Copper(I) acetate: A structurally simple but highly efficient dinuclear catalyst for copper-catalyzed azide-alkyne cycloaddition

Article abstract of DOI:10.1002/adsc.200900768

In this article, the structurally well-defined dinuclear complex copper(I) acetate was studied in detail and was developed as a highly practical and efficient catalyst for the copper(I)-catalyzed azide-alkyne cycloaddition. The "bare" phenylethynylcopper(

Full text of DOI:10.1002/adsc.200900768

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DOI: 10.1002/adsc.200900768
Copper(I) Acetate: A Structurally Simple but Highly Efficient
Dinuclear Catalyst for Copper-Catalyzed Azide-Alkyne
Cycloaddition
Changwei Shao,a Guolin Cheng,a Deyong Su,a Jimin Xu,a Xinyan Wang,a,*
and Yuefei Hua,*
a
Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of
Chemistry, Tsinghua University, Beijing 100084, Peopleꢀs Republic of China
Fax : (+86)-10-6277-1149; phone: (+86)-10-6279-5380; e-mail: wangxinyan@mail.tsinghua.edu.cnyfh@mail.tsinghua.edu.cn
Received: November 5, 2009; Revised: March 28, 2010; Published online: June 30, 2010
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.20090789.
Abstract: In this article, the structurally well-de-
fined dinuclear complex copper(I) acetate was stud-
ied in detail and was developed as a highly practical
and efficient catalyst for the copper(I)-catalyzed
azide-alkyne cycloaddition. The “bare” phenylethy-
nylcopper(I) (i.e., with no exogeneous ligands) was
isolated as an intermediate, which can be converted
into an active catalytic species by treatment with
acetic acid (in situ produced in the reaction) to effi-
ciently catalyze the azide-alkyne cycloaddition
under mild conditions.
In the past years, great progress has been made in
the development of the efficient catalytic procedures
for CuAAC. The first ligand-mediated CuAAC was
reported in 2004,[7] in which the ligand was hypothe-
sized to protect the Cu(I) species from oxidation and
disproportionation. Later, two mechanistic concepts
were developed: (a) a kinetic investigation[8] revealed
that the catalytic CuAAC had a strict second-order
dependence on Cu(I); (b) two DFT studies[9] indicat-
ed that dinuclear and tetranuclear alkynyl–Cu(I) com-
plexes could be intermediates and display both supe-
rior stability and high reactivity in CuAAC. The dis-
tances between CuA and CuB (2.54–2.88 ꢁ) in the di-
nuclear Cu(I) complexes were suggested to be rele-
vant in one of the studies (Figure 1).[9b] Although
several efficient ligand-mediated procedures have
been reported in the literature,[7,10] they are far from
practical because complicated or large amounts of li-
Keywords: acetylides; catalysts; click chemistry;
copper; cycloaddition
In 2002, the groups of Sharpless[1] and Meldal[2] dis- gands were employed. In spite of the obvious impor-
covered independently that the Huisgen 1,3-dipolar tance of the concept of a “dinuclear alkynyl–Cu(I) in-
cycloaddition[3] of an alkyne (1) and an azide (2) termediate” in the development of highly efficient
could be catalyzed by Cu(I) species under mild condi- catalysts for CuAAC, it was rarely applied in the
tions to regioselectively yield 1,4-disubstituted 1,2,3- design of catalysts.[11]
triazoles (3) (Scheme 1). To date, this copper-cata-
During a screen of Cu(I) sources for CuAAC, we
lyzed azide-alkyne cycloaddition (CuAAC) has found that the commercially available copper(I) ace-
become the most remarkable example for “click”
chemistry[4,5] and has been widely applied in organic
syntheses as well as in medicinal and materials re-
search.[6]
Scheme 1. Copper-catalyzed azide-alkyne cycloaddition
(CuAAc) reaction.
Figure 1. Dinuclear Cu(I) complexes.
Adv. Synth. Catal. 2010, 352, 1587 – 1592
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Changwei Shao et al.
