Syntheses of 5-substituted 1 H-tetrazoles catalyzed by reusable CoY zeolite

Article abstract of DOI:10.1021/jo201261w

A simple and efficient route for the synthesis of 5-substituted 1H-tetrazoles catalyzed by CoY zeolite is reported. The salient features of this atom-economical, cost-effective, and high-yield cobalt-catalyzed protocol are aerobic conditions, lower reaction time, and milder reaction conditions without additives. Other advantages include experimental ease of manipulation, safer alternative to hazardous, corrosive, and polluting conventional Lewis acid catalysts, recovery, and reusability with consistent catalytic activity. The results are rationalized by proposing a suitable mechanism.

Full text of DOI:10.1021/jo201261w

NOTE
pubs.acs.org/joc
Syntheses of 5-Substituted 1H-Tetrazoles Catalyzed by Reusable CoY
Zeolite
Velladurai Rama, Kuppusamy Kanagaraj, and Kasi Pitchumani*
School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
S Supporting Information
b
ABSTRACT: A simple and efficient route for the synthesis of
5-substituted 1H-tetrazoles catalyzed by CoY zeolite is reported.
The salient features of this atom-economical, cost-effective, and
high-yield cobalt-catalyzed protocol are aerobic conditions, lower
reaction time, and milder reaction conditions without additives.
Other advantages include experimental ease of manipulation, safer
alternative to hazardous, corrosive, and polluting conventional
Lewis acid catalysts, recovery, and reusability with consistent catalytic activity. The results are rationalized by proposing a suitable
mechanism.
etrazoles are nitrogen-rich compounds, covering a wide
range of applications.1 They are used in pharmaceuticals as
slow to be synthetically useful except when potent electron-with-
drawing groups activate the nitrile component and for aliphatic
nitriles. Thus, the development of environmentally friendly alter-
natives is desirable for the synthesis of tetrazoles.
T
lipophilic spacers and metabolically stable surrogates for the
carboxylic acid group and cis-amide bond,1a as antifoggants in
photographic materials,1b in information recording systems,1c in
biomedical applications,1d in agriculture,1e and in materials
science applications including propellants1f and explosives.1g
Tetrazole moieties are also important synthons in synthetic
organic chemistry.1h For example, proline-derived tetrazole
is used as an enantioselective catalyst in asymmetric synthesis
and multicomponent reactions and as ligands in coordination
chemistry.
Since the pioneering work of Kharasch, cobalt has been
extensively used as catalyst for many transformations12 asso-
ciated with homocoupling, cross-coupling, radical cyclizations,
Vollhardt [2 + 2 + 2] and [2 + 2] cycloaddition reactions,
Nicholas reaction, PausonÀ Khand reaction, and Heck-type
reactions. Zeolite-encapsulated cobalt clusters are the first
shape-selective FischerÀTropsch (FÀT) catalysts.12b Cobalt as
a biological constituent of organometallic species via coenzyme
B12, can be used as replacement for the corrosive Lewis acid and
expensive metals Pd, Pt, and Cu, making the process more
practical and viable. Cobalt complexes can also undergo a facile
switch among several oxidation states (CoIII, CoII, CoI, and Co0),
resulting in a high reactivity with good catalytic active sites.
