Synthesis and characterization of benzannelated thienyl oligomers

Article abstract of DOI:10.1002/ejoc.200800244

An array of 1,3-diarylbenzo[c]thiophenes have been synthesized by the ring-opening of lactones followed by thionation using Lawesson's reagent with concurrent intramolecular cyclization. Photophysical studies of the various benzo[c]thiophene analogues are presented. The results of a cyclic voltammetric investigation of the benzo[c]thiophenes are also reported.

Full text of DOI:10.1002/ejoc.200800244

FULL PAPER
DOI: 10.1002/ejoc.200800244
Synthesis and Characterization of Benzannelated Thienyl Oligomers
Pitchamuthu Amaladass,[a] J. Arul Clement,[a] and Arasambattu K. Mohanakrishnan*[a]
Keywords: Lactones / Lawesson’s reagent / Benzothiophene / Oligomers / Cyclic voltammetry / Thiophenes
An array of 1,3-diarylbenzo[c]thiophenes have been synthe-
sized by the ring-opening of lactones followed by thionation
using Lawesson’s reagent with concurrent intramolecular cy-
clization. Photophysical studies of the various benzo[c]thio-
phene analogues are presented. The results of a cyclic vol-
tammetric investigation of the benzo[c]thiophenes are also
reported.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
dently by four groups.[16–19] In addition, Cava and co-
workers have outlined detailed synthetic studies of 1,3-di-
thienylbenzo[c]thiophene analogues.[20] An FeCl3-mediated
oligomerization of 1,3-dithienylbenzo[c]thiophene has also
been carried out. The synthesis of a novel nucleoside ana-
logue in which a DNA base is replaced by a 1,3-dithienyl-
benzo[c]thiophene has also been reported.[21] Nucleosides
of this type are useful as potential probes for understanding
the structures and dynamics of nucleic acids and can also
be used as fluorescent labels. The enhanced photolumines-
cence behavior of a 1,3-dithienylbenzo[c]thiophene deriva-
tive during photobleaching has also been observed.[22]
Substitution at the reactive α-positions of the terminal
thiophenes results in chemically stable oligomers.[23] Several
workers have reported the electrochemical/chemical synthe-
sis of dialkylsexithiophenes and their use in field-effect tran-
sistors (FETs).[24] In recent years, there has been consider-
able interest in the synthesis of new, low-band-gap oligo-
mers in view of their superior conductivity and nonlinear
optical properties. An optoelectronic study of polymers
from 1 gave a band gap of ca. 1.7 eV,[16] which is less than
that of polythiophenes (ca. 2 eV).[1c]
Introduction
During the past few years, the synthesis and application
of thienyl oligomers has been of great interest to chemists
and material scientists because of their intrinsic photophysi-
cal and redox properties.[1] Thienyl oligomers are also
widely used as building blocks in the synthesis of organic
materials with potential as organic light-emitting diodes
(OLEDs),[2,3] organic solar cells (OSC),[4,5] organic field-
effect transistors (OFETs),[6–9] and in photorefractive holo-
graphy.[10–12] In this regard, thiophene derivatives have
played a very significant role. For example, polythiophene
is superior to polyphenylene as a semiconductor and poly-
(thienylenevinylene) has attracted considerable interest as a
material with enhanced third-order nonlinear susceptibil-
ities. Arylenevinylenes and heteroarylenevinylenes have also
attracted attention in the fabrication of electroluminescent
devices.[13] The synthesis and investigation of well-defined
model oligomers have recently allowed a greater insight into
the structural and electronic peculiarities of the correspond-
ing polymers. The properties of oligomers can exceed those
of polymers not only because of their defined chemical
structures and conjugation length, but also because of their
superior solubility and the convenient processability of
these materials. In particular, the extent of conjugation does
not have a major effect on thienyl oligomers compared with
the corresponding polymers because electronic properties
become saturated beyond a particular chain length.[14] An
organic transistor containing sexithienylene as the active
semiconducting material has been reported.[15]
The exciting photophysical properties of thienyl oligo-
mers prompted us to explore further the synthesis of
benzo[c]thiophene derivatives. It has been well established
that the annellation of aromatic rings to thiophenes, for ex-
ample, as in benzo[c]thiophene,[25] greatly changes the prop-
erties of materials derived from such a substrate, and thus
synthetic work has been undertaken to modify 1,3-dithien-
ylbenzo[c]thiophenes so as to provide routes to new ex-
tended oligomers, for example, vinylenes. This may also
provide an opportunity to analyze the spectroscopic and
Since 1992 the synthesis and electrochemical behavior of
1,3-dithienylbenzo[c]thiophene have been reported indepen-
[a] Department of Organic Chemistry, University of Madras,
Guindy Campus,
Chennai 600025, Tamil Nadu, India
Fax: +91-44-22352494
E-mail: mohan_67@hotmail.com
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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Benzannelated Thienyl Oligomers
electrochemical behavior of 1,3-diarylbenzo[c]thiophene-ex-
tended systems.
As a continuation of our work on benzo[c]thiophene an-
alogues,[26,27] we report herein a detailed study on the syn-
thesis of the diarylbenzo[c]thiophene derivatives 2–5.
Scheme 2.
Results and Discussion
The related lactones are considered as crucial intermedi-
ates in the synthesis of various 1,3-diarylbenzo[c]-
thiophenes and their oligomers. Similarly to the known
phthalides 8a and 8b,[20] phthalides 8c and 8d were synthe-
sized by conventional Friedel–Crafts phthaloylation fol-
lowed by NaBH4 reduction and intramolecular cyclization
(Scheme 1).
Scheme 3.
Ring-opening of the various types of lactones 8a–n with
aryl/heteroaryl Grignard reagents was then attempted. The
1-aryl-3-thienylbenzo[c]thiophene analogues 9a and 9b were
readily prepared by the interaction of known lactone 8a
with commercially available aryl Grignard reagents fol-
lowed by thionation using Lawesson’s reagent (Scheme 4).
Scheme 1.
As the conventional Friedel–Crafts phthaloylation was
feasible only with thiophene derivatives, it was decided to
explore other methods[28–31] that can deliver highly substi-
tuted lactones in reasonable yields. We next attempted to
prepare the lactones by the magnesio protocol published
by Kato et al.[32] Notably, different types of lactones were
Scheme 4.
Alternatively, the interaction of lactones 8e–g, 8k, and 8l
synthesized by metallation of 2-bromobenzoic acid by using with 2-thienylmagnesium bromide followed by thionation
a combination of Bu2Mg and nBuLi under noncryogenic afforded unsymmetric 1-aryl-3-thienylbenzo[c]thiophenes
conditions. By adopting this procedure, lactones 8e–j were 9c–g. Under similar conditions, aryl lactones 8i, 8j, 8m, and
synthesized in better yields (Scheme 2). Some additional 8n were also smoothly transformed into the corresponding
lactones 8k–n were synthesized through the reaction of benzo[c]thiophenes 9h–k.
freshly prepared aryl Grignard reagents with 2-formylben-
The interaction of lactone 8a with 5-alkyl-2-thienylmag-
nesium bromide followed by thionation led to the isolation
zoic acid[33] (Scheme 3).
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P. Amaladass, J. A. Clement, A. K. Mohanakrishnan
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of highly soluble one-end-blocked 1,3-dithienylbenzo[c]- lective oligomerization of 3-(alkylsulfanyl)thiophenes using
thiophene analogues 9l–n (Scheme 5). Similarly, the inter- FeCl3 has also been reported.[35] Mustafa and Shephered
action of lactones 8b and 8d with 5-alkyl-2-thienylmagnes- reported a simple dimerization of β-trimethylsilyl-substi-
ium bromide followed by thionation furnished benzo[c]- tuted terthiophenes using ceric ammonium nitrate
thiophene analogues 9o–q (Scheme 6).
(CAN).[36] Recently, Kita and co-workers reported a syn-
thesis of 2,2Ј-bithiophene derivatives that involved oxidative
coupling of the corresponding alkylthiophenes using a com-
bination of phenyl iodide bis(trifluoroacetate) and
BF3·OEt2.[37] A mild FeCl3-mediated oligomerization of β-
substituted 1,3-dithienylbenzo[c]thiophenes led to the isola-
tion of annelated sexithiophene and nonithiophene ana-
logues.[20] Various conditions using CAN, FeCl3, PIFA/
BF3·OEt2, and CuCl2 were explored for the dimerization of
benzo[c]thiophene analogues.
End-blocked and highly soluble benzannelated quaterthi-
enyl derivatives 2a–d were prepared by the treatment of the
appropriate freshly prepared 5-alkyl-2-thienylmagnesium
Scheme 5.
Having synthesized the one-end-blocked benzo[c]thio- bromide with commercially available biphthalide 10 fol-
phenes, the next plan was to dimerize them in a controlled lowed by thionation and cyclization (Scheme 7). Ring-
manner to afford the corresponding dimerization products opening of the biphthalide 10 with aryl Grignard reagents
in reasonable yields. The controlled dimerization of several followed by thionation led to the isolation of the corre-
thienyl monomers has been reported by oxidation of the sponding benzo[c]thiophene analogues 11a and 11b
corresponding thienyl α-carbanion using CuCl2.[34] Regiose- (Scheme 8).
Scheme 6.
Scheme 7.
Scheme 8.
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Benzannelated Thienyl Oligomers
Scheme 9. [a] Yield obtained using FeCl3. [b] Yield obtained using PIFA/BF3·Et2O.
Scheme 10. [a] Yield obtained using FeCl3. [b] Yield obtained using PIFA/BF3·Et2O.
Of these conditions, anhydrous FeCl3 at room tempera-
ture and PIFA/BF3·OEt2 at a low temperature were found
to yield the dimerization products in reasonable yields.
Contrary to the FeCl3 conditions,[20] the dimerization of
benzo[c]thiophene 12 could be selectively performed by
using PIFA/BF3·OEt2 at a low temperature to afford the
known dimeric product 3 in 75% yield (Scheme 9). Simi-
larly, benzo[c]thiophenes 9l–n, 9c, and 9f could also be
smoothly dimerized to the corresponding products 4a–c,
5a, and 5b by using FeCl3 as well as PIFA/BF3·OEt2
(Schemes 9 and 10).
Scheme 11.
The push–pull system containing 1,3-diarylbenzo[c]thio-
phene as a conjugated system is regarded as potential non-
linear optical material. In particular, unsymmetrical donor–
acceptor-type 2,5-diarylated thiophenes that possess both
electron-donating and -withdrawing groups are of much
interest in single-layer electroluminescent devices that oper-
ate by hole transportation, light emission, or electron trans-
portation.[38–41] Hence, the synthesis of benzo[c]thiophene
analogues with an electron-acceptor group at one end and
a donor group at the other was planned. Accordingly, the
one-end-blocked benzo[c]thiophenes 9a, 9c–d, 9f–g, 9l–n,
and 9p were formylated under Vilsmeier–Haack conditions
to afford the corresponding monoaldehydes 13a–e and 14a–
e (Schemes 11 and 12). The monoaldehydes 13b–e under-
Scheme 12.
