Double-Stranded Helical Oligomers Covalently Bridged by Rotary Cyclic Boronate Esters

Article abstract of DOI:10.1002/asia.201700162

Novel double helices covalently bridged by cyclic boronate esters were synthesized from complementary dimers with an m-terphenyl backbone joined by a chiral or achiral phenylene linker bearing diethyl boronates and diols, respectively. The X-ray crystallographic analysis and variable-temperature NMR and circular dichroism measurements, along with theoretical calculations, revealed that the double helices function as a “molecular rotor” in which the cyclic boronate ester units rotate, yielding two stable rotamers at low temperatures. Moreover, our data indicates that the covalently bonded double helices can undergo a unique helix-inversion simultaneously with a rotational motion of the boronate esters.

Full text of DOI:10.1002/asia.201700162

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Double-Stranded Helical Oligomers Covalently-Bridged by Rotary
Cyclic Boronate Esters
Authors: Hiroki Iida, Kenji Ohmura, Ryuta Noda, Soichiro Iwahana,
Hiroshi Katagiri, Naoki Ousaka, Taku Hayashi, Yuh Hijikata,
Stephan Irle, and Eiji Yashima
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To be cited as: Chem. Asian J. 10.1002/asia.201700162
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Chemistry - An Asian Journal
10.1002/asia.201700162
FULL PAPER
Double-Stranded Helical Oligomers Covalently-Bridged by Rotary
Cyclic Boronate Esters
[
a,b]
[a]
[a]
[a]
[c]
[a]
Hiroki Iida,* Kenji Ohmura, Ryuta Noda, Soichiro Iwahana, Hiroshi Katagiri, Naoki Ousaka,
[
d]
[d]
[d]
[a]
Taku Hayashi, Yuh Hijikata, Stephan Irle,* and Eiji Yashima*
[
5]
Abstract: Novel double helices covalently-bridged by cyclic
boronate esters were synthesized from complementary dimers with
a m-terphenyl backbone joined by a chiral or achiral phenylene linker
bearing diethyl boronates and diols, respectively. The X-ray
crystallographic analysis and variable-temperature NMR and circular
dichroism measurements, along theoretical calculations, revealed
that the double helices function as a “molecular rotor” in which the
cyclic boronate ester units rotate, yielding two stable rotamers at low
temperatures. Moreover, our data indicates that the covalently-
handedness (Figure 1A).
Fully detailed studies of the
thermodynamic and kinetic stabilities of the complementary
double helices demonstrated that the chain exchange between
the strands and helix-inversion of the double helices take place
depending on the linker structures and the substituents on the
[
5g]
amidine residues.
A Non-covalently assembled double helices
salt bridge
bonded double helices can undergo
a unique helix-inversion
simultaneously with a rotational motion of the boronate esters.
R
R
O
O
N
H
N
H
R
R
X
X
R
R
H
N
H
N
O
O
R
R
Introduction
X : linker
B Covalently-bridged double helices
rotational
motion
The design and synthesis of oligomers and polymers that adopt
a specific conformation reminiscent of the DNA double-helix has
been challenging and is of intense current interest in the
supramolecular and polymer chemistry and chiral materials
B
R
R
X
X
O
O
R
R
[
1,2]
[2a]
O
O
science fields.
Metal-directed coordination,
hydrogen-
[2d,4]
B
[
2b,g,3]
bonding,
and/or aromatic-aromatic interactions
have
been mostly utilized to direct self-assembly of the strands to
construct homo-double helices. We previously developed a
modular strategy to construct a series of hetero-double helical
oligomers and polymers that consist of crescent-shaped m-
terphenyl backbones joined by various linkers bearing
complementary chiral amidine and achiral carboxyl groups,
respectively, in which the double-helix formations rely on the
non-covalent amidinium-carboxylate salt bridges, thus providing
the first artificial complementary double helices with a controlled
Left-handed
Helix-inversion
B
R
R
O
O
R
R
O
O
X
X
B
Right-handed
Figure 1. Structures of (A) non-covalently assembled complementary double-
helix stabilized by amidinium-carboxylate salt bridges and (B) covalently-
bridged complementary double-helix through cyclic boronate esters that
[
a]
b]
Prof. H. Iida, K. Ohmura, R. Noda, Dr. S. Iwahana, Prof. N. Ousaka,
Prof. E. Yashima
undergoes
a helix-inversion accompanied by a rotational motion of the
Department of Molecular Design and Engineering, Graduate School
of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603
boronate ester units.
(
Japan)
E-mail: yashima@apchem.nagoya-u.ac.jp
Prof. H. Iida
Department of Chemistry, Interdisciplinary Graduate School of
Science and Engineering, Shimane University, 1060 Nishikawatsu,
Matsue 690-8504 (Japan)
[
Boronic acids and their esters are known to readily react with
diols to form thermodynamically-stable cyclic boronate esters,
and the dynamic properties of the cyclic boronate esters has
been exploited to build diverse self-assembled supramolecular
structures, such as nanotubes, macrocycles, molecular capsules,
E-mail: iida@riko.shimane-u.ac.jp
Prof. H. Katagiri
[
c]
d]
Graduate School of Science and Engineering, Yamagata University,
[6]
and organic frameworks. We anticipated that the dynamic
4-3-16 Jonan, Yonezawa, Yamagata 992-8510 (Japan)
boronate ester structure would provide a novel covalently-
[
T. Hayashi, Dr. Y. Hijikata, Prof. S. Irle
Institute of Transformative Bio-Molecules (WPI-ITbM) and
Department of Chemistry, Graduate School of Science, Nagoya
University, Nagoya 464-8602 (Japan)
bridged,
complementary
pair
in
addition
to
the
amidine/carboxylic acid pair, resulting in a hetero-double helix
with higher thermodynamic and kinetic stabilities than the
previously reported, non-covalently assembled double helices
(Figure 1B). Covalently-linked homo-double helical molecules
E-mail: sirle@chem.nagoya-u.ac.jp
Supporting information for this article is given via a link at the end of
the document.
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A
B
and macrocycles have attracted much attention because of their
unique structures coupled with their specific properties and
X
B
OEt
EtO
B
B
[
7]
EtO
OEt
TMS
R
O
O
TMS
R
functions. We considered that the bridged cyclic boronate ester
units located within the helical cavity of the obtained hetero-
BB, (R)-BB*, or (S)-BB*
R1
R1
+
[
8,9]
double helices likely achieve a rotational motion.
Single and
R = TMS B-D
or
X
R = H BH-D
[
2f]
double helices often undergo an inversion of their helicity, and
if this is the case, the double helices may function as a dynamic
molecular rotor composed of two bridged cyclic boronate esters
as a rotator encased in the dynamic double-stranded helical
framework as an interconvertible helical stator, which suggests
that the double helical molecules may simultaneously perform
dual motions (rotation and helical inversion) as illustrated in
Figure 1B. In this study, the dynamic molecular motions
occurring in the double helices were investigated using X-ray
crystallographic analysis and variable-temperature NMR and
chiroptical measurements along with theoretical calculations.
Because the molecular rotors as well as motors stand out
as essential components to operate complex machine-like
OH
HO
DD
OH
HO
=
R1
R1
toluene
90 °C
BB-DD
B
(CH2)9
O
R
R
X
O
O
R
R
O
O
B
O
(
R)-BB*-DD
(CH2)9
O
R = TMS BB-DD , (R)-BB*-DD, or (S)-BB*-DD
Bu4N+F–, THF
O
(S)-BB*-DD
R = H (R)-BBH*-DDH
Scheme 1. Synthesis and structures of (A) double helices BB-DD, (R)-BB*-
[
10]
functions as observed in biological systems,
construction of artificial molecular rotors that perform
sophisticated rotary motion have attracted considerable interest
the design and
DD, (S)-BB*-DD, and (R)-BB
-D.
H
*-DD
H
and (B) monomeric duplexes B-D and
B
H
a
[
9-11]
in the context of molecular machines.
However, most rotors
A Rotamer X (
φ = 197˚)
B Rotamer Y (φ = 17˚)
(c)
prepared to date consist of a central linear rotator linked to a
shielding stator, and artificial molecular rotors composed of
multi-rotators covalently linked to a double-helix as a helically
(
a)
b)
[
12]
twisted stator have thus far never been reported.
