Facile method for the conversion of semicarbazones/thiosemicarbazones into azines (Under Microwave Irradiation) and oxadiazoles (By Grinding)

Article abstract of DOI:10.1080/00397911.2010.515334

In an effective transformation, semicarbazones/thiosemicarbazones are smoothly converted into azines under microwave irradition. Oxadiazoles are also obtained from semicarbazones by reaction with bromine generated in situ via a grinding reaction in the solid phase. Taylor &Francis Group, LLC.

Full text of DOI:10.1080/00397911.2010.515334

This article was downloaded by: [McGill University Library]
On: 06 October 2012, At: 10:04
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
Facile Method for the Conversion of
Semicarbazones/Thiosemicarbazones
into Azines (Under Microwave
Irradiation) and Oxadiazoles (by
Grinding)
Gautam Chattopadhyay a & Partha Sinha Ray a
a Postgraduate Department of Chemistry, Presidency College,
Kolkata, India
Version of record first published: 29 Jun 2011.
To cite this article: Gautam Chattopadhyay & Partha Sinha Ray (2011): Facile Method for the
Conversion of Semicarbazones/Thiosemicarbazones into Azines (Under Microwave Irradiation)
and Oxadiazoles (by Grinding), Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 41:17, 2607-2614
To link to this article: http://dx.doi.org/10.1080/00397911.2010.515334
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
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.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,

demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Synthetic Communications1, 41: 2607–2614, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.515334
FACILE METHOD FOR THE CONVERSION OF
SEMICARBAZONES/THIOSEMICARBAZONES INTO
AZINES (UNDER MICROWAVE IRRADIATION) AND
OXADIAZOLES (BY GRINDING)
Gautam Chattopadhyay and Partha Sinha Ray
Postgraduate Department of Chemistry, Presidency College, Kolkata, India
GRAPHICAL ABSTRACT
Abstract In an effective transformation, semicarbazones/thiosemicarbazones are smoothly
converted into azines under microwave irradition. Oxadiazoles are also obtained from semi-
carbazones by reaction with bromine generated in situ via a grinding reaction in the solid
phase.
Keywords Azines; grinding; microwave; oxadiazoles; semicarbazones
INTRODUCTION
In continuation of our synthetic studies on heterocycles[1] and related method-
ology,[2] and in view of the biological importance of the oxadiazole system,[3–6] we
are interested in synthesizing the 2-amino-5-aryl-1,3,4-oxadiazole for possible incor-
poration in the imidazole ring for an entry into novel purine derivatives.[7] Various
methods are reported in the literature for the oxidation of acyl hydrazones as well as
semicarbazones to 1,3,4-oxadiazoles with various oxidizing agents,[8] including
sodium hypobromite, iodine–potassium iodide in aqueous sodium carbonate, and
lead tetraacetate, and by electrochemical oxidation.
The main drawbacks of these methods include longer reaction times, high tem-
peratures, and difficult workup procedures. Recently, many solventless organic reac-
tions have been studied. In comparison with the reaction in organic solvents, these
reactions are often rapid, occur in good yields, and have environmental and economic
Received April 21, 2010.
Address correspondence to Gautam Chattopadhyay, Postgraduate Department of Chemistry,
Presidency College, Kolkata 700073, India. E-mail: g_chattopadhyay2002@yahoo.co.in
2607

2608
G. CHATTOPADHYAY AND P. S. RAY
Scheme 1. Conversion of semicarbazones=thiosemicarbazones into azines and oxadiazoles.
advantages. Thus, the applications of solid-state organic chemistry (SSOR)[9–14]
coupled with microwave-assisted organic synthesis (MAOS)[15] attracted our atten-
tion, and we proposed to exploit the combined protocol to achieve our goal.
