A dicationic, podand-like, ionic liquid water system accelerated copper-catalyzed azide-alkyne click reaction

Article abstract of DOI:10.1016/j.cclet.2014.09.005

In this work, an effective, task specific, dicationic, podand-like ionic liquid was synthesized and applied to improve the capability features of click reaction. Moreover, to broaden the scope and decreasing the serious limitations of preparation methods of organic azides, a simple green procedure for the preparation of alkyl azides, the fundamental starting materials in click reactions, from alcohols under solvent-free conditions and microwave irradiation has been reported, for the first time.

Full text of DOI:10.1016/j.cclet.2014.09.005

G Model
CCLET 3086 1–5
Chinese Chemical Letters xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
1
2
Original article
3
4
A dicationic, podand-like, ionic liquid water system accelerated
copper-catalyzed azide-alkyne click reaction
b
a
Q1 Mohammad Javaherian a, , Foad Kazemi , Masoumeh Ghaemi
*
5
6
7
a Department of Chemistry, College of Science, Shahid Chamran University, Ahvaz, Iran
b Department of Chemistry, University for Advanced Studies in Basic Sciences, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
In this work, an effective, task specific, dicationic, podand-like, ionic liquid was synthesized and applied
to improve the capability features of click reaction. Moreover, to broaden the scope and decreasing the
serious limitations of preparation methods of organic azides, a simple green procedure for the
preparation of alkyl azides, the fundamental starting materials in click reactions, from alcohols under
solvent-free conditions and microwave irradiation has been reported, for the first time.
ß 2014 Mohammad Javaherian. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All
rights reserved.
Received 8 April 2014
Received in revised form 25 June 2014
Accepted 30 July 2014
Available online xxx
Keywords:
Dicationic ionic liquid
Click chemistry
1,2,3-Triazoles
Alkyl azides
Alkynes
Microwave irradiation
8
9
1. Introduction
attention in various fields of science due to their unique properties, 29
such as extremely low vapour pressure, non-flammability, 30
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11
12
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15
16
17
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19
20
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23
24
25
26
27
28
The 1,3-dipolar cycloaddition of azides with alkynes (CuAAC)
was first reported more than 100 years ago and investigated in
detail by Huisgen [1]. In 2001, Sharpless and co-workers
discovered that copper(I) catalysts in solution can improve the
rate and regioselectivity of the cycloaddition reaction [2–4]. Fre-
quently, 1,2,3-triazoles are potential targets due to numerous
applications in biology, agrochemicals, drug discovery and also as
dyes [5,6]. The use of benign solvents, such as water and ionic
liquids, is significant in the practice of green chemistry. While
water is a preferable solvent because of its abundance, safety, non-
toxicity, cheapness and environmentally-friendly aspects in click
reaction, and furthermore, the limited solubility of the less polar
reactants can cause difficulties in a reaction step. The possibility of
using a variety of solvents is one of the remarkable features of
CuAAC reactions, which often are mixture of water and water-
miscible organic solvents, such as DMSO, THF, t-BuOH or even
biphasic media, which have been traditionally used as solvent
system [7]. The use of ionic liquids is an acceptable way to meet the
principles of green chemistry [8]. Ionic liquids have received great
tunability, high thermal stability and also solubility of many 31
substances [9,10]. Moreover, it has been shown that ionic liquids, 32
especially imidazolium based ones, have substantial effects on 33
chemical reactions as catalysts or alternative to conventional 34
solvents [9–11]. It has been noticed that multifunctional, cationic, 35
ionic liquids may be more effective than conventional mono- 36
cationic analogs [12].
37
2. Experimental
38
The alkyl tosylates were synthesized according to the method in 39
reference [13]. Melting points were recorded on Buchi Melting 40
point apparatus D-545; IR Spectra (KBr disks) were recorded on St- 41
jean Baptist Ave Bomem 450 instrument. NMR Spectra were 42
recorded on Bruker Avance DPX (400 MHz) in DMSO and D2O with 43
TMS as internal standard for protons and solvent signals as internal 44
standard for carbon spectra. Chemical shift values are reported in
d
45
(ppm) and coupling constants are given in Hz. MW irradiation was 46
done by Micro SYNTH Labstation med CHEM Kit P/N 70140. The 47
progress of all reactions was monitored by TLC on 2 cm  5 cm pre- 48
coated silica gel-60 F-254 plates of thickness of 0.25 mm (Merck). 49
The chromatograms were visualized under UV 254–336 nm and 50
*
Corresponding author.
E-mail addresses: Mohamad.javaherian@gmail.com, m.javaherian@scu.ac.ir
iodine tank.
