Synthesis and characterization of new blue-greenish electroluminescent materials based on 1,3,4-oxadiazole-triazolopyridinone hybrids

Article abstract of DOI:10.1002/hc.20285

New functionalized oxadiazole-triazolopyridinone derivatives were synthesized via arcycloaddition. With the chromophores of triazolopyridinone, the photoluminescence spectra of these compounds in dichloromethane solution showed emission peaks between 430 and 520 nm. Following the spectroscopic studies, and the measurements of cyclic voltammogram, 1,3,4-oxadiazole- triazolopyridinone hybrids possess a great potential as highly efficient, blue-greenish, organic light-emitting devices materials.

Full text of DOI:10.1002/hc.20285

Heteroatom Chemistry
Volume 18, Number 3, 2007
Synthesis and Characterization of New
Blue-Greenish Electroluminescent Materials
Based on 1,3,4-Oxadiazole-triazolopyridinone
Hybrids
Ming-Hsiang Shin,1 Fung Fuh Wong,2 Chun-Min Lin,1
Wen-Yi Chen,1 and Mou-Yung Yeh1,3
1Department of Chemistry, National Cheng Kung University, No 1, Ta Hsueh Rd.,
Tainan, Taiwan 70101, Republic of China
2Graduate Institute of Pharmaceutical Chemistry, China Medical University, No. 91, Hsueh-Shih
Rd., Taichung, Taiwan 40402, Republic of China
3Nan Jeon Institute of Technology, No.178, Chaocin Rd., Yanshuei Township,
Tainan County Taiwan 737, Republic of China
Received 10 May 2005; revised 23 February 2006
tions in displays and electronic industries [1–3]. Fur-
ABSTRACT: New functionalized oxadiazole-
thermore, blue light-emitting materials have been
triazolopyridinone derivatives were synthesized
essential because of their wild applicability [4–7].
via arcycloaddition. With the chromophores of
In 1990, Adachi et al. reported 2-(biphenyl-4-
triazolopyridinone, the photoluminescence spectra
yl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as
of these compounds in dichloromethane solution
an excellent electron transport material in an
showed emission peaks between 430 and 520 nm.
organic multilayer electroluminescent (EL) diode
Following the spectroscopic studies, and the mea-
[8]. After this report, 1,3,4-oxadiazole deriva-
surements of cyclic voltammogram, 1,3,4-oxadiazole-
tives have been widely exploited as electron-
triazolopyridinone hybrids possess a great potential as
transporting, hole-blocking materials in EL de-
highly efficient, blue-greenish, organic light-emitting
vices because of their electron-deficient nature,
ꢀ
C
devices materials.
2007 Wiley Periodicals, Inc. Het-
high thermal stability, and high photoluminescence
quantum yield (PLQL) [9–10]. 1,3,4-Oxadiazole-
based heterocyclic compounds were also enthusias-
tically investigated. For example, 1,3,4-oxadiazole-
pyridine hybrids [11], 1,3,4-oxadiazole-pyrimidine
hybrids [11],1,3,4-oxadiazole-carbazole [12], and
1,3,4-oxadiazole-spirobifluorene [13] were well stud-
ied. The heterocyclic moieties on the molecular
structure can provide the improved hole injection,
transport properties, and confer rigidity.
eroatom Chem 18:212–219, 2007; Published online in
Wiley InterScience (www.interscience.wiley.com). DOI
10.1002/hc.20285
INTRODUCTION
Organic light-emitting devices have been an impor-
tant subject in recent years because of their applica-
In
this
work,
novel
1,3,4-oxadiazole-
Correspondence to: Fung Fuh Wong; e-mail: ffwong@
mail.cmu.edu.tw.
2007 Wiley Periodicals, Inc.
triazolopyridinone derivatives were synthesized
to explore the effect of modification of the
c
ꢀ
212

Synthesis and Characterization of New Blue-Greenish Electroluminescent Materials 213
triazolopyridinone moiety [14]. We synthesized
in CH2Cl2 and CHCl3 solutions. UV-vis absorption
maxima of 4a–4c are between 286 and 292 nm. 1,3,4-
Oxadiazole-triazolopyridinone derivatives 5a–5i
with the moiety of triazolopyridinone have gradual
red shifts to 291–305 nm because of the extension of
conjugation (see Table 1). The photoluminescence
(PL) spectra of 1,3,4-oxadiazol-2-ylpyridine deriva-
tives 4a–4c and 1,3,4-oxadiazole-triazolopyridinone
derivatives 5a–5i were shown in Table 1. The
emission wavelengths for 4a–4c are between 356
a series of 6-(1,3,4-oxadiazol-2-yl)-[1,2,4]triazodone
derivatives (5a–5i) in which N1-phenyl group and
C-10 of 1,3,4-oxadiazole ring were modified in sev-
eral ways. Following the spectroscopic studies and
the measurements of cyclic voltammogram, 1,3,4-
oxadiazole-triazolopyridinone derivatives were
highly efficient, blue-greenish EL.
