Selective and mild oxidation of sulfides to sulfoxides or sulfones using H2O2 and Cp′Mo(CO)3Cl as catalysts

Article abstract of DOI:10.1016/j.tetlet.2008.05.126

Dialkyl, aryl-alkyl, benzylic, and benzothiophenic sulfides are selectively oxidized to sulfoxides or sulfones, with stoichiometric amounts of H₂O₂ (aq) or TBHP, in the presence of complexes Cp′Mo(CO)₃Cl, CpMoO₂Cl and the mesoporous material MCM-41-2 as catalysts. The use of the thianthrene 5-oxide (SSO) probe shows that CpMo(CO)₃Cl/H₂O₂ or TBHP are electrophilic oxidants (Xso ≤ 15). The same conclusion is drawn from competition experiments with a mixture of p-ClC₆H₄SCH₃ and C₆H₅SOCH₃.

Full text of DOI:10.1016/j.tetlet.2008.05.126

Tetrahedron Letters 49 (2008) 4708–4712
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Selective and mild oxidation of sulfides to sulfoxides or sulfones
0
using H O and Cp Mo(CO) Cl as catalysts
2
2
3
a,b,*
a
a
a
Carla A. Gamelas
, Tiago Lourenço , André Pontes da Costa , Ana L. Simplício ,
a
a,
*
Beatriz Royo , Carlos C. Romão
Instituto de Tecnologia Química e, Biológica da Universidade Nova de Lisboa, Av. República, EAN, 2780-157 Oeiras, Portugal
a
b
Escola Superior de Tecnologia, Instituto Politécnico de Setúbal, 2910-761 Setúbal, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Dialkyl, aryl–alkyl, benzylic, and benzothiophenic sulfides are selectively oxidized to sulfoxides or sulf-
Received 20 April 2008
Revised 25 May 2008
Accepted 28 May 2008
Available online 2 June 2008
0
ones, with stoichiometric amounts of H
CpMoO
SSO) probe shows that CpMo(CO)
clusion is drawn from competition experiments with a mixture of p-ClC
O
2 2
(aq) or TBHP, in the presence of complexes Cp Mo(CO)
3
Cl,
2
Cl and the mesoporous material MCM-41-2 as catalysts. The use of the thianthrene 5-oxide
Cl/H or TBHP are electrophilic oxidants (Xso 6 15). The same con-
SCH and C SOCH
(
3
2 2
O
H
6 4
3
H
6 5
3
.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Sulfoxide
Sulfone
Hydrogen peroxide
Molybdenum complexes
Sulfoxides and sulfones play important roles in synthetic organ-
ic chemistry and are important bioactive compounds.1 Further-
more, sulfoxidation catalysis has assumed special relevance
in the deep desulfurization of fuels, due to environmental
O
O
O
S
Cp'Mo(CO)3Cl , ∼1 eq. H2O2
S
S
R1
R2
Acetone:MeOH, low to rt
R1
R2
R1
R2
2
constraints.
Cp'Mo(CO)3Cl
Although there are many reported methods for the oxidation of
3
,4
~2 eq. H2O2/NCMe or TBHP/CH2Cl2, rt
sulfides to sulfoxides, metal-mediated oxidizing systems for the
5
preparation of sulfones are unusual in literature. Only a few re-
Scheme 2.
ports are available for the selective synthesis of sulfoxides and sulf-
ones with the same reagent system, under adjusted reaction
6
conditions.
Si
2 2 2
Although complexes MoO X L are important catalysts for oxy-
7
O
O
O
O
gen atom transfer reactions, organometallic oxo complexes have
0
not been so extensively used. Nevertheless, several Cp MoO
2
X
X
Si
Si
O
O
0
(
X = halide, alkyl) species or more practically their Cp Mo(CO)
3
Si
N
H
OEt
OC
OC
R
R
R
R
CO Cl
R
R
R
R
MCM-41 -2 (4 )
R
Mo
TBHP
R
Mo
OC
OC
Cl
CH2Cl2
CO
O
Cl
R = H (3 )
precursors (Scheme 1) were found to efficiently catalyze olefin
epoxidation, with tert-butyl hydroperoxide (TBHP), but not with
O
R = H (1 ), CH3 (2 ), Bz
Scheme 1.
