Nanodomain cubic cuprous oxide as reusable catalyst in one-pot synthesis of 3-alkyl/aryl-3-(pyrrole-2-yl/indole-3-yl)-2-phenyl-2,3-dihydro-isoindolinones in aqueous medium

Article abstract of DOI:10.1039/c3ra46168h

An environmentally benign one-pot protocol has been developed for the syntheses of 3-alkyl/aryl-3-(pyrrole/indole-2/3-yl)-2-phenyl-2,3-dihydro- isoindolinones via a multi-component one-pot reaction involving 2-iodo-N-phenylbenzamides, terminal alkyne and substituted indoles/pyrroles in aqueous medium using cubic cuprous oxide nanoparticles as catalyst. It involves domino Sonogashira-5-exo-dig-cyclization followed by regioselective nucleophilic addition of indoles or pyrroles, in aqueous medium without using any surfactants or additional ligands. The Royal Society of Chemistry 2014.

Full text of DOI:10.1039/c3ra46168h

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Nanodomain cubic cuprous oxide as reusable
catalyst in one-pot synthesis of 3-alkyl/aryl-3-
(pyrrole-2-yl/indole-3-yl)-2-phenyl-2,3-dihydro-
isoindolinones in aqueous medium†
Cite this: RSC Adv., 2014, 4, 7024
Received 28th October 2013
Accepted 24th December 2013
Swarbhanu Sarkar,‡a Nivedita Chatterjee,‡a Manas Roy,‡b Rammyani Pal,‡a
DOI: 10.1039/c3ra46168h
c
a
*
Sabyasachi Sarkar and Asish Kumar Sen
www.rsc.org/advances
An environmentally benign one-pot protocol has been developed for
the syntheses of 3-alkyl/aryl-3-(pyrrole/indole-2/3-yl)-2-phenyl-2,3- for various pharmaceuticals and natural products.5 Because of
dihydro-isoindolinones via multi-component one-pot reaction the structural diversity of biologically active indoles and
Different indoles and pyrroles are essential building blocks
a
involving 2-iodo-N-phenylbenzamides, terminal alkyne and substituted pyrroles, there is always a challenge to develop new or improved
indoles/pyrroles in aqueous medium using cubic cuprous oxide nano- methods for the syntheses of indole and pyrrole derivatives.
particles as catalyst. It involves domino Sonogashira-5-exo-dig-cycli- Palladium, rhodium, and ruthenium salts having bidentate N,P-
zation followed by regioselective nucleophilic addition of indoles or or N,N-ligands are widely used as catalysts in selective C–H and
pyrroles, in aqueous medium without using any surfactants or addi- C–C bond functionalization.6 However, these limit their wide
tional ligands.
applications in industry, as the catalysts are expensive. Utiliza-
tion of coordinated copper(I) complexes are supposed to be one
of the most enthralling alternatives.3c,7 The presence of ancillary
ligands prevent the aggregation of central metal ion by
chelating the metal or by increasing its solubility and thus
increases the efficiency of the metal catalyst. However, the use
of copper may introduce Glaser-type homocoupling products.8
The signicant difference of the nanostructured copper(I)
oxide in comparison to bulk materials with respect to reactivity,
stability in aqueous medium, environmental compatibility,
non-toxicity and large surface/volume ratio,9 makes nano-cop-
per(I) oxide more promising compared to expensive palladium
systems for the Sonogashira-type cross-coupling reactions.
Various methods have been reported for the production of
nanodomain copper(I) oxide having varied morphologies viz.
