Lewis acid catalysed M-ene, H-ene, and cycloaddition reactions of allylic stannanes and silanes with methyl propiolate

Article abstract of DOI:10.1016/S0022-328X(97)00246-5

The products of the reaction of methyl propiolate with cyclohexene and some allyl and cyclohex-2-enyl silanes and stannanes (H-ene and M-ene adducts, and [2+2] and [3+2] cycloadducts) have been determined, and rationlised in terms of the probable reaction mechanism. The allylstannanes show only the M-ene reactions to give a mixture of the E- and Z-adducts, and it has been confirmed that the reaction of allylsilanes can give both the [2+2] (cyclobutene) and [3+2] (cyclopentene) cycloadducts, which has been a matter of some dispute.

Full text of DOI:10.1016/S0022-328X(97)00246-5

Ž
.
Journal of Organometallic Chemistry 553 1998 67–72
Lewis acid catalysed M-ene, H-ene, and cycloaddition reactions of
allylic stannanes and silanes with methyl propiolate
)
Hai-Shan Dang, Alwyn G. Davies
Chemistry Department, UniÕersity College London, 20 Gordon Street, London WC1H OAJ, UK
Received 1 March 1997
Abstract
The products of the reaction of methyl propiolate with cyclohexene and some allyl and cyclohex-2-enyl silanes and stannanes H-ene
Ž
w
x
w
x
.
and M-ene adducts, and 2q2 and 3q2 cycloadducts have been determined, and rationlised in terms of the probable reaction
mechanism. The allylstannanes show only the M-ene reactions to give a mixture of the E- and Z-adducts, and it has been confirmed that
w
x Ž
.
w
x Ž
.
the reaction of allylsilanes can give both the 2q2 cyclobutene and 3q2 cyclopentene cycloadducts, which has been a matter of
some dispute. q 1998 Elsevier Science S.A.
Keywords: Ene reaction; Metalloene reaction; Sakurai reaction; Allylsilanes; Allylstannanes
w x
w x
Ž
1. Introduction
A5B is an aldehyde 6 or singlet oxygen 4 , and in
.
the presence of Lewis acids when M is R3Sn or R3Si
Ž
.
w
x
The metalloene M-ene reaction, 1™2 where M is
and A5B is an enone 7–9 , and these reactions have
been exploited in organic synthesis for constructing
metallocyclopentane and metallocyclopentene rings
an organometallic group, is a variant of the hydrogen
Ž
.
w x
ene H-ene reaction, 1™2 where M is hydrogen 1 ;
the enophile A5B can be 1O2 , RN5NR, RCH5O,
RCH5CHR, RC[CR, SO2 , etc. The Sakurai reaction
w
x
7,8,10,11 .
w
x
2q2 Cycloadducts 5 are sometimes observed in
w x
2 , in which an allylsilane adds to an enone in the
presence of usually TiCl4 may be regarded as a
variant of the metalloene reaction.
the reaction of hydrocarbon enes with singlet oxygen
Ž
.
Ž
. w x
A5BsO5O to give a 1,2-dioxetan 12,13 , with
Ž
.
N-methyltriazolinedione A5BsN5N to give a di-
w
x
azetidine 14 , or of propene with methyl propiolate
Ž ..
Ž
.
Ž
w x
A5BsC[C to give a cyclobutene Eq. 2 15 .
Ž .
1
Under some conditions, the M-ene product 2 may be
Ž .
2
w
x
accompanied by the H-ene product 3, andror the 3q2
Ž
cycloadduct 4 involving a 1,2-shift of an organometal-
.
lic group . This last type of reaction is known, for
w
x
The first 2q2 cycloaddition with allylmetallic
example, where M is R3Si, R3Ge, R3Sn, or R3Pb and
compounds was reported in 1975 by Abel and Rowley
who showed that allyltrimethylsilane reacted with per-
w
x
A5B is a triazolinedione 3–5 , where M is R3Sn and
w
x
fluoroacetone at y208C to give the oxetan 16 . In 1979
Snider reported that allyltrimethylsilane and methyl pro-
piolate reacted in the presence of AlCl3 to give the
)
w
x
Ž
Ž ..
w x
2q2 cycloadduct 6 Eq. 3 15 , and several reports
Corresponding author.
0022-328Xr98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.