A tremendous upsurge of interest has been evident recently in
chemical transformations performed on solid supports,13 which
make the reaction processes convenient to perform (simple
isolation of reaction products by filtration), faster, more eco-
nomical, environmentally benign, and recyclable with minimal
metallic waste. In this context, heterogeneous catalysis by zeolites
with exchangeable metal cations possessing tunable larger pore
sizes and inherent acid/base catalytic properties are excellent
catalysts with their well-optimized isolated active sites providing
greener alternatives to homogeneous catalysis.14 Zeolite Y is a
faujasite (FAU) type, microporous aluminosilicate built from
infinitely extending three-dimensional network of SiO4 and AlO4
tetrahedra that are linked together through oxygen bridges. The
presence of Al3+ instead of Si4+ creates a negative charge, which is
Conventional synthesis of 5-substituted 1H-tetrazoles via [3 + 2]
cycloaddition of azide to the corresponding nitriles, first reported by
Hantzsch and Vagt,2 suffered from drawbacks including use of
expensive and toxic metalÀorganic azide complexes such as tin or
silicon,3 highly moisture-sensitive reaction conditions, and use of
amine salts, strong Lewis acid,4 and hydrazoic acid which are extre-
mely toxic, water-sensitive, explosive, and volatile.5 Later, Demko
and Sharpless reported an innovative and safe procedure in water
with Zn salts as catalysts.6 Stoichiometric amounts of inorganic salts
and metal complexes7 as catalysts, use of TMSN3 and TBAF8
instead of metal salts under solvent-free conditions in micellar media
and ionic liquids, and use of various catalysts9 such as BF3 OEt2,
4
3
Pd(OAc)2/ZnBr2,9a Yb(OTf)3,9b Zn(OTf)3,9c AlCl3,9d and Pd-
(PPh3)49e were also employed for the same purpose. However, a
drawback of these homogeneous catalytic processes is difficulty in
separation and recovery of the catalysts. Therefore, heterogeneous
alternatives are highly desirable and have attracted increasing
attention. Several heterogeneous catalytic systems10,11 using nano-
crystalline ZnO, Zn/Al HT,10a Zn hydroxyapatite,10b Cu2O,11a,b
Sb2O3, FeCl3ÀSiO2,11c CdCl2,11d BaWO4, γ-Fe2O3,11e ZnS,11f and
natural natrolite zeolite11g were reported. These methods require a
large excess of sodium azide, higher temperature, longer reaction
time, and expensive metals. In spite of this, the cycloaddition is too
Received: June 25, 2011
Published: September 12, 2011
r
2011 American Chemical Society
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|

The Journal of Organic Chemistry
NOTE
Table 1. Synthesis of 5-Substituted 1H-Tetrazole with
the search toward ecocompatible and more economical transi-
tion-metal-catalyzed procedures, Cobalt-catalyzed reactions are
promising,12 as they are favorably comparable to nickel and
palladium, although in the framework of sustainable develop-
ment, cobalt is less interesting than iron or manganese. On the
other hand, several reactions performed under cobalt catalysis are
specific to this metal. For instance, iron-catalyzed cross coupling
between aryl Grignard reagents and functionalized secondary
alkyl bromides generally failed where as excellent yields are
obtained under cobalt catalysis.
To optimize the reaction conditions and to explore the
catalytic activity of cobalt-exchanged Y zeolite, phenylacetonitrile
(1i) and sodium azide (2) were used as test substrates to yield
5-benzyltetrazole (3i), and the results are summarized in Table 1.
CoY zeolite shows better catalytic performance than other metal
ion exchanged zeolites such as Fe, Ni, Cu, Zn, Cd, Al, and Sn
(Table 1, entries 3, and 5À10), and HY zeolite (Table 1, entry 1).
Poor yield is obtained with unmodified solid support, NaY zeolite
(Table 1, entry 2). No addition product is obtained when the
reaction is carried out without catalyst (Table 1, entry 11),
despite prolonged reaction time, thus highlighting the specific
role of cobalt present in the solid support.
Various Catalystsa
entry
catalyst
time (h)
yieldb (%)
1
2
HY
24
48
24
14
24
24
24
24
24
24
48
22
10
40
80
38
42
45
38
45
45
nil
NaY
FeY
CoY
NiY
CuY
ZnY
CdY
AlY
3
4
5
6
7
8
9
10
11
SnY
a Phenylacetonitrile (1 mmol), sodium azide (2.0 mmol), catalyst
(20 mg), DMF, 120 °C. b Isolated yield.
Table 2. Catalytic Performance of CoY Zeolite under Various
Reaction Conditionsa
To identify the best cobalt source, catalytic activities of various
cobalt forms are investigated under our experimental conditions.
The results, including yields and turnover number (TON), are
summarized in Table 2. Cobalt chloride has provided the desired
product in low but promising yield (Table 2, entry 1). However,
the separation and reuse of the catalyst pose problems due to
its complete dissolution in DMF. Use of solid supports led to
sharply ascending efficiencies in the synthesis of tetrazoles except
for Co/Al-HT and CoÀAlÀMCM41 (Table 2, entries 5À8).
Cobalt-exchanged zeolite is a better catalyst than others and gives
a very high yield of tetrazoles (Table 2, entry 5). CoY zeolite was
prepared by an ion-exchange method16 and characterized17
by powder XRD, SEM-EDX, ICP-AES, AAS analysis, UV-DRS,
and FT-IR spectra. The XRD (see the Supporting Information,
Figure S1) confirmed the dispersion of cobalt on NaY frame-
work, the heterogeneity in shape, and highly crystalline nature
of zeolite. The size and morphology of the catalyst were analyzed
by SEM image (see the Supporting Information, Figure S2).
