An Expeditious Ultrasound-Initiated Green Synthesis of 1,2,4-Thiadiazoles in Water

Article abstract of DOI:10.1007/s10593-020-02632-5

[Figure not available: see fulltext.] A convenient, environmentally benign, metal- and catalyst-free protocol has been developed for the conversion of thioamides to the corresponding 1,2,4-thiadiazole derivatives with chloranil under ultrasound irradiation in water at room temperature. This paper describes a general procedure for the synthesis of different 1,2,4-thiadiazoles in excellent yield in short reaction time via sonochemistry.

Full text of DOI:10.1007/s10593-020-02632-5

DOI 10.1007/s10593-020-02632-5
Chemistry of Heterocyclic Compounds 2020, 56(1), 123–126
An expeditious ultrasound-initiated green synthesis
of 1,2,4-thiadiazoles in water
Swati Chauhan1, Pratibha Verma1, Ankush Mishra1, Vandana Srivastava1*
1 Department of Chemistry, Indian Institute of Technology, Banaras Hindu University,
Varanasi 221005, India; e-mail: vsrivastava.apc@itbhu.ac.in
Submitted June 5, 2019
Accepted June 26, 2019
Published in Khimiya Geterotsiklicheskikh Soedinenii,
2020, 56(1), 123–126
A convenient, environmentally benign, metal- and catalyst-free protocol has been developed for the conversion of thioamides to the
corresponding 1,2,4-thiadiazole derivatives with chloranil under ultrasound irradiation in water at room temperature. This paper
describes a general procedure for the synthesis of different 1,2,4-thiadiazoles in excellent yield in short reaction time via sonochemistry.
Keywords: aqueous medium, heterocycles, metal- and catalyst-free, one-pot synthesis, oxidative coupling, ultrasound irradiation.
The 1,2,4-thiadiazole is a priviledged heterocyclic
N
N
OMe
N
S
scaffold because of its various biological activities and
associated therapeutic applications. Despite these facts, the
only commercially available 1,2,4-thiadiazole medication
is antibiotic cefozopran,1,2 but 1,2,4-thiadiazoles have a
number of biological activities (Fig. 1).3–10 1,2,4-Thia-
diazoles are privileged building blocks in the synthesis of
many bioactive molecules for the treatment of human
leukemia,11 as cathepsin B inhibitors,12 allosteric modu-
lators,13 factor XIIIa inhibitors,14 non-ATP competitive
glycogen synthase kinase 3 inhibitors,15 dual 5-lipoxy-
genase and cyclooxygenase inhibitors.16 Some of 1,2,4-
thiadiazoles have superb thiol-catching properties17 and
show pronounced muscarinic18 and cardioprotective
properties.19,20 They have been observed to have useful
insecticidal, herbicidal, and fungicidal properties.21
N
N
H
H2N
NH
S
O
N
N
O
O
O
Cefozopran (antimicrobial activity)
O
H
H
N
N
S
S
Cl
N
OH
Me
Me
N
N
H
O
N
N
Me
SEt
Neuroprotective activity
-Secretase inhibitory activity
OMe
N
S
MeO
In order to synthesize 1,2,4-thiadiazole derivatives under
environmentally benign conditions, the combination of
water and ultrasound technique has been applied. In this
communication, metal- and catalyst-free dimerization of
primary thioamide derivatives with chloranil in aqueous
N
N
Cl
N
Cl
Anticancer activity
Figure 1. Biologically active 1,2,4-thiadiazoles.
0009-3122/20/56(1)-0123©2020 Springer Science+Business Media, LLC
123

Chemistry of Heterocyclic Compounds 2020, 56(1), 123–126
medium under ultrasound irradiation is being reported for
thiobenzamide derivatives, and the results are summarized
in Table 2. These reaction conditions with chloranil as
oxidant show extensive functional group tolerance and
prove to be a general method for the synthesis of 3,5-disub-
stituted 1,2,4-thiadiazoles. It was found that the reaction
proceeds smoothly and provides an excellent yield of
desired product within short period of time using thio-
benzamide with electron-donating or electron-withdrawing
substituent. Interestingly, thiobenzamide bearing halogen
substituents such as chlorine and fluorine could also be
reacted in efficient manner to obtain the desired products in
good yield. Likewise, naphthalene-1-carbothioamide (1i)
was successfully transferred into 3,5-di(naphthalen-1-yl)-
the first time.
