Immobilization of copper in organic-inorganic hybrid materials: a highly efficient and reusable catalyst for the Ullmann diaryl etherification

Article abstract of DOI:10.1016/j.tetlet.2006.11.001

The immobilization of copper in organic-inorganic hybrid materials catalyzing the Ullmann reaction has been described. Phenols reacted with aryl iodides, aryl bromides and aryl chlorides smoothly in the presence of a 3-(2-aminoethylamino)propyl functionalized silica gel immobilized copper catalyst. The protocol involved the use of DMSO as the solvent, and potassium fluoride as the base. The reactions generated the corresponding cross-coupling products in good to excellent yields. Furthermore, the silica-supported copper could be recovered and recycled by a simple filtration of the reaction solution and used for 10 consecutive trials without loss of its reactivity.

Full text of DOI:10.1016/j.tetlet.2006.11.001

Tetrahedron Letters 48 (2007) 95–99
Immobilization of copper in organic–inorganic hybrid materials:
a highly efficient and reusable catalyst for the Ullmann
diaryl etherification
Tao Miaoa and Lei Wanga,b,
*
aDepartment of Chemistry, Huaibei Coal Teachers College, Huaibei, Anhui 235000, PR China
bState Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, Shanghai 200032, PR China
Received 25 June 2006; revised 31 October 2006; accepted 1 November 2006
Available online 21 November 2006
Abstract—The immobilization of copper in organic–inorganic hybrid materials catalyzing the Ullmann reaction has been described.
Phenols reacted with aryl iodides, aryl bromides and aryl chlorides smoothly in the presence of a 3-(2-aminoethylamino)propyl func-
tionalized silica gel immobilized copper catalyst. The protocol involved the use of DMSO as the solvent, and potassium fluoride as
the base. The reactions generated the corresponding cross-coupling products in good to excellent yields. Furthermore, the silica-sup-
ported copper could be recovered and recycled by a simple filtration of the reaction solution and used for 10 consecutive trials with-
out loss of its reactivity.
ꢀ 2006 Elsevier Ltd. All rights reserved.
The transition-metal-catalyzed aryl carbon–carbon and
carbon–heteroatom bond-forming reactions are
important fundamental transformations in synthetic
chemistry.1 The formation of diaryl ethers via a C–O
cross-coupling reaction represents a powerful and
straightforward method in organic synthesis.2 Diaryl
ethers are not only important structures in biological
systems, but also common moieties in pharmaceutical
research and materials interest.3 Copper-catalyzed
Ullmann-type arylation procedures of phenols with aryl
halides are traditional methods to approach these
compounds. However, these reactions are carried out
at high temperatures and many functional groups
cannot be tolerated for a long time. In addition, these
reactions often require the use of stoichiometric
amounts of copper reagents (copper powder or copper
salts), which leads to problems of waste disposal.4
scribed the C–O coupling of aryl halides and phenols by
using palladium catalysis in the presence of electron-rich
2-(di-tert-butylphosphino)biphenyl as a ligand.6
Nevertheless, the use of expensive palladium and non-
commercial sophisticated phosphines limits the attrac-
tiveness of this method for large-scale or industrial
applications. Meanwhile, Buchwald and co-workers also
developed an alternative approach to copper(II) triflate
catalyzed C–O formation.7 Due to the relatively high
cost of copper triflate and its air sensitivity, it is still
desirable to develop more robust and more cost-effective
processes for this important reaction. Since then, con-
siderable efforts have been devoted to the discovery of
more efficient copper-catalyzed Ullmann O-aryla-
tion methods. A number of groups showed that certain
additives, such as Chxn–Py–Al, N,N-dimethylglycine,
2,2,6,6-tetramethylheptane-3,5-dione, 1,10-phenanthro-
line or neocuproine, and phosphazene P4–But, which
probably act as copper ligands, enhance reaction rates
and allow the couplings to be carried out at milder tem-
peratures, in the presence of reduced amounts of copper
and cesium carbonate as the base.8
To overcome these drawbacks, a palladium-catalyzed
coupling reaction between sodium phenoxides and elec-
tron-deficient aryl bromides was reported by Mann and
Hartwig5 based on a ligand (dppf). Later, Buchwald de-
Keywords: Ullmann reaction; Diaryl etherification; Immobilization of
copper; Organic–inorganic hybrid materials.
