Facile and quick synthesis of 1-monosubstituted aryl 1,2,3-triazoles: A copper-free [3+2] cycloaddition

Article abstract of DOI:10.1016/j.tet.2010.11.051

An efficient copper-free synthesis of 1-monosubstituted aryl 1,2,3-triazoles from sodium acetylide and aryl azides was developed, which was found suitable for various aryl azides and completed within 15 min at room temperature with moderate to excellent y

Full text of DOI:10.1016/j.tet.2010.11.051

Tetrahedron 67 (2011) 289e292
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Tetrahedron
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Facile and quick synthesis of 1-monosubstituted aryl 1,2,3-triazoles:
a copper-free [3þ2] cycloaddition
,
b
Yubo Jiang a, Chunxiang Kuang a , Qing Yang
*
a Department of Chemistry, Tongji University, Siping Road 1239, Shanghai 200092, China
b Department of Biochemistry, School of Life Sciences, Fudan University, Handan Road 220, Shanghai 200433, China
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient copper-free synthesis of 1-monosubstituted aryl 1,2,3-triazoles from sodium acetylide and
aryl azides was developed, which was found suitable for various aryl azides and completed within 15 min
at room temperature with moderate to excellent yields.
Received 16 September 2010
Received in revised form 6 November 2010
Accepted 12 November 2010
Available online 18 November 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Copper-free
1-Monosubstituted aryl 1,2,3-triazoles
Sodium acetylide
Aryl azides
Room temperature
1. Introduction
electron-deficient alkynes,12 and arynes,13 in which the reactivity of
the alkyne groups was increased,14 as shown in Fig 1.
Since the Huisgen 1,3-dipolar cycloaddition of azides and alkynes
was developed into the ‘click chemistry’ at the beginning of this
century,1 the significance of synthesis of 1,2,3-triazoles has increased
in medicinal,2 material,3 and biological4 research owing tothe unique
properties of this heterocycle. Recently, the utilization of 1,2,3-tri-
azoles in catalysts and ligands has also been reported.5 The fast
growing requirements of this heterocycle necessitate the
development of effective methods for the preparation of diverse
1,2,3-triazole derivatives. In addition, the procedure is commonly
performed in the presence of copper.6 With consideration on the
cytotoxicity of copper residue in particular cases,7 the processes in-
volvingdifferenttransitionmetals (Ru, Ni, Pd, Pt, and Fe) and different
ligands (PMDETA, bipyridine derivatives, terpyridine derivatives, and
Me6Tren) have also been examined in recent years.8 Acetylides, in-
cluding lithium and magnesium, were used for the preparation of
1,2,3-triazole under the copper-free conditions by Akimova et al. in
the 1960s.9 These methods, however, suffered from several draw-
backs: difficulty in preparing the 1-monosubstituted 1,2,3,-triazoles,
low yields (<30% for some substrates), and long reaction time (>72 h
in most cases). Recently, several metal catalyst-free azideealkyne
cycloadditions were reported to be used in the fields of biology and
material science. The reactions employed special kinds of alkyne
moieties, such as substituted cyclooctynes,10 activated alkynes,11
F
F
OEt
(OC)5W
Ph
R1
Substituted cyclooctynes
Activated akynes
O
TMS
R4
OR3
OTf
R2
Electron-deficient alkynes
Arynes
in situ
Fig. 1. Reported Alkynes in metal-catalyst free cycloaddition.
Although there are numerous methods for the preparation of 1,
4-disubstituted 1,2,3-triazoles, literature concerning the synthesis of
1-monosubstituted aryl 1,2,3-triazoles is relatively rare. One strategy
is the decarboxylation of triazoles bearing carboxylic acid sub-
stituent, which requires extreme temperature and long reaction
time.15 Another method is the [3þ2] cycloaddition of azides to
acetylene and its analogs under the conditions of heating and pres-
ence of copper catalyst.16aed,6j Recently, we have efficiently synthe-
sized a series of 1-monosubstituted aryl 1,2,3-triazoles utilizing
calcium carbide as a source of acetylene.16b Thus, for this study, we
report on the successful use of commercially available sodium ace-
tylide for the efficient and quick synthesis of 1-monosubstituted aryl
1,2,3-triazoles in the absence of coppercatalyst at room temperature.
