Optimization of asymmetric oxidation of sulfides with the Fe(salan) complex in water and the expanded scope of its application

Article abstract of DOI:10.1055/s-2008-1078427

The scope of asymmetric oxidation of sulfides using Fe(salan) complex as a catalyst and aqueous hydrogen peroxide as an oxidant in water was broadened by optimizing the reaction conditions with respect to reaction temperature, catalyst loading, and amount of water solvent. The oxidation proceeded with high enantioselectivity under the optimized conditions. The undesired over-oxidation of the resultant sulfoxides was significantly suppressed and the yields of sulfoxides were improved. Various functional groups were tolerant of the conditions.

Full text of DOI:10.1055/s-2008-1078427

CLUSTER
1543
Optimization of Asymmetric Oxidation of Sulfides with the Fe(salan) Complex
in Water and the Expanded Scope of its Application
Asymmetric
O
xida
i
tion of
r
Sulfides
o
w
ith the Fe
m
salan) Complex in W
i
ater chi Egami, Tsutomu Katsuki*
Department of Chemistry, Faculty of Science, Graduate School, Kyushu University, Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan
Fax +81(92)6422607; E-mail: katsuscc@chem.kyushu-univ.jp
Received 8 January 2008
We recently studied asymmetric oxidation of sulfides us-
Abstract: The scope of asymmetric oxidation of sulfides using
ing hydrogen peroxide, which is a highly atom-efficient
Fe(salan) complex as a catalyst and aqueous hydrogen peroxide as
an oxidant in water was broadened by optimizing the reaction con-
ditions with respect to reaction temperature, catalyst loading, and
oxidant,7,8 and found that cis-b Ti(salen)9 and Al(sala-
len)10 complexes could efficiently catalyze the oxidation
amount of water solvent. The oxidation proceeded with high enan- in methanol. However, simple application of these cata-
tioselectivity under the optimized conditions. The undesired over-
lysts to the oxidation in water produced poor results in
oxidation of the resultant sulfoxides was significantly suppressed
terms of enantioselectivity and the number of turnover
and the yields of sulfoxides were improved. Various functional
with the catalysts. This is perhaps because these complex-
groups were tolerant of the conditions.
es are not very stable in water due to the high oxophilicity
of Ti and Al ions and the presence of imine moieties in the
ligands, which may undergo hydrolysis under aqueous
Key words: asymmetric catalysis, oxidation of sulfides, iron, hy-
drogen peroxide, salan ligand
conditions. It has been recently found that the salan
ligand, which is structurally similar to the salen and sala-
Avoiding waste of limited resources is a major research
len ligands but has no hydrolyzable imino bond, can also
induce high asymmetry.11,12 Thus, we were intrigued by a
combination of the salan ligand and iron ion that is com-
paratively nitrogenophilic and exerts versatile oxidation
catalysis. A quick survey showed that the Fe(salan) com-
plex 1 is stable in water and shows excellent asymmetric
catalysis for oxidation of sulfides in water (Scheme 1).13
objective for sustainable chemistry. Enhancement in the
efficiency of reagent(s) use and elimination of inefficient
use of organic materials are ways to decrease wastes in
chemical transformation. In most reactions, organic sol-
vents that are used for dissolving substrate(s) and re-
agent(s) are discarded after completion of the reaction: the
amount of the solvent is typically larger than substrate(s)
and reagent(s). Therefore, development of alternatives to
organic solvents is an important objective. Water is abun-
dant and innocuous, and it is the best alternative, though
there are many problems to be solved in performing or-
ganic reactions in water: Most organic substrates and cat-
alysts are poorly soluble to water and the reactions in
water are usually too slow to be practical. In addition,
some metal-based catalysts are not stable in water. Asym-
metric catalysis has been a topic in synthetic chemistry
and a great deal of effort has been expended to realize
metal-catalyzed asymmetric reactions in water.1 As an ap-
proach to this end, formation of a specific space around a
metal complex in water has been explored with the use of
a polymer support and linker,2 a chiral metal-complex-
combined surfactant3 or by adding surfactant.4 On the oth-
er hand, utilization of interaction(s) between substrate and
catalyst such as hydrogen bonding or ion pairing is anoth-
er promising approach, especially in reactions using orga-
O–
S+
1 (1 mol%)
aq H2O2 (1.5 equiv)
O
O
S
S
+
R2
R1
R2
R1
R2
R1
H2O, 3 h, 20 °C
76 to >99%
24 to <1%
R1 = aryl or alkyl
2 = Me or Et
R
R
1 = aryl; 81–96% ee
1 = alkyl; 87–94% ee
R
(S)
Cl
N
O
N
O
Fe
Ph
Ph
(R)
1
Scheme 1 Asymmetric oxidation of sulfides with Fe(salan)
nocatalysts.5 Indeed, highly enantioselective catalytic Not only aromatic but also aliphatic sulfides could be ox-
asymmetric reactions in water have been achieved by in- idized at room temperature with high enantioselectivity.
