Base-free palladium-catalyzed cross-coupling of arylsulfonium salts with sodium tetraarylborates

Article abstract of DOI:10.1055/s-0035-1560476

Palladium-catalyzed cross-coupling reactions of arylsulfonium salts with sodium tetraarylborates were found to proceed smoothly without recourse to an additional base, providing a new, reliable route to biaryls from organosulfur compounds.

Full text of DOI:10.1055/s-0035-1560476

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2015, 47, 3286–3291
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feature
D. Vasu et al.
Feature
Synthesis
Base-Free Palladium-Catalyzed Cross-Coupling of Arylsulfonium
Salts with Sodium Tetraarylborates
Dhananjayan Vasua
Hideki Yorimitsu*a,b
Atsuhiro Osukaa
R
S
Pd2(dba)3 (0.5 mol%)
SPhos (1.0 mol%)
Ar
B
Ar
+
Ar
Ar
R
THF, 80 °C, 1–6 h
base-free
Ar Na
SbF6
a Department of Chemistry, Graduate School of Science, Kyoto University,
Sakyo-ku, Kyoto 606-8502, Japan
19 examples
72–98% yield
yori@kuchem.kyoto-u.ac.jp
b ACT-C, JST, Sakyo-ku, Kyoto 606-8502, Japan
Received: 12.07.2015
Accepted after revision: 24.08.2015
Published online: 08.09.2015
Although aryl sulfides are generally challenging sub-
strates in cross-coupling reactions,6–8 Liebeskind pioneered
the use of cyclic arylsulfonium salts as activated sub-
strates.9 Cyclic arylsulfonium salts employed here were
readily available from the corresponding thiols in two
steps: conventional S-alkylation10 followed by intramolecu-
lar cyclization with silver hexafluoroantimonate(V),3,11 as
shown in Scheme 1.
DOI: 10.1055/s-0035-1560476; Art ID: ss-2015-z0431-fa
Abstract Palladium-catalyzed cross-coupling reactions of arylsulfo-
nium salts with sodium tetraarylborates were found to proceed
smoothly without recourse to an additional base, providing a new, reli-
able route to biaryls from organosulfur compounds.
Key words C–S cleavage, C–C bond formation, cross-coupling, sulfo-
nium salts, sodium tetraarylborates, palladium
Br(CH2)4Cl (1.1 equiv)
NaOH (1.0 equiv)
SH
S(CH2)4Cl
92%
EtOH–H2O (1:1), r.t., 8 h
The Suzuki–Miyaura cross-coupling reaction is one of
the most powerful methods in organic synthesis.1 Advanta-
geously, organoboron reagents show modest reactivity,
which leads to the broad scope of the cross-coupling. In
most cases, a base is necessary to activate the humble orga-
noboron reagents for efficient transmetalation.2 Even
though the coupling reactions usually proceed under mildly
basic conditions, some base-sensitive substrates can be in-
compatible.
We indeed suffered from such a situation. We have re-
cently discovered the palladium-catalyzed arylative ring-
opening of base-sensitive S-alkyldibenzothiophenium
salts,3 where sodium tetraarylborates exceptionally worked
as effective arylating agents among various combinations of
arylboron reagents and bases we tested. The ring-opening
reactions proceeded efficiently under neutral conditions
without any additional activators. Encouraged by the suc-
cess of the arylative ring-opening, we investigated palladi-
um-catalyzed base-free cross-coupling of more general ar-
ylsulfonium salts with sodium tetraarylborates, which we
disclose herein. Although there are some reports for base-
free cross-coupling reactions with anionic tetraarylbo-
rates,4,5 there is no example of base-free Suzuki–Miyaura-
type cross-coupling of arylsulfonium salts as substrates, ex-
cept for our previous work.3
AgSbF6 (1.0 equiv)
DCE, r.t., 8 h
S
SbF6
1a 96%
Scheme 1 Synthesis of cyclic phenylsulfonium salt 1a
Unfortunately, our previous conditions,3 using bis(tri-
tert-butylphosphine)palladium(0) [Pd(Pt-Bu3)2],12 were un-
satisfactory for the reaction of 1a with sodium tetra-4-tol-
ylborate at 35 °C, giving a moderate yield of the desired bi-
phenyl 2b (Table 1, entry 1). The yield was slightly im-
proved to 55% with 2-(dicyclohexylphosphino)-2′,6′-
dimethoxy-1,1′-biphenyl (SPhos)13 as a ligand with a higher
catalytic loading (Table 1, entry 2). Interestingly, at an ele-
vated temperature of 80 °C, both Pt-Bu3 and SPhos worked
well as ligands and delivered 2b in 72% and 91% yield, re-
spectively (Table 1, entries 3 and 4). To our delight, the cata-
lyst loading can be lowered to 0.5 mol% tris(dibenzylidene-
acetone)dipalladium(0) [Pd2(dba)3] and 1.0 mol% SPhos to
afford 2b in a comparable yield of 90% in a slightly longer
reaction time (Table 1, entry 5). When 0.50 equivalents of
the borate were employed, the reaction did not proceed to
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D. Vasu et al.
