Mechanistic studies on the hydrosilylation of an acetylene cobalt complex; trapping an active catalyst Co2(CO)6 causing olefin-isomerization and O-silylation

Article abstract of DOI:10.1016/S0040-4020(02)00659-2

We have recently reported a hydrosilylation reaction of acetylene cobalt complexes to produce the corresponding vinylsilanes. It has become clear that olefin-isomerization and O-silylation occurred under some hydrosilylation conditions. To avoid these side reactions, we found that hydrosilylation should be carried out in the presence of bis(trimethylsilyl)acetylene. The Co₂(CO)₆, which would cause side reactions, migrates to bis(trimethylsilyl)acetylene to form an acetylene cobalt complex. Mechanisms of olefin-isomerization and O-silylation are also discussed.

Full text of DOI:10.1016/S0040-4020(02)00659-2

Tetrahedron 58 (2002) 6485–6492
Mechanistic studies on the hydrosilylation of an acetylene cobalt
complex; trapping an active catalyst Co2(CO)6 causing
olefin-isomerization and O-silylation
Kazunobu Kira, Hiromichi Tanda, Akinari Hamajima, Takayuki Baba, Shigeyuki Takai
*
and Minoru Isobe
Laboratory of Organic Chemistry, School of Bioagricultural Sciences, Nagoya University, Chikusa, 464-8601 Nagoya, Japan
Received 19 March 2002; revised 5 April 2002; accepted 22 April 2002
This article is dedicated to Professor Yoshito Kishi for his Tetrahedron Prize
Abstract—We have recently reported a hydrosilylation reaction of acetylene cobalt complexes to produce the corresponding vinylsilanes. It
has become clear that olefin-isomerization and O-silylation occurred under some hydrosilylation conditions. To avoid these side reactions,
we found that hydrosilylation should be carried out in the presence of bis(trimethylsilyl)acetylene. The Co2(CO)6, which would cause side
reactions, migrates to bis(trimethylsilyl)acetylene to form an acetylene cobalt complex. Mechanisms of olefin-isomerization and O-silylation
are also discussed. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
hydrosilylation of 1 was conducted with Et3SiH by heating
at 608C in 1,2-dichloroethane. This hydrosilylation reaction
provided the vinylsilanes regioselectively together with an
inseparable mixture of O-silylated 2 (50–80%) and
O-silylated 3 (10–30%), the terminal olefin of the latter
being isomerized into an inner olefin, unexpectedly
(Scheme 1). The alcohol at C-22 was completely silylated
under this condition. If large excess of EtOH was added as a
co-solvent, it was possible to prevent the O-silylation.4 We,
however, could not control the olefin-isomerization at all.
The amounts of the olefin-isomerization were remarkably
dependent on the reaction scale; thus, the larger scale, the
more side reaction.
Biscobalthexacarbonyl complexes of acetylenes are becom-
ing increasingly important in synthetic organic chemistry,
not only as protection of intermediate-triple bonds1 but also
as bond formation reactions,2 and sometimes as a key step in
natural product synthesis.3 We have already reported a
reductive decomplexation of these acetylene cobalt com-
plexes with trialkylsilane to produce the corresponding
vinylsilanes (hydrosilylation).4 From our recent research, it
became clear that some side reactions, such as olefin-
isomerization and O-silylation, occurred during this hydro-
silylation. In the current paper, we propose several
conditions for hydrosilylation in the presence of bis(tri-
methylsilyl)acetylene to avoid the side reactions. Mechan-
isms of the side reactions are also discussed.
It is known that the reaction of R3SiH with Co2(CO)8 takes
place smoothly even at room temperature to give HCo(CO)4
and R3SiCo(CO)4 (step a in the following equation).8,9 In
the presence of excess amount of R3SiH, HCo(CO)4 reacts
with R3SiH to give R3SiCo(CO)4 and molecular hydrogen
(step b).
In our synthetic studies5 on Ciguatoxin6 (CTX-1B), the
hydrosilylation of acetylene cobalt complex 1 occasionally
turned out to be problematic in larger scales;7 thus,
Scheme 1.
Keywords: acetylene cobalt complex; hydrosilylation; olefin-isomerization; O-silylation; bis(trimethylsilyl)acetylene.
*
Corresponding author. Tel.: þ81-52-789-4109; fax: þ81-52-789-4111; e-mail: isobem@agr.nagoya-u.ac.jp
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00659-2

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K. Kira et al. / Tetrahedron 58 (2002) 6485–6492
Scheme 2.
reactions, HCo(CO)4 and R3SiCo(CO)4 play important
roles.
On the basis of these published reports, we made a working
hypothesis of the olefin-isomerization and O-silylation
during the hydrosilylation as shown in Scheme 2. The
hydrosilylation of acetylene cobalt complex 1 generated a
desired vinylsilane 4 and Co2(CO)6 species A (step c in
Scheme 2). This species A was assumed to be the active
catalyst of the catalytic hydrosilylation reactions13
(Scheme 3) and to be identical with the active species of
catalytic Pauson–Khand reactions.14 This A reacted with
Et3SiH to give HCo(CO)3 B and Et3SiCo(CO)3 C (step d in
Scheme 2). It is likely that the olefin-isomerization should
occur by B (step e, insertion and b-elimination) and the
O-silylation by C (step f). It would be possible to diminish
the side reactions (O-silylation and olefin-isomerization) by
trapping the Co2(CO)6 A with additives (step g).
Scheme 3.
