Recyclable Heterogeneous Copper(II)-Catalyzed Oxidative Cyclization of 2-Pyridine Ketone Hydrazones towards [1,2,3]Triazolo[1,5-a]pyridines

Article abstract of DOI:10.1055/s-0037-1610726

The heterogeneous copper(II)-catalyzed oxidative cyclization of 2-pyridine ketone hydrazones was achieved in ethyl acetate at room temperature in the presence of an MCM-41-anchored bidentate 2-aminoethylamino copper(II) catalyst [MCM-41-2N-Cu(OAc) _2<

Full text of DOI:10.1055/s-0037-1610726

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2019, 51, A–K
paper
A
en
G. Jiang et al.
Paper
Synthesis
Recyclable Heterogeneous Copper(II)-Catalyzed Oxidative Cycliza-
tion of 2-Pyridine Ketone Hydrazones Towards [1,2,3]Triazolo[1,5-
a]pyridines
Gan Jianga
Yang Lina
Mingzhong Cai*b
Hong Zhao*a
R1
R1
MCM-41-2N-Cu(OAc)2
(5 mol%)
N
R
N
R
0
0
0
0-0
0
0
2-1
0
5
6-
2
8
4
6
N
N
NH2
EtOAc, r.t., air
N
33 examples
up to 94% yield
a School of Chemistry & Chemical Engineering, Guangdong
Cosmetics Engineering & Technology Research Center,
Guangdong Pharmaceutical University, Guangzhou
510006, P. R. of China
R1
R1
N
1. N2H4·H2O, AcOH (0.1 equiv)
EtOH, reflux, 6 h
O
R
R
zhaohong1001@sina.com
N
N
b College of Chemistry & Chemical Engineering, Jiangxi
Normal University, Nanchang 330022, P. R. of China
mzcai@jxnu.edu.cn
N
MCM-41-2N-Cu(OAc)2
(5 mol%)
2.
23 examples
up to 96% yield
EtOAc/EtOH (5:1), r.t., air
Recyclable copper catalyst!
Received: 15.06.2019
Accepted after revision: 06.08.2019
Published online: 03.09.2019
metric amount of an oxidant such as Ag2O,6 nickel perox-
ide,7 Pb(OAc)2,8 MnO2,9 copper salts,10 or hypervalent io-
dine.11
DOI: 10.1055/s-0037-1610726; Art ID: ss-2019-h0326-op
Copper-catalyzed organic reactions are particularly im-
portant in modern organic synthesis owing to low cost and
low toxicity of copper catalysts. To develop economic and
environmentally benign catalytic oxidative reactions, em-
ployment of a copper salt as a catalytic oxidant is highly de-
sirable. As a result, copper-catalyzed oxidative C–H bond
functionalization12 and C–N bond-forming reaction have
received much attention.13 In spite of significant progress
made in N–N bond formation reactions,14 there are very
few reports on catalytic methods for the construction of the
N–N bond.15 Recently, Nagasawa and coworkers reported a
copper(I)-catalyzed tandem addition/oxidative cyclization
of nitriles with 2-aminopyridines towards 3-substituted
[1,2,4]triazolo[1,5-a]pyridines and a copper(II)-catalyzed
oxidative cyclization of 2-pyridine ketone hydrazones for
the construction of [1,2,3]triazolo[1,5-a]pyridines.16 Al-
though these copper-catalyzed N–N bond formation reac-
tions are highly efficient for the construction of triazolopyr-
idines, the use of 5–10 mol% of copper salts with or without
a ligand was required to obtain high yields, and these ho-
mogeneous copper catalysts are difficult to recover from
the reaction mixture and cannot be recycled. Furthermore,
homogeneous catalysis might lead to unacceptable contam-
ination of the product by copper, because triazolopyridines
as strong ligands could easily coordinate with copper salts
to produce the corresponding stable complexes,17 thus re-
stricting their applications in the synthesis of drug mole-
cules containing triazolopyridines, which must be free of
any residual metal. Anchoring of homogeneous copper cat-
alysts on various insoluble supports with high surface areas
is usually the strategy of choice for the solution to these
Abstract The heterogeneous copper(II)-catalyzed oxidative cyclization
of 2-pyridine ketone hydrazones was achieved in ethyl acetate at room
temperature in the presence of an MCM-41-anchored bidentate 2-ami-
noethylamino copper(II) catalyst [MCM-41-2N-Cu(OAc)2], in the pres-
ence of air as the oxidant, yielding a wide variety of [1,2,3]triazolo[1,5-
a]pyridines in mostly good to high yields. The present method was also
applied to the direct one-pot synthesis of [1,2,3]triazolo[1,5-a]pyri-
dines from 2-acylpyridine derivatives and hydrazine monohydrate. Im-
portantly, this supported copper(II) catalyst could be conveniently ob-
tained via a simple procedure from easily available and inexpensive
reagents, recovered by filtration of the reaction mixture, and reused at
least seven times without a significant loss of catalytic activity.
Key words copper catalysis, [1,2,3]triazolo[1,5-a]pyridines, oxidative
cyclization, heterogeneous catalysis, N–N coupling
Triazolopyridine structures are important building
blocks for many pharmaceutical and functional materials.
Among various triazolopyridine derivatives, [1,2,3]triazo-
lo[1,5-a]pyridines have been investigated by the Jones1 and
Abarca2 groups since the early 1980s. Although pharmaco-
logical studies of [1,2,3]triazolo[1,5-a]pyridine derivatives
are rare,3 their unique fluorescent properties and coordina-
tion chemistry have been extensively explored and applied
to materials science.4 Additionally, they are frequently used
as useful synthetic intermediates in organic synthesis.5 Be-
cause of the versatility of [1,2,3]triazolo[1,5-a]pyridines,
considerable effort has been devoted to developing efficient
synthetic routes for their preparation. The most commonly
used synthesis of [1,2,3]triazolo[1,5-a]pyridines involves
the oxidative cyclization of 2-pyridylcarboxaldehyde or
2-pyridyl ketone hydrazones by using at least a stoichio-
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
G. Jiang et al.
Paper
Synthesis
problems, because the supported catalysts can be easily
separated from the reaction product via a simple filtration
process after reactions and reused several times.18 Recently,
application of supported copper catalysts in various car-
bon–heteroatom bond-forming reactions has attracted con-
siderable interest.19 However, to the best of our knowledge,
heterogeneous copper-catalyzed oxidative N–N bond for-
mation for the construction of [1,2,3]triazolo[1,5-a]pyri-
dines has not been explored until now.
OH
OH
1. (MeO)3Si(CH2)3NH(CH2)2NH2
toluene, 110 °C, 24 h
OH
2. Me3SiCl, r.t., 24 h
MCM-41
OSiMe3
O
Si
O
CuXn
N
H
NH2
DMF, r.t., 12 h
OMe
Recently, the mesoporous silica material MCM-41 has
been widely employed as an ideal solid support for anchor-
ing homogeneous metal catalysts due to its advantageous
properties over other solid supports, including an extreme-
ly high surface area, large pore volume, tunable and uni-
form pore size, and excellent thermal stability.20 To date,
palladium,21 rhodium,22 molybdenum,23 gold,24 and cop-
per19f–h complexes anchored onto MCM-41 have been pre-
pared and applied to various organic reactions as recyclable
heterogeneous catalysts. In continuation of our interest in
developing green and sustainable catalytic systems for or-
ganic transformations,19f–j,21e–g,24d herein we report a het-
erogeneous copper(II)-catalyzed oxidative cyclization of 2-
pyridine ketone hydrazones leading to [1,2,3]triazolo[1,5-
a]pyridines by using an MCM-41-anchored bidentate 2-am-
inoethylamino copper(II) complex [MCM-41-2N-Cu(OAc)2]
as the catalyst and air as the oxidant (Scheme 1).
