Sequential electrophilic and photochemical cyclizations from bis(bithienyl)acetylene to a tetrathienonaphthalene core

Article abstract of DOI:10.1021/ol303107y

Photoirradiation of bis(bithienyl)acetylenes in the presence of iodine undergoes sequential electrophilic and photochemical cyclizations to produce tetrathienonaphthalenes (TTN) in one pot. The TTN framework is readily transformed into cruciform π-extended derivatives, which form ordered nano/microstructures.

Full text of DOI:10.1021/ol303107y

ORGANIC
LETTERS
2013
Vol. 15, No. 1
80–83
Sequential Electrophilic and
Photochemical Cyclizations from
Bis(bithienyl)acetylene to a
Tetrathienonaphthalene Core
Chuandong Dou, Shohei Saito, Libin Gao, Naoki Matsumoto, Takashi Karasawa,
Hongyu Zhang, Aiko Fukazawa, and Shigehiro Yamaguchi*
Department of Chemistry, Graduate School of Science, Nagoya University, and CREST,
Japan Science and Technology Agency, Furo, Chikusa, Nagoya 464-8602, Japan
yamaguchi@chem.nagoya-u.ac.jp
Received November 12, 2012
ABSTRACT
Photoirradiation of bis(bithienyl)acetylenes in the presence of iodine undergoes sequential electrophilic and photochemical cyclizations to
produce tetrathienonaphthalenes (TTN) in one pot. The TTN framework is readily transformed into cruciform π-extended derivatives, which form
ordered nano/microstructures.
Flatand rigid π-conjugated organicmolecules have been
extensively studied as promising materials for various
applications including organic light-emitting diodes, or-
ganic field-effect transistors, and organic photovoltaics.1
With the increasing demands for the two-dimensionally (2-D)
extended scaffolds with intriguing electronic structures as well
as favorable aggregation properties, a number of synthetic
methodologies have been developed for the preparation
of novel polycyclic π frameworks. The representative
methods are oxidative coupling between adjacent aro-
matic rings such as the Scholl reaction,2 transition-metal-
catalyzed intramolecular CꢀH arylations,3 and Mallory
photochemical cyclization.4 An alternative approach is
the cyclization of arylacetylenes triggered by oxidants,
acids, or electrophilic reagents including metal complexes.5
In particular, bis(biaryl)acetylenes are useful precursors
for the direct construction of polycyclic scaffolds (Figure 1).
For example, Swager and Yamaguchi reported the oxi-
dative cyclization of bis(biphenyl)acetylenes using SbCl5
as an oxidant, which doubly undergoes an electrophilic
(1) For recent reviews of flat and rigid π-conjugated systems, see: (a)
€
Grimsdale, A. C.; Mullen, K. Macromol. Rapid Commun. 2007, 28, 1676.
(b) Zang, L.; Che, Y.; Moore, J. S. Acc. Chem. Res. 2008, 41, 1596. (c)
Fukazawa, A.; Yamaguchi, S. Chem. Asian J. 2009, 4, 1386. (d) Skabara,
P. J. In Handbook of Thiophene-Based Materials; Perepichka, I. F.,
Perepichka, D. F., Eds.; Wiley-VCH: Weinheim, 2009; Vol. 1, 219. (e)
Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E. Adv. Mater. 2011,
23, 4347. (f) Chen, L.; Hernandez, Y.; Feng, X.; Mullen, K. Angew.
Chem., Int. Ed. 2012, 51, 7640.
(4) (a) Mallory, F. B.; Mallory, C. W. Organic Reactions; Wiley &
Sons: New York, 1984; Vol. 30, p 1. (b) Liu, L.; Yang, B.; Katz, T. J.;
Poindexter, M. K. J. Org. Chem. 1991, 56, 3769.
(5) (a) Larock, R. C.; Harrison, L. W. J. Am. Chem. Soc. 1984, 106,
4218. (b) Goldfinger, M. B.; Crawford, K. B.; Swager, T. M. J. Am.
