One-pot synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles by silica supported-zinc bromide in the aerobic condition

Article abstract of DOI:10.1016/j.crci.2012.11.007

An efficient one-pot cross-coupling/1,3-dipolar cycloaddition sequence was developed for a convenient synthesis of 4,5-disubstituted-1,2,3-(NH)-triazoles, starting from various acid chlorides, terminal alkynes and sodium azide in the presence of silica su

Full text of DOI:10.1016/j.crci.2012.11.007

C. R. Chimie 16 (2013) 239–243
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´
Full paper/Memoire
One-pot synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles by silica
supported-zinc bromide in the aerobic condition
*
Ali Keivanloo , Mohammad Bakherad, Sayed Ali Naghi Taheri, Shahrzad Samangooei
School of Chemistry, Shahrood University of Technology, Daneshgah avenue, Shahrood 3619995161, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
An efficient one-pot cross-coupling/1,3-dipolar cycloaddition sequence was developed for
a convenient synthesis of 4,5-disubstituted-1,2,3-(NH)-triazoles, starting from various
acid chlorides, terminal alkynes and sodium azide in the presence of silica supported-zinc
bromide under aerobic conditions.
Received 9 May 2012
Accepted after revision 15 November 2012
Available online 5 January 2013
´
ß 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Keywords:
Copper free
Cross-coupling
Dipolar cycloaddition
1,2,3-(NH)-triazoles
Silica supported
Aerobic condition
Zinc bromide
1. Introduction
offered an efficient route to the synthesis of 1,4-disubsti-
tuted-1,2,3-triazoles. Also the Ru-catalyzed reaction of
1,2,3-triazoles are important nitrogen heterocyles which
display many interesting properties including antibacterial
[1], herbicidal, fungicidal [2], antiallergic [3], anti-HIV [4],
GSK-3 inhibiting [5], and antineoplastic activities [6].
Moreover, they have been widely used in various research
fields, such as biological [7], and material sciences [8],
medicinal [9], and synthetic organic chemistry [10].
One-pot multi-step reactions have a number of advan-
tages including minimizing waste, saving energy, and
reducing operating times. This process is especially useful
when the reaction intermediates are unstable and difficult
to isolate. Recently, efforts have been developed for the
synthesis of 1,2,3-triazoles by copper(I)-catalyzed azide-
alkyne cycloaddition (CuAAC) using a multi-step, one-pot
synthetic approach [11]. Copper(I)-catalyzed 1,3-cycload-
dition reaction often referred to as ‘‘click-chemistry’’ [12]
terminal alkynes with alkyl azides was discovered to be a
unique way to synthesize 1,5-disubstituted-1,2,3-triazoles
[13]. In these methods inorganic azides, NaN3 and KN3 are
not active enough under mild conditions and it is inconve-
nient to prepare 4,5-disubstituted 1,2,3-(NH)-triazoles.
Only a few methods for the synthesis of 4,5-disubstituted
1,2,3-(NH)-triazoles have been reported [14]. It is therefore
necessary to develop novel ways of synthesizing 4,5-
disubstituted 1,2,3-(NH)-triazoles.
2. Results and discussion
Some new approachs for constructing 4,5-disubstituted
1,2,3-(NH)-triazoles are based on Sonogashira coupling
reaction [15]. These methods are efficient, but they have
several drawbacks, which include the requirements of
expensive palladium catalyst, dry solvents, and inert
atmosphere.
In this article, we report an efficient, one-pot, copper
and palladium free method for the synthesis of 4,5-
disubstituted 1,2,3-(NH)-triazoles 4 via cross coupling
* Corresponding author.
E-mail addresses: akeivanloo@yahoo.com,
keivanloo@shahroodut.ac.ir (A. Keivanloo).
