One-pot three-component synthesis of 1,4-disubstituted 1H-1,2,3-triazoles using green and recyclable cross-linked poly(4-vinylpyridine)-supported copper sulfate/sodium ascorbate in water/t-BuOH system

Article abstract of DOI:10.1007/s13738-014-0446-2

Cross-linked poly(4-vinylpyridine)-supported copper sulfate, [P₄-VP]CuSO4 as a green and recyclable, heterogeneous catalyst in the presence of sodium ascorbate (NaAsc), is reported for the regioselective synthesis of 1,4-disubstituted-1,2,3-tri

Full text of DOI:10.1007/s13738-014-0446-2

J IRAN CHEM SOC
DOI 10.1007/s13738-014-0446-2
ORIGINAL PAPER
One-pot three-component synthesis of 1,4-disubstituted 1H-1,2,3-
triazoles using green and recyclable cross-linked poly(4-
vinylpyridine)-supported copper sulfate/sodium ascorbate
in water/t-BuOH system
Mohammad Ali Karimi Zarchi Fatemeh Nazem
•
Received: 4 September 2013 / Accepted: 5 March 2014
Ó Iranian Chemical Society 2014
Abstract Cross-linked poly(4-vinylpyridine)-supported
copper sulfate, [P -VP]CuSO4 as a green and recyclable,
reported. The most popular method for the synthesis of
1,2,3-triazole is Huisgen 1,3-dipolar cycloaddition reaction
of azides with alkynes [1, 8–18], but this reaction suffered
from a lack of selectivity yielding a mixture of the 1,4- and
the 1,5-regioisomers. Furthermore, this transformation
requires elevated temperature, typically in refluxing con-
ditions and long reaction times to go to completion.
Therefore, it is desirable to develop a new, convenient and
regiospecific synthetic approach for the formation of
triazoles.
4
heterogeneous catalyst in the presence of sodium ascorbate
(
NaAsc), is reported for the regioselective synthesis of 1,4-
disubstituted-1,2,3-triazoles from benzyl halides, sodium
azide and terminal alkyne in water/t-BuOH (1/1:V/V) at
7
0 °C. Various alkyl halides and benzyl halides, with
electron-withdrawing groups as well as electron-donating
groups, were used for synthesis of various 1,4-disubsti-
tuted-1,2,3-triazoles in high yields. The present procedure
offers as short reaction time and simple reaction work up.
This catalyst can be recovered by simple filtration and
recycled several consecutive runs without any loss of its
efficiency.
The copper(I)-catalyzed Huisgen 1,3-dipolar cycload-
dition of organic azides and terminal alkynes (also called
‘‘click chemistry’’) resulting in the formation of only 1,4-
disubstituted 1,2,3-triazoles [9–17]. The sources of cop-
per(I) are the most commonly used directly (e.g., CuI) [11–
17], or generated by in situ oxidation of a copper metal,
reduction of a Cu(II) salts, and/or Cu(II)/Cu(0) [10], and
the redox couple copper(II)/ascorbic acid in organic or
organo-aqueous systems [8, 15–17]. Copper(I) salts have
been less used because of their thermodynamic instability
and the formation of undesired alkyne–alkyne coupling
products is sometimes observed [11]. While the use of
soluble Copper(I) salts complexes to promote this reaction
is well established (high reactivity and high selectivity) [7,
8, 14]. Homogeneous catalysis is generally connected with
the problem of separation (purity of the products), recovery
and regeneration of the catalysts, low regioselectivity and
long reaction times. In small-scale synthesis, these prob-
lems are solved by purification using chromatography
accompanied by the loss of the catalysts, but for synthesis
of industrial interest the costs of the catalyst materials are
of importance. In addition to the separation problems,
deactivations of the homogeneous catalysts by formation of
inactive colloidal species are encountered at the compara-
tively high reaction temperature. The problems discussed
Keywords Polymer-supported copper sulfate Á 1,2,3-
Triazole Á 1,3-Dipolar cycloaddition reaction Á Click
chemistry Á Sodium azide
Introduction
The chemistry of heterocyclic compounds has been an
interesting field of study for a long time. 1,2,3-Triazoles
are an important class of heterocyclic compounds due to
their wide range of applications [1] and biological activities
such as anti-HIV activity [2], anticonvulsant [3], anti-
allergic [4] and anti-microbial agents [5]. Recently, syn-
thesis of 1,2,3-triazole derivatives and evaluation of their
anticancer activity [6] and antibiotic activity [7] have been
M. A. Karimi Zarchi (&) Á F. Nazem
Department of Chemistry, College of Science, Yazd University,
P. O. Box 89195-741, Yazd, Iran
e-mail: makarimi@yazd.ac.ir
123

J IRAN CHEM SOC
could be principally minimized by a heterogeneously cat-
alyzed such as heterogeneous copper(I) catalysts based on
silica [19–21], montmorillonite [22], copper nanoparticles
carried out on a Buck Scientific atomic absorption spec-
trometer (SEM). SEM images were recorded using Jeol
make T-300 Scanning Electron Microscope. The copper in
[P -VP]CuSO determination was carried out on a Buck
[
[
23, 24], zeolites [25], Cu in charcoal [26, 27] and polymer
28, 29], have been developed. Nitrogen-containing poly-
4
4
Scientific atomic absorption spectrometer (Model 210
VGP, USA) with a hollow cathode lamp at a wavelength of
327.4 nm using air–acetylene flame.
