Electrogenerated acid (EGA)-catalyzed addition of diaryl disulfides to carbon carbon multiple bonds

Article abstract of DOI:10.1246/cl.130255

Addition of diaryl disulfides to carboncarbon multiple bonds was achieved with a catalytic amount of an electrogenerated acid (EGA), which was produced by the electrolysis of Bu₄N⁺B(C₆F ₅)₄^-/CH₂Cl₂. The anti-addition products of two ArS groups across the carboncarbon multiple bond were obtained in good yields.

Full text of DOI:10.1246/cl.130255

doi:10.1246/cl.130255
Published on the web May 29, 2013
843
Electrogenerated Acid (EGA)-catalyzed Addition of Diaryl Disulfides
to Carbon-Carbon Multiple Bonds
Kouichi Matsumoto,1 Hayato Shimazaki,1 Tomonari Sanada,1 Kazuaki Shimada,1
Shino Hagiwara,1 Seiji Suga,2 Shigenori Kashimura,1 and Jun-ichi Yoshida*3
1Faculty of Science and Engineering, Kinki University, 3-4-1 Kowakae, Higashi-osaka, Osaka 577-8502
2Division of Chemistry and Biotechnology, Graduate School of Natural Science and Technology,
Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530
3Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering,
Kyoto University, Nishikyo-ku, Kyoto 615-8510
(Received March 24, 2013; CL-130255; E-mail: yoshida@sbchem.kyoto-u.ac.jp)
step 1
Addition of diaryl disulfides to carbon-carbon multiple
bonds was achieved with a catalytic amount of an electro-
generated acid (EGA), which was produced by the electrolysis
electrolysis
Bu4N+B(C6F5)4−/CH2Cl2
EGA
¹
of Bu4N+B(C6F5)4 /CH2Cl2. The anti-addition products of
step 2
two ArS groups across the carbon-carbon multiple bond were
obtained in good yields.
catalytic
amount of EGA
R1
R2
R3
R4
R3
R4
ArS
R1
+
ArS-SAr
R2
SAr
Addition of diaryl disulfides (ArSSAr) to carbon-carbon
multiple bonds is one of the most efficient methods for
synthesizing organosulfur compounds. Several methods using
a catalytic or stoichiometric amount of transition-metal com-
plexes, BF3¢OEt2, GaCl3, AlCl3, FeCl3, TfOH, PhIO-OTf, and
I2, have been reported so far.1 Recently, we have reported the
addition reaction of ArSSAr to carbon-carbon multiple bonds
using a stoichiometric2 and catalytic3 amount of electrogener-
ated ArS(ArSSAr)+. Because it is well known that electro-
generated acids (EGAs)4 serve as powerful acid catalysts for
various organic reactions, we envisioned that an EGA might be
effective for this type of reaction. EGA is defined as a Brønsted
acid produced by the anodic process.5,6 The proton source might
be contaminating water or solvents, although the detailed
mechanism of its formation and its nature are not clear at
present.
Scheme 1. EGA-catalyzed addition reaction of ArSSAr to
alkenes.
Table 1. The addition reaction of ArSSAr 1a to (E)-¢-
methylstyrene using EGAa
1) ArS-SAr
(1a, Ar = p-FC6H4)
C6H5
ArS
SAr
electrolysis
Bu4N+X−/
CH2Cl2
EGA
C H
2)
CH3
6
5
(2a, Ar = p-FC6H4)
CH3
Electricity based on
(E)-¢-methylstyrene
Counter anion
(X )
Temperature Yield of
¹
/°C
2a/%b
¹1
/F mol
¹
ClO4
BF4
1.2
1.2
1.2
1.2
0
0
0
N.D.
21c
Herein, we report that an EGA generated by the electrolysis
¹
¹
of Bu4N+B(C6F5)4 /CH2Cl2 catalyzes the addition reaction
¹
B(C6F5)4
B(C6F5)4
B(C6F5)4
B(C6F5)4
B(C6F5)4
B(C6F5)4
B(C6F5)4
38c
of ArSSAr to carbon-carbon multiple bonds of alkenes and
alkynes. The reactions consist of two steps, in which the
generation of EGA is followed by the addition of ArSSAr to a
carbon-carbon multiple bond by a catalytic amount of EGA
(Scheme 1, steps 1 and 2).
