CuO-Nanoparticles Catalyzed Synthesis of 1,4-Disubstituted-1,2,3-Triazoles from Bromoalkenes

Article abstract of DOI:10.1007/s12039-018-1452-1

Abstract: A novel and efficient protocol involving commercially available CuO nanoparticles (CNP) as catalyst has been developed for the synthesis of 1,2,3-triazoles. A library of 1,4-disubstituted 1,2,3-triazoles has been constructed with good to excellent yields. Graphical Abstract: SynopsisA novel and efficient protocol involving commercially available CuO nanoparticles (CNP) as catalyst has been developed for the synthesis of 1,2,3-triazoles. A library of 1,4-disubstituted 1,2,3-triazoles has been constructed with good to excellent yields.[Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-018-1452-1

J. Chem. Sci. (2018) 130:44
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-018-1452-1
RAPID COMMUNICATION
CuO-Nanoparticles Catalyzed Synthesis of
1,4-Disubstituted-1,2,3-Triazoles from Bromoalkenes
JOHN PAUL RAJb, DASARI GANGAPRASADb, MURUGESAN VAJJIRAVELb,
KESAVAN KARTHIKEYANb and JEBAMALAI ELANGOVANa,∗
aDepartment of Chemistry, Rajah Serfoji Government College, Thanjavur, Tamilnadu 613 005, India
bDepartment of Chemistry, B. S. Abdur Rahman Crescent Institute of Science & Technology, Seethakathi Estate,
Vandalur, Chennai, Tamilnadu 600 048, India
E-mail: elangoorganic@gmail.com
MS received 4 January 2018; revised 3 March 2018; accepted 15 March 2018
Abstract. AnovelandefficientprotocolinvolvingcommerciallyavailableCuOnanoparticles(CNP)ascatalyst
has been developed for the synthesis of 1,2,3-triazoles. A library of 1,4-disubstituted 1,2,3-triazoles has been
constructed with good to excellent yields.
Keywords. 1,2,3-Triazoles; [3+2] Cycloaddition; bromoalkenes; CuO nanoparticles.
1. Introduction
This was ingeniously accomplished by oxidative azide-
olefin cycloaddition (OAOC) and eliminative azide-
olefin cycloaddition (EAOC). In OAOC, the triazoline
formed by azide-olefin cycloaddition would concomi-
tantly be oxidized into the corresponding triazole (Eq.
1a, Scheme 1). Whereas in EAOC, the olefin bearing
a leaving group would undergo cycloaddition with the
azide and the resulting triazoline would subsequently
undergo elimination reaction to furnish the triazole (Eq.
1b, Scheme 1). In OAOC, electron-deficient olefins have
been subjected to react with azides using various cat-
alysts such as Cu(OTf)2, Ce(OTf)3, Cu(OAc)2, CuI,
CuO and Fe2O3-nanoparticles.21–26 Whereas in EAOC,
olefins bearing the leaving groups such as alkoxy,27,28
acetate,29 nitro30–34 and sulfone35,36 would be treated
with azides to afford the triazoles. Another flamboy-
ant category of EAOC is ‘organo click reactions’ in
which electron-rich olefins such as enamines generated
in situ would be treated with azides in the presence of
organo catalysts such as secondary or tertiary amines.37
In continuation of our previous contributions in azide-
olefin cycloaddition of electron-deficient olefins and
organic azides using CuO nanoparticles,38–41 we were
prompted to examine the azide-olefin cycloaddition on
Despite the traditional Huisgen cycloaddition,1,2 1,2,3-
triazoles have drawn the attention of the scientific
fraternity after the invention of copper-catalyzed azide-
alkyne cycloaddition (CuAAC)3,4 owing to its amazing
regio-selectivity, functional group tolerance and opera-
tional simplicity. Even though 1,2,3-triazoles have not
been isolated from natural sources,5 they have unveiled
new horizons in various areas such as drug discov-
ery,6,7 materials,8,9 polymers10 and supramolecules.11,12
Besides their usage as synthetic intermediates,13–15 they
have also enormously contributed to the industry as
photo stabilizers, corrosion inhibitor, dyes, fluorescent
whiteners and optical brightening agents.16,17 Subse-
quently, Ruthenium-catalyzed azide-alkyne cycloaddi-
tion (RuAAC) was developed to prepare the com-
plementary 1,5-disubstituted 1,2,3-triazoles.18–20 How-
ever, alternative methods were sought out in the place
of azide-alkyne cycloaddition since the synthetic and
economic viability of alkynes emerged as a serious
difficulty. In response to this need, olefins were envis-
aged in the place of alkynes since they have a better
synthetic and commercial accessibility than alkynes.
