Design, synthesis, and antimicrobial activity of novel spiroisoxazolo[2,3- b[[1,2,4]thiadiazole-2,2-thiazolidine-4-ones and spiroisoxazolo[2,3-b[[1,2,4] oxadiazole-2, 2-thiazolidine-4-ones

Article abstract of DOI:10.1080/17415993.2012.703671

A new synthetic strategy for the synthesis of novel 6-methyl-3-aryl spiro[isoxazolo[2,3-b][1,2,4]thiadiazole-2,2-thiazolidin]-4-ones (9a-9e) and 6-methyl-3-aryl spiro[isoxazolo[2,3-b][1,2,4]oxadiazole-2,2-thiazolidin]-4-ones (12a-12e) analogs is described. These compounds showed significant antimicrobial activity against all the standard strains.

Full text of DOI:10.1080/17415993.2012.703671

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Design, synthesis, and antimicrobial
activity of novel spiroisoxazolo[2,3-b]
[1,2,4]thiadiazole-2,2′-thiazolidine-
4′-ones and spiroisoxazolo[2,3-b]
[1,2,4]oxadiazole-2, 2′-thiazolidine-4′-
ones
Rajanarendar Eligeti a , Ramakrishna Saini a & Nagaraju Dharavath
a
a Department of Chemistry, Kakatiya University, Warangal, AP, 506
009, India
Version of record first published: 10 Aug 2012.
To cite this article: Rajanarendar Eligeti , Ramakrishna Saini & Nagaraju Dharavath (2012):
Design, synthesis, and antimicrobial activity of novel spiroisoxazolo[2,3-b][1,2,4]thiadiazole-2,2′-
thiazolidine- 4′-ones and spiroisoxazolo[2,3-b][1,2,4]oxadiazole-2, 2′-thiazolidine-4′-ones, Journal
of Sulfur Chemistry, 33:4, 427-438
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Journal of Sulfur Chemistry
Vol. 33, No. 4, August 2012, 427–438
Design, synthesis, and antimicrobial activity of novel
spiroisoxazolo[2,3-b][1,2,4]thiadiazole-2,2ꢀ-thiazolidine-
4ꢀ-ones and spiroisoxazolo[2,3-b][1,2,4]oxadiazole-2,
2ꢀ-thiazolidine-4ꢀ-ones
Rajanarendar Eligeti*, Ramakrishna Saini and Nagaraju Dharavath
Department of Chemistry, Kakatiya University, Warangal, AP 506 009, India
(Received 2 May 2012; final version received 13 June 2012)
A new synthetic strategy for the synthesis of novel 6-methyl-3ꢀ-aryl spiro[isoxazolo[2,3-b][1,2,4]
thiadiazole-2,2ꢀ-thiazolidin]-4ꢀ-ones(9a–9e)and6-methyl-3ꢀ-arylspiro[isoxazolo[2,3-b][1,2,4]oxadiazole-
2,2ꢀ-thiazolidin]-4ꢀ-ones (12a–12e) analogs is described. These compounds showed significant antimicro-
bial activity against all the standard strains.
S
S
N
S
N
O
H3C
H3C
N
N
N
N
O
O
O
O
Ar
Ar
9a–9e
12a–12e
Keywords: cyclocondensation reaction; spiro[isoxazolo[2,3-b][1,2,4]thiadiazole-2,2ꢀ-thiazolidin]-4ꢀ-
ones; 6-methyl-3ꢀ-aryl spiro[isoxazolo[2,3-b][1,2,4]oxadiazole-2,2ꢀ-thiazolidin]-4ꢀ-ones; antibacterial
activity; antifungal activity
1. Introduction
The increasing incidence of bacterial and fungal resistance to a large number of antimicrobial
agents has prompted studies on the development of new potential antimicrobial compounds. The
molecular manipulation of promising lead compounds is still a major line of approach to develop
new drugs. It involves efforts to combine separate pharmacophoric groups of similar activity
into one compound, thus making structural changes in the biological activity. So, the discovery
of novel and potent antimicrobial agents is the best way to overcome microbial resistance and
develop effective therapies (1).
*Corresponding author. Email: rajanarendareligeti@gmail.com
ISSN 1741-5993 print/ISSN 1741-6000 online
© 2012 Taylor & Francis
http://dx.doi.org/10.1080/17415993.2012.703671
http://www.tandfonline.com

428 R. Eligeti et al.
S
O
H2N
N
O
N
O
H H
N
CCl3
N
+
S
N
N
H
N
N
H
N
N
N
O
N
N
S
O
O
S
N
O
O
O. .HCl
1,2,4-thiadiazolyl-spiroisobenzofuran
-1,4-piperidine-1'-carboxamide (3)
Terrazole (1)
Firstcin (2)
O
H
H
N
N
NH2
NH
N
N
N
HN
NMe2
R
S
O
N
N
H
1. R = Br
2. R = H
Dendrodoine (4)
Phidianidines A(1) and B(2) (5)
Scheme 1. Examples of commercial [1,2,4]thiadiazole derivatives and naturally occurring
[1,2,4]oxadiazoles with potential pharmacological activity.