51
(M. Javaherian).
http://dx.doi.org/10.1016/j.cclet.2014.09.005
1001-8417/ß 2014 Mohammad Javaherian. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Please cite this article in press as: M. Javaherian, et al., A dicationic, podand-like, ionic liquid water system accelerated copper-catalyzed
azide-alkyne click reaction, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.09.005

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CCLET 3086 1–5
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M. Javaherian et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
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2.1. The synthesis of ionic liquid b
(100 MHz, DMSO-d6):
d
98.71, 122.07, 125.63, 128.39, 129.27,
115
116
117
118
119
120
121
122
123
124
129.36, 130.33, 130.56, 135.45, 147.16.
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54
55
56
57
58
59
60
61
62
63
An agate mortar was charged with dry K2CO3 (5 g), tetra-
ethylene glycol (10 mmol, 1.72 mL), TsCl (24 mmol, 4.57 g) and
grinded for 5 min. Upon reaction completion, monitored by TLC
(CCl4/EtOAc, 4:1, v/v), the excess of TsCl was removed by wetting
the reaction mixture with drops of t-BuOH and irradiating in a
domestic microwave oven for 2 min. The prepared tetraethylene
glycol ditosylate, was isolated by extraction with ether (3Â 10 mL).
Then, 1-methylimidazole (25 mmol, 2 mL) was added to the
tetraethylene glycol ditosylate (10 mmol, 4.74 g) and allowed to
stir at r.t. for 30 min. The work-up was performed by washing the
synthesized ionic liquid with ether (3Â 50 mL).
3-Phenyl-1-propyl-1H-1,2,3-triazole: IR (KBr, cmÀ1):
v 744,
1115, 1370, 1453, 1495, 1602, 2857, 2938, 3026; 1H NMR
(400 MHz, DMSO-d6):
d 2.33 (q, 2H, J = 7.20 Hz), 2.72 (t, 2H,
J = 7.30 Hz), 4.43 (t, 2H, J = 7.08 Hz), 7.21–7.33 (m, 2H, J = 7.08 Hz),
7.34–7.37 (t, 3H, J = 7.40 Hz), 7.43–7.47 (t, 2H, J = 7.28 Hz), 7.84 (s,
1H), 7.85 (d, 2H, J = 7.90 Hz); 13C NMR (100 MHz, DMSO-d6):
22.27, 33.36, 51.27, 119.07, 125.31, 126.61, 127.83, 127.96, 128,
130.27, 142.16, 142.72.
d
3. Results and discussion
125
Even though, many benign properties of ionic liquids make
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
64
2.2. General procedure for the synthesis of triazoles
them attractive from
a green chemistry standpoint, their
preparation procedures continue to suffer from historical limita-
tions, such as use of a large amount of toxic solvents, long reaction
times, low yields. Herein, we report a facile synthesis of a podand
task specific and water soluble imidazolium based ionic liquid; 3-
alkyl-1-methylimidazolium tosylate under neat reaction condition
and used for [3+2] cycloaddition of different organic azides with a
terminal alkyne i.e., click reaction. In the presence of ionic liquids
and water, the reactions of terminal alkyne with organic azides
underwent easily to generate the corresponding regiospecific 1,4-
disubstituted-1,2,3-triazoles in excellent yields and short reaction
times at r.t., Scheme 1 and Table 1.
As shown in Table 1, a green approach for the scalable
preparation of alkyl tosylates under solvent free conditions has
been applied from alcohols as available starting materials, instead
of traditional use of a large amount of a toxic solvent like pyridine
and laborious procedure. Ethanol and tetraethylene glycol were
reacted with tosyl chloride in the presence of potassium carbonate
as a cheap and weak basic solid support [13]. Then the prepared
alkyl tosylates reacted with 1-methylimidazole to generate the
corresponding ionic liquids a and b in short reaction times and high
yields, under neat conditions without use of any toxic solvents,
such as toluene, acetonitrile, etc. [9,10,14]. Additionally, recovery
of these two task specific ionic liquids was quantitatively done
from the reaction mixture by simple extracting and reused for
several times in similar reactions. In direct alkylation reactions,
care should be taken during addition of the alkylating agent. The
addition should be slow and under an inert atmosphere to a cool
controlled temperature solution. Therefore, a small excess of
nucleophile is advised to avoid traces of the alkylating agent in the
product. According to our literature survey, ionic liquids compris-
ing tosylate as counter ion may be prepared from alcohols in the
presence of pyridine as base, and toluene as solvent with
1-methylimidazole under nitrogen atmosphere and refluxing for
65
66
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70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
A mixture of an alkyl azide (1 mmol), phenylacetylene (1 mmol,
0.109 mL), CuSO4Á5H2O (0.1 mmol, 0.02 g), sodium ascorbate
(0.1 mmol, 0.01 g), was dissolved in 5 mL of ionic liquid/H2O
(1:1) and stirred vigorously at room temperature. After the
completion of the reaction, monitored by TLC, the product was
isolated by extraction with ether (3Â 10 mL) and the solvent was
removed by a rotary evaporator. The prepared 1,2,3-triazole was
purified by recrystalization technique in water and ethanol.
