Synthesis and spectral characterization of novel 1,3,4-oxadiazole and 1,2,4-triazole derivatives: Synthesis for potential pharmacological activities

Article abstract of DOI:10.1080/10426500210235

Oxadiazole derivatives (3a,b) and (4a,b) were obtained in a good yield by the reaction of the benzylidene derivatives (2a,b) with acetic anhydride and yellow mercuric oxide respectively. Cyclodesulfurization of the thiosemicarbazide derivatives (5a-c) with yellow mercuric oxide afforded the oxadiazoles (7a-c). On the other hand, reaction of (5a-c) with sodium hydroxide gave the triazoles (6a-c). The structures of the isolated products were fully determined by spectral methods.

Full text of DOI:10.1080/10426500210235

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Phosphorus, Sulfur, and Silicon and the Related
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Synthesis and Spectral Characterization of Novel 1,3,4-
Oxadiazole and 1,2,4-Triazole Derivatives: Synthesis
for Potential Pharmacological Activities
Hassan M. Faidallah a , Essam M. Sharshira a , Salem A. Basaif b & Abd El-Kader A-Ba-Oum b
a Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt
b Chemistry Department, Faculty of Science, University of King Abdulaziz, Jaddah, Saudi
Arabia
Published online: 27 Oct 2010.
To cite this article: Hassan M. Faidallah , Essam M. Sharshira , Salem A. Basaif & Abd El-Kader A-Ba-Oum (2002) Synthesis and
Spectral Characterization of Novel 1,3,4-Oxadiazole and 1,2,4-Triazole Derivatives: Synthesis for Potential Pharmacological
Activities, Phosphorus, Sulfur, and Silicon and the Related Elements, 177:1, 67-79, DOI: 10.1080/10426500210235
To link to this article: http://dx.doi.org/10.1080/10426500210235
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Phosphorus, Sulfur and Silicon, 2002, 177:67–79
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SYNTHESIS AND SPECTRAL CHARACTERIZATION
OF NOVEL 1,3,4-OXADIAZOLE AND 1,2,4-TRIAZOLE
DERIVATIVES: SYNTHESIS FOR POTENTIAL
PHARMACOLOGICAL ACTIVITIES
Hassan M. Faidallah,a Essam M. Sharshira,a
Salem A. Basaif,b and Abd El-Kader A-Ba-Oumb
aChemistry Department, Faculty of Science, Alexandria
University, Alexandria, Egypt and bChemistry Department,
Faculty of Science, University of King Abdulaziz, Jaddah,
Saudi Arabia
(Received May 11 2001.)
Oxadiazole derivatives (3a,b) and (4a,b) were obtained in a good yield
by the reaction of the benzylidene derivatives (2a,b) with acetic anhy-
dride and yellow mercuric oxide respectively. Cyclodesulfurization of
the thiosemicarbazide derivatives (5a–c) with yellow mercuric oxide
afforded the oxadiazoles (7a–c). On the other hand, reaction of (5a–c)
with sodium hydroxide gave the triazoles (6a–c). The structures of the
isolated products were fully determined by spectral methods.
Keywords: 1,2,4-triazole; 1,3,4-oxadiazole; thiosemicarbazide
INTRODUCTION
It has been reported that disubstituted thiosemicarbazides derivatives
undergo oxidative cyclization to oxadiazoles,1,2 mercaptotriazoles,3 and
thiadiazoles4 depending on the oxidizing reagent used. Moreover, oxida-
tive cyclization of benzylidene derivatives were also extensively used
8
as a good precursor for the synthesis of oxadiazole derivatives.5 In
this study, we have explored the generality of that type of ring closure
in the synthesis of new 1,3,4-oxadiazole and 1,2,4-triazole derivatives.
1,3,4-oxadiazoles were reported to show many biological activities for
example, bactericide9 and fungicide8 10 properties. It is also reported in
the literature that some 1,2,4-triazoles have shown biological applica-
tion such as antiinflammatory,11 and antihistaminic properties.12 These
Address correspondence to Essam M. Sharshira, Chemistry Department, Faculty of
Science, Alexandria University, Alexandria, Egypt.
67