mer is used to generate metal complexes with transition
metal, in which nitrogen atoms are coordinative bounded to
metal ions [30, 31]. There are a few polymer-supported
copper catalysts reported in the literature for the synthesis
of 1,2,3-triazole derivatives such as polymer-supported
azide and copper(I) [32], copper iodide nanoparticles on
poly(4-vinylpyridine) [33], polymer-supported cop-
per(I) catalysts [34] and macroporous polymer-supported
azide and nanocopper (I) [35]. The present paper also refers
Preparation of [P -VP]CuSO
4
4
Cross-linked poly(4-vinylpyridine) (1.00 g) was added to a
5 mL of 1 M aqueous solution of CuSO Á5H O, and the
4
2
mixture was slowly stirred for 24 h at room temperature. The
blue polymer, [P -VP]CuSO , was filtered and the excessive
4
4
2
?
to the complexation between Cu
ions with poly(4-
copper ions in the complex were washed by deionized water
(3 9 5 mL). It was then dried under vacuum in the presence
of P O at 40 °C overnight. The excessive copper ions in the
vinylpyridine) cross-linked with 2 % divinyl benzene, [P4-
VP] 2 % DVB.
2
5
Although numerous applications of solid supported
reagents and catalysts are reported in the literature [30–44],
but, there are only a few reports in the literature based on
polymer-supported copper ion [30–35].
filtrate determination were carried out on a Buck Scientific
atomic absorption spectrometer (Model 210 VGP, USA)
with a hollow cathode lamp at a wavelength of 327.4 nm
using air–acetylene flame. The single-line flow-injection
system consisting of peristaltic pump (Ismatic, MS-REGLO/
8-100, Switzerland), and rotary injection valve (Rheodyne,
CA, USA) with a loop of 100-lL capacity was used for the
effective control of the amount of sample and reproducibility
of the measurements. The absorbance time response was
monitored on an x–t–chart recorder (L-250) and quantitative
analysis was based on the measurement of the peak height of
transient signals.
In continuation of our studies on development of
application of polymeric reagents and catalysts in organic
transformations [38–44] herein, we wish to report an
improved, fast and general convenient procedure for one-
pot three-component synthesis of 1,4-disubstituted 1H-
1
,2,3-triazoles via cycloaddition of alkyl azides (that in situ
generated from sodium azide and alkyl halides) to a ter-
minal alkyne such as phenyl acetylene using [P4-
2
?
VP]CuSO /NaAsc in mixture of water/t-BuOH (1/1:v/v), at
4
The amount of the Cu ions in complex was obtained
2?
7
0 °C.
by difference of the amount of Cu ions that used for loading
of the polymer and the excess of remained in the filtrates and
consequently, the capacity of the polymer was determined to
2?
-1
Experimental
be 1.5 mmol of Cu ion g of the polymer.
General
General procedure for synthesis of 1,4-disubstituted
1
H-1,2,3-triazoles
Chemicals were purchased from Fluka (Buchs, Switzer-
land), Aldrich (Milwaukee, WI) and Merck chemical
companies. Poly(4-vinylpyridine) cross-linked with 2 %
To a solution of phenylacetylene (1.2 mmol), alkyl halide
(1 mmol), and NaN (1 mmol), in mixture of tert-butyl
3
divinyl benzene (DVB), [P -VP] 2 % DVB was purchased
4
alcohol (3 mL) and water (3 mL) were added [P4-
VP]CuSO4 (1.5 g) and sodium ascorbate (0.1 g). The
resulting mixture was stirred at 70 °C for appropriate time
as indicated in Table 2. The progress of reaction was
monitored by TLC (n-hexane/ethyl acetate: 8/2). After
completion, ethanol (8 mL) was added to the reaction
mixture and heated at 70 °C for 5 min. The reaction mix-
ture was filtered off and washed with hot ethanol. Solvent
was removed under vacuum, and the residue was precipi-
tated in water. The precipitate was collected by filtration.
After washing with water, the precipitate was dried at room
temperature. For further purification, the solid was re-
crystallized in ethanol/water.
from Fluka company (Buchs, Switzerland). The reactions
were monitored by thin layer chromatography (TLC) using
silica gel Poly Gram SIL G/UV 254 plates. All products
were characterized by the comparison of their melting
1
points, FT-IR, and HNMR spectral data, with those of
known samples and all yields referring to the isolated pure
products. Melting points were determined with a Buchi
melting point B-540 B.V. CHI apparatus. FT-IR spectra
were obtained using a Bruker, Equinox (model 55) and
NMR spectra were recorded on a Bruker AC 400, Avance
DPX spectrophotometer at 400 MHz in CDCl solutions.
3
The excessive copper ions in the filtrate determination were
1
23

J IRAN CHEM SOC
Regeneration of [P -VP]CuSO4
4
hot ethanol, and consequently, the capacity of the polymer
2
?
-1
was determined to be 1.5 mmol of Cu ion g of the
polymer. Our effort for preparing the oxidation state of
copper sulfate on the spent polymer was not successful.
Based on changing the blue color of catalyst to greenish
species when the reaction was occurred, we proposed that
The spent green colored polymer (1.00 g) was slowly
stirred with ethanol for 24 h. The mixture was filtered and
washed with hot ethanol, and dried under vacuum in the
presence of P O at 40 °C overnight. The regenerated
2
5
2
?
polymer can be recovered several consecutive runs without
Cu ion in the [P -VP]CuSO in the presence of NaAsc
4 4
1
reduces to Cu ion. Also, based on changing the color of
?
significant loss of its efficiency.
the spent polymer in air to original color (blue), we pro-
2?
