CuI-catalyzed cross-coupling reaction of (E)-vinyl bromides with nitrogen-containing heterocycles

Article abstract of DOI:10.1055/s-2008-1077955

An efficient and straightforward copper-catalyzed method allowing vinylation of N-nucleophiles with various substituted (E)-vinyl bromides under palladium-free and ligand-free conditions has taken a high yield (up to 95%). Noteworthy is that the doublebond geometry of these vinyl halides was retained with our protocol.

Full text of DOI:10.1055/s-2008-1077955

LETTER
2011
CuI-Catalyzed Cross-Coupling Reaction of (E)-Vinyl Bromides
with Nitrogen-Containing Heterocycles
C
opper-
C
i
nc
on heng Mao,*a Qiongqiong Hua,b Jun Guo,a Daqing Shi,a,b Shunjun Jia
a
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry and Chemical Engineering, Suzhou University,
Suzhou 215123, P. R. of China
Fax +86(512)65880089; E-mail: jcmao@suda.edu.cn
Department of Chemistry, Xuzhou Normal University, Xuzhou 221116, P. R. of China
b
Received 18 April 2008
arylation of imidazoles with vinyl halides has rarely been
described.
Abstract: An efficient and straightforward copper-catalyzed meth-
od allowing vinylation of N-nucleophiles with various substituted
(E)-vinyl bromides under palladium-free and ligand-free conditions
has taken a high yield (up to 95%). Noteworthy is that the double-
bond geometry of these vinyl halides was retained with our proto-
col.
N-(1-Alkenyl)azoles or N-vinylimidazoles are important
compounds in organic synthesis, and can be found in nu-
merous biologically active molecules.18 However, al-
though there are many methods to prepare these
compounds, most of these suffer from either harsh reac-
tion conditions or lack of stereocontrol of the double-bond
geometry.19 Thus, the relevant reports about the mild and
stereoselective coupling of vinyl halides with azoles are
very few. In 2002, Voskoboynikov reported the vinylation
of various azoles and phenothiazine with vinyl bromides
catalyzed by palladium–phosphine complexes.20 Recent-
ly, Taillefer disclosed the finding of highly effective cop-
per-catalyzed vinylation of various azoles promoted by a
tetradentate ligand.21 Bao also reported the synthesis of N-
vinylimidazoles by using CuI/L-proline catalytic system
performed in ionic liquids.22 Therefore, more readily
available copper-catalytic systems are still desirable.
Key words: halides, nucleophiles, copper, cross-coupling, hetero-
cycles
It is well known that transition-metal-catalyzed formation
of C–N bonds via cross-coupling reactions represents one
of the powerful means for the preparation of numerous
important products in pharmaceutical industry and mate-
rial science.1 Although copper-catalyzed Ullmann-type
couplings were discovered more than a century ago,2 their
application in N-vinylation reactions has been limited,
due to their harsh reaction conditions such as high temper-
atures (120–220 °C), the requirement of a stoichiometric
amount of copper catalyst. Thus, it is of great interest to
develop copper-catalyzed C–N coupling under milder
conditions. Recently, Buchwald and co-workers3 discov-
ered and developed copper-catalytic reactions for N-
arylation of nitrogen-containing heterocycles with aryl
halides under relatively mild conditions. This work led to
a resurgence of interest in Ullmann-type couplings with
copper-based catalysts.
Based on our interest in the copper-catalyzed coupling re-
actions,23 we intended to study the efficiency of copper-
catalyzed C–N coupling between (E)-vinyl halides with
azoles using different ligands. Meanwhile, we wondered
whether the configuration of the double bond could be re-
tained after the reaction.
In order to explore copper catalysts for the C–N coupling
reactions, coupling of (E)-b-bromostyrene24 with imida-
zole was chosen as the model reaction. All the reactions
For the past decades, a notable achievement has been the
use of copper catalyst combined with ligands. The effi-
cient ligands included diamines,3 amino acids,4 1,10-
phenanthrolines,3a,5 8-hydroxyquinolines,6 (S)-pyrrolidi-
nylmethylimidazoles,7 aminoarenethiolates,8 phosphin-
idenes,9 phosphoramidities,10 oximephosphine oxides,11
amino alcohols,12 bidentate phosphines,13 diphenyl pyrro-
lidine-2-phosphonate,14 salicylamides,15 and others.16 De-
spite significant results were realized in the copper-
catalyzed C–N couplings using the ligands mentioned
above, relatively little progress has been made for the N-
arylation of imidazoles and aryl halides.3a,7,10,17 Mean-
while, the majority of aryl halides investigated to date
were limited to the use of aryl iodides, bromides, and
chlorides. However, application of these protocols to N-
O
N
OH
OH
N
N
N
N
H
OH
N
N
A
B
C
D
N
N
N
N
N
N
SYNLETT 2008, No. 13, pp 2011–2016
Advanced online publication: 15.07.2008
x
x
.x
x
.2
0
0
8
F
E
G
DOI: 10.1055/s-2008-1077955; Art ID: W06208ST
© Georg Thieme Verlag Stuttgart · New York
Figure 1 The ligands evaluated in the study

