Carboxylation of anisole derivatives with CO and O2 catalyzed by Pd(OAc)2 and molybdovanadophosphates

Article abstract of DOI:10.1039/b411934g

Anisole and its homologues were carboxylated under the influence of CO and O₂ catalyzed by Pd(OAc)₂ combined with molybdovanadophosphates (HPMoV) under mild conditions to give the corresponding carboxylic acids in fair to good yields; for instance, anisole underwent the carboxylation under a mixed gas of CO (0.5 atm) and O₂ (0.5 atm) in the presence of Pd(OAc)₂ (5 mol%) and H₅PMo ₁₀V₂O₄₀·nH₂O (2 mol%) to form an isomeric mixture of anisic acids in good yield.

Full text of DOI:10.1039/b411934g

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COMMUNICATION
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Carboxylation of anisole derivatives with CO and O catalyzed by
2
Pd(OAc) and molybdovanadophosphates
2
Shinichiro Ohashi, Satoshi Sakaguchi and Yasutaka Ishii*
Received (in Corvallis, OR, USA) 3rd August 2004, Accepted 11th October 2004
First published as an Advance Article on the web 2nd December 2004
DOI: 10.1039/b411934g
Anisole and its homologues were carboxylated under the
influence of CO and O catalyzed by Pd(OAc) combined with
2
2
molybdovanadophosphates (HPMoV) under mild conditions
to give the corresponding carboxylic acids in fair to good yields;
for instance, anisole underwent the carboxylation under a
2
mixed gas of CO (0.5 atm) and O (0.5 atm) in the presence of
Pd(OAc) (5 mol%) and H PMo V O ?nH O (2 mol%) to
2
5
10
2
40
2
form an isomeric mixture of anisic acids in good yield.
Benzenes react stoichiometrically with Pd(II) salts to undergo
1
chlorination, acetoxylation, carbonylation, carboxylation, etc.
2
3
4
The direct carboxylation of benzene with CO was first reported by
Scheme 1
Fujiwara et al. by the use of a stoichiometric amount of
5
Pd(OAc) . Thereafter, they reported the Pd-catalyzed carboxyla-
2
6
tion of benzene derivatives with CO using t-BuOOH or K
7
2
S
2
O
8
carboxylation of 1 by the use of CO and O can be achieved by
2
as reoxidants in trifluoroacetic acid. Pd(II)-catalyzed carboxylation
8
of hydrocarbons was reviewed by their group. However,
the Pd(OAc) /HPMoV system, since the same reaction using
2
5
2 2
PdCl /CuCl under these conditions provided no carboxylated
carboxylation using trifluoroacetic acid as a solvent is difficult to
carry out on a large scale, since trifluoroacetic acid is an intractable
compound. If molecular oxygen as an oxidant and acetic acid as a
solvent can be used in place of K S O and trifluoroacetic acid,
products at all (Run 10). The carboxylation was carried out under
varying pressures of CO and O (Runs 1 to 3). It was found that
the carboxylation of 1 to 2 was considerably influenced by the
partial pressures of CO and O . The best result was obtained when
a 1 : 1 mixed gas of CO and O was employed as shown in Run 2.
