Stereoselective synthesis of silacyclohexanols by silicon tethered Type II ene cyclisation

Article abstract of DOI:10.1016/S0040-4020(00)00737-7

Vinyl silane precursors for intramolecular ene reaction were prepared either by sequential organometallic substitution of appropriate silyl halides or by ring opening of oxasilacyclopentanes with 2-propenyllithium. The oxasilacyclopentane intermediates were prepared by free-radical cyclisation, intramolecular hydrosilylation, or intramolecular Diels-Alder reaction. Treatment of the ene precursors with methylaluminium dichloride resulted in the formation of silacyclohexanols with high stereoselectivity. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00737-7

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 8309±8320
Stereoselective Synthesis of Silacyclohexanols by Silicon Tethered
Type II Ene Cyclisation
a
a
b
Jeremy Robertson,a, Garry O'Connor, Tsarina Sardharwala and Donald S. Middleton
*
aDyson Perrins Laboratory, South Parks Road, Oxford OX1 3QY, UK
bDiscovery Chemistry, P®zer Central Research, Sandwich, Kent CT13 9NJ, UK
Received 4 July 2000; revised 1 August 2000; accepted 17 August 2000
AbstractÐVinyl silane precursors for intramolecular ene reaction were prepared either by sequential organometallic substitution of
appropriate silyl halides or by ring opening of oxasilacyclopentanes with 2-propenyllithium. The oxasilacyclopentane intermediates were
prepared by free-radical cyclisation, intramolecular hydrosilylation, or intramolecular Diels±Alder reaction. Treatment of the ene precursors
with methylaluminium dichloride resulted in the formation of silacyclohexanols with high stereoselectivity. q 2000 Elsevier Science Ltd.
All rights reserved.
Introduction
that had already been documented by the time we initiated
our own investigations in the area there were no reported
cases of silicon tethered ene reactions.5 We set out to
explore the reactions of aldehyde enophiles which were
expected to respond favourably to Lewis acid catalysis.6
The site of attachment of the silicon tether to the ene com-
ponent is open to variation so that both Type I and Type II7
variants could be explored; coupled with oxidative cleavage
of the C±Si bonds we envisaged that this method could
constitute a novel stereoselective approach to polyhydroxyl-
ated molecules (Scheme 1). This paper provides full experi-
mental details of our previously communicated8 results that
establish the methodology connected with the Type II
variant. In the accompanying paper we describe the current
status of our progress in identifying successful substrates for
the Type I variant.
The introduction in the mid 1980s of the temporary silicon
connection, in the context of free-radical cyclisation1 and
hydrosilylation,2 and of reliable procedures for the oxidative
cleavage of C±Si bonds with retention of con®guration,3 has
led to a proliferation of reports in which a silicon tether is
used to confer the rate and selectivity advantages of intra-
molecularity to equivalent intermolecular processes.4 Most
commonly the tethered components are linked to the silicon
atom through an oxygen or nitrogen atom giving rise to oxa-
and azasilacyclic intermediates; less common are examples
in which both interacting components are attached to silicon
through carbon atoms.
In spite of the many examples of silicon tethered reactions
Scheme 1.
Keywords: cyclisation; ene reactions; silicon and compounds; silicon heterocycles.
* Corresponding author. Tel.: 144-1865-275660; fax: 144-1865-275674; e-mail: jeremy.robertson@chem.ox.ac.uk
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00737-7

8310
J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
Scheme 2. Reagents: (i) Mg, THF then dimethyl(2-propenyl)silyl chloride; (ii) p-TsOH, aq. THF or HCl (aq., 1 M), acetone.
Results and Discussion
Synthesis of ene precursors
siloxanes were reactive to ring-opening with a diverse
range of organometallics.14 Our studies initiated with cyclic
siloxanes prepared by 5-exo-trig free-radical cyclisation of
precursors 10 and 11 (Scheme 3). The cyclisation of pre-
cursor 10 proceeded smoothly under standard conditions
(tributyltin hydride, AIBN, benzene) but, on a small scale,
removal of the solvent from the volatile product 12 proved
to be troublesome. Fortunately, ether was an acceptable
solvent for this reaction and a solvent-free sample of the
oxasilacyclopentane 12 could be obtained after distillation
at atmospheric pressure. Under these conditions the product
was contaminated with the directly reduced material,
1-trimethylsilyloxy-3-methylbut-2-ene, which generally
constituted ca. 15% of the product mixture. The cyclic
siloxane 13 obtained from precursor 111b was much less
volatile and could be obtained in a reasonably pure form,
unaccompanied by the direct reduction product, after
running the reaction in benzene. We were pleased to ®nd
that both oxasilacyclopentanes 12 and 13 were readily
opened with 2-propenyllithium to generate alcohols 14
and 15 in yields of around 40% from precursors 10 and
11; PDC oxidation gave the desired aldehydes 16 (74%)
and 17 (72%).
Our ®rst route (Scheme 2) to suitable ene precursors
involved displacement of chloride ion from chloro-
dimethyl(dimethylamino)silane9 with 2-propenyllithium10
followed by displacement with the Grignard reagents
derived from known bromides 1±311 after conversion of
the dimethylamino substituent to chloride.12 The so-formed
acetals 4±6 were hydrolysed under standard conditions to
give substrates 7, 8, and 9 in yields over the two steps of 47,
30, and 27%, respectively.
This route was effective in providing structurally simple
substrates for testing purposes in only two synthetic steps
but the overall yields were poor and it became clear that
applications to structurally more complex molecules would
be limited by the availability of appropriate organometallic
nucleophiles required for the second displacement at
silicon. A much more ¯exible approach was therefore
required.
Many published silicon tethered processes afford oxasila-
cyclopentane derivatives, rather labile intermediates that
are generally not isolated but characterised after either
direct oxidation affording diols or ring-opening with
methyllithium to form 3-trialkylsilylpropanol derivatives.
We hoped that if this latter reaction could be routinely
achieved with 2-propenyllithium (instead of methyllithium),
and the product alcohols oxidised to the corresponding
aldehydes, the synthesis of ene precursors would be greatly
facilitated.
The free-radical route made available ene precursors
bearing alkyl substitution a- to the aldehyde but, for
substrates bearing b-substitution, intramolecular hydrosilyl-
ation of silylated allylic alcohols2 became the method of
choice (Scheme 4). In our hands dimethyl- or diphenylsilane
derivatives of cinnamyl alcohol proved inconveniently
labile, therefore the known diisopropylsilane derivative 18
was prepared.15 This compound had been shown previously
to cyclise in 50% yield to siloxane 19 using [Rh((S,S)-
chiraphos)]2(ClO4)2 (2 mol%) in acetone at 258C for
48 h;15 we found a convenient alternative procedure that
employed Wilkinson's catalyst16 [Rh(PPh3)3Cl, 0.2 mol%]
in THF at re¯ux (3.5 h) to give siloxane 19 in essentially
quantitative yield. This, in turn, was opened (66%) with
2-propenyllithium and the product 20 oxidised as before
to give precursor 21 (64%).
A survey of the literature revealed just a few examples of the
ring-opening reaction of oxasilacyclopentanes with organo-
metallic reagents other than methyllithium.13 The most
direct precedent, however, was found in the investigations
of Corriu and co-workers who showed, during a study of
the stereochemistry of substitution at silicon, that cyclic
Ê
Scheme 3. Reagents: (i) Bu3SnH, AIBN, Et2O or PhH; (ii) 2-propenyllithium, THF; (iii) PDC, MS4A, CH2Cl2.

