Poly(N-vinylpyrrolidone)-H2O2 and poly(4-vinylpyridine)-H2O2 complexes: Solid H 2O2 equivalents for selective oxidation of sulfides to sulfoxides and ketones to gem-dihydroperoxides

Article abstract of DOI:10.1039/c4gc00586d

Complexes of poly(N-vinylpyrrolidone) (PVD) and poly(4-vinylpyridine) (PVP) with hydrogen peroxide have been prepared and their synthetic utility as solid H₂O₂ equivalents for the selective oxidation of sulfides to sulfoxides and ketones to gem-dihydroperoxides has been studied. These complexes are convenient and safe alternatives to H₂O₂ solutions and it is found that various symmetric as well as unsymmetrical sulfides undergo oxidation under mild conditions to provide the respective sulfoxides in high yields. A series of gem-dihydroperoxides were obtained from the corresponding ketones in good yields under ambient conditions. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4gc00586d

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PAPER
Poly(N-vinylpyrrolidone)–H2O2 and
poly(4-vinylpyridine)–H2O2 complexes: solid H2O2
equivalents for selective oxidation of sulfides to
sulfoxides and ketones to gem-dihydroperoxides†
Cite this: Green Chem., 2014, 16,
3616
G. K. Surya Prakash,* Anton Shakhmin, Kevin E. Glinton, Sneha Rao,
Thomas Mathew* and George A. Olah
Complexes of poly(N-vinylpyrrolidone) (PVD) and poly(4-vinylpyridine) (PVP) with hydrogen peroxide have
been prepared and their synthetic utility as solid H2O2 equivalents for the selective oxidation of sulfides to
sulfoxides and ketones to gem-dihydroperoxides has been studied. These complexes are convenient and
safe alternatives to H2O2 solutions and it is found that various symmetric as well as unsymmetrical sulfides
undergo oxidation under mild conditions to provide the respective sulfoxides in high yields. A series of
gem-dihydroperoxides were obtained from the corresponding ketones in good yields under ambient
conditions.
Received 2nd April 2014,
Accepted 2nd June 2014
DOI: 10.1039/c4gc00586d
www.rsc.org/greenchem
the “classic” use of simple hydrogen peroxide due to its high
oxygen content, reliable reactivity and the formation of only
Introduction
Oxidation reactions play a vital part in both the natural and water as the byproduct of its reactions.1 However, even hydro-
scientific world from cellular respiration to the oxidation of gen peroxide poses risks due to its oxidative strength and reac-
hydrocarbons as fuels. Oxidants themselves come in a great tivity.2 It also, for instance, reacts violently with metals and
variety of forms but in synthetic applications, there has been a reducing agents, can become explosive above certain concen-
growing search for oxidants that more accurately mimic the trations, and acts as a strong bleaching agent. Hydrogen per-
environmentally friendly characteristics of natural ones. Apart oxide can also be destabilized by extreme pH’s and form
from transition-metal based oxidants, some of the most acces- explosive mixtures with organics upon prolonged exposure. On
sible ones among these reagents are usually organic peroxides the other hand, H2O2 can also form extended hydrogen-
and related peroxy compounds. From very early on, however, it bonded complexes with organic bases and many see these
was well recognized that many peroxy compounds possess sig- compounds as a safer way to store and access the peroxides for
nificant drawbacks that can make their use both limited and, oxidations. Indeed, such complexes can reduce the volatility of
at times very dangerous.
the hydrogen peroxide allowing its storage at higher concen-
One of the most popular reagents, m-chloroperoxybenzoic trations for extended periods of time more safely without
acid (m-CPBA) for instance, is known to be shock sensitive and seriously affecting the reactivity.
