High-yield diastereoselective synthesis of planar chiral [2]- and [3]rotaxanes constructed from per-ethylated pillar[5]arene and pyridinium derivatives

Article abstract of DOI:10.1002/chem.201200122

Planar chiral [2]- and [3]rotaxanes constructed from pillar[5]arenes as wheels and pyridinium derivatives as axles were obtained in high yield using click reactions. The process of rotaxane formation was diastereoselective; the obtained [2]rotaxane was a racemic mixture consisting of (pS, pS, pS, pS, pS) and (pR, pR, pR, pR, pR) forms of the per-ethylated pillar[5]arene (C2) wheel, and other possible types of the [2]rotaxane did not form. Isolation of the enantiopure [2]rotaxanes with one axle through (pS, pS, pS, pS, pS)-C2 or (pR, pR, pR, pR, pR)-C2 wheels was accomplished. Furthermore, pillar[5]arene-based [3]rotaxane was successfully synthesized by attachment of two pseudo [2]rotaxanes onto a bifunctional linker. [3]Rotaxane formed in a 1:2:1 mixture with one axle threaded through two (pS, pS, pS, pS, pS)-C2, one (pS, pS, pS, pS, pS)-C2 and one (pR, pR, pR, pR, pR)-C2 (meso form), or two (pR, pR, pR, pR, pR)-C2 wheels. The [3]rotaxane enantiomers and the meso form were successfully isolated using appropriate chiral HPLC column chromatography. The procedure developed in this study is the starting point for the creation of pillar[5]arene-based interlocked molecules. Copyright

Full text of DOI:10.1002/chem.201200122

FULL PAPER
DOI: 10.1002/chem.201200122
High-Yield Diastereoselective Synthesis of Planar Chiral [2]- and
[3]Rotaxanes Constructed from per-Ethylated Pillar[5]arene and Pyridinium
Derivatives
Tomoki Ogoshi,*[a] Daiki Yamafuji,[a] Takamichi Aoki,[a] Keisuke Kitajima,[a]
Tada-aki Yamagishi,[a] Yoshihiro Hayashi,[b] and Susumu Kawauchi[b]
Abstract: Planar chiral [2]- and [3]ro-
taxanes constructed from pillar[5]ar-
enes as wheels and pyridinium deriva-
tives as axles were obtained in high
yield using click reactions. The process
of rotaxane formation was diastereose-
lective; the obtained [2]rotaxane was
a racemic mixture consisting of (pS, pS,
pS, pS, pS) and (pR, pR, pR, pR, pR)
forms of the per-ethylated pillar[5]ar-
ene (C2) wheel, and other possible
types of the [2]rotaxane did not form.
Isolation of the enantiopure [2]rotax-
anes with one axle through (pS, pS, pS,
pS, pS)-C2 or (pR, pR, pR, pR, pR)-C2
wheels was accomplished. Further-
more, pillar[5]arene-based [3]rotaxane
was successfully synthesized by attach-
ment of two pseudo [2]rotaxanes onto
axle threaded through two (pS, pS, pS,
pS, pS)-C2, one (pS, pS, pS, pS, pS)-C2
and one (pR, pR, pR, pR, pR)-C2
(meso form), or two (pR, pR, pR, pR,
pR)-C2 wheels. The [3]rotaxane enan-
tiomers and the meso form were suc-
cessfully isolated using appropriate
chiral HPLC column chromatography.
The procedure developed in this study
is the starting point for the creation of
pillar[5]arene-based interlocked mole-
cules.
a
bifunctional linker. [3]Rotaxane
formed in a 1:2:1 mixture with one
Keywords: chirality
·
inclusion
compounds · macrocycles · nano-
structures · rotaxanes
Introduction
Rotaxanes[1–6] are an important class of interlocked chemical
species that have attracted increasing attention because of
their unique structural features and wide potential applica-
tion in molecular machines and devices. [n]Pseudorotaxanes
can be described as a molecular system in which macrocy-
cles (wheels) are threaded by a linear subunit (axle). The in-
sertion of two bulky stoppers at the ends of the axle yields
[n]rotaxanes. Cyclodextrins,[2] cucurbit[n]urils,[3] crown
ethers,[4] calix[n]arenes,[5] and cyclobis(paraquat-p-phenyl-
ene)[6] compounds have been used as wheel components to
construct [n]rotaxanes.
