Rhodium-catalyzed carbonylation of spiropentanes

Article abstract of DOI:10.1021/ja0732779

Spiropentanes undergo carbonylation under an atmosphere of carbon monoxide in the presence of a rhodium(I)-phosphine catalyst, giving 3-methylcyclopent-2-enones. The catalytic cycle involves two mechanistically different carbon-carbon cleavage processes.

Full text of DOI:10.1021/ja0732779

Published on Web 10/03/2007
Rhodium-Catalyzed Carbonylation of Spiropentanes
Takanori Matsuda, Tomoya Tsuboi, and Masahiro Murakami*
Department of Synthetic Chemistry and Biological Chemistry, Kyoto UniVersity, Katsura, Kyoto 615-8510, Japan
Received May 8, 2007; E-mail: murakami@sbchem.kyoto-u.ac.jp
Spiropentanes,1 the smallest spirocyclic hydrocarbons, possess
Scheme 1. Mechanism of Spiropentane Carbonylation
unique rigid and strained structures and have been the subject of
extensive investigation in terms of synthesis,2 biological activity,3
and spectroscopy.4 However, the reactivities of spiropentanes5
toward transition metals, in particular, are yet to be explored.
Hydrogenation of spiropentane occurs in the presence of PtO2 to
produce a mixture of three hydrogenated hydrocarbons.6 In the
cobalt-promoted carbonylation reactions of vinyl- and methyl-
enespiropentanes, one cyclopropane ring was cleaved with the other
cyclopropane ring remaining unscathed.7 Our studies on the C-C
bond activation of cyclobutanones8 led us to target spiropentane
Table 1. Rhodium-Catalyzed Carbonylation of Spiropentanes
1b-ga
substrates for investigation. In this communication, we describe a
catalytic carbonylation reaction of spiropentanes forming cyclo-
pentenones through two successive carbon-carbon bond cleavage
processes.8b
When a solution of 1-(benzyloxymethyl)-1-methylspiropentane
(1a) in p-xylene was heated at 130 °C for 2.5 h under an argon
atmosphere in the presence of a rhodium(I) catalyst generated in
situ from [RhCl(cod)]2 (5 mol %, 10 mol % Rh) and DPPP (10
mol %),9 no reaction occurred, and 1a was largely recovered. In
contrast, when the same reaction was carried out under an
atmosphere of carbon monoxide, the carbonylation of 1a took place
to afford cyclopentenone 2a in 84% yield (eq 1).10,11
The formation of cyclopentenone 2a from spiropentane 1a is
explained by assuming the pathway shown in Scheme 1. Initially,
the C4-C5 bond of spiropentane 1a oxidatively adds to rhodium-
(I) to form spirocyclic rhodacyclobutane 3. Insertion of carbon
monoxide generates rhodacyclopentanone 4.12 Then, the methylene
carbon (C2) selectively migrates onto rhodium through a â-carbon
elimination13 to convert the spirocyclic skeleton into six-membered
rhodacycle 5.14 Finally, reductive elimination furnishes 3-methyl-
enecyclopentanone 6, which isomerizes to the enone 2a under the
reaction conditions.
a 5 mol % of [RhCl(cod)]2, 10 mol % of DPPP, CO (1 atm), p-xylene
(0.05 M), 130 °C, 2.5 h, unless otherwise noted. b Isolated yield by
preparative TLC. c 1b and (HCHO)n (10 equiv) were reacted for 6 h. d 5 h.
Scheme 2. Carbonylation of Trisubstituted Spiropentane 1ha
Various disubstituted spiropentanes underwent the carbonylation
reaction under similar conditions (Table 1). 1,1-Disubstituted
spiropentanes 1b-e afforded the corresponding 4,4-disubstituted
3-methylcyclopent-2-enones 2b-e in good yields (entries 1-5).
Paraformaldehyde could be used as a carbonyl source instead of
gaseous carbon monoxide (entry 2).15 Cyclopropylspiropentane 1e
reacts only at the spiropentane moiety, leaving the pendant
cyclopropyl group untouched, demonstrating the inertness of the
isolated cyclopropane ring under the reaction conditions (entry 5).
A pair of cis/trans isomers of 1,2-disubstituted spiropentanes (1f
and 1g) was subjected to the carbonylation to test the stereospeci-
ficity of the reaction. The secondary carbons migrated onto rhodium
with retention of the stereochemistry to furnish the corresponding
bicyclic ketones 2f and 2g, respectively (entries 6 and 7).
a Conditions: 5 mol % of [RhCl(cod)]2, 10 mol % of DPPP, p-xylene,
130 °C, CO (1 atm), 2.5 h.
The carbonylation reaction of spiropentanes with other substitu-
tion patterns was also examined. The reaction of trisubstituted
spiropentane 1h was complicated, yielding cyclopentenone 2h
(37%) and diene 7 (18%) as the only identifiable products (Scheme
2). The following pathway accounts for the formation of 2h and 7.
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10.1021/ja0732779 CCC: $37.00 © 2007 American Chemical Society

