Rhodium-catalyzed silylcarbocyclization (SiCaC) and carbonylative silylcarbocyclization (CO-SiCaC) reactions of enynes

Article abstract of DOI:10.1021/ja0258982

The reaction of a 1,6-enyne with a hydrosilane catalyzed by Rh(acac)(CO)₂, Rh₄(CO)₁₂, or Rh₂-CO₂(CO)₁₂ under ambient CO atmosphere or N₂ gives 2-methyl-1-silylmethylidene-2-cyclo

Full text of DOI:10.1021/ja0258982

Published on Web 07/10/2002
Rhodium-Catalyzed Silylcarbocyclization (SiCaC) and
Carbonylative Silylcarbocyclization (CO-SiCaC) Reactions of
Enynes
Iwao Ojima,* An T. Vu, Seung-Yub Lee, James V. McCullagh, Andrew C. Moralee,
Masaki Fujiwara, and Tram H. Hoang
Contribution from the Department of Chemistry, State UniVersity of New York at Stony Brook,
Stony Brook, New York 11794-3400
Received February 11, 2002
Abstract: The reaction of a 1,6-enyne with a hydrosilane catalyzed by Rh(acac)(CO)2, Rh4(CO)12, or Rh2-
Co2(CO)12 under ambient CO atmosphere or N2 gives 2-methyl-1-silylmethylidene-2-cyclopentane or its
heteroatom congener in excellent yield through silylcarbocycization (SiCaC) process. The same reaction,
but in the presence of a phosphite such as P(OEt)3 and P(OPh)3 under 20 atm of CO, affords the
corresponding 2-formylmethyl-1-silylmethylidene-2-cyclopentane or its heteroatom congener with excellent
selectivity through carbonylative silylcarbocycization (CO-SiCaC) process. The SiCaC reaction has also
been applied to a 1,6-enyne bearing a cyclohexenyl group as the alkene moiety and a 1,7-enyne system.
The functionalized five- and six-membered ring systems obtained by these novel cyclization reactions serve
as useful and versatile intermediates for the syntheses of natural and unnatural heterocyclic and carbocyclic
compounds. Possible mechanisms for the SiCaC and CO-SiCaC reactions as well as unique features of
these processes are discussed.
tannanes,7 and silastannanes7 are among the commonly used
reducing agents for these processes.8 The resulting tandem
Introduction
Development of practical and effective cyclization reactions
for the syntheses of carbocycles and heterocycles of medicinal
interest or intermediates useful for functional materials has been
the subject of extensive research. Among numerous annulation
methods available to synthesize these compounds, the power
and efficiency of transition metal-promoted carbocyclization
processes1 has been demonstrated in a number of elegant
syntheses of complex molecules and natural products.2 Recently,
significant advances have been made in the transition metal-
catalyzed carbocyclization reactions with the use of a stoichio-
metric amount of a reducing agent in the process. Hydrosilanes,3
hydrostannanes,4 borylsilanes,5 borylstannanes,6 disilanes,7 dis-
addition/cyclization reactions are particularly useful for yielding
functionalized carbocycles or heterocycles with concomitant
incorporation of metal or heteroatom groups that are amenable
for further synthetic manipulations.
In the course of our extensive research program to develop
silicon-initiated carbometalation processes, silylformyla-
tion,9,3b silylcarbocyclization (SiCaC),3a-d silylcarbobicyclization
(SiCaB),10,3d silylcyclocarbonylation (SiCCa),11 and silylcar-
botricyclization (SiCaT)12 have been discovered. We have also
reported the silylcarbocyclization-hydrosilylation (SiCaC-HS)
(3) (a) Ojima, I.; Donovan, R. J.; Shay, W. R. J. Am. Chem. Soc. 1992, 114,
6580 (b) Ojima, I.; Tzamarioudaki, M.; Tsai, C.-Y. J. Am. Chem. Soc. 1994,
116, 3643. (c) Ojima, I.; McCullagh, J. V.; Shay, W. R. J. Organomet.
Chem. 1996, 521, 421. (d) Ojima, I.; Zhu, J.; Vidal, E. S.; Kass, D. F. J.
Am. Chem. Soc. 1998, 120, 6690. (e) Widenhoefer, R. A.; DeCarli, M. A.
J. Am. Chem. Soc. 1998, 120, 3805. (f) Uozumi, Y.; Tsuji, H.; Hayashi, T.
J. Org. Chem. 1998, 63, 6137. (g) Stengone, C. N.; Widenhoefer, R. A.
Tetrahedron Lett. 1999, 40, 1451. (h) Widenhoefer, R. A.; Vadehra, A.
Tetrahedron Lett. 1999, 40, 8499. (i) Widenhoefer, R. A.; Stengone, C. N.
J. Org. Chem. 1999, 64, 8681. (j) Molander, G. A.; Corrette, C. P. J. Org.
Chem. 1999, 64, 9697. (k) Perch, N. S.; Widenhoefer, R. A. J. Am. Chem.
Soc. 1999, 121, 6960. (l) Perch, N. S.; Pei, T.; Widenhoefer, R. A. J. Org.
Chem. 2000, 65, 3836. (m) Pei, T.; Widenhoefer, R. A. Org. Lett. 2000, 2,
1469. (n) Muci, A. R.; Bercaw, J. E. Tetrahedron Lett. 2000, 41, 7609.
(4) Lautens, M.; Smith, N. D.; Ostrovsky, D. J. Org. Chem. 1997, 62, 8970.
Lautens, M.; Macuso, J. Org. Lett. 2000, 2, 671. Smith, N. D.; Mancuso,
J.; Lautens, M. Chem. ReV. 2000, 100, 3257.
(5) Suginome, M.; Matsuda, T.; Ito, Y. Organometallics 1998, 17, 5233.
Onozawa, S.-Y.; Hatanaka, Y.; Tanaka, M. Chem. Commun. 1997, 1229.
(6) Onozawa, S.-Y.; Hatanaka, Y.; Choi, N.; Tanaka, M. Organometallics 1997,
16, 5389.
(7) Obora, Y.; Tsuji, Y.; Kakehi, T.; Kobayashi, M.; Shinkai, Y.; Ebihara,
M.; Kawamura, T. J. Chem. Soc., Perkin Trans. 1 1995, 599.
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53, 3539. Chatani, N.; Morimoto, T.; Muto, T.; Murai, S. J. Organomet.
Chem. 1994, 473, 335.
* To whom correspondence should be addressed. E-mail: iojima@
notes.cc.sunysb.edu.
(1) For recent reviews on metal-catalyzed carbocyclization, see: (a) Grotjahn,
D. B. In ComprehensiVe Organometallic Chemistry II; Hegedus, L. S., Ed.;
Pergamon/Elsevier Science: Kidlington, 1995; Vol. 12; p 741. (b) Trost,
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Engl. 1995, 34, 259. (d) Lautens, M.; Klute, W.; Tam, W. Chem. ReV.
1996, 96, 49. (e) Negishi, E.-I.; Coperet, C.; Ma, S.; Liou, S.-Y.; Liu, F.
Chem. ReV. 1996, 96, 365. (f) Ojima, I.; Tzamarioudaki, M.; Li, Z.;
Donovan, R. J. Chem. ReV. 1996, 96, 635. (g) Fru¨hauf, H. W. Chem. ReV.
1997, 97, 523. (h) Trost, B. M.; Krische, M. J. Synlett 1998, 1. (i) Takacs,
J. M.; Boito, S. C.; Myoung, Y.-C. Curr. Org. Chem. 1998, 2, 233. (j)
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9
9164
J. AM. CHEM. SOC. 2002, 124, 9164-9174
10.1021/ja0258982 CCC: $22.00 © 2002 American Chemical Society

Silylcarbocyclization Reactions of Enynes
A R T I C L E S
Scheme 1
Results and Discussion
Silylcarbocyclization (SiCaC) of 1,6-Enynes. The scope of
the SiCaC reaction has been investigated systematically by
looking at the key elements and reaction variables involved in
this process. First, the efficacy of Rh and Rh-Co complexes
as catalyst for this process was examined using 4,4-bis-
(carbethoxy)hept-6-en-1-yne (1a) as the 1,6-enyne substrate.
Results are summarized in Table 1. As Table 1 shows, the
reaction of 1a with Me2PhSiH (1.0 equiv) catalyzed by Rh-
(acac)(CO)2 (1.0 mol %) in toluene at 70 °C under ambient
pressure of CO for 18 h gives a 3:1 mixture of SiCaC product
4,4-bis(carbethoxy)-1-(E)-dimethylphenylsilylmethylidene-2-
methylcyclopentane (2a) and CO-SiCaC product 4,4-bis-
(carbethoxy)-1-(E)-dimethylphenylsilylmethylidene-2-(formyl-
methyl)cyclopentane (3a) in 75% yield, accompanied by a small
amount of hydrosilylation product (∼5%) (Table 1, entry 1).
The use of (tBuNC)4RhCo(CO)4, which is the best catalyst for
intramolecular silylformylation of ω-siloxyalkynes,9e in xylene
increased the overall yield of the carbocyclization products, but
the product selectivity remains the same, that is, 2a:3a ) 3:1
(entry 2). However, the product selectivity is remarkably
improved to 10:1 when the same reaction is carried out in hexane
at 65 °C (entry 3). Thus, the efficacy of various rhodium
catalysts has been examined in hexane. It is worth mentioning
that the use of Rh and Rh-Co carbonyl clusters such as Rh4-
Scheme 2
reaction of 1,6-enynes3d as well as the carbonylative carbotri-
cyclization (CO-CaT) reaction of enediynes.13
The first silylcarbocyclization was discovered serendipitously
during our detailed product analysis of the silylformylation of
1-hexyne catalyzed by Rh and Rh-Co carbonyl clusters, which
gave dibutylcyclopentenone by incorporating two molecules of
1-hexyne, one molecule of hydrosilane, and one molecule of
CO.3a Following up this discovery, we investigated the intra-
molecular version of this reaction using a couple of 1,6-enynes
catalyzed by Rh and Rh-Co complexes, which led to the
discovery of the novel silylcarbocyclization (SiCaC) reaction
in 1992 (Scheme 1).3a When the SiCaC reaction of allyl
propargyl ether with Et3SiH catalyzed by Rh(acac)(CO)2 was
carried out under higher pressure of CO (10 atm), the first
carbonylative SiCaC reaction (CO-SiCaC) took place to give
the corresponding 3-exo-silylmethylidene-4-formylmethyl-tet-
rahydrofuran as minor product (15-20%) together with the
simple silylformylation product (70-75%) (Scheme 2). Our
discoveries of these two novel silicon-initiated carbocyclization
reactions have spurred substantial interests in this field for the
exploration of similar carbocyclization processes. We will
describe here a full account of our study on the silylcarbo-
cyclization (SiCaC) and carbonylative silylcarbocyclization
(CO-SiCaC) reactions of 1,6-enynes and related systems.
14
15
(CO)12 and Rh2Co2(CO)12 allows the SiCaC reaction of 1a
to occur instantaneously at ambient temperature, yielding 2a
as almost exclusive product (entries 4-10). Increasing the
hydrosilane ratio to 1a from 1.0 to 1.5 or higher gives 2a as
essentially the sole product based on GC analysis (2a:3a g 130:
1) (entries 5, 6, 9). SiCaC product 2a can be isolated in excellent
yield through removal of solvent followed by simple flash
chromatography on silica gel (entry 5). As expected, at higher
dilution (0.13 vs 0.4 M), the CO concentration increases thereby
somewhat decreasing the selectivity for 2a to 60:1 (entry 7).
