Oxidation of 1,4-disubstituted-1,2,3-triazoles with H2O2–CF3CO2H: efficient synthesis of 1,2,3-triazole 3-oxides

Article abstract of DOI:10.1080/00397911.2019.1566473

A collection of 1,2,3-triazole-3-oxides was obtained from oxidation of the corresponding 1,4-disubstituted-1,2,3-triazoles mediated by a H₂O₂–CF₃CO₂H system through a simple protocol in good yields showing high

Full text of DOI:10.1080/00397911.2019.1566473

Synthetic Communications
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Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Oxidation of 1,4-disubstituted-1,2,3-triazoles with
H2O2–CF3CO2H: efficient synthesis of 1,2,3-triazole
3-oxides
Norberto González-Mojica, Leticia Almazán-Sánchez, Jesús G. García-Torres,
Ivette Santana-Martinez, Diego Martínez-Otero, Miguel A. Sánchez-Carmona
& Erick Cuevas-Yañez
To cite this article: Norberto González-Mojica, Leticia Almazán-Sánchez, Jesús G. García-Torres,
Ivette Santana-Martinez, Diego Martínez-Otero, Miguel A. Sánchez-Carmona & Erick Cuevas-
Yañez (2019): Oxidation of 1,4-disubstituted-1,2,3-triazoles with H2O2–CF3CO2H: efficient synthesis
of 1,2,3-triazole 3-oxides, Synthetic Communications
To link to this article: https://doi.org/10.1080/00397911.2019.1566473
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https://doi.org/10.1080/00397911.2019.1566473
Oxidation of 1,4-disubstituted-1,2,3-triazoles with
H2O2–CF3CO2H: efficient synthesis of 1,2,3-triazole 3-oxides
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Norberto Gonzalez-Mojica, Leticia Almazan-Sanchez, Jesus G. Garcıa-Torres, Ivette
ꢀ
ꢀ
Santana-Martinez, Diego Martınez-Otero, Miguel A. Sanchez-Carmona, and Erick
~
Cuevas-Yanez
ꢀ
ꢀ
ꢀ
ꢀ
Centro Conjunto de Investigacion en Quımica Sustentable UAEM-UNAM, Universidad Autonoma del
ꢀ
Estado de Mexico, Toluca, Estado de Mexico, Mexico
ABSTRACT
ARTICLE HISTORY
Received 10 August 2018
A collection of 1,2,3-triazole-3-oxides was obtained from oxidation of
the corresponding 1,4-disubstituted-1,2,3-triazoles mediated by a
H2O2–CF3CO2H system through a simple protocol in good yields
showing high efficiency.
KEYWORDS
Hydrogen peroxide;
oxidation; trifluoroacetic
acid; 1,2,3-triazole 3-oxides
GRAPHICAL ABSTRACT
R2
R2
O
N
N
N
H2O2
N
N
N
CF3CO2H
R1
R1
Introduction
A new synthetic challenge has emerged as a result of the development of new applications
in coupling and cycloaddition reactions for 1,2,3-triazole N-oxides used as departure
materials,[1–7] which requires more synthetic procedures for these last compounds.
Nowadays, the available methods to prepare 1,2,3-triazole N-oxides involve the cyclization
of a-azoxyoximes,[8] hydrazonoximes,[9–14] and nitroso azoxy compounds.[15] In addition,
an alternative approach to obtain 1,2,3-triazole N-oxides is based on direct oxidation of
1,2,3-triazole moiety. Described first by Begtrup and Jonsson,[16] this method has the out-
standing characteristic that takes a previously synthesized heterocyclic ring as starting
material, similar to other heterocyclic systems such as pyridines.[17] However, the reaction
times are slow, affording the corresponding product in poor yields, besides only 1-methyl-
or unsubstituted 1,2,3-triazoles have been used in this process.
These facts motivated us to investigate thoroughly the oxidation on 1,4-disubstituted-
1,2,3-triazoles which are easily available from Copper-catalyzed Azide–Alkyne cycloadd-
ition (CuAAC), the most important click reaction. Initially developed by the Meldal[18]
~
ꢀ
ꢀ
Centro Conjunto de Investigacion en Quımica Sustentable
CONTACT Erick Cuevas-Yanez
ecuevasy@uaemex.mx
ꢀ
ꢀ
UAEM-UNAM, Universidad Autonoma del Estado de Mexico, Carretera Toluca-Atlacomulco Km 14.5, Toluca, Estado de
ꢀ
Mexico 50200, Mexico.
Supplemental data for this article is available online at on the publisher’s website.
ß 2019 Taylor & Francis Group, LLC

