Decarboxylative Heck-Type Reactions of Thioacrylic Acid with Aryl Bromides

Full text of DOI:10.1002/bkcs.11735

Communication
DOI: 10.1002/bkcs.11735
BULLETIN OF THE
M. Jang et al.
KOREAN CHEMICAL SOCIETY
Decarboxylative Heck-Type Reactions of Thioacrylic Acid with Aryl
Bromides
†
‡,
†
†,
†,
*
*
*
Mihee Jang, Kyungho Park, Jeongah Lim, Jonghoon Oh, and Sunwoo Lee
†Department of Chemistry, Chonnam National University, Gwangju 61186, Republic of Korea.
*
E-mail: jnoh@chonnam.ac.kr; sunwoo@chonnam.ac.kr
‡
Corporate R&D, LG Chem, Daejeon 34122, Republic of Korea. *E-mail: kyunghopark@lgchem.com
Received March 25, 2019, Accepted August 4, 2019
Keywords: Decarboxylative coupling, Heck reaction, Vinyl sulfide, Acrylic acid.
Development of palladium-catalyzed cross-coupling reac1-
tions has greatly contributed to organic synthesis.
Alkenylations of aryl halides in the presence of Pd-catalysts
so called Heck reaction, for instance, have been compre-
hensive reaction to append vinyl fragments to arenes with
proving to be reliable and versatile tool that can tolerate a
Vinyl carboxylic acids as an alkenyl surrogate are attrac-
tive reagents for organic synthesis because they are not
only readily available, but also stable for handling and stor-
age. Palladium-catalyzed decarboxylative coupling reac-
tions of cinnamic acids have been reported previously
6
(Scheme 1(d) and (e)). Wu demonstrated the coupling
2
wide range of functional groups.
reaction with aryl iodide and cinnamic acids, and
Satoh/Miura reported the coupling with vinyl bromide and
cinnamic acids. However, to the best of our knowledge,
there has not been any report on decaboxylative coupling
reactions of sulfur-containing acrylic acids.
The scarcity of studies on Heck coupling reactions of
vinyl sulfides and the privilege of acrylic acids as a reactant,
with this in mind, have encouraged the development of
alternative methods involving the decarboxylation of thio-
acrylic acids. Herein, we report the first decarboxylative
Heck-type reaction of thio-acrylic acid and aryl bromides.
Vinyl thioether has been an attractive functional group
for organic synthesis and materials, but a few examples of
Heck coupling reactions of vinyl sulfides have been
reported. Yoshida described the coupling reaction of vinyl
3
2
-pyrimidyl sulfide with aryl iodide (Scheme 1(a)). Doucet
and Santelli described the Heck reaction of aryl bromides
using a palladium complex derived from a tetraphosphine,
employing ethyl vinyl sulfide in the coupling reaction and
4
reporting moderate yields (Scheme 1(b)). Gillingham et al.
reported the coupling reaction with aryl bromide and phe-
5
nyl vinyl sulfide using Pd[P(t-Bu) ] (Scheme 1(c)). How-
3
2
ever, they all showed very few examples in the coupling
reaction with vinyl sulfides. One possible reason for the
scarcity of the studies could be the low reactivity of the
sulfur-containing functional group.
R2
R1
PCy2
-
r
-
r
i P
i P
P
R1
Ph
2
P
PPh
2
-
-
n
i P
r
i P
r
N
N
-
L5: n
L6: n
=
=
1
2
Ph
2
P
PPh
2
Cl
L1: R1,
2
=
,
t Bu
-
-
R
i Pr i Pr
-
-
r
L2: R1 Ph R2 i P
L3: R1 Ph R2 Cy
=
L7
L4 (XPh
os
L
,
=
)
8
=
We chose phenyl thio-acrylic acid and bromobenzene as
the standard substrates and tested various reaction parame-
ters. The results are summarized in Table 1. First, we
screened a variety of ligands. Sterically bulky mono-
phosphine ligands such as L1, L2, and L3 afforded the
desired product 3a in moderate yields (entries 1–3). When
Xphos was employed as a ligand, 3a was formed in 95%
yield (entry 4). However, chelating phosphine ligands such
as L5, L6, and L7 provided unsatisfactory results (entries
(
a)
.
-
N
ca
t Pd Pd t B
u
)
3
]
+
+
[
(
2
N
S
I
A
r
A
r
N
S
S
N
S
S
(
(
b)
c)
.
cat PdCl allyl
)]
[
(
2
A
r
Br Ar
Br Ar
Tedicyp
.
-
cat Pd Pd t Bu
)
3
]
2
+
[
(
A
r
S
(
(
d)
e)
5–7). Unfortunately, imidazolium salt L8, which is a pre-
.
cat PdCl
2
Ar
CO H
2
A
r
A
r
cursor to the carbene ligand, did not give the desired cou-
pling product (entry 8). Keeping L4 as the ligand, we then
tested several palladium sources. Pd(II) sources such as
Pd(OAc) and Pd(acac) furnished 3a in yields of 36 and
Ar
Ar
+
I
CyJoh
nPhos
c
.
