Insights into the reaction of trans-diarylethenes with thionyl chloride: A practical synthesis of chlorobenzo[b]thiophenes

Article abstract of DOI:10.1016/j.tet.2011.09.060

The reactivity of a variety of trans-1,2-diarylethenes with thionyl chloride has been investigated. All the substrates could readily afford 3-chlorobenzo[b]thiophenes in moderate yields and a pair of threo- and erythro-1,2-dichloro-1,2-diarylethanes as th

Full text of DOI:10.1016/j.tet.2011.09.060

Tetrahedron 67 (2011) 8865e8872
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Insights into the reaction of trans-diarylethenes with thionyl chloride: a practical
synthesis of chlorobenzo[b]thiophenes
*
Jie Han , Qiong Wang, Xiaoyong Chang, Yuxin Liu, Yanmei Wang, Jiben Meng
Department of Chemistry and State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 August 2011
Received in revised form 7 September 2011
Accepted 16 September 2011
Available online 22 September 2011
The reactivity of a variety of trans-1,2-diarylethenes with thionyl chloride has been investigated. All the
substrates could readily afford 3-chlorobenzo[b]thiophenes in moderate yields and a pair of threo- and
erythro-1,2-dichloro-1,2-diarylethanes as the minor products under mild condition. The diastereoisomers
of 1,2-dichloro-1,2-diarylethanes with a methoxy group on the benzene ring were found for the first time
to be also converted into cholobenzo[b]thiophenes under treatment of thionyl chloride. The chemical
transformations have been mechanistically rationalized and successfully applied to a one-pot synthesis
of novel fluorescent liquid crystalline compounds containing benzo[b]thiophene and 1,3,4-oxadiazole
units. Their spectroscopic and mesogenic behaviours are also described.
Keywords:
Benzo[b]thiophene
trans-Diarylethene
Thionyl chloride
Oxadiazole
Ó 2011 Elsevier Ltd. All rights reserved.
Liquid crystals
1. Introduction
include that the reaction precursors are readily available, and most of
the synthetic routes are very short, practical and free of expensive
Benzo[b]thiophene and its related derivatives have been exten-
sively documented as bioactive substances1 as well as optoelectronic
materials.2 To date, much work has been done to develop new and
convenient synthetic approaches to benzo[b]thiophenes.3,4 These
approaches may be categorized into two major types according to the
source of sulfur: one is from organic sulfur source; the other is from
inorganic sulfur source. As for the former, many kinds of sulfur-
containing precursors, such as ortho sulfur-containing arylalkynes5
and styrene,4b,6 2-mercaptobenzaldehydes,7 2-methylsulfanyl ben-
zamides,8 polarized ketene dithioacetals,9 methylthiobenzene,10 and
thio-ketones11 have been used for syntheses of various benzo[b]
thiophenes. Although most of the methods are quite efficient, they
usually suffer from certain drawbacks: (1) most of the reaction pre-
cursors are not commercially available, and should be prepared via
multi-step procedures using unpleasant organic sulfur-containing
reagents; (2) these synthetic methods often use expensive transi-
tion metal-catalysts, and the reactions should be carried out under
rigid conditions, such as anhydrous and free of oxygen. In contrast,
examples of syntheses of benzo[b]thiophenes using inorganic sulfur
sources are relatively limited in literature. Inorganic sulfur sources
include elemental sulfur,7b,12 thionyl chloride,13 sulfur dichloride14
and sodium sulfide.15 The common merits of these methods
transition metal-catalyst.
Thionyl chloride, as one of the inorganic sulfur precursors, was
first used to prepare 3-chlorobenzo[b]thiophenes by Krubsack,13
and the procedure was subsequently investigated by several
other research groups. The reported substrates are limited to cin-
namic acid,16 phenylpropanoic acid,13,17 phenyl propynoic,18,19 and
trans-p-nitrostilbene as the only example of 1,2-diarylethenes.17b
This methodology has not been properly investigated in detail,
and its application in synthesis of functional organic compounds is
very scarce.20 To develop convenient one-pot routes to prepare
novel fluorescent liquid crystalline compounds containing benzo[b]
thiophene and 1,3,4-oxadiazole moieties, we re-investigated the
reaction of trans-diarylethenes with thionyl chloride and gained
some interesting insights into the relevant chemistry. Herein, we
wish to report the results from such investigation.
2. Results and discussion
Our initial efforts focused on the synthesis of 3-chloro-2-(4-
methoxy)phenyl-6-methoxybenzo[b]thiophene 2a by the reaction
of readily available (E)-1,2-bis(40-methoxyphenyl)ethene 1a with
thionyl chloride (Scheme 1). The first attempt was carried out by
treatment of (E)-1,2-bis(40-methoxyphenyl)ethene 1a (4.2 mmol)
with excess of thionyl chloride without catalyst at room tempera-
ture. We were pleased to observe that the reaction occurred
smoothly to yield the desired product 2a in 42% yield after 24 h.
* Corresponding author. Tel./fax: þ86 22 2350 9933; e-mail address: hanjie@
nankai.edu.cn (J. Han).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.09.060

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J. Han et al. / Tetrahedron 67 (2011) 8865e8872
Interestingly, a pair of diastereoisomers of 1,2-dichloro-1,2-bis(4-
methoxyphenyl)ethane 4a (the erythro- and threo-isomers with
the ratio of 4:1) and a pair of E/Z isomers of 1,2-dichloro-1,2-bis(4-
methoxyphenyl)ethenes (5a and 6a) were separated as side prod-
ucts in 23% and 4% yield, respectively. Elongation of reaction time to
48 h led to slight increase of the yields of 2a, 4a and 6a with the
ratio of erythro-4a and threo-4a changed from 4:1 into 2:1 (Table 1,
entry2). When the reaction was carried out at reflux, the reaction
time could be shortened to 4 h, furnishing products 2a, 4a (with
a ratio of 2:1 for erythro-4a and threo-4a), 5a and 6a 37%, 11%, 3%,
and 12% yields, respectively (Table 1, entry3). However, when the
reaction time was prolonged to 24 h, both 2a and 4a disappeared
completely, and a new product dichlorobenzo[b]thiophene 3a was
obtained in 41% yield, accompanied by compounds 5a and 6a in 4%
and 12% yields, respectively (Table 1, entry 4). The structure of 3a
was unambiguously determined by single crystal X-ray analysis21
as shown in Fig. 1. In order to elucidate the relationship between
2a and 3a, a solution of isolated 2a in thionyl chloride was refluxed
for 24 h, giving 3a in 84% yield. This result indicated that mono-
chlorobenzo[b]thiophene 2a could be chlorinated by thionyl chlo-
ride to transform into dichlorobenzo[b]thiophene 3a in good yield.
