Pd-catalyzed olefination of perfluoroarenes with allyl esters

Article abstract of DOI:10.1021/ol202859b

An efficient Pd(II)-catalyzed direct olefination of perfluoroarenes with allyl esters is demonstrated. Under the typical conditions, the coupling reaction of fluorinated-arenes with allylic esters proceeded via a β-H elimination rather than a β-OAc elimin

Full text of DOI:10.1021/ol202859b

ORGANIC
LETTERS
2012
Vol. 14, No. 1
74–77
Pd-Catalyzed Olefination of
Perfluoroarenes with Allyl Esters
Zejiang Li, Yuexia Zhang, and Zhong-Quan Liu*
State Key Laboratory of Applied Organic Chemistry, Lanzhou University,
Lanzhou Gansu 730000, P. R. China
liuzhq@lzu.edu.cn
Received October 23, 2011
ABSTRACT
An efficient Pd(II)-catalyzed direct olefination of perfluoroarenes with allyl esters is demonstrated. Under the typical conditions, the coupling
reaction of fluorinated-arenes with allylic esters proceeded via a β-H elimination rather than a β-OAc elimination to give the corresponding
γ-substituted allylic esters.
Fluorinatedarenesandderivativesrepresent alargeclass
of important pharmaceuticals and agrochemicals.1 In the
past decades, a variety of methods have been developed to
prepare these useful compounds.2 Recently, Zhang,3 Zhao,4
Hirano and Miura,5 Su,6 and Shi7 et al. reported several
efficient protocols to synthesize substituted fluoroarenes
by transition-metal-catalyzed coupling reactions of per-
fluoroarenes via CÀH bond activation to form some new
CÀC bonds. Of particular interest is the oxidative Heck
reaction of ArH with alkenes catalyzed by palladium
which is also named the FujiwaraÀMoritani reaction.8
Although many efficient oxidative Heck-type coupling
reactions of alkenes with arenes and heteroarenes have
been developed, there is only one example of the direct
olefination of highly electron-deficient perfluoroarenes via
a FujiwaraÀMoritani reaction reported by Zhang et al. in
2010.3a However, only the electron-deficient olefins, ali-
phatic olefins, and styrene derivatives were effective sub-
strates in that system. Herein, we wish to report a first
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Diederich, F. Angew. Chem., Int. Ed. 2003, 42, 1210. (b) Kirsch, P.
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Tamborski, C. J. Org. Chem. 1964, 29, 2385. (b) Albeniz, A. C.; Espinet,
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H. M.; Ritter, T. Angew. Chem., Int. Ed. 2008, 47, 5993. (g) Ball, N. D.;
Sanford, M. S. J. Am. Chem. Soc. 2009, 131, 3796. (h) Furuya, T.; Strom,
A. E.; Ritter, T. J. Am. Chem. Soc. 2009, 131, 1662. (i) Powers, D. C.;
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Chem., Int. Ed. 2011, 50, 9081.
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Jiang, Z.-X. J. Am. Chem. Soc. 2010, 132, 4506. (b) He, C.-Y.; Fan, S.;
Zhang, X. J. Am. Chem. Soc. 2010, 132, 12850. (c) Fan, S.; He, C.-Y.;
Zhang, X. Chem. Commun. 2010, 46, 4926.
(4) Sun, Z.-M.; Zhang, J.; Manan, R. S.; Zhao, P. J. Am. Chem. Soc.
2010, 132, 6935.
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Heck reactions, see: (a) Moritani, I.; Fujiwara, Y. Synthesis 1973, 524.
(b) Dyker, G. Angew. Chem., Int. Ed. 1999, 38, 1698. (c) Fujiwara, Y.;
Jia, C. Pure Appl. Chem. 2001, 73, 319. (d) Jia, C.; Kitamura, T.;
Fujiwara, Y. Acc. Chem. Res. 2001, 34, 633. (e) Ritleng, V.; Sirlin, C.;
Pfeffer, M. Chem. Rev. 2002, 102, 1731. (f) Kakiuchi, F.; Chatani, N.
Adv. Synth. Catal. 2003, 345, 1077. (g) Chen, X.; Engle, K. M.; Wang,
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Sanford, M. S. Chem. Rev. 2010, 110, 1147. (i) Satoh, T.; Miura, M.
Synthesis 2010, 3395. (j) Le Bras, J.; Muzart, J. Chem. Rev. 2011, 111,
1170. For selected examples, see:(a) Boele, M. D. K.; van Strijdonck, G.
P. F; de Vries, A. H. M.; Kamer, P. C. J.; de Vries, J. G.; van Leeuwen, P.
W. N. M. J. Am. Chem. Soc. 2002, 124, 1586. (b) Cai, G.; Fu, Y.; Li, Y.;
Wan, X.; Shi, Z. J. Am. Chem. Soc. 2007, 129, 7666. (c) Patureau, F. W.;
Glorius, F. J. Am. Chem. Soc. 2010, 132, 9982. (d) Li, H.; Li, Y.; Zhang,
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r
10.1021/ol202859b
Published on Web 12/08/2011
2011 American Chemical Society