Hx
(
(d)
Hx
Results and Discussion
Racemic (BB-DD) and optically-active double-stranded helical
dimers ((R)- or (S)-BB*-DD) joined by p-phenylene and (R)- or
(
S)-dioxa[11]paracyclophane linkages bridged by two cyclic
dihedral angle
φ )
ROE cross-peaks
f
C
(
boronate esters, respectively, were prepared by
a
bH
transesterification reaction between the corresponding strands
H
f
bH
H
H
bearing the diethyl boronates (BB and (R)- or (S)-BB*) and diol
xH
Hx
Hz
OO
z
[
13]
H
TMS
H
TMS
TMS
groups (DD) in anhydrous toluene at 90 ˚C (Scheme 1). For
comparison, monomeric duplexes (B-D and B -D) were also
y
OO y
TMS
B
B
H
[
13,14]
synthesized in a similar way.
Rotamer X
Rotamer Y
φ = 17˚
An X-ray crystallographic analysis of BB-DD measured at
120 ˚C clearly revealed that BB-DD adopted a double-stranded
in crystal structure
Hx
φ = 197˚
–
φ2
helical structure in which the two m-terphenyl-based strands
were intertwined with one another covalently linked by the two
cyclic boronate esters (Figures 2 and S18). The crystal structure
around the cyclic boronate esters was disordered because of
two rotational conformers (rotamers X and Y, Figure 2C) that
exist at –120 ˚C in the crystals; rotamer X has the methine
protons (Hx) directed to the central phenylene linkers (dihedral
angle f = 197˚), while the Hx protons are directed to the opposite
terminal TMS groups in the rotamer Y (f = 17˚), and the two
rotamers differ by a 180˚ rotation. The crystal structure also
suggests that the double-helical BB-DD can be considered to be
a helically-twisted macrocage with two rotors bridged to the
double-stranded helical framework as a stator.
D
φ1
Conformer XX (φ = 175˚, φ = 175˚)
1
2
Figure 2. (A, B) X-ray structures of a left-handed helical BB-DD: (a,c) top view
and (b,d) side view. Carbon, black or pale blue; oxygen, red; boron, pink;
silicon, yellow; hydrogen, white. The disordered structures were observed
around the cyclic boronate esters, giving two rotamers
X and Y. (C)
Conformational change through rotation of the bridged cyclic boronate ester
unit. (D) DFT optimized most stable structure of conformer XX (see Figure
S17).
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1
The H NMR spectrum of BB-DD in CDCl
3
at 25 ˚C was
k
B
rather broad and complicated when compared to those of BB
and DD (Figures 3Ab and S8) due to the presence of
conformers mainly derived from the restricted rotational motion
of the bridged-boronate esters, which, however, became sharper
j
l
i
m
B
h
n
A
q
r
p
z
O
O
z
H
TMS
TMS
o
H
H
y
H y
Hx
in [D
8
]THF at high temperatures (Figures 3Aa, S14, and S15A),
D
a C
g
b
f
showing a set of well-resolved signals at 50 ˚C. The 2D ROESY
spectrum of BB-DD displayed clear ROE cross-peaks between
the interstrand aromatic protons of the m-terphenyl residues,
and the aliphatic protons (x, y, and z) of the cyclic boronate
esters and the aromatic protons of the m-terphenyl residues of
the DD strand, indicating the intertwined double-stranded helical
structure that remains in solution and the cyclic boronate esters
rotate too fast to distinguish the diastereotopic pair of protons (z
and y) on the NMR time scale at 50 ˚C (Figures 2B, 2C, 3B, and
S9-S12).
c
e
d
A
#
z
y
(
a) THF-d8 a,g
m
h
c
x
(b) CDCl3
(c) CD2Cl2
7
.8
7.4
7
3.8
3.4
δ / ppm
δ / ppm
q, r
b
Upon cooling to a low temperature in [D
8
]THF and CD
NMR signals of BB-DD gradually broadened,
accompanied by splitting into number of signals, thus
producing complicated spectra with overlapped broad signals
Figures S14 and S16, respectively and see the Supporting
2 2
Cl ,
B
d
1
a, g
f
j
the
H
m
h
k
l
n
i
e
c
a
7.7
7.6
7.5
7.4
7.3
7.2
7.1
(
c
m
Information). Interestingly, the singlet signal of the terminal TMS
groups (o) of the DD strand of the duplex gradually broadened
as the temperature decreased and coalesced at ca. –36 ˚C in
e
n
m-n
l
l-m
c-d
i
j
d
d-e
e-f
f
[
D
8
]THF, which finally appeared as two sets of nonequivalent
q, r
b
j-k
δ
k
signals below −40 °C (0.263 and 0.315 ppm), thus showing a
relative intensity ratio of 7:3 at –60 ˚C (Figures 3Da, S14, and
S15A). Since BB-DD is racemic, existing in a 1:1 mixture of
right- and left-handed helices, the observed uneven splitting of
the TMS protons (7:3) is not due to the interconvertible helices
b-c
/ ppm
k-l
h
h-i
a-i
(
helix-inversion), but can be reasonably assigned to two
a-h a-b
g-m
diastereomeric conformers, such as rotamers X and Y (Figure 2).
Probably, the pair of rotamers (X or Y) formed in the single BB-
DD helix may not have direct communication with each other,
thereby showing no signals corresponding to three conformers
a, g
g-f
g-n
7.7
7.6
7.5
7.4
δ / ppm
7.3
7.2
7.1
(
XX, XY, or YY) in its NMR spectrum even at low temperatures.
The fact that the optically-active BB*-DD also showed a similar
Tc (–35 ± 2 ˚C in [D ]THF) supports this conclusion (Figures S29
and S30A). The Tc of BB-DD was also estimated in CD Cl (Tc
]THF (Tc = –36 ±
˚C), indicating a noticeable solvent effect on the rotary motion
C
y z #
D (a)
(b)
k (s-1
)
x
o
*
*
–20 °C
8
3
.0 x 102
y-f z-f
x-f
2
2
7.25
–
–
–
30 °C
40 °C
50 °C
δ
80
f
=
2
–18 ± 2 ˚C), which was higher than that in [D
8
/ ppm
7
7
.3
b
y-b z-b
x-b
27
12
.35
of the cyclic boronate esters (Figures S15B and S16). The
3.7 3.6 3.5 3.4 3.3
δ / ppm
–60 °C
area ratio
optically-active BB*-DD linked by a relatively bulky cyclophane
:
= 3 : 7
2.0
linker showed similar Tc values (–35 ± 2 ˚C in [D
2 ˚C in CD Cl , Figures S29–S31).
The rate constants (k) for the dynamic process between
8
]THF and –17
0
.35
0.2
0.35
0.2
δ / ppm
±
2
2
δ / ppm
1
Figure 3. (A) Partial H NMR spectra of BB-DD in (a) [D
8
]THF, (b) CDCl
3
, and
the two diastereomeric conformers of BB-DD were calculated
1
2 2
(c) CD Cl at 25 °C. # denotes the protons from the solvent. The peak
based on the dynamic H NMR spectral changes using line-
assignments were performed on the basis of 2D COSY and ROESY spectra of
BB-DD (see Figures S9–S12). (B,C) Partial ROESY spectrum of BB-DD in
[
15]
shape simulations (Figures 3Db).
The free energies of
‡
1
activation (ΔG ) for the rotation of the cyclic boronate ester units
[D
8
]THF at 50 °C; mixing time = 200 ms. (D) Variable-temperature H NMR
spectra of the TMS signal (o) of BB-DD. Experimental spectra measured in
were calculated based on the Eyring equation and were 50 ± 8
–
1
–1
[D
8
]THF (a) and line-shape simulation obtained with the rate constants (b).
kJ mol in [D
8
]THF and 55 ± 4 kJ mol in CD
2
Cl
2
at 25 ˚C
‡
–1
(
Figure S32). In addition, similar ΔG values (51 ± 5 kJ mol in
–
1
8 2 2
[D ]THF and 56 ± 6 kJ mol in CD Cl ) were also obtained for
Based on the crystal structure of BB-DD and its dynamic
the optically-active BB*-DD. As a result, the rotational motion of
the cyclic boronate ester units was almost independent of the
linker structures and excess single-handedness.