1?
posed that Cu ion oxidizes to Cu ion with oxygen in
the air. The process for the preparation of [P -VP]CuSO ,
Results and discussion
4
4
the structure of P -VP] 2 % DVB and [P -VP]CuSO is
4
4
4
In preliminary experiments, we investigated the template
reaction of sodium azide, alkyl halide, phenyl acetylene
using [P -VP]CuSO /NaAsc system in a 1:1 (v/v) mixture
shown in Scheme 1, and the FT-IR spectra of [P -VP] 2 %
4
DVB and [P -VP]CuSO are compared in Fig. 1.
4
4
4
4
Direct evidence for the formation of the coordination
complex can be obtained from the FT-IR of the support and
complex. It is known that the C=N and C=C stretching
frequencies in vinylpyridine polymers shifts to higher fre-
quencies upon complexation with metal ions. Belfiore et al.
[47] have observed displacements in the stretching band of
the poly(4-vinylpyridine) ring and related this to the for-
mation of coordination compounds formed with the metal
and the polymer. The wavenumber increases according to
the force of interaction with the metallic ion. Hasik et al.
[48] discussed the possibility for the formation of a coor-
of water and tert-butyl alcohol, and the reaction only gave
the corresponding 1,4-disubstituted 1,2,3-triazoles in high
yields. The process is experimentally simple and appears to
have enormous scope. Although, a number of cop-
per(I) sources can be used as catalyst for the synthesis of
triazoles directly [11–17] but, copper(I) salts have been less
used because of their thermodynamic instability and the
formation of undesired alkyne–alkyne coupling products is
sometimes observed [11]. Hence in this study, we used
in situ reduction of Cu(II) salts, which are less costly and
often purer than CuI salts (CuSO Á5H O serves well). As
2
?
4
2
dination bond in the poly(4-vinylpyridine)-Pd
(PVP–
2
Pd ) complex, and found a new vibration bond at
-
1,612 cm . In our case, the frequency of C=N and C=C
?
the reductant, ascorbic acid and/or sodium ascorbate
proved to be excellent (for a review of reactions of ascorbic
acid with transition metals, see [45, 46] and references
therein) for they allow preparation of a broad spectrum of
1
-
1
stretch in the support was seen at 1,597 and 1,414 cm for
C=N and C=C stretching, respectively. These peaks suffer
shift towards higher wave numbers at 1,616 and
1
,4-triazole products in high yields and purity. Comparison
-
1
with an authentic sample established that the triazole was
formed in a completely regioselective manner with no
contamination by the 1,5-regioisomer. [P -VP]CuSO was
1,449 cm , respectively, when [P -VP] 2 % DVB was
4
treated with aqueous solution of CuSO and [P -VP]CuSO
4
4
4
4
4
complex was formed. This interaction increases the stiffness
of the associated ring and, consequently, more energy is
required to deform the aromatic cycle, reflected at higher
frequencies. On the other hand, the specific characteristics of
easily prepared in a one-step procedure as described in
experimental section by stirring the suspension of [P -VP]
4
2
% DVB in aqueous solution of CuSO Á5H O. After fil-
4
2
2-
tration, the excessive copper ions in the filtrate determi-
nation were carried out on a Buck Scientific atomic
absorption spectrometer (Model 210 VGP, USA) with a
hollow cathode lamp at a wavelength of 327.4 nm using
air–acetylene flame. The single-line flow-injection system
consisting of peristaltic pump (Ismatic, MS-REGLO/8-100,
Switzerland), and rotary injection valve (Rheodyne, CA,
USA) with a loop of 100-lL capacity was used for the
effective control of the amount of sample and reproduc-
ibility of the measurements. The absorbance time response
was monitored on an x–t–chart recorder (L-250), and
quantitative analysis was based on measurement of the
thestretching bands of the SO anion and S–Ovibrations of
4
2
-
SO4 groups in FT-IR spectrum of [P -VP]CuSO complex
4
4
-1
appeared between 900 and 1,300 cm
(1,120) and
-1
610 cm , respectively, that are absent in FT-IR spectrum of
[P -VP] 2 % DVB copolymer (Fig. 1). The obtained results
4
are supported by Belfiore et al. [47], Hasik et al. [48], Li [49],
Wu et al. [50], and Santana et al. [51]. In this work, we also
studied the scanning electron microscopy (SEM) of [P -VP]
4
2 % DVB and [P -VP]CuSO . The SEM of [P -VP] 2 %
4
4
4
DVB (a) and [P -VP]CuSO (b) is shown in Fig. 2. [SEM
4
4
photographs of (a) and (b) at 2,7109 magnification]. It is seen
from the Fig. 2 that the surface of the polymer is distinctly
altered in supported catalysts (b) and with comparison of
2
?
peak height of transient signals. The amount of the Cu
ions in complex was obtained by different amount of
particle size diameter of [P -VP] 2 % DVB (a) (7.7 lm) with
4
2
?
selected Cu for loading on polymer and the excess of
remained in the filtrates after filtration and washing with
[P -VP]CuSO (b) (14.2 lm) can be concluded that chelating
4
4
occurred between pyridine pendant group of [P -VP] 2 %
4
123

J IRAN CHEM SOC
Scheme 1 Preparation of
-VP]CuSO
)
)
9
(
(
(
[
P
4
4
2
8
)
2(
)
98
N
..
N
(
..
CuSO .5H O (aq)
)
4
2
2
Cu2 SO42-
+
)
(
2
.
