Bi2O3 catalyzed asymmetric oxidation of sulfides

Article abstract of DOI:10.1016/j.tetlet.2012.08.029

Bismuth based catalytic system for the asymmetric oxidation of alkyl and aryl benzyl sulfides using t-BuOOH as the oxidant has been investigated. This method affords sulfoxides with high enantioselectivities (up to 98% ee) and good yields in reasonable time. The over oxidized product namely the sulfone was not observed. The described method has wide range of applications, exhibits chemoselectivity/enantioselectivity, and proceeds under mild and environmentally friendly reaction conditions.

Full text of DOI:10.1016/j.tetlet.2012.08.029

Tetrahedron Letters 53 (2012) 5652–5655
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Bi O catalyzed asymmetric oxidation of sulfides
2
3
⇑
Payal Malik, Debashis Chakraborty
Department of Chemistry, Indian Institute of Technology Madras, Chennai-600 036, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Bismuth based catalytic system for the asymmetric oxidation of alkyl and aryl benzyl sulfides using t-
BuOOH as the oxidant has been investigated. This method affords sulfoxides with high enantioselectiv-
ities (up to 98% ee) and good yields in reasonable time. The over oxidized product namely the sulfone
was not observed. The described method has wide range of applications, exhibits chemoselectivity/
enantioselectivity, and proceeds under mild and environmentally friendly reaction conditions.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 6 July 2012
Revised 6 August 2012
Accepted 8 August 2012
Available online 14 August 2012
Keywords:
Asymmetric oxidation
t-BuOOH
Enantioselective
Sulfoxide
Kinetics
The field of enantioselective synthesis is one of the most impor-
tant focal areas in organic synthesis. Numerous catalytic asymmet-
ric reactions have been discovered often with spectacular results in
terms of efficiency and selectivity.1 Enantiomerically pure sulfox-
oxidation of sulfides.35–40 The main factor responsible for the effi-
ciency and versatility of BINOL/Ti catalysts is essentially the struc-
ture arising from the combination of the ligand and metal. In fact,
titanium alkoxides exhibit peculiar fluxionality in solution. They
feature various coordination numbers, geometries and undergo li-
gand addition, elimination, and exchange reactions easily. Probably
the fluxional behavior is responsible for the catalytic activity of
–6
ides play an important role in the asymmetric synthesis either as
chiral building blocks or stereo directing groups.7
–11
Owing to their
biological activity, the enantioselective oxidation of sulfides is a
well investigated area of organic synthesis.1
2–23
For the first time,
alkoxides. In 1992, for the first time Uemura et al. have used
38
i
in mid-eighties Kagan et al. have reported enantioselective oxida-
(R)-BINOL with Ti(O Pr)
4
to catalyze the enantioselective oxidation
tion of sulfides by using modified Sharpless oxidation.24 Later, tre-
of prochiral sulfides to sulfoxides by hydroperoxides in toluene or
carbon tetrachloride and they have obtained an enantiomeric ex-
2
5–28
mendous work has been done by Bolm et al. in this area.
A
3
3
number of metals like aluminum, iron, manganese, copper, nio-
bium, tungsten, molybdenum, and osmium have been used as cat-
alyst for the oxidation of sulfides.29
A rational approach to the control of stereoselectivity is based
on the use of molecules possessing only symmetry elements of
cess (up to 73% ee) with high chemical yield.
Herein, we have investigated the catalytic activity of Bi
combination with (S)-BINOL (L ) for the asymmetric oxidation of
sulfides. As a matter of fact, the oxidation of sulfides to sulfoxides
using Bi(NO O as well as BiBr –Bi(NO ꢀ5H O has been de-
ꢀ5H
scribed in the literature. However, no stereoselectivity was re-
2 3
O in
1
3
)
3
2
3
3
)
3
2
4
1,42
n n
pure rotation and belonging to the C or D symmetry groups,
allowing the prediction of the enantioselectivity due to the pres-
ence of only a single defined reactive species in solution. Under
ported. Besides, these were not high yielding methods.
In the preliminary phase of optimization, methyl methyl
(phenyl)sulfide was chosen as a standard substrate and the trials
were performed with different Bi(III) compounds, chiral ligands,
and solvents in the presence of various oxidants at room
temperature.
