A mild and clean Baeyer-Villiger oxidation of ketones using sodium peroxydisulfate as oxidant catalyzed by silica-supported aluminum chloride

Article abstract of DOI:10.1007/s13738-011-0064-1

Sodium peroxydisulfate was used as the oxidant for Baeyer-Villiger oxidation of a variety of cyclic and acyclic ketones at room temperature in the presence of Silica-supported aluminum chloride (silica-AlCl3) as catalyst. The catalyst was prepared by a simple procedure, which exhibited high catalytic activity for the Baeyer- Villiger oxidation of ketones using environmental friendly sodium peroxydisulfate as oxidizing agent. Iranian Chemical Society 2012.

Full text of DOI:10.1007/s13738-011-0064-1

J IRAN CHEM SOC (2012) 9:521–528
DOI 10.1007/s13738-011-0064-1
ORIGINAL PAPER
A mild and clean Baeyer–Villiger oxidation of ketones
using sodium peroxydisulfate as oxidant catalyzed
by silica-supported aluminum chloride
•
Nosrat Ollah Mahmoodi Seyedeh Zahra Dalil Heirati
•
Kamel Ekhlasi-Kazaj
Received: 18 February 2011 / Accepted: 10 October 2011 / Published online: 5 January 2012
Ó Iranian Chemical Society 2012
Abstract Sodium peroxydisulfate was used as the oxi-
dant for Baeyer–Villiger oxidation of a variety of cyclic
and acyclic ketones at room temperature in the presence of
Silica-supported aluminum chloride (silica-AlCl3) as cata-
lyst. The catalyst was prepared by a simple procedure,
which exhibited high catalytic activity for the Baeyer–
Villiger oxidation of ketones using environmental friendly
sodium peroxydisulfate as oxidizing agent.
In this regard, a number of different catalytic systems
have been developed to accomplish Baeyer–Villiger oxi-
dation. The catalysts based on polymer-anchored metal
complexes [8–10], solid acids [11, 12], zeolites [13], tita-
nium silicalite [14], Sn-MCM-41 [15], sulphonated resins
[16], Sn-synthesized hydrotalcites [17], Sn-b zeolite [18],
hydrotalcite-supported Sb catalyst [19], Pt [20], Zr [21], Re
[22], Se [23], As [24] and Mo [25] are examples of some of
the heterogeneous and homogeneous catalysts used to
perform the Baeyer–Villiger oxidation. These catalysts
activate H2O2 as a clean oxidant by increasing its nucleo-
philicity and facilitate attack by the oxidizing species on
the carbonyl carbon atom [26]. Most of these processes,
however, suffer from some disadvantages like low activity
or selectivity and expensive catalyst or the need for high
concentration of H2O2.
Keywords Baeyer–Villiger oxidation Á Silica-supported
aluminum chloride Á Sodium peroxydisulfate Á Silica-AlCl3
Introduction
The Baeyer–Villiger oxidation is one of the major reactions
in organic chemistry, particularly, in conversion of cyclic
and acyclic ketones into lactones or esters by regioselective
oxygen insertion into C–C bond [1]. Baeyer–Villiger oxi-
dations traditionally have conducted using organic peracids
such as trifluoroperacetic acid, perbenzoic acid and
m-chloroperbenzoic acid. Excess utilization of these oxidants
potentially produces large amounts of harmful wastes that
lead to serious environmental problems [2–5]. In addition,
the preparation of these reagents requires hazardous con-
centration levels of hydrogen peroxide (H2O2). Recently,
there have been many researches trying to find chemically
green reagents, oxidants and catalysts, which can overcome
to abovementioned disadvantages [6, 7].
In order to overcome the above problems, the new
effective heterogeneous catalysts based on cellulose-sup-
ported dendritic Sn complex [27] montmorillonite (MMT)
supported tin (II) chloride [28], Sn-palygorskite [29] and
aminomethyl polystyrene resin-supported tin complex [30]
were reported for the chemoselective Baeyer–Villiger
oxidation of a variety of cyclic and acyclic that can
selectively activate the ketone instead of the H2O2. This
way readily leads to increase of the positive charge on the
carbon atom of the carbonyl group and facilitates the
nucleophilic attack on this group by H2O2. Therefore, high
yields and excellent selectivities can obtain in low con-
centration of H2O2 using these catalytic systems.
