Lewis acid-mediated intramolecular addition of silyl enol ethers to internal unactivated alkynes

Article abstract of DOI:10.1139/v01-134

The EtAlCl₂-mediated intramolecular addition of silyl enol ethers to both terminal and internal unactivated alkynes, bearing alkyl and phenyl susbstituents at the alkyne moiety, gave mono- and bicyclic β,γ-unsaturated ketones in good to excelle

Full text of DOI:10.1139/v01-134

1624
Lewis acid-mediated intramolecular addition of
silyl enol ethers to internal unactivated alkynes
Ken-ichiro Imamura, Eiji Yoshikawa, Vladimir Gevorgyan, Tomoko Sudo,
Naoki Asao, and Yoshinori Yamamoto
Abstract: The EtAlCl2-mediated intramolecular addition of silyl enol ethers to both terminal and internal unactivated
alkynes, bearing alkyl and phenyl susbstituents at the alkyne moiety, gave mono- and bicyclic b,ꢀ-unsaturated ketones
in good to excellent yields. On the other hand, the silyloxy-substituted cyclic vinylsilanes were obtained in moderate to
high yields when the reactions were catalyzed by B(C6F5)3 in the presence of triethylsilane. All the reactions proceeded
via endo-fashion exclusively. The mechanisms of these regiospecific Lewis acid-assisted carbocyclizations are proposed.
Key words: Lewis acid, silyl enol ethers, carbocyclization, alkynes.
Résumé : La réaction, catalysée par le EtAlCl2, d’addition intramoléculaire d’éthers énoliques silylés sur des alcynes
internes ou en position terminale portant des substituants alkyles et phényles au niveau de l’alcyne conduit à la forma-
tion de cétones b,ꢀ-insaturées mono- et bicycliques, avec des rendements allant de bons à excellents. Par ailleurs, les
réactions catalysées par du B(C6F5)3 en présence de triéthylsilane conduisent à la formation de vinylsilanes cycliques,
substitués par des groupes silyloxy, avec des rendements allant de modérés à élevés. Toutes les réactions se produisent
exclusivement de façon endo. On propose des mécanismes pour ces carbocyclisations régiospécifiques assistées par des
acides de Lewis.
Mots clés : acide de Lewis, éthers énoliques, carbocyclisation, alcynes.
[Traduit par la Rédaction] Imamura et al. 1631
Introduction
trans-addition product 6 is obtained through syn-addition of
enolate to the ꢁ2 neutral 3 (pathway A) or anti-addition to the
ꢁ2 cationic 5 (pathway B) species, respectively.
The development of new selective carbocyclization meth-
odologies is an important task for synthetic organic chemists
(for reviews see ref. 1). Carbocyclization of alkynes is of par-
ticular interest since it provides an access to unsaturated carbo-
and heterocycles (for a review, see for example ref. 2). Among
several known methods of carbocyclization of alkynes (1, 2),
the intramolecular addition of silyl enol ethers to acetylenes
has proven to become one of the effective complementary
tools towards medium-sized carbocycles. Two approaches are
known to date to encourage a weak nucleophile, such as a
silyl enol ether, to add intramolecularly across a carbon—car-
bon triple bond (3).2 First is a well explored HgCl2-mediated
exo-carbocyclization (eq. [1]) (4, 5),3 in which mercury acti-
vates an enolate moiety of 1 by forming a transient a-keto
mercurial species 2. Either the product 4 or the isomeric
The second is a very recent approach where a W complex
catalytically activates an alkyne moiety (toward nucleophilic
addition of enolate) via formation of the alkyne–vinilydene
intermediate 7, which, after concomitant anti-addition of
silyl enol ether to its electrophilic central carbon, forms an
endo-carbocyclization product 8 (eq. [2]) (6).4
Despite the obvious synthetic importance of the men-
tioned methodologies (7),5 the scope of their application is
limited to use of terminal (4–6)3,4 and masked terminal
(silyl-protected) (4c-4d, 7)5 alkynes. Recently, we reported
the first examples of the third alternative approach: Lewis
acid-mediated intramolecular addition of silyl enol ethers to
both terminal and internal unactivated alkynes (8). Now we
report the B(C6F5)3-catalyzed cyclization reactions of the
carbon-tethered alkynyl silyl enol ether in the presence of
Received January 31, 2001. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on October 30, 2001.
This paper is dedicated to Professor Victor Snieckus in recognition of his contributions to organic chemistry.
K. Imamura, E. Yoshikawa, V. Gevorgyan, T. Sudo, N. Asao, and Y. Yamamoto.1 Department of Chemistry, Graduate School
of Science, Tohoku University, Sendai 980–8578, Japan.
1Corresponding author (telephone: +81-22-217-6581; fax: +81-22-217-6784; e-mail: yoshi@yamamoto1.chem.tohoku.ac.jp).
2There are reports on the intermolecular addition of silyl enol ethers to terminal alkynes mediated by the SnCl4–Bu3N system and
by GaCl3, proceeding via syn-addition of metal enolates to metalacetylides. See ref. 3.
3There are reports in which the authors state an exclusive anti-selective addition of a-keto carbons to the terminal alkynes mediated
by mercuric chloride. See ref. 5.
4When this project was undergoing in our labs, a paper describing a W-catalyzed endo-selective carbocyclization of silyl enol ethers
with terminal alkynes had appeared. See ref. 6.
5Mercury-mediated carbocylization approach was recently successfully used for the natural products syntheses. See ref. 7.
Can. J. Chem. 79: 1624–1631 (2001)
DOI: 10.1139/cjc-79-11-1624
© 2001 NRC Canada

Imamura et al.
1625
O
SYN
exo
D+
O
O
Hg
Cl
Hg
Cl
D
3
4
A
O-SiMe3
O
HgCl2
[1]
Hg
Cl
-TMSCl
2
1
B
D+
ANTI
exo
O
O
O
_
Hg
Cl
D
+
Hg
Cl
5
6
[W]
R3Si-O
R3Si-O
•
[W]
7
[2]
H+
ANTI
endo
_
[W]
H
+
O
O
8
SiR3
triethylsilane along with a detailed study on the EtAlCl2-mediated reactions (Lewis acid-catalyzed intramolecular
carbosilylation of alkynes are reported; see ref. 9).