.
..
N
N
N
)
2
(
P -VP 2% DVB
[
4
]
(
(
)
)
9
8
2
P -VP CuSO
4
[
4
]
Fig. 1 FT-IR spectra of
a [P -VP] 2 % DVB, and
b [P -VP]CuSO
4
4
4
DVB chain with CuSO and sandwiched between two poly-
4
This polymeric catalyst with NaAsc, catalyzed Huisgen
mer chain of [P -VP] 2 % DVB. Also, as Fig. 2 reveals no
4
1,3-dipolar cycloaddition reaction between phenylacety-
lene and alkyl azides that in situ generated from sodium
azide and alkyl halides. Since organic azides are often
definite size particles are observed in [P -VP] 2 % DVB
4
(
a) with uniform morphology.
1
23

J IRAN CHEM SOC
Fig. 2 Scanning electron
microscopy (SEM) images of
4 4
a [P -VP] 2 % DVB, and b [P -
VP]CuSO
4
Scheme 2 [P
NaAsc-catalyzed synthesis of
,4-disubstituted 1,2,3-triazoles
4 4
-VP]CuSO /
X
N
N
1
N
[
P4-VP]CuSO4 NaAsc
,
+
+
NaN3
R
70 °C
R
unstable to heat and light, the in situ preparation recom-
mends a great choice to their use and handling. All alkyl
azides were prepared in situ and subjected to multicom-
ponent click cyclization with phenylacetylene. A variety of
alkyl halides were also subjected to one-pot three-compo-
nent reaction for synthesis of 1,4-disubstituted 1,2,3-tria-
zoles under heterogeneous conditions (Scheme 2).
achieved high yield (entries 5, 15 and 16) which is one of
the most popular solvent system used for click reaction. In
these solvent systems, sodium azide and sodium ascorbate
were dissolved in water and alkyl halide and phenyl acet-
ylene were dissolved in organic solvent t-BuOH. The
reaction between 4-nitrobenzyl bromide, phenylacetylene
and sodium azide in the presence of 1.50 g of [P4-
To exploit a method for preparation of 1,2,3-triazole
derivatives, the reaction of 4-nitrobenzyl bromide, phen-
ylacetylene and sodium azide in the presence of [P4-
VP]CuSO and 0.10 g of sodium ascorbate furnished the
4
1,4-disubstituted triazole product in 93 % isolated yield
after stirring for 95 min at 70 °C. Also during our opti-
mization studies, it was found that, 1/1.2/1 molar ratios of
VP]CuSO /NaAsc via a 1,3-dipolar Huisgen cycloaddition
4
reaction was chosen as a model reaction. This reaction is
known to give high yields of triazoles with homogeneous
catalysts. The model reaction behavior was studied under a
variety of conditions, and the results are summarized in
Table 1. First we began to test in acetonitrile, methylene
chloride, ethanol and water as solvents. Unluckily, we did
not get good results at room temperature with various
amounts of heterogeneous catalysts and reagents with each
of solvents after 4 h. Therefore, the reaction was followed
at various solvent systems such as H O/t-BuOH, H O/i-
4-nitrobenzyl bromide/phenyl acetylene/NaN in the above
3
conditions were the best to achieve the highest yield of the
product (Table 1, entry 5). Then the amount of catalyst,
[P -VP]CuSO and reducing agent (NaAsc) were exam-
4
4
ined. As Table 1 reveals (entries 5 and 11–14) the best
result was obtained when the reaction took place in the
presence of 1.50 g of [P -VP]CuSO and 0.10 g of NaAsc
4
4
(Table 1, entry 5), for multicomponent click cyclization.
Furthermore, [P -VP]CuSO , in the absence of a reducing
4
4
agent, was also evaluated, and negative results were
observed (Table 1, entry 10).
2
2
PrOH, H O/EtOH, H O/THF and H O/CH CN and it was
2
2
2
3
found that the solvent plays a significant role in terms of
We then applied these conditions for synthesis of vari-
ous 1,4-disubstituted-1H-1,2,3-triazoles, and the results are
summarized in Table 2. Various alkyl or benzyl halides
with both electron-donating and -withdrawing substituents
were subjected to the same reaction conditions to furnish
the corresponding 1,2,3-triazole derivatives. When benzyl
reaction rate, isolated yield, and selectivity. H O/t-BuOH
2
clearly stands out as the solvent of choice with its fast
reaction rate, high isolated yield and selectivity. As can be
seen from Table 1, THF and CH CN afforded low yield
3
(
entry 17, 18), while the mixed solvent H O/alcohol
2
123

J IRAN CHEM SOC
Table 1 Optimization of the
reaction conditions for model
substrate (after 95-min stirring)
Entry MS
(
NaN
(mmol)
3
PA
(mmol)
Catal
c
(g)
NaAsc
d
(g)
RT
(°C)
Solvent (v/
v = 1/1)
Yield
f
(%)
a
b
e
mmol)
at 70 °C using [P
4 4
-VP]CuSO /
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1.5
1
1
1
1
1
1
1
1
1
1
1
1
1
1.5
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1.50
1.50
1.50
1.50
1.50
1.50
1.50
1.50
1.50
1.50
1.50
1.50
2.00
1.50
1.50
1.50
1.50
1.50
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
–
70
70
70
70
70
70
70
70
rt
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/t-BuOH
Water/i-PrOH
Water/EtOH
75
75
75
75
93
42
52
93
38
–
NaAsc to furnish the
corresponding 1,2,3-triazole
derivatives
1
1
1.5
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
0
1
2
3
4
5
6
7
8
70
70
70
70
70
70
70
70
70
0.20
0.05
0.10
0.10
0.10
0.10
0.10
0.10
93
48
93
61
92
92
20
32
a
MS model substrate (4-
