Iodotrimethylsilane-Promoted 1,4-Addition of Copper Acetylides to α,β-Unsaturated Ketones and Aldehydes

Article abstract of DOI:10.1021/jo960393d

In the presence of iodotrimethylsilane (TMSI) and lithium iodide in tetrahydrofuran, the otherwise unreactive copper acetylides add to enones present as s-trans conformers to provide good yields of the silyl enol ethers of β-acetylido carbonyl compounds.

Full text of DOI:10.1021/jo960393d

182
J . Org. Chem. 1997, 62, 182-187
Iod otr im eth ylsila n e-P r om oted 1,4-Ad d ition of Cop p er Acetylid es
to r,â-Un sa tu r a ted Keton es a n d Ald eh yd es
Magnus Eriksson, Tommy Iliefski, Martin Nilsson,* and Thomas Olsson
Department of Organic Chemistry, Chalmers University of Technology, S-412 96 Go¨teborg, Sweden
Received February 27, 1996X
In the presence of iodotrimethylsilane (TMSI) and lithium iodide in tetrahydrofuran, the otherwise
unreactive copper acetylides add to enones present as s-trans conformers to provide good yields of
the silyl enol ethers of â-acetylido carbonyl compounds. Typically good substrates are 2-cyclopen-
tenone, 2-cyclohexenone, R,â-unsaturated aldehydes, and â-alkoxy-R-enones. Copper acetylide
reagents prepared from CuI and an alkynyllithium give considerably higher yields than those
prepared from CuBr or CuCN. Iodotrimethylsilane is by far the most efficient silane, although
trimethylsilyl triflate is useful in some cases.
In tr od u ction
onstrated conjugate addition of RCtCCu‚LiCN to R-enones
in the presence of tert-butyldimethylsilyl triflate.8
Several of the existing methods for conjugate addition
of alkynyl groups to R,â-unsaturated ketones involve
organoaluminum or organoboron reagents. For example,
alkynyldiethylalanes9 add to enones capable of adopting
an s-cis conformation, whereas cyclic enones give only
1,2-addition. Nickel-catalyzed addition10 of organoalu-
minum acetylides is also effective for s-trans substrates.
Alkynylboron reagents11,12 add only to R,â-enones that
assume an s-cis conformation, whereas lithium acetyli-
doaluminates13 add both to s-cis and to s-trans enones.
Trialkylsilyl triflates promote conjugate addition of alky-
nylzinc reagents.14 Conjugate alkynylation with lithium
acetylides alone is possible to both cyclic and acyclic
R-enones if the carbonyl group is blocked by a bulky
aluminum complex.15
In this paper we demonstrate the conjugate addition
of copper acetylides in THF together with iodotrimeth-
ylsilane (TMSI) and LiI to enones and to R,â-unsaturated
aldehydes. This protocol gives good to excellent yields
of silyl enol ethers of γ,δ-acetylenic carbonyl compounds.
We have previously demonstrated that alkyl- and aryl-
copper reagents, RCu‚LiI, in the presence of TMSI add
to a variety of R,â-unsaturated enones and enoates.1 We
now report extensions of our previous observation that
pentynylcopper(I)‚LiI and TMSI add to 2-cyclopenten-
one.2
Conjugate addition of alkyl, alkenyl, and aryl groups
via organocuprates and mono-organocopper compounds
is a widely used synthetic method.3 Activating agents
like TMSI,4 TMSCl,5 and BF3 have extended the scope,
6
especially for the mono-organocopper compounds. Lithium
iodide is often important in these reactions, and we
therefore denote the copper reagents as RCu‚LiI or
RCtCCu‚LiI in the text. So far alkynyl ligands have
been considered unreactive in copper-promoted conjugate
additions and are often used as nontransferable groups
in mixed lithium diorganocuprates.7 Lithium bis(acetyli-
do)cuprates on the other hand give 1,2-addition to R,â-
unsaturated aldehydes.5b However, a recent report dem-
Resu lts
Treatment of an acetylene with butyllithium followed
by copper(I) iodide, or addition of the lithium acetylide
to a suspension of CuI, gives copper acetylide and lithium
iodide. (Trimethylsilyl)acetylene and 5-(benzyloxy)pen-
tyne give the copper acetylides as solutions in THF (ca.
0.35 M), whereas those from pentyne or phenylacetylene
form suspensions. TMSI is added to the copper acetylide
at -78 °C. In contrast to alkylcopper reagents, there is
often a distinct change when TMSI is added to the
alkynyl reagents; for example, [(trimethylsilyl)ethynyl]-
copper(I) goes from a greenish-yellow solution to a light-
green suspension. This indicates the formation of a
complex between the organocopper compound and TMSI.
On adding 2-cyclohexenone (1) or 2-cyclopentenone (2)
to the RCtCCu‚LiI-TMSI preparations, at -78 °C, we
sometimes observe a color change toward yellow, which
X Abstract published in Advance ACS Abstracts, December 15, 1996.
(1) (a) Bergdahl, M.; Lindstedt, E.-L.; Nilsson, M.; Olsson, T.
Tetrahedron 1988, 44, 2055. (b) Bergdahl, M.; Lindstedt, E.-L.; Nilsson,
M.; Olsson, T. Tetrahedron 1989, 45, 535. (c) Bergdahl, M.; Nilsson,
M.; Olsson, T. J . Organometal. Chem. 1990, 391, C19. (d) Bergdahl,
M.; Nilsson, M.; Olsson, T. Stern, K. Tetrahedron 1991, 47, 9691. (e)
Eriksson, M.; Nilsson, M.; Olsson, T. Synlett 1994, 271.
(2) Bergdahl, M.; Eriksson, M.; Nilsson, M.; Olsson, T. J . Org. Chem.
1993, 58, 7238.
(3) (a) Lipshutz, B. H.; Sengupta. S. Org. React. 1992, 41, 135. (b)
Perlmutter, P. Conjugate Addition Reactions in Organic Synthesis;
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React. 1990, 38, 225.
(4) (a) Eriksson, M.; Hjelmencrantz, A.; Nilsson, M.; Olsson, T.
Tetrahedron 1995, 51, 12631. (b) Bergdahl, M.; Iliefski, T.; Nilsson,
M.; Olsson, T. Tetrahedron Lett. 1995, 36, 3227. (c) Nilsson, K.;
Ullenius, C. Tetrahedron 1994, 50, 13173. (d) Eriksson, M.; J ohansson,
A.; Nilsson, M.; Olsson, T. J . Am. Chem. Soc. 1996, 118, 10904.