¹
¹50
¹78
¹50
¹50
¹50
¹50
¹
77
54
86
81 (79)d
86 (83)d
71 (66)d
¹
1.2
¹
0.60
0.30
0.15
0.05
¹
¹
Because the nature of the EGA depends on the supporting
electrolyte, we first examined the effect of the supporting
electrolyte for the addition of ArSSAr (1a, Ar = p-FC6H4) to
(E)-¢-methylstyrene (Table 1). The typical procedure is as
¹
aA typical procedure: a solution of Bu4N+X /CH2Cl2 (0.1 M,
8.0 mL) was electrolyzed. The electricity was used based on
(E)-¢-methylstyrene. ArSSAr (Ar = p-FC6H4, 1.00 mmol) was
added to the anodic chamber, and the mixture was stirred for
20 min at the same temperature. Then, (E)-¢-methylstyrene
(0.50 mmol) was added to the anodic chamber, and the mixture
was stirred for 60 min at the same temperature. The reaction
was quenched by the addition of Et3N (1.0 mL) to the anodic
camber. b 1H NMR yields of crude product using CH2Br2 as an
¹
follows. In a divided cell, the electrolysis of Bu4N+X /CH2Cl2
¹
¹
¹
(0.1 M, 8.0 mL) (X = ClO4 , BF4 , and B(C6F5)4 ) was carried
out under constant-current conditions to generate the EGA in the
¹1
anodic chamber (1.2 F mol of electricity based on (E)-¢-
methylstyrene was used). 1a (1.00 mmol) was added to the
anodic chamber, and the mixture was stirred for 20 min at
the same temperature. In the next step, (E)-¢-methylstyrene
(0.50 mmol) was added, and the mixture was stirred for 60 min at
the same temperature. To our surprise, the EGA generated from
c
internal standard. The total yield of two diastereomers. The
ratio of diastereomers could not be determined because of the
¹
Bu4N+ClO4 /CH2Cl2, which is well known to catalyze various
overlapping of the signals in H NMR spectrum of the crude
1
d
organic reactions, did not give the desired product at all. In the
product. Isolated yields.
Chem. Lett. 2013, 42, 843-845
© 2013 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

844
Table 2. The addition of various ArSSAr to (E)-¢-methylsty-
rene using a catalytic amount of EGAa
Table 3. The addition of ArSSAr (1a, Ar = p-FC6H4) to
various alkenes and alkynes using a catalytic amount of EGAa
Electricity based on
Yield of
Electricity based on
Entry
Substrate
Product
Yield/%b
the substrate/F mol–1
ArSSAr
(E)-¢-methylstyrene
2/%b
¹1
/F mol
1a (Ar = p-FC6H4)
1b (Ar = C6H5)
0.15
0.30
0.15
0.30
0.15
0.30
0.15
0.30
2a 83
2a 79
Me
0.15
1
3
4
71
Me
(d.r. = 2.1:1)c
ArS
SAr
2b 50 (52)c
2b 66
1c (Ar = p-ClC6H4)
1d (Ar = p-CH3C6H4)
2c 67 (62)c
2c 86 (81)c
2d 48
2
3
0.15
0.30
39
28
5
7
6
8
ArS
SAr
2d 64 (59)c
SAr
0.15
0.30
traced
tracee
4
5
aIn all cases, the reactions were carried out at ¹50 °C in
ArS
¹
Bu4N+B(C6F5)4 /CH2Cl2. bIsolated yields. cThe product
contained
a small amount of inpurity. The yields in
parentheses were determined by 1H NMR analysis of the crude
product using CH2Br2 as an internal standard.
