Synthesis and characterization of 1,3,4-oxadiazole-triazolopyridinone hybrid derivatives as new blue-greenish photoluminescent materials

Article abstract of DOI:10.1002/jhet.5570440313

(Chemical Equation Presented) Recently, New functionalized oxadiazole-triazolopyridinone hybrid compounds were investigated as photoluminescent materials. In this work, we introduce triazolopyridinone to synthesize a series of oxadiazole-triazolopyridinon

Full text of DOI:10.1002/jhet.5570440313

May-Jun 2007
591
Synthesis and Characterization of 1,3,4-Oxadiazole-
Triazolopyridinone Hybrid Derivatives as New Blue-Greenish
Photoluminescent Materials
Kuo-Chen, Chiang,c,e Fung Fuh Wong,*,a Chih-Shiang Chang,a Mann-Jen Hour,d Yu-
Ling, Wang,e Shaw-Bing Wen,c Mou-Yung Yeh*,b,e
aGraduate Institute of Pharmaceutical Chemistry, China Medical University, No. 91 Hsueh-Shih Rd.
Taichung, Taiwan 40402, R.O.C.
bDepartment of Chemistry, National Cheng Kung University, No 1, Ta Hsueh Rd., Tainan, Taiwan 70101 R. O. C.
cDepartment of Resources Engineering, National Cheng Kung University, No 1, Ta Hsueh Rd.,
Tainan, Taiwan 70101 R. O. C.
dSchool of Pharmacy, China Medical University, No. 91 Hsueh-Shih Rd. Taichung, Taiwan 40402, R.O.C
eSustainable Environment Research Center, National Cheng Kung University,
No 500, Sec. 3, An-ming Rd., Tainan City, Taiwan 709 R.O.C
*Corresponding Author. Tel.: +886 4 2205 3366 ext. 5603; Fax: +886 4 2207 8083.
E-mail address: ffwong@mail.cmu.edu.tw (F. F. Wong).
Received June 20, 2006
5f. R1 = Me, R2 = OMe
5g. R1 = Cl, R2 = H
5a. R1 = H, R2 = H
5b. R1 = H, R2 = Me
O
R1
N
O
5c. R1 = H, R2 = OMe 5h. R1 = Cl, R2 = Me
N
5d. R1 = Me, R2 = H
5e. R1 = Me, R2 = Me
5i. R1 = Cl, R2 = OMe
N
R2
N
N
Recently, New functionalized oxadiazole-triazolopyridinone hybrid compounds were investigated as
photoluminescent materials. In this work, we introduce triazolopyridinone to synthesize a series of
oxadiazole-triazolopyridinone hybrid derivatives as potential photoluminescent materials and explore
the effect of modification of the triazolopyridinone moiety. The ꢀmax values of the photoluminescence
(PL) spectra of 1,3,4-oxadiazole–triazolopyridinone hybrids are promoted to longer wavelengths (470–
486 nm) than the traditional 1,2,3-triazole derivatives (410–425 nm) in solutions. PL spectra 5a, 5d,
and 5g of the vacuum evaporated films on quartz substrates, with a maximum at 487 nm, shows a red-
shift (~15–20 nm), with respect to the solution spectrum. The solution fluorescence quantum yields
(ꢁf) were measured, all of which fell into the range 0.65–0.76, and were determined relative to that of
2-phenyl-5-(4-biphenyl)-1,3,4-oxadiazole in benzene (ꢁf = 0.80). 1,3,4-Oxadiazole–triazolopyridinone
hybrid derivatives show clearly non-reversible reduction processes in cyclic voltammogram
measurements. Following spectroscopic studies and observation of the electrochemical behaviors,
1,3,4-oxadiazole–triazolopyridinone derivatives were determined to be potential efficient blue-
greenish photoluminescent materials.
J. Heterocyclic Chem., 44, 591 (2007).
carbazole [12] and 1,3,4-oxadiazole-spirobifluorene [13]
were well studied. The heterocyclic moieties on the
molecular structure can provide improved hole/injection,
transport properties and confer rigidity.