RESULTS AND DISCUSSION
and 360 nm in CH2Cl2 or CHCl3 solution. The λmax
s
of photoluminescence are around 465–477 nm of
1,3,4-oxadiazole-triazolopyridinone derivatives 5a–
5i with the moiety of triazolopyridinone exhibiting
blue fluorescence in CH2Cl2 or CHCl3 solution. The
long range of substitution effects on R1 and R2
positions is clearly not a function for absorption
and emission spectra (see Table 1). The solution flu-
orescence quantum yields (ꢀf) of 5a–5i, all of which
fall in the range 0.68–0.76, were determined relative
to that of 2-phenyl-5-(4-biphenyl)-1,3,4-oxzdiazole
in benzene (ꢀf = 0.80, see Table 1) [18]. The PL
spectra 5c, 5f, and 5i of the vacuum evaporated
films on quartz substrates, with a maximum at 498
nm, show a red-shift (∼30 nm), with respect to the
solution spectrum as shown in Fig. 1.
Synthesis of 1,3,4-oxadiazol-2-yl-[1,2,4]triazolo[4,3-
a]pyridin-3(2H)-one Derivatives (5a–5i).
The synthetic route of 3-(5-phenyl-1,3,4-
oxadiazol-2-yl)pyridine derivatives (4a–4c) is shown
in Scheme 1. Isonicotinyl chloride 1 reacted with
hydrazine monohydrhydrate to generate isoni-
cotinyl hydrazine 2 [15]. Then various benzoyl
chloride (para-R1 = H, Me, and Cl) were treated with
isonicotinyl hydrazine 2 to give the corresponding
1-isonicotinyl-2-nicotinyl hydrazines 3a–3c [16].
1-Isonicotinyl-2-nicotinyl hydrazines 3a–3c were
subjected to dehydration–cyclization by using
fresh POCl3 to produce 1,3,4-oxadiazol-2-ylpyridine
derivatives 4a–4c.
α-Chloroformylarylhydrazines
hydrochloride
were synthesized through our previous published
procedures [17]. 1,3,4-Oxadiazol-2-ylpyridine deri-
vatives 4a–4c reacted with α-chloroformylaryl-
hydrazine in i-PrOH at 80◦C for 2 h to generate 1,3,4-
oxadiazole-triazolopyridinone derivatives 5a–5i in
65–72% yields (see Scheme 2).
Cyclic Voltammetry Measurements
The electrochemical behavior of 1,3,4-oxadiazole-
triazolopyridinone derivatives 5a–5i was investi-
gated by cyclic voltammetry. The measurements
were carried out with a platinum electrode in CH2Cl2
containing tetrabutylammonium hexafluorophos-
phate (TBAPF6). The potential was measured against
Ag/AgCl as reference electrode, and each measure-
ment was calibrated with an internal standard,
ferrocene/ferrocenium (Fc) redox system [19–20].
Photophysical Properties
The ultraviolet-visible (UV-vis) spectra of 1,3,4-
oxadiazol-2-ylpyridine 4a–4c and 1,3,4-oxadiazole-
triazolopyridinone derivatives 5a–5i were measured
SCHEME 1
Heteroatom Chemistry DOI 10.1002/hc

214 Shin et al.
SCHEME 2
The data were summarized in Table 2, and
the HOMO energy (Ip) for 1,3,4-oxadiazole-
triazolopyridinone derivatives 5a–5i were calcu-
lated on the basis of the value of −4.8 eV for
Fc with respect to zero vacuum level [19]. Upon
the anodic sweep, 5a–5i showed irreversible reduc-
tion processes. As an example, the cyclic voltam-
mogram of 5f is shown in Fig. 2. In the case
of 5f, the reversibility of oxidation was estimated
and the HOMO value is −5.60 eV with respect
to Ag/AgCl (−5.66 eV with respect to Fc). The
bandgap energies (3.68–3.70 eV) of 1,3,4-oxadiazole-
triazolopyridinone derivatives 5a–5i were estimated
from the onset wavelength (λonset) of the UV-vis
absorption. The substitution effects on R1 and
R2 positions do not promote the electronic
properties characterization of 1,3,4-oxadiazole-
triazolopyridinone derivatives 5a–5i. From the high
electron affinities, 5a–5i possess the potential of
electron-transporting and highly efficient, blue-
greenish, EL materials.
zine hydrochloride. Triazolopyridinone moiety plays
an excellent assistant role in controlling fundamen-
tal photolytic process.
