Recyclable, magnetic ionic liquid bmim[FeCl4]-catalyzed, multicomponent, solvent-free, green synthesis of quinazolines

Article abstract of DOI:10.1039/c3ra42039f

An atom-efficient, eco-friendly, solvent-free, high yielding, multicomponent green strategy to synthesize highly functionalized quinazoline derivatives by the one-pot reaction of 2-aminobenzophenone, aromatic aldehyde and ammonium acetate is presented. Ma

Full text of DOI:10.1039/c3ra42039f

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Recyclable, magnetic ionic liquid bmim[FeCl4]-
catalyzed, multicomponent, solvent-free, green
Cite this: DOI: 10.1039/c3ra42039f
synthesis of quinazolines3
Sumit Kumar Panja and Satyen Saha*
An atom-efficient, eco-friendly, solvent-free, high yielding, multicomponent green strategy to synthesize
highly functionalized quinazoline derivatives by the one-pot reaction of 2-aminobenzophenone, aromatic
aldehyde and ammonium acetate is presented. Magnetic IL, butylmethylimidazolium tetrachloroferrate
(bmim[FeCl4]) has been used successfully as a catalyst in a multicomponent synthetic strategy for the first
time. The catalytic cycle and a tentative reaction mechanism were discussed and experimentally verified.
Structural and optical properties of the synthesized quinazolines are also described.
Received 25th April 2013,
Accepted 20th May 2013
DOI: 10.1039/c3ra42039f
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knowledge pertaining to its storage, stability etc. In this regard,
information on the electronic properties of quinazoline
Introduction
moieties is very helpful.9 Several attempts have been made to
introduce a combinatorial library of this valuable binuclear
heterocycle over the last few decades, but most of the
syntheses were done without concern for environmental
friendliness, and involve the use of hazardous and volatile
solvents10 as well as toxic and expensive metal catalysts,11
cumbersome chromatographic separations,13g and high tem-
perature conditions.12 Cost effectiveness, commercial unavail-
ability of starting materials, prolonged reaction times and
multistep reaction processes13 are among the other major
concerns. A catalyst-free, solvent-free, microwave assisted
reaction methodology was developed by Prajapati and cow-
orkers recently to synthesise quinazoline and dihydroquinazo-
line derivatives.13g Though this method is brilliant, it lacks
selectivity. Zhang et al. have developed an iodine-catalyzed
quinazoline synthesis where an extra oxidant additive is used
at high temperature; a relatively prolonged reaction time was
also required.13h Dabiri et al. synthesized quinazolines using
an ionic liquid as a catalyst but at a high temperature.13i
Considering the above mentioned drawbacks, which include
eco-suitability factors, we intend to provide an eco-friendly,
green protocol to fabricate these biologically significant
substituted Quinazolines.
Nowadays, synthetic organic chemistry is focused on the
conversion of difficult synthetic protocols to easier and
greener strategies to produce known complexes as well as
entirely new organic moieties.1 One useful synthetic technique
which has been very recently explored by some research
groups, is the multicomponent strategy by which a multistep
reaction can be done within a single operation in one pot,2
with the use of environmentally benign, nonhazardous ionic
liquids as solvents as well as catalysts3 or by doing a reaction
under solvent-free conditions.4 Although, performing an
organic reaction in an environmentally suitable manner is a
challenge to chemists. Our main area of research is to explore
the synthesis and utility of different ionic liquids for
application in greener versions of organic syntheses.5
Quinazoline is an important class of binuclear heterocyclic
organic scaffold which is present as a core entity in several
naturally occurring alkaloids,6a–e microorganisms,6f and in
several life saving drugs such as gefitinib (Iressa),6g–h and
erlotinib6i–j (Tarceva). Some suitably substituted quinazoline
derivatives have been shown to have anticancer,7a–b antitu-
bercular,7c antibacterial,7d–f and antiviral activities.7g–h A few of
them are known to act as selective inhibitors of the tyrosine
kinase activity of the epidermal growth factor receptor
(EGFR).8 As this moiety is ubiquitous in modern drugs, its
use on bacteria and other microorganisms demands sound
Recently a new class of ionic liquid, namely magnetic ionic
liquids, has attracted lots of attention due to its unique
characteristics.14
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi-
221005, India. E-mail: ssahabhu@yahoo.com; Fax: +91-542-2368127;
Tel: +91-542-6702464
Butylmethylimidazoliumtetrachloroferrate (bmim[FeCl4])
(Fig. 1) is a representative of this class of ionic liquid and
has interesting physical properties.15 Due to the presence of
Electronic supplementary information (ESI) available: detailed experimental
3
procedure, separation techniques, electronic spectra, NMR spectra of all
compounds. CCDC 871913 (4n) and 915059 (isolated intermediate C). For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3ra42039f
2
the paramagnetic FeCl4 anion, this class of ionic liquid
responds to the presence of a magnet.15a Due to its remarkable
catalytic activity, stability and ease of synthesis,15a,16 it has
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Fig. 1 Chemical structure of bmim[FeCl4].