spheres,10 wires,11 cubes,12 polyhedral,13 and hollow-struc-
tures.14 But, only few applications of copper(I) oxide nano-
particles as catalyst are reported in organic synthesis.15 In the
present study we have envisaged the application of cubic
cuprous oxide nanoparticles as reusable catalyst for the
synthesis of 3-alkyl/aryl-3-(pyrrole/indole-2/3-yl)-2-phenyl-2,3-
dihydro-isoindolinones via one-pot multi-component reaction
involving 2-iodo-N-phenylbenzamides, terminal alkyne and
substituted indoles/pyrroles in aqueous medium. The protocol
involves domino Sonogashira-5-exo-dig-cyclization followed by
regioselective nucleophilic addition of indoles or pyrroles. The
process eliminates the use of palladium, organic solvents,
ligands, or the presence of any additional activator and
surfactants. Cubic cuprous oxide nanoparticles used in the
reaction was synthesized by the reduction of cupric chloride
There has been an increasing demand for the development of
environment friendly chemical processes for the syntheses of a
variety of organic compounds on industrial and laboratory
scales.1 Among the different methodologies, considerable
attention has been given to executing organic reactions in
water.2 A number of organic transformations together with
metal-mediated coupling reactions have now been accom-
plished at ambient temperature using water as the only
solvent.2,3 Substantial attention has also been given for the use
of sonochemical processes3b,4 for the syntheses of different
pharmacophores. These processes may afford products from
relatively simple starting materials and in high yield. Ultrasonic
techniques disperse soluble or insoluble molecules with
uniform shapes and geometry4b and thus, they oen provide a
high reaction rate compared to conventional procedures. So,
the use of ultrasonication is a better option for the emerging
concept of ‘Green chemistry’.
aChemistry Division, CSIR-Indian Institute of Chemical Biology, 4 Raja S. C. Mullick
Road, Jadavpur, Kolkata-700032, India. E-mail: asishksen@yahoo.com; aksen@iicb.
res.in; Fax: +91 33 24735197; Tel: +91 33 24995720
bDepartment of Chemistry, Indian Institute of Technology, Kanpur-208016, India
cDepartment of Chemistry, Bengal Engineering and Science University, Shibpur,
Howrah-711103, India
† Electronic supplementary information (ESI) available. CCDC 967591. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3ra46168h
‡ Contributed equally to the work.
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dihydrate in aqueous medium using fructose as reducing as
well as stabilizing agent at 60–65 ꢀC. Using this methodology, a
library of substituted isoindolinones was synthesized in high
yield and in short reaction time. In this context, it is worthwhile
to mention that cuprous oxide nanoparticles were synthesized
under non-hazardous condition as mentioned earlier. The
uniqueness of the protocol lies in its eco-friendly operation,
effective one-pot synthesis, reusability of the catalyst and
generation of unique scaffolds in excellent yield.
At the outset, we opted 2-iodo-N-(4-urophenyl)benzamide
(1a), phenylethyne (2a) and pyrrole (3a) as model reactants and
investigated the feasibility of our domino one-pot strategy to
produce pyrrolyl isoindolinone (4a) in water using commercially
available bulk copper(I) salts as catalyst under sonication
(Scheme 1). However, it gave poor to moderate yield (47%) in
presence of K3PO4 and various organic or inorganic bases and
even aer prolonged heating at elevated temperature. K3PO4
acts as base as well as stabilizer of the metal ions.16 The poor
yield compelled us to add n-Bu4NCl, n-Bu4NBr or n-Bu4NBF4 in
the reaction medium as activator.15a Even so the yield of the
reaction remained unaffected. The use of other bases did not
signicantly improve the outcome of the reaction. Our previous
approach towards the synthesis of similar scaffolds using cop-
per(I) iodide as catalyst and the utilization of various ionic or
non-ionic surfactants along with extra ligands produced the
products in good to moderate yield.3d Therefore, we re-designed
the reaction strategy.
Fig. 1 (a) FTIR spectrum; (b) powder XRD patterns; (c) SEM and (d) TEM
image of the synthesized cuprous oxide nanoparticles.
and in the presence of cuprous oxide nanoparticles instead of
bulk salts the yield of the reaction increased signicantly by 15–
20% even in the absence of surfactants/activators or ligands.