EXPERIMENTAL
General
Nicotinohydrazide [14] and α-chloroformylaryl-
hydrazines hydrochloride [21] were synthesized
according to literature procedures. All chemicals
were reagent grade and used as purchased. All reac-
tions were carried out under nitrogen atmosphere
and monitored by thin-layer chromatography
(TLC) analysis. Flash column chromatography was
carried out on silica gel (230–400 mesh). Com-
mercially available reagents were used without
further purification unless otherwise noted. Ethyl
acetate, dimethyl sulfoxide, diisopropyl ether,
hexanes, glacid acetic acid, and methanol were
purchased from Mallinckrodt Chemical Co.
Tetrahydrofuran (reagent grade) was purchased
from Aldrich. The following compounds were
purchased from Acoros Chemical Co: Benzoyl
chloride, p-toluoyl chloride, 4-chlorobenzoyl
We successfully prepared a series of new blue
EL materials on the basis of 1,3,4-oxadiazole-
triazolopyridinone moiety by using 1,3,4-oxadiazole-
pyridine derivatives with α-chloroformylarylhydra-
TABLE 1 UV-Vis Absorption Maxima and Photoluminescence Peak Wavelength of 1,3,4-Oxadiazole-Triazolopyridinone
Derivatives 5a–5i
λ
max/nm of UV-Vis
CH2Cl2
λ
max/nm of PL
Compound
R1
R2
CHCl3
CHCl3
CH2Cl2
ꢀfa
4a
4b
4c
5a
5b
5c
5d
5e
5f
H
Me
Cl
H
H
–
–
–
288
288
292
296
295
293
298
297
295
305
301
300
286
285
290
294
294
291
295
295
291
301
298
297
356
356
358
469
470
471
470
468
472
476
477
475
358
358
361
465
468
468
469
466
471
475
472
470
–
–
–
H
0.75
0.72
0.68
0.76
0.69
0.74
0.65
0.68
0.69
Me
OEt
H
Me
OEt
H
H
Me
Me
Me
Cl
Cl
Cl
5g
5h
5i
Me
OEt
aꢀf: Fluorescence quantum efficiency, relative to 2-phenyl-5-(4-biphenyl)-1,3,4-oxadiazole in benzene (ꢀf = 0.8).
Heteroatom Chemistry DOI 10.1002/hc

Synthesis and Characterization of New Blue-Greenish Electroluminescent Materials 215
FIGURE 2 Cyclic voltammogram of 5f in CH2Cl2 containing
0.1 M TBAPF6 at a scan rate.
FIGURE 1 Normalized photoluminescence spectra of 5c, 5f,
and 5i (vacuum evaporated film).
(400 MHz) spectrometer by use of chloroform-
d/DMSO-d6as solvent. Carbon-13 NMR spectra were
obtained on a Varian Unity-400 (100 MHz) spec-
trometer or a Bruker-400 (100 MHz) spectrometer
by use of chloroform-d as solvent. Carbon-13 chem-
ical 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, coupling constant
(hertz). Elemental analyses were carried out on a
Heraeus CHN–O RAPID element analyzer.
chloride, sodium hydrogen carbonate, sodium
hydroxide, and tributyl amine.
Analytical TLC was performed on precoated
plates (silica gel 60 F-254), purchased from
Merck Inc. Mixtures of ethyl acetate and hexanes
were used as eluants. Purification by gravity col-
umn 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) spec-
tra were measured on a Bomem Michelson Series
FT-IR spectrometer. The wave numbers reported are
referenced to the polystyrene 1601 cm−1 absorption.
Absorption intensities are recorded by the follow-
ing abbreviations: s, strong; m, medium; w, weak.
