Heterogeneous bimetallic ZnFe2O4 nanopowder catalysed facile four component reaction for the synthesis of spiro[indoline-3,2′-quinoline] derivatives from isatins in water medium

Article abstract of DOI:10.1016/j.tetlet.2015.02.030

The bimetallic ZnFe₂O₄ nanopowder, a dual Lewis acid-base combined catalyst is found to efficiently catalyse a four component reaction for the synthesis of functionalized tetrahydrospiro[indoline-3,2′-quinoline] derivatives from aryl

Full text of DOI:10.1016/j.tetlet.2015.02.030

Accepted Manuscript
Heterogeneous bimetallic ZnFe2O4 nanopowder catalysed facile four compo-
nent reaction for the synthesis of spiro[indoline-3,2′-quinoline] derivatives from
isatins in water medium
Kamalesh Debnath, Animesh Pramanik
PII:
S0040-4039(15)00289-0
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.02.030
TETL 45898
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
18 December 2014
6 February 2015
8 February 2015
Please cite this article as: Debnath, K., Pramanik, A., Heterogeneous bimetallic ZnFe2O4 nanopowder catalysed
facile four component reaction for the synthesis of spiro[indoline-3,2′-quinoline] derivatives from isatins in water
medium, Tetrahedron Letters (2015), doi: http://dx.doi.org/10.1016/j.tetlet.2015.02.030
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
Heterogeneous bimetallic ZnFe2O4
nanopowder catalysed facile four component
reaction for the synthesis of spiro[indoline-
3,2′-quinoline] derivatives from isatins in
water medium
Leave this area blank for abstract info.
Kamalesh Debnath, Animesh Pramanik*
COOR4
COOR4
O
O
O
O
O
O
O
NH2
R4
O
ZnFe2O4
R2
R5
R5
R1
O
R5
R5
H2O, Stirring
2 h, r.t.
+
+
+
N
N
N
O
R4
R3
R1
R3
R2
31 Examples
67-82 % Yield

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Heterogeneous bimetallic ZnFe2O4 nanopowder catalysed facile four component
reaction for the synthesis of spiro[indoline-3,2′-quinoline] derivatives from
isatins in water medium
Kamalesh Debnath, Animesh Pramanik*
Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata-700 009, India
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The bimetallic ZnFe2O4 nanopowder, a dual Lewis acid-base combined catalyst is found to
efficiently catalyze four component reaction for the synthesis of functionalized
tetrahydrospiro[indoline-3,2΄-quinoline]
derivatives from arylamines, dialkyl
acetylenedicarboxylates, isatin derivatives and cyclohexane-1,3-diones in water medium at room
temperature. Reduced reaction time, operational simplicity, elimination of hazardous solvent and
more importantly, easy recoverability and reusability of the nanopowder make the present
methodology economical, green and sustainable.
a
Available online
Keywords:
green chemistry
multicomponent reaction
heterogeneous catalysis
nanocatalyst
2009 Elsevier Ltd. All rights reserved.
spiro compounds
1. Introduction
Spirooxindole ring system is present in a large number of
bioactive naturally occurring alkaloids and medicinally
imperative compounds.5-8 Especially, 3-spiroheterocyclic 2-
oxindole cores are present in a number of natural products, such
as tabernoxidine,9 and medicinally important NITD 609 (Figure
1).10 These compounds also have emerged as potential
fluorescent materials.11,12 For the synthetic organic chemist, the
construction of structurally diverse spiro-heterocyclic
frameworks is always a challenging task since it often requires
specific strategy based on the synthetic design.13 Recently, Yan et
al. reported a four-component reaction of arylamines, dialkyl
acetylenedicarboxylates, isatin derivatives and cyclohexane-1,3-
diones to prepare spiro[indoline-3,2′-quinoline] derivatives in
Development of efficient methods and strategies for the
combinatorial synthesis of organic compounds is of interest,
especially for the organic compounds with potential biological
and medicinal activities.1 Now-a-days, Mixed Metal Oxide Nano
(MMON) particles have drawn much attention for the
development of green synthetic methodology due to their easy
separation procedure and recyclability, operational simplicity,
environmentally safe disposal and cleaner reaction profiles for
reducing the organic waste.2 In fact, the MMONs are better in
terms of their catalytic activity and selectivity since the active
sites are carefully tuned by the mixing of one oxide catalyst with
another metal oxide which attributes dual characteristic in the
catalysis. Moreover, the nano-surface of MMONs provides better
surface area-to-volume ratio which allows greater contact
between the reactants and the catalysts. Highly stable,
heterogeneous, bimetallic ZnFe2O4 nanopowder is such an
example where the Fe3+ cation and counter anionic O2- act as
Lewis acid and base respectively3 and Zn2+ acts as π-bond
activator. This interesting property of the ZnFe2O4 nanopowder
has not been explored widely, especially in important
multicomponent reactions for synthesis of bio-active building
blocks.4
AcOH medium under stirring for 24h.14
Cl
F
Cl
N
HN
H
O
H
OH
CO2Me
N
HN
N
O
H
H
O
________________
Tabernoxidine
NITD 609
Figure 1. Natural products and anti-malarial drug with 3-spiro-
oxindole core structures.
