[Et3NH][HSO4] catalyzed solvent‐free synthesis of new 1,2,3‐triazolidene‐indolinone derivatives

A series of new 1,2,3‐triazolidene‐indolinone derivatives (17a‐j) were designed and synthesized via [Et3NH] [HSO4] catalyzed solvent‐free approach. The synthesis strongly relied on Knoevenagel condensation of 1,4‐disubstituted 1,2,3‐triazolyl aldehydes (15a‐j) and oxindole (5). The solvent‐free approach and Brønsted acidity of [Et3NH] [HSO4] ionic liquid increased the rate of reaction and provided the corresponding 1,2,3‐triazolidene‐indolinone derivatives (17a‐j) in excellent yields. The reusability of ionic liquid is also established with persistent effective yields up to four cycles. These novel 1,2,3‐triazolidene‐indolinone derivatives may exhibit potential biological response due to the presence of potent moieties and presence of triazolidene‐exocyclic double bond. Present work describes a solvent‐free green approach for the efficient synthesis of 1,2,3‐triazolidene‐indolinones derivatives using reusable ionic liquid, triethyl amine sulfuric acid at 80 °C within short reaction time 20 min.