A novel ionic liquid mediated synthesis of 4(1H)-quinolones, 5H-thiazolo[3,2-a]pyrimidin-5-one and 4H-pyrimido[2,1-b]benzothiazol-4-ones

Article abstract of DOI:10.1016/j.tetlet.2011.12.024

A new, convenient, environmentally benign two-step synthesis of 4(1H)-quinolones, 5H-thiazolo[3,2-a]pyrimidin-5-one and 4H-pyrimido[2,1-b] benzothiazol-4-ones have been developed by first condensing substituted arylamine/2-aminothiazole/2-aminobenzenethia

Full text of DOI:10.1016/j.tetlet.2011.12.024

Tetrahedron Letters 53 (2012) 859–862
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A novel ionic liquid mediated synthesis of 4(1H)-quinolones, 5H-thiazolo
[3,2-a]pyrimidin-5-one and 4H-pyrimido[2,1-b]benzothiazol-4-ones
⇑
Ashok K. Yadav , Gopi Ram Sharma, Pankaj Dhakad, Tripti Yadav
Department of Chemistry, University of Rajasthan, Jaipur 302004, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A
new, convenient, environmentally benign two-step synthesis of 4(1H)-quinolones, 5H-thiazolo
Received 29 September 2011
Revised 30 November 2011
Accepted 7 December 2011
Available online 16 December 2011
[3,2-a]pyrimidin-5-one and 4H-pyrimido[2,1-b]benzothiazol-4-ones have been developed by first con-
densing substituted arylamine/2-aminothiazole/2-aminobenzenethiazole with Meldrum’s acid and
trimethylorthoformate in 1-butyl-3-methylimidazolium bromide at a moderate temperature to afford
5-{(substituted aryl/4-methylthiazolyl/substituted benzothiazolyl)methylene}-2,2-dimethyl-1,3-diox-
ane-4,6-dione. The resulting compounds upon cyclization in 1-butyl-3-methyl tetrafluoroborate/triflate
at a moderate temperature gave the title compounds in excellent yields.
Keywords:
Thiazoles
Cyclization
Ionic liquid
Ó 2011 Elsevier Ltd. All rights reserved.
4(1H)-Quinolones constitute an important class of heterocyclic
such as anti-viral,1,2 anti-platelet,3 anti-tumor4 and positive cardiac
compounds because of their important pharmaceutical properties,
R4
R4
R3
R3
O
O
H
O
O
O
[BMIM]Br
+
HC(OMe)3
+
O
O
40 2 °C
R2
NH2
N2-atm.
R2
N
H
O
R1
R1
4a-e
2
3
1a-e
[BMIM]BF4/OTf
80 2°C
–Acetone , –CO2
R4
O
R3
R2
N
H
R1
5a-e
Scheme 1. Synthesis of 4(1H)-quinolones.
⇑
Corresponding author. Tel.: +91 141 2552609.
E-mail address: drakyada@yahoo.co.in (A.K. Yadav).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.12.024

860
A. K. Yadav et al. / Tetrahedron Letters 53 (2012) 859–862
effects.5 These compounds have been exploited as precursors for
anti-cancer6 and anti-malarial agents.7
unsubstituted 4(1H)-quinolones have been reported, viz. addition
of anilines to methylacetylene carboxylate and further
cyclization,16 thermolysis of aminomethylene Meldrum’s acid
derivatives17 and reaction between polymer bound cyclic malonic
ester with anilines.18 The serious drawbacks of these methods form
the necessity to employ harsh cyclization conditions, including
temperatures above 200 °C or strong acids such as polyphosphoric
acid or Eaton’s reagent.18 Also, the yield of the products were mod-
erate to good. The thiazolo[3,2-a]pyrimidine derivatives have been
synthesized by reacting 1,2,3,4-tetrahydropyrimidine-2-thione
with chloroacetic acid and appropriate benzaldehyde.10 In this
method the cyclization step occurs at 220–40 °C.
In view of diversified applications of 4(1H)-quinolones, thiazol-
o[3,2-a]pyrimidines and pyrimido[2,1-b]benzothiazoles and our
interest in developing environmentally friendly room temperature
ionic liquid mediated synthetic methodologies,19 we herein report
for the first time a clean, smooth and efficient two step synthesis of
4(1H)-quinolones, 5H-thiazolo[3,2-a]pyrimidine, and 4H-pyrimi-
do[2,1-b]benzothiazoles at a moderate temperature.
