Easy one-pot synthesis of 1-monosubstituted aliphatic 1,2,3-triazoles from aliphatic halides, sodium azide and propiolic acid by a click cycloaddition/decarboxylation process

Article abstract of DOI:10.1002/cjoc.201300155

1-Monosubstituted aliphatic 1,2,3-triazoles were synthesized by a one-pot reaction from aliphatic halides (Cl and Br), sodium azide and propiolic acid. The yields ranged from moderate to good. The reaction was easily carried out in DMF with Cs₂CO₃ at 100°C by copper-catalyzed click cycloaddition/decarboxylation. The synthesis of 1-monosubstituted aliphatic 1,2,3-triazoles was achieved in a one-pot reaction from aliphatic halides (Cl, Br), sodium azide and propiolic acid with yields ranging from moderate to good. Copyright

Full text of DOI:10.1002/cjoc.201300155

FULL PAPER
DOI: 10.1002/cjoc.201300155
Easy One-Pot Synthesis of 1-Monosubstituted Aliphatic
1,2,3-Triazoles from Aliphatic Halides, Sodium Azide and
Propiolic Acid by a Click Cycloaddition/Decarboxylation
Process
Zhongkui Zhanga and Chunxiang Kuang*,a,b
a Department of Chemistry, Tongji University, Shanghai 200092, China
b Key Laboratory of Yangtze River Water Environment, Ministry of Education, Shanghai 200092, China
1-Monosubstituted aliphatic 1,2,3-triazoles were synthesized by a one-pot reaction from aliphatic halides (Cl
and Br), sodium azide and propiolic acid. The yields ranged from moderate to good. The reaction was easily carried
out in DMF with Cs2CO3 at 100 ℃ by copper-catalyzed click cycloaddition/decarboxylation.
Keywords click chemistry, copper-catalyzed, decarboxylation, 1-monosubstitued aliphatic 1,2,3-triazole
Introduction
Scheme 1
Our previous work:
1,2,3-Triazole is an important structural unit of nu-
merous pharmaceuticals, agrochemicals, and chemical
reagents. Various 1,2,3-triazole derivatives also have
wide-ranging applications in the fields of materials sci-
ence and molecular structure design.[1] The Cu-cata-
lyzed “click chemistry” reaction between azide and ter-
minal alkyne is extensively used for the practical and
efficient preparation of 1,4-disubstituted 1,2,3-triazoles
since the robust Huisgen 1,3-dipolar cycloaddition was
established.[2] However, reports on the synthesis meth-
ods of 1-monosubstituted 1,2,3-triazoles are limited.
One strategy is the decarboxylation of triazoles bearing
a carboxylic acid substituent, but the reactions require
long reaction times and extreme temperatures.[3] An-
other protocol is the cycloaddition of azides to acety-
lene[4] and its analogs such as acetylides[5] as well as the
cycloaddition of vinyl compounds.[6] A method has also
been developed for the synthesis of monosubstitued
1-aryl-1H-1,2,3-triazoles from arylboronic acids and
prop-2-ynoic acid or CaC2.[7]
CuI, Na ascorbate
DBU, DMF
ArN3
Ar N
COOH
N
N
This work:
CuI, Na ascorbate
Cs2CO3, DMF
NaN3
RX
R N
COOH
N
N
R = Bn, Alkyl, etc.
X = Cl, Br
Experimental
Melting points were recorded using a Krüss Optronic
GmbH KSPII melting-point apparatus and were uncor-
1
rected. H NMR and 13C NMR spectra were recorded
with a Bruker ARX400 spectrometer on CDCl3 solu-
tions with SiMe4 as an internal standard. IR spectra
were obtained on a Thermo FT-IR spectrophotometer.
MS data were measured with a Varian-310 mass spec-
trometer. High resolution mass spectra were determined
using a Finnigan-MAT GC/MS/DS 8430 spectrometer.
Commercially obtained reagents were used without fur-
ther purification. All reactions were monitored by TLC
with a Huanghai GF 254 system and silica gel coated
plates. Column chromatography was carried out using
300－400 mesh silica gel at medium pressure.
In a preliminary paper,[8] we reported a novel and
useful protocol for the synthesis of 1-monosubstitued
1,2,3-triazoles by click reaction/decarboxylation[9] under
mild conditions. In the present study, we developed an
easy one-pot synthesis of 1-monosubstituted aliphatic
1,2,3-triazoles from aliphatic halides (Cl and Br), so-
dium azide and propiolic acid by a click cycloaddition/
decarboxylation process. These previous and present
methods are compared in Scheme 1.
Preparation of compound 2
A solution of aliphatic halides (Cl and Br; 0.2 mmol),
NaN3 (16 mg, 0.24 mmol), propiolic acid (17 mg, 0.24
mmol), CuI (8 mg, 0.04 mmol), Na ascorbate (16 mg,
0.08 mmol), and Cs2CO3 (33 mg, 0.1 mmol) in DMF (2
*
E-mail: kuangcx@tongji.edu.cn; Tel.: 0086-021-65983191; Fax: 0086-021-65983191
Received March 6, 2013; accepted April 1, 2013; published online May 29, 2013.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201300155 or from the author.
Chin. J. Chem. 2013, 31, 1011—1014
© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1011