[1,2,4]Thiadiazoles have been widely claimed to be useful insecticidal, herbicidal, and fungici-
dal agents (2). In recent years, many biologically active [1,2,4]thiadaizoles, exhibiting interesting
medicinal properties for the potential treatment of human diseases have been disclosed (3–9).
For example, 5-ethoxy-3-(trichloromethyl)-[1,2,4]thiadiazole 1 is a soil fungicide marketed as
etridiazole or terrazole (10). The injectable cephalosporin antibiotic cefozopran hydrochloride
known as Firstcin 2, possess a thiadiazole group (11). The [1,2,4]thiadiazole system is present in
potential pharmaceuticals (12) and cytotoxic natural products 3,4 (13). New bioactive [1,2,4]oxa-
diazoles phidianidines A(1) and B(2) 5 isolated from marine organisms (14) are found to exhibit
in vitro cytotoxicity on various tumor and non-tumor mammalian cells (15) (Scheme 1). However,
the role and importance of the thiadiazole moiety in all of these compounds, with regard to the
mechanism of the biological response of the targeted enzymes are not clearly understood at the
molecular level.
Isoxazole derivatives have been reported with diverse structural features and versatile biolog-
ical properties such as antitumor (16), CNS–active (17), analgesic (18), antimicrobial (19), and
muscle relaxant (20) activity for the treatment of hyper cholsteremia and hyperlipidemia (21), as
organic electrolytes for non-aqueous batteries (22), in photographic emulsions (23), as synthetic
intermediates (24), and as chemotherapeutic agents (25).
New hybrid moieties secured by linking isoxazoles with [1,2,4]thiadiazole-2,2ꢀ-thiazolidinone
and [1,2,4]oxadiazole-2,2ꢀ-thiazolidinone promise to offer fascinating scaffolds of fundamen-
tal interest to both sulfur and medicinal chemistry. Design of synthetic methods for the
efficient preparation of these tri-heterocyclic compounds, however, is necessary. Hence, we
embarked on the synthesis and bioassay of the compounds having isoxazolo-[1,2,4]thiadiazole-
2,2ꢀ-thiazolidinone, and [1,2,4]oxadiazole-2,2ꢀ-thiazolidinone moieties embedded in a fused
molecular framework to improve specificity and efficacy of these scaffolds against microorgan-
isms. As a sequel to our work on the synthesis of fuse disoxazoles (26), we report herein the
synthesis and biological evaluation of novel 6-methyl-3ꢀ-aryl[spiro[2,3-b][1,2,4]thiadiazole-2,2ꢀ-
thiazolidin]-4ꢀ-ones (9) and 6-methyl-3ꢀ-aryl[spiro[2,3-b][1,2,4]oxadiazole-2,2ꢀ-thiazolidin]-4ꢀ-
ones (12).

Journal of Sulfur Chemistry 429
2. Chemistry
The synthesis of the compounds 7–12 was accomplished by the synthetic sequence shown
in Scheme 2. The reaction of commercially available 3-amino-5-methyisoxazole 6 with
aryl isothiocyanate and aryl isocyanate in the presence of K2CO3 in CH3CN afforded
the key intermediates, viz. 1-(5-methyl-3-isoxazolyl)-3-arylthioureas 7 (27) and 1-(5-methyl-
3-isoxazolyl)-3-arylureas 10 (28), respectively. Compounds 7 and 10 upon refluxing in
ethanol in the presence of I2 led to the formation of the cyclized products (Z)-N-(6-
methyl-2H-isoxazolo [2,3-b][1,2,4]thiadiazol-2-ylidene)-anilines 8 and (Z)-N-(6-methyl-2H-
isoxazolo[2,3-b][1,2,4]oxadiazol-2-ylidene)-anilines 11, respectively. Cyclocondensation of 8
and 11 with mercaptoacetic acid in ethanol led to the formation of novel 6-methyl-3ꢀ-
aryl[spiro[2,3-b][1,2,4]thiadiazole-2,2ꢀ-thiazolidin]-4ꢀ-ones (9) and 6-methyl-3ꢀ-aryl[spiro[2,3-
b][1,2,4]oxadiazole-2,2ꢀ-thiazolidin]-4ꢀ-ones (12), respectively. The structures of the products
1
7–12 have been elucidated on the basis of IR, H NMR, 13C NMR and MS spectral data. Ele-
mental analyses are satisfactory and confirm elemental composition and purity of the newly
synthesized compounds 7–12.
Compound 8 displayed a characteristic absorption band in the IR spectra around 1615 cm−1
=
due to the C N functional group. The absence of NH functional group absorption bands in the
IR of 8 clearly confirms the cyclization. In the 1H NMR spectra of 8, the absence of NH proton
signals, which are present in its precursor 7, also establishes the cyclization. The mass spectrum of
8 agrees well with the cyclized structure, which shows the molecular ion peak, [M]+, at m/z 231.
1
The H NMR spectrum of 9 displayed a distinct signal at δ 4.11 due to the methylene protons
of the thiazolidinone ring confirming the formation of the spirothiazolidinone ring. The mass
spectrum of 9 confirmed the structure by exhibiting the molecular ion peak [M]+ at m/z 305.
