General synthesis of thiophene and selenophene-based heteroacenes

Article abstract of DOI:10.1021/ol0523650

(Chemical Equation Presented) A new intramolecular triple cyclization of bis(o-haloaryl)diacetylenes, via dilithiation followed by reaction with chalcogen elements, produces π-conjugated compounds containing heterole-1,2-dichalcogenin-heterole fused tricy

Full text of DOI:10.1021/ol0523650

ORGANIC
LETTERS
2005
Vol. 7, No. 23
5301-5304
General Synthesis of Thiophene and
Selenophene-Based Heteroacenes
Toshihiro Okamoto, Kenichi Kudoh, Atsushi Wakamiya, and
Shigehiro Yamaguchi*
Department of Chemistry, Graduate School of Science, Nagoya UniVersity,
and SORST, Japan Science and Technology Agency (JST), Chikusa,
Nagoya 464-8602, Japan
yamaguchi@chem.nagoya-u.ac.jp
Received September 30, 2005
ABSTRACT
A new intramolecular triple cyclization of bis(o-haloaryl)diacetylenes, via dilithiation followed by reaction with chalcogen elements, produces
-conjugated compounds containing heterole 1,2-dichalcogenin heterole fused tricyclic skeletons. The subsequent dechalcogenation with
copper metal affords a series of thiophene- and selenophene-based heteroacenes.
π
−
−
Fused polycyclic aromatic hydrocarbons (PAHs) are an
important class of molecules as fundamental skeletons for
functional organic materials.1 Their rigid π-conjugated
frameworks, free from conformational disorder, are a decisive
characteristic leading to unique electronic properties. A
representative example is a linearly fused acene such as
pentacene.2,3 The flat π-conjugated framework realizes
densely packed solid-state structures that are beneficial in
achieving high carrier mobility. This class of molecules is
currently among the most extensively investigated materials
for organic thin film transistors.4 In this context, thiophene-
and selenophene-based heteroacenes are also of interest,5-9
since the heteroatom effects not only on the electronic
structures but also on the solid-state structures10 would make
(4) (a) Dimitrakopoulos, C. D.; Malenfant, P. R. L. AdV. Mater. 2002,
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W.; Hintzsche, E.; Felicetti, M.; Spitzner, R.; Sieler, J.; Kempe, R. Angew.
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H.; Jende, T.; Spitzner, R.; Thondorf, I. Tetrahedron 1997, 53, 7509.
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10502.
(8) Oyaizu, K.; Iwasaki, T.; Tsukahara, Y.; Tsuchida, E. Macromolecules
2004, 37, 1257.
(9) Other thiophene-based heteroacenes: (a) Li,. X.-C.; Sirringhaus, H.;
Garnier, F.; Holmes, A. B.; Moratti, S. C.; Feeder, N.; Clegg, W.; Teat, S.
J.; Friend, R. J. J. Am. Chem. Soc. 1998, 120, 2206. (b) Rajca, R.; Wang,
H.; Pink, M.; Rajca, S. Angew. Chem., Int. Ed. 2000, 39, 4481. (c) Zhang,
X.; Matzger, A. J. J. Org. Chem. 2003, 68, 9813. (d) Nenajdenko, V. G.;
Sumerin, V. V.; Chernichenko, K. Y.; Balenkova, E. S. Org. Lett. 2004, 6,
3437.
(1) (a) Harvery, R. G. Polycyclic Aromatic Hydrocarbons; Wiley-VCH:
New York, 1997. (b) Watson, M. D.; Fechtenko¨tter, A.; Mu¨llen, K. Chem.
ReV. 2001, 101, 1267.
(2) (a) Nelson, S. F.; Lin, Y.-Y.; Gundlach, D. J.; Jackson, T. N. Appl.
Phys. Lett. 1998, 72, 1854. (b) Bre´das, J. L.; Calbert, J. P.; da Silva Filho;
D. A.; Cornil, J. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 5804. (c) Mattheus,
C. C.; de Wijs, G. A.; de Groot, R. A.; Palstra, T. T. M. J. Am. Chem. Soc.
2003, 125, 6323. (d) Bendikov, M.; Duong, H. M.; Starkey, K.; Houk, K.
N.; Carter, E. A.; Wudl, F. J. Am. Chem. Soc. 2004, 126, 7416.
(3) (a) Takahashi, T.; Kitamura, M.; Shen, B.; Nakajima, K. J. Am. Chem.
