A modular procedure for the synthesis of functionalised β-substituted terthiophene monomers for conducting polymer applications

Article abstract of DOI:10.1016/j.tet.2007.08.022

An efficient modular strategy has been developed for the synthesis of β-functionalised terthiophene monomers using Suzuki-Miyaura and Wittig/Horner-Emmons chemistries. This paper discusses the problems encountered with converting the β-terthiophene aldehyde building block to the β-terthiophene phosphonium salt and the use of this material in a Wittig condensation. An improved strategy using the β-terthiophene phosphonate building block constructed via Suzuki-Miyaura coupling protocols was developed. We have synthesised and characterised a broad range of functionalised terthiophene materials that have been designed for specific end-use applications. The availability of these building blocks has dramatically increased access to a range of key monomers.

Full text of DOI:10.1016/j.tet.2007.08.022

Tetrahedron 63 (2007) 11141–11152
A modular procedure for the synthesis of functionalised
b-substituted terthiophene monomers for
conducting polymer applications
a,b,*
a
Anthony K. Burrell, Esther J. Blandford and David L. Officer
b
b
Gavin E. Collis,
a
Materials Chemistry, MPA-MC, Mail Stop J514, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
b
Nanomaterials Research Centre and MacDiarmid Institute for Advanced Materials and Nanotechnology, Massey University,
Private Bag 11222, Palmerston North, New Zealand
Received 27 March 2007; revised 14 July 2007; accepted 8 August 2007
Available online 14 August 2007
Abstract—An efficient modular strategy has been developed for the synthesis of b-functionalised terthiophene monomers using Suzuki–
Miyaura and Wittig/Horner–Emmons chemistries. This paper discusses the problems encountered with converting the b-terthiophene alde-
hyde building block to the b-terthiophene phosphonium salt and the use of this material in a Wittig condensation. An improved strategy using
the b-terthiophene phosphonate building block constructed via Suzuki–Miyaura coupling protocols was developed. We have synthesised and
characterised a broad range of functionalised terthiophene materials that have been designed for specific end-use applications. The availability
of these building blocks has dramatically increased access to a range of key monomers.
Ó 2007 Elsevier Ltd. All rights reserved.
CHO
1. Introduction
P
S
S
S
S
S
R
As a part of our continued efforts to use functionalised con-
ducting polythiophenes for targeted applications we focused
on developing a method that would allow rapid construction
of highly functionalised monomers. Using a building
R
S
1
Base
S
FGI
1
0
S
block approach, we reported that both 3 -formylterthio-
0
O
phene 1 and terthiophene-3 -methylenephosphorus deriva-
P
R
H
3
tive 2 served as ideal platforms from which different
monomers, such as 3, could be accessed using Wittig or
Horner–Emmons chemistries (Scheme 1). This methodology
eliminated the need to design new syntheses for each
different target monomer. Recent work has been directed at
obtaining practical quantities of phosphonium salt of type
S
Base
2
P = Phosphorus group
Scheme 1.
2
; unfortunately, this proved to be problematic for several
reasons. These difficulties were overcome by the design
and synthesis of the phosphonate derivative of 2. The current
paper describes synthetic routes to these phosphorus deriva-
tives and the implementation of this building block approach
in the synthesis of a variety of desirable functionalised
monomers.
2
. Results
2.1. Synthesis of terthiophene-methylene phosphonium
salt building block
0
2
Since 3 -formylterthiophene could be easily prepared on
a 50–100 g scale, it was envisaged that functional group in-
terconversion (FGI) of the aldehyde group would provide an
easy route to the terthiophene phosphonium salt building
*
0
Corresponding author at present address: CSIRO Molecular and Health
Technologies, Ian Wark Laboratory, Bayview Avenue, Clayton,
Melbourne, Victoria 3169, Australia. Tel.: +61 3 9545 2458; fax: +61 3
1
block. As reported previously, reduction of aldehyde 1
with sodium borohydride proceeded smoothly to give the al-
cohol 4 (Scheme 2). Analysis of the alcohol by H NMR
1
9545 2446; e-mail: gavin.collis@csiro.au
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.08.022

11142
G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
spectroscopy indicated the aromatic protons of the thiophene
rings and two new up-field signals. These signals at 4.76 and
CH OH
CH2OMs
S
2
S
S
i
S
1
.80 ppm were attributed to the methylene protons and the
S
S
hydroxyl group, respectively. Following known procedures
to form aryl phosphonium salts directly from aryl methylene
alcohols, a solution of 4 in benzene was heated in the pres-
4
7
3
,4
ence of triphenylphosphine hydrogen bromide (PPh .HBr)
3
ii
to give the desired bromide salt 5, albeit in surprisingly
poor yield (34%) (Method A). Attempts to improve the yield
by employing a mild two-step procedure proved tedious and
provide only marginally better yields. Treatment of the alco-
hol 4 at low temperature with thionyl chloride presumably
X
S
S
S
CH PPh OMs
2 3
S
S
O
0
S
affords 3 -(chloromethyl)terthiophene. Attempts to isolate
S
S
and purify this chloride before proceeding to the following
step were unsuccessful; the chloride was unstable and de-
composed on handling. Instead, the crude chloride was
heated in the presence of triphenylphosphine in benzene
and after cooling and crystallisation afforded the chloride
phosphonium salt 6 in 52% yield (Method B).
S
8
9
ꢀ
Scheme 3. Reagents and conditions: (i) MsCl, 0 C, THF, pyridine; (ii)
PPh , reflux.
3
2
.3.). Reaction of either 5 or 6 with the commercially avail-
able 4-pyridylaldehyde 10 under Wittig conditions produced
geometric isomers and the by-product triphenylphosphine
oxide 12 (Scheme 4). This crude material was then subjected
to iodine in dichloromethane to enable isomerisation of the
cis-isomer to the all trans-product. However, given the simi-
lar physical properties of trans-11 and triphenylphosphine
oxide, attempts to isolate 11 using chromatographic or
even recrystallisation techniques were unfruitful. The syn-
thetic difficulties in obtaining the phosphonium salts and
the purification problems of the subsequent Wittig reaction
led us to devise an alternative building block (Scheme 4).
CHO
CH OH
2
S
S
i
S
S
S
S
1
4
CH PPh X
2
3
ii or iii
S
S
5
X = Br
X = Cl
S
6
Scheme 2. Reagents and conditions: (i) NaBH
4
, THF, EtOH, 84%; (ii)
$HBr, benzene, reflux, 34% or (iii) Method B: (a) SOCl
, reflux, 52%.
Method A: PPh
ꢀ
3
2
,
N
pyridine, 0 C; (b) PPh
3
N
Because of the unexpected difficulty in synthesising phos-
phonium salts 5 and 6, we believed a closer examination
of these reactions was warranted. Since 3 -(chloromethyl)-
CHO
S
S
0
i, ii
S
10
terthiophene could not be isolated, we sought to form a leav-
ing group that could be detected by NMR spectroscopy and
aid in determining the effectiveness of this step. Attempts to
+
11
+
CH PPh X
5
2
3
convert 4 under standard conditions (Scheme 3) to the
mesylate confirmed our concerns. Analysis of the crude
product by H NMR indicated a relatively simple spectrum,
O
P
Ph
S
S
1
S
Ph
Ph
however, the key methyl signal expected from the mesylate
group of 7 could not be detected. Apart from some minor
shifts in the aromatic region the only noticeable change
was an up-field shift of the methylene signal from
5
X = Br or 6 X = Cl
12
Scheme 4. Reagents and conditions: (i) DBU, THF; (ii) I
2 2 2
, CH Cl .
4.76 ppm of 4 to 4.64 ppm in the product. Attempts to purify
and isolate this product for further characterisation were un-
2.2. Synthesis of terthiophene-methylene phosphonate
ester building block
successful as the oily substance readily decomposed when
subjected to column chromatography. Based on the
1
H
The reaction of carbonyl compounds under Horner–Emmons
conditions to construct olefins was investigated as an alterna-
tive to the triarylphosphorane chemistry (Scheme 5). It was
envisaged that the terthiophene phosphonate 16 could be
accessed using Suzuki–Miyaura chemistry as shown in
Scheme 5. The known phosphonate 13 was synthesised from
NMR data of the crude compound, we concluded that the
bis-terthiophene ether 9 was formed. Formation of only 9
under these mild conditions may explain the low yields
from the earlier phosphonium salt syntheses described in
Scheme 2.
6
,7
3
-methylthiophene following the literature procedures.
With access to phosphonium salts 5 and 6, we decided to eval-
uate the reactivity of these salts in typical Wittig reactions.
The need to develop and study functionalised monomers
that have the capacity to co-ordinate transition metal ions di-
rected our attention to pyridyl complexes (see later, Section
Bromination of 13 was easily achieved using biphasic
bromine in aqueous hydrobromic acid and diethyl ether.
The dibromophosphonate 14 was purified by distillation to
give a dense golden liquid, obtained in an improved yield
8
over the reported method.