As another potential catalyst for this reaction, Lei et al.
[31] have recently used a silica-supported aluminum
chloride heterogeneous catalyst containing 2.65% Al with
H2O2 as oxidant, for the chemoselective Baeyer–Villiger
oxidation of a variety of cyclic and acyclic ketones at
70 °C. The utilization of hydrogen peroxide as oxidizing
N. O. Mahmoodi Á S. Z. D. Heirati (&) Á K. Ekhlasi-Kazaj
Department of Chemistry, Faculty of Science,
University of Guilan, P.O. Box 41335-1914, Rasht, Iran
e-mail: raha.heirati@gmail.com
123

522
J IRAN CHEM SOC (2012) 9:521–528
agent produces water (byproduct) which may decrease the
activity of the catalyst and even hydrolyze reaction product
in reaction media. In order to solve these problems, we
employed sodium peroxydisulfate as good alternative to
H2O2 for selective oxidation of a wide variety of cyclic and
acyclic ketones into the corresponding lactones and esters
in the presence of silica-supported aluminum chloride as
catalyst. Since peroxydisulfate ion is one of the strongest
oxidizing agents and is even stronger than H2O2 (Standard
redox potential in aqueous solution is estimated to be 2.01
compared to 1.77 for H2O2) [32], we expected to obtain
higher yields with sodium peroxydisulfate under mild
conditions (room temperature) compared to H2O2 (at
70 °C). Hence, to show the ability of this new oxidation
system we successfully prepared the silica-supported alu-
minum chloride and used it along with sodium peroxydi-
sulfate for Baeyer–Villiger oxidation of cyclic and acyclic
ketones under mild conditions (room temperature). In
continuation of work, some of the results of our experi-
ments are compared with some of those reported for the
current heterogeneous catalysts with respect to their yield,
selectivity and the reaction temperature.
O
O
O
Na2S2O8, silica-AlCl3
1,4-dioxane, r.t
Scheme 1 Baeyer–Villiger oxidation of cyclohexanone into e-
caprolactone
for 1 h. Aluminum chloride (2 g) was then added to the
mixture and resultant slurry was stirred at room tempera-
ture for 2 days. The precipitates were collected by filtration
under reduced pressure, washed with excess amounts of
°
ethanol, and dried at 100 C under vacuum for 3 h. In order
to determine the amount of AlCl3 on the silica surface,
0.5 g of solid catalyst was fused with Na metal, extracted
with 5 ml of water and filtered. The aluminum and chloride
content of the filtrate was determined by the Mohr titration
method [33].
Ketone oxidation
A typical procedure for the Baeyer–Villiger oxidation is as
the following: silica-supported aluminum chloride (0.97 g)
was added to a stirred mixture of cyclohexanone (0.25 mL,
2.5 mmol) and sodium peroxydisulfate (1.19 g, 5 mmol) in
5 mL of 1,4-dioxane. The suspension was stirred at room
temperature for 24 h (Scheme 1). The progress of the
reaction was monitored by thin-layer chromatography
(TLC) (eluent: diethyl ether/ethyl acetate: 3/1). After the
completion of reaction, the catalyst was removed by fil-
tration, and washed twice with 1,4-dioxane. The combined
filtrates were evaporated to remove the solvent in vacuo
and then the resulting residue was identified by GC/MS
analysis procedure. Other cyclic and acyclic ketones were
also oxidized in this oxidation system to give the corre-
sponding lactones or esters. All of the products were
known, and their structures determined by comparing mass
spectra and fragmentation patterns with a GC/MS instru-
ment library search (Wiley 275) and those of the authentic
compounds [34].
Experimental
Aluminum chloride, peroxydisulfate salts, silica gel
(chromatographic-grade, 70–230 mesh), and all the ketones
used in the experiments were purchased from Merck
Company and used without further purification. All sol-
vents obtained from commercial sources were used as
received.