nitrobenzylbromide)
b
PA phenyl acetylene
c
Catalyst, [P4-VP]CuSO4
d
Sodium ascorbate
Water/THF
e
RT reaction temperature
3
Water/CH CN
f
Isolated yield
bromide and benzyl chloride were compared for the syn-
thesis of 1-benzyl-4-phenyl-1H-1,2,3-triazol product, we
observed that benzyl bromide reacted faster with higher
isolated yield (see Table 2, entries 9 and 10). This result
was also observed when 4-nitrobenzyl bromide and
pharmaceutical applications. The leaching of active species
from heterogeneous catalysts in solution is a crucial
question to identify whether the active centers are solid
surfaces or dissolved catalyst complexes. In this study, we
used the cross-linked poly(4-vinylpyridine)-supported
copper sulfate that does not dissolve in any solvent. The
reaction occurred on the surface of the pores of the poly-
mer. One reason for the observed different reaction times
in different solvents perhaps could be the swelling of the
reagent in the proper solvent. Hence, instead of leaching of
the catalyst reusability of the catalyst was studied. The
results obtained with [P -VP]CuSO that was recycled for
4
-nitrobenzyl chloride were used (entries 7 and 8). This can
be attributed to this fact that bromide is a better leaving
group than chloride in reaction with NaN for the forma-
3
tion of the corresponding benzyl azide intermediates. This
new, simple method can be successfully applied for the
synthesis of a wide range of 1,4-disubstituted-1H-1,2,3-
triazoles starting from the corresponding alkyl halides such
as substituted benzyl bromide, substituted benzyl chloride,
4
4
the chosen model reaction for six runs are shown in Fig. 3.
The original [P -VP]CuSO gave similar results concern-
1
-chloromethyl naphthalene (Table 2, entry 13) and
-phenylethyl bromide (Table 2, entry 14). As expected,
4
4
2
ing the recovery of the heterogeneous catalyst. As Fig. 3
reveals, when the polymer was reused after six runs under
identical conditions and in the same reaction times, the
isolated yield of the product was decreased only a few
percent (4 %).
the halide-leaving group and the electronic and steric
effects of substituted benzyl halides also play a significant
role in terms of reaction rate and isolated yield. As Table 2
reveals, using benzyl halides with electron-donating groups
at 4-position of the ring, results in bout higher isolated
yields and shorter reaction times (see entries 3 and 8) but,
when benzyl halides with a substituent group at 2-position
of the ring steric effect were observed and result in bout
lower yields and longer reaction times (see entries 2 and 7).
This polymeric catalyst is used in one-pot three-com-
ponent reaction, its main advantage over non-polymeric-
supported catalyst is its insolubility in the reaction medium
and consequently its easier work up by a simple filtration.
An important point concerning the use of heterogeneous
catalysts is its lifetime, particularly for industrial and
Our mechanistic proposal for the catalytic cycle is
2
?
shown in Scheme 3. Cu ion, in the [P -VP] CuSO (blue
4
4
1
?
species) in the presence of NaAsc reduced to Cu , and its
color was changed to greenish species that catalyzed the
2
?
reaction. The spent polymer oxidized to Cu in the pre-
sence of air and its color returned to original color (blue). It
begins unexceptionally with the formation of the cop-
per(I) acetylide (I) [52], which proceeds in addition to
in situ generated alkyl azides (from sodium azide and alkyl
halide) via the intriguing six-membered copper-containing
intermediate (II) [53]. Finally, by cyclization, formation of
1
23

J IRAN CHEM SOC
Table 2 Preparation of 1,4-disubstituted-1H-1,2,3-triazole from benzyl halides/NaN
water/t-BuOH (1/1) at 70 °C
3 4 4
/phenyl acetylene catalyzed by [P -VP]CuSO /NaAsc in
Entry
Substrate
Product
Time (min)
Yield (%)
88
M.p.(°C)
Found
Lit [References]
–
1
Cl
N
105
135
141–143
N
N
Cl
Cl
Cl
Ph
Cl
2
Cl
N
69
145–147
–
N
Ph
N
NO2
NO2
3
4
5
Br
N
30
95
93
90
108–110
107–108
84–86
110[27]
N
N
Me
Cl
Ph
Me
Cl
N
85
–
–
N
Br
Ph
N
Cl
N
125
N
Cl
Cl
Ph
Ph
N
6
7
Br
N
35
96
79
153–154
158–159
152–152.5 [27],
150–151 [19],
152–152.5 [33]
N
Br
N
Br
Cl
N
N
130
156–157 [27], 140–142
[19], 140–141 [33]
N
N
O N
2
Ph
O N
2
8
9
Br
95
93
158–159
156–157 [27], 140–142
[19], 140–141 [33]
N
N
O N
2
Ph
O N
2
Cl
Br
N
60
40
45
77
91
94
129–130
129–130
96–97
129–129.5 [27],
N
N
1
1
28–130 [19],
28–129 [33]
Ph
Ph
1
1
0
1
N
129–129.5 [27],
N
N
1
1
28–130 [19],
28–129 [33]
Me
N
109–110 [19], 110 [33]
N
N
Me
Cl
Ph
123

J IRAN CHEM SOC
Table 2 continued
Entry
Substrate
Product
Time (min)
120
Yield (%)
90
M.p.(°C)
Found
Lit [References]
–
1
2
3
F
N
156–158
N
N
F
Ph
Cl
Cl
Cl
Cl
1
N
135
75
128–129
–
N
Ph
N
1
4
Br
N
95
89
138–140
139 [27]
N
N
Ph
a
Yields refer to isolated and pure products
1
given below, and the FT-IR and H NMR spectra of 1-(4-
Chlorobenzyl)-4-phenyl-1H-1,2,3-triazole product are
given in Figs. 4, 5, 6.