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36, 2305. (b) Ibid. 1981, 37, 1385. (c) Corey, E. J .; Boaz, N. W.
Tetrahedron Lett. 1985, 26, 6015. (d) Ibid. 1985, 26, 6019. (e) Mat-
suzawa, S.; Horiguchi, Y.; Nakamura, E.; Kuwajima, I. Tetrahedron
1989, 45, 349. (f) J ohnson, C. R.; Marren, T. J . Tetrahedron Lett. 1987,
28, 27.
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16, 783.
(9) Hooz, J .; Layton R. B. J . Am. Chem. Soc. 1971, 93, 7320.
(10) (a) Hansen, R. T.; Carr, D. B.; Schwartz, J . J . Am. Chem. Soc.
1978, 100, 2244. (b) Schwartz, J .; Carr, D. B.; Hansen, R. T.; Dayrit,
F. M. J . Org. Chem. 1980, 45, 3053.
(11) (a) Sinclair, J . A.; Molander, G. A.; Brown, H. C. J . Am. Chem.
Soc. 1977, 99, 954. (b) Molander, G. A.; Brown, H. C. J . Org. Chem.
1977, 42, 3106.
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1992, 695.
(6) Yamamoto, Y. Angew. Chem., Int. Ed. Engl. 1986, 25, 947.
(7) (a) Corey, E. J .; Beames, D. J . J . Am. Chem. Soc. 1972, 94, 7210.
(b) Posner, G. H.; Chapdelaine, M. J .; Lentz, C. M. J . Org. Chem. 1979,
44, 3661.
(13) Kim, S.; Park, J . H. Synlett 1995, 163.
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1994, 519.
S0022-3263(96)00393-3 CCC: $14.00 © 1997 American Chemical Society

1,4-Addition of Copper Acetylides to Enones
J . Org. Chem., Vol. 62, No. 1, 1997 183
Sch em e 1
Sch em e 2
Sch em e 3
Ta ble 1. Con ju ga te Ad d ition of RCtCCu (LiI)-TMSIa to
2-Cycloh exen on e (1), 2-Cyclop en ten on e (2),
2-Meth yl-2-cyclop en ten on e (3), a n d Ch r om on e (5). Th e
Yield s Refer to Isola ted Ad d u ct Keton es
temp (°C),
time
yield
product (%)
entry enone
R
solvent
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
3
3
5
5
C3H7
C3H7
C3H7
C3H7(-LiI) THF
C3H7
Ph
Me3Si
t-Bu
t-Bu
C3H7
Ph
THF
Et2O
-30, 30 min
-30, 30 min
1a
1a
1a
1a
1a
1b
1c
1d
1d
2a
2b
2b
2c
2c
2c
2d
3a
3b
5a
5b
89
32
33
ethynyl)-2-cyclohexenone (30%). Additions of [(trimeth-
ylsilyl)ethynyl]copper(I) and (tert-butylethynyl)copper(I)
to chromone17 (5) give excellent yields of addition prod-
ucts (Table 1, entries 19 and 20).
Acyclic En on es. Additions of copper acetylide‚LiI
and TMSI to acyclic enones were less successful: (phen-
ylethynyl)copper(I) and ethyl vinyl ketone (6) gave 37%
of conjugate adduct 6a and 4-hexen-3-one gave only 12%
yield. For acyclic enones in general the s-cis conforma-
tion is favored.18 Pentynylcopper(I)‚LiI-TMSI added
neither to 1-acetyl-1-cyclohexene nor to chalcone. At-
tempted additions of RCtCCu‚LiI-TMSI to methyl
acrylate were unsuccessful.
To summarize so far, the cycloalkenones, which have
s-trans geometry, give fast reactions and good yields,
whereas acyclic alkenones, known to be present mainly
as s-cis conformers, give rather poor results. We there-
fore predicted that acyclic substrates such as R,â-
unsaturated aldehydes and (E)-4-methoxy-3-buten-2-one
(7), known to prefer s-trans conformation,2,5e,19 should
react better. The prediction was valid and additions of
(phenylethynyl)copper(I) and [(trimethylsilyl)ethynyl]-
copper(I) to (E)-4-methoxy-3-buten-2-one gave good yields
of the substitution products after hydrolysis. Also a
functionalized acetylene, prepared from geranylacetone,20
added in good yield. The products are the result of initial
conjugate addition to give the silyl enol ethers followed
by elimination of MeOH during hydrolysis giving net
substitution of the methoxy group (Scheme 3).2,21
(Phenylethynyl)copper(I)‚LiI-TMSI also adds in rea-
sonable yields both to acrylaldehyde (8) and to crotonal-
dehyde (9) to give predominantly E-silyl enol ethers. We
presume that the reaction is general for R,â-unsaturated
aldehydes (Scheme 4).
CH2Cl2 -30, 30 min
-30, 1 h
32
THF
THF
THF
THF
Et2O
THF
THF
-30, 30 min
-30, 30 min
-30, 30 min
-78, 45 min
-78, 45 min
-30, 30 min
-30, 1 h
52b
90
88
97
11
68e
75
Ph
CH2Cl2 -40, 2 h
41
Me3Si
Me3Si
Me3Si
BnO(CH2)3 THF
C3H7 THF
BnO(CH2)3 THF
THF
THF
THF
-30, 30 min
92
-30, 30 min
-30, 30 min
-30, 1 h
70b
68c
94
-50, 4 h
-50, 4 h
-30, 70 min
-30, 70 min
45d
54d
98
Me3Si
t-Bu
THF
THF
90
a
All copper reagents contain LiI from the preparation unless
otherwise noted. b Substrate:copper compound:TMSI ) 1:1:1. c Sub-
d
strate:copper compound:TMSI ) 1:1:1.5. Substrate:copper com-
pound:TMSI ) 1:1.5:3. e Taken from ref 2.
indicates formation of a π-complex.16 In some cases the
conjugate addition proceeds at -78 °C, but we generally
observe the reaction leading to acetylenic silyl enol ethers
around -30 °C. These can be isolated after addition of
triethylamine at low temperature or hydrolyzed directly
to the corresponding γ,δ-acetylenic ketones (Scheme 1).