Pillar[5]arenes,[7] first reported by our group in 2008,[7b]
are cyclic pentamers composed of electron-donating di-
Figure 1. Chemical structure and conformers of pillar[5]arene.
AHCTUNGTREGaNNNU lkoxybenzene units connected by methylene bridges at the
[a] Dr. T. Ogoshi, D. Yamafuji, T. Aoki, K. Kitajima,
Prof. T.-a. Yamagishi
para-positions to form a unique symmetrical pillar architec-
ture (Figure 1). Because of their symmetrical pillar architec-
ture, facile and high yield synthesis,[7c] and versatile functio-
nality,[7d–l] the chemistry of pillar[5]arenes has developed
rapidly. One of the features of pillar[5]arenes that differs
from traditional macrocycles is their planar chirality, which
is caused by the substitution position of the alkoxy moie-
ties.[7l,m] The units rotate around the methylene bridges as
the axis; thus pillar[5]arene has eight conformers, as shown
in Figure 1: four diastereomers ꢀ two enantiomers: (pS, pS,
pS, pS, pS), (pR, pR, pR, pR, pR), (pR, pS, pS, pS, pS), (pS,
pR, pR, pR, pR), (pR, pR, pS, pS, pS), (pS, pS, pR, pR, pR),
Graduate School of Natural Science
and Technology, Kanazawa University
Kakuma-machi, Kanazawa, 920-1192 (Japan)
Fax : (+81)76-234-4800
E-mail: ogoshi@t.kanazawa-u.ac.jp
[b] Y. Hayashi, Dr. S. Kawauchi
Graduate School of Science
and Engineering
Tokyo Institute of Technology
Ookayama, Meguro-ku
Tokyo, 152-8552 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200122.
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(pR, pR, pS, pR, pS), and (pS, pS, pR, pS, pR). These con-
formers are interconverted by rotation of the units at 258C
in solution.[7n]
based [2]rotaxane from the host–guest complex formed be-
tween per-methylated pillar[5]arene and 1,8-diaminooctane
by reacting the primary amino groups of the guest with 3,5-
di-tert-butylbenzaldehyde.[7k] However, the yield was poor
(7%) and the planar chirality of the [2]rotaxane was not in-
vestigated. Herein, we report high-yield syntheses of [2]-
and [3]rotaxanes consisting of pillar[5]arene wheels and
a pyridinium axle using a click reaction between terminal al-
kynes and azides.[1b,c] The diastereoselective synthesis and
planar chirality of [2]- and [3]rotaxanes is described.
Inhibiting the rotational motion is necessary to isolate
these conformers. One approach to inhibit the rotational
motion is to modify both rims with bulky substituents.[7l] In-
troducing bulky cyclohexylmethyl groups inhibited the rota-
tional motion of the unit, and the obtained product was
a mixture of the eight conformers. Silica gel and chiral
column chromatography allowed the enantiopure conform-
ers (pS, pS, pS, pS, pS) and (pR, pR, pR, pR, pR), in which
all of the substituents at both rims have the same orienta-
tion, to be successfully obtained. Another approach that can
be used to inhibit rotation is the inclusion of a guest into the
pillar[5]arene cavity.[7n] Pillar[5]arene possesses interesting
host–guest properties with electron-accepting molecules
such as viologen and pyridinium derivatives.[7b,e,n–p] Inclusion
of a viologen derivative slowed the rotation of the units on
the NMR timescale and afforded a mixture of conformers at
low temperature. However, host–guest complexation is an
equilibrium state between complexed- and free forms and
the exchange is very fast, so we could not isolate these con-
formers. We propose to prevent this exchange by formation
of a rotaxane structure between pillar[5]arene wheels and
guest axles, allowing these conformers to be isolated. Stod-
dart et al. reported the first synthesis of a pillar[5]arene-
Results and Discussion
per-Ethylated pillar[5]arene[7q] (C2; Scheme 1a) was used as
a
wheel, whereas pyridinium derivatives (1 and 2;
Scheme 1a) bearing alkyne and trans-azobenzene moieties
at either end were prepared as axles. The trans-azobenzene
moiety is too large to thread though the cavity of C2,[7o] thus
1
it was used as a stopper. Figure 2c shows the H NMR spec-
trum of a mixture of C2 and axle 1. Upon addition of C2,
upfield shifts were observed for the proton signals from pyr-
idinium (peaks a and b), methylene (peak c), and alkyne
moieties (peak f). This indicates formation of a host–guest
complex between C2 and axle 1, and inclusion of the pyri-
AHCTUNGTREGdNNNU inium and alkyne regions of axle 1 into the C2 cavity. The
Scheme 1. Synthesis of a) [2]- and b) [3]rotaxanes.
