AgN(CN)2/DIPEA/H2O-EG: a highly efficient catalytic system for synthesis of 1,4-disubstituted-1,2,3 triazoles at room temperature

Article abstract of DOI:10.1016/j.tetlet.2015.09.025

A novel, efficient and robust method for silver-catalyzed azide-alkyne cycloaddition (AgAAC) reactions in H₂O/Ethylene glycol (EG) at room temperature has been developed. The protocol addresses silver dicyanamide/DIPEA as a highly effective cat

Full text of DOI:10.1016/j.tetlet.2015.09.025

Accepted Manuscript
AgN(CN) /DIPEA/H O-EG: A highly efficient catalytic system for synthesis of
2
2
1
,4-disubstituted-1,2,3 triazoles at room temperature
Abdul Aziz Ali, Mitali Chetia, Bishwajit Saikia, Prakash J. Saikia, Diganta
Sarma
PII:
S0040-4039(15)30067-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.09.025
TETL 46697
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
10 August 2015
5 September 2015
7 September 2015
Please cite this article as: Ali, A.A., Chetia, M., Saikia, B., Saikia, P.J., Sarma, D., AgN(CN) /DIPEA/H O-EG: A
2
2
highly efficient catalytic system for synthesis of 1,4-disubstituted-1,2,3 triazoles at room temperature, Tetrahedron
Letters (2015), doi: http://dx.doi.org/10.1016/j.tetlet.2015.09.025
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AgN(CN)
2
/DIPEA/H
2
O-EG: a highly
Leave this area blank for abstract info.
efficient catalytic system for synthesis of 1,4-
disubstituted-1,2,3 triazoles at room
temperature
a
a
a
b
a
Abdul Aziz Ali, Mitali Chetia, Bishwajit Saikia, Prakash J. Saikia, and Diganta Sarma*
a
Department of Chemistry, Dibrugarh University, Dibrugarh-786004, Assam, INDIA.
b
Analytical Chemistry Division, CSIR-North East Institute of Science and Technology, Jorhat-785006, Assam, INDIA.
N
AgN(CN) , DIPEA
R
2
N
N
R N3
R'
H O/EG, rt
2
R'

1
Tetrahedron Letters
AgN(CN) /DIPEA/H O-EG: A highly efficient catalytic system for synthesis of 1,4-
2
2
disubstituted-1,2,3 triazoles at room temperature
a
a
a
b
a
Abdul Aziz Ali, Mitali Chetia, Bishwajit Saikia, Prakash J. Saikia, and Diganta Sarma*
a
Department of Chemistry, Dibrugarh University, Dibrugarh-786004, Assam, INDIA.
b
Analytical Chemistry Division, CSIR-North East Institute of Science and Technology, Jorhat-785006, Assam, INDIA.
ARTICLE INFO
ABSTRACT
Article history:
Received
A novel, efficient and robust method for silver-catalyzed azide–alkyne cycloaddition (AgAAC)
reactions in H O/Ethylene glycol (EG) at room temperature has been developed. The protocol
2
Received in revised form
Accepted
addresses silver dicyanamide/DIPEA as a highly effective catalyst system for the regioselective
formation of 1,4-disubstituted-1,2,3 triazoles under mild conditions.
Available online
2
009 Elsevier Ltd. All rights reserved.
Keywords:
Silver
Alkyne
Azide
Click chemistry
1
,4-disubstituted-1,2,3 triazoles
In recent years, 1,2,3-triazole compounds have received
Perhaps the most useful and powerful procedure for the
synthesis of 1,2,3-triazoles is the Huisgen 1,3-dipolar
cycloaddition of organic azides with acetylene. However, the
enhanced considerable attention due to their spacious range of
1
3
applications in organic and medicinal chemistry. Some of these
classes of drug molecules, now available in the market or in the
final stage of clinical trials, include the anticancer compound
carboxyamidotriazole (CAI), the nucleoside derivative non-
conventional thermal conditions normally require high
temperature and proceed with limited regioselectivity. The
copper-catalyzed version of Huisgen 1,3-dipolar azide-alkyne
cycloaddition (CuAAC), reported independently by the groups of
nucloside
reverse
transcriptase
inhibitor
tert-
4
5
butyldimethylsilylspiroaminooxathioledioxide
(known
as
Sharpless and Meldal in 2002, is generally recognized as the
most prime example of click chemistry. The Cu (I)- catalyzed
azide-alkyne cycloaddition (CuAAC) reaction is an important
advance in the chemistry of 1,2,3-triazoles because of its 100%
atom economy, exclusive regioselectivity (1,4-disubstituted
TSAO), β-lactum antibiotic Tazobactum, the cephalosporine
2
Cefatrizine and so on (Scheme 1). Consequently, the
development of straightforward and efficient approach for the
construction of 1,2,3-triazoles is likely to be enormously
demanded.
