Facile one-pot synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles through sonogashira coupling/ 1,3-dipolar cycloaddition of acid chlorides, terminal acetylenes, and sodium azide

Article abstract of DOI:10.1021/ol901040d

A novel and efficient way of synthesizing 4,5-disubstituted-1,2,3-(NH)- triazoles through palladium-catalyzed and ultrasonic promoted Sonogashira coupling/1,3-dipolar cycloaddition of acid chlorides, terminal acetylenes, and sodium azide in one pot is dev

Full text of DOI:10.1021/ol901040d

ORGANIC
LETTERS
2009
Vol. 11, No. 14
3024-3027
Facile One-Pot Synthesis of
4,5-Disubstituted 1,2,3-(NH)-Triazoles
through Sonogashira Coupling/
1,3-Dipolar Cycloaddition of Acid
Chlorides, Terminal Acetylenes, and
Sodium Azide
Jihui Li,† Dong Wang,† Yuanqing Zhang,† Jiting Li,‡ and Baohua Chen*,†
State Key Laboratory of Applied Organic Chemistry, Lanzhou UniVersity,
Gansu Lanzhou 730000, P. R. China, and College of Chemical Engineering,
Northwest Minoritise UniVersity, Gansu Lanzhou730030, P. R. China
chbh@lzu.edu.cn
Received May 12, 2009
ABSTRACT
A novel and efficient way of synthesizing 4,5-disubstituted-1,2,3-(NH)-triazoles through palladium-catalyzed and ultrasonic promoted Sonogashira
coupling/1,3-dipolar cycloaddition of acid chlorides, terminal acetylenes, and sodium azide in one pot is developed. The reaction scope is
quite general, and the methodology can produce excellent yields. The regioselective 1,4,5-trisubstituted-1,2,3-(NH)-triazoles can be made easily
from 4,5-disubstituted-1,2,3-(NH)-triazoles.
During the last decades, 1,2,3-triazoles have become one of
the best synthesized classes for chemists as they display many
interesting properties including antibacterial,1 herbicidal,
fungicidal,2 antiallergic,3 anti-HIV,4 GSK-3 inhibiting,5 and
antineoplastic activities.6 Moreover, they have been widely
used in various research fields, including biological science,7
material chemistry,8 medicinal chemistry,9 and synthetic
organic chemistry.10
Many methods have been developed to synthesize 1,2,3-
triazoles by now.11 Traditionally, the Huisgen 1,3-dipolar
cycloaddition between organic azides and terminal alkynes
is a useful and extensively applicable method for the
synthesis of N-substituted triazoles. However, the efficiency
of this method is dependent on the steric and electronic
properties of the alkyne, and the regioselectivities of these
† Lanzhou University.
‡ Northwest Minoritise University.
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Emmert, D. E.; Garmon, S. A.; Graber, D. R.; Grega, K. C.; Hester, J. B.;
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10.1021/ol901040d CCC: $40.75
Published on Web 06/19/2009
 2009 American Chemical Society