30
0
0
these assumptions, 1,1 -binaphthyl-2,2 -diol (BINOL) and related
symmetrical ligands possessing axial chirality have found a wide
C
2
31
utility in asymmetric catalysis. Since 1990, the enantiomeric
atropoisomers of BINOL are widely used ligands for both stoichi-
ometric and catalytic asymmetric reactions.32 An impressive vari-
ety of organic reactions were promoted and stereocontrolled by
BINOL ligands in combination with different metals.3
To inspect the effect of catalyst, Bi
2
O
3, Bi(NO
3
)
3
ꢀ5H
2
O, BiCl3, and
BiBr were used in different concentrations. Methyl methyl
3
3,34
(phenyl)sulfane was treated with t-BuOOH (3 equiv.), (S)-BINOL
In modern organic synthesis titanium(IV) BINOL complexes
are one of the most widely used antioselective catalysts for the
(1 mol%), and Bi(III) compounds in EtOAc at room temperature.
Results revealed that Bi
alyst among the Bi(III) compounds. Nevertheless, Bi(NO
BiCl , and BiBr were also active in the oxidation reaction, the de-
sired product was obtained in poor yields (Table 1, entries 2–4).
2
O
3
(10 mol%) was the most efficacious cat-
3
)
3
ꢀ5H O,
2
⇑
Corresponding author. Tel.: +91 44 22574223; fax: +91 44 22574202.
E-mail address: dchakraborty@iitm.ac.in (D. Chakraborty).
3
3
0
040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.08.029

P. Malik, D. Chakraborty / Tetrahedron Letters 53 (2012) 5652–5655
5653
Table 1
Table 2
2 3
Bi O
catalyzed selective oxidation of sulfides to sulfoxidesa
Optimization of reaction conditions for the conversion of methyl(phenyl)sulfane to
methylsulfinylbenzene with different solvents, oxidants, and Bi(III) compounds
a
O
oxidant, catalyst
S
S
BINOL(1 mol %)
solvent, rt
Entry Catalyst
Ligand Solvent Oxidant
Time (h)b Yield (%)c
1
2
3
4
5
6
7
8
9
1
1
Bi
Bi(NO
BiCl
BiBr
2
O
3
L
L
L
L
L
L
L
L
L
L
L
1
1
1
1
1
1
1
1
1
2
1
EtOAc
EtOAc
EtOAc
EtOAc
t-BuOOH 16
90
71
75
60
82
80
79
81
75
88
65
Entry Substrate
1
Timeb (h) Yieldc (%) eed (%) Confg.e
3
)
3
ꢀ5H
2
O
t-BuOOH 23
t-BuOOH 21
t-BuOOH 21
t-BuOOH 25
t-BuOOH 22
t-BuOOH 24
t-BuOOH 20
t-BuOOH 22
t-BuOOH 17
3
S
3
15
14
90
83
97.4
96.8
(S)
(S)
Bi
Bi
Bi
Bi
Bi
Bi
Bi
2
2
2
2
2
2
2
O
3
3
3
3
3
3
3
2 2
CH Cl
O
O
O
O
O
O
MeCN
MeNO
DMSO
DMF
EtOAc
EtOAc
S
2
2
0
1
S
S
S
H
2
O
2
30
3
20
16
24
20
23
81
90
87
89
84
97.5
91.6
94
(S)
(S)
(S)
(S)
(S)
a
With methyl(phenyl)sulfane (1 mmol), (S)-BINOL (1 mol%), 70% t-BuOOH
water) (3 equiv), and Bi(III) salts (10 mol%) at room temperature.
Monitored using TLC until all the sulfide was found consumed.
Isolated yield after column chromatography of the crude product.