1-(3,5-Dichlorobenzyl)-4-phenyl-1H-1,2,3-triazole
(
Table 2, entry 1): White solid, m.p. = 141–143 °C; FT-
-
1
IR (neat) m (cm ) = 3,089, 1,466, 1,425, 1,400, 1,255,
1
,224, 1,206, 1,140, 1,080, 1,046, 1,030, 977, 890, 838,
1
16, 777, 763, 689, 547, 514; H NMR (400 MHz, CDCl )
8
3
d (ppm) = 5.55 (s, 2H), 7.16 (d, J = 8.0 Hz, 1H), 7.36 (t,
J = 7.2 Hz, 1H), 7.42–7.49 (m, 4H), 7.73 (s, 1H), 7.83 (d,
J = 7.2 Hz, 2H).
1-(2-Nitrobenzyl)-4-phenyl-1H-1,2,3-triazole (Table
2
, entry 2): Yellow solid, m.p. = 145–147 °C; FT-IR
-
1
Fig. 3 Recovery studies: cycloaddition of 4-nitrobenzyl bromide,
phenylacetylene and sodium azide successively catalyzed by the same
(neat) m (cm ) = 3,091, 1,609, 1,527, 1,463, 1,340, 1,222,
1
,205, 1,074, 1,049, 977, 863, 791, 762, 730, 687, 600; H
1
4 4
recovered [P -VP]CuSO under the same reaction conditions as for
the initial run
NMR (400 MHz, CDCl ) d (ppm) = 6.02 (s, 2H), 7.16 (d,
3
J = 7.6 Hz, 1H), 7.37 (t, J = 7.6 Hz, 1H), 7.45 (t,
J = 7.6 Hz, 2H), 7.56 (t, J = 7.6 Hz, 1H), 7.64 (t,
J = 7.6 Hz, 1H), 7.87 (d, J = 7.6 Hz, 2H), 7.96 (s, 1H),
8.18 (d, J = 8.4 Hz, 1H).
intermediate (III) occurred that is converted to 1,4-disub-
stituted 1H-1,2,3 triazole product by proton abstraction
from reaction media (Scheme 3).
The solid products were easily recrystallized from a
mixture of ethanol/water (1:3 v/v). The 1,2,3-triazole
1-(4-Methylbenzyl)-4-phenyl-1H-1,2,3-triazole
(Table 2, entry 3): White solid, m.p. = 108–110 °C; FT-
1
derivatives products were characterized by FT-IR; H- and
-1
IR (neat) m (cm ) = 3,120, 1,609, 1,516, 1,483, 1,463,
1,445, 1,348, 1,223, 1,188, 1,134, 1,076, 1,047, 974, 913,
1
3
C NMR spectroscopy and physical properties were
1
832, 762, 691, 540, 511, 478; H NMR (400 MHz, CDCl )
compared with the literature values of known compounds.
Click condensations were confirmed by the appearance of a
1
singlet in the region of 8–8.5 ppm in H NMR spectra,
3
d (ppm) = 2.28 (s, 3H), 5.46 (s, 2H), 7.11–7.15 (m, 4H),
7.23 (t, J = 7.6 Hz, 1H), 7.32 (t, J = 7.6 Hz, 2H), 7.56 (s,
1H), 7.72 (d, J = 8.4 Hz, 2H).
which corresponds to the hydrogen on 5-position of triazole
ring and confirms the regioselective synthesis of 1,4-
disubstituted triazole regioisomers. Selected spectral data
of some 1,4-disubstituted 1H-1,2,3-triazole products are
1-(3-Chlorobenzyl)-4-phenyl-1H-1,2,3-triazole (Table
2, entry 4): White solid, m.p. = 107–108 °C: FT-IR (neat)
-
1
m (cm ) = 3,083, 1,575, 1,462, 1,435, 1,342, 1,222,
1
23

J IRAN CHEM SOC
Scheme 3 Proposed catalytic
cycle for P -VP]CuSO -
4 4
catalyzed ligation
NaAsc
-
2+
-
+
[
P VP]Cu
[P VP] Cu + Ph
4
C
C
-H
4
Cu+
[
P4- VP]
_
NaN3
+
P4-VP]H+
Ph
R-N=N=N
R-X
+
C
[
C-Cu
+
(
I)
Air
N
N
R
R
[P4-VP]H+
H
N
N
R
N
Cu
Cu
Ph
N
N
+
Cu [P -VPH] +
4
N
N
(
II)
(
III) Ph
Ph
Fig. 4 The FT-IR spectrum of
1
1
-(4-chlorobenzyl)-4-phenyl-
H-1,2,3-triazole
1
,078, 1,046, 973, 912, 888, 864, 840, 760, 692, 511; H
1
1-(4-Bromobenzyl)-4-phenyl-1H-1,2,3-triazole (Table
2, entry 6): White solid, m.p. = 153–154 °C; FT-IR (neat)
NMR (400 MHz, CDCl ) d (ppm) = 5.58 (s, 2H), 7.21 (d,
3
-
1
J = 6.8 Hz, 1H), 7.33-7.36 (m, 4H), 7.44 (t, J = 7.2 Hz,
m (cm ) = 3,126, 1,589, 1,484, 1,461, 1,435, 1,324,
1,216, 1,182, 1,073, 1,048, 1,013, 917, 849, 808, 763, 694,
2
H), 7.72 (s, 1H), 7.84 (d, J = 7.2 Hz, 2H).