Cycloa lk en on es. The scope of the reaction between
some cyclic enones and alkynylcopper(I)‚LiI-TMSI re-
agents is summarized in Table 1, where yields are given
for the ketones obtained after hydrolysis.
As seen from Table 1, the different alkynylcopper
reagents add to 2-cyclopentenone and 2-cyclohexenone
in good to excellent yields. Additions to 2-methyl-2-
cyclopentenone (3) are slow and give lower yields. Here,
cleavage of THF by TMSI competes to give 1-iodo-4-
[(trimethylsilyl)oxy]butane, consuming TMSI. The reac-
tion with RCtCCu‚LiI and trimethylsilyl triflate is slow
but gives higher yields without significant THF cleavage
(Table 2, entry 11). Addition of RCtCCu‚LiI-TMSOTf
to 3-methyl-2-cyclopentenone (4) is slow, and the yield
is poor (Table 2, entry 12).
Rea ction Con d ition s. In order to optimize the
reactions we checked for suitable solvents and reagent
proportions for the substrates 2-cyclopentenone and
2-cyclohexenone. The reactions in THF give considerably
(17) Fo¨hlisch, B. Chem. Ber. 1971, 104, 348.
(18) (a) Montaudo, G.; Librando, V.; Caccamese, S.; Maravigna, P.
J . Am. Chem. Soc. 1973, 95, 6365. (b) Oelichmann, H.-J .; Bougeard,
D.; Schrader, B. Angew. Chem. Suppl. 1982, 1404. (c) Chamberlin, A.
R.; Reich, S. H. J . Am. Chem. Soc. 1985, 107, 1440.
(19) Gung, B. W.; Gerdeman, M. S.; Fouch, R. A.; Wolf, M. A. J .
Org. Chem. 1994, 59, 4255.
Addition of (phenylethynyl)copper(I) to 3-ethoxy-2-
cyclohexenone gives the substitution product, 3-(phenyl-
(20) Bergstro¨m, G.; J ohansson, A.; Olsson, T. Tetrahedron Lett. 1996,
37, 7127.
(21) Cahiez, G.; Alami, M. Tetrahedron Lett. 1989, 30, 3541.
(16) Vellekoop, A. S.; Smith, R. A. J . J . Am. Chem. Soc. 1994, 116,
2902.

184 J . Org. Chem., Vol. 62, No. 1, 1997
Eriksson et al.
Ta ble 3. Th e In flu en ce of Cu (I) P r ecu r sor s. Con ju ga te
Ad d ition of RCtCCu (LiX)-TMSI in THF to
2-Cycloh exen on e (1) a n d 2-Cyclop en ten on e (2). Th e
Yield s Refer to Isola ted Ad d u ct Keton es.
Sch em e 4
entry enone
R
X
temp, (°C), time product yield (%)
1
2
3
4
5
6
7
8
1
1
1
1
2
2
2
2
C3H7
I
-30, 0.5 h
-30, 1 h
-30, 1 h
-30, 1 h
-30, 1 h
-30, 1 h
-40, 2 h
-40, 2 h
1a
1a
1c
1c
2b
2b
2b
2b
89
7
7
<1
75
73a
6
C3H7 Br
SiMe3 CN
SiMe3 OTf
Ph
Ph
Ph
Ph
I
I
Ta ble 2. Th e In flu en ce of Differ en t Ad d itives.
Con ju ga te Ad d ition of RCtCCu (LiI)-X in THF to
2-Cycloh exen on e (1), 2-Cyclop en ten on e (2),
2-Meth yl-2-cyclop en ten on e (3), a n d
3-Meth yl-2-cyclop en ten on e (4). Th e Yield s Refer to
Isola ted Ad d u ct Keton es.
Br
CN
0
a
CuI (Aldrich 99.999%) was used.
compounds to R,â-unsaturated carbonyl compounds. The
conjugate addition of copper acetylide‚LiI-TMSI requires
a reactive substrate. Enoates do not react, and among
enones only cycloalkenones and those that preferentially
assume an s-trans conformation are good substrates.
Other distinctive features are the importance of THF as
solvent and the strong effect of LiI present.
The preference for reactions with s-trans conformers
parallels the reactions of reactive mono-organocopper
compounds and TMSI with enoates, which are less
reactive than enones. We have also seen this in additions
to naphthylbornyl crotonates1d and allylic enoates.1e The
present discussion therefore strongly connects to that in
our recent paper on conjugate addition to allylic
acrylates.4a
The results from all these investigations indicate a
common mechanism for reactions of moderately reactive
copper acetylides/TMSI with reactive substrates and of
reactive mono-organocopper compounds/TMSI with the
moderately reactive enoates.
NMR investigations of the reaction between organo-
cuprates and R,â-unsaturated carbonyl compounds have
shown that formation of a π-complex probably takes place
prior to the transfer of the organic ligand.16,24 A similar
complexation seems probable also for the mono-organo-
copper reactions, including those of the copper acetylides,
but remains to be proven. We have not yet been able to
observe π-complexes between mono-organocopper com-
pounds and enones by NMR methods, but we have seen
color changes which indicate such complexes.16
yield
temp (°C), time product (%)
entry enone
R
X
1
2
1
1
1
2
2
2
2
2
2
2
3
4
C3H7 TMSI
C3H7 TMSBr
C3H7 TMSCl
Ph
Ph
Ph
-30, 30 min
-30, 30 min
-30, 30 min
-30, 1 h
1a
1a
1a
2b
2b
2b
2a
2a
2a
2c
3c
4a
89
<2
0
75
0
3
4
5
6
TMSI
BF3
TMSCN
-40, 2 h
-40, 2 h
-30, 30 min
0
7
8
9
C3H7 TMSI
68
25
0
0
81
16
C3H7 TMSOTf -30, 30 min
C3H7 BF3
SiMe3 BF3
-30, 30 min
-30, 2 h
10
11
12
SiMe3 TMSOTf -30, 1 h
SiMe3 TMSOTf -40 to 0, 5 h
higher yields and rates than those in diethyl ether or
dichloromethane. A moderate excess of copper acetylide
was beneficial and the best proportions of substrate:
copper acetylide‚LiI:TMSI were around 1:1.5:1.5.