UV-vis spectra were measured with an HP 8452A
diode-array spectrophotometer. PL spectra were ob-
tained on a Perkin-Alemer fluorescence spectropho-
tometer (LS 55). Proton NMR spectra were obtained
on a Varian Unity-400 (400 MHz) or a Bruker-300
Cyclic Voltammetry Measurements
Cyclic voltammetry (CV) and differential pulse
voltammetry (DPV) measurements were performed
on a PGSTAT 20 electrochemical analyzer. The ox-
idation and reduction measurements were carried
out, respectively, in anhydrous CH2Cl2 and anhy-
drous THF containing 0.1 M tetrabutylammonium
TABLE 2 Electrochemical Properties of 1,3,4-Oxadiazole-Triazolopyridinone Derivatives 5a–5i
E onseta
(v)
E ꢁ onsetb
(v)
Ipc,d = EHOMO
Egd,f = Bandgap
Eae,f = ELUMO
Compound
(eV)
energy (eV)
(eV)
5a
5b
5c
5d
5e
5f
5g
5h
5i
1.27
1.17
0.98
1.07
1.04
0.99
1.12
1.46
1.41
1.08
0.98
0.79
0.88
0.85
0.80
0.93
1.27
1.22
–5.88
–5.78
–5.59
–5.68
–5.63
–5.60
–5.93
–6.07
–6.02
3.67
3.68
3.68
3.68
3.69
3.70
3.68
3.68
3.69
–2.21
–2.10
–1.91
–2.00
–1.96
–1.90
–2.05
–2.39
–2.33
aMeasured vs. ferrocene/ferrocenium.
bE ꢁ onset = E onset − 0.19 eV (Measured vs. Ag/AgCl).
cIp = −(Eꢁ onset + 4.8) [19].
dEg: the bandgap energy estimated from the onset wavelength of UV-vis absorption.
eEa = Ip + Eg.
f 1 eV = 96.5 kJ/mol.
Heteroatom Chemistry DOI 10.1002/hc

216 Shin et al.
hexafluorophosphate (TBAPF6) as the supporting
electrolyte at a scan rate of 50 mV s−1. The potentials
were measured against an Ag/Ag+ (0.01 M AgCl) ref-
erence electrode using ferrocene as the internal stan-
dard. The onset potentials were determined from the
intersection of two tangents drawn at the rising cur-
rent and background current of the cyclic voltam-
mogram [19].
1H), 9.22 (s, 1H), 10.58 (s, 1H, NH), 10.95 (s, 1H,
NH).
Standard Procedure for Dehydroxyl-cyclolization
[16]
A solution of benzoic acid(pyridine-3-carbonyl)-
hydrazide compounds 3a–3c in POCl3 (15 mL) was
stirred at 100◦C for 2–4 h. After the reaction was
completed, the reaction mixture was added with cold
water (50 mL) and neutralized with NaOH aque-
ous solution (50 mL) to precipitate. The product
was washed with cold water, filtrated, and dried in
vacuum oven overnight to give the desired product
(4a–4c).
Standard Procedure for Acylation [16]
A solution of nicotinohydrazide and pyridine was
mixed and stirred in CH2Cl2 solution at room
temperature. Benzoyl chloride was added drop-
wise into the reaction mixture and stirred at room
temperature for 3 h. After the reaction was com-
pleted, the reaction mixture was filtered and washed
with CH2Cl2. The filtrate solid was dried in vacuum
oven overnight and crystallized from CH2Cl2 to give
the desired product (3a–3c).
3-(5-Phenyl-1,3,4-oxadiazol-2-yl)pyridine(4a). A
solution of benzoic acid(pyridine-3-carbonyl)-
hydrazide (2a, 3.40 g, 14.1 mmol, 1.0 equivalent)
in POCl3 (15 mL) was stirred at 100◦C for 2–4 h.
After the reaction was completed, the reaction
mixture was added with cold water (50 mL) and
neutralized with NaOH aqueous solution (50 mL)
to precipitate. The product was washed with cold
water, filtrated, and dried in vacuum oven overnight
to obtain a pure 4a (2.64 g, 11.8 mmol) as white
solid in 84% isolated yield: 1H NMR (DMSO-d6,
200 MHz) δ 7.68–7.60 (m, 4H), 8.15 (d, J = 4.1 Hz,
2H, ArH), 8.49 (d, J = 4.2 Hz, 1H), 8.82 (d, J = 4.5,
1H), 9.30 (s, 1H); 13C NMR (DMSO-d6, 50 MHz):
δ 120.45, 122.26, 124.22, 127.18, 130.62, 142.66,
147.73, 152.78, 162.35, 164.66.
Benzoic acid(pyridine-3-carbonyl)hydrazide (3a).
A solution of nicotinohydrazide (2, 2.50 g, 18.2
mmol, 1.0 equivalent) and pyridine (126 mg, 20.1
mmol, 1.1 equivalent) was mixed and stirred in
CH2Cl2 (50.0 mL) solution at room temperature.
