Palladium-catalyzed Suzuki-Miyaura coupling with aryl and heteroaryl bromides using N,N,N',N'-tetra(diphenylphosphinomethyl)-1,2-ethylenediamine

Article abstract of DOI:10.1002/aoc.2869

An easily prepared tetraphosphine N,N,N',N'-tetra(diphenylphosphinomethyl)- 1,2-ethylenediamine (1) combined with PdCl₂ affords an efficient catalytic system for Suzuki cross-coupling of aryl and heteroaryl bromides. A high turnover number of 7

Full text of DOI:10.1002/aoc.2869

Full Paper
Received: 13 January 2012
Revised: 30 March 2012
Accepted: 31 March 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2869
Palladium-catalyzed Suzuki–Miyaura coupling
with aryl and heteroaryl bromides using N,N,N′,
N′-tetra(diphenylphosphinomethyl)-1,2-
ethylenediamine
Kun Wang, Tao Yi, Xiaojun Yu, Xueli Zheng, Haiyan Fu, Hua Chen and
Ruixiang Li*
An easily prepared tetraphosphine N,N,N′,N′-tetra(diphenylphosphinomethyl)-1,2-ethylenediamine (1) combined with PdCl2
affords an efficient catalytic system for Suzuki cross-coupling of aryl and heteroaryl bromides. A high turnover number of 750
000 is obtained with the catalyst loading as low as 1 ppm. This catalyst system exhibits good stability and longevity. In this study,
a broad scope of substrates is investigated and satisfactory yields are obtained. Copyright © 2012 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: Suzuki–Miyaura coupling; palladium; tetraphosphine
multidentate ligands increases their coordination ability to palla-
dium, so tetraphosphine improves the stability of the catalyst
Introduction
Palladium-catalyzed Suzuki cross-coupling is one of the most
efficient methods for the formation of biaryl compounds.[1–5] In
the past decades, much effort was devoted to this field and many
efficient catalyst systems were developed.[6–15] However, palla-
dium catalyst brings a high cost as well as significant efficiency.
Relevant reviews by Farina[16] and by Corbet and Mignani[17]
illustrated that if the catalyst loadings could be reduced to a level
of less than 10À1 mol% (turnover number ≥ 1000), not only the
cost of catalyst could be minimized but also its recovery from
the final product could be avoided. Recently, attention has
shifted towards ultra-low catalyst loading to make these
reactions more economical and practical.[18–23] Buchwald and
coworkers disclosed a new class of monophosphine ligands,
which conferred unprecedented activity even at low catalyst
loadings. For example, the coupling of 4-tert-butylbromobenzene
with 2-methylphenylboronic acid using 5 ppm Pd(OAc)2 provided
89% isolated yield after 24 h. Strong s-donor capability and steric
hindrance of these monophosphines is the key to achieving the
catalyst activity.[24–27] Since 2000, a few multidentate phosphine
ligands have been synthesized;[28–31] however, most of them were
poorly exploited in palladium catalysis. Doucet and Santelli
designed a cyclopentane alkyl backbone tetraphosphine: Tedicyp.
A remarkable turnover number (TON) of 2 500 000 was obtained
for the Suzuki reaction of 4-bromoanisole after 135 h.[32–36]
Recently, a cyclodextrin–tetraphosphine hybrid coined a-Cytep
was synthesized and assessed in the Suzuki reaction, which dis-
played exceptionally high TONs and turnover frequencies (TOFs).
For the coupling of 4-bromoanisole and phenylboronic acid, an
outstanding TON of 60 000 000 was achieved.[37] Kinetic experi-
ments and poisoning studies indicated that soluble Pd(0)
species generated by the decomposition of palladium complexes
performed the catalytic reaction.[38–43] The chelating effect of
and extends the catalyst longevity, which also sheds light on
the development of ultra-low loading catalytic processes.
However, the long synthetic route of the above-mentioned
tetraphosphines limits their applications.[28,32,37] A tetraphosphine,
N,N,N′,N′-tetra(diphenylphosphinomethyl)-1,2-ethylenediamine
1
(Fig. 1),[44] which is easily prepared from commercially available
reactants in three steps combining [Pd(Z3-C3H5)Cl]2 showed good
activity for the Heck reaction and the catalyst loading could be
lowered to 0.1 mol%.[45] In this paper, 1 associated with the conven-
tional catalytic precursor PdCl2 was used for Suzuki–Miyaura
coupling to investigate its catalytic performance.
