Rearrangement of 1-(1-alkynyl)cyclopropanols to 2-cyclopentenones via their hexacarbonyldicobalt complexes. A new use of alkyne-CO2(CO)6 complexes in organic synthesis

Article abstract of DOI:10.1021/ja9734004

A novel rearrangement of 1-(1-alkynyl)cyclopropanols to 2-cyclopenten- 1-ones proceeded on complexation of their alkynyl part with octacarbonyldicobalt (Co₂(CO₈)). 1-(1-Alkynyl)cyclopropanols with a wide range of substituents on thei

Full text of DOI:10.1021/ja9734004

J. Am. Chem. Soc. 1998, 120, 3903-3914
3903
Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones
via Their Hexacarbonyldicobalt Complexes. A New Use of
Alkyne-Co2(CO)6 Complexes in Organic Synthesis
Nobuharu Iwasawa,*,† Takeshi Matsuo, Mari Iwamoto, and Taketo Ikeno
Contribution from the Department of Chemistry, Graduate School of Science, The UniVersity of Tokyo,
Hongo, Bunkyo-ku, Tokyo 113
ReceiVed September 29, 1997
Abstract: A novel rearrangement of 1-(1-alkynyl)cyclopropanols to 2-cyclopenten-1-ones proceeded on
complexation of their alkynyl part with octacarbonyldicobalt (Co2(CO8)). 1-(1-Alkynyl)cyclopropanols with
a wide range of substituents on their alkyne terminus rearranged to the corresponding 3-substituted 2-cyclopenten-
1-ones in good yield. In case of the reactions of 1-alkynylcyclopropanols with an alkyl substituent on the
cyclopropane ring, either 4-substituted or 5-substituted 2-cyclopenten-1-ones could be selectively obtained by
appropriate choice of stereochemistry and protective group of the substrates. This rearrangement was
successfully applied to cyclopentenone annulation reactions onto cycloalkenes. An efficient synthesis of alkynyl-
substituted bicyclo[n.1.0]alkanol derivatives from the corresponding cycloalkenes according to Danheiser’s
protocol was developed, and bicyclic cyclopentenones were obtained in moderate to good yield by applying
to these the cobalt-mediated rearrangement. Furthermore, the rearrangement was found to proceed catalytically
on addition of triaryl phosphite as a ligand. In particular, when tri(o-isopropylphenyl) phosphite was used as
ligand, 5-10 mol % of Co2(CO)8 and 10-20 mol % of the phosphite sufficed for the efficient conversion of
1-alkynylcyclopropanols to 2-cyclopentenones. Mechanistic studies revealed that the rate-determining step
was the thermal or oxidative dissociation of a carbonyl ligand from the alkyne-Co2(CO)6 complex and that
the coordinately unsaturated cobalt moiety so-formed inserted into the neighboring carbon-carbon bond of
the cyclopropane to give a metallacyclic intermediate. This further rearranged to a metallacyclohexanone
intermediate, which gave the cyclopentenone with liberation of a coordinatively unsaturated cobalt species.
Unlike the well-known chemistry of the vinylcyclopropane-
cyclopentene rearrangement,1 there has been no precedent for
the corresponding alkynylcyclopropane rearrangement to cy-
clopentene derivatives with the exception of one specific
example, that is, the pyrolysis of 2-methyl-1-ethynylcyclopro-
pane to methylcyclopentene and other compounds.2 This
difficulty in achieving the rearrangement of alkynylcyclopro-
panes to cyclopentene derivatives presumably lies in the longer
distance between the alkyne terminus and the cyclopropane ring
compared to that between the latter and an alkene terminus.
Various transition metal catalysts are known to promote the
vinylcyclopropane-cyclopentene rearrangement by forming a
complex with the olefinic part of the molecule, and the reactions
generally proceed under milder conditions than those of
equivalent thermal reaction.3 It is expected that by appropriate
complexation with transition metal compounds, alkynylcyclo-
propanes could also be made to rearrange to cyclopentene
derivatives, provided that the complexed transition metal moiety
can activate the neighboring cyclopropane ring effectively.
Alkyne-hexacarbonyldicobalt (Co2(CO)6) complexes can be
easily synthesized from alkynes and octacarbonyldicobalt (Co2-
(CO)8) simply by mixing, and these complexes are usually
chromatographically isolable, stable compounds.4 These alkyne-
Co2(CO)6 complexes have been employed in organic synthesis
mostly for three types of reaction, that is (1) as a protective
group for alkynyl functionality;5 (2) as a means to stabilize
propargylic cations for nucleophilic attack (Nicholas type
reaction);6 and (3) as a component in the Pauson-Khand reaction
to give 2-cyclopenten-1-ones by reaction with olefins.7 Al-
(4) (a) Sternberg, H. W.; Greenfield, H.; Friedel, R. A.; Wotiz, J.;
Markby, R.; Wender, I. J. Am. Chem. Soc. 1954, 76, 1457. (b) Greenfield,
H.; Sternberg, H. W.; Friedel, R. A.; Wotiz, J. H.; Markby, R.; Wender, I.
J. Am. Chem. Soc. 1956, 78, 120. (c) Hu¨bel, W. In Organic Syntheses Via
Metal Carbonyls; 1, Wender, I., Pino, P., Eds.; Interscience: New York,
1968; Vol. 1. (d) Kemmitt, R. D. W.; Russell, D. R. In ComprehensiVe
Organometallic Chemistry; Wilkinson G., Ed.; Pergamon Press: Oxford,
1982; Vol. 5, p1.
(5) For examples, see: (a)Seyferth, D.; Wehman, A. T. J. Am. Chem.
Soc. 1970, 92, 5520. (b) Nicholas, K. M.; Pettit, R. Tetrahedron Lett. 1971,
3475. (c) Melikyan, G. G.; Vostrowsky, O.; Bauer, W.; Bestmann, H. J.;
Khan, M.; Nicholas, K. M. J. Org. Chem. 1994, 59, 222. (d) Milgrom, L.
R.; Rees, R. D.; Yahioglu, G. Tetrahedron Lett. 1997, 38, 4905.
(6) (a) Varghese, V.; Saha, M.; Nicholas, K. M. Org. Synth. 1988, 67,
141. (b) Nicholas, K. M. Acc. Chem. Res. 1987, 20, 207. (c) Caffyn, A. J.
M.; Nicholas, K. M. In ComprehensiVe Organometallic Chemistry II, Vol
12: Transition Metal Alkyne Complexes: Transition Metal-stabilized
Propargyl System; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon Press: Oxford, 1995; p 685. For some recent examples, see:
(d) Schreiber, S. L.; Klimas, M. T.; Sammakia, T. J. Am. Chem. Soc. 1987,
109, 5749. (e) Tanaka, S.; Isobe, M. Synthesis 1995, 859. (f) Nakamura,
T.; Matsui, T.; Tanino, K.; Kuwajima, I. J. Org. Chem. 1997, 62, 3032. (g)
Caddick, S.; Delisser, V. M. Tetrahedron Lett. 1997, 38, 2355.
† Phone number 81-3-3812-2111 ext 4643. FAX number 81-3-5800-6891.
E-mail niwasawa@chem.s.u-tokyo.ac.jp.
(1) (a) Hudlicky, T.; Reed, J. W. In ComprehensiVe Organic Synthesis,
Vol 5: Rearrangements of Vinylcyclopropane and Related Systems; Trost,
B. M., Ed.; Pergamon Press: Oxford, 1991; p 899. (b) Goldschmidt, Z.;
Crammer, B. Chem. Soc. ReV. 1988, 17, 229. (c) Hudlicky, T.; Kutchan, T.
M.; Naqvi, S. M. Org. React. 1985, 33, 247.
(2) Dalacker, V.; Hopf, H. Tetrahedron Lett. 1974, 15.
(3) See ref 1. For a recent example, see: Ryu, I.; Ikura, H.; Tamura, Y.;
Maenaka, J.; Ogawa, A.; Sonoda, N. Synlett 1994, 941. References are cited
therein.
S0002-7863(97)03400-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/11/1998

3904 J. Am. Chem. Soc., Vol. 120, No. 16, 1998
Iwasawa et al.
Table 1. Reactions of Various 1-Alkynylcyclopropanols 1 Using
a Stoichiometric Amount of Co2(CO)8
Scheme 1
R
solvent
reaction timea/h
yield of 3/%
n-C6H13(1a)
Ph(1b)
t-Bu(1c)
SiMe3(1d)
SiPh3(1e)
SiPh3(1e)
Sii-Pr3(1f)
Sii-Pr3(1f)
CH2OTBS(1g)
CH2St-Bu(1h)
CH2CH2OTBS(1i)
CH2CH2OH(1j)
Sn-Bu(1k)
COOEt(1l)
DME
DME
DME
DME
DME
THF
DME
THF
DME
DME
DME
THF
1.5
1
1.25
1.5
0.5
3
0.16
1.5
1.5
1.5
6
71
91
73
77
73
85
62
67
61
68
81
68
45
33
though the unique properties of alkyne-Co2(CO)6 complexes
are obvious from these reactions, it is expected that other useful
reactions using alkyne-Co2(CO)6 complexes still remain to be
explored. In this paper is described another use of alkyne-
Co2(CO)6 complexes in organic synthesis, a novel rearrangement
of 1-(1-alkynyl)cyclopropanols to 2-cyclopenten-1-ones via their
Co2(CO)6 complexes.8
2
1.25
1.25
DME
DME
a Reaction time indicates the approximate time required for the cobalt
complex 2 to disappear as judged by TLC.
Stoichiometric Reactions. 1-Alkynylcyclopropanols with no
substituents at the 2- and 3-positions of the cyclopropane ring
were easily prepared in good yields by the reaction of alkynyl
Grignard reagents with cyclopropanone hemiacetal.9
t-BuOH, EtOAc, and CCl4 gave lower yields of the products
(benzene, 3a, 40%, 4a, 40%; t-BuOH, 3a, 27%, 4a, 30%;
EtOAc, 3a, 35%, 4a, 10%) or a complex mixture of unidentified
products (CCl4).
When 1-(1-octynyl)cyclopropanol 1a (R ) n-C6H13) was
treated with 1.1 molar amounts of Co2(CO)8 in THF at room
temperature under an argon atmosphere, complete formation of
the Co2(CO)6 complex 2a was observed within 30 min by thin-
layer chromatography. This complex was stable at room
temperature, but when the solution was heated to reflux for 8 h
under argon, it disappeared completely, and 3-hexyl-2-cyclo-
penten-1-one 3a was produced in 62% yield (Scheme 1). The
intermediate alkyne-Co2(CO)6 complex 2a was easily isolated
by silica gel column chromatography under argon. Heating this
isolated complex in refluxing THF gave the same rearranged
product 3a in a comparable yield. In general, 1-(1-alkynyl)-
cyclopropanols themselves are thermally more stable than
1-alkyl or 1-alkenyl cyclopropanols, and in practice 1a was
recovered unchanged when it was heated in refluxing benzene
for 2.5 h. Thus, complexation of Co2(CO)6 to the alkynyl part
of 1a is essential for the rearrangement.
As a novel 1-alkynylcyclopropanol-cyclopentenone rear-
rangement had been observed, we decided to investigate this
reaction in detail. Examination of the effect of the solvent on
this reaction using 1-(1-octynyl)cyclopropanol 1a as a substrate
revealed that use of ethereal solvents generally favored the
formation of the cyclopentenone 3a, and by carrying out the
reaction in refluxing dimethoxyethane (DME) for 1.5 h, 3a was
obtained in 71% yield. On the other hand, use of hydrocarbon
solvents favored another reaction pathway, that is, rearrangement
of the 1-octynylcyclopropanol-Co2(CO)6 complex 2a to an ethyl
1-octynyl ketone-Co2(CO)6 complex 4a. For example, by
carrying out the reaction in refluxing hexane, the complex 4a
could be obtained in about 70% yield, along with the cyclo-
pentenone 3a in 13% yield. Other solvents such as benzene,
Various other transition metal compounds known to form
complexes with alkynes were also examined in this reaction
but failed to give satisfactory results.10 We also examined
whether the presence of the unprotected hydroxyl group on the
cyclopropane was essential for the success of this reaction. The
reactions of various cyclopropanol derivatives such as the benzyl
ether, acetate, and various silyl ethers were carried out under
similar conditions, and it was found that while the reactions of
the benzyl ether or acetate of 1a were sluggish and the
rearranged product 3a was obtained in low yield, the reaction
of the corresponding TBS ether gave the cyclopentenone 3a in
good yield.11
The results of the reactions of 1-alkynylcyclopropanols with
various substituents on the alkyne using a stoichiometric amount
of Co2(CO)8 are summarized in Table 1. Not only alkyl-
substituted alkyne derivatives but also aryl- or silyl-substituted
alkyne derivatives gave the corresponding 3-substituted 2-cy-
clopenten-1-ones in good to high yields. In particular, the
efficient preparation of 3-silyl-substituted cyclopentenones is
noteworthy as hitherto no good method has been reported for
the synthesis of such compounds.12 Interestingly, bulkiness of
the substituent on the alkyne has a large effect on the reaction
rate. In case of the reaction of the TMS derivative 1d, it took
about 1.5 h for the completion of the reaction in refluxing DME.
On the other hand, the reaction of the triphenylsilyl derivative
1e needed only 0.5 h, and furthermore, the reaction went to
completion within 10 min when the triisopropylsilyl(TIPS)
derivative 1f was employed as substrate. Thus, the bulkier the
substituent on the alkyne becomes, the faster the reaction
proceeds. Various alkynyl substituents containing a functional
group can also be employed in this reaction. A tert-butyldi-
methylsilyl ether, alkylthio group, and even an unprotected
hydroxyl group are tolerated, and the corresponding function-
(7) (a) Schore, N. E. Org. React. 1991, 40, 1. (b) Schore, N. E. In
ComprehensiVe Organic Synthesis, Vol. 5: The Pauson-Khand Reaction;
Trost, B. M., Ed.; Pergamon Press: Oxford, 1991; p 1037. (c) Pauson, P.
L. In Organometallics in Organic Synthesis. Aspects of a Modern Inter-
dicsciplinary Field; Meijere, A. de., Dieck, H. T., Eds.; Springer: Berlin,
1988; p 233. (d) Pauson, P. L. Tetrahedron 1985, 41, 5855. (e) Schore, N.
E. In ComprehensiVe Organometallic Chemistry II, Vol 12: Transition Metal
Alkyne Complexes: Pauson-Khand Reaction; Abel, E. W., Stone, F. G.
A., Wilkinson, G., Eds.; Pergamon Press: Oxford, 1995; p 703.
(8) Preliminary communications: (a) Iwasawa, N. Chem. Lett. 1992, 473.
(b) Iwasawa, N.; Matsuo, T. Chem. Lett. 1993, 997. (c) Iwasawa, N.;
Iwamoto, M. Chem. Lett. 1993, 1257.
(10) Followings are the complexes examined. In some cases rearranged
products were obtained in low yield, but reactions were generally sluggish
and no satisfactory results were obtained: Ni(COD)2, Ni(PPh3)4, Fe2(CO)9,
W(CO)5‚THF, Pd(PPh3)4, Pd(dba)2, Cp2W2(CO)4, Cp2Mo2(CO)4.
(11) At present, we suppose that the hydrogen at the 2-position of the
cyclopentenone comes from the small amount of water present in the
reaction medium, because rigorous elimination of water from the reaction
mixture by carrying out the reaction in the presence of MS 4A made the
reaction sluggish and the yield of the product decreased considerably.
(12) See for an example: Kim, S. H.; Jin, Z.; Fuchs, P. L. Tetrahedron
Lett. 1995, 36, 4537.
(9) Salau¨n, J.; Bennani, F.; Compain, J.-C.; Fadel, A.; Ollivier, J. J. Org.
Chem. 1980, 45, 4129.

Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones
J. Am. Chem. Soc., Vol. 120, No. 16, 1998 3905
Table 2. Examination of the Regioselectivity of the Rearrange-
ment of 2-Methyl-1-phenylethynylcyclopropanol 7a and 2,2-Dimeth-
yl-1-phenylethynylcyclopropanol 10a and Their Silyl Ethers
Scheme 2
R3
solvent reaction timea/h yield/% 8a:9a (11a:12a)
2-1. R ) Ph, R1 ) Me, R2 ) H (7acis)
H
DME
DME
1.5
1.5
1.25
5
75
73
83
77
70
50:50
70:30
91:9
94:6
94:6
SiMe3
Sit-BuMe2 DME
Sit-BuMe2 THF
Sii-Pr3
THF
3
2-2. R ) Ph, R1 ) H, R2 ) Me (7atrans
)
H
DME
1.5
1.25
5
86
88
47
<1:>99
1:99
Sit-BuMe2 DME
Sii-Pr3
DME
2:98
2-3. R ) Ph, R1 ) R2 ) Me (10a)
H
DME
1
80
88
<1:>99
Sit-BuMe2 DME
1.5
3:97
a Reaction time indicates the approximate time required for the cobalt
complex 2 to disappear as judged by TLC.
alized cyclopentenones were obtained in moderate to good yield.
Furthermore, when a 1-(1-alkynyl)cyclopropanol having an
electron-donating n-butylthio group, or an electron-withdrawing
ethoxycarbonyl group, directly bonded to the alkyne was
employed, the corresponding 3-n-butylthio- or 3-ethoxycarbonyl-
2-cyclopentenone was obtained in moderate yields.
Table 3. Reactions of Various 2-Substituted 1-(1-Alkynyl)-
Cyclopropanols
reaction yield/
8:9
(or 11:12)
compd
7btrans Ph
7bcis Ph
7ctrans n-Hex H
7ccis n-Hex Me
7dtrans n-Hex H
R
R1
R2 R3 solvent timea/h
%
In the case of transformation of alkynylcyclopropanols with
a substituent on the 2-position of the cyclopropane ring, two
regioisomers, that is, the 4-substituted and/or 5-substituted
2-cyclopentenones, could be formed depending on which bond
of the cyclopropane is cleaved. The required substrates could
not be prepared according to the same procedure used for the
preparation of compounds 1 due to the instability of the
corresponding substituted cyclopropanone hemiacetals. Ac-
cordingly, we employed the following procedure: Alkynyl
ketones 5 were converted to the corresponding silyl enol ethers
6, and then cyclopropanation was carried out according to the
modified Simmons-Smith reaction using diethylzinc and di-
iodomethane.13 Finally, the silyl group was removed using a
catalytic amount of TMSCl in MeOH to give the desired
substituted cyclopropanols 7 in good yield. Since either E or
Z silyl enol ethers can be prepared with good to high selectivities
depending on the enolization conditions,14 by this procedure
selective preparation of either cis or trans substituted cyclopro-
panols (7cis or 7trans) is possible as shown in Scheme 2.
H
i-Pr
i-Pr
H
Me
H
i-Pr
H
H
DME
TBS THF
DME
TBS THF
DME
TBS THF
2.5
7
2.5
86
75
83
71
88
85
83
81
<1:>99
96:4
<1:>99
77:23
<1:>99
85:15
<1:>99
<1:>99
H
14
H
2
32
1
7dcis
10b
10c
n-Hex i-Pr
Ph
n-Hex Me Me
-(CH2)5- H
DME
DME
H
1.5
a Reaction time indicates the approximate time required for the cobalt
complex 2 to disappear as judged by TLC.
Scheme 3
NMR, while when silyl ethers of 7atrans were employed as
substrates, the same 5-substituted isomer 9a was obtained also
in high regioselectivity, which however fell slightly as the
bulkiness of the silyl group increased (Table 2, part 2-2).
First the reaction of (1R*,2S*)-2-methyl-1-phenylethynylcy-
clopropanol 7acis (R ) Ph, R1 ) Me, R2 ) R3 ) H) according
to the standard procedure was examined. Heating the Co2(CO)6
complex of 7acis for 1.5 h in DME under an argon atmosphere
gave almost equal amounts of 4-methyl-3-phenyl-2-cyclopenten-
1-one 8a and 5-methyl-3-phenyl-2-cyclopenten-1-one 9a in a
combined yield of 75%. As this rearrangement was nonregi-
oselective, the reaction of various silyl ethers of 7acis was next
examined. As shown in Table 2, part 2-1, the bulkiness of the
silyl group greatly influences the regioselectivity of the rear-
rangement. Using the TMS ether, the ratio of 8a and 9a was
70:30 but by using the bulkier tert-butyldimethylsilyl or
triisopropylsilyl ether and by carrying out the reaction in
refluxing THF, the regioselectivity could be improved to 94:6
without lowering the yield of the products. On the other hand,
in the reaction of (1R*,2R*)-2-methyl-1-phenylethynylcyclo-
propanol 7atrans (R ) Ph, R1 ) R3 ) H, R2 ) Me) 5-substituted
To make clear whether a methyl group cis to the alkyne or
trans to the alkyne would play a dominating role in determining
the regioselectivity, the reactions of 2,2-dimethyl-1-phenylethy-
nylcyclopropanol 10a (R ) Ph, R1 ) R2 ) Me, R3 ) H) and
its TBS ether were also examined. When 10a itself was
employed as substrate, 5,5-dimethyl-3-phenyl-2-cyclopenten-
1-one 12a was obtained as the sole product. The reaction of
the corresponding TBS ether gave the same regioisomer as the
major product with a small amount of the other regioisomer
11a (Table 2, part 2-3). These results indicate that the
substituent cis to the alkynyl group plays a dominant role in
determining the regioselectivity of the reaction.
As will be discussed later, it is assumed that the reaction
proceeds by the oxidative addition of the carbon-carbon bond
of the cyclopropane to cobalt species to make a metallacyclic
intermediate. The regioselectivity of this reaction is controlled
by the relative ease of insertion of the cobalt species into the
C1-C2 and the C1-C3 bonds of the cyclopropane. On the
basis of these assumptions the regioselectivity of the reaction
can be explained by considering the conformations available
1
isomer 9a was obtained as the sole isomer detectable by H
(13) (a) Simmons, H. E.; Cairns, T. L.; Vladuchick, S. A.; Heiness, C.
M. Org. React. 1973, 20, 1. (b) Furukawa, J.; Kawabata, N.; Nishimura, J.
Tetrahedron Lett. 1968, 3495. (c) Furukawa, J.; Kawabata, N. AdV.
Organomet. Chem. 1974, 12, 83.
(14) Ireland, R. E.; Mueller, R. H.; Willard, A. K. J. Am. Chem. Soc.
1976, 98, 2868.

