Temperature-controlled selective reduction of arenesulfonyl chlorides promoted by samarium metal in DMF

Article abstract of DOI:10.1016/S0040-4039(03)00814-1

Promoted by samarium in DMF, arenesulfonyl chlorides can be selectively reduced to diaryldisulfones, diarylthiosulfonates and diaryldisulfides in good to excellent yields by reaction temperature control without the need to pretreat or activate the metallic samarium.

Full text of DOI:10.1016/S0040-4039(03)00814-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 4291–4294
Temperature-controlled selective reduction of arenesulfonyl
chlorides promoted by samarium metal in DMF
Yongjun Liua and Yongmin Zhanga,b,
*
aDepartment of Chemistry, Zhejiang University (Campus Xixi ), Hangzhou 310028, PR China
bState Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, PR China
Received 16 December 2002; revised 10 March 2003; accepted 21 March 2003
Abstract—Promoted by samarium in DMF, arenesulfonyl chlorides can be selectively reduced to diaryldisulfones, diarylthiosul-
fonates and diaryldisulfides in good to excellent yields by reaction temperature control without the need to pretreat or activate
the metallic samarium. © 2003 Elsevier Science Ltd. All rights reserved.
Diaryldisulfones and diarylthiosulfonates have interest-
ing properties and have been exploited in synthetic,
pharmaceutical and polymer chemistry.1,2 Diaryl-
disulfides are important intermediates in various
organic transformations especially in natural product
synthesis.3 There are many reports involving the synthe-
ses of diaryldisulfides4 and diaryldisulfones;5 however,
most of these methods require unusual substrates and
relatively harsh reaction conditions. In addition, reports
concerning the synthesis of diarylthiosulfonates are
rare.6
by metallic samarium without any activator or
pretreatment.11
In our investigations on the applications of metallic
samarium, we found that when N,N-dimethylform-
amide (DMF) is used as the solvent instead of THF,
metallic samarium, without the need to be activated or
pretreated, can selectively reduce arenesulfonyl chlo-
rides 1 to diaryldisulfones 2, diarylthiosulfonates 3 or
diaryldisulfides 4, by controlling the reaction tempera-
ture over three different temperature ranges (Scheme
1).12
Though samarium diiodide (SmI2) is a useful reducing
reagent,7 its application in organic synthesis is limited.
Its storage is difficult because it is very sensitive to air
oxidation, which seriously restricts its application in
large scale reactions. Furthermore, Sm2+ can only
donate one electron. Therefore, the direct use of metal-
lic samarium as a reducing agent in organic transforma-
tions has attracted the attention of many organic
chemists.8 However, in most cases, reactions promoted
by samarium are usually carried out in THF,9 and
metallic samarium has to be activated or pretreated by
various methods so as to ensure the reactions proceed
smoothly. Generally, metallic samarium is activated by
other reagents such as iodine, hydrochloric acid, alkyl
halides, etc.9,10 Until now, only a few reports can be
found concerning organic reactions promoted efficiently
A variety of diaryldisulfones 2, diarylthiosulfonates 3
and diaryldisulfides 4 were obtained in good to excel-
lent yields in the Sm/DMF system, as shown in Table
1.13 We found that the substituents on the arenesulfonyl
Keywords: samarium; DMF; arenesulfonyl chloride; diaryldisulfone;
diarylthiosulfonate; diaryldisulfide.
* Corresponding author. E-mail: yminzhang@mail.hz.zj.cn
Scheme 1.
