Gemini basic ionic liquid as bi-functional catalyst for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones at room temperature

Article abstract of DOI:10.1016/j.tetlet.2019.151587

A cascade synthesis of 2,3-dihydroquinazolin-4(1H)-ones has been developed from 2-aminobenzonitriles and carbonyl analogues using Gemini basic ionic liquid as green catalyst cum solvent at room temperature. Both aldehydes and ketones were condensed with 2-aminobenzonitriles affording good to excellent yields of products. Moreover, the ionic liquids can be reused up to 5^th cycle without significant loss of catalytic activity.

Full text of DOI:10.1016/j.tetlet.2019.151587

Journal Pre-proofs
Gemini basic ionic liquid as bi-functional catalyst for the synthesis of 2,3-di-
hydroquinazolin-4(1H)-ones at room temperature
Apurba Dutta, Krishnaiah Damarla, Arvind Kumar, Prakash J. Saikia, Diganta
Sarma
PII:
S0040-4039(19)31386-3
DOI:
https://doi.org/10.1016/j.tetlet.2019.151587
TETL 151587
Reference:
Tetrahedron Letters
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Received Date:
Revised Date:
Accepted Date:
2 December 2019
26 December 2019
28 December 2019
Please cite this article as: Dutta, A., Damarla, K., Kumar, A., Saikia, P.J., Sarma, D., Gemini basic ionic liquid as
bi-functional catalyst for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones at room temperature, Tetrahedron
Letters (2019), doi: https://doi.org/10.1016/j.tetlet.2019.151587
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dihydroquinazolin-4(1H)-ones
at
room
temperature
Apurba Duttaa, Krishnaiah Damarlab, Arvind
Kumarb, Prakash J. Saikia c and Diganta Sarma*a

1
Tetrahedron Letters
Gemini basic ionic liquid as bi-functional catalyst for the synthesis of 2,3-
dihydroquinazolin-4(1H)-ones at room temperature
Apurba Duttaa, Krishnaiah Damarlab, Arvind Kumarb, Prakash J. Saikia c and Diganta Sarma*a
a Department of Chemistry, Dibrugarh University, Dibrugarh-786004, Assam, India E-mail: dsarma@dibru.ac.in.
b AcSIR, Salt and Marine Chemicals Division, CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar 364002, India.
cAnalytical Chemistry Division, CSIR-North East Institute of Science and Technology, Jorhat 785006, Assam, India
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A cascade synthesis of 2,3-dihydroquinazolin-4(1H)-ones has been developed from 2-
aminobenzonitriles and carbonyl analogues using Gemini basic ionic liquid as green catalyst
cum solvent at room temperature. Both aldehydes and ketones were condensed with 2-
aminobenzonitriles affording good to excellent yields of products. Moreover, the ionic liquids
can be reused up to 5th cycle without significant loss of catalytic activity.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Green chemistry
Gemini ionic liquids
2,3-Dihydroquinazolin-4(1H)-ones
Cascade synthesis
Introduction
also developed two synthetic methodologies by using K3PO4 [13]
and choline hydroxide [14] respectively as catalysts, but both the
In organic synthesis, 2,3-dihydroquinazolin-4(1H)-one
scaffold is one of the significant heterocycles since it has many
biological and pharmaceutical activity as well as found in a
plethora of natural products [1-3]. A large number of methods
have been developed for the synthesis of this pharmaceutically
active 2,3-dihydroquinazolin-4(1H)-one. Due to the importance
of 2,3-dihydroquinazolin-4(1H)-ones in diverse area, various
synthetic strategies have been developed by using different
starting materials. Some of the well established methods were
condensation of 2-aminobenzamides with carbonyl compounds,
benzyl alcohols, acid chlorides [4-6], one pot reaction between
isatoic anhydride, amines and aldehydes [7-8] or high-pressure
condensation of CO2 with 2-aminobenzonitriles [9-10]. Despite
these protocols are useful in many aspects but limited derivatives
of 2-aminobenzamide and isatoic anhydride, need of higher
temperature, longer reaction time and difficulty in the recycling
of the catalyst are some of the major shortcomings of these
methods. Therefore, scientists have tried to developed new
synthetic pathway for the construction of this valuable molecule
to overcome these drawbacks. In 2010, Tang et al. [11]
developed a method in which 2-aminobenzontrile reacts with
aromatic aldehydes in presence of ZnCl2 as catalyst. However,
this protocol suffers few drawbacks such as use of DMF as
solvent at reflux conditions, comparatively longer reaction time,
low yield of products and only aromatic aldehydes were
condensed with 2-aminobenzonitrile. In 2014, Tamaddon et al.
[12] have reported Amberlyst A26-OH catalyzed synthesis of
2,3-dihydroquinazolin-4(1H)-ones, but use of binary solvent
mixture and comparatively longer reaction time are the major
disadvantages of the system. Later, Wu et al. and Borase et al.
methods require very high temperature. Very recently Safaei et
al. [15] developed a synthetic pathway for the preparation of 2,3-
dihydroquinazolin-4(1H)-ones from 2-aminobenzonitrile and
aldehydes in presence of polyethylene glycol-bonded tetraethyl
ammonium hydroxide [PEG-TEA]OH as
a new reusable
biodegradable surfactant-combined base catalyst at high
temperature (Scheme 1). Till date, no room temperature synthetic
approach has been reported for the synthesis of 2,3-
dihydroquinazolin-4(1H)-ones from 2-aminobenzonitrile and
carbonyl compounds. Based on the above limitations, the
development of an inexpensive and eco-friendly catalyst for the
synthesis of 2,3-dihydroquinazolin-4(1H)-ones from 2-
aminobenzonitrile and carbonyl compounds at room temperature
is a very challenging topic.