The reaction conditions were first optimized using
equimolar amounts of thiobenzamide (1a) as a test
substrate and chloranil. The reaction was carried out in
H2O while stirring at room temperature for 3 h and yielded
only 20% of product 2a. In the second run, the reaction
mixture was refluxed for 3 h which gave low yield of the
desired product (Table 1, entry 2). Further on heating the
reaction mixture by conventional method at 50, 80, and
120°C under solvent-free conditions gave the desired
product in 50–70% yield after 3 h (Table 1, entries 3–5). In
order to improve the yield of the product, the reaction was
performed under ultrasound irradiation at room temperature
in H2O. To our surprise, 95% yield was obtained in 3 min.
To investigate the effect of solvents, the reaction was
carried out in different polar and nonpolar solvents.
Although the desired product was obtained in both polar
(H2O, MeCN, THF, EtOH, 1,4-dioxane, CHCl3, CH2Cl2,
DCE, DMSO) and nonpolar solvents (PhH, PhMe), H2O
was found to be the best solvent for the dimerization of
thiobenzamide with chloranil under ultrasound irradiation.
The formation of product 2a was confirmed by spectral
data. 1H NMR spectrum shows doublets at 8.40 (2H,
H-13,17), 8.06 ppm (2H, H-7,11), and multiplet at 7.56–
7.48 ppm (6H, H-8,9,10,14,15,16).22 13C NMR spectrum shows
the characteristic peaks at 188.3 (C-3) and 174.0 ppm (C-5)
which correspond to the 1,2,4-thiadiazole ring carbon atoms
along with other aromatic carbon atoms at 133.1 (C-12);
132.1 (C-15); 130.9 (C-6); 130.5 (C-9); 129.4 (C-14,16);
128.9 (C-8,10); 128.5 (C-13,17); 127.7 ppm (C-7,11).
With optimized reaction conditions, the applicability of
this methodology was examined with the different primary
Table 2. Synthesis of thiadiazole derivatives 2a–j*
Time, Yield**,
Entry
1
Substrate
Product
min
%
3
95
2
3
6
5
95
94
N
S
N
MeO
OMe
2c
4
8
89
Table 1. Effect of reaction conditions
on the yield of model compound 2a*
5
6
7
8
6
7
6
5
91
88
90
94
S
NH2
Entry
Reaction conditions
Solvent
Time
Yield**, %
Cl
1f
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Stirring, rt
Stirring, reflux
50°C
80°C
120°C
Ultrasound (US), rt
US, rt
H2O
H2O
Solvent-free
Solvent-free
Solvent-free
H2O
MeCN
THF
EtOH
1,4-Dioxane 12 min
CHCl3
CH2Cl2
DCE
DMSO
PhH
3 h
3 h
3 h
3 h
3 h
3 min
5 min
10 min
15 min
20
40
50
70
70
95
75
70
85
65
78
79
82
78
71
75
N
S
N
F
F
2g
US, rt
US, rt
US, rt
US, rt
US, rt
US, rt
US, rt
US, rt
9
8
5
87
87
8 min
9 min
7 min
10 min
12 min
15 min
10
US, rt
PhMe
* Reaction conditions: substrate (1.0 mmol) and chloranil (1.1 mmol)
were irradiated with ultrasound in H2O (3 ml) at room temperature.
** Isolated yield.
* Thiobenzamide (1.0 mmol) and chloranil (1.1 mmol), solvent (3 ml).
** Isolated yield.
124

Chemistry of Heterocyclic Compounds 2020, 56(1), 123–126
Scheme 1. Proposed mechanism for the chloranil-mediated condensation of thiobenzamide.
1,2,4-thiadiazole 2i in 87% yield (Table 2, entry 9) within
few minutes. The results established that no significant
electronic and steric effects of the substituents on the
phenyl ring were observed. This reaction also gave good
yield for 3,5-dibenzyl-1,2,4-thiadiazole 2j (Table 2, entry 10).
The corresponding products were obtained in good yield
which show the wide scope of current methodology.