INTRODUCTION
Organic light-emitting devices (OLEDs) have been an
important subject in recent years due to their
applications in displays and electronic industries [1-3].
Furthermore, blue light-emitting materials have been
essential because of their wild applicability [4-7].
Adachi, et al. reported 2-(biphenyl-4-yl)-5-(4-tert-
butylphenyl)-1,3,4-oxadiazole (PBD) as an excellent
electron transport material (ETM) in an organic
multilayer electroluminescent (EL) diode [8]. After this
report, 1,3,4-oxadiazole derivatives have been widely
exploited as electron-transporting, hole-blocking
(ETHB) materials in electroluminescent (EL) devices
due to their electron-deficient nature, high thermal
stability and high photoluminescence quantum yield
(PLQL) [9-10]. 1,3,4-Oxadiazole-based heterocyclic
compounds were also enthusiastically investigated. For
example, 1,3,4-oxadiazole-pyridine hybrids [11], 1,3,4-
oxadiazole-pyrimidine hybrids [11], 1,3,4-oxadiazole-
In this work, novel 1,3,4-oxadiazole-triazolopyridinone
hybrid derivatives were synthesized in order to explore
the effect of modification of the triazolopyridinone moiety
[14]. We synthesized a series of 8-(1,3,4-oxadiazol-2-yl)-
[1,2,4]triazodone derivatives (5a–5i) in which N1-phenyl
group and the substituted phenyl in 1,3,4-oxadiazole ring
were modified in several ways. Following the spectro-
scopic studies and the measurements of cyclic voltam-
mogram, 1,3,4-oxadiazole-triazolopyridinone derivatives
were highly efficient blue-greenish electroluminescent.
RESULTS AND DISCUSSION
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 4-(5-phenyl-1,3,4-oxadiazol-2-yl)pyridine deriv-
atives (4a–4c) is shown in Scheme 1. Isonicotinyl

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K.-C., Chiang, F. F. Wong, C.-S. Chang, M.-J. Hour, Y.-L., Wang, S.-B. Wen, M.-Y. Yeh
Vol 44
chloride 1 reacted with hydrazine monohydrhydrate to
generate isonicotinyl 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-Isonico-
tinyl-2-nicotinyl hydrazines 3a–3c were performed by the
dehydration–cyclization using fresh POCl3 to produce
1,3,4-oxadiazol-2-ylpyridine derivatives 4a–4c.
are shown in Table 1. The emission wavelengths for 4a–
4c are between 410 nm and 425 nm in CHCl3 solution.
The ꢁmax values of photoluminescence are around 470–486
nm of 1,3,4-oxadiazole-triazolopyridinone derivatives 5a–
5i with the moiety of triazolopyridinone exhibit blue-
greenish fluorescence in CHCl3 solution. The long range
of substitution effects on R1 and R2 positions are not
clearly function for absorption and emission spectra (see
R1
COCl
O
O
NH2NH2. H2O
EtOH
N
N
CH2Cl2
Cl
NHNH2
1
2
R1
O
O
POCl3
N
O
NHNH
N
R1
N
N
3a. R1 = H, 80%
3b. R1 = Me, 84%
3c. R1 = Cl, 76%
4a. R1 = H, 67%
4b. R1 = Me, 72%
4c. R1 = Cl, 70%
Scheme 1
ꢀ-Chloroformylarylhydrazines hydrochloride were
synthesized through our previous published procedures
[17]. 1,3,4-Oxadiazol-2-ylpyridine derivatives 4a–4c
reacted with ꢀ-chloroformylarylhydrazine in i-PrOH at 80
°C for 2 h to generate 1,3,4-oxadiazole-triazolopyridinone
derivatives 5a–5i in 45–66 % yields (see Scheme 2).