Sonication played a crucial role in the reaction. It dispersed all
the molecules and insoluble nanocatalyst in water allowing them
to come to close proximity for better reaction. It is worth
mentioning that in absence of sonication the yield of the product
was found to be reduced. The effect of different organic and
Being low-priced and non-toxic in nature, cuprous oxide or
cuprous oxide nanoparticles were long been used as an active
catalyst in many reactions.15 The nanodomain copper(I) oxide
was synthesized from cupric chloride using fructose as reducing
as well as capping agent. The formation of the nanoparticle was
conrmed using various techniques. The FTIR spectrum
[Fig. 1(a)] showed strong peak at 627 cmꢁ1 and was assigned as
the characteristic Cu(I)–O vibrational frequency for cuprous
oxide.17 The powder XRD pattern [Fig. 1(b)] of the synthesized
cuprous oxide nanoparticles clearly indicated the typical
reection patterns of cuprite (JCPDS no. 77-0199).18 The peaks
with 2q values at 29.4ꢀ, 36.4ꢀ, 42.4ꢀ, 61.4ꢀ, 73.4ꢀ and 77.5ꢀ were
attributed to the crystal plane of 110, 111, 200, 220, 311 and 222
respectively. The scanning electron microscopy (SEM) [Fig. 1(c)]
and transmission electron microscopy (TEM) images [Fig. 1(d)]
showed the regular cubic shape of the Cu2O particles with an
average edge length of 180 ꢂ 20 nm.
i
inorganic bases, viz. Et3N, DBU, Pr2EtN, K3PO4, Na2CO3, K2CO3
and Cs2CO3 was also explored subsequently (Table 1). Cs2CO3
appeared to be the most effective when employed in 2.0 molar
equiv. and afforded the product in maximum yield (Table 1, entry
9). It may therefore be concluded that the inorganic bases worked
better in comparison to organic bases.
The scope and generality of this methodology was then
tested with a variety of N-substituted benzamides and pyrroles/
indoles (Table 2). All reactions yielded pyrrolyl- or indolyl-
dihydro-isoindolinones as major product and structures of all
Table 1 Effect of the different bases on the yield of 4a
Entrya
Base
Amount (mol equiv.)
Time (min)
Yieldb (%)
1
2
3
4
7
8
9
10
11
12
Et3N
DBU
2.0
2.0
2.0
2.0
2.0
2.0
2.0
1.5
2.5
2.0
30
30
30
30
30
30
30
30
30
40
63
59
67
60
82
84
87
83
87
87
The relevance for the synthesis of 3-alkyl/aryl-3-(pyrrole/
indole-2/3-yl)-2-phenyl-2,3-dihydro-isoindolinones with cuprous
oxide nanoparticles was investigated next. It was found that
under similar reaction condition as described earlier (Scheme 1)
iPr2EtN
K3PO4
Na2CO3
K2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
a
All reactions were performed using 1a (1 mmol), 2a (1.5 mmol) and 3a
(1.5 mmol) in water at 50 ꢀC under sonication in aerobic condition.
Cubic Cu2O nanomaterial (10 mol%) was used. Increase in reaction
time or temperature did not provide better yield of the product.
b
Yield of isolated pure product; some loses during isolation is
unavoidable in certain cases.
Scheme 1 Synthesis of 4a in aqueous medium.
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Table 2 Reactions of 2-iodo-N-phenylbenzamide (1a–d), ethynes (2a–d) and pyrroles/indoles (3a, 4a–e) leading to pyrrolyl/indolyl-dihydro-
isoindolinones (5a–k) in aqueous medium
Amide
Alkynes
Pyrroles/indole
Product
Entrya
Yieldb (%)
1
2
3
1a: R1 ¼ F
1a
2a: R2 ¼ H
2b: R2 ¼ F
2a
3a: R3 ¼ H
5a: R1 ¼ F, R2 ¼ H, R3 ¼ H
5b: R1 ¼ F, R2 ¼ F, R3 ¼ H
5c: R1 ¼ OMe, R2 ¼ H, R3 ¼ H
87
91
85
3a
3a
1b: R1 ¼ OMe
4
1b
3a
78
2c
5d: R1 ¼ OMe, R3 ¼ H
5
1a
3a
72
2d
5e: R1 ¼ F, R3 ¼ H
6
2c
3a
70
1c
5f
7
2e: R2 ¼ OMe
3a
80
1d
5g
8
1a
2a
81
4a: R3 ¼ H; R4 ¼ H
5h: R1 ¼ H, R3 ¼ H, R4 ¼ H
5i: R1 ¼ H, R3 ¼ H, R4 ¼ NO2
5j: R1 ¼ H, R3 ¼ H, R4 ¼ OMe
9
10
1a
1a
2a
2a
4b: R3 ¼ H; R4 ¼ NO2
4c: R3 ¼ H; R4 ¼ OMe
80
87
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Table 2 (Contd.)
