An electrochemical multicomponent [3 + 1 + 1] annulations to synthesize polysubstituted 1,2,4-triazoles

Article abstract of DOI:10.1016/j.tet.2021.132111

An electrochemical multicomponent [3 + 1 + 1] annulation used for the synthesis of 1,3,5-trisubstituted 1,2,4-triazoles has been developed under transition-metal-, acid-, base- and external-oxidant-free conditions. In an undivided cell, a variety of hydrazones and aldehydes smoothly participate in this transformation to furnish a range of substituted 1,2,4-triazoles. The reaction constitutes a new transformation from hydrazones, aldehydes and NH₄OAc into 1,2,4-triazoles, providing a unifying, simple and environmentally friendly approach to the currently available methods.

Full text of DOI:10.1016/j.tet.2021.132111

Tetrahedron 87 (2021) 132111
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
An electrochemical multicomponent [3 þ 1 þ 1] annulations to
synthesize polysubstituted 1,2,4-triazoles
,
,
,
Zhiheng Zhao a 1, Yonghui He a 1, Ming Li a, Jiazhe Xu a, Xiangguang Li c *, Lizhu Zhang a,
, b, **
Lijun Gu a
a Key Laboratory of Chemistry in Ethnic Medicinal Resources, State Ethnic Affairs Commission & Ministry of Education, Yunnan Minzu University, Kunming,
650500, China
b Key Laboratory of Green Pesticide and Agricultural Bioengineering, Ministry of Education, Guizhou University, Guiyang, 550025, China
c School of Chemistry and Chemical Engineering, Kunming University, Kunming, 650214, China
a r t i c l e i n f o
a b s t r a c t
Article history:
An electrochemical multicomponent [3 þ 1 þ 1] annulation used for the synthesis of 1,3,5-trisubstituted
1,2,4-triazoles has been developed under transition-metal-, acid-, base- and external-oxidant-free con-
ditions. In an undivided cell, a variety of hydrazones and aldehydes smoothly participate in this trans-
formation to furnish a range of substituted 1,2,4-triazoles. The reaction constitutes a new transformation
from hydrazones, aldehydes and NH4OAc into 1,2,4-triazoles, providing a unifying, simple and envi-
ronmentally friendly approach to the currently available methods.
Received 4 February 2021
Received in revised form
17 March 2021
Accepted 19 March 2021
Available online 30 March 2021
© 2021 Elsevier Ltd. All rights reserved.
Keywords:
Electrochemical synthesis
[3 þ 1 þ 1] Annulation
1,2,4-Triazoles
Multicomponent
Green chemistry
1. Introduction
and additional competing side-reactions [7e9]. Thus, the explora-
tion of multicomponent reactions for the synthesis of aromatic N-
The development of green and sustainable ways for the con-
struction of chemical products is a fundamental goal in modern
organic synthesis [1]. Multicomponent reactions provide a new
method for constructing fine chemicals. Multicomponent reactions
are a prominent approach for the generation of structurally com-
plex and diverse scaffolds from simple building blocks, thereby
affording the advantages of operational simplicity, high chemical
efficiency, convergence and atom economy [2e6]. However, the
development of multicomponent reactions used to construct aro-
matic N-heterocyclic compounds remains a daunting task for syn-
thetic chemists because, with an increase in the number of starting
materials, multicomponent reactions may suffer from inefficiency
heterocycles is still a crucial challenge.
In this context, 1,2,4-triazoles are omnipresent aromatic N-
heterocyclic motifs in numerous biologically active compounds and
they also have widespread applications in biological and pharma-
ceutical fields as well as materials science [10e14]. Given their
applications, several strategies have been implemented for the
synthesis of 1,2,4-triazoles [15e23]. Traditional methods for the
preparation of substituted 1,2,4-triazoles include the Pellizzari and
Einhorn-Brunner reactions [24]. More recent methods involve
transition-metal-catalysed or transition-metal-free dehydrogen-
ative annulations. Although the previously reported protocols have
certain merits of their own, still they suffer from many shortcom-
ings such as the use of a super-stoichiometric amount of reagents or
oxidants, low chemo-selectivity, narrow functional group toler-
ance, multiple reaction steps and the production of copious waste.
Transition-metal-, acid-, base-, external-oxidant-free and step-
economical processes for efficient synthesis of substituted 1,2,4-
triazoles are in demand.
* Corresponding author.
** Corresponding author. Key Laboratory of Chemistry in Ethnic Medicinal Re-
sources, State Ethnic Affairs Commission & Ministry of Education, Yunnan Minzu
University, Kunming, 650500, China.
Organic electrochemistry represents an environmentally benign
and sustainable method using electrons as reagents. Using
E-mail addresses: lixiangguang@iccas.ac.cn (X. Li), gulijun2005@126.com
(L. Gu).
1
These authors contributed equally.
https://doi.org/10.1016/j.tet.2021.132111
0040-4020/© 2021 Elsevier Ltd. All rights reserved.

Z. Zhao, Y. He, M. Li et al.
Tetrahedron 87 (2021) 132111
Table 1
electrons as mass-free reagents, the use of a stoichiometric amount
of a chemical oxidant can be avoided, thereby eliminating the
production of waste [25e29]. Over the past decade, electro-
chemical synthesis has attracted increasing attention and has been
subjected to considerable development [30e39]. The electro-
chemical multicomponent reactions dramatically shorten the
pathway to construct complex ring systems. Recently, Yuan and co-
workers reported an electrosynthesis of 1,5-disubstituted and 1-
aryl 1,2,4-triazoles via an electrochemical multicomponent reac-
tion [40]. However, a strong base was used in this method and
1,2,4-triazoles bearing alkene or alkyne substituents were not
found to be viable products. Thus, an electrosynthesis of 1,2,4-
triazole products bearing alkene or alkyne substituents via a
convergent route under transition-metal-, acid-, base- and
external-oxidant-free conditions has remained elusive. Herein, we
report the successful development of an electrochemical multi-
component [3 þ 1 þ 1] annulation used for the synthesis of 1,3,5-
trisubstituted 1,2,4-triazoles from hydrazones, aldehydes and
NH4OAc. Advantageously, this method proceeds in a transition-
metal-, acid-, base- and external oxidant-free fashion to provide a
variety of functionalized 1,2,4-triazoles (Scheme 1).
a
Optimization of the reaction conditions
.
b
Entry
Variation from the standard reaction conditions
Yield (%)
1
2
3
4
5
6
7
8
None
3 h instead of 6 h
NaI instead of TBAI
HI instead of TBAI
NH4I instead of TBAI
nBu4NBr instead of TBAI
NIS instead of TBAI
86
59
70
66
71
53
n.d.
