Derivation of saddle shaped cyclooctatetrathiophene: Increasing conjugation and fabricating pentamer

Article abstract of DOI:10.1016/j.tet.2013.12.002

With cyclooctatetrathiophene (COTh) as building block, two α,α,α,α-tetraaryl COThs, COThP and COThTh have been efficiently synthesized. Phenyl and thienyl were employed as end-capping groups to introduce to COTh and increase its conjugation. For enlarging the special 'saddle' shaped structure, a pentamer of COTh was synthesized via Negishi reaction and CuCl₂-promoted oxidative coupling reaction. The pentamer (COThF) is a new type of dendrimer with COTh as dendron, which presents an artistic configuration possessing a large saddle shape. All compounds were fully characterized by ¹H NMR, ¹³C NMR, HRMS and IR. The crystal structures of COThP and COThTh were confirmed by X-ray analysis. The molecular configuration of COThF was optimized by theoretical calculations. Their UV-vis properties, electrochemical behaviours and thermo-gravimetric analysis of COThP, COThTh and COThF were also described.

Full text of DOI:10.1016/j.tet.2013.12.002

Tetrahedron 70 (2014) 631e636
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Derivation of saddle shaped cyclooctatetrathiophene: increasing
conjugation and fabricating pentamer
,
,
c
,
a
a
Yong Wang a b, Dewen Gao a, Jianwu Shi a , Yuhe Kan , Jinsheng Song , Chunli Li ,
*
*
,
Hua Wang a
*
a Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004, China
b Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, China
c Jiangsu Province Key Laboratory for Chemistry of Low Dimensional Materials, School of Chemistry and Chemical Engineering, Huaiyin Normal
University, Huaian 223300, China
a r t i c l e i n f o
a b s t r a c t
Article history:
With cyclooctatetrathiophene (COTh) as building block, two a,a,a,a-tetraaryl COThs, COThP and COThTh
Received 20 September 2013
Received in revised form 25 November 2013
Accepted 1 December 2013
Available online 7 December 2013
have been efficiently synthesized. Phenyl and thienyl were employed as end-capping groups to introduce
to COTh and increase its conjugation. For enlarging the special ‘saddle’ shaped structure, a pentamer of
COTh was synthesized via Negishi reaction and CuCl2-promoted oxidative coupling reaction. The pen-
tamer (COThF) is a new type of dendrimer with COTh as dendron, which presents an artistic configu-
ration possessing a large saddle shape. All compounds were fully characterized by 1H NMR, 13C NMR,
HRMS and IR. The crystal structures of COThP and COThTh were confirmed by X-ray analysis. The
molecular configuration of COThF was optimized by theoretical calculations. Their UVevis properties,
electrochemical behaviours and thermo-gravimetric analysis of COThP, COThTh and COThF were also
described.
Keywords:
Cyclooctatetrathiophene
Aryl substitution
Pentamer
Synthesis
Ó 2013 Elsevier Ltd. All rights reserved.
Crystal structure
Theoretical calculation
1. Introduction
in the process of synthesizing COTh and its derivatives limits its
advanced development.
Thiophene derivatives have attracted more attentions due to
their potential applications in organic optoelectronics.1 Usually,
these derivatives are possessing linear/planar structures with ex-
COTh was firstly synthesized with yield of 18% and 23% by
Kauffmann et al.7 in 1978 via CuCl2 promoting oxidative homo-
coupling of 3,30-dilithio[2,20]bithiophene and 2,20-dilithio[3,30]
bithiophene, respectively. Until twenty years later, Marsella et al.3,8
reported a series work about the synthesis of dimer and oligomer of
COTh and their application in organic electronics. In our previous
work, we reported an improvement of the efficient synthesis of
COTh with yield up to 40%6 and a dithieno[2,3-b:30,20-d]thiophene
fused COTh forming double helicene,9 in which the sophisticated
structure not only possesses the general COTh character, but also
shows a double helical configuration. Although COTh has been
reported for about 40 years, however, only a few papers about COTh
derivatives were achieved.3a,6e11 It is still a huge challenge to effi-
ciently synthesize its derivatives with various architectures.