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N. GONZALEZ-MOJICA ET AL.
2
O
N
N
N
Oxidizing
Agent
N
N
N
2
1
Scheme 1. Synthesis of triazole 3-oxide 2 from 1,2,3-triazole 1.
Table 1. Synthesis of triazole 2 using oxidzing agents.
Entry
Oxidzing agent
Solvent
Oxidzing agent ratio
Temperature, ꢀC
Reaction time, h
% Yield
1
2
3
4
5
6
7
8
mCPBA
mCPBA
mCPBA
mCPBA
mCPBA
mCPBA
mCPBA
mCPBA
mCPBA
H2O2
AcOEt
AcOEt
AcOEt
AcOEt
AcOEt
AcOEt
AcOEt
AcOEt
AcOEt
1.25 molar equiv.
2.5 molar equiv.
5.0 molar equiv.
1.25 molar equiv.
2.5 molar equiv.
5.0 molar equiv.
1.25 molar equiv.
2.5 molar equiv.
5.0 molar equiv.
1 ml/mmol
5 ml/mmol
10 ml/mmol
5 ml/mmol
10 ml/mmol
5 ml/mmol
10 ml/mmol
1 ml/mmol
5 ml/mmol
10 ml/mmol
1 ml/mmol
5 ml/mmol
10 ml/mmol
5 ml/mmol
10 ml/mmol
5 ml/mmol
R.T.
R.T.
R.T.
45
45
96
96
96
72
72
72
72
72
72
72
48
48
48
48
48
48
12
10
5
5
7
10
10
12
15
20
20
25
25
30
30
30
35
35
38
60
75
89
60
65
80
0
45
reflux
reflux
reflux
reflux
reflux
reflux
40
9
10
11
12
13
14
15
16
15
16
17
18
19
20
21
22
23
24
AcOH
AcOH
AcOH
H2O2
H2O2
H2O2-Urea
H2O2-Urea
H2O2-Urea
H2O2-Urea
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
CF3CO2H
No solvent
No solvent
No solvent
No solvent
40
reflux
reflux
40
40
40
reflux
Reflux
Reflux
40
40
reflux
reflux
5
5
5
24
24
24
24
H2O2
H2O2
H2O2
0
0
0
10 ml/mmol
and Sharpless–Fokin[19] groups, CuAAC reaction is the biggest source of 1,2,3-triazoles
and also the molecular assembly method par excellence.[20–22]
This report summarizes our most recent findings of the oxidation on 1,2,3-triazoles
derived from CuAAC reaction aiming to develop a new, mild and efficient procedure to
prepare triazole N-oxides.
Results and discussion
In order to reproduce and extend initial triazole oxidation conditions described by
Begtrup and Jonsson[16] to 1,4-disubstituted-1,2,3-triazoles, 1.25 molar equivalents of m-
chloroperoxybenzoic acid were added to an AcOEt solution of 1-benzyl-4-phenyl-1,2,3-
triazole 1 at room temperature as a model reaction. After 96 h, a compound that was
identified as 1-benzyl-4-phenyl-1,2,3-triazole 3-oxide 2 was obtained under these condi-
tions in only 5% yield (Scheme 1). Experiments with different amounts of mCPBA were
made in combination with various reaction times and temperatures, the results

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3
H2O2
O
O
N
F3C
OH
N
N
O
N
O
H
F3C
O
2
H
Ph
O
O
N
O
N
F3C
Ph
N
Bn
N
N
1
Bn
Scheme 2. Mechanism of formation of triazole 3-oxide 2 from 1,2,3-triazole 1.
R2
R2
O
N
N
N
H2O2
N
N
N
CF3CO2H
R1
R1
Scheme 3. Synthesis of 1,2,3-triazole 3-oxides from 1,2,3-triazoles.
summarized in Table 1 show an improvement of reaction yields to 25%. In a sequential
series of experiments, other oxidizing agents were compared with mCPBA such as
H2O2–AcOH,[23,24] H2O2–urea–(CF3CO)2O,[25] and H2O2–CF3CO2H,[26] which have
been used previously in the preparation of pyridine N-oxides. Results in Table 1 state
that optimal conditions (entry 17, Table 1) are achieved using a H2O2–CF3CO2H oxi-
dizing system affording triazole 3-oxide 2 in 88.8% yield, requiring only 5 h to complete
the reaction at 40 ꢀC, in contrast to traditional conditions to prepare pyridine
N-oxides.[23–26]
The use of additives like urea did not increase reaction yields, however, the presence
of acidic organic solvent together with the use of H2O2 as an oxidizing agent is funda-
mental in this process. As results in Table 1 indicate (entries 21–24), direct treatment of
triazole 1 with H2O2 in the absence of an organic acid did not give triazole 3-oxide 2,
recovering only starting material. This feature suggests that organic acid plays a role,
not only in solubilizing the triazole but also in the in situ generation of a peroxy acid,
in our case, trifluoroperoxyacetic acid presumably formed from CF3CO2H and H2O2.[27]
Subsequent trifluoroperoxyacetic acid interaction with the N3 of 1,2,3-triazole provides
triazole 3-oxide 2 according to the mechanism proposed in Scheme 2.
The success of this process prompted us to extrapolate the procedure to other 1,2,3-
triazoles, which were prepared from adaptations of methodologies described by the
[28,29]
groups of Meldal[18] and Cuevas-Yanez.
From these 1,2,3-triazoles used as starting
~
materials, a simple synthetic protocol was developed and a series of 1,2,3-triazole 3-
oxides were synthesized with high efficiency (Scheme 3, Table 2).
All compounds were characterized by the conventional spectroscopic techniques and
compound 2 was a crystalline solid which was studied by X-ray crystallography,