2. Results and discussion
Many reactions have been reported to occur under
various combinations of Co2(CO)8 and R3SiH; for
example, hydrosilylation of olefins,8,10 O-silylation,11
isomerization8,12 and polymerization.11,12 In these
We became interested in finding some trapping reagents of
the Co2(CO)6 A to avoid these side reactions with a simpler
model compound 12, which possessed the same endo-cobalt
Scheme 4. (a) CBr4, PPh3/CH2Cl2; (b) EVE, PPTS/CH2Cl2, 82% in 2 steps; (c) 10, nBuLi/THF then hydrocinnamaldehyde; (d) Amberlyst-15E/MeOH, 76% in
2 steps; (e) Co2(CO)8/CH2Cl2 then BF3·OEt2 94%. EVE¼ethyl vinyl ether, PPTS¼pyridinium p-toluenesulfonate.

K. Kira et al. / Tetrahedron 58 (2002) 6485–6492
6487
Table 1.
Entry
Et3SiH
Additive
Time (h)
Yield (%)
12 (recovery)
13
14
15
1
2
3
4
5
6
7
8
5 equiv.
5 equiv.
1.3 equiv.
5 equiv.
4 equiv.
3 equiv.
2 equiv.
6 equiv.
2 equiv.
4 equiv.
5 equiv.
5 equiv.
2 equiv.
None
None
None
2
24
24
2
1.5
24
2.5
2
–
–
18
–
–
–
28
16
26
–
–
–
77
–
19
–
53
9
–
–
–
64
–
–
–
–
80
–
–
–
–
–
–
–
–
–
–
–
18
90
86
92
64
16
64
94
90
95
96
16 (50 equiv.)
17 (6 equiv.)
17 (6 equiv.)
17 (4 equiv.)
17 (3 equiv.)
18 (4 equiv.)
18 (6 equiv.)
19 (2 equiv.)
19 (2 equiv.)
19 (1.1 equiv.)
9
2
10
11
12
13
2.5
1.5
24
2
–
–
–
complex and terminal olefin. This model 12 was synthesized
as summarized in Scheme 4. The aldehyde 97 was converted
into dibromoolefin 10.15 Treatment of the dibromoolefin 10
with 2.2 equiv. of n-BuLi generated the corresponding
acetylide, which was mixed with hydrocinnamaldehyde to
give the coupling product. After deprotection of the
hydroxyl group, it was successively treated with Co2(CO)8
and then BF3·OEt2 in one-pot to afford the cyclization
With the model compound 12 in hand, hydrosilylation was
performed under various conditions to check whether the
side reactions took place or not in the presence of additives.
The results are summarized in Table 1. When the reaction
was run without any additive and interrupted after 2 h, the
products were a mixture of the vinylsilane 13 and its isomer
14 (entry 1), while when the reaction was prolonged to 24 h,
the product was exclusive to give 15 (entry 2). It was
expected that 14 might transform into 15 by the partici-
pation of large excess Et3SiH. In fact, when small excess
Et3SiH (1.3 equiv.) was added to the cobalt complex 12, 15
was not observed (entry 3). Next, large excess 1-hexene 16
was added as a dummy terminal olefin to prevent the
isomerization of 13, but the olefin-isomerization reaction
was only partly diminished (entry 4). These results showed
the importance of trapping the active species A to prevent
the primary product 13 from isomerization. As a candidate
to trap A, propargyl alcohol 17 was chosen to add to the
reaction mixture. This choice turned out to be right; addition
of 17 prevented 13 from the isomerization completely, even
though the reaction was prolonged to 24 h (entries 5, 6). It is
noteworthy that the vinylsilane (22, 23) was derived from
the trapping reagent 17 to be isolated (Scheme 5). The
formation of these vinylsilanes (22, 23) suggested that
reagent 17 could trap the active species A (step i in
Scheme 5), then cobalt complex 20 also hydrosilylated into
vinylsilane 22 or 23 (step j). Since Et3SiH was consumed by
20 (step j), more than 3 equiv. of Et3SiH is necessary to
complete the reaction (entry 7 in Table 1); thus, the
competition between step h and step j. Apparently, it was
necessary to add more excess trapping reagent 17 than
Et3SiH to stop the isomerization and to complete the
reaction (entry 8). If the rate of step j is much slower than
product 12 as
relationship.16
a single stereoisomer having syn
Scheme 5.

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K. Kira et al. / Tetrahedron 58 (2002) 6485–6492
Table 2.
Entry
7 (equiv.)
Et3SiH (equiv.)
Additive
24/25
1
2
3
4
5
6
7
1
1
1
1
2
4
10
1
1
–
–
–
–
–
50:50
0:100
21:79
55:45
18:82
0:100
100:0
1
0.5
0.5
0.5
Scheme 6.
EtOH (5 equiv.)
19 (2 equiv.)
1
step h, it would be possible to complete the reaction with
less than 3 equiv. of Et3SiH. Then sterically hindered
2-methyl-3-butyn-2-ol 18 was selected as a trapping reagent
because of its slower reactivity with Et3SiH. Although 18
was effective to stop the isomerization, it was still necessary
to add more than 4 equiv. of Et3SiH to complete the reaction
as the same efficiency as 17 (entries 9, 10). Finally, a much
bulky acetylene, bis(trimethylsilyl)acetylene 19 was the
best choice as a trapping reagent because of our recent
finding that it would be difficult to hydrosilylate the cobalt
complex 21 into vinylsilane (Scheme 6, step l). The effect of
bis(trimethylsilyl)acetylene 19 as trapping reagent was
almost perfect as shown in short or long reaction time
(entries 11–13). There was no side product under this
condition. It is noted that cobalt complex 21, which came
from the trapping reagent 19, was isolated from the reaction
mixture. It means that the Co2(CO)6 in 12 migrates to 19 to
form cobalt complex 21.17 This cobalt complex 21 provided
strong evidence for the existence of the active species
Co2(CO)6 A.
than 11 mmol scale under this condition. In this scale, we
were successful in getting 4 (94% yield) along with 21 (86%
yield of the theoretical value). Since 21 is a nonpolar
compound, it is easy to separate 4 from 21 by silica gel
column chromatography.