6
regioisomer), wide substrate scope and mild reaction conditions.
Nevertheless, the scope of triazole chemistry is not confined to
drug discovery, there are a growing number of applications in
numerous other areas of modern chemical sciences, such as
O
N
N
NH2
H2N
H2N
N
N
7
TBSO
N
O
biological science, polymer science, and material chemistry. In
O
N
comparison to copper, silver-based catalysts seemed to be less
Cl
OTBS
8
O
effective; only recently, several Ag (I)-catalyzed azide-alkyne
S
O
9
O
O
cycloaddition reactions have been reported for the synthesis of
Cl
1,4- disubstituted-1,2,3 triazoles which is still considered a
TSAO
challenge in the silver catalysis. Especially, Cu free catalyst
systems that allow for alternative azide-alkyne cycloaddition to
Cl
1
0
CAI
take place efficiently are of great value due to cytotoxic nature
of redox active copper (I) which prevents the use of CuAAC
NH2
11
H
COOH
CH3
H
N
O
S
reaction in living biological systems. The advantage of silver
N
N
catalysis for the avoidance of the Glaser–Hay coupling
N
N
O
N
S
S
HO
O
N
N
commonly encountered with terminal alkynes in CuAAC
O
H
O
COOH HN
12
reaction is also noteworthy. Although, gold (I) and other
13
acetylides were also explored in the azide-alkyne cycloaddition
reaction, the addition of copper (I) salts is often required to affect
the cycloaddition. The majority of reported silver catalysts are
based on the preparation of Ag–ligand complexes by using
highly expensive and laborious methods. Likewise, the use of
organic solvents, an inert atmosphere and refluxed conditions are
required to exploit the catalytic performance. Nowadays,
Tazobacta
m
Cefatrizine
Scheme1. Potential pharmaceutical based on 1,2,3-triazoles
*
Corresponding author. Tel.: +91 9854403297
E-mail address: dsarma22@gmail.com; dsarma22@dibru.ac.in

2
Tetrahedron
tremendous efforts have been made for the development of
11
Ag O (10%)
DIPEA
DIPEA
DIPEA
DIPEA
DIPEA
DIPEA
DIPEA
DIPEA
DIPEA
DIPEA
DIPEA
H O
24h
0
0
0
0
0
0
0
0
0
0
0
0
2
2
catalytic processes to achieve a greener synthesis by reduction of
chemical waste and the number of synthetic steps as well as use
of environmentally friendly solvent. Water as solvent has
received remarkable concern because it is most abundant, non-
toxic, non-corrosive, 4as well as non-flammable and
environmentally benign. In several instances, water is the ideal
reaction solvent, providing the best yields of the product with the
highest rates.
12 AgN(CN) (10%)
DMSO
24h 50
24h 48
24h 40
2
1
1
1
1
1
1
1
3
4
5
6
7
8
9
AgN(CN)
AgN(CN)
AgN(CN)
AgN(CN)
AgN(CN)
AgN(CN)
2
2
2
2
2
2
(10%)
(10%)
(10%)
(10%)
(10%)
(10%)
(5%)
DMF
Toluene
2
H O/THF 24h 45
THF
EG
24h 66
12h 78
2h 98
2h 95
2h 80
1
H
H
H
H
2
2
2
2
O/EG
O/EG
O/EG
O/EG
6
AgN(CN)
2
2
Silver dicyanamide, a coordination polymer has been shown
20 AgN(CN)
(1%)
to consist of infinite -Ag-NC-N-CN-Ag- spiral chains (μ1,5
coordination mode) and proved to be excellent, high yielding,
simply prepared catalyst. To continue our interest on ‘click
reactions’, we wish to report herein an efficient and
preparatively straightforward approach for the generation of
diverse 1,2,3-triazoles of high purity and in excellent yields. The
reaction is experimentally simple proceeding well in
-
21
a
-
2h
0
15
Reactions were performed on a scale of 1 mmol of 1a and 1.5 mmol of
2a and additive (1 mmol) in a given solvent was stirred at room temperature
16
17
b
in air otherwise stated; Isolated yields.
