Synthesis and characterization of benzo[c]thiophene analogs incorporating benzo[b]thiophene/1-hexylindole/benzo[b]furan

Article abstract of DOI:10.1016/j.tet.2009.03.059

Synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating heterocycles such as benzo[b]thiophene/1-hexylindole/benzo[b]furan and thiophene units is described. Optical and electrochemical studies of the benzo[c]thiophene analogs are also reported.

Full text of DOI:10.1016/j.tet.2009.03.059

Tetrahedron 65 (2009) 4113–4123
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and characterization of benzo[c]thiophene analogs incorporating
benzo[b]thiophene/1-hexylindole/benzo[b]furan
*
J. Arul Clement, Pethaiah Gunasekaran, Arasambattu K. Mohanakrishnan
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 January 2009
Received in revised form 15 March 2009
Accepted 22 March 2009
Available online 27 March 2009
Synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating heterocycles such as benzo-
[b]thiophene/1-hexylindole/benzo[b]furan and thiophene units is described. Optical and electrochemical
studies of the benzo[c]thiophene analogs are also reported.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Friedel–Crafts reaction
Benzo[b]thiophene
1-Hexylindole
Benzo[b]furan
Thionation
Benzo[c]thiophene
1. Introduction
groups.8 During the last 15 years, synthesis and characterization of
wide variety of 1,3-disubstituted benzo[c]thiophene analogs have
Synthesis and application of thienyl oligomers have been of
great interest for chemists and material scientists due to their
intrinsic photo physical and redox properties.1 Indeed, the thienyl
oligomers have been widely used as components in Organic Light-
Emitting Diodes (OLEDs),2 Organic Solar Cells (OSC),3 Organic Field-
Effect Transistors (OFETs),4 and photo refractive holography.5 On
the other hand, polythiophene is superior to polyphenylene as
a semiconductor. In general, arylenevinylenes as well as hetero-
arylenevinylenes have also attracted attention in the fabrication of
electroluminescent devices.6 Specifically, poly(thienylenevinylene)
has attracted considerable interest as a material with enhanced
third-order nonlinear susceptibilities. The synthesis and in-
vestigation of well-defined model oligomers have recently become
useful in gaining insight into the structural and electronic pecu-
liarities of the corresponding polymers. Indeed, the extent of con-
jugation does not make major difference between thienyl
oligomers and polymers, since electronic properties are saturated
after a particular chain length.7
been realized.9 The synthesis of a novel nucleoside analog replacing
a DNA base with 1,3-dithienylbenzo[c]thiophene has been explored
as fluorescent labels.10 The benzo[c]thiophene analogs are also
explored as components in OLEDs11 as well as photovoltaics.12 Very
recently, Swager and co-workers reported push–pull type benzo-
[c]thiophenes as near-IR fluorophores.13
In continuation of our interest on synthesis and characterization
of 1,3-diarylbenzo[c]thiophenes,14 we have recently reported syn-
thesis of benzo[c]thiophenes containing other heterocycles such as
benzo[b]thiophene and 1-hexylindole.15 We report herein our
detailed study on synthesis and characterization of benzo[c]thio-
phenes incorporating benzo[b]heterocycles, which can be used as
potential electro-optical materials.
Ar1
Ar2
S
S
S
S
1
2
The synthesis and characterization of 1,3-dithienylbenzo[c]-
thiophene 1 have been reported independently by four different
2. Results and discussion
Benzo[b]heterocycles 3a–c on Friedel–Crafts phthaloylation in
the presence of anhydrous AlCl3 in dry DCM at room temperature
for 4 h followed by routine workup furnished keto-acids 5a–c in
* Corresponding author. Tel.: þ91 44 22202813; fax: þ91 44 22300488.
E-mail address: mohan_67@hotmail.com (A.K. Mohanakrishnan).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.03.059

4114
J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
45–68% yields. Selective reduction of the ketone-carbonyl function
of 5a–c using NaBH4 in THF/EtOH (2:5) at reflux for 12 h followed
by acid catalyzed cyclization and subsequent column chromato-
graphic purification led to the isolation of the respective hetero-
aryl phthalides 6a–c as colorless solid in 52–60% yields, Scheme 1.
by thionation led to the isolation of benzo[c]thiophenes 7h–j as
thick orange liquids in 45–56% yields (entry 4). Reaction of 1-hex-
ylindolyl lactone 6c with heteroaryl/aryl Grignards followed by
thionation afforded the corresponding benzo[c]thiophenes 7k–o as
thick orange liquids in 40–48% yields (entries 6 and 7).
Conventional Friedel–Crafts phthaloylation of 3-methyl-
benzo[b]furan 816 in the presence of anhydrous AlCl3 in DCM at
room temperature for 4 h furnished keto-acid 9 in 45% yield. As
mentioned earlier, the selective reduction of the ketone-carbonyl
function of 9 using NaBH4 in THF/EtOH (2:5) at reflux followed by
acid catalyzed cyclization furnished 3-methylbenzo[b]furanyl
phthalide 10 as colorless solid in 72% yield, Scheme 3. It should be
noted that an attempted preparation of 3-(benzofuran-3-yl)iso-
benzofuran-1(3H)-one via Friedel–Crafts phthaloylation of parent
benzo[b]furan followed by reductive cyclization was unsuccessful
due to the highly insoluble nature of the corresponding keto-acid.
Treatment of phthalide 10 with thienyl Grignards followed by
thionation using 0.5 equiv of Lawesson’s reagent and subsequent
column chromatographic purification led to the isolation of 1-
(benzo[b]furan-3-yl)-3-(2-thienyl)benzo[c]thiophenes 11a/11b as
red solid/thick orange liquid in 58 and 55% yields, respectively.
Similarly, the ring opening of the lactone 10 with aryl Grignards
followed by thionation furnished the corresponding benzo[c]thio-
phenes 12a–d as an orange solid in 52–62% yields, Scheme 4.
Having synthesized the benzo[b]heterocycle incorporated ben-
zo[c]thiophenes, the next plan was to dimerize some of these
compounds in a controlled manner to afford the respective di-
merization products in acceptable yields. Survey of literature
revealed that regio-selective oligomerization of thienyl monomers
using FeCl3 has been reported.9a,17
O
AlCl3/DCM
O
CO2H
4 h, rt
R1
O
X
R1
4
X
O
3a X = S, R1 = H
5a (68%)
5b (65%)
5c (45%)
3b X = S, R1 = n-C6H13
3c X = N-C6H13, R1 = H
i) NaBH4/EtOH-THF
reflux, 12 h
5a-c
O
O
ii) Conc.HCl/H2O
rt, 2 h
R1
X
6a-c
52-60%
Compound
5a/6a
X
R1
H
n-C6H13
H
Yield (%)
S
S
54
60
52
5b/6b
5c/6c
N-C6H13
Scheme 1.
Ring opening of the phthalides 6a–c using freshly prepared aryl/
hetero-aryl Grignards followed by aq NH4Cl quenching and DCM
extraction gave the corresponding keto-alcohol. The DCM solution
of the resulting keto-alcohol on interaction with 0.5 equiv of Law-
esson’s reagent at room temperature led to the thionation of ke-
tone-carbonyl function followed by intramolecular cyclization and
subsequent aromatization to yield crude benzo[c]thiophenes. Col-
umn chromatographic purification of the crude products furnished
benzo[c]thiophene analogs 7a–o in 40–60% yields, Scheme 2.
Recently Kita and co-workers18 reported a synthesis of 2,20-
bithiophene derivatives involving an oxidative coupling of the
corresponding alkylthiophenes using a combination of phenyl-
iodide bis(trifluoroacetate) and BF3$OEt2. As expected the di-
merization of benzo[c]thiophenes 7a,b and 7h,i could be
successfully carried out using either anhydrous FeCl3 in DCM at
room temperature or PIFA/BF3$OEt2 at ꢀ78 ꢁC to yield the re-
spective dimers 13a,b and 13c,d as a dark solids in 40–60% yields,
Scheme 5. To our delight, the dimerization of benzo[c]thiophens
7a/7b proceeded selectively at the thiophene-2-position rather
than the 2-position of benzo[b]thiophene. Interaction of indolyl
benzo[c]thiophene 7k as well as benzofuranyl benzo[c]thiophene
11b with anhydrous FeCl3 led to the formation of expected dimers
14 and 15 in 40 and 45% yields, respectively. Even with the ben-
zo[c]thiophenes 7k/11b, gratifyingly the expected dimerization
proceeded preferentially at the thiophene-2-position rather than
the 2-position of indole or benzo[b]furan.
i) Ar1MgBr/THF
ii) NH4Cl
6a-c
iii) Lawesson's reagent
(0.5 eq.)
Ar1
S
7a-o
X
R
40-60%
Scheme 2.
The nature of the phthalide as well as Grignards employed and
the resulting benzo[c]thiophenes obtained along with their yields
and physical characteristics are outlined in Table 1.
Next, the synthesis of push–pull type benzo[c]thiophene analog
is planned. Accordingly, Vilsmeier–Haack formylation of 7a/7k
using DMF/POCl3 in dry DCM at room temperature followed by
basic workup and column chromatographic purification led to the
isolation of respective monoaldehyde 16a/16b as red solid/thick red
liquid in 70 and 49% yields. Under similar conditions, the for-
mylation of benzofuranyl benzo[c]thiophene 11a afforded corre-
sponding monoaldehyde 17 as brown solid in 62% yield, Scheme 6.
Having prepared the required aldehydes 16a,b and 17, prepa-
ration of benzo[c]thiophene based cyanovinylene is planned. As
expected, condensation of the aldehyde 16a with malononitrile/
thiophene-2-acetonitrile using piperidine/t-BuOK as a base led to
the isolation of cyanovinylenes 18a and 18b in 55 and 60% yields,
respectively. Under identical conditions, the aldehyde 17 could also
be converted into the corresponding cyanovinylenes 19a and 19b.
As a representative case, Wittig reaction of the aldehyde 16a with
4-N,N-dibutylaminobenzylphosphonium iodide19 using n-BuLi in
THF/MeOH followed by workup and column chromatographic
purification gave compound 21 as a thick red liquid. The trans-
As expected, reaction of hetero-aryl phthalides 6a–c with aryl as
well as hetero-aryl Grignards followed by thionation furnished
expected benzo[c]thiophenes 7a–o in moderate yields. The ring
opening of benzo[b]thienyl phthalide 6a using thienyl-2-magne-
sium bromide followed by thionation and column chromatographic
purification gave benzo[c]thiophene 7a as an orange solid in 54%
yield (entry 1). Similarly, the reaction of 6a with hexyl-substituted-
2-thienylmagnesium bromides followed by interaction with
Lawesson’s reagent led to the isolation of corresponding ben-
zo[c]thiophenes 7b and 7c as thick yellow liquids in 60 and 56%
yields, respectively (entry 1). As expected, the interaction of 6a with
aryl Grignards followed by subsequent thionation also yielded
benzo[c]thiophenes 7d–f in 48–55% yields (entry 2). Under iden-
tical conditions, 1-naphthyl-benzo[c]thiophene 7g could also be
prepared (entry 3). The ring opening of the 2-hexyl-substituted
benzo[b]thiophenyl phthalide 6b with thienyl Grignards followed

J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
4115
Table 1
Synthesis of benzo[c]thiophene analogs containing benzo[b]thiophene/benzo[b]pyrrole
Entry
Lactone
ArMgBr
Product
Yielda (%) mp
R1
R1
7a R1¼H, R2¼H
54 (118 ꢁC)
60 (thick liquid)
56 (thick liquid)
1
6a
7b R1¼n-C6H13, R2¼H
7c R1¼H, R2¼n-C6H13
R2
S
MgBr
S
S
R2
S
MgBr
R1
R1
7d R1¼Me, R2¼H
7e R1¼H, R2¼Me
7f R1¼H, R2¼OMe
50 (62 ꢁC)
48 (thick liquid)
55 (105 ꢁC)
2
3
6a
6a
S
R2
R2
S
MgBr
7g
40 (78 ꢁC)
S
S
S
R1
MgBr
R1
7h R1¼H, R2¼H
45 (thick liquid)
56 (thick liquid)
50 (thick liquid)
4
6b
7i R1¼n-C6H13, R2¼H
7j R1¼H, R2¼n-C6H13
R2
S
S
S
S
R2
n-C6H13
R1
S
R1
MgBr
7k R1¼H, R2¼H
45 (thick liquid)
48 (thick liquid)
5
6c
7l R1¼H, R2¼n-C6H13
S
R2
R2
N
n-C6H13
7m R1¼Me
7n R1¼OMe
42 (thick liquid)
45 (thick liquid)
6
6c
MgBr
S
R1
N
e
n-C6H13
R1
7
6c
MgBr
7o
40 (thick liquid)
S
N
n-C6H13
a
Isolated yield after column chromatography.
stereochemistry of 21 was assigned on the basis 1H NMR coupling
constant value of the vinylic proton (Scheme 7).