1631-0748/$ – see front matter ß 2012 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2012.11.007

240
A. Keivanloo et al. / C. R. Chimie 16 (2013) 239–243
O
R2
N
R1
1) SiO2/ZnBr2 DIPEA
,
O
rt
,
3h
CH3CN
3h
R2
CH
N
R1
Cl
+
2) NaN3
,
/
H2O
N
H
50 °C
,
4
1
2
Scheme 1. Synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles from various acid chlorides, terminal alkynes and sodium azide in the presence of silica
supported-zinc bromide under aerobic conditions.
reaction/1,3-dipolar cycloaddition of acid chlorides 1,
terminal alkynes 2 and sodium azide in the presence of
silica supported-zinc bromide under aerobic conditions
(Scheme 1).
Recently we reported the synthesis of ynones by the
cross-coupling reaction of acid chlorides with terminal
alkynes in the presence of silica-supported zinc bromide
(ZnBr2/SiO2) under solvent free conditions [16]. We
decided to use the same procedure followed by 1,3-dipolar
cycloaddition for the synthesis of 4,5-disubstituted 1,2,3-
(NH)-triazoles.
In our starting experiment, phenyl acetylene, 4-
chlorobenzoyl chloride, sodium azide were put in one-
pot in the presence of ZnBr2 (1.2 eq) and a base (DIPEA or
Et3N) in various solvents (CH3CN, dioxane, THF, DMF) was
added to the mixture and the reaction was carried out at
room temperature for 10 h, after which the temperature
was raised to 50 8C and the reaction was continued for a
further 5 h. Unfortunately, only a very poor yield of the
desired product were formed. But when the reaction of
phenyl acetylene and 4-chlorobenzoyl chloride were
carried out using ZnBr2 (1.2 eq) or ZnBr2/SiO2 (10 mol%)
catalyst in various solvents or under solvent free condition
at room temperature, in advance, followed by sodium
azide 1,3-dipolar cycloaddition at 50 8C, (4-bromophe-
nyl)(5-phenyl-2H-1,2,3-triazol-4-yl)methanone, 4c was
obtained in 62–96% isolated yield (Table 1). Optimization
of the conditions was reached when ZnBr2/SiO2 (10 mol%)
was used as the catalyst under solvent free condition at
room tempreture followed by sodium azide cycloaddition
in CH3CN/H2O (3:1) at 50 8C (Table 1, entry 7).
In order to explore the scope and generality of this
protocol, we examined various benzoyl chlorides and
different 1-alkynes using the optimized procedure (Table
2). The results show that this reaction is equally facile with
both electron-donating and electron-withdrawing substi-
tuents present on the benzoyl chloride, resulting in good-
to-high yields of the corresponding triazoles. Aliphatic
terminal alkynes also reacted smoothly, affording the
desired product in 88–95% yield. The structure of
compounds was established by spectroscopic data and
elemental analysis.
The proposed mechanism for the steps involved in the
reactions is shown in Scheme 2. The key step of the
reaction is the cross-coupling reaction of terminal alkynes
with benzoylchlorides to afford the ynone intermediate 3.
Subsequent 1,3-dipolar cycloaddition with sodium azide
completes the reaction mechanism.
O
R1COCl
1
ZnBr2
2
1
R
CH
R
CZnBr
R
DIPEA
2
R
3
ZnBr
NaN3
2
O
O
O
2
2
1
1
2
R
R
R
R
R
1
R
N
N
N
N-
+
2-
N
N-
N
N
N
+
i
( -pr) EtNH
O
2
2
1
R
R
N
N
N
H
Scheme 2. Proposed mechanism for the formation of 4,5-disubstituted-1,2,3-(NH)-triazoles, from acyl chlorides, terminal alkynes and sodium azide in the
presence of silica supported-zinc bromide.

A. Keivanloo et al. / C. R. Chimie 16 (2013) 239–243
241
Table 1
Silica supported-zinc bromide coupling reaction of p-chlorobenzoyl chloride 1b with phenylacetylene followed by sodium azid 1,3-dipolarcycloaddition in
the presence of different bases and solventsa.
