A simple and efficient copper-catalyzed amination of aryl halides by aqueous ammonia in water

Article abstract of DOI:10.1139/v11-051

The copper(I) iodide/1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)piperazine (CuI-L2) system catalyzed the cross-coupling reactions between aryl halides and aqueous ammonia in water to produce primary aromatic amines in good yields. The protocol was simple and efficient, avoiding the need for inert atmosphere, additional base, or other additives.

Full text of DOI:10.1139/v11-051

6
45
A simple and efficient copper-catalyzed amination
of aryl halides by aqueous ammonia in water
Yefeng Zhu and Yunyang Wei
Abstract: The copper(I) iodide/1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)piperazine (CuI–L2) system catalyzed the cross-
coupling reactions between aryl halides and aqueous ammonia in water to produce primary aromatic amines in good yields.
The protocol was simple and efficient, avoiding the need for inert atmosphere, additional base, or other additives.
Key words: copper, catalysis, cross coupling, water chemistry, aqueous ammonia, primary arylamine.
Résumé : Le système iodure de cuivre(I)/1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)pipérazine (CuI–L2) catalyse les réac-
tions de couplages croisées entre les halogénures d’aryles et une solution aqueuse d’ammoniaque pour conduire à la forma-
tion d’amines aromatiques primaires avec de bons rendements. Le protocole est simple et efficace, il ne nécessite pas
d’atmosphère inerte, de base additionnelle ou d’autres additifs.
Mots‐clés : cuivre, catalyse, couplage croisé, chimie dans l’eau, solution aqueuse d’ammoniaque, arylamine primaire.
[
Traduit par la Rédaction]
water.11 We now report a ligand-assisted copper(I)-catalyzed
method for the coupling of aryl halides with aqueous ammo-
nia in water. This method utilizes inexpensive CuI as the cat-
alyst and simple synthesized Mannich bases as ligands and
tolerates a wide range of functional groups. Inert atmosphere
and additional base were not needed. The use of aqueous am-
monia makes the reaction easier to handle than the cases
where gaseous ammonia or ammonia in organic solvent was
used.
Introduction
Ammonia is an attractive source of nitrogen in organic
synthesis owing to its great abundance and low cost. In re-
cent years, the palladium- or copper-catalyzed coupling of
aryl halides with ammonia has attracted increasing attention
because of the value of primary aromatic amines in the prep-
aration of natural products, agrochemicals, dyes, polymers,
1
2
and medicinal compounds. While palladium catalysts devel-
oped by Buchwald and Hartwig proved most useful for this
3
reaction, less progress has been achieved with copper cata-
lysts. Recently, Kim and Chang reported a proline-derived
4
Results and discussion
copper complex catalyzed arylation of ammonium chloride
or aqueous ammonia with aryl iodides. Following these pio-
We initially selected iodobenzene as a model substrate for
optimization of the reaction conditions. The standardized pro-
tocol was carried out by using iodobenzene (1 equiv.), CuI
(10 mol%), L2 (10 mol%), and aqueous ammonia (2 mL) in
water at 120 °C for 12 h. The results are summarized in Ta-
ble 1.
It can be seen from Table 1 that the CuI–L combination
successfully promoted the coupling reaction with yields from
75% to 90% (Table 1, entries 1–4), whereas no product was
detected without the ligand under similar conditions (Table 1,
entry 5). Among the ligands used, 1,4-bis(2-hydroxy-3,5-di-
tert-butylbenzyl)piperazine (L2) displayed the best catalytic
activity (Table 1, entry 2). Thus, L2 was chosen as the ligand
for further optimization of the reaction conditions. Different
copper sources have also been examined, the catalysis by
5
neering works, a lot of catalytic systems have been reported,
5
a
such as CuI/diketone ligands, CuI/2-pyridinyl-b-ketone li-
5
b
5c
gands, CuI/4-hydroxy-L-proline, etc. Furthermore, Rao et
6
a
al. also introduced a ligand-free copper-catalyzed arylation
of aqueous ammonia with aromatic boronic acids at room
temperature. These reactions are generally performed in or-
7
ganic solvents, which lead to environmental problems. It is
highly desirable to find a procedure to carry out these cou-
pling reactions in cheap, nontoxic, and nonflammable
“
green” solvents. Obviously, water is the most cheap and en-
8
vironmentally benign solvent. However, to the best of our
knowledge, there are only a few well-established methods to
effectively synthesize anilines from aryl halides and aqueous
9
9b
ammonia in water. More recently, Wu et al. reported the
coupling reactions of aryl halides with aqueous ammonia by
a sulfonato–Cu(salen) complex in water, but an additional
base was essential.
