Copper-catalyzed synthesis of 2-imidazolines and their N-hydroxyethyl derivatives under various conditions

Article abstract of DOI:10.1016/j.tetlet.2011.01.082

A rapid and efficient method for the synthesis of 2-imidazolines and their N-hydroxyethyl derivatives from the reaction of aromatic nitriles with ethylenediamine (EDA) or N-(2-aminoethyl)ethanolamine (AEEA) using cupric indole-3-acetate (Cu(II)-(IAA)₂) as a reusable catalyst under reflux and microwave conditions is reported. And seven new N-hydroxyethyl-imidazolines were reported for the first time.

Full text of DOI:10.1016/j.tetlet.2011.01.082

Tetrahedron Letters 52 (2011) 1578–1582
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Copper-catalyzed synthesis of 2-imidazolines and their N-hydroxyethyl
derivatives under various conditions
⇑
Jin Zhang, Xiao Wang, Meipan Yang, Kerou Wan, Bing Yin, Yunxia Wang, Jianli Li , Zhen Shi
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education and College of Chemistry & Materials Science, Northwest University, Xi’an
Shaanxi 710069, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A rapid and efficient method for the synthesis of 2-imidazolines and their N-hydroxyethyl derivatives
from the reaction of aromatic nitriles with ethylenediamine (EDA) or N-(2-aminoethyl)ethanolamine
(AEEA) using cupric indole-3-acetate (Cu(II)–(IAA)2) as a reusable catalyst under reflux and microwave
conditions is reported. And seven new N-hydroxyethyl-imidazolines were reported for the first time.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 3 December 2010
Revised 8 January 2011
Accepted 18 January 2011
Available online 21 January 2011
Keywords:
Imidazolines
Cupric indole-3-acetate
Solvent free
Microwave-assisted synthesis
Imidazolines and their derivatives are an important class of bio-
active molecules in the field of drugs and pharmaceuticals.1 They
exhibit significant activity against several diseases including
hyperglycaemia,2 inflammation,3 hypertension,4 hypercholesterol-
emia5 and cancer.6 Moreover, some imidazoline derivatives have
been demonstrated to be imidazoline receptors,7 phase transfer
catalysts8 and synthetic intermediates.9 They can also act as li-
gands coordinated to transition metals for asymmetric catalysis.10
A number of methods have been developed for the synthesis of
imidazolines and their derivatives from carboxylic acids,11 esters,12
nitriles,13 orthoesters,14 hydroximoylchlorides15 and hydroxya-
mides.16 However, there are some disadvantages in these methods
such as long reaction time, high temperature, tedious work-up,
corrosive reagents and large amounts of toxic solid supports. Thus,
an efficient, simple and environmentally friendly synthesis method
is worthwhile endeavour. In this context, direct access of imidazo-
lines by the utilization of diamines and nitriles has attracted signif-
icant attention from academic community. Due to usage of Lewis
acids as catalysts, the reaction becomes efficient, environmentally
friendly and economical. Until now, many ordinary Lewis acids
have been reported as catalysts such as ZrOCl2Á8H2O,17 supported
12-tungstophosphoric acid18 1,3-dibromo-5,5-dimethylhydan-
toin,19 thioacetamide.20 Since copper was first used as a catalyst
in synthesis chemistry in 1901,21 copper-catalyzed reactions have
received considerable attentions because of their efficiency and
low cost.22 However, as far as we know, only CuCl had been used
as a catalyst by Rousselet and it was not efficient enough in the
preparation of imidazolines.23 The catalytic activity of copper has
not been fully explored in this reaction.
Indole-3-acetic acid (IAA) is a substance with essential and mul-
tifunctional biological significance,24 and the metal complexes of
IAA have been reported recently.25 But to the best of our knowl-
edge, there are no reports on direct use of the metal complexes
of IAA as a heterogeneous catalyst in organic reaction, especially
in the synthesis of imidazolines.
In consequence, we explored the capability of cupric indole-3-
acetate as an efficient and reusable heterogeneous catalyst for the
synthesis of imidazolines and their N-hydroxyethyl derivatives
from the reaction of aromatic nitriles and EDA or AEEA under either
reflux conditions or under microwave irradiation (Scheme 1).