Feature
Synthesis
Table 1 Optimization
catalyst
(4-Tol)4BNa (1.1 equiv)
S
Me
THF (0.04 M)
2b
1a
SbF6
Entry
Catalyst
Pd(Pt-Bu3)2 (3 mol%)
Temp (°C)
Time (h)
Yield (%)
1
2
3
4
5
6
35
25
80
80
80
80
24
24
1
42
55
72
91
90
48a
Pd2(dba)3 (5 mol%), SPhos (10 mol%)
Pd(Pt-Bu3)2 (3 mol%)
Pd2(dba)3 (5 mol%), SPhos (10 mol%)
0.5
1
Pd2(dba)3 (0.5 mol%), SPhos (1.0 mol%)
Pd2(dba)3 (0.5 mol%), SPhos (1.0 mol%)
5
a (4-Tol)4BNa (0.50 equiv) was used; 42% of 1a was recovered.
completion (Table 1, entry 6). This incomplete conversion
clearly suggests that only one of the four aryl groups is
transferrable for arylation.
With the optimized conditions in hand (Table 1, entry
5), the scope of the reaction was investigated. A variety of
sodium tetraarylborates reacted with arylsulfonium salt 1a
Biographical Sketches
Dhananjayan Vasu was born
in Arumbakkam, India in 1983.
He obtained his B.Sc. from Dr.
Ambedkar Government Arts
College, University of Madras,
India in 2003 and his M.Sc. from
the same university in 2005. He
received his Ph.D. from National
Tsing Hua University, Taiwan un-
der the supervision of Professor
Rai-Shung Liu in 2011 and, until
2013, carried out his postdoc-
toral research at the same labo-
ratory in the field of gold- and
platinum-catalyzed new organic
moved to Kyoto University, Ja-
pan in the same year as a JSPS
postdoctoral fellow working
with Professor Hideki Yorimitsu,
where he conducted research
on organosulfur-based organic
synthesis.
transformations.
He
then
Hideki Yorimitsu was born in
Kochi, Japan in 1975. He ob-
tained his Ph.D. in 2002 from
Kyoto University under the su-
pervision of Professor Koichiro
Oshima. He then served as a
JSPS postdoctoral fellow with
Professor Eiichi Nakamura at the
University of Tokyo. He became
an Assistant Professor in 2003
and an Associate Professor in
2008 at the Graduate School of
Engineering, Kyoto University.
He moved to the Graduate
School of Science at the same
university in 2009 and became
a Full Professor in 2015. His re-
search program focuses on the
development of new organic
transformations for creating
new molecules, phenomena
and concepts. He received the
Chemical Society of Japan
Award for Young Chemists in
2009 and the Young Scientists’
Prize from MEXT in 2011.
Atsuhiro Osuka received
a
search interests cover many as-
pects of synthetic approaches
toward novel porphyrin-related
compounds with intriguing
structures, properties and func-
tions, which were recognized
with the Chemical Society of Ja-
pan Award in 2010. Representa-
tive molecules explored in his
laboratory include artificial pho-
tosynthetic reaction center
models, meso–meso-linked por-
phyrin arrays, porphyrin tapes,
expanded porphyrins, subpor-
phyrins, and Möbius aromatic
and antiaromatic molecules.
Ph.D. from Kyoto University in
1982. In 1979, he started his ac-
ademic career at Ehime Univer-
sity as an Assistant Professor. In
1984, he returned to Kyoto Uni-
versity, where he has been a
Professor since 1996. His re-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 3286–3291

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D. Vasu et al.