G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
11143
O
O
formation of substantial quantities of the mono-coupled
product. The reluctance of 14 to be completely consumed
was solved by changing the halide substituents on the phos-
phonate precursor. The thiophene phosphonate 13 was in-
stead reacted with pyridine–iodine monochloride and
P(OEt)2
P(OEt)2
i or ii
X
X
S
S
13
14 X = Br
7 X = I
10
mercuric(II) nitrate to afford the diiodo-derivative 17 in
1
excellent yield. Using the typical large-scale Suzuki condi-
tions described previously, terthiophene phosphonate 16
was easily obtained in excellent yield (76%) (Method D).
Having developed large-scale syntheses to both the building
blocks, we now directed our efforts to synthesising function-
alised terthiophene monomers.
O
P(OEt)2
iii or iv
S
S
S
16
2.3. Metallated macrocycles and ligand functionalised
terthiophene monomers
Scheme 5. Reagents and conditions: (i) Method A: Br
2
, 48% HBr, ether,
ꢀ
0
C: 2-thiophene boronic acid 15, Pd
Method D: 2-thiophene boronic acid 15, Pd(PPh
DME, 76%.
C–rt, 67%; (ii) Method B: Py$ICl, MeOH, HgCl
2
, 86%; (iii) Method
P, K PO , 70%; (iv)
, aq 1 M Na CO
t
, THF, Bu
2
(dba)
3
3
3
4
3
)
4
2
3
,
As a part of our ongoing efforts to use porphyrins in photovol-
taics, sensor and electrocatalysis applications, we recently
reported how the architecture of porphyrin/oligothiophene
monomers (i.e., compound 18) was important in under-
standing and controlling the efficiency of photo-energy
Utilising the Suzuki-Miyaura conditions developed in the
synthesisof3 -formylterthiophene1, anaqueousdimethoxy-
0
ethane (DME) solution containing the dibromophosphonate
2
1
1
conversion.
1
Pd(PPh ) . Unfortunately the reaction afforded a mixture of
4 was reacted with excess boronic acid 15 and catalytic
Prior to this research, we were also interested in using ferro-
cene-appended polythiophenes, such as 19, for use as redox
active biosensors or in electrocatalysis applications (Fig. 1).
As an alternative to the three-step literature procedure to
3
4
unreacted starting material 14, mono-coupled product and
the desired terthiophene phosphonate 16 as determined by
HPLC and H NMR data. Attempts to drive the reaction to
1
1
2
completion by modifying the conditions were unsuccessful.
The similar R values of the thiophene, bithiophene and ter-
(ferrocenylmethylene)triphenylphosphonium iodide, we
found that the reaction of ferrocenemethanol with PPh $HBr
f
3
thiophene phosphonate materials prevented separation of
these compounds using chromatographic techniques.
in dry toluene directly gave ferrocene phosphonium salt 20
in essentially quantitative yield: this is in stark contrast to ef-
forts to make terthiophene phosphonium salt 5 via the same
procedure. The synthesis of 19 via Wittig olefination gave
a mixture of geometric isomers, which were isomerised to
Given the somewhat sluggish reactivity of 14 under this
Suzuki–Miyaura coupling protocol, a range of reported
1
13
modified coupling conditions were investigated. Only the
heterogeneous system reported by Littke and Fu allowed
the all trans-product (49%). Polymerisation of this mono-
mer gave electroactive films that were found to be effective
as a redox sensor for the detection of cytochrome c in aque-
9
the Suzuki reaction of 14 with 15 to be driven to completion.
After purification by chromatography and distillation, the
terthiophene phosphonate 16 was obtained as a viscous
yellow oil in high yield (70%). As with the characterisation
of 1, the long range COSY spectrum enabled the full assign-
ment of all thiophene protons. The AMX spin systems of the
two outer thiophene rings were easily determined from the
coupling constants, COSY spectrum and the long range cou-
1
3
ous solution. The recent availability of practical amounts
of 16 has enabled easier access to 19 via the Horner–
Emmons reaction of terthiophene phosponate 16 with the
commercially available ferrocene aldehyde 21 (Scheme 6).
More importantly, the crude reaction is essentially clean as
the phosphonate by-products are removed during the aque-
ous workup and the reaction conditions afford only the
trans-product.
0
00
pling correlation between H4 and H3 . The methylene
group is observed as a doublet at 3.31 ppm (J¼21.3 Hz)
due to coupling with the phosphorus nuclei. The electronic
spectrum shows an absorbance maximum at 342 nm, which
is consistent for the terthiophene chromophore.
R1
R1
R1
R1
R1
R1
With the new building block 16 in hand, the synthesis of the
pyridyl compound 11 was revisited (Scheme 4). Reaction of
N
M
N
1
0 and 16 under Horner–Emmons conditions gave 11 in
N
S
N
good yield and without the complications described previ-
ously. Having established the terthiophene phosphonate 16
as the complementary building block to the terthiophene al-
dehyde 1, our final objective was to have access to large
quantities of the phosphonate. Although the Suzuki coupling
reaction (Scheme 5) was successful on a gram scale,
attempts to perform the reaction on multi-gram scales using
the conditions optimised for 16 were unsuccessful (Method
C). Large-scale reactions were again complicated by in-
complete consumption of dibromophosphonate 14 and the
Fe
R1
R1
S
S
S
S
S
1
8 R1 = H or Me and M = 2H or Zn
19
Figure 1.

11144
G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
1
PPh Br
As expected, the aromatic region in the H NMR spectrum
of this compound is extremely congested. However, using
coupling constants and the long range COSY experiment it
was possible to fully assign all the signals. As in all the cases
where the terthiophene phosphonate was used, only the
trans-product was observed. Currently, the syntheses of a
variety of metal–ligand complexes are being explored.
3
CHO
Fe
Fe
20
21
i
ii
+
19
+
O
CHO
P(OEt)2
S
S
S
S
N
N
S
S
1
16
N
N
t
Scheme 6. Reagents and conditions: (i) Method A: (a) KO Bu, THF, rt; (b)
I , DCM, rt, 49%; (ii) Method B: KO Bu, THF, rt, 62%.
2
CHO
t
i
2
4
S
S
+
The fabrication of hybrid materials consisting of conducting
polythiophenes and transition metal complexes has created
a tremendous amount of interest in the field of ECPs.
O
S
P(OEt)2
1
4–18
25
S
S
Metallopolymers have been synthesised from functionalised
monomers, which fit one of the three structurally different
S
1
8
morphologies. The simplest approach has been to tether
the metal complex to the thiophene backbone via an alkyl
linker. The metal system can also be fused directly onto
the monomer backbone or, alternatively, inserted into the
monomer sequence. The last two methods have been used
to produce many metal complex materials, including
16
t
Scheme 8. Reagents and conditions: (i) KO Bu, THF, 88%.
2.4. Cross-linked polymers for studying electronic
properties
1
9,20
19,21–23
23,24
25,26
27
23
Cu,
exhibit different redox, optical and electronic properties.
Ni,
Pd,
Ru,
Mo and Au, that
Polythiophenes that are cross-linked through the b-position
have been of interest since the early 1990s. It is well known
that the regiochemistry and architecture of the monomer
play a dramatic role in determining the electronic, physical
and chemical properties of the resultant polymer. How-
ever, the advantages or disadvantages of using cross-linked
materials in homopolymers and copolymers are not well
understood.
In this context, we focused our efforts on the synthesis of ter-
thiophene monomers containing polypyridyl ligands that
would be suitable to form metal complexes. As mentioned
earlier, condensing the terthiophene phosphonate building
block and 4-formylpyridine under Horner–Emmons condi-
tions gave the all trans-11 product in good yield (Scheme
2
9
7
). Similarly, reaction of 16 with 2-formylpyridine 22
Early work by Tanaka and Kumei showed that the cross-
afforded the all trans-ortho-product 23 in satisfactory yield.
Both the compounds were easily purified by column chro-
matography and characterised by the usual analytical tech-
niques.
0
0
0
0
00
linked monomer 3 ,3 -bis-(2,2 :5 ,2 -terthiophene) upon
electrochemical polymerisation formed materials with in-
creased electroactive properties with respect to polyterthio-
3
0
phene. In their efforts to develop nanowire materials, Tour
and colleagues used oligothiophene monomer 26 rigidly
linked via a spirobicyclic system to control the 3-D geome-
N
3
1
32
try of the resulting polymer. Cherioux and colleagues,
N
CHO
and more recently Liu and colleagues, have investigated
the properties of polymers derived from star-shaped mono-
mers, such as 27 (Fig. 2). While Roncali and colleagues
10 para
22 ortho
33
i
S
S
have elegantly shown that b-thiophene monomers linked
via polyethers act as pseudo-crown ethers in the presence
of cations.
+
S
3
4
O
1
1 para, 53%.
P(OEt)2
23 ortho, 66%.
S
S
R
R
S
S
S
S
S
S
S
S
S
1
6
t
Scheme 7. Reagents and conditions: (i) KO Bu, THF.
S
S
The use of a bipyridyl ligand system in metal complexes is
well known and therefore compound 25 was considered an
ideal target. Reaction of bipyridyl-mono-aldehyde 24
with the phosphonate 16 under the conditions described pre-
viously produced the bipyridyl-terthiophene 25 in excellent
yield (88%) as a yellow microcrystalline solid (Scheme 8).