Zhang & Kuang
FULL PAPER
mL) in a sealed tube was stirred under nitrogen. The
reaction mixture was heated to a certain temperature
until the starting aliphatic halides were completely con-
sumed (monitored by TLC). The reaction solution was
diluted with water and extracted three times with EtOAc.
The combined organic layers were washed with satu-
rated brine, dried over anhydrous Na2SO4, and concen-
trated under reduced pressure to afford a crude product.
This product was subjected to column chromatography
(silica gel and EtOAc-petroleum ether) to afford
1-monosubstituted 1,2,3-triazoles 2.
1-(2,6-Difluorobenzyl)-1H-1,2,3-triazole
(2h)
1
Light yellow solid. m.p. 114.0－115.0 ℃; H NMR
(CDCl3, 400 MHz) δ: 7.69 (s, 1H, TrH), 7.63 (s, 1H,
TrH), 7.33－7.41 (m, 2H, ArH), 6.95－7.00 (m, 2H,
ArH), 5.66 (s, 2H, CH2). 13C NMR (100 MHz, CDCl3) δ:
41.15, 111.69, 123.47, 131.42, 134.07, 160.10, 162.67;
IR (KBr) ν: 3142, 3122, 1629, 1594, 1472, 1213, 1165,
1078, 1024 cm−1. HRMS m/z caled for C9H7F2N3:
195.0608 [M]＋; found 195.0610.
1-(4-Nitrobenzyl)-1H-1,2,3-triazole (2i)[13]
1H
NMR (CDCl3, 400 MHz) δ: 8.24 (d, J＝8.8 Hz, 2H,
ArH), 7.79 (s, 1H, TrH), 7.58 (s, 1H, TrH), 7.40 (d, J＝
8.4 Hz, 2H, ArH), 5.70 (s, 2H, CH2).
Spectral data of all synthesized compounds 2a－2j
1-Benzyl-1H-1,2,3-triazole (2a)[10]
1H NMR
1-(1-Phenylethyl)-1H-1,2,3-triazole (2j)[13]
1H
(CDCl3, 400 MHz) δ: 7.70 (s, 1H, TrH), 7.49 (s, 1H,
TrH), 7.25－7.37 (m, 5H, ArH) , 5.56 (s, 2H, CH2).
1-(4-Methylbenzyl)-1H-1,2,3-triazole (2b) Light
NMR (CDCl3, 400 MHz) δ: 7.68 (s, 1H, TrH), 7.47 (s,
1H, TrH), 7.25－7.38 (m, 5H, ArH), 5.85 (q, J＝7.2 Hz,
1H, CH), 1.99 (d, J＝7.2 Hz, 3H, CH3).
1
yellow solid. m.p. 55.7－56.6 ℃; H NMR (CDCl3,
400 MHz) δ: 7.68 (s, 1H, TrH), 7.47 (s, 1H, TrH), 7.17
(s, 4H, ArH) , 5.51 (s, 2H, CH2), 2.34 (s, 3H, CH3); 13C
NMR (100 MHz, CDCl3) δ: 21.15, 53.75, 123.26,
128.07, 129.75, 131.71, 134.15, 138.63; IR (KBr) ν:
3132, 2914, 1605, 1254, 1213, 1176, 1068, 1048 cm−1.
HRMS m/z caled for C10H11N3: 173.0953 [M]＋; found
173.0954.
Results and Discussion
The optimum reaction conditions were preliminarily
screened using benzyl chloride (0.3 mmol), NaN3 (1.2
equiv.), and propiolic acid (1.2 equiv.) as the model
substrates (Table 1). We first investigated the effects of
different bases (none, 1,8-diazabicyclo[5.4.0]undec-
7-ene (DBU), Et3N, K2CO3, and Cs2CO3) on the forma-
tion of 1-benzyl-1H-1,2,3-triazole (2a) (Table 1, Entries
1－5). Among the bases we tested, Cs2CO3 (0.5 equiv.)
gave the highest yield of 90% in DMF at 100 ℃ for
0.5 h (Table 1, Entry 5). The reason may be that cesium
propiolate is more soluble in DMF than potassium
propiolate, and the solubility drives faster reaction.
However, the organic bases often cause more side reac-
tions in the transition metal catalyzed reactions. On the
other hand, the solvent system significantly affected the
reaction outcome, and DMF was much more effective
