Toward Functionalized Conducting Polymers: Synthesis and Characterization of Novel β-(Styryl)terthiophenes

Article abstract of DOI:10.1021/jo034855g

Metal-catalyzed coupling methodologies have been employed in the synthesis of the key building block 3′-formyl-2,2′:5′,2″ -terthiophene. Wittig olefinations with this aldehyde have produced five novel β-styryl-substituted terthiophene monomers. These materials have been fully characterized by NMR spectroscopy, microanalysis, mass spectrometry, and X-ray crystal structure analysis. The results from the UV/visible spectroscopy and cyclic voltammetric investigations are reported.

Full text of DOI:10.1021/jo034855g

Tow a r d F u n ction a lized Con d u ctin g P olym er s: Syn th esis a n d
Ch a r a cter iza tion of Novel â-(Styr yl)ter th iop h en es
Gavin E. Collis and Anthony K. Burrell*
Actinide, Catalysis and Separations Chemistry, C-SIC, Mail Stop J 514, Los Alamos National Laboratory,
Los Alamos, New Mexico 87545
Sonya M. Scott† and David L. Officer
Nanomaterials Research Centre, Massey University, Private Bag 11222, Palmerston North, New Zealand
burrell@lanl.gov
Received J une 18, 2003
Metal-catalyzed coupling methodologies have been employed in the synthesis of the key building
block 3′-formyl-2,2′:5′,2′′-terthiophene. Wittig olefinations with this aldehyde have produced five
novel â-styryl-substituted terthiophene monomers. These materials have been fully characterized
by NMR spectroscopy, microanalysis, mass spectrometry, and X-ray crystal structure analysis. The
results from the UV/visible spectroscopy and cyclic voltammetric investigations are reported.
In tr od u ction
A number of these applications require tailored elec-
tronic properties, which influence polymer characteris-
tics, such as p- or n-type doping,18 redox cycling,19 band
gap,20,21 and photovoltaic behavior.22,23 Typically, aromatic
substituents have been utilized in this regard. Thus, poly-
(3-arylthiophenes) (1) have improved doping capacity and
Since the Nobel prize-winning discovery by Heeger,
MacDiarmid, and Shirakawa1,2 that doped polyacetylene
is conducting, conjugated polymers have been intensely
studied.3 While the initial interest was in the intriguing
structure and electronic properties of these materials,
subsequent work has been driven by the diversity of
potential applications for conducting “plastics”.4,5 Promi-
nent among the conjugated materials studied to date are
the oligo- and polythiophenes, since a wide variety of
functionality can be readily built on to the parent
thiophene, bithiophene, or terthiophene monomers.6,7
Oligo- and polythiophenes have been investigated as
advanced electrode materials;7 as suitable materials for
electronic,8,9,10 optoelectronic,8,11,12 and chemosensor13,14,15
devices; and for photovoltaics.16,17
cyclability over polythiophene,24,25 and fusing benzene to
thiophene leads to poly(isothianaphthene) (2), the pro-
totypical small band gap polymer.26
Other conjugated substituents have also been used to
influence the electronic nature and resulting properties
of polythiophenes. A new variety of low band gap
* Corresponding author.
† Current address: Department of Chemistry, Cambridge Univer-
sity, Lensfield Rd, Cambridge, CB2 1EW.
(1) Chiang, C. K.; Fincher, C. R., J r.; Park, Y. W.; Heeger, A. J .;
Shirakawa, H.; Louis, E. J .; Gau, S. C.; MacDiarmid, A. G. Phys. Rev.
Lett. 1977, 39, 1098.
(2) Shirakawa, H.; Louis, E. J .; MacDiarmid, A. G.; Chiang, C. K.;
Heeger, A. J . J . Chem. Soc., Chem. Commun. 1977, 578.
(3) Nalwa, H. S., Ed. Handbook of Advanced Electronic and Photonic
Materials and Devices, Volume 8: Conducting Polymers; Academic:
San Diego, 2001.
(4) Hsieh, B. R.; Wei, Y. ACS Symp. Ser. 1999, 735, 1.
(5) Spinks, G. M.; Innis, P. C.; Lewis, T. W.; Kane-Maguire, L. A.
P.; Wallace, G. G. Mater. Forum 2000, 24, 125.
(6) Roncali, J . Chem. Rev. 1992, 92, 711.
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M. R.; Friend, R. H. Nature 1998, 395, 257.
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Innovation 2000, 30, 14.
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Theander, M.; Ingana¨s, O. J . Mater. Chem. 1999, 9, 1933.
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99-23, 104.
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S. E.; Vaid, T. P.; Walt, D. R. Chem. Rev. 2000, 100, 2595.
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A. IEEE Trans. Electron Devices 1997, 44, 1315.
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Geri, A.; Bertarelli, C. Adv. Funct. Mater. 2003, 13, 307.
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10.1021/jo034855g CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/21/2003
8974
J . Org. Chem. 2003, 68, 8974-8983

Novel â-(Styryl)terthiophenes
SCHEME 1
For example, Higgins and Mirkin have found that the
terthiophene monomer (9b) forms an electroactive mater-
ial, whereas the analogous thiophene (9a ) does not.34 An
added advantage to using 8 is that the substituents will
be on alternate sides of the polymer chain, reducing steric
interactions that may lead to structural irregularities.
To our knowledge, there are no examples of aryl
â-conjugatively linked terthiophene derivatives, and
therefore, we set out to establish a general methodology
to these materials.35 Since the formation of the aryl
alkenic linkage to the terthiophene structure should be
readily accessible by Wittig chemistry using a variety of
aryl-substituted ylides that have been reported in the
literature, the key building block for the syntheses is 3′-
formylterthiophene (10) (Scheme 2). The chemistry of
assembling terthiophene structures using metal-cata-
lyzed aryl-coupling reactions is well-documented, and so
it was envisioned that the terthiophene backbone with
the necessary functionality at the 3′-position could be
efficiently constructed by Kumada coupling36 (Scheme 2).
It is also noteworthy that the Wittig reaction can give
rise to cis/trans isomers, which may provide distinct
polymers with interesting properties.
polymers has been developed from the methylenecyclo-
pentadithiophene moiety (3).27,28,29 More recently, Green-
wald and co-workers used a styryl substituent in a
copolymer (5) (Scheme 1) to improve the photoconductiv-
ity of polythiophene.30
This was not the first time that styryl side chains had
been introduced into polythiophene in an attempt to
tailor the electronic structure of the polymer. In 1994,
Smith et al. reported that electrochemical homopoly-
merization of (4) produced a nonconductive material,
presumably through side-chain polymerization.31 Other
styryl derivatives showed similar behavior. However,
electrically conducting polymers (7) have been obtained
by copolymerization of styryl derivatives with 3-meth-
ylthiophene.32 We have recently confirmed and extended
these findings.33 Although copolymers such as 5 and 7
are extremely promising, they have irregular and random
structures and provided limited information on the role
the conjugated substituents play in influencing the
physical and chemical properties of the polymer.
Resu lts
1. Syn th esis a n d Ch a r a cter iza tion . The necessary
thiophene precursors, 12 and 17 (Scheme 3), were
prepared efficiently and easily from commercially avail-
able materials. Monobromination of thiophene (11) under
mild conditions, following the procedure of Brandsma and
Keegstra,37 gave 2-bromothiophene (12) in excellent yield
(Scheme 3). Using an adaptation of a procedure from the
same paper,37 2,5-dibromo-3-formylthiophene (15) was
synthesized in moderate yield (73%) via a one-step
dibromination of 3-formylthiophene (14). This reaction
can be performed on larger scales (50-100 g) and gives
good yields of purified 15 (55-73%). This method im-
proves on those previously reported; Fournari and co-
workers38 used a conventional method to brominate the
aldehyde (14) in low yield (28%), while Coyle and co-
workers39 used a cumbersome three-step synthesis to
convert 3-methylthiophene to the dibromoaldehyde (15)
in moderate yield (66%). During the course of this work,
Gallazzi and co-workers40 reported that the more recent
technique used to brominate oligothiophenes, employing
NBS in DMF, could be used to convert 14 to 15.