S
R
R
S
S
2
8
26
27a R = H
7b R = 2-thienyl
2
Figure 2.

G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
11145
Interest has also been directed at cross-linked polymers con-
taining alkene or alkyne linkers, as these materials have been
species. The UV–vis spectrum shows three absorption bands
that occur at 251, 317 and 348 nm. The lower and higher ab-
sorption bands are reminiscent of the thiophene and terthio-
phene chromophores, respectively, while the centre band is
presumably a result of the conjugative linker connecting
the central thiophene moieties.
3
5
suggested as low band gap polymers. Although the compu-
tational and physical data for these thiophene monomers are
encouraging, conclusive experimental results for these poly-
3
6
mer materials are needed. Marani and Emtezami’s previous
effortstochemicallyoxidiseanumberofa-andb-vinylcross-
linked thiophene monomers resulted in poor films. Our group
and others have also found that the electrochemical polymer-
isation of similar styryl linked 3-thienyl substituted mono-
To obtain practical quantities of 29 for further studies and
device testing, large-scale McMurray reactions were per-
formed, however, they provided poor yields. Access to
both terthiophene building blocks allowed the condensation
between 1 and 16 providing bis-(terthiophene)alkene in
excellent yield (86%) (Method B). Interestingly, neither
this route nor the McMurray coupling afforded any detect-
able amount of the cis-isomer.
3
7–39
mers produces electro-inactive homopolymers.
Based on our earlier success with the electrochemistry of
styryl-substituted b-terthiophenes, we expected that the
2
block monomer bis-(terthiophene)alkene 29 would elimi-
nate these problems observed with thiophene derivatives.
Initially, it was envisioned that cross-metathesis of alkene
A comparison of the X-ray structure for trans-1,2-bis-
0 00 00 000 00
(2 ,2 :5 ,2 -terthiophen)-3 -yl)ethene 29 to that reported
28 would provide the target 29 (Scheme 9). The alkene 28
has been previously accessed via the palladium catalysed
reaction of 3 -bromoterthiophene with vinylmagnesium
0 00 00 000 00
previously for trans-1-((2 ,2 :5 ,2 -terthiophen)-3 -yl)-2-
0
0000
2
(4 -cyanophenyl)ethene 30 shows some differences.
Most noticeable is that four of the thiophene rings and the
vinylic bond of structure 29 (Fig. 3) are essentially co-pla-
nar, thereby allowing significant p orbital overlap through
these rings. The two remaining thiophene rings are twisted
4
0
bromide. In this case, 28 was generated by Wittig conden-
sation of the aldehyde 1 with triphenylphosphinemethylene
ylide to give the identical product in excellent yield (90%).
Surprisingly, treatment of 28 with Grubb’s first generation
ruthenium catalyst ((Ph]RuCl (PCy ) ) under argon in
ꢀ
by an angle of 45.2 , presumably to compensate for the steric
2
3 2
DCM or even at elevated temperatures in toluene did not
result in the formation of any metathesis product.
congestion caused by the proximity of the vinylic protons.
The mean plane through the atoms of the central thiophene
ring and the cyano-substituted aryl ring of 30 was calculated
ꢀ
to have a dihedral angle of 26.5 . Interestingly, the central
CHO
S
S
i
S
S
S
S
1
28
Cross
Metathesis
X
S
ii or iii
S
S
S
S
S
29
t
Scheme 9. Reagents and conditions: (i) PPh MeI, KO Bu, THF, 90%; (ii)
3
t
Method A: TiCl
rt, 86%.
4
, Zn, THF, reflux, 66%; (iii) Method B: 16, KO Bu, THF,
A successful synthesis of bis-(terthiophene)alkene 29 was
achieved following McMurray coupling
4
1
protocols
Method A). The reaction of the low-valent titanium reagent,
(
generated from the in-situ reduction of TiCl , with 3 -for-
0
myl-2,2 :5 ,2 -terthiophene 1 afforded the trans-alkene 29
4
0
in good yield (66%) (Method A). Surprisingly, no cis-isomer
0
00
CN
1
was detected in the crude sample by H NMR spectroscopy.
The C2v symmetry of pure 29 is evident from the relatively
simple H NMR spectrum. The vinylic protons are present
1
as a singlet at 7.29 ppm. The two AMX spin systems of
the outer thiophene rings were fully assigned using proton
coupling constants and long range coupling correlation be-
S
S
S
0
0
000
2
30
tween H4 and H3 . The low resolution mass spectrum
of 29 indicated a relatively strong parent ion at M 520
+
Figure 3. Side view and top view ORTEP diagrams of compound 29 and
structure of compound 30.
(
95%), supporting the formation of a stable radical cation

11146
G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
bis-(thienyl)ethene unit of 29 is essentially planar having
ꢀ
full agreement with the structure of 32. Interestingly, the
presence of the additional styryl component of 32 compared
to compound 29 is clearly observed in the UV–vis absorption
spectra. In addition to the similar absorption bands found in
compound 29, the presence of the shoulder seen at 490 nm
in the visible region is presumably caused by the extensive
conjugated system connecting the two terthiophene rings.
a dihedral angle of only 7.7 .
We considered whether materials where the key component
was conjugatively positioned between two monomer linkers,
such as type 32, could result in polymeric systems with su-
perior electronic properties (Scheme 10). Reaction of 1
with the bis-phosphonium salt 31 under Wittig conditions
gave the product in good yields (68%) (Method A). How-
ever, we also found the cross-linked material 32 could be
made in better yield (80%) by the reaction of 19 with com-
mercially available p-terephthaldehyde 33 (Method B).
Electrochemical studies with bis-terthiophene alkene 29 and
its fabrication into photovoltaic devices have provided some
information on polymer opto-electronic properties. Homo-
polymers of 29 provide materials that are electroactive.
However, the best photovoltaic response was found to be
achieved from a blend of 29 with terthiophene, rather than-
homopolymers derived from either poly-29 or polyterthio-
PPh Br
3
CHO
4
2
S
S
phene. These preliminary results suggest that careful
control of conjugative cross-linking in the polymer can be
used to alter polymer architecture and opto-electronic prop-
erties.
+
S
1
31
PPh Br
3
i (68%)
2.5. Synthesis of the building block homologue, penta-
thiophene aldehyde
S
S
Initial efforts were directed at expanding the modular ap-
proachused toconstructthebuilding blocks1and16toaccess
the analogous compounds, such as the pentathiophene alde-
hyde 35. The reaction of 3-formyl-2,5-dibromothiophene
with bithiophene-2-boronic acid under Suzuki conditions
unfortunately gave complex mixtures of unreacted starting
material, mono-coupledproduct, bithiophene(i.e.,deboronyl-
ation by-product)and small amounts of the desired pentathio-
phene. Attempts to effectively isolate the various products
by chromatographic or recrystallisation methods were
S
S
S
3
2
S
i (80%)
O
CHO
P(OEt)2
4
3
problematic.
S
S
+
S
Asanalternative, thestepwisethiopheneelongationoftheini-
tial terthiophene aldehyde 1 was explored as a route to 35
(Scheme11). FollowingB €a uerleandco-workers’protocols,
CHO
1
6
33
4
4
t
Scheme 10. Reagents and conditions: (i) KO Bu/THF.
terthiophene aldehyde1 wassubjected toNBSin DMFto give
the dibromide 34 in high yield (80%). The proton NMR spec-
trum of 34 is simple, consisting of an aldehyde signal down-
1
Irrespective of the method used, analysis of the crude H
NMR spectrum revealed that only one of the three possible
geometric isomers was present; this was determined to be
the all trans,trans-product 32 based on the vinylic coupling
constant (16.2 Hz). Surprisingly, the C symmetry of 32 pro-
0
field at 10.02 ppm, a singlet at 7.48 ppm for H4 and two AB
quartet spin systems between 7.13 and 6.95 ppm (J¼3.9 Hz)
for the remaining four b-thiophene protons. Suzuki coupling
of the terthiophene dibromide 34 with thiophene boronic acid
under conditions as described for 1 and 16 proceeded
smoothly with the complete consumption of 34 as indicated
by TLC. This crude material was recrystallised to give the
2
v
1
vides a very simple H NMR spectrum that along with cou-
pling constants and long range COSY data enabled full
assignment of all signals. The other spectroscopic data is in
CHO
CHO
S
S
i
S
S
ii
Br
Br
S
S
1
34
R
S
CHO
S
S
S
S
S
S
S
S
S
35
36
3 4 2 3
Scheme 11. Reagents and conditions: (i) NBS, DMF, darkness, 80%; (ii) 2-thiophene boronic acid 15, Pd(PPh ) , DME, 1 M aq Na CO , 71%.

G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
11147
analogous pentathiophene aldehyde 35 as a deep red solid in
good yield (71%). Analysis of the H NMR spectrum of 35
Anhydrous tetrahydrofuran was obtained by distillation
from benzophenone ketyl, while anhydrous CH Cl was
1
2
2
was, as expected, extremely complex in the aromatic region.
Most distinguishable are the two singlets at 10.14 and
distilled off calcium hydride. Reactions requiring anhydrous
reagents or solvents were carried out under an inert atmo-
sphere of nitrogen or argon.
