c2cy20438j

2216 Catal. Sci. Technol., 2012, 2, 2216–2220 This journal is c The Royal Society of Chemistry 2012
Cite this: Catal. Sci. Technol., 2012, 2, 2216–2220
Self-assembled monolayer coated gold-nanoparticle catalyzed aerobic
oxidation of a-hydroxy ketones in water: an efficient one-pot synthesis
of quinoxaline derivativesw
Tamalika Bhattacharya, Tridib K. Sarma* and Sampak Samanta*
Received 10th May 2012, Accepted 3rd July 2012
DOI: 10.1039/c2cy20438j
For the first time, 4-aminothiophenol self-assembled monolayer-
coated gold-nanoparticles (Au-NPs) which catalyze the aerobic
oxidation of aryl substituted a-hydroxy ketones to aryl 1,2-diketones
are reported. In addition, a one-pot synthesis of quinoxalines has
been successfully achieved via in situ oxidation of a-hydroxy ketones
and subsequent condensation with aryl 1,2-diamines in water. This
method offers the potential for simple self-assembled monolayer-
coated Au-NPs to exhibit catalytic activity for the aerobic
oxidation reaction in a green and efficient manner.
Introduction
The exploration of gold nanoparticles (Au-NPs) as catalysts has
attracted tremendous attention in recent years in the context of
developing environmentally friendly and sustainable routes to a
myriad of important organic transformations.1
This development
is fuelled by the benign character of Au-NPs and their simplistic
synthesis with controlled sizes and compositions. The high
activity of Au in the nanometer dimension has led to several
reports of catalytically active Au-NP systems prepared in the
presence of supports, such as poly(N-vinyl-2-pyrrolidone),
polyaniline, coordination polymers, dendrimers and solid
oxide surfaces such as TiO2, CeO2, SiO2, Al2O3 etc.2
In these
systems, investigations related to the catalytic activity of Au has
been oriented towards the morphology of the nanoparticles and
the nature of the support, where the Au-NPs are bound by weak
coordination to the supported polymeric or solid surfaces.
However, there is no report which studies the catalytic properties
of Au-NPs, governed mainly by the intrinsic surface properties of
the nanoparticles, while stabilized with only a self-assembled
monolayer, e.g. surface bound via the strong Au–S bond.
Undoubtedly, understanding the catalytic behaviour of
self-assembled monolayer-coated Au-NPs would be helpful
in establishing the guiding principles for the rational design of
active Au-NP-based catalytic systems.
As part of our continuing interest in the development of
environmentally friendly protocols in organic transformations3
as well as the synthesis of nanoparticle-based composite
materials,4
we have been trying to develop Au-NP-based mild
catalytic systems for the oxidation of alcohols to give carbonyl
compounds. In this regard, developing a simple self-assembled
monolayer-coated Au-NP-based catalytic system for the oxidation
of a-hydroxy ketones and the synthesis of biologically significant
quinoxaline derivatives in water has great significance. Aryl
substituted 1,2-diketones and quinoxaline derivatives are
utilized as intermediates in the synthesis of chiral ligands
and biologically active compounds.5,6
In addition to their
medicinal use, these derivatives have also found technological
importance in dyes, semiconductors, anticorrosion in mild
steels, as photosensitive coatings in photocurable agents etc.7
Investigations, such as oxalyl chloride with organostannanes,8a
oxidation of alkynes,8b
aldehyde condensation8c
and oxidation
of alcohols8d,e,f
on the preparation of benzil derivatives have
been reported. Similarly, for the preparation of quinoxaline
derivatives, generally acid or transition metal (Mn, Ru, Pd, Cu,
Ce etc.) catalyzed condensations of an aryl 1,2-dicarbonyl
compound with a 1,2-diamine have been reported.9
There
are several other approaches reported for the synthesis of
quinoxaline compounds, e.g. the combination of phenyl
epoxides or phenacyl bromides with o-phenylenediamines,
using catalysts such as Bi(0),10a
HClO4/SiO2,10b
b-cyclodextrin
(b-CD)10c
and TMSCl.10d
Recently, a few reports of one pot
syntheses of quinoxaline from a-hydroxy ketones using solid
supports, such as KF/Al2O3,11a
Ru/C in the presence of
b–CD,11b
manganese oxide octahedral molecular sieves
(OMS-2),11c
HgI2,11d
RuCl2(PPh3)3–TEMPO,11e
MnO2
11f
etc. have
been published. However, they often suffer from one or more
disadvantages, such as the use of organic solvents, unsatisfactory
product yields, tedious experimental procedures, non-catalytic,
multi step, harsh reaction conditions, difficult operation etc. To
overcome all these disadvantages, the development of an effective
nanoparticle-based catalytic system is highly desirable for the
synthesis of benzils and quinolaxine derivatives that leads to better
yields under mild reaction conditions, specifically in water, which is
very significant in the context of green chemistry.
Herein, we report an efficient, simple and green procedure
for the aerobic oxidation of aryl substituted a-hydroxy ketones
to afford 1,2-diketones in water (Scheme 1), catalyzed by
4-aminothiophenol self-assembled monolayer-coated Au-NPs.
We also extended this procedure for the one-pot direct synthesis
Department of Chemistry, Indian Institute of Technology Indore,
Indore-452017, India. E-mail: tridib@iiti.ac.in, sampaks@iiti.ac.in;
Fax: +91-731-2364182; Tel: +91-731-243-8706
w Electronic supplementary information (ESI) available. See DOI:
10.1039/c2cy20438j
Catalysis
Science & Technology
Dynamic Article Links
www.rsc.org/catalysis COMMUNICATION
Publishedon04July2012.Downloadedon13/08/201515:54:04. View Article Online / Journal Homepage / Table of Contents for this issue