Results and Discussion
In order to optimize the reaction parameters, we initially tested
the coupling of 4-bromoanisole with phenylboronic acid as the
model reaction. After examining the effects of various bases and
solvents, we found the best result was provided when dioxane
and KOH were used as solvent and base, respectively. The
electron-rich substrate 4-bromoanisole was almost completely
converted into the desired product using 0.1 mol% PdCl2 and
0.1 mol% tetraphosphine 1 in 1 h at 90 ꢀC (Table 1, entry 1).
*
Correspondence to: Ruixiang Li, Key Laboratory of Green Chemistry and Tech-
nology, Ministry of Education, Department of Chemistry, Sichuan University,
Chengdu, Sichuan 610064, People’s Republic of China. Email: liruixiang@scu.
edu.cn; scu.ruixiang@gmail.com
Key Laboratory of Green Chemistry and Technology, Ministry of Education,
Department of Chemistry, Sichuan University, Chengdu, Sichuan 610064,
People’s Republic of China
Appl. Organometal. Chem. 2012, 26, 342–346
Copyright © 2012 John Wiley & Sons, Ltd.

A tetraphosphine used in palladium-catalyzed Suzuki–Miyaura coupling
PPh2
longevity, which is probably attributed to stabilization of the tet-
raphosphine to the active palladium species. The results also
demonstrated that multidentate ligand had advantages for the
exploring of low loading catalyst. It is noteworthy that when
the catalyst loading was minimized to 0.001 mol% KOH was not
suitable as base (Table 1, entries 5, 7). Strong basicity seems to
influence the catalytic efficiency and benefit the formation of
by-product biphenyl when the palladium loading was reduced
to a low level. A weaker base, K2CO3, could be more favorable
(Table 1, entries 6, 8, 9).
N
N
PPh2
PPh2
PPh2
Subsequently, we investigated the scope of the palladium–
tetraphosphine 1 catalyst for the Suzuki–Miyaura reaction. A
survey of catalytic cross-coupling of aryl and heteroaryl
bromides with phenylboronic acid is provided in Table 2.
Electron-rich as well as electron-poor aryl bromides could couple
efficiently in the presence of 0.01 mol% catalyst (Table 2, entries
1–13). As expected, the steric hindrance of aryl bromides had an
effect on the reaction rate. We studied the influence of the ortho
substituent on the aryl bromides (Table 2, entries 3–5). 4-Bromoto-
luene and 2-bromotoluene coupled with phenylboronic acid gave
isolated yields of 92% (Table 2, entry 3) and 88% (Table 2, entry
4), respectively, which elucidated that one ortho substituent might
not influence the reaction rate. However, just 75% yield of product
was obtained when 2,6-dimethylbromobenzene was used (Table 2,
entry 5), even when the reaction time was prolonged to 4 h. The
presence of two ortho substituents reduced the reaction rate
obviously. Some activated substrates bearing functional groups
(Table 2, entries 7–13) were sensitive to the strong basicity of
KOH, which led to the formation of undesired products. Thus
K3PO4 was used instead.
Figure 1. Tetraphosphine N,N,N′,N′-tetra(diphenylphosphinomethyl)-1,2-
ethylenediamine (1)
Intriguingly, when the catalyst loading was decreased to 0.01 mol
%, 4-bromoanisole could not be detected after 2 h (Table 1,
entry 2). The above results showed the high activity of the catalyst
system.
Next, we tried to evaluate the importance of the presence of
tetraphosphine 1. We performed the reaction with 0.01 mol%
PdCl2 as catalyst in the absence of ligand. After 2 h a low yield
of 15% was obtained (Table 1, entry 3). It is suggested that the
addition of ligand 1 improved the activity or stability of the
palladium species.
We then tried to determine the limitation of the catalyst load-
ing. For the coupling of 4-bromoanisole with phenylboronic acid,
a yield of 98% was still achieved in the presence of 0.001 mol%
catalyst after 20 h (Table 1, entry 6). Finally, the reaction could
be performed with a catalyst loading as low as 0.0001 mol%. In
order to shorten the reaction time, the temperature was raised
to 110 ꢀC. After 40 h, only 41% conversion of 4-bromoanisole
was observed (Table 1, entry 8). When the reaction time
extended to 100 h a high TON of 750 000 was achieved (Table 1,
entry 9), and the yield of product did not increase any further
even when the reaction time was further prolonged to 120 h.
