4-(N,N-Dimethylamino)pyridinium acetate as a recyclable catalyst for the synthesis of 5-substituted-1H-tetrazoles

Article abstract of DOI:10.1016/j.tetlet.2014.12.106

An efficient method for the synthesis of 5-substituted-1H-tetrazoles through the reaction of nitriles with sodium azide using 4-(N,N-dimethylamino)pyridinium acetate as a recyclable catalyst with ionic liquid character is described. The reactions proceed well at 100 °C and provide the corresponding tetrazoles in good to excellent yields. This method has the advantage of easy work-up of the product without the requirement of HCl. Mono [3+2] cycloaddition products were obtained from dicyanides via this method.

Full text of DOI:10.1016/j.tetlet.2014.12.106

Accepted Manuscript
4
-(N,N-Dimethylamino)pyridinium acetate as a recyclable catalyst for the syn-
thesis of 5-substituted-1H-tetrazoles
Najmeh Nowrouzi, Soghra Farahi, Maryam Irajzadeh
PII:
S0040-4039(14)02184-4
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.12.106
TETL 45631
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
13 September 2014
9 December 2014
17 December 2014
Please cite this article as: Nowrouzi, N., Farahi, S., Irajzadeh, M., 4-(N,N-Dimethylamino)pyridinium acetate as a
recyclable catalyst for the synthesis of 5-substituted-1H-tetrazoles, Tetrahedron Letters (2014), doi: http://
dx.doi.org/10.1016/j.tetlet.2014.12.106
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Graphical Abstract
Leave this area blank for abstract info.
4-(N,N-Dimethylamino)pyridinium acetate
as a recyclable catalyst for the synthesis of
5-substituted-1H-tetrazoles
catalyst (15 mol%)
N
N
N
CN
+
NaN
3
100 °C
N
H
no solvent
(1.0 mmol)
(1.0 mmol)
NMe
2
Catalyst:
N
CH CO
3
2
H
*
Najmeh Nowrouzi , Soghra Farahi, Maryam Irajzadeh