Thus, we could successfully control the side reactions using
trapping reagents, and our attention was turned to the
mechanisms of these side reactions. To investigate the
validity of this olefin-isomerization mechanism (Scheme 2,
working hypothesis), subsequent experiments were carried
out with a simple terminal olefin 24. For this propose,
acetylene cobalt complex 713,14 was selected as a source of
Co2(CO)6 A due to the fact that 7 is easy to prepare and is
shelf stockable crystal. The results are summarized in
Table 2. Under these conditions, olefin-isomerization went
on to give 25 in quantitative yield as a mixture of olefin-
regioisomers. At first, an effect of Et3SiH/7 ratio was
examined (entries 1–4). Taking into account the supposed
mechanism of isomerization in Scheme 8, 2 mol of Et3SiH
to 1 mol of 7 would be a best ratio to generate the HCo(CO)3
B (steps m and n) that is supposed to be a real catalyst of
olefin-isomerization. Actually, the olefin-isomerization
under that condition (Et3SiH/7¼2) is faster than other
ratio (entry 2). If the ratio Et3SiH/7 is more than 2, part of
HCo(CO)3 B is supposed to transform into Et3SiCo(CO)3 C
(step o). Next, EtOH was added to transform Et3SiCo(CO)3
C into HCo(CO)3 B (step p, R¼Et). As compared with
entry 5, adding EtOH surely accelerate the isomerization
We employed this condition for the synthesis of the desired
vinylsilane 4 (Scheme 7). It was clear that the trapping
reagent 19 played important roles in stopping the side
reactions. No olefin-isomerization and O-silylation were
observed. In spite of our previous report,4 EtOH was not
necessary as a co-solvent to prevent the alcohol at C-22
from O-silylation because of the presence of a trapping
reagent. This result indicated that the O-silylation also
occurred by the participation of Co2(CO)6 A. Until now, this
hydrosilylation reaction was performed in a higher scale
Scheme 7.

K. Kira et al. / Tetrahedron 58 (2002) 6485–6492
6489
Scheme 8.
Scheme 9.
(entry 6). It should be noted that these isomerization did not
occur at all if bis(trimethylsilyl)acetylene 19 was added
(entry 7). These results would support the working
hypothesis. It appears that HCo(CO)3 B is unstable species
at 608C, because the olefin-isomerization gradually became
slow with the elapsing of time and finally stopped.
3. Experimental
3.1. General
Infrared spectra (IR) were recorded on a JASCO FT/IR-
8300 spectrophotometer and are reported in wave number
(cm21). Proton nuclear magnetic resonance (1H NMR)
spectra were recorded on Brucker ARX-400 (400 MHz) and
Varian Gemini-2000 (300 MHz) spectrometers. Carbon
nuclear magnetic resonance (13C NMR) spectra were
recorded on Brucker ARX-400 (100 MHz) and Varian
Gemini-2000 (75 MHz) spectrometers. Optical rotations
were measured on a JASCO DIP-370 digital polarimeter.
Mass spectra were recorded on a Micromass Q-TOF (ESI),
and are reported in m/z. Elemental analyses were performed
by Analytical Laboratory at School of Bioagricultural
Sciences, Nagoya University. Reactions were monitored
by thin-layer chromatography carried out on 0.25 mm silica
gel coated glass plates 60F254 (Cica Merck, Art 1.05715)
using UV light as visualizing agent and 7% ethanolic
phosphomolybdic acid, or p-anisaldehyde solution as
developing agents. Cica Merck silica gel 60 (particle size
0.063–0.2 mm ASTM) was used for open-column chroma-
tography. Unless otherwise noted, nonaqueous reactions
were conducted in oven-dried (2008C) or flame-dried
glassware under inert atmosphere of dry nitrogen or argon.
Dry THF was distilled from potassium metal with benzo-
phenone. Dry CH2Cl2 was distilled from CaH2 under nitrogen
atmosphere. BF3·OEt2 were distilled from CaH2. All other
commercially available reagents were used as received.
Hyflo Super-Celw (nacalai tesque) was used as filter aid.
Subsequent experiments were carried out to investigate the
validity of the O-silylation mechanism (Scheme 2). If the
working hypothesis is correct, this condition would be
applicable to 7 for a catalytic O-silylation (Scheme 8, step
p). For this propose, 1.5 equiv. of Et3SiH and 2 mol% of 7
was added to geraniol 26 in 1,2-dichloroethane at 608C to
generate the Et3SiCo(CO)3 C that was supposed to be a real
catalyst of O-silylation. In this case, excess Et3SiH would
transform HCo(CO)3 B into Et3SiCo(CO)3 C (step o). As we
expected, 7 catalyzed O-silylation proceeded to give 27
(Scheme 9). It is noteworthy that O-silylation did not occur
at all if bis(trimethylsilyl)acetylene 19 was added. These
results also support the working hypothesis.
Thus, we have successfully developed a hydrosilylation
reaction of an acetylene cobalt complex in the presence of a
trapping reagent of the active species A. Although
bis(trimethylsilyl)acetylene 19 is recommended as the
trapping reagent, cheaper acetylenic additives 17 and 18
were also effective to stop the side reactions. The formation
of the cobalt complex 21 should provide the evidence that
the active species A should be ‘Co2(CO)6’. Further studies
on the improvement and limitation of 7 catalyzed olefin-
isomerization and O-silylation are now in progress.