The results indicated that the catalyst system might have a good
Heteroaryls have important biological properties.[46–48] For
electronic or poisoning reasons, Suzuki reactions with heteroaryl
halides as substrates generally proceed slowly and require high
catalyst loadings.[49–51] In the presence of PdCl2/tetraphosphine
1, electron-poor heteroaromatics such as pyridine, pyrimidine
and quinoline led to coupling products in morderate to good
Table 1. The effect of catalyst loadings in the Suzuki cross-coupling reactiona
Entry
Pd loading (mol%)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
0.1
1
2
99
99
15b
95c
82
98c
27d
41c,e
75c,e
0.01
0.01
2
0.01
2
0.001
0.001
0.001
0.0001
0.0001
20
20
20
40
100
aReaction conditions: 4-bromoanisole 1 mmol, phenylboronic acid 1.5 mmol, KOH 2 mmol, 1/PdCl2 = 1/1, dioxane 3 ml, temperature 90 ꢀC, yield
analysed by gas chromatography.
bNo ligand.
cK2CO3 as base (2 mmol).
dKOH 4 mmol.
eTemperature 110 ꢀC.
Appl. Organometal. Chem. 2012, 26, 342–346
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K Wang et al.
Table 2. Suzuki coupling of phenylboronic acid with aryl and heteroaryl halidesa
Entry
Substrate
4-Bromoanisole
Base
Time (h)
Yield (%)
1
KOH
2
2
99
97
92
88
75
99
99
97
99
99
97
96
94
38b
93c
99
55
99b
10b
7b
2
3-Bromoanisole
KOH
3
4-Bromotoluene
KOH
2
4
2-Bromotoluene
KOH
2
5
2,6-Dimethylbromobenzene
4-Bromobenzotrifluoride
4-Bromonitrobenzene
2-Bromonitrobenzene
4-Bromobenzonitrile
4-Bromoacetophenone
3-Bromoacetophenone
4-Bromobenzaldehyde
3-Bromobenzaldehyde
2-Bromopyridine
KOH
4
6
KOH
1
7
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K3PO4
K3PO4
2
8
2
9
2
10
11
12
13
14
15
16
17
18
19
20
2
4
2
4
6
3-Bromopyridine
6
5-Bromopyrimidine
3-Bromoquinoline
6
6
2-Bromothiophene
4-Chloronitrobenzene
4-Chlorobenzotrifluoride
20
20
20
aReaction conditions: aryl or heteroaryl halides 1 mmol, phenylboronic acid 1.5 mmol, base 2 mmol, 1/PdCl2 = 1/1, substrate/catalyst = 10 000,
dioxane 3 ml, temperature 90 ꢀC, isolated yield.
bSubstrate/catalyst = 1000.
cSubstrate/catalyst = 2000.
yield (Table 2, entries 14–17). We studied the influence of the
position of bromide on the pyridine ring, and an obvious effect
on the reaction rate was observed. Ideally, owing to the
electronegativity of the nitrogen atom, 2-bromopyridine
should be more susceptible to the oxidative addition step than
3-bromopyridine. In fact, our results were contrary. The coupling
of phenylboronic acid with 3-bromopyridine resulted in a good
yield of 93% (Table 2, entry 15), but with 2-bromopyridine a
low yield of 38% was obtained even if the catalyst loading was
increased to 0.1 mol% (Table 2, entry 14). This is generally
assumed to be an interaction between nitrogen atom and palla-
dium, restraining the reaction rate. Thiophene is a p-electron
excessive heteroaromatic, which is unfavorable for the oxidative
addition process, but 2-bromothiophene coupled with phenyl-
boronic gave an excellent yield of 99% in the presence of
0.1 mol% catalyst (Table 2, entry 18).
