Rapid Syntheses of Oligo(2,5-thiophene ethynylene)s with Thioester Termini: Potential Molecular Scale Wires with Alligator Clips

Article abstract of DOI:10.1021/jo962335y

The syntheses of soluble oligo(3-ethyl-2,5-thiophene ethynylene)s via an iterative divergent/ convergent approach starting from 3-ethyl-2-(trimethylsilylethynyl)thiophene are described. The monomer, dimer, tetramer, octamer, and 16-mer were synthesized. The 16-mer is 100 A long in its minimized extended zigzag conformation. At each stage in the iteration, the length of the framework doubles. Only three sets of reaction conditions are needed for the entire iterative synthetic sequence: an iodination, a protodesilylation, and a Pd/Cu-catalyzed cross coupling. The oligomers were characterized spectroscopically and by mass spectrometry. The optical properties are presented which show that at the octamer stage, the optical absorbance maximum is nearly saturated. The size exclusion chromatography values for the number average weights, relative to polystyrene, illustrate the tremendous differences in the hydrodynamic volume of these rigid rod oligomers verses the random coils of polystyrene. These differences become quite apparent at the octamer stage. Attachment of thiol end groups, protected as the thioacetyl moieties, was achieved. These serve as binding sites for adhesion to gold surfaces. In some cases, one end of the oligomeric chains were capped with a thiol group so that the surface attachments to gold could be studied. In other cases, thiol groups were affixed to both ends of the molecular chains so that future conduction studies could be done between proximal metallic probes. The rigid rod conjugated oligomers may act as molecular wires in molecular scale electronic devices, and they also serve as useful models for understanding analogous bulk polymers.

Full text of DOI:10.1021/jo962335y

1376
J . Org. Chem. 1997, 62, 1376-1387
Ra p id Syn th eses of Oligo(2,5-th iop h en e eth yn ylen e)s w ith
Th ioester Ter m in i: P oten tia l Molecu la r Sca le Wir es w ith Alliga tor
Clip s
Darren L. Pearson and J ames M. Tour*
Department of Chemistry and Biochemistry, University of South Carolina,
Columbia, South Carolina 29208
Received December 13, 1996X
The syntheses of soluble oligo(3-ethyl-2,5-thiophene ethynylene)s via an iterative divergent/
convergent approach starting from 3-ethyl-2-(trimethylsilylethynyl)thiophene are described. The
monomer, dimer, tetramer, octamer, and 16-mer were synthesized. The 16-mer is 100 Å long in
its minimized extended zigzag conformation. At each stage in the iteration, the length of the
framework doubles. Only three sets of reaction conditions are needed for the entire iterative
synthetic sequence: an iodination, a protodesilylation, and a Pd/Cu-catalyzed cross coupling. The
oligomers were characterized spectroscopically and by mass spectrometry. The optical properties
are presented which show that at the octamer stage, the optical absorbance maximum is nearly
saturated. The size exclusion chromatography values for the number average weights, relative to
polystyrene, illustrate the tremendous differences in the hydrodynamic volume of these rigid rod
oligomers verses the random coils of polystyrene. These differences become quite apparent at the
octamer stage. Attachment of thiol end groups, protected as the thioacetyl moieties, was achieved.
These serve as binding sites for adhesion to gold surfaces. In some cases, one end of the oligomeric
chains were capped with a thiol group so that the surface attachments to gold could be studied. In
other cases, thiol groups were affixed to both ends of the molecular chains so that future conduction
studies could be done between proximal metallic probes. The rigid rod conjugated oligomers may
act as molecular wires in molecular scale electronic devices, and they also serve as useful models
for understanding analogous bulk polymers.
In tr od u ction
ducting when doped,5 we only recently determined how
thiol-ended rigid rod conjugated molecules orient them-
selves on gold surfaces,6 and how we could record
electronic conduction through single undoped conjugated
molecules that are end-bound onto a metal probe surface.7
Here we describe the synthetic details for the formation
Future computational systems will likely consist of
logic devices that are ultradense, ultrafast, and molecular-
sized.1-3 The slow step in existing computational archi-
tectures is not usually the switching time, but the time
it takes for an electron to travel between devices. By
using molecular scale electronic interconnects,4 the trans-
mit times could be minimized, resulting in computational
systems that operate at far greater speeds than is
presently attainable from conventional patterned archi-
tectural arrays.1 There is another technical advantage
that might also be gained from molecular scale devices.
A powerful computational system presently utilizes ca.
1010 silicon-based devices. If devices were to be based
upon single molecules,3r using routine chemical synthe-
ses, one could prepare ca. 1023 devices in a single reaction
flask. Of course, the task of addressing large arrays of
ordered molecular scale devices is presently unattainable;
however, the potential is certainly enough to maintain
current and future interests.
(3) For some recent background work on the formation of molecular-
based transporters and devices, see: (a) Grosshenny, V.; Harriman,
A.; Ziessel R. Angew. Chem., Int. Ed. Engl. 1995, 34, 1100. (b) Langler,
L.; Stockman, L.; Heremans, J . P.; Bayor, V.; Olk, C. H.; Van
Haesendonck, C.; Bruynseraede, Y.; Issi, J .-P. Synth. Met. 1995, 70,
1393. (c) Pascual, J . I.; Me´ndez, J .; Go´mez-Herrero, J .; Baro´, A. M.;
Garcia, N.; Landman, U.; Luedtker, W. D.; Bogachek, E. N.; Cheng,
H.-P. Science 1995, 267, 1793. (d) Purcell, S. T.; Garcia, N.; Binh, V.
T.; J ones, L., II; Tour, J . M. J . Am. Chem. Soc. 1994, 116, 11985. (e)
Martin, C. R. Science 1994, 266, 1961. (f) Seth, J .; Palaniappan, V.;
J ohnson, T. E.; Prathapan, S.; Lindsey, J . S.; Bocian, D. F. J . Am.
Chem. Soc. 1994, 116, 10578. (g) Gust, D. Nature 1994, 372, 133. (h)
Wu, C.; Bein, T. Science 1994, 266, 1013. (i) Wagner, R. W.; Lindsey,
J . S.; Seth, J .; Palaniappan, V.; Bocain, D. F. J . Am. Chem. Soc. 1996,
118, 3996. (j) Sailor, M. J .; Curtis, C. L. Adv. Mater. 1994, 6, 688. (k)
Brigelletti, F.; Flamigni, L.; Balzani, V.; Collin, J .; Sauvage, J .; Sour,
A.; Constable, E. C.; Thompson, A. M. W. C. J . Am. Chem. Soc. 1994,
116, 7692. (l) Wu, C.; Bein, T. Science 1994, 264, 1757. (m) Moerner,
W. E. Science 1994, 265, 46. (n) Sessler J . L.; Capuano, V. L.;
Harriman, A. J . Am. Chem. Soc. 1993, 115, 4618. (o) Farazdel, A.;
Dupuis, M.; Clementi, E.; Aviram. A. J . Am. Chem. Soc. 1990, 112,
4206. (p) Tour, J . M.; Wu, R.; Schumm, J . S. J . Am. Chem. Soc. 1991,
113, 7064. (q) Dai, H.; Wong, E. W.; Lieber, C. M. Science 1996, 272,
523. (r) Wu, R.; Schumm, J . S.; Pearson, D. L.; Tour, J . M. J . Org.
Chem. 1996, 61, 6906. (s) Ward, M. D. Chem. Ind. 1996, 569.
(4) “Molecular electronics” is a poorly defined term since some
authors refer to it as any molecular-based system such as a film or a
liquid crystalline array. Other authors, including us, have preferred
to reserve the term “molecular electronics” for single molecule tasks,
such as single molecule-based devices or single molecular wires. Due
to this confusion, we have chosen here to follow the Petty et al.
(Introduction to Molecular Electronics, Petty, M. C., Bryce, M. R., Bloor,
D., Eds.; Oxford Univ. Press: New York, 1995) terminology by using
two subcategories, namely “molecular materials for electronics” for bulk
applications and “molecular scale electronics” for single molecule
applications.
Though it is well-documented that bulk conjugated
organic materials can be semiconducting or even con-
X Abstract published in Advance ACS Abstracts, February 15, 1997.
(1) For some recent background work on molecular scale electronics,
see: (a) Molecular Electronics: Science and Technology; Aviram, A.,
Ed.; Confer. Proc. No. 262, American Institute of Physics: New York,
1992. (b) Miller, J . S. Adv. Mater. 1990, 2, 378, 495, 601. (c) Molecular
and Biomolecular Electronics; Birge, R. R., Ed.; Advances in Chemistry
Series 240, American Chemical Society: Washington, DC, 1991. (d)
Nanostructures and Mesoscopic Systems; Kirk, W. P., Reed, M. A., Eds.;
Academic: New York, 1992.
(2) For some theoretical considerations on molecular scale wires,
see: (a) Samanta, M. P.; Tian, W.; Datta, S.; Henderson, J . I.; Kubiak,
C. P. Phys. Rev. B 1996, 53, R7626. (b) Mujica, V.; Kemp, M.; Roitberg,
A.; Ratner. M. J . Phys. Chem. 1996, 104, 7296. (c) J oachim, C.; Vinuesa,
J . F. Europhys. Lett. 1996, 33, 635.
(5) Handbook of Conducting Polymers; Skotheim, T. A., Ed.; Dek-
ker: New York, 1986.
S0022-3263(96)02335-3 CCC: $14.00 © 1997 American Chemical Society