7
.55 ppm that were identified as the aldehyde proton and
0
0
H4 , respectively. With the aid of coupling constants
and long range COSYexperiments the proton NMR spectrum
of35wasassigned. Wehaverecentlyshownthatthepentathio-
phene aldehyde reacts in a similar fashion to the terthiophene
aldehyde allowing access to a meso-bis-pentathiophene por-
0
0
0
A stirred solution of 3 -formyl-2,2 :5 ,2 -terthiophene 1
00
4.1.1. 3 -(Hydroxymethyl)-2,2 :5 ,2 -terthiophene (4).
0
0
0
00
2
(500 mg, 1.81 mmol) in ethanol (10 mL) and THF (5 mL)
at rt was treated with sodium borohydride (48 mg,
1.27 mmol). After 3 h the reaction mixture was quenched
with ice-cold water (20 mL), then treated with a solution
of 1 M HCl (40 mL) and extracted with CH Cl
1
1
45
phyrin analogue of interest in photovoltaic studies.
2
2
3. Conclusion
(3ꢁ40 mL). The organic extracts were combined and
washed with water (60 mL) and dried (MgSO ). The solvent
4
The modular strategy described in the present work allows the
rapidandefficient constructionofthebuilding blocks, terthio-
phene aldehyde and terthiophene-methylene phosphonate,
by employing Suzuki–Miyaura coupling methodology. As
shown in this paper, this approach is extremely versatile. Irre-
spective of whether the coupling partner is commercially
available, had to be synthesised or has the desired chemical
reactivity, all the target monomers could ultimately be ob-
tained in good yields and purity. As a result, a range of func-
tionalised terthiophene monomers have been generated for
study in specific conducting polymer applications. In addi-
tion, these types of monomeric materials are of current in-
terest as novel materials for use in plastic electronics. The
synthesis of the pentathiophene aldehyde analogue was also
achieved by applying this modular approach. Current work
is directed at using b-functionalised thiophene boronic acids
in the Suzuki–Miyaura coupling reaction to give second gen-
eration building blocks with tuned physical, chemical and
electronic properties. The results of this work will be pub-
lished in the near future.
was removed under reduced pressure to give a faint yellow
oily/solid. This material was then subjected to column chro-
matography with gradient elution (EtOAc/toluene) to afford
a solid that was recrystallised from ether/petroleum ether to
give the alcohol 4 as fluffy pale yellow crystals (423 mg,
ꢀ
1
84%), mp 85 C. H NMR (400 MHz) d 7.35 (dd, 1H,
0
J¼5.1, 1.2 Hz, H5); 7.25 (s, 1H, H4 ); 7.24 (dd, 1H,
0
0
J¼5.1, 1.2 Hz, H5 ); 7.22 (dd, 1H, J¼3.6, 1.2 Hz, H3);
0
0
7.19 (dd, 1H, J¼3.6, 1.2 Hz, H3 ); 7.10 (dd, 1H, J¼5.1,
0
0
3.6 Hz, H4); 7.03 (dd, 1H, J¼5.1, 3.6 Hz, H4 ); 4.76 (s,
1
3
2H, CH OH); 1.80 (br s, 1H, CH OH).
C NMR
(100.6 MHz) d 138.1, 136.8, 135.9, 134.7, 132.1, 128.0,
2
2
4
6
127.9, 126.5, 126.1, 125.7, 124.7, 123.7, 59.1. IR (KBr)
3078, 2954, 2924, 2854, 1459, 1421, 1379, 1320, 1226,
ꢂ1
1177, 1030, 833, 699 cm . UV–vis (CHCl ) l
nm/
(log 3) 253 (4.10), 348 (4.32). LRMS (EI) m/z 280 (15),
3
max
+
279 (17), 278 (M , 100%), 261 (28), 245 (19), 216 (12),
127 (11). Anal. Calcd for C H OS : C, 56.08; H, 3.62;
S, 34.55. Found: C, 56.29; H, 3.74; S, 34.43.
1
3
10
3
0
nium bromide (5). A stirred solution of 3 -hydroxymethyl-
0
00
0
4
.1.2. ((2,2 :5 ,2 -Terthiophen)-3 -yl)methylene phospho-
0
,2 :5 ,2 -terthiophene 4 (200 mg, 0.72 mmol) in dry
4. Experimental
0
benzene (15 mL) at rt was treated with PPh $HBr
0
00
2
4
.1. General
3
(247 mg, 0.72 mmol) with vigorous stirring. The mixture
Melting points were determined on a Reichert Hot Stage ap-
paratus and are uncorrected. Microanalyses were performed
by Campbell Microanalytical Laboratory (Dunedin, New
Zealand). Nuclear Magnetic Resonance (NMR) spectra
was then heated at reflux for 10 h, then cooled and diluted
with petroleum ether (50 mL). The precipitate was collected
and dried under vacuum to give a yellow/grey powder 5
ꢀ
1
(149 mg, 34%), mp 247–248 C. H NMR (400 MHz)
d 7.82–7.73 (m, 3H, ArH); 7.73–7.58 (m, 12H, ArH); 7.22
1
13
were measured at 400 MHz ( H), 100.6 MHz ( C) and
1
13
00
3
3
00 MHz ( H), 75 MHz ( C) on a Bruker Avance 400 and
00 Ultrashield spectrometers. All NMR spectra were re-
(dd, 1H, J¼5.2, 1.1 Hz, H5 ); 7.19 (dd, 1H, J¼5.1, 1.1 Hz,
H5); 7.03 (dd, 1H, J¼3.6, 1.1 Hz, H3); 6.96 (dd, 1H,
0
0
corded in deuterochloroform unless otherwise stated, with
reference to tetramethylsilane. Signals are described in
terms of chemical shifts, multiplicity, intensity, coupling
constants and assignment. The following abbreviations
have been used: s (singlet), d (doublet), t (triplet), q (quartet),
m (multiplet) or br (broad). COSYexperiments were used to
J¼5.1, 3.6 Hz, H4); 6.92 (dd, 1H, J¼5.2, 3.6 Hz, H4 );
0 00
H,P
6.72–6.80 (m, 2H, H4 , H3 ); 5.57 (d, 2H, J ¼13.8 Hz,
1
3
CH PPh ). C NMR (100.6 MHz) d 137.2 (d, JC,P¼2.7 Hz),
2
3
135.2 (d, JC,P¼2.9 Hz), 134.7, 134.6, 134.2 (d, J ¼9.9 Hz),
C,P
133.0 (d, JC,P¼2.5 Hz), 130.3 (d, J ¼12.6 Hz), 128.0,
C,P
0
127.9, 127.8, 126.9, 126.3 (d, J ¼2.7 Hz, C4 ), 125.3,
C,P
1
assign signals in H NMR spectra.
124.4, 123.9 (d, JC,P¼9.0 Hz), 117.5 (d, J ¼85.6 Hz),
C,P
2
5.6 (d, JC,P¼48.1 Hz). Anal. Calcd for C H BrPS :
31
24
3
Analytical Thin Layer Chromatography (TLC) was carried
out using Merck (Art. 1.05554) silica gel 60 F254 pre-coated
on aluminium sheets. Flash and column chromatography
were performed using Merck Kieselgel 60 as adsorbent.
Both the chromatographic techniques used increasing pro-
portions of ethyl acetate in petroleum ether as eluting sol-
vent, unless stated otherwise. Fractions were monitored by
TLC and appropriate fractions were combined.
C, 61.69; H, 4.01; S, 15.94. Found: C, 61.67; H, 3.89;
S, 16.10.
0
0
00
0
nylphosphonium chloride (6). Anice-coldsolutionof3 -hy-
4.1.3. ((2,2 :5 ,2 -Terthiophen)-3 -yl)methylene triphe-
0
0
0
00
droxymethyl-2,2 :5 ,2 -terthiophene 4 (248 mg, 0.89 mmol)
and dry pyridine (0.50 mL, 6.24 mmol, 493 mg) in anhy-
drous CH Cl (50 mL) was treated dropwise with distilled
2
2

11148
G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
thionyl chloride (0.26 mL, 3.56 mmol, 424 mg, 4 equiv).
After 30 min, analysis by TLC indicated that all the starting
material had been consumed and the reaction mixture was
quenched with ice water (50 mL). The reaction mixture
was washed with 10% sodium bicarbonate solution
was extracted with CH Cl (4ꢁ80 mL), dried (MgSO )
2
2
4
and concentrated. The crude product was vacuum distilled
(192 C/0.01 mmHg) with a Vigreux column to give 17 as
ꢀ
a faint yellow oil (17.86 g, 86%). H NMR (400 MHz)
1
d 7.11 (d, 1H, JH,P¼1.3 Hz, H4); 4.05 (dq, 4H, OCH CH );
2
3
(
(
2ꢁ30 mL), saturated copper sulfate solution (20 mL), water
3.11 (d, 2H, J ¼21.1 Hz, ThCH P); 1.25 (dt, 6H,
H,P
2
1
3
60 mL) and dried (MgSO ). Attempts to purify the material
4
OCH CH ). C NMR (100.6 MHz) d 138.7 (d, J¼
C,P
2 3
by chomatographic means resulted in decomposition and
thus the chloride was used immediately in the next step.
