Green synthesis of 1-monosubstituted 1,2,3-triazoles via 'click chemistry' in water

Article abstract of DOI:10.1515/hc-2013-0151

The copper-catalyzed click reaction of organic azides with acetylene gas to give 1,2,3-triazoles using water as solvent was studied. The best yields are obtained in the presence of 10 mol% of CuI and 20 mol% of Et₃N. Several 1-substituted triaz

Full text of DOI:10.1515/hc-2013-0151

ꢁꢁꢁꢂ
ꢀHeterocycl. Commun. 2013; 19(6): 397–400
DOI 10.1515/hc-2013-0151ꢀ
Luyong Wu*, Bo Yan, Guo Yang and Yuxue Chen
Green synthesis of 1-monosubstituted
1,2,3-triazoles via ‘click chemistry’ in water
Abstract: The copper-catalyzed click reaction of organic trimethylsilyl acetylene [17], calcium carbide [18–20],
azides with acetylene gas to give 1,2,3-triazoles using and sodium acetylide [21]. Although good results have
water as solvent was studied. The best yields are obtained been achieved, organic solvents are necessary in these
in the presence of 10 mol% of CuI and 20 mol% of Et3N. preparations. Influenced by increasing environmental
Several 1-substituted triazoles were prepared in the yields consciousness, the use of water as a green medium has
of 29–96%.
attracted considerable attention in chemical society in the
past decades [22–24]. It is fascinating to establish novel
Keywords: azide; click chemistry; green chemistry; methods for the synthesis of 1-monosubstituted 1,2,3-tri-
1,2,3-triazole.
azoles via a green process (for the selected examples for
click reaction in water, see [25–33]). Herein, we wish to
report an efficient and green synthesis method of 1,2,3-tri-
azoles from organic azides with acetylene gas in water
under CuI catalysis.
*Corresponding author: Luyong Wu, College of Chemistry and
Chemical Engineering, Hainan Normal University, No. 99, Longkun
South Road, 571158 Haikou, P.R. China,
e-mail: wuluyong@hainnu.edu.cn
Bo Yan, Guo Yang and Yuxue Chen: College of Chemistry and
Chemical Engineering, Hainan Normal University, No. 99, Longkun
South Road, 571158 Haikou, P.R. China
Results and discussion
In continuation of our previous research [16] and taking
into account other reports on the CuAAC reaction [6–8],
the initial studies were conducted using phenyl azide (1a,
1.0 mmol), water (1 mL), base (0.2 mmol), and Cu(I) salt
(0.1 mmol) under the atmosphere of acetylene (1 atm) at
Introduction
1,2,3-Triazoles exhibit important biological activities such room temperature for 24 h, as shown in Scheme 1.
as antiviral, antibacterial, antiepileptic, and antiallergic Previously, our group and the Kuang group found that
behaviors and are important industrial compounds. Their high water content in organic solvents was disadvanta-
synthetic strategies have received broad attention [1, 2]. In geous in the click chemistry of organic azide with acety-
numerous methods, thermal 1,3-dipolar cycloaddition of lene gas or calcium carbide. Surprisingly, the reaction of
azides and alkynes is the most utilitarian one [3]. However, Scheme 1 underwent smoothly and afforded the desired
elevated temperature and long reaction time are obligatory triazole 2a in 90% yield in the presence of 10 mol% of CuI
in the thermal cycloaddition. In 2002, the Meldal group [4] and 20 mol% of Et3N. Encouraged by this positive result,
and the Sharpless group [5] independently reported Cu(I)- optimization of the reaction conditions was carried out
catalyzed azide-alkyne cycloaddition (CuAAC) reaction to using different amines. Et3N proved to be the best cata-
construct 1,4-disubstituted 1,2,3-triazoles. Because of its lyst, and in the absence of Et3N the yield decreased to
mild conditions, high yield and high regioselectivity, the 29%. Subsequently, when Et3N was dosed to 10 mol%, the
CuAAC reaction has become the most widely used reac- yield increased to 69%. Many different nitrogen-contain-
tion in ‘click chemistry’ [6–8].
