H14[NaP5W30O110] as a Heterogeneous Recyclable Catalyst for the Synthesis of 6,8-Dimethyl-3-aryl-[1,2, 4]triazolo[3,4-b][1,3,4]thiazepine Derivatives

Article abstract of DOI:10.1080/00397910903161785

6,8-Dimethyl-3-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiazepine derivatives were synthesized by cyclodehydration of 3-aryl-4-amino-5-mercapto-1,2,4-triazole with 2,4-pentanedione in the presence of a catalytic amount of Preyssler catalyst under very mild conditions. Copyright

Full text of DOI:10.1080/00397910903161785

This article was downloaded by: [Stony Brook University]
On: 07 October 2014, At: 07:10
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
H14[NaP5W30O110] as a Heterogeneous
Recyclable Catalyst for the Synthesis of
6,8-Dimethyl-3-aryl-[1,2,4]triazolo[3,4-
b][1,3,4]thiazepine Derivatives
Rahim Hekmatshoar a , Sodeh Sadjadi a , Samaheh Sadjadi a , Majid
M. Heravi a & Fatemeh F. Bamoharram b
a Department of Chemistry , School of Science, Alzahra University ,
Vanak, Tehran, Iran
b Department of Chemistry, School of Sciences , Azad University ,
Khorasan Branch, Mashad, Iran
Published online: 17 May 2010.
To cite this article: Rahim Hekmatshoar , Sodeh Sadjadi , Samaheh Sadjadi , Majid M. Heravi &
Fatemeh F. Bamoharram (2010) H14[NaP5W30O110] as a Heterogeneous Recyclable Catalyst for the
Synthesis of 6,8-Dimethyl-3-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiazepine Derivatives, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
40:12, 1778-1783, DOI: 10.1080/00397910903161785
To link to this article: http://dx.doi.org/10.1080/00397910903161785
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Synthetic Communications1, 40: 1778–1783, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903161785
H14[NaP5W30O110] AS A HETEROGENEOUS
RECYCLABLE CATALYST FOR THE SYNTHESIS
OF 6,8-DIMETHYL-3-ARYL-[1,2,4]TRIAZOLO[3,4-b]
[1,3,4]THIAZEPINE DERIVATIVES
Rahim Hekmatshoar,1 Sodeh Sadjadi,1 Samaheh Sadjadi,1
Majid M. Heravi,1 and Fatemeh F. Bamoharram2
1Department of Chemistry, School of Science, Alzahra University, Vanak,
Tehran, Iran
2Department of Chemistry, School of Sciences, Azad University, Khorasan
Branch, Mashad, Iran
6,8-Dimethyl-3-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiazepine derivatives were synthesized
by cyclodehydration of 3-aryl-4-amino-5-mercapto-1,2,4-triazole with 2,4-pentanedione in
the presence of a catalytic amount of Preyssler catalyst under very mild conditions.
Keywords: 3-Aryl-4-amino-5-mercapto-1,2,4-triazole; heteropolyacids; 2,4-pentanedione; Preyssler
catalyst
INTRODUCTION
In recent years, some fused heterocycles have been found to possess many
unique properties in the synthesis of condensed S-triazole heterocycles and have
attracted a great deal of attention from chemists and pharmacologists because of
their broad spectra of biological activities such as antifungal, antibacterial, hypoten-
sive, and central nervous system–depressant activities.[1] Various methods have been
reported for the synthesis of fused heterocyclic compounds using mineral acids such
as H2SO4 and polyphosphoric acid.
These catalysts have their own disadvantages and drawbacks. They generate
pollution, require great care in handling, have safety issues, cause corrosion, and
need tedious workup procedures. Strong solid acids and solid acids based on sup-
ported transition-metal oxides are suitable for replacement of liquid acids to decrease
these disadvantages.[2]
Recently, Nizamuddin et al. prepared some substituted 1,2,4-triazolo[3,4-b]-
[1,3,4]thiadiazepines (II) by cyclodehydration of 3-aryl-4-amino-5-mercapto-1,2,4-
triazole (I) with 2,4-pentanedione by refluxing in acetic acid.[3] All compounds were
screened[3] for their fungicidal activity against Aspergillus niger and Helminthosporium
Received April 19, 2009.
Address correspondence to Rahim Hekmatshoar, Department of Chemistry, School of Science,
Alzahra University, Vanak, Tehran, Iran. E-mail: rhekmatus@yahoo.com
1778