Unfortunately, the catalyst system combining PdCl2 with tetra-
phosphine 1 is not active for aryl chlorides. Even with substrates
bearing electron-withdrawing groups, very low yields were
obtained (Table 2, entries 19, 20). Ligands always play important
roles in some or all of the catalytic steps. Electron-rich ligands
facilitate oxidative addition, and those with steric pressure may
accelerate the reductive elimination step. The combination of
both electronic and steric properties in these ligands are efficient
for the Suzuki reactions of non-activated substrates. The lack of
sufficient steric pressure in tetraphosphine 1, which is ascribed
to the flexibility of the 1,2-ethylenediamine backbone, probably
leads to the catalytic system being unfavorable for the reactions
of aryl chlorides. We are designing and preparing new ligands
possessing a fine balance of electronic and steric properties in
the hope that these ligands will exhibit a better catalytic
performance.
In the past decade, some effort has been devoted to the cou-
pling of sterically hindered aryl halides and arylboronic
acids.[23,52–55] However, arylboronic acids possessing two ortho
substituents are less involved.[24,35] We investigated the efficiency
of our catalytic system for the coupling of 2,6-dimethylphenyl-
boronic acid with sterically hindered aryl bromides (Table 3).
Compared to the reaction of 2,6-dimethylbromobenzene with
phenylboronic acid (Table 2, entry 5), the coupling of bromoben-
zene with 2,6-dimethylphenylboronic acid was much more
difficult. Only a trace amount (<3%) of biaryl adduct was
detected in the presence of 0.01 mol% catalyst (Table 3, entry
1). This result indicated that the transmetallation of sterically
hindered arylboronic acid with palladium occurred more slowly
than the oxidative addition of sterically hindered arylbromides.
As expected, a steric effect for the substituted arylbromides in
ortho position was observed. For the coupling of 2-bromotoluene
with 2,6-dimethylphenylboronic acid, 1 mol% PdCl2 resulted in a
yield of 74% (Table 3, entry 5); however, 6% product was obtained
under the same conditions when 2,6-dimethylbromobenzene was
used (Table 3, entry 6). The low reaction rate suggested that the
transmetallation of boronic acid with the palladium centre seems
to be the rate-determining step.
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Appl. Organometal. Chem. 2012, 26, 342–346

A tetraphosphine used in palladium-catalyzed Suzuki–Miyaura coupling
Table 3. Suzuki coupling of sterically hindered aryl bromides with 2,6-dimethylphenylboronic acida
Entry
Aryl bromide
Bromobenzene
Pd loading (mol%)
Yield (%)
1
2
3
4
5
6
7
0.01
0.1
1
trace b,c
32b
97
2-Bromotulene
0.1
1
8b
74
2,6-Dimethylbromobenzene
1
6d
2
9d
aReaction conditions: aryl bromide 1 mmol, 2,6-dimethylphenylboronic acid 1.5 mmol, KOH 2 mmol, 1/PdCl2 = 1/1, dioxane 3 ml, temperature 100 ꢀC,
20 h, isolated yield.
bGas chromatographic yield.
cTemperature 90 ꢀC.
dGas chromatographic–mass spectrometric yield.
with an isolated yield. See supporting information for general
experimental details, synthetic procedure of the ligand and
Conclusion
In summary, PdCl2 associated with an easily synthesized
tetraphosphine N,N,N′,N′-tetra(diphenylphosphinomethyl)-1,2-
ethylenediamine 1 affords an efficient catalytic system for
Suzuki cross coupling reaction. With the catalyst loading of
0.0001 mol%, the electron-rich substrate 4-bromoanisole couples
with phenylboronic acid in a high TON of 750,000. A broad scope
of aryl and heteroaryl bromides can generate the desired products
in good yields, and the coupling of 2,6-dimethylphenylboronic
acid with sterically hindered aryl bromides leads to lower
reaction rates. The advantages of this catalyst system may be
attributed to the strong coordination ability of ligand 1 with
palladium. However, this system is not active for aryl chlorides.
Further work to improve the structure of the ligand is planned.
characterization data for the catalytic products.
References
[1] N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457.
[2] R. Capdeville, E. Buchdunger, J. Zimmermann, A. Matter, Nat. Rev.
Drug Discov. 2002, 1, 493.
[3] M. Vilaró, G. Arsequell, G. Valencia, A. Ballesteros, J. Barluenga, Org.
Lett. 2008, 10, 3243.
[4] J. P. Heiskanen, O. E. O. Hormi, Tetrahedron 2009, 65, 518.
[5] K. Pomeisl, A. Holý, R. Pohl, K. Horská, Tetrahedron 2009, 65, 8486.