CuI, CuCl, and CuSO with L2 afforded the aniline product
4
in good yields of 90%, 85%, and 87%, respectively (Table 1,
entries 2, 7, and 8, respectively). However, the use of the
CuCl –L2 combination resulted in a moderate yield of 51%
2
We have identified Mannich bases10 (Fig. 1) as efficient li-
gands for the Cu-catalyzed N-arylation of imidazoles in
(Table 1, entry 9). It must be pointed out that in the absence
of copper catalysis, no aniline derivative was obtained
Received 10 November 2010. Accepted 15 February 2011. Published at www.nrcresearchpress.com/cjc on 22 June 2011.
Y. Zhu and Y. Wei. School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.
Corresponding author: Yunyang Wei (e-mail: ywei@mail.njust.edu.cn).
Can. J. Chem. 89: 645–649 (2011)
doi:10.1139/V11-051
Published by NRC Research Press

646
Can. J. Chem. Vol. 89, 2011
Fig. 1. Structures of Mannich bases L1–L4.
Table 1. Results of amination of iodobenzene with aqueous ammonia in water.
[Cu] , L
I
+
NH (aq)
3
NH2
Entry
Cu
Ligand
L1
L2
L3
L4
NH3(aq) (mL)
Yield (%)a
1
2
3
4
5
6
7
8
9
CuI
CuI
CuI
CuI
CuI
2
2
2
2
2
2
2
2
2
1
3
1
2
2
75
90
80
78
0
L2
L2
L2
L2
L2
L2
L2
L2
L2
0
CuCl
CuSO4
CuCl2
CuI
CuI
CuI
85
87
51
57
91
10
11
12
13
14
b
32
c
CuI
CuI
70
d
<5
Note: Unless otherwise noted, the reactions were carried out with iodobenzene (1 mmol),
2
5%–28% aqueous ammonia (2 mL) at 120 °C for 12 h.
a
Isolated yields.
b
H O (1 mL) was added.
2
c
Reaction time was 8 h.
d
Reaction temperature was 100 °C.
(
Table 1, entry 6). Further investigation revealed that 2 mL
tophenone. However, when the highly activated 4-nitro-
iodobeneze was used, a slightly lower yield (61%; Table 2,
entry 3) was obtained because of the formation of a small
amount of unidentified byproduct.
aqueous ammonia was needed for the reaction to take place.
When we decreased the amount or the concentration of aque-
ous ammonia, the reaction rate decreased (Table 1, entries
1
0–12). In addition, a lower temperature decelerated the reac-
Next, we were intrigued by the possibility of using aryl
bromides as coupling partners, which are less reactive sub-
strates but of much greater interest for industrial applications.
It can be seen from Table 2 that all the electron-deficient aryl
bromides afforded the aniline products with excellent yields
ranging from 72% to 92% under the optimized conditions
(Table 2, entries 5–9). The reactions with the electron-rich
aryl bromides were slower, but the products could be isolated
in good yields by extending the reaction time to 24 h (Ta-
ble 2, entries 10–14). It is noteworthy that the catalytic sys-
tem displayed a great tolerance for multiple groups including
the nitro, acetyl, and ether groups. However, the steric hin-
tion rate and led to a lower yield (Table 1, entry 14). In sum-
mary, the proper conditions for amination of aryl halides by
aqueous ammonia in water consist of the combination of CuI
(
1
10 mol %), L2 (10 mol %), and aqueous ammonia (2 mL) at
20 °C for 12 h in air.
