A novel one-pot synthesis of 2-aryl-4(3H)-quinazolinones using room temperature ionic liquid as reaction medium as well as promoter

Article abstract of DOI:10.1081/SCC-200048433

An efficient one-pot synthesis of 2-aryl-4(3H)-quinazolinones from 2-amino benzamides and substituted benzoyl chlorides in a room temperature ionic liquid is described. Compared with the classical reaction conditions, this new synthetic method has the advantages of recyclability of ionic liquid, very good to excellent yields (78-92%), the absence of hazardous and expensive catalysts, and easy workup procedures giving rise to a process with minimum waste.

Full text of DOI:10.1081/SCC-200048433

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A Novel One‐Pot Synthesis of
2‐Aryl‐4(3H)‐Quinazolinones
Using Room Temperature Ionic
Liquid as Reaction Medium as
well as Promoter
a
a
a
T. M. Potewar , R. N. Nadaf , Thomas Daniel , R.
a
a
J. Lahoti & K. V. Srinivasan
a
Division of Organic Chemistry; Technology, National
Chemical Laboratory, Dr. Homi Bhabha Road, Pune,
411 008, India
Version of record first published: 28 Jul 2007.
To cite this article: T. M. Potewar, R. N. Nadaf, Thomas Daniel, R. J. Lahoti & K. V.
Srinivasan (2005): A Novel One‐Pot Synthesis of 2‐Aryl‐4(3H)‐Quinazolinones Using
Room Temperature Ionic Liquid as Reaction Medium as well as Promoter, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:2, 231-241
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Synthetic Communications , 35: 231–241, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200048433
A Novel One-Pot Synthesis of
-Aryl-4(3H)-Quinazolinones Using
2
Room Temperature Ionic Liquid as
Reaction Medium as well as Promoter
T. M. Potewar, R. N. Nadaf, Thomas Daniel,
R. J. Lahoti, and K. V. Srinivasan
Division of Organic Chemistry; Technology,
National Chemical Laboratory, Pune, India
Abstract: An efficient one-pot synthesis of 2-aryl-4(3H)-quinazolinones from 2-amino
benzamides and substituted benzoyl chlorides in a room temperature ionic liquid
is described. Compared with the classical reaction conditions, this new synthetic
method has the advantages of recyclability of ionic liquid, very good to excellent
yields (78–92%), the absence of hazardous and expensive catalysts, and easy
workup procedures giving rise to a process with minimum waste.
Keywords: Ionic liquid, 2-amino benzamide, benzoyl chlorides, 2-aryl-4(3H)-
quinazolinones
INTRODUCTION
One of the most frequently encountered heterocycles in medicinal chemistry
is 4(3H)-quinazolinone with wide applications including anticonvulsant,
antihypertensive, antidiabetic, antibacterial, antitumor, antihistaminic, and
Received in India November 1, 2004
Address correspondence to K. V. Srinivasan, Division of Organic Chemistry; Tech-
nology, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, India.
Fax: þ91-20-25893614; E-mail: kvsri@dalton.ncl.res.in