Rea gen ts. TMSI proved uniquely effective for the
reactions as demonstrated in Table 2. TMSCl, TMSBr,
TMSCN, and BF3 are all ineffective. TMSI is clearly
more effective than TMSOTf, and the latter requires the
presence of LiI for reaction. Reaction of TMSOTf with
LiI could give TMSI. A reagent from lithium (trimeth-
ylsilyl)acetylide and copper(I) triflate did not add to
2-cyclohexenone in the presence of TMSOTf; the THF
polymerized instead.22 On the other hand, this acetylide
added to 2-cyclohexenone in the presence of TMSI,
although only in trace amounts (Table 3, entry 4). Still
TMSOTf can be useful in combination with copper
acetylide‚LiI for hindered enones (Table 2, entries 11 and
12).
There are important differences between the mono-
organocopper and the organocuprate reactions. Mono-
organocopper compounds in general require an additive,
at least LiI from their preparation and preferably also
TMSI. Such additives are not needed for the organocu-
prates, even though TMSCl often increases the reactivity
of cuprates quite strongly and can affect the stereochem-
ical outcome as well.5 Coordination of the lithium of a
diorganocuprate to the carbonyl oxygen of the substrate
is crucial, however, and can be counteracted by THF,
which slows down the reaction considerably.25 For
RCtCCu‚LiI-TMSI reactions, on the other hand, THF
increases the rates. We believe that coordination of Li
to the carbonyl oxygen is less important, whereas iodide
from LiI and TMSI is important for the reactivity of the
mono-organocopper compounds.
The copper acetylide preparations obtained by treat-
ment of an acetylene with butyllithium, followed by
addition of solid copper iodide, are superior for the
conjugate additions. They naturally contain lithium
iodide. Removal of the dissolved lithium iodide gives a
distinct drop in yield (Table 1, entry 4). Use of the
complex CuI.0.75DMS (dimethyl sulfide), CuI purified via
KCuI2 or 99.999% CuI gave comparable results (see
Experimental Section). Still the dimethyl sulfide complex
is probably more soluble than the other preparations.
Attempts to use CuBr‚DMS complex or CuCN instead
of CuI gave poor yields (Table 3). These findings are in
line with the results of Bertz and Dabbagh for conjugate
addition of BuCu‚LiX reagents to 2-cyclohexenone in
THF.23
Organocuprates and monoorganocopper‚LiI-TMSI re-
agents give different epimers when reacted with chiral
Discu ssion
The present results further demonstrate the usefulness
of TMSI in conjugate additions of mono-organocopper
(24) (a) Hallnemo, G.; Olsson, T.; Ullenius, C. J . Organomet. Chem.
1985, 282, 133. (b) Christenson, B.; Olsson, T.; Ullenius, C. Tetrahedron
1989, 45, 523. (c) Bertz, S. H.; Smith, R. A. J . J . Am. Chem. Soc. 1989,
111, 8276. (d) Krause, N. J . Org. Chem. 1992, 57, 3509.
(22) Hrkach, J . S.; Matyjaszewski, K. Macromolecules 1990, 23,
4042.
(23) Bertz, S. H.; Dabbagh, G. Tetrahedron 1989, 45, 425.
(25) House, H. O.; Wilkins, J . M. J . Org. Chem. 1978, 43, 2443.

1,4-Addition of Copper Acetylides to Enones
J . Org. Chem., Vol. 62, No. 1, 1997 185
Sch em e 5
Exp er im en ta l Section
Gen er a l. All reactions were performed under argon and
in cooled oven-dried glassware (140 °C). NMR spectra were
recorded at 400 MHz or 500 MHz with CDCl3 as solvent and
TMS as internal standard (δ ) 0). Coupling patterns are
abbreviated as: s, singlet; d, doublet; t, triplet; q, quartet; m,
multiplet; J , coupling constants are given in hertz (Hz). High
resolution mass spectra (HRMS) were recorded at 70 eV,
capillary column, DB-1. IR spectra were recorded on an FT-
IR instrument. Elemental analyses were performed by Ana-
lytische Laboratorien in Engelskirchen, Germany.
Ch em ica ls. All starting materials are commercially avail-
able from Aldrich, Merck, Fluka, or J anssen, unless otherwise
noted. Copper(I) cyanide (99%) from Aldrich and CuBr‚DMS
complex prepared according to House et al.28 were used.
Diethyl ether (Et2O) and tetrahydrofuran (THF) were distilled
from sodium benzophenone ketyl. Triethylamine (Et3N) and
dichloromethane (CH2Cl2) were distilled from CaH2 under
argon and used immediately. BuLi (1.6 M in hexane) was
purchased from Aldrich and titrated prior to use. Iodotri-
methylsilane (TMSI) was purchased from J anssen or Sigma
and stored septum-capped at -25 °C under argon with copper
chips in a light-protected bottle.
enoates.1c,d This difference indicates that the two types
of reagents react with different conformations of the
substrate. The organocuprate predominantly reacts with
an enoate in the s-cis conformation, whereas the mono-
organocopper‚LiI-TMSI reactions prefer the s-trans
conformation. On the other hand, TMSI can change the
course of organocuprate additions as recently observed
for allylic acrylates.4a
As also discussed in a recent paper, these observations
have led us to propose the following common mechanism
for additions of mono-organocopper compounds‚LiI-
TMSI to enones and enoates:
P u r ification of Copper Iodide.28 Copper(I) iodide (Merck,
99%) was dissolved in an Et2O/DMS mixture and filtered.
Dilution with hexane precipitated the new CuI‚1.5DMS com-
plex29 as white crystals. This complex was dried at room
temperature under vacuum for 1-2 h to give CuI‚0.75DMS
as a white powder. The complex is stable at room temperature
and does not spontaneously lose DMS on standing. Anal.
Calcd for CuI‚0.75DMS: C; 7.60. H; 1.91. Found: C; 7.42.
H; 1.76. It should be pointed out that CuI (Aldrich 99.999%)
or CuI purified via KCuI230 are also useful precursors in these
reactions.
Typ ica l P r oced u r e for th e TMSI-P r om oted Con ju ga te
Ad d ition of Alk yn ylcop p er Rea gen ts. BuLi (7.5 mmol) is
added at -10 °C to a stirred solution of the acetylene (7.5
mmol) in 20 mL of dry THF. The solution is stirred for 20
min at -10 °C after which CuI‚0.75DMS (8.25 mmol) is added
in one batch. After stirring the copper acetylide suspension/
solution for 45 min at -10 °C, the temperature is lowered to
-78 °C and TMSI (7.5 mmol) added. The mixture is stirred
at -78 °C another 5 min, and then the R,â-unsaturated
substrate (5 mmol), dissolved in 5 mL of dry THF, is added
slowly via the cold flask wall (this procedure cools down the
substrate solution).
