Highly efficient and green synthesis of spiro[indoline-3,9′-xanthene]trione and spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives in water catalyzed by graphene oxide-supported dicationic ionic liquid

Article abstract of DOI:10.1007/s11164-021-04405-x

In this article, a mild and highly efficacious synthetic route has been developed for the synthesis of spiro[indoline-3,9′-xanthene]trione and spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives using graphene oxide-supported dicationic ionic liquid (DIL@GO) as a heterogeneous catalyst in aqueous media. Targeted spiro[indoline-3,9′-xanthene]trione derivatives were synthesized via one-pot condensation of substituted isatins and 1,3-diketone compounds (1,3-cyclohexanedione/dimedone), and spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives were synthesized via one-pot reaction of substituted isatins, malononitrile, and enolizable C-H-activated compounds (2-hydroxynaphthalene-1,4-dione/dimedone). The DIL@GO catalyst demonstrated outstanding catalytic capabilities in all the tested reactions and yielded excellent isolated yields of the final products within a short reaction time. Additionally, the heterogeneous nature of the catalyst facilitates catalyst separation through centrifugation, and its reusability up to five successive reaction cycles with retention in activity makes this methodology more advantageous and environmentally benign. Graphic abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11164-021-04405-x

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-021-04405-x
Highly efcient and green synthesis
oꢀ spiro[indoline‑3,9′‑xanthene]trione and spiro[chromene
‑4,3′‑indoline]‑3‑carbonitrile derivatives in water catalyzed
by graphene oxide‑supported dicationic ionic liquid
1
1
1
Nipun Patel · Unnati Patel · Abhishek Dadhania
Received: 22 October 2020 / Accepted: 19 January 2021
©
The Author(s), under exclusive licence to Springer Nature B.V. part of Springer Nature 2021
Abstract
In this article, a mild and highly efcacious synthetic route has been developed
ꢀ
or the synthesis oꢀ spiro[indoline-3,9′-xanthene]trione and spiro[chromene-4,3′-
indoline]-3-carbonitrile derivatives using graphene oxide-supported dicationic
ionic liquid (DIL@GO) as a heterogeneous catalyst in aqueous media. Targeted
spiro[indoline-3,9′-xanthene]trione derivatives were synthesized via one-pot con-
densation oꢀ substituted isatins and 1,3-diketone compounds (1,3-cyclohexanedione/
dimedone), and spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives were syn-
thesized via one-pot reaction oꢀ substituted isatins, malononitrile, and enolizable
C-H-activated compounds (2-hydroxynaphthalene-1,4-dione/dimedone). The DIL@
GO catalyst demonstrated outstanding catalytic capabilities in all the tested reac-
tions and yielded excellent isolated yields oꢀ the ꢁnal products within a short reac-
tion time. Additionally, the heterogeneous nature oꢀ the catalyst ꢀacilitates catalyst
separation through centriꢀugation, and its reusability up to ꢁve successive reaction
cycles with retention in activity makes this methodology more advantageous and
environmentally benign.
*
Abhishek Dadhania
abhishekdadhania.bt@charusat.ac.in
1
Department oꢀ Chemical Sciences, P. D. Patel Institute oꢀ Applied Sciences, Charotar University
oꢀ Science and Technology (CHARUSAT), Changa, Gujarat 388421, India
Vol.:(012
1
3456789)
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N. Patel et al.
Graphic abstract
Keywords Spiro[indoline-3,9ʹ-xanthene]trione · Spiro[chromene-4,3′-indoline]-3-
carbonitrile · Graphene oxide · Ionic liquid · Heterogeneous catalyst
Introduction
Over the past decades, polyheterocyclic compounds have gained considerable
importance in academia as well as industrial research and been extensively investi-
gated due to their signiꢁcant biological activity [1–3]. These heterocycles are widely
distributed and have a great inꢂuence as structural subunits oꢀ medicinally important
classes oꢀ natural products, pharmaceuticals, agrochemicals and many other addi-
tives and modiꢁers having wide industrial applications [4, 5]. In the class oꢀ polyhet-
erocycles, spiro-heterocyclic compounds have received special attention because oꢀ
the wide-ranging biological activity associated with them due to their unique struc-
tural ꢀeatures [6–9]. A good number oꢀ spiro-heterocycles are reported ꢀor highly
pronounced applications in medicinal chemistry including antituberculosis agents
[
10, 11], antidermatitis agents [12], anticancer agents [13], antibacterial agents [14],
antimicrobial agents [15], and anticonvulsant agents [16].
Categorically, spiro-oxindole derivatives represent an important class oꢀ pharma-
ceutically promising compounds with enhanced biological activities due to sterically
constrained ring system obtained through spiro-annulation oꢀ indole 3-carbon with
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Highly efcient and green synthesis oꢀ…
heterocycles [17]. Some naturally occurring and synthetic spiro-oxindole derivatives
have shown their activity as inhibitors oꢀ MDM2-p53 interaction [18, 19], inhibi-
tors oꢀ microtubule assembly [20, 21], antiproliꢀerative ꢀor malignant glioma and
neuroblastoma [22], modulate the ꢀunction oꢀ muscarinic serotonin receptors [23],
antitumor [24], antiꢀungal [25], and anticancer [26]. Hence, studies on the synthe-
sis oꢀ spiro-oxindole derivatives observed an exponential growth to produce highly
potential therapeutic agents [27, 28]. Accordingly, spiro[indoline-3,9ʹ-xanthene]
trione and spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives get reasonable
attention due to their essential medicinal properties [29–31]. Nevertheless, the syn-
thesis oꢀ these derivatives remains a challenge ꢀor synthetic organic chemists due to
their steric strain and hence is scantly explored [32–39]. Moreover, some oꢀ these
reported methods suꢃer ꢀrom one or more pitꢀalls such as harsh reaction conditions,
tiresome synthetic procedure, longer reaction time, poor reusability oꢀ catalyst and
lower to moderate yields.