Results and discussion
EtAlCl2-mediated intramolecular addition of silyl enol ether to alkynes
As we have previously shown, the intramolecular addition of silyl enol ethers of 9 to internal alkynes is mediated by EtAlCl2 to
give cyclic products 10 in good to high yields (eq. [3], Table 1). The reaction of 9a in the presence of stoichiometric amounts of
EtAlCl26 afforded the cyclization product 10a in 70% isolated yield (entry 1). The reaction of 9b bearing t-Bu-Me2Si group instead
of Me3Si group also proceeded smoothly to give 10a in 63% (entry 2). Optimization experiments revealed that the reaction under
0.1 mol L–1 concentration gave the best result (entries 1, 3–5). The carbocyclizations of methyl- (9c) and butyl-substituted (9d)
alkynyl silyl enol ethers gave b,ꢀ-unsaturated ketones 10b–c in 57 and 80%, respectively. The reaction of the silyl enol ether con-
taining trisubstituted alkene 9e also proceeded smoothly to give 10d in 76% yield. In all above cases, the b,ꢀ-unsaturated ketones
10a–d were accompanied with detectable amounts of isomeric a,b-unsaturated cyclohexenones 11a–d, which are obviously the
thermodynamic products.7 It should be pointed out that in all cases the carbocyclizations proceeded in exclusive endo-fashion and
no traces of exo-cyclization product 12 were detected by GC–MS and NMR analyses of the crude reaction mixtures.
R1
R1
R1
R1 EtAlCl2
Toluene
[3]
+
R2
R2
R2
R2
O
O
OSi
O
9
10
11
12
not detected
6 Other Lewis acids such as HfCl4, ZrCl4, and InCl3 did not mediate this carbocyclization, whereas the use of AlBr3, MeAlCl2, Et2AlCl, and
GaCl3 in some cases gave the carbocyclization products although the chemical yields with these Lewis acids were low (?40%).
7 The control experiments have confirmed that b,ꢀ-enone 10 is the kinetic product, which isomerized into the thermodynamic product (a,b-
enone 11) under the reaction conditions. Thus, normally the carbocyclization of 9c gives about a 95:5 ratio of 10c:11c (eq. [3]); after being
stirred for an additional 3 h at room temperature, the mentioned ratio changed to 44:56, whereas after 12 h, the isomeric 11c became the
major reaction product accompanied by traces of 10c.
© 2001 NRC Canada

1626
Can. J. Chem. Vol. 79, 2001
Table 1. EtAlCl2-mediated cyclization reaction of 9.a
Yield (%)
Lewis acid
(equiv)
Entry
Si
R1
R2
9
(mol L–1)
10
11
1
2
3
4
5
6
7
8
Me3Si
t-Bu-Me2Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Ph
Ph
Ph
Ph
Ph
Me
Bu
Ph
H
H
H
H
H
H
H
Me
9a
9b
9a
9a
9a
9c
9d
9e
EtAlCl2
EtAlCl2
EtAlCl2
EtAlCl2
EtAlCl2
EtAlCl2
EtAlCl2
EtAlCl2
(1.2)
(1.2)
(1.2)
(1.5)
(1.2)
(1.2)
(1.2)
(1.2)
0.4
0.4
0.1
0.08
0.01
0.1
0.1
0.1
10a
10a
10a
10a
10a
10b
10c
10d
70
63
75
77
60
57
80
76
11a
11a
11a
11a
11a
11b
11c
11d
6
11
4
5
4
11
6
8
aReactions were conducted in toluene at 0°C for 3 h.
EtAlCl2-mediated carbocyclization of cyclic substrates 13, as well as that of their acyclic analogues 9, proceeded in exclu-
sive endo-fashion to give bicylic b,ꢀ-cyclohexenones 14 in good yields (eq. [4]). Substrates possessing both terminal (13a) and
internal (13b) alkynyl moieties effectively cyclized to give the bicylic 14a and 14c in 78 and 84% isolated yields, respectively.
Furthermore, quenching the reaction mixtures with electrophiles, such as D2O and I2, afforded the corresponding D- (14b) and
I-containing (14d) products in good yields.
R
E
R
OSiMe3
1) EtAlCl2
2) E+
O
[4]
13
a: R=H
b: R=Me
14 a: R=E=H, 78%
b: R=H, E=D, 71%
c: R=Me, E=H, 84%
d: R=Me, E=I, 75%
We propose the following plausible mechanism for the observed Lewis acid-mediated exclusive endo-carbocyclization of
carbon-tethered alkynyl silyl enol ethers. As we previously proposed for the Lewis acid-catalyzed hydro- and allylmetalation
of alkynes (9), the coordination of the triple bond of 15 to Lewis acid would form zwitterionic intermediate 16 (eq. [5]). The
double bond of silyl enol ether moiety would attack the vinyl cation of 16 at the most nucleophilic terminal position in an
anti-fashion affording the endo-mode cyclization intermediate 17. The elimination of the TMSCl from 17 would form the vi-
nyl metal 18, which after trapping with an electrophile would produce 19.
X3Al
R
AlX3
AlX3
R
R
O
O
O
Me3Si
15
17
16
Me3Si
Me3Si
[5]
AlX2
E
R
R
E
-TMSCl
18
19
O
O
An application of the above methodology is shown in eq. [6]. Naphthol 21 could be synthesized from the unsaturated ana-
1
logue 20, although in modest unoptimized yield (40% by H NMR, eq. [6]).
1) EtAlCl2
[6]
2) H+
OSiMe3
OH
20
21
© 2001 NRC Canada

Imamura et al.
1627
Fig. 1. Mechanism of the B(C6F5)3-catalyzed hydrosilylation of
the carbonyl group.
B(C6F5)3-catalyzed intramolecular addition of silyl enol
ether to alkynes
Although the above mentioned carbocyclization reaction
demonstrated the first example of the Lewis acid-mediated
addition of silyl enol ethers to internal unactivated alkynes,
the synthetic utility of this methodology is limited by the
fact that a stoichiometric amount of EtAlCl2 is needed. This
prompted us to search for a more synthetically useful cata-
lyst for this reaction. Attempted reaction of 9b in the pres-
ence of a catalytic amount of B(C6F5)3 did not proceed at all.
However, the B(C6F5)3-catalyzed reaction proceeded dramati-
cally by addition of triethylsilane and the silyloxy-substituted
cyclic vinylsilane 22a was obtained in 49% yield (eq. [7])
(10).8 The compound 10a, which was produced in the EtAlCl2-
mediated reaction, was not formed at all. The B(C6F5)3-cata-
lyzed cyclization reaction using other substituted substrates
9f and 9g also proceeded smoothly under the same condi-
tions as those in the case of 9b to afford 22b and 22c in 61
and 63% yield, respectively.