6490
K. Kira et al. / Tetrahedron 58 (2002) 6485–6492
3.1.1. Dibromoolefin (10). To a solution of CBr4 (5.78 g,
17.4 mmol) in 24 mL of CH2Cl2 was added a solution of
PPh3 (9.14 g, 34.8 mmol) in 10 mL of CH2Cl2 at 08C. After
stirring for 10 min at 08C, aldehyde 9 (2.04 g, 4.36 mmol) in
10 mL of CH2Cl2 was added and the resulting mixture was
stirred for 30 min at 08C. Then the reaction mixture was
poured into an ice-cold sat. NaHCO3 solution and extracted
with CH2Cl2 (£2). The combined extract was washed with
brine, dried over Na2SO4, and concentrated in vacuo, which
was filtered through a silica gel short column.
(1H, d, J¼1.5 Hz, –OH ), 2.22–2.34 (1H, m, H-8a), 2.53
(1H, dm, J¼17.0 Hz, H-14a), 2.57–2.62 (1H, m, H-8b),
2.68 (1H, dm, J¼17.0 Hz, H-14b), 2.79 (2H, t, J¼8.0 Hz,
H-19a, 19b), 3.26–3.53 (5H, m, H-9, 10, 11, 12, 13), 4.35
(1H, br, H-17), 4.66 (1H, d, J¼11.0 Hz, –OCH2Ph), 4.75
(1H, d, J¼11.0 Hz, –OCH2Ph), 4.86 (1H, d, J¼11.0 Hz,
–OCH2Ph), 4.96 (1H, d, J¼11.0 Hz, –OCH2Ph), 5.02 (1H,
dm, J¼10.0 Hz, H-6a), 5.09 (1H, dm, J¼17.0 Hz, H-6b),
5.92 (1H, ddt, J¼17.0, 10.0, 6.0 Hz, H-7), 7.16–7.38 (15H,
m, aromatic). 13C NMR (CDCl3, 75 MHz) d 22.3, 31.3,
35.7, 39.4, 61.9, 73.4, 75.0, 75.3, 76.9, 78.6, 81.5, 81.8,
82.8, 86.6, 117.1, 126.0, 127.9, 128.0, 128.4, 128.6, 128.7,
134.6, 138.1, 138.5, 141.5. Anal. Calcd for C34H38O5: C,
77.54; H, 7.27. Found: C, 77.53; H, 7.29.
To a solution of the above dibromoolefin in 44 mL of
CH2Cl2 were successively added ethyl vinyl ether (1.25 mL,
13.1 mmol) and pyridinium p-toluenesulfonate (50 mg).
After stirring for 6 h at room temperature, the reaction
mixture was poured into an ice-cold sat. NaHCO3 solution.
The resulting mixture was extracted with CH2Cl2 (£2). The
combined extract was dried over Na2SO4, and concentrated
under reduced pressure. The residue was purified by silica
gel column chromatography (ethyl acetate/hexane¼5:95)
to give the dibromoolefin 10 (2.21 g, 82% in 2 steps). IR
(KBr) nmax 2980, 2900, 2360, 1498, 1455, 1359, 1121,
3.1.3. Cyclic acetylene cobalt complex (12). To a solution
of the diol 11 (489 mg, 0.93 mmol) in 47 mL of CH2Cl2 was
added a solution of Co2(CO)8 (635 mg, 1.86 mmol) in
3.0 mL of CH2Cl2. After stirring for 30 min at room
temperature, BF3·OEt2 (0.12 mL, 0.93 mmol) was added
at 08C. After stirring for 15 min at 08C, the reaction mixture
was poured into an ice-cold sat. NaHCO3 solution and
extracted with CH2Cl2 (£3). The combined extract was
washed with brine, dried over Na2SO4, and concentrated in
vacuo. The residue was purified by silica gel column
chromatography (ethyl acetate/hexane¼5:95) to give 12
(686 mg, 93%) as a dark red oil. [a]2D7¼2728 (c 0.155,
CHCl3). IR (KBr) nmax 2360, 2343, 2094, 2053, 2026, 1085,
1
1090, 1056, 1028, 993, 735, 698 cm21. H NMR (CDCl3,
300 MHz)
d
1.06, 1.21 (total 3H, t, J¼7.0 Hz,
–OCH2CH3), 1.24, 1.35 (total 3H, d, J¼5.0 Hz,
–OCH(O)CH3), 2.16–2.29 (2H, m, H-8a, 14a), 2.51–2.63
(1H, m, H-8b), 2.76 (1H, ddd, J¼16.0, 7.5, 3.0 Hz, H-14b),
3.18–3.62 (6H, m, H-9, 10, 11, 12, 13, –OCH2CH3), 3.82,
3.89 (total 1H, q, J¼7.0 Hz, –OCH2CH3), 4.61, 4.63 (total
1H, d, J¼11.0 Hz, –OCH2Ph), 4.75–5.03 (4H, m,
–OCH(CH3)O–, –OCH2Ph, –OCH2Ph, –OCH2Ph), 5.08
(1H, dm, J¼12.0 Hz, H-6a), 5.09 (1H, dm, J¼16.0 Hz,
H-6b), 5.80–5.96 (1H, m, H-7), 6.55 (1H, ddd, J¼7.0, 6.0,
1.0 Hz, H-15), 7.22–7.39 (10H, m, aromatic). 13C NMR
(CDCl3, 75 MHz) d 15.2, 15.4, 20.5, 21.2, 35.6, 35.7, 35.8,
61.7, 63.1, 75.1, 75.3, 75.5, 77.2, 78.0, 78.5, 78.8, 81.8,
82.0, 86.0, 87.2, 89.4, 101.6, 101.7, 117.1, 117.2, 127.4,
127.5, 127.6, 127.7, 127.9, 128.3, 128.5, 134.6, 134.9,
135.8, 138.1, 138.5. Anal. Calcd for C29H36Br2O5: C, 55.78;
H, 5.81. Found: C, 55.78; H, 5.80.