Over the past ꢀew decades, ionic liquids (ILs) have gained signiꢁcant consid-
eration in many areas oꢀ chemistry due to their special properties, such as negli-
gible vapor pressure, solvating ability, high chemical and thermal stability, inher-
ent Lewis/Brønsted acidity, and high polarity [40, 41]. However, the homogeneous
nature oꢀ most ionic liquids limits their application in catalysis due to poor recycla-
bility. Hence, supported ionic liquids (SILs) have emerged due to their heterogene-
ous nature and distinctive properties because oꢀ the collaborative eꢃect oꢀ ILs and
supports [42–44]. Among the class, supported dicationic ionic liquids (DILs) are
an emerging catalytic material constructed through linking oꢀ two cations with each
other by connecting groups [45–47]. Unique physicochemical properties, a great
extent oꢀ tunability and more active sites make DILs more advantageous as com-
pared to conventional monocationic ILs and ꢁnd applications in material ꢀabrication
[
48–50], reaction medium [51, 52], separation [53–55] and catalysis [56–62]. To
the best oꢀ our knowledge, there is no report on the synthesis oꢀ spiro[indoline-3,9ʹ-
xanthene]trione and spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives cata-
lyzed through supported DILs. Thereꢀore, developing an eꢃective and environment-
ꢀ
riendly route ꢀor the synthesis oꢀ these derivatives catalyzed through supported
DILs is an attractive goal.
Recently, graphene oxide (GO)-supported heterogeneous catalysts have gained
huge recognition in the ꢁeld oꢀ catalysis due to the unique structural and physi-
ochemical properties oꢀ GO [63]. Additionally, solid support ꢀacilitates the easy
recovery and reusability oꢀ the catalysts as compared to its homogeneous coun-
terpart. Numerous reports have been published on the exploitation oꢀ GO as solid
support ꢀor the immobilization oꢀ homogeneous catalysts [64, 65]. The oxygenated
ꢀ
unctional groups present on the surꢀace oꢀ GO ꢀacilitate the anchoring oꢀ homoge-
neous moiety through covalent bonding, and a larger surꢀace area keeps the catalytic
sites available ꢀor reactants [66, 67].
In continuation oꢀ our ongoing research about the development oꢀ environmen-
tally benign methodologies ꢀor the synthesis oꢀ heterocyclic compounds [68–71],
herein we employed graphene oxide-supported dicationic ionic liquid (DIL@
GO) as an efcient heterogeneous catalyst ꢀor the synthesis oꢀ spiro[indoline-3,9ʹ-
xanthene]trione and spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives. All
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N. Patel et al.
the syntheses were carried out in the water, and targeted compounds were obtained
in high to excellent yield. The catalyst was easily separated ꢀrom the reaction mix-
ture via centriꢀugation and successively reused in subsequent reaction cycles with-
out any signiꢁcant loss oꢀ its catalytic activity.
Experimental
Materials and methods
All the reagents were obtained ꢀrom Sigma-Aldrich (India) and SDFCL and used as
received. Melting points were determined using VMP-D melting point apparatus by
capillary technique and were uncorrected. FTIR spectra were recorded on Thermo
1
13
Nicolet 6700 FTIR spectrophotometer via KBr. The H and C NMR spectra were
recorded on BRUKER 400 MHz using DMSO-d6 as a solvent. Elemental analy-
sis was perꢀormed on elementar vario MICRO CUBE analyzer. XRD patterns were
recorded on Bruker D-2 Phaser XRD instrument. TG analysis was perꢀormed on
Mettler-Toledo Thermal Analyzer.
Synthesis of catalyst (DIL@GO)
Graphene oxide-supported dicationic ionic liquid (DIL@GO) was synthesized
according to the procedure reported by us [70]. Initially, GO was ꢀunctionalized
through treatment with (3-chloropropyl)trimethoxysilane. The resulting solid mate-
rial was treated with the sodium salt oꢀ imidazole ꢀollowed by 1,4-dibromobutane
and ꢀurther with imidazolium salt to generate covalent graꢀting oꢀ two imidazole
moieties on the surꢀace oꢀ GO. The obtained material was treated with 1,4-butane-
sultone, ꢀollowed by conc. H SO to obtain a dicationic ionic liquid on the surꢀace
2
4
oꢀ GO.