SiR3
O
(C6F5)3B H
or
R3Si
H
chromatography was carried out employing Merck silica gel
(Kieselgel 230–400 mesh), and analytical thin layer chroma-
tography (TLC) was performed on 0.2-mm precoated silica
gel plates (Kieselgel 60 F254). All manipulations were con-
ducted under an argon atmosphere using standard Schlenk
techniques. Anhydrous solvents were purchased from Kanto
Chemicals. Alkyl-tethered alkynyl silyl enol ethers 9 were
obtained by consecutive ester propargylation (for a review
see ref. 13), conversion to ketone, and silyl enolization (for a
review see ref. 14). All other compounds used were com-
mercially available and purchased from Aldrich.
R
SiEt3
R
B(C6F5)3 (20 mol%)
[7]
Et3SiH (2 equiv)
toluene, 0°C, 15 min
OSitBuMe2
OSitBuMe2
9b: R=Ph
22a: R=Ph 49%
Preparation of alkynyl silyl enol ethers 9
: R=Me
: R=Me 61%
: R=Bu 63%
9f
22b
22c
The preparation of 9e is representative. (i) To a solution of
diisopropylamine (6.73 mL, 48 mmol) in THF (40 mL) was
added n-BuLi (1.61 M in hexane, 28.6 mL) at 0°C. After be-
ing stirred for 30 min, the mixture was cooled to –78°C. To the
solution was added methyl isobutyrate (4.58 mL, 40 mmol), and
the reaction mixture was stirred for 1 h. To the resulting
mixture, phenylpropargyl p-toluenesulfonate (11.4 g, 40 mmol)
in THF (20 mL) – 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-
pyrimidinone (5.0 mL) was added. The mixture was stirred
for 15 min, and then allowed to warm to 0°C. After being
stirred for additional 10 min at this temperature, the mixture
was quenched with ice-cold saturated, aq NH4Cl solution
and three times extracted with ether. The combined organic
phase was washed with H2O, brine, dried over MgSO4, fil-
tered, and concentrated. The crude product was purified by
column chromatography (silica gel, eluent: hexane – ethyl
acetate, 15:1) to give methyl 2,2-dimethyl-5-phenyl-4-pentylate
: R=Bu
9g
Piers and co-workers (10)8 proposed the interesting silane
activation mechanism in the B(C6F5)3-catalyzed hydrosilylation
of aldehydes and ketones; the ordinary mechanism, in which
the carbonyl oxygen of the electrophiles coordinates to B(C6F5)3
and thus carbonyl substrates are activated, is not operative in
the B(C6F5)3-catalyzed reduction. Their extensive mechanis-
tic studies clarify that B(C6F5)3 activates the silane via hy-
dride abstraction to form the incipient silylium species which
enhances the electrophilicity of carbonyl group, facilitating
the reduction by [HB(C6F5)3]– or R3SiH (Fig. 1).
Most probably, silylium species 23 is generated here also and
a plausible mechanism for the B(C6F5)3-catalyzed cyclization re-
action of 9 is shown in Scheme 1. The ꢂ-coordination of
acetylenic bond of 9 to the silylium species would form the
cationic intermediate 24. The silyl enol ether moiety would
attack the electron deficient triple bond from the side oppo-
site to the silylium species to produce an oxonium cation 25.
The reduction of an intermediate 25 by [HB(C6F5)3]– would
form cyclization products 22 and regenerate B(C6F5)3.
1
(6.96 g, 80% yield). H NMR (300 MHz, CDCl3) d: 7.41–
7.35 (m, 2H), 7.30–7.24 (m, 3H), 3.71 (s, 3H), 2.66 (s, 2H),
1.34 (s, 6H). (ii) To a solution of methyl 2,2-dimethyl-5-
phenyl-4-pentylate (1.92 g, 8.9 mmol) in THF (18 mL) were
added sequentially TMSCH2Li (1.0 M in pentane, 19.5 mL) and
1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (2.15 mL,
18 mmol) at –78°C. After being stirred for 30 min, the mix-
ture was quenched with ice-cold saturated, aq NH4Cl solu-
tion and three times extracted with ether. The combined
organic phase was washed with H2O, brine, dried over MgSO4,
filtered, and concentrated. The crude product was purified
by column chromatography (silica gel, eluent: hexane – ethyl
acetate, 30:1) to give 1-(trimethylsilyl)-3,3-dimethyl-6-phenyl-
Experimental
1H and 13C NMR spectra were recorded on a JEOL LA-
300 (300 MHz) and JEOL a–500 (500 MHz) spectrometers.
IR spectra were recorded on a Shimadzu FT IR-8200A spec-
trometer. High-resolution mass spectra were recorded on a
JEOL HX-110 spectrometer. Elemental analyses were car-
ried out at the Analytical Center of Tohoku University. GC–
MS analysis was performed on a Hewlett-Packard Model
6890 GC interfaced to a Hewlett-Packard Model 5973 mass
selective detector (30 m × 0.25 mm capillary column). Column
1
5-hexyn-2-one (1.85 g, 76% yield). H NMR (300 MHz,
CDCl3) d: 7.40–7.34 (m, 2H), 7.30–7.24 (m, 3H), 2.59 (s,
8 Piers and his co-workers found that B(C6F5)3-catalyzed hydrosilylation of carbonyl functions, such as aldehydes, ketones, and esters, pro-
ceeded very smoothly to give the corresponding reduced compounds in high yields.
© 2001 NRC Canada

1628
Can. J. Chem. Vol. 79, 2001
Scheme 1.
