Silica supported-boron sulfonic acid: a versatile and reusable catalyst for synthesis of bis(indolyl)methane in solvent free and room temperature conditions

Silica supported-boron sulfonic acid (SBSA) was used as a cheap and mild bronsted acidic in the reaction of indole with aldehydes to afford the corresponding bis(indolyl)methanesin in solvent free grinding and room temperature. The catalyst is also effective in the reaction in good yields. This methodology offers several advantages, such as good yields, reusability of catalyst, short reaction times, simple procedure, and mild conditions. The catalyst can be recovered and reused without loss of activity. The work-up of the reaction consists of a simple filtration, followed by concentration of the crude product and purification.