Highly efficient aerobic oxidation of oximes to carbonyl compounds catalyzed by metalloporphyrins in the presence of benzaldehyde

Article abstract of DOI:10.1016/j.tetlet.2009.11.078

Highly efficient oxidation of oximes to carbonyl compounds by molecular oxygen with benzaldehyde as an oxygen acceptor in the presence of metalloporphyrins has been reported. The simple structural manganese porphyrin showed an excellent activity for the oxidative deoximation reactions of various oximes. Moreover, different factors influencing oximes oxidation, that is, catalyst, solvent, and temperature, have been investigated. A possible mechanism for the deoximation reaction has been proposed.

Full text of DOI:10.1016/j.tetlet.2009.11.078

Tetrahedron Letters 51 (2010) 613–617
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Tetrahedron Letters
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Highly efficient aerobic oxidation of oximes to carbonyl compounds
catalyzed by metalloporphyrins in the presence of benzaldehyde
Xian-Tai Zhou a, Qiu-Lan Yuan b, Hong-Bing Ji a,
*
a School of Chemistry and Chemical Engineering, Sun Yat-sen University, 510275 Guangzhou, PR China
b School of Chemistry and Materials Science, Longyan University, Longyan, FuJian 364000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Highly efficient oxidation of oximes to carbonyl compounds by molecular oxygen with benzaldehyde as
an oxygen acceptor in the presence of metalloporphyrins has been reported. The simple structural man-
ganese porphyrin showed an excellent activity for the oxidative deoximation reactions of various oximes.
Moreover, different factors influencing oximes oxidation, that is, catalyst, solvent, and temperature, have
been investigated. A possible mechanism for the deoximation reaction has been proposed.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 4 October 2009
Revised 9 November 2009
Accepted 17 November 2009
Available online 20 November 2009
Keywords:
Oxime
Carbonyl compound
Oxidation
Metalloporphyrins
1. Introduction
oxidation of fluorenone oxime catalyzed by iron porphyrin under
high pressure conditions was reported by Groves group, in which
Oximes are extensively used for purification and characteriza-
tion of carbonyl compounds and preparation of amides via Beck-
mann rearrangement.1 At the same time, the synthesis of oximes
from noncarbonyl compounds also provides an alternative for pre-
paring aldehydes and ketones.2 So far, a variety of methods for
deoximation based on acid-catalytic hydrolysis,3 reductive cleav-
age,4 oxidative cleavage,5 and photosensitized oxidative deprotec-
tion6 have been developed. The oxidation methods employed
several oxidizing agents, that is, chromium reagents,7 KMnO4,8
manganese triacetate,5c N-bromosuccinimide,9 N2O4,10 NaIO4,11
and tert-butylhydroperoxide.5d Most of the reagents used in the
methods are hazardous or very toxic, usually causing severe envi-
ronmental pollution. Therefore, using clean and inexpensive oxi-
dants such as dioxygen for deoximation reactions are extremely
significant and particularly attractive from an environmental and
cost effective viewpoint.
the reaction rate increased with the increasing pressure of dioxy-
gen.14 When the pressure of molecular oxygen was about
3.5 MPa, fluorenone could be obtained with the yield of 86%.
In previous studies, a series of efficient catalytic systems for the
metalloporphyrins-catalyzed aerobic oxidation of olefin, sulfide,
alcohol, ketone, etc. have been developed in the presence of alde-
hyde as an oxygen acceptor.15 In continuation of our ongoing re-
search on the metalloporphyrins-catalyzed oxidations, herein the
efficient deoximation reaction catalyzed by manganese porphyrins
by dioxygen in the presence of benzaldehyde under ambient con-
ditions is reported (Scheme 1). Various oximes were readily re-
As model catalysts of cytochrome P-450, metalloporphyrins
have been widely used for the oxygenation of various organic com-
pounds, that is, alkanes, alkenes, and alcohols.12 However, few
studies on deoximation have ever been reported. Chauhan and
co-workers reported the oxidation of C@NOH bonds in ionic liquid
catalyzed by water soluble iron(III) porphyrins (Cl8TPPS4FeIII) with
hydrogen peroxide, in which various carbonyl compounds could be
obtained with yields of 45–80%.13 The only example on the aerobic
N
N
N
N
Mn
Cl
OH
R2
O
N
toluene,benzaldehyde, O2(1 atm), 50oC
R1
R2
R1
* Corresponding author. Tel.: +86 2084113658; fax: +86 2084113654.