than other single solvents or mixed solvents (Table 1,
Entries 5－8). Moreover, product 2a was not obtained
when water was used as a solvent. The reason may be
the decrease in the reactant solubility in this reaction
system. We also studied the effects of various amounts
of CuI and sodium ascorbate on the formation of the
triazole 2a (Table 1, Entries 9－13). As expected, CuI
(0.2 equiv.) and sodium ascorbate (0.4 equiv.) were
necessary. Eventually, the optimum reaction conditions
were concluded to be CuI (0.2 equiv.), Cs2CO3 (0.5
equiv.), and sodium ascorbate (0.4 equiv.) in DMF sol-
vent at 100 ℃ for 0.5 h (Table 1, Entry 5).
1-(3-Methylbenzyl)-1H-1,2,3-triazole (2c)[11] 1H
NMR (CDCl3, 400 MHz) δ: 7.71 (s, 1H, TrH), 7.50 (s,
1H, TrH), 7.27 (t, J＝7.2 Hz, 1H, ArH), 7.17 (d, J＝7.2
Hz, 1H, ArH), 7.08 (s, 1H, ArH), 7.07 (d, J＝7.2 Hz,
1H, ArH), 5.53 (s, 2H, CH2), 2.34 (s, 3H, CH3).
1-(2-Methylbenzyl)-1H-1,2,3-triazole (2d)[10] 1H
NMR (CDCl3, 400 MHz) δ: 7.68 (s, 1H, TrH), 7.38 (s,
1H, TrH), 7.27－7.31 (m, 1H, ArH), 7.20－7.23 (m, 2H,
ArH), 7.13－7.17 (m, 1H, ArH), 5.56 (s, 2H, CH2), 2.27
(s, 3H, CH3).
1-Phenethyl-1H-1,2,3-triazole (2e)[12] 1H NMR
(CDCl3, 400 MHz) δ: 7.61 (s, 1H, TrH), 7.30 (s, 1H,
TrH), 7.08－7.28 (m, 5H, ArH), 4.62 (t, J＝7.2 Hz, 2H,
ArCH2), 3.20 (t, J＝7.2 Hz, 2H, TrCH2).
1-(2-Phenoxyethyl)-1H-1,2,3-triazole (2f) White
solid. m.p. 91.8－92.4 ℃; 1H NMR (CDCl3, 400 MHz)
δ: 7.78 (s, 1H, TrH), 7.70 (s, 1H, TrH), 7.28 (t, J＝8.0
Hz, 2H, ArH), 6.98 (t, J＝7.2 Hz, 1H, ArH), 6.86 (d,
J＝8.0 Hz, 2H, ArH), 4.79 (t, J＝4.8 Hz, 2H, ArOCH2),
4.34 (t, J＝4.8 Hz, 2H, TrCH2); 13C NMR (100 MHz,
CDCl3) δ: 49.63, 66.37, 114.55, 121.72, 124.64, 129.69,
133.93, 157.83; IR (KBr) ν: 3147, 3113, 2926, 1603,
1489, 1252, 1219, 1171, 1085, 1043 cm−1. HRMS m/z
caled for C10H11N3O: 189.0902 [M]＋; found 189.0904.
1-(4-Fluorobenzyl)-1H-1,2,3-triazole (2g) Light
Under the optimized conditions, the substrate scope
of this one-pot synthesis of 1-monosubstituted aliphatic
1,2,3-triazoles from aliphatic halides (Cl and Br), so-
dium azide and propiolic acid by a click cycloaddition/
decarboxylation process was investigated.
The newly established conditions appeared to be
general for most aliphatic halides (Cl and Br) and af-
forded 1-momosubstitued 1,2,3-triazoles in moderate to
good yields (Table 2). Nevertheless, 1-(2-methyl-
benzyl)-1H-1,2,3-triazole (2d) suffered from a low re-
1
yellow solid. m.p. 51.3－52.2 ℃; H NMR (CDCl3,
400 MHz) δ: 7.71 (s, 1H, TrH), 7.51 (s, 1H, TrH), 7.25
－7.29 (m, 2H, ArH), 7.05 (t, J＝8.8 Hz, 2H, ArH),
5.54 (s, 2H, CH2); 13C NMR (100 MHz, CDCl3) δ:
53.17, 116.18, 123.31, 129.84, 134.29, 161.57, 164.04;
IR (KBr) ν: 3103, 1609, 1514, 1266, 1238, 1211, 1082
cm−1. HRMS m/z caled for C9H8FN3: 177.0702 [M]＋;
found 177.0705.
1012
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© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2013, 31, 1011—1014

