Construction of terminal conjugated enynes: Cu-mediated cross-coupling reaction of alkenyldialkylborane with (trimethylsilyl)ethynyl bromide

Article abstract of DOI:10.1055/s-2006-942373

The cross-coupling reaction of (E)- and (Z)-alk-1-enyldialkylborane with (trimethylsilyl)ethynyl bromide proceeds in the presence of a catalytic amount of copper(II) acetylacetonate and a base under extremely mild conditions to provide conjugated enynes w

Full text of DOI:10.1055/s-2006-942373

PAPER
1961
Construction of Terminal Conjugated Enynes: Cu-Mediated Cross-Coupling
Reaction of Alkenyldialkylborane with (Trimethylsilyl)ethynyl Bromide
C
onstruction of Termin
a
al Conjuga
s
ted Enyne
a
s
yuki Hoshi,* Noritsugu Kawamura, Kazuya Shirakawa
Department of Applied and Environmental Chemistry, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
Fax +81(157)247719; E-mail: hoshi-m@chem.kitami-it.ac.jp
Received 2 December 2005
tions with (trimethylsilyl)ethynyl halide as an ethynyl unit
Abstract: The cross-coupling reaction of (E)- and (Z)-alk-1-enyl-
so far;8c,9–11 however, to the best of our knowledge, the Su-
dialkylborane with (trimethylsilyl)ethynyl bromide proceeds in the
presence of a catalytic amount of copper(II) acetylacetonate and a
base under extremely mild conditions to provide conjugated enynes
zuki–Miyaura cross-coupling reaction12 with (trimethyl-
silyl)ethynyl halide has not been demonstrated. The cross-
with a distal carbon–carbon triple bond. Employing sodium meth- coupling reaction using organoboranes requires base to-
oxide (1 M) as the base results in not only cross-coupling but also
desilylation affording both (E)- and (Z)-alk-3-en-1-ynes, exclusive-
ly, while lithium hydroxide monohydrate gives both (E)- and (Z)-1-
cleavage of the carbon–silicon bond is controlled during
(trimethylsilyl)alk-3-en-1-ynes with high regio- and stereoselectiv-
ity. On the other hand, the cross-coupling reaction of (Z)-1-(tri-
gether with catalyst, while the sp-hybridized carbon–sili-
con bond can be readily cleaved by basic methanolysis. If
the cross-coupling reaction between alkenylborane and
(trimethylsilyl)ethynyl halide, terminal conjugated
enynes with and without a trimethylsilyl group are fur-
nished selectively, which are of great significance for fur-
ther transformations.13 Thus we were interested in
applying a Cu-mediated cross-coupling reaction of alke-
nylborane in the presence of base to (trimethylsilyl)ethy-
nyl halide in an effort to obtain a single product in a
selective fashion.14 Herein, we report the successful syn-
theses of not only (E)- and (Z)-alk-3-en-1-ynes with or
without the trimethylsilyl group at the 1-position but also
(Z)-3-(trimethylsilyl)alk-3-en-1-ynes also with or without
the trimethylsilyl group at the terminal position via Cu-
mediated cross-coupling reaction.
methylsilyl)alk-1-enyldicyclohexylborane with (trimethylsilyl)ethy-
nyl bromide proceeds in the presence of a small amount of copper(I)
iodide and aqueous sodium hydroxide under extremely mild condi-
tions to afford (Z)-1,3-bis(trimethylsilyl)alk-3-en-1-yne with high
regio- and stereoselectivity. In addition, treatment of the resulting
product with sodium methoxide (1 M) leads to the stereoselective
formation of (Z)-3-(trimethylsilyl)alk-3-en-1-yne in a one-pot syn-
thesis.
Key words: alkenyldialkylborane, (trimethylsilyl)ethynyl bro-
mide, cross-coupling, alk-3-en-1-yne, 1,3-bis(trimethylsilyl)alk-3-
en-1-yne
Conjugated enynes are valuable precursors for a variety of
functionalized compounds such as stereodefined conju-
gated dienes via stereospecific reduction of their triple
bond1 and polysubstituted benzenes via benzannulation
reactions.2 Enyne systems are also found in a number of
natural products such as the neocarzinostatin chro-
mophore.3 Among conjugated enynes, there has been a
lively interest in terminal conjugated enyne, alk-3-en-1-
yne, due to its synthetic utility; the acetylenic hydrogen
can be converted into various functionalities as well as un-
dergo carbon–carbon bond formation. Furthermore, the
terminal conjugated enyne is a useful building block for
the synthesis of natural products in organic synthesis, be-
cause the terminal conjugated enyne unit occurs in natural
products such as laurencin,4 dactylyne,5 quinolizidine,6
and histrionicotoxin.7 Although a large number of meth-
ods have been developed for constructing conjugated
enynes, cross-coupling reactions appear to be the most re-
liable and straightforward methodology due to their high
regio- and stereoselectivity and high product yields.8
There have been several reports on the synthesis of termi-
nal conjugated enynes employing cross-coupling reac-
We initially focused our attention on the use of (trimeth-
ylsilyl)ethynyl bromide in the cross-coupling reaction.
This substrate was easily prepared from (trimethylsil-
yl)ethyne by a known procedure;15 (E)-oct-1-enyldialkyl-
borane (1a) was chosen as a coupling partner. The cross-
coupling reaction of 1a with (trimethylsilyl)ethynyl bro-
mide was optimized by using Cu(acac)2 as the catalyst,
THF as solvent, and a variety of bases (Scheme 1). The re-
action proceeded under very mild conditions (–15 °C to
r.t.) to yield two products, (E)-dec-3-en-1-yne (2a) and
(E)-1-(trimethylsilyl)dec-3-en-1-yne (3a, Table 1). The
ratio of product 2a to product 3a was dependent on the
base employed. Thus, the reaction using NaOMe gave
product 2a exclusively (Table 1, entries 1, 8, and 9), while
the reaction using LiOH·H2O gave product 3a preferen-
tially (Table 1, entries 6 and 7). In addition, making use of
an excess amount of 1a (1.5 equiv) increased the yield of
the products (Table 1, entries 7 and 9). It was also ob-
served that the ratio and the yield of the products were af-
fected by changing the dialkylboryl group of 1a (Table 1,
entry 6 vs 10 and entry 1 vs 8). In coupling reactions using
organoboron compounds such as the Suzuki–Miyaura re-
action, the substituent on the boron atom influences the re-
activity of the boron compounds.12 The reaction using
(E)-oct-1-enyldisiamylborane and NaOMe provided the
best results for the synthesis of 2a (desilylated cross-cou-
SYNTHESIS 2006, No. 12, pp 1961–1970
x
x.
x
x
.
2
0
0
6
Advanced online publication: 05.05.2006
DOI: 10.1055/s-2006-942373; Art ID: F20505SS
© Georg Thieme Verlag Stuttgart · New York

1962
M. Hoshi et al.
PAPER
Cu(acac)2/Me3SiC CBr
base
R2B
C
H
HC
C
H
H
Me3SiC
C
H
H
C
C
C
+
C
C
–15 °C to r.t.