-(2-Chlorobenzyl)-4-phenyl-1H-1,2,3-triazole (Table
, entry 5): White solid, m.p. = 84–86 °C; FT-IR (neat) m
1
1
515, 490; H NMR (500 MHz, CDCl ) d (ppm) = 5.56 (s,
3
2
2H), 7.22 (d, J = 8.4 Hz, 2H), 7.36 (t, J = 7.4 Hz, 1H),
7.44 (t, J = 7.4 Hz, 2H), 7.55 (d, J = 8.4 Hz, 2H), 7.72 (s,
1H), 7.84 (d, J = 8 Hz, 2H).
-
1
(
cm ) = 3,123, 1,573, 1,463, 1,356, 1,277, 1,220, 1,082,
,046, 977, 915, 812, 750, 692; 1H NMR (400 MHz,
CDCl ) d (ppm) = 5.74 (s, 2H),7.24 (d, J = 7.6 Hz, 1H),
1
1-(4-Nitrobenzyl)-4-phenyl-1H-1,2,3-triazole (Table
2, entries 7, 8-12): Yellow solid, m.p. = 158–159 °C;
3
7
.28–7.37 (m, 3H), 7.43 (t, J = 7.2 Hz, 2H), 7.48 (d,
-
1
J = 6.4 Hz, 1H), 7.80 (s, 1H), 7.84 (d, J = 7.2 Hz, 2H);
3
FT-IR (neat) m (cm ) = 3,081, 1,519, 1,647, 1,350,
1,222, 1,110, 1,078, 1,045, 861, 802, 763, 732, 690,
1
C NMR (100 MHz, CDCl ) d (ppm) = 51.45, 119.81,
3
1
1
1
25.74, 127.66, 128.22, 128.83, 129.94, 130.25, 130.27,
510; H NMR (500 MHz, CDCl ) d (ppm) = 5.74 (s,
3
30.49, 132.57, 133.44, 148.19.
2H), 7.39 (t, J = 7.4 Hz, 1H), 7.45–7.49 (m, 4H),
123

J IRAN CHEM SOC
1
68, 746, 699, 596, 511, 464, 436; H NMR (400 MHz,
7
CDCl ) d (ppm) = 2.37 (s, 3H), 5.56 (s, 2H), 7.14 (s,
3
1
H), 7.20 (d, J = 7.6 Hz, 1H), 7.30–7.35 (m, 3H), 7.42
t, J = 7.6 Hz, 2H), 7.68 (s, 1H), 7.83 (d, J = 8.4 Hz,
H).
-(2-Chloro-6-fluorobenzyl)-4-phenyl-1H-1,2,3-tria-
zole (Table 2, entry 16): White solid, m.p. = 156–158 °C;
(
2
1
-
1
FT-IR (neat) m (cm ) = 3,129, 1,608, 1,579, 1,484,
1
1
4
7
,459,1,430, 1,352, 1,248, 1,218, 1,179, 1,155, 1,128,
,078, 1,043, 976, 950, 912, 853,824, 795, 763, 691,
1
73; H NMR (400 MHz, CDCl ) d (ppm) = 5.80 (s, 2H),
3
.13 (t, J = 8.4 Hz, 1H), 7.30–7.37 (m, 3H), 7.40 (t,
J = 8.0 Hz, 2H), 7.78 (s, 1H), 7.83 (d, J = 7.2 Hz, 2H).
-(Naphthylmethyl)-4-phenyl-1H-1,2,3-triazole
Table 2, entry 17): White solid, m.p. = 128–129 °C; FT-
1
(
-
1
IR (neat) m (cm ) = 3,119, 3,089, 1,602, 1,511, 1,483,
1
,462, 1,432, 1,396, 1,341, 1,217, 1,194, 1,168, 1,081,
1
Fig. 5 H NMR spectrum of 1-(4-chlorobenzyl)-4-phenyl-1H-1,2,3-
triazole
1
,044, 976, 913, 940, 776, 725, 692, 624, 595, 539; H
1
NMR (400 MHz, CDCl ) d (ppm) = 5.95 (s, 2H), 7.20 (t,
3
J = 7.2 Hz, 1H), 7.27(t, J = 7.2 Hz, 2H), 7.40–7.47 (m,
4
H), 7.44 (s, 1H), 7.66 (d, J = 7.2 Hz, 2H), 7.82-7.86 (m,
H), 7.94 (t, J = 5.6 Hz, 1H).
2
1-(2-phenylethyl)-4-phenyl-1H-1,2,3-triazole (Table
2
, entry 18): White solid, m.p. = 138–140 °C; FT-IR
-
1
(
neat) m (cm ) = 3,082, 3,028, 1,606, 1,483, 1,456,
1
5
,371, 1,223, 1,196, 1,048, 974, 911, 845, 764, 734, 695,
19; 1H NMR (400 MHz, CDCl ) d (ppm) = 3.28 (t,
3
J = 7.2 Hz, 2H), 4.66 (t, J = 7.2 Hz, 2H), 7.16 (d,
J = 6.4 Hz, 2H), 7.30–7.36 (m, 4H), 7.43 (t, J = 7.4 Hz,
1
H), 7.49 (s, 1H), 7.79 (d, J = 6.8 Hz, 2H); C NMR
3
2
(
100 MHz, CDCl ) d (ppm) = 36.82, 51.76, 119.91,
3
1
1
25.70, 127.15, 128.08, 128.75, 128.81, 128.86, 130.67,
37.08, 147.