We envisaged that reaction of benzaldehyde-semicarbazone (1, R1 ¼ R2 ¼ H,
X ¼ O) (Scheme 1) with bromine (acting as an oxidant and generated in situ) in
solvent-free conditions under microwave irradiation might afford the required oxa-
diazole derivative. To verify this view, benzaldehyde-semicarbazone was intimately
mixed with potassium bromide, potassium bromate, and oxalic acid dehydrate,
and the mixture was then subjected to microwave irradiation. To our surprise, after
the usual workup of the yellow mixture, benzalazine (2, R1 ¼ R2 ¼ H) was obtained
as a major product together with a very small amount of the desired oxadiazole (3,
R2 ¼ H) (Scheme 1). This serendipitous formation of azine pointed out that the
required cyclization in this condition was not favored, and instead the benzaldehyde
semicarbazone underwent self-condensation to afford the azine. This was supported
by the fact that when the semicarbazone alone or a mixture of benzaldehyde, semi-
carbazide hydrochloride, and sodium acetate (i.e., the semicarbazone formed in situ)
was subjected to microwave irradiation, the same azine was isolated in comparable
yield. Moreover, instead of semicarbazone, when the corresponding thiosemicarba-
zone of benzaldehyde (1, R1 ¼ R2 ¼ H, X ¼ S) was subjected to microwave
irradiation, benzalazine was again obtained in moderate yield. To the best of our
knowledge such deoxygenation of thiosemicarbazone to azine has not been reported
earlier. To generalize this transformation, semicarbazones=thiosemicarbazones of
several carbonyl compounds were subjected to similar treatment under microwave
irradiation (15–20 min) when the respective azines (2) were obtained in good yields.
The identities of the known azines (entries 1–9) were established by comparison
of their physical and spectroscopic data with those reported earlier,[16,17] and the
results are summarized in Table 1.
In the infrared (IR) spectra, an absorption band between 1610 and 1640cmꢀ1
(except entry 12, 1585cmꢀ1) due to the C N group is clearly indicative of the
=

SEMICARBAZONES TO AZINES/OXADIAZOLES
2609
Table 1. Synthesis of azines from thiosemicarbazones=semicarbazones under microwave irradiation
Entry
R1
R2
Yield (%)a
Time (min)
Mp=lit. mp (ꢁC)
1
2
H
H
H
3-NO2
4-OMe
4-Cl
45
57
70
55
45
70
80
76
62
50
70
75
20
16
18
15
20
16
15
15
16
18
15
15
93–94=92–93[17]
195–196=197–199[17]
173–174=174[16]
209–210=207–209[17]
218–220=215[16]
156–158=152–153[17]
217–218=216[16]
125–126=123[16]
162–163=163–165[17]
202–203=—
3
H
4
H
5
H
4-NMe2
4-CH3
2-OH
H
6
H
7
H
8
CH3
Ph
CH3
H
9
H
10
11
12
3-NO2
3,4-diOMe
194–195[16]
2-Acetylthiophene
92–93=—
aYields (isolated) correspond to the products obtained from semicarbazones.
1
formation of azine. In the H NMR spectra of the aldehyde-azines, the CH signal of
=
the CH N appeared around d 8.5–d 8.7 as a singlet. Isolation of the same azine from
either semicarbazone or thiosemicarbazone of a particular aldehyde in identical con-
ditions ruled out the possibility of the isocyanate intermediate documented else-
where,[18] because there is no sulfur analog of carbon monoxide that has to be
eliminated in the final step if the reported mechanism is taken into account. Moreover,
the yields of the products were also not mentioned in the reported observations. This
prompted us to suggest an alternative mechanism for the azine formation, especially
from thiosemicarbazones. It is assumed that the reaction is initiated by the elimination
of HNCS (or HNCO) under microwave conditions from thiosemicarbazone (or semi-
carbazone) (1) to provide the hydrazone (1a) of the parent carbonyl, which then reacts
with another molecule of 1 to afford the azine (2) with concomitant loss of a molecule
of thiosemicarbazide (or semicarbazide) (Scheme 2).