Herein, we demonstrate an efficient approach to build up COTh
tended
linear/planar structure but also can present 3D conformation with
large flexible -con-
-conjugated skeleton.3 These large flexible
p
system.2 In fact, thiophene derivatives not only possess
p
p
jugated skeleton structures may be potentially applied in electro-
mechanical actuators,3 molecular tweezers,4 and self-assembly
building blocks.5 Cyclooctatetrathiophene (tetra[2,3-thienylene],
COTh) composed of four thiophene rings, is one of the special
flexible p-conjugated skeletons with an 8p annulene as centre. The
single crystal of [TMS]4-COTh6 indicates that the four thiophene
rings present ‘saddle’ form, which can be transformed into ‘planar’
form for aromaticity of the reduced 10p dianion or the oxidized 6p
dication.3 Furthermore, COTh may be also developed in the field of
organic electronics because of the rich thiophene units, which can
be modified with various functional groups. However, the low yield
derivatives
with
aryl
groups,
a,
a,
a,
a-tetraphenyl-cyclo-
octatetrathiophene (COThP) and
a,a,a,a-tetra(3-thienyl)-cyclo-
octatetrathiophene (COThTh) via Suzuki reaction with high yields
of 83% and 71%, respectively. Their crystal structures indicate that
the end-capping groups of phenyl and thienyl are approximately
coplanar with the thiophene rings of COTh. Furthermore, a novel
pentamer, COThF, has also been prepared via Negishi reaction and
* Corresponding authors. Tel.: þ86 378 3897112; fax: þ86 378 3881358; e-mail
addresses: jwshi@henu.edu.cn (J. Shi), kyh@hytc.edu.cn (Y. Kan), hwang@henu.edu.
cn (H. Wang).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.12.002

632
Y. Wang et al. / Tetrahedron 70 (2014) 631e636
CuCl2-promoted oxidative coupling reaction. More interestingly,
the molecular configuration of COThF optimized by theoretical
calculation, presents an artistic configuration possessing a large
saddle shape, which is composed of five independent saddle sha-
ped COTh units. This architecture of COThF is different from the
thiophene-based dendrimers with terthiophene12 or tetrakis(-
thiophene-2-yl)ethene13 as dendrons as reported. In addition, the
UVevis properties, electrochemical behaviours and thermo-
gravimetric analysis of COThP, COThTh and COThF were also
described.
and 4 were also tried for COThF (Scheme 2), and both were failed
again. This failure may be due to the decreased activity and in-
creased steric hindrance arising from the larger COTh substituents.
TMS
TMS
S
S
S
S
TMS
TMS
TMS
TMS
TMS
TMS
TMS
1) n-BuLi
2) ZnCl
3
S
S
S
S
S
S
3) 2, Pd(PPh
)
TFA
51%
X
Negishi Rxn
S
S
TMS
TMS
TMS
TMS
S
S
S
S
S
2. Results and discussion
S
S
S
TMS
TMS
1) n-BuLi
2.1. Synthesis of COThP and COThTh
2) Bu SnCl
3) 2, Pd(PPh
4
S
S
S
S
S
)
X
S
S
S
Stille Rxn
The synthetic route to COThP and COThTh are shown in
Scheme 1. Tetrabromo-COTh (2)10a is the key scaffold for the prep-
Ph -B(OH)
74%
TMS
TMS
TMS TMS
COThF
aration of
a,a,a,a-tetraaryl COThs. Normally, it is hard to be effi-
TMS
TMS
S
ciently functionalized to each
a-position available on the parent
S
2, Pd(PPh
) , K CO
COTh. To avoid such problem, we directly made COTh bearing four
functionalized groups, namely tetrabromo-COTh (2) through an
efficient synthetic route (Scheme 1), which was developed by two
steps: bromine dance (BD) reaction9,14 of 2,20-dibromo-[3,30]
bithiophene (1)6 and following CuCl2-promoted oxidative coupling.
The yield of 47% of 2 was efficiently obtained in one-pot. Thus, using
2 as a versatile building block, we first synthesized COThP in 83% via
four-fold Suzuki couplings between 2 and phenylboronic acid. Fur-
thermore, we successfully prepared COThTh in 72% yield with the
same process by using 2 and thiophen-3-boronic acid (Scheme 1).
X
Suzuki Rxn
S
S
B(OH)2
TMS
5
Scheme 2. The first synthetic route to COThF.
To overcome this problem, we tried another synthetic route as
shown in Scheme 3 to respond to the challenge of making COThF.