Fig. 1. The crystal structure of 3a.
(Path C), which further expels another molecule of hydrogen
chloride by a 1,4-elimination process to give rise to mono-
chlorobenzo[b]thiophene 2a. As observed in this work, compound
2a can be chlorinated by thionyl chloride at the C7 position to
furnish the dichlorobenzo[b]thiophene 3a. In addition, the in-
termediate ii could be converted into the isomeric (E)- and (Z)-1,2-
dichloro-1,2-bis(4-methoxyphenyl) ethene (5a and 6a) by elimi-
nation of one molecule of HSCl (Path D), which decomposes into
hydrogen chloride and sulfur, as evidenced by the observation of
elemental sulfur in the reaction.
SOCl2
OCH3
H3CO
1a
It’s worthy to note that thionyl chloride could be used as
a chlorinating agent to transform trans-1,2-di(4-methoxyphenyl)
ethene 1a into 1,2-dichloro-1,2-di(4-methoxyphenyl)ethane 4a in
moderate yields at room temperature or reflux (Table 1, entries
1e3). However, 4a disappeared upon refluxing for prolonged time
(Table 1, entry 4). In order to better understand the reaction path-
way, a solution of isolated 4a in thionyl chloride was refluxed and
monitored by TLC. The results were shown in Scheme 3 and Table 2.
When the reaction mixture was refluxed for 4 h, products 2a, 5a
and 6a were afforded in 12%, 6%, and 15% yield, respectively. When
refluxed for 24 h, dichlorobenzo[b]thiophene 3a emerged and was
obtained in 15% yield, as well as compounds 2a (10%), 5a (8%) and
6a (48%). Further elongation of the reaction time to 40 h, resulted in
the disappearance of 4a and 2a, and afforded products 3a, 5a and 6a
in 21%, 18% and 61% yields, respectively. It’s found that the reactions
of 1a and 4a with thionyl chloride afforded the same products, but
with different ratios.
Cl
H3CO
H3CO
H3CO
H3CO
S
S
OCH3
+
OCH3
+
Cl
Cl
3a
5a
2a
Cl
H Cl
C C
Cl
OCH3
+
OCH3
+
H
Cl
4a
Cl
Cl
H3CO
OCH3
6a
Scheme 1. Reaction of 1a with thionyl chloride.
According to the results, a possible pathway for the reaction of
4a with thionyl chloride is shown in Scheme 4. Initially, compound
4a undergoes a C-sulfinylation reaction23 to give the sulfinyl chlo-
ride iv, which is subsequently converted to sulfenyl chloride ii by
a Pummerer-like reaction. Products 2a, 5a and 6a are formed from
ii by a process depicted in Scheme 3. The ratio of 2a, 5a and 6a from
4a is different from that from 1a. This difference may be ascribed to
the different ratios of isomeric intermediate ii, although an exact
reason is not clear at present.
Table 1
Reaction of the 1a with thionyl chloride
Entry
Temp
Time (h)
2a (%)
3a (%)
4a (%)b (ratio)c
5a
6a
1
2
3
4
rt
rt
24
48
4
42
43
37
0
0
0
0
23 (4:1)
27 (2:1)
11 (2:1)
0 (/)
Trace
Trace
3
4
6
12
10
Refluxa
Refluxa
24
41
4
a
The temperature of the oil bath is 90e95 ꢀC.
Under the optimized conditions,
a series of trans-1,2-
b
c
Isolated yields.
diarylethenes 1bee were examined to explore the scope of the
cyclization reaction (Scheme 5). The results were summarized in
Table 3. Substrates 1b and 1c with an electron-donating methoxy
group readily afforded the corresponding monochlorobenzo[b]
thiophenes (2b,c) and isomers of 1,2-diaryl-1,2-dichloroethanes
(4b,c) in moderate yields after refluxed in thionyl chloride for
3e6 h (Table 3, entries 1, 5 and 6). When the reaction was refluxed
for 48 h (Table 3, entries 4 and 8), both the monochlorobenzo[b]
thiophenes (2b,c) and the 1,2-diaryl-1,2-dichloroethanes (4b,c)
were transformed into the corresponding dichlorobenzo[b]thio-
phenes (3b,c). For the substrate 1d, no benzo[b]thiophene de-
rivatives were detected upon refluxing for 24 h, with only a minor
of 1,2-dichloro-1,2-diphenylethanes 4d isolated. With addition of
a catalytic amount of pyridine, however, the reaction of 1d could
Calculated by 1H NMR spectroscopy of the crude products.
On the basis of the above results, a probable pathway leading to
products 2ae6a from 1a is outlined in Scheme 2. The initial step of
the reaction is an electrophilic addition of thionyl chloride across
the double bond of 1a to form sulfinyl chloride i. Intermediate i
undergoes a thermolysis process to form the isomers 4a (Path A),
and competitively i undertakes a typical Pummerer reaction with
thionyl chloride to form intermediate ii (Path B).22 The sulfenyl
chloride ii subsequently undergoes a concerted eliminationecyc-
lization process, namely, loss of hydrogen chloride from the ben-
zylic carbon and the sulfur simultaneously, to form intermediate iii

J. Han et al. / Tetrahedron 67 (2011) 8865e8872
8867
Cl
O
H Cl
C C
Cl H
H S
H3CO
OCH3
H3CO
C C
Cl H
OCH3
OCH
4a
Path A
Cl
Cl
O
H S
H S
SOCl2
SOCl
2 H3CO
C C
OCH3
OCH3
H3CO
H3CO
C C
Cl H
i
3 Path B
H3CO
Cl Cl
i
i
1a
Cl
H3CO
SOCl2
H
H3CO
H3CO
S
S
Cl
S
Path C
OCH3
OCH3
OCH3
Cl
Cl
H
Cl
iii
2a
Cl
3a
Cl
Cl
-HSCl
Path D
OCH3
+
Cl
H3CO
OCH3
6a
5a
Scheme 2. Probable pathway for the reaction of 1a with thionyl chloride.
