Stereoselective synthesis of (E)- and (Z)-acetals of pent-2-en-4-yn-1-al and related dienynes and dienediynes

Article abstract of DOI:10.1002/(sici)1099-0690(199911)1999:11<2957::aid-ejoc2957>3.0.co;2-7

(3E)-5,5-Diethoxypent-3-en-1-yne was stereospecifically prepared by Sonogashira-Linstrumelle cross-coupling between (E)-3-iodoacrolein diethylacetal and (trimethylsilyl)acetylene. The (Z) isomer was obtained by Stille cross-coupling between the corresponding (Z)-vinyltin and 1-bromo-2- (trimethylsilyl)acetylene. In the case of the (E) isomer, transacetalisation occurred without isomerization affording a large variety of (E)-enynals protected as acetals. It has also been shown to be possible to obtain the corresponding (E,E)-dienediyne through sp-sp homo-coupling under appropriate experimental conditions.

Full text of DOI:10.1002/(sici)1099-0690(199911)1999:11<2957::aid-ejoc2957>3.0.co;2-7

FULL PAPER
Stereoselective Synthesis of (E)- and (Z)-Acetals
of Pent-2-en-4-yn-1-al and Related Dienynes and Dienediynes
[
a]
[a,b]
and Jean-Paul Quintard*[a]
Franck Suzenet, Jean-Luc Parrain,
Keywords: Sonogashira–Linstrumelle cross-coupling / Stille cross-coupling / Protected enynals / Transacetalisation / Pent-
-en-4-yn-1-al / Deca-2,8-diene-4,6-diyne-1,10-dial / Dienediynes
2
(3E)-5,5-Diethoxypent-3-en-1-yne was stereospecifically
isomer, transacetalisation occurred without isomerization
prepared by Sonogashira–Linstrumelle cross-coupling affording a large variety of (E)-enynals protected as acetals.
between (E)-3-iodoacrolein diethylacetal and (trimethylsilyl)-
acetylene. The (Z) isomer was obtained by Stille cross-
coupling between the corresponding (Z)-vinyltin and 1-
bromo-2-(trimethylsilyl)acetylene. In the case of the (E)
It has also been shown to be possible to obtain the
corresponding (E,E)-dienediyne through sp–sp homo-
coupling under appropriate experimental conditions.
Introduction
Polyenic building blocks with fixed configurations appear
to be of great importance for the synthesis of bioactive
[
1]
compounds such as arachidonic acid derivatives, retinoids
Scheme 1. Stannylcupration of pent-2-en-4-yn-1-al dioxolanyl
[2]
[3]
and nor-retinoids,
macrolide antibiotics
mones. Furthermore, such structures could be of con-
siderable use in producing materials having possible appli- stereodefined protected enynals. The literature contains nu-
or phero- acetal
[
4]
[5]
cations because of potential nonlinear optical properties
merous possibilities for reaching enynes by coupling be-
or high conductivity.[ Stereodefined dienyltin compounds tween activated alkenes
6]
[12]
or vinylmetal compounds
[13][14]
are good candidates for this purpose because of their fairly with alkynyl halides, or by coupling of alkynylmetal com-
good stability and ease of control of their stereochemistry, pounds[ or alkynes
15]
[16]
with vinyl halides, in our case,
the more usual access to this type of precursors requiring however, we have to take into account the availability of
the regio- and stereoselective stannylation of α,β-en- the desired compounds and the nature of the experimental
[
7][8]
ynes.
a mixture of isomers and because palladium-catalyzed
hydrostannation increases the rate of formation of branched can be prepared in good yields as a clean (E) isomer 1a-
While free-radical hydrostannation usually affords conditions in order to avoid unwanted isomerizations.
[8]
The fact that 1-tributylstannyl-3,3-diethoxyprop-1-ene
[
9][10]
[17]
[18]
dienyltins,
Pancrazi
it has been recently demonstrated by
E
or as a clean (Z) isomer 1a-Z
from commercially
[
8][11]
[10]
and ourselves
that the regioselectivity of available 3,3-diethoxyprop-1-yne was first considered in or-
the syn-stannylcupration of α,β-enynes can be controlled der to obtain the vinylic moiety. Indeed, vinyltin acetals can
using appropriate experimental conditions. When the stan- be either directly used in Stille cross-coupling reactions with
nylcupration was achieved in the presence of proton alkynyl halides[ or as precursors of vinyl iodides, which
14]
sources, the kinetic vinyltin cuprate was trapped before re- can be subsequently used in SonogashiraϪLinstrumelle
tro-stannylcupration.[
8][11]
In the presence of a functional cross-coupling reactions.[16] Due to the number of papers
group, like an acetal group, however, we have been able to which report the use of this last approach, we first at-
drive the reaction to the “thermodynamic adduct” because tempted to reach the desired compounds according to this
of intra- and intermolecular chelations,[ as exemplified in route.
10]
Scheme 1.
In order to obtain a dienyltin precursor having both a
nucleophilic site (SnϪC bond) and an electrophilic site (ace- Synthesis of Protected Enynals by
tal function), we need to have an efficient route to obtain Sonogashira؊Linstrumelle Cross-Coupling
Reactions
[
a]
Laboratoire de Synth e` se Organique, UMR 6513 du CNRS,
Facult e´ des Sciences et des Techniques de Nantes,
Optimization of the Experimental Conditions
2
, rue de la Houssini e` re, BP 92208, F-44322 Nantes Cedex 3,
France
The most appropriate experimental conditions are usu-
ally dependent on the substrate and must be optimized in
terms of relative rates of reagents, catalysts, bases or tem-
perature.[ Therefore, taking as “basic experimental con-
Fax: (internat.) ϩ 33-2/51125412
E-mail: quintard@chimie.univ-nantes.fr
Current address: Laboratoire de Synth e` se Organique associ e´ au
CNRS, Facult e´ des Sciences de Saint J e´ r oˆ me,
Avenue Escadrille Normandie-Niemen, Case postale D12, F-
[
b]
16]
[19]
13397 Marseille, France
ditions” those described by Lee for obtaining α,β-enynes,
Eur. J. Org. Chem. 1999, 2957Ϫ2963
 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ193X/99/1111Ϫ2957 $ 17.50ϩ.50/0
2957

F. Suzenet, J.-L. Parrain, J.-P. Quintard
FULL PAPER
we studied the influence of the above-mentioned param- Note that fulvene-type compounds such as 7 have been pre-
eters on the yield of desired product and on the rate of by- viously described in these reactions,[ but obtaining com-
products. The results obtained are reported in Table I (En- pounds like 6 simultaneously has not been reported. Under
tries 1Ϫ3). While the desired product 4a-E was often ob- these experimental conditions, one should mention that 4a-
tained as the major compound (Scheme 2), considerable E and 6 were obtained by an anti-retrohydropalladation.[
amounts of side products were also observed when the reac- Obviously, obtaining 4a-E according to Scheme 3 is one
tion was performed at room temperature. Using triethyl- possibility among more conventional ones.[
19]
22]
15][16]
amine as the base and Pd(PPh ) Cl as the catalyst at room
Taking into account the difficulties encountered in avoid-
3
2
2
temperature, the best results were obtained using a 1.5 al- ing the formation of side products using PdCl (PPh ) as
2
3 2
kyne/vinyl iodide ratio (Entry 2). In these experimental con- catalyst and triethylamine as base, modifications were
ditions, the desired compound 4a-E was obtained in fairly made, in agreement with Linstrumelle,[
16e]
with
good yield but with an important contamination by side PdCl (MeCN) used as the catalyst and piperidine as the
2
2
product 5.
