Modified conditions for copper-catalyzed ipso-thiolation of arylboronic acid esters with thiosulfonates

Article abstract of DOI:10.1246/cl.170907

An efficient ipso-thiolation of arylboronic acid esters with thiosulfonates has been achieved under mild and odorless conditions using a copper catalyst. The use of TMEDA and cesium fluoride as the ligand and base, respectively, dramatically facilitated the desired transformation. The method exhibited a broad substrate scope, which allowed for the expeditious synthesis of diverse aryl sulfides from easily available starting materials.

Full text of DOI:10.1246/cl.170907

Advance Publication Cover Page
Modified Conditions for Copper-Catalyzed ipso-Thiolation of
Arylboronic Acid Esters with Thiosulfonates
Kazuya Kanemoto, Suguru Yoshida,* and Takamitsu Hosoya*
Advance Publication on the web October 27, 2017
doi:10.1246/cl.170907
© 2017 The Chemical Society of Japan
Advance Publication is a service for online publication of manuscripts prior to releasing fully edited, printed versions. Entire
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Publication manuscripts.

1
Modified Conditions for Copper-Catalyzed ipso-Thiolation of
Arylboronic Acid Esters with Thiosulfonates
Kazuya Kanemoto, Suguru Yoshida,* and Takamitsu Hosoya*
Laboratory of Chemical Bioscience, Institute of Biomaterials and Bioengineering,
Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062
E-mail: s-yoshida.cb@tmd.ac.jp; thosoya.cb@tmd.ac.jp
1
2
3
4
5
6
7
8
An efficient ipso-thiolation of arylboronic acid esters
with thiosulfonates has been achieved under mild and
odorless conditions using a copper catalyst. The use of
TMEDA and cesium fluoride as the ligand and base,
conditions
+
Ts
p-Tol
p-Tol
S
Yield (%)
Bpin
R
S
3
R
100
1
2a
respectively,
dramatically
facilitated
the
desired
conditions A; CuSO4, NaHCO3, rt
conditions B; CuSO , K CO , 50 °C
conditions C; [Rh(OH)(cod)]
79
transformation. The method exhibited a broad substrate
scope, which allowed for the expeditious synthesis of
diverse aryl sulfides from easily available starting materials.
4
2
3
80
60
40
20
0
2
, K
3
PO4
, 50 °C
48
41
9
Aromatic sulfur compounds have broad applications in
30
25
10 various fields, such as medicinal chemistry,1,2
11 agrochemistry,3 and materials science.4 Although many
12 synthetic methods have been developed, the preparation of
13 aromatic sulfur compounds by conventional methods is still
14 limited.
16
14
13
12
8
3
3
A
B
C
A
B
C
A
B
C
A
B
C
OMe
MeO2C
MeO
15
In this context, to render a variety of aryl sulfides
Bpin
Bpin
Bpin
16 easily available, our group has recently developed the
17 copper-catalyzed and rhodium-catalyzed ipso-thiolation
18 methods of arylboronic acids with thiosulfonates.5,6 These
19 reactions are advantages because of the readily available
20 starting materials and broad substrate scope, and mild and