The optical properties of selected benzo[c]thiophenes are
went smooth condensation with malononitrile/2-thienyl- listed in Table 1. The UV/Vis absorption spectra of them
acetonitrile to give the corresponding cyanovinylenes 15a– showed an interesting pattern analogous to that observed
d and 16a–c (Scheme 13).
previously in the case of oligothiophene derivatives. The
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P. Amaladass, J. A. Clement, A. K. Mohanakrishnan
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λmax value (ca. 25 nm). Dimerization of one-end-blocked
benzo[c]thiophenes (9l–n Ǟ 2a–d and 9c/9f Ǟ 2a–d) caused
a redshift of the absorption maxima of ca. 70 nm. Com-
pared to the parent α,αЈ-dihexylsexithiophene (ca.
444 nm),[42] the benzannelated sexithienyl system 4c ex-
hibited a λmax value at a higher wavelength (520 nm) which
confirms the enhancement of conjugation through annel-
ation. A representative UV/Vis absorption spectrum of
compound 4c is presented in Figure 1.
Scheme 13.
monomeric benzo[c]thiophene analogues exhibited a highly
intense absorption band around 400 nm due to π–π* elec-
tron transfer of the entire conjugated backbone. As ex-
pected, benzannelation of the quaterthienyl system (9o–q)
caused a redshift of the λmax value of 75–90 nm. The intro-
duction of α-alkyl substituents (n-hexyl, 2-ethylhexyl, and
n-butyl) into 1 increased the longer-wavelength absorption
from 412 to 440 nm. The introduction of an electron-releas-
ing group such as NMe2, OMe, or Me at one end of the
benzo[c]thiophene caused a redshift of the absorption max-
ima of 10–25 nm. However, with the electron-releasing SMe
group the λmax value was shifted to a maximum extent (ca.
50 nm). The presence of electron-withdrawing groups at one
end of the benzo[c]thiophenes (9e and 13a–e) resulted in a
redshift of the λmax value, which confirms the enhancement
of π-electron delocalization. Increasing the number of
benzannelations (9o–q Ǟ 2a–d) significantly enhanced the
Figure 1. UV/Vis absorption spectrum of 4c.
The photoluminescence spectra of the benzo[c]thiophene
analogues exhibited emission in the orange region, which
was gradually redshifted with increasing conjugation. Of
the benzo[c]thiophene analogues 9a–g, only 9b and 9g emit-
ted light in the relatively high energy region of 510–518 nm.
As in the case of the absorption spectra, the luminescence
of the benzo[c]thiophenes was also redshifted with increas-
ing π-conjugation. The emission spectrum of compound 2d
is presented in Figure 2.
Table 1. Physical data for selected benzo[c]thiophenes.
[a]
[b]
[c]
[d]
onset
Compound λmax
λlum
Eg
1Epa
Eox
[eV]
HOMO[e] LUMO[f]
[nm]
[nm] [eV]
[V]
[eV]
[eV]
1
2a
2b
2d
3
4a
4b
4c
5b
9a
9b
9d
9e
9f
433
520
468
494
484
504
510
520
480
416
476
445
470
412
440
442
468
532
661
531
602
582
600
587
630
588
566
518
526
611
525
561
600
592
2.66 0.87
2.08 0.43
2.43 0.57
2.33 0.64
2.43 0.66
2.26 0.68
2.27 0.65
2.25 0.75
2.31 0.62
2.59 0.71
2.53 0.81
2.53 0.59
2.45 1.10
2.69 0.75
2.65 0.82
2.53 0.87
2.38 0.77
0.64
0.41
0.51
0.50
0.59
0.52
0.63
0.71
0.56
0.54
0.73
0.50
0.98
0.70
0.69
0.74
0.67
5.08
4.85
4.95
4.94
5.03
4.96
5.07
5.09
5.00
4.98
5.17
4.94
5.42
5.14
5.13
5.18
5.11
2.42
2.77
2.52
2.61
2.06
2.70
2.80
2.84
2.69
2.39
2.64
2.41
2.97
2.45
2.48
2.65
2.73
9l
9m
9o
[a] Measured in dilute dichloromethane solution. [b] Excited at the
absorption maxima. [c] Estimated from the onset of absorption
1
(Eg = 1240/λonset). [d] Epa denotes the first anodic peak potential.
[e] Calculated using the empirical equation: HOMO = (4.44 +
Eoxonset). [f] Calculated from LUMO = HOMO – Eg.
Figure 2. Emission spectrum of 2d.
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Benzannelated Thienyl Oligomers
The oxidation potentials and the onset oxidation values tion of highly soluble and stable sexithiophenes (4a–c) in
of the benzo[c]thiophenes are presented in Table 1. Increas- moderate yields. The ter-, quater-, and quinque-heterocycles
ing the ratio of nonclassical thiophene to thiophene (9o–q were studied by fluorescence spectroscopy and cyclic vol-
Ǟ 2a–d) significantly reduced its oxidation potential. Of tammetry. The highly soluble nature of the benzannelated
the thienyl oligomers, the quaterthienyl system 2a, which α,ω-dialkylsexithiophenes could find use in transistor appli-
contains two benzo[c]thiophene units, exhibited the lowest cations.
oxidation potential (0.43 eV). Dimerization of the thienyl
oligomers significantly enhances its electro-oxidative behav-
ior. The cyclic voltammogram of benzo[c]thiophene 2d is
Experimental Section
presented in Figure 3.
General Methods: All melting points (Toshnival) are uncorrected.
NMR spectra (JEOL 400 MHz, Bruker 300 and 500 MHz) were
determined in CDCl3 solution containing TMS as internal stan-
dard unless otherwise stated. Organic extracts were dried with an-
hydrous Na2SO4. All UV/Vis spectra were recorded with an Elico
SL-159 spectrophotometer using 10–3  solutions of the diaryl-
benzothiophenes in CH2Cl2. The emission spectra were recorded
with a Perkin-Elmer LS-45 Model spectrophotometer using 10–3

solutions of the diarylbenzothiophenes in CH2Cl2. Cyclic voltam-
metry of 10–3  solutions of the diarylbenzothiophenes was carried
out with a CHI 600C electrochemical analyzer. All the measure-
ments were carried out under oxygen-free conditions using a three-
electrode cell in which a glassy carbon electrode was employed as
a working electrode, a saturated Ag/AgCl electrode as the reference
electrode, and platinum wire as the auxiliary electrode. Tetra-
butylammonium hexafluorophosphonate (TBAPF6) was used as
the supporting electrolyte at a concentration of 10–1 . All the
potentials were calibrated with ferrocene as the internal standard.
3-(2-Thienyl)phthalide (8a): A hot solution of 2-(2-thenoyl)benzoic
acid (30.0 g, 0.129 mmol) in aqueous sodium hydrogen carbonate
(16.0 g in 2 L of H2O) was treated with NaBH4 (49. 0 g, 1.29 mmol)
in portions. After standing overnight, it was heated in a steam bath
for 1 h, cooled to room temperature, and then cautiously acidified
with 12% aqueous hydrochloric acid to pH = 2. The mixture was
stirred at room temperature for 2 h, and the white solid obtained
was filtered to give 8a[20] (22.0 g, 80%).
Figure 3. Cyclic voltammogram of 2d.
The HOMO and LUMO energy levels of selected
benzo[c]thiophenes were calculated from the corresponding
absorption onset and the onset oxidation potential and the
values are presented in Table 1. In general, annelation of
the benzene ring to terthiophene reduced the Eg value from
3 to 2.6 eV (terthiophene Ǟ 1). Of the benzo[c]thiophene
analogues, compound 2a, which has a 1:1 ratio of classical/
nonclassical thiophene, has the lowest Eg value (2.1 eV). Di-
merization of benzo[c]thiophene 9f led to a decrease and
increase in the HOMO and LUMO energy levels, respec-
tively. Consequently, the Eg value of the resulting product
5b is reduced. Dimerization of the α-alkyl-substituted
benzo[c]thiophenes (9l,m Ǟ 4a,b) also resulted in a lower-
ing of the Eg value. Compared with α,ω-dihexylsexithi-
ophene (Eg = 2.7 eV),[44] the benzannelated sexithiophene
4c exhibited a low band-gap value (Eg = 2.2 eV). The corre-
sponding β,βЈ-dihexylbenzannelated thiophene 3 has a
slightly enhanced band-gap value (Eg = 2.4 eV).
3-(2,2Ј-Bithienyl-5-yl)phthalide (8b): The bithenoylbenzoic acid
(12.0 g) was prepared from 2,2Ј-bithiophene (8.4 g, 0.051 mol) and
phthalic anhydride (7.5 g, 0.051 mol) in CH2Cl2 in 76% yield. M.p.
161 °C. The above intermediate acid was reduced to phthalide 8b
in 77% yield by a procedure similar to that of 2-thienylphthalide
8a. M.p. 164 °C. 1H NMR (400 MHz, CDCl3): δ = 7.97 (d, J =
7.7 Hz, 1 H), 7.74 (t, J = 7.3 Hz, 1 H), 7.61 (t, J = 7.6 Hz, 1 H),
7.50 (d, J = 7.1 Hz, 1 H), 7.22 (d, J = 4.1 Hz, 1 H), 7.12 (d, J =
4.1 Hz, 1 H), 7.08–7.10 (m, 2 H), 6.99–7.01 (m, 1 H), 6.62 (s, 1 H)
ppm. MS (EI): m/z (%) = 298 (100) [M]+. C16H10O2S2 (298.01):
calcd. C 64.40, H 3.38, S 21.49; found C 64.29, H 3.33, S 21.53.
3-(5-Hexyl-2-thienyl)phthalide (8c): The phthalide 8c was obtained
in 40% yield by a procedure similar to that of 2-thienylphthalide
8a. M.p. 90 °C. 1H NMR (400 MHz, CDCl3): δ = 7.92 (d, J =
8.0 Hz, 1 H), 7.67 (t, J = 7.4 Hz, 1 H), 7.55 (t, J = 7.6 Hz, 1 H),
7.46 (d, J = 8.0 Hz, 1 H), 6.94 (d, J = 3.2 Hz, 1 H), 6.67 (d, J =
3.0 Hz, 1 H), 6.58 (s, 1 H), 2.72 (t, J = 7.6 Hz, 2 H), 1.59 (m, 2 H),
1.28 (m, 6 H), 0.85 (t, J = 5.8 Hz, 3 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 169.72, 148.73, 148.58, 135.74, 134.13, 129.58, 127.94,
125.95, 125.45, 123.79, 123.12, 78.26, 31.37, 30.14, 29.59, 28.60,
22.41, 13.96 ppm. MS (EI): m/z (%) = 300 (100) [M]+. C18H20O2S
(300.12): calcd. C 71.96, H 6.71, S 10.67; found C 71.82, H 6.80, S
10.75.
Conclusions
A range of 1,3-diarylbenzo[c]thiophenes have been syn-
thesized by using Lawesson’s sulfur transfer reagent. The
diarylbenzothiophenes were functionalized to give alde-
hydes, vinylenes, and cyanovinylenes. For the first time the
one-end-blocked benzannelated quaterthienyl systems have
been prepared in reasonable yields. Dimerization of the
3-(5Ј-Hexyl-2,2Ј-bithienyl-5-yl)phthalide (8d): The phthalide 8d was
obtained in 50% yield by a procedure similar to that of 2-thienyl-
1
one-end-blocked terthienyl system (9l–n) led to the forma- phthalide 8a. M.p. 102 °C. H NMR (300 MHz, CDCl3): δ = 7.95
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P. Amaladass, J. A. Clement, A. K. Mohanakrishnan
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(d, J = 7.8 Hz, 1 H), 7.70 (t, J = 7.0 Hz, 1 H), 7.59 (t, J = 7.5 Hz,
1 H), 7.48 (d, J = 7.5 Hz, 1 H), 7.02 (d, J = 3.6 Hz, 1 H), 7.0 (d,
1Ј,3Ј-Dihydro-1,5Ј-bibenzo[c]furan-3(1H)-one (8h): The phthalide 8h
was obtained in 66% yield by a procedure similar to that used for
J = 3.9 Hz, 1 H), 6.91 (d, J = 3.9 Hz, 1 H), 6.64 (d, J = 3.6 Hz, 1 the preparation of 2-thienylphthalide 8a (metalation method). M.p.