R
Et3Si•HB(C6F5)3
OSitBuMe2
Et3SiH
23
9
SiEt3
B(C6F5)3
R
HB(C6F5)3
SiEt3
OSitBuMe2
R
24
SiEt3
R
OSitBuMe2
22
O
H B(C6F5)3
25
tBuMe2Si
2H), 2.27 (s, 2H), 1.27 (s, 6H), 0.13 (s, 9H). (iii) To a mix-
ture of 1-(trimethylsilyl)-3,3-dimethyl-6-phenyl-5-hexyn-2-one
(1.85 g, 6.8 mmol) and NaI (1.22 g, 8.1 mmol) in CH3CN
(14 mL) were added sequentially Et3N (4.54 mL, 33 mmol)
and TMSCl (2.58 mL, 20 mmol) at room temperature. After
being stirred for 30 min, the mixture was quenched with sat-
urated, aq NaHCO3 solution and three times extracted with
pentane. The combined organic phase was washed with brine,
dried over MgSO4, filtered, and concentrated. The crude
product was purified by column chromatography (silica gel,
eluent: hexane – ethyl acetate – pyridine, 20:1:0.1) to give
9a (1.81 g, 98% yield). (iv) To a solution of 9a (1.33 g,
4.9 mmol) in THF (9.8 mL) was added n-BuLi (1.54 M in
hexane, 3.32 mL) at 0°C, and the mixture was stirred for
20 min. To the resulting mixture was added MeI (455 L,
7.3 mmol), and the mixture was allowed to warm to room
temperature. After being stirred for 25 min, the reaction
mixture was quenched with ice-cold saturated, aq NH4Cl so-
lution and three times extracted with ether. The combined
organic phase was washed with brine, dried over MgSO4,
filtered, and concentrated. The crude product was purified
by column chromatography (silica gel, eluent: hexane –
ethyl acetate, 30:1) to give 4,4-dimethyl-7-phenyl-6-heptyn-
was quenched with saturated, aq NaHCO3 solution and three
times extracted with pentane. The combined organic phase
was washed with brine, dried over MgSO4, filtered, and con-
centrated. The crude product was purified by column chro-
matography (silica gel, eluent: hexane – ethyl acetate –
pyridine, 20:1:0.1) to give 9e (302 mg, 81% yield).
2-(Trimethylsilyloxy)-3,3-dimethyl-6-phenyl-1-hexen-5-yne (9a):
colorless oil. HRMS calcd. for C17H24OSi 272.1597; found
272.1600. IR (neat) (cm–1): 3125, 1654, 1624, 1599, 1254,
1
1021, 847, 755, 691. H NMR (300 MHz, CDCl3) d: 7.41–
7.36 (m, 2H), 7.30–7.24 (m, 3H), 4.18 (d, J = 1.7 Hz, 1H),
4.04 (d, J = 1.7 Hz, 1H), 2.48 (s, 2H), 1.19 (s, 6H), 0.23 (s,
9H). 13C NMR (75.5 MHz, CDCl3) d: 164.4, 131.5, 128.1,
127.4, 124.2, 88.4, 87.4, 82.2, 40.0, 30.8, 25.4, 0.2. Anal.
calcd. for C17H24OSi: C 74.94, H 8.88; found: C 74.72, H
8.68.
2-(tert-Butyldimethylsilyloxy)-3,3-dimethyl-6-phenyl-1-hexen-
5-yne (9b): colorless oil. HRMS calcd. for C20H30OSi:
1
314.2066; found: 314.2067. H NMR (300 MHz, CDCl3) d:
7.41–7.37 (m, 2H), 7.28–7.26 (m, 2H), 4.15 (d, J = 1.8 Hz,
1H), 4.03 (d, J = 1.8 Hz, 1H), 2.50 (s, 2H), 1.20 (s, 6H),
0.96 (s, 9H), 0.21 (s, 6H). 13C NMR (75.5 MHz, CDCl3) d:
164.4, 134.5, 128.1, 127.4, 124.2, 88.4, 86.2, 82.2, 40.4,
30.9, 25.8, 25.5, 18.2, –4.8. Anal. calcd. for C20H30OSi: C
76.37, H 9.61; found: C 76.22, H 9.56.
1
3-one (327 mg, 31% yield). H NMR (300 MHz, CDCl3) d:
7.40–7.33 (m, 2H), 7.30–7.24 (m, 3H), 2.61 (s, 2H), 2.59 (q,
J = 7.2 Hz, 2H), 1.28 (s, 6H), 1.06 (t, J = 7.2 Hz, 3H).
(v) To a solution of 4,4-dimethyl-7-phenyl-6-heptyn-3-one
(281 mg, 1.3 mmol) in CH2Cl2 (2.8 mL) were added sequen-
tially Et3N (274 L, 2.0 mmol) and TMSOTf (304 L,
1.6 mmol) at 0°C. The mixture was stirred for 30 min, and
then allowed to warm to room temperature. After being
stirred for an additional 1 h at this temperature, the mixture
2-(Trimethylsilyloxy)-3,3-dimethyl-1-hepten-5-yne (9c): col-
orless oil. HRMS calcd. for C12H22OSi: 210.1440; found:
210.1422. IR (neat) (cm–1): 3125, 1655, 1622, 1254, 1021,
1
848. H NMR (300 MHz, CDCl3) d: 4.12 (d, J = 1.6 Hz,
1H), 3.99 (d, J = 1.6 Hz, 1H), 2.20 (q, J = 2.6 Hz, 2H), 1.78
© 2001 NRC Canada

Imamura et al.
1629
(t, J = 2.6 Hz, 3H), 1.10 (s, 6H), 0.21 (s, 9H). 13C NMR
(75.5 MHz, CDCl3) d: 164.9, 87.2, 39.7, 30.2, 25.2, 3.5, 0.1.
Anal. calcd. for C12H22OSi: C 68.51, H 10.54; found:
C 68.50, H 10.21.
1.42 (m, 1H), 1.06 (s, 3H), 0.17 (s, 9H). 13C NMR
(75.5 MHz, CDCl3) d: 155.3, 102.4, 77.04, 76.95, 38.1,
35.1, 29.1, 24.6, 24.2, 19.3, 0.4. Anal. calcd. for C14H24OSi:
C 71.12, H 10.23; found: C 70.93, H 10.06.
2-(Trimethylsilyloxy)-3,3-dimethyl-1-decen-5-yne (9d): color-
less oil. HRMS calcd. for C15H28OSi: 252.1909; found:
252.1911. IR (neat) (cm–1): 3125, 1658, 1622, 1254, 1021,
a-(Trimethylsilyloxy)-o-(1-pentynyl)styrene (20): colorless oil.
HRMS calcd. for C16H22OSi: 258.1439; found: 258.1465. IR
(neat) (cm–1): 2963, 2933, 2235, 1621, 1480, 1307, 1253,
1
846. H NMR (300 MHz, CDCl3) d: 4.11 (d, J = 1.7 Hz,
1
1014, 848. H NMR (300 MHz, CDCl3) d: 7.54–7.45 (m,
1H), 3.99 (d, J = 1.7 Hz, 1H), 2.22 (t, J = 2.3 Hz, 2H), 2.15
(tt, J = 6.8, 2.3 Hz, 2H), 1.51–1.34 (m, 4H), 1.10 (s, 6H),
0.90 (t, J = 7.2 Hz, 3H), 0.21 (s, 9H). 13C NMR (75.5 MHz,
CDCl3) d: 164.8, 87.2, 81.9, 77.9, 39.8, 31.3, 30.2, 25.2,
21.9, 18.4, 13.6, 0.1. Anal. calcd. for C15H28OSi: C 71.36, H
11.18; found: C 71.22, H 10.92.