An alternative approach to the formation of styryl-
functionalized polythiophenes such as 6, without the
complication of the regioirregular alkyl substituent, is
to polymerize substituted terthiophenes such as 8. Since
terthiophene polymerizes more readily than thiophene,
these polymers should be easier to form and less likely
to produce branched structures through the vinylic group.
Treatment of the dibromoaldehyde (15) with neopentyl
glycol (16) and a catalytic amount of p-toluenesulfonic
acid in benzene under Dean-Stark conditions provided,
after distillation, the acetal (17) as a white crystalline
solid in quantitative yield. The key advantages of using
this 1,3-diol as a protecting group is that the acetal is
(27) Kozaki, M.; Tanaka, S.; Yamashita, Y. J . Chem. Soc., Chem.
Commun. 1992, 1137.
(28) Ferraris, J . P.; Lambert, T. L. J . Chem. Soc., Chem. Commun.
1991, 1268.
(34) Higgins, T. B.; Mirkin, C. A. Chem. Mater. 1998, 10, 1589.
(35) Collis, G. E.; Burrell, A. K.; Officer, D. L. Tetrahedron Lett.
2001, 42, 8733.
(36) Kumada, M. Pure Appl. Chem. 1980, 52, 669.
(37) Keegstra, M. A.; Brandsma, L. Synthesis 1988, 890.
(38) Fournari, P.; Guilard, R.; Person, M. Bull. Soc. Chim. Fr. 1967,
11, 4115.
(29) Roncali, J.; Brisset, H.; Thobie-Gautier, C.; Jubault, M.; Gorgues,
A. J . Chim. Phys. Phys.-Chim. Biol. 1995, 92, 771.
(30) Greenwald, Y.; Cohen, G.; Poplawski, J .; Ehrenfreund, E.;
Speiser, S.; Davidov, D. J . Am. Chem. Soc. 1996, 118, 2980.
(31) Smith, J . R.; Campbell, S. A.; Ratcliffe, N. M.; Dunleavy, M.
Synth. Met. 1994, 63, 233.
(32) Welzel, H.-P.; Kossmehl, G.; Engelmann, G.; Plieth, W. Eur.
Polym. J . 1997, 33, 299.
(33) Cutler, C. A.; Burrell, A. K.; Officer, D. L.; Too, C. O.; Wallace,
G. G. Synth. Met. 2001, 128, 35.
(39) Coyle, J . D.; Haws, E. J .; Oduntan, O.; Rogers, J . T. Heterocycles
1984, 22, 1175.
(40) Gallazzi, M. C.; Toscano, F.; Paganuzzi, D.; Bertarelli, C.;
Farina, A.; Zotti, G. Macromol. Chem. Phys. 2001, 202, 2074.
J . Org. Chem, Vol. 68, No. 23, 2003 8975

Collis et al.
SCHEME 2
SCHEME 3
the H 3 denoted as the thiophene ring nearest to the
acetal group. The acetal functionality of 18 is clearly
identified in the 1H NMR spectrum and all its signals
are deshielded due to the π systems of the nearby
aromatic rings.
Attempts to remove the acetal group from 18 using
conventional procedures45 resulted in recovery of the
acetal or poor conversion to the desired aldehyde material
only after long reaction periods (Scheme 4). It was
eventually found that the aldehyde could be efficiently
deprotected by employing a procedure used by Magnus
and co-workers46 for the removal of diethyl acetals.
Treatment of the acetal in a two-phase trifluoroacetic
acid/chloroform/water mixture (ratio of 3:3:1) gave, after
chromatography, the terthiophene aldehyde (10) in excel-
lent yield (95%). The 1H NMR spectrum of 10 at 400 MHz
shows an aldehyde proton resonance at 10.08 ppm, while
the singlet at 7.57 ppm corresponds to H 4′. COSY and
NOESY experiments were used to assign the outer
thiophene rings; long-range coupling between H 4′ and
H 3′′ was detected, while a NOE difference between the
aldehyde proton and H 3 of 1.1% was observed. The IR
robust under acidic conditions and has characteristic
signals that are easily identifiable in 1H NMR spectra.
With the necessary precursors available to construct
the terthiophene system, small scale (1 g) Kumada
coupling reactions were investigated.36,41,42,43 Treatment
of an ethereal solution of 2-bromothiophene with mag-
nesium metal gave 2-bromomagnesiothiophene (13)
(Scheme 3) with minimal formation of the Wurtz byprod-
uct, 2,2′-bithiophene. Heating the Grignard reagent (13)
with dibromo acetal (17) and NiCl2(dppp) catalyst af-
forded a complex mixture which, when subjected to radial
chromatography, resulted in the isolation of the ter-
thiophene acetal (18) in good yield (71%), as well as a
small amount of 2,2′-bithiophene and unreacted acetal
(17) (Scheme 4).
spectrum of 10 shows an absorption band at 1676 cm-1
,
typical of an aromatic aldehyde.
Unfortunately, attempts to perform the coupling reac-
tion on a preparative scale (>5 g) and isolate suitable
quantities of the terthiophene acetal gave discouraging
results. Modification of the conditions, by varying the
addition time and quantity of the Grignard reagent or
prolonged reaction periods, only resulted in poor yields.
Attempts to increase the yield by using another nickel
catalyst, Ni(dppe)Cl2, under the conditions used before
gave only trace amounts of the desired product. In
addition, conventional methods for purifying the ter-
thiophene acetal (18) by rapid silica filtration or column
chromatography proved laborious and inefficient for
large-scale crude mixtures. It was found, however, that
adsorption of the crude material onto chromatographic
silica gel and extraction with hexane using a Soxhlet
apparatus circumvented the need for chromatographic
purification. Concentration of this filtrate and cooling
1
Analysis of the terthiophene acetal (18) by H and 13C
NMR spectroscopy, with the aid of COSY and NOE
experiments, allowed the unambiguous assignment of all
three thiophene rings. The COSY experiment allowed
conclusive assignment of the AMX spin system of each
outer thiophene ring. A five bond long-range coupling44
interaction between H 3′′ and the H 4′ was identified.
The NOE difference also supported the assignment of the
two external thiophene rings. Irradiation of the methine
proton of the acetal group indicated a NOE difference of
0.9% and 2.7% between the H 4′ of the center ring and
SCHEME 4
8976 J . Org. Chem., Vol. 68, No. 23, 2003

Novel â-(Styryl)terthiophenes
SCHEME 5
the target molecules in excellent yields ranging from 80
to 92%. The target materials 23, 25, 27, 29, and 31, were
successfully characterized using microanalysis, mass
spectrometry, IR, NMR, and UV/visible spectroscopy (see
later). Wittig olefination involving aryl phosphonium
salts with electron-withdrawing groups or no substituent,
such as 21, 24, or 26, were best performed by treatment
with DBU in the presence of the aldehyde (10) in
dichloromethane at reflux. In the case of the nitro salt
(21), using these conditions gave, as expected, a mixture
of geometric isomers (22 and 23) (Scheme 6). Analysis of
resulted in precipitation of the terthiophene acetal (18),
which was then recrystallized in 51% yield. Due to the
limited success of this Kumada chemistry on a larger
scale, alternative coupling methodologies were investi-
gated.
1
the crude mixture by H NMR spectroscopy indicated a
cis/trans ratio of 1.5:1; this was determined from integra-
tion of the vinylic protons of the cis isomer appearing as
an AB quartet (6.70 and 6.74 ppm, 12.0 Hz) and the trans
isomer consisting of two doublets at 7.05 and 7.49 ppm
(16.2 Hz). No attempt was made to isolate the cis isomer,
as cis/trans isomerization was found to occur after
exposure of a solution of 22 and 23 to sunlight. In
practice, the isomerization of 22 to 23 was achieved by
irradiating the mixture with a 240-W lamp to afford, after
chromatography and recrystallization, the all-trans prod-
uct 23 as orange crystals (82%). The IR spectrum shows
the characteristic absorption bands at 1336 and 1508
cm-1 of the nitro group.
