Mild and efficient deoxygenation of sulfoxides with a WCl6/indium system

Article abstract of DOI:10.1080/00397910600773676

Dialkyl, diaryl, and aryl alkyl sulfoxides can be rapidly converted to the corresponding sulfides with a WCl6/In system in excellent yields under mild conditions. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910600773676

This article was downloaded by: [Stony Brook University]
On: 26 October 2014, At: 14:44
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office:
Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An International
Journal for Rapid Communication of
Synthetic Organic Chemistry
Publication details, including instructions for authors and subscription
information:
http://www.tandfonline.com/loi/lsyc20
Mild and Efficient Deoxygenation of
Sulfoxides with a WCl6/Indium System
Byung Woo Yoo a , Min Chol Park a & Min Suk Song a
a Department of Advanced Materials Chemistry , Korea University ,
Jochiwon, Chungnam, South Korea
Published online: 19 Nov 2007.
To cite this article: Byung Woo Yoo , Min Chol Park & Min Suk Song (2007) Mild and Efficient Deoxygenation
of Sulfoxides with a WCl6/Indium System, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 37:22, 4079-4083, DOI: 10.1080/00397910600773676
To link to this article: http://dx.doi.org/10.1080/00397910600773676
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”)
contained in the publications on our platform. However, Taylor & Francis, our agents, and our
licensors make no representations or warranties whatsoever as to the accuracy, completeness, or
suitability for any purpose of the Content. Any opinions and views expressed in this publication
are the opinions and views of the authors, and are not the views of or endorsed by Taylor &
Francis. The accuracy of the Content should not be relied upon and should be independently
verified with primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities
whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or
arising out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any substantial
or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or
distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use
can be found at http://www.tandfonline.com/page/terms-and-conditions

Synthetic Communicationsw, 37: 4079–4083, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600773676
Mild and Efficient Deoxygenation of
Sulfoxides with a WCl6/Indium System
Byung Woo Yoo, Min Chol Park, and Min Suk Song
Department of Advanced Materials Chemistry, Korea University,
Jochiwon, Chungnam, South Korea
Abstract: Dialkyl, diaryl, and aryl alkyl sulfoxides can be rapidly converted to the
corresponding sulfides with a WCl6/In system in excellent yields under mild
conditions.
Keywords: Deoxygenation, indium, sulfide, sulfoxides, WCl6
The deoxygenation of sulfoxides to sulfides is a valuable transformation in the
application of organosulfur compounds in organic synthesis. Particularly, sulf-
oxides deserve much attention as important chiral auxiliaries in asymmetric
synthesis.[1] Accordingly, a good number of methodologies have been
developed for the reduction of sulfoxides to the corresponding sulfides.[2]
However, they often suffer from serious disadvantages, such as functional
group incompatibility, difficult workup procedures, harsh reaction conditions,
or not readily available reagents. Further, some of these methods are associ-
ated with low yields and prolonged reaction times. Therefore, there still
exists a need for new, improved methods based on easily accessible
reagents and operationally simple procedures for the reduction of sulfoxides.
The use of low-valent oxophilic d-block metals has become important in
deoxygenation of various types of organic substrates.[3] In this regard,
deoxygenations of sulfoxides and oximes are readily performed with low-
valent tungsten generated by reacting WCl6 with either NaI or Zn.[4] It is
Received in Japan February 19, 2006
Address correspondence to Byung Woo Yoo, Department of Advanced Materials
Chemistry, Korea University, Jochiwon, Chungnam 339-700, South Korea. E-mail:
bwyoo@korea.ac.kr
4079