MCM-41-2N
OSiMe3
O
H
N
Si
NH2
O
OMe
CuXn
MCM-41-2N-CuI [A], CuXn = CuI
MCM-41-2N-CuBr2 [B], CuXn = CuBr2
MCM-41-2N-Cu(OAc)2 [C], CuXn = Cu(OAc)2
MCM-41-2N-Cu(OTf)2 [D], CuXn = Cu(OTf)2
MCM-41-2N-CuSO4 [E], CuXn = CuSO4
MCM-41-2N-Cu(NO3)2 [F], CuXn = Cu(NO3)2
Scheme 2 Synthesis of the MCM-41-2N-CuXn catalysts
the effect of various heterogeneous copper catalysts on the
model reaction was examined with DMF as the solvent at
60 °C under air (entries 1–6). The best result was obtained
by using MCM-41-2N-Cu(OAc)2 (C) as catalyst, to give
3-phenyl[1,2,3]triazolo[1,5-a]pyridine (2a) in 90% yield
(entry 3). The use of MCM-41-2N-CuI (A) and MCM-41-2N-
CuBr2 (B) as catalyst provided the desired 2a in 67 and 78%
yield (entries 1 and 2), while other heterogeneous copper
catalysts such as MCM-41-2N-Cu(OTf)2 (D), MCM-41-2N-
CuSO4 (E), and MCM-41-2N-Cu(NO3)2 (F) were ineffective
(entries 4–6). The reaction did not work without any cop-
per catalyst, revealing the catalytic role of copper in this
transformation (entry 7). Next, the effect of the solvent on
the model reaction was explored with MCM-41-2N-
Cu(OAc)2 (C) as the catalyst at 60 °C (entries 8–12). The re-
action also proceeded smoothly in acetonitrile, toluene, and
ethyl acetate, yielding the desired 2a in 84–88% yield (en-
tries 8–10). In the case of EtOAc as solvent, the starting ma-
terial 1a was completely converted into 2a within 0.5 h, be-
cause EtOAc could accelerate the reaction (entry 10). The
use of 1,2-dimethoxyethane and ethanol as solvents led to
decreased yields due to the hydrolytic decomposition of
starting material 1a (entries 11 and 12). To our delight, the
reaction in EtOAc could also proceed efficiently at room
temperature to give the target product 2a in 87% yield with-
in 0.5 h (entry 13). In contrast, complete consumption of 1a
was not observed with MeCN or toluene as solvent even af-
ter 3 h (entries 14 and 15). Therefore, EtOAc was selected as
the solvent, because of the high reaction rate at room tem-
perature (entry 13). Reducing the loading of the copper cat-
alyst to 2.5 mol% resulted in a decreased yield and required
a longer reaction time (entry 16). Increasing the loading of
the copper catalyst to 10 mol% did not increase the yield of
R1
R1
MCM-41-2N-Cu(OAc)2
(5 mol%)
N
N
R
R
N
NH2
N
EtOAc, r.t., air
N
Scheme 1 Heterogeneous copper(II)-catalyzed synthesis of [1,2,3]tri-
azolo[1,5-a]pyridines
MCM-41-anchored bidentate 2-aminoethylamino cop-
per(I) or (II) complexes [MCM-41-2N-CuXn] were facilely
synthesized via a simple procedure from easily available
andinexpensive[3-(2-aminoethylamino)propyl]trimethox-
ysilane according to our previous method (Scheme 2).19f
The condensation reaction of the mesoporous material
MCM-4120a with [3-(2-aminoethylamino)propyl]trime-
thoxysilane at 110 °C in toluene for 24 hours, followed by
treatment with Me3SiCl in toluene at room temperature
provided the MCM-41-anchored bidentate 2-aminoethyl-
amino ligand (MCM-41-2N). Subsequent reaction of
MCM-41-2N with various copper salts [CuXn = CuI, CuBr2,
Cu(OAc)2, Cu(OTf)2, CuSO4, and Cu(NO3)2] at room tempera-
ture in DMF afforded a series of MCM-41-anchored biden-
tate 2-aminoethylamino copper(I) or (II) complexes [MCM-
41-2N-CuXn] as pale blue powders.
In our initial screening experiments, the oxidative cy-
clization of 2-benzoylpyridine hydrazone (1a) was selected
as the model reaction to determine the optimal reaction
conditions, and the results are summarized in Table 1. First,
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K

C
G. Jiang et al.
Paper
Synthesis
2a significantly (entry 17). When homogeneous Cu(OAc)2
(5 mol%) was used as catalyst, the desired 2a was isolated in
88% yield (entry 18), indicating that the catalytic efficiency
of MCM-41-2N-Cu(OAc)2 was comparable to that of
Cu(OAc)2. When the reaction was carried out under argon,
the desired 2a was not detected, confirming that the oxida-
tive N–N bond formation reaction did not occur in the ab-
sence of air or oxygen (entry 19). The use of 2 mmol of 1a as
substrate also gave 2a in high yield (entry 20). Thus, the op-
timized reaction conditions for this oxidative cyclization
are the use of MCM-41-2N-Cu(OAc)2 (5 mol%) with EtOAc
as solvent at room temperature under air for 0.5 hours (en-
try 13).
conditions; the results are summarized in Scheme 3. A vari-
ety of substituted 2-benzoylpyridine hydrazones 1b–j bear-
ing various substituents on the phenyl group, regardless of
their electronic properties or substitution positions, were
converted into the corresponding triazolopyridines 2b–j in
mostly good to excellent yields within 0.5 h. Methoxy-sub-
stituted 2-benzoylpyridine hydrazones 1c and 1i with a
strongly electron-donating group furnished the target
product 2c and 2i in relatively low yields of 40 and 59% due
to the presence of competitive hydrolytic decomposition of
the hydazones to the ketones, since the stability of the hy-
drazone strongly depends on the basicity of its imino nitro-
gen atom. The cyclization reactions of the hydrazones 1k–
m having a rigid biphenyl or a bulky naphthalene group
also worked well, providing the desired products 2k–m in
78–85% yields, but the reaction of hydrazone 1k with a rig-
id biphenyl group required heating at 60 °C for a longer re-
action time to achieve complete consumption of 1k. 2,2′-
Dipyridylketone hydrazone 1n showed similar reactivity
with aryl pyridyl ketone hydrazones and gave the expected
product 2n in 89% yield within 0.5 h. In addition to aryl pyr-
idyl ketone hydrazones, alkyl pyridyl ketone hydrazones 1o
and 1p were also compatible with the standard conditions
and afforded the corresponding products 2o and 2p, respec-
tively, in 83 and 85% yield. Notably, substitution on the pyr-
idine ring was also tolerated in this transformation. For ex-
ample, aryl (5-bromopyridyl) ketone hydrazones 1q–y
bearing various substituents on the benzene ring could un-
dergo the cyclization reaction smoothly to give the corre-
sponding triazolopyridines 2q–y in mostly good to high
yields. Cyclohexyl (5-bromopyridyl) ketone hydrazone 1z
also gave the desired 2z in 82% yield. Additionally, hydra-
zones 1a′–d′ having 5-fluoro or 3-methyl groups on the
pyridine ring also reacted well, providing the corresponding
products 2a′–d′ in good yields. However, (6-bromopyridyl)
methyl ketone hydrazone 1e′ and (6-methylpyridyl) methyl
ketone hydrazone 1f′ displayed a relatively lower reactivity,
and the reactions required a higher temperature (60 °C) and
a longer reaction time, giving 2e′ and 2f′ in only 63 and 65%
yield. Interestingly, quinoline hydrazone 1g′ could undergo
the oxidative cyclization at 60 °C to give the corresponding
triazoloquinoline 2g′ in 52% yield. The relatively lower reac-
tivity of substrates 1e′–g′ may be due to the steric hin-
drance resulting from substitution at the 6-position on the
pyridine ring.