1
698, 519 cm21. H NMR (CDCl3, 400 MHz) d 2.08 (1H,
ddt, J¼13.0, 9.5, 6.5 Hz, H-18a), 2.19 (1H, ddt, J¼13.0,
9.5, 6.5 Hz, H-18b), 2.20–2.26 (1H, m, H-8a), 2.55–2.62
(1H, m, H-8b), 2.84 (2H, td, J¼9.5, 6.5 Hz, H-19a, 19b),
2.92 (1H, dd, J¼16.0, 9.0 Hz, H-14a), 3.31 (1H, t,
J¼9.0 Hz, H-10), 3.32–3.34 (1H, m, H-9), 3.42 (1H, td,
J¼9.0, 4.5 Hz, H-13), 3.49 (1H, t, J¼9.0 Hz, H-12), 3.63
(1H, dd, J¼16.0, 4.5 Hz, H-14b), 3.64 (1H, t, J¼9.0 Hz,
H-11), 4.53 (1H, t, J¼6.5 Hz, H-17), 4.64 (1H, d,
J¼11.0 Hz, –OCH2Ph), 4.87 (2H, d, J¼11.0 Hz,
–OCH2Ph), 4.99 (1H, d, J¼11.0 Hz, –OCH2Ph), 5.08
(1H, dm, J¼7.0 Hz, H-6a), 5.09 (1H, dm, J¼17.5 Hz,
H-6b), 5.88 (1H, ddt, J¼17.5, 10.0, 7.0 Hz, H-7), 7.26–
7.40 (15H, m, aromatic). 13C NMR (CDCl3, 100 MHz) d
32.2, 36.0, 39.1, 39.4, 75.0, 75.7, 76.0, 77.9, 81.1, 81.6,
85.9, 87.9, 93.9, 101.4, 117.2, 126.0, 127.5, 127.6, 127.7,
127.8, 128.2, 128.4, 134.6, 138.2, 138.8, 141.4, 199.1,
199.5. ESI Q-TOF MS calcd for C40H37Co2O10 [MþH]þ
795.105, found 795.107.
3.1.2. Diol (11). To a solution of the dibromoolefin 10
(1.27 g, 2.04 mmol) in 20 mL of THF was added a solution
of n-BuLi (1.59 M in hexane, 2.94 mL, 4.68 mmol) at
2788C. After stirring for 15 min at 2788C, hydro-
cinnamaldehyde (0.32 mL, 2.65 mmol) in 2.7 mL of THF
was added and the resulting mixture was stirred for 60 min
at 278 to 08C. Then the reaction mixture was poured into an
ice-cold sat. NH4Cl solution and extracted with ether (£3).
The combined extract was washed with brine, dried over
Na2SO4, and concentrated in vacuo.
3.1.4. Vinylsilane (13); hydrosilylation in the presence of
bis(trimethylsilyl)acetylene. To a solution of the acetylene
cobalt complex 12 (39.2 mg, 49.3 mmol) and bis(trimethyl-
silyl)acetylene (22.3 mL, 98.6 mmol) in 0.5 mL of 1,2-
dichloroethane was added Et3SiH (39.4 mL, 0.25 mmol).
After stirring for 1.5 h at 608C, the reaction mixture was
concentrated under reduced pressure. The residue was
purified by silica gel column chromatography (ethyl
acetate/hexane¼5:95) to give the vinylsilane 13 (30.8 mg,
99%). [a ]2D4¼þ298 (c 0.48, CHCl3). IR (KBr) nmax 2361,
To a solution of the above coupling product in 20 mL of
MeOH was added Amberlyst-15E (300 mg). After stirring
for 90 min at room temperature, the reaction mixture was
filtered through a pad of Super-Celw, the resin was washed
thoroughly with ethyl acetate. The filtrate was concentrated
in vacuo. The residue was purified by silica gel column
chromatography (ethyl acetate/hexane¼30:70) to give 11
(0.82 g, 76% in 2 steps). IR (KBr) nmax 3406, 2913, 2862,
1643, 1604, 1497, 1455, 1359, 1087, 1028, 1002, 915, 750,
737, 699 cm21. 1H NMR (CDCl3, 300 MHz) d 1.79 (1H, d,
J¼5.0 Hz, –OH ), 1.94–2.06 (2H, m, H-18a, 18b), 2.18
1
2343, 2054, 1600, 1508, 1457, 1087, 697, 669 cm21. H
NMR (CDCl3, 400 MHz) d 0.61 (6H, q, J¼8.0 Hz,
–SiCH2CH3), 0.93 (9H, t, J¼8.0 Hz, –SiCH2CH3), 1.89
(1H, dddd, J¼14.0, 9.0, 7.0, 5.0 Hz, H-18a), 2.03 (1H, dtd,
J¼14.0, 9.0, 5.5 Hz, H-18b), 2.25 (1H, m, H-8a), 2.47–2.60

K. Kira et al. / Tetrahedron 58 (2002) 6485–6492
6491
(3H, m, H-8b, 14a, 14b), 2.73 (1H, ddd, J¼14.0, 9.0,
7.0 Hz, H-19a), 2.82 (1H, ddd, J¼14.0, 9.0, 5.5 Hz, H-19b),
2.98 (1H, ddd, J¼10.0, 8.5, 3.0 Hz, H-13), 3.32 (1H, t,
J¼8.5 Hz, H-10), 3.33–3.37 (1H, m, H-9), 3.54 (1H, t,
J¼8.5 Hz, H-12), 3.64 (1H, t, J¼8.5 Hz, H-11), 4.00 (1H,
dt, J¼9.0, 5.0 Hz, H-17), 4.12 (1H, d, J¼11.0 Hz,
–OCH2Ph), 4.32 (1H, d, J¼11.0 Hz, –OCH2Ph), 4.40
(1H, d, J¼11.0 Hz, –OCH2Ph), 5.05 (1H, dm, J¼10.0 Hz,
H-6a), 5.07 (1H, dm, J¼17.0 Hz, H-6b), 5.08 (1H, d,
J¼11.0 Hz, –OCH2Ph), 5.89 (1H, ddt, J¼17.0, 10.0,
6.0 Hz, H-7), 6.07 (1H, dd, J¼5.0, 2.5 Hz, H-16), 7.13–
7.38 (15H, m, aromatic). 13C NMR (CDCl3, 100 MHz) d
2.5, 7.5, 31.8, 36.0, 36.3, 37.8, 75.0, 75.2, 75.9, 78.4, 81.4,
85.6, 88.6, 116.8, 125.8, 127.5, 127.6, 127.7, 127.9, 128.4,
128.5, 134.7, 138.5, 138.9, 140.5, 141.9, 146.6. Anal. Calcd
for C40H52O4Si: C, 76.88; H, 8.39. Found: C, 76.89; H, 8.51.