Rapid Syntheses of Oligo(2,5-thiophene ethynylene)s
J . Org. Chem., Vol. 62, No. 5, 1997 1377
of soluble oligo(3-ethyl-2,5-thiophene ethynylene)s, po-
tential molecular scale wires, by a rapid iterative diver-
gent/convergent doubling approach.8,9 Additionally, the
syntheses and attachments of protected thiol moieties to
one or both ends of the oligomers are presented. These
thiols serve as molecular scale alligator clips for adhesion
of the molecular scale wires to the gold probes.6,7
F igu r e 1. Schematic presentation of the iterative divergent/
convergent approach to molecular length doubling.
to Y′. The two portions are then brought back together
to form the dimer XMMY with loss of X′Y′. Since the
same end groups that were present in the monomer are
now present in the dimer, the procedure can be repeated
with a doubling of molecular length at each iteration. The
advantages of this approach are that the molecular
length grows rapidly, at a rate of 2n were n ) the number
of iterations, and incomplete reactions yield unreacted
material that is half the size of the desired compound.
Thus, purification at each step is far simpler since
separation involves, for example, an octamer from a 16-
mer. This iterative divergent/convergent approach is
therefore particularly attractive.10,11
There has been considerable recent effort to prepare
large conjugated molecules of precise length and consti-
tution.10 Our approach to these compounds maintains
several key features that make it well-suited for the
requisite large molecular architectures for molecular
scale electronics studies. Specifically, the route involves
(1) a rapid construction method that permits doubling
molecular length at each coupling stage to afford an
unbranched 100 Å oligomer, the approximate size of
present nanopatterned probe gaps,1 (2) an iterative
approach so that the same high yielding reactions can
be used throughout the sequence, (3) the syntheses of
conjugated compounds that are semiconducting in the
bulk, (4) products that are stable to light and air so that
subsequent engineering manipulations will not be im-
peded, (5) products that could easily permit independent
functionalization of the ends to serve as molecular
alligator clips that are required for surface contacts to
metal probes, (6) products that are rigid in their frame-
works so as to minimize conformational flexibility yet
containing substituents for maintaining solubility and
processability, (7) alkynyl units (cylindrically symmetric)
separating the aryl units so that ground state contiguous
π-overlap will be minimally affected by rotational varia-
tions, (8) molecular systems that do not have degenerate
ground state resonance forms and are thus not subject
to Peierls distortions,5 and finally, (9) products that serve
as useful models for the understanding of bulk polymeric
materials.5
Resu lts a n d Discu ssion
Mon om er Syn th eses. The syntheses of several mono-
mers were conducted as shown in eqs 1 and 2. Oligomers
derived solely from 1 had minimal solubility. Oligomers
derived from 9 were too difficult to purify since the butyl
groups promoted excessively rapid migration on silica gel
chromatography even with hexane as an eluent. Oligo-
mers that were prepared from 10 or mixtures of 1 and
10 required protection of the hydroxyl moieties as tert-
butyldimethylsilyl ethers, and they suffered from silyl
migration reactions. The use of monomer 8, however,
proved to be optimal; there were no protection/deprotec-
tion steps necessary and acceptable Rf values on silica
gel could be maintained.
Con tr olled Oligom er Syn th eses. The iterative di-
vergent/convergent synthetic approach is outlined in
Scheme 1. The sequence involves partitioning 8 into two
portions, iodinating the 5-position in one of the portions
to form 11, and protodesilylating the alkynyl end of the
second portion to form 12. Bringing the two portions
back together in the presence of a soluble Pd/Cu catalyst
mixture12 couples the aryl iodide to the terminal alkyne,
thus generating the dimer 13. Iteration of this reaction
sequence doubles the length of the dimer 13 to afford the
tetramer 16, and so on to the octamer 19, and finally the
16-mer 22. The silylated alkynes showed good oxidative
stability; however, upon protodesilylation, the tetramer
18 and octamer 21 were air sensitive and immediate
workup and further coupling was necessary to minimize
oxidative decomposition of these terminal alkyne inter-
mediates. Similarly, the Pd/Cu coupling reactions to
form 19 and 22 required the strict exclusion of oxygen;
The iterative divergent/convergent approach is outlined
in Figure 1.10,11 A batch of monomer material M, with
inactive end groups X and Y, is divided into two portions.
In one portion, the end group X is activated by conversion
to X′. In the second portion, Y is activated by conversion
(6) (a) Tour, J . M.; J ones, L., II; Pearson, D. L.; Lamba, J . S.; Burgin,
T.; Whitesides, G. W.; Allara, D. L.; Parikh, A. N.; Atre, S. J . Am. Chem.
Soc. 1995, 117, 9529. (b) Dhirani, A.; Zehner, R. W.; Hsung, R. P.;
Guyot-Sionnest, P., Sita, L. R. J . Am. Chem. Soc. 1996, 118, 3319.
(7) Bumm, L. A.; Arnold, J . J .; Cygan, M. T.; Dunbar, T. D.; Burgin,
T. P.; J ones, L., II, Allara, D. L.; Tour, J . M.; Weiss, P. S. Science 1996,
271, 1705.
(8) Schumm, J . S.; Pearson, D. L.; Tour, J . M. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1360.
(9) Pearson, D. L.; Schumm, J . S.; Tour, J . M. Macromolecules 1994,
27, 2348.
(10) Tour, J . M. Chem. Rev. 1996, 96, 537.
(11) (a) Wegner, G. In Thermoplastic Elastomers, A Comprehensive
Review; Legge, N. R., Holden, G., Schroeder, H. E., Eds.; Hanser: New
York, 1987; p 405. (b) Young, J . K.; Nelson, J . C.; Moore, J . S. J . Am.
Chem. Soc. 1994, 116, 10841. (c) Nelson, J . C.; Young, J . K.; Moore, J .
S. J . Org. Chem. 1996, 61, 8160.
(12) Suffert, J .; Ziessel, R. Tetrahedron Lett. 1991, 32, 757.

1378 J . Org. Chem., Vol. 62, No. 5, 1997
Pearson and Tour
Sch em e 1
degassing and use of a dry box was required to attain
reasonable yields.
The 16-mer, in its minimum-energy extended zigzag
conformation, has a molecular length of approximately
100 Å. The zigzag conformation is significantly lower in
energy, by molecular mechanics calculations,13 than other
nonextended forms. Once one end of the molecule binds
to a gold probe, the other end could affix to the proximal
probe with 2 eV stabilization14 on each end from the
Au-S bonds.

Rapid Syntheses of Oligo(2,5-thiophene ethynylene)s
J . Org. Chem., Vol. 62, No. 5, 1997 1379
F igu r e 2. The optical absorbance maximum (λmax) in CH2Cl2
versus the number of units in the oligomer (n) for 8, 13, 16,
19, and 22.
F igu r e 3. The values of Mn determined by SEC in THF
(relative to polystyrene standards) versus the actual molecular
weights of the monomer through 16-mer, 8, 13, 16, 19, and
22, respectively.
Oligom er Ch a r a cter iza tion . The monomer through
16-mer, 8, 13, 16, 19, and 22, have been characterized
spectroscopically. While the tetramer 16 and octamer
19 afforded molecular ions by direct exposure via electron
impact mass spectrometry (MS), neither this method nor
FAB or electrospray MS sufficed for obtaining a molec-
ular ion of 22. However, matrix-assisted laser desorption
MS (MALDI-MS) did afford an M + 1 peak for 22
(sinapinic acid matrix, positive ion mode).
The optical spectra are interesting in that a near
saturation of the systems appears to have occurred by
the octamer stage so that doubling the conjugation length
to the 16-mer caused little change in the absorbance
maximum (Figure 2). We observed a similar near
saturation for the third order (ø(3)) nonlinear optical
intensities.15
The results of the size exclusion chromatography (SEC)
are also quite intriguing (Figure 3). SEC is not a direct
measure of molecular weight but a measure of the
hydrodynamic volume. Thus, by SEC using randomly
coiled polystyrene standards, the number average mo-
lecular weights (Mn) of rigid rod polymers are usually
greatly inflated relative to the actual molecular weights
(MW). Accordingly, the SEC-recorded Mn values of the
octamer 19 (Mn ) 1610, actual MW) 1146) and 16-mer
22 (Mn ) 3950, actual MW) 2218) were much greater
than the actual MWs. Conversely, the monomer 8
through tetramer 16 had Mn values that were very close
to the actual MWs (slope ∼1.0 in Figure 3) because they
are in the low MW region, prior to significant polystyrene
coiling. Therefore Figure 2 could serve as a useful
calibration chart for determining the MW of rigid rod
polymers. In all cases, the SEC-determined values of Mw/
Mn ) 1.02-1.05 were within the detectable range limits.
Atta ch m en t of Th iol En d Gr ou p s. We then sought
to affix protected thiol moieties to the ends of the
oligomers. These thiols were used as molecular alligator
clips for adhesion to gold probe surfaces.6,7 In some cases,
we prepared monothiol-terminated systems for adhesion
of these oligomers to single gold surfaces. In other cases,
we prepared the R,ω-difunctionalized systems for adhe-
sion between two gold probe surfaces. We found that the
terminal aromatic thiols were most difficult to manipu-
late since they were unstable, undergoing disulfide
formation in the presence of oxygen, often resulting in
insoluble oligomers. However, the acetyl-protected thiols
were resilient enough for manipulations in air, yet they
could be readily hydrolyzed with NH4OH, in situ, once
exposed to the gold probe surfaces.6a Initially, we at-
tached phenylene bromides to the ends of the thiophene-
ethynylene oligomers and then converted the halide
moieties to protected thiols via a one-pot lithiation-
sulfide-acetylation protocol (eq 3).16 This thioacetyl-
generating protocol was low-yielding, and it only worked
(13) Oligomer lengths were simulated using standard molecular
modeling procedures. All calculations were performed on a Power
Macintosh 8100/80 AV using Personal CAChe version 3.7 for both
structure drawing and minimization. The CAChe mechanics applica-
tion implements a standard MM2 force field. All energy calculations
were minimized over a large number of iterations to convergence at
local minima nearest in energy to the starting compounds’ energies.
(14) Ulman, A. An Introduction to Ultrathin Organic Films; Aca-
demic: Boston, 1991.
for the monomeric thiophene case. For instance, we
made the corresponding R,ω-dibromoaryl-16-mer 29 that
we were unable to transform into the R,ω-dithioacetyl
oligomer using the sequence of t-BuLi, S8, AcCl (Scheme
2).
(15) Samuel, I. D. W.; Ledoux, I.; Delporte, C.; Zyss, J .; Pearson,
L.; Tour, J . M. Chem. Mater. 1996, 8, 819.

1380 J . Org. Chem., Vol. 62, No. 5, 1997
Pearson and Tour
Sch em e 2
Sch em e 3
We then decided to follow a more convergent approach
by synthesizing the two complementary alligator clips,
30 and 31, from a common intermediate, and then to affix
the thioester-containing units directly to the ends of the
oligomers (eq 4). During the final protodesilylation for
the formation of 31, if acidic conditions were not used,
as well as desilylation. Moreover, addition of acetic
anhydride increased the yield of 31, presumably by
reacylating any thiol intermediate that formed. The aryl
iodide 30 can be coupled to the alkynyl end (head) of the
oligomers while the alkynyl arene 31 can be coupled to
the thienyl iodide end (tail) of the oligomers.
Scheme 3 shows the attachment of 30 to the heads of
the monomer through octamer (12, 15, 18, and 21,
respectively). The yield for the attachment of 30 to the
octamer 21 was low, and we were unable to obtain any
desired material when we attempted the same reaction
(16) For sulfur quench without acylation, see: J ones, E.; Moodie, I.
M. Org. Synth. 1970, 50, 104. Note that we also used thienylthiols as
alligator clips; however, dimerization reactions via conjugate addition
on thiol tautomers ensued. For analogous dimerizations, see: Ponti-
cello, G. S.; Habecker, C. N.; Varga, S. L.; Pitzenbeger, S. M. J . Org.
Chem. 1989, 54, 3223.
the fluoride was nucleophilic enough to cause deacylation