troduction of sophisticated catalysts or reaction systems However, significant overoxidation of the resultant sulf-
based on the above approaches.6
oxides was observed in the oxidation of some sulfides un-
der these conditions. Fortunately, the minor enantiomers
of the sulfoxides were oxidized in an enantiomer-differen-
tiating manner to the corresponding sulfones, so that
enantiomeric excesses of the sulfoxides increased as the
reactions proceeded, at the expense of desired sulfoxides.
SYNLETT 2008, No. 10, pp 1543–1546
x
x
.x
x
.2
0
0
8
Advanced online publication: 16.05.2008
DOI: 10.1055/s-2008-1078427; Art ID: Y00208ST
© Georg Thieme Verlag Stuttgart · New York

1544
H. Egami, T. Katsuki
CLUSTER
In the present study, we describe the optimization of the Under the optimized conditions, we examined oxidation
conditions to obtain highly enantioselective oxidation of of various sulfides (Table 2). Overoxidation of sulfoxides
sulfides in water with a much smaller contribution of was well suppressed under these conditions, albeit not
enantiomer-differentiating overoxidation and a broadened completely. For the oxidation of aryl methyl sulfides un-
degree of oxidation.
der the original conditions, a considerable quantity of sul-
fones were formed, especially when the aryl group has an
electron-withdrawing group at the para position: for ex-
ample, the oxidation of 4b gave the sulfoxide 5b of 92%
ee in 84%, together with 16% of the sulfone. Under the
present conditions, the oxidation of 4b gave 5b of 92% ee
in 96%. Moreover, the present oxidation is highly
chemoselective. Oxidation of the sulfide S atom selective-
ly occurred in the presence of hydroxy or alkenyl groups,
while the oxidation of 4d was somewhat slow (entries 3
Oxidation of sulfides and the corresponding sulfoxides is
usually catalyzed by a common catalyst, though the oxi-
dation of the latter is slower than that of the former. How-
ever, Jackson et al. have reported that the optimized
temperatures for asymmetric oxidation of sulfides and ki-
netic resolution (enantiomer differentiation) of the corre-
sponding sulfoxides using the same vanadium catalyst
differ from one other and the optimized conditions for ki-
netic resolution are also influenced by several other fac-
tors.14 Thus, we expected that we could improve the
enantioselectivity in the oxidation of the sulfide with sig-
nificantly reduced overoxidation by optimizing the reac-
tion conditions. We first examined the influences of
reaction temperature, amount of water, catalyst loading,
etc. on the Fe(salan)-catalyzed oxidation of n-octyl meth-
yl sulfide (Table 1). Under the original conditions,13 18%
of the sulfoxide was oxidized to the sulfone, before the
sulfide was completely consumed (entry 1). When the cat-
alyst loading was reduced to 0.2 mol%, the overoxidation
was diminished to 10%, with a slight decrease in the enan-
tiomeric excess (entry 2). Lowering the reaction tempera-
ture to 0 °C significantly suppressed the overoxidation
without eroding the enantiomeric excess of the sulfoxide,
though the reaction did not proceed to completion even
for lengthy reaction times (entry 3). Fortunately, the reac-
tion proceeded to completion at that temperature without
diminishing the enantiomeric excess, when the amount of
water solvent was reduced (entry 4). Further lowering the
temperature to –10 °C slowed the reaction and deteriorat-
ed the enantioselectivity (entry 5).