poor in terms of its oxygen content. Other peroxides such as
Well before its molecular structure was agreed upon,3
tert-butyl hydroperoxide can become unstable and explosive hydrogen peroxide was known to form adducts with various
making them difficult to both implement into a large scale bases. Urea–H2O2 for instance, was the first such adduct dis-
process and dispose of after the reaction is completed. In covered and for almost a century has been the model for sub-
response to these concerns, many have begun to look back to sequent peroxide complexes. Commercially available urea–
H2O2 is a crystalline, white, hygroscopic solid that is generally
stable at room temperature. With such favorable character-
istics, it comes as no surprise that urea–H2O2 is known as a
Loker Hydrocarbon Research Institute and the Department of Chemistry, University
dependable, solid alternative to hydrogen peroxide with estab-
lished utility in a range of oxidative applications.4 Such reac-
of Southern California, Los Angeles, CA 90089, USA. E-mail: gprakash@usc.edu,
tmathew@usc.edu; Fax: +1-213-740-6679; Tel: +1-213-740-5984
tions include epoxidations,5 the oxidation of sulfides,6
†Electronic supplementary information (ESI) available: Characterization (NMR)
selenium compounds,7 benzylic carbons8 and many other
reactions.9 Hydrogen peroxide also forms a stable complex
data and copies of 1H and 13C spectra of the products. See DOI:
10.1039/c4gc00586d
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with 1,4-diazabicyclo[2.2.2]octane (DABCO),10 though com- 3–5 molecules of hydrogen peroxide being preferred over a cyclic
plexes with other tertiary amines have been known to degrade structure.28 Compared to urea–H2O2, a 1 : 1 complex, PVD–H2O2
easily and are less useful.11
(1 : 4.5) and PVP–H2O2 (1 : 3.5) carry more equivalents of H2O2
Interestingly, some of the more effective supports or car- content making them better H2O2 carriers.
riers for hydrogen peroxide are polymeric bases and hetero-
Interestingly, it has been found that PVD–H2O2 performs sig-
cycles. In particular, poly(N-vinylpyrrolidone) has been known nificantly better than PVP–H2O2 in most applications though
to form stable, free flowing, solid complexes with various con- this may be simply a difference in H2O2 loading between the
centrations of hydrogen peroxide. Since their discovery during two. Nonetheless, as efficient, solid forms of hydrogen peroxide,
the 1960s,12 PVD–H2O2 complexes have been used as peroxide both complexes showed impressive promise as efficient oxidiz-
surrogates in many different capacities. Many differing formu- ing agents. In our efforts in exploring the applications of hydro-
lations have been proposed13 and most of them are used for gen peroxide complexes in oxygenation and oxidation reactions,
surface sterilizations,14 tissue preservations,15 acne treatments,16 we found that they are efficient oxidizing agents and our results
tooth whiteners17 and radical polymerization initiations.18 are reported here in the selective partial oxidation of sulfides to
However, while its industrial and cosmetic applications have sulfoxides as well as in preparation of gem-dihydroperoxides
been well documented, PVD–H2O2 has only within the last few from the corresponding ketones.
decades been shown useful in synthetic organic transform-
ations. Unlike other complexes, hydrogen peroxide within PVD–
H2O2 has been shown to preferentially bond with the carbonyl
Results and discussion
Selective oxidation of sulfides to sulfoxides
moiety of the amido group.19 Inevitably, this alternative bond
site and the presence of a polymeric backbone have both led to
interesting and new applications of these complexes.
The oxidation of sulfides to sulfoxides is one of the most
PVD–H2O2 for instance has been used by Pourali and simple, yet particularly important transformations in organic
associates in the production of iodinated arene.20 The complex chemistry. Sulfoxides are indispensable as they appear in
was used in conjunction with KI or molecular iodine and cata- numerous natural products and drug molecules, act as chiral
lytic amounts of hydrated tungstophosphoric acid and pro- auxiliaries and C–C bond forming reagents, and even partici-
duced a range of products in good yields. The complex was pate as intermediates in some molecular rearrangements and
also used in the epoxidation of ketones and α,β-enones in the transformations. Because of this, numerous reagents and
presence of sodium hydroxide21 and Mn porphyrins22 as cata- methods have been developed in an effort to produce sulfox-
lysts. Recently, our group has sought to expand the synthetic ides as selectively and inexpensively as possible. Among these,
role of hydrogen peroxide complexes. We have reported the use the oxidation of sulfides has been proven as one of the most
of both PVD–H2O2 and the newly formed poly(4-vinylpyridine) durable and pervasive methods in synthetic organic chem-
hydrogen peroxide complex (PVP–H2O2).23 PVP–H2O2, similar to istry.24 Sulfoxides have been made from sulfides using nitrates
other peroxide complexes, is formed by hydrogen bonds in combination with halogens,25 hypervalent iodine or peri-
through the amine functionality and forms a free-flowing, light odic acids,26 and peroxyacids and peroxides in conjunction
yellow solid. Both complexes were used in the synthesis of with multiple transition metal catalysts.27 However, with the
phenols and halophenols from arylboronic acids under very growing emphasis on environmentally benign processes, more
mild conditions (Scheme 1). Calculations were also performed and more chemists have sought out ways to bring about this
to help elucidate the extended structure of the complexes and transformation with greater selectivity with minimal by-pro-
it was found that both PVD and PVP form stable, extended ducts and waste as possible. In many instances, overoxidation
hydrogen bonded structures with a linear arrangement of to sulfones hinder the selectivity of the process. The use of the
many inorganic oxidants for instance is seen as less than
optimal due to their tendency to over-oxidize sulfides and
interfere with sensitive functional groups while peroxyacids
can be hazardous and lead to excessive waste streams.