[b]-thiophene based optoelectronic materials. A series of novel
light-emitting liquid crystal compounds 9a,b and 10a,10b con-
taining benzo[b]thiophene and 1,3,4-oxadiazole units have been
synthesized by a simple and efficient one-pot procedure as shown
in Scheme 6. Thionyl chloride plays a critical role in construction of
both benzo[b]thiophene and 1,3,4-oxadiazole units. 1,3,4-
Oxadiazole unit was selected as a mesogenic core, for this struc-
tural moiety has become an important synthon in design and
synthesis of various liquid crystals with interesting properties,24
and the 1,3,4-oxadiazole derivatives have also enjoyed wide-
spread use as electron-transporting materials and emitting layers
in electroluminescent diodes due to their electron-deficiency, high
photoluminescence quantum yield and good thermal and chemical
stability.25 The combination of the unique feature of self-assembly
and intrinsic light emitting capabilities may find potential appli-
cation in the field of emissive LC displays and anisotropic OLEDs.
The liquid crystal properties of compounds 9a,b and 10a,b were
investigated by means of differential scanning calorimetry (DSC)
and polarizing optical microscopy (POM). The mesophases are
identified according to the classification system reported by
Dierking.26 All the DSC thermograms show clear-cut peaks both in
the heating and cooling runs, which are well consistent with the
respective observations of textures under the polarizing optical
microscopy. The phase transitions and associated enthalpies of
these products are summarized in Table 4, and the selected POM
images are shown in Fig. 2. All compounds display thermotropic
liquid crystalline properties with different mesophases, which are
determined by the terminal and lateral groups. Compounds 9a and
10a exhibit smectic A phase with wide temperature range due to
the terminal cyano group, while 9b and 10b with an end methoxy
group tend to display nematic phase with relatively narrow tem-
perature range. Compared to 9a and 10a, the corresponding ana-
logues 9b and 10b facilitate to produce nematic phase with
suppression of the smectic A phase due to the lateral chlorine,
which may broaden the core of the mesogen, and the mesophases
can show a decrease in range or even disappear.27
H Cl
C C
Cl H
SOCl2
Reflux
H3CO
OCH3
erythro-4a : threo-4a = 4 : 1
Cl
H3CO
H3CO
S
S
+
OCH3
OCH3
OCH3
+
Cl
Cl
2a
3a
Cl
Cl
Cl
+
H3CO
Cl
5a
H3CO
OCH3
6a
Scheme 3. Reaction of 4a with thionyl chloride.
Table 2
Reaction of the 4a with thionyl chloridea
Entry
Time (h)
2a (b/%)
3a (b/%)
5a (b/%)
6a (b/%)
1
2
3
4
24
40
12
10
0
0
15
21
6
8
18
15
48
61
a
The erythro/threo ratio is 4:1.
Yields determined by 1H NMR.
b
afford 3-chloro-2-phenylbenzo[b]thiophene 2d and 1,2-diaryl-1,2-
dichloroethanes 4d in 42% and 12% yields, respectively. Further
elongation of the reaction time to 48 h resulted in no apparent
change in the yields of 2d and 4d, and no formation of diclorobenzo
[b]thiophene 3d. This result implicated that compounds 2d and 4d
could not be further transformed into 3d as observed in the cases of
1aec. To confirm this speculation, the isolated 2d and 4d were
treated with refluxing thionyl chloride for 24 h, respectively, and no
reactions happened as expected. As for the substrate 1e bearing an
ester group, similar results were observed to those of 1d. (Table 3,
entries 12e14).
The UVevis absorption and photoluminescence properties for
9a,b in CH2Cl2 were investigated as shown in Fig. 3. Both 9a and 9b
exhibit an intense absorption band peaking at 352 and 346 nm with
high molar absorptivity (1.88ꢁ104 L molꢂ1 cmꢂ1 for 9a and
2.05ꢁ104 L molꢂ1 cmꢂ1 for 9b), respectively, and display an intense
emission with moderate photoluminescence quantum yields (16%
for 9a and 46% for 9b). The Stokes shifts for 9a and 9b are 3382 and
On the basis on the established methodology for construction of
benzo[b]thiophenes, we then turn our attention to develop benzo

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J. Han et al. / Tetrahedron 67 (2011) 8865e8872
H Cl
C C
Cl H
H Cl
H Cl
C C
SOCl2
OCH3
SOCl
-HCl
2H3CO
C C
H3CO
OCH3
H3CO
OCH3
Cl
Cl
Cl
Cl
S
S
ii
O
Cl
4a
iv
Cl
Cl
OCH3
+
-HSCl
Path D
H3CO
Cl
H3CO
H3CO
OCH3
5a
6a
Cl
H3CO
SOCl2
H
H3CO
S
S
Cl
S
-HCl
OCH3
OCH3
OCH3
Cl
Cl
2a
H
Cl
iii
3a
Scheme 4. Probable pathway for the reaction of 4a with thionyl chloride.
Cl
H Cl
C C
R1
R1
S
S
R1
R2
SOCl2
+
R2
R2
+
R2
Cl
H
4b-4e
R1
Cl
3b-3e
Cl
2b-2e
1b-4b: R1 = CH3O, R2 = H; 1c, 2c, 4c: R1 = CH3O, R2 = CO2CH3; 1d,2d, 4d: R1 = R2 = H; 1e, 2e, 4e: R1 = H, R2 = CO2CH3.
