Gold(III) catalyzed oxidation of sulfides to sulfoxides with hydrogen peroxide

Article abstract of DOI:10.1016/j.tetlet.2007.09.146

Au(III) catalyzed oxidation of sulfides to sulfoxides with 30% hydrogen peroxide in good yields and chemoselectivities was developed. It was shown that the catalyst loading can be decreased to 0.01 mol % with the good activity and chemoselectivity. Meanwhile, the catalyst was stable in the reaction system, which can be reused at least six cycles with similar activity and chemoselectivity.

Full text of DOI:10.1016/j.tetlet.2007.09.146

Available online at www.sciencedirect.com
Tetrahedron Letters 48 (2007) 8518–8520
Gold(III) catalyzed oxidation of sulfides to sulfoxides
with hydrogen peroxide
*
Yu Yuan and Yubo Bian
College of Chemistry and Chemical Engineering, Yangzhou University, 225002 Yangzhou, PR China
Received 14 June 2007; revised 24 September 2007; accepted 25 September 2007
Available online 22 October 2007
Abstract—Au(III) catalyzed oxidation of sulfides to sulfoxides with 30% hydrogen peroxide in good yields and chemoselectivities
was developed. It was shown that the catalyst loading can be decreased to 0.01 mol % with the good activity and chemoselectivity.
Meanwhile, the catalyst was stable in the reaction system, which can be reused at least six cycles with similar activity and
chemoselectivity.
ꢀ
2007 Elsevier Ltd. All rights reserved.
The use of Lewis-acid catalysts in modern organic
synthesis has been studied extensively during the last
afford sulfoxides in high yields and good
chemoselectivities.
1
4
1
,2
decade. Nowadays the research is focused on the more
versatile, more selective, and more reactive catalyst. It
has been found that gold Lewis acids are effective in
catalyzing the formation of C–C and oxidation reactions
O
S
S
HAuCl ·4H O
4 2
30% H O , r.t.
2
2
3
as the heterogeneous or the homogeneous catalysts. In
particular, gold catalyzed oxidation reactions have been
At the beginning, methyl phenyl sulfide was treated with
4
,5
applied in the epoxidation, oxidation of alcohols and
3
4
1
0% hydrogen peroxide in the presence of HAuCl4Æ
6
aldehydes, and the oxidative cleavage of C–C double
H O (1 mol % based on the sulfide) in methanol (Table
2
7
bonds. Sulfides oxidation is one of the most important
). After stirring the reaction mixture at room tempera-
organic processes, because the corresponding organo-
sulfur compounds are versatile intermediates in organic
synthesis and are useful for the preparation of biologi-
cally and medically important products.8–10 To the best
of our knowledge, two examples of gold Lewis acids
reveal the catalytic property in the reaction of sulfides
to sulfoxides. Gasparrini and co-workers applied the
gold(III) halides to catalyze the oxidation of sulfides to
sulfoxides by nitric acid under phase-transfer conditions
ture for 1 h, the methyl phenyl sulfide was completely
converted to the corresponding sulfoxide and sulfone
in good chemoselectivity (97:3) (entry 1). On decreasing
the catalyst loading under this condition, the reaction
time was prolonged for the satisfied conversion whereas
the ratio of the sulfoxide and sulfone was increased
Table 1. Oxidation of methyl phenyl sulfide with 30% hydrogen
1
1
in high yields. Hill developed a homogeneous aerobic
oxidation of thioethers with the molecular oxygen cata-
a
peroxide catalyzed by HAuCl
4 2
Æ4H O
b
b
1
2
Entry HAuCl Æ4H O Solvent
Time Convn
SO:SO2
4
2
lyzed by Au(III) clusters in water with good yields.
(
mmol)
(h)
(%)
Recently, the oxidation of sulfides to sulfoxides by
hydrogen peroxide has been proved to be one of the
1
2
3
4
5
6
0.01
CH
CH
CH
CH
CH
3
3
3
3
3
OH
OH
OH 12
OH
CN
1
6
99
96
94
42
94
97:3
98:2
99:1
88:12
93:7
100:0
1
3
0.001
0.0001
None
0.01
most attractive methods. Herein, we reported an easy
way to accomplish catalytic sulfoxidation process with
hydrogen peroxide in the presence of HAuCl Æ4H O to
1
3
1
4
2
0.01
Ether
<10
a
Reactions were carried out with 1:2 molar ratio of substrate and
at 25 ꢁC under an initial substrate concentration of 1.3 M.
Determined by GC on the crude reaction mixture.
*
Corresponding author. Fax: +86 0514 7975244; e-mail:
yyuan@yzu.edu.cn
2 2
H O
b
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.09.146