been efficiently used as a catalyst for Friedel–Crafts acyla-
tion,17a aryl Grignard cross-coupling of alkyl halides,17b and
glycolysis of poly(ethylene terephthalate),17c and also as a
‘liquid fixed-bed’ catalyst in flow applications.17d To the best of
our knowledge, bmim[FeCl4] has never been used as a catalyst
in any multicomponent reaction. Herein we report the
bmim[FeCl4]-catalyzed, multicomponent, solvent-free, one-
pot reaction of substituted 2-aminoarylketone, substituted
benzaldehyde and ammonium acetate at moderate tempera-
ture, to produce quinazolines in excellent yields.
Scheme 1 Optimization of the reaction conditions.
Table 2 Recycling and reuse of the catalyst (bmim[FeCl4])a
Entry
Reaction Cycles
Yieldb(%)
1
2
3
4
1st
95
93
93
91
2nd
3rd
4th
a
Substrate 1a (1 mmol), 2a (1 mmol) and ammonium acetate (2.5
mmol) were heated and stirred with 5 mol% of bmim[FeCl4] under
optimized reaction conditions. After reaction completion, the
Results and discussion
Initially, we started our investigation by placing 1 mmol of
2-aminobenzophenone 1a, 1 mmol of benzaldehyde 2a, 2.5
mmol of ammonium acetate 3 and 0.1 mmol of freshly
prepared15a magnetic ionic liquid (bmim[FeCl4]) in one pot
under solvent-free conditions. This mixture was then stirred at
room temperature for 8 h which provided the desired
quinazoline 4a in 80% yield, with 17% of 1a remaining
unreacted. But when the reaction was performed at a slightly
elevated temperature (40 uC), it is interesting to note that the
complete conversion of the starting material to the desired
product (94% yield) was observed within 2.5 h. To optimise the
reaction conditions i.e., temperature, catalyst loading etc., we
performed a few sets of the above mentioned reaction by
varying one or more of the reaction parameters as presented in
Table 1 and Scheme 1.
b
catalyst was recovered and successively reused. Isolated pure yield.
intermediate 49a was formed after 10 h of heating at 60 uC
(Table 1, entry 9–11). When 49a was separated from the
reaction mixture and 2.5 equivalents of NH4OAc and 0.05
equivalents of bmim[FeCl4] catalyst were added and stirred for
2.5 h at 40 uC, the desired product 4a was obtained. This
observation unambiguously highlights the merit of
bmim[FeCl4] as a catalyst in these multicomponent reactions.
