Chemistry Reference
In-Depth Information
gave isotactic polymers, all of which showed positive optical rotations of [
]
365
+786 to
+939 ° . The poly -
218
exhibits reversible helix-to-helix transition in which the excess of
screw sense is dependent on the solvent [306]. Cyclopolymerizations of bifunctional meth-
acrylate (
219
) [307,308] and related monomers [309] under anionic or radical conditions
are feasible to obtain single-handed helical polymers.
α
O
Ph
Ph
NMe
H
O
O
O
O
O
Ph
O
O
Ph
Ph
Ph
218
219
13.3.2.3. Polymerization of Alkynes
Helical polyacetylenes with excess screw sense
can be obtained by metal-catalyzed polymerization of optically active alkynes [310].
Among transition metal catalysts ever reported, rhodium catalysts are remarkably pow-
erful because of their nature to form exclusive
cis
-transoidal structures in the obtained
polymer, which leads to the induction of helical conformations. In 1993, Aoki and
coworkers reported the synthesis of helical poly(arylacetylene)s (
221
) by [RhCl(nbd)]
2
-
catalyzed polymerization of arylacetylenes (
220
) (Scheme 13.25) [311]. Since the report,
a variety of single-handed helical poly(arylacetylene)s having optically active substitu-
ents such as carbamoyloxy groups [312], minidendric moieties [313,314], sugar-derived
groups [315] oligopeptide pendants [316], and mesogenic groups [317] have been syn-
thesized by rhodium-catalyzed polymerization. A series of helical disubstituted poly-
acetylenes have also been investigated [318 - 321] .
n
H
[RhCl(nbd)]
2
THF
O
O
O
O
220
221
Scheme 13.25.
Masuda and coworkers have made signifi cant contributions to the fi eld of helical
polyacetylene chemistry by synthesizing various optically active polyacetylenes,
including poly(propionic ester)s [322 - 325] , poly(propargyl alcohol)s [326] ,
poly(
N
- propargylamide)s [327 - 350] , poly(
N
- butynylamide)s [351] , poly(
N
- propargyl-
carbamate)s [352,353] , and poly(
N
- propargylphosphonamidate)s [354 - 356] , and
poly(arylacetylene)s [357-368]. Their chiroptical properties, as well as helical conforma-
tion and helicity inversion behavior, have been intensely investigated.