base. Under these new experimental conditions, at room
Side product 5 can be seen as the result of the syn ad- temperature, the vinyl iodide was consumed in about 30 min
dition of the excess of 2 on 4a-E. The addition might occur (against 12 h under previous experimental conditions) and
through the alkynylcopper intermediate in agreement with contamination by 5 appeared to be less (Entry 4). However,
the absence of 5 when the reaction was performed without an increase in the concentration of the reagents induced the
cuprous iodide (Entry 3).[ Another possibility might be formation of the desilylated compound 8a-E and of the sub-
the carbopalladation of 1,4-bis(trimethylsilyl)but-1,3-diyne sequent homocoupling product 9a-EE (Entry 5). On the
20]
by a vinylpalladium compound resulting from the oxidative other hand, the increased reactivity allowed the achieve-
addition of 3a-E on PdL2.[
21]
ment of the reaction at 0°C and the clean obtaining of 4a-
E (75% isolated yield) after 2 h (Entry 6).
Scope and Limitations of the Method
The above-mentioned results demonstrate that the Sono-
gashiraϪLinstrumelle cross-coupling can be efficient in ob-
taining cleanly (3E)-5,5-diethoxy-1-(trimethylsilyl)pent-3-
en-1-yne (4a-E) and, subsequently, (3E)-5,5-diethoxypent-3-
en-1-yne (8a-E) upon treatment with tetrabutylammonium
fluoride[ according to Scheme 4.
23]
The desilylation reaction occurs without isomerization of
the E double bond in this case and transacetalisation of 8a-
E with diols can also be achieved under mild experimental
conditions without isomerization to afford the correspond-
ing cyclic acetals in good yields (Scheme 5).
Scheme 2. Cross-coupling of (E)-3,3-diethoxy-1-iodoprop-1-ene
with (trimethylsilyl)acetylene
However, while the above-mentioned method appears to
The formation of the side compounds obtained in the be satisfactory in obtaining numerous (E)-protected α,β-en-
absence of cuprous iodide might be explained by several ynals, problems arise when similar reactions were attempted
competitive reactions involving the first formed organopal- in order to obtain the 8-Z isomers. The first problem was
ladium intermediate which can generate 4a-E, 6 or 7 ac- the poor configurational stability of the vinyl iodide 3a-Z
cording to Scheme 3, while alkynylcopper intermediates which is usually obtained as a mixture of (E) and (Z) iso-
drive the reaction to 4a-E because of a direct cross-coupling mers when the iododestannylation of 1a-Z was performed
reaction with the first-formed vinylpalladium compound. at 0°C, prohibiting a clean stereochemical control for the
Table 1. Optimization of the synthesis of 4a-E by SonogashiraϪLinstrumelle cross-coupling reaction
Entry
2/3aE
3aE
mol LϪ1]
Pd catalyst
CuI
[%]
base
T [°C],
time [h]
Product 4aE
By-products
(yield in%)
[a]
[
(yield in%)
1
2
3
2.5
1.5
2
0.156
0.26
Pd(PPh
Pd(PPh
Pd(PPh
3
3
3
)
)
)
2
2
2
Cl
Cl
Cl
2
2
2
5
5
0
Et
Et
Et
3
3
3
N
N
N
20, 12
20, 12
20, 12
60
5 (30)
(70)
(50)
5 (30)
0.195
6 (25) ϩ
7
(25)
4
5
2
2.5
0.195
0.325
Pd(MeCN)
Pd(MeCN)
2
2
Cl
Cl
2
2
10
10
piperidine
piperidine
20, 0.5
20, 0.25
62
17
5 (15)
8aE (25) ϩ
9
Ϫ
aEE (8)
6
2.5
0.195
Pd(MeCN)
2
Cl
2
10
piperidine
0, 2
75
[
a]
Reported values are isolated yields or conversion rates (values in parentheses).
2958
Eur. J. Org. Chem. 1999, 2957Ϫ2963

Stereoselective Synthesis of (E)- and (Z)-Acetals of Pent-2-en-4-yn-1-al
FULL PAPER
Scheme 3. Sonogashira cross-coupling of 3a-E with (trimethylsilyl)acetylene and possible explanation for the formation of the products
in the absence of CuI
with some isomerization, prohibiting attempts to reach cle-
anly the (Z)-protected enynal according to this route.
Selective Preparation of Dienynes and Dienediynes
Scheme 4. Desilylation of 4a-E
Compound 5 was selectively desilylated by tetrabutylam-
monium fluoride at the sp-carbon atom affording the
monosilylated dienyne 10 (Scheme 6).
Scheme 6. Desilylation of 5
Scheme 5. Transacetalisation of 8a-E
More interesting is the possible homocoupling of the α,β-
enyne 8a-E to afford the dienediyne 9a-EE. Although
SonogashiraϪLinstrumelle cross-coupling (at 0°C) to reach known in principle, the homocoupling of alkynes is de-
a-Z. Furthermore, while 1a-Z is fairly stable under neutral scribed in only a limited number of publications.[ Under
24]
8
conditions, the transacetalisation of this isomer also occurs experimental conditions close to those used in Sonogashira
Eur. J. Org. Chem. 1999, 2957Ϫ2963
2959

F. Suzenet, J.-L. Parrain, J.-P. Quintard
FULL PAPER
cross-coupling, results of this type have been obtained for
The (E) isomer was efficiently prepared by Sonogashira-
[
25]
arylacetylenes
and very recently for aryl- and alkylacety- ϪLinstrumelle cross-coupling between (trimethylsilyl)acety-
[
26]
lenes.