(
)
68
H.-S. Dang, A.G. DaÕiesrJournal of Organometallic Chemistry 553 1998 67–72
followed of the formation of cyclobutenes from allylsi-
allylsilanes and allylstannanes with methyl propiolate as
the enophile. The aim was to determine the relative
course of the reactions when MsR3Sn, R Si, or H,
w
x
lanes and yneones 17 , or cyclobutanes from allylsi-
w
x
lanes and eneones 18–22 , under Sakurai conditions.
3w
x
and to investigate further the question of the 2q2 or
w
x
3q2 structures of the cycloadducts.
2. Results
Methyl propiolate was chosen as the eneophile to
Ž .
3
allow a direct comparison with the results obtained by
Snider et al. on its H-ene reaction with allylic hydrocar-
However, in 1990, Knolker showed that the cyclic
products from the Sakurai reaction of some allylsilanes
and eneones or yneones in the presence of TiCl4 are not
¨
w
x
bons and allyltrimethylsilane 15 . Ethylaluminium
dichloride was used as the catalyst because it acts both
as a Lewis acid and also as a Brønsted base which will
scavenge adventitiously formed protic acids which might
cause decomposition or rearrangement of the reactants
w
x
the 2q2 cycloadducts as was believed, but rather the
w
x
Ž
Ž ..
w
x
3q2 cycloadducts Eq. 4 8,23 ; the evidence in-
Ž
Ž .
cluded unambiguous X-ray crystallography. In Eq. 4 ,
the Sakurai reaction is represented as involving conju-
gate 1,4-addition across the eneone or yneone system;
1,2-addition can not be excluded, but the silyl group is
hydrolysed off during the hydrolytic work-up, and the
mode of addition does not appear to have been estab-
w
x
or products 31 . One molar equivalent of EtAlCl2 was
used as it complexes more strongly with the acrylate
w
x
products than the propiolate reactant 31 .
The reactivity followed the sequence MsH-SiR3
-SnR3; in the presence of the catalyst, the stannanes
reacted exothermically with methyl propiolate at room
temperature with the development of a brown colour,
and these reactions were therefore carried out at 08C.
The potential initial products corresponding to com-
.
lished.
Ž .
pounds 2–5 are shown in Eq. 5 , but vinylmetallic
w
x
groups are susceptible to protodemetallation 32,33 dur-
ing chromatography on silica gel, and from these prod-
ucts, only the demetallated hexadienoic acids, MsH,
Ž .
4
Ž
.
10, 11, 13, and 19 were isolated. The products were
identified mainly by H and 13C NMR spectroscopy.
1
At this time, the nature of all the cyclobutanes re-
ported as byproducts of the Sakurai reactions was under
w
x
question, but in 1994 Monti et al. 24 showed that the
reaction of 1-trimethylsilylmethylcyclohexene with 3-
w
x
butyn-2-one in the presence of ZnI2 did give the 2q2
Ž
.
w
x
Ž
adduct 19% rather than the 3q2 adduct together
Ž .
5
with 11% of the Sakurai product and 70% of the H-ene
product . In particular, they reinvestigated Snider’s reac-
tion 15 of allyltrimethylsilane with methyl propiolate
in the presence of AlCl Eq. 3 and showed that it did
.
x
w
The reaction conditions and products are given in
Table 1.
Ž
Ž ..
w
x3
Ž
.
indeed give the 2q2 cycloadduct 6 96% , but that a
As protodestannylation of the metallohexadienoate
products occurred on work-up, compounds such as 10
and 11 could in principle be formed by either an M-ene
or an H-ene process. To check this, the reaction of
w
x
Ž
.
small amount of the 3q2 adduct 7 4% was also
formed. There continues to be a great deal of interest in
w
x
the way various factors such as the temperature 25 , the
w
x
Ž .
size of the alkyl groups in the silane 26 , the nature of
allyltributyltin 9 and methyl propiolate was carried out
w
x
the catalyst 27 , and the substituents on the allylic
double bond 27 can be used to control the size of the
ring which is formed.
We have studied the ene reactions of allylstannanes
and related compounds of Group 14 metals where the
enophile A5B is either singlet oxygen or an azo com-
pound 4,5,28–30 . There appears to have been no
report of the metalloene reaction of allylstannanes with
alkynes, and we now describe the results of an investi-
gation of the ene reactions of cyclohexene and of
in a sealed NMR tube. After 16 h at 08C, the mixture
1
w
x
Ž
showed two H NMR triplets, one at d 6.17 J 6.87, J
119Sn 55.19, J Sn 52.79 Hz and the other at d 7.78
117
.
