The Ireland-Claisen rearrangement as a probe for the diastereoselectivity of nucleophilic attack on a double bond adjacent to a stereogenic centre carrying a silyl group

Article abstract of DOI:10.1039/b305881f

The E- and Z-silyl enol ethers 4 derived from allyl 3-R-3-dimethyl(phenyl)silylpropanoate (R = Me, Prⁱ and Ph) and the Z-silyl enol ethers 7 derived from 4-R-4-dimethyl(phenyl)silylbut-2-enyl acetate (R = Me and Prⁱ) undergo Ireland-

Full text of DOI:10.1039/b305881f

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The Ireland–Claisen rearrangement as a probe for the
diastereoselectivity of nucleophilic attack on a double bond
adjacent to a stereogenic centre carrying a silyl group
Mark S. Betson and Ian Fleming*
Department of Chemistry, Lensfield Road, Cambridge, UK CB2 1EW.
E-mail: if10000@cam.ac.uk; Fax: ϩ44 (0)1223 336362; Tel: ϩ44 (0)1223 336372
Received 23rd May 2003, Accepted 15th September 2003
First published as an Advance Article on the web 6th October 2003
The E- and Z-silyl enol ethers 4 derived from allyl 3-R-3-dimethyl(phenyl)silylpropanoate (R = Me, Pri and Ph) and
the Z-silyl enol ethers 7 derived from 4-R-4-dimethyl(phenyl)silylbut-2-enyl acetate (R = Me and Pri) undergo
Ireland–Claisen rearrangements largely in the same stereochemical sense, with C–C bond formation taking place anti
to the silyl group in the conformations 22, 23 and 24 in which the hydrogen atom on the stereogenic centre is inside,
more or less eclipsing the double bond. The E-silyl enol ether E-7a derived from 4-methyl-4-dimethyl(phenyl)silylbut-
2-enyl acetate shows low diastereoselectivity in the alternative sense, probably because C–C bond formation takes
place anti to the silyl group in the conformation 26 with the methyl group inside, but the silyl enol ether E-7b derived
from 4-isopropyl-4-dimethyl(phenyl)silylbut-2-enyl acetate shows low diastereoselectivity in the normal sense. The
E- and Z-silyl enol ethers 33 derived from cis-crotyl 3-phenyl-3-dimethyl(phenyl)silylpropanoate and the E-silyl enol
ether 39 derived from trans-crotyl 3-phenyl-3-dimethyl(phenyl)silylpropanoate undergo Ireland–Claisen rearrange-
ments largely in the same stereochemical sense as their allyl counterparts, but with moderately high levels of
diastereocontrol in setting up the third stereogenic centre following from chair-like transition structures.
originally wanted to tackle, but they do shed some light on a
different matter, namely on the sense of the diastereoselectivity
of nucleophilic attack on a double bond adjacent to a stereo-
genic centre carrying a silyl group 3.
Introduction
We established at length how effectively a silyl group can con-
trol the stereochemistry of electrophilic attack on a double
bond in the sense 1, anti to the silyl group, for a wide variety of
Earlier work in this area had been largely about attack on a
reactions, some of which take place with bond formation at
carbonyl group, analogous to the control exerted by the Felkin–
C-2,1,2 some at C-3,3,4 and some for cycloadditions taking place
Anh rule. For somewhat complicated but essentially steric
with bonds forming at both C-2 and C-3.5 We have also been
reasons, the attack is largely anti to the silyl group in the usual
much exercised to determine whether the sense and the high
Felkin–Anh conformation with the R group inside, more or less
level of control for all these reactions stems from the steric or
eclipsing the double bond.9 There have also been two papers on
from the electronic effect of the neighbouring Si–C bond. We
the attack on the C᎐O double bond of oxenium ions derived
᎐
have had little substantive success, managing only to show that
the stereochemistry of the SE2Љ reaction 2,6 taking place at C-5,
further away from the steric effect, was much less stereoselective
with small electrophiles than the corresponding SE2Ј reaction
at C-3. Separating steric and electronic effects is a notorious
problem, beset with pitfalls. It is clearly important for our
understanding of chemical reactions, but applied to dia-
stereoselectivity it has led so far to substantial but largely
unresolved debate.7
from acetals, in which the stereogenic centre was attached to the
oxygen atom.10 For attack on a C᎐C double bond, there has
᎐
only been our own work, described in the preceding paper, on a
system in which a cuprate attacked at the β carbon of an enone
having the stereogenic centre attached to the α carbon.11 In all
cases, attack takes place predominantly anti to the silyl group.
In the acetal reactions, it is not clear what the conformation is at
the time of reaction, and in the enone the cyclic system imposes
extra rigidity. None of these cases has the attack at C-2 in the
sense 3.
The device that we chose to use was the diastereoselectivity
of the Ireland–Claisen rearrangement12 of the complementary
pair of silyl enol ethers 4 and 7 (Scheme 1). We reasoned that the
former, 4, with two oxygen atoms as substituents on the double
bond adjacent to the stereogenic centre, would have nucleo-
philic character at C-3 in the [3,3]-sigmatropic rearrangement,
and hence some of the character of electrophilic attack
adjacent to the stereogenic centre, symbolised by the curly
arrows drawn in an anti-clockwise direction. We expected that
we would see the same sense of diastereoselectivity anti to the
silyl group as we had seen in the corresponding enolate alkyl-
ations,1 just as Yamazaki found that the new bond is largely
formed syn to a trifluoromethyl group for the same type of
Ireland–Claisen rearrangement.13 The more interesting case
was the latter, 7, where the [3,3]-sigmatropic rearrangement
would have the nucleophilic character at C-3Ј and some of the
character of nucleophilic attack at C-3, symbolised by the curly
arrows drawn in a clockwise direction. Would the two reactions
Our approach to the problem reported here was flawed from
the start—we planned to study how changing the electronic
balance from electrophilic attack to nucleophilic attack might
affect the sense of the diastereoselectivity. In the meantime it
has become clearer that there is no compelling reason to expect
nucleophilic attack to differ fundamentally in the sense of its
diastereoselectivity from the otherwise analogous electrophilic
attack. Indeed, the most provocative of the theories for electro-
nically controlled diastereoselectivity positively suggests that
nucleophilic and electrophilic attack ought to take place in the
same sense, anti to the best donor substituent.8 In consequence,
the results reported here do not address the problem we
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
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Scheme 2 Reagents and conditions: i, CBr4, Ph3P, CH2Cl2; ii, BunLi,
THF; iii, RMe2SiCl; iv, ButLi, THF, TMEDA; v, PhMe2SiCl; vi,
AgNO3, KCN, EtOH, H2O; vii, LDA, THF; viii, ClCO2Me; ix, LiAlH4,
Et2O; x, Ac2O, Et3N, DMAP, Et2O; xi, H2, Pd/BaSO4, MeOH xii,
CH2O; xiii, DIBAL.
Scheme 1
show the same sense of diastereoselectivity, and which would
have the higher degree?
intermediates analogous to those in Scheme 2 as well as in other
routes that we tried.
The idea of a complementary pair of Claisen rearrangements
is not without precedent—it has been used by le Noble to probe
stereoelectronic effects exocyclic to an adamantyl framework.
He found that both the nucleophilic and electrophilic version
took place with attack syn to a remote electron-withdrawing
group, and therefore anti to the better donor substituent, and
to a very similar extent.14 There is also some support for the
idea that the complementary pairs would have an opposite
electronic bias of the kind that we wanted to use. The transition
structure for the Ireland–Claisen rearrangement is even further
above the diagonal line in a More O’Ferrall–Jencks diagram
than the transition structure for an unsubstituted Claisen
rearrangement,15 implying even more bond-breaking ahead of
bond-making. There is also some evidence for an unequal dis-
tribution of electron population in Claisen rearrangements,
which can have a significant solvent effect, implying that the
transition structure can have zwitterionic as well diradical
character.16 On the other hand, it is not reassuring to know that
the transition structure for an Ireland–Claisen rearrangement
appears to have four times as much bond breaking as bond
making.17
The Ireland–Claisen rearrangements took place on refluxing
the freshly-prepared solutions of the silyl enol ethers in THF
for 8 hours. A brief treatment with sodium hydroxide solution
converted the silyl esters into the carboxylic acids, which we
1
analysed as their methyl esters by integration of the H-NMR
spectra of the mixtures. The overall yields from the esters
used to prepare the silyl enol ethers to the methyl esters used
in the analysis were in the range 43–66%. The ratios of
diastereoisomers are summarised in Table 1.
We assigned relative stereochemistry to the products 5 and 6
by preparing authentic samples of the methyl esters (Scheme 3).
For the a and b series, we prepared mixtures rich in the anti
isomer by allylation of the enolates derived from the esters 14a
and 14b, for which the sense of the diastereoselectivity is
reliably high. In practice, the ratio 15a : 16a was 97 : 3, and the
ratio 15b : 16b was 89 : 11. To identify with more confidence
the NMR signals of the minor diastereoisomers 16a and 16b,
we formed the enolates from the mixtures rich in the anti
isomers using LDA, and reprotonated them with ammonium
chloride solution, to give mixtures richer in the syn isomers 16a
and 16b. This procedure gave products in the ratio 15a : 16a
of 60 : 40 and 15b : 16b of 48 : 52, with clearly identifiable
1H-NMR signals from the isomers that had been the minor
products in the Ireland–Claisen rearrangements. Furthermore,
we also carried out a conjugate addition of the silyl cuprate
Results and discussion
We carried out reactions using the silyl enol ethers 4 in three
series, labelled a (R = Me), b (R = Pri) and c (R = Ph), each of
which was prepared separately as an E and a Z isomer. We
prepared the allyl esters used to make the silyl enol ethers from
the known methyl esters1,2 by acid-catalysed ester exchange,
and the silyl enol ethers themselves using Ireland’s recipes for
E and Z isomers.18 There was little doubt that the E isomers,
made with LDA in THF at Ϫ78 ЊC, would be close to 94%
configurationally pure, since this is a well tested and reliable
method. We checked only one case, that of 4a, which appeared
1
to be a single isomer from its H-NMR spectrum. In contrast,
we were unable to confirm the stereochemical purity of any of
the Z silyl enol ethers, prepared similarly, but in a mixture
of HMPA and THF. The trimethylsilyl enol ethers were not
isolable, because the HMPA could only be removed using an
aqueous wash, during which the silyl enol ethers were hydro-
lysed even in the most careful workup, and the tert-butyl-
dimethylsilyl enol ethers, which might have been isolable, were
not formed cleanly. We reassured ourselves that we were getting
mixtures rich in the Z-isomer, when we examined the reactions
of the crotyl esters, as described below (Scheme 5).
We carried out reactions using the silyl enol ethers 7 in only
two series, labelled a (R = Me) and b (R = Pri). The esters 11 and
13 used to make the silyl enol ethers 7a and 7b were prepared
by the standard routes shown in Scheme 2. The third series 7c
(R = Ph) defeated us, because of low yields, probably because
the silyl group was too easily lost from the simultaneously
benzylic and propargylic carbon during the preparation of the
Scheme 3 Reagents and conditions: i, LDA, THF; ii, allyl bromide; iii,
(PhMe2Si)2CuLi, THF; iv, NH4Cl, H2O; v, O3, CH2Cl2; vi, H2O2,
NaOH; vii, Me3SiCHN2, MeOH.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
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Table 1 Ratios of diastereoisomers produced by the Ireland–Claisen rearrangements in Scheme 1
“Electrophilic attack”
“Nucleophilic attack”
R
Starting material
E or Z
5 : 6
98 : 2
93 : 7
86 : 14
69 : 31
>98 : 2
>97 : 3
Starting material
E or Z
8 : 9
Me
Me
Pri
Pri
Ph
Ph
4a
4a
4b
4b
4c
4c
E
Z
E
Z
E
Z
7a
7a
7b
7b
–
Z
E
Z
E
–
93 : 7
38 : 62
98 : 2
52 : 48
–
–
–
–
reagent to the α,β-unsaturated ester 17b followed by proton-
ation of the enolate, and obtained a similar mixture of the
esters 15b and 16b in a ratio of 45 : 55. The products 15c and
16c, produced in this work by allylation in the ratio 98 : 2, were
already known.1
We assigned relative stereochemistry to the products 8 and 9
by ozonolysis of the mixtures of their methyl esters 20 and 21,
followed by oxidation and esterification, to give the diesters 18
and 19 (Scheme 3). We compared the 1H-NMR spectra of these
mixtures with the spectra of similar mixtures derived by the
same sequence from the esters 15 and 16.
All but one of the Ireland–Claisen rearrangements gave more
of the anti isomer 5 or 8 than of the syn isomer 6 or 9 (Table 1,
but note that the E-isomers of the silyl enol ethers 4 match the
Z-isomers of the silyl enol ethers 7). In the “electrophilic
attack” series, the ratios match the ratios obtained in the allyl-
ation of the enolates derived from the ester 14, with the highest
ratio for R = Ph, intermediate for R = Me, and lowest for
R = Pri, which in turn match our earlier results for the corre-
sponding methylation reactions.1 We can be reasonably con-
fident that the preferred geometries in the transition structures
resemble the somewhat simplified drawings 22 and 23 for the
E- and Z-isomers, respectively, with the hydrogen inside and
attack anti to the silyl group in all six cases.
propyl substituent E-7b. Normally a large group like this avoids
being inside, but a molecular modelling calculation (MOPAC
PM3) supports this explanation in this case by finding that
the conformation 26 (R = Pri) is actually 0.84 kJ molϪ1 lower
in energy than that with the hydrogen inside 25 (R = Pri). As
expected, similar calculations on the corresponding Z-isomer
have the transition structure with the isopropyl inside 14.7 kJ
molϪ1 higher in energy than the conformation with the
hydrogen atom inside 24 (R = Pri). It is clear from the high
diastereoselectivity with both Z-isomers in the “nucleophilic
attack” series that this translates into a highly favourable path-
way leading to the products 8 by attack anti to the silyl group.
Our results in the “electrophilic attack” series 4
be compared with those of Beslin,20 and our results in the
“nucleophilic attack” series 7 8 ϩ 9 can be compared with
5 ϩ 6 can
those of Cha21 (Scheme 4). In Beslin’s and in Cha’s work, the
heteroatom substituent on the stereogenic centres is an electro-
negative element, in contrast to our electropositive element.
Beslin’s Claisen rearrangements of the thioenol ethers 27 were
highly diastereoselective, taking place in the sense syn to the
oxygen atom in the conformation with the hydrogen atom
inside, making these results with an electronegative element
opposite to ours with the electropositive element. In contrast,
Cha’s Ireland–Claisen rearrangements of the silyl enol ethers 30
showed low diastereoselectivity in favour of the anti isomer
31, corresponding to attack anti to the oxygen atom in the
conformation with the hydrogen atom inside.
In the “nucleophilic attack” series, the Z-isomers Z-7a and
Z-7b show remarkably high levels of diastereoselectivity, pre-
sumably because they also have a preferred transition structure
24 with the hydrogen inside and attack anti to the silyl group.
The one result in which the syn isomer is the major product is
with the silyl enol ether E-7a, which gives more (62 : 38) of the
isomer 9a than 8a. The explanation is probably not related to
any change in an electronic effect. The silyl enol ether E-7a,
where the carbon group on the stereogenic centre is a methyl
group and the substituent on the double bond cis to it is only
a hydrogen atom, can have a conformation 26 (R = Me)
significantly populated in which the methyl group is inside.