[6] M. B. Andrus, C. Song, Org. Lett. 2001, 3, 3761.
[7] R. C. Smith, R. A. Woloszynek, W. Z. Chen, T. Ren, J. D. Protasiewicz,
Tetrahedron Lett. 2004, 45, 8327.
[8] T. Itoh, T. Mase, Tetrahedron Lett. 2005, 46, 3573.
[9] C. Wolf, K. Ekoue-Kovi, Eur. J. Org. Chem. 2006, 1917.
[10] E. A. B. Kantchev, C. J. O’Brien, M. G. Organ, Angew. Chem. Int. Ed.
2007, 46, 2768.
[11] F. W. Li, S. Q. Bai, T. S. A. Hor, Organometallics 2008, 27, 672.
[12] D. H. Lee, Y. H. Lee, D. I. Kim, Y. Kim, W. T. Lim, J. M. Harrowfield, P.
Thuéry, M. J. Jin, Y. C. Park, I. M. Lee, Tetrahedron 2008, 64, 7178.
[13] V. Polshettiwar, A. Decottignies, C. Len, A. Fihri, ChemSusChem 2010,
3, 502.
[14] H. Bonin, E. Fouquet, F. X. Felpin, Adv. Synth. Catal. 2011, 353, 3063.
[15] A. Fihri, M. Bouhrara, B. Nekoueishahraki, J. M. Basset, V. Polshettiwar,
Chem. Soc. Rev. 2011, 40, 5181.
[16] V. Farina, Adv. Synth. Catal. 2004, 346, 1553.
[17] J. P. Corbet, G. Mignani, Chem. Rev. 2006, 106, 2651.
[18] D. A. Albisson, R. B. Bedford, S. E. Lawrence, P. N. Scully, Chem.
Commun. 1998, 2095.
[19] A. Zapf, A. Ehrentraut, M. Beller, Angew. Chem. Int. Ed. 2000, 39, 4153.
[20] J. C. Hierso, A. Fihri, R. Amardeil, P. Meunier, H. Doucet, M. Santelli,
Tetrahedron 2005, 61, 9759.
[21] A. Scrivanti, M. Bertoldini, U. Matteoli, S. Antonaroli, B. Crociani,
Tetrahedron 2009, 65, 7611.
[22] D. Yuan, H. V. Huynh, Organometallics 2010, 29, 6020.
[23] D. Schaarschmidt, H. Lang, ACS Catal. 2011, 1, 411.
[24] J. P. Wolfe, R. A. Singer, B. H. Yang, S. L. Buchwald, J. Am. Chem. Soc.
1999, 121, 9550.
[25] T. E. Barder, S. D. Walker, J. R. Martinelli, S. L. Buchwald, J. Am. Chem.
Soc. 2005, 127, 4685.
[26] K. Billingsley, S. L. Buchwald, J. Am. Chem. Soc. 2007, 129, 3358.
[27] R. Martin, S. L. Buchwald, Acc. Chem. Res. 2008, 41, 1461.
Experimental
General Procedure of Suzuki Coupling Reactions
All reactions were carried out under argon atmosphere with the
standard Schlenk techniques. Tetraphosphine
1
(8.5 mg,
0.01 mmol) and PdCl2 (1.8 mg, 0.01 mmol) were added to a
Schlenk tube equipped with a magnetic bar, and then degassed
DMF (1 ml) was added. The mixture was stirred overnight at room
temperature. 4-Bromoanisole (125 ml, 1 mmol), phenylboronic
acid (183 mg, 1.5 mmol) and KOH (112 mg, 2 mmol) were added
to another Schlenk tube with a magnetic bar. The dissolved mix-
ture of tetraphosphine 1/PdCl2 (10 ml, 0.0001 mmol) was trans-
ferred to the Schlenk tube of reactants by syringe. Then, dioxane
(3 ml) was added. The reaction mixture was heated at 90 ꢀC for
2 h. At the end of the reaction, the solution was cooled to room
temperature and water (5 ml) was added. The mixture solution
was extracted with ethyl acetate (3 Â 5 ml) and the organic layer
was dried over magnesium sulfate. The dried solution was filtered
and reduced to approx. 1–2 ml under vacuum, then purified with
silica gel chromatography to give the corresponding product
Appl. Organometal. Chem. 2012, 26, 342–346
Copyright © 2012 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

K Wang et al.
