Palladium(II)-catalyzed oxidative ring cleavage of tert-cyclobutanols under oxygen atmosphere [25]

Full text of DOI:10.1021/ja984259h

J. Am. Chem. Soc. 1999, 121, 2645-2646
2645
Scheme 1
Scheme 2
Scheme 3
Palladium(II)-Catalyzed Oxidative Ring Cleavage of
tert-Cyclobutanols under Oxygen Atmosphere
Takahiro Nishimura, Kouichi Ohe, and Sakae Uemura*
Department of Energy and Hydrocarbon Chemistry
Graduate School of Engineering
Kyoto UniVersity, Sakyo-ku, Kyoto 606-8501, Japan
ReceiVed December 10, 1998
Transition-metal alcoholates have been widely explored in
organic and inorganic chemistry, since they have the interesting
reactivity and structural diversity.1 In sharp contrast to stability
of early transition-metal alcoholates, late transition-metal ones
are labile due to weak M-O bond.2b Thus, the late transition-
metal alcoholates, although they lack M-C bonds, show certain
similarities to alkyls and are prone to â-hydrogen elimination to
give a carbonyl compound and a reduced metal as shown in
Scheme 1.2 On the other hand, the examples of dealkylation
reactions of tert-alcoholates via â-carbon elimination catalyzed
by the late transition metal (Scheme 2) similar to â-hydrogen
elimination are still few in number.3
Scheme 4
Recently, we have succeeded in the aerobic oxidation of
primary and secondary alcohols to aldehydes and ketones in the
Pd(OAc)2/pyridine/MS3A catalyst system.4 This dehydrogenative
reaction proceeds via a palladium alcoholate and catalytically on
palladium under oxygen atmosphere. Thus, we undertook the
reaction of tert-alcohols. Cyclic tert-cyclobutanol could merit
being used to pursue the â-carbon elimination without the loss
of the carbon atom because it was expected to favor â-carbon
elimination at the endo-carbon by relief of the ring strain.5,6 Now
we wish to report the novel palladium-catalyzed reaction of several
tert-cyclobutanols involving selective â-carbon elimination (bond
a breaking) from the palladium alcoholate under the aerobic
conditions (Scheme 3).
find a different bond-cleavage reaction is performed by the
application of the recently discovered aerobic conditions employ-
ing Pd(II) (vide supra)4 to tert-cyclobutanols. Treatment of
7-vinylbicyclo[4.2.0]octan-7-ol8 (1a) (0.5 mmol) in toluene at 80
°C for 20 h with 10 mol % Pd(OAc)2, pyridine (1.0 mmol) and
MS3A (50 mg) under oxygen atmosphere afforded 1-(2-methyl-
enecyclohexan-1-yl)-2-propen-1-one (2a) in 56% isolated yield
as a dehydrogenative ring opening product (eq 1). This result
Ring expansion reaction of 1-alkenyl or 1-alkynyl cyclobutanols
is a well-investigated reaction that can be promoted or catalyzed
by a divalent palladium.7 This reaction is suggested by the required
formation of palladium alkene or alkyne π-complex prior to
migration of a secondary carbon (Scheme 4). Our approach to
(1) For review, see: Bryndza, H. E.; Tam, W. Chem. ReV. 1988, 88, 1163.
(2) (a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. In
Principles and Applications of Organotransition Metal Chemistry; University
Science Books: Mill Valley, CA, 1989; pp 59-61. (b) Crabtree, R. H. In
The Organometallic Chemistry of the Transition Metals, 2nd ed.; Wiley: New
York, 1994; pp 57-59.
(3) (a) Harayama, H.; Kuroki, T.; Kimura, M.; Tanaka, S.; Tamaru, Y.
Angew. Chem., Int. Ed. Engl. 1997, 36, 2352. (b) Kondo, T.; Kodoi, K.;
Nishinaga, E.; Okada, T.; Morisaki, Y.; Watanabe, Y.; Mitsudo, T. J. Am.
