Silica-supported ferric chloride (FeCl3-SiO2): An efficient and recyclable heterogeneous catalyst for the preparation of arylaminotetrazoles

Article abstract of DOI:10.1080/00397910903370683

An efficient method for preparation of 5-arylamino-1H-tetrazole and 1-aryl-5-amino-1H-tetrazole derivatives is reported using FeCl ₃-SiO₂ as an effective heterogeneous catalyst. Generally, when the substituent in arylcyanamide is a strongly electron-withdrawing group, the position of the equilibrium would shift toward 5-arylamino-1H-tetrazole, whereas with an electron-releasing substituent, the position of the equilibrium would shift toward 1-aryl-5-amino-1H-tetrazole. Copyright Taylor & Francis Group, LLC.

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Silica-Supported Ferric Chloride (FeCl3-
SiO2): An Efficient and Recyclable
Heterogeneous Catalyst for the
Preparation of Arylaminotetrazoles
Davood Habibi a & Mahmoud Nasrollahzadeh a
a Department of Organic Chemistry, Bu-Ali Sina University, Hamedan,
Iran
Version of record first published: 04 Oct 2010.
To cite this article: Davood Habibi & Mahmoud Nasrollahzadeh (2010): Silica-Supported Ferric
Chloride (FeCl3-SiO2): An Efficient and Recyclable Heterogeneous Catalyst for the Preparation of
Arylaminotetrazoles, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 40:21, 3159-3167
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Synthetic Communications1, 40: 3159–3167, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903370683
SILICA-SUPPORTED FERRIC CHLORIDE (FeCl3-SiO2):
AN EFFICIENT AND RECYCLABLE HETEROGENEOUS
CATALYST FOR THE PREPARATION OF
ARYLAMINOTETRAZOLES
Davood Habibi and Mahmoud Nasrollahzadeh
Department of Organic Chemistry, Bu-Ali Sina University, Hamedan, Iran
An efficient method for preparation of 5-arylamino-1H-tetrazole and 1-aryl-5-amino-1H-
tetrazole derivatives is reported using FeCl3-SiO2 as an effective heterogeneous catalyst.
Generally, when the substituent in arylcyanamide is a strongly electron-withdrawing group,
the position of the equilibrium would shift toward 5-arylamino-1H-tetrazole, whereas with
an electron-releasing substituent, the position of the equilibrium would shift toward
1-aryl-5-amino-1H-tetrazole.
Keywords: 1-Aryl-5-amino-1H-tetrazole; 5-arylamino-1H-tetrazole; arylcyanamide; FeCl3-SiO2; hetero-
geneous catalyst
INTRODUCTION
The growth of tetrazole chemistry over the past 25 years has been significant,
mainly as a result of the roles played by tetrazoles in coordination chemistry as ligands,
in medicinal chemistry as stable surrogates for carboxylic acids, and in material appli-
cations, including explosives, agriculture, and photography.[1–4] Another important
application of tetrazoles is preparation of imidoylazides.[5] The earliest published
methods for preparation of aminotetrazole derivatives included the following: (1) dia-
zotation of aminoguanidine derivatives,[6] (2) azidation of carbodiimides,[7] cyana-
mides,[8] and aminoiminomethanesulfonic acid,[9] and (3) nucleophilic substitution
by Nꢀ3 of sulfur from thioureas in the presence of mercury[10] or lead salts.[6]
More recently, 5-monosubstituted amino-1H-tetrazoles were synthesized by
thermal isomerization of 1-substituted-5-amino-1H-tetrazoles in boiling ethylene
or melt state (180–200 ꢁC)[6,8b] Herbst and Garbrecht have shown that cyanamides
may be converted to aminotetrazoles using hydrazoic acid, which often results in
a mixture of isomers (Scheme 1).[8a]
These methods suffer from one or more disadvantages such as poor yield,
long reaction times, harsh reaction conditions, lack of easy availability or easy
preparation of the starting materials, and use of expensive and toxic reagents (the
in situ–generated hydrazoic acid is highly toxic and explosive). If hydrazoic acid is
Received August 5, 2009.