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tate is a structurally well-defined dinuclear polymer were treated with a high loading of catalyst (10 mol%
[(CH3CO2Cu)2]n.[12] It has a desirable Cu Cu distance or 5 mol%), both Cat-1 and Cat-2 gave the excellent
À
(2.56 ꢁ, Figure 1), which may serve as a template for results (entries 1–4). When 1 mol% of these catalysts
the expected “dinuclear alkynyl–Cu(I) intermediate”. was used, the desired product 3a was obtained in ex-
If the acetate anion is considered as a bidentate cellent yields, but with prolonged reaction times
ligand, it should be the structurally simplest bidentate (entries 5 and 6). Interestingly, by replacement of
ligand to exist in CuAAC. However, the literature t-BuOH/H2O with cyclohexane as a solvent, the same
search showed that copper(I) acetate was rarely used reaction catalyzed by Cat-1 was finished within 8 min
as a catalyst for CuAAC.[13] In another few arti- to give 3a in 98% yield (entry 7), while the Cat-2-cat-
A
ACHTUNGRTEN(NUNG OAc)2/sodium ascor- alyzed reaction gave 3a in 93% yield after 110 min
copper(I) acetate may be generated in situ. However,
Further solvent tests proved that the non-polar sol-
these procedures were usually associated with using a vents benefit the reaction rate very much (entries 9–
large excess of catalyst, a high temperature or a pro- 11). However, the polar organic solvents significantly
longed reaction time. To our disappointment, no de- decreased the catalytic activity of Cat-1 (entries 13–
tailed study on the reaction conditions or scope was 16). It is well known that Cu(I) can be easily oxidized
discussed in those articles.
to Cu(II) by air; even so, the reactions of entries 7, 9–
To explore the catalytic properties of copper(I) ace- 11 were performed conveniently open to the air. It
tate for CuAAC, a group of experiments catalyzed by was not necessary to use inert gas protection for two
pure [(CH3CO2Cu)2]n (Cat-1) or a combination of reasons: (a) very short reaction time was used; (b)
CuACHTUNGTRENNUNG(OAc)2/sodium ascorbate (1:5 mol/mol) (Cat-2) the reaction proceeded in a reductive system, by
was undertaken. As shown in Table 1, when the which Cu(II) can be reduced to Cu(I) by coupling of
model substrates phenylethyne (1a, 1.0 equiv.) and acetylenes. Although Cat-1 is sensitive to humidity to
benzyl azide (2a, 1.05 equiv.) in t-BuOH/H2O (1:1 v/v) decompose into Cu2O and HOAc as an equilibrium,
the reaction in H2O was finished within 11 min to
give a 95% yield (entry 12).
Table 1. Effects of catalysts and solvents on CuAAC.[a]
We interestingly observed that a bright yellow color
was produced at the beginning of each reaction in en-
tries 7–16 and it disappeared at the end of the reac-
tion in entries 7–12. In the absence of 2a, a bright
yellow solid was isolated from the stoichiometric reac-
tion between Cat-1 and 1a (Scheme 2). To our sur-
Entry
Catalyst[b]
(mol%)
Solvent[c]
Time
[min]
Yield of
G
N
3a [%][e]
1
2
3
4
5
6
7
8
Cat-1 (10)
Cat-2 (10)
Cat-1 (5)
Cat-2 (5)
Cat-1 (1)
Cat-2 (1)
Cat-1 (1)
Cat-2 (1)
Cat-1 (1)
Cat-1 (1)
Cat-1 (1)
Cat-1 (1)
Cat-1 (1)
Cat-1 (1)
Cat-1 (1)
Cat-1 (1)
t-BuOH/H2O
t-BuOH/H2O
t-BuOH/H2O
t-BuOH/H2O
t-BuOH/H2O
t-BuOH/H2O
cyclohexane
cyclohexane
CH2Cl2
CHCl3
MeC6H5
H2O
MeCN
10
10
36
32
270
240
8
110
16
97
96
95
98
93
92
98
93
92
93
98
95
65
43
20
89
ꢀ
Scheme 2. PhC CCu (4) was identified as an intermediate.
ꢀ
prise, its structure was assigned as PhC CCu (4) by
elemental analyses and by comparing its IR spectra
with that of a commercial sample or samples obtained
by reference methods.[15,16] Since 4 when treated with
2a gave the desired product 3a in 98% yield, it was
proved to be an intermediate in the CuAAC.
