Formation of nickeladihydropyran by oxidative addition of cyclopropyl ketone. Key intermediate in nickel-catalyzed cycloaddition

Article abstract of DOI:10.1021/ja060220y

Cyclopropyl phenyl ketone underwent oxidative addition to Ni(PCy₃) generated from Ni(cod)₂ and PCy₃ to give a nickeladihydropyran, which is a key intermediate for the Ni(0)-catalyzed homo- or heterocycloaddition to give cyclopentane compounds having two carbonyl substituents at the 1,3-position. Copyright

Full text of DOI:10.1021/ja060220y

Published on Web 03/30/2006
Formation of Nickeladihydropyran by Oxidative Addition of Cyclopropyl
Ketone. Key Intermediate in Nickel-Catalyzed Cycloaddition
Sensuke Ogoshi,* Midue Nagata, and Hideo Kurosawa*
Department of Applied Chemistry, Faculty of Engineering, Osaka UniVersity, Suita, Osaka 565-0871, Japan
Received January 11, 2006; E-mail: ogoshi@chem.eng.osaka-u.ac.jp
Scheme 1. Oxidative Addition of Cyclopropyl Ketone
Scheme 2. Reaction of Cyclopropyl Ketone with Ni(0)
The oxidative addition of cyclopropanes to a transition metal
has been reported; however, its application to a catalytic reaction
has been limited due to the poor coordination ability of the cyclo-
propanes.1 In the case of the cyclopropyl compounds having an
unsaturated bond, such as methylenecyclopropane and vinylcyclo-
propane, the transition metal-catalyzed ring opening reaction is a
very powerful method to construct cyclic compounds.2 The key to
the success of the ring opening reaction might be the η2-coordination
of an unsaturated bond to locate the cyclopropyl ring on a transition
metal, which was suggested by a computational study on a rhodium
complex.2f According to this, cyclopropyl ketones are another
candidate for the ring opening reaction.2g Although the coordination
of an aldehyde or ketone in the η2-mode is very rare for the late
transition metals, the synthesis and reactivity of several η2-aldehyde
and η2-ketone complexes of nickel have been reported.3,4 Thus it
seems very promising to attain a nickeladihydropyran complex by
the oxidative addition of cyclopropyl ketones to nickel(0) (Scheme
1). Moreover, a nickeladihydropyran might be a transient key
intermediate in the reaction of cyclopropyl ketone with AlMe3 in
the presence of a catalytic amount of Ni(acac)2.5 Here, we report
the formation of a nickeladihydropyran by the oxidative addition
of cyclopropyl ketones to nickel(0). Furthermore, catalytic cycload-
dition of cyclopropyl ketones to give cyclopentane derivatives
proceeding through the nickeladihydropyran is also discussed.
The reaction of cyclopropyl ketone with Ni(cod)2 and PBu3 at
100 °C in toluene-d8 gave an η2-enonenickel complex (1a, 1b)
quantitatively (Scheme 2). The treatment of 1a and 1b with carbon
monoxide (5 atm) led to the dissociation of the coordinated enones,
(E)-3-penten-2-one and (E)-1-phenyl-2-buten-1-one, respectively.
In the presence of PCy3, the ring opening reaction of cyclopropyl
methyl ketone also occurred to give µ-η2:η1-enonenickel dimer
complex (2a) quantitatively (Scheme 3). 2a was generated quan-
titatively as well even in the presence of 2 equiv of PCy3. The
molecular structure of 2a was confirmed by the X-ray structure
analysis. The reaction of cyclopropyl phenyl ketone under the same
condition gave not only the corresponding µ-η2:η1-enonenickel
complex (2b) but also a mixture of cyclopentane products (3b, 3b′).6
The cycloaddition of cyclopropyl phenyl ketone proceeded
catalytically (Scheme 4) to give a mixture of 3b and 3b′ in 93%
yield. At the end of the reaction, the formation of 2b (76% based on
Ni(cod)2) was observed. Formally, 3b and 3b′ can be formed by the
[3 + 2] cycloaddition of cyclopropyl phenyl ketone with (E)-1-
phenyl-2-buten-1-one. Somewhat surprisingly, addition of 1 equiv of
(E)-1-phenyl-2-buten-1-one to the above catalysis mixture gave only
a trace amount of a mixture of 3b and 3b′, due to the rapid forma-
tion of 2b at the initial stage.7 Although cyclopropyl methyl ketone
did not undergo the cycloaddition reaction at all under the reaction
condition in Scheme 4, the cross cycloaddition with cyclopropyl
phenyl ketone competed with the homocycloaddition of cyclopropyl
phenyl ketone to give a mixture of 3b, 3b′, 4b, and 4b′ (Scheme 5).
The reaction of cyclopropyl phenyl ketone (2 equiv) with Ni-
(cod)2 (1 equiv) and PCy3 (1 equiv) in C6D6 was followed at the
Scheme 3. Reaction of Cyclopropyl Ketone with Ni(0)
Scheme 4
Scheme 5
lower temperature (40 °C) by 1H and 31P NMR. The rapid formation
of the η2-ketonenickel complex (5, 32% based on Ni) was observed
in 5 min.8 Then, 5 decreased gradually, and a new complex (6)
having a resonance at δ 5.2 in the 1H NMR spectrum was generated
(40%). After 48 h, 6 disappeared, and 2b (60%) and a mixture of
3b and 3b′ (40% as a mixture) were generated with cyclopropyl
phenyl ketone (1 equiv) and 40% of Ni(cod)2 and PCy3 remaining
intact. To confirm if 6 is the expected nickeladihydropyran
intermediate, the isolation of 6 was attempted. At room temperature
for 5 h in THF, the reaction of cyclopropyl phenyl ketone with
Ni(cod)2 and PCy3 generated 6 in 60% yield as confirmed by 31P
NMR. THF and COD were removed completely under reduced
pressure. The residue was dissolved in a minimum amount of
toluene, and the precipitation gave 6 as pale orange solids in 25%
isolated yield. Elemental analysis is consistent with the expected
composition.9 The 13C NMR resonance of the methylene carbon
attached to Ni is coupled with phosphorus. The 1H and 13C chemical
shifts of the nickel enolate moiety (-NiOC(Ph)dCH-) are in the
range of those for reported nickel enolates.10,11 The treatment of 6
9
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J. AM. CHEM. SOC. 2006, 128, 5350-5351
10.1021/ja060220y CCC: $33.50 © 2006 American Chemical Society