Br
(
S
b
4
5
6
7
c
To analyze the solvent effect, the reaction was carried out in dif-
ferent solvents like nitromethane, DMF, DMSO, CH Cl , and EtOAc
2 2
Cl
Cl
S
following the same protocol. On the basis of the results, EtOAc
was found to be the most efficient reaction medium. In the case
of other solvents the reactions were slow and low yields of products
were obtained (Table 1). To examine the effect of oxidant on the
oxidation of methyl methyl(phenyl)sulfide, the reaction was per-
formed with different oxidants by using the same reaction condi-
78.1
95.4
tions. When 3 equiv of 30% H
reaction was sluggish and gave the corresponding sulfoxide in
5% yield (Table 1, entry 11). In case of 5M t-BuOOH (decane) the
isolated yield was only 50%. In the presence of 3 equiv of 70% t-
BuOOH (water) the reaction was exceedingly facile and found to
be completed within 16 h with 90% isolated yield (Table 1, entry
2
O
2
(water) was used as oxidant, the
S
S
8
9
20
18
89
90
85.2
94.7
(S)
(S)
6
1
). To optimize the oxidant concentration, the reaction was carried
out with 2 equiv of 70% t-BuOOH (water), the reaction took a longer
time (24 h) to complete and gave the sulfoxide in 75% yield, when
S
10
22
85
80.1
(S)
5
equiv of 70% t-BuOOH (water) was used as oxidant, no consider-
able effect was observed on the reaction rate. The (S)-BINOL and BI-
43
a
NOL based phosphoramidate (L
sulfoxidation (Table 1, entries 1 and 10), and the results showed
that (S)-BINOL (L ) has good stereocontrol over the oxidation as
compared to the BINOL based phosphoroamidate ligand. The (S)-BI-
NOL (L ) gave a maximum 98% ee and at the same time the BINOL
based phosphoroamidate (L ) could produce only 10% ee. When
2
)
were used as ligand for the
2 3
Reactions performed in EtOAc with sulfide (1 mmol), (S)-BINOL (1 mol%), Bi O
45
(
10 mol%), and 70% t-BuOOH (3 equiv) at room temperature.
b
Monitored using TLC until all sulfide was found consumed.
Isolated yield after column chromatography of the crude reaction mixture.
Enantiomeric excess was determined by HPLC with a chiral stationary phase.
Absolute configurations were assigned by comparing the optical rotations and
1
c
d
e
1
HPLC retention times with the literature.44
2
the reaction was carried out in the absence of (S)-BINOL, the reac-
tion provided only a racemic mixture of sulfoxide, which shows
that there was no stereocontrol over the reaction. Conversely, the
ligand is mandatory for the enantioselective oxidation of sulfides.
withdrawing) of the substituents. The catalytic system is selective,
without affecting the other functionalities and the sulfides were
oxidized to the respective sulfoxides. However, the overoxidized
product sulfone was not observed. The interesting aspect of this
catalytic system is that the reactions were carried out at room tem-
In fact, in the absence of Bi
On the ground of the optimization studies, Bi
S)-BINOL (1 mol%) with 3 equiv 70% t-BuOOH (water) in EtOAc at
2
O
3
the reaction was very slow.
2 3
O
(10 mol%) and
(
room temperature were the best reaction conditions for the oxida-
tion of prochiral methyl methyl(phenyl)sulfide to methylsulfinyl-
benzene (Table 1).
perature, with environmentally friendly Bi
The proposed catalytic cycle (Scheme 1) for the oxidation reac-
tion involves the coordination of (S)-BINOL to Bi . The second
2 3
O .
2 3
O
Having optimized the reaction conditions, in order to test the
efficiency of the developed catalytic system, various alkyl and aryl
benzyl sulfides were used for the oxidation reaction. The results
are summarized in Table 2. A high degree of enantioselectivity
with good to excellent yields was observed (Table 2).
step is insertion of t-BuOOH followed by the addition of sulfide.
In the final step the transfer of oxygen takes place through a four
member cyclic rearrangement.
The kinetic studies of the sulfoxidation with methyl(4-tolyl)sul-
fide was explored in detail. Waters HPLC was used to determine
the various starting materials and products present as a function
of time. The concentration of reactant and product for the oxida-
The results revealed that the enantioselectivity is independent
of the electronic properties (electron-donating and electron-

5
654
P. Malik, D. Chakraborty / Tetrahedron Letters 53 (2012) 5652–5655
tion of methyl(4-tolyl)sulfane is shown in Figure 1. The concentra-
tion of the sulfide decreases steadily while that of the sulfoxide in-
creases. The rate of reaction was calculated for the conversion of
methyl(4-tolyl)sulfane to the corresponding sulfoxides. van’t Hoff
differential method was used to determine the order (n) and rate
constant (k) (Fig. 2). From Figure 2, the rate of the reaction at dif-
ferent concentrations can be estimated by evaluating the slope of
the tangent at each point on the curve corresponding to that of
methyl phenyl sulfide.
O
O
O
Bi
Bi
O
S
Ph
S
tBuOOH
Ph
Bi
With these data, log10(rate) versus log10(concentration) was
plotted. The order (n) and rate constant (k) are given by the slope
of the line and its intercept on the log10(rate) axis, respectively.
