Palladium/Me3SiOTf-catalyzed bis-silylation of α,β-unsaturated carbonyl compounds without involving oxidative addition of disilane

Article abstract of DOI:10.1021/ja0272944

In the presence of a catalytic amount of Me₃SiOTf and palladium(0), the addition of disilane to α,β-unsaturated carbonyl compounds proceeds under very mild conditions via η³-siloxyallylpalladium generated by the reaction of enone, en

Full text of DOI:10.1021/ja0272944

Published on Web 09/10/2002
Palladium/Me3SiOTf-Catalyzed Bis-silylation of r,â-Unsaturated Carbonyl
Compounds without Involving Oxidative Addition of Disilane
Sensuke Ogoshi,* Sadayuki Tomiyasu, Masaki Morita, and Hideo Kurosawa*
Department of Applied Chemistry, Faculty of Engineering, Osaka UniVersity, Suita, Osaka 565-0871, Japan
Received June 14, 2002
The conjugate silylation of enone has been studied well, which
can be classified into two reactions. One is the stoichiometric
conjugate addition of silyl anion to enones,1 and the other is the
palladium-catalyzed reaction of disilane with enones to give
γ-siloxyallylsilane (Scheme 1).2,3 Oxidative addition of disilanes
reported transition metal-catalyzed conjugate silylation,2,3 this
reaction proceeds much more rapidly under very mild conditions.
Thus, the conjugate addition product of methyl vinyl ketone or
acrolein (1, 2) was obtained quantitatively, which had previously
been prepared in poor to modest yields. Furthermore, both di-
phenyltetramethyldisilane and even hexamethyldisilane can be
employed in this reaction, while the reported palladium-catalyzed
reaction of disilanes with enones required more active halogenated
disilanes.
Scheme 1
is suggested to be a crucial process in the palladium-catalyzed bis-
silylation of the unsaturated bond.4 The requirement of the reactive
disilanes and heating conditions in Scheme 1 would be due to the
hardness of the oxidative addition. Thus, the construction of catalytic
bis-silylation of R,â-unsaturated carbonyl compounds, which does
not proceed via oxidative addition of disilane, would expand the
scope of bis-silylation of the unsaturated bond. As a new method
to this goal, we envisaged the silylation of the η3-siloxyallylpal-
ladium complex with disilane to give the desired product under
milder conditions, because the reaction of the η3-allylpalladium
intermediate with disilane has been known to give allylsilanes rather
facilely (Scheme 2).5 Efficient generation of η3-siloxyallylpalladium
Scheme 2
The reaction would proceed as shown in Scheme 3. The
electrophilic addition of Me3SiOTf to η2-enonepalladium leads to
the formation of η3-siloxyallylpalladium intermediates followed by
transmetalation of disilane with η3-siloxyallylpalladium intermedi-
ates to regenerate Me3SiOTf.11 Thus, only a catalytic amount of
Me3SiOTf was required. The reductive elimination then occurs to
give the conjugate addition products and regenerate palladium(0)
species. In this reaction, even symmetrical disilanes can be
employed, which is similar to the formation of allylsilanes via η3-
allylpalladium(II) species as depicted in Scheme 2.
The addition of PPh3 suppressed the reaction completely possibly
due to the formation of unreactive complex.12 In fact, a stoichio-
metric reaction of Pd(η2-RCHdCHCHO)(PPh3)2 (R ) H or Ph)
with Me3SiOTf gave (η3-1-siloxyallyl)palladium complex (6, 7)
quantitatively, which did not react with disilane at room temperature
(eq 2).13 In the absence of PPh3, more reactive η3-siloxyallylpal-
ladium would be generated.
is then the key to the new catalytic conjugate silylation. We searched
for suitable conditions to generate η3-siloxyallylpalladium by
referring to the reaction of Lewis acid with η2-enonepalladium
complex leading to the formation of zwitterionic η3-metalloxyal-
lylpalladium complexes.6,7 Here, we report the palladium/Me3SiOTf-
catalyzed addition of disilane to R,â-unsaturated carbonyl com-
pounds via η3-siloxyallylpalladium generated by the reaction of
enone, enal, or aromatic aldehyde with palladium and Me3SiOTf.