The UV–vis spectra of monomeric benzo[c]thiophenes
exhibited a strong absorption in the region of 435–464 nm due to
CH3
O
Me
the
p
–
p electronic transition of the conjugated backbone system.
*
AlCl3 / DCM
rt, 4 h
CO2H
Compared to parent 1,3-dithienylbenzo[c]thiophene 1, re-
placement of thiophene ring by benzo[b]thiophene has increased
the lmax value around 12 nm (1 to 7a). On contrary to the 1,3-
dithienylbenzo[c]thiophene 1,9a the introduction of hexyl sub-
stituent in the case of 7a enhanced the lmax value. Replacement of
benzo[b]thiophene unit of 7a with 1-hexylindole has led to the
O
+
O
O
O
9
8
4
O
CH3
i) NaBH4 / EtOH-THF
reflux, 10 h
ii) Conc.HCl/H2O
rt, 2 h
enhancement of p-conjugation. However, exchange of benzo[b]-
O
O
O
thiophene unit with 3-methylbenzo[b]furan has only slightly in-
creased (w5 nm) the lmax value (7a to 7k). The presence of
electron-withdrawing groups such as aldehyde/cyanovinylenes
10
72%
Scheme 3.

4116
J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
R1
MgBr
R1
H3C
DMF/POCl3
i)
ii) NH4Cl
7a/7k
S
S
S
Dry DCM
S
S
10
CHO
O
X
11a R1 = H
16a X = S (70%)
16b X = N-C6H13 (49%)
iii) Lawesson's reagent
(0.5 eq.)
55-58%
11b R1 = C6H13
CH3
O
H3C
i) Ar1MgBr/THF
ii) NH4Cl
Ar1
S
DMF/POCl3
Dry DCM
S
S
11a
10
O
iii) Lawesson's reagent
(0.5 eq.)
52-62%
CHO
17
12a-d
62%
Scheme 6.
Compound
Ar1
Yield(%)
12a
12b
12c
Phenyl
p-Tolyl
p-Anisyl
62
53
56
The qualitative emission data of selected benzo[b]heterocycles
incorporated benzo[c]thiophenes were recorded in DCM solution
and the emission values are also presented in Table 2. The mono-
meric benzo[c]thiophenes showed emission in the range of 510–
567 nm. As observed in the case of absorption spectra, the emission
values of these benzo[c]thiophenes are also red shifted with in-
12d
1-Naphthyl
52
Scheme 4.
creasing
p-conjugation. The presence of electron-withdrawing
at one end of benzo[c]thiophenes (16a,b, 17, 18b, and 19) resulted
groups such as aldehyde/cyanovinylenes at one end of benzo[c]-
thiophenes (16a,b, 17, 18b, and 19) exhibited emission values in the
range of 584–720 nm. The dimeric benzo[c]thiophenes (13a,d, 14,
and 15) displayed emission values in the range of 690–730 nm. The
HOMO and LUMO energy levels of benzo[c]thiophenes were calcu-
lated from the absorption and the onset oxidation potential. The Eg,
HOMO, and LUMO values obtained for representative benzo[c]thio-
phenes are presented in Table 2. The monomeric benzo[c]thiophene
analogs showed Eg values in the range of 2.7–2.8 eV. Introduction of
electron-withdrawing aldehyde/cyanovinylene function at one end
of the benzo[c]thiophenes has reduced band gap value w0.4 eV/
0.7 eV. The dimerization of benzo[c]thiophenes also reduced the Eg
values around w0.7 eV. Indeed, the dimerization has significantly
enhanced the LUMO energy levels (w2.4 eV to w3.0 eV). However,
relatively HOMO energy levels were only slightly (w5.2 eV to
w5.1 eV) reduced.
in red shift of absorption value in the range of 60–81/153–161 nm,
which confirms the significant enhancement of
p-electron de-
localization. The dimerization of monomeric benzo[c]thiophenes
red shifted the lmax values in the range of 162–171 nm, which is
more than twice as observed in the case of dimerization of parent
benzo[c]thiophene 1.9a Of course compared to dibenzohetero-
cycles containing benzo[c]thiophenes,14e the enhancement of
lmax value for the dimerization of 7a is almost tripled. The exact
absorption lmax values of representative benzo[c]thiophenes are
presented in Table 2.
R2
R2
S
S
i) FeCl3/DCM
ii) NH2.NH2.H2O
(or)
S
The electrochemical properties of representative benzo[c]thio-
phenes are summarized in Table 3. The anodic peak potential of
benzo[c]thiophene 7a was observed at þ0.60 V at scan rate of
100 mV Sꢀ1. The anodic peak potential of 7a was less compared to
S
7a,b
7h,i
R1
R1
13a-d
i) PIFA/BF3.OEt2
-78 °C, 6 h
ii) aq. NaHCO3
S
S
13a R1 = H, R2 = H (55%, 40%)
13b R1 = H, R2 = n-C6H13 (60%, 55%)
13c R1 = n-C6H13, R2 = H (52%, 42%)
13d R1 = n-C6H13, R2 = n-C6H13 (49%, 53%)
CH2(CN)2/Piperidine
(or)
CN
16a
S
S
CN/tBuOK
R
S
S
18a R = CN (55%)
S
S
18b R = 2-thienyl (60%)
S
S
i) FeCl3/DCM
ii) NH2.NH2.H2O
Me
CH2(CN)2/Piperidine
(or)
7k
14
40%
N
N
17
CN
R
S
C6H13
C6H13
S
CN/tBuOK
S
O
19a R = CN (52%)
19b R = 2-thienyl (53%)
C6H13
C6H13
S
S
CH2PPh3I
n-BuLi
S
S
H3C
ii) NH2.NH2.H2O
i) FeCl3/DCM
THF-MeOH
Me
O
S
11b
15
S
16a
O
45%
S
N(n-Bu)2
20
21 (48%)
Scheme 7.
N(n-Bu)2
Scheme 5.

J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
4117
Table 2
Summary of the physical measurements for some selected benzo[c]thiophenes
4. Experimental
HOMOd
(eV)
LUMOe
(eV)
a
b
c
onset
4.1. General
Comp.
lmax
lemiss
Eg
E
ox
(nm)
(nm)
(eV)
(eV)
1
7a
7b
7h
7i
433
445
455
455
464
458
449
459
615
635
620
625
505
525
530
598
610
532
515
533
521
539
549
542
567
691
730
725
720
584
620
615
720
705
2.66
2.78
2.72
2.72
2.67
2.70
2.76
2.70
2.01
1.95
2.00
1.98
2.45
2.36
2.34
2.07
2.03
0.64
0.54
0.84
0.63
0.55
0.72
0.60
0.71
0.54
0.64
0.71
0.58
0.79
0.65
0.69
1.00
0.95
5.08
4.98
5.28
5.07
4.99
5.16
5.04
5.15
4.98
5.08
5.15
5.02
5.23
5.09
5.13
5.44
5.39
2.42
2.20
2.56
2.35
2.32
2.46
2.28
2.45
2.97
3.13
3.15
3.04
2.78
2.73
2.79
3.37
3.36
All melting points are uncorrected. IR spectra were recorded on
a SHIMADZU FT-IR 8300 instrument. 1H and 13C NMR spectra were
recorded in CDCl3 using TMS as an internal standard on a Bruker-
300 spectrometer. Mass spectra were recorded on a JEOL DX 303 HF
spectrometer. Elemental analyses were carried out on a Perkin–
Elmer series II 2400 (IIT Madras) instrument. All UV–vis spectra
were recorded in CH2Cl2 solution. The emission spectra were
recorded on Perkin–Elmer LS-45 spectrophotometer. The cyclic-
voltammogram of 10ꢀ3 M solution of benzo[c]thiophenes was
carried out on a CHI 600C electrochemical analyzer. All the mea-
surements were carried out under oxygen free condition using
three electrode cells in which glassy carbon electrode was working
electrode, saturated Ag/AgCl electrode was reference electrode, and
platinum wire was used as an auxiliary electrode. Tetrabutyl-
ammonium hexafluoro phosphate (TBAPF6) was used as supporting
electrolyte and its concentration was 10ꢀ1 M.
7k
11a
11b
13a
13d
14
15
16a
16b
17
18b
19a
a
Measured in dilute dichloromethane solution.
Excited at absorption maxima.
b
c
Estimated from the absorption (Eg¼1240/lmax).
d
e
Calculated using the empirical equation: HOMO¼(4.44þEoonxset).
Calculated from: LUMO¼HOMO-Eg.
4.2. A representative procedure for the preparation of lactone
from heterocycle 3a (procedure A)
Table 3
4.2.1. 3-(Benzo[b]thiophen-3-yl)isobenzofuran-1(3H)-one (6a)
Redox behavior of some selected benzo[c]thiophenes
To
a stirred suspension of phthalic anhydride (6.07 g,
Compound
1Epa (V)
1Epc (V)
1DEpc (mV)
2Epaa (V)
a
b
41.01 mmol) in dry DCM (150 mL), powdered anhydrous AlCl3
(6.47 g, 48.50 mmol) was added in two portions, resulted in yellow
solution which was then cooled to 0 ꢁC. The benzo[b]thiophene 3a
(5 g, 37.31 mmol) in DCM (20 mL) was added dropwise to the above
solution at 0 ꢁC and stirred for 4 h at room temperature. The re-
action mixture was quenched with ice water containing HCl and
extracted with DCM (2ꢂ30 mL). Evaporation of the solvent gave
crude keto-acid, which was dissolved in THF/EtOH (2:5). To this,
NaBH4 (7.08 g, 186.56 mmol) was added in small portions and
refluxed for 10 h. The reaction mixture was poured into water and
concd HCl was added dropwise under stirring (pH¼1–2). It was
then extracted with EtOAc and dried (Na2SO4). Solvent was evap-
orated in vacuo to give the crude product, which was purified by
column chromatography (10% EA/Hexane) to give the title com-
pound 6a [5.35 g, 54% (two steps)].