232
T. M. Potewar et al.
[
1–6]
anti-inflammatory properties.
prising the 4(3H)-quinazolinone moiety have been isolated from natural
In addition, more than 40 alkaloids com-
sources, some of which have interesting biological properties such as antima-
larial activity, biofungicide, and diuretic properties.
[7–11]
The 2-substituted
quinazolinones in particular have been used as peptidomimetic scaffolds
with specificity for cholecystokinin, angiotensin, and certain cell adhesion
[12,13]
receptors.
In view of the importance of quinazolinones and their derivatives, a variety
of preparatory methods have been reported in literature. The main synthetic
[
14,15]
routes to such compounds use 2-aminobenzoic acid or its derivatives
[
16,17]
and 2-aminobenzonitrile as starting materials. In addition, quinazoli-
nones were also synthesized by reaction of isatoic anhydride with
[18]
benzamide,
[19]
by intramolecular Aza–Wittig reaction,
[
by thermolysis
20]
of anil at 3008C
and a two-step reaction from benzoyl chloride and
Furthermore, quinazolinones have been prepared
from 2-aminobenzamide and aldehyde by using bases such as sodium
[
21]
2
-aminobenzamide.
[
22]
hydrogen sulfite and sodium hydroxide.
23]
Quinazolinones have also been
by using a different variety of Lewis
[
prepared by solid-phase synthesis,
[
24]
[25]
acid in solvent-free condition, and by using various
transition metals such as copper, ruthenium, platinum and palladium
by microwave,
[26,27]
complexes.
However, despite their potential utility, many of the reported methods
have drawbacks such as long reaction time, unsatisfactory yields, multistep
synthetic protocol, harsh reaction conditions, cumbersome product isola-
tion procedures, and use of hazardous and often expensive acid and base
catalysts. Moreover, the synthesis of these heterocycles has been usually
carried out in volatile and polar solvents such as THF, benzene, pyridine,
DMF, and DMSO, leading to complex isolation and recovery procedures.
These processes also generate waste-containing solvent and catalysts, which
have to be recovered, treated, and disposed of.
The increasing attention during the last decades for environmental pro-
tection has influenced both academic and industrial groups to develop
chemical processes with maximum yield and minimum cost while using
nontoxic reagents, catalysts, and solvents or even better, without solvents.
In this context, in recent times, the use of room temperature ionic liquids
(ILs) as “green” solvents in organic synthetic processes has gained consi-
derable importance due to their solvating ability, negligible vapor pressure,
[
28–32]
and easy recyclability.
They have the potential to be highly polar
yet noncoordinating. In addition to the above-mentioned salient features of
ILs as a reaction media, we have also recently shown that they can
promote and catalyze organic transformation, particularly heterocyclization,
under mild condition. The various heterocyclization reactions that we inves-
[
35]
tigated include regioselective synthesis of 1,5 benzodiazepines,
dropyrimidin-2-(1H)-ones under ultrasound irradiation
3,4-dihy-
and substituted
[33]

One-Pot Synthesis with Ionic Liquid
233
quinoline and fused polycyclic quinolines using the Friedlander
heteroannulation.
[34]
In continuation, herein we report for the first time a novel and facile route
to the one-pot synthesis of 2-aryl-4(3H)-quinazolinone in very good to
excellent isolated yields using the room temperature ionic liquid, 1,3-di-n-
butylimidazolium bromide [bbim]Br as a reaction medium as well as
promoter. The nonvolatile IL can be efficiently recovered and reused, and
the process does not require any additional catalyst.
RESULTS AND DISCUSSION
A variety of benzoyl chlorides and thiophene-2-carbonyl chloride were
condensed with 2-amino benzamide and 2-amino-5-chlorobenzamide,
respectively, in the IL 1,3-di-n-butylimidazolium bromide, ([bbim]Br) at
1
208C to afford 2-aryl-4(3H)-quinazolinones (Scheme 1).
A typical reaction of 2-amino benzamide 1a with benzoyl chloride 2a
was carried out in the ionic liquid, [bbim]Br, at ambient conditions to form
-phenyl-4(3H)-quinazolinone 3a. However, at room temperature, reaction
2
stops short of the formation of 2-(N-benzoylamino) benzamide and does not
proceed further to afford the 2-phenyl-4(3H)-quinazolinone even in trace
amounts. Consequently, the reaction was carried out at higher temperatures,
and the optimum results were obtained at 1208C (92%).
Scheme 1.

