CeO2 NPs/rGO composite catalyzed chemoselective synthesis of 2,8-dioxabicyclo[3.3.1]nonanes in aqueous medium via aldol condensation/Michael addition/bicyclization reaction sequence

Abstract

CeO2 NPs decorated reduced graphene oxide (CeO2 NPs/rGO) composite has been synthesized and characterized by XRD, TEM, SEM, UV–vis, FT-IR, cyclic voltammetery and EDX analyses. The results show that the CeO2 NPs have an average size of approximately 10 nm and homogeneously distributed onto the surface of rGO. The activity of the catalyst was probed through the synthesis of 2,8-dioxabicyclo[3.3.1]nonanes via one pot aldol condensation/Michael addition/bicyclization reaction sequence of 2-hydroxybenzaldehydes, acetophenones and 4-hydroxycoumarin in aqueous medium under microwave irradiation. One CC bond, two CO bonds, two stereogenic centers and two six-membered cycles were formed in a single operation with excellent yields and high selectivity. Moreover, 5,5-dimethyl-1,3-cyclohexanedione and indane-1,3-dinone were also found appropriate for the reactions. At the end of the reaction, catalyst could be easily recovered by simple filtration and recycled for 7 times without noteworthy loss in catalytic activity. Advantages of combination of water and CeO2 NPs/rGO nanocatalyst under microwave irradiation was observed in the form high turnover frequency (TOF).