The total cobalt content was found to be 7.06 atom % by EDX
analyzer (see the Supporting Information, Figure S3). The UVÀ
DRS spectra provided a “fingerprint” of the specific transition of
cobalt environment in the zeolite, indicating the presence of
cobalt in +2 state.17 The three bands around 530, 574, and
634 nm were assigned to Co2+ in zeolite, which was absent in the
unmodified solid support, NaY zeolite (see the Supporting Infor-
mation, Figure S4). The results obtained from ICP-AES and AAS
analyses also confirmed the presence of cobalt (7.06%) in CoY
zeolite (see the Supporting Information). FT-IR spectra (see the
Supporting Information, Figure S5) of recycled catalyst shows
that the structural integrity remains unaltered after the reaction
and thus proves the efficiency of cobalt exchanged zeolite as a
recyclable catalyst.
entry
catalyst
solvent
yieldb (%)
TONc
1d
2d
3d
4d
5
CoCl2 6H2O
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
toluene
EtOH
dioxan
THF
56
21
3
Co(NO3)2 6H2O
nil
3
Co(OAc)2 4H2O
nil
3
CoSO4 7H2O
27
1
3
CoY
80
29
6
CoÀK10 Mont.
Co/AlÀHT
CoÀAlÀMCM41
CoY
72
26
7
12
4
8
9e
10
3
35, 80
58
15, 29
18
10
11
12
13
14
15
16f
17g
18h
19i
CoY
CoY
55
18
CoY
35
16
CoY
50
17
CoY
62
23
CoY
ACN
DMF
DMF
DMF
DMF
25
14
CoY
50, 80
30, 80
30, 80
70, 80
17, 29
8, 29
14, 29
24, 29
CoY
CoY
CoY
a Phenylacetonitrile (1 mmol), sodium azide (2 mmol), catalyst (20
mg), DMF (2 mL), 120 °C for 14 h. b Isolated yield. c Moles of tetrazole
formed per mole of catalyst. d Reaction carried out with 0.01 g of
cobalt salts. e Yield and TON of the reaction carried at 100 and 120 °C,
f
respectively. Yield and TON of the reaction carried for 12 and 14 h,
respectively. g Yield and TON of the reaction carried with 10 mg and 20
mg of catalyst, respectively. h Yield and TON when the reaction carried
with 1.0 and 2.0 mmol of sodium azide, respectively. i Yield and TON
when the reaction carried with solvent 0.5 and 1 mL, respectively.
The influence of other experimental parameters such as
solvent, temperature, amount of catalyst, and reaction time was
also optimized. The solvent has a prominent influence on the
yield (Table 2, entries 10À15). The experimental results show
that toluene, THF, and DMF are good solvents in sharply
ascending efficiencies in the synthesis of tetrazoles, whereas a
protic solvent namely ethanol is not suitable for this reaction. An
increase in temperature from 100 to 120 °C accelerates the
compensated by exchangeable transition-metal cations which,
after dehydration, may occupy different sites in zeolite.
In continuation of our ongoing works on development of
efficient, reusable supports, and catalysts using zeolites/clays15
which are readily impregnated with metal ions, herein we report a
simple, green, and efficient protocol for the synthesis of tetrazoles
with environmentally friendly CoY zeolites as a novel catalyst. In
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NOTE
Table 3. Synthesis of 5-Substituted 1H-Tetrazoles Catalyzed
Table 4. Sheldon Test Carried out with CoY Zeolite Cata-
by CoY Zeolitea
lyzed Synthesis of 5-Substituted 1H-Tetrazolesa
yieldb (%)
catalyst
CoY
7h
7 + 7h
reused catalyst (TON)c
35.4
38.2
79.8 (29)
a Phenylacetonitrile (1 mmol), sodium azide (2.0 mmol), catalyst (20
mg), DMF (1 mL) at 120 °C. b HPLC yield. c Moles of tetrazole formed
per mole of catalyst.
entry
R
product
yieldb (%)
TONc
1
C6H5-
3a
3b
3c
3d
3e
3f
90, 92d
91
37
40
40
31
37
34
30
26
29
37
38
39
60
46
2
p-ClC6H4-
p-NO2C6H4-
p-NH2C6H4-
2- pyridinyl-
4-pyridinyl-
1-naphthyl-
Table 5. Reusability of CoY Zeolite in the Synthesis 5-Sub-
3
95
stituted 1H-Tetrazolesa
4
77
runb
first
second
third
fourth
fifth
5
92
6
90
yield (%)
TONc
80
29
78
29
79
29
77.4
28
77.5
29
7
3g
3h
3i
68
8
9-anthracenyl-
62
a Reactions are performed with phenylacetonitrile (1 mmol), sodium
azide (2.0 mmol), catalyst (20 mg), DMF (1 mL) for 14 h at 120 °C.
b After completion of the reaction, catalyst was filtered and washed three
times with ethyl acetate, air-dried, activated at 450 °C, and reused for
successive runs. c Moles of tetrazole formed per mole of catalyst.