Address correspondence to Mahmoud Nasrollahzadeh, Department of Organic Chemistry, Bu-Ali
Sina University, Hamedan, Iran. E-mail: mahmoudnasr81@gmail.com
3159

3160
D. HABIBI AND M. NASROLLAHZADEH
Scheme 1. Conversion of arylcyanamide to the corresponding aminotetrazole using hydrazoic acid.
used, care must be taken by monitoring the concentration of hydrazoic acid in the
reaction mixture to avoid an explosion.[2a] Because of the safety considerations,
we required a method that does not use hydrazoic acid or an azide source that
produced hydrazoic acid in situ because of the associated hazards.
Great efforts in catalysis researches have been devoted in recent years to the
introduction and application of effective and safe heterogeneous catalysts.[11]
Organic synthesis on silica-supported reagents[12–14] have received considerable
attention because of the ease of handling, enhanced reaction rates, greater selectivity,
simple workup, and recoverability of the catalysts.[13,14]
In continuation of our recent work on the synthesis of heterocycles[15] and
application of heterogeneous reagents for development of the useful synthetic meth-
odologies,[16] we herein report a new protocol for preparation of arylaminotetrazole
3–8 derivatives from cyanamides 1 using FeCl3-SiO2 as a heterogeneous catalyst
(Scheme 2, Table 1). This catalyst is safe, easy to handle, and environmentally benign
Scheme 2. Conversion of arylcyanamides to the corresponding arylaminotetrazoles using FeCl3-SiO2.
Table 1. Synthesis of various arylaminotetrazoles 3–8 in the presence of FeCl3-SiO2 by reaction of sodium
azide 2 and cyanamides 1 at 110 ꢁC
Entry
R
Product
Yield (%)a
Time [min]
Ratio of isomers (A=B)b
1
2
3
4
5
6
2,5-(Cl)2C6H3
2-ClC6H4
3
4
5
6
7
8
76
75,73c
75
120
120
125
75
1.9
1.7
1.8
0.5
0.5
0.4
4-NO2C6H4
4-OCH3C6H4
2,4-(CH3)2C6H3
4-CH3C6H4
74
77
75
75
73
aYield refer to the pure isolated product.
bDetermined by 1H NMR analysis.
cYield after the third cycle.

SILICA-SUPPORTED FERRIC CHLORIDE (FeCl3-SiO2)
3161
with fewer disposals problems. Silica-supported ferric chloride was prepared from
the reaction of silica gel with anhydrous ferric chloride.[14e,15a]
EXPERIMENTAL
General
All reagents were purchased from Merck and Aldrich and used without further
1
purification. 13C NMR and H NMR spectra were recorded on Brucker 300- and
500-MHz instruments using tetramethylsilane (TMS) as an internal standard.
Chemical shifts are reported in parts per million, and coupling constants are
reported in hertz. Infrared (IR) spectra were recorded on a Shimadzu 470 spectro-
photometer. Thin-layer chromatography (TLC) was performed on Merck precoated
silica-gel 60-F254 plates.
General Procedure for Preparation of 3–8
FeCl3-SiO2 (0.1 g, mmol% loading of FeCl3: ꢂ0.04[15a]) was added to a mixture
of cyanamide 1 (2 mmol), NaN3 2 (3 mmol), and distilled dimethylformamide (7 mL)
and stirred at 110 ꢁC for the appropriate time (Table 1). After completion of the reac-
tion (as monitored by TLC), the mixture was cooled to room temperature. The cata-
lyst was filtered, and the filtrate was treated with ethyl acetate (35 mL) and 5 N HCl
(20 mL) and stirred vigorously. The resultant organic layer was separated, and the
aqueous layer was again extracted with ethyl acetate (25 mL). The combined organic
layers were washed with water, and the solvent was removed and crystallized with
aqueous ethanol to give the crystalline arylaminotetrazoles 3–8. The pure products
were characterized by IR and NMR.
Spectroscopic Data
R ¼ 2,5-(Cl)2 in Scheme 2 and Table 1, Entry 1. IR (KBr): 3320, 3165, 1649,
1
1575, 1524, 1481, 1450, 1396, 1301, 1240, 880, 817, 665, 641, 581 cmꢀ1; H NMR
(500 MHz, acetone-d6) isomer A: d 6.12 (1H, s, br), 6.98 (1H, dd, J ¼ 8.6 Hz,
J ¼ 2.5 Hz), 7.37 (1H, d, J ¼ 8.6 Hz), 7.88 (1H, s, br), 8.49 (1H, s, J ¼ 2.5 Hz); 13C
NMR (125 MHz, DMSO-d6) isomer A: d 119.4, 119.6, 121.8, 130.3, 131.8, 138.0,
1
155.3; H NMR (500 MHz, acetone-d6) isomer B: d 6.46 (2H, s, br), 7.70 (1H, dd,
J ¼ 8.7 Hz, J ¼ 2.4 Hz), 7.76 (1H, d, J ¼ 8.7 Hz), 7.81 (1H, d, J ¼ 2.4 Hz); 13C NMR
(125 MHz, DMSO-d6) isomer B: d 130.0, 130.2, 131.6, 131.7, 132.2, 132.5, 155.7.
