New Crown Ether-Based Nano Ionic Liquid ([DB-18-C-6K+][OH?] nIL): A Versatile Nanocatalyst for the Synthesis of Spiro[indoline-3,2″-quinoline] Derivatives via the Cascade Four-Component Reaction of Arylamines, Dialkylacetylenedicarboxylates, Isatins and Dimedone

Article abstract of DOI:10.1007/s10562-018-2391-7

Abstract: A new nano-size crown ether-based ionic liquid on the basis of dibenzo-18-crown-6 ([DB-18-C-6K⁺][OH^?] nIL) has been synthesized via a simple procedure and characterized through fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, high-resolution scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric/differential thermal analysis, and UV–Vis spectroscopy techniques The obtained catalyst has been utilized for the one-pot, four-component synthesis of spiro[indoline-3,2′-quinoline] derivatives from the combination of isatins, amines, dimedone, and dialkylacetylenedicarboxylates. The advantages of this protocol included the use of common and easily-available starting materials, utilizing ambient temperature, non-toxic and inexpensive reagent usage, high yields of products, and operationally simple procedure.

Full text of DOI:10.1007/s10562-018-2391-7

Catalysis Letters
https://doi.org/10.1007/s10562-018-2391-7
New Crown Ether-Based Nano Ionic Liquid ([DB-18-C-6K+][OH−] nIL):
A Versatile Nanocatalyst for the Synthesis of Spiro[indoline-3,2′-
quinoline] Derivatives via the Cascade Four-Component Reaction
of Arylamines, Dialkylacetylenedicarboxylates, Isatins and Dimedone
Kobra Nikoofar1 · Shiva Khani1
Received: 17 January 2018 / Accepted: 15 April 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
A new nano-size crown ether-based ionic liquid on the basis of dibenzo-18-crown-6 ([DB-18-C-6K+][OH−] nIL) has been syn-
thesized via a simple procedure and characterized through fourier transform infrared spectroscopy, nuclear magnetic resonance
spectroscopy, high-resolution scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric/differential
thermal analysis, and UV–Vis spectroscopy techniques The obtained catalyst has been utilized for the one-pot, four-component
synthesis of spiro[indoline-3,2′-quinoline] derivatives from the combination of isatins, amines, dimedone, and dialkylacetylen-
edicarboxylates. The advantages of this protocol included the use of common and easily-available starting materials, utilizing
ambient temperature, non-toxic and inexpensive reagent usage, high yields of products, and operationally simple procedure.
Graphical Abstract
Extended author information available on the last page of the article
Vol.:(0123456789)
1 3

K. Nikoofar, S. Khani
Keywords Crown ether-based nano ionic liquid · Spiro[indoline-3,2′-quinoline] · Spiro compounds · Multi-component
reaction · Isatin · Dialkylacetylenedicarboxylates
catalyze the three-component reactions of aromatic alde-
hydes and malononitrile with cyclic β-dicarbonyls or cyclic
β-enaminoketones to obtain tetrahydro-4H-chromenes and
1,4-dihydropyridines by respectively [17].
1 Introduction
Ionic liquids (ILs) possess green properties such as non-
flammability, chemical and thermal stability, extended sol-
vation nature, and negligible vapor pressure [1]. Brönsted
acidic ionic liquids has been replaced with mineral acids
such as sulfuric acid and hydrochloric acid in chemical and
industrial processes [2–4]. In recent years, many task-spe-
cific ionic liquids (TSILs) were designed and utilized for
accelerating various organic transformations [5–7].
2 Results and Discussion
2.1 Characterization of the Nanocatalyst
Crown ether-based nIL ([DB-18-C-6K+][OH−] nIL) has
been prepared through the simple mixing of an equimolar
ratio of dibenzo-18-crown-6 and potassium hydroxide in
methanol as solvent (Scheme 1). After workup procedure,
the obtained yellow powder was characterized with fourier
transform infrared spectroscopy (FT-IR), high-resolution
scanning electron microscopy (HR-SEM), energy-dispersive
X-ray spectroscopy (EDAX), nuclear magnetic resonance
spectroscopy (1H NMR), thermogravimetric/differential
thermal analysis (TGA/DTG), and UV–Vis techniques.