With these promising results in hand, the scope of the method
was investigated with a range of different azides and alkynes. As
exemplified in Scheme 2, all the reactions proceeded efficiently
to completion, and the products were isolated in good to
excellent yields with high purity. As expected, the reaction of
benzyl, aryl and aliphatic azides with aromatic acetylene afforded
the corresponding triazole products in excellent yields (90−97%;
Scheme 2). In addition to aromatic acetylenes, aliphatic
acetylenes are also suitable substrates to produce 1,4-
disubstituted 1,2,3-triazoles in 90- 94% (Scheme 2, entries 3f-3h,
2
H O/ethylene glycol without protection from oxygen, and
generating nearly no by-products. The unique aspects of this
route are the enormous scope, high selectivity, and nearly
quantitative yields of the desired products under mild condition.
Initially, the cycloaddition reaction between benzyl azide and
phenyl acetylene was selected to optimize the reaction conditions
by using 10 mol % silver dicyanamide as a catalyst (Table 1). To
our delight, we indeed obtained 1,4-disubstituted triazole
regioisomer in moderate yield along with small amount of 1,5-
isomer (Table 1, entry 1). This exciting transformation to the
3r) yields under the same reaction condition. Pleasantly, a variety
of reactive functional groups were tolerated, including alcohol,
ester functionalized alkyne also delivered the expected product in
superior yields under our optimized conditions.
1
,2,3-triazole encouraged us to further examine the feasibility of
this efficient cycloaddition. After many optimization efforts, the
use of 5 mol% AgN(CN) as the catalyst and DIPEA as a
base/ligand in H O/ethylene glycol at room temperature turned
R
N
2
AgN(CN)2, DIPEA
N
N
R
1
N3
R'
2
H2O/Ethylene glycol, rt
R'
out to give the optimum result (Table 1, entry 18). However, it is
apparent that the reaction also proceeded in other solvents, such
as dimethyl sulfoxide (DMSO), toluene, N,N-dimethylformamide
2
3
N
N
N N
N
N
N
N
N
.
Br
(
DMF) and tetrahydrofuran (THF), but gave the products in
inferior yields (Table 1, entries 12–16). The necessity of using
AgN(CN) was confirmed in a control experiment (Table 1,
entry 21); other silver salts, such as AgNO and Ag O, were
3a, 2h, 95%
3b, 5h, 95%
3c, 5h, 94%
2
3
2
totally ineffective (Table 1, entries 10 and 11). Notably, no
undesirable byproduct could be detected under optimized
condition and gratifyingly, the catalyst loading could be lowered
to 1 mol % [Ag] while keeping short reaction times (Table 1,
entry 20).
N N
N
N
N
N
N
N
N
Cl
3d, 5h, 95%
3f, 5h, 90%
3
e, 5h, 90%
N
N
N
N
N
N
N
a
N
N
OH
Table 1. Optimization of reaction conditions.
Br
3h, 6h, 94%
3i, 6h, 88%
3g, 5h, 90%
N3
[Ag], Additive
Bn
N
Bn
N
N
N
N
N
solvent, rt
Ph
Ph
3b
N
N
N N
N
N
N
O
1a
2a
3a
OH
N
N
O
O2N
Time Yield (%)b
3b
24h 40 10
Br
Entry Catalyst (mol%)
Additive
Solvent
3k, 2h, 92%
3l, 5h, 90%
3
j,6h, 85%
3
a
1
2
3
4
5
6
7
8
AgN(CN)
AgN(CN)
AgN(CN)
AgN(CN)
AgN(CN)
AgN(CN)
AgN(CN)
AgN(CN)
2
2
2
2
2
2
2
2
(10%)
(10%)
(10%) Diethyl amine
(10%)
(10%)
(10%)
(10%)
-
H
H
H
H
H
H
H
H
2
2
2
2
2
2
2
2
O
O
O
O
O
O
O
O
N
N
N
L-Proline
24h 54
24h 55
24h 51
24h 52
24h 56
24h 70
0
0
0
0
0
0
N
N
N N
O
N
N
O
OMe
Br
NEt
3
30, 5h, 92%
3
m, 5h, 90%
3n, 5h, 90%
DABCO
DBU
N N
N
N
DIPEA
N
N
N
N
N
(10%) (DHQD)
2
PHAL
24h 45 10
MeO
NC
Pyridine-2-
aldehyde
DIPEA
9
AgN(CN)
2
(10%)
H
H
2
2
O
O
24h 43 13
3r, 5h, 90%
3p, 5h, 95%
3q, 5h, 93%
1
0
AgNO
3
(10%)
24h
0
0

3
Scheme 2. Silver (I) catalyzed azide–alkyne cycloaddition
reaction.
