New domino sequences involving successive cleavage of carbon-carbon and carbon-oxygen bonds: Discrete product selection dictated by catalyst ligands [5]

Full text of DOI:10.1021/ja981993s

J. Am. Chem. Soc. 1998, 120, 9949-9950
9949
Cyclobutanone equipped with a phenoxymethyl side chain (1a)7
was heated in refluxing xylene in the presence of [Rh(nbd)(dppe)]-
PF6 (2a, 5 mol %)8,9 and diphenylacetylene (20 mol %). After
New Domino Sequences Involving Successive
Cleavage of Carbon-Carbon and Carbon-Oxygen
Bonds: Discrete Product Selection Dictated by
Catalyst Ligands
Masahiro Murakami,* Tamon Itahashi, Hideki Amii,†
Kunio Takahashi, and Yoshihiko Ito*
(2)
Department of Synthetic Chemistry and Biological Chemistry
Kyoto UniVersity, Yoshida, Kyoto 606-8501, Japan
ReceiVed June 8, 1998
24 h, 1a was consumed, and chromatographic isolation afforded
olefinic ester 5a in 88% yield.10 The production of 5a can be
explained by assuming the pathway pictured in eq 2. Initially,
rhodium(I) inserts into the bond between the carbonyl carbon and
the R-carbon of 1a.11 The resultant five-membered cyclic
acylrhodium intermediate 3 undergoes â-oxygen elimination,
rather than â-hydrogen elimination5a,6a,12 to produce acylrhodium
coordinated by a C-C double bond (4). Subsequent reductive
elimination gives rise to the olefinic ester 5a and rhodium(I).
When the reaction was carried out in the absence of diphenyl-
acetylene, the yield of 5a decreased to 46%. It is assumed that
â-oxygen elimination of 3 to form 4 is reversible and that
diphenylacetylene coordinates to the rhodium of 4 to expel the
olefinic moiety from the coordination sphere, thus promoting the
reaction forward.
Transition metal-mediated C-C bond cleavage has received
much attention in recent years.1 Oxidative addition of a C-C
bond onto a transition metal provides a direct method to break a
C-C bond.2 Catalytic reactions involving this elementary step,
however, are still limited due to the inertness of C-C σ-bonds
toward transition metals.3,4 On the other hand, while common
with alkali metal and alkali earth organometallics, C-O bond
cleavage by â-oxygen elimination has been observed more rarely
in late transition metal systems.5,6 We recently found that the
bond between the carbonyl carbon and the R-carbon of a
cyclobutanone is catalytically cleaved by a rhodium(I) complex.4
We envisaged that situating an ether linkage appropriately in the
substrate would lead to development of a new domino sequence
in which C-C and C-O bonds are sequentially cleaved.
Other examples of successive cleavage of C-C and C-O
bonds are shown in eqs 3 and 4. Spirocyclobutanone 1b7 yielded
(1)
(3)
(4)
We report herein successive cleavage of C-C and C-O bonds
catalyzed by a cationic rhodium complex having a bidentate
diphosphine ligand. Furthermore, this study provides a striking
example wherein a slight modification of the tether length of an
employed diphosphine ligand completely changes the reaction
course.
the corresponding olefinic ester 5b in 91% yield. The reaction
of cyclobutanone having a hydrogen atom at the 3-position (1c)7
also resulted in the formation of olefinic ester 5c.
† Present address: Department of Applied Chemistry, Faculty of Engineer-
ing, Okayama University, Tsushimanaka 3-1-1, Okayama 700-0082, Japan.
(1) For a review, see: Crabtree, R. H. Chem. ReV. 1985, 85, 245.
(2) (a) Suggs, J. W.; Jun, C.-H. J. Am. Chem. Soc. 1984, 106, 3054. (b)
Periana, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1986, 108, 7346. (c) Hughes,
R. P.; King, M. E.; Robinson, D. J.; Spotts, J. M. J. Am. Chem. Soc. 1989,
111, 8919. (d) Bennett, M. A.; Nicholls, J. C.; Rahman, A. K. F.; Redhouse,
A. D.; Spencer, J. L.; Willis, A. C. J. Chem. Soc., Chem. Commun. 1989,
1328. (e) Suzuki, H.; Takaya, Y.; Takemori, T. J. Am. Chem. Soc. 1994, 116,
10779. (f) Rybtchinski, B.; Vigalok, A.; Ben-David, Y.; Milstein, D. J. Am.