General procedure for the synthesis of spiro[indoline‑3,9ʹ‑xanthene]trione
derivatives
In a typical synthesis, isatin (1 mmol), dimedone or 1,3-cyclohexanedione (2 mmol)
and water (5 mL) were added to the reaction vessel. Aꢀter that, the catalyst DIL@
GO (100 mg) was introduced into the reaction system, and the temperature was
raised to reꢂux the reaction mixture ꢀor the appropriate time. The reaction progress
was monitored by TLC, and aꢀter the completion oꢀ the reaction, the obtained mass
was ꢁltered and added to the hot ethanol. The catalyst was separated through cen-
triꢀugation, and the crude product was crystallized to aꢃord a pure spiro[indoline-
3
,9ʹ-xanthene]trione derivatives. The recovered catalyst was washed with ethanol
and dried under vacuum at 60 °C ꢀor ꢀurther use in subsequent reactions. All syn-
1
13
thesized compounds were characterized through melting points, FTIR, H and
C
NMR spectra.
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Highly efcient and green synthesis oꢀ…
Spectral data of representative compounds
3
ʹ,3ʹ,6ʹ,6ʹ‑tetramethyl‑3ʹ,4ʹ,6ʹ,7ʹ‑tetrahydrospiro[indoline‑3,9ʹ‑xanthene]‑1ʹ,2,8ʹ
(2ʹH,5ʹH)‑trione (3a)
−
1
1
IR (KBr; cm ) ν : 3332, 2959, 1724, 1692, 1599, 1232, 1126, 904; H NMR
max
3
(
400 MHz, CDCl ): δ (ppm) 1.02 (s, 6H), 1.11 (s, 6H), 2.10 (dd, 4H, J=48 Hz),
2
.41 (dd, 4H, J=46 Hz), 6.83–6.89 (m, 3H), 7.13–7.17 (m, 1H), 7.60 (s, 1H);
1
3
C NMR (400 MHz, CDCl ): δ (ppm) 27.18, 29.00, 31.98, 41.27, 50.98, 109.29,
3
1
13.65, 121.95, 122.37, 128.48, 133.63, 142.22, 163.51, 178.79, 195.32.
5
‑bromo‑3ʹ,3ʹ,6ʹ,6ʹ‑tetramethyl‑3ʹ,4ʹ,6ʹ,7ʹ‑tetrahydrospiro[indoline‑3,9ʹ‑xanthene
]‑1ʹ,2,8ʹ (2ʹH,5ʹH)‑trione (3b)
−
1
1
IR (KBr; cm ) ν : 3394, 2955, 1731, 1667, 1474, 1185, 1031, 877; H NMR
max
3
(
400 MHz, CDCl ): δ (ppm) 1.05 (s, 6H), 1.11 (s, 6H), 2.13 (dd, 4H, J=36 Hz),
2
.44 (dd, 4H, J=32 Hz), 6.71 (d, 1H, J=8 Hz), 6.95 (d, 1H, J=2 Hz), 7.25 (d, 1H,
1
3
J=7.6 Hz), 7.6 (s, 1H); C NMR (400 MHz, CDCl ): δ (ppm) 27.56, 28.71, 32.03,
3
4
1
1.23, 50.94, 110.70, 113.23, 114.35, 125.56, 131.26, 135.65, 141.50, 163.84,
78.14, 195.43.
3
1
ʹ,3ʹ,6ʹ,6ʹ‑tetramethyl‑5‑nitro‑3ʹ,4ʹ,6ʹ,7ʹ‑tetrahydrospiro[indoline‑3,9ʹ‑xanthene]‑
ʹ,2,8ʹ (2ʹH,5ʹH)‑trione (3d)
−
1
IR (KBr; cm ) ν : 3410, 2957, 1739, 1664, 1617, 1341, 1171, 1072, 904, 839;
max
1
H NMR (400 MHz, CDCl ): δ (ppm) 1.06 (s, 6H), 1.12 (s, 6H), 2.14 (dd, 4H,
3
J=36 Hz), 2.55 (d, 4H, J=4 Hz), 6.90 (d, 1H, J=8 Hz), 7.79 (d, 1H, J=2.4 Hz),
1
3
8
4
1
.12–8.16 (m, 2H); C NMR (400 MHz, CDCl ): δ (ppm) 27.71, 28.53, 32.11,
3
1.20, 50.84, 108.83, 112.84, 118.16, 125.91, 143.04, 148.51, 164.50, 178.73,
95.77.
3
ʹ,3ʹ,6ʹ,6ʹ‑pentamethyl‑3ʹ,4ʹ,6ʹ,7ʹ‑tetrahydrospiro[indoline‑3,9ʹ‑xanthene]‑1ʹ,2,8ʹ
(2ʹH,5ʹH)‑trione (3f)
−
1
IR (KBr; cm ) ν : 3412, 2958, 1719, 1674, 1346, 1219, 1127, 1025, 903, 752;
max
1
H NMR (400 MHz, CDCl ): δ (ppm) 1.01 (s, 6H), 1.10 (s, 6H), 2.06 (dd, 4H,
3
J=36 Hz), 2.41 (dd, 4H, J=48 Hz), 3.32 (s, 3H), 6.81 (d, 1H, J=8 Hz), 6.87–6.89
1
3
(
m, 2H), 7.19–7.24 (m, 1H); C NMR (400 MHz, CDCl ): δ (ppm) 26.71, 27.15,
3
2
1
9.07, 31.99, 41.26, 50.97, 107.69, 113.70, 121.84, 121.95, 128.60, 133.04, 145.32,
63.52, 177.68, 195.31.