Table 2 Asymmetric Oxidation of Various Sulfides Using 1a
1 (0.2 mol%)
aq H2O2 (1.5 equiv)
O–
S+
O O
S
S
+
R
R
R
H2O, 0 °C, 6 h
4
5
6
Entry
1
R
Yield of 5 Yield of 6 ee of5
(%)b
(%)b
(%)c
a
b
c
96
4
96 (S)
2
3
96
97
4
3
92 (S)
F
94
HO
3
4d
d
88
9
95
O
Table 1 Optimization of Asymmetric Oxidation of Methyl Octyl
Sulfide Using 1a
5e
e
f
96
4
5
95
92
O
O–
O O
S
1, aq H2O2 (1.5 equiv)
S+
S
+
O
n-C8H17
n-C8H17
n-C8H17
H2O
6e
92f
2
3
O
Entry
Temp
Time
(h)
Yield of 2 Yield of 3 ee of 2
(°C)
20
20
0
(%)b
(%)b
18
10
2
(%)c
O
1d
2
3
3
82
89 (S)
87 (S)
86 (S)
87 (S)
62 (S)
7
8
g
98
96
1
4
87 (S)
87 (S)
90
h
3
6
62
4e
5e
0
6
96
4
a The reactions were carried out on a 0.5 mmol scale in H2O (0.5 ml)
in the presence of 30% H2O2 (1.5 equiv) and 1 (0.2 mol%) at 0 °C, un-
less otherwise mentioned.
–10
12
85
2
a The reactions were carried out on a 0.5 mmol scale in H2O (1.25 mL)
in the presence of 30% H2O2 (1.5 equiv) and 1 (0.2 mol%), unless oth-
erwise mentioned.
b Determined by 1H NMR (400 MHz) spectroscopic analysis.
c Determined by HPLC analysis (DAICEL CHIRALCEL OB-H).
d Run with 0.4 mol% of 1.
b Determined by 1H NMR (400 MHz) spectroscopic analysis.
c Determined by HPLC analysis(DAICEL CHIRALCEL OB-H).
d Run with 1 (1 mol%).
e Run with 0.3 mol% of 1.
f Formation of a small amount (3%) of benzaldehydes derived from 4f
and 5f was observed.
e Run in H2O (0.5 mL).
Synlett 2008, No. 10, 1543–1546 © Thieme Stuttgart · New York

CLUSTER
Asymmetric Oxidation of Sulfides with the Fe(salan) Complex in Water
1545
[hexane–i-PrOH (80:20), 0.8 mL/min]: tR (major) = 11.3 min, tR
(minor) = 16.2 min. 1H NMR (400 MHz, CDCl3): d = 7.70–7.63 (m,
2 H), 7.27–7.20 (m, 2 H), 2.72 (s, 3 H).
and 4). No hydrolysis of the ester group was observed un-
der these conditions (entry 5). Moreover, benzylic acetal,
a highly acid-sensitive group, is almost compatible with
the present conditions: only 3% of the acetal was decom-
posed under the present conditions, while the decomposi-
tion amounted to 13% under the original conditions (entry
6). It is noteworthy that the oxidation of cyclohexyl meth-
yl sulfoxide 5g was also well suppressed under the present
conditions (entry 7).
