Pyrimidine derivatives and related compounds VI. A novel synthesis of 3,5‐diacetamidopyrazole and of 2‐aminopyrazolo [1,5‐α] pyrimidines

3,5‐Diaeetamidopyrazole (2) could be prepared via arylazo group decoupling from 3,5‐diamino‐4‐arylazopyrazoles ( 1a‐c ) by the action of acetic acid‐sulfuric acid mixture. Arylazo group removal could also be effected when 2‐amino‐5‐melhyl‐7‐oxo‐6,7‐dihydro‐3‐phenylazopyrazolo‐[1,5‐α]pyrimidine ( 5 ) was similarly treated. The 2‐aminopyrazolo[1,5‐α]pyrimridine derivative was obtained in this case. On the other hand, under the same experimental conditions compounds 7a‐c and 8 were recovered almost unaffected. The mechanism of the reaction is discussed.