3
ʹ,3ʹ,5,6ʹ,6ʹ‑pentamethyl‑3ʹ,4ʹ,6ʹ,7ʹ‑tetrahydrospiro[indoline‑3,9ʹ‑xanthene]‑1ʹ,2
,8ʹ (2ʹH,5ʹH)‑trione (3g)
−
1
IR (KBr; cm ) ν : 3368, 2958, 1732, 1668, 1619, 1492, 1349, 1222, 1030,
max
1
8
79; H NMR (400 MHz, CDCl ): δ (ppm) 1.03 (s, 6H), 1.11 (s, 6H), 2.11 (d, 2H,
3
1
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N. Patel et al.
J=16 Hz), 2.20 (s, 3H), 2.22 (d, 2H, J=16 Hz), 2.42 (dd, 4H, J=40 Hz), 6.65
1
3
(
(
s, 1H), 6.72 (d, 1H, J=8 Hz), 6.94 (d, 1H, J=8 Hz), 7.45 (s, 1H); C NMR
400 MHz, CDCl ): δ (ppm) 21.16, 27.39, 28.88, 31.98, 41.27, 51.00, 108.86,
3
1
13.70, 123.26, 128.87, 131.69, 134.01, 140.20, 163.39, 179.12, 195.35.
General procedure for the preparation of spiro[chromene‑4,3′‑indoline]‑3‑carbon
itrile derivatives
In a round-bottom ꢂask equipped with a magnetic stirrer, isatin (1 mmol), malo-
nonitrile (1 mmol), 2-hydroxy-1,4-naphthoquinone or 5,5-dimethylcyclohexane-
1
,3-dione (1 mmol) and DIL@GO (100 mg) were added in 5 mL water. The reaction
mixture was stirred at reꢂux temperature ꢀor an appropriate time. Aꢀter completion
oꢀ the reaction (as indicated by TLC), the resultant product was ꢁltered and washed
thoroughly with water. The obtained solid was then dissolved in hot ethanol and
centriꢀuged to remove the catalyst. Desired pure products were obtained by recrys-
tallization ꢀrom ethanol. The separated catalyst was ꢀurther washed with ethanol and
dried under vacuum at 60 °C to use in subsequent reactions. The synthesized deriva-
1
13
tives were characterized by melting points, FTIR, H and C NMR spectra.
Spectral data of representative compounds
2
3
‑amino‑7,7‑dimethyl‑2′,5‑dioxo‑5,6,7,8‑tetrahydrospiro[chromene‑4,3′‑indoline]‑
‑carbonitrile (4a)
−
1
IR (KBr; cm ) ν : 3375, 3311, 3140, 2960, 2926, 2192, 1723, 1655, 1604, 1469,
max
1
1
349, 1323, 1231, 1220, 1165, 1054, 902, 746; H NMR (400 MHz, CDCl ): δ
3
(
ppm) 1.00 (s, 3H), 1.03 (s, 3H), 2.07 (d, J=12.8 Hz, 1H), 2.15 (d, J=12.8 Hz,
1
H), 2.51 (d, J=14.4 Hz, 2H), 6.77 (d, J=6 Hz, 1H), 6.87 (t, J=6 Hz, 1H), 6.96
1
3
(
(
d, J=5.6 Hz, 1H), 7.12 (t, J=6 Hz, 1H), 7.22 (s, 2H), 10.39 (s, 1H); C NMR
400 MHz, CDCl ): δ (ppm) 26.99, 27.57, 31.91, 46.78, 49.97, 57.46, 109.20,
3
1
1
10.76, 117.30, 121.64, 122.98, 128.13, 134.38, 142.03, 158.73, 164.10, 177.99,
94.84.
2
‑amino‑7,7‑dimethyl‑5′‑nitro‑2′,5‑dioxo‑5,6,7,8‑tetrahydrospiro[chromene‑4,3′‑i
ndoline]‑3‑carbonitrile (4d)
−
1
IR (KBr; cm ) ν : 3389, 3246, 3199, 2960, 2873, 2190, 1741, 1679, 1600, 1519,
max
1
1
478, 1339, 1251, 1226, 1169, 1061, 988, 828, 739, 694; H NMR (400 MHz,
CDCl ): δ (ppm) 1.03 (s, 6H), 2.12 (d, J=12.8 Hz, 1H), 2.18 (d, J=12.8 Hz, 1H),
3
2
.54 (s, 1H), 2.65 (d, J=14 Hz, 1H), 7.02 (d, J=6.8 Hz, 1H), 7.46 (s, 2H), 7.970
1
3
(
d, J=2 Hz, 1H), 8.14 (dd, J=6.8 Hz, 1H), 11.18 (s, 1H); C NMR (400 MHz,
CDCl ): δ (ppm) 26.98, 27.64, 32.02, 46.95, 49.78, 55.88, 109.41, 109.75, 117.02,
3
1
18.83, 125.77, 135.34, 142.39, 148.63, 159.07, 165.17, 178.57, 195.32.
