Efficient synthesis of 3,6-dialkoxythieno[3,2-b]thiophenes as precursors of electrogenerated conjugated polymers

Article abstract of DOI:10.1039/c0ob00585a

A series of 3,6-dialkoxythieno[3,2-b]thiophenes have been synthesized through three synthetic pathways. Symmetrical derivatives have been obtained from 3,6-dibromothieno[3,2-b]thiophene or by trans-etherification of 3,6-dimethoxythieno[3,2-b]thiophene while unsymmetrical derivatives have been easily prepared from the readily accessible dimethyl 3-hydroxythiophene-2,5- dicarboxylate. These compounds have been used as precursors for electropolymerisation and a first characterisation of the electronic properties of the resulting polymers is presented.

Full text of DOI:10.1039/c0ob00585a

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Organic &
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PAPER
Efficient synthesis of 3,6-dialkoxythieno[3,2-b]thiophenes as precursors of
electrogenerated conjugated polymers†
No e´ mie Hergu e´ , Pierre Fr e` re* and Jean Roncali
Received 15th August 2010, Accepted 17th September 2010
DOI: 10.1039/c0ob00585a
A series of 3,6-dialkoxythieno[3,2-b]thiophenes have been synthesized through three synthetic
pathways. Symmetrical derivatives have been obtained from 3,6-dibromothieno[3,2-b]thiophene or by
trans-etherification of 3,6-dimethoxythieno[3,2-b]thiophene while unsymmetrical derivatives have been
easily prepared from the readily accessible dimethyl 3-hydroxythiophene-2,5-dicarboxylate. These
compounds have been used as precursors for electropolymerisation and a first characterisation of the
electronic properties of the resulting polymers is presented.
Introduction
engineering of functional p-conjugated systems with tailored
26,27
electronic properties.
The strong electron-donor effect of the
The control of the electronic properties of thiophene-based
ethylenedioxy group raises the HOMO level and thus decreases
the oxidation potential of the resulting oligomers or polymers and
enhances the stability of the conducting oxidized state. Further-
more, the alkoxy groups at the b-position of thiophene units induce
the planarization and rigidification of the p-conjugated system by
means of non-covalent intramolecular S---O interactions between
polymers remains at the forefront of research on p-conjugated
1–3
systems. Motivated by their potential technological applications
in the field of plastic electronics, a major goal consists of the
control of the energy of the HOMO and LUMO frontier orbitals
in order to tune crucial electronic properties such as absorp-
tion and emission properties, ionization potential and electron
affinity.
26–29
adjacent thiophene units.
As a further step, one can envision developing a syner-
gistic combination of the two approaches by combining in-
trinsically rigid TT units with constructive non-covalent in-
tramolecular S---O interactions. Recently, the combination
In this context, synthetic approaches aiming at the rigid-
ification and planarization of the conjugated backbone have
been developed in order to minimize the limitations imposed
to p-electron delocalization by the rotational disorder between
thiophene rings. Recently, several groups have reported on
the incorporation of the intrinsically rigid thieno[3,2-b]thiophene
of EDOT and TT moieties has been reported to favour
2,4
30,31
the planarity of conjugated systems.
On the other hand,
32
we have shown that 3,6-dimethoxythieno[3,2-b]thiophene and
(
TT) block in p-conjugated oligomers or polymers in order to
33
3
,4-ethylenedioxythieno[2,3-b]thiophene are efficient building
improve their electronic properties and optimize the performances
of electronic devices such as field-effect transistors or solar cells
blocks for the development of self-rigidified conjugated systems.
On this basis, soluble poly(3,6-dialkoxythieno[3,2-b]thiophene)s
have recently been reported to lead to highly conjugated rigid,
5
–17
based on these materials. Despite some significant improvement
in hole mobility, the use of the TT unit does not suppress rotational
freedom between adjacent units. Furthermore, the introduction of
solubilizing alkyl chains at the b position of the TT unit leads to
steric interactions and thus to distortions of conjugated chains that
enlarge the energy gap.
have been described but the lengthening of the conjugated
chain is rapidly limited by synthetic difficulties.
few years 3,4-ethylenedioxythiophene (EDOT) has progressively
emerged as an important versatile building block for the molecular
9
rod-like structures in solution.
As part of our research aimed at the development of new
synthetic routes to substituted thiophenes, we are developing
the access to alkoxythiophene derivatives from easily available
starting materials. We have recently reported the synthesis of 3,4-
10,14
Rigidified oligothiophene derivatives
33
dialkoxythieno[2,3-b]thiophenes and 3-substituted thieno[3,2-
18–25
In the past
34
b]furanes from 3-hydroxythiophene derivatives. As a further step,
we report here on different synthetic pathways leading to various
dialkoxythieno[3,2-b]thiophenes (Scheme 1). Symmetrical deriva-
tives 3 have been first synthesized from 3,6-dibromothieno[3,2-
b]thiophene or 3,6-dimethoxythieno[3,2-b]thiophene, and we
show that alkoxythienothiophenes can be easily prepared from the
readily available dimethyl 3-hydroxythiophene-2,5-dicarboxylate.
Moreover this new synthetic pathway gives access to unsymmet-
rical derivatives 4, difficult to obtain by already known methods.