Corresponding author. Tel.: +91-33-2484-1647; fax: +91-33-2351-
9755; e-mail: animesh_in2001@yahoo.co.in

2
Tetrahedron Letters
next sought to find out the effect of different solvents
Although the method is helpful for the preparation of spiro-
(CH3CN, EtOH etc.) with careful tuning of the catalyst load (10-
40 mol %) and additives (Table 1, entries 12-16). Though the
reaction in EtOH medium gave the product 5a in good yield,
~62% (Table 1, entry 13), from the economical and
environmental point of view, H2O was chosen as the reaction
medium for all further reactions. The addition of L-Proline (1
mmol) as additive to ZnFe2O4 also did not produce higher yield
of product 5a under similar reaction conditions (Table 1, entry
16). Therefore, the best yield of 5a (~77%) was achieved when a
mixture of isatin, dimedone, p-toluidine, and dimethyl
acetylenedicarboxylate taking 1 mmol each was stirred with
ZnFe2O4 catalyst (20 mol%) in water medium for 2 h at room
temperature. With the optimized condition in hand, next the
scope and generality of this protocol was assessed by employing
heterocyclic framework, the reaction suffers from some serious
limitations such as prolong reaction time (24 h), use of AcOH
and poor to moderate yields of the products. In continuation of
our research work on the synthesis of isatin based heterocycles15
and development of green synthetic methodologies,16-18 herein,
we explore the potential of the bimetallic ZnFe2O4 nanopowder
as heterogeneous catalyst in this four component reaction to
make it green. Moreover the study will provide valuable insights
into the mechanism of the reaction and the mode of catalytic
activity of the catalyst. This will help in expanding the scope of
the catalyst for new synthetic design.
During our studies in exploring the potential of ZnFe2O4
nanopowder as catalyst for the one pot four component synthesis
of 3-spiroheterocyclic 2-oxindoles in water medium, we
attempted to optimize the reaction condition taking isatin,
dimedone, p-toluidine, and dimethylacetylenedicarboxylate in
1:1:1:1 molar proportion (Scheme 1). In this process various
parameters such as the effect of catalysts, solid support,
temperature and solvents at different experimental conditions
were investigated (Table 1). Initially we assumed that carrying
out the reaction under solvent free condition using solid acid
support such as silica sulphuric acid (SSA) might produce better
results, but the reaction failed to give the desired product 5a on
the solid surface of SSA (500 mg) under continuous stirring at
room temperature for 24 h (Table 1, Entry 1). But when the same
reaction was carried out in EtOH medium at a slightly elevated
temperature, around 60 ºC, the product 5a was formed in low
yield ~15% (Table 1, Entry 2). The isolated product was purified
through column chromatography and the structure of the product
5a was assigned and confirmed by IR, 1H NMR, 13C NMR,
elemental analysis and X-ray diffraction study (Figure 2).