When the addition is complete the temperature is raised to
the values indicated in the Tables 1-3, and the mixture is
stirred for 0.5-5 h. Saturated NH4Cl (10 mL) is added at low
temperature, and the mixture is then stirred at room temper-
ature for 30 min. To affect complete hydrolysis, 2 mL of 3 M
HCl is added and the mixture stirred another 30 min at room
temperature. The layers are separated, and the aqueous phase
is extracted twice with ether. The combined ethereal layer is
washed once with 5% Na2S2O3, once with brine, and dried over
Na2SO4. Evaporation of the solvent gives the crude product,
generally as a slightly yellow oil, which is further purified by
flash chromatography and bulb-to-bulb distillation.
The first step is the formation of a π-complex, in which
the enone can adopt either of the s-cis or s-trans confor-
mations. Due to the strong interactions between the
copper and the acetylide ligand,26 we expect π-complexes
between copper acetylides and enones to be weaker than
those of alkylcopper compounds. Coordination of the
silicon in TMSI to one of the electron pairs of the carbonyl
oxygen then activates the substrate for the subsequent
addition. For the s-trans conformer of the substrate, this
arrangement is suitable for additional stabilization of the
π-complex by interaction between copper and the iodine
of TMSI. The arrangement also allows further reaction
of the π-complex, either through direct decomposition
yielding the silyl enol ether or formation of an R-cuprio
ketone27 with subsequent decomposition to product
(Scheme 5). In this scheme an interaction between
copper and TMSI is also possible, increasing the electro-
philicity of silicon and also the reactivity of the copper
acetylide.
For an s-cis conformer the stabilizations outlined above
are not possible. For steric reasons the silicon must
coordinate to the electron pair pointing away from the
carbon-carbon double bond. Thus there is no good path
for the decomposition of the intermediate π-complex to
product.
The mechanism proposal given in Scheme 5 accounts
for the s-trans selectivity in the mono-organocopper
reactions and for the superiority of TMSI as an additive,
since it can coordinate well to both the carbonyl oxygen
and the copper. The solvation of Li+ by THF leaves the
carbonyl group open for interaction with TMSI and the
iodide ion open for interaction with copper. In conjugate
additions of reactive mono-organocopper compounds/
TMSI to reactive substrates the selectivity is lower and
formation of Z enol ethers often dominates, indicating a
preferred path via s-cis conformers.
Typ ica l P r oced u r e Wh en Oth er Ad d itives Ar e Used .
The same procedure as above is used substituting TMSI for
TMSCl, TMSCN, BF3, etc.
Typ ica l P r oced u r e for Isola tion of TMS En ol Eth er s.
When the reaction is complete, dry Et3N is added at low
temperature (ca. 3 mol equiv versus TMSI) instead of NH4Cl.
The reaction mixture is stirred at room temperature for 1 h
and then diluted with Et2O or pentane. The organic layer is
washed once with saturated NaHCO3 and once with brine and
dried over Na2SO4. Evaporation of the solvent gives the crude
product, generally as a slightly brown-yellow oil, which is
In conclusion, the activation of copper acetylides by
TMSI has provided new synthetic possibilities and also
some new aspects of the mechanism of conjugate addi-
tions of organocopper reagents.
(28) House, H. O.; Chu, C.-Y.; Wilkins, J . M.; Umen, M. J . J . Org.
Chem. 1975, 40, 1460.
(29) Maelger, H.; Olbrich, F.; Kopf, J .; Abeln, D.; Weiss, E. Zeit.
Naturforsch. B 1992, 47(9), 1276.
(26) van Koten, G.; Noltes, J . G. In Comprehensive Organometallic
Chemistry; Pergamon: New York, 1982; Vol. 4, Chapt 14.
(27) Berlan, J .; Battioni, J . P.; Koosha, K. Bull. Soc. Chim. Fr. 1979,
183.
(30) Kauffman, G. B.; Teter, L. A. Inorg. Synth. 1963, 7, 9.

186 J . Org. Chem., Vol. 62, No. 1, 1997
Eriksson et al.
further purified by bulb-to-bulb distillation. Small amounts
of the cleavage product of THF and TMSI, 4-iodo-1-[(trimeth-
ylsilyl)oxy]butane,2 often remains in the product even after
bulb-to-bulb distillation.
83.9, 33.6, 33.1, 29.9, 0.4, 0.2. IR (neat): 2170 (CtC), 1643
(CdC) cm-1. HRMS: Calcd for C13H24OSi2: 252.136. Found:
252.137.
3-[5-(Ben zyloxy)-1-p en tyn yl]cyclop en ta n on e (2d ). Ob-
tained as a colorless oil after flash chromatography (30% ether
in pentane, Rf ) 0.27) followed by bulb-to-bulb distillation
(125-130 °C/0.06 mbar), 94% yield. 1H NMR: δ 7.22-7.38
(m, 5H), 4.51 (s, 2H), 3.54 (t, J ) 6, 2H), 2.95-3.05 (m, 1H),
1.74-2.50 (m, 10H). 13C NMR: δ 217.9, 138.7, 128.6, 127.8,
127.7, 82.0, 81.4, 73.1, 68.9, 45.7, 37.6, 30.7, 29.2, 27.8, 15.8.
3-(1-P en tyn yl)cycloh exa n on e (1a ). Obtained as a color-
less oil after flash chromatography (30% ether in pentane, Rf
) 0.51) followed by bulb-to-bulb distillation (175-176 °C/3
mbar), 89% yield. 1H NMR: δ 2.82-2.92 (m, 1H), 1.42-2.58
(m, 12H), 0.90 (t, J ) 7.0, 3H). 13C NMR: δ 209.7, 82.8, 81.4,
47.6, 41.3, 31.3, 30.3, 24.0, 22.4, 20.7, 13.5. IR (neat): 2254
(CtC), 1715 (CdO) cm-1
.
HRMS: Calculated for C11H16O:
IR (neat): 1745 (CdO) cm-1
. HRMS: Calcd for C17H20O2:
164.120. Found: 164.120. Anal. Calcd for C11H16O: C, 80.44;
H, 9.82. Found: C, 80.21; H, 9.84.