Soc. 2000, 122, 12876. (b) Anthony, J. E.; Brooks, J. S.; Eaton, D. A.;
Parkin, S. R. J. Am. Chem. Soc. 2001, 123, 9482. (c) Payne, M. M.; Parkin,
S. R.; Anthony, J. E. J. Am. Chem. Soc. 2005, 127, 8028. (d) Perepichka,
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S. H.; Lee, H. K.; Wang, Y. M.; Fu, N. Y.; Chen, X. M.; Cai Z. W.; Wong,
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124, 10638.
10.1021/ol0523650 CCC: $30.25
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carbon atoms of the diacetylene moiety, followed by trapping
with the remaining chalcogen element to afford a doubly
cyclized intermediate 5. Then, through the counterion
exchange of lithium with sodium by the addition of 1 M
NaOH aqueous solution, and in the final step, potassium
ferricyanide(III) is employed as an oxidant to convert 5 to
the target heteroacene, according to Schroth’s report.5 This
sequential procedure affords fused thiophene derivative 2a
or selenophene derivative 2b in good yields.
Scheme 1. General Scheme for the Synthesis of Heteroacenes
There are several features for the present cyclization: (1)
The cyclization proceeds via an anionic mechanism. This is
supported by a trapping of the intermediate 5 with benzyl
bromide, which produces a corresponding bis(benzylthio)
compound 6 in 69% yield. (2) There are two important
precedent reactions related to the present cyclization: that
is, the heteroannulation of (o-alkynylphenyl)thiolate to
benzothiophene via a 5-endo-dig cyclization11 and the
oxidation of 2,2′-bithiophene-3,3′-dithiolate to dithieno-fused
1,2-dithiin.5 Notably, the simple idea of employing of the
diacetylenic compound as a starting material allows us to
achieve the facile one-pot synthesis of the fused tricyclic
structure via the two aforementioned transformations. (3) The
present cyclization proceeds in a regiospecific manner. No
other regioisomer, in terms of the position of a six-membered
dichalcogenin ring, was obtained. (4) The cyclization pro-
ceeds well, not only with sulfur, but also with selenium. This
is the first synthesis of fused polycyclic diselenin compounds.
Scheme 2. Intramolecular Triple Cyclization
On the basis of this procedure, a series of fused 1,2-
dichalcogenin π-electron systems, including not only benzo-
annulated derivatives 2a-d, but also thieno- or benzothieno-
annulated derivatives 2e-g, were synthesized from appropriate
diacetylenes,12 as shown in Scheme 3.
them more attractive candidates. However, only a limited
number of this class of molecules have been reported to date,
such as dibenzo-annulated dithieno[3,2-b:2′,3′-d]thiophene,5
fused oligothiophenes consisting of five or seven thiophene
rings,6,7 and a fully fused polythiophene.8 This may be due
to a lack of useful synthetic routes in terms of efficiency as
well as accessible structural diversity. The exploration of
conceptually new methodology is thus a compelling subject
in this chemistry.
We now report a general and facile synthetic route to the
thiophene- and selenophene-containing heteroacenes based
on a new intramolecular triple cyclization of bis(o-haloaryl)-
diacetylenes 1, as shown in Scheme 1. This cyclization
constructs a heterole-1,2-dichalcogenin-heterole fused
tricyclic skeleton in one pot. The subsequent dechalcogena-
tion with copper metal5 produces a series of thiophene- and
selenophene-based heteroacenes. The structures and funda-
mental properties of the fused 1,2-dichalcogenin compounds
2 and the heteroacenes 3 are also described in this Letter.
A typical example of the intramolecular triple cyclization
with bis(o-bromophenyl)diacetylene 1a as a starting material
is shown in Scheme 2. This cyclization involves three
reaction steps. The first step is the dilithiation of 1a with
t-BuLi in THF, followed by trapping with a chalcogen
element (4 mol amounts) to produce a dianionic intermediate
4. In the second step, the dianion centers attack on the inner
Schroth has already reported the copper-mediated dechal-
cogenation from 1,2-dithiin 2a to 3a at high temperature.5a
In a similar manner, the produced 1,2-dichalcogenin deriva-
tives 2b-g were successfully converted into the correspond-
ing heteroacenes 3b-g (Scheme 3). Whereas some of the
dichalcogenin derivatives have very poor solubility, the
reaction can be conducted only by heating a mixture of
powdered 2 and Cu nanopowder (ca. 100 nm) without use
of any solvent. The reaction starts upon melting of the
dichalcogenin at ca. 250-350 °C and finishes within a few
minutes. The subsequent purification by recrystallization or
sublimation affords pure heteroacene compounds. The newly
produced heteroacenes 3 were identified with use of NMR
spectroscopies and elemental analysis, except for the seven-
ring-fused derivatives 3f and 3g, which have almost no
solubility toward common organic solvents at ambient
temperature and could not be chracterized by the NMR
spectroscopy. All the product compounds are very stable
toward heat and light and can be handled without special
care.
