12-Tungstosilicic Acid Supported on Different Carriers: Pronounced Catalytic Activity in the Synthesis of Bis(indolyl)methanes Under Solvent-Free Conditions

Abstract

12-Tungstosilicic acid supported on different metal oxides was used as catalyst in the synthesis of bis(indolyl)methanes via electrophilic substitution reactions of indole with structurally diverse aldehydes and cyclohexanone. The effects of solvent, catalyst loading, and the nature of substituents on the aromatic ring of aldehydes were investigated. The workup of the reaction consists of simple filtration, followed by concentration of the crude product, and purification. A mechanism for the catalytic activity is proposed, and corresponding products were obtained in good to excellent yields in relatively short reaction times. The catalysts were reusable without significant loss of activity.

Keywords:

• Bis(indolyl)methanes
• indole
• solvent-free conditions
• supported catalysts
• 12-tungstosilicic acid

ACKNOWLEDGMENTS

The authors thank the Razi University Research Council and Kermanshah Oil Refining Company for support of this work.

Notes

^a Isolated yields.

^a Isolated yields.

^a Isolated yields.

^b Results in parentheses show the yield of product 2.

^c 4 mmol of indole were used in this reaction.