Mild and efficient reduction of sulfoxides to sulfides with titanium tetrachloride-indium system

Article abstract of DOI:10.1081/SCC-120015558

TiCl₄/In system was found to be a new reagent for reducing various sulfoxides to the corresponding sulfides in good yields under mild conditions.

Full text of DOI:10.1081/SCC-120015558

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Mild and Efficient Reduction of Sulfoxides to Sulfides
with Titanium Tetrachloride–Indium System
Byung Woo Yoo a c , Kwang Hyun Choi a , Dong Yoon Kim a , Kyung Il Choi b & Joong Hyup Kim
b
a Department of Chemistry , Korea University , Jochiwon, Chungnam, Korea
b Biochemicals Research Center , Korea Institute of Science and Technology , Cheongryang,
Seoul, Korea
c Department of Chemistry , Korea University , Jochiwon, Chungnam, 339-700, Korea
Published online: 29 Jun 2011.
To cite this article: Byung Woo Yoo , Kwang Hyun Choi , Dong Yoon Kim , Kyung Il Choi & Joong Hyup Kim (2003) Mild and
Efficient Reduction of Sulfoxides to Sulfides with Titanium Tetrachloride–Indium System, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:1, 53-57, DOI: 10.1081/SCC-120015558
To link to this article: http://dx.doi.org/10.1081/SCC-120015558
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 1, pp. 53–57, 2003
Mild and Efficient Reduction of
Sulfoxides to Sulfides with Titanium
Tetrachloride–Indium System
1
Byung Woo Yoo,1, Kwang Hyun Choi,
*
Dong Yoon Kim,1 Kyung Il Choi,2
and Joong Hyup Kim2
1Department of Chemistry, Korea University,
Jochiwon, Chungnam, Korea
2Biochemicals Research Center, Korea Institute of Science
and Technology, Cheongryang, Seoul, Korea
ABSTRACT
TiCl4/In systemwas found to be a new reagent for reducing various
sulfoxides to the corresponding sulfides in good yields under mild
conditions.
Key Words: Sulfoxide; Sulfide; Titanium; Indium.
*Correspondence: Byung Woo Yoo, Department of Chemistry, Korea University,
Jochiwon, Chungnam, 339-700, Korea. Fax: 82-41-867-5396; E-mail: bwyoo@
korea.ac.kr.
53
DOI: 10.1081/SCC-120015558
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
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54
Yoo et al.
The chemical reactivity of TiCl4/M system(M ¼ Te, Mg, Zn, Sm) has
been the subject of considerable interest and the reducing ability of these
systems has been extensively studied.[1] It has recently been reported that
[2]
TiCl4/Smsystemis used as a reagent for reducing sulfoxides to sulfides.
The reduction of sulfoxides to sulfides is a valuable transformation in the
application of organosulfur compounds in organic synthesis and a good
number of reagents have been developed for the reduction of sulfoxides
to sulfides.[3] However, many of these procedures require harsh reaction
conditions, and prolonged reaction times. There still exists a need for
the development of new efficient and readily available reagents for
this conversion. We considered that TiCl4/In systemcan be an efficient
reducing agent for the conversion of sulfoxides to sulfides. We have
investigated the reactions of TiCl4/In systemwith various sulfoxides
and found that they can be rapidly reduced to the corresponding sulfides
in good yields (Eq. (1)). The new reducing systemwas generated by the
addition of indiumpowder to a stirred solution of titaniumtetrachloride
in THF under nitrogen. In continuation of our work on the applications
[4]
of low-valent titaniumreagent in various transformations,
herein
we report a mild and efficient procedure for the deoxygenation of
sulfoxides using TiCl4/In system. Some control experiments revealed
that sulfoxides could not be reduced by indiumalone and were recovered
unchanged.
ð1Þ
In comparison with other procedures, TiCl4/In systemreduces
sulfoxides more rapidly (10 min) in higher yields (84–95%) and showed
a good chemoselectivity. The functional group tolerance of this method is
evident from Entries 3–6 which show that bromo, methoxy, aldehyde,
and vinyl are unaffected under the reaction conditions. All the com-
pounds obtained showed IR, NMR, and mass spectral data compatible
with the structure. Sulfoxides as the substrate were prepared according to
theliteratureprocedure.[5] Inordertoassessthegeneralityoftheprocess,the
reaction was studied with a variety of sulfoxides. As shown in Table 1,
the methodology is applicable to aromatic, aliphatic, and aralkyl sulfox-
ides. Thus, we have been able to demonstrate the utility of easily
accessible TiCl4/In systemas a convenient reagent for effecting