Chem. Soc. 1998, 120, 5587.
suggested that our reaction condition favored the cleavage of C-C
bond of cyclobutanol giving a less hindered primary alkylpalla-
dium intermediate (bond a breaking). The amount of pyridine
used was crucial to obtain the product 2a selectively. Reducing
the amount of pyridine to 0.2 mmol, the yield of 2a decreased
(30%).9 Next, the reaction of 7-phenylbicyclo[4.2.0]octan-7-ol
(1b) under the same conditions for 48 h afforded 2-methylenecy-
clohexan-1-yl phenyl ketone (2b) in 60% isolated yield. Interest-
ingly, the addition of a catalytic amount of ethyl acrylate (0.2
mmol) dramatically increased the yield of 2b up to 97% isolated
yield.10 These successful reaction conditions could be applied to
(4) Nishimura, T.; Onoue, T.; Ohe, K.; Uemura, S. Tetrahedron Lett. 1998,
39, 6011.
(5) The ring expansion reactions of siloxycyclopropanes, see: (a) Kuwa-
jima, I.; Nakamura, E. Top. Curr. Chem. 1990, 155, 1. (b) Kirihara, M.;
Ichinose, M.; Takizawa, S.; Momose, T. Chem. Commun. 1998, 1691 and
references therein. The oxidative rearrangement reactions of cyclobutanols,
see: Schlecht, M. F. In ComprehensiVe Organic Synthesis; Trost, B. M.,
Fleming, I., Ley, S. V., Eds.; Pergamon: Oxford, U.K., 1991; Vol.7, pp 824-
826. The recent advance of â-carbon elimination in the reaction sequence
using spiro cyclobutanones, see: Murakami, M.; Takahashi, K.; Amii, H.;
Ito, Y. J. Am. Chem. Soc. 1997, 119, 9307.
(6) The study on the strain energy, see: Schleyer, P. v. R.; Williams, J.
E.; Blanchard, K. R. J. Am. Chem. Soc. 1970, 92, 2377.
(7) For some previous works on the palladium-catalyzed ring expansion
of cyclobutanols, see: (a) Boontanonda, P.; Grigg, R. J. Chem. Soc., Chem.
Commun. 1977, 583. (b) Clark, G. R.; Thiensathit, S. Tetrahedron Lett. 1985,
26, 2503. (c) Liebeskind, L. S.; Mitchell, D.; Foster, B. S. J. Am. Chem. Soc.
1987, 109, 7908. (d) Demuth, M.; Pandey, B.; Wietfeld, B.; Said, H.; Viader,
J. HelV. Chim. Acta 1988, 71, 1392. (e) de Almeida Barbosa, L.-C.; Mann, J.
J. Chem. Soc., Perkin Trans. 1 1990, 177. (f) Mitchell, D.; Liebeskind, L. S.
J. Am. Chem. Soc. 1990, 112, 291. (g) Nemoto, H.; Nagamochi, M.; Fukumoto,
K. J. Chem. Soc., Perkin Trans. 1 1993, 2329. (h) Nemoto, H.; Nagamochi,
M.; Ishibashi, H.; Fukumoto, K. J. Org. Chem. 1994, 59, 74. (i) Nemoto, H.;
Shiraki, M.; Fukumoto, K. Synlett 1994, 599. (j) Nemoto, H.; Miyata, J.;
Fukumoto, K. Tetrahedron 1996, 52, 10363. (k) Nemoto, H.; Yoshida, M.;
Fukumoto, K. J. Org. Chem. 1997, 62, 6450. (l) Nemoto, H.; Miyata, J.;
Yoshida, M.; Raku, N.; Fukumoto, K. J. Org. Chem. 1997, 62, 7850.
(8) Cyclobutanols are readily accessible from the corresponding cyclobu-
tanones and Grignard reagent or alkyllithium. Typical methods for cyclobu-
tanones, see: (a) Krepski, L. R.; Hassner, A. J. Org. Chem. 1978, 43, 2879.
(b) Greene, A. E.; Luche, M.-J.; Serra, A. A. J. Org. Chem. 1985, 50, 3957.
