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 Bronsted 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.