1
H NMR spectral changes, the cyclic boronate ester units of BB-
DD possess either the rotamer X or Y, giving three possible
conformers (XX, XY, or YY, Figure S17) with respect to the
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rotation of the bridged-boronate esters. The density functional
theory (DFT) calculations revealed that the conformer XX
catalyzed the cyclic ether bond cleavage (ring-opening)
[
19]
reaction
of the optically-active cyclophane linkage of the
-
1
(
dihedral angles, f
1
and f
2
= 175˚) is 4.85 and 6.04 kJ mol more
double-helix, resulting in racemization via helix-inversion, and
the reaction was monitored by CD spectroscopy (Scheme 2 and
Figure S34). The reaction slowly proceeded at –10 ˚C and
stable than the other conformers XY and YY (See the
Supporting Information for details of the DFT calculations).
Therefore, the two major and minor signals that appeared at
approximately 30% of (R)-BB
H
*-DD
H
was converted to yield the
-2 and BB -DD -3) after 1
0
.263 and 0.315 ppm (Figure 3D) upon cooling can be assigned
ring-opened double helices (BB
H
-DD
H
H
H
to rotamers X and Y, respectively.
h. During the reaction at –10 ˚C, the CD intensities of the
reaction mixture gradually decreased to 72% (Figure S34),
which is almost proportional to the conversion of the (R)-BB*-DD,
indicating that (R)-BB*-DD rapidly racemized at –10 ˚C once the
chiral linker unit was converted to the achiral one. These
findings clearly provide convincing evidence that the double
helices of BB-DD and BB*-DD adopt a dynamic double-helical
structure and the helix-inversion readily took place under the
experimental conditions noted above.
We first expected that the helical conformation of the BB-
DD duplex was stable in solution because each strand was
covalently bridged, and could be separated into enantiomers by
[
16]
chiral HPLC as well as by enantioselective adsorption, but all
attempts of separation were unsuccessful. We also attempted to
discriminate the enantiomeric right- and left-handed BB-DD
double helices by NMR using a series of chiral shift reagents,
such
as
tris(heptafluoropropylhydroxymethylene-(+)-
camphorato)europium(III), β- or γ-cyclodextrins, and optically
active amines, but all these attempts failed. The circular
dichroism (CD) spectra of the optically-active (R)- and (S)-BB*-
We previously demonstrated that a helix-inversion of
analogous complementary double helices stabilized by non-
covalent amidinium-carboxylate salt bridges (R = isopropyl,
Figure 1A) took place coupled with a rotation along the C–C
bond between the amidine and m-terphenyl groups based on the
2 2
DD were then measured in CH Cl to evaluate their chiroptical
and dynamic properties in solution (Figure 4). Both enantiomers
of BB*-DD showed perfectly mirror-imaged CD spectra in the
range of 240-400 nm, whose CD spectral patterns differed from
those of the (R)- and (S)-BB* strands, suggesting that the BB*-
DD adopts a preferred-handed double-stranded helical structure
biased by the planar chiral paracyclophane linkage (Figure 4A),
which was also supported by 2D NMR studies (Figures S20-
S27). However, the CD intensity of (S)-BB*-DD gradually
increased with the decreasing temperature from 25 to -90 °C
accompanied by changes in its absorption and CD spectral
patterns (Figure 4B), while the corresponding single strand (S)-
BB* did not show such significant temperature-dependent CD
changes under the same conditions (Figure S33). These results
suggested that the optically-active BB*-DD double-helix is
dynamic and an equilibrium exists between the diastereomeric
right- and left-handed double helices through a helix-inversion,
which shifts to an excess of one helical sense at low
1
temperature-dependent H NMR measurements of the racemic
[
5g]
dimer duplex carrying achiral amidine residues. These results
imply that the present covalently bound, helically-twisted
macrocage BB-DD can also undergo a similar helix-inversion
coupled with rotational motions of the bridged-boronate ester
units, thus providing a unique chiral molecular rotor, in which
dual rotary and inverting (twisting) motions can occur. In
particular, when the optically active BB*-DD double helix was
used, a quite intriguing unidirectional rotational motion of the
bridged-boronate ester units regulated by
a unidirectional
twisting motion of the double helix (helix-inversion) was
anticipated. However, it remains difficult to demonstrate such
correlation between the three conformational changes, namely,
the helical inversion motion of the stator and each rotational
[
20]
motion of the two rotamers, based on the present results.
[
17,18]
temperature.
(CH2)9
HO
HO
O
Me3SiI
+
CDCl3
OH
2
5 °C
O
2 9
O–(CH ) –I
A
B
0 °C
–10 ˚C, 1 h
(
R)-BB*-DD
R)-BB*
–20 °C
–40 °C
–
–
–
(
R)-BB *-DD
BB -DD -2
BB -DD -3
H H
4
0
H
H
H
H
2
0
0
60 °C
80 °C
90 °C
conversion: 30%
(
2
0
25 °C after –90 °C
0
Scheme 2. Ring-opening reaction of the cyclophane units of (R)-BB*
with Me SiI.
H H
-DD
(
S)-BB*
ε
ε
–20
3
–
20
(
S)-BB*-DD
1
0
0
1
0
0
Conclusions
3
00
400
300
Wavelength / nm
400
ε
ε
Wavelength / nm
In summary, we have successfully synthesized covalently-
bridged novel hetero-double helices composed of
Figure 4. (A) CD and absorption spectra of (R)- and (S)-BB*, and (R)- and
S)-BB*-DD in CH Cl (0.02 mM) at ca. 25 °C. (B) CD and absorption spectral
changes of (S)-BB*-DD in CH Cl (0.02 mM) at various temperatures.
(
2
2
complementary m-terphenyl dimer strands (racemic BB-DD and
optically active BB*-DD) via the cyclic boronate ester formation
between the corresponding strands bearing the alkyl boronates
and diol groups. We found that; (1) the two cyclic boronate ester
units of BB-DD and BB*-DD encased in the double-stranded
helical framework dynamically rotate, thus the double helices
could function as unprecedented artificial molecular rotors
2
2
In order to obtain direct evidence for the helix inversion of
BB*-DD and its barrier, (R)-BB *-DD derived from (R)-BB*-DD
Scheme 1A) was treated with Me SiI in CDCl at –10 ˚C, which
H
H
(
3
3
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composed of multi-rotators covalently linked to a double helical
stator; (2) the helically twisted stator are also able to perform an
interconvertible helical inversion motion concurrently with the
rotation of the cyclic boronate ester units. We believe that the
bound carbon was not detected due to quadrupolar relaxation. HRMS
+
(
ESI+): m/z calcd for C32
H
39BO
2
Si
2
(M+Na ), 545.2486; found, 545.2506.
Synthesis of Diethyl Boronates (2 and B
H
). A solution of TBAF in THF
(
25 mM, 2.00 mL, 0.500 µmol) was added portionwise (500 µL at a time)
present helically-twisted macrocages composed of
a
to a solution of B (268 mg, 0.512 µmol) in anhydrous THF (5.7 mL) at
room temperature, and the mixture was stirred for 30 min. To this were
added aqueous HCl (1.0 M, 40 µL) and EtOH (2 mL), and the mixture
complementary double-helical framework bridged by two rotary
cyclic boronate esters could be further applied to constructing a
novel optically-active molecular rotor by introducing chiral
substituents at the boronate ester units; the two boronate esters
could rotate in the same direction controlled by the helical sense
of the double-helical framework and the direction of the
correlated rotational motion would be switched by the helical
was then extracted with CH
washed with a mixture of water and EtOH (25:1 (v/v), 50 mL x 2), dried
over anhydrous MgSO , and filtered. After the solvent was removed by
evaporation, the residue was subjected to SEC fractionation to obtain 2
76.2 mg, 33% yield) and B (53.9 mg, 28% yield) as white solids.
2 2
Cl (50 mL x 2). The organic extracts were
4
(
H
[
11a,c,d,21]
inversion triggered by external stimuli.
Further studies
–
1
Spectroscopic Data of 2. Mp: 146.2–149.2 °C. IR (KBr, cm ): 3282 (νC≡C-
along this line, together with deeper investigations of the
molecular motions in the solid state, are now in progress.
