Nickel-Catalyzed CO2Rearrangement of Enol Metal Carbonates for the Efficient Synthesis of β-Ketocarboxylic Acids

Article abstract of DOI:10.1002/anie.201609338

4-Methylene-1,3-dioxolan-2-ones underwent oxidative addition of a Ni⁰catalyst in the presence of Me₂Al(OMe), followed by a coupling reaction with alkynes, to form δ,?-unsaturated β-ketocarboxylic acids with high regio- and stereoselectivity. The reaction proceeds by [1,3] rearrangement of an enol metal carbonate intermediate and the formal reinsertion of CO₂.

Full text of DOI:10.1002/anie.201609338

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201609338
German Edition: DOI: 10.1002/ange.201609338
Multicomponent Coupling
Nickel-Catalyzed CO Rearrangement of Enol Metal Carbonates for
2
the Efficient Synthesis of b-Ketocarboxylic Acids
Ryo Ninokata, Tatsuya Yamahira, Gen Onodera, and Masanari Kimura*
0
Abstract: 4-Methylene-1,3-dioxolan-2-ones underwent oxida-
with alkynes and Me Al(OMe) in the presence of a Ni
2
0
tive addition of a Ni catalyst in the presence of Me Al(OMe),
catalyst. This reaction directly provides d,e-unsaturated b-
2
followed by a coupling reaction with alkynes, to form d,e-
unsaturated b-ketocarboxylic acids with high regio- and
stereoselectivity. The reaction proceeds by [1,3] rearrangement
of an enol metal carbonate intermediate and the formal
reinsertion of CO2.
ketocarboxylic acids under a N atmosphere without decarb-
oxylation occurring.
2
The reaction was examined with the catalyst [Ni(cod) ],
2
1,3-dioxolan-2-one 1a, and 4-octyne by treatment with
Me Al(OMe) at 608C under a N atmosphere in a wide
2
2
variety of solvents (Table 1). Nonpolar solvents, such as
b-Ketocarboxylic acids are useful and valuable key
For example, crassulacean acid metabolism (CAM) is an
[1]
intermediates en route to biologically active molecules.
Table 1: Coupling of cyclic carbonate 1a with 4-octyne and Me Al-
2
[a]
(OMe).
important carbon-resource-utilization process in the photo-
synthesis of oxaloacetate from CO by pyruvate carboxylase
2
[
2]
of green plants. However, as b-ketocarboxylic acids are
thermodynamically unstable, many problems, such as the
ready extrusion of CO by decarboxylation processes, often
2
[
b]
[
3]
Entry
Solvent
Product(s) (yield [%] )
arise. Although metal enolates are highly reactive and
convenient nucleophilic intermediates for the synthesis of
carbonyl compounds, little attention has been focused on the
1
2
3
4
5
6
7
8
hexane
toluene
DME
dioxane
THF
DMA
DMF
DMSO
DMSO
trace
2a (20)
trace
2a (10)
trace
2a (34)
2a (27)
2a (70)
2a (82), 3a (14)
[4]
fixation of CO by metal enolates.
2
1
,3-Dioxolan-2-ones are among the most important
industrial materials, for example, as electrolytes in lithium-
ion-battery half-cells and as predominant monomers for
[
5]
polycarbonates. Although cyclic carbonates are utilized as
fine chemicals and as monomers for polymerization in
modern industrial synthesis, most synthetic applications of
[
c]
9
[a] Reaction conditions: 1a (1.0 mmol), 4-octyne (1.0 mmol), Me Al-
2
[
6]
1
,3-dioxolan-2-ones face difficulties due to decarboxylation.
Nickel-catalyzed CÀC bond transformations are powerful
(
OMe) (1.2 mmol), [Ni(cod) ] (0.1 mmol), solvent (3 mL), 608C, 24 h,
nitrogen atmosphere. [b] Yield of the isolated product. [c] The reaction
was carried out with 1a (1.2 mmol), 4-octyne (1.0 mmol), and Me Al-
(OMe) (1.2 mmol) in the presence of [Ni(cod) ] (0.05 mmol). cod=1,5-
cyclooctadiene, DMA=N,N-dimethylacetamide, DME=1,2-dimethoxy-
ethane, DMF=N,N-dimethylformamide, DMSO=dimethyl sulfoxide.
2
[
7]
tools in modern organic synthesis. Insertion reactions of
CO2, reductive coupling with alkynes and enones, and
multicomponent coupling reactions with unsaturated hydro-
2
[8]
[9]
2
[
10]
carbons
are extremely attractive methods for efficient
organic synthesis. Recently, we developed a nickel-catalyzed
multicomponent coupling of diketene and alkynes with
organometallic reagents to provide unsaturated carboxylic
hexane, toluene, and cyclic ethers were ineffective, with the
desired product 2a obtained in low yields and most of
substrate 1a remaining (Table 1, entries 1–5). Among aprotic
polar solvents, DMSO was especially efficient and afforded
2a in 82% yield, along with ketone 3a as a minor product,
[
11]
acids and phenylacetic acids. In that case, the combination
of a Ni catalyst and Et Al(OEt) had a very important role in
2
promoting the C=C double-bond cleavage of diketene to
enable reconstruction of the molecular framework through
cycloaddition and migratory processes.
even in the presence of 5 mol% of the [Ni(cod) ] catalyst
2
(Table 1, entry 9).
