A facile synthesis of (Z)-5-(substituted)-2-(methylthio)thiazol-4(5H)-one using microwave irradiation and conventional method

Article abstract of DOI:10.1016/j.tetlet.2013.12.113

A new effective approach to the synthesis of some new (Z)-5-(substituted)- 2-thioxothiazolidin-4-one 3a-l and (Z)-5-(substituted)-2-(methylthio)thiazol- 4(5H)-one 5a-l is reported under microwave irradiation as well as conventional conditions.

Full text of DOI:10.1016/j.tetlet.2013.12.113

Accepted Manuscript
A facile synthesis of (Z)-5-(substituted)-2-(methylthio)thiazol-4(5H)-one using
microwave irradiation and conventional method
Dattatraya N. Pansare, Devanand B. Shinde
PII:
S0040-4039(13)02211-9
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.12.113
TETL 44027
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
16 November 2013
28 December 2013
28 December 2013
Please cite this article as: Pansare, D.N., Shinde, D.B., A facile synthesis of (Z)-5-(substituted)-2-
(methylthio)thiazol-4(5H)-one using microwave irradiation and conventional method, Tetrahedron Letters (2013),
doi: http://dx.doi.org/10.1016/j.tetlet.2013.12.113
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A facile synthesis of (Z)-5-(substituted)-2-(methylthio)thiazol-4(5H)-one using
microwave irradiation and conventional method
Dattatraya N. Pansare and Devanand B. Shinde*
Department of Chemical Technology, Dr. Babasaheb Ambedkar Marathwada University,
Aurangabad 431 004, MS, India.
*Corresponding author E-mail: dbsdattatraya10@rediffmail.com
Tel No.: 0240-2403308 Fax No.: 0240-2400413
Abstract
A new effective approach to the synthesis of some new (Z)-5-(substituted)-2-
thioxothiazolidin-4-one 3a-l and (Z)-5-(substituted)-2-(methylthio)thiazol-4(5H)-one 5a-l is
reported under microwave irradiation as well as conventional conditions.
Keywords: aromatic aldehydes, 2-thioxothiazolidin-4-one, microwave irradiation,
In recent years, thiazolidinone and their derivatives have become among the most
extensively investigated compounds. They constitute a very important group of heterocyclic
compounds, having valuable biological activities in the areas of medicine as well as agriculture.
The rhodanine scaffold is a central part of biologically active compounds with various
applications and uses1,2 such as antimicrobial,3,4 antimalarial,5 anti-HIV agents,6-9 anti-
inflammatory,10,11 antifungal,12,13 anticancer,14 antidiabetic15 and anti-tubercular.16,17 For the
discovery of new lead structures in drug discovery, based on high throughput screening,
synthetic methodologies are required which deliver highly diverse derivatives in a timely
manner. Under these circumstances, microwave-assisted chemistry appears to be a promising
synthetic method.18 Utility of microwave irradiation19 (MW) to carry out organic reaction has
now become a regular feature. The main benefits of performing the reaction under microwave
conditions are the significant rate-enhancements and the higher product yields and minimum
time requirement. Here, we wish to mention the development and implementation of a
methodology allowing for the synthesis of some new (Z)-5-(substituted)-2-thioxothiazolidin-4-
one 3a-l and (Z)-5-(substituted)-2-(methylthio)thiazol-4(5H)-one 5a-l derivatives. The reported
reactions under microwave irradiation as well as by conventional method proceed in short
1