University of Angers, Moltech Anjou UMR CNRS 6200, Group Linear
Conjugated Systems, Department of Chemistry, UFR Sciences, 2 Boulevard
Lavoisier, Angers, France. E-mail: pierre.frere@univ-angers.fr; Fax: (33)2
4
1735005; Tel: (33)241735063
1
†
Electronic supplementary information (ESI) available: Copies of H and
C NMR of the new compounds. See DOI: 10.1039/c0ob00585a
1
3
5
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Scheme 1 Symmetrical 3 and unsymmetrical 4 3,6-dialkoxythieno-
3,2-b]thiophenes.
[
Finally a first analysis of the potential of the dialkoxythienothio-
phenes as precursors of electrogenerated conjugated polymers is
presented.
Scheme 2 Synthesis of symmetrical derivatives 3
Results and discussion
Synthesis
The synthesis of dialkoxy-TT derivatives has been envisaged along
three routes. The first involves a nucleophilic substitution of
3
,6-dibromothienothiophene 2 using a concentrated solution of
alcoholate (Scheme 2). Bromination of TT or thienothiophene-
2
-carboxylic acid (prepared in two or four steps from 3-
16,35,36
bromothiophene),
leads to tetrabromothienothiophene 1
which is reduced to the dibromo derivative 2 by treatment with
zinc in acetic acid under microwave activation. Treatment of 2 by
sodium methanolate (4 M in MeOH) in the presence of CuO and
32
KI gives 3,6-dimethoxy-TT 3a in 76% yield.
This procedure is less efficient with longer alcoholates, thus 2-
methoxyethanol leads to the corresponding TT derivative 3b in
5
6% yield while with 2-(2-ethoxyethoxy)ethanol the reaction fails.
An alternative method involves the transetherification of
dimethoxy-TT 3a in the presence of para-toluenesulfonic acid
PTSA) and a slight excess of alcohol to afford dialkoxy-TT 3c–e
(
in 43–80% yield.
The dissymmetrical derivative bearing methoxy and 2-
cyanoethoxy groups (4a) was prepared by the transetherification
of TT 3a using 1 eq. of 3-hydroxypropionitrile (Scheme 3). The
reaction also gives compound 3e as a side-product, the mixture is
easily separated by flash chromatography to give 4a and 3e in 40%
and 25% yields respectively. The cyanoethoxy group is known
Scheme 3 First approach for the synthesis of unsymmetrical derivatives
4
indicates the presence of 67% of the hydroxy form 5 and 33% of
ketone 6 in equilibrium. However, addition of iodopentane to a
basic solution of 4a gives derivative 4b in only 20% yield, indicating
that this procedure is not the most efficient for the synthesis of new
dialkoxy TT derivatives.
37
to give alcoholate anions by reaction with a hydroxide anion.
Thus, reaction of 4a with 1 equivalent of Bu NOH followed by
4
1
acidification leads to a mixture of 5 and 6. H NMR in DMSO
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Scheme 4 General synthesis of unsymmetrical derivatives 4
The third synthetic route proceeds via the easily available
dimethyl 3-hydroxythiophene-2,5-dicarboxylate 7 synthesized in
microwave irradiation in presence of copper chromite affords the
target molecules 4b,c in 65–71% yields for the two steps.
8
5% yield by a Michael reaction of the thiolate of methyl
thioglycolate and the dimethyl acetylenedicarboxylate followed by
Electronic properties
34,38
intramolecular cyclization (Scheme 4).
Compound 7 is easily
purified in large quantities by precipitation after acidification.
Treatment of 7 by 2 equivalents of LDA followed by the successive
addition of sulfur and methyl bromoacetate leads to compound
The optical and electrochemical properties of compounds 3a–e
and 4a–c have been analysed by UV-Vis absorption spectroscopy
and cyclic voltammetry (CV). The resulting data are listed in
Table 1. The absorption spectrum of the monomers presents a well-
resolved vibrational fine structure with two maxima as expected
for rigid TT systems. Comparison of the data for unsubstituted TT
and 3,6–dialkylthienothiophenes, shows that the introduction of
the donor alkoxy groups provokes a bathochromic shift of 17 nm
and 10 nm respectively.
8
which is not isolated. Further addition of a slight excess of
LDA (1.5 eq.) produces a second intramolecular cyclization to
give 9 in 50% yield after acidification. If the low solubility of 9
limits the interest of this route for the synthesis of symmetrical TT,
this synthetic pathway appears promising for the development of
unsymmetrical dialkoxy derivatives difficult to obtain by the first
route. Application of this procedure to the methoxy derivative
14
The CV of compounds 3 and 4 were recorded in acetonitrile in
the presence of tetrabutylammonium perchlorate as the support-
ing electrolyte. The CV of all compounds presents an irreversible
1
0, obtained in 91% yield from the reaction of 7 with methyl
iodide in DMF in the presence of K CO , leads to compound 11
in 77% yield. Reaction of compound 11 with various alkylating
reagents in the presence of K CO in DMF gives compounds 12
2
3
anodic peak (E ) around 1.30 V vs. Ag/AgCl corresponding to
pa
2
3
the formation of the radical cation. The slight positive shift of Epa
in 50% yield. Finally, decarboxylation of the acids resulting from
the saponification of compounds 12 at 200 C in quinoline under
to 1.34 V and 1.37 V for compounds 4a and 3e is probably due to
the long distance electron-withdrawing effect of the cyano group.