reactions are generally low within unsymmetrical alkynes
giving rise to regioisomeric mixtures of triazoles until
recently.12 In addition, the low molecular weight organic
azides are sometimes unstable and difficult to handle.13
Therefore, it is highly desirable to develope more efficient
synthetic and operationally simple methodologies used for
synthesizing a diverse array of [1,2,3]-triazoles.
Many new methods of synthesizing 1,2,3-triazoles were
developed in the past two years inspired by the “click”
chemistry and their broad application in many fields.14
However, most of these developed methods are for N-
substituted 1,2,3-triazoles, and only a few are for N-
unsubstituted 1,2,3-triazoles which also have wide utilities.15
Thus, it is very necessary and complementary to find novel
ways of synthesizing N-unsubstituted 1,2,3-triazoles in the
future. In this paper, an efficient, convenient and safe one-
pot procedure was developed to synthesize 4,5-disubstituted-
1,2,3-(NH)-triazoles through palladium-catalyzed and ultra-
sonic promoted Sonogashira coupling/1,3-dipolar cycloaddition
of acid chlorides, terminal acetylenes and sodium azide.
Enlightened by the application of Sonogashira coupling
in one-pot synthetic organic processes,16 it was assumed that
a three-component reaction of acid chlorides, terminal
acetylenes and sodium azide would provide an efficient route
for the synthesis of 4,5-disubstituted-1,2,3-(NH)-triazoles. In
our starting experiments, where phenyl acetylene, benzoyl
chloride, sodium azide were put in one pot with the catalyst
of PdCl2(PPh3)2 (1 mmol %)/CuI (2 mmol %) and the base
Et3N together in various solution(Et3N, dioxane, toluene,
THF, DMSO), and reacted under nitrogen at room temper-
ature (rt) for 24 h, we only achieved trace of the triazole 3a
and byproducts. In the latter experiments, where phenyl
acetyleneandbenzoylchloridewerecatalyzedbyPdCl2(PPh3)2/
CuI and promoted by ultrasonic (32 kHz, 160 W) at rt in
advance, followed by NaN3-1,3-dipolar cycloaddition in
DMSO, 4,5-disubstituted-1,2,3-(NH)-triazoles, 3a was ob-
tained with 98% isolated yield (Table 1, entry 1). The impact
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Table 1. Screening the Impact of Bases, Solutions and
Catalystsa
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V. V. Angew. Chem., Int. Ed. 2006, 45, 1435. (d) Wang, J.; Sui, G.;
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yield
entry
cat.(mmol %)
solvent
base
(%)b
1
PdCl2(PPh3)2(1)/CuI(2) DMSO
PdCl2(PPh3)2(1)/CuI(2) DMSO
PdCl2(PPh3)2(1)/CuI(2) DMSO
PdCl2(PPh3)2(1)/CuI(2) DMSO
PdCl2(PPh3)2(1)/CuI(2) DMF
PdCl2(PPh3)2(1)/CuI(2) Dioxane
PdCl2(PPh3)2(1)/CuI(2) Enthanol
PdCl2(PPh3)2(1)/CuI(2) CHCl3
PdCl2(PPh3)2(1)/CuI(2) THF
PdCl2(PPh3)2(1)/CuI(2) acetonitrile
Et3N
pyridine
98
2
trace
3
diisopropylamine 70
(10) (a) Wacharasindhu, S.; Bardhan, S.; Wan, Z.-K.; Tabei, K.;
Mansour, T. S. J. Am. Chem. Soc. 2009, 131, 4174. (b) Liu, Y.; Yan, W.;
Chen, Y.; Petersen, J. L.; Shi, X. Org. Lett. 2008, 10, 5385. (c) Katritzky,
A. R.; Bobrov, S.; KirichenkoKostyantyn; Ji, Y.; Steel, P. J. J. Org. Chem.
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L. M.; Zhang, X. J. Org. Chem. 2006, 71, 3928.
4
tert-butylamine trace
5
Et3N
-
92
6
45
7
-
35
8
-
40
9
-
20
10
11
12
13
14
15
16
-
30
PdCl2(5)
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
-
90
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2006, 8, 4505. (f) Boren, B. C.; Narayan, S.; Rasmussen, L. K.; Zhang, L.;
Zhao, H.; Lin, Z.; Jia, G.; Fokin, V. J. Am. Chem. Soc. 2008, 130, 8923.
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46, 1800. (c) Howell, S. J.; Spencer, N.; Philp, D. Tetrahedron 2001, 57,
4945.
Pd/C(5)
-
trace
trace
70
CuI(5)
-
Pd(PPh3)4(5)
Pd(dba)2(5)
PdCl2(PPh3)2(5)
-
-
65
trace
-
a The reaction was carried out with 1a (0.5 mmol), 2a (0.5 mmol) and
Et3N (3 equiv, 1.5 mmol) in the presence of catalyst promoted by ultrasonic
(32 kHz, 160 W) at room temperature for 1 h first under nitrogen, then
NaN3 (1.2 equiv, 0.6 mmol) and 1 mL solvent was added to the mixture
and the reaction continued at rt for one more hour. b Isolated yields after
column chromatography.
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Rasmussen, L. K.; Boren, B. C.; Fokin, V. V. Org. Lett. 2007, 9, 5337. (b)
Kalisiak, J.; Sharpless, K. B.; Fokin, V. V. Org. Lett. 2008, 10, 3171. (c)
Sengupta, S.; Duan, H.; Lu, W.; Petersen, J. L.; Shi, X. Org. Lett. 2008,
10, 1493. (d) Balducci, E.; Bellucci, L.; Petricci, E.; Taddei, M.; Tafi, A.
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11, 1587. (f) Yang, D.; Fu, N.; Liu, Z.; Li, Y.; Chen, B. Synlett 2007, 278.
of bases, solvents and catalystes was investigated in detail
for the reaction (Table 1). When using other bases, the
reaction gave low yields (Table 1, entries 2, 3, 4). The
reaction can be performed in various solutions including
Org. Lett., Vol. 11, No. 14, 2009
3025