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Figure 2. 1H NMR spectra of a) C2, b) axle 1, c) a 1:1 mixture of axle 1 and C2, d) axle 2, and e) a 1:1 mixture of axle 2 and C2 (5 mm in CDCl3 at 258C).
stoichiometry of the complex determined from a Job plot
was 1:1 (Figure S18 in the Supporting Information) and the
association constant (K) for the C2-axle 1 complex was
found to be (2.7Æ0.4ꢀ104)mÀ1 (Figure S19 in the Support-
higher than the K value of the complexes formed between
the cationic molecules and pillar[5]arenes in polar solvents
(K=100–2,000mÀ1).[7f,l–p,x,8] In [D6]acetone, the K value of
the axle 2–C2 complex was found to be (1.5Æ0.3ꢀ102)mÀ1
(see the Supporting Information), which is in the same
range. Cation–p interaction depends on the type of solvent
used,[7f] and is weakened in polar solvents and strengthened
in nonpolar solvents. Due to the low solubility of the cation-
ic guests, polar solvents such as acetone and dimethyl sulfox-
ide (DMSO) have been used as complexation media. How-
ever, axle 2 was highly soluble in a range of solvents includ-
ing chloroform. The high solubility of axle 2 in chloroform
led to the high K value. The changes in chemical shift be-
tween the free and complexed species were large for the sig-
nals from pyridinium (peaks a and b) and methylene (peaks
c and h–k) groups, and small for the other signals including
that from the alkyne proton (peak f). This indicates that C2
was mainly located on the pyridinium and alkyl moieties,
and that the alkyne group was not included in the C2 cavity.
The click reaction of axle 2 with stopper 3 in the presence
of C2 was carried out under the same reaction conditions
that were used for axle 1 and stopper 3 in the presence of
C2. Purification of the crude product from the reaction mix-
ture by silica gel chromatography afforded [2]rotaxane 6
ing Information).
A
copper(I)-catalyzed Huisgen-type
azide–alkyne cycloaddition was used to synthesize the [2]ro-
taxane. An azide-terminated stopper (3; Scheme 1a) was
added to the mixture of C2 and axle 1 together with [Cu-
ACHTUNGTRENNUNG(CH3CN)4PF6] and tris[(1-benzyl-1H-1,2,3-triazol-4-yl)me-
thyl]amine (TBTA). However, the isolated product was
a dumbbell (4; Scheme 1a, yield 47%) and the [2]rotaxane
(5; Scheme 1a) was not obtained. This was because the reac-
tive part of the alkyne moiety of axle 1 was located in the
1
cavity of C2, as confirmed by H NMR measurements (Fig-
ure 2c). The presence of C2 on the alkyne moiety hindered
the click reaction, so the reaction proceeded after dethread-
ing of C2 from axle 1. Based on this result, a pyridinium de-
rivative with a long alkyl linker between the pyridinium and
alkyne moieties (axle 2) was used instead of axle 1. Fig-
1
ure 2e shows the H NMR spectrum of a mixture of C2 and
axle 2. Upon addition of C2, new peaks (peaks in Figure 2e)
appeared and the original signals disappeared, indicating
formation of a host–guest complex between C2 and axle 2.
