Efficient copper-catalyzed ullmann reaction of aryl bromides with imidazoles in water promoted by a pH-Responsive ligand

Article abstract of DOI:10.1002/cctc.201300257

A series of 1,10-phenanthroline derivatives were used as supporting ligands for copper-catalyzed Ullmann reaction in neat water. The catalytic system based on 4,7-dihydroxy-1,10-phenanthroline has demonstrated the promising catalytic performances for aryl

Full text of DOI:10.1002/cctc.201300257

CHEMCATCHEM
FULL PAPERS
DOI: 10.1002/cctc.201300257
Efficient Copper-Catalyzed Ullmann Reaction of Aryl
Bromides with Imidazoles in Water Promoted by a pH-
Responsive Ligand
Rui Lv,[a, b] Yangxin Wang,[a, b] Chunshan Zhou,[a] Liuyi Li,[a] and Ruihu Wang*[a]
A series of 1,10-phenanthroline derivatives were used as sup-
porting ligands for copper-catalyzed Ullmann reaction in neat
water. The catalytic system based on 4,7-dihydroxy-1,10-phe-
nanthroline has demonstrated the promising catalytic perform-
ances for aryl bromides. The catalytic system was applicable to
a wide scope of substrates, high catalytic activity and selectivi-
ty were observed for the reactions of electron-deficient, elec-
tron-rich, and heterocyclic aryl bromides with imidazoles con-
taining different steric hindrance. The superior promoting
effect of 4,7-dihydroxy-1,10-phenanthroline is attributed to its
water solubility under the basic conditions.
Introduction
Transition-metal catalyzed cross-coupling reaction is an effi-
cient and versatile tool in organic synthesis for the connection
of two fragments through CÀC or CÀN formation.[1,2] Among
them, Ullmann-type coupling reactions are particularly attrac-
tive because they often allow the usage of low-cost starting
materials and readily available copper complexes.[3–7] However,
the initial protocols required harsh conditions, such as high
temperatures and stoichiometric proportion of copper re-
agents.[3] Recent approaches, which are involved in the judicial
combination of organic ligands and copper ions, enable the re-
actions to be efficiently performed under the milder condi-
tions.[4–7] Various types of ligands have been developed to facil-
itate the copper-catalyzed N-arylation of azoles with aryl hal-
ides. The use of the ligands not only increases the solubility of
copper salts in reaction media and prevents their aggregation
in the reaction process, but also enhances the reaction rate by
varying the electronic and steric characters of the catalytic spe-
cies.[5,6] Some elegant concepts for homogenous[4–6] and heter-
ogeneous[7] protocols were developed based on the strategies,
but these reactions were generally operated in volatile organic
solvents or the mixed H2O/organic solvents.
try have resulted from organic solvents.[8] Although the reac-
tion rate in water may be slower than those in organic sol-
vents, water is regarded as an environmentally benign and
cheap medium, in which the unique reactivity is often ob-
served.[9] Furthermore, the use of water-soluble catalytic sys-
tems may help simplify separation, recovery, and recycling of
the catalysts.[10] Obviously, smooth implementation of the cata-
lytic reactions in water requires the catalysts to be water-solu-
ble. It is a common method to make metal complexes water-
soluble by attaching ionic groups, such as sulfonate,[11] carbox-
ylate,[12] and ammonium[13] to hydrophobic ligands. The majori-
ty of studies for transition-metal-catalyzed cross-coupling reac-
tions in water have been concentrated on expensive palladium
catalysts. In contrast, little progress has been reported for
copper-catalyzed coupling reactions of aryl halide and azoles
in neat water.[14]
During the investigation of Cu-catalyzed Ullmann-type cross-
coupling reactions, it was noted that high catalytic activity was
usually achieved in the Cu/bidentate N,N-[5a,6,15] and N,O-sys-
tems,[16] owing to the formation of stable copper-chelating
species in catalytic reactions. Moreover, the steric and electron-