3906 J. Am. Chem. Soc., Vol. 120, No. 16, 1998
Iwasawa et al.
Scheme 4
Scheme 5
separately to the Simmons-Smith cyclopropanation using diio-
doethane and diethylzinc. In both cases, two isomeric cyclo-
propanol TBS ethers were obtained, one of which was a
common product of both reactions. This isomer could be
definitely assigned as the 2,3-trans isomer 13. The remaining
two compounds were therefore the 2,3-cis isomers 14 and 15,
respectively, as fixed by the geometry of the silyl enol ethers
employed.
to the various 1-alkynylcyclopropanol-Co2(CO)6 complexes
Due to the instability of the corresponding desilylated
cyclopropanols reactions were directly carried out employing
TBS ethers 13-15. When each of these three diastereomers
was treated with Co2(CO)8 and heated in refluxing THF, the
reaction proceeded to give cyclopentenones, but the situation
was not so simple as in previously discussed cases. In the case
of the reaction of 2,3-trans isomer 13, trans 4,5-dimethyl-3-
phenylcyclopentenone 16 was obtained almost exclusively in
good yield. When the reaction of 2,3-cis isomer 14 was carried
out in refluxing THF for 15 min, 4,5-cis isomer 17 was obtained
as the major product with a substantial amount of recovered
14, while prolonged reaction time resulted in the formation of
an inseparable mixture of 4,5-trans isomer 16, cis isomer 17,
and 2,3-dimethyl-4-phenyl-2-cyclopenten-1-one 18 in 79% yield
in a ratio of 33:15:52. The formation of 16 and 18 indicates
that both partial epimerization and migration of the double bond
of 17 occurred during the reaction. Rearrangement of the other
2,3-cis isomer 15 did not proceed smoothly, and decomplexation
occurred as the major reaction pathway presumably due to
severe steric hindrance imposed on the alkyne-Co2(CO)6 moiety
by the two methyl groups on the same side of the cyclopropane
ring (Scheme 5). These results strongly suggest that migration
occurs chiefly with retention of configuration at the migrating
carbon.
Cyclopentenone Annulation Reaction. To expand the
synthetic utility of this reaction, we next examined the possibility
of applying it to cyclopentenone annulation onto cycloalkenes.
For this purpose, it is necessary to develop a new method for
the preparation of alkynyl-substituted bicyclo[n.1.0]alkanol
derivatives from the corresponding cycloalkenes. Danheiser and
co-workers have reported that various substituted cyclopropanols
can be synthesized by the reaction of gem-lithiobromocyclo-
propanes with alkylboranes such as trialkylboranes or cat-
echolborane utilizing 1,2-migration of an alkyl group or
hydrogen from boron to carbon.15 We employed this protocol
using alkynylboranes as the boron component.
(Scheme 4). In the case of reaction of (1R*,2R*)-isomer 7atrans
,
5-methyl-3-phenyl-2-cyclopenten-1-one 9a is produced via TS2
without any serious steric repulsion, while the 4-methyl isomer
8a must be produced via TS1 in which severe steric repulsion
between the methyl group and the cobalt moiety exists. In the
case of reaction of (1R*, 2S*)-isomer 7acis, the unprotected
derivative 7acis gave equal amounts of 8a and 9a because the
reaction can proceed via either TS3 or TS4 with equal efficiency.
When the silyl derivatives of 7acis are employed, the silyl groups
would take a position to minimize the repulsion with the methyl
group as shown in TS5 and TS6. Of these two conformations,
TS5 is thought to be favored as in this case there is no steric
repulsion between the phenyl group on the alkyne and the silyl
group. Thus, the bulkier the silyl group becomes, the higher
the selectivity becomes in favor of the formation of 8a. As
can obviously be seen from Scheme 4, the methyl group cis to
the alkynyl group plays a dominant role in determining the
regioselectivity.
The generality of these observations is supported by the data
in Table 3. In the case of the reactions of monosubstituted 1-(1-
alkynyl)cyclopropanols 7, 5-substituted cyclopentenones were
obtained with complete selectivity when 7trans were used as
substrates. On the other hand, 4-substituted cyclopentenones
were obtained in good to high regioselectivity by employing
tert-butyldimethylsilyl ethers of 7cis as substrates. Furthermore,
5,5-disubstituted cyclopentenones including a spirocyclic deriva-
tive were obtained selectively starting from 2,2-disubstituted
1-(1-alkynyl)cyclopropanols 10. As either diastereomer of the
monosubstituted 1-(1-alkynyl)cyclopropanols can be prepared
selectively depending on the reaction conditions used in
preparation of the silyl enol ethers, either 4- or 5-substituted
cyclopentenones can be synthesized selectively by appropriate
choice of reaction procedure.
We next examined the reaction of 2,3-disubstituted 1-alky-
nylcyclopropanol derivatives to clarify the stereochemistry at
the migrating carbon. As substrates, three diastereomers of 2,3-
dimethyl-1-(phenylethynyl)cyclopropanol, that is, (2S*,3S*)-13,
(1S*,2R*,3S*)-14, and (1R*,2R*,3S*)-15, were prepared by the
same procedure used in the preparation of monosubstituted
1-alkynylcyclopropanols 7, except that 1,1-diiodoethane was
employed instead of 1,1-diiodomethane. The relative stere-
ochemistries of these isomers were determined as follows. (E)-
and (Z)-Silyl enol ethers, (E)-6 and (Z)-6 (R ) Ph, R′ ) Me),
were separated by silica gel column chromatography (silica
deactivated with 10% H2O) and both isomers were subjected
Optimization of this reaction employing 7,7-dibromobicyclo-
[4.1.0]heptane 19 (n ) 1) and several phenylethynylborane
derivatives 21a (R ) Ph) revealed that while B-phenylethynyl
9-BBN did not give the desired product at all, probably due to
facile migration of the sp3-carbon of 9-BBN, use of the
corresponding borates, in particular cyclic borates, gave the
desired product 24a (n ) 1, R ) Ph) in good yields. For
example, treatment of 7,7-dibromobicyclo[4.1.0]heptane with
(15) Danheiser, R. L.; Savoca, A. C. J. Org. Chem. 1985, 50, 2401.

Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones
J. Am. Chem. Soc., Vol. 120, No. 16, 1998 3907
Scheme 6
Scheme 7
Table 4. Preparation of Various Bicyclic Cyclopropanols
be controlled by choice of the alkynylborate. By using a bulky
borate such as 4,4,5,5-tetramethyl-1,3-dioxa-2-borolane, the exo
isomer 27d was obtained preferentially (26d:27d ) 12:88),
while using a less sterically demanding 1,3-dioxa-2-borinane
derivative, the endo isomer 26d was obtained as the major
product (26d:27d ) 93:7). Assignment of the stereochemistry
of these compounds was based on the rate of silylation of the
hydroxyl group. Silylation of the endo isomers 24c,d was much
faster than that of the exo isomers 25c,d due to the steric
congestion imposed on the hydroxyl group by the cycloheptane
ring. Also the reactivity of each isomer in the alkynylcyclo-
propanol-cyclopentenone rearrangement supported this assign-
ment as is described below.
With several bicyclic alkynylcyclopropanols in hand, the
alkynylcyclopropanol-cyclopentenone rearrangement of these
compounds was examined. The reaction of 7-phenylethynyl-
bicyclo[4.1.0]heptan-7-ol 24a (n ) 1, R ) Ph) gave the desired
bicyclo[4.3.0]non-8-en-7-one derivative 28a in 86% yield on
carrying out the reaction in refluxing DME for 2 h according
to the standard procedure. However, the reaction of the
corresponding hexynyl derivative 24b (n ) 1, R ) n-Bu) was
sluggish, and the desired product 28b was obtained in only 19%
yield under similar reaction conditions (Scheme 7). This can
probably be ascribed to the fact that the reactions of phenyl-
ethynyl derivatives generally proceed quickly compared to the
reactions of alkyl-substituted ethynyl derivatives, while decom-
plexation and decomposition of the substrate competed under
these conditions due to the severe steric repulsion between the
alkyne-Co2(CO)6 moiety and the cyclohexane ring.
We next examined the reaction of the endo bicyclo[5.1.0]-
octanol derivatives 24c,d and the exo TBS ethers 27c,d. In
contrast to the case of the bicyclo[4.1.0]heptan-7-ol derivatives
24a,b, both of the endo isomers 24c and 24d gave the
corresponding bicyclo[5.3.0]dec-9-en-8-one derivatives 28c,d
in good yield on carrying out the reaction in refluxing DME.
This higher yield of the hexynyl derivative 24d compared to
that of 24b is probably due to their being less congestion over
the cycloheptane than the cyclohexane ring. Interestingly, the
reactions of the silyl ethers of the exo isomers 27c and 27d
proceeded much faster than those of the corresponding endo
isomers 24c,d, and the reaction went to completion within
n-BuLi at -100 °C generated the corresponding gem-lithiobro-
mocyclopropane 20 (n ) 1), which was reacted with a
phenylethynylborate derivative to give an ate complex 22a (n
) 1, R ) Ph). On slowly warming to room temperature and
then heating to reflux migration of the phenylethynyl group
occurred to give a cyclopropylborane derivative 23a, which was
oxidized with H2O2 to give the desired product 24a in 65%
yield (Scheme 6). In this reaction only one diastereomer was
obtained, whose stereochemistry was assigned as the endo-
alkynyl isomer as shown in 24a by analogy with the results of
Danheiser.15
Several other bicyclic alkynylcyclopropanols were prepared
from the corresponding dibromocyclopropanes and alkynylbo-
rates as summarized in Table 4. Some features of this
preparative method should be pointed out here. The reaction
of gem-lithiobromobicyclo[4.1.0]heptane with 1-hexynylborate
also gave only one diastereomer 24b (n ) 1, R ) n-Bu) in
good yield. In the case of the reaction of 8,8-dibromobicyclo-
[5.1.0]octane 19 (n ) 2) with phenylethynylborate and 1-hexy-
nylborate, the products, in particular the exo isomers 25c (n )
2, R ) Ph) and 25d (n ) 2, R ) n-Bu), were insufficiently
stable to be purified, and the crude products were directly treated
with TBSOTf and Et3N to give the corresponding silylated
mixture of endo isomers 26c,d and exo isomers 27c,d. These
isomers were easily separable, and, interestingly, their ratio could

3908 J. Am. Chem. Soc., Vol. 120, No. 16, 1998
Iwasawa et al.
several hours in refluxing THF.16 This clear difference in
reactivity of the endo and exo isomers is probably due to easy
access of the cobalt moiety of the complexed exo isomers 27c,d
to the carbon-carbon bonds of the cyclopropane. The cobalt
moiety is severely hindered from approaching these in the endo
isomers 24c,d.
Scheme 8
Finally this annulation reaction was applied to the steroidal
skeleton. According to the above procedure, alkynylcyclopro-
panol 29 was prepared from cholest-2-ene in good overall yield.
The rearrangement was carried out by the standard procedure
to give two isomeric cyclopentenones in a ratio of about 3:1 in
60% yield. Careful NMR analysis suggested that the major
product has the structure shown in 30.17
As dibromocyclopropanation can be easily carried out by
reacting a cycloalkene and bromoform in the presence of a
base,18 this method affords an alternative procedure for cyclo-
pentenone annulation onto cyclic olefins. It should be noted
that in the Pauson-Khand reaction, which is probably the most
direct cyclopentenone annulation reaction, the reaction using
cyclohexene gives the product only in very low yield.7,19 Also
the position of the original alkynyl substituent on the product
double-bond is opposite to that in the present reaction.7 Thus
the two reactions are complementary.
Catalytic Reactions. All the reactions described so far were
carried out using a stoichiometric amount of Co2(CO)8. How-
ever, it was thought that a coordinatively unsaturated Co2(CO)6
species is liberated when the rearrangement proceeds and that
if this cobalt species could form an alkyne-Co2(CO)6 complex
with another molecule of 1-(1-alkynyl)cyclopropanol, the reac-
tion should proceed with only a catalytic amount of Co2(CO)8.20
In practice, when 1-phenylethynylcyclopropanol 1b was treated
with a 10 or 20 mol % amount of Co2(CO)8, the rearranged
product 3b was obtained in 43 and 59% yield, respectively.
Thus, the reaction did in fact proceed with a catalytic amount
of Co2(CO)8; however, the efficiency was low, and a complex
mixture of byproducts was also obtained. As we thought this
low efficiency could be ascribed to instability of the liberated
cobalt species, it was expected that the catalytic reaction could
be made more efficient by the addition of an additive stabilizing
this. As additives we chose to investigate phosphines and
phosphites since it was known that carbonyl ligands of alkyne-
Co2(CO)6 complexes are easily replaced by one or two
molecules of phosphines or phosphites21 and the electronic and
steric character of the cobalt complexes should be changed by
such ligand substitution.
examined in the presence of various additives using 1-(phenyl-
ethynyl)cyclopropanol 1b as a substrate. Although no change
was observed at room temperature on addition of a phosphine
or a phosphite to 1b-Co2(CO)6 complex 2b, complete formation
of a new complex was observed within a few minutes at reflux
temperature, and the reaction was observed to proceed from
this new complex to give the cyclopentenone 3b. The new
complex was isolated in the case of triphenyl phosphite and
was shown on the basis of integration of its NMR spectrum to
be the ligand-exchanged complex 32b (RdOPh) where two
carbonyl ligands of the complex 2b had been exchanged for
two molecules of triphenyl phosphite. These results indicate
that the reaction also proceeds from the ligand-exchanged
complexes 32b with comparable yields to the reaction of the
hexacarbonyldicobalt complex 2b (Scheme 8). The reactions
in the presence of several representative phosphines or phos-
phites were carried out in THF to compare on the basis of
reaction time the reactivity of the ligand-exchanged complexes.
It was found that the reactivity of the ligand-exchanged
complex 32b was mainly controlled by the steric characteristics
of the ligand. There was no big difference in reaction time
between the reactions in the presence of tributylphosphine and
triphenyl phosphite, which are electronically different but whose
cone angles22 are nearly the same (5 h, 71% yield for
tributylphosphine; 6 h, 86% yield for triphenyl phosphite; 6 h,
90% yield without additive). On the other hand, the bulkiness
of the ligand had a considerable effect on reactivity, and the
bulkier the ligand became, (that is, the larger the cone angle of
the ligand became), the faster the reaction proceeded. The
reaction went to completion in 1 h in refluxing THF when
triphenylphosphine was used as additive (84% yield), while the
reaction in the presence of trimethyl phosphite was not complete
even after 17 h in refluxing THF (43% yield). The amount of
additive also had a large effect on reaction time, and use of 4
molar amounts of triphenyl phosphite retarded the reaction
considerably (6 h, 4% yield) although further ligand exchange
of the complex 32b was not observed. Furthermore, when an
equimolar amount of a bidentate phosphine ligand dppm was
added, the reaction became much slower, and even after heating
for 3 h in refluxing DME 3b was obtained only in 20% yield,
42% of the dppm substituted complex 32b ((PR3)2 ) dppm)
being recovered.
First in order to make clear their influence on this reaction,
the reaction with a stoichiometric amount of Co2(CO)8 was
(16) The reaction of the parent cyclopropanols 25c,d was not examined
due to thier instability. The reaction of 26c,d took nearly the same reaction
time as that of 24c,d and gave the corresponding products in comparable
yield.
(17) See the Experimental Section for the details of the determination
of the regio and stereochemistries of 30 and 31.
(18) (a) Skattebøl, L. Acta Chem. Scand. 1963, 17, 1683. (b) Last, L.
A.; Fretz, E. R.; Coates, R. M. J. Org. Chem. 1982, 47, 3211.
(19) Khand, I. U.; Pauson, P. L. J. Chem. Res. (M), 1978, 168.
(20) For catalytic Pauson-Khand reaction using cobalt complex, see: (a)
Rautenstrauch, V.; Megard, P.; Conesa, J.; Ku¨ster, W. Angew. Chem., Int.
Ed. Engl. 1990, 29, 1413. (b) Jeong, N.; Hwang, S. H.; Lee, Y.; Chung, Y.
K. J. Am. Chem. Soc. 1994, 116, 3159. (c) Lee, B. Y.; Chung, Y. K.; Jeong,
N.; Lee, Y.; Hwang, S. H. J. Am. Chem. Soc. 1994, 116, 8793. (d) Lee, N.
Y.; Chung, Y. K. Tetrahedron Lett. 1996, 37, 3145. (e) Pagenkopf, B. L.;
Livinghouse, T. J. Am. Chem. Soc. 1996, 118, 2285.
(21) (a) Chia, L. S.; Cullen, W. R.; Franklin, M.; Manning, A. R. Inorg.
Chem. 1975, 14, 2521. (b) Bonnet, J.-J.; Mathieu, R. Inorg. Chem. 1978,
17, 1973. (c) Kemmitt, R. D. W.; Russell, D. R. In ComprehensiVe
Organometallic Chemistry; Wilkinson G., Ed.; Pergamon Press: Oxford,
1982; Vol. 5, p198.
As it had been confirmed that the stoichiometric reaction in
the presence of 2 molar amounts of phosphines or phosphites
proceeded in the same manner as the reaction without additives,
we next examined reactions using a 10 mol % amount of Co2-
(CO)8 and 20 mol % amount of these additives. As shown in
Table 5, the addition of either phosphines or phosphites
improved the yield of the rearranged product considerably in
all cases. Significantly, the electronic parameter of the ligand
became more influential in these catalytic reactions, and
phosphites, which are less electron-donating than phosphines,
gave better results than the latter. When triphenyl phosphite
was employed as additive, 3b was obtained in 91% yield, which
is equal to the yield of the stoichiometric reaction. This can
be explained by assuming that catalyst deactivation occurs by
dimerization or oligomerization of the coordinatively unsaturated
(22) Tolman, C. A. Chem. ReV. 1977, 77, 313.

Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones
J. Am. Chem. Soc., Vol. 120, No. 16, 1998 3909
Table 5. Effect of Additives on the Catalytic Reactionsa
of tri(o-isopropylphenyl)phosphite. Not only the 1-phenylethy-
nylcyclopropanol 1b but also alkyl- or silyl-substituted deriva-
tives gave the corresponding 3-substituted 2-cyclopentenones
in good to high yields (Table 6). This catalytic reaction is also
applicable to the reaction of 2-methyl-1-(phenylethynyl)cyclo-
propanol, 7atrans (10 mol % Co2(CO)8, 20 mol % P(OPh)3, DME
reflux, 1.6 h, 80% yield of 9a), but the reaction of the silylated
cyclopropanol derivative 7acis was not promoted effectively. This
is presumably because the alkynyl part of the molecule was so
crowded that the recomplexation step was retarded, resulting
in interruption of the catalytic cycle.
additives
PR3/mol %
reaction timeb/min
yield/%
none
P(n-Bu)3
PPh3
P(Oi-Pr)3
P(OPh)3
P(OPh)3
60
30
20
30
60
43
59
79
74
91
91
20
20
20
20
40
240
a Reactions were run using 10 mol % amount of Co2(CO)8 in
refluxing DME using 1b as substrate. b Reaction time indicates the
approximate time at which that the ligand-exchanged cobalt complex
disappeared as judged by TLC.
Mechanism of the Reaction. Several reports have appeared
on the effect of additives on the Pauson-Khand reaction. For
example, addition of phosphine oxide improves the yield of
cyclopentenones,24 while addition of dimethyl sulfoxide ac-
celerates the reaction considerably.25 Furthermore, it has been
reported that the Pauson-Khand reaction proceeds even at room
temperature when a tertiary amine N-oxide such as trimethyl-
amine N-oxide or N-methylmorpholine N-oxide is added to the
alkyne-Co2(CO)6 complex in the presence of olefins.26 With
this knowledge in mind, we examined further the effect of
various other additives on the reaction to obtain information
on the mechanism of this rearrangement.
Table 6. Effect of the ortho Substituent of Triphenylphosphite on
the Catalytic Reactions
cone
reaction
R
R′ angle X/mol % timea/min yield/%
Ph
Ph
Ph
n-C6H13
CH2OSit-BuMe2
CH2CH2OSit-BuMe2 i-Pr
SiMe3 i-Pr
H
Me
i-Pr 148
i-Pr
i-Pr
128
141
5
5
5
10
10
5
420
120
15
30
60
30
30
76b
84
95
82
62
85
63
The reaction using 1a as a substrate was examined employing
several oxides as additive, and the reaction time necessary for
consumption of the complex 2a was compared. It revealed that
addition of tributylphosphine oxide, hexamethylphosphoric
triamide, and dimethyl sulfoxide all accelerated the reaction
considerably. For example, the original reaction using a
stoichiometric amount of Co2(CO)8 without an additive took
about 90 min in refluxing DME for completion, while the
reaction went to completion within 10 min on addition of 10
molar amounts of tributylphosphine oxide. It has been reported
that phosphine oxide facilitates CO-13CO exchange of Co4-
(CO)12,27 and the acceleration of the rearrangement is thought
to be related to the dissociation of the carbonyl ligand.
10
a Reaction time indicates the approximate time at which the starting
material 1 disappeared as judged by TLC. b 1 was recovered in 7%
yield.
cobalt species to give cluster complexes.23 This process is
expected to be retarded when the electron density on cobalt is
lowered by the less electron-donating phosphite ligand. In these
reactions, the presence of ligand-exchanged complex 32b was
observed during the reaction, and Co2(CO)4(P(OPh)3)2 is thought
to act as the real catalyst.
When the amount of the catalyst was reduced to 5 mol % of
Co2(CO)8 and 10 mol % of P(OPh)3 in the above reaction, the
reaction did not go to completion even after prolonged reaction
times, and 3b was obtained in 76% yield with recovery of 7%
of 1b. As it was expected from the results obtained so far that
a bulkier triaryl phosphite might accelerate the catalytic reaction
more efficiently, we examined the reaction using various ortho-
substituted triphenyl phosphites as additive with the results
summarized in Table 6.
As expected, use of tri(o-tolyl) phosphite as additive promoted
the reaction more effectively, and the reaction went to comple-
tion within 2 h even with only a 5 mol % amount of Co2(CO)8
and 10 mol % amount of phosphite giving the product in 84%
yield. Furthermore, when a 10 mol % amount of tri(o-
isopropylphenyl) phosphite was employed as additive, the
reaction was dramatically accelerated, and the reaction was
complete after 15 min, the cyclopentenone 3b being obtained
in 95% yield. However, tri(2,6-xylyl) phosphite was too bulky
to replace carbonyl ligand of alkyne-cobalt complex 2b and
formation of a new complex was not observed during the
reaction, nearly the same result being obtained as in the reaction
with no additive.
It is known that tertiary amine N-oxides attack the carbonyl
ligands of transition metal carbonyl complexes generating
coordinatively unsaturated species along with carbon dioxide
and an amine.28 When about 10 molar amounts of N-
methylmorpholine N-oxide (NMO) was added to the alkyne-
cobalt complex 2b in THF, the reaction proceeded even at room
temperature, and cyclopentenone 3b was obtained in 37% yield
accompanied by another rearranged product, methylene cy-
clobutanone 33, obtained in 23% yield as a mixture of
geometrical isomers. Further examination of effect of solvent
revealed that when the reaction was carried out in ethanol, 3b
was obtained in 47% yield along with 9% of a cyclopentenone
34 having an ethoxycarbonyl group in the 2-position (Scheme
9). These facts indicate that dissociation of the carbonyl ligand
of the alkyne-cobalt complex 2 is the rate determining step in
this rearrangement. This is also supported by the fact that
(24) Billington, D. C.; Helps, I. M.; Pauson, P. L.; Thomson, W.;
Willison. D. J. Organomet. Chem. 1988, 354, 233.
(25) Chung, Y. K.; Lee, B. Y.; Jeong, N.; Hudecek, M.; Pauson, P. L.
Organometallics 1993, 12, 220.
(26) (a) Shambayati, S.; Crowe, W. E.; Schreiber, S. L. Tetrahedron
Lett. 1990, 31, 5289. (b) Jeong, N.; Chung, Y. K.; Lee, S. H.; Yoo, S.-E.
Synlett 1991, 204. (c) Ornum, S. G. V.; Cook, M. Tetrahedron Lett. 1997,
38, 3657. (d) Jamison, T. F.; Shambayati, S.; Crowe, W. E.; Schreiber, S.
L. J. Am. Chem. Soc. 1997, 119, 4353.
(27) Darensbourg, D. J.; Darensbourg, M. Y.; Walker, N. Inorg. Chem.
1981, 20, 1918.
The reactions of various 1-(1-alkynyl)cyclopropanols were
examined using 5-10 mol % of Co2(CO)8 and 10-20 mol %
(28) (a) Alper, H.; Edward, J. T. Can. J. Chem. 1970, 48, 1543. (b) Shi,
Y.-L.; Gao, Y.-C.; Shi, Q.-Z.; Kershner, D. L.; Basolo, F. Organometallics
1987, 6, 1528.
(23) Khand, I. U.; Knox, G. R.; Pauson, P. L.; Watts, W. E.; Foreman,
M. I. J. Chem. Soc., Perkin Trans. 1, 1973, 977.

