Pd-catalyzed arylation of chlorotrifluoroethylene using arylboronic acids

Article abstract of DOI:10.1021/ol3014107

The palladium-catalyzed cross-coupling of chlorotrifluoroethylene and arylboronic acids proceeds in the presence of a base and H₂O to provide α,β,β-trifluorostyrene derivatives in satisfactory yields.

Full text of DOI:10.1021/ol3014107

ORGANIC
LETTERS
2012
Vol. 14, No. 13
3454–3457
Pd-Catalyzed Arylation of
Chlorotrifluoroethylene Using
Arylboronic Acids
Tetsuya Yamamoto and Tetsu Yamakawa*
Catalysis Group, Sagami Chemical Research Institute, 2743-1 Hayakawa, Ayase,
Kanagawa 252-1193, Japan
t_yamakawa@sagami.or.jp
Received May 22, 2012
ABSTRACT
The palladium-catalyzed cross-coupling of chlorotrifluoroethylene and arylboronic acids proceeds in the presence of a base and H2O to provide
R,β,β-trifluorostyrene derivatives in satisfactory yields.
R,β,β-Trifluorostyrene derivatives are important inter-
mediates for functional materials such as proton exchange
membranes1 and liquid crystals.2 In the past three decades,
several processes for R,β,β-trifluorostyrene derivative
syntheses through the Pd-catalyzed cross-coupling of
trifluorovinylzinc,3 tin,4 and boron5 reagents with aryl
halides have been developed (eq 1 in Scheme 1). Although
these processes are superior to the classical ones in regards
to the yields of the products,6 the raw materials for the
Scheme 1. Pd-Catalyzed Synthesis of R,β,β-Trifluorostyrene
Derivatives
(1) (a) Peckham, T. J.; Schmeisser, J.; Holdcroft, S. J. Phys. Chem. B
2008, 112, 2848. (b) Hickner, M. A.; Ghassemi, H.; Kim, Y. S.; Einsla,
B. R.; McGrath, G. E. Chem. Rev. 2004, 104, 4587. (c) Basura, V. I.;
Chuy, C.; Beattie, P. D.; Holdcroft, S. J. Electroanal. Chem. 2001, 501,
77. (d) Stone, C.; Daynard, T. S.; Hu, L.-Q.; Mah, C.; Steck, A. E. J. New
Mater. Electrochem. Syst. 2000, 3, 43. (e) Momose, T.; Kitazumi, T.;
Ishigaki, I.; Okamoto, J. J. Appl. Polym. Sci. 1990, 39, 1221. (f) Nikitina,
T. S. Usp. Khim. 1990, 59, 995. (g) Wodzki, R.; Narebska, A.; Ceynowa,
J. Angew. Makromol. Chem. 1982, 106, 23.
(2) Yokokoji, O.; Miyajima, T.; Irisawa, J.; Shimizu, T.; Inoue, S.
Liq. Cryst. 2009, 37, 799.
(3) (a) Raghavanpillai, A.; Burton, D. J. J. Org. Chem. 2004, 69, 7083.
(b) Anilkumar, R.; Burton, D. J. Tetrahedron Lett. 2002, 43, 2731. (c)
Burton, D. J.; Yang, Z. Y.; Morken, P. A. Tetrahedron 1994, 2993. (d) Ji,
G.; Shi, W.; Guo, H.; Jiang, X. Chin. Chem. Lett. 1992, 3, 791. (e) Heinze,
P. L.; Burton, D. J. J. Org. Chem. 1988, 53, 2714. (f) Heinze, P. L.;
Burton, D. J. J. Fluorine Chem. 1986, 31, 115.
(4) (a) Sorokina, R. S.; Rybakova, L. F.; Kalinovskii, I. O.; Beletskaya,
I. P. Izv. Akad. Nauk SSSR, Ser. Khim. 1985, 1647. (b) Sorokina, R. S.;
Rybakova, L. F.; Kalinovskii, I. O.; Chernoplekova, V. A.; Beletskaya, I. P.
Zh. Org. Chim. 1982, 18, 2458.
(5) Duric, S.; Schmidt, B. M.; Ninnemann, N. M.; Lentz, D.;
Tzschucke, C. C. Chem.;Eur. J. 2012, 18, 437.
(6) (a) Anilkumar, R.; Burton, D. J. Tetrahedron Lett. 2003, 44, 6661.
(b) Sigalov, A. B.; Beletskaya, I. P. Izv. Akad. Nauk SSSR, Ser.Khim.
1988, 445. (c) McGrath, T. F.; Levine, R. J. Am. Chem. Soc. 1955, 77,
4168. (d) Dixon, S. J. Org. Chem. 1956, 21, 400. (e) Prober, M. J. Am.
Chem. Soc. 1953, 75, 968. (f) Cohen, S. G.; Wolosinski, H. T.; Scheuer,
P. J. J. Am. Chem. Soc. 1949, 71, 3439.
preparation of trifluorovinyl metal reagents are unsuitable
for practical use: expensive and hazardous bromotrifluoro-
ethylene for trifluorovinylzinc and tin and thermally
unstable trifluorovinyllithium for trifluorovinylboron.
Very recently, Ogoshi and co-workers succeeded in the
(7) Ohashi, M.; Kambara, T.; Hatanaka, T.; Saijo, H.; Doi, R.;
Ogoshi, S. J. Am. Chem. Soc. 2011, 133, 3256.
r
10.1021/ol3014107
Published on Web 06/12/2012
2012 American Chemical Society