The reaction under a 1 : 2 mixture of CO (0.33 atm) and O
2
2
2 8
2
respectively, in the carboxylation of benzene derivatives, such a
method would provide an important practical synthetic route to
the corresponding benzoic acids. Recently, we have found that
2
2
(0.67 atm) resulted in the decrease of conversion of 1 and the
selectivity of 2, although the product ratio was almost the same
Pd(OAc)
2
combined with molybdovanadophosphoric acids
(
HPMoV) is an efficient catalytic system for the direct activation
(Run 1). Under a 2 : 1 mixture of CO (0.67 atm) and O
the conversion of 1 to 2 was considerably decreased (Run 3). When
the amount of Pd(OAc) was halved under these conditions, the
2
(0.33 atm),
of the C–H bond of arenes using molecular oxygen as the
reoxidant. Thus, the Heck–Mizoroki reaction of benzene with
2
acrylate was first achieved by using the Pd(OAc) /HPMoV/O
2
2
conversion of 1 was decreased to 44%, but the selectivity to 2 was
9
system. We have now found that the Pd(OAc) /HPMoV system
2
catalyzes efficiently the carboxylation of anisole derivatives under
Table 1 Carboxylation of anisole (1) to anisic acid (2) with CO and
a
the influence of a mixed gas of CO and O
2
to give the
O
2
by Pd(II) combined with HPMo10
V
2
under various conditions
corresponding anisic acids in fair to good yields (Scheme 1).
b
Conv. (%) Select. (%)
Run Pd(II) CO : O (atm) Solv.
2
In order to confirm the optimum reaction conditions, anisole (1)
1
2
3
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
0.33 : 0.67 AcOH
0.50 : 0.50 AcOH
0.67 : 0.33 AcOH
0.50 : 0.50 AcOH
0.50 : 0.50 AcOH
0.50 : 0.50 AcOH
0.50 : 0.50 EtCOOH
80
88
17
44
83
74
81
88 (23 : 77)
97 (26 : 74)
20 (26 : 74)
96 (26 : 74)
99 (23 : 77)
91 (23 : 77)
85 (23 : 77)
n.d.
2
was allowed to react under a mixed gas of CO and O in the
presence of catalytic amounts of Pd(OAc) and HPMoV in acetic
2
c
acid under various conditions (Table 1).
4
5
Pd(OAc)2
d
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
2
2
The reaction of 1 under a 1 : 1 mixture of CO (0.5 atm) and O
0.5 atm) in the presence of catalytic amounts of Pd(OAc)2
5 mol%) and H PMo10 40?15.2H O (HPMo10 ) (2 mol%) in
2
e
6
(
7
8
(
5
2
V O
2
V
2
0.50 : 0.50 CH
3
CN
4
11
acetic acid at 70 uC for 15 h afforded a 74 : 26 isomeric mixture of
p- and o-anisic acids (p- and o-2) in 88% conversion and 97%
selectivity (Run 2).{ This is the first successful direct carboxylation
9
0.50 : 0.50 DMF
0.50 : 0.50 AcOH
0.50 : 0.50 AcOH
n.d.
f
0
1
PdCl
4 2
Pd(SO )
2
no reaction
no reaction
1
1
a
1
(2 mmol) was allowed to react in the presence of Pd(OAc)
(0.1 mmol), HPMo10 (0.04 mmol) in solvent (7 mL) at 70 uC for
15 h. Numbers in parentheses show the ratio of o-2 and p-2.
2
2
of benzene derivatives like 1 using CO and O catalyzed by
V
2
b
Pd(OAc) and HPMoV. It is important to note that the
2
c
d
e
f
Pd(OAc)
2
(0.05 mmol) was used. At 80 uC. At 90 uC. CuCl
2
(
0.04 mmol) was used instead of HPMo10V .
2
*ishii@ipcku.kansai-u.ac.jp
4
86 | Chem. Commun., 2005, 486–488
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not changed (Run 4). The conversion of 1 to 2 was slightly
decreased in the reaction at 80 uC, but the reaction at 90 uC under
these conditions resulted in the decrease of the conversion of 1
Table 3 Carboxylation of various anisoles and phenol with CO and
O by the Pd(OAc) /HPMo10V system
2 2 2
a
Conv. Select.
(%) (%)
(Runs 5 and 6). The formation of m-anisic acid was not observed
Run Substrate
1
Products
at all in the present carboxylation.