8
2 2
H O .
These results prompted us to verify the possibility of achieve-
ment of a new procedure for the oxidation of sulfides. Herein, we
5
describe the use of complexes [(
g
-C
5
R
5
)Mo(CO)
3
Cl] (R = H (1),
*
Corresponding authors. Tel.: +351 214469758; fax: +351 214411277 (C.A.G.).
8
b,9a
5
8b,9b
E-mail address: carla.gamelas.reis@hotmail.com (C. A. Gamelas).
CH
3
(2))
5 5 2
and [(g -C H )MoO Cl] (3)
and the mesoporous
0
040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.05.126

C. A. Gamelas et al. / Tetrahedron Letters 49 (2008) 4708–4712
4709
material MCM-41-2 (4)10 as catalysts for the efficient and selective
oxidation of sulfides either to sulfoxides or sulfones (Scheme 2).
Recently, Poli has revealed the remarkable stability of
corresponding sulfones (Table 1), near to room temperature, using
aq (in NCMe) or TBHP. This is a clean, straightfor-
ꢀ2 equiv of H
2 2
O
ward synthetic method, in which sulfones are readily precipitated
0
12
Cp Mo(VI) oxo species in aqueous media (through analytical inves-
as the pure product, in high yields.
1
1
tigations). To the best of our knowledge, our study represents the
The oxidation of BTP is remarkably fast when TBHP is used as
oxidant with CH Cl as solvent (entries 12 and 15). The time
2 2
0
first example wherein Cp MoO
2
Cl is found to be catalytically effi-
cient with H
2
O
2
(aq) as oxidant.
needed for completion of these reactions catalyzed by complexes
1 and 3 is comparable (15 min, at 35 °C). This suggests that the
in situ oxidative decarbonylation of complex 1 by TBHP (see
Aryl–alkyl (namely with the electron-withdrawing nitro group),
diaryl, and benzothiophenic sulfides were easily oxidized to the
Table 1
2 2
Selective oxidation of various functionalized substrates to sulfones using H O
or TBHP and complexes 1–4a
Entry
Substrate
Catalyst
complex
Oxidant
Time (h)
Yieldb (%) (Conv. %)
Temperature (°C)
S
CH3
1
1
TBHP
15 min
1
(96)c
(100)
rt
2
3
1 and 2
3
H
H
2
O
O
2
2
0.5
2
99 (100)
(100)
rt
rt
2
S
CH3
4
1
TBHP
1
85 (100)
rt
H3CO
S
CH
3
5
6
1
1
TBHP
TBHP
6
4
87
76
rt
2
O N
S
CH
3
35
OHC
7
8
2
1
H
2
O
2
2
1
99
35
35
O
S
TBHP
92 (100)
H
3
C
CH
3
O
S
9
2
1
2
H
H
H
2
O
2
O
2
O
2
2
2
4
3
5
98
ꢁ20 °C to rt
ꢁ20 °C to rt
35
S
1
1
0
1
98
3
H C
S
100
1
1
2
3
1 and 2
1
TBHP
TBHP; solv.: MeOH
15 min
3
8
85 (100)
(28)
78
35
35
S
14
15
16
17
2
3
4
H
2
O
2
5
70
97 (100)
71
35
35
55
55
TBHP
TBHP
TBHP
15 min
4
1.5
1 and 2
80
S
S
18
19
20
1
1
1
H
2
O
2
7
5
12
69
100
90
35
rt
35
TBHP
; solv: MeOH/CH
H
2
O
2
2
Cl
2
(4:1)
a
Reaction conditions: 3.5 mmol of sulfide; 2.0–2.5 equiv of oxidant; 2 mol % of catalyst; 8 ml of solvent: CH
2
Cl
2 2 2
for TBHP, NCMe for H O .
b
6a,13
Isolated yield. Spectra were compared with literature.
