Synthesis of 4-(5-aryl-1,3,4-oxadiazol-2-yl)phenyl-hydrazine derivatives from 3-(4-hydrazinocarbonyl-phenyl)sydnones

Article abstract of DOI:10.1002/hc.20318

The synthesis of potential fluorescent active 4- (5-aryl-1,3,4-oxadiazol-2- yl)phenylhydrazine derivatives was accomplished in three steps. The key step was the dehydration cyclization of 1,2-diacylhydrazines to form the 1,3,4-oxadiazole ring by use of ac

Full text of DOI:10.1002/hc.20318

Heteroatom Chemistry
Volume 18, Number 4, 2007
Synthesis of 4-(5-Aryl-1,3,4-oxadiazol-
2-yl)phenyl-hydrazine Derivatives from
3-(4-Hydrazinocarbonyl-phenyl)sydnones
Hung-Te Chang,2 Kuo-Chen Chiang,3,4 Fung Fuh Wong,1
Chun-Sheng Huang,2 Yang-Ming Liao,2 Wen-Fa Kuo,4
Shaw-Bing Won,3 and Mou-Yung Yeh2
1Graduate Institute of Pharmaceutical Chemistry, China Medical University, No. 91 Hsueh-Shih
Rd., Taichung, Taiwan 40402, R.O.C.
2Department of Chemistry, National Cheng Kung University, No 1, Ta Hsueh Rd., Tainan,
Taiwan 70101, R.O.C.
3Department of Resources Engineering, National Cheng Kung University, No 1, Ta Hsueh Rd.,
Tainan, Taiwan 70101, R.O.C.
4Sustainable Environment Research Center, National Cheng Kung University, No 500, Sec. 3,
An-ming Rd., Tainan City, Taiwan 709, R.O.C.
Received 5 June 2006; revised 4 August 2006
INTRODUCTION
ABSTRACT: The synthesis of potential fluorescent
active 4-(5-aryl-1,3,4-oxadiazol-2-yl)phenylhydrazine
derivatives was accomplished in three steps. The
key step was the dehydration cyclization of 1,2-
diacylhydrazines to form the 1,3,4-oxadiazole ring by
use of acetic anhydride/perchloric acid mixture as
the dehydrating agent. The sydnone moiety served as
the masked hydrazines, which could be demasked by
1,3,4-Oxidiazoles have been reported to be biolog-
ically versatile compounds displaying a variety of
biological effects [1–5]. 1,3,4-Oxadiazole-based het-
erocyclic compounds are also the most widely stud-
ied class of electron-injection and/or hole-blocking
organic electroluminescent materials [6]. The most
common synthetic approach to 1,3,4-oxidiazoles
involves cyclodehydration of 1,2-diacylhydrazines
ꢀ
C
HCl for further application.
2007 Wiley Periodicals,
Inc. Heteroatom Chem 18:438–442, 2007; Published on-
line in Wiley InterScience (www.interscience.wiley.com).
DOI 10.1002/hc.20318
by use of
a dehydrating agent [11–15]. An
alternative route to 1,3,4-oxidiazoles by oxidative
cyclization from the corresponding aldehyde N-
acylhydrazones proceeds with an oxidating agent
[12–17]. Herein, we reported the synthesis of 4-
(5-aryl-1,3,4-oxadiazol-2-yl)phenylhydrazine deriva-
tives from 3-(4-hydrazinocarbonylphenyl)sydnones
in three steps to prepare the precursor of the
1,3,4-oxadiazol derivatives as electroluminescent
materials. Description of the formation of the
1,3,4-oxidiazole ring can be found in a previ-
ous work, where a mixture of acetic anhydride
Correspondence to: Fung Fuh Wong; e-mail: wongfungfuh@
yahoo.com.tw.
Contract grant sponsor: National Science Council of Republic
of China.
Contract grant number: 95-2221-E-006-398.
2007 Wiley Periodicals, Inc.
c
ꢀ
438

Synthesis of 4-(5-Aryl-1,3,4-oxadiazol-2-yl)phenyl-hydrazine Derivatives 439
and perchloric acid was used as the dehydrating
agent [18].
