CuFe2O4 nanoparticles: A magnetically recoverable and reusable catalyst for the synthesis of 5-substituted 1H-tetrazoles

Article abstract of DOI:10.1016/j.tetlet.2011.04.094

An efficient and economical protocol for the synthesis of 5-substituted 1H-tetrazoles from various nitriles and sodium azide is described using magnetically recoverable and reusable CuFe₂O₄ nanoparticles. A wide variety of aryl nitriles underwent [2+3] cycloaddition under mild reaction conditions to afford tetrazoles in good to excellent yields. The catalyst was magnetically separated and reused five times without significant loss of catalytic activity.

Full text of DOI:10.1016/j.tetlet.2011.04.094

Tetrahedron Letters 52 (2011) 3565–3569
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
CuFe2O4 nanoparticles: a magnetically recoverable and reusable catalyst
for the synthesis of 5-substituted 1H-tetrazoles
⇑
B. Sreedhar , A. Suresh Kumar, Divya Yada
Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology (Council of Scientific and Industrial Research), Hyderabad 500 607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient and economical protocol for the synthesis of 5-substituted 1H-tetrazoles from various nitriles
and sodium azide is described using magnetically recoverable and reusable CuFe2O4 nanoparticles. A
wide variety of aryl nitriles underwent [2+3] cycloaddition under mild reaction conditions to afford tet-
razoles in good to excellent yields. The catalyst was magnetically separated and reused five times without
significant loss of catalytic activity.
Received 16 March 2011
Revised 21 April 2011
Accepted 24 April 2011
Available online 10 May 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
[2+3] Cycloaddition
Aryl nitriles
CuFe2O4 nanoparticles
5-Substituted 1H-tetrazoles
1. Introduction
inorganic azide salts, trimethylsilyl,11 trialkyl tin12 and organoalu-
minum azides13 have been introduced as comparatively safe azide
Tetrazoles are an increasingly popular functionality with wide
ranging applications.1 Interest in tetrazole chemistry over the past
few years has been increasing rapidly, mainly as a result of the role
played by this heterocyclic functionality in medicinal chemistry as
these offer a more favorable pharmacokinetic profile and a meta-
bolically stable surrogate for carboxylic acid functionalities.2 In
particular, by the widespread incorporation of the tetrazole func-
tionality into angiotensin II antagonist structures (sartans, Fig. 1),
several methods have been reported in literature during the past
few years for the synthesis of tetrazoles.3
This functionality has also been frequently used as lipophilic
spacers, ligands, precursors of a variety of nitrogen containing het-
erocycles in coordination chemistry4,5 and in material sciences
including photography, information recording systems, and
explosives.6
In general, the most direct and versatile method of the synthesis
of 5-substituted 1H-tetrazoles is [2+3] the cycloaddition between
nitriles and azides. A plethora of synthetic protocols and variations
on this general theme have been reported in the literature.6 In the
majority of cases, sodium azide (NaN3) has been used as an inor-
ganic azide source in combination with an ammonium halide as
the additive employing dipolar aprotic solvents.6,7 In some in-
stances, Brønsted8 or Lewis acids,9 or stoichiometric amounts of
Zn(II) salts10 have been reported as suitable additives to afford
the desired azide–nitrile addition process. As an alternative to
sources (sometimes prepared in situ), which have the added bene-
fit of being soluble in organic solvents under homogeneous condi-
tions. Unfortunately, with very few exceptions, all of these
methods require long reaction times (several hours to days) in
combination with high reaction temperatures.
Heterogeneous catalysis is particularly attractive as it allows
the production and ready separation of large quantities of products
with the use of a small amount of catalyst. Recently, several heter-
ogeneous catalytic systems were reported using, for example,
nanocrystalline ZnO,14a Zn/Al hydrotalcite,14b Zn hydroxyapatite14c
and Cu2O,15 tungstate salts16 as catalysts. Very recently, Zheng Xu
et al. have reported the synthesis of 5-substituted 1H-tetrazoles
using mesoporous ZnS nanospheres.17
In recent years, magnetic nanoparticles have emerged as a use-
ful group of heterogeneous catalysts due to their numerous appli-
cations in synthesis and catalysis.18 Separation of magnetic
nanoparticles is simple, economical, and an attractive alternative
to filtration or centrifugation as it prevents loss of catalyst and en-
hances reusability, making the catalyst cost-effective and promis-
ing for industrial applications.
As a part of our research program directed toward the utility of
magnetic nanoparticles,19 in the present study, we exploit magnet-
ically separable CuFe2O4 nanoparticles20 for the synthesis of 5-
substituted 1H-tetrazoles from a wide variety of organic nitriles
with sodium azide (Scheme 1).
Initially, in an effort to develop better reaction conditions, dif-
ferent solvents were screened for the preparation of 5-substituted
1H-tetrazole from the reaction of benzonitrile with sodium azide in
⇑
Corresponding author. Tel.: +91 40 27193510; fax: +91 40 27160921.
E-mail address: sreedharb@iict.res.in (B. Sreedhar).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.04.094