With this promising result in hand, we started to exam-
ine the substrate scope of this heterogeneous copper-cata-
lyzed oxidative cyclization reaction under the optimized
Table 1 Optimization of the Reaction Conditionsa
Ph
Ph
copper catalyst
(5 mol%)
N
N
N
NH2
N
solvent, temp, air
N
1a
2a
Entry
Copper cata- Solvent
lyst
Temp (°C) Time (h) Yield (%)b
1
2
A
DMF
60
60
60
60
60
60
60
60
60
60
60
60
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
3
3
67
78
90
0
B
DMF
3
C
DMF
3
4
D
DMF
12
12
12
12
3
5
E
DMF
0
6
F
DMF
0
7
–
DMF
0
8
C
MeCN
toluene
EtOAc
DME
84
88
85
72
74
87
71
75
80
89
88
0
9
C
3
10
11
12
13
14
15
16c
17d
18
19e
20f
C
0.5
C
3
C
EtOH
EtOAc
MeCN
toluene
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
3
C
0.5
3
C
C
3
C
1
C
0.5
0.5
Because the pyridine ketone hydrazones could be easily
obtained by the reaction of the corresponding 2-acylpyri-
dines with hydrazine monohydrate, we next attempted the
one-pot synthesis of [1,2,3]triazolo[1,5-a]pyridines to im-
prove the convenience of the present reaction; the results
are listed in Scheme 4. Optimization of the reaction condi-
tions indicated that the treatment of 2-benzoylpyridine 3a
with hydrazine monohydrate (1.5 equiv) in EtOH in the
presence of acetic acid (0.1 equiv) under reflux for 6 hours,
followed by oxidative cyclization in EtOAc/EtOH (5:1) in the
Cu(OAc)2
C
C
12
0.5
86
a Reaction conditions: 1a (0.2 mmol), copper catalyst (5 mol%), solvent
(1.5 mL), under air.
b Isolated yield.
c Catalyst (2.5 mol%) was used.
d Catalyst (10 mol%) was used.
e The reaction was performed under argon.
f Modified conditions: 1a (2 mmol), C (0.1 mmol), EtOAc (10 mL).
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K

D
G. Jiang et al.
Paper
Synthesis
R1
R1
MCM-41-2N-Cu(OAc)2
(5 mol%)
N
N
R
F
R
N
NH2
N
EtOAc, r.t., air
N
1
2
Me
Cl
CF3
OMe
N
N
N
N
N
N
N
2c, 0.5 h, 40%
N
N
N
N
N
N
N
N
N
N
N
2e, 0.5 h, 84%
2b, 0.5 h, 81%
2a, 0.5 h, 87%
2f, 0.5 h, 86%
2d, 0.5 h, 94%
Ph
Me
CF3
Me
Me
OMe
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
2k,a 2 h, 82%
2l, 1 h, 85%
2j, 0.5 h, 75%
2g, 0.5 h, 83%
2h, 0.5 h, 86%
2i, 0.5 h, 59%
OMe
Me
Me
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Br
N
N
N
2m, 1 h, 78%
N
Br
2o, 0.5 h, 83%
2p, 0.5 h, 85%
2q, 0.5 h, 85%
2n, 0.5 h, 89%
2r, 0.5 h, 42%
Cl
F
F3C
Me
Me
MeO
Me
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Br
N
Br
Br
N
N
Br
N
Br
Br
2x, 0.5 h, 76%
2w, 0.5 h, 55%
2u, 0.5 h, 78%
2v, 0.5 h, 86%
2t, 0.5 h, 74%
2s, 0.5 h, 82%
Ph
Me
Me
Me
Me
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
F
F
Br
N
Br
2d′, 3 h, 74%
2y,a 2 h, 72%
2a′, 0.5 h, 81%
2b′, 0.5 h, 77%
2c′, 3 h, 70%
2z, 0.5 h, 82%
Me
Me
N
N
N
N
N
N
N
N
N
Br
Me
2e′,a 4 h, 63%
2f′,a 4 h, 65%
2g′,a 24 h, 52%
Scheme 3 Heterogeneous copper(II)-catalyzed synthesis of substituted [1,2,3]triazolo[1,5-a]pyridines. Reagents and conditions: 1 (0.2 mmol), MCM-
41-2N-Cu(OAc)2 (5 mol%), EtOAc (1.5 mL), r.t. (unless indicated otherwise), under air; isolated yields given. a Reaction was conducted at 60 °C.
presence of MCM-41-2N-Cu(OAc)2 (5 mol%) at room tem-
perature under air for 0.5 hours afforded the desired 2a in
84% yield. Subsequently, a variety of 2-acylpyridines were
applied to the one-pot construction of [1,2,3]triazolo[1,5-
a]pyridine derivatives. As shown in Scheme 4, 2-(4-methyl-
benzoyl)pyridine (3b), 2-(4-trifluoromethylbenzoyl)pyri-
dine (3f), and 2-acetyl-6-bromopyridine (3e′) afforded the
corresponding triazolopyridines 2b, 2f, and 2e′ in excellent
yields. Substituted 2-benzoylpyridines 3c–e, 3i, and 3j
bearing either an electron-donating or electron-withdraw-
ing group on the benzene ring underwent the one-pot reac-
tion smoothly to give the corresponding products 2c–e, 2i,
and 2j in good yields. The other 2-acylpyridines also react-
ed well in this transformation, thus providing triazolopyri-
dines 2l, 2n-v, 2z, 2a′, and 2f′–g′ in good yields. Notably, the
yields of products 2c, 2i, 2r, and 2e′–g′ were significantly
improved to 74, 76, 75, 91, 89, and 80%, respectively,
through the one-pot reaction compared with the direct
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K

E
G. Jiang et al.
Paper
Synthesis
synthesis from the corresponding hydrazones. The im-
provements in the yields may be due to inhibition of the hy-
drolytic decomposition of the intermediate hydrazones in
the presence of excess hydrazine monohydrate. Thus, we
have developed a general, efficient and practical one-pot
route to [1,2,3]triazolo[1,5-a]pyridine derivatives from 2-
acylpyridines.
To ensure that the observed catalysis arises from the
heterogeneous catalyst MCM-41-2N-Cu(OAc)2 and not from
the leached copper species in solution, we focused on the
oxidative cyclization of 2-benzoylpyridine hydrazone (1a).
The reaction was carried out until an approximately 50%
conversion of 1a. Then the copper catalyst was removed by
filtration of the reaction solution and the catalyst-free fil-
trate was allowed to react further under air for 0.5 h. We
found that after removal of the catalyst, no increase in the
conversion of 2-benzoylpyridine hydrazone (1a) was ob-
served. The copper content in the filtrate was also deter-
mined by ICP-AES analysis, and no copper was detected in
the clear solution. These results rule out any contribution to
the observed conversion from the leached copper species,
indicating that MCM-41-2N-Cu(OAc)2 was stable during the
oxidative cyclization and the observed cyclization reaction
was intrinsically heterogeneous.