The complexation process was slow on the NMR timescale
at 258C. A Job plot showed that the stoichiometry of the
C2-axle 2 complex was 1:1 (see Figure S20 in the Supporting
Information). From the integration ratio between the com-
(Scheme 1a) in 75% yield, whereas
a dumbbell (7;
Scheme 1a) was not isolated. The high association constant
of the C2–axle 2 complex in CDCl3 and protrusion of the
alkyne moiety from the C2 cavity led to the synthesis of
[2]rotaxane 6 in high yield. The chemical structure of 6 was
fully characterized by 1H, 13C, 2D 1H-1H COSY, HSQC,
1
plex and free species determined from H NMR signals, K
of the complex in CDCl3 was found to be (7.6Æ1.1ꢀ104)mÀ1
(see the Supporting Information), which is significantly
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T. Ogoshi et al.
HMBC, ROESY NMR spec-
troscopy, and by high-resolution
electrospray ionization mass
spectrometry (HRMS ESI).
The HRMS of [2]rotaxane 6
contained a peak at m/z 1804
(see Figure S22 in the Support-
ing Information), corresponding
À
to the loss of one PF6 anion.
This is consist with the forma-
tion of [2]rotaxane 6.
1H NMR spectra of [2]rotax-
ane 6 (Figure 3b) and dumbbell
7[9] (Figure 3a) indicates the lo-
cation of C2 in [2]rotaxane 6.
Upfield shifts of the signals
from pyridinium (peaks a and
b) and methylene linker (peaks
c and h–k) protons were ob-
served because of the aromatic
shielding effect of C2, whereas
other protons were only slightly
affected. Figure 4 shows a 2D
ROESY NMR spectrum of
[2]rotaxane 6. Correlations be-
tween the signals from the
phenyl proton (peak a’) of the
C2 moiety and methylene pro-
tons (peaks i, j, and k) of the
axle, and between the methyl-
ene group adjacent to the O
atom of the C2 moiety (peaks
b and b’) and methylene (peaks
i, j, and k) and pyridinium
(peak a) moieties of the axle
were observed. These results in-
dicate that the C2 wheel was lo-
cated on the methylene linker
between the pyridinium and tri-
azole moieties. The same peak
shifts were observed in differ-
ent deuterated solvents (see
Figure S23 in the Supporting
Information), strongly suggest-
ing that dethreading of the
wheel C2 does not take place
and that [2]rotaxane 6 is stable.
The rotational motion of the
units of C2 was fast on the
NMR timescale, and the eight
conformers interconverted at
258C.[7n] We speculate that
there are eight possible con-
formers of [2]rotaxane 6. Two
singlet peaks (peaks a and aꢂ in
Figure 3b) from the aromatic
Figure 3. 1H NMR spectra of a) dumbbell 7 and b) [2]rotaxane 6 (5 mm in CDCl3 at 258C).
protons of C2 were observed in Figure 4. 2D NOESY analysis of [2]rotaxane 6 (5 mm in CDCl3 at 258C).
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the 1H NMR spectrum of [2]rotaxane 6, whereas the aro-
matic proton signal of pristine C2 was observed as one sin-
glet because of its symmetrical structure. The axle segment
in [2]rotaxane 6 is nonsymmetric, so the proton signals of
C2 were distinguished between the upper and lower rims.
The equivalent splitting patterns for the aromatic protons of
C2 in [2]rotaxane 6 indicated that the structure of C2 in
[2]rotaxane 6 was highly symmetric and stereoregular. Con-
sidering the eight possible [2]rotaxanes, the obtained prod-
uct was a racemic mixture of [2]rotaxane 6 consisting of (pS,
pS, pS, pS, pS) and (pR, pR, pR, pR, pR) forms of C2, and
the other possible conformers of [2]rotaxane were not
formed (Figure 5).
Figure 5. Diastereoselective pseudorotaxanation between C2 and axle 2.
These results indicate that rotaxanation between C2 and
axle 2 is diastereoselective, which is probably due to the fact
that (pS, pS, pS, pS, pS)-C2 and (pR, pR, pR, pR, pR)-C2
conformers should be of lower energy and possess a larger
cavity than the other conformers. These two conformers
should possess cavities large enough to thread onto axle 2,
but the other conformers should not. The signals from the
protons of wheel component C2 in [2]rotaxane 6 did not
change when the sample was cooled and heated (see Fig-
ure S24 in the Supporting Information), indicating that rota-
tion of the wheel C2 in [2]ro-
[3]Rotaxane 8, with one axle threaded through two
wheels, was also synthesized from C2, axle 2, and diazido-
propane 9 (Scheme 1b). Purification of the crude product
from the reaction mixture by silica gel chromatography af-
forded [3]rotaxane 8 in 45% yield. The chemical structure
of [3]rotaxane 8 was fully characterized by 1H, 13C, 2D
1H-1H COSY, HSQC and ROESY NMR spectroscopy and
by HRMS (ESI). The HRMS of [3]rotaxane 8 contained
taxane 6 did not take place on
the NMR timescale in the tem-
perature range investigated.