Scheme 5. Reaction of 1bee with thionyl chloride.
2603 cmꢂ1, respectively, which are comparable to those of the
reported 1,3,4-oxadiazole derivatives.28 Compared to 9b, com-
pound 9a showed a larger red shift of absorption and a longer
photoluminescent emission wavelength due to the elongated
conjugation length of the cyano group in conjunction with the
mesogenic core. According to the emission energy and quantum
yields, the photoluminescence of the mesogens 9a,b may be at-
Table 3
Reaction of 1bee with thionyl chloride
a
Entry
Substrate
Time (h)
2 (%)b
3 (%)b
4 (%) b (ratio)c
1
2
3
4
5
6
7
8
1b
1b
1b
1b
1c
1c
1c
1c
1d
1d
1d
1e
1e
1e
4
8
24
48
3
45
38
25
0
26
42
26
0
0
5
15
48
0
4 (1.6:1)
21 (1.6:1)
0 (/)
0 (/)
Trace (/)
0 (/)
tributed to spin-allowed pep
* fluorescence.
6
0
24
48
24
24
48
24
24
48
28
45
0
0
0
0
0
0
0 (/)
0 (/)
3. Conclusions
9
0
7 (4.8:1)
12 (2.4:1)
12 (1.8:1)
Trace (/)
6 (1.7:1)
9 (1.5:1)
10d
11d
12
13d
14d
42
44
0
15
18
The reactions between trans-1,2-diaylethenes and thionyl
chloride have been systematically investigated, and new insights
have been made. The main results are summarized as following: (1)
the reactivity is affected greatly by the electronic nature of the
substituents on the phenyl rings, the substrates bearing a methoxy
group can react readily with thionyl chloride to provide mono-
chlorobenzo[b]thiophenes, which may be further chlorinated by
thionyl chloride to afford the dichlorobenzo[b]thiophenes. While
a
The temperature of the oil bath is 90e95 ꢀC.
b
c
Isolated yields.
The erythro-4/threo-4 ratio was determined by 1H NMR of the crude products.
d
With 0.1 equiv of pyridine.
O
O
R
COCl
C10H21
O
HN NH2
C10H21
O
OC2H5
Pyridine
O
7
1f
S
S
SOCl2
R
R
C10H21
O
N
N
reflux, 6h
Cl
Cl
O
O
9a-9b
R
C10H21
O
HN NH
Cl
O
SOCl2
8a-8b
C10H21
O
N
N
reflux 48h
10a-10b
Scheme 6. One-pot preparation of the mesogenic compounds 9a,b and 10a,b.

J. Han et al. / Tetrahedron 67 (2011) 8865e8872
8869
Table 4
500
400
300
200
100
0
Phase transitions and enthalpies of 9a,b and 10a,b
0.20
Phase transitionsa T[ꢀC]( H [kJ molꢂ1])
D
9a
9b
Compds
9a
Cr1 121.9 (ꢂ15.6) Cr2183.3 (34.1) SmA 242.3 (3.2) Iso
Iso 240.3 (ꢂ3.1) SmA 154.5 (ꢂ12.7) Cr2 128.3 (ꢂ5.0) Cr1
Cr 166.7 (46.3) N 172.0b Iso
0.15
0.10
0.05
0.00
9b
Iso 168.7 (ꢂ0.6) N 145.8 (ꢂ49.8) Cr
Cr 179.5 (49.4) SmA 218.5 (0.9) N 224.1 (0.8) Iso
Iso 222.4 (ꢂ1.0) N 216.8 (ꢂ1.1) SmA 138.3 (ꢂ51.5) Cr
Cr 170.6b Iso
10a
10b
Iso 160.5b N 135b Cr
a
Cr or Crn¼crystal phases (nth); SmA¼smectic A; N¼nematic phase;
Iso¼isotropic.
b
Optical microscopy data.
250
300
350
400
450
500
550
600
Wavelength (nm)
Fig. 3. Normalized UVevis absorption and emission spectra of 9a and 9b in CH2Cl2 at
298 K (concentration¼1ꢁ10ꢂ5 mol dmꢂ3).
4. Experimental
4.1. General
Melting points were determined with an X-4 digital melting
point apparatus with thermometer uncorrected. 1H and 13C{1H}
NMR spectra were recorded on Bruker AV400 instrument. Ele-
mental analyses were performed on an Elementar Vario EL appa-
ratus. ESI-MS were recorded on
spectrometer.
a Finnigan LCQ Advantage
The single crystals of 3a suitable for X-ray diffraction
determination were obtained from slowly grown in CH2Cl2 at room
temperature. Data for single X-ray structure were collected using
Rigaku diffractometer with graphite monochromatized Mo K
a
X-ray radiation (
l
¼0.71073) and Saturn CCD area detector. The
X-ray crystal structure was solved by direct method and expanded
using Fourier syntheses technique. The non-hydrogen atoms were
refined using riding model. Structural refinement based on full-
matrix least-squares refinement on jFj2 was performed by using
Crystal Structure of SHELXL97 suite program.29
The phase transition temperatures and enthalpy changes were
measured on a NETZSCH DSC 204 differential scanning calorimeter
with a heating rate of 5 ꢀC/min and calibrated with a pure indium
sample. The optical textures were observed on an optical polarized
microscopy (OLYMPUS BX51) equipped with a heating stage.
UVevis absorption spectra were recorded with a Cary 300 spec-
trophotometer. Steady-state emission spectra were recorded with
an SPEX 1681 Fluorolog-2 series F111AI spectrophotometer. The
emission quantum yields were determined using the method of
Demas and Crosby with quinine sulfate in degassed 1 N sulfuric
acid as a standard reference solution (4r¼0.546).30
^
Fig. 2. Optical photomicrographs (200ꢁ) in the cooling cycle: (a) the batonnets and
fan-shaped texture of SmA phase for 9a at 228 ꢀC; (b) the schilieren texture of N phase
for 9b at 169 ꢀC isotropic.
