One-pot synthesis of various 2-amino-4H-chromene derivatives using a highly active supported ionic liquid catalyst

Article abstract of DOI:10.1039/c6ra06523f

In this paper, a supported ionic liquid catalyst (SILC) was synthesized by dissolving palladium acetate in [BMIM][OH] and immobilizing it on the surface of HAP. Further, it was characterized by SEM, TEM, TGA, FTIR, AAS and EDAX. This SILC was then used to

Full text of DOI:10.1039/c6ra06523f

RSC Advances
View Article Online
View Journal | View Issue
PAPER
One-pot synthesis of various 2-amino-4H-
chromene derivatives using a highly active
Cite this: RSC Adv., 2016, 6, 32052
supported ionic liquid catalyst†
a
a
Pankaj Sharma, Monika Gupta, Rajni Kantb and Vivek K. Guptab
*
In this paper, a supported ionic liquid catalyst (SILC) was synthesized by dissolving palladium acetate in
[BMIM][OH] and immobilizing it on the surface of HAP. Further, it was characterized by SEM, TEM, TGA,
FTIR, AAS and EDAX. This SILC was then used to synthesize various derivatives of chromenes under
solvent-free conditions in excellent yields. The products obtained were characterized by 1H NMR, 13C
NMR and mass analysis. One of the products, 2-amino-4-(3-nitrophenyl)-6,6,8,8-tetrahydro-7,7-
dimethyl-5-oxo-4H-chromene-3-carbonitrile, was also characterized by single crystal X-ray
crystallography.
Received 11th March 2016
Accepted 14th March 2016
DOI: 10.1039/c6ra06523f
www.rsc.org/advances
of ionic liquids and heterogeneous catalysis such as desig-
nability, good solubility of catalytically active species, ease of
Introduction
handling, separation and recycling. In this context, ionic liquids
are now widely used for immobilization of homogeneous cata-
lysts.6–9 Recently, ionic liquids are also used as hybrid materials
called ionogels well reviewed by Bideau et al.10
Recently, the growing awareness to environmental issues has
focused the need for greener and more sustainable technologies
in the chemical industry. Ionic liquids, which consist of cations
and anions with low melting points and very low vapor pres-
sures,1–3 are in tremendous demand and undergoing serious
growth. Many different ionic liquids have been prepared and
have been successively used as solvents as well as modied
catalysts. Zhang et al. have reviewed the recent advances in ionic
liquid catalysis and expressed briey the recent used catalytic
techniques.4 Heterogeneous catalysis is preferred in industrial
processes compared to homogeneous catalysis as the extraction
of product and catalyst recovery is easier in heterogeneous
catalysis.5 A catalytic system which has advantages of both
homogeneous and heterogeneous catalysis can be a better
option. The homogeneous catalysts in ionic liquids usually
provide the advantages of high catalytic activity and good
selectivity. However, their widespread use in homogeneous
conditions is associated with some drawbacks such as product
isolation, catalyst recovery and large amount of expensive ionic
liquids are used which may cause possible toxicological
concerns. The use of ionic liquids in heterogeneous form has
been established to overcome these drawbacks and moreover,
supported solid catalysts with ionic liquid combine the benets
Because of considerable and attractive properties of sup-
ported ionic liquid catalysis, earlier also we reported the
synthesis of various compounds using these catalysts.11–14 Here,
we intend to design a catalyst combining the homogeneous
nature of ionic liquid and palladium having high activity and
selectivity with heterogeneous support to provide large interfa-
cial reaction areas. The supported ionic liquid phase catalysis
concept is based on a classical homogeneous catalyst that is
dissolved in a thin lm of ionic liquid which is further
dispersed over the high internal surface of a porous support. In
supported ionic liquid phase materials, the dissolved catalyst
still acts microscopically as a homogeneously dissolved metal
complex in its uniform ionic liquid environment while macro-
scopically dry solid form that can be recycled easily.