9
10
11
12
13
14
15
16
15
10
11
60[d]
60[d]
60[d]
60[d]
We also observed that the conversion of 4 and 2a
into 3a could be influenced by HOAc only, but not by
other proton sources, such as t-BuOH, H2O or t-
BuOH/H2O. Although the phenomenon[17] that ace-
tate enhances the catalytic activity of Cu(I) in
CuAAC has been reported (without sufficient investi-
gation), no acetate enhancement was observed when
this conversion was conducted in a solution of
NaOAc in t-BuOH, H2O or t-BuOH-H2O. Therefore,
these results clearly showed that the acidity of HOAc
may play an important role in this conversion.
EtOH
EtOAc
THF
[a]
The mixture of 1a (2.0 mmol), 2a (2.1 mmol) and Cu(I)
catalyst in various solvents (1 mL) was stirred at room
temperature without protection by inert gas.
The molecular weight of Cat-1 was calculated based on
CH3CO2Cu.
Ratio of t-BuOH/H2O was 1:1 v/v.
Incomplete conversions were observed.
Yields of isolated products.
[b]
[c]
[d]
[e]
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Copper(I) Acetate: A Structurally Simple but Highly Efficient Dinuclear Catalyst
During the revision of this article, Heaney[11a] re-
ported that 4 could be used as a catalytic species for
CuAAC when it was heated at 1008C with microwave
irradiation in MeCN. His reaction conditions and the
phenomena we described above together indicate that
4 alone is not an active catalytic species for CuAAC,
but it could be converted into an active catalytic spe-
cies under suitable conditions.
Further investigation showed that 4 is a very stable
À
polymeric dinuclear complex with an extended Cu
Cu ladder structure, in which both Cu atoms adopt
1,2
[18]
ꢀ
the same m,h -C C bridging mode. Therefore, we
hypothesized that the polymeric structure of 4 may be
dissociated initially by HOAc to give monomeric di-
nuclear complexes. Then, AcOÀ coordinates with
Cu(I) of monomer to produce an active catalytic spe-
cies (its structure remains unclear).
Since the coordination ability of MeCN with Cu(I)
was emphasized in Heaneyꢀs work, the Cat-1 cata-
lyzed reaction in MeCN was re-tested. As shown in
Scheme 3, when a stoichiometric reaction proceeded
in MeCN, 4 was formed and converted into 3a even
more efficiently than in cyclohexane.
Figure 2. Structurally well-defined copper(I) carboxylates.
Scheme 3. The stoichiometric reaction in MeCN.
Scheme 4. Cat-1-catalyzed solvent-free CuAAC reaction.
Thus, MeCN did not have any negative influence
on the formation of 4. The low efficiency of the cata-
To efficiently control the exothermic effect for safe
lytic reaction in MeCN (see entry 13 in Table 1, performance, the reaction with lower loadings of cata-
60 min, 65% yield) may be caused by a competitive lyst was tested. As shown in Table 2, when 0.1 mol%
coordination between MeCN and AcOÀ with Cu(I) in of Cat-1 was used, the product 3a formed gradually
the active catalytic species.
and the reaction finished mildly within 7 min
Encouraged by the results from Cat-1, other struc- (entry 4). By using 0.05 mol% of Cat-1, the reaction
turally well-defined copper(I) benzoate,[19] copper(I) finished within 12 min at room temperature (entry 5)
trifluoroacetate[20] and copper(I) pivalate[21] samples or within 4 min at 508C (entry 6). Even 0.01 mol% of
were tested under the same conditions (see: entry 7 in
Table 1). As shown in Figure 2, each of them repre-
Table 2. Effect of the amount of Cat-1 on CuAAC.[a]
sents an amazing polynuclear Cu(I) complex or poly-
nuclear Cu(I) complex polymer, in which the carbox-
ylic acid anions serve as bidentate ligands for Cu(I)
ions. As was expected, all of them showed highly cata-
lytic activity for CuAAC and gave 3a in excellent
yields.
Then, the solvent-free CuAAC was tested (the first
solvent-free CuAAC was reported by Nolan in
2008).[5b] To our great surprise, when 1a (1.0 equiv.),
2a (1.05 equiv.) and Cat-1 (1 mol%) were mixed at
room temperature, 3a was produced in 98% yield
within 3 seconds accompanied by a strong exothermic
effect. As shown in Scheme 4, Cat-1 was so powerful
that the same reaction finished within 35 min at 08C.
