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

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