3-Ethyl-1-methylimidazolium tosylate: IR (neat, cmÀ1):
1011, 1456, 1189, 1570, 1655, 2924, 2974, 3152; 1H NMR
(400 MHz, D2O): 1.28 (t, 3H. J = 7.36 Hz), 2.13 (s, 3H), 3.66 (s,
v 819,
d
3H), 3.93–3.98 (q, 2H, J = 7.34 Hz), 7.05–7.07 (d, 2H. J = 8 Hz), 7.17–
7.23 (d, 2H), 7.54–7.55 (d, 2H, J = 4.1 Hz), 8.43(s, 1H); 13C NMR
(100 MHz, D2O): d 14.55, 20.61, 35.66, 44.70, 121.78, 123.41,
123.45, 125.41, 129.22, 135.18, 140.96, 141.45.
Tetraethylene glycol bis(1-methyl-3-imidazolium) ditosylate:
IR (neat, cm À1):
v
819, 1011, 1217, 1454, 1575, 1647, 2873, 2961,
3112; 1H NMR (400 MHz, D2O):
d
2.11 (s, 3H), 3.41–3.46 (t, 4H,
J = 7.2 Hz), 3.48–3.50 (t, 2H. J = 7 Hz), 3.55 (s, 6H), 3.56–3.66 (t,
4H, J = 6.4 Hz), 4.14 (s, 2H), 6.82–6.88 (d, 4H, J = 8 Hz), 7.04–7.06
(d, 4H, J = 8 Hz), 7.20–7.22 (d, 2H, J = 8 Hz), 7.51–7.53 (d, 2H,
J = 8 Hz), 8.51 (s, 2H); 13C NMR (100 MHz, D2O):
d 21.73, 36, 51.47,
65.80, 70.37, 71.50, 123.69, 124.06, 125.38, 128.98, 138.16,
142.26, 144.53.
1-Octyl-4-phenyl-1H-1,2,3-triazole: mp: 100–102 8C, IR (KBr,
cmÀ1): 962, 759, 1078, 1494, 2848, 2919, 2954, 3121; 1H NMR
v
(400 MHz, DMSO-d6): d 0.83 (t, 3H, J = 7 Hz), 1.24–1.28 (m, 10H,
J = 4 Hz), 1.84 (q, 2H, J = 7.12 Hz), 4.38 (t, 2H, J = 7.04 Hz), 7.31–7.35
(m, 1H, J = 5.01 Hz), 7.44–7.46 (t, 2H, J = 6.39 Hz), 7.83–7.85 (2H, q,
J = 5.12 Hz), 8.58 (1H, s); 13C NMR (100 MHz, DMSO-d6):
d 14.40,
22.51, 26.30, 28.81, 28.96, 30.06, 31.62, 49.97, 121.69, 125.55,
128.23,129.35,131.35.
97
98
Diethyleneglycol bis-1H-1,2,3-triazole: mp: 155–157 8C, IR
(KBr, cmÀ1): 759, 805, 916, 1113, 1464, 2866, 2886, 3135; 1H
v
99
NMR (400 MHz, DMSO-d6): d 3.94 (t, 2H, J = 5.10 Hz), 4.59 (t, 2H,
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
J = 5.08 Hz), 7.28 (m, 3H, J = 5.26 Hz), 7.74 (d, 2H, J = 7.66 Hz), 7.79
(s, 1H); 13C NMR (100 MHz, DMSO-d6):
d 50.40, 69.30, 120.76,
25.80, 128.32, 128.88, 147.71.
Triethylene glycol bis-1H-1,2,3-triazole: mp: 159–161 8C, IR
(KBr, cmÀ1): 757, 805, 916, 1115, 1462, 2868, 2891, 3130; 1H
NMR (400 MHz, DMSO-d6): 3.58 (s, 4H), 3.86 (t, 4H, J = 5.80 Hz),
4.52 (t, 4H, J = 5.80 Hz), 7.28–7.34 (m, 3H, J = 9.14 Hz), 7.44 (d, 2H,
J = 12.17 Hz), 7.87 (s, 1H); 13C NMR (100 MHz, DMSO-d6):
50.45,
v
d
d
69.46, 70.47, 125.61, 128.19, 128.91, 130.68, 146.60; Anal. Calcd.
for C22H24N6O2. (H2O): C, 62.58; H, 6.15; N, 19.89. Found: C, 62.92;
H, 6.07; N, 19.31.