ic properties of the bidentate ligands, which dictate activity, se-
lectivity, and stability of the catalysts, could be modified by
variation of the substituents in organic ligands. Among biden-
tate ligands, 1,10-phenanthroline and its derivatives[6] are one
type of promising ligands for copper-catalyzed N-arylation of
imidazoles with aryl halides owing to their strong electron-do-
nating ability and ready availability (Scheme 1). However, the
catalytic reactions were performed in organic solvents, and the
hydrophobicity of these organic ligands limited their applica-
tion in water. In our continuous effort to develop catalytic pro-
tocols in neat water,[17] we are interested in 4,7-dihydroxy-1,10-
phenanthroline (L1), which is water-soluble under basic condi-
tions; this provides a possibility for the development of
copper-catalyzed organic reactions in neat water. Herein, we
report a simple and efficient catalytic system for Ullmann
Organic reactions in water are of highly practical value be-
cause most wastes per mass unit produced in chemical indus-
[a] R. Lv, Y. Wang, Dr. C. Zhou, Dr. L. Li, Prof. R. Wang
State Key Laboratory of Structural Chemistry
Key Laboratory of Coal to Ethylene Glycol and Its Related Technology
Fujian Institute of Research on the Structure of Matter
Chinese Academy of Science
Fuzhou, Fujian, 350002 (China)
Fax: (+86)591-83714946
E-mail: ruihu@fjirsm.ac.cn
[b] R. Lv, Y. Wang
University of Chinese Academy of Sciences
Beijing 100049 (China)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201300257.
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 2978 – 2982 2978

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
water, but it can dissolve in water after deprotona-
tion of two hydroxyl groups in the presence of base
(Figure 1), which results in high catalytic activity in
the cross-coupling reaction. Although L4 also con-
tains two hydroxyl groups, L4 is water-insoluble
under basic conditions. It is not surprising that no
Scheme 1. 1,10-Phenanthroline and its derivatives employed in this work.
cross-coupling coupling reactions of aryl bromides with imida-
zoles promoted by L1 under mild conditions in neat water.
Results and Discussion
To test the catalytic performances of L1-supported copper spe-
cies and optimize reaction conditions, as shown in Table 1, the
cross-coupling reaction of 4-bromotoluene and imidazole was
initially performed by using 20 mol% L1, 10 mol% CuI in the
presence of tetrabutylammonium bromide (TBAB) and Cs2CO3
Figure 1. The pH-responsive behavior of L1.
Table 1. Screening reaction conditions for N-arylation of imidazole with
product was observed in the absence of the supporting ligand
(entry 6). If the molar ratio of L1 to CuI was decreased from 2
to 1, the GC yield sharply decreased to 34% (entry 7). To deter-
mine the most suitable reaction conditions for N-arylation of
imidazole, the catalytic system was examined by using differ-
ent copper sources, bases, and additives. It was found that
CuBr, CuCl2, Cu2O, and CuO were considerably inferior to CuI,
and the target product was obtained in moderate yields (en-
tries 9–12), CuCl was less efficient and only gave 35% GC yield
under similar conditions (entry 8). It was known that phase-
transfer catalysts may favor a better contact between the sub-
strates and the aqueous catalytic species, and may accelerate
the reaction rate in aqueous solution. The absence of TBAB re-
sulted in 41% GC yield (entry 13). Sodium dodecyl sulfate
(SDS) and sodium dodecylbenzene sulfonate (SDBS) were also
used as phase-transfer catalysts. The reaction was promoted
by them, but SDS and SDBS were less effective than TBAB and
N-(4-tolyl)imidazole was formed in 83% and 67% GC yields, re-
spectively (entries 14 and 15). Bu4NOH was usually employed
as both base and phase-transfer catalyst, but the presence of
25% aqueous Bu4NOH resulted in a 48% GC yield (entry 16),
which was slightly higher than that in the absence of TBAB.