The high costs of transition metal catalysts coupled with
the toxic effects associated with many transition metals
has led to an increased interest in immobilizing catalysts
*
Corresponding author. Tel.: +86 561 380 2069; fax: +86 561 309
0518; e-mail: leiwang@hbcnc.edu.cn
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.11.001

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T. Miao, L. Wang / Tetrahedron Letters 48 (2007) 95–99
onto a support. This class of supported reagents can
facilitate both the isolation and recycling of the catalyst
by filtration thus providing environmentally cleaner pro-
cesses.9 Recent examples have immobilized palladium
complexes onto amphiphilic polystyrene supports for
effecting Suzuki coupling reaction in an aqueous med-
ium as well as a modified aminomethyl polystyrene-sup-
ported palladium reagent for use as a catalyst in a range
of Sonogashira coupling reactions.10 The development
of organic reagents grafted onto silica gels has attracted
increasing attention in recent years because the industry
seeks more environmentally friendly chemical manufac-
turing processes.11 Recently, we have developed a silica-
supported copper(I) catalyzed Sonogashira coupling
reaction.12 To the best of our knowledge, there is no re-
port on the Ullmann diaryl etherification in the presence
of supported copper or palladium catalyst.
When we searched for a cross-coupling protocol of iodo-
benzene and phenol, we observed that iodobenzene
could react with phenol in the presence of 5 mol % of sil-
ica-supported copper(II) catalyst and 2 equiv of K2CO3
in DMF at 130 ꢁC to afford the desired cross-coupling
product in 53% yield. Encouraged by this result, we con-
tinued our research to improve the yield of product by
the optimization of reaction conditions.
In the presence of potassium fluoride, the Ullmann dia-
ryl etherification could be catalyzed by either Cu(I) or
Cu(II) in the absence of any palladium. However, no
reaction occurred in the absence of any copper and
palladium catalyst. As can be seen from Table 1, sil-
ica-supported Cu(II) catalysts were superior. Among
silica-supported Cu(II) catalysts, which were prepared
from different copper(II) sources, silica-supported
Cu(II) catalyst from copper(II) acetate was found to
be the most effective one (Table 1, entries 1–8). This
may be the effect of anion in silica-supported Cu(II) cat-
Here, we wish to report the synthesis of 3-(2-aminoeth-
ylamino)propyl functionalized silica gel immobilized
copper(II) catalyst (Scheme 1), and it was subsequently
used as an effective catalyst for the Ullmann cross-
coupling reactions of phenols with aryl iodides, aryl bro-
mides and aryl chlorides in the presence of potassium
fluoride in DMSO. The reactions generated the corre-
sponding diaryl ethers in good to excellent yields. It is
important to note that the silica-supported copper cata-
lyst could be recovered and recycled by a simple filtration
of the reaction solution and used for 10 consecutive trials
without significant loss of its reactivity.
Table 1. Effect of copper source on the Ullmann diaryl etherificationa
Cu source
KF, DMSO
OH
O
+
I
Entry
Copper source/amount
Yieldb (%)
1
2
3
4
5
6
7
8
9
No
N/A
25
34
43
41
73
65
92
93
93
74
31
CuI (5 mol %)
CuSO4 (5 mol %)
Cu(OAc)2 (5 mol %)
Silica supported Cu(I)c (5 mol %)
Silica supported Cu(II)d (5 mol %)
Silica supported Cu(II)e (5 mol %)
Silica supported Cu(II)f (5 mol %)
Silica supported Cu(II)f (10 mol %)
Silica supported Cu(II)f (15 mol %)
Silica supported Cu(II)f (3 mol %)
Silica supported Cu(II)f (1 mol %)
The synthesis of the organic–inorganic hybrid materials
immobilized copper catalyst illustrated in Scheme 1. It
was readily prepared through a two-step procedure.
