Synthesis of Polymers Bearing Proline Moieties in the Side Chains and Their Application as Catalysts for Asymmetric Induction

Novel polyphenylacetylene and polystyrene derivatives carrying L-proline moieties at the side chains were synthesized by the rhodium-catalyzed and radical polymerizations of the corresponding monomers. The polyphenylacetylene derivatives showed Cotton effects at the absorption region of the main chain, indicating that the polymers adopt helical conformations with predominantly one-handed screw sense. The polymers catalyzed the asymmetric aldol reactions of acetone with aromatic aldehydes, and cyclohexanone with p-nitrobenzaldehyde. The enantioselectivities largely depended on the reaction conditions. In the asymmetric aldol reaction of acetone with aromatic aldehydes, the R-enantiomeric products were predominantly obtained except the cases with the polymer catalyst in CHCl3. The ee of the products became higher as the reaction temperature was decreased. The polymeric catalysts were recoverable from the reaction mixture by filtration, and the recovered ones catalyzed the asymmetric aldol reaction of acetone with p-nitrobenzaldehyde without decreasing the product yield and ee. The ee was improved using the copolymers of L-proline-based and nonchiral monomers as catalysts. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3783-3796,2011