Synthesis of benzothieno[2,3-b]thiophenes, [2,3-b:3′,2′-d]- dithienothiophenes and their selenium derivatives via electrophilic cyclization and McMurry cyclization

Article abstract of DOI:10.1016/j.tet.2012.01.088

Benzothieno[2,3-b]thiophenes, [2,3-b:3′,2′-d]- dithienothiophenes, and their selenium derivatives were synthesized in good yields from readily available 3-ethynyllithio-benzo[b]thiophenyllithio compounds, sulfur or selenium, and 2 equiv of acid chlorides.

Full text of DOI:10.1016/j.tet.2012.01.088

Tetrahedron 68 (2012) 5283e5289
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Synthesis of benzothieno[2,3-b]thiophenes, [2,3-b:30,20-d]-dithienothiophenes
and their selenium derivatives via electrophilic cyclization and McMurry
cyclization
,
b,
*
Weizhi Geng a, Hanliu Wang a, Zitao Wang a, Shaoguang Zhang a, Wen-Xiong Zhang a, Zhenfeng Xi a
a Beijing National Laboratory of Molecular Sciences (BNLMS) and Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry,
Peking University, Haidian District, Beijing 100871, China
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry (SIOC), CAS, Shanghai 200032, China
a r t i c l e i n f o
a b s t r a c t
Benzothieno[2,3-b]thiophenes, [2,3-b:30,20-d]-dithienothiophenes, and their selenium derivatives were
synthesized in good yields from readily available 3-ethynyllithio-benzo[b]thiophenyllithio compounds,
sulfur or selenium, and 2 equiv of acid chlorides. Two heteroarene rings were constructed by a twofold
cyclization via an acid chloride-induced electrophilic ring closing and the McMurry cyclization using Zn/
TiCl4 reagents.
Article history:
Received 17 November 2011
Received in revised form 16 December 2011
Accepted 23 December 2011
Available online 3 February 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Benzothieno[2,3-b]thiophene
Dilithio reagent
Dithienothiophene
Electrophilic cyclization
McMurry cyclization
1. Introduction
Benzothieno[2,3-b]thiophenes, dithienothiophenes, and their
selenium derivatives have been increasingly attractive due to their
utility for electronic materials.1 For the further development of new
materials based on thienothiophenes, it is of primary importance to
develop effective synthetic methods to construct thiophene rings.
Chalcogen elements, such as sulfur and selenium, are among the
cheapest and simplest sources.2 A challenge topic is the efficient
cyclization of sulfur- and selenium-containing species. Sashida and
co-workers employed the thiol- or selenol-induced electrophilic
cyclization to construct benzothiophenes and their analogs.2a
Yamaguchi and co-workers developed a double/triple cyclization
to construct thiophene or selenophene-fused polycyclic aromatic
hydrocarbons.3
Although the synthetic methods of dithieno[3,2-b: 20,30-d]
thiophenes (A) are well established,1h,3a,4 the synthetic method
toward [2,3-b:30,20-d]-dithienothiophenes (B) or its seleno de-
rivative (C) is limited (Scheme 1).5e7 In principle, the reported
methods for B type of compounds can be categorized into two
pathways: one is the cyclization of bithiophenyl and (PhSO2)2S as
Scheme 1. Synthetic strategy for benzothieno[2,3-b]thiophenes and their selenium
derivatives via electrophilic cyclization and the McMurry coupling.
* Corresponding author. Tel.: þ86 10 6275 9728; fax: þ86 10 6275 1708; e-mail
address: zfxi@pku.edu.cn (Z. Xi).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.01.088

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W. Geng et al. / Tetrahedron 68 (2012) 5283e5289
reported by Rajca and co-workers,6 the other is the coupling of two
C(sp2)eBr bonds in bis(3-bromothiophen-2-yl)sulfanes.7 There-
fore, it is of great importance to develop general and efficient
methods to synthesize B type of compounds and their selenium
derivatives such as (C) (Scheme 1).
Table 1
Synthesis of benzothieno[2,3-b]thiophene derivatives 2 via electrophilic cyclization
Recently, we reported the synthesis of benzothiophene de-
rivatives from o-lithiophenylethynyllithium via electrophilic cycli-
zation (Scheme 1).11 On the basis of this work, we developed a step-
by-step method to construct unsymmetric benzothieno[2,3-b]
thiophenes 2, [2,3-b:30,20-d]-dithienothiophenes 5, and their sele-
nium derivatives from commercially available 3-ethynylbenzo[b]
thiophene. The first thiophene ring was constructed by using the
electrophilic cyclization and the other one was formed by McMurry
coupling (Scheme 1).
RCOCl
Product 2
Yielda (%)
92b (90%)
2. Results and discussion
71b (63%)
3-Ethynylbenzo[b]thiophene was treated with 2 equiv of t-
BuLi in Et2O for 1 h to afford 3-ethynyllithia-benzo[b]thiophen-2-
yl-lithium 1, a dilithio reagent,12 to which was then added
0.25 equiv of S8 (Table 1). After stirring at room temperature for
2 h, the intermediate 1 was formed and applied for further
reactions.
71
61
When 2 equiv of an acyl chloride was added to 1, an electro-
philic cyclization occurred to afford the corresponding di-
substituted benzothieno[2,3-b]thiophene 2. Acyl chloride with
either alkyl or aromatic substituents could all afford their corre-
sponding benzothieno[2,3-b]thiophenes 2ae2c in moderate to
high isolated yields. Benzoic anhydride and butyric anhydride
could also induce this electrophilic cyclization, leading to the
cyclized products 2a and 2b in 90% and 63% isolated yields, re-
spectively. The structure of 2a has been determined by single-
crystal X-ray structural analysis (Fig. 1). Heteroaromatic acyl
chlorides, such as thiophene-2-carbonyl chloride and 5-methyl-
thiophene-2-carbonyl chloride, were also applicable, yielding 2d,
2e in good yields. Aryl acyl chlorides bearing either electron-
donating or electron-withdrawing substituents on the phenyl
ring could also afford their corresponding products 2f and 2g in
good isolated yields.