Among the bases tested, K3PO4 was found to be the most ef-
fective, an almost quantitative yield was achieved (entry 20),
whereas Cs2CO3, K2CO3, NaOH, and NEt3 were slightly less effec-
tive and gave moderate to excellent GC yields under the same
conditions (entries 1, 17–19). If copper loading was decreased
to 1%, an 18% GC yield was obtained under the same condi-
tions (entry 21). Wang et al. reported a 90% GC yield in the
cross-coupling reaction of 4-bromotoluene and imidazole by
using 1 mol% CuI as the copper source and 2 mol% 6,7-dihy-
droquinolin-8(5H)-one oxime as the supporting ligand, but the
reaction was operated at 1208C for 48 h.[14g]
4-bromotoluene.[a]
Entry
Cu source
Ligand
Base
Additive
Yield [%][b]
1
2
3
4
5
6
7[c]
8
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuCl
CuBr
CuCl2
Cu2O
CuO
CuI
CuI
CuI
CuI
CuI
L1
L2
L3
L4
L5
–
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Bu4NOH
NaOH
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
–
SDS
SDBS
–
TBAB
TBAB
TBAB
TBAB
TBAB
90 (82)
<1
<1
<1
<1
<1
34
35
75
75
59
66
41
83
67
48
67
71
85
L1
L1
L1
L1
L1
L1
L1
L1
L1
L1
L1
L1
L1
L1
L1
9
10
11[d]
12
13
14
15
16[e]
17
18
19
20
21
CuI
CuI
CuI
CuI
Net3
K2CO3
K3PO4
K3PO4
99 (95)
18
[a] Reaction conditions: 4-bromotoluene (0.50 mmol), imidazole
(0.60 mmol), base (1.00 mmol), Cu source (0.05 mmol), ligand
(0.10 mmol), additive (0.25 mmol), H2O (2.0 mL), 1008C, under N2, 24 h;
[b] GC yields, isolated yields are given in parentheses; [c] The molar of
CuI-to-L ratio was 1:1; [d] An amount of 0.025 mmol Cu2O was used;
[e] 25% aqueous Bu4NOH solution (1.05 mL) was used as the base; [f] An
amount of 0.005 mmol CuI was used.
at 1008C in neat water; N-(4-tolyl)imidazole was obtained in
90% GC yield after 24 h (entry 1). However, if 1,10-phenanthro-
line and its derivatives (L2–L5) were used as supporting li-
gands, only trace amount of the target product was detected
under the same conditions (entries 2–5). The water insolubility
of L2–L5 under the reaction conditions was responsible for
their poor catalytic activity in water. L1 is also insoluble in
The scope and generality of aryl bromides were then investi-
gated under the optimized reaction conditions. As shown in
Table 2, the effect of varying aryl bromides was explored by
using imidazole as the nucleophile (entries 1–11). The para-
substituted electron-rich and electron-deficient aryl bromides
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 2978 – 2982 2979

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
Table 2. N-Arylation of imidazoles with aryl bromides catalyzed by CuI/L1
in water.[a]
Table 2. (Continued)
Entry
Ar-X
Nucleophile
Product
Yield[b]
[%]
Entry
Ar-X
Nucleophile
Product
Yield[b]
[%]
20
99 (93)
1
2
3
4
5
6
7
99 (95)
99 (93)
99 (93)
95
[a] Reaction conditions: aryl bromides (0.50 mmol), N-nucleophile
(0.60 mmol), K3PO4 (1.00 mmol), CuI (0.05 mmol), L1 (0.10 mmol), TBAB
(0.25 mmol), H2O (2.0 mL), 1008C, N2; [b] GC yields, isolated yields are
given in parentheses; [c] An amount of 0.25 mmol 2,6-dibromopyridine
was used.
afforded the desirable products in almost quantitative yields
(entries 1–5). A variety of functional groups, such as acetyl,
ether, trifluoromethyl, and hydroxyl, were tolerated well in the
catalytic system, In addition, the electronic nature in para-posi-
tioned substituents of aryl bromides did not seem to affect the
cross-coupling reaction.