3-[4-(Methylsulfinyl)phenyl]propan-1-ol (5c)
Colorless viscous liquid; 94% ee (c = 0.925, acetone). HPLC Anal-
ysis on DAICEL CHIRALCEL OB-H [hexane–i-PrOH (80:20), 0.8
1
mL/min]: tR (major) = 15.0 min, tR (minor) = 34.0 min. H NMR
(400 MHz, CDCl3): d = 7.57 (d, 2 H, J = 8.1 Hz), 7.36 (d, 2 H,
J = 8.1 Hz), 3.68 (t, 2 H, J = 6.3 Hz), 2.78 (t, 2 H, J = 7.8 Hz), 2.72
(s, 3 H), 1.95–1.86 (m, 2 H).
Although the detailed mechanism is unclear at the present,
we have observed that the crystalline and water-insoluble
complex 1 becomes liquid upon addition of sulfide and
the oxidation begins.15 This suggests that the coordination
of sulfide to the complex 1 is essential for this reaction. A
few substrates precipitated out upon cooling and their sug-
gested coordination would have been disturbed. Indeed,
the oxidation of p-chlorophenyl methyl sulfide that crys-
tallized out below 10 °C became sluggish.
4-(Allyloxymethyl)phenyl Methyl Sulfoxide (5d)
Colorless oil; 95% ee (c = 1.266, acetone). HPLC Analysis on
DAICEL CHIRALCEL OB-H [hexane–i-PrOH (80:20), 0.8 mL/
min]: tR (major) = 14.4 min, tR (minor) = 24.6 min. 1H NMR (400
MHz, CDCl3): d = 7.63 (d, 2 H, J = 8.1 Hz), 7.52 (d, 2 H, J = 8.1
Hz), 6.03–5.90 (m, 1 H), 5.33 (dd, 1 H, J = 1.7, 17.1 Hz), 7.24 (dd,
1 H, J = 1.7, 10.5 Hz), 4.58 (s, 2 H), 4.07 (d, 2 H, J = 5.4 Hz), 2.72
(s, 3 H).
4-(Methylsulfinyl)benzyl Acetate (5e)
In conclusion, optimizing the reaction conditions with re-
spect to reaction temperature, amount of water solvent,
and catalyst loading significantly expanded the scope of
the oxidation of sulfides using Fe(salan) complex 1 as a
catalyst in water and improved its enantio- and chemose-
lectivity.
Colorless viscous liquid; 95% ee (c 1.191, acetone). HPLC Analysis
on DAICEL CHIRALCEL OB-H [hexane–i-PrOH (50:50), 0.5 mL/
min]: tR (major) = 22.9 min, tR (minor) = 28.7 min. 1H NMR (400
MHz, CDCl3): d = 7.65 (d, 2 H, J = 8.3 Hz), 7.52 (d, 2 H, J = 8.3
Hz), 5.16 (s, 2 H), 2.73 (s, 3 H), 2.13 (s, 3 H).
2-[4-(Methylsulfinyl)phenyl]-1,3-dioxolane (5f)
Colorless solid; 92% ee (c = 1.241, acetone). HPLC Analysis on
DAICEL CHIRALCEL OB-H [hexane–i-PrOH (80:20), 0.8 mL/
min]: tR (major) = 25.9 min, tR (minor) = 30.9 min. 1H NMR (400
MHz, CDCl3): d = 7.70–7.63 (m, 4 H), 5.86 (s, 1 H), 4.18–4.03 (m,
4 H), 2.72 (s, 3 H).
General Experimental Procedure
The Fe(salan) complex 1 (1 mg, 0.2 mol%) was weighed into a
Schlenk tube followed by the addition of sulfide (0.5 mmol). Water
(0.5 ml) was added to the mixture and stirred for 10 min at 0 °C.
Then, H2O2 (82 mL, 1.5 equiv) was added to the suspension in one
portion and stirred for 6 h at that temperature in air. The reaction
mixture was diluted by H2O and brine (5 mL, each) and extracted.
The organic phase was passed through anhyd Na2SO4. The residue
was purified by chromatography on SiO2 (EtOAc) to give the cor-
responding sulfoxide. The ee was determined by HPLC analysis.