6,8-DIMETHYL-3-ARYL-[1,2,4]TRIAZOLO[3,4-b][1,3,4]THIAZEPINE DERIVATIVES 1779
oryzae at 1000, 100, and 10 ppm. In general, all compounds showed moderate activity.
The greatest antifungal activity was observed only in compound IIa.
Heteropolyacids (HPAs), supported or in bulk form, are very interesting solid
acid catalysts and can act as green and ecofriendly catalysts. HPAs are widely used
as catalysts for the synthesis of fine and specific chemicals.[4] Being stronger acids,
they generally exhibit higher catalyst activities than conventional catalysts such as
mineral acids, ion exchange resins, mixed oxides, and zeolites.
Catalysis by HPAs and related compounds is a field of increasing importance
worldwide. The reactions in which they can be used, from dehydration, cyclization,
and esterification to amine oxidation and olefin epoxidation, find wide application in
industrial chemical production, such as fragrances, pharmaceuticals, and foods.[5–8]
The application of Preyssler catalyst is mostly limited, and only a few demonstra-
tions of catalytic activity have been reported.[9] The important advantages of this
HPA are strong Brønsted acidity with 14 acidic protons, high thermal stability, high
hydrolytic stability (pH 0–12), reusability, safety, little waste, easy separability, low
corrosiveness, high oxidation potential, and environmental friendliness along with its
unique structure.
Recently, we have explored the application of the Preyssler catalyst in various
organic reactions.[10,11] In this article, we report an improved catalytic and general
approach for the synthesis of 6,8-dimethyl-3-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiazepine
derivatives, using Pressyler’s anion (Scheme 1).
The performance of this catalyst as pure acid and supported on silica was
compared with a Keggin type, H3[PW12O40], and traditional acids in homogeneous
conditions.
The reactions were in most cases completed within 1.5 h as evidenced by thin-
layer chromatography (TLC). The effect of temperature was studied by carrying out
the model reaction in solvent-free condition and at different temperatures in the
presence of these catalysts (room temperature, 45, and 90 ꢀC). Interestingly, in the
presence of classical acids such as H2SO4, only a trace of product was observed at
45 ꢀC. When these reactions were carried out at 90 ꢀC, the products were obtained
in moderate yields. In the presence of HPAs as pure acid and in supported form,
it was observed (Table 1) that yield is a function of temperature; the yield increased
as the reaction temperature was raised.
The results showed that the greatest yields of the products were achieved when
H14[NaP5W30O110] was used as catalyst. Comparison of the catalysts in Table 1
showed that H14[NaP5W30O110] is the catalyst of choice. Comparison of supported
and unsupported catalysts showed that, in all cases, the supported polyacid is less
active than the unsupported one. One plausible interpretation of this observation
Scheme 1. Synthesis of 6,8-dimethyl-3-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiazepine derivatives.

