Polystyrene-supported aluminum chloride as an efficient and reusable catalyst for condensation of indole with various carbonyl compounds

Crosslinked poly styrene-supported aluminum chloride (PS-AlCl 3) is a sta ble, recy clable an d enviro nmental friendl y heterogeneou s cat alyst for th e condensation of indole with aldehydes a nd ketone s to af ford diindoly lme- thanes. In addit ion, PS-AlCl 3 shows sati sfactory selectivity in the reaction of mixtures of an aldehyde and a ketone with i ndole. Althoug h AlCl3 is a w ater sensitive, corrosive and environmentally harmful compound, PS-AlCl3 is a stable and water-tolerant species. The mild reaction conditions, short reaction ti mes, easy work-up, high to excellent yields, chemoselectivity, reuse of the catalyst for at least te n ti mes witho ut sign ificant chang e i n its cataly tic a ctivity, low cost, and easy preparation and handling of the polymeric catalyst are obvious advan- tages of the present method.