Rapid Syntheses of Oligo(2,5-thiophene ethynylene)s
J . Org. Chem., Vol. 62, No. 5, 1997 1381
Sch em e 4
on the corresponding 16-mer, the protodesilylation prod-
uct of 22. Again, the sensitivity of the terminal alkynes
increases with increased conjugation length.
Exp er im en ta l P r oced u r es
Gen er a l. Unless otherwise noted, all operations were
carried out under a dry, oxygen-free nitrogen atmosphere.
Molecular weight analyses were performed using two 30 × 75
cm GPC columns (105 Å 10 µm and 500 Å 5 µm) eluted with
THF at 60 °C (flow rate 1.0 mL/min). Molecular weight results
were based on eight polystyrene standards (Mw ) 52000,
30300, 9200, 7000, 5050, 2950, 1060, and 580 with a correla-
tion coefficient > 0.9998) purchased from Polymer Laboratories
Ltd. 3-Bromothiophene was purchased from Lancaster Syn-
thesis Ltd. and used without purification. Alkyllithium re-
agents were obtained from Aldrich Chemical Co. Inc. or FMC.
Reagent grade diethyl ether and tetrahydrofuran (THF) were
distilled under nitrogen from sodium benzophenone ketyl.
Reagent grade benzene and dichloromethane were distilled
over calcium hydride. Bulk grade hexane was distilled prior
to use. The Pd/Cu couplings were conducted in a manner
analogous to that described by Suffert.12 The 2-halogenations
of 3-alkylthiophenes were performed according to the proce-
dure of Uhlenbroek and Reinecke.17 The terminal alkynes
larger than the dimer stage were oxidatively unstable, and
they were used immediately after their preparation. The
synthetic procedures for the preparation of 1, 2, 5, 8, 11-16,
and 18 have been described previously.3r Unless otherwise
noted, all compounds were >95% pure as judged by NMR, GC,
or combustion analyses. The oligomers’ purities can be as-
sessed by their polydispersity indexes Mw/Mn.
We then synthesized tail-functionalized dimer through
16-mer, 36-39, respectively, as outlined in Scheme 4. As
before, direct functionalization of the iodinated 16-mer
was unsuccessful; however, coupling of the protodesil-
ylated product of 38 did afford 39, albeit in low yield.
We also prepared R,ω-difunctionalized oligomers based
on some of our larger conjugated systems. For example,
the R,ω-diphenylthioacetyl-octamer 40 has been pre-
pared. Additionally, the phenylthioacetyl-containing tet-
ramer 37, after protodesilylation, was coupled to the R,ω-
diiodo-nonamer 42 to afford the 128 Å long R,ω-di-
phenylthioacetyl-17-mer 43 (Scheme 5).13 These are the
macromolecules that we are presently using in our
attempts to bridge proximal gold probes.
Su m m a r y
We outlined the rapid syntheses of oligo(3-ethyl-2,5-
thiophene ethynylene)s via an iterative divergent/con-
vergent approach starting from 3-ethyl-2-[(trimethylsilyl)-
ethynyl]thiophene (8). At each stage in the iteration, the
length of the framework doubled. Only three sets of
reaction conditions were needed for the entire iterative
synthetic sequence: an iodination, a protodesilylation,
and a Pd/Cu-catalyzed cross coupling. Convergent at-
tachment of the complementary thiol end groups, pro-
tected as thioester moieties, was achieved. These serve
as binding units for adhesion to gold surfaces. The rigid
rod conjugated oligomers may act as molecular wires in
molecular scale electronic devices. Moreover, they also
serve as useful models for understanding analogous bulk
polymers as judged by the optical spectra and SEC-
determined values.
3-n -Bu tylth iop h en e (3).18a A procedure analogous to that
of Kumada and co-workers was used as follows.18b To mag-
nesium turnings (1.82 g, 75 mmol) in ether (20.0 mL) was
added dropwise butyl bromide (10.3 g, 75 mmol) in ether (20.0
(17) (a) Uhlenbroek, J . H.; Bijloo, J . D. Rec. Trav. Chim. 1960, 79,
1181. (b) Reinecke, M. G.; Adickes, H. W.; Pyrn, C. J . Org. Chem. 1971,
36, 2690.
(18) (a) Pham, C. V.; Mark, H. B.; Zimmer, H. Synth. Commun.
1986, 16, 689. (b) Tamao, K.; Kodama, S.; Nakajima, I.; Kumada, M.;
Minato, A.; Suzuki, K. Tetrahedron 1982, 38, 3347. (c) Campaigne,
E.; Yokley, O. E. J . Org. Chem. 1963, 28, 914.
(19) Tour, J . M.; Wu, R. Macromolecules 1992, 25, 1901.

1382 J . Org. Chem., Vol. 62, No. 5, 1997
Pearson and Tour
Sch em e 5
mL) at room temperature, and an ice bath was used occasion-
ally to maintain a mild reflux. The mixture was stirred at
room temperature for 1 h and transferred via cannula to a
solution of 3-bromothiophene (8.15 g, 50 mmol) and dichloro-
[(diphenylphosphino)propane]nickel(II) (30 mg, 0.055 mmol)
in ether (20.0 mL) at 0 °C . The mixture was then allowed to
warm to room temperature and stir overnight before being
poured into water with a few drops of 3 N hydrochloric acid.
The aqueous layer was extracted with ether, and the organic
extracts were washed with brine and dried over magnesium
sulfate. The solvent was removed by rotary evaporation, and
the residue was purified by flash chromatography on silica gel
(hexane) to provide 5.93 g (85%) of the title product as colorless
washed with brine and dried over magnesium sulfate. The
solvent was removed by rotary evaporation and the residue
was purified by a column chromatography on silica gel
(hexane) to provide 8.06 g (72%) of the title product as colorless
liquid. IR (neat) 2929, 2857, 2361, 1464, 1398, 966, 829, 715
cm-1
.
1H NMR (300 MHz, CDCl3) δ 7.36 (d, J ) 5.51 Hz, 1
H), 6.73 (d, J ) 5.46 Hz, 1 H), 2.48 (t, J ) 7.63 Hz, 2 H), 1.54
(p, J ) 7.70 Hz, 2 H), 1.35 (sext, J ) 7.29 Hz, 2 H), 0.93 (t, J
) 7.21 Hz, 2 H).
3-(Hyd r oxyeth yl)-2-iod oth iop h en e (7). See the prepara-
tion of 6 for the synthetic protocol. Used were 3-(hydroxyeth-
yl)thiophene (10.6 g, 82.8 mmol), benzene (100 mL), mercuric
oxide (17.9 g, 82.9 mmol), iodine (21.0 g, 82.8 mmol), and flash
chromatography on silica gel (3:2 hexane/ethyl acetate) to
afford 17.11 g (81%) of the title product as a clear light yellow
liquid. IR (neat) 2929, 2859, 1466, 1079, 857, 834, 768 cm-1
.
1H NMR (300 MHz, CDCl3) δ 7.23 (m, 1 H), 6.91 (m, 2 H),
2.62 (t, J ) 7.62 Hz, 2 H), 1.60 (pent, J ) 7.58 Hz, 2 H), 1.32
(sext, J ) 7.38 Hz, 2 H), 0.92 (t, J ) 7.32 Hz, 3 H).
liquid. IR (neat) 2929, 2857, 1464, 1397, 965, 829 cm-1 1H
.
NMR (300 MHz, CDCl3) δ 7.41 (d, J ) 5.5 Hz, 1 H), 6.81 (d, J
) 5.5 Hz, 1 H), 3.82 (t, J ) 6.6 Hz, 2 H), 2.84 (t, J ) 6.6 Hz,
2 H), 1.39 (br s, 1 H).
3-(Hyd r oxyeth yl)th iop h en e (4).18c To a 1 L flame-dried
vessel were added ether (300 mL) and tert-butyllithium (212
mL, 467 mmol, 2.2 M in pentane), and the vessel was cooled
to -78 °C. To the solution was added 3-bromothiophene (19.5
mL, 208 mmol) dropwise, and the reaction was stirred at -78
°C for 1 h at which time ethylene oxide (45.8 mL, 229 mmol,
5 M in ether) was added. The reaction was allowed to warm
to room temperature and stir overnight. The mixture was
poured into water and extracted with ether (3 × 20 mL) and
the organic layer dried over magnesium sulfate and filtered.
The product was purified by flash chromatography (1:1 hexane/
ethyl acetate) to afford 23 g (87%) the title compound as a clear
colorless liquid. IR (neat) 3356, 2933, 1410, 1047, 909, 835,
3-n -Bu tyl-2-[(tr im eth ylsilyl)eth yn yl]th iop h en e (9). To
a 100 mL flame-dried vessel containing 3-n-butyl-2-iodo-
thiophene (20.93 g, 78.7 mmol), bis(triphenylphosphine)-
palladium(II) chloride (1.1 g, 1.57 mmol), copper(I) iodide (0.44
g, 2.3 mmol), and THF (150 mL) was added diisopropylamine
(11.9 mL, 85 mmol) at room temperature. The resulting clear
brown solution was stirred for 5 min before (trimethylsilyl)-
acetylene (12.0 mL, 85 mmol) was added. The nitrogen outlet
was removed and the septum capped. The reaction was stirred
overnight at room temperature and poured into water, and
the aqueous layer was extracted with ether (3 × 20 mL). The
organic layer was dried over magnesium sulfate, and the crude
product was concentrated in vacuo. The product was distilled
at 100 °C/1 mmHg to afford 15.0 g (81%) of the title compound
as a clear yellow liquid. IR (neat) 2958, 2144, 1458, 1250, 1084
774 cm-1
.
1H NMR (500 MHz, CDCl3) δ 7.29-7.27 (m, 1 H),
7.04-7.03 (m, 1 H), 6.97-6.96 (m, 1 H), 3.83 (q, J ) 6.1 Hz, 2
H), 2.89 (t, J ) 6.4 Hz, 2 H), 1.43 (t, J ) 5.9 Hz, 1 H).
3-n -Bu tyl-2-iod oth iop h en e (6). To a solution of 3-bu-
tylthiophene (5.89 g, 42 mmol) in benzene (10.0 mL) were
alternately added mercuric oxide (8.41 g, 38.9 mmol) and
iodine (10.93 g, 43.1 mmol) in small portions at 0 °C . The
mixture was stirred at room temperature overnight before
filtration. The filtrate was poured into water, the aqueous
layer was extracted with ether, and the organic extracts were
cm-1
.
1H NMR (500 MHz, CDCl3) δ 7.10 (d, J ) 5.2 Hz, 1 H),
6.81 (d, J ) 5.1 Hz, 1 H), 2.67 (t, J ) 7.6 Hz, 2 H), 1.58 (p, J
) 7.5 Hz, 2 H), 1.32 (sext, J ) 7.3 Hz, 2 H), 0.91 (t, J ) 7.3
Hz, 3 H), 0.22 (s, 9 H).
2-(H y d r o x y e t h y l)-1-[(t r im e t h y ls ily l)e t h y n y l]t h io -
p h en e (10). See the preparation of 9 for the synthetic