9
C6H5CH2-
80
10
11
12
13e
14f
15g
16g
p-NO2C6H4CH2-
p-H3COC6H4CH2-
1-cyclohexenyl-CH2-
CH3-
3j
91
3k
3l
87
93
3m
3n
3o
3p
74
CNCH2-
86
with longer reaction time without any additives (Table 3, entry
13).18 Malononitrile afforded only monoaddition product even
on addition of 2 equiv of sodium azide (Table 3, entry 14).
Phenylacetonitrile, 4-nitrophenylacetonitrile, 4-nitrophenyla-
cetonitrile, and 1-cyclohexenylacetonitrile provided moderate
to good yields with shorter reaction time (Table 3, entries
9À12) than the methods reported previously.8,10 CoY catalyst
exhibited negligible activity for N,N-dimethylbenzonitrile, and
α-cyano-4-hydroxycinnamic acid (Table 3, entries 15 and 16)
despite prolonged reaction time because azide ion would not
add to the cyanide group of the nitriles of carboxylic acid and
electron-rich nitriles, respectively.19 All synthesized tetrazoles
p-(CH3)2NC6H4-
nil
p-OHC6H4CHdC(COOH)-
nil
a Nitrile (1 mmol), sodium azide (2.0 mmol), catalyst (20 mg), DMF
(1 mL) for 14 h at 120 °C. b Yield of isolated product. c Moles of tetrazole
formed per mole of catalyst. d Yield of gram-scale reaction with
benzonitrile (10 mmol), sodium azide (20.0 mmol). e Reaction carried
for 20 h in a pressure tube. f Reaction carried in a pressure tube with 2
and 4.0 mmol of sodium azide. g Reaction carried at 140 °C.
reaction to give the desired product in high yield (Table 2, entry 9).
Moderate to good yield is obtained on increasing the quantity
of sodium azide from 1 equiv to 2 equiv (Table 2, entry 18). The
effects of reaction times and the amount of catalyst on the
reaction were also evaluated (Table 2, entries 16 and 17). There
was no appreciable increase in the yield on prolonging the
reaction time or increasing the amount of catalyst. Consequently,
the optimal reaction conditions have been identified as 120 °C
in DMF for 14 h.
1
were characterized by H and 13C NMR, FT-IR, and UVÀvis
spectroscopy. The IR spectra of synthesized compounds
showed a sharp absorption at 3421 cmÀ1 (NÀH) and group of
bands at 1455 (CÀH), 1285 (NÀNdNÀ), 1208, 1120, and
1048 cmÀ1 caused by the presence of secondary amino group
and tetrazole ring and absence of band at 2200 cmÀ1 due to
CN group.
In order to verify real heterogeneity of CoY zeolite, a Sheldon
test20 was performed to evaluate possible metal leaching. Thus,
the reaction mixture after 7 h at 120 °C was filtered, and the
filtrate was further heated at 120 °C for an additional 7 h. Sodium
azide and phenylacetonitrile were further added to the recovered
solid catalyst, and the mixture was heated at 120 °C for 14 h. The
obtained results clearly indicated that there is no appreciable
leaching of metal ions under the present reaction conditions
(Table 4). The absence of leaching was also confirmed from
chemical and ICP-AES analyses of the filtrate from the reaction
mixture and also of the filtrate from a stirred solution of CoY in
DMF (at 120 °C for 14 h) (for details, see the Supporting
Information).
As recyclability is important for industrial applications of a
good catalyst, reuse performance of CoY zeolite was investigated.
It is noteworthy that the recovered catalyst was recycled by
calcinating at 450 °C and even after the fifth cycle exhibited
comparable activity with 77.5% yield and a turnover number
of 29 as shown in Table 5. The reusability was also confirmed
To understand the scope and generality of CoY zeolite
catalyzed [3 + 2] cycloaddition reaction, various structurally
divergent benzonitriles were employed as substrates. As depicted
in Table 3, various aromatic, heteroaromatic and aliphatic nitriles
were tested. All reactions proceeded to completion within 14 h,
and tetrazoles were isolated in moderate to excellent yields. The
isolated yield obtained for gram-scale reaction was comparable to
that for small-scale reaction (Table 3, entry 1). This demon-
strates the potential utility of this method for preparative
purposes. The aromatic benzonitriles give moderate to good
yields (Table 3, entries 1À8). The best results are obtained with
nitriles containing an electron-withdrawing substituent (Table 3,
entries 2 and 3) than with an electron-donating substituent
(Table 3, entry 4). Heteroaromatic nitriles such as 2-pyridine-
carbonitrile and 4-pyridinecarbonitrile gave the corresponding
tetrazoles in excellent yields (Table 3, entries 5 and 6). Moderate
yield was obtained in the reaction of sterically demanding
cyanoanthracene and cyanonaphthalene (Table 3, entries 7 and
8). Among aliphatic nitriles, acetonitrile provided moderate yield
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NOTE
Scheme 1. Plausible Mechanism for CoY Zeolite Catalyzed [3 + 2] Cycloaddition of Tetrazoles
by ICP-AES analysis of reused CoY zeolite, which proved the
presence of 7.06% of cobalt, and this strongly supports the
heterogeneous nature of CoY zeolite.
