Bmim(OH)/chitosan/C2H5OH synergy: Grinding induced, a new route for the synthesis of spiro-oxindole and its derivatives

Article abstract of DOI:10.1039/c4ra03483j

Here we report a synthetic strategy based on the synergistic effect of a catalyst system incorporating Bmim(OH), chitosan and C₂H ₅OH. This powerful catalyst system is very effective and has several advantages such as being cost effective, involving shorter reaction times, being high yielding, involving the formation of no by-products and most importantly its easy recyclability (at least three times) with negligible reduction in its catalytic properties.

Full text of DOI:10.1039/c4ra03483j

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Bmim(OH)/chitosan/C2H5OH synergy: grinding
induced, a new route for the synthesis of spiro-
oxindole and its derivatives
Cite this: RSC Adv., 2014, 4, 30592
a
a
b
a
*
Madhulika Srivastava, Pratibha Rai, Jaya Singh and Jagdamba Singh
Here we report a synthetic strategy based on the synergistic effect of a catalyst system incorporating
Bmim(OH), chitosan and C2H5OH. This powerful catalyst system is very effective and has several
advantages such as being cost effective, involving shorter reaction times, being high yielding, involving
the formation of no by-products and most importantly its easy recyclability (at least three times) with
negligible reduction in its catalytic properties.
Received 17th April 2014
Accepted 9th June 2014
DOI: 10.1039/c4ra03483j
www.rsc.org/advances
The reason behind the incorporation of 1-Bmim(OH) in the
catalyst system is that a basic ionic liquid can dissolve many
Introduction
polar and non polar organic and inorganic molecules and also
has good catalytic activity in base catalyzed reactions.10
In addition, 2-chitosan has amino and hydroxyl group, both
of which are basic.11 We have made continuous efforts to syn-
thesise biologically active spiro compounds example spiro-
oxindole compounds12 which have been known to exhibit
countless useful properties in the eld of agriculture and
pharmaceutical industry for example antioxidant,13a anti-
fungal,13b anti-malarial,13c anti-tumor,13d anti-mycobacterial,13e
anti-microbial13f properties, etc. Melanoderma is a form of skin
cancer which is very dangerous. SOID-8, a derivative of spiro
[pyrrolidin-3,30-oxindole], inhibits growth and induces
apoptosis of melanoma cells (Scheme 2).
A major challenge in the eld of synthetic chemistry is to avoid a
multistep synthetic method and the use of hazardous solvents
and toxic chemicals.1 Multi component reactions are a precise
synthetic tool which can offer easy access to the synthesis of a
multi functionalised compound in an easy way with atom and
time economy.2 In addition, a neat synthesis is the only way to
save the environment from the harmful effects of the solvent.3
An alternative route to escape the solvent is a grinding induced
reaction in which mechanical action is used for the reaction.4
First of all the reactants are broken down into ne particles
which facilitate the reaction amongst them.5 Without a query,
catalysis gives an alternative path with a better yield, greater
energy efficiency and improved economy.6 According to litera-
ture a mono-catalyst system was famous and very successful but
since last 37 years multi catalyst system made a place in the
form of synergistic catalysis.7 In this type of catalysis all
components give the additive effect in the catalytic process.7
Many research groups have focused on this type of catalysis.
Result and discussion
Spiro-oxindole serves as an intermediate for alkaloid potential
drugs and has varying pharmacological activities. The desired
compound is prepared by the starting material isatin, malono-
nitrile and dimedone.14 Initially we took staring materials in
stoichiometric amounts in mortar and grinded with the help of
pestle.
˜
Eder. J. Lenardao synthesised vinyl sulphides and tellurides in
the recyclable catalyst system – glycerol/CuI/Zn,8 Jing and his co-
worker reported our work, Henery-micheal by synergically
catalysed by graed chiral bases and inherent achiral hydroxyl
on mesoporous surface.9a Our recent work5b involved the
synthesis of functionalised pyrazoles with time economy by the
use of a catalyst system which was prepared from ionic liquid
and water. In extension to our recent work we have now used a
catalyst which is prepared by 10 mol% Bim(OH), 10 mol%
chitosan9b and 1 mL ethanol (Scheme 1). This catalyst system
shows additive effect and serves as a superb catalyst.
