A rational design for the directed helicity change of polyacetylene using dynamic rotaxane mobility by means of through-space chirality transfer

Article abstract of DOI:10.1002/chem.201101727

Directed helicity control of a polyacetylene dynamic helix was achieved by hybridization with a rotaxane skeleton placed on the side chain. Rotaxane-tethering phenylacetylene monomers were synthesized in good yields by the ester end-capping of pseudorotax

Full text of DOI:10.1002/chem.201101727

FULL PAPER
DOI: 10.1002/chem.201101727
A Rational Design for the Directed Helicity Change of Polyacetylene Using
Dynamic Rotaxane Mobility by Means of Through-Space Chirality Transfer
Fumitaka Ishiwari, Kei-ichiro Fukasawa, Takashi Sato, Kazuko Nakazono,
Yasuhito Koyama, and Toshikazu Takata*[a]
Abstract: Directed helicity control of a
polyacetylene dynamic helix was ach-
ieved by hybridization with a rotaxane
skeleton placed on the side chain. Ro-
taxane-tethering phenylacetylene mon-
omers were synthesized in good yields
by the ester end-capping of pseudoro-
taxanes that consisted of optically
active crown ethers and sec-ammonium
salts with an ethynyl benzoic acid. The
monomers were polymerized with
posal that N-acylative neutralization of
the sec-ammonium moieties of the
side-chain rotaxane moieties enables
asymmetric induction of a one-handed
helix as the wheel components ap-
proach the main chain is strongly sup-
ported by observation of the Cotton
effect around the main-chain absorp-
tion region. A polyacetylene with a
side-chain rotaxane that has a shorter
axle component shows a Cotton effect
despite the ammonium structure of the
side-chain rotaxane moiety, thereby
suggesting the importance of proximity
between the wheel and the main chain
for the formation of a one-handed
helix. Through-space chirality induc-
tion in the present systems proved to
be as powerful as through-bond chirali-
ty induction for formation of a one-
handed helix, as demonstrated in an
experiment using non-rotaxane-based
polyacetylene that had an optically
active binaphthyl group. The present
protocol for controlling the helical
structure of polyacetylene therefore
provides the basis for the rational
design of one-handed helical polyacety-
lenes.
[{RhClACHTUNGTRENNUNG(nbd)}2] (nbd=norbornadiene)
to give the corresponding polyacety-
lenes in high yields. Polymers with opti-
cally active wheel components that are
far from the main chain show no
Cotton effect, thereby indicating the
formation of racemic helices. Our pro-
Keywords: chirality · helical struc-
tures · polyacetylene · rotaxanes ·
supramolecular chemistry
Introduction
taining polyacetylenes capable of changing their helical
sense in response to varying solvent polarity and tempera-
ture.[5]
Artificial helical molecules and architectures have been ex-
tensively studied, inspired mainly by the biological function
and importance of the one-handed helix in biomolecular sys-
tems such as DNA and proteins.[1] For helical polymers syn-
thesized artificially to date, several important functions have
been reported, including chiral discrimination,[2] asymmetric
catalysis,[3] and optical resolution,[4] which eventually led to
their practical usage. The functions of helical polymers are
often strongly related to their higher-order structures. Artifi-
cial helical polymers such as polyisocyanate and polyacety-
lene change their helical form in response to varying stimuli
such as solvent and temperature, and are thus known as “dy-
namic helical polymers.”[1] In a pioneering work, Yashima
et al. reported a variety of optically active side-chain-con-
The larger class of structure-variable polymers to which
dynamic helical polymers belong are expected to show
structure-dependent dynamic functions. Many reports on
structure changes in dynamic helical polymers have ap-
peared, but most of the reported changes were not designed
a priori. Thus, the rational design of protocols for intention-
al, directed control of helical-structure change is highly de-
sirable.
Along these lines, Feringa et al. reported an ingenious
switching system of a polyisocyanate helix driven by a pho-
toswitchable group introduced in the polymer terminus,[6]
but few reports exist of such dynamic systems.[7] Meanwhile,
the excellent capability of rotaxanes to function as switching
devices, based on the high degree of freedom of the compo-
nents, has recently attracted attention because of possible
their application in molecular motors and actuators.[8] We
became intrigued by the possibility of directed structure
control of the polyacetylene dynamic helix by hybridization
with rotaxane placed on the side chain, which we would ac-
complish by controlling the mobility of the rotaxane compo-
nents—a reasonable next step for us, as we had already ach-
ieved the regular arrangement of rotaxane functions in the
synthesis of side chain-type polyrotaxanes.[9] Masuda et al.
