Nickel-catalyzed intermolecular codimerization of acrylates and alkynes

Article abstract of DOI:10.1039/c0cc04061d

The linear codimerization of acrylates and alkynes to produce 1,3-dienes is successfully demonstrated using a nickel catalyst in association with 2-aminopyridine as an additive.

Full text of DOI:10.1039/c0cc04061d

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COMMUNICATION
Nickel-catalyzed intermolecular codimerization of acrylates and alkynesw
Hiroaki Horie, Ichiro Koyama, Takuya Kurahashi* and Seijiro Matsubara*
Received 24th September 2010, Accepted 9th December 2010
DOI: 10.1039/c0cc04061d
The linear codimerization of acrylates and alkynes to produce
1,3-dienes is successfully demonstrated using a nickel catalyst in
association with 2-aminopyridine as an additive.
Table 1 Codimerization between a methyl acrylate 1a and an
4-octyne 2a to afford a 1,3-diene 4aaa
Transition-metal-catalyzed cooligomerizations of alkynes and
alkenes that involves an s–p isomerization are powerful
methodologies for an efficient construction of complex
molecules from readily accessible starting materials.1
Therefore, development of cooligomerization has been a
research topic of great interest.2–5 Recently, we reported an
intermolecular cotrimerization of alkenes and alkynes by
tuning the nickel catalyst allowing access to 1,3-dienes
and 1,3,5-trienes. It was found that sterically hindered
N-heterocyclic carbene ligands (IPr) give 1,3-dienes
(Scheme 1b), while P(4-MeO–C6H4)3 gives 1,3,5-trienes
(Scheme 1c).6 Herein, we wish to report an unprecedented
nickel-catalyzed codimerization, which incorporates an
acrylate and an alkyne into a 1,3-diene (Scheme 1a).7–10
During the exploration of different cooligomerization
conditions, we found that on addition of 2-aminopyridine,
the reaction of methyl acrylate (1a) and 4-octyne (2a) affords
1,3-diene 4aa as a preferred product. The reaction of 1a and 2a
in the presence of N-methyl-2-aminopyridine 3a (20 mol%)
gave 4aa in 56% yield along with 5aa in 25% yield (Table 1,
Entry R (3)
Ligand Solvent
4aab/5aac yield (%)
1
2
Me (3a)
—
PCy3
PCy3
PBu3
PPh3
IPr
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
56/25
o5/39
d
3
4
5
6
Me (3a)
Me (3a)
Me (3a)
Ph (3b)
42/36
52/27
41/(24)e
95/o5
95/o5
91/o5
91/o5
PCy3
7
8
3-CF3–C6H4 (3c) PCy3
4-MeO–C6H4 (3d) PCy3
9
2-Me–C6H4 (3e)
Ph (3b)
Ph (3b)
PCy3
PCy3
PCy3
PCy3
10
11
12
1,4-Dioxane 87/o5
MeCN
Pyridine
80/o5
Ph (3b)
o5/o5
a
Reactions were carried out using Ni(cod)2 (10 mol%), ligand
(10 mol%), 2-aminopyridine 3 (20 mol%), 1 (0.6 mmol, 1.2 equiv.),
b
and 2 (0.5 mmol) in 5 mL of solvent at 100 1C for 24 h. NMR yields
based on 2 (0.5 mmol). NMR yields based on 2 (0.25 mmol). The
reaction was carried out without an addition of 2-aminopyridine
e
3. (2E,4Z)-Dimethyl-4,5-dipropylocta-2,4-dienedioate was obtained
c
d
in 24% yield as a minor product. For details, see ref. 6.
entry 1). While in the absence of 2-aminopyridine, the reaction
afforded 5aa in 39% yield as a sole product (entry 2). Among
phosphine ligands examined, PCy3 gave the best yield of 4aa
(entries 3 and 4). IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-
2-ylidene) afford 4aa in 41% yield (entry 5). It was found after
thorough screening that a N-aryl-2-aminopyridine is the most
effective for the selective codimerization to give 1,3-diene 4aa
(entry 6). Almost same results were obtained when trifluoro-
methyl-, methoxy- or methyl-substituted N-phenyl-2-amino-
pyridine was employed as an additive (entries 7–9). In other
solvents, such as 1,4-dioxane, MeCN, or pyridine, yields and
selectivity were even lower (entries 10–12).
Scheme
1 Nickel-catalyzed cooligomerization of acrylates and
alkynes.
