Rapid and highly chemoselective biomimetic oxidation of organosulfur compounds with tetrabutylammonium peroxymonosulfate in the presence of manganese meso-tetraphenylporphyrin and imidazole

Article abstract of DOI:10.1016/j.tetlet.2004.03.082

A novel and efficient method is described for the immediate oxidation of different organosulfur compounds using tetrabutylammonium peroxymonosulfate in the presence of manganese meso-tetraphenylporphyrin and imidazole. The method is highly chemoselective and the yields are excellent.

Full text of DOI:10.1016/j.tetlet.2004.03.082

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 3811–3815
Rapid and highly chemoselective biomimetic oxidation of
organosulfur compounds with tetrabutylammonium
peroxymonosulfate in the presence of manganese meso-
tetraphenylporphyrin and imidazole
*
*
Nasser Iranpoor, Daryoush Mohajer and Abdol-Reza Rezaeifard
Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Iran
Received 15 January 2004; revised 1 March 2004; accepted 12 March 2004
Abstract—A novel and efficient method is described for the immediate oxidation of different organosulfur compounds using tetra-
butylammonium peroxymonosulfate in the presence of manganese meso-tetraphenylporphyrin and imidazole. The method is highly
chemoselective and the yields are excellent.
Ó 2004 Published by Elsevier Ltd.
The oxidation of organosulfur compounds, which are a
major source of environmental pollution, is very
important from both industrial and green chemistry
S
R
R
S
B
1
points of view. On the other hand, their oxidation
products are useful precursors for biologically and
S
R
RSH
R
S
O
A
2;3
chemically important compounds. For example, sul-
fones (C, Scheme 1) and thiosulfonates (D, Scheme 2),
C
4
both of which occur in some pharmaceuticals, have been
extensively used as versatile intermediates in organic
S
R
R
S
5;6
synthesis. Recently, sulfones have been employed for
7
O
O
8
D
stabilizing a-radicals, a-anions, and acting as cationic
synthons. Thiosulfonates, with strong sulfenylating
9
Scheme 2.
power, have found wide industrial applications both in
polymer production and in photographic processes.
10
Decontamination procedures require very fast and
selective chemical transformations. In this regard, many
efficient catalysts for oxidative degradation of various
types of pollutants and residual wastes have been
S
R1
R2
A
4b;11
developed.
Biomimetic catalysts, in particular
O
S
metalloporphyrins, have been of considerable interest
for chemoselective oxidation of organosulfur com-
O
R1
O
R2
S
R1
R2
12
pounds, especially with respect to the catalytic role of
cytochrome P-450 and vitamin B12 in the oxidation of
B
C
13
biological sulfides and thiols.
Scheme 1.
In the course of our studies on tetrabutylammonium
peroxymonosulfate (TBAO) for oxidation of organic
compounds, we have explored it as an efficient oxidant
for the selective transformation of imines to oxazir-
Keywords: Sulfone; Thiosulfonate; Tetrabutylammonium peroxy-
monosulfate; Manganese porphyrin.
*
Corresponding authors. Tel.: +98-711-2284822; fax: +98-711-2280-
26; e-mail addresses: iranpoor@chem.susc.ac.ir; dmohajer@chem.
susc.ac.ir
14
9
idines. Its use in oxyfunctionalization of hydrocarbons
required activation by Mn-porphyrin. TBAO has also
15
0
040-4039/$ - see front matter Ó 2004 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2004.03.082