(S)-Decyl Methyl Sulfoxide (5h)
Colorless solid; 87% ee (c 0.958, CHCl3), lit. R-isomer:17 >98% ee
(c 1, CHCl3)]. HPLC Analysis on DAICEL CHIRALCEL OB-H
[hexane–i-PrOH (98:2), 0.7 mL/min): tR (major) = 18.1 min, tR (mi-
nor) = 20.3 min. 1H NMR (400 MHz, CDCl3): d = 2.79–2.60 (m, 2
H), 2.56 (s, 3 H), 1.82–1.70 (m, 2 H), 1.53–1.20 (m, 14 H), 0.88 (t,
3 H, J = 6.8 Hz).
3-[4-(Methylthio)phenyl]propan-1-ol (4c)
Colorless oil. 1H NMR (400 MHz, CDCl3): d = 7.20 (d, 2 H, J = 8.3
Hz), 7.12 (d, 2 H, J = 8.3 Hz), 3.65 (t, 2 H, J = 6.3 Hz), 2.68 (t, 2 H,
J = 7.6 Hz), 2.46 (s, 3 H), 1.90–1.81 (m, 2 H). 13C NMR (100 MHz,
CDCl3): d = 138.7, 135.1, 128.8, 127.0, 62.1, 34.2, 31.6, 16.4.
Acknowledgment
Financial support from Specially Promoted Research 18002011 and
the Global COE Program, ‘Science for Future Molecular Systems’
from the Ministry of Education, Science, and Culture, Japan is gra-
tefully acknowledged. H. E. is grateful for the JSPS Research Fel-
lowships for Young Scientists.
4-(Allyloxymethyl)phenyl Methyl Sulfide (4d)
Colorless oil. 1H NMR (400 MHz, CDCl3): d = 7.30–7.19 (m, 4 H),
5.88–5.33 (m, 1 H), 5.30 (ddd, 1 H, J = 1.7, 3.4, 17.2 Hz), 5.23–5.15
(m, 1 H), 4.48 (s, 2 H), 4.03–3.99 (m, 2 H), 2.48 (s, 3 H). 13C NMR
(100 MHz, CDCl3): d = 137.5, 135.1, 134.5, 128.2, 126.6, 117.0,
71.7, 7.1, 16.2.
References and Notes
4-(Methylthio)benzyl Acetate (4e)
Colorless oil. 1H NMR (400 MHz, CDCl3): d = 7.31–7.21 (m, 4 H),
5.05 (s, 2 H), 2.47 (s, 3 H), 2.08 (s, 3 H). 13C NMR (100 MHz,
CDCl3): d = 170.5, 138.6, 132.5, 128.8, 126.4, 65.9, 21.1, 15.9.
(1) (a) Kobayashi, S.; Manabe, K. Acc. Chem. Res. 2002, 35,
209. (b) Lindström, U. M. Chem. Rev. 2002, 102, 2751.
(c) Li, C.-J.; Chen, L. Chem. Soc. Rev. 2006, 35, 68.
(2) (a) Uozumi, Y.; Shibatomi, K. J. Am. Chem. Soc. 2001, 123,
2919. (b) Uozumi, Y.; Tanaka, H.; Shibatomi, K. Org. Lett.
2004, 6, 281. (c) Li, X.; Wu, X.; Chen, W.; Hancock, F. E.;
King, F.; Xiao, J. Org. Lett. 2004, 6, 3321. (d)Otomaru, Y.;
Senda, T.; Hayashi, T. Org. Lett. 2004, 6, 3357. (e) Nikai,
Y.; Uozumi, Y. Org. Lett. 2005, 7, 291. (f) Lee, B. S.;
Mahajan, S.; Janda, K. D. Tetrahedron Lett. 2005, 46, 4491.
(g) Uozumi, Y.; Suzuka, T. J. Org. Chem. 2006, 71, 8644.