Attack anti to the silyl group in this conformation gives the syn
product 9a, in contrast to the usual attack when the hydrogen
atom is inside 25 (R = Me). As we have pointed out in our
earlier work,4,19 the diastereoselectivity in many reactions is
unpredictable when the carbon substituent on the stereogenic
centre is small and there is only a hydrogen atom cis to it,
unless a closely analogous reaction has been investigated. The
same explanation may account for the unusually low dia-
stereoselectivity in the corresponding reaction with an iso-
Scheme 4
We also carried out a few Ireland–Claisen rearrangements
with a methyl substituent at the terminus of the allyl fragment
in the “electrophilic attack” series (Scheme 5). If we can rely on
the preference for the chair transition structure established by
Ireland’s work,22 we can expect that the double bond geometry
in a crotyl ester would control a third stereocentre. This had the
added advantage that it would provide some check on whether
the geometry of the silyl enol ethers had been controlled to
give largely the E- and Z-isomers in our earlier work. There
were earlier reports of reactions controlling three contiguous
stereocentres using Claisen rearrangements with electro-
negative substituents on the stereogenic centre, in contrast to
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
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with nucleophilic character does not change the sense of the
diastereoselectivity, and that, in the latter case, when the con-
formation is well controlled, it is actually much higher.
Experimental
General
Infrared spectra were recorded on a Perkin-Elmer FT-IR 1600
spectrometer, using sodium chloride plates. NMR spectra were
recorded on Bruker AC 250 and Bruker AM 400 spectrometers.
Chemical shifts were measured relative to tetramethylsilane
(1H δ 0.0) or chloroform (14C δ 77.0). Coupling constants J
are expressed in Hertz are the measured values correct to one
decimal place. 14C-NMR spectra taken using the APT protocol
are labelled ϩ for quaternary and methylene carbons, and – for
methine and methyl carbons. Flash column chromatography
was carried out using Merck Kieselgel 60 (230–400 mesh). Thin
layer chromatography was performed using plates coated with
Kieselgel 60 PF254. Ether and THF were distilled from lithium
aluminium hydride immediately before use. Toluene, hexane,
dichloromethane and acetonitrile were distilled from calcium
hydride. Light petroleum refers to the fraction boiling between
40 ЊC and 60 ЊC. Organolithium reagents were titrated using the
method of Gilman.25
Scheme 5 Reagents and conditions: i, THF, reflux, 8 h; ii, NaOH; iii,
CH2N2; iv, TBAF, THF.
our electropositive substituent. In one of them, a hydroxyl
group sat inside in a lithium enolate providing coordination
to the lithium ion, and attack was then anti to the alkyl group.23
In another, a sulfoxide group is the stereogenic centre and a
thio-Claisen rearrangement takes place anti to the lone pair.24
We prepared the cis-crotyl ester used to make the silyl
enol ethers 33 from methyl 3-dimethyl(phenyl)silyl-3-phenyl-
propanoate, using acid-catalysed ester exchange with but-3-
ynol, followed by Lindlar hydrogenation, and prepared the
E- and Z-silyl enol ethers 33 using Ireland’s recipes. We
analysed the mixtures of silyl esters by hydrolysis and esterifi-
cation in the same way as before. Four diastereoisomers must
have been present, but we could detect clearly only two, to
which we assign the structures 34 and 35. The recipe expected
to give largely the E-silyl enol ether gave the two products
in a ratio of 86 : 14, whereas the recipe expected to give the
Z-isomer gave a complementary ratio of 32 : 68, supporting our
belief that we had been able to control to a reasonable extent
the double bond geometry in all the silyl enol ethers. The poorer
ratio from the mixture rich in the Z-isomer may well be a con-
sequence of the less effective control of geometry of the silyl
enol ether with that recipe. We confirmed that the two isomers
differed in relative configuration between C-2 and C-3 by
removing the benzylic silyl group, which give the esters 37 and
38 in a ratio close to that of the starting materials, and in a ratio
unchanged by how long the treatment with TBAF was. We also
prepared the same two esters in a similar ratio by carrying
out the Ireland–Claisen rearrangement from the silyl enol ether
E-36, supporting our assignment of which diastereoisomer was
which.
Methyl 3-dimethyl(phenyl)silylbutanoate26 (78%), methyl 4-
methyl-3-dimethyl(phenyl)silylpentanoate1 (80%) and methyl
3-phenyl-3-dimethyl(phenyl)silylpropanoate1 (69%) were pre-
pared by the methods referred to.
General method for the preparation of allyl esters
Typically, the methyl ester (8.4 mmol), allyl alcohol (15 cm3)
and concentrated sulfuric acid (1 cm3) were refluxed overnight
and allowed to cool to room temperature before being par-
titioned between ether (20 cm3) and saturated aqueous sodium
bicarbonate solution (20 cm3). The aqueous layer was extracted
with ether (3 × 10 cm3) and the combined organic layers washed
with saturated aqueous sodium bicarbonate solution (3 ×
10 cm3), brine (10 cm3). The organic layer was dried (MgSO4)
and the solvent removed under reduced pressure. The residue
was chromatographed (SiO2, light petroleum–EtOAc, 95 : 5) to
give the allyl ester.
The following esters were prepared by this method.
Allyl 3-dimethyl(phenyl)silylbutanoate27 (63%). Rf (light
petroleum–EtOAc, 97 : 3) 0.24; νmax (film)/cmϪ1 2955 (CH),
2870 (CH), 1735 (CO), 1251 (SiMe) and 1112 (SiPh); δH (250
MHz; CDCl3) 7.50 (2 H, m, SiPh), 7.35 (3 H, m, SiPh), 5.92
(1 H, ddt, J 17.7, 10.8 and 5.7, CH᎐CH ), 5.31 (1 H, d, J 17.7,
᎐
2
CH᎐CH H ), 5.22 (1 H, d, J 10.8, CH᎐CH H ), 4.55 (2 H, d,
᎐
᎐
A
B
A
B
J 5.7 OCH CH᎐CH ), 2.43 (1 H, dd, J 15.2 and 4.1, CH H -
᎐
2
2
A
B
Finally, we prepared the trans-crotyl ester used to make the
silyl enol ether 39 from 3-dimethyl(phenyl)silyl-3-phenyl-
propanoic acid, esterifying with trans-but-3-enol. Ireland–
Claisen rearrangement gave the same two esters as before, but
now the E-silyl enol ether 39 gave more of the isomer 35 than of
the isomer 34. Thus the stereocontrol at the third stereocentre
can be controlled either by changing the geometry of the silyl
enol ether or by changing the geometry in the allyl group. The
internal consistency of all these results shows that our struc-
tures are almost certainly correct.
CO2), 2.10 (1 H, dd, J 15.2 and 11.1, CHAHBCO2), 1.47 (1 H,
ddq, J 11.1, 7.3 and 4.1, CHSi), 1.0 (3 H, d, J 7.3, CH3CHSi)
and 0.30 (6 H, s, SiMe2).
Allyl 4-methyl-3-dimethyl(phenyl)silylpentanoate6 (81%). Rf
(light petroleum–EtOAc, 95 : 5) 0.30; νmax (film)/cmϪ1 3020
(C᎐CH), 2956 (CH), 1738 (C᎐O) and 1649 (C᎐C); δ (250
᎐
᎐
᎐
H
MHz; CDCl3) 7.54 (2 H, m, SiPh), 7.35 (3 H, m, SiPh), 5.90
(1 H, dddd, J 17.3, 10.4, 9.1 and 5.8 CH᎐CH ), 5.29 (1 H, dd,
᎐
2
J 17.3 and 2.9, CH᎐CH H ), 5.22 (1 H, dd, J 9.1 and 1.2,
᎐
A
B
In conclusion, the Ireland–Claisen rearrangement is quite
highly controlled in the sense anti to the silyl group in a con-
formation with the hydrogen atom inside, whether it is carried
CH᎐CH H ), 4.47 (2 H, dt, J 5.8 and 1.2 OCH CH᎐CH ), 2.41
᎐
᎐
A
B
2
2
(1 H, dd, J 16.0 and 7.6, CHAHBCO2), 2.35 (1 H, dd, J 16.0 and
6.2, CHAHBCO2), 1.94 (1 H, d sept, J 3.9 and 6.8, CHMe2), 1.53
(1 H, ddd, 7.5, 6.2 and 3.9, CHSi), 0.93 (3 H, d, J 6.8,
CHMeAMeB), 0.85 (3 H, d, J 6.8, CHMeAMeB), 0.34 (3 H, s,
SiMeAMeB) and 0.33 (3 H, s, SiMeAMeB).
out in the sense 4
ester enolate, or in the sense 7
5 ϩ 6, analogous to the allylation of an
8 ϩ 9, provided that the
double bond is cis, ensuring that the conformation with the
hydrogen inside 24 is much the most highly populated. It
appears that changing the electronic balance from a rearrange-
ment with electrophilic character in the attack at C-3 to one
Allyl 3-phenyl-3-dimethyl(phenyl)silylpropanoate28 (70%). Rf
(light petroleum–EtOAc, 97 : 3) 0.17; νmax (film)/cmϪ1 3030
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
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(CH), 2956 (CH), 1737 (CO), 1649 (PhH), 1600 (PhH), 1493
(PhH), 1250 (SiMe) and 1114 (SiPh); δH (250 MHz; CDCl3)
7.45–7.35 (5 H, m, Ph), 7.20 (2 H, t, J 7.4, m-PhH), 7.10 (1 H, t,
J 7.4, p-PhH), 6.96 (2 H, d, J 7.5, o-PhH) 5.70 (1 H, ddt, J 16.1,
δH (250 MHz; CDCl ) 6.37 (1 H, t, J 7.2, CH᎐CBr ), 2.10
᎐
3 2
(2 H, qt, J 7.4 and 7.2, MeCH CH᎐C) and 1.02 (3 H, t,
᎐
2
J 7.5, MeCH2); δC (500 MHz, CDCl3) 139.8Ϫ, 88.0ϩ, 26.3ϩ
and 12.0Ϫ, which was used in the next step without further
purification.
12.0, and 5.6, CH᎐CH ), 5.12 (1 H, d, J 16.1, CH᎐CH H ),
᎐
᎐
2
A
B
5.10 (1 H, d, J 12.2, CH᎐CH H ), 4.37 (2 H, d, J 5.7,
᎐
A
B
OCH CH᎐CH ), 2.87 (1 H, dd, J 10.8 and 3.5, CHSi), 2.79
1,1-Dibromo-4-methylpent-1-ene
᎐
2
2
(1 H, dd, J 10.8 and 14.0, CHAHBCO2), 2.66 (1 H, dd, J 14.0
and 3.4, CHAHBCO2), 0.27 (3 H, s, SiMeAMeB) and 0.23 (3 H, s,
SiMeAMeB).
Isovaleraldehyde (1.7 cm3, 15 mmol) was similarly converted
to the dibromoalkene,31 which was obtained as an oil (3.1 g);
δH (250 MHz; CDCl ) 6.39 (1 H, t, J 7.3, CH᎐CBr ), 1.99 (2 H,
᎐
3
2
t, J 7.2, CH CH᎐CBr ), 1.75 (1 H, nonet, J 6.7, CHMe ) and
0.94 (6 H, d, J 6.7, CHMe2), which was used in the next step
without further purification.
᎐
2
2
2
1-Allyloxy-1-trimethylsilyloxy-3-dimethylphenylsilyl-4-methyl-
pent-2-ene E-4b
Method A. Diisopropylamine (freshly distilled over calcium
hydride under argon, 0.06 cm3, 0.44 mmol) in dry ether
(0.5 cm3) was cooled to 0 ЊC under nitrogen and treated with
n-butyllithium (2.0 mol dmϪ3 in hexanes, 0.22 cm3, 0.44 mmol).
The mixture was stirred at 0 ЊC for 15 min before being cooled
to Ϫ95 ЊC. Triethylamine (0.1 cm3) and trimethylsilyl chloride
(0.04 cm3, 0.3 mmol) were added, followed after 5 min by
allyl 4-methyl-3-dimethyl(phenyl)silylpentanoate (0.075 g, 0.26
mmol) in dry ether (0.2 cm3). The mixture was stirred for 1 h
and then allowed to warm to room temperature over 30 min.
Solvents were removed under reduced pressure and the residue
dissolved in dry hexane. Insoluble materials were removed by
filtration and solvents removed under reduced pressure to give
the silyl enol ether (0.05 g) as a yellow oil; δH (400 MHz; CDCl3)
7.52 (2 H, m, SiPh), 7.31 (3 H, m, SiPh), 5.85 (1 H, dddd, J 17.2,
1-Dimethyl(phenyl)silylbut-1-yne
n-Butyllithium (2.2 mol dmϪ3 in hexanes, 23.3 cm3, 51.2 mmol)
was added to a stirred solution of 1,1-dibromobut-1-ene (10.4
g, 48.7 mmol) in dry ether (100 cm3) at Ϫ78 ЊC under argon.
After 1 h at Ϫ78 ЊC, the solution was allowed to warm to 0 ЊC
and dimethylphenylsilyl chloride (9.2 cm3, 55 mmol) in dry
ether (5 cm3) was added. The solution was stirred at 0 ЊC for a
further 15 min, water (20 cm3) and ether (20 cm3) were added,
and the layers separated. The aqueous layer was washed with
ether (3 × 15 cm3) and the combined organic layers were washed
with water (2 × 15 cm3), brine (15 cm3), and dried (MgSO4).
Solvents were removed under reduced pressure, and the residue
was distilled to give the alkyne3 (6.6 g, 72%) as an oil (bp 115–
117 ЊC at 20 mm Hg, lit.3 116–118 ЊC at 17 mmHg); νmax (film)/
10.4, 5.5 and 5.4, CH᎐CH ), 5.26 (1 H, dq, J 17.2 and 1.7, CH᎐
᎐
᎐
2
cmϪ1 2175 (C᎐C), 1249 (SiMe) and 1115 (SiPh); δH (250 MHz;
᎐
᎐
CH H ), 5.13 (1 H, dq, 10.4 and 1.4, CH᎐CH H ), 4.18 (1 H,
᎐
A
B
A
B
CDCl3) 7.7–7.3 (5 H, m, PhH), 2.32 (2 H, q, J 7.0, CH2Me),
1.20 (3 H, t, J 7.0 CH2Me) and 0.39 (6 H, s, SiMe2).
ddt, J 13.0, 5.5 and 1.5, OCHAHB), 4.07 (1 H, ddt, 13.0, 5.4 and
1.5, OCH H ), 3.62 (1 H, d, J 11.6, C᎐CHCHSi), 1.95 (1 H, dd,
᎐
A
B
J 11.6 and 4.3, CHSi), 1.78 (1 H, dsept, J 4.3 and 6.8, CHMe2),
0.83 (3 H, d, J 6.8, CHMeAMeB), 0.75 (3 H, d, J 6.8,
CHMeAMeB), 0.27 (3 H, s, SiMeAMeB), 0.26 (3 H, s, Si-
MeAMeB) and 0.21 (9H, s, SiMe3), and there was no sign of the
stereoisomer. This material was used in the next step without
further purification.
1-Trimethylsilyl-4-methylpent-1-yne
1,1-Dibromo-4-methylpent-1-ene (5.0 g, 20.7 mmol) was simi-
larly converted to the alkyne32 (2.50 g, 78%) as an oil (bp 120–
126 ЊC at 760 mm Hg); δH (250 MHz; CDCl3) 2.08 (2 H, d, J 6.6,
CH2CHMe2), 1.78 (1 H, nonet, J 6.6, CH2CHMe2), 0.96 (6 H,
d, J 6.6, CHMe2) and 0.13 (9 H, s, SiMe3).