97 (94)
93
Noteworthy, the reaction between 4-bromophenol and imi-
dazole selectively gave rise to 1-(4-hydroxyphenyl)-1H-imida-
zole in a 94% isolated yield regardless of the hydroxyl groups
in the supporting ligand (entry 5), moreover, no formation of
diaryl ether was observed, suggesting good chemoselectivity
of the catalytic system in neat water. The cross-coupling reac-
tions between imidazole and meta-substituted aryl bromides,
such as 3-bromoanisole and 3-bromotoulene, were also
smoothly carried out, 1-(3-methoxyphenyl)-1H-imidazole and
1-m-tolyl-1H-imidazole were obtained in 93% and 95% GC
yields, respectively (entries 6 and 7). Interestingly, N-arylation
reaction between imidazole and 5-bromo-m-xylene gave the
target product in a 73% GC yield (entry 8). In comparison, if 2-
bromotoluene was used as the substrate, 1-o-tolyl-1H-imida-
zole was produced in a 27% GC yield (entry 9), which was
much lower than the yields if 3- or 4-bromotoluene was used,
attributed to the steric effect of the methyl group. The catalyt-
ic system was also applied to N-arylation reactions of nitrogen-
containing heteroaryl bromides with imidazole. The coupling
reactions of imidazole with 2-bromopyridine and 2,6-dibromo-
pyridine gave the corresponding N-arylimidazoles in almost
quantitative yields (entries 10 and 11). These products are po-
tentially good candidates for the preparation of N-heterocyclic
carbene compounds, and their palladium(II) complexes have
shown the excellent activities in many organic transformation-
s.[12a,18] Thus, this catalytic system provides a valuable route for
the preparation of functionalized N-heterocyclic carbene pre-
cursors.
95 (88)
8
73
9
27
10
99 (80)
11[c]
99
12
13
14
15
93
72
99 (87)
99 (84)
16
17
99 (87)
79
The excellent catalytic performances of the catalytic system
encouraged us to further examine N-arylation reactions be-
tween imidazole derivatives and aryl bromides. Aryl bromides
with electron-withdrawing groups, such as 4-bromoacetophe-
none, were efficiently coupled with the sterically hindered nu-
cleophiles, such as 2-methyl-, 2-ethyl-, and 2-isopropylimida-
zole, the corresponding products were obtained in almost
quantitative yields (entries 14–16). However, the cross-coupling
reaction of 4-bromotoluene with 2-methyl- and 2-ethylimida-
zole gave the resulting products in 93 and 72% GC yields, re-
18
19
99 (97)
99 (94)
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 2978 – 2982 2980

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
spectively (entries 12 and 13). Interestingly, the N-arylation re-
action of 2-phenylimidazole and benzimidazole with 4-bro-
moacetophenone generated the desirable products in 79 and
99% GC yields, respectively (entries 17 and 18). 2-Bromopyri-
dine was also successfully arylated with 2-methylimidazole and
2-ethylimidazole and gave rise to the target products in almost
quantitative yields (entries 19 and 20).
Acknowledgements
This work was financially supported by 973 Program
(2010CB933501, 2011CBA00502), Natural Science Foundation of
China (21273239), Natural Science Foundation of Fujian Province
(2011J01064) and “One Hundred Talent Project” from Chinese
Academy of Sciences.
Keywords: chelates · copper · cross-coupling · homogeneous
catalysis · green chemistry
Conclusions
We have developed an efficient protocol for Cu-catalyzed Ull-
mann cross-coupling reactions of a variety of imidazoles with
aryl bromides, in which the catalytic system was promoted by
4,7-dihydroxy-1,10-phenanthroline in neat water. 4,7-Dihy-
droxy-1,10-phenanthroline is insoluble in water, but it can dis-
solve in water under basic conditions, resulting in superior cat-
alytic performances in N-arylation reactions of imidazoles with
aryl bromides. However, no catalytic activity was observed if
water-insoluble 1,10-phenathroline and its derivatives were
used as supporting ligands under the same conditions. This
study further extends the scope of copper-catalyzed Ullmann
cross-coupling reactions in water, and provides a new route for
the development of highly efficient catalytic systems. Further
investigation to broaden the scope of this catalytic system to
other reactions is currently on progress.
[1] a) F. Bellina, R. Rossi, Chem. Rev. 2010, 110, 1082–1146; b) G. Evano, N.