(h) Uozumi, Y.; Kimura, M. Tetrahedron: Asymmetry 2006,
17, 161.
2-[4-(Methylthio)phenyl]-1,3-dioxolane (4f)
Colorless oil. 1H NMR (400 MHz, CDCl3): d = 7.39 (d, 2 H, J = 8.2
Hz), 7.25 (d, 2 H, J = 8.2 Hz), 5.77 (s, 1 H), 4.14–3.98 (m, 4 H),
2.47 (s, 3 H). 13C NMR (100 MHz, CDCl3): d = 139.5, 134.5, 126.8,
126.1, 103.3, 65.3, 15.8.
(S)-4-Fluorophenyl Methyl Sulfoxide (5b)
Colorless oil; 92% ee (c 1.575, acetone), lit. S-isomer:16 98.6% ee;
(c 1.5, acetone).; HPLC Analysis on DAICEL CHIRALCEL OB-H
Synlett 2008, No. 10, 1543–1546 © Thieme Stuttgart · New York

1546
H. Egami, T. Katsuki
CLUSTER
(3) (a) Azoulay, S.; Manabe, K.; Kobayashi, S. Org. Lett. 2005,
7, 4593. (b) Gu, Y.; Ogawa, C.; Kobayashi, J.; Mori, Y.;
Kobayashi, S. Angew. Chem. Int. Ed. 2006, 45, 7217.
(c) Boudou, M.; Ogawa, C.; Kobayashi, S. Adv. Synth.
Catal. 2006, 348, 2585.
(4) (a) Sinou, D.; Rabeyrin, C.; Nguefack, C. Adv. Synth. Catal.
2003, 345, 357. (b) Rabeyrin, C.; Sinou, D. Tetrahedron:
Asymmetry 2003, 14, 3891. (c) Rabeyrin, C.; Sinou, D.
J. Mol. Catal. A: Chem. 2004, 215, 89. (d) Hamada, T.;
Manabe, K.; Kobayashi, S. J. Am. Chem. Soc. 2004, 126,
7768. (e) Scarso, A.; Strukul, G. Adv. Synth. Catal. 2005,
347, 1227. (f) Hamada, T.; Manabe, K.; Kobayashi, S.
Chem. Eur. J. 2006, 12, 1205. (g) Colladon, M.; Scarso, A.;
Strukul, G. Adv. Synth. Catal. 2007, 349, 797..
Synthesis, 2nd ed., Vol. 2; Beller, M.; Bolm, C., Eds.; Wiley-
VCH: Weinheim, 2004, 479–495. (b) Bolm, C. Coord.
Chem. Rev. 2003, 237, 245.
(8) For recent examples of asymmetric sulfoxidation using H2O2
as terminal oxidant, see: (a) Page, P. B.; Heer, J. P.; Bethell,
D.; Lund, B. L. Phosphorus, Sulfur Silicon Relat. Elem.
1999, 153-154, 247. (b) Pelotier, B.; Ason, M. S.; Campbell,
I. B.; Macdonald, S. J. F.; Priem, G.; Jackson, R. F. W.
Synlett 2002, 1055. (c) Ohta, C.; Shimizu, H.; Kondo, A.;
Katsuki, T. Synlett 2002, 161. (d) Legros, J.; Bolm, C.
Angew. Chem. Int. Ed. 2003, 42, 5487. (e) Miyazaki, T.;
Katsuki, T. Synlett 2003, 1046. (f) Thakur, V. V.; Sudalai,
A. Tetrahedron: Asymmetry 2003, 14, 407. (g) Weix, D. J.;
Ellman, J. A. Org. Lett. 2003, 5, 1317. (h) Legros, J.; Bolm,
C. Angew. Chem. Int. Ed. 2004, 43, 4225. (i) Legros, J.;
Bolm, C. Chem. Eur. J. 2005, 11, 1086.
(5) Dalko, P. I.; Moison, L. Angew. Chem. Int. Ed. 2004, 43,
5138.
