Efficient silver-catalyzed direct sulfenylation and selenylation of rich arenes

Article abstract of DOI:10.1039/c4ob01992j

An efficient protocol for silver/copper-cocatalyzed direct sulfenylation and selenylation of arenes with aryl disulfides and diselenides has been developed. This strategy exhibits excellent functional group tolerance and high regioselectivity. Mono sulfenylation and selenylation products can be exclusively achieved. This reaction provides a simple and practical route to the preparation of aryl sulfides and selenides. This journal is

Full text of DOI:10.1039/c4ob01992j

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Efficient silver-catalyzed direct sulfenylation and
selenylation of rich arenes†
Cite this: Org. Biomol. Chem., 2014,
12, 9557
Guobing Yan,* Arun Jyoti Borah* and Lianggui Wang
Received 18th September 2014,
Accepted 3rd October 2014
An efficient protocol for silver/copper-cocatalyzed direct sulfenylation and selenylation of arenes with
aryl disulfides and diselenides has been developed. This strategy exhibits excellent functional group toler-
ance and high regioselectivity. Mono sulfenylation and selenylation products can be exclusively achieved.
This reaction provides a simple and practical route to the preparation of aryl sulfides and selenides.
DOI: 10.1039/c4ob01992j
www.rsc.org/obc
Organochalcogenides are very important molecules frequently C(sp2)–H functionalization of electron-rich arenes using Cu and
found in the biological and pharmaceutical fields.1 Apart from Pd respectively as catalysts. With these methods, the yields of the
the conventional methods of coupling aryllithiums/aryl products were found to be moderate and corresponding selenide
Grignard reagents with chalcogenide precursors towards for- analogues are less available. Recently, Lee and co-workers15p
mation of carbon–chalcogen (S, Se) bond,2 one of the more reported the Cu-catalyzed, highly regioselective synthesis of aryl
powerful approaches is based on transition-metal-catalyzed chalcogenides using arenes as coupling partners. However, it pro-
coupling of aryl halides,3–11 triflates4d,12 or boronic acids13 ceeded through tandem C–H borylation and copper-catalyzed
with a suitable chalcogenide precursor. Complexes and salts of C–S coupling reactions. Continuing the study on metal catalyzed
Pd4,12 Ni,5 Cu,6,13 Fe,7 Co,8 Rh,9 In,10 and Ru11 have been intro- C–S/Se bond formation of arenes, in this paper we have intro-
duced as efficient catalysts for this type of reaction. However, duced silver in combination with copper as cocatalysts that can
prefunctionlization of the starting material can be considered efficiently carry out the formation of C–S/Se bond in the presence
a drawback of this approach in comparison to another of various dichalcogenides.
approach through the direct C–H bond activation process.
Initially, we carried out sulfenylation of 1-methoxynaphthal-
While in the area of C–H bond functionalization, much atten- ene using diarydisulfide (2a) with AgSbF6 as a Lewis acid cata-
tion has been paid to transition metal catalyzed C–C, C–O, and lyst at room temperature (Table 1, entry 1). The reaction was
C–N bond-forming reactions,14 the formation of intermolecu- carried out in 1,2-dichloroethane (DCE) as solvent, but only
lar C–S/C–Se bonds through transition-metal catalyzed direct trace amounts of product were detected by GC-MS. To our
C–H activation is relatively rare.15 Metal-free C–S bond for- delight, increasing the temperature to 100 °C (Table 1,
mation is also reported but to a very small extent.16
entry 2), the sulfenylation was found to occur with 47% yield
In general, the metal-catalyzed processes involve predomi- (product 3a). The NMR spectral data revealed the sulfenylation
nantly the use of thiols or disulfides as coupling partners. process at the para position of the naphthalene ring. We then
However, thiols are prone to undergo oxidative S–S coupling reac- changed the Ag source under this improved reaction condition
tions, resulting in the undesired formation of disulfides. There- to get a better yield (Table 1, entries 3–5) but the reaction did
fore, the use of dichalcogenides is preferred. Since the pioneering not occur in all cases. In an attempt using Cu(OAc)2·H2O as an
Cu-mediated direct intermolecular thioetherification of the arene additive15k (Table 1, entry 6) at 100 °C, the product 3a was iso-
C–H bond reported by Yu and co-workers,15a there have been a lated with excellent yield (85%) within 12 h of reaction time.