Among other solvents that were used in representative sets of
these reactions, only ethanol provided the desired product 4a
in 93% yield within 2.5 h (Table 1, entry 6). It was noticed that
if acetonitrile and toluene were used as a reaction medium,
the reaction stopped at its initial step and only the
intermediate 49a was produced (Table 1, entry 7–8). Hence, 5
mol% of bmim[FeCl4] at 40 uC in the absence of solvent were
It was observed that in the absence of catalyst, the reaction
did not occur and the starting materials remained unreacted
(Table 1, entry 12). Interestingly, when either FeCl3, bmim[PF6]
or bmim[BF4] was used as the catalyst, only the uncyclized
Table 1 Optimization of the reaction conditionsa
Entry
Catalyst (mol %)
3 (equivalents)
Temp. (uC)
Solvent
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
bmim[FeCl4] (10)
bmim[FeCl4] (10)
bmim[FeCl4] (10)
bmim[FeCl4] (5)
bmim[FeCl4] (2)
bmim[FeCl4] (5)
bmim[FeCl4] (5)
bmim[FeCl4] (5)
FeCl3 (10)
NH4OAc (2.5)
NH4OAc (2.5)
NH4OAc (5)
25
40
40
40
40
40
60
60
60
60
60
60
Neat
Neat
Neat
Neat
8
80
94
92
95
2.5
2.5
2.5
5
2.5
10
10
10
10
10
10
NH4OAc (2.5)
NH4OAc (2.5)
NH4OAc (2.5)
NH4OAc (2.5)
NH4OAc (2.5)
NH4OAc (2.5)
NH4OAc (2.5)
NH4OAc (2.5)
NH4OAc (2.5)
Neat
82
Ethanol
MeCN
Toluene
Neat
Neat
Neat
93
53c
42c
74c
70c
65c
9
10
11
12
bmim[PF6] (10)
bmim[BF4] (10)
None
d
Neat
—
a
Reaction conditions: 1a (1 mmol), 2a (1 mmol) and ammonium acetate (2.5 mmol) were heated with stirring, with varying concentrations of
b
c
d
catalyst, either in ethanol or under solvent-free (neat) conditions. Isolated pure yield. Uncyclized product 49a. No reaction.
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Table 3 Synthesis of quinazoline derivatives
Table 3 (Continued)
Time Yielda
Time Yielda
Entry Reactant 1 Reactant 2 Product 4
(h)
(%)
Entry Reactant 1 Reactant 2 Product 4
(h)
(%)
1
1a
2a
2.5
95
13
14
1c
1c
2c
3.5
91
2
3
4
1a
1a
1a
2b
2c
2d
2.5
2.5
2.5
94
92
91
2d
3.5
86
a
Isolated pure yield.
determined to be the optimum reaction conditions for the
reaction of substituted 2-aminobenzophenone 1, substituted
benzaldehyde 2, and 2.5 mmol of ammonium acetate to
produce the desired quinazolines 4 in maximum yield in the
minimum time (Table 1, entry 4).
5
6
7
1a
1b
1b
2e
2a
2b
1.5
2.5
2.5
92
95
94
Since for any catalytic reaction, recyclability of the catalyst
is a very important parameter, we investigated the recyclability
of this magnetic ionic liquid. For this purpose, after comple-
tion of the reaction, 20 mL of diethylether was added to the
reaction mixture. It was then shaken well and the ethereal
layer was decanted before washing the crude reaction mixture
with ether (3 6 10 mL). The residue was dried under vacuum
at 45 uC for 2 h, yielding the ionic liquid in its activated form.
This was then subjected directly to another reaction, affording
again the desired product in high yield. The ethereal layer was
evaporated and washed with water, followed by ethanol, to
obtain the pure product. Finally, the product was crystallized
from ethanol. Even after recycling the catalyst four times, the
activity of the catalyst remained the same and almost
quantitative yield was obtained each time (Table 2).
8
9
1b
1b
2c
2.5
2.5
91
91
We have examined the suitability of this method for a
variety of aromatic aldehydes (Table 3). It can be clearly
observed that substitution of the aldehyde did not appreciably
affect the yield of the desired product. However, the presence
of a nitro group at the C-5 position of 2-aminobenzophenone
affects the reaction time significantly (Table 3, entry 11–14). In
all cases, the products were characterized by detailed analysis
2d
1
of H and 13C NMR, FT–IR and ESI–MS. Further regioselective
10
1b
2e
1.5
93
formation of the desired product (4n, Table 3, entry 14) and
the structure of isolated intermediate C were confirmed by
single crystal X-ray diffraction (SCXRD) data analysis. ORTEP
diagrams of the structures obtained from SCXRD are
presented in Fig. 2 and 3.18
The as-described bmim[FeCl4]-catalyzed transformation of
isolated intermediate 49a into quinazoline 4a indicates that
the first step of these multicomponent reactions is the
condensation of the aldehyde with 2-aminobenzophenone,
and not the attack of ammonium acetate as presumed
previously in the literature.12b,13g
11
12
1c
1c
2a
2b
3.5
3.5
89
92
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Fig. 2 ORTEP diagram of 6-nitro-2-(2-nitrophenyl)-4-phenylquinazoline (4n)
(atoms at 50% ellipsoid probability).
