Ionic liquids vs. microporous solids as reusable reaction media for the catalytic C–H functionalization of indoles with alcohols

High performance reusable catalysts and reaction media are evaluated for the green alkylation of indoles with alcohols under mild and solvent-free conditions. For a range of Brønsted and Lewis acid catalytic sites in different environments, such as inexpensive ionic liquids or microporous solids, we show a correlation between the acid strength and catalytic activity, achieving the highest turnovers reported for strong acid sites upon five reuses under mild conditions.