General Method for the Synthesis of 1,4-Disubstituted 5-Halo-1,2,3-triazoles

Article abstract of DOI:10.1002/ejoc.201700925

A general method for the synthesis of 1,4-disubstituted 5-halo-1,2,3-triazoles has been developed. The one-pot two-step process consists of a CuAAC reaction of a copper(I) acetylide with an organic azide catalyzed by (aNHC)CuCl, followed by halogenation with N-chlorosuccinimide, N-bromosuccinimide, or I₂.

Full text of DOI:10.1002/ejoc.201700925

A Journal of
Accepted Article
Title: General method of synthesis of 1,4-disubstituted-5-halo-1,2,3-
triazoles
Authors: Pavel Gribanov, Maxim Topchiy, Iuliia Karsakova, Gleb
Chesnokov, Alexander Smirnov, Lidiya Minaeva, Andrey
Asachenko, and Mikhail Sergeevich Nechaev
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201700925
Link to VoR: http://dx.doi.org/10.1002/ejoc.201700925
Supported by

10.1002/ejoc.201700925
European Journal of Organic Chemistry
COMMUNICATION
General method of synthesis of 1,4-disubstituted-5-halo-1,2,3-
triazoles
Pavel S. Gribanov,[a] Maxim A. Topchiy,[a] Iuliia V. Karsakova,[b] Gleb A. Chesnokov,[b] Alexander Yu.
Smirnov[a], Lidiya I. Minaeva[c], Andrey F. Asachenko[a,c] and Mikhail S. Nechaev*[a,b]
Abstract: General method of synthesis of 1,4-disubstituted-5-halo-
1,2,3-triazoles have been developed. The one-pot two-step process
consists of CuAAC of copper(I) acetylide with organic azide
catalyzed by (aNHC)CuCl, and following halogenation using NCS,
NBS or I2.
reaction with organic azide. Contrary, NCS, as lower strength
electrophile, reacts with copper(I) phenylacetylide at lower rate.
Thus, copper(I) phenylacetylide predominantly reacts with
benzyl azide to give copper(I) 1,2,3,-triazolide 3a. Then, 3a
reacts with NCS to give 4a in high yield. Arguably, this is due to
lower lability of copper-carbon bond in 2a than in 3a, since 2a is
a polymeric complex.
Introduction
The discovery of copper catalyzed azide acetylene cycloaddition
reaction (CuAAC) made 1,2,3-triazoles easily accessible
compounds.[1] This have led to their broad utilization in various
applications.[2] However this approach is not suitable, in most
cases, for synthesis of 1,4,5-trisubstituted-1,2,3-triazoles. It have
been recently shown that 1,4,5-trisubstituted-1,2,3-triazoles
have high practical significance in organic synthesis, biomedical
and material applications.[3] Convenient precursors for this class
of compounds are 1,4-disubstituted-5-iodo-1,2,3-triazoles that
3m, 3q, 4]
can be functionalized via Sonogashira alkynylation,[3l,
3p, 6]
7]
alkylation,[5] arylation,[3g,
Heck reaction,[3k,
nucleophilic
substitution,[3n, 8] and intramolecular cyclization (Scheme 1).[3f, 3h,
3i]
Recently, Yuefei Hu et al. reported on the development of the
new original approach for synthesis of 1,4-disubstituted-5-
chloro-1,2,3,-triazoles by mixing copper(I) aryl acetylides with
benzyl azide in CH2Cl2 in presence of NCS (Scheme 2).[9]
However, this approach is not applicable for synthesis of bromo-
and iodo-derivatives using NBS and NIS, correspondingly.
The proposed method enabled to obtain 1-benzyl-4-phenyl-5-
chloro-1,2,3-triazole (4a) in high yield (88%). However, upon
substitution of NCS with NBS the target 5-bromo-1,2,3-triazole
(5a) was obtained in only 2% yield. The main product of the
reaction was 1,4-diphenylbutadiyne. The reaction in presence of
NIS gave exclusively 1-iodophenylacetylene (98%). The
obtained results were rationalized in terms of relative strengths
of NXSs as electrophiles. Stronger electrophiles NBS and NIS
quench copper(I) phenylacetylide, thus preventing its CuAAC
Scheme 1. Functionalization of 5-iodo-1,2,3-triazoles.[10]
Using the developed protocol, Yuefei Hu performed synthesis of
20 examples of 5-chloro-1,2,3-triazoles in good to high yields.
