Catalytic systems containing p-toluenesulfonic acid monohydrate catalyzed the synthesis of triazoloquinazolinone and benzimidazoquinazolinone derivatives

Article abstract of DOI:10.1007/s00706-014-1273-y

A variety of quinazolinones are readily prepared via one-pot three-component reaction in good to excellent yields. The desired products were obtained from the reaction of dimedone, various aldehydes with 2-aminobenzimidazole or 3-amino-1,2,4-triazole unde

Full text of DOI:10.1007/s00706-014-1273-y

Monatsh Chem
DOI 10.1007/s00706-014-1273-y
ORIGINAL PAPER
Catalytic systems containing p-toluenesulfonic acid monohydrate
catalyzed the synthesis of triazoloquinazolinone
and benzimidazoquinazolinone derivatives
•
Mir Rasul Mousavi Malek Taher Maghsoodlou
Received: 22 March 2014 / Accepted: 22 June 2014
Ó Springer-Verlag Wien 2014
Abstract A variety of quinazolinones are readily prepared
via one-pot three-component reaction in good to excellent
yields. The desired products were obtained from the reaction
of dimedone, various aldehydes with 2-aminobenzimidazole
or 3-amino-1,2,4-triazole under mild reaction conditions
using p-toluenesulfonic acid monohydrate as effective cat-
alyst in acetonitrile as solvent. Starting from the
corresponding available materials, this friendly and envi-
ronmentally free-metal procedure has been successfully
extended to the synthesis of triazoloquinazolinones and
benzimidazoquinazolinones. The salient advantages of this
method are mild reaction conditions, nontoxic and inex-
pensive catalyst, environmentally benign, high to excellent
yields, shorter reaction times, easy operation, and no column
chromatographic separation.
(MCRs), leading to interesting heterocyclic scaffolds, are
particularly useful for combinatorial chemistry as powerful
tools [5] because of their valuable features such as atom
economy, environmental friendliness, straightforward
reaction design, and the opportunity to construct target
compounds by the introduction of several diversity ele-
ments in a single chemical operation [6, 7].
Five- and six-membered heterocyclic compounds are
important constituents that often exist in biologically active
natural products and synthetic compounds of medicinal
interest [8, 9]. Among them quinazolinones and 1,2,4-
triazoloquinazolinone derivatives are known for diverse
pharmacological activities as hypnotic [10], analgesic [11],
neuroleptic [12], anticonvulsant [13], muscle relaxant [14],
antifertility [15], latent leishmanicidal [16], antihistaminic
[17–19], antihypertensive [11, 20–22], anti-inflammatory
[23], anticancer [24], and anti-HIV [25]. In spite of their
importance from a pharmaceutical, industrial, and synthetic
point of view, a few methods for their preparation are
reported in the literature. These include condensation
reactions of dimedone, various aldehydes with 2-amino-
benzimidazole or 3-amino-1,2,4-triazole in the presence of
Keywords Triazoloquinazolinone Á
3-Amino-1,2,4-triazole Á 2-Aminobenzimidazole Á
p-Toluenesulfonic acid
Introduction
molecular
iodine
(I2)
[26],
microwave
[27],
The growth of organic synthesis has been facilitated by the
development of one-pot methods, since they generate less
waste, minimize isolation of intermediates in multistep
syntheses of complex molecular targets, and save time and
minimize cost [1]. One-pot reactions can be classified
roughly as cascade, domino, or tandem reactions [2–4]. Of
one-pot synthetic strategies, multicomponent reactions
H6P2W18O62Á18H2O [28], and refluxing in DMF [29, 30].
Some of these processes suffer from some limitations such
as drastic reaction conditions, expensive reagents, and low-
to-moderate yields, relatively long reaction times and high
temperature. Therefore, the development of clean, high-
yielding and environmentally friendly approaches is
desirable.
The use of organic catalysts has received considerable
attention in organic synthesis owing to their important
advantages such as the possibility of performing reactions
with acid-sensitive substrates, milder reaction conditions,
and selectivity [31–33]. p-Toluenesulfonic acid
M. R. Mousavi Á M. T. Maghsoodlou (&)
Department of Chemistry, Faculty of Science, University of
Sistan and Baluchestan, P.O. Box 98135-674, Zahedan, Iran
e-mail: mt_maghsoodlou@chem.usb.ac.ir
123

