Preparation Of Hollow Polymeric Bowl-supported BIONL-Derived Phosphonic Acids And Their Application In Asymmetric Catalysis

In recent years,the rapid development of organic small molecule catalyst has been environmentally friendly due to its non-metallic hazards,and has become one of the hot topics in asymmetric catalysis.Since Akiyama and Terada pioneered BINOL-derived phosphonic acids as catalysts,BINOL-derived phosphonic acids have been proven to be very successful multifunctional catalysts.These Br?nsted acids,which can be consider-ed as metal-free chiral Lewis acids,have been used in various asymmetric catalytic tran-sformations such as Friedel-Craft alkylation,transfer hydrogenation,multicomponent reactions and?trans?-acetalization.The substituents on the 3,3'position of BINOL-deri-ved phosphonic acid have a strong influence on the activity and enantioselectivity.Am-ong all the reported structures,the 2,4,6-triisopropyl derivative is said to be TRIP and has been widely used in asymmetric catalytic reactions.As a Br?nsted acid catalyst,it has a good three-dimensional control capability.However,BINOL-derived phosphonic acids have some important drawbacks,mainly due to their cumbersome synthesis steps.In order to achieve the best enantioselectivity,the different substituents at 3,3'positions are needed to be introduced,which leads to an increase in synthesis steps and costs.Therefore,the immobilization of such catalyst on a carrier is an effective method to achieve the recovery and reuse of the catalyst.The recovery and reuse of expensive or-ganic catalysts in heterogeneous catalysis with high catalytic performances are the new challenges for researchers.Based on the concept of green chemistry,in this paper hol-low polymeric bowl-supported BIONL-derived phosphonic acids are fabricated to im-prove the catalytic performance of heterogeneous TRIP,and good catalytic results are obtained in heterogeneous asymmetric reactions.In this paper,using bis-naphthalenediol as chiral material,the 6,6'-styrene-attached BINOL derivative monomer was synthesized through several reaction steps including methylation,iodination,Grignard reaction,Suzuki coupling and bromination.The ethyl-ene glycol dimethacrylate?EGDMA?-crosslinked copolymer of BINOL derivative mo-nomer and styrene?St?was coated on the surface of PS core to prepare the core-shelled nanospheres Poly?St-co-EGDMA-co-?R?-6?.After treated with N,N-dimethylform-amide?DMF?,phosphorus oxychloride?POCl₃?and acidified by HCl,PS cores were etched and naphthalene hydroxyls were functionalized to fabricate the hollow polymeric bowl-supported BIONL-derived phosphonic acids Poly?St-co-EGDMA-co-?R?-7?.The well-shaped morphologies and optimal catalytic performances of Poly?St-co-EGDMA-co-?R?-7?were regulated by optimizing temperature,reaction time and used amounts of KPS and monomers.Moreover,N₂ adsorption-desorption,SEM,TEM,IR and ICP were used to characterize the hollow structure,morphology and loaded amount of TRIP.In the asymmetric allylation of benzaldehyde with allyl boronic acid pinacol ester was used as a template reaction,the influences of temperature,solvent,used amount of catalyst and reaction time on the catalytic performance of Poly?St-co-EGDMA-co-?R?-7?were investigated to screen out the optimal catalytic reaction conditions.Under the optimal catalytic reaction conditions,the good to excellent 70–98%yield and 88–98%ee for various substrates were achieved.After the completion of the reaction,the catalyst was recovered by simple filtration or centrifugation,and 5^th–reused catalyst dis-played good catalytic performances including yields and enantioselectivities.