direct synthesis of R,β,β-trifluorostyrene derivatives by
Pd-catalyzed cross-coupling using tetrafluoroethylene
and arylzinc reagents (eq 2 in Scheme 1).7 Their report is
of significance from the academic and practical points of
view, because (i) it discusses the first example of the
catalytic transformation of tetrafluoroethylene through
a carbonÀfluorine bond and (ii) tetrafluoroethylene is
economically viable feedstock. Chlorotrifluoroethylene
(CTFE) is considered to be an alternative readily available
raw materialfor R,β,β-trifluorostyrene derivative synthesis
by Pd-catalyzed cross-coupling. Herein we reported the
Pd-catalyzed coupling of CTFE and arylboronic acid to
obatin R,β,β-trifluorostyrene derivatives.
This is consistent with the general trend that the addi-
tion of water accelerates Pd-catalyzed SuzukiÀMiyaura
coupling.8 The formation of 3a can be explained by the
protodeborylation that occasionally occurs in the SuzukiÀ
Miyaura coupling.9 On the other hand, the mechanism of
4a formation probably through aryl scrambling10 is now
unclear. Since the suppression of these byproducts should
bring about improvement of the yield of the desired
product, further mechanistic investigation is necessary.
Table 2. Pd-Catalyzed Coupling of CTFE and 2-Naphthalene-
boronic Acida
When a mixture of CTFE, 2-naphthaleneboronic acid,
PdCl2(dppf), and Na2CO3 in 1,4-dioxane and H2O
were heated at 100 °C for 2 h, 2-(1,2,2-trifluorovinyl)-
naphthalene was obtained in 78% isolated yield. Then, we
examined the effect of the other base on this cross-
coupling. The results are summarized in Table 1. When
using K2CO3, the corresponding product 2a was obtained
in a good yield (entry 3), but Li2CO3 and Cs2CO3 were
Table 1. PdCl2(dppf)-Catalyzed Coupling of CTFE and
2-Naphthaleneboronic Acida
yield (%)b
entry
Pd catalyst
PdCl2(dppf)
2a
3a
4a
1
84
76
62
76
74
82
67
23
59
35
3
1
4
1
3
3
2
5
1
11
7
2c
3
Pd(dba)2/dppf
PdCl2(dppm)
PdCl2(dppe)
PdCl2(dppp)
PdCl2(dppb)
PdCl2(PPh3)2
PdCl2(dtBpf)
PdCl2(PCy3)2
Pd(dba)2/
4
9
4
6
yield (%)b
5
8
6
4
entry
base
2a
3a
4a
7
10
26
15
16
1
2
3
4
5
6
7
8
9d
Na2CO3
Li2CO3
K2CO3
Cs2CO3
K3PO4
NaF
84 (78)c
32
3
7
8
1
2
9
10d
71
3
11
19
9
39
18
8
P(t-Bu)3 HBF4
3
56
11
12
SPhos-palladacycle
Pd(PPh3)4
20
2
2
1
6
2
6
1
2
KF
73
2
8
a The reaction was conducted with Pd catalyst (0.01 mmol), 1a
(1.0 mmol), CTFE (4 mmol), and Na2CO3 (2.0 mmol) in 1,4-dioxane
(2.0 mL) and H2O (0.1 mL) at 100 °C for 2 h. b Yields were determined by
CsF
73
8
9
Na2CO3
21
0
2
GC based on the used amount of 1a. c [dppf]/[Pd] = 1.0. d [P(t-Bu)3
a The reaction was conducted with PdCl2(dppf) (0.01 mmol), 1a
(1.0 mmol), CTFE (4 mmol), and base (2.0 mmol) in 1,4-dioxane
(2.0 mL) and H2O (0.1 mL) at 100 °C for 2 h. b Yields were determined
by GC, based on the used amount of 1a. c Isolated yield. d The reaction
was carried out in the absence of H2O.
3
HBF4]/[Pd] = 2.0.
Next, we surveyedvarious palladium complexes, and the
results are summarized in Table 2. Of the Pd complexes
tested, PdCl2(dppf) showed the highest activity (entry 1).
The combination of Pd(dba)2 and dppf also provided a
satisfactory yield (entry 2). The diphenylphosphino-
alkanes, which generally work as a bidentate ligand, pro-
vided the moderate yields (entries 3À6). In particular, the
yield obtained when using PdCl2(dppb) was virtually equal
not effective for the reaction (entries 2 and 4). K3PO4 also
afforded the product in a low yield (entry 5). While the use
of NaF led to poor conversion of 2-naphthaleneboronic
acid (entry 6), the reaction proceeded in good yields with
other metal fluorides, KF and CsF (entries 7 and 8). Even
though Na2CO3 exhibited the highest yield (entry 1), the
yield reduced drastically in the absence of H2O (entry 9).
(9) Hardy, J. J. E.; Hubert, S.; Macquerrie, D. J.; Wilson, A. J. Green
Chem. 2004, 6, 53.
(10) Wallow, T. I.; Novak, B. M. J. Org. Chem. 1994, 59, 5034.
(8) (a) Chai, D. I.; Lautens, M. J. Org. Chem. 2009, 74, 3054. (b)
Batey, R. A.; Quach, T. D. Tetrahedron Lett. 2001, 42, 9099.
Org. Lett., Vol. 14, No. 13, 2012
3455