In our case (homocoupling of protected enynals) lene and (E)-β-iodoacrolein diethylacetal or by Stille cross-
nothing had been described previously. Nevertheless, using coupling between (E)-β-(tributylstannyl)acrolein diethylace-
Pd(PPh ) and CuI as catalysts, in the presence of piperi- tal and 1-bromo-2-(trimethylsilyl)acetylene. The desilylation
3
4
dine, a good yield of the homocoupling product was ob- reaction was performed with tetrabutylammonium fluoride.
tained after 8 h at 0°C (Scheme 7).
In this case, a large variety of (E)-protected enynals can be
subsequently obtained by transacetalisation of the diethyl-
acetal with diols. For the less stable (Z) isomer, Stille cross-
coupling must be used in order to avoid isomerization of
the double bond. Finally, the optimization of an homo-
coupling side reaction has been exploited in order to reach
functional (E,E)-dienediynes. Accordingly, bis(diethylace-
tal) of deca-2,8-diene-4,6-diyne-1,10-dial was obtained in
good yield as (E,E) isomer in a clean fashion.
The polyunsaturated compounds obtained are useful
building blocks by themselves and also offer interesting
possibilities after regio- and stereoselective stannylcupr-
ation reaction. Work is in progress in order to evaluate their
effective potential in organic synthesis both as precursors
of new materials or as precursors of molecules of biologi-
cal interest
Scheme 7. Homocoupling of 8a-E
This product, which can be easily deprotected to afford
the corresponding deca-2,8-diene-4,6-diyne-1,10-dial on
wet silica, constitutes an interesting precursor in order to
obtain polyunsaturated materials.
Synthesis of Protected Enynals by Stille Cross-
Coupling Reaction
The problems encountered with isomerization of com-
pounds of the type 1-Z in transacetalisation reactions and
the poor configurational stability of the vinyl iodide 3a-Z
prohibits the use of Sonogashira-type reactions to reach the
Experimental Section
General and Starting Materials: H- and 13C-NMR spectra were
recorded with Bruker AC 200 or Bruker AC 400 spectrometers.
Chemical shifts are given as δ values related to tetramethylsilane
1
(Z)-protected enynals. Considering the good isomeric sta-
bility of 1a-Z under neutral conditions, the more appropri-
ate route to circumvent these difficulties was the use of a
Stille cross-coupling between this vinyltin compound and
3
and coupling constants in Hz (solvent ϭ CDCl ). Ϫ Mass spectra
were obtained in EI mode (70 eV) with a Hewlett-Packard appar-
atus (Engine 5989A) in direct introduction mode or in GC-MS
mode. Organotin fragments are given for Sn. Ϫ IR spectra were
recorded with a Bruker IFS apparatus. Ϫ (Trimethylsilyl)acetylene
1
-bromo-2-(trimethylsilyl)acetylene (11) using experimental
120
conditions for cross-couplings of this type previously de-
scribed by our group.[
14b]
The reaction was performed on is a commercially available compound (Aldrich) which was con-
both isomers of 1-tributylstannyl-3,3-diethoxyprop-1-ene verted into 1-bromo-2-(trimethylsilyl)acetylene upon treatment
and afforded the expected silylated enynes without signifi- with n-butyllithium (diethyl ether, Ϫ78°C) and quenching with bro-
mine. β-(Tributylstannyl)acrolein diethylacetal was obtained cleanly
cant isomerization of the double bond (Scheme 8).
as a pure (E) isomer 1a-E by stannylcupration of 3,3-diethoxypro-
pyne by Lipshutz reagent according to a previously described pro-
cedure.[ Similarly, its (Z) isomer 1a-Z was obtained by titanation
of 1-(tributylstannyl)-3,3-diethoxyprop-1-yne as already de-
17]
scribed.[ When corresponding iodides were desired, they were ob-
18]
tained by iododestannylation of 1a-E or 1a-Z,[
17][18]
however, while
Scheme 8. Preparation of 4a-E and 4a-Z by Stille cross-coupling re-
action
vinyl iodide 3a-E can be obtained easily as a pure compound from
a-E, the preparation of 3a-Z from 1a-Z, even possible at low tem-
1
perature, is much more tedious since partial isomerization occurs
at 0°C (temperature required for further coupling).
Desilylation of the compounds obtained with tetrabu-
tylammonium fluoride, as previously described, afforded
the desired terminal enynes 8a-E (80% yield) and 8a-Z (70%
yield) with complete retention of the stereochemistry at the
double bond. Therefore, starting from the appropriate acet-
als of prop-2-yn-1-al, this method should proceed to every
type of acetal of pent-2-en-4-yn-1-al with complete control
of the E or Z stereochemistry of the double bond.
(
E)-3,3-Diethoxy-1-(tributylstannyl)prop-1-ene (1a-E): 1H NMR:
3
δ ϭ 0.80Ϫ0.95 (m, 15 H), 1.22 (t, J2H ϭ 7.1, 6 H), 1.22Ϫ1.60 (m,
2
3
2
1
9
7
6
2 H), 3.47 (qd, J1H ϭ 9.5, J3H ϭ 7.1, 2 ϫ 1 H), 3.62 (qd, J1H
ϭ
3
3
4
4
.5, J3H ϭ 7.1, 2 ϫ 1H), 4.78 (dd, J1H ϭ 4.8, J1H ϭ 1.1, JSnH
ϭ
3
3
3
.9, 1 H), 5.94 (dd, J1H ϭ 19.3, J1H ϭ 4.8, JSnH ϭ 60/63, 1 H),
3
1H ϭ 19.3, 4J1H ϭ 1.1, 2JSnH ϭ 68/71, 1 H). Ϫ
13
.33 (dd,
J
C
1
NMR: δ ϭ 9.3 (3 C, JSnC ϭ 328/344), 13.5 (3 C), 15.1 (2 C), 27.5
3
2
3
(
7
3 C, JSnC ϭ 54), 29.1 (3 C, JSnC ϭ 21), 60.4 (2 C), 102.7 ( JSnC ϭ
2), 132.0 (1JSnC ϭ 362/377), 145.7 ( JSnC ϭ 43). Ϫ 119Sn NMR:
δ ϭ Ϫ46.4. Ϫ MS; m/z (%): organotin fragments: 363 (17), 319 (8),
07 (2), 291 (2), 235 (5), 179 (9), 177 (13), 165 (9), 121 (8); organic
fragments: 129 (100), 103 (6), 101 (6), 85 (27), 75 (7), 73 (7), 57
2
Conclusion
3
Acetals of pent-2-en-4-yn-1-al have been obtained selec-
Ϫ1
tively as (E) or (Z) isomers without isomerization of the (15), 55 (5),47 (9). Ϫ IR: ν˜ ϭ 2957Ϫ2865 cm , 1653, 1615, 1465,
double bond using appropriate experimental conditions. 1377, 1343, 1185, 1126, 1064, 1000, 970, 876, 692, 668.