Table 1 and Figure 1). The solution fluorescence quantum
yields (ꢂf) of 5a–5i, all of which fall in the range 0.66–
0.76, were determined relative to that of 2-phenyl-5-(4-
biphenyl)-1,3,4-oxzdiazole in benzene (ꢂf = 0.80, see
Table 1) [18]. The PL spectra 5a, 5d, and 5g of the
vacuum evaporated films on quartz substrates, with a
O
R1
N
Cl
+
O
R2
N
i-PrOH
NH2 HCl
N
N
R2 = H, Me, OMe
4a. R1 = H, 4b. R1 = Me, 4c. R1 = Cl
5f. R1 = Me, R2 = OMe, 50%
5g. R1 = Cl, R2 = H, 66%
5h. R1 = Cl, R2 = Me, 65%
5i. R1 = Cl, R2 = OMe, 63%
5a. R1 = H, R2 = H, 50%
O
N
R1
5b. R1 = H, R2 = Me, 53%
5c. R1 = H, R2 = OMe, 45%
5d. R1 = Me, R2 = H, 60%
5e. R1 = Me, R2 = Me, 57%
O
N
N
R2
N
N
Scheme 2
Photophysical properties. The UV-vis spectra of
1,3,4-oxadiazol-2-ylpyridine 4a–4c and 1,3,4-oxadiazole-
triazolopyridinone derivatives 5a–5i was measured in
CH2Cl2 solutions. The ꢁmax values of 4a–4c are between
310 and 314 nm. 1,3,4-oxadiazole-triazolopyridinone
derivatives 5a–5i with the moiety of triazolopyridinone
have gradual red shifts to 300–318 nm due to extension of
conjugation (see Table 1). The photoluminescence (PL)
spectra of 1,3,4-oxadiazol-2-ylpyridine derivatives 4a–4c
and 1,3,4-oxadiazole-triazolopyridinone derivatives 5a–5i
maximum at 487 nm, shows a red-shift (~15–20 nm), with
respect to the solution spectrum as shown in Figure 2.
Cyclic Voltammetry Measurements: The electro-
chemical behavior of 1,3,4-oxadiazole-triazolopyridinone
derivatives 5a–5i were investigated by cyclic voltammetry.
The measurements were carried out with a platinum
electrode in CH2Cl2 containing tetrabutylammonium
hexafluorophosphate (TBAPF6). The potential was
measured against Ag/AgCl as reference electrode and
each measurement was calibrated with an internal

May-Jun 2007
Synthesis and Characterization of 1,3,4-Oxadiazole-Triazolopyridinone Hybrid Derivatives
593
energy (Ip) for 1,3,4-oxadiazole-triazolopyridinone
derivatives 5a–5i were calculated based on the value of –
4.8 eV for Fc with respect to zero vacuum level [19].
Upon the anodic sweep, 5a–5i showed irreversible
reduction processes. As an example, the cyclic voltam-
mogram of 5e is shown in Figure 3. In the case of 5e, the
reversibility of oxidation was estimated and the HOMO
value is –5.35 eV with respect to Ag/AgCl. The bandgap
energies (3.56–3.69 eV) of 1,3,4-oxadiazole-triazolo-
pyridinone derivatives 5a–5i were estimated from the
onset wavelength (ꢀonset) 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
photoluminescent materials.
Table 1. UV-Vis Absorption Maxima and Photoluminescence Peak
Wavelength of 1,3,4-oxadiazole-triazolopyridinone derivatives 5a–5i
a
Compound
ꢂf
ꢀmax /nm of
UV-Vis
ꢀmax /nm of
PL
R1
R2
CH2Cl2
CHCl3
4a
4b
4c
5a
5b
5c
5d
5e
5f
H
Me
Cl
H
H
H
Me
Me
Me
Cl
Cl
Cl
-
-
-
314
310
312
314
308
302
316
318
304
304
301
300
425
425
410
479
476
470
480
486
486
484
482
486
-
-
-
H
0.76
0.71
0.72
0.71
0.69
0.73
0.66
0.65
0.71
Me
OEt
H
Me
OEt
H
5g
5h
5i
Me
OEt
[a] ꢂf: Fluorescence quantum efficiency, relative to 2-phenyl-5-(4-
biphenyl)-1,3,4-oxadiazole in benzene (ꢂf = 0.8).