[a] F. Ishiwari, K.-i. Fukasawa, Dr. T. Sato, Dr. K. Nakazono,
Dr. Y. Koyama, Prof. T. Takata
Department of Organic and Polymeric Materials
Tokyo Institute of Technology
2-12-1 (H126) Ookayama Meguro-ku
Tokyo 152-8552 (Japan)
Fax : (+81)3-5734-2888
E-mail: ttakata@polymer.titech.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101727.
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showed that polymers such as polyacetylene that possess an
optically active group in the side chain can form a one-
handed helix when the optically active group is close to the
main chain, and a racemic helix when the optically active
group is far from the main chain.[10] Scheme 1 shows helix
formation for a polyacetylene that has a pendant rotaxane
moiety with a wheel component that is optically active.
From this figure, it is conceivable that polyacetylene can
form a racemic helix when the wheel is far from the main
chain and a one-handed helix when the wheel is close to the
main chain. As mentioned above, this protocol seems rea-
sonable for directed structure control of the dynamic helix
of polyacetylene.
ane driven by through-space chirality transfer. We discuss
the synthesis of acetylene monomers and polyacetylenes
that have pendant rotaxanes with optically active wheel
components, position control of the wheel component on
the axle, and the structure change between racemic helix
and one-handed helix that corresponds to the rotaxane
structure change.
Results and Discussion
Design and synthesis of rotaxane-containing phenylacety-
lene monomers and their polymers: We designed and syn-
thesized various sec-ammonium salt/crown-ether-type rotax-
ane-containing phenylacetylene monomers (Scheme 2 and
Scheme 3). The monomers con-
Herein we report for the first time the dynamic helix con-
trol of polyacetylene by using the dynamic nature of rotax-
sist of pendant rotaxane moiet-
ies with a few types of wheel
components that have optically
active groups. Monomers (S)-1,
(R)-2, (S)-2, and
prepared in yields of 22–77%
according to tributylphos-
ACHTUNGTRENUN(NG R,R)-3 were
a
phane-catalyzed ester end-cap-
ping protocol (Scheme 2 and
Scheme 3).[9,11] Non-rotaxane-
type monomer 4, which lacks a
wheel component, was pre-
pared as a reference monomer.
The structures of these mono-
mers were determined by 1H
and 13C NMR spectroscopy, IR,
Scheme 1. Schematic illustration of a polyacetylene helix controlled by the position of the optically active
wheel on the pendant rotaxane axle.
Scheme 2. Synthesis of rotaxane-containing polyacetylene and N-acylation of polymers.
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Helicity Change of Polyacetylene
FULL PAPER
axle in the case of [2]rotaxane,
similar to the case for mono-
mers 1–3 (Scheme 4). That is,
N-acylation moves the wheel to
the less-hindered side.[17] If
movement of the wheel of 1–3
occurs similarly, the optically
active wheel component must
approach the main chain to
exert some influence over it.
Scheme 3. Synthesis of rotaxane-containing acetylene monomers.
UV/Vis, circular dichroism (CD), and FAB HRMS spectros-
copy.[12]
The various polyacetylenes were prepared by polymeri-
zation of the monomers with a typical polymerization cata-
lyst [{RhClACHTUNGTRENNUNG(nbd)}2]/Et3N in CHCl3 (in DMF for 4; nbd=nor-
bornadiene) at room temperature for 4 h (Scheme 3).[9,13]
Despite the presence of sec-ammonium salt groups,[9,14] poly-
merization of all monomers proceeded successfully to give
the corresponding polyacetylenes poly-(S)-1, poly-(R)-2,
poly-(S)-2, poly-(R,R)-3, and poly-4 in high yields (89–
98%). The polymers were isolated by reprecipitation from
Et2O. The polymer structures were determined by IR, UV/
1
Vis, CD, and Raman spectroscopy. H and 13C NMR spec-
troscopy proved unsatisfactory for this purpose, as their sig-
nals were too broad to assign in all cases, possibly because
of the structural disorderliness of the coalescent rotamers.[12]
The IR spectra proved particularly useful; the absorption at
around 3300 cmÀ1 of the monomers, attributable to the C H
À
stretching vibration of the terminal acetylene group, disap-
pears in the spectra of the polymers, whereas the other ab-
sorptions of the polymers, including those in the fingerprint
region, are in a good agreement with those of the mono-
mers.