M. R. Mousavi, M. T. Maghsoodlou
monohydrate (p-TsOHÁH2O) has received considerable
attention in organic synthesis owing to its advantages such
as low cost and ease of handling and isolation [34–36].
Encouraged by the remarkable results obtained from above
conditions, and also, in continuation of our ongoing green
chemistry program that utilizes homogeneous systems [37–
39] in various organic transformations, we report a simple,
mild, and convenient procedure for effecting one-pot,
three-component reaction of aryl aldehydes, dimedone and,
2-aminobenzimidazole/3-amino-1,2,4-triazole for prepara-
tion of triazolo/benzimidazolo-quinazolinone derivatives
using p-toluenesulfonic acid monohydrate as a homoge-
neous catalyst under mild reaction conditions at 40–50 °C
(Scheme 1).
it is noteworthy that the reaction did not progress even after
180 min in the absence of catalyst (Table 1, entry 1).
Next, we tested the influence of different temperatures
on the synthesis of quinazolinones in the presence of p-
toluenesulfonic acid (15 mol %) in acetonitrile, the results
are summarized in Table 2. It was found that the best
results were obtained at 40–50 °C, efficiency of 96 % was
generated (Table 2, entry 3) at the higher temperature that
did not increase the reaction yield (Table 2, entries 4, 5,
and 6).
During the course of the screening of a variety of reac-
tion conditions such as reaction temperature, the amount of
the catalyst and solvent, we found that the use of acetonitrile
as a solvent was essential for the efficient formation cor-
responding compounds. To estimate the generality and
versatility of the catalyst, the same reaction was applied for
the synthesis of 1,2,4-triazolo[5,1-b]quinolin-8(4H)-one
derivatives by replacing 2-aminobenzimidazole with
3-amino-1,2,4-triazole. In this case, the products were
obtained in excellent yields. To explore the scope of the
procedure, we extended this reaction to various aromatic
aldehydes in the presence of electron-withdrawing (NO2,
Cl, F) and electron-releasing (Me, OMe) substituents, both
of which gave the desired product. We observed that the
activity of 3-amino-1,2,4-triazole is better than 2-amino-
benzimidazole. The results are shown in Table 3. Results
show that the substituent groups did not play any significant
role in the reactivity of the substrate.
Results and discussion
In the present study, the authors examine the catalytic
behavior of p-toluenesulfonic acid as a catalyst for the
coupling reaction, and to optimize the reaction conditions,
we have performed a set of preliminary experiments on
benzaldehyde, dimedone, and 2-aminobenzimidazole in
acetonitrile at room temperature as a model reaction. The
reaction was completed in 60 min when 15 mol % of p-
TsOHÁH2O was used. Rate enhancement was observed
when higher molar ratios were used but no significant
improvement in the yield was observed. The results are
shown in Table 1. As could be seen in Table 1, to deter-
mine the catalytic amount of p-toluenesulfonic acid,
different ratios of the catalyst were examined and the
admissible result was obtained from using 15 mol % of p-
toluenesulfonic acid in acetonitrile (Table 1, entry 4). Also,
In this procedure, the products were easily isolated by
simple filtration; no need for column chromatography and
further recrystallization. All known products were charac-
terized by comparison of the melting points and the
analytical data (IR, NMR) with those reported for authentic
Scheme 1
123