R ¼ 2-Cl in Scheme 2 and Table 1, Entry 2. IR (KBr): 3420, 3315, 3190,
1651, 1590, 1528, 1497, 1438, 1355, 1313, 1122, 1091, 1078, 1033, 755, 731, 689,
1
651 cmꢀ1; H NMR (300 MHz, acetone-d6) isomer A: d 5.98 (1H, s, br), 6.95 (1H,
td, J ¼ 7.8 Hz, J ¼ 1.6 Hz), 7.23 (1H, td, J ¼ 8.6 Hz, J ¼ 1.4 Hz), 7.35 (1H, dd,
J ¼ 8.0 Hz, J ¼ 1.5 Hz), 8.31 (1H, dd, J ¼ 8.4 Hz, J ¼ 1.5 Hz); 13C NMR (125 MHz,
1
acetone-d6) isomer A: d 121.8, 121.9, 123.4, 129.4, 131.6, 137.8, 156.3; H NMR
(300 MHz, acetone-d6) isomer B: d 6.30 (2H, s, br), 7.58–7.74 (4H, m); 13C NMR
(125 MHz, acetone-d6) isomer B: d 128.1, 129.7, 130.6, 131.9, 132.7, 133.1, 156.8.

3162
D. HABIBI AND M. NASROLLAHZADEH
R ¼ 4-NO2 in Scheme 1 and Table 1, Entry 3. IR (KBr, cmꢀ1) : 3390, 3300,
3125, 1637, 1588, 1517, 1490, 1341, 1291, 1258, 1125, 1090, 1069, 1048, 872, 863, 855,
840, 746, 689; 1H NMR (500 MHz, acetone): isomer A: d 5.94 (1H, d, br), 7.77 (2H,
d, J ¼ 9.2 Hz), 8.14 (2H, d, J ¼ 9.2 Hz), 9.16 (1H, s, br); 13C NMR (125 MHz,
1
DMSO-d6): isomer A: d 116.8, 125.1, 140.3, 147.1, 155.0; H NMR (500 MHz, acet-
one): isomer B: d 6.58 (2H, s, br), 8.01 (2H, d, J ¼ 7.2 Hz), 8.49 (2H, d, J ¼ 7.2 Hz);
13C NMR (125 MHz, DMSO-d6): isomer B: d 124.6, 125.3, 138.6, 146.9, 155.4.
R ¼ 4-(OMe) in Scheme 2 and Table 1, Entry 4. IR (KBr): 3425, 3300,
3130, 2985, 2975, 2830, 1645, 1575, 1545, 1505, 1339, 1290, 1249, 1167, 1080,
1
1015, 834, 817, 629, 610, 551 cmꢀ1; H NMR (500 MHz, DMSO-d6) isomer A: d
3.67 (3H, s), 5.70 (1H, s), 6.78 (2H, d, J ¼ 8.7 Hz), 7.26 (2H, d, J ¼ 8.7 Hz), 8.33
(1H, s); 13C NMR (125 MHz, DMSO-d6) isomer A: d 55.1, 113.8, 119.4, 133.7,
1
153.9, 156.2; H NMR (500 MHz, DMSO-d6) isomer B: d 3.81 (3H, s), 6.73 (2H,
s), 7.11 (2H, d, J ¼ 8.7 Hz), 7.45 (2H, d, J ¼ 8.7 Hz); 13C NMR (125 MHz, DMSO-
d6) isomer B: d 55.6, 114.9, 126.0, 126.1, 155.1, 159.7.
