Functionalization of a simple dithienylethene via palladium-catalyzed regioselective direct arylation

Article abstract of DOI:10.1021/ol2026069

The direct arylation on the thienyl groups of a diarylethene with various aryl iodides efficiently provided arylated dithienylethenes under palladium catalysis. Unsymmetrically substituted dithienylethenes were also synthesized by this protocol. This proc

Full text of DOI:10.1021/ol2026069

ORGANIC
LETTERS
2011
Vol. 13, No. 24
6394–6397
Functionalization of a Simple
Dithienylethene via Palladium-Catalyzed
Regioselective Direct Arylation
Hiroki Kamiya,† Shuichi Yanagisawa,‡ Satoru Hiroto,† Kenichiro Itami,*,‡ and
Hiroshi Shinokubo*,†
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University,
Chikusa-ku, Nagoya 464-8603, Japan, and Department of Chemistry, Graduate School
of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
hshino@apchem.nagoya-u.ac.jp; itami.kenichiro@a.mbox.nagoya-u.ac.jp
Received October 9, 2011
ABSTRACT
The direct arylation on the thienyl groups of a diarylethene with various aryl iodides efficiently provided arylated dithienylethenes under palladium
catalysis. Unsymmetrically substituted dithienylethenes were also synthesized by this protocol. This procedure allows a rapid access to a variety
of aryl-substituted dithienylethenes from a single substrate of a simple dithienylethene.
In recent years, organic photochromic compounds
have attracted much attention due to the potential
applications for photoswitching materials.1 Among var-
ious photochromic systems, diarylethene is one of the
most prospective organic molecules owing to their ad-
vantageous property over other photochromic com-
pounds in terms of their thermal stability and fatigue
resistance as well as their intriguing photochromic
behavior.2 Diarylethenes often consist of arylated thie-
nyl groups, of which aryl substituents can control the
absorption property of the diarylethenes, thus tuning the
color change of the photochromic reaction. However,
the synthesis of such aryl-substituted dithienylethenes has
been carried out through multistep synthesis, which com-
menced with the preparation of arylated thiophenes.3
In the past decade, transition-metal-catalyzed direct
CꢀH arylation of aromatic and heteroaromatic com-
pounds has been an active area of research in organic
synthesis and organometallic chemistry.4,5 In particular, a
ligand-controlled regiodivergent direct arylation of thio-
phenes has been recently reported.6 The employment of
2,20-bipyridyl as a ligand proceeded with R-selectivity to
† Department of Applied Chemistry, Graduate School of Engineering.
‡ Department of Chemistry, Graduate School of Science.
(3) (a) Hanazawa, R.; Sumiya, R.; Horikawa, Y.; Irie, M. J. Chem.
Soc., Chem. Commun. 1992, 206. (b) Irie, M.; Sakemura, K.; Okinaka,
M.; Uchida, K. J. Org. Chem. 1995, 60, 8305.
(1) (a) Brown, G. H. Photochromism; Wiley-Interscience: New York,
NY, 1971. (b) D€urr, H.; Bouas-Laurent, H. Photochromism: Molecules and
Systems; Elsevier: Amsterdam, 1990. (c) Irie, M. Photo-reactive Materials
for Ultrahigh Density Optical Memory; Elsevier: Amsterdam, 1994.
(d) Raymo, F. M.; Tomasulo, M. Chem. Soc. Rev. 2005, 34, 327. (e) Gust,
D.; Moore, T. A.; Moore, A. L. Chem. Commun. 2006, 1169. (f) Irie, M.
Bull. Chem. Soc. Jpn. 2008, 81, 917.
(2) (a) Irie, M. Chem. Rev. 2000, 100, 1685. (b) Matsuda, K.; Irie, M.
J. Photochem. Photobiol. C 2004, 5, 169. (c) Irie, M.; Uchida, K. Bull.
Chem. Soc. Jpn. 1998, 71, 985. (d) Morimoto, M.; Irie, M. Chem.
Commun. 2005, 3895. (e) Tian, H.; Wang, S. Chem. Commun. 2007, 781.
(4) For recent reviews on CꢀH bond arylation of arenes, see:
(a) Ackermann, L.; Vicente, R.; Kapdi, A. R. Angew. Chem., Int. Ed.
2009, 48, 9792. (b) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev.
2008, 107, 174. (c) Seregin, I. V.; Gevorgyan, V. Chem. Soc. Rev. 2007,
36, 1173. (d) Chen, X.; Engle, K. M.; Wang, D.-H.; Yu, J.-Q. Angew.
Chem., Int. Ed. 2009, 48, 5094. (e) Kakiuchi, F.; Kochi, T. Synthesis 2008,
3013. (f) Bellina, F.; Rossi, R. Tetrahedron 2009, 65, 10269. (g) Lei, A.; Liu,
W.; Liu, C.; Chen, M. Dalton Trans. 2010, 39, 10352. (h) Wencel-Delord, J.;
€
Droge, T.; Liu, F.; Glorius, F. Chem. Soc. Rev. 2011, 40, 4740. (i) Ackermann,
L. Chem. Rev. 2011, 111, 1315. (j) Hirano, K.; Miura, M. Synlett 2011, 294.
r
10.1021/ol2026069
Published on Web 11/22/2011
2011 American Chemical Society