Tetrahedron Letters
1
TETRAHEDRON
LETTERS
Pergamon
4
-(N,N-Dimethylamino)pyridinium acetate as a recyclable
catalyst for the synthesis of 5-substituted-1H-tetrazoles
*
a
b
Najmeh Nowrouzi , Soghra Farahi , Maryam Irajzadeh
a
a
Department of Chemistry, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Iran
b
Department of Chemistry, Faculty of Sciences, Behbahan Khatam Alanbia University of Technology, Behbahan 63616, Iran
Abstract— An efficient method for the synthesis of 5-substituted-1H-tetrazoles through the reaction of nitriles with sodium azide using 4-
N,N-dimethylamino)pyridinium acetate as a recyclable catalyst with ionic liquid character is described. The reactions proceed well at 100
C and provide the corresponding tetrazoles in good to excellent yields. This method has the advantage of easy work-up of the product
(
°
without the requirement of HCl. Mono [3+2] cycloaddition products were obtained from dicyanides via this method. © 2014 Elsevier Ltd.
All rights reserved.
Tetrazoles are an important class of heterocycles with a
wide range of applications in medicinal chemistry and
between nitriles and trimethylsilyl azide was reported by
9
Yamamoto et al. However, trimethylsilyl azide is a
volatile and toxic reagent. Recent work on the synthesis of
5-substituted-1H-tetrazoles via the reaction of nitriles with
sodium azide has included the use of catalytic amounts of
1
materials science.
They have applications in
pharmaceuticals as lipophilic spacers and in medicinal
chemistry as metabolically stable carboxylic acid
2
surrogates. They have found applications in coordination
10
11
12
nanocrystalline ZnO, Zn/Al hydrotalcite, FeCl
13
3
-SiO
-SiO
2
,
3
chemistry as nitrogen-containing heterocyclic ligands, and
14
,
mesoporous ZnS nanospheres,
5
I
2
or NaHSO
17
4
2
1
16
in materials science as speciality explosives and
4
information recording systems.
ZrOCl ·8H O, CuSO ·5H O, InCl3, silica sulfuric
2
18 19 20
2
4
2
3 2
acid, Ln(OTf) -SiO , and CAN-HY zeolites. Ionic
The most common method for the preparation of 5-
substituted-1H-tetrazoles involves the addition of azide
salts to organic nitriles using acid or base catalysis. Earlier
work encountered difficulties such as using strong Lewis
acids, expensive and toxic metals or the presence of
liquids as solvents and promoters have also been employed
2
1
for the preparation of tetrazoles. The preparation of 5-
substituted-1H-tetrazoles from aldehydes through the
reaction of acetohydroxamic acid and sodium azide using
2
2
Bi(OTf) as the catalyst has also been reported.
3
5
hydrazoic acid which is extremely toxic and explosive.
However, most of these methods suffer from using DMF or
DMSO as the solvent and extraction of the products
requires acidification prior to work-up. Therefore, versatile
methods for the synthesis of tetrazoles through safe
protocols are still required.
Later, Sharpless and co-workers reported the preparation of
tetrazoles from nitriles in water using sodium azide and
stoichiometric amounts of Zn(II) salts. This proved to be an
innovative and safe procedure and showed good generality
for structurally diverse nitriles. However, the reaction of
4-(N,N-Dimethylamino)pyridine (DMAP) is an effective
nucleophilic basic catalyst. After the first report on the use
23
of DMAP in acylation reactions, its applications have
unactivated nitriles required high temperatures (140-170
6
°C) and the products were obtained after acidification.
Pizzo and co-workers reported the synthesis of tetrazoles
by the addition of trimethylsilyl azide to organic nitriles
7
using TBAF (50 mol%). The preparation of aryltetrazole-
been studied extensively. DMAP is extremely toxic and
several strategies have been developed in order to
24
circumvent this problem. However, they have been
boronate esters by microwave-assisted addition of
trimethylsilyl azide to arylnitrile-boronate esters in the
presence of dibutyltin oxide as a catalyst has also been
accompanied with loss of activity or recycling difficulties.
In recent years, DMAP salts have been introduced as
promising catalysts for organic reactions.
In our research group we have investigated the catalytic
activity of 4-(N,N-dimethylamino)pyridinium acetate,
which has ionic liquid character, in several reactions and
the results will be published soon.
2
5
8
reported. The copper-catalyzed [3+2] cycloaddition
Key Words: 5-substituted-1H-tetrazole, nitriles, sodium azide,
cycloaddition reaction, catalyst.
* Corresponding author. Tel.:+98-771-4222341; Fax: +98-771-4541494;
e-mail: nowrouzi@pgu.ac.ir