Compound 11 displayed a characteristic absorption band in the IR spectra around 1617 cm−1
=
duetotheC NfunctionalgroupanddidnotexhibitabsorptionbandsduetoNHandCOfunctional
groups present in its precursor 10, confirming the cyclization. Similarly, the cyclization was
1
supported by the H NMR spectrum of 11 that did not contain the NH proton signals that are
present in its precursor 10. The mass spectrum of the product 11 also agrees with the cyclized
1
structure that shows the molecular ion [M]+ peak at m/z 215. The H NMR spectrum of 12
displayed a characteristic signal at δ 4.23 due to the methylene protons of the thiazolidinone ring
confirming the formation of the spirothiazolidinone ring.
3. Antibacterial activity
Antibacterial activities of 9a–9e and 12a–12e in acetone were performed by the broth dilution
method using nutrient agar against Gram-negative bacteria Pseudomonas aeruginosa, Klebsiella
aerogenes, Chormobacteium violaceum, and Gram-positive bacteria Bacillus subtilis, Bacillus
sphaericus, and Staphylococcus aureus at 100 μg/ml concentration. The minimum inhibitory
concentration (MIC) was done by the broth dilution method (29). Ciprofloxacin was used as a
standard for comparison. The ready-made nutrient broth medium (HiMedia, 24 g) was suspended
in distilled water (100 ml) and heated until it dissolved completely. The medium and test tubes
were autoclaved at a pressure of 15 lb/inc2 for 20 min. A set of sterilized test tubes with nutrient
broth medium was capped with cotton plugs. The test compound is dissolved in acetone at a
concentration of 100 μg/ml and is added to the first test tube, which is serially diluted. A fixed
0.5 ml volume of overnight culture is added to all the test tubes and then incubated at 37◦C for
24 h. After 24 h, these tubes were measured for turbidity. Results are given in Tables 1 and 2.

430 R. Eligeti et al.
NH2
N
H3C
O
6
ARNCO
CH3CN
ARNCS
CH3CN
K2CO3,
K2CO3,
O
S
N
H
AR
N
H
N
H
AR
N
H
N
N
H3C
H3C
O
O
7
10
I2
ethanol
I2
ethanol
stirring, RT
stirring, RT
N
AR
N
N
AR
OH
N
N
O
N
S
H3C
O
H3C
O
11
8
OH
HS
HS
O
O
ethanol ,
ethanol,
S
N
S
N
H3C
H3C
N
N
N
O
S
N
O
O
O
O
AR
AR
9
12
7–12
AR
AR
C6H5
4-CH3C6H4
a
b
c
d
4-CLC6H4
4-BRC6H4
4-CH3OC6H4
e
Scheme 2. Synthesis of spiroisoxazolo[2,3-b][1,2,4]thiadiazole-2,2ꢀ-thiazolidine-4ꢀ-ones and
spiroisoxazolo[2,3-b][1,2,4]oxadiazole-2,2ꢀ-thiazolidine-4ꢀ-ones.

Journal of Sulfur Chemistry 431
Table 1. Antibacterial activity of 9a–9e.
MICa,b
Gram-positive
Gram-negative
Compound
B. subtilis
B. sphaericus
S. aureus
P. aeruginosa
K. aerogenes
C. violaceum
9a
9b
9c
9d
14
12
15
16
11
20
16
10
17
15
9
17
8
18
19
13
25
20
13
22
25
17
30
15
11
18
15
15
25
18
14
17
13
13
25
9e
Ciprofloxacin
20
Notes: aNegative control (acetone) – no activity.
bConcentration 100 μg/ml.
Table 2. Antibacterial activity of 12a–12e.
MICa,b
Gram-positive
Gram-negative
Compound
B. subtilis
B. sphaericus
S. aureus
P. aeruginosa
K. aerogenes
C. violaceum
12a
12b
12c
12d
12e
Ciprofloxacin
16
10
9
13
15
20
18
13
11
16
17
20
20
16
15
19
11
25
19
12
18
24
21
30
21
17
16
22
16
25
23
14
12
19
12
25
Notes: aNegative control (acetone) – no activity.
bConcentration 100 μg/ml.
The results of antibacterial screening (Tables 1 and 2) reveal that compounds 9a–9e and 12a–
12e displayed better activity and are more active than the standard drug Ciprofloxacin. In series 9,
compounds 9b and 9e possessing chloro and methoxy groups as substituent on the benzene ring
showed a better activity, whereas in series 12, compounds 12b and 12c carrying chloro and bromo
groups as substituents on the benzene ring imparted remarkable activity. However, the degree of
inhibition varied both with the test compound as well as with the bacteria used in the present
investigation. In conclusion, almost all the series of compounds, 9a–9e and 12a–12e exhibited
good activity by inhibiting growth of all the six bacteria to a greater extent in comparison to
the standard drug Ciprofloxacin. These remarkable results may be due to the presence of the
isoxazole–thiadiazole–thiazolidone and isoxazole–oxadiazole–thiazolidone ring systems. Some
of the compounds may be used as bacteriocides after a detailed study.