1
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Highly efcient and green synthesis oꢀ…
2
‑amino‑5′,7,7‑trimethyl‑2′,5‑dioxo‑5,6,7,8‑tetrahydrospiro[chromene‑4,3′‑indolin
e]‑3‑carbonitrile (4g)
−
1
IR (KBr; cm ) ν : 3369, 3136, 2960, 2191, 1716, 1660, 1603, 1492, 1351,
max
1
1
1
324, 1223, 1164, 1051, 880, 812, 661; H NMR (400 MHz, CDCl ): δ (ppm)
3
.01 (d, J = 7.6 Hz, 6H), 2.12 (d, J = 4.8 Hz, 2H), 2.19 (s, 3H), 2.55 (s, 2H), 6.66
(
d, J = 6 Hz, 1H), 6.78 (s, 1H), 6.92 (dd, J = 6 Hz, 1 H), 7.20 (s, 2H), 10.28 (s,
1
3
1
5
1
H); C NMR (400 MHz, CDCl ): δ (ppm) 20.63, 27.19, 27.43, 31.93, 46.82,
3
0.01, 57.68, 108.95, 110.82, 117.35, 123.57, 128.40, 130.40, 134.49, 139.60,
58.68, 164.00, 177.95, 194.83.
2
‑amino‑5′‑nitro‑2′,5,10‑trioxo‑5,10‑dihydrospiro[benzo[g]chromene‑4,3′‑indoline
]‑3‑carbonitrile (4k)
−
1
IR (KBr; cm ) ν : 3438, 3357, 3206, 2216, 1750, 1675, 1628, 1596, 1518,
max
1
1
481, 1407, 1339, 1275, 1208, 1158, 1095, 1069, 985, 835, 722; H NMR
(
400 MHz, CDCl ): δ (ppm) 7.11 (d, J = 7.2 Hz, 1H), 7.79–7.81 (m, 2H),
3
7
.82–7.84 (m, 2H), 7.85–7.89 (m, 2H), 8.20 (dd, J = 6.8 Hz, 1H), 8.32 (d,
1
3
J = 1.6 Hz, 1H), 11.44 (s, 1H); C NMR (400 MHz, CDCl ): δ (ppm) 48.07,
3
5
1
5.58, 109.75, 116.66, 118.02, 120.39, 126.02, 126.24, 130.41, 130.43, 134.54,
34.75, 135.17, 142.57, 148.18, 151.00, 158.86, 176.21, 178.02, 182.05.
2
‑amino‑5′‑ꢁuoro‑2′,5,10‑trioxo‑5,10‑dihydrospiro[benzo[g]chromene‑4,3′‑indolin
e]‑3‑carbonitrile (4l)
−
1
IR (KBr; cm ) ν : 3453, 3343, 2202, 1731, 1662, 1629, 1589, 1485, 1457,
max
1
1
339, 1270, 1237, 1205, 1179, 1070, 984, 821, 719; H NMR (400 MHz, CDCl ):
3
δ (ppm) 6.86(dd, J = 6.8 Hz, 1H), 7.02 (m, 1H), 7.02–7.06 (m, 2 Hz, 1H), 7.22
(
(
dd, J = 6.8 Hz, 1H), 7.65 (s,2H), 7.81–7.89 (m, 3H), 8.07–8.08 (m, 1H), 10.71
1
3
s,1H); C NMR (400 MHz, CDCl ): δ (ppm) 48.45, 56.42, 112.00, 115.20,
3
1
1
16.80, 118.86, 126.00, 126.20, 130.27, 130.51, 134.45, 134.81, 136.02, 137.91,
50.54, 156.96, 158.65, 159.32, 176.34, 177.52, 181.81.
2
‑amino‑1′‑methyl‑2′,5,10‑trioxo‑5,10‑dihydrospiro[benzo[g]chromene‑4,3′‑indoli
ne]‑3‑carbonitrile (4m)
−
1
IR (KBr; cm ) ν : 3456, 3348, 2200, 1721, 1666, 1628, 1591, 1490, 1468,
max
1
1
405, 1341, 1302, 1204, 1157, 1125, 1059, 983, 800, 762, 720; H NMR
(
400 MHz, CDCl ): δ (ppm) 3.24 (s, 3H), 6.98 (td, J = 6, 0.8 Hz, 1H), 7.09 (d,
3
J = 6 Hz, 1H), 7.30–7.33 (m, 2H), 7.64 (s, 2H), 7.78–7.87 (m, 3H), 8.06 (dd,
1
3
J = 6 Hz, 1H); C NMR (400 MHz, CDCl ): δ (ppm) 26.56, 47.59, 56.53, 108.55,
3
1
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N. Patel et al.
1
1
16.81, 119.24, 122.66, 123.99, 125.98, 126.22, 129.05, 130.30, 130.48, 133.54,
34.44, 134.76, 143.13, 150.46, 158.70, 176.00, 176.26, 181.77.
Results and discussion
Considering the pervasive biological activities and distinct medicinal properties oꢀ
spiro-oxindole moieties, we decided to synthesize spiro[indoline-3,9ʹ-xanthene]tri-
one and spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives via one-pot con-
densation using graphene oxide-supported dicationic ionic liquid as heterogeneous
catalyst under aqueous reaction condition.