Department of Material Chemistry, Graduate School of Engineering,
Kyoto University, Kyoto 615-8510, Japan.
E-mail: tkuraha@orgrxn.mbox.media.kyoto-u.ac.jp,
matsubar@orgrxn. mbox.media.kyoto-u.ac.jp;
Fax: +81 75 383 2461; Tel: +81 75 383 2462
The scope of the codimerization of various alkenes with
alkynes is briefly examined and summarized in Table 2. Under
the optimized reaction conditions, tert-butyl acrylate (1b) also
provides 1,3-diene 4ba in 92% yield (entry 2). The reaction
with unsymmetrical alkynes, such as 3-octyne and 2-octyne,
w Electronic supplementary information (ESI) available: Experimental
details and NMR spectra. See DOI: 10.1039/c0cc04061d
c
2658 Chem. Commun., 2011, 47, 2658–2660
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Table 2 Codimerization of acrylate 1 and alkyne 2a
nickelacyclopentene complex C, in which the steric repulsive
interaction is minimal between the bulkier RL and the PCy3
ligand on the nickel. b-Hydride elimination and reductive
elimination would afford 4 and regenerate the starting nickel(0).
It should be noted that 2-aminopyridines have lesser effects on
the regioselectivity of the reaction. The reaction of 1a and 2d with
various derivatives of aminopyridine in place of N-phenyl-2-
aminopyridine 3b was examined, and it was found that the
reaction afforded 1,3-diene 4ad consisting of regioisomers in 5/1
ratio (Table 3, entries 1–4). The phosphine ligands have more
influence on the regioselectivity of the reaction (entry 5).
Therefore, it might be reasonable to presume that N-phenyl-2-
aminopyridine has effects on the formation of intermediate A, but
not on the formation of intermediate B or intermediate C.
We next speculated that an assembly of two molecules of
acrylamide 6a in the coordination sphere of a nickel metal
center through hydrogen bonding (vide infra Scheme 3, A0),
also reacted with alkyne to provide a nickelacyclopentene
complex C0, and this led to selective codimerization of acryl-
amide 6a and alkyne 2a to furnish 1,3-diene 7aa. To test our
hypothesis, we examined a reaction of N-phenylacrylamide
(6a) and 4-octyne (2a) with Ni(cod)2/PCy3 catalyst, and found
that the reaction gave 1,3-diene 7aa in 77% yield (Scheme 4).
Considering that the reaction of N-methyl-N-phenylacrylamide
(6b) with 2a gave 1,3,5-triene 8ba exclusively via cotrimerization,
we suggest that the proton on the nitrogen atom of 6a may
contribute to form intermediate A0.
Entry 1 R1 (equiv.) 2 R2
R3
3
4
Yieldb (%)
1
2
1a Me (1.2) 2a Pr
1b tBu (1.2) 2a Pr
Pr
Pr
3b 4aa 95
3b 4ba 92
3
4
5
6
7
8
9
10
11
12
13
1a Me (1.2)
1a Me (1.2)
1a Me (1.2)
1a Me (1.2)
1a Me (1.2)
1a Me (1.2)
1a Me (2.0)
1a Me (2.0)
1a Me (2.0)
1a Me (2.0)
1a Me (2.0)
2b C5H11 C5H11
2c Bu Et
2d C5H11 Me
2d C5H11 Me
3b 4ab 90
3b 4ac 82 (1/1)c
3b 4ad 76 (5/1)c
3e 4ad 79 (5/1)c
3b 4ae 64 (10/1)c
3e 4ae 69 (10/1)c
3b 4af 58
2e iPr
2e iPr
2f Pr
2f Pr
Me
Me
Ph
Ph
3c 4af 62
2g C5H11 4-MeO–C6H4– 3c 4ag 87
3c 4ah 67
3c 4ai 53
2h C5H11 4-F–C6H4–
2i cPr Ph
a
Reactions were carried out using Ni(cod)2 (10 mol%), PCy3
(10 mol%), 3 (20 mol%), 1 (0.6 mmol, 1.2 equiv.), and 2 (0.5 mmol)
b
in 5 mL of toluene at 100 1C for 24 h. Isolated yields based on alkyne
2 (0.5 mmol). Ratio of isomers.
c
gave the 1,3-dienes consisting of regioisomers in a range of 1/1
to 5/1 ratio (entries 4–6), whereas the reaction of 4-methyl-2-
pentyne (2e) gave 4ae regioselectively (entries 7 and 8).