Blanchard, M. Toumi, Chem. Rev. 2008, 108, 3054–3131; c) M. Carril, R.
SanMartin, E. Domꢂnguez, Chem. Soc. Rev. 2008, 37, 639–647.
[2] a) P. Larsson, A. Correa, M. Carril, P. Norrby, C. Bolm, Angew. Chem. 2009,
121, 5801–5803; Angew. Chem. Int. Ed. 2009, 48, 5691–5693; b) V. Pol-
shettiwar, A. Decottignies, C. Len, A. Fihri, ChemSusChem 2010, 3, 502–
522; c) R. Z. Zhang, C. X. Miao, Z. Q. Shen, S. F. Wang, C. G. Xia, W. Sun,
ChemCatChem 2012, 4, 824–830.
[3] J. Lindley, Tetrahedron 1984, 40, 1433–1456.
[4] a) G. Franc, Q. Cacciuttolo, G. Lefꢃvre, C. Adamo, I. Ciofini, A. Jutand,
ChemCatChem 2011, 3, 305–309; b) F. Monnier, M. Taillefer, Angew.
Chem. 2009, 121, 7088–7105; Angew. Chem. Int. Ed. 2009, 48, 6954–
6971; c) M. Taillefer, A. Ouali, B. Renard, J. F. Spindler, Chem. Eur. J. 2006,
12, 5301–5313; d) H. Rao, Y. Jin, H. Fu, Y. Jiang, Y. Zhao, Chem. Eur. J.
2006, 12, 3636–3646; e) L. Zhu, L. Cheng, Y. Zhang, R. Xie, J. You, J. Org.
Chem. 2007, 72, 2737–2743.
[5] a) B. Chen, F. Li, Z. Huang, F. Xue, T. Lu, Y. Yuan, G. Yuan, ChemCatChem
2012, 4, 1741–1745; b) D. Jiang, H. Fu, Y. Jiang, Y. Zhao, J. Org. Chem.
2007, 72, 672–674; c) X. Lv, W. Bao, J. Org. Chem. 2007, 72, 3863–3867;
d) B. de Lange, M. H. Lambers-Verstappen, L. Schmieder-van de Vonder-
voort, N. Sereinig, R. de Rijk, A. H. M. de Vries, J. G. de Vries, Synlett
2006, 3105–3109; e) Z. Zhang, J. Mao, D. Zhu, F. Wu, H. Chen, B. Wan,
Tetrahedron 2006, 62, 4435–4443.
Experimental Section
L1,[6b] L3,[19] L4,[19] L5[20] were synthesized according to literature
methods, the others chemicals were purchased from commercial
suppliers and were used without further purification. 1H and
13C NMR spectra were recorded on a Bruker AVANCEIII NMR spec-
trometer at 400 and 100 MHz, respectively, by using deuterated
CDCl3 as locking solvent except otherwise indicated. GC analyses
were performed on a Shimadzu GC-2014 equipped with a capillary
[6] a) J. C. Antilla, J. M. Bassin, T. E. Barder, S. L. Buchwald, J. Org. Chem.
2004, 69, 5578–5587; b) R. A. Altman, A. Shafir, A. Choi, P. A. Lichtor,
S. L. Buchwald, J. Org. Chem. 2008, 73, 284–286; c) H. Maheswaran,
G. G. Krishna, K. L. Prasanth, V. Srinivas, G. K. Chaitany, K. Bhanuprakash,
Tetrahedron 2008, 64, 2471–2479; d) R. Q. Zhuang, J. Xu, Z. S. Cai, G.
Tang, M. J. Fang, Y. F. Zhao, Org. Lett. 2011, 13, 2110–2113.
[7] a) A. Ouali, R. Laurent, A. M. Caminade, J. P. Majoral, M. Taillefer, J. Am.
Chem. Soc. 2006, 128, 15990–15991; b) X. Lv, Z. Wang, W. Bao, Tetrahe-
dron 2006, 62, 4756–4761; c) W. Chen, Y. Zhang, L. Zhu, J. Lan, R. Xie, J.