23
70
54
67
25
33
30
Trace
72
67
57
75
14
n.d.
76
Pt(þ)|Pt(ꢁ) instead of GF(þ)|GF(ꢁ)
C(þ)|C(ꢁ) instead of GF(þ)|GF(ꢁ)
20 mA instead of 23 mA
26 mA instead of 23 mA
DMSO instead of MeCN
DMF instead of MeCN
DCE instead of MeCN
EtOH instead of MeCN
nBu4NBF4 instead of LiClO4
nBu4NPF6 instead of LiClO4
R.T. instead of 40 ꢀC
Air instead of Ar
9
10
11
12
13
14
15
16
17
18
19
20
21
22
2. Results and discussion
We chose 1-benzylidene-2-phenylhydrazine 1a, benzaldehyde
2a and NH4OAc as model substrates to perform our study. To
optimise the electrolytic conditions, the electrolysis was carried out
at a constant current in an undivided cell equipped with a graphite
felt (GF) anode and cathode. The reaction was conducted using 1.0
equiv of 2a and 3.0 equiv of NH4OAc at 40 ꢀC in the presence of
20 mol% LiClO4 and 20 mol% nBu4NI (TBAI). When the reaction was
carried out in MeCN under a constant current (23 mA) in the un-
divided cell, the [3 þ 1 þ1] annulation product 3aa was obtained in
86% yield (Table 1, entry 1). A shorter reaction time was insufficient
form the product 3aa effectively (entry 2). Several other mediators,
including NaI, HI, NH4I and nBu4NBr were subsequently investi-
gated and they were found to be less effective than TBAI (entries
3e7). The variation of electrodes had the biggest influence on this
reaction. Carbon-based materials showed good activity at both the
anode and cathode (entries 8, 9), which is attributed to the high
surface area of the porous carbon materials. Both increasing or
decreasing the current afforded the final product in lower yield
(entries 10, 11). A solvent screen revealed that MeCN was the most
suitable solvent for this transformation (entries 12e15). As for the
choice of the electrolyte, nBu4NBF4 and nBu4NPF6 exhibited lower
efficiencies than LiClO4 (entries 16, 17). Lowering the reaction
temperature decreased the yield (entry 18). A relatively low yield
was obtained when the reaction was conducted under an air at-
mosphere (entry 19). Performing the reaction with NH4HCO3
resulted in a decreased yield (entry 20). A control experiment
indicated that galvanization was necessary for this transformation
NH4HCO3 instead of NH4OAc
No current
Large-scale reaction
a
Reaction conditions: GF anode, GF cathode, constant current ¼ 23 mA, 1a
(0.3 mmol), 2a (0.3 mmol), NH4OAc (0.9 mmol), TBAI (20 mol%), LiClO4 (0.1 M),
MeCN (6 mL), Ar, 40 ꢀC, undivided cell.
b
Isolated yield.
(entry 21). The scale of this reaction between 1a, 2a and NH4OAc
was increased to 10 mmol and the desired product 3aa was ob-
tained in 76% yield (entry 22).
To demonstrate the applicability of this transformation, a variety
of hydrazones 1 were then applied to react with benzaldehyde 2a
and NH4OAc under the optimized reaction conditions (Table 2). The
reaction proceeded successfully with respect to the hydrazones
prepared from various substituted aromatic aldehydes. A variety of
hydrazones substituted at the para position with electron-donating
alkyl or alkoxy groups on the benzene ring were viable in the re-
action (3 ab, 3ac). It is particularly noteworthy that functional
groups such as F, Cl, Br, CN and CO2Me were well-tolerated in the
reaction (3ad-3ah). Regarding the steric hindrance in the substrate,
an ortho-substituted starting material was also tolerated and pro-
vided the desired 1,2,4-triazole in 50% yield (3ai). Moreover, sub-
strate 1j also reacted smoothly and the desired product 3aj was
obtained in 48% yield. A substrate bearing a furan ring was suc-
cessfully applied in the reaction, furnishing the 1,2,4-triazole
product in 52% yield. Interestingly, hydrazones derived from an
unsaturated aldehyde or aliphatic aldehyde could participate in the
reaction (3 al, 3am). To highlight the utility of this transformation,
hydrazones derived from different aromatic hydrazines and benz-
aldehyde were subjected to the reaction and good to excellent
product yields were observed (3an-3ap).
Next, the scope of the reaction with respect to the aldehyde was
investigated. As shown in Table 3, the substituents on the phenyl
ring of the benzaldehydes studied had no obvious effect on the
reaction and the expected 1,2,4-triazole products were produced in
good to high yield. The electrolysis reaction exhibited excellent
compatibility with the electron-donating groups on the phenyl
ring, thereby providing a high yield of substituted 1,2,4-triazoles
Scheme 1. The electrochemical multicomponent reaction for the synthesis of 1,2,4-
triazole derivatives.
2

Z. Zhao, Y. He, M. Li et al.
Tetrahedron 87 (2021) 132111
Table 2
Table 3
Scope of hydrazones 1 used in the reaction a
.
Scope of aldeaydes 2 used in the reaction.a.
reaction of 1a with 2a was carried out in the presence of a stoi-
chiometric amount of iodine as an oxidant, no desired product was
obtained at 40 ꢀC. Cyclic voltammetry experiments were performed
to investigate the possible reaction mechanism. In the TBAI case
(Figure S1, curve e), an obvious oxidation peak occurred at 0.45 V vs
Ag/AgCl (SCE), which was due to the electro-oxidation of Iꢁ ions.
These results suggest that the electrochemical oxidation of Iꢁ at the
anode was the main process.
(3ba, 3ca). Substrates bearing electron-withdrawing groups on the
phenyl ring produced good product yields (3da, 3ea). Steric hin-
drance did not affect the reaction yields, employing ortho- and
meta-substituted benzaldehydes as the starting materials, the re-
actions occurred smoothly and gave the cyclization products in
good to high yields.