139.0, 140.7, 142.0, 146.6. ESI Q-TOF MS calcd for
C40H54O4SiNa [MþNa]þ 649.369, found 649.373.
3.1.7. Vinylsilane (4) and acetylene cobalt complex (21);
hydrosilylation in the presence of bis(trimethylsilyl)-
acetylene. To a solution of the acetylene cobalt complex 1
(8.42 g, 10.6 mmol) and bis(trimethylsilyl)acetylene
(4.82 mL, 21.3 mmol) in 200 mL of 1,2-dichloroethane
was added Et3SiH (8.46 mL, 53.0 mmol). After stirring for
2 h at 608C, the reaction mixture was filtered through Super-
Celw and concentrated under reduced pressure. The residue
was purified by silica gel column chromatography
(hexane¼100) to give the acetylene cobalt complex 21
(4.17 g, 86%) and (ethyl acetate/hexane¼25:75) to give the
vinylsilane 4 (6.28 g, 94%)
Acetylene cobalt complex 21: IR (KBr) nmax 2085, 2042,
2015, 1544, 1249, 839, 521. 1H NMR (CDCl3, 300 MHz) d
0.29 (18H, s, –CH3). 13C NMR (CDCl3, 75 MHz) d 0.9,
92.8, 201.0. Anal. Calcd for C14H18O6Co2: C, 36.85; H,
3.98. Found: C, 36.91; H, 3.97.
3.1.5. Vinylsilane olefin isomer (14). [a]2D4¼þ438 (c 0.55,
CHCl3). IR (KBr) nmax 2951, 2904, 2873, 2360, 2343, 1560,
1
1498, 1455, 1087, 1029, 748, 736, 698 cm21. H NMR
(CDCl3, 300 MHz) d 0.60 (6H, q, J¼8.0 Hz, –SiCH2CH3),
0.92 (9H, t, J¼8.0 Hz, –SiCH2CH3), 1.74 (3H, d, J¼7.5,
1.5 Hz, –CH3), 1.84–1.95 (1H, m, H-18a), 1.98–2.20 (1H,
m, 18b), 2.48 (1H, ddd, J¼14.5, 9.0, 2.0 Hz, H-14a), 2.60
(1H, dd, J¼14.5, 2.5 Hz, H-14b), 2.68–2.90 (2H, m, H-19a,
19b), 3.04 (1H, td, J¼9.0, 2.5 Hz, H-13), 3.31 (1H, t,
J¼9.0 Hz, H-10), 3.53 (1H, t, J¼9.0 Hz, H-9), 3.63 (1H, t,
J¼9.0 Hz, H-12), 3.72 (1H, t, J¼9.0 Hz, H-11), 3.98 (1H,
dt, J¼9.0, 4.5 Hz, H-17), 4.61 (1H, d, J¼11.0 Hz,
–OCH2Ph), 4.76 (1H, d, J¼11.0 Hz, –OCH2Ph), 4.85
(1H, d, J¼11.0 Hz, –OCH2Ph), 5.05 (1H, d, J¼11.0 Hz,
–OCH2Ph), 5.44 (1H, ddd, J¼15.0, 7.5, 1.5 Hz, H-8), 5.87
(1H, dq, J¼15.0, 7.5 Hz, H-7), 6.07 (1H, dd, J¼4.5,
2.0 Hz, H-16), 7.13–7.40 (15H, m, aromatic). 13C NMR
(CDCl3, 75 MHz) d 2.3, 7.4, 18.0, 31.7, 36.4, 37.8, 74.9,
75.1, 76.1, 76.7, 80.2, 82.3, 84.9, 88.3, 125.8, 127.5, 127.7,
127.9, 128.2, 128.4, 128.6, 128.8, 130.9, 138.4, 139.0,
140.3, 142.0, 146.9. Anal. Calcd for C40H52O4Si: C, 76.88;
H, 8.39. Found: C, 76.89; H, 8.64.