Chem. Soc. 1997, 119, 4578. (c) Alonso, F.; Beletskaya, I. P.; Yus, M.
Chem. Rev. 2004, 104, 3079. (d) Yue, D.; Yao, T.; Larock, R. C. J. Org.
Chem. 2005, 70, 10292. (e) Soriano, E.; Marco-Contelles, J. Organome-
tallics 2006, 25, 4542. (f) Kashiki, T.; Shinamura, S.; Kohara, M.;
Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H. Org. Lett.
2009, 11, 2473. (g) Mehta, S.; Larock, R. C. J. Org. Chem. 2010, 75,
1652. (h) Godoi, B.; Schumacher, R. F.; Zeni, G. Chem. Rev. 2011, 111,
2937. (i) Hayashi, M.; Toshimitsu, F.; Sakamoto, R.; Nishihara, H.
J. Am. Chem. Soc. 2011, 133, 14518. (j) VanVeller, B.; Robinson, D.;
Swager, T. M. Angew. Chem., Int. Ed. 2012, 51, 1182.
€
(2) (a) Scholl, R.; Seer, C. Justus Liebigs Ann. Chem. 1912, 394, 111.
€
(b) Wu, J.; Pisula, W.; Mullen, K. Chem. Rev. 2007, 107, 718. (c) King,
B. T.; Kroulık, J.; Robertson, C. R.; Rempala, P.; Hilton, C. L.;
Korinek, J. D.; Gortari, L. M. J. Org. Chem. 2007, 72, 2279.
(3) (a) Shen, H.-C.; Tang, J.-M.; Chang, H.-K.; Yang, C.-W.; Liu,
R.-S. J. Org. Chem. 2005, 70, 10113. (b) Alberico, D.; Scott, M. E.;
Lautens, M. Chem. Rev. 2007, 107, 174. (c) Pascual, S.; Mendoza, P.;
Echavarren, A. M. Org. Biomol. Chem. 2007, 5, 2727. (d) Yamaguchi, J.;
Yamaguchi, A. D.; Itami, K. Angew. Chem., Int. Ed. 2012, 51, 8960.
r
10.1021/ol303107y
Published on Web 12/12/2012
2012 American Chemical Society

Scheme 1. Double Cyclization of Bis(biphenyl)acetylene
Figure 1. Direct construction of polycyclic π-scaffolds from
bis(biaryl)acetylenes and a series of TTN derivatives.
cyclization in a 6-endo mode to produce a dibenzo[g,
p]chrysene skeleton.6 Liu and co-workers also reported
sequential reactions from bis(biaryl)acetylenes combin-
ing the ICl-induced cyclization and the Pd-catalyzed
coupling reaction to synthesize various polycyclic aro-
matic hydrocarbons, in which the first monocyclized
intermediates need to be isolated.7
During the course of our acetylene cyclization chemistry
for polycyclic π-electron materials,8 we have now found
that the photoirradiation of bis(bithienyl)acetylenes cleanly
produces a tetrathienonaphthalene (TTN) skeleton 1. The
high yields and facile one-pot protocol are the advantages of
this method over the conventional synthesis of the TTN
skeleton.9 The regiocontrolled functionalization can be also
conducted for synthesizing more π-extended derivatives on
demand. It has turned out that the TTN core is a useful 2-D
scaffold as an intersection to extend π-conjugation in a
cruciform fashion. With a series of tetraaryl-substituted
derivatives 2ꢀ4 in hand (Figure 1), we have also investi-
gated the electronic impacts of their π-extension modes as
well as their aggregation properties.
A THF solution of bis(silyl)-substituted bis(3,30-bithio-
phen-2-yl)acetylene 5a with an excess amount (10 equiv)
of I2 was irradiated by a high-pressure mercury lamp at
room temperature under an argon atmosphere (Scheme 1).