E-mail address: jihb@mail.sysu.edu.cn (H.-B. Ji).
Scheme 1. Oxidation of oximes catalyzed by MnTPPCl in the presence of dioxygen
and benzaldehyde.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.11.078

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X.-T. Zhou et al. / Tetrahedron Letters 51 (2010) 613–617
Table 2
acted to afford the corresponding carbonyl compounds under mild
conditions. Furthermore, high-valent oxo intermediate was veri-
fied by UV–vis spectroscopy in the deoximation reaction, and a
plausible mechanism was proposed.
Effect of temperature on the aerobic oxidation of cyclohexanone oximea
Entry
T (°C)
Time (h)
Conv. (%)
Yield (%)
1
2
3
4
5
40
45
50
55
60
10
6
5
3
1.5
2
48
93
94
97
2
43
90
82
80
2. Oxidation of cyclohexanone oxime catalyzed by various
metalloporphrins
a
MnTPPCl (1 Â 10À3mmol), cyclohexanone oxime (1 mmol), toluene (5 mL),
The catalytic activity and selectivity of different metalloporphy-
rins for the oxidation of oxime to carbonyl compounds by molecu-
lar oxygen were investigated by using cyclohexanone oxime as a
model substrate.16 The engaged catalysts for the oxidation reac-
tions were simple structural metalloporphyrins that have the same
ligand meso-tetraphenylporphyrin (TPP) but different metals,
including MnTPPCl, RuTPPCl, FeTPPCl, and CoTPPCl. The results
are summarized in Table 1.
benzaldehyde (15 mmol), O2 bubbling.
idly to 93%, while the temperature rose to 50 °C (entry 3). With
the elevated temperature from 50 °C to 60 °C, no obvious incre-
ment was observed for the conversion of cyclohexanone oxime,
but its selectivity for cyclohexanone lowered. The substrate was
further converted to lactone at higher temperature (entries 5–6).
Such results indicated that 50 °C was the optimal reaction temper-
ature for the aerobic oxidation of cyclohexanone oxime.
The oxidation of cyclohexanone oxime catalyzed by these cata-
lysts produced cyclohexanone as the main product. As listed in Ta-
ble 1, almost no reaction was observed in blank experiment even
though the reaction time was prolonged to 8 h (entry 5). The cata-
lytic activity of metalloporphyrins for oxidation appeared to be
dependent on the nature of central ions. Manganese porphyrin
showed the best activity among the four simple structural metallo-
porphyrin catalysts, and presented excellent catalytic performance
for the oxidation of cyclohexanone oxime under mild condition
(entries 1–4). The catalytic activation of the four metalloporphy-
rins was in the sequence of MnTPPCl > FeTPPCl > CoTPPCl > RuT-
PPCl. The differences of the catalytic activities for various
metalloporphyrins were probably influenced by the stability of dif-
ferent valences of metal atoms and their electric potential.17 Man-
ganese porphyrin, the most reactive among the studied catalysts,
was chosen for further investigations. Attempts to obtain higher
activities of the electron-withdrawing metalloporphyrins (tetra-
(o-nitrophenyl) and tetra-(o-chlorophenyl) manganese porphyrin,
abbreviated as T(o-NO2)MnPPCl and T(o-Cl)MnPPCl)) for oxime
oxidation were unsuccessful, in which the conversions of cyclohex-
anone oxime were 91% and 87%, respectively (entries 6 and 7).
4. Effect of solvent on the oxidation of cyclohexanone oxime
With MnTPPCl as a catalyst, the aerobic oxidation of cyclohex-
anone oxime in various solvents has been investigated and the re-
sults are summarized in Table 3. The engaged solvents for the
oxidation reactions are toluene, acetonitrile, isopropanol, and
cyclohexane.