1
H
3
), 2154 (νC≡C), 1329 (νB-O). H NMR (500 MHz, 25 °C, CDCl ): δ 7.53 (d,
J = 8.5 Hz, 2H, ArH), 7.51 (d, J = 8.5 Hz, 2H, ArH), 7.46 (t, J = 7.8 Hz, 1H,
ArH), 7.41 (d, J = 5.9 Hz, 2H, ArH), 7.39 (d, J = 5.9 Hz, 2H, ArH), 7.37 (d,
J = 2.6 Hz, 1H, ArH), 7.36 (dd, J = 3.3, 1.1 Hz, 1H, ArH), 3.51 (q, J = 7.0
Experimental Section
Hz, 4H, CH
2
), 3.12 (s, 1H, C≡CH), 0.86 (t, J = 7.0 Hz, 6H, CH
3
), 0.27 (s,
1
3
9
1
1
H, TMS). C NMR (125 MHz, 25 °C, CDCl ): δ 145.12, 145.02, 143.87,
3
43.45, 132.32, 132.20, 129.08, 128.60, 128.49, 128.06, 128.00, 122.22,
Synthesis of Boronate Esters B, B
H
, BB, and BB*. Boronate esters B,
21.15, 105.02, 95.00, 83.62, 77.88, 59.73, 16.54, 0.12. HRMS (ESI+):
B
H
, BB, and (R)- and (S)-BB* were prepared according to Scheme 3.
+
m/z calcd for C64
H
64
B
2
O
4
Si
2
(M+Na ), 473.2090; found, 473.2086.
R1
R1
R1
R1
EtO
OEt
I
B
-
1
1
. n-BuLi, THF
Spectroscopic Data of B
H
. Mp: 111.4–113.7 °C. IR (KBr, cm ): 3254
C≡C-H), 1315 (νB-O). H NMR (500 MHz, 25 °C, CDCl ): δ 7.54 (d, J = 8.5
Hz, 4H, ArH), 7.48-7.45 (m, 1H, ArH), 7.41 (d, J = 8.5 Hz, 4H, ArH), 7.37
1
(
ν
3
2
3
. B(OEt)3
. HCl
R1
TMS
H
=
1
B
R2 =
(
d, J = 7.5 Hz, 2H, ArH), 3.51 (q, J = 7.0 Hz, 4H, CH
2
), 3.12 (s, 2H,
1
3
C≡CH), 0.82 (t, J = 7.0 Hz, 6H, CH
3
). C NMR (125 MHz, 25 °C, CDCl ):
3
R1
EtO
R2
R2
EtO
OEt
R2
OEt
B
B
δ 144.97, 144.12, 132.30, 128.90, 128.56, 127.88, 121.03, 83.70, 77.77,
TBAF
THF
59.91, 16.61. The boron-bound carbon was not detected due to
+
quadrupolar relaxation. Anal. Calcd for C26
Found: C, 82.35; H, 6.16.
2
H23BO : C, 82.55; H, 6.13.
2
BH
I
I
Synthesis of Boronate Ester Dimer (BB). A mixture of 2 (76.2 mg,
0.167 mmol), 3a (24.9 mg, 0.075 mmol), Pd(PPh (9.64 mg, 8.34 µmol),
3
a
3
a, (R)-3b, or (R)-3b
3 4
)
BB, (R)-BB*, or (S)-BB*
(
CH2)9
(CH2)9
CuI (1.53 mg, 8.03 µmol), and diisopropylamine (600 µL) in anhydrous
toluene (2.3 mL) was stirred at 60 °C for 45 h. After evaporation to
Pd(PPh3)4, CuI
iPr2NH, toluene
O
O
I
I
,
I
I
O
dryness, the residue was purified by column chromatography (SiO
CHCl ) and was then subjected to SEC fractionation to obtain BB (52.2
mg, 71% yield) as a white solid. Mp: 216.1–217.3 °C. IR (KBr, cm ):
2
,
O
(
R)-3b
(S)-3b
3
–
1
1
Scheme 3. Synthesis of boronate esters B, B
H
, BB, and (R)- and (S)-BB*.
2157 (νC≡C), 1322 (νB-O). H NMR (500 MHz, 25 °C, CDCl
3
): δ 7.58 (d, J =
.5 Hz, 4H, ArH), 7.53 (s, 4H, ArH), 7.52 (d, J = 8.5 Hz, 4H, ArH), 7.49-
.44 (m, 6H, ArH), 7.42-7.36 (m, 8H, ArH), 3.53 (q, J = 7.1 Hz, 8H, CH ),
), 0.27 (s, 18H, TMS). C NMR (125 MHz,
): δ 145.06, 145.04, 143.81, 143.77, 132.16, 131.79, 131.71,
8
7
0
2
1
9
2
1
3
.85 (t, J = 7.1 Hz, 12H, CH
5 °C, CDCl
3
Synthesis of Diethyl Boronate (B). n-BuLi (1.6 M in n-hexane, 5.50 mL,
.79 mmol) was added dropwise to a solution of iodide 1 (3.98 g, 7.25
mmol) in anhydrous THF (150 mL) at –78 ˚C, and the mixture was stirred
at –78 °C for 1 h. To this was added B(OEt) (5.30 mL, 37.4 mmol) at –
8 °C, and the mixture was further stirred at –78 °C for 3 h then at room
3
8
28.87, 128.66, 128.46, 127.88, 127.84, 123.28, 122.06, 121.94, 105.15,
4.85, 91.42, 89.83, 59.92, 16.69, 0.14. The boron-bound carbon was
3
not detected due to quadrupolar relaxation. HRMS (MALDI+): m/z calcd
7
+
•
64 2 4 2
for C64H B O Si (M ), 974.4529; found, 974.4565.
2
temperature for 6.5 h. HCl in Et O (1.0 M, 9.60 mL, 9.60 mmol) and dry
EtOH (20 mL) was then added to the mixture. After stirring at room
temperature for 5 min, the mixture was extracted with CH Cl (100 mL x
), and the organic extracts were washed with a mixture of water and
EtOH (25:1 (v/v), 100 mL x 2), dried over anhydrous MgSO , and filtered.
Synthesis of Optically Active Cyclophanes ((R)- and (S)-3b). A
mixture of 2,5-diiodo-1,4-hydroquinone (398 mg, 1.10 mmol) and 1,9-
dibromononane (223 mL, 1.10 mmol) in anhydrous DMF (34 mL) was
2
2
2
4
2 3
added dropwise to a suspension of K CO (382 mg, 2.76 mmol) in
After the solvent was removed by evaporation, the residue was subjected
anhydrous DMF (56 mL) at 120 °C within 6 h, and the mixture was stirred
at 120 °C for 3 h. After filtration, the solvent was removed by evaporation.
The residue was dissolved in EtOAc (60 mL), and the solution was
to SEC fractionation to obtain B (2.47 g, 65% yield) as a white solid. Mp:
–
1
1
5
2
9.0–65.3 °C. IR (KBr, cm ): 2158 (νC≡C), 1324 (νB-O). H NMR (500 MHz,
5 °C, CDCl ): δ 7.51 (d, J = 8.5 Hz, 2H, ArH), 7.45 (t, J = 7.5 Hz, 1H,
3
washed with aqueous HCl (1 M, 60 mL), saturated aqueous NaHCO
mL), and water (70 mL x 2), dried over anhydrous Na SO , and filtered.
After the solvent was removed under reduced pressure, the residue was
purified by column chromatography (SiO , EtOAc/n-hexane = 0/1 to 5/95
v/v)) to afford rac-3b (304 mg, 57 %) as a white solid. IR (KBr, cm ):
3
(60
ArH), 7.39 (d, J = 8.5 Hz, 2H, ArH), 7.36 (d, J = 7.5 Hz, 2H, ArH), 3.50 (q,
J = 7.1 Hz, 4H, CH ), 0.84 (t, J = 7.1 Hz, 6H, CH ), 0.27 (s, 18H, TMS).
