Synthesis of 3-Indole Substituted Sulfonyl 4H-Chromenes Using Recyclable Cyclometrix Polyphosphazene-Base Catalysts

摘要

In order to build a library of 3-indole substituted sulfonyl 4H-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 (cPOPs) 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 cPOPs intrinsically bear multiple amine moieties on their surface. The resultant cPOP 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 cPOPs catalysts were recyclable up to six cycles without leeching and deactivation, satisfying green chemistry principles.