Construction of pyrimido[5,4‐e]‐as‐triazine, purine, v‐triazolo‐[4,5‐d]pyrimidine and pyrazolo[3,4‐d]pyrimidine ring systems from 5‐arylazo‐6‐arylidenehydrazino‐1,3‐dimethyluracils

Abstract Reaction of 5‐arylazo‐6‐arylidenehydrazino‐1,3‐dimethyluracils (II), prepared by the treatment of 6‐aryl‐idenehydrazino‐1,3‐dimethyluracils (I) with diazotized arylamines, with dimethylformamide dimethylacetal resulted in the formation of pyrimido[5,4‐e]‐as‐triazine (V) system, while the thermolysis of II resulted in the formation of purine (X), v‐triazolo[4,5‐d]pyrimidine (XII), and pyrazolo[3,4‐d]pyrimidine (XIV, XIX) systems in lieu of the expected V. Reasonable mechanisms have been proposed for the formation of the various ring systems in these reactions.