Rapid Syntheses of Oligo(2,5-thiophene ethynylene)s
J . Org. Chem., Vol. 62, No. 5, 1997 1383
protocol. Used were 3-(hydroxyethyl)-2-iodothiophene (34.6 g,
136 mmol), bis(triphenylphosphine)palladium(II) chloride (1.9
g, 2.7 mmol), copper(I) iodide (1.3 g, 6.8 mmol), THF (200 mL),
diisopropylamine (19.0 mL, 136 mmol), (trimethylsilyl)acety-
lene (19.2 mL, 136 mmol), and flash chromatography (3:1
hexane/ethyl acetate) to afford 16.37 g (81%) of the title
compound as a clear yellow liquid. IR (neat) 3356, 2958, 2898,
provide 0.70 g (63%) of the title product as a fluorescent yellow
liquid which darkened upon standing. IR (film) 2967, 2930,
2872, 2180, 2140, 1698, 1514, 1460, 1384, 1319, 1262, 1249,
1062, 902, 842, 740 cm-1
.
1H NMR (300 MHz, CDCl3) δ 7.062
(s, 3 H), 7.058 (s, 2 H), 7.036 (s, 2 H), 7.014 (s, 1 H), 2.71
(overlapping q, J ) 7.6 Hz, 16 H), 1.26-1.25 (overlapping t, J
) 7.6 Hz, 24 H), 0.25 (s, 9 H). 13C NMR (100 MHz, CDCl3) δ
151.22, 150.78, 150.33, 149.90, 149.64, 149.59, 137.79, 132.93,
132.59, 132.50, 132.40, 123.97, 123.47, 123.40, 122.56, 120.08,
119.50, 119.45, 119.36, 102.74, 96.71, 92.61, 90.49, 90.07,
89.84, 89.77, 86.80, 86.72, 86.09, 85.85, 75.18, 23.28,, 23.08,
22.90, 22.82, 14.82, 14.77, 14.68, 14.60, 14.37, 14.26, 14.01,
0.00. LRMS calcd for C67H57IS8Si: 1272. Found: 1272.
Dep r otected Octa m er 21. To a solution of 19 (0.77 g, 0.67
mmol) in methanol (5 mL) and dichloromethane (5 mL) was
added potassium carbonate (0.69 g, 5.0 mmol). The solution
was allowed to stir for 6 h before being poured into water. The
aqueous layer was extracted with methylene chloride, and the
organic extracts were washed with brine. The combined
organic layers were dried over magnesium sulfate. The solvent
was removed by rotary evaporation. No further purification
was necessary to afford 0.72 g (100%) of the title compound
as a yellow-orange solid. IR (film) 3298, 2967, 2932, 2872,
2180, 2097, 1460, 1321, 1262, 1187, 1061, 901, 843, 739, 661
2144, 1418, 1250, 1047, 843 cm-1 1H NMR (300 MHz, CDCl3)
.
δ 7.15 (d, J ) 5.1 Hz, 1 H), 6.88 (d, J ) 5.1 Hz, 1 H), 3.86 (q,
J ) 6.4 Hz, 2 H), 2.96 (t, J ) 6.5 Hz, 2 H), 1.41 (t, J ) 5.9 Hz,
1 H), 0.23 (s, 9 H).
Iod in a ted Tetr a m er 17. To a solution of diisopropylamine
(7.89 g, 11 mL, 78 mmol) in ether (40 mL) at -78 °C was added
dropwise n-butyllithium (44 mL, 65 mmol, 1.49 M in hexanes).
The solution was warmed to 0 °C for 30 min and then recooled
to -78 °C. 16 (4.35 g, 7.1 mmol) in ether (15 mL) at room
temperature was then added to the -78 °C lithium diisopro-
pylamide solution. This solution was warmed from -78 °C to
0 °C for 10 min and then recooled to -78 °C. While at -78
°C, iodine (19.98 g, 78 mmol) in ether (140 mL) was added via
cannula, and the solution was allowed to warm to room
temperature overnight. The reaction was quenched with
water, the aqueous layer was extracted with methylene
chloride, and the organic extracts were washed with brine and
aqueous sodium thiosulfate. The organic layers were dried
over magnesium sulfate. The solvent was removed by rotary
evaporation, and the residue was purified by flash chroma-
tography (silica gel, hexane) to provide 4.86 g (93%) of the title
product as a fluorescent yellow liquid which darkened upon
cm-1
.
1H NMR (300 MHz, CDCl3) δ 7.21 (d, J ) 5.17 Hz, 1
H), 7.064 (s, 3 H), 7.059 (s, 2 H), 7.039 (s, 1 H), 7.030 (s, 1 H),
6.90 (d, J ) 5.15 Hz, 1 H), 3.489 (s, 1 H), 2.71 (overlapping q,
16 H), 1.25 (overlapping t, J ) 7.6 Hz, 24 H). 13C NMR (100
MHz, CDCl3) δ 152.40, 150.31, 149.90, 149.84, 149.67, 149.63,
132.87, 132.61, 132.55, 132.45, 132.35, 132.23, 127.89, 127.03,
124.52, 124.05, 124.01, 123.77, 123.56, 123.46, 123.01, 119.42,
119.37, 119.33, 119.11, 118.90, 118.78, 118.68, 117.28, 89.78,
89.55, 89.48, 89.44, 88.33, 87.25, 87.02, 86.84, 86.76, 86.71,
86.08, 84.65, 81.34, 76.08, 23.19, 23.06, 23.04, 22.82, 14.73,
14.65, 14.57, 14.52.
standing. IR (neat) 2966, 2140, 1459, 1249, 1020, 844 cm-1
.
1H NMR (300 MHz, CDCl3) δ 7.05 (s, 1 H), 7.03 (s, 1 H), 7.01
(s, 1 H), 2.69 (11 line m, 8 H), 1.25 (t, J ) 7.60 Hz, 3 H), 1.24
(t, J ) 7.56 Hz, 6 H), 1.22 (t, J ) 7.63 Hz, 3 H), 0.25 (s, 1 H).
13C NMR (100 MHz, CDCl3) δ 151.24, 149.88, 149.59, 149.57,
137.78, 132.58, 132.51, 132.39, 123.43, 123.38, 123.34, 122.54,
120.07, 119.46, 119.35, 102.69, 96.65, 89.98, 89.76, 89.67,
86.61, 86.01, 85.75, 75.03, 23.02, 23.02, 22.86, 22.78, 22.71,
14.62, 14.55, 14.54, 14.32, -0.04. HRMS calcd for C35H33IS4-
Si: 736.0279. Found: 736.0294.
16-m er 22. See the preparation of 19 for the synthetic
protocol. Used were 20 (0.68 g, 0.53 mmol), THF (3 mL), 21
(0.70 g, 0.65 mmol), diisopropylamine (0.30 g, 0.42 mL, 3.0
mmol), bis(triphenylphosphine)palladium(II) chloride (0.02 g,
0.02 mmol), copper(I) iodide (0.01 g, 0.03 mmol), and silica gel
flash chromatography by first using hexane and then slowly
increasing to 9:1 hexane/methylene chloride and finally 7:3
hexane/methylene chloride to provide 0.60 g (50%) of the title
product as a red-orange solid. IR (neat) 2968, 2933, 2180,
Octa m er 19. To a solution of 17 (0.23 g, 0.32 mmol) in THF
(5 mL) were added 18 (0.36 g, 0.67 mmol) and diisopropy-
lamine (0.10 g, 0.10 mL, 0.71 mmol). This solution was
allowed to stir under N2 in a dry box for 1 h. The catalysts
bis(triphenylphosphine)palladium(II) chloride (0.01 g, 0.02
mmol) and copper iodide (0.002 g, 0.01 mmol) (degassed in
vacuo for 1 h) were added, and the reaction was allowed to
stir for 3 days. The reaction was quenched with water, the
aqueous layer was extracted with ether, and the organic
extracts were washed with brine. The ether layers were dried
over magnesium sulfate. The solvent was removed by rotary
evaporation, and the residue was purified by silica gel flash
chromatography by first using hexane then slowly increasing
to 9:1 hexane/methylene chloride to provide 0.26 g (72%) of
the title product as a yellow-orange solid. IR (neat) 2967, 1511,
2140, 1460, 1321, 1249, 1187, 1062, 906, 844, 734 cm-1
.
1H
NMR (300 MHz, CDCl3) δ 7.21 (d, J ) 5.15 Hz, 1 H), 7.064 (s,
7 H), 7.057 (s, 3 H), 7.045 (s, 2 H), 7.035 (s, 3 H), 6.90 (d, J )
5.17 Hz, 1 H), 2.71 (overlapping q, J ) 7.6 Hz, 32 H), 1.25-
1.24 (overlapping t, J ) 7.6 Hz, 48 H), 0.26 (s, 9 H). 13C NMR
(125 MHz, CDCl3) δ 150.30, 150.24, 150.08, 150.03, 133.02,
132.95, 132.87, 132.71, 132.63, 128.96, 128.86, 128.27, 127.39,
124.86, 124.37, 124.04, 123.92, 123.83, 119.79, 119.68, 119.56,
119.25, 119.05, 117.64, 90.08, 90.02, 89.79, 88.65, 87.57, 87.09,
23.62, 23.54, 23.41, 23.23, 15.13, 15.08, 15.01, 14.92, 14.68,
14.31, 0.33. UV (CH2Cl2) λmax 442 nm, ꢀmax 2.1 × 105. Laser
1460, 1321, 1264, 1187, 1061, 900, 844, 739 cm-1
.
1H NMR
desorption MS (sinapic acid matrix) M + 1 calcd for C131H106S16
-
Si + 1 at statistical isotopic maximum with two 13C: 2221.37.
Found 2219.98 ( 1.20. SEC: Mn ) 3950, Mw ) 4160.
(300 MHz, CDCl3) δ 7.21 (d, J ) 5.15 Hz, 1 H), 7.06 (s, 4 H),
7.04 (s, 2 H), 7.02 (s, 1 H), 6.90 (d, J ) 5.14 Hz, 1 H), 2.72
(overlapping q, J ) 7.6 Hz, 16 H), 1.26 (overlapping t, J ) 7.6
Hz, 24 H), 0.26 (s, 9 H). 13C NMR (125 MHz, CDCl3) δ 150.30,
150.24, 150.07, 150.03, 150.00, 133.00, 132.94, 132.85, 132.80,
132.63, 128.27, 127.40, 124.44, 124.40, 124.17, 132.95, 123.87,
123.85, 123.83, 123.73, 122.94, 120.47, 119.88, 119.83, 119.82,
119.80, 119.71, 119.29, 119.24, 119.06, 117.67, 117.66, 103.10,
97.04, 90.17, 90.13, 90.08, 89.83, 89.78, 88.69, 88.68, 87.62,
97.60, 87.19, 87.13, 87.10, 87.03, 86.40, 23.57, 23.44, 23.42,
23.26, 15.10, 15.03, 14.94, 14.71, 0.34. UV (CH2Cl2) λmax 432
nm, ꢀmax 2.5 × 105. LRMS calcd for C67H58S8Si at statistical
isotopic maximum with one 13C: 1147. Found: 1147. SEC:
Mn ) 1610, Mw ) 1660.
Iod in a ted Octa m er 20. See the preparation of 17 for the
synthetic protocol. Used were diisopropylamine (3.18 g, 4.4
mL, 31.4 mmol), ether (20 mL), n-butyllithium (16 mL, 23.8
mmol, 1.49 M in hexanes), 19 (1.00 g, 0.87 mmol) in ether (10
mL), iodine (6.48 g, 25.5 mmol) in ether (45 mL), and flash
chromatography (silica gel, 9:1 hexane/methylene chloride) to
1-Br om o-4-[(tr im eth ylsilyl)eth yn yl]ben zen e. See the
preparation of 19 for the synthetic protocol. Used were
1-bromo-4-iodobenzene (2.83 g, 10 mmol) in THF (15 mL),
(trimethylsilyl)acetylene (1.47 g, 2.10 mL, 15 mmol), bis-
(triphenylphosphine)palladium(II) chloride (0.21 g, 0.30 mmol),
copper(I) iodide (0.06 g, 0.30 mmol), and diisopropylamine (2.16
g, 3.00 mL, 21.42 mmol) for 1 day. The reaction was passed
through a silica gel plug to remove the catalyst using a 1:1
hexane/methylene chloride eluent. The solvent was removed
by rotary evaporation, and the residue was purified by gravity
chromatography (silica gel) using hexane as the eluent to
provide 0.62 g (24%) of the title product as a light yellow-brown
solid. IR (KBr) 2960, 2157, 1896, 1581, 1484, 1393, 1247, 1070,
1009, 846 cm-1
.
1H NMR (300 MHz, CDCl3) δ 7.41 (d, J )
8.39 Hz, 2 H), 7.31 (d, J ) 8.37 Hz, 2 H), 0.27 (s, 9 H). 13C
NMR (100 MHz, CDCl3) δ 133.38, 131.49, 122.79, 122.15,
103.97, 95.56, -0.03. HRMS calcd for C11H13BrSi: 251.9970.
Found: 251.9966.