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4
N. GONZALEZ-MOJICA ET AL.
Table 2. Synthesis of N-unsubstituted triazoles.Table Layout
Compound
R1
R2
% Yield
2
3
4
5
6
7
8
9
10
11
12
13
14
PhCH2
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
88.8
63.7
57.7
87.5
49.5
72.0
75.5
90.0
84.9
58.7
56.4
85.0
67.6
4-CH3C6H4
4-CH3OC6H4
4-NO2C6H4
4-ClC6H4
4-BrC6H4
PhCH2
PhCH2
Ph
4-CH3C6H4CH2
2-BrC6H4CH2
CH2O(4-NO2)C6H4
CH2O(2-Cl)C6H4
CH2O(4-Cl)C6H4
Ph
Ph
N3
Cl
CH2O(4-CO2CH3)C6H4
O
Cl
Cl
Table 3. Crystal data and structure refinement of X-ray diffraction for compound 2.
Crystal data
2
Empirical formula
Formula weight
Temperature (K)
Wavelength Å
Crystal system
Space group
C15H13N3O
251.28
100(2)
0.71073
Monoclinic
P 21/c
ꢀ
ꢀ
Unitcell dimensions (Å,
)
–
a
b
c
a
b
c
9.2438(3)
6.2011(2)
21.7126(7)
90
91.5434(7)
90
Volume (Å3)
1244.15(7)
ꢀ
Z
4
Calculated densityD (mgm-3)
1.342
F(000)
528
2.552
Absorption coefficient m (mm-1)
Crystal size (mm3)
0.440 x 0.171 x 0.080
25.349
hmax(ꢀ)
hmin(ꢀ)
1.877
h
k
l
ꢁ11!11
ꢁ7!7
ꢁ26!26
Reflections collected
Independent reflection
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r (I)]
R indices (all data)
15819
2282 [R(int) ¼ 0.0163]
2282 / 0 / 172
1.036
R1 ¼ 0.0327,wR2 ¼ 0.0822
R1 ¼ 0.0352,wR2 ¼ 0.0842
confirming the proposed structure for this compound; crystallographic data and struc-
tural refinement parameters of 2 are summarized in Table 3. From single-crystal X-ray
diffraction analysis, crystal structure of 2 displays a distance between nitrogen and oxy-
gen atoms in N-oxide, N3–O1 ¼ 1.2815 Å and angles O1–N3–N2 (120.0ꢀ), O1–N3–C2
(127.31ꢀ) and N2–N3–C2 (112.68ꢀ), which demonstrate not only the N-oxide formation

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5
Figure 1. ORTEP diagram and atom labeling system for compound 2.
R
HO
O
N
N
N
N
H2O2
N
N
CF3CO2H
17
15 R=Me
16 R=iPr
Scheme 4. Generation of 1-benzyl-1,2,3-triazol-4-yl methanol 17 from compounds 15 and 16.
in 1,2,3-triazole moiety but also the selectivity of this process in the N3-position of
1,2,3-triazole ring (Figure 1).
On the other hand, this synthesis of 1,2,3-triazole 3-oxides has one important limita-
tion. Some (4-alkyl)phenoxymethyl-1,2,3-triazoles, in our case compound 15
(R ¼ methyl) and compound 16 (R ¼ isopropyl) are converted to 1-benzyl-1,2,3-triazol-
4-yl methanol 17 (Scheme 4), probably derived from an oxidative ether cleavage which
is described for propargyl and homoallyl ethers using a Hg(OCOCF3)2/HCl/CF3CO2H/
OsO4 oxidizing system,[30] as well as Ag2O,[31] RuH2(CO)(PPh3)3,[32] and IBX,[33] used
in oxidative dealkylation of methyl aryl ethers.
The examples described above demonstrate that oxidation of 1,2,3-triazoles with
H2O2–CF3CO2H represents a useful method to synthesize 1,2,3-triazole 3-oxides. In
addition, a novel small library of 1,4-disubstituted-1,2,3-triazoles N-oxides was easily
obtained in good yields and purity levels. As a consequence, a mild methodology was
developed with promising applications in synthetic organic chemistry.