◦
5
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Table 1 UV-Vis Absorption and cyclic voltammetric data for compounds
and 4
free electrolytic medium presents a first anodic wave of weak
intensity at -0.18 V followed by a main oxidation wave peaking
at + 0.34 V associated with the p-doping process of the polymer.
The narrowness of the main oxidation wave is consistent with the
formation of a relatively homogenous polymer chain. Compound
3
a
b
Compound
lmax/nm
Epa/V
3
3
3
3
3
4
4
4
a
b
c
d
e
a
b
c
286, 297
286, 297
285, 296
286, 296
285, 295
285, 296
286, 297
286, 297
1.31
1.30
1.29
1.30
1.37
1.34
1.29
1.29
3
b with two short diether groups was also electropolymerized but
-2
the monomer concentration had to be increased to 5 ¥ 10 M. The
CV of poly(3b) also presents a broad redox-system with two
distinct oxidation waves at -0.050 V and 0.82 V. For compounds
bearing longer alkoxy groups, no coherent polymer film could
deposited on the electrode, presumably because of the excessive
solubility of the coupled products.
a
0-5 M in CH
Cl . 10 M in 0.1 M Bu NClO in CH CN, ref. Ag/AgCl,
2 2 4 4 3
-1
b
-3
1
v = 100 mV s .
In the same conditions, the electropolymerization of dissym-
metrical compound 4c leads to a thin film of the polymer (Fig. 1
bottom). Unlike poly(3a), the CV of films of poly(4c) shows a
broad redox system extending from -0.12 V to 1.00 V suggesting
the formation of a polymer with higher polydispersity. The
dissymmetry introduced in the structure of the monomer probably
leads to the formation of a regio-random polymer.
Application of recurrent potential scans between -0.5 V and
1.30 V to a solution of compound 3a (1 ¥ 10 M) in acetonitrile,
-
3
+
leads to the progressive development of a new redox systems
at lower potential associated with the electrodeposition of a
polymer (Fig. 1 top). The CV of poly(3a) recorded in monomer-
Fig. 1 Left: electropolymerization of compound 3a (top) and 4c (bottom) at 1 ¥ 10 mol L-1 in 0.1 M Bu
-
3
NClO
in CH
CN, ref. Ag/AgCl, v =
CN, ref. Ag/AgCl, v =
4
4
3
-1
1
00 mV s . Right: CV of the resulting electrodeposited materials poly(3a) (top) and poly(4c) (bottom) in 0.1 M Bu NClO
4
4
in CH
3
-1
1
00 mV s .
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Table 2 Electrochemical and optical data of electrodeposited polymer
oxidation wave at ca 0.30 V, the main absorption band decreases
and two bands around 800 and 1600 nm emerge which is attributed
to the polaron state. For higher applied potentials, the spectrum
presents a very large band with maxima at 1600 nm for poly(3a)
and poly(3b) and 1200 nm for poly(4c) which should correspond
to the bipolaronic state. Visually the color of the polymers change
from violet to pale blue for poly(3a) and poly(3b) and dark blue
for poly(4c) during the oxidation process.
films
a
b
c
Polymer
E
pa/V
l
max/nm
g
E /eV
Poly(3a)
Poly(3b)
Poly(4c)
-0.18
-0.05
-0.12
0.34
0.82
0.70
586
580
541
1.60
1.69
1.68
a
Film deposited on Pt electrode, 0.1 M Bu
4
NClO
4
in CH CN, v = 50 mV
3
-1
b
c
s . Film deposited on ITO electrode. Calculated from the foot of the
absorption band.
Conclusion
The optical properties of the polymers have been analyzed on
thin films electrodeposited on ITO electrodes and the optical
data are gathered in Table 2. As shown in Fig. 2, the absorption
spectrum of poly(3a) (top) shows a lmax at 586 nm and presents
a fine structure consistent with a rigid backbone. A band gap of
In summary, we have presented herein three methods for the syn-
thesis of dialkoxythieno[3,2-b]thiophenes. The first two, inspired
from already known procedures, lead easily to symmetrical deriva-
tives. The last one, previously unknown, is promising due to its
synthetic pathway which allows the formation of both symmetrical
and unsymmetrical systems. This route proceeds from the easily
available dimethyl 3-hydroxythiophene-2,5-dicarboxylate which
leads to 3-hydroxythienothiophene derivatives via a sequence of
one-pot reactions.
Electroactive conjugated polymers have been obtained by
electrochemical polymerization. The polymers present broad
oxidation waves extending from -0.2 V to +1.0 V and moderate
band gaps of 1.60–1.70 eV depending on the size and composition
of the side substituents.
1
.60 eV has been estimated from the onset of the absorption band.
The lengthening of the alkoxy groups in poly(3b) leads to a slight
blue shift of lmax to 580 nm with a band gap of 1.70 eV. With the
unsymmetrical unit 4c, the polymer presents a broad absorption
band with a 39 nm blue shift of lmax while the width of the band
gap remains unchanged at 1.70 eV, which is consistent with a larger
polydispersity (Fig. 2 bottom).