A possible reaction mechanism for this heterogeneous
copper(II)-catalyzed synthesis of [1,2,3]triazolo[1,5-a]pyri-
dines is illustrated in Scheme 5.16b Firstly, coordination of
the pyridine ketone hydrazone 1 to MCM-41-2N-Cu(OAc)2
provides intermediate A. Then two electrons from the hy-
drazone immediately transfer to each of the two copper(II)
ions in intermediate A, to generate MCM-41-2N-CuOAc C
and the diazo intermediate B. The formation of the diazo in-
termediate was also suggested by a previous report on di-
azoketone formation from ketohydrazone by Cu(acac)2 oxi-
dation.25 The formed diazo intermediate B easily converts
into the triazolopyridine product 2 since the cyclized struc-
ture is highly dominant in the equilibrium between the di-
azo form and product 2.9c,25 Finally, the resulting MCM-41-
2N-CuOAc C is oxidized by atmospheric oxygen to regener-
ate the MCM-41-2N-Cu(OAc)2 complex and complete the
catalytic cycle.
For the practical application of a supported metal cata-
lyst, its ease of separation and recyclability are important
factors to be examined. The MCM-41-2N-Cu(OAc)2 catalyst
can be facilely separated and recovered by a simple filtra-
tion of the reaction mixture. We next studied the recycling
of the catalyst by using the one-pot reaction of 2-(4-trifluo-
romethylbenzoyl)pyridine (3f) with hydrazine monohy-
R1
R1
1. N2H4·H2O, AcOH (0.1 equiv)
EtOH, reflux, 6 h
O
R
N
R
N
N
2. MCM-41-2N-Cu(OAc)2 (5 mol%)
EtOAc/EtOH (5:1), r.t., air
N
2
3
Cl
F
CF3
Me
OMe
OMe
Me
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
2d,a 4 h, 75%
2e,a 4 h, 74%
2f, 1 h, 96%
OMe
2i, 2 h, 76%
2j, 4 h, 71%
2c, 2 h, 74%
2a, 0.5 h, 84%
2b, 1 h, 91%
F
Me
Me
Me
Me
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Br
N
N
N
2t,a 4 h, 71%
N
N
Br
Br
Br
2n, 2 h, 75%
2l, 2 h, 83%
2o, 2 h, 82%
2q, 2 h, 76%
2p, 2 h, 87%
2r, 4 h, 75%
2s, 2 h, 75%
Cl
F3C
Me
N
Me
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Me
N
Br
Br
Br
F
N
Br
2g′, 2 h, 80%
2f′, 2 h, 89%
2a′, 2 h, 78%
2e′, 2 h, 91%
2u,a 4 h, 75%
2z, 2 h, 85%
2v, 2 h, 84%
Scheme 4 Heterogeneous copper(II)-catalyzed one-pot synthesis of [1,2,3]triazolo[1,5-a]pyridine derivatives. Reagents and conditions: 1. 3 (0.2
mmol), N2H4·H2O (0.3 mmol), AcOH (0.02 mmol), EtOH (1.0 mL), 80 °C, 6 h; 2. MCM-41-2N-Cu(OAc)2 (5 mol%), EtOAc (5 mL) r.t. (unless indicated
otherwise), under air, 0.5–4 h; isolated yields given. a Reaction was conducted at 60 °C.
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K

F
G. Jiang et al.
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Synthesis
catalyst can facilely be obtained via a simple procedure
from easily available and cheap reagents and recovered by
filtration of the reaction mixture, and reused at least seven
times with only a slight decrease in activity. Thus, the pres-
ent method is an attractive alternative to prepare [1,2,3]tri-
azolo[1,5-a]pyridine derivatives.
R
H2O
2 L-CuII(OAc)2
L = MCM-41-2N
N
N
NH2
1
2 AcOH
+ 1/2 O2
OAc
CuII
R
All chemicals were purchased from different commercial suppliers
and used as received without purification. All solvents were dried and
distilled before use. MCM-41-2N-CuI (A), MCM-41-2N-CuBr2 (B),
MCM-41-2N-Cu(OAc)2 (C), MCM-41-2N-Cu(OTf)2 (D), MCM-41-2N-
CuSO4 (E), and MCM-41-2N-Cu(NO3)2 (F) were prepared according to
our previous procedure;19f the copper content was determined to be
0.57, 0.59, 0.64, 0.66, 0.61, and 0.62 mmol/g, respectively. 2-Acylpyri-
dine derivatives26 and 2-pyridyl ketone hydrazones16b were prepared
according to literature methods. The products were isolated by flash
column chromatography on 100–200 mesh silica gel with a mixture
of light petroleum ether and ethyl acetate as eluent. All 1H and 13C
NMR spectra were recorded on a Bruker Avance 400 NMR spectrome-
ter (400 MHz or 100 MHz, respectively); CDCl3 was used as solvent
with TMS as internal reference. Melting points were determined on
an X-5 Data microscopic melting point apparatus and are uncorrect-
ed. The copper content was determined on a Perkin-Elmer Optima
3100 XL ICP-AES spectrometer. High-resolution mass spectra (HRMS)
were obtained with a GCT-TOF instrument with an EI source.
2 L-CuIOAc
L
C
O
O
N
H
N
N
H
L
A
CuII
AcO
O
O
R
R
N
N
+ 2 AcOH
N
N
N
N
triazolopyridine 2
B
diazo form
Scheme 5 Proposed catalytic cycle
drate for the synthesis of 3-(4-trifluoromethylphe-
nyl)[1,2,3]triazolo[1,5-a]pyridine 2f. After the reaction was
carried out, the reaction mixture was diluted with ethyl ac-
etate, and the catalyst was recovered by simple filtration
and washed with distilled water and acetone. After being
air-dried, it can be reused directly without further purifica-
tion. The recovered copper catalyst was employed in the
next run, and the yield of the target product 2f was found to
be 95, 96, 95, 94, 94, 93, and 92% in seven consecutive cy-
cles, respectively. Compared with the fresh catalyst (96%
yield), only a slight decrease in activity was observed for the
recovered catalyst. In addition, the copper leaching in the
supported catalyst was also examined by ICP analysis. The
copper content of the catalyst after eight consecutive runs
was determined to be 0.62 mmol/g, indicating that only
3.1% of copper had been lost from the MCM-41 support.
In conclusion, we have developed a highly efficient het-
erogeneous copper(II)-catalyzed oxidative cyclization of
2-pyridyl ketone hydrazones for the construction of
[1,2,3]triazolo[1,5-a]pyridine derivatives. The present ap-
proach was also applied to the direct synthesis of [1,2,3]tri-
azolo[1,5-a]pyridines from 2-acylpyridines and hydrazine
monohydrate by using a one-pot reaction. In contrast to the
classical synthetic route to these compounds, the present
heterogeneous oxidative cyclization method shows many
attractive features, including: (a) the starting materials are
easily available, and a wide range of 2-acylpyridine deriva-
tives are allowed; (b) a wide variety of [1,2,3]triazolo[1,5-
a]pyridines could be produced in mostly good to high
yields; (c) the reaction conditions were mild and atmo-
spheric oxygen was used as the oxidant, producing water as
the sole side-product; and (d) this heterogeneous copper(II)
Heterogeneous Copper(II)-Catalyzed Synthesis of [1,2,3]Triazo-
lo[1,5-a]pyridines 2a–g′ from Hydrazones 1a–g′; General Proce-
dure
A dried reaction tube was charged with hydrazone 1 (0.2 mmol),
MCM-41-2N-Cu(OAc)2 (16 mg, 0.01 mmol), and EtOAc (1.5 mL). The
reaction mixture was stirred at room temperature or 60 °C for the in-
dicated time. The mixture was diluted with EtOAc (15 mL) and fil-
tered. The copper catalyst was washed with acetone (2 × 5 mL), air-
dried for 2 h, and reused in the next run. The filtrate was washed with
brine (10 mL) and dried over MgSO4. Then the organic phase was con-
centrated under vacuum and the residue was purified by column
chromatography (silica gel, light PE/EtOAc, 3:1) to afford the desired
product 2.
