Solvent-free Suzuki and Stille cross-coupling reactions of 4- and 5-halo-1,2,3-triazoles

Article abstract of DOI:10.1016/j.mencom.2019.03.009

An environmentally friendly and efficient synthesis of fully substituted 1,2,3-triazoles comprises solvent-free palladium-catalyzed Suzuki cross-coupling of halo-1,2,3-triazoles with pinacol arylboronates. The efficiencies of Stille and Suzuki reactions w

Full text of DOI:10.1016/j.mencom.2019.03.009

Mendeleev
Communications
Mendeleev Commun., 2019, 29, 147–149
Solvent-free Suzuki and Stille cross-coupling
reactions of 4- and 5-halo-1,2,3-triazoles
Pavel S. Gribanov,a,b Gleb A. Chesnokov,a,c Pavel B. Dzhevakov,a Nikita Yu. Kirilenko,a,c
Sergey A. Rzhevskiy,a,c Alexandra A. Ageshina,c Maxim A. Topchiy,a,c
Maxim V. Bermeshev,*c Andrey F. Asachenko*a,c and Mikhail S. Nechaev*a,c
a Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation
b A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
Russian Federation
c A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 119991 Moscow,
Russian Federation. E-mail: bmv@ips.ac.ru, aasachenko@ips.ac.ru, m.s.nechaev@org.chem.msu.ru
DOI: 10.1016/j.mencom.2019.03.009
Me
Me
An environmentally friendly and efficient synthesis of fully
substituted 1,2,3-triazoles comprises solvent-free palladium-
catalyzed Suzuki cross-coupling of halo-1,2,3-triazoles with
pinacol arylboronates. The efficiencies of Stille and Suzuki
reactions with halotriazoles under solvent-free conditions
were compared.
O
O
Ar
B
or Ar SnBu3
R1
R1
N
N
Me
Me
N
N
N
N
Hal
[Pd], base, solvent-free
Ar
R2
R2
23 examples
up to 95%
1,2,3-Triazoles are extensively used as medicines,1 functional
coatings,2 find application in supramolecular chemistry,3 organic
synthesis,4 transition metal catalysis5 and can be employed as
sensing materials.6 Therefore, development of new universal
syntheses of 1,2,3-triazoles is topical.7 1,4,5-Trisubstituted
1,2,3-triazoles and their derivatives comprise an important and
intensively studied chemotype of compounds,1(a),8 however they
are not readily accessible via classical click reactions9 and cross-
coupling of relevant halotriazoles. Notably, 5-halotriazoles were
poorly available until recently.10 Therefore, the development of
a new reliable versatile procedure for the synthesis of fully
substituted 1,2,3-triazoles is of importance.
coupling, pinacol arylboronates ArBPin were chosen as the
counterparts since they can be readily accessed using the boryla-
tion16(c),17,18 methods, are easy to handle and are stabile in air.19
In addition, pinacol arylboronates are often liquid at room
temperature and readily soluble in aprotic solvents, which makes
their use in solvent-free cross-coupling reactions beneficial.16(a),(c)
N
N
N
N
i or ii or iii
N
R1
N
R1
Ar
Hal
R2
R1 R2 Ar
R2
R1 R2 Hal
A number of procedures for the synthesis of 1,4,5-trisubstituted
1,2,3-triazoles via the Suzuki7,9(b),11 and Stille12 cross-coupling
reactions have been documented. Recently, we reported a general
highly efficient ‘green’ synthesis of 1,4,5-trisubstituted 1,2,3-tri-
azoles13 in water through the Suzuki reaction of 4- and 5-halo-
1,2,3-triazoles10 advantageous by low catalyst loadings, avoidance
of organic solvents in favor of water, and tolerance to various
functional groups. We were the first to show that 4- and 5-chloro-
1,2,3-triazoles could be used as the coupling partners.
One of the main directions of our research is the develop-
ment of solvent-free copper,14 gold,15 and palladium16 mediated
reactions. Here, we report on a ‘greener’ solvent-free synthetic
procedure providing fully substituted 1,2,3-triazoles.
1a Bn Me Br
2a Bn Me 4-MeC6H4
2b Bn Me 2-MeC6H4
2c Bn Me 4-FC6H4
2d Bn Me 1-naphthyl
2e Bn Me 3-thienyl
2f Ph Me 4-MeC6H4
2g Ph Me 2-MeC6H4
2h Ph Me 4-FC6H4
2i Ph Me 1-naphthyl
2j Ph Me 3-thienyl
1b Bn Me
I
1c Ph Me Br
Ph Pr
Cl
1d
2k Ph Pr
4-MeC6H4
N
N
N
N
i or ii or iii
N
Bn
N
Bn
Ph
Ph
Ar
Initially, we compared performances of the Suzuki and Stille
reactions of model 1-benzyl-4-bromo-5-methyl-1,2,3-triazole
1a under solvent-free conditions (Scheme 1).† In the Suzuki
Hal
4a Ar = 4-MeC6H4
4b Ar = 4-FC6H4
4c Ar = 1-naphthyl
4d Ar = 3-thienyl
3a Hal = Cl
3b Hal = Br
3c Hal = I
†
Solvent-free preparation of 1,4,5-trisubstituted 1,2,3-triazoles.
General procedure A based on the Suzuki–Miyaura cross-coupling.
A screw cap vial equipped with a magnetic stirring bar was charged with
the corresponding 4- or 5-halo-1,2,3-triazole (0.5 mmol, 1.0 equiv.),
ArBPin (0.525 mmol, 1.05 equiv.), Pd(OAc)2 (0.005 mmol, 0.01 equiv.),
SPhos (0.01 mmol, 0.02 equiv.), and powdered 85% KOH (0.85 mmol,
1.7 equiv.). All the components were thoroughly mixed together. The vial
was placed into a preheated oil bath (110°C). After 24 h, the reaction
Scheme 1 Reagents and conditions: i, procedure A, halotriazole (0.5 mmol),
ArBPin (0.525 mmol), Pd(OAc)2 (0.005 mmol, 1 mol%), SPhos (0.01 mmol,
2 mol%), KOH (0.85 mmol), neat, 110°C, 24 h; ii, procedure B, halotriazole
(0.5 mmol), ArBPin (0.525 mmol), Pd(PPh3)2Cl2 (0.005 mmol, 1 mol%),
KOH (0.85 mmol), neat, 110°C, 24 h; iii, procedure C, halotriazole (0.5 mmol),
ArSnBu3 (0.55 mmol), Pd(OAc)2 (0.005 mmol, 1 mol%), PCy3 (0.01 mmol,
2 mol%), CsF (0.75 mmol), neat, 110°C, 24 h.
© 2019 Mendeleev Communications. Published by ELSEVIER B.V.
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
– 147 –