2960
Eur. J. Org. Chem. 1999, 2957Ϫ2963

Stereoselective Synthesis of (E)- and (Z)-Acetals of Pent-2-en-4-yn-1-al
FULL PAPER
(
Z)-3,3-Diethoxy-1-(tributylstannyl)prop-1-ene (1a-Z): 1H NMR:
844, 760. Ϫ C12
H
22
O
2
Si (226.39): calcd. C 63.73, H 9.73; found C
3
3
δ ϭ 0.88 and 0.91 (2t, J ϭ 7.1, 15 H), 1.22 (t, J2H ϭ 7.1, 6 H), 63.46, H 9.68.
1
3
2
.23Ϫ1.58 (m, 12 H), 3.50 (qd, J2H ϭ 7.1, J1H ϭ 9.5, 2 ϫ 1H),
6
,6-Diethoxy-1-(trimethylsilyl)-3-[(trimethylsilyl)methylene]hex-4-
3
2
3
3
.65 (qd, J2H ϭ 7.1, J1H ϭ 9.5, 2 ϫ 1 H), 4.83 (dd, J1H ϭ 5,
1H ϭ 1.1, JSnH ϭ 8.5, 1 H), 6.20 (dd, J1H ϭ 13.4, J1H ϭ 1.1,
1
en-1-yne (5): H NMR: δ ϭ 0.18 (s, 9 H), 0.23 (s, 9 H), 1.25 (t,
4
4
3
4
J
3
3
2
J
2H ϭ 7.1, 6 H), 3.54 (qd, J3H ϭ 7.1, J1H ϭ 9.4, 2 ϫ 1 H), 3.69
2JSnH ϭ 60/63, 1 H), 6.51 (dd, J1H ϭ 13.4, J1H ϭ 5, JSnH ϭ 129/
1
C), 15.3 (2 C), 27.3 (3 C, JSnC ϭ 56/59), 29.1 (3 C, JSnC ϭ 21),
3
3
3
3
2
3
(
qd, J3H ϭ 7.1, J1H ϭ 9.4, 2 ϫ 1 H), 5.05 (br. d, J1H ϭ 4.6, 1
35, 1 H). Ϫ 13C NMR: δ ϭ 10.9 (3 C, JSnC ϭ 333/349), 13.7 (3
1
3
3
H), 6.16 (dd, J1H ϭ 15.3, J1H ϭ 4.6, 1 H), 6.33 (s, 1 H), 6.59 (br.
3
2
3
⋅
ϩ
d, J1H ϭ 15.3, 1 H). Ϫ MS; m/z (%): 324 (1) [M ], 295 (4), 279
7), 251 (4), 207 (6), 206 (7), 177 (18), 147 (16), 133 (10), 129 (34),
03 (36), 83 (11), 75 (43), 73 (100), 59 (15), 47 (16), 45 (20), 29 (34).
3
1
6
(
0.5 (2 C), 102.3 ( JSnC ϭ 31), 134.2 ( JSnC ϭ 351/368), 144.7
(
1
2
119
J
SnC ϭ 6.5). Ϫ
Sn NMR: δ ϭ Ϫ61.2. Ϫ MS; m/z (%): or-
ganotin fragments: 363 (17), 317 (32), 235 (1), 179 (5), 177 (7), 121
7); organic fragments: 129 (100), 103 (1), 101 (13), 85 (19), 75 (2),
(
7
1
7,7-Diethoxy-1,3-bis(trimethylsilyl)hepta-3,5-dien-1-yne (6): A sin-
gle isomer obtained as a mixture with 7. Ϫ H NMR: δ ϭ 0.14 (s,
9 H), 0.24 (s, 9 H), 1.23 (t, J2H ϭ 6.9, 6 H), 3.4Ϫ3.8 (m, 4 H), 5.0
Ϫ1
1
3 (12), 57 (15), 47 (6), 29 (9). Ϫ IR: ν˜ ϭ 2956 cm , 2926, 2872,
3
610, 1465, 1376, 1118, 1053, 1002, 875, 670.
3
4
3
3
(
5
(
3
dd, J1H ϭ 5.2, J1H ϭ 1.1, 1 H), 5.83 (m, J1H ϭ 15.4, J1H ϭ
1
(
E)-3,3-Diethoxy-1-iodoprop-1-ene (3a-E): H NMR: δ ϭ 1.22 (t,
4
3
4
.2, J1H ϭ 0.6, 1 H), 6.57 (dd, J1H ϭ 10.7, J1H ϭ 0.6, 1 H), 6.96
3
3
2
J
2H ϭ 7.1, 6 H), 3.50 (qd, J3H ϭ 7.1, J1H ϭ 9.8, 2 ϫ 1 H), 3.62
3
3
4
m, J1H ϭ 15.4, J1H ϭ 10.7, J1H ϭ 1.1, 1 H). Ϫ MS; m/z (%):
3
2
3
4
(
qd, J2H ϭ 7.1, J1H ϭ 9.8, 2 ϫ 1 H), 4.85 (dd, J1H ϭ 2.2, J1H
ϭ
⋅
ϩ
24 (2) [M ], 295 (10), 279 (10), 251 (5), 191 (5), 147 (14), 133
.9, 1 H), 6.56 (dd, J1H ϭ 16.5, J1H ϭ 0.9, 1 H), 6.57 (dd, 3J1H
3
4
ϭ
0
1
8
1
(
2
(
12), 103 (20), 75 (20), 73 (100), 45 (15), 29 (15).