The Suzuki coupling of aromatic halides with aryl
boronic acids has been used extensively and is well-
documented in the literature.47,48 Gronowitz and co-
workers49 have successfully shown that 2,2′:5′,2′′-ter-
thiophene can be constructed in satisfactory yield (40%)
using the Suzuki coupling methodology. Using this
strategy we envisioned that the key precursor, 3′-formyl-
terthiophene (10), could be accessed by the reactions
represented in Scheme 5, eliminating the need for the
protection/deprotection chemistry used in the Kumada
coupling approach. Treatment of thiophene (11) at low
temperature with n-butyllithium, followed by reverse
addition to trisisopropyl borate and acidic workup gave
2-thienyl boronic acid (19) in high yield. Other literature
methods describe relatively small-scale syntheses or
crude isolation of 19,50,51,52 but with this reverse addition
high yields and purity can be easily obtained on a
multigram scale. A slight excess of the boronic acid (19)
was treated with the previously prepared dibromoalde-
hyde (15) and tetrakis(triphenylphosphine)palladium
catalyst under the Suzuki coupling conditions employed
by Gronowitz49 (Scheme 5). After the requisite aqueous
workup and chromatography, terthiophene aldehyde (10)
was isolated, as well as the monocoupled product, 5-bromo-
3-formyl-2,2′-bithiophene (20). Interestingly, only one
monocoupled product was observed, implying that the
first coupling step is regioselective, and this is presum-
ably due to the electronic nature of the nearby aldehyde
functionality. Such regioselectivity has also been noted
in an analogous system that involves Suzuki coupling
with 15.53 It was determined that use of an excess of the
boronic acid (see Experimental Section) was required to
ensure the complete formation of the aldehyde (10),
which was obtained after purification in excellent yield
(76%). This procedure was readily scaled-up to provide
a rapid and efficient multigram synthesis of the ter-
thiophene aldehyde building block.
Using the same procedure, treatment of the aldehyde
(10) with (4-cyanobenzyl)triphenylphosphonium bromide
(24) or benzyltriphenylphosphonium bromide (26) under
basic conditions gave the target compounds, 25 and 27,
respectively, in excellent yields (Scheme 7). Surprisingly,
1
in each of the crude H NMR spectra no cis isomer was
observed and both pure trans materials were easily
isolated after chromatography and recrystallization as
yellow crystalline solids. The IR spectrum of terthio-
phene (25) displays a strong absorption at 2221 cm-1
,
typical of a cyano function in conjugation with an aryl
group.
The synthesis of compounds 29 and 31 that contain
electron-donating groups on the aryl ring required slightly
different reaction conditions than those previously em-
ployed. The reaction of excess phosphonium salt, 28 or
30, with the strong base potassium tert-butoxide ensured
the generation of the ylide to which the terthiophene
aldehyde (10) was then added (Scheme 8). This procedure
furnished the most satisfactory yields of the pure trans
isomers 29 and 31 after an aqueous workup and chro-
matography (80 and 81%, respectively). The main feature
of the IR spectrum of 29 is a C-O-C stretch at 1172
and 1247 cm-1, indicative of the methoxy substituent,
while the spectrum of 31 has a strong absorption at 1366
cm-1 attributed to the tertiary aromatic amine.
Wittig reactions between 3′-formylterthiophene (10)
and ylides, derived from various phosphonium salts, gave
SCHEME 6
J . Org. Chem, Vol. 68, No. 23, 2003 8977

Collis et al.
SCHEME 7
deshielding effect of the nitro group. On the other hand,
the spectrum of the phenyl derivative 27, as expected, is
more complicated.
In all the spectra of the target compounds, the vinylic
proton resonances appear as two doublets with a coupling
of approximately 16 Hz, typical of a trans configuration,
with variations in chemical shift, presumably arising
from shielding and deshielding effects induced by the R
group.
Due to the unsymmetrical nature of the terthiophene
compounds, all five molecules have two AMX spin
systems that are attributed to the outer thiophene rings.
The assignment of the H 3, H 4, and H 5 of each ring
was achieved by the extraction of coupling constants and
with the aid of COSY experiments. The actual assign-
ment as to which of the two rings is connected to either
side of the central ring was established using long-range
COSY experiments. Analysis of all the proton spectra for
the target compounds reveals the H 4′′ as a singlet [e.g.
see structure 23 (Scheme 6)] occurring in the range of
7.41-7.45 ppm. The COSY spectra indicate a correlation
between the H 4′′ and the vinylic proton assigned as H
1. More significantly, H 4′′ coupling through five bonds
to the proton of an adjacent thiophene ring is observed,
which can only be associated with the H 3′′′. Conversely,
the thiophene ring denoted as being the nearest to the
aryl-substituted system shows no evidence for long-range
coupling to the H 4′′ of the central ring (i.e. six bond
coupling). This long range coupling was clearly observed
in all the terthiophene systems studied.
SCHEME 8
The absence of cis isomers in all but the reaction of
the nitrophenyl phosphonium salt (21) is unusual but
presumably reflects the influence of the bulky ter-
thiophene aldehyde (10) in the transition states of the
reactions. In the case of 21, the presence of the cis isomer
could either be caused by π-π interactions or a favorable
interaction of the nitro group on the ylide with a sulfur
atom of one of the thiophene rings in the betaine
formation of the Wittig reaction.
Finally, use of HETCOR experiments allowed assign-
ment and distinction between carbon atoms attached to
the aryl and thiophene protons, the vinylic protons, and
H 4′′. Carbon-13 spectra of 29 and 31 also clearly show
the key signals of the methoxy substituent at 55.3 ppm
and the methyl groups of the amino functionality at 40.4
ppm.
2. NMR Sp ectr oscop y of Ar yl-Su bstitu ted Ter -
th iop h en e Ma ter ia ls. Analysis of the target compounds
by NMR spectroscopy reveals characteristic signals that
are observed in all spectra. Molecules 23, 25, 29, and 31
all contain para-substituted aromatic rings. As a result,
AA′XX′ patterns are easily distinguished in these spectra.
For example, in the proton NMR spectrum of 23 the
AA′XX′ spin pattern occurs at 8.16-8.22 and 7.55-7.60
ppm; where the downfield signal is a result of the strong
3. X-r a y Str u ctu r e An a lysis of tr a n s-1-((2′,2′′:5′′,2′′′-
Ter th iop h en )-3′′-yl)-2-(4′′′′-cya n op h en yl)eth en e (25).
Considering the ongoing interest in synthesizing and
utilizing terthiophene block monomers, there is a dearth
of X-ray crystallography data for simple â-substituted
2,2′:5′,2′′-terthiophenes in the literature. Structural analy-
sis of the parent terthiophene (32) in 1989 by Van Bolhuis
(41) Tamao, K.; Kodama, S.; Nakajima, I.; Kumada, M.; Minato, A.;
Suzuki, K. Tetrahedron 1982, 38, 3347.
(42) Chaloner, P. A.; Gunatunga, S. R.; Hitchcock, P. B. J . Chem.
Soc., Perkin Trans. 2 1997, 8, 1597.
(43) Van Pham, C.; Burkhardt, A.; Shabana, R.; Cunningham, D.
D.; Mark, H. B., J r.; Zimmer, H. Phosphorus, Sulfur Silicon 1989, 46,
153.
(44) Gu¨nther, H. NMR Spectroscopy: Basic Principles, Concepts and
Applications in Chemistry; 2nd ed.; J ohn Wiley and Sons: Chichester,
England, 1995.
(45) Greene, T. W. Protecting Groups in Organic Synthesis; J ohn
Wiley and Sons: New York, 1981.
(46) Magnus, P.; Davies, M. J . Chem. Soc., Chem. Commun. 1991,
1522.
(47) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(48) Kalinin, V. N. Synthesis 1992, 5, 413.
(49) Gronowitz, S.; Peters, D. Heterocycles 1990, 30, 645.
(50) Cullen, K. E.; Sharp, J . T. J . Chem. Soc., Perkin Trans. 1 1995,
2565.
(51) Caze, C.; El Moualij, N.; Hodge, P.; Lock, C. J . Polymer 1995,
36, 621.
and co-workers54 revealed that in the solid state, the
thiophene rings are in antiparallel positions and the
molecule itself is nearly, but not completely, planar. The
two outer thiophene rings, which are coplanar, are
(52) Ho¨rnfeldt, A.-B.; Gronowitz, S. Arkiv Kemi 1963, 21, 239.
(53) Evans, N. Honours Report, Massey University, 2000.