Parameter optimization, comparison with reported catalysts
and substrate screening using DIL@GO catalyst for the synthesis
of spiro[indoline‑3,9ʹ‑xanthene]trione derivatives
To optimize the reaction conditions, reactions with diꢃerent parameters such as cat-
alyst loading and temperature were conducted using isatin and dimedone as model
substrates exploiting DIL@GO as the heterogeneous catalyst under aqueous con-
ditions. The experimental details and optimized reaction parameters are shown in
Table 1. Initially, blank reactions oꢀ model substrates were perꢀormed at ambient
and reꢂux temperatures in water. It was observed that no or trace amount oꢀ prod-
uct was obtained in the absence oꢀ catalyst aꢀter a prolonged reaction time (Table 1,
entries 1 and 2). However, in the presence oꢀ 50 mg DIL@GO at 60 °C, 80 °C and
reꢂux temperature, a substantial rise was noticed in the % yield oꢀ the targeted prod-
uct (Table 1, entries 3–5). It was apparent ꢀrom these experiments that the catalyst is
essential ꢀor this transꢀormation. Interestingly, the noteworthy growth in % yield and
a huge reduction in reaction time were witnessed in the presence oꢀ 100 mg catalyst
under reꢂux condition (Table 1, entry 6). Subsequently, the eꢃect oꢀ catalyst loading
on the reaction was checked by utilizing a higher amount oꢀ catalyst under the same
conditions (Table 1, entries 7 and 8). However, no signiꢁcant change was observed
in reaction yield and time. Hence, the catalyst loading oꢀ 100 mg was considered to
be the optimum under reꢂux condition. The efciency oꢀ the present catalyst was
compared with the reported results oꢀ other catalytic systems ꢀor the synthesis oꢀ
spiro[indoline-3,9ʹ-xanthene]trione derivatives. As shown in Table 1 (entries 9–14),
the graphene oxide-supported dicationic ionic liquid catalyst was ꢀound superior
than other reported catalysts with respect to reaction times and yields oꢀ the ꢁnal
product. Retaining the same reaction parameters, the substrate scope ꢀor the synthe-
sis oꢀ spiro[indoline-3,9ʹ-xanthene]trione derivatives was investigated by utilizing
structurally diverse isatins and dimedone or 1,3-cyclohexanedione (Table 2). All the
reactions were aꢃorded excellent isolated yields oꢀ targeted compounds in shorter
reaction time.
1
3

Highly efcient and green synthesis oꢀ…
a
Table 1 Optimization oꢀ the reaction conditions ꢀor the synthesis oꢀ compound 3a and comparison with
other reported catalysts
Entry Catalyst (mg)
Solvent/temperature (°C) Time (min) Yield (%)b
1
2
3
4
5
6
7
8
9
1
1
1
1
1
No catalyst
No catalyst
Water/r. t
Water/reꢂux
Water/60
24 (h)
24 (h)
120
120
120
20
20
20
30
20
2 (h)
10 (h)
24 (h)
60
–c
Trace
48
56
71
95
95
96
85
90
85
83
75
88
DIL@GO (50)
DIL@GO (50)
DIL@GO (50)
DIL@GO (100)
DIL@GO (150)
DIL@GO (200)
Oxalic acid dehydrate: proline LTTM [32] None/90
SBA-15-Pr-SO H [33]
ZnO [35]
Water/80
Water/reꢂux
Water/reꢂux
Water/reꢂux
Water/reꢂux
0
1
2
3
4
None/130
None/100
Ethanol: H O/80
Water/reꢂux
Ethanol/reꢂux
3
Mg(ClO ) [39]
4
2
2
PTSA, water [72]
Fe O @PS@His[HSO −]d [73]
3
4
4
a
Reaction conditions: isatin (1 mmol), dimedone (2 mmol), water (5 mL)
Isolated yields
No reaction
For the synthesis oꢀ 3ꢀ
b
c
d
Parameter optimization, comparison with reported catalysts and substrate
screening using DIL@GO catalyst for the synthesis of spiro[chromene‑4,3′‑indolin
e]‑3‑carbonitrile derivatives
The optimization oꢀ the reaction conditions ꢀor the synthesis oꢀ spiro[chromene-4,3′-
indoline]-3-carbonitrile was carried out via reaction between isatin, malononitrile
and dimedone as the model substrates, and results are summarized in Table 3. At
ꢁ
rst, the blank reaction was perꢀormed at ambient and reꢂux temperatures (Table 3,
entries 1 and 2). It was observed that in the absence oꢀ catalyst, reactions become
sluggish and proceeded with no or negligible amount oꢀ the desired product. Fur-
ther, the reactions were carried out at diꢃerent temperatures in the presence oꢀ
5
0 mg oꢀ catalyst (Table 3, entries 3–5). The reꢂux condition was ꢀound to be good
ꢀ
or the reaction to complete with a reasonable isolated yield oꢀ the ꢁnal product. The
eꢃect oꢀ catalyst loading was checked by utilizing the diꢃerent amount oꢀ catalyst
1
3

