Ruthenium-catalyzed β-allyl elimination leading to selective cleavage of a carbon-carbon bond in homoallyl alcohols

Full text of DOI:10.1021/ja980714y

J. Am. Chem. Soc. 1998, 120, 5587-5588
5587
generally irreversible, neither stoichiometric nor catalytic C-C
cleavage via â-alkyl elimination from an (alkoxy)metal intermedi-
ate has yet been reported (eq 2 reverse). On the basis of our
recent study of ruthenium-catalyzed C-C bond activation3g as
well as allylruthenium chemistry,8 we assume that successful
catalytic C-C cleavage via â-alkyl elimination from an (alkoxy)-
metal intermediate can be attained by using tertiary homoallyl
alcohols as a substrate, since the formation of a stable allylru-
thenium species by â-allyl elimination should contribute signifi-
cantly to the driving force of this catalytic reaction. After many
trials, we finally found the first example of catalytic deallylation
of tertiary homoallyl alcohols via selective cleavage of a C-C
bond. We report here the development of this new catalyst system
and a synthetic application of â-allyl elimination.
Ruthenium-Catalyzed â-Allyl Elimination Leading
to Selective Cleavage of a Carbon-Carbon Bond
in Homoallyl Alcohols
Teruyuki Kondo,* Kouichi Kodoi, Eiji Nishinaga,
Takumi Okada, Yasuhiro Morisaki, Yoshihisa Watanabe, and
Take-aki Mitsudo*
Department of Energy and Hydrocarbon Chemistry
Graduate School of Engineering, Kyoto UniVersity
Sakyo-ku, Kyoto 606-8501, Japan
ReceiVed March 4, 1998
The development of efficient methods for the selective forma-
tion1 and cleavage2,3 of C-C bonds catalyzed by transition-metal
complexes is a central and challenging subject of modern organic
synthesis. Among various processes catalyzed by transition-metal
complexes, alkene insertion into metal-alkyl bonds is recognized
as a fundamental model reaction of alkene polymerization (eq 1
forward). The reverse reaction, i.e., C-C cleavage via â-alkyl
elimination (eq 1 reverse), has recently received growing attention,
especially in the field of polymer chemistry.4 Since Watson and
Roe reported the first example of â-methyl elimination in the
decomposition of (C5Me5)2LuCH2CHMe2,5 several examples of
reversible â-alkyl insertion-elimination at both early and late
transition metal centers have been reported.6
The treatment of tertiary homoallyl alcohol 1a with an excess
of allyl acetate in the presence of 5 mol % RuCl2(PPh3)3 in THF
under 10 atm of carbon monoxide at 180 °C for 15 h gave a
deallylated product, acetophenone 2a, in an isolated yield of 91%
(eq 3). General tertiary homoallyl alcohols bearing either an aryl
or alkyl substituent (1b-d) were smoothly deallylated by the
present catalyst system to give the corresponding ketones (2b-
d) in high isolated yields. Gas analysis showed the generation
of propene (54% yield) in the reaction of 1a and of isobutene
(42% yield) in the reaction of 1d.9 The presence of both carbon
monoxide and allyl acetate was crucial. Carbon monoxide
operates as an effective π-acid.10 While the role of allyl acetate
is not yet clear, we believe that it is required for the generation
and stabilization of a catalytically active ruthenium species.11
Attempts to effect the reaction at temperatures lower than 150
°C resulted in drastically diminished yield.
Several transition-metal complexes as well as ruthenium
complexes were examined with regard to their ability to catalyze
the deallylation of 1a to 2a. The results are summarized in Table
1. All of the ruthenium complexes showed catalytic activity, and
among them, RuCl2(PPh3)3 showed the highest activity. Besides
ruthenium complexes, only RhCl(PPh3)3 showed a moderate
catalytic activity.
On the other hand, the addition of metal-alkyls to carbonyl
compounds is another excellent method for the selective formation
of C-C bonds (eq 2 forward).7 However, since this reaction is
(1) Hegedus, L. S. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, U.K., 1995;
Vol. 12.
(2) For reviews, see: (a) Bishop, K. C. Chem. ReV. 1976, 76, 461. (b)
Crabtree, R. H. Chem. ReV. 1985, 85, 245. (c) Jennings, P. W.; Johnson, L.