* Corresponding author. Tel./fax: þ86 21 6598 3191; e-mail address: kuangcx@
tongji.edu.cn (C. Kuang).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.11.051

290
Y. Jiang et al. / Tetrahedron 67 (2011) 289e292
Table 2
2. Results and discussion
,
b
Copper-free quick synthesis of 1-monosubstituted aryl 1,2,3-triazolesa
N
To screen the suitable reaction conditions, 1-azido-4-methyl-
benzene 1a was used as model substrate with sodium acetylide.
Initially, non-toxic EtOH was employed as solvent at 80ꢀC. Forty
percent isolated yield was obtained when CuI and sodium ascor-
bate catalyst system was used while no product was observed in
the absence of catalyst (Table 1, entries 1 and 2). Moderate yields
were obtained at both room temperature and 80 ꢀC in the presence
of CuI catalyst when DMF was used as solvent (Table 1, entries 3 and
4). Surprisingly, the yield increased to 65% when the reaction was
conducted at room temperature without the use of catalyst (Table 1,
entry 5). Motivated by this result, we examined other solvents, such
as benzene, MeCN, MeCNeH2O mixture, and DMSO at room tem-
perature in the absence of CuI (Table 1, entries 6e9). DMSO showed
more vigorous compared with the others and achieved a significant
yield of 70%. Moreover, the system is highly efficient and completed
the process within 15 min (Table 1, entry 9). Excellent yield of 81%
was achieved when the quantity of sodium acetylide was increased
to 6 equiv (Table 1, entry 10). Seemingly, increase in temperature, or
use CuI were not necessary (Table 1, entry 11 and 12).
N
N
Ar N3
1
+
Na
Ar
DMSO, r.t., 15 min
2
Product 2
Yieldb(%)
81
Product 2
Yieldb(%)
93
N
N
N
N
N
N
2a
2k
Cl
N
N
N
N
N
Cl
N
2l
2b
88
55
58
75
N
N
N
N
N
N
N
N
Cl
F
N
2m
2c
N
N
N
N
Under the optimized conditions, the substrate scope of the
copper-free quick synthesis of 1-monosubstituted aryl 1,2,3-tri-
azoles was investigated and the conditions appeared to be gener-
ally similar for a spectrum of aryl azides (Table 2).
2n
2d
75
93
90
68
82
75
96
81
73
83
Br
Br
N
N
N
N
N
2e
O
2o
2p
2q
Table 1
Optimization of copper-free cycloaddition of 1a with sodium acetylidea
N
N
N
N
N
N
N
N3
N
Conditions
+
Na
2f
F3C
N
1a
2a
O
Entry
Solvent
Temp
Catalyst
Time
Yieldb (%)
N
N
N
N
N
1c
2
3
4
5
EtOH
EtOH
DMF
DMF
DMF
Toluene
MeCN
MeCN/H2O
DMSO
DMSO
DMSO
80 ꢀC
80 ꢀC
80 ꢀC
rt
rt
rt
d
12 h
4 h
4 h
6 h
6 h
8 h
8 h
8 h
15 min
15 min
15 min
15 min
0
2g
H2N
O2N
N
CuI(20%)
CuI(20%)
CuI(20%)
d
40
50
55
65
20
46
0
70
81
48
66
N
N
N
N
N
2h
N
2r
6
d
7
rt
rt
rt
rt
d
8c
9
d
Et2N
F
H2NO2S
d
10d
11
12
d
N
N
N
N
N
N
80 ꢀC
rt
d
2i
72
75
52
2s
DMSO
CuI(20%)
The significant of bold value is the optimized conditions.
a
Unless otherwise noted, the reaction conditions are as follows: 1-azido-4-
N
methylbenzene 1a (0.3 mmol), sodium acetylide (4 equiv), in solvent (3 mL).