example of Pd-catalyzed oxidative olefination of perfluor-
oarenes with allyl esters.
Table 1. Modification of the Typical Reaction Conditionsa
Allylic esters have been widely used as allylation re-
agents in organic synthesis.9 However, Pd-catalyzed Heck-
type coupling reactions of organic halides and boronic acids
with allyl esters are rarely achived. Recently, Jiao,10White,11
and Xiao12 et al. reported several examples of Heck re-
actions of allylic esters with arylhalides, arenes, and
arylboronic acids proceeding via β-H elimination rather
than β-OAc elimination (Scheme 1). We report herein an
efficient olefination of fluorinated arenes with allylic esters
via a highly selective β-H elimination process in the
oxidative Heck reaction.
solvent
(v/v)
yield
entry
catalyst
additive
(%)b
1
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
Ag2CO3
Ag2O
DMSO
12
43
34
55
73
65
64
51
21
41
40
3
2
THF
3
5% DMSO/DMF
5% DMSO/DCE
5% DMSO/THF
10% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
5% DMSO/THF
4
5
Scheme 1. β-H Elimination vs β-OAc Elimination in Heck-Type
Reactions of Allylic Esters with Arylhalides and/or Arylboronic
Acids
6
7
8
Pd(TFA)2
Pd(PCy3)2Cl2
Pd(acac)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
9
10
11
12
13
14
15
16c
17d
18e
Ag2SO4
Cu(OAc)2
BQ
9
11
trace
82
72
44
AgOAc
AgOAc
AgOAc
Initially, we chose pentafluorobenzene and allyl acetate
as the model substrates to optimize suitable conditions for
this reaction (Table 1). It was found that the solvent,
catalysts, and additives affect the reaction efficiency criti-
cally. The solvent suchas DMSO, THF, 5%DMSO/DMF
(v/v), and 5% DMSO/DCE (v/v) were not effective
(entries 1À4). The desired products were isolated in a yield
of 73% by using a mixed solvent of 5% DMSO in THF
(entry 5). The yield slightly decreased by using 10%
DMSO/THF as the solvent (entry 6). The solvent effect
indicates that a specified volume of DMSO plays an
important role in this reaction. As the catalyst, Pd(OAc)2
was more efficient than PdCl2, Pd(O2CCF3)2, PdCl2(Cy3P)2,
and Pd(acac)2 (entries 7À10). The additive AgOAc was
better than others such as Ag2CO3, Ag2O, Ag2SO4, Cu-
(OAc)2, and BQ (entries 11À15). Moreover, the yield
decreased when the reaction mixture was stirred at 80 °C
and was charged with equal moles of fluoroarene and allyl
ester (entries 17 and 18). The desired products were
obtained in 82% isolated yield under the typical condi-
tions: 3.0 equiv of fluoroarene, 1.0 equiv of allyl ester,
5 mol % Pd(OAc)2, 2.0 equiv of AgOAc, 5% DMSO/THF,
110 °C, 12 h (entry 16; also see Supporting Information).
To examine the scope of this system, the coupling
reactions of various fluoroarenes with substituted allylic
a Reaction conditions: pentafluorobenzene (1.5 mmol), allyl acetate
(0.5 mmol), additive (1 equiv), catalyst (5 mol %), 110 °C, 12 h, unless
otherwise noted. b Isolated yields of the E/Z and B isomers. c AgOAc
(2 equiv). d 2 equiv AgOAc, 80 °C. e 1/2 = 1/1.
esters and ethers were studied (Table 2). A variety of
fluorinated arenes have been proved to be very efficient
substrates under the typical conditions. In these cases,
olefination was generally observed at the more sterically
accessible position (3e, 3g, 3h). Such selectivity might be
attributed to the acidity of CÀH of the fluorinated arenes
even though it was located at a more sterical position.13
Fluorinated arenes with an electron-donating methoxy
group gave an excellent yield of the corresponding product
(3b). Tetrafluorobenzene also gave a very high yield of the
desired product (3c). It seems that the yields decrease with
the decrease in the number of F-atoms substituted in the
aromatic core (3c, 3d, 3h, 3i, 3j). Fluorobenzene gave an
81% yield of the olefination product when the reaction was
carried out in a mixed solvent of 5% DMSO/fluoroben-
zene (3k). 2,6-Difluorotoluene gave only a 30% yield of the
product(3e). Perfluoroarenewithanelectron-withdrawing
group like CF3 (3f) is also effective. Interestingly, the
desired product with retention of the Br-atom was isolated
(10) (a) Pan, D.; Chen, A.; Su, Y.; Zhou, W.; Li, S.; Jia, W.; Xiao, J.;
Liu, Q.; Zhang, L.; Jiao, N. Angew. Chem., Int. Ed. 2008, 47, 4729. (b) Su,
Y.; Jiao, N. Org. Lett. 2009, 11, 2980. (c) Pan, D.; Yu, M.; Chen., W.;
Jiao, N. Chem.;Asian J. 2010, 5, 1090.
(11) Delcamp, J. H.; White, M. C. J. Am. Chem. Soc. 2006, 128,
15076.
(13) (a) Garcia-Cuadrado, D.; Braga, A. A. C.; Maseras, F.; Echavarren,
A. M. J. Am. Chem. Soc. 2006, 128, 1066. (b) Garcia-Cuadrado, D.; de
Mendoza, P.; Braga, A. A. C.; Maseras, F.; Echavarren, A. M. J. Am.
Chem. Soc. 2007, 129, 6880. (c) Campeau, L.-C.; Parisien, M.; Jean, A.;
Fagnou, K. J. Am. Chem. Soc. 2006, 128, 581. (d) Lafrance, M.; Rowley,
C. N.; Woo, T. K.; Fagnou, K. J. Am. Chem. Soc. 2006, 128, 8754. (e)
ꢀ
(12) Ruan, J.; Li, X.; Saidi, O.; Xiao, J. J. Am. Chem. Soc. 2008, 130,
2424.
Rene, O.; Fagnou, K. Org. Lett. 2010, 12, 2116. (f) Ackermann, L.;
Fenner, S. Chem. Commun. 2011, 430.
Org. Lett., Vol. 14, No. 1, 2012
75