C NMR (125 MHz, 25 °C, CDCl ): δ 145.00, 143.75, 132.12, 128.83,
28.42, 127.83, 121.97, 105.12, 94.80, 59.88, 16.69, 0.14. The boron-
2
4
2
3
1
3
3
1
2
-
1
(
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1
O
O
1
190 (νC-O). H NMR (500 MHz, CDCl
3
): δ 7.37 (s, 2H, ArH), 4.39-4.32 (m,
), 1.88-1.79 (m, 2H, OCH CH ), 1.62-
), 1.06-0.86 (m, 8H, CH ), 0.83-0.72 (m, 2H,
). The rac-3b was separated into the enantiomers ((R)-3b and (S)-
O
O
OH OH
I
EtO
OEt
2
H, OCH
2
), 4.23-4.17 (m, 2H, OCH
CH
2
2
2
Cl
Cl
CuI, Cs2CO3
EtO
Cl
OEt
Cl
1. DIBAL-H, Et O
2
1
.47 (m, 2H, OCH
2
2
2
[
22]
2. H O+
3
Cl
Cl
picolinic acid
dioxane
CH
2
3
b) using a chiral HPLC column (Chiralpak IA, 2 (i.d.) x 25 cm, n-
4
-
1
5
6
2 2
hexane/CH Cl = 9/1 (v/v), 5.9 mL min ), and the enantiomeric excess
R1
(
ee) values of (R)-3b and (S)-3b were estimated to be >99% using a
chiral HPLC column (Chiralpak IA, 0.46 (i.d.) x 25 cm, n-hexane/CH Cl
2
2
=
HO
OH OH
OH OH
B
-
1
[20]
R1
R1
R1
R2
8
/2 (v/v), 1 mL min ).
OH
TBAF
THF
Pd(OAc)2
Synthesis of Chiral Boronate Ester Dimers ((R)-BB* and (S)-BB*). A
typical procedure for the synthesis of (S)-BB* is described below. A
mixture of 2 (49.3 mg, 0.109 mmol), (S)-3b (24.3 mg, 0.0500 mmol),
S-Phos, K3PO4
toluene
D
7
Pd(PPh
diisopropylamine (440 µL) in anhydrous toluene (1.6 mL) was stirred at
0 °C for 22 h. After evaporation to dryness, the residue was purified by
column chromatography (SiO , CHCl /EtOH = 4/1 (v/v)) and was then
subjected to SEC fractionation to obtain (S)-BB* (40.5 mg, 72% yield) as
3
)
4
(6.4 mg, 5.6 µmol), CuI (1.1 mg, 5.8 µmol), and
3a
R1
=
TMS
R2 =
H
DD
Pd(PPh3)4
6
i
CuI, Pr2NH
2
3
toluene
–
1
a white solid. Mp: 147.0–147.7 °C. IR (KBr, cm ): 2157 (νC≡C), 1323 (νB-
Scheme 4. Synthesis of diols D and DD.
1
O
), 1251 (νC-O). H NMR (500 MHz, 25 °C, CDCl
H, ArH), 7.51 (d, J = 8.5 Hz, 4H, ArH), 7.49-7.44 (m, 6H, ArH), 7.43-
.36 (m, 8H, ArH), 7.23 (s, 2H, ArH), 4.56-4.49 (m, 2H, OCH CH ), 4.33-
.27 (m, 2H, OCH CH ) 3.52 (q, J = 7.1 Hz, 8H, OCH CH ), 1.93-1.83 (m,
H, OCH CH ), 1.70-1.60 (m, 2H, OCH CH ), 1.17-0.89 (m, 10H, CH ),
.86 (t, J = 7.1 Hz, 12H, CH ), 0.27 (s, 18H, TMS). C NMR (125 MHz,
5 °C, CDCl ): δ 155.70, 145.07, 145.06, 143.81, 143.77, 132.16, 131.81,
3
): δ 7.60 (d, J = 8.5 Hz,
4
7
4
2
0
2
1
1
1
2
2
Synthesis of Diethyl (2,6-Dichlorophenyl)malonate (5).
malonate (61.0 mL, 404 mmol) was added to a mixture of 4 (10.9 g, 40.0
mmol), 2-picolinic acid (2.96 g, 24.1 mmol), Cs CO (39.2 g, 120 mmol),
Diethyl
2
2
2
3
2
2
2
2
2
1
3
2
3
3
and CuI (2.30 g, 12.1 mmol) in anhydrous 1,4-dioxane (80 mL), and the
mixture was stirred at 70 ˚C for 40 h. After cooling to room temperature,
3
28.87, 128.62, 128.46, 127.86, 127.86, 125.44, 122.17, 122.06, 118.18,
05.15, 95.51, 94.84, 86.38, 72.36, 59.92, 30.57, 28.20, 26.20, 25.68,
6.71, 0.14. The boron-bound carbon was not detected due to
saturated aqueous NH
and the mixture was then extracted with EtOAc (400 mL x 3). The
organic extracts were washed with saturated aqueous NH Cl (400 mL x
), dried over anhydrous MgSO , and filtered. After the solvent was
removed by evaporation, the residue was purified by column
chromatography (SiO , n-hexane/EtOAc = 10/0 to 85/15 (v/v)) to afford 5
4
Cl (400 mL) was added to the reaction mixture,
4
81 2 6 2
quadrupolar relaxation. HRMS (APCI+): m/z calcd for C73H B O Si
2
4
+
(
M+H ), 1131.5752 ; found. 1131.5752.
2
–
1
-
1
Spectroscopic Data of (R)-BB*. Mp: 147.2–148.5 °C. IR (KBr, cm ):
(
4.33 g, 36% yield) as a white solid. Mp: 59.2–59.4 °C. IR (KBr, cm ):
1
2
157 (νC≡C), 1323 (νB-O), 1250 (νC-O). H NMR (500 MHz, 25 °C, CDCl
δ 7.60 (d, J = 8.5 Hz, 4H, ArH), 7.51 (d, J = 8.5 Hz, 4H, ArH), 7.49-7.44
m, 6H, ArH), 7.45-7.36 (m, 8H, ArH), 7.23 (s, 2H, ArH), 4.56-4.50 (m, 2H,
3
):
1
1
3
748 (νC=O), 1285, 1039 (νC-O). H NMR (500 MHz, 25 °C, CDCl ): δ 7.35
(
d, J = 8.0 Hz, 2H, ArH), 7.21 (dd, J = 8.9, 7.4 Hz, 1H, ArH), 5.45 (s, 1H,
1
3
(
CH), 4.26 (q, J = 7.2 Hz, 4H, CH
2
), 1.28 (t, J = 7.2 Hz, 6H, CH
): δ 166.52, 136.51, 131.03, 129.74,
28.83, 62.22, 54.07, 14.14. Anal. Calcd for C13 : C, 51.17; H,
.62. Found: C, 51.25; H, 4.55.
3
).
C
OCH
2
CH
2
), 4.34-4.27 (m, 2H, OCH
), 1.93-1.83 (m, 2H, OCH CH
), 0.86 (t, J = 7.1 Hz, 12H, CH
TMS). C NMR (125 MHz, 25 °C, CDCl ): δ 155.69, 145.07, 145.05,
43.81, 143.77, 132.15, 131.81, 128.87, 128.62, 128.46, 127.88, 127.85,
2
CH
), 1.70-1.60 (m, 2H, OCH
), 0.27 (s, 18H,
2
) 3.53 (q, J = 7.1 Hz, 8H,
NMR (125 MHz, 25 °C, CDCl
3
OCH
2
CH
3
2
2
2
CH ),
2
1
4
2 4
H14Cl O
1
.18-0.89 (m, 10H, CH
2
3
1
3
3
1
1
5
Synthesis of 2-(2’,6’-Dichlorophenyl)propane-1,3-Diol (6). A solution
of DIBAL-H in n-hexane (1.0 M, 117 mL, 117 mmol) was added dropwise
25.44, 122.16, 122.06, 118.17, 105.14, 95.51, 94.84, 86.38, 72.36,
9.92, 30.56, 28.19, 26.20, 25.68, 16.70, 0.14. The boron-bound carbon
to a solution of 5 (3.59 g, 11.8 mmol) in anhydrous Et
2
O (74 mL) at –
was not detected due to quadrupolar relaxation. HRMS (APCI+): m/z
7
8 °C, and the mixture was stirred at –78 °C for 2 h and then at room
+
81 2 6 2
calcd for C73H B O Si (M+H ), 1131.5752 ; found. 1131.5752.
temperature for 36 h. The mixture was cooled to 0 °C and carefully
quenched with methanol (60 mL) followed by aqueous HCl (2 M, 60 mL).
Synthesis of Diols D and DD. Diols D and DD were prepared according
The solution was extracted with Et
was then made alkaline (pH 9-10) with saturated aqueous K
extracted with Et O (500 mL). The combined organic extracts were
washed with saturated aqueous K CO (500 mL), dried over MgSO , and
filtered. After the solvent was removed by evaporation, the residue was
purified by column chromatography (SiO , CHCl /MeOH = 10/0 to 24/1
v/v)) and then recrystallization to give 6 (2.22 g, 85% yield) as a white
2
O (500 mL x 2). The aqueous layer
to Scheme 4.