afford R-arylated thiophenes,6a,c while the reaction with a
P[OCH(CF3)2]3 ligand exhibited high β-selectivity in Pd-
catalyzed CꢀH arylation of thiophenes.6a,b This feature is
quite useful to construct a diverse list of arylated thio-
phenes. Here we have applied this synthetic protocol for
regioselective functionalization of dithienylethenes. We
anticipated that direct arylation on thienyl groups of one
single dithienylethene substrate would offer a useful and
convenient protocol to access diarylethenes with various
aryl-substituted thienyl groups (Scheme 1).
Table 1. Direct R-Arylation on the Thiophene Moieties of 1,
2-Di-(2-methylthien-3-yl)cyclopentenes 1 with Various Aryl
Iodidesa
Scheme 1
We optimized the reaction conditions for direct aryla-
tion of 1,2-di(2-methylthien-3-yl)perfluorocyclopentene
(1a), since a perfluorocyclopentene unit exhibits the
highest reversible durability and photoresponsibility
among various platforms for diarylethenes.3 The dithie-
nylethene 1a was prepared via SuzukiꢀMiyaura cross-
coupling of 1,2-dichlorohexafluorocyclopentene with
2-methyl-3-thienylboronic acid.7 The reaction of 1a with
4-iodoanisole (3.0 equiv), PdCl2, 2,20-bipyridyl, and
Ag2CO3 in m-xylene at 120 °C accomplished R,R0-
disubstitution on the thiophene moieties to afford 3a
in 72% yield (Table 1, entry 1). The similar procedure
can be applied to various aryl iodides. The reaction with
2- and 3-iodoanisoles provided the corresponding pro-
ducts 3b and 3c in 67 and 64% yields, respectively
(entries 2 and 3). Utilization of aryl iodides bearing
electron-withdrawing groups such as carbonyl and tri-
fluoromethyl substituents was shown to be effective
(entries 5 and 6), indicating no noticeable substituent
effect. 4-Bromoiodobenzene (2g) also participated in
this reaction without debromination to furnish the cor-
responding diarylethene 3g in 67% yield (entry 7). This
feature would be useful for further elaboration of 3g
on the basis of the bromide functionality. A 1-naphthyl
group could also be introduced efficiently by the
a Reaction conditions: dithienylethene 1 (1.0 equiv), aryl iodide
(3.0 equiv), PdCl2 (30 mol %), 2,20-bipyridyl (30 mol %), Ag2CO3
b
(3.0 equiv), 120 °C. PdCl2 (10 mol %) and 2,20-bipyridyl (10 mol %)
were used under otherwise the same reaction conditions. c The reaction
time was 17 h.
(5) For selected papers on CꢀH arylation of thiophenes with haloar-
enes, see: (a) Yanagisawa, S.; Sudo, T.; Noyori, R.; Itami, K. J. Am.
Chem. Soc. 2006, 128, 11748. (b) Join, B.; Yamamoto, T.; Itami, K.
Angew. Chem., Int. Ed. 2009, 48, 3644. (c) Roger, J.; Gottumukkala,
reaction with 1-iodonaphthalene (2h) to afford 3h in
good yield (entry 8). The reaction also proceeded with
1,2-dithienylcyclopentene 1b to produce diarylated pro-
duct 3i in 44% yield (entry 9).
Importantly, the employment of 1.0 equiv of aryl
iodides resulted in R-arylation on one of the two thienyl
groups under otherwise identical reaction conditions.
The reaction of 4-iodoanisole, ethyl 4-iodobenzoate,
and iodobenzene afforded the corresponding monoary-
lated dithienylethenes 4aꢀ4c predominantly in moderate
yields (Table 2). In each case, diarylated product 3 was also
formed in ca. 10% yield to reduce the yield of the desired
ꢀ
A. L.; Doucet, H. ChemCatChem 2010, 2, 20. (d) Liegault, B.; Lapointe,
D.; Caron, L.; Vlassova, A.; Fagnou, K. J. Org. Chem. 2009, 74, 1826.
(e) Kobayashi, K.; Sugie, A.; Takahashi, M.; Masui, K.; Mori, A. Org.
Lett. 2005, 7, 5083. (f) Gozzi, C.; Lavenot, L.; Ilg, K.; Penalva, V.;
ꢀ
Lemaire, M. Tetrahedron Lett. 1997, 38, 8867. (g) Liegault, B.; Petrov, I.;
Gorelsky, S. I.; Fagnou, K. J. Org. Chem. 2010, 75, 1047. (h) Glover, B.;
Harvey, K. A.; Liu, B.; Sharp, M. J.; Tymoschenko, M. F. Org. Lett.
2003, 5, 301.
(6) (a) Yanagisawa, S.; Ueda, K.; Sekizawa, H.; Itami, K. J. Am.
Chem. Soc. 2009, 131, 14622. (b) Ueda, K.; Yanagisawa, S.; Yamaguchi,
J.; Itami, K. Angew. Chem., Int. Ed. 2010, 49, 8946. (c) Yanagisawa, S.;
Itami, K. Tetrahedron 2011, 67, 4425.
(7) Hiroto, S.; Suzuki, K.; Kamiya, H.; Shinokubo, H. Chem. Com-
mun. 2011, 47, 7149.
Org. Lett., Vol. 13, No. 24, 2011
6395