4. Antifungal activity
Antifungal activities of 9a–9e and 12a–12e were determined by using the agar cup bioassay
method (30) with Clotrimazole as the standard. The compounds were tested for their antifungal
activity against five test organisms, Aspergillus niger, Chrysosporium tropicum, Rhizopus oryzae,
Fusarium moniliforma and Curvularia lunata using the agar cup bioassay method at 100 μg/ml
concentrations. The ready-made potato dextrose agar medium (HiMedia, 39 g) was suspended in

432 R. Eligeti et al.
Table 3. Antifungal activity of 9a–9e.
Zone of inhibitiona,b
Compound
A. niger
C. tropicum
R. oryzae F. moniliformae C. lunata
9a
9b
9c
9d
32
38
41
51
31
29
39
41
52
48
47
30
38
37
45
47
35
28
31
41
51
39
29
23
29
39
39
41
30
20
9e
Clotrimazole
Notes: aNegative control (acetone) – no activity.
bConcentration 100 μg/ml.
Table 4. Antifungal activity of 12a–12e.
Zone of inhibitiona,b
R. oryzae F. moniliformae C. lunata
Compound
A. niger
C. tropicum
12a
12b
12c
12d
12e
Clotrimazole
34
33
44
37
49
29
41
40
48
44
56
30
51
40
51
38
53
28
29
29
48
28
44
23
27
26
50
31
49
20
Notes: aNegative control (acetone) – no activity.
bConcentration 100 μg/ml.
distilled water (1000 ml) and heated until it dissolved completely. The medium and Petri dishes
were autoclaved at a pressure of 15 lb/inc2 for 20 min. The medium was poured into sterile
Petri dishes under aseptic conditions in a laminar flow chamber. When the medium in the plates
solidified, 0.5 ml of (week-old) culture of the test organism was inoculated and uniformly spread
over the agar surface with a sterile L-shaped rod. Solutions were prepared by dissolving plant
extract in acetone (100 μg/ml). Agar inoculation cups were scooped out with a 6 mm sterile cork
borer and the lids of the dishes were replaced. To each cup, 100 (μg/ml) of the test solution was
added. Controls were maintained with acetone and Clotrimazole (100 μg/ml). The treated and
the controls were kept at room temperature for 72–96 h. Inhibition zones were determined and
their diameter was calculated in millimeter. Three to four replicates were maintained for each
treatment. Results are given in Tables 3 and 4.
The antifungal activity results (Tables 3 and 4) indicated that compounds 9a–9e and 12a–12e
are significantly toxic toward all five fungi and they are lethal even at 100 μg/ml concentration. In
series 9, compounds 9c and 9d exhibited high antifungal activity which may be due to the presence
of bromo and methyl groups as substituents on the benzene ring. In series 12, compounds 12c and
12e possessing bromo and methoxy groups are highly toxic toward fungi. The antifungal activity
of these compounds was compared with the standard drug Clotrimazole, which demonstrated
that they have promising activity. In conclusion, almost all the series of compounds, 9a–9e and
12a–12e arehighlytoxictowardthefungiunderinvestigationandtheyarelethalevenat100 μg/ml
concentration in comparison with standard Clotrimazole at the same concentration. This may be
duetothepresenceofisoxazole–thiadiazole–thiazolidoneandisoxazole–oxadiazole–thiazolidone
ring systems. It is noteworthy that some of the compounds may be exploited after a detailed study
for control of wilt diseases of different crops as fungicides.

Journal of Sulfur Chemistry 433
5. Conclusion
A new synthetic strategy has been utilized for the synthesis of title compounds. The title
compounds 9a–9e and 12a–12e exhibited promising antimicrobial activity.
6. Experimental
All the melting points were determined on a Cintex melting point apparatus and are uncorrected.
Analytical TLC was performed on Merck precoated 60 F254 silica gel plates and visualization
was done by exposing the plates to iodine vapor. IR spectra (KBr pellet) were recorded on a
Perkin Elmer BX series FT–IR spectrometer. 1H NMR spectra were recorded on a Varian Gemini
300 MHz spectrometer. 13C NMR spectra were recorded on a Bruker 75 MHz spectrometer.
Chemical shift values are given in ppm (δ) with tetramethylsilane as an internal standard. Mass
spectral measurements were carried out by EI method on a Jeol JMC-300 spectrometer at 70 eV.
Elemental analyses were performed on a Carlo Erba 106 and Perkin Elmer model 240 analyzers.
6.1. Synthesis of 1-(5-methyl-3-isoxazolyl)-3-arylthioureas (7a–7e)/1-(5-methyl-
3-isoxazolyl)-3-arylureas (10a–10e) – general procedure
A mixture of 3-amino-5-methylisoxazole (6) (0.01 mol) and aryl isothiocyanate (0.01 mol)/aryl
isocyanate (0.01 mol) was added to acetonitrile (15 ml) in the presence of K2CO3 (0.5 g). The
reaction mixture was refluxed while stirring for 4 h.After completion of the reaction (monitored by
TLC), the reaction mixture was poured onto crushed ice and the solid filtered off and recrystallized
from ethylacetate to produce (7a–7e)/(10a–10e) in good yields.