CO H
R
ca
2
t Pd OA
(
+ Br
)
2
R
Ar
2
2
This work
21%, respectively (entries 9 and 10). However, the
.
cat Pd
Pd(0) source such as Pd(dba) did not yield the desired
CO2
H
Ar
2
+
I
A
r
PhS
PhS
product (entry 11). Inferior results were obtained when
K CO , DBU, and Et N were used in the decarboxylative
Scheme 1. Coupling reaction of vinyl sulfides and cinnamic acids.
2
3
3
Bull. Korean Chem. Soc. 2019
© 2019 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Communication
ISSN (Print) 0253-2964 | (Online) 1229-5949
BULLETIN OF THE
KOREAN CHEMICAL SOCIETY
Table 1. Optimal conditions for decarboxylative heck-type
reaction.
Pd MeCN Cl 10 mol%
(
)
2
2
(
)
a
L4 20 mol
(
%
)
CO
2
H
+
Br Ar
Ar
PhS
C
s
-
.
u v
2CO3 (2 0 eq i )
PhS
,
,
o
,
Pd 10 mol%
1 4 Dioxane 100 C 9h
(
)
2
3
1
Ligand 20 mol%
(
)
CO H
+
2
PhS
-
.
.
PhS
u
Br
Base 2 0 equiv
M
e
t B
(
)
, -
,
o
,
3a
2
a
1 4 Dioxane 100 C 9h
1
PhS
PhS
PhS
b 88%
)
3
c 87%
( )
3
b
3a 92%
(
(
)
Entry
Pd
Ligand
Base
Yield(%)
Me
OMe
Cl
O
1
2
3
4
5
6
7
8
9
Pd(MeCN) Cl
Pd(MeCN) Cl
Pd(MeCN)
Pd(MeCN) Cl
Pd(MeCN) Cl
Pd(MeCN)
Pd(MeCN) Cl
Pd(MeCN) Cl
Pd(OAc)
Pd(acac)2
Pd(dba)2
Pd(MeCN)
Pd(MeCN) Cl
L1
L2
L3
L4
L5
L6
L7
L8
L4
L4
L4
L4
L4
L4
L4
Cs CO
54
17
35
95
16
15
5
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
Cs CO
2
2
PhS
PhS
PhS
PhS
PhS
2
Cl
2
Cs CO
3
d 88%
3e (45%)
3f (94%)
(
)
Cs CO
2
2
Cs CO
F
Ph
2
2
CH3
2
Cl
Cs CO
2
PhS
Cs CO
2
2
Cs CO
0
2
2
3g
2
3h 81%
3i 96%
( )
(
9 %)
(
)
2
Cs
2
CO
36
21
0
64
69
24
35
Scheme 2. Decarboxylative heck-type reactions of 1 with aryl bro-
mides: Reaction conditions: 1 (2.0 mmol), 2 (2.0 mmol),
(0.2 mmol), L4 (0.4 mmol), and Cs
4.0 mmol) were reacted in 1,4-dioxane at 100 C for 9 h. num-
1
1
1
1
1
1
a
0
1
2
3
4
5
Cs CO
2
Cs CO
2
Pd(MeCN)
2
Cl
2
2
CO
3
2
Cl
2
2
2
2
K
2
CO
3
ꢀ
(
DBU
2
bers in parenthesis indicate isolated yields.
Pd(MeCN) Cl
Pd(MeCN)
Et N
2
3
c
2
Cl
Cs
2
CO
3
bromides. We found that the combination of
Pd(MeCN) Cl2 and XPhos provided the best results.
Reaction conditions: 1 (0.3 mmol), 2a (0.3 mmol), Pd (0.03 mmol),
2
ligand (0.06 mmol), and base (0.6 mmol) were reacted in
Although it is not clear in which step the decarboxylation
took place, this is the first report on the decarboxylative
coupling reaction of sulfur-containing acrylic acids. Further
investigations into the detailed mechanism are underway in
our laboratory.
ꢀ
1
,4-dioxane at 100 C for 9 h.
b
c
Determined by gas chromatography.
Pd(0.015 mmol) and ligand (0.03 mmol).
coupling reaction (entries 12–14). When the amounts of
palladium and ligand were decreased to 5 and 10 mol %,
respectively, the yield of the product was 34% (entry 15).
From these results, we found that the best catalytic system
for the decarboxylative Heck-type reaction, consisted of
XPhos in combination with Pd(MeCN) Cl , delivered 95%
Acknowledgment. This research was supported by the
National Research Foundation of Korea (NRF) grant
funded by the Korean Government (MSIT) (NRF-
2
015R1A4A1041036). Spectral data were obtained from
Gwangju Center of Korea Basic Science Institute.
2
2
and full conversion, and with no trace of by-products
derived from dehalogenation.
The coupling reactions between different aryl bromides
and phenylthio-acrylic acid 1 under optimal conditions are
presented in Scheme 2.
As expected, 3a was obtained successfully in 92% isolated
yield. The coupling of 4-alkyl-substituted bromobenzenes
furnished the desired products 3b and 3c in good yields.
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We developed the palladium-catalyzed decarboxylative
Heck type reaction of phenylthio-acrylic acid with aryl
Bull. Korean Chem. Soc. 2019
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2