Interestingly, we observed that there is a steady progress of the
reaction for first 1 h as monitored by TLC. But when the reaction
was carried out for a longer period of time, the desired product
started to decompose and finally disappeared. This result
suggests that the elevated temperature and strong acidity of SSA
are not suitable for this multicomponent reaction (MCR). In
search of better yield and cleaner reaction profile, magnetically
retrievable nano Fe3O4@SO3H was employed in place of SSA as
catalyst and the reaction was carried out in ethanol medium under
stirring condition at room temperature for 24 h (Table 1, Entry
3). Unfortunately, the yield of the product 5a was still poor
(~23%) along with considerable amount of side product. To
obtain the desired product 5a with satisfactory yield under
greener and milder acidic conditions, we tested Brønsted acid
catalyst p-TSA and organo-acid catalyst L-Proline in water
medium (Table 1, entries 4 and 5). But in both the cases the
product was not formed even after 24 h stirring at room
temperature. Subsequently we employed several Mixed Metal
Oxide Nano (MMON) particles such as MFe2O4 spinel (M = Co,
Cu, Zn) for the catalysis of the reaction. Although CoFe2O4 failed
to produce any product in EtOH medium on stirring at room
temperature, CuFe2O4 catalysed reaction produced the product 5a
in 42% yield within 2 h under similar reaction conditions (Table
1, Entry 7). The addition of SSA as additive to the catalyst
CuFe2O4 in EtOH medium enhanced the yield of the product upto
52% (Table 1, Entry 8). In an attempt to make the methodology
greener, when H2O was used as solvent in CuFe2O4 catalysed
reaction, the yield of the product was poor ~ 30% (Table 1, Entry
9). No improvement of yield was observed when sodium lauryl
sulphate was used as surfactant, even after a prolonged reaction
time (24 h) (Table 1, Entry 10). Gratifyingly, when ZnFe2O4
spinel was used as catalyst in H2O medium, the yield of the
product increased considerably (~77%) on stirring the reaction
mixture at room temperature for 2 h (Table 1, Entry 11). In an
attempt to enhance the catalytic activity of ZnFe2O4 spinel we
various
isatins,
dialkyl
acetylenedicarboxylates,
1,3-
cyclohexandiones and aniline derivatives 5a-e′ (Scheme 2, Table
2).19 The present methodology is more advantageous than the
previously reported method14 in many aspects such as drastic
reduction of reaction time from 24 h to 2 h, use of environmental
friendly solvent H2O in place of AcOH, and easier
isolation/purification of the products due to minimization of by-
products. In all cases, the formation of the final products was
1
confirmed by IR, H NMR, 13C NMR spectroscopy, elemental
analysis and also by matching the melting points of some
compounds with the reported values.14 The X-ray crystal
structures of products 5a and 5d are presented in Figure 2.
CO2Me
O
CO2Me
O
NH2
O
O
O
O
Catalyst
Solvent
NH
O
N
N
O
H
O
O
5a
Scheme 1. Optimization study for the synthesis of 5a
C29
C26
C27
C25
C28
C24
C23
N2
N1
C5
O1
C6
C17
C7
C8
C1
C18
C16
C19
C4
C3
C2
O2
C20
C14
C10
C13
C12
C15
C9
C21
O5
O3
O6
O4
C11
C22
5a
C21
C16
C15
O6
C20
C17
C14
C13
C18
C19
O5
O4
C11
C10
C9
C12
O3
C24
C25
C30
C26
C8
C7
N1
C22
O2
C27
C23
C5
C6
O1
C29
C28
C1
C2
C4
Br
N2
C3
5d
Figure 2. ORTEP representation of compound 5a and 5d.
Thermal ellipsoids are drawn at 50% probability level. (CCDC
No. 1013582 and 1016082 respectively).

3
.
Table 1. Optimization of reaction conditions for the synthesis of 5a
Entry
1
Solvent
__
Catalyst
Catalyst Load
Additive
__
Time (h)
24
Temperature(ºC)
r.t.
Yielda %
__
Silica sulphuric acid 500mg
(SSA)
2
3
4
Ethanol
Ethanol
H2O
SSA
20 mol%
20 mol%
20 mol%
__
__
__
1
60
r.t.
r.t.
15
23
__
Fe3O4-SO3H
24
24
p-toluenesulphonic
acid (PTSA)
L-Proline
5
6
7
H2O
20 mol%
20 mol%
20 mol%
__
__
__
24
24
2
r.t.
r.t.
r.t.
