Facile cuI-catalyzed arylation of azoles and amides using simple enaminones as efficient ligands

Article abstract of DOI:10.1055/s-0029-1217958

(E)-3-(Dimethylamino)-1-(2-hydroxyphenyl)prop-2-en-1-one was found to be an excellent ligand for copper-catalyzed N-arylation of azoles and amides with aryl halides under mild conditions. The reaction took place at 82 C in MeCN with broad functional-group compatibility. A combination of the ligand and CuI proved to be an efficient catalytic system to promote the coupling reactions of aryl halides with azoles and amides.

Full text of DOI:10.1055/s-0029-1217958

LETTER
2663
Facile CuI-Catalyzed Arylation of Azoles and Amides Using Simple
Enaminones as Efficient Ligands
Copper-Catalyzed
u
U
llmann–G
n
oldberg
R
ea
g
ctions ui Cheng,a Gonglei Sun,a Jieping Wan,b Cuirong Sun*b
a
Department of Chemistry, Zhejiang Normal University, Jinhua 321004, P. R. of China
Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. of China
Fax +86(571)87951629; E-mail: suncuirong@zju.edu.cn
b
Received 16 June 2009
ligand14 in Ullmann reactions. In this paper, based on the
rationale given in Buchwald’s first report of phenolic
ligands,8b we wish to report herein the use of a new phe-
nolic-type ligand (E)-3-(dimethylamino)-1-(2-hydroxy-
Abstract: (E)-3-(Dimethylamino)-1-(2-hydroxyphenyl)prop-2-en-
1-one was found to be an excellent ligand for copper-catalyzed N-
arylation of azoles and amides with aryl halides under mild condi-
tions. The reaction took place at 82 °C in MeCN with broad func-
tional-group compatibility. A combination of the ligand and CuI phenyl)prop-2-en-1-one in the efficient CuI-catalyzed N-
proved to be an efficient catalytic system to promote the coupling
arylation of both azoles and amides with a variety of aryl
reactions of aryl halides with azoles and amides.
halides.
Key words: copper, ligand, azoles, amides, arylation
O
O
NMe2
NMe2
Copper-catalyzed Ullmann reaction1 and the related Gold-
berg reactions2 are important methods for the formation of
C–N bond. Traditional Ullmann–Goldberg reactions are
generally conducted under harsh reaction conditions un-
der stoichiometric amounts of copper reagents, high tem-
perature, and with low tolerance of functional groups.
During the past decade, Buchwald3 and Hartwig4 have
made significant contribution in the palladium/phosphine-
ligand-promoted cross-coupling reactions, which pro-
ceeded under considerably milder conditions to construct
aryl C–N bond and other C–heteroatom bonds.5,6 Howev-
er, its large-scale application for industry is difficult, be-
cause palladium catalysts are expensive and phosphine
ligands are usually not easy to prepare, sensitive to air or
moisture, and toxic. As an alternative metal-catalyzed
protocol, copper-catalyzed coupling reactions7 attract
greater attention because of the low cost of copper re-
agents. Representatively, Buchwald8 and Ma,9,10a–c re-
spectively, accomplished the same transformation by
combining copper(I) iodide with salicylic amide deriva-
tives and proline. Thereafter, a number of efficient ligands
with N–N,10d,h N–O,9c,10d,g O–O,8b,i,10d N–S,10a–c,e and N–
P11 coordination sites that could form stable chelates with
copper were discovered. Recently, Hu12 and You13 report-
ed the copper-catalyzed N-arylation of nitrogen-contain-
ing heterocycles under ligand-free and mild conditions.
However, only aryl iodides were successfully applied in
their reactions. Neither aryl bromides nor other N-con-
taining substrates were reported as proper partners in their
ligand-free systems. Therefore, exploring new ligands
with broad application scope still plays an important role
in the Ullmann–Goldberg coupling reactions.7,9c,10,11 We
previously reported the 1,1-diamide motif as an efficient
Cl
O
L1
L2
NMe2
O2N
L3
O
O
NMe2
NHPh
NMe2
MeO
OH
L4
L5
O
O
O
NHPh
OH
OH
L6
L7
L8
O
HN
O
NHPh
EtO
EtO
L9
L10
Figure 1 The ligands screened for C–N coupling
Initially, we synthesized a series of analogous enaminone
compounds with N–O coordinate sites as candidate
ligands (Figure 1). To select the most efficient ligand, the
coupling reaction of iodobenzene with imidazole was
chosen as the model reaction, and this reaction was carried
out at 110 °C in the presence of 10 mol% of CuI, 20 mol%
of ligand, and 2 equivalents of Cs2CO3 in DMSO under N2
atmosphere for 12 hours.
Most of the ligand with N–O coordinate sites could pro-
mote the coupling reaction efficiently except L9 and L10,
which yielded the desired products in less than 5% yield
(Scheme 1). After analyzing the results from all entries in
this section, we found that ligand L5 was the best among
SYNLETT 2009, No. 16, pp 2663–2668
x
x
.x
x
.2
0
0
9
Advanced online publication: 04.09.2009
DOI: 10.1055/s-0029-1217958; Art ID: W09109ST
© Georg Thieme Verlag Stuttgart · New York