To examine the effect of microwaves in rate enhancement for this deoxygena-
tion, the same reactions were carried out in an oil bath at 250–260 ꢁC, where the reac-
tion took a longer reaction time (30 min) and comparatively very poor yields were
observed, particularly for the semicarbazones of ketones (entries 8–10 and 12) and
for the thiosemicarbazones in general.
The failure to obtain the desired oxadiazole in microwave conditions prompted
us to explore the oxidative cyclizations at room temperature, preferably in the solid
Scheme 2. Mechanistic pathway for azine formation.

2610
G. CHATTOPADHYAY AND P. S. RAY
Table 2. Synthesis of oxadiazole by oxidative cyclisation of semicarbazone by grinding
Entry
R2
Yield (%)
Mp=lit. mp (ꢀC)
1
2
3
4
5
6
7
8
H
4-Me
4-Cl
80
81
241–242=242[8]
260–261=263–264[8]
263–264=260–264[8]
252–253=250–251[8]
275–276
81
80
4-OMe
4-NMe2
3-NO2
4-NO2
3,4 di-OMe
72
96
71
253–254
250–251
268–269
Quantitative
phase using a grinding reaction.[14] As a model study to examine whether solid-phase
generation of bromine is feasible via simple grinding, commercially available acet-
anilide was taken as a substrate. Thus, finely powdered acetanilide was mixed well
with potassium bromide, potassium bromate, and oxalic acid dehydrate, and the
mixture was ground thoroughly in a mortar for a period of 20 min. A pink color
developed, and the whole mixture was then treated with excess of water. The
separated solid was collected by filtration and crystallized from water to afford
p-bromoacetanilide in 70% yield. Identity of the product was established by compari-
son (IR, mixed mp) with the authentic sample. This observation prompted us to
attempt oxidative cyclization of benzaldehyde semicarbazone under similar treat-
ment via in situ generation of bromine. After usual workup (vide Experimental),
the desired product, 2-amino-5-phenyl-1,3,4-oxadiazole (entry 1, Table 2) was
obtained in good yield.
To test the generality of this transformation, several aldehyde-semicarbazones
were subjected to grinding reaction, and the respective 2-amino-5-aryl-1,3,4-oxadia-
zoles were obtained in excellent yields. The results are summarized in Table 2. All the
semicarbazones=thiosemicarbazones required for our purpose were prepared follow-
ing the literature procedure.[19]
Azines constitute an important class of compounds with unexpected biological
activities[20] and are usually prepared from the reaction of aldehydes=ketones with
hydrazine hydrate.[16,17,21] These compounds can also be utilized for useful synthetic
transformations.[22,23] Our method of formation of azines under microwave
irradiation thus will be useful addition to the existing repertoire. Again, keeping in
view the importance of SSOR and biological activity of 1,3,4-oxadiazoles, simple
and efficient oxidative cyclization of semicarbazones via grinding reaction to obtain
2-amino-5-aryl-1,3,4-oxadiazoles assumes importance for our observations. It is per-
tinent to mention that no NMR spectral data has been incorporated in the literature
for the reported oxadiazoles.[8,24] In conclusion, the transformations we
accomplished are interesting and easy methods for the preparation of azines and
oxadiazoles from easily available starting materials involving a single workup step.
EXPERIMENTAL
Melting points were determined in open capillaries and are uncorrected. IR
spectra were recorded in KBr discs on a Shimadzu Fourier transform (FT–IR

SEMICARBAZONES TO AZINES/OXADIAZOLES
2611
8300 spectrophotometer. 1H NMR and 13C NMR spectra were recorded on a Bruker
AV 500 spectrometer in CDCl3 (for azines) and in dimethylsulfoxide (DMSO-d6 for;
oxadiazoles) with tetramethylsilane (TMS) as the internal standard.