The antibiotics, viz. norfloxacin and ciprofloxacin have been
found to possess 4(1H)-quinolone nuclei, which inhibit topoiso-
merase II (Gyrase-a subunit).8,9 Thiazolo[3,2-a]pyrimidine deriva-
tives have demonstrated a variety of pharmacological activities,
for example, anti-inflammatory,10 as inhibitors of matrix metallo
proteinases,11 etc. Pyrimido[2,1-b]benzothiazol-4-one has exhib-
ited potent pharmacological activities,12 for example, anti-bacte-
rial, anti-fungal, anti-inflammatory, etc. Various methods have
been reported for the syntheses of 4(1H)-quinolones, viz. addition
of (ethoxymethylene) malonates with anilines and subsequent
cyclization,13 addition of maleates to o-aminobenzoates followed
by cyclization.14 Conard–Limpach and Niementowski reactions15
generally focus on the condensation of amines, carboxyl deriva-
tives and subsequent cyclization. These methods, however, suffer
serious disadvantages for the synthesis of 2,3-unsubstituted
4(1H)-quinolones as the removal of ester groups present at these
positions involves several steps. Some elegant syntheses for the
In our strategy, we have performed the reaction between aryl-
amine 1a–e with Meldrum’s acid (2,2-dimethyl-1,3-dioxane-4,6-
dione, in which the nucleophilic attack occurs at C-4 and C-6 while
the electrophilic attack occurs at C-5 position) 2 and trimethyl
orthoformate 3 in the presence of ionic liquid, viz., 1-butyl-3-methyl
imidazolium bromide [BMIM]Br. The reaction has been carried out
by stirring the contents of the flask under nitrogen atmosphere at
40 2 °C. The products obtained were arylaminomethylene-1,
3-dioxane-4,6-dione 4a–e. Compounds 4a–e were then cyclized un-
der nitrogen current at 80 2 °C in ionic liquids, viz. [BMIM]BF4/OTf
to afford 4(1H)-quinolones 5a–e in excellent yields. (Scheme 1,
Table 1).
Table 1
Yields of the compounds 4a–e and 5a–e
Product
R1
R2
R3
R4
Yielda (%)/Time (min)
[BMIM]Br
[BMIM]BF4
[BMIM]OTf
4
5
5
a
b
c
d
e
H
H
H
H
H
H
H
H
H
H
Cl
H
H
Me
H
H
87/120
91/120
94/120
72/120
68/120
85/120
77/120
75/120
70/120
66/120
90/120
84/120
79/120
75/120
73/120
Me
Me
Cl
Cl
a
Isolated yield after purification.
R1
H3C
N
N
NH2
NH2
+ 2 + 3
S
S
R2
6
7a-e
[BMIM]Br
40 2°C
R1
H
O
H
O
O
O
H3C
N
S
N
S
N
O
N
H
O
H
R2
O
O
8
9a-e
[BMIM]BF4/OTf
80 2 °C
Nitrogen atmosphere
O
O
R1
H3C
N
N
N
N
S
S
R2
10
11a-e
Scheme 2. Synthesis of 5H-thiazolo [3,2-a]pyrimidin-5-one/4H-pyrimido[2,1-b]benzothiazol-4-ones.

A. K. Yadav et al. / Tetrahedron Letters 53 (2012) 859–862
861
Table 2
References and notes
Yields of the compounds 9a–e and 11a–e
1. Llinas-Brunet, M.; Bailey, M. D.; Ghiro, E.; Gorys, V.; Halmos, T.; Poirier, M.;
Rancourt, J.; Goureare, N. J. Med. Chem. 2004, 47, 6584.
Product
R1
R2
Yielda (%)/Time (min)
[BMIM]Br
9
[BMIM]BF4
[BMIM]OTf
2. Frutos, R. P.; Haddad, N.; Houpis, I. N.; Johnson, M.; Smith-Keenan, L. L.; Fuchs,
V.; Yee, N. K.; Farina, V.; Faucher, A.-M.; Brochu, C.; Hache, B.; Duceepe, J.-S.;
Beaulieu, P. Synthesis 2006, 256. and the references cited therein.
3. Huang, L.-J.; Hsich, M.-C.; Teng, C.-M.; Lee, K.-H.; Kno, S.-C. Bioorg. Med. Chem.
1998, 6, 1657.