Table 3 represents the efficiency of the introduced
method in comparison with some of the reported method-
ologies [7, 8, 10, 18, 19, 27, 32, 33, 35]. The superiority of
this work is that the catalyst is recoverable and reusable
many times without significant loss of their activity.
However, the yield of the product in our procedure is
comparable with reported methods. The reaction time in
the present method is shorter than in the previously
reported methods for homogeneous catalyst [7, 8] or in the
absence of catalyst [18]. This can probably be attributed to
1
Fig. 6 The expanded H NMR spectrum of 1-(4-chlorobenzyl)-4-
phenyl-1H-1,2,3-triazole
7
.80 (s, 1H), 7.86 (d, J = 7.5 Hz, 2H), 8.27 (d,
J = 8.6 Hz, 2H).
-Benzly-4-phenyl-1H-1,2,3-triazole (Table 2, entries
3, 14): White solid, m.p. = 129–130 °C; FT-IR (neat) m
2
?
1
the local concentration of Cu ion species inside the pores
of the polymer.
1
-
1
(
cm ) = 3,141, 1,606, 1,493, 1,468, 1,450, 1,360, 1,222,
The advantages to use this polymer-supported copper
sulfate in comparison with CuSO Á5H O [15–17] are
1
4
7
,139, 1,072, 1,044, 970, 922, 807, 768, 730, 695, 586, 506,
1
4
2
79; H NMR (500 MHz, CDCl ) d (ppm) = 5.61 (s, 2H),
recovery and regeneration of the catalysts, high regiose-
lectivity, short reaction times and very simple reaction
work up. In addition, there is a current research and
general interest in heterogeneous systems because such
systems are important in industry and developing tech-
nologies [54].
3
.37–7.45 (m, 8H), 7.72 (s, 1H), 7.85 (d, J = 7.7 Hz, 2H).
1
-(3-Methylbenzyl)-4-phenyl-1H-1,2,3-triazole
(
Table 2, entry 15): White solid, m.p. = 96–97 °C; FT-
-
1
IR (neat) m (cm ) = 3,119, 3,091, 1,608, 1,483, 1,463,
,436, 1,446, 1,221, 1,191, 1,077, 1,050, 976, 882, 825,
1
1
23

J IRAN CHEM SOC
Table 3 Evaluation of the introduced methodology in comparison with some of the previously reported methods
Entry
Reaction conditions
Time (h)
Isolated yield (%)
References
1
2
3
4
5
6
7
8
9
NaN
3
/Nano Cu(I) on charcoal/H
/Silica supported CuI/H
O, 25 °C
/Amberlyst A21CuI,EtOH, reflux
/Cu(0)/CuSO /t-BuOH/H O, MW
IRA-910 N /Amberlyst A21CuI/ CH CN, reflux
VPy-CuI/Water, reflux
2
O, 100 °C
0.5–8
72–91
85–92
70–92
84–93
78–92
75–89
14–96
52–98
[27]
NaN
3
2
10–20 min
1–2
[19]
IRA-400 N
NaN
3
[35]
3
4
2
10–15 min
1–1.75
15–45 min
24
[10]
3
3
[32]
NaN
NaN
NaN
NaN
NaN
3
3
3
3
3
/P
4
[33]
/CuSO
/CuSO
4
.5H O/Na ascorbate/Na
2
2
CO
3
/ L-proline/DMSO/65 °C
/DL-proline/DMSO/H
O (1/1)/60 °C
[7]
a
.5H O/Na ascorbate/Na
4 2
2
CO
3
2
24
[8]
b
/DMF/60-130 °C
/[P -VP]CuSO /NaAsc/t-BuOH/H
3–18
[18]
1
0
4
4
2
O
0.5–2.25
75–96
Present work
a
When CuSO
separation via extraction is needed
4
Á5H
2
O is used, for synthesis of 1,2,3-triazoles, copper azide that is explosive when dry is formed, and an additional step for its
b
In this method, the obtained sodium bromide and iodide are partially soluble in DMF and hinder the isolation of the desired reaction products,
and the mixture of 1,4- and 1,5-disubstituted-1H-1,2,3-triazoles is prepared in nearly equal amounts
Conclusions
10. P. Appukkuttan, W. Dehaen, V.V. Fokin, E.V. Eycken, Org. Lett.
, 3897 (2004)
1. C.W. Tornoe, C. Christensen, M. Meldal, J. Org. Chem. 67, 3057
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rahedron 61, 9331 (2005)
6
1
In conclusion, we have developed an efficient and one-pot
three-component method for [3 ? 2] cycloaddition of
in situ generated organic azides (from sodium azide and
alkyl halide) with terminal alkyne for the synthesis of 1,4-
disubstituted 1,2.3-triazoles using reusable polymer-sup-
ported copper sulfate catalyst/NaAsc. The present method
has the advantages of operational simplicity, mild reaction
conditions, ready availability, fast reaction rates, and sim-
ple reaction work up. The spent polymeric catalyst can be
recovered and reused several times without significant loss
of their activity.
(
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