The synthesis of 5,50-dibromo[3,30]bithiophene (6) was carried out
using BD reaction of 1, which was the key step in synthesis of
COThF. Compound 1 was treated with LDA in THF at ꢀ10 ꢁC and
then quenched with methanol, 6 was efficiently obtained in a yield
of 80%. The intermediate 7 was then prepared in 67% yield by two-
fold Negishi couplings between 4 and 6. Following the deproto-
nation on 7 with n-BuLi in ethyl ether, the resultant aryllithium
species was oxidized with CuCl2 to afford the target compound
COThF in 30% isolated yield. The star-shaped COThF is a pentamer
S
S
S
S
Ph-B(OH)2
Pd(PPh3)4
83%
Br
Br
Br
COThP
S
S
S
of COTh, in which four 4 units linked to the four peripheral a-po-
1) LDA
S
S
S
B(OH)2
S
S
sitions available on the cored COTh. The star-shaped COThF may
also be taken as a new type of all-thiophene based dendrimer with
COTh as new dendron. The 1H NMR spectrum behaviour of COThF
could be taken as a typical characteristic of dendrimers,12,15e17
which shows two broad peaks at both aromatic region of
7.03e7.10 ppm and alkyl region of 0.31e0.35 ppm in CDCl3. We
have also measured its 1H NMR spectrum at 333 K (60 ꢁC), however,
its spectral behaviour did not show any obvious change. HRMS data
of COThF clearly support its molecular structure (see
Supplementary data).
2) CuCl2
47%
S
Br
Br
S
S
S
Br
1
2
Pd(PPh3
72%
)
4
S
S
S
COThTh
Scheme 1. Synthetic route to COThP and COThTh.
2.2. Synthesis of COThF
A
1) LD
Br
The same strategy was also applied for the synthesis of pen-
tamer, COThF. The first synthetic route to COThF is shown in
Scheme 2. The first step was to obtain tri(trimethylsilyl)-COTh (4)
by directly treating tetra(trimethylsilyl)-COTh (3)6 with trifluoro-
acetic acid (TFA) in chloroform. At this step, one of the four TMS
groups in 3 was removed selectively. It was found that the use of
a high concentration of TFA led to complex products. Whereas
a good yield of 51% could be achieved by using a low concentration
of TFA (1.5%) in chloroform. At same time, 40% raw material could
also be recovered. COTh-boronic acid pinacol ester (5) was effi-
ciently prepared in 74% by using 4 and bis(pinacolato)diborane.
Then, the preparation of COThF was tested by Pd(PPh3)4-catalyzed
Suzuki coupling reaction between 2 and 5 in refluxing THF. Un-
fortunately, only complex mixtures were obtained and it is very
difficult to be separated by column chromatography. More cou-
plings including Stille coupling and Negishi coupling between 2
Br
2) CH3OH
80%
1
S
S
6
TMS
TMS
TMS
TMS
TMS
1) n-BuLi
1) n-BuLi
2) CuCl2
2) ZnCl2
S
S
S
S
S
S
S
S
3) 6, Pd(PPh
)
3
4
COThF
4
30%
67%
TMS
S
S
7
Scheme 3. The second synthetic route to COThF.
2.3. Crystal structures of COThP and COThTh
The crystal structures of COThP and COThTh are confirmed by
single-crystal X-ray analysis. Both of them belong to monoclinic,

Y. Wang et al. / Tetrahedron 70 (2014) 631e636
633
space group P2(1)/c, and reveal saddle-shaped structures (Fig.1). As
for the inner angles ( ) of the central eight-membered ring, the
a
average values in the X-ray structures of COThP and COThTh are
127.6ꢁ and 126.7ꢁ, respectively, which are close to that of COTh
(127.9ꢁ).3a,11 More structural data from X-ray analyses are sum-
marized in the Supplementary data (Table S1 and Fig. S25). The
dihedral angles between across thiophene rings are 71.1ꢁ for COThP
unit and 83.4ꢁ for COThTh as shown in Fig. 1e and f, respectively.
The average dihedral angels between end-capping groups and the
thiophene rings of COTh unit are 19.5ꢁ for COThP and 12.8ꢁ for
COThTh, respectively. It is obvious that the end-capping groups are
almost coplanar with the thiophene rings of COTh unit, which may
be indicate the expansion of
p conjugation.
Fig. 2. The intermolecular interactions (a and b) and crystal packings (c and d) of
COThP (left column) and COThTh (right column).
peak (347 nm, 345 nm), and COThF presents a weak absorption
weak (341 nm), while COTh does not exhibit obvious absorption
peak. As discussed above, the end-capping groups in COThP and
COThTh are almost planar with the thiophene rings of COTh unit as
shown in Fig. 1e and f. This co-planarity between the end-capping
groups and the thiophene rings of COTh enlarges the conjugations
of COThP and COThTh, which result in the strong absorption peaks
in band-II. This illustrates that it is an effective way to improve the
conjugation of COTh unit in four directions by utilizing aryl as end-
capping groups. For COThF, the weak absorption peak in band-II
may be attributed to that the dihedral angles between the adja-
cent thiophene rings on the neighbouring COTh units perhaps are
little large. More interesting, COThF exhibits an obvious absorption
peak (419 nm) in band-III, which may not originate from the large
conjugation of COThF due to the ‘saddle’ form of COTh unit. In
order to further understand this phenomenon, theoretical calcu-
lations were done.