2664
C. Cheng et al.
LETTER
with K2CO3 and K3PO4 (entries 7 and 9). However,
Cs2CO3 gave the optimal yield (entries 6 and 8).
After optimization, the best reaction conditions were 10
mol% CuI, 20 mol% ligand, and 2.0 equivalents of
Cs2CO3 in MeCN at 82 °C. Ullmann-type coupling reac-
tions of various aryl halides with different azoles were
conducted, and the results are summarized in Table 2. As
expected, aryl iodides showed better reactivity than aryl
bromides. The reaction of aryl bromides with azoles
yielded the desired products only in moderate yields (en-
tries 1–8, 13–16, and 24). Further studies disclosed that
aryl chlorides bearing electron-withdrawing groups were
reactive in this kind of conversion and different azoles
could be effectively arylated (entries 17–21). Moreover,
heterocyclic aryl bromides were compatible with the
present procedure and satisfactory results were obtained
(entries 22 and 23).
Scheme 1 Ligand performances in the CuI-catalyzed N-arylation of
imidazole
Table 1 N-Arylation of Imidazole under Different Conditionsa
CuI, L5
N
N
Table 2 CuI/L5-Catalyzed N-Arylation of Azoles with Different
+
HN
I
N
Aryl Halidesa
base, solvent
1a
2a
CuI (10 mol%), L5 (20 mol%)
+
HetNH
HetNAr
ArX
Cs2CO3 (2 equiv), MeCN
82 °C
Entry Solvent, base
CuI, ligand Temp
Yield
(%)b
1
2
(mol%)
10, 20
10, 10
5, 10
(°C)
110
110
110
110
110
82
Entry ArX
Product
Yield (%)b
88 (43)c
1
2
DMSO, Cs2CO3
DMSO, Cs2CO3
DMSO, Cs2CO3
DMF, Cs2CO3
dioxane, Cs2CO3
MeCN, Cs2CO3
MeCN, K2CO3
MeCN, MeONa
MeCN, K3PO4
MeCN, Cs2CO3
76
35
53
57
42
88
63
84
55
22
PhI (Br)
N
N
1
2
1a (1b)
1a (1b)
3
2a
4
10, 20
10, 20
10, 20
10, 20
10, 20
10, 20
10, 0
92 (45)c
78 (42)c
N
5
2b
6
7
82
3
4
1a (1b)
1a (1b)
N
8
82
2c
9
82
10
82
73 (29)c
a Reaction conditions: iodobenzene (0.5 mmol), imidazole (0.5
mmol), base (1.0 mmol) in the presence of L5 and CuI catalyst in sol-
vent (2 mL) under N2 atmosphere for 12 h.
N
N
2d
b Isolated yields.
4-ClC6H4 I (Br)
5
6
84 (38)c
79 (40)c
N
N
Cl
Cl
N
1c (1d)
the ligands tested, and the desired products N-phenylimi-
dazole was isolated in 76% yields (Table 1, entry 1).
2e
1c (1d)
1c (1d)
To determine the most suitable reaction conditions, differ-
ent parameters such as the amounts of CuI/L5, solvent,
and the nature of the base were optimized on the same re-
action (Table 1). It was found that a smaller amount of
CuI was inefficient for the reaction. Increasing the amount
of ligand L5 from 10 mol% to 20 mol% in the presence of
10 mol% CuI afforded N-phenylimidazole in higher yield
(entries 1 and 2). Without ligand L5,15 the yield was de-
creased greatly (entries 1 and 10). Among the tested sol-
vents, MeCN gave the best results (entries 1, 4–6). Both
MeONa and Cs2CO3 were efficient bases as compared
2f
7
8
89 (52)c
63 (33)c
N
N
Cl
Cl
2g
1c (1d)
N
2h
Synlett 2009, No. 16, 2663–2668 © Thieme Stuttgart · New York