Conversion (in brackets) was determined by GC on the reaction mixture (toluene as internal standard). Only
sulfone is formed.
c
Formation of sulfoxide and sulfone.

4
710
C. A. Gamelas et al. / Tetrahedron Letters 49 (2008) 4708–4712
Scheme 1) is fast and probably gives rise to the same active metal
species as complex 3. The use of MeOH produces a dramatic
rable isolated yields, in line with previous findings in epoxidation
catalysis.
8
b
10
slowing effect on the reaction (entry 13), perhaps due to the coor-
dination of this solvent to the Mo(VI) center.
The benzothiophenic compounds DBTP and 4,6-DMDBTP (en-
tries 17–20) could be oxidized in good yields, under very mild con-
ditions. In literature, the oxidation of thiophene derivatives to their
sulfones is known to take place over a limited range of metal cata-
The chemoselective oxidation of sulfides to sulfoxides was also
investigated (Scheme 2) and the sulfoxides in Table 2 were isolated
using ꢀ1 equiv of oxidant in the appropriate solvent (acetone/
14
1
6
2 2 2 2
MeOH 1:1 for H O ; CH Cl for TBHP), from low to rt. In the case
of DBTP (entry 9) sulfone formation could not be avoided. There are
6
c
few reports on the oxidation of DBTP to its sulfoxide, as the cor-
2
,6a,c
lysts and large excess of H
2
O
2
and higher reaction temperatures
responding sulfone is generally obtained.
To gain some mechanistic insight on the sulfoxidation reactions,
2
,15
are typically used.
The oxidation of DBTP at 55 °C, after 1.5 h,
in the presence of TBHP/complex 1 (entry 17) is remarkably
efficient.
Substrates containing sensitive functional groups such as alde-
hyde and alkene (entries 6, 7, 9, 10) were selectively oxidized at
kinetic experiments were performed where p-ClC
6
H
4
SCH
3
and
C
3).
6
H
5
SOCH
3
(1:1) were in competition for the oxidant (Table
1
7,18
6 4 3
A much higher oxidative reactivity of p-ClC H SCH
was
1
9,20
observed, as expected.
2 2
When H O is used as oxidant, the
the sulfur atom, without affecting the C–C double bond. It is impor-
protic solvent MeOH favors the chemoselective formation of
0
18,21a
tant to notice that Cp Mo(CO)
fin epoxidation catalyst.
3
Cl has been used as an efficient ole-
sulfoxide (entries 1 and 2), as in other catalytic systems
and
8
this has certainly permitted the straightforward synthesis of
sulfoxides in Table 2.
The above-mentioned catalytic systems are all homogeneous in
nature. At the exploratory level, we have tested the heterogeneous
MCM-41-2 (4) in the oxidation of BTP by TBHP (entry 16). Com-
pared to the non-supported catalyst (entry 12), longer reaction
times at higher temperature were necessary for obtaining compa-
We have also used the thianthrene 5-oxide (SSO) oxidation as a
2
1,22
mechanistic probe.