90
73
The reaction was examined in several solvents such as propionic
acid, CH CN and DMF. In a previous paper on the direct
3
2
coupling of benzene with ethyl acrylate by Pd(OAc) and HPMoV,
propionic acid was a better solvent than acetic acid. However, the
reaction in propionic acid resulted in a slight lowering of the
conversion and selectivity (Run 7). It was found that CH
DMF were not suited for the present carboxylation (Runs 8 and
). PdCl and PdSO combined with HPMo10 did not catalyze
at all the present carboxylation (Runs 10 and 11).
We next tried the carboxylation of 1 by Pd(OAc)
with several heteropoly acids (Table 2).
In the absence of HPMoV as a co-catalyst under the same
conditions, no reaction took place using Pd(OAc) (Run 1). The
carboxylation of 1 by Pd(OAc) was found to be considerably
affected by the vanadium content in HPMoV used (Runs 2 to 7).
No reaction was promoted by Pd(OAc) combined with
H PMo O (HPMo ) not containing vanadium (Run 2). The
3
CN and
b
2
82
72
9
2
4
V
2
2
combined
2
3
49
64
2
2
3
12 40
12
carboxylation of 1 was promoted by Pd(OAc)
PMo11 40?nH O (HPMo11 ) and H PMo
HPMo V ) containing vanadium to give 2 in 19% and 43%
2
combined with
H
4
V
1
O
2
V
1
10
6
9
V
3
2
O40?nH O
4
90
75
(
9
3
yields, respectively (Runs 3 and 4). Although the reaction was
examined using molybdotungstophosphoric acids (HPMo W
1
11
and HPMo10
under these conditions, no carboxylation was observed (Runs 6 to
). These results show that vanadium in heteropolyoxometalates is
2 2
W ) and vanadotungstophosphoric acid (HPW10V )
8
an essential component to catalyze the present carboxylation of 1.
5
89
92
Among heteropoly acids examined, HPMo V was the best
10 2
combination with Pd(OAc)
2
. Although several vanadium com-
were employed instead of
pounds such as V and VO(acac)
2
O
5
2
HPMoV, no carboxylation took place (Runs 9 and 10)
On the basis of these results, the carboxylation of several anisole
derivatives was carried out by the use of Pd(OAc)
2 2
and HPMo10V
c
6
90
59
in acetic acid at 70 uC for 15 h (Table 3).
In order to obtain information on the reaction path, the
carboxylation of 1 was compared with that of o-, m- and
p-methylanisoles (o-, m-, and p-3). The reactivity in the carboxyla-
tion was found to decrease in the order of o-3, m-3, and p-3. The
a
Substrate (2 mmol) was allowed to react under CO (0.5 atm) and
(0.5 atm) by Pd(OAc) (0.1 mmol) and HPMo10 (0.04 mmol)
Table 2 Carboxylation of anisole (1) to anisic acid (2) with CO and
a
O
2
2
V
2
O
2
catalyzed by Pd(OAc)
2
and heteropoly acids
b
c
in AcOH (7 mL) at 70 uC for 15 h. m-4 : m-49 5 ca. 50 : 50. In
AcOH (4 mL) at 60 uC; p-10 : o-10 5 ca. 90 : 10.
Run
HPA
Conv. (%)
Select. (%)
1
2
3
4
5
6
7
8
9
—
HPMo12
HPMo11
no reaction
2
30
53
27
1
2
—
64
81
57
—
—
selectivity in the carboxylation could be satisfactorily explained by
the electronic effect of the methoxy substituent. For instance, the
carboxylation of m-3 took place at the 4-position possessing
the highest electron density. The low reactivity of p-3 is due to the
occupation of its para-position by the methyl group. Additionally,
p-hydroxybenzoic acid (p-10) and o-hydroxybenzoic acid (o-10)
were obtained in 59% selectivity at 90% conversion in the reaction
of phenol (9) (Run 6). Unfortunately, however, benzene is inert for
the present carboxylation, giving a small amount of benzoic acid
V
1
HPMo
HPMo
9
V
3
4
8
V
HPMo11
HPMo10
W
W
1
2
HPW10
V
2
no reaction
no reaction
no reaction
2 5
V O
VO(acac)
2
10
a
1
(2 mmol) was allowed to react under CO (0.5 atm) and O
0.5 atm) by Pd(OAc) (0.1 mmol) and HPA (0.04 mmol) in AcOH
7 mL) at 70 uC for 15 h.
