A bifunctional molecular catalyst built up of l-proline grafted polyoxometalate for one-pot three-component green synthesis of heterocycles

Abstract

Both polyoxometalates (POMs) and organic small molecular catalysts show excellent performance in chemical synthesis. The incorporation of nanoscale POMs and organocatalysts allows the full expression of their respective merits and enables elusive reactions to be achieved in one catalytic system. However, the covalent combination of such two components has been rarely explored. Here, we have successfully designed and synthesized a bifunctional nanomolecular catalyst L-Pro-Mn-Anderson by grafting L-proline onto an Mn-Anderson POM for the first time, and catalytic experiments show that L-Pro-Mn-Anderson can realize the one-pot alcohol oxidation/three-component reaction to synthesize two types of heterocyclic compounds (5-aryl-pyrimido[4,5-b]quinoline-dione derivatives and pyrazolo[3,4-b] pyridine derivatives) in high yields up to 97%. The detailed characterization of the catalyst and the catalytic mechanism has shown that L-Pro-Mn-Anderson exhibits synergistic effects that combine both organic and inorganic catalytic functions, and the covalent linkage improves the overall redox activity of the molecular catalyst. This study opens up a new way for the design and application of covalently combined organic–inorganic molecular catalysts toward de novo organic synthesis.