Experimental
3
,6-Dimethoxythieno[3,2-b]thiophene (3a). To a solution of
methanolate in methanol (4 M, 15 mL) under nitrogen atmosphere
were added 1 g of 3,6-dibromothienothiophene 2 (3.35 mmol),
0
.56 g of CuO (7.1 mmol) and 30 mg of KI (0.1 mmol) and the
mixture was refluxed for 15 h. After cooling at room temperature,
the mixture was poured into 20 mL of water and the copper salts
were eliminated by filtration on a hyflosupercell then the aqueous
phase was extracted with CH
2
Cl
2
. The organic phase was dried
over MgSO and the solvent was removed at reduced pressure. A
4
purification by chromatography on silica gel (CH
2
2
Cl : PE, 1 : 2)
afforded 0.51 g of compound 3a (76%).
◦
1
3
a: white solid. Mp = 145 C. H NMR (CDCl
3
): 3.93 (s, 6H),
): 57.5, 97.3, 128.4, 150.8. HRMS
: 199.9966; found: 199.9969. Elemental
, calcd: C 47.98, H 4.03, O 15.98; found: C
1
3
6
(
.24 (s, 2H). C NMR (CDCl
3
EI): calcd for C
analysis for C
8
H
8
O
2
S
2
8
H
8
O
2
S
2
48.03, H 4.05, O 15.91.
3
,6-Bis(2-methoxyethoxy)thieno[3,2-b]thiophene (3b). Under
nitrogen atmosphere, 0.78 g of sodium (33.8 mmol) was added
to 11 mL of 2-methoxyethanol (0.13 mol) and the mixture was
stirred at room temperature. After the full reaction of sodium,
3
60 mg of 3,6-dibromothienothiophene 2 (1.20 mmol), 205 mg of
CuO (2.6 mmol) and 11 mg of KI (0.04 mmol) were added and the
mixture was refluxed for 15 h. After cooling at room temperature,
the mixture was poured into 20 mL of water and the copper salts
were eliminated by filtration on a hyflosupercell then the aqueous
Fig. 2 Electronic absorption spectra of thin films of poly(3a) (top) and
poly(4b) (bottom) on ITO.
phase was extracted with CH
2
Cl
2
. The organic phase was dried
over MgSO and the solvent was removed at reduced pressure. A
4
Oxidation of the three polymers leads to a similar change in
the optical spectrum. When the applied potential reaches the first
purification by chromatography on silica gel (CH
afforded 0.20 g of compound 3b (56%).
2
2
Cl : PE, 1 : 2)
5
92 | Org. Biomol. Chem., 2011, 9, 588–595
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◦
1
◦
1
3
b: white solid. Mp = 144 C. H NMR (CDCl
3
): 3.45 (s, 6H),
4a: white solid, Mp = 82–84 C. H NMR (CDCl ): 2.89 (t, 2H,
3
3
3
3
3
6
3
.77 (t, 4H, J = 4.77 Hz), 4.21 (t, 4H, J = 4.77 Hz), 6.29 (s, 2H).
J = 6.5 Hz), 3.92 (s, 3H) 4.29 (t, 2H, J = 6.5 Hz), 6.29 (d, 1H, J =
6 13
1
3
C NMR (CDCl
EI): calcd for C12
analysis for C12
0.06, H 5.66, O 22.07.
3
): 59.2, 69.8, 70.8, 98.5, 128.6, 149.7. HRMS
: 288.049; found: 288.0485. Elemental
, calcd: C 49.98, H 5.59, O 22.19; found: C
1.35 Hz), 6.33 (d, 1H, J = 1.35 Hz. C NMR (CDCl
3
): 18.4, 57.5,
(
H
16
O
4
S
2
64.6, 97.7, 99.4, 116.7, 128.1, 128.8, 148.5, 150.7. IR (KBr): nCN =
2235 cm .MS (EI): 239 (M ). Elemental analysis for C10
calcd C 50.19, H 3.79 found C 50.26, H 3.73.
-
1
+
H
16
O
4
S
2
H
9
NO
2
2
S ,
5
3
,6-Bis(2-hexyloxy)thieno[3,2-b]thiophene (3c). Under nitro-
3-Methoxy-6-hydroxythieno[3,2-b]thiophene (5) and 3-methoxy-
6-oxo-5H-dihydrothieno[3,2-b]thiophene (6). To a solution of
90 mg of 4a (0.37 mmol) in 5 mL of freshly distilled THF under
nitrogen atmosphere, was added 520 mL of tetrabutylammonium
1 M in methanol (0.414 mmol). After 30 min of stirring at room
temperature, the solution was poured on 15 mL of HCl (2 M) and
gen atmosphere, a solution of 0.20 g of 3a (1 mmol), 630 mL
of hexanol (5 mmol) and 40 mg of PTSA (0.20 mmol) in 20 mL of
toluene was refluxed for 20 h. The solvent was removed at reduce
pressure then the crude product was purified by chromatography
on silica gel (CH
2
Cl : PE, 2 : 1) to afford 0.24 g of compound 3c
2
(
70%).
c: white solid. Mp = 95 C. H NMR (CDCl
J = 6.80 Hz), 1.35 (m, 8H), 1.45 (m, 4H) 4.05 (t, 4H, J = 6.50
extracted with CH
then dried over anhydrous MgSO
2
Cl
2
. The organic phase was washed with water
. The solvent was removed at
◦
1
3
3
): 0.91 (t, 6H,
4
3
3
1
reduced pressure to give 60 mg of a pink pale solid (86%). The H
NMR reveals an equilibrium between compounds 5 and 6 with
proportions of 2/3 and 1/3 respectively.