Based on these observations and previous studies [18,37], a
plausable mechanism was proposed, as shown in Scheme 2. At the
anode, the electrochemical oxidation of Iꢁ leads to the formation of
iodine radicals. At the same time, 1a undergoes tautomerization to
give compound A. Thereafter, an iodine radical reacts with A to
afford intermediate B. Meanwhile, phenylmethanimine D is formed
through the condensation of benzaldehyde 2a with NH4OAc.
Anodic oxidation of B may give complex C and nucleophilic attack
of intermediate D leads to intermediate E, which undergoes tau-
tomerization to give F. With the aid of an iodine radical, F is readily
transformed into intermediate G, which will undergo a similar
process to the previous pathway to give H. Then, the intramolecular
attack of the nitrogen atom provides I. Finally, I gives the desired
aromatization product 3aa via an oxidative dehydrogenation re-
action. Alternatively, the nucleophilic attack of NH3 on complex C
gives intermediate J. The reaction of benzaldehyde 2a with J forms
intermediate E.
(3fa, 3ga). Notably, the 1-naphthaldehyde gave its desired
product 3ha in 51% yield. Apart from benzaldehyde 2a, thiophene-
2-carbaldehyde 2i gave the corresponding product 3ia in 67% yield.
The use of methyl 2-oxoacetate 2j gave the desired product in 49%
yield. Importantly, aliphatic aldehydes were also compatible with
the reaction system (3ka, 3la). Alkenyl- and alkynyl-substituted
aldehydes also displayed good activity under the conditions
(3ma, 3na). Unfortunately, paraformaldehyde did not deliver the
corresponding 1,2,4-triazole product under the optimal reaction
conditions.
To gain further information on the reaction mechanism, several
control reactions were performed. The reaction of 1a with 2a and
NH4OAc were conducted in the presence of a radical inhibitor (2.0
equiv), such as 2,6-di-tert-butyl-4-methylphenol, hydroquinone
and 2,2,6,6-tetramethyl-1-piperidinyloxy. The reaction was
completely suppressed. These results suggest that a radical process
may be involved in this transformation. As expected, when the
3

Z. Zhao, Y. He, M. Li et al.
Tetrahedron 87 (2021) 132111
(1 mmol) and CH3CN (50 mL) were combined and added. The bottle
was equipped with graphite felt as the anode and cathode and was
then charged with argon. The reaction mixture was stirred and
electrolyzed at a constant current of 23 mA for 16 h at 40 ꢀC. When
the reaction was finished, the reaction mixture was diluted in
80 mL ethyl acetate, washed with a saturated solution of brine
(2 ꢂ 20 mL), dried (Na2SO4) and concentrated in vacuum, and the
resulting residue was purified by silica gel column chromatography
(hexane/ethyl acetate) to afford the products desired product.
1,3,5-Triphenyl-1H-1,2,4-triazole (3aa): yield: 86%; 76.6 mg,
light yellow solid; 1H NMR (400 MHz, DMSO‑d6)
J ¼ 8.0 Hz, 1.6 Hz, 2H), 7.54-7.50 (m, 7H), 7.49-7.46 (m, 3H), 7.45-
7.39 (m, 3H); 13C NMR (100 MHz, DMSO‑d6)
: 160.7, 154.5, 137.9,
d: 8.15 (dd,
d
130.5, 130.1, 129.5, 129.2, 128.8, 128.7, 128.6, 127.6, 126.0, 125.8;
LRMS (EI 70 ev) m/z (%): 297 (Mþ, 100); HRMS m/z (ESI) calcd for
Scheme 2. Plausible mechanism for the reaction.
C
20H16N3 (M þ H)þ 298.1338, found 298.1335.
1,5-Diphenyl-3-p-tolyl-1H-1,2,4-triazole (3 ab): yield: 69%;
3. Conclusion
64.4 mg, light white solid; 1H NMR (400 MHz, DMSO‑d6)
d
: 8.02 (d,
J ¼ 7.6 Hz, 2H), 7.51-7.40 (m, 10H), 7.33 (d, J ¼ 8.0 Hz, 2H), 2.37 (s,
3H); 13C NMR (100 MHz, DMSO‑d6)
: 160.8, 154.4, 139.1, 137.9,
In summary, we introduced a novel sustainable multicompo-
nent 1,2,4-triazole synthesis. Hydrazones, aldehydes and NH4OAc
are assembled in three-component reactions. Our electrochemical
synthetic method is compatible with a wide range of hydrazones
and aldehydes. Readily available raw materials, good product
yields, scalability and an experimentally convenient catalytic pro-
cess make this protocol practical and attractive.
d
130.1, 129.5, 129.4, 129.2, 128.7, 128.6, 127.7, 127.6, 126.0, 125.8, 21.0;
LRMS (EI 70 ev) m/z (%): 311 (Mþ, 100); HRMS m/z (ESI) calcd for
C
21H18N3 (M þ H)þ 312.1495, found 312.1490.
3-(4-Methoxyphenyl)-1,5-diphenyl-1H-1,2,4-triazole (3ac):
yield: 70%; 68.7 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6)
7.48-7.45 (m, 3H), 7.44-7.39 (m, 2H), 7.08 (dd, J ¼ 6.8 Hz, 2.0 Hz, 2H),
3.82 (s, 3H); 13C NMR (100 MHz, DMSO‑d6)
: 160.7, 160.3, 154.3,
d
: 8.07 (dd, J ¼ 6.8 Hz, 2.0 Hz, 2H), 7.52-7.48 (m, 5H),
4. Experimental section
d
138.0,130.0,129.5,129.1,128.7,128.6,127.7,127.5,125.7,123.0,114.2,
55.2; LRMS (EI 70 ev) m/z (%): 327 (Mþ, 100); HRMS m/z (ESI) calcd
for C21H18N3O (M þ H)þ 328.1444, found 328.1440.