2012
J. Mao et al.
LETTER
Table 1 Screening of Copper Catalysts for N-Arylation of Imida-
zole with (E)-b-Bromostyrenea
were carried out with 10 mol% of copper salt, 20 mol%
ligand, and Cs2CO3 as the base in DMF (N,N-dimethylfor-
mamide) at 120 °C. These readily available ligands in-
cluded L-proline (A), rac-BINOL (1,1¢-binaphthyl-2,2¢-
diol, B), hexamethylenetetramine (C), DABCO {1,4-di-
aza-bicyclo[2.2.2]octane, D}, TMEDA (N,N,N¢,N¢-tet-
ramethyldiethylamine, E), 2,2¢-bipyridine (F), and 1,10-
phenanthroline (G, Figure 1). The results were listed in
Table 1. To our delight, all of these ligands afforded the
desired coupling products in moderate to good yields as
the pure E-isomers (Table 1, entries 1–7). It can be seen
that among them, DABCO (D) gave the best result of 85%
yield (entry 4). Using D as the best ligand, the optimal cat-
alytic conditions were screened subsequently. The differ-
ent solvents including DMF, DMSO (dimethyl sulfoxide),
1,4-dioxane, and toluene have been investigated and DMF
gave the best result (entry 4). Then, other various bases
were tested (such as K2CO3, K3PO4, KOt-Bu, KF, KOH,
and Et3N) in the coupling reaction (entries 8–13). It was
found that Cs2CO3 proved to be the best choice (entry 4).
CuI (10 mol%)
L (20 mol%)
N
Br
N
HN
N
+
DMF, Cs2CO3
120 °C, 36 h, Ar
Entry Catalyst
Ligand Base
Cs2CO3
Temp (°C) Yield (%)b
1
2
CuI
CuBr
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
–
A
B
C
D
E
F
G
D
D
D
D
D
D
D
–
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
80
80
73
76
85
79
75
80
54
66
69
24
66
22
19
95
54
53
83
–
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
K3PO4
KOt-Bu
KF
3
4
5
6
7
8
Control experiments were also conducted. As expected,
poor result was obtained in the absence of CuI (entry 14).
Subsequently, the CuI-catalyzed coupling reaction was
performed without using any ligand. However, we sur-
prisingly found that it afforded the corresponding product
with the retention of configuration in 95% yield (entry
15).25 The other control experiments showed that the cou-
pling reaction performed in air and at decreased tempera-
tures (such as 80 °C or 100 °C) gave moderate yields
(entries 16–18). When the catalytic reaction was per-
formed at room temperature, no product was obtained (en-
try 19).
9
10
11
12
13
14
15
16c
17
18
19d
KOH
Et3N
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
CuI
CuI
CuI
CuI
CuI
–
To the best of our knowledge, there are few papers that
deal with ligand-free C–N coupling reactions between
aryl halides and nitrogen-containing compounds.26 Thus,
in this paper, we disclose the copper-catalyzed cross-cou-
pling reaction of (E)-vinyl bromides or (E)-vinyl chlo-
rides with nitrogen-containing heterocycles under Pd-free
and ligand-free conditions.
–
–
100
r.t.
–
a Reaction conditions: CuI (0.05 mmol), ligand (0.1 mmol), (E)-b-
bromostyrene (0.5 mmol), imidazole (0.6 mmol), Cs2CO3 (1.0 mmol),
DMF (2 mL), 120 °C, 36 h, under an argon atmosphere.
b Isolated yield.
Using the optimized reaction conditions, we explored the
scope of the coupling reactions of vinyl bromides with ni-
trogen-containing heterocycles in the presence of 10
mol% of CuI and two equivalents of Cs2CO3 in DMF at
120 °C under an argon atmosphere. The results are sum-
marized in Table 2. As shown, the CuI-catalyzed coupling
reaction could also work for pyrazole, pyrrole, imidazole,
benzimidazole, pyrazole, indole, and substituted indoles
as the substrates. It could be seen that the N-vinylation of
heterocycles by vinyl bromides gave the corresponding
products in excellent yields (91–95%, Table 2, entries 1,
11, and 12). Noteworthy was that the results from the cou-
plings with substituted (E)-b-bromostyrenes were better
than those with (E)-b-bromostyrene, except for imidazole
and 4-(benzyloxy)-1H-indole (entries 1, 7, 10, 16).
c The catalytic reaction was performed in air.
d The catalytic reaction was performed at r.t.
lower yields than those of vinyl bromides (Scheme 1).
From the data listed, the results of couplings with substi-
tuted (E)-b-chlorostyrenes were better than those of (E)-
b-chlorostyrene, except for 4-(benzyloxy)-1H-indole. In
order to get satisfactory result, the coupling of (E)-vinyl
chloride was performed at a higher temperature (140 °C).
As shown in Scheme 2, the desired coupling product was
obtained in higher yield (66%).
In order to explore the scope of the coupling reactions, N-
arylations of (E)-b-bromostyrene with aromatic amines
(such as p-toluidine) or morpholine were investigated un-
der the standard conditions. To our surprise, no coupling
product was obtained (Scheme 3).
Under the similar conditions, coupling reactions of nitro-
gen-containing heterocycles and vinyl chlorides afforded
Synlett 2008, No. 13, 2011–2016 © Thieme Stuttgart · New York