Instead, the use of hydrogen peroxide (H2O2) as a sulfide
oxidant is seen as a more viable alternative due to its strong
oxygen content, safety and low cost. Hydrogen peroxide also
acts as a milder oxidant than other reagents and produces
water as the only waste by-product. The molecule has been
used to oxidize sulfides for decades both alone or in the pres-
ence of other catalysts.28 Such additives can help increase reac-
tivity, decrease reaction times and induce stereoselectivity
though an increase in the amounts of sulfone produced may
also occur as well. Khodaei and coworkers have, for instance,
reported the use of triflic anhydride (Tf2O) in conjunction with
Scheme 1 Solid H2O2 complexes and ipso-hydroxylation and halo-
genation of arylboronic acids.
H2O2 where the peroxy acid generated in situ acts as the oxidiz-
This journal is © The Royal Society of Chemistry 2014
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ing agent.29 In other cases, hydrogen-bonding additives can
Inspired by these successful examples, we decided to
play a part in the activation of peroxide. For example, Varma examine the use of PVD–H2O2 and PVP–H2O2 (both prepared
and Naicker have shown that commercially available urea– with 50% aqueous H2O2) as oxidants for arylsulfides. Initially,
H2O2 complexes are capable of such oxidations under solvent- as with many oxidizing reagents, by using PVD–H2O2 we
free conditions (Scheme 2).4
obtained mixtures of both sulfoxides and sulfones as products
with sulfoxide being more predominant at lower temperatures
while sulfone being the major one under prolonged heating at
elevated temperatures (Scheme 3).
However, unlike many other oxidants, PVD–H2O2 proved
highly amenable to control and optimization making the reac-
tion highly tunable. By monitoring the progress of reactions
with thin layer chromatography and modifying the reaction
temperature, selective formation of various sulfoxides deriva-
tives were achieved (Table 1).
Scheme 2 Oxidation of sulfides with urea–H2O2.
The relatively simple modifications led to excellent yields
and diverse side groups like alkenes, amines and alkyl chlor-
ides were tolerated. More importantly, by using a solid form of
H2O2, we were able to eliminate the steps associated with
workup as well as product separation and the amount of sol-
vents used has been significantly reduced.
Scheme 3 Oxidation of sulfides with PVD–H2O2.
Table 1 Selective oxidation of sulfides using PVP–H2O2 and PVD–H2O2 complexes
Entry
a
Substratea
Product
PVD–H2O2 Time (h)
PVD–H2O2 Yield (%)
PVD–H2O2 Time (h)
PVD–H2O2 Yield (%)
3
99
24
72
b
c
6
3
3
85
82
88
24
24
24
86
82
95
d
e
f
5
24
24
83
84
82
24
24
24
71
74
70
g
h
i
3
6
94
93
24
24
60
—
j
6
81
24
—
a Substrate to H2O2 ratio is 1 : 2.75.
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We also examined the use of PVP–H2O2 as an oxidant and many of the derivatives can indeed be explosive,34 the contin-
found the results similar to those obtained by the use of PVD– ued search for better pharmaceuticals and the abundance of
H2O2. PVP–H2O2 was also found to selectively oxidize aryl- peroxide containing targets have made gem-dihydroperoxides
sulfides to sulfoxides, however, reaction rates were generally more attractive and sought after targets for synthetic chemists.
much slower and required much higher H2O2 loading than The molecules, for instance, have been used as starting
expected (Table 1). Yields were generally lower than those materials or intermediates for a number of pharmaceuticals
observed in PVD–H2O2 reactions. Interestingly, a few substrates including 1,2-dioxolanes35 and 1,2,4,5-tetroxanes36 and by
such as 3i and 3j possessing sensitive groups seemed to themselves as oxidizing reagents in epoxidation reactions.37
undergo side reactions leading to complex mixtures when reac-
In terms of their own synthesis, gem-dihydroperoxides have
tion was conducted with PVP–H2O2. Nonetheless, PVP–H2O2 been made in only a few primary ways. Dihydroperoxides can
still proved effective as an environmentally friendly H2O2 sur- be synthesized through the ozonolysis of enol ethers as
rogate in oxidizing a range of sulfides.