Entry Cat-1
(mol%)
Temp.
[oC]
Time
[min]
Yield of 3a
[%][b]
1
2
3
4
5
6
7
1
1
0.5
0.1
0.05
0.05
0.01
0
35
0.05
3
7
12
4
99
98
99
99
99
99
99
25
25
25
25
50
50
20
[a]
The solvent-free mixture of 1a (2.0 mmol), 2a (2.1 mmol)
and Cat-1 (0.02–0.0002 mmol, 1–0.01 mol%) was stirred
at different temperatures.
[b]
Yields of isolated products.
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Scheme 6. Cat-1-catalyzed highly efficient CuAAC of al-
kynes 1b–f with 2a.
Scheme 5. Cat-1-catalyzed highly efficient CuAAC reaction
of 1a with azides 2a–l.
Table 3. The results of CuAAC reactions catalyzed by differ-
ent Cu(I) reagents without ligand or additive.[a]
Entry Catalyst Neat[b] (time,
Cyclohexane[b] (time,
yield of 3)
Cat-1 was sufficient to give an excellent yield at 508C
(entry 7).
yield of 3)
To generalize this novel procedure, the CuAAC be-
tween phenylethyne (1a) and different azides (2a–l)
was tested in cyclohexane solvent or under the safe
solvent-free conditions. As shown in Scheme 5, the
corresponding products (3a–l) were obtained in excel-
lent yields and significant substrate effects were ob-
served. Benzyl azides (2a–c) and the azides with func-
tional groups substituted on the b-carbon showed
higher reactivity (2d, e and 2i–k). As was expected,
aromatic azides 2f, g showed lower reactivity due to
their resonance stability. The alcohol 2h needed a pro-
longed reaction time, possibly because its hydroxy
group was involved in the coordination with Cu(I).
1
2
3
4
5
Cat-1
CuCl
CuBr
CuI
0.05 min, 98%
24 h, trace
24 h, trace
8 min, 98%
24 h, trace
24 h, trace
24 h, <10%
24 h, NR
24 h, <10%
CuCN 24 h, NR
[a]
The mixture of 1a (2.0 mmol), 2a (2.1 mmol) and differ-
ent catalysts (1 mol%) was stirred at room temperature.
Yields of isolated products.
[b]
ally well-defined dinuclear complex [(CH3CO2Cu)2]n
As shown in Scheme 6, the CuAAC reactions be- (Cat-1) was studied in detail. By using non-polar sol-
tween different acetylenes (1b–f) and benzyl azide vents or under the solvent-free conditions, a highly ef-
(2a) were finished smoothly to give the desired prod- ficient [(CH3CO2Cu)2]n (Cat-1)-catalyzed CuAAC
ucts 3m–q in 92–99% yields.
was developed, which is characterized by extremely
Finally, the control experiments proved that the low loading of catalyst, short reaction time, excellent
unique feature of our highly efficient Cat-1-catalyzed yield and simple work-up procedure. The “bare”
ꢀ
CuAAC is that no any additional ligand or additive [(PhC CCu)2]n (4) (i.e., with no exogeneous ligands)
was required, irrespective of whether the reaction was isolated as an intermediate and proved Àto be a
proceeded in hexane or under the solvent-free condi- catalytic species for CuAAC. Since CH3CO2 is one
tions. As shown in Table 3, the most often used Cu(I) of the structurally simplest bidentate ligands, this
reagents for CuAAC, such as CuCl, CuBr, CuI or method offers an unprecedented easy and atom-eco-
Cu2O, just afforded traces of the desired product in nomic ligand-mediated CuAAC procedure. Further
the absence of ligand or additive.
mechanistic studies on [(CH3CO2Cu)2]n (Cat-1)-cata-
In conclusion, based on the concept of a “dinuclear lyzed CuAAC reactions are under way in our labora-
alkynyl–Cu(I) intermediate” for CuAAC, the structur- tory.
