A novel pyrrolidinium ionic liquid with 1,1,2,2-tetrafluoro-2-(1,1,2,2-tetrafluoroethoxy)ethanesulfonate anion as a recyclable reaction medium and efficient catalyst for Friedel–Crafts alkylations of indoles with nitroalkenes

A series of pyrrolidinium-based salts with new fluorine-containing anions were synthesized. Different melting points could be obtained by changing the length of the fluoroalkyl chain of the anions. The pyrrolidinium 1,1,2,2-tetrafluoro-2-(1,1,2,2-tetrafluoroethoxy)ethanesulfonate ([C4H8NH2][H(CF2)4O(CF2)2SO3]) is highly fluid even below room temperature. It can be used both as a recyclable solvent and as an efficient catalyst for Friedel–Crafts alkylations of indoles with nitroalkenes.