0040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)00814-1

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Y. Liu, Y. Zhang / Tetrahedron Letters 44 (2003) 4291–4294
Table 1. Samarium-promoted temperature-controlled selective reduction of arenesulfonyl chlorides
Product 2a
T (°C) Time (min) Yield (%)b T (°C) Time (min) Yield (%)b T (°C) Time (min) Yield (%)b
Entry Substrate 1
Product 3
Product 4
1
2
3
4
5
6
7
8
9
C6H5SO2Cl (1a)
−10
−5
−5
−10
−10
−5
5
5
6
4
4
5
5
5
5
61 (2a)
55 (2b)
58 (2c)
51 (2d)
49 (2e)
54 (2f)
0
5
10
0
0
5
5
5
5
60
60
60
40
60
60
60
60
60
87 (3a)
85 (3b)
86 (3c)
83 (3d)
87 (3e)
84 (3f)
62 (3g)
50
60
60
50
60
60
60
60
60
10
10
10
10
10
10
20
30
30
93 (4a)
95 (4b)
92 (4c)
94 (4d)
96 (4e)
90 (4f)
86 (4g)
74 (4h)
68 (4i)
4-CH3-C6H4SO2Cl (1b)
4-CH3O-C6H4SO2Cl (1c)
4-Cl-C6H4SO2Cl (1d)
4-Br-C6H4SO2Cl (1e)
4-I-C6H4SO2Cl (1f)
3-NO2-C6H4SO2Cl (1g)
4-CH3CONH-C6H4SO2Cl (1h) −5
−5
c
−5
–
c
c
–
–
c
c
–
–
(1i)
a A considerable amount of product 3 was detected.
b Isolated yields based on arenesulfonyl chlorides.
c None of the expected product was obtained.
Scheme 2.
chloride influenced this reaction. Electron-withdrawing
groups on the aromatic ring (1d,e) induced the reduc-
tion of arenesulfonyl chlorides more easily than elec-
tron-donating groups (1b,c).
The initial stage of reduction of arenesulfonyl chlorides
to afford diaryldisulfones is relatively difficult to con-
trol, since the formation of the diarylthiosulfonate 3 is
usually unavoidable (generally, 2:3 have a ratio of
about 70:30 when the initial stage of reduction was
finished at a reaction temperature of −5 to −10°C), thus
leading to the relatively low yield of disulfone 2. In
contrast, the diarylthiosulfonates 3 can be obtained in
high yields after the second stage of reduction. In fact,
the three products can be detected in succession when
the reaction undergoes a temperature rise from −10 to
60°C (Scheme 2), and the experimental results show
that an excess amount of Sm metal has no effect upon
this reaction. These results indicate the mechanism of
this reaction is as shown in Scheme 2. According to
some reports,13b the formation of diarylthiosulfonates
of type 3 may proceed via an intermediate disulfoxide
(intermediate A).
Due to the strong electron-withdrawing effect of the
nitro group, reaction of the 3-nitrobenzenesulfonyl
chloride 1g could not be stopped at the first step of
reduction to the diaryldisulfone, therefore, only the
products 3g and 4g were obtained (entry 7). On the
other hand, the strong electron-donating effect of the
thiophene-ring made the initial reduction of 1i to the
diaryldisulfone and diarylthiosulfonate more difficult,
but at a relatively higher temperature, the only product
obtained was diaryldisulfide 4i because the diaryldisul-
fone and diarylthiosulfonate were very reactive toward
samarium metal at this temperature (entry 9).
Remarkably, this reaction shows high chemoselectivity.
Halo groups (chloro, bromo, iodo), thiophene-rings,
esters, amides and nitro groups all remain unaffected
by samarium in DMF under the reaction conditions,
although these groups, especially the iodo and nitro
groups, are usually reactive towards other samarium
reagents.7
In conclusion, the Sm-promoted stepwise reduction of
arenesulfonyl chlorides offers a facile, convenient and
efficient method for the synthesis of useful diaryldisul-
fones, diarylthiosulfonates and diaryldisulfides, selec-
tively, by controlling the reaction temperature. The

Y. Liu, Y. Zhang / Tetrahedron Letters 44 (2003) 4291–4294
4293
advantages of this method are the readily available
starting materials,14 the mild reaction conditions, the
simple operational procedures and high yields of prod-
ucts. In addition, the reaction selectivity of the temper-
ature-controlled procedure seems to offer a promising
strategy for large-scale preparations directly promoted
by metallic samarium. Finally, because the direct use of
samarium in organic synthesis without any activator
has rarely been reported, this reaction may become
useful.
