Metal-free Decarboxylative Annulation of 2-Aryl-2-isocyano-acetates with Aryldiazonium Salts: General Access to 1,3-Diaryl-1,2,4-triazoles

Article abstract of DOI:10.1002/adsc.202001016

Isocyanoacetates are versatile substrates for the synthesis of heterocyclic compounds, but the concomitant decarboxylation remains rare. Herein we report a decarboxylative annulation reaction of 2-aryl-2-isocyanoacetates with aryldiazonium salts. This metal-free, base-promoted protocol allows for the access to a broad collection of 1,3-diaryl-1,2,4-triazoles, including chiral triazole-based binaphthalene ligands, drug mimics, and synthetic intermediates of druglike molecules. (Figure presented.).

Full text of DOI:10.1002/adsc.202001016

Title: Metal-free Decarboxylative Annulation of 2-Aryl-2-isocyano-
acetates with Aryldiazonium Salts: General Access to 1,3-
Diaryl-1,2,4-triazoles
Authors: Yu-Ting Tian, Fa-Guang Zhang, Jing Nie, Chi Wai Cheung,
and Jun-An Ma
This manuscript has been accepted after peer review and appears as an
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.202001016
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10.1002/adsc.202001016
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.202((will be filled in by the editorial staff))
Metal-free Decarboxylative Annulation of 2-Aryl-2-isocyano-
acetates with Aryldiazonium Salts: General Access to 1,3-
Diaryl-1,2,4-triazoles
Yu-Ting Tian,ab Fa-Guang Zhang,ab Jing Nie,ab Chi Wai Cheungab* and Jun-An Maab*
[a] Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Frontiers Science Center for
Synthetic Biology (Ministry of Education), and Tianjin Collaborative Innovation Centre of Chemical Science &
Engineering, Tianjin University, Tianjin 300072, P. R. of China
[b]
Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University,
Binhai New City, Fuzhou 350207, P. R. of China
E-mail: zhiwei.zhang@tju.edu.cn; majun_an68@tju.edu.cn
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract. Isocyanoacetates are versatile substrates for
the synthesis of heterocyclic compounds, but the
concomitant decarboxylation remains rare. Herein we
report a decarboxylative annulation reaction of 2-aryl-
2-isocyanoacetates with aryldiazonium salts. This
metal-free, base-promoted protocol allows for the
access to a broad collection of 1,3-diaryl-1,2,4-
triazoles, including chiral triazole-based binaphthalene
ligands, drug mimics, and synthetic intermediates of
druglike molecules.
Keywords: aryldiazonium; isocyanoacetate; triazole;
decarboxylation; annulation
Introduction
1,2,4-Triazoles are prevalent nitrogen heterocyclic
compounds and paramount structural motifs of
biologically active molecules in pharmaceutical
industry.[1] Therefore, a vast number of functionalized
1,2,4-triazoles have been accessed by means of
annulation and cyclization reactions of various
synthons and substrates.[1-4] Among these methods,
aryldiazonium salts,[4-7] which are versatile and
readily accessible ‘N‒N’ synthons, have been utilized
for the synthesis of 1,2,4-triazoles.[5] In 1970’s,
Masumoto disclosed the first synthesis of 1,3-
disubstituted 1,2,4-triazoles via the base-promoted
annulation of aryldiazonium salts with methyl
isocyanoacetate,[5a] wherein only electron-rich aryl
groups could be harnessed to deliver methyl 1-aryl-
1,2,4-triazole-3-carboxylates (Scheme 1a). Such
limitation was recently addressed by Bi and co-
workers via the silver-catalyzed annulation of 2-
isocyanoacetates,[5b] allowing for incorporating both
electron-rich and electron-deficient aryldiazonium
salts to obtain broader range of 1-aryl-1,2,4-triazole-
3-carboxylates (Scheme 1b). On the other hand,
Scheme 1. Synthesis of 1,2,4-triazoles from 2-
isocyanoacetates and aryldiazonium salts.