Chem. Soc. 1996, 118, 12406. (g) Jun, C.-H. Organometallics 1996, 15, 895
and references therein.
(3) (a) Noyori, R.; Odagi, T.; Takaya, H. J. Am. Chem. Soc. 1970, 92,
5780. (b) Kaneda, K.; Azuma, H.; Wayaku, M.; Teranishi, S. Chem. Lett.
1974, 215. (c) Suggs, J. W.; Jun, C.-H. J. Chem. Soc., Chem. Commun. 1985,
92. (d) Huffman, M. A.; Liebeskind, L. S. J. Am. Chem. Soc. 1993, 115,
4895. (e) Edelbach, E. L.; Lachicotte, R. J.; Jones, W. D. J. Am. Chem. Soc.
1998, 120, 2843. (f) Liou, S.-Y.; van der Boom, M. E.; Milstein, D. Chem.
Commun. 1998, 687 and references therein.
(4) (a) Murakami, M.; Amii, H.; Ito, Y. Nature 1994, 370, 540. (b)
Murakami, M.; Amii, H.; Shigeto, K.; Ito, Y. J. Am. Chem. Soc. 1996, 118,
8285. (c) Murakami, M.; Takahashi, K.; Amii, H.; Ito, Y. J. Am. Chem. Soc.
1997, 119, 9307.
(5) (a) Komiya, S.; Shindo, T. J. Chem. Soc., Chem. Commun. 1984, 1672.
(b) Komiya, S.; Srivastava, R. S.; Yamamoto, A.; Yamamoto, T. Organo-
metallics 1985, 4, 1504. (c) Oishi, S.; Kihara, N.; Hosaka, A. Chem. Lett.
1985, 621. (d) Steinborn, D Angew. Chem., Int. Ed. Engl. 1992, 31, 401 and
references therein.
A surprising ligand effect was found during the course of a
detailed examination of the reaction conditions. The reaction
pattern of 1a was completely changed when the bidentate
phosphine ligand dppe was replaced with dppp,8 where the two
phosphorus atoms are separated by a three-carbon tether instead
of a two-carbon chain. In contrast to when the dppe was used to
give the olefinic ester 5a, the [Rh(nbd)(dppp)]PF6-catalyzed
reaction of 1a furnished cyclopentanone 7a in 81% isolated yield.
No formation of 5a was detected by capillary GC analysis of the
(7) Cyclobutanones 1a-d were readily prepared by [2 + 2] cycloaddition
of the corresponding allylic ethers with dichloroketene and the subsequent
dechlorination with zinc.
(8) nbd ) 2,5-norbornadiene, dppe ) Ph2PCH2CH2PPh2, dppp ) Ph2P(CH2)3-
PPh2, and dppb ) Ph2P(CH2)4PPh2.
(9) The hexafluorophosphate complexes 2a-c were prepared according to
a literature procedure for preparation of analogous tetrafluoroborate com-
plexes: Green, A.; Kuc, T. A.; Taylor, S. H. J. Chem. Soc. A 1971, 2334.
The details of the syntheses and crystal structures will be reported separately.
(10) Monitoring the reaction by capillary GC revealed that decarbonylated
cyclopropane 8a was formed as a sole side product (∼4.5%), and formation
of cyclopentanone 7a was not observed.
(11) Whereas a less substituted R-bond is cleaved in the hydrogenolysis
of an ordinary cyclobutanone,4b the more substituted R-bond is cleaved in the
present case. It is likely that coordination of the ether linkage to rhodium
facilitates insertion into the more substituted but proximate R-bond.
(12) Milstein, D.; Calabrese, J. C. J. Am. Chem. Soc. 1982, 104, 3773.
(6) For isolation of stable (â-oxyalkyl)metal complexes, see: (a) Majima,
T.; Kurosawa, H. Chem. Soc., Chem. Commun. 1977, 610. (b) Zlota, A. A.;
Frolow, F.; Milstein, D. J. Am. Chem. Soc. 1990, 112, 6411. (c) Chatt, J.;
Vallarino, L. M.; Venanzi, L. M. J. Chem. Soc. 1957, 2496. (d) Ref 5a.