H), 6.60 (s, 1 H), 2.76 (t, J = 7.5 Hz, 2 H), 1.59–1.62 (m, 2 H),
180 °C. 1H NMR (400 MHz, CDCl3): δ = 7.91 (d, J = 7.2 Hz, 1
1.28–1.32 (m, 6 H), 0.88 (t, J = 6.5 Hz, 3 H) ppm. 13C NMR H), 7.63 (t, J = 7.2 Hz, 1 H), 7.53 (t, J = 7.4 Hz, 1 H), 7.28 (d, J
(75 MHz, CDCl3): δ = 169.67, 148.44, 146.31, 140.39, 136.67,
134.36, 133.89, 129.86, 128.79, 125.97, 125.70, 124.87, 124.04,
123.19, 122.50, 78.08, 31.54, 30.14, 28.71, 22.55, 14.06 ppm.
C22H22O2S2 (382.11): calcd. C 69.07, H 5.80, S 16.76; found C
69.17, H 5.66, S 16.89.
= 7.6 Hz, 1 H), 6.78–6.80 (m, 2 H), 6.56 (s, 1 H), 6.29 (s, 1 H), 5.93
(s, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 170.30, 149.51,
148.52, 148.22, 134.27, 129.99, 129.36, 125.75, 125.55, 122.87,
121.47, 108.39, 107.23, 101.40, 82.69 ppm. C15H10O4 (254.06):
calcd. C 70.86, H 3.96; found C 70.70, H 4.05.
3-(2,4,6-Trimethoxyphenyl)benzo[c]furan-1(3H)-one
(8i):
The
Synthesis of Phthalides by the Metalation Method (Low-Tempera-
phthalide 8i was obtained in 65% yield by a procedure similar to
that used for the preparation of 2-thienylphthalide 8a (metalation
ture Conditions):
A solution of 2-bromobenzoic acid (1 g,
4.97 mmol) in THF (20 mL) was cooled below –15 °C under nitro-
gen, and 1.0  of Bu2Mg in hexane (2.6 mL, 2.6 mmol) was slowly
added to the solution below –5 °C. Then 1.6  n-BuLi in hexane
(3.4 mL, 5.30 mmol) was slowly added to the solution below –15 °C
over 20 min whilst stirring. The solution became a viscous slurry
during the addition of Bu2Mg and then gradually changed to a less
viscous yellowish slurry during the addition of nBuLi. After stirring
below –15 °C for 1 h, a solution of thiophene-2-carbaldehyde
(1.11 g, 9.95 mmol) in THF was added to the mixture below
–15 °C. After stirring below –15 °C for 1 h, the reaction mixture
was quenched with 2  HCl (10 mL). The resulting mixture was
stirred at room temperature overnight. EtOAc (30 mL) was added
to the resulting mixture and the mixture was stirred for a few min-
utes. The organic layer was separated and washed with H2O
(5 mL), 5% aqueous NaHCO3 (10 mL), and saturated brine solu-
tion (5 mL) successively. After drying with anhydrous Na2SO4, the
solvent was removed under reduced pressure, and the crude solid
thus obtained was purified by silica gel chromatography [hexane/
ethyl acetate (EA), 9:1] to afford phthalide 8a[20] as white solid
(1.32 g, 62%).
1
method). M.p. 122 °C. H NMR (400 MHz, CDCl3): δ = 7.94 (d,
J = 7.84 Hz, 1 H), 7.71 (t, J = 6.8 Hz, 1 H), 7.59 (t, J = 7.3 Hz, 1
H), 7.40 (d, J = 7.8 Hz, 1 H), 6.48 (s, 2 H), 6.35 (s, 1 H), 3.83 (s,
3 H), 3.81 (s, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 170.44,
153.67, 149.46, 138.69, 134.39, 131.39, 131.86, 129.49, 125.65,
125.47, 122.85, 103.99, 82.83, 60.80, 56.20 ppm. C17H16O5 (300.1):
calcd. C 67.99, H 5.37; found C 68.11, H 5.32.
3-(Anthracen-9-yl)benzo[c]furan-1(3H)-one (8j): The phthalide 8j
was obtained in 55% yield by a procedure similar to that used for
the preparation of 2-thienylphthalide 8a (metalation method). M.p.
1
142 °C. H NMR (400 MHz, CDCl3): δ = 8.58 (s, 1 H), 8.47–8.50
(m, 1 H), 8.16 (d, J = 7.4 Hz, 1 H), 8.01–8.11 (m, 2 H), 7.93 (s, 1
H), 7.55–7.63 (m, 5 H), 7.34–7.38 (m, 1 H), 7.28–7.32 (m, 1 H),
7.10 (d, J = 7.3 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
170.89, 151.36, 134.58, 131.69, 130.69, 129.55, 129.30, 127.51,
126.56, 126.35, 126.05, 124.98, 124.27, 123.98, 122.38, 79.06 ppm.
MS (EI): m/z (%) = 310 (20) [M]+. C22H14O2 (310.1): calcd. C
85.14, H 4.55; found C 85.01, H 4.50.
Synthesis of Phthalide by the Grignard Method
3-[4-(Hexyloxy)phenyl]isobenzofuran-1(3H)-one (8e): The phthalide
8e was obtained in 60% yield by a procedure similar to that used
for the preparation of 2-thienylphthalide 8a (metalation method).
3-(5-Hexyl-2-thienyl)phthalide (8c): A solution of 2-bromo-5-hexyl-
thiophene (1 g, 4.06 mmol) in dry diethyl ether (25 mL) was added
dropwise to a refluxing mixture of magnesium turnings (0.10 g,
4.47 mmol) containing a catalytic amount of iodine (20 mg) in dry
THF (20 mL) under nitrogen. After addition of the bromo com-
pound, the reaction mixture was heated at reflux for 2 h to ensure
complete formation of the Grignard reagent. The above Grignard
reagent was slowly added to a solution of 2-formylbenzoic acid
(0.60 g, 4.06 mmol) in THF at room temperature. The reaction
mixture was stirred at room temperature for 6 h. Then 2  HCl was
added to the above reaction mixture and stirred for 0.5 h. The sol-
vent was completely removed and the solid filtered and dried with
Na2SO4. The crude product was purified by column chromatog-
raphy (hexane/EA, 9:1) to afford phthalide 8c as white solid (0.76 g,
63%).
1
M.p. 61 °C. H NMR (400 MHz, CDCl3): δ = 7.91 (d, J = 7.2 Hz,
1 H), 7.60 (t, J = 7.0 Hz, 1 H), 7.50 (t, J = 7.6 Hz, 1 H), 7.27 (d,
J = 6.8 Hz, 1 H), 7.11 (d, J = 8.4 Hz, 2 H), 6.83 (d, J = 8.8 Hz, 2
H), 6.33 (s, 1 H), 3.89 (t, J = 6.6 Hz, 2 H), 1.70–1.77 (quint, J =
6.9 Hz, 2 H), 1.40–1.43 (m, 2 H), 1.28–1.32 (m, 4 H), 0.85 (t, J =
5.8 Hz, 3 H) ppm. MS (EI): m/z (%) = 310 (100) [M]+. C20H22O3
(310.16): calcd. C 77.39, H 7.14; found C 77.30, H 7.18.
3-(3,4-Dimethoxyphenyl)isobenzofuran-1(3H)-one (8f): The phthal-
ide 8f was obtained in 52% yield by a procedure similar to that
used for the preparation of 2-thienylphthalide (metalation method).
M.p. 138 °C. 1H NMR (400 MHz, CDCl3): δ = 7.97 (d, J = 7.3 Hz,
1 H), 7.66 (t, J = 7.3 Hz, 1 H), 7.56 (t, J = 7.5 Hz, 1 H), 7.33 (d,
J = 7.3 Hz, 1 H), 6.86 (br. s, 2 H), 6.68 (s, 1 H), 6.36 (s, 1 H), 3.88
(s, 3 H), 3.80 (s, 3 H) ppm. C16H14O4 (270.09): calcd. C 71.10, H
5.22; found C 70.92, H 5.31.
3-(4-Methoxyphenyl)benzo[c]furan-1(3H)-one (8k): The phthalide
8k was obtained in 55% yield by a procedure similar to that used
for the preparation of 3-(5-hexyl-2-thienyl)phthalide (Grignard
1
method). M.p. 117 °C. H NMR (400 MHz, CDCl3): δ = 7.95 (d,
3-(4-Nitrophenyl)isobenzofuran-1(3H)-one (8g): The phthalide 8g
was obtained in 40% yield by a procedure similar to that used for
the preparation of 2-thienylphthalide 8a (metalation method). M.p.
146 °C. 1H NMR (400 MHz, CDCl3): δ = 8.25 (d, J = 8.8 Hz, 2
H), 7.99 (d, J = 7.3 Hz, 1 H), 7.68 (t, J = 6.8 Hz, 1 H), 7.61 (t, J
= 7.5 Hz, 1 H), 7.53 (d, J = 8.7 Hz, 2 H), 7.35 (d, J = 6.8 Hz, 1
H), 6.50 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 169.85,
148.46, 143.53, 134.77, 129.99, 127.51, 126.13, 125.10, 124.27,
122.60, 80.95 ppm. MS (EI): m/z (%) = 255 (100) [M]+. C14H9NO4
(255.05): calcd. C 65.88, H 3.55, N 5.49; found C 65.96, H 3.61, N
5.42.
J = 7.3 Hz, 1 H), 7.65 (t, J = 7.5 Hz, 1 H), 7.55 (t, J = 7.5 Hz, 1
H), 7.30 (d, J = 6.8 Hz, 1 H), 7.16 (d, J = 8.8 Hz, 2 H), 6.88 (d, J
= 8.2 Hz, 2 H), 6.41 (s, 1 H), 3.80 (s, 3 H) ppm. MS (EI): m/z (%)
= 240 (100) [M]+. C15H12O3 (240.08): calcd. C 74.99, H 5.03; found
C 74.83, H 5.11.
3-(p-Tolyl)benzo[c]furan-1(3H)-one (8l): The phthalide 8l was ob-
tained in 60% yield by a procedure similar to that used for the
preparation of 3-(5-hexyl-2-thienyl)phthalide (Grignard method).
M.p. 130 °C. 1H NMR (400 MHz, CDCl3): δ = 7.94 (d, J =
7.32 Hz, 1 H), 7.62 (t, J = 6.8 Hz, 1 H), 7.52 (t, J = 7.3 Hz, 1 H),
3804
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 3798–3810

Benzannelated Thienyl Oligomers
7.31 (d, J = 6.8 Hz, 1 H), 7.13–7.19 (m, 4 H), 6.37 (s, 1 H), 2.35 1-(3,4-Dimethoxyphenyl)-3-(thiophen-2yl)benzo[c]thiophene
(9d):
(s, 3 H) ppm. MS (EI): m/z (%) = 224 (100) [M]+. C15H12O2
Reaction of 2-thienylmagnesium bromide from 2-bromothiophene
(224.08): calcd. C 80.34, H 5.39; found C 80.41, H 5.43.