Benzoyl chloride (156 mg, 20.3 mmol, 1.1 equiva-
lent) was added dropwise into the reaction mixture
and stirred at room temperature for 3 h. After the
reaction was completed, the reaction mixture was
filtered and washed with CH2Cl2 (150 mL). The fil-
trate solid was dried in vacuum oven overnight and
crystallized from CH2Cl2 to give the pure 3a as white
1
powder in 82% yield (3.60 g, 14.9 mmol): H NMR
(DMSO-d6, 200 MHz) δ 7.60–7.51 (m, 3H, ArH),
7.82 (t, J = 4.0 Hz, 1H), 7.92 (d, J = 4.4 Hz, 2H,
ArH), 8.54 (d, J = 4.0 Hz, 1H), 8.89 (d, J = 3.2 Hz,
1H), 9.19 (s, 1H), 10.69 (s, 1H, NH), 10.96 (s, 1H,
NH).
3-(5-(4-Methylpheny)l-1,3,4-oxadiazol-2-yl)pyri-
dine (4b). The standard procedure was followed,
and the desired product 4b was obtained as white
powder in 84% yield: 1H NMR (DMSO-d6, 200 MHz)
δ 2.39 (s, 3H, CH3), 7.42 (d, J = 3.8 Hz, 2H, ArH),
7.65 (t, J = 6.1 Hz, 1H), 8.02 (d, J = 3.3 Hz, 2H,
ArH), 8.46 (d, J = 3.7 Hz, 1H), 8.80 (d, J = 4.7 Hz,
1H), 9.27 (s, 1H); 13C NMR (DMSO-d6, 50 MHz)
δ 21.57, 120.43, 120.79, 124.73, 127.18, 130.38,
134.60, 142.85, 147.73, 152.84, 162.45, 164.89.
4-Methylbenzoic acid(pyridine-3-carbonyl)hydra-
zide (3b). The standard procedure was followed,
and the desired product 3b was obtained as white
powder in 85% yield: 1H NMR (DMSO-d6, 200 MHz)
δ 2.49 (s, 3H, CH3), 7.33 (d, J = 3.8 Hz, 2H, ArH),
7.86–7.78 (m, 3H), 8.57 (d, J = 3.9 Hz, 1H), 8.91 (d,
J = 3.5 Hz, 1H), 9.20 (s, 1H), 10.60 (s, 1H, NH), 10.93
(s, 1H, NH).
3-(5-(4-Chloropheny)l-1,3,4-oxadiazol-2-yl)pyri-
dine (4c). The standard procedure was followed,
and the desired product 4b was obtained as white
powder in 82% yield: 1H NMR (DMSO-d6, 200 MHz)
δ 7.72–7.65 (m, 3H), 8.15 (d, J = 4.1 Hz, 2H, ArH),
8.48 (d, J = 3.9 Hz, 1H), 8.80 (d, J = 4.2 Hz, 1H),
9.29 (s, 1H); 13C NMR (DMSO-d6, 50 MHz) δ 120.21,
122.44, 124.75, 129.02, 130.02, 134.71, 137.29,
147.84, 152.99, 162.96, 164.08.
4-Chlorobenzoic acid(pyridine-3-carbonyl)hydra-
zide (3c). The standard procedure was followed,
and the desired product 3c was obtained as white
powder in 85% yield: 1H NMR (DMSO-d6, 200
MHz) δ 7.40 (d, J = 3.9 Hz, 2H), 7.92–7.80 (m,
3H), 8.60 (d, J = 4.1 Hz, 1H), 8.88 (d, J = 3.8 Hz,
Heteroatom Chemistry DOI 10.1002/hc

Synthesis and Characterization of New Blue-Greenish Electroluminescent Materials 217
for C21H15N5O2: C, 68.28; H, 4.09; N, 18.96. Found:
C, 68.19; H, 4.09; N, 19.02.
Standard Procedure for Arcycloaddition [16]
A solution of 3-phenyl-1,3,4-oxadiazolpyridine (4a–
4c) was stirred in i-PrOH (15 mL) and triethylamine
(1.0 mL) solution. The reaction mixture was heated
up to 80◦C. α-Chloroformylarylhydrazine hydrochlo-
ride (0.29 g, 1.47 mmol, 1.1 equivalent) was added
into the reaction mixture. After the reaction was
completed, hot filtration was performed and washed
with cold ethanol (10 mL) to isolate the solid crude
product. The crude product was dried and crystal-
lized from CH2Cl2 to give pure 5a–5i as light yellow
solids in 65–72% yields.