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Copper(I) Acetate: A Structurally Simple but Highly Efficient Dinuclear Catalyst
[4] For references before 2008, see reviews: a) M. Meldal,
Experimental Section
C. W. Tornøe, Chem. Rev. 2008, 108, 2952–3015;
b) V. D. Bock, H. Hiemstra, J. H. van Maarseveen, Eur.
J. Org. Chem. 2006, 51–68.
Typical Procedure; Preparation of 1-Benzyl-4-phenyl-
1H-[1,2,3]triazole (3a) by [(CH3CO2Cu)2]n (Cat-1)-
Catalyzed CuAAC under Solvent-Free Conditions
[5] For selected references after 2007, see: a) N. Miller,
G. M. Williams, M. A. Brimble, Org. Lett. 2009, 11,
2409–2412; b) S. Diez-Gonzalez, S. P. Nolan, Angew.
Chem. 2008, 120, 9013–9016; Angew. Chem. Int. Ed.
2008, 47, 8881–8884; c) N. Candelon, D. Lastecoueres,
A. K. Diallo, J. R. Aranzaes, D. Astruc, J-M. Vincent,
Chem. Commun. 2008, 741–743; d) S. Diez-Gonzalez,
E. D. Stevensb, S. P. Nolan, Chem. Commun. 2008,
4747–4749; e) S. Chassaing, A. Sani Souna Sido, A.
Alix, M. Kumarraja, P. Pale, J. Sommer, Chem. Eur. J.
2008, 14, 6713–6721; f) L. Li, G. Zhang, A. Zhu, L.
Zhang, J. Org. Chem. 2008, 73, 3630–3633; g) I. S.
Park, M. S. Kwon, Y. Kim, J. S. Lee, J. Park, Org. Lett.
2008, 10, 497–500; h) L. Ackermann, H. K. Potukuchi,
D. Landsberg, R. Vicente, Org. Lett. 2008, 10, 3081–
3084; i) B. H. Lipshutz, D. M. Nihan, E. Vinogradova,
B. R. Taft, Z. V. Boskovic, Org. Lett. 2008, 10, 4279–
4282.
A solution of [(CH3CO2Cu)2]n in Et2O (1 mL) {it was made
from [(CH3CO2Cu)2]n (12.5 mg) in Et2O (10 mL)} was
evaporated under N2 to yield a powder of [(CH3CO2Cu)2]n
(1.25 mg, 0.01 mmol, 0.5 mol%, MW was calculated based
on CH3CO2Cu). To this powder was added a mixture of phe-
nylethyne (1a, 204 mg, 2 mmol) and benzyl azide (2a,
280 mg, 2.1 mmol) at room temperature. The resultant mix-
ture was stirred continuously until the reaction system had
solidified completely (ca. 3 min). After the crude product
had been diluted with CH2Cl2 (2 mL), it was purified by a
short chromatography (silica gel, EtOAc:PE=1:3) to give
3a as an off-white solid; yield: 464 mg (99%).
Typical Procedure; Preparation of 1-Benzyl-4-phenyl-
1H-[1,2,3]triazole (3a) by [(CH3CO2Cu)2]n (Cat-1)-
Catalyzed CuAAC in Cyclohexane
[6] For selected references after 2007, see: a) N. Mont,
V. P. Mehta, P. Appukkuttan, T. Beryozkina, S. Toppet,
K. Van Hecke, L. Van Meervelt, A. Voet, M. DeMaey-
er, E. Van der Eycken, J. Org. Chem. 2008, 73, 7509–
7516; b) Q. Zhang, J. M. Takacs, Org. Lett. 2008, 10,
545–548; c) S.-A. Poulsen, B. L. Wilkinson, A. Inno-
centi, D. Vullo, C. T. Supuran, Bioorg. Med. Chem.
Lett. 2008, 18, 4624–4627; d) Y. Chen, M. Lopez-San-
chez, D. N. Savoy, D. D. Billadeau, G. S. Dow, A. P. Ko-
zikowski, J. Med. Chem. 2008, 51, 3437–3448; e) T. J.
Wigglesworth, F. Teixeira, Jr., F. Axthelm, S. Eisler,
N. S. Csaba, H. P. Merkle, W. Meier, F. Diederich, Org.
Biomol. Chem. 2008, 6, 1905–1911; f) M. Anwarul
Karim, Y.-R. Cho, J. S. Park, S. C. Kim, H. J. Kim, J. W.