3566
B. Sreedhar et al. / Tetrahedron Letters 52 (2011) 3565–3569
N
N
N
N
N
N
N
N
N
H
H
N
O
N
NH
N
N
N
HO
HO
N
O
Cl
Losartan
Valsartan
Figure 1. Sartans.
BMS-183920
the expected tetrazoles in good yields (Table 2, entries 13 and
14). On the other hand, when 4-phenyl substituted benzonitriles,
2,2-dimethyl-2H-chromene-6-carbonitrile and thiophene-3-carbo-
nitrile were used, the product was formed in moderate yield (Table
2, entries 15–18). Unfortunately the present method is not amena-
ble for aliphatic nitriles.
N
HN
N
N
CN
40 mol% CuFe2O4
+ NaN3
R
DMF, 120 0
C
R
To check the reusability of the catalyst, as can be seen from Ta-
ble 3, the reaction was performed with benzonitrile and NaN3 un-
der the optimized reaction conditions. The catalyst was separated
from the reaction mixture by applying external magnetic field
and reused five times without significant loss of catalytic activity.
Atomic absorption spectroscopy (AAS) was employed to determine
the copper content of CuFe2O4 nanoparticles, and it was found to
be 27.32%. The leaching of the metal after the third cycle was
determined by AAS and was found to be negligible. (0.048%)
In conclusion we have developed a simple and efficient method
for the synthesis of 5-substituted 1H-tetrazoles using magnetically
separable CuFe2O4 nanoparticles as the catalyst under mild reac-
tion conditions. This catalyst has been used to generate a diverse
range of 5-substituted 1H-tetrazoles of using different nitriles in
good to excellent yields. Furthermore, the catalyst is magnetically
separable and eliminates the requirement of catalyst filtration
after completion of the reaction, which is an additional sustainable
attribute of this protocol.
Scheme 1. Magnetically separable CuFe2O4 catalyzed synthesis of 5-substituted
1H-tetrazoles.
the presence of 40 mol % of CuFe2O4 and the results are summa-
rized in Table 1. Among the different solvents screened DMF gave
the product in good yield at 120 °C and DMSO also was equally
effective at 130 °C (Table 1, entries 1–2). Other solvents, such as
NMP and toluene gave the desired products in low yield (Table 1,
entries 3–4). However, only a trace amount of the product was
formed in THF and water (Table 1, entries 5–6). On the other hand,
no product was formed when the reaction was carried out in the
absence of catalyst.
Under the optimized reaction conditions, we chose a variety of
structurally divergent benzonitriles to understand the scope and
generality of the CuFe2O4 promoted [2+3] cycloaddition reaction
to form 5-substituted 1H-tetrazoles and the results are presented
in Table 2. Unsubstituted as well as benzonitriles with electron-
donating substituents at both para and meta positions reacted well
and gave the corresponding products in good to excellent yields
(Table 2, entries 1–4). Further, the reaction was extended to di-
and tri- substituted benzonitriles, 3,5-dimethoxybenzonitrile, pip-
ernyl benzonitrile and 3,4,5-trimethoxybenzonitrile, respectively,
to generate tetrazoles in moderate to excellent yields (Table 2, en-
tries 5–7). 2-cyanonaphthalene and different halogen substituted
benzonitriles, such as 4-chlorobenzonitrile, 3-chlorobenzonitrile,
4-bromobenzonitrile and 3-bromobenzonitrile reacted smoothly
and gave the desired products in decent yields (Table 2, entries
8–12). Furthermore, the reaction was equally effective with benzo-
nitriles having substituted electron-withdrawing groups and gave
2. Spectroscopic data for the unknown products
2.1. 5-(Benzo[1,3]dioxol-5yl)-1H-tetrazole (Table 1, entry 5)
White solid. Mp: 250–252 °C. IR (KBr): 3448, 3065, 2895, 1852,
1576, 1459, 1254, 1043, 925, 818, 745 cmÀ1 1H NMR (300 MHz,
CDCl3 + DMSO): d 6.07 (s, 2H), 6.92 (d, 1H, J = 8.3 Hz), 7.54(d, 1H,
J = 1.5 Hz), 7.66 (dd, 1H, J = 1.5 Hz, 8.3 Hz). 13C NMR (75 MHz,
CDCl3 + DMSO): d 100.9, 106.5, 108.0, 117.3, 121.0, 147.5, 149.0,
154.9. EI-MS (m/z): 190 (M+).
2.2. 5-(3,5-Dimethoxyphenyl)-1H-tetrazole (Table 1, entry 6)
White solid. Mp: 204–206 °C. IR (KBr): 3091, 2970, 2843, 1730,
Table 1
1603, 1553, 1474, 1285, 1206, 1062, 837, 742, 538 cmÀ1 1H NMR
.
Screening of various solvents for the reaction of benzonitrile with sodium azidea
(300 MHz, CDCl3 + DMSO): d 3.86 (s, 6H,), 6.55 (t, 1H J = 2.2 Hz),
7.21 (d, 2H, J = 2.2 Hz).13C NMR (75 MHz, CDCl3 + DMSO): d 54.8,
102.6, 104.4, 125.4, 155.4, 160.5. ESI-MS (m/z): 207 (M+H).
Entry
Solvent
Temp °C
Yieldb (%)
1
2
3
4
5
6
DMF
DMSO
NMP
Toluene
THF
Water
120
130
80
110
65
0c, 82
80
28
35
Trace
Trace
2.3. 5-(3,4,5-Trimethoxyphenyl)-1H-tetrazole (Table 1, entry 7)
100
White solid. Mp: 202–203 °C . IR (KBr): 3442, 3184, 2977, 1594,
1503, 1467, 1252, 1125, 999, 855, 751 cmÀ1 1H NMR (300 MHz,
.
a
Reaction conditions: benzonitrile (1 mmol), NaN3 (1.5 mmol), CuFe2O4
(40 mol %) in DMF (5 mL) at 120 °C for 12 h.
CDCl3 + DMSO): d 3.81 (s, 3H,), 3.92 (s, 6H), 7.35 (s, 2H)13C NMR
(75 MHz, CDCl3 + DMSO): d 55.1, 59.6, 103.4, 118.5, 138.9, 152.5,
154.6. ESI-MS (m/z): 237 (M+H).
b
Yield of isolated products.
Reaction without catalyst.
c