Tetrahedron Lett. 1977, 25, 1195; (b) Kim, Y. H.; Takata,
T.; Oae, S. Tetrahedron Lett. 1978, 26, 2305.
7. (a) Girard, P.; Namy, J. L.; Kagan, H. B. J. Am. Chem.
Soc. 1980, 102, 2693; (b) Molander, G. A. Chem. Rev.
1992, 92, 29; (c) Molander, G. A.; Harris, C. R. Chem.
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8. Banik, B. K. Eur. J. Org. Chem. 2002, 2431.
9. (a) Ogawa, A.; Nanke, T.; Takami, N.; Sumino, Y.; Ryu,
I.; Sonoda, N. Chem. Lett. 1994, 379; (b) Molander, G.
A.; Etter, J. B. J. Org. Chem. 1986, 51, 1778; (c)
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Acknowledgements
10. (a) Banik, B. K.; Mukhopadhyay, C.; Venkatraman, M.
S.; Becker, F. F. Tetrahedron Lett. 1998, 39, 7243; (b)
Yanada, R.; Negora, N.; Yanada, K.; Fujita, T. Tetra-
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Chem. Pharm. Bull. 1994, 42, 402; (d) Ogawa, A.;
Takami, N.; Sckiguchi, M.; Ryu, I.; Kambe, N.; Sonoda,
N. J. Am. Chem. Soc. 1992, 114, 8729; (e) Wang, L.;
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66, 330.
We are grateful to the National Natural Science Foun-
dation of China (Project No. 20072033).
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12. Typical procedure:
Preparation of diphenyldisulfone: To a mixture of Sm
powder (2 mmol) in freshly distilled N,N-dimethylfor-
mamide (DMF, 10 mL), benzenesulfonyl chloride (2
mmol, freshly distilled) was added at −10°C with mag-
netic stirring under a nitrogen atmosphere. The resulting
solution turned yellow-green within 2 h. After the com-
pletion of the reaction (about 5 h at −10°C), the reaction
was quenched with dilute hydrochloric acid (0.1 mol/L, 5
ml) and the mixture was extracted with diethyl ether
(3×30 ml). The organic phase was washed with water (20
ml), saturated brine (15 ml), and dried over anhydrous
Na2SO4. The solvents were removed under reduced pres-
sure to give the crude product, which was purified by
column chromatography to afford diphenyldisulfone in
58% yield.
Preparation of diphenylthiosulfonate: To a mixture of Sm
powder (3 mmol) in freshly distilled N,N-dimethylfor-
mamide (DMF, 10 mL), benzenesulfonyl chloride (2
mmol, freshly distilled) was added at 5°C with magnetic
stirring under a nitrogen atmosphere. The resulting solu-
tion turned yellow-green within 15 min and an exother-
mic reaction was observed. After the completion of the
reaction (about 1 h at 5°C), a routine workup as men-
tioned above afforded diphenylthiosulfonate in 87%
yield.
4. (a) Dhar, P.; Ranjan, R.; Chandrasekaran, S. J. Org.
Chem. 1990, 55, 3728 and references cited therein; (b)
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135; (c) Guo, H. Y.; Wang, J. Q.; Zhang, Y. M. Synth.
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Org. Synth. 1951, Collect. Vol. 1, 220, 2nd ed.; Blatt, A.
H., Ed; (e) Wohlfahrt, T. J. Prakt. Chem. 1902, 66, 553.
Preparation of diphenyldisulfide: To a mixture of Sm
powder (4 mmol) in freshly distilled N,N-dimethylfor-
mamide (DMF, 10 mL) benzenesulfonyl chloride (2
mmol, freshly distilled) was added at 50°C with magnetic
stirring under a nitrogen atmosphere. The resulting solu-
tion turned yellow-green within 1 min and an exothermic
reaction was observed. After the completion of the reac-
tion (about 10 min), a routine workup as mentioned
above afforded diphenyldisulfide in 93% yield.
&
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Y. Liu, Y. Zhang / Tetrahedron Letters 44 (2003) 4291–4294
13. (a) All of the products obtained in this study were
characterized (1H NMR, MS, IR, EA).