2H), 7.28–7.23 (m, 2H), 5.13 (d, J = 1.2 Hz, 1H), 4.07 (d,
J = 1.2 Hz, 1H), 2.46 (t, J = 7.0 Hz, 2H), 1.68 (tq, J = 7.0,
7.0 Hz, 2H), 1.10 (t, J = 7.0 Hz, 3H), 0.27 (s, 9H). 13C NMR
(75.5 MHz, CDCl3) d: 154.8, 139.9, 133.5, 127.7, 127.4,
127.2, 121.4, 95.9, 94.3, 80.4, 22.1, 21.7, 13.6, 0.0.
EtAlCl2-mediated carbocyclization of 9 (general procedure)
EtAlCl2 (1.2 equiv) was added to a stirred solution of 9
(0.5 mmol) in toluene (5.0 mL) at 0°C. After being stirred
for 3 h, the reaction mixture was quenched with Et2NH, di-
luted with saturated, aq NaHCO3 solution, and extracted
with ether three times. The combined organic phase was
washed with brine, dried over MgSO4, filtered, and concen-
trated. The products (10 and 11) were purified by column
chromatography (silica gel, eluent: hexane – ethyl acetate).
3-(Trimethylsilyloxy)-4,4-dimethyl-7-phenyl-2-hepten-6-yne
(9e): colorless oil. HRMS calcd. for C18H26OSi: 286.1752;
found: 286.1758. IR (neat) (cm–1): 1664, 1598, 1253, 1074,
1
842, 755, 691. H NMR (300 MHz, CDCl3, a major isomer)
d: 7.41–7.36 (m, 2H), 7.30–7.24 (m, 3H), 4.70 (q, J =
6.8 Hz, 1H), 2.47 (s, 2H), 1.55 (d, J = 6.8 Hz, 3H), 1.18 (s,
6H), 0.26 (s, 9H). 13C NMR (75.5 MHz, CDCl3) d: 156.8,
131.5, 128.1, 127.4, 124.2, 99.3, 88.6, 82.4, 39.9, 31.1, 25.8,
11.8, 1.2.
2-(tert-Butyldimethylsilyloxy)-3,3-dimethyl-1-hepten-5-yne
(9f): colorless oil. HRMS calcd. for C15H28OSi: 252.1910;
found: 252.1908. H NMR (300 MHz, CDCl3) d: 4.08 (d,
J = 1.7 Hz, 1H), 3.97 (d, J = 1.7 Hz, 1H), 2.22 (q, J =
2.6 Hz, 2H), 1.78 (t, J = 2.6 Hz, 3H), 1.11 (s, 6H), 0.93 (s,
9H), 0.18 (s, 6H). 13C NMR (75.5 MHz, CDCl3) d: 164.9,
86.5, 77.2, 76.9, 40.0, 30.3, 25.8, 25.3, 18.2, 3.5, –4.8. Anal.
calcd. for C15H28OSi: C 71.36, H 11.18; found: C 71.34,
H 10.92.
6,6-Dimethyl-3-phenyl-3-cyclohexenone (10a): colorless oil.
HRMS calcd. for C14H16O: 200.1201; found: 200.1211. IR
(neat) (cm–1): 1714, 1672, 1599, 751, 694. 1H NMR
(300 MHz, CDCl3) d: 7.41–7.25 (m, 5H), 6.22 (tt, J = 4.2,
1.8 Hz, 1H), 3.31 (dt, J = 1.8, 1.8 Hz, 2H), 2.46 (dt, J = 4.2,
1.8 Hz, 2H), 1.20 (s, 6H). 13C NMR (75.5 MHz, CDCl3) d:
213.4, 139.4, 134.2, 128.5, 127.5, 124.9, 122.1, 43.3, 40.8,
40.1, 24.3. Anal. calcd. for C14H16O: C 83.96, H 8.05;
found: C 83.91, H 8.01.
1
2-(tert-Butyldimethylsilyloxy)-3,3-dimethyl-1-decen-5-yne (9g):
colorless oil. H NMR (300 MHz, CDCl3) d: 4.08 (d, J =
6,6-Dimethyl-3-phenyl-2-cyclohexenone (11a): colorless oil.
HRMS calcd. for C14H16O: 200.1201; found: 200.1201. IR
(CCl4) (cm–1): 1667, 1611, 1573, 725, 693. 1H NMR
(300 MHz, CDCl3) d: 7.58–7.52 (m, 2H), 7.44–7.38 (m,
3H), 6.35 (t, J = 1.5 Hz, 1H), 2.79 (td, J = 6.1, 1.5 Hz, 2H),
1.98 (t, J = 6.1 Hz, 2H), 1.18 (s, 6H). 13C NMR (75.5 MHz,
CDCl3) d: 204.7, 157.3, 138.5, 129.8, 128.7, 126.0, 123.8,
40.4, 36.4, 25.2, 24.1.
1
1.7 Hz, 1H), 3.97 (d, J = 1.7 Hz, 1H), 2.24 (t, J = 2.4 Hz,
2H), 2.15 (tt, J = 6.8 and 2.4 Hz, 2H), 1.51–1.34 (m, 4H),
1.11 (s, 6H), 0.94 (s, 9H), 0.90 (t, J = 7.2 Hz, 3H), 0.38 (s,
6H). 13C NMR (75.5 MHz, CDCl3) d: 164.8, 86.5, 81.8, 77.9,
40.1, 31.3, 30.3, 25.8, 25.3, 21.9, 18.4, 18.2, 13.6, –4.8.
Anal. calcd. for C18H34OSi: C 73.40, H 11.63; found:
C 73.32, H 11.57.
3,6,6-Trimethyl-3-cyclohexenone (10b): colorless oil. HRMS
2-(Trimethylsilyloxy)-3-methyl-3-(2-propynyl)-1-cyclohexene
(13a): colorless oil. HRMS calcd. for C13H22OSi: 222.1439;
found: 222.1446. IR (neat) (cm–1): 2962, 2933, 2118, 1713,
calcd. for C9H14O: 138.1045; found: 138.1067. IR (neat)
1
(cm–1): 3041, 1715. H NMR (300 MHz, CDCl3) d: 5.44
1
(ttq, J = 3.9, 1.8, 1.4 Hz, 1H), 2.80 (dtq, J = 1.8, 1.8, 0.9 Hz,
2H), 2.21 (dtq, J = 3.9, 1.8, 1.8 Hz, 2H), 1.70 (tdt, J = 1.8,
1.4, 0.9 Hz, 3H), 1.11 (s, 6H). 13C NMR (75.5 MHz, CDCl3)
d: 214.1, 131.5, 119.7, 43.3, 42.7, 40.6, 24.3, 22.4. Anal.
calcd. for C9H14O: C 78.21, H 10.21; found: C 77.92, H
10.67.