Palladium is known to catalyze many reactions and is also
reported in literature to synthesize chromene derivatives.15 The
HAP support was chosen to enhance the basic nature of the
catalyst and to provide heterogeneity to catalyst. Thus hetero-
geneous catalyst formed has its own advantages including
larger interfacial reaction area, ease of product separation, cost-
effective, recyclability and environment friendly.
aDepartment of Chemistry, University of Jammu, Jammu – 180006, India. E-mail:
monika.gupta77@rediffmail.com
Chromene derivatives are interesting heterocyclic
compounds with numerous pharmacological and biological
properties including antitumor,16 antiallergic,17 antimicrobial
and antifungal,18 anti-proliferative19 and antioxidant.20 These
compounds are also involved in central nervous system activi-
ties21 and also used in the eld of biodegradable agrochemi-
cals22 and pigments.23
bDepartment of Physics and Electronics, University of Jammu, Jammu – 180006, India
† Electronic supplementary information (ESI) available: Spectral data of the
products and crystallography data collection and renement and selected
geometric parameters (A, ꢀ) of the crystal structure. CCDC 1400076. For ESI and
˚
crystallographic data in CIF or other electronic format see DOI:
10.1039/c6ra06523f
32052 | RSC Adv., 2016, 6, 32052–32059
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
There are number of methods24–30 reported in literature for
RSC Advances
synthesis of these heterocycles using homogeneous and
heterogeneous catalysts. Recently, Majumdar et al. published
a review on catalytic synthesis of 2H-chromenes involving
different catalysts.15 Although these methods are effective but
are associated with some drawbacks like use of high tempera-
ture, long reaction times, low yield, difficult work-up procedures
and harsh reaction conditions. Savitha et al.31 synthesized
chromene derivatives involving complex strategy using
Pd(OAc)2 as catalyst with stoichiometric quantities of CuBr2 and
LiBr. Scheidt and coworkers32 developed enantioselective Pd-
catalyzed synthesis of 2-aryl chromenes. However, in this
method besides Pd catalyst potassium carbonate, methanol,
methylene chloride are used making the whole procedure
complex. Mondal et al. have synthesized these chromene
derivatives in facile way using metal-free mesoporous organo-
catalyst.33 However the time taken to complete the reaction is
longer and the preparation of catalyst is complex. Recently,
Kundu and Bhaumik have reported the synthesis of chromenes
using triazine based polymer catalyst.34 Although this method
involves recyclability and eco friendly synthesis but again the
reaction time is longer. Thus, our motto was to use supported
ionic liquid catalysis accompanying simple, cost effective,
reusable and co-benign method, providing high yields in lesser
time under solvent-free conditions.
Fig. 1 Illustration of the synthesis of supported ionic liquid catalyst.
TGA-DTA analysis (Fig. 4) was employed to investigate the
thermal stability of catalyst, since observed weight loss is
associated with loss of components attached to the surface.
ꢀ
The small amount of weight loss below 150 C was attributed
to desorption of physically adsorbed gases, water and minor
residual solvent. However the curve gradually starts decreasing
from 150 ꢀC onwards upto 277 ꢀC which was attributed to
decomposition of alkyl chains of ionic liquid and anionic part
of ionic liquid and showed sharp decline in weight upto 370 ꢀC
can be due to decomposition of cationic core of ionic liquid.
Results and discussion
Preparation of SILC (HAP–Pd–[BMIM][OH])
ꢀ
The loss above 370 C can be attributed to decomposition of
HAP.
[BMIM][OH] (0.78 g, 5 mmol) in methanol (5 mL) was mixed
with hydroxyapatite (HAP) (5 g) in a round-bottomed ask (100
mL) and stirred at room-temperature for 10 h under inert
atmosphere and then dried under reduced pressure until free
owing powder was obtained. In another round-bottomed ask
(100 mL), [BMIM][OH] (1.56 g, 10 mmol) and palladium acetate
(0.112 g, 0.5 mmol) were dissolved in methanol (10 mL) and
stirred for 5 min. Aer this, hydroxyapatite pre-treated with
ionic liquid was suspended in this solution and the mixture was
reuxed for 10 h under inert atmosphere. Then solvent was
evaporated under reduced pressure to get free owing powder.