0.8
COTh
COThF
Fig. 1. Molecular structures and conformations for COThP (left column) and COThTh
(right column). (a) and (b) top view, Carbon and sulfur atoms are depicted with
thermal ellipsoids set at 30% probability level and all hydrogen atoms are omitted for
clarity. (c) and (d) the spacefill mode; (e) and (f) side view.
COThTh
0.6
COThP
0.4
In the crystal of COThP, there exist multiple intermolecular in-
teractions of S/p, S/C and S/S between neighbouring molecules
as shown in Fig. 2a. For example, the distances of S1/C13, S1/C14,
S1/C15, S2/C2, S2/C3, C3/C24 and S1/S2 are found as 3.573,
3.447, 3.570, 3.652, 3.486, 3.570 and 3.884 A, respectively. For
0.2
0.0
ꢀ
COThTh, there also exist multiple intermolecular interactions of
S/p, S/C and S/S between neighbouring molecules as shown in
300
400
500
600
Fig. 2b. The S/S and S/C interactions are observed as S1/S7
Wavelength (nm)
ꢀ
ꢀ
ꢀ
(3.249 A), S2/S1 (3.448 A) and S1/C21 (3.384 A), respectively. For
their crystal packing mode as shown in Fig. 2c and d, COThP shows
close packing along b axis, while COThTh along a axis. These short
contacts and crystal packing modes in the crystals of COThP and
COThTh are important for them to be considered as possible
semiconductors for organic electronics.
Fig. 3. UVevis absorption spectra of COTh, COThP, COThTh and COThF in chloroform
at room temperature ([C]¼1ꢂ10ꢀ5 M).
Table 1
Optical and electrochemical parameters of COThP, COThTh and COThF
onset
Compd
l
(nm)
lonset
(nm)a
Eg
E
HOMO
(eV)d
ox
(eV)b
(V)c
2.4. UVevis properties
Band-I
Band-II
Band-III
COThP
COThTh
COThF
290
294
288
347
345
341
d
455
450
500
2.73
2.76
2.48
0.61
0.62
0.58
5.41
5.42
5.38
The UVevis spectra for COTh, COThP, COThTh and COThF are
shown in Fig. 3. There are three major absorption bands with the
range of 270e320 nm (Band-I), 320e380 nm (Band-II) and
380e480 nm (Band-III) as listed in Table 1. All four compounds
show similar peaks in band-I, which may be attributed to the
characteristic absorption peak of the thieno[3,2-b]thiophene unit in
COTh.18 In band-II, COThP and COThTh show a strong absorption
d
419
a
lonset was the onset value of absorption.
Eg (optical energy gap) calculated from the onset of absorption used the for-
b
mula: Eg¼1240/lonset
.
c
onset
þ
is the onset potential of the first oxidation wave relative to EFc=Fc .
E
ox
d
onset
HOMO was determined by CV with ferrocene [HOMO¼4.8þE
(vs Fc/Fcþ)].
ox

634
Y. Wang et al. / Tetrahedron 70 (2014) 631e636
2.5. Theoretical calculations
2.6. Electrochemical behaviours and thermogravimetric
analysis
Theoretical calculations were done at CAM-B3LYP/6-31þG(d,p)
level.19 Table 2 lists the electronic absorption energy, oscillator
strengths, and dominant electronic transitions. For COThP and
COThTh, the absorption peaks in experiments are consistent with
the results of theoretical calculations. So it can be concluded that
the absorption peaks of COThP and COThTh in band-II originate in
the transitions from H to Lþ1 and Hꢀ1 to L.
The electrochemical behaviours of COThP, COThTh and
COThF were investigated in dry CH2Cl2 with Ag/AgCl electrode as
the reference electrodes. The onset voltage and highest occupied
molecular orbits (HOMO) values of these compounds were
summarized in Table 1. COThF showed two pairs of quasi-
reversible redox waves (Fig. S28, Supplementary data) with the
onset voltage of the first oxidation potential at þ0.58 V (vs Fc/
Fcþ), while the COThP and COThTh only showed one irreversible
redox wave with the onset voltage of the first oxidation potential
at þ0.61 V and þ0.62 V, respectively. No redox process occurs at
negative potential for these compounds. These results demon-
strate that the central COTh moiety endows this skeleton with
high redox stability.19 From the onset voltages of oxidation peaks
with almost same value, it implies that the electrochemical
properties of these COTh derivatives are primarily dominated by
the COTh units.