The mixture of the crude chloride and triphenylphosphine
9.1 Hz), 138.3 (d, J¼3.0 Hz), 79.9 (d, J ¼15.1 Hz), 76.5
C,P C,P C,P
(d, J ¼3.0 Hz), 62.4 (d, J ¼7.0 Hz), 30.2 (d, J
¼
141.8 Hz), 16.4 (d, J ¼6.0 Hz). IR (NaCl) 3433, 1733,
C,P
(
701 mg, 2.67 mmol, 3 equiv based on alcohol) dissolved
1636, 1526, 1389, 1242, 1162, 1096, 1026, 992, 969, 846,
782, 644 cm . UV–vis (CHCl ) l
ꢂ1
in dry benzene (30 mL) was heated under reflux for 16 h. Af-
ter this period the reaction mixture was cooled, petroleum
ether (30 mL) was added and then cooled in ice. The precip-
itate that formed was collected and recrystallised from
CH Cl /ether to give the terthiophene phosphonium salt 6
nm/(log 3) 268
(4.95). LRMS (EI) m/z 486 (M , 11), 359 (100%), 349
3
+
max
(31), 331 (24), 303 (60), 239 (39), 95 (22), 80 (12). HRMS
(EI) M calcd for C H I O PS 485.8412. Found 485.8410.
+
9
13 2 3
2
2
0
4.1.6. Suzuki coupling to form diethyl ester (3 -methyl-
as yellow cream crystals (257 mg, 52% based on alcohol
ꢀ
1
0
0
00
used), mp 275 C. H NMR (400 MHz, CD Cl ) d 5.41 (d,
2
ene-2:2 ,5 :2 -terthiophene)phosphonic acid (16). Method
C. A mixtureof dibromophosphonate 14(1.00 g, 2.55 mmol),
tri(tert-butyl)phosphine (0.18 mL, 146 mg, 0.722 mmol),
2-thienylboronic acid 15 (653 mg, 5.10 mmol, 2 equiv) and
anhydrous K PO (1.30 g, 6.12 mmol, 2.4 equiv) in dry
2
2
H, J ¼13.9 Hz, CH PPh ); 6.75 (br d, 1H, J ¼1.3 Hz,
H,P
2
3
H,P
0
0
0
H4 ); 6.82 (br dd, 1H, J¼3.5 Hz, H3 ); 6.98 (dd, 1H,
00
J¼5.2, 3.6 Hz, H4 ); 7.02 (dd, 1H, J¼5.1, 3.6 Hz, H4);
7
1
(
.09 (dd, 1H, J¼3.6, 1.1 Hz, H3); 7.27 (dd, 1H, J¼5.1,
3
4
00
m, 12H, ArH); 7.79–7.86 (m, 3H, ArH). C NMR
.1 Hz, H5); 7.31 (dd, 1H, J¼5.2, 1.1 Hz, H5 ); 7.62–7.71
THF (25 mL) was stirred vigorously at rt to give a homoge-
neous slurry before tris(dibenzylideneacetone)dipalladium
[Pd (dba) ] (35 mg, 0.038 mmol, 1.5 mol %) was added.
1
3
(
100.6 MHz, CD Cl ) d 25.6 (d, J ¼48.1 Hz), 117.5 (d,
2
2
C,P
2
3
JC,P¼85.6 Hz), 123.9 (d, J ¼9.0 Hz), 124.4, 125.3, 126.3
C,P
The reaction mixture was then heated for 2 h under reflux,
when analysis of the mixture by HPLC indicated that
the reaction had ceased. The mixture was then charged
with additional tri(tert-butyl)phosphine (0.18 mL, 146 mg,
0.722 mmol) and 2-thienylboronic acid 15 (326 mg,
2.55 mmol, 1 equiv) and heated for another 2 h. The crude
mixture was then diluted with CH Cl and filtered. The or-
(
d, J ¼2.7 Hz), 126.9, 127.8, 127.9, 128.0, 130.3 (d,
C,P
JC,P¼12.6 Hz), 133.0 (d,
J
¼2.5 Hz), 134.2 (d,
C,P
C,P
JC,P¼9.9 Hz), 134.6, 134.7, 135.2 (d, J ¼2.9 Hz), 137.2
(
H, 4.33; S, 17.20. Found: C, 66.33; H, 4.03; S, 17.11.
d, J ¼2.7 Hz). Anal. Calcd for C H ClPS : C, 66.59;
C,P
31 24
3
2
2
4
.1.4. Diethyl ester (2,5-dibromo-3-thienylmethyl)phos-
phonic acid (14). A solution of bromine (28.7 g, 9.3 mL,
.180 mol) in 48% hydrobromic acid (26 mL) was added
ganic mixture was then subjected to normal aqueous workup
and the solvent removed under reduced pressure to afford
a dark brown oil. This material was subjected to column
chromatography to give a crude yellow oil, which was further
0
dropwise over 15 min to a vigorously stirred solution of
the phosphonate 13 (20.8 g, 0.085 mol) in 48% aqueous hy-
drobromic acid (26 mL) and ether (20 mL) cooled at 0 C.
The reaction was allowed to gradually warm to rt and left
to stir for 45 min. The mixture was then diluted with
CH Cl (200 mL) and water (150 mL) and the aqueous
7
ꢀ
purified by vacuum distillation (w 260–270 C/0.03 mmHg)
to give the terthiophene phosphonate 16 as a yellow viscous
ꢀ
1
oil (0.714 g, 70%). H NMR (400 MHz) d 7.35 (dd, 1H,
J¼5.2, 1.2 Hz, H5); 7.32–7.30 (m, 1H, H3); 7.23 (s,
0
00
1H, H4 ); 7.23 (dd, 1H, J¼5.1, 1.1 Hz, H5 ); 7.18 (dd, 1H,
2
2
0
0
phase removed. The organic layer was washed with 10% so-
dium hydrogen carbonate solution (5ꢁ75 mL), 10% sodium
thiosulfate solution (50 mL), water (2ꢁ75 mL) and dried
J¼3.6, 1.1 Hz, H3 ); 7.10 (dd, 1H, J¼5.2, 3.6 Hz, H4); 7.02
00
2 3
(dd, 1H, J¼5.1, 3.6 Hz, H4 ); 4.07 (q, 4H, OCH CH ); 3.31
(d, 2H, J ¼21.3 Hz, ThCH P); 1.28 (br t, 6H, OCH CH ).
H,P
2
2
3
1
3
(
MgSO ). The solvent was removed under reduced vacuum
C NMR (100.6 MHz) d 136.7, 135.9 (d, J ¼2.3 Hz),
C,P
4
to give a dark brown viscous oil, which was vacuum distilled
ꢀ
131.9 (d, JC,P¼11.5 Hz), 128.2 (d, J ¼9.4 Hz), 127.8,
C,P
(156–158 C/0.03 mmHg) with a Vigreux column to afford
product 14 as a golden liquid (22.5, 67%) (98% purity by
127.1, 126.8 (d, J ¼2.8 Hz), 126.2, 124.7, 123.9, 62.3
C,P
(d, JC,P¼6.6 Hz), 27.4 (d, J ¼141.5 Hz), 16.4 (d,
C,P
8
ꢀ
1
HPLC) (lit. 131–135 C/0.08 Torr). H NMR (400 MHz)
JC,P¼6.1 Hz). IR (KBr) 3464, 3075, 2984, 2908, 2362,
ꢂ1
d 6.98 (d, 1H, JH,P¼1.3 Hz, H4); 4.05 (dq, 4H, OCH CH );
1509, 1438, 1394, 1247, 1053, 1025, 965, 841, 697 cm
UV–vis (CHCl ) l
.
nm/(log 3) 249 (4.06), 342 (4.27).
2
3
3
.07 (d, 2H, J ¼21.1 Hz, ThCH P); 1.256 (dt, 6H,
H,P
2
3
max
1
3
+
+
OCH CH ). C NMR (100.6 MHz) d 32.2 (d, J ¼9.2 Hz),
LRMS (FAB) m/z 399 (MH , 84%), 398 (M , 100%), 371
(4.3), 343 (3.6), 261 (32), 227 (5), 203 (3), 179 (3). HRMS
2
3
C,P
1
31.5 (d, JC,P¼2.9 Hz), 111.0 (d, J ¼2.5 Hz), 110.6 (d,
C,P
+
JC,P¼13.7 Hz), 62.4 (d, J ¼6.7 Hz), 27.8 (d, J
C,P
¼
(EI) M calcd for C H O PS 398.0234. Found 398.0230.
3
C,P
17 19
3
1
nm/(log 3) 247 (4.94).