few reports on chelation-assisted C–S bond formation.15b–f However, Cu(OAc)2·H2O by itself cannot provide the sulfide
Though these methods are highly regioselective, success requires product 3a. (Table 1, entry 7). So the use of this additive is
a heteroatom in the molecule that acts as a directing group. The essential for the Ag catalyzed process. Cu(OAc)2·H2O is an
direct C–S/Se bond formation of non acidic C–H bonds of arenes oxidant and was used in catalytic amount in the presence of
is very challenging in comparision to acidic heterocycles.15g,h,j,n,o air. Then, we examined the reaction using Cu(OAc)2·H2O at
Cheng et al.15k and Beller15m reported a nonchelation-assisted other temperatures (Table 1, entries 11 and 12) but low yield
in comparision to entry 6 was recorded. Screening of different
solvents had shown that toluene (Table 1, entry 8) can provide
68% yield while in DMF (Table 1, entry 9) and DMSO (Table 1,
entry 10), the desired product could not be obtained. Though
Department of Chemistry, Lishui University, Lishui 323000, People’s Republic of
China. E-mail: gbyan@lsu.edu.cn; Fax: +86-578-2271250
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
decreased amounts of diarydisulfide (2a) results in compara-
c4ob01992j
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Table 1 Optimization of the reaction conditionsa
Table 2 Direct sulfenylation of 1-methoxynaphthalene with disulfidesa
Entry
Catalyst
Solvent
T (°C)
Yieldb (%)
Entry
RSSR (2a–p)
Product (3a–p)
Yieldb (%)
1
2
3
4
AgSbF6
AgSbF6
Ag2CO3
AgOAc
DCE
DCE
DCE
DCE
DCE
DCE
DCE
PhMe
DMF
DMSO
DCE
DCE
DCE
DCE
rt
Trace
47
—
—
—
85
—
68
—
1
2
3
4
5
6
7
8
R = 4-ClC6H4 2a
R = 3-ClC6H4 2b
R = 2-ClC6H4 2c
R = 4-BrC6H4 2d
R = 2-BrC6H4 2e
R = 4-FC6H4 2f
R = 2-FC6H4 2g
R = 4-MeC6H4 2h
R = 3-MeC6H4 2i
R = 2-MeC6H4 2j
R = 4-NO2C6H4 2k
R = 2-NH2C6H4 2l
R = C6H5 2m
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3o
3p
85
79
69
78
67
83
69
95
78
64
21
Trace
80
Trace
Trace
100
100
100
100
100
100
100
100
100
80
5
AgNO3
6c
AgSbF6
Cu(OAc)2·H2O
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
7c
8c
9c
10c
11c
12c
13c,d
14c,d,e
—
9
10
11
12
13
14
15
57
72
78
87
120
100
100
R = 2-Pyridinyl 2o
R = 4-Pyridinyl 2p
a Unless otherwise noted, the reaction conditions are: 1a (0.3 mmol),
2a (0.3 mmol), catalyst (0.15 eq.), solvent (2 mL), 12 h. b Isolated yield.
c Cu(OAc)2·H2O (0.4 eq.), 12 h. d 2a (0.2 mmol). e AgSbF6 (0.3 eq.).
a The reaction conditions are: 1a (0.3 mmol), 2a–p (0.3 mmol), AgSbF6
(0.15 eq.), Cu(OAc)2·H2O (0.4 eq.), DCE (2 mL), 100 °C, 12 h. b Isolated
yield.
tively lower yield during the process (Table 1, entry 13), with
higher loading of the catalyst (Table 1, entry 14), the system
enables the use of two RS in (RS)2. Hence the catalyst AgSbF6 in
combination with Cu(OAc)2·H2O at 100 °C using DCE as solvent
was found to be the best reaction condition (Table 1, entry 6)‡.
Having identified the optimal reaction conditions, this
approach was then applied to the coupling of 1-methoxy-
naphthalene to a variety of disulfides, the results of which are
shown in Table 2. The electronic effects of the substituents on
the aromatic ring of disulfides hardly influenced the reactivity
(Table 2, entries 1–10) and provided the sulfides in good to
excellent yield. However, the NO2 substituent on the aromatic
ring of the disulfide provided only 21% yield of the product
(3k), while the amine group (product 3l) provided a trace
amount. The position of the substituent on the benzene ring
had a slight impact on the reaction yield. Substituents at the
para position provided more yield in comparision to ortho and
meta. This is due to steric restriction of the disulfides. No
regioisomeric products or disulfenation products were
observed by 1H NMR spectroscopy. The process was also
extended to disulfides bearing heteroarenes (entries 14
and 15), but only a trace amount of product was obtained.