DMSO, DMF, dioxane, enthanol, chloroform, THF, aceto-
nitrile using PdCl2(PPh3)2/CuI as catalyst (Table 1, entries
1, 5-10); and the aprotic, polar solvent DMSO is the most
favorable for the reaction. When PdCl2(PPh3)2/CuI was
changed to other catalysts, the yields decreased (Table 1,
entries 11, 14, 15) and even trace product was obtained only
(Table 1, entries 12, 13, 16) with DMSO as solvent and Et3N
as base. Therefore, the Et3N, PdCl2(PPh3)2/CuI and DMSO
is the best system for this reaction.
employed, the reaction can conduct moderately since benzoyl
chloride is used (Table 2, entry 12). The reaction of the
aliphatic cyclohex-1-enecarbonyl chloride and hex-1-yne can
also produce good yiled (Table 2, entry 13).
The scope of the process related to other kinds of terminal
acetylenes was also examined (Table 3). When other kinds
Table 3. Substrate Scope of Terminal Acetylenesa
Encouraged by the efficiency of the reaction protocol
described above, the substrate scope was investigated next.
A variety of acid chlorides were tested under the optimized
conditions using phenylacetylene or hex-1-yne as the cou-
pling agent. It was found that several electron-rich phenyl
acid chlorides were suitable substrates for the reaction,
affording the corresponding 4,5-disubstituted-1,2,3-(NH)-
triazoles in excellent yields (85-99%, Table 2, entries 1, 2,
entry
R1
R2
product yield (%)b
1
2
3
4
5
6
4-CH3OPhenyl Phenyl
4a
4b
4c
4d
4e
4f
99
98
98
98
98
94
-
4-CH3Phenyl
3-Cl Phenyl
4-Cl Phenyl
3, 5-DiCH3Phenyl
funan-2-yl
-
-
-
-
Table 2. Substrate Scope of Acid Chloridesa
7
8
9
4-FPhenyl
n-C4H9
-
-
-
-
-
n-C5H11
n-C3H7
-
-
thiophen-3-yl
-
-
Fc
Phenyl
Phenyl
4-CH3Phenyl
2-CH3Phenyl
4-ClPhenyl
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
4t
98
90c
94c
92c
95c
95c
96c
95c
88c
90c
90c
97
10
11
12
13
14
15
16
17
18
19
20
21
22
entry
R1
R2
product
yieldb
99
3-ClPhenyl
3,5-DiCH3Phenyl
3,5-DiCH3Phenyl
Phenyl
3, 5-DiCH3Phenyl
3-ClPhenyl
4-CH3Phenyl
2-CH3Phenyl
3-ClPhenyl
4-CH3Phenyl
3,5-DiCH3Phenyl
1
2
3
4
5
6
7
8
Phenyl
4-CH3Phenyl
3-CH3Phenyl
2-CH3Phenyl
2-ClPhenyl
3b
3c
3d
3e
3f
3g
3h
3i
-
-
-
-
-
-
-
98
99
60(93)c
99
4-ClPhenyl
4-NO2Phenyl
4-CH3OPhenyl
3-Cl Phenyl
83d
85d
98
98
97
93
95
4u
4v
9
-
-
-
-
3,5-DiCH3Phenyl
2,6-DiCH3Phenyl
2,6-DiClPhenyl
funan-2-yl
3j
3k
3l
3m
3n
98
-
10
11
12
13
trace
trace
97
a The reaction was carried out with 1a (0.5 mmol), 2a (0.5 mmol) and
Et3N (3 equiv, 1.5 mmol) in the presence of PdCl2(PPh3)2 (1 mol %)/CuI
(2 mol %) promoted by ultrasonic (32 kHz, 160 W) at room temperature
for 1 h under nitrogen first, then NaN3 (1.2 equiv, 0.6 mmol) and 1 mL
DMSO was added to the mixture and the reaction continued for one more
hour. b Isolated yields after column chromatography. c The temperature is
increased to 45 °C as NaN3 and DMSO are added, and the reaction continued
for another three hours.
n-butyl
cyclohex-1-enyl
88
a The reaction was carried out with 1a (0.5 mmol), 2a (0.5 mmol) and
Et3N (3 equiv, 1.5 mmol) in the presence of PdCl2(PPh3)2 (1 mol %)/CuI
(2 mol %) promoted by ultrasonic (32 kHz, 160 W) at room temperature
for 1 h first under nitrogen, then NaN3 (1.2 equiv, 0.6 mmol) and 1 mL
DMSO are added to the mixture and the reaction continued at rt for one
more hour. b Isolated yields after column chromatography. c The reaction
was carried out with PdCl2 (5 mol %) as a catalyst. d The reaction
temperature is increased to 45 °C before NaN3 and DMSO are added.
of terminal acetylenes were employed, it was found that they
are efficient with very high yields when using phenyl
acetylene. For example, 4-methoxyl phenyl acetylene can
react with several phenyl acid chlorides or furan-2-carbonyl
chloride to produce excellent results, indicating that the
procedure did not depend on the electronic properties of aryl
terminal acetylenes and acid chlorides (Table 3, entries 1-6).
When aliphatic terminal acetylenes were used, this reaction
proceeded completely at proper temperature (rt or 45 °C),
and it was much slower than when using aryl terminal
acetylene; the chain length of aliphatic terminal acetylenes
did not affect the yields (Table 3, entries 7-16). The terminal
acetylene was also extended to 3-ethynylthiophene or ethynyl
ferrocene (Fc). They can react completely with acid chlorides
3, 7, 9). In addition, electron-deficient phenyl acid chlorides
provided the coupling/1,3-dipolar cycloaddition products in
consistent yields (83-99%, Table 2, entries 4, 5, 6, 8). Even
when the acid chloride incorporated strongly an electron-
withdrawing nitro group or an electron-rich methoxyl moiety,
the reaction also conducted reasonably at higher temperature
(Table 2, entries 6, 7). The sterically hindered benzoyl
chloride can react completely without yileds decreasing
(Table 2, Entries 3, 4). While the more sterically hindered
benzoyl chloride only gave trace products (Table 2, entries
10, 11). When heterocycle furan-2-carbonyl chloride was
3026
Org. Lett., Vol. 11, No. 14, 2009