The reaction can be carried out with catalyst loading as low as
0.05 mol % although these conditions require longer reaction
time (8 h vs <1 min), and the product selectivity is reduced to
35:1 (entry 8). The reaction employing Rh2Co2(CO)12 as catalyst
proceeds under nitrogen atmosphere, giving 2a as the single
product (>1000:1, i.e., the limit of GC analysis) (entry 10).16
Next, a range of hydrosilanes was examined for their efficacy
in the SiCaC reaction using 1a as the substrate. Results are
summarized in Table 2. As Table 2 shows, hydrosilanes
possessing aryl groups such as Me2PhSiH and MePh2SiH react
with 1a instantaneously to give 2a in excellent isolated yields
(entries 1, 2). Reactions with hydrosilanes containing alkoxy
groups are equally rapid, giving complete conversion to the
SiCaC products (entries 3-5). More sterically demanding Ph3-
SiH also gives product Ph3Si-2a, albeit higher temperature and
longer reaction time are required (entry 6). However, less
(9) (a) Ojima, I.; Ingallina, P.; Donovan, R. J.; Clos, N. Organometallics 1991,
10, 38. (b) Ojima, I.; Donovan, R. J.; Ingallina, P.; Clos, N.; Shay, W. R.;
Eguchi, M.; Zeng, Q.; Korda, A. J. Cluster Sci. 1992, 3, 423. (c) Eguchi,
M.; Zeng, Q.; Korda, A.; Ojima, I. Tetrahedron Lett. 1993, 34, 915. (d)
Ojima, I.; Donovan, R. J.; Eguchi, M.; Shay, W. R.; Ingallina, P.; Korda,
A.; Zeng, Q. Tetrahedron 1993, 49, 5431. (e) Ojima, I.; Vidal, E.;
Tzamarioudaki, M.; Matsuda, I. J. Am. Chem. Soc. 1995, 117, 6797. (f)
Ojima, I.; Li, Z.; Donovan, R. J.; Ingallina, P. Inorg. Chimica Acta 1998,
270, 279. (g) Ojima, I.; Li, Z. In Catalysis by Di- and Polynuclear Metal
Complexes; Adams, R. A., Cotton. F. A., Eds.; John Wiley & Sons:
Chichester, 1998; Chapter 9, pp 307. For contributions from other
laboratories, see: (h) Matsuda, I.; Ogiso, A.; Sato, S.; Izumi, Y. J. Am.
Chem. Soc. 1989, 111, 2332. (i) Matsuda, I.; Ogiso, A.; Sato, S. J. Am.
Chem. Soc. 1990, 112, 6120. (j) Tanke, R.; Crabtree, R. H. J. Am. Chem.
Soc. 1990, 112, 7984-7989. (k) Matsuda, I.; Sakakibara, J.; Nagashima,
H. Tetrahedron Lett. 1991, 32, 7431. (l) Matsuda, I.; Sakakibara, J.; Inoue,
H.; Nagashima, H. Tetrahedron Lett. 1992, 33, 5799. (m) Doyle, M. P.;
Shanklin, M. S. Organometallics 1993, 12, 11. (n) Wright, M. E.; Cochran,
B. B. J. Am. Chem. Soc. 1993, 115, 2059. (o) Doyle, M. P.; Shanklin, M.
S. Organometallics 1994, 13, 1081. (p) Zhou, J. Q.; Alper, H. Organo-
metallics 1994, 13, 1586. (q) Monteil, F.; Matsuda, I.; Alper, H. J. Am.
Chem. Soc. 1995, 117, 4419. (r) Leighton, J. L.; Chapman, E. J. Am. Chem.
Soc. 1997, 119, 12416. (s) Matsuda, I.; Fukuta, Y.; Tsuchihashi, T.,
Nagashima, H.; Itoh, K. Organometallics 1997, 16, 4327. (t) Muraoka, T.;
Matsuda, I.; Itoh, K. Tetrahedron Lett. 1998, 39, 7325.
t
reactive and bulky trialkylhydrosilane, BuMe2SiH, does not
yield any SiCaC product (entry 7), but gives only a small amount
(14) Martinengo, S.; Giordano, G.; Chini, P. Inorg. Synth. 1990, 28, 242.
(15) (a) Horva´th, I. T.; Bor, G.; Garland, M.; Pino, P. Organometallics 1986,
5, 1441. (b) Ojima, I.; Clos, N.; Donovan, R. J.; Ingallina, P. Organome-
tallics 1991, 10, 3211.
(16) The CO atmosphere appears to be necessary or at least preferred to stabilize
the active catalyst species for most catalyst precursors, especially Rh4(CO)12.
Rh2Co2(CO)12 seems to be sufficiently stable under N2 atmosphere to
catalyze the SiCaC reactions. Nevertheless, unless the reactions are very
fast, all catalysts decompose under N2 during the reaction over a longer
period of time.
(10) Ojima, I.; Fracchiolla, D. A.; Donovan, R. J.; Banerji, P. J. Org. Chem.
1994, 59, 7594. Ojima, I.; Fracchiolla, D. A.; Zhu, J. Organometallics 1996,
15, 5191.
(11) Ojima, I.; Machnik, D.; Donovan, R. J.; Mneimne, O. Inorg. Chim. Acta
1996, 251, 299.
(12) Ojima, I.; Vu, A. T.; McCullagh, J. V.; Kinoshita, A. J. Am. Chem. Soc.
1999, 121, 3230.
(13) Ojima, I.; Lee, S.-Y. J. Am. Chem. Soc. 2000, 122, 2385.
9
J. AM. CHEM. SOC. VOL. 124, NO. 31, 2002 9165

A R T I C L E S
Ojima et al.
Table 1. Rh-Catalyzed SiCaC Reaction of Enyne 1aa
entry
catalyst (mol %)
solvent
conc. (M)
Me2PhSiH (equiv.)
temp (°C)
time
yield (%)b
ratio (2a:3a)b
1
2
3
4
5
6
7
8
9
Rh(acac)(CO)2 (1.0)
(tBuNC)4RhCo(CO)4 (1.0)
Rh(acac)(CO)2 (1.0)
Rh4(CO)12 (0.5)
Rh4(CO)12 (0.5)
Rh4(CO)12 (0.5)
toluene
xylene
hexane
hexane
hexane
hexane
hexane
hexane
hexane
hexane
0.4
0.2
0.4
0.4
0.4
0.4
0.13
0.4
0.4
0.4
1.0
1.0
1.0
1.0
1.5
2.0
1.5
5.0
1.5
5.0
70
100
65
22
22
22
22
22
22
22
18 h
12 h
1.5 h
18 min
<1 min
<1 min
<1 min
8 h
<1 min
<1 min
75
90
98
100
99 (95)
100
99
99
100
100
3:1
3:1
10:1
30:1
130:1
>150:1
60:1
Rh4(CO)12 (0.5)
Rh4(CO)12 (0.05)
Rh2Co2(CO)12 (0.5)
Rh2Co2(CO)12 (0.5)
35:1
138:1c
>1000:1c
10
a Reactions were run on a 1 mmol scale. b Yields and ratios were determined by GC analysis. Isolated yields are in parentheses. c Reaction was run under
nitrogen atmosphere.
Table 2. Efficacy of Hydrosilanes in SiCaC Reaction of 1aa
a Rh or Rh-Co cluster catalyst is found to be slow at ambient
temperature. However, by running the reaction at 70 °C with
the use of Rh(acac)(CO)2 as the catalyst brings about a clean
conversion of 1j to SiCaC product 2j (entry 10). Methyl
substitution at the terminal alkyne carbon is also tolerated,
although longer reaction time (3 h vs <1 min) is necessary to
give 2k in high yield (entry 11). The formation of a six-
membered ring carbocycle is possible (entry 12) although it is
less effective than the five-membered ring formation, as
expected. Thus, the reaction of 4,4-bis(carbomethoxy)oct-7-en-
1-yne (1l) at 70 °C for 1 h gives the SiCaC product 2l in 34%
yield, accompanied by hydrosilylation (21%) and silylformy-
lation products (17%) (entry 12).
entry
R SiH
3
temp (°C)
time
product
yield (%)b
1
2
3
4
5
6
7
Me2PhSiH
MePh2SiH
(EtO)2MeSiH
(EtO)3SiH
(MeO)3SiH
Ph3SiH
22
22
22
22
22
70
22
<1 min 2a
95
94
>99
99
<1 min 2a-SiMePh2
<1 min 2a-SiMe(OEt)2
<1 min 2a-Si(OEt)3
<1 min 2a-Si(OMe)3
>99
50
3 h
2 h
2a-SiPh3
tBuMe2SiH
2a-SiMe2But
0c
a Reactions were run on a 1 mmol scale using 1.5 equiv of silane at 0.4
M concentration in hexane under ambient pressure of CO. b Isolated yields.
c Some hydrosilylation product formed.
The attempted SiCaC reactions of enynes bearing a substituted
alkene moiety, 1m and 1n, led exclusively to hydrosilylation
or silylformylation or both of the alkyne moiety (Chart 1).
However, the reaction of 4, wherein the olefin substitution is
constrained in a ring, with Me2PhSiH catalyzed by Rh(acac)-
(CO)2 at 50 °C resulted in the formation of bicyclo[4.3.0]nonene
6 in 84% isolated yield (Scheme 3). Bicyclic product 6 was
found to possess cis ring juncture in the fused ring system on
the basis of the unambiguous NOE experiments (See Experi-
mental Section). The observed exclusive formation of the cis
ring juncture is readily explained by taking into account the
transition-state model of the carbometalation step (see TS-5).
As TS-5 clearly illustrates, only possible approach of â-silyl-
vinyl-[Rh] moiety to the olefin moiety of cyclohexenyl group
of 4 is to form the cis juncture as observed. This carbometalation
also defines the stereochemical arrangement of the [Rh] moiety,
which is anti (or trans) to the bridgehead hydrogen. Accordingly,
the â-hydride elimination can take place only with one of the
methylene hydrogen syn (or cis) to the [Rh] moiety. Diene 1o
also failed to undergo carbocyclization under the standard SiCaC
reaction conditions (Chart 1).
Carbonylative Silylcarbocyclization (CO-SiCaC) of 1,6-
Enynes. As mentioned in the Introduction, the very first Rh-
catalyzed CO-SiCaC reaction of 1,6-diyne was discovered in
these laboratories with 1j as the substrate as a minor pathway
in the SiCaC reaction.3a Since this reaction gives versatile
intermediates for organic syntheses, systematic variation of
reaction parameters was performed for the CO-SiCaC reaction
of 1a, which was selected as the standard substrate, to optimize
the selectivity for the formation of product 3a. While our study
of the hydrosilylation product. The use of hydrosilanes bearing
aryl and alkoxy substituents is synthetically useful as the
resulting vinylsilane moieties of the SiCaC products could be
easily transformed into other functional groups via oxidation.17
As shown in Table 1, the optimal reaction conditions for the
SiCaC reaction include the use of Rh4(CO)12 or Rh2Co2(CO)12
clusters, 1.5 equiv of Me2PhSiH at 0.4 M (or higher) concentra-
tion in hexane at room temperature and ambient pressure of
CO or N2. Thus, a variety of 1,6-enynes has been subjected to
the optimal conditions for the SiCaC process to examine the
scope of this reaction in terms of functional group tolerance. A
1,6-enyne bearing an internal acetylene moiety (1k) and a 1,7-
enyne (1l) have also been empolyed. Results are summarized
in Table 3.
As Table 3 shows, the SiCaC reaction is applicable to a range
of substrates, allowing the rapid synthesis of highly function-
alized exo-silylmethylenecyclopentane and pyrrolidine deriva-
tives 2 in excellent isolated yields (entries 1-8). The reaction
tolerates various functional groups including ester, ether,
sulfonamide, and amine. The formation of product 2h indicates
that the Rh-catalyzed SiCaC reaction occurs exclusively at the
1,6-enyne moiety, but not at the 1,6-diene moiety (entry 8). Free
hydroxyl groups are tolerated under the SiCaC reaction condi-
tions albeit the yield of 2i is somewhat lower than others (entry
9). The reaction of allyl propargyl ether (1j), in the presence of
(17) Taber, D. F.; Bhamidipati, R. S.; Yet, L. J. Org. Chem. 1995, 60, 5537.
Jones, G. R.; Landais, Y. Tetrahedron 1996, 52, 7599.
9
9166 J. AM. CHEM. SOC. VOL. 124, NO. 31, 2002

Silylcarbocyclization Reactions of Enynes
A R T I C L E S
Table 3. Rhodium-Catalyzed SiCaC Reaction of Enynesa
a Reactions were run on a 1 mmol scale using 0.5 mol% of rhodium cluster and 1.5 equiv of Me2PhSiH at 0.4 M concentration in hexane under ambient
pressure. b Isolated yields. c Reaction in toluene. d 1 mol% of catalyst used.