We also attempted direct arylation of the thienyl group
at the β-position.8 The reaction of 1 with 3.0 equiv of
4-iodoanisole, PdCl2, P[OCH(CF3)2]3, and Ag2CO3 in
m-xylene at 100 °C afforded none of the desired products.
After several trials, we eventually found that the use of
1,4-dioxane as the reaction solvent effected β-arylation on
only one of the two thienyl groups to provide dithienylethene
6 in 41% yield with high regioselectivity (Scheme 2). Inter-
estingly, β,β0-diarylation was not observed even with the
use of an increased amount of 4-iodoanisole. Unfortu-
nately, the use of other iodoarenes such as iodobenzene
resulted in quite low yields under the optimized reaction
conditions. However, this type of reaction is promising
because a diarylethene bearing β-arylated thienyl groups is
difficult to synthesize through conventional protocols.9
Table 2. Selective R-Monoarylation on the Thiophene Moiety of
1,2-Dithienylcyclopentene 1aa
entry
R
product
yield (%)
1
2
3
OMe
CO2Et
H
2a
2e
2d
4a
4b
4c
32
36b
36
Scheme 2. Direct β-Arylation on the Thiophene Moiety of
1,2-Dithienylcyclopentene 1a
a Reaction conditions: dithienylethene 1a (1.0 equiv), aryl iodide
(1.0 equiv), PdCl2 (30 mol %), 2,20-bipyridyl (30 mol %), Ag2CO3
(1.0 equiv), m-xylene, 120 °C, 13 h. b PdCl2 (10 mol %) and 2,20-
bipyridyl (10 mol %) were used under otherwise the same reaction
conditions.
compound 4. The monoarylated products 4 are useful for
the construction of unsymmetrically substituted dithieny-
lethenes (Table 3). For example, the direct arylation of 4a
with ethyl 4-iodobenzoate provided unsymmetrically sub-
stituted dithienylethene 5a with 4-methoxyphenyl and
4-ethoxycarbonylphenyl groups in 40% yield.
Table 3. Synthesis of Unsymmetrically Substituted Dithieny-
lethene 5
Scheme 3
yield
entry
R1
R2
CO2Et
product
(%)
1
2
3
OMe
H
4a
4c
4c
2e
2a
2i
5a
5b
5c
40a
40b
37b
(8) For examples of β-arylation of thiophenes, see: (a) Okazawa, T.;
Satoh, T.; Miura, M.; Nomura, M. J. Am. Chem. Soc. 2002, 124, 5286.
(b) Vogler, T.; Studer, A. Org. Lett. 2008, 10, 129. (c) Nakano, M.;
Tsurugi, H.; Satoh, T.; Miura, M. Org. Lett. 2008, 10, 1851.
(d) Kirchberg, S.; Tani, S.; Ueda, K.; Yamaguchi, J.; Studer, A.; Itami,
K. Angew. Chem., Int. Ed. 2011, 50, 2387.
(9) Diarylethenes with methyl substituents at β-positions of the
thiophene moieties have been synthesized. (a) de Meijere, A.; Zhao,
L.; Belov, V. N.; Bossi, M.; Noltemeyer, M.; Hell, S. W. Chem.;Eur. J.
2007, 13, 2503. (b) Kobatake, S.; Muto, H.; Irie, M. Chem. Lett. 2006, 35,
102.
OMe
H
CO2Me
a Reaction conditions: diarylethene 4 (1.0 equiv), aryl iodide 2e
(3.9 equiv), PdCl2 (39 mol %), 2,20-bipyridyl (39 mol %), Ag2CO3
(3.9 equiv), m-xylene (0.30 mL), 120 °C, 13 h. b Aryl iodide 2 (3.0 equiv),
PdCl2 (30 mol %), and 2,20-bipyridyl (30 mol %) were used under
otherwise the same reaction conditions.
6396
Org. Lett., Vol. 13, No. 24, 2011

