3 research outputs found
Optically Active Helical Polyacetylene Bearing Ferrocenyl Amino-Acid Derivative in Pendants. Preparation and Application as Chiral Organocatalyst for Asymmetric Aldol Reaction
The
article reports a novel type of helical polymer-based chiral
catalyst for catalyzing asymmetric aldol reactions. Chiral acetylenic
monomers containing ferrocenyl amino-acid derivative substituent were
synthesized for the first time and structurally identified. The investigated
amino acids include alanine and threonine enantiomers. The obtained
monomers separately underwent solution homopolymerization and copolymerization
with an achirally substituted acetylene monomer in the presence of
[RhÂ(nbd)ÂCl]<sub>2</sub> and Et<sub>3</sub>N. Circular dichroism and
UV–vis absorption spectra demonstrated that the copolymer chains
adopted predominantly one-handed helices, endowing the copolymers
with optical activity. The resulting (co)Âpolymers were further used
to catalyze aldol reaction between cyclohexanone and <i>p</i>-nitrobenzaldehyde. Only threonine-derived copolymers efficiently
catalyzed the aldol reaction. A remarkable yield (up to 90%) and enantiomeric
excess (up to 93%) were obtained. A synergic effect between the helical
structures in the copolymer main chains and the pendent catalytic
moieties was found to play a crucial role in the asymmetric catalysis
Optically Active Helical Polyacetylene Self-Assembled into Chiral Micelles Used As Nanoreactor for Helix-Sense-Selective Polymerization
Chiral micelles have been drawing
ever-increasing attention because
of their potentials in mimicking the unique stereochemical effects
of enzymes. This article reports on the first success in preparing
chiral micelles through self-assembly of helical polyacetylene bearing
cholic acid pendants. The micelles were further used as chiral nanoreactor,
in which achiral acetylenic monomer smoothly underwent helix-sense-selective
polymerization (HSSP). The HSSPs directly established optically active
core/shell nanoparticles whose shell and core both were constructed
by helical polymers. The shells (or micelles) provided a protective
effect for the preferably induced one-handed helical polymer chains
in the cores. The present work provides insights into the self-assembly
of chiral helical polymers, and also provides a powerful strategy
for constructing novel chiral polymer nanoarchitectures