Mild and Efficient Reduction of Sulfoxides to Sulfides with Bis(cyclopentadienyl)titanium(IV) Dichloride-Indium System

Article abstract of DOI:10.1081/SCC-120001509

Cp2TiCl2/In system was found to be a new reagent for reducing various sulfoxides to the corresponding sulfides in good yield under mild and neutral conditions.

Full text of DOI:10.1081/SCC-120001509

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MILD AND EFFICIENT REDUCTION OF
SULFOXIDES TO SULFIDES WITH BIS-
(CYCLOPENTADIENYL)TITANIUM(IV)
DICHLORIDE–INDIUM SYSTEM
Byung Woo Yoo , Kwang Hyun Choi a , Sung Jae Lee a , Cheol Min Yoon b , Sung Hoon Kim c
& Joong Hyup Kim c
a Department of Chemistry, Korea University , Chochiwon, Chungnam, 339-700, Korea
b Department of Life Science and Biotechnology, Graduate School of Biotechnology,
Korea University , Seoul, Korea
c Biochemicals Research Center, Korea Institute of Science and Technology ,
Cheongryang, Seoul, 130-650, Korea
Published online: 21 Aug 2006.
To cite this article: Byung Woo Yoo , Kwang Hyun Choi , Sung Jae Lee , Cheol Min Yoon , Sung Hoon Kim & Joong Hyup
Kim (2002) MILD AND EFFICIENT REDUCTION OF SULFOXIDES TO SULFIDES WITH BIS-(CYCLOPENTADIENYL)TITANIUM(IV)
DICHLORIDE–INDIUM SYSTEM, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 32:1, 63-67, DOI: 10.1081/SCC-120001509
To link to this article: http://dx.doi.org/10.1081/SCC-120001509
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SYNTHETIC COMMUNICATIONS, 32(1), 63–67 (2002)
MILD AND EFFICIENT REDUCTION OF
SULFOXIDES TO SULFIDES WITH BIS-
(CYCLOPENTADIENYL)TITANIUM(IV)
DICHLORIDE–INDIUM SYSTEM
Byung Woo Yoo,1, Kwang Hyun Choi,1
*
Sung Jae Lee,1 Cheol Min Yoon,2
Sung Hoon Kim,3 and Joong Hyup Kim3
1Department of Chemistry, Korea University,
Chochiwon, Chungnam, 339-700, Korea
2Department of Life Science and Biotechnology,
Graduate School of Biotechnology,
Korea University, Seoul, Korea
3Biochemicals Research Center,
Korea Institute of Science and Technology,
Cheongryang, Seoul, 130-650, Korea
ABSTRACT
Cp2TiCl2/In system was found to be a new reagent for redu-
cing various sulfoxides to the corresponding sulfides in good
yields under mild and neutral conditions.
*Corresponding author.
63
Copyright & 2002 by Marcel Dekker, Inc.
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YOO ET AL.
The chemical reactivity of Cp2TiCl2/M system (M ¼ Na, Zn, Al, Mg,
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 Cp2TiCl2/samarium system is used as a reagent for reducing sulfoxides
to sulfides.1(d) The reduction of sulfoxides to sulfides is a valuable transfor-
mation in the application of organosulfur compounds in organic synthesis
and a number of methods have been developed for the reduction of sulf-
oxides.2 We considered that Cp2TiCl2/In system can be an efficient reducing
agent for the conversion of sulfoxides to sulfides. The application of process
is highly desired in which protected thios are directly transformed into dis-
ulfides indium reagents in organic synthesis has attracted more and more
interest in the last decade.3 We have investigated the reactions of Cp2TiCl2/
In system with various sulfoxides and found that they can be rapidly
reduced to the corresponding sulfides in good yields (Eq. 1). The new redu-
cing system was generated by the addition of indium powder to a stirred
solution of bis(cyclopentadienyl)titanium(IV) dichloride in THF under
nitrogen. Herein, we report the reduction of sulfoxides to sulfides by treat-
ment with Cp2TiCl2/In under mild conditions. Some control experiments
revealed that sulfoxides could not be reduced by Cp2TiCl2 or indium alone
and were recovered unchanged.
(1)
The reaction molar ratio of indium and Cp2TiCl2 is 1:2. If the molar
ratio is changed to In:Cp2TiCl2 ¼ 1:1, the reaction is not successful. In com-
parison with the Cp2TiCl2/Sm system, Cp2TiCl2/In system reduces sulfoxides
more rapidly (10 min) in higher yields (73–93%) and showed a good chemos-
electivity. The functional group tolerance of this method is evident from
entries 3–6 which show that bromo, methoxy, aldehyde and vinyl are unaf-
fected under the reaction conditions. All the compounds obtained showed IR,
NMR and mass spectral data compatible with the structure. Sulfoxides as the
substrate were prepared according to the literature procedure.4 In order to
assess the generality of the process, the reaction was studied with a variety of
sulfoxides. As shown in Table 1, the methodology is applicable to aromatic,
aliphatic and aralkyl sulfoxides. However, sulfones (entries 12 and 13) are not
reduced under the reaction conditions. Thus, we have been able to demon-

