Synthesis and properties of seleno-analog MK-organic dye for photovoltaic cells prepared by CH functionalization reactions of selenophene derivatives

Article abstract of DOI:10.1246/cl.2011.978

C-H arylation and homocoupling reactions of 2-formylselenophene were carried out with a palladium catalyst. By using these coupling reactions a seleno-analog of MK dye MK-49, which is an organic dye molecule of a dye-sensitized solar cell (DSSC), was synt

Full text of DOI:10.1246/cl.2011.978

doi:10.1246/cl.2011.978
978
Published on the web September 5, 2011
Pd-catalyzed Highly Regio- and Stereocontrolled Direct Alkenylation
of Electron-deficient Polyfluoroarenes
Fei Chen and Xingang Zhang*
Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, P. R. China
(Received May 30, 2011; CL-110453; E-mail: xgzhang@mail.sioc.ac.cn)
An effective and reliable method for Pd-catalyzed highly
Herein, we reported an effective method for Pd-catalyzed
direct alkenylation of polyfluoroarenes with alkenyl iodides. The
advantages of this reaction are high regio- and stereoselectivity,
mild reaction temperature (70 °C), and use of readily available
Pd(PPh3)4. This approach provides a useful access to the
fluorinated styrenyl products.
regio- and stereocontrolled direct alkenylation of electron-
deficient polyfluoroarenes with alkenyl iodides has been
developed. The advantages of this reaction are its high regio-
and stereoselectivity, mild reaction temperature (70 °C), and the
use of readily available Pd(PPh3)4. This approach provides a
useful access to polyfluoroarylated derivatives of interest in both
life and materials science.
We began this study by choosing pentafluorobenzene (1a)
and (Z)-ethyl 3-iodoacrylate (2a) as model substrates (Table 1).
Initially, from the viewpoint of synthetic convenience and cost
effectiveness, a Pd(OAc)2/PPh3 catalytic system, which was
successfully used in our previous work on the direct function-
alization of polyfluoroarenes,8 was investigated. However, no
desired product 3a was obtained (Table 1, Entry 1). Considering
that silver(I) salts are commonly employed to abstract halide
anions from transition-metal complexes thus rendering them
more electrophilic and facilitating the catalytic cycle,3c,9
Ag2CO3 was investigated, and provided compound 3a in 17%
NMR yield (Table 1, Entry 2). We were pleased to observe
that switching Pd source from Pd(OAc)2/PPh3 to Pd(PPh3)4
benefited the reaction, and 70% NMR yield of 3a was afforded
when the reaction was carried out with Pd(PPh3)4 (10 mol %)
and Ag2CO3 (0.75 equiv) in DMF at 120 °C (Table 1, Entry 3).
AgOAc was also found to be comparable with Ag2CO3, but
some by-products were formed (Table 1, Entry 4). The solvent
Due to the importance of polyfluoroarenes in materials and
