Fischer Indole Synthesis in Brønsted Acidic Ionic Liquids: A Green, Mild, and Regiospecific Reaction System

Abstract

Abstract A novel one‐pot Fischer indole synthesis approach has been developed by using Brønsted acidic ionic liquids as dual solvent‐catalysts. Yields of 83–97 % were obtained after reaction in BMImHSO 4 at 70–110 °C in 0.5–6 h, and exclusive formation of 2,3‐disubstituted indoles was observed in the reaction of alkyl methyl unsymmetrical ketones. The indoles produced could be conveniently separated from the reaction mixture without any volatile organic solvents, and the BMImHSO 4 could be readily reused without efficiency loss after simple treatment involving only 1 equiv. of HCl for neutralization followed by filtration.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)