The UV/Vis and CD spectra of the monomers and poly-
mers mentioned above were measured using THF as a sol-
vent. The UV/Vis spectra of poly-(S)-1, poly-(R)-2, poly-
(S)-2, and poly-(R,R)-3 show an absorption maximum
around 470 nm for the p-conjugated polyacetylene backbone
(poly-(S)-1: 472 nm, poly-(R)-2 and poly-(S)-2: 471 nm,
poly-(R,R)-3: 475 nm) that is not observed for the mono-
mers. In the CD spectra, these ammonium-type polymers
show no Cotton effect around 470 nm, thereby indicating a
good balance of right- and left-handed helices. The balanced
helix sense around the main chains can be explained by as-
suming that the optically active wheel components are locat-
ed at such a distance from the main chain that they do not
influence the main-chain conformation, because a strong hy-
drogen-bonding interaction operates between the compo-
nents of the rotaxane moiety to control the mobility of the
wheel.[15] This is consistent with our initial assumption de-
scribed in Scheme 1.
Scheme 4. N-Acetylation of (R)-2 and polymerization of (R)-2Ac.
N-Acylations of poly-(S)-1, poly-(R)-2, poly-(S)-2, and
poly-(R,R)-3 were performed by our previous method with
various acylating agents (acetic anhydride, benzoic anhy-
dride, and 2,2,2-trichloroethyl chloroformate) to give the
corresponding N-acylated neutral polymers (Scheme 3).[9,16]
The polymers were isolated by re-precipitation from MeOH
rather than Et2O, due to the increase in solubility in ordina-
ry organic solvents induced by N-acylation. We attempted to
estimate the molecular weights of the polymers by size-ex-
clusion chromatography (SEC); however, their values were
too high to measure correctly (Mn >2.0ꢁ106).[9] Large-mo-
lecular-weight polyacetylenes are not unusual.
In the IR spectra of the N-acylated polymers, the absorp-
tions at approximately 840 and 560 cmÀ1, which are assigna-
À
À
ble to the P F stretching vibration of counteranion PF6 ,
completely disappear and new absorptions at 1648 cmÀ1
(poly-(S)-1Ac, poly-(R)-2Ac, and poly-(S)-2Ac: aliphatic
amide) and 1636 cmÀ1 (poly-(R)-2Bz and poly-(R,R)-3Bz:
aromatic amide), assignable to the C=O stretching vibration
of the amide group, appear. This result strongly indicates
that all sec-ammonium salt groups were acylated. The IR
Synthesis and structure of N-aceylated polyacetylenes:
Movement of the wheel component from the ammonium
group in a crown-ether-based [2]rotaxane can be achieved
by N-acylation to neutralize the ammonium group.[16] The
crown ether wheel moves to the benzyl ester moiety on the
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T. Takata et al.
spectrum of poly-(R)-2Troc shows a strong absorption as-
signable to the C=O stretching vibration of the urethane
group in the same region as the ester group (around
1700 cmÀ1).
To determine the main-chain conformation or cis/trans
structure of the polyacetylene helix, we measured the
Raman spectra of all the polymers shown in Scheme 3. All
Actually, when the wheel component approached the main
chain, it changed the main-chain p conjugation. To investi-
gate the proximity effect of the optically active group on the
helicity of the polyacetylenes, we conducted detailed CD
spectral analyses. First, we studied the CD spectra of the
polymers that tether a point chirality at the carbon atom.
The spectra show no Cotton effect around the main-chain
absorption region (490 nm) for either poly-(S)-1 and poly-
(S)-1Ac (Figure 2), thus indicating that both polymers have
spectra show typical strong peaks at approximately 1540
À1
À
À
(cis-C=C), 1330 (trans-C C), and 840 cm (C H), which
are assignable to the cis-transoidal structure of polyacety-
lene.[13,14] This result agrees with results obtained for typical
polyacetylenes produced by polymerization with Rh cata-
lyst.[13,14]
In the UV/Vis spectra of the N-acylated polymers, peaks
appear around 490 nm ACTHNUGRTENUNG(poly-(S)-1Ac: 489 nm, poly-(R)-
2Ac and poly-(S)-2Ac: 492 nm, and poly-(R,R)-3Ac:
488 nm), which are assignable to the absorption maxima of
the main chains. Consistent with those assignments, the solu-
tion color changed from yellow before N-acylation to red
after it.[9] The remarkably large redshift (ꢀ20 nm) relative
to those of the corresponding ammonium polymers clearly
reveals the main-chain structural change. Namely, the N-
acylated polymers have
a longer effective conjugation
length and looser helix than do the ammonium polymers.[18]
We conclude, then, that the redshift results from the ap-
proach of the bulky wheel component to the main chain
during N-acylation, as we expected.[18] That the redshift does
not result simply from N-acylation is confirmed by the fol-
lowing experimental results for non-rotaxane-type polyace-
tylenes poly-4 and poly-4Ac: a UV/Vis absorption maxi-
mum is observed at 475 nm for poly-4 and at 448 nm for
poly-4Ac (Figure 1); in addition, a large blueshift (ꢀ30 nm)
Figure 2. CD and UV/Vis spectra (THF, 293 K, 0.14 mm: monomer unit)
of (S)-1, poly-(S)-1, and poly-(S)-1Ac.