Table 2. Electrochemical properties of 1,3,4-oxadiazole-
triazolopyridinone derivatives 5a–5i
Compound Eonseta E’onsetb Ipc,d
=
Egd,f
=
Ead,f
=
(v)
(v)
EHOMO
(eV)
Bandgap
energy (eV)
ELUMO
(eV)
5a
5b
5c
5d
5e
5f
5g
5h
5i
1.00
1.00
1.00
0.75
1.22
0.80
0.67
0.63
0.60
0.82
0.82
0.81
0.57
1.04
0.62
0.49
0.45
0.42
–5.62
–5.62
–5.51
–5.37
–5.35
–5.42
–5.39
–5.35
–5.32
3.66
3.69
3.65
3.58
3.57
3.56
3.57
3.58
3.57
–1.91
–1.93
–1.86
–1.79
–1.78
–1.86
–1.82
–1.77
–1.75
[a] Measured vs. ferrocene/ferrocenium. [b] E’onset = Eonset – 0.19
eV (Measured vs. Ag/AgCl). [c] Ip = - (E’onset + 4.8), [d] Eg: the
bandgap energy estimated from the onset wavelength of UV-vis
absorption. [e] Ea = Ip + Eg. [f] 1 eV = 96.5 kJ/mol
Figure 1. Normalized Photoluminescence Spectra of 4a, 5a, 5b, and 5c
in CHCl3 solution.
Figure 3. Cyclic voltammogram of 5e in CH2Cl2 containing 0.1 M
TBAPF6 at a scan rate of 0.01 eV/s.
Figure 2. Normalized Photoluminescence Spectra of 5a, 5d, and 5g
(Vacuum evaporated Film).
We successfully prepared a series of 1,3,4-oxadiazole-
triazolopyridinone hybrid compounds as the blue electro-
luminescent materials by using 1,3,4-oxadiazole-pyridine
derivatives with ꢁ-chloroformylarylhydrazine hydro-
standard, ferrocene/ferrocenium (Fc) redox system [19-
20]. The data are summarized in Table 2 and the HOMO

594
K.-C., Chiang, F. F. Wong, C.-S. Chang, M.-J. Hour, Y.-L., Wang, S.-B. Wen, M.-Y. Yeh
Vol 44
chloride (175 mg, 22.8 mmol, 1.1 equiv.) 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 filtrate solid
was dried in vacuum oven for overnight and crystallized from
CH2Cl2 to give the pure 3a as white powder in 80% yield (3.95
g, 16.3 mmol): 1H NMR (DMSO-d6, 200 MHz) ꢁ 7.46–7.65 (m,
3H, ArH), 7.72–7.95 (m, 4H, ArH), 8.82 (d, J = 4.6 Hz, 2H),
10.50 (s, 1H, NH), 10.64 (s, 1H, NH).
chloride. Triazolopyridinone moiety plays an excellent
assistant role in controlling fundamental photolytic process
EXPERIMENTAL
General. Nicotinohydrazide [14] and ꢀ-chloroformylaryl-
hydrazine hydrochlorides [21] were synthesized according to
literature procedures. All chemicals were reagent grade and used
as purchased. All reactions were carried out under nitrogen
atmosphere and monitored by TLC analysis. Flash column
chromatography was carried out on silica gel (230-400 mesh).
Commercially 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-toluoly chloride, 4-chloro-
benzoyl chloride, sodium hydrogen carbonate, sodium
hydroxide and tributyl amine.
4-Methylbenzoic acid(pyridine-4-carbonyl)hydrazide (3b).
The standard procedure was followed and the desired product 3b
1
was obtained as white powder in 84% yield: H NMR (DMSO-
d6, 200 MHz) ꢁ 2.37 (s, 3H, CH3), 7.32 (d, J = 8.1 Hz, 2H,
ArH), 7.78–7.85 (m, 4H, ArH), 8.79 (d, J = 5.9 Hz, 2H, ArH),
10.55 (s, 1H, NH), 10.83 (s , 1H, NH)
4-Chlorobenzoic acid(pyridine-4-carbonyl)hydrazide (3c).