Methods and instrumentations
The progress of the reactions were monitored by thin-layer
chromatography (TLC) carried out on Sigma-Aldrich silica
gel 60 F254 plates. The products were washed twice with
1,4-dioxane and then dried in the vacuo. The obtained
products were detected via retention times as measured by
GC/MS analysis on a Hewlet-Packard 6890 GC instrument
(Helium as carrier gas) furnished with an HP-5MS (30
m 9 0.25 mm 9 0.25 lm) column and Hewlet-Packard
5973N MSD instrument. The loading of AlCl3 in the cat-
alyst was determined by the Mohr titration. IR spectra were
recorded on a Shimadzu 470-IR spectrophotometer as neat
films on KBr pellets.
Results and discussion
Catalyst preparation and characterization
Aluminum chloride is very active catalyst in oxidation of
cyclic and acyclic ketones that is soluble in many organic
solvents and produces unwanted side reactions. Using
silica-supported aluminum chloride, the high reactivity of this
active Lewis acid is under control that leads to quantitative
and selective yields [35].
Catalyst preparation
Catalyst was prepared according to the literature method
[31]. Chromatographic-grade Silica gel (1 g, 70–230 mesh)
was leached with 1 M HCl (40 mL) at room temperature
123

J IRAN CHEM SOC (2012) 9:521–528
523
Silica-supported aluminum chloride that is a Brønsted
acid with a strength intermediate between zeolites and
magic acid was prepared by reacting of aluminum chloride
with silica under carefully controlled conditions [36]. At
the first, the silica was conditioned via leaching with 1 M
HCl to form a specified range of surface silanols. The silica
is then reacted with aluminum chloride by stirring at room
temperature (Scheme 2).
while there is not any peak at these positions in the spec-
trum of the natural silica. The loading of AlCl3 in the
catalyst based on its chloride determination was 1.6 mmol
AlCl3/g. The result confirms that silica-supported alumi-
num chloride catalyst was successfully prepared in this
work.
Oxidation mechanism
Figure 1 displays IR spectra of natural silica and silica-
supported aluminum chloride. Comparison of two IR
spectra reveals that the peak positions and shapes of the
main specific bands in the spectra are quite similar to each
other. For example, the bands corresponding to the sym-
metric and asymmetric vibrations of Si–O–Si are situated
at 829 and 1,110 cm-1, respectively, and are present in the
two spectra. The main differences between the two spectra
is due to the two additional bands at 600 and 660 cm-1
corresponding to backbone vibrations of Al–O groups,
A possible reaction mechanism using silica-supported
aluminum chloride as catalyst for the Baeyer–Villiger
oxidation of cyclopentanone is shown in Scheme 3.
First, the ketone is coordinated to the Lewis acid Al3?
center, and thereby, the carbonyl group is activated.
Sodium peroxydisulfate subsequently attacks the electro-
philic carbonyl carbon atom of coordinated ketone that
leads to Criegee adduct intermediate. After the intramo-
lecular rearrangement, the lactone product is replaced by a
Scheme 2 Reaction of AlCl3
with silica gel
Fig. 1 The IR spectra of natural
silica and silica-AlCl3
123

524
J IRAN CHEM SOC (2012) 9:521–528
Scheme 3 Catalytic
mechanism for the oxidation
of cyclopentanone with
Na2S2O8/silica-AlCl3
new substrate molecule. This mechanism is analogous to
that for peracids, which Corma et al. [6] have confirmed by
means of an 18O labeling experiment, infrared spectros-
copy and gas chromatography–mass spectrometry.
into corresponding lactone quantitatively when the reaction
was carried out using 1,4-dioxane as the solvent at room
temperature for 24 h.
Subsequently, as Table 1 shows, the effect of the molar
of substrate to oxidant under reaction conditions has been
investigated. The results show the molar ratio of cyclo-
hexanone to sodium peroxydisulfate had significant effect
on the oxidation reaction. When the molar ratio of cyclo-
hexanone to sodium peroxydisulfate was 2.5:2.5, the cor-
responding lactone was obtained in 74% yield (Entry 1).