R ¼ 2,4-(Me)2 in Scheme 2 and Table 1, Entry 5. IR (KBr): 3425, 3300,
3010, 2900, 1649, 1619, 1590, 1537, 1524, 1507, 1352, 1312, 1263, 1223, 1132,
1
1034, 825, 799, 758, 653, 614, 555 cmꢀ1; H NMR (500 MHz, DMSO-d6) isomer
A: d 2.15 (3H, s), 2.21 (3H, s), 5.92 (1H, s), 6.89 (1H, d, J ¼ 8.0 Hz), 6.93 (1H, s),
7.60 (1H, d, J ¼ 8.0 Hz), 7.61 (1H, s, br); 13C NMR (125 MHz, DMSO-d6) isomer
A: d 17.8, 20.3, 121.4, 126.4, 127.4, 130.5, 130.9, 135.5, 156.3; 1H NMR
(500 MHz, DMSO-d6) isomer B: d 2.01 (3H, s), 2.38 (3H, s), 6.68 (2H, s), 7.21
(1H, d, J ¼ 8.0 Hz), 7.24 (1H, d, J ¼ 8.0 Hz), 7.29 (1H, s); 13C NMR (125 MHz,
DMSO-d6) isomer B: d 16.8, 20.7, 127.3, 127.7, 129.5, 131.8, 134.9, 140.1, 155.7.
R ¼ 4-Me in Scheme 2 and Table 1, Entry 6. IR (KBr): 3415, 3304, 3145,
2980, 2915, 1648, 1589, 1568, 1542, 1514, 1118, 1092, 1087, 842, 811 cmꢀ1 1H
;
NMR (300 MHz, DMSO-d6) isomer A: d 2.19 (3H, s), 5.74 (1H, s), 6.99 (2H, d,
J ¼ 8.2 Hz), 7.25 (2H, d, J ¼ 8.2 Hz), 8.37 (1H, s); 13C NMR (75 MHz, DMSO-d6)
1
isomer A: d 20.3, 117.8, 123.9, 130.2, 138.1, 154.9; H NMR (300 MHz, DMSO-
d6) isomer B: d 2.38 (3H, s), 6.80 (2H, s), 7.39 (2H, d, J ¼ 8.1 Hz), 7.43 (2H, d,
J ¼ 8.1 Hz); 13C NMR (75 MHz, DMSO-d6) isomer B: d 20.7, 128.9, 129.6, 130.9,
138.9, 156.2.
RESULTS AND DISCUSSION
The general synthetic method is depicted in Scheme 2. Arylaminotetrazoles 3–8
were obtained from the reaction of cyanamides 1 with sodium azide 2 in the presence
of FeCl3-SiO2 as a heterogeneous catalyst at 110 ꢁC for appropriate time in excellent
yields, as summarized in Table 1.
We have studied the cycloaddition reaction of cyanamides with sodium azide
in the presence of PPh3, LiCl, and FeCl3-SiO2 (Table 2). Results show that in
all cases the products were obtained in good yields. However, PPh3 and LiCl,
being homogeneous reagents, could not be recycled from the reaction mixture. In
contrast to the reaction conditions with PPh3 and LiCl, FeCl3-SiO2 is a cheap and
nonhazardous solid acid catalyst that can be handled easily and is important from

SILICA-SUPPORTED FERRIC CHLORIDE (FeCl3-SiO2)
3163
Table 2. Comparison of different amounts of FeCl3-SiO2 catalyst with PPh3 and LiCl in synthesis of
5-(2,5-dichlorophenyl)amino-1H-tetrazole (A) and 1-(2,5-dichlorophenyl)-5-amino-1H-tetrazole (B) by
the reaction of sodium azide and 2,5-dichlorophenylcyanamide at 110 ꢁC
Entry
Reagent or catalyst (g)
Solvent
Time (min)
Yield (%)
Product
1
2
3
4
5
6
7
8
PPh3 (0.1)
LiCl (0.1)
DMF
DMF
DMF
DMF
DMSO
DMF
DMF
DMF
120a
120a
120
120
120
120
120
120
67
61
77
76
75
72
70
0b
A þ B
A þ B
A þ B
A þ B
A þ B
A þ B
A þ B
–
FeCl3-SiO2 (0.14)
FeCl3-SiO2 (0.1)
FeCl3-SiO2 (0.1)
FeCl3-SiO2 (0.08)
FeCl3-SiO2 (0.07)
None
aReaction was carried out at 120 ꢁC.
bIn the absence of catalyst at 110 ꢁC, no reaction occurred after 120 min.