4. Gasparotto, V.; Castagliuolo, I.; Chiarelotto, G.; Pezzi, V.; Montanaro, D.; Brun,
P.; Palu, G.; Viola, G.; Ferlin, M. G. J. Med. Chem. 2006, 49, 1910. and the
references cited therein.
11
11
a
b
c
d
e
H
CH3
H
H
H
H
H
CH3
OCH3
Cl
87/120
91/120
94/120
72/120
78/120
90/90
85/90
83/90
78/90
75/90
93/90
88/90
85/90
80/90
77/90
5. Osawa, T.; Ohta, H.; Akmoto, K.; Harada, K.; Soga, H.; Jinno, Y. EP 0343574,
1994.
a
Isolated yield after purification.
6. Ruchelman, A. L.; Singh, S. K.; Ray, A.; Wu, X. H.; Yang, J.-M.; Li, T.-K.; Liu, A.;
Liu, L. F.; LaVoie, E. J. Bioorg. Med. Chem. 2003, 11, 2061.
7. (a) Theeraladanon, C.; Arisawa, M.; Nishidi, A.; Nakagawa, M. Tetrahedron 2004,
60, 3017; (b) Nishida, A.; Sorimachi, H.; Iwaida, M.; Matsumizu, M.; Kawate, T.;
Na Kagawa, M. Synlett 1998, 389.
Table 3
Recyclability data for product 4a and 5a
8. Wentland, M. P.; Perni, R. B.; Dorff, P. H.; Brundage, R. P.; Castaldi, M. J.; Bailey,
T. R.; Carabatean, P. M.; Baeon, E. R.; Young, D. C.; Woods, M. G.; Rosi, D.; Drozd,
M. L.; Kullnig, R. K.; Dutko, F. J. J. Med. Chem. 1993, 36, 1580.
9. Schmidt, R. D. Taschenatlas der Biotechnologie and Gentechnik; Wiley-VCH:
Weinheim, 2002.
10. Tazkoparan, B.; Ertan, M.; Kelichen, P.; Demirdamar, R. IL Farmaco 1999, 54,
588. and the references cited therein.
11. Uwe, K.; Jochem, H. German patent Wo 2003089441A1 Oct 30, 2003.
12. Singh, H. P.; Sharma, C. S.; Gautam, C. P. Middle East J. Scientific Res. 2009, 4, 203.
13. Price, C. C.; Roberts, R. M. J. Am. Chem. Soc. 1946, 68, 1204.
14. Biere, H.; Seelen, W. Liebigs Ann. Chem. 1976, 1972.
Product
Cycle
Yielda (%)/Time (min)
[BMIM]BF4
[BMIM]Br
[BMIM]OTf
4a
0
1
2
0
1
2
87/120
83/120
79/120
—
—
—
—
—
—
85/120
79/120
76/120
—
—
—
90/120
85/120
80/120
5a
a
15. (a) Li, J. J. Conard–Limpach Reactions in Name Reactions: A Collection of Detailed
Reaction Mechanisms, 2nd ed.; Springer: Berlin, 2003; (b) Zewge, D.; Chem, C.-
Y.; Deer, C.; Domer, P. G.; Hughes, D. L. J. Org. Chem. 2007, 72, 4276. and the
references cited therein.
Isolated yield after purification.
We have attempted the cyclization of 4a–e in [BMIM]Br/BF4/
OTf at temperatures 40 2 °C, 80 2 °C with any of these three
ILs. However at 80 2 °C when cyclization was attempted with
[BMIM]BF4/OTf, we have obtained the products 5a–e in excellent
yields. This behavior appears to be due to the coordinating strength
between the cation, viz. [BMIM]+ and anion BrÀ/BFÀ4 /OTfÀ. As BFÀ4
and OTfÀ are weakly coordinated20 BrÀ > BFÀ4 > OTf–, the cyclization
occurs smoothly with [BMIM]BF4/OTf. The better results of
cyclization with anion OTfÀ in comparison to BFÀ4 are in conso-
nance with this preposition.
Next, we have attempted this methodology with 2-aminothia-
zole 6/2-aminobenzothiazole 7a–e, reactant 2 and 3 in the pres-
ence of [BMIM]Br under nitrogen atmosphere at 40 2 °C to
afford thiazolo-2-amino/benzothiazolyl-2-aminomethylene-1,3-
dioxane-4,6-dione 8/9a–e in excellent yields. These compounds
upon subsequent cyclization, as described above, afford 5H-thiaz-
olo[3,2-a]pyrimidine-5-one 10 in an 88% yield/4H-pyrimido
[2,1-b]benzothiazol-4-ones 11a–e in good yields (Scheme 2,
Table 2).