3-Phenyl[1,2,3]triazolo[1,5-a]pyridine (2a)
Yield: 34.1 mg (87%); white solid; mp 113–114 °C (Lit.16b 112–113 °C).
1H NMR (400 MHz, CDCl3):  = 8.74 (d, J = 7.2 Hz, 1 H), 8.01–7.94 (m, 3
H), 7.51 (t, J = 7.8 Hz, 2 H), 7.39 (t, J = 7.6 Hz, 1 H), 7.32–7.25 (m, 1 H),
7.00 (t, J = 6.8 Hz, 1 H).
13C NMR (100 MHz, CDCl3):  = 138.0, 131.5, 130.5, 129.0, 127.9,
126.7, 125.6, 125.5, 118.4, 115.2.
3-(4-Methylphenyl)[1,2,3]triazolo[1,5-a]pyridine (2b)
Yield: 33.9 mg (81%); white solid; mp 138–139 °C (Lit.7b 137–138 °C).
1H NMR (400 MHz, CDCl3):  = 8.75 (d, J = 6.4 Hz, 1 H), 7.99 (d, J = 8.4
Hz, 1 H), 7.86 (d, J = 7.2 Hz, 2 H), 7.35–7.26 (m, 3 H), 7.00 (t, J = 5.6 Hz,
1 H), 2.43 (s, 3 H).
13C NMR (100 MHz, CDCl3):  = 138.1, 137.8, 130.3, 129.7, 128.6,
126.6, 125.6, 125.3, 118.5, 115.2, 21.3.
3-(4-Methoxyphenyl)[1,2,3]triazolo[1,5-a]pyridine (2c)
Yield: 18.1 mg (40%); white solid; mp 133–134 °C (Lit.5c 134–135 °C).
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K

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G. Jiang et al.
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1H NMR (400 MHz, CDCl3):  = 8.73 (d, J = 6.8 Hz, 1 H), 7.95 (d, J = 9.2
Hz, 1 H), 7.88 (d, J = 8.4 Hz, 2 H), 7.27 (t, J = 7.8 Hz, 1 H), 7.05 (d, J = 8.4
Hz, 2 H), 6.98 (t, J = 6.8 Hz, 1 H), 3.88 (s, 3 H).
13C NMR (100 MHz, CDCl3):  = 159.5, 138.0, 130.1, 128.0, 125.6,
125.2, 124.1, 118.5, 115.3, 114.5, 55.4.
1H NMR (400 MHz, CDCl3):  = 8.69 (d, J = 7.2 Hz, 1 H), 7.86 (dd, J = 7.6,
1.6 Hz, 1 H), 7.82 (d, J = 9.2 Hz, 1 H), 7.42–7.37 (m, 1 H), 7.22–7.17 (m,
1 H), 7.11 (t, J = 7.6 Hz, 1 H), 7.04 (d, J = 8.0 Hz, 1 H), 6.94 (t, J = 6.4 Hz,
1 H), 3.85 (s, 3 H).
13C NMR (100 MHz, CDCl3):  = 156.4, 135.7, 131.8, 131.1, 129.6,
125.1, 124.3, 121.2, 120.5, 120.4, 115.1, 111.3, 55.4.
HRMS (ESI): m/z [M + H]+ calcd for C13H12N3O: 226.0980; found:
226.0981.
3-(4-Fluorophenyl)[1,2,3]triazolo[1,5-a]pyridine (2d)
Yield: 40.1 mg (94%); white solid; mp 133–134 °C (Lit.16b 134–135 °C).
1H NMR (400 MHz, CDCl3):  = 8.72 (d, J = 7.2 Hz, 1 H), 7.94–7.88 (m, 3
H), 7.29 (t, J = 7.8 Hz, 1 H), 7.18 (t, J = 8.8 Hz, 2 H), 7.00 (t, J = 6.8 Hz, 1
H).
3-(2-Methylphenyl)[1,2,3]triazolo[1,5-a]pyridine (2j)
Yield: 31.4 mg (75%); white solid; mp 105–106 °C (Lit.2f 106–107 °C).
13C NMR (100 MHz, CDCl3):  = 162.5 (d, J = 245.9 Hz), 137.0, 130.2,
128.3 (d, J = 8.1 Hz), 127.6 (d, J = 3.3 Hz), 125.8, 125.6, 118.1, 116.0 (d,
J = 21.6 Hz), 115.4.
1H NMR (400 MHz, CDCl3):  = 8.75 (d, J = 6.8 Hz, 1 H), 7.67 (d, J = 8.8
Hz, 1 H), 7.48–7.45 (m, 1 H), 7.38–7.28 (m, 3 H), 7.27–7.22 (m, 1 H),
7.00 (t, J = 6.8 Hz, 1 H), 2.44 (s, 3 H).
13C NMR (100 MHz, CDCl3):  = 138.4, 137.5, 131.5, 131.0, 130.1,
130.0, 128.4, 125.9, 125.4, 125.2, 118.3, 115.2, 20.5.
3-(4-Chlorophenyl)[1,2,3]triazolo[1,5-a]pyridine (2e)
Yield: 38.6 mg (84%); white solid; mp 158–159 °C (Lit.16b 159–160 °C).
1H NMR (400 MHz, CDCl3):  = 8.77 (d, J = 7.2 Hz, 1 H), 7.97 (d, J = 8.8
Hz, 1 H), 7.90 (d, J = 8.4 Hz, 2 H), 7.48 (d, J = 8.4 Hz, 2 H), 7.34 (dd, J =
8.8, 6.8 Hz, 1 H), 7.04 (t, J = 6.8 Hz, 1 H).
13C NMR (100 MHz, CDCl3):  = 136.9, 133.7, 130.4, 130.0, 129.2,
127.8, 126.0, 125.8, 118.2, 115.4.
3-Biphenyl-4-yl[1,2,3]triazolo[1,5-a]pyridine (2k)
Yield: 44.5 mg (82%); white solid; mp 178–179 °C.
1H NMR (400 MHz, CDCl3):  = 8.72 (d, J = 6.8 Hz, 1 H), 8.03 (d, J = 8.0
Hz, 2 H), 8.01–7.98 (m, 1 H), 7.73 (d, J = 8.0 Hz, 2 H), 7.65 (d, J = 7.6 Hz,
2 H), 7.46 (t, J = 7.6 Hz, 2 H), 7.36 (t, J = 7.2 Hz, 1 H), 7.31–7.26 (m, 1
H), 6.97 (t, J = 6.8 Hz, 1 H).
13C NMR (100 MHz, CDCl3):  = 140.6, 140.5, 137.6, 130.5, 128.9,
127.7, 127.5, 127.0, 126.9, 125.7, 125.6, 118.5, 115.3.
3-[4-(Trifluoromethyl)phenyl][1,2,3]triazolo[1,5-a]pyridine (2f)
Yield: 45.3 mg (86%); white solid; mp 184–185 °C (Lit.5a 178–179 °C).
HRMS (ESI): m/z [M + H]+ calcd for C18H14N3: 272.1188; found:
272.1179.