General Procedure for the Preparation of Azines: Synthesis of
Acetophenone Azine, (1E,2E)-1,2-Bis(1-phenylethylidene)hydrazine,
from Semicarbazone/Thiosemicarbazone (Entry 8, Table 1)
Powdered semicarbazone=thiosemicarbazone (1 mmol) of acetophenone was
dissolved in methylene chloride and adsorbed on the surface of silica gel (3 g). The
mixture was then taken in a 50-ml Erlenmeyer flask placed in a silica-gel bath inside
a microwave oven (BPL Sanyo BMO-700 T, 2450 MHz, 1200 W) and irradiated for a
period of 15 min (monitored by thin-layer chromatography, TLC), each time for a
pulse of 1 min with 30-s intervals. The reaction mixture was then allowed to attain
room temperature, and the product was purified by short-column chromatography
over silica gel by eluting with ethyl acetate–benzene (1:20). The practically pure
product was further purified by crystallization from ethanol.
General Procedure for the Preparation of 2-Amino-5-aryl-
1,3,4-oxadiazoles by Grinding Reaction: Synthesis of 2-Amino-5-
phenyl-1,3,4-oxadiazole from Benzaldehyde Semicarbazone (Entry
1, Table 2)
A
mixture of semicarbazone (0.25 g, 1.5 mmol), KBr (1 g, 9 mmol),
KBrO3(0.5 g, 3 mmol), and oxalic acid dehydrate (0.5 g, 4 mmol) was intimately
mixed by pestle and mortar at room temperature. The mixture was ground for
20 min and decomposed with an excess of water. The resulting light orange solution
was again stirred for a period of 30 min, and the separated solid was filtered. The
residue was then crystallized from large volume of ethanol to afford the title
compound in white needles.
Representative Spectral Data of Azines
1
=
Entry 3. H NMR d ppm, 8.60 (s, 2H, CH N), 7.77 (d, J ¼ 8.6 Hz, 4H), 6.95
(d, J ¼ 8.6 Hz, 4H), 3.85 (s, 6H, OCH3); 13C NMR d ppm, 162.0 (ꢂ2), 161.0 (ꢂ2),
130.1 (ꢂ 4), 127.0 (ꢂ2), 114.2 (ꢂ 4), 55.3 (ꢂ2).
1
=
Entry 5. H NMR d ppm, 8.56 (s, 2H, CH N), 7.68 (d, J ¼ 8.5 Hz, 4H), 6.70
(d, J ¼ 8.5 Hz, 4H), 3.0 (s, 12H, NMe2); 13C NMR d ppm, 160.7 (ꢂ2), 152.1 (ꢂ2),
129.8 (ꢂ 4), 122.2 (ꢂ2), 111.7 (ꢂ 4), 40.1 (ꢂ 4).
1
=
Entry 6. H NMR d ppm, 8.66 (s, 2H, CH N), 7.75 (d, J ¼ 7.7 Hz, 4H), 7.27
(d, J ¼ 7.7 Hz, 4H), 2.42 (s, 6H, CH3); 13C NMR d ppm, 161.8 (ꢂ2), 141.5 (ꢂ2),
131.5 (ꢂ2), 129.5 (ꢂ 4), 128.5 (ꢂ 4), 21.6 (ꢂ2).
Entry 8. 1H NMR d ppm, 7.88–7.94 (m, 4H, Ar), 7.39–7.46 (m, 6H, Ar), 2.31
(s, 6H, CH3); 13C NMR d ppm, 157.6 (ꢂ2) 138.4 (ꢂ2), 129.5 (ꢂ2), 128.3 (ꢂ 4), 126.5
(ꢂ 4), 15.0 (ꢂ2).

2612
G. CHATTOPADHYAY AND P. S. RAY
Entry 10. 1H NMR d ppm, 8.75 (s, 2H), 8.28 (d, J ¼ 6.5 Hz, 4H), 7.63 (t,
J ¼ 7.8 Hz, 2H), 2.41 (s, 6H, CH3); 13C NMR d ppm, 156.7, 148.5, 139.6, 132.3,
129.4, 124.4, 121.6, 15.1 (all ꢂ2).