Scheme 1 Scope of the sulfenylation process of rich arenes with di-
aryldisulfide (2a).
‡Typical procedure for the sulfenylation and selenylation of rich arenes: Under
air atmosphere, 1-methoxynaphthalene (47.4 mg, 0.3 mmol), diaryl disulfides or
diaryl diselenides (0.3 mmol), AgSbF6 (0.15 eq. or 0.20 eq.), Cu(OAc)2·H2O
(0.4 eq. or 1.0 eq.) were added to a screw-capped vial, followed by addition of a
stir bar and DCE (2 mL). The reaction vial was placed in a temperature-controlled
aluminium-heating block set at 100 °C. After 12 h of stirring, the vial was
removed from the heating block and was left at ambient temperature. The sol-
vents were removed under reduced pressure and the crude reaction mixture was
purified by silica gel column chromatography with Petroleum ether/EtOAc as an
eluent to give the desired product.
After successful investigation of the sulfenylation of
1-methoxynaphthalene, we also observed the efficiency of the
process with different aromatic systems as coupling partner to
2a. However, it was revealed that only electron rich arenes
(Scheme 1) are suitable for the sulfenylation process. Dis-
appointingly, the scope of the arenes is limited.
We next turned our attention towards the formation of C–Se
bonds. Under similar reaction conditions using diaryldi-
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Table 3 Direct selenylation of 1-methoxynaphthalene with diaryl
diselenidesa
Entry
RSeSeR (4a–f)
Product (5a–f)
Yieldb (%)
1
2
3
4
5
6
R = 4-ClC6H4 4a
R = 4-FC6H4 4b
R = 4-MeC6H4 4c
R = 2-MeC6H4 4d
R = 2-OMeC6H4 4e
R = 3-CF3C6H4 4f
5a
5b
5c
5d
5e
5f
83
78
87
60
75
71
Fig. 1 Proposed mechanism of the reaction.
a The reaction conditions are as: 1a (0.3 mmol), 4a–f (0.3 mmol),
AgSbF6 (0.20 eq.), Cu(OAc)2·H2O (1.0 eq.), DCE (2 mL), 120 °C, 12 h.
b Isolated yield.
transfer process. Subsequent reductive elimination of inter-
mediate B gave the desired product, along with Ag (0) species
which can be oxidized to Ag(I) by Cu(II) and/or air to complete
the catalytic cycle. Therefore, Ag(I) is used as a Lewis acid
through the classical electrophilic substitution providing
highly regioselective sulfenylation of 1-methoxynaphthalene at
the 4-position of naphthalene ring and only electron-rich
arenes were suitable under the reaction conditions. In
addition, the use of oxidant Cu(OAc)2 in catalytic amount
improves the reaction yield. We speculate the reduced Cu(I) is
oxidized back to Cu(II) in the presence of air.
In conclusion, we have developed a direct sulfenylation and
selenylation process of arenes using silver in combination with
copper as cocatalysts. The present method is very effective with
a number of dichalcogenides. However, only electron rich
arenes were found to be successful under the reaction
conditions.
selenides, selenide products of 1-methoxynaphthalene
(Table 3, 5a–5f) were isolated in very good yield of 60–87%.
However, use of 1 equivalent Cu(OAc)2·H2O at 120 °C was
found to be the best condition for the selenylation process and
also required slightly more catalyst loading (20 mol%) in com-
parision to the sulfenylation process. Both electron withdraw-
ing and electron donating substituents on the aryl ring of the
diselenide are equally effective and do not exhibit significant
differences. The extension of the process with another electron
rich arene was found to be effective under the reaction con-
ditions (Scheme 2).
The exact mechanistic path of the reaction is not clear at
this moment. We believe there is a radical reaction path since
the use of TEMPO (Scheme 3), a radical-trapping reagent, com-
pletely suppressed the formation of the desired product 3a.
However, under the reaction conditions it was not possible to
detect the formation of the TEMPO adduct.
We thank the Natural Science Foundation of Zhejiang Pro-
vince (no. LY12B02006 and LY13B020005) for financial
support.
On the basis of our observations, a plausible mechanism
has been proposed (Fig. 1). Initially, the interaction between
1-methoxynaphthalene and Ag(I) salt generated aryl-Ag(I)
species A at 4-position of the ring, which reacted with diarydi-
sulfide to afford intermediate B through a single-electron
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