C O M M U N I C A T I O N S
Scheme 6
oxidative addition and insertion are important key steps in the
catalytic cycloaddition of cyclopropyl phenyl ketone reported for
the first time in this paper. Further studies on the reactivity of
nickeladihydropyran as well as applications to cross cycloaddition
reactions are in progress in our group.
Acknowledgment. Partial support of this work through the
Sumitomo Chemical Foundation (S.O.) and Grants-in-Aid for
Scientific Research from the Ministry of Education, Science, and
Culture, Japan, is gratefully acknowledged.
Supporting Information Available: Experimental procedures
(PDF) and crystallographic information (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
Scheme 7
References
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(2) Methylenecyclopropane: (a) Noyori, R.; Odagi, T.; Takaya, H. J. Am.
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Dinjus, E.; Schindler, S. Organometallics 1998, 17, 98-103.
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with carbon monoxide (5 atm) led to the formation of the expected
lactone (7) quantitatively,12 which is also consistent with the
structure of 6 depicted in Scheme 6.
The isomerization of 6 to 2b in C6D6 proceeded slowly at room
temperature. The insertion of (E)-3-pentene-2-one proceeded smooth-
ly to give η3:η1-enolatoalkylnickel complex 8 quantitatively.13 In
the 13C NMR spectrum of 8, the methylene carbon attached to Ni
is found upfield and coupled with phosphorus. Both 1H and 13C res-
onances of the CH group R to acetyl group (-CHC(O)CH3) are coup-
led with phosphorus, which indicates that nickel is bound to the R
carbon. Furthermore, their chemical shifts (δ 4.96 for H, δ 78.14 for
C) are too low for an η1-bound C-enolate structure, and we assume
an η3-enolate structure for 8. The chemical shift of the central carbon
(δ 159.5) is also consistent with this structure. Under a carbon mon-
oxide pressure (5 atm), 8 underwent the reductive elimination to
give a mixture of 4b and 4b′. These observations suggest the
occurrence of the isomerization of 8 prior to the reductive elimination.
The cycloaddition reaction might proceed as follows (Scheme
7). The cyclopropyl ketone coordinates to Ni(0) to form η2-ketone
complex A followed by the oxidative addition to give a nickeladi-
hydropyran B. The â-elimination and reductive elimination followed
by the tautomerization might generate η2-enonenickel C.14 In the
catalytic reaction, the concentration of free enone, which is expected
to react with B to give E (see Scheme 6), is supposed to be low since
enones may coordinate to Ni(0) so strongly that cyclopropyl ketones
are unable to replace the enone ligand in C. Thus, we assume that
the second oxidative addition of cyclopropyl phenyl ketone takes
place at C, leading to the formation of D followed by the insertion
of an enone to generate E. The coordination ability of cyclopropyl
phenyl ketone is much higher than that of cyclopropyl methyl
ketone,15 which might be one reason only cyclopropyl phenyl ketone
undergoes the second oxidative addition to C. The generation of
the mixture of isomers could be rationalized by the rapid isomer-