4.1. General materials and methods
All glassware was oven dried at 110 ꢀC for hours and cooled
down under vacuum. Unless otherwise noted, materials were ob-
tained from commercial suppliers and used without further puri-
fication. The instrument for electrolysis was dual display
potentiostat (DJS-292 B) (made in China). Both of the anode elec-
3-(4-Fluorophenyl)-1,5-diphenyl-1H-1,2,4-triazole
(3ad):
yield: 49%; 46.3 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6)
: 8.17 (dd, J ¼ 8.8 Hz, 5.6 Hz, 2H), 7.53-7.45 (m, 8H), 7.43-
7.39 (m, 2H), 7.36-7.32 (m, 2H); 13C NMR (100 MHz, DMSO‑d6)
d
d:
164.2 (d, J ¼ 244.9 Hz), 159.9, 154.6, 137.8, 130.2, 129.5, 129.3, 128.7,
128.6 (d, J ¼ 37.0 Hz), 128.2, 127.5, 127.0 (d, J ¼ 2.8 Hz), 125.8, 115.9
(d, J ¼ 21.7 Hz); LRMS (EI 70 ev) m/z (%): 315 (Mþ, 100); HRMS m/z
(ESI) calcd for C20H15FN3 (M þ H)þ 316.1244, found 316.1240.
trode
and
cathodic
electrode
were
carbon
rod
(15 mm ꢂ 15 mm ꢂ 0.2 mm). Thin layer chromatography (TLC)
employed glass 0.25 mm silica gel plates. Flash chromatography
columns were packed with 200e300 mesh silica gel in petroleum
(bp. 60e90 ꢀC). 1H and 13C NMR data were recorded with Bruker
Advance III (400 MHz) spectrometers with tetramethylsilane as an
3-(4-Chlorophenyl)-1,5-diphenyl-1H-1,2,4-triazole
(3ae):
yield: 62%; 61.6 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6)
: 8.13 (dd, J ¼ 6.4 Hz, 1.6 Hz, 2H), 7.57 (dd, J ¼ 6.8 Hz,
2.0 Hz, 2H), 7.52-7.45 (m, 8H), 7.43-7.39 (m, 2H); 13C NMR
(100 MHz, DMSO‑d6) : 159.8, 154.7, 137.8, 134.2, 130.2, 129.5, 129.3,
d
internal standard. All chemical shifts (d) are reported in ppm and
coupling constants (J) in Hz.
d
129.3, 129.0, 128.7, 128.6, 127.7, 127.4, 125.8; LRMS (EI 70 ev) m/z
(%): 331 (Mþ, 100); HRMS m/z (ESI) calcd for C20H15ClN3 (M þ H)þ
332.0949, found 332.0951.
4.2. General procedure for synthesis of 6-aryl (heteroaryl)
substituted phenanthridines 3
3-(4-Bromophenyl)-1,5-diphenyl-1H-1,2,4-triazole
yield: 62%; 69.8 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6) : 8.07-8.04 (m, 2H), 7.73-7.70 (m, 2H), 7.53-7.45 (m, 8H),
7.44-7.40 (m, 2H); 13C NMR (100 MHz, DMSO‑d6)
: 159.8, 154.7,
137.8, 131.9, 130.3, 129.7, 129.6, 129.4, 128.7, 128.6, 128.0, 127.4,
125.8, 122.9; LRMS (EI 70 ev) m/z (%): 375 (Mþ, 100); HRMS m/z
(ESI) calcd for C20H15BrN3 (M þ H)þ 376.0443, found 376.0450.
4-(1,5-Diphenyl-1H-1,2,4-triazol-3-yl)benzonitrile (3 ag):
yield: 55%; 53.1 mg, light yellow solid; 1H NMR (400 MHz,
(3af):
In an oven-dried undivided three-necked bottle (15 mL)
equipped with a stir bar, hydrazones 1 (0.30 mmol), aldehydes 2
(0.30 mmol), NH4OAc (0.9 mmol), TBAI (0.06 mmol), LiClO4
(0.05 mmol) and CH3CN (5 mL) were combined and added. The
bottle was equipped with graphite felt as the anode and graphite
felt as the cathode and was then charged with argon. The reaction
mixture was stirred and electrolyzed at a constant current of 23 mA
for 6 h at 40 ꢀC. When the reaction was finished, the reaction
mixture was diluted in 40 mL ethyl acetate, washed with a satu-
rated solution of brine (2 ꢂ 10 mL), dried (Na2SO4) and concen-
trated in vacuum, and the resulting residue was purified by silica
gel column chromatography (hexane/ethyl acetate) to afford the
products desired product.
d
d
DMSO‑d6)
1.6 Hz, 2H), 7.55-7.47 (m, 8H), 7.45-7.41 (m, 2H); 13C NMR (100 MHz,
DMSO‑d6) : 159.3,155.1,137.7,134.7,133.1,130.4,129.7,129.6,128.8,
d: 8.28 (dd, J ¼ 6.8 Hz, 2.0 Hz, 2H), 7.99 (dd, J ¼ 6.8 Hz,
d
128.7, 127.3, 126.7, 125.9, 118.7, 111.9; LRMS (EI 70 ev) m/z (%): 322
(Mþ, 100); HRMS m/z (ESI) calcd for C21H15N4 (M þ H)þ 323.1291,
found 323.1295.
Large-scale experimental procedure: In an oven-dried undi-
vided three-necked bottle (100 mL) equipped with a stir bar, 1-
benzylidene-2-phenylhydrazine 1a (10.0 mmol), benzaldehyde 2a
(10.0 mmol), NH4OAc (30.0 mmol), TBAI (2.0 mmol), LiClO4
Methyl 4-(1,5-diphenyl-1H-1,2,4-triazol-3-yl)benzoate (3ah):
yield: 73%; 77.7 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6)
d: 8.27 (dd, J ¼ 6.8 Hz, 1.6 Hz, 2H), 8.11 (dd, J ¼ 6.4 Hz,
4

Z. Zhao, Y. He, M. Li et al.
Tetrahedron 87 (2021) 132111
1.6 Hz, 2H), 7.55-7.41 (m, 10H), 3.89 (s, 3H); 13C NMR (100 MHz,
(M þ H)þ 376.0443, found 376.0449.
DMSO‑d6)
d: 166.0, 159.8, 155.0, 137.8, 134.7, 130.4, 130.3, 129.9,
1,3-Diphenyl-5-p-tolyl-1H-1,2,4-triazole (3ba): yield: 77%;
129.7, 129.5, 128.8, 128.7, 127.4, 126.3, 125.9, 52.3; LRMS (EI 70 ev)
m/z (%): 355 (Mþ, 100); HRMS m/z (ESI) calcd for C22H18N3O2
(M þ H)þ 356.1393, found 356.1397.