LETTER
Copper-Catalyzed N-Vinylation
2013
Table 2 Catalytic N-Vinylation of Nitrogen-Containing Heterocy-
cles with (E)-Vinyl Bromides by CuIa
Table 2 Catalytic N-Vinylation of Nitrogen-Containing Heterocy-
cles with (E)-Vinyl Bromides by CuIa (continued)
Br
+
N-Het
Br
+
N-Het
CuI (10 mol%)
CuI (10 mol%)
Het-NH
Het-NH
DMF, Cs2CO3
120 °C, 36 h, Ar
DMF, Cs2CO3
120 °C, 36 h, Ar
R
R
R
R
1–17
R = H, OMe
1–17
R = H, OMe
Entry R
Product
Yield (%)b
95
Entry R
Product
Yield (%)b
57
N
N
N
N
1
2
H
H
1
10
11
OMe 10
MeO
N
N
2
3
78
80
N
N
N
N
OMe 11
OMe 12
93
91
MeO
MeO
MeO
MeO
3
4
5
6
7
H
H
H
H
H
12
13
14
15
16
17
4
5
6
7
70
63
48
71
OMe 13
OMe 14
OMe 15
OMe 16
OMe 17
82
80
74
64
75
N
N
N
N
CHO
CHO
O
N
N
N
O
MeO
MeO
MeO
OBn
OBn
8
9
H
H
8
9
69
70
N
N
N
N
N
a Reaction conditions: CuI (0.05 mmol), (E)-vinyl bromide (0.5
mmol), nitrogen-containing heterocycle (0.6 mmol), Cs2CO3 (1.0
mmol), DMF (2 mL), 120 °C, 36 h, under an argon atmosphere.
b Isolated yield based on vinyl bromides (average of two runs).
Synlett 2008, No. 13, 2011–2016 © Thieme Stuttgart · New York