described by McCullough and others although the reaction is
not general as ozone sensitive functionalities are not well toler-
ated.38 Hydroperoxidation of ketals39 has also been shown in
some cases to lead to gem-dihydroperoxides though, one is
limited to ketals as starting materials.40 In contrast to these
two paths, the mildest and most general route to gem-dihydro-
peroxides appears to be through the H2O2 oxidation of ketones
in the presence of an acid catalyst.
Several different acids have been used in such a process
including the original acid of choice, formic acid33,41 and,
more recently, phosphomolybdic42 and camphorsulfonic
acids.43 However, in terms of both strength and ease of use,
the most intriguing acid for such reactions could be sulfuric
acid.44 Terent’ev and co-workers for example, have shown that
acid activation of ketones can successfully lead to geminal
bishydroperoxides in good yields (Scheme 4).
Interestingly, the reactions were carried out in tetrahydro-
furan as a solvent, which the authors claim helps the solvation
of the products preventing further reaction. We sought there-
fore, to use hydrogen peroxide complexes in such a manner.
For the activation of ketone, instead of using a liquid acid, we
decided to use 1 : 5 PVP–H2SO4, the complex of poly(4-vinyl
pyridine) with 83 wt% H2SO4 as a convenient solid equivalent
of H2SO4 (Fig. 2b and 3c), which makes the reaction more eco-
friendly. We prepared PVP–H2SO4 (1 : 5) and by combining
Oxidation of ketones to gem-dihydroperoxides
With hundreds of millions of cases leading to over a million
deaths every year, malaria unfortunately continues to be one of
the most widespread and potent threats to lives and commu-
nities within the tropics.30 As a result, there has been a con-
certed effort to discover newer, more potent molecules for the
treatment of malaria.
One of the most promising of these is the naturally occur-
ring artemisinin, isolated by Chinese scientists in 1971 from
Artemisia annua.31 Artemisinin is toxic to malaria parasites at
micro and even nanomolar concentrations and the prime
factor behind its activity has been shown to be its character-
istic endoperoxide structure. However, while its antimalarial
properties cannot be denied, artemisinin is still only slightly
soluble in oil and water and has a very short half-life. This
means that complex formulations must be administered
repeatedly over several days. The other drawback is most of the
artemisinin is still isolated directly from natural sources.
Thus many synthetic variants of artemisinin were and are
still being developed for easy administration, longer lasting
effects and greater lipophilicity while retaining the all-impor-
tant peroxide linkage in active form.32 These include a range
of molecules from those closely mimicking the original artemi-
sinin framework with simpler structures that are easier to syn-
thesize. As is evident from looking at their structures (Fig. 1,
5a–h), one of the best synthetic paths to many of these com-
pounds could be through the use of gem-diperoxides.
gem-Diperoxides have been encountered as byproducts of
various oxidation reactions for a very long time but were very
rarely explored because of their perceived instability.33 Though
Scheme 4 Synthesis of gem-dihydroperoxides under acidic conditions.
Fig. 1 Artemisinin and related anti-malarial compounds with peroxy
linkages.
Fig. 2 SEM images of (a) PVP and (b) PVP–H2SO4 (1 : 5).
Green Chem., 2014, 16, 3616–3622 | 3619
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generally better for cyclic ketones such as cyclohexanone
derivatives though ring size also appeared to play an important
role. Benzylic ketones were found to be very resistant to reac-
tions though such difficulties have been noted by other groups
as well. Results were also dependent upon the amount of acid
used. Though Terent’ev and co-workers have described ratios
between 8 : 0.3 and 4 : 0.3 for hydrogen peroxide to acid as
optimal, we found most reactions to progress well with a 2 : 1
ratio of peroxide to acid. This may be due entirely to the
nature of our solid oxidant system compared to liquid systems.
Even though these systems have been found to exhibit slight
H2O2 leaching in solvents, their reactivity is still somewhat
tempered by the strong bonds between polymer and oxidant
molecules.
Fig. 3 (a) PVD–H2O2 (1 : 4.5), (b) PVP–H2O2 (1 : 3.5), and (c) PVP–H2SO4
(1 : 5).
