One-pot synthesis of 2,4,5-trisubstituted 1,2,3-triazoles through the cascade reactions of acid chlorides, terminal acetylenes, sodium azide and aryl halides

Article abstract of DOI:10.1039/c3nj40912k

An efficient one-pot reaction of acid chlorides, terminal acetylenes, sodium azide and aryl halides is developed for the regioselective synthesis of 2,4,5-trisubstituted 1,2,3-triazoles. The method is general, convenient, eco-friendly, atom-economical, an

Full text of DOI:10.1039/c3nj40912k

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One-pot synthesis of 2,4,5-trisubstituted 1,2,3-triazoles
through the cascade reactions of acid chlorides,
terminal acetylenes, sodium azide and aryl halides†
Cite this: NewJ.Chem., 2013,
37, 965
Received (in Montpellier, France)
10th October 2012,
Xiang Liu,ab Jihui Liab and Baohua Chen*ab
Accepted 11th January 2013
An efficient one-pot reaction of acid chlorides, terminal acetylenes, sodium azide and aryl halides is
developed for the regioselective synthesis of 2,4,5-trisubstituted 1,2,3-triazoles. The method is general,
convenient, eco-friendly, atom-economical, and could provide excellent yields and regioselectivities.
DOI: 10.1039/c3nj40912k
www.rsc.org/njc
cycloaddition/C–N coupling of acid chlorides, terminal acety-
lenes, sodium azide and aryl halides in one pot.
Introduction
Designing one-pot reactions is a major challenge for modern
organic chemistry. These reactions combine the two or more
step reactions of three or more components in one pot. Such
processes can easily produce a large library of related hetero-
cyclic compounds and complicated structures from simple
raw materials.1 What is more, they are quite close to an
‘‘ideal synthesis’’,2 and can minimize the time-consuming,
complex equipment, costly protection/deprotection steps and
purification processes, and can even provide excellent yields
and selectivities, they are also considered to be inherently
environmentally benign and atom economical.3 Therefore,
developing novel and highly selective one-pot reactions
from easily available materials is highly desirable in organic
synthetic chemistry.
1,2,3-triazoles have received significant attention as one of
the most important heterocycles displaying interesting bio-
logical activities, such as anti-HIV4 and GSK-3 inhibiting
activity,5 and have been widely applied in many research
fields.6 The existing synthetic methodologies have mostly
focused on the N-1 substituted 1,2,3-triazoles.7 Only several
methods have been developed for N-2 substituted 1,2,3-tri-
azoles until now, which is a challenging task for organic
synthesis chemists.8 Herein, we have developed a novel and
operationally simple way of regioselectively synthesizing 2,4,5-
trisubstituted 1,2,3-triazoles via Sonogashira coupling/1,3-dipolar
Results and discussion
Encouraged by the successful synthesis of 4,5-disubstitued
1,2,3-triazoles through the Sonogashira coupling/1,3-dipolar
cycloaddition of acid chlorides, terminal acetylenes and
sodium azide,9 we applied Sonogashira coupling to the one-
pot sequential reaction of acid chlorides, terminal acetylenes,
sodium azide and aryl halides to regioselectively construct
2,4,5-trisubstituted 1,2,3-triazoles. In our starting experiments,
we firstly performed the Sonogashira coupling of phenyl acetylene
and benzoyl chloride under PdCl2(PPh3)2/CuI-catalyzed and
ultrasonic promoted (32 kHz, 160 W, rt) conditions for 1 h,
then 2,5-difluoronitrobenzene 1a, NaN3 and DMF were added
to the mixture and the reaction continued at 100 1C. Fortu-
nately, the expected 2,4,5-trisubstituted 1,2,3-triazole product
1aa was obtained in 70% yield (Table 1, entry 1), and it was
found that there was still some 4,5-disubstituted 1,2,3-triazole
generated in situ after 6 h. A longer reaction time (12 h) also
achieved a similar result (Table 1, entry 1). It appears reason-
able that the acidic product NEt3HCl is generated from the
Sonogashira coupling reaction of phenyl acetylene and benzoyl
chloride. In order to improve the results, different bases were
added as shown in Table 1. When the reaction was carried out
with 1.0 eq. or 0.5 eq. K2CO3 as base, the reactions proceeded
smoothly and the in situ generated 4,5-disubstituted 1,2,3-
triazole almost completely converted into the corresponding
2,4,5-trisubstituted 1,2,3-triazoles, in 80% and 82% yield
respectively (Table 1, entries 2 and 3). Other bases, including
Cs2CO3, (CH3)3COK, NaOH, K3PO4, CH3COONa, were
employed, however, the reactions did not provide higher yields
(Table 1, entries 10–14). Using 0.5 eq. K2CO3 as the base,
various solvents were screened to optimize the reaction.