J 7.58, J 119Sn 88.69, J Sn 84.79 Hz , and these
117
Ž
.
signals were lost when trifluoroacetic acid was added.
This confirms that in the product, tin, which is acid-la-
bile, is coupled to a deshielded vinylic proton which is
adjacent to a methylene group, and would be compati-
ble with a mixture of the E and Z M-ene adducts
w
x
w
x
32,33 .

(
)
H.-S. Dang, A.G. DaÕiesrJournal of Organometallic Chemistry 553 1998 67–72
69
Table 1
Ž
.
products 14 80 : 20 which was obtained from cyclo-
EtAlCl2-catalysed reaction of allylic compounds with methyl propio-
late
Ž
.
hexene 12 is similar to that which was reported 83 : 17
where ethyl propiolate was the enophile and AlCl3 was
w
x
the catalyst 15 . Again the behaviour of AlCl3 and
EtAlCl2 is similar.
The reaction between triethylsilyl cyclohexene 15
w
x
and methylpropiolate gave the 2q2 cycloadduct 17
w
x
and the 2q3 cycloadduct with silyl shift 16 in the
1
ratio 18 : 82. In the H NMR spectrum, 16 and 17 are
clearly differentiated by the signals of the protons on
the bridgehead carbon atoms. As shown by decoupling
irradiation, in 17 H-1 couples with H-6 and H-2 with
the coupling constants 4.78 and 4.65 Hz respectively, to
give a distinctive triplet for H-1 at d 3.10. Coupling of
H-6 with H-1 and H-7, and with the axial and equatorial
protons at H-5 results in a more complex multiplet at d
2.85. In 16, the bridgehead protons H-1 and H-5 show
less well resolved multiplets at d 2.76 and 2.93 respec-
tively.
Compounds 16 and 17 were further characterised by
a detailed study of the 13C NMR spectra. The values of
1
Ž
.
J CH for the olefinic CH groups are within the range
which is normally observed for cyclo- and bicyclo-al-
w
x
kenes 34,35 . The chemical shifts for the carbon atoms
carrying the triethylsilyl groups were determined by the
INEPT and APT techniques, and found to be 41.86 for
16 and 18.45 for 17, in line with the rule that they
should be downfield for a bicyclic five-membered ring,
w
x
and up-field for a six-membered ring 35,36 .
In the H-ene reaction of allylic hydrocarbons with
methyl propiolate, Snider reported the formation of only
3. Discussion
w
x
the E-dienoates 15 , whereas in the M-ene reactions of
the allylstannanes, we obtain a mixture of the E- and
Z-products.
The mechanism which is normally accepted for the
reaction of an allylmetallic compounds and an enophile
is illustrated for the case of methyl propiolate in Scheme
1.
Our 1H and 13C NMR spectra of methyl 4- trimethyl-
silylmethyl cyclobut-1-ene-1-carboxylate 6 were iden-
tical to those reported by Monti et al. 24 . As they point
out, the presence of two signals at high field d 0.53
Ž
.
Ž .
w
x
Ž
2
.
and 1.24, J y14.6 Hz , coupled to one further proton,
identifies the Me3SiCH2CH5 group; the signal at higher
field suggests that the corresponding proton is located in
the shielding region of the carbonyl group. The small
Ž
.
w
x
amount 4% of the 3q2 cycloadduct which they
report may have escaped detection. In this system, the
products are similar whether AlCl3 or EtAlCl2 is used
as the catalyst.
No cyclic product could be detected from the reac-
tion of allyltrimethylstannane 9, cyclohexenyltrimethyl-
stannane 18, or cyclohexenyltributylstannane 20; all
three, particularly the cyclohexenylstannanes, gave only
the methyl hexa-2,5-dienoate, with a preponderance of
the E-isomer, though this does not necessarily reflect
Ž
.
the stereochemistry of the ene reactions see below .
w
x
The ratio of the 2q2 cycloaddition 13 and H-ene
Scheme 1.

(
)
70
H.-S. Dang, A.G. DaÕiesrJournal of Organometallic Chemistry 553 1998 67–72
When the eneophile is the carbonyl group of an
sterically unavailable, as in the reaction of adamantyli-
w
x
aldehyde or ketone, or the double or triple bond of an
unsaturated carbonyl compound, Lewis acids can catal-
yse the reaction by associating at the oxygen and in-
creasing the electrophilicity of the enophile, or some-
times by transmetallation of the allylmetallic reagent.