1384 J . Org. Chem., Vol. 62, No. 5, 1997
Pearson and Tour
1-Br om o-4-eth yn ylben zen e (23). See the preparation of
21 for the synthetic protocol. Used were 1-bromo-4-[(trimeth-
ylsilyl)ethynyl]benzene (1.42 g, 5.61 mmol), methanol (10 mL),
and potassium carbonate (2.77 g, 20.04 mmol) for 5 h. No
purification was necessary to afford 1.00 g (98%) of the title
compound as a brown liquid. IR (film) 3267, 2976, 1902, 1584,
193.40, 149.51, 134.27, 134.24, 132.87, 131.95, 131.89, 128.29,
124.11, 123.87, 123.18, 95.69, 93.80, 84.00, 83.51, 30.31, 22.94,
14.51. HRMS calcd for C26H20O2S3: 460.0625. Found:
460.0631.
Cou p lin g of 20 w ith 23. See the preparation of 19 for the
synthetic protocol. Used were 20 (0.33 g, 0.26 mmol), THF (5
mL), 23 (0.18 g, 0.99 mmol), bis(triphenylphosphine)palla-
dium(II) chloride (0.022 g, 0.03 mmol), copper(I) iodide (0.006
g, 0.03 mmol), and N,N-diisopropylethylamine (0.37 g, 0.50
mL, 2.86 mmol) for 1 day. The residue was purified by silica
gel flash chromatography by first using hexane then slowly
increasing to a 9:1 hexane/methylene chloride to provide 0.26
g (77%) of the desired product as a yellow-orange solid. IR
1484, 1069, 821 cm-1 1H NMR (400 MHz, CDCl3) δ 7.44 (d,
.
J ) 8.45 Hz, 2 H), 7.33 (d, J ) 8.49 Hz, 2 H), 3.11 (s, 1 H). 13
C
NMR (100 MHz, CDCl3) δ 133.55, 131.60, 123.15, 121.06,
82.59, 78.37.
Mon ofu n ction a lized Mon om er 24. See the preparation
of 19 for the synthetic protocol. Used were 11 (1.02 g, 3.04
mmol), THF (5 mL), 23 (0.64 g, 3.54 mmol), bis(triphenylphos-
phine)palladium(II) chloride (0.063 g, 0.09 mmol), copper(I)
iodide (0.017 g, 0.09 mmol), and N,N-diisopropylethylamine
(0.74 g, 1.0 mL, 5.74 mmol) for 1 day. Gravity chromatography
(silica gel) using hexane as the eluent provided 1.01 g (86%)
of the title product as a yellow liquid. IR (neat) 2962, 2931,
(film) 2966, 2933, 2873, 2180, 2140, 1460, 843 cm-1
.
1H NMR
(400 MHz, CDCl3) δ 7.46 (d, J ) 8.45 Hz, 2 H), 7.34 (d, J )
8.41 Hz, 2 H), 7.05-7.01 (4 line m, 8 H), 2.72 (overlapping q,
J ) 7.6 Hz, 16 H), 1.26 (overlapping t, J ) 7.6 Hz, 24 H), 0.25
(s, 9 H).
2872, 2198, 2146, 1489, 1248, 1068, 1007, 842 cm-1
.
1H NMR
Com p ou n d 27. See the preparation of 21 for the synthetic
protocol. Used were the 20/23 coupled product (0.22 g, 0.17
mmol), methanol (5 mL), methylene chloride (5 mL), and
potassium carbonate (1.42 g, 10.3 mmol) for 5 h. No purifica-
tion was necessary to afford 0.20 g (96%) of the title compound
as a yellow-orange solid which, due to its oxidative instability,
was carried on immediately for the preparation of 29.
Cou p lin g of 21 w ith 1-Br om o-4-iod oben zen e. See the
preparation of 19 for the synthetic protocol. Used were 21
(0.18 g, 0.17 mmol), THF (5 mL), 1-bromo-4-iodobenzene (0.04
g, 0.14 mmol), bis(triphenylphosphine)palladium(II) chloride
(0.022 g, 0.03 mmol), copper(I) iodide (0.006 g, 0.03 mmol), and
N,N-diisopropylethylamine (0.37 g, 0.50 mL, 2.86 mmol) for 1
day. The residue was purified by silica gel flash chromatog-
raphy by first using hexane and then slowly increasing to a
9:1 hexane/methylene chloride to provide 0.16 g (77%) of the
desired product as a yellow-orange solid. IR (film) 3074, 2960,
(400 MHz, CDCl3) δ 7.46 (d, J ) 8.60 Hz, 2 H), 7.33 (d, J )
8.61 Hz, 2 H), 7.01 (s, 1 H), 2.66 (q, J ) 7.60 Hz, 2 H), 1.21 (t,
J ) 7.65 Hz, 3 H), 0.25 (s, 9 H). 13C NMR (100 NMR, CDCl3)
δ 149.84, 132.81, 132.46, 131.67, 122.84, 122.60, 121.66,
119.85, 102.44, 96.58, 92.41, 83.81, 22.79, 14.24, -0.11. HRMS
calcd for C19H19BrSSi: 386.0160. Found: 386.0150. Anal.
Calcd for C19H19BrSSi: C, 59.07; H, 4.92. Found: C, 58.82;
H, 5.01.
2-[(4′-Br om op h e n yl)e t h yn yl]-4-e t h yl-5-e t h yn ylt h io-
p h en e. See the preparation of 21 for the synthetic protocol.
Used were 24 (1.01 g, 2.61 mmol), methanol (5 mL), methylene
chloride (5 mL), and potassium carbonate (1.60 g, 11.58 mmol)
for 5 h. No purification was necessary to afford 0.79 g (96%)
of the title compound as a brown liquid. IR (neat) 3298, 2968,
2933, 2874, 2204, 2098, 1899, 1487, 1393, 1085, 1068, 1010,
846 cm-1 1H NMR (400 MHz, CDCl3) δ 7.46 (d, J ) 8.48 Hz,
.
2 H), 7.33 (d, J ) 8.47, 2 H), 7.03 (s, 1 H), 3.47 (s, 1 H), 2.68
(q, J ) 7.60 Hz, 2 H), 1.21 (t, J ) 7.60 Hz, 3 H). 13C NMR
(100 MHz, CDCl3) δ 150.25, 132.83, 132.41, 131.70, 123.10,
122.94, 121.57, 118.53, 92.49, 84.37, 83.58, 76.03, 22.75, 14.43.
Dibr om o Difu n ction a lized Mon om er 25. See the prepa-
ration of 19 for the synthetic protocol. Used were 2-[(4′-
bromophenyl)ethynyl]-4-ethyl-5-ethynylthiophene (0.79 g, 2.51
mmol), THF (5 mL), 1-bromo-4-iodobenzene (1.45 g, 5.13
mmol), bis(triphenylphosphine)palladium(II) chloride (0.056 g,
0.08 mmol), copper(I) iodide (0.015 g, 0.08 mmol), and diiso-
propylamine (1.08 g, 1.50 mL, 10.71 mmol) for 1 day. Gravity
chromatography (silica gel) using hexane as the eluent pro-
vided 0.94 g (80%) of the title product as a yellow solid. IR
(film) 2960, 2202, 1631, 1530, 1481, 1391, 1064, 1003, 818
2932, 2872, 2181, 1460, 1069, 843 cm-1
.
1H NMR (400 MHz,
CDCl3) δ 7.47 (d, J ) 8.43 Hz, 2 H), 7.35 (d, J ) 8.45 Hz, 2 H),
7.21 (d, J ) 5.15 Hz, 1 H), 7.06 (s, 5 H), 7.04 (s, 2 H), 6.90 (d,
J ) 5.14 Hz, 1 H), 2.72 (overlapping q, J ) 7.60 Hz, 16 H),
1.26 (overlapping t, J ) 7.60 Hz, 24 H). 13C NMR (100 MHz,
CDCl3) δ 152.39, 149.89, 149.84, 149.67, 149.63, 149.34, 132.80,
132.72, 132.61, 132.54, 132.45, 132.23, 131.70, 127.87, 126.99,
123.44, 123.04, 122.78, 121.85, 119.70, 119.39, 117.25, 89.70,
89.40, 88.27, 87.17, 86.69, 23.15, 23.02, 22.97, 22.68, 14.68,
14.61, 14.52, 14.15.
Com p ou n d 28. See the preparation of 17 for the synthetic
protocol. Used were diisopropylamine (1.59 g, 2.2 mL, 15.71
mmol) in THF (2 mL), n-butyllithium (8.5 mL, 12.83 mmol,
1.51 M in hexanes), the 21/1-bromo-4-iodobenzene-coupled
product (0.28 g, 0.23 mmol) in ether (10 mL), and iodine (3.50
g, 13.79 mmol) in ether (40 mL). The residue was purified by
silica gel flash chromatography by first using hexane and then
slowly increasing to a 9:1 hexane/methylene chloride eluent
to provide 0.25 g (81%) of the title product as an reddish-orange
solid.
cm-1
.
1H NMR (400 MHz, CDCl3) δ 7.47 (d, J ) 8.53 Hz, 2
H), 7.46 (d, J ) 8.53 Hz, 2 H), 7.35 (d, J ) 8.55 Hz, 2 H), 7.34
(d, J ) 8.55 Hz, 2 H), 7.07 (s, 1 H), 2.73 (q, J ) 7.60 Hz, 2 H),
1.26 (t, J ) 7.60 Hz, 3 H). 13C NMR (100 MHz, CDCl3) δ
149.30, 132.82, 132.74, 132.72, 131.71, 123.14, 122.92, 122.78,
121.84, 121.62, 119.49, 95.37, 92.92, 83.81, 83.00, 22.95, 14.53.
HRMS calcd for C22H14Br2S: 467.9183. Found: 467.9186.
Dith ioester F u n ction a lized Mon om er 26. To a solution
of 25 (0.04 g, 0.085 mmol) in ether (2 mL) at -78 °C was added
dropwise tert-butyllithium (1.0 mL, 2.1 mmol, 2.1 M in
hexanes). The solution was stirred at -78 °C for 15 min.
Sulfur powder (0.08 g, 2.5 mmol) was added as a solid, and
the reaction was warmed to 0 °C for 30 min.16 The solution
was recooled to -78 °C, and acetyl chloride (3.31 g, 3.0 mL,
4.22 mmol) was added in one portion. The solution was
allowed to warm to room temperature overnight. The mixture
was extracted with methylene chloride and dried over mag-
nesium sulfate. The solvent was removed by rotary evapora-
tion, and the residue was purified by silica gel flash chroma-
tography using a 9:1 hexane/methylene chloride and finally a
7:3 hexane/methylene chloride eluent to provide 0.01 g (25%)
of the title product as a yellow-brown solid. IR (film) 2925,
1H NMR (400 MHz, CDCl3) δ 7.47 (d, J ) 8.48 Hz, 2
H), 7.35 (d, J ) 8.55 Hz, 2 H), 7.06 (s, 4 H), 7.03 (s, 4 H), 2.71
(overlapping q, J ) 7.6 Hz, 16 H), 1.25 (overlapping t, J ) 7.6
Hz, 24 H).
Com p ou n d 29. See the preparation of 19 for the synthetic
protocol. Used were 28 (0.23 g, 0.18 mmol), THF (1.0 mL), 27
(0.08 g, 0.06 mmol), bis(triphenylphosphine)palladium(II)
chloride (0.004 g, 0.006 mmol), copper(I) iodide (0.002 g, 0.01
mmol), and N,N-diisopropylethylamine (0.370 g, 0.40 mL, 2.30
mmol) for 1 day. The residue was purified by silica gel flash
chromatography by first using hexane and then slowly in-
creasing to a 9:1 hexane/methylene chloride eluent then a 7:3
hexane/methylene chloride eluent to provide 0.01 g (55%) of
the title product as a yellow-orange solid. 1H NMR (400 MHz,
CDCl3) δ 7.46 (d, J ) 8.41 Hz, 4 H), 7.34 (d, J ) 8.42 Hz, 4 H),
7.07 (s, 4 H), 7.06 (s, 10 H), 7.04 (s, 2 H), 2.72 (overlapping q,
J ) 7.6 Hz, 32 H), 1.26 (overlapping t, J ) 7.6 Hz, 48 H). 13C
NMR (100 MHz, CDCl3) δ 149.67, 132.95, 132.80, 132.69,
132.61, 131.70, 123.41, 119.39, 89.69, 86.66, 23.20, 23.00,
22.66, 14.72, 14.51, 14.13, 13.90.
2860, 1712, 1591, 1198, 1116, 1022, 958, 836 cm-1
.
1H NMR
(400 MHz, CDCl3) δ 7.52 (d, J ) 8.35 Hz, 2 H), 7.51 (d, J )
8.42 Hz, 2 H), 7.38 (d, J ) 8.37 Hz, 2 H), 7.37 (d, J ) 8.41 Hz,
2 H), 7.09 (s, 1 H), 2.73 (q, J ) 7.60 Hz, 2 H), 2.42 (s, 6 H),
1.25 (t, J ) 7.59 Hz, 3 H). 13C NMR (100 MHz, CDCl3) δ
1-Iod o-4-t h ioa cet ylben zen e (30). To a solution of 1,4-
diiodobenzene (4.95 g, 17.5 mmol) in ether (2 mL) at -78 °C