(1.0 g, 6.13 mmol) and magnesium turnings (0.161 g, 6.74 mmol)
with phthalide 8f (1.66 g, 6.13 mmol) followed by workup and
thionation using Lawesson’s reagent (1.24 g, 3.06 mmol) led to 9d
3-(1-Naphthyl)benzo[c]furan-1(3H)-one (8m): The phthalide 8m was
obtained in 58% yield by a procedure similar to that used for the
preparation of 3-(5-hexyl-2-thienyl)phthalide (Grignard method).
1
(1.19 g, 55%). M.p. 85 °C. H NMR (400 MHz, CDCl3): δ = 7.94
(d, J = 8.3 Hz, 1 H), 7.76 (d, J = 8.8 Hz, 1 H), 7.34–7.36 (m, 2 H),
7.21–7.25 (m, 2 H), 7.11–7.17 (m, 3 H), 6.98 (d, J = 8.3 Hz, 1 H),
3.95 (s, 6 H) ppm. MS (EI): m/z (%) = 352 (10) [M]+. C20H16O2S2
(352.06): calcd. C 68.15, H 4.58, S 18.19; found C 68.10, H 4.53, S
18.24.
1
M.p. 65 °C. H NMR (400 MHz, CDCl3): δ = 8.20 (d, J = 8.2 Hz,
1 H), 7.99 (d, J = 7.3 Hz, 1 H), 7.90 (d, J = 8.3 Hz, 1 H), 7.86 (s,
1 H), 7.81 (dd, J = 3.4, 2.44 Hz, 2 H), 7.53–7.62 (m, 2 H), 7.44
(dd, J = 3.4, 2.9 Hz, 2 H), 7.35–7.38 (m, 1 H), 7.21–7.23 (m, 1 H)
ppm. MS (EI): m/z (%) = 260 (100) [M]+. C18H12O2 (260.08): calcd.
C 83.06, H 4.65; found C 82.96, H 4.62.
1-(4-Nitrophenyl)-3-(thiophen-2-yl)benzo[c]thiophene (9e): Reaction
of 2-thienylmagnesium bromide from 2-bromothiophene (0.99 g,
6.11 mmol) and magnesium turnings (0.161 g, 6.74 mmol) with
phthalide 8g (1.56 g, 6.11 mmol) followed by workup and thion-
ation using Lawesson’s reagent (1.23 g, 3.05 mmol) led to 9e
(0.86 g, 42%). M.p. 116 °C. 1H NMR (400 MHz, CDCl3): δ = 8.34
(d, J = 8.8 Hz, 2 H), 8.02 (d, J = 2.4 Hz, 1 H), 7.83 (d, J = 9.2 Hz,
2 H), 7.44 (d, J = 4.8 Hz, 1 H), 7.40 (dd, J = 2.4, 1.2 Hz, 1 H),
7.17–7.24 (m, 4 H) ppm. MS (EI): m/z (%) = 338 (100) [M + 1]+.
C18H11NO2S2 (337.02): calcd. C 64.07, H 3.29, N 4.15, S 19.01;
found C 64.03, H 3.33, N 4.12, S 18.95.
N,N-Dimethyl-4-[3-(thiophen-2-yl)benzo[c]thiophen-1-yl]benzen-
amine (9a): Reaction of 4-(dimethylamino)phenylmagnesium bro-
mide (9.25 mL, 0.5 ) with phthalide 8a[20] (1.0 g, 4.62 mmol) fol-
lowed by workup and thionation using Lawesson’s reagent (0.93 g,
2.31 mmol) led to 9a (1.0 g, 65%). M.p. 84 °C. 1H NMR
(500 MHz, CDCl3): δ = 7.96 (d, J = 9.1 Hz, 1 H), 7.80 (d, J =
8.4 Hz, 1 H), 7.57 (d, J = 9.1 Hz, 2 H), 7.34–7.36 (m, 2 H), 7.05–
7.16 (m, 3 H), 6.84 (d, J = 8.4 Hz, 2 H), 3.04 (s, 6 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 150.10, 135.41, 130.22, 127.89,
124.97, 124.87, 124.63, 123.68, 121.80, 121.43, 112.81, 40.59 ppm.
MS (EI): m/z (%) = 335 (22) [M + 1]+. C20H17NS2 (335.08): calcd.
C 71.60, H 5.10, N 4.18, S 19.12; found C 71.50, H 5.07, N 4.20,
S 19.23.
1-(4-Methoxyphenyl)-3-(thiophen-2-yl)benzo[c]thiophene (9f): Reac-
tion of 2-thienylmagnesium bromide from 2-bromothiophene
(2.0 g, 12.26 mmol) and magnesium turnings (0.35 g, 14.58 mmol)
with phthalide 8k (2.94 g, 12.26 mmol) followed by workup and
thionation using Lawesson’s reagent (2.47 g, 6.10 mmol) led to 9f
(1.57 g, 40%). M.p. 107 °C. 1H NMR (300 MHz, CDCl3): δ = 7.98
(d, J = 8.7 Hz, 1 H), 7.77 (d, J = 8.4 Hz, 1 H), 7.61 (d, J = 8.4 Hz,
2 H), 7.37–7.40 (m, 2 H), 7.10–7.19 (m, 3 H), 7.05 (d, J = 8.7 Hz,
2 H), 3.90 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 159.43,
136.17, 135.32, 134.95, 134.04, 130.49, 127.80, 126.45, 125.42,
125.80, 125.21, 125.13, 124.58, 124.09, 121.41, 121.33, 114.59,
55.43 ppm. MS (EI): m/z (%) = 322 (100) [M + 1]+. C19H14OS2
(332.05): calcd. C 70.77, H 4.38, S 19.89; found C 70.70, H 4.36, S
19.80.
1-[4-(Methylthio)phenyl]-3-(thiophen-2-yl)benzo[c]thiophene
(9b):
Reaction of 4-(methylthio)phenylmagnesium bromide (9.28 mL,
0.5 ) with phthalide 8a[20] (1.0 g, 4.62 mmol) followed by workup
and thionation using Lawesson’s reagent (0.93 g, 2.31 mmol) led to
1
9b (62%). M.p. 79 °C. H NMR (400 MHz, CDCl3): δ = 7.95 (d,
J = 8.4 Hz, 1 H), 7.80 (d, J = 8.4 Hz, 1 H), 7.66–7.68 (m, 1 H),
7.55 (d, J = 7.6 Hz, 2 H), 7.12–7.35 (m, 6 H), 2.42 (s, 3 H) ppm.
C19H14S3 (338.03): calcd. C 67.41, H 4.17, S 28.42; found C 67.47,
H 4.20, S 28.33.
1-[4-(Hexyloxy)phenyl]-3-(thiophen-2-yl)benzo[c]thiophene (9c):
A
solution of 2-bromothiophene (2.89 g, 17.72 mmol) in dry THF
(20 mL) was added (15 min) to a refluxing mixture of magnesium
turnings (0.51 g, 21.27 mmol) containing a catalytic amount of io-
dine (20 mg) in dry THF (100 mL) under N2. After addition of the
bromo compound, the reaction mixture was heated at reflux for
2 h to ensure the completion of the Grignard reaction. Then the
above Grignard reagent was slowly added through an additional
funnel to a solution of phthalide 8f (5.0 g, 16.12 mmol) in dry THF
(30 mL) at room temperature. The reaction mixture was stirred at
room temperature for 6 h and poured into ice-cold water contain-
ing ammonium chloride solution. The crude product was extracted
with DCM (75 mL) and dried (Na2SO4). Then it was treated with
Lawesson’s reagent (3.26 g, 8.05 mmol) at room temperature for
6 h. The solvent (DCM) was removed, and the residue was gently
heated (fume hood) in a steam bath with ethanol (20 mL). The
crude product was purified by column chromatography on neutral
alumina using hexane as eluent to afford compound 9c as a yellow
1-(Thiophen-2-yl)-3-(p-tolyl)benzo[c]thiophene (9g): Reaction of 2-
thienylmagnesium bromide from 2-bromothiophene (2.0 g,
12.26 mmol) and magnesium turnings (0.32 g, 13.49 mmol) with
phthalide 8l (2.74 g, 12.23 mmol) followed by workup and thion-
ation using Lawesson’s reagent (2.47 g, 6.11 mmol) led to 9g
(2.24 g, 60%). M.p. 106 °C. 1H NMR (400 MHz, CDCl3): δ = 7.65
(d, J = 7.8 Hz, 2 H), 7.53–7.62 (m, 4 H), 7.33 (d, J = 3.4 Hz, 1 H),
7.11 (d, J = 7.3 Hz, 2 H), 6.97 (t, J = 4.4 Hz, 1 H), 6.83 (t, J =
4.1 Hz, 1 H), 2.25 (s, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 143.51, 139.72, 136.74, 133.72, 129.55, 128.68, 127.71, 125.07,
124.98, 124.58, 123.64, 121.88, 121.47, 121.33, 120.09, 119.82,
21.27 ppm. MS (EI): m/z (%) = 306 (100) [M]+. C19H14S2 (306.05):
calcd. C 74.47, H 4.60, S 20.93; found C 74.55, H 4.53, S 20.92.
3-(Thiophen-2-yl)-1-(2,4,6-trimethoxyphenyl)benzo[c]thiophene (9h):
Reaction of 2-thienylmagnesium bromide from 2-bromothiophene
(1.0 g, 6.13 mmol) and magnesium turnings (0.161 g, 6.74 mmol)
with phthalide 8i (1.84 g, 6.13 mmol) followed by workup and
1
solid (4.1 g, 65%). M.p. 80 °C. H NMR (300 MHz, CDCl3): δ =
7.92 (d, J = 8.4 Hz, 1 H), 7.72 (d, J = 8.4 Hz, 1 H), 7.52 (d, J = thionation using Lawesson’s reagent (1.24 g, 3.06 mmol) led to 9h
1
8.2 Hz, 2 H), 7.28 (d, J = 4.0 Hz, 2 H), 6.94–7.09 (m, 5 H), 3.95
(t, J = 6.2 Hz, 2 H), 1.77 (quint, J = 7.1 Hz, 2 H), 1.32–1.51 (m, 6
H), 0.90 (t, J = 6.1 Hz, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ
= 158.87, 136.24, 135.81, 135.15, 134.20, 130.30, 127.71, 127.01,
(1.26 g, 54%) as a viscous liquid. H NMR (400 MHz, CDCl3): δ
= 7.93 (d, J = 8.4 Hz, 1 H), 7.78 (d, J = 7.6 Hz, 1 H), 7.34–7.35
(m, 2 H), 7.08–7.14 (m, 3 H), 6.85 (s, 2 H), 3.92 (s, 9 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 153.59, 137.88, 135.78, 135.25,
126.61, 125.01, 124.94, 123.93, 121.27, 114.98, 68.05, 31.55, 29.18, 135.09, 134.89, 133.73, 129.35, 127.80, 126.45, 125.33, 124.57,
25.69, 22.58, 14.04 ppm. MS (EI): m/z (%) = 392 (49) [M]+. 124.40, 121.45, 121.14, 106.43, 60.95, 56.22 ppm. MS (EI): m/z (%)
C24H24OS2 (392.13): calcd. C 73.43, H 6.16, S 16.34; found C 73.35,
H 6.14, S 16.29.
