Nickel-catalyzed reactions between enone and two ethylenes

Article abstract of DOI:10.1246/cl.2009.1166

In the presence of a catalytic amount of Ni(cod)2 and PCy3, the reaction of (E)-l-phenylbut-2-en-l-one (la) with ethylene occurred to give three-component addition products, 1,6-enone 2a and 1,5-diketone 4a. The reaction of an enone with two ethylenes gav

Full text of DOI:10.1246/cl.2009.1166

1166
Chemistry Letters Vol.38, No.12 (2009)
Nickel-catalyzed Reactions between Enone and Two Ethylenes
Sensuke Ogoshi,ꢀ Akira Nishimura, Toshifumi Haba, and Masato Ohashi
Department of Applied Chemistry, Faculty of Engineering, Osaka University,
2-1 Yamadaoka, Suita, Osaka 565-0871
(Received September 14, 2009; CL-090826; E-mail: ogoshi@chem.eng.osaka-u.ac.jp)
In the presence of a catalytic amount of Ni(cod)2 and PCy3,
Table 1.
the reaction of (E)-1-phenylbut-2-en-1-one (1a) with ethylene
occurred to give three-component addition products, 1,6-enone
2a and 1,5-diketone 4a. The reaction of an enone with two ethyl-
enes gave 2a. The reaction of two enones with an ethylene gave
4a. On the other hand, 2-methyl-1-phenylprop-2-en-1-one (1b)
reacted with two ethylenes selectively to give a mixture of 2b
and 3b. The reaction might proceed via oxidative cyclization
of an enone and an ethylene with nickel(0).
10 mol%
Ni(cod)2/4PCy3
O
+
Ph
C6D6 or toluene
1a
O
O
O
O
Ph
Ph
+
+
Ph
Ph
2a
3a
4a
Yield/%
Run
Ethylene
Temp/ꢁC
Time/h
2a
3a
4a
1a
2a
3a
4b
5 atm
5 atm
8 atm
25
80
80
100
72
17
17
15
7
20
30
43
—
3
5
18
41
19
18
13
Ethylene is an important industrial feedstock and numerous
reactions have been developed to convert ethylene into more
valuable chemicals. The hydrovinylation reaction of alkenes
catalyzed by transition metal hydride complexes is one of the
most useful reactions for the introduction of ethylene into al-
kenes, however, a limited number of alkenes, such as vinylar-
enes, cyclic dienes, and norbornenes, are available for hydrovi-
nylation reactions due to the isomerization of terminal alkenes
to internal alkenes (eq 1).1 During the due course of the present
study of the formation of hetero-nickelacycles by oxidative
cyclization,2 we found nickel-catalyzed direct conjugate addi-
tion reactions of simple alkenes to enones, which is a very
straightforward method to introduce an alkenyl group to the
ꢀ-carbon of enones by the addition of a carbon–hydrogen bond
(eq 2).3,4 In this reaction, the oxidative cyclization of alkenes
and enones with nickel(0) to give a nickelacycle was proposed
as an important key reaction step. On the other hand, in the
presence of a nickel catalyst, the reaction of enones with al-
kynes to give three-component cycloaddition has been reported
(eq 3). Ikeda et al. reported nickel-catalyzed reactions of an
enone with two alkynes to give cyclohexadiene derivatives.5
Montgomery et al. reported nickel-catalyzed intramolecular
reactions of an alkyne and two enones to give cyclohexene
derivatives.6 In a similar reaction with alkenes, Hoberg et al.
have reported a nickel-catalyzed three-component addition
of a phenyl isocyanate with two ethylenes.7 Jamison et al. have
reported a nickel-catalyzed reaction of enoes with ethylene in
the presence of Et3SiOTf.4 However, the three-component
30 atm
a[1] = 0.4 M, C6D6, NMR yield. b[1] = 0.04 M, toluene, isolat-
ed yield.
addition of enones with alkenes to give terminal alkenes has not
been reported yet.8 Here, we report a nickel-catalyzed three-
component addition reaction of enones with ethylene.
In the presence of Ni(cod)2 and PCy3, the reaction of (E)-1-
phenylbut-2-en-1-one (1a) with ethylene (5 atm) at 25 ꢁC in
C6D6 gave a mixture of 1,6-enone 2a and 1,5-diketone 4a
(Table 1, Run 1).9 Both products were three-component addition
compounds. 2a was the product of an enone and two ethylenes.
On the other hand, 4a was the product of two enones and an eth-
ylene. At higher reaction temperature, the yields of 2a and its
isomer 3a increased and the yield of 4a decreased (Run 2). At
higher ethylene pressure (8 atm), the yield of 2a was improved
(Run 3). To attain selective formation of 2a and 3a, the reaction
was carried out under a much higher ethylene pressure (30 atm)
at lower concentration of 1a (0.04 M). A mixture of 2a, 3a, and
4a was obtained in 74% isolated yield, and the selectivity of 2a
and 3a toward 4a was also improved (Run 4). Under similar re-
action conditions, 2-methyl-1-phenylprop-2-en-1-one (1b) also
reacted with two ethylenes to give 2b and 3b in 65 and 9% iso-
lated yield, respectively (eq 4). In this reaction, the 1,5-diketone
product 4b was not obtained at all, which might be due to the
10 mol%
Ni(cod)2/4PCy3
cat. M-H
O
+
+
ð1Þ
ð2Þ
R
+
Ph
R
R
toluene, 100 °C, 18 h
1b
0.08 M
30 atm
O
cat. Ni(0)
O
+
R
R
O
O
O
O
ð4Þ
Ph
Ph
+
Ph
Ph
+
O
O
O
cat. Ni(0)
O
+
ð3Þ
2b
65%
3b
9%
4b
-
Copyright Ó 2009 The Chemical Society of Japan