1H NMR (400 MHz, CDCl3):  = 8.77 (d, J = 6.8 Hz, 1 H), 8.07 (d, J = 8.0
Hz, 2 H), 8.00 (d, J = 8.8 Hz, 1 H), 7.74 (d, J = 8.0 Hz, 2 H), 7.38 (dd, J =
8.8, 6.8 Hz, 1 H), 7.05 (t, J = 6.8 Hz, 1 H).
13C NMR (100 MHz, CDCl3):  = 136.3, 135.0, 130.8, 129.6 (q, J = 32.1
Hz), 126.6, 126.5, 125.9 (q, J = 3.8 Hz), 124.2 (q, J = 270.4 Hz), 118.0,
115.5.
3-Naphthalen-1-yl[1,2,3]triazolo[1,5-a]pyridine (2l)
Yield: 41.7 mg (85%); white solid; mp 122–123 °C.
1H NMR (400 MHz, CDCl3):  = 8.76 (d, J = 7.2 Hz, 1 H), 8.22 (d, J = 8.4
Hz, 1 H), 7.92–7.89 (m, 2 H), 7.69 (d, J = 6.8 Hz, 1 H), 7.61 (d, J = 9.2 Hz,
1 H), 7.56 (t, J = 7.6 Hz, 1 H), 7.53–7.45 (m, 2 H), 7.17 (t, J = 7.4 Hz, 1
H), 6.96 (t, J = 6.8 Hz, 1 H).
3-[3-(Trifluoromethyl)phenyl][1,2,3]triazolo[1,5-a]pyridine (2g)
Yield: 43.7 mg (83%); white solid; mp 144–145 °C.
13C NMR (100 MHz, CDCl3):  = 137.5, 134.1, 132.2, 131.7, 129.0,
128.4, 128.1, 127.9, 126.6, 126.2, 125.9, 125.5, 125.4, 118.4, 115.5.
HRMS (ESI): m/z [M + H]+ calcd for C16H12N3: 246.1031; found:
1H NMR (400 MHz, CDCl3):  = 8.78 (d, J = 7.2 Hz, 1 H), 8.23 (s, 1 H),
8.15 (t, J = 3.6 Hz, 1 H), 8.00 (d, J = 9.2 Hz, 1 H), 7.65–7.62 (m, 2 H),
7.38 (dd, J = 9.0, 6.6 Hz, 1 H), 7.06 (t, J = 7.0 Hz, 1 H).
13C NMR (100 MHz, CDCl3):  = 136.4, 132.3, 131.5 (q, J = 32.2 Hz),
130.6, 129.6, 129.5, 126.4, 125.9, 124.4 (q, J = 3.7 Hz), 124.1 (q, J =
270.8 Hz), 123.2 (q, J = 3.7 Hz), 118.0, 115.5.
246.1036.
3-Naphthalen-2-yl[1,2,3]triazolo[1,5-a]pyridine (2m)
HRMS (ESI): m/z [M + H]+ calcd for C13H9F3N3: 264.0749; found:
Yield: 38.3 mg (78%); yellow solid; mp 158–159 °C.
264.0744.
1H NMR (400 MHz, CDCl3):  = 8.65 (d, J = 3.6 Hz, 1 H), 8.30 (s, 1 H),
8.09 (dd, J = 8.4, 1.2 Hz, 1 H), 8.02–7.80 (m, 4 H), 7.50–7.42 (m, 2 H),
7.24–7.15 (m, 1 H), 6.93–6.86 (m, 1 H).
3-(3,5-Dimethylphenyl)[1,2,3]triazolo[1,5-a]pyridine (2h)
13C NMR (100 MHz, CDCl3):  = 137.8, 133.6, 132.8, 130.6, 128.9,
128.8, 128.1, 127.8, 126.5, 126.2, 125.9, 125.6, 125.1, 124.7, 118.4,
115.4.
HRMS (ESI): m/z [M + H]+ calcd for C16H12N3: 246.1031; found:
246.1029.
Yield: 38.4 mg (86%); white solid; mp 113–114 °C.
1H NMR (400 MHz, CDCl3):  8.72 (d, J = 6.8 Hz, 1 H), 7.99 (d, J = 8.8
Hz, 1 H), 7.57 (s, 2 H), 7.30–7.25 (m, 1 H), 7.03 (s, 1 H), 6.98 (t, J = 6.4
Hz, 1 H), 2.41 (s, 6 H).
13C NMR (100 MHz, CDCl3):  = 138.6, 138.2, 131.2, 130.4, 129.7,
125.5, 125.4, 124.5, 118.6, 115.3, 21.4.
HRMS (ESI): m/z [M + H]+ calcd for C14H14N3: 224.1188; found:
224.1191.
3-Pyridin-2-yl[1,2,3]triazolo[1,5-a]pyridine (2n)
Yield: 34.9 mg (89%); white solid; mp 127–128 °C (Lit.16b 126–127 °C).
1H NMR (400 MHz, CDCl3):  = 8.75 (d, J = 7.2 Hz, 1 H), 8.70 (d, J = 8.8
Hz, 1 H), 8.65 (d, J = 4.4 Hz, 1 H), 8.35 (d, J = 8.0 Hz, 1 H), 7.78 (td, J =
7.6, 1.6 Hz, 1 H), 7.38–7.32 (m, 1 H), 7.22–7.18 (m, 1 H), 7.03 (td, J =
6.8, 1.2 Hz, 1 H).
3-(2-Methoxyphenyl)[1,2,3]triazolo[1,5-a]pyridine (2i)
Yield: 26.6 mg (59%); white solid; mp 103–104 °C.
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K

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G. Jiang et al.
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Synthesis
13C NMR (100 MHz, CDCl3):  = 152.0, 149.3, 137.4, 136.6, 132.0,
HRMS (ESI): m/z [M + H]+ calcd for C12H8BrFN3: 291.9886; found:
126.4, 125.2, 122.0, 121.2, 120.4, 115.9.
291.9881.
3-Methyl[1,2,3]triazolo[1,5-a]pyridine (2o)
6-Bromo-3-(4-chlorophenyl)[1,2,3]triazolo[1,5-a]pyridine (2u)
Yield: 22.1 mg (83%); white solid; mp 81–82 °C (Lit.5b 78–80 °C).
Yield: 48.1 mg (78%); white solid; mp 178–179 °C.
1H NMR (400 MHz, CDCl3):  = 8.65 (d, J = 6.8 Hz, 1 H), 7.62 (d, J = 8.8
Hz, 1 H), 7.17 (dd, J = 8.2, 6.6 Hz, 1 H), 6.95–6.90 (m, 1 H), 2.63 (s, 3 H).
1H NMR (400 MHz, CDCl3):  = 8.88 (s, 1 H), 7.87–7.79 (m, 3 H), 7.46
(d, J = 8.4 Hz, 2 H), 7.36 (d, J = 9.2 Hz, 1 H).
13C NMR (100 MHz, CDCl3):  = 134.4, 131.6, 125.1, 123.6, 117.5,
13C NMR (100 MHz, CDCl3):  = 137.5, 134.2, 129.6, 129.3, 128.9,
114.9, 10.3.
127.8, 125.9, 118.5, 110.8.
HRMS (ESI): m/z [M + H]+ calcd for C12H8BrClN3: 307.9590; found:
307.9593.
3-Propyl[1,2,3]triazolo[1,5-a]pyridine (2p)
Yield: 27.4 mg (85%); yellow oil.