n-C6H13
41 (37)f,g
57f
n-C6H13
6
7
0.15
0.30
9
10
12
ArS
SAr
¹
case of Bu4N+BF4 /CH2Cl2, however, the addition product
SAr
94f
8
9
11
0.15
0.15
2a was obtained in 21% yield. The EGA generated by the
electrolysis of Bu4N+B(C6F5)4 /CH2Cl2 gave the product in
¹
SAr
SAr
38% yield. Cationic intermediates with a bulky and delocalized
counter anion seem to have higher reactivity, although the
reason is not clear at present. Temperature also plays an
important role. The reaction at ¹50 °C gave the best results
(77%). At this temperature, the amount of electricity could be
decreased, and only a catalytic amount of electricity based on
the amount of (E)-¢-methylstyrene was sufficient to drive the
reaction. For example, with 0.30 and 0.15 F mol¹1 of electricity,
the addition product was obtained in 81% and 86% yields,
respectively.7 Notably, the reaction proceeded stereoselectively,
and the anti addition of two ArS groups across the carbon-
carbon double bond was confirmed by the comparison of NMR
spectra of the product with those reported in the literature.2a
ArSSAr having various substituents on the aromatic ring
could be used for the reaction with (E)-¢-methylstyrene, as
shown in Table 2. Diphenyl disulfide and substituents bearing
electron-donating groups such as the CH3 group on the aromatic
ring and electron-withdrawing groups such as F and Cl groups
could also be used.
The method could be extended to various alkenes and
alkynes, as shown in Table 3. For example, (Z)-¢-methylstyrene
gave the corresponding addition product 4, which is a mixture of
two diastereomers. The reaction of (Z)-stilbene with ArSSAr
gave the product 6 in moderate yields (Entries 2 and 3), but the
reaction of (E)-stilbene did not proceed at all (Entries 4 and 5),
although the reason is not clear at present. 1-Octene, cyclo-
hexene, and 1-methylcyclohexene were also effective (Entries
6-9). It was also found that alkynes such as diphenylethyne and
methylphenylethyne gave the corresponding diarylthiolated
compounds 16 and 18 in moderate yields (Entries 10-13). The
reaction proceeded in a highly stereoselective manner except in
the case of (Z)-¢-methylstyrene (Entry 1).
13
14
16
80 (84)g
SAr
SAr
23h
63h
10
11
0.15
0.30
ArS
15
17
SAr
12
13
Me
0.15
0.30
41
53
18
ArS
Me
aIn all cases, the reactions were carried out at ¹50 °C in
¹
Bu4N+B(C6F5)4 /CH2Cl2. bIsolated yield. cThe ratio of
diastereomers. The major diastereomer was shown in the
table. d 1H NMR analysis of the crude product using CH2Br2 as
an internal standard indicated that 97% of (E)-stilbene was
recovered. e 1H NMR analysis of the crude product using
CH2Br2 as an internal standard indicated that ca. 87% of (E)-
stilbene was recovered. fThe reaction was carried out at
¹50 °C for 60 min, and then the temperature was raised to r.t.
g
gradually (30 min) before the addition of Et3N (1.0 mL). The
product contained a small amount of inpurity. The yield in the
1
parenthesis was determined by H NMR analysis of the crude
h
material using CH2Br2 as an internal standard. The product
contained a small amount of inpurity.
ArSSAr attacks the episulfonium ion intermediate to give the
corresponding product, regenerating “ArS+”, which triggers the
next reaction. Another possibility to be considered is that ArSH
attacks the episulfonium ion intermediate to give the product and
“H+”, which can be used in the next cycle to activate ArSSAr.
Although it is difficult to distinguish between the two mecha-
nisms at present, the current reaction seems to proceed by the
cation chain reaction2b,2c,2j,3,11 mediated by a catalytic amount of
“ArS+” or “H+” as a chain carrier.
Although the nature of the EGA is not clear at present, the
following mechanism seems to be plausible (Scheme 2). In the
initiation step, the EGA (= “H+”) reacts with ArSSAr to
produce “ArS+” 8,9 and ArSH (eq 1). “ArS+” reacts with the
alkene to generate an episulfonium ion intermediate (eq 2).10
Chem. Lett. 2013, 42, 843-845
© 2013 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

845
initiation
2006, 128, 7710.