1780
R. HEKMATSHOAR ET AL.
Table 1. Catalytic synthesis of 6,8-dimethyl-3-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiazepine (IIa) with 3-aryl-
4-amino-5-mercapto-1,2,4-triazole (Ia) and 2,4-pentanedione (refluxed at 45 and 90 ꢀC for 1.5 h in solvent-
free conditions) and the comparison of efficiency of HPAs in synthesis of 6,8-dimethyl-3-aryl-[1,2,4]
triazolo[3,4-b][1,3,4]thiazepine (IIa) after four times
Percentage yield
90 ꢀC
Entry
Catalyst
45 ꢀC
1
2
3
4
1
2
3
4
5
6
H
14[NaP5W30O110
]
65
58
87
85
78
71
68
61
85
83
75
69
—
—
83
80
72
66
—
—
80
78
70
64
—
—
H14[NaP5W30O110]=SiO2
H3PW12O40
51
46
H3PW12O40=SiO2
H2SO4
H2SO4=SiO2
Trace
Trace
is that in the supported type, there are polyanion–support interactions of an acid–
base nature. Some protons of the polyacid and some basic sites of the support (for
example, hydroxyl groups) can interact. This would lead to diminished availability
of hydrogens as a result of this extra ionic interaction.[12] Interestingly, this beha-
vior is similar to that of Keggin HPAs. However, when H3[PW12O40] was used
instead of H14[NaP5W30O110], the yield of product was decreased. The results point
out that the catalytic effectiveness may be enhanced as the number of tungsten
atoms (or the number of protons) is increased. Both possibilities stand to reason.
The larger number of protons may lower the activation barrier for the cycloconden-
sation reaction. In addition, the large anion also provides many sites on the
oval-shaped molecule that are likely to render the catalyst effective. Interestingly,
the comparison of Preyssler’s anion, with its exclusive properties, with Keggin
HPA, H2SO4, and supported silica sulfuric acid showed that the activity is the most
for H14[NaP5W30O110]. The catalytic activity is increased in the following order:
H14[NaP5W30O110] > H14[NaP5W30O110]=SiO2 > H3[PW12O40] > H3[PW12O40]=SiO2 >
H2SO4 > H2SO4=SiO2.
To establish the generality of this method, we investigated the cyclocondensa-
tion of various substituted 3-aryl-4-amino-5-mercapto-1,2,4-triazole with 2,4-
pentanedione. The reaction of various 3-aryl-4-amino-5-mercapto-1,2,4-triazole with
2,4-pentanedione afforded the corresponding 6,8-dimethyl-3-aryl-[1,2,4]triazolo[3,4-b]-
[1,3,4]thiazepine derivatives in 78–93% yields (Table 2). The reaction was compatible
with various electron-donating (Me and OMe) and electron-withdrawing (Cl and
NO2) substituents.
Consequently, we investigated the catalytic activity of recycled Preyssler catalyst
in the reaction of 3-aryl-4-amino-5-mercapto-1,2,4-triazole and 2,4-pentanedione.
The catalyst was filtered from the reaction, washed with diethyl ether, and dried in
an oven. It could be reused without appreciable loss of activity.
As shown in Table 1, Preyssler catalyst could be reused at least four
times without significant loss of activity. Our experiments exhibited that the
infrared (IR) spectrum of the used Preyssler catalyst was consistent with that of
the unused one.

6,8-DIMETHYL-3-ARYL-[1,2,4]TRIAZOLO[3,4-b][1,3,4]THIAZEPINE DERIVATIVES 1781
Table 2. Synthesis of IIa–e under different reaction conditions in the reaction of 3-aryl-4-amino-
5-mercapto-1,2,4-triazole and 2,4-pentanedione
Entry
Compound
R
Method A yield (%)
Method B[7] yield (%)
Mp (ꢀC)[7]
1
2
3
4
5
IIa
IIb
IIc
IId
IIe
4-Cl
4-NO2
4-CH3
3-CH3
3-OCH3
87
90
89
78
93
68
70
64
59
82
152
110
64
118
178
Notes. Method A: refluxed at 90 ꢀC for 1.5 h in solvent-free conditions in the presence of Preyssler
catalyst. Method B: refluxed in acetic acid for 4 h.
Finally, the efficacy of the present method for the synthesis of 6,8-dimethyl-3-
aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiazepine derivatives was compared with other
reported procedures (Table 2).[3] It revealed that H14[NaP5W30O110] is an efficient,
environmentally benign catalyst in the synthesis of 6,8-dimethyl-3-aryl-[1,2,4]triazolo
[3,4-b][1,3,4]thiazepine derivatives.
In summary, we describe a convenient and efficient protocol for the synthesis of
6,8-dimethyl-3-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiazepine derivatives via condensation
of 3-aryl-4-amino-5-mercapto-1,2,4-triazole with derivatives with 2,4-pentanedione
using H14[NaP5W30O110] as a green recyclable and heterogeneous catalyst (Table 2).
The simple experimental procedure combined with ease of recovery and reuse of this
catalyst make this procedure quite simple, more convenient, and environmentally
benign.
EXPERIMENTAL
Catalyst Preparation
Phosphotungstic acid and molybdophosphoric acid were purchased from
Merck Company. H3PW12O40=SiO2 was prepared by the known procedure.[13]
Preyssler-type HPA was prepared by passage of a solution of the potassium
salt in water through a column (50 cm ꢁ 1 cm) of Dowex 50 W ꢁ 8 in the Hþ form
and evaporation of the elute under a vacuum.
Supported HPA catalyst was synthesized according to our previous report[14]
by impregnating a support in the form of powder (SiO2) with an aqueous solution
of the H14-P5 (50% equivalent weight). After stirring the mixture, the solvent was
evaporated, and the catalyst was dried at 120 ꢀC and calcinated at 250 ꢀC in a furnace
prior to use.
Typical Experimental Procedure
The starting compounds 3-aryl-4-amino-5-mercapto-1,2,4-triazole (I) were
prepared by employing our published procedures.[15] A mixture of 3-aryl-4-amino-
5-mercapto-1,2,4-triazole (I, 1 mmol), 2,4-pentanedione (1 mmol), and catalyst
(0.01 mmol) was refluxed at 90 ꢀC for 1.5 h in solvent-free condition. After completion
of the reaction, the mixture was cooled and diluted with chloroform, and the catalyst