3
13
6.5, J1H ϭ 2.2, 1 H) . Ϫ C NMR: δ ϭ 15.2 (2 C), 61.1 (2 C),
⋅
ϩ
6-Diethoxymethyl-1,3-bis(trimethylsilyl)fulvene (7): A single isomer
obtained as a mixture with 6. Ϫ H NMR: δ ϭ 0.14 (s, 9 H), 0.24
(s, 9 H), 1.24 (t, J2H ϭ 6.9, 6 H), 3.4Ϫ3.8 (m, 4 H), 5.50 (d, J1H ϭ
1.4, 101.2, 143.4. Ϫ MS; m/z (%): 211 (75) [M Ϫ 45], 183 (100),
1
55 (11), 145 (37), 129 (58), 127 (5), 103 (25), 101 (29), 85 (13), 75
3
3
Ϫ1
25), 73 (33), 55 (30), 47 (37). Ϫ IR: ν˜ ϭ 3076 cm , 2974, 2928,
3
6
.8, 1 H), 6.30 (br. d, J1H ϭ 6.8, 1 H), 6.79 (br. s, 1 H), 6.86 (br.
877, 1610, 1481, 1444, 1391, 1332, 1128, 1051, 1005, 943.
⋅
ϩ
s, 1 H). Ϫ MS; m/z (%): 324 (2) [M ], 295 (7), 280 (10), 251 (7),
(
Z)-3,3-Diethoxy-1-iodoprop-1-ene (3a-Z, Mixture with 3a-E): 1H 192 (4), 163 (14), 147 (10), 133 (9), 103 (9), 75 (20), 73 (100), 45
3
3
2
NMR: δ ϭ 1.24 (t, J2H ϭ 7.1, 6 H), 3.58 (qd, J3H ϭ 7.1, J1H
9
ϭ
(14), 29 (15).
3
2
.3, 2 ϫ 1 H), 3.70 (qd, J2H ϭ 7.1, J1H ϭ 9.3, 2 ϫ 1 H), 5.10
Desilylation of 4a-E and 5: In a 100-mL three-necked reactor were
placed 3.65 mmol (0.826 g) of crude 4a-E in diethyl ether (20 mL).
After cooling at 0°C, 4 mL of Bu NF solution (1  in THF) were
4
3
4
3
3
(dd, J1H ϭ 6.3, J1H ϭ 0.9, 1 H), 6.39 (dd, J1H ϭ 7.9, J1H ϭ 6.3,
H), 6.54 (dd, 3J1H ϭ 7.9, J1H ϭ 0.9, 1 H). Ϫ C NMR: δ ϭ 15.5
4
13
1
(
2 C), 61.9 (2 C), 84.3, 103.4, 138.4. Ϫ GC MS; m/z (%): 255 (1)
added and the reaction mixture was stirred for 2 h at 0°C before
adding 15 mL of a saturated aqueous ammonium chloride solution.
After filtration and ether extraction, the organic phase was washed
with an aqueous solution of sodium chloride before drying with
magnesium sulfate. After removal of the solvents, 8a-E (0.67 g, 70%
yield from 1a-E) was obtained as a pure product by liquid chroma-
tography on silica gel 60 (hexane/triethylamine, 98:2). Similar treat-
ment was applied to 5 in order to obtain 10.
⋅
ϩ
[M
ϪH], 227 (2), 211 (74), 183 (100), 155 (6), 129 (47), 127 (5),
1
03 (6), 101 (19), 75 (9), 73 (20), 55 (17), 47 (20), 29 (38), 27 (24).
Cross-Coupling of 3a-E with (Trimethylsilyl)acetylene. ؊ Typical
Experimental Procedure (for Entry 6, Table 1): In a Schlenk tube
were placed 0.109 mmol (0.029 g) of PdCl (MeCN) and 0.218
2 2
mmol (0.042 g) of cuprous iodide in piperidine (10 mL). The reac-
tion mixture was degassed before addition of vinyl iodide 3a-E
(
(
2.18 mmol, 0.558 g) and further addition of trimethylsilylacetylene
5.45 mmol, 0.543 g) at 0°C. At the end of the reaction (monitored
1
(
E)-5,5-Diethoxypent-3-en-1-yne (8a-E): H NMR: δ ϭ 1.22 (t,
3
2
4
3
J
J
2H ϭ 7.0, 6 H), 2.96 (br. d, J1H ϭ 2.2, 1 H), 3.50 (qd, J3H ϭ 7,
1H ϭ 9.5, 2 ϫ 1 H), 3.64 (qd, J3H ϭ 7, J1H ϭ 9.5, 2 ϫ 1 H),
by TLC), 20 mL of water and 20 mL of hexane were added to
the reaction mixture before usual treatments (extraction, drying,
removal of solvents). The desired compound 4a-E was obtained as
a crude product which can be purified or directly used in desilyl-
ation reaction when the reaction has been conducted under the
experimental conditions described above. Ϫ For other attempts at
3
2
3
4
3
4
.95 (dd, J1H ϭ 4.4, J1H ϭ 1.4, 1 H), 5.84 (ddd, J1H ϭ 16.1,
4
4
3
3
J
1H ϭ 1.4, J1H ϭ 2.2, 1 H), 6.18 (ddd, J1H ϭ 16.1, J1H ϭ 4.4,
5J1H ϭ 0.5, 1 H). Ϫ C NMR: δ ϭ 15.3 (2 C), 61.2 ( 2 C), 79.3,
13
⋅
ϩ
8
(
(
3
9
6
1.2, 99.8, 112.3, 141.7. Ϫ MS; m/z (%): 154 (1) [M ], 125 (5), 110
15), 109 (100), 98 (9), 97 (11), 82 (12), 81 (87), 79 (6), 70 (8), 53
46), 52 (12), 51 (11), 47 (9), 43 (5), 29 (24), 27 (17). Ϫ IR: ν˜ ϭ
2978, 2920, 2876, 2105, 1640, 1339, 1138, 1056, 1000,
(154.21): calcd. C 70.15, H 9.09; found C
9.66, H 9.10. Ϫ Upon treatment with wet silica, pent-2-en-4-yn-
2 2
optimization, the amount of palladium catalyst PdCl L was main-
tained at 0.109 mmol and the amount of vinyl iodide 3a-E at 2.18
mmol, the solvent being the amine. The other parameters were
modified according to Table 1. After determination of the more
appropriate conditions, this coupling has been proved to be pos-
sible at higher scales.
Ϫ1,
300 cm
9 14 2
50, 610. Ϫ C H O
1
1
-al was obtained as a crude product: Ϫ H NMR: δ ϭ 3.73 (d,
4
3
3
J
1H ϭ 1.7, 1 H), 6.55 (dd, J1H ϭ 16.0, J1H ϭ 5.2, 1 H), 6.58 (br.
3
3
4
d, J1H ϭ 16.0, 1 H), 9.59 (dd, J1H ϭ 5.2, J1H ϭ 2.2, 1 H).
