Wacker-type oxidation of internal olefins using a PdCl2/N,N- dimethylacetamide catalyst system under copper-free reaction conditions

Article abstract of DOI:10.1002/anie.200905184

(Figure Presented) A simple catalyst system consisting of PdCl₂ and N,N-dimethylacetamide (DMA) as the solvent can successfully promote Wacker-type oxidation of internal olefins. This catalyst system does not require copper compounds and is tolerant of a wide range of substrates having internal olefins.

Full text of DOI:10.1002/anie.200905184

Communications
DOI: 10.1002/anie.200905184
Synthetic Methods
Wacker-Type Oxidation of Internal Olefins Using a PdCl /N,N-
2
Dimethylacetamide Catalyst System under Copper-Free Reaction
Conditions**
Takato Mitsudome, Keiichi Mizumoto, Tomoo Mizugaki, Koichiro Jitsukawa, and
Kiyotomi Kaneda*
0
Carbonyl groups are key moieties for the construction of
Pd species by O . This discovery opens a new route for the
2
[
1]
carbon skeletons and synthetic intermediates. Oxygenation
of olefins is one of the most straightforward routes for the
synthesis of carbonyl compounds. The industrially important
oxidation of ethylene to acetaldehyde, using a catalyst system
consisting of palladium with copper, is commonly known as
selective and direct synthesis of carbonyl compounds from
internal olefins.
We herein present a method by which a PdCl /DMA
2
catalyst system can be successfully applied to the oxidation of
various internal olefins to carbonyl compounds. This method-
ology is extremely simple, and the oxidation proceeds
efficiently without isomerization of the olefins. Interestingly,
the addition of copper compounds decreases the catalytic
activity of the palladium for internal olefins. It is revealed that
the lack of a requirement for copper is fundamental to
overcome the problem of low activity for internal olefins,
which the traditional Wacker–Tsuji oxidation reactions have
suffered from.
[
2–5]
the Wacker oxidation process.
Since the discovery of this
process, this Pd/Cu catalyst system has been extended to the
oxidation of diverse terminal olefins using water under liquid-
phase conditions (Wacker–Tsuji oxidation), which offers a
[6–8]
powerful method for the synthesis of methyl ketones.
However, this catalyst system has been inevitably limited to
the oxidation of terminal olefins. This limitation arises
because internal olefins show extremely low reactivity and
selectivity; that is, non-regioselective oxidations occur to yield
various undesired oxygenated products through isomerization
Initially, trans-4-octene (1) was treated with 5 mol%
PdCl in a mixture of an organic solvent and water with 3 atm
of O under copper-free reactions conditions. In a DMA
2
[
9–11]
of the olefinic bonds.
Therefore, the selective synthesis of
2
carbonyl compounds from internal olefins using water
remains a major challenge.
solution, oxidation of 1 proceeded to give 4-octanone (2) as
the sole product in 91% yield without isomerization or
chlorination of 1 (Table 1, entry 1). The use of N-methyl-
pyrrolidone (NMP) also gave 2 in good yield (Table 1,
entry 4). Other solvents, such as N,N-dimethylformamide
(DMF), dimethyl sulfoxide (DMSO), acetonitrile, and tolu-
ene resulted in low yields of 2, which was accompanied by the
formation of isomers of 1 or 2 (Table 1, entries 5–8). Among
the palladium compounds tested, PdCl and [PdCl (PhCN) ]
Recently, some advancements of the Wacker–Tsuji oxi-
dation method have successfully eliminated the requirement
[
12–15]
for copper additives.
of a PdCl2 catalyst system with N,N-dimethylacetamide
DMA) allows direct O -coupled Wacker-type oxidation of
We also found that the combination
(
2
various terminal olefins into the corresponding methyl
[
14]
ketones under copper-free reaction conditions. From the
study of cyclic voltammetry, kinetics, and X-ray absorption
fine structure (XAFS) data, DMA was found to act as the
most efficient solvent for promoting the reoxidation of the
2
2
2
[
a]
Table 1: Oxidation of trans-4-octene under various conditions.
[*] Dr. T. Mitsudome, K. Mizumoto, Dr. T. Mizugaki,
Prof. Dr. K. Jitsukawa, Prof. Dr. K. Kaneda
Department of Materials Engineering Science
Graduate School of Engineering Science, Osaka University
[
b]
[b]
Entry Catalyst
Solvent
Conv. of 1 [%]
Yield of 2 [%]
1
2
3
4
5
6
7
8
9
1
1
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
DMA
DMA
DMA
NMP
DMF
DMSO
91
91
–
–
76
12
6
8
–
87
–
–
[
[
c]
1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)
trace
trace
79
13
6
d]
Fax: (+81)6-6850-6260
E-mail: kaneda@cheng.es.osaka-u.ac.jp
Homepage: http://www.cheng.es.osaka-u.ac.jp/kanedalabo/
GSCLabo/index.html
Prof. Dr. K. Kaneda
Research Center for Solar Energy Chemistry, Osaka University
acetonitrile 13
toluene trace
1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)
[PdCl (PhCN) ] DMA
2
2
87
trace
trace
0
1
Pd(OAc)2
DMA
DMA
[
**] This work was supported by a Grant-in-Aid for Scientific Research on
Priority Areas (no. 18065016, “Chemistry of Concerto Catalysis”)
from Ministry of Education, Culture, Sports, Science, and Technol-
ogy (Japan).
[PdCl (NH ) ]
2
3 4
[
(
a] Reaction conditions: trans-4-octene (1 mmol), Pd catalyst
0.05 mmol), solvent (5 mL), H O (0.5 mL), 3 atm of O , 808C, 10 h.
2
2
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200905184
[b] Determined by GC methods using an internal standard. [c] Without
H O. [d] Ar was used instead of O .
2
2
1
238
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Angew. Chem. Int. Ed. 2010, 49, 1238 –1240

