A Novel Synthesis of 1‐Aryl‐6‐bromo‐3‐(5‐ethylthio‐4‐phenyl‐4 H ‐1,2,4‐triazol‐3‐yl)‐1 H ‐pyrazolo[4,3‐ b ]quinolin‐9(4 H )‐ones via Thermal Cyclization of 4‐Azidopyrazoles

2‐Aryl‐hydrazononitriles 3a , 3b , 3c were prepared by coupling 3‐ethylthio‐5‐cyanomethyl‐4‐phenyl‐1,2,4‐triazole ( 1 ) with diazonium salts 2a , 2b , 2c . Reacting 3a , 3b , 3c with both ethyl bromoacetate ( 4a ) and 4‐bromobenzyl bromide ( 4b ) in DMF, in the presence of K 2 CO 3 , at 80 °C for 3–4 h, gave the corresponding 4‐amino‐pyrazoles 6a , 6b , 6c , 6d , 6e , 6f . Diazotization of 6a , 6b , 6c , 6d , 6e , 6f , followed by reaction with NaN 3 , leads to the formation of 4‐azidopyrazoles 8a , 8b , 8c , 8d , 8e , 8f , a new heterocyclic ring system. Interestingly, fusion of 4‐azidopyrazoles 8d , 8e , 8f at temperature higher than their melting points with 5 °C for 2 min did not give the expected fused pyrazolo[4,3‐ c ]isoxazoles 9 but furnished instead the novel pyrazolo[4,3‐ b ]quinolinones 10a , 10b , 10c , in high yields.