the environmental point of view because it produces little waste. It also has excellent
activity and selectivity even on an industrial scale and in most cases can be recovered
from the reaction mixtures by simple filtration and reused. In addition, to improve
yield and because of the biological importance of aminotetrazole derivatives, we
started to study this reaction by examining the different amounts of FeCl3-SiO2
catalyst for the reaction involving 2,5-dichlorophenylcyanamide (2 mmol) and
sodium azide (3 mmol) to afford the product under thermal conditions. The best
result was obtained with a 0.1 g (mmol% loading of FeCl3: ꢂ0.04[15a]) of FeCl3-
SiO2 and gave a mixture of 1-(2,5-dichlorophenyl)-5-amino-1H-tetrazole (B) and
5-(2,5-dichlorophenyl)amino-1H-tetrazole (A) (3, Table 1, entry 1) in excellent yield.
The cyanamides 1 were prepared according to the literature.[17] To include a
reasonable range of electrical and steric effects, the aryl-substituted cyanamides were
studied including various groups in ortho, meta, and para positions. According to
Table 1, among the various cyanamides tested, electron-rich aromatic cyanamides
reach completion at 110 ꢁC after 75 min, whereas electron-poor aromatic species
require more times (compare entries 1–3 with 4–6 in Table 1).
In addition, there is an excellent correlation between the effect of substitution
on the benzene ring and the position of equilibrium. In other words, isomer ratios in
tetrazoles 3–8 are affected by different types of substituents in arylcyanamide 1.
Generally, when the substitution on the aryl ring is strongly electron-withdrawing,
the position of equilibrium would shift toward the isomer of 5-arylamino-1H-
tetrazole A via guanidine azide intermediate A0, which appears to be the major
product (Table 1, entries 1–3) and as the electropositivity of substituent increases,
the position of equilibrium is shifted toward the isomer of 1-aryl-5-amino-1H-tetra-
zoles B via guanidine azide intermediate B0 (Table 1, entries 4–6). This is similar to
the substituent effect on the aryl ring of the mechanism that was presented by Henry
and coworkers for thermal isomerization of A and B.[6,8a,8b,18]
FeCl3-SiO2 as catalyst was isolated from the reaction mixture by simple fil-
tration. The purified catalyst was achieved through washing the solid residue catalyst
by water and ethanol followed by drying in an oven at 100 ꢁC for 30 min. In every
experiment, more than 98% of the FeCl3-SiO2 was easily recovered from the reaction
mixture. Catalytic activity of the recovered catalyst was tested and showed to be the

3164
D. HABIBI AND M. NASROLLAHZADEH
Figure 1. 1H NMR spectrum (300 MHz) of 5-(2,5-dichlorophenyl)amino-1H-tetrazole 3A and 5-amino-1-
(2,5-dichlorophenyl)-1H-tetrazole 3B in acetone-d6.
same as FeCl3-SiO2 used for the first time. The recovered catalyst was reused three
times without any loss of activity (Table 1, entry 2).
All products are known compounds and were identified by comparison of some
1
of their spectral data [infrared (IR), H NMR, and 13C NMR] with those of auth-
entic samples.[6,8,9,18,19] Elimination of one strong and sharp absorption band (CN
stretching band) and appearance of two absorption bands in the range of
3140–3550 cmꢀ1 (NH stretching bands) in the IR spectrum confirmed the formation
of arylaminotetrazoles. The 13C NMR spectra displayed signals for tetrazole ring
carbons of arylaminotetrazoles in the range of 154–157 ppm (depending on the nat-
ure of the substituents in the amino functionality).[20]
1
A comparison of H NMR spectra revealed that 5-arylamino-1H-tetrazole A
generally shows a large separation in the chemical shifts of the aryl protons
(Fig. 1). Isomers 1-aryl-5-amino-1H-tetrazoles B had a small separation of the aryl
ring protons. Indeed, signals of the aryl ring protons of isomer 1-aryl-5-amino-
1H-tetrazoles B contracted their multiplicities and shifted downfield (Fig. 1).