Method B. Dimethylphenylsilyllithium (1.3 mol dmϪ3 solu-
tion in THF, 0.7 cm3, 0.91 mmol) was added to dimethylzinc
(2 mol dmϪ3 solution in toluene, 0.46 cm3, 0.91 mmol) at
Ϫ20 ЊC and the mixture stirred for 5 min before being cooled to
Ϫ78 ЊC. Allyl 4-methylpent-2-enoate (100 mg, 0.65 mmol) in
THF (1 cm3) was added over 1 min, and the mixture stirred for
15 min. Trimethylsilyl chloride (freshly distilled over calcium
hydride, 0.21 cm3, 1.63 mmol) was added, and the mixture
stirred for a further 1 h before being allowed to warm to room
temperature. Pentane (10 cm3) was added and the solution
filtered through celite and solvents removed under reduced
pressure to give an oil. Assignable 1H NMR signals were identi-
cal with those from the preparation using LDA. It appears that
conjugate addition of the silylzincate gives largely the E-isomer,
in contrast to our earlier results with the silycuprate, which gave
predominantly the Z-silyl enol ether.1
1,3-Bis[dimethyl(phenyl)silyl]butyne
tert-Butyllithium (1.9 mol dmϪ3 in hexanes, 26.3 cm3, 50 mmol)
was added to a solution of TMEDA (7.6 cm3, 50 mmol) in
dry THF (100 cm3) at Ϫ78 ЊC under nitrogen. 1-Dimethyl-
(phenyl)lsilylbutyne (9.4 g, 50 mmol) in dry THF (10 cm3) was
added dropwise over 10 min, and the mixture stirred at Ϫ78 ЊC
for 15 min. The mixture was allowed to warm to Ϫ40 ЊC and
stirred for 2 h. The mixture was cooled to Ϫ78 ЊC and di-
methyl(phenyl)silyl chloride (7.7 cm3, 51 mmol) was added. The
mixture was stirred for 15 min and then allowed to warm to
room temperature over 1 h. The solution was partitioned
between saturated aqueous ammonium chloride (50 cm3) and
ether (50 cm3), and the aqueous layer was washed with ether
(3 × 30 cm3). The combined organic layers were washed with
water (2 × 30 cm3) and brine (30 cm3). The organic layer was
dried (MgSO4) and solvents removed under reduced pressure.
The residue was chromatographed (SiO2, light petroleum–
CH2Cl2, 9 : 1) to give the alkyne33 (15.3 g, 95%) as an oil; Rf
1,1-Dibromobut-1-ene
Following Corey and Fuchs,29 carbon tetrabromide (45.0 g,
136 mmol) and triphenylphosphine (74.5 g, 284 mmol) were
stirred in dry dichloromethane (300 cm3) at Ϫ10 ЊC (ice/acetone
bath, 1 : 1) under nitrogen for 40 min, by which time the mixture
had turned deep red and had deposited an orange precipitate.
Propionaldehyde (freshly distilled, 4.9 cm3, 67.5 mmol) was
added dropwise, the mixture stirred for a further 2.5 h at 0 ЊC,
allowed to warm to room temperature, and solvents removed
under reduced pressure. The solid residue was extracted with
light petroleum (4 × 30 cm3), filtered through a silica plug and
solvents removed under reduced pressure to give the alkene30
(SiO2, light petroleum–CH2Cl2, 9 : 1) 0.25; νmax (film)/cmϪ1 2960
᎐
(CH), 2156 (C᎐C), 1248 (SiMe) and 1114 (SiPh); δ (250 MHz;
᎐
H
CDCl3) 7.65–7.54 (4 H, m, SiPh), 7.43–7.31 (6 H, m, SiPh), 2.02
(1 H, q, J 7.2, MeCH ), 1.18 (3 H, d, J 7.2, MeCH), 0.40 [6 H, s,
(SiMe2Ph)A], and 0.39 [6 H, s, (SiMe2Ph)B].
1-Trimethylsilyl-3-dimethyl(phenyl)silyl-4-methylpent-1-yne
1-Trimethylsilyl-4-methylpent-1-yne (1.0 g, 6.5 mmol) was
similarly converted to the alkyne (1.2 g, 60%) as an oil; Rf (SiO2,
as an oil (9.0 g); νmax (film)/cmϪ1 2970 CH) and 1618 (C᎐C);
hexane) 0.3; νmax (film)/cmϪ1 2959 (CH), 2151 (C᎐C), 1249
᎐
᎐
᎐
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
4009

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(SiMe) and 1113 (SiPh); δH (250 MHz; CDCl3) 7.61 (2 H, m,
SiPh), 7.37 (3 H, m, SiPh), 1.95 (1 H, d, J 4.2, CHSiPhMe2),
1.82 (1 H, septd, J 6.6 and 4.2, CHMe2), 0.97 (3 H, d, J 6.6,
CHMeAMeB), 0.93 (3 H, d, J 6.6, CHMeAMeB), 0.44 (3 H, s,
SiMeAMeBPh), 0.42 (3 H, s, SiMeAMeBPh) and 0.17 (9 H,
s, SiMe3); δC (400 MHz, CDCl3) 137.7ϩ, 134.5Ϫ, 129.2Ϫ,
127.9Ϫ, 107.5ϩ, 87.8ϩ, 30.2Ϫ, 28.0Ϫ, 24.2Ϫ, 20.5Ϫ, 0.5Ϫ,
Ϫ3.0Ϫ and Ϫ4.2Ϫ; m/z (EI) 288 (55%, Mϩ) and 135 (100,
PhMe2Si) (Found: Mϩ, 288.1723. C17H28Si2 requires M,
288.1730).
73.2ϩ, 52.3Ϫ, 13.9Ϫ, 13.4Ϫ, Ϫ4.6Ϫ and Ϫ5.6Ϫ; m/z (EI) 246
(45%, M) and 135 (100%, SiMe2Ph)(Found: Mϩ, 246.1080.
C14H18O2Si requires M, 246.1076).
Methyl 4-dimethyl(phenyl)silyl-5-methylhex-2-ynoate
3-Dimethyl(phenyl)silyl-4-methylpent-1-yne (0.65 g, 3 mmol)
in dry THF (5 cm3) was similarly converted to the ester, which
was obtained as as a colourless oil (0.6 g, 74%) together with
the starting alkyne (0.16 g, 25%); Rf (light petroleum–EtOAc,
95 : 5) 0.35; νmax (film)/cmϪ1 2960 (CH), 2321 (C᎐C), (2215
᎐
᎐
᎐
(C᎐C), 1712 (C᎐O), 1263 (SiMe) and 1113 (SiPh); δ (400 MHz;
᎐
᎐
H
3-Dimethy(phenyl)silylbutyne 10a
CDCl3) 7.57 (2 H, m, SiPh), 7.38 (3 H, m, SiPh), 4.14 (3 H, s,
Following the method of Schmidt and Arens34 and Rajagopa-
lan and Zweifel,35 silver nitrate (2.38 g, 14 mmol) in water
(6 cm3) and absolute ethanol (18 cm3), was added in four equal
portions, 15 min apart, to a stirred solution of 1,3-bis[dimethyl-
(phenyl)silyl]butyne (2.6 g, 7.9 mmol) in ethanol (20 cm3) at
0 ЊC. Fifteen minutes after the final addition a solution of
potassium cyanide (4.5 g, 70 mmol) in water (8 cm3) was added
at 0 ЊC, producing heavy precipitation, and the mixture allowed
to warm to 20 ЊC and stirred for 2 h. The mixture was partioned
between pentane (20 cm3) and water (20 cm3). The aqueous
layer was washed with pentane (3 × 20 cm3), the combined
organic layers were washed with water (3 × 20 cm3), brine
(20 cm3), dried (MgSO4) and solvents removed to give the
alkyne36 (1.5 g, 100%) as an oil; Rf (light petroleum–dichloro-
CO Me), 2.04 (1 H, d, J 4.1, CHC᎐C), 1.85 (1 H, dsept, J 4.1
᎐
᎐
2
and 6.6, Me2CH ), 0.97 (3 H, d, J 6.5, MeAMeBCH), 0.95 (3 H,
d, 6.4, MeAMeBCH), 0.46 (3 H, s, SiMeAMeB) and 0.43 (3 H, s,
SiMeAMeB); δC (500 MHz, CDCl3) 154.5ϩ, 136.4ϩ, 133.9Ϫ,
129.5Ϫ, 127.9Ϫ, 91.6ϩ, 76.2ϩ, 52.1Ϫ, 28.7Ϫ, 27.9Ϫ, 24.2Ϫ,
20.5Ϫ, Ϫ2.9Ϫ and Ϫ4.0Ϫ; m/z (ES) 297 (100%, MNaϩ)(Found:
MNaϩ, 297.1294. C16H22O2Si requires MϩNa, 297.1289).
(E )-Pent-4-dimethyl(phenyl)silylpent-2-en-1-ol
Lithium aluminium hydride (0.20 g, 5.0 mmol) was suspended
in dry THF under a nitrogen atmosphere and the mixture
cooled to Ϫ78 ЊC. Methyl 4-dimethyl(phenyl)silylpent-2-ynoate
(0.50 g, 2.0 mmol) in THF (2 cm3) was added and the mixture
stirred at Ϫ78 ЊC for 30 min before being allowed to warm to
room temperature. The mixture was then refluxed for 9 h before
being allowed to cool to room temperature. The mixture was
poured onto ice and left for 10 min. Dilute aqueous hydro-
chloric acid (5 cm3) and ether (2 cm3) were added, and the layers
separated. The aqueous layer was washed with ether (3 × 2 cm3)
and the combined organic layers washed with water (2 × 2 cm3)
and brine (2 cm3). The organic layer was dried (MgSO4) and
solvents removed under reduced pressure. The residue was
chromatographed (SiO2, light petroleum–EtOAc, 8 : 2) to give
the alcohol as an oil (0.19 g, 43%); Rf (light petroleum–EtOAc,
8 : 2) 0.17; νmax (film)/cmϪ1 3332 (OH), 2955 (CH), 1654
methane, 9 : 1) 0.50; νmax (film)/cmϪ1 3310 (C᎐C–H), 2959 (CH),
᎐
᎐
᎐
2095 (C᎐C), 1252 (SiMe) and 1117 (SiPh); δ (400 MHz;
᎐
H
CDCl3) 7.65–7.5 (2 H, m, SiPh), 7.45–7.3 (3 H, m, SiPh), 2.02
᎐
(1 H, d, J, 2.7, C᎐CH), 1.90 (1 H, dq, J 2.7 and 7.2, MeCH ),
᎐
1.15 (3 H, d, J 7.2, MeCH) and 0.40 (6 H, s, SiMe2Ph).
3-Dimethyl(phenyl)silyl-4-methylpent-1-yne 10b
1-Trimethylsilyl-3-dimethyl(phenyl)silyl-4-methylpent-1-yne
(0.50 g, 1.73 mmol) was similarly converted into the alkyne36
(0.35 g, 93%), which was obtained as an oil; Rf (light petrol-
eum–EtOAc, 90 : 10) 0.70; νmax (film)/cmϪ1 3309 (C᎐C–H), 2850
᎐
᎐
᎐
᎐
(CH), 2246 (C᎐C), 2096 (C᎐C), 1251 (SiMe) and 1112 (SiPh);
(C᎐C), 1248 (SiMe), 1112 (SiPh) and 971 (trans-H–C᎐C–H);
᎐ ᎐
᎐
᎐
δH (250 MHz; CDCl3) 7.62 (2 H, m, SiPh), 7.39 (3 H, m, SiPh),
δH (400 MHz; CDCl3) 7.51–7.45 (2 H, m, SiPh), 7.39–7.30
(3 H, m, SiPh), 5.70 (1 H, dd, J 15.3 and 7.6, HC᎐CHCH ), 5.40
᎐
2.15 (1 H, d, J 2.8, C᎐CH), 1.93 (1 H, dd, J 3.9 and 2.8, SiCH),
᎐
᎐
2
1.83 (1 H, dsept, J 4.2 and 6.6, CHMe2), 1.2 (3 H, d, J 6.6,
CHMeAMeB), 0.97 (3 H, d, J 6.6, CHMeAMeB), 0.46 (3 H, s,
SiMeAMeBPh) and 0.44 (3 H, s, SiMeAMeBPh).
(1 H, dt, J 15.3 and 6.3, HC᎐CHCH ), 4.05 (2 H, d, J 6.3,
᎐
2
CH2OH), 1.83 (1 H, dq, J 7.6 and 7.7, SiCHMe), 1.06 (3 H, d,
J 7.7, CHMe) and 0.27 (6 H, s, SiMe2); δC (500 MHz, CDCl3)
137.5ϩ, 136.5Ϫ, 133.9Ϫ, 129.0Ϫ, 127.6Ϫ, 125.5Ϫ, 64.3ϩ,
25.7Ϫ, 13.5Ϫ, Ϫ5.0Ϫ and Ϫ5.3Ϫ; m/z (ESI) 243.1 (85%,
MNaϩ)(Found: MNaϩ, 243.1185. C13H20OSi requires MϩNa,
243.1181).
Methyl 4-dimethyl(phenyl)silylpent-2-ynoate
n-Butyllithium (1.6 mol dmϪ3 solution in hexanes, 4.9 cm3, 7.9
mmol) was added to a solution of diisopropylamine (1.1 cm3,
7.9 mmol) in THF (15 cm3) at 0 ЊC and the solution stirred for
30 min before being cooled to Ϫ78 ЊC. 3-Dimethyl(phenyl)-
silylbutyne (10a) (1.5 g, 7.9 mmol) in THF (5 cm3) was added
and the solution stirred at Ϫ78 ЊC for 5 min before being
allowed to warm to Ϫ10 ЊC over a period of 1 h. The solution
was kept at Ϫ10 ЊC for 1 h before being cooled back to Ϫ78 ЊC.