The standard procedure was followed and the desired product 3c
1
was obtained as white powder in 76% yield: H NMR (DMSO-
d6, 200 MHz) ꢁ 7.59 (d, J = 8.5 Hz, 2H, ArH), 7.76–7.96 (m,
4H, ArH), 8.85 (d, J = 4.9 Hz, 2H, ArH), 10.76 (s, 1H, NH),
10.97 (s, 1H, NH).
Analytical thin-layer chromatography (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 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 wavenumbers reported are referenced to the polystyrene
1601 cm-1 absorption. Absorption intensities are recorded by the
following abbreviations: s, strong; m, medium; w, weak. UV-
visible spectra were measured with an HP 8452A diode-array
spectrphotometer. Photolumimesence (PL) spectra were
obtained on a Perkin-Alemer fluorescence spectrophotometer
(LS 55). Proton NMR spectra were obtained on a Varian Unity-
400 (400 MHz) or a Bruker-300 (400 MHz) spectrometer by use
of chloroform-d as solvent. Elemental analyses were carried out
on a Heraeus CHN–O RAPID element analyzer.
Standard Procedure for Dehydroxyl-cyclolization [16]. A
solution of N'-benzoylisonicotinohydrazide compounds 3a–3c in
POCl3 (15 mL) was stirred at 100 °C for 2–4 h. After the
reaction was complete, the reaction mixture was added to cold
water (50 mL) and neutralized with NaOH aqueous solution (50
mL) to form precipitate. The product was washed with cold
water, collected by filtration and dried in a vacuum oven
overnight to give the desired product (4a–4c).
4-(5-Phenyl-1,3,4-oxadiazol-2-yl)pyridine (4a). A solution
of N'-benzoylisonicotinohydrazide (3a, 3.26 g, 13.5 mmole, 1.0
equiv.) in POCl3 (15 mL) was stirred at 100 °C for 2–4 h. After
the reaction was completed, the reaction mixture was added to
cold water (50 mL) and neutralized with NaOH aqueous solution
(50 mL) to precipitate. The product was washed with cold water,
collected by filtration and dried in vacuum oven overnight to
obtain a pure 4a (2.02 g, 9.03 mmol) as white solid in 67%
1
isolated yield: H NMR (DMSO-d6, 200 MHz) ꢁ 7.63–7.68 (m,
Cyclic Voltammetry Measurements: Cyclic voltammetry
(CV) and differential pulse voltammetry (DPV) measurements
were performed on a PGSTAT 20 electrochemical analyzer. The
oxidation and reduction measurements were carried out,
respectively, in anhydrous CH2Cl2 and anhydrous THF
containing 0.1 M tetrabutylammonium 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) reference electrode using ferrocene as the
internal standard. The onset potentials were determined from the
intersection of two tangents drawn at the rising current and
background current of the cyclic voltammogram [19].
3H, ArH), 8.04–8.08 (m, 2H, ArH), 8.13–8.18 (m, 2H, ArH), 8.85
(d, J = 4.5 Hz, 2H, ArH); FABMS m/z (relative intensity) 224
(M+1, 31), 223 (M, 54), 77 (100). Anal. Calcd for C13H9N3O: C,
69.95; H, 4.06; N, 18.82. Found: C, 69.99; H, 4.03; N, 18.82.
4-(5-(4-Methylpheny)l-1,3,4-oxadiazol-2-yl)pyridine (4b).
The standard procedure was followed and the desired product 4b
1
was obtained as white powder in 72% yield: H NMR (DMSO-
d6, 200 MHz) ꢁ 2.40 (s, 3H, CH3), 7.44 (d, J = 8.1 Hz, 2H,
ArH), 8.02–8.06 (m, 4H, ArH), 8.85 (d, J = 5.9 Hz, 2H, ArH);
FABMS m/z (relative intensity) 238 (M+1, 24), 237 (M, 44).
Anal. Calcd for C14H11N3O: C, 70.87; H, 4.67; N, 17.71. Found:
C, 70.89; H, 4.66; N, 17.74.
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 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. The
filtrate solid was dried in vacuum oven for overnight and
crystallized from CH2Cl2 to give the desired product (3a–3c).
4-(5-(4-Chloropheny)l-1,3,4-oxadiazol-2-yl)pyridine (4c).