*
For correspondence
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s12039-018-1452-1) contains
supplementary material, which is available to authorized users.

44 Page 2 of 6
J. Chem. Sci. (2018) 130:44
2.2 General Procedure for the Synthesis
of 1-benzyl-4-phenyl-1H-1,2,3-triazole
Amixtureofbromostyrene(0.5mmol), benzylazide(1mmol),
CuO nanoparticles (50mol%) and piperidine (1mL) as a
solvent were heated at 110 ◦C for 12h. Completion of the
reaction was monitored by TLC and the reaction mixture was
cooled to room temperature. The resulting crude product was
purified by column chromatography.
2.3 Spectral data of representative compounds
2.3a 1-benzyl-4-phenyl-1H-1,2,3-triazole (3a): White solid,
1
M.p.: 126–128 ◦C, H NMR (400MHz, CDCl3): δ 7.81–7.79
(m, 2H), 7.66 (s, 1H), 7.42–7.36 (m, 5H), 7.33–7.29 (m, 3H),
5.58 (s, 2H) ppm.13C NMR (100MHz, CDCl3)δ 148.3, 134.7,
130.6, 129.2, 128.8, 128.2, 128.1, 125.7, 119.5, 54.3ppm.
Scheme 1. Background of EAOC of bromoalkenes and
organic azides.
3. Results and Discussion
bromoalkenes and organic azides. Our literature perusal
on this aspect revealed the palladium-catalyzed synthe-
sis of 1H-1,2,3-triazoles from sodium azide and alkenyl
bromides (Eq. 2, Scheme 1).42 Besides that, base-
promoted synthesis of 1,5-disubstituted 1,2,3-triazoles
from alkenyl bromides and organic azides also has
been reported in the literature (Eq. 3, Scheme 1).43
Kuang et al., described Cu-catalyzed synthesis of 1H-
1,2,3-triazoles from 1,1-dibromoalkenes and sodium
azide.44 Herein we report the synthesis of the com-
plementary 1,4-disubstituted-1,2,3-triazoles from bro-
moalkenes and organic azides catalyzed by commer-
cially available CuO nanoparticles (Eq. 4, Scheme 1).
At the outset, we embarked on our examination with β-
bromostyrene(1a)andbenzylazide(2a)asthereference
substrates with CuO nanoparticles in DMSO. Though
we initially anticipated the 4-bromo-1,2,3-triazole by
oxidative azide-olefin cycloaddition, we were surprised
to see 1,4-disubstituted triazole (3a) in 60% yield which
was accompanied by 15% of the other regioisomer
4a (Table 1, entry 1). When n-octane was employed
as the solvent in the place of DMSO, the yield of
the triazole (3a) subsided to 20% (Table 1, entry 2).