Then, it was dried in an oven at 200 ꢀC for 5 h. A general scheme
for the preparation of the catalyst is shown in Fig. 1.
According to EDX spectrum (Fig. 5) the presence of Pd is
indicated. The EDX spectrum also showed other elements
including C, N, O and Ca which are present in the SILC. The
amount of Pd loaded onto the surface of catalyst was deter-
mined by AAS analysis and found that 0.022 g of Pd was present
per gram of the catalyst.
FTIR spectrum (Fig. 6) of supported ionic liquid phase
catalyst displayed the PO43ꢁ bands at wave numbers 1093, 1062,
601 and 569 cmꢁ1. The hydroxyl bending bands of hydroxyap-
atite were identied at around 3570 cmꢁ1 and 624 cmꢁ1
whereas the hydroxyl bands of anionic part of ionic liquid were
displayed in a range from 3160–3392 cmꢁ1
.
Characterization of SILC
Optimization of reaction conditions
Particle morphology and textural properties of the catalyst were An efficient method for the preparation of chromene derivatives
studied carefully by scanning electron microscopy (SEM) and through the reaction of aldehydes, malononitrile and dimedone
transmission electron microscopy (TEM). The surface structure in the presence of catalytic amount of SILC as heterogeneous
of the catalyst was characterized by SEM micrographs. The catalyst has been described. In a preliminarily investigation on
views of surface are presented in Fig. 2. The SEM image of SILC the model reaction of 4-methoxybenzaldehyde, dimedone and
showed that the catalyst is a ne homogeneous powder with malononitrile (entry 10, Table 3), it was found that the reaction
porous structure. The TEM micrographs (Fig. 3) of the catalyst could be nished in the presence of catalytic amount of SILC
ꢀ
provided direct observation of the morphology. From TEM under solvent-free conditions at 80 C which gave the desired
micrographs it looks like that Pd with ionic liquid is distributed product in good yield. The effect of catalyst, reaction tempera-
on to the surface of HAP and there is no bulk aggregation of the ture, solvent and time of the reaction was systematically inves-
Pd–IL complex and is uniformly dispersed on to the surface of tigated. In order to optimize the amount of catalyst, model
HAP.
reaction was carried out with different amount of catalyst. With
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 32052–32059 | 32053

View Article Online
RSC Advances
Paper
Fig. 2 SEM micrograph of SILC.
Fig. 3 TEM images of SILC.
1 mmol of each reactant, reaction with 0.025 g, 0.05 g and 0.1 g increase in yield was observed with the increase in amount of
of catalyst was tried and it was found that 0.05 g of catalyst is catalyst. Thus, 0.05 g of catalyst was chosen as optimum
sufficient to get the product in good yield. No signicant amount to catalyze the reaction. In order to optimize the
Fig. 4 TGA-DTA curve of SILC.
32054 | RSC Adv., 2016, 6, 32052–32059
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
Fig. 5 EDX pattern of SILC.
ꢀ
temperature, model reaction was carried out at room- represented in Table 1. At room-temperature and 40 C, lower
ꢀ
temperature, 40 ꢀC, 60 ꢀC, 80 ꢀC and 100 ꢀC under solvent- yields of products were seen, whereas at 60 C, 70% yield was
free conditions using SILC as catalyst and results are obtained. The reaction was clean at 80 ꢀC and afforded excellent
Fig. 6 FTIR spectra of SILC.
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 32052–32059 | 32055

View Article Online
RSC Advances
Paper
Table 1 Effect of temperature studied in the synthesis of 2-amino- Table 2 Comparison of activity of the catalysts in the oxidation of
4H-chromenesa under solvent-free conditions benzyl alcohols and in the synthesis of chromene derivativesa
Entry
Temperature
Time (min)
Yieldb (%) Entry
Catalyst
Time (min)
Yieldb (%)
1
2
3
4
5
r.t.