life science,1 it is of great synthetic interest to develop efficient
methods for the preparation of fluoroarylated compounds. Of the
developed methods, the transition-metal-catalyzed direct func-
tionalization of simple polyfluoroarenes is the most attractive
approach, because this direct C-H bond functionalization
process provides a more effective strategy in terms of atom
and step economy.2 Since the first example of palladium-
catalyzed direct arylation of polyfluoroarenes with arylhalides
was reported by Fagnou,3 impressive progress in direct
functionalization of polyfluoroarenes has been made.4 However,
many of these efforts mainly focused on the direct arylation of
polyfluoroarenes.4a-4f Very recently, we successfully developed
a straightforward protocol for direct Pd-catalyzed alkenylation
of polyfluoroarenes,5 which represents one of the rare examples
of catalytic direct olefination of electron-deficient arenes.6
Unfortunately, when branched or aliphatic alkenes were inves-
tigated in this Fujiwara-Moritani oxidative Heck type reaction, a
mixture of constitutional isomers was generated.5 In fact, this is
the most difficult problem in the intermolecular Mizoroki-Heck
reaction.7 To continue our research, we envisioned that the
installation of a halogen substituent onto the alkenes would be
a reliable strategy to solve this difficult problem. Since these
“prefunctionalized” alkenes would direct Pd-catalyst to install
polyfluoroarenes at specific position, as a result, a high regio-
and stereoselectivity would be obtained (Scheme 1).
Table 1. Optimization of Pd-catalyzed regio- and stereocon-
trolled direct alkenylation of electron-deficient pentafluoro-
benzenea
F
F
F
F
cat. Pd, additive
solvent, temp
I
CO2Et
C6F5
CO2Et
+
H
3a
2a
F
1a
Catalyst
(mol %)
Additvie
(equiv)
Temp Yieldb
Entry
1
Solvent
/°C
/%
Pd(OAc)2 (10) K2CO3 (0.75) DMF
PPh3 (20)
100 N.R.
Previous work
2
Pd(OAc)2 (10) Ag2CO3 (0.75) DMF
PPh3 (20)
Pd(PPh3)4 (10) Ag2CO3 (0.75) DMF
Pd(PPh3)4 (10) AgOAc (1.5) DMF
Pd(PPh3)4 (10) Ag2CO3 (0.75) DMSO 120 83(68)
Pd(PPh3)4 (10) Ag2CO3 (0.75) Dioxane 120
Pd(PPh3)4 (5) Ag2CO3 (0.75) DMSO 120 86
Pd(PPh3)4 (5) Ag2CO3 (0.5) DMSO 120 86
100 17
F
F
F
F
cat. Pd(OAc)2
3
4
5
6
7
8
9
120 70
120 76
+
3CH3
CH3
constitutional isomers
C6F5
Ag2CO3, 120 °C
H
F
This work
0
F
R2
R2
F
F
F
C6F5
cat. [Pd(PPh3)4]
I
R3
+
R3
Ag2CO3, 70 °C
R1
only one product
H
R1
Pd(PPh3)4 (5) Ag2CO3 (0.5) DMSO
70 87(74)
F
aConditions: 1a (0.9 mmol) and 2a (0.3 mmol) in solvent
(2 mL), 10 h. bNMR yield determined by 19F NMR and number
in parentheses is isolated yield.
Scheme 1. Direct alkenylation of electron-deficient polyfluoro-
arenes.
Chem. Lett. 2011, 40, 978-979
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