The mixture smoothly turned into a deep brown solution.
After irradiation for 50 h, the reaction mixture was quenched
Figure 2. Crystal structures of a) 1a and b) 6a (50% probability
for thermal ellipsoids). Hydrogen atoms are omitted for clarity.
with a saturated Na2SO3 aqueous solution. Recrystalliza-
tion from CH2Cl2/hexane gave the TTN product 1a in
86% yield. Using 5b as a precursor, the corresponding
regioisomer 1b was also successfully synthesized in 73%
yield.
The structures of 1a and 1b were verified by NMR
spectroscopy and mass spectrometry and finally by an
X-ray diffraction analysis. The crystal structures showed
a completely planar geometry of the TTN skeleton (Figure 2a).
While the bulky triisopropylsilyl (TIPS) groups in 1a
prevented intermolecular π-stacking, 1b formed a
π-stacked dimer with the TIPS groups oriented outside.
The interfacial distance between the mean planes of the
˚
TTN cores is 3.41 A (see the Supporting Information).
(6) Yamaguchi, S.; Swager, T. M. J. Am. Chem. Soc. 2001, 123,
12087.
These different packing structures suggest that the self-
assembling mode of the TTN skeleton is controllable by
incorporating substituents at the appropriate positions.
Togaininsight intothemechanism ofthe doublecycliza-
tion, the reaction of 5a was monitored by 1H NMR spectro-
scopy (Figure 3). After UV light irradiation for 11 h, the
signals of 5a completely disappeared and a set of
new signals for an intermediate appeared together with
the small signals of the double-cyclized product 1a. When a
THF solution of 5a was stirred with I2 even in the dark at
room temperature, 5a was gradually consumed to even-
tually yield the intermediate without the formation of the
(7) (a) Li, C.-W.; Wang, C.-I.; Liao, H.-Y.; Chaudhuri, R.; Liu, R.-S.
J. Org. Chem. 2007, 72, 9203. (b) Chaudhuri, R.; Hsu, M.-Y.; Li, C.-W.;
Wang, C.-I; Chen, C.-J.; Lai, C. K.; Chen, L.-Y.; Liu, S.-H.; Wu, C.-C.;
Liu, R.-S. Org. Lett. 2008, 10, 3053. (c) Mukherjee, A.; Pati, K.; Liu,
R.-S. J. Org. Chem. 2009, 74, 6311. (d) Chen, T.-A.; Liu, R.-S. Org. Lett.
2011, 13, 4644.
(8) (a) Xu, C. H.; Wakamiya, A.; Yamaguchi, S. J. Am. Chem. Soc.
2005, 127, 1638. (b) Okamoto, T.; Kudoh, K.; Wakamiya, A.; Yama-
guchi, S. Chem.;Eur. J. 2007, 13, 548. (c) Zhang, H.; Wakamiya, A.;
Yamaguchi, S. Org. Lett. 2008, 10, 3591. (d) Fukazawa, A.; Yamada, H.;
Yamaguchi, S. Angew. Chem., Int. Ed. 2008, 47, 5582.
ꢀ
(9) (a) Fischer, E.; Larsen, J.; Christensen, J. B.; Fourmigue, M.;
Madsen, H. G.; Harrit, N. J. Org. Chem. 1996, 61, 6997. (b) Wang, Z.;
Shi, J.; Wang, J.; Li, C.; Tian, X.; Cheng, Y.; Wang, H. Org. Lett. 2010,
12, 456.
Org. Lett., Vol. 15, No. 1, 2013
81

Figure 3. Monitoring of a reaction of 5a upon photoirradiation
in the presence of I2 by 1H NMR spectroscopy.
Figure 4. Pictorial presentations of KohnꢀSham HOMOs and
LUMOs with their energy levels for models 20ꢀ40, calculated at
the B3LYP/6-31G* level.