The best evidence for the formation of an initial
complex between the ene and the enophile is the intra-
molecular isotope effects which are observed when
gem-, trans-, and cis-2,3-dimethylbut-2-ene-d6 reacts
deneadamantane with singlet oxygen 12,13 or with a
w
x
triazolinedione 14 .
When MsR3Si, the interaction with the b-positive
w
x
charge is more significant, but this 38 , and its reactiv-
ity towards the carbon nucleophile, is much weaker than
when MsR3Sn. The major reactions which are ob-
w
x
w
x
served are the 2q2 and the 3q2 cycloadditions,
though with other enophiles, the H-ene reaction may
predominate.
w
x
with methyl propiolate in the presence of EtAlCl2 37 .
The precise structure of this intermediate, which is
represented in Scheme 1 for the sake of simplicity as a
zwitterion, is open to question, but all the possibilities
involve the development of positive charge on the ene,
which can be stabilised by the interaction with the metal
M.
4. Conclusions
The chemoselectivity of the reaction of allylic com-
pounds with enophiles is very dependent on the identity
of the metallic group M, of the nature of the ene and
enophile and of any catalyst, and on the reaction condi-
tions.
The nature of the products is then governed by the
nature of the reaction between the nucleophilic and
electrophilic moieties of the intermediate. Nucleophilic
substitution by C-2 at M gives the M-ene product, and
at hydrogen gives the H-ene product; nucleophilic sub-
stitution at C-6 with displacement of M onto C-5 gives
Our results confirm Monti’s demonstration that, un-
der appropriate conditions, the reactions of allylsilanes
w
x
Ž
.
with acetylenes can lead to both 2q2 cyclobutene
w
x
Ž
.
w x
and 3q2 cyclopentene cycloadducts 24 .
The allylstannanes which we have investigated, un-
like the allylsilanes, react chemoselectively with methyl
propiolate by the M-ene route, to give, after hydrolysis,
the methyl hexa-2,5-dienoates. This reaction may be
useful in synthesis, though one limitation would be its
lack of stereoselectivity. Previous work has shown that
in general the M-ene reaction can be enhanced by the
w
x
the 3q2 cycloadduct, and nucleophilic addition at
w
x
C-5 gives the 2q2 cycloadduct.
The reactivity and chemoselectivity which we ob-
serve can be rationalised as follows.
The strength of the interaction of M with a positive
charge in the b-position is well established to increase
w
x
in the sequence H-R3Si-R3Sn 38 , and if the for-
mation of the intermediate is rate-determining, this will
account for the increase of reactivity HC–C5C-
R3SiC–C5C-R3SnC–C5C which we observe, what-
ever the fate of the intermediate.
Ž
use of a more electropositive metal e.g. Sn rather than
.
Si , by introduction of electronegative ligands at the
metal e.g. ClBu2 Sn rather than Bu3Sn , and by the use
Ž
.
w
x
of a polar solvent 30 .
Ž
Sterically hindering ligands on the metal e.g. R3Si
5 Pr3Si rather than Me3Si on the other hand slow the
When MsR3Sn, the principal route which is fol-
lowed is the M-ene reaction, with perhaps a small
H-ene component. This is in accord with the usual high
reactivity of a tin centre to a nucleophile. The vinyl–tin
bond in trimethylvinylstannane is 9 times more reactive
towards protic acids than is the corresponding bond in
i
.
M-ene reaction so that the cyclisation reactions may
w
x
become dominant 25,39 , and lower temperatures favour
w
x
w
x
the 2q2 cycloaddition over the 3q2 cycloaddition
w
x
25,26 .
By a judicious choice of these various parameters,
w
x
2-trimethylstannylacrylate 33 , and both are broken
during chromatography on silica. On hydrolysis, the
a-stannylacrylates give mixtures of the E and Z protic
the reactions can be directed towards the required prod-
uct.
w
x
acrylates 33 , hence the ratio of E- and Z-hexa-
dienoates which we observe reflects the stereochemistry
of the hydrolysis and not that of the M-ene reaction.
When MsH, there is now no possibility of a metal-
loene route. The interaction of the proton with the
5. Experimental
1H And 13C NMR spectra were recorded on solutions
in CDCl3 on a Varian VXR-400 spectrometer, shifts
being referenced to the solvent d H 7.24, dC 77.00 .