To further investigate the
planar chirality of [2]rotaxane
6, chiral HPLC measurements
were performed (Figure 6a).
Upon injection of [2]rotaxane 6
onto an appropriate chiral
HPLC column, two peaks of
equal area were observed, indi-
cating that rotaxane 6 was race-
mic, that is, a 1:1 mixture of
[2]rotaxanes with one axle
threaded through one (pS, pS,
pS, pS, pS)-C2 or one (pR, pR,
pR, pR, pR)-C2 wheel. This
also supports the occurrence of
diastereoselective rotaxanation.
Figure 6b shows UV/Vis and
circular dichroism (CD) spectra
of each fraction. The CD spec-
tra of the fractions were mirror
images, indicating isolation of
enantiopure [2]rotaxane 6. Cal-
culations (see Figure S25 in the
Supporting
Information)
showed that the first and
second fractions were [2]rotax-
anes 6 containing (pS, pS, pS,
pS, pS)-C2 and (pR, pR, pR,
pR, pR)-C2 wheels, respective-
ly.
Figure 6. Panels a) and c) HPLC trances, and b) and d) UV/Vis and CD spectra of b) first (i) and second (ii)
fractions of [2]rotaxane 6 (5 mm), and d) first (i), second (ii), and third (iii) fractions of [3]rotaxane 8 (3 mm) in
chloroform at 258C.
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T. Ogoshi et al.
Figure 7. 2D ROESY study of [3]rotaxane 8 (5 mm in CDCl3 at 258C).
peaks at m/z 3072 and 1536 (see Figure S26 in the Support-
in Figure 6d. The CD peak pattern of the first fraction was
the mirror image of that of the third fraction, indicating that
[3]rotaxane enantiomers were successfully isolated. No CD
signal was observed for the second fraction. This means that
the second fraction is the meso form of [3]rotaxane 8, in
which one (pS, pS, pS, pS, pS)-C2 wheel and one (pR, pR,
pR, pR, pR)-C2 wheel were locked on one axle.
ing Information), corresponding to the loss of one and two
À
PF6 anions, respectively, and indicating formation of [3]ro-
taxane 8. The location of C2 in [3]rotaxane 8 was investigat-
ed by a 2D ROESY study (Figure 7). Correlations between
phenyl (peak a’) and methylene (peaks b and b’) protons
adjacent to the O atom protons of the C2 wheel components
in [3]rotaxane 8 and methylene protons (peaks i and j) of
the axle component in [3]rotaxane 8 were observed. This in-
dicates that the wheel C2 was located on the methylene
linker between the pyridinium and triazole moieties, which
is similar to [2]rotaxane 6. The peaks for the aromatic pro-
tons (peaks a and a’) of C2 in [3]rotaxane 8 were split with
a 1:1 ratio. This indicates that the wheel components of C2
in [3]rotaxane 8 are either (pS, pS, pS, pS, pS) or (pR, pR,
pR, pR, pR) conformers and formation of [3]rotaxane 8 is
diastereoselective, which is the same as for [2]rotaxane 6.
The planar chirality of [3]rotaxane 8 was investigated by
chiral HPLC measurements (Figure 6c). Three peaks were
observed and the ratio of peak areas was calculated to be
26.9:51.1:22.0. The data indicates that 8 was a 1:2:1 mixture
of [3]rotaxanes with one axle threaded through either two
(pS, pS, pS, pS, pS)-C2, one (pR, pR, pR, pR, pR)-C2 and
one (pS, pS, pS, pS, pS)-C2, or two (pR, pR, pR, pR, pR)-C2
wheels. UV/Vis and CD spectra of each fraction are shown
Conclusion
Planar chiral[2]- and [3]rotaxanes constructed from pillar[5]-
arenes were synthesized in high yield using click reactions.