7a
7b
7c
7h
7i
7k
7l
11a
11b
þ0.60
þ0.89
þ0.80
þ0.66
þ0.59
þ0.79
þ0.53
þ0.65
þ0.76
þ0.47
130d
þ1.21
þ0.94
þ0.93
þ0.42
þ0.39
370e
260e
a
1Epa and 2Epa are the anodic peak potentials of the first and second redox process,
respectively.
b
1Epc is the cathodic peak potentials of the first redox process.
c
1DEp is the differences between the cathodic and anodic peak potentials of the
first redox process.
d
Quasireversible.
e
Irreversible.
parent 1,3-dithienylbenzo[c]thiophene (þ0.71).8 The introduction
4.2.2. 3-(Benzo[b]thiophen-3-yl)isobenzofuran-1(3H)-one (6a)
Colorless solid; mp 114 ꢁC [Found: C, 72.3; H, 3.8; S, 12.2.
C16H10O2S requires: C, 72.16; H, 3.78; S, 12.04%.] Rf (10% EA/Hexane)
of hexyl substituents at the a/b-position of benzo[c]thiophene 7a
significantly diminished its electro-oxidation behavior, which is in
agreement with our earlier observation.9a Surprisingly, the simul-
taneous introduction of two hexyl units on benzo[c]thiophene 7a
has only a minimum influence on its electro-oxidation potential.
Replacement of benzo[b]thineyl unit of 7a with 1-hexylindole/3-
methylfuran increased its anodic peak potential value and conse-
quently the electro-oxidation behavior has been slightly reduced.
0.62; nmax (KBr) 1759, 1595, 1500, 745 cmꢀ1
; dH (300 MHz, CDCl3)
8.03 (1H, d, J 7.5 Hz, ArH), 7.88 (1H, t, J 4.5 Hz, ArH), 7.74–7.68 (2H,
m, ArH), 7.63 (1H, t, J 7.5 Hz, ArH), 7.52 (1H, t, J 7.5 Hz, ArH), 7.41–
7.38 (2H, m, ArH), 7.35 (1H, s, ArH), 6.82 (1H, s, ArH); dC (75.6 MHz,
CDCl3) 170.2, 148.1, 140.8, 137.2, 134.4, 131.1, 128.7, 126.7, 126.3,
125.9, 125.1, 124.7, 123.1, 122.1, 77.7; MS (EI): m/z (%)¼266 [M]þ.
3. Conclusions
4.2.3. 3-(2-Hexylbenzo[b]thiophen-3-yl)isobenzofuran-1(3H)-
one (6b)
In summary, the synthesis of a variety of benzo[c]thiophene ana-
logs possessing heterocycles such as benzo[b]thiophene/1-hexyl-
indole/benzo[b]furan has been achieved in reasonable yields. The
highly soluble nature of these benzo[c]thiophenes may make them
suitable for transistor applications through spin-coating techniques.
Since, the emission values of dimeric benzo[c]thiophenes as well as
benzo[c]thiophenes possessing electron-withdrawing groups are in
the range of 700–730 nm, they may be regarded as potential NIR
contrast agents for biomedical applications.13 Additionally, the
higher-lying HOMO energy levels of these benzo[c]thiophenes (w5.0
to 5.3 eV) may find them as suitable candidates for application as
hole-transporting materials in double-layer OLEDs.
Following the above-mentioned procedure (A), lactone 6b
(4.81 g, 60%) was obtained using 2-hexyl benzo[b]thiophene 3b
(5 g, 22.93 mmol), phthalic anhydride (3.73 g, 25.22 mmol), AlCl3
(3.98 g, 29.81 mmol), and NaBH4 (4.35 g, 114.67 mmol) as a color-
less solid. Mp 115 ꢁC; [Found: C, 75.5; H, 6.2; S, 8.9. C22H22O2S re-
quires: C, 75.39; H, 6.33; S, 9.15%.] nmax (KBr) 2867, 1755, 1585, 1500,
741 cmꢀ1; Rf (10% EA/Hexane) 0.70; dH (300 MHz, CDCl3) 8.04 (1H,
d, J 6.3 Hz, ArH), 7.71 (1H, d, J 7.8 Hz, ArH), 7.62–7.57 (2H, m, ArH),
7.25–7.16 (2H, m, ArH), 7.06 (1H, t, J 7.5 Hz, ArH), 6.80–6.78 (2H, m,
ArH), 2.94 (2H, t, J 7.5 Hz, CH2), 1.74 (2H, t, J 7.05 Hz, CH2), 1.38–1.29
(6H, m, CH2), 0.91 (3H, t, J 7.8 Hz, CH3); dC (75.6 MHz, CDCl3); 170.6,
149.0, 148.6, 138.2, 137.8, 134.6, 129.6, 126.5, 125.7, 124.4, 123.9,

4118
J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
123.7, 122.6, 122.3, 121.4, 76.9, 32.1, 31.5, 28.9, 28.8, 22.5, 14.1; MS
2.81 mmol), 5-hexyl-2-thienyl magnesium bromide [prepared
from 2-bromo-5-hexylthiophene (1.04 g, 4.22 mmol) and Mg
(0.12 g, 5.00 mmol)], and Lawesson’s reagent (0.56 g, 1.40 mmol) as
a thick yellow liquid. [Found: C, 72.3; H, 5.7; S, 22.1. C26H24S3 re-
quires: C, 72.18; H, 5.59; S, 22.23%.] Rf (100% Hexane) 0.92; dH
(300 MHz, CDCl3) 8.0–7.91 (3H, m, ArH), 7.59 (1H, s, ArH), 7.54 (1H,
d, J 9.0 Hz, ArH), 7.42–7.38 (2H, m, ArH), 7.18 (1H, d, J 3.6 Hz, ArH),
7.11 (1H, t, J 6.2 Hz, ArH), 7.02 (1H, t, J 6.4 Hz, ArH), 6.81 (1H, d, J
3.6 Hz, ArH), 2.86 (2H, t, J 7.6 Hz, CH2), 1.79–7.72 (2H, m, CH2), 1.44–
1.30 (6H, m, CH2), 0.9 (3H, t, J 7.1 Hz, CH3); dC (75.6 MHz, CDCl3)
146.6, 140.3, 138.3, 137.0, 134.5, 133.2, 129.1, 127.9, 126.1, 125.4,
125.3, 124.8, 124.6, 124.4, 124.1, 123.4, 122.9, 121.7, 121.6, 31.6, 30.9,
28.8, 22.6, 14.1; MS (EI): m/z (%)¼432 [M]þ.
(EI): m/z (%)¼350 [M]þ.
4.2.4. 3-(1-Hexyl-1H-indol-3-yl)isobenzofuran-1(3H)-one (6c)
Following the above-mentioned procedure (A), lactone 6c
(4.30 g, 52%) was obtained using 1-hexyl-1H-indole 3c (5 g,
24.87 mmol), phthalic anhydride (4.04 g, 27.36 mmol), AlCl3 (4.31 g,
32.33 mmol), and NaBH4 (4.72 g, 124.37 mmol) as a thick yellow
liquid. [Found: C, 79.4; H, 7.1; N, 4.0. C22H23NO2 requires: C, 79.25; H,
6.95; N, 4.20%.] Rf (10% EA/Hexane) 0.58; nmax (KBr) 2811,1759,1605,
1500, 755, 685 cmꢀ1
; dH (300 MHz, CDCl3) 7.91 (1H, d, J 7.5 Hz, ArH),
7.67–7.46 (2H, m, ArH), 7.42 (1H, d, J 7.5 Hz, ArH), 7.32 (1H, d, J 8.4 Hz,
ArH), 7.17 (1H, t, J 8.7 Hz, ArH), 7.13–6.99 (2H, m, ArH), 7.02 (1H, d, J
6.9 Hz, ArH), 6.76 (1H, s, ArH), 4.05 (2H, t, J 7.05 Hz, CH2), 1.81–1.78
(2H, m, CH2), 1.35–1.25 (6H, m, CH2), 0.86 (3H, t, J 6.1 Hz, CH3); dc
(75.6 MHz, CDCl3) 170.6,149.4,136.8,134.1,129.3,128.2,126.8,126.4,
125.5,123.1,122.3,120.0,119.2,109.9,109.5, 77.7, 46.6, 31.3, 30.1, 26.6,
22.5, 13.9; MS (EI): m/z (%)¼333 [M]þ.
4.3.4. 3-(1-o-Tolylbenzo[c]thiophen-3-yl)benzo[b]thiophene (7d)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7d (0.50 g, 50%) was obtained using the lactone 6a (0.75 g,
2.81 mmol), o-tolylmagnesium bromide [prepared from o-bro-
motoluene (0.71 g, 4.23 mmol) and Mg (0.12 g, 5.01 mmol)], and
Lawesson’s reagent (0.56 g, 1.40 mmol) as a yellow solid. Mp
62 ꢁC; [Found: C, 77.6; H, 4.7; S, 18.1. C23H16S2 requires: C, 77.49; H,
4.52; S, 17.99%.] Rf (100% Hexane) 0.85; dH (300 MHz, CDCl3) 7.99–
7.91 (2H, m, ArH), 7.60 (1H, s, ArH), 7.58 (1H, d, J 3.7 Hz, ArH), 7.46
(1H, d, J 6.9 Hz, ArH), 7.42–7.28 (6H, m, ArH), 7.03–7.0 (2H, m,
ArH), 2.33 (3H, s, CH3); dC (75.6 MHz, CDCl3) 140.4, 138.4, 138.1,
136.2, 136.0, 133.1, 132.7, 132.2, 130.6, 129.4, 128.5, 126.3, 125.9,
125.8, 124.8, 124.5, 123.7, 123.4, 122.9, 121.6, 121.5, 20.7; MS (EI):
m/z (%)¼356 [M]þ.
4.3. A representative procedure for the preparation of benzo-
[c]thiophene (7a) from lactone (6a) (procedure B)
To a solution of lactone 6a (0.75 g, 2.81 mmol) in anhydrous THF
(25 mL) was added 2-thienylmagnesium bromide [prepared from
2-bromothiophene (0.68 g, 4.22 mmol) and magnesium turnings
(0.12 g, 5.0 mmol)] at 0 ꢁC under N2. The reaction mixture was
slowly raised to room temperature and stirred for 4 h. It was then
quenched with aq NH4Cl solution (30 mL), extracted with DCM
(2ꢂ20 mL), and dried (Na2SO4). The DCM solution was then stirred
with Lawesson’s reagent (0.56 g, 1.40 mmol) at room temperature
for 4 h. Solvent was evaporated in vacuo to give the crude product,
which was purified by column chromatography (100% Hexane) to
give the title compound 7a (0.52 g, 54%) as an orange solid.
4.3.5. 3-(1-p-Tolylbenzo[c]thiophen-3-yl)benzo[b]thiophene (7e)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7e (0.48 g, 48%) was obtained using the lactone 6a (0.75 g,
2.81 mmol), p-tolylmagnesium bromide [prepared from p-bromo-
toluene (0.71 g, 4.23 mmol) and Mg (0.12 g, 5.01 mmol)], and
Lawesson’s reagent (0.56 g, 1.40 mmol) as a thick orange liquid.
[Found: C, 77.3; H, 4.6; S,18.2. C23H16S3 requires: C, 77.49; H, 4.52; S,
17.99%.] Rf (100% Hexane) 0.85; dH (300 MHz, CDCl3) 7.98–7.86 (2H,
m, ArH), 7.62–7.56 (2H, m, ArH), 7.47 (2H, d, J 7.8 Hz, ArH), 7.41 (1H,
t, J 3.6 Hz, ArH), 7.32–7.21 (4H, m, ArH), 7.11–7.01 (2H, m, ArH), 2.37
(3H, s, CH3); dC (75.6 MHz, CDCl3) 140.3, 137.5, 137.0, 136.7, 133.1,
132.7, 131.3, 129.8, 129.4, 129.1, 126.8, 125.9, 124.8, 124.6, 124.1,
123.8, 123.4, 122.9, 121.7, 121.2, 21.1; MS (EI): m/z (%)¼356 [M]þ.