catalysts. Its reusability with consistent activity for at least five
cycles is also established, indicating CoY as a greener catalyst, it
can substitute metal salts or other heterogeneous catalysts, and
has potential value for industrial applications.
On the basis of the above results, and also in accordance
with previous literature reports,6 a plausible reaction pathway
is proposed as shown in Scheme 1. The pink CoY zeolite
(octahedral coordination) upon activation became blue because
of tetrahedral coordination, which was strongly supported by
UVÀDRS spectra (see the Supporting Information, Figure S4).
The three bands at 530, 574, and 634 nm were assigned to Co2+
in tetrahedral coordination in the zeolite framework. During the
course of reaction, the color changed from blue to deep blue and
then pink indicating a change in the coordination sphere, from
tetrahedral to octahedral.
’ EXPERIMENTAL SECTION
Preparation and Characterization of Cobalt-Exchanged
Zeolite. NaY zeolite powder was purchased and used as such. The
physio-chemical parameters of NaY zeolite are 2.43 Si/Al ratio, unit cell
size 24.65 Å and surface area, m2/g: 900 with supercages of a diameter of
ca. 1.3 nm. Cobalt-exchanged zeolite was prepared from NaY zeolite by
an ion-exchange method and was characterized by powder XRD, EDX,
ICP-AES, AAS analyses, and UVÀDRS spectra.
The structure of NaY zeolite was found to be retained as observed from
the retention of all the characteristic peaks in XRD patterns after cobalt-
exchange process. The diffraction patterns of the zeolite samples show the
reflections in the range 5À35°, typical of zeolites. This suggests that cobalt is
highly dispersed on the NaY framework. The sharp intense peaks at 15.54°,
23.52°, and 31.15° show the good crystallinity of the zeolite material.
The SEM image (see the Supporting Information, Figure S2) shows
that the surface consists of CoY zeolite granules with sizes ranging from
0.5 to 10 μm. It is noted that the shape of CoY grains is heterogeneous in
nature.
CoII bound to zeolite Y (to trivalent Al) coordinated readily to
the nitrile, and this is the dominant factor influencing [2 + 3]
cycloaddition. It is relevant to note here that, in the study of
azideÀnitrile cycloaddition catalyzed by Zn2+, Sharpless et al.
reported that coordination of the nitrile substrate to the Lewis
acidic zinc is the source of the catalysis in the formation of 1H-
tetrazoles which is supported by model calculations using density
functional theory and corroborated with experimental rate studies.
Subsequent neucleophilic attack by azide (via azide binding to CoII
ensures the formation of an 18-eÀ complex)21 followed by hydro-
lysis produces tetrazole as the end product, with CoII catalyst being
released for the next cycle of reactions as its structural integrity
remains unaltered (see the Supporting Information, Figure S5).