2-(4-Ethoxyphenyl)-6-(5-phenyl-1,3,4-oxadiazol-
2-yl)-[1,2,4]triazolo[4,3-a]pyridin-3(2 H)-one (5c).
The standard procedure was followed, and the de-
sired product 5c was obtained as a light yellow solid
1
in 68% yield: mp 214–216◦C; H NMR (DMSO-d6,
200 MHz) δ 1.31 (t, J = 6.9 Hz, 3H, CH3), 4.01 (q, J =
5.18 Hz, 2H, CH2), 4.01 (q, J = 5.18 Hz, 2H, CH2),
7.60–7.47 (m, 4H), 7.72 (d, J = 3.2 Hz, 2H, ArH),
7.78 (d, J = 3.7 Hz, 1H), 8.02 (d, J = 4.0 Hz, 2H,
ArH), 8.30 (d, J = 3.6 Hz, 2H, ArH), 8.81 (s, 1H); 13
C
NMR (DMSO-d6, 50 MHz) δ 14.60, 64.50, 120.12,
120.79, 123.31, 124.49, 126.60, 132.28, 136.90,
143.26, 146.72, 148.23, 153.21, 159.34, 161.21,
166.36, 167.56; IR (KBr) 1608 (m, C N), 1726 (m,
C O) cm−1; FABMS m/z (relative intensity): 400
(M + 1, 28), 354 (100), 77 (33). Anal. Calcd for
C22H17N5O3: C, 66.16; H, 4.29; N, 17.53. Found: C,
66.16; H, 4.26; N, 17.50.
2-Phenyl-6-(5-phenyl-1,3,4-oxadiazol-2-yl)-[1,2,4]-
triazolo[4,3-a]pyridin-3(2H)-one (5a). A solution
of 3-(5-phenyl-1,3,4-oxadiazol-2-yl)pyridine (4a,
0.30 g, 1.34 mmol, 1.0 equivalent) was stirred in
i-PrOH (15 mL) and triethylamine (1.0 mL) solu-
tion. The reaction mixture was heated up to 80˚C.
α-Chloroformylarylhydrazine hydrochloride (0.29
g, 1.47 mmol, 1.1 equivalent) was added into the
reaction mixture. After the reaction was completed,
hot filtration was performed and washed with cold
ethanol (10 mL) to isolate the solid crude product.
The crude product was dried and crystallized from
CH2Cl2 to give pure 5a as a light yellow solid in
65% yield (339 mg, 0.956 mmol): mp 187–189◦C; 1H
NMR (DMSO-d6, 200 MHz) δ 7.35 (t, J = 4.1 Hz,
1H, ArH), 7.67–7.48 (m, 6H), 7.86 (d, J = 3.9 Hz,
1H), 8.08 (d, J = 3.8 Hz, 2H, ArH), 8.24 (d, J = 4.0
Hz, 2H, ArH), 8.81 (s, 1H);13C NMR (DMSO-d6,
50 MHz) δ 120.12, 120.79, 124.31, 125.47, 126.22,
127.18, 130.21, 134.60, 142.85, 146.23, 147.72,
155.21, 157.34, 160.21, 167.36, 168.21; IR (KBr)
1605 (m, C N), 1725 (m, C O) cm−1; FABMS m/z
(relative intensity): 356 (M + 1, 27), 278 (69), 77
(100). Anal. Calcd for C20H13N5O2: C, 67.60; H, 3.69;
N, 19.71. Found: C, 67.66; H, 3.60; N, 19.63.
2-Phenyl-6-(5-(4-methylphenyl)-1,3,4-oxadiazol-
2-yl)-[1,2,4]triazolo[4,3-a]pyridin-3(2 H)-one (5d).
The standard procedure was followed, and the de-
sired product 5d was obtained as a light yellow solid
1
in 66% yield: mp 180–182◦C; H NMR (DMSO-d6,
200 MHz) δ 2.07 (s, 3H, CH3), 7.72 (d, J = 3.4 Hz,
2H, ArH), 7.58–7.48 (m, 3H), 7.33 (t, J = 4.1 Hz, 1H,
ArH), 7.83 (d, J = 4.1 Hz, 1H), 8.06 (d, J = 3.4 Hz,
2H, ArH), 8.24 (d, J = 4.3 Hz, 2H, ArH), 8.81 (s,
1H); 13C NMR (DMSO-d6, 50 MHz) δ 21.57, 120.80,
124.76, 125.92, 126.46, 127.25, 130.98, 134.35,
142.49, 147.76, 155.67, 157.11, 160.65, 167.59,
168.11; IR (KBr) 1602 (m, C N), 1726 (m, C O)
cm−1; FABMS m/z (relative intensity): 370 (M + 1,
21), 292 (100), 91 (60). Anal. Calcd for C21H15N5O2:
C, 68.28; H, 4.09; N, 18.96. Found: C, 68.20; H, 4.05;
N, 18.95.