A general method for the synthesis of these compounds is pre-
sented.21 All these compounds 4a–e, 5a–e, 8, 9a–e, and 11a–e were
characterized by IR, 1H NMR, 13C NMR, mass spectroscopy and
elemental analysis.22
We have studied the recyclability of the regenerated ionic
liquids for the products 4a and 5a. The yields of the products in
two cycles are presented in Table 3.
From the data presented in Table 3, it is clear that the yields of the
products 4a and 5a decrease in various cycles, yet the regenerated
ionic liquid can be reused with reasonably good success. Thus, this
procedure is advantageous over the reported conventional methods.
In conclusion, we have developed an environmentally benign
efficient methodology for the clean synthesis of 4(1H)-quinolones,
5H-thiazolo[3,2-a]pyrimidin-5-ones and 4H-pyrimido[3,2-a]ben-
zothiazol-4-ones.
16. Heindel, N. D.; Kennewell, P. D.; Fish, V. B. J. Heterocyl. Chem. 1969, 6, 77.
17. Rotzoll, S.; Reinke, H.; Fischer, C.; Langer, P. Synthesis 2009, 69.
18. Huang, X.; Lia, Z. J. Org. Chem. 2002, 67, 6731. and the references cited therein.
19. Yadav, A. K.; Kumar, M.; Yadav, T.; Jain, R. Tetrahedron Lett. 2009, 50, 5031.
20. Bini, R.; Bortolini, O.; Chiappe, C.; Pieraccini, D.; Siciliano, T. J. Phys. Chem. B.
2007, 111, 598–604.
21. (a) Typical experimental procedure for the synthesis of 4a–e: A mixture of
appropriate aniline
1
(5 mmol), Meldrum’s acid
2
(6 mmol), trimethyl
round
orthoformate (15 mmol) and [BMIM]Br (3 mL) is taken in
3
a
bottomed flask with the provision to perform the reaction under nitrogen
atmosphere. The contents of the flask were stirred magnetically at 40 2 °C.
The progress of the reaction was monitored on a TLC plate (Merck Silica gel
60F254) in pet.ether–ethyl acetate (8:2) and the visualization was accomplished
in an iodine chamber/UV-light. After the completion of the reaction, water
(10 mL) was added to it. The organic compound was precipitated, which was
filtered on a Buckner funnel applying vacuum. The product, so obtained, was
purified by crystallization with methanol/column chromatography (Merck
Silica gel 60–120 mesh) and elution of the product was carried out by
pet.ether–ethylacetate (8:2).
(b) Typical experimental procedure for the cyclization of 4a–e: Compound 4a–
e (5 mmol) and [BMIM]BF4/OTf (3 mL) were taken in a round bottomed flask
having provision to carry out the reaction under nitrogen atmosphere. The
contents of the flask were stirred magnetically at 80 2 °C. The progress of the
reaction was monitored on a TLC plate in pet.ether–ethyl acetate (8:2). After
completion of the reaction, the product was extracted with ethyl acetate
(3 Â 10 mL). The solvent was recovered under reduced pressure (5 mm of Hg).
The pasty mass thus obtained was extracted with diethyl ether (3 Â 10 mL),
dried over anhydrous sodium sulphate and ether was distilled. The product so
obtained was purified by crystallization with ethanol/column chromatography
(Merck Silica gel 60–120 mesh) and eluting TLC product with pet.ether–
ethylacetate (8:2).
22. Details of analytical data of compounds 4a,b, 5a,b,d,e, 8, 11a,b; Compound 4a.
5{(Phenylamino)methylene}-2,2-dimethyl, 1,3-dioxane-4,6-dione: Yellow
solid, mp 135–136 °C, Characteristic IR (KBr pellet, cmÀ1) 3169, 3067, 1728,
1675, 1630, 1608, 1440, 1270, 1028. 1H NMR (300 MHz, CDCl3) d 1.74 (s, 6H,
2 Â CH3), 7.18 (d, 3J = 7.8 Hz, 2H, Ar), 7.15 (dd, 3J = 7.6, 2H, Ar), 7.12 (dd, 1H, Ar),
8.68 (d, 3J = 13.9 Hz, 1H, @CH), 11.43 (br d, 3J = 13.8 Hz, 1H, NH). 13C NMR
(75 MHz, CDCl3) d = 27.1, 87.2, 105.4, 116.9, 125.2, 127.4, 131.5, 136.2, 137.6,
152.6, 163.6, 165.7. Anal. Calcd for C13H13NO4: C, 63.15; H, 5.26, N, 5.66%.
