CuI/Dabco as a highly active catalytic system for the Heck-type reaction

Article abstract of DOI:10.1016/j.tetlet.2005.05.106

An efficient catalytic system using CuI/Dabco (triethylenediamine) for the Heck-type cross-coupling reaction was developed. In the presence of 10 mol % of CuI and 20 mol % of Dabco, the coupling of various aromatic iodides and 1-((Z)-2-bromovinyl)benzene

Full text of DOI:10.1016/j.tetlet.2005.05.106

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 4941–4944
CuI/Dabco as a highly active catalytic system for the
Heck-type reaction
*
Jin-Heng Li, De-Ping Wang and Ye-Xiang Xie
Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research,
College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081, China
Received 21 January 2005; revised 24 May 2005; accepted 25 May 2005
Available online 9 June 2005
Abstract—An efficient catalytic system using CuI/Dabco (triethylenediamine) for the Heck-type cross-coupling reaction was develo-
ped. In the presence of 10 mol % of CuI and 20 mol % of Dabco, the coupling of various aromatic iodides and 1-((Z)-2-bromo-
vinyl)benzene with olefins was carried out efficiently and selectively to afford the corresponding internal olefins in moderate to
good yields.
Ó 2005 Elsevier Ltd. All rights reserved.
The Heck cross-coupling reaction represents one of the
most valuable methods for carbon–carbon bond forma-
10 mol% CuI
H
R'
H
2
0 mol% Dabco
I
+
R'
ð1Þ
R
2 3
K CO , EtOH, 80 C
o
R
1
–5
tion in organic synthesis. As a result, a number of effi-
cient and selective catalytic systems were developed for
1
2
3 - 10
1
–5
the Heck cross-coupling reaction.
Of these catalytic
systems, the palladium complexes, which are employed
efficiently in controlling the reactivity and selectivity,
The efficiency of CuI/Dabco for the Heck-type cross-
coupling reaction of 1-iodo-4-methylbenzene (1a) with
tert-butyl acrylate (2a) was first evaluated, and the
results are summarized in Table 1. The results showed that
Dabco was an effective ligand for the copper-catalyzed
Heck-type reaction. Without any ligand, only a 11%
yield of the corresponding cross-coupled product 3
was isolated in the presence of 10 mol % of CuI and
1
,2
are the most popular. In recent years, the applications
of complexes with other transition metals have been
3
,4
attracting much attention, including Ni, Co, Rh, Ir
and Cu. However, only one paper on CuX-catalyzed
4
,5
Heck-type cross-coupling reaction has been reported.
In the presence of 0.1–1 equiv of CuX (X = Br, I), only
moderate yields were obtained when treatment of
aromatic iodides with olefins was proceeded in NMP
under an elevated reaction temperature (150 °C). Thus,
the development of mild and efficient copper catalytic
systems for the Heck-type cross-coupling reaction still
remains a challenging area for organic chemists. Here,
we report an inexpensive and efficient CuI/Dabco
catalytic system for the Heck-type reactions of aromatic
2 equiv of K CO (entry 1), whereas the yield of 3 was
2 3
increased dramatically to 65% when 10 mol % of Dabco
was added (entry 2). A 91% yield of 3 was obtained
when the amount of Dabco was increased to 20 mol %
(entry 3). The yield was decreased slightly upon further
increasing of Dabco to 40 mol % (entry 4). TMEDA and
PPh were also tested as the ligands. The results indi-
3
cated that they were less effective (entries 5 and 6).
The use of solvents for the Heck reaction was also inves-
tigated, and EtOH gave the highest yield (entries 3 and
iodides and 1-((Z)-2-bromovinyl)benzene with olefins
6
(
Eq. 1).
8
–13). The results also demonstrated that higher reac-
tion temperatures favored the reaction (entries 3 and
). Finally, the loadings of CuI were tested. The desired
7
yields were obtained in the presence of 1–5 mol % of CuI
after prolonged heating (entries 14 and 15).
Keywords: CuI; Dabco; The Heck-type cross-coupling reaction; ArI;
Olefins.
*
Corresponding author. Tel.: +86 731 8872530; fax: +86 731
872531; e-mail: jhli@hunnu.edu.cn
Typical experimental procedure for the copper/Dabco-
catalyzed Heck-type cross-coupling reactions is as
8
0
040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.05.106