Feature
Synthesis
Table 2 Scope of Sodium Tetraarylborates in the Base-Free Cross-
Coupling of 1a
The present conditions were applicable to arylation of
the acyclic sulfonium salts 1b and 1c (Scheme 2). Advanta-
geously, odorless dodecyl methyl sulfide14 was liberated in
the reaction of 1c. Notably, the counteranion of the sulfo-
nium salt had no influence on the yield of product, as ex-
emplified in the reaction of 1c.
In conclusion, mild and base-free cross-coupling of aryl-
sulfonium salts with sodium tetraarylborates has been
achieved in good to excellent yields under palladium/SPhos
catalysis through C–S bond cleavage. A variety of functional
groups are tolerated in both coupling partners. Despite low
atom economy, preparation and handling of sulfonium salts
and sodium tetraarylborates are easy. These base-free con-
ditions offer a simple protocol for the synthesis of biaryls
from organosulfur compounds in excellent yields.
Pd2(dba)3 (0.5 mol%)
Ar
SPhos (1.0 mol%)
Ar
B
Ar
Ar Na
(1.1 equiv)
1a
+
Ar
2a–h
THF (0.04 M)
80 °C, 1–4 h
Entry
Ar
Ph
Time (h)
2
Yield (%)
1
2
3
4
5
6
7
8
3
1
1
4
4
1
1
1
2a
2b
2c
2d
2e
2f
88
90
92
88
89
92
96
72
4-Tol
3,5-(MeO)2C6H3
4-FC6H4
4-ClC6H4
2-furyl
Table 3 Scope of Sulfonium Salts in the Base-Free Cross-Coupling with
Sodium Tetraphenylborate
2-thienyl
4-CH2=CHC6H4
2g
2h
Pd2(dba)3 (0.5 mol%)
SPhos (1.0 mol%)
Ph4BNa (1.1 equiv)
R
R
to afford the corresponding functionalized biphenyls 2a–h
in good to excellent yields (Table 2). The electron-rich
tetrakis(3,5-dimethoxyphenyl)borate afforded the corre-
sponding biphenyl 2c in 92% yield (Table 2, entry 3). Elec-
tron-withdrawing substituents like fluoro in 2d and chloro
in 2e were totally compatible. Heteroaromatic borates re-
acted smoothly to furnish the corresponding biphenyls 2f
and 2g in excellent yields (Table 2, entries 6 and 7). The re-
active 4-styryl unit was also tolerated under the present
conditions (Table 2, entry 8).
S
THF (0.04 M)
80 °C, 1–6 h
4a–i
SbF6
3a–i
Entry Sulfonium cation
Time (h)
2
4
Yield (%)
98
1
2
3a
3b
4a
4b
S
Me
We prepared various arylsulfonium salts3,11 3a–i to as-
sess the generality in sulfonium salts (Table 3). Steric hin-
drance of the ortho methyl group in 3b and 3c gave rise to
lower yet satisfactory yields of 4b and 4c, respectively. In
contrast, the electronic nature of the sulfonium salts had no
significant effect on reaction efficiency: an electron-donat-
ing methoxy group, as well as electron-deficient carbonyl,
nitro, and trifluoromethyl groups, was tolerated (Table 3,
entries 4–8). 2-Pyridylsulfonium salt 3i also participated to
afford 4i in 84% yield (Table 3, entry 9).
6
6
78
79
S
Me
3
3c
4c
Me
S
S
4
5
3d
3e
1
3
4d
4e
96
91
MeO
O
S
Me
S
MeO
O
Me
Pd2(dba)3 (0.5 mol%)
6
3f
3
4f
93
S
SbF6 SPhos (1.0 mol%)
(4-Tol)4BNa (1.1 equiv)
1b
Me
or
THF (0.04 M), 80 °C, 1 h
Me
7
8
9
3g
3h
3i
3
3
1
4g
4h
4i
91
95
84
O2N
F3C
S
2b
S
89% from 1b
86% from 1c
C12H25
BF4
1c
S
Scheme 2 Cross-coupling of acyclic sulfonium salts
S
N
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D. Vasu et al.