CONCLUSION
In conclusion, we have developed a novel and highly efficient method for the
synthesis of various arylaminotetrazoles by treatment of cyanamides with sodium
azide in the presence of FeCl3-SiO2 as an effective catalyst. The significant advan-
tages of this methodology are good yields, elimination of dangerous and harmful
hydrazoic acid, simple workup procedure, and easy preparation and handling of

SILICA-SUPPORTED FERRIC CHLORIDE (FeCl3-SiO2)
3165
the catalyst. The catalyst can be recovered by simple filtration and reused without
loss of activity.
ACKNOWLEDGMENT
We are thankful to the Bu-Ali Sina University, Hamedan, Iran, for partial sup-
port of this work.
REFERENCES
1. Bulter, R. N. In Comprehensive Heterocyclic Chemistry II; A. R. Katritzky, C. W. Ress,
E. F. V. Scriven (Eds.); Pergamon: New York, 1996; vol. 4, p. 621.
2. (a) Herr, R. 5-Substituted-1H-tetrazoles as carboxylic acid isosteres: Medicinal chemistry
and synthetic methods. J. Bioorg. Med. Chem. 2002, 10, 3379; (b) Holland, G. F.; Pereira,
J. N. Heterocyclic tetrazoles, a new class of lipolysis inhibitors. J. Med. Chem. 1967, 10,
149; (c) Figdor, S. K.; Schach von Wittenau, M. Metabolism of 5-(3-pyridyl)tetrazole.
J. Med. Chem. 1967, 10, 1158; (d) Rhonnstad, P.; Wensbo, D. On the relative strength
of the 1H-tetrazol-5-yl- and the 2-(triphenylmethyl)-2H-tetrazol-5-yl-group in directed
ortho-lithiation. Tetrahedron Lett. 2002, 43, 3137.
3. Klapo¨tke, T. M.; Stierstorfer, J.; Weber, B. New energetic material: Synthesis and
characterization of copper 5-nitriminotetrazolates. Inorg. Chim. Acta 2009, 362, 2311.
4. John, E. O.; Kirchmeier, R. L.; Shreeve, J. M. Reactions of 5-(perfluoro-alkyl)tetrazolates
with cyanogen, nitrosyl, and cyanuric chlorides. Inorg. Chem. 1989, 28, 4629.
5. Modarresi-Alam, A. R.; Khamooshi, F.; Rostamizadeh, M.; Keykha, H.; Nasrollahzadeh,
M.; Bijanzadeh, H. R.; Kleinpeter, E. Dynamic 1H NMR spectroscopic study of the
restricted S-N rotation in aryl-N-(arylsulfonyl)-N-(triphenylphosphoranylidene)-
imidocarbamates. J. Mol. Struc. 2007, 841, 67.
6. Finnegan, W. G.; Henry, R. A.; Lieber, E. Preparation and isomerization of 5-
alkylaminotetrazoles. J. Org. Chem. 1953, 18(7), 779.
7. Percival, D. F.; Herbst, R. M. Alkylated 5-aminotetrazoles, their preparation and
properties. J. Org. Chem. 1957, 22, 925.
8. (a) Garbrecht, W. L.; Herbst, R. M. The synthesis of certain 5-aminotetrazole derivatives,
II: The action of hydrazoic acid on monoalkylcyanamides. J. Org. Chem. 1953, 18(8),
1014; (b) Henry, R. A.; Finnegan, W. G.; Lieber, E. Thermal isomerization of substituted
5-aminotetrazoles. J. Am. Chem. Soc. 1954, 76, 88.
9. Miller, A. E.; Feenay, D. J.; Ma, Y.; Zarcone, L.; Aziz, M. A.; Magnuson, E. The
synthesis of aminoiminoethanenitriles, 5-aminotetrazoles, N-cyanoguanidines, and
N-hydroxyguanidines from aminoiminomethanesulfonic acids. Synth. Commun. 1990,
20, 217.
10. (a) Batey, R. A.; Powell, D. A. A general synthetic method for the formation of
substituted 5-aminotetrazoles from thioureas: A strategy for diversity amplification.
Org. Lett. 2000, 2, 3237; (b) Yu, Y.; Ostresh, J. M.; Houghten, R. A. Solid-phase synthesis
of 5-aminotetrazoles. Tetrahedron Lett. 2004, 45, 7787.
11. (a) Das, B.; Thirupathi, P.; Mahender, I.; Reddy, K. R.; Ravikanth, B.; Nagarapu, L. An
efficient synthesis of 1,8-dioxo-octahydroxanthenes using heterogeneous catalysts. Catal.