2-(4-Methylphenyl)-6-(5-phenyl-1,3,4-oxadiazol-
2-(4-Methylphenyl)-6-(5-(4-methylphenyl)-1,3,4-
oxadiazol-2-yl)-[1,2,4]triazolo[4,3-a]pyridin-3(2 H)-
one (5e). The standard procedure was followed,
and the desired product 5e was obtained as a light
2-yl)-[1,2,4]triazolo[4,3-a]pyridin-3(2H)-one
(5b).
The standard procedure was followed, and the
desired product 5b was obtained as a light yellow in
1
1
65% yield: mp 178–180◦C; H NMR (DMSO-d6, 200
yellow solid in 70% yield: mp 189–191◦C; H NMR
MHz) δ 2.18 (s, 3H, CH3), 7.60–7.48 (m, 4H), 7.72 (d,
J = 4.1 Hz, 2H, ArH), 7.90 (d, J = 3.2 Hz, 1H), 8.07
(d, J = 3.5 Hz, 2H, ArH), 8.26 (d, J = 3.8 Hz, 2H,
ArH), 8.81 (s, 1H); 13C NMR (DMSO-d6, 50 MHz)
δ 22.80, 120.12, 124.31, 125.47, 126.22, 128.53,
135.36, 135.47, 141.25, 147.72, 155.25, 158.25,
163.34, 168.52, 169.35; IR (KBr) 1602 (m, C N),
1730 (m, C O) cm−1; FABMS m/z (relative inten-
sity): 372 (M + 1, 30), 148 (100), 91 (40). Anal. Calcd
(DMSO-d6, 200 MHz) δ 2.18–2.05 (m, 6H), 7.65–7.57
(m, 3H), 7.72 (d, J = 3.7 Hz, 2H, ArH), 7.86 (d,
J = 4.0 Hz, 1H), 8.08 (d, J = 4.0 Hz, 2H, ArH),
8.24 (d, J = 3.8, 2H, ArH), 8.82 (s, 1H); 13C NMR
(DMSO-d6, 50 MHz) δ 21.57, 25.67, 120.60, 120.80,
124.92, 126.46, 129.25, 132.98, 136.35, 143.49,
146.23, 157.67, 159.11, 163.64, 168.29, 169.25; IR
(KBr) 1600 (m, C N), 1720 (m, C O) cm−1; FABMS
m/z (relative intensity): 384 (M + 1, 50), 292 (80), 91
Heteroatom Chemistry DOI 10.1002/hc

218 Shin et al.
(100). Anal. Calcd for C22H17N5O2: C, 68.92; H, 4.47;
N, 18.27. Found: C, 68.86; H, 4.50; N, 18.30.
C, 62.46; H, 3.49; N, 17.34. Found: C, 62.52; H, 3.49;
N, 17.32.
2-(4-Ethoxyphenyl)-6-(5-(4-methylphenyl)-1,3,4-
oxadiazol-2-yl)-[1,2,4]triazolo[4,3-a]pyridin-3(2H)-
one (5f). The standard procedure was followed,
and the desired product 5f was obtained as a
light yellow solid in 72% yield: mp 216–218◦C;
1H NMR (DMSO-d6, 200 MHz) 1.31 (t, J = 6.9
Hz, 3H, CH3), 2.07 (s, 3H, CH3), 4.00 (q, J= 6.9
Hz, 2H, CH2), 7.67–7.54 (m, 3H), 7.68 (d, J = 4.1
Hz, 2H, ArH), 7.84 (d, J = 3.7 Hz, 1H), 8.02 (d,
J = 3.5 Hz, 2H, ArH), 8.27 (d, J = 3.2 Hz, 2H, ArH),
8.80 (s, 1H); 13C NMR (DMSO-d6, 50 MHz) δ 15.03,
21.60, 65.22, 120.80, 124.76, 125.92, 126.46, 127.65,
132.98, 134.35, 142.49, 146.23, 147.76, 155.21,
157.64, 160.21, 167.49, 168.35; IR (KBr) 1610 (m,
C N), 1715 (m, C O) cm−1; FABMS m/z (relative
intensity): 414 (M + 1, 17), 121 (100), 77 (41). Anal.