predominantly oxidized at the sulfide and the XSO values unequiv-
ocally indicate an electrophilic character for complex 1/H or
The results in Table 4 show that SSO was
2 2
O
Table 2
Selective oxidation of sulfides to sulfoxides using H
2
O
2
or TBHP and complexes 1 and 2a
Entry
1
Substrate
Catalyst complex
Oxidant
Time (h)
2.5
Yieldb (%) (Conv. %)
92
S
1
2
1
H
H
2
O
O
2
2
2
3
2
2
86
S
S
CH
3
TBHP
15 min, at ꢁ20 °C
(37)
89 (96)
2.5
S
CH
3
4
5
1
2
H
H
2
O
O
2
2
2
98
75
3
H CO
S
CH
3
2
3.5
O N
2
S
CH
3
6
1
H
2
O
2
5
96
Cl
7
8
1
1
H
H
2
O
O
2
2
5.5
7
92
95
S
S
2
9
1
H
2
O
2
6
60
S
a
Reaction conditions: 3.5 mmol of sulfide; 1.1 equiv of oxidant; 2 mol % of catalyst; solv.: CH
2
Cl
2
for TBHP, acetone/MeOH (1:1) for H
2
O
2
; ꢁ20 °C to rt.
b
4c,6a,13
Isolated yield. Spectra were compared with literature.
Conversion (in brackets) was determined by GC. Only sulfoxide is formed.

C. A. Gamelas et al. / Tetrahedron Letters 49 (2008) 4708–4712
4711
Table 3
Competitive oxidation of p-ClC
6
4
H SCH
3
and C
H
6 5
SOCH
3
using H
2
O
2
or TBHP and complex 1a
O
O
S
O
O
S
S
S
CH
3
CH3
CH
3
CH3
0
.7 eq. oxidant
ºC; Cat.
+
+
0
Cl
Cl
SCH b
Entry
Oxidant
Solvent
NCMe
Time (h)
Conv. of p-ClC
6
H
4
3
(%)
Conv. of C
6
H
5
SOCH b
3
(%)
1
2
H
H
2
O
O
2
2
0.5
3 h
30
33
66
69
9
2
Acetone/MeOH (1:1)
—
—
—
5
h 30
3
TBHP
2
CH Cl
2
2 h
a
Reaction conditions: 3.5 mmol of 4-ClTIOAN and 3.5 mmol of TIOANSO; 0.7 equiv of oxidant; 2 mol % of catalyst; at 0 °C.
Conversion determined by GC analysis on the crude reaction mixture (with mesitylene as internal standard).
b
Table 4
Oxidation of thianthrene 5-oxide (SSO) by H
2
O
2
or TBHP catalyzed by complex 1a
O
S
O
O
S
O
O
S
S
S
nucleophilic attack
electrophilic attack
+
S
S
S
O
O
Thianthrene 5-oxide (SSO)
2
Thianthrene 5,5-dioxide (SSO )
cis-SOSO
trans -S OS O
Conv.b (%)
Mass balanceb (%)
Product distributionb (%) SSO
X
c
Entry
Oxidant (equiv)
Solvent
Time (h)
2
/trans-SOSO/cis-SOSO
SO
1
2
3
H
H
2
O
O
2
2
(2.0)
(2.0)
CH
2
CH
2
CH
2
2
Cl /NCMe (2:9)
2
Cl /MeOH (1:4)
Cl
2
4
4
1
22
11
86
97
71
100
12/64/24
8/84/8
15/78/7
0.12
0.08
0.15
2
TBHP (1.0)
a
Reaction conditions: 0.05 mmol of SSO; 1.0–2.0 equiv of oxidant; 2 mol % of catalyst; at rt.
Determined by HPLC analysis of the crude reaction mixture. No over-oxidation product SOSO
XSO = sulfoxide oxidation/total oxidation; calculated according to Ref. 21.
b
c
2
was detected.
TBHP,21 in accordance with the competition experiments with
ClC SCH and C SOCH
The active species in this system is still unknown; a species con-
Tetrahedron Lett. 2005, 46, 3819–3822; (f) Mekmouche, Y.; Hummel, H.; Ho, R.
Y. N.; Que, L., Jr.; Schünemann, V.; Thomas, F.; Trautwein, A. X.; Lebrun, C.;
Gorgy, K.; Lepêtre, J.-C.; Collomb, M.-N.; Deronzier, A.; Fontecave, M.; Ménage,
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2005, 44, 2465–2471.