owing to the unique reaction patterns of 2-isocyano-
acetates, they could be employed as five-,[8] four-,[9]
three-,[10] or two-atom[11] synthons for the distinct
1
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10.1002/adsc.202001016
Advanced Synthesis & Catalysis
constructions of cyclic compounds. In particular,
isocyanoacetates bearing additional 2-substituents
undergo the annulations with the retention of the
carboxylate moieties.[10] Strikingly, despite the high
reactivity of 2-aryl-2-isocyanoacetates and aryl-
diazonium salts, the annulation reaction based on
these two substrates remains underdeveloped. Herein
we describe an alternative decarboxylative annulation
reaction between aryldiazonium salts and 2-aryl-2-
isocyanoacetates. This metal-free, base-promoted
annulation strategy provides an operationally simple
and expeditious access to 1,3-diaryl-1,2,4-triazoles in
conjunction with the elimination of carboxylate
groups (Scheme 1c). This protocol takes advantage of
2-aryl-2-isocyanoacetates as decarboxylative ‘C‒N‒C’
synthons, displaying an intriguing and unprecedented
mode of reactivity of isocyanoacetates and providing
an attractive means for diversifications in heterocycle
synthesis.
Under the optimized conditions (Table 1, entry 19),
a wide range of aryldiazonium salts underwent this
Table 1. Optimization of decarboxylative annulation[a]
Entry
Additive
(equiv)
Solvent
Yield/
%
[b]
1
2
3
4
5
6
7
8
Cu(OAc)2 (0.1)
Ag2CO3 (0.1)
Ag2CO3 (0.1)/Cs2CO3 (1)
Cs2CO3 (1)
Na2CO3 (1)
KOH (1)
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
toluene
DCM
1,4-
35
31
53
57
39
55
65
61
58
71
88
81
85
92
NaOH (1)
KOtBu (1)
9
DBU (1)
Et3N (1)
DABCO (1)
DABCO (1)
DABCO (1)
DABCO (1)
10
11
12
13
14
Results and Discussion
dioxane
DMF
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
15
16
17
18
DABCO (1)
DABCO (1)
DABCO (0.5)
DABCO (1.5)
DABCO (1)
DABCO (1)
none (1)
92
91
67
90
95
83
0
Methyl 2-isocyano-2-phenylacetate (1a) and
phenyldiazonium salt (2a) were employed as model
substrates for initial study (Table 1). By applying Cu
or Ag salt as a conventional catalyst in annulation
with aryldiazonium salts, [5b] 1a (1 equiv) reacted with
19 [c]
20[c, d]
21[c]
o
2a (1.5 equiv) in tetrahydrofuran solvent at 0 C in 1
[a]
h, delivering exclusively the decarboxylated product
1,3-diphenyl-1,2,4-triazole 3a in the yields of 31%
and 35%, respectively (Entries 1 and 2). The Ag-
catalyzed reaction was found to be promoted by
Cs2CO3 (1 equiv) to afford 3a in 53% yield (Entry 3).
Interestingly, subsequent survey revealed that the
presence of Cs2CO3 without metal catalyst was
sufficient to provide 3a in a similar yield (Entry 4).
Therefore, the effect of bases was explored (Entries
5‒11). Gratifyingly, the use of 1,4-diazabicyclo-
[2.2.2]octane (DABCO) as a weaker base in THF
enhanced the yield of 3a to 88% (Entry 11). When
1,4-dioxane, dimethylformamide (DMF), and
acetonitrile (MeCN) were used as solvents, the yields
could be further improved to 91‒92% (Entries 12‒16).
MeCN was employed as a more sustainable
solvent[12] for subsequent study (Entry 16). To further
increase the product yield, the effects of loadings of
base and substrates as well as the reaction
temperatures were examined (Entries 17‒20). The
product yield was slightly improved to 95% in the
presence of slightly excess of 1a (1.5 equiv, Entry 19).
Base was particularly indispensable for the reaction.
When base was excluded, most substrates remained
unreacted and the desired product 3a was not
detected (Entry 21).
Reaction conditions: 1a (0.2 mmol), 2a (0.3 mmol),
additive (0.1‒0.3 mmol), solvent (2 mL), 0 oC, air
atmosphere, 1 h.
[b] Isolated yield.
[c] 1a (0.3 mmol, 1.5 equiv), 2a (0.2 mmol, 1 equiv) were
used.