H
n-C6H13
n-C6H13
n-C6H13
2a
1a
3a
Scheme 1
Table 1 Effect of Base and Dialkylborane on the Cross-Coupling
Reaction of 1a with (Trimethylsilyl)ethynyl Bromidea
treatment of (Z)-1-haloalk-1-enyldialkylborane with
LiBEt3H (Scheme 2).16
Thus, 4 was subjected to the reaction with (trimethylsi-
lyl)ethynyl bromide under the same conditions as de-
scribed above (Table 3). The reactions using (Z)-alk-1-
enyldisiamylborane and NaOMe led to the selective for-
mation of (Z)-alk-3-en-1-yne (5) in satisfactory yields
(Table 3, entries 1–5) and tolerated a number of functional
groups. It is important to note that Et3B, liberated from
LiBEt3H, has to be removed from the reaction mixture to
give favorable results. In the presence of Et3B, for exam-
ple, the cross-coupling reaction of (Z)-oct-1-enyl-
disiamylborane decreased the yield of (Z)-dec-3-en-1-yne
(5a) substantially, probably due to the consumption of
NaOMe by forming NaBEt3OMe. In fact, further addition
of NaOMe (2 equiv) restored the formation of product 5a
to nearly the same yield. On the other hand, the reaction
using (Z)-alk-1-enyldicyclohexylborane and LiOH·H2O
was only applicable to a limited number of substrates
(Table 3, entries 6 and 7). The cross-coupling reaction of
(Z)-oct-1-enyldicyclohexylborane, prepared from (Z)-1-
iodooct-1-enyldicyclohexylborane, gave (Z)-1-(trimeth-
ylsilyl)dec-3-en-1-yne (6a) in only 14% yield, while DMF
as the co-solvent increased the yield of 6a to 49%
(Table 3, entry 6). Removing Et3B gave rise to the con-
comitant formation of desilylated product 5a, although re-
moval of Et3B is a critical process for the synthesis of 5.
The cross-coupling reaction of (Z)-3-benzyloxyprop-1-
enyldicyclohexylborane, prepared from (Z)-1-bromo-3-
benzyloxylprop-1-enyldicyclohexylborane, by contrast,
produced (Z)-3-benzyloxy-1-(trimethylsilyl)pent-3-en-1-
yne (6e) in 66% yield without using DMF (Table 3, entry
7). However, the cross-coupling reaction of (Z)-2-(cyclo-
hex-1-enyl)ethenyldicyclohexylborane or (Z)-5-chloro-
pent-1-enyldicyclohexylborane, prepared from (Z)-1-
bromoalk-1-enyldicyclohexylborane, gave low yields of
the corresponding products. In the case of (Z)-2-phe-
nylethenyldicyclohexylborane derived from (Z)-1-iodo-2-
phenylethenyldicyclohexylborane, the addition of DMF
was not very useful to gain a practical yield. The reason
why this method lacks generality for the synthesis of 6 is
unclear at present.
Entry
R
Base
Yield of products (%)b
2a
3a
1
1 M NaOMe
66
trace
2
3
¢¢
2 M NaOH
n-BuLi
56
39
15
21
2
2
12
14
1
¢¢
4
¢¢
t-BuOK
5
¢¢
CsF
6
¢¢
LiOH·H2O
LiOH·H2O
1 M NaOMe
1 M NaOMe
LiOH·H2O
50
78
0
7c
8
¢¢
1
Me2CHCHMe
71
75
17
9c
10
¢¢
¢¢
0
53
a Unless otherwise specified, the reaction of 1a (1 mmol) with (tri-
methylsilyl)ethynyl bromide (1 mmol) was carried out using Cu(acac)2
(0.05 mmol) and base (1 mmol) at –15 °C to r.t. overnight.
b Yields were estimated by GC and were based on the amount of (tri-
methylsilyl)ethynyl bromide employed.
c An excess of 1a (1.5 mmol) was used.
pling product) (Table 1, entry 9). In marked contrast, (E)-
oct-1-enyldicyclohexylborane and LiOH·H2O proved to
be the best conditions for the synthesis of 3a (silyl-re-
tained cross-coupling product) (Table 1, entry 7).
The optimized conditions were applied to the cross-cou-
pling reaction of a range of 1 with (trimethylsilyl)ethynyl
bromide. As shown in Table 2, the reactions proceeded
with satisfactory yields and high selectivity. The present
reaction was tolerant of functional groups including con-
jugated alkenyl, chloro, and ethers. The cross-coupling re-
actions using alkenyldisiamylborane and NaOMe
provided the corresponding products 2 with complete se-
lectivity (Table 2, entries 1–6), while the cross-coupling
reactions using alkenyldicyclohexylborane and LiOH·H2O
afforded the corresponding products 3, exclusively
(Table 2, entries 10 and 12) or together with very small
amounts of 2 (Table 2, entries 7–9 and 11). It should be
noted that the present reaction could be applied to an in-
ternal alkenyldialkylborane derived from a symmetric in-
ternal alkyne (Table 2, entries 6 and 12).
Continuing our investigation, we explored the cross-cou-
pling reaction of (Z)-1-(trimethylsilyl)alk-1-enyldicyclo-
hexylborane with (trimethylsilyl)ethynyl bromide. To
determine the optimized reaction conditions, (Z)-1-(tri-
R2B
X
H
LiBEt3H
H
H
To synthesize terminal conjugated enynes with the oppo-
site geometry, we next examined the reaction employing
(Z)-alk-1-enyldialkylborane (4), which was prepared by
C
C
C
C
R1
R2B
R1
–25 °C to r.t.
4
Scheme 2
Synthesis 2006, No. 12, 1961–1970 © Thieme Stuttgart · New York

PAPER
Construction of Terminal Conjugated Enynes
1963
Table 2 Cross-Coupling Reaction of (E)-Alk-1-enyldialkylborane with (Trimethylsilyl)ethynyl Bromidea
Cu(acac)2/Me3SiC CBr
Cu(acac)2/Me3SiC CBr
1 M NaOMe
HC
C
H
R2B
R2
H
Me3SiC
C
H
LiOH⋅H2O
C
C
C
C
C
C
R2
R1
R1
R2
R1
–15 °C to r.t.
–15 °C to r.t.
2
1
3
Entry
R
Base
1 M NaOMe
R1
R2
H
H
H
Product
2a
Yield (%)b
1
2
3
Me2CHCHMe
n-C6H13
70
70
63
¢¢
¢¢
Ph
2b
2c
4
5
¢¢
¢¢
Cl(CH2)3
H
H
2d
2e
67
74
CH2OCH2
6
7
¢¢
n-Pr
n-Pr
2f
70
LiOH·H2O
n-C6H13
H
3a
72c
8
9
¢¢
¢¢
H
H
3b
3c
73c
62c
10
11
¢¢
¢¢
Cl(CH2)3
H
H
3d
3e
72
63c
CH2OCH2
12
¢¢
n-Pr
n-Pr
3f
65
a The reaction of 1 (4 mmol) with (trimethylsilyl)ethynyl bromide (2.68 mmol) was carried out using Cu(acac)2 (0.2 mmol) and base (4 mmol)
at –15 °C to r.t. overnight.
b Isolated yields based on the amount of (trimethylsilyl)ethynyl bromide employed.
c A very small amount of 2 (1–4%) was formed.
Table 3 Cross-Coupling Reaction of (Z)-Alk-1-enyldialkylboranea with (Trimethylsilyl)ethynyl Bromideb
Cu(acac)2/Me3SiC CBr
Cu(acac)2/Me3SiC CBr
1 M NaOMe
H
C
H
H
H
H
C
H
LiOH⋅H2O
C
C
C
C
C
C
R1
–15 °C to r.t.
–15 °C to r.t.
HC
R1
R2B
R1
Me3SiC
5
4
6
Entry
R
Base
1 M NaOMe
R1
Product
5a
Yield (%)c
1
2
3
Me2CHCHMe
n-C6H13
Ph
75
66
57
¢¢
¢¢
5b
5c
4
5
¢¢
¢¢
Cl(CH2)3
5d
5e
70
60
CH2OCH2
6
7
LiOH·H2O
n-C6H13
6a
6e
14 (49)d,e
66
¢¢
CH2OCH2
a Compound 4 was prepared by the reaction of (Z)-1-haloalk-1-enyldialkylborane (4 mmol) with LiBEt3H (4 mmol) at –25 °C to r.t. over 1 h.
b The reaction of 4 (4 mmol) with (trimethylsilyl)ethynyl bromide (2.68 mmol) was carried out using Cu(acac)2 (0.2 mmol) and base (4 mmol)
at –15 °C to r.t. overnight.
c Isolated yields based on the amount of (trimethylsilyl)ethynyl bromide employed.
d A very small amount of 5a (3%) was formed.
e DMF was used as a co-solvent in the cross-coupling step.