N
b
Isolated yield.
Compound 1a was recovered.
Sodium acetylide (6 equiv) was used.
2j
N
c
d
Cl
a
It was observed that aryl azides carrying either an electron
donating substituent, such as methyl (Table 2, 2aec), methoxyl
(2eef), and amino-group (2geh), or an electron withdrawing group
including halogens (2ieo), trifluoromethyl (2p), nitryl (2q), and
sulfonamide (2r) could perform efficiently with moderate to ex-
cellent yields. Higher yields were obtained when the substrates had
a substituent at meta-position whether it was electron donating or
electron withdrawing (2b, 2e, 2k). Aryl azides bearing an ortho-
group could also complete the process within 15 min at room
temperature. However, the yield was lower (2c, 2l, 2s).
Reaction conditions: azides 1 (0.3 mmol), sodium acetylide (6 equiv), DMSO
(3 mL), rt.
b
Isolated yield.
It is believed that the reactivity of the alkynes group is increased
in the copper-free azideealkyne cycloadditions,14 although there is
minimal information available in literature about the mechanism.
In this case, the alkyne group in sodium acetylide is seemingly
activated in the system, allowing copper-free azideealkyne cyclo-
additions to occur with high efficiency at room temperature. Nev-
ertheless, the exact mechanism remains unknown. Owing to this,
further studies on the reaction mechanism are ongoing.
Compared to the other acetylides9 used in copper-free [3þ2]
cycloaddition, which have been reported, this system is easier to
manipulate and showed higher efficiency. The reactions can be
completed within 15 min and can produce the 1-monosubstitued
1,2,3-triazoles, which are not as easy to synthesize as the 1,4-
disubstituted 1,2,3-triazoles.
3. Conclusion
We have demonstrated copper-free azideealkyne cycloaddi-
tions, which showed high efficiency and speed; the process was

Y. Jiang et al. / Tetrahedron 67 (2011) 289e292
291
completed within 15 min at room temperature with moderate to
excellent yields. It provides a quick access to 1-monosubstitued aryl
1,2,3-triazoles, which are important kinds of heterocycle com-
pounds for medical, material, and biological research.
1H), 7.14e7.13 (m, 1H), 7.03e7.01 (m, 1H), 6.74e6.72 (m, 1H), 3.95
(s, 2H).18a
4.2.8. N,N-Diethyl-4-(1H-1,2,3-triazol-1-yl)aniline (2h). 1H NMR
(500 MHz, CDCl3)
d
7.85 (s, 1H), 7.78 (s, 1H), 7.50 (d, J¼9.0 Hz, 2H),
6.72 (d, J¼9.0 Hz, 2H), 3.39 (q, J¼7.1, 7.1, 7.0 Hz, 4H), 1.19 (t, J¼7.1,
7.1 Hz, 6H); 13C NMR (125 MHz, CDCl3): 148.0, 133.8, 125.8, 122.3,
121.6, 111.6, 44.5, 12. 4; ESI-MS: m/z (%)¼216 (Mþ, 100); HRMS calcd
for [MþH]þ: C12H17N4 217.2896, found: 217.2898.