4.3.1. 3-(1-(Thiophen-2-yl)benzo[c]thiophen-3-yl)-
benzo[b]thiophene (7a)
Mp 118 ꢁC; [Found: C, 69.1; H, 3.5; S, 27.8. C20H12S3 requires: C,
68.93; H, 3.47; S, 27.60%.] Rf (100% Hexane) 0.90; dH (300 MHz,
CDCl3) 8.73 (1H, d, J 7.8 Hz, ArH), 7.95 (1H, d, J 7.8 Hz, ArH), 7.80–
7.76 (2H, m, ArH), 7.71 (1H, d, J 4.2 Hz, ArH), 7.58–7.53 (2H, m, ArH),
7.47 (1H, t, J 7.8 Hz, ArH), 7.35 (1H, d, J 4.8 Hz, ArH), 7.31–7.18 (1H, m,
ArH), 7.10–7.04 (2H, m, ArH); dC (75.6 MHz, CDCl3) 140.8, 140.2,
139.8, 136.8, 133.9, 127.9, 127.1, 125.4, 125.3, 125.0, 124.9, 124.3,
123.8, 122.9, 122.7, 122.3, 122.0, 120.9, 119.8, 119.8; MS (EI): m/z
(%)¼348 [M]þ.
4.3.6. 1-(Benzo[b]thiophen-3-yl)-3-(4-methoxylphenyl)-
benzo[c]thiophene (7f)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7f (0.57 g, 55%) was obtained using the lactone 6a (0.75 g,
2.81 mmol), p-anisylmagnesium bromide [prepared from p-bro-
moanisole (0.78 g, 4.23 mmol) and Mg (0.12 g, 5.03 mmol)], and
Lawesson’s reagent (0.56 g, 1.40 mmol) as a yellow solid. Mp
105 ꢁC; [Found: C, 74.4; H, 4.4; S, 17.1. C23H16OS2 requires: C, 74.16;
H, 4.33; S, 17.22%.] Rf (100% Hexane) 0.80; dH (300 MHz, CDCl3)
7.87–7.81 (2H, m, ArH), 7.70 (1H, d, J 8.4 Hz, ArH), 7.53–7.45 (3H, m,
ArH), 7.35 (2H, d, J 8.7 Hz, ArH), 7.37–7.30 (1H, m, ArH), 6.99–6.91
(3H, m, ArH), 6.83 (1H, d, J 8.7 Hz, ArH), 3.75 (3H, s, OCH3); dC
(75.6 MHz, CDCl3) 159.4, 158.7, 140.3, 138.4, 137.0, 134.4, 133.5,
130.5, 129.4, 127.7, 126.7, 125.8, 124.8, 124.5, 124.1, 123.8, 123.4,
122.9, 121.7, 121.2, 114.6, 114.2, 55.4; MS (EI): m/z (%)¼372 [M]þ.
4.3.2. 1-(Benzo[b]thiophen-3-yl)-3-(3-hexylthiophen-2-yl)-
benzo[c]thiophene (7b)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7b (0.72 g, 60%) was obtained using the lactone 6a (0.75 g,
2.81 mmol), 3-hexyl-2-thienylmagnesium bromide [prepared from
2-bromo-3-hexylthiophene (1.04 g, 4.22 mmol) and Mg (0.12 g,
5.0 mmol)], and Lawesson’s reagent (0.56 g, 1.40 mmol) as a thick
yellow liquid. [Found: C, 72.3; H, 5.7; S, 22.1. C26H24S3 requires: C,
72.18; H, 5.59; S, 22.23%.] Rf (100% Hexane) 0.92; dH (300 MHz,
CDCl3) 7.97–7.92 (2H, m, ArH), 7.64–7.56 (3H, m, ArH), 7.43–7.37 (3H,
m, ArH), 7.11–7.01 (3H, m, ArH), 2.68 (2H, t, J 7.8 Hz, CH2), 1.62–1.55
(2H, m, CH2), 1.28–1.17 (6H, m, CH2), 0.81 (3H, t, J 6.9 Hz, CH3); dC
(75.6 MHz, CDCl3) 142.4,140.3,138.3,137.3,136.2,129.3,129.2,128.0,
127.6,126.2,125.9,125.3,124.9,124.6,124.2,123.9,123.4,122.9,121.6,
121.5, 31.6, 30.9, 29.2, 29.1, 22.6, 14.1; MS (EI): m/z (%)¼432 [M]þ.
4.3.7. 3-(1-(Naphthalen-1-yl)benzo[c]thiophen-3-yl)-
benzo[b]thiophene (7g)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7g (0.44 g, 40%) was obtained using the lactone 6a (0.75 g,
2.81 mmol), 1-napthylmagnesium bromide [prepared from 1-
bromnapthalene (0.87 g, 4.23 mmol) and Mg (0.12 g, 5.03 mmol)],
and Lawesson’s reagent (0.56 g, 1.40 mmol) as a yellow solid. Mp
4.3.3. 1-(Benzo[b]thiophen-3-yl)-3-(5-hexylthiophen-2-yl)-
benzo[c]thiophene (7c)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7c (0.67 g, 56%) was obtained using the lactone 6a (0.75 g,

J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
4119
78 ꢁC; [Found: C, 79.7; H, 4.2; S, 16.1. C26H16S2 requires: C, 79.55; H,
4.11; S, 16.34%.] Rf (100% Hexane) 0.85; dH (300 MHz, CDCl3) 8.37
(1H, d, J 6.9 Hz, ArH), 8.02–7.77 (5H, m, ArH), 7.66–7.41 (7H, m,
ArH), 7.22–7.05 (3H, m, ArH); dC (75.6 MHz, CDCl3) 140.4, 138.4,
136.9, 136.2, 134.3, 133.9, 132.8, 131.6, 130.9, 129.3, 128.7, 128.4,
126.5, 126.3, 126.2, 126.1, 126.0, 125.4, 124.9, 124.6, 123.9, 123.8,
123.5, 122.9, 121.8, 121.6; MS (EI): m/z (%)¼392 [M]þ.
bromothiophene (0.55 g, 3.37 mmol) and Mg (0.10 g, 4.04 mmol)],
and Lawesson’s reagent (0.45 g, 1.12 mmol) as a thick orange liquid.
[Found: C, 75.3; H, 5.9; N, 3.5; S,15.6. C26H25NS2 requires: C, 75.14; H,
6.06; N, 3.37; S,15.43%.] Rf (100% Hexane) 0.85; dH (300 MHz, CDCl3)
7.89–7.81 (2H, m, ArH), 7.62 (1H, d, J 8.7 Hz, ArH), 7.30–7.09 (6H, m,
ArH), 7.03–6.99 (2H, m, ArH), 6. 91 (1H, t, J 7.5 Hz, ArH), 4.02 (2H, t, J
7.2 Hz, NCH2), 1.79–1.74 (2H, m, CH2), 1.35–1.15 (6H, m, CH2), 0.77
(3H, t, J 6.2 Hz, CH3); dC (75.6 MHz, CDCl3) 135.5, 134.4, 133.9, 126.9,
126.6, 126.1,125.9,125.5, 124.7,123.6,123.6,123.2,122.1,121.3, 121.1,
120.2, 119.3, 119.1, 108.7, 107.3, 45.6, 30.3, 29.1, 25.6, 21.5, 12.9; MS
(EI): m/z (%)¼415 [M]þ.
4.3.8. 1-(2-Hexylbenzo[b]thiophen-3-yl)-3-(thiophen-3-yl)-
benzo[c]thiophene (7h)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7h (0.41 g, 45%) was obtained using the lactone 6b (0.75 g,
2.14 mmol), 2-thienylmagnesium bromide [prepared from 2-bro-
mothiophene (0.52 g, 3.21 mmol) and Mg (0.09 g, 3.82 mmol)], and
Lawesson’s reagent (0.43 g, 1.07 mmol) as a thick orange liquid;
[Found: C, 72.0; H, 5.6; S, 22.4. C26H24S3 requires: C, 72.18; H, 5.59;
S, 22.23%.] Rf (100% Hexane) 0.92; dH (300 MHz, CDCl3) 7.72–7.60
(3H, m, ArH), 7.36 (1H, d, J 3.8 Hz, ArH), 7.32–7.15 (3H, m, ArH),
7.09–6.99 (2H, m, ArH), 6.93–6.87 (1H, m, ArH), 6.83–6.78 (1H, m,
ArH), 2.89 (2H, t, J 7.8 Hz, CH2), 1.69–1.60 (2H, m, CH2), 1.31–1.08
(6H, m, CH2) 0.71 (3H, t, J 5.5 Hz, CH3); dC (75.6 MHz, CDCl3) 146.9,
139.3, 138.2, 134.0, 127.8, 125.4, 125.2, 124.6, 124.6, 124.2, 123.8,
123.5, 122.9, 122.5, 122.2, 122.2, 121.9, 120.6, 120.2, 119.7, 31.9, 31.6,
29.8, 29.0, 22.6, 14.1; MS (EI): m/z (%)¼432 [M]þ.
4.3.12. 1-Hexyl-3-(1-(5-hexylthiophen-2-yl)benzo[c]-
thiophen-3-yl)-1H-indole (7l)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7l (0.53 g, 48%) was obtained using the lactone 6c (0.75 g,
2.25 mmol), 5-hexyl-2-thienyl magnesium bromide [prepared
from 2-bromo-5-hexylthiophene (0.83 g, 3.37 mmol) and Mg
(0.10 g, 4.04 mmol)], and Lawesson’s reagent (0.45 g, 1.12 mmol) as
a thick orange liquid. [Found: C, 77.1; H, 7.3; N, 2.9; S, 13.1.
C32H37NS2 requires: C, 76.90; H, 7.46; N, 2.80; S, 12.83%.] Rf (100%
Hexane) 0.85; dH (300 MHz, CDCl3) 7.94 (1H, d, J 9.0 Hz, ArH), 7.91
(1H, d, J 7.8 Hz, ArH), 7.70 (1H, d, J 8.7 Hz, ArH), 7.41–7.38 (2H, m,
ArH), 7.31–7.21 (1H, m, ArH), 7.19–7.17 (1H, m, ArH), 7.14 (1H, d, J
3.3 Hz, ArH), 7.12–7.07 (1H, m, ArH), 7.02–6.98 (1H, m, ArH), 6.79
(1H, d, J 3.6 Hz, ArH), 4.16 (2H, t, J 7.2 Hz, NCH2), 2.84 (2H, t, J 7.6 Hz,
CH2),1.93–1.84 (2H, m, CH2),1.78–1.68 (2H, m, CH2),1.42–1.29 (12H,
m, CH2), 0.85–0.92 (6H, m, CH3); dC (75.6 MHz, CDCl3) 145.7, 136.5,
135.4, 134.6, 133.9, 127.2, 127.1, 125.2, 124.7, 124.5, 124.3, 123.1,
122.4, 122.2, 121.5, 120.4, 120.1, 109.7, 108.5, 46.6, 31.6, 31.4, 30.3,
30.2, 28.9, 26.7, 22.6, 22.5, 14.1, 14.0; MS (EI): m/z (%)¼499 [M]þ.