Feature
Synthesis
4-Methyl-1,1′-biphenyl (2b); Typical Procedure for the Cross-
Coupling of Arylsulfonium Salts with Sodium Tetraarylborates
(Table 2)
Unless otherwise noted, all reactions were performed under an argon
atmosphere. 1H NMR (600 MHz) and 13C NMR (151 MHz) spectra
were recorded on a JEOL ECA-600 spectrometer at r.t. Sulfonium salts
were analyzed in CD3CN (for 1H, δ = 1.94 ppm; for 13C, δ = 1.32 ppm as
internal references) and the other compounds were analyzed in CDCl3
(for 1H, δ = 7.26 ppm; for 13C, δ = 77.00 ppm). TLC analyses were per-
formed on commercial glass plates bearing a 0.25-mm layer of Merck
silica gel 60 F254. Purification was done by column chromatography
using silica gel (Wakogel 200 mesh). Mass spectra were obtained on a
Bruker micrOTOF II-KR (APCI) spectrometer. Pd2(dba)3, SPhos, NaBF4
and anhydrous solvents, such as 1,2-dichloroethane (DCE) and N,N-
dimethylformamide (DMF), were purchased from Aldrich. Na2SO4 and
MgSO4 were purchased from Wako Pure Chemicals. THF and Et2O
were directly obtained from a solvent purification system of Innova-
tion Technology Company. All other commercial reagents were used
without further purification, unless otherwise indicated.
A flame-dried Schlenk tube was charged with Pd2(dba)3 (5.71 mg,
0.006 mmol) and SPhos (5.12 mg, 0.012 mmol) under argon. To this,
anhydrous THF (31 mL) was added at r.t. The resulting dark brownish-
purple solution was brought to reflux at 80 °C for 10 min to generate
an active Pd–SPhos species, which was observed by a clear dark red
coloration from purple during the course of heating. After the reac-
tion mixture was cooled to r.t., 1a (0.50 g, 1.25 mmol) and sodium tet-
ra-4-tolylborate (0.55 g, 1.37 mmol) were added. The mixture was
again brought to 80 °C for 1 h. After completion, the reaction mixture
was filtered through a short bed of silica gel and the solvent was re-
moved using a rotary evaporator. The crude mixture was purified by
silica gel column chromatography (hexane) to provide 2b as a white
solid; yield: 189 mg (1.12 mmol, 90%).
The product biphenyls are known compounds and their spectra
agreed with the corresponding literature data: 2a,16a,c 2b,16b 2c,16f
2d,16d 2e,16a 2f,16e 2g,16d 2h,16i 4a,16b,d 4b,16f 4c,16h 4d,16b 4e,16c 4f,16g
4g,16b 4h16b and 4i.16d
(4-Chlorobutylsulfanyl)benzene (Scheme 1); Typical Procedure for
S-4-Chlorobutylation
S-Alkylation was conducted according to the literature,10 with some
modifications. Thiophenol (1.0 g, 9.08 mmol) was added to a solution
of NaOH (0.36 g, 9.08 mmol) in an EtOH–H2O (1:1) mixture (65 mL) at
r.t. After 10 min, 1-bromo-4-chlorobutane (1.15 mL, 9.98 mmol) was
added, and stirring was continued for 8 h at 25 °C. Then, the solvent
was removed with a rotary evaporator, and the residue was diluted
with Et2O and extracted with EtOAc. The organic layer was dried over
anhydrous MgSO4 and concentrated to furnish a yellow oil; yield: 1.68
g (8.37 mmol, 92%). In most cases, the crude products were pure
enough to carry out the next step without further purification.
Phenylsulfonium Salt 1a
Compound 1a was prepared from thiophenol by following the typical
procedure under the conditions given in Scheme 1; yield: 3.07 g (7.65
mmol, 88% over two steps); colorless crystals.
1H NMR (600 MHz, CD3CN): δ = 7.80–7.75 (m, 3 H), 7.69–7.67 (m, 2
H), 3.92–3.89 (m, 2 H), 3.66–3.64 (m, 2 H), 2.51–2.44 (m, 2 H), 2.38–
2.32 (m, 2 H).
13C NMR (151 MHz, CD3CN): δ = 135.0, 132.0, 131.0, 127.4, 49.4, 29.9.
Cyclic Sulfonium Salt 1a (Scheme 1); Typical Procedure3,11
HRMS (ESI): m/z [M]+ calcd for C10H13S (M – SbF6): 165.0732; found:
165.0734.