Coupling constants are in Hz. Mass spectra were
recorded on a VG 7070H spectrometer, and IR spectra
on a Perkin Elmer PE983 instrument. Column chro-
matography was carried out on Merck silica gel 60.
The reactants 9, 15, 18, and 20 were prepared as
Ž
.
w x
Ž
.
b-positive charge hyperconjugation is weak 38 , in-
w
x
hibiting migration in the 3q2 cyclisation, but permit-
ting attack of the carbon nucleophile at C-5, leaving the
w
x
2q2 cycloaddition and the H-ene reaction in competi-
tion to a degree depending on the structure of the alkene
x w
w
x
15 . 2q2 Cycloadditions can be observed in isolation
w x
when the relevant hydrogen atoms are absent or are
described previously 4 .

(
)
H.-S. Dang, A.G. DaÕiesrJournal of Organometallic Chemistry 553 1998 67–72
71
[
]
(
)
5.1. Reaction of allylmetallic compounds with methyl
propiolate
5.5. Methyl bicyclo 4.2.0 -oct-7-ene-7-carboxylate 13
Ž .
Ž
.
Ž
.
Ž
.
Oil. d H 1.30 1H, m , 1.40 2H, m , 1.54 2H, m ,
Ž . Ž . Ž
1.75 2H, m , 2.00 1H, m , 2.77 1H, ddd, J 10.30,
These reactions were carried out by Snider’s proce-
w
x
. Ž
5.45, and 1.15, H-2 , 3.04 1H, dd, J 10.13 and 5.40,
. Ž . Ž .
H-1 , 3.70 3H, s, OMe , 6.86 1H, d, J 1.15, H-8 .
dure 31 . The general method was as follows.
3
y3
Ž
Ethylaluminium dichloride 4.0 cm of a 1 mol dm
.
Ž .
Ž
.
Ž
.
solution in hexane was syringed dropwise under argon
into a solution of methyl propiolate 0.34 g, 4.0 mmol
in CH2Cl2 5 cm at room temperature. The mixture
was stirred for 30 min, then a solution of the corre-
d C 150.52 J H 174.3, C-7 , 141.63 C-8 , 40.06
Ž
.
Ž
Ž
. Ž . Ž . Ž .
C-2 , 38.38 C-1 , 23.80 C-6 , 23.59 C-5 , 18.92
3
Ž
.
. Ž . Ž . Ž .
C-4 , 18.33 C-3 , 51.10 OMe , 162.85 C5O .
Ž
.
Ž
sponding allyl compound 4.0 mmol in CH2Cl2
5
( ) ( )
5.6. Methyl E -3- cyclohex-2-enyl propenoate 14
(
)
cm3 at room temperature when MsSi, and at 08C
when MsSn. The mixture was then stirred at the
corresponding temperature for the period given in Table
1. The solvent was evaporated off, and the residue was
.
Ž .
Ž
.
Ž
.
Oil. d H 1.20–2.00 6H, m , 2.92 1H, m , 3.73
Ž
.
Ž
.
3H, s, OMe , 5.51 1H, dm, J 9.83 and 2.81, H-6 ,
5.78 1H, dd, J 15.73 and 1.40, H-2 , 5.79 1H, dm, J
9.83 and 2.21, H-5 , 6.91 1H, dd, J 15.73 and 7.06,
H-3 .
The H NMR spectra of the compounds 13 and 14
are consistent with those reported for the corresponding
Ž
.
Ž
Ž
chromatographed on silica gel using pentanerether 5 : 1
.
Ž
.
vrv as eluent. The mixture was examined by NMR to
.
1
determine the ratio of the products, which were then
separated by repeated chromatography.
Ž
.
Ž
.
w
x
ethyl ester 15 .
(
)
5.2. Methyl 4- trimethylsilylmethyl cyclobut-1-ene-1-
( ) [
]
carboxylate 6 15
[
]
5.7. Methyl 8-triethylsilylbicyclo 3.2.1 oct-6-en-6-
carboxylate 16
(
)
Ž .
Ž
.
Ž
Clear oil. d H y0.01 9H, s, SiMe3 , 0.55 1H, dd,
X
.
Ž
J 14.68 and 12.64, C H H Si , 1.26 1H, dd, J 14.68
Ž .
Ž
.