In order to identify the optimal reaction conditions for the reac-
tion, a number of copper catalysts were examined in the reaction of
EDA with 3-cyanopyridine under reflux condition for 4 h firstly.
26
Unexpectedly, only Cu(II)–(IAA)2 showed extraordinary reaction
⇑
Corresponding author.
E-mail address: lijianli@nwu.edu.cn (J. Li).
Scheme 1. Preparation of 2-imidazolines and N-hydroxyethyl derivatives from
nitriles and diamines.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.01.082

J. Zhang et al. / Tetrahedron Letters 52 (2011) 1578–1582
1579
Table 1
Effect of various copper salts on the reaction of 3-cyanopyridine with EDAa
Table 2
Solvent effects on the reaction of 3-cyanopyridine with EDAa
Entry
Catalyst
Yieldb (%)
Entry
Solvents
Temperature (°C)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Cupric chloride
Cupric nitrate
Cupric sulfate
Cupric benzoate
61
52
9
73
25
79
4
22
20
38
28
45
3
27
71
25
1
1
2
3
4
5
6
7
None
116c
77
40
65
78
4
4
4
4
4
4
4
85
5
3
41
22
73
3
EtOAc
CH2Cl2
CH3OH
C2H5OH
DMF
Cupric nicotinate
Cupric isonicotinate
Cupric 4-chlorobenzoate
Cupric oxalate
Cupric malonate
Cupric cinnamate
Cupric 2-aminobenzoate
Cupric 1-naphthoate
Cupric phthalate
Cupric 4-nitrobenzoate
Cupric 4-metoxybenzoate
Cupric 4-hydroxybenzoate
La(III)–(IAA)3
153
83
iPrOH
a
Reaction conditions: 3-cyanopyridine (4.0 mmol), EDA (32 mmol), Cu(II)–(IAA)2
(0.8 mmol).
b
Yield determined by GC–MS using an internal standard.
The boiling point of EDA.
c
cupric malonate, cupric cinnamate, cupric 2-aminobenzoate, cup-
ric 1-naphthoate, cupric phthalate, cupric 4-nitrobenzoate, cupric
4-metoxybenzoate and cupric 4-hydroxybenzoate were either less
active or inert as a catalyst. Moreover, the catalytic activity of other
metal complexes of indole-3-acetic acid was also investigated, and
the yield was not more than 2% (Table 1).
Zn(II)–(IAA)2
Sm(III)–(IAA)3
Cu(II)–(IAA)2
2
1
85
In continuation of this work, we have used Cu(II)–(IAA)2 as an
efficient catalyst to investigate the effect of different solvents un-
der their corresponding reflux temperature for the same reaction
as above (Table 2). Thus, optimal conditions were: Cu(II)–(IAA)2
as the catalyst, solvent free and 116 °C (the boiling point of EDA).
The chosen reflux reaction conditions have been used for the
successful preparation of a series of 2-substituted imidazolines.27
a
All reactions were carried out according to the typical experimental procedure.
Yield determined by GC–MS using an internal standard.
b
activity for this reaction, but other copper salts such as cupric chlo-
ride, cupric nitrate, cupric sulfate, cupric benzoate, cupric nicotin-
ate, cupric isonicotinate, cupric 4-chlorobenzoate, cupric oxalate,
Table 3
Preparation of imidazolines and N-hydroxyethyl-imidazolines from aromatic nitriles and diamines under reflux conditiona and under MW irradiationb
Entry
Nitriles (1)
Diamines (2)
Products (3)
Reflux conditions
MW irradiation
Time (min)
Time (min)
Yieldc (%)
Yieldc (%)
91
NH2
N
H2N
CN
2a
1
2
3
240
87
91
85
5
5
5
1a
N
H
3a
3b
3c
N
CN
CN
CN
2a
2a
240
240
92
92
N
N
H
1b
N
N
N
N
H
1c
N
N
N
N
4
5
6
2a
2a
2a
240
240
360
93
78
88
5
5
94
87
90
1d
N
H
3d
N
Cl
CN
CN
Cl
1e
1f
N
3e
N
N
NC
20
N
H
N
H
3f
N
NC
7
8
1f
2a
2a
120
360
75
85
5
80
89
N
H
3g
H
N
H
N
20
CN
NC
1g
N
N
3h
H
N
9
1g
2a
120
70
5
79
NC
N
3i
(continued on next page)

1580
J. Zhang et al. / Tetrahedron Letters 52 (2011) 1578–1582
Table 3 (continued)
Entry
Nitriles (1)
Diamines (2)
Products (3)
Reflux conditions
MW irradiation
Time (min)
Time (min)
Yieldc (%)
Yieldc (%)
91
H
N
N
H2N
OH
2b
10
1a
1b
1c
1d
180
85
5
5
N
OH
3j
3k
3l
N
N
11
2b
180
91
96
N
OH
OH
N
N
12
13
14
15
2b
2b
2b
2b
180
180
240
300
87
92
83
83
5
5
5
5
92
94
90
89
N
N
N
N
OH
3m
N
Cl
1e
N
OH
3n
N
N
H3C
CN
H3C
1h
OH
3o
N
N
N
N
16
17
18
1f
1f
1g
2b
2b
2b
300
120
120
81
89
88
20
85
93
91
OH
OH
N
3p
NC
N
5
OH
3q
OH
5
N
NC
N
3r
a
b
c
All reflux reactions were carried out according to the typical experimental procedure.