2
Tetrahedron Letters
The newly synthesized ILs were characterized by ESI-MS, FT-
IR, NMR and TGA analyses.
Characterization of the prepared [Nbmd][OH] ionic liquid
In order to justify the chemical structure of the ionic liquid
[Nbmd][OH], FT-IR study was carried out as shown in Fig 2.
The band at 3412 cm-1 is assigned to the stretching vibration of
O–H caused by residual ethanol. The two bands due to saturated
C–H stretching vibration were observed at 2925 and 2856 cm-1.
The three characteristic peaks at 1457, 1123 and 1071 cm-1
corresponds to –CH2 deformation vibration in alkanes, C–O–C
(stretching) vibration of the morpholine ring and C–N–C
(stretching) respectively. A band observed at 724 cm-1 is due to
the presence of long-chain alkanes in [Nbmd][OH].
Scheme 1 Synthesis of 2,3-dihydroquinazolin-4(1H)-ones from
2-aminobenzonitrile and carbonyls
From green chemistry viewpoint, ionic liquids (ILs) are
considered as environmentally benign solvents and catalysts
since they have low vapour pressure, low viscosities and high
thermal and chemical stability [16-19]. Due to the advantages of
ILs over conventional solvents, currently researchers have tried
to perform organic reactions with ILs as catalyst or solvents.
Gemini ionic liquids are a new type of amphiphilic molecules
having two head groups and two aliphatic chains which are
linked by a spacer group. Recently, in organic synthesis, gemini
basic ionic liquids have attracted unprecedented attention, due to
their high catalytic efficiency and easy recyclability of the
catalyst [20-25]. Herein, we have successfully synthesized four
dual core basic ionic liquids (Fig 1) and employed them for the
very first time in catalysis for the synthesis of 2,3-
dihydroquinazolin-4(1H)-ones from 2-aminobenzonitrile and
aldehydes at room temperature.
Fig 2 FT-IR spectrum of the synthesized [Nbmd][OH]
1H and 13C NMR spectra were studied which are comparable
to the reported one [26]. The spectra are shown in the supporting
information file. Further, the mass analysis of [Nbmd][OH] IL in
methanol was done and found LC-MS (ESI-Positive) m/z:
+
283.2870 calcd for C36H74N2O2 /2 or [(M2+/2)], found 283.2533
(100%) , 256.2635 calcd for C16H34NO+ (breaking of C-N bond),
found 256.3150 and 312.3261 calcd for C20H42NO+, found
312.3675. The thermal behavior of the dicationic ionic liquid is
illustrated in Fig 3. The first weight lost at 100 °C, corresponded
to the removal of the surface loosely physisorbed water
molecules. The second weight lost at 276 °C is attributed to the
decomposition of the ionic liquid which indicates wide
temperature range usefulness of the prepared ionic liquids.
Fig 1 Gemini basic ionic liquids used in this study
Synthesis of Gemini basic [Nbmd][OH] ionic liquid (IL): The
Gemini basic ionic liquid was prepared according to the reported
procedure [26]. In the first step, given amounts of 1-
bromododecane and NaOH were added to a dry round-bottomed
flask equipped with a condenser and heated to 40 °C. After that,
preheated morpholine solution in water at 70 °C was added
dropwise into the flask and stirring was continued for 7 h at 130
°C. Then, the reaction mixture was allowed to rest at room
temperature, and then, the upper layer was separated with a
separatory funnel as the intermediate product dodecyl morpholine
(molar ratio n1-bromododecane: nmorpholine: nNaOH : nwater = 1:1.2:1.5:5).
In the second step a given amount of dodecyl morpholine
obtained from step (1) was placed in a dry round-bottomed flask,
and then 1,4-dibromobutane was added under reflux condition
for 7 h at 110 °C. The resulting yellow sticky liquid was dried at
50 °C under high vacuum. After drying, an amount of the
remaining powder (bromododecyl morpholine) and KOH were
placed in a conical flask at a molar ratio of 1:2 (nbromododecyl
morpholine : nKOH) in anhydrous ethanol to dissolve the powder and
then the mixture was stirred for 48 h at room temperature to
allow sufficient ion exchange to proceed. After that KBr as a
white solid was separated with a centrifugal separator from the
liquid mixture and ethanol was removed from the remaining
liquid by vacuum distillation at 80 °C to obtain the resulting
gemini basic ionic liquids, which was termed as [Nbmd][OH]
(4,4'-(butane-1,4-diyl)bis(4-dodecylmorpholin-4-ium)hydroxide).
Fig 3 TGA and DTG curves of the synthesized [Nbmd][OH]
Results and discussion
The study was initiated by conducting the reaction of 2-
aminobenzonitrile (1 mmol) with 4-chlorobenzaldehyde (1.5
mmol). Firstly, we explored different organic bases, such as
Et3N, 2,6-lutidine and Et2NH (Table 1, entries 2-4) in H2O at
reflux condition but no desired product was obtained up to 7
hours. After that, the newly prepared Gemini basic ionic liquid,
[Nbmd][OH] was investigated to check the catalytic activity at
100 °C without any additional solvents. As expected,