However, no examples derived from aryl azides, substrates,
challenging for CuAAC reaction,[11] were reported. Moreover, the
proposed method is not suitable for synthesis of 5-bromo and 5-
iodo-1,2,3-triazoles which are valuable substrates for further
transformations.
[a]
Pavel S. Gribanov, Maxim A. Topchiy, Alexander Yu. Smirnov,
Andrey F. Asachenko, Prof. Mikhail S. Nechaev
A. V. Topchiev Institute of Petrochemical Synthesis
Russian Academy of Sciences
Lenynsky Prospect 29, Moscow, 119991,Russian Federation
E-mail: m.s.nechaev@org.chem.msu.ru
[b]
[c]
Iuliia V. Karsakova, Gleb A. Chesnokov, Prof. Mikhail S. Nechaev
M. V. Lomonosov Moscow State University
Leninskie Gory 1 (3), Moscow, 119991, Russian Federation
Lidiya I. Minaeva, Andrey F. Asachenko
Peoples' Friendship University of Russia
Miklukho-Maklay St., 6, Moscow, 117198, Russian Federation
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
Scheme 2. Synthesis of 1,4-disubstituted 5-halo-1,2,3-triazoles.
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10.1002/ejoc.201700925
European Journal of Organic Chemistry
COMMUNICATION
In this contribution, we report on the development of a general
approach for synthesis of 1,4-disubstituted-5-halo-1,2,3-triazoles
from copper(I) acetylides, organic azides, and halogenating
agents.
reaction temperature and decrease reaction time. As a result,
the yield of N-phenyl-4-phenyl-5-chloro-1,2,3-triazole (4b) was
raised to 87% (entry 6).
Results and Discussion
Initially, we tested the conditions, developed by Yuefei Hu[9] for
synthesis of N-aryl-5-halo-1,2,3-triazoles by taking a phenyl
azide as the azide component. The resulting N-phenyl-4-phenyl-
5-chloro-1,2,3-triazole 4b have been obtained in 41% yield
(Scheme 3).
Table 1. Optimization of reaction conditions of synthesis of N-phenyl-4-phenyl-
5-chloro-1,2,3-triazole.
Entry
Catalyst
Solvent
T, °C
NCS
(eq.)
Yield
(%)
1
2
3
4
5
6
5 mol% CuCl
CH2Cl2
25
25
60
60
60
60
1.2
1.2
1.2
1.2
2.0
2.0
50[a]
58[a]
41[b]
55[b]
77[b]
87[b]
1 mol% (aNHC)CuCl
5 mol% CuCl
CH2Cl2
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
1 mol% (aNHC)CuCl
5 mol% CuCl
Scheme 3. Preparation of N-phenyl-4-phenyl-5-chloro-1,2,3-triazole.
1 mol% (aNHC)CuCl
Then, we decided to sequence two reaction steps. First, phenyl
azide was mixed with copper(I) phenylacetylide in CH2Cl2
(Scheme 4). Then, after 24 h, NCS was added. The resulting
product 4b was isolated in the same 41% yield. Analogously, the
N-phenyl-4-phenyl-5-bromo-1,2,3-triazole 5b was obtained by
addition of NBS in 36% yield.
[a] CuAAC reaction time t = 24 h. [b] CuAAC reaction time t = 4 h.
Analogous optimization of synthesis of N-phenyl-4-phenyl-5-
bromo-1,2,3-triazole (5b) using CuBr or (aNHC)CuCl) as
catalysts (Table 2) enabled us to obtain the final product in
nearly quantitative yield (99%, entry 4).
Table 2. Optimization of reaction conditions of synthesis of N-phenyl-4-phenyl-
5-bromo-1,2,3-triazole.
Scheme 4. Sequential preparation of 5-chloro- and 5-brono N-phenyl-4-
phenyl-1,2,3-triazoles.
Entry
Catalyst
NBS (eq.)
