Palladium-catalyzed carbonylative dimerization of styrenes to 1,5-diarylpent-1-en-3-ones

Article abstract of DOI:10.1002/asia.201100836

A general palladium-catalyzed carbonylative dimerization of styrenes has been developed. Starting from commercial available styrenes, symmetrical 1,5-diarylpent-1-en-3-ones were produced in good to excellent yields (see scheme; dppp=1,3-bis(diphenylphosphino)propane). Copyright

Full text of DOI:10.1002/asia.201100836

DOI: 10.1002/asia.201100836
Palladium-Catalyzed Carbonylative Dimerization of Styrenes to 1,5-
Diarylpent-1-en-3-ones
Xiao-Feng Wu,[a, b] Helfried Neumann,[b] and Matthias Beller*[b]
Transition metal catalyzed reactions of alkenes represent
key transformations in the chemical industry.[1] Representa-
tive examples include catalytic hydrogenations, oxidations,
oligomerizations, polymerizations, metathesis, and so on. In
addition, carbonylation reactions of olefins are performed
annually on a million-ton scale to synthesize aliphatic alde-
hydes and alcohols. Based on this important methodology,
further refinement reactions have led to numerous inter-
mediates for the polymer, bulk and fine chemical industries.
Among the various homogeneous catalysts applied in this
area, palladium complexes proved to be especially useful for
the preparation of carboxylic acid derivatives.[2]
gated,[7] and no general synthetic methodology is known so
far.
Recently, our group have developed novel palladium-cata-
lyzed aminocarbonylations of aryl halides to primary
À
amides, carbonylative C H activations of heteroarenes, and
carbonylative Heck reactions of aryl halides and triflates.[8]
Based on our continuing interest in carbonylation reactions,
here we wish to present a convenient protocol for the car-
bonylative synthesis of 1,5-diarylpent-1-en-3-ones from com-
mercially available styrenes. The resulting products repre-
sent interesting building blocks for further functionalizations
towards potentially bioactive compounds.
More specifically, as shown in Scheme 1 palladium-cata-
lyzed copolymerization of alkenes with CO,[3] alkoxycarbo-
nylation of olefins,[4] hydroxy- and amino-carbonylation of
alkenes,[5 ]and even oxidative carbonylations of alkenes are
well developed.[6] However, the apparently simple related
carbonylative dimerization of alkenes was scarcely investi-
Recently, we examined palladium-catalyzed oxidative-car-
bonylative coupling reactions of arylboronic acids with styr-
enes to give chalcones as shown in Scheme 2.[9] In this reac-
Scheme 2. Oxidative carbonylation of arylboronic acids and alkenes.
tion, air was employed as an oxidant. To our surprise, in
some reactions decomposition of the corresponding arylbor-
onic acid was observed and carbonylative dimerization of
the alkene took place as a side reaction.
Based on this interesting result we studied the dimeriza-
tion of styrene in the presence of carbon monoxide in more
detail. As shown in Table 1 variation of the acid co-catalyst
was performed because of the importance of the active pal-
ladium hydride species (Scheme 3). When a combination of
Scheme 1. Palladium-catalyzed carbonylation reactions of alkenes.
PdACTHNUGTRENNG(U OAc)2 and 1,3-bis(diphenylphosphino)propane (dppp)
was used as the catalytic system no product was detected in
the absence of acidic additives, instead polymerization of
styrene occurred (Table 1, entry 1). In the presence of boric
acid, which should be one of the decomposition products or
arylboronic acids, 16% of 1,5-diphenylpent-1-en-3-one was
obtained. Other tested acids showed only traces of this de-
sired product (Table 1, entries 2–6). However, to our delight
80% of 1,5-diphenylpent-1-en-3-one was formed when
1 mmol of TsOH·H2O was added to the solution (Table 1,
entry 7). An almost quantitative yield (>95%) was obtained
by decreasing the amount of TsOH·H2O to 0.5 mmol
(Table 1, entries 8–10). Noteworthy, no regioisomers, which
might result from a head-to-tail carbonylative dimerization,
[a] Dr. X.-F. Wu
Department of Chemistry
Zhejiang Sci-Tech University
Xiasha Campus, Hangzhou, 310018 Zhejiang Province (Peopleꢀs Re-
public of China)
[b] Dr. X.-F. Wu, Dr. H. Neumann, Prof. Dr. M. Beller
Leibniz-Institut fꢁr Katalyse e.V. an der Universitꢂt Rostock
Albert-Einstein-Strasse 29a, 18059 Rostock (Germany)
Fax : (+49)381-1281-5000
E-mail: matthias.beller@catalysis.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100836.