1H NMR (400 MHz, CDCl3):  = 8.66 (d, J = 6.8 Hz, 1 H), 7.64 (d, J = 9.2
Hz, 1 H), 7.16 (dd, J = 8.8, 6.8 Hz, 1 H), 6.92 (t, J = 6.8 Hz, 1 H), 2.98 (t,
J = 7.6 Hz, 2 H), 1.89–1.82 (m, 2 H), 1.00 (t, J = 7.4 Hz, 3 H).
6-Bromo-3-[3-(trifluoromethyl)phenyl][1,2,3]triazolo[1,5-a]pyri-
dine (2v)
Yield: 58.8 mg (86%); white solid; mp 164–165 °C.
13C NMR (100 MHz, CDCl3):  = 138.8, 131.4, 125.2, 123.6, 117.6,
114.9, 27.3, 22.9, 13.9.
HRMS (ESI): m/z [M + H]+ calcd for C9H12N3: 162.1031; found:
162.1026.
1H NMR (400 MHz, CDCl3):  = 8.93 (s, 1 H), 8.19 (s, 1 H), 8.11 (d, J =
6.4 Hz, 1 H), 7.88 (d, J = 9.6 Hz, 1 H), 7.66–7.61 (m, 2 H), 7.43 (dd, J =
9.4, 1.4 Hz, 1 H).
13C NMR (100 MHz, CDCl3):  = 137.1, 131.7, 131.6 (q, J = 32.3 Hz),
130.1, 129.7, 129.6, 129.2, 126.1, 124.8 (q, J = 3.7 Hz), 124.0 (q, J =
270.8 Hz), 123.3 (q, J = 3.7 Hz), 118.3, 111.0.
6-Bromo-3-phenyl[1,2,3]triazolo[1,5-a]pyridine (2q)
Yield: 46.6 mg (85%); white solid; mp 161–162 °C (Lit.16b 162–163 °C).
HRMS (ESI): m/z [M + H]+ calcd for C13H8BrF3N3: 341.9854; found:
341.9857.
1H NMR (400 MHz, CDCl3):  = 8.89 (s, 1 H), 7.91 (d, J = 7.2 Hz, 2 H),
7.88 (d, J = 9.2 Hz, 1 H), 7.51 (t, J = 7.6 Hz, 2 H), 7.41 (t, J = 7.4 Hz, 1 H),
7.35 (dd, J = 9.4, 1.4 Hz, 1 H).
6-Bromo-3-(2-methoxyphenyl)[1,2,3]triazolo[1,5-a]pyridine (2w)
Yield: 33.4 mg (55%); white solid; mp 112–113 °C.
13C NMR (100 MHz, CDCl3):  = 138.7, 130.8, 129.3, 129.1, 129.0,
128.3, 126.7, 125.8, 118.8, 110.8.
1H NMR (400 MHz, CDCl3):  = 8.87 (s, 1 H), 7.87 (d, J = 7.2 Hz, 1 H),
7.75 (d, J = 9.2 Hz, 1 H), 7.41 (t, J = 7.4 Hz, 1 H), 7.27 (d, J = 8.4 Hz, 1 H),
7.12 (t, J = 7.4 Hz, 1 H), 7.04 (d, J = 8.0 Hz, 1 H), 3.86 (s, 3 H).
6-Bromo-3-(4-methoxyphenyl)[1,2,3]triazolo[1,5-a]pyridine (2r)
13C NMR (100 MHz, CDCl3):  = 156.3, 136.4, 131.1, 130.3, 129.9,
Yield: 25.5 mg (42%); white solid; mp 168–169 °C.
128.0, 125.3, 121.3, 121.0, 119.9, 111.3, 110.6, 55.5.
HRMS (ESI): m/z [M + H]+ calcd for C13H11BrN3O: 304.0085; found:
1H NMR (400 MHz, CDCl3):  = 8.85 (s, 1 H), 7.84–7.79 (m, 3 H), 7.29
(d, J = 9.2 Hz, 1 H), 7.03 (d, J = 8.8 Hz, 2 H), 3.87 (s, 3 H).
304.0078.
13C NMR (100 MHz, CDCl3):  = 159.8, 138.6, 128.7, 128.6, 128.0,
125.7, 123.4, 118.8, 114.6, 110.6, 55.4.
HRMS (ESI): m/z [M + H]+ calcd for C13H11BrN3O: 304.0085; found:
304.0082.
6-Bromo-3-o-tolyl[1,2,3]triazolo[1,5-a]pyridine (2x)
Yield: 43.8 mg (76%); white solid; mp 120–121 °C.
1H NMR (400 MHz, CDCl3):  = 8.91 (s, 1 H), 7.57 (d, J = 9.6 Hz, 1 H),
7.42 (d, J = 7.2 Hz, 1 H), 7.39–7.27 (m, 4 H), 2.43 (s, 3 H).
6-Bromo-3-(3,5-dimethylphenyl)[1,2,3]triazolo[1,5-a]pyridine
(2s)
13C NMR (100 MHz, CDCl3):  = 139.2, 137.6, 131.1, 130.1, 130.0,
129.4, 128.9, 128.8, 126.0, 125.6, 118.7, 110.7, 20.5.
Yield: 49.5 mg (82%); white solid; mp 141–142 °C.
HRMS (ESI): m/z [M + H]+ calcd for C13H11BrN3: 288.0136; found:
288.0139.
1H NMR (400 MHz, CDCl3):  = 8.86 (s, 1 H), 7.87 (d, J = 9.6 Hz, 1 H),
7.52 (s, 2 H), 7.32 (d, J = 9.2 Hz, 1 H), 7.04 (s, 1 H), 2.40 (s, 6 H).
13C NMR (100 MHz, CDCl3):  = 138.9, 138.7, 130.6, 130.0, 129.0,
125.7, 124.5, 119.0, 110.6, 21.4.
3-Biphenyl-4-yl-6-bromo[1,2,3]triazolo[1,5-a]pyridine (2y)
Yield: 50.4 mg (72%); white solid; mp 201–202 °C.
HRMS (ESI): m/z [M + H]+ calcd for C14H13BrN3: 302.0293; found:
302.0299.
1H NMR (400 MHz, CDCl3):  = 8.89 (s, 1 H), 7.99 (d, J = 8.0 Hz, 2 H),
7.90 (d, J = 9.2 Hz, 1 H), 7.74 (d, J = 8.4 Hz, 2 H), 7.65 (d, J = 7.2 Hz, 2 H),
7.47 (t, J = 7.6 Hz, 2 H), 7.41–7.33 (m, 2 H).
6-Bromo-3-(4-fluorophenyl)[1,2,3]triazolo[1,5-a]pyridine (2t)
13C NMR (100 MHz, CDCl3):  = 141.0, 140.4, 138.3, 129.8, 129.3,
Yield: 43.2 mg (74%); white solid; mp 159–160 °C.
129.0, 128.9, 127.8, 127.6, 127.1, 127.0, 125.9, 118.8, 110.8.
HRMS (ESI): m/z [M + H]+ calcd for C18H13BrN3: 350.0293; found:
1H NMR (400 MHz, CDCl3):  = 8.88 (s, 1 H), 7.88 (dd, J = 8.4, 5.6 Hz, 2
H), 7.82 (d, J = 9.2 Hz, 1 H), 7.36 (d, J = 9.6 Hz, 1 H), 7.20 (t, J = 8.6 Hz, 2
350.0298.
H).
13C NMR (100 MHz, CDCl3):  = 162.7 (d, J = 246.8 Hz), 137.8, 129.4,
128.8, 128.4 (d, J = 8.1 Hz), 127.0 (d, J = 3.2 Hz), 125.8, 118.5, 116.2 (d,
J = 21.6 Hz), 110.8.