1659, 1458, 1252, 1178. H NMR (300 MHz, CDCl3) d:
4.72 (t, J = 4.0 Hz, 1H), 2.35 (dd, J = 16.2, 2.7 Hz, 1H),
2.27 (dd, J = 16.2, 2.7 Hz, 1H), 2.03–1.95 (m, 2H), 1.95 (t,
J = 2.7 Hz, 1H), 1.87–1.74 (m, 1H), 1.60–1.48 (m, 3H), 1.10
(s, 3H), 0.17 (s, 9H). 13C NMR (75.5 MHz, CDCl3) d: 154.7,
102.6, 82.6, 69.8, 37.9, 35.0, 28.8, 24.5, 24.2, 19.2, 0.4.
2-(Trimethylsilyloxy)-3-(2-butynyl)-3-methyl-1-cyclohexene
(13b): colorless oil. HRMS calcd. for C14H24OSi: 236.1596;
found: 236.1600. IR (neat) (cm–1): 2962, 2932, 2126, 1656,
3,6,6-Trimethyl-2-cyclohexenone (11b): colorless oil. HRMS
calcd. for C9H14O: 138.1045; found: 138.1045. IR (neat)
1
(cm–1): 3031, 1670, 1638. H NMR (300 MHz, CDCl3) d:
1
1252, 1178, 842. H NMR (300 MHz, CDCl3) d: 4.70 (t, J =
5.77 (tq, J = 1.5, 1.3 Hz, 1H), 2.29 (tdq, J = 6.1, 1.5, 0.7 Hz,
2H), 1.92 (dt, J = 1.3, 0.7 Hz, 3H), 1.80 (t, J = 6.1 Hz, 2H),
1.08 (s, 6H). 13C NMR (75.5 MHz, CDCl3) d: 204.5, 160.3,
125.1, 40.1, 36.3, 28.4, 24.2, 24.0.
4.0 Hz, 1H), 2.28 (dq, J = 16.5, 2.5 Hz, 1H), 2.19 (dq, J =
16.5, 2.5 Hz, 1H), 1.98 (dt, J = 6.0, 4.0 Hz, 2H), 1.85–1.76
(m, 1H), 1.78 (t, J = 2.5 Hz, 3H), 1.58–1.46 (m, 2H), 1.50–
© 2001 NRC Canada

1630
Can. J. Chem. Vol. 79, 2001
3-Butyl-6,6-dimethyl-3-cyclohexenone (10c): colorless oil.
HRMS calcd. for C12H20O: 180.1514; found: 180.1510. IR
(neat) (cm–1): 3043, 1717, 1676. 1H NMR (300 MHz,
CDCl3) d: 5.45 (ttt, J = 3.9, 1.8, 1.3 Hz, 1H), 2.81 (dtt, J =
1.8, 1.7, 0.7 Hz, 2H), 2.23 (dtt, J = 3.9, 1.7, 1.6 Hz, 2H),
2.00 (ttdt, J = 6.8, 1.6, 1.3, 0.7 Hz, 2H), 1.44–1.24 (m, 4H),
1.12 (s, 6H), 0.90 (t, J = 7.2 Hz, 3H). 13C NMR (75.5 MHz,
CDCl3) d: 214.5, 135.6, 119.1, 43.5, 41.1, 40.6, 36.1, 29.5,
24.4, 22.3, 13.9. Anal. calcd. for C12H20O: C 79.94,
H 11.18; found: C 79.77, H 10.96.
(300 MHz, CDCl3) d: 5.54 (tq, J = 4.0, 1.5 Hz, 1H), 2.70 (t,
J = 3.0 Hz, 1H), 2.43 (ddq, J = 18.0, 4.0, 2.0 Hz, 1H), 2.27
(d, J = 18.0 Hz, 1H), 2.00–1.87 (m, 2H), 1.84–1.75 (m, 2H),
1.66 (dt, J = 2.0, 1.5 Hz, 3H), 1.62–1.46 (m, 2H), 1.01 (s,
3H). 13C NMR (75.5 MHz, CDCl3) d: 217.2, 133.8, 122.8,
52.8, 45.1, 44.7, 43.3, 31.5, 23.5, 21.3, 18.5. Anal. calcd. for
C11H16O: C 80.44, H 9.82; found: C 80.42, H 9.93.
2,5-Dimethyl-3-iodo-9-oxobicyclo[3,3,1]non-2-ene (14d):
colorless oil. HRMS calcd. for C11H15IO: 290.0167; found:
290.0177. IR (neat) (cm–1): 2932, 2864, 1720, 1446. 1H
NMR (300 MHz, CDCl3) d: 2.95 (t, J = 3.0 Hz, 1H), 2.95
(dd, J = 18.0, 2.0 Hz, 1H), 2.76 (d, J = 18.0 Hz, 1H), 2.05–
1.70 (m, 7H), 1.63–1.53 (m, 2H), 1.00 (s, 3H). 13C NMR
(75.5 MHz, CDCl3) d: 213.5, 138.3, 95.3, 57.0, 54.8, 49.0,
44.4, 31.9, 27.5, 22.6, 18.8. Anal. calcd. for C11H15IO:
C 45.54, H, 5.21, I 43.74; found: C 45.63, H 5.24, I 43.84.
3-Butyl-6,6-dimethyl-2-cyclohexenone (11c): colorless oil.
HRMS calcd. for C12H20O: 180.1514; found: 180.1515. IR
(neat) (cm–1): 3028, 1668, 1632. 1H NMR (300 MHz,
CDCl3) d: 5.76 (tt, J = 1.3, 0.9 Hz, 1H), 2.29 (tdt, J = 6.1,
1.3, 0.7 Hz, 2H), 2.18 (tdt, J = 7.4, 0.9, 0.7 Hz, 2H), 1.80 (t,
J = 6.1 Hz, 2H), 1.53–1.43 (m, 2H), 1.38–1.25 (m, 2H), 1.09
(s, 6H), 0.91 (t, J = 7.2 Hz, 3H). 13C NMR (75.5 MHz,
CDCl3) d: 204.8, 164.3, 124.1, 40.4, 37.4, 36.4, 29.2, 27.0,
24.2, 22.3, 13.8.