4.3.9. 2-Hexyl-3-(1-(3-hexylthiophen-2-yl)benzo[c]-
thiophen-3-yl)benzo[b]thiophene (7i)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7i (0.61 g, 56%) was obtained using the lactone 6b (0.75 g,
2.14 mmol), 3-hexyl-2-thienylmagnesium bromide [prepared from
2-bromo-3-hexylthiophene (0.79 g, 3.21 mmol) and Mg (0.09 g,
3.85 mmol)], and Lawesson’s reagent (0.43 g, 1.07 mmol) as a thick
orange liquid. [Found: C, 74.5; H, 7.1; S, 18.4. C32H36S3 requires: C,
74.37; H, 7.02; S, 18.61%.] Rf (100% Hexane) 0.92; dH (300 MHz,
CDCl3) 7.75–7.69 (2H, m, ArH), 7.38 (1H, d, J 7.2 Hz, ArH), 7.30–7.20
(4H, m, ArH), 7.05–7.0 (2H, m, ArH), 6.72 (1H, d, J 6.8 Hz, ArH), 2.91–
2.84 (4H, m, CH2), 1.80–1.71 (4H, m, CH2), 1.47–1.26 (12H, m, CH2),
0.82–0.73 (6H, m, CH3); dC (75.6 MHz, CDCl3) 146.6, 139.7, 138.3,
134.2, 128.0, 125.5, 125.3, 124.8, 124.6, 124.2, 123.7, 123.4, 122.9,
122.6, 122.5, 122.3, 122.0, 120.7, 119.6, 31.9, 31.5, 31.4, 30.8, 29.4,
29.1, 28.9, 22.5, 22.4, 14.2; MS (EI): m/z (%)¼516 [M]þ.
4.3.13. 1-Hexyl-3-(1-p-tolylbenzo[c]thiophen-3-yl)-1H-indole (7m)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7m (0.40 g, 42%) was obtained using the lactone 6c (0.75 g,
2.25 mmol), p-tolylmagnesium bromide [prepared from p-bromo-
toluene (0.57 g, 3.37 mmol) and Mg (0.10 g, 4.02 mmol)], and
Lawesson’s reagent (0.45 g, 1.12 mmol) as a thick orange liquid.
[Found: C, 82.5; H, 6.7; N, 3.4; S, 7.7. C29H29NS requires: C, 82.22; H,
6.90; N, 3.31; S, 7.57%.] Rf (100% Hexane) 0.65; dH (300 MHz, CDCl3)
7.92 (1H, d, J 7.8 Hz, ArH), 7.83 (1H, d, J 8.1 Hz, ArH), 7.72 (1H, d, J
8.4 Hz, ArH), 7.61 (2H, t, J 7.5 Hz, ArH), 7.42–7.28 (4H, m, ArH), 7.24–
7.19 (1H, m, ArH), 7.11–7.03 (3H, m, ArH), 4.20 (2H, t, J 6.7 Hz, NCH2),
2.42 (3H, s, CH3), 1.91–1.82 (2H, m, CH2), 1.55–1.25 (6H, m, CH2),
0.87 (3H, t, J 7.51 Hz, CH3); dC (75.6 MHz, CDCl3) 136.9, 136.5, 135.5,
131.8, 129.7, 129.0, 127.8, 127.0, 122.9, 122.3, 122.1, 121.2, 121.05,
120.92, 120.45, 120.0, 119.1, 109.3, 100.8, 46.6, 31.4, 30.2, 26.7, 22.5,
21.2, 14.0; MS (EI): m/z (%)¼423 [M]þ.
4.3.10. 2-Hexyl-3-(1-(5-hexylthiophen-2-yl)benzo[c]-
thiophen-3-yl)benzo[b]thiophene (7j)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7j (0.55 g, 50%) was obtained using the lactone 6b (0.75 g,
2.14 mmol), 5-hexyl-2-thienyl magnesium bromide [prepared
from 2-bromo-5-hexylthiophene (0.79 g, 3.21 mmol) and Mg
(0.09 g, 3.85 mmol)], and Lawesson’s reagent (0.43 g, 1.07 mmol)
as a thick orange liquid. [Found: C, 74.6; H, 7.1; S, 18.5. C32H36S3
requires: C, 74.37; H, 7.02; S, 18.61%.] Rf (100% Hexane) 0.92; dH
(300 MHz, CDCl3) 7.74–7.65 (2H, m, ArH), 7.41 (1H, d, J 7.4 Hz,
ArH), 7.30–7.18 (4H, m, ArH), 7.06–6.99 (2H, m, ArH), 6.84 (1H, d, J
6.5 Hz, ArH), 2.90–2.86 (4H, m, CH2), 1.82–1.66 (4H, m, CH2), 1.44–
1.26 (12H, m, CH2), 0.84–0.70 (6H, m, CH3); dC (75.6 MHz, CDCl3)
146.6, 139.5, 138.3, 134.1, 127.9, 125.5, 125.3, 124.7, 124.6, 124.2,
123.7, 123.4, 122.9, 122.7, 122.4, 122.3, 122.1, 120.6, 120.3, 119.6,
31.9, 31.6, 31.4, 30.8, 29.4, 29.2, 28.9, 22.5, 22.4, 14.3; MS (EI): m/z
(%)¼516 [M]þ.
4.3.14. 1-Hexyl-3-(1-(4-methoxyphenyl)benzo[c]-
thiophen-3-yl)-1H-indole (7n)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7n (0.44 g, 45%) was obtained using the lactone 6c (0.75 g,
2.25 mmol), p-anisylmagnesium bromide [prepared from p-bro-
moanisole (0.62 g, 3.37 mmol) and Mg (0.10 g, 4.04 mmol)], and
Lawesson’s reagent (0.45 g, 1.12 mmol) as a thick orange liquid.
[Found: C, 79.5; H, 6.7; N, 3.0; S, 7.4. C29H29NOS requires: C, 79.23;
H, 6.65; N, 3.19; S, 7.29%.] Rf (100% Hexane) 0.75; dH (300 MHz,
CDCl3) 7.92 (1H, d, J 7.8 Hz, ArH), 7.80–7.72 (2H, m, ArH), 7.63 (2H, d,
J 8.7 Hz, ArH), 7.48–7.39 (3H, m, ArH), 7.29–7.26 (1H, m, ArH), 7.19–
7.00 (3H, m, ArH), 6.94 (1H, d, J 9.0 Hz, ArH), 4.17 (2H, t, J 7.1 Hz,
NCH2), 3.86 (3H, s, OCH3), 1.92–1.88 (2H, m, CH2), 1.38–1.30 (6H, m,
CH2), 0.88 (3H, t, J 6.9 Hz, CH3); dC (75.6 MHz, CDCl3) 159.0, 136.6,
135.5, 134.6, 133.5, 130.4, 127.7, 127.3, 126.6, 123.9, 122.4, 122.1,
121.0, 120.4, 120.0, 114.5, 114.2, 113.5, 109.7, 108.8, 55.4, 46.6, 31.5,
30.2, 26.7, 22.6, 14.0; MS (EI): m/z (%)¼439 [M]þ.
4.3.11. 1-Hexyl-3-(1-thiophen-2-yl)benzo[c]thiophen-3-yl-
1H-indole (7k)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7k (0.42 g, 45%) was obtained using the lactone 6c (0.75 g,
2.25 mmol), 2-thienylmagnesium bromide [prepared from 2-

4120
J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
4.3.15. 1-Hexyl-3-(1-(napthalen-1-yl)benzo[c]-
thiophen-3-yl)-1H-indole (7o)
119.3, 113.9, 110.9, 31.8, 30.6, 30.4, 29.2, 22.7, 14.2, 9.1; MS (EI): m/z
(%)¼430 [M]þ.
Following the above-mentioned procedure (B), benzo[c]thio-
phene 7o (0.41 g, 40%) was obtained using the lactone 6c (0.75 g,
2.25 mmol), 1-napthylmagnesium bromide [prepared from 1-bro-
monapthalene (0.69 g, 3.37 mmol) and Mg (0.10 g, 4.01 mmol)],
and Lawesson’s reagent (0.45 g, 1.12 mmol) as a thick orange liquid.
[Found: C, 83.8; H, 6.5; N, 3.0; S, 7.1. C32H29NS requires: C, 83.62; H,
6.36; N, 3.05; S, 6.98%.] Rf (100% Hexane) 0.75; dH (300 MHz, CDCl3)
7.93–7.88 (2H, m, ArH), 7.83–7.80 (2H, m, ArH), 7.71 (1H, d, J 8.7 Hz,
ArH), 7.59 (1H, d, J 6.6 Hz, ArH), 7.48–7.40 (2H, m, ArH), 7.37–7.31
(3H, m, ArH), 7.23–7.15 (2H, m, ArH), 7.11 (1H, s, ArH), 6.92–6.83
(2H, m, ArH), 4.08 (2H, t, J 7.5 Hz, NCH2), 1.81 (2H, t, J 6.7 Hz, CH2),
1.29–1.16 (6H, m, CH2), 0.82 (3H, t, J 7.5 Hz, CH3); dC (75.6 MHz,
CDCl3) 134.7, 134.2, 132.3, 131.6, 130.5, 129.2, 127.4, 126.5, 126.4,
126.1,125.9, 124.8,124.7,124.1,123.9, 123.7,123.1,121.3,120.5,120.0,
119.6, 119.3, 118.1, 117.7, 107.4, 106.3, 44.3, 29.1, 27.8, 24.4, 20.2, 11.6;
MS (EI): m/z (%)¼459 [M]þ.
4.4.3. 3-Methyl-2-(1-phenylbenzo[c]thiophen-3-yl)-
benzofuran (12a)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 12a (0.60 g, 62%) was obtained using the lactone 10 (0.75 g,
2.84 mmol), phenylmagnesium chloride (0.93 g, 6.85 mmol), and
Lawesson’s reagent (0.57 g, 1.42 mmol) as an orange solid. Mp
114 ꢁC; [Found: C, 81.3; H, 4.9; S, 9.5. C23H16OS requires: C, 81.14; H,
4.74; S, 9.42%.] Rf (100% Hexane) 0.90; dH (300 MHz, CDCl3) 8.20
(1H, d, J 7.5 Hz, ArH), 7.82 (1H, d, J 7.8 Hz, ArH), 7.68 (2H, d, J 7.8 Hz,
ArH), 7.55–7.45 (4H, m, ArH), 7.38 (1H, d, J 7.5 Hz, ArH), 7.33–7.26
(2H, m, ArH), 7.20–7.09 (2H, m, ArH), 2.48 (3H, s, CH3); dC
(75.6 MHz, CDCl3) 154.3,147.2,137.0,135.9,134.7,133.9,130.7,129.3,
129.1, 127.8, 124.7, 124.4, 123.1, 122.6, 122.0, 120.9, 119.2, 112.3, 110.9,
9.7; MS (EI): m/z (%)¼340 [M]þ.
4.4.4. 3-Methyl-2-(1-p-tolylbenzo[c]hiophen-3-yl)-
benzofuran (12b)
4.4. 3-(3-Methylbenzofuran-2-yl)isobenzofuran-1-
(3H)-one (10)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 12b (0.53 g, 53%) was obtained using the lactone 10 (0.75 g,
2.84 mmol), p-tolylmagnesium bromide [prepared from p-bromo-
toluene (0.72 g, 4.26 mmol) and Mg (0.12 g, 5.07 mmol)], and
Lawesson’s reagent (0.57 g, 1.42 mmol) as a orange solid. Mp 90 ꢁC;
[Found: C, 81.5; H, 5.3; S, 9.3. C24H18OS requires: C, 81.32; H, 5.12; S,
9.05%.] Rf (100% Hexane) 0.90; dH (300 MHz, CDCl3) 8.10 (1H, d, J
7.8 Hz, ArH), 7.71 (1H, d, J 7.5 Hz, ArH), 7.50–7.42 (4H, m, ArH), 7.36
(2H, d, J 7.8 Hz, ArH), 7.21–7.18 (2H, m, ArH), 7.13–7.08 (2H, m, ArH),
2.39 (3H, s, CH3), 2.32 (3H, s, CH3); dC (75.6 MHz, CDCl3) 154.3,
138.3,137.8,137.0,136.7,136.3,134.5,131.1,129.8,129.4,129.2,126.8,
124.7, 124.5, 124.4, 123.0, 122.6, 121.0, 119.1, 112.2, 110.9, 21.3, 9.7;
MS (EI): m/z (%)¼354 [M]þ.