70
81
Furthermore, selenium and tellurium were also investigated. As
given in Table 2, when 3-ethynyllithia-benzo[b]-thiophen-2-yl-
lithium was treated with 2 equiv of selenium powder for 2 h, the
intermediate 3 was formed as yellow precipitation and then the
solvent was changed to THF. When 2 equiv of an acyl chloride was
added, a same type of electrophilic cyclization occurred to afford
the corresponding product 4 in this condition. Both alkyl and aro-
matic acyl chloride could all afford their corresponding benzo[b]
selenopheno[3,2-d]thiophenes 4ae4d in moderate yields. Hetero-
aromatic acyl chloride, such as thiophene-2-carbonyl chloride
could also give corresponding product 4e in 68% yields. However,
due to the low solubility of tellurium, when o-lith-
iophenylethynyllithium was treated with 2 equiv of tellurium
powder, the reaction was messy.
77
a
Isolated yields.
The yields in parenthesis were obtained with anhydride.
b
The compounds 2 and 4 featuring two carbonyl groups were
further applied to the synthesis of another thiophene ring. It is
well known that McMurry reaction is an efficient method to
construct C]C and C]X (X¼O, N) bonds.8 The use of low-valent
titanium species for C]C bond formation by intramolecular re-
ductive coupling between carbonyl groups and esters or amides
resulted in the formation of nitrogen-containing heterocycles.
However, the formation of chalcogen-containing heterocycles via
reductive coupling is unknown in the literature. The Mukaiyama
reagent (TiCl4/Zn) was found effective for reductive coupling of
two carbonyl groups in benzothiophenes 2 (and 4). To a well
stirred and cooled solution of 2 in dry dioxane, TiCl4 was added
dropwise under nitrogen atmosphere (Scheme 2). After the
Fig. 1. Single-crystal X-ray structure of 2a with 30% thermal ellipsoids. Hydrogen
atoms are omitted for clarity.

W. Geng et al. / Tetrahedron 68 (2012) 5283e5289
5285
Table 2
Synthesis of benzo[b]selenopheno[3,2-d]thiophene derivatives 4 via electrophilic
cyclization
RCOCl
Product 4
Yield (%)
62
57
77
65
68
Scheme 2. Synthesis of [2,3-b:30,20-d]-dithienothiophenes 5aeg and their selenium
derivatives 5hei via the McMurry cyclization from 2 and 4.
Particularly, the compound 5e bearing two methyl-thiophenyl
groups was an interesting precursor to construct larger planar
p-
conjugated systems as demonstrated by Pei and co-workers.10
mixture was stirred for 30 min, activated Zn powder was added
and then the mixture was refluxed for 9 h. Compounds 2aeg
were applied, aiming at the synthesis of the corresponding [2,3-
b:30,20-d]-dithienothiophenes 5aeg. As given in Scheme 2, the
yields of 5b and 5c were much lower than those of aromatic 5a,
5deg. With these results, we supposed that the stability of
thioesters caused by the aromatic substituted groups showed
significant influence in the reductive cyclization.9 The electron-
donating or electron-withdrawing substituents on the aromatic
rings did not greatly affect the cyclization. The structure of 5b
was determined by single-crystal X-ray structural analysis
(Fig. 2). Under the same condition, the benzo[b]selenopheno[3,2-
d]thiophenes 4d, 4e could also afford their corresponding [2,3-b]-
thieno-[30,20-d]-seleno-selenophenes 5h, 5i in good isolated
yields.
Thus, when 5e was treated with FeCl3, the oxidative CeC bond
formation between two
duced the compound 6 in 87% isolated yield (Scheme 3). According
to the literature, such a large planar -conjugated compound could
a-positions of the thiophene units pro-
p
show helical structure and potential application in organic
materials.6
In 5b, the dihedral angles of C4eC5eC6eC7 and
C5eC6eC7eC8 were 178.92ꢀ and 181.73ꢀ, indicating that all aro-
matic rings were nearly coplanar. From the crystal packing of 5b
ꢀ
(Fig. 3A and B), the distances of S1eS2# (3.579 A) and S1eS3#
ꢀ
(3.509 A) reveal that there exist strong interactions between those
S atoms of neighboring enantiomers. The head-to-head SeS in-
teractions are expected to provide new packing mode for charge
transport.1f
Fig. 2. Single-crystal X-ray structure 5b with 30% thermal ellipsoids. Hydrogen atoms
are omitted for clarity.

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W. Geng et al. / Tetrahedron 68 (2012) 5283e5289
2000) program package for 2a and 5b. The raw frame data were
processed using Crystal Structure (Rigaku/MSC 2000) for 2a and 5b
to yield the reflection data file. The structures of 2a and 5b were
solved by use of SHELXTL program. Refinement was performed on
F2 anisotropically for all the non-hydrogen atoms by the full-matrix
least-squares method. The hydrogen atoms were placed at the
calculated positions and were included in the structure calculation
without further refinement of the parameters. Crystallographic
data (excluding structure factors) have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publi-
cation nos. 2a (CCDC-790434) and 5b (CCDC-790435). Copies of
these data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_-
request/cif.
1H and 13C NMR spectra were recorded on a JEOL JNM-AL300
spectrometer (FT, 300 MHz for 1H; 75 MHz for 13C), a Varian Mer-
cury 300 spectrometer (FT, 300 MHz for 1H; 75 MHz for 13C) or
a Bruker ARX400 spectrometer (FT, 400 MHz for 1H; 100 MHz for
13C) at room temperature, unless otherwise noted. Infrared spectra
(IR) were recorded on a Thermo Nicolet Avatar 330 FT-IR spec-
trometer. High-resolution mass spectra (HRMS) were recorded on
a Bruker Apex IV FTMS mass spectrometer using ESI (electrospray
ionization).