3-Propyl-1-naphthol (21): colorless oil. HRMS calcd. for
C13H14O: 186.1044; found: 186.1045. IR (neat) (cm–1): 3393,
1
2958, 2929, 1638, 1599, 1578. H NMR (300 MHz, CDCl3)
2,6,6-Trimethyl-3-phenyl-3-cyclohexenone (10d): colorless
d: 8.13–8.08 (m, 1H), 7.75–7.71 (m, 1H), 7.48–7.38 (m,
2H), 7.22 (s, 1H), 6.67 (s, 1H), 5.39 (s, 1H), 2.67 (t, J =
7.5 Hz, 2H), 1.70 (tq, J = 7.5, 7.5 Hz, 2H), 0.96 (t, J =
7.5 Hz, 3H). 13C NMR (75.5 MHz, CDCl3) d: 151.2, 140.6,
134.8, 127.2, 126.4, 124.4, 122.8, 121.3, 119.2, 110.1, 38.2,
24.2, 13.8.
oil. HRMS calcd. for C15H18O: 214.1357; found: 214.1322.
1
IR (neat) (cm–1): 1710, 1599, 756, 698. H NMR (300 MHz,
CDCl3) d: 7.38–7.24 (m, 5H), 5.98 (ddd, J = 5.4, 3.3, 1.5 Hz,
1H), 3.48 (qddd, J = 7.3, 1.8, 1.5, 0.9 Hz, 1H), 2.43 (ddd,
J = 17.6, 3.3, 1.8 Hz, 1H), 2.37 (ddd, J = 17.6, 5.4, 0.9 Hz,
1H), 1.24 (s, 3H), 1.19 (s, 3H), 1.15 (d, J = 7.3 Hz, 3H). 13
C
NMR (75.5 MHz, CDCl3) d: 216.0, 141.2, 140.3, 128.4,
127.2, 126.1, 122.7, 43.0, 39.8, 25.2, 24.6, 15.4.
B(C6F5)3-mediated carbocyclization of 9 (general
procedure)
To a solution of B(C6F5)3 (0.1 mmol, 20 mol%) in toluene
(1.0 mL) were added triethylsilane (0.16 mL, 1.0 mmol) and
substrate 9 (0.5 mmol) at 0°C, successively. After being
stirred for 15 min, the reaction mixture was diluted with
pentane, quenched with Et2NH, filtered through Al2O3, and
concentrated. The product was purified by column chroma-
tography (silica gel, eluent: hexane).
2,6,6-Trimethyl-3-phenyl-2-cyclohexenone (11d): colorless
oil. HRMS calcd. for C15H18O: 214.1357; found: 214.1361.
IR (neat) (cm–1): 1665, 1625, 1599, 751, 701. 1H NMR
(300 MHz, CDCl3) d: 7.42–7.28 (m, 3H), 7.21–7.17 (m,
2H), 2.62 (tq, J = 6.0, 2.0 Hz, 2H), 1.93 (t, J = 6.0 Hz, 2H),
1.70 (t, J = 2.0 Hz, 3H), 1.18 (s, 6H). 13C NMR (75.5 MHz,
CDCl3) d: 204.7, 154.4, 141.4, 129.9, 128.3, 127.7, 127.1,
40.3, 36.1, 29.6, 24.6, 13.4.
[5-(tert-Butyldimethylsilyloxy)-4,4-dimethyl-2-(triethylsilyl)-
cyclohex-1-enyl]-benzene (22a): colorless oil. HRMS calcd.
for C26H46OSi: 430.3087; found: 430.3081. 1H NMR
(300 MHz, CDCl3) d: 7.27–7.23 (m, 3H), 7.10–7.07 (m,
2H), 3.57 (dd, J = 6.8 and 4.9 Hz, 1H), 2.45 (ddt, J = 18.3,
5.1, and 2.0 Hz, 1H), 2.18 (ddt, J = 18.3, 5.1, and 2.0 Hz,
1H), 2.12 (dt, J = 17.4 and 1.7 Hz, 1H), 1.89 (dt, J = 17.4
and 1.7 Hz, 1H), 0.96 (s, 3H), 0.92 (s, 3H), 0.89 (s, 9H),
0.79 (t, J = 6.4 Hz, 9H), 0.21 (q, J = 6.4 Hz, 6H), 0.04 (d,
J = 5.3 Hz, 6H). 13C NMR (75.5 MHz, CDCl3) d: 147.0,
145.8, 130.0, 128.3, 127.7, 126.5, 74.1, 42.3, 35.9, 33.9,
26.7, 25.8, 21.6, 18.0, 15.3, 7.5, 3.4, –4.1, –4.9. Anal. calcd.
for C26H46OSi: C 72.49, H 10.76; found: C 72.36, H 10.77.
5-Methyl-9-oxobicyclo[3,3,1]non-2-ene (14a): colorless oil.
HRMS calcd. for C10H14O: 150.1044; found: 150.1044. IR
(neat) (cm–1): 2929, 1718, 1445. 1H NMR (300 MHz,
CDCl3) d: 5.86 (dt, J = 9.5, 3.5 Hz, 1H), 5.55 (dddd, J = 9.5,
5.5, 2.0, 1.5 Hz, 1H), 2.91 (dt, J = 5.5, 3.0 Hz, 1H), 2.54
(ddd, J = 18.5, 3.5, 1.5 Hz, 1H), 2.37 (d, J = 18.5 Hz, 1H),
2.15–1.98 (m, 1H), 1.88–1.80 (m, 3H), 1.63–1.47 (m, 2H),
1.03 (s, 3H). 13C NMR (75.5 MHz, CDCl3) d: 217.1, 129.4,
127.1, 48.2, 46.3, 44.8, 44.5, 33.2, 23.7, 18.1.
3-Deuterio-5-methyl-9-oxobicyclo[3,3,1]non-2-ene (14b):
colorless oil. HRMS calcd. for C10H13DO: 151.1106; found:
151.1096. IR (neat) (cm–1): 2929, 1720, 1445. 1H NMR
(300 MHz, CDCl3) d: 5.58–5.53 (m, 1H), 2.91 (dt, J = 5.5,
3.0 Hz, 1H), 2.54 (dd, J = 18.5, 1.5 Hz, 1H), 2.37 (d, J =
18.5 Hz, 1H), 2.15–1.98 (m, 1H), 1.88–1.80 (m, 3H), 1.63–
1.47 (m, 2H), 1.03 (s, 3H). 13C NMR (75.5 MHz, CDCl3) d:
217.1, 129.4 (C—D), 129.1 (C—D), 128.8 (C—D), 126.9,
48.1, 46.3, 44.8, 44.4, 33.2, 23.7, 18.0.