Vinylsilane 4: [a ]D24¼þ218 (c 0.57, CHCl3). IR (KBr) nmax
3484, 3067, 3032, 2953, 2908, 2874, 2053, 2028, 1456,
1
1362, 1327, 1074, 1029, 1003, 913, 733, 698 cm21. H
NMR (CDCl3, 400 MHz) d 0.63 (6H, q, J¼7.5 Hz,
–SiCH2CH3), 0.95 (9H, t, J¼7.5 Hz, –SiCH2CH3), 1.58
(1H, q, J¼11.5 Hz, H-14a), 1.83 (1H, ddt, J¼14.5, 6.5,
4.0 Hz, H-21a), 1.95 (1H, dddd, J¼14.5, 9.5, 6.5, 4.5 Hz,
H-21b), 2.25 (1H, dt, J¼14.5, 7.5 Hz, H-8a), 2.37 (1H, dt,
J¼11.5, 4.0 Hz, H-14b), 2.50–2.60 (2H, m, H-8b, 17a),
2.62 (1H, dd, J¼14.5, 3.0 Hz, H-17b), 2.98 (1H, ddd,
J¼11.5, 8.5, 3.0 Hz, H-16), 3.12 (1H, t, J¼8.5 Hz, H-12),
3.12–3.16 (1H, m, H-13), 3.28 (1H, dd, J¼9.5, 8.5 Hz,
H-10), 3.37 (1H, ddd, J¼9.5, 7.5, 3.0 Hz, H-9), 3.51 (1H,
ddd, J¼11.5, 8.5, 4.5 Hz, H-15), 3.60 (1H, t, J¼8.5 Hz,
H-11), 3.78–3.82 (2H, m, H-22a, 22b), 4.24 (1H, ddd,
J¼9.5, 4.5, 4.0 Hz, H-20), 4.62 (1H, d, J¼11.0 Hz,
–OCH2Ph), 4.75 (1H, d, J¼11.5 Hz, –OCH2Php), 4.93
(1H, d, J¼11.0 Hz, –OCH2Ph), 4.95 (1H, d, J¼11.5 Hz,
–OCH2Php), 5.05 (1H, dm, J¼10.5 Hz, H-6a), 5.07 (1H,
dm, J¼17.5 Hz, H-6b), 5.86 (1H, dddd, J¼17.5, 10.5,
7.5, 6.5 Hz, H-7), 6.02 (1H, dd, J¼4.5, 2.5 Hz, H-19),
7.26–7.38 (10H, m, aromatic). 13C NMR (CDCl3,
75 MHz) d 2.3, 7.4, 35.9, 36.5, 37.0, 37.9, 60.9, 73.9,
75.1, 75.2, 78.9, 80.9, 82.5, 82.9, 84.2, 117.1, 127.8, 128.0,
128.2, 128.4, 128.5, 134.6, 139.4, 138.8, 141.2, 145.9. Anal.
Calcd for C37H52O6Si: C, 71.57; H, 8.44. Found: C, 71.57;
H, 8.58.
3.1.6. Vinylsilane saturated olefin (15). [a]2D6¼þ268 (c
0.67, CHCl3). IR (KBr) nmax 2955, 2910, 2874, 2360, 2343,
2054, 2029, 1498, 1456, 1074, 1029, 1005, 733, 696 cm21
.
1H NMR (CDCl3, 300 MHz) d 0.59 (6H, q, J¼8.0 Hz,
–SiCH2CH3), 0.87–0.93 (3H, m, –CH3), 0.92 (9H, t,
J¼8.0 Hz, –SiCH2CH3), 1.30–1.41 (1H, m, H-8a), 1.47–
1.57 (2H, m, H-7a, 7b), 1.72–1.79 (1H, m, H-8b), 1.88 (1H,
dddd, J¼14.0, 9.5, 7.0, 4.5 Hz, H-18a), 2.04 (1H, dtd,
J¼14.0, 9.0, 5.5 Hz, H-18b), 2.48 (1H, ddd, J¼14.5, 9.5,
2.5 Hz, H-14a), 2.55 (1H, dd, J¼14.5, 3.5 Hz, H-14b), 2.72
(1H, ddd, J¼14.0, 9.0, 7.0 Hz, H-19a), 2.82 (1H, ddd,
J¼14.0, 9.5, 5.5 Hz, H-19b), 2.96 (1H, td, J¼9.5, 3.5 Hz,
H-13), 3.19–3.23 (1H, m, H-9), 3.24 (1H, t, J¼9.0 Hz,
H-10), 3.54 (1H, t, J¼9.0 Hz, H-12), 3.62 (1H, t, J¼9.0 Hz,
H-11), 3.98 (1H, dt, J¼9.0, 4.5 Hz, H-17), 4.61 (1H, d,
J¼11.0 Hz, –OCH2Ph), 4.81 (1H, d, J¼11.0 Hz,
–OCH2Ph), 4.89 (1H, d, J¼11.0 Hz, –OCH2Ph), 5.07
(1H, d, J¼11.0 Hz, –OCH2Ph), 6.06 (1H, dd, J¼4.5,
2.5 Hz, H-16), 7.03–7.42 (15H, m, aromatic). 13C NMR
(CDCl3, 75 MHz) d 2.5, 4.5, 6.5, 7.4, 14.0, 18.7, 31.8, 34.0,
36.5, 37.8, 74.8, 75.1, 75.2, 75.9, 76.5, 78.8, 82.4, 85.7,
88.8, 125.8, 127.4, 127.6, 127.8, 127.9, 128.3, 128.5, 138.5,
3.1.8. Decene-1-ol olefin iosmers (25). To a solution of the
olefin 24 (21.1 mg, 87.8 mmol) in 1.8 mL of 1,2-dichloro-
ethane were added Et3SiH (28 mL, 0.18 mmol) and
acetylene cobalt complex 7 (32.5 mg, 87.8 mmol). After
stirring for 1 h at 608C, the reaction mixture was filtered
through Super-Celw and concentrated under reduced
pressure. The residue was purified by silica gel column
chromatography (ether/hexane¼1:20) to give the olefine-
isomers 25 (20.4 mg, 97%). IR (KBr) nmax 2929, 2856,
1
1455, 1201, 1138, 1121, 1079, 1035, 966, 870 cm21. H
NMR (CDCl3, 300 MHz) d 1.20–2.10 (22H, m, –CH2–),
3.38 (1H, dt, J¼9.5, 7.0 Hz, –OCH2–), 3.46–3.54 (1H, m,
–OCH2–), 3.73 (1H, dt, J¼9.5, 7.0 Hz, –OCH2–), 3.83–

6492
K. Kira et al. / Tetrahedron 58 (2002) 6485–6492
Synlett 2000, 587. (f) Liu, T.-Z.; Isobe, M. Tetrahedron 2000,
56, 5391. (g) Liu, T.-Z.; Li, J.-M.; Isobe, M. Tetrahedron
2000, 56, 10209. (h) Kira, K.; Isobe, M. Tetrahedron Lett.