Sydnones attract attention owing to their widely
useful properties, including biological and phar-
maceutical usage [19], synthetic application [20],
photochromic properties [21], and preparation of
electroluminescent materials [22]. In this work, syd-
nones were considered as the masked hydrazines,
which could be demasked by HCl for further appli-
cation [23].
dehydration–cyclization was smoothly performed to
yield the 1,3,4-oxidiazole ring (6). Finally, reaction
of 1,3,4-oxadiazole–sydnone hybrids 3a–3c with HCl
gave products derived from cleavage of the sydnone
ring to the corresponding hydrazines 4a–4c.
In conclusion, we have developed a synthetic
route for the precursor of electroluminescent materi-
als of 4-(5-aryl-1,3,4-oxadiazol-2-yl)phenylhydrazine
derivatives in three steps. The key dehydration
cyclization of 1,2-diacylhydrazines was performed
with acetic anhydride/perchloric acid mixture to
provide the 1,3,4-oxadiazole ring. In the last step, the
cleavage of sydnone ring was reacted with HCl aque-
ous solution to afford the 4-(5-aryl-1,3,4-oxadiazol-
2-yl)phenylhydrazines.
RESULTS AND DISCUSSION
The synthetic pathway of the 4-(5-aryl-1,3,4-
oxadiazol-2-yl)phenylhydrazine derivatives 4a–4c
is depicted in Scheme 1. 4-Hydrazinocarbonyl-
phenylsydnone 1a–1c were prepared by the pub-
lished procedure [24]. The sydnone compounds 1a–
1c were easily converted to the 1,2-diacylhydrazines
2a–2c by reacting with benozyl chloride (para-
R1 = H, Cl, and OMe) in CH2Cl2 solution for 3.0 h.
The isolated yields and the results are shown in
Table 1.
Treatment of the various 1,2-diacylhydrazines
2a–2c (para-R1 = H, Cl, and OMe) with the acetic
anhydride/perchloric acid mixture gave the 1,3,4-
oxadiazole–sydnone hybrids 3a–3c in 52%–60%
yields (see Table 1). The proposed dehydration–
cyclization mechanism is shown in Scheme 2. Upon
addition of perchloric acid to the acetic anhy-
dride solution, the sequence of the reaction can be
generated using the CH3CO+–ClO4 and acetic acid
species [25]. 1,2-Diacylhydrazines 5 can be reacted
with CH3CO+–ClO4 in the acidic condition to afford
the acetyl hydrazone intermediate (7) [26]. Further
EXPERIMENTAL
General
Analytical thin-layer chromatography (TLC) was
performed on precoated plates (silica gel 60
F-254), purchased from Merck Inc. Purification by
gravity column chromatography was carried out by
use of Merck Reagents Silica Gel 60 (particle size
0.063–0.200 mm, 70–230 mesh ASTM). Infrared (IR)
spectra were measured on a Bomem Michelson
Series FT-IR spectrometer. The wave numbers re-
ported are referenced to the polystyrene 1601 cm−1
absorption. Absorption intensities are recorded by
the following abbreviations: s, strong; m, medium;
w, weak. Proton NMR spectra were obtained on a
Bruker-300 (300 MHz) spectrometer by use of CDCl3
and-d6-DMSO as solvent. Carbon-13 NMR spectra
were obtained on a Varian Bruker-300 (75 MHz)
O
R1
O
H2NHN
O
O
Cl
N
N
R1
N
NHNH
R1 = H, Cl, OMe
O
N
O
O
O
1
2a(R1 = H), 2b(R1 =Cl), 2c(R1 = OMe)
O
HClO4
(CH3CO)2O
R1
N
HCl
N N
N
EtOH/H2O, at reflux
O
O
3a(R1 = H), 3b(R1 = Cl), 3c(R1 = OMe)
O
R1
NHNH2 HCl
N N
4a(R1 = H), 4b(R1 = Cl), 4c(R1 = OMe)
SCHEME 1 The synthetic route of 4-(5-aryl-1,3,4-oxadiazol-2-yl)phenylhydrazine derivatives 4a–4c.