71.8 mg, light yellow solid; 1H NMR (400 MHz, DMSO‑d6)
d: 8.13 (d,
J ¼ 7.6 Hz, 2H), 7.52-7.47 (m, 8H), 7.40 (d, J ¼ 8.0 Hz, 2H), 7.22 (d,
J ¼ 7.6 Hz, 2H), 2.31 (s, 3H); 13C NMR (100 MHz, DMSO‑d6)
d: 160.6,
3-(2-Chlorophenyl)-1,5-diphenyl-1H-1,2,4-triazole
(3ai):
154.6, 140.0, 138.0, 130.5, 129.5, 129.5, 129.2, 128.8, 128.7, 128.6,
126.0, 125.8, 124.7, 20.9; LRMS (EI 70 ev) m/z (%): 311 (Mþ, 100);
HRMS m/z (ESI) calcd for C21H18N3 (M þ H)þ 312.1495, found
312.1488.
yield: 50%; 49.7 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6) : 8.04-8.02 (m, 1H), 7.64-7.62 (m, 1H), 7.54-7.47 (m,
10H), 7.45-7.41 (m, 2H); 13C NMR (100 MHz, DMSO‑d6)
: 159.4,
d
d
153.9,137.8,131.7,131.5,131.5,130.9,130.8,130.3,129.6,129.4,128.8,
128.7, 127.4, 127.4, 125.8; LRMS (EI 70 ev) m/z (%): 331 (Mþ, 100);
HRMS m/z (ESI) calcd for C20H15ClN3 (M þ H)þ 332.0949, found
332.0956.
5-(4-Methoxyphenyl)-1,3-diphenyl-1H-1,2,4-triazole (3ca):
yield: 71%; 69.7 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6) d: 8.13-8.11 (m, 2H), 7.54-7.51 (m, 4H), 7.49-7.43 (m, 6H),
6.97 (dd, J ¼ 6.8 Hz, 2.0 Hz, 2H), 3.77 (s, 3H); 13C NMR (100 MHz,
3-(3-Chlorophenyl)-1,5-diphenyl-1H-1,2,4-triazole
yield: 48%; 47.7 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6) : 8.09-8.06 (m, 2H), 7.56-7.51 (m, 6H), 7.51-7.47 (m, 3H),
7.47-7.40 (m, 3H); 13C NMR (100 MHz, DMSO‑d6)
: 159.4, 154.8,
(3aj):
DMSO‑d6) d: 160.5, 160.5, 154.4, 138.1, 130.6, 130.2, 129.5, 129.4,
129.2, 128.8, 126.0, 125.8, 119.7, 114.1, 55.3; LRMS (EI 70 ev) m/z (%):
327 (Mþ, 100); HRMS m/z (ESI) calcd for C21H18N3O (M þ H)þ
328.1444, found 328.1443.
d
d
137.8, 133.7, 132.5, 131.0, 130.4, 129.7, 129.6, 129.5, 128.8, 128.7,
127.4, 125.9, 125.5, 124.6; LRMS (EI 70 ev) m/z (%): 331 (Mþ, 100);
HRMS m/z (ESI) calcd for C20H15ClN3 (M þ H)þ 332.0949, found
332.0953.
5-(4-Fluorophenyl)-1,3-diphenyl-1H-1,2,4-triazole
yield: 70%; 66.2 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6) :8.14-8.11 (m, 2H), 7.59-7.56 (m, 2H), 7.55-7.51 (m, 4H),
7.50-7.45 (m, 4H), 7.30-7.24 (m, 2H);13C NMR (100 MHz, DMSO‑d6)
(3da):
d
3-(Furan-2-yl)-1,5-diphenyl-1H-1,2,4-triazole (3ak): yield:
d
: 162.8 (d, J ¼ 247.0 Hz), 160.7, 153.7, 137.8, 131.2, 131.1, 130.4, 129.6
52%; 44.8 mg, brown red oil; 1H NMR (400 MHz, DMSO‑d6)
d: 7.87-
(d, J ¼ 2.7 Hz), 129.3, 128.8, 126.0, 125.8, 124.4 (d, J ¼ 3.1 Hz), 115.7
(d, J ¼ 22.0 Hz); LRMS (EI 70 ev) m/z (%): 315 (Mþ,100); HRMS m/z
(ESI) calcd for C20H15FN3 (M þ H)þ 316.1244, found 316.1241.
7.86 (m, 1H), 7.53-7.40 (m, 10H), 7.07 (dd, J ¼ 3.6 Hz, 0.8 Hz, 1H),
6.68 (dd, J ¼ 3.6 Hz, 2.0 Hz, 1H); 13C NMR (100 MHz, DMSO‑d6)
d:
154.3, 154.3, 145.7, 144.2, 137.7, 130.3129.6, 129.3, 128.7, 128.7, 127.3,
125.8, 111.8, 109.9; LRMS (EI 70 ev) m/z (%): 287 (Mþ,100); HRMS m/
z (ESI) calcd for C18H14N3O (M þ H)þ 288.1131, found 288.1136.
1,5-Diphenyl-3-styryl-1H-1,2,4-triazole (3 al): yield: 51%;
5-(4-Chlorophenyl)-1,3-diphenyl-1H-1,2,4-triazole
(3ea):
yield: 66%; 65.5 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6)
: 8.13 (dd, J ¼ 8.4 Hz, 1.6 Hz, 2H), 7.55-7.52 (m, 3H), 7.51-
7.47 (m, 9H); 13C NMR (100 MHz, DMSO‑d6)
: 160.8, 153.6, 137.7,
135.1, 130.5, 130.3, 129.7, 129.6, 129.4, 128.9, 128.8, 126.4, 126.0,
125.8; LRMS (EI 70 ev) m/z (%): 331 (Mþ, 100); HRMS m/z (ESI) calcd
for C20H15ClN3 (M þ H)þ 332.0949, found 332.0954.
d
d
49.4 mg, light yellow solid; 1H NMR (400 MHz, DMSO‑d6)
d
: 7.72 (d,
J ¼ 7.2 Hz, 2H), 7.66 (d, J ¼ 16.4 Hz, 1H), 7.52-7.47 (m, 5H), 7.46-7.39
(m, 7H), 7.36-7.32 (m, 1H), 7.29 (d, J ¼ 16.4 Hz, 1H); 13C NMR
(100 MHz, DMSO‑d6)
d: 160.5, 154.2, 137.9, 136.0, 133.8, 130.2, 129.6,
1,3-Diphenyl-5-o-tolyl-1H-1,2,4-triazole (3fa): yield: 75%;
129.2,128.9,128.8,128.7,128.6,127.6,127.1,125.7,117.5; LRMS (EI 70
ev) m/z (%): 323 (Mþ, 100); HRMS m/z (ESI) calcd for C22H18N3
(M þ H)þ 324.1495, found 324.1490.