a racemic helical structure in solution. These results mean
that the point chirality of the wheel component is insuffi-
cient to induce a one-handed helix.
In contrast, the CD spectra of poly-2Ac and poly-(R,R)-
3Ac, which have axially chiral or C2 chiral groups on the
wheel components of the pendant rotaxanes, show a clear
Cotton effect around the main-chain absorption regions
(Figure 3), thus indicating that these polymers can form
one-handed helices in solution. It is conceivable that the
one-handed helix emerges from the asymmetric field
formed by axial chirality, which is larger than that induced
by point chirality in this system. Meanwhile, the CD spectra
of poly-(R)-2Ac and poly-(S)-2Ac are mirror images of
each other, which indicates that the two polymers form one-
handed helices in solution with complementary helix senses.
Thus, the chirality of the wheel component was nicely trans-
ferred through space to the polyacetylene backbone. The
absorption maximum and CD intensity are almost independ-
ent of the bulkiness of the acyl groups (Figure 3), thereby
suggesting that any acyl group is sufficiently bulky to move
the wheel component to the main chain.
Figure 1. UV/Vis spectra (THF, 293 K, 0.14 mm: monomer unit) of poly-4
and poly-4Ac.
due to N-acylation is observed for both, in contrast to the
redshift observed for the rotaxane-type polymers. These
phenomena suggest that the steric and/or electronic repul-
sions of the sec-ammonium groups are larger than those of
Poly-(R,R)-3Bz shows an opposite Cotton effect to that
shown by poly-(R)-2Ac in the main-chain absorption
region. Thus, although the two polymers have similar CD in-
tensities (Figure 4), their helix senses differ. Direct compari-
son of the two is difficult since the wheel component of the
two pendant rotaxane moieties differs in the number of C2
chiral groups and in cavity size, but the difference in degree
À
the N Ac groups.
Asymmetric induction of a one-handed helix by means of
through-space chirality transfer: The above N-acylation was
performed to move the optically active wheel component of
the pendant rotaxane near the polyacetylene main chain.
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Helicity Change of Polyacetylene
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Figure 4. CD and UV/Vis spectra (THF, 293 K, 0.14 mm: monomer unit)
of poly-(R)-2, poly-(R)-2Ac, poly-(R,R)-3, and poly-(R,R)-3Bz.
Figure 3. CD and UV/Vis spectra (THF, 293 K, 0.14 mm: monomer unit)
of (R)-2, poly-(R)-2, poly-(S)-2, poly-(R)-2Ac, poly-(R)-2Bz, and poly-
(R)-2Troc.
should be high, because the typical chemical shifts in the
1H NMR spectroscopic signals of the indicator are similar to
those of the
a priori acetylated monomer (R)-2Ac
of proximity reasonably accounts for the difference in helix
sense. Namely, larger steric repulsion with the adjacent
wheel component and looser interaction with the axle O-
benzylic site for poly-(R,R)-3Bz than for poly-(R)-2Ac
might result in an incomplete approach to the main chain of
poly-(R,R)-3Bz, thus accounting for the different helix
sense of the main chain. This prediction is justified by their
absorption maxima for which poly-(R,R)-3Bz (488 nm) is at
a shorter wavelength than that of poly-(R)-2Ac (492 nm),
despite its bigger pendant group.[18] Therefore, the degree of
approach to the main chain is significant.