20
10
10
10
10
20
40
70
96
96
1
2
3
4
5
No catalyst
HAP
HAP–Pd(OAc)2
Pd(OAc)2–IL
SILC
10
10
10
10
10
No rxn
Traces
50
60
96
40 ꢀC
60 ꢀC
80 ꢀC
100 ꢀC
a
a
Reaction conditions; p-methoxybenzaldehyde (1 mmol), dimedone (1
Reaction conditions; p-methoxybenzaldehyde (1 mmol), dimedone (1
mmol), malononitrile (1 mmol) and catalyst (0.05 g). b Isolated yield.
mmol), malononitrile (1 mmol) and catalyst (0.05 g for entries 2 and
5, 0.01 g Pd(OAc)2 and 0.05 g HAP for entry 3, 0.01 g Pd(OAc)2 and
0.05 g [BMIM][OH] for entry 4) and stirring at 80 ꢀC under solvent-free
conditions. b Isolated yield.
yield of desired product. There was no signicant improvement
in percentage yield of product at 100 ꢀC. Thus, 80 ꢀC was chosen
to be best temperature for the synthesis of 2-amino-4H-chro-
menes. Further we explored the effect of different solvents on
model reaction and results are presented in Fig. 7. Among
various solvents used, ethanol gave reasonable yield of 70% and
all other solvents were ineffective to give good yields. From the
gure it was concluded that solvent-less conditions are best to
carry out the synthesis of chromenes.
nitrophenyl)-6,6,8,8-tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-
3-carbonitrile was characterized by single X-ray crystallography
(CCDC: 1400076†) and revealed that the compound crystallizes in
ꢀ
a triclinic crystal system with P1 space group. The ORTEP view of
the molecule has been shown in Fig. 8.
In order to identify the role of supported ionic liquid
catalyst (SILC) as a heterogeneous catalyst, in the synthesis of
chromene derivatives, the test reaction was carried out in the
presence of HAP, HAP–[BMIM][OH], HAP–palladium acetate
and without catalyst. Among various catalysts used, HAP was
unable to carry the reaction, whereas combination of HAP with
ionic liquid or palladium acetate also gave low yield but sup-
ported ionic liquid catalyst gave best results (Table 2). SILC
combines the advantage of homogeneous and heterogeneous
nature of the catalyst. Moreover, the supported ionic liquid
catalyst can be easily recovered and recycled for several runs,
thus making process cost-effective with easy work-up. So,
supported ionic liquid catalyst (SILC) was used as a catalyst to
catalyze the reactions.
With the optimized reaction conditions, the synthesis of
chromenes was tried with range of substrates to study the scope
of this method and examples are summarized in Table 3. It was
observed that aromatic aldehyde bearing various functional
groups on phenyl ring and heterocyclic aldehydes all yielded
good amount of products. One of the product 2-amino-4-(3-
Recyclability
Being heterogeneous in nature, the important feature of
catalyst was its recyclability. To check the recyclability of SILC,
a series of 7 consecutive runs for the synthesis of chromenes
using 4-methoxybenzaldehyde were carried out and the results
are represented in Fig. 9 which demonstrates that SILC is
highly active and recyclable upto 7th run with very little loss of
activity.
Although, no signicant change in the activity of the catalyst
was observed, we performed the AAS of the catalyst aer 7th use
to determine any change in the catalyst. We observed nearly
same weight loss aer 7th use indicating no signicant change
in the structure of catalyst. Also there is negligible change from
0.022 g to 0.021 g of palladium loaded on per gram surface of
the catalyst aer 7 uses in both recycled catalysts as measured
by AAS indicating proper interaction between ionic liquid and
palladium due to polarity of ionic liquid.
Proposed mechanism for synthesis of chromenes
The plausible mechanism is shown in Fig. 10. The step 1
involves the activation of dimedone by the catalyst to attack
intermediate 1, which was formed in second step by the
nucleophilic attack of activated malononitrile on aldehyde.