Methyl (E)-[2-(4-methoxyphenyl)ethenyl]benzoate 1c, Methyl
4-[(E)-2-phenylethenyl]benzoate 1e and methyl (E)-[2-(4-
decanoxyphenyl)ethenyl]benzoate 1f were prepared according to
the literature procedure.31 Other starting materials were commer-
cially available. Thionyl chloride was purified according to the
standard method.32 Dichloromethane used for photophysical
studies was washed with concentrated sulfuric acid, 10% sodium
hydrogencarbonate and water, dried with calcium chloride, and
distilled from calcium hydride. All other solvents were of analytical
grade used as received.
All the final products were fully characterized with spectro-
scopic analyses and combustion elemental analysis. Compound 3a
was further confirmed by single X-ray crystallography. The isomeric
ratios of the threo- and erythro-1,2-dichloro-1,2-diarylethanes
4aee were identified and determined by 1H NMR spectroscopy
the reaction between the stilbene derivatives with an electron-
withdrawing group must be carried out with addition of catalytic
pyridine at reflux temperature, and the corresponding mono-
chlorobenzo[b]thiophenes can not been chlorinated with thionyl
chloride; (2) for the first time, we found that thionyl chloride can
work as a chlorinating reagent to transform 1,2-diarylethene into
1,2-dichloro-1,2-diarylethanes in moderate yields, and the isomeric
1,2-dichloro-1,2-diarylethanes with methoxy group can further
react with thionyl chloride to give benzo[b]thiophenes; and (3)
owing to the accessibility of the precursors and the easy experi-
mental operation, this effective methodology has been applied to
synthesize novel fluorescent liquid crystals containing benzo[b]
thiophene and 1,3,4-oxadiazole units.

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J. Han et al. / Tetrahedron 67 (2011) 8865e8872
by the chemical shifts of the methane protons, which were earlier
used for identification of chlorination products of trans-1,2-
diarylethenes.33
J¼7.4 Hz,1H,), 7.17 (d, J¼8.8 Hz,1H), 4.02 (s, 3H); 13C NMR (100 MHz,
CDCl3):
d 153.07, 137.66, 135.31, 132.58, 132.12, 129.09, 128.75,
128.73, 121.09, 116.30, 114.89, 111.23, 56.94; EI-MS: m/z: 307.9; Anal.
Calcd for C15H10Cl2OS: C, 58.26; H, 3.26. Found C, 58.11; H 3.40.
4.2. Typical procedure for the reaction of 1a with thionyl
chloride
4.2.8. erythro-1,2-Dichloro-1-phenyl-2-(4-methoxyphenyl)ethane
4b. Mp 142e144 ꢀC, yield, 4%. 1H NMR (400 MHz, CDCl3):
Compound 1a (1 g, 4.2 mmol) was added to SOCl2 (15 mL), and the
reaction mixture was refluxed under a nitrogen atmosphere for 4 h.
Then, the excessive thionyl chloride was removed by vacuum distil-
lation. The crude solid was purified to afford the products 2a and
amixtureoftheisomericerythro-4aand threo-4ainsequencebysilica
gel column chromatography using petroleumether/dichloromethane
(1:1 in volume) as eluent. The isomers of 4a were further recrystal-
lized from ethanol to afford the pure erythro-4a. In another run, the
products 3a, 5a and 6a were afforded upon refluxing the reaction
mixture for 24 h under the same procedure and workup as above.
d
7.46e7.31 (m, 7H), 6.91 (d, J¼8.6 Hz, 2H), 5.20 (s, 2H, Note: the
signal is not split.), 3.83 (s, 3H); 13C NMR (100 MHz, CDCl3):
159.98, 138.52, 130.45, 129.32, 128.96, 128.55, 128.07, 113.91,
d
66.05, 65.69, 55.34; EI-MS: m/z: 280.1; Anal. Calcd for C15H14Cl2O:
C, 64.07; H, 5.02. Found C, 63.97; H, 5.07.
4.2.9. Methyl 4-(3-chloro-6-methoxybenzo[b]thiophen-2-yl) benzo-
ate 2c. Mp 176e177 ꢀC. yield, 42%. 1H NMR (400 MHz, CDCl3):
d 8.13
(d, J¼8.2 Hz, 2H), 7.87 (d, J¼8.2 Hz, 2H), 7.77 (d, J¼8.8 Hz, 1H), 7.28
(d, J¼2.2 Hz, 1H), 7.10 (dd, J¼8.8, 2.2 Hz, 1H), 3.96 (s, 3H), 3.91 (s,
3H); 13C NMR (100 MHz, CDCl3):
d 166.64, 158.71, 138.40, 137.05,
4.2.1. 3-Chloro-2-(4-methoxy)phenyl-6-methoxybenzo[b]thiophene
132.09, 131.82, 129.87, 129.57, 128.83, 123.31, 117.53, 115.39, 104.74,
55.72, 52.25; EI-MS: m/z: 322.1; Anal. Calcd for C17H13ClO3S: C,
61.35; H 3.94. Found C, 61.65; H 4.02.
2a34. White solid, yield, 37%. Mp 90e91 ꢀC. 1H NMR (400 MHz,
CDCl3):
d
7.77e7.67 (m, 3H), 7.26 (d, J¼1.5 Hz, 1H), 7.08 (dd, J¼8.7,
1.5 Hz, 1H), 7.00 (d, J¼8.6 Hz, 2H), 3.90 (s, 3H), 3.87 (s, 3H); 13C NMR
(100 MHz, CDCl3):
d
¼159.70, 158.15, 137.81, 133.43, 131.96, 130.36,
4.2.10. Methyl
4-(3,7-dichloro-6-methoxybenzo[b]thiophen-2-yl)
124.96, 122.79, 115.31, 114.92, 114.12, 104.86, 55.69, 55.38; EI-MS:
m/z: 304.0; Anal. Calcd for C16H12Cl2O2S: C, 63.05; H, 4.30. Found
C, 63.35; H 4.36.