Amide
Alkynes
Pyrroles/indole
Product
Entrya
Yieldb (%)
11
1a
2a
2a
76
4e
3a
5k
5a
12
70
1d
a
All reactions were performed using 1 (1 equiv.), 2 (1.0 equiv.) and 3–4 (1.5 equiv.) in water at 50 ꢀC for 30 min under aerobic condition in presence
b
of nanodomain cuprous oxide (0.1 equiv.) and Cs2CO3 (2 equiv.). Yield of isolated pure product; some loses during isolation is unavoidable in
certain cases.
compounds were characterized by NMR and MS spectroscopy.
The reusability of the nanoparticles towards the synthesis of
With pyrroles the reaction was found to occur at C-2 where as pyrrolyl dihydro-isoindolinones (5a) was also studied and the
with unsubstituted or N-substituted indoles, the reactions were results are summarized in Table 3. Aer each reaction, using
found to occur selectively at C-3 as expected, and the reaction the same reaction methodology, the nanocatalyst were sepa-
occurred at C-2 with 3-substituted indoles (Table 2, entry 11). rated by centrifugation and thoroughly washed with EtOH–H2O
The reaction also proceeded well with amide with an aliphatic for reuse. TEM images of the Cu2O nanocubes aer three times
group (Table 2, entry 6 and 7). It is interesting to mention that use indicated unchanged morphology of the nanoparticles
the aliphatic alkynes (Table 2, entry 4–6), and aryl bromides (Fig. 2). It was found that the catalyst exhibited a marginal loss
(Table 2, entry 12) gave equally good result under the same in activity aer three recycles. To ascertain of the reduced
reaction condition. It may be noted that no signicant reactivity of the nanodomain cuprous oxide due to surface
amount of Glaser coupling product was obtained in any case. oxidation, similar reactions were carried out under anaerobic
However, the reaction failed to proceed with substituted pyrrole condition. The results are also summarized in Table 3.
such as 1-benzyl-2-(benzyloxymethyl)-1H-pyrrole. Other nucleo-
In conclusion, we have established an efficient one
philic substrates such as furan and thiophene did not react under pot environmentally benign and cost-effective process for
the same reaction condition. This is possibly because of the the syntheses of pyrrolyl-/indolyl-dihydro-isoindolinones,
reduced nucleophilicity of the substrates.
in aqueous medium even under aerobic conditions. We
A plausible mechanism for the formation of pyrrolyl/indolyl demonstrated that inexpensive nanodomain cuprous oxide
isoindolinones (5a–k) is shown in Scheme 2. It is expected that could be used as a reusable and competent catalyst for this
copper(I) initially forms pi–alkyne complex, which makes the protocol. The capping of fructose may prevent the aerial
alkyne terminal proton acidic. Subsequently, in presence of oxidation of the nanodomain cuprous oxide. However its
base, copper acetylide is formed. The activated acetylide reacts reuse showed reduced catalytic activity. In the fourth cycle the
with iodobenzamides and Sonogashira product is generated in activity of cuprous oxide is signicantly dropped. To ascertain
situ. The triple bond is then again activated by nanodomain the reason we checked with a control reaction with freshly
cuprous oxide, which in presence of base undergoes 5-endo-dig synthesized nanocuprous oxide, which under nitrogen did
cyclization. Nanodomain cuprous oxide, presumably acting as not show surface oxidation for extended hours in water as
Lewis acid, activates the double bond which subsequently solvent used in the synthesis. However, under air, the catalyst
undergoes aromatic electrophilic substitution by indoles/ aer extended time of 16 h showed a positive test for the
pyrroles to form nal compounds.
presence of cupric ion conrming surface oxidation of the
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Scheme 2 Plausible mechanism for the formation of pyrrolyl/indolyl isoindolinones.