H
6 4
3
6
H
5
3
.
2
23
1
7b,14
taining
g -coordinated peroxide , g -tert-butylperoxo ligand,
8f
4. (a) Bortolini, O.; Di Furia, F.; Modena, G.; Seraglia, R. J. Org. Chem. 1985, 50,
or a non-cyclopentadienyl containing catalyst can be suggested
2688–2690; (b) Bonchio, M.; Carofiglio, T.; Di Furia, F.; Fornasier, R. J. Org. Chem.
on the basis of previous findings.
1995, 60, 5986–5988; (c) Batigalhia, F.; Zaldini-Hernandes, M.; Ferreira, A. G.;
Regardless of the nature of the intermediate, nucleophilic attack
of sulfur then occurs on the electrophilic oxygen atom activated by
Malvestiti, I.; Cass, Q. B. Tetrahedron 2001, 57, 9669–9676.
(a) Xu, L.; Cheng, J.; Trudell, M. L. J. Org. Chem. 2003, 68, 5388–5391; (b) Barker,
E.; Ren, T. Tetrahedron Lett. 2004, 45, 4681–4683.
(a) Sato, K.; Hyodo, M.; Aoki, M.; Zheng, X. Q.; Noyori, R. Tetrahedron 2001, 57,
2469–2476; (b) Sasaki, V.; Ushimaru, K.; Iteya, K.; Nakayama, H.; Yamaguchi,
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Commun. 2007, 8, 1112–1116.
5
.
.
the Mo(VI) center.
6
0
In conclusion, the Cp Mo(CO)
3
Cl complexes promote the
chemoselective and efficient oxidation of sulfides either to sulfox-
ides or sulfones, with stoichiometric amounts of TBHP or the ‘envi-
ronmentally friendly’ H
This is the first time Cp MoO
2
O
2
(aq), under mild reaction conditions.
Cl is found to be catalytically efficient
(aq) and further studies with this system
0
7. (a) Kühn, F. E.; Santos, A. M.; Lopes, A. D.; Gonçalves, I. S.; Herdtweck, E.;
Romão, C. C. J. Mol. Catal. A: Chem. 2000, 164, 25–38; (b) Kühn, F. E.; Groarke,
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Romão, C. C.; Gonçalves, I. S.; Lopes, A. D.; Pillinger, M. Chem. Eur. J. 2002, 8,
2
in oxidations with H
2
O
2
are being developed in our group.
2370–2383; (c) Kühn, F. E.; Santos, A. M.; Abrantes, M. Chem. Rev. 2006, 106,
2
455–2475.
References and notes
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2.
3.
(a) Kaczorowska, K.; Kolarska, Z.; Mitka, K.; Kowalski, P. Tetrahedron 2005, 61,
315–8327 and references cited therein; (b) Simpkins, N. S. Sulfones in
Organic Synthesis. In Baldwin, J. E., Magnus, P. D., Eds.; Oxford: Pergamon,
993.
(a) Te, M.; Fairbridge, C.; Ring, Z. Appl. Catal. A 2001, 219, 267–280; (b) Li, C.;
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Chem. Eur. J. 2004, 10, 2277–2280; (c) Campos-Martin, J.; Capel-Sanchez, M.;
Fierro, J. Green Chem. 2004, 6, 557–569.
2003, 22, 2112–2118; (c) Freund, C.; Abrantes, M.; Kühn, F. E. J. Organomet.
8
Chem. 2006, 691, 3718–3729; (d) Martins, A. M.; Romão, C. C.; Abrantes, M.;
Azevedo, M. C.; Cui, J.; Dias, A. R.; Duarte, M. T.; Lemos, M. A.; Lourenço, T.; Poli,
R. Organometallics 2005, 24, 2582–2589; (e) Zhao, J.; Santos, A. M.; Herdtweck,
E.; Kühn, F. E. J. Mol. Catal. A: Chem. 2004, 222, 265–271; (f) Pratt, M.; Harper, J.