Clear oil. d H 0.66 6H, q, J 7.98, CH2 Si , 0.96
9H, t, J 7.98, Me , 1.24 1H, m , 1.38–1.60 6H,
X
.
Ž
and 3.06, CH H Si , 1.98 1H, dt, J 15.38 and 1.56,
H-3 , 2.62 1H, ddd, J 15.38, 3.65, and 1.56, H -3 3.03
Ž
.
Ž
.
Ž
X
.
Ž
.
.
Ž
.
Ž
.
complex, ring protons , 2.76 1H, m , 2.93 1H, m ,
Ž .
Ž
.
1H, dddd, J 12.64, 3.65, 3.06, and 1.56, H-4 , 3.70
Ž .
Ž
.
Ž
.
3.71 3H, s, OMe , 6.99 1H, d, J 3.00, H-7 . d C
Ž
.
Ž
Ž
Ž
.
Ž
3H, s, OMe , 6.72 1H, m, H-2 . d C 144.05 J H
Ž
.
Ž
Ž
.
Ž
.
.
147.93 J H 168.2, C-7 , 140.2 C-6 , 42.84 C-5 ,
.
.
Ž
.
Ž
Ž
.
167.9, C-1 , 144.10 C-2 , 39.11 C-3 , 36.19 C-4 ,
20.28 C-5 , 50.95 OMe , 162.59 C5O y1.02
Ž
Ž
.
Ž
Ž
.
.
Ž
41.86 C-8 , 41.84 C-1 , 21.73 C-2 , 21.39 C-3 ,
Ž
.
.
.
.
.
.
Ž
.
17.81 C-8 , 51.22 OMe , 165.76 C5O , 4.42 and
Øq
Ž
SiMe3 .
Ž
.
Ž
.
Ž
.
Ž
.
7.70 SiEt3 . MS 70 eV 280 M , 2 , 251 45 , 133
Ž
.
Ž
.
Ž
.
Ž
100 , 117 35 , 105 44 . HRMS on mixture with
.
( ) ( )
5.3. Methyl Z -hexa-2,5-dieneoate 10
isomer 17 , found 280.1785; C16 H28O2 Si requires
280.1792.
Ž .
Ž
Clear oil. d H 3.42 2H, ttd, J 7.48, 6.25, and 1.54,
.
Ž
.
Ž
.
Ž
[
]
H-4 , 3.80 3H, s, OMe , 5.03 2H, m, H-6 , 5.78 1H,
dt, J 11.45 and 1.54, H-2 , 5.82 1H, ddt, J 16.63,
5.8. Methyl 2-triethylsilylbicyclo 4.2.0 oct-7-ene-8-
carboxylate 17
.
Ž
(
)
.
Ž
10.11, and 6.25, H-5 , 6.24 1H, dt, J 11.45 and 7.48,
Ž .
.
Ž
.
Ž
.
Ž
.
H-3 . d C 37.59 C-4 , 51.69 OMe , 116.50 C-6 ,
Ž .
Ž
.
Clear oil. d H 0.58 6H, quartet, J 7.86, CH2 Si ,
Ž
.
Ž
Ž
.
Ž
.
119.75 C-5 , 135.44 C-2 , 147.22 C-3 , 165.81
Ž
.
Ž
.
0.96 9H, t, J 7.86, CH3 , 1.22 1H, m , 1.40–1.55
Ž
.
.
C5O . nmax neat 2940, 2869, 1733, 1650, 1435, 1223
Ž
.
Ž
.
Ž
6H, complex , 2.85 1H, m , 3.01 1H, dd, J 4.78 and
cmy1. HRMS C7 H10O2 , found 126.0680, calculated
126.0688.
.
Ž
.
Ž
.
4.65 , 3.68 1H, s, OMe , 6.72 1H, d, J 1.28, H-7 .
d C 147.97 J H 173.1, C-7 , 144.00 C-8 , 39.15
C-1 , 38.59 C-6 , 26.24 C-5 , 24.00 C-4 , 20.30
C-3 , 18.45 C-2 , 50.91 OMe , 162.67 C5O , 2.29
Ž .
Ž
.
Ž
.
.
Ž
Ž
.
.
Ž
.
Ž
.
.
Ž
Ž
.
Ž
Ž
.
( ) ( )
5.4. Methyl E -hexa-2,5-dieneoate 11
Ž
.
Ž
.
and 7.70 SiEt3 . HRMS on mixture with isomer 16 ,
found 280.1785; C16 H28O2 Si requires 280.1792.