In conclusion, an efficient, atom-economical synthesis of
5-substituted 1H-tetrazoles is reported for the first time using
the heterogeneous CoY zeolite. This simple, environmentally
benign catalysis proceeds under aerobic conditions with no
additives, tolerates various nitriles particularly for aliphatic
nitriles, requires shorter reaction times with good to excellent
yields, and gives a higher turnover number. The present [2 + 3]
cycloaddition is associated with several advantages such as
simpler procedure, milder reaction conditions, and an alternative
to hazardous, corrosive, and polluting conventional Lewis acid
Typical Procedure for the Preparation of 5-Substituted
1H-Tetrazole. CoY zeolite was added (0.02 g) to a mixture of
phenylacetonitrile (1 mmol) and sodium azide (2 mmol) in DMF
(1 mL) and stirred at 120 °C for 14 h. After completion of reaction
(monitored by thin-layer chromatography, TLC), the reaction mixture
was treated with ethyl acetate (10 mL), the catalyst was filtered, and the
filtrate was washed with distilled water. The organic layer was treated
with 5 N HCl (10 mL) and stirred vigorously. The resultant organic layer
was separated, and the aqueous layer was again extracted with ethyl
acetate (10 mL). The combined organic layers were washed with water,
dried over anhydrous sodium sulfate, and concentrated to give the crude
solid crystalline 5-benzyltetrazole. Column chromatography silica gel
(60À120 mesh) afforded pure tetrazole. All products were characterized
by 1H and 13C NMR, FT-IR, UVÀvis, and emission spectra, which were
in agreement with literature.6a,8,10,22À28
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NOTE
Characterization of 5-Phenyl-1H-tetrazole6a (Table 3, Entry 1). Com-
pound 3a was prepared according to the general procedure and recrystal-
lized from ethanol to give a white solid (90% yield): mp 215À216 °C;
UVÀvis (EtOH) λmax 209, 243, 274 nm; emission (EtOH, λexci = 274 nm)
λemi 395 nm; FT-IR (KBr) γ cmÀ1 3419, 2924, 2827, 2717, 2656, 1620,
2731, 1616, 1597, 1518, 1491, 1373, 1357, 1259, 1120, 1101, 965, 863;
1H NMR (300 MHz, CDCl3, 25 °C, TMS, δ ppm) 7.48À7.64 (m, 4H),
7.94 (d, J = 8.1 Hz, 2H), 8.28 (d, J = 8.4 Hz, 2H), 8.47 (s, 1H); 13C NMR
(100 MHz, CDCl3, 25 °C, TMS, δ ppm) 125.0, 126.1, 128.8, 130.3,
132.5, 133.0, 133.2, 133.3, 162.8.
1
1600, 1460, 1350, 1383, 1163, 1057, 765; H NMR (300 MHz, CDCl3,
Characterization of 5-Benzyl-1H-tetrazole8 (Table 3, Entry 9). Com-
pound 3i was prepared according to the general procedure and
recrystallized from ethanol to give a white solid (80% yield): mp
123À125 °C; UVÀvis (EtOH) λmax 219, 257 nm; emission (EtOH,
λexci = 257 nm) λemi 437 nm; FT-IR (KBr) γ cmÀ1 3419, 2928, 2814,
25 °C, TMS, δ ppm) 3.92 (br s, 1H), 7.58 (m, 3H), 8.12 (m, 2H).
Characterization of 5-(p-Chlorophenyl)-1H-tetrazole10a (Table 3,
Entry 2). Compound 3b was prepared according to the general proce-
dure and recrystallized from ethanol to give a white solid (91% yield):
mp 261À263 °C; UVÀvis (EtOH) λmax 214, 254 nm; emission (EtOH,
λexci = 254 nm) λemi 416 nm; FT-IR (KBr) γ cmÀ1 3419, 2927, 2816,
1
2723, 1626, 1600, 1496, 1384, 1350, 1182, 1066, 831; H NMR (300
MHz, CDCl3, 25 °C, TMS, δ ppm) 4.29 (s, 2H), 7.20À7.56 (m, 5H),
8.52 (br s, 1H); 13C NMR (75 MHz, CDCl3, 25 °C, TMS, δ ppm) 29.8,
127.7, 128.8, 129.1, 134.3, 156.1.
1
2723, 1602, 1457, 1437, 1383, 1350, 1161, 1095, 1055, 875, 765; H
NMR (400 MHz, DMSO-d6, 25 °C, TMS, δ ppm) 7.64 (d, J = 8.8 Hz,
2H), 8.00 (d, J = 8.8 Hz, 2H); 13C NMR (100 MHz, DMSO-d6, 25 °C,
TMS, δ ppm) 123.1, 128.7, 129.5, 135.9, 155.0.
Characterization of 5-(4-Nitrophenylacetonitrile)-1H-tetrazole25
(Table 2, Entry 10). Compound 3j was prepared according to the general
procedure and recrystallized from ethanol to give a white solid (91%
yield): mp 184À186 °C; UVÀvis (EtOH) λmax 217, 289 nm; emission
(EtOH, λexci = 289 nm) λemi 421 nm; FT-IR (KBr) γ cmÀ1 3421, 2933,
Characterization of 5-(p-Nitrophenyl)-1H-tetrazole8,10a (Table 3,
Entry 3). Compound 3c was prepared according to the general proce-
dure and recrystallized from ethanol to give a white solid (95% yield):
mp 219À221 °C; UVÀvis (EtOH) λmax 219, 289 nm; emission (EtOH,
λexci = 289 nm) λemi 452 nm; FT-IR (KBr) γ cmÀ1 3421, 2933, 2818,
1
2818, 2719, 1627, 1599, 1273, 1174, 1016, 929, 852; H NMR (300
MHz, CDCl3, 25 °C, TMS, δ ppm) 2.54 (s, 2H), 5.25 (br s, 1H),
7.57À7.65 (m, 2H), 7.84À8.96 (m, 2H); 13C NMR (75 MHz, CDCl3,
25 °C, TMS, δ ppm) 29.47, 127.44, 129.44, 131.27, 156.67.