Fig. 3. SeS interaction in crystal packing in 5b. (A) Top view of crystal packing (B) S/S
distance in crystal packing.
4.2. Typical procedure for the preparation of benzothieno
[2,3-b]thiophenes 2aeg
In a 25 mL flask, t-BuLi (2 mmol, 1.6 M in pentane) was added
dropwise at ꢁ78 ꢀC to a stirred solution of 3-ethynylbenzo[b]
thiophene (1 mmol, 158 mg) in Et2O (5 mL) and the reaction mix-
ture was allowed to warm to room temperature. After stirring at
room temperature for 1 h, S8 (0.25 mmol, 64 mg) was added and
the reaction was stirred at room temperature for 2 h. The solvent of
the reaction mixture was evaporated under vacuum and THF (5 mL)
was added. After that, acid chloride (2 mmol) was added dropwise
at room temperature. After stirring at room temperature for 1 h, the
solvent of the reaction mixture was evaporated under vacuum. The
residue was purified by chromatography to give products 2ael.
Scheme 3. Synthesis of compound 6 via oxidative coupling of 5e.
3. Conclusion
In summary, we reported the synthesis of benzothieno[2,3-b]
thiophenes, [2,3-b:30,20-d]-dithienothiophenes, and their selenium
derivatives from readily available dilithio reagents, sulfur or sele-
nium, and 2 equiv of acid chlorides. By carefully controlling the
amount of sulfur or selenium, the first 2-thio-thiophene ring could
be conveniently constructed by acid chloride-induced electrophilic
cyclization. The second thiophene ring was achieved by C]C
double bond formation via the McMurry reaction. Study on the
opto-electronic property of these derivatives will be reported in
due course.
4.2.1. S-3-Benzoylbenzothieno[2,3-b]thiophen-2-yl
benzothioate
(2a). Yellow solid (mp 152.2e153.2 ꢀC), isolated yield 92%
(396 mg); 1H NMR (400 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼7.16e8.16 (m,
13
14H, CH); C NMR (100 MHz, CDCl3, Me4Si, 25 ꢀC):
d¼122.24 (1
CH), 122.97 (1 CH), 124.75 (1 CH), 124.86 (1 CH), 126.68 (1 quat. C),
127.59 (2 CH),128.72 (4 CH),129.91 (2 CH),131.56 (1 quat. C),134.00
(1 CH), 134.09 (1 CH), 135.31 (1 quat. C), 137.06 (1 quat. C), 139.35 (1
quat. C), 140.71 (1 quat. C), 142.88 (1 quat. C), 143.12 (1 quat. C),
188.50 (1 quat. C), 192.33 (1 quat. C). HRMS calcd for C24H14O2S3
[MþH]þ: 431.0229, found 431.0237.
4. Experimental section
4.1. General information
Unless otherwise noted, all starting materials were commer-
cially available and were used without further purification. Solvents
were purified by an Mbraun SPS-800 Solvent Purification System
and dried over fresh Na chips in the glovebox. t-BuLi was obtained
from Acros. All reactions were carried out under a dry and oxygen-
free nitrogen atmosphere in slight positive pressure by using
Schlenk techniques or under a nitrogen atmosphere in a Mikrouna
Super (1220/750) Glovebox. The nitrogen in the glovebox was
constantly circulated through a copper/molecular sieve catalyst
unit. The oxygen and moisture concentrations in the glovebox at-
mosphere were monitored by an O2/H2O Combi-Analyzer to ensure
both were always below 1 ppm.
4.2.2. S-3-Butyrylbenzothieno[2,3-b]thiophen-2-yl
(2b). Yellow oil, isolated yield 71% (257 mg); 1H NMR (400 MHz,
CDCl3, Me4Si, 25 ꢀC):
butanethioate
d
¼0.99 (t, J¼7.4 Hz, 3H, CH3), 1.00 (t, J¼7.4 Hz,
3H, CH3), 1.73e1.83 (m, 4H, CH2), 2.68 (t, J¼7.3 Hz, 2H, CH2), 2.96 (t,
J¼7.3 Hz, 2H, CH2), 7.34e7.38 (m, 2H, CH), 7.78e7.87 (m, 2H, CH);
13C NMR (100 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼13.39 (1 CH3), 13.79 (1
CH3), 17.53 (1 CH2), 18.87 (1 CH2), 45.06 (1 CH2), 46.12 (1 CH2),
122.27 (1 CH), 123.01 (1 CH), 124.86 (1 CH), 125.00 (1 CH), 125.84 (1
quat. C), 131.76 (1 quat. C), 138.85 (1 quat. C), 142.32 (1 quat. C),
142.57 (1 quat. C), 143.17 (1 quat. C), 195.96 (1 quat. C), 201.42 (1
quat. C). HRMS calcd for C18H18O2S3 [MþNa]þ: 385.0361, found
385.0359.