3812
N. Iranpoor et al. / Tetrahedron Letters 45 (2004) 3811–3815
a
b
Table 1. TBAO oxidation of sulfides, and sulfoxides, to sulfones catalyzed by Mn(TPP)OAc in the presence of Im
c
d
Entry
Substrate
Conversion%
Product
Yield% (Isolated)
Time (min)
O
O
O
S
S
1
100
100 (96)
<1
O
S
S
S
2
100
100
<1
O
O
O
O
S
S
3
4
100
100
100
100
<1
<1
S
S
O
O
5
6
100
100
S
100 (95)
100 (93)
<1
<1
O
O
S
S
O
O
O
S
S
7
8
100
100
100 (96)
100 (92)
<1
MeO
OMe
MeO
OMe
Me
O
S
S
3
O
2
N
Me
2
O N
O
O
NC
S
NC
S
9
100
100
100 (95)
100
3
Me
Me
1
1
0
1
S
S
<1
O
S
O
O
S
O
O
O
100
100
100
100
100
100
<1
<1
<1
O
S
O
O
S
S
1
1
2
3
O
S
O
a
b
c
The molar ratio for sulfide/TBAO/Im/Mn(TPP)OAc is 100:100:20:1.
The molar ratio for sulfoxide/TBAO/Im/Mn(TPP)OAc is 100:50:20:1.
The yields were based on the starting substrates determined by GLC (entries 1–4, 10–12) or H NMR (entries 5–9, 13). The identity of products were
1
18;11g
confirmed by comparison of their spectral data with known samples prepared according to the literature.
Isolated by silica gel column chromatography.
d
been introduced as a very sluggish oxygen source for the
oxidation of sulfides to sulfones (A ! C, Scheme 1).
corresponding sulfone. We found that the addition of
only 1 mol % of commercially available manganese
meso-tetraphenylporphyrin in the presence of imidazole
(Im) as co-catalyst, considerably improved the rate of
1
6
For example, oxidation of thioanisole by 3 equiv of
TBAO took four days to produce a 78% yield of the

N. Iranpoor et al. / Tetrahedron Letters 45 (2004) 3811–3815
3813
conversion (<3 min) and selectivity of sulfone formation
sulfones without formation of any benzylic oxidation
by-products.
(
pared TBAO,
100%) using a-stoichiometric amount of freshly pre-
16;17
at room temperature (A ! C, Scheme
1
).
The notable feature of this method is the efficient oxi-
dation of electron-deficient sulfides to sulfones. Most of
20
This catalytic system is very efficient for the oxygenation
the reported methods for this purpose, have some
limitations such as low yields or use of reagents, which
19
of sulfides to sulfones (Table 1). It leads to the com-
plete conversion of dialkyl, phenyl alkyl, phenyl allyl,
diphenyl, benzyl phenyl and dibenzyl sulfides to the
corresponding sulfones in excellent yields (100%) and
excellent selectivities (100%) within 1 min at room tem-
perature. Despite the efficiency of this method for the
11h
require special handling.
Sulfides having electron-
withdrawing substituents such as 4-nitrophenyl
4-methylphenyl sulfide and 3-cyanophenyl 4-methyl-
phenyl sulfide (entries 8 and 9), reacted completely
within 3 min with 100% selectivity for formation of their
corresponding sulfones. Oxidation of the electron-rich
sulfide, di-4-methoxyphenyl sulfide (entry 7) gave the
related sulfone as the sole product. This catalytic system
is also applicable to the efficient and rapid oxidation of
sulfoxides to sulfones (B ! C, Scheme 1, entries 11–13).
15
epoxidation of alkenes, a sulfide also having a carbon–
carbon double bond (entry 3), was cleanly transformed
11c
into the corresponding sulfone in excellent yield. In
addition, benzyl phenyl and dibenzyl sulfides (entries 5
and 6) were selectively oxidized to their corresponding
a
b
Table 2. TBAO oxidation of thiols and disulfides to thiosulfonates catalyzed by Mn(TPP)OAc in the presence of Im
c
Entry
Substrate
Conversion%
100
Product
Isolated yield%
Time (min)
O
O
O
S
1
96
<1
SH
S
O
Me
S
d
2
100
94 (100)
<1
Me
SH
S
Me
S
3
4
SH
SH
100
100
93
94
<1
<1
S
S
O
O
S
O
O
O
SH
d
e
5
6
7
100
100
100
S
O
95 (100)
3
S
O
S
O
97
<1
<1
S
S
S
O
Me
S
Me
S
O
95 (100)
d
S
Me
S
Me
S
S
8
9
S
100
100
96
94
<1
<1
S
O
O
S
S
S
S
O
O
O
S
d
10
100
S
O
92 (100)
<1
S
S
a
b
c
The molar ratio for thiol/TBAO/Im/Mn(TPP)OAc is 100:150:40:1.
The molar ratio for disulfide/TBAO/Im/Mn(TPP)OAc is 100:100:20:1.
The products were isolated by column chromatography and identified by comparison with known samples.
21
d
e
1
H NMR yields based on the starting materials.
H H
Conversion (100%) was observed within 1 min with the formation of 75% of thiosulfonate; d (ppm): 1.42, 1.60 along with 25% of thiosulfinate; d
22
1
(
ppm): 1.38, 1.56, using H NMR (250 MHz) analysis.