68
H. M. Faidallah et al.
observations, and our interest in the chemistry of oxadiazoles1,2,13 and
triazoles,13 prompted us to synthesize unreported derivatives of 1,3,4-
oxadiazole and 1,2,4-triazole.
DISCUSSION
2-substituted 3-benzylidenehydrazinocarbonyl-4, 5-dihydronaphtho
[1,2-c]pyrazoles (2a–c) for oxadiazoles (3a,b) and (4a,b) syntheses were
prepared by the condensation of hydrazides derivatives (1a–c) with
benzaldehyde.7 On the other hand, thiosemicarbazides (5a–c) for tri-
azoles (6a–c) and oxadiazoles (7a–c) syntheses were prepared by the
reaction of hydrazides (1a–c) with phenyl isothiocyanate. The results
of the reactions are outlined in Scheme 1, Table I and Table II.
SCHEME 1
The structure of the benzylidene derivatives (2a–c) was confirmed
1
from their spectral data. For example, their H NMR spectra showed
beside the aliphatic, aromatic, and NH protons a singlet of one proton
intensity at 8.55–8.62 for the CH. This high deshielded value for the
azomethine proton confirm the structure (See Experimental Section).

Oxadiazoles and Triazoles
69
TABLE I Characterization Data of Benzylidenes (2a–c), Oxadiazolines
(3a,b), and Oxadiazoles (4a,b)
Product
R
Yield (%)
Melting point ( C) Reaction time (h)
2a
2b
2c
3a
3b
4a
4b
Ph
74
57
69
64
55
60
51
112
214
287
86
195
150
172
3
3
3
2
2
p-ClC6H4
p-NH2SO2C6H4
Ph
p-ClC6H4
Ph
48
48
p-ClC6H4
Cyclization of the benzylidenes (2a,b) with acetic anhydride5 gave
the corresponding 2-aryl-3-(40-acetyl-50-phenyl-40, 50-dihydro-10,30,40-
oxadiazol-20-yl)-4, 5-dihydronaphtho[1, 2-c]pyrazoles (3a,b). The mech-
anism of the cyclization reaction5 is outlined in Scheme 2. The reaction
would be initiated by nucleophilic addition of acetic anhydride at the
SCHEME 2
TABLE II Characterization Data of Triazoles (6a–c) and Oxadiazolines
(7a–c)
Product
R
Yield (%)
Melting point ( C) Reaction time (hours)
6a
6b
6c
7a
7b
7c
Ph
72
68
63
61
57
64
138
281
218
119
167
260
1
1
1
4
4
4
p-ClC6H4
p-NH2SO2C6H4
Ph
p-ClC6H4
p-NH2SO2C6H4