6.2. 1-(5-Methyl-3-isoxazolyl)-3-phenylthiourea (7a)
1
Pale brown solid; yield 74%, m.p. 134–136◦C; IR (KBr) cm−1: 3310 (NH), 1220 (C S), H NMR
=
(300 MHz, CDCl3) δ (ppm): 2.31 (s, 3H, isoxazole–CH3), 6.16 (s, 1H, isoxazole–CH), 7.00–8.17
(m, 5H, Ar–H), 8.48 (bs, 1H, NH, D2O exchangeable), 8.82 (bs, 1H, NH, D2O exchangeable).
EI–MS [M]+ m/z 233. Anal. calcd. for C11H11N3OS: C, 56.63; H, 4.75; N, 18.01%. Found: C,
56.69; H, 4.68; N, 18.04%.
6.3. 1-(5-Methyl-3-isoxazolyl)-3-phenylurea (10a)
1
Brown solid; yield 77%, m.p. 138–140◦C; IR (KBr) cm−1: 3300 (NH), 1615 (C O), H NMR
=
(300 MHz, CDCl3) δ (ppm): 2.30 (s, 3H, isoxazole–CH3), 6.22 (s, 1H, isoxazole–CH), 7.11–
8.34 (m, 5H,Ar–H),8.52 (bs, 1H, NH, D2O exchangeable), 8.78 (bs, 1H, NH, D2O exchangeable).
EI–MS [M]+ m/z 217. Anal. calcd. for C11H11N3O2: C, 60.82; H, 5.10; N, 19.34%. Found: C,
60.78; H, 5.16; N, 19.39%.
6.4. Synthesis of (Z)-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]thiadiazol-2-ylidene)-anilines
(8a–8e) and (Z)-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]oxadiazol-2-ylidene)-anilines
(11a–11e) – general procedure
To a solution of 1-(5-methyl-3-isoxazolyl)-3-arylthioureas (7a) (0.01 mol)/1-(5-methyl-3-
isoxazolyl)-3-arylureas (10) (0.01 mol) in ethanol (10 ml), a solution of I2 (0.01 mol) in 10 ml

434 R. Eligeti et al.
of ethanol was added and the contents are stirred. After completion of the reaction (monitored by
TLC), the solvent was removed under pressure and 30 ml of water was added to the residue. The
resulting solution was then extracted with ethyl acetate to give a residue after evaporation that
was purified by recrystallization from methanol to produce 8a–8e/11a–11e in high yields.
6.5. (Z)-N-(6-Methyl-2H-isoxazolo[2,3-b][1,2,4]thiadiazol-2-ylidene)-aniline (8a)
1
Brown solid; yield 75%, m.p. 182–184◦C; IR (KBr) cm−1: 1615 (C N), H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.32 (s, 3H, isoxazole–CH3), 6.21 (s, 1H, isoxazole–CH), 7.20–8.00 (m, 5H,
Ar–H). EI–MS [M]+ m/z 231.13C NMR (75 MHz, CDCl3) δ (ppm): 16.42, 90.61, 124.31, 125.13,
126.42, 127.31, 127.86, 150.13, 163.42, 165.36, 186.41. Anal. calcd. for C11H9N3OS: C, 57.13;
H, 3.92; N, 18.17%. Found: C, 57.10; H, 3.97; N, 18.20%.
6.6. (Z)-4-Chloro-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]thiadiazol-2-ylidene)-aniline (8b)
Brown solid; yield 78%, m.p. 180–182◦C; IR (KBr) cm−1: 1620 (C N), H NMR (300 MHz,
1
=
CDCl3) δ (ppm): 2.28 (s, 3H, isoxazole–CH3), 6.14 (s, 1H, isoxazole–CH), 7.00–8.04 (m, 4H,
Ar–H). EI–MS [M]+ m/z 265.13C NMR (75 MHz, CDCl3) δ (ppm): 16.11, 90.81, 124.01, 125.34,
126.65, 127.52, 132.58, 150.01, 162.98, 165.54, 186.32.Anal. calcd. for C11H8N3OSCl: C, 49.72;
H, 3.03; N, 15.81%. Found: C, 49.77; H, 3.00; N, 15.88%.
6.7. (Z)-4-Bromo-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]thiadiazol-2-ylidene)-aniline (8c)
1
Brown solid; yield 75%, m.p. 185–187◦C; IR (KBr) cm−1: 1627(C N), H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.30 (s, 3H, isoxazole–CH3), 6.20 (s, 1H, isoxazole–CH), 7.01–7.83 (m, 4H,
Ar–H). EI–MS [M]+ m/z 309. Anal. calcd. for C11H8N3OSBr: C, 42.60; H, 2.60; N, 13.55%.
Found: C, 42.58; H, 2.65; N, 13.51%.