The silica gel (100–200 mesh, from Aldrich) was
reacted with 3-(2-aminoethylamino)propyltrimethoxy-
silane in dry toluene at 120 ꢁC for 24 h to afford the
3-(2-aminoethylamino)propyl functionalized silica gel.
The organic–inorganic hybrid materials then reacted
with copper(II) acetate in ethanol at room temperature
for 4 h to generate the silica-supported copper(II)
catalyst.
10
11
12
a Phenol (1.00 mmol), iodobenzene (1.00 mmol), Cu catalyst (contains
0.05 mmol of Cu), KF (2.00 mmol) in DMSO (4 mL) at 130 ꢁC for
16 h.
b Isolated yields.
c Catalyst prepared from CuI.
d Catalyst prepared from CuCl2.
In our initial screening experiments, the Ullmann reac-
tion of iodobenzene and phenol catalyzed by the silica-
supported copper catalyst was chosen as model reaction.
e Catalyst prepared from CuSO4.
f Catalyst prepared from Cu(OAc)2.
OH
OH
OH
OH
OH
OH
O
O
O
O
O
O
O
O
O
O
O
O
3-(2-aminoethyl-
amino)propyltri-
methyloxylsilane
Si
Si
N
H
Si
Si
NH
NH
NH2
NH2
NH2
Cu(II)
NH2
Cu(OAc)2
H
N
SiO2
SiO2
SiO2
[Cu] Cat.
[Cu] Cat. (5 mol %)
KF, DMSO, 130 oC
X
+
OH
O
R2
R1
X = I, Br, Cl
R2
R1
Scheme 1.

T. Miao, L. Wang / Tetrahedron Letters 48 (2007) 95–99
97
Table 3. Effect of solvent on the Ullmann diaryl etherificationa
alysts on its catalytic activity. So, silica-supported Cu(II)
from Cu(OAc)2 was used as a catalyst in the following
investigation for its high efficiency, easy separation
and recycling. In addition, the amount of silica-sup-
ported Cu(II) from Cu(OAc)2 was also examined and
the optimized loading of Cu(II) on silica was found to
be in the range of 5–15 mol % (Table 1, entries 8–12).
[Cu] cat. (5%)
KF, Solvent
O
OH +
I
Entry
Solvent/temperature (ꢁC)
Yieldb (%)
1
2
3
4
5
6
7
8
9
C2H5OH/78
THF/70
N.R.
N.R.
N.R.
N.R.
N.R.
N.R.
N.R.
72
Dioxane/100
CH3CN/80
Toluene/110
Benzene/80
HOCH2CH2OH/120
DMF/130
We tested several different bases for the Ullmann
coupling reactions catalyzed by the silica-supported
copper(II) in DMSO. KF was found to be the most
effective. Other bases such as K2CO3, Cs2CO3, K3PO4,
KOAc, triethylamine and piperidine were substantially
less effective (Table 2, entries 1–7).
DMSO/130
92
a Phenol (1.00 mmol), iodobenzene (1.00 mmol), silica-supported Cu
catalyst (0.05 mmol of Cu), KF (2.00 mmol) in solvent (4 mL) at the
temperature indicated in Table 3 stirring for 16 h.
b Isolated yields.
We then turned our attention to investigate the effect of
solvent on the coupling reaction. When the reactions
were conducted in DMF and DMSO, good to excellent
yields (72% and 92%, respectively) of products were iso-
lated. No desired cross-coupling product was observed
during reactions in EtOH, dioxane, THF, CH3CN,
HOCH2CH2OH, benzene and toluene (Table 3, entries
1–9).