2
Tetrahedron Letters
Herein, we report the development of an efficient process
for transforming a wide variety of nitriles into the
while the reaction of 4-methylbenzonitrile took a longer
time affording a 90% isolated yield (Table 2, entry 2). The
reaction of 4-chloro- and 3-chlorobenzonitriles with sodium
azide gave the corresponding tetrazoles in excellent yields
after two hours (Table 2, entries 4 and 5). However, 3-
aminobenzonitrile provided the corresponding product in a
poor 20% yield (Table 2, entry 6). Heteroaromatic nitriles
such as 4-pyridinecarbonitrile and 3-pyridinecarbonitrile
afforded the corresponding tetrazoles in excellent yields
after short reaction times (Table 2, entries 7 and 8). This
method was also suitable for the conversion of an aliphatic
nitrile into a 5-(R)-1H-tetrazole (Table 2, entry 9). The
reactions of 1,2-dicyanobenzene and malonitrile afforded
mono addition products (Table 2, entries 10 and 11), even
when the number of equivalents of sodium azide was
doubled (Table 2, entries 12 and 13).
corresponding
tetrazoles
using
4-(N,N-
dimethylamino)pyridinium acetate as the catalyst under
solvent-free conditions.
The catalyst was prepared from the reaction of 4-(N,N-
2 2
dimethylamino)pyridine with acetic acid in CH Cl . Next,
the effect of the catalyst on the [3+2] cycloaddition reaction
of nitriles with sodium azide was investigated. Thus,
benzonitrile (1.0 mmol) was treated with sodium azide (1.0
mmol) in the presence of different amounts of 4-(N,N-
dimethylamino)pyridinium acetate at 100 °C and the
obtained results are shown in Table 1.
Table 1. Effect of the amount of catalyst on the synthesis of
5-phenyl-1H-tetrazole.
Table 2. Synthesis of 5-substituted-1H-tetrazoles from the
reactions of nitriles with sodium azide in the presence of 4-(N,N-
a
dimethylamino)pyridinium acetate as the catalyst.
b
Time
h)
Yield
ref
(%)
Entry
1
Nitrile
Product
N
(
N
a
Entry
Catalyst (mol%)
Time (h)
Yield (%)
CN
N
2
6
N
2
95
H
N
1
2
3
4
5
6
60
30
15
10
7.5
-
2
2
96
95
95
82
70
-
N
CN
N
N
27,28
90
2
3
4
N
H
2.5
CH
3
2
CH
3
N
N
3
CN
30
min
22
98
N
H
4
CF
3
CF
Cl
3
N
24
N
CN
N
2
93
2
N
H
2
b
7
DMAP
24
-
Cl
a
Isolated yield.
5 mol% of DMAP in acetonitrile at reflux was used.
N
N
b
1
CN
N
N
2
8
H
2
3
90
When the reaction was carried out in the presence of 15
mol% of the catalyst, 5-phenyl-1H-tetrazole was obtained
in an excellent yield (Table 1, entry 4). Increasing the
amount of the catalyst had no additional beneficial effect
on the yield of the product (Table 1, entries 1 and 2).
However, a lower amount of the catalyst resulted in lower
yields (Table 1, entries 4 and 5). In the absence of the
catalyst no product was obtained (Table 1, entry 6). In
another experiment we used DMAP instead of DMAP
acetate, but no product was detected even after 24 hours
5
Cl
Cl
N
N
CN
N
N
H
2
9
6
7
8
20
96
94
NH
2
NH
2
N
N
CN
N
N
45
min
16
N
H
N
(
Table 1, entry 7).
N
The scope and generality of the catalyst for the [3+2]
cycloaddition reaction of structurally diverse benzonitriles
N
N
CN
2
2
possessing
a
wide range of functional groups was
N
H
1
N
investigated and the results are summarized in Table 2.
It is clear that this method is more suitable for nitriles with
electron-withdrawing groups. For example, the reaction of
N
4-trifluoromethylbenzonitrile provided the corresponding
product in 98% yield after 30 minutes (Table 2, entry 3),

