RhCl(PPh3)3/DPPF: A useful and efficient catalyst for cross-coupling reactions of activated alkenyl tosylates with arylboronic acids

Article abstract of DOI:10.1002/ejoc.200600469

A useful and effective rhodium catalyst system - [RhCl(PPh ₃)₃/DPPF] - for the Suzuki-Miyaura cross-coupling of activated alkenyl tosylates is described. The results not only represent the first examples of the rhodium-catalyzed Suzuki-Miyaura coupling of activated alkenyl tosylates with arylboronic acids under mild conditions, but also provide an efficient route for the synthesis of some natural product-like compounds, such as furan-2(5H)-one, coumarin, pyrone, and quinolin-2(1H)-one derivatives. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejoc.200600469

FULL PAPER
DOI: 10.1002/ejoc.200600469
RhCl(PPh ) /DPPF: A Useful and Efficient Catalyst for Cross-Coupling
3
3
Reactions of Activated Alkenyl Tosylates with Arylboronic Acids
Jie Wu,*[a,b] Liang Zhang, and Ke Gao
[a]
[a]
Keywords: Rhodium / 1,1Ј-Bis(diphenylphosphanyl)ferrocene / Cross-coupling / activated alkenyl tosylates / Natural
product-like compounds
A useful and effective rhodium catalyst system – [RhCl-
PPh /DPPF] – for the Suzuki–Miyaura cross-coupling of ac-
tivated alkenyl tosylates is described. The results not only
represent the first examples of the rhodium-catalyzed Su-
zuki–Miyaura coupling of activated alkenyl tosylates with ar-
ylboronic acids under mild conditions, but also provide an
efficient route for the synthesis of some natural product-like
compounds, such as furan-2(5H)-one, coumarin, pyrone, and
quinolin-2(1H)-one derivatives.
(
3 3
)
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
nent substrates in cross-coupling reactions. Although tosyl-
ates are relatively unreactive compared to their halide and
Transition-metal catalyzed cross-coupling reactions, ex- triflate counterparts in cross-coupling reactions, the use of
tensively employed in a wide range of areas in organic arenesulfonates as electrophiles has recently witnessed re-
[
5–11]
chemistry, are arguably one of the most powerful methods markable progress.
Among these, the Suzuki–
coupling reactions of arenesulfonates are the
for carbon–carbon bond formation.[1] While a large variety Miyaura
[12]
of organic electrophiles and organometallic reagents can be most attractive. Many inert, widely available arenesulfon-
applied in the coupling reactions, this field is largely domi- ates have been employed as coupling partners in palladium
nated by the use of palladium or nickel complexes as cata- or nickel-catalyzed Suzuki–Miyaura coupling reactions in-
[
1]
[5]
lysts. Recently, rhodium-catalyzed cross coupling reac- cluding reactions performed at room temperature. How-
tions have attracted much attention because an electron- ever, Suzuki–Miyaura couplings of arenesulfonates with bo-
rich arylrhodium intermediate may undergo oxidative ad- ronic acids with the utilization of rhodium as a useful cata-
dition of electrophilic aromatic substrates.[2] The stoichio- lyst have not yet been disclosed. In view of their ease of
metric activation of aryl chlorides on a phenylrhodium preparation, increased stability, and lower expense relative
complex has been realized.[ Moreover, these rhodium cata- to aryl triflates, as well as to broaden the application of
lysts have been employed in the catalytic cross-coupling of rhodium-catalyzed cross-coupling reactions, it is of signifi-
3]
[2]
arylboron reagents with acid anhydrides, aryl bromides, cant interest to develop general protocols for the employ-
and electron-deficient aryl chlorides,[ as well as in the ment of arenesulfonates in Rh-catalyzed Suzuki–Miyaura
4]
[
2]
cross-coupling of arylzinc reagents with aryl iodides.
cross-coupling reactions.
Missing is a system capable of handling triflates and arenes-
ulfonates.
With the use of a chemical genetic approach for the
analysis of biological systems – the use of interfaced librar-
Arenesulfonates are emerging as important alternatives ies of natural product-like molecules in connection with
[
13]
to aryl/vinyl triflates and halides in transition metal-cata- biological assays – we became interested in the develop-
lyzed cross-coupling reactions. They are often more stable ment of new approaches for the synthesis of some privileged
[
14]
and easier to handle than the corresponding triflates both scaffolds,
in the solid state and in solution. As a direct result of these and quinolin-2(1H)-one derivatives (Figure 1), because of
such as furan-2(5H)-one, coumarin, pyrone,
[
15–16]
described advantages, arenesulfonates are becoming promi- their extraordinary biological activities.
The structural
similarity of 4-hydroxycoumarin with 4-hydroxy-2(1H)-qui-
nolone, 4-hydroxy-pyrones, and 4-hydroxy-2(5H)-furanones
led us to envisage that their 4-tosyloxy species could be em-
ployed in transition metal catalyzed cross-coupling reac-
[
[
a] Department of Chemistry, Fudan University,
2
20 Handan Road, Shanghai 200433, China
Fax: +86-216-510-2412
E-mail: jie_wu@fudan.edu.cn
b] State Key Laboratory of Organometallic Chemistry, Shanghai tions as an ideal alternative to their corresponding triflates
Institute of Organic Chemistry, Chinese Academy of Sciences,
because of their increased stability, lower cost, and the com-
mercial availability of their synthetic precursors. Herein, we
disclose our preliminary results, which not only represent
3
54 Fenglin Road, Shanghai 200032, China
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
5260
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 5260–5263