= 382 (70) [M]+. C21H18O3S2 (382.07): calcd. C 65.94, H 4.74, S
16.77; found C 65.99, H 4.72, S 16.70.
Eur. J. Org. Chem. 2008, 3798–3810
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3805

P. Amaladass, J. A. Clement, A. K. Mohanakrishnan
FULL PAPER
1-(Anthracen-9-yl)-3-(thiophen-2-yl)benzo[c]thiophene (9i): Reaction
of 2-thienylmagnesium bromide from 2-bromothiophene (1.0 g,
6.13 mmol) and magnesium turnings (0.161 g, 6.74 mmol) with
phthalide 8j (1.90 g, 6.13 mmol) followed by workup and thion-
ation using Lawesson’s reagent (1.24 g, 3.06 mmol) led to 9i (1.08 g,
45%). M.p. 170 °C. 1H NMR (400 MHz, CDCl3): δ = 8.57 (s, 1
H), 8.05 (d, J = 8.3 Hz, 2 H), 7.88 (d, J = 8.8 Hz, 2 H), 7.84 (d, J
= 9.2 Hz, 1 H), 7.42–7.56 (m, 6 H), 6.89–7.32 (m, 4 H) ppm. MS
(EI): m/z (%) = 392 (10) [M]+. C26H16S2 (392.07): calcd. C 79.55,
H 4.11, S 16.34; found C 79.46, H 4.18, S 16.36.
0.90 (t, J = 7.0 Hz, 3 H) ppm. MS (EI): m/z (%) = 354 (46) [M]+.
C20H18S3 (354.06): calcd. C 67.75, H 5.12, S 27.13; found C 67.70,
H 5.10, S 27.20.
1-(5-Hexylthiophen-2-yl)-3-[5-(thiophen-2-yl)thiophen-2-yl]benzo-
[c]thiophene (9o): Reaction of 5-hexyl-2-thienylmagnesium bromide
from 2-bromo-5-hexylthiophene (0.45 g, 1.84 mmol) and magne-
sium turnings (0.052 g, 2.19 mmol) with phthalide 8b (0.5 g,
1.67 mmol) followed by workup and thionation using Lawesson’s
reagent (0.33 g, 0.83 mmol) led to 9o (0.42 g, 55%). M.p. 42 °C. 1H
NMR (500 MHz, CDCl3): δ = 7.94–7.97 (m, 2 H), 7.22–7.25 (m, 3
H), 7.18–7.21 (m, 1 H), 7.11–7.16 (m, 3 H), 7.03–7.05 (m, 1 H),
6.81 (d, J = 3.8 Hz, 1 H), 2.85 (t, J = 7.6 Hz, 2 H), 1.71–1.77 (quint,
J = 7.05 Hz, 2 H), 1.41–1.44 (m, 2 H), 1.27–1.36 (m, 4 H), 0.92 (t,
J = 6.87 Hz, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 146.86,
128.05, 125.82, 125.47, 125.01, 124.65, 124.60, 123.76, 31.70, 30.37,
28.96, 22.72, 14.23 ppm. MS (EI): m/z (%) = 464 (100) [M]+.
C26H24S4 (464.08): calcd. C 67.20, H 5.20, S 27.60; found C 67.08,
H 5.30, S 27.62.
1-(Naphthalen-1-yl)-3-(thiophen-2-yl)benzo[c]thiophene (9j): Reac-
tion of 2-thienylmagnesium bromide from 2-bromothiophene
(1.0 g, 6.13 mmol) and magnesium turnings (0.161 g, 6.74 mmol)
with phthalide 8m (1.54 g, 6.13 mmol) followed by workup and
thionation using Lawesson’s reagent (1.24 g, 3.06 mmol) led to 9j
(0.87 g, 43%) as a viscous yellow liquid. 1H NMR (400 MHz,
CDCl3): δ = 7.84 (d, J = 8.8 Hz, 1 H), 7.77 (d, J = 8.2 Hz, 1 H),
7.73 (d, J = 8.2 Hz, 1 H), 7.47 (d, J = 7.3 Hz, 1 H), 7.40 (d, J =
7.8 Hz, 1 H), 7.22 (d, J = 4.4 Hz, 2 H), 7.25–7.29 (m, 1 H), 7.34–
7.37 (m, 1 H), 7.03–7.15 (m, 4 H), 6.82–6.91 (m, 1 H) ppm. MS
(EI): m/z (%) = 342 (66) [M]+. C22H14S2 (342.05): calcd. C 77.15,
H 4.12, S 18.73; found C 77.10, H 4.10, S 18.80.
1-[5-(5-Hexylthiophen-2-yl)thiophen-2-yl]-3-(thiophen-2-yl)benzo[c]-
thiophene (9p): Prepared according to a procedure similar to that
for 9o. Yield: 60%, viscous red liquid. 1H NMR (300 MHz,
CDCl3): δ = 7.89–7.95 (m, 2 H), 7.29–7.34 (m, 2 H), 7.18 (d, J =
3.9 Hz, 1 H), 7.05–7.12 (m, 4 H), 7.00 (d, J = 3.3 Hz, 1 H), 6.67
(d, J = 3.6 Hz, 1 H), 2.77 (t, J = 7.7 Hz, 2 H), 1.64–1.71 (m, 2 H),
1.30–1.41 (m, 6 H), 0.89 (t, J = 6.6 Hz, 3 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 145.78, 137.87, 135.68, 135.37, 135.13,
134.43, 133.87, 127.90, 126.61, 126.37, 125.95, 125.56, 125.51,
124.94, 124.88, 124.84, 123.60, 123.47, 121.67, 121.62, 31.63, 31.60,
30.27, 28.83, 22.64, 14.15 ppm. C26H24S4 (464.08): calcd. C 67.20,
H 5.20, S 27.60; found C 67.10, H 5.40, S 27.50.
1-Phenyl-3-(thiophen-2-yl)benzo[c]thiophene (9k): Reaction of 2-thi-
enylmagnesium bromide from 2-bromothiophene (1.70 g,
10.47 mmol) and magnesium turnings (0.30 g, 12.51 mmol) with
phthalide 8n (2.0 g, 9.52 mmol) followed by workup and thionation
using Lawesson’s reagent (1.92 g, 4.74 mmol) led to 9k (1.75 g,
1
63%) as a viscous yellow liquid. H NMR (400 MHz, CDCl3): δ =
7.95 (d, J = 8.3 Hz, 1 H), 7.81 (d, J = 7.8 Hz, 1 H), 7.66 (d, J =
7.3 Hz, 2 H), 7.49 (t, J = 6.6 Hz, 2 H), 7.32–7.40 (m, 2 H), 7.11–
7.19 (m, 4 H) ppm. MS (EI): m/z (%) = 292 (22) [M]+. C18H12S2
(292.04): calcd. C 73.93, H 4.14, S 21.93; found C 73.73, H 4.20, S
22.07.
1-(3-Hexylthiophen-2-yl)-3-[5-(5-hexylthiophen-2-yl)thiophen-2-yl]-
benzo[c]thiophene (9q): Prepared according to a procedure similar
to that for 9o. Yield: 62%, viscous red liquid. 1H NMR (300 MHz,
CDCl3): δ = 7.98 (d, J = 8.4 Hz, 1 H), 7.60 (d, J = 8.4 Hz, 1 H),
7.38 (d, J = 5.1 Hz, 1 H), 7.24 (d, J = 3.3 Hz, 1 H), 7.10–7.15 (m,
2 H), 7.06–7.08 (m, 1 H), 7.04 (t, J = 3.0 Hz, 2 H), 6.70 (d, J =
3.6 Hz, 1 H), 2.80 (t, J = 8.0 Hz, 2 H), 2.64 (t, J = 7.8 Hz, 2 H),
1.66–1.72 (m, 2 H), 1.53–1.60 (m, 2 H), 1.20–1.41 (m, 12 H), 0.90
(t, J = 6.8 Hz, 3 H), 0.82 (t, J = 6.8 Hz, 3 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 145.76, 142.57, 137.91, 137.86, 134.45,
134.37, 134.01, 129.31, 127.98, 127.72, 126.03, 125.87, 124.91,
124.64, 124.30, 123.59, 123.44, 121.83, 121.27, 31.57, 30.82, 30.23,
29.08, 29.01, 28.76, 22.58, 22.54, 14.07, 14.03 ppm. C32H36S4
(548.17): calcd. C 70.02, H 6.61, S 23.37; found C 70.22, H 6.51, S
23.27.
1-(5-Hexylthiophen-2-yl)-3-(thiophen-2yl)benzo[c]thiophene (9l): Re-
action of 5-hexyl-2-thienylmagnesium bromide from 2-bromo-5-
hexylthiophene (1.25 g, 5.09 mmol) and magnesium turnings
(0.13 g, 5.41 mmol) with phthalide 8a (1 g, 4.62 mmol) followed by
workup and thionation using Lawesson’s reagent (0.93 g,
1
2.31 mmol) led to 9l (1.02 g, 58%) as a viscous orange liquid. H
NMR (400 MHz, CDCl3): δ = 7.92 (dd, J = 2.5, 3.5 Hz, 1 H), 7.11–
7.13 (m, 2 H), 7.08–7.12 (m, 2 H), 6.80–6.83 (m, 3 H), 6.78 (m, 1
H), 2.83 (t, J = 7.6 Hz, 2 H), 1.25–1.71 (m, 8 H), 0.89 (t, J =
7.1 Hz, 3 H) ppm. MS (EI): m/z (%) = 382 (100) [M]+. C32H36S4
(382.09): calcd. C 69.06, H 5.80, S 25.14; found C 69.16, H 5.85, S
24.99.
1-[5-(2-Ethylhexyl)thiophen-2-yl]-3-(thiophen-2-yl)benzo[c]thiophene
(9m): According to a procedure similar to that used for the prepara-
tion of 9l, benzothiophene 9m was prepared (2.08 g, 55%) as a
3,3Ј-Bis(thiophen-2-yl)-1,1Ј-bibenzo[c]thiophene (2a): A solution of
thienylmagnesium bromide in dry THF was prepared using 2-bro-
mothiophene (0.91 g, 5.58 mmol) and magnesium turnings (0.16 g,
6.66 mmol). Then the Grignard reagent was slowly added through
an addition funnel to a solution of diphthalide 10 (0.5 g,
1.87 mmol) in dry THF (30 mL) at room temperature. The reaction
mixture was then quenched with aq. ammonium chloride. It was
then extracted with DCM (75 mL) and treated with Lawesson’s rea-
gent (0.76 g, 1.87 mmol) at room temperature for 6 h. The solvent
(DCM) was removed, and the residue was gently heated (fume
1
viscous orange liquid. H NMR (400 MHz, CDCl3): δ = 8.06 (t, J
= 7.2 Hz, 1 H), 7.45–7.47 (m, 1 H), 7.22–7.29 (m, 2 H), 7.04 (t, J
= 3.8 Hz, 1 H), 6.97 (d, J = 3.6 Hz, 1 H), 6.91 (d, J = 7.8 Hz, 1
H), 6.89 (d, J = 7.6 Hz, 1 H), 6.63 (d, J = 3.2 Hz, 1 H), 2.81 (d, J
= 6.8 Hz, 2 H), 1.40–1.57 (m, 9 H), 0.99–1.08 (m, 6 H) ppm. MS
(EI): m/z (%) = 410 (22) [M]+. C24H26S3 (410.12): calcd. C 70.19,
H 6.38, S 23.43; found C 70.10, H 6.36, S 23.54.