The intermediate 2 formed undergoes cyclocondensation in
the presence of catalyst to give the nal product. Here,
catalyst is providing larger interfacial surface area to reaction
and moreover the structural and textural properties of the
catalyst are strongly inuenced by the presence of ionic
liquid which also provide polarity to catalytic system and
thus enhancing its activity. The whole catalytic system is
responsible to catalyze the reaction effectively and it is quite
difficult to justify the role of individual HAP, ionic liquid or
palladium acetate.
Fig. 7 Effect of different solvents studied in the synthesis of chromene
derivatives.
32056 | RSC Adv., 2016, 6, 32052–32059
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
Table 3 Supported ionic liquid catalyst catalyzed one-pot synthesis of 2-amino-4H-chromenesa
Entry
R
Time (min)
Yieldb (%)
Mp/Lit. (ꢀC)
1
2
3
4
5
6
7
8
C6H5
15
20
20
15
25
15
15
20
25
10
25
30
25
30
25
20
25
94
90
92
95
90
94
92
94
90
96
90
92
90
90
88
89
90
230–232/232–234 (ref. 35)
235–236/234–238 (ref. 36)
213–214/213–214 (ref. 35)
176–178/176–177 (ref. 35)
290–291/292–293 (ref. 37)
212–214/212–214 (ref. 35)
199–200/198–200 (ref. 35)
165–166/165–168 (ref. 35)
209–210/210–215 (ref. 38)
200–202/198–200 (ref. 35)
208–210/206–208 (ref. 35)
228–229/230 (ref. 38)
222–224/223–226 (ref. 35)
216–218/216–218 (ref. 39)
194–195/192–193 (ref. 40)
221–223/224–226 (ref. 41)
195–196/196–198 (ref. 38)
2-NO2C6H4
3-NO2C6H4
4-NO2C6H4
2-ClC6H4
4-ClC6H4
4-FC6H4
4-BrC6H4
9
4-MeC6H4
4-MeOC6H4
4-OHC6H4
4-OH-3-MeOC6H3
2-Furyl
10
11
12
13
14
15
16
17
2-Thienyl
2,4-Dichloro-C6H3
3-OHC6H4
2-MeOC6H4
a
Optimized reaction conditions: aldehyde (1 mmol), malononitrile (1 mmol), dimedone (1 mmol), SILC (0.05 g) and stirring at 80 ꢀC, solvent-free.
Isolated yield.
b
Fig. 8 The ORTEP view of 2-amino-4-(3-nitrophenyl)-6,6,8,8-tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-3-carbonitrile.
a SEM (JEOL) and TEM was recorded on a TECHNAI G2 20 S-
TWIN (FEI Netherlands). X-ray data of complex was collected
Experimental
General
on an X'calibur-Oxford Diffraction single crystal diffractometer
(Department of Physics and Electronics, University of Jammu,
Jammu) with CCD area-detector (graphite-monochromator, Mo-
The chemicals used were either prepared in our laboratory or
purchased from Sigma Aldrich or Merck chemical companies.
The 1H or 13C NMR data were recorded in CDCl3 or DMSO-d6 on
Bruker DPX 400 spectrometer. The FTIR spectra were recorded
on Perkin-Elmer spectrophotometer and mass spectral data
were recorded on Bruker Esquires 3000 (ESI). Thermal analysis
was carried out on DTG-60 Shimadzu thermal analyzer. The
amount of Pd in catalyst was determined by atomic absorption
spectrometric analysis (AAS) and was performed on an Avanta-
M atomic absorption spectrometer AAS. SEM was recorded on
˚
Ka radiations, l ¼ 0.71073 A).
General procedure for the synthesis of 2-amino-4H-
chromenes
SILC (0.05 g) was added to the mixture of an aldehyde (1
mmol), dimedone (1 mmol) and malononitrile (1 mmol) in
a round-bottomed ask (Scheme 1). Then, the reaction was
carried on a magnetic stirrer at 80 ꢀC for the appropriate time
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 32052–32059 | 32057

View Article Online
RSC Advances
Paper
Scheme 1 General procedure for synthesis of 2-amino-4H-chro-
menes using SILC.