It could be observed from Table 3 that solvent played an impor-
tant role in the oxidation system. It seemed that acetonitrile and
toluene were favorable to the aerobic oxidation of cyclohexanone
oxime to cyclohexanone, which gave the yield of 90% and 88%,
respectively (entries 1 and 2). When isopropanol and cyclohexane
were used instead, very low yield of product could be obtained (en-
tries 3 and 4). The distinct results should be attributed to the inher-
ent characteristic of each solvent. Toluene as a solvent is often the
choice for radical reactions because of its reluctance to undergo
radical addition,18 and acetonitrile is an ideal replacement in the
oxidations catalyzed by metalloporphyrins.19
3. Effect of temperature on the oxidation of cyclohexanone
oxime
5. Effect of the amount of benzaldehyde on the oxidation of
cyclohexanone oxime
The effect of reaction temperature on the aerobic oxidation of
cyclohexanone oxime to cyclohexanone catalyzed by MnTPPCl
has been investigated, and the results are summarized in Table 2.
As shown in Table 2, it seemed that the conversion of cyclohex-
anone oxime was closely related to reaction temperature, and the
reaction rate increased with the raising temperature from 40 °C to
60 °C. When the temperature was 40 °C, almost no cyclohexanone
oxime could be converted to the corresponding product, although
the mixture was stirred for the prolonged reaction time (entry 1).
However, the conversion of cyclohexanone oxime increased rap-
The effect of the amount of benzaldehyde on the aerobic oxida-
tion of cyclohexanone oxime under ambient conditions was inves-
tigated and the results are listed in Table 4.
As shown in Table 4, it can be found that benzaldehyde played
an important role in the cyclohexanone oxime oxidation system
when dioxygen was employed as the sole oxidant. The oxidation
reaction stopped completely in the absence of benzaldehyde (entry
1), indicating that the metalloporphyrins have excellent perfor-
mance for activating dioxygen in the presence of benzaldehyde.
It also seemed that the reaction rate was related closely with the
amount of benzaldehyde. The higher molar ratio of benzaldehyde
could accelerate the oxidation. The conversion increased with the
Table 1
Aerobic oxidation of cyclohexanone oxime catalyzed by various metalloporphyrinsa
Entry
Catalyst
Conv. (%)
Yield (%)
Table 3
1
2
3
MnTPPCl
FeTPPCl
CoTPPCl
RuTPPCl
—
93
32
14
15
5
90
30
14
11
4
Effect of solvent on the aerobic oxidation of cyclohexanone oximea
Entry
Solvent
Time (h)
Conv. (%)
Yield (%)
4
5b
6
1
2
3
4
Toluene
5
6
6
6
93
93
21
2
90
88
21
2
Acetonitrile
Isopropanol
Cyclohexane
Mn(o-NO2)TPPCl
Mn(o-Cl)TPPCl
91
87
86
80
7
Catalyst (1 Â 10À3mmol), substrate (1 mmol), toluene (5 mL), benzaldehyde
a
a
MnTPPCl (1 Â 10À3mmol), cyclohexanone oxime (1 mmol), solvent (5 mL),
(15 mmol), 50 °C, 5 h, O2 bubbling.
b
benzaldehyde (15 mmol), O2 bubbling, 50 °C.
Reaction time was 8 h.

X.-T. Zhou et al. / Tetrahedron Letters 51 (2010) 613–617
615
Table 4
dehyde during the reaction. However, no significant difference was
observed when the amount of benzaldehyde was higher than
15 mmol (entry 5). Some papers reported that isobutyraldehyde
was effective for epoxidation,20 but it has been found that the yield
of cyclohexanone was only 45% when isobutyraldehyde was used
as the only oxygen transfer agent in the oxidative system (entry 6).
Effect of the amount of benzaldehyde on the aerobic oxidation of cyclohexanone
oximea
Entry Amount of benzaldehyde (mmol) Time (h) Conv. (%) Yield (%)
1
2
3
4
0
5
10
15
20
15
7
7
7
5
5
5
0
40
70
93
92
50
0
39
66
90
88
45
6. Aerobic oxidation of various oximes catalyzed by MnTPPCl
5
6b
Different substrates were examined for the aerobic oxidation
catalyzed by the MnTPPCl and the typical results are summarized
in Table 5.
a
MnTPPCl (1 Â 10À3mmol), cyclohexanone oxime (1 mmol), toluene (5 mL), O2
bubbling, 50 °C.
b
Isobutyraldehyde (15 mmol).