ing bases were employed in the dosage of 20 mol%. No
1-Monosubstituted 1,2,3-triazoles play an important significant difference was observed when 2,6-lutidine or
role in some biologically active molecules [9–13] and iPr2EtN was used as the base. When changing to pyridine,
such molecules are normally synthesized by high-tem- NH3‧H2O, Et2NH, and ethane-1,2-diamine as the base, 2a
perature cycloaddition reaction [14, 15]. It is an attractive was obtained in 63%, 82%, 85%, and 29% yield, respec-
research to develop milder conditions for the synthesis. tively. In further studies, we chose 20 mol% Et3N as the
Recently, several groups have focused on the synthesis standard base. Different commercially available and inex-
of 1-monosubstituted triazoles via click chemistry from pensive copper(I) salts such as CuCl and CuBr were used
acetylene gas [16] or some acetylenic surrogates such as for the reaction, and the results showed that CuCl and
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ꢀL. Wu et al.: Green synthesis of 1-monosubstituted 1,2,3-triazoles
N3
CuI, base
N
Conclusion
N
HC CH
(1 atm)
N
H2O, rt, 24 h
In summary, the CuAAC reaction of organic azides with
acetylene gas using water as solvent was developed. The
use of 10 mol% CuI with 20 mol% Et3N catalyzed the click
reaction with good results. This green process provides a
simple and practical method to synthesize 1-substituted
1,2,3-triazoles.
1a
2a
Scheme 1ꢀ
CuBr exhibited relatively low activity as catalysts. When
the dosage of CuI was reduced to 5 mol%, the reaction
yield decreased considerably to 75%. Without CuI as a
catalyst, no desired product was observed. The reaction
under solvent-free conditions with 10 mol% of CuI and 20
mol% of Et3N yielded 73% of 2a.
Experimental
Under the optimized conditions, a variety of azides
were employed to demonstrate the efficiency and gener-
ality of this green process on a 1.0 mmol scale. As sum-
marized in Scheme 2, both aryl azides and alkyl azides
were successfully examined. In general, the reactions of
electron-rich and electron-poor aromatic azides proceed
efficiently in good to excellent yields except the aromatic
azides bearing ortho-substituents. Compared with other
click processes in organic solvents [16, 18–20], it was
found that the efficiency of this green process in water is
slightly lower or equivalent to that of the former processes.
The desired triazole 2k was not obtained in the attempted
reaction of p-nitrophenyl azide, for which heterogeneous
conditions were observed. However, the triazole 2k was
synthesized in 78% yield after a small amount of toluene
(0.8 mmol) was added to make a homogeneous solution.
Under the same conditions, triazole 2l was obtained from
3-azidobenzonitrile in 95% yield. Benzyl derivative 2n and
octyl derivative 2o were obtained in 67% and 41% yields,
respectively, when using water as solvent.
Melting points were measured using a Beijing-Taike X-4 apparatus
without correction. NMR spectra were recorded on Bruker DRX-400
spectrometer (400 MHz for 1H and 100 MHz for 13C). IR analyses were
performed with a Bruker FT-IR spectrophotometer. Elemental analy-
ses were performed at Midwest Microlabs. Column chromatography
was carried out on silica gel (200–300 mesh). All azides 1a–o were
prepared from arylamines [34] or organic bromides [35] according to
the literature procedures.
General procedure for synthesis
of 1,2,3-triazoles 2a–o
To a flask equipped with a stirring bar, azide (1.0 mmol), Et3N (0.2
mmol), water (1 mL), and CuI (0.1 mmol) were added successively.
Afer the atmosphere was excluded using a vacuum pump, acety-
lene gas was introduced from a balloon and the mixture was stirred
at room temperature for 24 h. Afer completion of the reaction, ethyl
acetate (25 mL) was added to dissolve the product and the mixture
was washed with brine (10 mL). The organic layer was dried over
anhydrous Na2SO4 and filtered. Afer the solvent was removed under
reduced pressure, the residue was purified by flash chromatogra-
phy to give the 1,2,3-triazole product. Warning: organic azides are
potentially explosive substances and should be handled with great
care.
CuI, 10 mol%
N
R
Et3N, 20 mol%
N
N
RN3
HC CH
H2O, rt, 1 atm, 24 h
1-Phenyl-1H-1,2,3-triazole (2a)ꢀYield 90% (lit. [18] yield 85%);
white solid; mp 52–53°C (lit. [16] mp 52–53°C); 1H NMR (CDCl3): δ
8.04 (s, 1H), 7.82 (s, 1H), 7.73 (d, J ꢀ= ꢀ 8.0 Hz, 2H), 7.52 (m, 3H); 13C NMR
(CDCl3): δ 136.8, 134.2, 129.5, 128.5, 121.7, 120.4.
1
2
R =
yield%
R =
yield%
86
2a
)
90
85
29
2i
3-ClC6H4 ( )
Ph (
4-MeC6H4 (2b)
2-MeC6H4 (2c)
4-EtOCOC6H4 (2j)
4-NO2C6H4 (2k)a
96
1-p-Tolyl-1H-1,2,3-triazole (2b)ꢀYield 85% (lit. [18] yield 88%);
78
1
white solid; mp 85–86°C (lit. [16] mp 86°C); H NMR (CDCl3): δ 7.98
a
2d
82
95
4-MeOC6H4 (
)
2l
3-CNC6H4 (
)
(s, 1H), 7.82 (s, 1H), 7.61 (d, J ꢀ= ꢀ 8.4 Hz, 2H), 7.30 (d, J ꢀ= ꢀ 8.0 Hz, 2H), 2.41
(s, 3H); 13C NMR (CDCl3): δ 138.8, 134.7, 134.3, 130.2, 121.7, 120.5, 21.0.