1
(
E)-5,5-Diethoxy-1-(trimethylsilyl)pent-3-en-1-yne (4a-E): H NMR:
3
3
6,6-Diethoxy-3-[(trimethylsilyl)methylene]hex-4-en-1-yne (10): 1H
1H ϭ 9.35, 2 ϫ 1 H), 3.63 (qd, J3H ϭ 7.1, J1H ϭ 9.35, 2 ϫ 1H), NMR: δ ϭ 0.17 (s, 9 H), 1.22 (t, J2H ϭ 7.1, 6 H), 3.02 (s, 1 H),
δ ϭ 0.19 (s, 9 H), 1.21 (t, J2H ϭ 7.1, 6 H), 3.48 (qd, J3H ϭ 7.1,
2
3
2
3
J
.93 (dd, 3
J
1H ϭ 4.3, 4
J
1H ϭ 1.2, 1 H), 5.86 (dd,
1H ϭ 1.2, 1 H), 6.12 (dd, J1H ϭ 16.2, J1H ϭ 4.3, 1 H). Ϫ
3
J
1H ϭ 16.2,
3.51 (qd, J3H ϭ 7.1, J1H ϭ 9.4, 2 ϫ 1 H), 3.66 (qd, J3H ϭ 7.1,
J1H ϭ 9.4, 2 ϫ 1 H), 5.03 (dd, J1H ϭ 4.5, J1H ϭ 1, 1 H), 6.17
3
2
3
4
4
3
3
13
2
3
4
J
C
3
3
3
NMR: δ ϭ 0.1 (3 C), 15.2 (2 C), 61.0 (2 C), 96.6, 99.9, 102.6, 113.2, (dd, J1H ϭ 15.4, J1H ϭ 4.5, 1 H), 6.32 (s, 1 H), 6.58 (br. d, J1H
ϭ
⋅
ϩ
15.4, 1 H). Ϫ 13C NMR: δ ϭ 1.1 (3 C), 16.3, 16.4, 62.0, 62.2, 79.1,
1
1
1
40.7. Ϫ MS; m/z (%): 226 (6) [M ], 211 (10), 197 (27), 182 (16),
81 (92), 153 (19), 139 (15), 137 (30), 125 (29), 117 (12), 113 (10), 83.8, 101.6, 132.1, 133.2, 135.1, 145.4. Ϫ MS; m/z (%): 252 (3)
11 (12), 109 (16), 103 (21), 97 (11), 83 (30), 79 (10), 77 (10), 75 [M· ], 223 (5), 207 (18), 179 (14), 163 (16), 135 (11), 129 (25), 106
ϩ
(
64), 73 (100), 47 (10), 45 (13), 41 (12), 29 (29). Ϫ IR: ν˜ ϭ (12), 105 (35), 103 (35), 91 (11), 89 (37), 85 (10), 83 (28), 77 (16),
Ϫ1
2976Ϫ2876 cm , 2170, 2130, 1630, 1251, 1137, 1053, 1000, 950,
75 (100), 73 (90), 59 (25), 55 (11), 47 (26), 45 (33), 43 (28), 31 (11),
Eur. J. Org. Chem. 1999, 2957Ϫ2963
2961

F. Suzenet, J.-L. Parrain, J.-P. Quintard
FULL PAPER
9 (81), 27 (24). Ϫ IR: ν˜ ϭ 3315 cmϪ1, 2976, 2962Ϫ2850, 2250,
550, 1340, 1251, 1134, 1053, 1000, 950, 905, 864, 735, 610.
(2E,8E)-1,1,10,10-Tetraethoxydeca-2,8-diene-4,6-diyne (9a-EE): H
1
2
1
3
3
2
NMR: δ ϭ 1.21 (t, J2H ϭ 7.1, 12 H), 3.49 (qd, J3H ϭ 7.1, J1H ϭ
.5, 4 ϫ 1 H), 3.63 (qd, J3H ϭ 7.1, J1H ϭ 9.5, 4 ϫ 1 H), 4.97
3
2
9
Transacetalisation of 8a-E: In a 100-mL flask, 10 g of molecular
3
4
3
4
˚
(dd, J1H ϭ 4.3, J1H ϭ 1.1, 2 ϫ 1 H), 5.94 (dd, J1H ϭ 15.7, J1H ϭ
sieves (4 A) was activated by warming under vacuum. After cooling
1
.1, 2 ϫ 1 H), 6.23 (dd, J1H ϭ 15.7, J1H ϭ 4.3, 2 ϫ 1 H). Ϫ 13C
3
3
under dry argon, dry dichloromethane (50 mL), p-toluenesulfonic
acid (18 mg, 0.0105 mmol) and the diol (2.3 mmol) were success-
ively added. The reaction mixture was stirred for 30 min at room
temperature before addition of 8a-E (0.3 g, 1.95 mmol). The reac-
tion was monitored by TLC before neutralization with triethyl-
amine. After filtration through neutral aluminium oxide (CH Cl )
2 2
and removal of the solvents, the (E)-enynals were directly isolated
and characterized.
1ЈE)-2-(But-1Ј-en-3Ј-yn-1Ј-yl)-1,3-dioxane (8b-E): 1H NMR: δ ϭ
NMR: δ ϭ 15.1 (4 C), 61.1 (4 C), 75.5 (2 C), 79.3 (2 C), 99.5 (2
C), 111.9 (2 C), 143.1 (2 C). Ϫ MS; m/z (%): 306 (8) [M ], 277
10), 261 (45), 232 (15), 221 (12), 203 (12), 176 (8), 175 (20), 159
17), 147 (16), 131 (35), 119 (11), 116 (15), 105 (11), 103 (25), 102
13), 91 (23), 77 (49), 76 (11), 75 (19), 51 (12), 47 (14), 29 (100). Ϫ
2204, 1625, 1371, 1337, 1250, 1123,
055, 1000, 950, 845. Ϫ C18H O (306.40): calcd. C 70.56, H 8.55;
26 4
found C 70.85, H 8.58 Ϫ Upon treatment with wet silica, deca-2,8-
diene-4,6-diyne-1,10-dial was obtained as a crude product which
could be used without further purification. Ϫ H NMR: δ ϭ 6.61
⋅
ϩ
(
(
(
Ϫ1,
IR: ν˜ ϭ 2976Ϫ2850 cm
1
(
1
J
1
J
.38 (br. d, J1H ϭ 13.4, 1 H), 2.12 (dtt, J1H ϭ 13.4, 3J2H ϭ 12.3,
2
2
1
3
4
2
2H ϭ 5.0, 1 H), 2.95 (d, J1H ϭ 2.1, 1 H), 3.83 (br. dt, J1H
ϭ
3
3
3
(
dd,
J
J
1H ϭ 16.0,
J1H ϭ 6.2, 2 ϫ 1 H), 6.99 (dd, J1H ϭ 16.0,
1H ϭ 1.1, 2 ϫ 1 H), 9.63 (dd, J1H ϭ 6.2, J1H ϭ 1.1, 2 ϫ 1 H).