B. Sreedhar et al. / Tetrahedron Letters 52 (2011) 3565–3569
3567
Table 2
Magnetically separable CuFe2O4 catalyzed preparation of 5-substituted 1H-tetrazolesa
Entry
Substrate
Product
Yield (%)
82
Melting point (°C)
213–214
CN
N
HN
(215–216)10
N
1
N
250–251
CN
N
HN
(248–249)21
N
2
3
85
90
N
231–233
CN
N
HN
(231–232)22
N
N
H3CO
H3CO
157–159
CN
N
HN
(158–160)11
N
N
4
5
6
88
73
80
OCH3
OCH3
CN
N
O
O
HN
N
O
250–252
204–206
N
O
H3CO
CN
N
HN
N
H3CO
N
OCH3
CN
OCH3
HN
H3CO
H3CO
N
N
H3CO
H3CO
N
7
93
202–203
OCH3
CN
OCH3
204–206
N
HN
(205–207)10
N
8
9
78
89
N
250–252
CN
N
HN
(252–253)23
N
N
Cl
Cl
138–139
CN
N
HN
(139–140)8a
N
N
10
11
12
13
87
90
86
80
Cl
Cl
267–269
CN
N
HN
(268–269)7a
N
N
Br
Br
155–156
CN
N
N
HN
(154–155)23a
N
Br
Br
220–222
CN
N
HN
(218–219)24
N
N
F3C
F3C
(continued on next page)