Table 2. Pd-Catalyzed Oxidative Heck Reaction of Fluoroarene with Allyl Estera
a Reaction conditions: fluoroarene (1.5 mmol, 3 equiv), allyl esters or ethers (0.5 mmol, 1 equiv), AgOAc (2 equiv), Pd(OAc)2 (5 mol %), 5% DMSO/
THF (v/v), 110 °C, unless otherwise noted. b Reaction time, indicated by TLC. c Isolated overall yields of the E/Z and B isomers. d Ratio of E/Z/B
determined by crude 1H NMR. e Solvent: 5% DMSO/fluoroarene (v/v), isolated yields of the 1,2,3,4/1,2,4,5 substituted isomers. f Solvent: 5% DMSO/
fluoroarene (v/v), isolated yields of the E isomer. g Solvent: 5% DMSO/fluoroarene (v/v), isolated yields of the 1,2,3/1,2,4 substituted isomers. h Solvent:
5% DMSO/fluoroarene (v/v), isolated yields of the 1,2/1,4 substituted isomers. i Ratio of B/E/Z.
in 68% yield by coupling of 1-bromo-2,4,6-trifluoroben-
zene with allyl acetate (3g).
olefination site was located at the allylic rather than the
acrylic double bond in this system. It is noteworthy that
allylic ether is also used successfully as the olefination
partner under these reaction conditions (3u and 3v).
A competing olefination would occur between the allylic
and the acrylic double bonds (Scheme 2). However, the
CÀC bond formation took place in the position of the ter-
minal allylic CdC bond rather than the acrylic double
bond under the typical conditions. The selectivity might be
attributed to the stability of the alkyl-Pd-intermediate via
chelation of Pd atom by the carbonyl O-atom which was
Various substituted allylic esters gave excellent to quan-
titative yields of the desired products in this reaction
(Table 2, 3lÀ3t). A branched coupling product was isolated
as the major product which might proceed via a β-elimina-
tion of the H-atom from the methyl group (3n). Both allyl
benzoate and allyl cinnamate gave excellent yields of the
products (3oÀ3r). Surprisingly, allyl acrylate and allyl
methacrylate gave the desired products 3w, 3p, and 3q in
moderate to good yields. It indicates that the oxidative
76
Org. Lett., Vol. 14, No. 1, 2012

previously proposed.9f,10,14 Additionally, this chelation
effect could also result in the high regioselectivity since
the (Pd)CÀC(O) bond cannot rotate freely.
Scheme 2. Competing Olefination of Fluoroarene between the
Allylic and Acrylic Double Bonds
In conclusion, we demonstrated an efficient Pd(II)-cata-
lyzed direct olefination of highly electron-deficient perfluoro-
arenes by using allylic esters and ethers. In this system,
various γ-substituted allylic esters have been prepared by an
oxidative Heck-type reaction via β-H elimination rather
than β-OAc elimination. As the olefination partner, a series
of allylic esters even bearing another CdC bond such as allyl
methacrylate and allylic ether give high yields of the desired
products. The present protocol could be useful for the
synthesis of perfluoroarenes and its derivatives which should
be valuable to materials and life science. Further investiga-
tion of this procedure is underway in our laboratory.
Acknowledgment. This project is supported by the
National Science Foundation of China (No. 21002045). We
also thank the State Key Laboratory of Applied Organic
Chemistry and Lanzhou University for financial support.
Supporting Information Available. Full experimental
details and characterization data for all products. This
material is available free of charge via the Internet at
http://pubs.acs.org.
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Org. Lett., Vol. 14, No. 1, 2012
77