When other solvents such as chloroform, tetrahydrofu-
ran, nitromethane, toluene and DMF were examined,
only trace amount of the product (3a) was obtained
(Table 1, entries 3–7). It is worth mentioning that the
water has also failed to promote the reaction with a pro-
nounceable yield of the product yield of 3a (Table 1,
entry 8). When we envisaged a basic condition for
this transformation, we employed piperidine entrusted
with a dual role as the base and solvent. Our expec-
tation was vindicated with 90% yield of 3a as the
2. Experimental
2.1 Materials and methods
All melting points were taken on Guna melting point appara-
tus and are uncorrected. High- resolution mass spectra were
recorded on a JEOL GC Mate using electron impact ion- sole product (Table 1, entry 9). When the tempera-
ture of the reaction was gradually elevated from 90 ◦C
ization (EI) techniques. NMR spectra were obtained on a
Bruker Ascend TM 400 NMR spectrometer;1H NMR and
13C NMR spectra were recorded at 400MHz and 100MHz
respectively. The chemical shifts were reported in ppm down-
field to TMS (δ = 0) for 1H NMR and relative to the middle
CDCl3 resonance (δ = 77.0) for 13C NMR. In the 13C NMR
spectra and the coupling constant (J) is given in Hz. For
thin-layer chromatography (TLC), silica gel plates Merck
60 F254 (0.25mm thick) were used and compounds were
visualized by irradiation with UV light and/or by treatment
with Iodine. Column chromatography was performed either
with Merck silica gel 60 (230–400 mesh) in common glass
columns.
to 110 ◦C, the yield of the product (3a) precipitously
hiked to 97% (Table 1, entries 9–11). Subsequently,
whileotherorganicbasesliketriethylamine, morpholine
and pyridine were examined in the place of piperi-
dine, morpholine could exhibit a comparable effect with
85% yield of the product (3a) while the others lagged
behind with a great margin (Table 1, entries 12–14).
Other catalysts such as Ce(OTf)3, Cu(OTf)2, AlCl3,
CuCl2, CuI and Copper nanopowder were tested in the
place of CuO nanoparticles (Table 1, entries 15–20).
To our surprise, only copper nanopowder has exhibited

J. Chem. Sci. (2018) 130:44
Page 3 of 6 44
Table 1. Optimization for the azide-olefin cycloaddition of β-bromostyrene and benzyl
azide[a]
.
Entry Solvent
Temp (◦C)
Catalyst
Yield of 3a (%)[b] Yield of 4a (%)[b]
1
2
3
4
5
6
7
8
9
10
DMSO
n-Octane
CHCl3
90
90
90
90
90
90
90
90
90
100
110
110
110
110
110
110
110
110
110
110
110
110
110
CNP
CNP
CNP
CNP
CNP
CNP
CNP
CNP
CNP
CNP
CNP
CNP
CNP
60
20
15
3
-
-
-
-
-
-
-
-
-
7
-
10
15
-
8
-
-
-
-
trace
trace
trace
trace
trace
10
90
95
97
45
85
30
50
70
40
69
65
90
THF
CH3 NO2
Toluene
DMF
Water
Piperidine
Piperidine
11[c,d] Piperidine
12
13
14
15
16
17
18
19
20
21
22
23
Et3N
Morpholine
Pyridine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
-
CNP
Ce(OTf)3
Cu(OTf)2
AlCl3
CuCl2
CuI
Cu nanopowder
CuO
70
45
40
CNP
-
12
15
Piperidine
[a] Reaction conditions: β-Bromostyrene (0.5mmol), Benzyl azide (1.0mmol), catalyst
(50mol%) and solvent (1.0mL) were heated for 12h. [b] Isolated yields. [c] Reaction
with 0.5mmol of azide led to 68% yield of 3a and 0.75mmol of azide furnished 84%
yield of 3a after 12h. [d] Upon performing the reaction with 10, 20, 40 and 60mol% of
CNP, the yields of 3a were 57, 83, 90 and 97%, respectively.
comparable efficiency as that of CuO nanoparticles bromoalkenes (Table 2, entries 1–9). As discussed in
which is evident from the yield (Table 1, entry 20). How- the optimization part, β-bromostyrene (1a) furnished
ever, it is worth mentioning that copper nanopowder is 97% yield of the required 1,2,3-triazole (3a) with ben-
costlier than the CuO nanoparticles. Most importantly, zyl azide (Table 2, entry 1). Methoxy substituent which
bulk CuO also failed to exhibit the efficiency as its nano is a mesomeric electron donor has dramatically boosted
brother as testified from the poor yield of the prod- up the reaction to an excellent yield (Table 2, entry 2).
uct (Table 1, entry 21). The decline of yields of the On the other hand, methyl substituent which is an induc-
products observed under solvent-free and catalyst-free tive electron donor has shown a slight lessening in the
conditions,ascertain the crucial role played by the sol- efficacy of this transformation (Table 2, entry 3).
vent and the catalyst in this protocol (Table 1, entries
22–23).