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REDUCTION OF SULFOXIDES TO SULFIDES
65
Table 1. Reduction of Sulfoxides with Cp2TiCl2/In System
Reaction Yield
Time (min) (%)*
Entry
R1
R2
Products
PhSPh
PhSCH3
1
2
3
4
5
6
7
8
9
10
11
12
13
Ph
Ph
Ph
CH3
CH3
10
10
93
85
90
92
81
73
90
80
83
85
82
4-BrC6H4
4-BrC6H4SCH3
10
10
4-CH3OC6H4 4-CH3OC6H4 (4-CH3OC6H4)2S
4-CHOC6H4
Ph
4-CH3C6H4
Ph
PhCH2
PhCH2
nC4H9
CH3
CH¼CH2
4-CHOC6H4SCH3
PhSCH¼CH2
4-CH3C6H4SCH3
PhSCH2CH3
(PhCH2)2S
10
10
CH3
10
10
CH2CH3
PhCH2
Ph
10
10
PhCH2SPh
( nC4H9)2S
nC4H9
10
no reaction
no reaction
PhCH2S(¼O)2Ph
PhS(¼O)2CH2CH3
*Isolated yield.
strate the utility of easily accessible Cp2TiCl2/In system as a convenient
reagent for effecting chemoselective deoxygenation of sulfoxides. Although
the role of bis(cyclopentadienyl)-titanium(IV) dichloride is still not clarified,
it is assumed that reduction of titanium(IV) with indium provides low valent
titanium,5 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 (10 min), simple operation, tolerance of some
functional groups on the aromatic ring.
In conclusion, we believe this procedure using Cp2TiCl2/In system will
present a useful and convenient alternative to the existing methods for
reduction of sulfoxides to sulfides. Further investigations of Cp2TiCl2/In
system as reducing agent in organic synthesis are currently in progress.
EXPERIMENTAL
Tetrahydrofuran was freshly distilled from sodium/benzophenone
1
ketyl before use. H NMR spectra were recorded on a FT-Bruker AF-300
1
(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

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YOO ET AL.
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
Bis(cyclopentadienyl)titanium(IV) dichloride (500 mg, 2.0 mmol),
indium powder (115 mg, 1.0 mmol) and THF (5 mL) were mixed under
nitrogen atmosphere and the resulting mixture was sirred at reflux for
30 min. A dark-red solution of the low-valent titanium-indium complex
was obtained and cooled to room temperature. To this solution, diphenyl-
sulfoxide (101 mg, 0.5 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 (87 mg, 93%).
ACKNOWLEDGMENT
This work was financially supported by Korea Institute of Science and
Technology (2E16800) and partially by Korea University.
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67
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Received in Japan December 25, 2000

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