(11) For example, see: Takimiya, K.; Kunugi, Y.; Konda, Y.; Niihara,
N.; Otsubo, T. J. Am. Chem. Soc. 2004, 126, 5084.
(12) The starting diacetylenes were readily synthesized in three steps
from appropriate bromoiodoarenes, via the Pd/Cu-catalyzed coupling with
Me3SiCtCH, alkaline desilylation, and Cu-mediated homocoupling.
5302
Org. Lett., Vol. 7, No. 23, 2005

Scheme 3. Synthesis of a Series of Fused 1,2-Dichalcogenins and Heteroacenes
Among the produced compounds, the crystal structures
has a nearly coplanar structure. Notably, this compound
forms a herringbone packing structure that is very similar
to that of pentacene.14 Considering this similarity, the
investigation on their solid-state properties, such as a carrier
mobility, would give important information about the
structure-properties relationships.15 Further research along
this line is in progress.
of 2b and 3a have been determined by X-ray crystal-
lography.13 As shown in Figure 1, while the six-membered
1,2-diselenin ring is highly deviated from a planar structure
with a C-Se-Se-C dihedral angle of 52°, heteroacene 3a
The photophysical and electrochemical data for the fused
1,2-dichalocogenin compounds 2 and the heteroacenes 3 are
collected in Table 1.
In UV-visible absorption spectra, while the fused 1,2-
dichalcogenin π-systems 2 have weak absorption bands with
maximum wavelengths around 460-520 nm, together with
intense structureless π-π* transition bands with maxima
around 330-380 nm, the heteroacenes 3 show vibronic
π-π* transition bands with the longest absorption maxima
around 340-420 nm (for detailed data, see the Supproting
Information). For example, the absorption spectra of 2e and
3e are shown in Figure 2a. According to the preliminary
TDDFT calculation of 2e with 6-31G(d) basis sets (λcalc, 545
nm, f ) 0.1414), its long wavelength absorption band
observed at 473 nm is assignable to the transition from the
HOMO consisting of the n-π conjugation between the lone
pair electrons on the chalcogen element and the π-conjugated
framework (Figure 2c) to the LUMO mainly consisting of
the S-S σ* orbital.
(13) Crystallographic data: 2b: C16H8Se4, FW ) 516.06, crystal
dimensions 0.20 × 0.20 × 0.20 mm3, monoclinic, space group P21/a, a )
12.632(8) Å, b ) 7.864(4) Å, c ) 14.964(10) Å, â ) 101.258(7)°, V )
1457.8(15) Å3, Z ) 4, Dc ) 2.351 Mg m-3, µ(Mo KR) ) 10.050 mm-1
,
T ) 173(2) K, F(000) ) 960, 2θmax ) 50°. 8281 reflections measured, of
which 2467 were unique. Final R1 ) 0.0510 with wR2 ) 0.1309 for 2467
observed reflections with I > 2σ(I). 3a: C16H8S3, FW ) 296.40, crystal
dimensions 0.20 × 0.20 × 0.02 mm3, orthorhombic, space group Pnma, a
) 7.933(4) Å, b ) 26.589(15) Å, c ) 5.906(3) Å, V ) 1245.9(11) Å3, Z
) 4, Dc ) 1.580 Mg m-3, µ(Mo KR) ) 0.573 mm-1, T ) 173(2) K, F(000)
) 608, 2θmax ) 55°. 6907 reflections measured, of which 1110 were unique.
Final R1 ) 0.0417 with wR2 ) 0.0913 for 1110 observed reflections with
I > 2σ(I).
(14) Holmes. D.; Kumaraswamy, S.; Matzger, A. J.; Vollhardt, K. P. C.
Chem. Eur. J. 1999, 5, 3399.
(15) (a) Bre´das, J. L.; Calbert, J. P.; da Silva Filho, D. A.; Cornil, J.