4942
J.-H. Li et al. / Tetrahedron Letters 46 (2005) 4941–4944
a
Table 1. CuI/Dabco-Catalyzed Heck reaction of 1a with 2a
H
COOC(Me)3
H
CuI/L
Me
I
+
COOC(Me)3
Me
K CO , 80 oC
2
3
1
a
2a
3
b
Entry
1
Ligand
Solvent
Yield (%)
—
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
DMF
THF
11
65
91
88
37
80
79
55
21
33
42
65
41
86
75
c
2
Dabco
Dabco
Dabco
TMEDA
3
d
4
5
6
PPh
3
e
7
Dabco
Dabco
Dabco
Dabco
Dabco
Dabco
Dabco
Dabco
Dabco
8
9
1
1
1
1
1
1
0
1
2
3
4
5
Toluene
MeCN
Dioxane
Acetone
EtOH
f
g
EtOH
a
Under otherwise indicated, the reaction conditions were as follows: 1a (1.0 mmol), 2a (1.5 mmol), CuI (10 mol %), ligand (20 mol %), K
CO
2 3
(
2
2 equiv), and solvent (3 mL) for 20 h at 80 °C under N .
b
c
d
e
f
Isolated yield.
Dabco (10 mol %).
Dabco (40 mol %).
At 50 °C.
CuI (5 mol %) at 100 °C for 48 h.
CuI (1 mol %) at 100 °C for 48 h.
g
a
Table 2. The Heck-type reactions of aryl iodides with olefins catalyzed by CuI/Dabco catalytic system
1
0 mol% CuI
H
R'
H
2
0 mol% Dabco
I
+
R'
R
K CO , EtOH, 80 C
o
2
3
R
1
2
3 - 11
b
Entry
1
ArX
Olefin
Time (h)
20
Product
Yield (%)
91
H
COOC(Me)3
(4)
O2N
I
COOC(Me)3 (2a)
(
1b)
O N
H
2
H
COOC(Me)3
I
H
(5)
2
3
(2a)
40
30
68
90
NO2
(1c)
NO2
H
COOC(Me)3
I
I
(2a)
(2a)
(2a)
H
(6)
(
1d)
1e)
H
COOC(Me)3
H
(7)
4
5
36
34
61
88
Me
(
Me
H
COOC(Me)3
MeO
I
MeO
H
(8)
(
1f)
n
H
COO Bu
9)
n
COO Bu
6
7
(1f)
(1f)
30
30
81
78
(
(
2b)
MeO
MeO
H
H
Ph
Ph
(
2c)
H
10)
(