70.0 mg, light yellow solid; 1H NMR (400 MHz, DMSO‑d6)
d
: 8.16-
8.13 (m, 2H), 7.54-7.47 (m, 3H), 7.45-7.35 (m, 7H), 7.32-7.24 (m, 2H),
2.10 (s, 3H); 13C NMR (100 MHz, DMSO‑d6)
: 160.7, 154.4, 137.4,
d
3-tert-Butyl-1,5-diphenyl-1H-1,2,4-triazole (3am): yield: 80%;
137.0, 130.5, 130.2, 130.2, 129.5, 129.3, 128.8, 128.5, 128.1, 126.0,
125.9, 124.1, 19.3; LRMS (EI 70 ev) m/z (%): 311 (Mþ, 100); HRMS m/z
(ESI) calcd for C21H18N3 (M þ H)þ 312.1495, found 312.1491.
1,3-Diphenyl-5-m-tolyl-1H-1,2,4-triazole (3ga): yield: 65%;
66.5 mg, white solid; 1H NMR (400 MHz, DMSO‑d6)
d
: 7.49-7.45 (m,
3H), 7.44-7.35 (m, 7H), 1.39 (s, 9H); 13C NMR (100 MHz, DMSO‑d6)
d
:
170.7, 153.4, 138.0, 129.9, 129.4, 128.8, 128.6, 128.6, 128.0, 125.6,
32.5, 29.5; LRMS (EI 70 ev) m/z (%): 277 (Mþ, 100); HRMS m/z (ESI)
calcd for C18H20N3 (M þ H)þ 278.1651, found 278.1649.
60.6 mg, light yellow solid; 1H NMR (400 MHz, DMSO‑d6)
d
: 8.13 (d,
J ¼ 7.6 Hz, 2H), 7.54-7.43 (m, 9H), 7.29-7.24 (m, 2H), 7.19-7.17 (m,
1H), 2.28 (s, 3H); 13C NMR (100 MHz, DMSO‑d6)
: 160.7, 154.6,
1-(4-Methoxyphenyl)-3,5-diphenyl-1H-1,2,4-triazole (3an):
yield: 74%; 72.6 mg, light yellow solid; 1H NMR (400 MHz,
d
138.1, 138.0, 130.8, 130.6, 130.5, 129.6, 129.5, 129.3, 129.3, 128.9,
128.5, 127.5, 126.0, 125.8, 20.9; LRMS (EI 70 ev) m/z (%): 311 (Mþ,
100); HRMS m/z (ESI) calcd for C21H18N3 (M þ H)þ 312.1495, found
312.1493.
DMSO‑d6) d: 8.13-8.10 (m, 2H), 7.54-7.50 (m, 5H), 7.49-7.40 (m, 5H),
7.06 (dd, J ¼ 6.8 Hz, 2.4 Hz, 2H), 3.81 (s, 3H); 13C NMR (100 MHz,
DMSO‑d6) d: 160.4, 159.6, 154.5, 130.8, 130.6, 130.0, 129.5, 128.8,
128.7, 128.6, 127.7, 127.4, 125.9, 114.6, 55.5; LRMS (EI 70 ev) m/z (%):
327 (Mþ, 100); HRMS m/z (ESI) calcd for C21H18N3O (M þ H)þ
328.1444, found 328.1438.
5-(Naphthalen-1-yl)-1,3-diphenyl-1H-1,2,4-triazole
(3ha):
yield: 51%; 53.1 mg, brown red oil; 1H NMR (400 MHz, DMSO‑d6)
d:
8.21-8.19 (m, 2H), 8.09 (dd, J ¼ 29.2 Hz, 8.0 Hz, 2H), 7.82 (d,
1-(4-Chlorophenyl)-3,5-diphenyl-1H-1,2,4-triazole
yield: 55%; 54.6 mg, light yellow solid; 1H NMR (400 MHz,
DMSO‑d6)
: 8.13 (dd, J ¼ 8.4 Hz, 2.0 Hz, 2H), 7.60 (dd, J ¼ 6.8 Hz,
2.4 Hz, 2H), 7.54-7.45 (m, 10H); 13C NMR (100 MHz, DMSO‑d6)
(3ao):
J ¼ 8.4 Hz, 1H), 7.63 (dd, J ¼ 7.2 Hz, 1.2 Hz, 1H), 7.58-7.49 (m, 6H),
7.36-7.30 (m, 5H);13C NMR (100 MHz, DMSO‑d6)
d:160.9, 153.6,
d
137.4, 133.0, 130.8, 130.6, 130.5, 129.6, 129.2, 129.2, 128.9, 128.6,
128.4, 127.3, 126.6, 126.1, 125.6, 125.1, 124.8, 124.3; LRMS (EI 70ev)
m/z (%): 347 (Mþ,100); HRMS m/z (ESI) calcd for C24H18N3 (M þ H)þ
348.1495, found 348.1499.
d
:
160.9, 154.7, 136.7, 133.6, 130.3, 129.6, 129.6, 128.9, 128.9, 128.8,
128.7, 127.5, 127.4, 126.0; LRMS (EI 70 ev) m/z (%): 331 (Mþ, 100);
HRMS m/z (ESI) calcd for C20H15ClN3 (M þ H)þ 332.0949, found
332.0950.