6-Bromo-3-cyclohexyl[1,2,3]triazolo[1,5-a]pyridine (2z)
Yield: 45.9 mg (82%); white solid; mp 85 °C.
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K

I
G. Jiang et al.
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Synthesis
1H NMR (400 MHz, CDCl3):  = 8.81 (s, 1 H), 7.60 (d, J = 9.2 Hz, 1 H),
7.20 (d, J = 9.6 Hz, 1 H), 3.09–3.01 (m, 1 H), 2.06–2.01 (m, 2 H), 1.96–
1.86 (m, 2 H), 1.82–1.69 (m, 3 H), 1.51–1.32 (m, 3 H).
13C NMR (100 MHz, CDCl3):  = 144.3, 129.1, 127.2, 125.4, 118.3,
110.3, 35.9, 32.8, 26.5, 26.0.
3,7-Dimethyl[1,2,3]triazolo[1,5-a]pyridine (2f′)
Yield: 19.2 mg (65%); yellow solid; mp 94–95 °C.
1H NMR (400 MHz, CDCl3):  = 8.01 (d, J = 7.6 Hz, 1 H), 7.63 (t, J = 7.8
Hz, 1 H), 7.16 (d, J = 7.6 Hz, 1 H), 2.60 (s, 3 H), 2.34 (s, 3 H).
13C NMR (100 MHz, CDCl3):  = 157.5, 157.4, 155.2, 136.4, 123.4,
118.2, 24.6, 13.9.
HRMS (ESI): m/z [M + H]+ calcd for C12H15BrN3: 280.0449; found:
280.0451.
HRMS (ESI): m/z [M + H]+ calcd for C8H10N3: 148.0875; found:
148.0871.
6-Fluoro-3-phenyl[1,2,3]triazolo[1,5-a]pyridine (2a′)
Yield: 34.5 mg (81%); white solid; mp 117–118 °C.
[1,2,3]Triazolo[1,5-a]quinoline (2g′)
Yield: 17.6 mg (52%); white solid; mp 111–113 °C (Lit.16b 112–114 °C).
1H NMR (400 MHz, CDCl3):  = 8.80 (d, J = 8.4 Hz, 1 H), 8.12 (s, 1 H),
7.85 (d, J = 8.0 Hz, 1 H), 7.77 (t, J = 7.6 Hz, 1 H), 7.61 (t, J = 7.6 Hz, 1 H),
7.58–7.50 (m, 2 H).
13C NMR (100 MHz, CDCl3):  = 131.9, 131.8, 130.1, 128.6, 127.6,
127.1, 126.7, 123.9, 116.4, 114.8.
1H NMR (400 MHz, CDCl3):  = 8.67 (s, 1 H), 8.01–7.97 (m, 1 H), 7.92
(d, J = 7.2 Hz, 2 H), 7.52 (t, J = 7.6 Hz, 2 H), 7.41 (t, J = 7.4 Hz, 1 H), 7.25
(t, J = 8.0 Hz, 1 H).
13C NMR (100 MHz, CDCl3):  = 154.7 (d, J = 243.8 Hz), 138.8, 130.9,
129.1, 128.4, 128.3, 126.7, 119.0 (d, J = 9.3 Hz), 118.3 (d, J = 26.0 Hz),
112.7 (d, J = 39.9 Hz).
HRMS (ESI): m/z [M + H]+ calcd for C12H9FN3: 214.0781; found:
214.0789.
Heterogeneous Copper(II)-Catalyzed One-Pot Synthesis of
[1,2,3]Triazolo[1,5-a]pyridines; General Procedure
6-Fluoro-3-o-tolyl[1,2,3]triazolo[1,5-a]pyridine (2b′)
A dried reaction tube was charged with 2-acylpyridine 3 (0.2 mmol),
hydrazine monohydrate (0.3 mmol), acetic acid (0.02 mmol), and eth-
anol (1.0 mL) at room temperature. The reaction mixture was stirred
at 80 °C for 6 h, and then EtOAc (5.0 mL) and MCM-41-2N-Cu(OAc)2
(16 mg, 0.01 mmol) were added. After stirring at room temperature
or 60 °C for the indicated time, the resulting mixture was diluted with
EtOAc (15 mL) and filtered. The copper catalyst was washed with dis-
tilled water (2 × 5 mL), acetone (2 × 5 mL), and air-dried for 2 h, and
reused in the next run. The filtrate was washed with water (10 mL)
and dried over MgSO4. Then the organic phase was concentrated in
vacuum and the residue was purified by column chromatography (sil-
ica gel, light PE/EtOAc, 3:1) to afford the desired product 2.
Yield: 34.9 mg (77%); white solid; mp 106–107 °C.
1H NMR (400 MHz, CDCl3):  = 8.69 (s, 1 H), 7.67 (dd, J = 9.6, 5.2 Hz, 1
H), 7.43 (d, J = 7.6 Hz, 1 H), 7.40–7.28 (m, 3 H), 7.23–7.17 (m, 1 H),
2.43 (s, 3 H).
13C NMR (100 MHz, CDCl3):  = 154.8 (d, J = 243.5 Hz), 139.2, 137.6,
131.1, 130.0, 129.5, 128.8, 126.0, 118.9 (d, J = 9.4 Hz), 118.0 (d, J = 26.1
Hz), 112.4 (d, J = 39.9 Hz). 20.5.
HRMS (ESI): m/z [M + H]+ calcd for C13H11FN3: 228.0937; found:
228.0931.
4-Methyl-3-o-tolyl[1,2,3]triazolo[1,5-a]pyridine (2c′)
Yield: 31.3 mg (70%); white solid; mp 84–85 °C.
1H NMR (400 MHz, CDCl3):  = 8.63 (d, J = 6.4 Hz, 1 H), 7.39–7.23 (m, 4
Funding Information
H), 6.96–6.87 (m, 2 H), 2.18 (s, 3 H), 2.14 (s, 3 H).
13C NMR (100 MHz, CDCl3):  = 138.5, 131.8, 131.6, 131.5, 129.9,
129.6, 128.9, 125.3, 124.4, 123.2, 115.4, 20.3, 18.3.
HRMS (ESI): m/z [M + H]+ calcd for C14H14N3: 224.1188; found:
We thank the National Natural Science Foundation of China (No.
21462021), the Natural Science Foundation of Jiangxi Province of Chi-
na (No. 20161BAB203086), and the Key Laboratory of Functional
Small Organic Molecules, Ministry of Education (No. KLFS-KF-
224.1186.
201704) for financial support.
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Yield: 31.9 mg (74%); white solid; mp 93 °C.
1H NMR (400 MHz, CDCl3):  = 8.50 (d, J = 7.2 Hz, 1 H), 6.85 (d, J = 6.0
Hz, 1 H), 6.77 (t, J = 6.8 Hz, 1 H), 3.17–3.11 (m, 1 H), 2.64 (s, 3 H),
2.01–1.88 (m, 6 H), 1.81–1.77 (m, 1 H), 1.47–1.35 (m, 3 H).
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1610726.
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13C NMR (100 MHz, CDCl3):  = 144.3, 130.6, 128.7, 123.5, 123.1,
114.8, 36.4, 33.9, 26.8, 26.0, 18.9.
References
HRMS (ESI): m/z [M + H]+ calcd for C13H18N3: 216.1501; found:
216.1509.
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© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K

J
G. Jiang et al.
Paper
Synthesis
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© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–K