An efficient, ionic liquid mediated one-pot, three component sequential synthesis of 3-benzothiazolyl-2-styrylquinazolin-4(3H)-ones

Article abstract of DOI:10.1016/j.tetlet.2012.11.104

An efficient and diversity oriented one-pot three component sequential synthetic method has been presented for the synthesis of 3-benzothiazolyl-2- styrylquinazolin-4(3H)-ones. The synthetic method involves the reaction of 3,1-benzoxazinone with 2-aminobe

Full text of DOI:10.1016/j.tetlet.2012.11.104

Tetrahedron Letters 54 (2013) 878–882
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Tetrahedron Letters
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An efficient, ionic liquid mediated one-pot, three component sequential
synthesis of 3-benzothiazolyl-2-styrylquinazolin-4(3H)-ones
Mahendra Kumar a, , Kailash Sharma a, Dinesh Kumar Sharma a, Anand Kumar Arya b
⇑
a Department of Chemistry, University of Rajasthan, Jaipur 302 055, India
b DESM, Regional Institute of Education (NCERT), Ajmer 305 004, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient and diversity oriented one-pot three component sequential synthetic method has been pre-
sented for the synthesis of 3-benzothiazolyl-2-styrylquinazolin-4(3H)-ones. The synthetic method
involves the reaction of 3,1-benzoxazinone with 2-aminobenzothiazole and subsequently with aromatic
aldehyde using SO3H-functionalized ionic liquids (SFILs) as solvent/ catalyst.
Received 28 September 2012
Revised 22 November 2012
Accepted 24 November 2012
Available online 1 December 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
One-pot reaction
Benzothiazolyl-styrylquinazolin-4(3H)-ones
Stilbenes
SFILs
O
Recently, combretastatin A-4 (CA-4) and its analogs have shown
unique potentialities for treatment of cancer and for cancer chemo-
prevention.1 The styryltriazole and resveratrol derivatives have
been evaluated as potential radio ligands for Ab plaque imaging.
The hybrid pharmacophores of stilbene-chalcones have also been
reported as antimalarial scaffolds that trigger cell death through
stage specific apoptosis.2,3 Quinazolin-4(3H)-one (compounds 1,
2) is considered to be a privileged structure and has been exten-
sively utilized as a drug like scaffold in medicinal chemistry.4
Among the various classes of stilbene-based compounds, 2-styryl-
quinazolin-4(3H)-ones derivatives form an interesting class of
pharmacologically active compounds.5 The 2-styrylsubstituted
derivatives of quinazolin-4(3H)-one 3 are associated with inhibi-
tory effects on tubulin polymerization and the growth of L1210
murine leukemia cells, while N-3-aryl-substituted analogs (piriqu-
alone, 4) have been shown to exhibit potent anticonvulsant activ-
ity.6 The stilbene based quinazolin-4-one derivatives CP-465,022 5
have also been reported as potent noncompetitive alpha-amino-3-
hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor
antagonists (Fig. 1).7 As a privileged structural fragment, benzo-
thiazoles are also the important key building blocks in drug
discovery.8
NHR
H3C
O
N
O
X
N
NH
N
O
N
Ar
N
CH3
Cl
Cl
1
3
2
methaqualone
Cl
O
O
N
N
F
N
N
N
N
4
5
piriqualone
CP-465,022
NEt2
Figure 1. Biologically active quinazolinones and 2-styrylquinazolinones.
4(3H)-one skeleton improves biological activity.5 Furthermore,
N3-substitution of the quinazolin-4(3H)-one ring with aromatic/
heteroaromatic rings considerably enhances their biologically
activity.6 There are only a few reports on the synthesis of 2-styryl-
quinazolin-4(3H)-ones and generally involves multistep
procedures.9 The reported synthetic protocols suffer from disad-
vantages such as relying on multi-step reactions, having low yields,
Among various studies on the structure–activity relationship of
stilbene, most of them concern with the modification in aromatic
rings and in linker alkene. The literature demonstrates that the
structural modification of one ring of stilbene with quinazolin-
⇑
Corresponding author. Tel.: +91 0141 2702720.
