Optically active helical polymers bearing cinchona alkaloid pendants: an efficient chiral organocatalyst for asymmetric Henry reaction

Abstract

Inspired by the highly efficient and enantioselective reactions catalyzed by biomacromolecules, developing artificial helical polymer-supported catalysts is an attractive and meaningful field. In this work, a series of helical polymers poly-1ns with controlled molecular mass (Mns) and narrow molecular mass distribution (Mw/Mns) bearing cinchona alkaloid pendants was obtained by asymmetric polymerization of corresponding monomer. The poly-1ns exhibited intense positive Cotton effect at 364 nm, indicating preferred righted-handed helix was formed in their backbone. Due to the catalytic groups on pendants and helix in the backbone, poly-1ns exhibited satisfied catalytic efficiency on asymmetric Henry reaction. Compared to small molecule (1) with similar structures, enantioselectivity of Henry reaction was significantly enhanced using poly-1n as catalyst. The enantiomeric excess (ee) value of the Henry reaction could be up to 75%. Furthermore, the helical polyisocyanide catalyst could be recovered and reused facilely at least five cycles without apparent significant loss of its enantioselectivity.