Single crystals of 2a and 5b suitable for X-ray analysis were
grown in CH2Cl2/hexane at room temperature for 3 days. Data
collections for 2a and 5b were performed at ꢁ100 ꢀC on a RIGAKU
CCD SATURN 724 diffractometer, using graphite-monochromated
4.2.3. S-3-Decanoylbenzothieno[2,3-b]thiophen-2-yl decanethioate
(2c). Yellow oil, isolated yield 71% (376 mg); 1H NMR (300 MHz,
ꢀ
Mo K
a
radiation (
l
¼0.71073 A). The determination of crystal class
and unit cell parameters was carried out by Rapid-AUTO (Rigaku
CDCl3, Me4Si, 25 ꢀC):
d
¼0.84e0.90 (m, 6H, CH3), 1.27 (br s, 24H,

W. Geng et al. / Tetrahedron 68 (2012) 5283e5289
5287
CH2), 1.69e1.79 (m, 4H, CH2), 2.68 (t, J¼7.5 Hz, 2H, CH2), 2.96 (t,
mixture was allowed to warm to room temperature. After stirring
at room temperature for 1 h, Se (2 mmol, 160 mg) was added and
the reaction was stirred at room temperature for 2 h. The solvent of
the reaction mixture was evaporated under vacuum and THF (5 mL)
was added. After that, acid chloride (2 mmol) was added dropwise
at room temperature. After stirring at room temperature for 1 h, the
solvent of the reaction mixture was evaporated under vacuum. The
residue was purified by chromatography to give products 4aee.
J¼7.2 Hz, 2H, CH2), 7.34e7.37 (m, 2H, CH), 7.77e7.86 (m, 2H, CH), 13
C
NMR (75 MHz, CDCl3, Me4Si, 25 ꢀC):
d¼14.47 (2 CH3), 23.03 (2 CH2),
24.44 (1 CH2), 25.74 (1 CH2), 29.29 (1 CH2), 29.58 (1 CH2), 29.60 (1
CH2), 29.63 (1 CH2), 29.72 (1 CH2), 29.78 (1 CH2), 29.81 (1 CH2),
30.07 (1 CH2), 32.20 (1 CH2), 32.22 (1 CH2), 43.72 (1 CH2), 44.65 (1
CH2), 122.71 (1 CH), 123.40 (1 CH), 125.26 (1 CH), 125.40 (1 CH),
126.28 (1 quat. C), 132.18 (1 quat. C), 139.28 (1 quat. C), 142.74 (1
quat. C), 142.96 (1 quat. C), 143.58 (1 quat. C), 196.48 (1 quat. C),
201.95 (1 quat. C). UVevis (CH2Cl2): lmax¼233 nm. HRMS calcd for
C30H42O2S3 [MþH]þ: 531.2420, found 531.2420.
4.3.1. Se-3-Butyrylbenzoylbenzo[b]selenopheno[3,2-d]thiophen-2-yl
butanethioate (4a). Yellow oil, isolated yield 62% (284 mg); 1H NMR
(400 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼0.87e1.17 (m, 6H, CH3),
4.2.4. S-3-(Thiophene-2-carbonyl)benzothieno[2,3-b]thiophen-2-yl
thiophene-2-carbothioate (2d). Yellow solid (mp 69.7e71.5 ꢀC),
isolated yield 61% (267 mg); 1H NMR (300 MHz, CDCl3, Me4Si,
1.16e1.77 (m, 4H, CH2), 2.61e2.84 (m, 4H, CH2), 7.20e7.29 (m, 2H,
CH), 7.55e7.73 (m, 2H, CH); 13C NMR (100 MHz, CDCl3, Me4Si,
25 ꢀC):
d
¼13.30 (1 CH3), 13.80 (1 CH3), 17.33 (1 CH2), 18.72 (1 CH2),
25 ꢀC):
25 ꢀC):
d
¼6.92e7.82 (m, 10H, CH); 13C NMR (75 MHz, CDCl3, Me4Si,
46.47 (1 CH2), 48.62 (1 CH2), 121.41 (1 CH), 122.91 (1 CH), 123.47 (1
quat. C), 124.25 (1 CH), 124.64 (1 CH), 132.63 (1 quat. C), 139.39 (1
quat. C), 144.17 (1 quat. C), 144.20 (1 quat. C), 144.64 (1 quat. C),
199.41 (1 quat. C), 204.14 (1 quat. C). HRMS calcd for C18H18O2SSe2
[MþH]þ: 458.9441, found 458.9433.
d¼122.16 (1 CH), 123.04 (1 CH), 124.89 (1 CH), 124.99 (1 CH),
128.19 (1 CH),128.70 (1 CH),131.44 (1 quat. C),132.66 (1 CH),133.79
(1 quat. C), 134.44 (1 CH), 135.56 (1 quat. C), 136.22 (1 CH), 136.74 (1
CH), 138.93 (1 quat. C), 139.59 (1 quat. C), 140.49 (1 quat. C), 143.08
(1 quat. C), 143.81 (1 quat. C), 180.49 (1 quat. C), 184.22 (1 quat. C).
HRMS calcd for C20H10O2S5 [MþH]þ: 442.9357, found 442.9359.
4.3.2. Se-(3-Heptanoyl)benzoylbenzo[b]selenopheno[3,2-d]
thio-
phen-2-yl heptaneselenoate (4b). Yellow oil, isolated yield 57%
1
4.2.5. S-3-(5-Methylthiophene-2-carbonyl)benzothieno[2,3-b] thio-
(309 mg); H NMR (300 MHz, CDCl3, Me4Si, 25 ꢀC):
d¼0.77e0.83
phen-2-yl 5-methylthiophene-2-carbothioate (2e). Yellow solid, iso-
(m, 6H, CH3), 1.18e1.32 (m, 12H, CH2), 1.58e1.72 (m, 4H, CH2),
2.64e2.69 (t, J¼7.5 Hz, 2H, CH2), 2.82e2.87 (t, J¼7.5 Hz, 2H, CH2),
7.24e7.28 (m, 2H, CH), 7.56e7.76 (m, 2H, CH); 13C NMR (75 MHz,
1
lated yield 70% (329 mg); H NMR (300 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼2.46 (s, 3H, CH3), 2.47 (s, 3H, CH3), 6.65e7.72 (m, 8H, CH); 13C NMR
(75 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼15.86 (1 CH3), 16.18 (1 CH3), 122.02
CDCl3, Me4Si, 25 ꢀC):
d
¼13.96 (1 CH3), 14.00 (1 CH3), 22.35 (1 CH2),
(1 CH), 122.93 (1 CH), 126.70 (1 CH), 126.91 (1 CH), 127.55 (1 CH),
131.41 (1 CH), 133.27 (1 quat. C), 135.42 (1 CH), 136.43 (1 quat. C),
136.93 (1 quat. C),137.617 (1 CH),138.87 (1 quat. C),140.37 (1 quat. C),
141.54 (1 quat. C),143.00 (1 quat. C),149.82 (1 quat. C),150.81 (1 quat.