3910 J. Am. Chem. Soc., Vol. 120, No. 16, 1998
Iwasawa et al.
Scheme 9
rearrangement of 1-(1-alkynyl)cyclopropanols to 2-cyclopen-
tenones is achieved via their Co2(CO)6 complexes. This reaction
has been applied to the synthesis of variously substituted
2-cyclopentenones, and furthermore found to be promoted by
a catalytic amount of Co2(CO)8 in the presence of triaryl
phosphite. Mechanistic studies have revealed that this reaction
has a close relation with the Pauson-Khand reaction.
Experimental Section
carrying out the reaction in refluxing THF but under a CO
atmosphere led to its complete suppression.
General Techniques. All reactions were carried out under an argon
atmosphere under anhydrous conditions, unless otherwise noted.
Solvents were distilled and stored over MS 4A. Tetrahydrofuran (THF)
and diethyl ether were freshly distilled from sodium-benzophenone.
Dimethoxyethane (DME) was distilled from CaH2 and dried over MS
4A. Solvents employed for the reaction using Co2(CO)8 were degassed
with sonication before use.
Column chromatography was conducted on silica gel (E. Merck,
7734, 70-230 mesh), unless otherwise noted. Preparative thin-layer
chromatography (TLC) was carried out on silica gel (Wakogel-B5F).
1H NMR spectra were recorded on Bruker AM500 (500 MHz)
spectrometer using CDCl3 as a solvent. IR spectra were recorded on
a Horiba FT-300S spectrometer. High-resolution mass spectra (HRMS)
were recorded on a JEOL JMS-D300 mass spectrometer operating at
70 eV.
(1) Syntheses of 1-(1-Alkynyl)cyclopropanols 1 and 2-Substituted
1-(1-Alkynyl)cyclopropanols 7 and 10. 1-(Phenylethynyl)cyclopro-
panols (1b) was prepared according to the literature.9 Other 1-(1-
alkynyl)cyclopropanols (1a, 1c-k) were prepared according to the same
procedure. 1-(Ethoxycarbonylethynyl)cyclopropanol (1l) (R ) COOEt)
was prepared from the literally known 1-ethynylcyclopropanol31 by the
following procedure. Hydroxyl group of 1-ethynylcyclopropanol was
silylated with TBSOTf and Et3N. The obtained 1-ethynyl-1-tert-
butyldimethylsiloxycyclopropane was deprotonated with n-BuLi fol-
lowed by reaction with ClCOOEt to give 1-tert-butyldimethylsiloxy-
1-(ethoxycarbonylethynyl)cyclopropane. Acidic deprotection of the
silyl group yielded 1l. 2-Substituted 1-(1-alkynyl)cyclopropanols 7a-d
and 10a-c were prepared as follows. Alkynones 532 were converted
to the corresponding TBS enol ethers by treatment with TBSOTf and
Et3N. The obtained silyl enol ethers were subjected to cyclopropanation
by treatment with Et2Zn and CH2I2. Cis and trans isomers were
separated at this stage. Acidic desilylation of the TBS ether of the
alkynylcyclopropanols gave 7a-d and 10a-c. See the Supporting
Information for the details of the preparation of these 1-alkynylcyclo-
propanols.
We also carried out a deuterium-labeling experiment to clarify
the source of the hydrogen at the 2-position of the cyclopen-
tenone. When the stoichiometric reaction was performed in
C2H5OD, more than 90% of the hydrogen at the 2-position of
cyclopentenone was deuterated. Therefore, the hydrogen at the
2-position of cyclopentenone was introduced as a proton.
These results suggest that this rearrangement of 1-(1-alkynyl)-
cyclopropanols to 2-cyclopentenones is closely related to the
Pauson-Khand reaction in its reaction mechanism. Although
none of the intermediate complexes has been isolated or
detected, we currently suppose the following mechanism for
this reaction (Scheme 10). The first step of the reaction is the
dissociation of a carbonyl ligand from the alkyne-Co2(CO)6
complex 2 to generate a coordinatively unsaturated alkyne-Co2-
(CO)5 complex A, which is formed thermally or by the addition
of tertiary amine N-oxide. The coordinatively unsaturated cobalt
species thus generated inserts into the carbon-carbon bond of
the cyclopropanol to give a four-membered metallacyclic
intermediate B, which rearranges into a metallacyclohexanone
intermediate C by C-Co bond cleavage with proton transfer
as indicated by path a. Reductive elimination between C1 and
C2 gives a cyclopentenone-cobalt carbonyl complex D, which
in turn gives the free cyclopentenone 3 with liberation of Co2-
(CO)5L (L ) CO or a solvent). The fact that the reaction using
tertiary amine N-oxide at room temperature gives rise to the
formation of the methylenecyclobutanone 33 indicates that the
reaction can also proceed via path b to give C′ and that in this
case reductive elimination between C1 and C3 occurs at room
temperature to give a methylenecyclobutanone-cobalt carbonyl
complex D′. Also the formation of ethoxycarbonylated product
34 under the oxidative conditions implies that alkenyl cobalt
species E might be formed in part in this case. The fact that
both bulky substituents on the alkyne and bulky ligands
accelerate the reaction can be ascribed to facilitation of ligand
dissociation due to steric congestion.
(2) General Procedure for the Stoichiometric Reaction of 1-(1-
Alkynyl)cyclopropanols with Co2(CO)8. To a THF or DME solution
(6 mL) of Co2(CO)8 (1.1 mmol) was added the same solution (10 mL)
of 1-(1-alkynyl)cyclopropanol 1 (1 mmol) at room temperature, and
after the complete formation of hexacarbonyldicobalt complex 2 was
observed by thin-layer chromatography (in most cases within 30 min),
the mixture was refluxed for an appropriate time under an atmospheric
pressure of argon. (Usually the reaction was monitored by TLC. The
end of the reaction was judged by the disappearance of the alkyne-
Co2(CO)6 complex 2.) Precipitated inorganic materials were removed
by filtration through a small pad of silica gel, and after purification of
crude product by silica gel TLC, 3-substituted-2-cyclopentenone 3 was
obtained.
Oxidative addition of the carbon-carbon bond of cyclopro-
panes to zerovalent cobalt species is not in general a facile
process.29 It is assumed that in this reaction the alkynyl part
of the molecule is working as an anchor for the cobalt carbonyl,
which enables an efficient insertion of the cobalt moiety into
the proximal carbon-carbon bond of the cyclopropane to
proceed. We have already found that direct substitution of the
alkynyl part onto the cyclopropanol is not essential for this type
of reaction,30 and thus appropriate design of substrates should
expand the scope of these synthetic reactions.
3a,33 3b,34 3c,35 3d,36 and 3l37 are known in the literatures. Full
data of these compounds are described in the Supporting Information.
(31) Wasserman, H, H.; Cochoy, R. E.; Baird. M. S. J. Am. Chem. Soc.
1969, 91, 2375.
(32) Ramachandran, P. V.; Teodorovic, A. V.; Rangaishenvi, M. V.;
Brown, H. C. J. Org. Chem. 1992, 57, 2379.
(33) Jones, D. N.; Meanwell, N. A.; Mirza, S. M. J. Chem. Soc., Perkin
Trans. 1 1985, 145.
(34) Corbel, B.; Decesare, J. M.; Durst, T. Can. J. Chem. 1978, 56, 505.
(35) Garbisch, E. W. Jr.; Sprecher, R. F. J. Am. Chem. Soc. 1969, 91,
6785.
(36) Reuter, J. M.; Sinha, A. Salomon, R. G. J. Org. Chem. 1978, 43,
2438.
Conclusion
A new use of alkyne-Co2(CO)6 complexes in organic
synthesis has been disclosed. A hitherto unknown type of
(29) Stille, J. K. In The Chemistry of the Metal-Carbon Bond; Hartley,
F. R., Patai, S., Eds.; John Wiley & Sons: New York, 1985; Vol. 2, p 718.
For an example of platinum complex, see: Ikura, K.; Ryu, I.; Kambe, N.;
Sonoda, N. J. Am. Chem. Soc. 1992, 114, 1520. References are cited therein.
(30) Iwasawa, N.; Matsuo, T. Chem. Lett., 1997, 341.
(37) Mori, K. Tetrahedron 1978, 34, 915.

Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones
J. Am. Chem. Soc., Vol. 120, No. 16, 1998 3911
Scheme 10
3-Triphenylsilyl-2-cyclopentenone (3e) (R ) SiPh3). IR (KBr)
2924, 1711, 1109 cm-1; 1H NMR δ ) 2.38-2.40 (2H, m), 2.83-2.85
(2H, m), 6.53 (1H, t, J ) 2.1 Hz), 7.38-7.41 (6H, m), 7.44-7.48 (3H,
m), 7.50-7.52 (6H, m); 13C NMR δ ) 33.0, 35.2, 128.2, 130.3, 131.7,
136.0, 145.9, 178.5, 210.8. Anal. Calcd for C23H20OSi: C, 81.13; H,
5.92. Found: C, 80.99; H, 6.02.
1H NMR δ ) 0.53 (3H, d, J ) 6.8 Hz), 1.01 (3H, d, J ) 6.8 Hz),
2.08-2.15 (1H, m), 2.34 (1H, d, J ) 18.7 Hz), 2.48 (1H, dd, J ) 6.6,
18.7 Hz), 3.51-3.53 (1H, m), 6.39 (1H, s), 7.41-7.46 (3H, m), 7.50-
7.54 (2H, m); 13C NMR δ ) 14.5, 21.8, 28.4, 36.4, 46.2, 127.1, 128.6,
129.8, 130.6, 134.0, 178.2, 208.6; HRMS calcd for C14H16O: 200.1201.
Found: 200.1177.
5-Isopropyl-3-phenyl-2-cyclopentenone (9b, R ) Ph, R1 ) H, R2
3-Triisopropylsilyl-2-cyclopentenone (3f) (R ) TIPS). IR (KBr)
1
2950, 2864, 1711, 1462, 1018 cm-1; H NMR δ ) 1.07 (18H, d, J )
) i-Pr). IR (neat) 2954, 2925, 1689, 1603, 1572, 1495, 1448, 1178
1
cm-1; H NMR δ ) 0.80 (3H, d, J ) 6.8 Hz), 1.02 (3H, d, J ) 6.9
7.4 Hz), 1.20-1.27 (1H, m), 2.30-2.32 (2H, m), 2.74-2.77 (2H, m),
6.41 (1H, t, J ) 2.0 Hz); 13C NMR δ ) 10.9, 18.5, 34.1, 34.7, 143.7,
181.5, 211.3. Anal. Calcd for C14H26OSi: C, 70.52; H, 10.99.
Found: C, 70.43; H, 11.02.
Hz), 2.27-2.33 (1H, m), 2.54-2.57 (1H, m), 2.74-2.79 (1H, m), 2.97-
3.04 (1H, m), 6.52 (1H, t, J ) 1.5 Hz), 7.42-7.44 (3H, m), 7.64-7.66
(2H, m); 13C NMR δ ) 17.1, 20.8, 28.9, 30.9, 51.9, 126.8, 127.7, 128.9,
131.2, 134.1, 172.9, 211.2; HRMS calcd for C14H16O: 200.1201.
Found: 200.1201.
3-Hexyl-4-methyl-2-cyclopentenone (8c, R ) n-Hex, R1 ) H, R2
) Me). IR (neat) 2931, 2925, 1709, 1614, 1458 cm-1; 1H NMR δ )
0.87 (3H, t, J ) 6.9 Hz), 1.16 (3H, d, J ) 7.2 Hz), 1.25-1.48 (6H,
m), 1.49-1.58 (2H, m), 1.97 (1H, dd, J ) 2.2, 18.6 Hz), 2.25 (1H,
ddd, J ) 5.9, 9.0, 16.0 Hz), 2.41 (1H, dt, J ) 8.1, 16.0 Hz), 2.61 (1H,
dd, J ) 6.6, 18.6 Hz), 2.80-2.86 (1H, m), 5.86 (1H, d, J ) 1.3 Hz);
13C NMR δ ) 14.0, 19.0, 22.5, 26.9, 29.1, 30.9, 31.5, 37.7, 44.0, 128.7,
187.0, 209.0. Anal. Calcd for C12H20O: C, 79.94; H, 11.18. Found:
C, 79.70; H, 11.14.
3-Hexyl-5-methyl-2-cyclopentenone (9c, R ) n-Hex, R1 ) H, R2
) Me). IR (neat) 2956, 2925, 1701, 1616, 1458 cm-1; 1H NMR δ )
0.87 (3H, t, J ) 6.3 Hz), 1.14 (3H, d, J ) 7.6 Hz), 1.23-1.36 (6H,
m), 1.49-1.58 (2H, m), 2.14 (1H, d, J ) 18.3 Hz), 2.35-2.41 (3H,
m), 2.79 (1H, dd, J ) 7.0, 18.3 Hz), 5.87 (1H, t, J ) 1.7 Hz); HRMS
calcd for C12H20O: 180.1515. Found: 180.1488.
3-(tert-Butyldimethylsiloxymethyl)-2-cyclopentenone (3 g) (R )
CH2OTBS). Mp 64.5-66.0 °C; IR (KBr) 2929, 2858, 1699, 1432,
1142, 1078, 843 cm-1; 1H NMR δ ) 0.65 (6H, s), 0.88 (9H, s), 2.39-
2.41 (2H, m), 2.51-2.52 (2H, m) 4.42 (2H, d, J ) 0.6 Hz), 6.12-6.13
(1H, m); 13C NMR δ ) -5.6, 18.2, 25.7, 27.8, 34.9, 63.2, 128.3, 181.4,
209.1. Anal. Calcd for C12H22O2Si: C, 63.67; H, 9.79. Found: C,
63.66; H, 9.52.
3-(tert-Butylthiomethyl)-2-cyclopentenone (3h) (R ) CH2St-Bu).
IR (neat) 2927, 1709, 1676, 1616, 1178 cm-1; 1H NMR δ ) 1.29 (9H,
s), 2.39-2.41 (2H, m), 2.67-2.69 (2H, m), 3.47 (2H, s), 6.07 (1H, t,
J ) 1.1 Hz); 13C NMR δ ) 30.5, 30.65, 30.74, 35.5, 43.3, 131.1, 178.6,
209.5; HRMS calcd for C10H16OS: 184.0923. Found: 184.0939.
3-(2-tert-Butyldimethylsiloxyethyl)-2-cyclopentenone (3i) (R )
1
CH2CH2OTBS). IR (neat) 2931, 1712, 1618, 1255, 1097 cm-1; H
NMR δ ) 0.01 (6H, s), 0.82 (9H, s), 2.32-2.34 (2H, m), 2.56-2.58
(4H, m), 3.79 (2H, t, J ) 6.3 Hz), 5.94 (1H, t, J ) 1.2 Hz); 13C NMR
δ ) -5.5, 18.1, 25.7, 31.9, 35.1, 36.6, 60.6, 130.5, 180.0, 209.9; HRMS
calcd for C13H24O2Si: 240.1546. Found: 240.1528.
3-(2-Hydroxyethyl)-2-cyclopentenone (3j) (R ) CH2CH2OH). IR
(neat) 3398, 2925, 1705, 1672, 1612, 1053 cm-1; 1H NMR δ ) 2.27-
2.29 (2H, m), 2.54-2.58 (4H, m), 3.55 (1H, br), 3.76 (2H, t, J ) 5.6
Hz), 5.90 (1H, t, J ) 1.2 Hz); 13C NMR δ ) 31.6, 35.0, 36.3, 59.4,
130.2, 180.9, 210.8; HRMS calcd for C7H10O2: 126.0681. Found:
126.0698.
3-Hexyl-4-isopropyl-2-cyclopentenone (8d, R ) n-Hex, R1 ) H,
1
R2 ) i-Pr). IR (neat) 2927, 1714, 1687, 1614, 1464 cm-1; H NMR
δ ) 0.59 (3H, d, J ) 6.8 Hz), 0.85 (3H, t, J ) 6.9 Hz), 0.95 (3H, d,
J ) 6.9 Hz), 1.21-1.34 (6H, m), 1.46-1.60 (2H, m), 2.09-2.15 (1H,
m), 2.12 (1H, dd, J ) 2.2, 18.5 Hz), 2.18-2.24 (1H, m), 2.25 (1H, dd,
J ) 6.8, 18.5 Hz), 2.33-2.40 (1H, m), 2.81-2.84 (1H, m), 5.91 (1H,
q, J ) 1.4 Hz); 13C NMR δ ) 14.0, 14.6, 21.7, 22.5, 26.9, 27.6, 29.1,
31.2, 31.5, 35.8, 48.7, 129.9, 185.3, 209.3. HRMS calcd for C14H24O:
208.1828. Found: 208.1820.
3-Butylthio-2-cyclopentenone (3k) (R ) Sn-Bu). IR (neat) 2929,
1
1701, 1682, 1547, 1265, 1178 cm-1; H NMR δ ) 0.91 (3H, t, J )
7.4 Hz), 1.41 (2H, sextet, J ) 7.4 Hz), 1.65 (2H, quint, J ) 7.4 Hz),
2.42-2.44 (2H, m), 2.70-2.73 (2H, m), 2.86 (2H, t, J ) 7.4 Hz), 5.87
(1H, t, J ) 1.3 Hz); 13C NMR δ ) 13.5, 21.9, 30.2, 31.7, 32.4, 35.1,
123.7, 180.2, 205.3; HRMS calcd for C9H14O2S: 170.0766. Found:
170.0774.
3-Hexyl-5-isopropyl-2-cycloopentenone (9d, R ) n-Hex, R1 ) H,
1
R2 ) i-Pr). IR (neat) 2924, 1697, 1618, 1464 cm-1; H NMR δ )
0.71 (3H, d, J ) 6.8 Hz), 0.85 (3H, t, J ) 6.9 Hz), 0.93 (3H, d, J )
7.0 Hz), 1.21-1.33 (6H, m), 1.54 (2H, quint, J ) 7.5 Hz), 2.16-2.23
(1H, m), 2.28-2.38 (3H, m), 2.52 (1H, ddd, J ) 1.3, 7.0, 18.4 Hz),
5.87 (1H, quint, 1.3 Hz); 13C NMR δ ) 14.0, 16.8, 20.7, 22.5, 27.0,
28.5, 28.9, 31.5, 33.48, 33.55, 51.8, 129.7, 182.3, 211.9. Anal. Calcd
for C14H24O: C, 80.71; H, 11.61. Found: C, 80.49; H, 11.75.
5,5-Dimethyl-3-phenyl-2-cyclopentenone (12a, R ) Ph, R1 ) R2
) Me). Mp 85.0-86.0 °C; IR (KBr) 2924, 1681, 1597, 1572, 1450,
1136 cm-1; 1H NMR δ ) 1.17 (6H, s), 2.86 (2H, d, J ) 1.6 Hz), 6.45
(1H, t, J ) 1.6 Hz), 7.40-7.42 (3H, m), 7.59-7.61 (2H, m); 13C NMR
δ ) 25.2, 44.1, 45.1, 124.6, 126.7, 128.8, 131.1, 133.9, 170.4, 213.7.
Anal. Calcd for C13H14O: C, 83.84; H, 7.57. Found: C, 83.89; H,
7.60.
(3) General Procedure for the Reaction of 2-Substituted 1-(1-
Alkynyl)cyclopropanols with Co2(CO)8. The reactions of 2-substituted
1-(1-alkynyl)cyclopropanols were carried out by the same procedure
as described for the stoichiometric reaction of unsubsituted 1-alkynyl-
cyclopropanols 1. 8a38 and 9a39 are known in the literatures. Full data
of these compounds are described in the Supporting Information.
4-Isopropyl-3-phenyl-2-cyclopentenone (8b, R ) Ph, R1 ) H, R2
) i-Pr). IR (neat) 2952, 2925, 1684, 1602, 1572, 1493, 1267 cm-1
;
(38) Gowda, G.; McMurry, T. B. H. J. Chem. Soc., Perkin Trans. 1 1979,
274.
(39) Binet du Jassonneix, C. Bull. Soc. Chim. Fr. 1975, 758.