[28] J. C. Hierso, A. Fihri, R. Amardeil, P. Meunier, H. Doucet, M. Santelli,
B. Donnadieu, Organometallics 2003, 22, 4490.
[42] D. E. Bergbreiter, P. L. Osburn, J. D. Frels, Adv. Synth. Catal. 2005,
347, 172.
[29] C. Bianchini, H. M. Lee, A. Meli, W. Oberhauser, F. Vizza, P. Brüggeller,
H. B. Rainer, C. Langes, Chem. Commun. 2000, 777.
[43] M. R. Eberhard, Org. Lett. 2004, 6, 2125.
[44] A. L. Balch, M. M. Olmstead, S. P. Rowley, Inorg. Chim. Acta 1990,
168, 255.
[45] X. J. Yu, R. Zhou, Y. Zhang, H. Y. Fu, R. X. Li, H. Chen, X. J. Li, Catal.
Commun. 2010, 12, 222.
[46] R. A. Hughes, C. J. Moody, Angew. Chem. Int. Ed. 2007, 46, 7930.
[47] V. F. Slagt, A. H. M. de Vries, J. G. de Vries, R. M. Kellogg, Org. Process
Res. Dev. 2010, 14, 30.
[30] P. Nair, G. K. Anderson, N. P. Rath, Organometallics 2003, 22, 1494.
[31] T. Imamoto, K. Yashio, K. V. L. Crépy, K. Katagiri, H. Takahashi, M.
Kouchi, I. D. Gridnev, Organometallics 2006, 25, 908.
[32] D. Laurenti, M. Feuerstein, G. Pèpe, H. Doucet, M. Santelli, J. Org.
Chem. 2001, 66, 1633.
[33] M. Feuerstein, D. Laurenti, C. Bougeant, H. Doucet, M. Santelli, Chem.
Commun. 2001, 325.
[48] D. B. Zhao, J. S. You, C. W. Hu, Chem. Eur. J. 2011, 17, 5466.
[49] E. Tyrrell, P. Brookes, Synthesis 2003, 4, 469.
[50] T. Cailly, F. Fabis, R. Legay, H. Oulyadi, S. Rault, Tetrahedron 2007,
63, 71.
[34] M. Feuerstein, H. Doucet, M. Santelli, Synlett 2001, 9, 1458.
[35] M. Feuerstein, H. Doucet, M. Santelli, Tetrahedron Lett. 2001,
42, 6667.
[36] M. Feuerstein, H. Doucet, M. Santelli, J. Organomet. Chem. 2003,
687, 327.
[51] N. A. Jones, J. W. Antoon, A. L. Bowie, J. B. Borak, E. P. Stevens, J.
Heterocycl. Chem. 2007, 44, 363.
[37] E. Zaborova, J. Deschamp, S. Guieu, Y. Bleriot, G. Poli, M. Menand, D.
Madec, G. Prestat, M. Sollogoub, Chem. Commun. 2011, 47, 9206.
[38] J. A. Widegren, R. G. Finke, J. Mol. Catal. A: Chem. 2003, 198, 317.
[39] I. P. Beletskaya, A. V. Cheprakov, J. Organomet. Chem. 2004, 689, 4055.
[40] J. Dupont, C. S. Consorti, J. Spencer, Chem. Rev. 2005, 105, 2527.
[41] K. Q. Yu, W. Sommer, J. M. Richardson, M. Weck, C. W. Jones, Adv.
Synth. Catal. 2005, 347, 161.
[52] N. Kataoka, Q. Shelby, J. P. Stambuli, J. F. Hartwig, J. Org. Chem. 2002,
67, 5553.
[53] G. Adjabeng, T. Brenstrum, J. Wilson, C. Frampton, A. Robertson, J.
Hillhouse, J. McNulty, A. Capretta, Org. Lett. 2003, 5, 953.
[54] T. Hoshi, I. Saitoh, T. Nakazawa, T. Suzuki, J. Sakai, H. Hagiwara, J. Org.
Chem. 2009, 74, 4013.
[55] J. L. Bolliger, C. M. Frech, Chem. Eur. J. 2010, 16, 4075.
wileyonlinelibrary.com/journal/aoc
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