Following the above-mentioned procedure (A), lactone 10 (7.2 g,
72%) was obtained using 3-methylbenzofuran 8 (5 g, 37.87 mmol),
phthalic anhydride (6.16 g, 41.66 mmol), AlCl3 (6.57 g, 49.24 mmol),
and NaBH4 (7.19 g, 189.39 mmol) as a colorless solid. Mp 146 ꢁC;
[Found: C, 77.4; H, 4.7. C17H12O3 requires: C, 77.26; H, 4.58%.] Rf (10%
EA/Hexane) 0.70; nmax (KBr) 1759, 1600, 1379, 1174, cmꢀ1
; dH
(300 MHz, CDCl3) 7.99 (1H, d, J 7.5 Hz, ArH), 7.67 (1H, t, J 7.5 Hz,
ArH), 7.60 (1H, d, J 7.5 Hz, ArH), 7.52 (1H, d, J 7.5 Hz, ArH), 7.37 (1H,
d, J 7.5 Hz, ArH), 7.29–7.28 (2H, m, ArH), 7.26–7.23 (1H, m, ArH),
6.64 (1H, s, ArH), 2.30 (3H, s, CH3); dC (75.6 MHz, CDCl3) 170.1,154.5,
146.7, 145.1, 134.4, 129.8, 129.3, 126.2, 125.8, 125.5, 122.9, 122.7,
119.8, 116.9, 111.4, 74.6, 7.9; MS (EI): m/z (%)¼264 [M]þ.
4.4.5. 2-(1-(4-Methoxyphenyl)benzo[c]thiophen-3-yl)-
3-methylbenzofuran (12c)
4.4.1. 3-Methyl-2-(1-(thiophen-2-yl)benzo[c]-
thiophen-3-yl)benzofuran (11a)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 12c (0.59 g, 56%) was obtained using the lactone 10 (0.75 g,
2.84 mmol), p-anisylmagnesium bromide [prepared from p-bro-
moanisole (0.79 g, 4.26 mmol) and Mg (0.12 g, 5.07 mmol)], and
Lawesson’s reagent (0.57 g, 1.42 mmol) as an orange solid. Mp
88 ꢁC; [Found: C, 77.9; H, 4.7; S, 8.9. C24H18O2S requires: C, 77.81; H,
4.90; S, 8.66%.] Rf (100% Hexane) 0.90; dH (300 MHz, CDCl3) 7.99
(1H, d, J 7.5 Hz, ArH), 7.72 (1H, d, J 7.8 Hz, ArH), 7.62 (1H, d, J 7.5 Hz,
ArH), 7.42–7.36 (2H, m, ArH), 7.26 (1H, d, J 7.2 Hz, ArH), 7.16–7.14
(2H, m, ArH), 6.92–6.89 (3H, m, ArH), 6.66 (1H, d, J 7.8 Hz, ArH), 3.75
(3H, s, OCH3), 2.54 (3H, s, CH3); dC (75.6 MHz, CDCl3) 158.8, 158.7,
154.3, 132.2, 130.7, 130.5, 126.1, 125.4, 125.1, 124.6, 124.1, 123.8,
122.6, 121.2, 120.2, 119.6, 118.9, 115.7, 114.6, 110.7, 55.4, 8.8; MS (EI):
m/z (%)¼370 [M]þ.
Following the above-mentioned procedure (B), benzo[c]thio-
phene 11a (0.56 g, 58%) was obtained using the lactone 10 (0.75 g,
2.84 mmol), 2-thienylmagnesium bromide [prepared from 2-bro-
mothiophene (0.69 g, 4.26 mmol) and Mg (0.12 g, 5.07 mmol)], and
Lawesson’s reagent (0.57 g, 1.42 mmol) as a red solid. Mp 86 ꢁC
[Found: C, 73.0; H, 3.9; S, 18.3. C21H14OS2 requires: C, 72.80; H, 4.07;
S, 18.51%.] Rf (100% Hexane) 0.90; dH (300 MHz, CDCl3) 8.09–8.11
(1H, m, ArH), 7.86 (1H, m, ArH), 7.42–7.38 (2H, m, ArH), 7.25–7.06
(4H, m, ArH), 6.92–6.83 (3H, m, ArH), 2.38 (3H, s, CH3); dC
(75.6 MHz, CDCl3) 154.3, 146.9, 136.8, 135.6, 134.7, 130.6, 127.9,
125.7, 125.1, 124.8, 124.5, 123.1, 122.7, 121.2, 121.1, 119.2, 112.6, 110.8,
9.7; MS (EI): m/z (%)¼346 [M]þ.
4.4.2. 2-(1-(3-Hexylthiophen-2-yl)benzo[c]thiophen-3-yl)-3-
methylbenzofuran (11b)
4.4.6. 3-Methyl-2-(1-(naphthalen-1-yl)benzo[c]-
thiophene-3-yl)benzofuran (12d)
Following the above-mentioned procedure (B), benzo[c]thio-
phene 11b (0.67 g, 55%) was obtained using the lactone 10 (0.75 g,
2.84 mmol), 3-hexyl-2-thienylmagnesium bromide [prepared
from 2-bromo-3-hexylthiophene (1.04 g, 4.26 mmol) and Mg
(0.12 g, 5.07 mmol)], and Lawesson’s reagent (0.57 g, 1.42 mmol)
as a thick orange liquid. [Found: C, 75.1; H, 6.3; S, 14.7. C27H26OS2
requires: C, 75.31; H, 6.09; S, 14.89%.] Rf (100% Hexane) 0.92; dH
(300 MHz, CDCl3) 8.09–8.06 (1H, m, ArH), 7.44–7.41 (1H, m, ArH),
7.25–7.15 (2H, m, ArH), 7.12–7.05 (2H, m, ArH), 6.82–6.77 (4H, m,
ArH), 2.52–2.47 (2H, m, ArH), 2.37 (3H, s, CH3), 1.52–1.46 (2H, m,
CH2), 1.24–1.14 (6H, m, CH2), 0.76 (3H, t, J 6.8 Hz, CH3); dC
(75.6 MHz, CDCl3) 154.8, 145.1, 137.1, 135.9, 131.2, 129.5, 129.4,
128.4, 126.3, 125.1, 124.8, 124.6, 124.5, 122.8, 121.5, 120.7, 119.9,
Following the above-mentioned procedure (B), benzo[c]thio-
phene 12d (0.57 g, 52%) was obtained using the lactone 10 (0.75 g,
2.84 mmol), 1-napthyllmagnesium bromide [prepared from 1-bro-
monaphthalene (0.87 g, 4.26 mmol) and Mg (0.12 g, 5.06 mmol)],
and Lawesson’s reagent (0.57 g, 1.42 mmol) as an orange solid. Mp
128 ꢁC; [Found: C, 83.3; H, 4.5; S, 8.1. C27H18OS requires: C, 83.05; H,
4.65; S, 8.21%.] Rf (100% Hexane) 0.90; dH (300 MHz, CDCl3) 8.36–
8.32 (1H, m, ArH), 8.19 (1H, d, J 7.8 Hz, ArH), 7.92–7.80 (4H, m, ArH),
7.55–7.45 (5H, m, ArH), 7.27–7.22 (2H, m, ArH), 7.09–6.99 (2H, m,
ArH), 2.59 (3H, s, CH3); dC (75.6 MHz, CDCl3) 154.4,145.1,138.8,134.3,
130.8,130.7,129.9,128.8,128.6,127.9,127.2,126.6,126.3,126.2,125.8,
125.6,125.5,125.3,124.3,123.3,123.2,122.8,121.2,119.7,119.1,110.9,
8.8; MS (EI): m/z (%)¼390 [M]þ.

J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
4121
4.5. A representative procedure for the preparation
of compound 13a (procedure C)
0.86 mmol), BF3$Et2O (0.10 g, 0.86 mmol) and PIFA (0.27 g,
0.86 mmol) as a dark solid (0.12 g, 42%).
To a stirred solution of 7a (0.3 g, 0.86 mmol) in dry DCM (20 mL)
was added FeCl3 (0.27 g, 1.72 mmol) under N2 atmosphere. The
reaction mixture was stirred for 12 h at room temperature and
quenched with dilute solution of N2H4$H2O. Then, it was filtered
through Celite, extracted with DCM and dried (Na2SO4). Evapora-
tion of solvent followed by column chromatographic purification
(Silica gel, hexane) afforded 13a as black solid (0.17 g, 55%).
Using PIFA/BF3$OEt2. BF3$Et2O (0.12 g, 0.86 mmol) and PIFA (0.37 g,
0.86 mmol) were added sequentially to a stirred solution of 7a (0.3 g,
0.86 mmol) in CH2Cl2 (10 ml) at ꢀ78 ꢁC under nitrogen atmosphere.
The reaction mixture was stirred at the same temperature for 6 h.
Aqueous workup with saturated NaHCO3 (10 mL) at 0 ꢁC followed by
column chromatographic purification gave the dimer 13a (0.13 g, 40%).
4.5.4. Hexyl-3-(1-(3-hexyl-5-(4-hexyl-5-(1-(2-hexylbenzo[b]-
thiophen-3-yl)benzo[c]thiophen-3-yl)thiophen-2-yl)thiophen-
2-yl)benzo[c]thiophen-3-yl)benzo[b]thiophene (13d)
Following the above-mentioned procedure (C), dimer 13d was
obtained using the monomer 7i (0.3 g, 0.58 mmol) and FeCl3
(0.18 g,1.11 mmol) as a thick red liquid (0.14 g, 49%). [Found: C, 74.8;
H, 7.0; S, 18.4. C64H70S6 requires: C, 74.51; H, 6.84; S, 18.65%.] Rf
(Hexane) 0.40; dH (300 MHz, CDCl3) 7.70 (2H, d, J 7.8 Hz, ArH), 7.42–
7.37 (2H, m, ArH), 7.28–7.10 (8H, m, ArH), 7.06–6.88 (6H, m, ArH),
2.89 (4H, t, J 7.0 Hz, ArH), 2.72 (4H, t, J 7.8 Hz, CH2),1.72–1.68 (8H, m,
CH2), 1.29–1.20 (24H, m, CH2), 0.89–0.80 (12H, m, CH3); dC
(75.6 MHz, CDCl3) 159.6, 147.0, 142.9, 140.7, 137.9, 137.2, 137.1, 136.8,
129.4, 126.8, 125.9, 125.7, 124.4, 124.1, 123.7, 122.8, 122.1, 121.6,
120.6, 119.8, 31.9, 31.6, 31.5, 30.9, 29.4, 29.1, 28.8, 22.6, 22.5, 14.1; MS
(EI): m/z (%)¼1030 [M]þ.
4.5.1. 3-(1-(5-(5-(1-(Benzo[b]thiophen-3-yl)benzo[c]thiophen-3-
yl)thiophen-2-yl)thiophen-2-yl)benzo[c]thiophen-3-
yl)benzo[b]thiophene (13a)
Using PIFA/BF3$OEt2. Following the above-mentioned procedure
(C), dimer 13d was obtained using the monomer 7e (0.3 g,
0.58 mmol), BF3$Et2O (0.08 g, 0.58 mmol) and PIFA (0.25 g,
0.58 mmol) as a thick red liquid (0.13 g, 45%).