2
CO and
3
2
2
3
4
2
3
(
-
1
1
solid. Mp: 72.8–74.8 °C. IR (KBr, cm ): 3336 (νO-H). H NMR (500 MHz,
2
4
2
1
4
5 °C, CDCl
.43-4.35 (m, 2H, CH
.17 (t, J = 4.8 Hz, 2H, OH). C NMR (125 MHz, 25 °C, CDCl
3
): δ 7.40–7.20 (br, 2H, ArH), 7.09 (t, J = 8.0 Hz, 1H, ArH),
), 4.18-4.11 (m, 1H, CH), 4.06-3.98 (m, 2H, CH ),
): δ 135.16,
: C,
2
2
1
3
3
30.01, 128.86, 128.74, 63.72, 48.51. Anal. Calcd for C
8.89; H, 4.56. Found: C, 49.02; H, 4.50.
9 2 2
H10Cl O
Synthesis of Diol (D).
A
mixture of
trimethylsilylethynyl)phenylboronic acid (8.89 g, 40.8 mmol), Pd(OAc)
149 mg, 0.656 mmol), K PO (8.64 g, 40.7 mmol), and S-Phos (704 mg,
.72 mmol) in anhydrous toluene (27.1 mL) was stirred at 100 °C for 39 h.
6 (1.51 g, 6.81 mmol), 4-
(
2
(
3
4
1
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To this was added Et
through a short-pass column of SiO
dissolved in anhydrous THF (70 mL). To the solution were added
aqueous H (30%, 5.66 mL, 69.9 mmol), water (13.0 mL), and sodium
acetate (1.14 g, 13.9 mmol), and the mixture was stirred at room
temperature. After 12 h, aqueous Na SO (0.55 M, 20 mL, 11.1 mmol)
was added at 0 °C, and the mixture was stirred at room temperature for
0 h, then extracted with CHCl (50 mL x 2). The organic extracts were
washed with water (50 mL), dried over anhydrous MgSO , and filtered.
After the solvents were removed by evaporation, the residue was purified
by column chromatography (SiO , n-hexane/EtOAc = 10/0 to 4/1 (v/v)) to
afford D (1.49 g, 44% yield) as a white solid. Mp: 238.0–240.0 °C. IR
2
O (70 mL), and the mixture was then passed
2
. After evaporation, the residue was
B
B
TMS
R
O
O
TMS
R
O
O
or
BH
+
D
2
O
2
B
benzene
0 °C
5
2
3
B-D R = TMS
or
3
3
B -D R = H
8
H
4
H
Scheme 5. Synthesis of monomeric duplexes B-D and B -D.
2
-
1
1
(
KBr, cm ): 3367 (νO-H), 2159 (νC≡C). H NMR (500 MHz, 25 °C, CDCl
3
): δ
7
.51 (d, J = 8.5 Hz, 4H, ArH), 7.25 (m, 5H, ArH), 7.13 (d, J = 8.0 Hz, 2H,
Synthesis of Monomeric Duplex (B-D). A mixture of B (1.06 mg, 2.02
mmol) and D (1.01 mg, 2.03 mmol) in anhydrous benzene (0.8 mL) was
stirred at 50 °C for 7 d. After evaporation, the residue was subjected to
SEC fractionation to obtain B-D (1.78 mg, 95% yield) as a white solid.
ArH), 3.60-3.50 (m, 4H, CH
2
), 3.42-3.34 (m, 1H, CH), 0.27 (s, 18H, TMS).
): δ 143.09, 142.89, 134.46, 131.70,
30.67, 129.55, 126.01, 122.34, 104.79, 95.10, 66.94, 48.26, 0.10. Anal.
Calcd for C31 Si : C, 74.95; H, 7.30. Found: C, 74.71; H, 7.06.
1
3
C NMR (125 MHz, 25 °C, CDCl
3
1
–
1
1
H
36
O
2
2
Mp: 148.6–150.2 °C. IR (KBr, cm ): 2157 (νC≡C), 1290 (νB-O). H NMR
500 MHz, 25 °C, CDCl ): δ 7.63 (d, J = 8.5 Hz, 4H, ArH), 7.34 (dd, J =
.3, 7.5 Hz, 1H, ArH), 7.26 (d, J = 8.5 Hz, 4H, ArH), 7.23 (m, 3H, ArH),
.15 (d, J = 8.3 Hz, 4H, ArH), 7.10-7.06 (m, 6H, ArH), 3.46 (dd, J = 10.5,
.5 Hz, 2H, CH ), 3.37 (dd, J = 10.5, 10.5 Hz, 2H, CH ), 3.20 (tt, J = 10.5,
.5 Hz, 1H, CH), 0.35 (s, 18H, TMS), 0.27 (s, 18H, TMS). C NMR (125
): δ 145.59, 144.20, 143.38, 142.40, 134.40, 132.12,
31.90, 130.80, 129.35, 128.66, 128.14, 127.26, 126.31, 122.92, 121.52,
05.54, 104.64, 95.69, 94.43, 65.59, 41.83, 0.33, 0.16. The boron-bound
(
3
8
7
4
4
Synthesis of Diol (7). A solution of TBAF in anhydrous THF (15 mM,
14 µL, 9.21 µmol) was added portionwise (307 µL at a time) to a
6
2
2
solution of D (448 mg, 0.902 mmol) in anhydrous THF (10 mL), and the
1
3
mixture was stirred for 20 min. To this were added aqueous HCl (1 M,
MHz, 25 °C, CDCl
3
5
00 µL) and water (50 mL) sequentially. The mixture was then extracted
with CHCl (50 mL x 2), and the organic extracts were dried over
anhydrous MgSO and filtered. After the solvent was removed by
evaporation, the residue was subjected to SEC fractionation to obtain 7
1
1
3
4
carbon was not detected due to quadrupolar relaxation. HRMS (ESI+):
+
–
2 4
m/z calcd for C59H63BO Si (M+Na ), 949.3906; found, 949.3906.
(
162 mg, 42% yield) as a white solid. Mp: 221.5–222.0 °C. IR (KBr, cm
1
1
)
: 3298 (νO-H), 2158 (νC≡C). H NMR (500 MHz, 25 °C, CDCl
J = 8.5 Hz, 2H, ArH), 7.51 (d, J = 8.5 Hz, 2H, ArH), 7.30-7.23 (m, 5H,
ArH), 7.13 (d, J = 7.5 Hz, 2H, ArH), 3.61-3.50 (m, 4H, CH ), 3.44-3.36 (m,
H, CH), 3.12 (s, 1H, C≡CH), 1.70 (t, J = 5.2 Hz, 2H, OH), 0.27 (s, 9H,
3
): δ 7.54 (d,
H H
Synthesis of Monomeric Duplex (B -D). A mixture of B (14.9 mg,
0.0394 mmol) and D (19.6 mg, 0.0394 mmol) in anhydrous benzene (10
2
1
mL) was stirred at 50 °C for 7 d. After evaporation, the residue was
1
3
TMS). C NMR (125 MHz, 25 °C, CDCl
3
): δ 143.28, 143.14, 143.07,
42.91, 134.47, 131.91, 131.71, 130.76, 130.67, 129.68, 129.57, 126.05,
22.44, 121.41, 104.82, 95.14, 83.44, 77.91, 66.85, 48.34, 0.11. Anal.