6.8. (Z)-4-Methyl-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]thiadiazol-2-ylidene)-aniline (8d)
1
Brown solid; yield 69%, m.p. 183–185◦C; IR (KBr) cm−1: 1618 (C N), H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.26 (s, 3H, isoxazole–CH3), 2.51 (s, 3H, Ar–CH3), 6.18 (s, 1H, isoxazole–CH),
7.03–8.11 (m, 4H,Ar–H). EI–MS [M]+ m/z 245.Anal. calcd. for C12H11N3OS: C, 58.76; H, 4.52;
N, 17.13%. Found: C, 58.80; H, 4.50; N, 17.18%.
6.9. (Z)-4-Methoxy-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]thiadiazol-2-ylidene)-aniline
(8e)
Brown solid; yield 72%, m.p. 179–181◦C; IR (KBr) cm−1: 1622 (C N), H NMR (300 MHz,
1
=
CDCl3) δ (ppm): 2.31 (s, 3H, isoxazole–CH3), 3.64 (s, 3H, OCH3), 6.22 (s, 1H, isoxazole–CH),
6.98–8.01 (m, 4H, Ar–H). EI–MS [M]+ m/z 261. Anal. calcd. for C12H11N3O2S: C, 55.16; H,
4.24; N, 16.08%. Found: C, 55.20; H, 4.20; N, 16.12%.
6.10. (Z)-N-(6-Methyl-2H-isoxazolo[2,3-b][1,2,4]oxadiazol-2-ylidene)-aniline (11a)
1
Brown solid; yield 70%, m.p. 165–167◦C; IR (KBr) cm−1: 1617 (C N), H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.30 (s, 3H, isoxazole–CH3), 6.19 (s, 1H, isoxazole–CH), 6.82–8.00 (m, 5H,
Ar–H). EI–MS [M]+ m/z 215.13C NMR (75 MHz, CDCl3) δ (ppm): 17.01, 89.98, 124.15, 125.55,

Journal of Sulfur Chemistry 435
126.47, 127.14, 132.42, 150.53, 163.11, 165.65, 186.12. Anal. calcd. for C11H9N3O2: C, 61.39;
H, 4.22; N, 19.53%. Found: C, 61.43; H, 4.26; N, 19.49%.
6.11. (Z)-4-Chloro-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]oxadiazol-2-ylidene)-
aniline (11b)
Brown solid; yield 74%, m.p. 171–173◦C; IR (KBr) cm−1: 1613 (C N), H NMR (300 MHz,
1
=
CDCl3) δ (ppm): 2.27 (s, 3H, isoxazole–CH3), 6.21 (s, 1H, isoxazole–CH), 6.93–7.65 (m, 4H,
Ar–H). EI–MS [M]+ m/z 249.13C NMR (75 MHz, CDCl3) δ (ppm): 16.67, 90.14, 124.01, 125.42,
126.11, 127.51, 132.37, 150.27, 162.65, 165.77, 186.57.Anal. calcd. for C11H8N3O2Cl: C, 52.92;
H, 3.23; N, 14.20%. Found: C, 52.87; H, 3.19; N, 14.26%.
6.12. (Z)-4-Bromo-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]oxadiazol-2-ylidene)-
aniline (11c)
1
Brown solid; yield 71%, m.p. 190–192◦C; IR (KBr) cm−1: 1621(C N), H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.31 (s, 3H, isoxazole–CH3), 6.18 (s, 1H, isoxazole–CH), 7.00–7.87 (m, 4H,
Ar–H). EI–MS [M]+ m/z 293. Anal. calcd. for C11H8N3O2Br: C, 44.92; H, 2.74; N, 14.29%.
Found: C, 44.89; H, 2.68; N, 14.35%.
6.13. (Z)-4-Methyl-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]oxadiazol-2-ylidene)-
aniline (11d)
1
Brown solid; yield 76%, m.p. 173–175◦C; IR (KBr) cm−1: 1621 (C N), H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.23 (s, 3H, isoxazole–CH3), 2.58 (s, 3H, Ar–CH3), 6.19 (s, 1H, isoxazole–CH),
7.13–8.16 (m, 4H,Ar–H). EI–MS [M]+ m/z 229.Anal. calcd. for C12H11N3O2: C, 62.87; H, 4.84;
N, 18.33%. Found: C, 62.81; H, 4.90; N, 18.38%.
6.14. (Z)-4-Methoxy-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]oxadiazol-2-ylidene)-
aniline (11e)
1
Brown solid; yield 75%, m.p. 177–179◦C; IR (KBr) cm−1: 1612 (C N), H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.29 (s, 3H, isoxazole–CH3), 3.62 (s, 3H, OCH3), 6.21 (s, 1H, isoxazole–CH),
6.88–7.86 (m, 4H,Ar–H). EI–MS [M]+ m/z 261.Anal. calcd. for C12H11N3O3: C, 58.77; H, 4.52;
N, 17.13%. Found: C, 58.72; H, 4.58; N, 17.18%.