5-(tert-Butyldimethylsilyloxy)-1,4,4-trimethyl-2-(triethylsilyl)-
cyclohexene (22b): colorless oil. HRMS calcd. for C21H44OSi2:
1
368.2931; found: 368.2938. H NMR (300 MHz, CDCl3) d:
3.46 (dd, J = 7.7 and 5.6 Hz, 1H), 2.17–1.76 (m, 4H), 1.70
(s, 3H), 0.91 (t, J = 7.9 Hz, 9H), 0.89 (s, 9H), 0.85 (s, 3H),
0.77 (s, 3H), 0.64 (q, J = 7.9 Hz, 6H), 0.03 (d, J = 2.8 Hz,
6H). 13C NMR (75.5 MHz, CDCl3) d: 141.2, 125.2, 74.3,
43.2, 40.8, 34.0, 27.2, 25.8, 23.1, 20.5, 18.3, 7.6, 4.2, –4.1,
–4.9. Anal. calcd. for C21H44OSi2: C 68.40, H 12.03;
found: C 68.27, H 12.17.
2,5-Dimethyl-9-oxobicyclo[3,3,1]non-2-ene (14c): colorless
oil. HRMS calcd. for C11H16O: 164.1200; found: 164.1205.
1
IR (neat) (cm–1): 2966, 2927, 1716, 1446, 1379. H NMR
© 2001 NRC Canada

Imamura et al.
1631
38, 2855 (1997); (c) H. Huang and C.J. Forsyth. J. Org. Chem.
1-Butyl-5-(tert-butyldimethylsilyloxy)-4,4-dimethyl-2-
62, 8595 (1997).
(triethylsilyl)-cyclohexene (22c): colorless oil. HRMS calcd.
for C24H50OSi2: 410.3401; found: 410.3400. 1H NMR
(300 MHz, CDCl3) d: 3.46 (dd, J = 7.5 and 5.5 Hz, 1H),
2.12–1.73 (m, 6H), 1.39–1.26 (m, 4H), 0.91 (t, J = 8.0 Hz,
9H), 0.88 (s, 3H), 0.77 (s, 3H), 0.62 (q, J = 8.0 Hz, 6H),
0.03 (d, J = 3.7 Hz, 6H). 13C NMR (75.5 MHz, CDCl3) d:
145.9, 125.1, 74.4, 43.1, 37.7, 37.4, 34.1, 31.6, 31.3, 27.1,
25.9, 23.1, 22.7, 20.7, 18.0, 14.2, 7.6, 4.3, –4.0, – 4.9.
3. (a) M. Yamamguchi, A. Hayashi, and M. Hirama. J. Am. Chem.
Soc. 115, 3362 (1993); (b) T. Tsukagoshi, Y. Kido, M. Arisawa,
T. Sugihara, and M. Yamaguchi. In Int. Symp. Carbanion Chem.
(ISCC-5), 5th, 1998. Sendai. pp. 144.
4. (a) J. Drouin, M.A. Boaventura, and J.M. Conia. J. Am. Chem.
Soc. 107, 1726 (1985); (b) J. Drouin and M.A. Boaventura. Tet-
rahedron Lett. 28, 3923 (1987); (c) M.A. Boaventura, J. Drouin,
F. Theobald, and N. Rodier. Bull. Soc. Chim. Fr. 1006 (1987);
(d) M.A. Boaventura and J. Drouin. J. Bull. Soc. Chim. Fr. 1015
(1987).
5. (a) C.J. Forsyth and J. Clardy. J. Am. Chem. Soc. 112, 3497
(1990); (b) H. Huang and C.J. Forsyth. J. Org. Chem. 60, 2773
(1995); (c) H. Huang and C.J. Forsyth. J. Org. Chem. 60, 5746
(1995).
6. K. Maeyama and N. Iwasawa. J. Am. Chem. Soc. 120, 1928
(1998).
7. (a) A.J. Frontier, S. Raghavan, and S.J. Danishefsky. J. Am.
Chem. Soc. 119, 6686 (1997); (b) H. Huang and C.J. Forsyth.
J. Org. Chem. 60, 5746 (1995).
Conclusion
We demonstrated for the first time an intramolecular addi-
tion of silyl enol ethers to both terminal and internal unactivated
alkynes by using Lewis acid. While the EtAlCl2-mediated
reaction gave cyclohexenone derivatives, the silyloxy-sub-
stituted cyclic vinylsilanes were produced in the B(C6F5)3-
catalyzed reaction in the presence of Et3SiH. The presented
endo-selective method could be used for the construction of
mono- and bicyclic compounds possessing a cyclohexenone
framework.
8. K.-i. Imamura, E. Yoshikawa, V. Gevorgyan, and Y. Yamamoto.
Tetrahedron Lett. 40, 4081 (1999).
9. (a) N. Asao and Y. Yamamoto. Bull. Chem. Soc. Jpn. 73, 1071
(2000); (b) N. Asao, T. Shimada, and Y. Yamamoto. J. Am.
Chem. Soc. 121, 3797 (1999); (c) K. Imamura, E. Yoshikawa,
V. Gevorgyan, and Y. Yamamoto. J. Am. Chem. Soc. 120,
5339 (1998).
10. (a) D.J. Parks and W.E. Piers. J. Am. Chem. Soc. 118, 9440
(1996); (b) D.J. Parks, J.M. Blackwell, and W.E. Piers. J. Org.
Chem. 65, 3090 (2000).
References
1. (a) I. Ojima, M. Tzamarioudaki, Z. Li, and R.J. Donovan.
Chem. Rev. 96, 635 (1996); (b) R. Grigg and V. Sridharan. In
Comprehensive organometallic chemistry II. Vol. 12. Edited by
E.W. Abel, F.G.A. Stone, and G. Wilinson. Pergamon, Oxford.
1995. pp. 299.
11. N. Petragnani and M. Yonashiro. Synthesis, 521 (1982).
12. P. Brownbridge. Synthesis, 1 (1983).
2. (a) M. Lautens, W. Klute, and W. Tam. Chem. Rev. 96, 49
(1996); (b) T. Harada, T. Otani, and A. Oku. Tetrahedron Lett.
© 2001 NRC Canada