Methyl chloroformate (0.61 cm3, 7.9 mmol) was added and the
mixture stirred at Ϫ78 ЊC for 30 min before being allowed to
warm slowly to room temperature. Water (15 cm3) was added
and the layers separated. The aqueous layer was washed with
ether (3 × 10 cm3), the combined organic layers washed with
water (2 × 10 cm3), brine (10 cm3), dried (MgSO4) and solvents
removed. The residue was chromatographed (SiO2, light
petroleum–CH2Cl2, 9 : 1) to give the ester (1.1 g, 46%) as an oil
together with the starting alkyne (36%); Rf (SiO2, light petrol-
eum–CH2Cl2, 95 : 5) 0.11; νmax (film)/cmϪ1 2959 (CH), 2219
(E )-5-Methyl-4-dimethyl(phenyl)silylhex-2-en-1-ol and
5-methyl-4-dimethyl(phenyl)silylhexa-1,2-diene
Methyl 4-dimethyl(phenyl)silyl-5-methylhex-2-ynoate (0.19 g,
0.7 mmol) was similarly converted into the alcohol which was
obtained as an oil (0.13 g, 75%); Rf (light petroleum–EtOAc,
8 : 2) 0.17; νmax (film)/cmϪ1 3356 (OH), 2956 (CH), 1655 (C᎐C),
᎐
1248 (SiMe) and 1112 (SiPh); δH (250 MHz; CDCl3) 7.50 (2 H,
m, SiPh), 7.35 (3 H, m, SiPh), 5.59 (1 H, dd, J 15.1 and 10.7,
SiCHCH᎐CH), 5.42 (1 H, dt, J 15.1 and 6.02, SiCHCH᎐CH ),
᎐
᎐
4.05 (2 H, d, J 6.1, CH2OH), 1.87 (1 H, dsept, J 5.3 and 6.7,
Me CH ), 1.67 (1 H, dd, J 10.7 and 5.2, SiCHCH᎐C), 0.97 (3 H,
᎐
2
d, J 6.7, MeAMeBCH), 0.90 (3 H, d, J 6.8, MeAMeBCH), 0.33
(3 H, s, SiMeAMeB) and 0.30 (3 H, s, SiMeAMeB); δC (500 MHz,
CDCl3) 138.7ϩ, 133.9Ϫ, 132.3Ϫ, 128.9Ϫ, 128.8Ϫ, 127.6Ϫ,
64.1ϩ, 40.9Ϫ, 28.3Ϫ, 23.8Ϫ, 20.9Ϫ, Ϫ3.3Ϫ and Ϫ3.4Ϫ; m/z
(ES) 271 (100%, MNaϩ)(Found: MNaϩ, 271.1481. C15H24OSi
requires MϩNa, 271.1494), together with the allene (34 mg,
21%); Rf (light petroleum–EtOAc, 8 : 2) 0.65; νmax (film)/cmϪ1
᎐
(C᎐C), 1712 (CO Me), 1254 (SiMe) and 1113 (SiPh); δ (400
᎐
2
H
MHz; CDCl3) 7.57–7.52 (2 H, m, SiPh), 7.42–7.33 (3 H, m,
SiPh), 3.73 (3 H, s, CO2Me), 2.05 (1 H, q, J 7.2, MeCH ), 1.17
(3 H, d, J 7.2, MeCH) and 0.43 (6 H, s, SiMe2Ph); δC (500 MHz,
CDCl3) 154.5ϩ, 135.3ϩ, 133.9Ϫ, 129.7Ϫ, 127.9Ϫ, 94.3ϩ,
3050 (CH), 2957 (CH), 1950 (C᎐C᎐C), 1249 (SiMe) and 1111
᎐ ᎐
(SiPh); δH (250 MHz; CDCl3) 7.55 (2 H, m, SiPh), 7.35 (3 H, m,
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
4010

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SiPh), 5.02 (1 H, dt, J 10.7 and 6.5, CH᎐C᎐CH ), 4.62 (1 H, dd,
᎐ ᎐
(light petroleum–EtOAc, 90 : 10) 0.10; νmax (film)/cmϪ1 3415
2
᎐
16.5 and 6.8, CH᎐C᎐CH H ), 4.56 (1 H, dd, J 16.6 and 6.5,
(OH), 2960 (CH), 2249 (C᎐C), 1251 (SiMe), 1112 (SiPh);
᎐ ᎐
᎐
A
B
CH᎐C᎐CH H ), 1.87 (1 H, dsept, J 5.3 and 6.8, Me CH ),1.60
᎐ ᎐
δH (250 MHz; CDCl3) 7.61 (2 H, m, SiPh), 7.37 (3 H, m, SiPh),
4.29 (2 H, d, J 2.2, CH2OH), 1.93 (1 H, dt, J 4.3 and 2.3, SiCH),
1.83 (1 H, dsept, J 4.3 and 6.6, CHMe2), 0.97 (3 H, d, J 6.6,
CHMeAMeB), 0.94 (3 H, d, J 6.6, CHMeAMeB), 0.43 (3 H, s,
SiMeAMeBPh) and 0.42 (3 H, s, SiMeAMeBPh); δC (400 MHz,
CDCl3) 137.7ϩ, 133.9Ϫ, 129.3Ϫ, 127.9Ϫ,86.5ϩ,81.5ϩ, 51.5ϩ,
28.1Ϫ, 28.0Ϫ, 24.2Ϫ, 20.3Ϫ, Ϫ3.0Ϫ and Ϫ3.8Ϫ; m/z (EI) 246
(9%, Mϩ) and 135 (100%, SiMe2Ph)(Found: Mϩ, 246.1432.
C15H22OSi requires M, 246.1440).
A
B
2
(1 H, dd, J 10.8 and 5.3, SiCHCHMe2), 0.92 (3 H, d, J 6.7,
MeAMeBCH), 0.87 (3 H, d, J 6.8, MeAMeBCH), 0.35 (3 H,s,
SiMeAMeB) and 0.33 (3 H, s, SiMeAMeB); δC (500 MHz, CDCl3)
209.1ϩ, 138.8ϩ, 134.1Ϫ, 128.7Ϫ, 127.6Ϫ, 88.3Ϫ, 73.4ϩ,
36.3Ϫ, 28.7Ϫ, 23.7Ϫ, 20.8Ϫ, Ϫ2.9Ϫ and Ϫ3.5Ϫ.
(E )-4-Dimethyl(phenyl)silylpent-2-enyl acetate 11a
(E)-5-Methyl-4-dimethyl(phenyl)silylhex-3-en-1-ol (0.17 g, 0.77
mmol), DMAP (0.01 g, 0.1 mmol), acetic anhydride (0.15 cm3,
1.2 mmol) and triethylamine (0.23 cm3, 1.5 mmol) were stirred
in ether (3 cm3) at room temperature for 9 h. Water (5 cm3) was
added and the layers separated. The aqueous layer was washed
with ether (3 × 2 cm3) and the combined organic layers washed
with water (2 × 2 cm3), brine (2 cm3), dried (MgSO4) and
solvents removed under reduced pressure. The residue was
chromatographed (SiO2, light petroleum–EtOAc, 9 : 1) to give
the acetate as an oil (0.19 g, 93%); Rf (light petroleum–EtOAc,
4-Dimethyl(phenyl)silyl-5-methylhex-2-ynyl acetate
4-Dimethyl(phenyl)silyl-5-methylhex-2-yn-1-ol
(0.055
g,
0.22 mmol), DMAP (0.007 g, 0.055 mmol), acetic anhydride
(0.036 g, 0.35 mmol) and triethylamine (freshly distilled,
0.06 cm3, 0.4 mmol) were stirred in dry ether (5 cm3) under
argon at room temperature for 16 h. Saturated aqueous
sodium bicarbonate solution (5 cm3) was added and the layers
separated. The aqueous layer was washed with ether (2 × 5 cm3)
and the combined organic layers washed with saturated
aqueous sodium bicarbonate solution (2 × 5 cm3), brine (5 cm3),
dried (MgSO4) and solvents removed under reduced pressure.
The residue was chromatographed (SiO2, light petroleum–
EtOAc, 90 : 10) to give the ester (0.05 g, 80%) as an oil; Rf (light
petroleum–EtOAc, 90 : 10) 0.35; νmax (film)/cmϪ1 2960 (CH),
9 : 1) 0.60; νmax (film)/cmϪ1 3048 (CH), 2955 (CH), 1740 (C᎐O),
᎐
1655 (C᎐C), 1248 (SiMe), 1112 (SiPh) and 970 (trans-CH᎐CH);
᎐
᎐
δH (400 MHz; CDCl3) 7.57–7.45 (2 H, m, SiPh), 7.38–7.30
(3 H, m, SiPh), 5.80 (1 H, dd, J 15.4 and 7.6, HC᎐CHCH ), 5.35
᎐
2
(1 H, dt, J 15.4 and 6.7, HC᎐CHCH ), 4.49 (2 H, d, J 6.7,
᎐
2
CH2OH), 2.03 (3 H, s, COMe), 1.85 (1 H, dq, J 7.6 and
7.2, SiCHMe), 1.05 (3 H, d, J 7.2, SiCHMe) and 0.27 (6 H,
s, SiMe2); δC (500 MHz, CDCl3) 170.9ϩ, 139.6Ϫ, 137.3ϩ,
134.0 Ϫ, 129.1Ϫ, 127.6Ϫ, 120.1Ϫ, 65.7ϩ, 26.0Ϫ, 21.1Ϫ, 13.3Ϫ,
Ϫ5.1Ϫ and Ϫ5.4Ϫ; m/z (ESI) 158.1 (100%, PhMe2SiNa) 285.1
(85%, MNa)(Found: Mϩ, 285.1279. C15H22O2Si requires
MϩNa, 285.1287).
᎐
᎐
2350 (C᎐C), 2262 (C᎐C), 1736 (C᎐O), 1250 (SiMe) and 1112
᎐
᎐
᎐
(SiPh); δH (400 MHz; CDCl3) 7.57 (2 H, m, SiPh), 7.36 (3 H, m,
SiPh), 4.72 (2 H, d, J 2.4, CH2OH), 2.08 (3 H, s, COMe), 1.92
(1 H, dt, J 4.1 and 2.3, SiCH), 1.80 (1 H, dsept, J 4.3 and 6.6,
CHMe2), 0.95 (3 H, d, J 6.6, CHMeAMeB), 0.91 (3 H, d, J 6.7,
CHMeAMeB), 0.41 (3 H, s, SiMeAMeBPh) and 0.39 (3 H, s,
SiMeAMeBPh); δC (400 MHz, CDCl3) 170.5ϩ, 137.5ϩ, 134.0Ϫ,
129.0Ϫ, 127.5Ϫ, 87.5ϩ, 77.1ϩ, 53.2ϩ, 28.2Ϫ, 28.0Ϫ, 24.1Ϫ,
20.4Ϫ, 20.2Ϫ, Ϫ3.0Ϫ and Ϫ3.8Ϫ; m/z (EI) 288.0 (30%, Mϩ)
and 135 (100%, SiMe2Ph)(Found: Mϩ, 288.1546. C17H24O2Si
requires M, 288.1545).
(E )-4-Dimethyl(phenyl)silyl-5-methylhex-2-enyl acetate 11b
(E)-5-Methyl-4-dimethyl(phenyl)silylhex-3-en-1-ol (0.125 g,
0.50 mmol) was similarly converted into the acetate, which was
obtained as an oil (80 mg, 54%); Rf (light petroleum–EtOAc,
9 : 1) 0.57; νmax (film)/cmϪ1 2955 (CH) 1740 (C᎐O), 1112 (SiPh),
᎐
(Z )-4-Dimethyl(phenyl)silyl-5-methylhex-2-enyl acetate 13b
and 970 (trans-CH᎐CH); δ (250 MHz; CDCl3) 7.44 (2 H, m,
᎐
H
SiPh), 7.35 (3 H, m, SiPh), 5.68 (1 H, dd, J 15.2 and 10.9,
SiCHCH᎐CH), 5.36 (1 H, dt, J 15.1 and 6.7, SiCHCH᎐CH ),
Quinoline (freshly distilled, 1 drop) was added to a suspension
of 5% palladium on barium sulfate in dry methanol (10 cm3)
and the mixture stirred under hydrogen for 5 min. 4-Dimethyl-
(phenyl)silyl-5-methylhex-2-ynyl acetate (0.05 g, 0.17 mmol) in
methanol (5 cm3) was added and the mixture stirred under
hydrogen at room temperature for 72 h, during which time the
reaction was monitored by TLC. Dilute hydrochloric acid
(3 mol dmϪ3, 5 cm3) was added and the layers separated. The
aqueous layer was washed with ether (3 × 5 cm3) and the com-
bined organic layers washed with dilute aqueous hydrochloric
acid (3 × 5 cm3), brine (5 cm3), dried (MgSO4) and solvents
removed under reduced pressure. The residue was chromato-
graphed (SiO2, light petroleum–EtOAc, 95 : 5) to give the alkene
as an oil (0.03 g, 68%); Rf (light petroleum–EtOAc, 95 : 5) 0.31;
᎐
᎐
4.51 (2 H, d, J 6.7, CH2CO2Me), 2.0 (3 H, s, COMe), 1.87 (1 H,
dsept, J 5.2 and 6.7, CHMe2), 1.68 (1 H, dd, J 10.9 and 5.2,
SiCHCHMe2), 0.85 (6 H, d, J 6.7, Me2CH), 0.30 (3 H, s, SiMeA-
MeB) and 0.27 (3 H, s, SiMeAMeB); δC (500 MHz, CDCl3)
170.8ϩ, 138.4ϩ, 135.5Ϫ, 133.9Ϫ, 128.8Ϫ, 127.6Ϫ, 123.5Ϫ,
65.5ϩ, 41.1Ϫ, 29.0Ϫ, 23.8Ϫ, 21.0Ϫ, 20.7Ϫ, Ϫ3.1Ϫ and Ϫ3.6Ϫ;
m/z (ES) 313 (68%, MNaϩ)(Found: MNaϩ, 313.1610.
C17H26O2Si requires MϩNa, 313.1600).
4-Dimethyl(phenyl)silyl-5-methylhex-2-yn-1-ol
n-Butyllithium (1.7 mol dmϪ3 solution in hexanes, 0.9 cm3,
1.4 mmol) was added dropwise to a solution of 3-dimethyl-
(phenyl)silyl-4-methylpent-1-yne (10b) (0.2 g, 0.9 mmol) in
THF (10 cm3) at Ϫ78 ЊC under argon. The mixture was allowed
to warm to Ϫ20 ЊC over a period of 1 h before being cooled to
Ϫ78 ЊC. Formaldehyde [cracked from paraformaldehyde (dried
over phosphorous pentoxide) at 160 ЊC] was bubbled through
the reaction mixture in a stream of argon for 15 min. The
mixture was allowed to warm to room temperature and
saturated aqueous ammonium chloride (10 cm3) and ether
(10 cm3) were added. The layers were separated, and the
aqueous layer washed with ether (3 × 10 cm3). The combined
organic phases were washed with water (2 × 10 cm3), brine
(10 cm3), dried (MgSO4) and the solvents removed. The residue
was chromatographed (SiO2, light petroleum–EtOAc, 90 : 10)
to give starting material (0.087 g, 0.4 mmol) and the alcohol as
an oil (0.072 g, 58% based on unrecovered starting material); Rf
νmax (film)/cmϪ1 2958 (CH), 1728 (C᎐O), 1250 (SiMe) and 1100
᎐
(SiPh); δH (250 MHz; CDCl3) 7.51 (2 H, m, SiPh), 7.29 (3 H, m,
SiPh), 5.58 (2 H, m, CH᎐CH ), 4.52 (1 H, dd, J 6.3 and 12.5,
᎐
CHAHBO), 4.24 (1 H, dd, J 4.9 and 12.6, CHAHBO), 2.02 (3 H,
s, COMe), 2.02 (1 H, m, SiCH), 1.88 (1 H, dsept, J 5.3 and 6.7,
CHMe2), 0.95 (6 H, d, J 6.7, CHMe2), 0.33 (3 H, s, SiMeAMeB)
and 0.31 (3 H, s, SiMeAMeB); δC (400 MHz, CDCl3) 171.0ϩ,
138.2ϩ, 133.9Ϫ, 133.7Ϫ, 129.0Ϫ, 127.7Ϫ, 122.6Ϫ, 60.6ϩ,
36.5Ϫ, 28.7Ϫ, 23.9Ϫ, 20.5Ϫ, 15.3Ϫ, Ϫ3.2Ϫ and Ϫ3.6Ϫ; m/z
(ES) 313 (100%, MNaϩ)(Found: MNaϩ, 313.1597. C17H26O2Si
requires MϩNa, 313.1600).