All MW reactions were carried out at 80 °C, with 1000 W applied power in a 50 mL round-bottom flask with a glass condenser.
Isolated yield.
Various aromatic and heteroaromatic nitriles reacted with EDA to
produce the corresponding imidazolines in high to excellent yields.
Bis-imidazolines can also be prepared from the same reaction in
the presence of Cu(II)–(IAA)2. As shown in Table 3, bis-imidazolines
were obtained from dinitriles in 85–88% yields with longer time
(6 h). If the reaction time was reduced to 2 h, mono-imidazolines
were generated in 70–75% yields. The synthesis of the mono-imi-
dazolines is very meaningful, because the remaining nitrile group
can also be converted to other functional groups.
In order to further verify the performance of this catalytic sys-
tem, we used AEEA instead of EDA to react with various aromatic
and heteroaroatic nitriles in the presence of catalytic amounts of
Cu(II)–(IAA)2, and the results were satisfactory. To the best of our
knowledge, this method of preparation of N-hydroxyethyl-imidaz-
olines and bis-N-hydroxyethyl-imidazolines from nitriles has not
been reported yet. In this way, seven N-hydroxyethyl-imidazolines
involved in this article are reported for the first time (3k–n, 3p–r28).
Previously, it was reported that microwave irradiation could be
used as an efficient approach to achieve good yields, short reaction
time, and mild reaction conditions. Therefore, we examined the ef-
fect of MW irradiation on the synthesis of imidazolines and bis-
imidazolines from the reaction of nitriles with EDA in the presence
29
of catalytic amount of Cu(II)–(IAA)2. A variety of nitriles and
dinitriles were used for this manner. The corresponding imidazo-
lines and bis-imidazolines were obtained in high yields (81–91%).
And N-hydroxyethyl-imidazolines can also be synthesized from ni-
triles and AEEA in high yields (85–93%) in the presence of Cu(II)–
(IAA)2 with the assistance of MW irradiation. The results are shown
in Table 3.
The reusability of catalysts is one of the important benefits for
large-scale operations and commercial applications. Therefore,
we investigated the reusability of Cu(II)–(IAA)2 catalyst in the reac-
tion of 3-cyanopyridine with EDA. The catalyst can be recovered by
simple filtration, washing and drying at 60 °C. Under either reflux
conditions or MW irradiation, the catalyst has been consecutively
reused five times without significant loss of activity (Table 4).
A plausible mechanism for the reaction has been proposed in
Scheme 2. Cu(II)–(IAA)2 first activates the nitrile group by the

J. Zhang et al. / Tetrahedron Letters 52 (2011) 1578–1582
1581
Table 4
5. Li, H.-Y.; Drummond, S.; De Lucca, I.; Boswell, G. A. Tetrahedron 1996, 52,
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Recycling no.
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MW irradiation
Time (min)
7. Kawamura, K.; Naganawa, M.; Konno, F.; Yui, J.; Wakizaka, H.; Yamasaki, T.;
Yanamoto, K.; Hatori, A.; Takei, M.; Yoshida, Y.; Sakaguchi, K.; Fukumura, T.;
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H.-M.; Chen, C.-T. Chem. Eur. J. 2008, 14, 11601–11609.