With this practical procedure in hand, we explored the
scope of this reaction and screened a wide range of aryl io-
dides and bromides. As shown in Table 2, most of the aryl
iodides with either electron-donating or electron-withdrawing
substituents afforded aniline derivatives in water in excellent
yields, and the highest yield was obtained by using 4-iodoace-
Published by NRC Research Press

Zhu and Wei
647
Table 2. CuI–L2 catalyzed amination of aryl halides with aqueous ammonia in water.
CuI, L2
X
+
NH
3
(aq)
NH2
Yield (%)a
R
120 °C
R
Entry
ArX
ArNH2
NH2
1
I
90
85
61
2
3
H C
3
I
I
H C
3
NH
2
O N
2
O N
NH
2
2
4
I
NH2
95
O
O
5
6
Br
85
90
NH2
O N
2
Br
O N
NH
2
2
7
8
9
Br
NH2
NH2
92
72
O
O
Cl
Br
Cl
Br
NH2
85
Cl
Cl
1
0
1
H C
3
Br
H C
85b
27b
83b
3
NH
2
Br
CH3
Br
NH2
1
1
1
2
3
H CO
3
Br
H CO
3
NH2
Br
OCH3
Br
NH
2
85b
88b
OCH3
NH2
1
4
1
5
6
Cl
0
NH2
1
O N
2
Cl
O N
2
NH2
<5b
Note: Reaction conditions: aryl halides (1 mmol), 25%–28% aqueous ammonia (2 mL), CuI
(
10 mmol%), L2 (10 mmol%), 120 °C, 12 h.
a
Isolated yield.
b
Reaction time was 24 h.
Published by NRC Research Press

648
Can. J. Chem. Vol. 89, 2011
drance has a huge influence on the coupling reaction. When
-methylbromobenzene was aminated with this catalytic sys-
tem, only a 27% isolated yield was obtained (Table 2, entry
(125 MHz, CDCl ) d: 153.1, 139.8, 134.6, 122.6, 122.2,
3
2
119.3, 61.0, 51.2, 33.9, 33.2, 30.7, 28.6. MS (ESI, m/z): 523
+
[M ].
1
1). Fortunately, when the reaction was performed with
1
,4-Bis(2-hydroxy-5-chlorobenzyl)piperazine (L3)
o-methoxybromobenzene, the corresponding o-methoxyani-
line was obtained in an 85% isolated yield (Table 2, entry
White solid; mp (recrystallization in methanol) 243–246 °C
(lit. value1 mp 243–245 °C). H NMR (300 MHz, CDCl3)
d: 2.48–2.78 (m, 8H), 3.70 (s, 4H), 6.77 (d, J = 8.6 Hz,
2H), 6.98 (d, J = 2.2 Hz, 2H), 7.15 (dd, J = 8.6, 2.2 Hz,
0a
1
1
3). Furthermore, attempts to use chlorobenzene as an aryl
source failed (Table 2, entry 15). When 4-nitrochlorobenzene,
an activated aryl chloride, was used as the arylating agent,
only a 5% yield of the corresponding coupling product was
detected (Table 2, entry 16).
13
2H). C NMR (125 MHz, DMSO-d6) d: 154.9, 128.2,
127.2, 124.2, 121.7, 116.3, 56.7, 51.6. MS (ESI, m/z): 368
+
[
M ].
Conclusion
1
,4-Bis(2-hydroxy-5-acetylbenzyl)piperazine (L4)
White solid; mp (recrystallization in methanol) 222–223 °C.
In summary, we have developed a ligand-assisted copper
I)-catalyzed method for coupling aryl halides with aqueous
(
1
H NMR (300 MHz, CDCl ) d: 2.54 (s, 6H), 2.67–2.86 (m,
3
ammonia in water. This protocol avoids the use of toxic or-
ganic solvents and eliminates the need for an inert atmos-
phere, additional base, or other additives, which greatly
facilitates operations. Excellent yields are obtained with a
wide range of aryl bromides and aryl iodides as substrates in
the catalytic system.
