Efficient and solvent-free synthesis of bis-indolylmethanes using silica gel supported aluminium chloride as a reusable catalyst

Stable and non-hygroscopic silica gel supported aluminium chloride (SiO2–AlCl3), which is prepared easily from cheap and commercially available compounds was found to be an environmentally friendly heterogeneous catalyst for the condensation of indole with aldehydes and ketones to afford bis-indolylmethanes at room temperature under solvent-free conditions. The catalyst can be reused up to five times after simple washing with ether.