(Z)-Methyl 4-dimethyl(phenyl)silylpent-2-enoate 12a
Methyl 4-dimethyl(phenyl)silylpent-2-ynoate (0.60 g, 2.4 mmol)
was similarly converted into the alkene, which was obtained as a
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
4011

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colourless oil (0.35 g, 59%); Rf (light petroleum–EtOAc, 95 : 5)
0.29; νmax (film)/cmϪ1 2951 (CH), 1715 (CO Me), 1622 (C᎐
CCO2Me), 1250 (SiMe), 1112 and (SiPh); δH (250 MHz; CDCl3)
7.55–7.47 (2 H, m, SiPh), 7.38–7.32 (3 H, m, SiPh), 6.05 (1 H, t,
tion was stirred at that temperature for 20 min and then cooled
to Ϫ78 ЊC. Methyl pent-4-enoate (0.30 g, 2.6 mmol) in THF
(3 cm3) was added and the mixture stirred at Ϫ78 ЊC for a
further 1 h. Isobutyraldehde (0.26 cm3, 2.9 mmol) was added
and the mixture allowed to warm to Ϫ10 ЊC over 2 h. Saturated
aqueous ammonium chloride solution (5 cm3) was added and
the layers separated. The aqueous layer was washed with ether
(3 × 3 cm3) and the combined organic layers were washed with
water (2 × 3 cm3) and brine (3 cm3), dried (MgSO4) and the
solvents removed. The residue was chromatographed (SiO2,
light petroleum–EtOAc, 9 : 1) to give methyl 4-methyl-3-
hydroxy-2-prop-2Ј-enylpentanoate as an oil (0.32 g, 66%) and
as a mixture of diastereoisomers; Rf (light petroleum–EtOAc,
9 : 1) 0.09; νmax (film)/cmϪ1 3499 (OH), 2960 (CH) and 1714
᎐
2
J 11.5, CHCH᎐CH), 5.63 (1 H, d, J 11.5, CH᎐CHCO Me), 3.66
᎐
᎐
2
(3 H, s, CO2Me), 3.55 (1 H, dq, 11.5 and 6.9, SiCHMe), 1.07
(3 H, d, J 6.9, SiCHMe) and 0.31(6 H, s, SiMe2); δC (500 MHz,
CDCl3) 167.1ϩ, 155.1Ϫ, 136.5ϩ, 133.8Ϫ, 128.9Ϫ, 127.4Ϫ,
114.9Ϫ, 50.5Ϫ, 25.2Ϫ, 14.5Ϫ, Ϫ4.8Ϫ and Ϫ5.9Ϫ; m/z (ESI)
271.1 (100%, MNaϩ)(Found: MNaϩ, 271.1140. C14H20O2Si
requires MϩNa, 271.1130).
(Z )-4-Dimethyl(phenyl)silylpent-2-en-1-ol
DIBAL (1.0 mmol dmϪ3 solution in hexane, 1.4 cm3, 1.4 mmol)
was added to a solution of (Z)-methyl 4-dimethyl(phenyl)-
silylpent-2-enoate 12a (0.18 g, 0.72 mmol) in hexane (1.5 cm3)
at Ϫ78 ЊC and the mixture stirred for 1 h at Ϫ78 ЊC and 2 h at
room temperature. The mixture was poured onto ice and left for
5 minutes. Ether (5 cm3) was added and the layers separated.
The aqueous layer was washed with ether (2 × 2 cm3) and the
combined organic layers were washed with dilute aqueous
hydrochloric acid (3 cm3), water (3 cm3), brine (3 cm3), dried
(MgSO4) and solvents removed under reduced pressure to give
the alcohol as a colourless oil (0.16 g, 97%); νmax (film)/cmϪ1
(C᎐O); δ (250 MHz; CDCl3) 5.75 (1 H, dddd, J 4.1, 7.1, 10.1
᎐
H
and 13.9, CH᎐CH ), 5.05 (2 H, m, CH᎐CH ), 3.68 (1.5 H, s,
᎐
᎐
2
2
OMe), 3.65 (1.5 H, s, OMe), 3.55 (1 H, dd, J 11.1 and 4.7,
CHOH) 2.75–2.32 (3 H, m, CH(OH)CHCH2), 1.65 (1 H, dsept,
J 4.7 and 6.7, Me2CH ), 0.97 (3 H, d, J 6.7 CHMeAMeB) and
0.90 (3 H, d, J 6.7, CHMeAMeB); δC (400 MHz, CDCl3) 175.7ϩ,
175.4ϩ, 135.8Ϫ, 134.9Ϫ, 117.2ϩ, 116.6ϩ, 77.0Ϫ, 76.7Ϫ,
48.6Ϫ, 47.8Ϫ, 34.3ϩ, 32.1Ϫ, 31.6ϩ, 31.0Ϫ, 17.6Ϫ and 14.2Ϫ;
m/z (ESI) 209.1 (100%, M)(Found: MNaϩ, 209.1162. C10H18O3
requires MϩNa, 209.1154). Triethylamine (1.4 cm3, 10 mmol)
was added dropwise to a stirred solution of methyl 4-methyl-3-
hydroxy-2-prop-2Ј-enylpentanoate (0.50 g, 2.7 mmol) and
methanesulfonyl chloride (0.32 cm3, 4.1 mmol) in THF (20 cm3)
at 0 ЊC under a argon. The cloudy mixture was stirred at 0 ЊC
for 1 h and then allowed to warm to room temperature before
being concentrated in vacuo. The residue was dissolved in ethyl
acetate (20 cm3) and washed with saturated aqueous ammo-
nium chloride solution (10 cm3), water (10 cm3) and brine
(10 cm3). The organic layer was dried (MgSO4), the solvents
were removed under reduced pressure, and the residue was
chromatographed (SiO2, light petroleum–ethyl acetate, 8 : 2) to
give methyl 4-methyl-3-hydroxymethanesulfonyl-2-prop-2Ј-enyl-
pentanoate as an oil (0.44 g, 67%) and as a mixture of separable
diastereoisomers (50 : 50); isomer A: Rf (light petroleum–
3332 (OH), 3068 (CH), 2956 (CH), 1640 (C᎐C), 1249 (SiMe)
᎐
and 1112 (SiPh); δH (400 MHz; CDCl3) 7.55–7.46 (2 H, m,
SiPh), 7.40–7.33, (3 H, m, SiPh), 5.42 (1 H, dt, J 11.0 and 6.7,
CHCH OH), 5.35 (1 H, t, J, 11.0, SiCHCH᎐CH), 3.96 (1 H, dd,
᎐
2
J 12.4 and 6.9, CHACHBOH), 3.75 (1 H, dd, J 12.4 and 6.5,
CHACHBOH), 2.08 (1 H, dq, J 11.0 and 7.1, SiCHMe), 1.06
(3 H, d, J 6.9, SiCHMe), 0.30 (3 H, s, SiMeAMeB) and 0.25 (3 H,
s, SiMeAMeB); δC (500 MHz, CDCl3) 137.4ϩ, 135.8Ϫ, 134.0Ϫ,
129.2Ϫ, 127.7Ϫ, 125.3Ϫ, 58.7ϩ, 22.6Ϫ, 15.2Ϫ, Ϫ5.2Ϫ and
Ϫ5.8Ϫ; m/z (EI) 220.1 (35%, M), 135.0 (50%, PhMe2Si) and 68
(100%, C5H8)(Found: Mϩ, 220.1291. C13H20OSi requires M,
220.1283).
EtOAc, 8 : 2) 0.25; νmax (film)/cmϪ1 2968 (CH) and 1732 (C᎐O);
᎐
(Z )-4-Dimethyl(phenyl)silylpent-2-enyl acetate 13a
δH (250 MHz; CDCl ) 5.73 (1 H, ddt, J 17.0, 7.0 and 6.7, CH᎐
᎐
3
CH ), 5.05 (2 H, m, CH᎐CH ), 4.80 (1 H, t, J 5.8, CHOSO Me),
᎐
2
2
2
(Z)-4-Dimethyl(phenyl)silyl-pent-2-en-1-ol (0.16 g, 0.72
mmol), acetic anhydride (0.15 cm3, 1.2 mmol), DMAP (0.01 g,
0.1 mmol) and triethylamine (0.23 cm3, 1.5 mmol) were stirred
in ether (3 cm3) at room temperature for 9 h. Water (5 cm3) was
added and the layers separated. The aqueous layer was washed
with ether (3 × 2 cm3) and the combined organic layers washed
with water (2 × 2 cm3), brine (2 cm3), dried (MgSO4) and the
solvents removed under reduced pressure. The residue was
chromatographed (SiO2, light petroleum–EtOAc, 9 : 1) to give
the acetate as a colourless oil (0.145 g, 77%); Rf (light petrol-
eum–EtOAc, 9 : 1) 0.56; νmax (film)/cmϪ1 3069 (CH), 2957 (CH),
3.68 (3 H, s, SO2Me), 3.05 (3 H, s, CO2Me), 2.80 (1 H, quintet,
J 5.8, CHCO Me), 2.30 (2 H, m, CH CH᎐CH ), 1.95 (1 H,
᎐
2
2
2
octet, J 6.5, CHMe2)1.03 (3 H, d, J 6.8, CHMeAMeB) and 1.0
(3 H, d, J 6.7, CHMeAMeB); isomer B: Rf (light petroleum–
EtOAc, 8 : 2) 0.25; δH (250 MHz; CDCl3) 5.73 (1 H, ddt, J 17.0,
10.1 and 6.7, CH᎐CH ), 5.10 (2 H, m, CH᎐CH ), 4.80 (1 H, dd,
᎐
᎐
2
2
J 7.4 and 4.5, CHOSO2Me), 3.70 (3 H, s, SO2Me), 3.05 (3 H, s,
CO2Me), 2.90 (1 H, ddd, J 9.5, 7.4 and 5.2, CHCO2Me), 2.36
(2 H, m, CH CH᎐CH ), 2.01 (1 H, m, CHMe )1.07 (3 H, d,
᎐
2
2
2
J 6.9, CHMeAMeB) and 0.98 (3 H, d, J 6.7, CHMeAMeB). The
mixture of mesylates (0.34 g, 1.3 mmol) and DBU (0.95 cm3,
6.4 mmol) were refluxed in toluene (5 cm3) for 2 h, and then
allowed to cool to room temperature. Saturated aqueous
ammonium chloride solution (5 cm3) was added and the layers
separated. The aqueous layer was washed with ether (3 × 3 cm3)
and the combined organic layers washed with saturated
aqueous ammonium chloride solution (3 cm3), water (3 cm3)
and brine (3 cm3), dried (MgSO4) and solvents removed under
reduced pressure to give the alkene (0.19 g, 87%); Rf (light
petroleum–EtOAc, 90 : 10) 0.42; νmax (film)/cmϪ1 3080 (CH),
1739 (C᎐O) and 1112 (SiPh); δ (250 MHz; CDCl3) 7.50–7.45
᎐
H
(2 H, m, SiPh), 7.37–7.30 (3 H, m, SiPh), 5.44 (1 H, t, J 10.8,
CH᎐CHCH OAc), 5.40 (1 H, ddd, J 11.1, 7.7 and 5.6, CH᎐
᎐
᎐
2
CHCH2OAc), 4.54 (1 H, dd, J 12.6 and 7.0, CHACHBOAc),
4.24 (1 H, dd, J 12.6 and 5.4, CHACHBOAc), 2.10 (1 H, dq,
J 10.7 and 7.1, SiCHMe), 2.05 (3 H, s, COMe), 1.03 (3 H, d,
J 7.1, SiCHMe), 0.27 (3 H, s, SiMeAMeB) and 0.25 93 H, s, (3 H,
s, SiMeAMeB); δC (500 MHz, CDCl3) 171.0ϩ, 138.2Ϫ, 137.0ϩ,
134.0Ϫ, 129.2Ϫ, 127.7Ϫ, 120.0Ϫ, 60.5ϩ, 22.7Ϫ, 15.1Ϫ, Ϫ5.1Ϫ
and Ϫ5.5Ϫ; m/z (ESI) 285.1 (100%, Mϩ)(Found: 285.1282.
C15H22O2Si requires MNaϩ 285.1287).
2962 (CH) and 1718 (C᎐O); δ (400 MHz; CDCl3) 6.63 (1 H,
᎐
H
d, J 10.0, Me2CHCH ), 5.80 (1 H, ddt, J 16.0, 11.6 and 5.9,
CH᎐CH ), 4.92–5.02 (2 H, m, CH᎐CH ), 3.70 (3 H, s, CO Me),
᎐
᎐
2
2
2
3.05 (2 H, d, J 6.0, CH CH᎐CH ), 2.65 (1 H, dsept, J 10.0 and
᎐
2
2
Methyl 4-methyl-2-prop-2Ј-enylpent-2-enoate 17b
6.1, Me2CH ) and 1.0 (6 H, d, J 6.0, Me2CH); δC (400 MHz,
CDCl3) 168.3ϩ, 150.4Ϫ, 135.9Ϫ, 127.3ϩ, 114.9ϩ, 51.7Ϫ,
30.8ϩ, 27.9Ϫ and 22.1ϩ; m/z (EI) 168.1 (100%, Mϩ) 153.0
(18%, M–CH3) and 109.0 (52%, M–CO2Me)(Found: Mϩ,
168.1139. C10H16O2 requires M, 304.1150).
Diisopropylamine (freshly distilled over calcium hydride under
an argon atmosphere, 0.41 cm3, 2.9 mmol) in THF (3 cm3) was
cooled to 0 ЊC under argon and treated with n-butyllithium
(1.6 mol dmϪ3 solution in hexane, 1.6 cm3, 2.9 mmol). The solu-
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
4012

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Preprations of the mixtures of esters 15 and 16, 20 and 21, 34 and
35 and 37 and 38
under argon for 25 min. The esters rich in the isomers 15a and
15b (0.58 g, 2.1 mmol) in THF (2 cm3) were added, and the
mixture stirred at 0 ЊC for 2.5 h before being cooled to Ϫ78 ЊC.
Saturated aqueous ammonium chloride solution (3 cm3) was
added and the mixture allowed to warm to room temperature.
The layers were separated, the aqueous layer washed with ether
(3 × 2 cm3) and the combined organic layers washed with water
(2 × 2 cm3) and brine (2 cm3), dried (MgSO4) and the solvents
removed under reduced pressure. The residue was chromato-
graphed (SiO2, hexane–EtOAc, 95 : 5) to give the mixtures of
esters.
Method A, by enolate allylation. Typically, diisopropylamine
(freshly distilled over calcium hydride under an argon
atmosphere, 1.5 eq.) in THF (2 cm3) was cooled to 0 ЊC under
argon and treated with n-butyllithium (1.5 eq). The solution
was stirred at that temperature for 20 min and then cooled to
Ϫ78 ЊC. Ester (1 eq.) in THF (1 cm3) was added dropwise and
the mixture stirred for 30 min at Ϫ78 ЊC before being allowed to
warm to Ϫ20 ЊC and stirred at that temperature for 30 min. The
mixture was cooled to Ϫ78 ЊC and allyl bromide (1.5 eq.) in
THF (0.5 cm3) added. The mixture was allowed to warm to
room temperature over 2 h and saturated aqueous ammonium
chloride solution (5 cm3) added. The layers were separated and
the aqueous layer washed with ether (3 × 2 cm3). The combined
organic layers were washed with water (2 × 2 cm3) and brine
(2 cm3). The organic layer was dried (MgSO4), and solvents
removed under reduced pressure. The residue was chromato-
graphed (SiO2, light petroleum–EtOAc, 95 : 5) to give the
authentic mixture of esters.
The following esters were prepared using these methods.