C), 152.80 (1 quat. C), 179.93 (1 quat. C), 183.646(1 quat. C). HRMS
calcd for C22H14O2S5 [MþH]þ: 470.9676, found 470.9667.
22.47 (1 CH2), 23.81 (1 CH2), 25.14 (1 CH2), 28.44 (1 CH2), 28.85 (1
CH2), 31.33 (1 CH2), 31.53 (1 CH2), 44.64 (1 CH2), 46.94 (1 CH2),
121.50 (1 CH), 122.95 (1 CH), 123.56 (1 quart. C), 124.30 (1 CH),
124.69 (1 CH), 132.73 (1 quart. C), 139.48 (1 quart. C), 144.25 (1
quart. C), 144.30 (1 quart. C), 144.66(1 quart. C), 199.52 (1 quart. C),
204.28 (1 quart. C). HRMS calcd for C24H30O2SSe2 [MþH]þ:
543.0373, found 543.0386.
4.2.6. S-3-(4-Methoxybenzoyl)benzothieno[2,3-b]thiophen-2-yl 4-
methoxybenzothioate (2f). Yellow solid, isolated yield 81%
4.3.3. Se-3-Benzoylbenzo[b]selenopheno[3,2-d]thiophen-2-yl benzo-
1
(397 mg); H NMR (300 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼3.78 (s, 3H,
thioate (4c). Yellow solid, isolated yield 77% (405 mg); 1H NMR
CH3), 3.82 (s, 3H, CH3), 6.84e6.88 (m, 4H, CH), 7.16e7.45 (m, 4H,
(300 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼7.10e7.60 (m, 10H, CH),
7.77e7.81 (m, 2H, CH), 7.96e7.98 (m, 2H, CH); 13C NMR (75 MHz,
CDCl3, Me4Si, 25 ꢀC):
CH), 7.77e8.00 (m, 4H, CH); 13C NMR (75 MHz, CDCl3, Me4Si, 25 ꢀC):
d¼55.43 (1 CH3), 55.52 (1 CH3), 113.93 (2 CH), 114.01 (2 CH), 122.18
d¼121.98 (1 CH), 122.76 (1 CH), 124.13 (1 CH),
(1 quat. C), 122.96 (1 quat. C), 124.74 (2 CH), 126.28 (1 quat. C),
128.08 (1 quat. C), 129.98 (2 CH), 130.06 (1 quat. C), 131.63 (1 quat.
C), 132.50 (2 CH), 139.23 (1 quat. C), 141.05 (1 quat. C), 142.69 (1
quat. C), 143.09 (1 quat. C), 164.31 (1 quat. C), 164.34 (1 quat.
C),186.99 (1 quat. C), 190.97 (1 quat. C). HRMS calcd for C26H18O4S3
[MþH]þ: 491.0440, found 491.0449.
124.51 (1 CH), 125.46 (1 quat. C), 127.39 (2 CH), 128.85 (2 CH),
129.04 (2 CH),130.05 (2 CH),132.73 (1 quat. C),134.13 (1 CH),134.40
(1 CH), 136.74 (1 quat. C), 137.26 (1 quat. C), 140.25 (1 quat. C),
141.53 (1 quat. C), 144.25 (1 quat. C), 144.40 (1 quat. C), 192.28 (1
quat. C), 194.43 (1 quat. C). HRMS calcd for C24H14O2SSe2 [MþNa]þ:
548.8940, found 548.8948.
4.2.7. S-3-(3-Chlorobenzoyl)benzothieno[2,3-b]thiophen-2-yl 3-
4.3.4. Se-3-(4-Hexylbenzoyl)benzoylbenzo[b]selenopheno[3,2-d]thi-
chlorobenzothioate (2g). Yellow solid, isolated yield 77% (383 mg);
ophen-2-yl-4-hexylbenzothioate (4d). Yellow oil, isolated yield 65%
1
1H NMR (300 MHz, CDCl3, Me4Si, 25 ꢀC):
13C NMR (75 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼7.19e7.98 (m, 12H, CH);
(451 mg); H NMR (300 MHz, CDCl3, Me4Si, 25 ꢀC):
d¼0.89e0.92
d¼122.12 (1 CH), 123.08 (1
(m, 6H, CH3), 1.28e1.33 (m, 12H, CH2), 1.58e1.63 (m, 4H, CH2),
2.60e2.66 (m, 4H, CH2), 7.15e7.43 (m, 8H, CH) , 7.71e7.95 (m, 4H,
CH), 124.87 (1 CH), 125.07 (1 CH), 125.68 (1 quat. C), 126.22 (1 CH),
127.45 (1 CH), 128.24 (1 CH), 129.37 (1 CH), 130.07 (1 CH), 130.08 (1
CH), 131.26 (1 quat. C), 134.00 (1 quat. C), 134.09 (1 quat. C), 135.03
(2 quat. C), 136.50 (1 quat. C), 138.46 (1 quat. C), 139.23 (1 quat. C),
140.07 (1 quat. C), 143.07 (1 quat. C), 143.33 (1 quat. C),187.35 (1
quat. C), 190.90 (1 quat. C). HRMS calcd for C24H12Cl2O2S3 [MþH]þ:
498.9449, found 498.9449.