Commun. 2007, 8, 535; (b) Das, B.; Thirupathi, P.; Mahender, I.; Reddy, V. S.; Rao, Y. K.
Amberlyst-15: An efficient reusable heterogeneous catalyst for the synthesis of
1,8-dioxo-octahydroxanthenes and 1,8-dioxo-decahydroacridines. J. Mol. Catal. A:
Chem. 2006, 247, 233.

3166
D. HABIBI AND M. NASROLLAHZADEH
12. (a) Das, B.; Laxminarayana, K.; Ravikanth, B. Application of heterogeneous catalysts for
an efficient synthesis of b-keto enol ethers. J. Mol. Catal. A: Chem. 2007, 271, 131; (b)
Das, B.; Damodar, K.; Chowdhury, N.; Kumar, R. A. Application of heterogeneous solid
acid catalysts for Friedlander synthesis of quinolines. J. Mol. Catal. A: Chem. 2007, 274,
148; (c) Wang, Y.; Sarris, K.; Sauer, D. R.; Djuric, S. W. An expeditious and convenient
synthesis of acylsulfonamides utilizing polymer-supported reagents. Tetrahedron Lett.
´
r, A. Silica-supported Pd catalysts for Heck
2007, 48, 5181; (d) Polshettiwar, V.; Molna
´
coupling reactions. Tetrahedron 2007, 63, 6949.
13. (a) Ahmed, N.; Van Lier, J. E. Silica-gel-supported TaBr5: New catalyst for the facile
and rapid cyclization of 20-aminochalcones to the corresponding 2-aryl-2,3-
dihydroquinolin-4(1H)-ones under solvent-free conditions. Tetrahedron Lett. 2006, 47,
2725; (b) Bandini, M.; Luque, R.; Budarin, V.; Macquarrie, D. J. Aryl alkynylation versus
alkyne homocoupling: Unprecedented selectivity switch in Cu, phosphine, and
solvent-free heterogeneous Pd-catalysed couplings. Tetrahedron 2005, 61, 9860; (c)
Ramesh, C.; Mahender, G.; Ravindranath, N.; Das, B. A simple, mild, and efficient
procedure for selective cleavage of prenylesters using silica-supported sodium hydrogen
sulphate as a heterogenous catalyst. Tetrahedron Lett. 2003, 44, 1465.
14. (a) Chari, M. A.; Shobha, D.; Mukkanti, K. Silica gel=FeCl3: An efficient and recyclable
heterogenous catalyst for one-step synthesis of 4(3H)-quinazolinones under solvent-free
conditions. Catal. Commun. 2007, 7, 787; (b) Dang, Q.; Brown, B. S.; Erion, M. D.
Efficient synthesis of purine analogues: An FeCl3-SiO2-promoted cyclization reaction of
4,5-diaminopyrimidines with aldehydes leading to 6,8,9-trisubstituted purines. Tetra-
hedron Lett. 2000, 41, 6559; (c) Morys, P.; Schlieper, T. Synthesis and catalytic activity
of silica-supported iron(III). J. Mol. Catal. A: Chem. 1995, 95, 27; (d) Funabiki, T.;
Ohashi, H.; Sugimoto, T.; Yoshida, S. Oxidation of hydroxybenzenes with oxygen cata-
lyzed by supported metal chloride catalysts in aprotic solvents, part 1: Effects of supports
and solvents on reactivity. J. Mol. Catal. 1991, 69, 407; (e) Kim, K. S.; Song, Y. H.; Lee,
B. H.; Hahn, C. S. Efficient and selective cleavage of acetals and ketals using ferric chlor-
ide adsorbed on silica gel. J. Org. Chem. 1986, 51, 404; (f) Fadel, A.; Salaun, J. Anhydrous
¨
ferric chloride adsorbed on silica gel induced ring enlargement of tertiary cyclobutanols:
Synthesis of isolaurolene and derivatives, campholenic ether, and (ꢃ) cuparene. Tetra-
hedron 1985, 41, 413; (g) Fadel, A.; Salaun, J. Anhydrous ferric chloride dispersed on silica
¨
gel induced ring enlargement of tertiary cycloalkanols, II: A convenient homologation of
cycloalkanones, preparation of spiro systems, and propella-c-lactones. Tetrahedron 1985,
41, 1267; (h) Tal, D. M.; Keinan, E.; Mazur, Y. Reactions in dry media: Reactions of
cholesterol and cholestanes on silica-bound ferric chloride: Cholestane- diacholestene
rearrangement. Tetrahedron 1981, 37, 4327; (i) Patney, H. K. A rapid mild and efficient
method of thioacetalization using anhydrous iron(III) chloride dispersed on silica gel.