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N. GONZALEZ-MOJICA ET AL.
6
Conclusions
In summary, 1,2,3-triazole 3-oxides are easily prepared from 1,4-disubstituted-1,2,3-tria-
zoles which in turn are obtained from CuAAC reaction. This simple synthetic protocol
allows a fast access to this kind of compounds, which will increase the research in
this area. The simplicity of the method suggests that this route to 1,2,3-triazole 3-oxides
will enjoy the widespread application.
Experimental
General remarks
The starting materials were purchased from Aldrich Chemical Co. and were used with-
out further purification. Solvents were distilled before use. Silica plates of 0.20 mm
thickness were used for thin layer chromatography. Melting points were determined
1
with a Kruss Optronic melting point apparatus and they are uncorrected. H and 13C
€
NMR spectra were recorded using a Bruker Avance 300 MHz (Bruker, MA, USA), and
a Varian 500 MHz (Varian, CA, USA); the chemical shifts (d) are given in ppm relative
to TMS as internal standard (0.00). For analytical purposes, the mass spectra were
recorded on a Shimadzu GCMS-QP2010 Plus (Shimadzu, Kyoto, Japan) in the EI mode,
70 eV, 200 ꢀC through a direct inlet probe. Only the molecular and parent ions (m/z)
are reported. IR spectra were recorded on a Bruker TENSOR 27 FT instrument. 1,2,3-
triazoles were prepared according to the literature.[18,27,28]
For the X-ray diffraction studies, crystals of compounds 5 and 8 were obtained by
slow evaporation of a dilute MeOH solution, and the reflections were acquired with a
Bruker APEX DUO diffractometer equipped with an Apex II CCD detector. Three
standard reflections every 97 reflections were used to monitor the crystal stability. The
structures were solved by direct methods; missing atoms were found by difference-
Fourier synthesis, and refined on F2 by a full-matrix least-squares procedure using
anisotropic displacement parameters using SHELX-97. Crystallographic data for the
structures reported herein have been deposited with the Cambridge Crystallographic
Data Centre (CCDC No. 1873609 for compound 2). Copies of available materials can
be obtained free of charge on application to the Director, CCDC, 12 Union Road,
Cambridge CB2 IEZ, UK (facsimile: (44) 01223 336033); e-mail: deposit@ccdc.ac.uk.
Synthesis of 1,2,3-triazole 3-oxides
Typical procedure
A 30% aqueous solution of H2O2 (5 mL) was added to a pre-cooled solution of the
appropriate 1,2,3-triazole (300 mg) in CF3CO2H (4 mL) at 0 ꢀC. The resulting reaction
mixture was stirred at room temperature during 1 h and an additional aliquot of 30%
H2O2 solution (5 mL) was added. The resulting mixture was heated at 40 ꢀC for 2 h. If
necessary, 30% H2O2 solution (2 mL) was added every hour (maximum 5 h) to total dis-
appearance of starting material monitored by TLC. The mixture was cooled to room
temperature and A saturated solution of NaHCO3 (10 mL) was added and the organic
layer was extracted with AcOEt (3 ꢂ 20 mL). The combined organic layers were dried

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7
over anhydrous Na2SO4, the solvent was removed under reduced pressure and the final
product was purified by column chromatography (SiO2, hexane/AcOEt 7:3). 1-benzyl-4-
phenyl-1,2,3-triazole 3-oxide (2). White solid, m. p. 193–195 ꢀC (88.8%). IR (ATR,
1
cmꢁ1): 3056, 2958, 1496, 1466, 1394 (N–O), 1164, 760. H NMR (300 MHz, CDCl3): d
7.93 (d, 2H), 7.55 (s, 1H), 7.39–7.28 (m, 8H), 5.22 (s, 2H). 13C NMR (75 MHz, CDCl3):
d 130.8, 129.4, 127.4, 127.0, 127.2, 126.7, 126.7, 124.4, 123.4, 119.8, 53.6. MS [EIþ] m/
z(%):251 [M]þ (32), 234 [M–O]þ (5), 116 [M–C7H7N2O]þ (23), 102 [M–C8H9N2O]þ
(30), 91 [C6H5–CH2]þ (100), 65 [C5H5]þ (25). HRMS (EIþ): for C15H13N3O calcd.
251.1059, found 251.1063.
Acknowledgments
~
The authors would like to thank N. Zavala, A. Nunez, and L. Triana for the technical support.
Funding
Financial support from SIEA-UAEMEX (Project No. 4326/2017/C1) and CONACYT (Project No.
135053) is gratefully acknowledged.
ORCID
~
Erick Cuevas-Yanez
http://orcid.org/0000-0002-9437-637X
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