CH); 13C NMR (75 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼13.99 (2 CH3), 22.44
(1 CH2), 22.46 (1 CH2), 28.77 (2 CH2), 30.75 (1 CH2), 30.81 (1 CH2),
31.51 (2 CH2), 35.94 (1 CH2), 35.99 (1 CH2), 121.96 (1 CH), 122.62 (1
CH), 123.94 (1 CH), 124.34 (1 CH), 122.55 (1 quart. C), 127.46 (2 CH),
128.83 (2 CH), 128.92 (2 CH), 130.15 (2 CH), 132.74 (1 quart. C),
134.48 (1 quart. C), 134.82 (1 quart. C), 140.16 (1 quart. C), 141.33(1
quart. C), 144.05 (1 quart. C), 144.18 (1 quart. C), 149.98 (1 quart. C),
150.39 (1 quart. C), 191.59 (1 quart. C), 194.02 (1 quart. C). HRMS
calcd for C36H38O2SSe2 [MþH]þ: 695.1001, found 695.1016.
4.3. Typical procedure for the preparation of benzo[b]
selenopheno[3,2-d]thiophenes 4aee
In a 25 mL flask, t-BuLi (2 mmol, 1.6 M in pentane) was added
dropwise at ꢁ78 ꢀC to a stirred solution of 3-ethynylbenzo[b]
thiophene (1 mmol, 158 mg) in Et2O (5 mL) and the reaction
4.3.5. Se-3-(Thiophene-2-carbonyl)
benzoylbenzo[b]selenopheno
[3,2-d]thiophen-2-yl thiophene-2-carbothioate (4e). Yellow solid,
isolated yield 68% (366 mg); 1H NMR (300 MHz, CDCl3, Me4Si,

5288
W. Geng et al. / Tetrahedron 68 (2012) 5283e5289
25 ꢀC):
d
¼6.98e7.79 (m, 10H, CH); 13C NMR (75 MHz, CDCl3, Me4Si,
C), 135.20 (1 quat. C), 135.89 (1 quat. C), 136.22 (1 quat. C), 138.52 (1
quat. C), 140.07 (1 quat. C), 141.33 (1 quat. C), 142.77 (1 quat. C).
HRMS calcd for C20H10S5 [MþH]þ: 410.9459, found 410.9454.
25 ꢀC): 121.91 (1 CH), 122.77 (1 CH), 124.23 (1 CH), 124.60 (1 CH),
125.14 (1 quart. C), 128.24 (1 CH), 128.74 (1 CH), 132.62 (1 quart. C),
132.82 (1 CH), 134.82 (1 CH), 136.24 (1 CH), 136.69 (1 CH), 139.80 (1
quart. C), 141.15 (1 quart. C), 141.33 (1 quart. C), 143.68 (1 quart. C),
144.17(1 quart. C), 144.72 (1 quart. C), 182.50 (1 quart. C), 186.28 (1
quart. C). HRMS calcd for C20H10O2S3Se2 [MþH]þ: 538.8254, found
538.8246.
4.4.5. 2,3-Bis(5-methylthiophen-2-yl)benzo[2,3-b:30,20-d]-dithieno-
thiophene (5e). White solid, isolated yield 71% (310 mg); 1H NMR
(300 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼2.39 (s, 3H, CH3), 2.62 (s, 3H,
CH3), 6.30e7.22 (m, 8H, CH); 13C NMR (75 MHz, CDCl3, Me4Si,
25 ꢀC):
d¼15.28 (1 CH3), 15.63 (1 CH3), 122.12 (1 quat. C), 122.59 (1
4.4. Typical procedure for the preparation of compound 5
CH), 123.27 (1 CH), 123.48 (1 CH), 124.25 (1 CH), 125.02 (1 CH),
125.73 (1 CH), 125.75 (1 CH), 130.47 (2 CH), 132.23 (1 quat. C),
133.64 (1 quat. C), 133.69 (1 quat. C), 134.48 (1 quat. C), 138.90 (1
quat. C), 139.80 (1 quat. C), 141.09 (1 quat. C), 141.39 (1 quat. C),
142.58 (1 quat. C), 142.74 (1 quat. C), 144.26(1 quat. C). HRMS calcd
for C22H14S5[MþH]þ: 438.9772, found 438.9763.
To a solution of 2 or 4 (1 mmol) in dry dioxane (50 mL), the
mixture was cooled to 0 ꢀC and TiCl4 (0.33 mL, 3 mmol) was added
dropwise under nitrogen atmosphere. After stirring at 0 ꢀC for
0.5 h, Zn powder (0.39 g, 6 mmol) was added in small lots and then
the mixture was refluxed for 9 h. The reaction mixture was
quenched by H2O and the product was extracted by Et2O. The
solvent of the organic layer was evaporated under vacuum. The
residue was purified by chromatography to give the products 5aei.