All products were isolated, purified by crystallization or
chromatographic separation and characterized by NMR
spectroscopy comparing their spectral data with those of the
authentic samples.45
both the solid polymeric complexes PVD–H2O2 and PVP–
H2SO4, gem-dihydroperoxides of several cyclic and acyclic
ketones have been synthesized.
Reactions were generally carried out by first stirring the
substrate of choice and our acid catalyst in tetrahydrofuran at
0 °C. PVD–H2O2 was then added followed by warming the
Conclusion
entire mixture to room temperature and allowing it to stir for The present study unveils an important application of the
24 h (Table 2). We found that the yields for the reaction are solid H2O2 equivalents PVD–H2O2 and PVP–H2O2 for the selec-
tive oxidation of the sulfides to sulfoxides with much safer and
more convenient handling of the oxidant H2O2 while reducing
the amount of side products. Conversion of aryl alkyl sulfides
Table 2 Acid catalyzed synthesis of gem-dihydroperoxides
to their corresponding sulfoxides was achieved in good to
excellent yields. Additionally, we found that these stable com-
plexes can be very useful for the preparation of the gem-
dihydroperoxy compounds from corresponding ketones in
Entry
a
Substratea
Product
Yield (%)
57
good yields. Reaction methodology, workup procedure and
purification of the products are safe and the reagents can be
easily handled compared to the one involving the use of other
oxidants such as tert-butyl hydroperoxide and peracids such as
m-CPBA or liquid H2O2. Moreover, the complexes are more
environmentally benign than other oxidants as they have the
potential to be recycled and reused (with the remaining
amount of H2O2 or enhancing the H2O2 content by additional
complexation) and water is the by-product. This, in fact,
prompts us to test the efficacy of these solid oxidizing reagents
for many selective oxidation/oxygenation reactions in the
future.
b
c
77
80
72
d
e
f
70
65
Acknowledgements
g
51
42
Financial Support by the Loker Hydrocarbon Research Insti-
tute is gratefully acknowledged.
h
i
j
64
71
Notes and references
1 J. M. Campos-Martin, G. Blanco-Brieva and J. L. G. Fierro,
Angew. Chem., Int. Ed., 2006, 45, 6962–2684.
2 C. W. Jones, Applications of Hydrogen Peroxide and Deriva-
tives, The Royal Society of Chemistry, Cambridge, 1999.
a Substrate to H2O2 ratio is 1 : 2.75.
3620 | Green Chem., 2014, 16, 3616–3622
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Paper
3 C. S. Lu, E. W. Hughes and P. A. Giguère, J. Am. Chem. Soc., 27 (a) K. Matsumoto, T. Yamaguchi and T. Katsuki, Chem.
1941, 63, 1507–1513.
4 R. S. Varma and K. P. Naicker, Org. Lett., 1999, 1,
189–191.
5 M. S. Cooper, H. Heaney, A. J. Newbold and
W. R. Sanderson, Synlett, 1990, 533–535.
6 R. Balicki, Synth. Commun., 1999, 29, 2235–2239.
7 L. Yu, B. Meng and X. Huang, Synth. Commun., 2008, 38,
3142–3150.
Commun., 2008, 1704–1706; (b) B. Karimi, M. Ghoreishi-
Nezhad and J. H. Clark, Org. Lett., 2005, 7, 625–628;
(c) S. Superchi, P. Scafato, L. Restaino and C. Rosini,
Chirality, 2008, 20, 592–596; (d) K. P. Bryliakov and
E. P. Talsi, Eur. J. Org. Chem., 2008, 3369–3376;
(e) H. Egami and T. Katsuki, J. Am. Chem. Soc., 2007, 129,
8940–8941.
28 (a) T. Noguchi, Y. Hirai and M. Kirihara, Chem. Commun.,
2008, 3040–3042; (b) F. Shi, M. K. Tse, H. M. Kaiser and
M. Beller, Adv. Synth. Catal., 2007, 349, 2425–2430.
8 S. Paul, P. Nanda and R. Gupta, Synlett, 2004, 531–533.
9 S. Taliansky, Synlett, 2005, 1962–1963.
10 M. A. Zolfigol, P. Salehi, S. E. Mallakpour and M. Torabi, 29 M. M. Khodaei, K. Bahrami and A. Karimi, Synthesis, 2008,
Bull. Chem. Soc. Jpn., 2003, 76, 1673–1674. 1682–1684.