Ž .
Ž
Clear oil. d H 2.96 2H, ttd, J 7.99, 6.55, and 1.41,
.
Ž
.
Ž
.
Ž
H-4 , 3.85 3H, s, OMe , 5.20 2H, m, H-6 , 5.82 1H,
dt, J 15.73 and 1.68, H-2 , 5.85 1H, dt, J 16.65,
( ) ( )
(
)
.
Ž
5.9. Methyl Z -3- cyclohex-2-enyl propenoate 19
.
Ž
10.15, and 7.99, H-5 , 7.06 1H, dt, J 15.73 and 6.55,
Ž .
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
H-3 . d C 35.95 C-4 , 51.24 OMe , 116.89 C-6 ,
Oil. 1.36 1H, m , 1.59 1H, m , 1.72 1H, m , 1.84
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
121.70 C-5 , 133.56 C-2 , 146.27 C-3 , 166.52
C5O . These spectra are consistent with those reported
1H, m , 1.98 2H, m , 3.68 3H, s, OMe , 4.06 1H, m,
H-4 , 5.46 1H, dm, J 9.96 and 2.24, H-6 , 5.71 1H,
dd, J 11.42 and 1.06, H-2 , 5.75 1H, dm, J 9.96 and
Ž
.
.
Ž
.
Ž
w
x
.
Ž
previously 15,40 .

(
)
72
H.-S. Dang, A.G. DaÕiesrJournal of Organometallic Chemistry 553 1998 67–72
w
x
15 B.B. Snider, D.J. Rodini, R.S.E. Conn, S. Sealfon, J. Am.
.
Ž
.
3.45, H-5 , 6.04 1H, dd, J 11.42 and 10.04, H-3 .
Ž
.
Chem. Soc. 101 1979 5283.
Ž .
Ž
.
d C 20.39, 24.72, 28.42, 34.85, 51.02 OMe , 118.07
C-6 , 127.07 C-2 , 128.38 C-5 , 153.57 C-3 , 166.66
C5O . nmax cm , neat 2929, 2846, 1720, 1633,
1432, 1195, 823. MS 70 eV 166 8, M , 150 7 ,
134 10 , 105 12 , 91 14 , 79 17 , 53 100 . HRMS,
found 166.0999, calculated for C10 H14O2 , 166.0994.
w
w
x
x
Ž
.
16 E.W. Abel, R.J. Rowley, J. Organomet. Chem. 84 1975 199.
17 G. Audran, H. Monti, G. Leandri, J.-P. Monti, Tetrahedron Lett.
Ž
Ž
.
Ž
.
Ž
.
Ž
.
´
y1
.
Ž
.
Ž
.
34 1993 3417.
Øq
Ž
Ž
.
Ž
.
.
.
Ž .
w
w
x
Ž
.
18 R. Pardo, J.-P. Zahra, M. Santelli, Tetrahedron Lett. 1979
4557.
Ž
.
Ž
.
.
Ž
Ž
x
19 A. Hosimi, H. Kobayashi, H. Sakurai, Tetrahedron Lett. 21
Ž
.
1980 955.
w
w
x
x
Ž
.
20 S. Danishefsky, M. Kahn, Tetrahedron Lett. 22 1981 485.
21 H.O. House, P.C. Gaa, D. VanDerveer, J. Org. Chem. 48 1983
Ž
.
.
Acknowledgements
1661.
w
w
w
w
w
w
x
Ž
22 G. Majetich, J. Defauw, C. Ringold, J. Org. Chem. 53 1988
50.
23 H.-J. Knolker, N. Foitzik, R. Graf, J.-B. Pannek, Tetrahedron 49
This work was supported by the SERC.
x
¨
Ž
.
1993 9955.
x
24 H. Monti, G. Audran, G. Leandri, J.-P. Monti, Tetrahedron Lett.
´
References
Ž
.
35 1994 3073.
x
Ž
.
25 G.P. Brengel, C. Rithner, A.I. Meyers, J. Org. Chem. 59 1994
w x
1
Ž
.
A.G. Davies, in: B.T. Golding, R.J. Griffin, H. Maskell Eds. ,
Organic Reactivity. Physical and Biological Aspects, Royal
Society of Chemistry, Cambridge, 1995, p. 263.