L. Chem. ReV. 1994, 94, 2241.
(3) For catalytic cleavage of a C-C-bond, see: (a) Noyori, R.; Odagi, T.;
Takaya, H. J. Am. Chem. Soc. 1970, 92, 5780. (b) Suggs, J. W.; Jun, C.-H. J.
Chem. Soc., Chem. Commun. 1985, 92. (c) Trost, B. M.; Tanoury, G. J. J.
Am. Chem. Soc. 1988, 110, 1636. (d) Aoki, S.; Fujimura, T.; Nakamura, E.;
Kuwajima, I. J. Am. Chem. Soc. 1988, 110, 3296. (e) Huffman, M. A.;
Liebeskind, L. S. J. Am. Chem. Soc. 1991, 113, 2771. (f) Rondon, D.; Chaudret,
B.; He, X.-D.; Labroue, D. J. Am. Chem. Soc. 1991, 113, 5671. (g) Mitsudo,
T.; Zhang, S.-W.; Watanabe, Y. J. Chem. Soc., Chem. Commun. 1994, 435.
(h) Perthuisot, C.; Jones, W. D. J. Am. Chem. Soc. 1994, 116, 3647. (i) Chatani,
N.; Morimoto, T.; Muto, T.; Murai, S. J. Am. Chem. Soc. 1994, 116, 6049.
(j) Murakami, M.; Amii, H.; Ito, Y. Nature 1994, 370, 540. (k) Tsukada, N.;
Shibuya, A.; Nakamura, I.; Yamamoto, Y. J. Am. Chem. Soc. 1997, 119, 8123.
(l) Harayama, H.; Kuroki, T.; Kimura, M.; Tanaka, S.; Tamaru, Y. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2352. (m) Murakami, M.; Takahashi, K.; Amii,
H.; Ito, Y. J. Am. Chem. Soc. 1997, 119, 9307 and references therein.
(4) (a) Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985, 18, 51. (b)
Resconi, L.; Piemontesi, F.; Franciscono, G.; Abis, L.; Fiorani, T. J. Am. Chem.
Soc. 1992, 114, 1025. (c) Kesti, M. R.; Waymouth, R. M. J. Am. Chem. Soc.
1992, 114, 3565. (d) Yang, X.; Jia, L.; Marks, T. J. J. Am. Chem. Soc. 1993,
115, 3392. (e) Hajela, S.; Bercaw, J. E. Organometallics 1994, 13, 1147 and
references therein.
A synthetic application of the present reaction is demonstrated
in the following ring-opening reaction of cyclic homoallyl alcohols
(eq 4). The treatment of 1e under the present reaction conditions
gave the ring-opening product, unsaturated ketone 3, as a mixture
of olefinic isomers (8-en:7-en ) 26:74, total 76% yield).
(8) Kondo, T.; Ono, H.; Satake, N.; Mitsudo, T.; Watanabe, Y. Organo-
metallics 1995, 14, 1945 and references therein.
(9) In the reaction of 1d, a small amount (0.36 mmol) of propene was
generated from allyl acetate (30 mmol) together with isobutene (1.68 mmol,
42%) from 1d.
(10) After the reaction, RuCl2(PPh3)3 was quantitatively converted into cis-
RuCl2(CO)2(PPh3)2 (Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem.
1966, 28, 945). In addition, carbon monoxide can be replaced by maleic
anhydride (yield of 1a, 65%; see the Supporting Information). These results
indicate that carbon monoxide and maleic anhydride may coordinate to an
active ruthenium center and promote the reductive elimination of propene
from a (hydrido)(allyl)ruthenium intermediate, as well as control the electronic
condition of an active ruthenium center.
(5) Watson, P. L.; Roe, D. C. J. Am. Chem. Soc. 1982, 104, 6471.
(6) (a) Etienne, M.; Mathieu, R.; Donnadieu, B. J. Am. Chem. Soc. 1997,
119, 3218. (b) McNeill, K.; Andersen, R. A.; Bergman, R. G. J. Am. Chem.
Soc. 1997, 119, 11244 and references therein.
(7) Addition of allylorganometallics to carbonyl compounds, see: Roush,
W. R. In ComprehensiVe Organic Synthesis: Trost, B. M.; Fleming, I., Eds.;
Pergamon: Oxford, U.K., 1991; Vol. 2, pp 1-53.