LETTER
Copper-Catalyzed Ullmann–Goldberg Reactions
2665
Table 2 CuI/L5-Catalyzed N-Arylation of Azoles with Different
Table 2 CuI/L5-Catalyzed N-Arylation of Azoles with Different
Aryl Halidesa (continued)
Aryl Halidesa (continued)
CuI (10 mol%), L5 (20 mol%)
CuI (10 mol%), L5 (20 mol%)
+
+
HetNH
HetNH
HetNAr
HetNAr
ArX
ArX
Cs2CO3 (2 equiv), MeCN
82 °C
Cs2CO3 (2 equiv), MeCN
82 °C
1
1
2
2
Entry ArX
Product
Yield (%)b
83
Entry ArX
Product
Yield (%)b
4-BrC6H4I
1e
N
N
Br
Br
9
20
21
1g
1g
90
N
N
CF3
2i
O2N
N
10
1e
81
91
2t
2j
89
11
12
1e
1e
N
CF3
N
N
N
Br
Br
O2N
2k
2u
2-BrPy
1h
N
22
23
79
92
61
N
N
N
N
2v
2l
4-MeC6H4Br
1f
13
14
43c
39c
N
N
1h
N
N
N
2m
N
2w
CF3
CF3
1f
1f
3,5-(F3C)2C6H3Br
1i
2n
N
24
25
39
N
15
16
51c
34c
2x
N
N
2o
N
2y-1
73
(2y-1/2y-
2 = 6.5:1)
1a
1f
N
N
N
2p
N
2-O2N-4-
F3CC6H3Cl
1g
N
N
CF3
2y-2
17
18
79
87
a Reaction conditions: aryl halide (0.5 mmol), azole (0.5 mmol), CuI
(0.05 mmol), Cs2CO3 (1.0 mmol) and L5 (0.1 mmol) in MeCN (2 mL)
at 82 °C under N2 atmosphere for 12 h.
O2N
2q
b Isolated yields.
c KI (0.5 mmol) was used.
N
CF3
1g
1g
O2N
Encouraged by the successful application of L5 in Ull-
mann-type reaction, we further employed our catalyst to
the Goldberg-type N-arylation of amides. We optimized
the coupling conditions of iodobenzene with 2-pyrroli-
done as shown in Table 3. The effects of solvent and base
in the coupling reaction were investigated by using 10
mol% CuI and 20 mol% ligand L5 (entries 1–4 and 6–8).
It was found that the transformation led to as low as only
14% yield without using ligand (entry 5). In the presence
of Cs2CO3 as a base, L5 as a ligand, and MeCN as a sol-
2r
19
88
N
CF3
O2N
2s
Synlett 2009, No. 16, 2663–2668 © Thieme Stuttgart · New York

