Silica-supported sodium sulfonate with ionic liquid: a neutral catalyst system for Michael reactions of indoles in water.

A neutral catalytic system for Michael reactions of indoles has been developed by combining silica-supported benzenesulfonic acid sodium salt with hydrophobic ionic liquid in water. An efficient hydrophobic environment could be created on the surface of the silica-sodium material under the conditions. Various indole derivatives and alpha,beta-unsaturated carbonyl compounds including some acid-labile substrates were successfully applied to this system with water as the sole solvent to afford the desired Michael adducts in high yields. [structure: see text].