41.9 Hz), 16.4 (d, J ¼6.0 Hz). UV–vis (CHCl ) l
C,P
3
max
Method D. A mixture of the boronic acid 15 (7.90 g,
.062 mmol, 3 equiv), di-iodophosphonate 17 (10.0 g,
0.071 mol) DME (180 mL) and 1 M Na CO solution
0
4.1.5. Diethyl ester (2,5-diiodo-3-thienylmethyl)phos-
phonic acid (17). A stirred mixture of the phosphonate 13
(10 g, 0.043 mol), Py$ICl (21.65 g, 0.090 mol, 2.1 equiv)
in methanol (105 mL) was treated with Hg(NO ) $H O
2
3
(130 mL) was stirred vigorously at rt. To this was added
Pd(PPh ) (1.19 g, 1.03 mmol, 5 mmol %) and the reaction
1
0
3
4
mixture was heated under reflux for 12 h. The mixture was
then cooled and the DME removed under reduced pressure.
The residual mixture was diluted with water (100 mL) and
3
2
2
(
2
29.95 g, 0.085 mol) at rt and in the dark. It was left for
.5 h and then diluted with brine (300 mL). The mixture

G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
11149
0
00
00
extracted with CH Cl (4ꢁ120 mL). The organic extracts
J¼5.1, 1.2 Hz, H5 ); 7.42 (s, 1H, H4 ); 7.36–7.30 (m, 2H,
2
2
0
were combined and washed with water (2ꢁ70 mL), dried
pyridyl H ); 7.27 (dd, 1H, J¼5.1, 1.2 Hz, H5 ); 7.22 (dd,
B
0
(
MgSO ) and concentrated. The crude product was sub-
4
1H, J¼3.6, 1.2 Hz, H3 ); 7.20 (dd, 1H, J¼3.6, 1.2 Hz,
ꢀ
000
000
jected to Kugelrohr distillation (208 C/0.01 mmHg) to
give a yellowish oil (6.25 g, 76%).
H3 ); 7.15 (dd, 1H, J¼5.1, 3.6 Hz, H4 ); 7.05 (dd, 1H,
0
13
J¼5.1, 3.6 Hz, H4 ); 6.93 (d, 1H, J¼16.2 Hz, vinyl H2).
C
NMR (100.6 MHz) d 150.1, 144.7, 136.5, 136.3, 135.3,
134.5, 133.7, 128.0 (2ꢁCH), 127.4 (2ꢁCH), 127.0, 125.8,
125.1, 124.4, 121.9, 120.8. IR (KBr) 3431, 1623, 1590,
4
.1.7. (Ferrocenemethylene)triphenylphosphonium bro-
mide (20). A stirred solution of hydroxymethylferrocene
790 mg, 3.66 mmol) in dry benzene (20 mL) was treated
ꢂ1
(
1500, 1415, 969, 831, 812, 696, 678 cm . UV–vis (CHCl3)
lmax nm/(log 3) 311 (4.24), 349 (sh) (4.03). LRMS (EI) m/z
353 (13), 352 (21), 351 (M , 100%), 350 (17), 318 (19),
273 (18), 240 (8), 127 (10). Anal. Calcd for C H NS : C,
64.92; H, 3.73; N, 3.98. Found: C, 64.21; H, 3.54; N, 3.95.
with finely ground PPh $HBr (1.24 g, 3.60 mmol,
3
ꢀ
+
0
.98 equiv) at rt. The reaction mixture was heated at 50 C
for 2 h, then cooled and the yellow precipitate was collected
and washed with petroleum ether (2ꢁ30 mL). The solid was
dried under vacuum (P O ) to give the ferrocene phosphoni-
1
9
13
3
2
5
0
2-(2 -pyridyl)ethene (23). The required fractions were
00 00 000
00
um salt 20 as fluffy yellow crystals (1.84 g, 94%), mp 223–
4.1.9.2. trans-(E)-1-((2 ,2 :5 ,2 -Terthiophen)-3 -yl)-
ꢀ
.10 (br s, 2H, CH); 4.40 (s, 5H, Cp); 5.09, d, 2H, J
1
0000
concentrated under vacuum to give a solid that was recrystal-
2
4
1
24 C decomp. H NMR (400 MHz) d 4.01 (br s, 2H, CH);
¼
2
H,P
1
3
1.7 Hz, CH PPh ); 7.62–7.88 (m, 15H, ArH). C NMR
3
lised from ether/pentane to afford product 23 as pale yellow
ꢀ
2
1
(
7
1
(
100.6 MHz) d 27.5 (d, JC,P¼45.8 Hz), 68.7, 69.9, 70.5,
micro-crystals (392 mg, 66%), mp 119 C. H NMR
0
000
3.7, 118.0 (d, JC,P¼84.6 Hz), 130.1 (d, J ¼12.6 Hz),
(400 MHz) d 8.60–8.56 (m, 1H, pyridyl H6 ); 7.82 (d,
1H, J¼16.0 Hz, vinyl H1); 7.65–7.62 (m, 1H, pyridyl
C,P
34.2 (d, JC,P¼9.9 Hz), 134.8 (d, J ¼2.8 Hz). LRMS
C,P
+
0000 00
H4 ); 7.47 (s, 1H, H4 ); 7.42–7.39 (m, 1H, pyridyl
FAB) m/z 462 (36), 461 (M ꢂBr, 100%), 200 (16), 199
0
000
0
(
87). Anal. Calcd for C H BrFeP: C, 64.35; H, 4.84; P,
2
H3 ); 7.39 (dd, 1H, J¼5.1, 1.1 Hz, H5 ); 7.26 (dd, 1H,
9 26
0
0
0
0
5
.72. Found: C, 64.32; H, 4.86; P, 5.70.
J¼5.1, 1.2 Hz, H5 ); 7.22 (dd, 1H, J¼3.6, 1.1 Hz, H3 );
000
7
.21 (dd, 1H, J¼3.6, 1.2 Hz, H3 ); 7.15–7.13 (m, 1H, pyr-
0
-yl)-2-(ferrocenyl)ethene (19). Method B. A stirred solu-
00 00 000
0000
0
4
3
.1.8. Synthesis of trans-(E)-1-((2 ,2 :5 ,2 -terthiophen)-
0
idyl H5 ); 7.13 (dd, 1H, J¼5.1, 3.6 Hz, H4 ); 7.11 (d, 1H,
0
000
C NMR (100.6 MHz) d 155.7, 149.7, 136.6, 136.4,
J¼16. Hz, vinyl H2); 7.04 (dd, 1H, J¼5.1, 3.6 Hz, H4 ).
1
3
tion of the ferrocene aldehyde 21 (500 mg, 2.34 mmol) and
terthiophene phosphonate 16 (1.02 g, 2.57 mmol, 1.1 equiv)
in dry THF (20 mL) was slowly treated at rt with KO Bu
136.1, 135.8, 134.9, 133.3, 129.9, 128.0 (2ꢁCH), 127.3,
t
126.7, 125.4, 124.9, 124.1, 122.3, 122.0, 121.6. IR (KBr)
3443, 3056, 1629, 1584, 1469, 1430, 967, 817, 697 cm
ꢂ1
(
283 mg, 257 mmol, 1.1 equiv). The reaction was exother-
.
+
mic and was left to stir for 2 h. After this period the reaction
mixture was quenched with water (20 mL), acidified with
LRMS (EI) m/z 352 (27), 351 (M , 85%), 350 (51), 319
(23), 318 (100), 272 (25), 268 (53), 79 (32). Anal. Calcd
for C H NS : C, 64.92; H, 3.73; N, 3.98. Found: C,
1
M solution of HCl (50 mL) and extracted with CH Cl2
2
19 13
3
(
(
3ꢁ60 mL). The organic extracts were combined, dried
64.74; H, 3.69; N, 4.04.
MgSO ) and pre-adsorbed onto silica. This crude material
4
0 00 00 000 00
4.1.10. trans-(E)-1-((2 ,2 :5 ,2 -Terthiophen)-3 -yl)-2-
(4 -(4 -methyl-2 ,2 -bipyridyl))ethene (25). A mix-
was subjected to rapid silica filtration to give the product,
which was further purified by recrystallisation from ether/
0
000
00000
0000 00000
ꢀ
0
0
petroleum ether (charcoal) (650 mg, 62%), mp 165 C
ꢀ
ture of 4-formyl-4 -methyl-2,2 -bipyridine 24 (300 mg,
1.51 mmol) and terthiophene phosphonate 16 (665 mg,
1
3
(
lit. mp 165 C).
1
.66 mmol) dissolved in dry THF (25 mL) was treated
t
4.1.9. General Horner–Emmons reaction procedure. A
stirred mixture of the appropriate aldehyde 10, or 22
(
with KO Bu (188 mg, 1.68 mmol) and was left to stir at rt
for 5 h. The reaction mixture was subjected to the normal
aqueous workup as described for the pyridyl-terthiophene
isomers. The crude product was adsorbed onto alumina
and subjected to column chromatography, first gradient elu-
tion with chloroform/petroleum ether, followed with 10%
methanol/chloroform. The necessary fractions were
combined, concentrated and the product recrystallised
from CH Cl /petroleum ether (charcoal) to give title
0 0 0 00
10 equiv) and diethyl ester (3 -methylene-2:2 ,5 :2 -terthio-
phene)phosphonic acid 16 (1 equiv,w600–750 mg) in anhy-
drous THF (30 mL) was treated with KO Bu (1 equiv). The
t
reaction mixture was stirred at rt for 4 h. The mixture was
quenched with water (20 mL) and acidified with a 1 M
HCl (70 mL) solution. The mixture was diluted with
CH Cl (50 mL) and neutralised with saturated Na CO
2
2
2
3
2
2
solution. The organic layer was removed and the aqueous
extracted with a further portion of CH Cl (30 mL), then
combined and dried (MgSO ). The crude product was pre-
compound 25 as a yellow microcrystalline solid (388 mg,
ꢀ
1
88%), mp 158–159 C. H NMR (400 MHz) d 8.63 (d, 1H,
0
2
2
000
J¼5.1 Hz, pyridyl H6 ); 8.55 (d, 1H, J¼4.9 Hz, pyridyl
4
0000 0000
adsorbed onto alumina and subjected to column chromato-
graphy using gradient elution with CH Cl /petroleum ether.