A. Hosomi, H. Sakurai, J. Am. Chem. Soc. 99 1977 1673.
S. Ohashi, W.E. Ruch, G.B. Butler, J. Org. Chem. 46 1981
5144.
x
26 H.-J. Knolker, G. Baum, R. Graf, Angew. Chem. Int. Ed. Engl.
¨
Ž
.
33 1994 1612.
w x
Ž
.
2
w x
3
x
27 H. Monti, G. Audran, M. Feraud, J.-P. Monti, G. Leandri,
´
Ž
.
.
Ž
.
Tetrahedron 52 1996 6685.
614.
w
w
x
x
Ž
.
28 H.-S. Dang, A.G. Davies, Synthesis 1992 833.
29 H.-S. Dang, A.G. Davies, J. Chem. Soc. Perkin Trans. 2 1992
w x
4
Ž
H.-S. Dang, A.G. Davies, J. Chem. Soc. Perkin Trans. 2 1991
Ž
.
2011.
1095.
w x
5
J. Cai, H.-S. Dang, A.G. Davies, in: E. Lukevics, L. Ignatovich
Eds. , Frontiers of Organogermanium, -tin and -lead Chemistry,
Latvian Institute of Organic Synthesis, Riga, 1993, p. 197.
M. Nakatsuka, J.A. Ragan, T. Sammakia, D.B. Smith, D.E.
Uehling, S.L. Schreiber, J. Am. Chem. Soc. 112 1990 5583.
J.W. Herndon, C. Wu, J.J. Harp, Organometallics 9 1990
w
w
x
x
Ž
.
30 H.-S. Dang, A.G. Davies, J. Organomet. Chem. 430 1992 287.
31 B.B. Snider, D.J. Rodini, M. Karras, T.C. Kirk, E.A. Deutsch,
Ž
.
Ž
.
R. Cordova, R.T. Price, Tetrahedron 37 1981 3927.
w x
6
w
w
w
w
w
x
32 A.J. Leusink, H.A. Budding, J.W. Marsman, J. Organomet.
Ž
.
Ž
.
Chem. 9 1967 285.
w x
7
Ž
.
x
33 J.C. Cochran, L.E. Williams, B.S. Bronk, J.A. Calhoun, J.
3157.
Ž
.
Fassberg, K.G. Clark, Organometallics 8 1989 804.
w x
Ž
.
8
w x
9
H.-J. Knolker, P.G. Jones, J.-B. Pannek, Synlett 1990 429.
K. Ohkata, K. Ishimaru, Y.-g. Lee, K.-y. Akiba, Chem. Lett.
1990 1725.
x
¨
34 F.W. Wehrli, A.P. Marchand, S. Wehrli, Interpretation of Car-
bon-13 NMR Spectra, Wiley, Chichester, 1988.
Ž
.
x
35 H.O. Kalinowski, S. Berger, S. Braun, Carbon-13 NMR Spec-
w
x
10 R.L. Danheiser, B.R. Dixon, R.W. Gleason, J. Org. Chem. 57
troscopy, Wiley, Chichester, 1988.
Ž
.
1992 6094.
x
36 W. Kitching, M. Marriott, W. Adcock, D. Doddrell, J. Org.
w
w
x
x
Ž
.
11 J.S. Panek, N.F. Jain, J. Org. Chem. 58 1993 2345.
12 W. Adam, in: S. Patai Ed. , The Chemistry of Peroxides,
Wiley, Chichester, 1983, p. 829.
13 W. Adam, M. Heil, T. Mosandl, C.R. Saha-Moller, in: W. Ando
Ed. , Organic Peroxides, Wiley, Chichester, 1992, p. 221.
14 R. Richter, H. Ulrich, in: A. Hassner Ed. , Heterocyclic Com-
Ž
.
Chem. 41 1976 1671.
Ž
.
w
w
w
x
x
Ž
Ž
.
.
37 B.B. Snider, E. Ron, J. Am. Chem. Soc. 107 1985 8160.
38 G. Hagen, H. Mayr, J. Am. Chem. Soc. 113 1991 4954.
x
39 H.-J. Knolker, N. Foitzik, H. Goesmann, R. Graf, Angew.
¨
w
x
¨
Ž
.
Ž
.
Chem. Int. Ed. Engl. 32 1993 1081.
w
x
Ž
.
w
x
40 F.K. Sheffy, J.P. Godschalx, J.K. Stille, J. Am. Chem. Soc. 106
pounds, vol. 42, part 2, Wiley, New York, 1983.
Ž
.
1984 4833.