Synthesis of enynes and epoxyenynes by coupling: Use of a new set of catalysts based on Pd-Ag salts

Article abstract of DOI:10.1016/S0022-328X(98)00681-0

The new couple of catalysts Pd(PPh₃)₄ and AgI are very efficient for the coupling of vinyltriflates and terminal alkynes in the presence of a bulky amine in dimethylformamide at room temperature. Enynes and epoxyenynes are obtained in good to excellent yields. As illustrated with several examples, a wide variety of functional groups are well tolerated in the described conditions. Silver acetylides have been proposed as intermediate in this reaction.

Full text of DOI:10.1016/S0022-328X(98)00681-0

Journal of Organometallic Chemistry 567 (1998) 173–180
Synthesis of enynes and epoxyenynes by coupling: use of a new set of
catalysts based on Pd–Ag salts
Philippe Bertus 1,a, Patrick Pale b,*
a Laboratoire des Re´actions Se´lecti6es et Applications, Associe´ au CNRS, Uni6ersite´ de Reims-Champagne Ardenne, BP 1039,
51687 Reims cedex 2, France
b Laboratoire de Synthe`se et Re´acti6ite´ Organique, Institut Le Bel, Uni6ersite´ L. Pasteur, 4 Rue B. Pascal, 67000 Strasbourg, France
Received 30 September 1997; received in revised form 9 February 1998
Abstract
The new couple of catalysts Pd(PPh3)4 and AgI are very efficient for the coupling of vinyltriflates and terminal alkynes in the
presence of a bulky amine in dimethylformamide at room temperature. Enynes and epoxyenynes are obtained in good to excellent
yields. As illustrated with several examples, a wide variety of functional groups are well tolerated in the described conditions.
Silver acetylides have been proposed as intermediate in this reaction. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Palladium; Silver; Epoxide; Vinyl triflate; Enynes; Coupling reactions
1. Introduction
mophores and the recently discovered N1999A2 3 [5]
thus possess an epoxydienediyne system laid on a bicy-
clo[7.3.0]dodecane backbone (Scheme 1).
A new class of antibiotic molecules has recently
emerged, the enediynes, [1,2] which are among the most
potent antitumor agents known to date. All of these
molecules exhibit a common moiety, a conjugated
enediyne system able, upon DNA complexation and
chemical initiation, to rearrange with concommitant
formation of a biradical species. Since it is complexed
to the DNA minor groove, this biradical then abstracts
hydrogen atoms from the deoxyribose part of DNA.
Oxydation then leads to DNA cleavage, and eventually
to cell death [1].
Since the epoxydienediyne system found in structures
1–3 is responsible for their particular mode of action
and biological activity, we embarked upon a program
devoted to the synthesis of this kind of system, with
total synthesis and synthesis of analogs as the ultimate
goals. As a preliminary part of this program, we in-
tended to find a mild method to create the C–C bond
between the multiple bonds of an epoxyenyne system
(Scheme 2) since such coupling was unprecedented.
A few enediynes exhibit a further degree of complex-
ity in their structure with the presence of an epoxide
group adjacent to one of the triple bonds of the
enediyne moiety included in a nine-membered ring. The
neocarzinostatin 1 [3] and kedarcidin 2 [4] chro-
2. Synthesis of epoxyenynes and enynes by coupling
The synthesis of enynes by palladium-catalyzed cou-
pling reaction between haloalkenes or enol triflates and
alkynes is well described in the literature [6,7]. The
Sonogashira–Linstrumelle procedure using both palla-
dium complexes and copper salts as catalysts is
amongst the most useful and has found many applica-
tions in the synthesis of natural products [1,6,8].
* Corresponding author. Tel.: +33 3 88416042; fax: +33 3
88416042; e-mail: ppale@chimie.u-strasbg.fr
1 Present address: Laboratoire de Synthe`se Organique Associe` au
CNRS, Ecole Nationale Supe`rieure de Chimie de Paris, 11 Rue P. et
M. Curie, 75231 Paris cedex 05, France.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00681-0