A control experiment was performed using (2,2,6,6-tetra-
methylpiperidin-1-yl)oxyl (TEMPO) as radical trapping
agent and it was observed that TEMPO does not quench
the reaction. This shows that reaction does not proceed via
radical intermediate and a nucleophilic pathway has been
proposed. On the basis of product analysis, a mechanism
for the chloranil-assisted dimerization of primary thio-
benzamide is proposed in Scheme 1. Oxidative addition of
thioamide 1a to chloranil leads to intermediate A, which
dimerizes forming intermediate B. Product 2a is formed
after cyclization of intermediate B.
In summary, we have developed a highly efficient and
rapid conversion of primary thiobenzamides by chloranil in
aqueous solution to the corresponding 1,2,4-thiadiazoles
under ultrasonic irradiation. Ultrasound-induced dimeriza-
tion of thiobenzamides using chloranil in water makes a
highly efficient promoter system for the synthesis of 1,2,4-
thiadiazoles in excellent yield in short reaction time. It is a
valuable addition to the prevailing methods available for
the synthesis of substituted 3,5-diaryl-1,2,4-thiadiazoles.
Synthesis of 1,2,4-thiadiazoles 2a–j (General method).
A flask was charged with primary thiobenzamide 1a–j
(1.0 mmol) and chloranil (270 mg, 1.1 mmol) in H2O
(3 ml). The reaction mixture was irradiated with ultrasound
at room temperature for appropriate time. The progress of
reaction was monitored with TLC. After completion of the
reaction, solvent was concentrated under reduced pressure,
and the obtained residue was subjected to silica gel column
chromatography purification (EtOAc–hexane) to obtain the
desired products.
3,5-Diphenyl-1,2,4-thiadiazole (2a). Yield 226 mg
(95%), white solid, mp 91–92°C (mp 90°C22,23), Rf 0.59
(hexane–EtOAc, 9:1). IR spectrum, ν, cm–1: 3050, 2922,
1599, 1464, 1407, 1315, 1270, 1171, 751. 1H NMR
spectrum, δ, ppm (J, Hz): 8.40 (2H, d, J = 8.1, H Ar); 8.06
(2H, d, J = 9.4, H Ar); 7.56–7.48 (6H, m, H Ar). 13C NMR
spectrum, δ, ppm: 188.3; 174.0; 133.1; 132.1; 130.9; 130.5;
129.4; 128.9; 128.5; 127.7. Found, m/z: 239.0636 [M+H]+.
C14H11N2S. Calculated, m/z: 239.0637.
3,5-Bis(4-methylphenyl)-1,2,4-thiadiazole (2b). Yield
253 mg (95%), white solid, mp 135°C (mp 135–137°C23),
Rf 0.55 (hexane–EtOAc, 9:1). IR spectrum, ν, cm–1: 2962,
1402, 1317, 1011, 842, 735. 1H NMR spectrum, δ, ppm
(J, Hz): 8.27 (2H, d, J = 8.1, H Ar); 7.94 (2H, d, J = 8.0,
H Ar); 7.36–7.29 (4H, m, H Ar); 2.48–2.39 (6H, m, 2CH3).
13C NMR spectrum, δ, ppm: 188.1; 173.9; 142.6; 140.6; 130.5;
130.0; 129.5; 128.4; 128.3; 127.6; 21.8; 21.7. Found, m/z:
267.0948 [M+H]+. C16H15N2S Calculated, m/z: 267.0950.
3,5-Bis(4-methoxyphenyl)-1,2,4-thiadiazole (2c). Yield
280 mg (94%), yellow solid, mp 139–140°C (mp 138–
140°C24), Rf 0.60 (hexane–EtOAc, 9:1). IR spectrum, ν, cm–1:
Experimental
IR spectra were recorded on a PerkinElmer Spectrum
100 FT-IR spectrometer in KBr pellets. The 1H and
13C NMR spectra were recorded on a Bruker Avance 500
spectrometer (500 and 125 MHz, respectively) using
CDCl3 as a solvent and TMS as internal standard. High-
resolution mass spectra were measured on a Waters Quattro
Micro mass spectrometer. Melting points were measured
with a Stuart melting point apparatus SMP10. Ultrasonic
irradiation was performed using a Sonics & Materials
Vibra Cell Ultrasonic Processor VCX750 with a fixed
power of 750 W, 20% amplitude, and a tapered micro tip
was used as ultrasonic probe operating at a frequency of
20 kHz. Thin-layer chromatography was performed using
pre-coated TLC silica gel 60 F254 plates from Merck. TLC
plates were visualized by exposure to UV light with
254 nm wavelength lamp or in I2 chamber. The column
chromatography was performed on silica gel (60–120 mesh)
using a mixture of EtOAc and hexane as an eluent. All the
solvents and chemicals were purchased from commercial
sources and were used without any further purification.