1,3-Diphenyl-5-(thiophen-2-yl)-1H-1,2,4-triazole (3ia): yield:
67%; 60.9 mg, white yellow solid; 1H NMR (400 MHz, DMSO‑d6)
d:
1-(4-Bromophenyl)-3,5-diphenyl-1H-1,2,4-triazole
yield: 61%; 68.6 mg, brown yellow solid; 1H NMR (400 MHz,
DMSO‑d6)
: 8.13 (dd, J ¼ 8.4 Hz, 2.0 Hz, 2H), 7.73 (dd, J ¼ 6.4 Hz,
2.0 Hz, 2H), 7.54-7.52 (m, 3H), 7.50-7.47 (m, 4H), 7.47-7.42 (m, 3H);
13C NMR (100 MHz, DMSO‑d6)
: 160.9, 154.7, 137.1, 132.5, 130.3,
(3ap):
8.11-8.08 (m, 2H), 7.75 (dd, J ¼ 5.2 Hz, 1.2 Hz, 1H), 7.66-7.62 (m, 5H),
7.53-7.47 (m, 3H), 7.07 (dd, J ¼ 4.8 Hz, 3.6 Hz, 1H), 6.99 (dd,
d
J ¼ 3.6 Hz, 1.2 Hz, 1H); 13C NMR (100 MHz, DMSO‑d6)
d: 160.6, 149.9,
137.5, 130.3, 130.2, 130.1, 129.9, 129.6, 129.6, 128.9, 128.8, 128.0,
127.0, 126.0; LRMS (EI 70 ev) m/z (%): 303 (Mþ, 100); HRMS m/z
(ESI) calcd for C18H14N3S (M þ H)þ 304.0902, found 304.0908.
Methyl 2,5-diphenyl-2H-1,2,4-triazole-3-carboxylate (3ja):
d
130.3, 129.6, 128.9, 128.8, 128.7, 127.7, 127.4, 126.0, 122.1; LRMS (EI
70 ev) m/z (%): 375 (Mþ, 100); HRMS m/z (ESI) calcd for C20H15BrN3
5

Z. Zhao, Y. He, M. Li et al.
Tetrahedron 87 (2021) 132111
yield: 49%; 41.0 mg, light brown red solid; 1H NMR (400 MHz,
Appendix A. Supplementary data
DMSO‑d6)
d
: 8.10-8.08 (m, 2H), 7.66-7.64 (m, 2H), 7.58-7.50 (m, 6H),
3.84 (s, 3H); 13C NMR (100 MHz, DMSO‑d6)
d: 160.7, 157.4, 145.4,
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2021.132111.
137.9, 130.0, 129.7, 129.6, 129.0,128.9,126.1, 125.9, 52.9; LRMS (EI 70
ev) m/z (%): 279 (Mþ, 100); HRMS m/z (ESI) calcd for C16H14N3O2
(M þ H)þ 280.1080, found 280.1084.
Supporting information available
1,3-Diphenyl-5-propyl-1H-1,2,4-triazole (3ka): yield: 78%;
61.5 mg, light yellow solid; 1H NMR (400 MHz, DMSO‑d6)
d: 8.07
Characterization data of 3 including the 1H and 13C NMR data.
(dd, J ¼ 8.4 Hz, 2.0 Hz, 2H), 7.62-7.42 (m, 8H), 2.80 (dd, J ¼ 10.0 Hz,
7.6 Hz, 2H), 1.76-1.67 (m, 2H),0.88 (t, J ¼ 7.4 Hz, 3H); 13C NMR
References
(100 MHz, DMSO‑d6) d: 160.2, 156.7, 137.2, 130.8, 129.5, 129.2, 128.9,
128.7, 125.8, 125.1, 27.8, 20.4,13.5; LRMS (EI 70 ev) m/z (%): 263 (Mþ,
100); HRMS m/z (ESI) calcd for C17H18N3 (M þ H)þ 264.1495, found
264.1498.
[1] Y. Kim, C.-J. Li, Green Synth. Catal. 1 (2020) 1e11.
[2] B. Ganem, Acc. Chem. Res. 42 (2009) 463e472.
€
[3] A. Domling, Chem. Rev. 106 (2006) 17e89.
[4] N. Deibl, K. Ament, R. Kempe, J. Am. Chem. Soc. 137 (2015) 12804e12807.
[5] J.-R. Chen, X.-Q. Hu, L.-Q. Lu, W.-J. Xiao, Chem. Rev. 115 (2015) 5301e5365.
5-cyclopropyl-1,3-diphenyl-1H-1,2,4-triazole (3la): yield:
65%; 50.9 mg, light yellow oil; 1H NMR (400 MHz, DMSO‑d6)
d: 7.90
^
[6] R. Echemendía, A.F. de La Torre, J.L. Monteiro, M. Pila, A.G. Correa,
~
B. Westermann, D.G. Rivera, M.W. Paixao, Angew. Chem. Int. Ed. 54 (2015)
(dd, J ¼ 1.6 Hz, 1.2 Hz, 2H), 7.57 (d, J ¼ 7.6 Hz, 2H), 7.50 (t, J ¼ 7.6 Hz,
2H), 7.41 (dd, J ¼ 7.2 Hz, 5.2 Hz, 1H), 7.35-7.30 (m, 3H), 1.92-1.87 (m,
1H), 1.01-0.98 (m, 2H), 0.97-0.92 (m, 2H); 13C NMR (100 MHz,
7621e7625.
[7] S. Brauch, S.S. van Berkel, B. Westermann, Chem. Soc. Rev. 42 (2013)
4948e4962.
[8] A.V. Gulevich, A.S. Dudnik, N. Chernyak, V. Gevorgyan, Chem. Rev. 113 (2013)
3084e3213.
[9] D.M. Flanigan, F. Romanov-Michailidis, N.A. White, T. Rovis, Chem. Rev. 115
(2015) 9307e9387.
DMSO‑d6) d: 160.0, 158.3, 137.1, 130.7, 129.6, 129.3, 128.8, 128.7,
125.9, 124.7, 9.2, 7.3; LRMS (EI 70 ev) m/z (%): 261 (Mþ, 100); HRMS
m/z (ESI) calcd for C17H16N3 (M þ H)þ 262.1344, found 262.1341.
1,3-Diphenyl-5-vinyl-1H-1,2,4-triazole (3ma): yield: 61%;
[10] D.J. Pennell, J.M. Bland, Lancet 361 (2003) 183e184.
[11] R. Tokala, S. Bale, I.P. Janrao, A. Vennela, N.P. Kumar, K.R. Senwar, C. Godugu,
N. Shankaraiah, Bioorg. Med. Chem. Lett 28 (2018) 1919e1924.
45.2 mg, light yellow oil; 1H NMR (400 MHz, DMSO‑d6)
d: 8.11-8.09
(m, 2H), 7.65-7.57 (m, 5H), 7.53-7.45 (m, 3H), 6.68 (dd, J ¼ 16.8 Hz,
€
[12] C. Lass-Florl, Drugs 71 (2011) 2405e2419.
