A new method for the synthesis of 4H-1,3,4-thiadiazino[5,6-b]quinoxalines

The reaction of 6-chloro-2-[1-methyl-2-(N-methylthiocarbamoyl)hydrazino]quinoxaline 4-oxide 5 with acetic anhydride or trifluoroacetic anhydride resulted in dehydrative cyclization to give 2-(N-acetyl)methylamino-8-chloro-4-methyl-4H-1,3,4-thiadiazino[5,6-b]quinoxaline 6 or 8-chloro-2-(N-trifluoroacetyl)methylamino-4-methyl-4H- 1,3,4-thiadiazino[5,6-b]quinoxaline 9, respectively. The oxidation of compound 6 or 9 with 2-fold molar amount of m-chloroperbenzoic acid afforded the 4H-1,3,4-thiadiazino[5,6-b]quinoxaline 1,1-dioxide 8 or 13, respectively. The acetyl group of compound 6 was hardly hydrolyzed, but the trifluoroacetyl group of compound 9 was easily hydrolyzed to change into 8-chloro-4-methyl-2-methylamino-4H-1,3,4 10. The acylation of compound 10 with acetic anhydride, trifluoroacetic anhydride, phenyl isocyanate, and chloroacetyl chloride furnished the 2-(N-acetyl)methylamino 6, 2-(N-trifluoroacetyl)methylamino 9, 2-(1-methyl-3-phenylureido) 11, and 2-(N-chloroacetyl)methylamino 12 derivatives, respectively.