This journal is c The Royal Society of Chemistry 2012 Catal. Sci. Technol., 2012, 2, 2216–2220 2217
of aryl substituted quinoxalines via in situ oxidation and
condensation reactions between aryl substituted a-hydroxy
ketones with aryl 1,2-diamines (Scheme 1).
Results and discussion
The 4-aminothiophenol monolayer-coated Au-NPs (A) were
prepared in a one-pot synthetic procedure using 4-aminothiophenol
as both the reducing and stabilizing agent, according to a literature
procedure.12
The Au-NPs were stabilized by thiolates adsorbed
onto the surfaces of the nanoparticles. Fig. 1a depicts a
representation of the self-assembled monolayer formation of
4-aminothiophenol on the surfaces of the Au-NPs. The
appearance of a plasmon resonance band at 530 nm (as shown
in Fig. 1b) confirmed the formation of Au-NPs. The formation
of Au-NPs was further confirmed from the powder X-ray
diffraction (XRD) pattern, where the intense peaks corres-
ponding to the (111), (200) and (220) Braggs’ reflections are in
good agreement with those reported for Au nanoparticles4a
(Fig. 1c). The TEM images taken of the synthesized Au-NPs
from the DMF–water mixture (1 : 1), as shown in Fig. 1d,
indicated the formation of Au-NPs with an average diameter
of 10 Æ 3 nm (see the histogram in the ESIw). In order to
compare the catalytic properties of the self-assembled monolayer
systems which have terminal thiolate functional groups on the
Au surface, we also synthesized undecanethiol-coated Au-NPs
(catalyst B) (details in the ESIw).
We chose the model reaction between benzoin (1.0 mmol),
K2CO3 (2.0 mmol) and water (10 mL) in the presence of
catalyst B (2.5 atom%) at 60 1C for 4 h under air. Although
the reaction did not progress well, we were able to isolate the
oxidized product in a 15% yield (Table 1, entry 5). As a
consequence, this significant result prompted us to investigate
the aerobic oxidation of benzoin in detail. It was observed that
the reaction proceeded very slowly in the absence of base,
catalyst and air (entries 1–3 and 12, Table 1). To improve the
catalytic activity of this reaction, catalyst A was examined. As
shown in Table 1, with a 2.5 atom% loading of catalyst A, the
desired oxidized product benzil was obtained in a 22% yield
after reacting at 40 1C for 4 h (entry 6). For this catalyst, on
further increasing the reaction temperature to 80 1C, the yield
improved dramatically from 22% to 83% for the same reaction
time (entry 8). Among the bases, K2CO3 was the best choice
compared to Na2CO3 and Cs2CO3 in terms of reactivity under
similar reaction conditions (entries 14 and 15). In particular, there
was a substantial enhancement in the yield when the amount of
catalyst was increased from 2.5 to 4 atom%. From various
reaction conditions, as shown in Table 1, it is obvious that a
superior result was obtained under the conditions mentioned in
entry 11 (91% yield). In particular, there was no significant
improvement in yield when the reaction was carried out in the
presence of oxygen instead of air (entry 13).
To understand the scope and limitation of this novel aerobic
oxidation reaction, we studied several aryl substituted a-hydroxy
ketones using the self-assembled monolayer-coated Au-NPs,
catalyst A (4 atom%), at standard reaction conditions and the
results are compiled in Table 2. As is evident from Table 2, aryl
a-hydroxy ketones with various substituents on the aromatic ring
all produced the desired oxidized product in good to excellent
yields (entries 2–4). It should be pointed out that electron
withdrawing substituents (entry 4) on the aromatic ring increased
the yield when compared to electron donating groups (entries 2
and 3). Hetero-aryl groups also afforded the desired oxidized
products in good yields at 60 1C. The reaction conditions were
mild enough to tolerate furan, thiophene and pyridine rings.
The isolated products were fully characterized from their
spectral data and by direct comparison with the reported data.
Scheme 1 Syntheses of aryl 1,2-diketones and quinoxaline derivatives.
Fig. 1 (a) Schematic presentation of 4-aminothiophenol-coated
Au-NPs (catalyst A). (b) UV-visible spectra of the Au-NPs formed
using 4-aminothiophenol as both the reducing and stabilizing agent in
a DMF–water mixture. (c) XRD pattern of the Au-NPs. The corres-
ponding lattice planes are marked. (d) TEM images of the Au-NPs in a
DMF–water mixture, scale bar 20 nm.
Table 1 Aerobic oxidation of benzoin to benzil, catalyzed by Au-NPs
Entry Catalysts Base Temp (1C) Yielda
(%)
1 Nil Nil 60 2
2 Nil Na2CO3 60 6
3 Nil K2CO3 60 10
4 A (4.0 atom% ) Nil 80 3
5 B (2.5 atom%) K2CO3 60 15
6 A (2.5 atom%) K2CO3 40 22
7 A (2.5 atom%) K2CO3 60 38
8 A (2.5 atom%) K2CO3 80 83
9 A (0.8 atom%) K2CO3 80 41
10 A (1.6 atom%) K2CO3 80 59
11 A (4.0 atom%) K2CO3 80 91
12 A (4.0 atom%) K2CO3 80 7b
13 A (4.0 atom%) K2CO3 80 92c
14 A (4.0 atom%) Na2CO3 80 27
15 A (4.0 atom%) Cs2CO3 80 83
Unless otherwise specified, all reactions were carried out with benzoin
(1.0 mmol), base (2.0 mmol) and water (10 mL) in the presence of air at
the specified temperature and catalysts. a
Isolated product after column
chromatography. b
Reaction was carried out in an argon atmosphere.
c
Reaction was carried out in an oxygen atmosphere.
Publishedon04July2012.Downloadedon13/08/201515:54:04. View Article Online