1
=
Entry 11. H NMR d ppm, 8.58 (s, 2H, CH N), 7.52 (s, 2H, Ar), 7.22 (d,
J ¼ 8.4 Hz, 2H, Ar), 6.89 (d, J ¼ 8.2 Hz, 2H, Ar), 3.96 (s, 6H, OCH3), 3.92 (s, 6H,
OCH3); 13C NMR d ppm, 161.20, 151.76, 149.33, 127.22, 123.94, 110.62, 108.69,
55.94, 55.92 (all ꢂ2).
Entry 12. 1H NMR d ppm, 7.40 (d, J ¼ 3.5 Hz, 2H), 7.36 (d, J ¼ 5 Hz, 2H),
7.05 (t, J ¼ 4.3 Hz, 2H), 2.43 (s, 6H, CH3); 13C NMR d ppm, 157.2, 144.6, 128.7,
127.5, 127.3, 15.1 (all ꢂ2).
Spectral Data of Oxadiazoles
Entry 1. 1H NMR d ppm, 8.15 (s, 1H), 7.82 (d, J ¼ 7.8 Hz, 2H), 7.37 (d,
J ¼ 7.8 Hz, 2H), 6.94 (2H); 13C NMR d ppm, 163.86, 157.32, 130.31, 129.18 (ꢂ2),
125.00 (ꢂ2), 124.38; IR (KBr): 3287, 3114, 1651, 1618, 1596, 1584, 1561, 1490,
1448, 1298, 1283, 1066, 1023, 965, 916, 767, 737, 687 cmꢀ1
.
Entry 2. 1H NMR d ppm, 7.66 (d, J ¼ 8.1 Hz, 2H), 7.31 (d, J ¼ 7.9 Hz, 2H),
7.17 (s, 2H), 2.34 (s, 3H); 13C NMR d ppm, 164.54, 158.30, 141.07, 130.61 (ꢂ2),
125.88 (ꢂ2), 122.57, 21.86; IR (KBr): 3268, 3092, 1673, 1656, 1605, 1582, 1560,
1504, 1418, 1378, 1296, 1285, 1074, 1031, 1016, 955, 823, 743 cmꢀ1
.
Entry 3. 1H NMR d ppm, 7.79 (d, J ¼ 8.6 Hz, 2H), 7.57 (d, J ¼ 8.6 Hz, 2H),
7.31 (s, 2H); 13C NMR d ppm, 163.98, 156.56, 134.87, 129.32 (ꢂ2), 126.71 (ꢂ2),
123.21; IR (KBr): 3288, 3110, 1661, 1594, 1578, 1486, 1308, 1293, 1276, 1177,
1091, 1040, 1010, 829, 744 cmꢀ1
.
Entry 4. 1H NMR d ppm, 7.72 (d, J ¼ 8.6 Hz, 2H), 7.13 (s, 2H), 7.05 (d,
J ¼ 8.6 Hz, 2H), 3.08 (s, 3H); 13C NMR d ppm, 163.45, 160.75, 157.27, 126.72
(ꢂ2), 116.89, 114.57 (ꢂ2), 55.27; IR (KBr): 3321, 3110, 1673, 1655, 1606, 1503,
1465, 1308, 1258, 1178, 1115, 1075, 1021, 833, 741 cmꢀ1
.
Entry 5. 1H NMR d ppm, 7.60 (d, J ¼ 8.2 Hz, 2H), 6.80 (d, J ¼ 8.2 Hz, 2H),
6.80 (s, 2H), 2.98 (s, 6H); 13C NMR d ppm, 162.94, 157.94, 151.32, 126.25 (ꢂ2),
111.83 (ꢂ2), 111.41, 39.98; IR (KBr): 3310, 3107, 1655, 1616, 1571, 1513, 1370,
1285, 1234, 1202, 1166, 1068, 1031, 953, 811, 741, 684 cmꢀ1
.