Angewandte
Chemie
were effective as catalysts in the DMA solvent (Table 1,
give cyclohexanone in good yield, and was accompanied by a
entries 1 and 9). The oxidation of 1 did not proceed in the
small amount of an allylic oxidation product (2-cyclohexene-
1-one; Table 2, entry 8). The oxidation of functionalized
internal olefins also proceeded efficiently wherein only the
carbon–carbon double bonds were oxidized to ketones, and
the functional groups (hydroxy, cyano, and ether groups)
remained intact under the present reaction conditions
(Table 2, entries 9–12). More interestingly, olefins having
functional groups in the allylic position were regioselectively
oxidized to give the respective b-functionalized ketones as the
sole products with excellent yields (Table 2, entries 10–12).
For example, in the oxidation of trans-3-pentenenitrile, an
oxygen atom was selectively incorporated at the g position
relative to the cyano group, affording 4-oxopentanenitrile in
absence of water. Under an argon atmosphere instead of O , a
2
trace amount of 2 together with a precipitate of palladium
1
8
black was observed. The use of O-labeled water provided
1
8
exclusively the O-labeled ketone with 99% selectivity. No
1
6
18
oxygen scrambling between O ketone and O water was
1
6
18
observed when 4-octanone ( O) was treated with O-labeled
water under identical conditions for 1 hour. These results
indicate that the oxygen atom incorporated into 2 is derived
not from molecular oxygen but from water.
The applicability of this catalyst system to other types of
olefins is shown in Table 2. The compounds trans-2-octene
and trans-3-octene provided 2- and 3-octanones, and 3- and 4-
octanones, respectively, suggesting that the oxygen atoms are
incorporated into the original olefinic position of the starting
materials (Table 2, entries 1 and 2). cis-4-Octene showed a
similar reactivity to the trans-4-octene, affording 2 as the sole
product (Table 2, entry 4). Although the long-chain olefin 7-
tetradecene does not undergo the oxidation under the
previously reported copper-free Wacker oxidation sys-
[17]
86% isolated yield (Table 2, entry 10).
All of the internal olefins that we tested were hardly
oxidized under the standard reaction conditions of traditional
the Wacker–Tsuji oxidation, using 10 mol% PdCl and
2
[
19]
100 mol% CuCl in a DMF solvent. In a control experiment
for the oxidation of 1, the addition of 10 mol% CuCl to the
2
PdCl /DMA mixture decreased the yield of 2 to 68% yield
2
[
15,16]
tems,
-tetradecene into 7-tetradecanone in excellent yield
Table 2, entry 7). A cyclic olefin, cyclohexene, reacted to
the present catalyst system effectively converted
after 6 hours. Moreover, increasing the amounts of CuCl to
2
7
(
the reaction mixture dramatically decreased the conversion of
[20]
1 (Figure 1). The above phenomenon is in sharp contrast
with the result obtained with 1-
octene for which an increase of
[
a]
Table 2: Wacker oxidation of various internal and cyclic olefins catalyzed by the PdCl /DMA system.
CuCl2 resulted in an increased
yield of 2-octanone (Figure 2). Pre-
sumably, the low activity of the
palladium species in the presence
of copper is due to the formation of
2
[
b]
[b]
Entry
Substrate
t [h]
Conv. [%]
Product
Yield [%]
6
3
5
4
2
6
4
4
1
10
98
[22]
a bulky Pd/Cu bimetallic complex
which cannot easily coordinate to
an internal olefin.
In conclusion, we have demon-
[
23]
2
10
98
strated the direct O -coupled
Wacker oxidation of internal olefins
into carbonyl compounds using a
3
4
5
6
7
10
10
10
10
20
91
83
98
86
81
91 (88)
83
2
PdCl /DMA catalyst system. The
98
2
presence of copper was shown to
have a negative effect on Wacker
oxidation of internal olefins. The
conventional Wacker–Tsuji oxida-
tion system may suffer from the
dilemmatic problem: the copper
species, which promotes the reox-
86 (80)
81 (77)
[
c,d,e]
[f]
8
9
10
10
85
92
73
4
4
7
5
0
II
[
c]
idation of Pd into Pd , inhibits the
oxidation of internal olefins. The
discovery of the direct O -coupled
2
[
[
[
c]
10
11
12
20
20
20
94
95
85
94 (86)
Wacker oxidation without the need
for copper as a co-catalyst will lead
to novel Wacker-type oxidations of
internal olefins.
c,d]
c]
[g]
91
[h]
80
[
a] Reaction conditions: substrate (1 mmol), PdCl (0.05 mmol), DMA (5 mL), H O (0.5 mL), 3 atm of
2
2
O , 808C. [b] Determined by GC methods using an internal standard. The values within parentheses are Experimental Section
2
the yields of the isolated products. [c] PdCl2 (0.1 mmol). [d] Substrate (0.5 mmol). [e] 708C. [f] 2- A typical procedure for the Wacker
Cyclohexene-1-one was formed as a by-product in 12% yield. [g] 1-Benzyloxy-2-hexanone formed as a oxidation of various olefins: To com-
minor product in 4% yield. [h] 1-Methoxy-2-octanone formed as a minor product in 5% yield.
pletely dissolve the PdCl in DMA, the
2
Angew. Chem. Int. Ed. 2010, 49, 1238 –1240
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1239