benzoate 3c. Mp 185e186 ꢀC, yield, 45%. 1H NMR (400 MHz, CDCl3):
d
8.14 (d, J¼8.2 Hz, 2H), 7.88 (d, J¼8.2 Hz, 2H), 7.74 (d, J¼8.8 Hz, 1H),
7.18 (d, J¼8.8 Hz, 1H), 4.02 (s, 3H), 3.96 (s, 3H); 13C NMR (100 MHz,
CDCl3):
d 166.54, 153.40, 137.86, 136.53, 133.92, 132.43, 129.91,
4.2.2. 3,7-Dichloro-2-(4-methoxy)phenyl-6-methoxybenzo[b]thio-
128.84, 121.40, 117.58, 114.87, 111.39, 56.92, 52.31; EI-MS: m/z:
366.0; Anal. Calcd for C17H12Cl2O3S: C, 55.60; H, 3.29. Found C,
55.70; H, 3.30.
phene 3a. White crystals, yield, 41%. Mp 128e130 ꢀC. 1H NMR
(400 MHz, CDCl3):
7.14 (d, J¼8.8 Hz, 1H), 7.00 (d, J¼8.7 Hz, 2H), 4.00 (s, 3H), 3.87 (s,
3H); 13C NMR (100 MHz, CDCl3):
d
7.72 (d, J¼8.7 Hz, 2H), 7.68 (d, J¼8.7 Hz, 1H),
d
¼159.96, 152.93, 137.36, 135.32,
4.2.11. 2-Phenyl-3-chlorobenzo[b]thiophene 2d5e,34. Mp 64e65 ꢀC.
132.74, 130.38, 124.52, 120.84, 115.39, 114.94, 114.20, 111.24, 56.98,
55.38; EI-MS: m/z: 338.0; Anal. Calcd for C16H12Cl2OS: C, 56.65; H
3.57. Found C, 56.51; H 3.59.
yield, 42%. 1H NMR (400 MHz, CDCl3):
d
7.88 (d, J¼8.0 Hz, 2H),
7.83e7.79 (m, 3H), 7.54e7.46 (m, 3H), 7.46e7.38 (m, 2H); 13C NMR
(100 MHz, CDCl3): 137.82, 136.76, 136.29, 132.34, 129.28, 128.67,
d
126.50, 125.46, 125.06, 122.27, 122.24, 116.64; EI-MS: m/z: 244.0;
4.2.3. erythro-1,2-Dichloro-1,2-bis(4-methoxyphenyl)ethane erythro-
Anal. Calcd for C14H9ClS: C, 68.71; H, 3.71. Found C, 69.35; H 4.07.
4a35. Yield, 11%. Mp 192e194 ꢀC. 1H NMR (400 MHz, CDCl3):
d 7.35
(d, J¼8.5 Hz, 4H), 6.91 (d, J¼8.5 Hz, 4H), 5.19 (s, 2H), 3.83 (s, 6H); 13C
4.2.12. erythro-1,2-Dichloro-1,2-diphenylethane 4d35. Mp 193e195
NMR (100 MHz, CDCl3):
55.32; EI-MS: m/z: 309.9; Anal. Calcd for C16H16Cl2O2: C, 61.75; H,
d
¼159.91, 130.70, 129.27, 113.86, 65.93,
ꢀC, yield, 12%. 1H NMR (400 MHz, CDCl3):
d
7.49e7.33 (m, 10H), 5.22
(s, 2H); 13C NMR (100 MHz, CDCl3):
d 138.36, 129.01, 128.56, 128.06,
5.18. Found C, 61.78; H, 5.30.
65.75; EI-MS: m/z: 250.0; Anal. Calcd for C14H12Cl2: C, 72.56; H,
5.22. Found C, 66.65; H, 4.85.
4.2.4. (E)-1,2-Dichloro-1,2-bis(4-methoxyphenyl)ethene
5a36. Mp
166e168 ꢀC, yield, 3%. 1H NMR (400 MHz, CDCl3):
J¼8.7 Hz, 4H), 6.94 (d, J¼8.7 Hz, 4H), 3.86 (s, 6H); EI-MS: m/z: 308.0.
d
7.56 (d,
4.2.13. Methyl 4-(3-chlorobenzo[b]thiophen-2-yl)benzoate 2e. Mp
120e122 ꢀC, yield, 15%. 1H NMR (400 MHz, CDCl3):
d 8.14 (d,
J¼7.9 Hz, 2H), 7.93e7.86 (m, 3H), 7.83 (d, J¼7.9 Hz, 1H), 7.50 (t,
4.2.5. (Z)-1,2-Dichloro-1,2-bis(4-methoxyphenyl)ethene
6a37. Mp
J¼7.5 Hz, 1H), 7.44 (t, J¼7.5 Hz, 1H), 3.96 (s, 3H); 13C NMR (100 MHz,
62e64 ꢀC, yield, 12%. 1H NMR (400 MHz, CDCl3):
7.15 (d, J¼8.5 Hz,
d
CDCl3): d 166.60, 137.75, 136.94, 136.82, 134.96, 129.96, 129.90,
4H), 6.71 (d, J¼8.5 Hz, 4H), 3.76 (s, 6H); EI-MS: m/z: 308.0.
The procedures for the reaction of 1bee with thionyl chloride
are similar to that of 1a, and the characterization data are listed in
the following.
129.13, 125.98, 125.29, 122.52, 122.36, 117.88, 52.31; EI-MS: m/z:
302.0; Anal. Calcd for C16H11Cl2O2S: C, 63.47; H, 3.66. Found C,
63.93; H, 3.76.