The β-arylated product 6 can be subjected to further
arylation of the remaining CꢀH bonds on the thiophene
moieties. Treatment of 6 with 3.0 equiv of 4-iodoanisole
under the standard R-arylation conditions induced
R,R0-disubstitution to afford diarylethene 7 in 43% yield
of diverse diarylethenes including unsymmetrically substi-
tuted dithienylethenes.
Acknowledgment. This work was supported by a
Grant-in-Aid for Scientific Research in Priority Areas
“New Frontiers in Photochromism (No. 471)” from the
Ministry of Education, Culture, Sports, Science and Tech-
nology (MEXT), Japan and the Global COE program in
Chemistry of Nagoya University. H.S. acknowledges Asa-
hi Glass Foundation for financial support.
1
(Scheme 3). The product was assigned by its H NMR
spectrum and high-resolution mass spectrum observed at
m/z = 686.1371 (calcd for (C36H28F6O3S2)þ = 686.1379).
This is the first example of a diarylethene with an
R,β-diarylated thienyl group.
In conclusion, we have demonstrated versatile functio-
nalization of a simple dithienylethene at the R- and
β-positions of the thiophene moieties through a Pd-catalyzed
direct CꢀH arylation strategy. The regioselectivity of
arylation can be controlled by the proper choice of ligands.
The present protocol would be useful for the construction
Supporting Information Available. General procedures
and spectral data for new compounds. This material
is available free of charge via the Internet at http://
pubs.acs.org.
Org. Lett., Vol. 13, No. 24, 2011
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