1-(4-Chlorobenzyl)-4-phenyl-1H-1,2,3-triazole: mp: 165–
168 8C, IR (KBr, cmÀ1):
v
763, 1016, 1221, 1351, 1411, 1492,
2995, 3113; 1H NMR (400 MHz, DMSO-d6):
5.66 (s, 2H), 7.33–7.47
(m, 7H, J = 6.59 Hz), 7.83 (d, 2H, J = 7.44 Hz); 8.64 (s, 1H); 13C NMR
d
Scheme 1. Synthesis of ionic liquid.
Please cite this article in press as: M. Javaherian, et al., A dicationic, podand-like, ionic liquid water system accelerated copper-catalyzed
azide-alkyne click reaction, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.09.005

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M. Javaherian et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
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Table 1
Preparation of the ionic liquids a and b.
Entry
a
Alkyl tosylate
Ionic liquid
Time (min)
30
Yield (%)
98
CH3CH2OTs
Et
N
OTs
N
a
CH3
O
O
O
b
30
95
TsO
OTs
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
hours [14]. But the current work has apparent superiority to other
works; due to its simplicity, high rate and, more importantly,
avoiding use of any solvent.
After preparing the alkyl azides, to determine the best volume 185
ratio of solvents, different volume ratios of IL(b) and water were 186
examined, Table 4.
187
Click chemistry reactions are, by definition, highly exothermic.
Therefore, presence of water in click reactions is beneficial, not just
for reactivity reasons, but also because water is the best heat-sink
for handling the enormous heat output when click reactions are
performed on larger scales [15]. Therefore, a combination of water
and ionic liquid medium was chosen to accelerate the reaction.
Initially, we focused on the catalytic activity of ionic liquids a and b.
So, these two task specific ionic liquids were investigated for a
typical [3+2] cycloaddition reaction of diethylene glycol diazide
and phenyl acetylene in the presence of different Cu catalysts, at r.t.
in water, that the ionic liquid b and CuSO4/NaAsc as a more useful
catalyst were selected, Scheme 2 and Table 2.
One restriction of the click-like reactions involving azides is the
limitations of selecting commercially available alkyl azides. In
CuAAC reactions, this problem can be decreased by developing
one-pot procedures for preparing organic azides [16]. In our
continuing efforts in developing simple and practical scalable
procedures in organic transformations, we explored the possibility
of developing one-pot procedure of preparing alky azides from
alcohols by grinding and microwave irradiation, sequentially,
Scheme 3 and Table 3.
Table 3
Q4
The sequential one-pot preparation of azides from alcohols in overall 7 min.
Entry
1
Alcohol
Alkyl azide
Yielda (%)
95
Ph
N3
Ph
OH
OH
N3
6
2
3
91
90
6
CH3
CH3
OH
H3C CH3
N3
H3C CH3
N3
OH
4
5
6
7
94
98
95
91
OH
N3
O2N
Cl
O2N
Cl
N3
OH
OH
N3
Cl
Scheme 2. Preparation of 1,2,3- triazole in the presence of ILs (a or b).
Cl
Table 2
OH
N3
Using of the prepared ionic liquids in a typical click reaction.
8
9
95
96
93
94
92
OCH3
O
Entry
Ionic liquid
Cu-catalyst
Time (min)
Yield (%)
OCH3
1
2
3
4
5
6
a
a
a
b
b
b
CuCl
40
40
15
20
15
5
71
70
81
78
81
89
O
CuI
OH
OH
N3
N3
N3
N3
CuSO4, NaAsc
CuCl
CuI
O
O
O
2
2
10
11
12
CuSO4, NaAsc
N3
HO
HO
OH
O
3
3
N3
OH
OH
N3
Scheme 3. One-pot preparation of alkyl azides from alcohols.
Please cite this article in press as: M. Javaherian, et al., A dicationic, podand-like, ionic liquid water system accelerated copper-catalyzed
azide-alkyne click reaction, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.09.005

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M. Javaherian et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
Table 4
Table 5
Determination of the best volume ratio of water and IL.
A [3+2] cycloaddition of the prepared alkyl azides with phenylacetylene in the
presence of CuSO4/NaAsc in a mixture of IL (b)/water.