4-ClC6H4 (2e)
86
54
86
84
2-HOC6H4 (2m)
40
67
41
2f
2n
Bn ( )
2-ClC6H4 (
)
1-o-Tolyl-1H-1,2,3-triazole (2c)ꢀYield 29% (lit. [16] yield 45%); yel-
2g
2o
1-octyl ( )
3-MeC6H4 (
)
1
low oil; H NMR (CDCl3): δ 7.85 (s, 1H), 7.78 (s, 1H), 7.39 (m, 4H), 2.20
2h
4-BrC6H4 (
)
(s, 3H); 13C NMR (CDCl3): δ 136.3, 133.6, 133.5, 131.4, 129.8, 126.7, 125.9,
125.0, 17.7.
a0.8 mmol toluene was added to homogenize the mixture,
otherwise the corresponding triazole was not observed
1-(4-Methoxyphenyl)-1H-1,2,3-triazole (2d)ꢀYield 82% (lit.
[19] yield 64%); white solid; mp 77–79°C (lit.[16] mp 78–80°C); 1H
NMR (CDCl3): δ 7.98 (s, 1H), 7.80 (s, 1H), 7.62 (d, J ꢀ= ꢀ 7.6 Hz, 2H), 6.99
Scheme 2ꢀThe synthesis of different triazoles under the optimal
conditions in water.
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(d, J ꢀ= ꢀ 7.6 Hz, 2H), 3.83 (s, 3H); 13C NMR (CDCl3): δ 159.4, 133.9, 130.0, (DMSO-d6): δ 9.06 (s, 1H), 8.47 (d, J ꢀ= ꢀ 8.8 Hz, 2H), 8.25 (d, J ꢀ= ꢀ 8.8 Hz,
121.9, 121.7, 114.4, 55.3.
2H), 8.01 (s, 1H); 13C NMR (DMSO-d6): δ 146.6, 140.9, 135.0, 125.5, 123.8,
120.6.
1-(4-Chlorophenyl)-1H-1,2,3-triazole (2e)ꢀYield 86% (lit. [16] yield
92%); pale yellow solid; mp 111–113°C (lit. [16] mp 111–113°C); 1H NMR 3-(1H-1,2,3-triazol-1-yl)benzonitrile (2l)ꢀYield 95%; pale yellow
(CDCl3): δ 7.98 (s, 1H), 7.85 (s, 1H), 7.80 (d, J ꢀ= ꢀ 7.6 Hz, 2H), 7.50 (d, J ꢀ= ꢀ 7.6 solid; mp 130.5–132°C; 1H NMR (CDCl3): δ 8.08 (s, 2H), 8.05 (d, J ꢀ= ꢀ 8.0
Hz, 2H); 13C NMR (CDCl3): δ 135.5, 134.6, 134.5, 129.9, 121.8, 121.6.
Hz, 1H), 7.89 (s, 1H), 7.73 (d, J ꢀ= ꢀ 7.2 Hz, 1H), 7.68 (dd, J ꢀ= ꢀ 7.6 Hz, 1H); 13
C
NMR (CDCl3): δ 137.5, 132.0, 130.9, 124.6, 123.7, 121.6, 114.1. Anal. Calcd
1-(2-Chlorophenyl)-1H-1,2,3-triazole (2f)ꢀYield 54% (lit. [16] yield for C9H6N4: C, 63.52; H, 3.55; N, 23.92. Found: C, 63.55; H, 3.52; N, 23.89.
54%); yellow oil; 1H NMR (CDCl3): δ 8.02 (s, 1H), 7.87 (s, 1H), 7.68–7.60 IR (KBr, cm-1): 3107, 2098, 1601, 1457, 1215.
(m, 2H), 7.50 (m, 2H); 13C NMR (CDCl3): δ 134.8, 133.5, 130.7, 128.6, 127.9,
127.8, 125.6.