Catalytic systems containing p-toluenesulfonic
Table 1 Condensation reaction of 2-aminobenzimidazole, benzaldehyde, and dimedone in the presence of different loading of the catalyst at
ambient conditionsa
Entry
Solvent/temp/ °C
Catalyst/mol %
Time/min
Yield/ %b
1
2
3
4
5
6
7
8
a
CH3CN/rt
CH3CN/rt
CH3CN/rt
CH3CN/rt
CH3CN/rt
CH3CN/rt
CH3CN/rt
-/rt
–
180
120
100
60
–
5
68
75
87
80
82
83
–
10
15
20
25
30
15
55
50
45
180
All reactions were carried out using 1 mmol benzaldehyde, 1 mmol dimedone, and 1 mmol 2-aminobenzimidazole with varying amounts of
catalyst in 5 cm3 CH3CN at room temperature
b
Yield refers to the pure isolated products
Table 2 Condensation reaction of 2-aminobenzimidazole, benzaldehyde, and dimedone in the presence of different loading of the catalyst at
different temperaturea
Entry
Solvent
T/°C
Time/min
Yield/%b
1
2
3
4
5
6
a
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
20–30 (r.t.)
30–40
60
60
30
55
50
40
87
89
96
91
90
92
40–50
50–60
60–70
70–80
All the reactions were carried out using 1 mmol benzaldehyde, 1 mmol dimedone, and 1 mmol 2-aminobenzimidazole with catalytic amount
of catalyst in 5 cm3 CH3CN at different temperatures
b
Yield refers to the pure isolated products
samples. The structure of new compounds 4h and 6j was
deduced on the basis of IR, 1H and 13C NMR spectroscopy,
mass spectrometry, and elemental analysis. For example,
the mass spectrum of 4h displayed the molecular ion peak
(M?) at m/z = 344, which is consistent with the proposed
structure. The 1H NMR spectrum of 4h exhibited two
singlet at d = 0.91 and 1.05 ppm for the geminal methyl
protons. Four doublets were observed at 2.07
(J = 16.0 Hz), 2.26 (J = 16.0 Hz), 2.52 (J = 16.0 Hz),
and 2.63 (J = 16.0 Hz) for the diastereotopic methylene
123

