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

The reaction of 6‐chloro‐2‐[1‐methyl‐2‐(Mmemylthiocarbamoyl)hydrazino]quinoxaline 4‐oxide 5 with acetic anhydride or trifluoroacetic anhydride resulted in dehydrative cyclization to give 2‐( N ‐acetyl)‐memylamino‐8‐chloro‐4‐methyl‐4 H ‐1,3,4‐thiadiazino[5,6‐ b ]quinoxaline 6 or 8‐chloro‐2‐( N ‐trifluoroacetyl)methylamino‐4‐methyl‐4 H ‐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 4 H ‐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‐memylamino‐4 H ‐1,3,4‐thiadiazino[5,6‐ b ]quinoxaline 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.