Silica Gel Supported TaBr₅ Catalyst

Significance

Silica gel supported TaBr₅ was developed as a new solid-support catalyst. A wide range of substituted 2′-aminochalcones 1 (12 varieties) adsorbed on silica gel supported TaBr₅ were reacted to give the corresponding 2-aryl-2,3-dihydroquinoline-4(1H)-ones 2 in 70-92% yield under solvent-free conditions. In this silica gel supported cyclization reaction, TaBr₅ served as a Lewis acid catalyst. The reaction did not take place in the presence of silica gel alone, while the solution-phase reaction with TaBr₅ in the absence of silica gel gave the dihydroquinoline products (30-40%), even after prolonged reaction times.