Synthesis 2006, No. 12, 1961–1970 © Thieme Stuttgart · New York

1964
M. Hoshi et al.
PAPER
Catalyst/Base
Me3SiC CBr
Me3SiC
C
H
)
2B
HC
C
H
H
C
C
+
C
C
C
C
–15 °C to r.t.
Me3Si
n-C4H9
Me3Si
n-C4H9
Me3Si
n-C4H9
8g
9g
7g
Scheme 3
two sp carbons at 93.6 and 109.0 ppm in the broadband
decoupled spectrum, the latter of which appeared as a
doublet (3JCH = 11.6 Hz) in the coupled spectrum. Also,
the internal sp carbon of product 9g appeared at 87.2 ppm
in the broadband decoupled spectrum, and the coupled
spectrum of it appeared as a doublet of doublets
(2JCH = 48.5 Hz, 3JCH = 11.2 Hz). The 3JCH coupling con-
stants for the E-isomer were larger (3JCH = 15.8 Hz).17 In
fact, these 3JCH values are larger than those in 1,2-disub-
stituted alkenes without a trimethylsilyl group on the al-
kenyl carbons. A similar tendency was observed in the
3JHH coupling constants for the alkenyl protons of 1-(tri-
methylsilyl)alk-1-enes.18
Table 4 Effect of Catalyst and Base for the Cross-Coupling
Reaction of 7g with (Trimethylsilyl)ethynyl Bromidea
Entry Catalyst
mol% Base
Yield of products (%)b
8g
10
30
43
83
78
28
63
22
93
73
9g
1
2
Cu(acac)2
5
10
5
1 M NaOMe
43
¢¢
1 M NaOMe
LiOH·H2O
1 M NaOH
2 M NaOH
1 M NaOMe
1 M NaOMe
LiOH·H2O
1 M NaOH
2 M NaOH
18
3
¢¢
trace
7
4
¢¢
5
5
¢¢
5
10
6
CuI
¢¢
5
25
Under the optimized conditions good to high yields of (Z)-
1,3-bis(trimethylsilyl)alk-3-en-1-ynes (8) could be ob-
tained from the cross-coupling reaction between different
types of (Z)-1-(trimethylsilyl)alk-1-enyldicyclohexylbo-
ranes (7) and (trimethylsilyl)ethynyl bromide. In addition,
the cross-coupling-desilylation sequence afforded (Z)-3-
(trimethylsilyl)alk-3-en-1-yne (9) in moderate to good
yields (Table 5). Both the cross-coupling and desilylation
reactions were not only tolerant of a variety of functional
groups, including conjugated alkenyl and chloro substitu-
ents (Table 5, entries 4, 5, 10, and 11) but also bulky tert-
butyl and trimethylsilyl groups (Table 5, entries 2, 6, 8,
and 12). It is noteworthy that the three trimethylsilyl
7
10
10
10
10
4
8
¢¢
trace
0
9
¢¢
10
¢¢
trace
a The reaction of 7g (1 mmol) with (trimethylsilyl)ethynyl bromide
(0.67 mmol) was carried out using copper catalyst and base (0.75
mmol) at –15 °C to r.t. overnight.
b Yields were estimated by GC and based on the amount of (trimeth-
ylsilyl)ethynyl bromide employed.
methylsilyl)hex-1-enyldicyclohexylborane (7g) was groups of (Z)-1,2,4-tris(trimethylsilyl)but-1-en-3-yne (8i)
coupled with (trimethylsilyl)ethynyl bromide under vari- are attached to unsaturated carbons in a conjugated system
ous conditions (Table 4). It was found that the reaction (Table 5, entry 6). For the reaction of (Z)-2-phenyl-1-(tri-
proceeded under very mild conditions (–15 °C to r.t.) to methylsilyl)ethenyldicyclohexylborane (7b), employing
yield two products, (Z)-1,3-bis(trimethylsilyl)oct-3-en-1- 2 M NaOH gave a better yield of (Z)-4-phenyl-1,3-bis(tri-
yne (8g; silyl-retained cross-coupling product) and (Z)-3- methylsilyl)but-3-en-1-yne (8b) (Table 5, entry 3).
(trimethylsilyl)oct-3-en-1-yne (9g; desilylated cross-cou-
In summary, we have developed a highly flexible protocol
pling product) (Scheme 3). In the presence of Cu(acac)2 as
for the synthesis of terminal conjugated enynes using (tri-
a catalyst, NaOMe resulted in the formation of a mixture
methylsilyl)ethynyl bromide as an ethynyl unit. This pro-
of products 8g and 9g (Table 4, entries 1 and 2), while
tocol allows the stereoselective synthesis of (E)- and (Z)-
LiOH·H2O gave product 8g exclusively, albeit in low
alk-3-en-1-yne as well as (E)- and (Z)-1-(trimethylsi-
lyl)alk-3-en-1-yne. Moreover, the synthesis of (Z)-1,3-
yield (Table 4, entry 3). When aqueous NaOH was em-
ployed, the reaction afforded product 8g preferentially in
bis(trimethylsilyl)alk-3-en-1-yne and (Z)-3-(trimethylsi-
higher yields (Table 4, entries 4 and 5). Changing the cat-
lyl)alk-3-en-1-yne has successfully been achieved. Tak-
alyst to CuI proved to be advantageous for this cross-cou-
ing also into account the mild reaction conditions, ready
pling, thus, the reaction was conducted in the presence of
availability of the starting materials, and simple experi-
mental conditions, this protocol provides a convenient
route to several types of terminal conjugated enynes that
are useful intermediates for organic synthesis. Studies on
CuI and NaOH, leading to the exclusive formation of 8g
in high yield (Table 4, entry 9). Unfortunately, selective
formation of 9g was not achieved during the cross-cou-
pling reaction. It is useful to note that subsequent treat-
the synthetic application of this protocol are ongoing in
ment of 8g with NaOMe gave product 9g exclusively in a
our laboratory.
one-pot synthesis. The configuration of the products 8g
and 9g were assigned on the basis of the 3JCH coupling of
NMR spectra were recorded on a JEOL JNM-A-500 spectrometer
the alkynyl carbon to the alkenyl proton. It is well known
with TMS, CHCl3 (7.26 ppm and 77.0 ppm) or CH2Cl2 (5.32 ppm
that 3JCH(cis) couplings are smaller than 3JCH(trans) couplings
and 53.1 ppm) as internal standard. IR spectra were recorded on a
Shimadzu FT-IR 8300 spectrometer, and only the strongest/struc-
in alkenes. The 13C NMR spectrum of product 8g revealed
Synthesis 2006, No. 12, 1961–1970 © Thieme Stuttgart · New York

PAPER
Construction of Terminal Conjugated Enynes
1965
Table 5 Cross-Coupling Reaction of 7 with (Trimethylsilyl)ethynyl Bromidea and Desilylation of 8b
CuI/Me3SiC CBr
1 M NaOH
HC
C
H
)
2B
H
Me3SiC
C
H
1 M NaOMe
r.t.
C
C
C
C
C
C
Me3Si
R1
R1
Me3Si
Me3Si
R1
–15 °C to r.t.
9
7
8
Entry
R1
Product
Yield (%)c
1
2
3
4
n-Bu
t-Bu
Ph
8g
8h
8b
8c
85
90
65 (75)d
73
5
6
7
8
9
Cl(CH2)3
Me3Si
n-Bu
8d
8i
72
64
77
70
40d
9g
9h
9b
t-Bu
10
9c
75
11
12
Cl(CH2)3
Me3Si
9d
9i
71
65
a The reaction of 7 (4 mmol) with (trimethylsilyl)ethynyl bromide (2.68 mmol) was carried out using CuI (0.4 mmol) and base (3 mmol) at
–15 °C to r.t. overnight.
b The reaction mixture containing 8 was treated with 1 M NaOMe (8 mmol) at r.t. overnight.
c Isolated yields based on the amount of (trimethylsilyl)ethynyl bromide employed.
d 2 M NaOH (3 mmol) was used instead of 1 M NaOH.
turally most important absorption peaks are listed. Mass spectra
were performed on a JEOL JMS-SX102A spectrometer (EI, 70 eV).