(54) Van Bolhuis, F.; Wynberg, H.; Havinga, E. E.; Meijer, E. W.;
Staring, E. G. J . Synth. Met. 1989, 30, 381.
8978 J . Org. Chem., Vol. 68, No. 23, 2003

Novel â-(Styryl)terthiophenes
TABLE 1. Electr on ic Absor p tion Sp ectr a l Da ta for
Com p ou n d s a t Room Tem p er a tu r e in CHCl3
compd
λ, nm (log ꢀ)
355 (4.34)
terthiophene (32)
23
25
27
29
31
345 (4.57), 411(sh) (4.25)
324 (4.65), 355(sh) (4.45)
312 (4.57), 353(sh) (4.34)
323 (4.74), 362(sh) (4.48)
348(br) (4.58)
TABLE 2. Electr och em ica l Da ta for Com p ou n d s in
CH2Cl2
E°, Va
initial
oxidation potential
polymerization
potential
compd
23
25
27
29
31
35
1.38
1.24
1.19
1.20
0.83
1.20
0.90
0.90
0.92
0.86
b
F IGURE 1. X-ray crystal structure of trans-1-((2′,2′′:5′′,2′′′-
terthiophen)-3′′-yl)-2-(4′′′′-cyanophenyl)ethene (25).
twisted slightly with respect to the central ring with a
torsional angle of 6.9°. Later studies by Barbarella and
co-workers55 on the simple â-substituted regioregular
thiophene trimer 3,4′,4′′-trimethyl-2,2′:5′,2′′-terthiophene
(33) gave similar supporting evidence for an essentially
planar structure where the outer thiophene rings are
twisted by 7° and 7.8° with respect to the central ring;
the thiophene rings themselves are in an anti-arrange-
ment.
0.81
a
b
Versus ferrocene. No visible film seen on the electrode
surface.
tion the rotation of the external thiophene rings about
the C(4)-C(5) and C(8)-C(9) bonds is not restricted by
a excessively large rotational energy barrier: this is
supported by the 2D COSY and NOESY NMR experi-
ments performed on terthiophene systems described in
this paper. The torsional angles between the outer rings
and the central thiophene ring is -148.6° [S(1a)-C(4)-
C(5)-C(6)] for the ring closest the alkene linker, while
the other lies at -151.2 [C(7)-C(8)-C(9)-S(3a)]. More
importantly, the mean plane through the atoms of the
central thiophene ring and the cyano-substituted aryl
ring has a dihedral angle of 26.5° as calculated. Thus, it
seems that the addition of the alkene spacer allows the
aryl and thiophene ring to assume a greater π orbital
overlap, which is in stark contrast to the geometry of 3′-
phenyl-2,2′:5′,2′′-terthiophene (34) described earlier.
4. Electr on ic Absor p tion Sp ectr a . A survey of the
literature indicates that terthiophenes that have aryl
substituents directly attached to the 3′ position have been
synthesized and their spectroscopic properties studied.
Kankare and co-workers56 have observed that these
compounds, such as 34 and 37, all have a major absorp-
tion band occurring around 350 nm that is characteristic
of terthiophene (32). However, the data obtained for the
functionalized terthiophenes prepared in this study, as
shown in Table 1 (see Supporting Information), is unusu-
ally complex. A DFT study has been undertaken to
explain the substituent effects observed, and the results
will be published elsewhere.
However, a significant deviation in the terthiophene
crystal geometry has been observed when simple sub-
stituents have been directly attached to the â-position
of the terthiophene backbone. Kankare and colleagues56
found it difficult to obtain accurate bond lengths, since a
substantial amount of conformational disorder was present
in the X-ray data of aryl-substituted terthiophenes. For
example, in the case of 3′-phenyl-2,2′:5′,2′′-terthiophene
(34), the thiophene rings were far from coplanar (-156°
and 138.4° with respect to the center thiophene ring) and
the aryl ring was also twisted at an angle of -116.7°;
this presumably occurs due to the close proximity of the
nearby thiophene ring. Disorder in the solid-state struc-
tures of 3′-methyl-2,2′:5′,2′′-terthiophene (35), 3,3′′-di-
methyl-2,2′:5′,2′′-terthiophene (36), and 5′-(2-thienyl)-2,2′:
3′,2′′-terthiophene (37) has also been reported recently
by Chaloner and co-workers.42 In their studies they found
that a range of conformational isomers was present in
the solid state and in no case were any of the thiophene
rings coplanar, where interplane angles between 29° to
88° were observed. Although there seems to be some
variation between early X-ray data and recent findings,
these results suggest that conformational disorder is
prevalent and the likelihood of disorder is increased by
the presence of sterically demanding substituents.
Crystallographic studies on trans-1-((2′,2′′:5′′,2′′′-ter-
thiophen)-3′′-yl)-2-(4′′′′-cyanophenyl)ethene (25) provided
similar findings to the conformational disorder of the
terthiophene systems found by Kankare and Chaloner.
The X-ray data of 25 indicates that the outer thiophene
rings exist as conformers with the general structure
having the antiparallel orientation shown in Figure 1.
The presence of these conformers suggests that in solu-
5. Electr och em istr y. Preliminary electrochemical
studies have been performed on this series of ter-
thiophenes using cyclic voltammetry. The data obtained
for the five styrylterthiophenes is presented in Table 2,
with the 3′-methyl-2,2′:5′,2′′-terthiophene (35) data in-
cluded for comparison.
The initial oxidation potential of the compounds is
found to vary depending on the nature of the substituent.
The strong electron-withdrawing substituent, NO2, is
observed to shift the potential of the oxidation to more
positive values, while the electron-donating substituent,
(55) Barbarella, G.; Zambianchi, M.; Bongini, A.; Antolini, L. Adv.
Mater. (Weinheim, Ger.) 1994, 6, 561.
(56) Kankare, J .; Lukkari, J .; Pasanen, P.; Sillanpa¨a¨, R.; Laine, H.;
Harmaa, K.; Visy, C. Macromolecules 1994, 27, 4327.
J . Org. Chem, Vol. 68, No. 23, 2003 8979

Collis et al.
utilizes Suzuki coupling methodology was developed that
provides multigram quantities of 10. Wittig chemistry
with 10 has been achieved to give several novel â-(styryl)-
substituted terthiophenes. X-ray crystal analysis of 25
confirms that placement of the alkene linkage between
the center thiophene and aryl ring reduces the steric
interaction, thereby allowing a greater degree of conjuga-
tion between the two moieties. This is reflected in the
electronic properties of the substituents attached to the
aryl ring, which are shown to influence the electronic
absorption properties and electrochemistry of the ter-
thiophene monomers. All terthiophene derivatives, 23,
25, 27, and 29, except 31, appear to form electroactive
polymers.
Current research has been directed at the development
of this building block approach for the attachment of a
variety of functionality to terthiophene. To date, func-
tionalized polymers have been studied in photovoltaic59,60
and biological sensor devices.61 Future work is also
directed at the synthesis of materials that may have
useful applications in LED, electrocatalytic, and metal
ion sensor devices. The results of these findings will be
published soon.
F IGURE 2. Cyclic voltammogram of (23), repeated cycles.
NMe2, shifts the potential to less positive values. This
effect has been noted before in similarly substituted
oligothiophene molecules.31,33,57,58 Somewhat surprisingly,
there was little difference in the oxidation potential of
25, 27, and 29. The first oxidation wave for all compounds
showed only a single oxidation peak with no peak
attributable to the oxidation of the double bond.31,33
Repeated cycles showed a growth in current that is
consistent with the formation of an electroactive polymer.
This differs from the electrochemical polymerization of
the analogous thiophene monomers, suggesting that the
alkene linker in these terthiophenes is not involved in
polymer formation.31,33 Typically, Figure 2 shows 23
under repeated cycling with formation of an apparent
electroactive polymer evident from the appearance and
growth of the shoulder at lower potential than the first
oxidation potential.57,58,59,60 The polymerization potential
quoted in Table 2 is an indication of the potential at
which the shoulder grows in at. In contrast, oxidation of
31 does not appear to form an electroactive polymer. The
availability of monomer 23 has, until now, allowed
homopolymers to be fabricated for testing in photovoltaic
devices.59 It has been of interest to determine to what
extent “high electron affinity” groups, such as nitro,
enhance the properties of the polymer that are necessary
in photocells.30
Exp er im en ta l Section
General experimental details are provided in the Supporting
Information.
