Synthetic approach for optically active polymers through the combination of asymmetric chirogenic polymerization and postpolymerization modification

A new type of asymmetric chirogenic polymerization by asymmetric allylic substitution catalyzed by planar-chiral ruthenium complexes was designed. The polymerization systems function in a highly stereoselective manner to afford optically active polymers with high selectivity. The asymmetric carbon in the main chain is precisely controlled. Each monomer unit of the polymer has a potentially reactive terminal olefin, which can be used for further transformations. Optically active polymers bearing chiral cyclic architecture were prepared by a combination of asymmetric allylic substitution and ring-closing metathesis reaction employing the terminal olefin of the side chains. Additionally, the efficient introduction of a wide range of substituents into the side chain of the optically active polymer without any racemization has been made possible by using the thiol-ene reaction. Poly-N-alkoxyamides obtained by our asymmetric polymerization can be transformed into nonnatural polypeptides containing an aromatic ring on the peptide backbone, called a poly arylopeptide, through reductive cleavage of the N-O bond in N-alkoxyamide. The resulting polymer adopts a one-handed stable helical conformation in solution.