Table 4. Silica-supported copper catalyzed Ullmann diaryl
etherificationa
Entry
Phenol
Aryl halide
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
C6H5OH
C6H5OH
C6H5OH
C6H5OH
C6H5OH
C6H5OH
C6H5OH
C6H5OH
p-CH3OC6H4I
C6H5I
90
92
99
98
84
82
95
73
78
81
88
99
80
91
93
78
94
During the course of our further optimization of the
reaction conditions, when using a 5 mol % loading of
the silica-supported copper(II), the reactions were gener-
ally completed in a matter of hours, but the time, as ex-
pected, was inversely proportional to the temperature. A
reaction temperature of 130 ꢁC was found to be optimal.
Thus, the optimized reaction conditions for this Ull-
mann reaction are the silica-supported copper
(5 mol %), KF (2 equiv) in DMSO at 130 ꢁC for 16 h.
p-NO2C6H4I
p-NO2C6H4Br
m-NO2C6H4Br
p-CH3COC6H4Br
p-CNC6H4Br
C6H5Br
p-NO2C6H4Cl
o-NO2C6H4Cl
p-NO2C6H4Br
p-CNC6H4Br
p-NO2C6H4Cl
p-CNC6H4Cl
o-NO2C6H4Cl
p-NO2C6H4Cl
p-CNC6H4Cl
C6H5OH
C6H5OH
p-CH3C6H4OH
p-CH3C6H4OH
p-CH3C6H4OH
p-CH3C6H4OH
p-CH3C6H4OH
p-ClC6H4OH
p-ClC6H4OH
We have investigated the reactions using a variety of
aryl iodides, aryl bromides and aryl chlorides, and phe-
nols as the substrates under the reaction conditions and
the results are summarized in Table 4. Electron-neutral,
electron-rich and electron-poor aryl iodides, as well as
electron-poor aryl bromides reacted with phenol very
well to generate the corresponding cross-coupling prod-
ucts in excellent yields under the standard reaction con-
ditions (Table 4, entries 1–7). For electron-neutral aryl
bromide, moderate yield of the desired product was ob-
tained (Table 4, entry 8). Fortunately, electron-poor aryl
a Phenol (1.00 mmol), aryl halide (1.00 mmol), silica-supported Cu(II)
catalyst (125 mg, contains 0.05 mmol of Cu), KF (2.00 mmol) in
DMSO (4 mL) at 130 ꢁC stirring for 16 h.
b Isolated yields.
chlorides also coupled with phenol to generate the corre-
sponding diaryl ethers in high yields (Table 4, entries 9
and 10). This cross-coupling was also tolerant of ortho
substitution in aryl halides and led to good yields (Table
4, entries 10 and 15). On the other hand, the substituted
phenols with both of electron-withdrawing and electron-
donating groups on aromatic rings underwent smoothly
with activated aryl bromides and aryl chlorides to pro-
duce the desired products in good yields (Table 4, entries
11–17). However, poor yields were obtained for inacti-
vated aryl bromides and aryl chlorides and phenol under
the present reaction conditions.
Table 2. Effect of base on the Ullmann diaryl etherificationa
[Cu] cat. (5%)
DMSO, Base
OH +
O
I
Entry
Base
KF
K2CO3
Cs2CO3
K3PO4
KOAc
Triethylamine
Piperidine
Yieldb (%)
1
2
3
4
5
6
7
92
81
51
40
67
53
59
The recyclability of the silica-supported copper was
also surveyed. After reaction, the solution was vacuum
filtered using a sintered glass funnel and washed with
CH2Cl2 (5 mL), Et2O (5 mL), C2H5OH (5 mL), and hex-
ane (5 mL), respectively. After being dried, they can be
a Phenol (1.00 mmol), iodobenzene (1.00 mmol), silica-supported Cu
catalyst (0.05 mmol of Cu), base (2.00 mmol) in DMSO (4 mL) at
130 ꢁC stirring for 16 h.
b Isolated yields.