Conclusion
In conclusion, we have explored the role of supported ionic
liquid catalysis in the synthesis of various derivatives of chro-
menes. SILC was prepared by simple method using HAP and
palladium acetate, and was quite efficient in synthesizing
derivatives of chromenes in excellent yields under solvent-free
conditions. This technique combines the most attractive
features of homogeneous catalysis like high activity and selec-
tivity with benets of heterogeneous catalysis such as large
surface area and easy product separation. Moreover it was
recyclable and catalyzed the reaction in less time with simple
work-up procedures and clean products were obtained. One of
the product 2-amino-4-(3-nitrophenyl)-6,6,8,8-tetrahydro-7,7-
dimethyl-5-oxo-4H-chromene-3-carbonitrile was also character-
ized by single crystal X-ray analysis and revealed that the
compound crystallizes in a triclinic crystal system.
Fig. 9 Recyclability graph of the SILC for the synthesis of chromene
derivatives.
as shown in Table 3. Aer completion of the reaction as
monitored by TLC, the mixture was treated with required
amount of ethylacetate and then catalyst was removed by
ltration at reduced pressure and washed with hot distilled
water. The ltrate was concentrated and cooled down to room
temperature until solid product was formed in crystalline
form. The product was ltered and crystallized from ethanol if
necessary. The products were characterized with 1H NMR, 13
NMR and mass spectrometry.
C
Fig. 10 Plausible mechanism for the synthesis of chromenes.
32058 | RSC Adv., 2016, 6, 32052–32059
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
18 (a) Z. Q. Xu, K. Pupek, W. J. Suling, L. Enache and
M. T. Flavin, Bioorg. Med. Chem., 2006, 14, 4610; (b) V. Jeso
and K. C. Nicolaou, Tetrahedron Lett., 2009, 50, 1161.
19 M. Brunavs, C. P. Dell, P. T. Gallagher, W. M. Owton and
C. W. Smith, Eur. Pat. Appl. EP, 557075 A1 19930825, 1993.
20 L. Alvey, S. Prado, V. Huteau, B. Saint-Joanis, S. Michel,
M. Koch, S. T. Cole, F. Tillequin and Y. L. Janin, Bioorg.
Med. Chem., 2008, 16, 8264; T. Symeonidis, M. Chamilos,
D. J. Hadjipavlou-Litina, M. Kallitsakis and K. E. Litinas,
Bioorg. Med. Chem. Lett., 2009, 19, 1139.
21 F. Eiden and F. Denk, Arch. Pharm., 1991, 324, 353.
22 E. A. A. Hafez, M. H. Elnagdi, A. G. A. Elagame and
F. M. A. A. El-Taweel, Heterocycles, 1987, 26, 903.
23 G. P. Ellis, The Chemistry of Heterocyclic of Compounds, ed. A.
Weissberger, Taylor EC John Wiley, New York, 1977, ch. II, p.
11.
24 S. M. Baghbanian, N. Rezaei and H. Tashakkorian, Green
Chem., 2013, 15, 3446.
25 Y. Peng and G. Song, Catal. Commun., 2007, 8, 111.
26 M. R. Naimi-jamal, S. Mashkouri and A. Shari, Mol.
Diversity, 2010, 14, 473.
27 R. Ballini, F. Bigi, M. L. Conforti, D. D. Santis, R. Maggi,
G. Oppici and G. Sartori, Catal. Today, 2000, 60, 305.
28 M. P. Surpur, S. Kshirsagar and S. Samant, Tetrahedron Lett.,
2009, 50, 719.
29 Z. Zhou, F. Yang, L. Wu and A. Zhang, Chem. Sci. Trans.,
2012, 1, 57.
Acknowledgements
We are thankful to the Director, Indian Institute of Integrative
Medicines Jammu for spectral facilities; Head of Central
Research facility section, Indian Institute of Technology Ropar
for SEM and Indian Institute of Technology Roorkee for TEM.