To a solution of (4-chlorobutylsulfanyl)benzene (1.6 g, 7.97 mmol) in
DCE (30 mL) was added AgSbF6 (2.74 g, 7.97 mmol). The resulting sus-
pension was stirred at r.t. for 8 h. Gray precipitates were formed and
were removed by filtration. The mother liquid was treated with
MgSO4 and filtered. The combined filtrate was condensed under re-
duced pressure to give a viscous yellow oil, which was further puri-
fied by precipitation with an Et2O–hexane (1:2) mixture to provide
sulfonium salt 1a in a pure form as colorless crystals; yield: 3.07 g
(7.65 mmol, 96%).
Dimethyl(phenyl)sulfonium Salt 1b
Compound 1b was prepared from thioanisole by simple S-methyla-
tion with MeI (1.1 equiv) and AgSbF6 (1.0 equiv); yield: 2.96 g (7.89
mmol, 98%); white powder.
1H NMR (600 MHz, CD3CN): δ = 7.90 (d, J = 8.2 Hz, 2 H), 7.81 (d, J = 7.6
Hz, 1 H), 7.72 (d, J = 8.3 Hz, 2 H), 3.13 (s, 6 H).
13C NMR (151 MHz, CD3CN): δ = 135.6, 132.0, 130.7, 126.1, 29.4.
HRMS (ESI): m/z [M]+ calcd for C8H11S (M – SbF6): 139.0581; found:
139.0571.
Sodium Tetra-4-tolylborate; Typical Procedure for the Synthesis of
Sodium Tetraarylborates
Sodium tetraarylborates were prepared according to the literature,3,15
with some modifications. NaBF4 (1.0 g, 9.11 mmol) and Mg turnings
(0.99 g, 41.00 mmol) were taken in an oven-dried sealed tube. The
tube was filled with argon by the standard Schlenk technique. To this
mixture, THF (20 mL) and 1,2-dibromoethane (40 μL, 0.46 mmol)
were added, and the resulting mixture was stirred for 1 min. Finally,
4-bromotoluene (4.7 mL, 38.3 mmol) was added in one shot at 0 °C. A
very exothermic reaction started immediately after the addition of
aryl halide. After the apparent exotherm had ceased, the resulting
suspension was stirred at r.t. for 12 h. The solution became gray and
white precipitates were formed. The reaction mixture was then add-
ed to aq Na2CO3. The resulting mixture was stirred for 30 min and
then extracted with MeCN (3 × 30 mL). The combined organic layer
was washed with brine (50 mL), dried over MgSO4, filtered and con-
centrated under reduced pressure with a rotary evaporator. The crude
residue was purified by precipitation using Et2O–hexane (1:2) to pro-
vide sodium tetra-4-tolylborate as a white powder; yield: 3.48 g (8.75
mmol, 96%).
Dodecyl(methyl)phenylsulfonium Salt 1c
Compound 1c was prepared from thioanisole by simple S-alkylation
with dodecyl iodide (1.1 equiv) and AgBF4 (1.0 equiv); yield: 8.54 g
(22.5 mmol, 93%); white semisolid.
1H NMR (600 MHz, CD3CN): δ = 7.95–7.94 (m, 2 H), 7.73–7.70 (m, 1
H), 7.66–7.63 (m, 2 H), 3.69–3.62 (m, 2 H), 3.25 (s, 3 H), 1.63–1.56 (m,
1 H), 1.53–1.46 (m, 1 H), 1.42–1.32 (m, 2 H), 1.24–1.14 (m, 16 H), 0.82
(t, J = 6.8 Hz, 3 H).
13C NMR (151 MHz, CD3CN): δ = 134.7, 131.2, 130.5, 122.8, 45.6, 31.7,
29.4 (2 × CH2), 29.3, 29.1, 29.0, 28.7, 27.8, 26.8, 24.4, 22.5, 13.9.
HRMS (ESI): m/z [M]+ calcd for C19H33S (M – BF4): 293.2297; found:
293.2301.
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D. Vasu et al.
Feature
Synthesis
2-Naphthylsulfonium Salt 3a
13C NMR (151 MHz, CD3CN): δ = 192.5, 140.7, 133.0, 132.0, 131.8,
49.4, 30.0.