Scheme 2 Proposed reaction mechanism.
In view of the above experimental facts, we propose a
tentative mechanism for this multicomponent reaction, which
is depicted in Scheme 2. Initially the counter-cation, bmim+, of
the ionic liquid, bmim[FeCl4], acts as a Lewis acid, catalyzing
the condensation of the NH2 group of substrate 1 with the
carbonyl group of aldehyde 2, to furnish intermediate 49x. This
intermediate is the only product when bmim[BF4] or
bmim[PF6] is used as the catalyst. In the next step, 49x is
transformed into A through condensation of the carbonyl
group with ammonia, which is obtained from NH4OAc. In the
third step, the proton from the ketimine intermediate A is
in the constituent naphthalene ring. Therefore, we further
extended our study to understand the optical behaviour, in
addition to the substitution effect on the ring, of various
synthesized quinazoline derivatives containing variable chro-
mophores and auxochromes at different positions. The UV–vis
absorption spectra of quinazoline derivatives in acetonitrile
consist of two main bands at 310–425 nm and 240–300 nm
(see Fig. 4). The shorter wavelength band is attributed to the p
A p* transition in the aromatic ring, and the longer
wavelength band was found to be due to the n A p* transition.
The overlapping band at the shorter wavelength region arises
due to the partial overlap of n and p* orbitals of auxochrome.
The electron withdrawing substituent at the 6th position of the
quinazoline ring significantly affects the absorption band
maximum (4a, 4d, 4l, 4m) and makes the band vibrationally
structured (4l). The peak positions and molar extinction
coefficients in acetonitrile solvent are tabulated and provided
2
abstracted by FeCl4 (the counter-anionic component of the
catalyst). Other ionic liquids such as bmim[BF4] or bmim[PF6]
2
2
are unable to catalyze this step as BF4 and PF6 are not
capable of abstracting the proton as mentioned earlier
(Table 1, entry 9–11). The catalyst is regenerated through H+
abstraction by intermediate B, giving rise to relatively stable
intermediate C.12b,13g The intermediate C is then converted to
the desired product 4 via aerial oxidation.
The stability of the H+FeCl42bmim+ intermediate plays an
important role in this reaction. Here, bmim[FeCl4] acts as an
efficient catalyst due to the synergistic effect of the cation and
anion in this reaction.17c
in the ESI.
3
UV-Visible measurements
These quinazoline derivatives reveal characteristic and inter-
esting optical properties due to the presence of a hetero-atom
Fig. 4 UV-Visible spectra of selected quinazoline derivatives in acetonitrile
(concentrations of 4a, 4d, 4m and 4l are 16.6, 36.6, 29.1 and 25.6 micromolar
respectively).
Fig. 3 ORTEP diagram of Intermediate C 2-(6-chloro-4-phenyl-1,2-dihydroqui-
nolin-2-yl)phenol (atoms at 50% ellipsoid probability).
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6 (a) A. L. D’yakonov and M. V. Telezhenetskaya, Chem. Nat.
Compd., 1997, 33, 221; (b) C. Wattanapiromsakul, P.
I. Forster and P. G. Waterman, Phytochemistry, 2003, 64,
609; (c) Z. Z. Ma, Y. Hano, T. Nomura and Y. J. Chen,
Heterocycles, 1997, 46, 541; (d) D. Yonghong, X. Rensheng
and Y. J. Yang, Chin. Pharm. Sci., 2000, 9, 116; (e)
B. Somanadhan, C. Leong, S. R. Whitton, S. Ng, A.
D. Buss and M. S. Butler, J. Nat. Prod., 2011, 74, 1500; (f)
S. Yoshida, T. Aoyagi, S. Harada, N. Matsuda, T. Ikeda,
H. Naganawa, M. Hamada and T. Takeuchi, J. Antibiot.,
1991, 44, 111; (g) K. Waisser, J. Gregor, H. Dostal, J. Kunes,
L. Kubicova, V. Klimesova and J. Kaustova, Farmaco, 2001,
56, 803; (h) J. Kunes, J. Bazant, M. Pour, K. Waisser,
M. Slosarek and J. Janota, Farmaco, 2000, 55, 725; (i)
S. Tanaka, Y. Sakamori, M. Niimi, M. Hazama, Y. H. Kim
and K. Yanagihara, Trials, 2011, 12, 120; (j) F. A. Shepherd,
J. R. Pereira and T. N. Ciuleanu, N. Engl. J. Med., 2005, 353,
123.