O
O
CH
Cl
1) catalyst, base
Cl
rt 3h
,
+
N
N
2) NaN3 solvent
,
N
H
Cl
50 °C 3h
,
1
2
4
Entry
Solvent
Base
Catalyst
Cyloaddition solvent
Yield (%)
c
1
2
3
4
5
6
7
8
9
10
CH3CN
CH3CN
DMF
DIPEAb
Et3N
ZnBr2
CH3CN/H2O
CH3CN/H2O
DMF/H2O
DMF/H2O
CH3CN/H2O
DMF/H2O
CH3CN/H2O
CH3CN/H2O
H2O
76
62
78
85
80
71
96
74
90
70
ZnBr2
Et3N
ZnBr2
DMF
DIPEA
DIPEA
DIPEA
DIPEA
Et3N
ZnBr2
e
CH3CN
DMF
SiO2/ZnBr2
SiO2/ZnBr2
SiO2/ZnBr2
SiO2/ZnBr2
SiO2/ZnBr2
SiO2/ZnBr2
d
–
d
–
d
–
DIPEA
DIPEA
d
–
DMSO/H2O
Bold elements represent optimized conditions.
a
Reaction conditions: p-chlorobenzoyl chloride (1.2 mmol), phenylacetylene (1.0 mmol), base (1.2 mmol), solvent (1 mL) and catalyst, stir room
temperature (3 h), followed by sodium azid (1.2 mmol) addition in solvent, 50 8C (3 h).
b
Diisopropylethylamine.
c
1.2 eq.
d
Without solvent.
e
10 mol%.
Table 2
Synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles in the presence of silica supported-zinc bromidea.
O
R2
N
R1
1) SiO2 /ZnBr2, DIPEA
O
rt
, 3h
R2
CH
N
R1
Cl
+
2) NaN3
,
CH3CN/H2O
N
H
50 °C
,
3h
4
1
2
Entry
R1
R2
Product
Mp (8C)
Yieldb (%)
Ref
1
C6H5
C6H5
C3H7
C6H5
C6H5
C3H7
C6H5
C3H7
C6H5
C6H5
C3H7
C6H13
C6H5
C6H5
C4H9
4a
4b
4c
4d
4e
4f
114–116
85–87
92–94
131–133
Oil
92
94
95
96
92
91
93
90
87
88
94
82
96
95
[15a]
[15a]
New
[15a]
New
[15a]
New
[15a]
[15a]
New
New
[15a]
New
[15a]
2
C6H5
3
4-BrC6H4
4-ClC6H4
2-ClC6H4
2-ClC6H4
4-ClC6H4
4
5
6
Oil
7
4g
4h
4i
75–77
117–119
89–91
Oil
8
4-MeC6H4
2-MeC6H4
2-MeC6H4
4-ClC6H4
9
10
11
12
13
14
4j
4k
4l
Oil
4-NO2C6H4
2,4-Cl2C6H4
4-ClC6H4
150–152
68–70
73–75
4m
4n
a
Reaction conditions: benzoyl chloride (1.2 mmol), terminal alkyne (1.0 mmol), base (1.2 mmol), SiO2/ZnBr2 (10 mol%), stir room temperature (3 h),
followed by addition of sodium azid (1.2 mmol), 50 8C (3 h).
b
Isolated yield.

242
A. Keivanloo et al. / C. R. Chimie 16 (2013) 239–243
3. Conclusion
4.4. (2-chlorophenyl)(5-propyl-2H-1,2,3-triazol-4-
yl)methanone (4e)
In conclusion, we have developed an efficient, facile,
convenient, one-pot, copper and palladium free method for
the synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles via
cross-coupling reaction/1,3-dipolar cycloaddition of acid
chlorides, terminal alkynes and sodium azide in the
presence of silica supported-zinc bromide in aerobic
conditions.