979
Table 2. Pd-Catalyzed regio- and stereocontrolled direct alke-
nylation of electron-deficient polyfluoroarenesa
alkenylation of electron-deficient polyfluoroarenes with alkenyl
iodides.10 The reaction was carried out under mild reaction
temperature (70 °C) and afforded good yields and high regio-
and stereoselectivity. Hence, it is a useful and reliable method
for the preparation of polyfluoroarylated derivatives of interest
in both life and materials science.
I
R2 [Pd(PPh3)4] (5 mol%)
ArF
R2
Fluoroarene
+
Ag2CO3 (0.5 equiv)
R3
R1
R1
R3
1
DMSO, 70 °C
2
3
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
The NSFC (Nos. 20902100 and 20832008), the Shanghai
Rising-Star Program (No. 09QA1406900), and SIOC are warm-
ly acknowledged for funding this work.
F
F
CO2Et
F
F
CO2Et
Ph
Ph
3a, 74%
3b, 79%
3c, 76%
3d, 66%
This paper is in celebration of the 2010 Nobel Prize
awarded to Professors Richard F. Heck, Akira Suzuki, and
Ei-ichi Negishi.
F
F
CN
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
CO2Et
Me
CO2Et
Me
6
6
References and Notes
3e, 66%
3f, 41%
3g, 70%b
3h, 87%
1
For recent selected reviews, see: a) K. Müller, C. Faeh, F.
Diederich, Science 2007, 317, 1881. b) A. R. Murphy, J. M. J.
Fréchet, Chem. Rev. 2007, 107, 1066. c) F. Babudri, G. M.
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2119.
Me
F
F
N
F
F
OMe
F
CF3
F
F
F
F
F
F
F
F
F
F
F
CO2Et
CO2Et
CO2Et
CO2Et
3k, 52%
3i, 54%
3j, 87%
3l, 70%
2
For selected recent reviews related to C-H bonds activation, see:
a) L.-C. Campeau, K. Fagnou, Chem. Commun. 2006, 1253. b)
O. Daugulis, V. G. Zaitsev, D. Shabashov, Q.-N. Pham, A.
Lazareva, Synlett 2006, 3382. c) D. Alberico, M. E. Scott, M.
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Engle, N. Maugel, J.-Q. Yu, Chem. Soc. Rev. 2009, 38, 3242. e)
L. Ackermann, R. Vicente, A. R. Kapdi, Angew. Chem., Int. Ed.
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Chem. Rev. 2010, 110, 1147.
aConditions: 1a (0.9 mmol) and 2a (0.3 mmol) in DMSO
(2 mL), 10 h. 8 equiv of fluoroarene was used.
b
effect also influenced the reaction efficiency (Table 1, Entries 5
and 6), and DMSO was the optimum reaction medium with 68%
isolated yield obtained (Table 1, Entry 6). Further optimization
revealed that the reaction could proceed smoothly in good yield
(74% isolated yield) with utilization of 5 mol % Pd(PPh3)4 and
0.5 equiv of Ag2CO3 at 70 °C (Table 1, Entry 9).
3
4
a) M. Lafrance, C. N. Rowley, T. K. Woo, K. Fagnou, J. Am.
Chem. Soc. 2006, 128, 8754. b) M. Lafrance, D. Shore, K.
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Under the optimum reaction conditions (Table 1, Entry 9),
the substrate scope of the regio- and stereocontrolled direct
alkenylation of polyfluoroarenes 1 was tested and the represen-
tative results are illustrated in Table 2. The fluorinated styrenyl
products could be obtained as a single Z- or E-isomer through
the present reaction. Notably, for the aliphatic alkenyl iodides,
especially for the linear aliphatic alkene 2e (Table 2, 3e), no
constitutional isomers were observed (Table 2, 3d-3f), which
is in sharp contrast to our previous results,5 thus providing
a complementary method to the Fujiwara-Moritani oxidative
Heck type reaction. The substrate scope of polyfluoroarene is not
restricted to pentafluorobenzene, variations of polyfluoroarenes
1 were also suitable substrates for the reaction (Table 2, 3g-3l).
Generally, the reaction efficiency depends on the nature of the
substituents on the fluoroaromatic ring. Substrates bearing an
electron-withdrawing group provided higher yields than that of
fluoroarenes containing an electron-donating group (Table 2,
3h-3k). Lewis basic functionality, a pyridyl group, was
tolerated, and provided 3l in good yield (Table 2, 3l). Impor-
tantly, nitrile groups are also compatible to the reaction
conditions with 87% yield obtained (Table 2, 3h), thus provid-
ing opportunities for further functionalization. For compounds
3f, 3i, and 3k, due to the low conversion of alkenyl iodide 3f
or formation of by-products 3i and 3k, modest yields were
provided.
For selected transition-metal-catalyzed direct functionalization of
polyfluoroarenes, see: a) H.-Q. Do, O. Daugulis, J. Am. Chem.
Soc. 2008, 130, 1128. b) H.-Q. Do, R. M. K. Khan, O. Daugulis,
J. Am. Chem. Soc. 2008, 130, 15185. c) H.-Q. Do, O. Daugulis,
Chem. Commun. 2009, 6433. d) Y. Wei, J. Kan, M. Wang, W. Su,
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5
6
7
8
9
a) S. Fan, C.-Y. He, X. Zhang, Chem. Commun. 2010, 46, 4926.
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5918.
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10 Supporting Information is available electronically on the CSJ-
Journal Web site, http://www.csj.jp/journals/chem-lett/index.
html.
In conclusion, we have developed an effective Pd(PPh3)4/
Ag2CO3-catalyzed system for regio- and stereocontrolled direct
Chem. Lett. 2011, 40, 978-979
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/