1-(5-Butylthiophen-2-yl)-3-(thiophen-2-yl)benzo[c]thiophene
(9n): hood) in a steam bath with ethanol (20 mL). The crude product
According to a procedure similar to that used for the preparation
was purified by column chromatography on neutral alumina (hex-
ane as eluent) to afford product 2a as a brown solid 0.48 g, 58%).
M.p. 175 °C. 1H NMR (300 MHz, CDCl3): δ = 8.03 (d, J = 8.4 Hz,
2 H), 7.89 (d, J = 8.1 Hz, 2 H), 7.36–7.42 (m, 4 H), 7.11–7.23 (m,
6 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 136.98, 135.57, 135.18,
128.50, 127.94, 125.70, 125.04, 124.81, 124.27, 121.89, 121.46 ppm.
of 9l, benzothiophene 9n was prepared (1.60 g, 49%) as a viscous
1
orange liquid. H NMR (400 MHz, CDCl3): δ = 7.91 (dd, J = 2.8,
3.6 Hz, 1 H), 7.29 (t, J = 5.2 Hz, 1 H), 7.07–7.12 (m, 3 H), 6.88 (t,
J = 4.4 Hz, 1 H), 6.80 (d, J = 3.2 Hz, 1 H), 6.75 (m, 1 H), 6.49 (d,
J = 4.2 Hz, 1 H), 2.70 (t, J = 7.8 Hz, 2 H), 1.34–1.64 (m, 4 H),
3806
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 3798–3810

Benzannelated Thienyl Oligomers
C24H14S4 (430.0): calcd. C 66.94, H 3.28, S 29.78; found C 66.89,
H 3.26, S 29.85.
gave the known dimer 3[20] as a red very viscous liquid (0.14 g,
75%).
1-[4-(Hexyloxy)phenyl]-3-[5-(5-{3-[4-(hexyloxy)phenyl]benzo[c]-
thiophen-1-yl}thiophen-2-yl)thiophen-2-yl]benzo[c]thiophene (5a).
Using FeCl3: A solution of benzo[c]thiophene 9c (0.2 g, 0.51 mmol)
in dry DCM (10 mL) was treated with anhydrous FeCl3 (0.09 g,
0.61 mmol) under nitrogen. The mixture was stirred at room tem-
perature for 10 h and diluted with more DCM (10 mL). The dark
mixture was treated with a dilute solution of NH2NH2·H2O
(10 mL). The crude product was extracted with DCM (30 mL),
dried (Na2SO4), and the solvent was removed. The crude product
was purified by column chromatography on neutral alumina (ethyl
acetate as eluent) to give dimer 5a (0.13 g, 65%) as a dark solid.
M.p. 220 °C. 1H NMR (400 MHz, CDCl3): δ = 8.00 (d, J = 8.8 Hz,
2 H), 7.75 (d, J = 8.8 Hz, 2 H), 7.57 (d, J = 8.76 Hz, 4 H), 7.24–
7.28 (m, 4 H), 7.14–7.18 (m, 2 H), 7.07–7.11 (m, 2 H), 7.01 (d, J
= 8.8 Hz, 4 H), 4.03 (t, J = 6.6 Hz, 4 H), 1.81 (q, J = 6.8 Hz, 4 H),
1.31–1.57 (m, 12 H), 0.92 (t, J = 6.8 Hz, 6 H) ppm. MS (MALDI-
TOF): m/z = 782 [M]+. C48H46O2S4 (782.24): calcd. C 73.62, H
5.92, S 16.38; found C 73.51, H 5.85, S 16.39. Using PIFA/
BF3·OEt2: BF3·Et2O (0.06 g, 0.45 mmol) and PIFA (0.19 g,
0.45 mmol) were added sequentially to a stirred solution of 9c
(0.2 g, 0.51 mmol) in CH2Cl2 (10 mL) at –78 °C under nitrogen.
The reaction mixture was stirred at the same temperature for 6 h.
Aqueous workup with saturated aq. NaHCO3 (10 mL) at 0 °C fol-
lowed by column chromatographic purification (silica gel; EA/hex-
ane, 1:1) gave the dimer 5a (0.07 g, 35%).
3,3Ј-Bis(5-hexylylthiophen-2-yl)-1,1Ј-bibenzo[c]thiophene (2b): Pre-
pared according to a procedure similar to that for 2a. Yield: 51%,
viscous orange liquid. H NMR (400 MHz, CDCl3): δ = 7.98 (d, J
= 8.8 Hz, 2 H), 7.82 (d, J = 8.2 Hz, 2 H), 7.08–7.19 (m, 6 H), 6.82
(d, J = 3.9 Hz, 2 H), 2.86 (t, J = 7.56 Hz, 4 H), 1.70–1.77 (quint,
J = 6.8 Hz, 4 H), 1.33–1.53 (m, 12 H), 0.90 (t, J = 6.8 Hz, 6 H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 146.76, 136.83, 134.74,
129.11, 125.33, 124.92, 124.66, 123.69, 121.88, 121.62, 31.58, 30.27,
28.83, 22.58, 14.08 ppm. C36H38S4 (598.19): calcd. C 72.19, H 6.39,
S 21.42; found C 72.11, H 6.42, S 21.47.
1
3,3Ј-Bis[5-(2-ethylhexyl)thiophen-2-yl]-1,1Ј-bibenzo[c]thiophene (2c):
Prepared according to a procedure similar to that for 2a. Yield:
55%, viscous orange liquid. 1H NMR (400 MHz, CDCl3): δ = 8.10
(d, J = 8.7 Hz, 2 H), 7.9 (d, J = 8.8 Hz, 2 H), 7.1–7.3 (m, 6 H), 6.9
(d, J = 3.4 Hz, 2 H), 2.8 (d, J = 6.3 Hz, 4 H), 1.3–1.7 (m, 16 H),
0.89–1.0 (m, 14 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 145.29,
136.83, 134.68, 133.26, 129.14, 125.98, 125.34, 124.92, 123.66,
121.64, 121.51, 34.2, 32.36, 28.8, 25.5, 23.0, 14.14, 10.8 ppm.
C40H46S4 (654.25): calcd. C 73.34, H 7.08, S 19.58; found C 73.30,
H 7.00, S 19.70.
3,3Ј-Bis(5-butylthiophen-2-yl)-1,1Ј-bibenzo[c]thiophene (2d): Pre-
pared according to a procedure similar to that for 2a. Yield: 62%.
1
M.p. 80 °C. H NMR (400 MHz, CDCl3): δ = 8.00 (d, J = 9.2 Hz,
2 H), 7.84 (d, J = 9.2 Hz, 2 H), 7.10–7.20 (m, 6 H), 6.82 (d, J =
3.0 Hz, 2 H), 2.88 (t, J = 7.2 Hz, 4 H), 1.71–1.77 (quint, J = 7.1 Hz,
4 H), 1.44–1.50 (m, 4 H), 1.00 (t, J = 3.8 Hz, 6 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 146.78, 136.92, 134.84, 133.11, 125.43,
125.06, 124.79, 123.82, 122.00, 121.74, 33.86, 30.07, 22.38,
13.99 ppm. C32H30S4 (542.12): calcd. C 70.80, H 5.57, S 23.63;
found C 70.71, H 5.60, S 23.69.
1-(4-Methoxyphenyl)-3-(5-{5-[3-(4-methoxyphenyl)benzo[c]-
thiophen-1-yl]thiophen-2-yl}thiophen-2-yl)benzo[c]thiophene (5b).
Using FeCl3: Prepared according to a procedure similar to that for
5a. Yield: 60%. M.p. 160 °C. 1H NMR (400 MHz, CDCl3): δ =
8.01 (d, J = 8.8 Hz, 2 H), 7.75 (d, J = 8.8 Hz, 2 H), 7.59 (d, J =
8.8 Hz, 4 H), 7.22–7.29 (m, 4 H), 7.15–7.19 (m, 2 H), 7.08–7.11 (m,
2 H), 7.03 (d, J = 8.8 Hz, 4 H), 3.89 (s, 6 H) ppm. MS (MALDI-
TOF): m/z = 642 [M]+. C38H26O2S4 (642.08): calcd. C 70.99, H
4.08, S 19.95; found C 70.95, H 4.04, S 19.99. Using PIFA/
BF3·OEt2: Prepared according to a procedure similar to that for 5a
(from PIFA/BF3·OEt2). Yield: 0.08 g (40%).
1-(p-Tolyl)-3-[1-(p-tolyl)benzo[c]thiophen-3-yl]benzo[c]thiophene
(11a): Reaction of p-tolylmagnesium bromide from 4-bromotoluene
(1.58 g, 9.34 mmol) and magnesium turnings (0.26 g, 10.83 mmol)
with diphthalide 10 (1.0 g, 3.75 mmol) followed by workup and
thionation with Lawesson’s reagent (1.52 g, 3.75 mmol) led to 11a
(0.88 g, 53%). M.p. 167 °C. 1H NMR (400 MHz, CDCl3): δ = 7.83–
7.86 (m, 4 H), 7.60 (d, J = 8.0 Hz, 4 H), 7.30 (d, J = 7. 0 Hz, 4 H),
7.09–7.11 (m, 4 H), 2.43 (s, 6 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 137.62, 136.89, 135.75, 134.87, 131.14, 129.79, 129.11,
124.35, 121.85, 121.21, 21.26 ppm. C30H22S2 (446.12): calcd. C
80.68, H 4.96, S 14.36; found C 80.60, H 4.92, S 14.48.
1-(5-Butylthiophen-2-yl)-3-(5-{5-[3-(5-butylthiophen-2-yl)-2-
benzothiophen-1-yl]thiophen-2-yl}thiophen-2-yl)benzo[c]thiophene
(4a). Using FeCl3: Prepared according to a procedure similar to
that for 5a. Yield: 55%, viscous red liquid. 1H NMR (400 MHz,
CDCl3): δ = 7.84 (d, J = 8.8 Hz, 2 H), 7.89 (d, J = 8.7 Hz, 2 H),
7.60 (d, J = 3.9 Hz, 2 H), 7.29 (d, J = 3.9 Hz, 2 H), 7.07–7.18 (m,
6 H), 6.71 (d, J = 3.4 Hz, 2 H), 2.78 (t, J = 7.5 Hz, 4 H), 1.60–1.65
(quint, J = 6.8 Hz, 4 H), 1.34–1.40 (m, 4 H), 0.89 (t, J = 7.3 Hz, 6
H) ppm. MS (GC): m/z = 706 [M]+. C40H34S6 (706.1): calcd. C
67.94, H 4.85, S 27.21; found C 67.91, H 4.90, S 27.28. Using PIFA/
BF3·OEt2: Prepared according to a procedure similar to that for 5a
(from PIFA/BF3·OEt2). Yield: 0.06 g (60%).