We also thank the Department of Chemistry, University of
Jammu for NMR, FTIR and TGA analysis. We are also thankful
to Department of Physics, University of Jammu for providing us
the XRD data of crystal obtained. One of the authors Rajni Kant
is thankful to Department of Science & Technology, Govern-
ment of India for the sanction of single crystal X-ray Diffrac-
tometer as a National Facility under Project No. SR/S2/CMP-47/
2003.
References
1 P. Wasserscheid and T. Welton, Ionic liquid in synthesis,
Wiley-VCH, Weinheim, 2008, vol. 1.
2 H. Weingartner, Angew. Chem., Int. Ed., 2008, 47, 654.
3 P. Wasserscheid and W. Keim, Angew. Chem., Int. Ed., 2008,
39, 3772.
4 Q. Zhang, S. Zhang and Y. Deng, Green Chem., 2011, 13, 2619.
5 I. F. J. Vankelecom and P. A. Jacobs, Catalyst immobilization
on inorganic supports, in Chiral Catalyst Immobilization and
Recycling, ed. D. E. De Vos, I. F. J. Vankelecom and P. A
Jacobs, Wiley – VCH Verlag GmbH, Weinheim, 2000, pp.
19–42.
6 C. P. Mehnert, Chem.–Eur. J., 2005, 11, 50.
7 A. Riisager, R. Fehrmann, M. Haumann and
P. Wasserscheid, Top. Catal., 2006, 40, 91.
8 Y. Gu and G. Li, Adv. Synth. Catal., 2009, 351, 817.
9 C. V. Doorslaer, J. Wahlen, P. Mertens, K. Binnemans and
D. D. Vos, Dalton Trans., 2010, 39, 8377.
30 R. Pratap and V. J. Ram, Chem. Rev., 2014, 114, 10476.
31 G. Savitha, K. Felix and P. T. Perumal, Synlett, 2009, 2079.
32 B. S. Zeng, X. Yu, P. W. Siu and K. A. Scheidt, Chem. Sci.,
2014, 5, 2277.
33 J. Mondal, A. Modak, M. Nandi, H. Uyama and A. Bhaumik,
RSC Adv., 2012, 2, 11306.
34 S. K. Kundu and A. Bhaumik, RSC Adv., 2015, 5, 32730.
35 H. Hu, F. Qiu, A. Ying, J. Yang and H. Meng, Int. J. Mol. Sci.,
2014, 15, 6897.
10 J. L. Bideau, L. Viau and A. Vioux, Chem. Soc. Rev., 2011, 40,
907.
11 P. Sharma and M. Gupta, Green Chem., 2015, 17, 1100.
12 P. Sharma, M. Gupta, R. Kant and V. K. Gupta, New J. Chem.,
2015, 39, 5116.
36 S. Zavar, Arabian J. Chem., DOI: 10.1016/j.arabjc.2012.07.011.
37 A. Akbaria and A. Hosseini-Nia, Iranian Journal of Organic
Chemistry, 2014, 6, 1183.
13 P. Sharma, M. Gupta, M. Gupta and R. Gupta, Aust. J. Chem.,
2016, 69, 230.
38 S. Rostamnia and A. Morsali, Inorg. Chim. Acta, 2014, 411,
113.
14 P. Sharma and M. Gupta, J. Chem. Sci., 2016, 128, 61.
15 N. Majumdar, N. D. Paul, S. Mandal, B. de Bruin and
W. D. Wulff, ACS Catal., 2015, 5, 2329.
16 S. J. Mohr, M. A. Chirigos, F. S. Fuhrman and J. W. Pryor,
Cancer Res., 1975, 35, 3750.
39 W. B. Sun, P. Zhang, J. Fan, S. H. Chen and Z. H. Zhang,
Synth. Commun., 2010, 40, 587.
40 K. Gong, H. L. Wang, J. Luo and J. L. Liu, J. Heterocycl. Chem.,
2009, 46, 1145.
41 D. Kumar, V. B. Reddy, S. Sharad, U. Dube and S. Kapur, Eur.
J. Med. Chem., 2009, 44, 3805.
17 K. Gorlitzer, A. Dehre and E. Engler, Arch. Pharm., 1983, 316,
264.
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 32052–32059 | 32059