Entry
Solvent
Ratio IL(b)/H2O
Yielda (%)
Entry
1
Alkyl azide
Triazole
Time
Yield
(%)a
1
2
3
IL(b)/H2O
IL(b)/H2O
IL(b)/H2O
1:1
2:1
1:2
89
80
58
(min)
15
80
N
N3
Ph
N
N
Ph
N
Ph
N
N
N3
6
2
3
15
15
5
91
89
63
82
82
63
87
89
91
92
79
6
Ph
CH3
CH3
Scheme 4. Preparation of 1,2,3-triazoles in the presence of IL(b).
N
N
N3
N
H3C CH3
H3C CH3
Ph
N
N
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
To improve the scope of our method, a serial reactions between
azides and phenyacetylene in the presence of CuSO4/NaAsc as the
best examined catalyst in a mixture of ionic liquid b and water with
the ratio of 1:1 was carried out, Scheme 4 and Table 5.
N
N3
4
Ph
As shown in Table 5, to explore the scope of this modification,
different kinds of alkyl azides, i.e., benzylic containing EDGs and
EWGs, aliphatic 18 and 28 with short and long chains and, more
importantly, the oligomers of ethylene glycol diazides were
submitted to the click reaction; which all of them afforded the
expected transformation and leading to their corresponding 1,4-
disubstituted-1,2,3-triazoles in short reaction times and high
yields, exclusively. Noticeably, the bis-triazole synthesized com-
pounds (Table 5, entries 9–11) are valuable nitrogen-electron
donors in coordination chemistry, such as transition metal
catalyzed, cross-coupling reaction types reported by Suzuki [17],
Stille [18], etc. Although, electronic effects are known to influence
click reactions [19], but with benzylic azides (entries 4–8) not any
significant differences between substituents were observed, even
though the less yield of 2-chlorobenzyl azide (entry 7) may be
attributed to steric hindrance. The oligomers of ethylene glycol
diazides (entries 9–11) showed nearly similar results, but longer
aliphatic chains and alicylic azizdes (entries 1–3) exhibit longer
reaction times; probably due to steric considerations of their
chains.
N
N
N3
N
5
5
O2N
Cl
O2N
Cl
Ph
N
N
N3
N
6
5
Ph
N
N
N3
Cl
N
7
5
Cl
Ph
N
N3
N
N
8
5
Ph
OCH3
OCH3
O
N
N
N
N
N
N
O
N
N
9
5
N3
N3
Ph
Ph
212
4. Conclusion
O
O
2
N
N
N
O
N
N
10
11
12
5
2
N3
N3
N3
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
Most of the published click methods involving combined
systems of water and an organic co-solvent, but most of them have
used of toxic solvents, such as DMF, DMSO, CHCl3, CH3CN etc. or
often entirely toxic organic solvents like PhCH3, benzene or have
shown long reaction times or use of especial additives and high
temperature [7,20–26]. Apparently, in this work an interesting
kind of podand IL was applied, not only as a safe modification, but
also to enhance the catalytic features and improve the reaction rate
and yield as a task specific IL or co-solvent. In conclusion, we have
Ph
Ph
3
N
N
N
O
N
N
5
3
N3
N3
Ph
Ph
N
N
N
15
Ph
developed
a versatile, highly efficient and environmentally
friendly system for the Huisgen [3+2] cycloaddition of organic
azides and terminal alkynes by using tetraethylene glycol bis-(1-
methyl-3-imidazolium) ditosylate as a co-solvent, or task specific
podand IL, at r.t. Thus, it can be claimed that, these results not only
have broaden the scope of this so-called click reaction, but also, we
have extended a simple, practical method, based on the green
chemistry principles, to supply the required azides as starting
material from alcohols without any laborious works. Moreover, it
should be emphasized that all of the reaction steps from starting
alcohols to triazoles includes only single products which were
separated by simple experimental methods, such as filtration for
triazoles and liquid-liquid extraction for alkyl azides without any
work-up difficulties.
234
235
Acknowledgments
236
Authors thank the Shahid Chamran University of Ahvaz for their Q23 237
financial support. Thanks are also due to JundiShapur University of
Medical Sciences for use of their microwave reactor.
238
239
Please cite this article in press as: M. Javaherian, et al., A dicationic, podand-like, ionic liquid water system accelerated copper-catalyzed
azide-alkyne click reaction, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.09.005

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M. Javaherian et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
5
240
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Please cite this article in press as: M. Javaherian, et al., A dicationic, podand-like, ionic liquid water system accelerated copper-catalyzed
azide-alkyne click reaction, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.09.005