4. Experimental
4.1. General
4.2.9. 1-(4-Fluorophenyl)-1H-1,2,3-triazole (2i). 1H NMR (500 MHz,
All commercially available reagents and solvent were obtained
from the commercial providers and used without further purifi-
cation. 1H NMR and 13C NMR spectra were recorded using a
Bruker AM-500 MHz spectrometer. Chemical shifts were reported
CDCl3)
d
7.95 (d, J¼1.0 Hz, 1H), 7.86 (d, J¼1.0 Hz, 1H), 7.75e7.71 (m,
2H), 7.25e7.21 (m, 2H).16b
relative to internal tetramethylsilane (
d
0.00 ppm) for 1H, and
4.2.10. 1-(4-Chlorophenyl)-1H-1,2,3-triazole (2j). 1H NMR (500 MHz,
CDCl3 (
d
77.0 ppm) for 13C. MS data were measured with a Varian-
CDCl3)
d
7.98 (s, 1H), 7.86 (s, 1H), 7.71 (d, J¼8.8 Hz, 2H), 7.52 (d,
J¼8.7 Hz, 2H).16b
310 mass spectrometer. High resolution mass spectra were de-
termined using a Finnigan-NAT GC/MS/DS 8430 spectrometer.
Flash column chromatography was performed on 300e400 mesh
silica gel. Aryl azides were prepared according to procedures in
literature.17
4.2.11. 1-(3-Chlorophenyl)-1H-1,2,3-triazole (2k). 1H NMR (500 MHz,
CDCl3)
d
8.00 (d, J¼0.9 Hz, 1H), 7.87 (d, J¼0.9 Hz, 1H), 7.81e7.80 (m,
1H), 7.68e7.66 (m, 1H), 7.50e7.47 (m, 1H), 7.45e7.43 (m, 1H).16a
4.2. General procedure for synthesis of 1-monosubstituted
aryl 1,2,3-triazoles 2
4.2.12. 1-(2-Chlorophenyl)-1H-1,2,3-triazole (2l). 1H NMR (500 MHz,
CDCl3)
2H).16b
d 8.03 (s, 1H), 7.87 (s, 1H), 7.63e7.57(m, 2H), 7.48e7.44(m,
DMSO (3 mL) and aryl azide 1 (0.3 mmol) were added to
a round-bottomed flask. (CAUTION! Aryl azides are poisonous and
potentially explosive due to heat, light, and pressure. Any azides
synthesized should be stored below 0 ꢀC and in the dark.) The flask
was equipped with a rubber septa and sodium acetylide (1.8 mmol,
18 wt % suspension in xylene) was subsequently added to the
system via syringe. (CAUTION! Sodium acetylide is moisture sen-
sitive and all apparatus should be dried thoroughly before use.)
After stirring the mixture for 15 min at room temperature, the re-
action was quenched with the addition of 20 mL water. The mixture
was extracted with ether (25 mL, three times) and the combined
organic layer was washed with water, and dried over MgSO4. The
solvent was evaporated and the crude product was purified by silica
gel column chromatography to derive 1-monosubstituted aryl
1,2,3-triazoles 2 as products.
4.2.13. 1-(3-Chloro-4-fluorophenyl)-1H-1,2,3-triazole (2m). 1H NMR
(500 MHz, CDCl3)
d 7.96 (s, 1H), 7.87e7.87(m, 2H), 7.66e7.33 (m,
1H), 7.34e7.31 (m, 1H).18b
4.2.14. 1-(4-Bromophenyl)-1H-1,2,3-triazole (2n). 1H NMR (500