4.4.6. 2,3-Bis(4-methoxyphenyl)benzo[2,3-b:30,20-d]-dithienothio-
phene (5f). Yellow solid, isolated yield 74% (339 mg); 1H NMR
(300 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼3.75 (s, 3H, CH3), 3.89 (s, 3H,
CH3), 6.15 (d, J¼8.1 Hz, 1H, CH), 6.75 (d, J¼8.7 Hz, 2H, CH),
6.84e6.88 (m, 3H, CH), 7.13e7.19 (m, 3H, CH), 7.32 (d, J¼8.4 Hz, 2H,
CH), 7.71 (d, J¼8.1 Hz, 1H, CH); 13C NMR (75 MHz, CDCl3, Me4Si,
4.4.1. 2,3-Diphenylbenzo[2,3-b:30,20-d]-dithienothiophene
(5a). White solid (mp 192.0e193.5 ꢀC), isolated yield 63% (249 mg);
1H NMR (300 MHz, CDCl3, Me4Si, 25 ꢀC):
d¼5.74e5.77 (m, 1H, CH),
25 ꢀC):
d
¼55.14 (1 CH3), 55.38 (1 CH3), 113.68 (2 CH), 114.05 (2 CH),
13
6.63e7.51(m, 13H, CH); C NMR (75 MHz, CDCl3, Me4Si, 25 ꢀC):
122.63 (1 CH), 123.29 (1 CH), 123.54 (1 CH), 124.04 (1 CH), 126.91 (1
quat. C), 129.24 (1 quat. C), 130.08 (1 quat. C), 130.25 (2 CH), 130.51
(1 quat. C), 132.21 (2 CH), 133.79 (1 quat. C), 135.47 (1 quat. C),
139.60 (1 quat. C), 141.01 (1 quat. C), 141.47 (1 quat. C), 142.79 (1
quat. C), 158.79 (1 quat. C), 159.46 (1 quat. C). HRMS calcd for
C26H18O2S3 [MþH]þ: 459.0542, found 459.0548.
d
¼122.64 (1 CH), 123.38 (1 CH), 123.51 (1 CH), 124.05 (1 CH), 127.42
(1 CH), 128.14 (1 CH), 128.30 (2 CH), 128.72 (2 CH), 129.11 (2 CH),
131.20 (2 CH), 131.55 (1 quat. C), 132.24 (1 quat. C), 133.77 (1 quat. C),
134.37 (1 quat. C), 136.41 (1 quat. C), 137.18 (1 quat. C), 139.87 (1 quat.
C),140.96 (1 quat. C),141.51 (1 quat. C),142.84(1 quat. C). HRMS calcd
for C24H14S3 [MþH]þ: 399.0330, found 399.0324.
4.4.7. 2,3-Bis(3-chlorophenyl)benzo[2,3-b:30,20-d]-dithienothiophene
4.4.2. 2,3-Dipropylbenzo[2,3-b:30,20-d]-dithienothiophene
(5g). Yellow solid, isolated yield 75% (350 mg); 1H NMR (300 MHz,
(5b). Colorless solid (mp 78.0e81.2 ꢀC): isolated yield 28% (95 mg);
CDCl3, Me4Si, 25 ꢀC):
CDCl3, Me4Si, 25 ꢀC):
d
¼6.94e7.62 (m, 12H, CH); 13C NMR (75 MHz,
1H NMR (300 MHz, CDCl3, Me4Si, 25 ꢀC):
d¼1.04e1.14 (m, 6H, CH3),
d¼122.84 (1 CH), 123.06 (1 CH), 123.61 (1 CH),
1.72e1.83 (m, 4H, CH2), 2.86 (t, J¼7.5 Hz, 2H, CH2), 3.10 (t, J¼7.8 Hz,
124.28 (1 CH), 127.26 (1 CH), 127.77 (1 CH), 128.58 (1 CH), 129.11 (1
CH), 129.31 (1 CH), 129.63 (1 CH), 130.05 (1 CH), 130.46 (2 quat. C),
131.01 (1 quat. C),131.98 (1 quat. C),133.30 (1 quat. C),134.26 (1 quat.
C), 134.72 (1 quat. C), 135.63 (1 quat. C), 137.14 (1 quat. C), 138.47 (1
quat. C),140.18 (1 quat. C),140.32 (1 quat. C),142.82 (1 quat. C). HRMS
calcd for C24H12Cl2S3 [MþH]þ: 466.9556, found 466.9556.
2H, CH2), 7.32e7.47 (m, 2H, CH), 7.85 (d, J¼7.8 Hz, 1H, CH), 8.19 (d,
J¼7.8 Hz, 1H, CH); 13C NMR (75 MHz, CDCl3, Me4Si, 25 ꢀC):
¼13.69
d
(1 CH3), 13.90 (1 CH3), 24.81 (1 CH2), 25.17 (1 CH2), 30.86 (1 CH2),
31.15 (1 CH2), 122.61 (1 CH), 123.33 (1 CH), 123.38 (1 CH), 124.44 (1
CH), 130.52 (1 quat. C), 132.66 (1 quat. C), 133.69 (1 quat. C), 134.77
(1 quat. C), 139.57 (1 quat. C), 139.83 (1 quat. C), 141.55 (1 quat. C),
143.06 (1 quat. C). HRMS calcd for C18H18S3 [MþH]þ: 331.0643,
found 331.0639.
4.4.8. 2,3-Bis(5-methylthiophen-2-yl)benzo[2,3-b]-thieno-[30,20-d]-
seleno-selenophene (5h). White solid (mp 218.2e219.5 ꢀC, decom-
posed), isolated yield 68% (344 mg); 1H NMR (300 MHz, CDCl3,
4.4.3. 2,3-Didecanoylbenzo[2,3-b:30,20-d]-dithienothiophene
Me4Si, 25 ꢀC):
Me4Si, 25 ꢀC):
d
¼6.88e7.72 (m, 10H, CH); 13C NMR (75 MHz, CDCl3,
(5c). Yellow oil, isolated yield 24% (119 mg); 1H NMR (300 MHz,
d
¼122.30 (1 CH), 123.13 (1 CH), 123.51 (1 CH), 123.97
CDCl3, Me4Si, 25 ꢀC):
d¼0.84e0.90 (m, 6H, CH3), 1.25e1.49 (m, 24H,
(1 CH), 126.58 (1 CH), 126.74 (1 CH), 126.76 (1 CH), 127.81 (1 CH),
128.16 (1 CH), 130.87 (1 CH), 133.54 (2 quat. C), 133.78 (1 quat. C),
136.97 (1 quat. C), 137.96 (1 quat. C), 137.97 (1 quat. C), 140.51 (1
quat. C),143.48(1 quat. C),143.83 (1 quat. C),14.38 (1 quat. C). HRMS
calcd for C20H10S3Se2 [MþH]þ: 506.8348, found 506.8354.