Methyl 3-dimethyl(phenyl)silyl-2-prop-2Ј-enylbutanoate 15a
؉ 16a. By method A, the mixture of esters (0.165 g, 71%,
15a : 16a, 97 : 3,) was obtained as an oil; νmax (film)/cmϪ1 3070
(CH), 1735 (CO), 1250 (SiMe) and 1112 (SiPh); δH (250 MHz;
CDCl3) (15a, major isomer) 7.53 (2 H, m, SiPh), 7.36 (3 H, m,
SiPh), 5.67 (1 H, ddt, J 17.1, 10.3 and 6.9, CH CH᎐CH ), 4.98
᎐
2
2
(1 H, dd, J 17.3 and 1.4, CH᎐CH H ), 4.95 (1 H, d, J 10.0, CH᎐
᎐
᎐
A
B
CHAHB), 3.53 (3 H, s, OMe), 2.50 (1 H, ddd, J 10.9, 5.8 and 3.5,
CHCO Me), 2.35 (1 H, ddd, J 14.0, 10.9 and 1.0, CH CH CH᎐
᎐
2
A
B
Method B, by Ireland–Claisen rearrangement using LDA in
THF. Typically, diisopropylamine (freshly distilled over
calcium hydride under an argon atmosphere, (1.5 eq.) in THF
(5 cm3) was cooled to 0 ЊC under argon and treated with
n-butyllithium (1.5 eq.). The solution was stirred at that
temperature for 20 min and then cooled to Ϫ78 ЊC. The allyl
ester (1 eq.) in THF (1 cm3) was added dropwise and the solu-
tion stirred at Ϫ78 ЊC for 1 h before the addition of trimethyl-
silyl chloride (freshly distilled, 1.6 eq.). The mixture was stirred
at Ϫ78 ЊC for 2 h before being allowed to warm to room
temperature. The mixture was then refluxed for 8 h before
being allowed to cool to room temperature. Aqueous sodium
hydroxide (10%, 3 cm3) was added and the solution stirred for
15 min. THF was removed under reduced pressure, and the
basic layer extracted with pentane (3 × 2 cm3). The basic
aqueous phase was carefully acidified with aqueous hydro-
chloric acid (3 mol dmϪ3), extracted with ether (4 × 1 cm3),
dried (MgSO4) and solvents removed under reduced pressure.
The residue was taken into dry ether (1.5 cm3), or dry methanol
(when trimethylsilyldiazomethane was used for esterification).
An ethanolic solution of diazomethane or trimethylsilyldiazo-
methane (2.0 mol dmϪ3 solution in hexanes) was added drop-
wise to the stirred solution at room temperature until there
was a permanent yellow colour. The mixture was stirred
for a further 30 min. Glacial acetic acid was added dropwise
until the evolution of nitrogen had ceased, followed by
saturated aqueous sodium bicarbonate solution. The layers
were separated and the aqueous phase washed with ether
(3 × 2 cm3). The combined organic layers were washed with
water (2 cm3), dried (MgSO4) and solvents removed under
reduced pressure. The residue was chromatographed (SiO2,
light petroleum–EtOAc, 95 : 5) to give the mixtures of esters.
CH ), 2.10 (1 H, dddd, J 14.0, 5.0, 3.5 and 1.5, CH CH CH᎐
᎐
2
A
B
CH2), 1.39 (1 H, dq, J 7.6 and 5.9, MeCHSi), 0.99 (3 H, d,
J 7.6, MeCHSi), 0.34 (3 H, s, SiMeAMeB) and 0.33 (3 H, s,
SiMeAMeB); (16a, minor isomer, where different from the major
isomer) 3.56 (3 H, s, OMe) and 0.97 (3 H, d, J 7.5, MeCHSi);
δC (500 MHz, CDCl3) 175.4ϩ, 137.7ϩ, 136.0Ϫ, 133.7Ϫ,
128.8Ϫ, 127.5Ϫ, 115.9ϩ, 50.9Ϫ, 46.4Ϫ, 33.4ϩ, 26.7Ϫ, 22.2Ϫ,
11.2Ϫ, Ϫ4.1Ϫ and Ϫ4.3Ϫ; m/z (ESI) 299.1 (100%, MNaϩ)-
(Found: MNaϩ, 299.1446. C16H24O2Si requires MϩNaϩ
299.1443). Method B gave the mixture of esters (56 mg,
53%, 15a : 16a, 98 : 2). Method C gave the mixture of esters
(45 mg, 43%, 15a : 16a, 93 : 7), together with methyl 3-
dimethyl(phenyl)silylbutanoate (13 mg, 15%). Method D gave
the mixture of esters (0.55 g, 95%, 15a : 16a, 48 : 52).
Methyl
4-methyl-3-dimethyl(phenyl)silyl-2-prop-2Ј-enyl-
pentanoate 15b ؉ 16b. By method A, the mixture of esters
(0.11 g, 95%, 15b : 16b, 89 : 11) was obtained as an oil; Rf (light
petroleum–EtOAc, 95 : 5) 0.23; νmax (film)/cmϪ1 2958 (CH),
2253 (C᎐C), 1727 (C᎐O), 1251 (SiMe) and 1109 (SiPh); δH (250
᎐
᎐
MHz; CDCl3) (15b, major isomer) 7.57 (2 H, m, SiPh), 7.30 (3
H, m, SiPh), 5.70 (1 H, dddd, J 16.0, 9.5, 7.3 and 6.5 CH᎐CH ),
᎐
2
5.00 (2 H, m, CH᎐CH ), 3.59 (3 H, s, CO Me), 2.70 (1 H, ddd,
᎐
2
2
J 9.0, 5.7 and 3.2, CHCO2Me), 2.47 (1 H, dt, J 14.0 and 7.8,
CH ᎐CHCH CH ), 2.13 (1 H, dt, J 14.1 and 7.1, CH ᎐
᎐
᎐
2
2
A
B
CHCHACHB), 2.00 (1 H, dsept, J 4.1 and 6.8, CHMe2), 1.33
(1 H, dd, J 3.9 and 3.3, SiCH), 0.92 (3 H, d, J 6.8, CHMeAMeB),
0.85 (3 H, d, J 6.9, CHMeAMeB), 0.43 (3 H, s, SiMeAMeB) and
0.42 (3 H, s, SiMeAMeB); δH (250 MHz; CDCl3) (16b, minor
isomer, where different from the major isomer) 3.62 (3 H, s,
CO2Me), 0.39 (3 H, s, SiMeAMeB) and 0.37 (3 H, s, SiMeAMeB);
δC (400 MHz, CDCl3) 177.7ϩ, 140.5ϩ, 137.0Ϫ, 134.0Ϫ,
128.5Ϫ, 127.5Ϫ, 116.5ϩ, 51.2Ϫ, 44.2Ϫ, 36.3ϩ, 36.0Ϫ, 28.0Ϫ,
23.8Ϫ, 21.5Ϫ, Ϫ0.7Ϫ and Ϫ1.7Ϫ; m/z (ESI) 327.18 (100%,
MNaϩ)(Found: MNaϩ, 327.1756. C18H28O2Si requires MϩNa,
327.1858). Method B gave the mixture of esters (63 mg, 60%,
15b : 16b, 84 : 16). Method C gave the mixture of esters (0.045 g,
43%, 15b : 16b, 69 : 31). Method D gave the mixture of esters
(0.07 g, 85%, 15b : 16b, 60 : 40).
Method C, by Ireland–Claisen rearrangement using LDA in
HMPA and THF. Typically, diisopropylamine (freshly distilled
over calcium hydride under an argon atmosphere, 0.85 eq.)
in THF (5 cm3) was cooled to 0 ЊC under argon and treated with
n-butyllithium (0.85 eq.). The solution was stirred at that tem-
perature for 20 min and then cooled to Ϫ78 ЊC. HMPA (freshly
distilled under nitrogen at reduced pressure, 1.6 cm3) was added
and the mixture stirred for 5 min. The allyl ester (1 eq.) in THF
(5 cm3) was added and the reaction and workup conducted in
the same way as in method B, to give the mixtures of esters.
Methyl
3-phenyl-3-dimethyl(phenyl)silyl-2-prop-2Ј-enyl-
propanoate 15c ؉ 16c. By method A, the mixture of esters1
(1.65 g, 98%, with the known minor isomer undetectable
in the 1H-NMR spectrum) was obtained as an oil; Rf (light pet-
roleum–EtOAc, 95 : 5) 0.23; νmax (film)/cmϪ1 3070 CH), 1736
(CO), 1640 (PhH), 1598 (PhH), 1492 (PhH), 1249 (SiMe) and
1113 (SiPh); δH (400 MHz; CDCl3) 7.40–7.27 (5 H, m, SiPh),
7.18 (2 H, t, J 7.2, m-PhH), 7.10 (1 H, t, J 7.4, p-PhH), 6.90
Method D, by enolate protonation. Diisopropylamine (freshly
distilled over calcium hydride under an argon atmosphere,
0.48 cm3, 3.2 mmol) in THF (2 cm3) and n-butyllithium
(1.7 mol dmϪ3 in hexanes, 2.1 cm3, 3.2 mmol) were kept at 0 ЊC
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
4013

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(2 H, d, J 7.8, o-PhH), 5.58 (1 H, dddd, J 14.3, 10.2, 8.0 and 6.2,
CH CH᎐CH ), 4.87 (1 H, d, J 10.2, CH᎐CH H ), 4.83 (1 H, d,
CHCH᎐CH2), 2.45 (1 H, dd, J 14.5 and 5.5, CH H CO Me)
᎐
A B 2
1.06 (1 H, dd, J 4.2 and 3.2, Me2CH ), 0.39 (3 H, s, SiMeAMeB)
and 0.37 (3 H, s, SiMeAMeB).
᎐
᎐
2
2
A
B
J 14.2, CH᎐CH H ), 3.31 (3 H, s, OMe), 2.95 (1 H, ddd, J 12.0,
᎐
A
B
10.4 and 3.9, CHCO2Me), 2.62 (1 H, d, J 12.0, PhCH ), 2.15–
1.95 (2 H, m, CH CH᎐CH ), 0.26 (3 H, s, SiMe Me ) and 0.07
(3 H, s, SiMeAMeB). Method B gave the mixture of esters
᎐
2
2
A
B
1-Phenyl-1-dimethyl(phenyl)silyl-2-methoxycarbonyl-3-
methylpent-5-ene 34 and 35. By method B, (Z)-but-2-enyl 3-
phenyl-3-dimethyl(phenyl)silylpropanoate (80 mg, 0.25 mmol)
gave the mixture of esters (58 mg, 66%, 34 : 35, 86 : 14) as an oil;
Rf (light petroleum–EtOAc, 95 : 5) 0.33; νmax (film)/cmϪ1 2957
(51 mg, 49%, >98 : 2, with the minor isomer undetectable in
1
the H-NMR spectrum). Method C gave the mixture of esters
(67 mg, 66%, >97 : 3, with the minor isomer undetectable in the
1H-NMR spectrum).
(CH), 2959 (CH), 1732 (C᎐O), 1248 (SiMe) and 1112 (SiPh);
᎐
δH (400 MHz; CDCl3) (major isomer 34) 7.38–7.25 (5 H, m,
SiPh), 7.17 (2 H, t, J 7.6, m-PhH), 7.07 (1 H, t, J 7.4, p-PhH),
6.82 (2 H, d, J 7.7, o-PhH), 5.75 (1 H, ddd, J 17.2, 10.2 and 8.6,
Methyl 4-dimethyl(phenyl)silyl-3-ethenyl-pentanoate 20a
and 21a. By method B, (Z)-4-dimethyl(phenyl)silylpent-2-enyl
acetate (13a) (100 mg, 0.38 mmol) gave the mixture of esters
(53 mg, 53%, 20a : 21a, 93 : 7) as an oil; Rf (light petroleum–
CH᎐CH ), 4.88 (1 H, d, J 10.3, CH᎐CH H ), 4.49 (1 H, d,
᎐
᎐
2
A
B
J 17.2, CH᎐CH H ), 3.37 (3 H, s, CO Me), 3.00 (1 H, dd, J 12.7
᎐
A
B
2
EtOAc, 95 : 5) 0.27; νmax (film)/cmϪ1 2998 (CH), 1738 (C᎐O),
᎐
and 4.0, CHCO2Me), 2.75 (1 H, d, J 12.7, PhCH ), 2.32 (1 H,
ddq, 8.6, 4.2 and 7.3, MeCH ), 0.89 (3 H, d, J 7.1, CHMe), 0.20
(3 H, s, SiMeAMeB) and 0.10 (3 H, s, SiMeAMeB), (minor isomer
35, where different from 34) 6.90 (2 H, d, J 7.01, o-PhH), 5.70
1251 (SiMe) and 1113 (SiPh); δH (400 MHz; CDCl3) (major
isomer, 20a) 7.54–7.47 (2 H, m, SiPh), 7.36–7.33 (3 H, m, SiPh),
5.70 (1 H, ddd, J 16.7, 10.7 and 8.3, CH᎐CH ), 4.95 (1 H, d,
᎐
2
J 16.7, CH᎐CH H ), 4.93 (1 H, d, J 10.7, CH᎐CH H ), 3.61
᎐
᎐
A
B
A
B
(1 H, ddd, J 17.2, 10.5 and 6.7, CH᎐CH ), 4.91 (1 H, d, J 10.7,
᎐
2
(3 H, s, OMe), 2.68 (1 H, dddd, J 12.4, 10.2, 8.5 and 4.1,
CHCH᎐CH ), 2.35 (1 H, dd, J 14.7 and 4.2, CH H CO Me),
CH᎐CH H ), 4.87 (1 H, d, J 17.2, CH᎐CH H ), 3.37 (3 H, s,
᎐
᎐
A
B
A
B
᎐
2
A
B
2
CO2Me), 3.10 (1 H, dd, J 12.4 and 4.2, CHCO2Me), 2.82 (1 H,
d, J 12.4, PhCH ), 2.32 (1 H, ddq, 6.7, 4.2 and 6.9, MeCH ), 0.86
(3 H, d, J 6.9, CHMe), 0.23 (3 H, s, SiMeAMeB) and 0.12 (3 H,
s, SiMeAMeB); δC (400 MHz, CDCl3) 173.6ϩ, 139.9ϩ, 138.4Ϫ,
136.8ϩ, 134.2Ϫ, 128.9Ϫ, 128.7Ϫ, 127.6Ϫ, 124.8Ϫ, 124.7Ϫ,
115.3ϩ, 50.5Ϫ, 50.3Ϫ, 37.5Ϫ, 36.4Ϫ, 18.7Ϫ, Ϫ3.0Ϫ and
2.20 (1 H, dd, J 14.7 and 10.2, CHAHBCO2Me), 1.07 (1 H, dq,
J 12.2 and 7.4, CHSi), 0.95 (3 H, d, J 7.4, MeCHSi), 0.34 (3 H,
s, SiMeAMeB) and 0.32 (3 H, s, SiMeAMeB); δC (500 MHz,
CDCl3) 173.3ϩ, 141.1Ϫ, 138.7ϩ, 133.Ϫ, 128.8Ϫ, 127.7Ϫ,
114.6ϩ, 51.4Ϫ, 42.6Ϫ, 37.7ϩ, 24.8Ϫ, Ϫ2.9Ϫ and Ϫ3.7Ϫ;
m/z (ESI) 299.1 (55%, MNaϩ)(Found: Mϩ, 299.1457. C16H24-
O2Si requires MϩNa, 299.1443). Method B starting with (E)-
4-dimethyl(phenyl)silylpent-2-enyl acetate (11a)(100 mg, 0.38
mmol) gave the mixture of esters (73 mg, 68%, 20a : 21a,
38 : 62); δH (400 MHz; CDCl3) signals from the minor isomer
20a (identical to the major isomer in the previous experiment)
and (major isomer, 21a) 7.54–7.45 (2 H, m, SiPh), 7.35–7.30
Ϫ4.6Ϫ; m/z (ESI) 375.2 (100%, MNaϩ), 316.2 (15%, MNaϩ
Ϫ
CO2Me)(Found: MNaϩ, 375.1740. C22H28O2Si requires MϩNa,
352.1859). Method C, starting from (Z)-but-2-enyl 3-phenyl-3-
dimethyl(phenyl)silylpropanoate (93 mg, 0.27 mmol), gave the
mixture of esters (70 mg, 87%, 34 : 35, 32 : 68). Method B,
starting from (E)-but-2-enyl 3-phenyl-3-dimethyl(phenyl)-
silylpropanoate (110 mg, 0.324 mmol), gave the mixture of
esters (70 mg, 61%, 34 : 35, 33 : 67).