Entry 6. 1H NMR d ppm, 8.41 (s, 1H), 8.28 (d, J ¼ 8.2 Hz, 1H), 8.16 (d,
J ¼ 7.8 Hz, 1H) 7.78 (t, J ¼ 8 Hz, 1H), 7.41 (2H); 13C NMR d ppm, 164.38, 155.86,
148.28, 131.31, 130.98, 125.83, 125.72, 119.45; IR (KBr): 3413, 3300, 3233, 3094,
1674, 1577, 1522, 1478, 1352, 1314, 1270, 1060, 1041, 970, 898, 875, 734, 691 cmꢀ1
.
Entry 7. 1H NMR d ppm, 8.25 (d, J ¼ 8.6 Hz, 2H), 7.98 (d, J ¼ 8.6 Hz, 2H),
7.17 (s, 2H); 13C NMR d ppm, 164.59, 156.05, 147.93, 129.84, 125.99 (ꢂ2), 124.59
(ꢂ2); IR (KBr): 3282, 3083, 1661, 1598, 1562, 1525, 1353, 1335, 1308, 1106, 1048,
1011, 855, 739, 695 cmꢀ1
.

SEMICARBAZONES TO AZINES/OXADIAZOLES
2613
Entry 8. 1H NMR d ppm, 7.29 (s, 1H), 7.25 (s, 1H), 7.21 (s, 1H), 7.13 (s, 2H),
3.84 (s, 3H) 3.79 (s, 3H); 13C NMR d ppm, 163.81, 155.90, 150.70, 148.02, 117.51 (all
q), 116.55, 112.93, 108.00 (all CH), 56.01, 55.52; IR (KBr): 3470, 3151, 2996, 2967,
2936, 1725, 1659, 1602, 1575, 1428, 1391, 1351, 1321, 1266, 1210, 1181, 1166, 1029,
975, 917, 860, 817, 756, 711 cmꢀ1
.
ACKNOWLEDGMENT
We are thankful to the Council of Scientific and Industrial Research, New
Delhi, India, for providing a junior research fellowship to one of the authors (P.S.R).
REFERENCES
1. Chattopadhyay, G.; Saha, T. K. A domino type one-flask synthesis of 1-substituted-5-
aminoimidazole-4-carboxamides and ring transformation to pyrazine under microwave
through suitable aminoimidazoliumcarboxamide. Indian J. Chem. 2005, 44B, 827–830.
2. Chattopadhyay, G.; Chakraborty, S.; Saha, C. Brine-mediated efficient benzoylation of
primary amines and amino acids. Synth. Commun. 2008, 38, 4068–4075.
3. Yale, H. L.; Losee, K. J. 2-Amino-5-substituted-1,3,4-oxadiazoles and 5-imino-2-
substitutedD2-1,3,4-oxadiazolines: A group of novel muscle relaxants. J. Med. Chem.
1966, 9, 478–483.
4. Park, Y.-D.; Kim, J.-J.; Chung, H.-A.; Kweon, D.-H.; Cho, S.-D.; Lee, S.-G.; Yoon, Y.-J.
Facile synthesis of symmetric and unsymmetric 1,3,4-oxadiazoles using 2-acyl(or aroyl)
pyridazine-3-ones. Synthesis 2003, 560–564.
5. Dolman, S. J.; Gosselin, F.; O’Shea, P. D.; Davies, I. W. Superior reactivity of thiosemi-
carbazides in the synthesis of 2-amino-1,3,4-oxadiazoles. J. Org. Chem. 2006, 71,
9548–9551.
6. Zhong, L.; Zhixiang, Z.; Gonghua, S.; Xuhong, Q.; Jie, S. The crystal structure of N-(5-
phenyl-1,3,4-oxadiazol-2-yl)-N0-benzoyl urea a novel insect-growth regulator. J. Chem.
Res., Synop. 1999, 66–67.
7. Chattopadhyay, G.; Saha, T. K. Aminoimidazoliumcarboxamide with dimethylforma-
mide-dimethylacetal: A novel ANRORC towards rearranged imidazole anchord with
one carbon fragment. Indian J. Chem. 2004, 43B, 1558–1560.
