Application of Nicotinic Acid Functionalized Chlorosulfonic Acid as a Green Catalyst for the Synthesis of Bis(2-methyl-1Hindole)Derivatives

3-Carboxy-1-sulfopyridin-1-ium chloride ([CPySO3H]+Cl-) as a novel ionic organocatalyst for thecondensation of aldehydes and 2-methylindole to synthesize bis(2-methyl-1H-indole) derivatives inacetonitrile at room temperature has been developed. Some tetrakis (2-methyl-1H-indole)derivatives have also been synthesized by the reaction of 2,2'-(butane-1,4-diylbis(oxy))dibenzaldehyde and 2-methylindole or indole in the presence of chlorosulfonic acidimmobilized on nicotinic acid ([CPySO3H]+Cl-) at room temperature. All products formed inexcellent yields over short reaction times under mild and environmentally friendly conditions. Thismethodology offers significant improvements for the synthesis of bis(2-methyl-1H-indole)derivatives with regard to the yield of products, simplicity in operation and reusability of thecatalyst.