Tetrahedron Letters
3
several of the previously reported methods require longer
reaction times and also excess amounts of sodium azide
need to be used for the reactions to proceed.
N
CN
1
6
9
N
3
90
HN
N
N
3
2,33
In conclusion, we have developed a convenient protocol
for the preparation of 5-substituted-1H-tetrazoles from a
variety of organic nitriles. This method provided 5-
substituted-1H-tetrazoles in good to excellent yields using
4-(N,N-dimethylamino)pyridinium acetate as a recyclable
catalyst. The procedure was simple and clean. Easy
isolation and purification of the product from reaction
mixture without the requirement of acidification (with HCl)
is an important advantage of the method. This method is
suitable for various nitriles, particularly those carrying
deactivating groups and furnishes the corresponding
products in excellent yields. Mono [3+2] cycloaddition
products of dicyanides were obtained by this method.
N
CN
N
3
73
0
1
0
1
N
H
1
4
CN
CN
N
CN
31
30
1
CN
CN
N
N
55
HN
N
N
N
CN
CN
c
1
2
3
N
H
1
6
65
CN
N
31
42
c
CN
1
CN
CN
N
Table 4. Comparison between 4-(N,N-dimethylamino)pyridinium
acetate and some other promoters for the synthesis of 5-phenyl-
1H-tetrazole from the reaction of benzonitrile with sodium azide.
HN
N
a
Reaction conditions: nitrile (1.0 mmol), sodium azide (1.0 mmol),
catalyst (15 mol%), 100 °C.
Catalyst
Solvent
Temp.
Nitrile
Azide
b
a
Isolated yield.
The reaction was performed using 2.0 mmol of sodium azide.
Yield
ref
(%)
Entry
c
Time
14 h
Catalyst
Recycling of the catalyst was explored on the [3+2]
cycloaddition reaction of 4-cyanopyridine with sodium
azide in the presence of 4-(N,N-dimethylamino)pyridinium
acetate as a model reaction. After completion of the
reaction, cold ethanol was added to the solvent-less
reaction mixture and the product was separated by
filtration. Evaporation of ethanol provided the catalyst,
which was dried in an oven and reused for six consecutive
runs without any considerable loss in the catalytic activity
being demonstrated. The results are shown in Table 3.
Nano ZnO
DMF
2.5 mmol
2.75 mmol
0.1 g
10
1
72
1
20 °C
Zn/Al hydrotalcite
DMF
2.0 mmol
3.0 mmol
0.1 g
11
2
3
12 h
12 h
84
79
1
20 °C
FeCl -SiO
3
2
2.0 mmol
3.0 mmol
0.09 g
12
DMF
Table 3. Recycling of the catalyst in the reaction of 4-
a
cyanopyridine with sodium azide.
120 °C
MZNSS
DMF
2.5 mmol
5.4 mmol
0.1 g
b
Run
Time (min)
Yield (%)
1
3
4
5
4
36 h
10 h
6 h
96
91
95
1
2
3
4
5
6
45
50
50
51
55
60
96
94
91
91
88
85
1
20 °C
NaHSO -SiO
4
2
1.0 mmol
1.5 mmol
45 g
14
DMF
1
20 °C
a
The reaction between 4-cyanopyridine and sodium azide (1.0 equiv)
was performed in the presence of 4-(N,N-dimethylamino)pyridinium
ZrOCl
DMF
00 °C
2
·8H
2
O
2.0 mmol
3.0 mmol
10 mol%
15
acetate (15 mol%) at 100 °C.
b
Isolated yield.
1
In order to show the merit of the catalyst, the synthesis of
5-phenyl-1H-tetrazole in the presence of 4-(N,N-
dimethylamino)pyridinium acetate was compared with
some previously reported methods (Table 4). As is obvious
from these results, the reactions in the presence of the other
catalysts were performed in solvents, whereas, we used
1
.0 mmol
1.0 mmol
mol%
CuSO
4 2
·5H O
1
6
6
7
1 h
98
95
DMSO 140 °C
2
InCl
3
0.01 mmol
0.012 mmol
10 mol%
17
DMF
MW
8 min
solvent-free
conditions.
In
fact,
4-(N,N-
dimethylamino)pyridinium acetate is applied as the
medium and as the promoter, and is also easily recyclable
and allows simple work-up of the products. In comparison,