7 (a) L. A. Doyle and D. D. Ross, Oncogene, 2003, 22, 7340; (b) E.
A. Henderson, V. Bavetsias, D. S. Theti, S. C. Wilson,
R. Clauss and A. L. Jackman, Bioorg. Med. Chem., 2006, 14,
5020; (c) K. Waisser, J. Gregor, H. Dostal, J. Kunes,
L. Kubicova, V. Klimesova and J. Kaustova, Farmaco, 2001,
56, 803; (d) P. P. Kung, M. D. Casper, K. L. Cook, L. Wilson-
Lingard, L. M. Risen, T. A. Vickers, R. Ranken, L. B. Blyn,
R. Wyatt, P. D. Cook and D. J. J. Ecker, J. Med. Chem., 1999,
42, 4705; (e) S. Jantova, K. Spirkova, S. Stankovsky and
P. Duchonova, Folia Microbiol., 1999, 44, 187; (f) G. Grovera
and S. G. Kini, Eur. J. Med. Chem., 2006, 41, 256; (g) T.
C. Chien, C. S. Chen, F.-H. Yu and J. W. Chern, Chem. Pharm.
Bull., 2004, 52, 1422; (h) T. Herget, M. Freitag, M. Morbitzer,
R. Kupfer, T. Stamminger and M. Marschall, Antimicrob.
Agents Chemother., 2004, 48, 4154.
Conclusions
We have described a simple, efficient, solvent-free, one-pot,
multicomponent reaction, catalyzed by
a magnetic IL
(bmim[FeCl4]) for the synthesis of quinazoline derivatives,
and established the reaction pathways and catalytic cycle with
the help of experimental evidence. It has been observed that
the reaction is much superior to other reported synthetic
methods, in terms of its simplicity, high yield, absence of any
chromatographic separation technique, easier recyclability
and high catalyst stability. Furthermore, UV-visible spectro-
scopic studies have revealed that the optical properties of
various derivatives are affected by the substitutions at the 6th
position of the quinazoline ring.
Acknowledgements
We gratefully acknowledge the generous financial support
from the Council of Scientific and Industrial Research (CSIR,
Project No. 01(2210)/08/EMR-II)). Department of Chemistry,
Banaras Hindu University is acknowledged for providing
infrastructure facilities.
References
1 (a) P. J. Dunn, Chem. Soc. Rev., 2012, 41, 1452; (b)
N. Isambert, M. del M. S. Duque, J.-C. Plaquevent,
Y. Genisson, J. Rodriguez and T. Constantieux, Chem. Soc.
Rev., 2011, 40, 1347.
2 (a) I. Ugi, Pure Appl. Chem., 2001, 73, 187; (b) Synthesis of
Heterocycles via Multicomponent Reactions, ed. R. V. A. Orru
and E. Ruijter, Springer, Heidelberg, New York, 2010, Vol-1
& Vol-2; (c) A. Domling, Chem. Rev., 2006, 106, 17; (d)
S. Maeda, S. Komagawa, M. Uchiyama and K. Morokuma,
Angew. Chem., Int. Ed., 2011, 50, 644; (e) E. Ruijter,
R. Scheffelaar and R. V. A. Orru, Angew. Chem., Int. Ed.,
2011, 50, 6234; (f) Multicomponent Reactions, ed. J. Zhu and
H. Bienayme, Wiley-VCH, Weinheim, Germany, 2005.
3 (a) M. A. P. Martins, C. P. Frizzo, D. N. Moreira, N. Zanatta
and H. G. Bonacorso, Chem. Rev., 2008, 108, 2015; (b) Ionic
Liquids in Organic Synthesis, ed. S. V. Malhotra, ACS,
Washington DC, 2007; (c) J. P. Hallett and T. Welton, Chem.