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COMMUNICATION
Table 1. Pd-catalyzed carbonylative synthesis of 1,5-diphenylpent-1-en-3-
one: The influence of acid co-catalysts.[a]
en), DPEphos (bis(2-diphenylphosphinophenyl)ether), PPh3,
PCy3, P(o-tolyl)3) gave even a trace of product, except in
AHCTUNGTRENNUNG
the presence of dppm where the product was obtained in
16% yield.
Moreover, the influence of solvents was examined
(Table 2). Using N,N-dimethylformamide (DMF) or N-
methyl-2-pyrrolidinone (NMP) gave moderate yields, while
Entry
Additive
Yield [%][b]
1
–
0
2
3
4
5
6
7
8
9
10
11
12
13
14
B(OH)3 (1 mmol)
AcOH (1 mmol)
TFA (1 mmol)
16
<1
<1
<1
<1
80
99
65
33
Table 2. Pd-catalyzed carbonylative synthesis of 1,5-diphenylpent-1-en-3-
one: Variation of solvents, temperature, and pressure.[a]
KH2PO4 (1 mmol)
K2HPO4 (1 mmol)
TsOH·H2O (1 mmol)
TsOH·H2O (0.5 mmol)
TsOH·H2O (0.2 mmol)
TsOH·H2O (0.1 mmol)
TsOH·H2O (1 mmol)
TsOH·H2O (1 mmol)
TsOH·H2O (0.5 mmol)
TsOH·H2O (0.5 mmol)
Entry
Solvent
Yield [%][b]
0[c]
0[d]
92[e]
89[f]
1
2
3
4
5
6
7
8
DMF
NMP
43
78
24
2
1,4-dioxane
Toluene
CH3CN
THF
DMSO
DMSO
8
[a] PdACHTUNGTRENNUNG(OAc)2 (0.02 mmol), dppp (0.02 mmol), DMSO (2 mL), styrene
(2 mmol), additive, CO (5 bar), air (5 bar), 608C, 16 h. [b] Yield was de-
termined by GC using hexadecane as an internal standard based on
1 mmol of styrene. [c] No PdACTHNUTRGNE(UGN OAc)2 was used. [d] No dppp was used.
53
31[c]
33[d]
[e] An atmospheric pressure of air. [f] The reaction was performed under
argon. TFA=trifluoroacetic acid; TsOH·H2O=para-toluenesulfonic acid
monohydrate.
[a] PdACTHUNGRTENUNG(OAc)2 (0.02 mmol), dppp (0.02 mmol), solvent (2 mL), styrene
(2 mmol), TsOH·H2O (0.5 mmol), CO (5 bar), 608C, 16 h. [b] Yield was
determined by GC using hexadecane as an internal standard based on
1 mmol of styrene. [c] 258C. [d] CO (1 bar).
in toluene and CH3CN even lower reactivity is observed
(Table 2, entries 1–6). Notably, in the case of CH3CN a sig-
nificant amount of N-(1-phenylethyl)acetamide resulting
from a Ritter amidation reaction was formed.[10] The tem-
perature and the pressure of CO proved to be also crucial
for the selective carbonylative dimerization. Hence, at room
temperature or at 1 bar of carbon monoxide significantly
lower yields (31–33%) of the product were formed (Table 2,
entries 7–8).
