A Facile Synthesis of Aryl‐Substituted Hydrazono‐Pyrazolyl[1,2,4]triazolo[3,4‐b][1,3,4][thiadiazol]‐coumarin Derivatives

Some inimitable and therapeutic coumarin‐substituted fused1,2,4]triazolo‐3,4‐b]1,3,4]thiadizole derivatives were synthesized by the cyclocondensation reaction of 2‐oxo‐2H‐chromene‐3‐carboxylic acid ( 1 ) and 4‐amino‐5‐hydrazinyl‐4H‐1,2,4]‐triazole‐3‐thiol ( 2 ) by using phosphorous oxychloride as a cyclizing agent. This cyclized intermediate 3‐(3‐hydrazino‐1,2,4]triazolo3,4‐b]1,3,4]thiadiazol‐6‐yl)‐chromen‐2‐one ( 3 ) later condensation with various ethyl 2‐(2‐arylhydrazono)‐3‐oxobutanoates ( 4 ) in NaOAc/MeOH under reflux conditions afforded the corresponding new series of aryl‐substituted hydrazono‐pyrazolyl‐1,2,4]triazolo3,4‐b]1,3,4]thiadiazol]‐coumarin derivatives ( 5 ) in good to excellent yields. The structures of newly synthesized compounds were established on the basis of elemental analysis, IR, ¹H NMR and mass spectroscopic studies.