Proc. Natl. Acad. Sci. 2002, 99, 5804. (b) Curtis, M. D.; Cao, J.; Kampf,
J. W. J. Am. Chem. Soc. 2004, 126, 4318.
Figure 1. ORTEP drawings of (a) 2b and (b) 3a (50% probability
for thermal ellipsoids) and (c) packing structure of 3a.
Org. Lett., Vol. 7, No. 23, 2005
5303

Table 1. Photophysical and Electrochemical Data for Fused
1,2-Dichalcogenins 2 and Heteroacenes 3
UV-vis absorptiona
redox potentialb
compd
λmax/nmc
log ꢀ
E1/2,ox1/V E1/2,ox2/V
Epc/V
2ad
2bd
2cd
2dd
2ed
2fe
2ge
3ad
3be
3ce
3dd
3ed
3f
468
498
473
471
473
480
516
344
356
356
350
370
399h
418h
3.41
2.12
3.56
3.49
3.81
3.99
3.51
4.51
4.56
4.43
4.59
4.65
3.98
3.08
+0.72
+0.64
+0.54
+0.87
+0.63
+0.67
+0.62
+0.99
(+0.90)g
(+0.43)g
+1.30
+0.68
i
+1.08
+1.03
+0.80
+1.22
+0.91
+1.02
+0.99
f
f
f
f
f
-1.54
-1.46
-1.51
-1.37
-1.46
-1.53
-1.45
f
f
f
f
f
3g
i
a In THF, unless otherwise stated. b Determined by cyclic voltammetry
(CV) under the following condition: Sample 1 mM; n-Bu4NPF6 (0.1 M)
in PhCN or o-dichlorobenzene. Potentials are given against the ferrocene/
ferrocenium couple (Fc/Fc+). While all reduction waves were irreversible,
all oxidation processes were reversible unless otherwise stated. c Only the
longest absorption maximum wavelengths are given. d CV measured in
PhCN. e CV measured in o-dichlorobenzene. f Not observed. g Irreversible
process. Oxidation peak potential (Epa) is given in the parentheses.
h Measured in CS2. i Could not be obtained due to poor solubiliy of the
sample.
Figure 2. Comparisons between fused 1,2-dichalcogenin com-
pound 2e (solid line) and heteroacene 3e (dashed line) in (a) UV-
vis absorption spectra in THF and in (b) cyclic voltammograms
and (c) Kohn-Sham HOMO of 2e calculated at the B3LYP/6-
31G(d) level.
In the cyclic voltammetry, both of the fused dichalcogenin
compounds 2 and heteroacenes 3 (except for 3b and 3c) show
reversible oxidation waves at rather low oxidation potentials.
For example, while 3e shows one reversible oxidation wave
at E1/2 ) +0.68 V (vs Fc/Fc+), 2e shows two reversible
oxidation waves at +0.63 and +0.91 V, as shown in Figure
2b. Considering the 1,2-dichalcogenin ring as the 8π-electron
system with two sets of lone pair electrons on the chalcogen
atoms, the redox stability of the 1,2-dichalcogenin systems
may be rationalized by thinking the aromatic stabilization
in the resultant two-electron oxidized 6π-electron species.
In both series of compounds 2a-d and 3a-d, the oxidation
potential can be tuned by the substituents R, while the
substituent effect is more significant in the heteroacenes
series. All these results indicate the potential utility of the
heteroacenes as well as the fused 1,2-dichalcogenin com-
pounds for the electronic applications.
Further studies on the applications of these materials to
electronic devices such as thin film transistors, as well as
the synthesis of more extended heteroacenes, are in progress
in our laboratory.
Acknowledgment. This work was supported by Grants-
in-Aid (Nos. 12CE2005 and 15205014) from the Ministry
of Education, Culture, Sports, Science, and Technology of
Japan, and SORST, Japan Science and Technology Agency.
T.O. thanks JSPS Research Fellowships for Young Scientists.
Supporting Information Available: Experimental pro-
cedures and spectral data for 1-3, and crystallographic data
for 2b and 3a in CIF format. This material is available free
of charge via the Internet at http://pubs.acs.org.
In summary, a new synthetic methodology based on the
intramolecular triple cyclization of bis(o-haloaryl)diacety-
lenes opens the door to the general synthesis of fused
dichalcogenin π-electron systems and heteroacenes. This
achievement will be relevant to further progress in this field.
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Org. Lett., Vol. 7, No. 23, 2005