Studies in the heterocyclic series. XXI. A novel tetraaza‐analog of phenothiazine

Abstract As a continuation of our search for new pharmaco‐active phenothiazine compounds, the synthesis of 1,4,6,8‐tetraazabenzo[ b ]phenothiazine ring system is described. Derivatives of this new heterocycle were prepared by converting 4,5‐diamino‐6‐hydroxypyrimidine to 4,5‐diaminopyrimidine‐6‐(1 H )thione followed by the action of 2,3‐dichloroquinoxaline in refluxing DMF or DMAC. The reaction of mixed nitric and sulfuric acids with 9‐amino‐12‐chloro‐1,4,6,8‐tetraazabenzo[ b ]phenothiazine gave 9‐amino‐12‐chloro‐13‐nitro‐1,4,6,8‐tetraazabenzo[ b ]phenothiazine 5‐oxide in satisfactory yields. Diazotization of 9‐amino‐1,4,6,8‐tetraazabenzo‐[ b ]phenothiazine led to 1,4,6,8‐tetraazatriazolo[4,5,1‐ kl ]benzo[ b ]phenothiazine which is a new heterocyclic compound and the parent compound of this ring system. The mechanistic pathways to these compounds are also proposed.