8. Scott, F. L.; Lambe, T. M.; Butler, R. N. Ambident oxidative ring closure of semicarba-
zones. J. Chem. Soc., Perkin I Tran. 1 1972, 1918–1923.
9. Toda, F.; Yagi, M.; Kiyoshige, K. Baeyer–Villiger reaction in the solid state. J. Chem.
Soc.,Chem. Commun. 1988, 958–959.
10. Toda, F. Solid-state organic chemistry: Efficient reactions, remarkable yields, and stereo-
selectivity. Acc. Chem. Res. 1995, 28, 480–486.
11. Wang, Z. X.; Qin, H. L. Solventless syntheses of pyrazole derivatives. Green Chem. 2004,
6, 90–92.
12. Toda, F.; Boy, J.; Kaupp, G. 2. Quantitative solid-solid synthesis of azomethine. J. Chem.
Soc., Perkin Trans. 2 1998, 2, 989–994.
13. Tanaka, K. Solvent-Free Organic Synthesis, 1st ed.; Wiley-VCH: New York, 2003.
14. Rao, V. S.; Chandra Sekhar, K. V. G. Iodobenzene diacetate–mediated solid-state
synthesis of heterocyclyl-1,3,4-oxadiazoles. Synth. Commun. 2004, 34, 2153–2157.
15. Lidstrom, P.; Tierney, J. Microwave Assisted Organic Synthesis, 1st ed.; Blackwell
Scientific: Oxford, UK, 2005.

2614
G. CHATTOPADHYAY AND P. S. RAY
16. Loghmani-Khouzani, H.; Sadeghi, M. M. M.; Safari, J.; Abdorrezaie, M. S.; Jafarpisheh,
M. A convenient synthesis of azines under solvent-free conditions using microwave
irradiation. J. Chem. Res., Synop. 2001, 80–81.
17. Nanjundaswamy, H. M.; Pasha, M. A. Rapid, chemoselective, and facile synthesis of
azines by hydrazine=I2. Synth. Commun. 2007, 37, 3417–3420.
18. Shah, S. N.; Chudgar, N. K. Thermolysis of semicarbazones to the corresponding azines
through reactive N-substituted isocyanate intermediates. Molecules 2000, 5, 657–664.
19. Campaigne, E.; Monroe, P. A.; Aruwine, B.; Archer, W. L. Thiosemicarbazones of
thiophene derivatives. J. Am. Chem. Soc. 1953, 75, 988–989.
20. Kolb, V. M.; Hua, D. H. Syn-anti isomerism in the opiate hydrazones and azines derived
from naloxons, naltrexone, and oxymorphone. J. Org. Chem. 1984, 49, 3824–3828.
21. Vogel, A. I. Textbook of Practical Organic Chemistry, 4th ed.; ELBS and Longman:
London, 1978.
22. Suschitzky, H.; Walrond, E. R.; Hill, R. Synthesis of heterocyclic compounds, part 34:
Reaction of chlorosulphonyl isocyanate with carbon–nitrogen double bonds. J. Chem.
Soc., Perkin Trans. 1 1977, 47–52.
23. Schweizer, E. E.; Cao, Z.; Rheingold, A. L.; Brunch, M. Reaction of azines, 16: Prep-
aration of 6-(phenylmethylene)-5H-pyrazolo[1,5-d][2,4]benzoxazepines,5H,7H-pyrazolo
[1,5-d][2]benzoxazepin-6-one, and indeno[2,3-c]pyridine-3,9-diones. J. Org. Chem. 1993,
58, 4339–4345.
24. Rivera, N. R.; Balsells, J.; Hansen, K. B. Synthesis of 2-amino-5-substituted-1,3,4-
oxadiazoles using 1,3-dibromo-5,5-dimethylhydantoin as oxidant. Tetrahedron Lett.
2006, 47, 4889–4891.