Time (min)
Yielda (%)
Yielda (%)
1
2
3
4
5
240
240
240
240
240
97
97
96
94
94
5
5
5
5
5
99
99
98
98
97
a
Yield determined by GC–MS using an internal standard.
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Hojati, S. F. Polyhedron 2008, 27, 750–758.
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Shafiezadeh, F.; Haghdoust, M. Can. J. Chem. 2010, 88, 135–141.
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26. The preparation of Cu(II)–(IAA)2. To
a solution of indole-3-acetic acid
(5.7 mmol, 1.0 g) in 15 mL of water, a solution of NaOH (5.7 mmol, 0.23 g) in
10 mL of water was slowly added under stirring. To this solution, an aqueous
solution of CuCl2 (previously prepared with 2.8 mmol CuCl2Á2H2O in 15 mL of
water) was added, then green precipitation generated. The precipitation was
washed with water and dried under vacuum. The identities of products were
confirmed by IR data, IR (KBr): 3381, 1598, 1417, 1282, 794, 743 cmÀ1
.
Scheme 2. Proposed mechanism for the synthesis of 2-imidazolines and their N-
27. The typical reaction procedure under reflux condition. In
a 50 mL round
hydroxyethyl derivatives catalyzed by Cu(II)–(IAA)2.
bottom flask equipped with a water condenser, magnetic stirrer and oil-bath, a
mixture of nitrile (4.0 mmol), EDA (32 mmol) and Cu(II)–(IAA)2 (0.8 mmol) was
heated under reflux condition. The progress of the reaction was monitored by
TLC (eluent: EtOAc/MeOH, 3:1). After completion of the reaction, CH2Cl2
(10 mL) was added and the catalyst was filtered. The solvent was evaporated
under reduced pressure and the crude products were obtained. Compound 3a–
i were purified by recrystallization from cyclohexane respectively, and 3j–r
were purified by a silica gel column (eluent: EtOAc/MeOH, 3:1). The identities
of products were confirmed by mp, 1H NMR, MS and IR data.
formation of nitrogen cation 1. EDA or AEEA attacks 1 to afford 2
and 3. Finally, the corresponding imidazoline or N-hydroxyethyl-
imidazoline is produced by releasing NH3 and the catalyst for the
next catalytic cycle.
In summary, we have first demonstrated that Cu(II)–(IAA)2 can
be used as a green and reusable catalyst for efficient synthesis of
imidazolines and their N-hydroxyethyl derivatives under either re-
flux condition or MW irradiation. The attractive features of this
procedure are the mild reaction conditions, high conversions, sol-
vent free and reusable catalyst, all of which make it a useful and
attractive strategy for the preparation of various imidazolines. In
addition, a new method of synthesizing the N-hydroxyethyl-imi-
dazolines is proposed and seven N-hydroxyethyl-imidazolines are
reported for the first time.
28. The characterization of the new compounds. Compond 3k: Light yellow liquid.
IR (KBr): 3372, 2943, 1659, 1532, 1460, 1434, 1052, 750, 692 cmÀ1 1H NMR
;
(CDCl3, 400 MHz) d: 2.90 (m, 2H, CH2), 2.99 (m, 2H, CH2), 3.47 (s, 1H, OH), 3.67
(m, 2H, CH2), 3.72 (m, 2H, CH2), 7.43 (m, 1H, ArH), 7.84 (m, 1H, ArH), 8.17 (d,
1H, ArH), 8.55 (d, 1H, ArH); MS m/z: 191 (9.6%), 160 (53.6%), 118 (4.2%), 105
(21.1%), 78 (34.8%), 56 (100%). Compond 3l: Light yellow liquid. IR (KBr): 3337,
2957, 1607, 1427, 1299, 1057, 749, 707 cmÀ1 1H NMR (CDCl3, 400 MHz) d:
;
2.52 (s, 1H, OH), 3.37 (m, 2H, CH2), 3.76 (m, 2H, CH2), 4.06 (m, 2H, CH2), 7.44
(m, 1H, ArH), 8.20 (d, 1H, ArH), 8.77 (d, 1H, ArH), 8.97 (s, 1H, ArH); MS m/z: 191
(11.4%), 160 (50.1%), 118 (13.0%), 56 (100%). Compond 3m: Light yellow liquid.