21 odorless conditions. However, we found that these methods
22 often provided insufficient results, particularly with the use
23 of arylboronic acid pinacol esters. For example, the
24 deborylthiolation of arylboronic acid pinacol esters 1a–1d
25 with S-p-tolyl p-toluenethiosulfonate (2a) under the copper-
26 catalyzed (Figure 1, conditions A or B, blue or orange bars,
27 respectively) or rhodium-catalyzed conditions (conditions C,
28 gray bars) generally afforded the corresponding sulfides 3a–
29 3d in low to moderate yields. These results indicated that
Bpin
1a
1b
1c
1d
49
50 Figure 1. ipso-Thiolation of arylboronic acid pinacol esters under the
51 reported conditions. Conditions A: PhBpin (1.5 equiv), CuSO4 (5
52 mol %), NaHCO3 (2.0 equiv), MeOH, rt, 24 h. Conditions B: PhBpin
53 (1.5 equiv), CuSO4 (5 mol %), K2CO3 (2.0 equiv), MeOH, 50 °C, 24 h.
54 Conditions C: PhBpin (2.0 equiv), [Rh(OH)(cod)]2 (2.5 mol %), K3PO4
55 (2.0 equiv), MeOH, 50 °C, 24 h. Yields were determined by HPLC.
56
57
Table 1. Optimization of the reaction conditions
Cu source (5 mol %)
Ligand, Base (2.0 equiv)
Ts
p-Tol
+
S
p-Tol
Solvent
50 °C, 24 h
Bpin
S
1c (1.5 equiv)
2a
3c
58
Cu source/
Yield
/%a
Entry
Base
Solvent
Ligand (mol %)
30 our
methods
demonstrate
limitations
for
the
1
2
CuSO4/–
CuSO4/–
K3PO4
KOAc
MeOH
MeOH
trace
14
31 deborylthiolation of arylboronic acid esters, which are
32 relatively less reactive than the corresponding arylboronic
33 acids because of the increased steric bulk of the boryl group
34 and σ-donation from the α-carbons to the oxygens resulting
35 in decrease of the Lewis acidity of the boron center.7–9
36 Considering the recent advances in the methods for the
37 synthesis of arylboronic acid esters by transition-metal-
38 catalyzed borylation reactions, including the palladium-
39 catalyzed borylation of aryl halides10 and iridium-catalyzed
40 C–H borylation of arenes,11 it is crucial to achieve an
41 efficient ipso-thiolation of arylboronic acid esters. Herein,
42 we report modified conditions for the efficient copper-
43 catalyzed ipso-thiolation of a wide range of arylboronic acid
44 esters.
3
4
CuSO4/–
CuSO4/–
KF
CsF
RbF
CsF
CsF
CsF
CsF
CsF
CsF
CsF
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
65
74
48
9
5
CuSO4/–
6
CuSO4/PPh3 (12)
CuSO4/Xantphos (6)
CuSO4/acac (6)
CuSO4/bpy (6)
CuSO4/1,10-phen (6)
CuSO4/TMEDA (6)
CuI/TMEDA (6)
Cu(OAc)2·H2O/
TMEDA (6)
7
12
63
63
53
81b
55
8
9
10
11
12
13
CsF
MeOH
DMF
60
45
After the extensive rescreening of conditions carried
14
15
CuSO4/TMEDA (6)
CuSO4/TMEDA (6)
CsF
CsF
trace
46 out for the copper-catalyzed reaction between
47 phenylboronic pinacol ester (1c) and thiosulfonate 2a
48 (Figure 1, conditions B), the addition of a ligand using a
1,4-dioxane trace
59
60
aYields were determined by HPLC analysis, unless otherwise noted.
bIsolated yield.