GC analyses were performed with a Shimadzu GC-14B gas chro-
matograph equipped with a glass column (5% FFAP on Uniport B,
1 m), a flame ionization detector, and a Shimadzu C-R8A digital in-
tegrator-recorder. TLC analyses were carried out using aluminum
sheets pre-coated with silica gel 60 F254 or glass plates pre-coated
with aluminum oxide 60 F254 purchased from Merck. Product puri-
fication was performed by flash chromatography using Merck silica
gel (Silica gel 60, 40–63 mm) or column chromatography using
Merck aluminum oxide (aluminum oxide 60 active basic, 70–230
mm). All reactions were carried out under an argon atmosphere.
Alk-1-yne, oct-4-yne, 2-methylbut-2-ene, cyclohexene, and DMF
were used after distillation over CaH2 under argon. THF was dis-
tilled from sodium benzophenone ketyl under argon before use. A
solution of LiBEt3H in THF, 1-(trimethylsilyl)hex-1-ene, 1-phenyl-
2-(trimethylsilyl)ethyne, and bis(trimethylsilyl)ethyne were pur-
chased from Aldrich. (Trimethylsilyl)ethynyl bromide,15 1-iodoalk-
1-yne (from hex-1-yne and phenylethyne),19 1-bromoalk-1-yne
(from cyclohex-1-enylethyne, 5-chloropent-1-yne, and 3-benzyl-
oxyprop-1-yne),15,20 1-(trimethylsilyl)alk-1-yne [from 3,3-dimeth-
ylbut-1-yne, (cyclohex-1-enyl)ethyne, and 5-chloropent-1-yne],21
solution of alkenyldisiamylborane in THF, thus prepared, was
cooled to –15 °C, and Cu(acac)2 (0.052 g, 0.2 mmol) was added to
the solution under a flow of argon, followed by dropwise addition
of (trimethylsilyl)ethynyl bromide (0.474 g, 2.68 mmol) and
NaOMe (1 M; 4 mL, 4 mmol). The resulting mixture was allowed
to warm gradually to r.t. and stirred overnight. The reaction mixture
was treated with an aq solution of NaOH (3 M; 4 mL) and H2O2 (30
wt%, H2O; 2 mL) at 0 °C and stirred for 1 h at the same temperature
to decompose the residual organoboron compound. The resultant
mixture was extracted with pentane (2 × 30 mL), washed with brine
(2 × 20 mL), dried (Na2SO4), and concentrated in vacuo. Purifica-
tion by flash chromatography on silica gel provided product 2.
(E)-Dec-3-en-1-yne (2a)
Flash chromatography (pentane) provided 2a.
IR (neat): 3315, 3024, 2956, 2927, 2856, 2104, 1629, 1465, 1436,
954 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.88 (t, J = 7.0 Hz, 3 H), 1.28–
1.44 (m, 8 H), 2.12–2.18 (m, 2 H), 2.76 (dd, J = 2.2, 0.4 Hz, 1 H),
5.47 (ddt, J = 16.0, 2.2, 1.5 Hz, 1 H), 6.22 (dtd, J = 16.0, 6.8, 0.4
Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 14.0 (CH3), 22.6 (CH2), 28.5
(CH2), 28.7 (CH2), 31.6 (CH2), 33.0 (CH2), 75.4 (≡CH), 82.6 (≡C),
108.5 (=CH), 146.9 (=CH).
22
and a THF solution of BH3 were prepared according to literature
procedures.
(E)-Alk-3-en-1-ynes (2); General Procedure
HRMS (EI): m/z calcd for C10H16 [M+]: 136.1252; found: 136.1254.
To a solution of BH3 (0.33 M, THF; 4 mmol) was added 2-methyl-
but-2-ene (0.56 g, 8 mmol) dropwise at –15 °C under argon, and the
reaction mixture was stirred for 2 h at 0 °C to form a solution of di-
siamylborane in THF. To this solution was added alkyne (4 mmol)
dropwise at –15 °C and the mixture was stirred for 2 h at 0 °C. A
(E)-1-Phenylbut-1-en-3-yne (2b)
Flash chromatography (pentane) provided 2b.
Synthesis 2006, No. 12, 1961–1970 © Thieme Stuttgart · New York

1966
M. Hoshi et al.
PAPER
IR (neat): 3292, 3058, 3031, 2923, 2852, 2098, 1490, 1448, 954,
748, 690 cm–1.
1H NMR (500 MHz, CDCl3): d = 3.04 (d, J = 2.4 Hz, 1 H), 6.11 (dd,
J = 16.2, 2.4 Hz, 1 H), 7.04 (d, J = 16.2 Hz, 1 H), 7.23–7.38 (m, 5
(E)-1-(Trimethylsilyl)alk-3-en-1-ynes (3); General Procedure
To a solution of BH3 (0.33 M, THF; 4 mmol) was added cyclohex-
ene (0.66 g, 8 mmol) dropwise at 0 °C under argon, and the reaction
mixture was stirred for 2 h at this temperature to form a white sus-
pension of dicyclohexylborane in THF. To this suspension was add-
ed alkyne (4 mmol) dropwise at 0 °C and the mixture was stirred for
2 h at this temperature. The solution of alkenyldicyclohexylborane
in THF, thus prepared, was cooled to –15 °C, and Cu(acac)2 (0.052
g, 0.2 mmol) was added to the solution under a flow of argon, fol-
lowed by addition of (trimethylsilyl)ethynyl bromide (0.474 g, 2.68
mmol) dropwise and LiOH·H2O (0.168 g, 4 mmol) under a flow of
argon. The resulting mixture was allowed to warm gradually to r.t.
and stirred overnight. After the reaction mixture was neutralized
with a sat. solution of NH4Cl, the resulting mixture was treated with
NaBO3·4H2O (1.846 g, 12 mmol) and H2O (4 mL) at r.t. under vig-
orous stirring for 2 h to decompose the residual organoboron com-
pound. The work-up was the same as described for 2. Purification
by flash chromatography on silica gel provided product 3.
H).
13C NMR (125 MHz, CDCl3): d = 79.2 (≡CH), 82.9 (≡C), 107.1
(=CH), 126.3 (2 × =CH), 128.7 (2 × =CH), 128.9 (=CH), 135.9
(=C), 143.1 (=CH).
HRMS (EI): m/z calcd for C10H8 [M+]: 128.0626; found: 128.0623.
(E)-1-(Cyclohex-1-enyl)but-1-en-3-yne (2c)
Flash chromatography (pentane) provided 2c.
IR (neat): 3305, 3031, 2931, 2860, 2829, 2098, 1625, 954 cm–1.
1H NMR (500 MHz, CDCl3): d = 1.55–1.70 (m, 4 H), 2.14–2.18 (m,
2 H), 2.58–2.62 (m, 2 H), 2.92 (d, J = 2.2 Hz, 1 H), 5.44 (ddd,
J = 16.0, 2.2, 0.9 Hz, 1 H), 5.85–5.87 (m, 1 H), 6.67 (d, J = 16.0 Hz,
1 H).
(E)-1-(Trimethylsilyl)dec-3-en-1-yne (3a)
Flash chromatography (pentane) provided 3a.
13C NMR (125 MHz, CDCl3): d = 22.2 (2 × CH2), 23.8 (CH2), 26.1
(CH2), 77.8 (≡CH), 83.7 (≡C), 102.9 (=CH), 133.1 (=CH), 135.3
(=C), 146.7 (=CH).
