Iodobenzene diacetate mediated solid-state synthesis of heterocyclyl-1,3,4-oxadiazoles

Article abstract of DOI:10.1081/SCC-120038493

A simple and efficient method has been developed for the oxidation of various heterocyclyl acylhydrazones 3 with iodobenzene diacetate (IBD) to heterocyclyl-1,3,4-oxadiazoles 4 in solid state. The reaction took place at room temperature within few minutes. The products were isolated by simple aqueous work-up in good yields.

Full text of DOI:10.1081/SCC-120038493

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Iodobenzene Diacetate Mediated Solid‐State
Synthesis of Heterocyclyl‐1,3,4‐oxadiazoles
V. S. Rao a & K. V. G. Chandra Sekhar a
a Chemistry Group , Birla Institute of Technology and Science , Pilani, 333 031,
Rajasthan, India
Published online: 17 Aug 2006.
To cite this article: V. S. Rao & K. V. G. Chandra Sekhar (2004) Iodobenzene Diacetate Mediated Solid‐State Synthesis
of Heterocyclyl‐1,3,4‐oxadiazoles, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 34:12, 2153-2157, DOI: 10.1081/SCC-120038493
To link to this article: http://dx.doi.org/10.1081/SCC-120038493
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 12, pp. 2153–2157, 2004
Iodobenzene Diacetate Mediated Solid-State
Synthesis of Heterocyclyl-1,3,4-oxadiazoles
*
V. S. Rao and K. V. G. Chandra Sekhar
Chemistry Group, Birla Institute of Technology and Science,
Pilani, Rajasthan, India
ABSTRACT
A simple and efficient method has been developed for the oxidation of
various heterocyclyl acylhydrazones 3 with iodobenzene diacetate
(IBD) to heterocyclyl-1,3,4-oxadiazoles 4 in solid state. The reaction
took place at room temperature within few minutes. The products were
isolated by simple aqueous work-up in good yields.
Key Words: Iodobenzene diacetate; 1,3,4,-Oxadiazoles; Heterocyclyl
acylhydrazones; Solid state synthesis.
INTRODUCTION
Presently, there is a considerable interest in organohypervalent iodine
reagents because of their versatile use in solid-state organic reactions
*
Correspondence: V. S. Rao, Chemistry Group, Birla Institute of Technology and
Science, Pilani 333 031, Rajasthan, India; E-mail: vsr@bits-pilani.ac.in.
2153
DOI: 10.1081/SCC-120038493
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Rao and Chandra Sekhar
(SSOR).[1] These reagents are used in the synthesis of several heterocyclic
compounds in liquid and solid state.[2] Innumerable methods are reported in
the literature for the oxidation of acyl hydrazones to 1,3,4-oxadiazoles
such as oxidation with lead tetra acetate[3] or electrochemical oxidation of
N-acylhydrazones.[4] The main drawback of these methods includes long
reaction periods, high temperatures, and difficult work-up procedures.
Keeping in view the importance of SSOR and biological activities of 1,3,4-
oxadiazoles,[5–8] we herein report, simple and efficient conversion of hetero-
cyclyl acylhydrazones to heterocyclyl-1,3,4-oxadiazoles using IBD under
solid-state conditions.
RESULTS AND DISCUSSIONS
Conventional synthesis of isonicotinoyl hydrazones[9] has been modified by
treating isonicotinic acid hydrazide (1) with various aromatic aldehydes (2) and
subjected to microwave irradiation in domestic microwave oven over a period
ranging from 1 to 3 min. After work-up, the resulting hydrazones were triturated
with IBD in a pestle and mortar at room temperature without any solvent. After
5 min, sudden exothermic reaction took place with the evolution of nitrogen gas.
Completion of reaction is marked by the change of state from solid to semi-
solid/liquid with characteristic smell of iodobenzene. All the synthesized
compounds (4a–4l) were characterized by elemental analysis (CHN) and spec-
tral (IR, 1H NMR) data. Formation of hydrazones (3a–3l) were confirmed by
previously reported melting points and the absence of primary amino group
at ꢀ3350cm21 in IR spectra. IR spectral analysis of the final compounds
(4a–4l) shows absorption band at ꢀ1600 and ꢀ1200cm21 due to C55N and
1
C–O–C functions, respectively. In H NMR spectra, peak at d 7.99–8.33
and 6.95–7.66 indicates the presence of pyridyl ring and phenyl ring, respect-
ively. Elemental (CHN) analysis indicated that the calculated and observed
values were within the acceptable limits (+0.4%).
EXPERIMENTAL SECTION
Melting points were determined in open capillaries using Buchi 530
apparatus and are uncorrected. The purity of the compounds was checked

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Synthesis of Heterocyclyl-1,3,4-oxadiazoles
Table 1. Physical constants for compounds 3a–3l.
2155
Reaction
period
(min)
M.p.
(lit.)[9]
Compound
number
Yield
(%)
Ar
(8C)
3a
3b
3c
C6H5
o-Cl–C6H4
m-NO2–C6H4
2.0
1.5
1.0
80
79
89
162–164
210–212
269–270
(269)
3d
p-NO2–C6H4
1.0
93
190–191
(190–191)
196–197
162–163
(162)
3e
3f
p-CH3–C6H4
p-OCH3–C6H4
2.5
2.5
87
91
3g
3h
3i
o-OH–C6H4
–CH55CH–C6H5
p-OH–m-OCH3–C6H3
3.0
2.5
3.0
87
72
96
265–266
199–201
200–202
(200–201)
212–214
206–207
221–223
3j
3k
3l
p-Cl–C6H4
m-CH3–C6H4
m-Cl–C6H4
2.0
2.5
2.0
81
95
89
Table 2. Physical constants of compounds 4a–4l.a
Compound
number
Yield
(%)
M.p.
(8C)
Ar
4a
4b
4c
4d
4e
4f
C6H5
o-Cl–C6H4
87
88
81
80
81
82
84
86
93
92
90
86
152–154
102–104
123–124
203–205
134–135
184–185
230–233
151–153
222–224
174–175
124–125
142–144
m-NO2–C6H4
p-NO2–C6H4
p-CH3–C6H4
p-OCH3–C6H4
o-OH–C6H4
4g
4h
4i
–CH55CH–C6H5
p-OH–m-OCH3–C6H3
p-Cl–C6H4
4j
4k
4l
m-CH3–C6H4
m-Cl–C6H4
aAll new compounds show satisfactory C, H, N analysis.