Chemistry Letters Vol.38, No.12 (2009)
1167
A might be less reactive due to steric hindrance around the eno-
late carbon.
H
+
O
Ni(0)
H
In conclusion, the reaction of an enone with two ethylenes to
give a 1,6-enone was demonstrated for the first time. This reac-
tion can be regarded as a cross-trimerization of alkenes with eth-
ylene to give a terminal alkene. Moreover, at a lower tempera-
ture, the reaction of two enones with an ethylene gave a 1,5-di-
ketone compound as the major product. In both reactions, ethyl-
ene reacted with an enone as a vinylation reagent.
O
B
Ni(0)
(not observed)
H
H
Ni
Ni
Ni
A
O
O
H
O
This work was supported by a Grant-in-Aid for Scientific
Research (Nos. 21245028 and 21750102) and a Grant-in-Aid
for Scientific Research on Priority Areas (No. 19028038, Chem-
istry of Concerto Catalysis) from the Ministry of Education, Cul-
ture, Sports, Science and Technology, Japan.
H
O
O
H
H
O
References and Notes
1
Ni
Ni
C
F
T. V. RajanBabu, Chem. Rev. 2003, 103, 2845, and refer-
ences cited therein.
O
O
2
S. Ogoshi, M. Oka, H. Kurosawa, J. Am. Chem. Soc. 2004,
126, 11802; S. Ogoshi, M. Ueta, T. Arai, H. Kurosawa,
J. Am. Chem. Soc. 2005, 127, 12810; S. Ogoshi, K.-I.
Tonomori, M.-A. Oka, H. Kurosawa, J. Am. Chem. Soc.
2006, 128, 7077; S. Ogoshi, H. Ikeda, H. Kurosawa, Angew.
Chem., Int. Ed. 2007, 46, 4930; S. Ogoshi, T. Arai, M.
Ohashi, H. Kurosawa, Chem. Commun. 2008, 1347.
S. Ogoshi, T. Haba, M. Ohashi, J. Am. Chem. Soc. 2009, 131,
10350.
A nickel-catalyzed reaction of enones with ethylene in the
presence of a trialkylsilyl triflate and triethylamine to give
corresponding silyl ethers incorporating one ethylene mole-
cule: C.-Y. Ho, H. Ohmiya, T. F. Jamison, Angew. Chem.,
Int. Ed. 2008, 47, 1893.
O
Ni
or
Ni
Ni
H
O
O
H
O
O
H
Ni(0)
Ni(0)
O
O
3
4
H
H
H
G
D
E
Scheme 1. A plausible mechanism.
reduced reactivity of the intermediate toward 1b (see later).
Under the same reaction conditions, methyl vinyl ketone, or
phenyl vinyl ketone underwent oligomerization. Neither chal-
cone nor 3-penten-2-one reacted changed.
5
S. Ikeda, N. Mori, Y. Sato, J. Am. Chem. Soc. 1997, 119,
4779; N. Mori, S. Ikeda, Y. Sato, J. Am. Chem. Soc. 1999,
121, 2722.
The reaction might proceed as follows (Scheme 1). The ox-
idative cyclization of an enone and ethylene with a nickel(0) spe-
cies generates a ꢁ3-oxaallylnickelacycle intermediate A. The