2014
J. Mao et al.
LETTER
catalyze the C–N coupling of aromatic amine or morpho-
line. We assumed that the nitrogen-containing heterocy-
cles could possibly serve not only as the substrate but also
as the ligand. Actually, benzotriazole could work as an ex-
cellent ligand for Cu-catalyzed N-arylation of imidazoles
with aryl and heteroaryl halides.29
Cl
N-Het
CuI (10 mol%)
Het-NH
+
DMF, Cs2CO3
120 °C, 50 h, Ar
R
R
R = H, OMe
N
N
N
N
MeO
R
N
CuI (10 mol%)
Br
HN
+
N
7%, R = H
13%, R = OMe
22%, R = H
15%, R = OMe
DMF, Cs2CO3
120 °C, 36 h, Ar
Me
Me
18
19
E/Z = 7:5
E/Z = 2:1
70% yield
CHO
N
N
R
R
CuI (10 mol%)
HN
N
7%, R = H
35%, R = OMe
17%, R = H
25%, R = OMe
+
+
byproducts
DMF, Cs2CO3
120 °C, Ar
N
Br
N
Scheme 1 Catalytic N-arylation of nitrogen-containing hetero-
cycles with vinyl chloride by CuI. Reagents and conditions: CuI (0.05
mmol), (E)-vinyl chloride (0.5 mmol), nitrogen-containing hetero-
cycle (0.6 mmol), Cs2CO3 (1.0 mmol), DMF (2 mL), 120 °C, 50 h, un-
der an argon atmosphere. Isolated yield based on vinyl chlorides
(average of two runs).
20
21
30% yield
61% yield
24 h
36 h
byproducts (GC-MS):
+
Based on the results as above, it can be seen that CuI could
directly catalyzed N-arylations of nitrogen-containing
heterocycles with (E)-vinyl bromides or chlorides and the
corresponding E-products were obtained as the only ste-
reoisomer. As shown in Scheme 4, when vinyl bromide
(E/Z = 7:5; 18) was used as the substrate, the coupling
product (E/Z = 2:1; 19) in 70% yield was obtained. In ad-
dition, when pure (Z)-b-bromostyrene (20)27 was em-
ployed as the substrate, the corresponding Z-product
(21)28 was acquired with only 30% yield in 24 hours and
61% yield in 36 hours (Scheme 4). It was shown that with
our protocol the more stable E-isomer was easily generat-
ed than the less stable Z-isomer of the corresponding
product. The GC-MS showed that the possible byproducts
were phenylacetylene (<2%) and 1,4-diphenylbut-1-en-3-
yne (<2%).21 In addition, our catalytic system could not
Scheme 4 The coupling of vinyl bromide (E/Z = 7:5) or (Z)-vinyl
bromide with imidazole by CuI
In summary, we have developed a versatile, simple and
effective copper-catalyzed coupling protocol for N-con-
taining heterocycles with (E)-vinyl bromides under
ligand-free and Pd-free conditions. The couplings of (E)-
vinyl chlorides were also performed with promising re-
sults. Notably, the corresponding coupling products could
retain the original double configuration. These N-contain-
ing heterocycles include pyrazole, pyrrole, imidazole,
benzimidazole, pyrazole, indole, and substituted indoles.
Particularly, our catalytic system could tolerate various
functional groups on the heterocycles substrates, such as
Me, CHO, MeO, MeCO, BnO. Thus, the procedures could
N
N
Cl
CuI (10 mol%)
HN
N
+
DMF, Cs2CO3
140 °C, 36 h, Ar
MeO
MeO
66% yield
Scheme 2 The coupling of (E)-vinyl chloride with imidazole by CuI at higher temperature (140 °C)
O
N
HN
O
CuI (10 mol%)
Br
H
N
+
DMF, Cs2CO3
120 °C, 36 h, Ar
H2N
Scheme 3 The coupling of (E)-b-bromostyrene with p-toluidine or morpholine by CuI
Synlett 2008, No. 13, 2011–2016 © Thieme Stuttgart · New York