As shown in Table 5, the oxidations of most oximes occurred
smoothly to afford selectively the corresponding carbonyl com-
pounds by dioxygen in the presence of MnTPPCl under mild condi-
tions. Among the cyclic oximes, it seems that six-membered cyclic
amount of benzaldehyde raised from 0 to 15 mmol (entries 1–4),
which could be attributed to the continual consumption of benzal-
Table 5
Aerobic oxidation of various oximes catalyzed by manganese porphyrina
Entry
Oxime
Product
Time (h)
5
Conv. (%)
93
Yield (%)
90
OH
O
N
1
OH
O
N
2b
8
56
56
OH
O
N
3
4
8
6
85
85
OH
H
O
O
O
N
N
N
H
>99
>99
OH
5
2
2
>99
98
>99
84
HO
6c
OH
O
N
OH
7
6
8
6
>99
15
95
15
30
OH
OH
N
N
NO2
8
NO2
OH
N
N
9c
30
N
N
a
b
c
MnTPPCl (1 Â 10À3 mmol), substrate (1 mmol), toluene (5 mL), benzaldehyde (15 mmol), O2, 50 °C.
Isobutyraldehyde (15 mmol).
Acetonitrile (5 mL).

616
X.-T. Zhou et al. / Tetrahedron Letters 51 (2010) 613–617
oxime was more efficiently oxidized than other cyclic oximes, that
is, cyclooctanone and cyclopentanone oximes (entries 1–3). The
catalytic system seems favorable for the conversion of aromatic
oximes in short reaction times (entries 4–9). For example, aceto-
phenone oxime could be converted to the corresponding acetophe-
none completely within 2 h (entry 5). Steric structure almost has
no effect on the conversion of oximes, but has a slight effect on
the selectivity of carbonyl compound such as benzophenone oxime
(entry 6).
The oxidation efficiency for this catalytic system seems very
dependent on the electronic property of substrates. It is interesting
to find that the obtained product was nitrile rather than carbonyl
compound for the substrates with electron-withdrawing groups
at ortho-position (entries 8 and 9). Meanwhile, the yield of nitrile
was very low even with long reaction time, indicating that elec-
tron-withdrawing effect retarded the deprivation of oxime group.
However, the oxidation efficiency was not affected by electron-
denoting group of substrate (entry 7).
catalyzed by manganese porphyrin should involve radical species.
As described in our previous works,15a,21 high-valent metal inter-
mediate is generated from a series of radical species in the pres-
ence of dioxygen and aldehyde.
High-valent porphyrin intermediate is generally accepted as the
active species for the oxidations catalyzed by metalloporphyrins.22
The presence of manganese-oxo porphyrin was confirmed by UV–
vis spectra for the oxidation of cyclohexanone oxime, as demon-
strated in Figure 1. Curves a, b, and c show the spectra of solution
at the beginning, reacted for 15 min and 30 min, respectively. The
strength of Soret band of MnTPPCl at 476 nm decreased gradually,
suggesting the consumption of the oxidant active species
(MnIV@O) by substrate.19a,22a,23 In addition, color changes of the
reaction mixture from dark green to tinge also indicated valence
change of manganese. The GC results for these reactions revealed
the formation of cyclohexanone, which is indicative of the pres-
ence of an active oxidation species.
While investigating the catalytic efficiency for various sub-
strates, it is interesting to find that nitrile was the only product
for the substrates with electron-withdrawing groups at ortho-posi-
tion (Table 5, entries 8 and 9), while carbonyl compound was the
main product for the substrates with electron-donating group
(Table 5, entry 7). Such extremely different results could be attrib-
uted to different electronic atmosphere of C@N bond.
To get a better understanding, calculations were performed
with the GAUSSIAN03W package using the density functional theory
(DFT).24 Full geometry optimizations of different substrates were
performed employing Becke’s three parameter Lee–Yang–Parr cor-
relation functions (B3LYP) combined with 6-31+G(d,p) basis set.