H6 ); 8.42 (br s, 1H, pyridyl H3 ); 8.24 (br s, 1H, pyridyl
0
H, H4 and H5 ); 7.38 (m, 1H, pyridyl H5 ); 7.28 (dd,
0000
H3 ); 7.62 (d, 1H, J¼16.2 Hz, vinyl H1); 7.44–7.41 (m,
2
2
00 000 0000
2
0
00 00 000
00
0
0
000
4
.1.9.1. trans-(E)-1-((2 ,2 :5 ,2 -Terthiophen)-3 -yl)-
000
1H, J¼5.1, 1.0 Hz, H5 ); 7.24–7.20 (m, 2H, H3 and H3 );
0
00000 0
2
-(4 -pyridyl)ethene (11). The required fractions were
7.16–7.13 (m, 2H, pyridyl H5 and H4 ); 7.057 (d, 1H,
concentrated under vacuum to give a solid that was recrystal-
lised from absolute ethanol/pentane to afford product 11 as
bright yellow fluffy crystals (307 mg, 53%), mp 128–
J¼16.2 Hz, vinyl H2); 7.056 (dd, 1H, J¼5.1, 3.6 Hz,
0
00
13
H4 ); 2.45 (s, 3H, CH ). C NMR (100.6 MHz) d 156.8,
3
155.8 (2ꢁCH), 149.4, 149.0, 148.1, 145.7, 136.45, 136.41,
135.5, 134.7, 133.6, 128.0 (2ꢁCH), 127.4, 126.9, 125.8,
125.1, 124.8, 124.3, 122.1, 122.0, 120.2, 118.9, 21.2. IR
ꢀ
1
1
29 C. H NMR (400 MHz) d 8.62–8.50 (m, 2H, pyridyl
H ); 7.54 (d, 1H, J¼16.2 Hz, vinyl H1); 7.43 (dd, 1H,
A

11150
G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
(
6
KBr) 3434, 3052, 1629, 1592, 1545, 1460, 964, 841, 828,
70 cm . LRMS (EI) m/z 444 (14), 443 (28), 442 (M ,
178 (100%), 165 (43), 73 (52), 57 (64), 55 (55), 43 (57),
41 (50). Anal. Calcd for C H S : C, 59.96; H, 3.10; S,
36.94. Found: C, 59.89; H, 3.12; S, 36.95.
ꢂ1
+
2
6 16 6
100%), 441 (29), 409 (6), 359 (10), 315 (14), 170 (28).
Anal. Calcd for C H N S : C, 67.84; H, 4.10; N, 6.33.
Found: C, 67.98; H, 4.18; N, 6.63.
2
5 18 2 3
Method B. A vigorously stirred mixture of the terthiophene
aldehyde (1) (1.61 g, 5.83 mmol) and terthiophene phospho-
nate 16 (2.44 g, 6.12 mmol, 1.05 equiv) in dry THF
0 0 0 00
.1.11. 3 -Vinyl-2:2 ,5 :2 -terthiophene (28). A slurry of
triphenylphosphonium methyl bromide (2.65 g, 7.42 mmol,
4
t
(100 mL) was slowly treated with KO Bu (687 mg,
ꢀ
4
.1 equiv) in dry THF (45 mL) at 0 C was treated dropwise
6.12 mmol) over a 10 min period at rt under an inert atmo-
sphere. The reaction was then left to stir at rt for 3 h by which
time a yellow precipitate had formed. The mixture was di-
luted with water (60 mL) and the yellow solid collected.
The crude solid was dissolved in hot toluene, dried
with a solution of n-BuLi in THF (2.5 M, 2.7 mL,
.75 mmol) and stirred for 2 h. The reaction mixture was
6
then allowed to warm to rt and stirred for a further 2 h, before
a solution of terthiophene aldehyde 1 (500 mg, 1.81 mmol) in
dry THF (20 mL) was added dropwise. After a further 2 h of
stirring at rt, the reaction mixture was quenched by the addi-
tion of 1 M HCl (50 mL) and then concentrated under re-
duced pressure to remove the solvent. This residue was
diluted with water (50 mL) and then extracted with CH Cl
(
with water (20 mL), dried (MgSO ) and concentrated under
vacuum to give a dark yellow oil. This crude material was ad-
sorbed onto silica and subjected to column chromatography
with gradient elution CH Cl /petroleum ether (with increas-
(MgSO ) and passed through a plug of silica. The filtrate
4
was concentrated and the residue recrystallised from
CH Cl /petroleum ether (charcoal) to afford alkene 29 as
bright yellow crystals (2.60 g, 86%).
2
2
2
2
0000 0000 0 00 00 000
4.1.13. trans,trans-(1 ,4 -Bis-[2-((2 ,2 :5 ,2 -terthio-
2ꢁ50 mL). The organic layers were combined, washed
0
0
phen)-3 -yl)vinyl]benzene (32). Method A. A stirred slurry
of the bis-phosphonium salt 31 (300 mg, 0.380 mmol) and
terthiophene aldehyde 1 (215 mg, 0.779 mmol) in dry THF
(10 mL) and CH Cl (10 mL) was treated with freshly sub-
4
2
2
2
2
t
ꢀ
ing concentration of CH Cl ). The appropriate fractions were
2
combined, concentrated and kept under high vacuum for sev-
eral hours to give the desired alkene 28 as a bright yellow oil
limed KO Bu (128 mg, 1.14 mmol, 3 equiv) at 0 C. The re-
action was allowed to warm to rt and stirred for 5 h. The
mixture was diluted with CH Cl (20 mL), then 1 M HCl
2
2
2
(
consistent with the compound that was made by Kagan and
Liu via the Kumada coupling route. UV–vis (CHCl3)
lmax nm/(log 3) 251 (4.23), 347 (4.29).
478 mg, 90%). The proton NMR spectrum of this material is
(50 mL) was added and vigorously stirred for 10 min. The
organic layer was removed and washed with water
(50 mL), dried (MgSO ) and concentrated under vacuum
4
0
4
to give a yellow solid. The crude material was adsorbed
onto silica and subjected to column chromatography begin-
ning with 50% toluene/petroleum ether, then gradually in-
creasing to toluene. This material was recrystallised from
CH Cl /petroleum ether (charcoal) to give product 32 as yel-
0
00 00 000
00
4
.1.12. trans-(E)-1,2 Bis((2 ,2 :5 ,2 -terthiophen)-3 -
yl)ethene (29). Method A. A stirred solution of TiCl4
11.7 mL, 0.105 mol, 20.25 g) in dry THF (150 mL) at rt
(
2
2
ꢀ
1
was treated with portions of zinc dust (4.63 g, 0.071 mol).
This mixture was then heated at reflux for 15 min before
a solution of the terthiophene aldehyde 1 (1.00 g,
low powdery solid (162 mg, 68%), mp 229–230 C. H
NMR (400 MHz, CD Cl ) d 7.10 (dd, 2H, J¼5.1, 3.6 Hz,
2
2
0
H4 ); 7.11 (d, 2H, J¼16.2 Hz, vinylic); 7.19 (dd, 2H,
0
00
000
3
1
.62 mmol) in dry THF (25 mL) was added dropwise. After
7 h the reaction mixture was cooled and cold water (50 mL)
J¼5.1, 3.6 Hz, H4 ); 7.27 (dd, 2H, J¼3.6, 1.2 Hz, H3 );
0
7.29 (dd, 2H, J¼3.6, 1.2 Hz, H3 ); 7.34 (dd, 2H, J¼5.1,
0
was added slowly. The mixture was then diluted CH Cl
2
1.2 Hz, H5 ); 7.44 (d, 2H, J¼16.2 Hz, vinylic); 7.47 (dd,
2
0
00
00
aryl H). C NMR (100.6 MHz, CD Cl ) d 121.8, 122.5,
(
100 mL) and a 1 M solution of HCl (70 mL) was added
2H, J¼5.1, 1.2 Hz, H5 ); 7.52 (s, 2H, H3 ); 7.38 (s, 4H,
2 2
1
3
and the mixture stirred for 30 min. The organic layer was
then separated and the aqueous layer extracted with
CH Cl (3ꢁ50 mL). The organic layers were combined,
124.6, 125.4, 127.0, 127.2, 127.4, 128.3, 128.4, 130.3,
132.0, 135.4, 136.4, 136.8, 137.0, 137.2. IR (KBr) 1512,
1420, 1309, 1232, 1175, 1069, 1045, 950, 834, 815,
2
2
then dried (MgSO ) and the solvent removed under reduced
4
ꢂ1
pressure to give bright yellow solid. This crude material was
then pre-adsorbed onto silica gel and subjected to column
chromatography. The column was first eluted with 10%
CH Cl /petroleum ether to remove some high R materials,
690 cm . UV–vis (CHCl ) l
nm/(log 3) 246 (4.39),
279 (4.09), 345 (4.84), 456 (4.65). LRMS (EI) m/z 460
3
max
+
(19), 459 (30), 458 (M , 100%), 304 (13), 303 (31), 69
(15), 57 (20), 55 (19), 43 (20), 41 (18). Anal. Calcd for
C H S : C, 65.56; H, 3.56; S, 30.88. Found: C, 65.32; H,
3.40; S, 31.01.