You, J. Am. Chem. Soc. 2007, 129, 13879–13886; d) T. Miao, L. Wang, Tet-
rahedron Lett. 2007, 48, 95–99; e) A. Dhakshinamoorthy, S. Navalon, D.
Sempere, M. Alvaro, H. Garcia, ChemCatChem 2013, 5, 241–246; f) L.
Wang, J. Zhang, J. Sun, L. Zhu, H. Zhang, F. Liu, D. Zheng, X. Meng, X.
Shi, F. S. Xiao, ChemCatChem 2013, 5, 1606–1613.
column (RTX-5, 30 mꢁ0.25 mm) by using
a flame ionization
detector.
General procedures for N-arylation of imidazoles with aryl
bromides
[8] a) J. G. Concepciꢄn, A. D. Curzons, D. J. C. Constable, V. L. Cunningham,
Int. J. Life Cycle Assess. 2004, 9, 114–121; <lit b>A. Loppinet-Serani, C.
Aymonier, F. Cansell, ChemSusChem 2008, 1, 486–503.
A 25 mL Schlenk tube equipped with a magnetic stirring bar was
charged with CuI (0.05 mmol), organic ligands (0.1 mmol), K3PO4
(1.0 mmol), TBAB (0.25 mmol), imidazole (0.6 mmol), and aryl bro-
mide (0.5 mmol). For solid aryl bromides, the tube was evacuated
and back-filled with nitrogen, and this procedure was repeated
three times; for liquid aryl bromides, the reaction components
were added after removal of air. Then, water (2.0 mL) was added at
RT under a stream of nitrogen and the tube was sealed and stirred
in a preheated oil bath (1008C). After 24 h, the mixture was cooled
with icy water, the product was extracted with ethyl acetate (3ꢁ
5 mL). The combined organic layer was dried over Na2SO4 and the
solvent was removed under reduced pressure. The crude products
were purified by flash column chromatography on silica gel to
afford the desired product. The identity of the products was con-
firmed by comparison with literature spectroscopic data.
[9] a) C. J. Li, Chem. Rev. 2005, 105, 3095–3165; b) T. Dwars, G. Oehme, Adv.
Synth. Catal. 2002, 344, 239–260; c) C. M. Kleiner, P. R. Schreiner, Chem.
Commun. 2006, 4315–4317; d) C. Rçhlich, A. S. Wirth, K. Kçhler, Chem.
Eur. J. 2012, 18, 15485–15494.
[10] a) K. H. Shaughnessy, Chem. Rev. 2009, 109, 643–710; b) H. Tꢅrkmen, R.
Can, B. Cetinkaya, Dalton Trans. 2009, 7039–7044; c) Y. L. Hu, Q. Ge, Y.
He, M. Lu, ChemCatChem 2010, 2, 392–396.
[11] a) C. A. Fleckenstein, H. Plenio, Chem. Eur. J. 2007, 13, 2701–2716;
b) E. J. Garcꢂa Suarez, A. Ruiz, S. Castillꢄn, W. Oberhauser, C. Bianchini, C.
Claver, Dalton Trans. 2007, 2859–2861; c) A. Riisager, K. M. Eriksen, J.
Hjortkjær, R. Fehrmann, J. Mol. Catal. A 2003, 193, 259–272; d) E. Paet-
zold, G. Oehme, C. Fischer, M. Frank, J. Mol. Catal. A 2003, 200, 95–103.
[12] a) B. Inꢆs, R. SanMartin, M. Moure, E. Domꢂngueza, Adv. Synth. Catal.
2009, 351, 2124–2132; b) D. Baskakov, W. A. Herrmann, J. Mol. Catal. A
2008, 283, 166–170; c) Y. Otomaru, T. Senda, T. Hayashi, Org. Lett. 2004,
6, 3357–3359; d) R. Amengual, E. Genin, V. Michelet, M. Savignac, J. P.
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 2978 – 2982 2981

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
Genꢆt, Adv. Synth. Catal. 2002, 344, 393–398; e) M. Kant, S. Bischoff, R.
Siefkan, E. Grꢅndemann, A. Kçckritz, Eur. J. Org. Chem. 2001, 477–481.