Herein, we disclose a highly efficient method for the
synthesis of b-ketocarboxylic acids from 4-methylene-1,3-
We screened a number of organometallic reagents for this
reaction (Table 2). In the presence of 5 mol% of [Ni(cod) ],
2
dioxolan-2-one as a CO and enolate equivalent, by treatment
a mixture of the cyclic carbonate 1a, 4-octyne, and Me B
2
3
underwent the coupling reaction at 608C in DMSO to give the
expected b-ketocarboxylic acid 2a in 18% yield, along with
the decarboxylated product 3a in 70% yield (Table 2,
[
*] R. Ninokata, T. Yamahira, Dr. G. Onodera, Prof. Dr. M. Kimura
Graduate School of Engineering, Nagasaki University
Bunkyo-machi 1-14, Nagasaki 852-8521 (Japan)
E-mail: masanari@nagasaki-u.ac.jp
entry 1). When Me Zn or Me Al was used, the desired
2
3
product 2a was obtained in 65 and 73% yield, respectively
entries 2 and 3). Me Al(OMe) was the most efficient
(
Supporting information for this article can be found under:
http://dx.doi.org/10.1002/anie.201609338.
2
organometallic reagent for the desired coupling reaction
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1
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[
a]
Table 2: Coupling of cyclic carbonate 1a with 4-octyne and an organo-
metallic reagent.
Table 3: Coupling of cyclic carbonates with 3-hexyne and Me Al(OMe).
2
[
a]
[
b]
Entry
RnM
Products (yield [%] )
1
2
3
4
5
6
Me3B
2a (18), 3a (70)
2a (65), 3a (19)
2a (73), 3a (21)
2a (82), 3a (14)
complex mixture
complex mixture
[
b]
Entry
Cyclic carbonate
Products (yield [%] )
Me Zn
2
Me Al
1
2
3
1
2
R =Me, R =Me (1a)
2c (79), 3c (13)
2h (52), 3h (35)
2i (15), 3i (72)
2j (60), 3j (25)
Me Al(OMe)
1
2
2
R =Me, R =Et (1h)
Et Al
[c]
1
2
3
3
4
R =Me, R =Ph (1i)
Et Al(OEt)
2
[c]
1
2
R =H, R =H (1j)
[
c]
c]
1
2
5
6
R =H, R =Me (1k)
2k (45), 2’k (18), 3k (11), 3’k (9)
2l (38), 2’l (12), 3l (36), 3’l (5)
[a] Reaction conditions: 1a (1.2 mmol), 4-octyne (1.0 mmol), organo-
[
1
2
R =H, R =Ph (1l)
metal (1.2 mmol), [Ni(cod) ] (0.05 mmol), DMSO (3 mL), 608C, 24 h,
2
nitrogen atmosphere. [b] Yield of the isolated product.
[
a] Reaction conditions: 1 (1.2 mmol), 3-hexyne (1.0 mmol), Me Al-
2
(
OMe) (1.2 mmol), [Ni(cod) ] (0.05 mmol), DMSO (3 mL), 608C, 24 h,
2
nitrogen atmosphere. [b] Yield of the isolated product. [c] b-Ketocar-
boxylic acids 2 and 2’ were isolated as the methyl ester by treatment of
the products with trimethylsilyldiazomethane.
(
entry 4). In contrast, Et Al and Et Al(OEt) were not
3 2
effective at promoting the coupling reaction with ethyl-
group insertion, thus resulting in complex mixtures (Table 2,
entries 5 and 6).
Next, we investigated the reaction of cyclic carbonate 1a
with various kinds of alkynes (Scheme 1). The symmetrical
(Table 3). The unsymmetrical 5-disubstituted carbonate 1h
1
2
(R = Me, R = Et) was converted into the unsymmetrical a-
disubstituted b-keto acid 2h as the major product, as well as
ketone 3h (Table 3, entry 2). The phenyl- and methyl-
substituted cyclic carbonate 1i was transformed into b-keto
acid 2i in low yield as a mixture with ketone 3i (entry 3). The
1
2
unsubstituted cyclic carbonate 1j (R = H, R = H) underwent
a similar coupling reaction to give a mixture of b-keto acid 2j
with ketone 3j as a minor product (entry 4). In the case of the
1
2
monosubstituted carbonate 1k (R = H, R = Me), a mixture
of regioisomers of a-methyl-b-keto acid 2k and g-methyl-b-
keto acid 2’k were produced in 63% yield in an approximately
3
2
:1 ratio, along with a small amount of ketone 3k and 3’k in
0% combined yield (entry 5). Apparently, the correspond-
ing 5-phenyl-substituted carbonate underwent the decarbox-
ylation to some extent (entry 6). The ratios of b-keto acid 2
and ketone 3 might depend on the stability of the key metal
1
enolate intermediate, as well as the steric bulk of the R and
R groups.