[d] Reaction was conducted at rt.
annulation with methyl 2-isocyano-2-phenylacetate
1a (Scheme 2). Electron-neutral (3a), electron-rich
(3b‒3j), and electron-withdrawing groups (3k‒3t) on
the phenyl ring of aryldiazonium salts were all
tolerated, giving the corresponding 1,3-diaryl-1,2,4-
triazoles in high to excellent yields. Notably, triazoles
bearing sterically bulky 2-anisoyl (3d), 2-tolyl- (3g),
and 1,1’-biphenyl (3j) groups were formed smoothly.
Various functional groups were compatible as well,
such as bromo (3k), chloro (3l‒3n), fluoro (3o),
trifluoromethyl (3p), ester (3q), and nitro (3r‒3t)
groups. The protocols allowed for the incorporation
of 2-, 3- and 4-substituted aryl, di-substituted aryl
(3u‒3w), as well as bioactive trimethoxyphenyl (3x)
counterparts. Furthermore, triazoles embedded with
naphthyl (3y) and thienyl (3z) moieties were also
accessible. The annulation with quinolyldiazonium
salt only afforded the corresponding triazole 3ao in
16% yield, presumably due to the participation of
nucleophilic quinolyl group in the decarboxylation
2
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10.1002/adsc.202001016
Advanced Synthesis & Catalysis
step that subsequently dampens the annulation. The
regioselectivity of annulation was further ascertained
by the X-ray crystallographic analysis of product 3a
(Supporting Information).[13]
desulfonylation to deliver the corresponding product
1,3-diphenyl-1,2,4-triazole 3a.
This protocol was also amendable to the one-pot
synthesis of triazoles 3a and 3al‒3ao based on the in
situ formed aryldiazonium salts and methyl 2-
isocyano-2-phenylacetate
(Scheme
4).
This
convenient approach was particularly valuable in
preparing triazoles bearing the protic functional
groups such as phenol (3al), alcohol (3am), and
carboxylic acid (3an). This streamlined synthesis also
slightly improved the yield of quinolyl-based triazole
3ao to 27%.
Scheme 3. Substrate scope of 2-aryl-2-isocyanoacetates.
Unless otherwise noted, methyl 2-aryl-2-isocyanoacetates
(1a’‒1k’) were used.
Scheme 2. Substrate scope of aryldiazonium salts.
This protocol proved to be equally general in the
annulation with a variety of 2-aryl-2-isocyanoacetates
(Scheme 3). Methyl 2-aryl-2-isocyanoacetates
bearing both electron-donating (3aa, 3ab) and
electron-withdrawing (3ac‒3ak) groups on the aryl
ring reacted well to afford the corresponding 1,3-
diaryl-1,2,4-triazoles. The effect of steric hinderance
of aryl groups on isocyanoacetates were insignificant,
giving 2-bromo- (3ad), 2-cyano- (3ah) and 2-
nitrophenyl (3ai, 3aj)-substituted triazoles in 87‒98%
yields. Sensitive bromo (3ac, 3ad), chloro (3ae),
fluoro (3af, 3ak), cyano (3ag, 3ah), and nitro (3ai,
3aj) groups on the aryldiazonium partners were also
compatible in the protocol. Likewise, ethyl (1l’),
isopropyl (1m’), tert-butyl (1n’), and benzyl (1o’) 2-
isocyano-2-phenylacetates as well as α-tosylbenzyl
isocyanide (1p’) also underwent decarboxylation or
Scheme 4. One-pot decarboxylative annulation.
The synthetic utility was showcased by several
chemical transformations. The reaction was scalable
to large-scale synthesis of 3a based on 5 mmol of
phenyldiazonium salt 2a without significant
diminishment of yield (Scheme 5a). Interestingly, 3a
was formed in equally high yield when water was
used as solvent, exhibiting the potential application
3
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10.1002/adsc.202001016
Advanced Synthesis & Catalysis
for greener and more sustainable organic synthesis.
suggesting that the decarboxylation of 1a does not
take place prior to the coupling reaction with
aryldiazonium salt 2a. Likewise, the reaction with
Additionally,
the
(S)-1,1'-binaphthalene-2,2'-
bis(diazonium) salt, which was readily prepared from
its diamine precursor, underwent annulation to afford
both bis-triazole- (4) and mono-triazole (5)-
substituted binaphthalenes without erosions of
enantiomeric excess (Scheme 5b). The chiral ligands
might be applicable in metal-catalyzed asymmetric
reactions. Moreover, under this protocol, 1-(3,4,5-
trimethoxy-phenyl)-3-(4-ethoxyphenyl)-1,2,4-trizole
6 could be obtained in 62% yield, which could exert
as a regio-analogue of an antitumor agent 6’[14]
(Scheme 5c). This method also provided an
alternative strategy to access an aminophenyl- and
(trifluoromethyl)-phenyl-substituted triazole 8, an
essential intermediate for synthesis of potent inhibitor
of vascular endothelial growth factors,[15] via the
annulation to 7 and the following hydrogenation
process (Scheme 5d).