The yield of reaction with 2.5 mmol of cyclohexanone
increased slowly with increasing the amount of sodium
peroxydisulfate up to 5 mmol, giving 84%. When the ratio
was increased to 2.5:6, the yield was 84% that was not
increased (Entry 5). Hence, the optimum molar ratio of
cyclohexanone to sodium peroxydisulfate was chosen
2.5:5.
Reaction optimization
Amount of catalyst is very important for a reaction, so we
investigated the effect of amount of silica-supported alu-
minum chloride catalyst on the Baeyer–Villiger oxidation
of cyclohexanone. Generally, the reaction yield was
increased over the amount of catalyst. It was found that
0.97 g of catalyst was appropriate amount for reaction.
The less amounts gave a low yield, and more amounts
could not cause the obvious increase for yield of product.
Hence, the optimum ratio of catalyst to substrates was
chosen 0.97 g: 5 mmol, and cyclohexanone was converted
123

J IRAN CHEM SOC (2012) 9:521–528
525
From Table 2, it can be observed the fact that using
sodium peroxydisulfate as oxidant exhibits the higher
conversion of cyclohexanone into corresponding lactone,
indicating that sodium peroxydisulfate is the best reagent
among all peroxydisulfate salts used in Baeyer–Villiger
oxidation of cyclohexanone. For this reason, sodium per-
oxydisulfate oxidation of other cyclic and acyclic ketones
in the presence of silica-supported aluminum chloride as
catalyst at room temperature has been developed.
Table 1 The effect of cyclohexanone/Sodium peroxydisulfate molar
ratio on Baeyer–Villiger oxidation of the cyclohexanone by silica-
AlCl3
O
O
O
Na2S2O8, silica-AlCl3
1,4-dioxane, r.t
Conversiona (%)
Oxidation of other cyclic and acyclic ketones
Entry
Substrate/oxidant
1
2
3
4
5
2.5:2.5
2.5:3
2.5:4
2.5:5
2.5:6
74
77
81
84
84
A series of cyclic and acyclic ketones were oxidized with
sodium peroxydisulfate catalyzed by silica-AlCl3 affording
the corresponding lactones or esters. Table 3 summarizes
the related results.
It can be seen from Table 3 that the yields of reactions
were good-to-excellent which shows sodium peroxydisul-
fate is an active and efficient oxidant in the Baeyer–
Villiger oxidation of cyclic and acyclic ketones in the
presence of silica-supported aluminum chloride as catalyst.
The conversion after 24 h of reaction for Entry 2 was
equal to 84% With substituted methylcyclohexanone
(Entry 4 in Table 3), the catalytic activity for the desired
product decreased to 74%. Actually, this result is consistent
with the proposed mechanism. In fact, the presence of two
methyl substitutes in methylcyclohexanone must hinder the
adsorption of the catalyst and hence the formation of the
Criegee adduct. This could be the reason why the catalyst
activity is lower for substituted methylcyclohexanone
compared to cyclohexanone. In case of unsymmetrical
ketones (Entries 10–13 in Table 3), the expected esters
were obtained in ratios depending on the migratory apti-
tude of the group adjacent to the carbonyl moiety. In fact,
less than 100% selectivity can be ascribed to their asym-
metry allowing the formation of two different esters. The
outstanding of this catalytic system was that the catalyst is
active for the oxidation of cyclic and acyclic ketones under
mild reaction conditions, and it may facilitate the devel-
opment of its industrial applications. Furthermore, the sil-
ica-supported aluminum chloride could be easily separated
from the reaction mixture only by filtration.
Reaction condition: Substrate 2.5 mmol, reagent 2.5–6 mmol, Cata-
lyst 0.97 g, 1,4-dioxane 5 ml, r.t, 24 h
a
Conversion percentage was determined by GC/MS analysis
Baeyer–Villiger oxidations of cyclohexanone
with different peroxydisulfate salts
Actually, commercially available compounds containing
peroxydisulfate ion are sodium peroxydisulfate, potassium
peroxydisulfate and di-ammonium peroxydisulfate. For
comparison of the effect of different peroxydisulfate salts
as oxidant on yield of cyclohexanone under established
optimum conditions, cyclohexanone has been used as the
substrate with different peroxydisulfate salts in the pres-
ence of silica-supported aluminum chloride. The mixture of
reaction was also stirred at room temperature for 24 h. The
results are summarized in Table 2.