Mp 130 ꢁC; [Found: C, 69.4; H, 3. 3; S, 27.5. C40H22S6 requires: C,
69.13; H, 3.19; S, 27.68%.] Rf (5% EA/Hexane) 0.70; dH (300 MHz,
CDCl3) 8.07 (2H, d, J 8.4 Hz, ArH), 7.98–7.94 (4H, m, ArH), 7.64 (2H, s,
ArH), 7.59 (2H, d, J 8.7 Hz, ArH), 7.44–7.39 (4H, m, ArH), 7.33–7.32
(2H, m, ArH), 7.28–7.17 (4H, m, ArH), 7.10–7.05 (2H, m, ArH); dC
(75.6 MHz, CDCl3) 140.3, 138.2, 137.2, 136.7, 135.0, 134.8, 126.8,
126.4, 125.9, 125.4, 124.9, 124.6, 124.4, 124.3, 123.5, 123.3, 122.9,
121.9, 121.7, 121.4; MS (EI): m/z (%)¼694 [M]þ.
4.5.5. 1-Hexyl-3-(1-(5-(5-(1-(1-hexyl-1H-indol-3-yl)benzo[c]-
thiophen-3-yl)thiophen-2-yl)thiophen-2-yl)benzo[c]-
thiophen-3-yl)-1H-indole (14)
Following the above-mentioned procedure (C), dimer 14 was
obtained using the monomer 7k (0.3 g, 0.72 mmol) and FeCl3
(0.23 g, 1.41 mmol) as thick red liquid (0.11 g, 40%). [Found: C, 75.1;
H, 6.0; N, 3.5; S, 15.3. C52H48N2S4 requires: C, 75.32; H, 5.83; N, 3.38;
S, 15.47%.] Rf (5% EA/Hexane) 0.50; dH (300 MHz, CDCl3) 7.97–7.94
(2H, m, ArH), 7.88–7.85 (2H, m, ArH), 7.67 (2H, d, J 7.5 Hz, ArH), 7.36–
7.30 (4H, m, ArH), 7.24–7.11 (6H, m, ArH), 6.98–6.93 (2H, m, ArH),
6.89–6.81 (4H, m, ArH), 4.04 (4H, t, J 7.6 Hz, NCH2),1.78–1.72 (4H, m,
CH2), 1.26–1.15 (12H, m, CH2), 0.80–0.70 (6H, m, CH3); dC (75.6 MHz,
CDCl3) 136.1, 135.6, 134.8, 134.1, 133.6, 130.9, 126.7, 126.2, 125.7,
125.2,124.9,123.8,123.6,122.4,121.6,121.3,120.4,119.4,111.6,107.6,
44.8, 31.1, 29.2, 26.1, 21.8, 13.4; MS (EI): m/z (%)¼828 [M]þ.
4.5.2. 3-(1-(5-(5-(1-(Benzo[b]thiophen-3-yl)benzo[c]thiophen-3-
yl)-4-hexylthiophen-2-yl)-3-hexylthiophen-2-yl)benzo[c]-
thiophen-3-yl)benzo[b]thiophene (13b)
Following the above-mentioned procedure (C), dimer 13b was
obtained using the monomer 7b (0.3 g, 0.69 mmol) and FeCl3
(0.22 g, 1.36 mmol) as a dark solid (0.17 g, 60%). Mp 180 ꢁC; [Found:
C, 72.6; H, 5.5; S, 22.0. C52H46S6 requires: C, 72.34; H, 5.37; S,
22.29%.] Rf (5% EA/Hexane) 0.80; dH (300 MHz, CDCl3) 7.98–7.90
(3H, m, ArH), 7.77–7.74 (3H, m, ArH), 7.62–7.57 (3H, m, ArH), 7.41–
7.34 (4H, m, ArH), 7.20–7.05 (7H, m, ArH), 2.69 (4H, t, J 7.5 Hz, CH2),
1.65–1.54 (4H, m, CH2), 1.24–1.17 (12H, m, CH2), 0.82 (6H, t, J 6.5 Hz,
CH3); dC (75.6 MHz, CDCl3) 143.1, 140.3, 138.3, 137.3, 137.2, 136.3,
129.1, 127.8, 127.3, 126.3, 126.0, 124.9, 124.8, 124.6, 124.4, 124.1,
123.8, 122.9, 121.6, 121.5, 31.6, 30.8, 29.4, 29.1, 22.6, 14.1; MS (EI):
m/z (%)¼862 [M]þ.
4.5.6. 3-Methyl-2-(1-(5-(5-(1-(3-methylbenzofuran-3-yl)benzo[c]-
thiophen-3-yl)thiophen-2-yl)thiophen-2-yl)benzo[c]-
thiophen-3-yl)benzofuran (15)
Following the above-mentioned procedure (C), dimer 15 was
obtained using the monomer 11b (0.3 g, 0.69 mmol) and FeCl3
(0.22 g, 1.39 mmol) as thick red liquid (0.13 g, 45%). [Found: C, 75.1;
H, 6.0; S, 15.2. C54H50O2S4 requires: C, 75.48; H, 5.87; S, 14.93%.] Rf
(10% EA/Hexane) 0.70; dH (300 MHz, CDCl3) 8.10–7.95 (4H, m, ArH),
7.41–7.32 (4H, m, ArH), 7.18–7.08 (4H, m, ArH), 6.92–6.81 (6H, m,
ArH), 2.62–2.51 (4H, m, CH2), 2.39 (6H, s, CH3), 1.56–1.48 (4H, m,
CH2), 1.26–1.12 (12H, m, CH2), 0.81–0.73 (6H, m, CH3); dC (75.6 MHz,
CDCl3) 155.1, 146.2, 138.2, 136.2, 130.3, 128.9, 128.5, 126.5, 126.1,
125.4, 125.2, 124.6, 124.1, 123.1, 122.4, 121.8, 121.2, 120.1, 114.4, 111.2,
31.9, 30.6, 30.5, 29.3, 22.9, 14.4, 9.2; MS (EI): m/z (%)¼858 [M]þ.
Using PIFA/BF3$OEt2. Following the above-mentioned procedure
(C), dimer 13b was obtained using the monomer 7b (0.3 g,
0.69 mmol), BF3$Et2O (0.10 g, 0.69 mmol) and PIFA (0.29 g,
0.69 mmol) as a dark solid (0.16 g, 55%).
4.5.3. 2-Hexyl-3-(1-(5-(5-(1-(2-hexylbenzo[b]thiophen-3-yl)-
benzo[c]thiophen-3-yl)thiophen-2-yl)thiophen-2-yl)-
benzo[c]thiophen-3-yl)benzo[b]thiophene (13c)
Following the above-mentioned procedure (C), compound 13c
was obtained using the compound 7h (0.3 g, 0.86 mmol) and FeCl3
(0.22 g, 1.36 mmol) as black solid (0.15 g, 52%). Mp 192 ꢁC; [Found:
C, 72.7; H, 5. 5; S, 22.0. C52H46S6 requires: C, 74.51; H, 5.37; S,
22.29%.] Rf (5% EA/Hexane) 0.90; dH (300 MHz, CDCl3) 7.78–7.70
(4H, m, ArH), 7.42 (2H, d, J 6.9 Hz, ArH), 7.35–7.25 (6H, m, ArH),
7.95–7.05 (4H, m, ArH), 6.87 (2H, t, J 7.5 Hz, ArH), 6.80–6.75 (2H, m,
ArH), 2.72–2.68 (4H, m, CH2), 1.52–1.48 (4H, m, CH2), 1.27–1.21
(12H, m, CH2), 0.79 (6H, t, J 6.9 Hz, CH3); dC (75.6 MHz, CDCl3) 143.1,
140.4, 138.3, 137.3,137.2,136.3, 129.0, 127.9, 127.4, 126.1, 126.0, 125.1,
124.9, 124.7, 124.5, 124.1, 123.4, 123.0, 121.6, 121.5, 31.6, 30.8, 29.4,
29.1, 22.6, 14.1. MS (EI): m/z (%)¼862 [M]þ.
4.6. A representative procedure for the preparation
of compound 16a (procedure D)
POCl3 (0.66 g, 4.31 mmol) was slowly added to a mixture of dry
DCM (30 mL) and DMF (0.31 g, 4.31 mmol) at 0 ꢁC. After the addi-
tion was completed, the reaction mixture was stirred at room
temperature until a pale yellow color (Vilsmeier reagent) formed.
Then it was added to a solution benzo[c]thiophene 7a (1.0 g,
2.87 mmol) in dry DCM (10 mL) at 0 ꢁC. The reaction mixture was
stirred at room temperature for additional 10 h. Then the solvent
was completely removed and treated with aqueous NaOH (5 g in
Using PIFA/BF3$OEt2. Following the above-mentioned procedure
(C), compound 13c was obtained using the compound 7h (0.3 g,

4122
J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
100 mL water) at room temperature for 15 min. The crude product
was then extracted into DCM (50 mL) dried (Na2SO4) and solvent
was removed. The column chromatographic purification of the
crude product on neutral alumina (eluent: 10% EA in hexane)
afforded product 16a (0.75 g, 70%) as a red solid.
0.31 mmol) was added. The reaction mixture was then stirred at
room temperature for 6 h. The solid obtained was filtered and
washed with ethanol and dried to give 18b (0.07 g, 60%). Black
solid; mp 177 ꢁC; [Found: C, 67.1; H, 3.4; N, 3.1; S, 26.3. C27H15NS4
requires: C, 67.33; H, 3.14; N, 2.91; S, 22.63%.] Rf (10% EA/Hexane)
0.62; nmax (KBr) 2215, 1490, 730 cmꢀ1
; dH (300 MHz, CDCl3) 8.09
4.6.1. 5-(1-(Benzo[b]thiophen-3-yl)benzo[c]thiophen-3-
yl)thiophene-2-carbaldehyde (16a)
(1H, d, J 8.4 Hz, ArH), 7.98–7.91 (2H, m, ArH), 7.65–7.58 (3H, m,
ArH), 7.50–7.41 (4H, m, ArH), 7.34 (1H, s, ArH), 7.26 (2H, d, J 6.6 Hz,
ArH), 7.18–7.07 (2H, m, ArH); dC (75.6 MHz, CDCl3) 140.9, 140.3,
139.1, 138.0, 137.3, 136.6, 135.3, 133.4, 131.6, 128.5, 128.2, 126.8,
126.7, 126.1, 125.9, 125.8, 125.2, 125.1, 124.7, 124.5, 123.2, 122.9,
122.1, 121.4, 117.2, 102.0; MS (EI): m/z (%)¼481 [M]þ.
Mp 148 ꢁC; [Found: C, 67.2; H, 3.4; S, 25.2. C21H12OS3 requires: C,
66.99; H, 3.21; S, 25.55%.] Rf (10% EA/Hexane) 0.70; nmax (KBr) 1660,
1510, 1500, 730 cmꢀ1
; dH (300 MHz, CDCl3) 9.92 (1H, s, CHO), 8.11
(1H, d, J 9.0 Hz, ArH), 7.98–7.91 (2H, m, ArH), 7.78 (1H, d, J 3.9 Hz,
ArH), 7.68 (1H, s, ArH), 7.62 (1H, d, J 9.0 Hz, ArH), 7.48–7.42 (3H, m,
ArH), 7.31–7.28 (1H, m, ArH), 7.15–7.10 (1H m, ArH); dC (75.6 MHz,
CDCl3) 182.3, 146.1, 141.8, 140.3, 137.9, 137.5, 135.9, 130.0, 128.3,
127.2, 126.4, 125.2, 125.1, 124.8, 124.5, 123.1, 123.0, 122.3, 121.1; MS
(EI): m/z (%)¼376 [M]þ.