The optimized structures for the substrates listed in Table 5 (en-
tries 7–9, o-hydroxy benzaldehyde oxime, o-nitro benzaldehyde
oxime and picolinaldehyde oxime as the substrates) are presented
in Figure 2. According to the calculated results, the Mulliken
charges for the carbon atom in C@N bond are À0.150 eV,
0.119 eV, and 0.086 eV, respectively. The oximes with electron-
withdrawing groups have a positive charge for the carbon atom,
which retards the nucleophilic attack of high-valent metal inter-
mediate to carbon atom. The oxidation of such oximes may pro-
ceed with another mechanism, in which the oximes tend to be
protonated firstly.
7. Plausible mechanism for the aerobic oxidation of oxime
catalyzed by MnTPPCl
When the oxidation of cyclohexanone oxime was conducted
with dioxygen and benzaldehyde in the absence of MnTPPCl, the
yield of cyclohexanone could only reach 4% (Table 1, entry 5). How-
ever, the yield was remarkably increased by adding 1 Â 10À3 mmol
of manganese porphyrin in the mixture (Table 1, 90%, entry 1). The
results clearly suggest that manganese porphyrin is crucial for the
deoximation reaction. Meanwhile, it was found that the reaction
was completely inhibited when the radical trap (2,6-di-tert-bu-
tyl-4-methylphenol) was used. Therefore, the deprivation of oxime
1.0
a
b
c
a:0 min
0.5
According to the above discussions, a plausible reaction mech-
anism for the deoximation reaction using MnTPPCl as a catalyst
has been proposed as shown in Figure 3. Based on the proposed
mechanism, the high-valent Mn porphyrins intermediate is gen-
erated as described in previous literatures. A adduct (a) could
be generated from the nucleophilic attack of the high-valent oxo
species to C@N bond, which produces the corresponding carbonyl
compounds 1 by decomposition (pathway A). Substrates with
electron-withdrawing groups tend to be protonated to give interme-
diate (b), which yields nitrile 2 via dehydration (pathway B).
b:15 min
c:30 min
0.0
460
480
500
520
wavelength/nm
Figure 1. UV–vis spectra of cyclohexanone oxime oxidation by molecular oxygen in
the presence of benzaldehyde and MnTPPCl.
Figure 2. Optimized structures and of oximes (1: o-hydroxy benzaldehyde oxime, 2: o-nitro benzaldehyde oxime, and 3: picolinaldehyde oxime) calculated at the B3LYP/6-
31+G(d,p) level of theory.

X.-T. Zhou et al. / Tetrahedron Letters 51 (2010) 613–617
617
OH
H
H+
PhCOOH
N
O
PorMnIV
R
PhCHO + O2
B
A
+
N OH2
R
C
H
PorMnIII
MnVPor
O
C
H
N O
(a)
R
R
C N
2
H2O
O
R
H
1
Figure 3. Plausible reaction mechanism of the oxidative deoximation catalyzed by MnTPPCl in the presence of molecular oxygen and benzaldehyde.
1612; (g) Ganguly, N. C.; De, P.; Sukai, A. K.; De, S. Synth. Commun. 2002, 32, 1–
7.
8. (a) Chrisman, W.; Blankinship, M. J.; Taylor, B.; Harris, C. E. Tetrahedron Lett.
2001, 42, 4775–4777; (b) Imanzadeh, G. H.; Hajipour, A. R.; Mallakpour, S. E.
Synth. Commun. 2003, 33, 735–740.
In conclusion, an efficient method for an aerobic oxidation of
oximes to the corresponding carbonyl compounds with manganese
porphyrin as a catalyst in the presence of benzaldehyde has been
developed. All the factors that effected cyclohexanone oxime oxi-
dation were well investigated. Various oximes could be success-
fully oxidized. The oxidative deoximation was through radical
process with the formation of high-valent manganese intermedi-
ate, which was confirmed by UV–vis spectroscopy. A possible
mechanism for the oxidative deoximation has been proposed.
9. Bandgar, B. P.; Kale, R. R.; Kunde, L. B. Monatsh. Chem. 1998, 129, 1057–1060.
10. Shim, S.; Kim, K.; Kim, Y. H. Tetrahedron Lett. 1987, 28, 645–648.
11. Varma, R. S.; Dahiya, R.; Saini, R. K. Tetrahedron Lett. 1997, 38, 8819–8820.
12. (a) Zhou, X. T.; Ji, H. B.; Pei, L. X.; She, Y. B.; Xu, J. C.; Wang, L. F. Chin. J. Org.