1-(o-Tolyl)-3-[1-(o-tolyl)benzo[c]thiophen-3-yl]benzo[c]thiophene
(11b): Reaction of o-tolylmagnesium bromide from 2-bromotoluene
(1.58 g, 9.34 mmol) and magnesium turnings (0.26 g, 10.83 mmol)
with diphthalide 10 (1.0 g, 3.75 mmol) followed by workup and
thionation using Lawesson’s reagent (1.52 g, 3.75 mmol) led to 11b
1
(0.83 g, 50%). M.p. 81 °C. H NMR (400 MHz, CDCl3): δ = 8.06
(d, J = 8.8 Hz, 2 H), 7.65 (d, J = 7.2 Hz, 2 H), 7.47–7.51 (m, 8 H),
7.42–7.27 (m, 4 H), 2.52 (s, 6 H) ppm. MS (EI): m/z (%) = 446 (26)
[M]+. C30H22S2 (446.12): calcd. C 80.68, H 4.96, S 14.36; found C
80.74, H 4.91, S 14.35.
1-[5-(2-Ethylhexyl)thiophen-2-yl]-3-[5-(5-{3-[5-(2-ethylhexyl)-
thiophen-2-yl]benzo[c]thiophen-1-yl}thiophen-2-yl)thiophen-2-yl]-2-
benzothiophene (4b). Using FeCl3: Prepared according to a pro-
cedure similar to that for 5a. Yield: 50%, viscous red liquid. 1H
NMR (400 MHz, CDCl3): δ = 7.83–8.06 (m, 4 H), 7.36–7.40 (m, 6
H), 7.16–7.21 (m, 4 H), 6.83–6.91 (m, 2 H), 2.85 (d, J = 5.8 Hz, 4
H), 0.9–1.71 (m, 30 H) ppm. MS (GC): m/z = 818 [M]+. C48H50S6
(818.22): calcd. C 70.37, H 6.15, S 23.48; found C 70.46, H 6.10, S
23.44. Using PIFA/BF3·OEt2: Prepared according to a procedure
similar to that for 5a (from PIFA/BF3·OEt2). Yield: 0.05 g (54%).
1-(3-Hexylthiophen-2-yl)-3-(5-{5-[3-(3-hexylthiophen-2-yl)-2-
benzothiophen-1-yl]thiophen-2-yl}thiophen-2-yl)benzo[c]thiophene
(3): BF3·Et2O (0.06 g, 0.47 mmol) and PIFA (0.20 g, 0.47 mmol)
were added sequentially to a stirred solution of 12 (0.2 g,
0.52 mmol) in CH2Cl2 (10 mL) at –78 °C under nitrogen. The reac-
tion mixture was stirred at the same temperature for 6 h. Aqueous
workup with saturated aq. NaHCO3 (10 mL) at 0 °C followed by 1-(5-Hexylthiophen-2-yl)-3-(5-{5-[3-(5-hexylthiophen-2-yl)-2-
column chromatographic purification (silica gel; EA/hexane, 1:1) benzothiophen-1-yl]thiophen-2-yl}thiophen-2-yl)benzo[c]thiophene
Eur. J. Org. Chem. 2008, 3798–3810
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3807

P. Amaladass, J. A. Clement, A. K. Mohanakrishnan
FULL PAPER
(4c). Using FeCl3: Prepared according to a procedure similar to
NMR (100 MHz, CDCl3): δ = 182.24, 146.44, 141.37, 138.46,
138.08, 137.11, 136.35, 135.51, 130.34, 129.88, 129.18, 126.21,
that for 5a. Yield: 60%, viscous red liquid. 1H NMR (400 MHz,
CDCl3): δ = 7.99–8.03 (m, 4 H), 7.73 (d, J = 3.6 Hz, 2 H), 7.39 (d, 124.80, 124.57, 121.84, 121.15, 21.29 ppm. MS (EI): m/z (%) = 334
J = 4.0 Hz, 2 H), 7.15–7.25 (m, 6 H), 6.82 (d, J = 3.2 Hz, 2 H), (57) [M]+. C20H14OS2 (334.05): calcd. C 71.82, H 4.22, S 19.17;
2.84 (t, J = 7.8 Hz, 4 H), 1.71 (quint, J = 6.9 Hz, 4 H), 1.25–1.42 found C 71.93, H 4.20, S 19.13.
(m, 12 H), 0.90 (t, J = 6.0 Hz, 6 H) ppm. MS (GC): m/z = 762
5-[3-(4-Methoxyphenyl)benzo[c]thiophen-1-yl]thiophene-2-carb-
aldehyde (13e): The aldehyde 13e was obtained in 62% yield ac-
[M]+. C44H42S6 (762.16): calcd. C 69.24, H 5.55, S 25.21; found C
69.31, H 5.58, S 25.11. Using PIFA/BF3·OEt2: Prepared according
cording to a procedure similar to that used for 13a. M.p. 130 °C.
to a procedure similar to that for 5a (from PIFA/BF3·OEt2). Yield:
1H NMR (400 MHz, CDCl3): δ = 9.87 (s, 1 H), 8.02 (d, J = 8.8 Hz,
0.06 g (65%).
1 H), 7.75 (d, J = 8.8 Hz, 1 H), 7.72 (dd, J = 1.2, 2.8 Hz, 1 H),
7.56 (d, J = 8.8 Hz, 2 H), 7.39 (dd, J = 2.4, 1.6 Hz, 1 H), 7.21–7.25
(m, 1 H), 7.10–7.13 (m, 1 H), 7.01 (d, J = 8.4 Hz, 2 H), 3.87 (s, 3
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 182.26, 159.88, 146.55,
141.50, 141.25, 137.13, 136.29, 130.54, 126.19, 125.61, 124.67,
121.44, 121.80, 121.28, 114.65, 55.39 ppm. MS (EI): m/z (%) = 350
(100) [M]+. C20H14O2S2 (350.04): calcd. C 68.54, H 4.03, S 18.30;
found C 68.42, H 4.09, S 18.40.
5-{3-[4-(Dimethyamino)phenyl]benzo[c]thiophen-1-yl}thiophene-2-
carbaldehyde (13a): POCl3 (0.06 mL, 0.65 mmol) was slowly added
to a mixture of dry DCM (10 mL) and DMF (0.05 mL, 0.65 mmol)
at 0 °C. After the addition was completed, the reaction mixture was
stirred at room temperature until it turned pale yellow (Vilsmeier
reagent). Then it was added to a solution benzo[c]thiophene 9a
(0.2 g, 0.59 mmol) in dry DCM (10 mL) at 0 °C. The reaction mix-
ture was stirred at room temperature for an additional 10 h. Then
the solvent was completely removed and the residue treated with
aqueous NaOH (5 g in 100 mL of water) at room temperature for
15 min. The crude product was then extracted with DCM (50 mL),
dried (Na2SO4), and the solvent removed. Column chromatography
of the crude product on neutral alumina (eluent: 10% EA in hex-
ane) afforded product 13a as an orange solid (0.13 g, 60%). M.p.
70 °C. 1H NMR (400 MHz, CDCl3): δ = 9.84 (s, 1 H), 8.02 (d, J =
8.4 Hz, 1 H), 7.79 (d, J = 8.8 Hz, 1 H), 7.68 (d, J = 3.4 Hz, 1 H),
7.53 (d, J = 8.0 Hz, 2 H), 7.34 (br. s, 1 H), 7.07–7.24 (m, 3 H), 6.82
(br. s, 1 H), 3.01 (s, 6 H) ppm. 13C NMR (100 MHz, CDCl3) δ =
182.50, 150.12, 140.69, 137.18, 134.89, 130.15, 126.21, 124.22,
123.97, 122.18, 121.11, 114.21, 112.70, 40.44 ppm. C21H17NOS2
(363.08): calcd. C 69.39, H 4.71, N 3.85, S 17.64; found C 69.45,
H 4.75, N 3.81, S 17.68.
5-{3-[5-(5-Hexylthiophen-2-yl)thiophen-2-yl]benzo[c]thiophen-1-
yl}thiophene-2-carbaldehyde (14b): The aldehyde 14b was obtained
in 60% yield as a viscous orange liquid according to a procedure
similar to that used for 13a. 1H NMR (300 MHz, CDCl3): δ = 9.85
(s, 1 H), 7.95 (t, J = 7.0 Hz, 2 H), 7.67 (d, J = 4.2 Hz, 1 H), 7.14–
7.24 (m, 3 H), 7.06 (d, J = 3.9 Hz, 1 H), 7.01 (d, J = 3.3 Hz, 1 H),
6.69 (d, J = 3.3 Hz, 1 H), 2.79 (t, J = 7.5 Hz, 2 H), 1.63–1.70 (m,
2 H), 1.31–1.40 (m, 6 H), 0.90 (t, J = 6.4 Hz, 3 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 182.18, 146.26, 145.80, 141.54, 139.00,
137.00, 136.40, 135.28, 134.06, 132.93, 130.41, 126.85, 126.48,
125.15, 125.02, 124.31, 123.81, 123.65, 122.09, 121.36, 31.59, 31.56,
30.25, 28.79, 22.60, 14.11 ppm. C27H24OS4 (492.07): calcd. C 65.81,
H 4.91, S 26.03; found C 65.71, H 4.81, S 26.16.
5-[3-(5-Hexylthiophen-2-yl)benzo[c]thiophen-1-yl]thiophene-2-
carbaldehyde (14c): The aldehyde 14c was obtained in 66% yield as
a viscous orange liquid according to a procedure similar to that
5-{3-[4-(Hexyloxy)phenyl]benzo[c]thiophen-1-yl}thiophene-2-carbal-
dehyde (13b): The aldehyde 13b was obtained in 64% yield accord-
ing to a procedure similar to that used for 13a. M.p. 86 °C. 1H
NMR (400 MHz, CDCl3): δ = 9.87 (s, 1 H), 8.02 (d, J = 8.8 Hz, 1
H), 7.76 (d, J = 8.8 Hz, 1 H), 7.72 (d, J = 4.0 Hz, 1 H), 7.55 (d, J
= 8.8 Hz, 2 H), 7.39 (d, J = 4.0 Hz, 1 H), 7.21–7.23 (m, 1 H), 7.09–
7.11 (m, 1 H), 7.00 (d, J = 8.8 Hz, 2 H), 3.99 (t, J = 6.6 Hz, 2 H),
1.77 (quint, J = 7.2 Hz, 2 H), 1.45–1.49 (m, 2 H), 1.32–1.38 (m, 4
H), 0.90 (t, J = 7.0 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 182.26, 159.60, 141.28, 137.14, 136.36, 135.32, 130.56, 126.24,
125.23, 124.68, 124.42, 121.90, 121.17, 115.23, 68.23, 31.57, 29.19,
25.71, 22.59, 14.01 ppm. MS (EI): m/z (%) = 420 (100) [M]+.
C25H24O2S2 (420.12): calcd. C 71.39, H 5.75, S 15.25; found C
71.50, H 5.70, S 15.30.
1
used for 13a. H NMR (500 MHz, CDCl3): δ = 9.87 (s, 1 H), 7.99
(d, J = 8.4 Hz, 1 H), 7.96 (d, J = 8.4 Hz, 1 H), 7.71 (d, J = 3.8 Hz,
1 H), 7.36 (d, J = 4.5 Hz, 1 H), 7.15–7.25 (m, 3 H), 6.81 (d, J =
3.0 Hz, 1 H), 2.84 (t, J = 7.6 Hz, 2 H), 1.69–1.75 (quint, J = 6.8 Hz,
2 H), 1.33–1.43 (m, 6 H), 0.90 (t, J = 6.8 Hz, 3 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 182.38, 148.01, 146.21, 141.45, 137.24,
136.45, 135.24, 132.32, 131.41, 126.53, 126.37, 125.27, 124.98,
124.95, 123.86, 122.31, 121.35, 31.67, 30.37, 28.92, 22.69,
14.21 ppm. C23H22OS3 (410.08): calcd. C 67.28, H 5.40, S 23.43;
found C 67.35, H 5.45, S 23.40.