Ku m a d a Cou p lin g Syn th esis. 2,5-Dibr om o-3-for m ylth -
iop h en e (15). A mixture of thiophene-3-carboxaldehyde (14)
(1.00 mL, 1.28 g, 11.4 mmol), 48% aqueous hydrobromic acid
(3.4 mL), and ether (3 mL) cooled at 0 °C was stirred vigorously
while a mixture of bromine (1.18 mL, 3.68 g, 23.0 mmol) and
48% aqueous hydrobromic acid (3.4 mL) was added dropwise.
The reaction mixture was then heated at 50 °C and monitored
by TLC. After 3 h the mixture was diluted with water (50 mL)
and extracted with ether (2 × 50 mL). The organic layers were
combined, washed with 10% sodium thiosulfate solution (2 ×
15 mL) and water (30 mL), and dried (MgSO4). The solvent
was removed under reduced pressure, diluted with dichlo-
romethane/hexane (1:2), and passed through a column of silica
to remove baseline material. The residue was vacuum distilled
(145 °C/10 mmHg) to give the product 15, which crystallized
upon cooling as a white solid (2.26 g, 73%). Recrystallization
from n-heptane afforded white fluffy needles that darken on
exposure to light and air: mp 46-7 °C (lit.32 mp 45-6 °C, lit.33
1
mp 48-9 °C); H NMR (270 MHz) δ 9.79 (s, 1H, CHO), 7.33
(s, 1H, H 4); 13C NMR (67.8 MHz) δ 183.0, 139.1, 128.5, 124.2,
113.3; MS m/z 272 (40), 271 (55), 270 (M, 78), 269 (100%), 268
(39), 267 (49), 81 (24), 80 (21); υmax/cm-1 3098, 2856, 1676,
1520, 1176, 1014, 832, 736; electronic spectrum λmax nm/(log
ꢀ) 252 (4.04), 299 (3.60).
2,5-D ib r o m o -3-(5,5-d im e t h y l-1,3-d io x a n -2-y l)t h io -
p h en e (17). A mixture of the aldehyde (15) (2.26 g, 8.37
mmol), p-toluenesulfonic acid (50 mg, 0.29 mmol), and 2,2-
dimethylpropane-1,3-diol (16) (0.95 g, 9.12 mmol) in dry
benzene (85 mL) was heated under reflux for 1 h using a
Dean-Stark apparatus. The reaction mixture was concen-
trated under vacuum, then diluted with dichloromethane (30
mL) and dried (MgSO4). To this solution was added an equal
volume of hexane and the mixture was then passed through a
pad of silica to remove the unreacted diol. The filtrate was
concentrated and vacuum distilled (120°/0.05 mmHg) to give
the acetal (17) as a white solid (2.92 g, 98%). Recrystallization
from 95% ethanol gave the analytical sample as fluffy white
needles: mp 86-7 °C; 1H NMR (270 MHz) δ 7.16 (s, 1H, H 4),
Con clu sion
A combination of Kumada coupling and protection/
deprotection chemistry has been employed in the syn-
thesis of 3′-formyl-2,2′:5′,2′′-terthiophene (10). Attempts
to use this route to synthesize this material on a large
scale proved complicated. An efficient synthesis that
(57) Audebert, P.; Catel, J .-M.; Le Coustumer, G.; Duchenet, V.;
Hapiot, P. J . Phys. Chem. B 1998, 102, 8661.
(58) Demanze, F.; Yasser, A.; Garnier, F. Macromolecules 1996, 29,
4267.
(59) Cutler, C. A.; Burrell, A. K.; Collis, G. E.; Dastoor, P. C.; Officer,
D. L.; Too, C. O.; Wallace, G. G. Synth. Met. 2001, 123, 225.
(60) Too, C. O.; Wallace, G. G.; Burrell, A. K.; Collis, G. E.; Officer,
D. L.; Boge, E. W.; Brodie, S. G.; Evans, E. J . Synth. Met. 2001, 123,
53.
(61) Chen, J .; Burrell, A. K.; Collis, G. E.; Officer, D. L.; Swiegers,
G. F.; Too, C. O.; Wallace, G. G. Electrochim. Acta 2002, 47, 2715.
8980 J . Org. Chem., Vol. 68, No. 23, 2003

Novel â-(Styryl)terthiophenes
5.41 (s, 1H, CH), AB quartet, A part of AB, 3.73 (2H, J AB
)
diluted with dichloromethane (30 mL) and the aqueous layer
separated. The organic layer was washed with 10% sodium
bicarbonate solution (4 × 30 mL), then water (20 mL) and
dried (MgSO4). The solvent was removed under reduced
pressure to afford a brown oil which slowly crystallized on
standing. This material was subjected to radial chromatogra-
phy (CH2Cl2/ hexane) to give the title compound (10) as a
bright yellow solid (83 mg, 95%): mp 68 °C; 1H NMR (400
MHz) δ 10.08 (s, 1H, CHO), 7.57 (s, 1H, H 4′), 7.51 (dd, 1H, J
) 5.1, 1.2 Hz, H 5), 7.32 (dd, 1H, J ) 3.6, 1.2 Hz, H 3), 7.30
(dd, 1H, J ) 5.1, 1.2 Hz, H 5′′), 7.23 (dd, 1H, J ) 3.6, 1.2 Hz,
H 3′′), 7.17 (dd, 1H, J ) 5.1, 3.6 Hz, H 4), 7.06 (dd, 1H, J )
5.1, 3.6 Hz, H 4′′); 13C NMR (67.8 MHz) δ 184.9, 145.8, 137.5,
136.7, 135.4, 132.0, 129.1, 128.6, 128.2, 127.9, 125.7, 124.9,
122.3; MS m/z 278 (15), 277 (17), 276 (M+, 100%), 249 (9), 248
(55), 247 (8), 231 (10), 203 (20); υmax/cm-1 3076, 1676, 1386,
1230, 1162, 824, 720, 693; electronic spectrum λmax nm/(log ꢀ)
263 (4.20), 322 (4.01), 358 (3.91). Anal. Calcd for C13H8OS3:
C, 56.49; H, 2.92. Found: C, 56.73; H, 2.75.
Su zu k i Cou p lin g Syn th esis. 2-Th ien ylbor on ic Acid
(19). A solution of thiophene (11) (9.51 mL, 10.0 g, 0.119 mol)
in dry THF (120 mL) cooled at -78 °C was treated dropwise
with n-BuLi (95 mL, 1.24 mol L-1, 0.118 mol). The mixture
was stirred at -78 °C for 30 min and then allowed to warm to
-20 °C slowly. This mixture was then cooled to -78 °C before
the 2-thienyllithium was added to a solution of trisisopropyl
borate (38.0 mL, 31.0 g, 0.165 mol) in dry THF (80 mL) also
at -78 °C. The reaction mixture was stirred at -78 °C for 1 h
before warming the solution to room temperature. The mixture
was then treated with 1 M HCl (200 mL) and the organic layer
separated. The aqueous layer was then extracted with dichlo-
romethane (5 × 120 mL), and the organic layers were
combined and dried (MgSO4). The solvent was then removed
under reduced pressure to afford a crude white solid, which
was recrystallized from water to give the boronic acid (19) as
a pure white solid (11.9 g, 78%): mp 125-127 °C (lit.44 mp
128-130 °C).
11.2 Hz, CHAHB) and B part of AB, 3.63 (2H, J AB ) 11.2 Hz,
CHAHB), 1.30 (s, 3H, CH3), 0.80 (s, 3H, CH3); 13C NMR (67.8
MHz) δ 139.3, 129.2, 111.4, 110.4, 97.2, 77.6, 30.2, 23.1, 21.9;
MS m/z 356 (M, 37), 272 (53), 271 (36), 270 (100%), 269 (43),
268 (50), 191 (23), 69 (73); υmax/cm-1 2943, 2854, 1559, 1462,
1437, 1392, 1376, 1360, 1177, 1105, 1010, 991, 977, 958, 926,
830; electronic spectrum λmax nm/(log ꢀ) 252 (3.92). Anal. Calcd
for C10H12Br2O2S: C, 33.73; H, 3.40; Br, 44.88. Found: C,
33.85; H, 3.29; Br, 44.83.