Chart 1. Substrates That Failed To Cyclize under SiCaC
From the results shown in Table 1, we anticipated that the
selectivity for CO-SiCaC product 3a should be improved by
Conditions
running the reaction with 1 equiv of a hydrosilane in higher
dilution of the Rh catalyst and a substrate, which should increase
dissolved CO concentration and hence the formation of carbo-
nylative SiCaC product 3a. Results obtained under various
conditions are summarized in Table 4. The reaction of 1a with
Scheme 3
Me2PhSiH (1.05 equiv) catalyzed by Rh(acac)(CO)2 (1.0 mol
%) at 0.2 M concentration in toluene at 50 °C and ambient
pressure of CO for 3 h gives a 1:3 mixture of 3a and 2a in
78% yield (entry 1). Addition of PPh3 or P(OPh)3 as ligand to
the reaction system reverses the product ratio, yielding 3a as
the major product (entries 2-5). It should be noted that the
3a:2a ratio has reached 19:1 in 95% yield when 4 mol % of
P(OPh)3 is used. Another effort to improve the selectivity for
3a is to increase CO pressure (entries 6-8). The reaction of 1a
at 70 °C and 20 atm of CO in 1,4-dioxane for 24 h favors the
formation of 3a over 2a in a 5:1 ratio even without phosphite
additive (entry 6). Lowering the substrate concentration from
0.1 to 0.02 M without phosphite additive affords 3a predomi-
nantly (3a:2a ) 8:1) (entry 7). However, only a slight
improvement is observed by increasing the CO pressure from
20 to 30 atm (entry 8). These results imply that a combination
was in progress, Matsuda et al. reported a similar process,
involving a silylformylation/carbocyclization process with the
use of a hydrosilane and CO in the presence of a Rh catalyst.18
(18) Fukuta, Y.; Matsuda, I.; Itoh, K. Tetrahedron Lett. 1999, 40, 4703.
of a ligand additive, low substrate concentration, higher tem-
9
J. AM. CHEM. SOC. VOL. 124, NO. 31, 2002 9167

A R T I C L E S
Ojima et al.
Table 4. Rhodium-Catalyzed CO-SiCaC Reaction of Enyne 1aa
entry
catalyst
ligand (equiv/Rh)
solvent
toluene
toluene
toluene
toluene
toluene
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
conc (M)
CO (atm)
temp (°C)
time (h)
yield (%)b
ratio (2a:3a)b
1
2
3
4
5
6
7
8
9
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh(acac)(CO)2
Rh4(CO)12
Rh4(CO)12
Rh4(CO)12
Rh4(CO)12
Rh4(CO)12
none
0.2
0.2
0.2
0.2
0.2
0.1
0.02
0.02
0.02
0.02
0.02
1
1
1
1
1
20
20
30
20
20
20
50
50
50
50
50
70
70
70
3
7
18
8
14
24
24
24
48
48
48
78
87
98
92
95
85
86
88
3:1
1:1.5
1:3
1:12
1:19
1:5
1:8
1:9
1:39
1:50
1:77
PPh3 (1)
PPh3 (3)
P(OPh)3 (2)
P(OPh)3 (4)
none
none
none
P(OPh)3 (5)
P(OEt)3 (3)
P(OEt)3 (5)
105
105
105
96(87)
98
99(91)
10
11
a Reactions were run on a 1 mmol scale using 1 mol% of Rh(acac)(CO)2 or 0.5 mol% of Rh4(CO)12 and 1.05 equiv of Me2PhSiH. b Yields and ratios were
determined by GC analysis. Isolated yields of 3a are in parentheses.
Table 5. Rh-Catalyzed CO-SiCaC Reaction of 1,6-Enynesa
purification by flash column chromatography on silica gel
(entries 2-5). The reaction of 4-methanesulfonyl-4-azahept-6-
en-1-yne 1p, bearing a sulfonamide group in the backbone, was
not as clean as other cases, giving 3p in 56% isolated yield
(entry 6). To our surprise, under the CO-SiCaC reaction
conditions, allyl(benzyl)propargylamine 1f led to the exclusive
formation of SiCaC product 2f, accompanied by a small amount
of hydrosilylation product.19 A possible explanation for this
result is discussed later in the Mechanism section (vide infra).
The optimal conditions mentioned above include high dilution
of reactants, which is not advantageous in practical syntheses.
Accordingly, we performed further optimization of the CO-
SiCaC process and have indeed found a synthetically more
favorable procedure. The improved procedure includes the
freezing of the substrate solution in dioxane before addition of
the catalyst and hydrosilane. The frozen reaction mixture is then
placed in an autoclave and pressurized with 20 atm of CO. This
a Reactions were run on a 1 mmol scale using 0.5 mol% of Rh4(CO)12,
“freeze and CO” protocol should prevent any reaction from
occurring before the system is subjected to the high pressure
of CO. Since the SiCaC product predominates at lower CO
concentration (i.e., lower CO pressure or higher concentration
of the substrate or both), this protocol should be able to block
the SiCaC reaction by freezing the reaction to start until the
whole reaction system is under high CO pressure and thus favors
the formation of the CO-SiCaC product.
First, this protocol was examined using substrate 1q, and the
results are summarized in Table 6. As Table 6 shows, this
protocol has a profound effect on the product selectivity. When
the reaction was carried out without phosphite ligand at 70 °C
and 20 atm of CO at 0.02 M concentration of 1q, a high
selectivity (1:27, i.e., 96.3%) is observed in favor of the
formation of CO-SiCaC product 3q (entry 1). However, the
selectivity drops to 1:6 when the same reaction is run at 1.0 M
concentration of 1q, which is not surprising though (entry 2).
When the reactions are carried out in the presence of P(OEt)3
at 105 °C, high selectivities (1:26-1:45) are observed even at
0.2-1.0 M concentrations (entries 3-5). It is noteworthy that
a practically useful high selectivity (1:26) is achieved even at
1.0 M concentration under these conditions (entry 5). These
results clearly indicate that the “freeze and CO” protocol allows
1.05 equiv of Me2PhSiH and 10 mol% of P(OEt)3 at 0.02 M concentration
in 1,4-dioxane under 20 atm of CO at 105 °C for 48 h. b Isolated yields.
perature, and sufficiently high CO pressure would maximize
the selectivity for CO-SiCaC product. In fact, the reaction using
P(OPh)3 as ligand (5 equiv to Rh) and low substrate concentra-
tion (0.02 M) at 105 °C and 20 atm of CO for 48 h gives 3a
with very high selectivity (3a:2a ) 39:1) in 96% yield (entry
9). Along this line of approach, the optimal conditions have
been found, which consist of Rh4(CO)12 (0.5 mol %) and
P(OEt)3 (10 mol %; 5 equiv to Rh) at 105 °C and 20 atm of
CO at 0.02 M substrate concentration in 1,4-dioxane. The
reaction under the optimal conditions affords 3a as essentially
the sole product (3a:2a ) 77:1 by GC analysis), which is
isolated in 91% yield after removal of solvent followed by
simple flash chromatography on silica gel (entry 11).
Next, various 1,6-enynes were subjected to the optimal CO-
SiCaC reaction conditions mentioned above and the results are
summarized in Table 5. The reaction of 1a giving 3a exclusively
(vide supra) is listed as reference (entry 1). As Table 5 shows,
the CO-SiCaC reaction provides an efficient route to highly
functionalized exo-silylmethylene-cyclopentane and pyrrolidine
derivatives 3 bearing a formylmethyl moiety at the C2 position.
The reaction also tolerates a variety of functional groups,
including ester, ketal, ether, and sulfonamide, to give CO-
SiCaC products 3b-e in high-to-excellent isolated yields after
(19) This rather peculiar phenomenon was also pointed out by Fukuta, Matsuda,
and Itoh, but without any interpretation. See ref 18.
9
9168 J. AM. CHEM. SOC. VOL. 124, NO. 31, 2002

Silylcarbocyclization Reactions of Enynes
A R T I C L E S
Table 6. Rhodium-Catalyzed CO-SiCaC Reaction of Enyne 1q
Scheme 4. Proposed Mechanism for the SiCaC and CO-SiCaC
Reactions
Using the “Freeze and CO” Protocola
entry
conc (M)
ligand (equiv./Rh)
temp (°C)
time (h)
ratio (2q:3q)b
1
2
3
4
5
0.02
1.0
0.2
0.5
1.0
none
none
P(OEt)3 (5)
P(OEt)3 (5)
P(OEt)3 (5)
70
70
105
105
105
24
24
48
48
48
1:27
1:6
1:45
1:38
1:26
a Reactions were run on 1 mmol scale using 0.5 mol% of Rh4(CO)12
and 1.05 equiv of Me2PhSiH under 20 atm of CO. Yield was >98% by
GC analysis for all cases. b Ratios were determined by GC analysis.
Table 7. CO-SiCaC Reaction of Enyne 1a Using the “Freeze and
CO” Protocola
entry
conc (M)
ligand (equiv/Rh)
temp (°C)
time (h)
ratio (2a:3a)b
1
2
3
4
0.02
0.2
0.5
1
P(OEt)3 (5)
P(OEt)3 (5)
P(OEt)3 (5)
P(OEt)3 (5)
105
105
105
105
48
48
48
48
1:125
1:95
1:65
1:64
into the â-silylvinyl-[M](H) complex takes place to form
â-silylacryloyl-[M](H) species, followed by reductive elimina-
tion, yielding a silylformylation product.9a,f,s
a Reactions were run on a 1 mmol scale using 0.5 mol% of Rh4(CO)12
and 1.05 equiv of Me2PhSiH under 20 atm of CO. Yield was >98% by
GC analysis for all cases. b Ratios were determined by GC analysis.
The most plausible mechanism for the silylcarbocyclization
of enyne 1, which can accommodate the formations of both
SiCaC product 2 and CO-SiCaC product 3, is proposed in
Scheme 4 by taking into account the mechanisms for hydro-
silylation and silylformylation mentioned above. As Scheme 4
illustrates, the silylcarbocyclization of enynes should begin with
formation of the active catalyst species, silyl-[Rh] complex I,
followed by insertion of the acetylene moiety of enyne 1 to
generate â-silylvinlyl-[Rh] complex II. Coordination of the
olefin moiety, followed by intramolecular carbometalation, leads
to the formation of exo-methylenecyclopentylmethyl-[Rh]
complex III. In the absence of CO or at very low concentration
of CO, hydrosilane-promoted reductive elimination occurs to
give SiCaC product 2 and regenerates silyl-[Rh] complex I.
At higher CO concentration, migratory insertion of CO into the
alkyl-[Rh] bond of III leads to the formation of acyl-[Rh]
complex IV.21 Subsequent hydrosilane-promoted reductive
elimination affords CO-SiCaC product 3 and regenerates the
active catalyst species I. A CO atmosphere is not essential for
the SiCaC process as exemplified in Table 3 (entries 2 and 3).
However, the use of a CO atmosphere appears to stabilize the
active [Rh] catalyst species, especially when Rh and Rh-Co
carbonyl clusters are used for a prolonged period of time.
It should be noted that the coordination of the alkene moiety
to the [Rh] metal appears to have a very strong directing effect
on the regioselective insertion of the alkyne moiety to the Si-
[Rh] bond in the conversion of I to II. As Table 3 shows (entry
11), the reaction of 1k bearing an internal alkyne moiety gives
the SiCaC product 2k in 89% isolated yield. Since a simple
hydrosilylation of 2-alkyne, for example, 5,5-di(carbethoxy)-
oct-2-yne, should give a mixture of 2-silylalkane and 3-silyl-
the CO-SiCaC reaction to be conducted at normal concentra-
tions (i.e., not high dilution) without compromising the selectiv-
ity for the CO-SiCaC product.
Next, the “freeze and CO” with P(OEt)3 protocol was applied
to the reaction of 1a for comparison with the results shown in
Table 4, wherein the best selectivity for 3a was 1:77 (i.e., 98.7%)
(see Table 4, entry 11). The results are summarized in Table 7.
As expected, the “freeze and CO” protocol increases the
selectivity dramatically, for example, the best selectivity for the
formation of 3a with this protocol is 1:125 (i.e., 99.2%) (entry
1) as compared to 1:77 obtained earlier (vide supra). A high
selectivity (1:64) is still achieved even at 1.0 M concentration
(entry 4). Accordingly, it can be said that the ultimate optimal
reaction conditions have been found for the CO-SiCaC reaction
through this study.