Y. Yuan, Y. Bian / Tetrahedron Letters 48 (2007) 8518–8520
8519
(
entries 2 and 3). Using 0.01 mol % gold catalyst, the
chemoselectivity of 99:1 could be achieved in 12 h with
4% conversion (entry 3). In comparison with 1 mol %
and high chemoselectivities. Introducing the bromo,
methyl, and amino group to the alkylarylsulfides, almost
no significant differences were obtained in the reaction
activity and the chemoselectivity (entries 2–6). However,
the chemoselectivity of oxidation of 4-methoxysulfide is
only 91:9 because the substrate is so active that H O
could readily react with it without catalyst (entry 7). It
was found that the nature of the starting sulfides con-
trols the reaction rate in the presence of the Au catalyst.
It was observed that the reaction rates of the electron-
withdrawing group at the para-position of alkylaryl-
sulfide and diarylsulfide were much lower than those
of other dialkylsulfides, which indicated that the elec-
tron-withdrawing group and the diaryl group produced
a strong deactivating effect in the oxidation process; on
the other hand, the chemoselectivity of the oxidation
was improved when the nitro function was present at
the para-position (entries 8–10).
9
catalyst loading, the 1 mol % catalyst loading possessed
the higher catalytic efficiency due to the short reaction
time. Other solvents were employed for the reaction,
including acetonitrile and ether. It was found that the
reaction in acetonitrile proceeded smoothly with the
high conversion and good chemoselectivity (93:7) (entry
2
2
5
). However, the reaction carried out in ether under the
same conditions was very sluggish with less than 10%
conversion (entry 6). An attempt to carry out the reac-
tion without the catalyst proved that the reaction could
occur with moderate conversion and chemoselectivity
in methanol at room temperature. It was shown that
HAuCl Æ4H O was an important catalyst for the high
4
2
conversion and chemoselectivity in the oxidation of
sulfides to sulfoxides.
With the good results in hand, the oxidations of a
variety of alkylarylsulfides and diarylsulfides with
hydrogen peroxide were investigated in the presence of
The gold mediated redox process has been studied from
a kinetic point of view. Considering the oxidation of
sulfides with H O in the absence of any catalyst, the
2
2
1
mol % HAuCl Æ4H O in methanol at room tempera-
possible reaction mechanism was proposed: It could
readily form the gold complexes of gold(III) and sulfides
4
2
ture. The reactions of all sulfides shown in Table 2 with
hydrogen peroxide took place smoothly to afford the
corresponding sulfoxides with good to excellent yields
1
5–17
under the substitution equilibria in the solution.
These gold(III) complexes were reacted with H O to give
2
1
2
the gold(I) complexes and sulfoxide. The reaction rate
of redox of gold(III)-sulfide complexes was much faster
than the direct oxidation of sulfides with H O in this
Table 2. Oxidation of sulfides to sulfoxides with hydrogen peroxide
catalyzed by HAuCl
a
2
2
4
2
Æ4H O
step. The obtained gold(I) complexes were immediately
oxidized to gold(III) complexes in the presence of
H O (Fig. 1).
b
b
2
c
Entry Substrate
Time Convn
SO:SO
Yield
(%)
(
h)
(%)
2
2
S
1
1
99
97:3
99:1
92
90
Due to the expense of the Au compounds, the recycled
uses of the Au catalyst are very necessary for saving
the catalyst cost. Upon completion of the reaction, the
S
2
7
96
aqueous layer containing HAuCl Æ4H O was collected
Br
4
2
and the catalyst was separated by removing water. The
recovered catalyst was reused for at least six cycles with
S
S
S
3
3
98
95
99:1
97:3
85
85
similar activity. It was shown that the HAuCl Æ4H O
Br
4
2
possesses high stability in the oxidation of sulfide
with hydrogen peroxide, which demonstrated that the
HAuCl Æ4H O can be totally reserved after the oxida-
4
0.8
Me
4
2
tion without any decomposition (see Table 3).
5
4
99
95
99:1
97
90
H2N
In conclusion, we have developed an Au(III) catalyzed
oxidation of sulfides to sulfoxides with 30% hydrogen
peroxide in good yields. The reactions were highly selec-
tive for the conversion of sulfides into the corresponding
S
6
0.7
100:0
Me N
2
S
7
0.7
99
95
94
96
91:9
85
94
92
95
MeO
-
AuCl4
S
R SR
1
2
8
27
21
20
100:0
100:0
99:1
NC
S
-
H O
2
9
AuCl (R SR )
n 1 2 4--n
O N
2
H O
2 2
O
S
1
0
R SR
1
2
+
(1-n)
a
AuCl (R SR )
n 1 2 2-n
Reactions were carried out with 1:2 molar ratio of substrate and
at 25 ꢁC under an initial substrate concentration of 1.3 M.
2 2
H O
b
c
Determined by GC on the crude reaction mixture.
Figure 1. The proposed mechanism of the oxidation of sulfides
catalyzed by HAuCl Æ4H O.
Isolated yield.
4
2