In case of halogen substitutions, chloro substitution
has revealed a remarkable improvement of yield than
Having fixed the optimized condition (Table 1, entry fluoro and bromo substitutions (Table 2, entries 4–
11) for CuO nanoparticles catalyzed synthesis of 1,4- 6). On the other hand, strongly electron withdrawing
disubstituted 1,2,3-triazoles via azide-olefin cycloaddi- nitro group has significantly suppressed the efficiency
tion of bromoalkenes and organic azides, a variety of
of this protocol which is evident from the slump
olefins and azides were studied and the results were of yield to 65% (Table 2, entry 7). When other aro-
summarized in Table 2. Initially, benzyl azide (2a) matic substitutions such as naphthyl and thiophenyl
was subjected to this reaction condition with various were investigated, thiophenyl sored up to a great

44 Page 4 of 6
J. Chem. Sci. (2018) 130:44
Table 2. CuO nanoparticles catalyzed synthesis of 1,4-
disubstituted 1,2,3-triazoles from bromoalkenes and azides[a]
.
Entry
R1
Ph
1
R2
2
3
Yield (%)[b]
1
2
3
4
5
6
7
8
1a
Bn
Bn
Bn
Bn
Bn
Bn
Bn
Bn
Bn
2a 3a
2a 3b
2a 3c
2a 3d
2a 3e
2a 3f
2a 3g
2a 3h
2a 3i
97
99
78
79
83
96
65
74
97
95
99
98
83
70
68
76
4-(MeO)Ph 1b
4-(Me)Ph 1c
4-(F)Ph 1d
4-(Br)Ph 1e
4-(Cl)Ph 1f
3-(NO2)Ph 1g
2-Napthyl 1h
2-Thiophenyl 1i
9
10
11
12
13
14
15
16
Ph
Ph
Ph
Ph
Ph
Ph
1a 4-(Me)Bn 2b 3j
1a 4-(MeO)Bn 2c 3k
1a Phenethyl 2d 3l
1a n-Hexyl 2e 3m
1a CH2CO2Et 2f 3n[c]
1a
Ph
2g 3o
4-(MeO)Ph 1b Phenethyl 2d 3p
[a] Reaction conditions: Bromoalkenes (0.5mmol), organic
azide (1.0mmol), CuO Nanoparticles (50mol%) and piperi-
dine (1.0mL) were heated for 12h. [b] Isolated yields. [c]
2-(4-phenyl-1H-1,2,3-triazol-1-yl)-1-(piperidin-1-yl)ethanone
forms as the solvent reacts with the ester group of the triazole.
Table 3. Recycling of CuO nanoparticles.
Entry
Catalyst
recovery (%)
Catalytic
Cycle
Yield (%)
Scheme 2. Synthesis of bis-triazole by azide-olefin
cycloaddition of (2-bromovinyl)triazole with benzyl azide.
1[a]
2[b]
3[b]
4[b]
97
92
86
82
1
2
3
4
97
94
90
88
margin while naphthyl slipped to poor yield (Table 2,
entries 8–9). On the other part of this study, fixing
the olefin (1a), various azides were subjected to this
condition and examined the outcome (Table 2, entries
10–15). Excellent yields of triazoles were registered
with methyl and methoxy benzyl azides (Table 2,
entries 10–11). In case of aliphatic azides, phenethyl
azide (2d) was found to be benign while n-hexylazide
[a] Reaction conditions: Bromoalkenes (2.5mmol), organic
azide (5.0mmol), CuO Nanoparticles (250mol%) and piperi-
dine (5.0mL) were heated for 12h. [b] The recovered catalyst
was under identical reaction conditions to those for the first
run.