Rapid Syntheses of Oligo(2,5-thiophene ethynylene)s
J . Org. Chem., Vol. 62, No. 5, 1997 1385
was added dropwise tert-butyllithium (16 mL, 33 mmol, 2.10
M in hexanes). The solution was stirred at -78 °C for 5 min.
Sulfur powder (0.08 g, 2.5 mmol) in THF (75 mL) at 0 °C was
added, and the reaction was warmed to 0 °C for 30 min.16 The
solution was recooled to -78 °C, and acetyl chloride (1.77 g,
1.6 mL, 22.5 mmol) was added in one portion. The solution
was allowed to warm to room temperature overnight. The
mixture was extracted with methylene chloride and dried over
magnesium sulfate. The solvent was removed by rotary
evaporation, and the residue was purified by silica gel flash
chromatography using a 25:1 hexane-ether eluent to provide
2.34 g (56%) of the title product as a yellowish white solid. IR
chromatography by first using hexane and then slowly in-
creasing to 9:1 hexane/methylene chloride and finally 7:3
hexane/methylene chloride to provide 0.20 g (68%) of the title
product as a yellowish-brown liquid. IR (neat) 3103, 2967,
2932, 2193, 1710, 1591, 1120, 827 cm-1
.
1H NMR (300 MHz,
CDCl3) δ 7.52 (d, J ) 8.34 Hz, 2 H), 7.38 (d, J ) 8.29 Hz, 2 H),
7.21 (d, J ) 5.16 Hz, 1 H), 7.05 (s, 1 H), 6.90 (d, J ) 5.16 Hz,
1 H), 2.76 (q, J ) 7.57 Hz, 2 H), 2.73 (q, J ) 7.53 Hz, 2 H),
1.26 (t, J ) 7.56 Hz, 3 H), 1.25 (t, J ) 7.61 Hz, 3 H). 13C NMR
(100 MHz, CDCl3) δ 193.31, 149.81, 149.47, 134.24, 132.24,
131.85, 128.27, 127.85, 126.92, 124.18, 123.64, 119.13, 117.25,
95.59, 88.89, 83.61, 30.27, 22.96, 14.64, 14.50. HRMS calcd
for C24H20OS3: 420.0676. Found: 420.0674.
1
(film) 3080, 1907, 1694, 1466, 1382, 1122, 1005, 811 cm-1. H
NMR (400 MHz, CDCl3) δ 7.72 (d, J ) 8.35 Hz, 2H), 7.11 (d,
J ) 8.35 Hz, 2 H), 2.40 (s, 3 H). 13C NMR (100 MHz, CDCl3)
δ 193.10, 138.36, 135.94, 127.79, 95.93, 30.25. HRMS calcd
for C8H7IOS: 277.9262. Found: 277.9272. Anal. Calcd for
C8H7IOS: C, 34.53; H, 2.52. Found: C, 34.67; H: 2.42.
1-Th ioa cetyl-4-[(tr im eth ylsilyl)eth yn yl]ben zen e. See
the preparation of 19 for the synthetic protocol. Used were
30 (1.11 g, 3.99 mmol), THF (5.0 mL), (trimethylsilyl)acetylene
(0.58 g, 0.84 mL, 5.90 mmol), bis(triphenylphosphine)palla-
dium(II) chloride (0.14 g, 0.2 mmol), copper iodide (0.04 g, 0.02
mmol), and N,N-diisopropylethylamine (0.83 g, 1.12 mL, 6.42
mmol) for 1 day. The residue was purified by silica gel flash
chromatography by first using hexane and then slowly in-
creasing to 9:1 hexane/methylene chloride to provide 0.88 g
(89%) of the title product as an off-white solid. IR (neat) 2960,
Com p ou n d 34. See the preparation of 19 for the synthetic
protocol. Used were 18 (0.85 g, 1.58 mmol), THF (1.0 mL), 30
(0.28 g, 1.01 mmol), bis(triphenylphosphine)palladium(II)
chloride (0.01 g, 0.02 mmol), copper iodide (0.002 g, 0.01 mmol),
and N,N-diisopropylethylamine (0.37 g, 0.50 mL, 2.87 mmol)
for 1 day. The residue was purified by silica gel flash
chromatography by first using hexane then slowly increasing
to 9:1 hexane/methylene chloride and finally 7:3 hexane/
methylene chloride to provide 0.37 g (54%) of the title product
as a reddish-brown liquid. IR (neat) 2968, 2933, 2874, 2249,
2194, 1709, 1460, 1120, 907, 827 cm-1
.
1H NMR (400 MHz,
CDCl3) δ 7.52 (d, J ) 8.21 Hz, 2 H), 7.38 (d, J ) 8.19 Hz, 2 H),
7.20 (d, J ) 5.12 Hz, 1 H), 7.07 (s, 1 H), 7.06 (s, 1 H), 7.04 (s,
1 H), 6.90 (d, J ) 5.13 Hz, 1 H), 2.74 (overlapping q, J ) 7.6
Hz, 8 H), 2.42 (s, 3 H), 1.25 (overlapping t, J ) 7.6 Hz, 12 H).
13C NMR (100 MHz, CDCl3) δ 193.33, 149.85, 149.64, 149.63,
149.54, 134.26, 132.62, 132.55, 132.23, 131.87, 128.33, 127.86,
126.97, 124.10, 123.94, 123.45, 123.12, 119.29, 118.83, 117.21,
95.86, 89.59, 89.33, 88.21, 87.10, 86.68, 86.42, 83.52, 30.28,
22.98, 22.95, 14.65, 14.50. HRMS calcd for C40H32OS5: 688.1057.
Found: 688.1046.
2159, 1713, 1484, 1250, 864 cm-1
.
1H NMR (300 MHz, CDCl3)
δ 7.46 (d, J ) 8.10 Hz, 2 H), 7.33 (d, J ) 8.07 Hz, 2 H), 2.40
(s, 3 H), 0.23 (s, 9 H). 13C NMR (100 MHz, CDCl3) δ 193.28,
134.04, 132.49, 128.32, 124.36, 104.15, 96.20, 30.24, -0.13.
HRMS calcd for C13H16OSSi: 248.0691. Found: 248.0694.
Anal. Calcd for C13H16OSSi: C, 62.90; H, 6.45. Found: C,
62.66; H, 6.19.
Com p ou n d 35. See the preparation of 19 for the synthetic
protocol. Used were 21 (0.20 g, 0.19 mmol), THF (0.5 mL), 30
(0.03 g, 0.11 mmol), bis(triphenylphosphine)palladium(II)
chloride (0.01 g, 0.02 mmol), copper iodide (0.002 g, 0.01 mmol),
and N,N-diisopropylethylamine (0.37 g, 0.50 mL, 2.87 mmol)
for 1 day. The residue was purified by silica gel flash
chromatography by first using hexane and then slowly in-
creasing to 9:1 hexane/methylene chloride and finally 7:3
hexane/methylene chloride to provide 0.03 g (22%) of the title
product as a yellow-orange film. IR (film) 2966, 2931, 2872,
4-Eth yn yl-1-th ioa cetylben zen e (31). To a solution of
1-thioacetyl-4-[(trimethylsilyl)ethynyl]benzene (0.17 g, 0.69
mmol) in THF (2 mL) at 0 °C were added acetic acid (0.01 g,
0.01 mL, 0.167 mmol) and acetic anhydride (0.01 g, 0.01 mL,
0.10 mmol) followed by the dropwise addition of tetrabutyl-
ammonium fluoride (2.88 g, 3.20 mL, 11.03 mmol). The
solution was allowed to warm to room temperature for 5 min.
The reaction was run through a silica gel plug to remove the
solid impurities. The solvent was removed by rotary evapora-
tion. No further purification was necessary to afford 0.20 g
(96%) of the title compound as a yellow-orange solid. IR (film)
2181, 1709, 1459, 1186, 1118, 903, 842 cm-1
.
1H NMR (400
MHz, CDCl3) δ 7.52 (d, J ) 8.50 Hz, 2 H), 7.38 (d, J ) 8.50
Hz, 2 H), 7.21 (d, J ) 5.19 Hz, 1 H), 7.07 (s, 1 H), 7.065 (s, 3
H), 7.058 (s, 1 H), 7.04 (s, 1 H), 6.90 (d, J ) 5.16 Hz, 1 H),
2.71 (overlapping q, J ) 7.6 Hz, 16 H), 2.42 (s, 3 H), 1.25
(overlapping t, J ) 7.6 Hz, 24 H).
3288, 2924, 1708, 1483, 1398, 1353, 1126, 951, 829 cm-1
.
1H
NMR (300 MHz, CDCl3) δ 7.50 (d, J ) 8.46 Hz, 2 H), 7.35 (d,
J ) 8.55 Hz, 2 H), 3.13 (s, 1 H), 2.41 (s, 3 H). 13C NMR (75
MHz, CDCl3) δ 193.26, 134.18, 132.73, 128.80, 123.35, 82.84,
78.85, 30.31. LRMS calcd for C10H8OS: 176. Found: 176.
Com p ou n d 32. See the preparation of 19 for the synthetic
protocol. Used were 12 (0.22 g, 1.61 mmol), THF (2.0 mL), 30
(0.29 g, 1.04 mmol), bis(triphenylphosphine)palladium(II)
chloride (0.041 g, 0.06 mmol), copper iodide (0.013 g, 0.07
mmol), and N,N-diisopropylethylamine (0.374 g, 1.0 mL, 5.74
mmol) for 1 day. The residue was purified by silica gel flash
chromatography by first using hexane and then slowly in-
creasing to 9:1 hexane/methylene chloride and finally 7:3
hexane/methylene chloride to provide 0.16 g (54%) of the title
product as a yellow-orange solid. IR (neat) 3103, 2967, 2932,
2873, 2201, 1709, 1592, 1486, 1459, 1396, 1258, 1117, 1015,
Com p ou n d 36. See the preparation of 19 for the synthetic
protocol. Used were 14 (0.14 g, 0.30 mmol), THF (0.5 mL), 31
(0.06 g, 0.34 mmol), bis(triphenylphosphine)palladium(II)
chloride (0.01 g, 0.02 mmol), copper iodide (0.003 g, 0.02 mmol),
and N,N-diisopropylethylamine (0.37 g, 0.50 mL, 2.87 mmol)
for 1 day. The residue was purified by silica gel flash
chromatography by first using hexane then slowly increasing
to 9:1 hexane/methylene chloride and finally 7:3 hexane/
methylene chloride to provide 0.03 g (19%) of the title product
as a yellow liquid. IR (neat) 2966, 2140, 1712, 1488, 1457,
1250, 1121, 1016, 949, 844 cm-1
.
1H NMR (300 MHz, CDCl3)
δ 7.51 (d, J ) 8.45 Hz, 2 H), 7.38 (d, J ) 8.45 Hz, 2 H), 7.07
(s, 1 H), 7.01 (s, 1 H), 2.70 (q, J ) 7.58 Hz, 2 H), 2.66 (q, J )
7.56 Hz, 2 H), 2.42 (s, 3 H), 1.21 (t, J ) 7.65 Hz, 3 H), 0.24 (s,
9 H). 13C NMR (100 MHz, CDCl3) δ 193.20, 149.89, 149.55,
134.21, 132.84, 132.41, 131.94, 128.53, 123.84, 123.41, 122.51,
120.03, 119.37, 102.65, 96.60, 93.41, 89.56, 85.94, 84.30, 30.28,
22.97, 22.83, 14.49, 14.28, -0.08. HRMS calcd for C29H28OS3-
Si: 516.1072. Found: 516.1066.
Com p ou n d 37. See the preparation of 19 for the synthetic
protocol. Used were 17 (1.83 g, 2.49 mmol), THF (3 mL), 31
(0.47 g, 2.67 mmol), bis(triphenylphosphine)palladium(II)
chloride (0.07 g, 0.1 mmol), copper(I) iodide (0.02 g, 0.01 mmol),
and N,N-diisopropylethylamine (0.74 g, 1.00 mL, 5.72 mmol)
for 2 days. The residue was purified by silica gel flash
chromatography by first using hexane then slowly increasing
950, 827 cm-1
.
1H NMR (300 MHz, CDCl3) δ 7.51 (d, J ) 8.54
Hz, 2 H), 7.37 (d, J ) 8.51 Hz, 2 H), 7.20 (d, J ) 5.17 Hz, 1 H),
6.90 (d, J ) 5.17 Hz, 1 H), 2.77 (q, J ) 7.60 Hz, 2 H), 2.42 (s,
3 H), 1.25 (t, J ) 7.60 Hz, 3 H). 13C NMR (100 MHz, CDCl3)
δ 193.35, 149.63, 134.25, 131.82, 127.99, 127.88, 126.65,
124.57, 117.51, 94.63, 84.14, 30.27, 22.98, 14.70. HRMS calcd
for C16H14OS2: 286.0486. Found: 286.0496. Anal. Calcd for
C16H14OS2: C, 67.13; H, 4.89. Found: C, 66.87; H: 4.91.
Com p ou n d 33. See the preparation of 19 for the synthetic
protocol. Used were 15 (0.26 g, 0.196 mmol), THF (0.5 mL),
30 (0.19 g, 0.70 mmol), bis(triphenylphosphine)palladium(II)
chloride (0.014 g, 0.02 mmol), copper iodide (0.004 g, 0.02
mmol), and N,N-diisopropylethylamine (0.21 g, 0.28 mL, 1.62
mmol) for 1 day. The residue was purified by silica gel flash