Although it would be premature to provide a complete
explanation of the reactivities and selectivities described
herein, a plausible mechanism for the multicomponent
coupling reaction of 5-substituted 4-methylene-1,3-dioxolan-
Scheme 1. Coupling of cyclic carbonate 1a with various alkynes and
2
the methylaluminum reagent Me Al(OMe). Reaction conditions: 1a
2
(
1.2 mmol), alkyne (1.0 mmol), Me Al(OMe) (1.2 mmol), [Ni(cod) ]
2 2
(
0.05 mmol), DMSO (3 mL), 608C, 24 h, nitrogen atmosphere. Yields
are for the isolated product. [a] The ratio shows the regioselectivity
with respect to the alkyne substituents. TMS=trimethylsilyl.
2
-ones with alkynes promoted by the Ni catalyst and Me Al-
2
(
OMe) is proposed in Scheme 2. Thus, oxidative addition of
0
alkynes 2-butyne, 3-hexyne, and 5-decyne reacted smoothly
the cyclic carbonate to the Ni catalyst at the allylic position,
with cyclic carbonate 1a in the presence of Me Al(OMe) to
as promoted by Me Al(OMe) as a Lewis acid, gives the
2
2
provide the corresponding b-ketocarboxylic acids 2b–d in
good yields (Scheme 1). In the case of the unsymmetrical
alkynes 4-methyl-2-pentyne, 1-trimethylsilyl-1-propyne, and
oxanickelacycle intermediate I, the stability of which seems to
depend on the substituents at the 5-position. Metallacycle I
readily isomerizes to the more stable nickelacycle III through
[
12]
1
-phenyl-1-propyne, the corresponding b-ketocarboxylic
s–p–s allylnickel interconversion.
The insertion of an
acids 2e–g were obtained in modest to good yields. The less
hindered substituted acetylenic carbon atom tended to attack
the methylene carbon atom of the carbonate. b-Keto acids 2e
and 2 f were obtained as a mixture of regioisomers, whereas
alkyne proceeds to form an eight-membered oxanickelacycle
intermediate V, which then undergoes transmetalation with
[
2e,13]
Me Al(OMe) to form an enol aluminum carbonate VII.
2
This enol metal carbonate VII readily undergoes [1,3]
[
14]
2
g was obtained as a single isomer.
rearrangement to afford a b-ketocarboxylic acid, followed
0
We examined the reaction of 3-hexyne with cyclic
by reductive elimination to generate a catalytically active Ni
carbonates containing different substituents at the 5-position
species.
2
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Acknowledgements
We gratefully acknowledge funding from Grants-in-Aid for
Scientific Research (B; 26288052) from the Ministry of
Education, Culture, Sports and Technology (MEXT), Japan.
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[12] In entries 5 and 6 of Table 3, a regioisomeric mixture of b-
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[14] For the [1,3] rearrangement of an enol zinc carbonate to provide
a b-ketocarboxylic acid, see: K. Kataoka, T. Tsuruta, Polym. J.
1977, 9, 595 – 604.
[
10] a) Y. Mori, T. Kawabata, G. Onodera, M. Kimura, Synthesis
016, 48, 2385 – 2395; b) Y. Ohira, T. Mori, M. Hayashi, G.
2
Onodera, M. Kimura, Heterocycles 2015, 90, 832 – 841; c) Y.
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d) T. Mori, Y. Mori, G. Onodera, M. Kimura, Synthesis 2014, 46,
Manuscript received: September 23, 2016
2287 – 2292; e) T. Mori, Y. Akioka, G. Onodera, M. Kimura,
Final Article published: && &&, &&&&
4
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Multicomponent Coupling
R. Ninokata, T. Yamahira, G. Onodera,
M. Kimura*
&&&& — &&&&
Let all the parts fall into place: A 4-Meth-
with high regio- and stereoselectivity (see
Nickel-Catalyzed CO Rearrangement of
Enol Metal Carbonates for the Efficient
Synthesis of b-Ketocarboxylic Acids
ylene-1,3-dioxolan-2-one underwent oxi-
dative addition to a Ni catalyst in the
scheme). The reaction proceeds via [1,3]
rearrangement of an enol metal carbon-
ate intermediate and the formal reinser-
tion of CO2.
2
0
presence of Me Al(OMe), followed by
2
a coupling reaction with alkynes to form
d,e-unsaturated b-ketocarboxylic acids
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!