ization between E and F prior to the reductive elimination.
In conclusion, we demonstrated that a carbonyl group adjacent
to cyclopropyl group is a nice direction group to locate the
cyclopropane ring on the Ni(0) center, and the oxidative addition
proceeds easily to generate a nickeladihydropyran. Moreover, this
complex underwent the insertion of (E)-3-penten-2-one. Both
(5) A nickeladihydropyran seems a likely intermediate, although authors did
not mention it. Ichiyanagi, T.; Kuniyama, S.; Shimizu, M.; Fujisawa, T.
Chem. Lett. 1997, 1149-1150.
(6) Selected spectral data for 2b: 1H NMR (C6D6): δ 1.13 (d, J ) 6.2 Hz,
3H, -CHdCHCH3), 1.84 (m, 1H, -CHdCHCH3), 5.77 (dd, J ) 11.1,
3.8 Hz, 1H, -CHdCHCH3). 31P NMR (C6D6): δ 41.1 (s). 13C NMR
(C6D6): δ 20.39 (s, -CHdCHCH3), 32.99 (s, -CHdCHCH3), 34.30 (d,
JCP ) 15.2 Hz, Cy), 78.79 (d, JCP ) 3.8 Hz, -CHdCHCH3), 166.17 (s,
-C(O)Ph). Anal. Calcd for C56H86Ni2O2P2: C, 69.30; H, 8.93. Found:
C, 69.23; H, 8.10. Stereochemistry of 3b and 3b′ was determined by NOE
measurements.
(7) By the use of 10 mol % of 2b as a catalyst, cyclopropyl phenyl ketone
underwent the cycloaddition only slowly to give a mixture of 3b and 3b′
at 100 °C (1.5 h 7%, 16 h 91% as a mixture).
(8) Selected spectral data for 5: 31P NMR (toluene-d8, -20 °C): δ 33.17 (d,
J ) 47.6 Hz), 40.91 (d, J ) 47.6 Hz). 13C NMR (toluene-d8, -20 °C):
δ 82.72 (dd, JCP ) 20.9, 1.9 Hz, -C(O)Ph). Anal. Calcd for C46H76
-
NiOP2: C, 72.15; H, 10.00. Found: C, 71.57; H, 9.79.
(9) Selected spectral data for 6: 1H NMR (C6D6): δ 0.80 (m, 1H, -NiCH2-
CH2-), 0.99 (m, 1H, -NiCH2CH2-), 5.29 (t, J ) 4.4 Hz, 1H, -CHd
CO-). 31P NMR (C6D6): δ 31.3(s). 13C NMR (C6D6): δ 4.94 (d, JCP
)
30.8 Hz, -NiCH2CH2-), 104.70 (s, -CHdCO-), 157.11 (s, -CHd
CO). Anal. Calcd for C56H86Ni2O2P2: C, 69.30; H, 8.93. Found: C, 69.31;
H, 9.00.
(10) (a) Amarasinghe, K. K. D.; Chowdhury, S. K.; Heeg, M. J.; Montgomery,
J. Organometallics 2001, 20, 370-371. (b) Campora, J.; Maya, C. M.;
Palma, P.; Carmona, E.; Graiff, C.; Tiripicchio, A. Chem. Commun. 2003,
1742-1743.
(11) We assume the O-bridging dimer structure for 6 tentatively, although a
trimer or higher order aggregated structures are possible.
(12) Salisova, M.; Toma, S.; Solcaniova, E. J. Organomet. Chem. 1987, 327,
77-84.
(13) Selected spectral data for 8: 1H NMR (C6D6): δ 0.43 (m, 2H, -NiCH2-
CH2-), 2.00 (s, 3H, -CHdC(CH3)ONi-), 4.96 (dd, JHH ) 10.0 Hz, JHP
) 2.7 Hz, 1H, -CHdC(CH3)ONi-). 31P NMR (C6D6): δ 35.1 (s). 13C
NMR (C6D6): δ 0.01 (d, JCP ) 12.9 Hz, -NiCH2CH2-), 22.18 (s, -CHd
C(CH3)ONi-), 78.14 (d, JCP ) 16.0 Hz, -CHdC(CH3)ONi-), 159.54
(s, -CHdC(CH3)ONi-), 202.14 (s, -CH(COPh)CH(CH3)-). Anal. Calcd
for C33H51NiO2P: C, 69.61; H, 9.03. Found: C, 68.61; H, 8.91. 8 is
depicted tentatively as a complex having the stereochemistry corresponding
to the major product 4b.
(14) The intermediate C may dimerize to the catalytically much less active 2
if the rate of conversion of C to D becomes comparably small.
(15) No ketone substitution was observed by the addition of cyclopropyl methyl
ketone to a solution of 5 in C6D6.
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