The codimerization reaction is also compatible with aryl-
substituted alkyne and afforded the corresponding 1,3-dienes
in good yields with excellent regioselectivities (entries 9–12).
Cyclopropyl-substituted alkyne 2i also reacted with 1a to
furnish 1,3-diene 4ai in 53% yield regioselectively (entry 13).
However, terminal alkynes, such as 1-octyne and phenyl-
acetylene, failed to participate in the reaction.
Indeed, a stoichiometric reaction of N-phenylacrylamide
(6a) with Ni(cod)2 and PCy3 gave an pseudodiene nickel
Table 3 Regioselectivity of the codimerization of 1a and 2da
A reaction pathway to account for the formation of
1,3-diene 4 based on the observed results is outlined in
Scheme 2. In view of the effects of 2-aminopyridine 3 on the
reaction, it is reasonable to consider that the catalytic cycle of
the present reaction may involve assembly of 2-aminopyridine
and acrylate 1 in the coordination sphere of a nickel metal
center through hydrogen bonding to form Ni(0) intermediate
A.11,12 Subsequent coordination of alkyne and dissociation of
2-aminopyridine affords Ni(0) intermediate B. Oxidative
cyclization of nickel(0) with an alkyne and an acrylate provides
Entry Ligand
3
Yieldb (%) (4ad/4ad0)c
1
2
3
PCy3
PCy3
PCy3
3b 76 (5/1)
3c 76 (5/1)
3d 73 (5/1)
4
PCy3
PPh3
3e 79 (5/1)
5
3f
40 (3/2)
a
Reactions were carried out using Ni(cod)2 (10 mol%), ligand
(10 mol%), additive (20 mol%), 1 (0.6 mmol, 1.2 equiv.), and 2d
b
(0.5 mmol) in 5 mL of solvent at 100 1C for 24 h. Isolated yields
based on 2d (0.5 mmol). Ratio of regioisomers.
c
Scheme 2 Plausible reaction pathway.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 2658–2660 2659

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crystal structure analysis. We also thank Prof. S. Ogoshi for
valuable discussions on the subject.
Notes and references
1 For pioneering works of ruthenium-catalyzed codimerization of
alkynes and alkenes, see: B. M. Trost and A. F. Indolese, J. Am.
Chem. Soc., 1993, 115, 4361. For reviews, see: (a) B. M. Trost,
F. D. Toste and A. B. Pinkerton, Chem. Rev., 2001, 101, 2067;
(b) B. M. Trost, M. U. Frederiksen and M. T. Rudd, Angew.
Chem., Int. Ed., 2005, 44, 6630.
2 For ruthenium-catalyzed codimerization of alkynes and alkenes to
provide 1,3-dienes, see: (a) T. Mitsudo, S.-W. Zhang, M. Nagao
and Y. Watanabe, J. Chem. Soc., Chem. Commun., 1991, 598;
(b) M. Murakami, M. Ubukata and Y. Ito, Tetrahedron Lett.,
1998, 39, 7361; (c) T. Nishimura, Y. Washitake and S. Uemura,
Adv. Synth. Catal., 2007, 349, 2563; (d) N. M. Neisius and
B. Plietker, Angew. Chem., Int. Ed., 2009, 48, 5752.
Scheme 3 Plausible reaction pathway.
3 For palladium-catalyzed codimerization and cotrimerization of
alkynes and alkenes to provide 1,3-dienes, see: (a) N. Tsukada,
H. Setoguchi, T. Mitsuboshi and Y. Inoue, Chem. Lett., 2006,
1164; (b) A. T. Lindhardt, M. L. H. Mantel and T. Skrydstrup,
Angew. Chem., Int. Ed., 2008, 47, 2668; (c) K. Itoh, K. Hirai,
M. Sasaki, Y. Nakamura and H. Nishiyama, Chem. Lett., 1981,
865; (d) L. Zhao and X. Lu, Org. Lett., 2002, 4, 3903;
(e) H. Horiguchi, K. Hirano, T. Satoh and M. Miura, Adv. Synth.
Catal., 2009, 351, 1431.
4 For rhodium-catalyzed codimerization of alkynes and alkenes to
provide 1,3-dienes, see: Y. Shibata, M. Hirano and K. Tanaka,
Org. Lett., 2008, 10, 2829.