4.2.14. erythro-Methyl
4-(1,2-dichloro-2-phenylethyl)benzoate
8.06 (d,
4.2.6. 2-Phenyl-3-chloro-6-methoxybenzo[b]thiophene 2b. Mp 82e84
4e. Mp 157e159 ꢀC, yield, 6%. 1H NMR (400 MHz, CDCl3):
d
ꢀC, yield, 45%. 1H NMR (400 MHz, CDCl3):
d
7.75 (d, J¼7.7 Hz, 2H), 7.71
J¼8.1 Hz, 2H), 7.50 (d, J¼8.1 Hz, 2H), 7.47e7.36 (m, 5H), 5.24 (d,
(d, J¼8.8 Hz, 1H), 7.44 (t, J¼7.5 Hz, 2H), 7.36 (t, J¼7.2 Hz, 1H), 7.22 (d,
J¼9.2 Hz, 1H), 5.20 (d, J¼9.2 Hz, 1H), 3.94 (s, 3H); 13C NMR
J¼2.2 Hz, 1H), 7.05 (dd, J¼8.8, 2.2 Hz, 1H), 3.84 (s, 1H); 13C NMR
(100 MHz, CDCl3):
d 166.51, 143.02, 137.86, 130.67, 129.81, 129.17,
(100 MHz, CDCl3):
d158.36, 138.17, 133.48, 132.57, 131.91, 129.11,
128.63, 128.23, 128.03, 65.45, 64.98, 52.30; EI-MS: m/z: 308.0; Anal.
128.68, 128.39, 123.03, 116.21, 115.09, 104.82, 55.70; EI-MS: m/z: 274.1;
EI-MS: m/z: 274.1; Anal. Calcd for C15H11ClOS: C, 65.57; H, 4.04. Found
C, 65.44; H 4.13.
Calcd for C16H14Cl2O2: C, 62.15; H, 4.56. Found C, 61.88; H, 4.71.
4.3. Synthesis of (E)-N-[2-(4-decanoxyphenyl)vinyl]benzoyl
hydrazide 7
4.2.7. 2-Phenyl-3,7-dichloro-6-methoxybenzo[b]thiophene 3b. Mp
130e132 ꢀC, yield, 15%. 1H NMR (400 MHz, CDCl3):
d
7.79 (d,
A suspension of 1f (12 g, 30 mmol) in 20 mL of hydrazine
J¼7.3 Hz, 2H), 7.72 (d, J¼8.7 Hz, 1H), 7.49 (t, J¼7.4 Hz, 2H), 7.42 (t,
monohydrate (80%) was dissolved in 150 mL of methanol and

J. Han et al. / Tetrahedron 67 (2011) 8865e8872
8871
100 mL of toluene, and the mixture was refluxed for 72 h. After
cooling, the reaction mixture was poured in water and the crude
solid was recrystallized from ethanol to afford 7 as white needle
115.30, 113.01, 70.26, 31.91, 29.56, 29.34, 29.24, 25.93, 22.69, 14.13;
EI-MS: m/z: 603.1; Anal. Calcd for C33H31Cl2N3O2S: C, 65.56; H, 5.17;
N, 6.95. Found C, 65.47; H, 5.08; N, 7.07.
Compounds 10a and 10b were prepared according to the same
procedure as that of 9a and 9b.
crystals. Yield, 83%. 1H NMR (CDCl3, 400 M):
d
9.65 (s, 1H), 7.80 (d,
J¼8.0 Hz, 2H), 7.59 (d, J¼8.0 Hz, 2H), 7.52 (d, J¼7.6 Hz, 2H), 7.26 (d,
J¼16.4 Hz, 1H), 7.09 (d, J¼16.4 Hz, 1H), 6.92 (d, J¼8.4 Hz, 2H), 4.48
(s, 2H), 3.97 (t, J¼6.0 Hz, 2H), 3.92 (s, 3H), 1.76e1.63 (m, 2H),
1.46e1.11 (m, 14H), 0.84 (t, J¼6.4 Hz).
4.5.3. (E)-2-(4-Methoxyphenyl)-5-[4-(3-chloro-6-decyloxybenzo [b]
thiophene-2-yl)phenyl]-1,3,4-oxadiazole 10a. Yield, 45%. 1H NMR
(400 MHz, CDCl3):
d
8.22 (d, J¼8.5 Hz, 2H), 8.11 (d, J¼8.9, 5.2 Hz,
4.4. Synthesis of (E)-[2-(4-decanoxyphenyl)vinyl] benzoic acid
N-(4-cyanobenzoyl)hydrazide 8a
2H), 7.96 (d, J¼8.5 Hz, 2H), 7.76 (d, J¼8.8 Hz, 1H), 7.28 (d, J¼2.2 Hz,
1H), 7.10 (dd, J¼8.9, 2.2 Hz, 1H), 7.06 (d, J¼8.8 Hz, 2H), 4.05 (t,
J¼6.5 Hz, 2H), 3.91 (s, 3H), 1.84 (quintet, 2H), 1.49 (quintet, 2H),
1.44e1.23 (m, 12H), 0.89 (t, J¼6.6 Hz, 3H); 13C NMR (100 MHz,
To a round-bottomed flask was added 4-cyanobenzoic acid
(330 mg, 2.2 mmol), 10 mL of thionyl chloride, and the mixture was
refluxed for 8 h. After cooling, the excess of thionyl chloride was
removed at reduced pressure to give the 4-fluorobenzoyl chloride,
which was added to a solution of compound 7 (790 mg, 2 mmol) in
10 mL of pyridine. The reaction mixture was stirred for 2 h at 90 ꢀC
and then poured into water. The solid was filtered and crystallized
from ethanol to give 8a as white crystals; yield, 76%. 1H NMR
CDCl3):
d 164.69, 163.79, 162.44, 158.30, 138.32, 135.79, 131.82,
131.69, 129.44, 128.77, 127.02, 123.51, 123.24, 117.49, 116.41, 115.82,
114.57, 105.51, 68.62, 55.49, 31.89, 29.56, 29.39, 29.32, 29.22, 26.05,
22.68, 14.11; EI-MS: m/z: 574.2; Anal. Calcd for C33H35ClN2O3S: C,
68.91; H, 6.13; N, 4.87. Found C, 68.80; H, 6.17; N, 4.91.
