Palladium(II)-catalyzed aerobic intermolecular cyclization of acrylic acid with alkenes to α-methylene-γ-butyrolactones

Article abstract of DOI:10.1002/adsc.201100006

The methodology in this article is a palladium(II)/copper(II)- or palladium(II)-catalyzed intermolecular cyclization of acrylic acid with alkenes to produce α-methylene-γ-butyrolactone derivatives using molecular oxygen as an environmentally benign oxidant. In this system, the carboxylato, especially trifluoroacetato, or trimethylacetato ligand, plays a quite important role to afford a high catalytic activity by suppressing the deposition of palladium(0) black. Copyright

Full text of DOI:10.1002/adsc.201100006

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DOI: 10.1002/adsc.201100006
Palladium(II)-Catalyzed Aerobic Intermolecular Cyclization of
Acrylic Acid with Alkenes to a-Methylene-g-butyrolactones
a,
a
a
a
Koji Yonehara, * Yasuyuki Miyoshi, Aki Tsukajima, Takeo Akatsuka,
a
and Makoto Saito
a
Advanced Materials Research Center, Nippon Shokubai Co., Ltd., 5–8 Nishi Otabi-cho, Suita, Osaka 564-8512, Japan
Fax : (+81)-6-5841-2992; phone: (+81)-6-5841-2250; e-mail: koji_yonehara@shokubai.co.jp
Received: January 4, 2011; Published online: May 3, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201100006.
Abstract: The methodology in this article is a palla-
dium(II)/copper(II)- or palladium(II)-catalyzed in-
termolecular cyclization of acrylic acid with alkenes
to produce a-methylene-g-butyrolactone derivatives
using molecular oxygen as an environmentally
benign oxidant. In this system, the carboxylato, es-
pecially trifluoroacetato, or trimethylacetato ligand,
plays a quite important role to afford a high catalyt-
ic activity by suppressing the deposition of palladi-
um(0) black.
satisfactory results seems to be due to the fact that
the Pd(II) salt is much more unstable in the presence
of acrylic acid in comparison with another aliphatic
acid, e.g., acetic acid, and it tends to be easily decom-
posed to an inactive Pd(0) black or mirror despite the
[
7]
presence of an oxidant. Therefore, the development
of an efficient catalytic oxidation system for these lac-
tones should be an ongoing synthetic challenge. Re-
cently, much effort has been made to elaborate palla-
[
8]
dium-catalyzed aerobic oxidations, and the many
fruitful results stimulated us to investigate a new pal-
ladium-catalyzed system for these lactones using mo-
lecular oxygen as an environmentally benign oxidant.
Initially, we examined as a model the reaction of
acrylic acid with 1-octene in toluene at 708C for 16 h
under an oxygen atmosphere to probe the activity of
the different combinations of Pd(II) catalyst
Keywords: homogeneous catalysis; a-methylene-g-
butyrolactones; oxidation; oxygen; palladium
Over the last several decades, the syntheses of lac- (1 mol%) and Cu(II) cocatalyst (1 mol%). The pres-
tones having a double bond, especially a-methylene- sure was kept at 0.2 MPa by a continuous supply of
g-butyrolactone derivatives, have received a great oxygen during the reaction. Typical results are sum-
deal of attention, mainly because they exist widely in marized in Table 1 (entries 1–6). A PdCl /CuCl com-
2
2
nature and have significant biological activities. Al- bination which displays a high catalytic activity in the
[
8]
though an extraordinary number of preparative meth- Wacker-type oxidation
was not effective at all
[1,2]
[3]
ods
ylenation of g-butyrolactone, Pd(0)-catalyzed heter- Cu
oannulation of a-iodo or a-bromoacrylic acid with tone 1 [5-hexyl-3-methylenedihydrofuran-2(3H)-one],
including the Reformatsky reaction, a-meth- (entry 1). The reaction in the presence of Pd(OAc) /
ACHTUNGTRENNUNG
2
[
4]
AHCTUNGTNERGUN( OAc) also gave a low yield of the methylenelac-
2
[5]
dienes has been reported, they usually need several mainly due to catalyst deactivation caused by the for-
steps for the syntheses of these compounds. Among mation of Pd(0) black (entry 2). On the other hand,
them, Pd(II)-catalyzed direct intermolecular cycliza- the catalytic system Pd ACHTGNUTERNN(UNG OAc) /Cu ACHTUNGTRENN(GU OCOCF ) dramat-
2 3 2
tion using commercially available and cheap acrylic ically increased the yield giving 1 as a major exo
acid and alkenes as substrates under oxidative condi- isomer (56%), along with its endo isomer 2 [5-hexyl-
tions seems to be potentially the most convenient pro- 3-methylfuran-2(5H)-one] (3%) and acyclic ester 3
[
9,10]
tocol for these products. In 1994, Waegell and co- (2-acryloxy-1-octene) (14%) (entry 3).