In addition, the bench-scale preparation of the oxidized product of
benzoin under our conditions was investigated. Catalyst A
(80 atom%) was added to a stirred reaction mixture containing
benzoin (20 mmol), K2CO3 (40 mmol) and water (200 mL) and
heated at 80 1C for 6 h. The benzil product was isolated with a
79% yield. This exciting result reveals that our present condi-
tions can be applied for milligram to gram scale syntheses.
The reusability of the Au-NPs catalysts was investigated. In a
typical experiment, the catalyst was reused twice (recovery
amount was 71% after 1st run and the 53% after the 2nd run
for entry 1, Table 2). The recovered nanoparticles after the 1st and
2nd oxidations were examined by TEM measurements, which
showed substantial agglomeration of the particles after the 2nd
run (as shown in Fig. 2). The agglomeration which took place
may be due to several factors, such as interactions among self-
assembled monolayers,12
effect of salt (base)13
and temperature.
We propose that the probable mechanism of this reaction
follows a similar path to that reported earlier for the Au-NP-
catalyzed aerobic oxidation reactions of alcohol.2i,k,l
At first,
the absorption of the oxy anion onto the Au surface enhanced
the electron density that facilitated the absorption of oxygen
molecules, probably in the superoxo-type form. The ketone is
formed due to the abstraction of hydrogen by the O2
À
species
(Fig. 3). From the reaction mechanism, the lower catalytic
efficiency of the 1-undecanethiol-protected Au-NPs when
compared to the 4-aminothiophenol-coated Au-NPs was not
surprising. The formation of a highly dense monolayer in the
case of the 1-undecanethiol-coated Au-NPs14
probably retarded
the absorption of bulky molecules onto the Au surface.
After successfully developing a simple, green and efficient
catalytic system for the aerobic oxidation of a-hydroxy ketones
to aryl a-diketones, catalyzed by Au-NPs, we then applied the
same procedure to a one-pot tandem oxidation and subsequent
condensation reactions of aryl a-hydroxy ketones with aryl
1,2-diamines for the synthesis of functionalized quinoxaline
derivatives using catalyst A in water. As shown in Table 3, a
Table 2 Syntheses of aryl 1,2-diketones
Entry Ar (Substrate) t (h) Yielda
(%)
1 Ph 4 91
2 4-MeC6H4 5 71
3 4-MeOC6H4 5 70
4 4-FC6H4 3.5 95
5 2-Pyridyl 4 90b
6 2-Thiophenyl 5 93b
7 2-Furyl 6 66b
8 4 82
Unless otherwise specified, all reactions were carried out with a-hydroxy
ketone (1.0 mmol), base (2.0 mmol), water (10 mL) and catalyst A
under air at the specified temperature. a
Isolated product after column
chromatography. b
Reactions were carried out at 60 1C.
Fig. 2 TEM images of the 4-aminothiophenol-protected Au-NP
catalyst after the 1st (a) and 2nd (b) oxidation of benzoin. The Au-NPs
were deposited from the separated and concentrated aqueous layer after
the removal of the organic products. Scale bar is 50 nm.
Fig. 3 Proposed mechanism for the aerobic oxidation of a-hydroxy
ketones by the self-assembled monolayer-protected Au-NPs.
Table 3 One-pot synthesis of quinoxaline
Entry Ar (Substrate) R t (h) Yielda
(%)
1 Ph H 4 92
2 Ph Me 4 93
3 Ph Cl 4 88
4 4-FC6H4 Me 2 89
5 4-FC6H4 Cl 2 91
6 4-MeOC6H4 Me 4 89
7 4-MeOC6H4 Cl 4 84
8 4-MeOC6H4 CO2H 5 85
9 2-Thiophenyl Cl 3 88
10 2-Thiophenyl CO2H 4 90
11 2-Furyl H 2 86
12 2-Furyl Me 2 82
13 2-Furyl CO2H 2 87
14 Me 4 91
Unless otherwise specified, all reactions were carried out with a-hydroxy
ketones (1.0 mmol), 1,2-diamine (1.1 mmol), K2CO3 (2.0 mmol), water
(10 mL) and catalyst A (4.0 atom%) under air at 80 1C. a
Yield of the
isolated product.