Heteroatom Chemistry DOI 10.1002/hc

440 Chang et al.
TABLE 1 The Yields of Aldehyde N-Acylhydrazones 2a–2c, 1,3,4-Oxidiazole–sydnone Hybrids 3a–3c, and 4-(5-Aryl-1,3,4-
oxadiazol-2-yl)phenylhydrazines 4a–4c
Entry R1
Compounds 2
Yield (%)
Compounds 3
Yield (%)
Compounds 4
Yield (%)
H
Cl
Ome
2a
2b
2c
87
90
91
3a
3b
3c
52
60
57
4a
4b
4c
68
77
70
spectrometer by use of CDCl3 as solvent. Carbon-13
chemical shifts are referenced to the center of
the CDCl3 triplet (δ 77.0 ppm). Multiplicities are
recorded by the following abbreviations: s, singlet;
d, doublet; t, triplet; q, quartet; m, multiplet; J, cou-
pling constant (Hz). Elemental analyses were carried
out on a Heraeus CHN–O RAPID element analyzer.
intensity): 325 (M + 1, 20), 324 (M+, 16); Anal. Calcd
for C16H12N4O4: C, 59.26; H, 3.73; N, 17.28. Found:
C, 59.32; H, 3.84; N, 17.27.
3-[4-(Nꢁ-4-Chlorobenzoylhydrazinocarbonyl)phen-
yl]sydnone 2b. mp (recrystallized from EtOAc):
199–201◦C; 1H NMR (DMSO-d6, 300 MHz) δ: 7.60 (d,
2H, J = 8.8 Hz), 7.88 (s, 1H), 7.90 (d, 2H, J = 8.8 Hz),
8.09 (d, 2H, J = 8.8 Hz), 8.18 (d, 2H, J = 8.8 Hz),
10.74 (s, 1H), 10.87 (s, 1H); IR (KBr) 3214 (s,
NH), 3136 (s), 1746 (m, C O) cm−1; FABMS m/z
(relative intensity): 361 (M + 3, 10), 360 (M + 2,
8), 359 (M + 1, 32), 358 (M+, 20); Anal. Calcd for
C16H11N4O4Cl: C, 53.57; H, 3.09; N, 15.62. Found: C,
53.70; H, 3.21; N, 15.43.
Standard Procedure for the Substitution
Reaction
To
a
solution of 4-hydrazinocarbonylphenyl-
sydnones (1, 0.38 g, 6.00 mmol, 1.0 equiv.) and ben-
zoyl chloride (0.80 mL, 6.00 mmol, 1.0 equiv.) in
CH2Cl2 (30 mL) was stirred at room temperature
for 3 h. After the reaction was completed, the re-
sultant precipitate was filtrated, washed with cold
CH2Cl2 (10 mL × 2), and dried in vacuum oven. The
residue was purified by recrystallization from EtOAc
to give pure 1,2-diacylhydrazines 2a–2c as light-
yellow powder in 87%–91% yields.
3-[4-(Nꢁ-4-Methoxylbenzoylhydrazinocarbonyl)-
phenyl]sydnone 2c. mp (recrystallized from EtOAc):
1
250–252◦C; H NMR (DMSO-d6, 300 MHz) δ: 3.84
(s, 3H, CH3), 7.05 (d, 2H, J = 8.9 Hz), 7.88 (s, 1H),
7.90 (d, 2H, J = 8.8 Hz), 7.91 (d, 2H, J = 8.9 Hz),
8.10 (d, 2H, J = 8.8 Hz), 8.19 (d, 2H, J = 8.8 Hz),
10.47 (s, 1H), 10.74 (s, 1H); IR (KBr) 3214 (s, NH),
3130 (s), 1749 (m, C O) cm−1; FABMS m/z (relative
intensity): 355 (M + 1, 31), 354 (M+, 22); Anal. Calcd
for C17H14N4O5: C, 60.35; H, 4.17; N, 16.56. Found:
C, 60.50; H, 4.23; N, 16.69.