__
__
42
Ethanol
Ethanol
CoFe2O4
CuFe2O4
8
Ethanol
H2O
CuFe2O4
CuFe2O4
CuFe2O4
ZnFe2O4
ZnFe2O4
ZnFe2O4
ZnFe2O4
ZnFe2O4
ZnFe2O4
20 mol%
20 mol%
20 mol%
20 mol%
20 mol%
20 mol%
10 mol%
40 mol%
20 mol%
SSA (100 mg)
__
2
2
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
52
50
30
77
55
62
60
68
75
9
10
11
12
13
14
15
16
H2O
Sodium lauryl sulphate 24
(1 mmol)
__
H2O
2
2
2
2
2
2
CH3CN
Ethanol
H2O
__
__
__
H2O
__
H2O
L-Proline (1 mmol)
aIsolated Yields
O
O
COOR4
O
O
O
NH2
O
COOR4
R4
O
R2
ZnFe2O4
H2O, Stirring
2 h, r.t.
R5
R5
R1
R5
R5
+
O
+
+
N
O
N
N
R4
R3
O
R1
1
2
4
3
R3
R2
5
Scheme 2. Synthesis of spiro[indoline-3,2′-quinoline] derivatives 5.
Table 2. Library synthesis of 3-spiroheterocyclic 2-oxindole compounds 5a-e′a
CO2Et
CO2Et
CO2Me
CO2Me
CO2Me
CO2Et
O
O
O
O
CO2Me
O
CO2Et
O
O
O
NH
NH
NH
NH
N
N
N
N
O
5b (75%)
Br
5a (77%)
Br
5c (72%)
5d (73%)
CO2Et
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
O
O
O
O
CO2Et
O
CO2Me
O
O
O
N
N
N
NH
N
N
N
N
Cl
5h (77%)
Br
O
O
Cl
O
5f (78%)
5e (80%)
5g (71%)

4
Tetrahedron
Table 2 (continued)…
CO2Me
CO2Me
CO2Et
CO2Et
CO2Me
CO2Me
O
CO2Me
O
O
O
CO2Me
O
O
O
O
N
NH
N
N
NH
N
N
N
Cl
5l (81%)
CO2Me
Cl
O
Cl
Cl
O
Br
5j (72%)
5k (76%)
5i (69%)
CO2Et
O
CO2Et
CO2Me
CO2Me
O
CO2Me
CO2Et
O
O
O
CO2Et
O
O
O
N
NH
N
N
N
N
N
N
Cl
Cl
Cl
O
Cl
5p (76%)
5o (74%)
5m (72%)
5n (70%)
CO2Et
CO2Et
CO2Et
CO2Et
O
O
CO2Et
O
O
CO2Et
O
O
CO2Et
O
CO2Et
O
NH
N
NH
NH
N
N
N
N
Cl
Cl
5s (79%)
Br
F
F
Cl
O
5q (78%)
5t (82%)
5r (73%)
CO2Et
CO2Et
CO2Me
CO2Et
O
O
CO2Et
CO2Me
O
O
CO2Et
O
CO2Et
O
O
O
NH
NH
NH
N
N
NH
N
N
Cl
O
Cl
Cl
Cl
5v(70%)
5x (77%)
5u (67%)
5w(69%)
CO2Me
CO2Et
CO2Me
CO2Me
CO2Me
CO2Me
O
O
O
CO2Me
CO2Et
O
O
O
O
O
NH
NH
NH
NH
N
N
N
N
Cl
Cl
Cl
5y (73%)
O
O
O
5b' (78%)
5z (67%)
5a' (78%)
CO2Et
CO2Et
CO2Et
O
CO2Me
CO2Me
O
CO2Et
O
O
O
O
NH
NH
N
NH
N
N
Cl
5e' (82%)
5d' (79%)
5c' (73%)
aIsolated Yields (%)

5
The zinc ferrite nanoparticles were prepared following a
reported procedure.20 The nanoparticles were characterized by
scanning electron microscopy (SEM), powder X-ray diffraction
(XRD), high-resolution transmission electron microscopic
(HRTEM) analysis, EDX with elemental analysis, and solid state
UV spectroscopy (For the preparation and other characterization
see ESI†).