1
2
3
4
5
6
7
8
9
fluoride salt as the base considerably improved the yield of
the desired sulfide 3c (Table 1). Instead of weak bases, such
as K2CO3, K3PO4, and KOAc, the use of alkali metal
fluorides, particularly cesium fluoride, dramatically
facilitated the reaction (Table 1, Entries 1–5). The addition
45
Various thiosulfonates 2 were also applied to the
46 modified method as demonstrated in the deborylthiolation of
47 phenylboronic acid pinacol ester (1c) (Figure 3). S-Aryl
48 thiosulfonates bearing an electron-donating or electron-
49 withdrawing substituent, including an unprotected amino,
50 carbamate, and amide group, on the aryl moiety successfully
51 furnished diaryl sulfides 3k–3q, demonstrating the excellent
52 functional-group tolerance of the method. Moreover, S-
53 heteroaryl and S-alkyl thiosulfonates also participated in the
54 reaction, affording 3-thienyl and phenethyl sulfides 3r and
55 3s, respectively.
of
a
catalytic
amount
of
N,N,Nʹ,Nʹ-
tetramethylethylenediamine (TMEDA) as the ligand further
improved the yield of 3c (Entry 11). In contrast, the addition
of other ligands, such as phosphines, acetylacetonate, and
10 pyridines, decreased the yield of 3c (Entries 6–10). Notably,
11 for the reaction conducted under the conditions shown in
12 Entry 11, the formation of di(4-tolyl) disulfide as the side
13 product, which exhibits polarity similar to that of the desired
14 diaryl sulfide making purification difficult, was not
15 detected.12 Changing the copper source from CuSO4 to CuI
16 or Cu(OAc)2·H2O decreased the yield of 3c (Entries 12 and
17 13). In addition, the use of other solvents, such as DMF and
18 dioxane, instead of methanol were completely unsuccessful
19 (Entries 14 and 15).
56
CuSO4 (5 mol %)
TMEDA (6 mol %)
CsF (2.0 equiv)
Ts
R
Ph
R
Ph Bpin
+
S
2
S
3
MeOH
50 °C, 24 h
1c
(1.5 equiv)
OMe
Ph
NH2
Ph
Ph
S
S
S
3k (73%)
3l (84%)
3m (50%)
20
The optimized conditions (Table 1, Entry 11) were
21 applicable to the ipso-thiolation of a wide range of aryl- and
22 alkenylboronic acid pinacol esters 1 as exemplified by the
23 reaction with thiosulfonate 2a affording sulfides 3a–3j
24 (Figure 2). Various diaryl sulfides 3a–3h were successfully
25 obtained in high yields from the corresponding arylboronic
26 acid pinacol esters 1. In particular, arylboronic acid pinacol
27 esters 1 bearing an electron-donating group, including
28 methoxy, dimethylamino, and an unprotected hydroxyl
29 group, underwent thiolated under the optimized conditions.
30 This result is in stark contrast to those observed for
31 reactions carried out under previously reported copper-
32 catalyzed conditions shown in Figure 1, wherein the
33 reaction of electron-rich arylboronic acid pinacol esters
34 afforded the desired sulfides only in low yields. Moreover,
35 the method was also applicable to the deborylthiolation of
36 heteroaryl- and alkenylboronic acid esters to afford products
37 such as 3-thienyl and (E)-styryl sulfides 3i and 3j,
NHBoc
Ph
Cl
Ph
Ph
S
Ph
S
S
NHBz
3p (71%)a
3n (82%)
3o (73%)
S
Ph
Ph
S
S
Ph
S
F
3s (87%)
3q (81%)a
3r (68%)
57
58 Figure 3. ipso-Thiolation of PhBpin (1c) with various thiosulfonates.
59 a10 mol % of CuSO4 and 12 mol % of TMEDA were used.
60
conditions
Ts
p-Tol
+
S
p-Tol
B
S
2a
(1.5 equiv)
3c
conditions A; CuSO4, NaHCO3, rt
conditions D; CuSO4, TMEDA, CsF, 50 °C
Yield (%)
ꢀꢄ
ꢀꢅ
ꢀꢁ
ꢀꢆ
ꢀꢁ
ꢀꢃ
ꢅꢀꢀ
ꢈꢀ
ꢈꢁ
ꢄꢀ
ꢃꢀ
ꢂꢀ
ꢁꢀ
ꢀ
ꢋ
ꢄꢀ
ꢉꢅꢃꢊ
38 respectively.
Unfortunately,
deborylthiolation
of
39 alkylboronic acid esters, including n-butyl- and allylboronic
40 acid pinacol ester, did not proceed.
ꢃꢃ
ꢆꢆ
ꢆꢇ
ꢂꢀ
41
ꢂꢃ
CuSO4 (5 mol %)
TMEDA (6 mol %)
CsF (2.0 equiv)
+
Ar
Ts
p-Tol
Ar
A
D
A
D
A
D
A
D
O
A
D
O
A
D
A
D
S
p-Tol
MeOH
50 °C, 24 h
S
3
Bpin
K
B
Ph
Ph
Ph
O
O
Ph
O
B
1
(1.5 equiv)
2a
B
B
PhB(OH)2
PhBpin
PhBF3K
O
O
O
O
4
1c
9
5
6
7
8
OMe
61
MeO2C
MeO
62 Figure 4. Comparison of the reactivity of various boronates with
63 thiosulfonate 2a under respective conditions. Conditions A: boronate
64 (1.5 equiv), CuSO4 (5 mol %), NaHCO3 (2.0 equiv), MeOH, rt, 24 h.
65 Conditions D: boronate (1.5 equiv), CuSO4 (5 mol %), TMEDA (6
66 mol %), CsF (2.0 equiv), MeOH, 50 °C, 24 h. aYield when the reaction
67 was conducted under conditions D without CsF is shown in brackets.
p-Tol
p-Tol
p-Tol
S
p-Tol
S
S
3a (92%)
3b (87%)
3d (73%)
Me2N
HO
Br
p-Tol
p-Tol
S
S
S
68
3e (68%)
3f (67%)
3g (91%)
69
The modified conditions established herein were
S
70 effective for the ipso-thiolation of other phenylboronic acid
71 alkanediol esters (Figure 4, conditions D, orange bars), e.g.,
72 trimethylene, neopentyl, and hexylene glycol esters 5–7,
73 affording the desired sulfide 3c in high yields. This result is
74 in stark contrast to that observed from the reactions carried
Ph
p-Tol
p-Tol
S
S
p-Tol
S
Br
3h (90%)
3i (74%)
3j (68%)
42
43 Figure 2. Deborylthiolation of various aryl- and alkenylboronic acid
44 pinacol esters 1 with thiosulfonate 2a.