MHz, CDCl3)
d
7.98 (s, 1H), 7.87 (s, 1H), 7.69e7.64(m, 4H).16a
4.2.15. 1-(3-Bromophenyl)-1H-1,2,3-triazole (2o). 1H NMR (500
MHz, CDCl3) d 8.00 (s, 1H), 7.96e7.95 (m, 1H), 7.86 (s, 1H), 7.72e7.70
(m, 1H), 7.59 (d, J¼8.0 Hz, 1H), 7.43e7.40 (m, 1H).16a
4.2.16. 1-(3-(Trifluoromethyl)phenyl)-1H-1,2,3-triazole
(2p). 1H
NMR (500 MHz, CDCl3)
d
8.09 (s, 1H), 8.05 (s, 1H), 7.99 (d, J¼7.6 Hz,
1H), 7.73e7.68 (m, 2H).18b
4.2.1. 1-p-Tolyl-1H-1,2,3-triazole (2a). 1H NMR (500 MHz, CDCl3)
4.2.17. 1-(3-Nitrophenyl)-1H-1,2,3-triazole (2q). 1H NMR (500 MHz,
d
7.96 (d, J¼0.9 Hz, 1H), 7.83 (d, J¼0.9 Hz, 1H), 7.62 (d, J¼8.4 Hz, 1H),
CDCl3) d 8.62e8.61 (m, 1H), 8.34e8.32 (m, 1H), 8.23e8.21 (m, 1H),
7.32 (d, J¼8.6 Hz, 1H), 2.43 (s, 3H).16b
8.13 (d, J¼1.1 Hz, 1H), 7.93 (d, J¼1.1 Hz, 1H), 7.79e7.76 (m, 1H).16a
4.2.2. 1-m-Tolyl-1H-1,2,3-triazole (2b). 1H NMR (500 MHz, CDCl3)
4.2.18. 4-(1H-1,2,3-Triazol-1-yl)benzenesulfonamide (2r). 1H NMR
d
7.98 (s, 1H), 7.85 (s, 1H), 7.59 (s, 1H), 7.52 (d, J¼8.1 Hz, 1H), 7.41 (t,
(500 MHz, DMSO-d6)
d
8.93 (s,1H), 8.14 (d, J¼8.5 Hz, 2H), 8.04e8.03
J¼7.8, 7.8 Hz, 1H), 7.26 (d, J¼6.8 Hz, 1H), 2.46 (s, 3H).16a
(m, 3H), 7.55 (s, 2H).16b
4.2.3. 1-o-Tolyl-1H-1,2,3-triazole (2c). 1H NMR (500 MHz, CDCl3)
d
4.2.19. 1-(Naphthalen-1-yl)-1H-1,2,3-triazole(2s). 1H NMR(500 MHz,
CDCl3)
8.06e8.02 (m, 1H), 7.98e7.96 (m, 3H), 7.62e7.53 (m, 5H).18c
7.87 (s, 1H), 7.76 (s, 1H), 7.44e7.31(m, 4H), 2.21 (s, 3H).16b
d
4.2.4. 1-Phenyl-1H-1,2,3-triazole (2d). 1H NMR (500 MHz, CDCl3)
Acknowledgements
d
8.00 (d, J¼0.9 Hz, 1H), 7.86 (d, J¼0.9 Hz, 1H), 7.76e7.75 (m, 2H),
7.57e7.53 (m, 2H), 7.47e7.44 (m, 1H).16b
We gratefully acknowledge the valuable support from the
Natural Science Foundation of China (No. 30873153), the Key Pro-
jects of Shanghai in Biomedical (No. 08431902700), and the Sci-
entific Research Foundation of the State Education Ministry for the
Returned Overseas Chinese Scholars. We would like to thank the
Center of Tongji University for the Instrumental Analysis.
4.2.5. 1-(3-Methoxyphenyl)-1H-1,2,3-triazole (2e). 1H NMR (500
MHz, CDCl3) d 8.00 (s, 1H), 7.84 (s, 1H), 7.43e7.36(m, 2H), 7.27e7.26
(m, 1H), 6.9e6.97 (m, 1H), 3.88 (s, 3H).6j
4.2.6. 1-(4-Methoxyphenyl)-1H-1,2,3-triazole (2f). 1H NMR (500
MHz, CDCl3)
d
7.91 (s, 1H), 7.83 (s, 1H), 7.64 (d, J¼9.0 Hz, 2H), 7.03 (d,
J¼9.0 Hz, 1H), 3.88 (s, 3H).16a
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d
7.95 (d, J¼1.1 Hz, 1H), 7.82 (d, J¼1.0 Hz, 1H), 7.29e7.27 (m,

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