Synthesis and asymmetric catalytic performance of one-handed helical poly(phenylacetylene)s bearing proline dipeptide pendants

One-handed helical substituted polyacetylene has received extensive attention due to its potential in chiral stationary phases and molecular recognition . Here, three one-handed helical poly(phenylacetylene)s bearing proline or proline dipeptide as the pendants ( PPA-Pro, PPA-Pro-Pro and PPA-Pro-Hyp ) were synthesized. As the catalyst, the three helical polymers separately catalyzed the asymmetric aldol reaction of acetone with p -nitrobenzaldehyde in a various media. The results indicate that PPA-Pro-Pro and PPA-Pro-Hyp bearing dipeptide pendants showed the higher catalytic activity and enantioselectivity than the PPA-Pro bearing proline pendants and the corresponding monomer catalysts. This indicates the synergistic effect of the dipeptide pendants with the one-handed helical mainchain of the polymer catalyst. The polymer catalysts can be recycled and maintain the catalytic performance after four circles. When imidazole was added to the reaction system, the reaction yield could be efficiently improved without affecting the enantioselectivity.