One-pot, efficient, and regioselective syntheses of 1,4-disubstituted 1,2,3-triazoles using aryldiazonium silica sulfates in water

Article abstract of DOI:10.1016/j.tetlet.2012.07.081

A one-pot, efficient, and straightforward procedure for the copper-catalyzed synthesis of 1,4-disubstituted 1,2,3-triazoles is studied by in situ generation of aryl azides via the reaction of aryldiazonium silica sulfates and sodium azide, followed by coupling with a terminal alkyne. These reactions are carried out in water at room temperature without using any additional ligands.

Full text of DOI:10.1016/j.tetlet.2012.07.081

Tetrahedron Letters 53 (2012) 5176–5179
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
One-pot, efficient, and regioselective syntheses of 1,4-disubstituted
1,2,3-triazoles using aryldiazonium silica sulfates in water
⇑
Amin Zarei
Department of Science, Fasa Branch, Islamic Azad University, PO Box 364, Fasa 7461713591, Fars, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 March 2012
Revised 5 July 2012
Accepted 19 July 2012
Available online 27 July 2012
A one-pot, efficient, and straightforward procedure for the copper-catalyzed synthesis of 1,4-disubsti-
tuted 1,2,3-triazoles is studied by in situ generation of aryl azides via the reaction of aryldiazonium silica
sulfates and sodium azide, followed by coupling with a terminal alkyne. These reactions are carried out in
water at room temperature without using any additional ligands.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Aryldiazonium silica sulfates
Click reaction
1,2,3-Triazoles
Cycloaddition
An important example of click chemistry1 is the copper(I)-cata-
lyzed Huisgen 1,3-dipolar cycloaddition of azides and terminal
alkynes (CuAAC)2 for the regioselective synthesis of 1,4-disubstiti-
uted 1,2,3-triazole derivatives. These compounds have received
significant attention because of their wide applications in chemi-
cal, material, and biological sciences.3 For example, some of these
compounds show a variety of properties including anti-HIV,4
antiallergic,5 antidiabetic,6 antifungal,7 and antibacterial.8 More-
over, 1,2,3-triazoles are stable and tolerant to many functional
groups and conditions. Therefore, they have been widely used in
organic synthesis, industrial applications, bioconjugation, and drug
discovery.9 Different methods have been reported to develop the
1,3-dipolar cycloaddition of alkynes with organic azides. For exam-
ple, using Cu(II) in the presence of reductants,2e,10 Cu(I) directly,11
a variety of ligands to stabilize the Cu(I) oxidation state,12 copper-
containing nanoparticles,13 copper(I) immobilized on various sup-
ports,14 the in situ generation of organic azides that not only sim-
plifies the experimental procedure, but also minimizes the risk of
handling hazardous azides,15 and the use of microwave or ultra-
sound irradiation to reduce reaction times.16 In view of environ-
mental and economic reasons, the development of catalytic
systems without employing an additional ligand and using water
instead of organic solvents are attractive fields in this area of
research.
prepared by the reaction of diazonium salts with azides. Although
organic azides are often stable under most reaction conditions,
derivatives with low molecular weight can sometimes be explo-
sive. Moreover, high temperatures lead to decomposition of the
aryl azides. Therefore, the in situ generation of organic azides fol-
lowed by their immediate reactions, is a desirable and attractive
method to minimize the potential explosive risks. In continuation
of our studies on the stabilization of diazonium salts on silica sul-
furic acid and their application in organic synthesis,17 we report
herein an efficient, convenient, and one-pot synthesis of 1,4-disub-
stituted 1,2,3-triazoles by the in situ generation of aryl azides via
reaction of aryldiazonium silica sulfates and sodium azide followed
by coupling with a terminal alkyne (Scheme 1). Unlike traditional
methods, these reactions were carried out in water at room tem-
perature without using any additional ligand.
Aryldiazonium salts are useful intermediates in organic synthe-
sis due to their ready availability and high reactivity.18 These com-
pounds, however, have a serious drawback in their intrinsic
instability and hence they are usually synthesized at around
10 °C and, to avoid their decomposition, they are handled at tem-
peratures below 0 °C. Moreover, because of this instability, subse-
quent reactions with diazonium salts must be carried out under
the same conditions. Thus, diazonium salts with higher stability
Aromatic azides are versatile intermediates with various appli-
cations in organic and bioorganic chemistry. They are very useful
starting materials for the click reaction and are commonly
Ar
N
CuSO4, Na ascorbate
CH,
N
NaN3
H2O, r.t.
N
ArN2OSO3-SiO2
ArN3
R
C
H2O, r.t.
R
⇑
Tel.: +98 9171302528; fax: +98 311 2289113.
E-mail address: aj_zarei@yahoo.com
Scheme 1. One-pot synthesis of 1,4-disubstituted 1,2,3-triazoles
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.07.081