3
10i
[Nbmd][Br]
(1)
H2O
25 °C
2
-
[Nbmd][OH] gives the desired products in quantitative yields
within 2 hours (Table 1, entry 5). A variety of basic ionic liquids
were also investigated in this reaction but no desired product was
obtained up to 5 hours (Table 1, entries 6-9). A reaction was
performed by using neutral Gemini ionic liquid, [Nbmd][Br] but
the reaction did not give the desired products within 2 hours
(Table 1, entry 10). To study the temperature effect, the reaction
was performed at room temperature and very surprisingly the
desired product was obtained in 98% isolated yield within 2
hours (Table 1, entry 11). In the last step of preparation of
[Nbmd][OH], KOH was used to exchange Br- ion by OH- ion.
Therefore, to check whether our reaction was catalyzed by
[Nbmd][OH] or KOH (that might present in trace amounts with
the IL), a reaction was carried out in presence of KOH in water.
Only a trace amounts of desired product was formed in 5 hours
which confirms superior catalytic activity of [Nbmd][OH] (Table
1, entry 12). Since in the presence of KOH, a trace amount of the
desired product was obtained, the reaction was performed in
presence of NaOH and LiOH but no satisfactory results were
obtained (Table 1, entry 13,14). We have also performed the
reaction with some other Gemini basic ILs but the results were
not satisfactory (Table 1, entries 15-17). The high yield of the
desired product in [Nbmd][OH] compared to the other Gemini
ILs used in this study may be due to the presence of oxygen atom
in the cationic counter part of [Nbmd][OH]. From green
chemistry perspective, only water was chosen as solvent to carry
out the condensation reaction because our aim was to avoid
organic solvents. The reaction did not proceed well in presence of
water as solvents (Table 1, entry 18). From the above study, we
confirmed that [Nbmd][OH] acts both as catalyst and solvent.
Further the amount of [Nbmd][OH] was also optimized and
found that 1 mL of [Nbmd][OH] was sufficient for quantitative
yields of products (Table 1, entry 11). Lowering the amounts of
[Nbmd][OH] gives slightly lower yield of products (Table 1,
entry 20).
11
[Nbmd][OH]
(1)
-
25 °C
1.5
98
12c
13c
14c
15j
KOH
NaOH
LiOH
H2O
H2O
H2O
-
25 °C
25 °C
25 °C
25 °C
5
3
3
2
20
15
trace
35
[Nbid][OH]
(1)
16k
17l
18
[Npid][OH]
(1)
-
25 °C
25 °C
25 °C
25 °C
25 °C
2
2
-
[Nbad][OH]
(1)
-
-
[Nbmd][OH]
(1)
H2O
2
50
97
80
19
[Nbmd][OH]
(2)
-
-
1.5
2
20
[Nbmd][OH]
(0.5)
aReaction conditions: 2-Aminobenzonitrile (1 mmol), 4-Chlorobenzaldehyde (1.5
mmol), ILs (‘n’ mL) at room temperature. bIsolated yield of pure product.
cCatalyst (1 mmol) was used. d[Nbmd][OH],4,4'-(butane-1,4-diyl)bis(4-
dodecylmorpholin-4
octahydropyrido[1,2-a]-[1,3]diazepin-1-ium acetate. f[Bmim][OH], 1-Butyl-3-
methylimidazolium hydroxide.
g[Omim][OH],1-methyl-3-octylimidazolium
h[Dom][OH],
4-dodecyl-4-octylmorpholin-4-ium
4,4'-(butane-1,4-diyl)bis(4-dodecylmorpholin-4
ium)hydroxide.
e[DBU]OAc,
2,3,4,5,7,8,9,10-
hydroxide.
i[Nbmd][Br],
hydroxide.
ium)bromide.
j[Nbid][OH], 3,3'-(butane-1,4-diyl)bis(1-dodecyl-1H-imidazol-3-ium)hydroxide.
k[Npid][OH], 3,3'-(propane-1,3-diyl)bis(1-dodecyl-1H-imidazol-3-ium)hydroxide.
l[Nbad][OH],N1,N4-didodecyl-N1,N1,N4,N4-tetraethylbutane-1,4-diaminium
hydroxide.
Table 1 Optimization of the Reaction Parametersa
To examine the substrate scope of this protocol, the optimized
reaction condition [29] was then applied to the synthesis of a
variety of 2,3-dihydroquinazolin-4(1H)-ones (Table 2). The
reactions with substituted aryl carbonyl compounds bearing
electron-donating or electron-withdrawing groups proceeded
smoothly to provide the desired products in 60-98% yields within
1-5 hours. The effect of steric hindrance on the phenyl ring of
carbonyl compounds were investigated and found that presence
of bulky group decreases the product yield as well as required
long reaction time (Table 2, entries 18,19,25,26). The effect of
substituent in 2-aminobenzonitrile was also examined which
gives almost identical results as 2-aminobenzonitrile (Table 2,
entries 1 vs 21-24). The advantage of our protocol was that
formaldehyde also gets condensed with amine to give the desired
product within short period of time (Table 2, entry 23).
Entry
Catalyst (mL)
Solvent
Temperature
Time
(h)
Yieldb
(%)
1
-
H2O
H2O
H2O
H2O
-
100 °C
100 °C
100 °C
100 °C
100 °C
7
7
-
-
2c
3c
4c
5d
Et3N
2,6-lutidine
Et2NH
6
-
7
-
[Nbmd][OH]
(1)
1.5
98
Table 2 Scope of the Reaction for Synthesis of Various 2,3-
Dihydroquinazolin-4(1H)-onesa
6e
7f
[DBU]OAc
(1)
-
-
-
-
100 °C
25 °C
25 °C
25 °C
5
4
-
-
-
-
[Bmim][OH]
(1)
Yieldb
(%)
8g
9h
[Omim][OH]
(1)
5
Carbonyl
s
Time
(h)
Entry
Amines
Products
[Dom][OH]
(1)
2.5
1
1.5
95