Found: C, 63.12; H, 5.18; N, 5.60%.
Compound 4b. 5{[(2-Methylphenyl)amino]methylene}, 2,2-dimethyl-1,3-
dioxane-4,6-dione: yellow solid, mp 142–143 °C, Characteristic IR (KBr pellet,
cmÀ1) 3165, 3058, 2985, 1722, 1672, 1640, 1609, 1440, 1270, 1025. 1H NMR
(300 MHz, CDCl3) d 1.76 (s, 6H, 2 Â CH3), 3.33 (d, 3H, CH3), 7.02 (d, 3J = 7.6 Hz,
1H, Ar), 7.15 (dd, 2H, Ar), 7.19 (d, 3J = 7.6 Hz, 1H, Ar), 8.65 (d, 3J = 13.9 Hz, 1H, –
CH), 11.40 (d, 3J = 13.9 Hz, 1H, NH). 13CNMR (75 MHz, CDCl3) d 21.1, 27.1, 87.1,
105.3, 117.4, 124.8, 127.5, 131.3, 136.7, 137.5, 152.7, 163.6, 165.7. Anal. Calcd
for C14H15NO4: C, 64.36; H, 5.74; N, 5.36%. Found: C, 64.28; H, 5.79; N, 5.44%.
Compound 5a. Quinolin-4(1H)-one: brownish solid, mp 190–191 °C,
Characteristic IR (KBr pellet, cmÀ1) 3240, 3080, 3150, 1640, 824. 1H NMR
(300 MHz, CDCl3) d 6.12 (d, 2J = 7.5 Hz, 1H, CH), 7.37 (dd, 3J = 7.5 Hz, 2H, Ar),
Acknowledgments
We thank the head, Chemistry Department, the University of
Rajasthan, Jaipur for providing laboratory facilities. Financial assis-
tance from UGC, New Delhi is thankfully acknowledged.

862
A. K. Yadav et al. / Tetrahedron Letters 53 (2012) 859–862
7.78 (d, 3J = 7.5 Hz, 1H, CH), 8.27 (d, 3J = 7.5 Hz, 2H, Ar), 10.97 (s, 1H, NH). 13C
NMR (75 MHz, CDCl3) d 108.1, 118.4, 121.2, 126.1, 128.4, 138.2, 138.7, 143.7,
171.8. Anal. Calcd for C9H7NO: C, 74.48; H, 4.82; N, 9.65%. Found: C, 74.43; H,
4.80; N, 9.75%.
(100), 185(55), 150(21), 123(14), 93(9) Anal. Calcd for C9H5Cl2NO: C, 50.50; H,
2.35; N, 6.54%. Found: C, 50.40; H, 2.25; N, 6.63%.
Compound 8. 3-Methyl 5H-thiazolo[3,2-a]pyrimidin-5-one: Yellow solid, mp
124–125 °C. Characteristic IR (KBr pellet, cmÀ1): 3114, 1665, 1618, 1590, 1482,
1419, 1285, 1235, 1148, 972, 815, 764. 1H NMR (300 MHz, CDCl2) d 2.83(d, 3H,
Compound 5b. 8-Methylquinolin-4(1H)-one: brownish solid, mp 196–197 °C,
Characteristic IR (KBr pellet, cmÀ1) 3168, 3110, 1610, 1560, 1519, 805. 1H NMR
(300 MHz, CDCl3) d 2.42 (s, 3H, CH3), 6.21 (d, 3J = 7.3 Hz, 1H, CH), 6.92 (d,
J = 1.35 Hz), 6.22 (d, 1H,
J 6.55 Hz), 6.45 (t, 1H, J = 1.35 Hz), 7.87 (d, 1H,
J = 6.55 Hz). 13C NMR (75 MHz, CDCl3) d 18.66, 105.83, 107.45, 135.92, 152.7,
161.9, 166.1. MS (EI, 70 eV): m/z (%) = 166 (M+, 100), 138 (74), 93 (19), 71 (28),
72 (19), 67 (16), 52 (11), 45 (33). Anal. Calcd. for C7H6N2OS: C, 50.58; H, 3.63;
N, 16.85%. Found: 50.50, H, 3.52; N, 16.76%.