1386 J . Org. Chem., Vol. 62, No. 5, 1997
Pearson and Tour
to a 9:1 hexane/methylene and then a 7:3 hexane/methylene
chloride eluent to provide 0.48 g (25%) of the title product as
a yellow-brown liquid. IR (film) 2967, 2933, 2874, 2184, 2140,
H), 7.380 (d, J ) 8.34 Hz, 2 H), 7.08 (s, 1 H), 7.07 (s, 1 H),
7.06 (s, 6 H), 2.71 (overlapping q, J ) 7.6 Hz, 16 H), 2.422 (s,
3 H), 2.420 (s, 3 H), 1.25 (overlapping t, J ) 7.6 Hz, 24 H). 13
C
1712, 1460, 1249, 1121, 845 cm-1
.
1H NMR (300 MHz, CDCl3)
NMR (125 MHz, CDCl3) δ 193.68, 193.63, 150.08, 150.04,
149.93, 134.64, 134.60, 133.24, 133.02, 132.34, 132.26, 128.93,
128.76, 124.50, 124.24, 123.92, 123.81, 119.81, 119.77, 119.75,
119.69, 93.83, 90.04, 87.01, 83.91, 30.67, 30.09, 23.38, 23.35,
14.88.
δ 7.51 (d, J ) 8.32 Hz, 2 H), 7.38 (d, J ) 8.29 Hz, 2 H), 7.082
(s, 1 H), 7.062 (s, 1 H), 7.056 (s, 1 H), 7.010 (s, 1 H), 2.71
(overlapping q, J ) 7.6 Hz, 8 H), 2.42 (s, 3 H), 1.25 (overlapping
t, J ) 7.6 Hz, 12 H), 0.24 (s, 9 H). 13C NMR (100 MHz, CDCl3)
δ 193.26, 149.90, 149.64, 149.60, 134.22, 132.86, 132.63,
132.40, 131.94, 128.52, 123.83, 123.52, 123.40, 123.29, 122.50,
120.03, 119.44, 119.37, 119.30, 102.67, 96.60, 93.48, 89.73,
89.67, 89.51, 86.65, 86.59, 85.96, 84.30, 30.30, 23.00, 22.83,
22.68, 14.53, 14.30, 14.17, -0.07. HRMS calcd for C45H40OS5-
Si: 784.1452. Found: 784.1440.
Com p ou n d 41. See the preparation of 19 for the synthetic
protocol. Used were 18 (1.42, 2.64 mmol), THF (2.5 mL), 2,5-
diiodothiophene18 (0.38 g, 1.1 mmol), bis(triphenylphosphine)-
palladium(II) chloride (0.07 g, 0.1 mmol), copper iodide (0.008
g, 0.04 mmol), and diisopropylamine (0.74 g, 1.0 mL, 5.74
mmol) for 1 day. The residue was purified by gravity chro-
matography (silica gel) using a 9:1 hexane/methylene chloride
eluent to provide 0.89 g (68%) of the title product as a yellow-
orange solid. IR (film) 3101, 2966, 2930, 2872, 2183, 1459,
Com p ou n d 38. See the preparation of 19 for the synthetic
protocol. Used were 20 (0.23 g, 0.18 mmol), THF (0.5 mL), 31
(0.09 g, 0.50 mmol), bis(triphenylphosphine)palladium(II)
chloride (0.01 g, 0.02 mmol), copper iodide (0.002 g, 0.01 mmol),
and N,N-diisopropylethylamine (0.37 g, 0.50 mL, 2.87 mmol)
for 1 day. The residue was purified by silica gel flash
chromatography by first using hexane and then slowly in-
creasing to 9:1 hexane/methylene chloride and finally 7:3
hexane/methylene chloride to provide 0.15 g (63%) of the title
product as a yellow-orange solid. IR (neat) 2967, 2933, 2140,
1188, 1060, 842 cm-1 1H NMR (400 MHz, CDCl3) δ 7.21 (d,
.
J ) 5.14 Hz, 2 H), 7.15 (s, 2 H), 7.07 (s, 2 H), 7.06 (s, 2 H),
7.05 (s, 2 H), 6.91 (d, J ) 5.14 Hz, 2 H), 2.73 (overlapping q,
J ) 7.6 Hz, 16 H), 1.26 (overlapping t, J ) 7.6 Hz, 24 H). 13C
NMR (100 MHz, CDCl3) δ 149.86, 149.82, 149.71, 149.65,
132.62, 132.56, 132.24, 132.09, 127.88, 127.01, 124.61, 123.98,
123.56, 119.26, 119.23, 118.86, 117.24, 89.61, 89.40, 89.27,
88.27, 87.18, 86.98, 86.77, 23.03, 23.01, 22.70, 14.70, 14.55,
14.18. LRMS calcd for C68H52S9: 1156. Found: 1156.
1711, 1459, 1249, 904, 843 cm-1 1H NMR (300 MHz, CDCl3)
.
δ 7.51 (d, J ) 8.50 Hz, 2 H), 7.38 (d, J ) 8.54 Hz, 2 H), 7.08
(s, 1 H), 7.06 (s, 5 H), 7.05 (s, 1 H), 7.01 (s, 1 H), 2.69
(overlapping q, J ) 7.6 Hz, 16 H), 2.42 (s, 3 H), 1.23
(overlapping t, J ) 7.6 Hz, 24 H), 0.25 (s, 9 H). 13C NMR (100
MHz, CDCl3) δ 193.22, 149.89, 149.67, 134.20, 132.84, 132.61,
132.39, 131.94, 128.52, 123.83, 123.41, 119.37, 89.66, 86.64,
30.28, 23.19, 22.99, 22.81, 14.71, 14.49, 14.26, 13.89, -0.10.
Com p ou n d 42. See the preparation of 17 for the synthetic
protocol. Used were n-butyllithium (16 mL, 25.0 mmol, 1.56
M in hexanes), diisopropylamine (5.06 g, 7.0 mL, 50.0 mmol)
in ether (5.0 mL), 41 (0.90 g, 0.78 mmol) in ether (30 mL),
and iodine (12.94 g, 51.0 mmol) in ether (80 mL). The residue
was purified by silica gel flash chromatography using a 9:1
hexane/methylene chloride eluent to provide 0.99 g of the title
product as a red-orange solid that was 90% pure by spectral
analysis. IR (film) 2965, 2929, 2871, 2184, 1459, 1262, 1185,
Desilyla tion of 38. To a solution of 38 (0.11 g, 0.08 mmol)
in THF (1 mL) at 0 °C was added acetic acid (0.01g, 0.01 mL,
0.18 mmol) followed by tetra-n-butylammonium fluoride (0.36
g, 0.40 mL, 1.38 mmol). The solution was allowed to warm to
23 °C for 5 min. The reaction mixture was run through a silica
gel plug using 1:1 hexane/methylene chloride eluent. The
solvent was removed by rotary evaporation. No further
purification was necessary to afford 0.07 g (67%) of the title
compound as a yellow-orange solid. IR (film) 3298, 2966, 2932,
1061, 902, 841, 801, 739 cm-1 1H NMR (400 MHz, CDCl3) δ
.
7.08 (s, 2 H), 7.06 (s, 3 H), 7.04 (s, 5 H), 2.71 (overlapping q,
J ) 7.6 Hz, 16 H), 1.25 (overlapping t, J ) 7.6 Hz, 24 H).
Desilyla tion of 37. See the desilylation of 38 for the
synthetic protocol. Used were acetic acid (0.01 g, 0.01 mL,
0.18 mmol), 37 (0.11 g, 0.14 mmol), THF (5.0 mL), and
tetrabutylammonium fluoride (2.71 g, 3.0 mL, 10.36 mmol).
