Novel sultone based Brønsted acidic ionic liquids with perchlorate counter-anion for one-pot synthesis of 2H‑indazolo[2,1‑b]phthalazine‑triones

Abstract

Three novel sultone based Brønsted acidic ionic liquids are introduced. These ionic liquids were prepared in three similar two-steps reactions. The ring opening of 1,4-butane sultone was performed using 1,4-dimethyl piperazine or 1,10-phenantroline as nitrogen nucleophile sources to obtain zwitterions and then followed by acidification by treatment with perchloric acid to give the introduced ionic liquids. FTIR, 1HNMR, 13C-NMR, TGA and CHNS analysis techniques were used for the characterization of these ionic liquids. These ionic liquids are completely water soluble and have good thermal stability. Their catalytic efficiency was checked for the preparation of polycyclic 2H‑indazolo[2,1‑b]phthalazine‑trione compounds. Small amount (3-7 mmol%) of the prepared acidic ionic liquid catalysts is required and targeted products are obtained in short times (6-25 min) at high yields (86-96%). Moreover, the introduced acidic ionic liquids are completely green, environmental benign and task specific and simply recoverable up to six consecutive runs without significant decrease in their catalytic.