Lee, Y.-S. Gald, S. H. Jin, Chem. Commun. 2008, 1929–
1931; g) D. K. Scrafton, J. E. Taylor, M. F. Mahon, J. S.
Fossey, T. D. James, J. Org. Chem. 2008, 73, 2871–2874;
h) M. A. Fazio, O. P. Lee, D. I. Schuster, Org. Lett.
2008, 10, 4979–4982.
A solution of [(CH3CO2Cu)2]n in Et2O (1 mL) {it was made
from [(CH3CO2Cu)2]n (25 mg) in Et2O (10 mL)} was evapo-
rated under N2 to yield a powder of [(CH3CO2Cu)2]n
(2.5 mg, 0.01 mmol, 1 mol%, MW was calculated based on
CH3CO2Cu). To this powder was added a solution of phe-
nylethyne (1a, 204 mg, 2 mmol) and benzyl azide (2a,
280 mg, 2.1 mmol) in cyclohexane (1 mL) at room tempera-
ture. The resultant mixture was stirred continuously until
phenylethyne was exhausted (ca. 8 min). After the crude
product had been diluted by CH2Cl2 (2 mL), it was purified
by a short chromatography (silica gel, EtOAc:PE=1:3) to
give 3a as an off-white solid; yield: 459 mg (98%).
A similar procedure was used in CuAAC for the prepara-
tion of triazole products 3b–q (see Scheme 4 and Scheme 5
in the text).
Supporting Information
The experimental details, characterization data, 1H NMR
and 13C NMR spectra for products 3a–q are available in the
Supporting Information.
[7] T. R. Chan, R. Hilgraf, K. B. Sharpless, V. V. Fokin,
Org. Lett. 2004, 6, 2853–2855.
[8] V. O. Rodionov, V. V. Fokin, M. G. Finn, Angew. Chem.
2005, 117, 2250–2255; Angew. Chem. Int. Ed. 2005, 44,
2210–2215.
[9] a) B. F. Straub, Chem. Commun. 2007, 3868–3870;
b) M. Ahlquist, V. V. Fokin, Organometallics 2007, 26,
4389–4391.
[10] For the selected references, see: a) S. Diez-Gonzalez,
S. P. Nolan, Angew. Chem. 2008, 120, 1–5; Angew.
Chem. Int. Ed. 2008, 47, 1–5; b) F. Wang, H. Fu, Y.
Jiang, Y. Zhao, Green Chem. 2008, 10, 452–456;
c) V. O. Rodionov, S. I. Presolski, S. Gardinier, Y.-H.
Lim, M. G. Finn, J. Am. Chem. Soc. 2007, 129, 12696–
12704; d) S. Diez-Gonzalez, A. Correa, L. Cavallo, S. P.
Nolan, Chem. Eur. J. 2006, 12, 7558–7564.
Acknowledgements
This work was supported by the NNSFC (20672066,
30600779) and CFKSTIP from Education Ministry of China
(706003).
References
[1] V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharp-
less, Angew. Chem. 2002, 114, 2708–2711; Angew.
Chem. Int. Ed. 2002, 41, 2596–2599.
[11] a) B. R. Buckley, S. E. Dann, D. P. Harris, H. Heaney,
E. C. Stubbs, Chem. Commun. 2010, 46, 2274–2276;
b) K. Namitharan, M. Kumarraja, K. Pitchumani,
Chem. Eur. J. 2009, 15, 2755–2758; c) K. Kamata, Y.
[2] C. Tornoe, C. Christensen, M. Meldal, J. Org. Chem.
2002, 67, 3057–3062.
[3] R. Huisgen, in: 1,3-Dipolar Cycloaddition Chemistry,
(Ed.: A. Padwa), Wiley, New York, 1984, pp 1–176.
Adv. Synth. Catal. 2010, 352, 1587 – 1592
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1591

Changwei Shao et al.
COMMUNICATIONS
Nakagawa, K. Yamaguchi, N. Mizuno, J. Am. Chem.
Soc. 2008, 130, 15304–15310.
[12] a) R. D. Mounts, T. Ogura, Q. Fernando, Inorg. Chem.