The FT-IR spectrum of [DB-18-C-6K+][OH−] nIL dem-
onstrated all the bands of crown ether in addition with the
band at 3647 cm−1 that belongs to the hydroxyl group in the
structure (Fig. 1).
Spirooxindoles have contained particular attention in
recent years because of their strong activity and interest-
ing structural properties as potent medicinal or biologi-
cally active agents. Many heterocycles including these
motifs could be used as therapeutic [8], anticancer [9],
anti-malaria [10], antimicrobial [11], anti-inflamtory [12],
and anti-tumor [13] agents. One group of these spiro-com-
pounds are spiro[indoline-3,2′-quinoline] derivatives. Yan
and co-workers in 2012 have reported a novel procedure
to obtain these products via a four-component reaction
of arylamines, dimethylacetylene dicarboxylate (DMAD),
isatins, and dimedone in acetic acid within 24 h [14]. In
2015 Pramanik and Debnath has also achieved these fuc-
tionalized heterocycles via the same four-component reac-
tion in the presence of bimettalic (ZnFe2O4) nanopowder
in water medium [15]. According to the literature surveys
there are no reports for this type four-component reactiond
expect the two mentioned above.
1H NMR spectrum of the nIL, which is recorded in
CDCl3, demonstrated two triplets at δ 4.05 J=6.7 Hz and
4.13 ppm J=5.78 Hz related to CH2 methylene groups of
the crown ether ring. Aromatic protons recorded as multiple
peak at δ 6.85–6.92 ppm The hydroxyl group appeared as a
singlet at 7.26 ppm (Fig. 2).
In this report, we synthesized and characterized a new
nano-size crown ether ionic liquid based on dibenzo-18-
crown-6 ([DB-18-C-6K+][OH−] nIL) for the first time
and examine its catalytic activity to get spiro[indoline-
3,2′-quinoline] derivatives via the one-pot, one-step, and
four-component reaction of arylamines, dialkylacetylen-
edicarboxylates (DAAD), isatins, and dimedone in EtOH
at room temperature. It must be mentioned that in 2011
Jing and co-workers prepared and characterized some new
crown ether complex cation ionic liquids (CECILs) based
on [15] crown-5-ether (15-C-5) and [18] crown-6-ether
(18-C-6), which have been utilized to promote Michael
addition of alkenes ([15-C-5Na][OH], [15-C-5Na][OAc],
[18-C-6K][OH], and [18-C-6K][OAc]), Henry reaction of
nitromethane and aromatic aldehydes ([18-C-6K][OH] and
[15-C-5Na][OH]), and Knoevenagel condensation of aro-
matic aldehydes and malononitrile ([18-C-6K][OH]) [16].
In addition Abaszadeh and Mohammad in 2017 synthe-
sized some new crown ether complex cation ionic liquids
(CECILs) via the reaction of crown ethers (18-C-6 and
DB-18-C-6) chelated with sodium benzenesulfonates to
The TGA/DTG diagram showed at Fig. 3. According to
the results, the negligible exothermic weight loss took placed
at 150–160 °C which related to losing the adsorbed water
on the surface of nIL. The main weight lost displayed at
265–380 °C in a single endothermic step.
The HR-SEM picture of [DB-18-C-6K+][OH−] nIL is
appeared at Fig. 4. This image reveals that the product con-
sists of nanorodes with the average diameter of 100–150 nm.
In continue, the EDAX of [DB-18-C-6K+][OH−] nIL in
Fig. 5 indicated that the catalyst is only made up of carbon,
potassium, and oxygen.
An efficient method for evaluating the Bronsted acidity is
based on the Hammett function (Eq. 1).