In the presence of 10 mol % of Me3SiOTf and Pd(OAc)2, the
reaction of methyl vinyl ketone with diphenyltetramethyldisilane
proceeded very rapidly and cleanly in 20 min to give the expected
1,4-bis-silylation product quantitatively (eq 1).8,9 In the absence of
Pd catalyst or Me3SiOTf, the reaction did not occur at all. Other
enones and enals also reacted with disilane under the same condition
to give the corresponding conjugate addition products. The hy-
drolysis of the conjugate silylation products gave â-silyl ketones,
of which structures were confirmed by the comparison of the NMR
spectra with those of the authentic samples.3 An alternative
precursor (η3-allyl)PdCp in 3 mol % was also effective for the
isolation of the â-silylcarbonyl compound.10 As compared with the
Scheme 3
* To whom correspondence should be addressed. E-mail: (S.O.) ogoshi@
chem.eng.osaka-u.ac.jp.
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J. AM. CHEM. SOC. 2002, 124, 11598-11599
10.1021/ja0272944 CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
References
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The reaction of cinnamaldehyde gave a mixture of 1,4- and 1,2-
addition products (8, 9) (eq 3), which is consistent with the reaction
path via the η3-allylpalladium intermediate in Scheme 3. Moreover,
this reaction leading to 9 could be extended to benzaldehyde or
naphthaldehyde to give the 1,2-addition product (10,14 1115) in
excellent yield where the η3-siloxybenzylpalladium intermediate
may be generated (eq 4). Equation 4 is the first example of the
addition of the Si-Si bond of acyclic disilanes across the carbon-
oxygen double bond. So far, only the reaction of strained four-
membered cyclic disilanes with the carbonyl compound in the
presence of Ni, Pd, or Pt catalyst had been reported.16
(3) Only one catalytic reaction using a metal other than Pd has been reported.
Cu: Ito, H.; Ishizuka, T.; Tateiwa, J.-i.; Sonoda, M.; Hosomi, A. J. Am.
Chem. Soc. 1998, 120, 11196.
(4) Suginome, M.; Ito, Y. In ActiVation of UnreactiVe Bonds and Organic
Synthesis; Murai, S., Ed.; Springer: Berlin, 1999; Vol. 3, p 131.
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1984, 57, 607. Tsuji, Y.; Funato, M.; Ozawa, M.; Ogiyama, H.; Kajita,
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(6) Ogoshi, S.; Yoshida, T.; Nishida, T.; Morita, M.; Kurosawa, H. J. Am.
Chem. Soc. 2001, 123, 1944.
(7) The formation of η3-1-siloxyallylnickel complexes by the reaction of enone
and Ni(0) complexes in the presence of chlorosilane and its application
to the catalytic reaction had been reported. Johnson, J. R.; Tully, P. S.;
Mackenzie, P. B.; Sabat, M. J. Am. Chem. Soc. 1991, 113, 6172. Grisso,
B. A.; Johnson, J. R.; Mackenzie, P. B. J. Am. Chem. Soc. 1992, 114,
5160.
(8) Typical procedure for 4: To a solution of Pd(OAc)2 (5.6 mg, 0.025 mmol),
benzalacetone (36.6 mg, 0.25 mmol), hexamethyldisilane (43.9 mg, 0.30
mmol), and toluene (internal standard) (23.0 mg, 0.25 mmol) in 0.5 mL
of C6D6 was added Me3SiOTf (5.6 mg, 0.025 mmol). The reaction was
followed by NMR.
(9) The reaction was not catalyzed by Ni(cod)2 in the presence of Me3SiOTf,
although Ni(cod)2 catalyzed the conjugate addition of organotin compounds
to enone in the presence of a stoichiometric amount of Me3SiCl.7
(10) Isolation of hydrolysis product of 4: To a solution of (η3-allyl)PdCp (6.4
mg, 0.03 mmol (3 mol %)), benzalacetone (146.2 mg, 1.0 mmol), and
hexamethyldisilane (175.7 mg, 1.2 mmol) in 0.5 mL of benzene was added
Me3SiOTf (6.7 mg, 0.03 mmol). The reaction mixture was stirred for 1 h
and concentrated in vacuo. The residue was separated by column (silica
gel) to give the corresponding â-silyl ketone (209.9 mg, 95%).3
(11) The reaction of enone with Me3SnSnMe3 under the same condition did
not occur.
(12) The stoichiometric reaction of η3-allylpalladium with disilanes had been
reported, in which the addition of PPh3 suppressed the transmetalation
with disilanes. Macsa´ri, I.; Hupe, E.; Szabo´, K. J. J. Org. Chem. 1999,
64, 9547.