[13] a) T. T. Hung, C. M. Huang, F. Y. Tsai, ChemCatChem 2012, 4, 540–545;
b) S. N. Chen, W. Y. Wu, F. Y. Tsai, Green Chem. 2009, 11, 269–274;
c) D. J. M. Snelders, R. Kreiter, J. Firet, G. van Koten, R. J. M. K. Gebbink,
Adv. Synth. Catal. 2008, 350, 262–266.
[14] a) H. J. Xu, F. Y. Zheng, Y. F. Liang, Z. Y. Cai, Y. S. Feng, D. Q. Che, Tetrahe-
dron Lett. 2010, 51, 669–671; b) Y. Wang, Z. Q. Wu, L. X. Wang, Z. K. Li,
X. G. Zhou, Chem. Eur. J. 2009, 15, 8971–8974; c) L. Liang, Z. K. Li, X. G.
Zhou, Org. Lett. 2009, 11, 3294–3297; d) J. S. Peng, M. Ye, C. J. Zong,
F. Y. Hu, L. T. Feng, X. Y. Wang, Y. F. Wang, C. X. Chen, J. Org. Chem. 2011,
76, 716–719; e) K. Swapna, S. N. Murthy, Y. V. D. Nageswar, Eur. J. Org.
Chem. 2010, 6678–6684; f) F. Ke, Y. Y. Qu, Z. Q. Jiang, Z. K. Li, D. Wu,
X. G. Zhou, Org. Lett. 2011, 13, 454–457; g) D. P. Wang, F. X. Zhang, D. Z.
Kuang, J. X. Yua, J. H. Lia, Green Chem. 2012, 14, 1268–1271.
Ku, T. Grieme, R. Henry, A. Bhatia, Tetrahedron Lett. 2006, 47, 149–153;
d) P. J. Fagan, E. Hauptman, R. Shapiro, A. Casalnuovo, J. Am. Chem. Soc.
2000, 122, 5043–5051.
[17] a) C. S. Zhou, J. Y. Wang, L. Y. Li, R. H. Wang, M. C. Hong, Green Chem.
2011, 13, 2100–2106; b) L. Y. Li, J. Y. Wang, C. S. Zhou, R. H. Wang, M. C.
Hong, Green Chem. 2011, 13, 2071–2077; c) L. Y. Li, J. Y. Wang, T. Wu,
R. H. Wang, Chem. Eur. J. 2012, 18, 7842–7851; d) F. Z. Kong, C. S. Zhou,
J. Y. Wang, Z. Y. Yu, R. H. Wang, ChemPlusChem 2013, 78, 536–545.
[18] a) Z. Xi, Y. Zhou, W. Chen, J. Org. Chem. 2008, 73, 8497–8501; b) M. Bor-
onat, A. Corma, C. G. Arellano, M. Iglesias, F. Sꢇnchez, Organometallics
2010, 29, 134–141.
[19] J. Ettedgui, Y. Diskin-Posner, L. Weiner, J. Am. Chem. Soc. 2011, 133,
188–190.
[20] G. I. Graf, D. Hastreiter, L. Everson da Silva, R. A. Rebelo, A. G. Montalban,
A. McKillop, Tetrahedron 2002, 58, 9095–9100.
[15] a) L. Y. Li, L. Zhu, D. G. Chen, X. L. Hu, R. H. Wang, Eur. J. Org. Chem.
2011, 2692–2696; b) H. J. Cristau, P. P. Cellier, J. F. Spindler, M. Taillefer,
Eur. J. Org. Chem. 2004, 695–709; c) W. Li, T. S. Andy Hor, Chem. Eur. J.
2009, 15, 10585–10592.
Received: April 6, 2013
[16] a) D. Ma, Q. Cai, Acc. Chem. Res. 2008, 41, 1450–1460; b) J. Niu, P. Guo,
J. Kang, Z. Li, J. Xu, S. Hu, J. Org. Chem. 2009, 74, 5075–5078; c) Y. Pu, Y.
Published online on June 21, 2013
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 2978 – 2982 2982