H0 = pK(I)aq + log ([I]s∕[HI+]s)
(1)
where the pKIaq is the pKa value of aqueous solution of indi-
cator, [IH+]s and [I]s are the molar concentrations of proto-
nated and unprotonated forms of the indicator in the solvent,
respectively. According to Lambert–Beer’s Law, the value
of [I]s/[IH+]s can be determined and calculated through
1 3

New Crown Ether-Based Nano Ionic Liquid ([DB-18-C-6K+][OH−] nIL): A Versatile Nanocatalyst…
UV–Vis spectrum [18, 19]. For this reason, 4-nitroaniline
pKIaq =0.99, as the basic indicator, and DMSO as the sol-
vent were chosen. As it has been cleared in Fig. 6, the maxi-
mal absorbance of the unprotonated form of the indicator
was observed at 383 nm in DMSO.
the reaction conditions, at first the reaction of isatin 1a
(1 mmol), 4-methoxyaniline 2d (1 mmol), DMAD 3a
(1 mmol), and dimedone 4 (1 mmol) was considered as the
model reaction to determine the effect of various parameters.
The catalyst amount investigation denoted that 0.008 g is
the best amount (Table 2, entries 1–3). The model reaction
performed in different solvents as well as solvent-free situ-
ations. The best results observed in ethanol. The results in
entries 7 and 8 of Table 2 validated that elevating the tem-
perature didn’t affect the progress of the reaction. All the
entries of Table 2 have been examined in a one-pot and one-
step manner. We also carried out this reaction in a domino
condition but the desired product didn’t achieved.
When [DB-18-C-6K+][OH−] nIL, as the ionic liquid
catalyst, was added to the indicator solution, the absorb-
ance of the unprotonated form of the indicator decreased,
which indicated that the indicator was partially in the form
of [IH+]. These results, Table 1, affirmed the acidity strength
of the nano IL.
2.2 Investigation the Catalytic Activity
of the Nanocatalsyt
Terminally, on the basis of the optimized conditions, the
reaction of isatins 1a–b, aniline derivatives 2a–h, DMAD
3a or DEAD 3b, and dimedone 4 followed by [DB-18-C-
6K+][OH−] nIL (0.008 g), as accelerator, in ethanol at room
temperature (Scheme 2). The resultant of this research are
summarized in Table 3.
In the next step the catalytic activity of [DB-18-C-
6K+][OH−] nIL has been examined for the synthesis of
spiro[indoline-3,2′-quinoline] derivatives. To optimize
According to the perceived data in Table 3 aniline 2a
and its electron-donating as well as electro-withdrawing
substituents reacted with isatin 1a, DMAD 3a, and dime-
done 4 to obtain the corresponding products successfully
(entries 1–5). 5-Chloroisatin 1b as another candidate per-
fumed the same transformations finely (entries 6–10). The
condensation of 1b, dimedone, and DMAD with 1-naph-
thylamine 2g, as a sterically hindered aromatic amine, has
also yielded to the adduct 5k very well (entry 11). DEAD
3b was another successful volunteer that utilized in these
examinations good (entries 12–15). All the known prod-
ucts has been isolated and characterized by their melting
O
O
O
O
O
O
O
O
H 70 o
C
,
e
M
O
K+
O
+
O
K H
O
O
O
H-
O
DB 18 6K
H- IL
O
+
-
- -
n
]
C
[
][
Scheme 1 Synthesis of [DB-18-C-6K+][OH−] nIL
Fig. 1 FT-IR spectrum for [DB-18-C-6K+][OH−] nIL
1 3

K. Nikoofar, S. Khani
Fig. 2 1H NMR spectra of [DB-18-C-6K+][OH−] nIL
Fig. 4 HR-SEM image of [DB-18-C-6K+][OH−] nIL
The recommended mechanism for this synthesis has
been demonstrated in Scheme 3. As the catalyst possessed
both acidic (K+) and also basic centers (OH−), at first the
catalyst, from its acidic moiety, activated the carbonyl of
isatin at its C3 position which reacted with arylamine to
give imine (A) On the other hand, the α-proton of dime-
done 4, which has been more acidic by the aid of its
Fig. 3 TGA/DTG diagram of [DB-18-C-6K+][OH−] nIL
point and spectroscopic data FT-IR, 1H NMR, and MASS
in comparison with their authentic samples.