5-{3-[5-(2-Ethylhexyl)thiophen-2-yl]benzo[c]thiophen-1-yl}thiophene-
2-carbaldehyde (14d): The aldehyde 14d was obtained in 54% yield
as a viscous orange liquid according to a procedure similar to that
used for 13a. 1H NMR (500 MHz, CDCl3): δ = 9.87 (s, 1 H), 7.91–
8.00 (m, 2 H), 7.77 (d, J = 3.8 Hz, 1 H), 7.37 (d, J = 3.8 Hz 1 H),
7.21–7.25 (m, 2 H), 7.16–7.20 (m, 1 H), 6.80 (d, J = 3.8 Hz, 1 H),
2.7 (d, J = 6.9 Hz, 2 H), 1.62–1.64 (m, 1 H), 1.40–1.42 (m, 2 H),
1.31–1.38 (m, 6 H), 0.8–0.9 (m, 6 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 182.38, 146.62, 146.24, 141.43, 137.25, 136.47, 135.20,
132.58, 131.45, 126.53, 126.33, 126.26, 124.95, 123.80, 122.34,
121.35, 41.55, 34.32, 32.48, 28.96, 25.64, 23.11, 14.26, 10.95 ppm.
MS (EI): m/z (%) = 438 (97) [M]+. C25H26OS3 (438.11): calcd. C
68.45, H 5.97, S 21.93; found C 68.40, H 6.00, S 22.02.
5-[3-(3,4-Dimethoxyphenyl)benzo[c]thiophen-1-yl]thiophene-2-
carbaldehyde (13c): The aldehyde 13c was obtained in 50% yield
according to a procedure similar to that used for 13a. M.p. 138 °C.
1H NMR (400 MHz, CDCl3): δ = 9.90 (s, 1 H), 8.05 (d, J = 8.8 Hz,
1 H), 7.80 (d, J = 8.8 Hz, 1 H), 7.75 (d, J = 3.9 Hz, 2 H), 7.42 (d,
J = 3.8 Hz, 2 H), 7.13–7.25 (m, 2 H), 7.00 (d, J = 8.3 Hz, 1 H),
3.96 (s, 6 H) ppm. MS (EI): m/z (%) = 380 (47) [M]+. C21H16O3S2
(380.05): calcd. C 66.29, H 4.24, S 16.86; found C 66.20, H 4.21, S
16.90.
5-[3-(p-Tolyl)benzo[c]thiophen-1-yl]thiophene-2-carbaldehyde (13d):
The aldehyde 13d was obtained in 52% yield according to a pro-
cedure similar to that used for 13a. M.p. 126 °C. 1H NMR
(400 MHz, CDCl3): δ = 9.90 (s, 1 H), 8.05 (d, J = 9.2 Hz, 1 H),
5-[3-(5-Butylthiophen-2-yl)benzo[c]thiophen-1-yl]thiophene-2-
carbaldehyde (14e): The aldehyde 14e was obtained in 33% yield as
a viscous orange liquid according to a procedure similar to that
7.81 (d, J = 8.8 Hz, 1 H), 7.76 (d, J = 3.9 Hz, 1 H), 7.56 (d, J = used for 13a. 1H NMR (400 MHz, CDCl3): δ = 9.80 (s, 1 H), 7.89–
7.8 Hz, 2 H), 7.43 (d, J = 3.8 Hz, 1 H), 7.31 (d, J = 8.3 Hz, 2 H), 7.94 (m, 2 H), 7.64 (d, J = 3.9 Hz, 1 H), 7.30–7.31 (d, J = 3.9 Hz,
7.24–7.28 (m, 1 H), 7.13–7.17 (m, 1 H), 2.44 (s, 3 H) ppm. 13C
1 H), 7.07–7.18 (m, 3 H), 6.74 (d, J = 3.4 Hz, 1 H), 2.80 (t, J =
3808
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Eur. J. Org. Chem. 2008, 3798–3810

Benzannelated Thienyl Oligomers
7.5 Hz, 2 H), 1.61–1.66 (quint, J = 6.9 Hz, 2 H), 1.34–1.40 (sept, J
= 6.7 Hz, 2 H), 0.89 (t, J = 7.32 Hz, 3 H) ppm. MS (EI): m/z (%)
= 382 (37) [M]+. C21H18OS3 (382.05): calcd. C 65.93, H 4.74, S
25.14; found C 65.82, H 4.72, S 25.19.
(525.13): calcd. C 70.82, H 5.18, N 2.66, S 18.30; found C 70.75,
H 5.20, N 2.60, S 18.36.
3-{5-[3-(3,4-Dimethoxyphenyl)benzo[c]thiophen-1-yl]thiophen-2-
yl}-2-(thiophen-2-yl)acrylonitrile (16b): The cyano derivative 16b
was obtained in 55% yield accoding to a procedure similar to that
2-[(5-{3-[4-(Hexyloxy)phenyl]benzo[c]thiophen-1-yl}thiophen-2-yl)-
methylene]malononitrile (15a): Monoaldehyde 13b (0.2 g,
0.47 mmol) and malononitrile (0.034 g, 0.52 mmol) were condensed
in the presence of tBuOK (0.064 g, 0.57 mmol) as base in dry etha-
nol. The above reaction mixture was stirred at room temperature
for 12 h, and the solid was filtered. The crude solid was purified
by column chromatography (hexane/EA, 90:10). Yield: 0.14 g
1
used for 16a. M.p. 166 °C. H NMR (400 MHz, CDCl3): δ = 8.01
(d, J = 9.2 Hz, 1 H), 7.78 (d, J = 8.8 Hz, 1 H), 7.52 (d, J = 3.8 Hz,
1 H), 7.42 (s, 1 H), 7.04–7.33 (m, 8 H), 6.98 (d, J = 8.3 Hz, 1 H),
3.95 (s, 6 H) ppm. C27H19NO2S3 (485.06): calcd. C 66.78, H 3.94,
N 2.88, S 19.81; found C 66.70, H 3.90, N 2.96, S 19.90.
3-{5-[3-(4-Methoxyphenyl)benzo[c]thiophen-1-yl]thiophen-2-yl}-2-
(thiophen-2-yl)acrylonitrile (16c): The cyano derivative 16c was ob-
tained in 61% yield according to a procedure similar to that used
1
(64%). M.p. 160 °C. H NMR (400 MHz, CDCl3): δ = 8.05 (d, J
= 8.76 Hz, 1 H), 7.99 (d, J = 9.28 Hz, 1 H), 7.70–7.81 (m, 2 H),
7.57–7.59 (m, 1 H), 7.46 (d, J = 3.9 Hz, 1 H), 7.39 (d, J = 3.9 Hz,
1 H), 7.02–7.19 (m, 3 H), 6.89 (s, 1 H), 4.01 (t, J = 6.6 Hz, 2 H),
1.83 (quint, J = 7.2 Hz, 2 H), 1.36–1.56 (m, 6 H), 0.90 (t, J =
7.0 Hz, 3 H) ppm. MS (EI): m/z (%) = 468 (17) [M]+. C28H24N2OS2
(468.13): calcd. C 71.76, H 5.16, N 5.98, S 13.68; found C 71.70,
H 5.10, N 6.06, S 13.77.
1
for 16a. M.p. 182 °C. H NMR (400 MHz, CDCl3): δ = 8.02 (d, J
= 6.3 Hz, 1 H), 7.75 (d, J = 6.9 Hz, 1 H), 7.52–7.57 (m, 3 H), 7.43
(s, 1 H), 7.21–7.33 (m, 4 H), 7.05–7.10 (m, 4 H), 3.88 (s, 3 H) ppm.
MS (EI): m/z (%) = 455 (19) [M]+. C26H17NOS3 (439.05): calcd. C
68.54, H 3.76, N 3.07, S 21.11; found C 68.42, H 3.66, N 3.00, S
21.20.
2-({5-[3-(3,4-Dimethoxyphenyl)benzo[c]thiophen-1-yl]thiophen-2-
yl}methylene)malononitrile (15b): The cyano derivative 15b was ob-
tained in 65% yield according to a procedure similar to that used
Supporting Information (see footnote on the first page of this arti-
cle): Emission spectra of selected benzo[c]thiophenes (2d, 4a, 9a,
9d, 13b, and 14d) and cyclic voltammograms of selected benzo[c]-
thiophenes (4a, 5a, 9c, 9d, 9m, and 15c).
1
for 15a. M.p. 202 °C. H NMR (400 MHz, CDCl3): δ = 8.04 (d, J
= 8.8 Hz, 1 H), 7.84 (d, J = 8.8 Hz, 1 H), 7.74 (s, 1 H), 7.68 (d, J
= 3.9 Hz, 1 H), 7.46 (d, J = 4.3 Hz, 1 H), 7.32–7.36 (m, 1 H), 7.18–
7.24 (m, 2 H), 7.16 (d, J = 1.4 Hz, 1 H), 7.01 (d, J = 8.3 Hz, 1 H),
Acknowledgments
3.90 (s, 6 H) ppm. MS (EI): m/z (%) = 428 (77) [M] +
.
C24H16N2O2S2 (428.07): calcd. C 67.27, H 3.76, N 6.54, S 14.97;
found C 67.20, H 3.70, N 6.60, S 15.00.
The authors thank the Department of Science and Technology
(DST), New Delhi and the University Grants Commission – Poten-
tial for Excellence for financial support. P. A. thanks the Council
of Scientific and Industrial Research (CSIR) for a Senior Research
Fellowship. The authors thank the Department of Science and
Technology Fund for Improvement of Science and Technology
(DST-FIST) for a 300-MHz NMR spectrometer.
2-({5-[3-(p-Tolyl)benzo[c]thiophen-1-yl]thiophen-2-yl}methylene)-
malononitrile (15c): The cyano derivative 15c was obtained in 50%
yield according to a procedure similar to that used for 15a. M.p.
257 °C. 1H NMR (400 MHz, CDCl3): δ = 8.05 (d, J = 8.8 Hz, 1
H), 7.84 (d, J = 8.8 Hz, 1 H), 7.76 (s, 1 H), 7.71 (d, J = 4.4 Hz, 1
H), 7.56 (d, J = 8.3 Hz, 2 H), 7.47 (d, J = 4.4 Hz, 2 H), 7.33 (d, J
= 8.3 Hz, 2 H), 7.18–7.22 (m, 1 H), 2.45 (s, 3 H) ppm. C23H14N2S2
(382.06): calcd. C 72.22, H 3.69, N 7.32, S 16.77; found C 72.12,
H 3.72, N 7.35, S 16.81.
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1
(60%). M.p. 100 °C. H NMR (400 MHz, CDCl3): δ = 8.02 (d, J
= 8.8 Hz, 1 H), 7.76 (d, J = 8.8 Hz, 1 H), 7.57–7.59 (m, 2 H), 7.56
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Eur. J. Org. Chem. 2008, 3798–3810
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3809

P. Amaladass, J. A. Clement, A. K. Mohanakrishnan
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Received: March 4, 2008
Published Online: June 24, 2008
3810
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 3798–3810