11 A. A. Oswald and D. L. Guertin, J. Org. Chem., 1963, 28, 30 World Malaria Report 2009, World Health Organization,
651–657.
Geneva, 2009.
12 D. A. Shiraeff, US Patent 3,376,110, 1968.
13 (a) J. S. Shih, J. J. Merianos, T. E. Smith and J.-C. Chuang,
31 R. K. Haynes and S. C. Vonwiller, Acc. Chem. Res., 1997, 30,
73–79.
US Patent 5,312,619, 1994; (b) J. J. Merianos, R. P. Login 32 (a) A. Robert, O. Dechy-Cabaret, J. Cazalles and B. Meunier,
and P. Garelick, US Patent 5,130,124, 1992; (c) R. B. Biss,
J. Cohen, J. J. Merianos and P. D. Taylor, US Patent
5,077,047, 1991.
Acc. Chem. Res., 2002, 35, 167–174; (b) G. H. Posner and
P. M. O’Neill, Acc. Chem. Res., 2004, 37, 397–404.
33 (a) T. Ledaal and T. Solbjor, Acta Chem. Scand., 1967, 21,
1658–1659; (b) P. L. Story, B. Lee, C. E. Bishop,
D. D. Denson and P. J. Busch, J. Org. Chem., 1970, 35,
3059–3062.
14 (a) J. J. Merianos, H. A. Lieberman and R. B. Login, US
Patent 5,008,106, 1991; (b) J. Gomori, US Patent 4,915,955,
1990; (c) J. J. Merianos, H. A. Lieberman, R. B. Login and
P. Garelick, WO Patent 91-07184 A1, 1990.
34 D. Swern, Organic Peroxides, Wiley-Interscience, New York,
1970.
15 R. Shanbrom, WO Patent 94-00011 A1, 1994.
16 J. J. Merianos and M. W. Helioff, US Patent 5,122,370, 35 A. Ramirez and K. A. Woerpel, Org. Lett., 2005, 7, 4617–
1992. 4620.
17 (a) W. E. Prosise, T. G. Bee and M. A. Drzewinski, US Patent 36 (a) K. Zmitek, S. Stavber, M. Zupan, D. Bonnet-Delpon and
6,893,629, 2005; (b) S. K. Chopra, L. Zaidel and
M. Prencipe, US Patent Application, 2007-0071695, 2007.
18 J. J. Merianos, R. B. Login, S. L. Kopolow and M. Tazi, US
Patent 5,159,033, 1992.
J. Iskra, Tetrahedron, 2006, 62, 1479–1484; (b) H. S. Kim,
K. Tsuchiya, Y. Shibata, Y. Wataya, Y. Ushigoe,
A. Masuyama, M. Nojima and K. J. J. McCullough, J. Chem.
Soc., Perkin Trans. 1, 1999, 1867–1870.
19 E. F. Panarin, K. K. Kalninsh and D. V. Pestov, Eur. Polym. 37 K. Jakka, J. Y. Liu and C. G. Zhao, Tetrahedron Lett., 2007,
J., 2001, 37, 375–379. 48, 1395–1398.
20 A. R. Pourali and M. Ghanei, Chin. J. Chem., 2006, 24, 38 (a) K. Tsuchiya, Y. Hamada, A. Masuyama, M. Nojima,
1077–1079.
K. J. McCullough, H. S. Kim, Y. Shibata and Y. Wataya,
Tetrahedron Lett., 1999, 40, 4077–4080; (b) I. Saito,
R. Nagata, K. Yuba and T. Matsuura, Tetrahedron Lett.,
1983, 24, 1737–1740; (c) J. C. Robertson and W. J. Verzino, Jr.,
J. Org. Chem., 1970, 35, 545–547.
21 A. R. Pourali and M. Ghanei, Bull. Korean Chem. Soc., 2006,
27, 1674–1676.
22 S. Zakavi, A. Abasi, A. R. Pourali and S. Rayati, Bull. Korean
Chem. Soc., 2008, 29, 866–868.
23 G. K. S. Prakash, S. Chacko, C. Panja, T. E. Thomas, 39 (a) A. O. Terent’ev, A. V. Kutkin, M. M. Platonov,
L. Gurung, G. Rasul, T. Mathew and G. A. Olah, Adv. Synth.
Catal., 2009, 351, 1567–1574.