IR (neat): 2958, 2927, 2856, 2175, 2133, 1249, 1085, 952, 842, 759
cm–1.
1H NMR (500 MHz, CDCl3): d = 0.17 (s, 9 H), 0.88 (t, J = 7.0 Hz,
3 H), 1.28–1.44 (m, 8 H), 2.12–2.18 (m, 2 H), 5.52 (dt, J = 15.8, 1.5
Hz, 1 H), 6.20 (dt, J = 15.8, 6.8 Hz, 1 H).
HRMS (EI): m/z calcd for C10H12 [M+]: 132.0939; found: 132.0948.
(E)-7-Chlorohept-3-en-1-yne (2d)
Flash chromatography (pentane–CH2Cl2, 9:1) provided 2d.
13C NMR (125 MHz, CDCl3): d = 0.0 (3 × CH3), 14.0 (CH3), 22.5
(CH2), 28.5 (CH2), 28.7 (CH2), 31.6 (CH2), 33.0 (CH2), 92.4 (≡C),
104.2 (≡C), 109.6 (=CH), 146.2 (=CH).
HRMS (EI): m/z calcd for C13H24Si [M+]: 208.1647; found:
208.1664.
IR (neat): 3296, 3026, 2958, 2848, 2104, 1629, 1444, 958, 731, 651
cm–1.
1H NMR (500 MHz, CDCl3): d = 1.83–1.89 (m, 2 H), 2.22–2.28 (m,
2 H), 2.79 (dd, J = 2.2, 0.4 Hz, 1 H), 3.53 (t, J = 6.4 Hz, 2 H), 5.48–
5.54 (m, 1 H), 6.19 (dt, J = 16.0, 6.8 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 30.0 (CH2), 31.3 (CH2), 43.9
(CH2), 76.2 (≡CH), 82.0 (≡C), 110.1 (=CH), 144.3 (=CH).
HRMS (EI): m/z calcd for C7H937Cl [M+]: 130.0364; found:
(E)-1-Phenyl-4-(trimethylsilyl)but-1-en-3-yne (3b)
Flash chromatography (pentane) provided 3b.
IR (neat): 3060, 3028, 2958, 2927, 2898, 2852, 2167, 2119, 1492,
1448, 1249, 1082, 1068, 952, 842, 746, 690 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.28 (s, 9 H), 6.22 (d, J = 16.2 Hz,
1 H), 7.05 (d, J = 16.2 Hz, 1 H), 7.23–7.38 (m, 5 H).
130.0347.
HRMS (EI): m/z calcd for C7H935Cl [M+]: 128.0393; found:
128.0376.
13C NMR (125 MHz, CDCl3): d = 0.0 (3 × CH3), 96.8 (≡C), 104.4
(≡C), 108.1 (=CH), 126.3 (2 × =CH), 128.7 (3 × =CH), 136.2 (=C),
142.3 (=CH).
(E)-5-Benzyloxypent-3-en-1-yne (2e)
Flash chromatography (pentane–CH2Cl2, 7:3) provided 2e.
IR (neat): 3292, 3031, 2852, 1496, 1454, 1359, 1116, 1076, 1028,
954, 738, 698 cm–1.
HRMS (EI): m/z calcd for C13H16Si [M+]: 200.1021; found:
200.1012.
1H NMR (500 MHz, CDCl3): d = 2.88 (dd, J = 2.2, 0.4 Hz, 1 H),
4.06 (ddd, J = 5.0, 1.7, 0.4 Hz, 2 H), 4.51 (s, 2 H), 5.76 (dt, J = 16.0,
1.7 Hz, 1 H), 6.30 (dt, J = 16.0, 5.0 Hz, 1 H), 7.25–7.40 (m, 5 H).
13C NMR (125 MHz, CDCl3): d = 69.5 (CH2), 72.4 (CH2), 77.8
(≡CH), 81.6 (≡C), 110.4 (=CH), 127.7 (3 × =HC), 128.4 (2 × =CH),
138.0 (=C), 141.4 (=CH).
(E)-1-(Cyclohex-1-enyl)-4-(trimethylsilyl)but-1-en-3-yne (3c)
Flash chromatography (pentane) provided 3c.
IR (neat): 3028, 2956, 2933, 2860, 2165, 2121, 1625, 1448, 1247,
1089, 1072, 952, 842, 759 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.18 (s, 9 H), 1.55–1.70 (m, 4 H),
2.15–2.20 (m, 2 H), 2.58–2.62 (m, 2 H), 5.49 (dd, J = 16.0, 0.6 Hz,
1 H), 5.83–5.85 (m, 1 H), 6.80 (d, J = 16.0 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 0.0 (3 × CH3), 22.2 (2 × CH2),
23.8 (CH2), 26.1 (CH2), 95.2 (≡C), 103.9 (=CH), 105.3 (≡C), 132.9
(=CH), 135.5 (=C), 146.1 (=CH).
EI-MS: m/z (%) = 172 (1, [M+]), 92 (14), 91 (100), 65 (13).
(E)-3-Propylhept-3-en-1-yne (2f)
Flash chromatography (pentane) provided 2f.
IR (neat): 3313, 2960, 2931, 2871, 1458, 1379, 896 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.91 (t, J = 7.3 Hz, 3 H), 0.92 (t,
J = 7.3 Hz, 3 H), 1.25 (br s, 1 H), 1.40 (sext, J = 7.3 Hz, 2 H), 1.54
(sext, J = 7.3 Hz, 2 H), 2.08 (q, J = 7.3 Hz, 2 H), 2.11 (t, J = 7.3 Hz,
2 H), 5.96 (t, J = 7.3 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 13.6 (CH3), 13.8 (CH3), 21.4
(CH2), 22.4 (CH2), 30.2 (CH2), 32.4 (CH2), 73.9 (≡CH), 86.1 (≡C),
122.0 (=C), 139.9 (=CH).
HRMS (EI): m/z calcd for C13H20Si [M+]: 204.1334; found:
204.1359.
(E)-7-Chloro-1-(trimethylsilyl)het-3-en-1-yne (3d)
Flash chromatography (pentane–CH2Cl2, 9:1) provided 3d.
IR (neat): 2958, 2900, 2177, 2135, 1444, 1249, 1085, 956, 844, 759,
655 cm–1.
HRMS (EI): m/z calcd for C10H16 [M+]: 136.1252; found: 136.1268.
Synthesis 2006, No. 12, 1961–1970 © Thieme Stuttgart · New York

PAPER
Construction of Terminal Conjugated Enynes
1967
1H NMR (500 MHz, CDCl3): d = 0.17 (s, 9 H), 1.83–1.89 (m, 2 H),
2.22–2.28 (m, 2 H), 3.52 (t, J = 6.4 Hz, 2 H), 5.57 (dt, J = 15.8, 1.3
Hz, 1 H), 6.13 (dt, J = 15.8, 6.8 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 0.0 (3 × CH3), 30.0 (CH2), 31.3
(CH2), 43.9 (CH2), 93.3 (≡C), 103.6 (≡C), 111.2 (=CH), 143.5
(=CH).
(Z)-1-Phenylbut-1-en-3-yne (5b)
Flash chromatography (pentane) provided 5b.
IR (neat): 3290, 3084, 3062, 3024, 2958, 2931, 2088, 1492, 1446,
779, 690 cm–1.
1H NMR (500 MHz, CDCl3): d = 3.33 (dd, J = 2.6, 0.9 Hz, 1 H),
5.67 (dd, J = 12.1, 2.6 Hz, 1 H), 6.70 (d, J = 12.1 Hz, 1 H), 7.30–
7.37 (m, 3 H), 7.80–7.90 (m, 2 H).
HRMS (EI): m/z calcd for C10H1737ClSi [M+]: 202.0761; found:
202.0759.