Chem. 2007, 27, 1039–1049; (b) Meunier, B. Biomimetic Oxidations Mediated by
Metal Complexes; Imperial College Press: London, 2000.
13. Jain, N.; Kumar, A.; Chauhan, S. M. S. Tetrahedron Lett. 2005, 46, 2599–2602.
14. Wang, C. C. Y.; Ho, D. M.; Groves, J. T. J. Am. Chem. Soc. 1999, 121, 12094–12103.
15. (a) Zhou, X. T.; Ji, H. B.; Yuan, Q. L. J. Porphyrins Phthalocyanines 2008, 12, 94–
100; (b) Ji, H. B.; Yuan, Q. L.; Zhou, X. T.; Pei, L. X.; Wang, L. F. Bioorg. Med. Chem.
Lett. 2007, 17, 6364–6368; (c) Zhou, X. T.; Ji, H. B.; Cheng, Z.; Xu, J. C.; Pei, L. X.;
Wang, L. F. Bioorg. Med. Chem. Lett. 2007, 17, 4650–4653; (d) Zhou, X. T.; Ji, H.
B.; Xu, H. C.; Pei, L. X.; Wang, L. F.; Yao, X. D. Tetrahedron Lett. 2007, 48, 2691–
2695.
16. General procedure for the aerobic oxidation of oximes to carbonyl compounds:
Typical procedure for the oxidation of oximes to carbonyl compounds
catalyzed by manganese porphyrin was described as: Dioxygen was bubbled
into a solution containing toluene (5 mL), oximes (1 mmol), benzaldehyde
(15 mmol), MnTPPCl (1 Â 10À3 mmol), and 0.8 mmol naphthalene (as an
internal standard) at 50 °C. The consumption of the starting oximes and the
formation of the corresponding carbonyl compounds were monitored by GC
(Shimadzu GC14C) and GC–MS (Shimadzu GCMS-QP2010).
Acknowledgments
The authors thank the National Natural Science Foundation of
China (20976203), the Key Fundamental Research Foundation
(2008CB617511), China Postdoctoral Science Foundation
(20080440792), and the Program for New Century Excellent Tal-
ents in University (NCET-06-740) for providing financial support
for this project.
References and notes
17. Guo, C. C.; Chu, M. F.; Liu, Q.; Liu, Y.; Guo, D. C.; Liu, X. Q. Appl. Catal., A 2003,
246, 303–309.
18. James, J. M.; Philip, J. O.; Gregg, A. U.; Bruno, L.; Dennis, P. C. Modern Solvents in
Organic Synthesis; Springer: New York, 1999.
1. Greene, T. W.; Wuts, P. G. Protective Groups in Organic Synthesis; John Wiley:
New York, 1999.
2. Kabalka, G. W.; Pace, R. D.; Wadgaonkar, P. P. Synth. Commun. 1990, 20, 2453–
2458.
19. (a) De Paula, R.; Simoes, M. M. Q.; Neves, M. G. P. M.; Cavaleiro, J. A. S. Catal.
Commun. 2008, 10, 57–60; (b) Liu, J. Y.; Li, X. F.; Li, Y. Z.; Chang, W. B.; Huang, A.
J. J. Mol. Catal. A 2002, 187, 163–167; (c) Naik, R.; Joshi, P.; Umbarkar, S.;
Deshpande, R. K. Catal. Commun. 2005, 6, 125–129; (d) Chan, W. K.; Liu, P.; Yu,
W. Y.; Wong, M. K.; Che, C. M. Org. Lett. 2004, 6, 1597–1599; (e) Kameyama,
H.; Narumi, F.; Hattori, T.; Kameyama, H. J. Mol. Catal. A 2006, 258, 172–
177.