C O M M U N I C A T I O N S
Scheme 3. Carbonylation of Monosubstituted Spiropentane 1i and
Reaction of Spirocyclic Cyclobutanone 8a
was synthesized from commercially available methyl 4-methylphe-
nyl ketone 11 in three steps: Wittig olefination of 11 with
cyclopropylidenephosphorane (82%), cyclopropanation of methyl-
enecyclopropane 12 with dibromocarbene (54%), and debromination
of 13 with zinc (56%). Carbonylation of 1j under the standard
conditions gave cyclopentenone 2j (82%). Finally, the nickel-
catalyzed conjugate addition of dimethylzinc17b furnished 14 in 75%
yield.
In summary, we have developed a rhodium-catalyzed carbony-
lation reaction of spiropentanes involving two different types of
carbon-carbon bond cleavage processes. The reaction allows for
the synthesis of a series of 3-methylcyclopent-2-enones, one of
which was utilized as an intermediate in the concise synthesis of
(()-â-cuparenone.
Acknowledgment. This work was supported by Grants-in-Aid
for Scientific Research on Priority Areas (No. 18037035) and for
Scientific Research (A) (No. 19205013) from the Ministry of
Education, Culture, Sports, Science and Technology, Japan. We
thank Dr. S. Kadowaki for assistance in the synthesis of the
spiropentanes.
a Conditions: 5 mol % of [RhCl(cod)]2, 10 mol % of DPPP, p-xylene,
130 °C, CO (1 atm), 2.5 h for 1h and 20 h for 8.
Scheme 4. Synthesis of (()-â-Cuparenone
Supporting Information Available: Experimental details and
selected spectral data for new compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
References
(1) For reviews, see: (a) de Meijere, A.; Kozhushkov, S. I. Chem. ReV. 2000,
100, 93. (b) de Meijere, A.; Kozhushkov, S. I.; Schill, H. Chem. ReV.
2006, 106, 4926.
(2) (a) Murray, M. J.; Stevenson, E. H. J. Am. Chem. Soc. 1944, 66, 314. (b)
Applequist, D. E.; Fanta, G. F.; Henrikson, B. W. J. Org. Chem. 1958,
23, 1715. (c) Charette, A. B.; Jolicoeur, E.; Bydlinski, G. A. S. Org. Lett.
2001, 3, 3293.
(3) (a) Li, D.; Zhou, H.-q.; Dakoji, S.; Shin, I.; Oh, E.; Liu, H.-w. J. Am.
Chem. Soc. 1998, 120, 2008. (b) Guan, H.-P.; Ksebati, M. B.; Cheng,
Y.-C.; Drach, J. C.; Kern, E. R.; Zemlicka, J. J. Org. Chem. 2000, 65,
1280. (c) Pellicciari, R.; Marinozzi, M.; Camaioni, E.; del Carmen Nu`nez,
M.; Costantino, G.; Gasparini, F.; Giorgi, G.; Macchiarulo, A.; Subra-
manian, N. J. Org. Chem. 2002, 67, 5497.
(4) (a) Cleveland, F. F.; Murray, M. J.; Gallaway, W. S. J. Chem. Phys. 1947,
15, 742. (b) Bechtold, W.; Goldstein, J. H. J. Am. Chem. Soc. 1981, 103,
4989. (c) Gleiter, R.; Krennrich, G.; Brinker, U. H. J. Org. Chem. 1986,
51, 2899.
(5) (a) Gajewski, J. J.; Burka, L. T. J. Am. Chem. Soc. 1972, 94, 8865. (b)
Wiberg, K. B.; Snoonian, J. R. J. Org. Chem. 1998, 63, 1390. (c) Maercker,
A.; Oeffner, K. S.; Girreser, U. Tetrahedron 2004, 60, 8245.
(6) Slabey, V. A. J. Am. Chem. Soc. 1947, 69, 475.
(7) (a) Kurahashi, T.; de Meijere, A. Synlett 2005, 2619. (b) Kurahashi, T.;
de Meijere, A. Angew. Chem., Int. Ed. 2005, 44, 7881.
Rhodacyclobutane 3h is formed from 1h, as with the case of 1a.
From this species, two six-membered rhodacycles 5h and 5′h result
depending on which carbon C1 or C2 migrates. Migration of the
secondary carbon (C2) predominates over migration of the tertiary
carbon (C1), thus reductive elimination from 5h gives 2h. With