We evaluated the helix stabil-
(Scheme 4). The fact that (R)-2Ac shows no polymerizabili-
ty also supports a high degree of approach of the wheel
component, because the bulky group that covers the reac-
tive ethynyl moiety lowers polymerizability remarkably
(Scheme 4). The clear upfield shift of the ethynyl proton
signal of the N-acetylated monomer (R)-2Ac in the
1H NMR spectra (Figure 5, from 2: d=3.18 ppm to 2Ac:
d=2.87 ppm)[9,16] is consistent with controlled polymerizabil-
ity—that is, with sufficient approach of the wheel compo-
nent during N-acetylation in the case of poly-(R)-2Ac, in
accordance with the above CD phenomena.
ity by examining the tempera-
ture dependence of the CD
spectra in various solvents.[12]
We observed no change in CD
intensity in the temperature
range À10 to 608C in THF and
no solvent dependence for
poly-(S)-2, poly-(R)-2Ac, poly-
(R)-2Bz, poly-(R)-2Troc, and
poly-(R,R)-3Ac. These results
suggest that the one-handed
helical conformation is stabi-
lized by steric hindrance be-
tween the bulky side-chain
units.
The degree to which the
wheel component approaches
the main chain in poly-(R)-2Ac Figure 5. Partial H NMR spectra of (R)-2 and (R)-2Ac (400 MHz, CDCl3, 298 K).
1
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T. Takata et al.
As mentioned above, the forced transfer of the optically
active rotaxane wheel near the polymer main chain during
N-acylation actually causes formation of the one-handed
helix of polyacetylenes by means of through-space chirality
transfer. N-Acylation certainly contributes to movement of
the wheel, but does not by itself induce formation of the
one-handed helix, although Masuda and co-workersꢂ results
strongly support the present proximity effect.[10] To clarify
whether the present one-handed helix induction arises only
from the approach of the optically active group to the main
chain and whether the disappearance of the ionic structure
relates to this effect, we studied the effect of the length of
the axle component of the pendant rotaxane moiety. We de-
signed a rotaxane monomer (R)-5 for which the distance be-
tween the ethynyl group and ammonium group is shorter
than that of 2—that is, its optically active group is closer to
the main chain than that of (R)-2. According to Scheme 5,
polyacetylene poly-(R)-5, with a short axle component, was
prepared by typical polymerization with an Rh catalyst fol-
lowed by N-acetylation with acetic anhydride. However,
(R)-5 had very low polymerizability and the yield was only
10% after reaction for 4 h. The low polymerizability can be
simply explained, similar to the case for (R)-2Ac described
above, by assuming effective shielding of the ethynyl moiety
by the nearby wheel component. The shortened distance be-
tween the wheel and the main chain in poly-(R)-5 was con-
firmed by UV/Vis spectroscopy: poly-(R)-5 has an absorp-
tion maximum at 481 nm. To our surprise, the main-chain
absorption region in the CD spectrum shows some clear
Cotton effects (Figure 6). Moreover, the CD profile and in-
tensity of poly-(R)-5 are similar to those of poly-(R)-2Ac.
These results suggest that poly-(R)-5 takes a one-handed
helical conformation similar to poly-(R)-2Ac, although all
ammonium-type rotaxane-containing polymers poly-2 do
not, thereby strongly supporting the proximity effect of the
optically active wheel component.
Figure 6. CD and UV/Vis spectra (THF, 293 K, 0.14 mm: monomer unit)
of poly-(R)-2, poly-(R)-2Ac, poly-(R)-5, and poly-(R)-5Ac.
the pendant rotaxane, its influence on the main chain, and
the sense of the helix. To evaluate the structural similarity,
we conducted MM2 calculations for the monomers (R)-2,
(R)-2Ac, (R)-5, and (R)-5Ac. Results show that the wheel
components of these compounds, except for (R)-2, have sim-
ilar positions close to the ethynyl group.[12] Thus, the short
distance between the main chain and the wheel component
is important for inducing formation of a one-handed helix,
independent of neutral or ionic property.
To compare the through-space chirality-transfer system
with the through-bond chirality-transfer system, we designed
a non-rotaxane-type phenylacetylene monomer (R)-6 that
bore an optically active C2 chiral group as a model for
through-bond chirality transfer. We also prepared the (R)-
binaphthyl-group-containing polyacetylene poly-(R)-6 in
89% yield by typical Rh-catalyzed polymerization of (R)-6
(Scheme 6). The structures of (R)-6 and poly-(R)-6 were de-
N-Acylation of poly-(R)-5 with acetic anhydride was per-
formed to give the neutral polymer poly-(R)-5Ac. The
structure was determined in the same manner as for poly-
(R)-2Ac. The CD and UV/Vis spectra show an absorption
maximum at 483 nm with a clear Cotton effect. The CD pro-
file and intensity are similar to those of poly-(R)-5 and
poly-(R)-2Ac (Figure 6). These results suggest the structural
similarity of poly-(R)-2Ac, poly-(R)-5, and poly-(R)-5Ac
with respect to the position of the optically active wheel in
1
termined by H NMR spectroscopy, IR, and SEC. The mo-
lecular weight of poly-(R)-6 was also too high to measure
correctly (Mn >2000ꢁ103).