3 ′-(5 ,5 -D i m e t h y l -1 ,3 -d i o x a n -2 -y l )-2 :2 ′,5 ′:2 ′′-t e r -
th iop h en e (18). (a ) Sm a ll Sca le. A stirred mixture of the
dibromoacetal (17) (1.00 g, 2.81 mmol) and NiCl2(dppp)62 (50
mg, 0.09 mmol, 3 mmol %) in dry ether (15 mL) was treated
dropwise at room temperature with 2-bromomagnesiothiophene
(13) [generated by reacting 2-bromothiophene (1.09 g, 6.69
mmol) with magnesium (179 mg, 7.36 mmol) in dry ether (9
mL) at ambient temperature over a period of a 30 min]. Once
the addition was completed, the mixture was heated under
reflux for 4 h. The reaction mixture was cooled and diluted
with ether (50 mL) and then quenched with 1 M HCl solution
(50 mL). The organic layer was separated and the aqueous
layer extracted with ether (3 × 60 mL). The ethereal extracts
were combined and washed with water (30 mL), dried (MgSO4),
and concentrated in vacuo to give a dark yellow solid. Purifica-
tion was achieved by radial chromatography to give the
materials in order of elution: bithiophene (73 mg), dibromoac-
etal (17) (139 mg), and the terthiophene product (18) (624 mg,
71% based on recovered starting material). Recrystallization
from ether/hexane afforded an analytical sample as yellow
1
flakes: mp 133 °C; H NMR (400 MHz) δ 7.42 (s, 1H, H 4′),
7.37 (dd, 1H, J ) 5.1, 1.2 Hz, H 5), 7.23 (dd, 1H, J ) 5.1, 1.2
Hz, H 5′′), 7.21 (dd, 1H, J ) 3.6, 1.2 Hz, H 3), 7.19 (dd, 1H, J
) 3.6, 1.2 Hz, H 3′′), 7.10 (dd, 1H, J ) 5.1, 3.6 Hz, H 4), 7.02
(dd, 1H, J ) 5.1, 3.6 Hz, H 4′′), 5.53 (s, 1H, CH), AB quartet,
A part of AB, 3.79 (2H, J AB ) 11.2 Hz, CHAHB) and B part of
AB, 3.67 (2H, J AB ) 11.2 Hz, CHAHB), 1.37 (s, 3H, CH3), 0.82
(s, 3H, CH3); 13C NMR (67.8 MHz) δ 136.8, 2 × 136.1, 134.2,
133.0, 2 × 127.6, 126.9, 126.5, 124.6, 123.9, 123.4, 97.5, 77.5,
30.3, 23.2, 21.9; MS m/z 364 (16), 363 (23), 362 (M+, 100%),
292 (40), 277 (13), 276 (53), 275 (18), 248 (53); υmax/cm-1 3100,
3072, 2952, 2852, 1466, 1459, 1420, 1394, 1362, 1117, 1104,
1013, 981, 837, 820, 709; electronic spectrum λmax nm/(log ꢀ)
251 (4.04), 343 (4.28). Anal. Calcd for C18H18O2S3: C, 59.63;
H, 5.00. Found: C, 59.41; H, 5.10.
5-Br om o-3-for m yl-2,2′-bith iop h en e (20). To a stirred
solution of the dibromide (15) (1.00 g, 3.68 mmol) and Pd-
(PPh3)4 (255 mg, 0.220 mmol) in 1,2-dimethoxyethane (30 mL)
was added 2-thiophene boronic acid (1.13 g, 8.83 mmol, 2.4
equiv) and a solution of 1 M Na2CO3 (22 mL). The mixture
was then heated under reflux for 8 h, cooled, and concentrated
under vacuum to remove nearly all of the DME. The crude
material was then diluted with DCM (100 mL) and washed
with water (2 × 50 mL), and the organic layer was dried
(MgSO4). The brown liquid was dissolved in DCM:petroleum
ether (1:1) and passed through a pad of silica to remove
unwanted baseline materials. This material was then sub-
jected to radial chromatography first with constant elution
with 50% toluene/hexane to give the monocoupled product
(b) La r ge Sca le. A stirred mixture of the dibromoacetal
(17) (5.00 g, 14.0 mmol) and NiCl2(dppp)58 (250 mg, 0.46 mmol,
3 mmol %) in dry ether (75 mL) was treated dropwise at room
temperature with 2-bromomagnesiothiophene (16) [generated
by reacting 2-bromothiophene (5.45 g, 33.4 mmol) with mag-
nesium (0.90 g, 37.0 mmol) in dry ether (60 mL) at ambient
temperature over a period of 1 h]. Once the addition was
completed, the mixture was heated under reflux for 16 h. After
this period, the reaction mixture was cooled and diluted with
ether (150 mL) and then quenched with 1 M HCl solution (150
mL). The organic layer was removed and the aqueous layer
was extracted with ether (3 × 80 mL). The ethereal extracts
were combined and washed with water (2 × 50 mL), dried
(MgSO4), and concentrated in vacuo to give a dark yellow solid.
This crude material was adsorbed onto chromatographic grade
silica and then extracted with hexane using a Soxhlet ap-
paratus for 12 h. Upon cooling the filtrate a yellow precipitate
was collected and this material was recrystallized from ether/
hexane to afford the terthiophene acetal (18) (2.58 g, 51%):
mp 133 °C.
5-bromo-3-formyl-2,2′-bithiophene (20) as
a faint yellow
solid: mp 76 °C (268 mg, 0.98 mmol, 27%); 1H NMR (400 MHz)
δ. 9.97 (d, 1H, J ) 0.3 Hz, CHO), 7.51 (dd, 1H, J ) 5.1, 1.2
Hz, H 5′), 7.49 (d, 1H, J ) 0.3 Hz, H 4), 7.27 (dd, 1H, J ) 3.6,
1.2 Hz, H 3′), 7.16 (dd, 1H, J ) 5.1, 3.6 Hz, H 4′); 13C NMR
(67.8 MHz) δ 183.9, 148.6, 137.6, 131.0, 129.6, 129.3, 129.2,
128.3, 112.8. Anal. Calcd for C9H5BrOS2: C, 39.57; H, 1.84;
Br, 29.25; S, 23.48. Found: C, 39.81; H, 1.73; Br, 29.48; S,
23.55; electronic spectrum (CHCl3) λmax nm/(log ꢀ) 253 (4.25),
336 (3.86). Elution with EtOAc/hexane (10% and then 20%)
gave the terthiophene aldehyde (10) (514 mg, 1.86 mmol, 51%)
(see earlier experimental for full characterization).
3′-F or m yl-2:2′,5′:2′′-ter th iop h en e (10). To a stirred mix-
ture of 2,5-dibromo-3-formylthiophene (15) (10.0 g, 37.0 mmol)
and tetrakis(triphenylphosphine)palladium [Pd(PPh3)4]63 (2.55
g, 2.21 mmol, 6 mmol %) in 1,2-dimethoxyethane (300 mL)
were added 2-thiophene boronic acid (10.83 g, 84.6 mmol) and
a solution of 1 M Na2CO3 (220 mL). The reaction mixture was
heated under reflux for 5 h. After this period another portion
of 2-thiophene boronic acid (2.18 g, 17.0 mmol) was added and
3′-F or m yl-2:2′,5′:2′′-ter th iop h en e (10). A mixture of the
terthiophene acetal (18) (115 mg, 0.32 mmol), chloroform (4
mL), trifluoroacetic acid (4 mL), and water (1.3 mL) were
stirred vigorously at room temperature and monitored by TLC.
After 1.5 h the reaction was complete and the mixture was
(62) Van Hecke, G. R.; D., H. J . W. Inorg. Chem. 1966, 5, 1968.
(63) Coulson, D. R. Inorg. Synth. 1972, 13, 121.