Easy One-Pot Synthesis of 1-Monosubstituted Aliphatic 1,2,3-Triazoles
Table 1 Reaction optimization
Table 2 Synthesis of 1-monosubstituted aliphatic 1,2,3-tria-
zoles (2) from aliphatic halides (Cl and Br) (1)
CO2H
CuI,
Cl
+
Na ascorbate
CuI, Ligand
N
N
NaN3
+
R N
+
NaN3
CO2H
RX
+
N
Base, solvent
N
N
1
2
Na
CuI/
equiv.
Yielda/%
of 2a
Entry
ascorbate/ Base Solvent T/℃ Time/h
equiv.
(T/℃)/ Yield of
Entry
1
2
(t/h)
2a/%
1
2
3
4
5
0.2
0.2
0.2
0.2
0.2
0.40
0.40
0.40
0.40
0.40
0
DMF 100 0.5
DMF 100 0.5
DMF 100 0.5
30
82
68
55
90
N
N
N
DBU
Et3N
Cl
N
100/0.5
90
1
2a
K2CO3 DMF 100 0.5
Cs2CO3 DMF 100 0.5
CH3CN/
N
N
Cl
Cl
100/0.5
100/0.5
82
80
6
0.2
0.40
Cs2CO3
100 0.5
12
2
3
H2O(9/1)
7
8
9
0.2
0.2
0.1
0.40
0.40
0.20
1.00
0.30
0
Cs2CO3 DMSO 100 0.5
Cs2CO3 H2O 100 0.5
Cs2CO3 DMF 100 0.5
Cs2CO3 DMF 100 0.5
Cs2CO3 DMF 100 0.5
Cs2CO3 DMF 100 0.5
75
0
2b
N
N
61
91
83
10
90
N
10 0.5
11 0.2
12 0.2
13 0.2
2c
N
N
0.40
Cs2CO3 DMF 100
2
N
Cl
120/1
70
4
a Isolated yields.
2d
action rate because of the steric hindrance effect with
70% yield at 120 ℃ for 1 h (Table 2, Entry 4).
N
Br
N
100/0.5
100/0.5
100/0.5
86
85
78
5
6
7
N
To elucidate this novel and useful protocol, we pro-
posed a mechanism as shown in Scheme 2. The azide B
is obtained from aliphatic halides (Cl and Br) (1) with
iodine anion catalysis in cycle I. Simultaneously, at the
initial stage of catalytic cycle II, the dehydrogenation of
propiolic acid with Cs2CO3 and CuLn produces the
copper acetylide carbonate ion A. Afterwards, the in-
termediate C is readily formed by the [3＋2] cycloaddi-
tion reaction between A and B. Immediately, intermedi-
ate D is obtained by electronic transition with CO2 re-
2e
O
O
N
Br
N
N
2f
N
Cl
N
N
F
F
2g
Scheme 2 Possible mechanism of the reaction
-HCO3
R
H
COO-
H
COOH
[Cu]Ln
N
N
N
2-
CO3
2-
CO3
2
-HCO3
RI
OOC
CuLn
X-
NaN3
A
Cycle II
Cycle I
I-
CuLn
H
D
RX
RN3
N
R
N
1
B
N
O
Ln
O
Cu
X= Cl , Br
R= Bn, Alkyl, etc.
N
N
CO2
R
N
C
Chin. J. Chem. 2013, 31, 1011—1014
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1013

Zhang & Kuang
FULL PAPER
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Conclusions
We developed an easy and useful protocol for the
synthesis of 1-monosubstitued 1,2,3-triazoles by click
reaction/decarboxylation under mild conditions. Pro-
piolic acid was found to be equivalent to gaseous acety-
lene and its analogs in the click cycloaddition and pro-
vided mild access to 1-monosubstitued aliphatic
1,2,3-triazoles, which are important heterocyclic comp-
ounds in medicinal chemistry and materials science.
Acknowledgement
The work was supported by the National Natural
Science Foundation of China (No. 21272174) and the
Key Projects of Shanghai in Biomedical (No.
08431902700). We thank the Center for Instrumental
Analysis, Tongji University, China.
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