13C NMR (125 MHz, CDCl3): d = 81.9 (≡C), 84.0 (≡CH), 106.3
(=CH), 128.2 (2 × =CH), 128.7 (3 × =CH), 136.1 (=C), 140.6
(=CH).
HRMS (EI): m/z calcd for C10H1735ClSi [M+]: 200.0788; found:
200.0811.
HRMS (EI): m/z calcd for C10H8 [M+]: 128.0626; found: 128.0617.
(E)-5-Benzyloxy-1-(trimethylsilyl)pent-3-en-1-yne (3e)
Flash chromatography (pentane–CH2Cl2, 7:3) provided 3e.
(Z)-1-(Cyclohex-1-enyl)but-1-en-3-yne (5c)
Flash chromatography (pentane) provided 5c.
IR (neat): 3064, 3031, 2958, 2898, 2852, 2177, 2133, 1496, 1454,
1359, 1249, 1116, 1085, 954, 854, 759, 698 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.24 (s, 9 H), 4.11 (dd, J = 5.0, 1.5
Hz, 2 H), 4.56 (s, 2 H), 5.86 (dt, J = 16.0, 1.5 Hz, 1 H), 6.30 (dt,
J = 16.0, 5.2 Hz, 1 H), 7.25–7.40 (m, 5 H).
13C NMR (125 MHz, CDCl3): d = –0.1 (3 × CH3), 69.6 (CH2), 72.2
(CH2), 95.1 (≡C), 103.1 (≡C), 111.6 (=CH), 127.6 (3 × =CH), 128.3
(2 × =CH), 138.0 (=C), 140.6 (=CH).
IR (neat): 3303, 3014, 2931, 2858, 2829, 2088, 1622, 1433, 848,
798 cm–1.
1H NMR (500 MHz, CDCl3): d = 1.55–1.70 (m, 4 H), 2.14–2.18 (m,
2 H), 2.58–2.62 (m, 2 H), 3.31 (d, J = 2.9 Hz, 1 H), 5.28 (dd,
J = 12.2, 2.4 Hz, 1 H), 5.96–5.99 (m, 1 H), 6.19 (d, J = 12.2 Hz, 1
H).
13C NMR (125 MHz, CDCl3): d = 21.8 (CH2), 22.4 (CH2), 26.1
(CH2), 26.8 (CH2), 82.2 (≡CH), 82.8 (≡C), 102.3 (=CH), 133.7
(=CH), 136.9 (=C), 144.3 (=CH).
EI-MS: m/z (%) = 229 (5, [M+ – 15]), 158 (8), 109 (7), 92 (11), 91
(100), 83 (5), 77 (6), 75 (8), 73 (15), 65 (5).
HRMS (EI): m/z calcd for C10H12 [M+]: 132.0939; found: 132.0945.
(E)-3-Propyl-1-(trimethylsilyl)hept-3-en-1-yne (3f)
Flash chromatography (pentane) provided 3f.
IR (neat): 2960, 2931, 2900, 2873, 2142, 1458, 1249, 840, 759 cm–1.
(Z)-7-Chlorohept-3-en-1-yne (5d)
Flash chromatography (pentane–CH2Cl2, 9:1) provided 5d.
1H NMR (500 MHz, CDCl3): d = 0.17 (s, 9 H), 0.90 (t, J = 7.3 Hz,
3 H), 0.92 (t, J = 7.3 Hz, 3 H), 1.39 (sext, J = 7.3 Hz, 2 H), 1.53
(sext, J = 7.3 Hz, 2 H), 2.06 (q, J = 7.3 Hz, 2 H), 2.09 (t, J = 7.3 Hz,
2 H), 5.93 (t, J = 7.3 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 0.1 (3 × CH3), 13.7 (CH3), 13.8
(CH3), 21.4 (CH2), 22.4 (CH2), 30.3 (CH2), 32.4 (CH2), 90.4 (≡C),
107.8 (≡C), 123.1 (=C), 139.3 (=CH).
IR (neat): 3294, 3026, 2958, 2869, 2088, 1444, 731, 650 cm–1.
1H NMR (500 MHz, CDCl3): d = 1.88–1.94 (m, 2 H), 2.45–2.52 (m,
2 H), 3.11 (d, J = 2.1 Hz, 1 H), 3.55 (t, J = 6.7 Hz, 2 H), 5.50–5.55
(m, 1 H), 5.98 (dt, J = 11.0, 7.3 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 27.6 (CH2), 31.6 (CH2), 44.2
(CH2), 80.0 (≡C), 82.0 (≡CH), 109.5 (=CH), 143.6 (=CH).
HRMS (EI): m/z calcd for C7H937Cl [M+]: 130.0364; found:
HRMS (EI): m/z calcd for C13H24Si [M+]: 208.1647; found:
208.1668.
130.0353.
HRMS (EI): m/z calcd for C7H935Cl [M+]: 128.0393; found:
128.0382.
(Z)-Alk-3-en-1-ynes (5); General Procedure
To a solution of disiamylborane (4 mmol) in THF (12 mL) was add-
ed 1-haloalk-1-yne (4 mmol) dropwise at –15 °C under argon, and
the reaction mixture was stirred for 2 h at 0 °C to form a THF solu-
tion of (Z)-1-haloalk-1-enyldisiamylborane. To this solution was
added LiBEt3H (1 M, THF; 4 mL, 4 mmol) dropwise at –25 °C, and
the mixture was allowed to warm gradually to r.t. over 1 h. Et3B, lib-
erated from LiBEt3H, was removed under reduced pressure, accom-
panied by the solvent. After the addition of THF (12 mL) to the
residue under argon, the resulting solution of (Z)-alk-1-enyldi-
siamylborane in THF was subjected to cross-coupling as described
in the general procedure for the synthesis of 2.
(Z)-5-Benzyloxypent-3-en-1-yne (5e)
Flash chromatography (pentane–CH2Cl2, 7:3) provided 5e.
IR (neat): 3288, 3031, 2858, 1496, 1454, 1336, 1099, 1076, 1028,
736, 698 cm–1.
1H NMR (500 MHz, CDCl3): d = 3.13 (dd, J = 2.2, 0.4 Hz, 1 H),
4.32 (ddd, J = 6.3, 1.5, 0.4 Hz, 2 H), 4.52 (s, 2 H), 5.60–5.65 (m, 1
H), 6.15 (dtd, J = 11.0, 6.4, 0.9 Hz, 1 H), 7.20–7.32 (m, 5 H).
13C NMR (125 MHz, CDCl3): d = 67.9 (CH2), 72.5 (CH2), 79.3
(≡C), 83.1 (≡CH), 110.4 (=CH), 127.7 (=CH), 127.8 (2 × =CH),
128.3 (2 × =CH), 138.1 (=C), 141.6 (=CH).
(Z)-Dec-3-en-1-yne (5a)
Flash chromatography (pentane) provided 5a.
IR (neat): 3313, 3024, 2956, 2927, 2856, 1465, 738 cm–1.
EI-MS: m/z (%) = 172 (1, [M+]), 129 (10), 92 (14), 91 (100), 65
(15).
(Z)-1-(Trimethylsilyl)alk-3-en-1-ynes 6; General Procedure
To a suspension of dicyclohexylborane (4 mmol) in THF (12 mL)
was added 1-haloalk-1-yne (4 mmol) dropwise at 0 ºC under argon,
and the reaction mixture was stirred for 2 h at this temperature to
form a solution of (Z)-1-haloalk-1-enyldicyclohexylborane in THF.
To this solution was added LiBEt3H (1 M, THF; 4 mL, 4 mmol)
dropwise at –25 °C, and the mixture was allowed to warm gradually
to r.t. over 1 h. The solution of (Z)-alk-1-enyldicyclohexylborane in
THF, thus prepared, was subjected to cross-coupling as described in
the general procedure for the synthesis of 3.