1782
R. HEKMATSHOAR ET AL.
was removed by simple filtration (the catalyst is not soluble in chloroform). After
evaporation of solvent, the reaction mixture was poured over cold water with stirring.
The resulting solid was filtered, washed with cold water, and recrystallized from
ethanol.
All products were known and characterized by comparison of their physical
and spectra data with those already reported.[3]
ACKNOWLEDGMENT
The authors are thankful to Alzahra Research Council for the partial financial
support.
REFERENCES
1. Eweiss, N. F.; Bahajaj, A. A. Synthesis of heterocycles, part VII: Synthesis and antimicrobial
activity of some 7H-s-triazolo[3,4-b][1,3,4]thiadiazine and s-triazolo[3,4-b][1,3,4]thiadiazole
derivatives. J. Heterocycl. Chem. 1987, 24, 1173–1182.
2. (a) Heravi, M. M.; Kivanloo, A.; Rahimzadeh, M.; Bakavoli, M.; Ghassemzaeh, M.
Pd–Cu–catalyzed heterocyclization during Sonogashira coupling: Synthesis of
3-benzylthiazolo[3,2-a]benzimidazole. Tetrahedron Lett. 2004, 45, 5747–5749; (b) Heravi,
M. M.; Kivanloo, A.; Rahimzadeh, M.; Bakavoli, M.; Ghassemzaeh, M.; Neumuller, B.
¨
Regioselective synthesis of 6-benzylthiazolo[3,2-b]1,2,4-triazoles during Sonogashira
coupling. Tetrahedron Lett. 2005, 46, 1607–1610.
3. Tiwari, N.; Singh, K.; Nizamuddin, N. Synthesis of [1,2,4]-triazolo[3,4-b][1,3,4]thiadiaze-
pines and [1,2,4]triazolo[3,4-b][1,3,4]benzothiadiazocines. Indian J. Heterocycl. Chem.
1993, 2, 195–198.
4. Mizuno, N.; Misono, M. Heteropolyanions in catalysis. J. Mol. Catal. 1994, 86, 319–342.
5. Izumi, Y.; Urabe, K.; Onaka, M. Zeolite, Clay, and Heteropoly Acid in Organic Reactions;
Kadansha: Tokyo, 1992.
6. Kozhevinkov, I. V. Catalysis by heteropoly acids and multicomponent polyoxometalates
in liquid-phase reactions. Chem. Rev. 1998, 98, 171–198.
7. (a) Kozhevinkov, I. V. Catalysis for fine chemicals. In Catalysis by Polyoxometalates;
John Wiley and Sons: New York, 2002; (b) Misono, M.; Nojiri, N. Recent progress in
catalytic technology in Japan. Appl. Catal. 1990, 64, 1–30.
8. Timofeeva, M. N. Acid catalysis by heteropoly acids. Appl. Catal. 2003, 256, 19–35.
9. Harrup, M. K.; Hill, C. L. Polyoxometalate catalysis of the aerobic oxidation of hydrogen
sulfide to sulfur. Inorg. Chem. 1994, 33, 5448–5455.
10. (a) Bamoharram, F. F.; Heravi, M. M.; Roshani, M.; Jahangir, M.; Gharib, A. Preyssler
catalyst, [NaP5W30O110]
14ꢂ: A green, efficient, and reusable catalyst for esterification of
salicylic acid with aliphatic and benzylic alcohols. Appl. Catal. 2006, 302, 42–47;
(b) Bamoharram, F. F.; Heravi, M. M.; Roshani, M.; Gharib, A.; Jahangir, M. A catalytic
method for synthesis of c-butyrolactone, e-caprolactone, and 2-cumaranone in the
presence of Preyssler’s anion, [NaP5W30O110]
14ꢂ, as a green and reusable catalyst. J.
Mol. Catal. 2006, 252, 90–95.
11. (a) Heravi, M. M.; Motamedi, R.; Seifi, N.; Bamoharram, F. F. Catalytic synthesis of
6-aryl-1H-pyrazolo[3,4-d]pyrimidin-4[5H]-ones by heteropolyacid: H14[NaP5W30O110
]
and H3PW12O40. J. Mol. Catal. 2006, 249, 1–3; (b) Heravi, M. M.; Bakhtiari, K.;
Bamoharram, F. F. 12-Molybdophosphoric acid: A recyclable catalyst for the synthesis
of Biginelli-type 3,4-dihydropyrimidine-2(1H)-ones. Catal. Commun. 2006, 7, 373–376;