(3 H, m, SiPh), 5.68 (1 H, dt, J 18.4 and 9.5, CH᎐CH ),
᎐
2
5.0–4.9 (2 H, m, CH᎐CH H ), 3.59 (3 H, s, OMe), 2.82 (1 H,
᎐
A
B
ddt, J 15.7, 9.5 and 4.0, CHCH᎐CH ), 2.38 (2 H, m,
᎐
2
1-Phenyl-2-methoxycabonyl-3-methylpent-5-ene 37 and 38.
Method B, starting from (Z)-but-2-enyl 3-phenylpropanoate
(100 mg, 0.5 mmol) gave the mixture of esters 37 and 38 (63 mg,
58%, 37 : 38, 80 : 20) as an oil, with the same signals (1H NMR)
as in the mixture produced by the experiment using TBAF,
described below.
CH2CO2Me), 1.07 (1 H, dq, J 15.1 and 7.4, CHSi), 0.93 (3 H, d,
J 7.4, MeCHSi), 0.32 (3 H, s, SiMeAMeB) and 0.27 (3 H, s,
SiMeAMeB).
Methyl 5-Methyl-4-dimethyl(phenyl)silyl-3-ethenyl-hexanoate
20b and 21b. By method B, (Z)-4-dimethyl(phenyl)silyl-5-
methylhex-2-enyl acetate (13b) (100 mg, 0.34 mmol) gave the
mixture of esters (0.045 g, 44%, 20b : 21b, 98 : 2) as an oil; Rf
(light petroleum–EtOAc, 95 : 5) 0.35; νmax (film)/cmϪ1 3070
(CH), 2954 (CH), 1740 (CH), 1251 (SiMe) and 1110 (SiPh);
δH (400 MHz; CDCl3) (major isomer 20b) 7.55–7.50 (2 H, m,
SiPh), 7.35–7.32 (3 H, m, SiPh), 5.82 (1 H, ddd, J 17.8, 10.0 and
8.1, CH᎐CH ), 4.97 (1 H, d, 17.8, CH᎐CH H ), 4.95 (1 H, d,
Preparation of the mixtures of diesters 18a ؉ 19a and 18b ؉ 19b
Typically, ozone was bubbled through a solution the mixtures
of esters 15 ϩ 16 or 20 ϩ 21 (0.45 mmol) in dry dichloro-
methane (5 cm3) at Ϫ78 ЊC, until there was a permanent blue
colour (approximately 5 min). The mixture was allowed to
warm to 0 ЊC. Aqueous hydrogen peroxide (30%, 5 cm3) was
added and the mixture stirred at room temperature for 16 h at
room temperature. Dilute aqueous hydrochloric acid (3 mol
dmϪ3, 2 cm3) was added and the layers separated. The aqueous
layer was washed with dichloromethane (3 × 2 cm3) and the
combined organic layers washed with brine (3 cm3), dried
(MgSO4) and solvents removed under reduced pressure. The
residue was dissolved in dry methanol (1 cm3) and trimethyl-
silyldiazomethane (2.0 mol dmϪ3) added dropwise until the
mixture was a permanent yellow colour. The mixture was
stirred for a further 30 min and glacial acetic acid added until
nitrogen evolution had ceased. Ether (3 cm3) was added and the
mixture was neutralised with aqueous sodium bicarbonate
solution (3 cm3). The layers were separated and the aqueous
layer washed with ether (3 × 3 cm3). The combined organic
layers were washed with water (3 cm3), aqueous sodium bi-
carbonate solution (3 cm3), dried (MgSO4) and solvents
removed under reduced pressure. The residue was chromato-
graphed (SiO2, light petroleum–EtOAc, 95 : 5) to give the
mixtures of diesters.
᎐
᎐
2
A
B
J 10.0, CH᎐CH H ), 3.62 (3 H, s, OMe), 2.96 (1 H, dddd, J 9.5,
᎐
A
B
8.2, 6.5 and 3.0, CHCH᎐CH ), 2.33 (1 H, dd, J 14.5 and 6.6,
᎐
2
CHACHBCO2Me), 2.31 (1 H, dd, J 14.5 and 8.5, CHACHB-
CO2Me), 1.97 (1 H, dsept, 3.7 and 6.9, MeAMeBCH ), 1.02 (1 H,
t, J 3.4, SiCH), 0.96 (3 H, d, J 6.9, MeAMeBCH), 0.93 (3 H, d,
J 6.9, MeAMeBCH), 0.40 (3 H, s, SiMeAMeB) and 0.38 (3 H, s,
SiMeAMeB); δC (400 MHz, CDCl3) 172.8ϩ, 141.7Ϫ, 140.1ϩ,
133.7Ϫ, 128.4Ϫ, 127.4Ϫ, 114.3ϩ, 51.1Ϫ, 39.8ϩ, 39.4Ϫ, 38.2Ϫ,
28.1Ϫ, 23.6Ϫ, 22.3Ϫ, Ϫ0.61Ϫ and Ϫ1.1Ϫ; m/z (EI) 304.2 (3%,
Mϩ) and 135.1 (100%, PhMe2Si)(Found: Mϩ, 304.1871.
C18H28O2Si requires M, 304.1858). Method B, starting with
(E)-4-dimethyl(phenyl)silyl-5-methylhex-2-enyl acetate (11b)
(55 mg, 0.24 mmol) gave the mixture of esters (20 mg, 29%,
20b : 21b, 52 : 48), together with recovered starting material 11b
(21 mg, 29%); δH (400 MHz; CDCl3) signals from the major
isomer 20b (identical to the major isomer in the previous
experiment) and (minor isomer 21b, where different from the
major isomer 20b) 7.55–7.50 (2 H, m, SiPh), 7.35–7.30 (3 H, m,
SiPh), 5.75 (1 H, m, CH᎐CH ), 4.95 (2 H, m, CH᎐CH ), 3.57
᎐
᎐
2
2
(3 H, s, OMe), 2.94 (1 H, dddd, J 13.8, 12.7, 5.0 and 3.9,
The following diesters were prepared using these methods.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
4014

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Methyl 4-dimethyl(phenyl)silyl-3-methoxycarbonylpentanoate
18a ؉ 19a. The mixture of esters 15a ϩ 16a gave the mixture
of diesters (0.10 g, 72%, 18a : 19a, 98 : 2) as an oil; Rf (light
petroleum–EtOAc, 95 : 5) 0.11; νmax (film)/cmϪ1 2951 (CH),
1732 (CO), 1252 (SiMe) and 1112 (SiPh); δH (400 MHz; CDCl3)
(major isomer) 7.55–7.47 (2 H, m, SiPh), 7.40–7.42 (3 H, m,
SiPh), 3.64 [3 H, s, (CO2Me)A], 3.62 [3 H, s, (CO2Me)B], 3.02
[1 H, dt, J 11.5 and 3.5, CH2CH(CO2Me)A], 2.70 [1 H, dd,
J 16.8 and 11.5, CHAHB(CO2Me)B], 2.15 [1 H, dd, J 16.8 and
3.2, CHAHB(CO2Me)B], 1.47 (1 H, dq, J 7.6 and 3.8, CHSi),
0.94 (3 H, d, J 7.6, MeCH) and 0.34 (6 H, s, SiMe2) (minor
isomer, where different from major isomer) 3.08 [1 H, dt, 10.0
and 3.5, CH2CH(CO2Me)A]; δC (400 MHz, CDCl3) 175.2ϩ,
172.6ϩ, 137.0ϩ, 133.6Ϫ, 129.1Ϫ, 129.0Ϫ, 51.6Ϫ, 51.4Ϫ,
41.8Ϫ, 32.8ϩ, 22.1Ϫ, 10.7Ϫ, Ϫ4.2Ϫ and Ϫ4.3Ϫ; m/z (ESI)
331.1 (100%, Mϩ)(Found: MNaϩ, 331.1345. C16H24O4Si
requires MϩNa 331.1342). The mixture of esters 20a ϩ 21a
(98 : 2) derived from the silylenol ether Z-7a gave the mixture of
diesters (27 mg, 50%), in which only the isomer 18a was detect-
able in the 1H-NMR spectrum.
(ESI) 359.14 (100%, MNaϩ)(Found: MNaϩ, 359.1426.
C21H24O2Si requires MϩNa, 359.1443).
But-2-ynyl 3-phenylpropanoate
DCC (7.3 g, 36.3 mmol) in dichloromethane (5 cm3) was added
to hydrocinnamic acid (5 g, 33 mmol), but-2-yn-1-ol (3.5 g,
50 mmol) and DMAP (0.35 g, 3 mmol) in dry dichloromethane
(50 cm3) at 0 ЊC, and the cloudy mixture stirred for 1 h before
being allowed to warm to room temperature. The mixture was
stirred for a further 2 h, and the precipitate filtered off. The
mixture was washed with saturated aqueous sodium bi-
carbonate solution (15 cm3) and saturated aqueous ammonium
chloride solution (15 cm3). The combined aqueous layers were
washed with dichloromethane (3 × 10 cm3) and the combined
organic layers washed with water (2 × 10 cm3) and brine
(15 cm3). The orgnaic layer was dried (MgSO4) and solvents
removed under reduced pressure. The residue was filtered
through a silica pad (light petroleum–EtOAc, 95 : 5) to give the
ester (5.5 g, 82%) as an oil; Rf (light petroleum–EtOAc, 95 : 5)
0.36; νmax (film)/cmϪ1 2933 (CH), 2240 (C᎐C), 1740 (C᎐O), 1604
᎐
᎐
᎐
(Ph) and 1496 (Ph); δH (400 MHz; CDCl3) 7.32–7.25 (2 H, m,
Ph), 7.23–7.17 (3 H, m, Ph), 4.64 (2 H, q, J 2.4, OCH2), 2.95
Methyl 4-dimethyl(phenyl)silyl-3-methoxycarbonyl-5-methyl-
hexanoate 18b ؉ 19b. The mixture of esters 15b ϩ 16b gave the
mixture of diesters (67 mg, 79%, 94 : 6) as an oil; Rf (light
petroleum–EtOAc, 95 : 5) 0.17; νmax (film)/cmϪ1 2954 (CH),
(2 H, t, J 7.6, PhCH2CH2), 2.65 (2 H, t, J, 7.6, PhCH2CH2) and
᎐
1.84 (3 H, t, J 2.4, C᎐CMe); δ (500 MHz, CDCl3) 172.1ϩ,
᎐
C
140.1ϩ, 128.2Ϫ, 128.0Ϫ, 126.0Ϫ, 82.9ϩ, 72.9ϩ, 52.7ϩ, 35.4ϩ,
30.6ϩ and 3.3 Ϫ; m/z (ESI) 225.09 (100%, MNaϩ) (Found:
MNaϩ, 225.0882. C13H14O2 requires MϩNa, 225.0891).
1736 (C᎐O), 1253 (SiMe) and 1110 (SiPh); δ (250 MHz;
᎐
H
CDCl3) (major isomer) 7.50–7.57 (2 H, m, SiPh), 7.30–7.36
(3 H, m, SiPh), 3.67 [3 H, s, (CO2Me)A], 3.65 [3 H, s, (CO2Me)B],
3.17 [1 H, ddd, J 10.7, 3.5 and 2.5, CH(CO2Me)A], 2.80 [1 H,
dd, J 16.4 and 10.7, CHAHB(CO2Me)B], 2.27 [1 H, dd, J 16.4
and 3.7, CHAHB(CO2Me)B], 1.88 (1 H, octet, J 6.7 CHMe2),
1.50 (1 H, dd, J 6.1 and 2.5, CHSi), 0.92 (3 H, d, J 6.8,
CHMeAMeB), 0.85 (3 H, d, J 6.8, CHMeAMeB), 0.42 (3 H, s,
SiMeAMeB) and 0.40 (3 H, s, SiMeAMeB) (minor isomer, where
different from the major isomer) 3.67 [3 H, s, (CO2Me)A], 3.59
[3 H, s, (CO2Me)B] and 3.30 [1 H, dt, J 7.1 and 3.5, CH(CO2-
Me)A]; δC (400 MHz, CDCl3) 176.3Ϫ, 172.6Ϫ, 139.2ϩ, 133.8Ϫ,
128.9Ϫ, 127.7Ϫ, 51.7Ϫ, 51.6Ϫ, 40.7Ϫ, 36.0Ϫ, 34.6ϩ, 28.1Ϫ,
24.0Ϫ, 22.8Ϫ, Ϫ1.2Ϫ and Ϫ1.8Ϫ; m/z (EI) 336.2 (10%, Mϩ)
135.1 (100%, SiMe2Ph)(Found: Mϩ, 336.1746. C18H28O4Si
requires M 336.1757). The mixture of esters 20b ϩ 21b (>98 : 2)
derived from the silylenol ether Z-7b gave the mixture of
diesters (20 mg, 45%), in which only the isomer 18b was detect-
able in the 1H-NMR spectrum.
(E )-But-2-enyl 3-phenyl-3-dimethyl(phenyl)silylpropanoate
3-Phenyl-3-dimethyl(phenyl)silylpropanoic acid (0.34 g,
1.2 mmol) and E-but-2-enol (0.18 g, 2.4 mmol) were similarly
converted into the ester (0.35 g, 72%), which was obtained as an
oil; Rf (light petroleum–EtOAc, 95 : 5) 0.35; νmax (film)/cmϪ1
3023 (CH), 2957 (CH, 1736 (C᎐O), 1250 (SiMe), 1113 (SiPh)
᎐
and 966 (HC᎐CH); δ (250 MHz; CDCl3) 7.44–7.30 (5 H, m,
᎐
H
SiPh), 7.18 (2 H, t, J 7.9, Ph) m-PhH), 7.10 (1 H, t, J 7.3,
p-PhH), 6.95 (2 H, d, J 7.7, o-PhH), 5.60 (1 H, dq, J 15.3 and
6.4, OCH CH᎐CH ), 5.35 (1 H, dt, J 15.3 and 6.4, OCH CH᎐
᎐
᎐
2
2
CH), 4.30 (2 H, d, J 6.4, OCH2), 2.86 (1 H, dd, J 10.8 and 4.2,
SiCHCHACHB), 2.75 (1 H, dd, J 14.8 and 10.8, SiCHCHA-
CHB), 2.65 (1 H, dd, J 14.7 and 4.2, SiCHCHACHB), 1.64 (3 H,
d, J 6.4, C᎐CMe), 0.25 (3 H, s, SiMe Me ) and 0.22 (3 H, s,
᎐
A
B
SiMeAMeB); δC (500 MHz, CDCl3) 172.7ϩ, 141.7ϩ, 136.4ϩ,
133.9Ϫ, 130.7Ϫ, 129.0Ϫ, 128.2Ϫ, 128.0Ϫ, 127.8Ϫ, 126.0Ϫ,
124.7Ϫ, 65.2ϩ, 34.7ϩ, 32.0Ϫ, 17.4Ϫ, Ϫ4.4Ϫ and Ϫ5.7Ϫ;
m/z (ESI) 361.16 (100%, MNaϩ) (Found: MNaϩ, 361.1613.
C21H26O2Si requires MϩNa, 361.1600).