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P. Bertus, P. Pale / Journal of Organometallic Chemistry 567 (1998) 173–180
Scheme 1.
Unfortunately, as we [9] and others [10] have experi-
Product structures were established by spectrocopic
correlation with products previously prepared when
possible or by full spectroscopic and analytic character-
ization (Section 7) in other cases. Nevertheless, the
formation of the expected coupling products was evi-
denced in all cases by the presence in the crude H-
NMR spectra of a new vinyl signal characterisic of the
conjugated enyne system.
With 1-hexyne, the vinyl triflate 4 led to the corre-
sponding enyne 5a in high yield (entry 1, Table 1). It is
noteworthy that this yield is by far better than the one
reported by Stille et al. for the same coupling but with
bis(triphenylphosphine)palladium dichloride as a cata-
lyst and in the presence of triethylamine in DMF at
75°C (entry 2) [12]. Our conditions still gave a better
yield of enyne than the best one reported [12] for the
same starting compound and obtained by catalysis with
tetrakis(triphenylphosphine)palladium in the presence
or not of an excess of lithium chloride in THF at 60°C
(75 or 50%, respectively, entry 3).
enced, this procedure proved to be inefficient for the
direct synthesis of epoxyenyne starting from ethynyl
oxiranes. In a preliminary work [9], we studied this
reaction with two model compounds and introduced
the use of silver iodide as a new mild cocatalyst.
Indeed, in the presence of a catalytic amount of tetrak-
is(triphenylphosphine)palladium and a slight excess of
diisopropylethylamine as base in dimethylformamide,
silver iodide led to the clean formation of epoxyenynes
in high yields. Other silver salts such as silver nitrate or
carbonate proved to be efficient in this reaction, al-
though lower yields were obtained [9].
In this communication, we described further investi-
gations dealing with the scope and limitations of this
new set of catalysts and we demonstrated here that
these conditions allow for the synthesis of a wide
variety of enynes and epoxyenynes. The probable in
situ formation of silver acetylides as intermediates in
this coupling reaction was also discussed.
1
The coupling with trimethylsilylacetylene also gave
the expected trimethylsilylenyne 5b in a very efficient
way with the Pd/Ag catalysts (entry 4). This product
has already been obtained by coupling [13]. The re-
ported procedure required the activation of the
trimethylsilylacetylene as a stannyl acetylide in order to
achieve an efficient coupling. Although the yields of
3. Synthesis of enynes
The usefulness of our method for enyne synthesis has
been studied by coupling the vinyl triflate 4 derived
from 4-tertbutylcyclohexanone, [11] with various alky-
nes. The choice of this triflate and of some alkynes was
guided by the literature availability of similar or identi-
cal compounds used in more conventional coupling
methods. Thus, direct comparison of the Pd–Ag cata-
lytic system with others catalysts and/or other methods
would be made possible.
Scheme 2.

P. Bertus, P. Pale / Journal of Organometallic Chemistry 567 (1998) 173–180
175
Table 1
Synthesis of enynes
a
Yields of isolated chromatographically pure products.
b Reaction carried out [11] in the following conditions: PdCl2(PPh3)2-NEt3-DMF-75°C.
c Reaction carried out [11,12] in the following conditions: Pd (PPh3)4-LiCl xs-THF-70°C
both coupling steps are quite similar (entry 5 vs. 4), our
method allows for a direct coupling and thus avoids the
additional activation step which lowers the overall yield
of the reported method.
With propargyl alcohol, the formation of the enyne
5c was very rapid compared to the precedings realized
with purely hydrocarbonated compounds. However,
slightly lower yields were obtained (entry 6 vs. 1, 4).
Protection of the alcohol function simply solved this
minor drawback, significantly improving the yield while
keeping a rapid, although slightly longer, reaction time
(entry 7 vs. 6). The presence of an electronwithdrawing
group at the propargylic position might well account
for the increased reactivity of these two alkynes.
More functionnalized alkynes have also been cou-
pled. For example, a carbonate function, a group which
is present in the neocarzinostatin structure (1, Scheme
1) was well tolerated. The carbonatoenyne 5e was in-