reaction times and give good to excellent yields. The structures of compounds 3a-l and 5a-l were
1
substantiated by IR, H NMR, 13C NMR and Mass spectral analysis and only the
thermodynamically more stable Z-isomers were obtained.20
We have developed the protocol for the synthesis of (Z)-5-(2-chlorobenzylidene)-2-
thioxothiazolidin-4-one 3 (Scheme 1) by condensation between active methylene compounds and
aromatic aldehydes. The reaction of 2-chlorobenzaldehyde (1 mmol) and 2-thioxothiazolidin-4-
one (rhodanine) (1 mmol) catalyzed by various bases and various solvents were selected as a
model reaction to optimize the reaction conditions. In terms of the effect of solvent on the
condensation reaction, acetic acid was found to be the best solvent for the reaction (Table 1,
entry 8); other solvents, including dichloromethane (DMF), ethanol, methanol and toluene were
less efficient (Table 1, entries 1, 2, 4-7, 9-10, 14, 15). Ethanol gave the corresponding product in
a 50-55% yield, which was the worst among these solvents (Table 1, entry 1, 6, 11).
Nevertheless, all of these yields were generally low before further optimizations. To increase the
efficiency of the condensation reaction, the effects of different bases were investigated (Table 1,
entries 1-15). Sodium acetate exhibited the best performance with acetic acid solvent (55-90%).
Ammonium acetate and piperidine gave lower yields with other solvents, but gave better yield in
combination with acetic acid as a solvent (Table 1, entries 3 and 13). All the reactions were
carried out in equimolar amounts of each compound in 1 mL of solvent. Among these reactions
same amounts of the solvent, namely 1 mL of acetic acid turned out to be the best choice with
yields of 75%, 90% and 80% (Table 1, entry 3, 8 and 13). We would like to mention here that
acetic acid as a solvent with sodium acetate as base was the best choice with a yield of 90% and
less time required for the completion of the reaction (Table 1, entry 8). Thus we decided to carry
out the reactions in acetic acid with sodium acetate.
The compounds 2a-l were then subjected to a Knoevenagel condensation with the
appropriate rhodanines, which were synthesized using the reported procedure,21,22 to provide new
series of target compounds 3a-l. Thiazolidinone based compounds were synthesized by
microwave irradiation (MW) as well as conventional heating with sodium acetate and glacial
acetic acid.23
We synthesized the new (Z)-5-(substituted)-2-thioxothiazolidin-4-one 3a-l (Scheme 2,
Table 2) derivatives and (Z)-5-(substituted)-2-(methylthio)thiazol-4(5H)-one 5a-l (Scheme 3,
2

Table 3) derivatives under microwave irradiation as well as conventional method. However, the
MW reaction provided cleaner reaction, short reaction time, and the products were only required
to be washed with ice-cold water. The yields were good to excellent. The IR spectrum of
representative compound (Z)-5-(2-chlorobenzylidene)-2-thioxothiazolidin-4-one 3a, shows a
strong absorption band at 1694 cm-1 which is due to a carbonyl group thiazolidinone moiety. The
mass spectrum revealed a molecular ion peak at m/z = 256 (M+H) corresponding to a molecular
formula C10H6ClNOS2. 1H NMR spectra of compounds 3a show only one signal for the methyne
proton in the range δ 7.79–7.91 ppm, at lower field values than those expected for the E-isomers.
This strongly indicates that the compounds have the Z-configuration. The compounds 5a-l were
synthesized from compound 3a-l and IR spectrum of representative compound (Z)-5-(2-
chlorobenzylidene)-2-(methylthio)thiazol-4(5H)-one 5a, showed a strong absorption band at
1697 cm-1 due to a carbonyl group. The mass spectrum revealed a molecular ion peak at m/z =
270 (M+H) corresponding to a molecular formula C11H8ClNOS2.
In conclusion, we have successfully developed an easy access to a new series of (Z)-5-
(substituted)-2-(methylthio)thiazol-4(5H)-one 5a-l derivatives. The mild reaction conditions,
good to excellent yields, easy workup, and easily available substrates make the reactions
attractive for the preparation of compounds 3a-l and 5a-l. Efforts towards the synthesis of other
important drug molecules with a Rhodanine moiety by MW irradiation as well as conventional
method are ongoing in our laboratory. Also work is in progress to obtain biological activity such
as antibacterial, antifungal and anticancer of these important compounds. Results in these areas
will be presented in due course.
Acknowledgement
The authors are thankful to The Head, Department of Chemical Technology, Dr.
Babasaheb Ambedkar Marathwada University, Aurangabad, 431004 (MS), India, for providing
the laboratory facility.
3