From Figure 2, it is clear that this reaction proceeds with
second-order kinetics (n = 2.01) and the rate constant
O
O
O
Bi
O
Bi
O
O
O
S
O
O
Bi
Ph
S
OH
Ph
ꢁ1
ꢁ1
k = 0.1089 L mol
h .
In conclusion, a variety of sulfides were converted into the cor-
responding sulfoxide with 70% t-BuOOH (water) as the oxidant in
the presence of (S)-BINOL as the chiral ligand and a catalytic
Scheme 1. Proposed mechanism for the catalytic cycle.
2 3
amount of Bi O . The described method has wide range of applica-
tions, exhibits chemoselectivity/enantioselectivity, and proceeds
under mild and environmentally friendly reaction conditions. The
resulting products were obtained in good yields with high ee.
Acknowledgments
The authors thank the Department of Science and Technology,
New Delhi, for financial support.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.
0
8.029.
References and notes
1
2
3
4
5
.
.
.
.
.
Drabowski, J.; Kielbasinski, P.; Mikolajczyk, M. Synthesis of Sulfoxides; John
Wiley and Sons: New York, 1994.
Pati, S.; Rappoport, Z. The Synthesis of Sulphones, Sulphoxides, and Cyclic
Sulphides; John Wiley and Sons: New York, 1994.
Kagan, H. B.; Luukas, T. In Transition Metals for Organic Synthesis; Beller, M.,
Bolm, C., Eds.; Wiley-VCH: Weinheim, 1998; p 361.
Kagan, H. B. In Catalytic Asymmetric Synthesis; Ojima, I., Ed., Second ed.; Wiley-
VCH: New York, 2000; p 327.
Bolm, C.; Mujiz, K.; J. Hildebrand, in Comprehensive Asymmetric Catalysis (Eds.
Jacobsen, A., Pfaltz, H., Yamamoto), Springer, Berlin 1999, pp. 697.
Stinson, S. C. Chem. Eng. News 2001, 79, 45–56.
Carrenõ, M. C. Chem. Rev. 1995, 95, 1717–1760.
Fernández, I.; Khiar, N. Chem. Rev. 2003, 103, 3651–3706.
Rouhi, A. M. Chem. Eng. News 2003, 81, 56–61.
Figure 1. Concentration vs. time in the oxidation of methyl(4-tolyl)sulfane with
0 mol% Bi , (S)-BINOL (1 mol%), and 3 equiv 70% t-BuOOH in EtOAc at room
temperature.
1
2 3
O
6.
7.
8.
9.
1
1
0. Wing, K. D.; Glickman, A. H.; Casida, J. E. Science 1983, 219, 63–65.
1. Glickman, A. H.; Wing, K. D.; Casida, J. E. Toxicol. Appl. Pharmacol. 1984, 73, 16–
22.
12. Matta, E. G. Phosphorus, Sulfur Silicon Relat. Elem. 1996, 117, 231–286.
13. Park, H. S.; Takahashi, Y.; Fukaya, H.; Aoyagi, Y.; Takeya, K. J. Nat. Prod. 2003, 66,
282–284.
1
1
4. Palucki, M.; Hanson, P.; Jacobsen, E. N. Tetrahedron Lett. 1992, 33, 7111–7114.
5. Noda, K.; Hosoya, N.; Yanai, K.; Irie, R.; Katsuki, T. Tetrahedron Lett. 1994, 35,
1870–1887.
1
1
1
6. Katsuki, T.; Saito, B. Tetrahedron Lett. 2001, 42, 3873–3876.
7. Miyazaki, T.; Katsuki, T. Synlett 2003, 1046–1048.
8. Sun, J.; Zhu, C.; Dai, Z.; Yang, M.; Pan, Y.; Hu, H. J. Org. Chem. 2004, 69, 8500–
8
503.
9. da Costa, A. P.; Reis, P. M.; Gamelas, C.; Romão, C. C.; Royo, B. Inorg. Chim. Acta
008, 361, 1915–1921.
0. Kirihara, M.; Yamamoto, J.; Noguchi, T.; Itou, A.; Naito, S.; Hirai, Y. Tetrahedron
009, 65, 10477–10484.