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P. Bertus, P. Pale / Journal of Organometallic Chemistry 567 (1998) 173–180
deed obtained cleanly without noticeable change in
yields (entry 8). However, the coupling rate was com-
parable to the one observed for the hydrocarbonated
alkynes (entry 8 vs. 1, 4) despite the presence of an
alcohol function at the propargylic position (entry 8 vs.
6, 7). A dissymmetrical 1,5-diyne [14] was also con-
verted to the corresponding enediyne 5f in high yield
(entry 9) again with a rate comparable to the one
observed for the hydrocarbonated alkynes (entry 9 vs.
1, 4)
tures showed in each case the sole presence of the
expected product together with some starting materials
left over, the purification by chromatography always
led to some decomposition. Morerover, 12a proved to
be particularly prone to double bond isomerization.
The stereochemistry of these enynones was deduced
from the chemical shift of the vinyl proton which
exhibits a typical [18] deshielding going from the Z to
the E isomer (5.67 and 6.24 ppm, respectively).
Even 1,2-diethynyloxiranes can be directly linked to a
alkenyl group through this new method. Indeed, when
the monosilylated 1,2-diethynyloxirane 7, obtained
from 6a, [16] was submitted to our standard conditions
in the presence of the vinyl triflate 4, the expected
epoxyenediyne 13 was formed.
4. Synthesis of epoxyenynes
In order to study the stability of the sensitive epoxide
function toward this new procedure and to create the
key epoxyenyne moiety present in the molecules 1–3,
we submitted various activated alkenes to the Pd–Ag
coupling conditions in the presence of the epoxyalkynes
6a,b [15] or 7 [16].
5. Mechanistic aspects
The coupling reaction leading to enynes is usually
thought to proceed in three successive steps: oxidative
addition, transmetallation and reductive elimination
(oa, tm and re, respectively in Scheme 3). The key
transmetallation step involves a reaction between an
organopalladium (II) species generated through oxida-
tive addition and a metal acetylide [6,19]. The acetylide
can be directly incorporated in the reaction mixture as
exemplified by the use of acetylenic tin reagents, [20]
magnesium acetylides [21] and zinc acetylides [22]
(Scheme 3, M=SnR3, MgX, ZnX). In each of these
cases, the acetylides must be independently prepared
and stœchiometricaly added to the coupling mixture.
Although widely used, the mechanistic bases of the
Sonogashira–Linstrumelle coupling are less clear. It
has been proposed ([7]a) that a copper acetylide would
be generated in situ from the copper catalyst used and
the terminal alkyne (Scheme 3, right part: M=Cu).
However, to the best of our knowledge, no proof nor
evidence have been obtained for such process. The
copper acetylide so formed would then enters the palla-
dium catalytic cycle at the transmetallation step, as the
other metal acetylides mentionned above. The copper
ion liberated during this step would be available for
another reaction with another alkyne molecule yielding
another copper acetylide. The overall process makes the
copper also a catalyst.
With the 4-tertbutylcyclohex-1-enyl triflate 4, the ex-
pected epoxyenyne 10a is obtained in high yield (entry
1, Table 2). As mentionned earlier, [9] use of the
standard Sonogashira–Linstrumelle protocols led to ex-
tensive decomposition mainly of the epoxyacetylenic
part of the molecules. In the Sonogashira or Lin-
strumelle condition, the presence of copper iodide
proved to be deleterious and the expected product
could only be isolated in low yield (entry 2). Since TLC
monitoring indicated that the triflate 4 was almost
unchanged while the epoxyalkyne 6a was rapidly con-
sumed, 6a was slowly added over the other components
of the reaction. With this modification, the yield was
doubled but still modest and decomposition was still
the major process (entry 3). Other Linstrumelle condi-
tions ([7]d) without copper required longer reaction
time and also led mainly to decomposition; neverthe-
less, the coupling product was detected and isolated in
very low yield (entry 4). Clearly, our method using
silver salts as cocatalyst greatly improves the direct
coupling of epoxyalkyne with vinyl triflate.
Acetylenic epoxyalcohols can also be directly coupled
without any protection as demonstrated by the reaction
between 2,3-epoxypent-4-yn-1-ol 6b [15] and the triflate
4 (entry 5). However, the yield of the epoxyenynol
obtained was somewhat lower than the one obtained
with the corresponding silylated product (entry 5 vs. 1),
as observed in the case of the propargyl alcohol (Table
1, entry 7 vs. 6).
More functionnalized vinyl triflates 8-9, conjugated
with a carbonyl group, [17] have also been coupled with
the epoxyalkyne 6a. The reactions led in an efficient
way to the expected epoxyenynones 11a-12a (entries 6,
7) as evidenced by their spectroscopic characteristics.
(Section 7). These compounds proved to be very sensi-
tive and although the NMR spectra of the crude mix-
When we observed that copper salts were responsible
for degradation during coupling with epoxyalkynes, we
looked for alternative catalysts. The analogy in elec-
tronic structure and chemical properties [23] led us to
envisaged the use of silver salts instead of copper salts
for coupling reactions. Since silver acetylides can be
obtained from the corresponding terminal acetylenes
using silver nitrate in the presence of ammonia, [23] we
reasoned that amines could a priori be also effective in
the formation of silver acetylides starting from terminal