The present study is the first example of inhibition of the ro-
tation of units of pillar[5]arene by rotaxanation and isolation
of planar chiral pillar[5]arene-based [2]rotaxane. Interesting-
ly, the process of rotaxane formation was diastereoselective.
This is because the (pS, pS, pS, pS, pS) and (pR, pR, pR, pR,
pR) forms of C2 wheels are of lower energy and have
a larger cavity than the other diastereomers. Furthermore,
a pillar[5]arene-based [3]rotaxane was synthesized for the
first time and the planar chirality of the [3]rotaxane was in-
vestigated. To the best of our knowledge, these are the only
examples of a planar chiral [3]rotaxane and a meso form of
[3]rotaxane.[1d] Future work will include the synthesis of a se-
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Experimental Section
Click reaction between axle 2 and stopper 3 in the presence of C2:
TBTA (53.1 mg, 0.100 mmol) was added to a solution of axle 2 (72.8 mg,
0.100 mmol), C2 (490 mg, 0.500 mmol), and stopper
0.100 mmol) in anhydrous chloroform (2 mL), and the reaction mixture
was stirred at 258C for 1 h. [Cu(CH3CN)4PF6] (37.3 mg, 0.100 mmol) was
3 (33.1 mg,
AHCTUNGTRENNUNG
added and the mixture was stirred at 258C for 24 h. The resulting solu-
tion was concentrated in vacuo. Column chromatography (silica gel;
ethyl acetate) afforded [2]rotaxane
6 (153 mg, 0.0751 mmol, 75%).
1H NMR (CDCl3, 500 MHz): d=7.96 (d, J=9 Hz, 2H; Ph-H), 7.76 (s,
2H; Ph-H), 7.54 (s, 1H; Ph-H), 7.32 (s, 1H; triazole), 7.11 (d, J=9 Hz,
2H; Ph-H), 7.03 (d, J=7 Hz, 2H; pyridinium), 6.95 (s, 5H; Ph-H of C2
moiety), 6.81 (s, 1H; Ph-H), 6.72 (s, 5H; Ph-H of C2 moiety), 6.49 (s,
2H; Ph-H), 6.03 (d, J=7 Hz, 2H; pyridinium), 4.77 (m, 2H; methylene),
4.62 (m, 2H; methylene), 4.36 (t, J=7 Hz, 2H; methylene), 3.70–4.00 (m,
30H; methylene bridge and methylene of C2), 3.14 (t, J=7 Hz, 2H;
methylene), 2.77 (t, J=8 Hz, 2H; methylene), 1.97 (m, 2H; methylene),
1.77 (m, 2H; methylene), 1.65 (m, 2H; methylene), 1.40–1.48 (m, 30H;
methyl of C2 moiety), 1.40 (s, 18H; tert-butyl), 1.30 (s, 18H; tert-butyl),
1.17 (m. 2H; methylene), 0.75 (m, 2H; methylene), 0.60 (m, 2H; methyl-
ene), À0.061 (m, 2H; methylene), À1.21 ppm (m, 2H; methylene).
13C NMR (CDCl3, 125 MHz): d=169.1, 160.4, 152.6, 151.7, 150.3, 149.4,
147.9, 147.5, 144.1, 129.9, 129.2, 124.8, 120.5, 117.1, 116.2, 115.0, 114.7,
112.3, 107.6 (C of phenyl, pyridinium and triazole), 70.1, 65.9 (C of meth-
ylene), 65.5, 64.0 (C of methylene of C2), 57.3, 50.1, 44.1 (C of methyl-
ene), 35.1, 34.8, 31.4 (C of tert-butyl), 31.0, 30.4, 30.2, 30.0, 29.8, 29.5 (C
of methylene), 29.2 (C of methylene of C2), 29.0, 27.6, 26.6, 26.3, 25.8 (C
of methylene), 15.4, 15.3 ppm (C of methyl of C2). HRMS (ESI): m/z
calcd for C113H156N7O12 [MÀPF6À]+: 1803.18119; found: 1803.18139.
Dumbbell 7 was not isolated.