N. Patel et al.
Table 2 Synthesis oꢀ spiro[indoline-3, 9ʹ-xanthene]trione derivatives
Entry
Product
R
R1
R2
Yield (%)a
Time (min)
Melting point (°C)
Found
Reported
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
3e
3f
3g
3h
3i
H
H
H
H
H
CH3
H
H
H
H
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
95
95
94
91
94
90
92
93
95
94
94
20
25
25
30
30
30
25
30
20
30
30
>300
290–292
>300
280–282
289–291
>300
>300
>300
>300
>300
>300 [32]
290 [72]
Br
Cl
NO2
F
H
CH3
I
H
Br
Cl
>300 [32]
280–281 [32]
286–288 [32]
>300 [32]
309 [34]
>300 [32]
>310 [33]
>310 [33]
>310 [33]
1
1
0
1
3j
3k
H
H
H
H
>300
aIsolated yield
under the same conditions (Table 3, entries 6–8). It was revealed that 100 mg oꢀ
catalyst (DIL@GO) in reꢂuxing water is the optimum condition ꢀor the reaction
to achieve an excellent isolated yield oꢀ the targeted product with improved reac-
tion time. In comparison with the other reported catalytic methods (Table 3, entries
9
–15), this method was ꢀound better in terms oꢀ catalytic perꢀormance and han-
dling, reaction time and excellent yield oꢀ the product. The overall eꢃectiveness oꢀ
the catalyst ꢀor the synthesis oꢀ spiro[chromene-4,3′-indoline]-3-carbonitriles was
determined under optimized reaction conditions through the reactions between sub-
stituted isatins, malononitrile and 5,5-dimethylcyclohexane-1,3-dione or 2-hydroxy-
1
,4-naphthoquinone. The results are summarized in Tables 4 and 5, respectively. In
all the examples, excellent isolated yields oꢀ the ꢁnal product were obtained. From
the results, it was apparent that 5,5-dimethylcyclohexane-1,3-dione tends to react at
a ꢀaster rate as compare to 2-hydroxy-1,4-naphthoquinone. This may be due to the
higher reactivity oꢀ enol ꢀorm oꢀ 5,5-dimethylcyclohexane-1,3-dione as compared to
2
-hydroxy-1,4-naphthoquinone.
1
3

Highly efcient and green synthesis oꢀ…
a
Table 3 Optimization oꢀ the reaction conditions ꢀor the synthesis oꢀ compound 4a and comparison with
other reported catalysts
Entry
Catalyst (mg)
Solvent/temperature (°C)
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
9
No catalyst
No catalyst
Water/r.t
Water/reꢂux
Water/60
24 (h)
24 (h)
120
120
120
10
10
10
90
120
180
120
20
45
150
–c
Trace
38
46
69
96
95
96
75
94
95
95
96
88
97
DIL@GO (50)
DIL@GO (50)
DIL@GO (50)
DIL@GO (100)
DIL@GO (150)
DIL@GO (200)
Water/80
Water/reꢂux
Water/reꢂux
Water/reꢂux
Water/reꢂux
InCl (20 mol%) [74]
CH CN/reꢂux
3
3
10
11
12
13
14
15
TEBA (20 mol%) [75]
Water/60 °C
Water/60 °C
Water/80 °C
Ethanol/reꢂux
Ethanol/r.t
Sodium stearate (10 mol%) [76]
MgO nanocrystalline (15 mol%) [77]
SiO –OSO H NPs (0.003 g) [78]
2
3
Fe O @APTPOSS (9 mg) [79]
3
4
SB-DBU (0.05 mmol) [80]
Ethanol/r.t
a
Reaction conditions: isatin (1 mmol), dimedone (1 mmol), malononitrile (1 mmol), water (5 mL)
Isolated yields
No reaction
b
c
Plausible mechanism for the synthesis of spiro[indoline‑3,9ʹ‑xanthene]trione
and spiro[chromene‑4,3′‑indoline]‑3‑carbonitrile derivatives
The reaction mechanism ꢀor the synthesis oꢀ spiro[indoline-3,9ʹ-xanthene]trione and
spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives is proposed on the basis oꢀ
structural nature oꢀ catalyst and previous reports [32, 75, 82] (Scheme 1). In the
synthesis oꢀ spiro[indoline-3,9ʹ-xanthene]triones, the catalyst activates the isatin
through hydrogen bonding and makes it susceptible to nucleophilic attack through
enolized dimedone or 1,3-cyclohexanedione to ꢀorm a product oꢀ aldol condensation,
aꢀter which, the Michael addition oꢀ another molecule oꢀ dimedone or 1,3-cyclohex-
anedione takes place, ꢀollowed by cyclization and dehydration to aꢃord the desired
product. In the synthesis oꢀ spiro[chromene-4,3′-indoline]-3-carbonitriles deriva-
tives; initially, the Knoevenagel condensation takes place between catalyst-activated
isatin and malononitrile to aꢃord the isatylidene malononitrile intermediate. Aꢀter-
ward, the intermediate undergoes Michael addition by enolizable C–H-activated
1
3

N. Patel et al.
Table 4 Synthesis oꢀ spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives using dimedone
Entry
Product
R
R1
Yield (%)a
Time (min)
Melting point (°C)
Found
Reported
1
2
3
4
5
6
7
4a
4b
4c
4d
4e
4f
H
H
H
H
H
CH3
H
H
Br
Cl
NO2
F
H
96
92
94
93
95
94
93
10
15
15
25
20
25
20
288–290
>300
>300
288–289 [36]
>300 [81]
>300 [81]
>300
>300 [81]
268–271
253–256
278–280
270–271 [36]
253–254 [36]
278–780 [36]
4g
CH3
aIsolated yield
Table 5 Synthesis oꢀ spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives using 2-hydroxynaphtha-
lene-1,4-dione
Entry
Product
R
R1
Yield (%)a
Time (min)
Melting point (°C)
Found
Reported
1
2
3
4
5
6
7
4h
4i
H
H
H
H
H
CH3
H
H
Br
Cl
NO2
F
H
95
93
96
93
94
92
95
15
25
20
30
25
25
20
295–298
275–278
>300
290–292
>300
273–275
>300
298–300 [36]
275–276 [36]
>310 [36]
290–291 [36]
312–313 [36]
270–272 [36]
310–311 [36]
4j
4k
4l
4m
4n
CH3
aIsolated yield
1
3

Highly efcient and green synthesis oꢀ…
Scheme 1 Proposed mechanism ꢀor the synthesis oꢀ spiro[indoline-3,9ʹ-xanthene]trione and
spiro[chromene-4,3′-indoline]-3-carbonitrile derivatives
Fig. 1 Reusability oꢀ the catalyst
ꢀor the synthesis oꢀ 3a
Fig. 2 Reusability oꢀ the catalyst
or the synthesis oꢀ 4a
ꢀ
1
3