Table 2 Oxidation of cyclohexanone with different peroxydisulfate
salts
O
O
O
Na2S2O8, silica-AlCl3
1,4-dioxane, r.t
Catalyst reuse
In order to investigate the recycling properties of silica-
supported aluminum chloride as the catalyst, three batches
of the experiments (Table 4) were carried out for 24 h at
room temperature in 1,4-dioxane. Then, cyclohexanone
was chosen as the test substrate for the oxidation with
sodium peroxydisulfate. The catalyst is repeatedly filtered
out and washed with excess 1,4-dioxane, afterward it was
submitted to a new reaction batch. At this step, it could be
Entry
Reagent
Conversiona (%)
1
2
3
Na2S2O8
K2S2O8
84
77
70
(NH4)2S2O8
Reaction condition: substrate 2.5 mmol, reagent 5 mmol, catalyst
0.97 g, 1,4-dioxane 5 ml, r.t, 24 h
a
Conversion percentage was determined by GC/MS analysis
123

526
J IRAN CHEM SOC (2012) 9:521–528
Table 3 Baeyer–Villiger oxidation of the ketones by Na2S2O8/silica-AlCl3
Entry
1
Substrate (a)
Selectivitya (%)
Conversiona (%)
Product (b)
100
100
O
O
O
O
2
100
84
O
O
3
4
100
100
73
72
O
O
O
O
O
O
5
100
90
O
O
O
But
t-Bu
O
6
7
100
100
85
82
O
O
O
O
O
8
100
65
O
O
O
O
O
O
9
100
83
78
72
71
10
11
O
O
O
73
O
O
O
12
13
72
75
78
82
O
O
O
O
O
O
Reaction condition: substrate 2.5 mmol, reagent 5 mmol, catalyst 0.97 g, 1,4-dioxane 5 ml, r.t, 24 h
a
Conversion percentage was determined by GC/MS analysis
123

J IRAN CHEM SOC (2012) 9:521–528
527
Comparison with other oxidation systems
Table 4 The recycling of silica-supported aluminum chloride
In Table 5, some of the results of the experiments are
compared with those reported by other methods. The
results show that when the oxidative activities of H2O2 and
sodium peroxydisulfate for the Baeyer–Villiger oxidation
of cyclopentanone in the presence of silica-supported alu-
minum chloride as catalyst were compared (Entries 1 and
5), using sodium peroxydisulfate as oxidant led to higher
yield and selectivity than using H2O2. The utilization of
hydrogen peroxide as oxidant produces water (byproduct)
which could decrease the activity of the catalyst and even
hydrolyze reaction product in Baeyer–Villiger oxidation. In
contrast, the usage of sodium peroxydisulfate as oxidizing
agent avoids the hydrolysis of products, since no water is
formed in reaction media. These could be the reasons why
the H2O2 shows low yield and selectivity compared to
sodium peroxydisulfate in the presence of same catalyst.
The oxidation under mild conditions (room temperature)
and high yield could be the obvious advantages for Bae-
yer–Villiger oxidation of cyclopentanone with sodium
peroxydisulfate in the presence of silica-supported alumi-
num chloride compared to those reported with H2O2 oxi-
dant in the presence of other catalysts (Entries 1–4).
O
O
O
Na2S2O8, silica-AlCl3
1,4-dioxane, r.t
Recycling time
Conversiona (%)
1
2
3
84
76
63
Reaction condition: substrate 2.5 mmol, reagent 5 mmol, catalyst
0.97 g, 1,4-dioxane 5 ml, r.t, 24 h
a
Conversion percentage was determined by GC/MS analysis
obtained that the activity is 76 and 63% after two and
three cycles, respectively. As shown in Table 4, silica-
supported aluminum chloride could be recycled as the
heterogeneous catalyst, even although the catalytic con-
version is lowered to about 63% from the original 84%
after three batches of the recycling experiment. Actually,
the reason of decreasing the catalytic activity is unclear. It
could be due to happening the continuous catalyst
leaching at each cycle or blocking of the active sites in the
catalyst by either products or intermediates involved in
the reaction.