2
(
(
2
(, 5%).
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 486–488 | 487

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Shinichiro Ohashi, Satoshi Sakaguchi and Yasutaka Ishii*
Department of Applied Chemistry, Faculty of Engineering & High
Technology Research Center, Kansai University, Suita, Osaka,
5
64-8680, Japan. E-mail: ishii@ipcku.kansai-u.ac.jp
Notes and references
{
(
(
1
Representative procedure: To an AcOH solution (7 mL) of Pd(OAc)
0.1 mmol) and H PMo10 40?15.2H O (0.04 mmol) was added 1
2 mmol). Then, the reaction mixture was stirred at 70 uC for 15 h under a
: 1 mixed gas (1 atm) of CO and O . After the reaction, the GC and GC-
2
5
2
V O
2
2
MS analyses were performed. The conversions and yields of products were
estimated from the peak areas based on the internal standard technique
using GC.
{
stage, a PdL
Although we could not determine the real active Pd(II) species at this
+
2
or a cationic Pd L (L: OAc) may be formed under these
reaction conditions.
1
2
P. Henry, J. Org. Chem., 1971, 36, 1886.
L. Eberson and L. Gomez-Gonzales, J. Chem. Soc., Chem. Commun.,
1971, 263.
P. Henry, Tetrahedron Lett., 1968, 2285.
T. Sakakibara and Y. Odaira, J. Org. Chem., 1976, 41, 2049.
Scheme 2
3
4
The carboxylation is rationally explained by a similar reaction
7
b
5 Y. Fujiwara, T. Kawauchi and H. Taniguchi, J. Chem. Soc., Chem.
Commun., 1980, 220.
6
path proposed by Fujiwara (Scheme 2). The ortho–para
orientation of the carboxylation of 1 by the present reaction
system suggests that the reaction involves the electrophilic
substitution of aromatic C–H bonds by Pd(II){ followed by the
CO insertion of the Ar–Pd(II) species leading to an aroylpalladium
species (A). The subsequent reductive elimination of Pd(0) and
acetic anhydride from A leads to anisic acid. The Pd(0) is
T. Jintoku, T. Taniguchi and Y. Fujiwara, Chem. Lett., 1987,
1159.
(a) T. Jintoku, Y. Fujiwara, I. Kawata, T. Kawauchi and T. Taniguchi,
J. Organomet. Chem., 1990, 385, 297; (b) Y. Taniguchi, Y. Yamaoka,
K. Nakata, K. Takai and Y. Fujiwara, Chem. Lett., 1995, 345 and
literature cited therein.
7
8 C. Jia, T. Kitamura and Y. Fujiwara, Acc. Chem. Res., 2001, 34, 633;
Y. Fujiwara, K. Takaki and Y. Taniguchi, Synlett, 1996, 591.
reoxidized by the action of HPMoV and O
species.
In conclusion, we have developed Pd-catalyzed direct
2
to the parent Pd(II)
9
T. Yokota, M. Tani, S. Sakaguchi and Y. Ishii, J. Am. Chem. Soc.,
003, 125, 1476.
0 D. M. Fenton and P. J. Steinwnd, J. Org. Chem., 1972, 37, 2034;
O. Hamed, A. El-Qisairi and P. M. Henry, J. Org. Chem., 2001, 66,
80.
2
1
carboxylation of anisole derivatives using CO and O
2
under
1
mild conditions.
4
88 | Chem. Commun., 2005, 486–488
This journal is ß The Royal Society of Chemistry 2005