4
Tetrahedron Letters
19
24
55
2
2
95
20
21
1.5
2
95
98
3
4
5
2
2
1
90
90
95
22
23
1
5
98
95
6
7
0.75
1.5
95
98
24
25
1
95
60
17
8
9
2
5
98
60
26
24
50
aReaction conditions: 2-Aminobenzonitriles (1 mmol), carbonyls (1.5 mmol),
[Nbmd][OH] (1 mL) at room temperature.
bIsolated yield of pure product.
The reusability of the IL was examined using the model
reaction under the optimized conditions (Scheme 2). After the
completion of the reaction the IL was recovered by adding
minimum amount of ethyl acetate to the reaction mixture. The IL
present in the water layer was separated from the ethyl acetate
layer which contains organic components. Then water was
evaporated under vacuum at 80 °C and reused the IL for next
consecutive runs after further addition of substrates in
appropriate amount and results are reported in Fig 4. The IL was
found to exhibit good catalytic activity up to five cycles for the
synthesis of 2,3-Dihydroquinazolin-4(1H)-ones.
10
11
12
13
14
15
1.5
5
98
80
96
90
95
90
1
4
2
Scheme 2
2
100
98
95
90
85
80
75
16
17
1
5
95
60
95
90
3
88
4
85
5
18
24
65
1
2
Run