intramolecular oxidative cyclization of an enone and an alkene
with nickel(0) to give the corresponding nickelacycle has been
reported.3 ꢀ-Hydrogen elimination of A followed by reductive
elimination would give the direct conjugate addition product B
as reported in the reaction with styrene under the same reaction
conditions;3 however, no direct conjugate addition product was
obtained in the reaction with ethylene. Only three-component
addition products were obtained. Therefore, the reaction of ꢁ3-
oxaallylnickelacycle intermediate A with either the second eth-
ylene or the second enone to generate a seven-membered nick-
elacycle intermediate C10 or F might proceed faster than the oc-
currence of ꢀ-hydrogen elimination to give B. The intermediate
C might undergo ꢀ-elimination followed by reductive elimina-
tion to give a mixture of a 1,6-enone compound D and its isomer-
ic 1,2-enone E. The conjugate addition of A to an enone also
generates a seven-membered nickelacycle intermediate F12 fol-
lowed by ꢀ-elimination and reductive elimination to give a
1,5-diketone G. As shown in eq 4, 4b was not obtained in the re-
action of 1b with ethylene, in which nickel enolate intermediate
6
7
8
J. Seo, H. M. P. Chui, M. J. Heeg, J. Montgomery, J. Am.
Chem. Soc. 1999, 121, 476.
H. Hoberg, E. Hernandez, J. Chem. Som., Chem. Commun.
1986, 544.
[2 þ 2 þ 2] Cycloadditions of electron-deficient olefins
with norbornadienes have been reported. M. Lautens, L. G.
Edwards, W. Tam, A. J. Lough, J. Am. Chem. Soc. 1995,
117, 10276.
9
An unidentified isomer of 4a (less than 1%) was also ob-
1
served in H NMR and 13C NMR spectra. Supporting Infor-
mation is available electronically on the CSJ-Journal Web
site, http://www.csj.jp/journals/chem-lett/index.html.
10 As an alternative reaction path to generate C, the oxidative
cyclization of (ꢁ2-CH2=CH2)2Ni(PCy3) followed by the in-
sertion of an enone into nickel–carbon bond is also possible.
In fact, at the end of the reaction, the formation of (ꢁ2-
CH2=CH2)2Ni(PCy3) was observed by 31P NMR spectra.11
11 K.-R. Porschke, J. Am. Chem. Soc. 1989, 111, 5691.
¨
12 The conjugate addition of cyclic nickel enolate to an enone
has been reported: S. Ogoshi, M. Nagata, H. Kurosawa,
J. Am. Chem. Soc. 2006, 128, 5350; T. Tamaki, M. Nagata,
M. Ohashi, S. Ogoshi, Chem.—Eur. J. 2009, 15, 10083.
Published on the web (Advance View) November 7, 2009; doi:10.1246/cl.2009.1166