Based on our experiments and the known mechanistic
studies of palladium-catalyzed olefin/CO copolymeriza-
tions,[3–5] a possible reaction mechanism is proposed in
Scheme 3. In the first step, formation of the active palladium
hydride complex should occur followed by coordination and
insertion of the alkene. Subsequent insertion of CO into the
palladium alkyl bond forms the corresponding palladium
acyl complex. Then, coordination and reaction with a
second alkene molecule takes place. Finally, the terminal
product is formed by b-hydride elimination to generate the
active palladium hydride complex for the next catalytic
cycle.
Next, the generality of this reaction was investigated. As
shown in Table 3, the carbonylative dimerization of 14 dif-
ferent styrenes proceeded with good to excellent yields (78–
97%). Para-, ortho-, and meta-alkyl-substituted styrenes
were smoothly transformed into the corresponding ketones
in good yields using 2 mol% of palladium catalyst (with re-
spect to olefin) (Table 3, entries 2–5). Both fluoride- and
chloride-substituted styrenes also dimerized well (Table 3,
entries 7–12). Styrenes with strong electron-withdrawing
Scheme 3. Proposed reaction mechanism.
are observed. As presumed, no conversion was obtained in
the absence of PdACHTUNGTRENNUNG(OAc)2 or the ligand dppp (Table 1, en-
tries 11 and 12). On the other hand, 89% of 1,5-diphenyl-
pent-1-en-3-one is produced in the absence of air (Table 1,
entry 14). As expected no oxidation reagents are necessary
in this reaction.
Next, ten different mono- and bidentate phosphines were
tested as ligands under the standard conditions (see Table 1,
entry 8). Interestingly, none of the other tested ligands such
as dppb (1,3-bis(diphenylphosphino)butane), dppm (bis(di-
phenylphosphino)metahne), dppe (1,2-bis(diphenylphosphi-
no)ethane), dpppe (1,5-bis(diphenylphosphino)pentane),
Xantphos (9,9-dimethyl-4,5-bis(diphenylphosphanyl)xanth-
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Carbonylative Dimerization of Styrenes
Table 3. Pd-catalyzed carbonylative synthesis of 1,5-diarylpent-1-en-3-
ones.[a]
failed to undergo carbonylative dimerization under the stan-
dard conditions.
Obviously, from a synthetic point of view, it is more
useful if the reaction can be carried out with two different
aromatic olefins. Indeed, as shown in Scheme 4 nonsymmet-
rical dimerizations of fluorinated styrenes with an excess of
styrene proceeded well. In addition to the cross dimeriza-
tion, the excess of the styrene underwent self-dimerization.
Unfortunately, chromatographic separation of the nonsym-
metrical products from the carbonylative self-dimerization
product 1,5-diphenylpent-1-en-3-one was not possible be-
cause of the similar polarity of the products.
In conclusion, the first general procedure for the carbony-
lative dimerization of aromatic olefins has been developed.
A Pd/dppp catalytic system in the presence of TsOH·H2O as
an acid co-catalyst is crucial for successful coupling. Starting
from commercially available styrenes, symmetrical 1,5-diary-
lpent-1-en-3-ones were produced in good yields.
Entry
1
Product
Yield [%][b]
92
2
3
4
5
89[c]
78[c]
88[c]
80[c]
6
7
82[c]
95
8
90
91
90
92
97
Scheme 4. Pd-catalyzed carbonylative reaction of two styrenes. PdACHTUNGTRENNUNG(OAc)2
9
(0.02 mmol), dppp (0.02 mmol), DMSO (2 mL), styrene (2 mmol), alkene
(1 mmol), TsOH·H2O (0.5 mmol), CO (5 bar), 608C, 16 h. Yields were
determined by GC, based on alkene.