70
H. M. Faidallah et al.
azomethine carbon of the carbazone moiety followed by tautomeriza-
tion. Subsequent nucleophilic attack by the unshared electron over the
oxygen atom of the hydroxyl group at the benzylic carbon and loss of
acetic acid afford the desired product (3a,b).
The infrared spectra of the dihydrooxadiazole derivatives (3a,b)
lacked the NH band but showed a carbonyl absorption at 1667–
1668 cm 1 for the acetyl group. Their structures were further confirmed
from 1H NMR spectra which lacked the CH singlet exist in the start-
ing benzylidene and exhibited a singlet of three proton intensity at
2.13–2.15 ppm for the COCH3. The 13C NMR spectrum of the N-acetyl
oxadiazole derivative (3b) exhibited beside the aromatic carbons, three
signals at 19.99, 29.99, and 92.00 for the C-4, C-5, and CH, respectively
as well as a carbonyl carbon at 167.83 ppm. These observations are in
accordance with mass spectrum of (3b). The probable structure of the
common prominent peaks as well as their fragmentation pathways are
shown in Scheme 3, which does not show molecular ion peak. However,
some other fragments are well observed which confirmed its structure.
The base peak appeared at m/z 57 and was assigned to the oxiranium or
oxadiaztium ions (14) or (15) respectively. Loss of three hydrogen atoms
from the molecular ion gives rise to the weak abundant ion at m/z 465.
Fragmentation of the molecular ion according to pathway (A) gives the
cation (8) and the radical cation (9) at m/z 279 and 189, respectively,
while loss of hydrogen atom (pathway B) yields the moderately intense
radical cations (10) and (11) at m/z 352 and 115 respectively. Successive
elimination of NCOCH3 and PhCH radicals from (10) gives rise to the
weakly intense peak at m/z 205 formulated as the radical cation (12).
The strong intense peak at m/z 149 is formulated as the radical cation
(13) formed by successive loss of NCO and N radicals from (12). Other
fragmentations are also shown in Scheme 3.
On the other hand, oxidation of benzylidene derivatives (2a,c) with
yellow mercuric oxide and iodine in anhydrous conditions afforded the
corresponding oxadiazole derivatives (4a,b). The plausible mechanism
for oxidative cyclization to oxadiazoles (4) are outlined in Scheme 4.
The benzylidene derivative (2) looses hydrogen atom under the in-
fluence of oxidizing I2/HgO to afford a radical (16) which undergoes
conjugation to afford radicals (17) and (18). Cyclization of radical (18)
with subsequent elimination of another hydrogen atom affords the de-
sired oxadiazole (4).
The structure of the oxadiazoles (4a,b) are supported by the infrared
spectra which does not reveal the presence of NH band present in the
1
starting benzylidenes (2a,b). Moreover, the H NMR spectra does not
show the benzylidene as well as the NH protons characteristic for the
starting compounds (2a,b).

71

72
H. M. Faidallah et al.
SCHEME 4
Next, treatment of thiosemicarbazide derivatives (5a–c)14 with aque-
ous sodium hydroxide afforded the desired 1,2,4-triazoles (6a–c). The
infrared spectra of (6a–c) indicating their existance in the thiol form
rather than thione one. It showed a SH stretching absorption at 2560–
1
2565 cm and lack of any NH stretching. Moreover, their 13C NMR
spectra further confirmed the thiol form over the thione one since no
C S signal was appeared in the spectra. The mass spectrum of the tria-
zole derivative (6b) showed no molecular ion peak but we could identify
some other fragments that confirmed the structure. Fragmentation of
the molecular ion gives rise to the species (20) and (21) at m/z 280
and 177 respectively. Elimination of N2 molecule from (21) leads to the
strong intense peak (22) at m/z 149, while successive loss of NPh and
hydrogen radicals from (21) gives rise to the cation (23) at m/z 84. The
base peak at m/z 163 arises from (21) by lossing nitrogen radical. Other
fragmentation are outlined in Scheme 5.
On the other hand, treatment of the thiocarbazide derivatives
(5a–c) with yellow mercuric oxide afforded the corresponding oxadi-
azoles (7a–c) in a good yield. Their structures were assigned on the

73

74
H. M. Faidallah et al.
SCHEME 6
basis of their elemental analyses and spectral data. The infrared spectra
1
revealed a C N stretching vibrations at 1583–1599 cm as well as
1
an NH absorptions at 3255–3349 cm 1. The H NMR showed also an
exchangeable NH signal. The structure of the oxadiazole derivatives
was further confirmed by mass spectra (Scheme 6).
EXPERIMENTAL
1H and 13C NMR spectra were recorded on Bruker DPX-400FT NMR
spectrometers using TMS as internal standard. Mass spectra were de-
termined on a Kratos MS 30. The infrared spectra were measured on