(100.00), 77 (11.52). Anal. calcd for C12H10S2: C, 66.01;
H, 4.62. Found: C, 66.02; H, 4.60%.
Diphenyldisulfone (2a) (Ref. 5e): White solid, mp 193–
196°C. wmax (KBr)/cm−1: 3062, 1349, 1143. lH (CDCl3):
7.84–7.86 (2H, m), 7.74–7.76 (2H, m), 7.58–7.66 (6H, m).
m/z (%): 282 (M+, 0.09), 141 (44.97), 77 (100.00). Anal.
calcd for C12H10O4S2: C, 51.05; H, 3.57. Found: C, 51.24;
H, 3.60%.
Di(4-methyl)phenyldisulfide (4b) (Ref. 4b): White solid,
mp 45–46°C. wmax (KBr)/cm−1: 2921, 485. lH (CDCl3):
7.39–7.41 (4H, m), 7.11–7.13 (4H, m), 2.34 (6H, s). m/z
(%): 246 (M+, 100.00), 123 (44.96), 91 (8.94). Anal. calcd
for C14H14S2: C, 68.25; H, 5.73. Found: C, 68.47; H,
5.69%.
Di(4-methyl)phenyldisulfone (2b) (Ref. 5e): White solid,
mp >200°C. wmax (KBr)/cm−1: 2947, 1344, 1137. lH
(CDCl3): 7.86–7.88 (4H, m), 7.44–7.46 (4H, m), 2.53 (6H,
s). m/z (%): 310 (M+, 0.18), 155 (53.37), 91 (100.00).
Anal. calcd for C14H14O4S2: C, 54.17; H, 4.55. Found: C,
54.22; H, 4.58%.
(b) The exact structure of the thiosulfonate is debatable.
The problem mainly focuses on which structure is the
more rational between I and II4a,15 shown below:
Diphenylthiosulfonate (3a) (Refs. 13b and 15a): White
solid, mp 44–45°C. wmax (KBr)/cm−1: 3054, 1381, 1139. lH
(CDCl3): 7.57–7.60 (4H, m), 7.37–7.44 (6H, m). m/z (%):
250 (M+, 25.10), 141 (33.15), 125 (82.04), 109 (42.75), 77
(100.00). Anal. calcd for C12H10O2S2: C, 57.57; H, 4.03.
Found: C, 57.28; H, 4.05%.
Di(4-methyl)phenylthiosulfonate (3b) (Refs. 13b and 15b):
White solid, mp 77–78°C. wmax (KBr)/cm−1: 2917, 1378,
1139. lH (CDCl3): 7.86–7.88 (2H, m), 7.22–7.28 (4H, m),
7.15–7.17 (2H, m), 2.44 (3H, s), 2.38 (3H, s). m/z (%): 278
(M+, 21.75), 155 (23.76), 139 (100.00), 123 (44.88), 91
(85.90). Anal. calcd for C14H14O2S2: C, 60.40; H, 5.07.
Found: C, 60.59; H, 5.10%.
Structure I was given by Beilstein,15a,b while structure II
was suggested to be more probable in other literature.15c
In fact, according to more recent literature, disulfoxides
of type I are known to rearrange readily to thiosulfonate
esters of type II.4a,15d,e
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62, 511.
15. (a) Beilsteins Handbuch Der Organichen Chemie 1921,
Band VI, 324; (b) Beilsteins Handbuch Der Organichen
Chemie 1921, Band VI, 427; (c) Gilman, H.; Smith, L. E.;
Parker, H. H. J. Am. Chem. Soc. 1925, 47, 851; (d)
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Kice, J. L. J. Am. Chem. Soc. 1976, 24, 7711.
Diphenyldisulfide (4a) (Ref. 4b): White solid, mp 59°C.
wmax (KBr)/cm−1: 3070, 464. lH (CDCl3): 7.52–7.54 (4H,
m), 7.24–7.34 (6H, m). m/z (%): 218 (M+, 0.09), 109