1.8, 3J1H ϭ 12.3, J1H ϭ 2.4, 2 ϫ 1 H), 4.15 (ddd, J1H ϭ 11.8,
3
2
4
3
4
3
1H ϭ 5.0, 3J1H ϭ 1.2, 2 ϫ 1 H), 5.00 (dd, J1H ϭ 3.9, J1H ϭ 1.0,
3
4
Ϫ1,
Ϫ IR: ν˜ ϭ 3012Ϫ2850 cm
68, 578.
2132, 1677, 1625, 1598, 1290, 1118,
3
4
4
1
H), 5.86 (ddd, J1H ϭ 16.1, J1H ϭ 2.1, J1H ϭ 1.0, 1 H), 6.13
dd, J1H ϭ 16.1, J1H ϭ 3.9, 1 H).
9
3
3
(
1
Synthesis of 4a-Z and 4a-E by Stille Cross-Coupling: In a Schlenk
tube were successively added 10 mL of DMF, 2 mmol (0.84 g) of
1a-Z, 2.2 mmol (0.390 g) of 1-bromo-2-(trimethylsilyl)acetylene
(11) and 0.1 mmol (0.011 g) of hydroquinone before addition of
(
1ЈE)-2-(But-1Ј-en-3Ј-yn-1Ј-yl)-1,3-dioxolane (8c-E): H NMR: δ ϭ
4
3
2
5
0
.98 (d, J1H ϭ 2.0, 1 H), 3.85Ϫ4.05 (m, 4 H), 5.32 (dd, J1H
ϭ
ϭ
4
3
4
4
.1, J1H ϭ 0.5, 1 H), 5.86 (ddd, J1H ϭ 16.0, J1H ϭ 2.0, J1H
.5, 1 H), 6.14 (dd, J1H ϭ 16.0, J1H ϭ 5.1, 1 H). Ϫ 13C NMR:
3
3
2 2
PdCl (MeCN) (0.1 mmol, 0.027 g). The reaction mixture was
δ ϭ 65.0 (2 C), 79.9, 80.7, 102.2, 113.2, 140.0. Ϫ MS; m/z (%): 124
38) [M ], 123 (28), 96 (10), 80 (21), 79 (38), 73 (23), 68 (78), 66
25), 65 (39), 64 (13), 63 (54), 62 (15), 53 (16), 52 (100), 51 (55), 50
40), 45 (34), 39 (19), 38 (25), 29 (29). Ϫ IR: ν˜ ϭ 3291 cm , 2957,
891, 2107, 1641, 1389, 1148, 1078, 1022, 960, 668. Ϫ C
124.14): calcd. C 67.71, H 6.50; found C 67.93, H 6.53.
ϩ
stirred at room temperature and the advancement of the reaction
was monitored by TLC until disappearance of 1a-Z. At the end of
the reaction (about 15 h), the reaction mixture was diluted in ethyl
acetate (10 mL) and vigorously stirred with a saturated aqueous
solution of sodium fluoride (10 mL) in order to precipitate tributyl-
stannyl fluoride. After filtration, extraction and drying of the or-
ganic phase with magnesium sulfate, the enyne 4a-Z was obtained
as a nearly chemically pure product (54%, isolated yield) which was
characterized by physicochemical methods before desilylation as
previously described to afford 8a-Z in 60% yield after liquid chro-
matography (cf. desilylation reactions). The same procedure was
similarly applied in order to obtain 4a-E and subsequently 8a-E.
(
(
(
2
(
Ϫ1
7 8 1
H O
dl-(1ЈE)-2-(But-1Ј-en-3Ј-yn-1Ј-yl)-4,5-dimethyl-1,3-dioxolane (8d-E):
H NMR: δ ϭ 1.25 (d, J1H ϭ 6.0, 3 H), 1.29 (d, J1H ϭ 5.8, 3 H),
.85 (d, J1H ϭ 2.3, 1 H), 3.56Ϫ3.72 (m, 2 H), 5.41 (d, J1H ϭ 5.3,
1
3
3
4
3
2
1
1
8
(
(
3
4
3
H), 5.84 (dd, J1H ϭ 16.0, J1H ϭ 2.3, 1 H), 6.16 (dd, J1H
ϭ
6.0, J1H ϭ 5.3, 1 H). Ϫ 13C NMR: δ ϭ 16.87, 16.94, 78.4, 79.8,
3
⋅
ϩ
0.1, 81.0, 101.3, 113.0, 141.2. Ϫ MS; m/z (%): 152 (42) [M ], 107
19), 101 (6), 81 (23), 80 (70), 79 (98), 73 (23), 64 (15), 63 (39), 55
46), 53 (25), 52 (100), 51 (26), 43 (57), 41 (15), 29 (22), 27 (23). Ϫ (Z)-5,5-Diethoxy-1-(trimethylsilyl)pent-3-en-1-yne (4a-Z): H NMR:
IR: ν˜ ϭ 3289 cm , 2964, 2933Ϫ2860, 2105, 1622, 1381, 1261,
180, 1100, 1021, 962, 800, 662.