The product was formed in 45 minutes with the formation of
some by products. In order to reduce the overall time of the
aEnvironmentally Benign Lab Department of Chemistry, University of Allahabad,
211002 India. E-mail: dr.jdsau@gmail.com; Tel: +91 9415218507
bL R PG College, Sahibabad, UP, India
Scheme 1 Catalyst system.
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Scheme 2 Synthesis of target compound.
Table 1 Optimization of ionic liquid as a catalyst for the synthesis of spiro-oxindole
Entry
Ionic liquid
Time (min)
Yielda
1
2
3
4
5
6
(Bmim)OH
(Bmim)BF4
(Hmim)HSO4
(Bmim)Cl
(Bmim)PF6
(Hmim)H2SO4
30
35
40
35
36
35
86
58
56
50
60
65
a
Is isolated yield in %, amount of ionic liquid is 20 mol%.
Table 2 Effect of different amounts of chitosan with ethanol on the
model reaction
catalyst, the performance of basic ionic liquid Bmim(OH)
(Table 1, entry 1) is best. We carried out further experiments in
order to improve the efficiency of the reaction.
Entry
Chitosanb
Time
Yielda
We grinded the staring material with varying amounts of
chitosan ranging from 5 mol% to 50 mol% with 1 mL
ethanol( Table 2). It was observed that there occurred a reduc-
tion in overall reaction time and an increase in yield by
increasing the amount of chitosan up to 20 mol% (Table 2 entry
4). Further increase in the amount of chitosan affected neither
the reaction time nor the yield of the product. Thus we
concluded that the best result was obtained with 20 mol% of
chitosan.
1
2
3
4
5
6
7
5
10
15
20
30
40
50
40
35
28
20
20
20
20
70
73
77
82
82
82
82
a
Is isolated yield in %. b Is amount of chitosan in mol%.
Next we performed the experiment with varying quantities of
both the catalysts in one mL ethanol and discovered that the
best yield of 92% was obtained with 10 mol% Bmim(OH) and
10 mol% chitosan (Table 3 entry 2). The adopted route was
atom, time and reagent economical. A further increase in the
amount of catalysts showed no benecial results. In this
synthesis use of ethanol as a solvent is to provides a homoge-
neous mixture of the reactants thus enhancing the reaction rate.
reaction and to inhibit the formation of by-products, we grinded
the starting materials in a sequential manner and introduced
the ionic liquid to the reaction mixture as a catalyst. This
alternative pathway proved to be benecial only in the reduction
of overall time but the reaction still took 30 minutes to
complete. Among the different types of ionic liquids used as
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recorded on a Perkin-Elmer 993 IR spectrophotometer, 1HNMR
spectra were recorded on a Bruker AVII 400 spectrometer in
CDCl3 using TMS as internal reference with chemical shi value
being reported in ppm. All coupling constants (J) are reported in
Hertz (Hz). 13C NMR spectra were recorded on the same
instrument at 100 MHz in CDCl3 and TMS was used as internal
reference. Elemental analyses were carried out in a Coleman
automatic carbon, hydrogen and nitrogen analyze.
Table 3 Effect of catalyst system of reaction rate and yield of the
product
Entry
Catalyst systemb
Time (min)
Yielda
1
2
3
4
5
5, 5
10
5
5
5
5
84
92
92
92
92
10, 10
20, 20
30, 30
40, 40
a
Is the isolated yield of the product. b Is the amount of Bmim(OH) and
General method
chitosan in mol%.
Isatin (1 mmol), malononitrile (1 mmol), and catalyst system,
were thoroughly grinded with pestle and mortar. Aer the
formation of Knoevenagel adduct, 1,3 diketone was added
(1 mmol) and again thoroughly grinded for an appropriate time
(Table 5). When the reaction was complete (checked by TLC
using authentic samples) 5 mL water was added and the
mixture was extracted with DCM (3 ꢀ 5 mL). The combined
organic phase was dried over MgSO4.
Chitosan and ionic liquid provide a basic medium which
increases the reactivity of each step of the reaction (Scheme 3).
Basicity of the reaction medium encourages it to run at a good
speed with a reduction in the formation of by-products.
To standardize the optimization condition we performed a
series of reactions and showed the electronic effect of the
substituent on reactant. We found then when an electron
withdrawing group is present on the isatin the reaction
becomes fast because it facilitates the Knoevenagel reaction. On
the other hand, when electron donating group is present on the
isatin then the reaction becomes slower. All starting materials
are activated by this catalyst system and moreover each step of
the reaction is catalysed by this system.