5
Fig
4
Reusability of [Nbmd][OH] ionic liquid in 2,3-
References and notes
Dihydroquinazolin-4(1H)-ones synthesis
1. DeSimone, R. W.; Currie, K. S.; Mitchell, S. A.; Darrow, J. W.;
Plausible reaction mechanism
Pippin, D. A. Comb. Chem. High Throughput Screening, 2004, 7,
473.
Based on the above experimental findings and literature
report [15,27] a plausible reaction mechanism has been proposed
as shown in Scheme 3. The mechanism involves one
[Nbdm][OH] molecule with two basic sites reacting with two
carbonyl compounds and two 2-aminoenzonitriles to form two
molecules of Schiff base intermediate. Then the two hydroxide
ions of [Nbdm][OH] attack the electrophilic carbon atom of
nitrile (two mocecules) which converts the nitrile group to an
amide group. In the final step, nucleophilic attack of amide
nitrogen takes place on the electron-deficient carbon of Schiff
base followed by a 1,5-proton shift to give the desired 2-
substituted 2,3-dihydroquinazolin-4(1H)-ones and the ionic
liquid, [Nbdm][OH]. Literature reveals that [28], Gemini ILs
show better catalytic performance compared to their
monocationic counterpart and the reason could be ascribed to the
following factors: firstly, Gemini ionic liquids have two basic
sites, possessing more basic sites than monocationic ionic liquids
with only one basic site. Secondly, two basic sites are adjacent in
Gemini ionic liquids, providing a good synergistic effect with
each other, which is crucial for improving the catalytic
efficiency. Finally, the basic strength of basic sites in Gemini
ionic liquids is higher than that in monocationic ILs, making the
abstraction of proton easier. Due to their stronger and more
intensive basic positions (cationic active sites), they exhibit
higher stability and stronger alkalinity.
2. Leeson, P. D.; Springthorpe, B. Nat. Rev. Drug Disc., 2007, 6,
881.
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Chem. Commun., 2015, 51, 9205.
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897.
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2012, 27, 179.
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Chandrasekhar, K. B.; Sarva, J. Synth. Commun., 2017, 47, 121.
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Catal. Today, 2009, 148, 355.
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Angew. Chem., 2014, 126, 6032.
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Biomol. Chem., 2014, 12, 1865.
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Commun., 2005, 6, 57.
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36, 2563.
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113, 9506.
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58.
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Chem. Soc., 2005, 127, 593.
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B, 2012, 116, 13239.
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29. Typical experimental procedure:2-Aminobezonitrile derivatives (1
mmol), substituted carbonyl compounds (1.5 mmol) and
[Nbmd][OH] (1 mL) were stirred at room temperature. The
progress of the reaction was monitored by TLC under UV light.
After completion of the reaction the mixture was extracted with
ethyl acetate (3 x 10 mL) and washed with water (3 x 10 mL). The
combined extract was dried over anhydrous Na2SO4. The filtrate
was concentrated under reduced pressure. The product was
purified by column chromatography over silica gel using n-
hexane/ethyl acetate (3:1 v/v) as eluent to get the purified product.
Scheme 3 Plausible reaction mechanism
Conclusion: In conclusion, we have successfully developed a
new and green approach for the construction of pharmaceutically
valuable 2,3-dihydroquinazolin-4(1H)-ones catalyzed by
[Nbdm][OH] ionic liquid at room temperature. To the best of our
knowledge, this is the first ever room temperature synthesis of
2,3-dihydroquinazolin-4(1H)-ones from 2-aminobenzonitiles and
carbonyl analogues. Bi-functional nature of the ionic liquid as
catalyst cum solvent is the major advantage of the present
protocol. Moreover, the ionic liquid can be reused up to 5th cycle
without significant loss of catalytic activity.
1
The products were then characterized by ESI-MS, H NMR, 13C
NMR and 1F NMR spectra.
Supplementary Material
Acknowledgments
1
General Information, Experimental and Analytical data, H 13C,
and 1F NMR spectra and characterization data of all the
synthesised compounds are available as Supplementary
Information.
DS is thankful to DBT, New Delhi, India for a research grant [No.
BT/PR24684/NER/95/810/2017]. AD thanks DBT, New Delhi for
Research Fellowship. The financial assistance of UGC-SAP
programme to the Department of Chemistry, Dibrugarh University is
also gratefully acknowledged.

6
Tetrahedron Letters
Highlights:
1. Bi-functional nature of the ionic liquid as
catalyst cum solvent.
2. Another benefit of the present strategy is
avoiding conventional organic solvents.
3. First room temperature protocol from 2-
aminobenzonitriles and carbonyls.
4. Some challenging aromatic ketones were
utilized as substrates for the first time.