2-(1H-1,2,3-triazol-1-yl)phenol (2m)ꢀYield 40%; pale reddish solid;
mp 150–151°C; 1H NMR (CDCl3): δ 9.86 (s, 1H), 8.13 (s, 1H), 7.91 (s, 1H),
1-m-Tolyl-1H-1,2,3-triazole (2g)ꢀYield 86% (lit. [16] yield 93%); yel- 7.43 (d, J ꢀ= ꢀ 8.0 Hz, 1H), 7.33 (t, J ꢀ= ꢀ 7.6 Hz, 1H), 7.21(d, J ꢀ= ꢀ 8.0 Hz, 1H),
low oil; 1H NMR (CDCl3): δ 8.00 (s, 1H), 7.80 (m, 1H), 7.57 (s, 1H), 7.50 (s, 7.01(t, J ꢀ= ꢀ 7.6 Hz, 1H); 13C NMR (DMSO-d6): 149.3, 133.8, 129.8, 122.7,
1H), 7.38 (d, J ꢀ= ꢀ 7.2 Hz, 1H), 7.23 (s, 1H), 2.43 (s, 3H); 13C NMR (CDCl3): δ 121.6, 120.3, 119.6, 119.5; IR (KBr, cm-1): 3436, 3125, 1643, 1397, 1044.
139.8, 136.8, 134.2, 129.4, 121.7, 121.1, 117.5, 21.2.
Anal. Calcd for C8H7N3O: C, 59.62; H, 4.38; N, 26.07. Found: C,
59.68; H, 4.34; N, 26.04.
1-(4-Bromophenyl)-1H-1,2,3-triazole (2h)ꢀYield 84% (lit. [16] yield
89%); white solid; mp 145–146°C (lit.[16] mp 145–146°C); 1H NMR 1-Benzyl-1H-1,2,3-triazoleꢀ(2n) Yield 67% (lit. [16] yield 85%);
(CDCl3): δ 7.98 (s, 1H), 7.85 (s, 1H), 7.73–7.65 (m, 4H); 13C NMR (CDCl3): δ white solid; mp 51–53°C (lit. [16] mp 51–53°C); 1H NMR (CDCl3): δ 7.68
136.0, 134.7, 132.9, 122.4, 122.0, 121.5.
(s, 1H), 7.50 (s, 1H), 7.34 (m, 3H), 7.26 (m, 2H), 5.55 (s, 2H); 13C NMR
(CDCl3): 134.6, 134.0, 128.9, 127.8, 128.5, 123.3, 53.7.
1-(3-Chlorophenyl)-1H-1,2,3-triazole (2i)ꢀYield 86% (lit. [16] yield
1
93%); pale yellow solid; mp 91–93°C (lit.[16] mp 91–93°C); H NMR 1-Octyl-1H-1,2,3-triazoleꢀ(2o) Yield 41% (lit. [16] yield 97%); pale
1
(CDCl3): δ 8.02 (s, 1H), 7.87 (s, 1H), 7.80 (s, 1H), 7.66 (d, J ꢀ= ꢀ 7.6 Hz, 1H), yellow oil (lit. [16] mp 18–20°C); H NMR (CDCl3): δ 7.71 (s, 1H), 7.56
7.52–7.40 (m, 2H); 13C NMR (CDCl3): δ 137.8, 135.6, 134.7, 130.8, 128.8, (s, 1H), 4.39 (t, J ꢀ= ꢀ 7.2 Hz, 2H), 1.91 (t, J ꢀ= ꢀ 6.4 Hz, 2H), 1.27 (m, 10H),
121.6, 120.9, 118.6.
0.85(t, J ꢀ= ꢀ 6.4 Hz, 3H). 13C NMR (CDCl3): δ 133.7, 123.1, 50.1, 31.6, 30.3,
29.0, 28.9, 26.4, 22.5, 14.0.
Ethyl 4-(1H-1,2,3-triazol-1-yl)benzoate (2j)ꢀYield 96% (lit. [16]
yield 90%); yellow solid; mp 94–96°C (lit.[16] mp 94–96°C); 1H NMR
(CDCl3): δ 8.22 (d, J ꢀ= ꢀ 7.6 Hz, 2H), 8.10 (s, 1H), 7.87 (d, J ꢀ= ꢀ 9.6 Hz, 3H),
4.42 (q, J ꢀ= ꢀ 6.8 Hz, 2H), 1.43 (t, J ꢀ= ꢀ 6.8 Hz, 3H); 13C NMR (CDCl3): δ 165.4,
139.9, 134.8, 131.3, 130.6, 121.6, 119.9, 61.4, 14.3.
Acknowledgments: The authors are grateful for the sup-
port of the Natural Science Foundation of Hainan Prov-
ince (No. 211017).
1-(4-Nitrophenyl)-1H-1,2,3-triazole (2k)ꢀYield 78% (lit. [16] yield
1
91%); yellow solid; mp 202–205°C (lit.[16] mp 202–205°C); H NMR Received May 12, 2013; accepted September 12, 2013
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