1 3

New Crown Ether-Based Nano Ionic Liquid ([DB-18-C-6K+][OH−] nIL): A Versatile Nanocatalyst…
Table 2 Screening the reaction conditions in the synthesis of
spiro[indoline-3,2′-quinoline] 5d
Entry Conditions [DB-18-C-6K+][OH−]
nIL (g)/solvent (8 mL)/temperature
(°C)
Time (min) Yielda (%)
1
2
3
4
5
6
7
8
0.004/EtOH/rt
0.008/EtOH/rt
0.012/EtOH/rt
0.008/–/rt
90
60
60
19 h
24 h
120
60
50
90
80
90
–
80
70
30
0.008/H2O/rt
0.008/EtOH/H2O 11/rt
0.008/EtOH/50
0.008/EtOH/reflux
90
aIsolated yield
Fig. 5 EDAX diagram of [DB-18-C-6K+][OH−] nIL
absorbed proton from ethanol to form D. Deporotonation
of D by means of EtO− from solvent yielded E that con-
densed with intermediate A to obtain F. Cycloaddition of
F give G which followed by dehydration afford the cor-
responding spiro[indoline-3,2′-quinoline] derivatives 5.
3 Conclusion
In conclusion, crown ether-based nano ionic liquid
([DB-18-C-6K+][OH−] nIL) has been prepared via eas-
ily-available precursors simply, and characterized by
1
Fig. 6 Diagram of the Hammett acidity for [DB-18-C-6K+][OH−]
FT-IR, EDAX, H NMR, HR-SEM, UV–Vis techniques.
It catalytic efficiency has been examined to produce
spiro[indoline-3,2′-quinoline] heterocycles from isatin
derivatives, arylamines, dialkylacetylenendicarboxylates,
and dimedone in ethanol via the one-pot four-component
reaction at room temperature. In general, the reported
protocol has several advantages such as (a) short reaction
times, (b) green reaction media because of no requirement
to hazardous solvents, (c) easily-handle, inexpensive, and
non-toxic nano reagent usage.
nIL
Table 1 Calculation of the Hammett acidity function H0 for
[DB-18-C-6K+][OH−] nIL
Catalyst
–
Amax
[I]%
[HI]%
H0
1.8177
1.5096
100
83.2
0
16.8
–
1.68
[DB-18-C-6K+]
[OH−] nIL
Condition for UV–Vis spectrum measurement solvent DMSO, indi-
cator: 4-nitroaniline (pKIaq =0.99, 1×10−5 mol/l, 2.5 mL); catalyst:
[DB-18-C-6K+][OH−] nIL (0.345 mg, 25 °C)
4 Experimental
All chemicals were purchased from Merck, Aldrich, and
Alfa Aesar and were used without further purification. FT-IR
spectra were recorded on FT-IR Bruker Tensor 27 instru-
ment from KBr disk. Melting points were determined on
neighbor carbonyl group, ruptured by basic part of the
nIL (OH−) and converted into its enol form (B) It must be
mentioned that the neighbor carbonyl moiety of this proton
has been more electrophilic through its coordination by
cationic center of the nIL (K+). It means that the reac-
tion could be promoted due to the synergistic effect (aid)
of the cation and also the anion parts of the [DB-18-C-
6K+][OH−] nIL [20]. Nucleophlic attack of B to dialky-
lacetylenendicarboxylate 3 produced intermediate C that
1
an Electrothermal 9200 analyzer and are uncorrected. H
NMR spectra were obtained with a Bruker drx 300 MHz
machine. Elemental analyses were determined using a
Thermo-Finnigan Flash EA 1112 Series. Mass spectroscopy
has been achieved by Gc-Mass 5973 network mass selec-
tive detector, Gc 6690 Agilent device. The scanning electron
1 3

K. Nikoofar, S. Khani
Scheme 2 One-pot synthesis of
spiro[indoline-3,2′-quinoline]
derivatives using [DB-18-C-
6K+][OH−] nIL
R'
CO2
O
R'
CO2
O
R'
CO2
CO2
O
O
[
O
+
H- IL 0 008
R
-
-
-
n
.