This journal is c The Royal Society of Chemistry 2012 Catal. Sci. Technol., 2012, 2, 2216–2220 2219
wide range of structurally varied aryl substituted and un-substituted
a-hydroxy ketones with aryl 1,2-diamine worked very well in this
procedure to provide the corresponding quinoxaline derivatives in
high to excellent yields. Several sensitive functional groups, such as
OMe, Cl, F and CO2H, remained unaffected under the present
reaction conditions. It is noteworthy that for the first time,
3,4-diaminobenzoic acid has been successfully used for this
condensation reaction, providing excellent yields (entries 8, 10,
and 13). Our Au-NP catalytic system is very efficient for
the synthesis of quinoxaline derivatives when compared to
established procedures.
Conclusion
In this manuscript, we have investigated the catalytic activity
of self-assembled monolayer-coated Au-NPs for the aerobic
oxidation of aryl substituted a-hydroxy ketones to aryl 1,2-
diketones and extended this reaction for a one-pot synthesis of
highly biologically significant quinoxaline derivatives in water.
Our current methods avoid the use of acid, highly toxic reagents,
hazardous organic solvents, multisteps etc. In addition, the
simplistic synthesis of the catalyst, operational simplicity, high
yields, catalytic and environmentally friendly reaction conditions
make them attractive. This result should encourage new applica-
tions for self-assembled monolayer-coated Au-NPs in organic
syntheses as efficient catalysts. In the present system, the
reusability of the catalyst was limited after few cycles of oxidation
due to agglomeration of the nanoparticles. However, the
development of suitable stabilizers to prevent agglomeration as
well as enhance the catalytic efficiency of the nanoparticles would
offer significant applications for self-assembled monolayer-
coated nanoparticles in organic syntheses.
Experimental section
Materials and reagents
Hydrogen tetrachloroaurate(III) hydrate, 4-aminothiophenol
and 1-undecanethiol were purchased from Aldrich Chemicals.
N,N-dimethylformamide (DMF) and hydrochloric acid (HCl)
were purchased from Merck India. All these chemicals were
used without further purification. Milli Q water was used
throughout the experiment. The starting materials were either
purchased from commercial sources or synthesized by known
literature procedures.
Synthesis of the catalysts
The details of the syntheses of the 4-aminothiophenol-coated
Au-NPs (catalyst A) and the 1-undecanethiol-coated Au-NPs
(catalyst B) are reported in the ESI.w The characterization of
the nanoparticles was performed using UV-visible spectroscopy
and X-ray diffraction. The particle size of the nanoparticles was
evaluated using TEM measurements. TGA experiments were
performed to estimate the Au content in the catalyst. Details of
the analyses are reported in the ESI.w
Oxidation of benzoin
K2CO3 (276 mg, 2.0 mmol) and catalyst A (28 mg, 4.0 atom%)
were added to a stirred heterogeneous mixture of benzoin
(212 mg, 1.0 mmol) in water (10 mL) at room temperature.
The reaction mixture was then heated at 80 1C for 4 h under
air. The progress of the reaction was monitored by TLC. After