workers first reported this type of palladium-cata- Pd(OCOCF ) /Cu(OAc) system also gave a similar
lyzed reaction using p-benzoquinone/MnO as an oxi- product distribution (entry 4). In both cases, there
The
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
3
2
2
2
[6]
dant. However, in their reaction system, acrylic acid was no deposition of Pd(0) black. Among the solvents
used as both substrate and solvent was partially poly- examined for this reaction, toluene or butyl acetate
merized because of the long reaction time and the was found to be the solvent of choice and solvents
product yield was moderate. Another reason for un- such as g-butyrolactone, chlorobenzene, dichlorome-
Adv. Synth. Catal. 2011, 353, 1071 – 1075
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Koji Yonehara et al.
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Table 1. Pd(II)-catalyzed aerobic intermolecular cyclization of acrylic acid with 1-octene in the presence or absence of
[a]
Cu(II) cocatalyst.
[b]
Entry
Catalyst (mol%)
Cocatalyst (mol%)
Yield [%]
+2 (ratio)
1
3
1
2
3
4
PdCl (1)
CuCl (1)
trace
trace
4
2
2
Pd
Pd
Pd
Pd
Pd
A
T
N
T
E
N
N
(OAc) (1)
Cu
Cu
Cu
Cu
Cu
A
T
N
T
E
N
N
(OAc) (1)
11 (91/9)
59 (95/5)
62 (97/3)
65 (95/5)
53 (96/4)
0
6 (83/17)
1 (100/0)
16 (94/6)
59 (93/7)
67 (93/7)
18 (89/11)
54 (87/13)
2
2
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
14
18
16
20
0
trace
0
6
5
4
2
4
2
3
2
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
3
3
3
2
2
2
2
[
[
c]
5
6
7
8
9
1
1
1
1
1
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
2
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
3
2
PdCl (5)
none
none
none
none
none
none
none
none
2
Pd
Pd
Pd
Pd
Pd
Pd
Pd
A
T
N
T
E
N
N
(OAc) (5)
2
d]
A
H
U
G
R
N
U
G
2
0
1
2
3
4
A
H
U
G
R
N
U
G
3
2
A
H
U
G
R
N
U
G
3
2
[
[
[
c]
e]
f]
A
H
U
G
R
N
U
G
3
2
A
H
U
G
R
N
U
G
2
A
H
U
G
R
N
U
G
2
[
a]
The reaction of acrylic acid (1 mmol) with 1-octene (10 mmol) was carried out in the presence of Pd(II) catalyst [and
Cu(II) cocatalyst] in toluene (5 mL) under oxygen (0.2 MPa) at 708C for 16 h.
The yield was determined by GLC based on acrylic acid. Numbers of parentheses show the ratio of 1/2 which was deter-
mined by GLC.
The oxygen pressure was 0.4 MPa.
Pyridine (10 mol%) was added.
[
b]
[
[
[
[
c]
d]
e]
f]
At 808C: acac; acetylacetonato.
At 808C: tmh; 2,2,6,6-tetramethyl-3,5-heptanedionato.