1.0
Yield (%)
57
1
2
3
4
5 mol% CuBr
Thus, contrary to previous results from Yuefei Hu’s group
(Scheme 2, 4),[9] upon sequential addition of copper
phenylacetylide and NCS/NBS the obtained yields were similar.
This have led us to the assumption that mixing of phenyl azide
with copper(I) phenylacetylide in CH2Cl2 leads to the formation
of copper(I) 1,2,3,-triazolide 3b in 24 h in approximately 40%
yield. Further, the obtained copper(I) 1,2,3,-triazolide reacts with
NCS/NBS in virtually quantitative yield.
5 mol% CuBr
2.0
88
1 mol% (aNHC)CuCl
1 mol% (aNHC)CuCl
1.0
82
2.0
>99
The optimized conditions were used for the synthesis of N-
phenyl-4-phenyl-5-iodo-1,2,3-triazole (6b) (Scheme 5). It was
found that elemental iodine, as electrophile, performs better than
NIS, corresponding yields are 63% and 38%.
To increase the yield of copper(I) 1,2,3,-triazolide 3b, and,
subsequently, to increase the overall yield of the reaction, we
performed optimization of reactions conditions.
It was previously shown that monomeric copper-acetylide
complexes are not reactive towards organic azides. However,
this reaction can be activated with corresponding copper
12]
catalysts.[10,
To enhance the rate of CuAAC reaction, we
tested CuCl[12] and (aNHC)CuCl,[13] complex bearing the
abnormal N-heterocyclic carbene ligand, as catalysts (Table 1).
We also tested the 1,2-dichloroethane (1,2-DCE), a solvent with
higher boiling temperature than for CH2Cl2, to increase the
Scheme 5. Preparation of N-phenyl-4-phenyl-5-iodo-1,2,3-triazole.
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10.1002/ejoc.201700925
European Journal of Organic Chemistry
COMMUNICATION
To determine the scope and limitations of the new synthetic
approach, we tested a series of reactions of different alkyl and
aryl azides[14] with copper(I) and arylacetylides quenched by
NCS (Scheme 6), and NBS or I2 (Scheme 7).
side products, bromination of 4-tolyloxy substituent. We have
also prepared two iodo-derivatives, 6a and 6b in good yields.
Main advantages of the new procedures of synthesis of 5-
bromo- and 5-iodo-1,2,3-triazoles are: (i) the method is
preparative; (ii) there is no need in high dilution of the reaction
Scheme 6: Preparation of 1,4-disubstituted-5-chloro-1,2,3-triazoles.[a]
[17]
media with expensive THF (0.018 mol/L)
or highly
hygroscopic CH3CN (0.12 mol/L);[18] (iii) absence of side
products, 5-H-1,2,3,-triazoles; (iv) high yields not only for alkyl-,
and benzyl azides, but also for aryl azides.[18-19]
We performed a scale-up of synthesis of 1,2,3,-triazoles 4a, 4c,
5a, 5b, 5g. Compounds 4a and 5a were obtained on a 50 mmol
scale, other examples were obtained on a 25 mmol scale.
Surprisingly, the yields in scale-up procedures reproduce small-
scale experiments. The isolation of analytically pure products is
simple. Notably, in certain cases solubility of products (4c) is low
and special care should be taken to achieve complete
dissolution of products upon isolation procedure.
A scale-up procedure is similar with the 1 mmol experiments,
except reaction vessel was immersed into room temperature
water bath due to moderate exothermicity upon addition of NXS.
Scheme 7: Preparation of 1,4-disubstituted 5-bromo- and 5-iodo-1,2,3-
triazoles.[a,b]
[a] Conditions: alkynyl copper(I) (1 mmol.), 1,2-dichloroethane (2 ml.), azide (1
mmol.), (aNHC)CuCl (1 mol.%), 60°C, 4 h, NCS (2 mmol., 2 eq.), 4 h. [b]
Room temperature.
