Reduction of arylsulfonyl derivatives with the Sm/Cp2TiCl2 system. A novel method for preparation of disulfides

Article abstract of DOI:10.1039/a805339a

The Sm/Cp₂TiCl₂ system reduces arylsulfonyl derivatives to the corresponding disulfides in good yield in refluxing THF.

Full text of DOI:10.1039/a805339a

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214 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
Reduction of Arylsulfonyl Derivatives with the
Sm/Cp TiCl System. A Novel Method for
1999, 214^215y
2
2
Preparation of Disulfidesy
a
b
a
c
You Huang, Hongyun Guo, Yongmin Zhang* and Yulu Wang
a
Department of Chemistry, Zhejiang University at Xixi Campus, Hangzhou, 310028, P.R. China.
Department of Chemistry, Zhejiang Normal University, Jinhua, 321004, P.R. China.
Department of Chemistry, Henan Normal University, Xinxiang, 453002, P.R. China.
b
c
The Sm/Cp TiCl system reduces arylsulfonyl derivatives to the corresponding disulfides in good yield in refluxing
2
2
THF.
Disul¢des are available as starting materials, and are useful
as a class of synthetic intermediates in organic synthesis.
Cp TiCl + Sm
[low valent titanium]
2
2
1� 4
O
S
O
O
S
O
S
Sulfonyl chlorides can be easily and e¤ciently prepared
+
e
coupling
5
by chlorosulfonation reactions of arenes and alkanes.
Ar
Cl
Ar S •
Ar
Ar
Therefore, the reduction of sulfonyl chlorides to disul¢des
is an important process in organic synthesis. As a result
many reagents for this purpose have been reported, such
O
O
O
O
Ti0
6
as piperdinium tetrathiotungstate, sodium cyanoboro-
7
8
9
hydride, iodotrimethylsilane, aluminium iodide, boron
1
0
11
TiII
TiIV
Ti0
triiodide, and diphosphorus tetraiodide.
Recently, samarium reagents have been widely applied to
organic synthesis, at the same time, many reports in which
ArSSAr
O
O
S
O
S
O
S
1
2
Ar
Ar
Ar
S
Ar
Cp2TiCl2 is used as a catalyst in organic synthesis have been
O
O
1
3;14
O
O
published.
In our previous work, the Sm=Cp2TiCl2
system, which our group has established, is a very e¡ective
reducing system.1
of this system and extend the scope of usage further, we
thought that samarium and catalytic amount of
5;16
In order to investigate the properties
Scheme 2
a
Cp2TiCl2 might be also a very e¡ective reducing system. Here
we report a new procedure for reduction of arylsulfonyl
derivatives to the corresponding disul¢des with samarium
and catalytic amount of Cp2TiCl2 (Scheme 1).
Table 1 Reduction of p-tolylsulfonyl chloride (1mmol) with
metallic samarium and various amounts of Cp2TiCl2
Entry Sm(mmol) Cp2TiCl2(mmol) Reaction conditions Yielda (%)
1
2
3
4
2
0
2
2
0
2
4
4
Reflux 5 h
Reflux 5 h
r.t. 5 h
Reflux 30 min,
r.t. 10 min.
Reflux 5 h
Reflux 5 h
Reflux 5 h
0
0
0
41
Sm=Cp2TiCl2
ArSO2X ������! ArSSAr
THF; reflux
Scheme 1 X ˆ Cl; Br; Na‡
To establish the optimum reaction conditions, reduction of
p-tolylsulfonyl chloride with metallic samarium and various
amounts of Cp2TiCl2 was examined in THF under a nitrogen
atmosphere. Table 1 shows that samarium (2 mmol) with
Cp2TiCl2 (0.8 mmol) under re£uxing THF is the best com-
bination for reduction of p-tolylsulfonyl chloride to the cor-
responding disul¢de (entry 5). The reaction also worked
well when various amounts of Cp2TiCl2 and samarium in
re£uxing THF (entries 4^7) were used. No reaction occurs
with only samarium or Cp2TiCl2 (entries 1 and 2) and no
reaction takes place with samarium and Cp2TiCl2 and room
temperature in THF (entry 3).
As shown in Table 2, this system not only can reduce
arylsulfonyl chlorides but also can reduce arylsulfonyl bro-
mide (entry 9) and sodium arylsul¢nate (entries 10 and 11)
e¤ciently. The reduction of arysulfonyl chlorides containing
electronic donating (entry 6) or electronic withdrawing
groups (entries 4, 5, 7 and 12) indicate that the electronic
environment of aryl group does not in£uence the reduction.
The high yields of the reduction products demonstrate the
e¤ciency of this new method.
5
6
7
2
2
2
0.8
0.2
0.1
86
60
51
a
Yield refers to isolated yield of di(p-tolyl) sulfide.
Table 2 Reduction of sulfonyl derivatives to disulfides with
Sm/Cp2TiCl2 a
Isolated
yield (%)
ꢀ
Entry
RSO2X
mp/ C (lit.)
43^44/44^461
36^38/38^39
58^59/58^60
91^92/93.5
7
86
76
83
80
84
72
84
79
81
73
77
1
2
3
4
5
6
7
8
9
4-MeC H SO Cl
6
4
2
1
8a
2-MeC6H4SO2Cl
C6H5SO2Cl
4-BrC6H4SO2Cl
4-ClC6H4SO2Cl
1
7
7
1
7
68^69/69^71
17
4-MeOC6H4SO2Cl
4-Cl,3-MeC6H3SO2Cl
2,4,6-Me C H SO Cl
40^42/41^43
19
48/48^50
17
3
6
2
2
121^123/123^125
1
7
7
4-MeC6H4SO2Br
C6H5SO2Na
4-MeC6H4SO2Na
44/44^46
59/58^60
1
1
0
1
7
11
43^45/44^46
Although the mechanism of the reduction process is not
clearly de¢ned a possible mechanism is shown in Scheme 2.
13 0/131^1321
8b
76
12
Br
SO2Cl
*
To receive any correspondence.
yThis is a Short Paper as de¢ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
therefore no corresponding material in J. Chem. Research (M).
aAll products gave satisfactory IR and 1H NMR spectra. Reaction
conditions: reflux for 5 h.

View Article Online
J. CHEM. RESEARCH (S), 1999 215
Current available methods have some disadvantages. For
example, when sodium cyanoborohydride is used in the
Received, 9th September 1998; Accepted, 30th November 1998
Paper E/8/05339A
7
reduction of arylsulfonyl chlorides, although good
chemoselectivity is observed, the reagents used are relatively
References
8
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1
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2
1
We thank the National Natural Science Foundation of
China and the Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, Chinese Academy
of Sciences for ¢nancial support.
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