completion of the reaction, the reaction mixture was extracted
with ethyl acetate (3 Â 10 mL), washed with water and brine
respectively and dried with Na2SO4. The organic phase was
evaporated on a rotary evaporator under reduced pressure to
give the crude product. The crude product was purified by
column chromatography over silica gel to furnish the pure
product (191 mg, 91% yield). The product was characterized
by the corresponding spectroscopic data, which was in good
agreement with the reported values.
One-pot synthesis of 2,3-diphenylquinoxaline
A mixture containing benzoin (212 mg, 1.0 mmol), o-phenyl-
enediamine (108 mg, 1.0 mmol), K2CO3 (276 mg, 2.0 mmol)
and catalyst A (28 mg, 4.0 atom%) in 10 ml of water was
stirred and heated at 80 1C under air. After completion of the
reaction (monitored by TLC), the reaction mixture was
extracted with ethyl acetate (3 Â 10 mL). The organic layer
was dried over anhydrous Na2SO4, followed by evaporation of
the solvent to obtain the crude product which was purified by
column chromatography over silica gel to give the pure
product (259 mg, 92% yield). The product was characterized
by the corresponding spectroscopic data, which was in good
agreement with the reported data. The spectroscopic data of
the unknown organic compounds is reported in the ESI.w
Acknowledgements
We acknowledge financial support from DST, the Govt. of
India (Project No. SR/S1/PC-32/2010). We are also thankful
to SAIC IIT Bombay for the TEM measurements and the
UGC-DAE Inter-University Consortium Indore for the powder
XRD measurement facilities.
Notes and references
1 (a) S. Biella and M. Rossi, Chem. Commun., 2003, 378;
(b) C. Milone, R. Ingoglia, M. Tropeano, G. Neri and
S. Galvango, Chem. Commun., 2003, 868; (c) M. Haruta,
T. Kobayashi, H. Sano and N. Yamamda, Chem. Lett., 1987,
405; (d) M. Haruta, Nature, 2005, 437, 1098; (e) C. D. Pina,
E. Falletta, L. Prati and M. Rossi, Chem. Soc. Rev., 2008,
37, 2077; (f) A. S. K. Hashmi and G. J. Hutchings, Angew. Chem.,
Int. Ed., 2006, 45, 7896; (g) A. S. K. Hashmi, Chem. Rev., 2007,
107, 3180; (h) E. Jimenez-Nunez and A. M. Echavarren, Chem.
Commun., 2007, 333.
2 (a) M. Haruta, Catal. Today, 1997, 36, 153; (b) T. Ishida and
M. Haruta, Angew. Chem., Int. Ed., 2007, 46, 7154; (c) B. K. Min
and C. M. Friend, Chem. Rev., 2007, 107, 2709; (d) G. J. Hutchings
and H. Brust, Chem. Soc. Rev., 2008, 37, 1759; (e) A. Corma and
H. Garcia, Chem. Soc. Rev., 2008, 37, 2096; (f) M. S. Chen and
D. W. Goodman, Science, 2004, 306, 252; (g) W. Fang, J. Chen,
Q. Zhang, W. Deng and Y. Wang, Chem.–Eur. J., 2011, 17, 1247;
(h) A. A. Herzing, C. J. Kiely, A. F. Carley, P. Landon and
G. J. Hutchings, Science, 2008, 321, 1331; (i) H. Tsunoyama,
N. Ichikuni, H. Sakurai and T. Tsukuda, J. Am. Chem. Soc.,
2009, 131, 7086; (j) H. Liu, Y. Liu, Y. Li, Z. Tang and H. Jiang,
J. Phys. Chem. C, 2010, 114, 13362; (k) T. Ishida, M. Nagaoka,
T. Akita and M. Haruta, Chem.–Eur. J., 2008, 14, 8456;
(l) T. Tsukuda, H. Tsunoyama and H. Sakurai, Chem.–Asian J.,
2011, 6, 736.
3 (a) B. C. Ranu, S. Samanta and S. K. Guchhait, J. Org. Chem.,
2001, 66, 4102; (b) B. C. Ranu, A. Das and S. Samanta, J. Chem.
Soc., Perkin Trans. 1, 2002, 1520; (c) B. C. Ranu, S. Samanta and