Rev., 2011, 111, 3508; (d) T. Welton, Chem. Rev., 1999, 99,
2071; (e) Handbook of Green Chemistry, ed. P. Wasserscheid
and A. Stark, WILEY-VCH Verlag, Weinheim, 2010.
4 (a) K. Tanaka and F. Toda, Solvent-free Organic Synthesis,
Wiley-VCH, Weinheim, 2003; (b) A. Corma and H. Garcia,
Chem. Rev., 2003, 103, 4307; (c) W. M. Nelson, Green
Solvents for Chemistry Perspectives and Practice, Oxford
University Press, Oxford, New York, 2003; (d) T. Chanda, R.
K. Verma and M. S. Singh, Chem.–Asian J., 2012, 7, 778; (e)
S. Choudhury and M. S. Singh, RSC Adv., 2012, 2, 4547.
5 (a) M. Shukla, N. Srivastava and S. Saha, J. Mol. Struct.,
2010, 975, 349; (b) S. Saha, S. Hayashi, A. Kobayashi and
H. Hamaguchi, Chem. Lett., 2003, 32, 740; (c) R. Ozawa,
S. Hayashi, S. Saha, A. Kobayashi and H. Hamaguchi,
Chem. Lett., 2003, 32, 948.
8 (a) P. A. Ple, T. P. Green, L. F. Hennequin, J. Curwen,
M. Fennell, J. Allen, C. L. Brempt and G. Costello, J. Med.
Chem., 2004, 47, 871.
9 (a) A. Militaru, A. Smarandache, A. Mahamoud, V. Damian,
`
P. Ganea, S. Alibert, J.-M. Pages and M.-L. Pascu, AIP Conf.
Proc., 2010, 13, 1364; (b) F. Arjmand, S. Parveen, M. Afzal,
L. Toupet and T. B. Hadda, Eur. J. Med. Chem., 2012, 49,
141; (c) J.-J. Aaron and M. Maafi, Spectrochim. Acta, Part A,
1995, 51, 603; (d) S. Bakalova and J. Kaneti, Spectrochim.
Acta, Part A, 2000, 56, 1443.
10 (a) P. Verhaeghe, N. Azas, M. Gasquet, S. Hutter, C. Ducros,
M. Laget, S. Rault, P. Rathelota and P. Vanelle, Bioorg. Med.
Chem. Lett., 2008, 18, 396; (b) C. Huang, Y. Fu, H. Fu,
Y. Jiang and Y. Zhaoa, Chem. Commun., 2008, 6333; (c)
W. Xu, Y. Jin, H. Liu, Y. Jiang and H. Fu, Org. Lett., 2011, 13,
1274; (d) B. Han, X.-L. Yang, C. Wang, Y.-W. Bai, T.-C. Pan,
X. Chen and W. Yu, J. Org. Chem., 2012, 77, 1136; (e) W. Xu
and H. Fu, J. Org. Chem., 2011, 76, 3846.
11 (a) J. Zhang, C. Yu, S. Wang, C. Wan and Z. Wang, Chem.
Commun., 2010, 46, 5244; (b) B. Han, C. Wang, R.-F. Han,
W. Yu, X. -Y. Duan, R. Fang and X.-L. Yang, Chem. Commun.,
2011, 47, 7818; (c) B. Ma, Y. Wang, J. Peng and Q. Zhu, J. Org.
Chem., 2011, 76, 6362; (d) J. Vicente, M. T. Chicote, A.
J. Martinez-Martinez, D. Bautista and P. G. Jones, Org.
Biomol. Chem., 2011, 9, 2279.
12 (a) M. Adib, S. Ansari, A. Mohammadi and H. R. Bijanzadeh,
Tetrahedron Lett., 2010, 51, 30; (b) Z.-H. Zhang, X.-N. Zhang,
L.-P. Mo, Y.-X. Li and F.-P. Ma, Green Chem., 2012, 14, 1502.
This journal is ß The Royal Society of Chemistry 2013
RSC Adv.

