Helicity Induction and Its Static Memory of Poly(biphenylylacetylene)s Bearing Pyridine N-Oxide Groups and Their Use as Asymmetric Organocatalysts

Novel poly(biphenylylacetylene) derivatives carrying different types of pyridine N-oxide units with a bulky or less-bulky substituent at a different position as the functional pendant groups (poly-2a and poly-2b) were synthesized by the rhodium-catalyzed polymerization of the corresponding monomers. The influence of the steric environment around the catalytically active pyridine N-oxide sites on the helicity induction and its static memory as well as the asymmetric catalytic activities of the resulting helical polymers with a macromolecular helicity memory was investigated. The polyacetylenes formed an excess one-handed helical conformation upon noncovalent interactions with optically active alcohols and the induced macromolecular helicities of the polyacetylenes were efficiently memorized after the removal of the chiral inducers. Poly-2b with the macromolecular helicity memory showed an enantioselectivity for the catalytic asymmetric allylation of benzaldehydes, producing optically active allyl alcohols, although their enantioselectivities were low. On the other hand, poly-2a exhibited a negligible catalytic activity probably due to the bulky substituent at the o-position of the pyridine N-oxide residues, while poly-2a underwent a unique helix-inversion with the increasing concentration of chiral alcohols and the opposite helicity of poly-2a was further successfully memorized. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019