(
r
t
,
)
DB 18 6K
C
O
g
)
H
3C
H
3C
][
Et H 8
]
r
A NH2
NH
+
+
+
N
O
m
L
O
(
N
r
A
H
H
C
3C
R'
3
H
4
a: r =
a:
:
=
=
2
A
A
A
A
A
A
A
H5
r
1
1b
C6
4 B H4
C6
4
4 M
4 M
4 N
r = -na
1 h h l
t
p
y
R
R
H
C
-
5
a o
R
:
r =
-
l
2b
a:
=
M
e
3
R'
c: r =
-
-
-
2
l
e
e
H4
C C6
O
:
=
3b R' Et
:
r =
2d
e: r =
2
:
r =
-
2f
O2
:
2
g
Table 3 Synthesis of
Entry
R
Ar
R′
Product
Time (min)
Yield (%)a
Mp (°C)b
spiro[indoline-3,2′-quinoline]
derivatives in the presence of
[DB-18-C-6K+][OH−] nIL
1
2
3
4
5
6
7
8
H
H
H
H
C6H5
4-BrC6H4
4-ClC6H4
4-OCH3C6H4
4-CH3C6H4
C6H5
4-BrC6H4
4-ClC6H4
4-NO2C6H4
4-OCH3C6H4
1-Naphthyl
4-BrC6H4
4-ClC6H4
4-OCH3C6H4
4-CH3C6H4
CH3
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
75
80
135
60
100
120
135
135
60
120
200
135
45
92
81
91
94
90
80
90
90
90
90
80
90
80
80
90
162–164 [15]
310–312 [14]
286–287 [15]
270–271 [15]
290–292 [14]
252–254 [15]
310–312 [14]
247–249 [14]
114–117
248–250 [15]
332–335
288–290 [14]
292–293 [15]
240–242 [14]
231–233 [15]
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
C2H5
C2H5
C2H5
C2H5
H
Cl
Cl
Cl
Cl
Cl
Cl
H
H
H
H
9
10
11
12
13
14
15
85
45
aIsolated yield
bRefrence of known compounds
microscope (HR-SEM, model ZEISS AMA) used to charac-
terize the nanostructures. Thermogravimetric analysis were
determined PYRIS DIAMOND apparatus. UV–Vis spectra
were recorded with Perkin-Elmer 45 LAMBADA quartz
cell, 1 cm machine. Progress of the reaction was monitored
by thin layer chromatography (TLC) technique using com-
mercially available silica gel sheets. Preparative layer chro-
matography (PLC) carried out on 20×20 cm2 plates, coated
with a 1 mm thick layer of Merck silica gel PF254, prepared
by applying the silica as slurry and drying in air.
4.2 General Procedure for the Synthesis
of Spiro[indoline‑3,2′‑quinoline] Derivatives
5a–o
A mixture of isatins 1a–b (1 mmol), arylamines 2a-g
(1 mmol), dialkylacetylenendicarboxylates 3a-b (1 mmol),
and dimedone 4 (1 mmol) in the presence of [DB-18-C-6K+]
[OH−] nIL (0.008 g) in ethanol (8 mL) was magnetically
stirred at room temperature for the desired reaction time
monitored by TLC (n-hexane/ethylacetate eluent). After
completion, purification of the products was performed
through plate chromatography to give the corresponding
solid products 5a-o in high yields. The characterization data
of the new compounds are given below.
4.1 Synthesis of Crown Ether‑Based nIL
([DB‑18‑C‑6K+][OH−] nIL)
A mixture of dibenzo-18-crown-6 (2 mmol, 0.36 g) and
potassium hydroxide (2 mmol, 0.056 g) in methanol (5 mL)
was stirred at 70 °C for 19 h. Then, the solvent was evapo-
rated to give a yellow powder which was centrifuged with
CCl4 (2 mL) within 5 min followed with drying in 70 °C
oven for 30 min.