The solution was allowed to warm to 23 °C over 8 min. The
reaction mixture was passed through a silica gel plug to
remove the solid impurities using a 1:1 hexane/methylene
chloride eluent. The solvent was removed by rotary evapora-
tion to afford the desired compound (0.10 g, 100%) as a brown
liquid. IR (neat) 3298, 2967, 2932, 2874, 2184, 2097, 1710,
2872, 2183, 2096, 1711, 1186, 903, 843 cm-1
.
1H NMR (300
MHz, CDCl3) δ 7.51 (d, J ) 8.53 Hz, 2 H), 7.38 (d, J ) 8.55
Hz, 2 H), 7.08(s, 1 H), 7.06 (s, 6 H), 7.03 (s, 1 H), 3.48 (s, 1 H),
2.71 (overlapping q, J ) 7.6 Hz, 16 H), 2.42 (s, 3 H), 1.23
(overlapping t, J ) 7.6 Hz, 24 H).
Com p ou n d 39. See the preparation of 19 for the synthetic
protocol. Used were 20 (0.18 g, 0.14 mmol), THF (1.0 mL),
desilylated 38 (0.08 g, 0.06 mmol), bis(triphenylphosphine)-
palladium(II) chloride (0.004 g, 0.006 mmol), copper iodide
(0.002 g, 0.01 mmol), and N,N-diisopropylethylamine (0.30 g,
0.40 mL, 2.32 mmol) for 3 days. The residue was purified by
silica gel flash chromatography by first using hexane and then
slowly increasing to 9:1 hexane/methylene chloride and finally
7:3 hexane/methylene chloride to provide 0.01 g (10%) of the
title product as a yellow-orange solid. IR (neat) 2967, 2930,
2181, 2140, 1712, 1634, 1461, 1320, 1250, 1186, 1092, 1015,
1591, 1460, 1396, 1121, 845, 738 cm-1
.
1H NMR (400 MHz,
CDCl3) δ 7.51 (d, J ) 8.46 Hz, 2 H), 7.38 (d, J ) 8.52 Hz, 2 H),
7.08 (s, 1 H), 7.06 (s, 1 H), 7.05 (s, 1 H), 7.03 (s, 1 H), 3.49 (s,
1 H), 2.70 (overlapping q, J ) 7.60 Hz, 8 H), 2.42 (s, 3 H), 1.25
(overlapping t, J ) 7.60 Hz, 12 H). 13C NMR (100 MHz, CDCl3)
δ 193.32, 150.31, 149.68, 149.64, 134.22 (2C), 132.86, 132.63,
132.61, 132.36, 131.94 (2C), 128.51, 123.82, 123.52, 123.41,
123.38, 122.96, 119.34, 119.30, 118.71, 93.48, 89.63, 89.50,
89.46, 86.65, 86.62, 85.99, 84.60, 84.30, 76.02, 30.30, 23.00,
22.77, 14.52, 14.48, 14.16.
948, 902, 844 cm-1 1H NMR (400 MHz, CDCl3) δ 7.51 (d, J )
.
8.42 Hz, 2 H), 7.38 (d, J ) 8.46 Hz, 2 H), 7.08 (s, 3 H), 7.06 (s,
11 H), 7.01 (s, 2 H), 2.71 (overlapping q, J ) 7.6 Hz, 32 H),
2.42 (s, 3 H), 1.25-1.23 (overlapping t, J ) 7.6 Hz, 48 H), 0.24
(s, 9 H).
Com p ou n d 43. See the preparation of 19 for the synthetic
protocol. Used were desilylated 37 (0.10 g, 0.14 mmol), 42
(0.09 g, 0.06 mmol), THF (0.5 mL), bis(triphenylphosphine)-
palladium(II) chloride (0.084 g, 0.12 mmol), copper iodide
(0.089 g, 0.47 mmol), and N,N-diisopropylethylamine (0.37 g,
0.5 mL, 2.87 mmol) for 2 days. The residue was purified by
silica gel flash chromatography. The eluent was initially
hexane and then increased to 9:1 hexane/methylene chloride
to provide the title product (0.03 g, 20%) as a red-orange solid.
IR (film) 2966, 2936, 2880, 2188, 1712, 1466, 1192, 1128, 850
Com p ou n d 40. See the preparation of 19 for the synthetic
protocol. Used were desilylated 38 (0.07 g, 0.06 mmol), THF
(0.3 mL), 30 (0.03 g, 0.11 mmol), bis(triphenylphosphine)-
palladium(II) chloride (0.01 g, 0.02 mmol), copper iodide (0.002
g, 0.01 mmol), and N,N-diisopropylethylamine (0.07 g, 0.10
mL, 0.57 mmol) for 3 days. The residue was purified by silica
gel flash chromatography by first using hexane then slowly
increasing to 9:1 hexane/methylene chloride, followed by 7:3
hexane/methylene chloride and finally 6:4 hexane/methylene
chloride to provide 0.05 g (63%) of the title product as a yellow-
orange solid. IR (neat) 2966, 2930, 2180, 1712, 1459, 1119,
cm-1
.
1H NMR (400 MHz, CDCl3) δ 7.51 (d, J ) 8.24 Hz, 4
H), 7.38 (d, J ) 8.27 Hz, 4H), 7.08 (s, 5 H), 7.07 (s, 13 H), 2.71
(overlapping q, J ) 7.6 Hz, 32 H), 2.42 (s, 6 H), 1.25
(overlapping t, J ) 7.6 Hz, 48 H). 13C NMR (300 MHz, CDCl3)
δ 193.67, 152.80, 150.31, 150.12, 150.09, 150.05, 134.61,
133.24, 133.02, 132.87, 132.35, 128.91, 124.85, 124.24, 124.03,
123.92, 123.86, 123.81, 119.75, 119.67, 119.54, 119.04, 93.82,
843 cm-1
.
1H NMR (400 MHz, CDCl3) δ 7.518 (d, J ) 8.41
Hz, 2 H), 7.512 (d, J ) 8.43 Hz, 2 H), 7.384 (d, J ) 8.36 Hz, 2

Rapid Syntheses of Oligo(2,5-thiophene ethynylene)s
J . Org. Chem., Vol. 62, No. 5, 1997 1387
90.02, 89.95, 89.83, 87.24, 87.11, 87.01, 84.65, 30.68, 23.57,
23.51, 23.38, 15.08, 14.97, 14.87, 14.50, 14.27.
acetylene, FMC for a gift of alkyllithium reagents, and
Molecular Design Ltd. for the use of their synthetic data
base.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra for
compounds 6, 7, 9, 10, 19-29, 33-40, 41, and 43 (28 pages).
This material is contained in libraries on microfiche, im-
mediately follows this article in the microfilm version of the
journal, and can be ordered from the ACS see any current
masthead page for ordering information.
Ack n ow led gm en t. We thank J effry Schumm for the
preparation of compound 10. Initial phases of this work
were supported by the Office of Naval Research and the
National Science Foundation (EHR-91-08772, DMR-
9158315). The present work is supported by the De-
fense Advanced Research Projects Agency. We thank
Farchan Laboratories for a gift of (trimethylsilyl)-
J O962335Y