Scheme 6. Mechanistic studies.
methyl 2-isocyanopropanoate instead of 1a also did
not lead to the product formation (Scheme 6b). The
result implied that an additional electron-withdrawing
and conjugating substituent such as aryl group is
requisite to facilitate deprotonation and/or
decarboxylation involved in the annulation process.
To probe the source of hydrogen at the 5-position of
triazole, the deuterium labelling effect was studied by
adding D2O into the reaction system. In the presence
Scheme 5. Synthetic utility of decarboxylative annulation.
To shed lights on the mechanism of the
decarboxylative annulation reaction, a series of
control experiments were conducted. When
phenylmethyl isocyanide without the ester linkage
was used in place of methyl 2-isocyano-2-
phenylacetate 1a, no reaction took place (Scheme 6a),
4
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10.1002/adsc.202001016
Advanced Synthesis & Catalysis
of 1 equivalent of D2O, 3a-d1 was formed with 30%
deuterium incorporation; when 30 equivalents of D2O
was added, the deuterium enrichment was boosted to
85% (Scheme 6c). On the other hand, when d3-
acetonitrile was employed as solvent, 3a was formed
without any D incorporation. Triazole 3a also did not
undergo deuterium exchange with excess D2O
(Scheme 6d). These results all suggested that water
could serve as the hydrogen source to protonate
triazole anion irreversibly for the product formation.
Furthermore, a radical mechanism is unlikely
involved, as 3a was still formed in 92% yield in
presence of 1 equivalent of (2,2,6,6-tetramethyl-
piperidin-1-yl)oxyl (TEMPO) as a radical trap
(Scheme 6e). Further, the electronic effect was
studied by competition experiments (Scheme 6f). In
the reaction with an equimolar ratio of electron-rich
4-methoxyphenyldiazonium 2b and electron-deficient
4-(methoxycarbonyl)benzenediazonium 2q, triazoles
3b and 3q were formed in 1:1.3 ratio. In the presence
of an equimolar ratio of electron-rich 4-tolyl- and
electron-deficient 4-cyanophenyl-isocyanide esters
(1b’ and 1g’), triazoles 3ab and 3ag were formed in
1:2.5 ratio. Likely, the reaction mechanism
encompasses the deprotonation, decarboxylation and
nucleophilic addition steps which could all be
promoted by electron-withdrawing groups.
Scheme 7. Proposed mechanism of decarboxylative
annulation.
Based on the above experiments, we proposed a
plausible mechanism of the decarboxylative
annulation (Scheme 7). Methyl 2-aryl-2-isocyano-
acetate 1 is initially deprotonated by DABCO to form
an anionic intermediate A, which then attacks the
terminal nitrogen of aryldiazonium salt to give the
species B. The species B cyclizes to form the
intermediate C, which could also be generated from
the cycloaddition reaction of A with aryldiazonium
salt. Subsequently, the Krapcho-type decarboxylation
and the isomerization furnish the desired triazole.
During such process, the protonated DABCO,
residual water, or the aqueous workup could provide
the proton source for the product formation.
Conclusion
Since Krapcho-type decarboxylation was proposed
in triazole synthesis with methyl diazoacetate,[16] we
also probed such feasibility in the protocol. In the
presence of excess sodium 4-tert-butylbenzoate as
base, 3a was formed with the concomitant isolation
of methyl 4-tert-butylbenzoate 9 in 40% yield
(Scheme 6g). In addition, the yield of triazoles
dropped accordingly with the elevation of steric
bulkiness of ester group in isocyanoacetates (1l’, 1m’,
1n’, Scheme 3), which is the distinctive feature of
In conclusion, we have developed a metal-free,
base-promoted
annulation
of
2-aryl-2-
isocyanoacetates with aryldiazonium salts. A diverse
array of 1,3-diaryl-1,2,4-triazoles are formed
regiospecifically with good functional group
compatibility. The protocol is scalable and allows for
access to chiral triazole-based ligands and
medicinally-relevant molecules. Mechanistic study
suggests that the annulation likely proceeds via a
Krapcho-type decarboxylation.