4.6.6. 2-((5-(1-(3-Methylbenzofuran-2-yl)benzo[c]thiophen-3-
yl)thiophen-2-yl)methylene)malononitrile (19a)
To a solution of 17 (0.1 g, 0.26 mmol) and malononitrile (0.02 g,
0.34 mmol) in dry ethanol piperidine (one drop) was added. The
reaction mixture was then stirred at room temperature for 6 h. The
solid obtained was filtered, washed with ethanol, and dried to give
19a (0.06 g, 52%). Black solid; mp 226 ꢁC; [Found: C, 71.3; H, 3.4; N,
6.5; S, 15.0. C25H14ON2S2 requires: C, 71.07; H, 3.34; N, 6.63; S,
15.18%.] Rf (10% EA/Hexane) 0.62; nmax (KBr) 2910, 2230, 1520,
4.6.2. 5-(1-(1-Hexyl-1H-indol-3-yl)benzo[c]thiophen-3-
yl)thiophene-2-carbaldehyde (16b)
Yield: 0.26 g (49%); thickred liquid; [Found: C, 73.4; H, 5.8; N, 3.3;
S, 14.2. C27H25NOS2 requires: C, 73.10; H, 5.68; N, 3.16; S, 14.46%.] Rf
(10% EA/Hexane) 0.62; nmax (KBr) 2890, 1680, 1530, 770 cmꢀ1
;
dH
720 cmꢀ1
; dH (300 MHz, CDCl3) 8.41 (1H, d, J 8.7 Hz, ArH), 8.07 (1H,
(300 MHz, CDCl3) 9.86 (1H, s, CHO), 8.07 (1H, d, J 9.0 Hz, ArH), 7.93
(1H, d, J 7.8 Hz, ArH), 7.80 (1H, d, J 8.7 Hz, ArH), 7.71 (1H, d, J 6.9 Hz,
ArH), 7.47 (1H, s, ArH), 7.42–7.39 (2H, m, ArH), 7.33 (1H, d, J 8.1 Hz,
ArH), 7.29 (1H, d, J 6.1 Hz, ArH), 7.26–7.21 (1H, m, ArH), 7.10–7.07 (1H,
m, ArH), 4.19 (2H, t, J 7.2 Hz, NCH2),1.96–1.86 (2H, m, CH2),1.36–1.25
(6H, m, CH2), 0.88 (3H, t, J 6.8 Hz, CH3); dC (75.6 MHz, CDCl3) 182.1,
147.2, 140.7,137.3, 136.6, 136.2, 135.8, 127.7, 126.7,126.5, 124.2,123.7,
122.8, 122.6, 121.2, 120.6, 120.2, 110.0, 108.1, 46.8, 31.4, 30.2, 26.7,
22.5, 14.0; MS (EI): m/z (%)¼443 [M]þ.
d, J 8.1 Hz, ArH), 7.77 (1H, s, ArH), 7.74–7.73 (1H, m, ArH), 7.61–7.53
(3H, m, ArH), 7.39–7.27 (4H, m, ArH), 2.58 (3H, s, CH3); dC
(75.6 MHz, CDCl3) 152.3, 149.1, 147.6, 144.1, 142.3, 140.1, 138.7, 137.7,
136.5, 134.5, 131.2, 127.6, 126.5, 125.3, 125.2, 123.9, 123.0, 122.1,
120.4, 117.5, 117.1, 10.1; MS (EI): m/z (%)¼422 [M]þ.
4.6.7. 3-(5-(1-(3-Methylbenzofuran-2-yl)benzo[c]thiophen-3-
yl)thiophen-2-yl)-2-(thiophen-2-yl)acrylonitrile (19b)
To a solution of 17 (0.1 g, 0.26 mmol) and thiophene-2-aceto-
nitrile (0.04 g, 0.34 mmol) in dry ethanol (10 mL), t-BuOK (0.03 g,
0.34 mmol) was added. The reaction mixture was then stirred at
room temperature for 6 h. The solid obtained was filtered washed
with ethanol and dried to give black solid 19b (0.07 g, 53%). Mp
165 ꢁC; [Found: C, 70.4; H, 3.4; N, 2.7; S, 20.2. C28H17NOS3 requires
C, 70.12; H, 3.57; N, 2.92; S, 20.06%.] Rf (10% EA/Hexane) 0.62; nmax
4.6.3. 5-(1-(3-Methylbenzofuran-2-yl)benzo[c]thiophen-3-
yl)thiophene-2-carbaldehyde (17)
Yield: 0.67 g (62%); brown solid; mp 190 ꢁC; [Found: C, 70.8; H,
3.9; S, 16.9. C22H14O2S2 requires: C, 70.56; H, 3.77; S, 17.13%.] Rf (10%
EA/Hexane) 0.62; nmax (KBr) 2851, 1672, 1490, 745 cmꢀ1
; dH
(KBr) 2900, 2220, 1495, 745 cmꢀ1
; dH (300 MHz, CDCl3) 8.27 (1H, d,
(300 MHz, CDCl3) 9.91 (1H, s, CHO), 8.32–8.30 (1H, m, ArH), 8.08–
8.06 (1H, m, ArH), 7.74–7.76 (1H, m, ArH), 7.56–7.46 (3H, m, ArH),
7.34–7.28 (4H, m, ArH), 2.52 (3H, s, CH3); dC (75.6 MHz, CDCl3) 182.3,
154.4,146.4,145.7,141.9,136.9,135.7,130.3,126.6,126.4,125.3,125.2,
123.7,122.9,120.8,119.5,114.2,110.9, 9.9; MS (EI): m/z (%)¼374 [M]þ.
J 7.8 Hz, ArH), 8.01 (1H, d, J 7.8 Hz, ArH), 7.53–7.45 (3H, m, ArH),
7.38–7.24 (8H, m, ArH), 7.04 (1H, d, J 3.9 Hz ArH), 2.49 (3H, s, CH3);
dC (75.6 MHz, CDCl3) 154.3, 146.7, 140.6, 139.1, 136.9, 136.7, 135.2,
133.4, 131.5, 130.5, 128.2, 127.3, 126.7, 126.2, 125.8, 125.4, 125.2,
124.9, 123.8, 123.6, 122.8, 121.1, 119.3, 117.2, 113.6, 110.9, 102.1, 9.9;
MS (EI): m/z (%)¼479 [M]þ.
4.6.4. 2-((5-(1-(Benzo[b]thiophen-3-yl)benzo[c]thiophen-3-
yl)thiophen-2-yl)methylene)malononitrile (18a)
4.6.8. 4-((E)-2-(5-(1-(Benzo[b]thiophen-3-yl)benzo-
To a solution of aldehyde 16a (0.1 g, 0.26 mmol) and malono-
nitrile (0.02 g, 0.30 mmol) in dry ethanol (10 mL), piperidine (one
drop) was added. The above reaction mixture was stirred at room
temperature for 6 h. The solid obtained was filtered, washed with
ethanol, and dried to give 18a (0.06 g, 55%). Black solid; mp 230 ꢁC;
[Found: C, 67.6; H, 2.9; N, 6.7; S, 22.8. C24H12N2S3 requires: C, 67.90;
H, 2.85; N, 6.60; S, 22.66%.] Rf (10% EA/Hexane) 0.62; nmax (KBr)
[c]thiophen-3-yl)thiophen-2-yl)vinyl)-N,N-dibutylbenzene-
amine (21)
The monoaldehyde 16a (0.2 g, 0.47 mmol) was reacted with
4-N,N-dibutylaminobenzylphosphonium iodide 20 (0.064 g,
0.52 mmol) in the presence of BuLi (0.064 g, 0.57 mmol) in dry THF/
MeOH (20 mL; 3:1). The reaction mixture was then stirred at room
temperature for 6 h, extracted into DCM (50 mL), and dried
(Na2SO4). Solvent was evaporated in vacuo togive the crude product,
which was purified by column chromatography to give compound
21 (0.06 g, 48%) as thick red liquid. [Found: C, 74.6; H, 6.0; N, 2.3; S,
16.9. C36H35NS3 requires C, 74.82; H, 6.10; N, 2.42; S, 16.65%.] Rf (10%
2210, 1500, 730 cmꢀ1
; dH (300 MHz, CDCl3) 8.12 (1H, d, J 9.0 Hz,
ArH), 8.0–7.93 (2H, m, ArH), 7.79 (1H, s, ArH), 7.74 (1H, d, J 4.2 Hz,
ArH), 7.72 (1H, s, ArH), 7.67 (1H, d, J 7.8 Hz, ArH), 7.52 (1H, d, J
4.2 Hz, ArH), 7.48–7.45 (2H, m, ArH), 7.21–7.16 (2H, m, ArH); dC
(75.6 MHz, CDCl3) 153.3, 149.6, 148.6, 145.4, 142.3, 140.4, 139.7,
137.7, 136.5, 133.5, 130.2, 127.6, 127.5, 125.3, 125.2, 124.9, 123.0,
122.6, 121.2, 117.5, 117.1; MS (EI): m/z (%)¼424 (67).
EA/Hexane) 0.62; nmax (KBr) 2851, 1610, 1330, 1210 cmꢀ1
; dH
(300 MHz, CDCl3) 8.07 (1H, d, J 9.0 Hz, ArH), 7.97–7.92 (2H, m, ArH),
7.61 (1H, s, ArH), 7.56 (1H, d, J 8.7 Hz, ArH), 7.54–7.40 (2H, m, ArH),
7.34 (2H, d, J 8.4 Hz, ArH), 7.25 (1H, d, J 5.1 Hz, ArH), 7.15 (1H, t, J
8.7 Hz, ArH), 7.07–6.98 (3H, m, ArH), 6.98 (1H, d, J 15.9 Hz, ArH), 6.46
(2H, d, J 8.4 Hz, ArH), 3.28 (4H, t, J 7.5 Hz, NCH2), 1.63–1.53 (4H, m,
CH2),1.42–1.32 (4H, m, CH2), 0.96 (6H, t, J 7.3 Hz, CH3); dC (75.6 MHz,
CDCl3) 147.9,144.3,140.3,138.3,137.2,134.5,133.1,129.1,129.0,127.9,
4.6.5. 3-(5-(1-(Benzo[b]thiophen-3-yl)benzo[c]thiophen-3-
yl)thiophen-2-yl)-2-(thiophen-2-yl)acrylonitrile (18b)
To a solution of 16a (0.1 g, 0.26 mmol) in dry ethanol (10 mL),
thiophene-2-acetonitrile (0.04 g, 0.34 mmol), and t-BuOK (0.03 g,

J. Arul Clement et al. / Tetrahedron 65 (2009) 4113–4123
4123
6. Hide, F.; Diaz-Garcia, M. A.; Schwartz, B. J.; Heeger, A. J. Acc. Chem. Res. 1997, 30,
127.7,126.2,125.7,125.4,124.9,124.6,124.1,123.4,122.9,121.8,121.6,
430–436.
116.6, 111.7, 50.80, 29.52, 20.37, 14.0; MS (EI): m/z (%)¼577 [M]þ
}
7. Ba¨uerle, P.; Gotz, G.; Segelbacher, U.; Huttenlocher, D.; Mehring, M. Synth. Met.
1993, 55, 1335–1342.
Acknowledgements
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We thank the Department of Science and Technology (DST),
New Delhi (SR/S1/OC-37/2005) for financial support. J.A.C. and P.G
thank CSIR for SRF and JRF fellowship, respectively. Financial as-
sistance from UGC-potential for excellence is also acknowledged.
The authors thank the Department of Science and Technology (DST-
FIST) for a 300-MHz NMR spectrometer.
10. Strassler, C.; Davis, N. E.; Kool, E. T. Helv. Chim. Acta 1999, 82, 2160–2171.
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