4R,5R,1ЈE)-2-(But-1Ј-en-3Ј-yn-1Ј-yl)-4,5-diphenyl-1,3-dioxolane
8e-E): H NMR: δ ϭ 3.03 (d, J1H ϭ 2.2, 1 H), 4.76 (d, J1H
.0, 1 H), 4.81 (d, J1H ϭ 8.0, 1 H), 5.88 (dd, J1H ϭ 5.3, J1H
.5, 1 H), 6.03 (ddd, J1H ϭ 16.0, J1H ϭ 2.2, J1H ϭ 0.5, 1 H),
.41 (dd, J1H ϭ 16.0, J1H ϭ 5.3, 1 H), 7.2Ϫ7.4 (m, 10 H). Ϫ
NMR: δ ϭ 80.2, 80.8, 84.9, 86.7, 103.1, 113.5, 126.5 (2 C), 126.8
2 C), 128.4 (2 C), 128.6 (4 C), 136.2, 137.2, 140.3. Ϫ MS; m/z (%):
97 (1), 170 (28), 169 (54), 142 (29), 141 (100), 115 (21), 105 (9),
1
Ϫ1
3
3
δ ϭ 0.20 (s, 9 H), 1.24 (t, J ϭ 7.0, 6 H), 3.58 (dq, J ϭ 7.0,
1
H
3H
2
3
2
1
3H 1H
J1H ϭ 9.5, 2 ϫ 1 H), 3.71 (dq, J ϭ 7.0, J ϭ 9.5, 2 ϫ 1 H),
J1H ϭ 0.6, 1 H), 5.69 (dd, J1H ϭ 11.2,
1H ϭ 0.6, 1 H), 5.95 (dd, J1H ϭ 11.2, J1H ϭ 7.5, 1 H). Ϫ
3
4
3
5
J
.35 (dd,
J1H ϭ 7.5,
(
(
8
0
6
4
3
3
13
1
4
3
C
ϭ
3
3
4
NMR: δ ϭ Ϫ0.1 (3 C), 15.4 (2 C), 62.1 (2 C), 66.0, 99.3, 100.6,
ϭ
⋅
ϩ
3
4
4
112.4, 140.3. Ϫ MS; m/z (%): 226 (4) [M ], 197 (25), 182 (14), 181
3
3
13
(67), 153 (25), 139 (13), 137 (23), 125 (28), 103 (21), 83 (31), 79
C
(
21), 75 (74), 73 (100), 47 (13), 45 (14), 43 (16), 29 (26). Ϫ IR: ν˜ ϭ
Ϫ1
3
065 cm , 3032, 2956, 2924, 2872, 1653, 1599, 1496, 1465, 1378,
330, 1160, 1100, 973, 832, 814, 764, 700, 664, 581, 548.
(
1
9
1
0 (9), 89 (17), 79 (10), 77 (16), 63 (15), 55 (22), 51 (12), 39 (5). Ϫ
(
Z)-5,5-Diethoxypent-3-en-1-yne (8a-Z): 1H NMR: δ ϭ 1.24 (t,
Ϫ1,
IR: ν˜ ϭ 3287 cm
1
C H O
19 16 2
3089Ϫ3040, 2890, 2105, 1641, 1605, 1498,
3
3
4
5
J
2H ϭ 7.0, 6 H), 3.15 (dd, J1H ϭ 2.4, J1H ϭ 0.8, 1 H), 3.57 (dq,
455, 1395, 1286, 1144, 1088, 1022, 955, 760, 700, 650, 534. Ϫ
(276.33): calcd. C 82.58, H 5.84; found C 82.85, H 5.93.
Synthesis of Dienediyne 9a-E,E: In a Schlenk tube were successively
placed 0.048 mmol (0.055 g) of Pd(PPh and 0.097 mmol (0.0185
g) of cuprous iodide in piperidine (7.5 mL). The reaction mixture
was cooled to 0°C and degassed before addition of 8a-E (0.3 g,
2
3
2
J
3H ϭ 7.0, J1H ϭ 9.5, 2 ϫ 1 H), 3.70 (dq, J3H ϭ 7.0, J1H ϭ 9.5,
3
4
2
1
H), 5.37 (br. d, J1H ϭ 7.5, 1 H), 5.68 (br. dd, J1H ϭ 2.4, 3J1H
ϭ
3
3
1H ϭ 7.5, 1 H). Ϫ 13C
1.2, 1 H), 6.20 (br. dd,
J1H ϭ 11.2,
J
3 4
)
NMR: δ ϭ 15.4 (2 C), 62.0 (2 C), 79.3, 83.2, 99.2, 111.4, 141.4. Ϫ
Ϫ1
IR: ν˜ ϭ 3299 cm , 3266, 2977, 2932, 2874, 2100, 1630, 1386, 1319,
1
118, 1056, 1002, 840, 758, 640.
1
.95 mmol). The reaction mixture was stirred at 0°C until disap-
pearance of 8a-E (TLC monitoring). At the end of the reaction,
water (20 mL) and hexane (20 mL) were successively added before
extraction of the organic products with ether. After usual treat-
ments and liquid chromatography on silica gel (hexane/ether/tri-
Acknowledgments
ethylamine, 78:20:2), the desired dienediyne 9a-E,E was obtained The authors are grateful to Chemetall GmbH, Continentale Parker,
in 70% yield (210 mg).
962
Schering and Rh oˆ ne Poulenc Companies for the gift of organomet-
2
Eur. J. Org. Chem. 1999, 2957Ϫ2963

Stereoselective Synthesis of (E)- and (Z)-Acetals of Pent-2-en-4-yn-1-al
allic starting materials, to MESR and AGISMED for financial sup-
port (F. S.) and to Drs. E. Blart and I. Beaudet for fruitful dis-
cussions.
FULL PAPER
Tetrahedron Lett. 1992, 33, 3647Ϫ3650. Ϫ [
14c]
S.-K. Kang, W.-
Y. Kim, X. Jiao, Synthesis 1998, 1252Ϫ1254.
[15] [15a]
H. P. Dang, G. Linstrumelle, Tetrahedron Lett. 1978, 25,
[15b]
1
1
91Ϫ194. Ϫ
R. Rossi, A. Carpita, A. Lezzi, Tetrahedron
[15c]
984, 40, 2773Ϫ2779. Ϫ
J. Lindley, Tetrahedron 1984, 40,
[
15d]
[
[
1] [1a]
1433Ϫ1456. Ϫ
O. A. King, E. I. Negishi, J. Org. Chem.
K. C. Nicolaou, J. Y. Ramphal, N. A. Petasis, C. N. Serhan,
[
15e]
[1b]
1978, 43, 358Ϫ360. Ϫ
B. P. Andreini, A. Carpita, R. Rossi,
[15f]
Angew. Chem. Int. Ed. Engl . 1991, 30, 1100Ϫ1116. Ϫ
Z. H.
Tetrahedron Lett. 1986, 27, 5533Ϫ5534. Ϫ
M. Abarbri, J.-
R. Rossi, F. Bellina, C. Bechini, L. Mannina, P. Vergamina,
Peng, Y. L. Li, W. L. Wu, C. X. Liu, Y. L. Wu, J. Chem. Soc.,
Perkin Trans. 1 1996, 1057Ϫ1066 and references therein.
L. Parrain, J.-C. Cintrat, A. Duch eˆ ne, Synthesis 1996, 82Ϫ86. Ϫ
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