The CD and UV/Vis spectra of poly-(R)-6 were measured
and compared with the spectra of the base polymer poly-
Scheme 5. Synthesis of poly-(R)-5 and N-acetylation of poly-(R)-5.
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Helicity Change of Polyacetylene
FULL PAPER
system in inducing formation of a one-handed helix. These
results confirm the successful rational design of a helical
polymer or oligomer with controlled helical structure. As an
extension of this work, we are now investigating the reversi-
ble structural change of the polyacetylene main chain by re-
versible shuttling of the wheel component.[19]
Scheme 6. Synthesis of poly-(R)-6.
Experimental Section
(R)-2Ac, in which through-space chirality transfer is known
to have taken place. The absorption maximum at 485 nm
shows a clear Cotton effect based on main-chain chirality
(Figure 7). Although the Cotton effects of the two polymers
are opposite, their CD and UV/Vis profiles and intensities
are similar. Thus it is evident that a through-space chirality-
transfer system is as effective as a through-bond chirality
transfer system for asymmetric induction of a one-handed
helix.
Materials and methods: Triethylamine (Wako Pure Chemical Industries,
Ltd.) was dried over calcium hydride and distilled prior to use. Commer-
cially available materials and solvents including 3-bromo-5-iodobenzoic
acid (Tokyo Chemical Industry Co., Ltd.), [Pd
ACHTUNGTRENNUNG
(Wako Pure Chemical Industries, Ltd.), [{RhClACHTUNGTRENNUNG
Chemical Industries, Ltd.), N,N-diisopropyl carbodiimide (Wako Pure
Chemical Industries, Ltd.), and (S)-2-phenylpropionic acid (Wako Pure
Chemical Industries, Ltd.) were used without further purification.
Column chromatography was performed using Wakogel C-400HG (Wako
Pure Chemical Industries Ltd.). 1H (400 MHz) and 13C NMR (100 MHz)
spectra were recorded using a JEOL AL-400 spectrometer with CDCl3 as
the solvent and tetramethylsilane as the internal standard. Purifications
by repeated preparative gel permeation chromatography (GPC) were
performed using a JAI Co., Ltd. LC-9204 system (JAIGEL-1H-40) with
CHCl3 as the eluent. Molecular weight and its distribution were mea-
sured by size-exclusion chromatography (SEC) using a JASCO Gulliver
system equipped with two consecutive linear polystyrene gel columns
(TOSOH TSKgel G5000HXL and GMHXL) at 308C, eluted with CHCl3
at a flow rate of 0.085 mLminÀ1, and calibrated using polystyrene stand-
ards. IR spectra were recorded using a JASCO FT/IR-230 spectrometer.
Melting points were measured using a Stuart Scientific SMP3 (Bibby Sci-
entific). UV/Vis spectra ware taken using a JASCO V-550 UV/VIS spec-
trophotometer. CD spectra were taken using a JASCO J-820 spectropo-
larimeter. Specific optical rotations were measured using a JASCO DIP-
1000 digital polarimeter in a 10 cm cuvette. The conformational analyses
of monomers were carried out by using MACROMODEL ver. 96. The
HRMS spectra were taken by the National University Corporation
Tokyo Institute of Technology Center for Advanced Materials Analysis
on request. Laser Raman spectra was taken by JASCO Co., Ltd. using a
NRS-3100 dispersive Raman spectrometer on request.