Reischer, R. J.; Ford, C. W.; Zurenko, G. E.; Hamel, J. C.;
Schaadt, R. D.; Stapert, D.; Yagi, B. H. J. Med. Chem. 2000, 43,
9
1
53–970; (e) Hawker, C. J.; Wooley, K. L. Science 2005, 309,
200–1205. (f) Wacharasindhu, S.; Bardhan, S.; Wan, Z.-K.;
A plausible mechanistic cycle involving AgN(CN)
2
as catalyst
Tabei, K.; Mansour, T. S. J. Am. Chem. Soc. 2009, 131, 4174-
4175; f) Liu, Y. X.; Yan, W. M.; Chen, Y. F.; Petersen, J. L.;
Shi, X. D. Org. Lett. 2008, 10, 5389–5392; (g) Tron, G. C.;
Pirali, T.; Billington, R. A.; Canonico, P. L.; Sorba, G.;
Genazzani, A. A. Med. Res. Rev. 2008, 28, 278–308; (h) Lauria,
A.; Delisi, R.; Mingoia, F.; Terenzi, A.; Martorana, A.; Barone,
G.; Almerico, A. M. Eur. J. Org. Chem. 2014, 3289-3306; (i) Li,
S.; Huang, Y. Curr. Med. Chem. 2014, 21, 113-123; (j)
Chuprakov, S.; Kwok, S. W.; Fokin, V. V. J. Am. Chem. Soc.
is depict in Scheme 3. Since the tertiary amine functions as both
18
a ligand and a base in CuAAC reactions, here DIPEA
contribute a same role in the intermediate step. We propose that
the catalytic cycle begins with the formation of silver phenyl
acetylide by DIPEA and then DIPEA act as a ligand to give A.
Nucleophilic attack on A by the azide generates B and the
process proceed through the pathway commonly accepted for this
transformation to form a transient silver metallacycle shown as
2
013, 135, 4652–4655; (k) Spangler, J. E.; Davies, H. M. L. J.
9b
C. Subsequent migration of nitrogen to carbon and protonation
leads to the formation of triazole. The observed regioselectivity is
due to a probable steric effect where the methyl groups of
isopropyl unit of DIPEA efficiently protect one side of the silver
metal, thereby blocking the cycloaddition to give up the sterically
more crowded 1,5- disubstituted product.
Am. Chem. Soc. 2013, 135, 6802–6805; (l) Zibinsky, M.; Fokin,
V.V. Angew. Chem. 2013, 125, 1547–1550; Angew. Chem. Int.
Ed. 2013, 52, 1507–1510; (m) Donnelly, K. F.; Petronilho, A.;
Albrecht, M. Chem. Commun. 2013, 49, 1145–1159; (n) Johnson,
T. C.; Totty, W. G.; Wills, M. Org. Lett. 2012, 14, 5230–5233;
(
o) Gulevich, A. V.; Dudnik, A. S.; Chernyak, N.; Gevorgyan,
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Gevorgyan, V. Angew. Chem. 2012, 124, 886–896; Angew.
Chem. Int. Ed. 2012, 51, 862–872.
N
2.
(a) Agalave, S. G.; Maujan, S. R.; Pore, V. S. Chem. Asian J.
R'
N
N
2
011, 6, 2696 – 2718; (b) Soltis, M. J.; Yeh, H. J.; Cole, K. A.;
H
R
R
AgN(CN)2
Whittaker, N.; Wersto. R. P.; Kohn, E. C. Drug Metab. Dispos.
1
2
996, 24, 799 – 806; (c) Sheng, C. Zhang, W. Curr. Med. Chem.
011, 18, 733 –766.
NH(CN)2
3
4
.
.
Huisgen, R. In 1,3-Dipolar Cycloaddition Chemistry; Padwa, A.,
Ed.; Wiley: New York, 1984; pp 1–176.
Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B.
Angew. Chem. 2002, 114, 2708–2711; Angew. Chem. Int. Ed.
N
R'
H
R
N
N
AgN(CN)2
R
Ag
i
N
Pr EtN
2
2
002, 41, 2596–2599.
Tornøe, C. W.; Christensen, C.; Meldal, M. J. Org.Chem. 2002,
7, 3057–3064.
5
6
7
.
.
.
NH(CN)2
N
6
Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem. Int.Ed.
2001, 40, 2004–2021.
R'
R
Ag
R'
N
N
N
A
(a) Thirumurugan, P.; Matosiuk, D.;
Jozwiak, K. Chem. Rev.
Ag
R
N
2013, 113, 4905–4979; b) Jewett, J. C.; Bertozzi, C. R. Chem.
Soc. Rev. 2010, 39, 1272–1279; (c) Debets, M. F.; Berkel, S. S.
van; Dommerholt, J.; Dirks, A. J.; Rutjes, F. P. J. T.; Delft, F.