234
T. M. Potewar et al.
For further optimization, several ILs based on 1,3-di-n-butylimidazolium
salts [bbim]X with varying anions (structure depicted in Fig. 1) were screened
for the typical reaction of 2-aminobenzamide 1a with benzoyl chloride 2a
at 1208C for complete conversions as monitored by TLC to afford
2
-phenyl-4(3H) quinazolinone 3a. The results are recorded in Table 1.
Evidently, [bbim]Br was found to be superior in terms of yield (92%) and
reaction time (3.5 hr) a compared with other ILs.
It was interesting to note that the corresponding reaction in molecular
solvents conventionally used for the reaction such as acetic acid and DMF
under reflux condition over a period of 10 hr afforded 3a in 32% and 25%
yields, respectively, and in pyridine, under similar condition no product was
obtained, thereby highlighting the role of IL in promoting the reaction
without the need for any added catalyst.
Consequently, all further reactions with other substrates were conducted
by using [bbim]Br as the reaction medium (Scheme 1). The results are
recorded in Table 2. All the products (3a–k) were fully characterized by
1
M.P., IR, H-NMR, and elemental analyses. For the known compounds, the
values were in agreement with those reported in literature.
Typically, for each case, after the reaction was completed (monitored by
TLC), the reaction mixture was diluted with water. The precipitated product
was filtered and dried. This crude product was homogeneous on TLC and
pure enough for all practical purposes. However, it was subjected to further
purification by column chromatography for characterization purposes. The
aqueous layer containing IL was subjected to distillation (808C at
1
0 mmHg) for 2 hr to remove water, leaving behind the IL in almost
complete recovery (.98%). The recovered IL was recycled twice with only
a marginal loss (1–2%) in yield.
To prove it is the IL that has promoted the benzoylation and the cyclode-
hydration and not the liberated hydrochloric acid, an appropriate amount of
potassium carbonate was externally added to trap the acid for the typical
reaction of 2-amino benzamide 1a with benzoyl chloride 2a under similar con-
ditions. The product 3a was formed with the same yield and purity as earlier.
The role of IL in the cyclization step was also supported by heating the
Figure 1. Ionic liquids screened for the reaction.

One-Pot Synthesis with Ionic Liquid
Table 1. Synthesis of 3a in [bbim]X at 1208C
235
a
Time (h)
b
Yield (%)
Sr. no.
Ionic liquid
1
2
3
4
5
[bbim]Br
[bbim]BF
[bbim]Cl
3.5
3.5
7
92
88
68
60
60
4
[bbim]ClO
[bbim]PF
4
5
6
7
a
Time for complete conversion.
Isolated yield after column chromatography.
b
isolated 2-(N-benzoylamino) benzamide in IL at 1208C to form the product in
same yield and of same purity. Thus, it was confirmed that the IL, by itself, has
promoted and catalyzed the reaction and not the librated hydrochloric acid.
The role of the IL may be postulated in terms of some Lewis/Brønsted
acidity of the imidazolium cation, leading to its interaction with the carbonyl
oxygen of the benzoyl group resulting in its increased polarization and thus
promoting the reaction both in the benzoylation and cyclization step.
Evidence for the interaction of the imidazolium cation with carbonyl oxygen
of the amide was obtained by recording the IR spectra of 2-amino benzamide
alone and 2-amino benzamide with one equivalent of IL [bbim]Br under
2
1
similar conditions. A significant shift to a lower wave number by 10 cm
was observed for C–O bond of amide for latter case. Based on this evidence,
a probable mechanism is postulated as shown in Scheme 2.
In conclusion, a novel method for the one-pot synthesis of the biologically
active 2-aryl-4(3H)-quinazolinones has been developed by the reaction of 2-
aminobenzamide and substituted 2-aminobenzamide with different substituted
benzoyl chlorides, including a heterocyclic carbonyl chloride in the ionic
liquid [bbim]Br in excellent isolated yields. In this green approach, the dual
role of the ionic liquid as a reaction medium and a promoter has excluded
the necessity of using hazardous acids or bases as catalysts. Experimental
evidence highlighting the role of the ionic liquid in promoting both the
acylation and cyclodehydration steps has been provided. The solvent IL was
recovered almost entirely and recycled successfully. The moderate reaction
conditions, absence of a catalyst, easy workup procedure and recyclability
of the non-volatile IL make this an environment friendly method amenable
for scaleup.
EXPERIMENTAL
NMR spectra were recorded on Bruker AC-200 spectrometer in CDCl3/
DMSO-d with TMS as an internal standard. Infrared spectra were recorded
6