2000, 41, 5951. (i) Saeeng, R.; Isobe, M. Heterocycles 2001,
54, 789. (j) Kira, K.; Isobe, M. Chem. Lett. 2001, 432. (k) Kira,
K.; Hamajima, A.; Isobe, M. Tetrahedron 2002, 58, 1875. (l)
Takai, S.; Isobe, M. Org. Lett. 2002, 4, 1183.
3.92 (1H, m, –OCH2), 4.57 (1H, dd, J¼4.5, 3.0 Hz,
–OCH(CH2–)–O–), 5.30–5.50 (2H, m, olefinic). 13C
NMR (CDCl3, 75 MHz) d 17.8, 19.6, 25.4, 26.1, 26.7,
29.0, 29.1, 29.3, 29.5, 29.7, 30.7, 32.5, 62.3, 67.7, 98.9,
123.7, 124.6, 130.9, 131.7.
3.1.9. Silyl ether (27). To a solution of geraniol 26 (227 mg,
1.47 mmol) in 3.8 mL of 1,2-dichloroethane were added
Et3SiH (0.35 mL, 2.20 mmol) and acetylene cobalt complex
7 (10.9 mg, 29.4 mmol). After stirring for 2 h at 608C, the
reaction mixture was concentrated under reduced pressure.
The residue was purified by silica gel column chromato-
graphy (ether/hexane¼1:20) to give 27 (344 mg, 87%). IR
(KBr) nmax 2956, 2937, 2913, 2877, 1458, 1379, 1239,
6. Structural studies: (a) Scheuer, P. J.; Takahashi, W.; Tsutsumi,
J.; Yoshida, T. Science 1967, 155, 1267. (b) Tachibana,
K. Ph.D. Thesis, University of Hawaii, 1980. (c) Nukina, M.;
Koyanagi, L. M.; Scheuer, P. J. Toxicon 1984, 22, 169.
(d) Murata, M.; Lebrand, A. M.; Ishibashi, Y.; Yasumoto, T.
J. Am. Chem. Soc. 1989, 111, 8929. (e) Murata, M.; Lebrand,
A. M.; Ishibashi, Y.; Fukui, M.; Yasumoto, T. J. Am. Chem.
Soc. 1990, 112, 4380. (f) Satake, M.; Morohashi, A.; Oguri,
H.; Oishi, T.; Hirama, M.; Harada, N.; Yasumoto, T. J. Am.
Chem. Soc. 1997, 119, 11325. Synthetic studies: (a) Takakura,
H.; Noguchi, K.; Sasaki, M.; Tachibana, K. Angew. Chem., Int.
Ed. 2001, 40, 1090. (b) Fujiwara, K.; Takaoka, D.; Kusumi,
K.; Kawai, K.; Murai, A. Synlett 2001, 691. (c) Clark, J. S.;
Hamelin, O. Angew. Chem., Int. Ed. 2000, 39, 372.
(d) Bond, S.; Perlmutter, P. Chem. Commun 2000, 567.
(e) Leeuwenburgh, M. A.; Kulker, C.; Overkleeft, H. S.; van
der Marel, G. A.; van Boom, J. H. Synlett 1999, 1945.
(f) Ravelo, J. D.; Regueiro, A.; Rodriguez, E.; Vera, J.; Martin,
J. D. Tetrahedron Lett. 1996, 37, 2869. (g) Soler, M. A.;
Palazon, J. M.; Martin, V. S. Tetrahedron Lett. 1993, 34, 5471
and references therein. Total synthesis of CTX-3C: Hirama,
M.; Oishi, T.; Uehara, H.; Inoue, M.; Maruyama, M.; Oguri,
H.; Satake, M. Science 2001, 294, 1904.
1104, 1067, 1008, 776, 745 cm21 1H NMR (CDCl3,
.
300 MHz) d 0.61 (6H, q, J¼8.0 Hz, –SiCH2CH3), 0.96
(9H, t, J¼8.0 Hz, –SiCH2CH3), 1.60 (3H, s, –CH3), 1.63
(3H, d, J¼1.0 Hz, –CH3), 1.68 (3H, d, J¼1.0 Hz, –CH3),
1.98–2.14 (total 4H, m, –CH2–), 4.18 (2H, dq, J¼6.5,
1.0 Hz, –CH2O–), 5.10 (1H, tt, J¼7.0, 1.5 Hz, olefinic ),
5.33 (1H, tq, J¼6.5, 1.0 Hz, olefinic ). 13C NMR (CDCl3,
75 MHz) d 4.4, 6.8, 16.2, 17.6, 25.6, 26.3, 39.5, 59.8, 124.2,
124.3, 131.6, 137.2. Anal. Calcd for C16H32OSi: C, 71.57;
H, 12.01. Found: C, 71.45; H, 12.19.
Acknowledgments
We are grateful to Mr Kitamura (analytical laboratory in this
school) for elemental analyses.
7. (a) Kira, K.; Isobe, M. Tetrahedron Lett. 2001, 42, 2821.
(b) Kira, K.; Hamajima, A.; Isobe, M. Tetrahedron 2002, 58,
1875.
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