Tetrahedron Lett. 1991, 32, 2259.
15. (a) Nasrollahzadeh, M.; Bayat, Y.; Habibi, D.; Moshaee, S. FeCl3-SiO2 as a reusable het-
erogeneous catalyst for the synthesis of 5-substituted 1H-tetrazoles via [2 þ 3] cycloaddi-
tion of nitriles and sodium azide. Tetrahedron Lett. 2009, 50, 4435; (b) Kamali, T. A.;
Bakherad, M.; Nasrollahzadeh, M.; Farhangi, S.; Habibi, D. Synthesis of 6-substituted
imidazo[2,1-b]thiazoles via Pd=Cu-mediated Sonogashira coupling in water. Tetrahedron
Lett. 2009, 50, 5459.
16. (a) Modarresi-Alam, A. R.; Nasrollahzadeh, M.; Khamooshi, F. Solvent-free preparation
of primary carbamates using silica sulfuric acid as an efficient reagent. Arkivoc 2007, 16,
234; (b) Modarresi-Alam, A. R.; Khamooshi, F.; Nasrollahzadeh, M.; Amirazizi, H. A.
Silica-supported perchloric acid (HClO4– SiO2): An efficient reagent for the preparation
of primary carbamates under solvent-free conditions. Tetrahedron 2007, 63, 8723; (c)
Modarresi-Alam, A. R.; Nasrollahzadeh, M.; Khamooshi, F. Al(HSO4)3-mediated for

SILICA-SUPPORTED FERRIC CHLORIDE (FeCl3-SiO2)
3167
the preparation of primary carbamates under solvent-free conditions. Scientia Iranica
2008, 15, 452; (d) Habibi, D.; Marvi, O. Montmorillonite KSF and montmorillonite
K-10 clays as efficient catalysts for the solventless synthesis of bismaleimides and
bisphthalimides using microwave irradiation. Arkivoc 2006, 13, 8; (e) Habibi, D.; Marvi,
O. Montmorillonite K-10–supported one-pot synthesis of some symmetric diimides and
3a,4,7,7a-tetrahydroisoindole-1,3-dione derivatives under solvent-free conditions using
microwaves. J. Serb. Chem. Soc. 2005, 70, 579.
17. Crutchley, R. J.; Nakicki, M. L. Pentaammineruthenium(III) complexes of neutral
and anionic (2,3-dichlorophenyl)cyanamide: A spectroscopic analysis of ligand to metal
charge-transfer spectra. Inorg. Chem. 1989, 28, 1955.
18. (a) Henry, R. A.; Finnegan, W. G.; Lieber, E. Kinetics of the isomerization of substituted
5-aminotetrazoles. J. Am. Chem. Soc. 1955, 77, 2264; (b) Garbrecht, W. L.; Herbst, R. M.
The synthesis of certain 5-aminotetrazole derivatives, I: The action of hydrazoic acid on
some dialkylcyanamides. J. Org. Chem. 1953, 18, 1003; (c) Garbrecht, W. L.; Herbst,
R. M. The synthesis of certain 5- aminotetrazole derivatives, III: The synthesis of certain
5- monoalkylaminotetrazoles. J. Org. Chem. 1953, 18, 1022.
19. (a) Schelenz, T.; Scha¨fer, W. Zur physikalisch-chemischen charakterisierung von
5-amino-1-aryl-1H-tetrazolen: Elektronische molekulparameter aus der thermischen iso-
¨
merisierung zu 5-arylamino-1H-tetrazolen. J. Prakt. Chem. 2000, 342, 197; (b) Katritzky,
A. R.; Jain, R.; Petrukhin, R.; Denisenko, S.; Schelenz, T. Qsar correlations of the
algistatic activity of 5-amino-1-aryl-1H-tetrazoles. SAR QSAR Environ. Res. 2001, 12, 259.
20. (a) Goljer, I.; Svetlik, J.; Hrusovsky, I. 13C-NMR of substituted tetrazoles. Monatsh.
Chem. 1983, 114, 65.