L. van Acc. Chem. Res. 2011, 44, 805–815; (d) Mamidyala, S.
K.; Finn, M. G. Chem. Soc. Rev. 2010, 39, 1252–1261; (e) Golas,
P. L.; Matyjaszewski, K. Chem. Soc. Rev. 2010, 39, 1338–1354;
R'
N
N
N
N N
C
N
R
Ag N
(
2
f) Qin, A.; Lam, J. W. Y.; Tang, B. Z. Chem. Soc. Rev. 2010, 39,
522–2544.
B
8
9
.
.
(a) Silvestri, I. P.; Andemarian, F.; Khairallah, G. N.; Yap, S.
W.; Quach, T.; Tsegay, S.; Williams, C. M.; O’ Hair, R. A. R.;
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6082–6088; (b) Aucagne, V.; Leigh, D. A. Org. Lett. 2006, 8,
Scheme 3. Proposed catalytic cycle for the Ag(I)-catalyzed AAC
reaction.
4
505–4507.
In summary, a simple and efficient method was effectively
developed for synthesizing 1,4-disubstituted 1,2,3-triazoles using
AgN(CN) /DIPEA as catalyst in H O/ethylene glycol at room
2 2
temperature without the exclusion of air. The ease and efficiency
of this catalyst system has been successfully demonstrated and
we envision that this procedure may release exciting perspectives
for use in various synthetic applications.
(a) McNulty, J.; Keskar, K.; Vemula, R. Chem. Eur. J. 2011, 17,
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Acknowledgement
DS is thankful to CSIR, New Delhi for a research grant [No.
12. Partyka, D. V.; Gao, L.; Teets, T. S.; Updegraff III, J. B.;
Deligonul, N.; Gray, T. G. Organometallics 2009, 28, 6171–
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02(0154)/13/EMR-II]. The authors also acknowledge the De-
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3. Zhou, Y.; Lecourt, T.; Micouin, L. Angew. Chem. 2010, 122,
661 – 2664; Angew. Chem. Int. Ed. 2010, 49, 2607–2610.
partment of Science and Technology for financial assistance
under DST-FIST Programme and UGC, New Delhi for Special
Assistance Programme (UGC-SAP) to the Department of
Chemistry, Dibrugarh University.
1
2
14. (a) Nezhad, A. K.; Panahi, F. Green Chem. 2011, 13, 2408–
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4
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1
1
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9. Synthesis of Silver Dicyanamide: Sodium dicyanamide (1 g, 11.2
mmol) was dissolved in deionized water (20 mL). Silver nitrate
1
1
(1.9 g, 11.2 mmol) was also dissolved in deionized water (20 mL)
and the two solutions were mixed together at room temperature.
A white precipitate of silver dicyanamide was formed, filtered and
washed with deionized water twice to eliminate the residual
sodium nitrate. The resulting material was dried in a vacuum oven
at 80 °C overnight to remove the trace amount of water. Silver
dicyanamide (1.92 g) was obtained as a white powder with a yield
of 98 %.
2
0. General procedure for the synthesis of 1,4-disubstituted-1H-
1
,2,3-triazole: To a mixture of azide (1 mmol, 1 equiv.) and
acetylene (1.1 mmol, 1.1 equiv.) in H O/ethylene glycol (1:1, 2
mL) was added sequentially catalyst AgN(CN) (5 mol%) and
2
2
DIPEA (1mmol.) The mixture was stirred at room temperature for
the given time period as mentioned in scheme 2. The progress of
the reaction was monitored by TLC. After completion of the
reaction it was extracted with EtOAc (2x20 mL), washed with
brine, dried over anhydrous sodium sulfate, and concentrated
under reduced pressure. The resulting residue was purified
through silica gel column chromatography (10–20%
EtOAc/hexanes) to afford the desired product.

5
Graphical Abstract
AgN(CN)
2
/DIPEA/H
2
O-EG: a highly
Leave this area blank for abstract info.
efficient catalytic system for synthesis of 1,4-
disubstituted-1,2,3 triazoles at room
temperature
a
a
a
b
a
Abdul Aziz ali, Mitali Chetia, Bishwajit Saikia, Prakash J. Saikia, and Diganta Sarma*
a
Department of Chemistry, Dibrugarh University, Dibrugarh-786004, Assam, INDIA.
b
Analytical Chemistry Division, CSIR-North East Institute of Science and Technology, Jorhat-785006, Assam, INDIA.
N
AgN(CN) , DIPEA
R
2
N
N
R N3
R'
H O/EG, rt
2
R'