Oxadiazoles and Triazoles
75
a Nicolet Magna FT 520 spectrophotometer using potassium bromide
pellets. Microanalyses were performed on a 2400 Perkin Elmer Series
2 CHNS analyzer. Melting points were determined on a Gallenkamp
melting point apparatus and are uncorrected.
2-phenyl-3-benzylidenehydrazinocarbonyl-4,
5-dihydronaphtho[1,2-c]pyrazole (2a)
A solution of benzaldehyde (0.17 g, 1.7 mmol) in ethanol (3 ml)
was added to a solution of an equimolar amount of 2-phenyl-4,5-
dihydronaphtho[1,2-c]pyrazole-3-carbohydrazide (1a, 0.5 g, 1.7 mmol)
in ethanol (15 ml). The reaction mixture was heated under reflux for
3 h, concentrated, and then left at room temperature overnight. The
product which separated was filtered off, washed with ethanol (3 ml),
dried, and recrystallized from ethanol to give 2a as cream needles.; ir
1
(potassium bromide): 1598 (C N), 1666 (C O), and 3262 cm (NH);
1H NMR (deuteriochloroform): 3.10 (m, 4H, H-4 and H-5), 7.34 (m,
ArH and NH), 8.58 (s, 1H, CH ). Anal. Calcd. for C25 H20N4O: C, 76.53;
H, 5.10; N, 14.29. Found: C, 76.62; H, 5.18; N, 14.38.
2-p-chlorophenyl-3-benzylidenehydrazinocarbonyl-4,
5-dihydronaphtho[1,2-c]pyrazole (2b)
Compound (2b) was obtained as cream crystals from ethanol in a man-
ner similar to the synthesis of (2a); ir (potassium bromide): 1544 (C N),
1
1666 (C O), and 3262 cm (NH); 1H NMR (DMSO-d6): 3.08 (m, 4H,
H-4 and H-5), 7.38 (m, ArH and NH), 8.55 (s, 1H, CH ). Anal. Calcd.
for C25 H19ClN4O: C, 70.34; H, 4.45; N, 13.13. Found: C, 70.45; H, 4.56;
N, 13.34.
2-p-sulfamylphenyl-3-benzylidenehydrazinocarbonyl-4,
5-dihydronaphtho[1,2-c]pyrazole (2c)
Compound 2c was obtained as pale yellow crystals from ethanol in a
manner similar to the synthesis of (2a); ir (potassium bromide): 1345–
1
1166 (SO2N). 1548 (C N), 1682 (C O), and 3331 cm (NH); 1H NMR
(DMSO-d6): 3.05 (m, 4H, H-4 and H-5), 7.53 (m, ArH and NH), 8.62
(s, 1H, CH ) Anal. Calcd. for C25 H21N5O3S: C, 63.69; H, 4.46; N, 14.86;
S. 6.79. Found: C, 63.81; H, 4.62; N, 14.77; S; 6.89.

76
H. M. Faidallah et al.
2-phenyl-3-(40-acetyl-50-phenyl-40, 50-dihydro-10,30,
40-oxadiazol-20-yl)-4,5-dihydronaphtho[1,2-c]pyrazole (3a)
A mixture of 2-phenyl-3-benzylidenehydrazinocarbonyl-4,5-dihydro-
naphtho[1,2-c]pyrazole (2a) (0.2 g, 0.5 mmol) and acetic anhydride
(10 ml) was heated under reflux for 3 h. After the reaction mixture
attained room temperature, it was poured into crushed ice and the
oily product deposited was decanted from water and extracted with
ether. The ether layer was washed with sodium bicarbonate, followed
by water, dried over anhydrous sodium sulphate, and evaporated to
give (3a) as yellow needles.; ir (potassium bromide): 1597 (C N) and
1668 cm 1 (C O); 1H NMR (deuteriochloroform): 2.15 (s, 3H, CH3CO),
3.05 (m, 4H, H-4 and H-5), 7.19 (m, ArH and OCHPh). Anal. Calcd. for
C27 H22N4O2: C, 74.65; H, 5.07; N, 12.90. Found: C, 74.85; H, 5.22;
N, 13.01.
2-p-chlorophenyl-3-(40-acetyl-50-phenyl-40, 50-dihydro-10,30,
40-oxadiazol-20-yl)-4,5-dihydronaphtho[1,2-c] pyrazole (3b)
Compound 2c was obtained as pale yellow crystals from ethanol in a
manner similar to the synthesis of (3a); ir (potassium bromide): 1590
1
(C N) and 1667 cm (C O); 1H NMR (deuteriochloroform/DMSO-d6):
2.13 (s, 3H, CH3CO), 3.08 (m, 4H, H-4, and H-5), 7.14 (m, ArH and
OCHPh). Ms: m/z (relative abundance) 465 (1), 422 (2), 352 (21), 324
(1), 296 (2), 279 (25), 244 (4), 205 (4), 189 (2), 168 (4), 163 (3), 151 (10),
149 (85), 145 (3), 129 (11), 115 (10), 105 (21), 97 (23), 91 (5), 77 (6), 71
(37), 69 (51), 64 (8), 57 (100). Anal. Calcd. for C27 H21ClN4O2: C, 69.16;
H, 4.48; N, 11.95. Found: C, 69.50; H, 4.82; N, 11.76.
2-phenyl-3-(50-phenyl-10,30,40-oxadiazol-20yl)-4,
5-dihydronaphtho[1,2-c]-pyrazol (4a)
A mixture of 2-phenyl-3-benzylidenehydrazinocarbonyl-4, 5-dihydr-
onaphtho[1,2-c]pyrazole (2a, 0.2 g, 0.5 mmol) in dry ether (50 ml) was
stirred with yellow mercuric oxide (1.0 g), magnesium oxide (0.4 g) and
iodine (1.0 g) at room temperature for 48 h under anhydrous condition.
The reaction mixture was filtered off and the ether layer washed with
5% potassium iodide (50 ml), 5% sodium thiosulphate (50 ml), water,
dried over anhydrous sodium sulphate, and evaporated to give (4a) as
1
1
yellow needles.; ir (potassium bromide): 1595 cm (C N); H NMR
(deuteriochloroform): 3.09 (m, 4H, H-4 and H-5), 7.25 (m, ArH). Anal.
Calcd. for C25 H18N4O: C, 76.92; H, 4.62; N, 14.36. Found: C, 77.13; H,
4.43; N, 14.58.