3J = 7.4 Hz, 2H, Ar), 7.23 (dd, 3J = 7.4 Hz, 1H, Ar), 7.73 (d, 3J = 7.3 Hz, 1H, CH). 13
C
NMR (75 MHz, CDCl3): d = 24.2, 111.6, 124.8, 125.4, 127.1, 133.2, 138.7, 139.4,
141.4, 182.6. Anal. Calcd for C10H9NO: C, 75.47; H, 5.66; N, 8.81%. Found: C,
75.58; H, 5.72; N, 8.90%.
Compound 5d. 8-Chloroquinolin-4(1H)-one: Brownish solid, mp 256–257 °C,
Characteristic IR (KBr pellet, cmÀ1): 3160, 3056, 2924, 1562, 1336, 1210, 1076.
1H NMR (300 MHz, CDCl3) d 6.19 (d, 3J = 7.5 Hz, 1H, CH), 7.87 (d, 3J = 7.5 Hz, 1H,
CH), 7.96 (d, 4J = 2.4 Hz, 2H, Ar), 7.01 (d, 4J = 2.4 Hz, 1H, Ar), 11.52 (s, 1H, NH).
13C NMR (75 MHz, CDCl3) d 107.9, 121.8, 122.7, 126.5, 126.9, 130.1, 134.2,
138.7, 176.8. Anal. Calcd for C9H6NOCl: C, 60.68; H, 3.36; N, 7.79%. Found: C,
60.72; H, 3.28; N, 7.70%.
Compound 5e. 6,8-Dichloroquinolin-4(1H)-one: brownish solid, mp 287–
288 °C, Characteristic IR (KBr pellet, cmÀ1): 3140, 3082, 2926, 1620, 1560,
1511, 1337, 1215, 1080. 1H NMR (300 MHz, CDCl3) d 6.18 (d, 3J = 7.5 Hz, 1H,
CH), 7.90 (d, 3J = 7.5 Hz, 1H, CH), 8.01 (d, 4J = 2.4 Hz, 1H, Ar), 7.05 (d, 4J = 2.4 Hz,
1H, Ar), 11.55 (s, 1H, NH). 13C NMR (75 MHz, CDCl3) d 108.7, 122.5, 126.3,
126.9, 130.7, 134.9, 135.1,139.4, 177.2. MS (EI, 70 eV): m/z (%) = 213 [M]+,
Compound 11a. 4H-Pyrimido[2,1-b]benzothiazol-4-one: Yellow solid, mp 165–
166 °C. Characteristic IR (KBr pellet, cmÀ1): 1681, 1578, 1503, 1258, 996, 826,
762. 1H NMR (300 MHz, CDCl3), d 6.43 (d, 1H, J = 6.52 Hz), 7.52–7.59 (m, 2H),
7.72–7.74 (m, 1H), 7.98 (d, 1H, J = 6.52 Hz), 9.12–9.15 (m, 1H). MS m/z
(%) = 202 (M+, 100), 174 (98), 146 (15), 134 (13), 120 (11), 108 (9), 90 (13), 69
(16). Anal. Calcd. for C10H6N2OS: C, 59.39; 2.98; N, 13.85%. Found 59.45; H,
2.91; N, 13.92%.
Compound 11b. 6-Methyl-4H-pyrimido[2,1-b]benzothiazol-4-one: Yellow
solid, mp 105–106°. Characteristic IR (KBr pellet, cmÀ1): 2932, 1695, 1578,
1498, 1476, 1386, 1278, 1245, 758. 1H NMR (300 MHz, CDCl3), d 2.64 (s, 3H),
6.32 (d, J = 6.52 Hz), 7.32–7.42 (m, 2H), 7.46–7.48 (m, 1H), 7.87 (d, 1H, J = 6.52).
13C NMR (75 MHz, CDCl3) d 24.26, 109.28, 119.24, 125.38, 126.93, 130.94,
132.01, 134.38, 151.25, 160.83, 163.15. Anal. Calcd. for C11H8N2OS: C, 61.09; H,
3.73; N, 12.95%. Found: C, 61.36; H, 3.93; N, 12.87%.