8520
Y. Yuan, Y. Bian / Tetrahedron Letters 48 (2007) 8518–8520
Table 3. Oxidation of methyl phenyl sulfide with 30% hydrogen
peroxide catalyzed by reused HAuCl Æ4H O
4 2
3. Hashmi, A. S. K.; Hutchings, G. J. Angew. Chem., Int. Ed.
2006, 45, 7896–7936.
a
4
. Chowdhury, B.; Bravo-Suarez, J. J.; Date, M.; Tsubota,
S.; Haruta, M. Angew. Chem., Int. Ed. 2006, 45, 412–415.
. Hughes, M. D.; Xu, Y.; Jenkins, P.; McMorn, P.; Landon,
P.; Enache, D. I.; Carley, A. F.; Attard, G. A.; Hutchings,
G. J.; King, F.; Stitt, E. H.; Johnston, P.; Griffin, K.;
Kiely, C. J. Nature 2005, 437, 1132–1135.
O
S
S
reused HAuCl ·4H O
4 2
5
2
eq 30% H O , r.t.
2 2
b
b
Entry
Catalyst
Convn (%)
SO:SO
2
6
. Guan, B.; Xing, D.; Cai, G.; Wan, X.; Yu, N.; Fang, Z.;
Yang, L.; Shi, Z. J. Am. Chem. Soc. 2005, 127, 18004–
1
2
3
4
5
6
1st use
2nd use
3rd use
4th use
5th use
6th use
99
100
99
100
100
100
97:3
94:6
96:4
95:5
93:7
93:7
1
8005.
7
8
9
. Xing, D.; Guan, B.; Cai, G.; Fang, Z.; Yang, L.; Shi, Z.
Org. Lett. 2006, 8, 693–696.
. Sulfur Reagents in Organic Synthesis; Metzner, P., Thu-
illier, A., Eds.; Academic Press: London, 1994.
. Drabowicz, J.; Kielbasinski, P.; Mikolajczyk, M. In The
Chemistry of Sulfones and Sulfoxides; Patai, S., Rappo-
port, Z., Stirling, C., Eds.; Wiley: Chichester, 1988; pp
a
The Reactions were carried out with 1:2 molar ratio of substrate and
at 25 ꢁC under an initial substrate concentration of 1.3 M.
Determined by GC on the crude reaction mixture.
2 2
H O
b
2
33–278.
1
1
0. Organosulfur Chemistry I, II; Page, P. C. B., Ed.; Springer:
Berlin, 1999.
1. Gasparrini, F.; Giovannoli, M.; Misiti, D. Tetrahedron
1983, 39, 3181–3184.
sulfoxides (up to 100:0). The catalyst loading can be
decreased to 0.01 mmol % with high yield and chemo-
selectivity, which showed the high activity of the cata-
lyst. Meanwhile, the catalyst was stable in the reaction
system, which can be reused at least six cycles with
similar activity and chemoselectivity.
12. Boring, E.; Geletii, Y. V.; Hill, C. L. J. Am. Chem. Soc.
2001, 123, 1625–1635.
1
3. Kaczorowska, K.; Kolarska, Z.; Mitka, K.; Kowalski, P.
Tetrahedron 2005, 61, 8315–8327.
1
4. Typical procedure of the sulfoxidation catalyzed by
HAuCl Æ4H O. A flask (10 mL) was charged with 118 lL
4
2
Acknowledgements
(
1.0 mmol) methyl phenyl sulfide, 4.1 mg (0.01 mmol)
HAuCl Æ4H O, and 0.5 mL methanol. To the resulting
mixture, 156 lL (2.0 mmol) of aqueous 30% H O was
4
2
This work was supported by the National Natural
Science Foundation of China (20702043), Jiangsu
Provincial Natural Science Foundation (BK2006549),
P.R. China, and by Program for New Century Excellent
Talents in Yangzhou University.
2
2
added and stirred at room temperature. The progress of
the reaction was followed by TLC. After disappearance of
the reactant, the product was extracted with EtOAc
(2 mL · 3) and washed with water. The organic layer
4
was dried over anhydrous MgSO . The solvent was
removed under vacuum and the residue was purified by
chromatography (eluting with 1:1 hexane/EtOAc).
5. Smith, G. M. J. Am. Chem. Soc. 1922, 44, 1769–1775.
6. Natile, G.; Bordignon, E.; Cattalini, L. Inorg. Chem. 1976,
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2