256.146. Found: 256.141. Anal. Calcd for C17H20O2: C,
79.65; H, 7.86. Found: C, 79.64; H, 7.75.
1-[(Tr im eth ylsilyl)oxy]-3-(1-pen tyn yl)cycloh exen e (1a′).
Obtained as a colorless oil after bulb-to-bulb distillation (70-
72 °C/0.8 mbar), 89% yield. 1H NMR: δ 4.86 (d, J ) 4.0, 1H),
3.05-3.15 (m, 1H), 1.42-2.17 (m, 10H), 0.96 (t, J ) 7.0, 3H),
0.19 (s, 9H). 13C NMR: δ 151.0, 106.2, 83.9, 79.7, 29.8, 29.7,
3-(1-P en tyn yl)-2-m eth ylcyclop en ta n on e (3a ). Obtained
as a colorless oil after flash chromatography (30% ether in
pentane, Rf ) 0.52 and 0.62) followed by bulb-to-bulb distil-
lation (54-56 °C/0.3 mbar), 45% yield. The presence of two
diastereomers in comparable amounts is evident from gas
chromatograms. 1H NMR: δ 3.14-3.22 (m, 1H), 1.96-2.50
(m, 7H), 1.42-1.58 (m, 2H), 1.15 (d, J ) 7.0, 3H), 0.97 (2t, J
) 7.0, 3H). 13C NMR: δ 219.6, 218.9, 84.6, 82.3, 81.2, 79.2,
51.4, 48.2, 37.1, 36.1, 35.7, 33.7, 28.6, 28.1, 22.6, 20.9, 13.6,
27.0, 22.7, 21.2, 20.9, 13.6, 0.51. IR (neat): 1667 (CdC) cm-1
.
HRMS: Calcd for C14H24OSi: 236.160. Found: 236.160.
3-(P h en yleth yn yl)cycloh exa n on e (1b).31 Obtained as a
colorless oil after flash chromatography (30% ether in pentane,
Rf ) 0.38) followed by bulb-to-bulb distillation (160-161 °C/
0.4 mbar), 90% yield. 1H NMR: δ 7.35-7.42 (m, 2H), 7.25-
7.31 (m, 3H), 3.06-3.15 (m, 1H), 2.65 (dd, J ) 14, 5, 1H), 2.52
(dd, J ) 14, 9, 1H), 2.37 (t, J ) 7, 2H), 2.04-2.24 (m, 2H),
1.74-1.96 (m, 2H). 13C NMR: δ 209.3, 131.8, 128.4, 128.1,
123.4, 90.8, 82.9, 47.2, 41.4, 31.2, 30.9, 24.2. IR (neat): 2233
(C≡C), 1715 (CdO) cm-1. HRMS: Calcd for C14H14O: 198.104.
Found: 198.106.
12.6, 11.2. IR (neat): 1745 (CdO) cm-1
. HRMS: Calcd for
C11H16O: 164.120. Found: 164.120. Anal. Calcd for
C11H16O: C, 80.44; H, 9.82. Found: C, 80.18; H, 9.80.
3-[5-(B e n z y lo x y )-1-p e n t y n y l]-2-m e t h y lc y c lo p e n -
ta n on e (3b). Obtained as a colorless oil (1:1 mixture of
diastereomers) after flash chromatography (30% ether in
pentane, Rf ) 0.35) followed by bulb-to-bulb distillation (125-
130 °C/0.05 mbar), 54% yield. The presence of two diastere-
omers in comparable amounts is evident from gas chromato-
grams. 1H NMR: δ 7.24-7.40 (m, 5H), 4.50-4.52 (2s, 2H),
3.51-3.58 (2t, J ) 6, 2H), 3.12-3.20 (m, 1H), 1.70-2.45 (m,
10H). 13C NMR: δ 219.5, 218.9, 138.7, 128.7, 128.6, 128.0,
127.9, 127.8, 84.0, 81.7, 81.5, 79.4, 73.2, 69.0, 51.4, 48.1, 37.1,
36.0, 35.6, 33.7, 29.4, 29.3, 28.5, 28.0, 15.8, 15.7, 12.6, 11.3.
3-[(Tr im eth ylsilyl)eth yn yl]cycloh exa n on e (1c).10b Ob-
tained as a colorless oil after flash chromatography (30% ether
in pentane, Rf ) 0.51) followed by bulb-to-bulb distillation
(123-125 °C/4 mbar), 88% yield. 1H NMR: δ 2.85-2.92 (m,
1H), 2.29-2.60 (m, 4H), 1.96-2.15 (m, 2H), 1.68-1.86 (m, 2H),
0.14 (s, 9H). 13C NMR: δ 209.1, 107.7, 86.7, 47.0, 41.2, 31.1,
IR (neat): 1742 (CdO) cm-1
. HRMS: Calcd for C18H22O2:
31.0, 24.1, 0.2. IR (neat): 2171 (CtC), 1715 (CdO) cm-1
.
270.162. Found: 270.160. Anal. Calcd for C18H22O2: C,
79.96; H, 8.20. Found: C, 79.84; H, 8.14.
HRMS: Calcd for C11H18OSi: 194.113. Found: 194.113.
3-(ter t-Bu tyleth yn yl)cycloh exa n on e (1d ).10b Obtained
as a colorless oil after flash chromatography (30% ether in
pentane, Rf ) 0.40) followed by bulb-to-bulb distillation (50-
51 °C/0.3 mbar), 97% yield. 1H NMR: δ 2.82-2.90 (m, 1H),
2.52 (dd, J ) 14.4, 5.2, 1H), 2.37 (dd, J ) 14.4, 8.4, 1H), 2.25-
2.36 (m, 2H), 2.03-2.16 (m, 1H), 1.88-2.00 (m, 1H), 1.68-1.82
(m, 2H), 1.17 (s, 9H). 13C NMR: δ 210.0, 91.8, 79.6, 47.8, 41.4,
3-[(Tr im et h ylsilyl)et h yn yl]-2-m et h ylcyclop en t a n on e
(3c). Obtained as a colorless oil after flash chromatography
(30% ether in pentane, Rf ) 0.44 and 0.56) followed by bulb-
to-bulb distillation (100°C/4 mbar), 82% yield. The presence
of two diastereomers in comparable amounts is evident from
gas chromatograms. 1H NMR: δ 3.22 (m, 1H), 1.80-2.54 (m,
5H), 1.18 (d, 3H), 0.17 (s, 9H), 0.14 (s, 9H). 13C NMR: δ 219.0,
218.3, 107.6, 105.7, 89.0, 86.5, 51.1, 47.7, 37.0, 36.7, 35.6, 34.4,
28.1, 27.7, 12.6, 11.2, 0.29, 0.23. IR (neat): 2173 (CtC), 1744
(CdO) cm-1. HRMS: Calcd for C11H18OSi: 194.115. Found:
194.113.