IR (KBr): 3349, 2950, 1650, 1549, 1419, 1307, 1062, 839, 752, 683 cmÀ1 1H
;
NMR (CDCl3, 400 MHz) d: 2.51 (s, 1H, OH), 2.83 (m, 2H, CH2), 2.92 (m, 2H, CH2),
3.55 (m, 2H, CH2), 3.73 (m, 2H, CH2), 7.51 (d, 1H, ArH), 7.70 (d, 1H, ArH), 8.65
(d, 1H, ArH), 8.70 (d, 1H, ArH); MS m/z: 191 (11.9%), 160 (53.2%), 118 (11.4%),
56 (100%). Compond 3n: Light yellow solid, mp 137–138 °C. IR (KBr): 3268,
Acknowledgements
2948, 1638, 1597, 1487, 1447, 1321, 1093, 1013, 843, 762 cmÀ1 1H NMR
;
(CDCl3, 400 MHz) d: 3.04 (m, 2H, CH2), 3.17 (m, 2H, CH2), 3.84 (s, 1H, OH), 3.99
(m, 2H, CH2), 4.18 (m, 2H, CH2), 7.37 (d, 1H, ArH), 7.43 (d, 1H, ArH), 7.85 (d, 1H,
ArH), 7.95 (d, 1H, ArH); MS m/z: 226 (2.9%), 224 (9.0%), 193 (34.3%), 56 (100%).
Compond 3p: White solid, mp 249–250 °C. IR (KBr): 3133, 2874, 2833, 1594,
The work was supported by the Natural Science Foundation of
China (No. 20972124), the China Postdoctoral Science Foundation
(No. 20080441180), the Chinese National Science Foundation for
Talent Training (No. J0830417) and the Chinese National Innova-
tion Experiment Program for University Students (No. 091069714).
1523, 1424, 1264, 1247, 1088, 859, 688 cmÀ1 1H NMR (DMSO-d6, 400 MHz) d:
;
2.60 (m, 4H, CH2), 2.69 (m, 4H, CH2), 3.50 (m, 4H, CH2), 3.75 (m, 4H, CH2), 4.82
(s, 2H, OH), 7.60 (m, 4H, ArH); MS m/z: 303[M+1+]. Compond 3q: White solid,
mp 162–163 °C. IR (KBr): 3157, 2879, 2834, 2227, 1590, 1553, 1431, 1363,
1251, 1064, 869, 848, 745 cmÀ1 1H NMR (CDCl3, 400 MHz) d: 2.19 (s, 1H, OH),
;
References and notes
3.22 (m, 2H, CH2), 3.63 (m, 2H, CH2), 3.77 (m, 2H, CH2), 3.96 (m, 2H, CH2), 7.72
(d, 2H, ArH), 7.80 (d, 1H, ArH); MS m/z: 215 (8.8%), 184 (34.4%), 142 (8.8%), 102
(8.3%), 56 (100%). Compond 3r: White solid, mp 120–121 °C. IR (KBr): 3141,
2901, 2230, 1613, 1588, 1495, 1430, 1362, 1256, 1093, 807, 706; 1H NMR
(CDCl3, 400 MHz) d: 2.33 (s, 1H, OH), 3.20 (m, 2H, CH2), 3.59 (m, 2H, CH2), 3.75
(m, 2H, CH2), 3.96 (m, 2H, CH2), 7.54 (m, 1H, ArH), 7.72 (d, 1H, ArH), 7.89 (d, 1H,
ArH), 7.97 (s, 1H, ArH); MS m/z: 215 (8.9%), 184 (35.2%), 142 (8.5%), 102 (7.8%),
56 (100%).
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J. Zhang et al. / Tetrahedron Letters 52 (2011) 1578–1582
29. The typical reaction procedure under MW irradiation. A mixture of nitrile
(10 mmol), EDA (40 mmol) and Cu(II)–(IAA)2 (2.0 mmol) was irradiated with
microwave (1000 W) for 5–20 min by pulsed irradiation. At the end of the
reaction (monitored by TLC, eluent: EtOAc/MeOH, 3:1), the mixture was cooled
to room temperature, CH2Cl2 was then added and the catalyst was filtered.
Evaporation of the solvent gave the almost pure product. Further purification
was performed as for the procedure used in the synthesis of imidazolines
under reflux condition. The identities of products were confirmed by mp, 1H
NMR, MS and IR data.