Hyperbranched polyethylene-supported l-proline: a highly selective and recyclable organocatalyst for asymmetric aldol reactions

Abstract

A novel hyperbranched polyethylene (HBPE)-supported L-proline has been developed via a bottom-up copolymerization strategy. The copolymerization of ethylene and protected proline acrylate comonomer with cationic Pd-diimine catalysts was conducted, followed by de-protection of the proline groups. Well-defined HBPE copolymers having molecular weights (MWs) of 10.3-50.3 kDa and 3.2-15.6 L-proline molecules per HBPE polymer chain were synthesized. The effects of the L-proline amount and HBPE MW on the catalyst performance were studied. The HBPE catalysts were efficient in asymmetric Aldol reactions of p-nitrobenzaldehyde (p-NBA) or benzaldehyde derivatives with cyclohexanone. High p-NBA conversions of up to 98% and excellent product selectivities with anti/syn = 98/2 and ee>99% were achieved. Moreover, the HBPE catalysts could be easily reclaimed by adding water into the product. The reclaimed catalysts could be reused for multiple times with only a slight decline in reactivity and selectivity.

Tailoring chain structures of l-lactide and ε-caprolactone copolyester macromonomers using rac-binaphthyl-diyl hydrogen phosphate-catalyzed ring-opening copolymerization with monomer addition strategy

“…Such catalysts are relatively easy to generate and remove from end-products. [19][20][21][22] The organocatalysts include organic acid, [23][24][25] phosphazene, 26,27 pyridine and carbene bases, [28][29][30][31] thiourea/amine complex, 32,33 and amidine/guanidine. 34 Hedrick et al 35 was the rst to report the successful catalysis of LA ROPs using strongly basic amines, 4-(dimethylamino)pyridine and 4-pyrrolidinopyridine.…”

Chiral Graphene Hybrid Materials: Structures, Properties, and Chiral Applications

“…[ 41 ] A variety of materials have been taken as supports to immobilize proline and its derivatives. The supports can be polymers, [ 65,66 ] inorganic materials like silica [ 67 ] and magnetic nanoparticles, [ 68 ] cyclodextrins, [ 69 ] and ionic liquids. [ 70 ] The layered structure and desirable properties of graphene enable it to be a new alternative for acting as supporting material for immobilizing proline.…”

On the Exceptionally High Loading of L-Proline on Multi-Wall Carbon Nanotubes

“…Asymmetric reactions catalyzed by small organic molecules (i.e., organo-catalysts) have the advantages of high enantioselectivity under mild reaction conditions [1,2]. However, the catalyst loading is usually high (~20 mol% or more) and the recovery of the catalyst is difficult [3,4]. As a result, the practical applications of organo-catalysts, especially in industrial setting, are greatly restricted [5,6].…”