DDAA-type 3, respectively, in 33 and 44% overall yields
in three steps. In essentially the same manner, the 3,4-
dioctyloxyphenyl-substituted DDDD-type compound 4
was also successfully prepared.
Scheme 2. Plausible Mechanism of the Double Cyclization from
5a to 1a
The cruciform compounds 2ꢀ4 are a suitable set for
studying the potentials of the TTN core as a π-conjugated
intersection. To investigate the impact of the π-extension
modes on the electronic structures, we first conducted the
DFT calculations at the B3LYP/6-31G* level using the
model compounds 20ꢀ40, in which the octyloxy groups of
2ꢀ4 are replaced with methoxy groups.12 The HOMOs
and LUMOs of 20 and 30 are mainly delocalized over the
dialkoxyphenyl and bis(trifluoromethyl)phenyl moieties,
respectively, through the TTN core skeletons (Figure 4).
The π-extension modes, namely, the diagonal or chevron-
shaped extension, only have a subtle effect on their energy
levels. For 40 with the four electron-donating groups, both
the HOMO and LUMO are delocalized over the entire
framework, resulting in the increased energy levels com-
pared to those of 20 and 30. These electronic structures
demonstrated that the TTN core is an effective intersection
that can extend the π-conjugation on demand.
These discussions are supported by cyclic voltammetry,
which were measured in THF for reduction and in
o-dichlorobenzene for oxidation (Figures S4 and S5, Sup-
porting Information). In the reduction process, both 2 and
3 showed two reversible redox waves with E1/2 at around
ꢀ2.13 and ꢀ2.31 V (vs Fc/Fcþ), while 4 only showed an
irreversible reduction wave with higher cathodic peak
potential (Epc) of ꢀ2.60 V. In the oxidation process, 2
showed two reversible redox waves, while 3 and 4 only
showed an irreversible oxidation wave. Their first anodic
peak potentials (Epa) are in the order of 4 (þ0.34 V),
double cyclized compound 1a. The crystal structure ana-
lysis demonstrated that the intermediate is a monocyclized
product 6a consisting of a tricyclic dithienobenzene skele-
ton with aniodine atom (Figure 2b). Thus, the initial stepis
likely an electrophilic monocyclization mediated by I2 to
give the intermediate 6a.10 The photoirradiation likely
promotes the second electrocyclization, which is followed
by aromatization to construct the TTN skeleton (Scheme 2).
The availability of the regiospecifically bis-silylated TTN
derivatives 1a and 1b enabled us to produce a series of
cruciform π-extended derivatives with electron-donating
(D) and electron-accepting (A) aryl groups in specific
positions (Schemes S1 and S2, Supporting Information).
Thus, the Pd-catalyzed direct CꢀH arylation11 of 1a or 1b
with 3,4-dioctyloxyphenyl iodide followed by desilylation
and the second direct CꢀH arylation with 3,5-bis(trifluo-
romethyl)phenyl iodide gave the DADA-type 2 and
(10) The possibility that this reaction is promoted by iodine radical or
through the charge-transfer process is not ruled out at this stage.
(11) Ueda, K.; Yanagisawa, S.; Yamaguchi, J.; Itami, K. Angew.
Chem., Int. Ed. 2010, 49, 8946.
(12) Frisch, M. J. et al. Gaussian 09, Rev. C.01. Gaussian, Inc.,
Wallingford, CT, 2009. See the Supporting Information for the full
reference.
82
Org. Lett., Vol. 15, No. 1, 2013

2 (þ0.49 V) and 3 (þ0.60 V). These trends are qualitatively
in agreement with their HOMO and LUMO energy levels
in Figure 4.
Figure 5. UVꢀvis absorption and fluorescence spectra for 2
(black), 3 (red), and 4 (blue) in THF.
Figure 6. SEM images of (a) 2, (b) 3, and (c) 4. The inset figures
are fluorescence microscopy images in which the scale bars
indicate 100 μm. (d) Fluorescence spectra of the fibers of 2ꢀ4.