thane, 1,2-dimethoxyethane, and cyclohexane were The employment of Pd ACHTUNGTRNEGNU( OCOCF ) slightly improved
3 2
less efficient. Also, the product yield was greatly di- the yield of 1, but the Pd(0) black formation was still
minished in cyclohexanone, tert-butyl alcohol, benzo- observed (entry 10). Eventually, we found that the
[
11]
[12]
nitrile, dimethyl sulfoxide (DMSO), and N,N-di- palladium complex bearing a trimethylacetato (piva-
[
13]
methylacetamide (DMA). When 4 mol% of copper lato) ligand had a high catalytic activity by suppress-
salt was used as a cocatalyst under a higher oxygen ing the Pd(0) black formation (entry 11). A higher
pressure (0.4 MPa), the yield of cyclic compounds was oxygen pressure (0.4 MPa) improved the yield of 1 to
slightly improved to 65% (entry 5). The combination 62% along with its isomer 2 (5%) and acyclic ester 3
of Pd ACHTUNGTRENNUNG( OCOCF ) with Cu ACHUTNGENRNUG( OCOCF ) could also be (4%) (entry 12). A Pd AHCTTRGNUNENGU( acac) (acac: acetylacetonato)
3
2
3
2
2
used as a catalytic system (entry 6). For practical pur- catalyst gave the products in much lower yield with
pose, a large-scale reaction of acrylic acid (150 mmol) Pd(0) black formation (entry 13). The application of
with 1-octene (900 mmol) in toluene (450 mL) in the 2,2,6,6-tetramethyl-3,5-heptanedionato (tmh) in place
presence of Pd
Cu(OAc) (3.6 mmol, 2.4 mol%) was carried out at the yield of 1 to 47% as a major isomer with its
08C for 24 h under oxygen (atmospheric pressure) to isomer 2 (7%) and acyclic ester 3 (4%) (entry 14). In
give 1+2 (70% GLC yield, 66% isolated yield). this case, Pd(0) black formation was not observed.
ACHTUNGTRENNUNG( OCOCF ) (0.9 mmol, 0.6 mol%) and of acetylacetonato as a ligand was shown to improve
3 2
ACHTUNGTRENNUNG
2
9
We then focused on the development of a direct These results suggest that a steric hindrance of the
molecular oxygen-coupled catalytic system in the ab- employed ligand is one of the important factors for
[
8]
sence of copper cocatalyst (Table 1, entries 7–14).
The reaction in the presence of PdCl or Pd(OAc)
the reaction to proceed efficiently without Pd(0)
[
15]
A
H
U
G
R
N
N
black precipitation.
Typical results of the application of these optimized
of Pd(0) black (entries 7 and 8). The use of a coordi- catalytic systems [A: Pd(OCOCF ) (1–5 mol%)/
2
2
did not proceed efficiently, resulting in the formation
AHCTUNGTRENNUNG
3
2
[
8j]
[14]
nating base, such as pyridine or sparteine,
had Cu AHCTUNGTREUNNN(G OAc) (4–20 mol%) and B: Pd ACHTUNGERTNNNU(G OCOCMe ) (5–
2
3
2
only a detrimental effect on the reaction (entry 9). 10 mol%)] to a variety of alkenes and acrylic acid are
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Adv. Synth. Catal. 2011, 353, 1071 – 1075

Palladium(II)-Catalyzed Aerobic Intermolecular Cyclization of Acrylic Acid with Alkenes
Table 2. Syntheses of a-methylene-g-butyrolactone deriva- system A smoothly proceeded to give the desired
tives catalyzed by Pd
ACHTUNGTREN(UNGN OCOCF ) /Cu AHCTUNGNNETUR(G OAc) (system A) or
3 2 2
[a]
products in good isolated yield (72% or 71% yield)
(entries 1 and 3, respectively). In both cases, acyclic
Pd(OCOCMe ) (system B).
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[16]
3
2
esters corresponding to 3 in Table 1 were also pro-
duced in 16–18% GLC yields. Furthermore, the
system A showed compatibility with many functional
groups such as a double bond (70% yield), tert-butyl-
dimethylsilyloxy ether (75% yield), methoxy ether
(
81% yield), or ester (75% yield) (entries 5, 7, 9, 11,
respectively). The catalytic system B was similarly ap-
plicable to the reaction of acrylic acid with 1-hexene
(
1
70% yield) (entry 2), 1-butene (70% yield) (entry 4),
,7-hexadiene (69% yield) (entry 6), 1-(tert-butyldi-
methylsilyloxy)-9-decene (72% yield) (entry 8), me-
thoxy-9-decene (81% yield) (entry 10), and butyl 10-
undecenate (80% yield) (entry 12) to produce the cor-
responding compounds in satisfactory yields. Unfortu-
nately, internal alkenes such as 2-octene and alkenes
having an electron-withdrawing group such as styrene
or methyl acrylate were not be applicable to these
catalytic systems because of their lower reactivity.