respectively. According to the cubic crystal structure of spinel
phase, the values of lattice parameter a determined from the most
intense (311) reflection of XRD patterns using the formula
(1/d2 = (h2 + k2 + l2)/a2, h k l = 3 1 1) are 8⋅503 Å, well
hkl
consistent with that of bulk ZnFe2O4.21
[311]
The SEM study of ZnFe2O4 sample (Figure 3a) reveals
that the homogeneous nanoparticles of the sample are in compact
arrangement with roughly spherical shape. Due to the clustering
of most of the nano-particles, it was difficult to determine the
exact size and shape of the particles. Hence, the exact size and
shape of the ZnFe2O4 particles were examined by HRTEM
images.
C
B
A
High-resolution transmission electron microscopic
(HRTEM) at an accelerating voltage of 200kV was employed to
know the morphology and size of prepared ZnFe2O4
nanoparticles calcined at 800 ºC (Figure 3b). It is clear from the
image in Figure 3(b) that the spherically shaped ZnFe2O4
nanoparticles have diameter within the range of ~95-150 nm
which is also in accordance with the result calculated using the
Scherrer formula. Elemental analyses of the as-synthesized
ZnFe2O4 nanoparticles were performed at EDX equipped onto
TEM. Quantitative EDX showed that Fe, Zn and O were the
main elemental components (Figure 3c).
20
30
40
50
60
2θ (Degree)
Figure 4. X-ray diffraction pattern of ZnFe2O4 nanopowder
calcined for 6h at different temperature (A) 30 °C, (B) 400 °C,
and (C) 800 °C.
(a)
(b)
A probable mechanism for the formation of 5a has been
depicted in Scheme 3 which emphasizes the dual role of ZnFe2O4
as a Lewis acidic site, as well as basic site.4 Normal spinel
structure of ZnFe2O4 can be represented as (Zn2+) (Fe3+)2 (O2−)4
where Fe3+ ions occupy the octahedral holes whereas diamagnatic
Zn2+ remains in the tetrahedral holes. Both the octahedral and the
tetrahedral holes of the spinel structure are well defined by the
O2− ions.22-24 Thus in ZnFe2O4 the Fe3+ ions of Fe2O3 part act as a
strong Lewis acid acceptor and the O2− ions, which remain in the
lattice site in the ZnFe2O4 spinel, act as a base in the reaction.
The strong Lewis acidic site Fe3+ activates the carbonyl oxygen
of isatin to facilitate the condensation between p-toluidine and
isatin in the formation of imine intermediate A. The enolisation
of dimedone is also catalysed by Fe3+, which is further assisted
by the proton abstraction of basic O2− ion. The nucleophilic
attack of the enol form of dimedone on dimethyl
acetylenedicarboxylate generates the intermediate B. This
process is probably catalyzed by Zn2+ through to the polarization
of the π-electron cloud. The intermediate B is converted to C
through the abduction of proton from water. Then C is converted
to intermediate D through the abstraction of proton by the O2−
ions of lattice sites which act as base. The negative charge on the
sp2 hybridised carbon atom of D is stabilised by the strong Lewis
acidic site Fe3+ which subsequently attacks intermediate A
leading to the formation of intermediate E. In the conversion of E
to F, Fe3+ of ZnFe2O4 plays a dual role by enhancing the
electrophilicity of carbonyl group of dimedone and also by
bringing the nitrogen centre of p-toluidine and carbonyl centre of
dimedone of E in close proximity for the ring closure. Finally
dehydration of F generates the product 5a.
(c)
Figure 3. (a) SEM image of ZnFe2O4 nanopowder; (b) TEM images
of ZnFe2O4 NPs and (c) TEM-EDX of ZnFe2O4 nanopowder.