Mechanism. It is logical to hypothesize that the mechanism
for the intramolecular silylcarbocyclization of enynes should
be closely related to that of hydrosilylation and silylformylation
of alkynes. Mechanistic studies performed in these laboratories
and others have revealed that both hydrosilylation20 and
silylformylation9a,f,s share the same fundamental reaction se-
quence, which includes the initial formation of silyl-[M](H)
species through the oxidative addition of a hydrosilane to a metal
complex, followed by insertion of an alkyne into the Si-[M]
bond of the silyl-[M](H) species to form the corresponding
â-silylvinyl-[M](H) species. Subsequent hydrosilane-induced
reductive elimination (hydride shift) gives a hydrosilylation
product.20 In the presence of CO, however, the insertion of CO
(20) (a) Ojima, I. In The Chemistry of Organic Silicon Compounds; Patai, S.,
Rappoport, Z., Eds.; Wiley: Chicheser, U.K., 1989; Vol. 2, p 1479. (b)
Ojima, I.; Clos, N.; Donovan, R. J.; Ingallina, P. Organometallics 1990, 9,
3127. (c) Hiyama, T.; Kusumoto, T. In ComprehensiVe Organic Synthesis;
Trost, B. M., Fleming, I., Paquette, L. A., Eds.; Pergamon Press: Oxford,
UK, 1991; Vol. 8, p 763.
(21) For reviews on migratory insertion of CO, see: Durfee, L. D.; Rothwell,
I. P. Chem. ReV. 1988, 88, 1059. Erker, G. Acc. Chem. Res. 1984, 17, 103.
Albers, M. O.; Coville, N. J. Coord. Chem. ReV. 1984, 53, 227.
9
J. AM. CHEM. SOC. VOL. 124, NO. 31, 2002 9169

A R T I C L E S
Ojima et al.
Scheme 5
due to the fact that this process is reversible because of a free
coordination site generated after the migration of the alkyl group
to the vicinal CO ligand. Trapping of this vacant site by addition
of an external ligand or CO thus suppresses the reversibility of
the CO insertion.22 As mentioned above, the CO-SiCaC process
requires a delicate stereoelectronic balance of ligands on the
active [Rh] species, in that the ligand(s) should stabilize the
acyl-[Rh] intermediate IV, but should not impose too much
steric hindrance for the approach of another molecule of a
hydrosilane to promote reductive elimination as well as the
coordination of an enyne to the Si-[Rh] sepecies I, forming
II. The fact that PPh3 possessing a better σ-donor property but
a much larger cone angle than P(OPh)3 or P(OEt)3 is not a good
ligand for this process (Table 4, entries 2 and 3) is a clear
indication of the delicate stereoelectronic balance in the
coordination sphere of the catalyst metal center and that
phosphites, especially P(OEt)3, are the appropriate ligands for
the CO-SiCaC process. The reaction rate should be reduced
when a strongly coordinating and bulky ligand is occupying a
coordination site of the [Rh] catalyst species. This is consistent
with the observation that more forced conditions are necessary
for the CO-SiCaC reaction to proceed smoothly in the presence
of a phosphtie ligand as compared to the SiCaC reaction. The
observed marked efficiency of the “freeze and CO” protocol is
also consistent with the discussion just mentioned above. Thus,
the combination of P(OEt)3 addition and the “freeze and CO”
protocol can achieve extremely high CO-SiCaC selectivity
without using high dilution conditions (Tables 6 and 7).
alkane, the insertion of the alkyne moiety of 2k is expected to
give a mixture of two regioisomeric â-silylvinyl-[Rh](H)
complexes (II and its regioisomer IIa), but it is obvious that
this is not happening. A simple molecular modeling inspection
of the hypothetical four-centered transition states indicates (i)
the transition state TS-A that leads to the formation of 3-silyl-
2-alkenyl-[Rh] intermediate IIa is sterically quite strained when
the alkene moiety is coordinating to the [Rh] metal and also
cannot undergo intramolecular carbometalation (i.e., carbo-
cyclization) due to extremely unfavorable geometry, and (ii)
the transition state TS-B that leads to 2-silyl-3-alkenyl-[Rh]
intermediate II, which is sterically much more favorable than
the transition state TS-A and ready for the subsequent carbo-
cyclization to give III (Scheme 5). Accordingly, it is clear that
the chelate formation involving the alkene moiety plays a key
role in the extremely regioselective addition of the Si-[M]
species to the alkyne moiety of 1, which leads to the formation
of II and then III (See Scheme 4).
As mentioned above, the reaction of allyl(benzyl)propar-
gylamine (1h) under the CO-SiCaC conditions (P(OEt)3, 105
°C and 20 atm of CO) does not give any trace of the expected
CO-SiCaC product 3h, but only affords SiCaC product 2h.
This rather peculiar result can be explained by taking into
account a very likely coordination of 1h to the [Rh] metal of
the intermediate III in a chelating manner using the π-acetylenic
bond (or π-olefinic bond) as well as the basic nitrogen atom.
This chelation evidently effectively blocks the migratory inser-
tion of CO into the alkyl-[Rh] bond, which is essential for the
formation of the acyl-[Rh] intermediate IV. The fact that this
peculiar phenomenon is observed only for 1,6-enyne substrates
with a trialkylamine moiety bearing a basic nitrogen strongly
supports the proposed explanation.
As Scheme 4 shows, it is apparent that the migratory CO
insertion to III and the hydrosilane-promoted reductive elimina-
tion of 2 from III are competing processes under the reaction
conditions. Accordingly, higher CO pressures surely favor the
CO insertion to form IV. However, higher pressures should also
favor the CO insertion to II, which leads to the formation of a
simple silylformylation product without carbocyclization.3a Thus,
an appropriate modification of the [Rh] coordination sites is
necessary to promote the CO insertion to III, but not to II. As
Table 4 indicates, addition of a phosphite, especially P(OEt)3,
exerts an remarkable influence on the selectivity for CO-SiCaC
(entries 9-11). It has been shown that phosphines and CO
greatly enhance the rate of migratory CO insertion.22 This is
Conclusions
A full account of our study on the scope and limitation of
unique SiCaC and CO-SiCaC reactions of enynes is described.
The SiCaC and CO-SiCaC reactions provide rapid access to
functionalized five-membered heterocyclic as well as carbocyclic
ring systems from 1,6-enynes, which serve as useful and
versatile intermediates for the syntheses of natural and unnatural
compounds of biological interest or intermediates useful for
functional materials. Either SiCaC products or CO-SiCaC
products can be obtained with extremely high selectivity under
the optimal conditions for each process. The SiCaC reaction is
applicable to the 1,7-enyne system albeit the yield is lower. The
most likely mechanism for these processes, which share key
intermediate complexes in the catalytic cycle, is proposed.
Experimental Section
General Method. All experiments were performed under a nitrogen
or CO atmosphere in oven-dried glassware using standard Schlenk
techniques. 1H and 13C NMR spectra were recorded on a Varian Inova-
600 (600 MHz 1H, 150 MHz 13C), Gemini-300 (300 MHz 1H, 75 MHz
1
13C), a General Electric QE-300 (300 MHz H, 75 MHz 13C), or a
Bruker AC-250 (250 MHz 1H, 62.5 MHz 13C) spectrometer in
deuterated solvents using residual protons (CHCl3: 7.26 ppm 1H, 77.0
ppm 13C) as the internal reference unless otherwise stated. NMR
solvents were dried over anhydrous K2CO3 or passed through a short
column of activated alumina. Chemical shifts (δ) are given in parts
per million downfield from tetramethylsilane (TMS). Infrared spectra
were recorded on a Mattson Galaxy Series-3000 FTIR spectrometer
using samples as neat oils or as KBr disks. Analytical gas chromatog-
raphy was performed with a Hewlett-Packard 5890 Series II gas
chromatograph (FID) with a Hewlett-Packard HP 3396A integrator
using either a 15 m J&W DB-1, a 30 m J&W DB-17, or a 25 m 3%
OV-101 capillary column. Elemental analyses were performed by
(22) Crabtree, R. H. In The Organometallic Chemistry of the Transition Metals,
Wiley: New York, 1994; Chapter 7, p 161.
9
9170 J. AM. CHEM. SOC. VOL. 124, NO. 31, 2002

Silylcarbocyclization Reactions of Enynes
A R T I C L E S
M-H-W Laboratories, Phoenix, Arizona. High-resolution mass spec-
trometric analyses were conducted at the Mass Spectrometry Facility
of the University of California at Riverside. Analytical thin-layer
chromatography (TLC) was carried out on Merck silica gel plates with
F-254 indicator.
IR (neat, cm-1) 3069 (m), 3048 (w), 2979 (m), 2933 (m), 2907 (w),
2872 (w), 1731 (s), 1625 (m), 1462 (w), 1447 (m), 1428 (m), 1389
(w), 1367 (m), 1268 (s), 1244 (s), 1178 (s), 1129 (m), 1109 (s), 1097
(s), 1067 (m), 1031 (m), 862 (w), 827 (m), 788 (m), 737 (m), 720 (s),
701 (s). Anal. Calcd for C26H32O4Si: C, 71.52; H, 7.39. Found: C,
71.63; H, 7.18.
Materials. All solvents used as reaction media were distilled under
nitrogen immediately before use; ether, THF, and toluene were distilled
from Na/benzophenone ketyl, and CH2Cl2 was distilled from CaH2.
Carbon monoxide was purchased from Liquid Carbonic Specialty Gases,
Oak Brook, Illinois, and passed through Drierite before use. Rh(acac)-
(CO)2, was provided by Mitsubishi Chemical Corporation and used as
4,4-Bis(carbethoxy)-1-(Z)-triphenylsilylmethylidene-2-methyl-
cyclopentane (2a-SiPh3): viscous, colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 5/1, Rf ) 0.34); 1H NMR (300 MHz, CDCl3) δ 0.59
(d, J ) 7.1 Hz, 3H, CH3CH), 1.23 (t, J ) 7.2 Hz, 3H, CH3CH2O),
1.24 (t, J ) 7.2 Hz, 3H, CH3CH2O), 1.79 (dd, J ) 13.2 Hz, 4.8 Hz,
1H, CH2CH), 2.33 (m, 1H, CH2CHCH3), 2.95 (d, J ) 16.4 Hz, 1H,
CH2CdC), 3.40 (d, J ) 16.4 Hz, 1H, CH2CdC), 4.18 (m, 4H,
CH3CH2O), 5.93 (s br, 1H, CdCH), 7.33 (m, 9H, Ph-H), 7.53 (m, 6H,
Ph-H); 13C NMR (75 MHz, CDCl3) δ 14.20, 14.26, 21.75, 37.13, 41.93,
45.15, 58.43, 61.78, 114.63, 127.98, 129.55, 135.57, 136.04, 168.28,
172.00, 172.30; IR (neat, cm-1) 3067 (m), 3048 (m), 2979 (s), 2934
(m), 2907 (m), 2871 (w), 1961 (w), 1892 (w), 1824 (w), 1728 (s), 1623
(m), 1588 (w), 1567 (w), 1483 (m), 1461 (m), 1446 (m), 1367 (m),
1267 (s), 1243 (s), 1177 (s), 1129 (s), 1108 (s), 1066 (s), 1030 (m),
998 (m), 918 (w), 904 (w), 861 (m), 820 (m), 791 (w), 742 (s), 704
(s). Anal. Calcd for C26H32O4Si: C, 74.66; H, 6.89. Found: C, 74.74;
H, 6.75.
received. Rhodium clusters, Rh4(CO)12 and Rh2Co2(CO)12,15 were
14
prepared according to literature methods. Hydrosilanes were purchased
from Aldrich Chemical Co. and Gelest, Inc., distilled under nitrogen,
and stored over activated molecular sieves 4 Å. Solvents for extraction
and chromatography were reagent grade and used as received. All other
reagents were purified by simple distillation or passing through a short
column of activated alumina or silica gel. Silica gel used for
chromatography, MN-Kieselgel 60, was purchased from Brinkman
Instruments Inc.
Caution: Since carbon monoxide is a toxic gas, all reactions using
carbon monoxide should be carried out with care in a hood with
sufficient ventilation.
4,4-Bis(carbethoxy)-1-(Z)-methyldiethoxysilylmethylidene-2-
methylcyclopentane (2a-SiMe(OEt)2): viscous, colorless liquid; H
General Procedure for the Catalytic SiCaC Reaction. A typical
procedure is described for the reaction of 4,4-bis(carbethoxy)hept-6-
en-1-yne (1a). A reaction vessel equipped with a stirring bar and a CO
inlet, was charged with Rh4(CO)12 (3.8 mg, 0.005 mol, 0.5 mol %).