2
2
f
then with toluene to allow isolation of the crude product. Re-
crystallisation from CH Cl /petroleum ether gave alkene 29
3
4 22 6
2
2
ꢀ
as yellow/greenish needles (625 mg, 66%), mp 202–203 C.
1
H NMR (400 MHz, CD Cl ) d 7.05 (dd, 2H, J¼5.1, 3.6 Hz,
Method B. A vigorously stirred mixture of the terephthaldi-
carboxaldehyde 33 (300 mg, 2.24 mmol) and terthiophene
phosphonate 16 (2.04 g, 5.12 mmol, 2.3 equiv) in dry THF
2
2
000
0
H4 ); 7.15 (dd, 2H, J¼5.2, 3.6 Hz, H4 ); 7.230 (dd, 2H,
0
000
J¼3.6, 1.2 Hz, H3 ); 7.235 (dd, 2H, J¼3.6, 1.2 Hz, H3 );
000
t
7
.28 (dd, 2H, J¼5.1, 1.2 Hz, H5 ); 7.285 (s, 2H, H1 and
(50 mL) was slowly treated with KO Bu (552 mg,
00
0
H2); 7.38 (s, 2H, H4 ); 7.43 (dd, 2H, J¼5.2, 1.2 Hz, H5 ).
4.94 mmol) and then left to stir at rt for 3 h. After this period
the reaction mixture was quenched with water (30 mL),
treated with 1 M solution of HCl (100 mL) to give a yellow
precipitate. This solid was filtered and dissolved in CH Cl
1
3
C NMR (100.6 MHz, CD Cl ) d 122.8, 124.0 (2ꢁCH)
2
2
1
1
1
24.8, 125.5, 127.0, 127.6, 128.4 (2ꢁCH), 132.2, 135.5,
36.5, 136.9, 137.0. IR (KBr) 1431, 1416, 1350, 1276,
167, 1049, 991, 960, 847, 831, 814, 691 cm . UV–vis
2
2
ꢂ1
(500 mL) with gentle heating. The solution was washed
with water (80 mL) and then organic layer was dried
(MgSO ). This crude solid was dissolved in a minimum
(
(
CHCl ) l
3
nm/(log 3) 251 (4.48), 317 (4.73), 348
max
+
4.66). LRMS (EI) m/z 520 (M , 95), 243 (40), 179 (44),
4

G. E. Collis et al. / Tetrahedron 63 (2007) 11141–11152
11151
amount of toluene and passed through a pad of silica using
rapid silica filtration to remove the first band of intensely
yellow material. The appropriate concentrations were con-
centrated to afford a yellow solid, which was recrystallised
from CH Cl /petroleum ether (charcoal) to give product
138.3, 138.2, 137.1, 136.8, 134.7, 131.3, 130.6, 127.7,
128.6, 126.3, 126.2, 125.7, 125.3, 125.2, 125.0, 124.8,
123.2. nmax/cm 3064, 1655, 1495, 1424, 1386, 1354,
ꢂ1
1221, 1203, 1166, 1056, 1047, 833, 786, 690. UV–vis
(CHCl ) l nm/(log 3) 257 (4.42), 369 (sh) (4.47), 412
max
2
2
3
+
3
2 (1.11 g, 80%) as a bright yellow solid.
(4.54). EIMS m/z 442 (27), 441 (28), 440 (M , 100%),
12 (15), 358 (4), 220 (9), 209 (6), 127 (29), 69 (7).
Anal. Calcd for C H OS : C, 57.24; H, 2.74; S, 36.38.
4
0
0
0
0
0
00
34). To a stirred solution of 3 -formyl-2:2 ,5 :2 -terthio-
4
(
.1.14. 5,5 -Dibromo-3 -formyl-2,2 :5 ,2 -terthiophene
00
2
1
12
5
0
0
0
Found: C, 57.25; H, 2.59; S, 36.46.
phene 1 (2.76 g, 10 mmol) in DMF (130 mL) kept in the
dark at rt was added NBS (3.74 g, 21 mmol) and was left
to stir for 5 h. After this period a yellow precipitate had
formed. The mixture was poured into ice-cold water and fil-
tered. The yellow solid was then dried (P O ) under vacuum
Acknowledgements
Thanks to Dr. Edwards for assistance with NMR experi-
ments, Dr. Wilde for the kind donation of compound 31
and Mr. Evans for exploratory studies on the pentathiophene
synthesis. The authors would like to thank New Economy
Research Fund for financial support.
2
5
and recrystallised chloroform/ether to give the dibromide 9
as bright yellow fluffy crystals (3.47 g, 80%), mp 163 C.
ꢀ
H NMR (300 MHz) d 10.02 (s, 1H, CHO); 7.48 (s, 1H,
1
0
H4 ); 7.12 (A part of ABq, 1H, J¼3.9 Hz, H4 or H3); 7.08
(
B part of ABq, 1H, J¼3.9 Hz, H3 or H4); 7.01 (A part of
00
ABq, 1H, J¼3.9 Hz, H4 ); 6.96 (B part of ABq, 1H,
Supplementary data
0
0
13
J¼3.9 Hz, H3 ). C NMR (75 MHz) d 184.4, 144.4,
1
1
1
1
7
37.8, 136.7, 136.1, 133.3, 131.2, 130.9, 129.5, 125.2,
23.0, 115.9, 112.9. IR (KBr) nmax/cm
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data
Centre, no. CCDC-652064. Copies of the data can be ob-
tained free of charge on application to CCDC, University
Chemical Lab, 12 Union Road, Cambridge CB2 1EZ, UK
fax: +44 1223/336 033; e-mail: deposit@ccdc.cam.ac.uk).
Processing data and the selected crystal data for compound
9 can be found in the Supplementary data. Supplementary
ꢂ1
3099, 3084,
673, 1509, 1434, 1422, 1374, 1324, 1301, 1233, 1225,
215, 1190, 1168, 1065, 981, 975, 954, 850, 842, 804,
79, 746, 735, 690. UV–vis (CHCl ) l
3
nm/(log 3) 264
max
(
(
4.29), 332 (4.19), 374 (sh) (4.14). EIMS m/z 437 (8), 436
61), 434 (M , 100%), 408 (9), 406 (15), 355 (14), 327
(
+
(
(
42), 311 (22), 309 (20), 246 (22), 205 (10), 201 (15), 123
15), 69 (17). Anal. Calcd for C H Br OS : C, 35.96; H,
2
1
3
6
2
3
data associated with this article can be found in the online
version, at doi:10.1016/j.tet.2007.08.022.
1
.39; S, 22.16. Found: C, 36.06; H, 1.19; S, 22.55.
00 0 0 00 00 000 000 0000
.1.15. 3 -Formyl-2,2 :5 ,2 :5 ,2 :5 ,2 -quinquethio-
phene (35). A stirred mixture of 5,5 -dibromo-3 -formyl-
4
00
0
References and notes
0
0
00
2
tetrakis(triphenylphosphine)palladium [Pd(PPh ) ] (1.28 mg,
,2 :5 ,2 -terthiophene 34 (0.803 g, 1.85 mmol) and
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2
3
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further elution with 75% CH Cl /petroleum ether to collect
2
2
an intense red band and to remove baseline impurities. This
crude material was adsorbed onto silica and subjected to col-
umn chromatography eluting with 50% toluene/petroleum
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2
the pentathiophene aldehyde 35 as deep red crystals
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ꢀ
CD Cl ) d 10.14 (s, 1H, CHO); 7.55 (s, 1H, H4 ); 7.33
1
(
0.578 g, 71%), mp 178 C.
NMR (300 MHz,
00
2
2
(
dd, 1H, J¼5.1, 1.1 Hz, H5); 7.32–7.26 (m, 3H,
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0000
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J¼3.9 Hz, H3, H4 , H5 ); 7.24 (d, 2H, J¼3.9 Hz, H3 ,
0
000
000
H3 ); 7.18 (A part of ABq, 1H, J¼3.8 Hz, H3 ); 7.14
000
(
B part of ABq, 1H, J¼3.8 Hz, H4 ); 7.08 (dd, 1H,
0
C NMR (75 MHz, CD Cl ) d 185.1, 145.6, 141.3,
000
J¼5.1, 3.6 Hz, H4); 7.06 (dd, 1H, J¼5.1, 3.6 Hz, H4 ).
1
3
2
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