1
2
2
2
2
2
2
2
1. O.’Mahony, G. E.; Ford, A.; Maguire, A. R. J. Org. Chem. 2012, 77, 3288–3296.
2. Miyazaki, T. T. Katsuki Synlett 2003, 1046–1048.
3. Takur, W. V. V.; Sudalai, A. Tetrahedron: Asymmetry 2003, 14, 407–410.
4. Pitchen, P.; Duiiach, E.; Deshmukh, M. N.; Kagan, H. B. J. Am. Chem. Soc. 1984,
1
06, 8188–8193.
Figure 2. van’t Hoff differential plot for the oxidation of methyl(4-tolyl)sulfane
25. Bolm, C.; Bienewald, F. Angew. Chem., Int. Ed. Engl. 1995, 34, 2640–2642.
26. Bolm, C.; Legros, J. Angew. Chem., Int. Ed. 2003, 42, 5487–5489.
2 3
with 10 mol% Bi O , (S)-BINOL (1 mol%), and 3 equiv 70% t-BuOOH in EtOAc at room
27. Legros, J.; Bolm, C. Angew. Chem., Int. Ed. 2004, 43, 4225–4228.
temperature.

P. Malik, D. Chakraborty / Tetrahedron Letters 53 (2012) 5652–5655
5655
2
2
8. Legros, J.; Dehli, J. R.; Bolm, C. Adv. Synth. Catal. 2005, 347, 19–31.
9. O’ Mahony, G. E.; Kelly, P.; Lawrence, S. E.; Maguire, A. R. ARKIVOC (Gainesville,
FL, U.S.) 2011, 1,1–110.
39. Wang, X.; Wang, X.; Guo, H.; Wang, Z.; Ding, K. Chem. Eur. J. 2005, 11, 4078–
4088.
40. Sahoo, S.; Kumar, P.; Lefebvre, F.; Halligudi, S. B. J. Catal. 2009, 262, 111–118.
41. Komatsu, N.; Uda, M.; Suzuki, H. Chem. Lett. 1997, 1229–1230.
42. Mashraqui, S.; Mudaliar, C.; Karnik, M. Synth. Commun. 1998, 939–943.
43. Gowda, R. R.; Chakraborty, D.; Ramkumar, V. Inorg. Chim Acta. 2011, 372, 88–
93.
3
3
3
3
0. Rosini, C.; Franzini, L.; Raffaelli, A.; Salvadori, P. Synthesis 1992, 503–517.
1. Brunel, J. M. Chem. Rev. 2005, 105, 857–897.
2. Chen, Y.; Yekta, S.; Yudin, A. K. Chem. Rev. 2003, 103, 3155–3211.
3. Komatsu, N.; Nishibayashi, Y.; Sugita, T.; Uemura, S. Tetrahedron Lett. 1992, 33,
5
391–5394.
4. Komatsu, N.; Hashizume, M.; Sugita, T.; Uemura, S. J. Org. Chem. 1993, 58,
529–4533.
44. Chakraborty, D.; Malik, P.; Goda, V. K. Appl. Organomet. Chem. 2012, 26, 21–26.
45. To a stirred suspension of sulfide (1 mmol), (S)-BINOL (1 mol%), and Bi O
2 3
3
3
3
3
3
4
(10 mol%) in 2.5 ml of EtOAc, 70% t-BuOOH (water) (3 mmol) was added at
room temperature. The progress of the reaction was monitored using TLC
periodically until all the sulfide was found to be consumed. The crude product
was extracted with EtOAc (3 ꢂ 5 ml). The organic layer was concentrated
under reduced pressure and further subjected to column chromatography. The
spectral data of the various sulfoxides were found to be satisfactory in
accordance with the literature.
5. Capozzi, M. A. M.; Cardellicchio, C.; Fracchiolla, G.; Naso, F.; Tortorella, P. J. Am.
Chem. Soc. 1999, 121, 4708–4709.
6. Capozzi, M. A. M.; Cardellicchio, C.; Naso, F.; Rosito, V. J. Org. Chem. 2002, 67,
7
289–7294.
7. Massa, A.; Siniscalchi, F. R.; Bugatti, V.; Lattanzi, A.; Scettri, A. Tetrahedron:
Asymmetry 2002, 13, 1277–1283.
8. Pescitelli, G.; Di Bari, L.; Salvadori, P. J. Organomet. Chem. 2006, 691, 2311–2318.