Mendeleev Commun., 2019, 29, 147–149
Table 1 Solvent-free Suzuki and Stille cross-coupling of halotriazoles 1, 3.
entries 8–14) and benzyl (entries 1–7 and 15–23) substituents at
the nitrogen atom. Various pinacol arylboronates bearing electron
donating (entries 1, 3, 4, 8, 9), electron withdrawing (entries 5,
10, 21) and sterically hindered (entries 6, 11, 22) substituents
in the aryl group can be efficiently used as coupling partners.
Also, we used reaction with 3-thienylboronic acid pinacol ester
(entries 7, 12, 23) to exemplify the reactivity of pinacol hetero-
arylboronates in the cross-coupling.
Organoelement counterpart
Halo-
triazole
Yield
(%)
Entry
Procedure Product
Ar
Leaving group
1
2
1a
1a
1b
1a
1a
1a
1a
1c
1c
1c
1c
1c
1d
1d
3a
3a
3b
3b
3c
3c
3c
3c
3c
4-MeC6H4 BPin
4-MeC6H4 SnBu3
4-MeC6H4 BPin
2-MeC6H4 BPin
A
C
B
A
A
A
A
A
A
A
A
A
A
C
A
C
A
C
B
C
B
B
B
2a
2a
2a
2b
2c
2d
2e
2f
94
46
73
71
70
82
74
71
78
60
82
65
37
25
52
65
37
35
96
62
95
50
68
3
4
Notably, in couplings of chloro- and bromo-1,2,3-triazoles
we used a well-recognized Buchwald catalytic system Pd(OAc)2/
SPhos.20 In cases of more active iodo-1,2,3-triazoles 2a and
5
4-FC6H4
1-naphthyl BPin
3-thienyl BPin
BPin
6
7
16(a)
4a–d, employment of a conventional catalyst Pd(PPh3)2Cl2
8
4-MeC6H4 BPin
2-MeC6H4 BPin
was sufficient to reach good-to-excellent yields of the target
compounds (see Table 1, entries 3, 19–23).
9
2g
2h
2i
10
11
12
13
14
15
16
17
18
19
20
21
22
23
4-FC6H4
1-naphthyl BPin
3-thienyl BPin
BPin
Couplings of 3-thienylboronic acid pinacol esters 2e,j and 4d
proceed in yields below 75% (see Table 1, entries 7, 12, 23),
which may be attributed to catalyst poisoning. It was documented
previously21 that admixtures of thiols and organic sulfides usually
contaminate the title organosulfur compounds. High affinity
of such impurities to palladium can be the cause of catalyst
deactivation.
In 5-iodo-1,2,3-triazole 3c, 1- and 4-positioned substituents
introduce steric encumbrance around 5-position, which might
hinder the cross-coupling. In fact, the coupling of this iodo-
hetarene with arylboronic esters of different electronic nature
proceeded very efficiently to provide products 4a,b in yields as
high as 96 and 95%, respectively (see Table 1, entries 19, 21).
Meanwhile, with bulky 1-naphthylboronic ester product 4c was
obtained in only 50% yield (entry 22). Therefore, 5-iodo-1,2,3-
triazoles are less sensitive to electronic nature of pinacol
arylboronates than to their steric properties.
In cases when the Suzuki coupling provided yields below
60% (see Table 1, entries 13, 15, 17), we additionally tested the
performance of Stille reaction. Regularly, on moving to the Stille
method the yields were even lower. However, in case of using
chloro derivative 3a some increase in the yield of product 4a from
52% (Suzuki) to 65% (Stille) was observed (entries 15 and 16).
In conclusion, a comparison between performances of the
Suzuki and Stille coupling reactions of 4- and 5-halo-1,2,3-tri-
azoles under solvent-free conditions revealed the preference of the
Suzuki method. The Buchwald catalytic system Pd(OAc)2/SPhos
is well suitable for the coupling of 4- and 5-bromo-1,2,3-triazoles,
whereas more active iodotriazoles react efficiently under catalysis
by conventional complex Pd(PPh3)2Cl2. The elaborated procedure
meets the requirements of ‘green’ chemistry for the following