Krapcho-type
decarboxylation.
These
two
observations indicated that the mechanism could
comprise of the Krapcho-type decarboxylation via
alkyl cation elimination followed by CO2 extrusion.
In a similar vein, when excess NaOPh was employed
in annulation with α-tosylbenzyl isocyanide 1p’, 3a
was produced whilst TsOPh 10 was formed in 35%
yield (Scheme 6h). The tosyl group is eliminated in
cationic form, in analogy to alkyl cation elimination
in Krapcho-type decarboxylation.
Experimental Section
General procedure for synthesis of triazoles via
metal-free decarboxylative annulation of 2-aryl-2-
isocyanoacetates with aryldiazonium salts.
An oven-dried 25-mL Schlenk tube equipped with a
magnetic stir bar was charged with 2-aryl-2-
isocyanoacetate 1 (0.45 mmol, 1.5 equiv), DABCO
(33.7 mg, 0.3 mmol, 1 equiv), followed by the
addition of MeCN (3 mL) via a syringe. The reaction
mixture was then cooled down to 0 oC. At this point,
aryldiazonium salt 2 (0.3 mmol, 1 equiv) was added
o
o
at 0 C. The resulting mixture was stirred at 0 C
under air for 1 h. After the reaction, the mixture was
concentrated under reduced pressure with the aid of
5
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10.1002/adsc.202001016
Advanced Synthesis & Catalysis
[2] K. T. Potts, Chem. Rev. 1961, 61, 87–127.
rotary evaporator. The residue was purified by a silica
gel column chromatography eluted with an eluent
(EtOAc/petroleum ether) to yield the 1,3-diaryl-1,2,4-
triazoles.
[3] For recent examples, see: a) K. Sudheendran, D.
Schmidt, W. Frey, J. Conrad, U. Beifuss, Tetrahedron
2014, 70, 1635–1645; b) J. Kuang, B. Chen, S. Ma,
Org. Chem. Front. 2014, 1, 186–189; c) H. Xu, S. Ma,
Y. Xu, L. Bian, T. Ding, X. Fang, W. Zhang, Y. Ren, J.
Org. Chem. 2015, 80, 1789−1794; d) M. Nakka, R.
Tadikonda, S. Rayavarapu, P. Sarakula, S. Vidavalur,
Synthesis 2015, 47, 517–525; e) W. S. Bechara, I. S.
Khazhieva, E. Rodriguez, A. B. Charette, Org Lett
2015, 17, 1184–1187; f) Z. Chen Z, H. Li, W. Dong, M.
Miao, H. Ren, Org. Lett. 2016, 18, 1334–1337; g) S. B.
Inturi, B. Kalita, A. J. Ahamed, Tetrahedron Lett. 2017,
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2018, 83, 11963−11969; i) A. V. Bogolyubsky, O.
Savych, A. V. Zhemera, S. E. Pipko, A. V.
Grishchenko, A. I. Konovets, R. O. Doroshchuk, D. N.
Khomenko, V. S. Brovarets, Y. S. Moroz, M. Vybornyi,
ACS Comb. Sci. 2018, 20, 461−466; j) J. Xia, X.
Huang, M. Cai, Synthesis 2019, 51, 2014–2022.
General procedure for synthesis of triazoles via
one-pot annulation based on anilines and methyl
2-isocyano-2-phenylpacetate.
An oven-dried Schlenk tube equipped with a
magnetic stir bar was charged with aniline (0.3
mmol), then dry THF (3 mL) were added. The
o
solution was cooled down to 0 C, added with HBF4
(74 μL, 50% in water, 0.6 mmol, 2.0 equiv), and
t
o
stirred at 0 C for 5 minutes. Then, BuONO (71 μL,
0.6 mmol, 2.0 equiv) was added, and the resulting
o
mixture was stirred at 0 C under air for 1 h to
prepare the in situ formed aryldiazonium salt. At this
point, methyl 2-isocyano-2-phenylacetate (78.8 mg,
0.45 mmol, 1.5 equiv) was added followed by
DABCO (101 mg, 0.9 mmol, 3 equiv). After the
addition was complete, the reaction mixture was
[4] a) For recent related review about the synthesis of N-
heterocycles via cycloaddition and cyclization of
aryldiazonium salts, see: F.-G. Zhang, Z. Chen, C. W.