P. Bertus, P. Pale / Journal of Organometallic Chemistry 567 (1998) 173–180
177
Table 2
Synthesis of epoxyenynes
a
Yields of isolated chromatographically pure products.
b CuI used instead of AgI.
c CuI used instead of AgI, and alkyne slowly added over the other compounds.
d Piperidine used instead of AgI, DIPEA and DMF.
e Quantitative if yield refered to triflate conversion.
acetylenes and silver salts. Furthermore, a few reactions
were known to proceed under silver salts catalysis, the
mechanisms of which probably involved silver-acetylene
complexes [24] or even silver acetylides [25,26]. There-
fore, a catalytic process comparable to the one involved
in coupling reactions using copper salts could also be
envisaged (Scheme 3, right part: M=Cu, Ag).
alkyne and amine in DMF leading to a silver acetylide
(Scheme 3, right part: M=Ag). [27] The latter would
then behave as other metal acetylides and thus react in
a transmetallation process with the organopalladium
species resulting from oxidative addition of the vinyl
triflate to a zerovalent palladium species. As silver
acetylides are probable intermediates in the present
coupling reaction, independent formation of silver
In our conditions, silver iodide may thus react with

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P. Bertus, P. Pale / Journal of Organometallic Chemistry 567 (1998) 173–180
Scheme 3.
acetylides and their uses in coupling reactions are now
actively pursued, and the results will be described in
due course.
7.2. Typical procedure for coupling:
1-(4-tert-butyl-1-cyclohexenyl)-1-hexyne 5a
A sample of diisopropylethylamine (154 vL, 0.89
mmol), tetrakis(triphenylphosphine) palladium (81 mg,
0.07 mmol) and silver iodide (33 mg, 0.14 mmol) were
added at r.t. under argon to a solution of 4-tert-butyl-
1-cyclohexenyl trifluoromethanesulfonate 4 (200 mg,
0.63 mmol) in dimethylformamide (10 ml). This solu-
tion was stirred for 10 min. in the dark, then 1-hexyne
(100 vl, 0.85 mmol) was added. The reaction was
monitored by TLC until the alkyne or the triflate was
consumed. The mixture was then quenched with satu-
rated aquous ammonium chloride (10 ml) and extracted
with ether (3×20 ml). The combined organic extracts
were washed with water (3×10 ml), dried (MgSO4) and
concentrated. The crude product was purified by flash
chromatography (silica gel-petroleum ether 100%) giv-
ing 125 mg (82%) of 5a as a colorless liquid. Spectro-
scopic data of 5a identical with the reported values [11].
6. Conclusion
The Pd–Ag catalyzed reaction between enol triflates
and alkynes provides a direct and efficient route to
highly functionnalized enynes. The examples described
here highlight the versatility of this coupling procedure
based on the new Pd–Ag set of catalysts. Good to
excellent yields of enynes were obtained even with
highly functionnalized alkynes. Interestingly enough,
acetylenic epoxydes can readily be coupled with various
enol triflates providing highly functionnalized
epoxyenynes in a single step.
This procedure is a good alternative to the well-
known Pd–Cu catalyzed coupling reaction and is far
better for the direct synthesis of epoxyenynes. Works
are currently in progress in our laboratory to explore
further and understand better this reaction.
7.3. Selected physical data of enynes 5c, 5d, 5e, 5f,
10a, 10b, 11a, 12a, 13
7. Experimental section
3-(4-Tert-butyl-1-cyclohexenyl)-2-propyn-1-ol (5c):
1
colorless oil. FT-IR (film): w=3353, 2218 cm−1. H‘-
7.1. General
NMR (250 MHz, CDCl3): l=0.85 (9H, s), 1.09–1.30
(2H, m), 1.76–1.92 (2H, m), 2.05–2.21 (4H, m), 4.36
(2H, s), 6.07–6.13 (1H, m). 13C-NMR. (62 MHz,
CDCl3): l=23.67, 27.02, 27.30, 30.55, 32.06, 43.13,
51.42, 84.81, 87.14, 119.86, 135.55. H.R.M.S (E.I.) m/
e=192.1507 (192.1514 calc. for C13H20O).
Yields are on isolated products. H-NMR and 13C-
1
NMR spectra were recorded on a Brucker AC-250. IR
spectra were recorded on a Spectrafile IRTM Plus MI-
DAC spectrometer. Mass spectra were measured on a
Jeol D300 (70 eV) mass spectrometer. Melting points
are uncorrected. Flash chromatography was carried out
on silica gel purchased from Merck (0.040–0.063
mesh). Amines and DMF were dried and distilled from
CaH2.
3-(4-Tert-butyl-1-cyclohexenyl)-1-tert-butyldiphenyl-
silyloxy-2-propyne (5d): colorless oil. FT-IR (film): w=
1
2220 cm−1. H-NMR (250 MHz-CDCl3): l=0.85 (9H,
s), 1.07 (9H, s), 1.15–1.45 (2H, m) 1.78–1.95 (2H, m),
2.10–2.21 (3H, m), 4.44 (2H, s), 6.00–6.06 (1H, m),