Powder XRD study was carried out to confirm the crystalline
nature of as-synthesized zinc ferrite nanoparticles. The XRD
pattern of ZnFe2O4 NPs, calcined at different temperature (400 ºC
and 800 ºC) and the comparison with the pattern of ZnFe2O4 NPs
at room temperature are displayed in Figure 4. The diffraction
peaks at 2θ values of 30.0, 35.0, 36.2, 42.8, 53.8, and 56.6 can be
assigned to the (220), (311), (221), (222), (400), (422), and (511)
planes which clearly index the cubic spinel structure of ZnFe2O4,

6
Tetrahedron
Fe3+
O
N
HO
NH
NH2
O
O
O
N
N
H
N
H
H
A
Fe3+
O
O
O
H
O
O
O
O
O
O
CO2Me
O
H
O
H
O
O
Zn2+
O
O
C
H
H
CO2Me
2-
2-
OO
-O
H
2-
O
2-
O
C
O
B
O
CO2Me
CO2Me
O
O
O
CO2Me
O
CO2Me
CO2Me
O
H
CO2Me
O
CO2Me
O
NH
NH
NH
N
N
N
O
_
N
OH
O
MeO2C
O
N
H
Fe3+
Fe3+
D
A
5a
F
E
Scheme 3. Plausible mechanism for the formation of 5a.
Stability, recovery and extension of reusability are very
In conclusion, ZnFe2O4 nanopowder has been emerged to be a
important factors for the practical application of a heterogeneous
catalyst. Therefore a series of experiments were carried out to
recover and reuse the ZnFe2O4 NPs for the reaction between
stable yet highly active recyclable bimetallic heterogeneous
catalyst for the facile one-pot four-component synthesis of 3-
spiroheterocyclic 2-oxindoles in water medium at room
temperature. These alkaloids analogous are readily prepared from
inexpensive starting materials in moderate to high yield under a
green, straightforward, efficient and highly economical reaction
conditions in shorter time. This is a promising approach from
sustainable and practical chemistry points of view. We believe
that the convenient and efficient ZnFe2O4 catalyzed 4CRs, and
the interesting activities of the catalyst as described in the
mechanism will encourage the fellow scientists to design new
methodologies within the frame of Green Chemistry principles.
isatin,
dimedone,
p-toluidine,
and
dimethyl
acetylenedicarboxylate under the optimized reaction conditions
(Table 1, entry 11). After the solvent extraction of the product 5a,
the solid catalyst was separated from the water medium by
simple filtration, which was then thoroughly washed with ethanol
and ethyl acetate, dried under vacuum and reused in a new cycle.
The catalyst was recovered and reused upto five times with
almost unaltered catalytic activity (Figure 5).
80
70
60
50
40
30
20
10
0
Acknowledgments
K.D. thanks UGC New Delhi, India for offering him Senior
Research Fellowship (SRF). The financial assistance of CSIR,
New Delhi is gratefully acknowledged [Major Research Project,
No. 02(0007)/11/EMR-II]. The authors are thankful for the
support and co-operation of Dibyendu Mondal, Department of
Polymer Science & Technology, University of Calcutta. We also
acknowledge DST-FIST for Single Crystal Diffractometer
Facility and Centre for Research in Nanoscience and
Nanotechnology (CRNN), University of Calcutta for
instrumental facilities.
1
2
3
4
5
1
2
3
4
5
Supplementary Material
Number of Runs
All spectroscopic data can be found in supporting information
file. Supplementary data to this article can be found online at
http://
Figure 5. Reusability of ZnFe2O4 NPs for the formation of 3-
spiroheterocyclic 2-oxindoles.

7
17. Pathak, S.; Debnath, K.; Pramanik, A. Beilstein J. Org. Chem.
2013, 9, 2344.
18. Pathak, S.; Debnath, K.;. Mollick, Md. M. R.; Pramanik, A. RSC
Adv. 2014, 4, 23779.
References and notes
19. General synthetic procedure for the preparation of 5a-eꢀ: A
mixture of arylamines (1.0 mmol), acetylenedicarboxylates (1.0
mmol), isatins (1.0 mmol), and cyclic 1,3-diketones (1.0 mmol)
was taken in a 100 ml round bottom flask. Then 10 ml water and
20 mol % of the ZnFe2O4 nanopowder were added to the flask.
The resultant mixture was stirred for 2h at room temperature.
1.
Bon, R. S.; Hong, C. G.; Bouma, M. J.; Schmitz, R. F.; Kanter, F.
J. J.; Lutz, M.; Spek, A. L.; Orru, R. V. A. Org. Lett. 2003, 5,
3759.
2.
3.
4.