CH2), 1.68e1.73 (m, 4H, CH2), 2.80 (t, J¼7.8 Hz, 2H, CH2), 3.03 (t,
J¼7.8 Hz, 2H, CH2), 7.25e7.40 (m, 2H, CH), 7.76e7.78 (m, 1H, CH),
13
8.12e8.15 (m, 1H, CH); C NMR (75 MHz, CDCl3, Me4Si, 25 ꢀC):
d¼14.12 (2 CH3), 22.67 (2 CH2), 22.69 (2 CH2), 29.03 (1 CH2), 29.09
(1 CH2), 29.30 (1 CH2), 29.35 (1 CH2), 29.36 (1 CH2), 29.45 (1 CH2),
29.55 (1 CH2), 29.59 (1 CH2), 31.70 (1 CH2), 31.87 (1 CH2), 31.90 (1
CH2), 31.94 (1 CH2), 122.62 (1 CH), 123.23 (1 CH), 123.29 (1 CH),
124.33 (1 CH), 130.55 (1 quat. C), 132.63 (1 quat. C), 133.68 (1 quat.
C), 134.70 (1 quat. C), 139.50 (1 quat. C), 139.79 (1 quat. C), 141.50 (1
quat. C), 143.02 (1 quat. C). HRMS calcd for C30H42S3 [MþH]þ:
498.2449, found 498.2447.
4.4.9. 2,3-Bis(4-hexylphenyl)benzo[2,3-b]-thieno-[30,20-d]-seleno-se-
lenophene (5i). Yellow solid (mp 152.4e153.8 ꢀC), isolated yield
72% (477 mg); 1H NMR (300 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼0.83e0.93 (m, 6H, CH3), 1.23e1.69 (m, 16H, CH2), 2.49 (t,
J¼7.5 Hz, 2H, CH2), 2.67 (t, J¼7.5 Hz, 2H, CH2), 5.77 (d, J¼6 Hz, 1H,
CH), 6.71 (t, J¼7.5 Hz, 1H, CH), 6.94e7.27 (m, 9H, CH), 7.66 (d,
J¼6 Hz, 1H, CH); 13C NMR (75 MHz, CDCl3, Me4Si, 25 ꢀC):
¼14.09 (1
d
4.4.4. 2,3-Di(thiophen-2-yl)benzo[2,3-b:30,20-d]-dithienothiophene
CH3), 14.18 (1 CH3), 22.59 (1 CH2), 22.70 (1 CH2), 28.90 (1 CH2),
29.00 (1 CH2), 31.14 (1 CH2), 31.67 (1 CH2), 31.81 (1 CH2), 31.94 (1
CH2), 35.56 (1 CH2), 35.85 (1 CH2),122.16 (1 CH), 122.82 (1 CH),
123.43 (1 CH), 124.20 (1 CH), 128.12 (2 CH), 128.84 (2 CH), 129.15 (2
CH), 131.08 (2 CH), 133.51 (1 quart. C), 133.80 (1 quart. C), 134.45 (1
quart. C), 135.32 (1 quart. C), 135.59(1 quart. C), 137.30 (1 quart. C),
140.02 (1 quart. C), 141.99 (1 quart. C), 142.83 (1 quart. C), 143.98 (1
(5d). Yellow solid, isolated yield 66% (269 mg); 1H NMR (300 MHz,
CDCl3, Me4Si, 25 ꢀC):
d
¼6.13 (d, J¼7.5 Hz, 1H, CH), 6.92e7.32 (m, 7H,
CH), 7.62e7.74 (m, 2H, CH); 13C NMR (75 MHz, CDCl3, Me4Si, 25 ꢀC):
d
¼122.43 (1 quat. C), 122.68 (1 CH), 123.03 (1 CH), 123.61 (1 CH),
124.42 (1 CH), 125.94 (1 CH), 126.43 (1 CH), 126.75 (1 CH), 127.79 (1
CH), 128.12 (1 CH), 130.64 (1 CH), 132.18 (1 quat. C), 133.60 (1 quat.

W. Geng et al. / Tetrahedron 68 (2012) 5283e5289
5289
Chem. 2010, 75, 1652e1658; (d) Sanz, R.; Guilarte, V.; Hernando, E.; Sanjuan, A.
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quart. C), 144.22 (1 quart. C) 147.39 (1 quart. C). HRMS calcd for
C36H38SSe2 [MþH]þ: 663.1109, found 663.1103.
4.5. Preparation of compound 6
3. (a) Okamoto, T.; Kudoh, K.; Wakamiya, A.; Yamaguchi, S. Org. Lett. 2005, 7,
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To a solution of 5e (88 mg, 0.1 mmol) in 150 mL of dry
dichloromethane was added a solution of FeCl3 (98 mg, 0.6 mmol)
in CH3NO2 (1 mL) at 0 ꢀC. After 15 min, 30 mL of anhydride meth-
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isolated yield 87% (76 mg); UVevis (CH2Cl2): lmax¼291, 324 nm.
HRMS calcd for C22H14S5[MþH]þ: 436.9615, found 436.9617. Anal.
calcd for C22H14S5: C, 60.51; H, 2.77. Found C, 60.47; H, 2.78.
Acknowledgements
The authors thank Prof. Jian Pei and Mr. Yan Zhou at Peking
University for discussion and support on experiments. This work
was supported by the Natural Science Foundation of China and the
Major State Basic Research Development Program (2011CB808705).
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Supplementary data
Supplementary data (experimental procedures, X-ray single-
crystal structural data for 2a and 5b, characterization data for all
new compounds, and copies of NMR spectra). Supplementary data
related to this article can be found online at doi:10.1016/
j.tet.2012.01.088.
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