Synthesis of (R)-2: PBu3 (1 drop) and diisopropyl carbodiimide (3.0 mL,
17 mmol) were added to a solution of 3-ethynyl-5-[(triisopropylsilyl)ethy-
nyl]benzoic acid (521 mg, 1.60 mmol), (R)-26-membered crown ether
(1.0 g, 1.6 mmol), and sec-ammonium salt (777 mg, 1.60 mmol) in CHCl3
(20 mL) at 08C, and the mixture was stirred for 12 h. The reaction solu-
tion was poured into hexane (70 mL), and the precipitate was collected
by decantation and purified by silica gel column chromatography
(CHCl3/EtOAc=1:1) and recycle preparative GPC (CHCl3) to give ro-
taxane-shaped phenylacetylene monomer (R)-2 (1.74 g, 77%) as a color-
less foam. M.p. 117.1–118.98C; [a]2D5 = +119.18 (c=0.14 in THF);
1H NMR (400 MHz, CDCl3, 298 K): d=8.12 (dd, 2H, J=1.5, 1.5 Hz),
7.94 (d, 1H, J=8.9 Hz), 7.89 (d, 1H, J=8.3 Hz), 7.84 (d, 1H, J=8.3 Hz),
7.79 (dd, 1H, J=1.5, 1.5 Hz), 7.78 (d, 1H, J=8.9 Hz), 7.43 (s, 1H), 7.40
(dd, 1H, J=8.3, 8.3 Hz), 7.36 (dd, 2H, J=8.3, 8.3 Hz), 7.35 (d, 1H, J=
8.9 Hz), 7.26 (s, 2H), 7.26 (dd, 1H, J=8.3, 8.3 Hz), 7.26 (dd, 1H, J=8.3,
8.3 Hz), 7.21 (d, 1H, J=8.3 Hz), 7.20 (d, 1H, J=8.3 Hz), 7.03 (d, 1H, J=
8.0 Hz), 7.01 (d, 1H, J=8.9 Hz), 6.94 (d, 1H, J=8.0 Hz), 6.86 (dd, 1H,
J=8.0, 8.0 Hz), 6.18 (dd, 1H, J=8.0, 8.0 Hz), 6.73 (d, 1H, J=8.0 Hz),
6.56 (d, 1H, J=8.0 Hz), 5.23 (s, 2H), 4.36–4.34 (m, 4H), 4.17–4.02 (m,
3H), 3.92–3.88 (m, 1H), 3.75–3.73 (m, 3H), 3.62–3.59 (m, 3H), 3.45–3.37
(m, 4H), 3.31–3.15 (m, 8H), 3.18 (s, 1H), 3.10–3.05 (m, 1H), 2.96–2.91
(m, 1H), 1.24 (s, 18H), 1.12–1.11 ppm (m, 21H); 13C NMR (100 MHz,
CDCl3): d=164.8, 154.4, 154.3, 151.6, 146.5, 146.4, 139.7, 139.6, 136.88,
133.9, 133.6, 133.0, 132.9, 132.7, 132.6, 130.9, 130.6, 130.6, 130.1, 140.0,
129.9, 129.8, 128.2, 128.1, 128.0, 127.9, 126.7, 125.4, 125.0, 124.7, 124.5,
124.3, 124.3, 123.8, 123.8, 123.6, 123.0, 122.2, 121.7, 120.7, 117.6, 116.7,
112.0, 104.6, 93.4, 81.6, 79.2, 79.1, 71.2, 70.9, 70.8, 70.7, 70.5, 70.3, 69.4,
Figure 7. CD and UV/Vis spectra (THF, 293 K, 0.14 mm: monomer unit)
of poly-(R)-2Ac and poly-(R)-6.
Conclusion
We achieved the rational transformation of the helical struc-
ture of polyacetylene by controlling the position of the ax-
ially chiral wheel on the side chain. In the synthesis of poly-
acetylenes with various optically active wheels, a wheel with
axial chirality as a large asymmetric field is needed for
asymmetric induction of a one-handed helix on the poly-
acetylene main chain. In the synthesis of polyacetylenes
with short axle components, proximity of the main chain
and the wheel component is essential for asymmetric induc-
tion of a one-handed helix, independent of neutral or ionic
property. Moreover,
a
through-space chirality-transfer
system is as effective as a through-bond chirality-transfer
Chem. Eur. J. 2011, 17, 12067 – 12075
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12073

T. Takata et al.
69.2, 68.2, 67.8, 66.3, 52.8, 52.1, 34.9, 31.3, 18.6, 11.2 ppm; IR (KBr): n˜ =
3278, 3064, 2948, 2866, 2155, 1731, 1592, 1505, 1457, 1436, 1362, 1309,
1249, 1221, 1129, 1069, 984, 950, 844, 750, 670, 557 cmÀ1; HRMS (FAB):
m/z calcd for C81H98NO10Si: 1272.6960 [MÀHPF6]+; found: 1272.6953.
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ACHTUNGTRENNUNG(nbd)}2] (4.0 mg, 8.7 mmol) and Et3N (10 mL) in CHCl3 (990 mL) was
added to a solution of (R)-2 (200 mg, 0.141 mmol) in CHCl3 (478 mL),
and the mixture was stirred for 4 h at room temperature. The solution
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polyacetylene poly-(R)-2 (190 mg, 95%) as a red solid. IR (KBr): n˜ =
3061, 2949, 2866, 2156, 1731, 1620, 1594, 1505, 1458, 1356, 1248, 1222,
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1126, 1058, 984, 947, 843, 750, 676, 557 cmÀ1
.