98
T. Miao, L. Wang / Tetrahedron Letters 48 (2007) 95–99
reused directly without further purification. The silica-
supported copper can be recovered, recycled and used
for 10 consecutive trials without loss of activity (Table
5).
(1.05 g). FT-IR (KBr, m cmÀ1): mSi–O = 1047; mC–H
=
2932. Anal. by ICP (Atomic %): Cu, 2.55.
Typical procedure for the Ullmann diaryl etherification:
Under nitrogen atmosphere, an oven-dried round-
bottomed flask was charged with the silica-supported
copper(II) (125 mg, contains 0.05 mmol of Cu), KF
(116 mg, 2.0 mmol), aryl halide (1.0 mmol), phenol
(1.0 mmol) and DMSO (4 mL). The reaction mixture
was refluxed at 130 ꢁC for 16 h. After cooling to room
temperature, the reaction mixture was vacuum filtered
using a sintered glass funnel and washed with CH2Cl2
(2 · 5 mL). The combined organic materials were dried
over Na2SO4, filtered, concentrated, and the residue
was purified by flash chromatography on silica gel to
give the desired cross-coupling product.
Preparation and characterization of the immobilization
of palladium catalyst in organic–inorganic hybrid mate-
rials: This catalyst was prepared in the following steps
from commercial silica.
Activation of silica. Silica (10 g) (100–200 mesh, Aldrich)
was introduced in a round-bottomed flask equipped
with a reflux condenser, 80 mL of concentrated H2SO4
and 15 mL of HNO3 were added and the mixture was
heated in oil-bath at 140 ꢁC for 24 h. The solution was
filtered and the white powder was washed with distilled
water until neutral pH was attained. The solid was again
washed with acetone, methanol and dichloromethane,
respectively, and dried under vacuum at 150 ꢁC for 48 h.
The recyclability of the silica-supported copper catalyst:
After reaction, the mixture was vacuum filtered using
a sintered glass funnel and washed with CH2Cl2
(5 mL), Et2O (5 mL), C2H5OH (5 mL), and hexane
(5 mL), respectively. After being dried on an oven, they
can be reused directly without further purification.
In a 50 mL round-bottomed flask were introduced suc-
cessively 20 mL of anhydrous toluene, 3 g of activated
silica and 10 mL of 3-(2-aminoethylamino)propyltri-
methoxylsilane (AAPTS). The solution was refluxed
for 24 h. The solution was filtered and the solid was
washed with acetone and dichloromethane, respectively,
and dried under reduced pressure at 60 ꢁC. Material
In conclusion, we have developed an efficient and eco-
nomic catalyst system for the Ullmann diaryl etherifica-
tion by using the organic–inorganic (silica) hybrid
materials-supported copper(II) as the catalyst in
DMSO. The cross-coupling reactions of phenols with
aryl iodides, aryl bromides and aryl chlorides generate
the corresponding coupling products in good to excel-
lent yields at the present reaction conditions. Further-
more, the silica-supported copper(II) can be recovered
and recycled by a simple filtration of the reaction solu-
tion and used for 10 consecutive trials without decreases
in activity.
(3.38 g) was obtained. FT-IR (KBr, m cmÀ1): mSi–O
=
1088; mC–H = 2941. Anal. Found: C, 6.56; H, 1.55; N,
2.56, corresponding to 0.914 mmol/g of 2-aminoethyl-
aminopropyl groups based on the nitrogen percentage.
In
a
small Schlenk tube, 1 g (0.914 mequiv
CH2CH2CH2NHCH2CH2NH2/g) of the above-func-
tionalized silica was mixed with 0.110 g (0.6 mmol) of
Cu(CH3CO2)2 in 5 mL of dry ethanol. The mixture
was stirred for 4 h under nitrogen atmosphere at room
temperature. The solution was filtered and the solid
was washed with acetone and methanol, respectively,
and the solid was dried under reduced pressure at room
temperature for 16 h, leading to a yellow powder
Acknowledgments
We gratefully acknowledge financial support by the
National Natural Science Foundation of China (No.