1
3
Hz), 6.23 (s, 2H). C NMR (CDCl
3
): 14.8, 22.5, 28.1, 28.8, 29.6,
0.8, 98.2, 128.7, 150.1. MS MALDI-TOF: calcd for C18
40.15; found 340.1. Elemental analysis for C18 , calcd C
3.48, H 8.29, O 9.40; found C 63.36, H 8.32, O 9.26.
7
3
6
H
28
O
2
S
2
1
H
28
O
2
S
2
H NMR (DMSO): compound 5: 3.86 (s, 3H), 6.39 (s, 1H), 6.68
(s, 1H), 10.28 (s, 1H); compound 6: 3.86 (s, 3H), 4.31 (s, 2H), 7.49
-
1
-1
(
1
s, 1H). IR (KBr): n
86 (M ).
C
O
= 1669 cm , n (OH) = 3400 cm . MS (EI):
3
,6-Bis(1,4,7-trioxanoylthieno[3,2-b]thiophene (3d). Under ni-
+.
trogen atmosphere, a solution of 0.30 g of 3a (1.48 mmol), 2 mL
of 2-(2-ethoxy)ethoxyethanol (14.5 mmol) and 60 mg of PTSA
Dimethyl 3-hydroxythiophene-2,5-dicarboxylate (7). To
stirred solution of dimethylacetylenedicarboxylate (10 mL,
81 mmol) and methyl thioglycolate (7.3 mL, 81 mmol) in 200 mL
a
◦
(
0.30 mmol) in 10 mL of benzene was heated at 60 C for 20 h.
After cooling at room temperature, the solution was poured on a
solution of NaHCO (2 M), extracted with CH Cl then washed
with water. The organic layer was dried over anhydrous MgSO
the solvent was removed at reduce pressure then the crude product
3
2
2
of dry methanol was added in small portion 22.6 g of K
2
CO
3
4
,
(163 mmol). Caution the reaction is highly exothermic and the
◦
temperature of the mixture should not exceed 80 C. The mixture
◦
was purified by chromatography on silica gel (CH
2
Cl
2
: AcOEt,
was maintained at 80 C for 2 h leading to an abundant yellow
9
: 1) to afford 0.26 g of compound 3d (43%).
precipitate. After treatment with H
2
SO at 10%, the precipitate
4
◦
1
3
d: white solid presenting decomposition from 80 C. H NMR
turned white, it was filtered, washed twice with water and twice
with methanol then dried in a desiccator to give 14.88 g of
compound 7 (85%).
3
3
(CDCl
3
3
): 1.22 (t, 6H, J = 7.15 Hz), 3.54 (q, 4H, J = 7.15 Hz), 3.62
3
3
(
t, 4H, J = 4.77 Hz), 3.73 (t, 4H, J = 4.77 Hz), 3.89 (t, 4H, J = 4.77
3
13
◦
1
Hz), 4.23 (t, 4H, J = 4.77 Hz), 6.28 (s, 2H). C NMR (CDCl
5.2, 66.7, 69.5, 69.9, 70.0, 71.0, 98.4, 128.6, 149.7. MALDI-TOF:
calcd for C18 404.13; found 404.19. HRMS (ESI): calcd for
+ Na 427.1250; found 427.1219. Elemental analysis
, calcd C 53.44, H 6.98, O 23.73; found C 53.81, H
3
):
7: white solid, Mp = 111 C. H NMR (CDCl
3
): 3.77 (s, 3H),
3.82 (s, 3H), 7.32 (s, 1H), 10.90 (s,1H). C NMR (CDCl ): 51.8,
62.7, 111.1, 125.3, 134.5, 159.2, 161.2, 161.8. IR (KBr) n
1
3
1
3
H
28
O
6
+
S
2
C
O
=
-1
-1
+.
C
for C18
18
H
18
O
6
S
2
1676 cm and 1718 cm .MS (EI): 216 (M ).
H
28
O
6
S
2
Dimethyl 3-methoxythiophene-2,5-dicarboxylate (10). To a
stirred solution of compound 7 (6.92 g, 32 mmol) in 60 mL of
DMF at room temperature were added 6.63 g of K
7
.06, O 23.74.
,6-Bis(2-cyanoethoxy)thieno[3,2-b]thiophene
pound 3e was obtained from 3a (0.31 g, 1.5 mmol), 525 ml of
-hydroxypropionitrile (7.7 mmol) and 2 mg of PTSA in 25 mL
of toluene following the procedure described for 3c. The crude
3
(3e). Com-
2
CO (48 mmol)
3
followed by 2 mL of methyl iodide (46 mmol). The mixture was
◦
3
stirred for 6 h at 80 C and 200 mL of water was added. The
suspension was filtered and washed with 50 mL of H
2
SO at 10%
4
product was purified by chromatography on silica gel (CH
2
Cl
2
) to
then twice with 50 mL of water. The solid was dried in a desiccator
afford 0.34 g of compound 3e (80%).
to give 6.74 g of compound 10 (91% yield).