S0002-7863(98)01993-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/11/1998

9950 J. Am. Chem. Soc., Vol. 120, No. 38, 1998
Communications to the Editor
reaction mixture.13 It is likely that, as is the case with dppe, the
olefin-coordinated acylrhodium intermediate 4 is initially formed
through successive cleavage of C-C and C-O bonds. Then,
instead of undergoing direct reductive elimination, 4 recyclizes
to a six-membered acylrhodium 614 by addition of the Rh-O
linkage across the C-C double bond15 in a 6-endo mode.16
Finally, reductive elimination forming a C-C bond affords 7a.
(96%).17 The wider P-Rh-P angle with dppb may cause larger
steric repulsions to favor a four-membered rhodacycle rather than
a five-membered one, thus promoting expulsion of the carbonyl
group from the five-membered cyclic skeleton.
Similar discrete product selection dictated by the diphosphine
ligand was observed with the benzyl ether analogue 1d7 of the
cyclobutanone 1a as shown in eq 7.
(5)
(7)
When an analogous reaction of 1a catalyzed by [Rh(nbd)-
(dppp)]PF6 (2b) was carried out in the presence of diphenylacety-
lene (20 mol %), the olefinic ester (5a) was produced (76%) in
preference to 7a (9%). This result can be explained by assuming
that diphenylacetylene drives out the internal coordination of the
olefinic moiety of 4 to disfavor recyclization.
A third distinct and exclusive reaction pathway of 1a was
identified when the bidentate diphosphine ligand dppp was
replaced with dppb.8 As reported previously,4b 1a having an
ether side chain underwent simple decarbonylation when catalyzed
by [Rh(nbd)(dppb)]PF6 (2c).9 Decarbonylated cyclopropane 8a,
keeping the ether side chain intact, was exclusively formed
Among the three pathways, however, the reaction that forms
cyclopentanone lacks generality. For example, olefinic ester 5b
was obtained in 86% yield from cyclobutanone 1b even when
2b was used as the catalyst.18
In summary, new rhodium-catalyzed domino sequences were
identified in which C-C and C-O bonds were successively
cleaved. A highlight is that the reaction patterns of the cyclo-
butanones 1a and 1d are affected enormously by the employed
bidentate diphosphine ligand. As the length of the carbon tether
between two phosphorus atoms was extended from ethylene to
trimethylene to tetramethylene, different compounds, ring-opened
olefinic ester, recyclized cyclopentanone, or decarbonylated
cyclopropane, were obtained respectively from the same reactant.
The mechanistic explanation for this unprecedented dramatic
divergence deserves careful study but could be very difficult to
work out. While the observed divergence presently requires
certain substitutions in the substrate, it clearly demonstrates the
possibility of controlling the reaction course itself by slight
modifications of the ligand of a transition metal catalyst.
(6)
Acknowledgment. Support from Monbusho (Grant-in-Aid for Sci-
entific Research on Priority Areas, No. 283: Innovative Synthetic
Reactions) is gratefully acknowledged.
(13) Decarbonylated cyclopropane 8a was observed by GC as the only
side product (∼12%).
Supporting Information Available: Experimental details and char-
acterization for 5, 7, and 8 (2 pages, print/PDF). See any current masthead
page for ordering and Web access instructions.
(14) Campbell, R. E., Jr.; Lochow, C. F.; Vora, K. P.; Miller, R. G. J. Am.
Chem. Soc. 1980, 102, 5824.
(15) For addition of a Rh-O linkage across a C-C double bond, see:
Evans, J. A.; Russell, D. R.; Bright, A.; Shaw, B. L. Chem. Commun. 1971,
841.
(16) Alternatively, recyclization of 4 by addition of the Rh-C linkage across
the C-C double bond in a 5-endo mode followed by reductive elimination
forming a C-O bond is also conceivable for the production of 7a.
JA981993S
(17) Neither 5a nor 7a was detected by GC.
(18) The reaction of 1b catalyzed by the dppb complex 2c afforded the
corresponding decarbonylated cyclopropane 8b in 93% yield, being in
accordance with other examples.