1974, 13, 802–805; b) M. G. B. Drew, D. A. Edwards,
R. Richards, J. Chem. Soc. Chem. Commun. 1973, 124–
125; c) T. Ogura, R. D. Mounts, Q. Fernando, J. Am.
Chem. Soc. 1973, 95, 949–951.
[15] a) W. Shi, Y. Luo, X. Luo, L. Chao, H. Zhang, J. Wang,
A. Lei, J. Am. Chem. Soc. 2008, 130, 14713–14720;
b) E. C. Y. Woon, A. Dhami, M. F. Mahon, T M. D.
Threadgill, Tetrahedron 2006, 62, 4829–4837; c) D. C.
Owsley, C. E. Castro, Org. Synth. 1972, 52, 128–131.
[16] The comparison sample was obtained by the method of
ref.[15b] The IR spectra for both our sample and the
comparison sample are presented in the Supporting In-
[13] a) T.-B. Yu, J. Z. Bai, Z. Guan, Angew. Chem. 2009,
121, 1117–1121; Angew. Chem. Int. Ed. 2009, 48, 1097–
1101; b) C.-B. Yim, O. C. Boerman, M. de Visser, M.
de Jong, A. C. Dechesne, D. T. S. Rijkers, R. M. J. Lis-
kamp, Bioconjugate Chem. 2009, 20, 1323–1331; c) M.
van Dijk, M. L. Nollet, P. Weijers, A. C. Dechesne, C. F.
van Nostrum, W. E. Hennink, D. T. S. Rijkers, R. M. J.
Liskamp, Biomacromolecules 2008, 9, 2834–2843; d) I.
Bae, H. Han, S. Chang, J. Am. Chem. Soc. 2005, 127,
2038–2039.
[14] a) T. L. Mindt, R. Schibli, J. Org. Chem. 2007, 72,
10247–10250; b) J. Zhang, H.-N. Chen, F.-I. Chiang,
J. Y. Takemoto, M. Bensaci, C.-W. T. Chang, J. Comb.
Chem. 2007, 9, 17–19; c) I. Dijkgraaf, A. Y. Rijnders,
A. Soede, A. C. Dechesne, G. W. van Esse, A. J. Brouw-
er, F. H. M. Corstens, O. C. Boerman, D. T. S. Rijkers,
R. M. J. Liskamp, Org. Biomol. Chem. 2007, 5, 935–
944; d) S. Groothuys, B. H. M. Kuijpers, P. J. L. M.
Quaedflieg, H. C. P. F. Roelen, R. W. Wiertz, R. H.
Blaauw, F. L. van Delft, F. P. J. T. Rutjes, Synthesis
2006, 3146–3152.
ꢀ À
formation, in which the vibrational absorption of C C
Cu was observed at 1930 cmÀ1. See: a) Y. Okamoto, S.
Kundu, J. Phys. Chem. 1973, 77, 2677–2680; b) V. T.
Aleksanyan, I. A. Garbuzova, I. R. Golding, A. M.
Sladkov, Spectrochim. Acta 1975, 31A, 517–524.
[17] a) W. S. Brotherton, H. A. Michaels, J. T. Simmons,
R. J. Clark, N. S. Dalal, L. Zhu, Org. Lett. 2009, 11,
4954–4957; b) K. R. Reddy, K. Rajgopal, M. L.
Kantam, Synlett 2006, 957–959; c) L. Zhu, V. M.
Lynch, E. V. Anslyn, Tetrahedron 2004, 60, 7267–7275.
[18] S. S. Y. Chui, M. F. Y. Ng, C.-M. Che, Chem. Eur. J.
2005, 11, 1739–1749.
[19] a) M. G. B. Drew, D. A. Edwards, R. Richards, J. Chem.
Soc. Dalton Trans. 1977, 299–303; b) D. A. Edwards,
R. Richards, J. Chem. Soc. Dalton Trans. 1973, 2463–
2468.
[20] F. A. Cotton, E. V. Dikarev, M. A. Petrukhina, Inorg.
Chem. 2000, 39, 6072–6079.
[21] T. Sugiura, H. Yoshikawa, K. Awaga, Inorg. Chem.
2006, 45, 7584–7586.
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