Table 2
The calculated electronic absorption energy (in nm), oscillator strengths f, and
dominant electronic transitions in chloroform for COThP, COThTh and COThF by
CAM-B3LYP/6-31þG(d,p)
Compd
Electronic
transition
Wavelengtha
f
Main Contributionsb
COThP
S0/S1
S0/S2
383.8
333.4 (347)
0.2223
1.4369
H/L (89%)
Hꢀ1/L (57%)
H/Lþ1 (35%)
H/Lþ1 (77%)
H/L (89%)
Hꢀ1/L (60%)
H/Lþ1 (32%)
H/Lþ1 (81%)
H/L (71%)
Hꢀ1/L (38%)
H/Lþ1 (35%)
Hꢀ1/Lþ2 (38%)
H/Lþ3 (20%)
In addition, the thermogravimetric analysis (TGA) reveals that
all COTh, COThP, COThTh and COThF possess the high thermal
stability. The decomposition temperatures for a 5% weight loss are
238, 451, 387 and 505 ꢁC (Fig. S27, Supplementary data) for COTh,
COThP, COThTh and COThF, respectively. This high stability is
attributable to the COTh moieties in these molecules and the re-
active C2 positions of thiophenes are capped by aryl sub-
S0/S3
S0/S1
S0/S2
296.7
387.8
335.2 (345)
0.0380
0.1900
1.1340
COThTh
COThF
S0/S3
S0/S1
S0/S2
297.6
427.7
400.8 (419)
0.0413
0.6458
1.9773
stituents.20 The multiple interactions of S/
p, p/p and S/S
observed in their solid states could be another main reason for
their high thermal stability.
S0/S3
374.4
0.2626
a
Data in parentheses in chloroform from experiment.
HOMO and LUMO are abbreviated as H and L, respectively.
b
3. Conclusion
The molecular configuration of COThF was optimized as shown
In summary, based on COTh as building block, we have suc-
in Fig. 4a and b. It is very interesting that the whole molecule
presents an artistic configuration possessing a large saddle shape,
which is composed of five independent saddle shaped COTh units.
The dihedral angles between across thiophene rings are about 71.1ꢁ
for the central COTh unit and 72.3ꢁ for the four cornered COTh
units, respectively. At the same time, the adjacent thiophene rings
on neighbour COTh units in COThF are also co-planar with dihedral
angle of 18.9ꢁ, which is responsible for the weak absorption peak in
band-II. For the absorption peak in band-III of COThF, the result of
the theoretical calculation can not give a reasonable explanation.
cessfully synthesized two
a,a,a,a-tetraaryl COThs, COThTh and
COThP, and an amazing pentamer COThF. The BD reaction plays
a key step in the synthesis of the title compounds. The derivation
by utilizing aryl as the end-capping groups can increase the con-
jugation of saddle shaped COTh, which makes such kind of large
p
-cored and flexible skeletons promising outcome in both opto-
electronic application and supermolecular chemistry. The pen-
tamer COThF has novel dendritic all-thiophene based
a
architecture and possesses a large saddle shape with flexible
skeletons, which may be act as elastic network for energy and
cation storages.
4. Experimental section
4.1. Materials and general methods
Ether and tetrahydrofuran (THF) for use were freshly distilled
from sodium/benzophenone prior to use. Concentration of n-BuLi
(hexane) was determined by titration with N-pivaloyl-o-tolui-
dine.21 Column chromatography was carried out on silica gel
(300e400 mesh). Analytical thin-layer chromatography was per-
formed on glass plates of Silica Gel GF254 with detection by UV.
Standard techniques for synthesis under inert atmosphere, using
gasbag and Schlenk glassware equipped with an 8-mm PTFE vac-
uum stop-cock, were employed.
Fig. 4. The molecular configurations of COThF optimized by theoretical calculations.
But it should be noticed that the absorption peak in band-III
comes from the transitions from Hꢀ1 to L and H to Lþ1 accord-
ing the theoretical result. The electrons distribution of HOMO and
LUMO for COThF is mainly on the central COTh unit (Fig. S26,
Supplementary data). This may be indicates that the circumambi-
ent COTh unit can act as electron donating group providing partial
electron to the central COTh unit in COThF. So COThF exhibits
a new absorption peak in band-III, which presents a red-shift
compared with COThP and COThTh.