The standard procedure was followed and the desired product 4b
was obtained as white powder in 70% yield: 1H NMR (DMSO-d6,
200 MHz) ꢁ 7.70 (d, J = 7.9 Hz, 2H, ArH), 8.05–8.17 (m, 4H,
ArH), 8.87 (d, J = 5.8 Hz, 2H , ArH) ; FABMS m/z (relative
intensity) 258 (M+1, 31), 257 (M, 93).Anal. Calcd for C13H8ClN3O:
C, 60.60; H, 3.13; N, 16.31. Found: C, 60.59; H, 3.16; N, 16.36.
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. ꢀ-Chloroformylaryl-
hydrazine hydrochloride (0.36 g, 1.82 mmole, 1.1 equiv) was
Isonicotinic acid hydrazide (3a).
A
solution of
isonicotinohydrazide (2, 2.81 g, 20.5 mmole, 1.0 equiv.) and
pyridine (142 mg, 22.6 mmol, 1.1 equiv.) was mixed and stirred
in CH2Cl2 (50.0 mL) solution at room temperature. Benzoyl

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595
added into the reaction mixture. After the reaction was
completed, hot-filtration was performed and the material 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–5i as light yellow solids in 45–66% yields.
light yellow solid in 50% yield: mp 236–238 °C (CHCl3); 1H NMR
(DMSO-d6, 200 MHz) ꢁ 2.07 (s, 3H, CH3), 3.80 (s, 3H, CH3), 7.09
(d, J = 8.8 Hz, 2H, ArH), 7.22 (d, J = 7.3 Hz, 1H, ArH), 7.63–7.67
(m, 3H, ArH), 7.95 (d, J = 8.8 Hz, 2H, ArH), 8.11–8.24 (m, 3H,
ArH); IR (KBr) 1718 (m, C=O) cm-1; FABMS m/z (relative intensity)
400 (M+1, 22), 399 (M, 43). Anal. Calcd for C22H17N5O3: C, 66.16;
H, 4.29; N, 17.53. Found: C, 66.12; H, 4.31; N, 17.51.
2-Phenyl-7-(5-phenyl-1,3,4-oxadiazol-2-yl)-[1,2,4]triazolo-
[4,3-a]pyridin-3(2H)-one (5a). A solution of 4-(5-phenyl-1,3,4-
oxadiazol-2-yl)pyridine (4a, 0.36 g, 1.61 mmole, 1.0 equiv) was
stirred in i-PrOH (15 mL) and triethylamine (1.0 mL) solution. The
reaction mixture was heated up to 80 °C. ꢀ-Chloroformylaryl-
hydrazine hydrochloride (0.35 g, 1.76 mmole, 1.1 equiv) was added
into the reaction mixture. After the reaction was completed, hot-
filtration was performed and the material was washed with cold
ethanol (10 mL) to isolate the solid crude product. The crude product
was dried and crystallized from CHCl3 to give pure 5a as a light
yellow solid in 50% yield (313 mg, 885 mmol): mp 257–259 °C
2-Phenyl-7-(5-(4-chlorophenyl)-1,3,4-oxadiazol-2-yl)-[1,2,4]-
triazolo[4,3-a]pyridin-3(2H)-one (5g). The standard procedure
was followed and the desired product 5g was obtained as a light
1
yellow solid in 66% yield: mp 263–265 °C (CHCl3); H NMR
(DMSO-d6, 200 MHz) ꢁ 7.51–7.78 (m, 7H, ArH), 8.05–8.25 (m, 5H,
ArH); IR (KBr) 1725 (m, C=O) cm-1; FABMS m/z (relative intensity)
390 (M+1, 34), 389 (M, 69). Anal. Calcd for C20H12ClN5O2: C, 61.63;
H, 3.10; N, 17.97. Found: C, 61.60; H, 3.12; N, 17.98.