References and notes
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4

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23. (a) General procedure for the synthesis of compounds (3a-l)
Method A: Microwave-assisted synthesis:
In a 100 ml round bottom flask, equimolar amounts of 2-thioxothiazolidin-4-one
1 (1 mmol), anhydrous sodium acetate (1 mmol) were added in glacial acetic acid (1
mL) and then aromatic aldehydes 2a-l (1 mmol) were added to the reaction mixture.
This mixture was subjected to MW irradiation (800 W), at 110 ºC temperature for 14-18
min. The progress of reaction was monitored by TLC (20% ethyl acetate: n-hexane).
After completion of the reaction, the reaction mixture was poured into the ice-cold
water. The precipitate was filtered off and washed with water (3×15 mL), dried, and
purified by recrystallization in ethanol as solvent to give 92-98% yield.
Method B: Conventional synthesis:
In a 100 ml round bottom flask, equimolar amounts of 2-thioxothiazolidin-4-one
1 (1 mmol), anhydrous sodium acetate (1 mmol) were added in glacial acetic acid (1
mL) and then aromatic aldehydes 2a-l (1 mmol) were added to the reaction mixture. The
5

mixture was stirred under reflux condition for 4-8 h. The progress of reaction was
monitored by TLC (20% ethyl acetate: n-hexane). After completion of the reaction, the
reaction mixture was poured into the ice-cold water. The precipitate was filtered off and
washed with water (3×15 mL), dried, and purified by recrystallization in ethanol as
solvent to give 85-90 % yield.
(Z)-5-(2-chlorobenzylidene)-2-thioxothiazolidin-4-one (3a)
Yellow solid. Yield: 98%. mp 180–182 ºC; ES-MS m/z (%): 256 (M+H). IR
νmax/cm–1: 3033 (NH), 2829 (CH–Ar), 1694 (C=O), 1581 (C=C), 1465 (C=N), 1189
(C=S), 1038 (C–N). 1H NMR (400 MHz, DMSO-d6): δppm = 7.23–7.48 (m, 4H, Ar–
13
CH), 7.79–7.91 (s, 1H, =CH), 13.71–13.92 (s, 1H, NH). C NMR (100 MHz, DMSO-
d6): δppm = 116.6, 126.5, 127.5, 129.4, 129.9, 133.4, 143.5, 168.7, 193.5. Molecular
formula C10H6ClNOS2
(Z)-5-(2,4-dichlorobenzylidene)-2-thioxothiazolidin-4-one (3b)
Yellow solid. Yield: 98%. mp 230–232 ºC; ES-MS m/z (%): 291 (M+H). IR
νmax/cm–1: 3039 (NH), 2929 (CH–Ar), 1728 (C=O), 1574 (C=C), 1442 (C=N), 1193
(C=S), 1047 (C–N). 1H NMR (400 MHz, DMSO-d6): δppm = 7.33–7.61 (m, 3H, Ar–
13
CH), 7.77–7.90 (s, 1H, =CH), 13.81–13.99 (s, 1H, NH). C NMR (100 MHz, DMSO-
d6): δppm = 116.2, 125.2, 126.5, 128.4, 130.9, 131.4, 136.5, 143.2, 168.3, 193.3.
Molecular formula C10H5Cl2NOS2
(Z)-5-(4-methoxybenzylidene)-2-thioxothiazolidin-4-one (3c)
Yellow solid. Yield: 95%. mp 247–249 ºC; ES-MS m/z (%): 252 (M+H). IR
νmax/cm–1: 3049 (NH), 2932 (CH–Ar), 1729 (C=O), 1575 (C=C), 1447 (C=N), 1198
1
(C=S), 1049 (C–N). H NMR (400 MHz, DMSO-d6): δppm = 3.71–3.83 (s, 3H, OCH3).
6.90–7.01 (d, 2H, Ar–CH), 7.40–7.51 (d, 2H, Ar–CH), 7.79–7.90 (s, 1H, =CH), 13.71–
13.93 (s, 1H, NH). 13C NMR (100 MHz, DMSO-d6): δppm = 55.8, 114.2, 116.3, 127.4,
130.2, 143.5, 159.3, 168.4, 193.5. Molecular formula C11H9NO2S2
(b) General procedure for the synthesis of compounds (5a-l)
Method A: Microwave-assisted synthesis:
In a 100 ml round bottom flask, the compound 3a-l (1 mmol) and triethylamine
(1.2 mmol) dissolved dichloromethane (1 mL) with iodomethane (1.2 mmol) were taken
6