S. K. Guchhait, Tetrahedron, 2002, 58, 983; (d) Y. Hayashi,
S. Samanta, H. Gotoh and H. Ishikawa, Angew. Chem., Int. Ed.,
2008, 47, 6634.
4 (a) T. K. Sarma, D. Chowdhury, A. Paul and A. Chattopadhyay,
Chem. Commun., 2002, 1048; (b) G. Majumdar, M. Goswami,
T. K. Sarma, A. Paul and A. Chattopadhyay, Langmuir, 2005,
21, 1663; (c) T. K. Sarma and A. Chattopadhyay, Langmuir, 2004,
20, 4733.
5 (a) E. J. Corey, D. H. Lee and S. Sarshar, Tetrahedron: Asymmetry,
1995, 6, 3; (b) A. Ryoda, N. Yajima, T. Haga, T. Kumamoto,
W. Nakanishi, M. Kawahata, K. Yamaguchi and T. Ishikawa,
J. Org. Chem., 2008, 73, 133; (c) L. R. Hillis and R. C. Ronald,
J. Org. Chem., 1985, 50, 470.
6 (a) A. Gomtsyan, E. K. Bayburt, R. G. Schmidt, G. Z. Zheng,
R. J. Perner, S. Didomenico, J. R. Koenig, S. Turner, T. Jinkerson,
I. Drizin, S. M. Hannick, B. S. Macri, H. A. McDonald,
P. Honore, C. T. Wismer, K. C. Marsh, J. Wetter,
K. D. Stewart, T. Oie, M. F. Jarvis, C. S. Surowy,
C. R. Faltynek and C. H. Lee, J. Med. Chem., 2005, 48, 744;
(b) R. Sarges, H. R. Howard, R. G. Browne, L. A. Label,
P. A. Seymour and B. K. Koe, J. Med. Chem., 1990, 33, 2240;
(c) L. E. Seitz, W. J. Suling and R. C. Reynolds, J. Med. Chem.,
2002, 45, 5604; (d) A. Jaso, B. Zarranz, I. Aldana and A. Monge,
J. Med. Chem., 2005, 48, 2019; (e) W. He, M. R. Myers,
B. Hanney, A. P. Spada, G. Bilder, H. Galzcinski, D. Amin,
S. Needle, K. Page, Z. Jayyosi and M. H. Perrone, Bioorg. Med.
Chem. Lett., 2003, 13, 3097; (f) G. Sakata, K. Makino and
Y. Kurasawa, Heterocycles, 1988, 27, 2481.
7 (a) E. D. Brock, D. M. Lewis, T. I. Yousaf and H. H. Harper,
U. S. Patent WO9951688, 1999; (b) S. Dailey, J. W. Feast,
R. J. Peace, I. C. Sage, S. Till and E. L. Wood, J. Mater. Chem.,
2001, 11, 2238; (c) B. I. Ita and O. E. Oﬃong, Mater. Chem. Phys.,
2001, 70, 330; (d) M. R. Ams and C. S. Wilcox, J. Am. Chem. Soc.,
2007, 129, 3966.
8 (a) T. Kashiwabra and M. Tanaka, J. Org. Chem., 2009, 74, 3958;
(b) A. Giraud, O. Provot, J. Franc, O. Peyrat, M. Alami and
J. D. Brion, Tetrahedron, 2006, 62, 7667; (c) Y. Shimakawa,
T. Morikawa and S. Sakaguchi, Tetrahedron Lett., 2010,
51, 1786; (d) C. Joo, S. Kang, S. M. Kim, H. Han and
J. W. Yang, Tetrahedron Lett., 2010, 51, 6006; (e) J. M. Khurana
and B. M. Kandpal, Tetrahedron Lett., 2003, 44, 4909; (f) D. Saio,