After purging the vessel with CO, hexane (1.0 mL) was added to
dissolve the catalyst. Me2PhSiH (68 mg, 0.5 mmol) was added via a
syringe. After stirring for 5 min at ambient temperature, the reaction
mixture was then cannulated into a 5-mL round-bottomed flask
containing a solution of 1a (238 mg, 1 mmol), Me2PhSiH (138 mg, 1
mmol) in hexane (1.5 mL) via CO pressure without stirring. The
resulting mixture was stirred for less than 1 min, and the reaction
mixture was submitted to GC analysis. After the reaction was complete,
all volatiles were removed under reduced pressure, and the crude
product was purified by column chromatography on silica gel.
4,4-Bis(carbethoxy)-1-(Z)-dimethylphenylsilylmethylidene-2-
methylcyclopentane (2a): viscous colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 5/1, Rf ) 0.51); 1H NMR (300 MHz, CDCl3) δ 0.35
(s, 3H, CH3Si), 0.36 (s, 3H, CH3Si), 0.95 (d, J ) 6.8 Hz, 3H, CH3-
CH), 1.25 (t, J ) 7.1 Hz, 6H, CH3CH2O), 1.85 (dd, J ) 13.0 Hz, 3.5
Hz, 1H, CH2CH), 2.35 (m, 1H, CH2CHCH3), 2.39 (dd, J ) 13.0 Hz,
8.5 Hz, 1H, CH2CH), 2.83 (d, J ) 16.4 Hz, 1H, CH2CdC), 3.28 (d, J
) 16.4 Hz, 1H, CH2CdC), 4.15 (q, J ) 7.1 Hz, 4H, CH3CH2O), 5.50
(s br, 1H, CdCH), 7.33 (m, 3H, Ph-H), 7.51 (m, 2H, Ph-H); 13C NMR
(75 MHz, CDCl3) δ -0.88, -0.89, 14.25, 14.29, 22.50, 36.98, 42.01,
44.87, 58.73, 61.63, 61.66, 118.72, 127.97, 129.03, 133.97, 139.73,
165.11, 172.00, 172.24; IR (neat, cm-1) 3048 (w), 2978 (m), 2933 (m),
2907 (w), 2872 (w), 1731 (s), 1625 (m), 1462 (w), 1449 (m), 1425
(m), 1389 (w), 1367 (m), 1268 (s), 1243 (s), 1177 (s), 1129 (m), 1111
(s), 1097 (s), 1065 (m), 1031 (m), 895 (w), 827 (m), 788 (m), 731 (m),
720 (s), 701 (s). Anal. Calcd for C21H30O4Si: C, 67.34; H, 8.07.
Found: C, 67.07; H, 7.83.
1
NMR (300 MHz, CDCl3) δ 0.17 (s, 3H, CH3Si), 1.15 (m, 6H, CH3-
CH2OSi), 1.23 (t, J ) 7.1 Hz, 6H, CH3CH2O2C), 1.88 (dd, J ) 13.4
Hz, 5.8 Hz, 1H, CH2CH), 2.65 (dd, J ) 13.4 Hz, 8.2 Hz, 1H, CH2-
CH), 2.80 (d, J ) 16.5 Hz, 1H, CH2CdC), 2.84 (m, 1H, CH2CHCH3),
3.40 (td, J ) 2.0 Hz, 16.5 Hz, 1H, CH2CdC), 3.80 (m, 4H, CH3CH2-
OSi), 4.18 (m, 4H, CH3CH2O2C), 5.25 (s br, 1H, CdCH); 13C NMR
(75 MHz, CDCl3) δ -2.77, 14.22, 18.50, 18.54, 22.01, 37.36, 42.22,
44.72, 58.27, 58.71, 61.61, 61.69, 115.25, 167.64, 171.89, 172.21; IR
(neat, cm-1) 2975 (m), 2929 (m), 2907 (m), 2878 (m), 1732 (s), 1629
(w), 1447 (w), 1390 (m), 1367 (w), 1244 (s), 1166 (m), 1102 (s), 1080
(s), 1035 (m), 952 (m), 838 (m), 825 (m), 762 (m). Anal. Calcd for
C18H32O6Si: C, 58.03; H, 8.66. Found: C, 57.81; H, 8.57.
4,4-Bis(carbethoxy)-1-(Z)-trimethoxysilylmethylidene-2-methyl-
cyclopentane (2a-Si(OMe)3): viscous, colorless liquid; 1H NMR (300
MHz, CDCl3) δ 1.12 (d, J ) 7.1 Hz, 3H, CH3CH), 1.21 (q, J ) 7.2
Hz, 3H, CH3CH2O), 1.88 (dd, J ) 13.5 Hz, 6.0 Hz, 1H, CH2CH), 2.67
(ddd, J ) 13.5 Hz, 8.2 Hz, 1.1 Hz, 1H, CH2CH), 2.82 (m, 1H,
CH2CHCH3), 2.84 (d, J ) 16.8 Hz, 1H, CH2CdC), 3.24 (td, J ) 2.2
Hz, 16.8 Hz, 1H, CH2CdC), 3.52 (s, 9H, CH3OSi), 4.16 (m, 4H,
CH3CH2O), 5.17 (d br, J ) 1.6 Hz, 1H, CdCH); 13C NMR (75 MHz,
CDCl3) δ 14.20, 21.78, 37.73, 42.16, 44.76, 50.48, 58.76, 61.64, 61.71,
109.07, 171.00, 171.75, 172.04; IR (neat, cm-1) 2977 (s), 2943 (s),
2873 (m), 2840 (s), 2022 (w), 2000 (w), 1895 (w), 1738 (s), 1628 (m),
1574 (w), 1566 (w), 1538 (w), 1474 (m), 1453 (m), 1390 (w), 1367
(m), 1271 (s), 1244 (s), 1191 (s), 1091 (s), 1033 (m), 920 (w), 903
(w), 856 (m), 842 (m), 822 (s), 804 (s), 754 (m), 722 (w). Anal. Calcd
for C16H28O7Si: C, 53.31; H, 7.83. Found: C, 53.06; H, 7.62.
4,4-Bis(carbethoxy)-1-(Z)-triethoxysilylmethylidene-2-methyl-
cyclopentane (2a-Si(OEt)3): viscous, colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 3/1, Rf ) 0.57); 1H NMR (300 MHz, CDCl3) δ 1.16
(d, J ) 7.1 Hz, 3H, CH3CH), 1.21 (t, J ) 7.1 Hz, 9H, CH3CH2OSi),
1.23 (m, 6H, CH3CH2O2C), 1.91 (dd, J ) 13.4 Hz, 6.0 Hz, 1H, CH2-
CH), 2.69 (ddd, J ) 13.4 Hz, 7.9 Hz, 1.1 Hz, 1H, CH2CH), 2.84 (d, J
) 16.5 Hz, 1H, CH2CdC), 2.94 (m, 1H, CH2CHCH3), 3.27 (td, J )
2.2 Hz, 16.5 Hz, 1H, CH2CdC), 3.80 (q J ) 7.1 Hz, 6H, CH3CH2-
OSi), 4.17 (m, 4H, CH3CH2O2C), 5.21 (d br, J ) 2.2 Hz, 1H, CdCH);
13C NMR (75 MHz, CDCl3) δ 14.22, 18.38, 21.92, 37.58, 42.15, 44.74,
58.44, 58.76, 61.60, 61.69, 110.73, 169.94, 171.82, 172.17; IR (neat,
cm-1) 2976 (s), 2929 (m), 2886 (m), 1734 (s), 1630 (w), 1462 (w),
1446 (m), 1390 (m), 1367 (m), 1283 (m), 1271 (m), 1243 (s), 1168
(s), 1100 (s), 1080 (s), 1036 (m), 960 (s), 862 (w), 854 (w), 836 (m),
4,4-Bis(carbethoxy)-1-(Z)-methyldiphenylsilylmethylidene-2-
methylcyclopentane (2a-SiMePh2): viscous, colorless liquid; TLC
1
(silica gel, hexanes/EtOAc ) 5/1, Rf ) 0.49); H NMR (300 MHz,
CDCl3) δ 0.66 (s, 3H, CH3Si), 0.82 (d, J ) 7.0 Hz, 3H, CH3CH), 1.26
(t, J ) 7.1 Hz, 6H, CH3CH2O), 1.85 (dd, J ) 13.0 Hz, 3.5 Hz, 1H,
CH2CH), 2.57 (m, 1H, CH2CHCH3), 2.59 (dd, J ) 13.0 Hz, 8.5 Hz,
1H, CH2CH), 2.91 (d, J ) 16.4 Hz, 1H, CH2CdC), 3.34 (d, J ) 16.4
Hz, 1H, CH2CdC), 4.20 (q, J ) 7.1 Hz, 2H, CH3CH2O), 4.21 (q, J )
7.1 Hz, 2H, CH3CH2O), 5.71 (s br, 1H, CdCH), 7.33 (m, 6H, Ph-H),
7.53 (m, 4H, Ph-H); 13C NMR (75 MHz, CDCl3) δ -1.87, 14.23, 14.27,
22.16, 37.05, 42.01, 44.95, 58.62, 61.65, 61.68, 116.64, 127.97, 127.98,
129.28, 129.34, 134.82, 134.95, 137.47, 137.93, 166.83, 171.99, 172.29;
9
J. AM. CHEM. SOC. VOL. 124, NO. 31, 2002 9171

A R T I C L E S
Ojima et al.
811 (m), 780 (m), 718 (w). Anal. Calcd for C19H34O7Si: C, 56.69; H,
8.51. Found: C, 56.48; H, 8.66.
1112 (s), 1095 (s), 1042 (s), 1017 (m), 834 (s), 819 (s), 775 (m), 732
(s), 702 (s). Anal. Calcd for C21H27NO2SSi: C, 65.41; H, 7.06; N, 3.63.
Found: C, 65.25; H, 6.83; N, 3.50.
2-(Z)-Dimethylphenylmethylidene-3,8,8-trimethyl-7,9-dioxaspiro-
[4,5]decane (2b): viscous, colorless liquid; TLC (silica gel, hexanes/
EtOAc ) 15/1, Rf ) 0.49); 1H NMR (300 MHz, CDCl3) δ 0.35 (s, 3H,
CH3Si), 0.38 (s, 3H, CH3Si), 0.97 (d, J ) 7.1 Hz, 3H, CH3CH), 1.13
(dd, J ) 13.7 Hz, 5.5 Hz, 1H, CH2CH), 1.42 (s, 6H, (CH3)2C), 1.83
(dd, J ) 13.7 Hz, 8.5 Hz, 1H, CH2CH), 2.51 (m, 3H, CH2CdC and
CH2CHCH3), 3.52 (s, 2H, OCH2C), 3.64 (d, J ) 11.2 Hz, 1H, OCH2C),
3.72 (d, J ) 11.2 Hz, 1H, OCH2C), 5.52 (s br, 1H, CdCH), 7.33 (m,
3H, Ph-H), 7.53 (m, 2H, Ph-H); 13C NMR (75 MHz, CDCl3) δ -0.74,
-0.60, 22.61, 23.60, 25.46, 35.97, 40.11, 41.31, 45.03, 68.14, 70.24,
1-Benzyl-3-(E)-dimethylphenylsilylmethylidene-4-methylpyrro-
lidine (2f): viscous, colorless liquid; TLC (silica gel, hexanes/EtOAc
) 5/1, Rf ) 0.30); 1H NMR (300 MHz, CDCl3) δ 0.39 (s, 3H, CH3Si),
0.40 (s, 3H, CH3Si), 1.07 (d, J ) 6.9 Hz, 3H, CH3CH), 2.41 (dd, J )
8.2 Hz, 3.0 Hz, 1H, CH2CH), 2.66 (m, 1H, CH2CHCH3), 2.72 (dd, J
) 8.2 Hz, 6.6 Hz, 1H, CH2CH), 3.10 (dd, J ) 13.7 Hz, 1.6 Hz, 1H,
CH2C)), 3.41 (d, J ) 13.7 Hz, 1H, CH2CdC), 3.60 (s, 2H, NCH2Ph),
5.47 (d br, J ) 1.6 Hz, 1H, CdCH), 7.25-7.37 (m, 8H, Ph-H), 7.55
(m, 2H, Ph-H); 13C NMR (75 MHz, CDCl3) δ -0.82, -0.78, 21.57,
37.31, 60.66, 62.76, 63.01, 116.05, 127.11, 127.91, 128.41, 128.93,
129.00, 133.98, 139.20, 139.91, 165.19; IR (neat, cm-1) 3066 (m), 3026
(w), 2957 (s), 2927 (m), 2871 (m), 2786 (m), 1688 (m), 1633 (m),
1452 (m), 1427 (m), 1373 (w), 1340 (m), 1299 (m), 1249 (s), 1153
(m), 1140 (m), 1113 (s), 882 (w), 832 (s), 797 (s), 773 (m), 730 (s),
699 (s). Anal. Calcd for C21H27NSi: C, 78.44; H, 8.46; N, 4.36.
