Synthesis And Asymmetric Catalytic Performance Of Functionalized Helical Poly(Phenylacetylene)s With Proline Derivatives

The optically active helically substituted polyacetylene has received extensive attention due to its conjugated structure.This unique structure gives the helically substituted polyacetylene unique properties and can be widely used in chiral stationary phases and molecular recognition.Inspired by the enzyme-catalyzed reaction,the scientists used helical polymer to simulate the catalysis of the enzyme,and introduced a catalytically-active group to the helically substituted polyacetylene side group to prepare a catalyst.In this paper,three kinds of helical poly（phenylacetylene）s-beared proline derivatives were synthesized to discuss the catalytic ability of the monomers and corresponding polymers as chiral catalysts.The 4-ethynylanilin was prepared by Sonogashira coupling reaction and off-protecting group TMS reaction,three proline derivatives functionalized phenylacetylene monomers PAA-Fmoc-Pro,PAA-Fmoc-dPro,PAA-Fmoc-dPro-OH were synthesized by amidation reaction.Polymers were synthesized by the rhodium-catalyzed and polymerization of PAA-Fmoc-Pro,PAA-Fmoc-dPro and PAA-Fmoc-dPro-OH.The monomers and polymers with Fmoc protecting group were deprotected by morpholine to obtain the monomers PAA-Pro,PAA-dPro,PAA-dPro-OH and polymers PPAA-Pro PPAA-dPro,PPAA-dPro-OH with free secondary amino groups.The product obtained in each reaction stage was characterized by ¹H NMR and IR.The optical activity of the monomers and polymers were investigated by optical rotation and CD spectro.The results showed that the synthesized polymers have dynamic helical conformation,and the polymers secondary structure could be adjusted by changing temperature and mixed solvent.Monomers PAA-Pro,PAA-dPro,PAA-dPro-OH and polymers PPAA-Pro,PPAA-dPro PPAA-dPro-OH catalyzed the asymmetric aldol reaction of acetone and4-nitrobenzaldehyde.When the reaction solvent was strongly polar DMF or DMSO,the catalytic products had higher ee values.The catalytic effects of polymer catalysts PPAA-dPro and PPAA-dPro-OH in these two solvents were better than corresponding monomers.It might be that the synergistic effect of the polymer helical structure and the side groups increased the catalytic effect.Increasing the amount of the catalyst,within a certain range,could increase the yield and the ee value.The polymer-catalyzed reaction could obtain a higher ee value in DMSO,and a larger yield could be obtained in H₂O,when a small amount of H₂O was added to DMSO and changed the proportion of the mixed solvent could achieve adjustment of the catalytic reaction.When the imidazole additive was added to the reaction system,the reaction efficiency could be improved;the polymer catalysts could be recycled for many times to maintain good catalytic performance.