1H NMR (500 MHz, CDCl3): d = 0.88 (t, J = 7.0 Hz, 3 H), 1.28–
1.45 (m, 8 H), 2.32–2.38 (m, 2 H), 3.05 (d, J = 2.2 Hz, 1 H), 5.45
(ddt, J = 11.0, 1.3, 0.9 Hz, 1 H), 5.98 (dtd, J = 11.0, 7.3, 0.9 Hz, 1
H).
13C NMR (125 MHz, CDCl3): d = 14.0 (CH3), 22.6 (CH2), 28.7
(CH2), 28.8 (CH2), 30.2 (CH2), 31.6 (CH2), 80.6 (≡CH), 81.1
(≡CH), 108.0 (=CH), 146.2 (=CH).
HRMS (EI): m/z calcd for C10H16 [M+]: 136.1252; found: 136.1253.
Synthesis 2006, No. 12, 1961–1970 © Thieme Stuttgart · New York

1968
M. Hoshi et al.
PAPER
(Z)-1-(Trimethylsilyl)dec-3-en-1-yne (6a)
13C NMR (125 MHz, CDCl3): d = 0.1 (3 × CH3), 0.2 (3 × CH3), 21.8
(CH2), 22.3 (CH2), 25.3 (CH2), 27.9 (CH2), 95.2 (≡C), 109.6 (≡C),
123.0 (=C), 126.8 (=CH), 137.1 (=C), 155.5 (=CH).
HRMS (EI): m/z calcd for C16H28Si2 [M+]: 276.1730; found:
276.1733.
In addition to the general procedure, DMF (16 mL) was added to the
reaction mixture after treatment with LiBEt3H. Flash chromatogra-
phy (pentane) provided 6a.
IR (neat): 3020, 2958, 2927, 2856, 2148, 1249, 842, 759 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.19 (s, 9 H), 0.88 (t, J = 7.0 Hz,
3 H), 1.28–1.45 (m, 8 H), 2.32–2.38 (m, 2 H), 5.48 (dt, J = 11.0, 1.3
Hz, 1 H), 5.94 (dt, J = 11.0, 7.3 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 0.0 (3 × CH3), 14.0 (CH3), 22.5
(CH2), 28.6 (CH2), 28.7 (CH2), 30.2 (CH2), 31.5 (CH2), 98.4 (≡C),
102.2 (≡CH), 109.1 (=CH), 145.5 (=CH).
(Z)-7-Chloro-1,3-bis(trimethylsilyl)hept-3-en-1-yne (8d)
Column chromatography (pentane–CH2Cl2, 9:1) provided 8d.
IR (neat): 2958, 2898, 2121, 1249, 848, 759 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.17 (s, 9 H), 0.24 (s, 9 H), 1.84–
1.90 (m, 2 H), 2.34–2.39 (m, 2 H), 3.55 (t, J = 6.3 Hz, 2 H), 6.64 (t,
J = 7.3 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = –0.2 (3 × CH3), 0.1 (3 × CH3),
29.6 (CH2), 32.0 (CH2), 44.3 (CH2), 94.6 (≡C), 108.4 (≡C), 125.1
(=C), 153.0 (=CH).
HRMS (EI): m/z calcd for C13H24Si [M+]: 208.1647; found:
208.1671.
(Z)-5-Benzyloxy-1-(trimethylsilyl)pent-3-en-1-yne (6e)
Flash chromatography (pentane–CH2Cl2, 7:3) provided 6e.
HRMS (EI): m/z calcd for C13H2537ClSi2 [M+]: 274.1158; found:
IR (neat): 3031, 2958, 2852, 2150, 1496, 1454, 1336, 1249, 1090,
852, 759 698 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.23 (s, 9 H), 4.36 (dd, J = 6.3, 1.5
Hz, 2 H), 4.58 (s, 2 H), 5.71 (dt, J = 11.0, 1.5 Hz, 1 H), 6.15 (dt,
J = 11.0, 6.3 Hz, 1 H), 7.32–7.43 (m, 5 H).
274.1156.
HRMS (EI): m/z calcd for C13H2535ClSi2 [M+]: 272.1183; found:
272.1183.
(Z)-1,3-Bis(trimethylsilyl)oct-3-en-1-yne (8g)
Column chromatography (pentane) provided 8g.
IR (neat): 2956, 2923, 2856, 2119, 1579, 1456, 1247, 840, 758 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.16 (s, 9 H), 0.21 (s, 9 H), 0.89
(t, J = 7.0 Hz, 3 H), 1.30–1.47 (m, 4 H), 2.16–2.23 (m, 2 H), 6.70 (t,
J = 7.7 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = –0.1 (3 × CH3), 67.8 (CH2), 72.3
(CH2), 100.6 (≡C), 100.7 (≡C), 111.6 (=CH), 127.6 (=CH), 127.8
(2 × =CH), 128.3 (2 × =CH), 138.0 (=C), 140.5 (=CH).
EI-MS: m/z (%) = 244 (1, [M+]), 92 (11), 91 (100), 73 (31).
(Z)-1,3-Bis(trimethylsilyl)alk-3-en-1-ynes (8); General Proce-
dure
13C NMR (125 MHz, CDCl3): d = –0.1 (3 × CH3), 0.2 (3 × CH3),
13.8 (CH3), 22.3 (CH2), 31.5 (CH2), 32.2 (CH2), 93.6 (≡C), 109.0
(≡C), 123.3 (=C), 155.8 (=CH).
HRMS (EI): m/z calcd for C14H28Si2 [M+]: 252.1730; found:
252.1687.
To a suspension of dicyclohexylborane (4 mmol) in THF (12 mL)
was added 1-(trimethylsilyl)alk-1-yne (4 mmol) dropwise at 0 °C
under argon, and the reaction mixture was stirred for 2 h at this tem-
perature to form a solution of (Z)-1-(trimethylsilyl)alk-1-enyldicy-
clohexylborane in THF. The solution was cooled to –15 °C, and CuI
(0.076 g, 0.4 mmol) was added under a flow of argon, followed by
dropwise addition of (trimethylsilyl)ethynyl bromide (0.474 g, 2.68
mmol) and NaOH (1 M; 3 mL, 3 mmol) or NaOH (2 M; 1.5 mL, 3
mmol, for 8b). The resulting mixture was allowed to warm gradual-
ly to r.t. and stirred overnight. The work-up was the same as that de-
scribed in the general procedure for the synthesis of 2, except the
organic phase was not washed with brine. Purification by column
chromatography on aluminum oxide (basic) provided product 8.
(Z)-5,5-Dimethyl-1,3-bis(trimethylsilyl)hex-3-en-1-yne (8h)
Column chromatography (pentane) provided 8h.
IR (neat): 2958, 2900, 2131, 2110, 1249, 840, 759 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.16 (s, 9 H), 0.28 (s, 9 H), 1.11
(s, 9 H), 6.92 (s, 1 H).
13C NMR (125 MHz, CDCl3): d = 0.1 (3 × CH3), 1.9 (3 × CH3), 30.6
(3 × CH3), 35.0 (C), 92.5 (≡C), 111.3 (≡C), 120.8 (=C), 167.4
(=CH).
(Z)-4-Phenyl-1,3-bis(trimethylsilyl)but-3-en-1-yne (8b)
Column chromatography (pentane) provided 8b.
HRMS (EI): m/z calcd for C14H28Si2 [M+]: 252.1730; found:
252.1731.
IR (neat): 3058, 3026, 2958, 2898, 2854, 2117, 1249, 866, 839, 758,
698 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.13 (s, 9 H), 0.26 (s, 9 H), 7.25–
7.42 (m, 5 H), 7.79 (s, 1 H).
(Z)-1,2,4-Tris(trimethylsilyl)but-1-en-3-yne (8i)
Column chromatography (pentane) provided 8i.