Found: C, 78.35; H, 8.33; N, 4.33.
97.96, 119.00, 127.91, 128.97, 133.89, 140.03, 167.09; IR (neat, cm-1
)
3068 (m), 3048 (w), 2991 (m), 2954 (s), 2856 (m), 1626 (m), 1453
(m), 1428 (m), 1382 (m), 1369 (m), 1346 (w), 1247 (s), 1200 (s), 1155
(m), 1114 (s), 1069 (s), 1043 (m), 1033 (m), 934 (m), 917 (w), 845
(s), 834 (s), 786 (m), 770 (m), 731 (s), 701 (s). Anal. Calcd for
C20H30O2Si: C, 72.67; H, 9.15. Found: C, 72.46; H, 9.02.
4,4-Bis(methoxymethyl)-1-(Z)-dimethylphenylsilylmethylidene-2-
methylcyclopentane (2c): viscous, colorless liquid; TLC (silica gel,
(S)-1-(1-Phenylethyl)-3-(E)-dimethylphenylsilylmethylidene-4-
methylpyrrolidine (2 g): viscous, colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 5/1, Rf ) 0.33); 1H NMR (300 MHz, CDCl3) δ [0.37
(s, CH3Si), 0.42 (s, CH3Si), (1:1.2), 6H], 1.04 (d, J ) 6.0 Hz, 3H,
CH3CH), [1.35 (d, J ) 2.1 Hz), 1.36 (d, J ) 2.1 Hz), (1:1.2), 3H,
CH3C(H)Ph], [2.24 (d, J ) 5.7 Hz), 2.43 (dd, J ) 7.2 Hz, 11.2 Hz),
(1:1.2), 1H, CH2CH], 2.65 (m, 1H, CH2CHCH3), 2.67 (m, 1H, CH2-
CH), [3.03 (d, J ) 14.1 Hz), 3.15 (d, J ) 14.1 Hz), (1:1.2), 1H, CH2Cd
], 3.17 (m, 1H, (CH3)PhCH), [3.24 (d, J ) 14.1 Hz), 3.48 (d, J ) 14.1
Hz), (1:1.2), 1H, CH2Cd], [5.43 (s, br), 5.46 (s, br), (1:1.2), 1H, Cd
CH], 7.25-7.37 (m, 8H, Ph-H), 7.56 (m, 2H, Ph-H); 13C NMR (75
MHz, CDCl3) δ -0.81, -0.78, [21.54, 21.68, (1:1.2)], [23.22, 23.28,
(1:1.2)], [37.17, 37.26, (1:1.2)], [61.40, 61.76, (1:1.2)], [61.96, 62.40,
(1:1.2)], [65.98, 66.01, (1:1.2)], [115.76, 115.84, (1:1.2)], 127.04,
127.37, 127.89, [128.46, 128.50, (1:1.2)], 128.98, 133.98, 139.98,
[145.73, 145.74, (1:1.15)], 165.32; IR (neat, cm-1) 3066 (m), 3050 (m),
3024 (m), 2969 (s), 2930 (m), 2901 (m), 2871 (m), 2777 (m), 1631
(m), 1492 (w), 1451 (m), 1492 (w), 1451 (m), 1427 (m), 1371 (m),
1316 (w), 1308 (w), 1248 (m), 1157 (m), 1112 (m), 862 (m), 832 (s),
800 (m), 765 (m), 729 (s), 700 (m). Anal. Calcd for C22H29NSi: C,
78.75; H, 8.71; N, 4.17. Found: C, 78.53; H, 8.52; N, 4.07.
1
hexanes/EtOAc ) 35/1, Rf ) 0.37); H NMR (300 MHz, CDCl3) δ
0.36 (s, 3H, CH3Si), 0.38 (s, 3H, CH3Si), 0.98 (d, J ) 6.7 Hz, 3H,
CH3CH), 1.24 (dd, J ) 13.5 Hz, 5.5 Hz, 1H, CH2CH), 1.80 (dd, J )
13.5 Hz, 8.5 Hz, 1H, CH2CH), 2.18 (d, J ) 15.4 Hz, 1H, CH2CdC),
2.50 (d, J ) 15.4 Hz, 1H, CH2CdC), 2.53 (m, 1H, CH2CHCH3), 3.14
(m, 2H, OCH2C), 3.30 (m, 2H, OCH2C), 3.34 (s, 3H, OCH3), 3.35 (s,
3H, OCH3), 5.46 (s br, 1H, CdCH), 7.35 (m, 3H, Ph-H), 7.55 (m, 2H,
Ph-H); 13C NMR (75 MHz, CDCl3) δ -0.62, -0.53, 23.65, 36.40,
40.27, 43.88, 46.05, 59.47, 59.51, 75.46, 77.67, 117.73, 127.86, 128.90,
133.92, 140.34, 168.62; IR (neat, cm-1) 3068 (m), 3049 (w), 3018 (w),
2954 (m), 2923 (m), 2874 (s), 2825 (m), 2808 (m), 1626 (m), 1476
(w), 1457 (m), 1427 (m), 1390 (w), 1248 (m), 1198 (m), 1166 (m),
1154 (m), 1110 (s), 966 (m), 846 (s), 834 (s), 788 (m), 770 (m), 729
(m), 700 (m). Anal. Calcd for C19H30O2Si: C, 71.64; H, 9.49. Found:
C, 71.52; H, 9.25.
4,4-Bis(acetoxymethyl)-1-(Z)-dimethylphenylsilylmethylidene-2-
methyl-cyclopentane (2d): viscous, colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 5/1, Rf ) 0.31); 1H NMR (300 MHz, CDCl3) δ 0.37
(s, 3H, CH3Si), 0.38 (s, 3H, CH3Si), 0.99 (d, J ) 7.1 Hz, 3H, CH3-
CH), 1.27 (dd, J ) 13.5 Hz, 5.5 Hz, 1H, CH2CH), 1.86 (dd, J ) 13.5
Hz, 8.2 Hz, 1H, CH2CH), 2.06 (s, 6H, CH3CO), 2.22 (d, J ) 15.3 Hz,
1H, CH2CdC), 2.58 (d, J ) 15.3 Hz, 1H, CH2CdC), 2.56 (m, 1H,
CH2CHCH3), 3.84 (d, J ) 11.0 Hz, 1H, OCH2C), 3.93 (d, J ) 11.0
Hz, 1H, OCH2C), 4.03 (s, 1H, OCH2C), 4.04 (s, 1H, OCH2C), 5.51 (s
br, 1H, CdCH), 7.35 (m, 3H, Ph-H), 7.54 (m, 2H, Ph-H); 13C NMR
(75 MHz, CDCl3) δ -0.80, -0.72, 21.02, 21.05, 23.47, 36.05, 40.20,
43.67, 44.09, 66.13, 68.24, 119.31, 127.92, 128.99, 133.87, 139.82,
186.20, 171.17, 171.23; IR (neat, cm-1) 3018 (w), 2956 (m), 2895 (w),
2870 (w), 1744 (s), 1628 (w), 1467 (w), 1428 (m), 1379 (m), 1366
(m), 1246 (s), 1112 (m), 1037 (s), 844 (m), 837 (m), 805 (m), 786 (w),
772 (w), 732 (m), 702 (m). Anal. Calcd for C21H30O4Si: C, 67.34; H,
8.07. Found: C, 67.58; H, 7.89.
1-(Prop-2-enyl)-3-(E)-dimethylphenylsilylmethylidene-4-meth-
ylpyrrolidine (2h): viscous colorless liquid; TLC (silica gel, hexanes/
EtOAc ) 2/1, Rf ) 0.49); 1H NMR (300 MHz, CDCl3) δ 0.38 (s, 6H,
CH3Si), 1.05 (d, J ) 6.8 Hz, 3H, CH3CH), 2.37 (dd, J ) 8.4 Hz, 3.4
Hz, 1H, CH2CH), 2.66 (m, 1H, CH2CHCH3), 2.75 (dd, J ) 8.4, 6.6
Hz, 1H, CH2CH), 3.07 (d, J ) 6.6 Hz, 2H, NCH2CHdCH2), 3.11 (dd,
J ) 13.7 Hz, 1.8 Hz, 1H, CH2C)), 3.38 (d, J ) 13.7 Hz, 1H, CHCd),
5.10 (dd, J ) 10.2 Hz, 1.9 Hz, 1H, HCdCH2), 5.20 (ddd, J ) 17.1
Hz, 2.3 Hz, 1.6 Hz, 1H, HCdCH2), 5.50 (dd, J ) 3.5 Hz, 1.9 Hz, 1H,
CdCH(Si)), 5.91 (tdd, J ) 6.3 Hz, 17.1 Hz, 10.2 Hz, 1H, HCdCH2),
7.34 (m, 3H, Ph-H), 7.55 (m, 2H, Ph-H); 13C NMR (75 MHz, CDCl3)
δ -0.99, -0.92, 21.37, 37.06, 59.45, 62.79, 62.93, 116.32, 117.20,
128.00, 129.11, 134.09, 135.99, 139.93, 165.03; IR (neat, cm-1) 3068
(w), 3049 (w), 3008 (w), 2998 (w), 2958 (s), 2928 (s), 2907 (m), 2871
(m), 2784 (m), 1633 (m), 1472 (w), 1449 (w), 1427 (m), 1372 (w),
1338 (m), 1300 (m), 1248 (s), 1155 (m), 1113 (s), 995 (m), 919 (m),
884 (w), 842 (s), 832 (s), 798 (m), 772 (m), 729 (s), 700 (s). Anal.
Calcd for C17H25NSi: C, 75.21; H, 9.28; N, 5.15. Found: C, 75.40; H,
9.07; N, 4.91.
1-(4-Toluenesulfonyl)-3-(E)-dimethylphenylsilylmethylidene-4-
methylpyrrolidine (2e): viscous, colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 5/1, Rf ) 0.40); 1H NMR (300 MHz, CDCl3) δ 0.34
(s, 3H, CH3Si), 0.36 (s, 3H, CH3Si), 0.93 (d, J ) 7.1 Hz, 3H, CH3-
CH), 2.44 (s, 3H, CH3Ph), 2.64 (m, 1H, CH2CHCH3), 3.09 (dd, J )
13.5 Hz, 5.5 Hz, 1H, CH2CH), 3.18 (dd, J ) 9.4 Hz, 1.3 Hz, 1H, CH2-
CH), 3.61 (dd, J ) 14.3 Hz, 1.6 Hz, 1H, CH2CdC), 4.06 (d, J ) 14.3
Hz, 1H, CH2CdC), 5.46 (s br, 1H, CdCH), 7.33 (m, 5H, Ph-H), 7.46
(m, 2H, Ph-H), 7.70 (m, 2H, Ph-H); 13C NMR (75 MHz, CDCl3) δ
-1.18, -1.03, 20.80, 21.70, 37.49, 54.00, 55.61, 119.18, 127.95,
128.02, 129.30, 129.79, 133.09, 133.78, 138.71, 143.68, 159.29; IR
(neat, cm-1) 3068 (w), 3047 (w), 2960 (m), 2929 (m), 2898 (m), 2871
(m), 1635 (m), 1598 (m), 1494 (w), 1427 (m), 1405 (m), 1375 (m),
1347 (s), 1306 (m), 1290 (m), 1249 (m), 1183 (m), 1166 (s), 1095 (s),
4,4-Bis(hydroxymethyl)-1-(Z)-dimethylphenylsilylmethylidene-2-
methylcyclopentane (2i): viscous, colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 1/2, Rf ) 0.23); 1H NMR (300 MHz, CDCl3) δ 0.37
(s, 3H, CH3Si), 0.38 (s, 3H, CH3Si), 0.99 (d, J ) 6.8 Hz, 3H, CH3-
CH), 1.17 (dd, J ) 13.4 Hz, 5.2 Hz, 1H, CH2CH), 1.82 (ddd, J ) 13.4
Hz, 8.5 Hz, 1.1 Hz, 1H, CH2CH), 2.29 (d, J ) 15.4 Hz, 1H, CH2Cd
C), 2.37 (s br, 2H, OH), 2.48 (td, J ) 1.9 Hz, 15.4 Hz, 1H, CH2CdC),
9
9172 J. AM. CHEM. SOC. VOL. 124, NO. 31, 2002

Silylcarbocyclization Reactions of Enynes
A R T I C L E S
2.55 (m, 1H, CH2CHCH3), 3.53 (s, 2H, CH2OH), 3.70 (s, 2H, CH2-
OH), 5.51 (s, br, 1H, CdCH), 7.35 (m, 3H, Ph-H), 7.54 (m, 2H, Ph-
H); 13C NMR (75 MHz, CDCl3) δ -0.73, -0.63, 23.61, 36.16, 39.88,
43.36, 46.71, 68.46, 71.62, 118.62, 127.90, 128.96, 133.87, 140.06,
167.40; IR (neat, cm-1) 3350 (s), 3341 (s), 2953.8 (s), 2928 (s), 2870
(s), 1626 (m), 1457 (w), 1427 (m), 1247 (m), 1112 (s), 1023 (m), 843
(s), 834 (s), 798 (m), 776 (m), 730 (m), 700 (m). Anal. Calcd for
C17H26O2Si: C, 70.29; H, 9,02. Found: C, 70.09; H, 8.87.