P. Bertus, P. Pale / Journal of Organometallic Chemistry 567 (1998) 173–180
179
7.33–7.45 (6H, m), 7.69–7.76 (4H, m). 13C-NMR (62
MHz, CDCl3): l=19.18, 23.75, 26.77, 27.13, 27.33,
30.54, 32.15, 43.22, 53.24, 85.13, 86.70, 120.22, 127.61,
129.65, 133.40, 134.97, 135.67. H.R.M.S (E.I.) m/e=
430.2708 (430.2692 calc. for C29H38OSi).
(1H, t, J=2.9), 7.32–7.41 (6H, m), 7.66–7.72 (4H, m).
13C-NMR (62 MHz, CDCl3): l=19.18, 19.18, 22.94,
26.71, 28.80, 38.31, 52.09, 63.81, 64.82, 81.77, 97.79,
110.94, 127.71, 129.74, 133.06, 133.36, 135.52, 148.70,
205.29.
5-(4-Tert-butyl-1-cyclohexenyl)-3-methyl-4-pentyne-
1,2,3-triol 1,2-carbonate (5e): colorless oil. FT-IR
Cis (Z)-2-(6-tert-butyldiphenylsilyloxy-4,5-epoxy-4-
methyl-2-hexynylidene)-cyclopentanone (12a): yellow
1
(film): w=3428, 2218, 1806–1777 cm−1. H-NMR (250
1
oil. FT-IR (film): w=2216 cm−1. H‘-NMR (250 MHz,
MHz, CDCl3): l=0.85 (9H, s), 1.05–1.29 (2H, m),
1.56 (3H, s), 1.73–1.90 (2H, m), 2.02–2.20 (3H, m),
2.89 (1H, s), 4.47–4.65 (3H, m), 6.11–6.18 (1H, m).
13C-NMR (62 MHz, CDCl3): l=23.51, 26.39, 27.00,
27.32, 30.23, 32.06, 43.00, 66.45, 68.81, 80.02, 83.98,
87.91, 118.96, 137.22, 154.89. H.R.M.S (E.I.) m/e=
292.1674 (292.1674 calc. for C17H24O4).
CDCl3): l 1.08 (9H, s), 1.62 (3H, s), 1.92 (2H, tt,
J=7.7, J=7.2), 2.32 (2H, t, J=7), 2.71 (2H, td,
J=7.2, J=2.4), 3.20 (1H, dd, J=5.4, J=4.8), 3.97
(1H, dd, J=11.7, J=5), 4.07 (1H, dd, J=11.7, J=
4.8), 5.67 (1H, t, J=2.4), 7.34–7.43 (6H, m), 7.70–7.74
(4H, m). 13C-NMR (62 MHz, CDCl3): l=19.22, 19.79,
22.90, 26.77, 31.27, 39.05, 52.24, 63.92, 65.20, 81.77,
95.64, 110.43, 127.60, 129.53, 133.42, 133.67, 135.61,
147.44, 203.62.
6-(4-Tert-butyl-1-cyclohexenyl)-3-tert-butyldiphenyl-
silyloxy-1-trimethylsilyl-1,5-hexadiyne (5f): colorless oil.
FT-IR (film): w=2218, 2177 cm−1 1H-NMR (250
.
Cis 6-(4-tert-butyl-1-cyclohexenyl)-1-tert-butyldime-
thylsilyl-3,4-epoxy-4-methyl-1,5-hexa-diyne (13): yellow
MHz, CDCl3): l=0.05 (9H, s), 0.85 (9H, s), 1.11–1.34
(2H, m), 1.75–1.92 (2H), 2.05–2.18 (3H, m), 2.73 (2H,
br d, J=6.5), 4.50 (1H, t, J=6.5), 5.98–6.03 (1H, m),
7.32-7.46 (6H, m), 7.72–7.81 (4H, m). 13C-NMR (62
MHz, CDCl3): l= −0.35, 19.37, 23.85, 26.91, 27.14,
27.31, 29.88, 30.84, 32.17, 43.31, 63.48, 83.38, 83.99,
89.71, 105.85, 120.67, 127.33, 127.51, 129.53, 129.63,
133.45, 133.63, 133.98, 135.99, 136.13.
1
oil. FT-IR (film): w=2222, 2174 cm−1. H-NMR (250
MHz, CDCl3): l=0.13 (6H, s), 0.86 (9H, s), 0.95 (9H,
s), 1.12–1.32 (2H, m), 1.55 (3H, s), 1.78–1.93 (2H, m),
2.09–2.26 (3H, m), 3.44 (1H, s), 6.15–6.21 (1H, m).