1
2990, 2872, 1632, 1443, 1255, 1295, 1032, 835. H NMR
spectrum, δ, ppm (J, Hz): 8.32 (2H, d, J = 8.9, H Ar); 7.98
(2H, d, J = 8.8, H Ar); 7.02–6.99 (4H, m, H Ar); 3.91–3.86
(6H, m, 2OCH3). 13C NMR spectrum, δ, ppm: 187.5; 173.5;
162.6; 161.4; 130.0; 129.3; 126.2; 123.9; 114.7; 114.1;
55.7; 55.5. Found, m/z: 299.0845 [M+H]+. C16H15N2O2S.
Calculated, m/z: 299.0849.
3,5-Bis(4-tert-butylphenyl)-1,2,4-thiadiazole (2d). Yield
312 mg (89%), white solid, mp 91–92°C (mp 91–93°C24),
Rf 0.52 (hexane–EtOAc, 9:1). IR spectrum, ν, cm–1: 2974,
1
2905, 1724, 1609, 1472, 1495, 1323, 1134, 835. H NMR
spectrum, δ, ppm (J, Hz): 8.32 (1H, d, J = 8.4, H Ar); 7.98
(1H, d, J = 8.3, H Ar); 7.59 (2H, d, J = 8.4, H Ar); 7.55–
7.52 (2H, m, H Ar); 7.48 (2H, d, J = 8.4, H Ar); 1.38 (9H,
s, C(CH3)3); 1.33 (9H, s, C(CH3)3). 13C NMR spectrum,
δ, ppm: 188.0; 174.0; 155.7; 153.7; 130.5; 128.3; 128.3;
127.5; 126.3; 125.8; 35.3; 35.0; 31.4; 31.3. Found, m/z:
351.1887 [M+H]+. C22H27N2S. Calculated, m/z: 351.1889.
125

Chemistry of Heterocyclic Compounds 2020, 56(1), 123–126
1
3,5-Bis[4-(trifluoromethyl)phenyl]-1,2,4-thiadiazole (2e).
Yield 340 mg (91%), white solid, mp 82–83°C (mp 81°C23),
Rf 0.56 (hexane–EtOAc, 9:1). IR spectrum, ν, cm–1: 2927,
1742, 1469, 1319, 1268, 1128, 1063, 894. 1H NMR
spectrum, δ, ppm (J, Hz): 8.51 (2H, d, J = 8.0, H Ar); 8.18
(2H, d, J = 8.0, H Ar); 7.83–7.75 (4H, m, H Ar). 13C NMR
spectrum, δ, ppm (J, Hz): 187.0; 172.7; 135.6; 133.7 (q,
J = 32.7); 132.46; 132.2 (q, J = 32.4); 128.7; 127.9; 126.4
(q, J = 3.7); 125.8 (q, J = 3.7); 124.0 (q, J = 271.0); 123.7
(q, J = 271.0). Found, m/z: 375.0412 [M+H]+. C16H9F6N2S.
Calculated, m/z: 375.0385.
Supplementary information file containing HRMS, H
and 13C NMR spectra of products 2a–j is available at the
journal website at http://link.springer.com/journal/10593.
Swati Chauhan thanks Indian Institute of Technology of
Banaras Hindu University for the financial support. Vandana
Srivastava gratefully acknowledges the Central Instrumen-
tation Facility Center of Indian Institute of Technology of
Banaras Hindu University for the NMR facilities.