N. Patel et al.
Fig. 3 FTIR spectra oꢀ (a) GO, (b) pristine DIL@GO, (c) recovered DIL@GO aꢀter ꢁve catalytic cycles
ꢀor the synthesis oꢀ 3a and (d) recovered DIL@GO aꢀter ꢁve catalytic cycles ꢀor the synthesis oꢀ 4a
Fig. 4 TG analysis oꢀ (a) GO, (b) ꢀresh DIL@GO, (c) recovered DIL@GO aꢀter ꢁve catalytic cycles ꢀor
the synthesis oꢀ 3a and (d) recovered DIL@GO aꢀter ꢁve catalytic cycles ꢀor the synthesis oꢀ 4a
1
3

Highly efcient and green synthesis oꢀ…
Fig. 5 XRD patterns oꢀ (a) GO, (b) synthesized DIL@GO, (c) recovered DIL@GO aꢀter ꢁve reaction
cycles ꢀor the synthesis oꢀ 3a and (d) recovered DIL@GO aꢀter ꢁve reaction cycles ꢀor the synthesis oꢀ
4
a
compounds (2-hydroxynaphthalene-1,4-dione/dimedone) ꢀollowed by intramolec-
ular cyclization reaction between hydroxyl and cyano groups to yield the desired
product.
Recyclability of the catalyst
It is noteworthy that catalyst can be easily recovered ꢀrom the reaction through
centriꢀugation and washed thoroughly with ethanol ꢀor the removal oꢀ any unre-
acted starting materials and then vacuum-dried ꢀor the appropriate time ꢀor its
reuse in successive cycles. The efciency oꢀ the recovered catalyst was checked
ꢀ
or the synthesis oꢀ 3ʹ,3ʹ,6ʹ,6ʹ-tetramethyl-3ʹ,4ʹ,6ʹ,7ʹ-tetrahydrospiro[indoline-3,9ʹ-
xanthene]-1ʹ,2,8ʹ(2ʹH,5ʹH)-trione and 2-amino-7,7-dimethyl-2′,5-dioxo-5,6,7,8-
tetrahydrospiro[chromene-4,3′-indoline]-3-carbonitrile. Aꢀter each cycle, the cata-
lyst was easily recovered and reused ꢀor at least ꢁve successive cycles ꢀor both the
model reactions without losing its signiꢁcant catalytical activity and all the products
were obtained in excellent yield (Figs. 1 and 2).
The recycled catalyst DIL@GO aꢀter ꢁve reaction cycles in both model reac-
tions was characterized by FTIR, TGA, XRD and elemental analysis to examine the
chemical and thermal stability. As shown in Fig. 3, recycled catalyst in both reac-
tions retains the characteristic bands in FTIR spectra, which advocates the ꢀunctional
integrity oꢀ the material. Further, TGA and XRD patterns (Figs. 4 and 5) oꢀ recy-
cled DIL@GO in both cases also revealed a good match with the pattern oꢀ pristine
material. Additionally, elemental analysis oꢀ recycled catalyst ꢀrom both model reac-
tions (recovered ꢀrom the synthesis oꢀ 3a: 43.07%C, 4.06%H, 2.62%N and 5.13%S;
recovered ꢀrom the synthesis oꢀ 4a: 43.64%C, 4.38%H, 2.42%N and 5.46%S) was
1
3

N. Patel et al.
matched well with the result oꢀ synthesized catalyst (43.37%C, 4.49%H, 2.36%N
and 5.68%S) suggesting the chemical and thermal stability oꢀ the catalyst.
Conclusions
In conclusion, we reported a highly eꢃective and environmentally benign route ꢀor
the synthesis oꢀ spiro-oxindole derivatives, namely spiro[indoline-3,9ʹ-xanthene]
triones and spiro[chromene-4,3′-indoline]-3-carbonitriles using graphene oxide-
supported dicationic ionic liquid (DIL@GO) as a heterogeneous catalyst in aqueous
media. Present synthetic approach witnessed enhanced reaction rates, easy workup,
operational simplicity, green reaction media and excellent yields oꢀ targeted deriva-
tives. The catalyst can be recovered easily and reused ꢀor ꢁve successive cycles in
both reactions without signiꢁcant loss in catalytical perꢀormance. The chemical and
thermal stability oꢀ recycled catalyst was conꢁrmed through FTIR, TGA, XRD and
elemental analyses. Overall, the methodology provides a highly promising alterna-
tive to conventional methods ꢀor the synthesis oꢀ spiro-oxindole derivatives.
Supplementary Inꢀormation The online version contains supplementary material available at https://doi.
org/10.1007/s11164-021-04405-x.
Acknowledgements We grateꢀully acknowledge the support and research ꢀacilities provided by the P. D.
Patel Institute oꢀ Applied Sciences, CHARUSAT.
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