1H and 13C NMR spectra were recorded at ambient temperature
on a Bruker AVANCE 400 NMR spectrometer using chloroform-
d (CDCl3) as solvent. The chemical shift references were as follows:
(1H) CDCl3, 7.26 ppm (CHCl3); (13C) CDCl3, 77.00 ppm (CDCl3).
HRMS spectra were recorded on GCT-MS Micromass UK or IonSpec
4.7 T FTMS or Bruker Apex IV FTMS spectrometer. IR spectra were
obtained using
a Bruker VERTEX 70 spectrometer in KBr
(4000e400 cmꢀ1). Melting point determination was taken on a XT4

Y. Wang et al. / Tetrahedron 70 (2014) 631e636
635
Melt-Temp apparatus and was uncorrected. UVevis spectra were
performed on a TU-1900 (Beijing Purkinje General Instrument Co.
Ltd.). TGA data were performed on a Mettler Toledo TGA/SDTA851e
instrument. Theoretical calculations were done at CAM-B3LYP/6-
31þG(d,p) level. All calculations were performed with Gaussian09
program in Intel Core i7 computer.
7.29 (m, 4H), 7.11 (s, 4H); 13C NMR (CDCl3, 100 MHz):
d
140.46,
137.15, 134.82, 130.38, 126.61, 125.78, 125.73, 120.11. HRMS (TOF MS
EIþ) m/z calcd for [C32H16S8] 655.9018, found 655.9024. IR (KBr):
3096.0 (CeH) cmꢀ1
.
4.2.4. Synthesis of tri(trimethylsilyl)-COTh (4). Compound
3
X-ray diffraction measurements were performed on a Bruker
SMART APEX II CCD diffractometer. The X-ray crystallographic
analyses were performed using crystals of compounds COThP,
COThTh with the size 0.45ꢂ0.09ꢂ0.07, 0.35ꢂ0.11ꢂ0.07 mm, re-
spectively. The data were corrected for Lorentz and polarization
effects and absorption corrections were performed using SADABS
program.22 The crystal structures were solved using the SHELXTL
program23 and refined using full matrix least squares. The positions
of hydrogen atoms were calculated theoretically and included in
the final cycles of refinement in a riding model along with attached
carbons. Further details are in the deposited CIFs. Single crystals of
COThP and COThTh suitable for X-ray analysis were obtained by
slow evaporation from hexane and CHCl3eCH3OH (4:1 v/v),
respectively.
(0.2160 g, 0.35 mmol) was dissolved in 30 mL CHCl3, TFA (1.5%,
4.5 mL) was added dropwise at room temperature. The reaction
procedure was monitored by TLC analysis. After stirring at room
temperature for 4 h, the reaction mixture was quenched with sat-
urated NaHCO3 (15 mL), then washed with water then dried over
MgSO4. After removing the solvent in vacuo, the residue was pu-
rified by column chromatography on silica gel with petrol ether
(60e90 ꢁC) as eluent to yield 4 (0.0972 g, 51%) as a yellow solid, and
0.0864 g of 3 (40%) was recovered. Mp 114e116 ꢁC. 1H NMR
(400 MHz, CDCl3)
d
7.36 (d, 1H, J¼5.2 Hz), 7.08 (s, 2H), 7.06 (s, 1H),
6.98 (d, 1H, J¼5.2 Hz), 0.34 (s, 18H), 0.33 (s, 9H). 13C NMR (CDCl3,
100 MHz)
d 142.40, 142.37, 137.80, 137.77, 137.63, 137.43, 137.28,
137.24, 136.75, 136.70, 136.64, 136.08, 132.42, 130.05, 126.85, ꢀ0.16,
ꢀ0.17, ꢀ0.19. HRMS (MALDI/DHB) m/z calcd for [C25H32S4Si3]
544.0695, found 544.0689. IR (KBr): 2955.0, 2925.0, 2898.0, 2853.0
4.2. Synthesis and characterization
(CeH) cmꢀ1
.