31.5, 31.4, 30.2, 27.5, 24.0. IR (neat): 1719 (CdO) cm-1
.
HRMS: Calcd for C12H18O: 178.136. Found: 178.136. Anal.
Calcd for C12H15O: C, 80.85; H, 10.18. Found: C, 80.60; H,
10.11.
3-(P h en yleth yn yl)cyclop en ta n on e (2b). Obtained as a
colorless oil after flash chromatography (20% ether in pentane,
Rf ) 0.22) followed by bulb-to-bulb distillation (115-120 °C/
1.5 mbar), 68% yield. 1H NMR: δ 7.37-7.42 (m, 2H), 7.27-
7.32 (m, 3H), 3.24-3.33 (m, 1H), 2.08-2.63 (m, 6H). 13C
NMR: δ 217.3, 131.8, 131.7, 128.5, 128.2, 123.3, 91.1, 82.0,
45.4, 37.7, 30.5, 28.4. IR (neat): 2228 (C≡C), 1744 (CdO)
cm-1. HRMS: Calcd for C13H12O: 184.089. Found: 184.089.
Anal. Calcd for C13H12O: C, 84.75; H, 6.56. Found: C, 84.42;
H, 6.58.
3-Met h yl-3-[(t r im et h ylsilyl)et h yn yl]cyclop en t a n on e
(4a ). Obtained as a yellow oil after flash chromatography
(30% ether in pentane, Rf ) 0.48), 16% yield. 1H NMR: δ 2.68
(d, J )18, 1H), 2.43-2.70 (m, 1H), 2.22-2.36 (m, 2H), 2.14 (d,
J )18, 1H), 1.84-1.94 (m, 1H), 1.40 (s, 3H), 0.14 (s, 9H). 13C
NMR: δ 217.7, 111.9, 85.2, 53.3, 37.7, 37.5, 36.2, 27.4, 0.3. IR
(neat): 2160 (CtC), 1748 (CdO) cm-1
. HRMS: Calcd for
C11H18OSi: 194.113. Found: 194.112.
2-[(Tr im eth ylsilyl)eth yn yl]-4-ch r om a n on e (5a ). Ob-
tained as a white solid after flash chromatography (10% EtOAc
in hexane, Rf ) 0.31) followed by bulb-to-bulb distillation (80-
82 °C/0.06 mbar), 98% yield, mp 56-58 °C. 1H NMR: δ 7.88-
7.91 (m, 1H), 7.48-7.53 (m, 1H), 7.02-7.08 (m, 2H), 5.20-
5.26 (m, 1H), 2.92-3.04 (m, 2H), 0.17 (s, 9H). 13C NMR: δ
190.7, 160.4, 136.4, 127.1, 122.2, 121.2, 118.4, 100.6, 93.4, 68.1,
3-[(Tr im eth ylsilyl)eth yn yl]cyclop en ta n on e (2c).32 Ob-
tained as a colorless oil after flash chromatography (20% ether
in pentane, Rf ) 0.35) followed by bulb-to-bulb distillation (42-
45 °C/4 mbar), 92% yield. 1H NMR: δ 3.03-3.12 (m, 1H),
1.98-2.54 (m, 6H), 0.15 (s, 9H). 13C NMR: δ 217.3, 108.1,
86.1, 45.3, 37.6, 30.4, 28.6, 0.3. IR (neat): 2178 (CtC), 1747
(CdO) cm-1. HRMS: Calcd for C10H16OSi: 180.097. Found:
180.098.
1-[(Tr im eth ylsilyl)oxy]-3-[(tr im eth ylsilyl)eth yn yl]cy-
clop en ten e (2c′).32 Obtained as a colorless oil after bulb-to-
bulb distillation (25-30 °C/0.08 mbar), 78% yield. 1H NMR:
δ 4.61 (d, J ) 2.0, 1H), 3.44-3.52 (m, 1H), 1.83-2.42 (m, 4H),
0.22 (s, 9H), 0.14 (s, 9H). 13C NMR: δ 156.3, 111.2, 103.5,
43.6, -0.2. IR (neat): 2187 (CtC), 1688 (CdO) cm-1
.
HRMS: Calcd for C14H16O2Si: 244.092. Found: 244.094.
Anal. Calcd for C14H16O2Si: C, 68.83; H, 6.61; Si, 11.46.
Found: C, 68.69; H, 6.56; Si, 11.30.
2-(ter t-Bu tyleth yn yl)-4-ch r om a n on e (5b). Obtained as
a slightly yellow syrup after flash chromatography (10% ether
in pentane, Rf ) 0.29) followed by bulb-to-bulb distillation (90-
92 °C/0.1 mbar), 90% yield. 1H NMR: δ 7.86-7.92 (m, 1H),
7.46-7.53 (m, 1H), 7.01-7.07 (m, 2H), 5.17-5.28 (m, 1H), 2.88-
2.98 (m, 2H), 1.20 (s, 9H). 13C NMR: δ 191.2, 160.6, 136.3,
127.0, 122.0, 121.3, 118.5, 97.2, 74.8, 68.2, 44.2, 30.8, 27.6. IR
(31) Barbero, A.; Cuadrado, P.; Fleming, I.; Gonzalez, A. M.; Pulido,
F. J .; Rubio, R. J . Chem. Soc., Perkin Trans. 1 1993, 1657.
(32) Salau¨n, J .; Ollivier, J . Nouv. J . Chim. 1981, 5(11), 587.

1,4-Addition of Copper Acetylides to Enones
(neat): 2244 (CtC), 1697 (CdO) cm-1
J . Org. Chem., Vol. 62, No. 1, 1997 187
.
HRMS: Calcd for
244.185. In spite of the convincing spectral data the mixture
gave a high carbon analysis. Anal. Calcd for C17H24O: C,
83.55; H, 9.90. Found: C, 82.62; H, 10.20.