8
7
H), 3.81 (s, 4H), 6.86 (d, J = 8.5 Hz, 2H), 7.68 (s, 2H),
.83 (dd, J = 8.6, 2.0 Hz, 2H). 13C NMR (125 MHz,
CDCl ) d: 195.7, 161.4, 129.5, 128.5, 128.3, 119.4, 115.1,
5
3
+
9.8, 51.1, 25.2. MS (ESI, m/z): 383 [M ]. Elemental anal.
calcd. (%): C 68.75, H 7.15, N 7.06; theoretical: C 69.09, H
.85, N 7.32.
6
Aniline9a
Experimental
1
Pale yellow oil. H NMR (500 MHz, CDCl ) d: 7.24–7.28
3
General method
(
2
1
m, 2H), 6.87–6.88 (m, 1H), 6.75–6.86 (m, 2H), 3.66 (s,
All reactions were carried out in a Teflon septum screw-
capped tube under air atmosphere. All chemicals were ob-
tained from a commercial source (Sinopharm Chemical Re-
agent Company, Ltd., Shanghai, China, and Aladdin
Reagent, Shanghai, China) and used without further purifica-
tion. Ligands L1–L4 were synthesized according to the liter-
ature.10 Column chromatography was performed on silica
H). 13C NMR (125 MHz, CDCl ) d: 145.7, 128.5, 117.6,
14.3, 19.6.
3
-Toluidine9a
4
Slight yellow solid; mp (recrystallization in methanol) 43–
12a
1
4
5 °C (lit. value
mp 43–44 °C). H NMR (500 MHz,
CDCl ) d: 6.99 (d, J = 10.0 Hz, 2H), 6.63 (d, J = 10.0 Hz,
3
1
13
2
00–300 mesh. H NMR and C NMR spectra was recorded
13
2
H), 3.46 (s, 2H), 2.26 (s, 3H). C NMR (125 MHz,
on a Bruker Avance 300, 400, or 500 and 125 spectrometer
at ambient temperature in CDCl3 or DMSO-d6. Chemical
shifts are reported in parts per million relative to TMS.
DMSO-d ) d: 145.5, 128.7, 123.4, 113.5.
6
-Nitroaniline9b
4
Yellow solid; mp (recrystallization in methanol) 148–149 °C
Typical procedure for the coupling
12b
1
(
lit. value mp 146–149 °C). H NMR (500 MHz, CDCl )
3
Aryl halides (1 mmol), CuI (0.1 mmol), 1,4-bis(2-hydroxy-
,5-di-tert-butylbenzyl)piperazine (0.1 mmol), and aqueous
d: 8.09 (d, J = 10.0 Hz, 2H), 6.64 (d, J = 10.0 Hz, 2H), 4.40
3
(s, 2H). 13C NMR (125 MHz, DMSO-d ) d: 155.2, 135.1,
6
ammonia (2 mL) were added to a Teflon septum screw-
capped tube. The reaction mixture was stirred at 120 °C for
125.6, 111.8.
4-Aminoacetophenone9b
12 h and then cooled to room temperature and extracted
with ethyl acetate. The organic layer was then dried with an-
hydrous Na SO , and the solvent was removed under reduced
pressure. The aniline product was finally obtained by column
chromatography on silica gel.
Slight yellow solid; mp (recrystallization in methanol)
12c
1
2
4
105–106 °C (lit. value
mp 103–105 °C). H NMR
(500 MHz, CDCl ) d: 7.82 (d, J = 5.0 Hz, 2H), 6.66 (d, J =
3
13
5.0 Hz, 2H), 4.22 (s, 2H), 2.51 (s, 3H). C NMR (125 MHz,
DMSO-d ) d: 194.5, 153.1, 130.1, 124.4, 112.0, 25.3.
6
1,4-Bis(2-hydroxy-5-methoxybenzyl)piperazine (L1)
4-Chloroaniline9b
White solid; mp (recrystallization in methanol) 184–186 °C
0a
1
(
lit. value1 mp 184–186 °C). H NMR (300 MHz, CDCl )
Pale white solid; mp (recrystallization in methanol) 69–
3
71 °C (lit. value1 mp 69–72 °C). H NMR (500 MHz,
2b
1
d: 2.40–2.90 (m, 8H), 3.69 (s, 4H), 3.72 (s, 6H), 6.57–6.76
1
3
(
1
m, 6H), 10.25 (br s, 2H). C NMR (125 MHz, CDCl ) d:
CDCl ) d: 7.12 (d, J = 10.0 Hz, 2H), 6.62 (d, J = 10.0 Hz,
3
3
13
51.7, 150.2, 120.4, 115.6, 113.6, 112.9, 60.2, 54.8, 51.2.