3-[4-(Nꢁ-Benzoylhydrazinocarbonyl)phenyl]syd-
none 2a. mp (recrystallized from EtOAc): 214–
1
216◦C; H NMR (DMSO-d6, 300 MHz) δ: 7.48–7.61
(m, 3H), 7.89 (s, 1H), 7.90–7.99 (m, 2H), 8.12 (d,
2H, J = 8.8 Hz), 8.20 (d, 2H, J = 8.8 Hz), 10.63 (s,
1H), 10.83 (s, 1H); IR (KBr) 3220 (s, NH), 3130
(s), 1695 (m, C O) cm−1; FABMS m/z (relative
Standard Procedure for the
Dehydration–Cyclization
1,2-Diacylhydrazines 2a–2c (0.32 g, 1.00 mmol, 1.0
equiv.) was dissolved in acetic anhydride (5.0 mL)
and added to 4 drops of 60% perchloric acid aqueous
solution (HClO4aq). The reaction mixture was stirred
at room temperature for 36 h. After the reaction was
completed, the reaction mixture was filtrated to re-
move the solid residue. The filtrate was mixed with
cold water (10.0 mL) and the resultant precipitate
was filtrated, washed with cold EtOAc (10 mL × 2),
and dried in vacuum oven. The residue was purified
by recrystallization from EtOAc to give the 1,3,4-
oxadiazole–sydnone hybrids 3a–3c as light-yellow
powder in 52%–60% yields.
O
O
HClO4
O
Ar1
Ar2
Ar2
Ar1
NHNH
(CH3CO)2O
N N
5
6
HClO4
+
(CH3CO)2O
HClO4
CH3CO ClO4
+
CH3COOH
ClO4
Ac
O
O
Ar2
Ar1
NNH
7
3-[4-(5-Phenyl-1,3,4-oxadiazol-2-yl)phenyl]sydnone
3a. mp (recrystallized from EtOAc) > 250◦C; 1H
NMR (DMSO-d6, 300 MHz) δ: 7.61–7.67 (m, 3H),
SCHEME 2 The proposed mechanism of the oxidative
cyclization.
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of 4-(5-Aryl-1,3,4-oxadiazol-2-yl)phenyl-hydrazine Derivatives 441
7.93 (s, 1H), 8.15–8.22 (m, 4H), 8.43 (d, 2H, J = 8.8
7.12 (d, 2H, J = 8.7 Hz), 8.95 (br, 1H), 10.47 (br,
3H), IR (KBr) 3208 (s, NH) cm−1; MS m/z (relative
intensity): 286 (M+ – 36, 76), 256 (7), 165 (18), 139
(41), 135 (100), 111 (34), 90 (27), 75 (32); Anal.
Calcd for C14H12N4OCl2: C, 52.03; H, 3.74; N, 17.33.
Found: C, 52.05; H, 3.70; N, 17.51.
Hz), IR (KBr) 3124 (s), 1770 (m, C O) cm−1; MS m/z
(relative intensity): 306 (M+, 3), 280 (4), 276 (11),
248 (100), 221 (10), 164 (21), 105 (53), 88 (33), 77
(63); Anal. Calcd for C16H10N4O3: C, 62.74; H, 3.29;
N, 18.29. Found: C, 62.83; H, 3.14; N, 18.18.
3-[-4-(5-(4-Chlorophenyl)-1,3,4-oxadiazol-2-yl)-
phenyl]sydnone 3b. mp (recrystallized from EtOAc)
4-(5-(4-Methoxylphenyl-1,3,4-oxadiazol-2-yl)phenyl-
hydrazine Hydrochloride 4c. mp (recrystallized from
1
1
> 250◦C; H NMR (DMSO-d6, 300 MHz) δ: 7.70 (d,
EtOH): 228–230◦C; H NMR (DMSO-d6, 300 MHz)
2H, J = 8.5 Hz), 7.92 (s, 1H), 8.15 (d, 2H, J = 8.7 Hz),
8.18 (d, 2H, J = 8.5 Hz), 8.41 (d, 2H, J = 8.7 Hz);
IR (KBr) 3124 (s), 1755 (m, C O) cm−1; MS m/z
(relative intensity): 340 (M+, 10), 310 (11), 282 (100),
255 (15), 198 (15), 164 (16), 139 (40), 90 (39); Anal.