C15H16O2: 228.115. Found: 228.114. Anal. Calcd for
C15H16O2: C, 78.91; H, 7.07. Found: C, 78.67; H, 7.02.
7-P h en yl-6-h ep tyn -3-on e (6a ). Obtained as a slightly
orange oil after flash chromatography (10% ether in pentane,
Rf ) 0.29), 37% yield. 1H NMR: δ 7.34-7.40 (m, 2H), 7.25-
7.30 (m, 3H), 2.64-2.78 (2m, 2H each), 2.49 (q, J ) 7.2, 2H),
1.09 (t, J ) 7.2, 3H). 13C NMR: δ 209.7, 131.7, 128.4, 127.9,
123.8, 88.9, 81.1, 41.4, 36.2, 14.3, 8.0. IR (neat): 2239 (CtC),
5-P h en yl-4-p en tyn a l (8a ). Obtained as a slightly yellow
oil after flash chromatography (10% ether in pentane, Rf )
0.17), 71% yield. 1H NMR: δ 9.85 (t, J ) 1, 1H), 7.35-7.42
(m, 2H), 7.26-7.32 (m, 3H), 2.71-2.81 (m, 4H). 13C NMR: δ
200.8, 131.8, 128.4, 128.1, 123.5, 87.9, 81.6, 42.8, 12.9. IR
(neat): 2234 (CtC), 1725 (CdO) cm-1
. HRMS: Calcd for
1716 (CdO) cm-1
. HRMS: Calcd for C13H14O: 186.104.
C11H10O: 158.073. Found: 158.078.
Found: 186.108.
3-Meth yl-5-p h en yl-4-p en tyn a l (9a ). Obtained after flash
chromatography (30% ether in pentane , Rf ) 0.53), followed
by bulb-to-bulb distillation (54-55 °C/0.3 mbar), 67% yield.
The product is a colorless oil which rapidly turns orange at
room temperature. 1H NMR: δ 9.85 (t, J ) 2.0, 1H), 7.35-
7.42 (m, 2H), 7.27-7.32 (m, 3H), 3.16-3.26 (m, 1H), 2.69 (ddd,
J ) 2.0, 7.6, 16.6, 1H), 2.59 (ddd, J ) 2.0, 6.4, 16.6, 1H), 1.33
(d, J ) 6.8, 3H). 13C NMR: δ 201.2, 131.8, 128.4, 128.3, 128.2,
128.1, 123.5, 92.3, 81.9, 50.2, 21.4, 21.2. IR (neat): 2230
(CtC), 1730 (CdO) cm-1. HRMS: Calcd for C12H12O: 172.089.
Found: 172.088.
(E)-6-P h en yl-3-h exen -5-yn -2-on e (7a ).33 Obtained as a
light-yellow solid (trans:cis ) 96:4) after flash chromatography
(20% ether in pentane, Rf ) 0.32), 88% yield, mp 45-47 °C.
1H NMR: δ 7.46-7.53 (m, 2H), 7.33-7.42 (m, 3H), 6.84 (d, J
) 16, 1H), 6.58 (d, J ) 16, 1H), 2.30 (s, 3H). 13C NMR: δ
197.3, 138.0, 132.2, 129.6, 128.8, 128.7, 124.0, 122.3, 99.9, 86.9,
27.9. IR (neat): 2192 (CtC), 1744 (CdO) cm-1. HRMS: Calcd
for C12H10O: 170.073. Found: 170.077. Anal. Calcd for
C12H10O: C, 84.68; H, 5.92. Found: C, 84.79; H, 5.94.
(E)-6-(Tr im eth ylsilyl)-3-h exen -5-yn -2-on e (7b).34 Ob-
tained as a light-yellow oil (trans:cis ) 97:3) after flash
chromatography (5% ether in pentane, Rf ) 0.23), 78% yield.
1H NMR: δ 6.59 (d, J ) 16, 1H), 6.51 (d, J ) 16, 1H), 2.26 (s,
3H), 0.22 (s, 9H). 13C NMR: δ 197.3, 138.9, 123.7, 106.6, 101.8,
27.8, 0.2. IR (neat): 2128 (CtC), 1696, 1678 cm-1. HRMS:
Calcd for C9H14OSi: 166.081. Found: 166.080.
Ack n ow led gm en t. We are grateful to Dr. Anders
J ohansson for the preparation of the functionalized
acetylenes used in some of the experiments and to Dr.
Gunnar Stenhagen for high resolution mass measure-
ments. We appreciate helpful feedback and comments
by Dr. Steven H. Bertz regarding this manuscript. We
acknowledge the financial support from The Swedish
Research Council for Engineering Sciences.
(E)-10,14-Dim eth ylpen tadeca-3,9,13-tr ien -5-yn -2-on e or
(E)-7-Ger a n yl-3-h ep ten -5-yn -2-on e (7c). Obtained as a
slightly greenish oil (trans:cis ) 95:5) after flash chromatog-
raphy (10% ether in pentane, Rf ) 0.28), 67% yield. 1H NMR:
δ 6.61 (dt, J ) 16.0, 2.4, 1H), 6.41 (d, J ) 16.0, 1H), 5.20-
5.14 (m, 1H), 5.12-5.07 (m, 1H), 2.44-2.38 (m, 2H), 2.30-
2.23 (m, 2H), 2.26 (s, 3H), 2.12-1.97 (m, 4H), 1.68 (s, 3H), 1.63
(s, 3H), 1.60 (s, 3H). 13C NMR: δ 197.7, 137.7, 137.3, 131.7,
125.2, 124.3, 122.3, 102.6, 78.4, 39.9, 27.6, 27.1, 26.8, 25.9, 20.6,
17.9, 16.3. HRMS: Calcd for C17H24O: 244.183. Found:
Su p p or tin g In for m a tion Ava ila ble: NMR (1H and 13C)
spectra for new substances which were not characterized by
combustion analysis (14 pages). This material is contained
in libraries on microfiche, immediately follows this article in
the microfilm version of the journal, and can be ordered from
the ACS; see any current masthead page for ordering
information.
(33) J effery, T. Synthesis 1987, 70.
(34) Boronoeva, T. R.; Belyaev, N. N.; Stadnichuk, M. D.; Petrov,
A. A. Zh. Obshch. Khim. 1974, 44(9), 1949.
J O960393D