24 (a) M. Madesclaire, Tetrahedron, 1986, 42, 5459–5495;
Y. N. Ogibin and G. I. Nikishin, Tetrahedron Lett., 2003, 44,
7359–7163; (b) C. W. Jefford, Y. L. A. Jaber and
J. Boukouvalas, Synth. Commun., 1990, 20, 2589–2596.
(b) J. E. Bäckvall, Modern Oxidation Methods, Wiley-VCH, 40 J. L. Vennerstrom, Y. Dong, S. L. Andersen, A. L. Ager Jr.,
Weinheim, 2004.
H. N. Fu, R. E. Miller, D. L. Wesche, D. E. Kyle, L. Gerena,
S. M. Walters, J. K. Wood, G. Edwards, A. D. Holme,
W. G. McLean and W. K. Milhous, J. Med. Chem., 2000, 43,
2753–2758.
25 (a) H. Zhang, C. Y. Chen, R. H. Liu and Q. Xu, Synth.
Commun., 2008, 38, 4445–4451; (b) C. O. Kinen, L. I. Rossi
and R. H. de Rossi, J. Org. Chem., 2009, 74, 7132–1739;
(c) M. A. Zolfigol, K. Amani, A. Ghorbani-Choghamarani, 41 H. S. Kim, Y. Nagai, K. Ono, K. Begum, Y. Wataya,
M. Hajjami, R. Ayazi-Nasrabadi and S. Jafarii, Catal.
Commun., 2008, 9, 1739–1744.
Y. Hamada, K. Tsuchiya, A. Masuyama, M. Nojima and
K. J. McCullough, J. Med. Chem., 2001, 44, 2357–2361.
26 (a) W. Qian and L. Pei, Synlett, 2006, 709–712; (b) S. S. Kim, 42 (a) Y. Li, H. D. Hao, Q. Zhang and Y. Wu, Org. Lett., 2009,
K. Nehru, S. S. Kim, D. W. Kim and H. C. Jung, Synthesis,
2002, 2484–2486.
11, 1615–1618; (b) Y. Li, H. D. Hao and Y. Wu, Org. Lett.,
2009, 11, 2691–2694.
This journal is © The Royal Society of Chemistry 2014
Green Chem., 2014, 16, 3616–3622 | 3621

View Article Online
Paper
Green Chemistry
43 A. Bunge, H. J. Hamann and J. Liebscher, Tetrahedron Lett.,
2009, 50, 524–526.
Chem. Soc., 2011, 8, 142–148; (d) R. B. Rama, S. Sarkar,
R. U. Chandramoulali and A. K. Saikia, J. Mol. Catal. A:
Chem., 2009, 308, 169–173; (e) A. A. Kumar, Tetrahedron
Lett., 2007, 48, 7857–7860; (f) Y. H. Liu, J. Deng, J.-W. Gao
and Z.-H. Zhang, Adv. Synth. Catal., 2012, 354, 441–447;
(g) L. Cui, N. Tada, H. Okubo, T. Miura and A. Itoh, Green
Chem., 2011, 13, 2347–2350; (h) N. Tada, L. Cui, H. Okubo
and T. Miura, Chem. Commun., 2010, 46, 1772–1774;
(i) K. V. Sashidhara, S. R. Avula, L. R. Singh and
G. R. Palnati, Tetrahedron Lett., 2012, 53, 4880–4884;
( j) M. Krishnaiah and P. Balasubramanyam, J. Mol. Catal.
A: Chem., 2008, 284, 116–119.
44 (a) A. O. Terent’ev, M. M. Platonov, Y. N. Ogibin and
G. I. Nikishin, Synth. Commun., 2007, 37, 1281–1287;
(b) B. Das, B. Veeranjaneyulu, M. Krishnaiah and
P. Balasubramanyam, J. Mol. Catal. A: Chem., 2008, 284,
116–119; (c) Y. Dong, H. Matile, J. Chollet, R. Kaminsky,
J. K. Wood and J. L. Vennerstrom, J. Med. Chem., 1999, 42,
1477–1480.
45 (a) Y. Yuan;, X. Shi and W. Liu, Synlett, 2011, 4, 559–564;
(b) X.-F. Wu, Tetrahedron Lett., 2012, 53, 4328–4431;
(c) A. Ghorbani-Choghamarani and P. Zamani, J. Iran
3622 | Green Chem., 2014, 16, 3616–3622
This journal is © The Royal Society of Chemistry 2014