4.2.1. Synthesis of tetrabromo-COTh (2). n-BuLi (2.38 M in hexane,
1.82 mL, 4.33 mmol, 2.56 equiv) was slowly added to a solution of
diisopropylamine (0.68 mL, 4.81 mmol, 2.85 equiv) in dry THF
(25 mL) at 0 ꢁC. After 1 h at 0 ꢁC, the prepared LDA was slowly
added to a solution of 1 (0.5480 g, 1.69 mmol) in dry THF (60 mL) at
ꢀ10 ꢁC. After 20 h at ꢀ10 ꢁC, dry CuCl2 (0.676 g, 5.03 mmol,
3.0 equiv) was added at ꢀ78 ꢁC, the reaction mixture was kept at
ꢀ78 ꢁC for 1 h, ꢀ50 ꢁC for 2 h, and then warmed slowly to ambient
temperature overnight. The reaction mixture was quenched with
water, extracted with ethyl ether. The organic layer was washed
with water and then dried over MgSO4. After removing the solvent
in vacuo, the residue was purified by column chromatography on
silica gel with petrol ether (60e90 ꢁC) as eluent to yield 2
(0.2581 g, 47%) as a pale white solid. Mp >300 ꢁC. 1H NMR (CDCl3,
4.2.5. Synthesis of 5. n-BuLi (2.29 M in hexane, 0.15 mL,
0.34 mmol, 1.05 equiv) was added to 4 (0.1734 g, 0.32 mmol,
1.0 equiv) in dry ethyl ether (30 mL) in a Schlenk vessel at ꢀ78 ꢁC.
After 2 h at ꢀ78 ꢁC, the homogeneous reaction mixture was
treated with bis(pinacolato)-diboron (0.0808 g, 0.32 mmol,
1.0 equiv) in 10 mL ethyl ether, then warmed slowly to ambient
temperature overnight. The reaction mixture was quenched with
water, extracted with ethyl ether, and finally dried over anhydrous
MgSO4. After the solvent was removed in vacuo, the residue was
purified by column chromatography on silica gel with petroleum
ether (60e90 ꢁC) as eluent to yield 5 (0.1580 g, 74%) as a light
yellow solid. Mp >300 ꢁC. 1H NMR (CDCl3, 400 MHz):
d 7.48 (s,
1H), 7.08 (s, 1H), 7.07 (s, 1H), 7.05 (s, 1H), 1.34 (s, 6H), 1.32 (s, 6H),
0.32 (s, 9H), 0.31 (s, 9H), 0.30 (s, 9H); 13C NMR (100 MHz, CDCl3):
400 MHz):
d
6.90 (s, 4H). 13C NMR (CDCl3, 100 MHz):
d
136.10,
d 142.85, 142.44, 142.42, 139.75, 139.61, 137.76, 137.70, 137.46,
132.45, 132.05, 114.98. HRMS (TOF MS EIþ) m/z calcd for
137.41, 137.31, 137.05, 136.96, 136.92, 136.74, 136.66, 84.22, 24.85,
24.56, ꢀ0.18, ꢀ0.20, ꢀ0.21. IR (KBr): 3053.0, 2977.0, 2956.0, 2897.0
(CeH) cmꢀ1. HRMS (TOF MS ESþ) m/z calcd for [C31H43BO2S4Si3]
670.1547, found [Mþ1]þ 671.1629.
[C16H4S749Br4]
639.5929,
found
[C16H4S749Br4]
639.5939,
[C16H4S749Br381Br] 641.5913, [C16H4S749Br821Br2] 643.5900, [C16H4
S749Br81Br3] 645.5878, [C16H4S481Br4] 647.5852. IR (KBr): 3078.6
(CeH) cmꢀ1
.
4.2.6. Synthesis of 5,50-dibromo-3,30-bithiophene (6). n-BuLi
(2.50 M in hexane, 0.52 mL, 1.30 mmol, 2.5 equiv) was slowly
added to a solution of diisopropylamine (0.22 mL, 1.56 mmol,
3.0 equiv) in dry THF (8 mL) at 0 ꢁC. After 1 h at 0 ꢁC, the prepared
LDA solution was transferred by syringe into a solution of 1
(0.1660 g, 0.51 mmol) in THF (16 mL) at ꢀ10 ꢁC. After 18 h at
ꢀ10 ꢁC, methanol was added to quench the reaction. The reaction
mixture was extracted with CHCl3 and washed with water, and
then dried over MgSO4. After the removal of the solvent under
vacuum, the residue was purified by column chromatography on
silica gel with petrol ether (60e90 ꢁC) as eluent to yield 6
(0.1330 g, 80%) as a white solid. Mp 117e119 ꢁC. 1H NMR (CDCl3,
4.2.2. Synthesis
of
a,a,a,a-tetraphenylcyclooctatetrathiophene
(COThP). Under argon, 2 (0.3032 g, 0.47 mmol), phenylboronic acid
(0.3537 g, 2.90 mmol, 6.0 equiv), K2CO3 (0.6500 g, 4.70 mmol,
10 equiv) and Pd(PPh3)4 (43.5 mg, 37.6
mmol, 0.08 equiv) were
added in a Schlenk vessel, then THF (30 mL) and water (2 mL) were
added. The reaction mixture was stirred for 36 h at 95 ꢁC. After
cooling to room temperature, the reaction mixture was extracted
with CHCl3 and dried with MgSO4. The product was purified by
silica chromatography with petrol ether (60e90 ꢁC) as an eluent.