Ikegami, S.; Hamamoto, H. Chem. Rev. 2009, 109, 583.
Wang, C. T.; Willey R. J. J. Catal. 2001, 202, 211.
Das, P.; Dutta, A.; Bhaumik, A.; Mukhopadhyay, C. Green
Chem. 2014, 16, 1426.
Dandia, A.; Singh, R.; Khaturia, S.; Mérienne, C.; Morgant, G.;
Loupy, A. Bioorg. Med. Chem. 2006, 14, 2409.
Edmondson, S.; Danishefsky, S. J.; Sepp-lorenzinol, L.; Rosen,
N. J. Am. Chem. Soc. 1999, 121, 2147.
After completion of the reaction (when the starting materials were
completely disappeared as per thin layer chromatography
projection), the reaction mixture was ultrasonicated by ethyl
acetate (10 ml) for 10 min. The separated organic phase was
concentrated to get the crude product which was purified by silica
gel column chromatography (ethyl acetate/hexanes) to afford the
spiro-compounds (5a-eꢀ). The solid catalyst was collected from
water layer by simple filtration with sintered funnel. The
recovered catalyst was washed several times with water, ethyl
acetate and finally by acetone, dried in a desiccator and used for
another run.
5.
6.
7. Galliford, C.V.; Scheidt, K.A. Angew Chem Int Ed 2007, 46,
8748.
8.
Venkatesan, H.; Davis, M. C.; Altas, Y.; Snyder, J. P.; Liotta, D.
C. J. Org. Chem. 2001, 66, 3653.
9. Joshi, B. S.; Rao, P. G.; Rogers, D.; Singri, B. P.; Williams, D. J.
Indian J. Chem., Sect. B 1984, 23B, 101.
20. Sato, T.; Haneda, K.; Seki, N.; Iijima, T. Appl. Phys. A: Solid Surf.
10. Rottmann, M.; McNamara, C.; Yeung, B. K. S.; Lee, M. C. S.;
Zou, B.; Russell, B.; Seitz, P.; Plouffe, D. M.; Dharia, N. V.; Tan,
J.; Cohen, S. B.; Spencer, K. R.; Gonzalez-Paez, G. E.;
Lakshminarayana, S. B.; Goh, A.; Suwanarusk, R.; Jegla, T.;
Schmitt, E. K.; Beck, H. B.; Brun, R.; Nosten, R.; Renia, L.;
Dartois, V.; Keller, T. H.; Fidock, D. A.; Winzeler, E. A.;
Diagana, T. T. Science, 2010, 1175.
11. Schönhaber, J.; Müller, T. J. J. Org. Biomol. Chem. 2011, 9, 6196.
12. D’Souza, D. M.; Rominger, F.; Müller, T. J. J. Angew. Chem., Int.
Ed. 2005, 44, 153.
1990, A50, 13.
21. Swamy, P. M. P.; Basavaraja, S.; Lagashetty, A.; Rao, N. V. S.;
Nijagunappa, R.; Venkataraman, A. Bull. Mater. Sci. 2011, 34,
1325.
22. Anantharaman, M. R.; Jagatheesan, S.; Malini, K. A.; Sindhu, S.;
Narayanasamy, A.; Chinnasamy, C. N.; Jacobs, J. P.; Reijne, S.;
Seshan, K.; Smits, R. H. H.; Brongersma, H. H. J. Magn. Magn.
Mater. 1998, 189, 83.
23. Thomas, M.; George, K. C. Indian J. Pure Appl. Phys. 2009, 47,
81.
13. Singh, G. S.; Desta, Z. Y. Chem. Rev. 2012, 112, 6104.
14. Sun, J.; Sun, Y.; Gao, H.; Yan, C.-G. Eur. J. Org. Chem. 2012,
2012, 1976.
24. Mohai, I.; Szépvölgyi, J.; Bertóti, I.; Mohai, M.; Gubicza, J.;
Ungár, T. Solid State Ionics 2001, 141, 163.
15. Kundu, A.; Pathak, S.; Pramanik, A. Asian J. Org. Chem. 2013, 2,
869.
16. Debnath, K.; Pathak, S.; Pramanik, A. Tetrahedron Lett. 2014, 55,
1743.
Click here to remove instruction text...