Polyacrylamide Bearing Chiral BINOL–derived Pendant Group: Synthesis And Preliminary Application In Asymmetric Catalysis

Biomolecules exist almost exclusively as single enantiomers,and different enantiomers can exhibit markedly different biological activities.Thus,stereochemistry is of great importance in chemical interactions,such as in the natural molecular recognition events that occur within living organisms,and in interactions between drugs and their targets.Accordingly,there is enormous demand for methods that allow the preparation of chiral compounds in enantiomerically pure forms.Asymmetric catalysis and synthesis are one of the most efficiently methods to obtained the chiral compounds in enantiomerically pure forms.The BINOL as chiral pool have been well applied in a series of model reactions.Polymeric BINOL-derived ligands make it easy for the recycle and reuse of the expensive ligand compare to small-molecule ligands.Thus,three polyacrylamides bearing Chiral BINOL–derived pendant group we have been designed and synthesized by us.Applied the obtained chiral polymeric ligands in the asymmetric addition of diethyl zinc to aryl aldehyde?asymmetric addition of triethyl aluminum to aryl aldehyde and the asymmetric epoxidation of enone.As fellows:(1)Poly[(S)-3-acrylamide-2,2'-dihydroxy-1,1'-binaphthyl] was synthesized through radical polymerization and applied in the asymmetric addition of diethylzinc to aromatic aldehydes,giving the optically active products up to 95% enantiomeric excess(ee)with up to 97% yield.Besides,The polymeric ligand could be recycled up to six times without erosion of the enantioselectivity.(2)Poly[(S)-6-acrylamide-2,2'-dihydroxy-1,1'-binaphthyl] was synthesized through radical polymerization.Applied the obtained polymer in the epoxidation of enone,gave the optically active products up to 98% enantiomeric excess(ee).Most importantly,the chiral polymeric ligand could be easily seperated from the reaction mixture and recycled up to four times without erosion of the enantioselectivity.(3)Poly[(S)-3-phenyl-3'-acrylamide-2,2'-bis(methoxymethoxy)-1,1'-binathphyl] was synthesized through radical polymerization,which was preferred to keep a stable helical conformation in solutions comfirmed by the CD spectra and the specific optical rotation by comparing with the monomer and the model compound(S)-3-phenyl-3'-propanamide-2,2'-bis(methoxymethoxy)-1,1'-binathphyl.The obtaind polymer deprotectd the protecting group and applied in the enantioselective addition of triethylaluminum(Et3Al)to various aromatic aldehydes,gave the optically active products with up to 96% ee.Most importantly,the helical L3 could be easily recovered and recycled many times without erosion of the catalytic activity as well as enantioselectivity.