P2O5/SiO2 as an efficient, mild, and heterogeneous catalytic system for the condensation of indoles with carbonyl compounds under solvent-free conditions

An efficient solvent-free procedure for the preparation of bis(indolyl)methanes via the condensation of indoles with aldehydes as well as ketones in the presence of catalytic amount of phosphorus pentoxide/silica gel (P2O5/SiO2) at room temperature is described. The advantages of this method are generality, high yields, short reaction times, ease of product isolation, low cost and ecologically friendly.