Isatin and malononitrile are added through Knoevenagel
reaction. Proton is abstracted by the base from active methylene
group and is attached on the Knoevenagel adduct. Aer that
tautomerisation occurs and enol form of active methylene
attaches on nitrile.
At the end of the reaction, catalyst system is recovered and
reused (Table 4). The recovered catalyst system was further used
with the same substrate as a catalyst to check the yield obtained
and catalytic activity of the recovered catalyst system. As shown
in Table 4, the yield of spiro-oxindoles aer three cycles was
almost the same.
Recovery of catalyst system
Aer isolation of the product, the remaining mother liquid
containing the ionic liquid and chitosan was poured in ethyl-
acetate (to remove any organic impurity.) in separating funnel.
Chitosan and ionic liquid separate from organic layer. Chitosan
was recovered aer centrifugation of water layer and further
used in reaction. The recovery of the ionic liquid was also
examined. Water layer dried under vacuum at 90 ꢁC afforded
(Bmim)OH, which was used in subsequent runs without
purication.
4a 2-Amino-7,7-dimethyl-20,5-dioxo-5,6,7,8-tetrahydrospiro
[chromene-4,30-indoline]-3-carbonitrile. White solid, mp 289–
290 ꢁC 1H NMR (400 MHz, DMSO-d6) d 1.00 (s, 3H), 1.02 (s, 3H),
2.10 (d, J ¼ 16.0 Hz, 1H), 2.14 (d, J ¼ 16.0 Hz, 1H), 2.57 (s, 2H),
6.77 (d, J ¼ 7.6 Hz, 1H), 6.86 (t, J ¼ 7.4 Hz, 1H), 6.99 (d, J ¼ 6.8
Hz, 1H), 7.15 (t, J ¼ 8.2 Hz, 1H), 7.13 (s, 2H), 10.40 (s, 1H); 13C
NMR (100 MHz, DMSO-d6) d 27.59, 28.17, 32.43, 47.21, 50.39,
57.89, 109.74, 111.19, 117.82, 122.13, 123.52, 128.59, 134.56,
142.48, 159.25, 164.56, 178.48, 195.30. Anal. calcd for
Conclusion
C
19H17N3O3: C, 68.05; H, 5.11; N, 12.53. Found: C, 67.06; H,
In summary, we have disclosed a new catalyst system which
proves to be very effective not only in reducing the reaction
time, but also in increasing the yield of the product. It involves
simple procedure, is environment friendly and also incorpo-
rates special features like reagent economy, easy workup and
easy handling.
4.98; N, 12.49%.
4b 2-Amino-50-chloro-7,7-dimethyl-20,5-dioxo-5,6,7,8-tetrahy-
drospiro[chromene-4,30-indoline]-3-carbonitrile. White solid,
1
ꢁ
mp 293–295 C H NMR (400, MHz, DMSO-d6) d 1.01 (s, 3H),
1.02 (s, 3H), 2.16 (s, 2H), 2.48–2.57 (m, 2H), 6.79 (d, J ¼ 8.0 Hz,
1H), 7.09 (s, 1H), 7.19 (d, J ¼ 5.6 Hz, 1H), 7.28 (s, 2H), 10.52 (s,
1H). 13C NMR (100 MHz, DMSO-d6) d 27.76, 27.98, 32.45, 47.52,
50.43, 57.15, 110.68, 111.14, 117.77, 123.79, 126.15, 128.57,
136.93, 141.57, 159.34, 165.12, 178.30, 195.64. Anal. calcd for
Experimental
General information
C
19H16ClN3O3: C, 61.71; H, 4.36; N, 11.36. Found: C, 61.68; H,
Reagents were obtained from commercial suppliers, and used 4.30; N, 11.26%.
without further purication unless otherwise specied by a
4c 2-Amino-50-bromo-7,7-dimethyl-20,5-dioxo-5,6,7,8-tetrahy-
reference. All reactions were performed using oven-dried drospiro[chromene-4,30-indoline]-3-carbonitrile. Mp > 300 ꢁC
glassware. Organic solutions were concentrated using a Buchi 1H NMR (DMSO-d6, 400 MHz) d: 1.04 (s, 6H), 2.14 (d, J ¼ 16.8 Hz,
rotary evaporator. TLC was performed using silica gel GF254 1H), 2.21 (d, J ¼ 16.8 Hz, 1H), 2.50 (d, J ¼ 17.6 Hz, 1H), 2.60 (d, J
(Merck) plates. Melting points were determined by open glass ¼ 17.6 Hz, 1H), 6.76 (d, J ¼ 8.4 Hz, 1H), 7.21 (s, 1H), 7.32 (d, J ¼
capillary method and are uncorrected. IR spectra in KBr were 7.2 Hz, 1H), 7.33 (s, 2H), 10.56 (s, 1H).