(2e) was hostile to this reaction condition as reflected the efficacy of the protocol since the yield decreased
in the difference of yields of the products (Table 2, to 68% (Table 2, entry 15). Unlike its reaction with β-
entries 12–13). Being aliphatic and electron deficient, bromostyrene (1a), phenethyl azide (2d) has furnished
ethyl-2-azidoacetate seemingly suppressed the yield a diminished yield of the product when it confronts 4-
(Table 2, entry 14). Phenyl azide, being aromatic as methoxy-β-bromostyrene(1b)asstatedinTable2, entry
well as electron deficient, has also markedly retarded 16.

J. Chem. Sci. (2018) 130:44
Page 5 of 6 44
Even the (2-bromovinyl)triazole (1j) was submissive
to this reaction condition and furnished excellent yield
of bis-triazole (3q) by using this protocol (Scheme 2).
Finally, recyclability of the heterogeneous CuO
nanoparticles was also examined. The catalyst was
recovered from the reaction mixture after each cycle as
follows. The reaction mixture was concentrated in vacuo
and diluted with water (10mL). The resulting heteroge-
neous mixture was filtered and the solid residue was
washed with ethylacetate and dried in the hot air oven at
110 ◦C for 2h. It was observed that the catalyst remains
active even for four cycles (Table 3).
copper(I)-catalyzed 1,3-dipolar cycloadditions of termi-
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less K B 2002 A stepwise Huisgen cycloaddition
process: copper(I)-catalyzed regioselective ligation of
azides and terminal alkynes Angew. Chem. Int. Edit. 41
2596
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istry: 1,2,3-triazoles as pharmacophores Chem. Asian J.
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4. Conclusions
In conclusion, a method commercially available CuO
nanoparticles-catalyzed synthesis of 1,2,3-triazoles via
azide-olefin cycloaddition of bromoalkenes and organic
azides has been developed and a diverse array of 1,4-
disubstituted 1,2,3-triazoles is built up. This method
is distinct from the existing Cu-catalyzed azide-alkyne
cycloaddition due to the accessibility of the starting
material and less cytotoxicity of the CuO nanoparticles
than the conventional copper(I) reagents.45 This method
is different from the existing Pd-catalyzed synthesis of
1,2,3-triazoles from bromoalkenes by the economic via-
bility of the CuO nanoparticles over the Pd catalysts.
This method is also unique from the t-BuOK-promoted
azide-alkene cycloaddition of bromoalkenes because
of its complementary regioselectivity and versatility of
azides employed (benzyl, alkyl and aryl). These salient
attributes make this method as a highly desirable one
among the other existing methods.
12. Schulze B and Schubert U S 2014 Beyond click
chemistry supramolecular interactions of 1,2,3-triazoles
Chem. Soc. Rev. 43 2522
13. Chattopadhyay B and Gevorgyan V 2012 Transition-
metal-catalyzed denitrogenative transannulation: con-
verting triazoles into other heterocyclic systems Angew.
Chem. Int. Edit. 51 862
14. Seo B, Jeon W H, Kim J, Kim S and Lee P H 2015
Synthesis of fluorenes via tandem copper-catalyzed
[3+2]cycloadditionandrhodium-catalyzeddenitrogena-
tive cyclization in a 5-exo mode from 2-ethynylbiaryls
and N-sulfonyl azides in one pot J. Org. Chem. 80
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Supplementary Information (SI)
Additional experimental data and spectroscopic characteriza-
tion data are given. Supplementary Information is available
at www.ias.ac.in/chemsci.
15. Kim C-E, Park Y, Park S and Lee P H 2015
Diastereoselective synthesis of tetrahydrofurano-
and tetrahydropyrano-dihydropyrroles containing N,O-
acetal moieties via rhodium-catalyzed transannulation
of N-sulfonyl-1,2,3-triazoles with oxacycloalkenes Adv.
Synth. Catal. 357 210
Acknowledgements
We thank the SERB (New Delhi) for financial support
(SB/EMEQ-260/2014). D. G. thanks CSIR (New Delhi) for
Senior Research Fellowship (09/1166(0001)/2017-EMR-I).
16. Fan W-Q and Katritzky A R 1996 In Comprehensive
heterocyclic chemistry Vol. II A R Katritzky, C W
Rees and E F V Scriven (Ed.) (Oxford: Elsevier) p. 1–
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