COThP (0.2468 g, 83%) was obtained as a yellow solid. Mp >300 ꢁC.
1H NMR (CDCl3, 400 MHz):
d 7.61 (m, 8H), 7.40 (m, 8H), 7.32 (m,
4H), 7.25 (s, 4H); 13C NMR (CDCl3, 100 MHz):
d
145.65, 137.48,
400 MHz):
d
7.22 (d, 2H, J¼2.0 Hz), 7.20 (d, 2H, J¼2.0 Hz); 13C NMR
133.63,131.53,128.97,127.98,125.79,125.62. HRMS (TOF MS EIþ) m/
z calcd for [C40H24S4] 632.0761, found 632.0767. IR (KBr): 3061.5,
(CDCl3, 100 MHz): d
136.7, 128.6, 121.3, 113.3. HRMS (EIþ) m/z calcd
for [C8H4S2Br2] 321.8121, found 321.8122. IR (KBr): 3095.8, 3075.7
3023.8 (CeH) cmꢀ1
.
(CeH) cmꢀ1
.
4.2.3. Synthesis of
a
,
a
,
a
,
a
-tetra(3-hienyl)cyclooctatetrathiophene
4.2.7. Synthesis of 7. n-BuLi (2.30 M in hexane, 0.20 mL, 0.46 mmol,
1.2 equiv) was slowly added to a solution of 4 (0.2121 g, 0.39 mmol,
1.0 equiv) in dry THF (45 mL) in a Schlenk vessel at ꢀ78 ꢁC. After 2 h
at ꢀ78 ꢁC, the pale yellow homogeneous reaction mixture was
treated with ZnCl2 (0.0800 g, 0.60 mmol, 1.5 equiv), kept stirring at
ꢀ78 ꢁC for 30 min, then kept at ambient temperature for 3 h. 6
(COThTh). The procedure in preparation of COThTh is same to that
of making COThP. On the scales of 0.1078 g of 2 (0.17 mmol) and
0.1287 g of thiophene-3-boronic acid (1.01 mmol, 6.0 equiv),
COThTh (0.0792 g, 72%) was obtained as a yellow solid. Mp
>300 ꢁC. 1H NMR (CDCl3, 400 MHz):
d 7.40 (m, 4H), 7.36 (m, 4H),

636
Y. Wang et al. / Tetrahedron 70 (2014) 631e636
(0.0539 g, 0.17 mmol, 0.44 equiv) and Pd(PPh3)4 (0.0192 g,
0.017 mmol) were added to the reaction mixture under argon. The
reaction mixture was stirred for 72 h at 110 ꢁC. After quenching
with water, the reaction mixture was extracted with CHCl3 and
dried over MgSO4. The product was purified by silica chromatog-
raphy with petrol ether (60e90 ꢁC) as eluent. 7 (0.1395 g, 67%) was
obtained as a yellow solid. Mp >300 ꢁC. 1H NMR (400 MHz, CDCl3)
Supplementary data
The NMR, HRMS spectra and X-ray crystallographic data are
available. Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.tet.2013.12.002.
References and notes
d
7.37 (d, 2H, J¼1.2 Hz), 7.27 (d, 2H, J¼1.2 Hz), 7.11 (s, 2H), 7.10 (s,
2H), 7.10 (s, 2H), 7.09 (s, 2H), 0.35 (s, 18H), 0.34 (s, 36H). 13C NMR
(CDCl3, 100 MHz) 142.77, 142.71, 138.23, 138.17, 138.10, 137.49,
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142.83, 142.74, 138.52, 138.25, 138.17, 137.51, 137.36, 137.30, 137.22,
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d
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Acknowledgements
This research was supported by NSFC (21270255, 51273055,
U1204212), Program for SRFDP (20124103110004), the Natural
Science Foundation of Jiangsu Province (BK2011408), the Opening
Project of Key Laboratory for Chemistry of Low-Dimensional Ma-
terials of Jiangsu Province (JSKC12109), and the Cultivation Fund of
the Key Scientific Innovation Project of Huaiyin Normal University
(11HSGJBZ11). The authors would like to thank Institute of Func-
tional Material Chemistry, NENU, for providing computational
support.
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