6,8-DIMETHYL-3-ARYL-[1,2,4]TRIAZOLO[3,4-b][1,3,4]THIAZEPINE DERIVATIVES 1783
(c) Bamoharram, F. F.; Heravi, M. M.; Roshani, M.; Takakoli, N. N-Oxidation of
pyridine carboxylic acids using hydrogen peroxide catalyzed by a green heteropolyacid
catalyst: Preyssler’s anion, [NaP5W30O110]
14ꢂ. J. Mol. Catal. 2006, 252, 219–225; (d)
Heravi, M. M.; Bakhtiari, K.; Bamoharram, F. F. An efficient and chemoselective
synthesis of acylals from aromatic aldehydes and their regeneration, catalyzed by
12-molybdophosphoric acid. Catal. Commun. 2006, 7, 499–501.
12. Lefebvre, F. 31P MAS NMR study of H3PW12O40 supported on silica: Formation of
(ꢃSiOHþ2 )(H2PW12O4ꢂ0). J. Chem. Soc., Chem. Commun. 1992, 10, 756–757.
13. Kozhevnikov, I. V.; Kloetstra, K. R.; Sinnema, A.; Zandbergen, H. W.; Van Bekkum, H.
Study of catalysts comprising heteropoly acid H3PW12O40 supported on MCM-41
molecular sieve and amorphous silica. J. Mol. Catal. 1996, 114, 287–298.
14. Alizadeh, M. H.; Razavi, H.; Bamoharram, F. F.; Hassanzadeh, M. K. Novel catalytic
acetylation of alcohols with Preyssler’s anion, [NaP5Wa30O110]
14ꢂ1. Kinet. Catal. 2003,
44, 524–528.
15. (a) Sharfi, T.; Heravi, M. M.; Ghassemzadeh, M.; Neumuller, B. Synthesis, characterization,
and crystal structure of the dimeric silver(I) complex containing 4-amino-5-methyl-2H-
1,2,4-triazole-3(4H)-thione. Z. Anorg. Allg. Chem. 2005, 631, 2297–2299; (b) Ghassemzadeh,
M.; Tabatabaee, M.; Pouramin, M. M.; Heravi, M. M.; Eslami, A.; Neumuller, B. Synthesis
and characterization of a novel 1,2,4-thiotriazine derivative (CAMTTO), and copper(I) and
silver(I) complexes thereof (CAMTTO¼ {(4-[(4-chlorobenzylidene)-amino]-6-methyl-3-
thioxo-[1,2,4]-triazin-3,4-dihydro(2H)-5-one)}. Z. Anorg. Allg. Chem. 2006, 632, 786–792.