RhCl(PPh
3 3
) /DPPF: A Useful and Efficient Catalyst for Cross-Coupling Reactions
FULL PAPER
the first examples of the rhodium-catalyzed Suzuki– Table 1. Reaction of 4-tosyloxy-2(5H)-furanone 1a with 4-meth-
[a]
3 3
oxyphenylboronic acid catalyzed by RhCl(PPh ) .
Miyaura coupling of activated alkenyl tosylates with aryl-
boronic acids under mild conditions, but also provide an
efficient route for the synthesis of 4-substituted furan-
2(5H)-ones, coumarins, pyrones, and quinolin-2(1H)-ones.
Figure 1. Some privileged scaffolds.
Entry
Ligand
Solvent
Base
Yield [%][b]
Results and Discussion
1
2
3
4
5
6
7
8
9
none
dppf
dppp
bpy
P(o-tolyl)
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
DMF
CsF
CsF
CsF
CsF
CsF
CsF
CsF
CsF
CsF
CsF
CsF
CsF
CsF
CsF
KF
47
82
72
n.r.
58
trace
45
These tosylates were simply prepared from the corre-
sponding 4-hydroxy species with p-toluenesulfonyl chloride
in the presence of triethylamine (Figure 2). At the outset of
our research, 4-tosyloxy-2(5H)-furanone (1a) was selected
for model studies. Gratifyingly, in an initial experiment, we
found that the coupling of 1a with 4-methoxyphenylboronic
acid in the presence of CsF catalyzed by RhCl(PPh3)3
3
PCy
P1
3
P2
P3
27
n.r.
n.r.
n.r.
n.r.
n.r.
n.r.
53
42
50
58
29
(
2 mol-%) in toluene heated at 50 °C under a nitrogen at- 10
dppf
dppf
dppf
dppf
dppf
dppf
dppf
dppf
dppf
dppf
dppf
dppf
1
1
1
1
2
3
DMSO
dioxane
THF
mosphere proceeded smoothly to afford the desired prod-
uct, 2a, in 47% yield (Table 1, Entry 1). Under the same
conditions, [RhCl(cod)] and [RhCl(C H ) ] proved less ef-
2
2
4 2 2
17]
14
EtOH
fective (results not shown in the Table).[ With this promis- 15
toluene
toluene
toluene
toluene
toluene
toluene
toluene
1
1
1
1
6
7
8
9
Cs
2
CO
CO
CO
PO
LiOH
NaOH
3
ing result in hand, a number of ligands were then screened.
As shown in Table 1, bidentate dppf and dppp were found
to be good ligands for this coupling (Entries 2 and 3) and
K
2
3
Na
2
3
K
3
4
afforded 2a in 82% and 72% yield, respectively. Other li- 20
gands, including PCy3 and Buchwald’s arylphos- 21
n.r.
n.r.
[
5b,18]
phanes,
tries 4–9). Further studies established that the product 0.25 mmol),
RhCl(PPh
.0  in H
showed results that were disappointing (En-
[
a] Reaction conditions: 4-tosyloxy-2(5H)-furanone (1a,
(4-methoxyphenyl)boronic acid (2.0 equiv.),
/ligand (1:1, 2 mol-%), solvent (4.0 mL), base (1.0 mL,
O), 50 °C, 12–24 h. [b] n.r.: no reaction. Isolated yield
3 3
)
2
yields decreased with a decreasing amount of catalyst (e.g.
mol-%, 45% yield). Toluene was the best choice among
1
1
based on 4-tosyloxy-2(5H)-furanone (1a).
the solvents screened (toluene, dioxane, DMF, DMSO,
EtOH, and THF), and the results indicated that it was very
critical for this reaction. We also found that CsF was the
best base, and the reaction temperature could be lowered to
Thus, with the optimized catalyst system, a variety of
activated alkenyl tosylates were examined in the Rh -cata-
I
lyzed cross-coupling reaction with arylboronic acids; the re-
sults are summarized in Table 2. In most cases, the activated
alkenyl tosylates reacted efficiently with both electron-rich
and electron-poor arylboronic acids to afford the corre-
sponding coupling products in good to excellent yields. The
failure of 1a in the coupling with thiophene-2-boronic acid
was possibly due to the deactivation of the catalyst by sulfur
50 °C at the expense of the reaction time. The trend for the
choice of solvent and base was similar to that reported by
[
4]
Satoh and Miura. Interestingly, hydroxide bases, usually
favored in palladium catalyst systems, were found to be in-
effective (Table 1, Entries 20 and 21).
(Entry 4). Substituted 4-tosyloxycoumarins showed broad
generality when coupled with various arylboronic acids,
and substrates with electron-withdrawing groups provided
better results. For example, an almost quantitative yield was
obtained (99%) when 6-fluoro-4-tosyloxycoumarin (1f) re-
acted with 4-fluorophenylboronic acid (Table 2, Entry 16).
4-Tosyloxypyrone (1g) was also a good partner in this coup-
ling reaction and excellent yields were obtained with vari-
ous arylboronic acids (Entries 17–20), whereas reactions of
4-tosyloxyquinolin-2(1H)-one (1h) afforded moderate yields
Figure 2. Tosylates.
(Entries 21–22).
Eur. J. Org. Chem. 2006, 5260–5263
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5261