References
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3,5-Bis(4-chlorophenyl)-1,2,4-thiadiazole (2f). Yield
270 mg (88%), white solid, mp 161–162°C (mp 159.7–
160.8°C25), Rf 0.55 (hexane–EtOAc, 9:1). IR spectrum,
ν, cm–1: 2925, 1741, 1464, 1424, 1091, 1013, 829, 738.
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H Ar); 7.98 (2H, d, J = 8.6, H Ar); 7.52–7.46 (4H, m, H Ar).
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[M+H]+. C14H9Cl2N2S. Calculated, m/z: 306.9858.
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3,5-Bis(4-fluorophenyl)-1,2,4-thiadiazole (2g). Yield
246 mg (90%), white solid, mp 186–187°C (mp 188.1–
188.6°C25), Rf 0.54 (hexane–EtOAc, 9:1). IR spectrum,
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1
739. H NMR spectrum, δ, ppm (J, Hz): 8.37 (2H, dd,
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J = 8.9, J = 5.5, H Ar); 8.04 (2H, dd, J = 8.8, J = 5.2,
H Ar); 7.23–7.16 (4H, m, H Ar). 13C NMR spectrum,
δ, ppm (J, Hz): 187.1; 172.9; 165.1 (d, J = 252.0); 164.4 (d,
J = 249.0); 130.6 (d, J = 8.6); 129.8 (d, J = 8.8); 129.3 (d,
J = 3.1); 127.2 (d, J = 3.3); 116.7 (d, J = 22.1); 115.9 (d,
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3,5-Bis(4-nitrophenyl)-1,2,4-thiadiazole (2h). Yield
309 mg (94%), yellow solid, mp 200–201°C (mp 201–
203°C24), Rf 0.54 (hexane–EtOAc, 9:1). IR spectrum, ν, cm–1:
1
2924, 2853, 1602, 1536, 1470, 1351, 851, 716. H NMR
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8.37 (4H, m, H Ar); 8.25 (2H, d, J = 8.8, H Ar). 13C NMR
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129.5; 128.6; 124.9; 124.3.
3,5-Di(naphthalen-1-yl)-1,2,4-thiadiazole (2i). Yield
294 mg (87%) white solid, mp 119–120°C (mp 120–
121°C23), Rf 0.52 (hexane–EtOAc, 9:1). IR spectrum, ν, cm–1:
3040, 2925, 1722, 1476, 1384, 1241, 1049, 795, 76.
1H NMR spectrum, δ, ppm (J, Hz): 9.22 (1H, d, J = 8.5,
H Ar); 8.96 (1H, d, J = 8.1, H Ar); 8.50 (1H, dd, J = 7.2,
J = 1.2, H Ar); 8.09–8.05 (2H, m, H Ar); 8.03 (1H, d,
J = 8.2, H Ar); 7.99–7.95 (2H, m, H Ar); 7.69–7.57 (6H,
m, H Ar). 13C NMR spectrum, δ, ppm: 187.1; 174.1; 134.3;
134.2; 132.4; 131.3; 131.2; 130.3; 130.2; 130.1; 129.4;
128.8; 128.7; 128.2; 127.9; 127.4; 126.9; 126.5; 126.2;
125.6; 125.3. Found, m/z: 339.0948 [M+H]+. C22H15N2S.
Calculated, m/z: 339.0950.
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3,5-Dibenzyl-1,2,4-thiadiazole (2j). Yield 231 mg (87%),
yellow oil, Rf 0.63 (hexane–EtOAc, 9:1). IR spectrum,
1
ν, cm–1: 3089, 1590, 1398, 1032, 832. H NMR spectrum,
δ, ppm (J, Hz): 8.50 (2H, d, J = 7.2, H Ar); 7.72–7.66 (1H,
m, H Ar); 7.57–7.53 (2H, m, H Ar); 7.43–7.33 (4H, m, H Ar);
7.29–7.25 (1H, m, H Ar); 4.47 (4H, s, 2CH2). 13C NMR
spectrum, δ, ppm: 187.3; 177.0; 136.9; 134.8; 134.3; 131.3;
129.3; 128.9; 128.8; 127.1; 39.7; 37.6. Found, m/z:
267.0954 [M+H]+. C16H15N2S. Calculated, m/z: 267.0950.
126