10
11
12
Experimental Section
Typical reaction procedure for the synthesis of 1,5-diphenylpent-1-en-3-
one
A 4 mL vial was charged with PdACTHNUTRGNE(NUG OAc)2 (0.02 mmol), dppp (0.02 mmol),
TsOH·H2O (0.5 mmol), and a stirring bar. Then, DMSO (2 mL) and
2 mmol of styrene were added by syringe under air. The vial (or several
vials) was placed in an alloy plate, which was transferred into a 300 mL
autoclave of the 4560 series from Parr Instruments under an atmosphere
of air. Then, a pressure of 5 bar of CO was adjusted at ambient tempera-
ture. The reaction was performed for 16 h at 608C. After the reaction is
finished, the autoclave was cooled down to room temperature and the
pressure was released carefully. The cooled mixture was partitioned be-
tween ethyl acetate and saturated NH4Cl. The organic layer was washed
with brine, dried over Na2SO4, and concentrated in vacuo. The residue
was purified by column chromatography on silica gel using n-heptane/
AcOEt (40:1) as an eluent, thus providing the desired product in 92%
yield.
13
90
91
14
[a] PdACHTUNGTRENNUNG(OAc)2 (0.02 mmol), dppp (0.02 mmol), DMSO (2 mL), styrenes
(2 mmol), TsOH·H2O (0.5 mmol), CO (5 bar), 608C, 16 h. [b] Isolated
yield. [c] Pd(OAc)2 (0.04 mmol), dppp (0.04 mmol).
ACHTUNGTRENNUNG
Typical reaction procedure for the synthesis of nonsymmetric 1,5-
diarylpent-1-en-3-ones
groups on the arene ring also gave the desired products in
excellent yields under our standard conditions (Table 3, en-
tries 13 and 14). However, 4-nitrostyrene gave no desired
product and unfortunately, both vinyl ethers and acrylates
A 4 mL vial was charged with PdACTHNUTRGNE(NUG OAc)2 (0.02 mmol), dppp (0.02 mmol),
TsOH·H2O (0.5 mmol), and a stirring bar. Then, DMSO (2 mL), 2 mmol
of styrene, and 1 mmol of a second aromatic olefin were added by syringe
under an atmosphere of air. The vial (or several vials) was placed in an
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M. Beller et al.
COMMUNICATION
alloy plate, which was transferred into a 300 mL autoclave of the 4560
series from Parr Instruments under an atmosphere of air. Then, a pres-
sure of 5 bar of CO was adjusted at ambient temperature. The reaction
was performed for 16 h at 608C. After the reaction is finished, the auto-
clave was cooled down to room temperature and the pressure was re-
leased carefully. Hexadecane (0.1 mmol) was added as an internal stan-
dard, after thorough mixing with reaction mixture, an aliquot of the solu-
tion was taken for GC and GC-MS analysis. The yield of the nonsymmet-
rical products was calculated based on a response factor of 1,5-diphenyl-
pent-1-en-3-one.
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Acknowledgements
The authors thank the state of Mecklenburg-Vorpommern and the Bun-
desministerium fꢁr Bildung und Forschung (BMBF) for financial support.
We also thank Dr. W. Baumann, and Dr. C. Fischer (all LIKAT) for ana-
lytical support.
Keywords: carbonylation · dimerization · oxo reaction ·
palladium · styrene
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Received: October 7, 2011
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COMMUNICATION
Carbonylative Dimerization
X.-F. Wu, H. Neumann,
M. Beller*
&&& — &&&
Palladium-Catalyzed Carbonylative
Dimerization of Styrenes to 1,5-Diary-
lpent-1-en-3-ones
A general palladium-catalyzed carbon-
ylative dimerization of styrenes has
been developed. Starting from com-
mercial available styrenes, symmetrical
1,5-diarylpent-1-en-3-ones were pro-
duced in good to excellent yields (see
scheme; dppp=1,3-bis(diphenylphos-
phino)propane).
Chem. Asian J. 2012, 00, 0 – 0
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