20372024), the Excellent Scientist Foundation of Anhui
Province, China (No. 04046080), the Scientific Research
Foundation for the Returned Overseas Chinese Schol-
ars, State Education Ministry, China (No. 2002247),
the Excellent Young Teachers Program of MOE, China
(No. 2024), and the Key Project of Science and Technol-
ogy of State Education Ministry, China (No. 0204069).
Table 5. Successive trials by using recoverable Cu(II) catalysta
[Cu] cat. (5%)
KF, DMSO
OH
+
I
O
Trial
Yieldb (%)
1
2
3
4
5
6
7
8
9
92
92
91
92
90
90
91
90
89
88
References and notes
1. (a) Mino, T.; Shirae, Y.; Sakamoto, M.; Fujita, T. Synlett
2003, 882; (b) Jonckers, T. H. M.; Maes, B. U.; Lemiere,
G. L. F.; Rombouts, G.; Pieters, L.; Haemers, A.;
Dommisse, R. A. Synlett 2003, 615; (c) Gonthier, E.;
Breinbauer, R. Synlett 2003, 1049; (d) Iyer, S.; Jayanthi,
A. Synlett 2003, 1125; (e) Nicolaou, K. C.; Christopher, N.
C. B. J. Am. Chem. Soc. 2002, 124, 10451; (f) Strurmer, R.
Angew. Chem., Int. Ed. 1999, 38, 3307; (g) Wolfe, J. P.;
Wagaw, S.; Marcoux, J. F.; Buchwald, S. L. Acc. Chem.
Res. 1998, 31, 805.
10
a Phenol (1.00 mmol), iodobenzene (1.00 mmol), silica-supported Cu
catalyst (0.05 mmol of Cu), KF (2.00 mmol) in DMSO (4 mL) at
130 ꢁC for 16 h.
b Isolated yields.

T. Miao, L. Wang / Tetrahedron Letters 48 (2007) 95–99
99
2. (a) Theil, F. Angew. Chem., Int. Ed. 1999, 38, 2345; (b)
Nicolaou, K. C.; Boddy, C. N. C. J. Am. Chem. Soc. 2002,
124, 10451; (c) Evans, D. A.; Wood, M. R.; Trotter, B. W.;
Richardson, T. I.; Barrow, J. C.; Katz, J. L. Angew.
Chem., Int. Ed. 1998, 37, 2700; (d) Evans, D. A.;
Dinsmore, C. J.; Watson, P. S.; Wood, M. R.; Richardson,
T. I.; Trotter, B. W.; Katz, J. L. Angew. Chem., Int. Ed.
1998, 37, 2704.
3. (a) Islas-Gonzalez, G.; Bois-Choussy, M. Z. J. Org.
Biomol. Chem. 2003, 1, 30; (b) Evans, D. A.; DeVries,
M. K. In Glycopeptide Antibiotics, Drugs and the Phar-
maceutical Sciences; Nagarajan, R., Ed.; Marcel Decker:
New York, 1994; p 63; (c) Eicher, T.; Fey, S.; Puhl, W.;
Buchel, E.; Speicher, A. Eur. J. Org. Chem. 1998, 877; (d)
Iyoda, M.; Sakaitani, M.; Otsuka, H.; Oda, M. Tetrahe-
dron Lett. 1985, 26, 4777; (e) Evans, D. A.; Wood, M. R.;
Trotter, B. W.; Richardson, T. I.; Barrow, J. C.; Katz, J.
L. Angew. Chem., Int. Ed. 1998, 37, 2700; (f) Evans, D. A.;
Dinsmore, C. J.; Watson, P. S.; Wood, M. R.; Richardson,
T. I.; Trotter, B. W.; Katz, J. L. Angew. Chem., Int. Ed.
1998, 37, 2704; (g) Zhang, A. J.; Burgess, K. Angew.