2666
C. Cheng et al.
LETTER
Table 4 CuI/L5-Catalyzed N-Arylation of Amides with Different
Table 3 N-Arylation of Amide under Different Conditionsa
Aryl Halidesa
O
O
O
O
CuI, L5
CuI (10 mol%), L5 (20 mol%)
R2
R2
+
I
N
HN
R1
R1
+
ArX
N
N
base, solvent
Cs2CO3 (2 equiv), MeCN
82 °C
H
Ar
3a
1a
1
3
Entry
Solvent, base
CuI, ligand Temp
Yield
(%)b
Entry ArX
Product
Yield (%)b
86 (50)c
(mol%)
10, 20
10, 20
10, 20
10, 20
10, 0
(°C)
O
1
2
3
4
5
6
7
8
MeCN, Cs2CO3
MeCN, K2CO3
MeCN, MeONa
MeCN, K3PO4
MeCN, Cs2CO3
DMSO, Cs2CO3
DMF, Cs2CO3
dioxane, Cs2CO3
82
86
72
83
34
14
36
29
27
PhI (Br)
1a (1b)
1
2
N
82
3a
82
O
82
1a (1b)
1a (1b)
79 (32)c
81 (46)c
N
H
82
10, 20
10, 20
10, 20
110
110
110
3b
O
3
4
N
H
a Reaction conditions: iodobenzene (0.5 mmol), 2-pyrrolidone (0.5
mmol), CuI (0.05 mmol), base (1.0 mmol) and L5 (0.1 mmol) in sol-
vent (2 mL) under N2 atmosphere for 12 h.
F
3c
b Isolated yields.
O
N
H
1a (1b)
1a (1b)
71 (36)c
vent, the desired product N-phenyl-pyrrolidin-2-one was
obtained in the highest yields (entry 1).
To probe the generality of the optimized conditions, the
reactions of aryl halides and amides were investigated
(Table 4). It was easily found that all of aryl iodides, aryl
bromides, and activated aryl chlorides could perform this
transformation successfully, but aryl iodides were more
active and led to better yields than aryl bromides (entries
1–8, 12–16, and 18). Meanwhile, the reaction of para-
substituted aryl bromides and iodides bearing electron-
withdrawing substituent gave the corresponding products
in excellent yields (entries 1, 3, and 5–8).
3d
O
MeO
N
78 (42)c
H
5
OMe
3e
O
4-ClC6H4I
(Br)
1c (1d)
6
7
92 (61)c
81 (39)c
N
Cl
Additionally, we also tried N-arylation of azoles and
amides with various aryl bromides under harsh conditions
at 130 °C in DMSO in the presence of 10 mol% of CuI, 20
mol% of L5, and 2 equivalents of Cs2CO3 under N2 atmo-
sphere for 12 hours. However, the yields were similar to
the same transformation at 82 °C in MeCN with adding 1
equivalent of KI.
3f
Cl
O
1c (1d)
1c (1d)
N
H
F
3g
In summary, we have developed a ligand (E)-3-(di-meth-
ylamino)-1-(2-hydroxyphenyl)prop-2-en-1-one for the ef-
ficient copper-catalyzed Ullmann-type N-arylation of
azoles and Goldberg-type N-arylation of amides. By using
MeCN as a solvent, various azoles and amides were ary-
lated with a broad range of aryl halides compared with tra-
ditional strategies. This protocol bears advantages of mild
conditions and wide application scope. Therefore, this ap-
proach provided a simple and useful supplement for
known methods.
Cl
O
MeO
N
8
9
83 (37)c
H
OMe
O
3h
Br
4-BrC6H4I
1e
73
N
H
F
3i
Synlett 2009, No. 16, 2663–2668 © Thieme Stuttgart · New York

LETTER
Copper-Catalyzed Ullmann–Goldberg Reactions
2667
Table 4 CuI/L5-Catalyzed N-Arylation of Amides with Different
Table 4 CuI/L5-Catalyzed N-Arylation of Amides with Different
Aryl Halidesa (continued)
Aryl Halidesa (continued)
O
O
O
O
CuI (10 mol%), L5 (20 mol%)
CuI (10 mol%), L5 (20 mol%)
R2
R2
R2
R2
R1
R1
R1
R1
+
+
ArX
ArX
N
N
N
N
Cs2CO3 (2 equiv), MeCN
82 °C
Cs2CO3 (2 equiv), MeCN
82 °C
H
H
Ar
Ar
1
3
1
3
Entry ArX
Product
Yield (%)b
Entry ArX
18 3,5-
Product
Yield (%)b
42
CF3
Br
O
(F3C)2C6H3Br
1i
O
N
H
10
11
1e
1e
71
67
N
H
CF3
F
3j
3r
a Reaction conditions: aryl halides (0.5 mmol), amides (0.5 mmol),
CuI (0.05 mmol), Cs2CO3 (1.0 mmol), and L5 (0.1 mmol) in MeCN
(2 mL) at 82 °C under N2 atmosphere for 12 h.
b Isolated yields.
Br
O
MeO
N
H
c KI (0.5 mmol) was used.
OMe
3k
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.
O
4-MeC6H4Br
1f
12
13
58c
41c
N
Acknowledgment
3l
The authors are grateful to National Natural Science Foundation of
China (No. 20775069) and NCET-06-0520 of the National Ministry
of Education of China for financial support on this work.
O
1f
1f
N
H
References and Notes
3m
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O2N
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Synlett 2009, No. 16, 2663–2668 © Thieme Stuttgart · New York

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LETTER
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(15) General Procedure
All chemicals were obtained from commercial source and
used without further purification. A stirred suspension of
aryl halides (0.5 mmol), azoles or amides (0.5 mmol), CuI
powder (0.05 mmol), Cs2CO3 (1.0 mmol), and L5 (0.1
mmol) in MeCN was refluxed for 12 h (monitored by TLC)
under nitrogen. After the mixture was cooled to r.t., the
MeCN was removed in vacuo. The solid was then extracted
with EtOAc (3 × 10 mL), washed with H2O (3 × 10 mL), and
dried over Na2SO4. After the solvent was removed, the crude
mixture was purified by silica gel column chromatography
to provide the desired product.
Synlett 2009, No. 16, 2663–2668 © Thieme Stuttgart · New York