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Scheme 3 Plausible mechanism for the synthesis of spiro-oxindole.
Table 4 Recovery and performance of catalyst system
4d Ethyl 2-amino-7,7-dimethyl-20,5-dioxo-5,6,7,8-tetrahy-
drospiro[chromene-4,30-indoline]-3-carboxylate. White solid,
Cyclesa
Yieldb (%)
Recoveredc (%)
1
ꢁ
mp 278–280 C H NMR (400 MHz, DMSO-d6) d 0.78 (t, J ¼ 6.8
Hz, 3H), 0.95 (s, 3H), 1.02 (s, 3H), 2.01 (d, J ¼ 16.0 Hz, 1H), 2.15
(d, J ¼ 16.0 Hz, 1H), 2.54 (m, 2H), 3.68 (q, J ¼ 6.8 Hz, 2H), 6.67
(d, J ¼ 7.6 Hz, 1H), 6.76 (t, J ¼ 7.2 Hz, 1H), 6.83 (d, J ¼ 7.2 Hz,
1H), 7.04 (t, J ¼ 7.2 Hz, 1H), 7.85 (s, 2H), 10.11 (s, 1H); 13C NMR
(100 MHz, DMSO-d6) d 13.64, 27.17, 28.22, 32.08, 47.12, 51.14,
59.39, 76.85, 108.60, 113.63, 121.06, 122.79, 127.66, 136.47,
144.53, 159.68, 162.83, 168.16, 180.28, 195.19. Anal. calcd for
Native
94
92
91
90
90
87
85
84
1
2
2
a
All reactions were carried out using isatin (1.0 mmol), malononitrile
b
(1.0 mmol), 1,3 diketone (1.0 mmol) and catalyst system. Is isolated
yield of the product. c Is isolated yield of the catalyst system.
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Table 5 Reaction of isatin, malononitrile and enol form of 1,3 cyclic diketones. All reactions were carried out using isatin (1.0 mmol), malo-
nonitrile (1.0 mmol), 1,3 diketone (1.0 mmol) and catalyst system
Entry
R
R1
R2
R3
Timeb
Yielda
1
2
3
4
5
6
7
8
9
H
Cl
H
H
H
H
H
H
CH3
H
H
CN
CN
CN
COOC2H5
CN
COOC2H5
CN
CN
CN
CN
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
10
8
8
20
22
25
22
8
94
96
96
93
91
89
92
93
95
95
Br
H
CH3
CH3
H
H
Cl
Br
H
H
7
7
10
H
a
Is isolated yield of the product. b Is time in minutes.
C21H22N2O5: C, 65.96; H, 5.80; N, 7.33. Found: C, 65.80; H, 5.72, (m, 2H), 2.51–2.66 (m, 2H), 6.78 (d, J ¼ 7.6 Hz, 1H), 6.89 (t, J ¼
N, 7.36%.
7.6 Hz, 1H), 7.01 (d, J ¼ 7.2 Hz, 1H), 7.14 (t, J ¼ 7.6 Hz, 1H), 7.19
4e
2-Amino-7,7,70-trimethyl-20,5-dioxo-5,6,7,8-tetrahy- (s, 2H), 10.38 (s, 1H). 13C NMR (100 MHz, DMSO-d6) d 20.25,
drospiro[chromene-4,30-indoline]-3-carbonitrile. White solid, 27.22, 36.88, 47.35, 58.09, 109.63, 112.30, 117.85, 122.16,
mp 296–297 ꢁC 1H NMR (400 MHz, DMSO-d6) d 0.98 (s, 3H), 1.02 123.68, 128.64, 135.02, 142.47, 159.14, 166.59, 178.64, 195.53.
(s, 3H), 2.06 (d, J ¼ 16.0 Hz, 1H), 2.17 (d, J ¼ 16.0 Hz, 1H), 2.22 (s, Anal. calcd for C17H13N3O3: C, 66.44; H, 4.26; N, 13.67. Found:
3H), 2.51–2.59 (m, 2H), 6.78 (t, J ¼ 6.8 Hz, 1H), 6.83 (s, 1H), 6.96 C, 66.49; H, 4.30; N, 13.69%.