The developed reaction protocol enabled us to obtain N-
substituted-4-phenyl-5-chloro-1,2,3-triazoles from phenyl azide
(4b), aryl azides bearing electron withdrawing (4c, 4d, 4e) as
well as electron donating (4f, 4g) substituents. The presence of
ortho- substituents in aryl azide has no negative effect on the
yields (4d, 4g). Alkyl azides were also found to be suitable
substrates for the developed protocol. Benzyl derivative 4a was
obtained in 80% yield, for the reaction of the (2-
azidoethyl)benzene (4i) the yield was virtually quantitative. Due
to high volatility of methyl azide, the first stage of the reaction
was performed at room temperature for 12 h. The obtained yield
of 4h was 49%.
The new method of synthesis of N-substituted-4-phenyl-5-
chloro-1,2,3-triazoles have several prominent advantages: (i)
suitable substrates are not only reactive alkyl and benzyl
azides,[9] but also less reactive aryl azides; (ii) mild reaction
temperature. We avoid the use of (iii) expensive solvents
(MeCN), special equipment (microwave);[3n] (iv) toxic organotin
derivatives (Bu3SnOMe);[15] and (v) flammable and functional
groups intolerant reagents (dialkylalkynylaluminium).[16]
[a] Conditions: alkynyl copper (I) (1 mmol), 1,2-dichloroethane (2 ml), azide (1
mmol), (aNHC)CuCl (1 mol.%), 60°C, 4h, NBS (2 mmol, 2 eq.), 4h. [b]
Conditions: alkynyl copper (I) (1 mmol), 1,2-dichloroethane (2 ml), azide (1
mmol), (aNHC)CuCl (1 mol.%), 60°C, 4h, I2 (2 mmol, 2 eq.), 4h. [c] NBS
(1eq.).
A series of 5-bromo triazoles were obtained from copper(I) aryl-
(5a – 5e, 5i - 5l), and propargyl ether acetylides (5f – 5h, 5m)
upon reactions with phenyl azide (5b, 5f), aryl azides, bearing
electron withdrawing (5c – 5e, 5g, 5h), and electron donating
(5k, 5l) substituents, as well as alkyl azides (5i, 5j, 5m). The
yield of N-methyl substituted 1,2,3,-triazole 5i was moderate
(51%) due to high volatility of starting methyl azide. Notably,
1,2,3,-triazoles 5f-5h and 5m were obtained using 1 eq. of NBS.
Upon utilization of 2 eq. of NBS we observed the formation of
All compounds were characterized with 1H and 13С NMR.
Characteristic signals in 1H NMR are low-filed doublets of 2H
intensity corresponding to protons of aromatic ring attached to
carbon atom. This is due to magnetic anisotropic effect of the
1,2,3,-triazole ring. This effect is not observed in 1,2,3,-triazoles
obtained from propargyl ether derivative due to different
molecular geometry.
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10.1002/ejoc.201700925
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COMMUNICATION
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atom attached to 1,2,3,-triazole ring.
Conclusions
In conclusion, we developed a general approach for the
synthesis of 1,4-disubstituted-5-halo-1,2,3-triazoles (Cl, Br, I).
The one-pot two-step procedure consists of CuAAC reaction of
copper(I) acetylides with organic azides (including challenging
aryl azides) followed by quenching of copper(I) 1,2,3,-triazolide
with the corresponding electrophile NCS, NBS or I2 to obtain
resulting 5-halo-1,2,3-triazoles in good to quantitative yields.
The developed method has several notable advantages: i) wide
scope of azides, ii) high yields, iii) low amount of side products
(5-H-1,2,3,-triazole), iv) simple and robust, v) easily scalable, vi)
short reaction times and easy work-up. Thus, a new approach
might find broad utilization in laboratory practice.
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The reported study was supported by the Russian Science
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Entry for the Table of Contents (Please choose one layout)
Layout 1:
COMMUNICATION
High yielding, robust, easily scalable
one-pot two-step approach for
synthesis of 1,4-disubstituted-5-halo-
1,2,3-triazoles.
1,2,3-Triazole Synthesis
Pavel S. Gribanov, Maxim A. Topchiy,
Iuliia V. Karsakova, Gleb A. Chesnokov,
Alexander Yu. Smirnov, Lidiya I.
Minaeva, Andrey F. Asachenko, Mikhail
S. Nechaev*
Page No. – Page No.
General method of synthesis of 1,4-
disubstituted-5-halo-1,2,3-triazoles
*one or two words that highlight the emphasis of the paper or the field of the study
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