4.2.1 Dimethyl 5-chloro-7′,7′-dimethyl-1′-(4-nitrophe
nyl)-2,5′-dioxo-5′,6′,7′,8′-tetrahydro-1′H-spiro[indoli
ne-3,2′-quinoline]-3′,4′-dicarboxylate (5i)
Mp decomp. 114–117 °C. IR (KBr, cm−1) υ 3420, 2957,
1716, 1648, 1617, 1510, 1474, 1368, 1248, 1183, 670. 1H
1 3

New Crown Ether-Based Nano Ionic Liquid ([DB-18-C-6K+][OH−] nIL): A Versatile Nanocatalyst…
Scheme 3 Proposed route for the synthesis of spiro[indoline-3,2′-quinoline]s using [DB-18-C-6K+][OH−] nIL
NMR DMSO-d6 (δ, ppm) 0.96 (s, 6H, 2CH3), 2.03–2.10
(m, 2H, CH2), 2.53 (s, 2H, CH2), 3. 32 (br s, 6H, 2OCH3),
6.66 (d, J = 8.17, 2H, -ArH), 6.71–6.90 (m, 2H, -ArH),
6.93 (s, 1H, -ArH), 7.09 (d, J= 8.17, 2H, -ArH), 9.93 (br
s, 1H, NH). m/z 346 ([M+]- p-nitrophenyl-cyclohexenyl),
331 ([M+]- p-nitrophenyl- 5-methylcyclohexenyl), 281
([M+]- CO2MeCHCHCO2Me- p-nitrophenyl -Me), 254
([M+]- CO2MeCHCHCO2Me- p-nitrophenyl -isopropyl),
221 ([M+]- p-nitrophenyl -5-chlorooxindolyl- CMe3), 163
([5-chlorooxindolyl]+), 125 ([nitrophenyl]+). Anal Calcd for
C28H24N3O8Cl: C 59.42, H 4.27, N 7.42%, Found C 59.40,
H 4.22, N 7.39%.
4.2.2 Dimethyl 5-chloro-7′,7′-dimethyl-1′-(naphthalen-
1-yl)-2,5′-dioxo-5′,6′,7′,8′-tetrahydro-1′H-spiro
[indoline-3,2′-quinoline]-3′,4′-dicarboxylate (5k)
Mp decomp. 330–335 °C. IR (KBr, cm−1) υ 3396, 2955,
1714, 1617, 1436–1569, 1222, 1183, 669. 1H NMR DMSO-
d6 (δ, ppm) 0.91 (s, 6H, 2CH3), 1.83–1.97 (m, 1H, CH2),
2.03–2.26 (m, 1H CH2), 2.53 (s, 2H, CH2), 3.35 (s, 3H,
OCH3), 3.54 (s, 3H OCH3), 6.31–7.14 (m, 10H, -ArH), 7.14
(s, 1H, NH). m/z 282 ([M+]-naphthyl-5-chlorooxindolyl),
217 ([M+]-naphthyl-5-chlorooxindolyl-CMe3), 185
([3-nitro-5-chlorooxindolyl]+), 163 ([5-chlorooxindolyl]+),
141 ([CO2MeCHCHCO2Me]+), 126 ([naphthyl]+). Anal
Calcd for C32H26N2O6Cl: C 67.43, H 4.60, N 4.91% Found
C 67.40, H 4.64, N 4.87%.
1 3

K. Nikoofar, S. Khani
10. Yeung BKS, Zou B, Rottmann M, Lakshminarayana SB, Ang SH,
Leong SY et al (2010) Spirotetrahydro β-carbolines (spiroindolo-
nes): a new class of potent and orally efficacious compounds for
the treatment of malaria. J Med Chem 53(14):5155–5164
11. Bhaskar G, Arun Y, Balachandran C, Saikumar C, Perumal PT
(2012) Synthesis of novel spirooxindole derivatives by one pot
multicomponent reaction and their antimicrobial activity. Eur J
Med Chem 51:79–91
Acknowledgements The researchers appreciate Alzahra University
research council for partial financial support of this work.
Compliance with Ethical Standards
Conflict of interest The authors declare that they have no conflict of
interest.
12. Liu J, Sun Y, Zhang X, Liang X, Wu Y, Wang Y, Jiang X (2014)
Spirooxindoles, a potential novel class of anti-inflammatory agent.