Conclusion
At this work, an efficient and mild method has been
described for the Baeyer–Villiger oxidation of cyclic and
acyclic ketones to the relevant lactones or esters at room
temperature using sodium peroxydisulfate in the presence
of silica-AlCl3 as catalyst. This procedure leads to high
product yields together with the complete absence of
byproduct problems. However, the proposed method could
strongly be considered as a procedure for the future works
due to mild reaction conditions, reasonable results, ease of
workup and reusability of the catalyst as well.
Table 5 Comparison of some of the results obtained from Na2S2O8/
Silica-AlCl3 and some of those reported with H2O2/Sn-MMT, H2O2/
Sn-palygorskite, H2O2/Sn-PS and H2O2/Silica-AlCl3
O
O
Na2S2O8, silica-AlCl3
1,4-dioxane, r.t
O
Mass spectroscopic data
Entry Oxidation system Conversionb Selectivity Temp Ref.
Compound 1b: GC–MS (EI?, 70 eV): m/z 100 (M?), 70,
56, 42, 41 (100%), 28, 27.
(%)
(%)
(°C)
Compound 2b: GC–MS (EI?, 70 eV): m/z 114(M?), 84,
70, 55 (100%), 56, 42, 41, 28, 27.
1
Na2S2O8/Silica-
AlCla3
100
100
r.t
–
Compound 3b: GC–MS (EI?, 70 eV): m/z 128(M?), 98,
84, 70, 69, 55 (100%), 41, 31, 29, 27.
2
3
H2O2/Sn-MMT
45
81
100
100
90
70
[28]
[29]
H2O2/Sn-
palygorskite
Compound 4b: GC–MS (EI?, 70 eV): m/z 142(M?)
(100%), 127, 114, 98, 84, 70, 56, 42, 28, 15.
Compound 5b: GC–MS (EI?, 70 eV): m/z 170(M?), 155,
137, 125, 114 (100%), 97, 86, 68, 57.
Compound 6b: GC–MS (EI?, 70 eV): m/z 210 (M?), 127,
111, 99, 83 (100%), 71, 55, 43.
4
5
a
H2O2/Sn-PS
22
37
100
75
70
70
[30]
[31]
H2O2/Silica-AlCl3
Reaction condition: substrate 2.5 mmol, Na2S2O8 5 mmol, catalyst
0.97 g, 1,4-dioxane 5 ml, r.t, 24 h
b
Conversion percentage was determined by GC/MS analysis
123

528
J IRAN CHEM SOC (2012) 9:521–528
Compound 7b: GC–MS (EI?, 70 eV): m/z 166 (M?, 5),
122, 107, 93, 80 (100), 67, 53, 41.
12. A. Lambert, D.J. Macquarrie, G. Carr, J.H. Clark, New J. Chem.
24, 485 (2000)
13. J. Fischer, W.F. Holderich, Appl. Catal. A Gen. 180, 435 (1999)
14. B. Notari, Adv. Catal. 41, 253 (1996)
15. A. Corma, M.T. Navarro, L. Nemeth, M. Renz, J. Catal. 219, 242
(2003)
16. W.F. Holderich, J. Fischer, G. Schindler, P. Arntz, German Patent
DE 19745442 (1999)
17. R.P. Unnikrishnan, S.D. Endalkachew, J. Mol. Catal. A Chem.
191, 93 (2003)
18. M. Renz, T. Blasco, A. Corma, V. Fornes, R. Jensen, L. Nemeth,
Chem. Eur. J. 8, 4708 (2002)
19. Y. Liu, C.L. Chen, N.P. Xu, Chin. J. Catal. 25, 801 (2004)
20. R. Gavagnin, M. Cataldo, F. Pinna, G. Strukul, Organometallics
17, 661 (1998)