View Article Online
Paper
RSC Advances
13 (a) S. V. Niementowski, J. Prakt. Chem., 1895, 51, 564; (b)
Y. Kabri, A. Gellis and P. Vanelle, Green Chem., 2009, 11,
201; (c) S. Ferrini, F. Ponticelli and M. Taddei, Org. Lett.,
2007, 9, 69, and the references therein; (d) F. Portela-
Cubillo, J. S. Scott and J. C. Walton, J. Org. Chem., 2009, 74,
4934; (e) X. Li, Z. Mao, Y. Wang, W. Chen and X. Lin,
Tetrahedron, 2011, 67, 3858; (f) J. R. Li, X. Chen, S. D. X. hi,
S. L. Ma, Q. Li, Q. Zhang and J. H. Tang, Org. Lett., 2009, 11,
1193; (g) R. Sarma and D. Prajapati, Green Chem., 2011, 13,
718; (h) J. Zhang, D. Zhu, C. Yu, C. Wan and Z. Wang, Org.
Lett., 2010, 12, 2841; (i) M. Dabiri, P. Salehi and
M. Bahramnejad, Synth. Commun., 2010, 40, 3214; (j) V.
Z. Parchinsky, O. Shuvalova, O. Ushakova, D.
V. Kravchenko and M. Krasavin, Tetrahedron Lett., 2006,
47, 947; (k) W. Szczepankiewicz, P. Wagner, M. Danicki and
J. Suwinski, Tetrahedron Lett., 2003, 44, 2015; (l) J. M. Cobb,
M. T. Fiorini, C. R. Goddard, M.-E. Theoclitou and C. Abell,
Tetrahedron Lett., 1999, 40, 1045; (m) R. Alonso,
A. Caballero, P. J. Campos, D. Sampedro and M.
F. Sun, S. Ling and J.-Z. Zhang, J. Phys. Chem. B, 2012, 116,
6461; (d) I. de. Pedro, D. P. Rojas, J. Albo, P. Luis,
A. Irabien, J. A. Blanco and J. R. Fernandez, J. Phys.:
Condens. Matter, 2010, 22, 296006.
15 (a) S. Hayashi and H. Hamaguchi, Chem. Lett., 2004, 33,
1590; (b) S. Hayashi, S. Saha and H. Hamaguchi, IEEE
Trans. Magn., 2006, 42, 12; (c) Y. Yoshida and G. J. Saito, J.
Mater. Chem., 2006, 16, 1254.
16 (a) M. S. Sitze, E. R. Schreiter, E. V. Patterson and R.
G. Freeman, Inorg. Chem., 2001, 40, 2298; (b) Q. Zhang,
J. Yang, X. Lu, J. Gui and M. Huang, Fluid Phase Equilib.,
2004, 226, 207.
17 (a) M. H. Valkenberg, C. de Castro and W. F. Holderich,
Appl. Catal., A, 2001, 215, 185; (b) K. Bica and P. Gaertner,
Org. Lett., 2006, 8, 733; (c) H. Wanga, R. Yan, Z. Li, X. Zhang
and S. Zhang, Catal. Commun., 2010, 11, 763; (d) V. Misuka,
¨
D. Breucha and H. Lowea, Chem. Eng. J., 2011, 173, 536.
18 The crystallographic coordinates have been deposited with
the Cambridge Crystallographic Data Centre; deposition
nos. CCDC 871913 (4n) and CCDC no. 915059 for isolated
intermediate C. This data can be obtained free of charge
from the Cambridge Crystallographic Data Centre, 12
Union Rd., Cambridge CB2 1EZ, UK or via www.ccdc.ca-
m.ac.uk/conts/retrieving.html.
´
A. Rodrıguez, Tetrahedron, 2010, 66, 4469; (n) Y. Cheng,
Synth. Commun., 1996, 26, 475.
14 (a) M. Okuno and H. Hamaguchi, Appl. Phys. Lett., 2006, 89,
132506; (b) R. H. Herber, I. Nowik, M. E. Kostner,
V. Kahlenberg, C. Kreutz, G. Laus and H. Schottenberger,
Int. J. Mol. Sci., 2011, 12, 6397; (c) J.-G. Li, Y.-F. Hu, S.-
RSC Adv.
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