4.5.4. (E)-2-(4-Methoxyphenyl)-5-[4-(3,7-dichloro-6-decyloxy benzo
(400 MHz, DMSO-d6):
d
10.78 (s,1H), 10.58 (s,1H), 8.05 (d, J¼8.5 Hz,
[b]thiophene-2-yl)phenyl]-1,3,4-oxadiazole 10b. Yield, 23%. 1H NMR
2H), 8.02 (d, J¼8.5 Hz, 2H), 7.90 (d, J¼8.3 Hz, 2H), 7.68 (d, J¼8.3 Hz,
2H), 7.55 (d, J¼8.6 Hz, 2H), 7.35 (d, J¼16.4 Hz,1H), 7.15 (d, J¼16.4 Hz,
1H), 6.94 (d, J¼8.6 Hz, 2H), 3.96 (t, J¼6.4 Hz, 2H), 2.36 (s, 3H), 1.68
(quintet, 2H), 1.38 (quintet, 2H), 1.33e1.18 (m, 12H,), 0.83 (t,
J¼6.8 Hz, 3H).
(400 MHz, CDCl3):
d
8.23 (d, J¼8.5 Hz, 2H), 8.11 (d, J¼8.9 Hz, 2H),
7.98 (d, J¼8.6 Hz, 2H), 7.73 (d, J¼8.8 Hz, 1H), 7.17 (d, J¼8.8 Hz, 1H),
7.06 (d, J¼8.9 Hz, 2H), 4.16 (t, J¼6.6 Hz, 2H), 3.91 (s, 3H), 1.88
(quintet, 2H), 1.53 (quintet, 2H), 1.43e1.20 (m, 12H), 0.89 (t,
J¼6.8 Hz, 3H); 13C NMR (100 MHz, CDCl3):
d 164.73, 163.68, 162.47,
153.16, 137.85, 135.32, 133.78, 132.40, 129.49, 128.78, 127.07, 123.91,
121.31, 117.61, 116.39, 114.58, 113.02, 70.30, 55.50, 31.92, 29.56,
29.34, 29.27, 25.95, 22.69, 14.11; EI-MS: m/z: 608.1; Anal. Calcd for
C33H34Cl2N2O3S: C, 65.02; H, 5.62; N, 4.60. Found C, 65.05; H, 5.42;
N, 4.73.
4.4.1. (E)-[2-(4-Decanoxyphenyl)vinyl]benzoic acid N-(4-
methoxybenzoyl)hydrazide 8b. Compound 8b was prepared
according to the procedure as 8a. Yield, 78%. 1H NMR (400 MHz,
DMSO-d6):
d
10.40 (s, 1H), 10.34 (s, 1H), 7.89 (d, J¼8.4 Hz, 4H), 7.67
(d, J¼8.4 Hz, 2H), 7.54 (d, J¼8.8 Hz, 2H), 7.34 (d, J¼16.4 Hz, 1H), 7.14
(d, J¼16.4 Hz, 1H), 7.04 (d, J¼8.8 Hz, 2H), 6.93 (d, J¼8.8 Hz, 2H), 3.96
(t, J¼6.4 Hz, 2H), 3.81 (s, 3H), 1.68 (quintet, 2H), 1.38 (quintet, 2H),
1.34e1.14 (m, 12H), 0.83 (t, J¼6.8 Hz, 3H).
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (20772064), and the authors are
grateful to Prof. Zhengjie He (Department of Chemistry, Nankai
University) for helpful suggestions and discussion.
4.5. Synthesis of compounds 9a and 9b
Compound 8a (524 mg, 1 mmol) was added to SOCl2 (15 mL),
and the reaction mixture was refluxed under a nitrogen atmo-
sphere for 12 h. Then, the excessive thionyl chloride was removed
by vacuum distillation. The crude solid was purified to afford the
products 9a and 9b in sequence by silica gel column chromatog-
raphy using dichloromethane as eluent.
Supplementary data
Supplementary data (proton NMR and carbon NMR for 2a, 3a,
3b, erythro-4b, 2c, 2d, erythro-4d, 2e, erythro-4e, 9a, 9b, 10a, and
10b). Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2011.09.060. These data
include MOL files and InChiKeys of the most important compounds
described in this article.
4.5.1. (E)-2-(4-Cyanophenyl)-5-[4-(3-chloro-6-decyloxy
thiophene-2-yl)phenyl]-1,3,4-oxadiazole 9a. Yield, 29%. 1H NMR
(400 MHz, CDCl3):
benzo[b]
d
8.29 (d, J¼8.3 Hz, 2H), 8.23 (d, J¼8.3 Hz, 2H),
7.99 (d, J¼8.3 Hz, 2H), 7.86 (d, J¼8.3 Hz, 2H), 7.77 (d, J¼8.9 Hz, 1H),
7.28 (d, J¼2.0 Hz, 1H), 7.11 (dd, J¼8.9, 2.0 Hz, 1H), 4.05 (t, J¼6.5 Hz,
2H), 1.84 (quintet, 2H), 1.49 (quintet, 2H), 1.44e1.20 (m, 12H), 0.89
References and notes
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d 165.03, 163.18,
158.41, 138.37, 136.60, 132.94, 131.65, 131.49, 129.58, 127.75, 127.40,
127.33, 123.33, 122.68, 117.90, 117.80, 115.93, 115.27, 105.48, 68.63,
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ham, M. A. Sci. Synth. 2001, 10, 155.
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(400 MHz, CDCl3):
d
8.29 (d, J¼8.3 Hz, 2H), 8.24 (d, J¼8.4 Hz, 2H),
8.00 (d, J¼8.4 Hz, 2H), 7.86 (d, J¼8.3 Hz, 2H), 7.73 (d, J¼8.8 Hz, 1H),
7.17 (d, J¼8.9 Hz, 1H), 4.16 (t, J¼6.5 Hz, 2H), 1.88 (quintet, 2H), 1.53
(quintet, 2H), 1.45e1.20 (m, 12H), 0.89 (t, J¼6.8 Hz, 3H); 13C NMR
(100 MHz, CDCl3):
d 164.94, 163.23, 153.26, 137.89, 136.12, 133.43,
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