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Reduction of Sulfoxides to Sulfides with TiCl4/In
55
Table 1. Reduction of sulfoxides with TiCl4/In system.a
Reaction
Yield
Entry
R1
R2
Products
time (min) (%)b
1
2
3
4
5
6
7
8
9
Ph
Ph
4-BrC6H4
Ph
CH3
CH3
PhSPh
PhSCH3
4-BrC6H4SCH3
10
10
10
10
10
10
10
10
10
10
10
91
93
93
95
91
84
95
87
89
93
85
4-CH3OC6H4 4-CH3OC6H4 (4-CH3OC6H4)2S
4-CHOC6H4
Ph
4-CH3C6H4
Ph
PhCH2
PhCH2
nC4H9
CH3
CH¼CH2
CH3
CH2CH3
PhCH2
Ph
4-CHOC6H4SCH3
PhSCH¼CH2
4-CH3C6H4SCH3
PhSCH2CH3
(PhCH2)2S
10
11
PhCH2SPh
(nC4H9)2S
nC4H9
aMole ratio of sulfoxide:TiCl4:Indium ¼ 1:1:0.5.
bIsolated yield.
chemoselective deoxygenation of sulfoxides. Although the role of
titaniumtetrachloride is still not clarified, it is assumed that reduction
of titanium(IV) with indium provides low valent titanium,[6] which might
be reducing the sulfoxides 1 to give the corresponding sulfides 2. The
notable advantages of this methodology are mild reaction condition,
fast reaction time, simple operation, and tolerance of some functional
groups on the aromatic ring. The utility of TiCl4/In systemas a new
reducing agent is also demonstrated by the high yields of dibenzyl sulfide
(Entry 9) and phenyl benzyl sulfide (Entry 10) obtained after the reduc-
tion of the corresponding sulfoxides. Usually the sulfoxides which con-
tain a benzyl group are difficult to reduce by other reagents.[7]
In conclusion, we believe that this procedure using TiCl4/In system
will present a useful and convenient alternative to the existing methods
for reduction of sulfoxides to sulfides. Further investigations of TiCl4/In
systemas reducing agent in organic synthesis are currently in progress.
EXPERIMENTAL
Tetrahydrofuran was freshly distilled fromsodium/benzophenone
1
ketyl before use. H NMR spectra were recorded on a FT-Bruker AF-

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56
Yoo et al.
1
300 (300 MHz for H NMR; 75 MHz for 13C NMR) using TMS as an
internal standard. The solvent was CDCl3 unless otherwise noted. IR
spectra were obtained on a Perkin Elmer 16F PC FT-IR Shimadzu. GC-
MS was recorded on a Hewlett-Packard 5890 GC. High resolution mass
spectra (HRMS) were obtained on a Varian MATCH-50F instrument.
General Procedure for the Reaction
Indium powder (58 mg, 0.5 mmol), titanium tetrachloride (226 mg,
1.2 mmol) and THF (10 mL) were mixed under nitrogen atmosphere
and the resulting mixture was stirred at room temperature for 1 h.
A dark-blue solution of the low-valent titanium–indium complex was
obtained and cooled to roomtemperature. To this solution, diphenylsulf-
oxide (202 mg, 1.0 mmol) was added. The reaction mixture was stirred for
10 min at room temperature under nitrogen. The solvent was evaporated
under reduced pressure and the residue was diluted with ether
and filtered. The crude product was purified by silica gel column
chromatography (hexane : ethyl acetate ¼ 6 : 1) to afford diphenylsulfide
(169 mg, 91%).
ACKNOWLEDGMENTS
This work was financially supported by the Korea University Grant
and we are thankful to Korea Institute of Science and Technology for
providing general facilities for this work.
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Received in Japan October 15, 2001

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