Synthesis of 3‐Indole Substituted Sulfonyl 4 <i>H</i> ‐Chromenes Using Recyclable Cyclometrix Polyphosphazene‐Base Catalysts
Sirigireddy Sudharsan Reddy, Anuraj Varyambath, Reddi Mohan Naidu Kalla, Wenliang Song, Il Kim
Abstract
Abstract In order to build a library of 3‐indole substituted sulfonyl 4 H ‐chromenes in green protocol the three‐component one‐pot coupling reactions of substituted salicylaldehydes, sulfonyl acetonitriles and indoles have been performed using recyclable and metal‐free heterogeneous base catalysts. The highly cross‐linked cyclometrix polyphosphazenes ( c POPs) synthesized via a single‐step precipitation polymerization of hexachlorocyclotriphosphazene with 4,4’‐oxydianiline or 3,3’‐diaminobenzidine without using any other additives or surfactants were used as catalysts considering the resultant c POPs intrinsically bear multiple amine moieties on their surface. The resultant c POP microspheres showed excellent catalytic activity for variety of substrates at mild reaction conditions using a minimum amount of non‐hazardous solvent. No laborious product workup and purification procedures were needed and the c POPs catalysts were recyclable up to six cycles without leeching and deactivation, satisfying green chemistry principles.