1
2719, 1627, 1599, 1273, 1174, 1016, 929, 852; H NMR (400 MHz,
DMSO-d6, 25 °C, TMS, δ ppm) 3.44 (br s, 1H), 7.60 (m, 2H), 8.04 (m,
2H); 13C NMR (100 MHz, DMSO-d6, 25 °C, TMS, δ ppm) 124.2,
126.9, 129.4, 131.2, 155.3.
Characterization of 5-(4-Methoxybenzyl)-1H-tetrazole26 (Table 3,
Entry 11). Compound 3k was prepared according to the general
procedure and recrystallized from ethanol to give a white solid (87%
yield): mp 156À158 °C; UVÀvis (EtOH) λmax 217, 283 nm; emission
(EtOH, λexci = 283 nm) λemi 394 nm; FT-IR (KBr) γ cmÀ1 3415, 2962,
2814, 2718, 1627, 1600, 1247, 1178, 1383, 1350, 1111, 1033, 829; 1H
NMR (300 MHz, CDCl3 and DMSO-d6, 25 °C, TMS, δ ppm) 3.78 (s,
3H), 4.22 (s, 2H), 6.85 (d, J = 6.3 Hz, 2H), 7.21 (d, J = 6 Hz, 2H), 8.65
(br s, 1H); 13C NMR (75 MHz, CDCl3 and DMSO-d6, 25 °C, TMS, δ
ppm) 28.9, 55.1, 114.1, 127.3, 129.3, 158.7.
Characterization of 5-(p-Aminophenyl)-1H-tetrazole22 (Table 3,
Entry 4). Compound 3d was prepared according to the general proce-
dure and recrystallized from ethanol to give a white solid (77% yield):
mp 265À267 °C; UVÀvis (EtOH) λmax 218, 286 nm; emission (EtOH,
λexci = 286 nm) λemi 434 nm; FT-IR (KBr) γ cmÀ1 3485, 1622, 1510,
1457, 1407, 1377, 1191, 1139, 1056, 991, 837, 750; 1H NMR (400 MHz,
DMSO-d6, 25 °C, TMS, δ ppm) 6.12 (br s, 3H), 6.59 (d, J = 8.8 Hz, 2H),
7.37 (d, J = 8.4 Hz, 2H); 13C NMR (100 MHz, DMSO-d6, 25 °C, TMS,
δ ppm) 113.4, 113.5, 133.3, 133.5, 152.9.
Characterization of 5-(Cyclohexenylmethyl)-1H-tetrazole (Table 3,
Entry 12). Compound 3l was prepared according to the general
procedure and recrystallized from ethanol to give white solid (93%
yield): mp 180À182 °C; UVÀvis (EtOH) λmax 220 nm; emission
(EtOH, λexci = 220 nm) λemi 428 nm; FT-IR (KBr) γ cmÀ1 3427, 3139,
Characterization of 2-(1H-Tetrazol-5-yl)pyridine6,10a (Table 3, Entry 5).
Compound 3e was prepared according to the general procedure and recry-
stallized from ethanol to give a white solid (92% yield): mp 210À213 °C;
UVÀvis (EtOH) λmax 214, 246 nm; emission (EtOH, λexci = 246 nm) λemi
401 nm; FT-IR (KBr) γ cmÀ1 3417, 2818, 2724, 1623, 1599, 1512, 1384,
1350, 1039, 833; 1H NMR (400 MHz, CDCl3, 25 °C, TMS, δ ppm) 7.61
(m, 1H), 8.06 (m, 1H), 8.21 (d, J = 8 Hz, 1H), 8.78 (d, J = 4.8 Hz, 1H).
Characterization of 5-(4-Pyridyl)-1H-tetrazole8 (Table 3, Entry 6).