J . Org. Chem, Vol. 68, No. 23, 2003 8981

Collis et al.
heating continued for 8 h. The reaction mixture was concen-
trated and then diluted with dichloromethane (300 mL) and
separated. The organic residue was washed with water (2 ×
50 mL), dried (MgSO4), and concentrated in vacuo to give a
brown liquid. This crude material was dissolved in CH2Cl2/
hexane (1:1) and passed through a pad of silica to remove
baseline material and the palladium catalyst. Further puri-
fication was achieved with column chromatography (CH2Cl2/
hexane), followed by recrystallization from ether to give the
title compound (10) as a bright yellow solid (7.76 g, 76%): mp
68°. The spectral data of this material is consistent with
compound derived from the Kumada coupling synthesis.
Wittig Rea ction s. tr a n s-1-((2′,2′′:5′′,2′′′-Ter th iop h en )-3′′-
yl)-2-(4′′′′-n itr op h en yl)eth en e (23). A mixture of the ter-
thiophene aldehyde (10) (160 mg, 0.58 mmol), (4-nitrobenzyl)-
triphenylphosphonium bromide (21)64 (322 mg, 0.67 mmol, 1.2
equiv), and DBU (0.10 mL, 0.67 mmol, 102 mg) in dichlo-
romethane (8 mL) was heated under reflux. After 8 h the
reaction mixture was diluted with dichloromethane (60 mL)
and washed with a 1 M solution of HCl (2 × 20 mL), 10%
sodium bicarbonate solution (20 mL), and water (30 mL). The
organic layer was dried and concentrated to give a crude
Hz, H 4′), 7.06 (dd, 1H, J ) 5.1, 3.6 Hz, H 4′′′), 7.01 (d, 1H, J
) 16.2 Hz, H 2); 13C NMR (67.8 MHz) δ 141.8, 136.4, 136.3,
135.4, 134.5, 133.4, 2 × 132.4, 128.1, 2 × 127.9, 127.3, 126.8,
126.7, 2 × 125.0, 124.3, 121.7, 119.0; MS m/z 377 (16), 376
(27), 375 (M+, 100%), 374 (14), 342 (7), 341 (7), 273 (15), 127
(10); υmax/cm-1 2221, 1599, 1409, 1172, 966, 949, 818, 698;
electronic spectrum λmax nm/ (log ꢀ) 324 (4.65), 355 (4.45). Anal.
Calcd for C21H13NS3: C, 67.16; H, 3.49; N, 3.73. Found: C,
66.84; H, 3.30; N, 3.83.
tr a n s-1-((2′,2′′:5′′,2′′′-Ter t h iop h en )-3′′-yl)-2-(p h en yl)-
eth en e (27). A mixture of the terthiophene aldehyde (10) (150
mg, 0.54 mmol), benzyltriphenylphosphonium bromide (26)66
(282 mg, 0.65 mmol, 1.2 equiv), and DBU (0.10 mL, 0.65 mmol,
99 mg) in dry dichloromethane (15 mL) was heated under
reflux. After 6 h the reaction mixture was diluted with
dichloromethane (60 mL) and washed with a 1 M solution of
HCl acid (2 × 30 mL), 10% sodium bicarbonate solution (30
mL), and water (40 mL). The organic layer was dried and
concentrated to give a crude yellow solid. Analysis of this crude
material by 1H NMR spectroscopy indicated it consisted of the
desired trans product. The material was then subjected to
radial chromatography (dichloromethane/hexane) to afford a
yellow oil which crystallized on standing. Recrystallization
from ether/pentane gave the product (27) as fluffy yellow
orange solid. This was dissolved in
a small quantity of
dichloromethane/hexane (1:1) and passed through a column
of silica with continued elution with the same solvent system
until the yellow/orange material had been collected. Analysis
of the material by 1H NMR spectroscopy indicated it consisted
of a mixture of the cis and trans isomers in a ratio of 1.5:1.
This material was dissolved in dry chloroform (30 mL) and
irradiated for 3 h using a 250-W flood lamp. After removal of
1
crystals (168 mg, 88%): mp 93-4 °C; H NMR (400 MHz) δ
7.53-7.48 (m, 2H, aryl H), 7.45 (s, 1H, H 4′′), 7.40 (dd, 1H, J
) 5.2, 1.2 Hz, H 5′), 7.38 (d, 1H, J ) 16.1 Hz, H 1), 7.40-7.34
(m, 2H, aryl H), 7.28 (dd, 1H, J ) 5.1, 1.1 Hz, H 5′′′), 7.30-
7.24 (m, 1H, aryl H), 7.24 (dd, 1H, J ) 3.6, 1.1 Hz, H 3′′′),
7.22 (dd, 1H, J ) 3.6, 1.2 Hz, H 3′), 7.14 (dd, 1H, J ) 5.2, 3.6
Hz, H 4′), 7.06 (dd, 1H, J ) 5.1, 3.6 Hz, H 4′′′), 7.06 (d, 1H, J
) 16.1 Hz, H 2); 13C NMR (67.8 MHz) δ 137.4, 136.8, 136.4,
136.0, 135.2, 131.6, 130.4, 128.7, 127.9, 127.8, 127.7, 127.0,
126.5, 126.4, 124.9, 124.2, 122.3, 121.7; MS m/z 352 (16), 351
(26), 350 (M+, 100%), 349 (14), 317 (12), 316 (14), 273 (15),
127 (8); υmax/cm-1 3056, 1595, 1506, 1188, 952, 842, 813, 752,
691; electronic spectrum λmax nm/(log ꢀ) 312 (4.57), 359 (4.34).
Anal. Calcd for C20H14S3: C, 68.53; H, 4.03. Found: C, 68.40;
H, 3.81.
1
the solvent, analysis of the sample by H NMR spectroscopy
indicated it consisted of essentially the trans product. The
material was recrystallized from dichloromethane/ether to give
23 as orange crystals (188 mg, 82%): mp 179 °C; 1H NMR
(400 MHz) δ 8.22-8.16 (2H, AA′ part of AA′XX′), 7.60-7.55
(2H, XX′ part of AA′XX′), 7.49 (d, 1H, J ) 16.2 Hz, H 1), 7.44
(dd, 1H, J ) 5.1, 1.2 Hz, H 5′), 7.41 (s, 1H, H 4′′), 7.28 (dd,
1H, J ) 5.1, 1.1 Hz, H 5′′′), 7.22 (dd, 1H, J ) 3.6, 1.1 Hz, H
3′′′), 7.20 (dd, 1H, J ) 3.6, 1.2 Hz, H 3′), 7.15 (dd, 1H, J ) 5.1,
3.6 Hz, H 4′), 7.05 (dd, 1H, J ) 5.1, 3.6 Hz, H 4′′′), 7.05 (d, 1H,
J ) 16.2 Hz, H 2); 13C NMR (67.8 MHz) δ 146.7, 143.8, 136.5,
136.3, 135.4, 134.5, 133.9, 127.9, 127.7, 127.4, 126.9, 126.7,
125.9, 125.1, 124.4, 124.1, 121.7; MS m/z 397 (17), 396 (26),
395 (M+, 100%), 394 (9), 365 (11), 316 (16), 273 (12), 127 (12);
tr a n s-1-((2′,2′′:5′′,2′′′-Ter t h iop h en )-3′′-yl)-2-(4′′′′-m et h -
oxyp h en yl)eth en e (29). A mixture of (4-methoxybenzyl)-
triphenylphosphonium chloride (28)67 (484 mg, 1.16 mmol, 2
equiv) and KOBut (130 mg, 1.16 mmol) in dry THF (10 mL)
was heated under reflux for 15 min. To this was added a
solution of the terthiophene aldehyde (10) (160 mg, 0.58 mmol)
in dry THF (10 mL). After 8 h the reaction was stopped, diluted
with dichloromethane (60 mL), and washed with a 1 M solution
of HCl (2 × 30 mL), 10% sodium bicarbonate solution (30 mL).