10.1021/ja984259h CCC: $18.00 © 1999 American Chemical Society
Published on Web 03/05/1999

2646 J. Am. Chem. Soc., Vol. 121, No. 11, 1999
Table 1. Pd(OAc)2 Catalyzed Reaction of Cyclobutanols*
Communications to the Editor
methylenecyclopentanone. In the case of substrate 15 having
phenyl group instead of vinyl, the interesting reaction took place
to give ketone 1611 in 91% yield (eq 3). The formation of 16 can
be explained by assuming the reaction sequence shown in Scheme
5. An alkylpalladium intermediate by â-carbon elimination
undergoes intramolecular endo cyclization with phenyl ring to
give trans-organopalladium complex 17. This trans-complex
isomerizes via palladium enolate 18 to cis-organopalladium
complex 19, which affords the product 16 via â-hydrogen syn-
elimination.
Scheme 5
* Reaction conditions: alcohol (0.5 mmol), Pd(OAc)2 (0.05 mmol),
pyridine (1.0 mmol), ethyl acrylate (0.2 mmol), MS3A (50 mg), toluene
(5 mL), at 80 °C under atmospheric O2. a Isolated yield. b In the absence
of ethyl acrylate.
the reaction of alkyl-substituted bicyclic cyclobutanol 1c leading
to â,γ-unsaturated ketone 1-(2-methylenecyclohexan-1-yl)pentan-
1-one (2c) in 71% yield. This means that the formation of
palladium alcoholate is a crucial step and the pre-coordination
of π-bond with palladium is not required prior to C-C bond
cleavage. Other examples of the selective C-C bond cleavage
of cyclobutanols are listed in Table 1. Several bicyclic cyclobu-
tanols 3, 5, and 7 produced the corresponding â,γ-unsaturated
ketones 4, 6, and 8 in good to high yields (entries 1-3).
Cyclobutanol 9 yielded R,â-unsaturated ketone 10 (81%) isomer-
ized from the initially formed â,γ-unsaturated ketone (entry 4).
The reaction of monocyclic cyclobutanol 11 was relatively slow,
but R,â-unsaturated ketone 12 was obtained in moderate yield
(entry 5).
The reaction could also be applied to bicyclic cyclobutanols
13a-c having an angular substituent (eq 2). Cyclobutanols 13a-c
afforded cyclopentanones 14a-c in good yield. Each product was
apparently different from products obtained in the previous
palladium(II)-mediated reactions.7 These results show that an
alkylpalladium intermediate which is formed by â-carbon elimi-
nation from palladium alcoholate undergoes cyclization in 5-exo
mode and subsequent â-hydrogen elimination to give an R-
We suppose that these catalytic reactions proceed via the
formation of a Pd(II)-alcoholate species12 from alcohol and Pd-
(II)-pyridine complex13 followed by â-carbon elimination giving
an alkylpalladium species. This alkylpalladium species is prone
to eliminate palladium with â-hydride to give â,γ-unsaturated
ketones or cyclize with an alkenyl bond in the same molecule to
give cyclic ketones. The Pd(II)-hydride species produced at the
final stage can be converted again to active Pd(II) species by
molecular oxygen. The salient features of this catalytic behavior
deserves detailed study in this C-C bond cleavage reaction as
well as in the aerobic oxidation of primary and secondary
alcohols.
Supporting Information Available: Experimental procedures and
analytical and spectroscopic data of compounds (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
(9) The byproduct, 7-methylenebicyclo[4.3.0]nonan-8-one (2a′) was also
obtained in 21% yield. The formation of 2a′ might stem from bond b breaking
as indicated in Scheme 3 or palladium catalyzed rearrangement as shown in
Scheme 4.
JA984259H
(11) 1H NMR for compound 16, see: Thompson, H. W.; Long, D. J. J.
Org. Chem. 1988, 53, 4201. Ring juncture was isomerized in some stage during
the reaction. The stereochemistry of 16 was confirmed by X-ray crystal-
lographic analysis in our hands: see Supporting Information.
(12) Blackburn, T. F.; Schwartz, J. J. Chem. Soc., Chem. Commun. 1977,
157.
(10) This effect of ethyl acrylate is not clear at present, but it might
accelerate the â-carbon and hydrogen elimination. In the reaction of 1-vinyl-
cyclobutanols the addition of ethyl acrylate did not show significant difference
in the yield of the products.
(13) Kravtsova, S. V.; Romm, I. P.; Stash, A. I.; Belsky, V. K. Acta
Crystallogr. 1996, C52, 2201.