a State Key Laboratory of Applied Organic Chemistry, Lanzhou University,
Gansu Lanzhou 730000, P. R. China. E-mail: chbh@lzu.edu.cn;
Fax: +86-0931-8912582
b Key Laboratory of Nonferrous Metal Chemistry and Resources
Utilization of Gansu Province, Lanzhou, 730000, P. R. China
† Electronic supplementary information (ESI) available. CCDC 752728. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3nj40912k
c
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Table 1 Effect of bases and solvents on the reactiona
Table 2 Regioselective synthesis of 2,4,5-trisubstituted 1,2,3-triazoles through
the reactions of phenyl acetylene and benzoyl chloride, sodium azide, and aryl
halidesa
Entry
Base
Solvent
t (h)
Yieldb (%)
1
2
3
4
5
6
7
8
None
K2CO3 (1 eq.)
DMF
DMF
DMF
6(12)
6
68(70)
80
Entry
1
R1X
t (h)
T (1C)
Yieldb (%)
4-NO2-C6H4Cl
1b
2-NO2-C6H4F
1c
4-NO2-C6H4I
1d
2-NO2-C6H4I
1e
2-NO2-C6H4Cl
1f
3-NO2-C6H4Cl
1g
2-CN-C6H4Cl
1h
C6H5Cl
1i
2-CH3-C6H4Cl
1j
2-Cl-3-NO2-Pyridine
1k
2-CN-4-NO2-C6H3Cl
1l
2,4-diNO2-C6H3Cl
1m
4-CH3-2-NO2-C6H3Cl
1n
3,4-diF-C6H3NO2
1o
2,5-diBr-C6H3NO2
1p
48
120
63
1ba
88
1ca
75
1ba
80
K2CO3(0.5 eq.)
K2CO3 (0.5 eq.)
K2CO3 (0.5 eq.)
K2CO3 (0.5 eq.)
K2CO3 (0.5 eq.)
K2CO3 (0.5 eq.)
K2CO3 (0.5 eq.)
Cs2CO3 (0.5 eq.)
(CH3)3COK (0.5 eq.)
NaOH (0.5 eq.)
K3PO4(0.5 eq.)
CH3COONa(0.5 eq.)
6
6
6
6
6
6
6
6
6
6
6
17
82
87
Trace
Trace
Trace
15
DMSO
Dioxane
THF
Ethanol
Acetone
Toluene
DMSO
DMF
2
3
36
36
36
36
48
48
48
12
6
120
120
120
120
120
120
120
120
120
100
rt
3
4
9
8
85
40
60
75
55
1ca
74
10
11
12
13
14
5
1ca
Trace
1da
Trace
1ea
0
1fa
0
1ga
80
1ha
90
1ia
95
1ja
Trace
1ka
87
1la
55
DMF
DMSO
DMF
6
7
a
Firstly, the reaction was carried out with phenyl acetylene (0.25 mmol),
benzoyl chloride (0.25 mmol) and Et3N (0.75 mmol) in the presence of
PdCl2(PPh3)2/CuI promoted by ultrasonic (32 kHz, 160 W) at room
temperature for 1 h under nitrogen, then NaN3 (0.25 mmol), base, 2,5-
diF-C6H4NO2 (0.375 mmol) and 3 mL solvent was added to the mixture
8
9
b
and the reaction continued at 100 1C. Isolated yield after column
chromatography.
10
11
12
13
14
15
3
Switching the solvent from DMF to DMSO enhanced the yield of
the 2,4,5-trisubstituted 1,2,3-triazole from 82% to 87% (Table 1,
entry 4). Other solvents, such as dioxane, THF, ethanol, acetone
and toluene, provided unfavourable results (Table 1, entries 5–9).
Thus, 0.5 eq. K2CO3/DMSO is the optimal system for this
reaction.