Oxadiazoles and Triazoles
77
2-p-chlorophenyl-3-(50-phenyl-10,30, 40-oxadiazol-20yl)-4,
5-dihydronaphtho-[1,2-c]-pyrazol (4b)
Compound (4b) was obtained as pale yellow crystals from ethanol in
a manner similar to the synthesis of (4a); ir (potassium bromide):
1
1
1598 cm (C N); H NMR (deuteriochloroform): 3.07 (m, 4H, H-4
and H-5), 7.12 (m, ArH). Anal. Calcd. for C25 H17ClN4O: C, 70.67; H,
4.00; N, 13.19. Found: C, 70.75; H, 4.11; N, 13.25.
2-phenyl-3-(50-mercapto-40-phenyl-10,20, 40-triazol- 30-yl)-4,
5-dihydronaphtho[1,2-c]pyrazol (6a)
A
solution of N-phenyl-N0-(2-phenyl-4, 5-dihydronaphtho [1,2-c]
pyrazol-3-yl-carbonyl)thiosemicarbazide (5a) (0.3 g, 0.7 mmol) in 5%
sodium hydroxide (5 ml) was heated to reflux for 1 h. The reaction mix-
ture was filtered while hot, cooled, and acidified with dilute HCl to pH 6.
The separated product was filtered off, washed with water till neutral
washings, dried, and recrystallized from ethanol-benzene mixture (2:1)
to yield (6a) as yellow needles.; ir (potassium bromide): 1596 (C N) and
1
2565 cm (SH); 1H NMR (deuteriochloroform): 3.05 (m, 4H, H-4 and
H-5), 7.36 (m, ArH). Anal. Calcd. for C25 H19N5S: C, 71.26; H, 4.51; N,
16.60; S, 7.60, Found: C, 71.40; H, 4.46; N, 16.82; S, 7.80.
2-p-chlorophenyl-3-(50-mercapto-40-phenyl-10,20,
40-triazol-30-yl)-4,5-dihydronaphtho[1,2-c]pyrazol (6b)
Compound (6b) was obtained as pale yellow crystals from ethanol-
benzene mixture (2:1) in a manner similar to the synthesis of (6a);
1
ir (potassium bromide): 1593 (C N) and 2560 cm (SH); 1H NMR
(deuteriochloroform/DMSO-d6): 2.88 (m, 4H, H-4 and H-5), 7.16 (m,
ArH). Ms: m/z (relative abundance) 455 (M+, 1), 280 (1), 266 (69, 252 (2),
177 (1), 164 (11), 163 (11), 150 (1), 149 (21), 135 (4), 109 (2), 104 (7), 84
(6), 77 (14), 71 (9), 57 (19), 56 (10). Anal. Calcd. for C25 H18N5S: C, 65.86;
H, 3.95; N, 15.37; S, 7.03. Found: C, 65.96; H, 4.00; N, 15.28; S, 7.20.
2-p-chlorophenyl-3-(50-mercapto-40-phenyl-10,20,
40-triazol-30-yl)-4,5-dihydronaphtho[1,2-c]pyrazol (6c)
Compound (6c) was obtained as cream needles from ethanol-benzene
mixture (2:1) in a manner similar to the synthesis of (6a); ir (potassium
bromide): 1332, 1160 (SO2N), 1594 (C N) and 2575 cm 1 (SH); 1H NMR
(deuteriochloroform/DMSO-d6): 3.06 (m, 4H, H-4 and H-5), 7.45 (m,
ArH). Anal. Calcd. for C25 H20N6O2S2: C, 60.00; H, 4.00; N, 16.80; S,
12.80. Found: C, 60.12; H, 3.95; N, 16.61; S, 12.45.