J. Wu, L. Zhang, K. Gao
Table 2. Reaction of arenesulfonates 1 with arylboronic acid cata- Suzuki–Miyaura coupling of activated alkenyl tosylates
FULL PAPER
[
a]
3 3
lyzed by RhCl(PPh ) .
with arylboronic acids under mild conditions, but also pro-
vide an efficient route for the synthesis of furan-2(5H)-one,
coumarin, pyrone, and quinolin-2(1H)-one derivatives,
which could be directly used for biological assays.
Experimental Section
Entry
1
ArB(OH)
4-OMeC
B(OH)
2-ClC B(OH)
thiophene-2-B(OH)
B(OH)
4-OMeC
4-FC
2
Product Yield [%][b]
I
General Procedure for the Rh -catalyzed Suzuki–Miyaura Coupling
1
2
3
4
5
6
7
8
9
1a
1a
1a
1a
1b
1b
1b
1c
1c
1c
1d
1e
1e
1f
6
H
4
B(OH)
2
2
2a
2b
2c
2d
2e
2f
82
50
93
–
C
6
H
5
of Arenesulfonates with Arylboronic Acids: A mixture of the acti-
vated alkenyl tosylate (0.25 mmol), arylboronic acid (2.0 equiv.),
RhCl(PPh3)3 (2 mol-%), and DPPF (2 mol-%) was added into a
reaction tube under a nitrogen atmosphere. Toluene (4.0 mL) and
aqueous cesium fluoride (1.0 mL, 1.0  solution) were then added.
The reaction mixture was stirred at 50 °C. After the reaction was
completed as monitored by TLC, the organic phase was separated
and purified directly by flash chromatography (silica gel) to afford
the corresponding product.
6
H
4
2
2
C
6
H
5
2
60
88
88
61
70
78
74
79
95
91
89
99
98
93
93
99
51
50
6
H
4
B(OH)
B(OH)
B(OH)
4-OMeC
4-FC
2
6
H
4
2
2g
2h
2i
2j
2k
2l
C
6
H
5
2
6
4 2
H B(OH)
10
11
12
13
14
15
16
17
18
19
20
21
22
6
H
B(OH)
B(OH)
4
B(OH)
2
C
C
6
H
H
5
5
2
6
2
Supporting Information (see also the footnote on the first page of
this article): All the products are known compounds. The charac-
4-FC
6
H
4
B(OH)
B(OH)
4-MeC B(OH)
4-FC B(OH)
B(OH)
4-MeC B(OH)
4-ClC B(OH)
4-FC B(OH)
B(OH)
B(OH)
2
2m
2n
2o
2p
2q
2r
2s
2t
C
6
H
5
2
terizations of these compounds are identical with the literature re-
1f
1f
6
H
4
2
2
ports.[
19–29]
For details, please see Supporting Information.
6
H
4
2
1g
1g
1g
1g
1h
1h
C
6
H
5
2
6
H
4
Acknowledgments
6
H
4
2
6
H
4
2
C
6
H
5
2
2u
2v
We thank Professor Pengyuan Yang for his invaluable advice dur-
ing the course of this research. Financial support from the National
Natural Science Foundation of China (20502004), Ministry of Edu-
cation of China, the Science and Technology Commission of
Shanghai Municipality (05ZR14013), and Fudan University is
gratefully acknowledged.
4-FC
6
H
4
2
[
a] Reaction conditions: arenesulfonate 1 (0.25 mmol), arylboronic
acid (2.0 equiv.), RhCl(PPh /dppf (1:1, 2 mol-%), toluene
4.0 mL), CsF (1.0 mL, 1.0  in H O), 50 °C, 12 h. [b] Isolated yield
based on arenesulfonate 1.
3 3
)
(
2
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In summary, we have described a useful and effective
rhodium catalyst system for the Suzuki–Miyaura cross-
coupling of activated alkenyl tosylates. These results not
only represent the first examples of the rhodium-catalyzed
5262
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 5260–5263

3 3
RhCl(PPh ) /DPPF: A Useful and Efficient Catalyst for Cross-Coupling Reactions
FULL PAPER
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Received: May 31, 2006
Published Online: September 28, 2006
Eur. J. Org. Chem. 2006, 5260–5263
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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