Finally, we demonstrated that the catalytic system
A, Pd
ACHTUNGTRENNUNG( OCOCF ) (2 mol%)/Cu ACHTUNGTREUNNGN( OAc) (8 mol%), was
3 2 2
very effective for the intramolecular cyclization of 2-
[
17]
(
cyclopent-2-enyl)acrylic
acid
under
oxygen
(
0.4 MPa) at 658C for 24 h to give the methylenelac-
tone 5 in 91% isolated yield (Scheme 1).
Scheme 1. Pd(II)-catalyzed aerobic intramolecular cycliza-
tion of 2-(cyclopent-2-enyl)acrylic acid.
[
[
[
a]
b]
c]
The reaction of acrylic acid (1 mmol) with an alkene
10 mmol) was carried out in toluene (5 mL) under
oxygen (0.4 MPa) at 708C for 24 h.
Catalytic system A: Pd(OCOCF ) (1 mol%) and Cu-
(
A
H
N
T
E
N
G
We believe that the reaction proceeds via oxypalla-
dation intermediates which are formed by nucleophil-
ic attack of the a,b-unsaturated carboxylic acid to al-
kenes coordinated to the palladium followed by an in-
tramolecular carbopalladation and then b-hydride
elimination. The active palladium species are regener-
ated by molecular oxygen (Scheme 2)
In summary, we have developed a novel palladium-
catalyzed aerobic intermolecular cyclization of acrylic
acid with alkenes afford to a-methylene-g-butyrolac-
tone derivatives in the presence or absence of copper
cocatalyst. In these catalytic systems, the carboxylato
3
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(OAc) (4 mol%). Catalytic system B: Pd
A
H
U
G
R
N
U
G
2
(
5 mol%).
The main product (exo isomer) was isolated as a mixture
with its endo isomer. Numbers in parentheses show the
ratio of exo isomer/endo isomer which was determined
1
by H NMR.
[
[
d]
e]
The oxygen pressure was 0.6 MPa.
The amounts of catalyst and cocatalyst were 5 mol% and
20 mol%, respectively.
[
f]
The amount of catalyst was 10 mol%.
shown in Table 2. The reaction was carried out at ligand on palladium plays a quite important role to
7
0
08C under oxygen, and the pressure was kept at 0.4– afford a high catalytic activity by suppressing the dep-
.6 MPa by continuous supply of oxygen during the osition of Pd(0) black and overcomes the drawback of
[
18]
reaction. A reaction time was prolonged for 24 h to using acrylic acid as substrate. To the best of our
convert acrylic acid completely. The reaction of acryl- knowledge, this is the first example of the use of a
ic acid with 1-hexene or 1-butene using the catalytic palladium-catalyzed intermolecular reaction for the
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Koji Yonehara et al.
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Emeritus T. Hosokawa (Kochi University of Technology) for
their invaluable discussions. We are also indebted to Dr. K.
Kuwata (Kyoto University) for high-resolution mass spectra
(
HR-MS) analysis. We thank Mr. M. Makino (Nippon Sho-
kubai Co., Ltd.) for his active collaboration.
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A thick-walled test-tube was charged with Pd ACHTUGNTRNEUNG( OCOCF )
3 2
[
7] In our experiments, Pd
2 mL) saturated by oxygen was quite stable at 908C
for at least 5 days. On the other hand, all of the Pd-
(OAc) (15 mg) in acrylic acid (2 mL) saturated by
ACHTUNGENTRNUNG( OAc) (15 mg) in acetic acid
2
(
(
PdACHTUNGTRENNUNG
0.01 mmol, 1 mol% to acrylic acid)/Cu
0.04 mmol, 4 mol% to acrylic acid) (catalytic system A) or
(OCOCMe ) (0.05 mmol, 5 mol% to acrylic acid) (cata-
ACHTUNGTNERUNNG( OAc) ·H O
2 2
(
3
2
AHCTUNGTRENNUNG
2
lytic system B) followed by the addition of toluene (5 mL),
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Palladium(II)-Catalyzed Aerobic Intermolecular Cyclization of Acrylic Acid with Alkenes
[
6b]
[
9] In ref. 1-acryloxy-2-octene was obtained as by-prod-
uct through the p-allylpalladium intermediate. But, in
our system, only traces were detected.
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endo isomer is sometimes difficult by one-path column
chromatography on silica gel. If necessary, the purifica-
tion procedure must be repeated several times to sepa-
rate them.
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3
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3
251.
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water removal from the reaction solution in a large
scale-experiment. The details of these results will be re-
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[
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Adv. Synth. Catal. 2011, 353, 1071 – 1075
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