M. R. Mousavi, M. T. Maghsoodlou
Table 3 Synthesis of 3,3-dimethyl-12-phenyl-3,4,5,12-tetrahydrobenzo[4,5]imidazo[2,1-b]quinazolin-1(2H)-one
b]quinolin-8(4H)-one 6 derivatives in the presence of p-TsOHÁH2O
4
and 1,2,4-triazolo[5,1-
Entry
R
Amine
Product
Time/min
Yield/%a
M.p./°C
Lit. m.p./°C
1
H
3
3
3
3
3
3
3
3
5
5
5
5
5
5
5
5
5
5
4a
4b
4c
4d
4e
4f
25
35
20
40
15
18
15
25
30
45
10
15
18
18
20
14
16
15
95
94
98
87
95
91
96
97
96
89
96
95
97
85
90
98
97
98
[300
[300 [28]
2
4-Br
[300
[300 [28]
3
4-NO2
4-F
[300
[300 [29]
4
[300
[300 [27]
5
4-OMe
4-Cl
[300
[300 [29]
6
[300
[300 [28]
7
2,4-Cl2
4-pyridin-
H
4g
4h
6a
6b
6c
6d
6e
6f
[300
[300 [26]
8
[300
This workb
248–250 [30]
307–309 [28]
304–306 [26]
264–269 [28]
323–325 [26]
210–212 [26]
258–260 [27]
266–269 [26]
287–290 [26]
This workb
9
248–250
305–306
302–304
263–265
320–322
208–210
256–258
265–267
268–270
306–308
10
11
12
13
14
15
16
17
18
a
4-OH
4-Cl
4-Me
2,4-Cl2
2,4-(OMe)2
4-F
6g
6h
6i
3-NO2
2-Naphthyl-
2,6-Cl2
6j
Yields refer to the pure isolated products
b
The new compounds synthesized in this work
protons of H-4, H’-4, H-2 and H’-2, respectively. The
methine proton of the central ring (H-12) was observed as a
singlet at 6.47 ppm. The aromatic protons’ resonance
observed as the mixture of doublets and triplets at
6.97–8.45 ppm. Therefore, all the spectral data were in
agreement with the proposed structure.
To show the merit of the present work in comparison
with reported results in the literature, we compared results
of p-TsOHÁH2O with molecular iodine (I2) [26], micro-
wave [27], H6P2W18O62Á18H2O [28], and refluxing in DMF
[29, 30] in the synthesis benzimidazolo/1,2,4-triazoloqui-
nazolinone derivatives. As shown in Table 4, p-TsOHÁH2O
can act as productive and effective catalyst with respect to
reaction times and yields of products.
p-Toluenesulfonic acid exhibited remarkable reactivity
as a homogenous organocatalyst and considerably accel-
erated the reactions. In the end, we turned our attention
towards mechanistic studies for this transformation. On the
basis of the proposed mechanism in the literature, and all
our experimental results possible mechanism for this three-
component reaction for the formation of benzimidazolo/
1,2,4-triazoloquinazolinone derivatives 4a-4h and 6a-6j in
the presence of p-toluenesulfonic is shown in Scheme 2. At
first, the described transformations proceed via the initial
formation of respective a,b-unsaturated carbonyl com-
pounds 11 upon the loss of water molecule via
Knoevenagel condensation. Next, the a,b-unsaturated car-
bonyl compounds, undergoing more nucleophilic
endocyclic nitrogen attack in the 2-aminobenzimidazole 3,
yield the corresponding acyclic intermediate 12. Therefore,
the endocyclic nitrogen is more nucleophilic than the pri-
mary amino group [40, 41]. Further intermediate 12
undergoes intra-molecular cyclization giving rise to inter-
mediate 13 and by the loss of water molecule to yield the
corresponding quinazolinones 4.
In summary, we have developed a novel, simple, con-
venient and efficient synthetic protocol for the synthesis of
triazolo/benzimidazolo-quinazolinone derivatives using
cheap, readily available and nontoxic p-toluenesulfonic
acid monohydrate as a homogeneous catalyst in a catalytic
amount. This reaction can be regarded as an efficient
approach for the preparation of synthetically and pharma-
ceutically important quinazolinone, triazole, imidazole,
pyrazole, and tetrazole systems. This one-pot reaction has
some important advantages such as the easy workup pro-
cedure, simple and readily available precursors, nontoxic
and inexpensive catalyst, and good to high yields. The
products were collected easily by simple filtration and no
need for further purification.
Experimental
Melting point and IR spectra of all compounds were
obtained on an Electrothermal 9100 apparatus and a
123