A. Zarei / Tetrahedron Letters 53 (2012) 5176–5179
5177
Table 1
One-pot synthesis of 1,4-disubstituted 1,2,3-triazoles using aryldiazonium silica sulfates
Entry
Diazonium salt
Alkyne
Product
Time (h)
5
Yielda (%)
1
C6H5N2+ÀOSO3-SiO2
87
81
73
78
80
79
86
82
65
90
81
78
72
60
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
2
4-MeC6H4N2+ÀOSO3-SiO2
2-MeC6H4N2+ÀOSO3-SiO2
4-MeOC6H4N2+ÀOSO3-SiO2
4-BrC6H4N2+ÀOSO3-SiO2
2-ClC6H4N2+ÀOSO3-SiO2
3-ClC6H4N2+ÀOSO3-SiO2
4-ClC6H4N2+ÀOSO3-SiO2
2-NO2C6H4N2+ÀOSO3-SiO2
3-NO2C6H4N2+ÀOSO3-SiO2
4-NO2C6H4N2+ÀOSO3-SiO2
4-NCC6H4N2+ÀOSO3-SiO2
4-MeCOC6H4N2+ÀOSO3-SiO2
2-HO2CC6H4N2+ÀOSO3-SiO2
4-PhCOC6H4N2+ÀOSO3-SiO2
6
7
6
6
6
5
6
6
5
6
6
6
6
7
Me
Me
3
4
OMe
Br
5
Cl
6
Cl
7
8
Cl
O2N
9
N
NO2
10
11
12
13
14
15
N
N
N
N
NO2
CN
O
Me
HO2C
N
N
O
79
N
N
Ph
(continued on next page)

