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‐(1H)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.