◦
1
◦
1
3
e: white solid, Mp = 189 C. H NMR (CDCl
3
): 2.90 (t, 4H,
10: white solid, Mp = 120 C. H NMR (CDCl
3
): 3.86 (s, 3H),
3.91 (s, 3H), 3.99 (s, 3H), 7.50 (s, 1H). C NMR (CDCl ): 52.1,
52.7, 59.2, 115.0, 120.6, 135.3, 160.7, 161.6, 161.8. IR (KBr) n
3
3
13
13
J = 6.0 Hz), 4.30 (t, 4H, J = 6.0 Hz), 6.35 (s, 2H). C NMR
3
(
2
2
CDCl
3
): 18.5, 64.8, 99.8, 116.7, 128.6, 148.5. IR (KBr): nCN
=
288.049; found
, calcd C 51.78,
C
O
=
-
1
-1
+.
240 cm . HRMS (EI): calcd for C12
88.0485. Elemental analysis for C12
H
16
O
O
4
S
S
2
1720 cm . MS (EI): 230 (M ).
H
10
N
2
2
2
Dimethyl 3-hydroxy-6-methoxythieno[3,2-b]thiophene-2,5-
dicarboxylate (11). To a stirred solution of compound 10 (2.0 g,
8.68 mmol) in 130 mL of dry THF at -78 C under nitrogen
H 3.62, O 11.50; found C 51.43, H 3.63, O 11.86.
◦
3
-Cyanoethoxy-6-methoxythieno[3,2-b]thiophene (4a). Com-
pound 4a was obtained by following the same procedure de-
scribed for 3e from 0.25 g of 3a (1.25 mmol) and 225 ml
of 3-hydroxypropionitrile (3.2 mmol) in presence of 6 mg of
PTSA in 20 mL of toluene. The crude product was purified by
atmosphere was added 1.5 equivalent of LDA. After 30 min of
stirring, 0.53 g of sulfur (16.4 mmol) was added and the mixture
was stirred for 1 h and the temperature was allowed to rise to
◦
-50 C. Then 1.6 equivalents of methyl bromoacetate were added
chromatography on silica gel (CH
2
Cl
2
: EP, 2 : 1) to afford 120 mg
and the mixture was stirred for 1 h. Finally 1.5 equivalents of
of 4a (40%) and 90 mg of 3e (25%).
LDA were added and the temperature was allowed to rise to
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◦
1
room temperature. The mixture was poured on 250 mL of H
2 M) to give a precipitate. The solid was filtered, washed twice
with water and dried in a desiccator to give 2.0 g of compound 11
2
SO
4
12b: white solid, Mp = 104 C. H NMR (CDCl
3
): 0.93 (t, 3H,
3
(
J = 7.0 Hz), 1.39 (m, 4H), 1.83 (m, 4H), 3.88 (s, 6H), 4.27 (s, 3H),
4.47(t, 2H, J = 6.8 Hz). MS (EI): 288 (M ).
3
+.
(
77% yield).
1: beige solid, decomposition from 217 C. H NMR (CDCl
.89 (s, 3H), 3.95 (s, 3H), 4.26 (s, 3H), 9.88 (s, 1H). C NMR
3
-Methoxy-6-(pentyloxy)thieno[3,2-b]thiophene 4b. This com-
◦
1
1
3
):
pound has been prepared by using the same protocol described
for 4c from 190 mg of 12b (0.51 mmol) and 0.8 g of NaOH. The
intermediate carboxylic acid was not characterized and it was
directly engaged for the decarboxylation reaction with 150 mg of
1
3
3
(CDCl
3
): 52.2, 52.4, 60.1, 106.9, 129.9 (2 C), 154.7, 156.9, 161.9,
-
1
+.
1
66.7. IR (KBr) n
C
O
= 1686 and 1718 cm . MS (EI): 302 (M ).
Cr
2
Cu
2
O in 2 mL of quinoline. The compound was purified by
5
Dimethyl
phene-2,5-dicarboxylate (12a). To a suspension of 400 mg of
1 (1.3 mmol) in 10 mL of DMF were added 1.8 g of K CO
3-methoxy-6-(2-methoxyethoxy)thieno[3,2-b]thio-
chromatography on silca gel (pentane : CH
of compound 4b (71% yield for the two steps).
4
2
Cl
2
, 5 : 1) to give 93 mg
1
2
3
◦
3
b: white solid, Mp = 59 C. NMR (CDCl
3
): 0.94 (t, 3H, J =
and 2 equivalents of 1-bromo-2-ethoxyethane. The mixture was
◦
3
7
.1 Hz), 1.42 (m, 4H), 1.83 (q, 2H, J = 6.9 Hz), 3.91 (s, 3H),
stirred for 16 h at 80 C. After cooling to room temperature, the
3
1
3
4
.05 (t, 2H, J = 6.5 Hz), 6.24 (s, 1H), 6.26 (s, 1H). C NMR
): 14.0, 22.4, 28.1, 28.8, 57.5, 70.5, 97.2, 97.7, 128.1, 128.7,
50.1, 150.8. HRMS (EI): calcd for C12 256.0592; found
56.0591. Elemental analysis for C12 , calcd C 56.22, H
mixture was acidified with a solution of H
2
SO (2 M) and the
4
(CDCl
3
obtained precipitate was filtered, washed with water and dried in
1
2
H
16
O
2
S
2
a desiccator to give 244 mg of compound 12a (51% yield).