4
Tetrahedron Letters
1
1
1
2. Nasrollahzadeh, M.; Bayat, Y.; Habibi, D.; Moshaee, S.
Tetrahedron Lett. 2009, 50, 4435.
3. Lang, L.; Li, B.; Liu, W.; Jiang, L.; Xu, Zh.; Yin, G.
Chem. Commun. 2010, 46, 448.
4. Das, B.; Reddy, Ch. R.; Kumar, D. N.; Krishnaiah, M.;
Narender, R. Synlett 2010, 391.
silica sulfuric acid
DMF
1.0 mmol
1.2 mmol
1.0 mmol
1
8
8
9
5 h
88
reflux
Ln(OTf)
DMF/MeOH
00 °C
3
-SiO
2
1.0 mmol
2.0 mmol
0.2 g
19
7.5 h
4 h
88
93
15. Reddy, M.; Gowd, M. B.; Pasha M. A. J. Chem. Sci.
011, 123, 75.
6. Akhlaghinia, B.; Rezazadeh, S. J. Braz. Chem. Soc.
012, 23, 2197.
2
1
1
CAN-HY zeolite
DMF
1.0 mmol
3.0 mmol
30 mol%
2
20
1
0
17. Patil, V. S.; Nandrea, K. P.; Borseb, A. U.; Bhosale, S.
V. E.-J. Chem. 2012, 9, 1145.
1
10 °C
1
1
2
2
8. Du, Zh.; Si, Ch.; Li, Y.; Wang, Y.; Lu, J. Int. J. Mol.
Sci. 2012, 13, 4696.
9. Meshram, G. A.; Deshpande, Sh. S.; Wagh, P. A.; Vala,
V. A. Tetrahedron Lett. 2014, 55, 3557.
DMAP·HOAc
no solvent
1.0 mmol
1.0 mmol
15 mol%
1
1
2 h
95
1
00 °C
0. Sivaguru, P.; Bhuvaneswari, K.; Ramkumar, R.; Lalitha,
A. Tetrahedron Lett. 2014, 55, 5683.
1. (a) Schmidt, B.; Meid, D.; Kieser, D. Tetrahedron 2007,
a
Isolated yield.
63, 492; (b) Legeay, J. Ch.; Vanden Eynde, J. J.;
Bazureau, J. P. Tetrahedron 2008, 64, 5328; (c) Dighe,
S. N.; Jain, K.S.; Srinivasan, K. V. Tetrahedron Lett.
Acknowledgements
2
009, 50, 6139.
2
2
2. Sridhar, M.; Mallu, K. K. R.; Jillella, R.; Godala, K. R.;
Beeram, Ch. R.; Chinthala, N. Synthesis 2013, 45, 507.
3. (a) Litvinenko, L. M.; Kirichenko, A. I. Dokl. Akad.
Nauk SSSR 1967, 176, 97; (b) Steglich, W.; Hofle, G.
Angew. Chem., Int. Ed. Engl. 1969, 8, 981.
We thank the Persian Gulf University Research Council for
generous partial financial support of this study.
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4. (a) Bergbreiter, D. E.; Osburn, P. L.; Smith, T.; Li, C.;
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21, 905; (b) Butler, R. N. in Comprehensive
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3
.
.
25. (a) Sakakura, A.; Kawajiri, K.; Ohkubo, T.; Kosugi, Y.;
Ishihara, K. J. Am. Chem. Soc. 2007, 129, 14775; (b)
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32. Preparation of 4-(N,N-dimethylamino)pyrridinium
2 2
acetate: To a round-bottom flask containing CH Cl (5
mL), 4-(N,N-dimethylamino)pyridine (5.0 mmol, 0.61
g) was added. While the mixture was stirring, AcOH
(5.0 mmol, 0.28 mL) was added dropwise over 10 min
and the mixture was allowed to stir for 3 h at room
temperature. Evaporation of the solvent followed by
drying of the precipitate under vacuum for 24 h afforded
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Catal. A: Chem. 2006, 247, 186.

Tetrahedron Letters
-(N,N-dimethylamino)pyridinium acetate as colorless
5
4
crystals in quantitative yield. m.p. 60-62 C; H-NMR
o
1
(
250 MHz, DMSO-d ) δ (ppm): 8.75 (d, J= 7.5 Hz, 2H),
6
7
.11 (d, J= 7.0 Hz, 2H), 6.66 (s, 1H), 4.65 (s, 6H), 1.88
13
(
s, 3H); C-NMR (62.9 MHz, DMSO-d
6
) δ (ppm):-
1
72.2, 154.5, 146.8, 141.2, 72.1, 21.26; IR (KBr) v (cm
1
)
: 3600-3200, 3080, 2720, 1640, 1565, 1550, 1440.
3. Typical procedure for the preparation of 5-(3-pyridyl)-
H-tetrazole (Table 2, entry 8): To a round-bottom flask
containing 4-(N,N-dimethylamino)pyridinium acetate
0.15 mmol, 0.02 g) at 100 °C, 3-cyanopyridine (1.0
3
1
(
mmol, 0.104 g) and sodium azide (1.0 mmol, 0.06 g)
were added and the mixture was stirred. After 1 h, the
reaction was complete. The mixture was cooled and
washed with cold EtOH (2×5 mL), each time it was
permitted to stir for 1 h. Filtration followed by drying of
the precipitate gave the corresponding pure tetrazole as
1
a white solid. Yield (0.14 g, 94%); mp 242-244 °C; H-
NMR (400 MHz, DMSO-d
(
6
) δ (ppm): 9.10 (s, 1H), 8.42
d, J= 7.9 Hz, 1H), 8.22 (d, J= 7.9 Hz, 1H), 7.38 (t, J=
13
8
1
.0 Hz, 1H); C-NMR (100 MHz, DMSO-d
62.7, 151.9, 149.8, 137.1, 126.4, 125.3; IR (KBr) v
6
) δ (ppm):
-
1
(
cm ): 3389, 2129, 2036, 1644, 1423, 1144, 1014, 754,
39, 410.
6