaz ino[5,6-b] quinoxaline 7b, respectively. The reaction of compound 7b w ith phosphorus pentasulfide gave roacetylhydrazino)-2-thioxo-1,2-dihyd roquinoxaline 11, whose dehydration with sulfuric acid in acetic acid afforded ro-4-methyl-2-trifluoromethyl-4H-1,3,4-thiadiazino [5,6-b]qui noxaline 12.