T. Amaya and T. Hirao, Adv. Synth. Catal., 2010, 352, 2177.
9 (a) R. S. Bhosale, S. R. Sarda, S. S. Ardhapure, W. N. Jadhav,
S. R. Bhusare and R. P. Pawar, Tetrahedron Lett., 2005, 46, 7183;
(b) S. V. More, M. N. V. Sastry, C. C. Wang and C. F. Yao,
Tetrahedron Lett., 2005, 46, 6345; (c) H. R. Darabi, S. Mohandessi,
K. Aghapoor and F. Mohsenzadeh, Catal. Commun., 2007, 8, 389;
(d) M. M. Heravi, S. Taheri, K. Bakhtiari and H. A. Oskooie,
Catal. Commun., 2007, 8, 211; (e) T. K. Huang, R. Wang, L. Shi
and X. X. Lu, Catal. Commun., 2008, 9, 1143; (f) C. Srinivas,
C. N. S. S. P. Kumar, V. J. Rao and S. Palaniappan, J. Mol. Catal.
A: Chem., 2007, 265, 227; (g) S. S. Katkar, P. H. Mohite,
L. S. Gadekar, Arbad, B. R. Lande and M. K. Cent, Eur. J.
Chem., 2010, 8, 320; (h) H. Alinezhad, M. Tajbakhsh and
P. Biparva, Bull. Korean Chem. Soc., 2011, 32, 3720;
(i) M. M. Heravi, K. Bhaktiari, F. F. Bamoharram and
M. H. Tehrani, Monatsh. Chem., 2007, 138, 465.
10 (a) S. Antoniotti and E. Donach, Tetrahedron Lett., 2002, 43, 3971;
(b) B. Das, K. Venkateswarlu, K. Suneel and A. Majhi, Tetrahedron
Lett., 2007, 48, 5371; (c) B. Madhav, S. N. Murthy, V. P. Reddy,
K. R. Rao and Y. V. D. Nageswar, Tetrahedron Lett., 2009,
50, 6025; (d) J. P. Wan, S. F. Gan, J. M. Wu and Y. J. Pan, Green
Chem., 2009, 11, 1633.
11 (a) S. Paul and B. Basu, Tetrahedron Lett., 2011, 52, 6597;
(b) V. K. Akkilagunta, V. P. Reddy and R. R. Kakulapati, Synlett,
2010, 2571; (c) S. Sithambaram, Y. Ding, W. Li, X. Shen,
F. Gaenzler and S. L. Suib, Green Chem., 2008, 10, 1029;
(d) S. A. Kotharkar and D. B. Shinde, Bull. Korean Chem. Soc.,
2006, 27, 1466; (e) R. S. Robinson and R. J. K. Taylor, Synlett,
2005, 1003; (f) S. A. Raw, C. D. Wilfred and R. J. K. Taylor,
Chem. Commun., 2003, 2286.
12 J. Sharma, S. Nahima, B. A. Kakade, R. Pasricha, A. B. Mandale
and K. Vijayamohanan, J. Phys. Chem. B, 2004, 108, 13280.
13 C. A. Mirkin, Inorg. Chem., 2000, 39, 2258.
14 (a) J. C. Love, L. A. Estroﬀ, J. K. Kriebel, R. G. Nuzzo and
G. M. Whitesides, Chem. Rev., 2005, 105, 1103; (b) D. Samanta
and A. Sarkar, Chem. Soc. Rev., 2011, 40, 2567; (c) M. C. Daniel
and D. Astruc, Chem. Rev., 2004, 104, 293.

c2cy20438j

Recommended

Recommended

More Related Content

What's hot

What's hot (19)

Similar to c2cy20438j

Similar to c2cy20438j (20)

c2cy20438j