(11) Oxidative addition of allyl trifluoroacetate to Ru(0) has already been
reported, see: Komiya, S.; Kabasawa, T.; Yamashita, K.; Hirano, M.; Fukuoka,
A. J. Organomet. Chem. 1994, 471, C6.
S0002-7863(98)00714-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 05/22/1998

5588 J. Am. Chem. Soc., Vol. 120, No. 22, 1998
Communications to the Editor
Table 1. Catalytic Activity of Several Transition-Metal Complexes
in Deallylation of 1a to 2aa
Scheme 1
catalyst
yield of 2a (%)b
RuCl2(PPh3)3
(91)
65
64
45
53
0
cis-RuCl2(CO)2(PPh3)2
Cp*RuCl(cod)
c
Ru3(CO)12
RhCl(PPh3)3
NiBr2(PPh3)2
PdCl2(PPh3)2
cis-PtCl2(PPh3)2
0
0
a Compound 1a (4.0 mmol), catalyst (0.20 mmol), allyl acetate (30
mmol), THF (8.0 mL), CO (10 atm), 180 oC, 15 h. b GLC yield (isolated
yield). c Ru3(CO)12 (0.067 mmol).
Considering all of our findings, the most plausible mechanism
is illustrated in Scheme 1. The initial step might consist of
oxidative addition of the hydroxy group in 1 to an active ru-
thenium center. Subsequent â-allyl elimination from an (alkoxy)-
ruthenium intermediate gives ketone 2 together with a (hydrido)-
(allyl)ruthenium intermediate, which undergoes reductive
elimination to give propene. Carbon monoxide may promote the
final reductive elimination of propene as an effective π-acid (vide
supra).
In summary, we have developed the first and practical
ruthenium-catalyzed deallylation of tertiary homoallyl alcohols
via selective cleavage of a C-C bond. The mechanistic aspects
and scope of the transfer-allylation reaction13 are currently under
investigation, but we believe that this C-C bond cleavage
involves the first â-alkyl (â-allyl) elimination from an (alkoxy)-
ruthenium intermediate in its catalytic cycle.
Hydrogenation of 3 by PtO2 catalyst gave the saturated ketone 4
in an overall isolated yield of 73%. Thus, the present reaction
may offer a novel method for the catalytic ring-opening reaction
of general 2-vinylcycloalkanols.12
The following reactions using 5a, 6a, and 7a, illustrated in
eqs 5-7, provided insight into the mechanism. First, treatment
of 5a did not give 2a at all, which indicates that the first step of
the reaction is oxidative addition of a hydroxy group of 1a to
ruthenium. Second, the failure of the depropylation of 6a to 2a
Acknowledgment. This work was supported in part by a Grant-in-
Aid for Scientific Research from the Ministry of Education, Science,
Sports and Culture, Japan. T.K. acknowledges financial support from the
Kurata Foundation. Y.M. appreciates Research Fellowships from the Japan
Society for the Promotion of Science for Young Scientists. Thanks are
also due to Dr. K. Ohe of this department for his helpful discussion.
Supporting Information Available: Experimental details and char-
acterization of compounds 1e and 4 (4 pages, print/PDF). See any current
masthead page for ordering information and Web access instructions.
JA980714Y
(13) The following novel ruthenium-catalyzed transfer-allylation of al-
dehydes with 1a or 1d also supports the formation of an allylruthenium
intermediate. For example, the treatment of benzaldehyde with an equimolar
amount of 1a or 1d in the presence of RuCl2(PPh3)3 catalyst and an excess
amount of allyl acetate in THF gave the transfer-allylated product, (E)-1-
phenyl-2-buten-1-one (8a) and 3-methyl-1-phenylbut-2-en-1-one (9a) in yields
of 68 and 35%, respectively (eq 8). Of course, no reaction occurred in the
absence of 1a or 1d, even in the presence of allyl acetate.
suggests that the driving force of this reaction is the formation
of an allylruthenium species. Furthermore, substrate 7a, which
has both a â-hydrogen and a â-allyl group, gave the R,â-
unsaturated ketone 8a exclusively via â-hydrogen elimination.
(12) The thermal ring-opening reaction (retro-ene reaction) of 2-vinyl-
cyclohexanols is generally carried out in the vapor phase at ca. 500 °C. Marvell,
E. N.; Rusay, R. J. Org. Chem. 1977, 42, 3336.