236
T. M. Potewar et al.

One-Pot Synthesis with Ionic Liquid
237

238
T. M. Potewar et al.
Scheme 2.
with ATI MATT-SON RS-1 FTIR spectrometer. Melting points were
recorded in open capillary and were uncorrected. All solvents and
chemicals were of research grade and were used as obtained from Merck
and Lancaster. The imidazolium-based ionic liquids investigated were
[34]
prepared according to the procedure reported in the previous literature.
Typical Procedure
Synthesis of 3a–k; General Procedure
A mixture of 2-aminobenzamides 1a–b (1 mmol) and substituted benzoyl
chlorides including thiophene-2-carbonyl chloride 2a–f (1 mmol) was
heated in [bbim]Br at 1208C for appropriate time as reported in Table 2.
The completion of reaction was monitored by TLC using 40% ethyl acetate
in petroleum ether as eluent. After completion of reaction, the reaction
mixture was diluted with water (25 mL). The quinazolinones, which
separated out, were filtered, washed with water, and dried. The crude
products, thus isolated, were pure (single spot on TLC). They were
subjected to further purification by chromatography through a column of
silica gel using 20% EtOAc in petroleum ether as eluent to afford the
desired substituted quinazolinones in 78–92% yield and were fully character-
ized. The aqueous layer containing the IL was subjected to distillation (808C
at 10 mmHg) for 2 hr to remove water, leaving behind the IL [bbim]Br
(recovery .98%), which was recycled.

One-Pot Synthesis with Ionic Liquid
239
Characterization Data For New Compounds
Compound 3f
2
1
1
Mp 2838C. IR (Nujol): 1460, 1668, 3124 cm
.
H-NMR (CDCl3):
d ¼ 7.16–7.18 (d, 1H), 7.43–7.47 (dd, 1H), 7.65–7.71 (m, 2H), 7.74–7.79
dd, 1H), 8.14–8.17 (dd, 1H), 8.22–8.24 (dd, 1H), 12.55 (brs, 1H). Anal.
Calcd. for C H N OS: C, 63.14; H, 3.53; N, 12.27; S, 14.05; Found: C,
(
1
2 8 2
6
3.01; H, 3. 43; N, 12.05; S, 13.87%.
Compound 3h
Mp 2228C. IR (Nujol): 1464, 1683, 3041 cm
2
1
1
.
H-NMR (CDCl3,
DMSO-d ): d ¼ 7.41–7.42 (d, 1H), 7.49–7.50 (d, 1H), 7.58–7.63 (t, 1H),
6
7.69–7.71 (d, 2H), 7.79–7.85 (t, 1H), 8.18–8.21 (d, 1H), 12.51 (brs, 1H).
Anal. Calcd. for C H CI N O: C, 57.76; H, 2.77; N, 9.62; Found: C,
1
4
8
2 2
5
7.53; H, 2.38; N, 9.01%.
Compound 3j
2
1 1
Mp 2688C. IR (Nujol): 1465, 1683, 3157 cm . H-NMR (CDCl3,
DMSO-d ): d ¼ 2.42 (s, 3H), 7.32–7.34 (d, 2H), 7.39–7.42 (d, 1H), 7.49–
6
7
1
1
.52 (d, 1H), 7.67–7.70 (d, 1H), 7.76–7.79 (dd, 1H), 8.11–8.12 (d, 1H),
2.55 (brs, 1H). Anal. Calcd. for C H CIN O: C, 66.55; H, 4.10; N,
1
5
11
2
0.35; Found: C, 66.45; H, 3.97; N, 10.10%.
Compound 3k
2
1 1
Mp 2638C.IR (Nujol): 1465, 1674.8, 3099 cm . H-NMR (CDCl3,
DMSO-d ): d ¼ 7.16–7.19 (t, 1H), 7.62–7.65 (d, 1H), 7.70–7.74 (m, 2H),
6
8.06–8.07 (d, 1H), 8.22–8.24 (d, 1H), 12.73 (brs, 1H). Anal. Calcd. for
C H CIN OS: C, 54.86; H, 2.69; N, 10.66; S, 12.20, Found: C, 54.53; H,
1
2
7
2
2
.33; N, 11.01; S, 12.11%.
ACKNOWLEDGMENTS
TMP thanks CSIR, New Delhi, for providing a Junior Research Fellowship.
The authors also acknowledge financial assistance from Department of
Science and Technology (DST), New Delhi, vide Project No. SR/S5/OC-
2
3/2002).
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