Helical Poly(phenylacetylene) Bearing Chiral and Achiral Imidazolidinone-Based Pendants that Catalyze Asymmetric Reactions due to Catalytically Active Achiral Pendants Assisted by Macromolecular Helicity.

Abstract

A series of optically active helical copolymers of phenylacetylenes are prepared by the rhodium-catalyzed copolymerization of the imidazolidinone-linked, catalytically active achiral phenylacetylenes and catalytically inactive chiral phenylacetylenes. The obtained chiral/achiral copolymers exhibit an induced circular dichroism in the UV-vis regions of the copolymer backbones resulting from a preferred-handed helical conformation biased by the chiral imidazolidinone units incorporated in the copolymers. The copolymers are found to catalyze the asymmetric Diels-Alder reaction and produce the products with a moderate enantioselectivity in spite of the fact that the catalytically active units of the copolymers are achiral, indicating that the observed enantioselectivity totally originates from the helical chirality dynamically induced by the optically active, but catalytically inactive imidazolidinone units incorporated in the copolymers.