Table
3 Recoverability of cuprous oxide nanoparticles for the
environment friendly and eliminates the use of heavy metal
catalysts.
synthesis of pyrrolyl dihydro-isoindolinones (entry 5a)a
Reusability of the catalyst
1st
2nd
3rd
4th
Experimental
Synthesis of cubic Cu2O nanoparticles
Yield (%) under aerobic condition
Yield (%) under anaerobic condition
87
89
84
86
80
84
72
82
a
Typically, the nanodomain Cu2O was synthesized by the
following procedure. To a solution of CuCl2 in water (0.01 M,
100 mL), NaOH (0.2 M, 10 mL) was added drop wise under
constant stirring. The colour of the solution changes from green
to blue due to the formation of Cu(OH)2. Fructose (1 M, 10 mL)
in water was then added to it and stirring was continued at 60 ꢀC
for 1 h. The precipitates gradually changed from green to yellow
indicating the formation of Cu2O nanoparticles. The solution
was then allowed to settle for 1 h for complete nucleation. It was
then centrifuged, and the precipitate was washed with water
(ꢃ3) and ethanol (ꢃ3) and dried under vacuum.
Yield of isolated pure product; some loses during isolation is
unavoidable in certain cases.
Characterization of Cu2O nanoparticles
The powder XRD of cubic Cu2O nanoparticles was carried out by
X-ray diffraction (ISO-DEBYEFLEX-2002-RICH, SEIFERT & CO)
using CuKa radiation with graphite monochromator. FT-IR
spectra of the sample were recorded using Bruker Fourier
transforms infrared spectrometer with a KBr beam splitter and
Fig. 2 (a) TEM image of cuprous oxide nanoparticles before reaction;
(b) TEM image of cuprous oxide nanoparticles after 3 times use.
catalyst and this could be the reason for reduced reactivity. DTGS/KBr detector. Morphology of Cu2O nanoparticles was
Therefore, for extended use of the same catalyst, the same characterized by SUPRA 40VP Field Emission Scanning Electron
reaction should be carried out under anaerobic conditions. Microscope (CARL ZEISS NTS GmbH, Oberkochen (Germany))
Cuprous oxide acts as a heterogeneous catalyst. The use of equipped with energy dispersive X-ray (EDX) facility. Samples
ultrasound dispersed the catalyst evenly and increases its for SEM were prepared by dispersing Cu2O (3 mg) nano-parti-
surface area making the reaction efficient. Even then, there is cles in ethanol (10 mL) and dispersed sample (50 mL) was
always a scope for the development of soluble catalysts. deposited onto brass stubs and vacuum dried. Samples for TEM
Exclusion of surfactants, additional activators or extra ligands were prepared by dropping dispersed solution (5 mL) of Cu2O on
makes the protocol signicantly simple, less expensive, a carbon coated copper TEM grid (400 mess) and then allowing
tolerant and versatile. Most importantly the process is to dry under vacuum. Imaging was performed by using Tecnai
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General procedure for the preparation of 3-alkyl/aryl-3-(pyrrole/
indole-2/3-yl)-2-phenyl-2,3-dihydro-isoindolinones derivatives
In an open round-bottomed ask containing water (20 mL),
iodobenzamides (1, 1.0 equiv.), alkynes (2, 1.5 equiv.), indoles
or pyrroles (3 or 4, 1.5 equiv.), cuprous oxide nanomaterials
(0.1 equiv.) and Cs2CO3 (2.0 equiv.) were added and stirred
vigorously under sonication for 30 min at 50 ꢀC when TLC
indicated completion of the reaction. The mixture was then
centrifuged to separate nanoparticles; supernatant was extrac-
ted with ethyl acetate (3 ꢃ 30 mL) and washed thoroughly with
water. Column chromatography (petroleum–EtOAc) produced
pure product (5a–k). The nanoparticles were washed with
ethanol–water twice for reuse.
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