The reaction between 3‐amino‐2,3‐dihydro‐7,9‐dimethyl‐2‐thioxo‐pyrido3′,2′:4,5]thieno3,2‐d]‐pyrimidin‐4(1H)‐one 4 or its 2‐methylthio derivative 5 with hydrazonoyl halides 6 in dioxane in the presence of triethylamine under reflux has followed heterocyclization reaction to yield pyrido3″,2″:4′,5′]‐thieno3′,2′:4,5]pyrimido2,1‐c]1,2,4,5]tetrazin‐6(4H)‐ones 9 . On the other hand, reaction of compound 4 with hydrazonoyl halides 6 in sodium ethoxide at room temperature led to formation of hydrazonothioate compounds 10 . The latter on treatment with glacial acetic acid produced tetracyclic compounds, namely 2‐arylhydrazonopyrido3″,2″:4′,5′]thieno 3′,2′:4,5]pyrimido2,1‐b]1,3,4]thiadiazinones 11 . An alternative method was carried out to prove the structure of product 11 . The mechanism of the reaction under study was proposed and the products were screened for their biological activity.