E-mail address: mahendrakpathak@gmail.com (M. Kumar).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.11.104

M. Kumar et al. / Tetrahedron Letters 54 (2013) 878–882
879
Table 1
harsh reaction conditions, prolonged reaction times, and using acid
Optimization of the reaction conditions
catalysts. Therefore, the development of new, efficient, and envi-
ronmentally benign routes for the synthesis of 2-styrylquinazoli-
nones incorporating medicinally privileged heterosystems by
employing non-toxic reagents and solvents is highly desirable from
the point of view of green chemistry and would be of great rele-
vance to both synthetic and medicinal chemists.
Entry
Solvent
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
DMF
Acetonitrile
24
25
19
24
12
09
09
18
17
35
33
68
43
81
87
79
68
61
Glacial acetic acid
Ethanol
[MIM(CH2)4SO3H][CH3PhSO3] IL-1
[MIM(CH2)4SO3H][HSO4] IL-2
Zwitterion [MIM(CH2)4SO3ꢀ] IL-2
[bmim][PF6]
Recently, the quinazolin-4(3H)-ones have been synthesized by
green protocols involving the reaction of 3,1-benzoxazin-4-one
with substituted anilines/ammonium acetate (as source of ammo-
nia) and substituted aldehydes.10 But in view of synthetic potenti-
alities of multicomponent reactions to incorporate structural
diversity and in continuation of our research program on the syn-
thesis of therapeutically interesting heterocycles,11–17 we have
synthesized structurally diverse 3-benzothiazolyl-2-styrylquinaz-
olin-4(3H)-ones 5 involving one-pot sequential reaction of 2-
methyl-3,1-benzoxazin-4-one 1 with 2-aminobenzothiazoles 2
and subsequently with substituted aromatic aldehyes 4 using
SO3H-functionalized ionic liquids (SFILs) as solvent/catalyst. High-
er yields, simplicity of the method, ease of the product isolation,
mild reaction conditions, and use of ionic liquid as the reaction
medium/catalyst make this method more attractive. To the best
of our knowledge the synthesis of 3-benzothiazolyl-2-styrylqui-
nazolin-4(3H)-ones in SO3H functionalized ionic liquid has not
been documented in the literature.
We started our study with the optimization of the one pot
sequential synthesis of 3-benzothiazolyl-2-styrylquinazolin-
4(3H)-ones as model reaction (Scheme 1). Because of the advanta-
ges of the use of ionic liquid in terms of their unique solvating,
catalytic, and recycling abilities, we also investigated the effects
of ionic liquids on the reaction time and the product yield of the
model reaction.
The reaction was performed in the different organic solvents
(entries 1–4, Table 1) and ionic liquids (entries 5–9, Table 1) and
the effects of the different solvents and ionic liquids were evalu-
ated on the basis of reaction time and product yield for this model
reaction and the results are summarized in Table 1.
The ionic liquids provided higher yields with shorter reaction
times as compared with those obtained using organic solvents (Ta-
ble 1, entries 5–9 vs entries 1–4). The IL [MIM(CH2)4SO3H][HSO4]
also proved to be slightly superior to their analogous as well as
other ionic liquids for this reaction (Table 1, entry 6). It was also
observed that the [MIM(CH2)4SO3H][HSO4] ionic liquid system
provided comparatively a better yield of the product in lesser time
than other catalytic systems. Moreover, it was also observed that
SO3H-functionlized ionic liquids (IL-1 and IL-2) provided a better
yield of the product as compared to that obtained when the reac-
tions were carried out with halogen containing ionic liquids (en-
tries 5 and 6). It was also observed that the 5 mol % ionic liquid
is sufficient to provide excellent results and further increase in
[bmim][BF4]
2-Methyl-3,1-benzoxazin-4-one 1 (1 mmol), 2-amino-5-methylbenzothiazole 2a
(1 mmol), p-anisaldehye 4a (1 mmol), temperature 80 °C.
the amount up to 10 mol % did not improve the results to a greater
extent.