Calcd for C23H19N5O3: C, 66.82; H, 4.63; N, 16.94.
Found: C, 66.86; H, 4.60; N, 16.88.
2-(4-Ethoxyphenyl)-6-(5-(4-chlorophenyl)-1,3,4-
oxadiazol-2-yl)-[1,2,4]triazolo[4,3-a]pyridin-3(2H)-one
(5i). The standard procedure was followed, and the
desired product 5i was obtained as a light yellow
solid in 70% yield: mp 210–212◦C; 1H NMR (DMSO-
d6, 200 MHz) δ 1.30 (t, J = 6.9 Hz, 3H, CH3), 4.00
(q, J = 6.9 Hz, 2H, CH2), 7.68–7.52 (m, 3H), 7.78 (d,
J = 4.1 Hz, 2H, ArH), 7.85 (d,J = 3.6 Hz, 1H), 8.10
(d, J = 4.0 Hz, 2H, ArH), 8.30 (d, J = 3.9 Hz, 2H,
ArH), 8.79 (s, 1H); 13C NMR (DMSO-d6, 50 MHz)
δ 14.25, 21.57, 65.22, 120.50, 124.22, 126.46, 127.55,
130.58, 134.15, 142.69, 146.83, 147.26, 155.37,
157.51, 160.15, 167.29, 168.18; IR (KBr) 1608 (m,
C N), 1718 (m, C O) cm−1; FABMS m/z (relative
intensity): 434 (M + 1, 6), 312 (100), 179 (36). Anal.
Calcd for C22H16N5O3: C, 60.91; H, 3.72; N, 16.14.
Found: C, 60.98; H, 3.69; N, 16.10.
2-Phenyl-6-(5-(4-chlorophenyl)-1,3,4-oxadiazol-
2-yl)-[1,2,4]triazolo[4,3-a]pyridin-3(2 H)-one (5g).
The standard procedure was followed, and the
desired product 5g was obtained as a light yellow
solid in 60% yield: mp 243–245◦C; 1H NMR (DMSO-
d6, 200 MHz) δ 7.33 (t, J = 4.1 Hz, 1H, ArH),
7.64–7.54 (m, 3H), 7.70 (d, J = 3.9 Hz, 2H, ArH),
7.81 (d, J = 3.9 Hz, 1H), 8.05 (d, J = 4.0 Hz, 2H,
ACKNOWLEDGMENTS
We are grateful to the National Science Council of
Republic of China for financial support.
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ArH), 8.25 (d, J = 4.1 Hz, 2H, ArH), 8.81 (s, 1H); 13
C
NMR (DMSO-d6, 50 MHz) δ 120.25, 120.86, 124.25,
125.53, 126.98, 127.56, 131.98, 136.35, 142.26,
146.95, 147.46, 155.35, 157.69, 159.21, 166.89,
167.11; IR (KBr) 1600 (m, C N), 1710 (m, C O)
cm−1; FABMS m/z (relative intensity): 490 (M + 1,
11), 179 (100), 111 (36). Anal. Calcd for C20H12N5O2:
C, 61.63; H, 3.10; N, 17.97. Found: C, 61.68; H, 3.08;
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2-(4-Methylphenyl)-6-(5-(4-chlorophenyl)-1,3,4-
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one (5h). The standard procedure was followed,
and the desired product 5h was obtained as a light
1
yellow solid in 62% yield: mp 202–204◦C; H NMR
(DMSO-d6, 200 MHz) δ 2.18 (s, 3H, CH3), 7.60–7.50
(m, 3H), 7.68 (d, J = 3.4 Hz, 2H, ArH), 7.76 (d,
J = 3.0 Hz, 1H), 8.08 (d, J = 3.8 Hz, 2H, ArH), 8.26
(d, J = 4.0 Hz, 2H, ArH), 8.82 (s, 1H); 13C NMR
(DMSO-d6, 50 MHz) δ 25.57, 120.69, 120.88, 124.56,
125.72, 126.48, 127.26, 130.98, 134.33, 142.49,
146.23, 147.76, 156.67, 159.26, 160.26, 167.57,
168.12; IR (KBr) 1602 (m, C N), 1732 (m, C O)
cm−1; FABMS m/z (relative intensity): 404 (M + 1,
25), 312 (40), 91 (100). Anal. Calcd for C21H14N5O2:
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Heteroatom Chemistry DOI 10.1002/hc