1H NMR (400 MHz, DMSO-d6):
d7.90 (d, J = 7.4 Hz, 1H,
ArH), 7.46–7.75 (m, 3H, ArH), 6.82 (s, 1H, NH), 2.71 (t,
J = 7.4 Hz, 2H, CH2), 1.52 (m, 2H, CH2), 0.98 (t, J = 7.6 Hz, 3H,
CH3); 13C NMR (100 MHz, DMSO-d6):
d 187.61, 152.69,
142.74, 138.34, 136.85, 133.57, 131.20, 129.14, 127.82,
30.23, 20.66, 13.42. IR (KBr): 3300 (NH), 2920, 1680 (C O),
1590, 1420, 1320, 760 cmÀ1; Anal. Calcd for C12H12ClN3O: C,
57.72; H, 4.84; N, 16.83; Found: C, 57.70; H, 4.85; N, 16.85.
4. Experimental
4.5. (4-chlorophenyl)(5-propyl-2H-1,2,3-triazol-4-
All the reagents used were of general reagent grade. IR
spectra were obtained as potassium bromide pellets or
solvent in the range of 400–4000 cmÀ1 on a Shimadzu
Model 460 spectrometer. 1H NMR spectra were recorded
on a Brucker BRX 400 AVANCE spectrometer. Elemental
analyses were performed on a Thermo Finnigan Flash EA
microanalyzer.
yl)methanone (4g)
1H NMR (400 MHz, DMSO-d6):
ArH), 7.50 (d, J = 8.4 Hz, 2H, ArH,), 6.50 (s, 1H, NH), 2.94 (t,
J = 7.6 Hz, 2H, CH2), 1.60 (m, 2H, CH2), 1.00 (t, J = 7.5 Hz, 3H,
CH3); 13C NMR (100 MHz, DMSO-d6):
141.81, 139.56, 134.38, 131.82, 129.04, 30.22, 20.64, 13.55.
IR (KBr): 3285 (NH), 2950, 1678 (C O), 1588, 1425, 1310,
750 cmÀ1; Anal. Calcd for C12H12ClN3O: C, 57.72; H, 4.84;
N, 16.83; Found: C, 57.73; H, 4.83; N, 16.84.
d 8.10 (d, J = 8.3 Hz, 2H,
d 187.26, 153.70,
4.1. Preparation of silica-supported zinc bromide
Silica gel (Wakogel C-100, 3.65 g) was added to a
solution of ZnBr2 (6 mmol, 1.35 g) in EtOH (20 ml), and the
mixture was heated at reflux for 1 h. The solvent was
removed on a rotary evaporator, and the product was
dried under vacuum at 150 8C for 10 h. Inductively
coupled plasma atomic absorption spectrometry (ICP)
indicated that 1.2 mmol of ZnBr2 was supported on 1 g of
ZnBr2/SiO2.
4.6. (2-methylphenyl)(5-propyl-2H-1,2,3-triazol-4-
yl)methanone (4j)
1H NMR (400 MHz, DMSO-d6):
d 7.66 (d, J = 7.7 Hz, 1H,
ArH), 7.20–7.45 (m, 3H, ArH), 2.61 (t, J = 7.7 Hz, 2H, CH2),
2.22 (s, 3H, CH3), 1.68 (m, 2H, CH2), 0.83 (t, J = 7.4 Hz, 3H,
CH3); 13C NMR (100 MHz, DMSO-d6):
d 185.02, 152.80,
141.77, 140.23, 137.33, 132.58, 132.43, 131.62, 125.76,
29.88, 20.64, 20.33, 13.67. IR (KBr): 3300 (NH), 2950, 1640
(C O), 1540, 1445, 1380, 1240, 840, 750 cmÀ1; Anal. Calcd
for C13H15N3O: C, 68.10; H, 6.59; N, 18.33; Found: C, 68.18;
H, 6.61; N, 18.35.