reasons: (i) no use of solvents; (ii) aerobic conditions; (iii) low
catalyst loadings; and (iv) easily available, environmentally
benign KOH as a base. Notably, we have previously shown that
the Suzuki coupling of aryl halides can be efficiently performed
under solvent-free conditions.16(a) Herein, we have demonstrated
that this methodology can be extended to heteroaromatic halides,
particularly, challenging 4- and 5-halo-1,2,3-triazoles. This
contribution presents no more than the second example of their
Suzuki cross-coupling.13
2j
4-MeC6H4 BPin
4-MeC6H4 SnBu3
4-MeC6H4 BPin
4-MeC6H4 SnBu3
4-MeC6H4 BPin
4-MeC6H4 SnBu3
4-MeC6H4 BPin
4-MeC6H4 SnBu3
2k
2k
4a
4a
4a
4a
4a
4a
4b
4c
4d
4-FC6H4
1-naphthyl BPin
3-thienyl BPin
BPin
The coupling of either 4-MeC6H4BPin or 4-MeC6H4SnBu3
with bromotriazole 1a upon 24 h heating afforded the same
product 2a (see Scheme 1, Table 1). For the catalytic systems,
special Suzuki [Pd(OAc)2/SPhos, KOH]16(a) and Stille [Pd(OAc)2/
PCy3, CsF]16(f) versions were chosen since they are known to be
suitable for the solvent-free procedures. The product 2a was isolated
by flash chromatography in 94% yield in case of Suzuki reaction
and 46% in case of Stille reaction (Table 1, entries 1 and 2).
Me
Me
Bu
O
Me
B
Me
Sn Bu
Bu
Me
Me
O
4-MeC6H4BPin
4-MeC6H4SnBu3
Since the Stille method provided only moderate yield of
product 2a in the model experiments, the further studies of the
scope and limitations of solvent-free coupling of 4(5)-chloro/
bromo/iodo-substituted 1,2,3-triazoles were performed based
on the Suzuki coupling (Table 1). Target 1,4,5-trisubstituted
1,2,3-triazoles 2 and 4 were obtained in good-to-excellent yields
from 4- and 5-halotriazoles 1, 3 containing aryl (see Table 1,
mixture was cooled and treated with CH2Cl2–H2O (1:1) mixture, the
organic phase was separated and the solvent was evaporated in vacuo. The
pure product was isolated by silica gel chromatography using hexane–
EtOAc (10:1) mixture as eluent.
General procedure B based on the Suzuki–Miyaura cross-coupling.
A mixture of 4- or 5-halo-1,2,3-triazole (0.5 mmol, 1.0 equiv.), ArBPin
(0.525 mmol, 1.05 equiv.), Pd(PPh3)2Cl2 (0.005 mmol, 0.01 equiv.) and
powdered 85% KOH (0.85 mmol, 1.7 equiv.) was treated as in General
Procedure A.
General procedure C based on the Stille cross-coupling. A mixture of
4- or 5-halo-1,2,3-triazole (0.5 mmol, 1.0 equiv.), tributyl(4-methylphenyl)-
stannane (0.55 mmol, 1.1 equiv.), Pd(OAc)2 (0.005 mmol, 0.01 equiv.),
tricyclohexylphosphine (0.01 mmol, 0.02 equiv.), and anhydrous CsF
(0.75 mmol, 1.5 equiv.) was treated as in General Procedure A.
P. S. Gribanov, G. A. Chesnokov, N. Yu. Kirilenko, S. A.
Rzhevskiy, M. A. Topchiy, A. F. Asachenko, and M. S. Nechaev
are grateful to the Russian Science Foundation for support
(project no. 17-13-01076). Part of this study was performed by
A. A. Ageshina and M. V. Bermeshev within the framework of
the A. V. Topchiev Institute of Petrochemical Synthesis, Russian
Academy of Sciences State Plan. Authors are grateful to the
M. V. Lomonosov Moscow State University for the opportunity
to use the NMR facilities of the Center for Magnetic Tomography
and Spectroscopy.
– 148 –

Mendeleev Commun., 2019, 29, 147–149
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Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2019.03.009.
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