36
3
120
100
100
3
1ma
Under the optimized conditions, the substrate scope of aryl
halides was examined. As illustrated in Table 2, when the
strongly electron-deficient aryl halides 1b–1f were used, the
reactions progressed sluggishly and regioselectively produced
the corresponding 2,4,5-trisubstituted 1,2,3-triazoles in good
yields (Table 2, entries 1–5). In contrast, the use of 3-NO2-C6H4Cl
1g and another electron-poor aryl chloride 1h only provided
trace amounts of the products (Table 2, entries 6 and 7). In
a
The reaction was carried out with phenyl acetylene (0.25 mmol),
benzoyl chloride (0.25 mmol) and Et3N (0.75 mmol) in the presence
of PdCl2(PPh3)2/CuI promoted by ultrasonic (32 kHz, 160 W) at room
temperature for 1 h under nitrogen, then NaN3 (0.25 mmol), K2CO3
(0.125 mmol), R1X (0.375 mmol) and 3 mL solvent were added to the
b
mixture and the reaction continued. Isolated yield after column
chromatography.
addition, phenyl chloride 1i and the electron-rich aryl chloride good yields. The structure of 1la was confirmed by X-ray crystallo-
1j did not yield any desired product. As well as the strongly graphy. The details of this structure have previously been
electron-deficient aryl halides, the heterocyclic compound reported by our group.10 It is evident that the electronic proper-
2-chloro-3-nitro-pyridine 1k also exhibited high reactivity, form- ties of the aryl halides have a significant impact on the reaction
ing the 2,4,5-trisubstituted 1,2,3-triazole 1ha in 80% yield and the strongly electron-withdrawing group NO2 is crucial for
(Table 2, entry 10). The aryl chlorides 1l and 1m, bearing two the reaction.
strongly electron-withdrawing groups, accelerated the reaction
The scope of the protocol for other terminal acetylenes and
and gave excellent yields (Table 2, entries 11 and 12). The acid chlorides was also investigated. As shown in Table 3,
reaction of 1m was carried out at room temperature, while various terminal acetylenes and acid chlorides were well-suited
the aryl chloride 1n, bearing NO2 and CH3, only yielded a for the one-pot two-step reaction system. For example, electron-
trace amount of product (Table 2, entry 13). Consistent with rich aryl acid chlorides including 4-Cl-C6H4COCl, 3-Cl-C6H4COCl,
2,5-diF-C6H4NO2, the reactions of 3,4-diF-C6H3NO2 1o and 2-Cl-C6H4COCl and 4-NO2-C6H4COCl could easily convert into
2,5-diBr-C6H3NO2 1p also selectively took place at the 4- and the corresponding 2,4,5-trisubstituted 1,2,3-triazoles in good yields
2-position of 1o and 1p respectively and afforded the corres- (Table 3, entries 1–3 and 8). The electron-poor aryl acid chlorides
ponding 2,4,5-trisubstituted 1,2,3-triazoles 1la and 1ma in 3-CH3-C6H4COCl, 3,5-diCH3-C6H3COCl and 4-CH3O-C6H4COCl
c
966 New J. Chem., 2013, 37, 965--968
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Table 3 Regioselective synthesis of 2,4,5-trisubstituted 1,2,3-triazoles through
the reactions of terminal acetylenes, acid chlorides, sodium azide and aryl halidea
Entry
1
R1
R2
t (h)
Yieldb (%)
C6H5
4-Cl-C6H4
3
89
2aa
87
2ba
82
2ca
82
2da
89
2ea
88
2fa
92
2ga
50
2ha
88
2ia
88
2ja
87
2ka
70
2la
72
2ma
68
2na
88
2oa
86
Scheme 1 A plausible reaction mechanism.
2
C6H5
3-Cl-C6H4
2-Cl-C6H4
3-CH3-C6H4
3,5-diCH3-C6H3
4-CH3O-C6H4
2-C2H5O-C6H4
4-NO2-C6H4
Furan-2-yl
C6H5
3
36
36
3
3c
4d
5
C6H5
transformed into the desired 2,4,5-trisubstituted 1,2,3-triazoles
in high yields (Table 3, entries 15 and 16).
C6H5
The mechanism of the reaction is shown in Scheme 1.
Firstly, ynone A is produced via the palladium and copper co-
catalyzed Sonogashira coupling of a terminal alkyne and an acyl
chloride; then sequential 1,3-dipolar cycloaddition/nucleophilic
arylation of A with sodium azide and aryl halide provides the
target product (C).