Calcd for C16H9N4O3Cl: C, 56.40; H, 2.66; N, 16.44.
Found: C, 56.30; H, 2.67; N, 16.45.
δ: 3.83 (s, 3H, CH3), 7.13 (d, 2H, J = 8.8 Hz), 7.15 (d,
2H, J = 8.8 Hz), 8.01 (d, 2H, J = 8.8 Hz), 8.03 (d, 2H,
J = 8.8 Hz), 8.95 (br, 1H), 10.52 (br, 3H); IR (KBr)
3214 (s, NH) cm−1; MS m/z (relative intensity):
282 (M+ −36, 65), 267 (63), 252 (9), 210 (24), 196
(27), 135 (100), 120 (83), 77 (62); Anal. Calcd for
C15H15N4O2Cl: C, 56.56; H, 4.74; N, 17.58. Found: C,
56.35; H, 4.68; N, 17.39.
3-[4-(5-(4-Methoxylphenyl)-1,3,4-oxadiazol-2-yl)-
phenyl]sydnone 3c. mp (recrystallized from EtOAc):
1
241–243◦C; H NMR (DMSO-d6, 300 MHz) δ: 3.87
(s, 3H, CH3), 7.18 (d, 2H, J = 8.9 Hz), 7.92 (s, 1H),
8.10 (d, 2H, J = 8.9 Hz), 8.18 (d, 2H, J = 8.9 Hz),
8.40 (d, 2H, J = 8.7 Hz); IR (KBr) 3142 (s), 1743 (m,
C O) cm−1; MS m/z (relative intensity): 336 (M+, 3),
306 (13), 278 (100), 251 (18), 208 (7), 194 (14), 152
(18), 135(85), 90 (35); Anal. Calcd for C17H12N4O4:
C, 60.71; H, 3.59; N, 16.66. Found: C, 60.53; H, 3.38;
N, 16.37.
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Standard Procedure for the Demasking
Reaction [16]:
1,3,4-Oxadiazole–sydnone hybrids 3a–3c (1.80 g,
5.88 mmol, 1.0 equiv.) was stirred in EtOH solu-
tion (60 mL) and added to 3.0 mL of 37% HCl
aqueous solution. The reaction mixture was stirred
at reflux for 4 h. After the reaction was com-
pleted, the resultant precipitate was filtrated, washed
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from EtOH to afford the 4-(5-aryl-1,3,4-oxadiazol-2-
yl)phenylhydrazine derivatives 4a–4c as light-yellow
powder in 68%–77% yields.
4-(5-Phenyl-1,3,4-oxadiazol-2-yl)phenylhydrazine
Hydrochloride 4a. mp (recrystallized from EtOH):
1
247–249◦C; H NMR (DMSO-d6, 300 MHz) δ: 7.18
(d, 2H, J = 8.8 Hz), 7.57–7.61 (m, 3H), 7.86 (d,
2H, J = 8.8 Hz), 8.02–8.12 (m, 3H), 9.03 (br, 1H),
10.58 (br, 3H); IR (KBr) 3184 (s, NH) cm−1; MS m/z
(relative intensity): 252 (M+ −36, 59), 180 (9), 165
(17), 135 (100), 119 (16), 105 (46), 90 (22), 77 (72);
Anal. Calcd for C14H13N4OCl: C, 58.24; H, 4.54; N,
19.40. Found: C, 58.35; H, 4.47; N, 19.40.
4-(5-(4-Chlorophenyl-1,3,4-oxadiazol-2-yl)phenyl-
hydrazine Hydrochloride 4b. mp (recrystallized from
1
EtOH) > 250◦C; H NMR (DMSO-d6, 300 MHz) δ:
Heteroatom Chemistry DOI 10.1002/hc

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