and water (20 mL). The organic layer was dried (MgSO4) and
concentrated to give a crude yellow solid. This solid was
dissolved in a small quantity of dichloromethane/hexane (1:1)
and passed through a column of silica with continued elution
with the same solvent system until the yellow material had
been collected. This material was subjected to radial chroma-
tography to give a yellow solid which was recrystallized from
ether/pentane to afford the product (29) as yellow crystals (175
mg, 80%): mp 94 °C; 1H NMR (400 MHz) δ 7.46-7.44 (2H,
AA′ part of AA′XX′), 7.43 (s, 1H, H 4′′), 7.40 (dd, 1H, J ) 5.1,
1.2 Hz, H 5′), 7.27 (dd, 1H, J ) 5.1, 1.2 Hz, H 5′′′), 7.25 (d, 1H,
J ) 16.2 Hz, H 1), 7.23 (dd, 1H, J ) 3.6, 1.2 Hz, H 3′′′), 7.21
(dd, 1H, J ) 3.6, 1.2 Hz, H 3′), 7.14 (dd, 1H, J ) 5.1, 3.6 Hz,
H 4′), 7.06 (dd, 1H, J ) 5.1, 3.6 Hz, H 4′′′), 7.01 (d, 1H, J )
16.2 Hz, H 2), 6.94-6.88 (2H, XX′ part of AA′XX′), 3.85 (s, 3H,
OMe); 13C NMR (67.8 MHz) δ 159.4, 136.9, 136.7, 135.9, 135.4,
130.8, 130.1, 130.0, 127.9, 2 × 127.8, 126.8, 126.2, 124.8, 124.1,
122.2, 119.7, 114.2, 55.3; MS m/z 382 (16), 381 (26), 380 (M+,
100%), 379 (8), 303 (7), 273 (6), 272 (5), 127 (8); υmax/cm-1 3104,
1602, 1510, 1247, 1172, 1035, 956, 846, 826, 816, 804, 699;
υ
max/cm-1 1586, 1508, 1336, 1107, 970, 955, 703, 690; electronic
spectrum λmax nm/(log ꢀ) 345 (4.57), 411 (4.25). Anal. Calcd
for C20H13NO2S3: C, 60.73; H, 3.31; N, 3.54. Found: C, 60.76;
H, 3.08; N, 3.58.
tr a n s-1-((2′,2′′:5′′,2′′′-Ter th iop h en )-3′′-yl)-2-(4′′′′-cya n o-
p h en yl)eth en e (25). A mixture of the terthiophene aldehyde
(10) (200 mg, 0.72 mmol), (4-cyanobenzyl)triphenylphospho-
nium bromide (24)65 (398 mg, 0.87 mmol, 1.2 equiv), and DBU
(0.13 mL, 0.87 mmol, 132 mg) in dry dichloromethane (20 mL)
was heated under reflux. After 3 h the reaction mixture was
diluted with dichloromethane (80 mL) and washed with a 1
M solution of HCl (2 × 30 mL), 10% sodium bicarbonate
solution (30 mL), and water (40 mL). The organic layer was
dried and concentrated to give a crude yellow solid. Analysis
of this crude material by 1H NMR spectroscopy indicated it
contained the triphenylphosphine oxide byproduct and only
the trans product. The material was then subjected to radial
chromatography (dichloromethane/hexane) to afford a yellow
solid which was recrystallized from ether/pentane to give
yellow crystals of 25 (249 mg, 92%): mp 154 °C; 1H NMR (400
MHz) δ 7.64-7.61 (2H, AA′ part of AA′XX′), 7.56-7.53 (2H,
XX′ part of AA′XX′), 7.46 (d, 1H, J ) 16.2 Hz, H 1), 7.44 (dd,
1H, J ) 5.1, 1.2 Hz, H 5′), 7.42 (s, 1H, H 4′′), 7.29 (dd, 1H, J
) 5.1, 1.1 Hz, H 5′′′), 7.23 (dd, 1H, J ) 3.6, 1.1 Hz, H 3′′′),
7.20 (dd, 1H, J ) 3.6, 1.2 Hz, H 3′), 7.16 (dd, 1H, J ) 5.1, 3.6
(66) Tinnemans, A. H. A.; Laarhoven, W. H. J . Chem. Soc., Perkin
Trans. 2 1976, 1104.
(67) Ketcham, R.; J ambotkar, D.; Martinelli, L. J . Org. Chem. 1962,
27, 4666.
(64) McDonald, R.; Campbell, T. W. J . Org. Chem. 1959, 24, 1969.
(65) Brettle, R.; Dunmur, D. A.; Hindley, N. J .; Marson, C. M. J .
Chem. Soc., Perkin Trans. 1 1993, 775.
8982 J . Org. Chem., Vol. 68, No. 23, 2003

Novel â-(Styryl)terthiophenes
electronic spectrum λmax nm/(log ꢀ) 323 (4.74), 3.62 (4.48). Anal.
Calcd for C21H16OS3 requires C, 66.28; H, 4.24. Found: C,
66.47; H, 4.16.
Hz, H 3′′′), 7.21 (dd, 1H, J ) 3.6, 1.2 Hz, H 3′), 7.20 (d, 1H, J
) 16.1 Hz, H 1), 7.12 (dd, 1H, J ) 5.2, 3.6 Hz, H 4′), 7.05 (dd,
1H, J ) 5.1, 3.6 Hz, H 4′′′), 7.00 (d, 1H, J ) 16.1 Hz, H 2),
6.76-6.70, 2H (XX′ part of AA′XX′), 3.00, s, 6H, NMe2. 13C
NMR (67.8 MHz) δ 150.2, 137.2, 137.1, 2 × 135.7, 130.7, 129.8,
127.9, 2 × 127.7, 127.6, 126.0, 125.7, 124.7, 124.0, 122.4, 117.6,
112.5, 40.4; MS m/z 395 (13), 394 (28), 393 (M+, 100%), 392
(9), 316 (5), 197 (9), 196 (4), 40 (4); υmax/cm-1 3064, 1601, 1522,
1366, 1185, 1170, 957, 829, 802, 703; electronic spectrum λmax
nm/(log ꢀ) 348 (4.58). Anal. Calcd for C22H19NS3: C, 67.13; H,
4.87; N, 3.56. Found: C, 67.13; H, 4.85; N, 3.58.
tr a n s-1-((2′,2′′:5′′,2′′′-Ter th iop h en )-3′′-yl)-2-(4′′′′-N,N-d i-
m eth ylp h en yl)eth en e (31). A mixture of (4-N,N-dimethyl-
benzyl)triphenylphosphonium iodide (30)68 (597 mg, 1.14
mmol, 2.1 equiv) and KOBut (128 mg, 1.14 mmol) in dry THF
(10 mL) was heated under reflux for 15 min and then cooled.
To this was added a solution of the terthiophene aldehyde (10)
(150 mg, 0.54 mmol) in dry THF (10 mL) and heated under
reflux. After 6 h the reaction was stopped, diluted with
dichloromethane (60 mL), and washed with a 1 M solution of
HCl (2 × 30 mL), 10% sodium bicarbonate solution (30 mL),
and water (20 mL). The organic layer was dried (MgSO4) and
concentrated to give a crude yellow solid. This solid was
dissolved in a small quantity of dichloromethane/hexane (1:1)
and passed through a column of silica with continued elution
with the same solvent system until the yellow material had
been collected. This material was subjected to radial chroma-
tography to give a yellow oil which crystallized from ether to
afford the product (31) as yellow crystals (173 mg, 81%): mp
154-5 °C; 1H NMR (400 MHz) δ 7.43 (s, 1H, H 4′′), 7.44-7.39
(2H, AA′ part of AA′XX′), 7.37 (dd, 1H, J ) 5.2, 1.2 Hz, H 5′),
7.26 (dd, 1H, J ) 5.1, 1.2 Hz, H 5′′′), 7.23 (dd, 1H, J ) 3.6, 1.2
Ack n ow led gm en t. This work has been made pos-
sible by the financial support to Dr. G. Collis through
Massey University Research Fund and New Economical
Research Fund Fellowships. We would like to also thank
Dr. Edwards for his NMR assistance and Dr. Hall for
use of his electrochemical instruments.
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal details,1H, 13C, and 2D LRCOSY NMR spectra, X-ray
crystallographic data for 25, cyclic voltammograms and elec-
tronic absorption spectra for compounds 23, 25, 27, 29, and
31 are provided. This material is available free of charge via
the Internet at http://pubs.acs.org.
(68) Bredereck, H.; Simchen, G.; Griebenow, W. Chem. Ber. 1973,
106, 3732.
J O034855G
J . Org. Chem, Vol. 68, No. 23, 2003 8983