2H), 3.65 (s, 2H). C NMR (125 MHz, DMSO-d ) d: 147.1,
6
+
MS (ESI, m/z): 359 [M ].
128.0, 118.2, 114.7.
3-Chloroaniline6
1
,4-Bis(2-hydroxy-3,5-di-tert-butylbenzyl)piperazine (L2)
1
White solid; mp (recrystallization in methanol) 258–260 °C
Slight yellow oil. H NMR (400 MHz, CDCl ) d: 7.02–
3
lit. value1 mp > 250 °C). H NMR (300 MHz, CDCl ) d:
.31 (s, 18H), 1.43 (s, 18H), 2.39–2.90 (m, 8H), 3.72 (s,
0b
1
7.06 (m, 1H), 6.65–6.71 (m, 2H), 6.52–6.54 (m, 1H), 3. 63
(
3
1
4
(s, 2H). 13C NMR (125 MHz, CDCl ) d: 146.9, 133.8,
3
13
H), 6.84–7.27 (m, 4H), 10.75 (br s, 2H). C NMR
129.5, 117.4, 114.0, 112.4.
Published by NRC Research Press

Zhu and Wei
649
2
-Toluidine9b
Colorless oil. H NMR (500 MHz, CDCl ) d: 7.09–7.12
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3
13
(
m, 2H), 6.72–6.80 (m, 2H), 3.59 (s, 2H), 2.23 (s, 3H).
C
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NMR (125 MHz, CDCl ) d: 143.8, 129.6, 126.2, 121.5,
3
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1
17.8, 114.1, 16.5.
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-Methoxyaniline9b
4
Pale white solid; mp (recrystallization in methanol) 54–
12a
1
56 °C (lit. value mp 57 °C). H NMR (400 MHz, CDCl )
3
d: 6.72–6.74 (m, 2H), 6.62–6.65 (m, 2H), 3.73 (s, 3H), 2.92
s, 2H). 1 C NMR (125 MHz, DMSO-d ) d: 150.2, 141.8,
3
(
1
6
14.2, 114.1, 54.7.
-Methoxyaniline9b
2
1
Slight yellow oil. H NMR (500 MHz, CDCl ) d: 6.85–
3
6
.88 (m, 2H), 6.76–6.81 (m, 2H), 3.90 (s, 3H), 3.75 (s, 2H).
1
3
C NMR (125 MHz, CDCl ) d: 146.4, 135.4, 120.2, 117.5,
3
(
h) Taillefer, M.; Xia, N. PTC 051701, 2008; (i) Gaillard, S.;
114.1, 109.6, 54.5.
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Thomas, C. M.; Renaud, J. L. Chem. Commun. (Camb.) 2010,
b-Aminonaphthalene6
Dark brown solid; mp (recrystallization in methanol) 109–
11 °C (lit. value1 mp 107–109 °C). H NMR (400 MHz,
2a
1
1
4
6 (6), 925. doi:10.1039/b916569j; (k) Ntaganda, R.; Dhud-
CDCl ) d: 7.51–7.63 (m, 3H), 7.27–7.31 (m, 1H), 7.13–7.19
3
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(
m,1H), 6.86–6.92 (m, 2H), 3.76 (s, 2H).
C NMR
(
125 MHz, DMSO-d ) d: 146.1, 134.5, 128.0, 127.0, 125.8,
6
1
25.3, 124.5, 120.3, 117.9, 105.3.
(
Supplementary data
Supplementary data for this article ( H NMR and 13C
1
NMR spectra for all products) are available on the journal
Web site (www.nrcresearchpress.com/cjc).
(
Acknowledgements
We are grateful to Nanjing University of Science and
Technology for financial support.
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