The proposed mechanism for the formation of 3-benzothiazol-
yl-2-styrylquinazolin-4(3H)-ones catalyzed by SO3H functional-
ized ionic liquid is presented in Scheme 2. In this reaction the
ionic liquid not only behaves as solvent but also facilitates the
reaction as a catalyst.
Under these optimal conditions, the sequential reaction of 2-
methyl-3,1-benzoxazin-4-one 1 with substituted 2-aminobenzo-
thiazoles 2(a–d) and subsequently with aromatic aldehydes
4(a–b) were carried out in the presence of SO3H-functionalized
ionic liquid (IL-1/IL-2) as catalyst/solvent in a single vessel to
obtain 3-benzothiazolyl-2-styrylquinazolin-4(3H)-ones 5(a–h) in
excellent yields.18 The results in terms of product yields and
reaction time were compared and are summarized in Table 2.
The overall yields obtained are excellent considering the number
of steps involved in the sequential reaction. The SO3H-function-
lized ionic liquids were prepared by the method reported.12
It was observed that the ionic liquid, SFILs, could be easily quan-
titatively recovered after completion of the reaction and readily
recycled and reused for at least five cycles without any appreciable
loss of activity to provide structurally diverse 3-benzothiazolyl-2-
styrylquinazolin-4(3H)-ones in excellent yields (Fig. 2).
In conclusion, we have developed an efficient and eco-compatible
synthetic methodology for the synthesis of structurally diverse
3-benzothiazolyl-2-styrylquinazolin-4(3H)-ones
in
excellent
yields using a halogen-free SO3H functionalized ionic liquid as
recyclable medium. The present method demonstrates the favor-
able reasons for using ionic liquid as a reaction medium (‘green-
ness’, solvent recoverability, non-inflammability, etc.) in parallel
to the synthesis of target compounds in conventional organic reac-
tion media such as DMF, CH3CN, glacial acetic acid, and ethanol.
This method is bestowed with its unique merits, such as mild reac-
tion conditions, operational simplicity, and use of ionic liquid as a
solvent.
CHO
Me
O
N
N
N
NH2
O
Me
O
N
N
S
N
S
Me
OMe
4a
O
2a
S
N
N
CH3
CH3
1
3
5a
OMe
Scheme 1. Model reaction.

880
M. Kumar et al. / Tetrahedron Letters 54 (2013) 878–882
-
HO3S
HSO4
IL with dual
acidic character
Me
O
N
O
S
N
H
IL
N
S
O
NH2
NH
N
CH3
Me
-
HO3S
H3C
O
HSO4
2a
1
Me
O
N
Me
Me
O
N
O
N
S
N
S
CH3
OH
S
N
N
-H2O
N
H
N
H
CH2
H
N
CH3
-
HO3S
HSO4
3
-
O
HO3S
HSO4
C
4a
OMe
N
Me
O
N
Me
O
N
N
S
N
S
H
C
N
H
-H2O
CH
CH
CH
HO
OMe
OMe
-
5a
HO3S
HSO4
Scheme 2. Proposed mechanism for the synthesis of 3-benzothiazolyl-2-styrylquinazolin-4(3H)-ones catalyzed by SO3H functionalized ionic liquid.