IR (neat): 2956, 2900, 2104, 1249, 840, 758 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.15 (s, 9 H), 0.17 (s, 9 H), 0.23
13C NMR (125 MHz, CDCl3): d = 0.0 (3 × CH3), 0.1 (3 × CH3), 96.8
(≡C), 109.2 (≡C), 127.9 (=C), 127.9 (2 × =CH), 128.3 (2 × =CH),
128.7 (=CH), 138.5 (=C), 152.3 (=CH).
HRMS (EI): m/z calcd for C16H24Si2 [M+]: 272.1417; found:
272.1396.
(s, 9 H), 7.12 (s, 1 H).
13C NMR (125 MHz, CDCl3): d = 0.0 (3 × CH3), 0.1 (3 × CH3), 0.5
(3 × CH3), 96.5 (≡C), 110.7 (≡C), 143.4 (=C), 158.1 (=CH).
HRMS (EI): m/z calcd for C13H28Si3 [M+]: 268.1499; found:
268.1452.
(Z)-4-(Cyclohex-1-enyl)-1,3-bis(trimethylsilyl)but-3-en-1-yne
(8c)
(Z)-3-(Trimethylsilyl)alk-3-en-1-ynes (9); General Procedure
The cross-coupling reaction of (Z)-1-(trimethylsilyl)alk-1-enyldi-
cyclohexylborane (4 mmol) in THF (12 mL) with (trimethylsi-
lyl)ethynyl bromide (0.474 g, 2.68 mmol) was carried out as
described in the general procedure for the synthesis of 8. To the re-
action mixture containing (Z)-1,3-bis(trimethylsilyl)alk-3-en-1-yne
was added 1 M NaOMe (8 mL, 8 mmol) dropwise at 0 °C under ar-
Column chromatography (pentane) provided 8c.
IR (neat): 2956, 2935, 2896, 2858, 2833, 2117, 1247, 842, 759 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.17 (s, 9 H), 0.18 (s, 9 H), 1.53–
1.65 (m, 4 H), 1.93–2.10 (m, 4 H), 5.60–5.64 (m, 1 H), 7.00 (s, 1 H).
Synthesis 2006, No. 12, 1961–1970 © Thieme Stuttgart · New York

PAPER
Construction of Terminal Conjugated Enynes
1969
gon, and the mixture was stirred at r.t. overnight. The resulting mix-
ture was treated as described in the general procedure for the
synthesis of 8.
HRMS (EI): m/z calcd for C10H1735ClSi [M+]: 200.0788; found:
200.0787.
(Z)-1,2-Bis(trimethylsilyl)but-1-en-3-yne (9i)
Column chromatography (pentane) provided 9i.
(Z)-3-(Trimethylsilyl)oct-3-en-1-yne (9g)
Column chromatography (pentane) provided 9g.
IR (neat): 3315, 2958, 2929, 2873, 2860, 1249, 840, 759 cm–1.
IR (neat): 3313, 2956, 2902, 1249, 867, 837, 754 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.17 (s, 9 H), 0.24 (s, 9 H), 3.18
(s, 1 H), 7.17 (s, 1 H).
13C NMR (125 MHz, CDCl3): d = 0.0 (3 × CH3), 0.5 (3 × CH3), 79.3
(≡CH), 89.1 (≡C), 142.4 (=C), 159.5 (=CH).
HRMS (EI): m/z calcd for C10H20Si2 [M+]: 196.1104; found:
196.1119.
1H NMR (500 MHz, CDCl3): d = 0.22 (s, 9 H), 0.90 (t, J = 7.0 Hz,
3 H), 1.30–1.47 (m, 4 H), 2.16–2.23 (m, 2 H), 2.91 (s, 1 H), 6.74 (t,
J = 7.6 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = –0.2 (3 × CH3), 13.8 (CH3), 22.3
(CH2), 31.4 (CH2), 32.2 (CH2), 76.6 (≡CH), 87.2 (≡C), 122.1 (=C),
156.8 (=CH).
HRMS (EI): m/z calcd for C11H20Si [M+]: 180.1334; found:
180.1335.
Acknowledgment
This work was partially supported by a Grant-in-Aid for Scientific
Research (C) (KAKENHI 13650898) from the Japanese Society for
the Promotion of Science.
(Z)-5,5-Dimethyl-3-(trimethylsilyl)hex-3-en-1-yne (9h)
Column chromatography (pentane) provided 9h.
IR (neat): 3313, 2956, 2925, 2866, 1560, 1458, 1375, 1363, 1249,
842, 761 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.00 (s, 9 H), 0.83 (s, 9 H), 2.58
(s, 1 H), 6.67 (s, 1 H).
References
(1) For examples see: (a) Zweifel, G.; Polston, N. L. J. Am.
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(c) Rossi, R.; Carpita, A.; Quirici, M. G.; Gaudenzi, M. L.
Tetrahedron 1982, 38, 631. (d) Cabezas, J. A.;
13C NMR (125 MHz, CDCl3): d = 1.8 (3 × CH3), 30.6 (3 × CH3),
35.0 (C), 75.8 (≡CH), 89.5 (≡C), 119.6 (=C), 168.4 (=CH).
HRMS (EI): m/z calcd for C11H20Si [M+]: 180.1334; found:
180.1326.
Oehlschlager, A. C. Synthesis 1999, 107. (e) Crousse, B.;
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(Z)-4-Phenyl-3-(trimethylsilyl)but-3-en-1-yne (9b)
Column chromatography (pentane) provided 9b.
IR (neat): 3307, 3057, 3026, 2956, 2896, 1249, 840, 752, 698 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.13 (s, 9 H), 3.19 (s, 1 H), 7.25–
7.38 (m, 5 H), 7.84 (s, 1 H).
13C NMR (125 MHz, CDCl3): d = –0.1 (3 × CH3), 79.3 (≡CH), 87.5
(≡C), 125.9 (=C), 127.9 (2 × =CH), 127.9 (=CH), 128.3 (2 × =CH),
138.4 (=C), 153.4 (=CH).
HRMS (EI): m/z calcd for C13H16Si [M+]: 200.1021; found:
200.1029.
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(Z)-1-(Cyclohex-1-enyl)-2-(trimethylsilyl)but-1-en-3-yne (9c)
Column chromatography (pentane) provided 9c.
IR (neat): 3313, 2925, 2856, 1247, 842, 759 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.19 (s, 9 H), 1.53–1.65 (m, 4 H),
1.93–2.10 (m, 4 H), 2.99 (s, 1 H), 5.61–5.65 (m, 1 H), 7.05 (s, 1 H).
13C NMR (125 MHz, CDCl3): d = 0.2 (3 × CH3), 21.8 (CH2), 22.3
(CH2), 25.3 (CH2), 28.0 (CH2), 77.9 (≡CH), 87.8 (≡C), 122.1 (=C),
126.9 (=CH), 137.1 (=C), 156.4 (=CH).
HRMS (EI): m/z calcd for C13H20Si [M+]: 204.1334; found:
204.1349.
(Z)-7-Chloro-3-(trimethylsilyl)hept-3-en-1-yne (9d)
Column chromatography (pentane–CH2Cl2, 9:1) provided 9d.
IR (neat): 3305, 2956, 2898, 1583, 1249, 842, 759 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.24 (s, 9 H), 1.84–1.90 (m, 2 H),
2.35–2.40 (m, 2 H), 2.96 (s, 1 H), 3.55 (t, J = 6.3 Hz, 2 H), 6.68 (t,
J = 7.8 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = –0.2 (3 × CH3), 29.6 (CH2), 32.0
(CH2), 44.2 (CH2), 77.5 (≡CH), 86.7 (≡C), 124.0 (=C), 154.1
(=CH).
HRMS (EI): m/z calcd for C10H1737ClSi [M+]: 202.0761; found:
202.0751.
Synthesis 2006, No. 12, 1961–1970 © Thieme Stuttgart · New York

1970
M. Hoshi et al.
PAPER
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Synthesis 2006, No. 12, 1961–1970 © Thieme Stuttgart · New York