3
1
2
3
4
5
6
7
8
9
out under the previously reported conditions (conditions A,
blue bars), where the result considerably depended on the
boronates used.7,13 The decrease in the yield of 3c was
observed with the increase in the steric bulk around the
boron moiety. These contrasting results indicated that the
new catalytic system using copper(II) sulfate and TMEDA
with cesium fluoride as the Lewis base significantly
facilitates deborylthiolation compared to the previous
system, probably via the acceleration of transmetalation.
51
This work was supported by the Platform Project for
52 Supporting Drug Discovery and Life Science Research
53 funded by Japan Agency for Medical Research and
54 Development (AMED); JSPS KAKENHI Grant Numbers
55 15H03118 (B; T.H.), 16H01133 (Middle Molecular
56 Strategy; T.H.), 26350971 (C; S.Y.); Suntory Foundation
57 for Life Sciences (S.Y.); Naito Foundation (S.Y.).
58
59
Supporting
Information
is
available
on
10 Moreover, phenylcyclic-triolborate potassium salt 8 was
11 deborylthiolated under the new conditions, whereas
12 potassium phenyltrifluoroborate (9) afforded 3c in poor
13 yields under both conditions.
60 http://dx.doi.org/ 10.1246/cl.xxxxxx.
61
62 References and Notes
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
1
For selected reviews of bioactive sulfur-containing compounds,
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14
As various arylboronic esters can be easily prepared
15 from simple starting materials by the transition-metal-
16 catalyzed borylative transformation of C–X,10 C–H,11 C–F,14
17 C–S,15 and C–COSR16 bonds, performing the ipso-thiolation
18 just after borylation facilitated the two-step synthesis aryl
19 sulfides. For example, formal C–H thiolation was
20 accomplished by the iridium-catalyzed C–H borylation11 of
21 1,2-dimethoxybenzene (10)17 followed by deborylthiolation,
22 affording desired sulfide 3t in high yield (Scheme 1). In this
23 case, the use of the modified conditions was crucial to
24 efficiently achieve ipso-borylation as the previous
25 conditions afforded 3t only in low yield. Notably, in
26 addition, the transformation of 10 to 3t was achieved with
27 the same efficiency even when the sequential reaction was
28 conducted in a same pot without purifying intermediate 1k.
29 This procedure demonstrated promise as a rapid route to
30 synthesize aryl sulfides from boron-free substrates.
31
2
3
4
5
6
7
S. Yoshida, Y. Sugimura, Y. Hazama, Y. Nishiyama, T. Yano, S.
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Chem. Commun. 2017, 53, 10640.
For a review comparing the properties of boronic acid derivatives,
see: A. J. J. Lennox, G. C. Lloyd-Jones, Chem. Soc. Rev. 2014,
43, 412.
Ts
p-Tol
S
2a
CuSO4 (5 mol %)
TMEDA (6 mol %)
CsF (2.0 equiv)
(Bpin)2
cat. Ir
MeO
MeO
MeO
MeO
MeO
MeO
MeOH
50 °C, 24 h
p-Tol
Bpin
S
87% [10%]a
10
1k
76%
3t
8
For selected examples describing the low reactivity of boronic
acid esters, see: a) M. Prieto, E. Zurita, E. Rosa, L. Muñoz, P.
Lloyd-Williams, E. Giralt, J. Org. Chem. 2004, 69, 6812. b) K. A.
McGarry, A. A. Duenas, T. B. Clark, J. Org. Chem. 2015, 80,
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Yi, T.-J. Liu, J.-H. Cheng, C.-F. Lee, Eur. J. Org. Chem. 2013,
3910. b) Z. Qiao, N. Ge, X. Jiang, Chem. Commun. 2015, 51,
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Sproules, A. J. B. Watson, J. Am. Chem. Soc. 2017, 139, 4769.
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Ishiyama, N. Miyaura, Chem. Rec. 2004, 3, 271. b) W. K. Chow,
O. Y. Yuen, P. Y. Choy, C. M. So, C. P. Lau, W. T. Wong, F. Y.
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M. R. Smith, III, J. Am. Chem. Soc. 1999, 121, 7696. b) J.-Y.
Cho, C. N. Iverson, M. R. Smith, III, J. Am. Chem. Soc. 2000,
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Am. Chem. Soc. 2002, 124, 390. For ortho-selective borylation,
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1. (Bpin)2, cat. Ir, heptane
2. evaporation, then
2a, cat. Cu
61%
same pot
32
33 Scheme 1. Formal C–H thiolation of 1,2-dimethoxybenzene (10).
34 aYield of 3t when the reaction was carried out under the previous
35 copper-catalyzed conditions (Conditions A: CuSO4 (5 mol %), NaHCO3
36 (2.0 equiv), MeOH, rt, 24 h) in brackets.
9
37
38
In summary, the efficient ipso-thiolation of arylboronic
102 10
103
39 acid esters with thiosulfonates using modified copper-
40 catalyzed conditions was reported. The use of cesium
41 fluoride and catalytic amount of TMEDA as the base and
42 ligand, respectively, dramatically facilitated the desired
43 transformation, affording diverse aryl sulfides from easily
44 available starting materials. In addition, the formal C–H
45 thiolation of a simple arene was achieved via the iridium-
46 catalyzed C–H borylation followed by ipso-thiolation. This
47 sequential reaction was conducted in the same pot,
48 considerably expanding the range of synthesizable sulfides
49 in an expeditious manner.
104
105
106 11
107
108
109
110
111
112
113
114
115
50
116
117

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