Communications
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9
[
[
2
Figure 1. Effect of the amount of CuCl upon the oxidation of 1.
2
Reaction conditions: trans-4-octene (1 mmol), H O (0.5 mL), DMA
2
[
5] P. M. Henry, Handbook of Organopalladium Chemistry for
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2 2
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[
[
[
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2
Reaction conditions: 1-octene (1 mmol), H O (0.5 mL), DMA (5 mL),
2
PdCl (0.002 mmol), 3 atm of O , 808C.
2
2
[
17] The high selectivity for b-functionalized ketones might be due to
a precoordination of a functional group of the olefin with a
palladium prior to the attack of water to the olefin. See
reference [18].
[
24]
following pretreatment protocol was conducted:
PdCl2 (5 ꢀ
À2
1
5
0
mmol), DMA (5 mL), and H O (0.5 mL) were placed in a
0 mL stainless-steel autoclave (with a Teflon inner cylinder) along
2
[
18] J. A. Wright, M. J. Gaunt, J. B. Spencer, Chem. Eur. J. 2006, 12,
with a Teflon-coated magnetic stir bar, and the mixture was stirred at
949.
room temperature for 1 h under 9 atm of O . After the pretreatment,
2
[19] J. Tsuji, H. Nagashima, H. Nemoto, Org. Synth. 1984, 62, 9.
[
trans-4-octene (1 mmol) was added. The vessel was pressurized to
À
20] It is well-known that the concentration of Cl is inversely
proportional to the reaction rate for Wacker oxidation of
terminal olefins (see reference [21]). To determine if the
3
1
atm of O , and then the mixture was vigorously stirred at 808C for
0 h. After the reaction, the reactor was cooled to room temperature,
2
and then the O pressure was carefully released to the atmospheric
2
decrease in the yield of 2 was a result of the increase in the
pressure [CAUTION: the reaction temperature was beyond the flash
point of DMA (778C)]. GC analysis of the solution, using naphtha-
lene as an internal standard, indicated 4-octanone as the sole product
with 91% yield. The product was then extracted using a 1:1 diethyl
ether/brine mixture (2 ꢀ 30 mL). The diethyl ether layer containing
À
concentration Cl , we assayed the effect of replacing CuCl with
2
Cu(OAc) . The conversion of 1 decreased as the amount of
2
added Cu(OAc) was increased. See Figure 1S in the Supporting
2
Information.
[
[
[
21] J. A. Keith, R. J. Niesen, J. Oxgaard, W. A. Goddard, J. Am.
the products was dried over MgSO , filtered, and then concentrated
4
Chem. Soc. 2007, 129, 12342.
under reduced pressure. The resultant crude mixture was purified by
column chromatography (silica gel) using EtOAc/n-hexane (1:4) as
the eluent to obtain pure 4-octanone (0.11 g, 88%).
22] T. Hosokawa, T. Nomura, S.-I. Murahashi, J. Organomet. Chem.
1998, 551, 387.
23] The exact mechanism of this Wacker-type reaction is not yet
known. However, evidence indicates these reactions are depen-
dent upon experimental conditions (see reference [5]). Thus, it is
not surprising that the observed rate law for this reaction, which
does not utilize copper salts, is different from that of the
industrial process, which does utilize copper salts (see the
Supporting Information).
Received: September 16, 2009
Revised: November 28, 2009
Published online: December 28, 2009
[
24] The structure of PdCl /DMA complexes have been studied in
2
the following papers: a) M. Donati, D. Morelli, F. Conti, R. Ugo,
Chim. Ind. 1968, 50, 231; b) S. N. Kurskov, V. I. Labunskaya,
E. V. Trushina, Koord. Khim. 1990, 16, 1671.
Keywords: aerobic oxidation · alkenes · homogeneous catalysis ·
palladium · oxidation
.
1
240
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