(13) Selected spectral data for 6: 1H NMR (270 MHz, C6D6) δ -0.19 (s, 9H),
3.08 (ddd, JHH ) 7.5, 2.5 Hz, JHP ) 7.7 Hz, 1H), 3.72 (ddd, JHH ) 12.5,
2.5 Hz, JHP ) 9.5 Hz, 1H), 4.95 (ddd, JHH ) 7.7, 12.5, 10.5 Hz, 1H),
6.90-7.56 (m, 30H), 7.96 (dd, JHH ) 10.5 Hz, JHP ) 9.5 Hz).13C NMR
(67.9 MHz, CDCl3) δ 62.7 (dd, JCP ) 1.6, 26.9 Hz), 104.8 (dd,
JCP ) 4.4, 5.6 Hz). The resonance of the other allyl carbon is hidden
by the resonance of Ph groups. 31P NMR (109 MHz, C6D6) δ 25.63 (d,
JPP ) 35.6 Hz), 26.59 (d, JPP ) 35.6 Hz). 7: 1H NMR (270 MHz, C6D6)
δ -0.13 (s, 9H), 5.39 (dd, JHH ) 11.5 Hz, JHP ) 10.4 Hz, 1H), 5.51 (dd,
JHH ) 11.5, 9.7 Hz, 1H), 6.62-7.42 (m, 35H), 8.47 (dd, JHH ) 9.7 Hz,
JHP ) 8.9 Hz).13C NMR (67.9 MHz, C6D6) δ 77.4 (dd, JCP ) 5.5, 27.5
Hz), 102.4 (dd, JCP ) 4.7, 6.9 Hz), 136.8 (dd, JCP ) 3.4, 7.0 Hz). 31P
NMR (109 MHz, C6D6) δ 25.33 (d, JPP ) 42.8 Hz), 27.53 (d, JPP ) 42.8
Hz).
In summary, we demonstrated that the Me3SiOTf/palladium
catalyst system is very efficient for the addition of disilanes to
enones and enals including aryl aldehydes via the η3-siloxyallylpal-
ladium intermediate, which allows us to employ methyl vinyl ketone
and acrolein as a substrate and unreactive disilanes as a silylation
reagent. The present reaction without involving the oxidative
addition of disilane is a very new method to introduce two silyl
groups into the unsaturated bond. Further studies of this theme are
ongoing in our group.
(14) Barrett, A. G. M.; Hill, J. M.; Wallace, E. M. J. Org. Chem. 1992, 57,
386.
(15) Isolation of hydrolysis product of 11: To a solution of Pd(OAc)2 (22.4
mg, 0.1 mmol), naphthaldehyde (156.2 mg, 1.0 mmol), and diphenyltet-
ramethyldisilane (324.6 mg, 1.2 mmol) in 0.5 mL of benzene was added
Me3SiOTf (22.2 mg, 0.1 mmol). The reaction mixture was stirred for 1
h. The reaction mixture was added to 0.01 N HCl solution in 2 mL of
EtOH(95%), and the mixture was stirred for 12 h. To the mixture was
added 50 mg of NaHCO3, and the solvent was removed in vacuo. The
concentrate was stirred for 18 h and separated by column (silica gel,
EtOAc/hexane ) 1/20) to give the corresponding alcohol (267.7 mg, 92%).
Spectral data for the hydrolysis product of 11: 1H NMR (270 MHz,
CDCl3) δ 0.21 (s, 3H), 0.31 (s, 3H), 1.75 (s, 1H), 5.62 (s, 1H), 7.28-
7.86 (m, 12H). 13C NMR (67.9 MHz, CDCl3): δ -5.8, -4.4, 65.9, 122.9,
123.6, 125.1, 125.4, 125.6, 126.3, 127.8, 128.7, 129.5, 130.0, 133.5, 134.4,
136.3, 140.0.
Acknowledgment. Partial support of this work through the
Tokuyama Science Foundation (S.O.), CREST of Japan Science
and Technology Corporation, Grants-in-Aid for Scientific Research
from Ministry of Education, Science, and Culture, Japan, and the
Japanese Government’s Special Coordination Fund for Promoting
Science and Technology is gratefully acknowledged.
(16) Seyferth, D.; Goldman, E. W.; Escudie, J. J. Organomet. Chem. 1984,
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tallics 1994, 13, 4994. Kusukawa, T.; Kabe, Y.; Nestler, B.; Ando, Y.
Organometallics 1995, 14, 2556.
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