(d, J ¼ 6.8 Hz, 1H), 7.23 (s, 2H), 10.45 (s, 1H). 13C NMR (100
4i 2-Amino-70-chloro-20,5-dioxo-5,6,7,8-tetrahydrospiro[chro-
MHz, DMSO-d6) d 16.83, 27.44, 28.13, 32.41, 47.56, 50.52, 58.37, mene-4,30-indoline]-3-carbonitrile. White solid, mp > 300 ꢁC 1H
111.43, 117.85, 118.77, 120.83, 122.05, 130.02, 134.50, 141.43, NMR (400 MHz, DMSO-d6) d 1.94 (t, J ¼ 6.0 Hz, 2H), 2.18–2.27
159.22, 164.45, 178.96, 195.22. Anal. calcd For C20H19N3O3: C, (m, 2H), 2.65–2.69 (m, 2H), 6.94 (t, J ¼ 8.0 Hz, 1H), 7.02 (d, J ¼
68.75; H, 5.48; N, 12.03. Found: C, 68.74; H, 5.47; N, 12.02%.
7.2 Hz, 1H), 7.22 (d, J ¼ 8.1 Hz, 1H), 7.33 (s, 2H), 10.84 (s, 1H).
4f Ethyl 2-amino-7,7,70-trimethyl-20,5-dioxo-5,6,7,8-tetrahy- 13C NMR (100 MHz, DMSO-d6) d 20.22, 27.28, 36.72, 48.25,
drospiro[chromene-4,30-indoline]-3-carboxylate. White solid, 57.49, 112.01, 113.92, 117.05, 122.48, 1239, 128.76, 136.73,
mp 289–291 ꢁC 1H NMR (400 MHz, DMSO-d6) d 0.78 (t, J ¼ 7.24 140.27, 159.24, 166.82, 178.64, 195.65. Anal. calcd for
Hz, 3H), 0.95 (s, 3H), 1.03 (s, 3H), 2.01 (d, J ¼ 15.6 Hz, 1H), 2.14
C17H12ClN3O3: C, 59.75; H, 3.54; N, 12.30. Found: C, 59.75; H,
(d, J ¼ 16 Hz, 1H), 2.16 (s, 3H), 2.44–2.62 (m, 2H), 3.61–3.73 (m, 3.60; N, 12.35%.
2H), 6.66 (d, J ¼ 6.4 Hz, 1H), 6.67 (t, J ¼ 7.2 Hz, 1H), 6.87 (d, J ¼
4j
2-Amino-50-bromo-20,5-dioxo-5,6,7,8-tetrahydrospiro
6.8 Hz, 1H), 7.84 (s, 2H), 10.18 (s, 1H). 13C NMR (100 MHz, [chromene-4,30-indoline]-3-carbonitrile. Mp: 291–292 ꢁC 1H
DMSO-d6) d 13.32, 16.81, 27.04, 28.32, 32.05, 47.31, 51.12, 59.32, NMR (DMSO-d6, 400 MHz) d: 1.92–1.97 (m, 2H), 2.23–2.25 (m,
77.02, 113.72, 117.51, 120.21, 121.02, 128.95, 136.01, 142.92, 2H), 2.74 (t, J ¼ 6.6 Hz, 2H), 6.75 (d, J ¼ 8.0 Hz, 1H), 7.23–7.28
159.51, 162.71, 168.21, 180.72, 195.04. Anal. calcd for (m, 1H), 7.33 (s, 3H), 10.57 (s, 1H).
C
22H24N2O5: C, 66.65; H, 6.10; N, 7.07. Found: C, 65.29; H, 6.15;
N, 7.08%.
4h
2-Amino-20,5-dioxo-5,6,7,8-tetrahydrospiro[chromene-
Acknowledgements
4,30-indoline]-3-carbonitrile. White solid, mp 251–253 ꢁC 1H
NMR (400 MHz, DMSO-d6) d 1.93 (t, J ¼ 6.0 Hz, 2H), 2.17–2.28
We sincerely thank SAIF, Punjab University, Chandigarh, for
providing micro-analyses and spectra. The authors are also
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thankful to UGC, New Delhi, for the award of Junior Research
Fellowship (JRF).
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