Facile conversion of acyldiithiocarbazinate salts to 1,3,4-oxadiazole derivatives under microwave irradiation

Article abstract of DOI:10.1081/SCC-120001516

Microwave irradiation is found to be especially suitable for salts, as illustrated by the conversion of acyldithocarbazinate salts 1 to 5-substituted-2-mercapto 1,3,4-oxadiazoles 2. This method reduced the reaction time to a few seconds.

Full text of DOI:10.1081/SCC-120001516

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FACILE CONVERSION OF ACYLDIITHIOCARBAZINATE
SALTS TO 1,3,4-OXADIAZOLE DERIVATIVES UNDER
MICROWAVE IRRADIATION
a
Sachin Joshi & A. V. Karnik
a
Department of Chemistry, University of Mumbai , Vidyanagari, Kalina, Mumbai, 400
098, India
Published online: 21 Aug 2006.
To cite this article: Sachin Joshi & A. V. Karnik (2002) FACILE CONVERSION OF ACYLDIITHIOCARBAZINATE SALTS TO 1,3,4-
OXADIAZOLE DERIVATIVES UNDER MICROWAVE IRRADIATION, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 32:1, 111-114, DOI: 10.1081/SCC-120001516
To link to this article: http://dx.doi.org/10.1081/SCC-120001516
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SYNTHETIC COMMUNICATIONS, 32(1), 111–114 (2002)
FACILE CONVERSION OF
ACYLDIITHIOCARBAZINATE SALTS
TO 1,3,4-OXADIAZOLE DERIVATIVES
UNDER MICROWAVE IRRADIATION
Sachin Joshi and A. V. Karnik*
Department of Chemistry, University of Mumbai,
Vidyanagari, Kalina, Mumbai-400 098, India
ABSTRACT
Microwave irradiation is found to be especially suitable for
salts, as illustrated by the conversion of acyldithocarbazinate
salts 1 to 5-substituted-2-mercapto 1,3,4-oxadiazoles 2. This
method reduced the reaction time to a few seconds.
The rapid heating effect of microwave irradiation has caught the atten-
tion of synthetic chemists in the recent times due to the remarkable reduc-
1
–3
tion of reaction time. The dielectric heating effect is suitable to substrates
with a permanent dipole. Synthesis of heterocycles necessarily involve the
use of polar substrates and hence the microwave dielectric heating is
4
–6
reportedly to give excellent results for the same. It is therefore reasonable
to expect polar salts to become ideal receptors and benefit the most from the
novel thermal-dielectric heating route.
*
Corresponding author. Fax: 91-22-6528547; E-mail: avkarnik@chem.mu.ac.in
11
1
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

ORDER
REPRINTS
1
12
JOSHI AND KARNIK
5-Substituted-2-mercapto-1,3,4-Oxadiazoles, 2, are important biologi-
cally active compounds. 1,3,4-Oxadizoles are known to exhibit antimalar-
7
8
ial, nematocidal, antimicrobial
9,10
activities and also have other important
medicinal properties. Potassium salt of 2-acyldithiocarbazinic acids 1 are
1
1
1
2
known to give the 5-Substituted-2-mercapto-1,3,4-Oxadiazoles 2. The
synthesis of 5-Substituted-2-mercapto-1,3,4-Oxadiazoles, 2, 5-Substituted-
2-mercapto-1,3,4-Oxadiazoles, 2, from acyldithocarbazinate salts 1 seemed
ideal for the microwave dielectric heating considering the polar nature of the
1
than the conventional thermal method.
. Microwave irradiation gave dramatic reduction in time with better yields
1
2
Scheme.
When the classical heating was employed for conversion of 1 to 2 in
pyridine, required about 30 min. The same reaction under microwave irra-
diation was found to take place in just 30 s by using DMF and DMSO as
solvents and 120 s in case of Pyridine. The yields obtained were satisfactory
(69% to 84%). Thus reaction time has been reduced by 60 folds when
conventional heating is replaced by microwaves. (Table)
In summary, the salts as expected gave very rapid conversion to the
desired products. It has also been observed that dipolar-aprotic, high boiling
1
3
solvents (DMF & DMSO) gave better results compared to pyridine
Table). The microwave irradiation is seen to be a simple and convenient
(
methodology for synthesis of heterocyclic systems with polar starting
materials such as salts.
EXPERIMENTAL
2-Mercapto-5-phenyl-1,3,4-oxadiazole (2a): Potassium-3-benzoyldithio-
carbazinate (500 mg, 2.0 mmole) and 2 ml solvent (DMF/DMSO) were
irradiated to microwaves for 30 s. The reaction mixture was diluted with
water and acidified with conc. HCl. The solid precipitated out was washed
with water dried and crystallized from alcohol. The melting point of the

ORDER
REPRINTS
1
,3,4-OXADIAZOLE DERIVATIVES
113
Table. Data for the Synthesis of 2-Mercapto-5-substituted-1,3,4-oxadiazoles Under
Microwave Irradiation
MWI DMF
Time 30 s
Yield %
MWI DMSO
Time 30 s
Yield %
MWI Pyridine
Time 120 s
Yield %
M.P.
ꢀ
Entry
R
( C)
a
b
c
d
e
f
g
h
i
Ph
4-ClC
21870
175
170
150
204
205
230
20874
125
72
69
6
H
4
4
72
80
70
81
80
84
76
78
71
80
75
82
71
72
70
78
73
76
2-ClC H
6
4-CH
4-OCH
3
C
6
H
4
3
C
6
H
4
3-CH C H
4
3
6
4-Pyridyl
4-OHC
C H CH
2
6
H
4
72
71
74
72
72
6
5
MWI: Microwave irradiation.
All the compounds were characterized on the basis of physical constants, IR and
(
1
H NMR spectroscopy; where appropriate data were in agreement with literature
values).
ꢀ
12
ꢀ
compound obtained was 218 C (lit m.p. 218ꢁ9 C) yield obtained was
2
50 mg (70%).
ꢁ1
Its IR (KBr) spectrum shows peaks at 3150 cm , 2950 cm ,
ꢁ
1
ꢁ
1
ꢁ1
1
1
610 cm , 1500 cm . H NMR (CDCl þ DMSO) spectrum showed sig-
3
nals at d 12.04 (s, 1H, SH), d 7.3–7.9 (m, 5H, Ar-H).
By following similar procedure remaining compounds 2b–2i were
synthesised.
REFERENCES
1. Saber Chatti; Michael Bortolussi; Andre Loupy Tetrahedron Lett. 2000,
41, 3367–3370.
2
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J.J. Synlett 1998, 147.
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4

ORDER
REPRINTS
1
14
JOSHI AND KARNIK
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8
9
. Hutt, M.P.; Elslager, E.F.; Werbal, L.M.; J. Heterocycl. Chem. 1970,
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(
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14. In a typical experiment acyldithiocarbazinate (2.5 mmol) was taken in
2
ml solvent (DMF/DMSO/Pyridine) and irradiated to microwaves for
the time described (Table). A commercial microwave oven with 900 W
power output was used. The reaction mixture on acidification with
conc. HCl gave corresponding solid, which was crystallized to afford
pure product.
Received in the Netherlands February 28, 2001

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