Compound 3f was prepared according to the general procedure and
recrystallized from ethanol to give a white solid (90% yield): mp
254À255 °C; UVÀvis (EtOH) λmax 214, 233, 271 nm; emission
(EtOH, λexci = 271 nm) λemi 419 nm; FT-IR (KBr) γ cmÀ1 3414, 2814,
2725, 1626, 1597, 1512, 1384, 1350, 1039, 833; 1H NMR (300 MHz, D2O,
25 °C, TMS, δ ppm) 5.91 (d, J = 1.5 Hz, 2H), 6.26 (d, J = 3.9 Hz, 2H); 13C
NMR (75 MHz, D2O, 25 °C, TMS, δ ppm) 119.1, 137.0, 137.3, 151.1.
Characterization of 5-(1-Naphthyl)-1H-tetrazole23 (Table 3, Entry 7).
Compound 3g was prepared according to the general procedure and recrys-
tallized from ethanol to give a white solid (68% yield): mp 264À267 °C;
UVÀvis (EtOH) λmax 227, 288 nm; emission (EtOH, λexci = 288 nm) λemi
358 nm; FT-IR (KBr) γ cmÀ1 3421, 3053, 2812, 2721, 1626, 1599, 1518,
1491, 1383, 1352, 1257, 1121, 1102, 966, 864; 1H NMR (400 MHz, DMSO-
d6, 25 °C, TMS, δ ppm) 7.63À7.72 (m, 3H), 7.97À7.99 (m, 1H),
8.02À8.08 (m, 1H), 8.10À8.18 (m, 1H), 8.59À8.61 (m, 1H); 13C NMR
(100MHz,DMSO-d6,25°C, TMS, δppm) 125.3, 126.0, 127.4, 128.1, 128.5,
130.9, 133.3, 162.3.
1
3002, 2931, 1571,1541, 1438, 1344, 1251, 1088, 840; H NMR (300
MHz, CDCl3, 25 °C, TMS, δ ppm) 1.56À1.60 (m, 4H), 1.92 (s, 2H),
2.02 (m, 2H), 3.55 (s, 2H), 5.54 (s, 1H), 7.76 (br s, 1H); 13C NMR (75
MHz, CDCl3, 25 °C, TMS, δ ppm) 23.6, 26.2, 27.3, 30.1, 37.8, 122.9,
138.1, 157.5. Elemental Analysis Anal. Calcd for C8H12N4: C, 58.51; H,
7.37; N, 34.12. Found: C, 58.64; H, 7.42; N, 34.12.
Characterization of 5-Methyl-1H-tetrazole27 (Table 3, Entry 13).
Compound 3m was prepared according to the general procedure and
recrystallized from ethanol to give a white solid (74% yield): mp
145À148 °C; UVÀvis (EtOH) λmax 210, 262 nm; emission (EtOH,
λexci = 262 nm) λemi 443 nm; FT-IR (KBr) γ cmÀ1 3443, 2945, 2814,
1
2723, 1628, 1247, 1600, 1489, 1180, 1095, 931, 767; H NMR (300
MHz, D2O, 25 °C, TMS, δ ppm) 1.84 (s, 3H), 8.32 (br s, 1H); 13C
NMR (75 MHz, DMSO-d6, 25 °C, TMS, δ ppm) 22.1, 180.4.
Characterization of 5-Cyanomethyl-1H-tetrazole28 (Table 3, Entry
14). Compound 3n was prepared according to the general procedure and
recrystallized from ethanol to give a white solid (86% yield): mp
116À118 °C; UVÀvis (EtOH) λmax 216, 262 nm; emission (EtOH,
λexci = 262 nm) λemi 429 nm; FT-IR (KBr) γ cmÀ1 3414, 2854, 2204,
1602, 1498, 1386, 1348, 837, 771; 1H NMR (300 MHz, CDCl3, 25 °C,
TMS, δ ppm) 3.71 (s, 2H), 7.84 (br s, 1H).
Characterization of 5-(9-Anthracenyl)-1H-tetrazole24 (Table 3, En-
try 8). Compound 3h was prepared according to the general procedure
and recrystallized from ethanol to give a white solid (62% yield): mp
215À216 °C; UVÀvis (EtOH) λmax 215, 255 nm; emission (EtOH,
λexci = 255 nm) λemi 446 nm; FT-IR (KBr) γ cmÀ1 3441, 3058, 2819,
’ ASSOCIATED CONTENT
S
Supporting Information. General methods, preparation
b
of catalyst, and analytical data for all compounds 3aÀn. This
9094
dx.doi.org/10.1021/jo201261w |J. Org. Chem. 2011, 76, 9090–9095

The Journal of Organic Chemistry
NOTE
material is available free of charge via the Internet at http://
pubs.acs.org.
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’ AUTHOR INFORMATION
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Corresponding Author
*E-mail: pit12399@yahoo.com.
’ ACKNOWLEDGMENT
Financial support from UGC Hyderabad for an award under
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