the six-membered rhodacycle 5′h, reductive elimination forming a
quaternary carbon failed to occur because of the steric reasons.
Instead, this species undergoes â-hydride elimination prior to
reductive elimination to afford 7.
When monosubstituted spiropentane 1i was subjected to the
reaction conditions, an isomeric mixture of cyclopentenones 2i
(55%) and 2′i (21%) was obtained (Scheme 3). Product 2i resulting
from migration of the primary carbon (C2) predominated over the
product 2′i resulting from migration of the secondary carbon (C1)
(2i:2′i ) 72:28). A control experiment was performed to obtain
some mechanistic information. Spirocyclic cyclobutanone 8 isomer-
ized in the presence of the rhodium catalyst to afford a mixture of
2i and 2′i (73:27), as previously reported.8b This result suggests
the possibility of a mechanistic similarity between the reaction of
8 and the carbonylation of 1i.
(8) (a) Murakami, M.; Amii, H.; Shigeto, K.; Ito, Y. J. Am. Chem. Soc. 1996,
118, 8285. (b) Murakami, M.; Takahashi, K.; Amii, H.; Ito, Y. J. Am.
Chem. Soc. 1997, 119, 9307. (c) Matsuda, T.; Shigeno, M.; Murakami,
M. Chem. Lett. 2006, 35, 288 and references therein.
(9) Abbreviations: cod ) cycloocta-1,5-diene; DPPP ) 1,3-bis(diphenylphos-
phino)propane.
(10) Results with other conditions: 10 mol % of RhCl(PPh3)3 (70%); 2.5 mol
% of [RhCl(cod)]2 and 5 mol % of DPPP (70%); 10 mol % of [Rh(cod)2]-
BF4 and 10 mol % of DPPP (0%).
(11) The reaction under 10 atm of CO was less productive (29% of 2a and
54% recovery of 1a).
(12) Related complexes have been generated from cyclobutanones8 and
cyclopropanes. For the latter examples, see: (a) Roundhill, D. M.; Lawson,
D. N.; Wilkinson, G. J. Chem. Soc. A 1968, 845. (b) McQuillin, F. J.;
Powell, K. C. J. Chem. Soc., Dalton Trans. 1972, 2129.
For comparison, cyclopropane 916 and spiro[3.2]hexane 10 were
subjected to similar reaction conditions. Unlike the case of
spiropentanes 1, no reaction occurred, and after 2.5 h, 9 and 10
remained intact. The contrasting results and the result of the reaction
of 1e indicate that the reactivity toward carbonylation under these
conditions is peculiar to the highly strained structure of 1.
(13) (a) Nishimura, T.; Uemura, S. Synlett 2004, 201. (b) Satoh, T.; Miura,
M. Top. Organomet. Chem. 2005, 14, 1. (c) Murakami, M.; Makino, M.;
Ashida, S.; Matsuda, T. Bull. Chem. Soc. Jpn. 2006, 79, 1315.
(14) The possibility of occurrence of â-carbon elimination from 3 prior to CO
insertion cannot be ruled out.
(15) (a) Morimoto, T.; Kakiuchi, K. Angew. Chem., Int. Ed. 2004, 43, 5580.
(b) Shibata, T. AdV. Synth. Catal. 2006, 348, 2328.
(16) Ring opening of cyclopropylmethyl ethers in the presence of Wilkinson’s
catalyst was reported. Bart, S. C.; Chirik, P. J. J. Am. Chem. Soc. 2003,
125, 886.
(17) (a) Lansbury, P.; Hilfiker, F. R. Chem. Commun. 1969, 619. (b) Greene,
A. E.; Charbonnier, F.; Luche, M.-J.; Moyano, A. J. Org. Chem. 1984,
49, 931. (c) Srikrishna, A.; Sundarababu, G. Tetrahedron 1991, 47, 481.
(d) Ray, D.; Ray, J. K. Org. Lett. 2007, 9, 191 and references therein.
The utility of this transformation was demonstrated in a short
synthesis of a sesquiterpene, (()-â-cuparenone (12) (Scheme 4).17
Spiropentane 1j, required for the preparation of cyclopentenone 2j,
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