◦
1
H
16
O
2
S
2
1
2a: yellow pale solid, Mp = 131 C. H NMR (CDCl
3
): 3.45 (s,
3
6.29; found C 56.36, H 6.22.
3
4
H), 3.76 (t, 2H, J = 4.5 Hz), 3.87 and 3.88 (2 s, 6H), 4.27 (s, 3H),
.55 (t, 2H, J = 4.5 Hz). C NMR (CDCl
3
13
3
): 52.1, 52.2, 59.3, 60.2,
7
1.3, 73.2, 115.0, 117.5, 129.5, 132.3, 153.8, 154.6, 161.6, 161.9.
Notes and references
-
1
+.
IR (KBr) n
C
O
= 1706 and 1720 cm . MS (EI): 360 (M ).
1
Handbook of conducting Polymers, ed. T. A. Skotheim and
J. R. Reynolds, CRC Press, Boca Raton, FL 3rd edn, 2007.
J. Roncali, Macromol. Rapid Commun., 2007, 28, 1761.
3
-Methoxy-6-(2-methoxyethoxy)thieno[3,2-b]thiophene 4c. To
2
3
a suspension of 200 mg of 12a (0.55 mmol) in 5 mL of ethanol
was added a solution of 0.9 g of NaOH in 15 mL of water. The
mixture was refluxed for 3 h. After cooling to room temperature,
the mixture was acidified with H
precipitate was filtered, washed with water and dried in adesiccator
to give 170 mg of carboxylic acid.
G. Barbarella, M. Melucci and G. Sotgiu, Adv. Mater., 2005, 17, 1581.
4 J. Roncali, Chem. Rev., 1997, 97, 173.
5
I. McCulloch, M. Heeney, M. L. Chabinyc, D. DeLongchamp, R. J.
Kline, M. C o¨ lle, W. Duffy, D. Fischer, D. Gundlach, B. Hamadani, R.
Hamilton, L. Richter, A. Salleo, M. Shkunov, D. Sparrowe, S. Tierney
and W. Zhang, Adv. Mater., 2009, 21, 1091.
2
SO to pH = 1 and the obtained
4
6 M. O. Ahmed, C. Wang, P. Keg, W. Pisula, Y.-M. Lam, B. S. Ong, S.-C.
◦
1
Ng, Z.-K. Chen and S. G. Mhaisalkar, J. Mater. Chem., 2009, 19, 3449.
Yellow pale solid, Mp >260 C. H NMR (DMSO): 3.28 (s,
7
Y. He, W. Wu, G. Zhao, Y. Liu and Y. Li, Macromolecules, 2008, 41,
3
3
3
1
1
H), 3.63 (t, 2H, J = 4.5 Hz), 4.17 (s, 3H), 4.48 (t, 2H, J = 4.5 Hz),
13
9
760.
3.28 (s, 2H). C NMR (DMSO): 58.2, 60.1, 70.7, 73.0, 116.0,
8 L. DeCremer, S. Vandeleene, M. Maesen, T. Verbiest and G. Koeckel-
+.
berghs, Macromolecules, 2008, 41, 591.
18.6, 129.9, 131.6, 152.7, 153.5, 161.9, 162.1. MS (EI): 288 (M
CO ).
A 10 mL tube equipped with a magnetic stirring bar was filled
with 170 mg (0.51 mmol) of carboxylic acid dissolved in 2 mL of
9
L. DeCremer, T. Verbiest and G. Koeckelberghs, Macromolecules, 2008,
-
2
4
1, 568.
1
0 L. SanMiguel and A. J. Matzger, Macromolecules, 2007, 40, 9233.
11 D. M. DeLongchamp, R. J. Kline, E. K. Lin, D. A. Fischer, L. J. Richter,
L. A. Lucas, M. Heeney, I. McCulloch and J. E. Northrup, Adv. Mater.,
quinoline and60 mg of Cr
with a rubber cap and irradiated for 3 min at 200 C with a reactor
power of 200 W. The mixture was cooled to room temperature,
poured on 20 mL of H
pentane (2 ¥ 20 mL) and the organic phase was dried on MgSO
After evaporation of the solvent the residue was purified by a flash
chromatography on silica gel (pentane, CH Cl , 2/1) to give 87 mg
of compound 4c (65% yield for the two steps).
2
Cu
2
O
5
(0.20 mmol). The tube was sealed
2
007, 19, 833.
◦
1
2 M. L. Chabinyc, M. F. Toney, R. J. Kline, I. McCulloch and M. Heeney,
J. Am. Chem. Soc., 2007, 129, 3226.
13 Y. Y. Noh, R. Azumi, M. Goto, B. J. Jung, E. H. Lim, H. K. Shim, Y.
2
SO
4
solution (2 M), extracted twice with
Yoshida, K. Yase and D. Y. Kim, Chem. Mater., 2005, 17, 3861.
4
.
1
4 X. N. Zhang, M. Kohler and A. J. Matzger, Macromolecules, 2004, 37,
6
306.