Acetylation of poly-(R)-2: Ac2O (1 mL) was added to a solution of poly-
(R)-2 (20.0 mg, 141 mmol) in DMF (1 mL) and Et3N (1 mL), and the
mixture was stirred for 24 h at 408C. The solution was poured into
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polyacetylene poly-(R)-2Ac (17.8 mg, 96%) as a red solid. IR (KBr): n˜ =
3062, 2950, 2866, 2153, 1725, 1648, 1624, 1592, 1505, 1459, 1361, 1249,
1214, 1125, 1070, 986, 804, 741, 679 cmÀ1
.
Synthesis of (R)-2Ac: Ac2O (1 mL) was added to a solution of (R)-2
(192 mg, 0.135 mmol) in DMF (1 mL) and Et3N (1 mL), and the solution
was stirred for 24 h at 408C. The solvent was evaporated and added
CH2Cl2, washed with saturated aqueous NaHCO3 solution, dried over
MgSO4, and concentrated in vacuo. The residue was purified by flash
silica gel column chromatography (CHCl3/EtOAc=1:1) and recycle prep-
arative GPC (CHCl3) to give N-acetylated monomer (R)-2Ac (70.1 mg,
45%) as a colorless foam. M.p. 99.9–111.58C; [a]2D5 = +119.68 (c=0.15 in
THF); 1H NMR (400 MHz, CDCl3, 298 K): d=8.12–8.10 (m, 1H), 8.09–
8.06 (m, 1H), 7.90–7.82 (m, 2H), 7.77–7.69 (m, 2H), 7.58–7.56 (m, 1H),
7.42–7.13 (m, 12H), 7.03 (s, 1H), 6.95 (s, 1H), 6.80–6.66 (m, 4H), 6.62–
6.60 (m, 1H), 5.40–5.36 (m, 2H), 4.52–4.51 (m, 2H), 4.31–4.30 (m, 2H),
4.02–3.93 (m, 3H), 3.87–3.80 (m, 1H), 3.75–3.68 (m, 1H), 3.58–3.43 (m,
2H), 3.38–3.09 (m, 16H), 2.93–2.87 (m, 1H), 2.89, 2.86 (2ꢁs, 1H), 2.18,
2.14 (2ꢁs, 3H), 1.33, 1.32 (2ꢁs, 18H), 1.12–1.11 ppm (m, 21H);
13C NMR (100 MHz, CDCl3, 298 K): d=171.0, 170.8, 165.3, 154.4, 154.3,
154.2, 151.6, 151.0, 148.3, 148.2, 148.2, 148.1, 139.0, 138.9, 136.6, 135.8,
135.8, 135.5, 135.4, 134.8, 134.0, 133.7, 133.5, 133.4, 133.3, 131.3, 131.2,
130.8, 130.6, 129.4, 129.3, 129.2, 127.9, 126.8, 126.0, 125.9, 125.6, 125.5,
125.3, 123.6, 123.5, 123.4, 123.3, 123.2, 122.4, 122.2, 121.5, 121.3, 120.5,
120.4, 120.3, 119.6, 119.5, 119.4, 115.1, 115.0, 114.8, 111.7, 111.6, 105.4,
105.3, 92.1, 91.9, 82.2, 82.1, 78.0, 77.9, 70.2, 70.1, 70.0, 69.9, 69.8, 69.7,
69.6, 69.3, 69.2, 68.8, 68.3, 68.2, 67.6, 67.5, 67.2, 50.9, 50.5, 48.1, 47.6, 34.9,
34.8, 31.5, 31.4, 21.8, 21.6, 18.6, 11.3 ppm; IR (KBr): n˜ =3277, 3063, 2957,
2866, 2154, 1718, 1624, 1592, 1506, 1458, 1434, 1362, 1310, 1251, 1222,
1126, 1068, 985, 879, 804, 775, 737, 669 cmÀ1; HRMS (FAB): m/z calcd
for C83H99NO11SiNa: 1336.6885 [M+Na]+; found: 1336.6876.
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This work was financially supported by a Grant-in-Aid for Scientific Re-
search (no. 19655013) and by a KAKENHI on Innovative Areas (Coordi-
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Received: June 7, 2011
Published online: September 16, 2011
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12075