20. (a) Nam, W.; Baek, S. J.; Lee, K. A.; Ahn, B. T.; Muller, J. G.; Burrows, C. J.;
Valentine, J. S. Inorg. Chem. 1996, 35, 6632–6633; (b) Nam, W.; Kim, H. J.; Kim,
S. H.; Ho, R. Y. N.; Valentine, J. S. Inorg. Chem. 1996, 35, 1045–1049; (c)
Ravikumar, K. S.; Barbier, F.; Begue, J. P.; Delpon, D. B. Tetrahedron 1998, 54,
7457–7464; (d) Qi, J. Y.; Qiu, L. Q.; Lam, K. H.; Yip, C. W.; Zhou, Z. Y.; Chan, A. S.
C. Chem. Commun. 2003, 1058–1059.
3. (a) De, S. K. Tetrahedron Lett. 2003, 44, 9055–9056; (b) Chavan, S. P.; Soni, P.
Tetrahedron Lett. 2004, 45, 3161–3162; (c) Lee, S. Y.; Lee, B. S.; Lee, C. W.; Oh, D.
Y. J. Org. Chem. 2000, 65, 256–257; (d) Martin, M.; Martinez, G.; Urpi, F.;
Vilarrasa, J. Tetrahedron Lett. 2004, 45, 5559–5561; (e) Shirini, F.; Zolfigol, M. A.;
Mallakpour, B.; Mallakpour, S. E.; Hajipour, A. R.; Baltork, I. M. Tetrahedron Lett.
2002, 43, 1555–1556.
4. Curran, D. P.; Brill, J. F.; Rakiewicz, D. M. J. Org. Chem. 1984, 49, 1654–1656.
5. (a) Davey, D. D.; Lumma, W. C. J. Org. Chem. 1989, 54, 3211–3213; (b) Shinada,
T.; Yoshihara, K. Tetrahedron Lett. 1995, 36, 6701–6704; (c) Demir, A. S.; Tanyeli,
C.; Altinel, E. Tetrahedron Lett. 1997, 38, 7267–7270; (d) Barhate, N. B.; Gajare,
A. S.; Wakharkar, R. D.; Sudalai, A. Tetrahedron Lett. 1997, 38, 653–656.
6. (a) Saravanselvi, C.; Somasundaram, N.; Vijaikumar, S.; Srinivasan, C.
Photochem. Photobiol. Sci. 2002, 1, 607–608; (b) de Lijser, H. J. P.; Fardoun, F.
H.; Sawyer, J. R.; Quant, M. Org. Lett. 2002, 4, 2325–2328; (c) Yang, Y.; Zhang,
D.; Wu, L. Z.; Chen, B.; Zhang, L. P.; Tung, C. H. J. Org. Chem. 2004, 69, 4788–
4791.
21. Chen, H. Y.; Ji, H. B.; Zhou, X. T.; Xu, J. C.; Wang, L. F. Catal. Commun. 2009, 10,
828–832.
22. (a) Rebelo, S. L. H.; Pereira, M. M.; Simoes, M. M. Q.; Neves, M. G. P. M.;
Cavaleiro, J. A. S. J. Catal. 2005, 234, 76–87; (b) Meunier, B.; Bernadou, J. Top.
Catal. 2002, 21, 47–54; (c) Meunier, B.; de Visser, S. P.; Shaik, S. Chem. Rev.
2004, 104, 3947–3980; (d) Stephenson, N. A.; Bell, A. T. J. Am. Chem. Soc. 2005,
127, 8635–8643.
7. (a) Bendale, P. M.; Khadilkar, B. M. Tetrahedron Lett. 1998, 39, 5867–5868; (b)
Shirini, F.; Mamaghani, M.; Rahmanzadeh, A. Arkivoc 2007, 34–39; (c) Shirini,
F.; Zolfigol, M. A.; Pourhabib, A. Russ. J. Org. Chem. 2003, 39, 1191–1192; (d)
Chakraborty, V.; Bordoloi, M. J. Chem. Res. 1999, 120–121; (e) Salehi, P.;
Khodaei, M. M.; Goodarzi, M. Synth. Commun. 2002, 32, 1259–1263; (f)
Ganguly, N. C.; Sukai, A. K.; De, S.; De, P. Synth. Commun. 2001, 31, 1607–
23. Nunes, G. S.; Mayer, I.; Toma, H. E.; Araki, K. J. Catal. 2005, 236, 55–61.
24. Frisch, M. J. GAUSSIAN W03, Revision D. 01; Gaussian: Wallingford, CT, 2004.