21. C. Bolm, O. Beckmann, Chirality 12, 523 (2000)
22. A.M. Phillips, C. Romao, Eur. J. Org. Chem. 64, 1767 (1999)
23. G.J.T. Brink, J.M. Vis, I.W.C.E. Arends, R.A. Sheldon, J. Org.
Chem. 66, 2429 (2001)
Compound 8b: GC–MS (EI?, 70 eV): m/z 102 (M?), 87,
75, 57 (100%), 45, 43, 29, 27, 15
Compound 9b: GC–MS (EI?, 70 eV): m/z 130 (M?), 101,
89, 71 (100%), 60, 43, 27, 15.
Compound 10b: GC–MS (EI?, 70 eV): m/z 88 (M?), 73,
70, 61, 43 (100%), 29.
Compound 11b: GC–MS (EI?, 70 eV): m/z 115 (M - 1),
101, 86, 73, 61, 56, 43 (100%), 29.
Compound 12b: GC–MS (EI?, 70 eV): m/z 102 (M?), 87,
61, 43 (100%), 31, 27, 15.
Compound 13b: GC–MS (EI?, 70 eV): m/z 116 (M?),
101, 57, 43 (100%), 29, 15.
Acknowledgments Authors thank the Research Committee of
University of Guilan for partial support given to the current research.
24. T. Miyauchi, H. Kurata, Japanese Patent 7109284A2 (1993)
25. S.E. Jacobson, R. Tang, F.J. Mares, J. Chem. Soc. Chem. Com-
mun. 888, (1978)
26. G. Strukul, Angew. Chem. Int. Ed. 37, 1198 (1998)
27. C. Li, J. Wang, Z. Yang, Z. Hu, Z. Lei, Catal. Commun. 8, 1202
(2007)
References
28. Z. Lei, G. Ma, C. Jia, Catal. Commun. 8, 305 (2007)
29. Z. Lei, Q. Zhang, J. Luo, X. He, Tetrahedron Lett. 56, 3505
(2005)
30. Q. Zhang, S. Wen, Z. Lei, React. Funct. Polym. 66, 1278 (2006)
31. Z. Lei, L. Wei, R. Wang, G. Ma, Catal. Commun. 9, 2467 (2008)
32. D.A. House, Chem. Rev. 62, 185 (1962)
33. I.M. Kolthoff, E.B. Sandell, in: (third ed.), Textbook of Quanti-
tative Inorganic Analysis, Macmillan Company, New York, 1965
34. National Institute of Advanced Industrial Science and Technol-
ogy, Japan. Spectral Database for Organic Compounds, SDBS.
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi.
(Last accessed: March 2010)
1. A. Baeyer, V.B. Villiger, Ber. Deut. Chem. Ges. 32, 3625 (1899)
2. G.R. Krow, Org. React. 43, 251 (1993)
3. B.M. Trost, Science 254, 1471 (1991)
4. W.F. Sager, A. Duckworth, J. Am. Chem. Soc. 77, 188 (1955)
5. S.L. Friess, N. Farnham, J. Am. Chem. Soc. 72, 5518 (1950)
6. A. Corma, L.T. Nemeth, M. Renz, S. Valencia, Nature 412, 423
(2001)
7. G. Strukul, Nature 412, 388 (2001)
8. G. Strukul, A. Varagnolo, F. Pinna, J. Mol. Catal. A Chem. 117,
413 (1997)
9. C. Palazzi, F. Pinna, G. Strukul, J. Mol. Catal. A Chem. 151, 245
(2000)
35. J.H. Clark, Acc. Chem. Res. 35, 791 (2002)
36. T. Xu, N. Kob, R.S. Drago, J.B. Nicholas, J.F. Haw, J. Am.
Chem. Soc. 119, 12231 (1997)
10. R. Bernini, E. Mincione, M. Cortese, R. Saladino, G. Gualandi,
M.C. Belfiore, Tetrahedron Lett. 44, 4823 (2003)
11. A. Berkessel, M.R.M. Andrae, Tetrahedron Lett. 42, 2293 (2001)
123