EGA (= ''H+''
)
3
4
5
6
K. Matsumoto, T. Sanada, H. Shimazaki, K. Shimada, S.
Hagiwara, S. Fujie, Y. Ashikari, S. Suga, S. Kashimura, J.-i.
Yoshida, Asian J. Org. Chem. 2013, 2, 325.
K. Uneyama, in Electrochemistry I in Topics in Current
Chemistry, ed. by E. Steckhan, Springer, 1987, Vol. 142,
pp. 167-188. doi:10.1007/3-540-17871-6_15.
''ArS+''
ArS-SAr
(1)
ArSH
propagation
''ArS+''
Ar
S
R1
R2
R3
R4
R1
R2
R3
R4
M. F. Nielsen, in Encyclopedia of Electrochemistry, ed. by
A. J. Bard, M. Stratmann, Wiley VCH, Weinheim, 2004,
Vol. 8, Chap. 14, pp. 453-465, and references therein.
The review of the electro-organic chemistry: a) J.-i. Yoshida,
K. Kataoka, R. Horcajada, A. Nagaki, Chem. Rev. 2008, 108,
2265. b) K. D. Moeller, Tetrahedron 2000, 56, 9527. c) J. B.
Sperry, D. L. Wright, Chem. Soc. Rev. 2006, 35, 605.
As for the effect of the temperature, the following results
+
(2)
(3)
Ar
S
R3
R4
SAr
ArS
R1
R1
R2
R3
R4
''ArS+''
+
ArS-SAr
+
R2
Scheme 2. The plausible reaction mechanism.
7
¹1
were obtained. 0.15 F mol of the electricity based on (E)-
In conclusion, we have developed the addition of ArSSAr
across carbon-carbon multiple bonds with a catalytic amount of
an EGA.12 The reaction seems to proceed by the cation chain
mechanism. Because the EGA can be easily generated and
utilized in one pot, the present method serves as an efficient and
convenient way to synthesize diarylthiolated compounds. Fur-
ther studies on other types of cation chain reactions using an
EGA are in progress in our laboratories.
¢-methylstyrene was used. (a) The generation of EGA at
0 °C and the subsequent reaction with ArSSAr (Ar =
p-FC6H4) at ¹50 °C followed by the reaction with (E)-¢-
methylstyrene at ¹50 °C gave the product in 68% (1H NMR
yield). (b) The generation of EGA at ¹50 °C and the
subsequent reaction with ArSSAr (Ar = p-FC6H4) at 0 °C
followed by the reaction with (E)-¢-methylstyrene at ¹50 °C
gave the product in 58% (1H NMR yield). (c) The generation
of EGA at ¹50 °C and the subsequent reaction with ArSSAr
(Ar = p-FC6H4) at ¹50 °C followed by the reaction with
(E)-¢-methylstyrene at 0 °C gave the product in 40%
(1H NMR yield).
This work was financially supported in part by a Grant-in-
Aid for Scientific Research from the Japan Society for the
Promotion of Science.
8
9
The electrochemical generation of “ArS+” from ArSSAr.
For example: Q. T. Do, D. Elothmani, J. Simonet, G.
Le Guillanton, Electrochim. Acta 2005, 50, 4792, and
references therein.
References and Notes
1
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2
a) S. Fujie, K. Matsumoto, S. Suga, T. Nokami, J.-i. Yoshida,
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10 For example: S. E. Denmark, W. R. Collins, M. D. Cullen,
J. Am. Chem. Soc. 2009, 131, 3490, and references therein.
11 a) M. P. Doyle, D. J. DeBruyn, D. J. Scholten, J. Org. Chem.
1973, 38, 625. Kennedy and Smith’s INIFER (INIFER:
initiator transfer) method is also recognized as a cation chain
reaction; for example: b) J. P. Kennedy, R. A. Smith,
J. Polym. Sci., Polym. Chem. Ed. 1980, 18, 1523. c) H.
Mayr, C. Schade, Makromol. Chem., Rapid Commun. 1988,
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12 Supporting Information is available electronically on the
CSJ-Journal Web site, http://www.csj.jp/journals/chem-lett/
index.html.
Chem. Lett. 2013, 42, 843-845
© 2013 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/