Table 2
Comparison of ionic liquids (IL-1 & IL-2)
SO3H
-
SO3H
N
N
N
N
-
CH3PhSO3
HSO4
IL-2
Entry
3-Benzothiazolyl-2-styryl-quinazolin-4(3H)-ones
IL-1
Time (h)
Yield (%)
81
Time (h)
Yield (%)
Me
O
N
N
N
S
S
N
N
5a
12.0
09.0
87
90
OMe
OMe
O
N
5b
12.30
80
10.15
OMe

M. Kumar et al. / Tetrahedron Letters 54 (2013) 878–882
881
Table 2 (continued)
SO3H
-
SO3H
N
N
N
N
-
CH3PhSO3
HSO4
IL-2
Entry
3-Benzothiazolyl-2-styryl-quinazolin-4(3H)-ones
IL-1
Time (h)
Yield (%)
Time (h)
Yield (%)
Cl
Cl
O
N
N
S
N
5c
12.5
81
11.5
85
88
OMe
H3C
CH3
O
N
N
S
N
N
N
5d
12.10
81
10.15
OMe
Me
O
N
N
S
5e
5f
11.0
11.5
79
80
09.5
87
88
Cl
OMe
O
N
N
S
09.40
Cl
Cl
Cl
O
N
N
S
N
5g
5h
13.25
11.35
75
77
12.1
86
89
Cl
H3C
CH3
O
N
N
S
N
10.20
Cl
2. Sharma, N.; Mohanakrishnan, D.; Shard, A.; Sharma, A.; Saima Sinha, A.; Sahal,
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Imaging 2008, 35, 75.
Figure 2. Reusability of IL-1 and IL-2.
References and notes
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(b) Lin, C. M.; Ho, H. H.; Pettit, G. R.; Hamel, E. Biochemistry 1989, 28, 6984; (c)
Simoni, D.; Roberti, M.; Invidiata, F. P.; Rondanin, R.; Baruchello, R.; Malagutti,
C.; Mazzali, A.; Rossi, M.; Grimaudo, S.; Dusonchet, L.; Meli, M.; Raimondi, M.
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Y.; Shan, W.; Lei, M.; Hu, L. Tetrahedron Lett. 2012, 53, 5923; (c) Ramesh, K.;
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NMR (300 MHz, DMSO-d6) d ppm: 3.69 (3H, s, OCH3), 6.80 (1H, d, olefinic CH),
7.01–8.71 (10H, m, ArH). 13C NMR (75 MHz, DMSO-d6) d (ppm): 55.6, 114.9,
117.2, 118.4, 121.1, 122.1, 122.9, 126.2, 127.7, 128.0, 129.3, 130.4, 130.9, 133.6,
138.1, 145.2, 150.2, 152.2, 161.6, 162.4, 163.1. Anal. Calcd. (%) for
11. Arya, A. K.; Gupta, S.; Kumar, M. Tetrahedron Lett. 2012, 53, 6035.
12. Kumar, M.; Sharma, K.; Arya, A. K. Tetrahedron Lett. 2012, 56, 4604.
13. Arya, A. K.; Kumar, M. Green Chem. 2011, 13, 1332.
C
24H15Cl2N3O2S:
(3.17%), N (8.73%).
3-(40,60-Dimethylbenzothiazol-2-yl)-2-(40-methoxystyryl)quinazolin-4(3H)-one
(5d). Mp 183–185 °C, IR (KBr): 1700, 1592, 1668, 1260–1145 cmꢀ1 1H NMR
C (60.01%), H (3.15%), N (8.75%). Found: C (60.03%), H
14. Arya, A. K.; Kumar, M. Mol Divers. 2011, 15, 781.
.
15. (a) Rathor, B. S.; Kumar, M. Bioorg. Med. Chem. 2006, 14, 5678; (b) Kumar, M.;
Sharma, K.; Samarth, R. M.; Kumar, A. Eur. J. Med. Chem. 2010, 45, 4467.
16. (a) Kumar, M.; Sharma, K.; Sharma, D. K. Org. Med. Chem. Lett. 2012, 2, 10; (b)
Rathor, B. S.; Gupta, V.; Gupta, R. R.; Kumar, M. Heteroatom Chem. 2007, 18, 81.
17. Gupta, R. R.; Kumar, M. Synthesis, Reactions and Properties of Phenothiazines’.
In Phenothiazines and 1,4-Benzothiazines. Chemical and Biomedical Aspect;
Elsevier: Amsterdam, 1988.