J.-H. Li et al. / Tetrahedron Letters 46 (2005) 4941–4944
4943
Table 2 (continued)
b
Entry
ArX
Olefin
Time (h)
36
Product
Yield (%)
O
8
(1f)
O
45
52
88
28
(
11)
(
2d)
MeO
H
H
H
H
H
H
9
(2b)
(2b)
(2a)
40
40
36
Br
COOC(Me)3
(
1g)
(
12)
H
H
c
1
1
0
Br
COOC(Me)3
12)
(
1g)
(
H
COOC(Me)3
(4)
d
1
O2N
Br
O N
H
(
1h)
2
H
H
COOC(Me)3
(4)
c,d
1
1
2
(1h)
(2a)
(2a)
36
36
30
O N
H
2
COOC(Me)3
(8)
d
3
MeO
Br
<5
MeO
H
(1i)
a
Under otherwise indicated, the reaction conditions were as follows: 1 (1.0 mmol), 2 (1.5 mmol), CuI (10 mol %), Dabco (20 mol %), K
2 equiv) and EtOH (3 mL) at 80 °C under N
Isolated yield.
CuI (1 equiv).
At 100 °C.
2 3
CO
(
2
.
b
c
d
follows: A mixture of aryl iodide 1a (1.0 mmol), olefin
a (1.5 mmol), CuI (10 mol %), Dabco (20 mol %),
K CO (2 equiv) and EtOH (3 mL) was added to a tube.
yield of the desired product 12 in the presence of
10 mol % of CuI and 20 mol % of Dabco (entry 9).
The yield of 12 was increased to 88%, when 1 equiv of
CuI and 200 mol % of Dabco were added (entry 10).
Unfortunately, the CuI/Dabco catalytic system was less
effective for the reaction of aryl bromides (entries 11–
13). The treatment of activated aryl bromide 1h with
2a afforded a lower yield of 4 even in the presence of
1 equiv of CuI (entries 11 and 12). Attempt to couple
1-bromo-4-methoxybenzene 1i with 2a was not success-
ful (entry 13).
2
2
3
Then, the tube was sealed with septum under N , and
2
the mixture was then stirred at 80 °C for an appropriate
period of time until there was complete consumption of
the starting material, as monitored by TLC. After the
mixture was filtered and evaporated, the residue was
purified by flash column chromatography (hexane/ethyl
acetate) to afford the desired coupled products.
As shown in Table 2, the treatment of various aryl iod-
ides (1b–f) or 1-((Z)-2-bromovinyl)benzene (1g) with
olefins (2a–d), CuI (10 mol %) and Dabco (20 mol %)
was carried out efficiently and selectively to afford the
corresponding cross-coupled products 4–12 in moderate
to good yields. The results indicated that the CuI/Dabco
catalytic system is remarkably active and tolerant of a
range of functionalities. For example, treatment of aryl
iodides 1b with 2a afforded 91% yields of the corre-
sponding cross-coupled product 4 in the presence of
A possible mechanism was proposed as shown in
,5b
2
Scheme 1.
The reaction of intermediate 3, a four-cen-
7
tered transition state proposed by Castro and Stephens,
with ArI afforded intermediate 4. Then, the complex of
intermediate 4 with olefin form intermediate 5, followed
by a reductive elimination of intermediate 5, gave the
coupled product 2 and regenerated the active copper(I)
complex 3.
1
0 mol % of CuI and 20 mol % of Dabco (entry 1).
In summary, an efficient CuI/Dabco catalytic system for
the Heck-type cross-coupling reaction has been devel-
oped. In the presence of CuI and Dabco, coupling of
various aryl iodides with olefins were carried out effi-
ciently and selectively to afford the desired products in
moderate to excellent yields. Currently, further efforts
to extend the application of this catalytic system and this
protocol in organic synthesis are underway in our
laboratory.
For the coupling of substrates 1c–e with 2a, the corre-
sponding coupled products 5–7 were obtained in 68%,
9
to good yields were obtained when deactivated aryl io-
dide 1e coupled with 2a–d, respectively, in the presence
of 10 mol % of CuI and 20 mol % of Dabco (entries 5–
0% and 61% yields, respectively (entries 2–4). Moderate
8). The reaction of 1-((Z)-2-bromovinyl)benzene (1g)
with 2a was also carried out smoothly to afford 52%

4944
J.-H. Li et al. / Tetrahedron Letters 46 (2005) 4941–4944
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L
L
3
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3
ArI + K
2 3
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Ar
2
L + KI
2
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2
L
L
Cu
I
4
Cu
L
Ar
L
Ar
I
5
3
L
Scheme 1. A possible mechanism for the copper-catalyzed Heck
reaction.
Acknowledgements
4
5
. For the paper on CuI-catalyzed Heck-type cross-coupling
reaction, see: Iyer, S.; Ramesh, C.; Sarkar, A.; Wadgaon-
kar, P. P. Tetrahedron Lett. 1997, 38, 8113.
We thank the National Natural Science Foundation of
China (No. 20202002) for financial support.
. For recent selected papers on CuX-catalyzed reaction of
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2
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1
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1
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3
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