Keggin heteropolyacid in auto-tandem catalysis: confinement effects over ordered mesoporous silica in the synthesis of 2-pyridones.

It is necessary to design and develop simpler, more efficient, and cleaner synthetic methodologies to prepare increasingly complex molecules. One interesting strategy is multicatalysis. The aim of this study was to synthesize a multicatalytic hybrid system by the immobilization of H₃PW₁₂O₄₀ (HPW), a polyoxometalate, on ionic liquid-functionalized mesoporous silica (SBA-15 or MCF). The resulting catalysts were characterized by different techniques, including N₂ adsorption–desorption, Boehm titration of the acid site, SEM-EDS, FT-IR, XPS, CP-MAS, and NMR. To test the active site acid-oxidant duality of HPW, 2-pyridones were synthesized in a one-pot methodology with auto-tandem catalysis involving the ring-opening/ring-closure/oxidation sequence of 4H-pyrans. The morphology of the support structure affects the duality of HPW. Whereas the MCF complex favors oxidation, the SBA-15 complex favors Brønsted acidity (finding greater oxidation when adding water). The hybrid catalyst was recovered and reused for eight consecutive reaction cycles with no significant loss in activity. [ABSTRACT FROM AUTHOR]