4080
B. W. Yoo, M. C. Park, and M. S. Song
anticipated that a WCl6/In system can be an efficient reducing agent for the
reduction of sulfoxides to sulfides. We have investigated the reactions of
the WCl6/In system with various sulfoxides and found that they can be
rapidly reduced to the corresponding sulfides in high yields [Eq. (1)].
Metal–metal salt binary systems have long been used as reducing agents for
many functional groups.[5] In this communication, the use of the WCl6/In
system for the selective reduction of sulfoxides to sulfides in high yields
under mild conditions is reported. Recently, we reported that TiCl4/In or
Cp2TiCl2/In could be used for the deoxygenation of various sulfoxides.[6]
In comparison with other procedures, the WCl6/In system reduces sulfoxides
more rapidly (5 min) in higher yields (85–96%) and showed good chemo-
selectivity. Some control experiments revealed that sulfoxides could not be
deoxygenated by WCl6 or indium alone under the present condition, and
starting materials were recovered unchanged. The new reducing system was
generated by the addition of indium powder to a stirred solution of tungsten
hexachloride in tetrahydrofuran (THF) under nitrogen. A 2:1 ratio of
indium and WCl6 was the best ratio in terms of yield and reaction time. The
sulfoxides are prepared by oxidation of the corresponding sulfides with
sodium metaperiodate in aqueous methanol.[7] All the compounds obtained
showed IR, NMR, and mass spectral data compatible with the structure. To
assess the scope and limitations of this reagent system, the reaction was
studied with various sulfoxides bearing other potentially labile functional
Table 1. Reduction of sulfoxides with the WCl6/In system
Time
(min)
Yield
(%)a
Entry
R1
R2
Products
PhSPh
PhSCH3
1
2
Ph
Ph
Ph
5
5
5
5
5
5
5
5
5
5
5
5
92
96
91
91
93
95
89
89
91
85
87
88
CH3
CH3
3
4-BrC6H4
4-ClC6H4
4-CH3OC6H4
4-CHOC6H4
4-CH3C6H4
4-CH3C6H4
Ph
4-BrC6H4SCH3
(4-ClC6H4)2S
(4-CH3OC6H4)2S
4-CHOC6H4SCH3
4-CH3C6H4SCH3
(4-CH3C6H4)2S
PhSCH2CH3
(PhCH2)2S
4
4-ClC6H4
4-CH3OC6H4
CH3
5
6
7
CH3
8
4-CH3C6H4
CH2CH3
PhCH2
Ph
9
10
11
12
PhCH2
PhCH2
nC4H9
PhCH2SPh
(nC4H9)2S
nC4H9
aIsolated yields.

Sulfoxide Deoxygenation with WCl6/In
4081
groups. As shown in Table 1, the methodology is equally applicable to dialkyl,
diaryl, and aryl alkyl sulfoxides. The functional group tolerance of this method
is evident from entries 3–6, which show that bromo, chloro, methoxy, and
aldehyde functionalities are unaffected under the reaction conditions. Thus
we have been able to demonstrate the utility of the easily accessible WCl6/
In system as a useful reagent for effecting chemoselective deoxygenation of
sulfoxides. Although the reaction mechanism is still unclear, it can be ration-
alized as the result of a two-stage process. In the first step, tungsten(VI)
chloride is probably reduced by indium to form a low-valent tungsten
species, which, in the subsequent step, reductively deoxygenates sulfoxides
1 to give the corresponding sulfides 2. The reducing property exhibited by
metal–metal salt combinations proceeds through transfer of one electron
from the metal surface to the substrate. We believe that the present
reduction reaction using the WCl6/In system proceeds through a SET
(single-electron transfer) process. The method offers advantages such as
mild reaction conditions, short reaction times, simple experimental
operation, and tolerance of some functional groups. The utility of the
WCl6/In system as a new reducing agent is also demonstrated by the high
yields of dibenzyl sulfide (entry 10) and phenyl benzyl sulfide (entry 11)
obtained after the reduction of the corresponding sulfoxides. Usually the sulf-
oxides that contain a benzyl group are difficult to reduce by other reagents.[8]
In conclusion, we believe that this procedure using the WCl6/In system
will present a useful and efficient alternative to the existing methods for
reduction of sulfoxides to sulfides. Further investigation of the WCl6/In
system as a reducing agent in organic synthesis is currently in progress.
EXPERIMENTAL
1
The H NMR spectra were recorded on a FT-Bruker AF-300 (300 MHz for
1H NMR; 75 MHz for 13C NMR) using TMS as an internal standard.
Infrared (IR) spectra were obtained on a Perkin-Elmer 16F PC FT-IR
Shimadzu. Thin-layer chromatography (TLC) analysis was performed on
silica-gel plates (Merck, 60 F-254). All products were purified by flash
column chromatography using silica gel 60 (79–230 mesh, Merck).
General Procedure for the Reaction
A typical procedure for the deoxygenation of sulfoxides is as follows:
Tungsten hexachloride (238 mg, 1.0 mmol) was added to a solution of
indium (230 mg, 2.0 mmol) and diphenylsulfoxide (101 mg, 0.5 mmol) in
anhyd. THF (1 mL). The mixture was stirred at room temperature, and the
progress of the reaction was followed by TLC. After completion of the
reaction (5 min), the reaction was quenched with aq. NaOH (10%) and