Cheung, J.-A. Ma, Chin. J. Chem. 2020, 38,
1132−1152; b) J. Liu, J. Jiang, L. Zheng, Z.-Q. Liu,
o
stirred at 0 C under air for additional 1 hour. After
the reaction, the mixture was concentrated under
reduced pressure, and the residue was further purified
by a silica gel column chromatography to yield the
corresponding 1,3-diaryl-1,2,4-triazoles.
Adv.
Synth.
Catal.
2020,
DOI:
10.1002/adsc.202000700.
[5] For synthesis of 1,2,4-triazoles using aryldiazonium
salts and isocyanoacetates as synthons, see: a) K.
Matsumoto, M. Suzuki, M. Tomie, N. Yoneda, M.
Miyoshi, Synthesis 1975, 9, 609–610; b) J.-Q. Liu, X.
Shen, Y. Wang, X.-S. Wang, X. Bi, Org. Lett. 2018,
20, 6930−6933.
Acknowledgements
We thank the National Key Research and Development
Program of China (No. 2019YFA0905100), the National
Natural Science Foundation of China (No. 21772142,
[6] For examples of synthesis of other nitrogen
heterocycles via annulation of aryldiazonium salts, see:
a) M. Ramanathan, Y.-H. Wang S.-T. Liu, Org. Lett.
2015, 17, 5886−5889; b) G.-B. Deng, H.-B, Li, X.-H.
Yang, R.-J. Song, M. Hu, J.-H. Li, Org. Lett. 2016, 18,
2012−2015; c) R. Patouret, T. M. Kamenecka,
Tetrahedron Lett. 2016, 57, 1597–1599; d) C. Zhu, H.
Zeng, F. Chen, C. Liu, R. Zhu, W. Wu, H. Jiang, Org.
Chem. Front. 2018, 5, 571−576; e) S. Chuprun, D.
Dar’in, G. Kantin, M. Krasavin, Synthesis 2019, 51,
3998−4005; f) M. Wang, B.-C. Tang, J.-C. Xiang, X.-
L. Chen, J.-T. Ma, Y.-D. Wu, A.-X. Wu, Org. Lett.
2019, 21, 8934−8937; g) C. Zhu, H. Zeng, F. Chen, C.
Liu, H. Jiang, Adv. Synth. Catal. 2019, 361,
5149−5159; h) P. Wu, Y. He, H. Wang, Y.-G. Zhou, Z.
Yu, Org. Lett. 2020, 22, 310−315; i) J. Liu, E. Xu, J.
Jiang, Z. Huang, L. Zheng, Z.-Q. Liu, Chem. Commun.
2020, 56, 2202–2205.
[7] Our group have been interested in harnessing
aryldiazonium salts for synthesis of nitrogen
heterocyclic compounds, see: a) Z. Chen, S.-Q. Fan, Y.
Zheng, J.-A. Ma, Chem. Commun. 2015, 51,
16545−16548; b) X. Peng, M.-Y. Xiao, J.-L. Zeng, F.-
G. Zhang, J.-A. Ma, Org. Lett. 2019, 21, 4808−4811; c)
S.-J. Zhai, X. Peng, F.-G. Zhang, J.-A. Ma, Org. Lett.
2019, 21, 9884−9888; d) H.-N. Liu, H.-Q. Cao, C. W.
21901181, 21971186), Tianjin Municipal Science
&
Technology Commission (19JCQNJC04700), and Tianjin
University (Start-up grants) for financial support.
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FULL PAPER
Metal-free Decarboxylative Annulation of 2-Aryl-
2-isocyanoacetates with Aryldiazonium Salts:
General Access to 1,3-Diaryl-1,2,4-triazoles
Adv. Synth. Catal. Year, Volume, Page – Page
Yu-Ting Tian, Fa-Guang Zhang, Jing Nie, Chi Wai
Cheung,* and Jun-An Ma*
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