Si: C, 79.20; H, 6.65. Found: C, 79.18; H, 6.68.
subjected to SEC fractionation to obtain B
H
-D (26.8 mg, 87% yield) as a
–
1
1
1
white solid. Mp: 219.7–220.4 °C. IR (KBr, cm ): 3294 (νC≡C-H), 2159
1
3
(νC≡C), 1290 (νB-O). H NMR (500 MHz, 25 °C, CDCl ): δ 7.63 (d, J = 8.3
Calcd for C28
H
28
O
2
Hz, 4H, ArH), 7.36 (dd, J = 7.6, 7.3 Hz, 1H, ArH), 7.28 (d, J = 8.3 Hz, 4H,
ArH), 7.25-7.20 (m, 3H, ArH), 7.15 (d, J = 8.3 Hz, 4H, ArH), 7.12 (d, J =
8
2
.3 Hz, 4H, ArH), 7.06 (d, J = 7.6 Hz, 2H, ArH), 3.50 (dd, J = 11, 4.8 Hz,
H, CH ), 3.45 (dd, J = 11, 11 Hz, 2H, CH2), 3.23 (tt, J = 11, 4.8 Hz, 1H,
Synthesis of Bisdiol (DD). A mixture of 7 (63.8 mg, 0.150 mmol), 3a
24.8 mg, 75.1 µmol), Pd(PPh (8.42 mg, 7.29 µmol), CuI (1.53 mg,
.03 µmol), and diisopropylamine (530 µL) in anhydrous toluene (2.0 mL)
was stirred at 60 °C for 24 h. After evaporation to dryness, the residue
was purified by column chromatography (SiO , CHCl /MeOH = 10/0 to
/1 (v/v)) to afford DD (63.6 mg, 92%) as a yellowish solid. Mp: 345 °C
2
(
3 4
)
1
3
CH), 3.20 (s, 2H, C≡CH), 0.28 (s, 18H, TMS). C NMR (125 MHz, 25 °C,
CDCl ): δ 145.44, 144.38, 143.47, 142.38, 132.16, 131.95, 131.77,
30.93, 129.37, 128.75, 128.16, 127.55, 126.33, 122.95, 120.62, 104.70,
5.82, 83.88, 77.84, 65.55, 41.88, 0.12. The boron-bound carbon was
8
3
1
9
2
3
4
–
1
1
not detected due to quadrupolar relaxation. Anal. Calcd for C53
C, 81.31; H, 6.05. Found: C, 81.16; H, 6.02.
2 2
H47BO Si :
(
dec). IR (KBr, cm ): 3436 (νO-H), 2157 (νC≡C). H NMR (500 MHz, 25 °C,
CDCl ): δ 7.59 (d, J = 8.0 Hz, 4H, ArH), 7.55 (s, 4H, ArH), 7.52 (d, J = 8.0
Hz, 4H, ArH), 7.32 (d, J = 8.0 Hz, 4H, ArH), 7.29-7.25 (m, 6H, ArH), 7.17
dd, J = 7.5, 1.4 Hz, 2H, ArH), 7.15 (dd, J = 7.5, 1.4 Hz, 2H, ArH), 3.65-
3
(
Synthesis of Model Compound (8). A mixture of phenylboronic acid
(183 mg, 1.50 mmol) and 2-phenyl-1,3-propanediol (228 mg, 1.50 mmol)
in anhydrous toluene (75 mL) was stirred under reflux for 6 h and the
water formed during the reaction was removed azeotropically using a
Dean-Stark apparatus. After the solvent was removed by evaporation,
3
0
1
1
.54 (m, 8H, CH
2
), 3.47-3.40 (m, 2H, CH), 1.68 (t, J = 5.1 Hz, 4H, OH),
1
3
.27 (s, 18H, TMS). C NMR (125 MHz, 25 °C, CDCl
3
): δ 143.18, 142.94,
34.54, 131.77, 131.73, 131.41, 130.75, 130.74, 129.78, 129.59, 126.07,
23.28, 122.45, 122.35, 104.83, 95.15, 91.09, 89.90, 66.92, 48.40, 0.12.
+
HRMS (MALDI+): m/z calcd for C62
45.3769.
H
58
O
4
Si
2
(M+Na ), 945.3771; found,
the residue was purified by column chromatography (SiO
2
, n-
9
hexane/EtOAc = 10/0 to 7/3 (v/v)) to afford 8 (316 mg, 88% yield) as a
–
1
1
white solid. Mp: 102.5-103.7 °C. IR (KBr, cm ): 1318 (νB-O). H NMR
500 MHz, 25 °C, CDCl ): δ 7.84-7.80 (m, 2H, ArH), 7.43 (tt, J = 7.4, 1.5
Hz, 1H, ArH), 7.39-7.33 (m, 4H, ArH), 7.29 (tt, J = 7.4, 1.4 Hz, 1H, ArH),
(
3
Synthesis of Monomeric Duplexes B-D and
duplexes B-D and B -D were prepared according to Scheme 5. The
model compound of B-D (8, Table S2) was also prepared.
H
B -D. Monomeric
H
7
.24-7.20 (m, 2H, ArH), 4.29 (dd, J = 11.0, 4.7 Hz, 2H, CH
11.0, 11.0 Hz, 2H, CH ), 3.31 (tt, 1H, J = 10.9, 4.7 Hz, CH). C NMR
): δ 137.57, 133.97, 130.89, 129.07, 127.95,
27.77, 127.76, 66.95, 43.43. The boron-bound carbon was not detected
due to quadrupolar relaxation. HRMS (EI+): m/z calcd for C15
2
), 4.20 (dd, J
1
3
=
2
(
125 MHz, 25 °C, CDCl
3
1
H
15BO
2
+
•
(
M ), 238.1165; found, 238.1169.
For internal use, please do not delete. Submitted_Manuscript
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Chemistry - An Asian Journal
10.1002/asia.201700162
FULL PAPER
Synthesis of Double Helices BB-DD, BB*-DD, and BB
H
*-DD
H
. Double-
were added aqueous HCl (1 M, 20 µL) and CHCl
and the organic layer was washed with water (30 mL x 2), dried over
anhydrous Na SO , and filtered. After the solvent was removed by
evaporation, the residue was subjected to SEC fractionation to obtain
R)-BB *-DD (2.2 mg, 50% yield) as a white solid. Mp: >300 °C. IR (KBr,
cm ): 3296(νC≡C-H), 1290 (νB-O), 1248 (νC-O). H NMR (500 MHz, 25 °C,
3
(30 mL) sequentially,
H H
stranded helical BB-DD, BB*-DD, and BB *-DD
were prepared
according to Scheme 1A.
2
4
(
H
H
Synthesis of Racemic Double Helix (BB-DD). A mixture of BB (5.83
mg, 5.98 µmol) and DD (5.52 mg, 5.98 µmol) in anhydrous toluene (120
mL) was stirred at 90 °C for 24 h. After evaporation, the residue was
subjected to SEC fractionation to obtain BB-DD (5.53 mg, 54% yield) as
–
1
1
-
1
ca. 0.1 mg mL , CDCl
ArH), 7.34-7.06 (m, 34H, ArH), 7.02 (s, 2 H, ArH), 4.54-4.47 (m, 2H,
OCH CH ), 4.28-4.20 (m, 2H, OCH CH ), 3.80-3.54 (m, 8H, OCH CH),
.48-3.34 (m, 2H, OCH CH), 3.24 (s, 2H, C≡CH), 3.22 (s, 2H, C≡CH),
.90-1.80 (m, 2H, OCH CH ), 1.70-1.58 (m, 2H, OCH CH ), 1.16-0.88 (m,
0H). Due to the low solubility of (R)-BB *-DD in organic solvents, it
3
): δ 7.80-7.66 (m, 8H, ArH), 7.46-7.35 (m, 6H,
–
1
a white solid. Mp: 350 °C (dec). IR (film, cm ): 2156 (νC≡C), 1290 (νB-O).
2
2
2
2
2
1
3
1
1
2
H NMR (500 MHz, 50 °C, THF-d
d, J = 8.2 Hz, 4H, ArH), 7.33 (t, J = 7.7 Hz, 2H, ArH), 7.32-7.24 (m, 26H,
ArH), 7.18-7.12 (m, 12 H, ArH), 7.10-7.07 (m, 8H, ArH), 3.67-3.64 (dd, J
8
): δ 7.72 (d, J = 8.0 Hz, 8H, ArH), 7.39
(
2
2
2
2
H
H
1
3
was difficult to obtain the C NMR spectrum. HRMS (APCI+): m/z calcd
=
11.3, 11.3 Hz, 4H, CH
2 2
), 3.64-3.58 (dd, J = 11.3, 4.5 Hz, 4H, CH ),
+
82 2 6
for C115H B O (M+H ), 1581.6370; found, 1581.6381.