6.15. Synthesis of 6-methyl-3ꢀ-aryl[spiro[2,3-b][1,2,4] thiadiazole-2,2ꢀ-thiazolidin]-4ꢀ-ones
(9a–9e) and 6-methyl-3ꢀ-aryl[spiro[2,3-b][1,2,4]oxadiazole-2, 2ꢀ-thiazolidin]-4ꢀ-ones
(12a–12e) – general procedure
To solutions of (Z)-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]thiadiazol-2-ylidene)-anilines
(8) (0.01 mol)/(Z)-N-(6-methyl-2H-isoxazolo[2,3-b][1,2,4]oxadiazol-2-ylidene)-anilines (11)
(0.01 mol) in ethanol (15 ml), mercaptoacetic acid (0.01 mol) was added and the contents
were refluxed for 6 h. After completion of the reaction (monitored by TLC), the solvent was
removed under pressure and 30 ml of water was added to the residue. The resulting solution was
then extracted with ethyl acetate which when evaporated gave a residue that was purified by
recrystallization from ethyl acetate to produce 9a–9e/12a–12e in high yields.

436 R. Eligeti et al.
6.16. 6-Methyl-3 ꢀ-phenyl spiro[isoxazolo[2,3-b][1,2,4]thiadiazole-2,2ꢀ-thiazolidin]-
4ꢀ-one (9a)
1
Brown solid; yield 70%, m.p. 194–196◦C; IR (KBr) cm−1: 1675 (C O); H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.30 (s, 3H, isoxazole–CH3), 4.11 (s, 2H, thiazole–CH2), 6.11 (s, 1H, isoxazole–
CH), 7.11–8.20 (m, 5H,Ar–H). EI–MS [M]+ m/z 305.13CNMR(75MHz, CDCl3) δ (ppm):16.12,
30.45, 86.13, 90.53, 124.35, 125.33, 126.02, 127.52, 127.67, 150.21, 165.48, 172.43, 186.30.Anal.
calcd. for C13H11N3O2S2: C, 51.13; H, 3.63; N, 13.76%. Found: C, 51.18; H, 3.68; N, 13.81%.
6.17. 3ꢀ-(4-Chlorophenyl)-6-methyl-spiro[isoxazolo[2,3-b][1,2,4]thiadiazole-2,
2ꢀ-thiazolidin]-4ꢀ-one (9b)
1
Brown solid; yield 76%, m.p. 201–203◦C; IR (KBr) cm−1: 1655 (C O); H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.28 (s, 3H, isoxazole–CH3), 4.18 (s, 2H, thiazole–CH2), 6.21 (s, 1H, isoxazole–
CH), 6.98–8.00 (m, 4H,Ar–H). EI–MS [M]+ m/z 339.13CNMR(75MHz, CDCl3) δ (ppm):17.02,
30.15, 84.13, 90.31, 124.65, 125.46, 126.08, 127.12, 127.72, 150.38, 165.33, 172.00, 186.45.Anal.
calcd. for C13H10N3O2S2Cl: C, 45.95; H, 2.97; N, 12.37%. Found: C, 45.89; H, 2.93; N, 12.45%.
6.18. 3ꢀ-(4-Bromophenyl)-6-methyl-spiro[isoxazolo[2,3-b][1,2,4]thiadiazole-2,2ꢀ-
thiazolidin]-4ꢀ-one (9c)
1
Brown solid; yield 76%, m.p. 198–200◦C; IR (KBr) cm−1: 1671 (C O); H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.30 (s, 3H, isoxazole–CH3), 4.21 (s, 2H, thiazole–CH2), 6.11 (s, 1H, isoxazole–
CH), 6.88–7.75(m, 4H,Ar–H). EI–MS[M]+ m/z 383.Anal. calcd. forC13H10N3O2S2Br:C, 40.63;
H, 2.62; N, 10.94%. Found: C, 40.58; H, 2.68; N, 10.87%.
6.19. 6-Methyl-3ꢀ-p-tolyl-spiro[isoxazolo[2,3-b][1,2,4]thiadiazole-2,
2ꢀ-thiazolidin]-4ꢀ-one (9d)
1
Brown solid; yield 71%, m.p. 207–209◦C; IR (KBr) cm−1: 1666 (C O); H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.27 (s, 3H, isoxazole–CH3), 2.57 (s, 3H, Ar–CH3), 4.25 (s, 2H, thiazole–CH2),
6.18 (s, 1H, isoxazole–CH), 6.93–7.67 (m, 4H, Ar–H). EI–MS [M]+ m/z 319. Anal. calcd. for
C14H13N3O2S2: C, 52.65; H, 4.10; N, 13.06%. Found: C, 52.59; H, 4.16; N, 13.11%.
6.20. 3ꢀ-(4-Methoxyphenyl)-6-methyl-spiro[isoxazolo[2,3-b][1,2,4]thiadiazole-2,2ꢀ-
thiazolidin]-4ꢀ-one (9e)
1
Brown solid; yield 76%, m.p. 203–205◦C; IR (KBr) cm−1: 1646 (C O); H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.21 (s, 3H, isoxazole–CH3), 3.60 (s, 3H, OCH3), 4.18 (s, 2H, thiazole–CH2),
6.10 (s, 1H, isoxazole–CH), 6.88–7.97 (m, 4H, Ar–H). EI–MS [M]+ m/z 335. Anal. calcd. for
C14H13N3O3S2: C, 50.13; H, 3.91; N, 12.53%. Found: C, 50.09; H, 9.86; N, 12.58%.