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N. Iranpoor et al. / Tetrahedron Letters 45 (2004) 3811–3815
Structurally different sulfoxides were readily oxidized to
their corresponding sulfones under the same reaction
conditions as sulfides, using 0.5 equiv of TBAO.
References and notes
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23
Scheme 2) has been of interest. Using this catalytic
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with excellent yields and selectivities at room tempera-
3
4
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5
6
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11e
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thiols, it is expected that disulfides should also be easily
oxidized to their corresponding thiosulfonates (B ! D,
9
1
1
0. Zefirof, N. S.; Zyk, N. V.; Beloglazkina, E. K.; Ku-
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5
Scheme 2) by this simple method. Inspection of our
results in Table 2 (entries 6–10) shows high chemo-
selectivity for the conversion of some symmetric aryl
and alkyl disulfides to the corresponding thiosulfonates
without the formation of any thiosulfinate (C, Scheme 2)
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3
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coupling of thiols to symmetrical disulfides (A ! B,
Scheme 2) under controlled conditions using a smaller
amount of Im. The gradual addition of a solution of
TBAO (0.25 mmol in 2 mL CH Cl ) over a 30 min per-
2
003, 68, 150–155; (g) Anisimov, A. V.; Fedorova, E.;
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2
2
iod to a cooled solution (ꢀ5 °C) of 4-methylbenzenethiol
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(
1
2. (a) Groves, J. T.; Viski, P. J. Org. Chem. 1990, 55, 3628–
3
2
2
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1
(
10%) determined by H NMR analysis. It was also
observed that the molar ratio of catalyst versus substrate
has a significant effect upon the selectivity of the oxi-
dation reactions. For example, the use of 0.0, 0.01, 0.02,
0
.1 and 1 mol % of Mn(TPP)OAc in the oxidation of
thioanisole (Table 1, entry 1) led to sulfoxide/sulfone
molar ratios of 0.8, 0.15, 0.12, 0.09 and 0.0, respectively.
It seems to us that the isolation of the intermediate
products [sulfoxide (B, Scheme 1) and thiosulfinate (C,
Scheme 2)] could be possible under controlled condi-
tions. Further investigations in this regard are under-
way.
1
1311.
1
3. (a) Brouwer, W. M.; Piet, P.; German, A. L. J. Mol. Catal.
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III
In conclusion, the remarkable efficiency of Mn meso-
tetraphenylporphyrin in the presence of Im for the
extremely rapid and highly chemoselective oxidation of
different organosulfur groups with TBAO under very
mild reaction conditions is described.
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1
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19. General procedure: TBAO (1 mmol) was added to a
solution of sulfide (1 mmol), Im (0.2 mmol), Mn(TPP)OAc
The research was supported by the Shiraz University
Research Council.

N. Iranpoor et al. / Tetrahedron Letters 45 (2004) 3811–3815
3815
(
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1
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2
6
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(0.01 mmol) in CH Cl (5 mL) and the mixture stirred
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1
by TLC and the yield of product was determined by H
NMR analysis of the reaction mixture or after purification
by chromatography over silica gel (eluent: cyclohexane/
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25. The procedure is similar to that mentioned in Ref. 19 only
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