Chem., Int. Ed. 1999, 38, 634.
4. (a) Ullmann, F. Chem. Ber. 1904, 37, 853; (b) Lindley, J.
Tetrahedron 1984, 40, 1433; (c) Sawyer, J. S. Tetrahedron
2000, 56, 5045; (d) Theil, F. Angew. Chem., Int. Ed. 1999,
38, 2345.
5. Mann, G.; Hartwig, J. F. Tetrahedron Lett. 1997, 46, 8005.
6. Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.;
Sadighi, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1999,
121, 4369.
7. Marcoux, J.-F.; Doye, S.; Buchwald, S. L. J. Am. Chem.
Soc. 1997, 119, 10539.
8. For recent copper-catalyzed direct coupling reaction of
aryl halides and phenols, see: (a) Cristau, H.-J.; Cellier, P.
P.; Hamada, S.; Spindler, J.-F.; Taillefer, M. Org. Lett.
2004, 6, 913; (b) Ma, D.; Cai, Q. Org. Lett. 2003, 5, 3799;
(c) Buck, E.; Song, Z. J.; Tschaen, D.; Dormer, P. G.;
Volante, R. P.; Reider, P. J. Org. Lett. 2002, 4, 1623; (d)
Gujadhur, R. K.; Bates, C. G.; Venkataraman, D. Org.
Lett. 2001, 3, 4315; (e) Palomo, C.; Oiarbide, M.; Lopez,
R.; Gomez-Bengoa, E. Chem. Commun. 1998, 2091; (f)
Kalinin, A. V.; Bower, J. F.; Riebel, P.; Snieckus, V. J.
Org. Chem. 1999, 64, 2986; (g) Ouali, A.; Spindler, J.-F.;
Cristau, H.-J.; Taillefer, M. Adv. Synth. Catal. 2006, 348,
499.
9. (a) Kirschnig, A.; Monenschein, H.; Wittenberg, R.
Angew. Chem., Int. Ed. 2001, 40, 650; (b) Clapham, B.;
Reger, T. S.; Janda, K. D. Tetrahedron 2001, 57, 4637.
10. (a) Uozumi, Y.; Nakai, Y. Org. Lett. 2002, 4, 2997; (b)
Gonthier, E.; Breinbauer, R. Synlett 2003, 1049; (c)
Tyrrell, E.; Al-Saardi, A.; Millet, J. Synlett 2005, 487;
(d) Djakovitch, L.; Rollet, P. Tetrahedron Lett. 2004, 45,
1367.
11. (a) Clark, J. H. Chemistry of Waste Minimisation; Chap-
man and Hall: Glasgow, 1995; (b) Clark, J. H.; Macquar-
rie, D. J. Chem. Commun. 1998, 853; (c) Price, P. M.;
Clark, J. H.; Macquarrie, D. J. J. Chem. Soc., Dalton
Trans. 2000, 101; For recent application of transition-
metal immobilized on silica in organic reaction, see: (d)
Breynaert, E.; Hermans, I.; Lambie, B.; Maes, G.; Peeters,
J.; Maes, A.; Jacobs, P. Angew. Chem., Int. Ed. 2006, 45, 1;
(e) Li, P.; Wang, L. Adv. Synth. Catal. 2006, 348, 681; (f)
Karimi, B.; Ghoreishi-Nezhad, M.; Clark, J. H. Org. Lett.
2005, 7, 625; (g) Hamza, K.; Abu-Reziq, R.; Avnir, D.;
Blum, J. Org. Lett. 2004, 6, 925; (h) Heckel, A.; Seebach,
D. Angew. Chem., Int. Ed. 2000, 39, 163; (i) Gelman, F.;
Blum, J.; Avnir, D. J. Am. Chem. Soc. 2000, 122, 11999.
12. Zhang, L.; Li, P.; Wang, L. Lett. Org. Chem. 2006, 3, 282.