New synthesis of [1,3,4] thiadiazolo [2,3-c][1,2,4] triazinone; transfer of active electron by microwaves

Article abstract of DOI:10.1080/10426500214296

Reaction of various aromatic aldehydes with 4-amino-6-methyl-1,2,4-triazin-5-one supported on to montmorillonite-K10 in the presence of nitrobenzene under microwaves irradiation, afforded the corresponding [1,3,4] thiadiazole [2,3-c][1,2,4]-triazinones.

Full text of DOI:10.1080/10426500214296

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New Synthesis of [1,3,4] Thiadiazolo [2,3-C][1,2,4]
Triazinone; Transfer of Active Electron by Microwaves
S. H. Abdi Oskooie a , M. M. Heravi a , P. Khosrofar a & F. Faridbod a
a Department of Chemistry, School of Science , Azzahra University , Vanak, Tehran, Iran
Published online: 27 Oct 2010.
To cite this article: S. H. Abdi Oskooie , M. M. Heravi , P. Khosrofar & F. Faridbod (2002) New Synthesis of [1,3,4] Thiadiazolo
[2,3-C][1,2,4] Triazinone; Transfer of Active Electron by Microwaves, Phosphorus, Sulfur, and Silicon and the Related
Elements, 177:10, 2399-2402, DOI: 10.1080/10426500214296
To link to this article: http://dx.doi.org/10.1080/10426500214296
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Phosphorus, Sulfur and Silicon, 2002, Vol. 177:2399–2402
C
Copyright 2002 Taylor & Francis
1042-6507/02 $12.00 + .00
DOI: 10.1080/10426500290110450
NEW SYNTHESIS OF [1,3,4] THIADIAZOLO
[2,3-C][1,2,4] TRIAZINONE; TRANSFER OF ACTIVE
ELECTRON BY MICROWAVES
S. H. Abdi Oskooie, M. M. Heravi, P. Khosrofar, and F. Faridbod
Department of Chemistry, School of Science, Azzahra University,
Vanak, Tehran, Iran
(Received December 11, 2001; accepted January 29, 2002)
Reaction of various aromatic aldehydes with 4-amino-6-methyl-1,2,4-
triazin-5-one supported on to montmorillonite-K10 in the presence of
nitrobenzene under microwaves irradiation, afforded the correspond-
ing [1,3,4] thiadiazole [2,3-c][1,2,4]-triazinones.
Keywords: Aromatic aldehydes; electron transfer; microwave irradia-
tion; thiadiazolotriazine
INTRODUCTION
[1,3,4] Thiadiazolo [2,3-c][1,2,4] triazines constitute a class of com-
pounds that is interesting from the view point of chemical reactivity
and biological activity.1–5 Reaction of 4-amino-6-methyl-1,2,4-triazin-
5-one 1 (R1 = Me) with a variety of carboxylic acids in phosphorus
oxychloride has afforded 2-substituted, [1,3,4] thiadiazolo [2,3-c][1,2,4]
triazine-4-one 3.6,7 1 also has been reacted with a variety of carboxylic
acids in the presence of sulfuric acid to give 3 in good to high yields.8,9
Microwave irradiation in organic synthesis presently is used widely.
Its application in the case of inorganic solid supported reactions recently
has been reported.10 Solvent free organic reactions or dry media tech-
niques under microwave irradiation are one of main topics of research
in our laboratory.11–13 The use of microwave iradiation in the formation
of radical-cation in oxidation of benzothiazolines to benzothiazole has
been recently reported.14
Azzahra University Research Council is gratefully acknowledged for its Financial
support.
Address correspondence to S. H. Abdi Oskooie, Department of Chemistry, School of
Science, Azzahra University, Vanak, Tehran, Iran.
2399

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S. H. Abdi Oskooie et al.
Armed with these experiences in this communication we report a new
route to thiadiazolo [2,3-c][1,2,4] triazinones starting from aromatic
aldehydes.
RESULTS AND DISCUSSION
As mentioned above the synthetic route to [1,3,4] thiadiazolo
[2,3-c][1,2,4] triazinone has been achieved through condensation and
ring closure of 3-thio-4-amino-1,2,4-trazin-5-one 115 and a variety of
carboxylic acids. Phosphours oxychloride and sulfuric acid have been
used as dehydrating agents.6–9 In contrast to this procedure, we at-
tempted to use aldehyde and an oxidizing agent in an one pot reaction
to obtain 1,3,4-thiadiazolo[2,3-c][1,2,4] triazinone.
Treatment of 1 (R = Me) with benzaldehyde in the presence of
nitrobenzene did not give either the cyclized product 2 or the cyclized
and aromatized product 3. The isolated product was only the imine 4
(Scheme 1).
However, when a mixture of 1, benzaldehyde and nitrobenzene were
irradiated by microwave in the presence of montmorillonite K-10 the
corresponding thiadiazolo [2,3-c][1,2,4] triazinone 3 (R = Me, R1 = ph)
was obtained in 58% yield (Scheme 1). When montmorillonite K-10 was
exchanged with silica gel, in the same condition, the yield of the reaction
decreased to 23%.
To establish the generality of the method, a variety of aromatic alde-
hydes were used to obtain different substituted 3 (Table I). It is note-
worthy to mention that this reaction is not successful with aliphatic
aldehydes and thus it can be considered to be limited to aromatic
aldehyde.
SCHEME 1

Transfer of Active Electron by Microwaves
2401
TABLE I Physical Properties and Yields of the Prepared 3
R
R1
MP( C)
MP(C lit)7
Yield(%)
CH3
CH3
CH3
CH3
CH3
Ph
268
214
224
231
268
265
215
227
230
270
56
58
62
51
50
p-CH3C6H4
p-CH3OC6H4
p-ClC6H4
p-NO2C6H4
Most probably the above reaction proceeds through formation of rad-
ical cations. Microwave irradiation has caused the electron transfer.
Montmorillonite K-10 probably facilitates the transfer of electrons by
generating an electric field 16 and water molecules prevent the reverse
of electron transfer17 (Scheme 2).
SCHEME 2
In conclusion we have introduced a simple one-pot synthesis of [1,3,4]
thiadiazolo [2,3-c][1,2,4] triazinone starting from aromatic aldehydes.
The reaction conditions are mild and relatively eco-friendly. The yields
of reactions are good to high. Solvent free condition and using mi-
crowave irradiation has apparently facilitated the electron transfer
and water molecules have prevented the reverse of electron transfer
processes.
EXPERIMENTAL
All products are known compounds and were identified by comparison
of their physical data with those of authentic samples.

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S. H. Abdi Oskooie et al.
SYNTHESIS OF THIADIAZOLO [2,3-C][1,2,4]
TRIAZIN-4-ONES, TYPICAL PROCEDURE
6-Methyl-3-thio-4-amino-1,2,4-triazin-5-one (10 mmol), benzaldehyde
(20 mmol) and nitrobenzene (10 ml) were mixed with montmorillonite
K-10 (1 g) to make an intimate mixture in a flask. The flask was placed
in a house hold microwave oven and irradiated for 15 min 3 times with
an interval of 5 min. The reaction mixture was filtered, washed with
chloroform, and from the filtrate the solvent distilled off to dryness. The
residue was triturated with dilute sodium hydroxide solution to remove
unreacted product. The solid residue was crystallized from acetic acid
to afford the corresponding [1,3,4] thiadiazolo [1,2,4] triazine (Table I).
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