18. Typical Experimental Procedure: A dry 50 mL round bottom flask was charged
with 2-methyl-3,1-benzoxazin-4-one 1 (1 mmol), 2-aminobenzothiazoles 2(a–
d) (1 mmol) and ionic liquid, SFILs (IL-1/IL-2) (0.05 g). The mixture was stirred
at 80 °C for 4–7 h to complete the reaction (monitored by TLC). The aromatic
aldehyde 4(a–b) (1 mmol) was added to the above reaction mixture, and stirred
at 80 °C for 9–13 h until the reaction was completed as monitored by TLC using
n-hexane/EtOAc; 7:3 as eluent. The mixture was cooled and 10 mL water was
added. The solid was filtered off and washed with water. The crude product was
purified by recrystallization from ethanol to give 5. The ionic liquid was reused
after drying under vacuum at 90 °C.
(300 MHz, CDCl3) d ppm: 2.25 (3H, s, CH3), 2.29 (3H, s, CH3), 3.78 (3H, s, OCH3),
6.71 (1H, d, olefinic CH), 6.78–7.96 (10H, m, ArH). 13C NMR (75 MHz, DMSO-d6)
d (ppm): 16.2, 20.8, 55.5, 114.1, 118.9, 120.1, 121.5, 122.7, 125.3, 126.1, 127.7,
128.2, 129.3, 130.4, 131.4, 134.0, 138.5, 145.3, 150.2, 152.4, 160.4, 162.3, 163.1.
Anal. Calcd. (%) for C26H21N3O2S: C (71.05%), H (4.82%), N (9.56%). Found: C
(71.09%), H (4.80%), N (9.55%).
3-(60-Methylbenzothiazol-2-yl)-2-(40-chlorostyryl)quinazolin-4(3H)-one (5e). Mp
218–220 °C; IR (KBr): 1693, 1535, 1615, 1035 cmꢀ1 1H NMR (300 MHz,
.
DMSO-d6) d ppm: 2.36 (3H, s, CH3), 6.99 (1H, d, olefinic CH), 7.12–8.75 (11H,
m, ArH). 13C NMR (75 MHz, DMSO-d6) d (ppm): 20.8, 117.4, 121.1, 121.7, 122.4,
126.3, 126.2, 126.9, 127.1, 128.5, 129.2, 130.7, 133.3, 134.1, 134.6, 135.2, 137.2,
149.4, 150.8, 151.4, 162.2, 163.1. Anal. Calcd. (%) for C24H16ClN3OS: C (67.05%), H
(3.75%), N (9.77%). Found: C (67.08%), H (3.78%), N (9.79%).
3-(60-Methoxybenzothiazol-2-yl)-2-(40-chlorostyryl)quinazolin-4(3H)-one (5f). Mp
203–206 °C, IR (KBr): 1737 1520, 1635, 1290–1145, 1070 cmꢀ1 1H NMR
.
(300 MHz, DMSO-d6) d ppm: 3.68 (3H, s, OCH3), 6.73 (1H, d, olefinic CH), 6.86–
7.54 (12H, m, ArH). 13C NMR (75 MHz, DMSO-d6) d (ppm): 55.7, 104.8, 114.2,
118.5, 121.4, 122.9, 126.7, 126.9, 127.6, 128.1, 129.7, 131.9, 133.4, 134.8, 135.7,
137.8, 145.2, 149.1, 151.2, 155.4, 162.6, 163.1; Anal. Calcd. (%) for
Spectral data of synthesized of 3-benzothiazolyl-2-styrylquinazolin-4(3H)-
ones. 3-(60-Methylbenzothiazol-2-yl)-2-(40-methoxystyryl)quinazolin-4(3H)-one
(5a). Mp 210–212 °C, IR (KBr): 1710, 1542, 1642, 1220–1162 cmꢀ1
.