Table 3. Pd-Catalyzed Arylation of CTFE Using Arylboronic Acidsa
a The reaction was conducted with PdCl2(dppf) (0.005À0.03 mmol), arylboronic acid 1bÀs (1.0 mmol), CTFE (4 mmol), and Na2CO3 (2.0 mmol) in
1,4-dioxane (2.0 mL) and H2O (0.1 mL) at 100 °C. b Isolated yield by silica gel column chromatography was determined based on the amounts of
arylboronic acids 1bÀs. c Yields were determined by GC based on the used amounts of arylboronic acid 1bÀs. d Not analyzed. e The reaction was
conducted at 120 °C.
to that obtained with PdCl2(dppf). PdCl2(PPh3)2, the most
readily available Pd(II)-phosphine complex, also gave a
moderate yield (entry 7). In contrast, the alkylphosphines
having a tert-butyl group or cyclohexyl group afforded the
product in low yields (entries 8À11), indicating that the
presence of phenyl groups on the phosphorus atom is
3456
Org. Lett., Vol. 14, No. 13, 2012

advantageous for this coupling. Nevertheless, Pd(PPh3)4
exhibited a lower activity than PdCl2(PPh3)2 (entry 12).
The scope of various arylboronic acids in this coupling is
summarized in Table 3. The results obtained when using
para- and meta-substituted arylboronic acids are shown in
entries 1À14. The reactions with substrates having various
functional groups such as alkyl, trialkylsilyl, phenyl, and acyl
groups smoothly proceeded to give the corresponding pro-
ducts in excellent yields (entries 1À5). Alkoxy substituted
arylboronic acids gave the products in good yields even when
0.5 mol % of the catalyst (entries 6 and 7) was used. The
chloro atom on the phenyl ring was unaffected during the
reaction. Preparation of arylzinc reagents having a nitro or
formyl group for the Negishi coupling using tetrafluoro-
ethylene ought to be difficult, because corresponding aryl-
magnesium reagents should be prepared.7 In contrast, these
groups can be tolerated in the synthesis of the corresponding
arylboronic acids. Indeed, the substrates with nitro and
formyl groups provided the desired products in good yields
(entries 11À14). Sterically bulky arylboronic acids provided
the corresponding products in good yields, although 2À
3 mol % of catalyst were required (entries 16À18).
In conclusion, we demonstrated the Pd-catalyzed arylation
of CTFE via the SuzukiÀMiyaura coupling. The reaction
gives ready access to various functionalized R,β,β-trifluoro-
styrene derivatives, regardless of the nature and position of
functional groups. Further examinations of other functiona-
lizations of CTFE and arylation of other fluorine-containing
alkenyl halides11 are underway in our laboratory.
Acknowledgment. We thank the Instrumental Analysis
Laboratory, University of Toyama for the HRMS mea-
surements. We are also grateful to Tosoh F-Tech Inc. for
the generousgiftof CTFE (chlorotrifluoroethylene). Tech-
nical assistance by Mr. Tomoyuki Morita (graduate stu-
dent of Tokai University) is gratefully acknowledged.
Supporting Information Available. Experimental pro-
cedures and spectral data for isolated products. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(11) (a) Kobayashi, O.; Uraguchi, D.; Yamakawa, T. J. Fluorine
Chem. 2009, 130, 591. (b) Kobayashi, O.; Uraguchi, D.; Yamakawa, T.
J. Mol. Catal. A 2009, 302, 7.
The authors declare no competing financial interest.
Org. Lett., Vol. 14, No. 13, 2012
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