3568
B. Sreedhar et al. / Tetrahedron Letters 52 (2011) 3565–3569
Table 2 (continued)
Entry
Substrate
Product
Yield (%)
78
Melting point (°C)
O
O
H
N
14
197–199
CN
CN
N
N
N
N
HN
N
N
15b
70
72
247–249
238–240
CN
N
HN
N
N
16b
H3CO
H3CO
196–198
CN
N
N
HN
(195–197)11a
N
17
70
68
O
O
245–247
CN
N
(244–246)25
HN
N
N
18
S
S
Reaction conditions: aryl nitrile (1 mmol), NaN3 (1.5 mmol), CuFe2O4 (40 mol %) in DMF (3 mL) at 120 °C for 12 h.26
Reaction carried out at 130 °C for 20 h.
a
b
Table 3
2.6. 5-(4-Methoxy-biphenyl-4-yl)-1H-tetrazole (Table 2, entry
16)
Recovery and reuse of CuFe204 catalyst for the reaction between benzonitrile and
sodium azidea
Yield(%)
Third
80
Average yield (%)
79
White solid. Mp: 238–240 °C. IR (KBr): 3468, 3010, 2924, 2853,
1606, 1493, 1247, 1175, 1032, 824, 753, 523 cmÀ1 1H NMR
.
First
82
Second
80
Fourth
78
Fifth
75
(300 MHz, CDCl3 + DMSO): d 3.85 (s, 3H), 6.96 (d, 2H, J = 7.6 Hz),
7.56 (d, 1H, J = 7.6 Hz), 7.69 (d, 2H, J = 7.4 Hz), 8.11 (d, 2H,
a
J = 7.3 Hz). 13C NMR (75 MHz, CDCl3 + DMSO):
d 53.8, 112.9,
Reaction conditions: benzonitrile (1 mmol), NaN3 (1.5 mmol), CuFe204
(40 mol %) in DMF (5 mL) at 120 °C for 12 h.
121.2, 125.5, 126.2, 126.5, 130.4, 141.5, 155.2, 158.2. ESI-MS (m/
z): 253 (M+H).
Acknowledgments
2.4. Phenyl-[4-(1H-tetrazol-5-yl)-phenyl]-methanone (Table 2,
entry 14)
ASK thanks the university grant commission for the award of
Senior Research Fellowship and Council of Scientific and Industrial
Research, New Delhi for the financial support.
White solid. Mp: 197–199 °C . IR (KBr) : 3014, 2857, 1657, 1563,
1435, 1277, 1156, 1054, 926, 865, 696, 657 cmÀ1.1H NMR
(300 MHz, CDCl3 + DMSO): d 7.47–7.56 (m, 2H), 7.63 (t, 1H,
J = 7.4 Hz), 7.78 (d, 2H, J = 8.3 Hz), 7.91 (d, 2H, J = 8.3 Hz), 8.24 (d,
2H, J = 8.3 Hz).13C NMR (75 MHz, CDCl3 + DMSO): d 126.2, 127.6,
129.0, 129.7, 132.0, 136.1, 138.4, 155.4, 194.7. ESI-MS (m/z): 251
(M+H).
References and notes
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was taken in a round-bottomed flask and stirred at 120 °C temperature for
12 h. After completion of the reaction the catalyst was separated from the
reaction mixture with an external magnet and reaction mixture was treated
with ethyl acetate (30 mL) and 5 N HCl (20 mL). The resultant organic layer
was separated and the aqueous layer was again extracted with ethyl acetate
(20 mL). The combined organic layers were washed with water, concentrated,
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