3-(E)-Dimethylphenylsilylmethylidene-4-methyltetrahydro-
furan (2j): viscous colorless liquid; TLC (silica gel, hexanes/EtOAc
) 5/1, Rf ) 0.43); 1H NMR (300 MHz, CDCl3) δ 0.38 (s, 3H, CH3Si),
0.39 (s, 3H, CH3Si), 1.01 (d, J ) 6.9 Hz, 3H, CH3CH), 2.64 (m, 1H,
CH2CHCH3), 3.62 (dd, J ) 8.2 Hz, 1.9 Hz, 1H, CH2CH), 3.82 (dd, J
) 8.2, 5.5 Hz, 1H, CH2CH), 4.17 (dd, J ) 13.7 Hz, 1.9 Hz, 1H, CH2Cd
), 4.44 (dd, J ) 1.2, 13.7 Hz, 1H, CH2Cd), 5.46 (s br, 1H, CdCH),
7.32 (m, 3H, Ph-H), 7.56 (m, 2H, Ph-H); 13C NMR (75 MHz, CDCl3)
δ -0.74, -0.62, 20.65, 38.41, 73.71, 77.85, 115.31, 128.34, 129.41,
134.16, 139.66, 164.38. Anal. Calcd for C14H20OSi C, 72.36; H, 8.67.
Found: C, 72.37; H, 8.52.
4,4-Bis(carbethoxy)-1-(Z)-(1-dimethylphenylsilylethylidene)-2-
methylcyclopentane (2k): 1H NMR (300 MHz, CDCl3) δ 0.38 (s,
6H), 0.86 (d, J ) 7.5 Hz, 3H), 1.24 (m, 6H), 1.67 (m, 3H), 2.01 (m,
1H), 2.47 (m, 1H), 2.76 (m, 1H), 2.94 (d, J ) 17.5 Hz, 1H), 3.16 (d,
J ) 17.5 Hz, 1H), 4.19 (m, 4H), 7.37 (m, 5H); 13C NMR (CDCl3) δ
-0.88, 14.05, 19.50, 22.84, 37.46, 38.49, 41.16, 58.38, 61.47, 123.76,
127.70, 128.73, 133.83, 140.00, 157.64, 173.00. IR (neat) 3068 (w),
3049 (w), 2977 (w), 1730 (s), 1625 (m), 1250 (s), 1185 (m), 1109 (m),
823 (m). Anal. Calcd for C22H32O4Si C, 68.00; H, 8.30. Found: C,
68.22; H, 8.06.
5,5-Bis(carbomethoxy)-1-(Z)-methyldiphenylsilylmethylidene-2-
methylcyclohexane (2l): viscous, colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 5/1, Rf ) 0.49); 1H NMR (300 MHz, CDCl3) δ 0.32
(s, 3H, CH3Si), 0.36 (s, 3H, CH3Si), 1.01 (d, J ) 7.1 Hz, 3H, CH3-
CH), 1.42 (d br, J ) 13.7 Hz, 1H, CH2CH2CHCH3), 1.70 (ddt, J ) 4.2
Hz, 4.4 Hz, 13.7 Hz, 1H, CH2CH2CHCH3), 1.91 (dt, J ) 4.1 Hz, 13.7
Hz, 1H, CH2CH2CHCH3), 2.18 (d br, J ) 13.7 Hz, 1H, CH2CH2-
CHCH3), 2.60 (m, 1H, CH2CH2CHCH3), 2.74 (d, J ) 13.8 Hz, 1H,
CH2CdC), 2.85 (d, J ) 13.8 Hz, 1H, CH2CdC), 3.73 (s, 6H, CH3-
OCO), 5.40 (s, br, 1H, CdCH), 7.34 (m, 3H, Ph-H), 7.50 (m, 2H,
Ph-H); 13C NMR (75 MHz, CDCl3) δ -0.83, -0.49, 18.46, 25.84,
29.65, 35.34, 39.59, 52.48, 52.92, 57.77, 123.28, 127.87, 128.96, 133.85,
140.01, 159.32, 170.95, 172.60; IR (neat, cm-1) 3069 (w), 3048 (w),
2998 (w), 2954 (s), 2869 (w), 1737 (s), 1616 (m), 1457 (M), 1430
(m), 1319 (m), 1284 (m), 1248 (s), 1223 (s), 1213 (s), 1194 (m), 1176
(s), 1155 (m), 1134 (m), 1113 (m), 1063 (m), 1028 (m), 878 (w), 853
(m), 836 (s), 793 (m), 773 (m), 731 (m), 701 (m). Anal. Calcd for
C20H28O4Si: C, 66.63; H, 7.83. Found: C, 66.54; H, 7.82.
9-(Z)-Dimethylphenylsilylmethylidene-7,7-bis(carbethoxy)bicyclo-
[4.3.0]non-2-ene (6): 1H NMR (600 MHz) δ 0.35 (3H, s), 0.38 (3H,
s), 1.18-1.28 (7H, m), 1.42 (1 H, m), 1.84-1.91 (1H, m), 1.92-2.00
(1H, m), 2.73 (1H, d, J ) 16.2 Hz), 2.93 (1H, ddd, J ) 12.6, 7.8, 4.8
Hz), 3.20 (1H, m), 3.43 (1H, dt, J ) 16.2, 2.4 Hz), 4.10-4.28 (4H,
m), 5.56 (1H, s), 5.61 (1H, m), 5.64 (1H, m), 7.34 (3H, m), 7.52 (2H,
m); 13C NMR (75 MHz, CDCl3) δ -1.0, -0.6, 14.1, 22.3, 23.3, 42.3,
43.3, 61.3, 61.4, 62.6, 119.3, 126.8, 127.8, 128.2, 128.9, 133.8, 161.4,
169.8, 171.4; IR (neat, cm-1) 3036 (w), 2955 (s), 2331 (m), 1731 (s),
1625 (m), 1443 (m), 1361 (m), 1249 (s), 832 (s), 732 (m). Anal. Calcd
for C24H32O4Si C, 69.87; H, 7.82. Found: C, 69.79; H, 7.91.
The structure of 6 was determined on the basis of 2D NMR analyses
(COSY and HETCOR) as well as 1D difference NOE experiments (see
Supporting Information). The 1D difference NOE experiments unam-
biguously established the cis ring juncture and Z geometry of PhMe2-
Si-methylidene moiety at the C-9 position in that strong NOE was
observed between H-C(1) and H-C(5), but no NOE was observed
between H-C(1) and the vinyl proton of the 9-silyl-exo-methylene
moiety. Similar results on the NOE experiments of closely related 9-exo-
methylenebicyclo[4.3.0]nonene23a,bor nonan-2-one23c systems have been
reported, which further support our assignments of the stereochemistry
of 6.
General Procedure for the Catalytic CO-SiCaC Reaction. A
typical procedure is described for the reaction of 1a. A reaction vessel
equipped with a stirring bar and a CO inlet, was charged with Rh4-
(CO)12 (3.8 mg, 0.005 mmol, 0.5 mol %). After purging the vessel
with CO, 1,4-dioxane (2 mL) was added to dissolve the catalyst. After
stirring for 5 min at ambient temperature, P(OEt)3 (17 mg, 0.10 mmol;
5 equiv to Rh) in 1,4-dioxane (2 mL) was added via a syringe, and the
mixture was stirred for an additional 10 min. The color of the solution
turned from bright red to dark red during this period. The resulting
catalyst solution was then cannulated into a 100-mL round-bottomed
flask containing a solution of 1a (238 mg, 1 mmol), Me2PhSiH (145
mg, 1.05 mmol) in 1,4-dioxane (50 mL) via CO pressure without
stirring. The resulting mixture was placed in a 300-mL stainless steel
autoclave, pressurized with CO gas (20 atm) and then heated to 105
°C with stirring for 48 h. After releasing CO, the reaction mixture was
submitted to GC analysis. All volatiles were removed under reduced
pressure and the crude product was purified by silica gel column
chromatography using hexanes/EtOAc (15/1) as eluant.
General Procedure for the “Freeze and CO” Protocol for the
CO-SiCaC Reaction. A Schlenk-type flask containing Rh4(CO)12 (3.8
mg, 0.005 mmol) and a stirring bar was purged with CO, and 1,4-
dioxane (2.0 mL) was added to dissolve the catalyst. After stirring for
5 min at ambient temperature, P(OEt)3 (17 mg, 0.10 mmol) in dioxane
(1.0 mL) was added via syringe. The catalyst solution was stirred for
an additional 10 min and cannulated into a reaction flask containing
an enyne (1.0 mmol) in dioxane (2.0 mL), which had been purged with
CO and frozen by submerging in liquid nitrogen under CO. Me2PhSiH
in dioxane (1.0 mL) was added via syringe and the reaction flask placed
into a 300-mL stainless steel autoclave that had been purged with CO.
Then, the autoclave was charged with CO (20 atm) and heated at 105
°C for 48 h. The autoclave was cooled to 0 °C and the pressure released
to take out the reaction flask. Then, the reaction mixture was subjected
to GC analysis.
4,4-Bis(carbethoxy)-1-(Z)-dimethylphenylsilylmethylidene-2-formyl-
methylcyclopentane (3a): viscous, colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 5/1, Rf ) 0.23); 1H NMR (300 MHz, CDCl3) δ 0.34
(s, 3H, CH3Si), 0.35 (s, 3H, CH3Si), 1.24 (t, J ) 7.1 Hz, 3H, OCH2CH3),
1.25 (t, J ) 7.1 Hz, 3H, OCH2CH3), 1.92 (dd, J ) 13.7 Hz, 4.9 Hz,
1H, CH2CH), 2.32 (m, 2H, CH2CHO), 2.66 (dd, J ) 13.7 Hz, 8.2 Hz,
1H, CH2CH), 2.90 (d, J ) 16.5 Hz, 1H, CH2CdC), 2.98 (m, 1H,
CH2CHCH2), 3.19 (dt, J ) 16.5 Hz, 2.2 Hz, 1H, CH2CdC), 4.18 (q,
J ) 7.1 Hz, 2H, OCH2CH3), 4.19 (q, J ) 7.1 Hz, 2H, OCH2CH3),
5.61 (s br, 1H, CdCH), 7.35 (m, 3H, Ph-H), 7.51 (m, 2H, Ph-H), 9.38
(d, J ) 1.1 Hz, 1H, CHO); 13C NMR (75 MHz, CDCl3) δ -1.29, -0.94,
14.18, 14.24, 36.42, 39.66, 44.96, 50.17, 58.65, 61.74, 61.85, 120.58,
128.16, 129.39, 133.97, 139.07, 161.86, 171.55, 172.09, 200.71; IR
(neat, cm-1) 3069 (w), 3049 (m), 2980 (s), 2959 (s), 2905 (m), 2821
(w), 2721 (w), 1729 (s), 1629 (m), 1463 (m), 1446 (m), 1428 (s), 1405
(m), 1390 (m), 1366 (m0, 1281 (s), 1248 (s), 1186 (s), 1162 (s), 1111
(s), 1096 (s), 1082 (s), 1064 (s), 1029 (m), 905 (w), 836 (s), 784 (m),
733 (s), 702 (s). Anal. Calcd for C22H30O5Si: C, 65.64; H, 7.51;
Found: C, 65.45; H, 7.36.