(6) (a) Luo, S.; Mi, X.; Liu, S.; Xu, H.; Cheng, J.-P. Chem.
Commun. 2006, 3687. (b) Hayashi, Y.; Sumiya, T.;
Takahashi, J.; Gotoh, H.; Urushima, T.; Shoji, M. Angew.
Chem. Int. Ed. 2006, 45, 958. (c) Hayasi, Y.; Aratake, S.;
Okano, T.; Takahashi, J.; Sumiya, T.; Shoji, M. Angew.
Chem. Int. Ed. 2006, 45, 5527. (d) Mase, N.; Nakai, Y.;
Ohara, N.; Yoda, H.; Takabe, K.; Tanaka, F.; Barbas, C. F.
III J. Am. Chem. Soc. 2006, 128, 734. (e) Mase, N.;
Watanabe, K.; Yoda, H.; Takabe, K.; Tanaka, F.; Barbas, C.
F. III J. Am. Chem. Soc. 2006, 128, 4966. (f) Zhong, L.;
Gao, Q.; Gao, J.; Xiao, J.; Li, C. J. Catal. 2007, 250, 360.
(g) Cao, Y.-J.; Lai, Y.-Y.; Wang, X.; Li, Y.-J.; Xiao, W.-J.
Tetrahedron Lett. 2007, 48, 21. (h) Giacalone, F.;
Gruttadauria, M.; Marculescu, A. M.; Noto, R. Tetrahedron
Lett. 2007, 48, 255. (i) Teo, Y.-C. Tetrahedron: Asymmetry
2007, 18, 1155. (j) Sathapornvajana, S.; Vilaivan, T.
Tetrahedron 2007, 63, 10253. (k) Luo, S.; Xu, H.; Li, J.;
Zhang, L.; Mi, X.; Zheng, X.; Cheng, J.-P. Tetrahedron
2007, 63, 11307. (l) Alza, E.; Cambeiro, X. C.; Jimeno, C.;
Pericás, M. A. Org. Lett. 2007, 9, 3717.
(9) Saito, B.; Katsuki, T. Tetrahedron Lett. 2001, 42, 3873.
(10) Yamaguchi, T.; Matsumoto, K.; Saito, B.; Katsuki, T.
Angew. Chem. Int. Ed. 2007, 46, 4729.
(11) (a) Sawada, Y.; Matsumoto, K.; Kondo, S.; Watanabe, H.;
Ozawa, T.; Suzuki, K.; Saito, B.; Katsuki, T. Angew. Chem.
Int. Ed. 2006, 45, 3478. (b) Matsumoto, K.; Sawada, Y.;
Katsuki, T. Synlett 2006, 3545.
(12) Sun, J.; Zhu, C.; Dai, Z.; Yang, M.; Pan, Y.; Hu, H. J. Org.
Chem. 2004, 69, 8500.
(13) The preliminary results have been communicated: Egami,
H.; Katsuki, T. J. Am. Chem. Soc. 2007, 129, 8940.
(14) (a) Drago, C.; Caggiano, L.; Jackson, R. F. W. Angew.
Chem. Int. Ed. 2005, 44, 7221. (b) Mohammadpoor-
Baltork, I.; Hill, M.; Caggiano, L.; Jackson, R. F. W. Synlett
2006, 3540.
(15) In 1H NMR analysis (D2O), signals of methyl phenyl sulfide
were broadened in the presence of 1 (sulfide/1 = 1:1).
(16) Wang, X.; Wang, X.; Guo, H.; Wang, Z.; Ding, K. Chem.
Eur. J. 2005, 11, 4078.
(17) Capozzi, M. A. M.; Cardellicchio, C.; Fracchiolla, G.; Naso,
F.; Tortorella, P. J. Am. Chem. Soc. 1999, 121, 4798.
(7) (a) Kagan, H. B.; Luukas, T. O. Catalytic Asymmetric
Sulfide Oxidations, In Transition Metals for Organic
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