Compound 3a was prepared from 2-thionaphthol by following the
typical procedure under the conditions given in Scheme 1; yield: 0.88
g (1.95 mmol, 87% over two steps); brown solid.
HRMS (ESI): m/z [M]+ calcd for C11H13SO (M – SbF6): 193.0687; found:
193.0689.
1H NMR (600 MHz, CD3CN): δ = 8.43 (d, J = 1.4 Hz, 1 H), 8.19 (d, J = 8.9
Hz, 1 H), 8.08 (d, J = 8.3 Hz, 1 H), 8.06 (d, J = 8.3 Hz, 1 H), 7.79–7.72 (m,
3 H), 3.99–3.95 (m, 2 H), 3.77–3.73 (m, 2 H), 2.57–2.54 (m, 2 H), 2.40–
2.37 (m, 2 H).
[4-(Methoxycarbonyl)phenyl]sulfonium Salt 3f
Compound 3f was prepared from methyl 4-mercaptobenzoate by fol-
lowing the typical procedure under the conditions given in Scheme 1;
yield: 0.76 g (1.66 mmol, 38% over two steps); white solid.
13C NMR (151 MHz, CD3CN): δ = 135.9, 133.8, 133.4, 132.5, 130.9,
1H NMR (600 MHz, CD3CN): δ = 8.22–8.20 (m, 2 H), 7.91–7.89 (m, 2
H), 3.96–3.92 (m, 5 H), 3.74–3.69 (m, 2 H), 2.47–2.42 (m, 2 H), 2.40–
2.34 (m, 2 H).
129.7, 129.6, 129.1, 124.6, 124.0, 49.4, 30.3.
HRMS (ESI): m/z [M]+ calcd for C14H15S (M – SbF6): 215.0894; found:
215.0894.
13C NMR (151 MHz, CD3CN): δ = 166.1, 136.0, 132.2, 132.0, 131.2,
2-Tolylsulfonium Salt 3b
53.5, 49.4, 29.9.
HRMS (ESI): m/z [M]+ calcd for C12H15SO2 (M – SbF6): 223.0793;
found: 223.0788.
Compound 3b was prepared from 2-methylbenzenethiol by following
the typical procedure under the conditions given in Scheme 1; yield:
0.85 g (2.05 mmol, 86% over two steps); white solid.
1H NMR (600 MHz, CD3CN): δ = 7.65–7.62 (m, 2 H), 7.53–7.48 (m, 2
H), 3.94–3.90 (m, 2 H), 3.61–3.57 (m, 2 H), 2.62 (s, 3 H), 2.52–2.49 (m,
2 H), 2.37–2.35 (m, 2 H).
(4-Nitrophenyl)sulfonium Salt 3g
Compound 3g was prepared from 4-nitrobenzenethiol by following
the typical procedure under the conditions given in Scheme 1; yield:
0.90 g (2.02 mmol, 92% over two steps); yellow solid.
13C NMR (151 MHz, CD3CN): δ = 142.3, 134.8, 133.2, 129.9, 129.2,
1H NMR (600 MHz, CD3CN): δ = 8.43–8.41 (m, 2 H), 8.03–8.01 (m, 2
H), 3.99–3.95 (m, 2 H), 3.79–3.75 (m, 2 H), 2.46–2.38 (m, 4 H).
126.8, 48.8, 30.0, 20.3.
HRMS (ESI): m/z [M]+ calcd for C11H15S (M – SbF6): 179.0894; found:
13C NMR (151 MHz, CD3CN): δ = 151.9, 134.1, 132.5, 126.4, 49.6, 30.0.
179.0899.
HRMS (ESI): m/z [M]+ calcd for C10H12SNO2 (M – SbF6): 210.0589;
found: 210.0614.
(2,4-Dimethylphenyl)sulfonium Salt 3c
Compound 3c was prepared from 2,4-dimethylbenzenethiol by fol-
lowing the typical procedure under the conditions given in Scheme 1;
yield: 0.71 g (1.65 mmol, 94% over two steps); off-white solid.
1H NMR (600 MHz, CD3CN): δ = 7.52 (d, J = 8.7 Hz, 1 H), 7.34 (d, J = 8.7
Hz, 1 H), 7.32 (s, 1 H), 3.92–3.89 (m, 2 H), 3.55–3.52 (m, 2 H), 2.57 (s, 3
H), 2.54–2.46 (m, 2 H), 2.39 (s, 3 H), 2.36–2.30 (m, 2 H).