C6H5
6
C6H5
3
7c
8e
9
C6H5
3
C6H5
3
C6H5
3
Conclusions
10
11
12
13
14
15
16
3-CH3-C6H4
4-F-C6H4
n-C4H9
tert-C4H9
n-C8H17
Fc
3
In summary, we have successfully combined a Sonogashira
coupling, 1,3-dipolar cycloaddition and N-arylation of acid
chlorides, terminal acetylenes, sodium azide and aryl halides
to regioselectively construct 2,4,5-trisubstituted 1,2,3-triazoles
in one pot. This methodology will easily provide an access to a
variety of N-2 substituted triazoles in terms of atom- and
step-economy, operational simplicity, and environmental
friendliness. Further applications of the Sonogashira coupling
in one-pot reactions are currently under investigation in our
research group.
C6H5
3
C6H5
2
C6H5
2
C6H5
2
C6H5
2
Thiophen-3-yl
C6H5
3
2pa
a
The reaction was carried out with terminal acetylene (0.25 mmol),
acid chloride (0.25 mmol) and Et3N (0.75 mmol) in the presence of
PdCl2(PPh3)2/CuI promoted by ultrasonic (32 kHz, 160 W) at room
temperature for 1 h under nitrogen, then NaN3 (0.25 mmol), K2CO3
(0.125 mmol), 2,5-diF-C6H4NO2 (0.375 mmol) and 3 mL solvent were
Experimental section
The general procedure of the reaction between acid chlorides,
terminal acetylenes, sodium azide and alkyl halides: regio-
selective synthesis of [2-(4-fluoro-2-nitrophenyl)-5-phenyl-2H-
1,2,3-triazol-4-yl](phenyl)methanone 1aa:
All reactions are performed on a 0.25 mmol scale relative to
the acid chlorides. A round-bottom side-arm flask (10 mL)
b
added to the mixture and the reaction continued at 100 1C. Isolated
c
yields after column chromatography. R3X: 2-NO2-C6H4F, reaction
d
temperature: 120 1C. R3X: 4-NO2-C6H4Cl, reaction temperature: 120 1C.
e
The temperature of Sonogashira coupling is increased to 45 1C.
also reacted moderately and afforded the desired products in containing PdCl2(PPh3)2 (0.0025 mmol), CuI (0.005 mmol)
excellent yields (Table 3, entries 4–6). Moreover, the sterically was subjected to the Schlenk-line procedures of evacuation
hindered benzoyl chloride 2-C2H5O-C6H4COCl and the hetero- and purging of N2 for three cycles. Phenyl acetylene
cyclic furan-2-carbonyl chloride were suitable for the reaction (0.25 mmol), benzoyl chloride (0.25 mmol) and 3 eq. Et3N
without decreasing the yields and regioselectivities (Table 3, (0.75 mmol) were successively added, and the flask was put
entries 7 and 9). Similarly, both electron-rich and electron-poor into an ultrasonicator (32 KHz, 160 W) to react at room
aryl acetylenes produced good yields (Table 3, entries 10 and 11). temperature for 1 h, the flask was taken out, then NaN3
As the terminal acetylenes were extended to aliphatic terminal (0.25 mmol), K2CO3 (0.125 mmol), 2,5-diF-C6H3NO2
acetylenes, the reaction proceeded smoothly and gave good (0.375 mmol) and 3 mL DMSO were added to the mixture and
yields and excellent selectivities (Table 3, entries 12–14). Inter- the reaction was allowed to continue at 100 1C for 3 h. Follow-
estingly, when heterocyclic 3-ethynylthiophene and ethynyl ing this, water (2 mL) and 20% HCl solution (1 mL) were added
ferrocene (Fc) were employed, they were also completely to the reaction mixture. The mixture was then extracted with
c
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concentrated in vacuo. The residue was subjected to flash
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to obtain the desired product (1aa) (84 mg, 87% yield). mp:
128–130 1C. IR (cmÀ1): 3071, 1656, 1549. 1H NMR (400 MHz,
CDCl3): d 8.14–8.27 (m, 5H), 7.87–7.89 (m, 2H), 7.64 (t, J =
7.4 Hz, 1H), 7.51 (t, J = 7.6 Hz, 2H), 7.43–7.45 (m, 3H). 13CNMR
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133.8, 130.4, 129.7, 128.8, 128.6, 128.5, 128.4, 127.8, 127.7,
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Acknowledgements
We are thankful for the support of the Project of National
Science Foundation of P. R. China (no. J1103307) and the
project by the Scientific Research Foundation for the State
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This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013