6.21. 6-Methyl-3ꢀ-phenyl spiro[isoxazolo[2,3-b][1,2,4]oxadiazole-2,2ꢀ-
thiazolidin]-4ꢀ-one (12a)
1
Brown solid; yield 68%, m.p. 204–206◦C; IR (KBr) cm−1: 1663 (C O); H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.27 (s, 3H, isoxazole–CH3), 4.23 (s, 2H, thiazole–CH2), 6.27 (s, 1H, isoxazole–
CH), 6.94–8.11 (m, 5H,Ar–H). EI–MS [M]+ m/z 289.13CNMR(75MHz, CDCl3) δ (ppm):16.83,
31.01, 90.25, 110.21, 124.23, 125.54, 126.21, 127.62, 127.81, 150.11, 165.27, 172.59, 186.45.

Journal of Sulfur Chemistry 437
Anal. calcd. for C13H11N3O3S: C, 53.97; H, 3.83; N, 14.52%. Found: C, 53.91; H, 3.87; N,
14.48%.
6.22. 3ꢀ-(4-Chlorophenyl)-6-methyl-spiro[isoxazolo[2,3-b][1,2,4]oxadiazole-2,2ꢀ-
thiazolidin]-4ꢀ-one (12b)
Brown solid; yield 75%, m.p. 211–213◦C; IR (KBr) cm−1: 1675 (C O); H NMR (300 MHz,
1
=
CDCl3) δ (ppm): 2.30 (s, 3H, isoxazole–CH3), 4.18 (s, 2H, thiazole–CH2), 6.11 (s, 1H, isoxazole–
CH), 7.12–8.34 (m, 4H,Ar–H). EI–MS [M]+ m/z 339.13CNMR(75MHz, CDCl3) δ (ppm):17.01,
32.06, 91.00, 110.45, 124.11, 125.36, 126.45, 127.17, 127.92, 150.32, 165.28, 172.23, 186.67.
Anal. calcd. for C13H10N3O3SCl: C, 48.23; H, 3.11; N, 12.98%. Found: C, 48.18; H, 3.18; N,
12.91%.
6.23. 3ꢀ-(4-Bromophenyl)-6-methyl-spiro[isoxazolo[2,3-b][1,2,4]oxadiazole-2,2ꢀ-
thiazolidin]-4ꢀ-one (12c)
Brown solid; yield 79%, m.p. 208–210◦C; IR (KBr) cm−1: 1663 (C O); H NMR (300 MHz,
1
=
CDCl3) δ (ppm): 2.31 (s, 3H, isoxazole–CH3), 4.27 (s, 2H, thiazole–CH2), 6.18 (s,
1H, isoxazole–CH), 7.11–8.34 (m, 4H, Ar–H). EI–MS [M]+ m/z 367. Anal. calcd. for
C13H10N3O3SBr: C, 42.41; H, 2.74; N, 11.41%. Found: C, 42.48; H, 2.80; N, 11.37%.
6.24. 6-Methyl-3ꢀ-p-tolyl-spiro[isoxazolo[2,3-b][1,2,4]oxadiazole-2,2ꢀ-thiazolidin]-4ꢀ-
one (12d)
Brown solid; yield 73%, m.p. 217–219◦C; IR (KBr) cm−1: 1660 (C O); H NMR (300 MHz,
1
=
CDCl3) δ (ppm): 2.20 (s, 3H, isoxazole–CH3), 2.61 (s, 3H, Ar–CH3), 4.11 (s, 2H, thiazole–CH2),
6.10 (s, 1H, isoxazole–CH), 7.10–7.97 (m, 4H, Ar–H). EI–MS [M]+ m/z 303. Anal. calcd. for
C14H13N3O3S: C, 55.43; H, 4.32; N, 13.85%. Found: C, 55.38; H, 4.38; N, 13.91%.
6.25. 3ꢀ-(4-Methoxyphenyl)-6-methyl-spiro[isoxazolo[2,3-b][1,2,4]oxadiazole-2,
2ꢀ-thiazolidin]- 4ꢀ-one (12e)
1
Brown solid; yield 78%, m.p. 215–217◦C; IR (KBr) cm−1: 1677 (C O); H NMR (300 MHz,
=
CDCl3) δ (ppm): 2.23 (s, 3H, isoxazole–CH3), 3.58 (s, 3H, OCH3), 4.24 (s, 2H, thiazole–CH2),
6.16 (s, 1H, isoxazole–CH), 7.03–8.13 (m, 4H, Ar–H). EI–MS [M]+ m/z 319. Anal. calcd. for
C14H13N3O4S: C, 52.66; H, 4.10; N, 13.16%. Found: C, 52.71; H, 4.17; N, 13.11%.
Acknowledgements
The authors are thankful to the Head, Department of Chemistry, Kakatiya University, Warangal for facilities and to the
Director, Indian Institute of Chemical Technology, Hyderabad for recording 1H NMR, 13C NMR and Mass Spectra.
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