Chiral amplification during asymmetric-induced copolymerization of phenylacetylenes with tight cis-cisoidal main chains

摘要

A novel phenylacetylene (1) having two hydroxyl groups and a chiral pinanyl group together with the other three related phenylacetylenes has been synthesized and (co)polymerized by using an achiral catalytic system. Among the four monomers, only 1 is suitable to the asymmetric-induced polymerization (AIP). Chiral amplification phenomenon is only observed in the copolymerization of 1 with an achiral phenylacetylene having two hydroxyl groups (3). The tight helical cis-cisoidal main chain formed by making intramolecular hydrogen bonds between the hydroxyl groups in the copoly(1/3) enhances the efficiency of chiral induction and as a result chiral amplification phenomenon is observed during the copolymerization. The efficiency of chiral amplification during the asymmetric-induced copolymerization of achiral and chiral phenylacetylenes with two hydroxyl groups is enhanced due to the tight helical cis-cisoidal conformations maintained by making intramolecular hydrogen bonds between the hydroxyl groups in copoly(phenylacetylene)s. The closer spatial position between the chiral pendant groups in the cis-cisoidal polyacetylene can control the helical sense more efficiently.