2-(Z)-Dimethylphenylsilylethylidene-8,8-dimethyl-3-formylmethyl-
7,9-dioxaspriro[4,5]decane (3b): viscous, colorless liquid; TLC (silica
gel, hexanes/EtOAc ) 5/1, Rf ) 0.21); 1H NMR (300 MHz, CDCl3) δ
0.34 (s, 6H, CH3Si), 1.05 (dd, J ) 13.7 Hz, 6.1 Hz, 1H, CH2CH), 1.38
(s, 6H, CH3C), 1.89 (dd, J ) 13.7 Hz, 8.3 Hz, 1H, CH2CH), 2.25 (m,
2H, CH2CHO), 2.35 (d, J ) 15.9 Hz, 1H, CH2CdC), 2.53 (d, J )
15.9 Hz, 1H, CH2CdC), 2.80 (m, 1H, CH2CHCH2), 3.57 (m, 4H,
(23) (a) Backva¨ll, J.-E.; Nilsson, Y. I. M.; Andersson, P. G.; Wu, J. Tetrahedron
Lett. 1994, 35, 5713. (b) Nilsson, Y. I. M.; Gatti, R. G. P.; Andersson, P.
G.; Backva¨ll, J.-E. Tetrahedron 1996, 52, 7511 (c) Hintz, S.; Mattay, J.;
Eldik, R.; Fu, W.-F. Eur. J. Org. Chem. 1998, 1583.
9
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A R T I C L E S
Ojima et al.
OCH2C), 5.61 (s br, 1H, CdCH), 7.32 (m, 3H, Ph-H), 7.49 (m, 2H,
Ph-H), 9.33 (d, J ) 1.1 Hz, 1H, CHO); 13C NMR (75 MHz, CDCl3) δ
-1.37, -1.16, 22.02, 25.48, 35.02, 38.90, 40.27, 45.33, 51.35, 67.37,
69.56, 97.88, 120.88, 127.95, 129.14, 133.70, 139.05, 163.48, 200.82;
IR (neat, cm-1) 3069 (m), 3048 (m), 2992 (s), 2952 (s), 2858 (s), 2717
(m), 2360 (m), 2342 (w), 1723 (s), 1626 (m), 1477 (w), 1453 (m),
1428 (m), 1405 (m), 1383 (s), 1371 (s), 1347 (m), 1304 (m), 1249 (s),
1198 (s), 1156 (m), 1110 (s), 1061 (s), 1033 (m), 998 (w), 932 (m),
919 (m), 834 (s), 731 (s), 701 (s). Anal. Calcd for C21H30O3Si: C,
70.35; H, 8.43. Found: C, 70.57; H, 8.54.
4,4-Bis(carbomethoxy)-1-(Z)-dimethylphenylsilylmethylidene-2-
formylmethylcyclopentane (3c): viscous, colorless liquid; TLC (silica
gel, hexanes/EtOAc ) 5/1, Rf ) 0.20); 1H NMR (300 MHz, CDCl3) δ
0.35 (s, 3H, CH3Si), 0.36 (s, 3H, CH3Si), 1.26 (dd, J ) 14.0 Hz, 5.3
Hz, 1H, CH2CH), 1.82 (dd, J ) 14.0 Hz, 9.0 Hz, 1H, CH2CH), 2.19
(d, J ) 15.6 Hz, 1H, CH2CdC), 2.34 (m, 2H, CH2CHO), 2.49 (d br,
J ) 15.6 Hz, 1H, CH2CdC), 2.84 (m, 1H, CH2CHCH2), 3.10 (s, 1H,
OCH2C), 3.11 (s, 1H, OCH2C), 3.24 (s, 2H, OCH2C), 3.29 (s, 3H,
OCH3), 3.30 (s, 3H, OCH3), 5.54 (s br, 1H, CdCH), 7.32 (m, 3H,
Ph-H), 7.49 (m, 2H, Ph-H), 9.37 (d, J ) 1.1 Hz, 1H, CHO); 13C NMR
(75 MHz, CDCl3) δ -1.32, -1.04, 35.79, 37.39, 43.61, 46.14, 51.15,
59.14, 59.25, 75.40, 76.83, 119.29, 127.84, 129.00, 133.69, 139.35,
165.23, 201.31; IR (neat, cm-1) 3068 (m), 3048 (m), 2953 (s), 2925
(s), 2886 (s), 2880 (s), 2826 (m), 2720 (w), 1724 (s), 1626 (m), 1475
(m), 1458 (m), 1450 (m), 1428 (m), 1404 (m), 1389 (m), 1339 (w),
1302 (w), 1250 (s), 1198 (m), 1167 (m), 1113 (s), 998 (w), 966 (m),
879 (m), 837 (s), 784 (m), 732 (s), 701 (s). Anal. Calcd for C20H30O3-
Si: C, 69.32; H, 8.73. Found: C, 69.05; H, 8.54.
4,4-Bis(acetoxymethyl)-1-(Z)-dimethylphenylsilylmethylidene-2-
formylmethylcyclopentane (3d): viscous, colorless liquid; TLC (silica
gel, hexanes/EtOAc ) 5/1, Rf ) 0.15); 1H NMR (300 MHz, CDCl3) δ
0.34 (s, 3H, CH3Si), 0.36 (s, 3H, CH3Si), 1.25 (dd, J ) 14.0 Hz, 6.1
Hz, 1H, CH2CH), 1.95 (m, 2H, CH2CHO), 2.03 (s, 3H, CH3CO), 2.04
(s, 3H, CH3CO), 2.23 (d, J ) 16.2 Hz, 1H, CH2CdC), 2.31 (d, J )
6.1 Hz, 1H, CH2CH), 2.50 (d, J ) 16.2 Hz, 1H, CH2CdC), 2.86 (m,
1H, CH2CHCH2), 3.90 (m, 4H, COOCH2C), 5.59 (s br, 1H, CdCH),
7.33 (m, 3H, Ph-H), 7.49 (m, 2H, Ph-H), 9.34 (s, 1H, CHO); 13C NMR
(75 MHz, CDCl3) δ -1.49, -1.14, 20.80, 20.84, 35.27, 37.88, 43.89,
44.23, 51.13, 65.67, 67.65, 121.00, 128.00, 129.20, 133.72, 138.92,
162.82, 170.90, 170.99, 200.59; IR (neat, cm-1) 3068 (m), 3048 (m),
3008 (w), 2999 (m), 2955 (m), 2894 (m), 2831 (m), 2722 (w), 1742
(s), 1627 (m), 1466 (m), 1428 (m), 1380 (m), 1366 (m), 1247 (s), 1234
(s), 1113 (m), 1039 (m), 998 (w), 983 (m), 903 (m), 838 (s), 786 (m),
734 (m), 702 (m). Anal. Calcd for C22H30O5Si: C, 65.64; H, 7.51.
Found: C, 65.39; H, 7.44.
0.30 (s, 3H, CH3Si), 0.31 (s, 3H, CH3Si), 1.99 (d, J ) 19.0 Hz, 1H,
CH2CH), 2.42 (s, 6H, Ph-CH3), 2.50 (dd, J ) 19.0 Hz, 10.7 Hz, 1H,
CH2CH), 2.97 (m, 2H, CH2CHO), 2.23 (m, 1H, CH2CHCH2), 3.50 (dd,
J ) 14.6 Hz, 1.9 Hz, 1H, CH2CdC), 3.50 (d, J ) 14.6 Hz, 1H, CH2Cd
C), 5.53 (s, 1H, CdCH), 7.32 (m, 5H, Ph-H), 7.49 (m, 2H, Ph-H),
7.64 (m, 2H, Ph-H), 9.36 (s, 1H, CHO); 13C NMR (75 MHz, CDCl3)
δ -1.91, -1.53, 21.54, 36.55, 48.02, 53.48, 53.84, 120.98, 127.84,
128.09, 129.42, 129.70, 132.42, 133.68, 138.04, 143.77, 156.44, 199.42;
IR (neat, cm-1) 3067 (w), 3048 (w), 3018 (w), 3006 (w), 2999 (w),
2954 (m), 2922 (w), 2897 (w), 2854 (w), 1721 (s), 1635 (m), 1597
(w), 1494 (w), 1476 (w), 1453 (w), 1427 (m), 1403 (m), 1347 (s), 1305
(m), 1291 (w), 1251 (m), 1220 (w), 1184 (m), 1165 (s), 1113 (s), 1093
(s), 1042 (m), 1017 (m), 997 (w), 967 (w), 832 (s), 703 (s). Anal. Calcd
for C22H27NO3SSi: C, 63.89; H, 6.58, N, 3.39; S, 7.75. Found: C,
63.70; H, 6,59; N, 3.36; S, 7.71.
1-Methanesulfonyl-3-(E)-dimethylphenylsilylmethylidene-4-formyl-
methylpyrrolidine (3p): viscous, colorless liquid; TLC (silica gel,
hexanes/EtOAc ) 5/1, Rf ) 0.15); 1H NMR (300 MHz, CDCl3) δ 0.36
(s, 3H, CH3Si), 0.38 (s, 3H, CH3Si), 2.05 (dd, J ) 18.4 Hz, 1.9 Hz,
1H, CH2CH), 2.61 (dd, J ) 18.4 Hz, 11.0 Hz, 1H, CH2CH), 2.79 (s,
3H, CH3-SO2), 3.09 (m, 1H, CH2CHCH2), 3.24 (m, 2H, CH2CHO),
3.74 (dd, J ) 14.8 Hz, 1.9 Hz, 1H, CH2CdC), 4.10 (d br, J ) 14.8
Hz, 1H, CH2CdC), 5.63 (s br, 1H, CdCH), 7.32 (m, 3H, Ph-H), 7.47
(m, 2H, Ph-H), 9.40 (s, 1H, CHO); 13C NMR (75 MHz, CDCl3) δ -1.96,
-1.56, 34.80, 36.88, 47.67, 53.17, 53.58, 121.38, 128.06, 129.39,
133.64, 137.94, 156.21, 199.34; IR (neat, cm-1) 3068 (m), 3048 (m),
3013 (w), 2953 (m), 2897 (m), 2855 (m), 2727 (w), 1721 (s), 1685
(w), 1637 (m), 1479 (w), 1458 (w), 1427 (m), 1407 (m), 1387 (m),
1335 (s), 1251 (s), 1221 (w), 1158 (s), 1112 (s), 1092 (m), 1050 (s),
998 (m), 960 (m), 835 (s), 787 (m), 772 (m), 738 (s), 703 (s). Anal.
Calcd for C16H23NO3SSi: C, 56.94; H, 6.87; N, 4.15; S, 9.50. Found:
C, 56.72; H, 6.97; N, 3.96; S, 9.31.
Acknowledgment. This research was supported by grants
from the National Institutes of Health (NIGMS) and the National
Science Foundation. Generous support from Mitsubishi Chemi-
cal Corp. and Central Glass Co. Ltd. is gratefully acknowledged.
One of the authors (A.T.V.) thanks the National Institutes of
Health (NIGMS) for granting him an Individual National
Research Service Award (NRSA) for his postdoctoral research.
Supporting Information Available: Synthesis, spectral data
for all enynes 1a-1q and 4 as well as NOE experiments for
elucidation of the structure of 6 (PDF). This material is available
free of charge via the Internet at http://pubs.acs.org.
1-(4-Toluenesulfonyl)-3-(E)-dimethylphenylsilylmethylidene-4-
formylmethylpyrrolidine (3e): viscous colorless liquid; TLC (silica
gel, hexanes/EtOAc ) 5/1, Rf ) 0.15); 1H NMR (300 MHz, CDCl3) δ
JA0258982
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9174 J. AM. CHEM. SOC. VOL. 124, NO. 31, 2002