13C NMR (151 MHz, CD3CN): δ = 146.2, 142.2, 133.7, 130.7, 129.3,
123.4, 49.0, 29.9, 21.3, 20.2.
HRMS (ESI): m/z [M]+ calcd for C12H17S (M – SbF6): 193.1051; found:
193.1052.
[4-(Trifluoromethyl)phenyl]sulfonium Salt 3h
Compound 3h was prepared from 4-(trifluoromethyl)benzenethiol
by following the typical procedure under the conditions given in
Scheme 1; yield: 0.82 g (1.75 mmol, 87% over two steps); off-white
solid.
1H NMR (600 MHz, CD3CN): δ = 8.02–7.98 (m, 4 H), 4.00–3.95 (m, 2
H), 3.78–3.74 (m, 2 H), 2.49–2.38 (m, 4 H).
13C NMR (151 MHz, CD3CN): δ = 135.5 (q, J = 33.3 Hz), 132.1, 132.0,
128.7–128.6 (m, 1 × CH), 124.4 (q, J = 275.4 Hz), 49.5, 30.0.
HRMS (ESI): m/z [M]+ calcd for C11H12F3S (M – SbF6): 233.0612; found:
233.0613.
4-Anisylsulfonium Salt 3d
Compound 3d was prepared from 4-methoxybenzenethiol by follow-
ing the typical procedure under the conditions given in Scheme 1;
yield: 0.76 g (1.76 mmol, 95% over two steps); white powder.
1H NMR (600 MHz, CD3CN): δ = 7.72 (d, J = 9.6 Hz, 2 H), 7.17 (d, J = 9.6
Hz, 2 H), 3.89–3.85 (m, 5 H), 3.55–3.51 (m, 2 H), 2.50–2.46 (m, 2 H),
2.33–2.31 (m, 2 H).
13C NMR (151 MHz, CD3CN): δ = 165.2, 133.4, 117.4, 117.2, 56.9, 49.8,
29.9.
HRMS (ESI): m/z [M]+ calcd for C11H15SO (M – SbF6): 195.0844; found:
195.0841.
2-Pyridylsulfonium Salt 3i
Compound 3i was prepared from pyridine-2-thiol by following the
typical procedure under the conditions given in Scheme 1; yield: 0.92
g (2.29 mmol, 81% over two steps); white solid.
1H NMR (600 MHz, CD3CN): δ = 8.75 (d, J = 8.3 Hz, 1 H), 8.08–8.05 (m,
1 H), 7.94 (d, J = 8.3 Hz, 1 H), 7.71–7.69 (m, 1 H), 3.95–3.91 (m, 2 H),
3.82–3.77 (m, 2 H), 2.42–2.36 (m, 2 H), 2.32–2.25 (m, 2 H).
13C NMR (151 MHz, CD3CN): δ = 152.8, 147.3, 140.9, 129.1, 128.7,
47.8, 30.1.
HRMS (ESI): m/z [M]+ calcd for C9H12SN (M – SbF6): 166.0690; found:
166.0694.
(4-Formylphenyl)sulfonium Salt 3e
Compound 3e was prepared from 4-mercaptobenzaldehyde by fol-
lowing the typical procedure under the conditions given in Scheme 1;
yield: 0.89 g (2.07 mmol, 87% over two steps); off-white powder.
1H NMR (600 MHz, CD3CN): δ = 10.10 (s, 1 H), 8.14–8.12 (m, 2 H),
7.99–7.97 (m, 2 H), 3.98–3.93 (m, 2 H), 3.76–3.72 (m, 2 H), 2.47–2.42
(m, 2 H), 2.41–2.35 (m, 2 H).
Acknowledgment
This work was supported by Grants-in-Aid from MEXT (No. 25107002
‘Science of Atomic Layers’) and from the JSPS [Nos. 24685007 (Young
Scientists (A)) and 26620081 (Exploratory Research)]. D.V. acknowl-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 3286–3291

3291
D. Vasu et al.
Feature
Synthesis
edges a JSPS Postdoctoral Fellowship. H.Y. acknowledges the Japan As-
sociation for Chemical Innovation for financial support.
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Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1560476.
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