4082
B. W. Yoo, M. C. Park, and M. S. Song
extracted with ether. The combined ethereal extracts were washed successively
with brine (20 mL) and H2O (20 mL). The organic layer was separated and
dried over anhydrous Na2SO4. The crude product was purified by silica-gel
column chromatography (hexane–ethyl acetate ¼ 1:1) to afford diphenylsul-
fide (86 mg, 92%).
ACKNOWLEDGMENT
We are very grateful to Korea University for financial support.
REFERENCES
1. (a) Carreno, M. C. Applications of sulfoxides to asymmetric synthesis of biologi-
cally active compounds. Chem. Rev. 1995, 95, 1717; (b) Solladie, G. Asymmetric
synthesis using nucleophilic reagents containing a chiral sulfoxide group.
Synthesis 1981, 185.
2. (a) For a review, see Madesclaire, M. Reduction of sulfoxides to thioethers. Tetra-
hedron 1988, 44, 6537; (b) For an earlier review, see Drabowicz, J.; Togo, H.;
Mikolajczyk, M.; Oae, S. Org. Prep. Proc. Int. 1984, 16, 171; (c) Schmizu, M.;
Shibuya, K.; Hayakawa, R. Chemoselective deoxygenation of sulfoxides with
titanium tetraiodide. Synlett 2000, 1437; (d) Khurana, J. M. Deoxygenation of sulf-
oxides and selenoxides with nickel boride. Tetrahedron Lett. 1998, 39, 3829;
(e) Yadav, J. S.; Reddy, B. V. S.; Srinivas, C.; Srihari, P. Ultrasound-promoted
deoxygenation of sulfoxides by samarium-NH4Cl. Synlett 2001, 854;
(f) Balicki, R. Mild and efficient deoxygenation of sulfoxides with titanium (IV)
chloride/sodium iodide reagent system. Synthesis 1991, 155; (g) Miller, S. J.;
Collier, T. R.; Wu, W. Efficient reduction of sulfoxides with 2,6-dihydroxypyridine.
Tetrahedron Lett. 2000, 41, 3781.
3. Cintas, P. Activated Metals in Organic Synthesis; CRC: Boca Raton, FL., 1993.
4. (a) Firouzabadi, H.; Jamalian, A.; Karimi, B. Efficient reductive deoximation by
tungusten (VI) chloride (WCl6) or molybdenum (V) chloride (MoCl5) in presence
of Zn powder in CH3CN. Bull. Chem. Soc. Jpn. 2002, 75, 1761; (b) Habib, F.;
Babak, K. Efficient deoxygenation of sulfoxides to thioethers and reductive
coupling of sulfonyl chlorides to disulfides with tungsten hexachloride. Synthesis
1999, 500.
.
5. (a) Sarmah, B. K.; Barua, N. C. Al-NiCl2 6H2O-THF: A new, mild and neutral system
for selective reduction of organic functional groups. Tetrahedron 1991, 47, 8587;
(b) Bezbarua, M. S.; Bez, G.; Barua, N. C. A facile procedure for the conversion of
.
nitroolefins into carbonyl compounds using Al-NiCl2 6H2O-THF system. Chem.
Lett. 1999, 325; (c) Wang, W. B.; Shi, L. L.; Huang, Y. Z. A novel reduction
system—SbCl3-Al/or SbCl3-Zn/DMF-H2O—for conversion of aldehydes to
alcohols. Tetrahedron Lett. 1990, 31, 1185; (d) Barua, M.; Boruah, A.; Prajapati, D.;
Sandhu, J. S. A new method for the chemoselective reduction of aryl and aroyl
azides. Tetrahedron Lett. 1996, 37, 4559; (e) Raju, B. R.; Devi, G.; Nongpluh, Y. S.;
Saikia, A. K. A facile and efficient method for the reduction of sulfoxides into
.
sulfides with an Al-NiCl2 6H2O system. Synlett 2005, 358.

Sulfoxide Deoxygenation with WCl6/In
4083
6. (a) Yoo, B. W.; Choi, K. H.; Kim, D. Y.; Choi, K. I.; Kim, J. H. Mild and efficient
reduction of sulfoxides to sulfides with titanium tetrachloride–indium system.
Synth. Commun. 2003, 33, 53; (b) Yoo, B. W.; Choi, K. H.; Lee, S. J.;
Yoon, C. M.; Kim, S. H.; Kim, J. H. Mild and efficient reduction of sulfoxides to
sulfides with (cyclopentadienyl) titanium (IV) dichloride–indium system. Synth.
Commun. 2002, 32, 63.
7. Vogel’s Textbook of Practical Organic Chemistry, 5th ed; Longman: London, 1978,
p. 792.
8. (a) Alper, H.; Kenney, E. C. H. Deoxygenation of sulfoxides by iron pentacarbonyl.
Tetrahedron Lett. 1970, 11, 53; (b) Chasar, D. W. Quantitative reduction of sulf-
oxides. J. Org. Chem. 1971, 36, 613.