4.2. General procedure for the preparation of 4,5-
disubstituted 1,2,3-(NH)-triazoles (3a-n)
A
test-tube was charged with the acyl chloride
(1.2 mmol), a terminal alkyne (1.0 mmol), ZnBr2/SiO2
(0.1 g, 0.12 mmol), and DIPEA (1.2 mmol), and the mixture
was stirred at room temperature for 3 h under anhydrous
conditions. Upon completion of the coupling reaction
(monitored by TLC), sodium azide (1.2 mmol) in CH3CN/
H2O (3:1) (2 ml) was added and and the mixture was
heated at 50 8C with stirring for a further 3 h. After
completion of the reaction (monitored by TLC), the solvent
was evaporated and residue extracted with CH3CN.
Concentrating the solution gave the crude product which
was subjected to column chromatography using CHCl3–
CH3OH (98:2) as eluent to obtain an analytically pure
product. Characterization data for new compounds are
given below.
4.7. (4-chlorophenyl)(5-hexyl-2H-1,2,3-triazol-4-
yl)methanone (4k)
1H NMR (400 MHz, DMSO-d6):
d 7.82 (d, J = 8.3 Hz, 2H,
ArH), 7.35 (d, J = 8.3 Hz, 2H, ArH), 2.62 (t, J = 6.8 Hz, 2H,
CH2), 1.58 (m, 2H, CH2), 1.20 (m, 4H, 2CH2), 0.82 (t,
J = 6.4 Hz, 3H, CH3); 13C NMR (100 MHz, DMSO-d6):
187.26, 153.65, 142.00, 139.79, 134.48, 131.71, 128.93,
31.75, 30.85, 29.40, 27.52, 23.18, 14.13; IR (KBr): 3300
(NH), 2900, 1690 (C O), 1580, 1450, 1380, 1258,
750 cmÀ1; Anal. Calcd for C15H18ClN3O: C, 61.75; H,
6.22; N, 14.40; Found: C, 61.73; H, 6.23; N, 14.38.
d
4.8. (2,4-dichlorophenyl)(5-phenyl-2H-1,2,3-triazol-4-
4.3. (4-bromophenyl)(5-phenyl-2H-1,2,3-triazol-4-
yl)methanone (4m)
yl)methanone (4c)
1H NMR (400 MHz, DMSO-d6):
(d, J = 8.5 Hz, 2H, ArH), 7.68 (s, 1H, ArH), 7.57–7.26 (m, 5H,
ArH); 13C NMR (100 MHz, DMSO-d6):
185.92, 153.37,
138.65, 138.08, 134.48, 133.82, 131.00, 130.60, 130.45,
129.35, 128.45, 128.13, 127.54; IR (KBr): 3293 (NH), 2900,
1648 (C O), 1590, 1540, 1380, 1320, 820, 780 cmÀ1; Anal.
Calcd for C15H9Cl2N3O: C, 56.63; H, 2.85; N, 13.21; Found:
C, 56.65; H, 2.83; N, 13.22.
d 9.23 (s, 1H, NH), 8.14
1H NMR (400 MHz, CDCl3):
7.72 (d, J = 8.0 Hz, 2H, ArH), 7.67–7.47 (m, 5H, ArH), 5.77 (s,
1H, NH); 13C NMR (100 MHz, CDCl3):
188.52, 132.72,
132.41, 132.20, 131.56, 130.53, 130.00, 129.93, 129.62,
129.41, 128.60. IR (KBr): 3290 (NH), 1640 (C O), 1590,
1560, 1490, 740 cmÀ1; Anal. Calcd for C15H10BrN3O: C,
54.90; H, 3.07; N, 12.80; Found: C, 54.88; H, 3.13; N, 12.78.
d7.85 (d, J = 8.0 Hz, 2H, ArH),
d
d

A. Keivanloo et al. / C. R. Chimie 16 (2013) 239–243
243
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