5 For cobalt-catalyzed codimerization of alkynes and alkenes, see:
S. Mannathan and C.-H. Cheng, Chem. Commun., 2010, 46, 1923.
6 H. Horie, T. Kurahashi and S. Matsubara, Chem. Commun., 2010,
46, 7229.
7 For related Ni-catalyzed addition reaction of alkynes to carbon–
carbon unsaturated bonds, see: (a) M. Shirakura and M. Suginome,
J. Am. Chem. Soc., 2008, 130, 5410; (b) K. Ogata, H. Murayama,
J. Sugasawa, N. Suzuki and S. Fukuzawa, J. Am. Chem. Soc., 2009,
131, 3176; (c) M. Shirakura and M. Suginome, J. Am. Chem. Soc.,
2009, 131, 5060; (d) K. Ogata, J. Sugasawa and S. Fukuzawa, Angew.
Chem., Int. Ed., 2009, 48, 6078; (e) M. Shirakura and M. Suginome,
Org. Lett., 2009, 11, 523; (f) K. Ogata, J. Sugasawa, Y. Atsuumi and
S. Fukuzawa, Org. Lett., 2010, 12, 148; (g) M. Shirakura and
M. Suginome, Angew. Chem., Int. Ed., 2010, 49, 3827.
Scheme 4 Cooligomerization of acrylamide and alkyne.
complex A0 quantitatively. The molecular structure of A0 was
unambiguously confirmed by the X-ray crystal structure
analysis, which showed that two amides and one phosphine
ligand are coordinated to the nickel in a trigonal planar
arrangement (Fig. 1). A short intermolecular Nꢀ ꢀ ꢀO distance
(2.816 A) may indicate that two amides are intermolecularly
NHꢀ ꢀ ꢀOQC hydrogen-bonded, forming
a
pseudodiene
complex.13 It was also found that a stoichiometric reaction
of complex A0 with an equivalent of 2a in dioxane at 40 1C
afforded 1,3-diene 7aa in 43% yield.14
8 For Ni-catalyzed intramolecular codimerization, see: T. N.
Tekavec and J. Louie, Tetrahedron, 2008, 64, 6870.
In summary, we have developed a new nickel-catalyzed
codimerization of an acrylate and an alkyne to provide 1,3-
diene. We demonstrated for the first time that 2-aminopyridine
acts as a ligand and contributes for selective formation of
1,3-dienes via codimerization of an acrylate and an alkyne.
Furthermore, we discovered that two molecules of acrylamides
are able to form a pseudodiene complex with nickel(0); such a
complex allows exclusive intermolecular codimerization of an
acrylamide and an alkyne.
9 For related Ni-catalyzed cyclo-oligomerization, see: (a) S.-i. Ikeda,
N. Mori and Y. Sato, J. Am. Chem. Soc., 1997, 119, 4779; (b) N. Mori,
S.-i. Ikeda and Y. Sato, J. Am. Chem. Soc., 1999, 121, 2722; (c) J. Seo,
H. M. P. Chui, M. J. Heeg and J. Montgomery, J. Am. Chem. Soc.,
1999, 121, 476; (d) S. Ogoshi, A. Nishimura and M. Ohashi, Org. Lett.,
2010, 12, 3450.
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D. K. Rayabarapu and C.-H. Cheng, J. Org. Chem., 1999, 64,
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and T. Hiyama, J. Am. Chem. Soc., 2009, 131, 15996; (e) S. Ogoshi,
A. Nishimura, T. Haba and M. Ohashi, Chem. Lett., 2009, 1166.
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Soc., 2006, 128, 4188; (c) I. Usui, S. Schmidt, M. Keller and
B. Breit, Org. Lett., 2008, 10, 1207.
This work was supported by Grants-in-Aid from MEXT,
Japan. T.K. also acknowledges Asahi Glass Foundation,
Kansai Research Foundation and Mizuho Foundation for
the Promotion of Sciences. We thank Dr T. Fujihara for X-ray
12 (a) T. Yamamoto, K. Igarashi, J. Ishizu and A. Yamamoto, J. Chem.
Soc., Chem. Commun., 1979, 554; (b) T. Yamamoto, K. Igarashi,
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14 The reaction of 6a (0.40 mmol) and 2a (0.60 mmol) in the presence
of catalytic amount of the nickel complex A0 (0.05 mmol) in
dioxane (80 1C) also afforded 7aa in 77% yield.
Fig. 1 ORTEP drawing of A0.
c
2660 Chem. Commun., 2011, 47, 2658–2660
This journal is The Royal Society of Chemistry 2011