Inflamm Cell Signal 1(4):372–375
References
13. Girgis AS, Mabied AF, Stawinski J, Hegazy L, George RF, Farag
H, Shalaby EM (2015) Farag ISA synthesis and DFT studies of
an antitumor active spiro-oxindole. New J Chem 39:8017–8027
14. Sun J, Sun Y, Gao H, Yan C-G (2012) Synthesis of spiro [indo-
line-3, 2′-quinoline] derivatives through a four-component reac-
tion. Eur J Org Chem 2012(10):1976–1983
1. Parvulescu VI, Hardacre C (2007) Catalysis in ionic liquids. Chem
Rev 107(6):2615–2665
2. Cole AC, Jensen JL, Ntai I, Tran KLT, Weaver KJ, Forbes DC et al
(2002) Novel brønsted acidic ionic liquids and their use as dual
solvent-catalysts. J Am Chem Soc 124(21):5962–5963
3. Amarasekara AS (2016) Acidic ionic liquids. Chem Rev
116(10):6133–6183
15. Debnath K, Pramanik A (2015) Heterogeneous bimetallic
ZnFe
2O4 nanopowder catalysed facile four component reaction
for the synthesis of spiro[indoline-3,2′-quinoline] derivatives from
isatins in water medium. Tetrahedron Lett 56(13):1654–1660
16. Song Y, Jing H, Li B, Bai D (2011) Crown ether complex cation
ionic liquids: preparation and applications in organic reactions.
Chem Eur J 17:8731–8738
4. Vafaeezadeh M, Alinezhad H (2016) Brønsted acidic ionic liq-
uids: green catalysts for essential organic reactions. J Mol Liq
218:95–105
5. Davis JH Jr (2004) Task-specific ionic liquids. Chem Lett
33(9):1072–1077
17. Abaszadeh M, Seifi M (2017) Crown ether complex cation ionic
liquids: synthesis and catalytic applications for the synthesis of
tetrahydro-4H-chromene and 1,4-dihydropyridine derivatives. J
Sulfur Chem 38(4):440–449
6. Yue C, Fang D, Liu L, Yi TF (2011) Synthesis and application
of task-specific ionic liquids used as catalysts and/or solvents in
organic unit reactions. J Mol Liq 163(3):99–121
7. Singh H, Sindhu J, Khurana JM, Sharma C, Aneja KR (2014)
Ultrasound promoted one pot synthesis of novel fluorescent
triazolyl spirocyclic oxindoles using DBU based task specific
ionic liquids and their antimicrobial activity. Eur J Med Chem
77:145–154
18. Shirini F, Langarudi MSN, Seddighi M, Jolodar OG (2015) Bi-
SO3H functionalized ionic liquid based on DABCO as a mild
and efficient catalyst for the synthesis of 1,8-dioxo-octahydro-
xanthene and 5-arylmethylene-pyrimidine-2,4,6-trione deriva-
tives. Res Chem Intermed 41(11):8483–8497
8. Galliford CV, Scheidt KA (2007) Pyrrolidinyl-spirooxindole
natural products as inspirations for the development of potential
therapeutic agents. Angew Chem 46:8748–8758
19. Xing H, Wang T, Zhou Z, Dai Y (2007) The sulfonic acid-
functionalized ionic liquids with pyridinium cations: acidities
and their acidity–catalytic activity relationships. J Mol Catal A
264(1–2):53–59
9. Satyamaheshwar P (2009) 3-Substituted-3-hydroxyl-2-oxindole,
an emerging new scaffold for drug discovery with potential
anticancer and other biological activities. Curr Bioact Compd
5(1):20–38
20. Wang J, Liang Y, Zhou D, Ma J, Jing H (2018) New crown ether
complex cation ionic liquids with N-heterocycle anions: prepara-
tion and application in CO2 fixation. Org Chem Front 5:741–748
Affiliations
Kobra Nikoofar1 · Shiva Khani1
1
* Kobra Nikoofar
Chemistry Department, School of Physics and Chemistry,
kobranikoofar@yahoo.com; k.nikoofar@alzahra.ac.ir
Alzahra University, Vanak, Tehran, Iran
1 3