and this mixture subjected to MW irradiation (800 W), at 40 ºC temperature for 2-5 min.
The progress of reaction was monitored by TLC (10% chloroform: methanol). After
completion of reaction, the reaction mixture was concentrated in vacuo. The residue was
washed with water (3×15 mL) to afford the crude product. The crude product was
recrystallized using ethanol as solvent to give yield in the range 88-92%.
Method B: Conventional synthesis:
In a 100 ml round bottom flask, the compound 3a-l (1 mmol) and triethylamine
(1.2 mmol) were added to dichloromethane (1 mL) at room temperature. To the stirred
reaction mixture, iodomethane (1.2 mmol) was added and stirred for 1-2 h at room
temperature. The progress of the reaction was monitored by TLC (10% chloroform:
methanol). After completion of reaction the reaction mixture was concentrated in vacuo.
The residue was washed with water (3×15 mL) to afford the crude product. The crude
product was recrystallized using ethanol as solvent to give yield in the range 60-77%.
(Z)-5-(2-chlorobenzylidene)-2-(methylthio)thiazol-4(5H)-one (5a)
Yellow solid. Yield: 92%. mp 170–172 ºC; ES-MS m/z (%): 271 (M+H). IR
νmax/cm–1: 3021 (CH–Ar), 1697 (C=O), 1603 (C=C), 1504 (C=N), 1154 (C-S), 982 (C–
1
N). H NMR (400 MHz, DMSO-d6): δppm = 2.71–2.87 (s, 3H, S–CH3), 7.41–7.71 (m,
13
4H, Ar–CH), 7.82–7.95 (s, 1H, =CH). C NMR (100 MHz, DMSO-d6): δppm = 14.2,
126.5, 127.6, 129.4, 129.9, 132.2, 133.1, 134.2, 152.2, 162.8, 167.2. Molecular formula
C11H8ClNOS2.
(Z)-5-(2,4-dichlorobenzylidene)-2-(methylthio)thiazol-4(5H)-one (5b)
Yellow solid. Yield: 90%. mp 165–167 ºC; ES-MS m/z (%): 305 (M+H). IR
νmax/cm–1: 3009 (CH–Ar), 1705 (C=O), 1579 (C=C), 1478 (C=N), 1137 (C-S), 980 (C–
1
N). H NMR (400 MHz, DMSO-d6): δppm = 2.71–2.87 (s, 3H, S–CH3), 7.31–7.61 (m,
13
3H, Ar–CH), 8.02–8.13 (s, 1H, =CH). C NMR (100 MHz, DMSO-d6): δppm = 14.3,
125.3, 126.5, 128.8, 130.2, 131.2, 132.2, 136.2, 152.1, 162.7, 167.1. Molecular formula
C11H7Cl2NOS2.
7

Scheme 1
Screening of model reaction (Z)-5-(2-chlorobenzylidene)-2-thioxothiazolidin-4-one (3)a
aReaction condition (3a). 2-thioxothiazolidin-4-one (1) (1 mmol), 2-chlorobenzaldehyde (2) (1 mmol), Base (1
mmol), solvent 1mL, reflux 6-13 h.
Scheme 2
Synthesis of (Z)-5-(substituted)-2-thioxothiazolidin-4-one (3a-l)a
aReaction condition (3a-l). 1 (1mmol), 2a-l (1mmol), sodium acetate (1mmol), 1 mL acetic acid, Method A:
Microwave-assisted synthesis: 110 ºC, 14-18 min. Method B: Conventional synthesis: reflux 4-8 h.
8

Scheme 3
Synthesis of (Z)-5-(substituted)-2-(methylthio)thiazol-4(5H)-one (5a-l)a
aReaction condition (5a-l). Compounds 3a-l (1 mmol), 4 (1.2 mmol), Method A: Microwave-assisted synthesis:
40ºC, triethylamine (1.2 mmol), 1 mL dichloromethane, 2-5 min. Method B: Conventional synthesis: triethylamine
(1.2 mmol), 1 mL dichloromethane, stirring room temperature, 1-2 h.
9