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Rao and Chandra Sekhar
by TLC using silica gel-coated Al plates (Merck). Microwave irradiations
were carried out in domestic microwave oven (LG Electronics, model
MG-605AP, 2450 MHZ, 900 W). IR spectra were recorded using KBr pellets
on a Jasco IR Repot-100 infrared spectrophotometer (nmax in cm21); 1H NMR
spectra on Bruker DRX300 spectrometer using TMS as internal standard
1
Table 3. IR and H NMR spectral data of compounds 4a–4l.
IR (KBr) (cm21
)
Compound
number
C55N
C–O–C
1,210
1H NMR (CDCl3) d (ppm)
4a
4b
4c
4d
1,620
7.31–7.42 (m, 5H, Ar-H)
8.02–8.14 (m, 4H, Py)
7.27–7.35 (m, 4H, Ar-H)
8.12–8.22 (m, 4H, Py)
7.49–7.57 (m, 4H, Ar-H)
8.06–8.15 (m, 4H, Py)
7.57–7.66 (m, 4H, Ar-H)
8.11–8.21 (m, 4H, Py)
2.46 (s, 3H, CH3)
1,600
1,650
1,640
1,180
1,190
1,210
4e
4f
1,590
1,610
1,640
1,650
1,200
1,220
1,200
1,200
7.26–7.38 (m, 4H, Ar-H)
8.02–8.16 (m, 4H, Py)
3.91 (s, 3H, OCH3)
7.04–7.26 (m, 4H, Ar-H)
7.99–8.12 (m, 4H, Py)
5.25 (br s, 1H, OH)
4g
4h
6.82–6.95 (m, 4H, Ar-H)
8.10–8.21 (m, 4H, Py)
6.65 (s, 2H, –CH55CH–)
7.24–7.36 (m, 5H, Ar-H)
8.02–8.11 (m, 4H, Py)
3.82 (s, 3H, OCH3)
5.71 (br s, 1H, OH)
4i
4j
1,640
1,610
1,220
1,180
6.95–7.21 (m, 3H, Ar-H)
8.12–8.21 (m, 4H, Py)
7.25–7.32 (m, 4H, Ar-H)
8.02–8.14 (m, 4H, Py)
2.48 (s, 3H, CH3)
4k
4l
1,620
1,600
1,190
1,200
7.17–7.26 (m, 4H, Ar-H)
8.21–8.30 (m, 4H, Py)
7.27–7.33 (m, 4H, Ar-H)
8.01–8.12 (m, 4H, Py)

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Synthesis of Heterocyclyl-1,3,4-oxadiazoles
2157
(chemical shifts in d, ppm), and elemental analysis on a Carla Erba 1108
elemental analyzer.
Heterocyclyl acylhydrazones 3: general procedure. Isonicotinic acid
hydrazide 1 (5 mmol), corresponding benzaldehyde 2 (5 mmol) in ethanol
with a few drops of glacial acetic acid were subjected to microwave irradiation
at 60% power output (540 W) for the period indicated in Table 1. After com-
pletion of the reaction (monitored by TLC), the reaction mixture was kept in
the refrigerator overnight. The resultant product was filtered, washed with
water, and recrystallized from ethanol to afford 3 (Table 1).
Oxidation of heterocyclyl acylhydrazones 3 to heterocycyl-1,3,4-
oxadiazoles 4: general procedure. A mixture of appropriate heterocyclyl
acylhydrazone 3 (2 mmol) and IBD (2.4 mmol) was ground by pestle and
mortar at room temperature. After 5 min, evolution of nitrogen gas occurred.
The solid was diluted with water, filtered and recrystallized from ethanol to
afford 4. Characterization data is given in Tables 2 and 3.
ACKNOWLEDGMENT
We wish to thank the RSIC, CDRI, Lucknow, India for analytical and
spectral data.
REFERENCES
1. Perrin, R.; Lamartine, R.; Perrin, M.; Thozet, A. Organic Solid State
Chemistry; Desiraju, G.R., Ed.; Elsevier: Amsterdam, 1987; 217.
2. Zhdankin, V.V.; Stang, P.J. Chem. Rev. 2002, 102, 2523–2584.
3. Stolle, R. J. Prakt. Chem. 1906, 73, 77.
4. Chiba, T.; Mitsuhiro, O. J. Org. Chem. 1992, 57, 1375.
5. Sharma, R.S.; Bahd, S.C. J. Indian Chem. Soc. 1982, 59, 877.
6. Ramalingam, T.; Deshmukh, A.A.; Sattur, P.B.; Sheth, U.K.; Naik, S.R.
J. Indian Chem. Soc. 1981, 58, 269.
7. Ram, V.J.; Pandey, H.N. J. Indian Chem. Soc. 1974, 51, 634.
8. Ponticello, G.S.; Engelhardt, E.L.; Baldwin, J.J. J. Hetrocyclic Chem.
1980, 17, 425.
9. Bayer, A.G. GB Pat. 737271, 1955.
Received in India February 10, 2004

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