3912 J. Am. Chem. Soc., Vol. 120, No. 16, 1998
Iwasawa et al.
3-Phenylspiro[4.5]-2-decen-1-one (12b, R ) Ph, R1 ) R2
)
;
The stereochemistries of the products were determined by the
differential NOE spectra of these compounds. In the case of the 4,5-
cis isomer 17, 8.7% of NOE was observed between the methine protons
of C-4 and C-5, while no NOE was observed between these protons in
the case of 4,5-trans isomer 16. Furthermore, the coupling constants
between these protons (for 16, J ) 1.8 Hz and for 17, J ) 7.2 Hz)
supported this assignment.
(CH2)5). IR (neat) 2929, 2852, 1687, 1603, 1573, 1448, 1194 cm-1
1H NMR δ ) 1.30-1.44 (5H, m), 1.62-1.79 (5H, m), 2.89 (2H, d, J
) 1.6 Hz), 6.48 (1H, t, J ) 1.6 Hz), 7.42-7.44 (3H, m), 7.65-7.66
(2H, m); 13C NMR δ ) 23.0, 25.2, 33.5, 41.5, 49.3, 125.2, 126.8, 128.8,
131.1, 134.1, 171.0, 213.8; HRMS calcd for C16H18O: 226.1358.
Found: 226.1346.
3-Hexyl-5,5-dimethyl-2-cyclopentenone (12c, R ) n-Hex, R1 )
R2 ) Me). IR (neat) 2956, 2927, 1705, 1618, 1468 cm-1; 1H NMR δ
) 0.86 (3H, t, J ) 6.9 Hz), 1.07 (6H, s), 1.25-1.32 (6H, m), 1.54
(2H, quint, J ) 7.3 Hz), 2.34 (2H, t, J ) 7.6 Hz), 2.40 (2H, d, J ) 1.0
Hz), 5.82 (1H, t, J ) 1.0 Hz); 13C NMR δ ) 14.0, 22.5, 25.1, 26.9,
28.9, 31.5, 33.4, 44.0, 48.2, 126.7, 179.8, 214.5; HRMS calcd for
C13H22O:194.1671. Found: 194.1662.
trans-4,5-Dimethyl-3-phenyl-2-cyclopentenone (16). IR (neat)
1
2962, 1697, 1595, 1448, 1186 cm-1; H NMR δ ) 1.23 (3H, d, J )
7.0 Hz), 1.26 (3H, d, J ) 7.5 Hz), 2.14 (1H, dq, J ) 1.8, 7.5 Hz), 3.02
(1H, dq, J ) 1.8, 7.0 Hz), 6.34 (1H, s), 7.42-7.43 (3H, m), 7.52-
7.54 (2H, m); 13C NMR δ ) 16.0, 19.5, 44.0, 50.1, 126.7, 127.4, 128.8,
130.6, 133.6, 177.6, 210.9; HRMS calcd for C13H14O: 186.1045.
Found: 186.1040.
cis-4,5-Dimethyl-3-phenyl-2-cyclopentenone (17). 1H NMR δ )
1.10 (3H, d, J ) 7.2 Hz), 1.18 (3H, d, J ) 7.5 Hz), 2.73 (1H, quint,
J ) 7.5 Hz), 3.59 (1H, quint, J ) 7.2 Hz), 6.42 (1H, s), 7.42-7.45
(3H, m), 7.54-7.60 (2H, m).
(4) Preparation of 2,3-Dimethyl-1-(1-phenylethynyl)cyclopro-
panols. (E)- and (Z)-TBS enol ethers of 1-phenyl-1-pentyn-3-one were
prepared as described in the preparation of 2-substituted 1-(1-alkynyl)-
cyclopropanols. The products were carefully separated using silica gel
deactivated with 10% water. Then each isomer was treated with Et2-
Zn and CH3CHI2. From both isomers, diastereomeric pairs of TBS
ethers of 2,3-dimethylcyclopropanols were obtained. The isomer which
was obtained from both (E)- and (Z)-isomers was assigned as 2,3-trans
isomer 14. The remaining two isomers were assigned as 2,3-cis isomers
13 and 15 based on the geometry of the silyl enol ether employed.
2,3-Dimethyl-4-phenyl-2-cyclopentenone (18). 1H NMR δ ) 1.77
(3H, s), 1.80 (3H, s), 2.34 (1H, dd, J ) 2.1, 18.8 Hz), 2.88 (1H, dd, J
) 7.0, 18.8 Hz), 3.78 (1H, dd, J ) 2.1, 7.0 Hz), 7.05-7.07 (2H, m),
7.19-7.22 (1H, m), 7.28-7.31 (2H, m).
(6) General Procedure for the Preparation of Bicyclic Alkynyl-
cyclopropanols. Alkynylborates were prepared according to the
literature procedure.40
(E)- and (Z)-Silyl Enol Ethers 6. (Z)-3-tert-Butyldimethylsiloxy-
1-phenyl-3-pentene-1-yne ((Z)-6:R1 ) Ph, R2 ) Me). IR (neat) 2858,
1641, 1489, 1319 cm-1; 1H NMR δ ) 0.28 (6H, s), 1.00 (9H, s), 1.70
(3H, d, J ) 7.0 Hz), 5.24 (1H, q, J ) 7.0 Hz), 7.29-7.32 (3H, m),
7.41-7.43 (2H, m); 13C NMR δ ) -4.2, 11.1, 18.2, 25.7, 86.8, 87.6,
114.8, 122.9, 128.2, 128.3, 131.2, 133.0; HRMS calcd for C17H24OSi:
272.1597. Found: 272.1567.
To a THF solution (2.5 mL) of a dibromocyclopropane (2.0 mmol)
was added dropwise a 1.65 M hexane solution (1.2 mL, 2.0 mmol) of
n-BuLi at -100 °C, and the mixture was stirred at this temperature for
10 min. Then a THF solution (1.8 mL) of alkynylborate (2.1 mmol)
was added to this mixture at -100 °C, and the mixture was slowly
warmed to room temperature overnight. Then the mixture was heated
to reflux for 10 h. At 0 °C, 10% aqueous NaOH solution (3 mL) and
30% H2O2 solution (3 mL) were added successively, and the mixture
was further stirred at room temperature overnight. Then the products
were extracted with ether three times, and the combined extracts were
dried over MgSO4. After evaporation of the solvent, the crude product
was purified by silica gel column chromatograpy to give the bicyclic
alkynylcyclopropanol.
(E)-3-tert-Butyldimethylsiloxy-1-phenyl-3-pentene-1-yne ((E)-6:
R1 ) Ph, R2 ) Me). IR (neat) 2929, 1633, 1489, 1338, 1252, 1192
1
cm-1; H NMR δ ) 0.21 (6H, s), 0.94 (9H, s), 1.79 (3H, d, J ) 7.2
Hz), 5.36 (1H, q, J ) 7.2 Hz), 7.30-7.32 (3H, m), 7.42-7.45 (2H,
m); 13C NMR δ ) -4.4, 13.3, 18.2, 25.7, 85.1, 92.6, 115.0, 122.9,
128.33, 128.35, 131.3, 133.9; HRMS calcd for C17H24OSi: 272.1597.
Found: 272.1584.
In the case of the reaction of 8,8-dibromobicyclo[5.1.0]octane, the
crude product was directly treated with TBSOTf and Et3N in CH2Cl2,
and the product was isolated as their TBS ether. Due to their instability,
25c,d were employed as their TBS ether for the rearrangement reaction.
24c,d were deprotected just before use by the procedure described for
the preparation of 2-substituted 1-(1-alkynyl)cyclopropanols.
(1R*,6S*,7R*)-7-(Phenylethynyl)bicyclo[4.1.0]heptan-7-ol (24a).
TBS Ethers of 2,3-Dimethylcyclopropanols 13-15. (2S*,3S*)-
1-tert-Butyldimethylsiloxy-2,3-dimethyl-1-(phenylethynyl)cyclopro-
pane (13). IR (neat) 2927, 1596, 1490, 1251, 1221 cm-1; 1H NMR δ
) 0.20 (3H, s), 0.25 (3H, s), 0.70 (1H, quint, J ) 6.4 Hz), 0.80 (1H,
quint, J ) 6.4 Hz), 0.89 (9H, s), 1.16 (3H, d, J ) 6.4 Hz), 1.17 (3H,
d, J ) 6.4 Hz), 7.25-7.29 (3H, m), 7.36-7.39 (2H, m); 13C NMR δ
) -4.2, -3.8, 11.9, 14.9, 18.0, 25.8, 29.2, 29.3, 54.7, 84.2, 90.7, 123.5,
127.7, 128.2, 131.3; HRMS calcd for C19H28OSi: 300.1910. Found:
300.1930.
1
IR (KBr) 3203, 2935, 1599, 1491, 1188, 1091 cm-1; H NMR δ )
1.15-1.22 (2H, m), 1.34-1.41 (2H, m), 1.43-1.48 (2H, m), 1.70-
1.75 (2H, m), 1.88-1.92 (2H, m), 2.41 (1H, br), 7.28-7.30 (3H, m),
7.41-7.43 (2H, m); 13C NMR δ ) 19.6, 21.0, 25.1, 54.9, 87.4, 89.6,
123.1, 128.1, 128.3, 131.4. Anal. Calcd for C15H16O: C, 84.87; H,
7.60. Found: C, 84.79; H, 7.71.
(1R*,6S*,7R*)-7-(1-Hexynyl)bicyclo[4.1.0]heptan-7-ol (24b). IR
(neat) 3344, 2935, 1448, 1194, 1092 cm-1; 1H NMR δ ) 0.89 (3H, t,
J ) 7.2 Hz), 1.09-1.22 (2H, m), 1.25-1.32 (4H, m), 1.38-1.45 (2H,
m), 1.47-1.52 (2H, m), 1.58-1.63 (2H, m), 1.79-1.84 (2H, m), 2.20
(1H, br), 2.28 (2H, t, J ) 6.9 Hz); 13C NMR δ ) 13.6, 18.7, 19.5,
20.9, 21.9, 24.0, 30.9, 54.9, 77.7, 90.4; HRMS calcd for C13H20O:
192.1514. Found: 192.1538.
(1S*,2R*,3S*)-1-tert-Butyldimethylsiloxy-2,3-dimethyl-1-(phenyl-
ethynyl)cyclopropane (14). IR (neat) 2929, 1599, 1248, 1043 cm-1
;
1H NMR δ ) 0.25 (6H, s), 0.90 (9H, s), 0.98 (6H, d, J ) 4.0 Hz), 1.21
(2H, q, J ) 4.0 Hz), 7.25-7.27 (3H, m), 7.35-7.37 (2H, m); 13C NMR
δ ) -3.7, 6.4, 18.5, 23.8, 26.0, 49.9, 81.4, 94.2, 123.5, 127.7, 128.2,
131.3. Anal. Calcd for C19H28OSi: C, 75.94; H, 9.39. Found: C,
75.72; H, 9.16.
(1R*,2R*,3S*)-1-tert-Butyldimethylsiloxy-2,3-dimethyl-1-(phenyl-
ethynyl)cyclopropane (15). IR (neat) 2929, 1596, 1491, 1255, 1184,
1120 cm-1; 1H NMR δ ) 0.20 (6H, s), 0.87 (9H, s), 1.04 (6H, d, J )
4.0 Hz), 1.25 (2H, q, J ) 4.0 Hz), 7.27-7.29 (3H, m), 7.39-7.40
(2H, m); 13C NMR δ ) -4.0, 8.8, 17.7, 25.7, 56.4, 87.3, 87.7, 123.5,
127.8, 128.2, 131.4. Anal. Calcd for C19H28OSi: C, 75.94; H, 9.39.
Found: C, 75.72; H, 9.19.
(1R*,7S*,8R*)-8-tert-Butyldimethylsiloxy-8-(phenylethynyl)bicyclo-
[5.1.0]octane (24c). IR (neat) 2920, 2854, 1490, 1253, 1130 cm-1
;
1H NMR δ ) 0.20 (6H, s), 0.87 (9H, s), 1.09-1.19 (1H, m), 1.22-
1.36 (6H, m), 1.78-1.81 (2H, m), 1.88-1.90 (1H, m), 2.12-2.17 (2H,
m), 7.27-7.30 (3H, m), 7.40-7.43 (2H, m); 13C NMR δ ) -4.1, 17.7,
25.7, 27.0, 29.3, 32.8, 32.9, 58.5, 87.3, 88.6, 123.5, 127.9, 128.2, 131.4.
Anal. Calcd for C22H32OSi: C, 77.59; H, 9.47. Found: C, 77.53; H,
9.49.
(5) Procedure for the Reaction of 2,3-Dimethyl-1-(phenylethy-
nyl)cyclopropanols with Co2(CO)8. The reactions of TBS ethers of
2,3-dimethyl-1-(phenylethynyl)cyclopropanols 13-15 were carried out
by the same procedure as describe for the stoichiometric reaction of
unsubsituted 1-alkynylcyclopropanols 1. The products were usually
obtained as an inseparable mixture of 16-18, and the ratios were
determined by integration of 1H NMR. As 16 was obtained as a single
isomer, satisfactory characterization was carried out, but only 1H NMR
data are shown for 17 and 18.
(1R*,7S*,8S*)-8-tert-Butyldimethylsiloxy-8-(phenylethynyl)bicyclo-
[5.1.0]octane (25c). IR (neat) 2927, 1599, 1491, 1244, 1089 cm-1
;
(40) Brown, H. C.; Bhat, N. G.; Srebnik, M. Tetrahedron Lett. 1988,
29, 5289.

Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones
J. Am. Chem. Soc., Vol. 120, No. 16, 1998 3913
1H NMR δ ) 0.26 (6H, s), 0.94 (9H, s), 1.10-1.20 (1H, m), 1.33-
1.37 (6H, m), 1.79-1.83 (2H, m), 1.89-1.91 (3H, m), 7.25-7.28 (3H,
m), 7.35-7.39 (2H, m); 13C NMR δ ) -3.8, 18.5, 23.5, 26.2, 29.0,
31.6, 32.9, 53.3, 81.6, 93.8, 123.5, 127.7, 128.2, 131.2. Anal. Calcd
for C22H32OSi: C, 77.59; H, 9.47. Found: C, 77.88; H, 9.58.
(1R*,7S*,8R*)-8-tert-Butyldimethylsiloxy-8-(1-hexynyl)bicyclo-
[5.1.0]octane (24d). IR (neat) 2956, 1471, 1230, 1132, cm-1; 1H NMR
δ ) 0.14 (6H, s), 0.83 (9H, s), 0.89 (3H, t, J ) 7.2 Hz), 1.04-1.19
(5H, m), 1.23-1.30 (2H, m), 1.39-1.43 (2H, m), 1.45-1.50 (2H, m),
1.75-1.76 (2H, m), 1.83-1.86 (1H, m), 2.04-2.06 (2H, m), 2.25 (2H,
t, J ) 7.0 Hz). Anal. Calcd for C20H36OSi: C, 74.93; H, 11.32.
Found: C, 74.85; H, 11.18.
(1R*,7S*,8S*)-8-tert-Butyldimethylsiloxy-8-(1-hexynyl)bicyclo-
[5.1.0]octane (25d). IR (neat) 2927, 1250, 1082, cm-1; 1H NMR δ )
0.18 (6H, s), 0.87 (3H, t, J ) 7.3 Hz), 0.89 (9H, s), 1.10-1.14 (3H,
m), 1.26-1.36 (4H, m), 1.37-1.47 (4H, m), 1.76-1.86 (5H, m), 2.15
(2H, t, J ) 7.1 Hz); 13C NMR δ ) -3.9, 13.6, 18.4, 18.5, 22.0, 23.5,
26.2, 29.1, 30.8, 31.1, 32.9, 53.2, 81.8, 84.2; HRMS calcd for C20H36-
OSi: 320.2536. Found: 320.2555.
(1R*,7S*,8R*)-8-(Phenylethynyl)bicyclo[5.1.0]octan-8-ol (24c). IR
(neat) 3298, 2922, 1600, 1490, 1321, 1097 cm-1; 1H NMR δ ) 1.07-
1.15 (1H, m), 1.20-1.38 (4H, m), 1.43-1.49 (2H, m), 1.77-1.80 (2H,
m), 1.87-1.90 (1H, m), 2.14-2.17 (2H, m), 2.44 (1H, br), 7.29-7.30
(3H, m), 7.43-7.45 (2H, m); 13C NMR δ ) 26.9, 29.1, 32.6, 32.7,
57.6, 87.3, 87.7, 123.1, 128.1, 128.2, 131.6. Anal. Calcd for
C16H18O: C, 84.91; H, 8.02. Found: C, 84.66; H, 7.99.
(1R*,7S*,8R*)-8-(1-Hexynyl)bicyclo[5.1.0]octan-8-ol (24d). IR
(KBr disk) 3259, 2921, 1459, 1107 cm-1; 1H NMR δ ) 0.90 (3H, t, J
) 7.3 Hz), 1.05-1.15 (4H, m), 1.26-1.31 (4H, m), 1.39-1.44 (2H,
m), 1.47-1.52(2H, m), 1.74-1.80 (2H, m), 1.84-1.90 (1H, m), 2.05-
2.08 (2H, m), 2.28 (2H, t, J ) 7.0 Hz); 13C NMR δ ) 13.6, 18.6, 21.9,
26.9, 29.2, 31.0, 31.8, 32.8, 57.7, 78.0, 88.0; HRMS calcd for
C14H22O: 206.1670. Found: 206.1658.
Steroidal Cycloparopanol 29. IR (neat) 3354, 2943, 1442, 1365,
1093, 754 cm-1; 1H NMR δ ) 0.63 (3H, s), 0.75 (3H, s), 0.84 (3H, d,
J ) 2.2 Hz), 0.85 (3H, d, J ) 2.1 Hz), 0.88 (3H, d, J ) 6.4 Hz),
1.72-1.76 (1H, m), 2.05-2.10 (1H, m), 2.58 (1H, s), 7.30-7.31 (3H,
m), 7.39-7.41 (2H, m); 13C NMR δ ) 12.0, 12.1, 18.7, 20.9, 22.5,
22.8, 23.8, 24.19, 24.23, 24.5, 25.4, 28.0, 28.2, 29.6, 32.0, 33.5, 33.8,
35.8, 36.0, 36.2, 39.1, 39.5, 40.0, 42.3, 53.6, 55.0, 56.3, 56.4, 87.3,
89.5, 123.2, 128.0, 128.4, 131.2; HRMS Calcd for C36H52O: 500.4018.
Found: 500.4029.
Figure 1.
m), 2.50-2.54 (1H, m), 2.91-2.97 (1H, m), 5.93 (1H, s); 13C NMR δ
) 13.8, 22.5, 27.8, 28.2, 29.0, 29.1, 30.9, 31.1, 49.2, 51.6, 128.8, 185.3,
211.7; HRMS Calcd for C14H22O: 206.1670. Found: 206.1672.
Steroidal Cyclopenetenone 30. IR (neat) 2941, 2856, 1693, 1570,
1464, 1381 cm-1; H NMR δ ) 0.61 (3H, s), 0.82 (3H, s), 0.83 (3H,
1
d, J ) 1.9 Hz), 0.84 (3H, d, J ) 1.8 Hz), 0.88 (3H, d, J ) 6.5 Hz),
1.91-1.96 (1H, m), 2.10 (1H, dd, J ) 7.7, 13.5 Hz), 2.73 (1H, dt, J )
13.5, 6.3 Hz), 3.54-3.58 (1H, m), 6.18 (1H,. d, J ) 1.8 Hz), 7.42-
7.43 (5H, m); 13C NMR δ ) 11.3, 12.0, 18.6, 20.8, 22.5, 22.8, 23.8,
24.2, 28.0, 28.2, 28.6, 28.8, 31.5, 35.59, 35.63, 35.8, 36.1, 38.7, 39.5,
39.8, 39.9, 41.4, 42.4, 44.3, 53.7, 56.2, 56.4, 127.4, 127.8, 128.8, 130.0,
134.3, 177.5, 211.9; HRMS Calcd for C36H52O: 500.4018. Found:
500.4017.
Steroidal Cyclopentenone 31. IR (neat) 2931, 2868, 1684, 1597,
1446, 1190, 1092 cm-1; H NMR δ ) 0.65 (3H, s), 0.83 (3H, d, J )
1
2.4 Hz), 0.85 (3H, d, J ) 2.3 Hz), 0.87 (3H, d, J ) 6.5 Hz), 0.93 (3H,
s), 2.31 (1H, dd, J ) 6.4, 11.3 Hz), 2.40-2.44 (1H, m), 3.44-3.47
(1H, m), 6.35 (1H,. s), 7.41-7.42 (3H, m), 7.53-7.55 (2H, m); 13C
NMR δ ) 12.1, 16.6, 18.7, 21.6, 22.5, 22.8, 23.8, 24.1, 26.0, 26.4,
28.0, 28.2, 31.4, 35.6, 35.7, 35.8, 35.9, 36.2, 39.5, 40.0, 40.2, 42.6,
43.0, 50.0, 55.3, 56.3, 56.4, 127.1, 127.9, 128.8, 130.4, 133.8, 176.5,
211.0; HRMS Calcd for C36H52O: 500.4018. Found: 500.4027.
In this reaction 30 and 31 were obtained in about 3:1 ratio.
Assignment of the regiochemistry of the products was carried out as
follows. The major isomer 30 has the olefinic proton Ha at δ ) 6.18
which is coupled (J ) 1.8 Hz) with the bridgehead proton Hb (δ )
3.54-3.58). Also moderate NOE is observed between Hb and the ortho
proton of the phenyl group. The signal at δ ) 2.73 is assigned as Hc
because strong NOE is observed with Hb, and CH-COSY and DEPT
spectra indicate that this signal is a methine proton. HH-COSY
spectrum also indicates that Hb is coupled with Hc and one of Hd (δ
) 1.6, dt, J ) 8.5, 13.4 Hz), while Hc is coupled with Hb and both of
He (δ ) 2.10, dd, J ) 7.5, 13.5 Hz and δ ) 0.96, coupling uncertain
due to overlapping). The fact that one of Hd appears as a double triplet
suggests that this proton is further coupled with another proton with a
coupling constant of 8.5 Hz. This is compatible with 30 but not with
31 due to the presence of the bridgehead methyl group as shown in
Figure 1. The fact that one of He clearly appears as a double doublet
also supports this assignment.
(7) General Procedure for the Reaction of Bicyclic Alkynylcy-
clopropanols with Co2(CO)8. The reactions of bicyclic alkynylcy-
clopropanols were carried out by the same procedure as described for
the stoichiometric reaction of unsubsituted 1-alkynylcyclopropanols 1.
9-Phenylbicyclo[4.3.0]nona-8-en-7-one (28a). IR (neat) 2935,
1
1684, 1589, 1568, 1446, 1174 cm-1; H NMR δ ) 0.98-1.06 (1H,
Facial selectivity of this annulation reaction was determined at the
cyclopropanation step. Although we have not been successful in
assigning the structure at this stage, we have observed moderate NOE
between Hc and the bridgehead methyl group (δ ) 0.82), which enabled
the assignment as shown in 30. This assignment is quite reasonable
because attack from â-face is thought to be unfavorable due to the
presence of the axial methyl group.
m), 1.15-1.24 (1H, m), 1.27-1.36 (1H, m), 1.52-1.70 (3H, m), 2.12-
2.22 (2H, m), 2.65 (1H, dt, J ) 3.5, 6.5 Hz), 3.45 (1H, dt, J ) 6.5,
10.1 Hz), 6.44 (1H, s), 7.41-7.45 (3H. m), 7.60-7.63 (2H, m); 13C
NMR δ ) 21.9, 22.35, 22.40, 30.7, 40.5, 47.6, 125.2, 127.1, 128.9,
130.8, 133.3, 177.5, 210.0. Anal. Calcd for C15H16O: C, 84.87; H,
7.60. Found: C, 84.67; H, 7.70.
9-Butylbicyclo[4.3.0]nona-8-en-7-one (28b). IR (neat) 2927, 1701,
As the cyclopropanation gave one isomer selectively and the
employed alkynylcyclopropanol was diastereomerically pure, the other
isomer 31 obtained on the rearrangement was assigned as the regio-
isomer of the major isomer 30.
1
1610, 1450 cm-1; H NMR δ ) 0.92 (3H, t, J ) 7.4 Hz), 1.05-1.12
(1H, m), 1.20-1.40 (5H, m), 1.47-1.67 (4H, m), 1.90-2.00 (2H, m),
2.24-2.31 (1H, m), 2.38-2.45 (2H, m), 2.77-2.82 (1H, m), 5.86 (1H,
d, J ) 1.1 Hz); 13C NMR δ ) 13.8, 21.4, 21.7, 22.53, 22.55, 28.1,
28.9, 31.0, 43.0, 46.6, 127.0, 185.6, 211.2; HRMS Calcd for C13H20O:
192.1514. Found: 192.1526
(8) Stoichiometric Reaction in the Presence of Additive. To a
DME solution (5 mL) of Co2(CO)8 (0.50 mmol) was added a DME
solution (5 mL) of 1-alkynylcyclopropanol (0.45 mmol) at room
temperature under an argon atmosphere. After the mixture was stirred
for 30 min, a DME solution (5 mL) of an additive (usually 1.00 mmol)
was added to the mixture. The mixture had been heated to reflux until
the starting material disappeared. After filtration through a small pad
of silica gel, the filtrate was concentrated, and the residue was subjected
to silica gel TLC to give the corresponding 2-cyclopentenone derivative.
(9) Catalytic Reaction in the Presence of Tri(o-isopropylphenyl)-
phosphite. To a DME solution (1 mL) of Co2(CO)8 (0.027 mmol)
was added a DME solution (1 mL) of 1-alkynylcyclopropanol (0. 53
mmol) at room temperature under an argon atmosphere. After the
10-Phenylbicyclo[5.3.0]deca-9-en-8-one (28c). IR (neat) 2924,
1693, 1674, 1593, 1446 cm-1; 1H NMR δ ) 1.33-1.46 (4H, m), 1.62-
1.65 (3H, m), 1.67-1.76 (1H, m), 1.87-1.91 (1H, m), 2.06-2.12 (1H,
m), 2.73-2.78 (1H, m), 3.59-3.63 (1H, m), 6.40 (1H, d, J ) 1.3 Hz),
7.40-7.44 (3H, m), 7.50-7.53 (2H, m); 13C NMR δ ) 27.3, 27.6,
28.2, 30.1, 31.0, 46.9, 52.0, 127.1, 128.2, 128.8, 130.4, 134.1, 177.9,
210.9; HRMS Calcd for C16H18O: 226.1358. Found: 226.1350
10-Butylbicyclo[5.3.0]deca-9-en-8-one (28d). IR (neat) 2918, 1699,
1
1614, 1456 cm-1; H NMR δ ) 0.91 (3H, t, J ) 7.4 Hz), 1.33-1.70
(12H, m), 1.89-1.96 (2H, m), 2.21-2.27 (1H, m), 2.37-2.44 (1H,

3914 J. Am. Chem. Soc., Vol. 120, No. 16, 1998
Iwasawa et al.
mixture was stirred for 30 min, a DME solution (7 mL) of tri(o-
isopropylphenyl) phosphite (0.053 mmol) was added to the mixture.
The mixture had been heated to reflux until the starting material
disappeared. After filtration through a small pad of silica gel, the filtrate
was concentrated, and the residue was subjected to silica gel TLC to
give the corresponding 2-cyclopentenone derivative.
(10) Oxidative Reaction Employing NMO. To a CH2Cl2 solution
(2 mL) of Co2(CO)8 (0.41 mmol) was added a CH2Cl2 solution (2 mL)
of 1-phenylethynylcyclopropanol (0.32 mmol) at room temperature
under an argon atmosphere. After the mixture was stirred for 30 min,
20 mL of CH2Cl2 was added, and then NMO (3.80 mmol) was added
to the mixture in one portion. After the mixture was stirred at room
temperature overnight, it was filtered through a small pad of silica gel,
and the filtrate was concentrated. The residue was subjected to silica
gel TLC to give the products.
2-Ethoxycarbonyl-3-phenyl-2-cyclopentenone (34). IR (neat)
2979, 1734, 1699, 1616, 1446, 1346, 1230, 1188, 1026 cm-1; 1H NMR
δ ) 1.23 (3H, t, J ) 7.2 Hz), 2.61-2.63 (2H, m), 3.03-3.05 (2H, m),
4.28 (2H, q, J ) 7.2 Hz), 7.40-7.47 (3H, m), 7.50-7.52 (2H, m); 13
C
NMR δ ) 13.9, 29.6, 34.8, 61.4, 127.5, 128.7, 131.2, 134.0, 134.1,
165.1, 172.3, 203.6; HRMS Calcd for C14H14O3: 230.0943. Found:
230.0943.
Acknowledgment. We are grateful to Professor Koichi
Narasaka (the University of Tokyo) for helpful discussions and
encouragement during this work. This research was supported
by grants from Tokuyama Science Foundation and the Ministry
of Education, Science, Sports and Culture of Japan.
(Z)-2-Benzylidenecyclobutanone ((Z)-33). IR (neat) 1732, 1630,
1088, 1070, 1024 cm-1; 1H NMR δ ) 2.70 (2H, dt, J ) 2.3, 8.6 Hz),
2.90-2.94 (2H, m), 6.29 (1H, t, J ) 2.3 Hz), 7.33-7.39 (3H, m), 7.94-
7.96 (2H, m); 13C NMR δ ) 21.3, 42.0, 128.5, 129.8, 129.9, 133.4,
134.7, 145.7, 196.9; HRMS Calcd for C11H10O: 158.0732. Found:
158.0717.
(E)-2-Benzylidenecyclobutanone ((E)-33). IR (neat) 2935, 1738,
1645, 1452, 1296, 1101 cm-1; 1H NMR δ ) 2.96 (2H, dt, J ) 2.7, 7.8
Hz), 3.10-3.13 (2H, m), 7.01 (1H, t, J ) 2.7 Hz), 7.36-7.39 (3H, m),
7.48-7.50 (2H, m); 13C NMR δ ) 23.5, 45.7, 126.4, 128.9, 129.9,
130.0, 134.5, 146.1, 199.5; HRMS Calcd for C11H10O: 158.0732.
Found: 158.0721.
Supporting Information Available: Complete experimental
details for the preparation of 1l and general procedure for the
preparation of 2-substituted 1-(1-alkynyl)cyclopropanols 7 and
10. 1H NMR, 13C NMR, IR, and elemental analysis or HRMS
data for 1-(1-alkynyl)cyclopropanols 1a-l, 2-substituted 1-(1-
alkynyl)cyclopropanols 7a-d, 10a-c, and their TBS ethers,
cyclopentenones 3a-d, 3l, 8a, and 9a, and H NMR data for
alkynylborates (11 pages, print/PDF). See any current masthead
page for ordering information and Web access instructions.
1
JA9734004