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jima, S. Fujinami, T. Yamagishi, Chem. Commun. 2011, 47, 10106–
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F. Yao, X. Jia, Org. Biomol. Chem. 2010, 8, 1568–1576; q) T. Ogoshi,
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[3]Rotaxane 8: TBTA (23.4 mg, 0.0440 mmol) was added to a solution of
axle 2 (32.0 mg, 0.0440 mmol), C2 (196 mg, 0.240 mmol), and 9 (2.52 mg,
0.0200 mmol) in anhydrous chloroform (1 mL), and the reaction mixture
was stirred at 258C for 1 h. [CuACTHNUTRGEN(UNG CH3CN)4PF6] (16.4 mg, 0.0440 mmol)
was added and the mixture was stirred at 258C for 24 h. The resulting so-
lution was concentrated in vacuo. Column chromatography (silica gel;
ethyl acetate) afforded [3]rotaxane 8 (30.0 mg, 0.00892 mmol, 45%).
1H NMR (CDCl3, 500 MHz): d=7.97 (d, J=7 Hz, 4H; Ph-H), 7.76 (s,
4H; Ph-H), 7.68 (br, 2H; triazole), 7.55 (s, 2H; Ph-H), 7.45 (d, J=7 Hz,
4H; Ph-H), 6.96 (s, 10H; Ph-H of C2), 6.93 (d, J=6 Hz, 4H; pyridinium),
6.70 (s, 10H; Ph-H of C2), 5.82 (d, J=6 Hz, 4H; pyridinium), 4.71 (m,
4H; methylene), 4.60 (m, 4H; methylene), 4.45 (m, 4H; methylene),
3.60–4.10 (m, 60H; methylene bridge and methylene of C2), 2.79 (br,
4H; methylene), 2.58 (br, 2H; methylene), 1.77 (br, 4H; methylene),
1.63 (m, 30H; methyl of C2), 1.40 (m, 66H; methyl of C2 and tert-butyl),
1.29 (m, 8H; methylene), 0.65–0.98 (m 12H; methylene), 0.073 (br, 4H;
methylene), À1.04 ppm (m, 4H; methylene). 13C NMR (CDCl3,
125 MHz, ppm): d=168.7, 160.3, 152.6, 151.8, 150.4, 149.4, 147.6, 144.2,
130.0, 129.2, 125.0, 124.7, 122.0, 117.1, 116.3, 115.1, 114.7, 112.2 (C of
phenyl, pyridinium and triazole), 69.7, 65.8 (C of methylene), 65.5, 64.1
(C of methylene of C2), 57.5, 46.9 (C of methylene), 35.1, 31.4 (C of tert-
butyl), 30.9 (C of methylene), 30.1, 29.9 (C of methylene) 29.2 (C of
methylene bridge of C2), 27.9, 26.6, 25.8 (C of methylene), 15.5, 15.4 (C
of methyl of C2), 14.1 ppm (C of methylene). HRMS (ESI): m/z calcd
À
for C189H250N12O24 [MÀ2PF6
]
2+: 3071.87108; found: 3071.87104.
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Chem. Eur. J. 2012, 00, 0 – 0
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www.chemeurj.org
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T. Ogoshi et al.
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[9] This compound was prepared by using the same conditions as those
for the preparation of [2]rotaxane 6 in the absence of C2.
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Received: January 12, 2012
Published online: && &&, 2012
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Planar Chiral Rotaxanes
FULL PAPER
Wheels in motion: Planar chiral [2]-
and [3]rotaxanes constructed from pil-
lar[5]arenes as wheels and pyridinium
derivatives as axles (see figure) were
obtained in high yield using click re-
Chiral Rotoxanes
T. Ogoshi,* D. Yamafuji, T. Aoki,
K. Kitajima, T.-a. Yamagishi,
Y. Hayashi, S. Kawauchi .... &&&& — &&&&
ACHTUNGTRENNUNGactions. The procedure developed in
High-Yield Diastereoselective
Synthesis of Planar Chiral [2]- and
[3]Rotaxanes Constructed from per-
Ethylated Pillar[5]arene and Pyridi-
nium Derivatives
this study is a starting point for the
creation of pillar[5]arene-based inter-
locked molecules.
Chem. Eur. J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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These are not the final page numbers!