LETTER
Copper-Catalyzed N-Vinylation
2015
72, 672. (b) Xie, Y.; Pi, S.; Wang, J.; Yin, D.; Li, J. J. Org.
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be performed easily, and it would be potentially useful for
the scale-up application. Further work is in progress in
this laboratory with the aim of extending the application
of these readily available catalytic systems in other cou-
pling transformations.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.
Acknowledgment
The authors would like to thank the Natural Science Foundation of
Education Committee of Jiangsu Province (06KJB150099), China
Postdoctoral Science Foundation, and the Key Laboratory of Orga-
nic Synthesis of Jiangsu Province for financial support.
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added to a screw-capped test tube. The tube was then
evacuated and backfilled with argon (3 cycles). N,N-
Dimethylformamide (2 mL), nitrogen-containing
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mixture was heated to 120 °C and stirred for 36–50 h. After
cooling to r.t., the mixture was diluted with H2O, and the
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EtOAc. The organic layers were combined, dried over
Na2SO4, and concentrated to yield the crude product, which
was further purified by silica gel chromatography, using PE
and EtOAc as eluents to provide the desired product.
Characteristic Data of Representative Products
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ArH), 7.05 (s, 1 H, ArH), 7.01–7.05 (m, 2 H, CH=CHPh and
ArH). 13C NMR (CDCl3): d = 136.1, 134.8, 130.8, 129.4,
128.5, 126.6, 123.1, 119.3, 116.7. HRMS: m/z calcd for
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(16) (a) Jiang, D.; Fu, H.; Jiang, Y.; Zhao, Y. J. Org. Chem. 2007,
Synlett 2008, No. 13, 2011–2016 © Thieme Stuttgart · New York

2016
J. Mao et al.
LETTER
C11H10N2 [M+ + H]: 170.0844; found: 170.0843.
Guo, P.; Li, G.; Lan, J.; Xie, R.; You, J. J. Org. Chem. 2007,
72, 8535.
Compound 12: 91%; mp 78–80 °C. 1H NMR (CDCl3): d =
7.63 (d, J = 8.0 Hz, 2 H, in ArH), 7.49–7.58 (m, 3 H, in
CH=CHPh and ArH), 7.39 (d, J = 8.8 Hz, 2 H, ArH), 7.15–
7.30 (m, 2 H, ArH), 6.91 (d, J = 8.8 Hz, 2 H, ArH), 6.64–
(27) (Z)-b-Bromostyrene was synthesized according the
references: (a) Kuang, C.; Senboku, H.; Tokuda, M.
Tetrahedron Lett. 2001, 42, 3893. (b) Kuang, C.; Yang, Q.;
Senboku, H.; Tokuda, M. Tetrahedron 2005, 61, 4043.
(c) Colorless oil. 1H NMR (CDCl3): d = 7.68 (d, J = 7.2 Hz,
1 H, ArH), 7.30–7.40 (m, 3 H, ArH), 7.06 (d, J = 8.0 Hz, 1
H, CH=CHPh), 6.42 (d, J = 8.0 Hz, 1 H, CH=CHPh).
(28) Colorless oil. 1H NMR (CDCl3): d = 7.48 (s, 1 H, ArH),
7.27–7.29 (m, 3 H, ArH), 7.09–7.12 (m, 2 H, ArH), 7.04 (s,
1 H, ArH), 6.86 (s, 1 H, ArH), 6.74 (d, J = 9.2 Hz, 1 H,
CH=CHPh), 6.36 (d, J = 9.2 Hz, 1 H, CH=CHPh). 13C NMR
(CDCl3): d = 137.4, 134.1, 130.0, 129.1, 128.9, 128.7, 123.8,
122.8, 118.9.
6.68 (m, 2 H, CH=CHPh and ArH), 3.84 (s, 3 H, CH3O). 13
C
NMR (CDCl3): d = 159.2, 136.0, 129.5, 129.0, 127.3, 124.3,
123.0, 122.4, 121.6, 121.2, 114. 7, 110.0, 105.3, 55.7.
HRMS: m/z calcd for C17H15NO [M+ + H]: 249.1154; found:
249.1153.
(26) During the course of our research on the ligand-free C–N
coupling reaction, we found the following relevant reports:
(a) CuI-catalyzed N-arylation of nitrogen heterocycles with
aryl iodides in the presence of n-Bu4NBr as the phase-
transfer catalyst: Chang, J. W. W.; Xu, X.; Chan, P. W. H.
Tetrahedron. Lett. 2007, 48, 245. (b) Cu2O-catalyzed N-
arylation of nitrogen nucleophiles: Correa, A.; Bolm, C. Adv.
Synth. Catal. 2007, 349, 2673. (c) CuI-catalyzed N-
(29) Verma, A. K.; Singh, J.; Sankar, V. K.; Chaudhary, R.;
Chandra, R. Tetrahedron Lett. 2007, 48, 4207.
arylation of nitrogen nucleophiles with aryl halides: Zhu, L.;
Synlett 2008, No. 13, 2011–2016 © Thieme Stuttgart · New York