Catalytic systems containing p-toluenesulfonic
Scheme 2
p-TsO H
p-TsO H
O
O
HO
O
O
O
O
O
p-TsOH
p-TsOH
H
H
R
R
1
7
9
8
2
p-TsO H
R
O
O
O
O
HO
HO
-H2O
H
H
R
O
O
R
p-TsO H
7
9
10
11
N
NH2
N
H
3
R
H
R
N
R
O
O
O
-H2O
N
N
O
N
H
HN
N
N
N
H
N
H
OH
p-TsO H
4
13
12
1
(1.0 mmol), and 15 mol % p-TsOHÁH2O was stirred in
5 cm3 acetonitrile as solvent at 40–50 °C for the appro-
priate time (Table 3). The progress of the reaction was
monitored by TLC. After completion of the reaction, a
thick precipitate was obtained. The solid product was
filtered off and washed with acetonitrile and subsequently
dried in air. The pure product was characterized by
conventional spectroscopic methods.
JASCO FT/IR-460 plus spectrometer, respectively. H and
13C NMR spectra of compounds were recorded on a Bruker
DRX-400 Avance instrument in DMSO-d6 or CDCl3. The
mass spectra for the new compounds were recorded on an
Agilent Technology HP 5973 MSD mass spectrometer
operating at an ionization potential of 70 eV. Elemental
analyses for C, H, and N were determined using a Perkin-
Elmer 2400 instrument. All commercial reagents were used
without further purification.
3,3-Dimethyl-12-(4-pyridyl)-3,4,5,12-tetrahydrobenzo[4,5]-
imidazo[2,1-b]quinazolin-1(2H).one (4h, C21H20N4O)
Whitesolid;yield97 %;m.p.:[300 °C;IR(KBr): vꢀ = 3419,
3030, 2957, 2922, 1640, 1615, 1596, 1570, 1460, 1377,
748 cm-1; 1H NMR (400 MHz, DMSO-d6): d = 0.91 (s, 3H,
CH3), 1.05 (s, 3H, CH3), 2.07 (d, J = 16.0 Hz, 1H, H-4), 2.26
(d, J = 16.0 Hz, 1H, H’-4), 2.52 (d, J = 16.0 Hz, 1H, H-2),
General procedure for the synthesis of 3,4,5,12-tetra-
hydrobenzo[4,5]imidazo[2,1-b]quinazolin-1(2H).ones
4
and 1,2,4-triazolo[5,1-b]quinazolin-8(4H)-ones 6 using p-
TsOHÁH2O as the reaction medium
A mixture of 2-aminobenzimidazole or 3-amino-1,2,4-
triazole (1.0 mmol), arylaldehyde (1.0 mmol), dimedone
123

M. R. Mousavi, M. T. Maghsoodlou
1369, 1255, 1191, 772 cm-1; 1H NMR (400 MHz, DMSO-
d6): d = 0.99 (s, 3H, CH3), 1.04 (s, 3H, CH3), 2.03 (d,
J = 16.0 Hz, 1H, H-5), 2.20 (d, J = 16.0 Hz, 1H, H’-5), 2.41
(d, J = 16.0 Hz, 1H, H-7), 2.54 (d, J = 20.0 Hz, 1H, H’-7),
7.02(s, 1H, H-9), 7.27(d, J = 4.0 Hz, 1H, Ar–H), 7.29(s, 1H,
Ar–H), 7.48 (dd, J = 4.0, 8.0 Hz, 1H, Ar–H), 7.68 (s, 1H,
H-2), 11.28 (s, 1H, NH) ppm; 13C NMR (100 MHz, DMSO-
d6):d = 21.2, 27.2, 29.0, 32.3, 50.3, 55.4, 103.6, 125.9, 128.9,
130.3, 133.9, 134.2, 137.0, 147.9, 150.5, 152.4, 193.4 ppm;
MS (EI, 70 eV): m/z (%) = 363 (M?, 9), 362 (22), 327 (100),
291 (67), 269 (1), 243 (8), 217 (31), 189 (3), 161 (23), 133 (8),
107 (5), 83 (8), 55 (8).
Table 4 Comparison result of p-TsOHÁH2O with molecular iodine
(I2) [26], microwave [27], H6P2W18O62Á18H2O [28], and refluxing in
DMF [29, 30] in the synthesis of benzimidazolo/ [1–4, 6, 7] triazo-
loquinazolinone derivatives
Entry Comp. Catalyst/conditions
Time/
min
Yield/
%
1
2
3
4
5
4a
4c
6c
6d
6h
I2/CH3CN, reflux
10
3
84.6
95
Silica gel/microwave
H6P2W18O62Á18H2O/CH3CN,
15
96
reflux
DMF/reflux
–
65
p-TsOHÁH2O/CH3CN, 40–50 °C 25
I2/CH3CN, reflux
95
10
97.1
94
Acknowledgments Financial support from the Research Council of
the University of Sistan and Baluchestan is gratefully acknowledged.
Silica gel/microwave
3
H6P2W18O62Á18H2O/CH3CN,
10
99
reflux
DMF/reflux
–
53
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98
10
96.1
93
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