1H NMR
C24H16ClN3O2S: C (64.64%), H (3.62%), N (9.42%). Found: C (64.65%), H (3.62%),
(300 MHz, DMSO-d6) d ppm: 2.14 (3H, s, CH3), 3.80 (3H, s, OCH3), 6.90 (1H, d,
olefinic CH), 7.02–8.77 (11H, m, ArH). 13C NMR (75 MHz, DMSO-d6) d (ppm):
20.2, 55.6, 114.9, 117.2, 118.4, 120.5, 120.7, 121.1, 124.2, 126.2, 127.7, 128.0,
129.3, 130.4, 133.6, 134.5, 138.1, 139.3, 149.4, 150.2, 152.2, 161.6, 162.4, 163.1;
Anal. Calcd. (%) for C25H19N3O2S: C (70.57%), H (4.50%), N (9.88%). Found: C
(70.56%), H (4.50%), N (9.89%).
N (9.41%).
3-(40,50-Dichlorobenzothiazol-2-yl)-2-(40-chlorostyryl)quinazolin-4(3H)-one (5g).
Mp 185–187 °C, IR (KBr): 1739, 1534, 1612, 1090 cmꢀ1 1H NMR (300 MHz,
.
DMSO-d6) d ppm: 6.81 (1H, d, olefinic CH), 6.88–7.61 (10H, m, ArH). 13C NMR
(75 MHz, DMSO-d6) d (ppm): 120.9, 121.7, 122.3, 126.7, 126.8, 127.0, 127.6,
127.4, 128.2, 129.8, 130.2, 131.1, 133.4, 134.2, 135.9, 137.5, 148.8, 150.1, 151.9,
162.8, 163.1. Anal. Calcd. (%) for C23H12Cl3N3OS: C (56.98%), H (2.49%), N (8.67%).
Found: C (56.95%), H (2.45%), N (8.67%).
3-(60-Methoxybenzothiazol-2-yl)-2-(40-methoxystyryl)quinazolin-4(3H)-one (5b).
Mp 238–240 °C; IR (KBr): 1740, 1532, 1640, 1250–1164 cmꢀ1 1H NMR
.
(300 MHz, DMSO-d6) d ppm: 3.49 (3H, s, OCH3), 3.58 (3H, s, OCH3), 6.93 (1H,
d, olefinic CH), 6.97–8.43 (11H, m, ArH). 13C NMR (75 MHz, DMSO-d6) d (ppm):
55.6, 57.4, 108.2, 110.6, 114.9, 117.2, 118.4, 121.2, 123.4, 126.2, 127.7, 128.0,
129.3, 130.4, 133.6, 138.1, 145.2, 149.4, 152.2, 159.2, 161.6, 162.4, 163.1; Anal.
Calcd. (%) for C25H19N3O3S: C (68.01%), H (4.39%), N (9.52%). Found: C (68.01%),
H (4.35%), N (9.51%).
3-(40,60-Dimethylbenzothiazol-2-yl)-2-(40-chlorostyryl)quinazolin-4(3H)-one (5h).
Mp 227–232 °C, IR (KBr): 1700, 1530, 1650, 1020 cmꢀ1 1H NMR (300 MHz,
.
DMSO-d6) d ppm: 2.24 (3H, s, CH3), 2.56 (3H, s, CH3), 6.83 (1H, d, olefinic CH),
7.02–8.65 (10H, m, ArH). 13C NMR (75 MHz, DMSO-d6) d (ppm): 18.4, 21.2, 39.4,
118.2, 120.7, 122.1, 124.2, 126.1, 126.9, 127.2, 127.9, 128.5, 129.5, 131.2, 133.4,
134.0, 134.7, 135.9, 137.8, 144.5, 149.1, 150.7, 162.9, 163.1. Anal. Calcd. (%) for
3-(40,50-Dichlorobenzothiazol-2-yl)-2-(40-methoxystyryl)quinazolin-4(3H)-one
C25H18ClN3OS: C (67.64%), H (4.09%), N (9.47%). Found: C (67.68%), H (4.06%), N
(5c). Mp 215–217 °C, IR (KBr): 1692, 1555, 1610, 1280–1154, 1085 cmꢀ1 1H
.
(9.42%).