B.; Colbran, S. B. Dalton Trans. 2007, 2746–2748.
(a) Kubas, G. J.; Kiss, G.; Hoff, C. D. Organometallics 1991, 10, 2870–2876; (b)
Cousins, M.; Green, M. L. H. J. Chem. Soc. 1964, 1567.
0. Abrantes, M.; Gago, S.; Valente, A. A.; Pillinger, M.; Gonçalves, I. S.; Santos, T.
M.; Rocha, J.; Romão, C. C. Eur. J. Inorg. Chem. 2004, 4914–4920.
1. Poli, R. Chem. Eur. J. 2004, 10, 332–341.
1
9.
(a) Yuan, Y.; Bian, Y. Tetrahedron Lett. 2007, 48, 8518–8520; (b) De Rosa, M.;
Lamberti, M.; Pellechia, C.; Scettri, A.; Villano, R.; Soriente, A. Tetrahedron Lett.
1
2
2
006, 47, 7233–7235; (c) Massa, A.; De Lorenzo, E. M.; Scettri, A. J. Mol. Catal. A
006, 250, 27–29; (d) Hosseinpoor, F.; Golchoubian, H. Tetrahedron Lett. 2006,
1
1
2. General procedure for preparation of sulfones: 2.0–2.5 equiv of H
2 2
O (30% aq) or
47, 5195–5197; (e) Velusamy, S.; Kumar, A. V.; Saini, R.; Punniyamurthy, T.
anhydrous TBHP (5–6 M in decane) was added to a solution of the catalyst

4
712
C. A. Gamelas et al. / Tetrahedron Letters 49 (2008) 4708–4712
(
H
(
2 mol %) and sulfide (3.5 mmol), in 8 ml of the appropriate solvent (NCMe for
; CH Cl for TBHP), at rt (or 35 °C). The reaction was monitored by TLC
and GC). After completion, the product precipitated by adding Et O/hexane.
Pure sulfones were obtained upon recrystallization from CH Cl /hexane. The
purity was ascertained by H NMR, MS and EA. Vinyl phenyl sulfone (entry 9,
4
layers were dried over anhydrous MgSO and concentrated in vacuum. Pure
2
O
2
2
2
sulfoxides were isolated upon flash chromatography on silica gel (AcOEt/
hexane). The purity was ascertained by 1H NMR, MS and EA.
2
2
2
17. Competitive oxidation of p-ClC
TBHP was added to a solution containing equal amounts (3.5 mmol) of p-
ClC SCH and C SOCH , CpMo(CO) Cl (2 mol %) and mesitylene (internal
6 4 3 6 5 3 2 2
H SCH and C H SOCH : 0.7 equiv of H O (aq) or
1
ꢁ
1
Table 1): white solid. IR (
306, 1250, 1152. 1H NMR (300 MHz; CDCl
J = 18.0, 1H), 6.64–6.55 (m, 1H), 7.59–7.46 (m, 3H, Ph), 7.83 (d, 2H, Ph). Anal.
Calcd C S: C, 57.14; H, 4.76; S, 19.07. Found: C, 56.95; H, 4.92; S, 19.32.
Allyl methyl sulfone (entry 10): orange oil. IR (
m
max, KBr, cm ): 3108, 3046, 1607, 1583, 1447, 1385,
6
H
4
3
H
6 5
3
3
1
3
, d): 5.97 (d, J = 12.0, 1H), 6.39 (d,
standard), in the selected solvent (5 ml), at 0 °C. The conversion of the
substrates was determined by GC analysis.
18. Patonay, T.; Adam, W.; Lévai, A.; Kövér, P.; Németh, M.; Peters, E.-M.; Peters, K.
J. Org. Chem. 2001, 66, 2275–2280.
19. Ballistreri, F. P.; Tomaselli, G. A.; Toscano, R. M.; Conte, V.; Di Furia, F. J. Am.
Chem. Soc. 1991, 113, 6209–6212.