5178
A. Zarei / Tetrahedron Letters 53 (2012) 5176–5179
Table 1 (continued)
Entry
Diazonium salt
Alkyne
Product
Time (h)
Yielda (%)
Ph
O
N
N
N
N
N
16
2-PhCOC6H4N2+ÀOSO3-SiO2
7
76
3-PyridylN2+ÀOSO3-SiO2
5
7
75
80
N
17
18
N
Me
Me
Me
Me
C6H5N2+ÀOSO3-SiO2
N
N
N
N
N
19
20
4-MeC6H4N2+ÀOSO3-SiO2
7
77
83
Me
N
N
C6H5N2+ÀOSO3-SiO2
5
6
N
N
N
O
4-MeCOC6H4N2+ÀOSO3-SiO2
78
N
21
N
Me
a
10b,c,11b,12f,13a,d,15
The yield refers to isolated pure products which were characterized from their spectral data and by comparison with those reported in the literature.
and versatility, and that can be easily made and stored under solid-
state conditions with explosion-proof properties are desirable.19,20
For example, many diazonium tetrafluoroborates are relatively sta-
ble and can be stored over extended periods of time without
decomposition.21 Recently, we reported an efficient, fast, and con-
venient method for the preparation of aryldiazonium salts sup-
terminal alkynes in water catalyzed by copper nanoparticles on
activated carbon. These reactions were carried out at 70 °C in 2–
8 h without using any ligand. However, it was necessary to use
an organic solvent and relatively expensive materials for the syn-
thesis of the copper nanoparticles.13c
By using aryldiazonium silica sulfates as heterogeneous sys-
tems with high surface areas, contamination of the desired prod-
ucts with residual copper decreased due to the reduction of Cu(I)
leaching from the surface. Furthermore, by supporting the aryldi-
azonium salt on silica sulfuric acid, the surface area of the reaction
increased thereby lowering the reaction time.17,25 Another advan-
tage of this method was the easy work-up since the crude products
were extracted with ethyl acetate and, if necessary, were purified
by short column chromatography.
To summarize, we have reported an efficient, one-pot, safe, and
experimentally simple method for the synthesis of 1,4-disubsti-
tuted 1,2,3-triazoles in good yields. These reactions were carried
out using aryldiazonium silica sulfates, sodium azide, terminal al-
kynes, and a catalytic amount of CuSO4 in the presence of sodium
ascorbate. It was notable that all the reactions took place in pure
water at room temperature without using any additional ligand.
ported on the surface of silica sulfuric acid (aryldiazonium silica
17a
sulfates).
We found that these new aryldiazonium salts (ArN2
+ÀOSO3-SiO2) were stable and could be stored at room temperature
under anhydrous conditions and used under different reaction
conditions.17
Initially, to minimize the potential explosive risk, in situ gener-
ation of aryl azides was studied by the reaction of aryldiazonium
silica sulfates with sodium azide in water. These reactions were
17c
carried out at room temperature in a few minutes.
After com-
pletion of azide formation, an aqueous solution of sodium ascor-
bate and a catalytic amount of CuSO4 were added to generate the
Cu(I) catalyst in situ, followed by addition of the corresponding ter-
minal alkyne. To examine the generality of the process, the reac-
tions of a variety of aryldiazonium silica sulfates and alkynes
were studied in water at room temperature.22,23
As shown in Table 1, the reactions were carried out under mild
heterogeneous conditions and the corresponding 1,4-disubstituted
1,2,3-triazoles were obtained in relatively short reaction times and
in good yields. Aryldiazonium silica sulfates with electron-with-
drawing or electron-donating groups also reacted effectively. The
steric effects of ortho substituents on the aryl rings of the aryldi-
azonium silica sulfates had relatively little influence on the yields
and reaction times (Table 1, entries 3, 6, 9, 14 and 16).
Although most CuAAC reactions proceed either in organic sol-
vents or in mixtures with water (i.e. water/MeCN or water/t-
BuOH), only a few reactions have been reported in water alone.24
However, in all of these, it was necessary to use an appropriate
ligand to accelerate the reaction rate. Moreover, in most of these
methods, raised temperatures were required to allow the reaction
to progress. Recently, Alonso and coworkers13c developed a one-
pot method for the CuAAC reaction using ArN2+BF4À, NaN3, and
Acknowledgement
Funding support for this project from the Islamic Azad Univer-
sity, Fasa Branch is gratefully acknowledged.
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22. Typical procedure for the synthesis of 1,4-diphenyl-1H-1,2,3-triazole (Table 1,
entry 1): To a stirred solution of NaN3 (0.15 g, 2.3 mmol) in H2O (5 mL), freshly
prepared phenyldiazonium silica sulfate17 (1 mmol) was gradually added and
the mixture was stirred at room temperature for 5 min. Next, a mixture of
CuSO4Á5H2O (0.04 g, 15 mol %), sodium ascorbate (0.18 g, 0.9 mmol), and
phenylacetylene (0.25 mL, 2.3 mmol) in H2O (5 mL) was added and the mixture
stirred for 5 h at room temperature. The mixture was diluted with EtOAc
(15 mL) and filtered after vigorous stirring. The filtrate was extracted with
EtOAc (3 Â 12 mL) and the combined organic layer washed with H2O (15 mL).
The organic layer was dried over anhydrous Na2SO4 and evaporated. The
residue was washed with n-hexane (5 mL) to afford the pure product (0.19 g,
87%). Column chromatography was used for some cases to obtain the pure
product.
23. Spectral data of new compounds: phenyl [4-(4-phenyl-1H-1,2,3-triazol-1-
yl)phenyl]ketone (Table 1, entry 15): Pale yellow solid; mp 206–208 °C; 1H
NMR (500 MHz, DMSO-d6) d 9.45 (1 H, s), 8.17 (2 H, d, J = 8.6 Hz), 8.00–7.96 (4
H, m), 7.79 (2 H, d, J = 7.6 Hz), 7.72 (1 H, t, J = 7.4 Hz), 7.60 (2 H, t, J = 7.6 Hz),
7.52 (2 H, t, J = 7.6 Hz), 7.40 (1 H, t, J = 7.4 Hz); 13C NMR (125 MHz, DMSO-d6) d
195.82, 148.52, 140.13, 137.61, 137.58, 133.84, 132.41, 130.86, 130.55, 129.93,
129.58, 129.32, 126.29, 120.59, 120.55; IR (KBr): 3130, 3055, 1647, 1604, 1411,
1319, 1281, 1230, 1041, 927, 852, 771, 703 cmÀ1; Anal. Calcd for C21H15N3O: C,
77.52; H, 4.65; N, 12.91%; Found: C, 77.39; H, 4.69; N, 12.81. Phenyl [2-(4-
phenyl-1H-1,2,3-triazol-1-yl)phenyl]ketone (Table 1, entry 16): Yellow solid; mp
108–110 °C; 1H NMR (500 MHz, DMSO-d6) d 9.06 (1 H, s), 7.89–7.84 (2 H, m),
7.77 (2 H, d, J = 7.8 Hz), 7.76–7.71 (2 H, m), 7.61 (2 H, d, J = 7.7 Hz), 7.52 (1 H, t,
J = 7.3 Hz), 7.45–7.39 (4 H, m), 7.33 (1 H, t, J = 7.4 Hz); 13C NMR (125 MHz,
DMSO-d6) d 194.83, 147.90, 136.91, 135.24, 134.74, 134.22, 132.77, 130.85,
130.62, 130.44, 129.80, 129.41, 129.09, 126.15, 125.05, 122.91; IR (KBr): 3136,
3103, 3061, 1663, 1600, 1579, 1501, 1483, 1449, 1316, 1288, 1262, 1226, 929,
767, 749, 691 cmÀ1; Anal. Calcd for C21H15N3O: C, 77.52; H, 4.65; N, 12.91%;
Found: C, 77.43; H, 4.76; N, 12.83.
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