∼10ꢀ3 M started to form aggregates upon reducing the
temperature below 60 °C (Supporting Information). Upon
slow evaporation of their THF solutions (5 ꢁ 10ꢀ5 M) at
room temperature, they gradually formed yellow nano/
microfibers. Their scanning electronic microscopy (SEM)
images showed the formation of smooth fibers of 2 with
widths of 0.5ꢀ1 μm and thicknesses of 100ꢀ200 nm, while
3 and 4 formed hierarchically assembled fibers with the
fibrous unit diameter of about 200 nm (Figure 6). The
fibers of 3 and 4 emitted a yellow fluorescence with the
peaks centered at 561 and 551 nm, respectively, while the
fibers of 2 emitted a green fluorescence with a broad
emission band around 525ꢀ544 nm. The difference in their
emission maxima should be attributed to the different
packing structures in their nanostructures (Supporting
Information).
In summary, we have developed an efficient and facile
one-pot sequential double cyclization for the construction
of a planar tetrathienonaphthalene (TTN) skeleton. The
TTN derivatives showed the effective extension of
π-conjugation on demand and exhibited strong aggregation
properties, indicative of a significant potential as a cruci-
form scaffold for nanostructured π-electron materials.
Table 1. Photophysical Properties of TTN Derivatives 2ꢀ4
THF solution
fibers
a
b
b
λabs
(nm)
εmax
(Mꢀ1 cmꢀ1
λem
λem
c
c
compd
)
(nm)
ΦF
(nm)
ΦF
2
373
89600
17800
78900
104000
497
0.10
535
0.04
448 (sh)
378
3
4
483
444
0.15
0.08
561
551
0.05
0.06
373
a Only the longest absorption maxima are shown. b Emission maxima
upon excitation at the absorption maximum wavelengths. c Absolute
quantum yield determined by a calibrated integrating sphere system
within errors of (3%.
To further investigate the structureꢀproperty relation-
ship, we next evaluated the photophysical properties of
2ꢀ4 (Figure 5 and Table 1). In the absorption spectra in
THF, while all the derivatives have the strongest absorp-
tion bands around 380 nm, the longest wavelength bands
of these compounds depend on the modes of the π-exten-
sion. The diagonal extension in 2 produces a distinct
shoulder band at 448 nm, whereas the chevron-shaped or
four-directional π-extension in 3 and 4 only results in
obscure shoulder bands. The TDꢀDFT calculations
(Supporting Information) suggested that the shoulder
band in 2 is assignable to the electronic transition from
the HOMO to LUMO, which are orthogonally extended
to each other. In the fluorescence spectra in THF, while the
four-directionally extended 4 showed a structured emis-
sion, 2 and 3 exhibited broad emission bands at the longer
wavelengths. The difference in the emission maxima be-
tween 2 and 4 exceeds 50 nm, demonstrating the impact of
the π-extension modes. As for the solvent effects, while 4
did not show any solvent-dependence, 2 and 3 showed
slightred-shiftsofthe emissionbands from toluene toTHF
by 13 and 26 nm, respectively.
Acknowledgment. This work was supported by CREST,
JST, and a Grant-in-Aid for Young Scientists (B)
(24750038). We thank Dr. H. Yoshikawa and Prof. K.
Awaga (Nagoya University) for use of the scanning
electronic microscopy (SEM) and T. Hikage (High
Intensity X-ray Diffraction Laboratory, Nagoya
University) for powder XRD measurements.
Supporting Information Available. Experimental pro-
cedures, X-ray crystallographic details, photophysical
properties, theoretical calculations, and aggregation
properties. This material is available free of charge via
the Internet at http://pubs.acs.org.
All of the π-extended TTN derivatives 2ꢀ4 exhibited
strong self-assembling properties. Even their diluted solu-
tions in tetrachloroethane with the concentration of
The authors declare no competing financial interest.
Org. Lett., Vol. 15, No. 1, 2013
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