13C-NMR (62 MHz, CDCl3): l= −4.74, 16.42, 22.81,
23.66, 25.99, 27.08, 27.41, 30.39, 32.14, 43.16, 53.36,
54.51, 81.42, 87.49, 88.07, 102.87, 119.54, 136.93.
H.R.M.S (E.I.) m/e=306.2537 (306.2535 calc. for
C23H36OSi).
Cis
phenylsilyloxy-2,3-epoxy-3-methyl-4-pentyne (10a): col-
orless solid. M.p. 75°C. FT-IR (film): w=2222 cm−1
5-(4-tert-butyl-1-cyclohexenyl)-1-tert-butyldi-
.
1H-NMR (250 MHz, CDCl3): l=0.85 (9H, s), 1.07
(9H, s), 1.00–1.26 (2H, m), 1.53 (3H, s), 1.73–1.85 (2H,
m), 1.90–2.05 (3H, m), 3.13 (1H, t, J=5.2), 3.87 (1H,
dd, J=11.5, J=5.2), 3.93 (1H, dd, J=11.5, J=5.2),
5.91–5.97 (1H, m), 7.33–7.45 (6H, m), 7.68–7.72 (4H,
m). 13C-NMR (62 MHz, CDCl3): l=19.22, 23.38,
23.60, 26.76, 27.06, 27.31, 30.30, 32.11, 43.10, 52.36,
63.91, 64.61, 83.62, 85.98, 119.47, 127.64, 129.61,
133.28, 133.59, 135.58, 136.26. H.R.M.S (E.I.) m/e=
486.2935 (486.2954 calc. for C32H42O2Si).
Acknowledgements
P. Bertus thanks the ‘Ministe`re de l’Education Na-
tionale, de l’Enseignement Supe´rieur et de la
Recherche’ for a doctoral fellowship.
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2222 cm−1. H-NMR (250 MHz-CDCl3): l=0.83 (9H,
s), 1.05–1.30 (3H, m), 1.55 (3H, s), 1.75–1.90 (2H, m),
2.00–2.20 (3H, m), 3.12 (1H, dd, J=6.1, J=4.6), 3.81
(1H, dd, J=12.2, J=6.1), 3.89 (1H, dd, J=12.2,
J=4.6), 6.10–6.15 (1H, m). 13C-NMR (62 MHz,
CDCl3): l=23.50, 23.59, 27.03, 27.34, 30.40, 32.10,
43.07, 52.39, 62.57, 64.27, 83.39, 86.32, 119.35, 136.75.
M.S (E.I.) m/e=248 (M+).
Cis (E)-2-(6-tert-butyldiphenylsilyloxy-4,5-epoxy-4-
methyl-2-hexynylidene)-cyclopentanone (11a): yellow
1
oil. FT-IR (film): w=2216 cm−1. H-NMR (250 MHz,
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115564h.
CDCl3): l 1.09 (9H, s), 1.59 (3H, s), 1.85 (2H, tt,
J=7.8, J=7.4), 2.35 (2H, t, J=7.8), 2.49 (2H, td,
J=7.4, J=2.9), 3.23 (1H, t, J=5.2), 3.90 (1H, dd,
J=11.4, J=5.2), 3.93 (1H, dd, J=11.4, J=5.2), 6.24

180
P. Bertus, P. Pale / Journal of Organometallic Chemistry 567 (1998) 173–180
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[14] This diyne was obtained from propargyl alcohol, see reference
17.
[15] This alkyne is easily obtained from the commercially available
(Fluka) Z 3-methyl pent-2-en-4-yn-1-ol after mCPBA epoxida-
[27] Isolation of silver acetylides in the conditions we used was so far
unsuccessfull. However, 1H-NMR of the crude mixture obtained
from alkynes and silver salts in the presence of tertiary amines
exhibited changes suggesting the formation of such complexes.
.
.