when phenyl acetylene is used (Table 3, entries 17-21).
Notably, the reaction conditions are compatible with a variety
of terminal acetylenes and acid chlorides. Consistent with
the previous studies, the electronic properties of the substrates
almost do not have any negative impact on the process.
Finally, the coupling of N-unsubstituted triazoles and aryl
chlorides was studied with a series of new N-unsubstituted
triazoles in hand. To our excitement, when 1-chloro-4-
nitrobenzene was used as coupling agent, they can react
moderately in DMSO using K2CO3 as base and give only
N-2 alkylation 1,2,3-(NH)-triazoles (Scheme 1: 5a, 5b, 5c),
agent was changed to other aryl chlorides, no reaction
occurred (Scheme 1: 5d, 5e, 5f). It is showed that this
reaction is dependent on the electronic properties of aryl
chlorides.
In conclusion, we have developed a novel, facile and
efficient method for synthesizing 4,5-disubstituted-1,2,3-
(NH)-triazoles directly from acid chlorides, terminal alkynes,
and sodium azide based on Sonogashira coupling. The
procedure is suitable for many substrates and various 4,5-
disubstituted-N-unsubstituted 1,2,3-triazoles can be produced
with excellent yields conveniently in short time using cheap
and easily available starting materials. Especially, the reaction
is hardly impacted by the electronic properties of the
subtracts, complementary to the classic Huisgen 1,3-dipolar
cycloaddition. The regioselective N-2 alkylation 1,4,5-
trisubstituted-1,2,3-(NH)-triazoles can be made simply with-
out regioisomers by the reaction of 4,5-disubstituted-1,2,3-
(NH)-triazoles and 1-chloro-4-nitrobenzene. New ways of
synthesizing regioselective 1, 4,5-trisubstituted-1,2,3-(NH)-
triazoles and Sonogashira coupling in the multicomponent
reaction (MRC) application are currently under investigation
in our research group.
Scheme 1. N-2-Aryl-1,2,3-triazoles Synthesis
Acknowledgment. We are grateful to the project spon-
sored by the Scientific Research Foundation for the State
Education Ministry (No. 107108).
because the N-2-substituted triazoles are thermodynamically
more stable with less steric hindrance.17 when the coupling
Supporting Information Available: Experimental details
and characterization data of all compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
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OL901040D
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Org. Lett., Vol. 11, No. 14, 2009
3027