8
H
8
O
2
ꢁ
1
m
max, KBr, cm ): 3093, 2296,
258, 2055, 1967, 1416, 1302, 1138. H NMR (300 MHz; CDCl , d): 1.92 (s, 3H);
.66 (d, 2H, J = 7.2 Hz); 5.43–5.36 (m, 2H); 5.82–5.91 (m, 1H). ESI-MS m/z Calcd
1
2
3
C
3
+
4
H
8
2
NaO S ([M+Na] ): 143.07. Found: 143.1.
20. Ballistreri, F. P.; Tomaselli, G. A.; Toscano, R. M.; Bonchio, M.; Conte, V.; Di
Furia, F. Tetrahedron Lett. 1994, 35, 8041–8044.
1
1
1
3. (a) The Sadtler Standard Spectra, NMR; Sadtler Research Laboratories, 12327M,
1
972.; (b) Ali, M. H.; Stevens, W. C. Synthesis 1997, 764–768.
21. (a) Adam, W.; Golsch, D.; Görth, F. C. Chem. Eur. J. 1996, 2, 255–258; (b) Adam,
W.; Golsch, D. Chem. Ber. 1994, 127, 1111–1113; (c) Bonchio, M.; Conte, V.; De
Concilis, M. A.; Di Furia, F.; Ballistreri, F. P.; Tomaselli, G. A.; Toscano, R. M. J.
Org. Chem. 1995, 60, 4475–4480; (d) Adam, W.; Golsch, D. J. Org. Chem. 1997,
62, 115–119; (e) Adam, W.; Mitchell, C. M.; Saha-Möller, C. R. J. Mol. Catal. A
2000, 154, 251–255; (f) Adam, W.; Corma, A.; García, H.; Weichold, O. J. Catal.
2000, 196, 339–344.
4. Veiros, L. F.; Prazeres, A.; Costa, P. J.; Romão, C. C.; Kühn, F. E.; Calhorda, M. J.
Dalton Trans. 2006, 1383–1389.
5. (a) Hulea, V.; Fajula, F.; Bousquet, J. J. Catal. 2001, 198, 179–186; (b) Abrantes,
M.; Valente, A. A.; Pillinger, M.; Gonçalves, I. S.; Rocha, J.; Romão, C. C. Chem.
Eur. J. 2003, 9, 2685–2695; (c) Chica, A.; Gatti, G.; Moden, B.; Marchese, L.;
Iglesia, E. Chem. Eur. J. 2006, 12, 1960–1967.
1
6. General procedure for preparation of sulfoxides: 1.1 equiv of H
was added to a solution of the catalyst (2 mol %) and sulfide (3.5 mmol), in 8 ml
of the appropriate solvent (acetone/MeOH 1:1 for H ; CH Cl for TBHP), at
20 °C. The mixture gradually came to rt. The reaction was monitored by TLC
and GC). After completion, a saturated solution of NaHCO (or Na , 10 ml)
was added and it was extracted with CH Cl or AcOEt. The combined organic
2
O
2
(aq) or TBHP
22. General procedure for the oxidation of SSO: 1.0–2.0 equiv of H
was added to solution containing SSO (0.05 mmol) and CpMo(CO)
(2 mol %) in the selected solvent (7 ml), at rt. Aliquots were withdrawn,
diluted in CH Cl /EtOH (1:1) and analyzed by quantitative HPLC.
23. (a) Mimoun, H. J. Am. Chem. Soc. 1986, 108, 3711–3718; (b) Chong, A.;
Sharpless, K. B. J. Org. Chem. 1977, 42, 1587–1590.
2
O
2
(aq) or TBHP
a
3
Cl
2
O
2
2
2
ꢁ
2
2
(
3
2
S
2
O
5
2
2