10.8 Hz, 1H), 6.40 (dd, J ¼ 17.2 Hz, 2.0 Hz, 1H), 5.75 (dd, J ¼ 11.2 Hz,
[13] R. Romagnoli, P.G. Baraldi, O. Cruz-Lopez, C.L. Cara, M.D. Carrion, A. Brancale,
E. Hamel, L.-C. Chen, R. Bortolozzi, G. Basso, G. Viola, J. Med. Chem. 53 (2010)
4248e4258.
2.0 Hz, 1H); 13C NMR (100 MHz, DMSO‑d6)
d: 160.7, 152.7, 136.6,
130.4, 129.7, 129.5, 129.3, 128.8, 126.0, 125.4, 124.0, 121.7; LRMS (EI
70 ev) m/z (%): 247 (Mþ, 100); HRMS m/z (ESI) calcd for C16H14N3
(M þ H)þ 248.1182, found 248.1185.
[14] K.T. Potts, Chem. Rev. 61 (1961) 87e127.
[15] A. Tam, I.S. Armstrong, T.E. La Cruz, Org. Lett. 15 (2013) 3586e3589.
[16] H. Huang, W. Guo, W. Wu, C.-J. Li, H. Jiang, Org. Lett. 17 (2015) 2894e2897.
[17] J. Kuang, B. Chen, S. Ma, Org. Chem. Front. 1 (2014) 186e189.
[18] Z. Chen, H. Li, W. Dong, M. Miao, H. Ren, Org. Lett. 18 (2016) 1334e1337.
[19] S. Ueda, H. Nagasawa, J. Am. Chem. Soc. 131 (2009) 15080e15081.
[20] S.T. Staben, N. Blaquiere, Angew. Chem. Int. Ed. 49 (2010) 325e328.
[21] Z. Ye, M. Ding, Y. Wu, Y. Li, W. Hua, F. Zhang, Green Chem. 20 (2018)
1732e1737.
[22] M.M. Guru, S. De, S. Dutta, D. Koley, B. Maji, Chem. Sci. 10 (2019) 7964e7974.
[23] J.-Q. Liu, X. Shen, Y. Wang, X.-S. Wang, X. Bi, Org. Lett. 20 (2018) 6930e6933.
[24] A. Moulin, M. Bibian, A.-L. Blayo, S. El Habnouni, J. Martinez, J.-A. Fehrentz,
Chem. Rev. 110 (2010) 1809e1827.
5-Ethynyl-1,3-diphenyl-1H-1,2,4-triazole (3na): yield: 52%;
38.2 mg, light yellow solid; 1H NMR (400 MHz, DMSO‑d6)
d
: 8.08
(dd, J ¼ 8.0 Hz, 2.0 Hz, 2H), 7.84-7.82 (m, 2H), 7.65-7.61 (m, 2H),
7.59-7.49 (m, 4H), 5.08 (s, 1H); 13C NMR (100 MHz, DMSO‑d6)
d
:
161.1, 137.9, 136.5, 130.0, 129.6, 129.5, 129.4, 129.0, 126.1, 123.3, 89.5,
71.1; LRMS (EI 70 ev) m/z (%): 245 (Mþ, 100); HRMS m/z (ESI) calcd
for C16H12N3 (M þ H)þ 246.1025, found 246.1028.
[25] E.J. Horn, B.R. Rosen, P.S. Baran, ACS Cent. Sci. 2 (2016) 302e308.
[26] P. Xiong, H.-C. Xu, Acc. Chem. Res. 52 (2019) 3339e3350.
[27] H.-T. Tang, J.-S. Jia, Y.-M. Pan, Org. Biomol. Chem. 18 (2020) 5315e5333.
[28] Y. Yuan, A. Lei, Acc. Chem. Res. 52 (2019) 3309e3324.
[29] P. Qian, Z. Zhou, K. Hu, J. Wang, Z. Li, Z. Zha, Z. Wang, Org. Lett. 21 (2019)
6403e6407.
[30] Y. Jiang, K. Xu, C. Zeng, Chem. Rev. 118 (2018) 4485e4540.
[31] J. Yoshida, A. Shimizu, R. Hayashi, Chem. Rev. 118 (2018) 4702e4730.
[32] Q.-L. Yang, Y.-Q. Li, C. Ma, P. Fang, X.-J. Zhang, T.-S. Mei, J. Am. Chem. Soc. 139
(2017) 3293e3298.
Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Acknowledgement
[33] S. Tang, Y. Liu, A. Lei, Inside Chem. 4 (2018) 27e45.
[34] Y. Liang, F. Lin, Y. Adeli, R. Jin, N. Jiao, Angew. Chem. Int. Ed. 58 (2019)
4566e4570.
[35] Z. Zhang, L. Zhang, X. Zhang, J. Yang, Y. Yin, Y. Jiang, C. Zeng, G. Lu, Y. Yang,
F. Mo, Chem. Sci. 11 (2020) 12021e12028.
[36] I.M. Ogbu, J. Lusseau, G. Kurtay, F. Robert, Y. Landais, Chem. Commun. 56
(2020) 12226e12229.
[37] L. Zeng, J. Li, J. Gao, X. Huang, W. Wang, X. Zheng, L. Gu, G. Li, S. Zhang, Y. He,
Green Chem. 22 (2020) 3416e3420.
[38] W. Yan, M. Lin, R.D. Little, C.-C. Zeng, Tetrahedron 73 (2017) 764e770.
[39] A.O. Terent’ev, O.M. Mulina, D.A. Pirgach, A.I. Ilovaisky, M.A. Syroeshkin,
N.I. Kapustina Nikishin, I. G, Tetrahedron 73 (2017) 6871e6879.
[40] N. Yang, G. Yuan, J. Org. Chem. 83 (2018) 11963e11969.
We are grateful for financial support from the National Natural
Science Foundation of China (21662045, 22065019), the Opening
Foundation of the Key Laboratory of Green Pesticide and Agricul-
tural Bioengineering, Ministry of Education, Guizhou University
(2018GDGP0103), the Applied Basic Research Programs of Yunnan
Science and Technology Department (2018FB020, 2019FH001-011),
the Kunming “Spring City Program” for Youth Top-Notch Talents,
and the Program for Innovative Research Team (in Science and
Technology) in Universities of Yunnan Province.
6