But-2-ynyl 3-phenyl-3-dimethyl(phenyl)silylpropanoate
Methyl 4-phenyl-3-dimethyl(phenyl)silylpentanoate (1.50 g,
5.0 mmol), but-2-yn-1-ol (20 cm3) and concentrated sulfuric
acid (0.5 cm3) were refluxed overnight and allowed to cool to
room temperature before being partitioned between ether
(25 cm3) and saturated aqueous sodium bicarbonate solution
(25 cm3). The aqueous layer was extracted with ether (3 ×
20 cm3) and the combined organic layers washed with saturated
aqueous sodium bicarbonate solution (3 × 20 cm3) and brine
(20 cm3). The organic layer was dried (MgSO4) and solvent
removed under reduced pressure. The residue was chromato-
graphed (SiO2, light petroleum–EtOAc, 97 : 3) to give the ester
(0.64 g, 33%) as an oil; Rf (light petroleum–EtOAc, 95 : 5)
(Z )-But-2-enyl 3-phenyl-3-dimethyl(phenyl)silylpropanoate
Quinoline (freshly distilled, 0.5 cm3) was added to a suspension
of 5% palladium on barium sulfate (4 mg) in dry methanol
(20 cm3) and the mixture stirred under hydrogen for 30 min,
after which time the catalyst had turned black. But-2-ynyl
3-phenyl-3-dimethyl(phenyl)silylpropanoate (0.35 g, 1.0 mmol)
in methanol (5 cm3) was added and the mixture stirred under
hydrogen at room temperature for 3 h, when TLC showed the
reaction to have gone to completion. The catalyst was removed
by filtration and solvent removed by evaporation. The residue
was taken into ether (5 cm3) and extracted with hydrochloric
acid solution (3 mol dmϪ3, 5 cm3). The aqueous layer was
washed with ether (3 × 5cm3) and the combined organic layers
washed with dilute aqueous hydrochloric acid (3 × 5 cm3)
and brine (5 cm3). The organic layer was dried (MgSO4) and
solvents removed under reduced pressure. The residue was
chromatographed (SiO2, light petroleum–EtOAc, 95 : 5) to give
the alkene (0.30 g, 89%) as an oil; Rf (light petroleum–EtOAc,
0.29; νmax (film)/cmϪ1 2995 (CH), 2241 (C᎐C), 1740 (C᎐O), 1250
᎐
᎐
᎐
(SiMe) and 1114 (SiPh); δH (400 MHz; CDCl3) 7.35 (5 H,
m, Ph), 7.18 (2 H, t, J 6.5, m-PhH), 7.07 (1 H, t, J 7.4, p-PhH),
6.94 (2 H, d, J 7.8, o-PhH) 4.45 (1 H, dq, J 15.3 and 2.4 CHA-
᎐
᎐
H ᎐CMe), 4.37 (1 H, dq, J 15.2 and 2.4, CH H ᎐CMe), 2.85
᎐
᎐
B
A
B
(1 H, dd, J 11.2 and 3.9, CHAHBCO2), 2.77 (1 H, dd, J 15.1 and
11.2, CHSi), 2.66 (1 H, dd, J, 15.0 and 3.9, CHAHBCO2), 1.79
᎐
(3 H, t, J 2.4, C᎐CMe), 0.23 (3 H, s, SiMe Me ) and 0.21 (3 H,
᎐
A
B
s, SiMeAMeB); δC (400 MHz, CDCl3) 172.5ϩ, 141.5ϩ, 136.5ϩ,
134.0 Ϫ, 129.5Ϫ, 128.0Ϫ, 127.8Ϫ, 127.5Ϫ, 125.0Ϫ, 83.0ϩ,
73.0ϩ, 52.5ϩ, 34.8ϩ, 32.0 Ϫ, 3.0 Ϫ, Ϫ4.0Ϫ and Ϫ6.0Ϫ; m/z
95 : 5) 0.22; νmax (film)/cmϪ1 3025 (CH), 2958 (CH), 1738 (C᎐O),
᎐
1250 (SiMe) and 1114 (SiPh); δH (250 MHz; CDCl3) 7.35 (5 H,
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
4015

View Article Online
m, Ph), 7.17 (2 H, t, J 7.0, m-PhH), 7.07 (1 H, t, J 7.3, p-PhH),
of diastereoselectivity in the reaction 7b
8b (Scheme 1), but
6.94 (2 H, d, J 7.8, o-PhH), 5.61 (1 H, dq, J 10.9 and 7.0, CH᎐
left us with the problem of finding out in what stereochemical
sense the reaction had taken place. We thank the EPSRC for a
maintenance award (MSB) and Dr David Fox for help with the
modelling calculations.
᎐
CHMe), 5.34 (1 H, dt, J 10.9 and 7.0, OCH2CH ), 4.44 (1 H, dd,
J 12.6 and 7.0, OCHAHB), 4.38 (1 H, dd, J 12.6 and 6.9,
OCHAHB), 2.85 (1 H, dd, J 10.7 and 4.5, CHAHBCO2), 2.75
(1 H, 14.8 and 10.7, CHSi), 2.63 (1 H, dd, J 14.8 and 4.3,
CH H CO ), 1.57 (1 H, d, J 7.0, C᎐CHCH ), 0.25 (3 H, s,
᎐
A
B
2
3
References
SiMeAMeB) and 0.22 (3 H, s, SiMeAMeB); δC (500 MHz, CDCl3)
172.7ϩ, 141.5ϩ, 136.2ϩ, 130.7Ϫ, 129.5Ϫ, 129.0Ϫ, 128.0Ϫ,
127.8Ϫ, 127.5Ϫ, 125.0Ϫ, 123.9Ϫ, 59.7ϩ, 34.5ϩ, 32.0Ϫ, 13.3,
Ϫ4.4Ϫ and Ϫ5.5Ϫ; m/z (ESI) 361.16 (100%, MNaϩ)(Found:
MNaϩ, 361.1598. C21H26O2Si requires MϩNa, 361.1600).
1 R. A. N. C. Crump, I. Fleming, J. H. M. Hill, D. Parker, N. L. Reddy
and D. Waterson, J. Chem. Soc., Perkin Trans. 1, 1992, 3277.
2 I. Fleming and J. D. Kilburn, J. Chem. Soc., Perkin Trans. 1, 1992,
3295.
3 I. Fleming and N. J. Lawrence, J. Chem. Soc., Perkin Trans. 1, 1992,
3309.
4 M. J. C. Buckle, I. Fleming and S. Gil, Tetrahedron Lett., 1992, 33,
4479; M. J. C. Buckle and I. Fleming, Tetrahedron Lett., 1993, 34,
2383.
5 I. Fleming, N. J. Lawrence, A. K. Sarkar and A. P. Thomas, J. Chem.
Soc., Perkin Trans. 1, 1992, 3303.
6 I. Fleming, G. R. Jones, N. D. Kindon, Y. Landais, C. P. Leslie,
I. T. Morgan, S. Peukert and A. K. Sarkar, J. Chem. Soc., Perkin
Trans. 1, 1996, 1171 See also ref. 25.
7 Fourteen papers in the May issue of, Chem. Rev., 1999, 99, p. 1067.
8 A. S. Cieplak, J. Am. Chem. Soc., 1981, 103, 4540.
9 I. Fleming, D. Hrovat and W. T. Borden, J. Chem. Soc., Perkin Trans.
2, 2001, 331 and references therein.
(Z )-But-2-enyl 3-phenylpropanoate
But-2-ynyl 3-phenylpropanoate (3.0 g, 14.8 mmol) was similarly
converted into the alkene (2.8 g, 92%), which was obtained as
an oil; Rf (light petroleum–EtOAc, 95 : 5) 0.22; νmax (film)/cmϪ1
3028 (CH), 2934 (CH), 1733 (CO), 1604 (PhH), 1496 (PhH) and
1454 (PhH); δH (400 MHz; CDCl3) 7.35–7.25 (2 H, m, Ph),
7.23–7.18 (3 H, m, Ph), 5.74 (1 H, m, OCH2CH ), 5.55 (1 H, m,
C᎐CHCH ), 4.66 (2 H, d, J 6.9, OCH ), 3.07 (2 H, t, J 7.6,
᎐
3
2
PhCH2), 2.65 (2 H, t, J 7.6, PhCH2CH2) and 1.71 (3 H, d, J 6.9,
C᎐CCH ).
᎐
3
10 R. J. Linderman and T. V. Anklekar, J. Org. Chem., 1992, 57, 5078;
J. Cossrow and S. D. Rychnovsky, Org. Lett., 2002, 4, 147.
11 I. Fleming, P. Maiti and C. Ramarao, Org. Biomol. Chem., 1,
10.1039/b305880h preceding paper I. Fleming and C. Ramarao,
Chem. Commun., 2000, 2185.
12 R. E. Ireland and R. H. Mueller, J. Am. Chem. Soc., 1972, 94, 5897;
For a review, see Y. Chai, S. Hong, H. A. Lindsay, C. M. McFarland
and M. C. McIntosh, Tetrahedron, 2002, 58, 2905.
13 T. Yamazaki, N. Shinohara, T. Kitazume and S. Sato, J. Org. Chem.,
1995, 60, 8140 See also T. Yamazaki, S. Takei, S. Kawashita,
T. Kitazume and T. Kubota, Org. Lett., 2001, 3, 2915.
14 A. Mukherjee, Q. Wu and W. J. le Noble, J. Org. Chem., 1994, 59,
3270.
15 J. J. Gajewski and J. Emrani, J. Am. Chem. Soc., 1984, 106, 5733.
16 R. M. Coates, B. D. Rogers, S. J. Hobbs, D. R. Peck and
D. P. Curran, J. Am. Chem. Soc., 1987, 109, 1160.
17 L. Kupczyk-Subotkowska, W. H. Saunders, Jr., H. J. Shine and
W. Subotkowski, J. Am. Chem. Soc., 1994, 116, 7088.
18 R. E. Ireland, P. Wipf and J. D. Armstrong, III, J. Org. Chem., 1991,
56, 650.
19 I. Fleming, A. Barbero and D. Walter, Chem. Rev., 1997, 97, 2063.
20 P. Beslin and S. Perrio, Tetrahedron, 1991, 47, 6275.
21 J. K. Cha and S. C. Lewis, Tetrahedron Lett., 1984, 25, 5263.
22 R. E. Ireland, R. H. Mueller and A. K. Willard, J. Am. Chem. Soc.,
1976, 98, 2868.
23 M. J. Kurth and C.-M. Yu, J. Org. Chem., 1985, 50, 1840.
24 S. Nowaczyk, C. Alayrac, V. Reboul, P. Metzner and
M.-T. Averbuch-Pouchot, J. Org. Chem., 2001, 66, 7841.
25 M. V. George, D. J. Peterson and H. Gilman, J. Am. Chem. Soc.,
1960, 82, 403.
26 I. Fleming and J. D. Kilburn, J. Chem. Soc., Perkin Trans. 1, 1992,
3295.
27 I. Fleming, A. K. Sarkar, M. J. Doyle and P. R. Raithby, J. Chem.
Soc., Perkin Trans. 1, 1989, 2023.
28 R. A. N. C. Crump, I. Fleming and C. J. Urch, J. Chem. Soc., Perkin
Trans. 1, 1994, 701.
1-Phenyl-2-methoxycabonyl-3-methylpent-5-ene 37 and 38
1-Phenyl-1-dimethyl(phenyl)silyl-2-methoxycarbonyl-3-methyl-
pent-5-ene (an 81 : 19 mixture of the diastereoisomers 34 and
35, 46 mg, 0.128 mmol) and TBAF (1.0 mol dmϪ3 in hexane,
0.26 cm3, 0.26 mmol) were stirred in THF (0.5 cm3) room tem-
perature for 12 h. Ether (2 cm3) and water (2 cm3) were added,
and the aqueous layer was washed with ether (2 × 2 cm3). The
organic layers were combined and washed with water (2 cm3)
and brine (1 cm3), the organic layer dried (MgSO4), and the
solvents removed under reduced pressure. The residue was
chromatographed (SiO2, light petroleum–EtOAc, 98 : 2) to
give the esters (21 mg, 75%, 37 : 38, 85 : 15) as an oil; Rf (light
petroleum–EtOAc, 95 : 5) 0.30; νmax (film)/cmϪ1 3028 (CH),
2959 (CH), 1737 (C᎐O), 1257 (SiMe) and 1119 (SiPh); δ (400
᎐
H
MHz; CDCl3) (major isomer 37) 7.30–7.22 (2 H, m, Ph), 7.20–
7.04 (3 H, m, Ph), 5.71 (1 H, ddd, J 17.1, 10.2 and 9.0, HC᎐
᎐
CH ), 5.10 (1 H, d, J 17.1, HC᎐CH H ), 5.08 (1 H, d, J 10.3,
᎐
2
A
B
HC᎐CH H ), 3.53 (3 H, s, CO Me), 2.88 (1 H, dd, J 13.7 and
᎐
A
B
2
4.5, PhCHACHB), 2.77 (1 H, dd, J 13.6 and 10.5, PhCHACHB),
2.54 (1 H, ddd, J 10.5, 8.4 and 4.4, CHCO2Me), 2.47 (1 H, sext,
J 7.5, MeCH ) and 1.04 (3 H, d, J 6.6, CHMe); (minor isomer
38, where different from the major isomer) 5.81 (1 H, ddd,
J 16.9, 10.2 and 8.0, HC᎐CH ), 5.05 (1 H, d, J 10.2, HC᎐
᎐
᎐
2
CH H ), 5.02 (1 H, d, J 17.0, HC᎐CH H ), 2.87 (1 H, dd,
᎐
A
B
A
B
J 13.7 and 10.2, PhCHACHB), 2.79 (1 H, dd, J 13.7 and 4.8,
PhCHACHB), 2.64 (1 H, ddd, J 10.3, 6.5 and 4.9, CHCO2Me)
and 1.12 (3 H, d, J 6.9, CHMe); δC (400 MHz, CDCl3) (major
isomer) 174.8ϩ, 141.1Ϫ, 139.4ϩ, 128.5Ϫ, 128.4Ϫ, 128.1Ϫ,
125.9Ϫ, 115.1ϩ, 53.3Ϫ, 50.9Ϫ, 40.7Ϫ, 36.4ϩ and 18.1Ϫ;
(minor isomer) 174.3ϩ, 140.5Ϫ, 139.4ϩ. 128.5Ϫ, 128.4Ϫ,
128.1Ϫ, 125.9Ϫ, 114.7ϩ, 53.0Ϫ, 50.9Ϫ, 40.0Ϫ, 35.2ϩ and
17.4ϩ; m/z (EI) 218.1 (25, Mϩ), 162.1 (48%, M Ϫ C4H8) 131.0
29 E. J. Corey and P. L. Fuchs, Tetrahedron Lett., 1972, 36, 3769.
30 G. B. Bachman, J. Am. Chem. Soc., 1933, 55, 4279.
31 E. Piers and A. V. Gavai, J. Org. Chem., 1990, 55, 2374.
32 M. Marakami, M. Hayashi and Y. Ito, J. Org. Chem., 1994, 25,
7910.
33 I. Fleming, I. T. Morgan and A. K. Sarkar, J. Chem. Soc., Perkin
Trans. 1, 1998, 2749.
[45%, M Ϫ (C4H8) Ϫ OMe] and 57.0 [100%, (CO2CH)2ϩ
(Found: Mϩ, 218.1305. C18H28SiO4 requires M, 218.1307).
]
34 H. M. Schmidt and J. F. Arens, Recl. Trav. Chim. Pays-Bas., 1967,
86, 1138.
35 S. Rajagopalan and G. Zweifel, Synth. Commun., 1984, 111.
36 I. Fleming and J. M. Mwaniki, J. Chem. Soc., Perkin Trans. 1, 1998,
1237.
Acknowledgements
We acknowledge the early work on this project by the late
Professor John Hill, who established the intriguingly high level
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 0 0 5 – 4 0 1 6
4016