2
2
15 E. Lim, B. J. Jung and H. K. Shim, Macromolecules, 2003, 36, 4288.
1
6 P. Leriche, J. M. Raimundo, M. Turbiez, V. Monroche, M. Allain, F. X.
◦
1
Sauvage, J. Roncali, P. Fr e` re and P. J. Skabara, J. Mater. Chem., 2003,
4
c: Yellow pale solid, Mp = 104 C. H NMR (CDCl ): 3.46
3
1
3, 1324.
3
3
(
s, 3H), 3.78 (t, 2H, J = 4.7 Hz), 3.91 (s, 3H), 4.22 (t, 2H, J =
1
7 L. Ying, D. Chong-an, D. Chunyan, L. Yunqi, L. Kun, Q. Wenfeng and
Y. Gui, Chem.–Eur. J., 2010, 16, 2231.
6
6
13
4
.7 Hz), 6.26 (d, 1H, J = 1.6 Hz), 6.29 (d, 1H, J = 1.6 Hz).
): 57.6, 57.9, 69.9, 70.9, 97.4, 98.5, 128.4, 128.7,
49.9, 150.8. HRMS (EI): calcd for C10 244.0228; found
, calcd C 49.16, H
C
1
1
8 J. Roncali and C. Thobie-Gautier, Adv. Mater., 1994, 6, 846.
9 P. Blanchard, P. Verlhac, L. Michaux, P. Fr e` re and J. Roncali, Chem.–
Eur. J., 2006, 12, 1244.
NMR (CDCl
3
1
2
4
H
12
O
3
S
2
44.0224. Elemental analysis for C10
.95; found C 49.56, H 4.92.
H
12
O
3
S
2
20 M. He and F. Zhang, J. Org. Chem., 2007, 72, 442.
2
2
1 X. Zhang, J. P. Johnson, J. W. Kampf and A. J. Matzger, Chem. Mater.,
006, 18, 3470.
2 K. Xiao, Y. Liu, T. Qi, W. Zhang, F. Wang, J. Gao, W. Qiu, Y. Ma, G.
Cui, S. Chen, X. Zhan, G. Yu, J. Qin, W. Hu and D. Zhu, J. Am. Chem.
Soc., 2005, 127, 13281.
2
Dimethyl 3-methoxy-6-(pentyloxy)thieno[3,2-b]thiophene-2,5-
dicarboxylate 12b. This compound has been prepared by using
the same protocol described for 12a from 300 mg of compound 10
23 T. Okamoto, K. Kudoh, A. Wakamiya and S. Yamaguchi, Org. Lett.,
2005, 7, 5301.
(
1 mmol), 276 mg of K
2
CO
3
(2 mmol) and 0.2 mL of iodopentane
SO the
2
4 X. N. Zhang, A. P. Cote and A. J. Matzger, J. Am. Chem. Soc., 2005,
27, 10502.
5 K. Oyaizu, T. Iwasaki, Y. Tsukahara and E. Tsuchida, Macromolecules,
2004, 37, 1257.
(
1.6 mmol) in 10 mL of DMF. After acidification with H
2
4
1
obtained precipitate was filtered, washed with water and dried in
a desiccator to give 330 mg of compound 12b (50% yield).
2
5
94 | Org. Biomol. Chem., 2011, 9, 588–595
This journal is © The Royal Society of Chemistry 2011

View Article Online
2
2
6 J. Roncali, P. Blanchard and P. Fr e` re, J. Mater. Chem., 2005, 15, 1589.
7 M. Turbiez, P. Fr e` re, M. Allain, C. Videlot, J. Ackermann and J.
Roncali, Chem.–Eur. J., 2005, 11, 3742.
8 J. M. Raimundo, P. Blanchard, P. Fr e` re, N. Mercier, I. Ledoux Rak, R.
Hierle and J. Roncali, Tetrahedron Lett., 2001, 42, 1507.
32 M. Turbiez, P. Fr e` re, P. Leriche, N. Mercier and J. Roncali, Chem.
Commun., 2005, 1161.
33 N. Hergu e´ and P. Fr e` re, Org. Biomol. Chem., 2007, 5, 3442.
34 N. Hergu e´ , C. Mallet, J. Touvron, M. Allain, P. Leriche and P. Fr e` re,
Tetrahedron Lett., 2008, 49, 2425.
2
2
3
9 M. Turbiez, P. Fr e` re and J. Roncali, J. Org. Chem., 2003, 68, 5357.
0 M. Turbiez, N. Hergu e´ , P. Leriche and P. Fr e` re, Tetrahedron Lett., 2009,
35 L. Fuller, S. B. Iddon and K. A. Smith, J. Chem. Soc., Perkin Trans. 1,
1997, 3465.
5
0, 7148.
36 J. T. Henssler and A. J. Matzger, Org. Lett., 2009, 11, 3144.
37 B. Jousselme, P. Blanchard, M. Ocafrain, M. Allain, E. Levillain and J.
Roncali, J. Mater. Chem., 2004, 14, 421.
3
1 G. J. McEntee, P. J. Skabara, F. Vilela, S. Tierney, I. D. W. Samuel,
S. Gambino, S. J. Coles, M. B. Hursthouse, R. W. Harrington and W.
Clegg, Chem. Mater., 2010, 22, 3000.
38 H. Fiesselmann and P. Schipprack, Chem. Ber., 1954, 87, 835.
This journal is © The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 588–595 | 595