Table 1 Screening of catalyst, solvents, reaction time, and yield for the synthesis (3)a
Entry
1
Base
Solvent
Ethanol
DMF
Time (h)
10
Yieldb (%)
Ammonium acetate
Ammonium acetate
Ammonium acetate
Ammonium acetate
Ammonium acetate
Sodium acetate
Sodium acetate
Sodium acetate
Sodium acetate
Sodium acetate
Piperidine
50
55
75
60
50
55
58
90
65
60
55
58
80
60
52
2
12
3
Acetic acid
Methanol
Toluene
Ethanol
DMF
11
4
10
5
11
6
11
7
10
8
Acetic acid
Methanol
Toluene
Ethanol
DMF
6
9
12
10
11
12
13
14
15
10
12
Piperidine
11
Piperidine
Acetic acid
Methanol
Toluene
12
Piperidine
12
Piperidine
13
a All the reaction was carried out in equimolar amounts of each compound in 1 mL of solvent .
b Isolated yield.
10

Table 2 Synthesis of (Z)-5-(substituted)-2-thioxothiazolidin-4-one (3a-l)a
Entry
Ar
Product
Time
Conventional
Yieldb (%)
Conventional
M.P. (ºC)
MW
(min)
18
MW
(h)
6
1
2
2-chlorobenzyl
2,4-dichlorobenzyl
4-methoxybenzyl
4-chlorobenzyl
4-fluorobenzyl
4-hydroxybenzyl
benzyl
98
98
95
95
94
95
95
95
92
94
95
92
90
90
88
86
85
85
85
90
85
85
85
85
180-182
230-232
247-249
131-133
226-228
265-267
204-206
255-257
231-233
271-273
198-200
219-221
3a
3b
3c
3d
3e
3f
18
6
3
15
6
4
15
7
5
14
7
6
18
6
7
14
5
3g
3h
3i
8
4-nitrobenzyl
14
4
9
2-Thiophenyl
18
8
10
11
12
2,4-dimethoxybenzyl
3-fluorobenzyl
4-Methylbenzyl
15
8
3j
16
7
3k
3l
18
8
aReaction condition (3a-l).
Method A: Microwave-assisted synthesis: Acetic acid, Sodium acetate, 110 ºC, 14-18 min.
Method B: Conventional synthesis: Acetic acid, Sodium acetate, reflux 4-8 h.
bIsolated yields.
11

Table 3 Synthesis of (Z)-5-(substituted)-2-(methylthio)thiazol-4(5H)-one (5a-l)a.
Entry
Ar
Product
Time
Conventional
Yieldb (%)
Conventional
M.P. (ºC)
MW
MW
(min)
(h)
1
1
2
2-chlorobenzyl
2,4-dichlorobenzyl
4-methoxybenzyl
4-chlorobenzyl
4-fluorobenzyl
4-hydroxybenzyl
benzyl
2
4
2
2
3
3
5
5
3
4
5
4
92
90
90
92
90
90
88
92
92
90
90
90
75
72
65
65
75
65
75
65
67
77
72
60
170-172
165-167
162-164
160-162
143-145
222-224
145-147
160-162
150-152
172-174
160-162
175-177
5a
5b
5c
5d
5e
5f
1
3
1
4
1
5
1
6
2
7
2
5g
5h
5i
8
4-nitrobenzyl
1
9
2-Thiophenyl
2
10
11
12
2,4-dimethoxybenzyl
3-fluorobenzyl
4-Methylbenzyl
2
5j
1
5k
1
5l
aReaction condition (5a-l).
Method A: Microwave-assisted synthesis: Triethylamine, Dichloromethane , 40 ºC, 2-5 min.
Method B: Conventional synthesis: Triethylamine, Dichloromethane, room temperature, 1-2 h.
bIsolated yields.
12

Research highlights:
• Synthesis of important drug molecules with a Rhodanine moiety by MW irradiation as
well as conventional method.
• We have successfully developed an easy access to a new series of (Z)-5-(substituted)-2-
(methylthio)thiazol-4(5H)-one.
• Developed the mild reaction conditions, well to excellent yields, easy workup.
13

A facile synthesis of (Z)-5-(substituted)-2-(methylthio)thiazol-4(5H)-one using
microwave irradiation and conventional method
Dattatraya N. Pansare and Devanand B. Shinde*
Department of Chemical Technology, Dr. Babasaheb Ambedkar Marathwada University,
Aurangabad 431 004, MS, India.
*Corresponding author E-mail: dbsdattatraya10@rediffmail.com
Tel No.: 0240-2403308 Fax No.: 0240-2400413
Graphical Abstract
14