3
.43-3.35 (tt, J = 11.3, 4.5 Hz, 2H, CH), 0.37 (s, 18H, TMS), 0.28 (s, 18H,
1
3
TMS). C NMR (125 MHz, 50 °C, 1,1,2,2-tetrachloroethane-d
2
): δ 145.45,
1
1
1
9
44.54, 143.64, 142.41, 142.07, 131.99, 131.56, 131.48, 131.43, 131.28,
H H 3
Ring-Opening Reaction of (R)-BB* -DD with Me SiI
31.24, 131.20, 130.61, 129.60, 128.99, 128.52, 128.04, 128.01, 127.69,
27.37, 126.24, 122.91, 122.69, 122.46, 121.39, 121.33, 105.23, 104.51,
5.58, 94.54, 90.84, 90.34, 90.09, 89.66, 65.28, 41.73, 0.16, 0. The
The cyclic ether bond cleavage (ring-opening) reaction of the optically
active cyclophane linkage of (R)-BB *-DD derived from (R)-BB*-DD
according to Scheme 2. (R)-BB *-DD
was used instead of (R)-BB*-DD because Me SiI also catalyzed the
deprotection of the terminal trimethylsilyl (TMS) groups of (R)-BB*-DD,
giving a series of TMS- deprotected products including (R)-BB *-DD . A
solution of Me SiI in distilled CDCl (11 mM, 5.3 µL, 0.059 µmol) was
added to a solution of (R)-BB* -DD in distilled CDCl (0.12 mM, 500 µL,
H
H
[
23]
boron-bound carbon was not detected due to quadrupolar relaxation.
was conducted using Me
3
SiI
H
H
+
•
HRMS (MALDI+): m/z calcd for C118
712.6844.
98 2 4 4
H B O Si (M ), 1712.6775; found,
3
1
H
H
Synthesis of Optically Active Double Helix Bearing a Cyclophane
Linker ((R)-BB*-DD and (S)-BB*-DD). A typical procedure for the
synthesis of (S)-BB*-DD is described below. A mixture of (S)-BB* (16.9
mg, 0.0150 mmol) and DD (13.8 mg, 0.0150 mmol) in anhydrous toluene
3
3
H
H
3
0.059 µmol) in a 0.1-cm quartz cell under nitrogen at -10 ˚C, and the
reaction was immediately monitored by CD spectroscopy (Figure S33A).
After 1 h, the reaction was quenched by the addition of water (5 µL), and
the absorption, CD, NMR, and ESI mass spectra of the reaction mixture
were measured, indicating that the ring-opening reaction partially
(
300 mL) was stirred at 90 °C for 24 h. After evaporation, the residue was
subjected to SEC fractionation to obtain (S)-BB*-DD (14.8 mg, 53%
–
1
yield) as a white solid. Mp: >300 °C. IR (KBr, cm ): 2156 (νC≡C), 1290
1
(
ν
B-O), 1250 (νC-O). H NMR (500 MHz, 25 °C, CDCl
3
): δ 7.78-7.64 (m, 8H,
H H H H
occurred, giving the corresponding helices BB -DD -2 and BB -DD -3 in
1
ArH), 7.48-7.34 (m, 6H, ArH), 7.32-7.06 (m, 34H, ArH), 7.04 (s, 2 H, ArH),
30% conversion based on its H NMR spectrum (Scheme 2).
4
8
.54-4.46 (m, 2H, OCH
H, OCH CH), 3.44-3.30 (m, 2H, OCH
CH ), 1.70-1.58 (m, 2H, OCH CH ), 1.16-0.85 (m, 10H), 0.38 (s,
8H, TMS), 0.28 (s, 18H, TMS). C NMR (125 MHz, 25 °C, CDCl ): δ
2
CH
2
), 4.28-4.20 (m, 2H, OCH
2 2
CH ), 3.76-3.48 (m,
2
2
CH), 1.90-1.80 (m, 2H,
OCH
2
2
2
2
1
3
Acknowledgements
1
1
1
1
1
7
3
55.46, 145.83, 145.05, 143.97, 142.40, 142.35, 133.82, 132.20, 131.92,
31.82, 131.77, 131.48, 131.36, 130.87, 129.80, 129.31, 128.81, 128.17,
28.09, 127.95, 127.57, 126.42, 125.25, 123.16, 122.95, 122.81, 121.84,
21.55, 117.97, 105.55, 104.73, 95.67, 94.95, 94.39, 90.79, 90.20, 86.10,
2.05, 65.82, 65.64, 41.99, 30.53, 28.17, 26.24, 25.77, 0.37, 0.19. The
This work was supported in part by a Grant-in-Aid for Scientific
Research (S) (no. 25220804 to E.Y.) and a Grant-in-Aid for
Young Scientists (B) (no. 26810068 to H.I.) from the Japan
Society for the Promotion of Science (JSPS). The authors thank
Prof. Takahisa Ikeue of Shimane University for his valuable
advice for the line-shape simulation of the variable-temperature
NMR spectra of the double helices.
boron-bound carbon was not detected due to quadrupolar relaxation.
+
HRMS (APCI+): m/z calcd for C127
869.7967.
114 2 6 4
H B O Si (M+H ), 1869.7951; found,
1
–
1
Spectroscopic Data of (R)-BB*-DD. Mp: >300 °C. IR (KBr, cm ): 2156
1
(
ν
C≡C), 1290 (νB-O), 1250 (νC-O). H NMR (500 MHz, 25 °C, CDCl
.80-7.63 (m, 8H, ArH), 7.48-7.34 (m, 6H, ArH), 7.32-7.06 (m, 34H, ArH),
.04 (s, 2 H, ArH), 4.56-4.46 (m, 2H, OCH CH ), 4.28-4.18 (m, 2H,
CH ), 3.80-3.48 (m, 8H, OCH CH), 3.45-3.30 (m, 2H, OCH CH),
.90-1.80 (m, 2H, OCH CH ), 1.70-1.58 (m, 2H, OCH CH ), 1.18-0.86 (m,
0H), 0.38 (s, 18H, TMS), 0.28 (s, 18H, TMS). C NMR (125 MHz, 25 °C,
): δ 155.45, 145.82, 145.03, 143.97, 142.40, 142.35, 133.83,
32.21, 131.92, 131.82, 131.77, 131.48, 131.36, 130.87, 129.80, 129.31,
3
):
δ
Keywords: helical structures • double helix • chirality • molecular
7
7
rotor • helix inversion
2
2
OCH
2
2
2
2
[
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2
2
2
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3
CDCl
3
1
1
1
9
2
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+
(
M+H ), 1869.7951; found, 1869.7964.
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anhydrous THF (5.0 mL), and the mixture was stirred for 10 min. To this
For internal use, please do not delete. Submitted_Manuscript
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Chemistry - An Asian Journal
10.1002/asia.201700162
FULL PAPER
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2
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H
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[18] We first anticipated that some H NMR signals of the optically active
BB*-DD double-helix gave rise to nonequivalent signals due to the
1
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diastereomeric right- and left-handed helices. However, the H NMR
1
signals of BB*-DD gradually broadened accompanied by splitting into a
number of signals, thus producing complicated spectra upon cooling to
a low temperature, even at temperatures as low as -90 ˚C (Figures S29
and S31), and we could not unambiguously assign signals due to the
diastereomeric helices. Thus, based on the variable-temperature NMR
measurement results, we could not conclude if the rate of helix
inversion of the BB*-DD double-helix was fast or slow on the NMR time
scale, thereby leading to difficulty to estimate the helix-sense excess of
the BB*-DD double-helix by NMR. On the other hand, the variable-
temperature CD measurement results of BB*-DD (Figure 4B) indicated
that the BB*-DD double-helix is dynamic even at -90 ˚C
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[
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013, 52, 6849-6853; c) Y. Suzuki, T. Nakamura, H. Iida, N. Ousaka, E.
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407-1416.
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Novel double-stranded helices
covalently-bridged by two cyclic
boronate esters were prepared via a
simple mixing of two complementary
dimer strands bearing diethyl
H. Iida,* K. Ohmura, R. Noda, S.
Iwahana, H. Katagiri, N. Ousaka, T.
Hayashi, Y. Hijikata, S. Irle,* E.
Yashima*
boronates and diols. A rotational
motion of the encased cyclic boronate
ester units can take place
Page No. – Page No.
Double-Stranded Helical Oligomers
Covalently-Bridged by Rotary Cyclic
Boronate Esters
simultaneously with helix-inversion of
the double-stranded helical
framework, thus providing a unique
molecular rotor that undergoes dual
rotary and inverting (twisting) motions.
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Title
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