2-(4-Methylphenyl)-7-(5-(4-chlorophenyl)-1,3,4-oxadiazol-
2-yl)-[1,2,4]triazolo[4,3-a]pyridin-3(2H)-one (5h). The standard
procedure was followed and the desired product 5h was obtained
as a light yellow solid in 65% yield: mp 238–239 °C (CHCl3);
1H NMR (DMSO-d6, 200 MHz) ꢁ 2.27 (s, 3H, CH3), 7.08–7.20
(m, 3H, ArH), 7.56 (d, J = 8.6 Hz, 2H, ArH), 7.68–7.72 (m, 4H,
ArH), 8.13 (d, J = 8.6 Hz, 2H, ArH); IR (KBr) 1726 (m, C=O)
cm-1; FABMS m/z (relative intensity) 404 (M+1, 32), 403 (M,
72). Anal. Calcd for C21H14ClN5O2: C, 62.46; H, 3.49; N, 17.34.
Found: C, 62.50; H, 3.47; N, 17.30.
2-(4-Ethoxyphenyl)-7-(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 63% yield: mp 223–225 °C (CHCl3);
1H NMR (DMSO-d6, 200 MHz) ꢁ 3.85 (s, 3H, CH3), 7.01 (d, J
= 8.9 Hz, 2H, ArH), 7.28 (d, J = 7.2 Hz, 2H, ArH), 7.56–7.59
(m, 3H, ArH), 7.97–8.16 (m, 5H, ArH); IR (KBr) 1726 (m,
C=O) cm-1; FABMS m/z (relative intensity) 420 (M+1, 42), 419
(M, 89), 179 (36). Anal. Calcd for C21H14N5O3: C, 60.08; H,
3.36; N, 16.68. Found: C, 60.11; H, 3.33; N, 16.69.
1
(CHCl3); H NMR (DMSO-d6, 200 MHz) ꢁ 7.20–7.33 (m, 2H,
ArH), 7.37–7.47 (m, 5H, ArH), 8.05–8.27 (m, 6H, ArH); IR (KBr)
1710 (m, C=O) cm-1; FABMS m/z (relative intensity) 356 (M+1, 20),
355 (M, 39), 77 (100). Anal. Calcd for C20H13N5O2: C, 67.60; H,
3.69; N, 19.71. Found: C, 67.63; H, 3.70; N, 19.68.
2-(4-Methylphenyl)-7-(5-phenyl-1,3,4-oxadiazol-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 53% yield: mp 250–252 °C (CHCl3); 1H NMR
(DMSO-d6, 200 MHz) ꢁ 2.22 (s, 3H, CH3), 7.06–7.15 (m, 4H,
ArH), 7.43–7.62 (m, 6H, ArH), 8.03–8.09 (m, 2H, ArH); IR
(KBr) 1711 (m, C=O) cm-1; FABMS m/z (relative intensity) 370
(M+1, 31), 369 (M, 83), 91 (40). Anal. Calcd for C21H15N5O2:
C, 68.28; H, 4.09; N, 18.96. Found: C, 68.31; H, 4.11; N, 18.98.
2-(4-Methoxyphenyl)-7-(5-phenyl-1,3,4-oxadiazol-2-yl)-
[1,2,4]triazolo[4,3-a]pyridin-3(2H)-one (5c). The standard
procedure was followed and the desired product 5c was obtained
as a light yellow solid in 45% yield: mp 253–255 °C (CHCl3); 1H
NMR (DMSO-d6, 200 MHz) ꢁ 3.80 (s, 3H, CH3) , 7.11 (d, J = 8.8
Hz, 2H, ArH), 7.21 (d, J = 7.4 Hz, 1H, ArH), 7.64–7.68 (m, 3H,
ArH), 7.95 (d, J = 8.8 Hz, 2H, ArH), 8.11–8.23 (m, 4H, ArH); IR
(KBr) 1709 (m, C=O) cm-1; FABMS m/z (relative intensity) 386
(M+1, 31), 385 (M, 55). Anal. Calcd for C21H15N5O3: C, 65.45; H,
3.92; N, 18.17. Found: C, 65.41; H, 3.95; N, 18.22.
Acknowledgement. We are grateful to the National Science
Council of Republic of China for financial support..
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triazolo[4,3-a]pyridin-3(2H)-one (5d). The standard procedure
was followed and the desired product 5d was obtained as a light
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