78
H. M. Faidallah et al.
2-phenyl-3-(50-phenylamino-10,30, 40-oxadiazol-20-yl)-4,
5-dihydronaphtho[1,2-c]pyrazole (7a)
Finally powdered yellow mercuric oxide (0.18 g, 0.8 mmol) was
added portionwise over a period of 30 min to a boiling solution
of N-phenyl-N0-(2-phenyl-4,5-dihydronaphtho[1,2-c]pyrazol-3-yl-carbo-
nyl)thiosemicarbazide (5a) (0.3 g, 0.7 mmol) in ethanol (20 ml). The
suspension was stirred and heated to reflux for 4 h and then filtered.
The black precipitate (HgS) formed was washed with boiling ethanol
(10 ml). The combined filtrate and washings were concentrated and set
aside overnight at room temperature. The separated product were re-
crystallized from ethanol to yield 7a as cream needles.; ir (potassium
bromide): 1598 (C N) and 3279 cm 1 (NH). Anal. Calcd. for C25 H19N5O:
C, 74.07; H, 4.69; N, 17.28. Found: C, 73.96; H, 4.40; N, 17.50.
2-p-chlorophenyl-3-(50phenylamino-10,30,40-oxadiazol-
20-yl)-4,5-dihydronaphtho[1,2-c]pyrazole (7b)
Compound (7b) was obtained as cream needles from ethanol in a man-
ner similar to the synthesis of (7a); ir (potassium bromide): 1599 (C N)
and 3255 cm 1 (NH); 1H NMR (deuteriochloroform): 3.08 (m, 4H, H-4
and H-5), 7.27 (m, ArH), 9.52 (broad s, 1H, NH). Ms: m/z (relative abun-
dance) 337 (1), 322 (1), 303 (1), 266 (6), 252 (2), 177 (2), 163 (100), 149
(13), 139 (1), 125 (1), 111 (1), 104 (7), 84 (7), 77 (14), 69 (9), 57 (21). Anal.
Calcd. for C25 H18N5O: C, 68.26; H, 4.10; N, 15.93. Found: C, 68.67; H,
3.98; N, 16.02.
2-p-sulfamylphenyl-3-(50-phenylamino-10,30,40-oxadiazol-
20-yl)-4,5-dihydronaphtho [1,2-c]pyrazole (7c)
Compound (7c) was obtained as cream needles from ethanol in a man-
ner similar to the synthesis of (7a); ir (potassium bromide): 1330, 1164
1
1
(SO2N), 1583 (C N), and 3265, 3344 cm (NH and NH2); H NMR
(DMSO-d6): 3.10 (m, 4H, H-4 and H-5), 7.37 (m, ArH and NH2), 9.62
(broad s, 1H, NH). Anal. Calcd. for C25 H20N6O3: C, 61.98; H, 4.13; N,
17.63; S, 6.61. Found: C, 61.32; H, 3.93; N, 16.95; S, 6.43.
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