J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
8311
Ê
Scheme 4. Reagents: (i) (Ph3P)3RhCl (0.2 mol%), MS4A, THF; (ii) 2-propenyllithium, THF; (iii) PDC, MS4A, CH2Cl2.
Ê
Ê
Scheme 5. Reagents: (i) 2-propenyllithium, THF; (ii) PDC, MS4A, CH2Cl2.
Finally we wished to consider sequences in which the oxa-
silacyclopentane intermediates were generated as part of a
more complex conversion, an obvious example being a
silicon tethered Diels±Alder reaction of a vinyl silane
derivative of a dienyl alcohol.17 In the published work,
having performed the job of tethering the reaction, the
silicon atom is either removed by oxidation or rendered
inert by treatment with methyllithium. The idea of using
the cyclic siloxane intermediates to allow subsequent
carbon±carbon bond forming processes appealed to us as
a way of maximising the synthetic value of silicon tethered
reactions in general. Thus, in converting this proposal into
practice, a mixture of Si-endo-(22) and Si-exo-(23) adducts,
previously prepared by both Stork17a and Sieburth,17b and
obtained by us in a 65:35 ratio (unseparated), was treated
directly with 2-propenyllithium to give separable alcohols
24 and 25 in isolated yields (from the starting triene) of 40
and 27%, respectively (Scheme 5). The sequence was
completed by oxidation to generate ene precursors 26 and
27 without complication.
adjacent positive charge22 in an asynchronous ene reaction23
may be contributory factors.8a
These cyclisation conditions were found to be general;
applied to the methyl analogues 8 and 9 the stereochemical
aspects of the reaction were found to parallel those found by
Snider for the all-carbon analogues 2,5- and 3,5-dimethyl-
hex-5-enal.24 Thus, in the a-methyl case (8) both diastereo-
mers of the cyclised product were formed (13:1 cis:trans)
which were separable by careful chromatography. Assign-
ment of stereochemistry was based on the assumption that
the major conformer of the cis-adduct would be that shown
(B) in Fig. 1 wherein the substituent with the smaller
A-value25 occupies the axial site and the destabilising syn-
pentane interaction (in A) is avoided. The CHOH resonance
1
in the H NMR spectrum appears at d 3.77 ppm (ddd,
Jˆ4.4, 2.3, 1.9 Hz) for the cis-isomer 29 and at d
3.16 ppm (td, Jˆ10.1, 3.7 Hz) for the trans-isomer 30
which indicate, respectively, predominantly axial and
equatorial hydroxyl groups. Under the same conditions
b-methyl precursor 9 cyclised with a higher stereo-
selectivity with only resonances corresponding to the
Ene reactions
With eight ene precursors in hand, bearing alkyl substituents
a- and/or b- to the aldehyde, a study of the stereochemical
features of the cyclisation could be pursued and reasonable
comparisons drawn with all-carbon analogues. Conditions
for the ene reaction were optimised with the unsubstituted
precursor 7. Early results were disappointing with no signs
of product formation at dry-ice/acetone temperatures either
with dimethylaluminium chloride18 or titanium(IV) chloride.
Higher temperatures led to complex product mixtures.
Fortunately, treatment of a DCM solution of substrate
7 with the more potent Lewis acid methylaluminium
dichloride19 (1.5 equiv., 2788C, 6±7 h) resulted in clean
conversion to a single compound assigned as the silacyclo-
hexanol 28 (80% isolated yield, Table 1). In comparison
with the results of Andersen,20 in which 4,4,5-trimethyl-
hex-5-enal was shown to cyclise within 0.5 h at 2728C
(diethylaluminium chloride), the reaction of the sila-ana-
logue 7 is signi®cantly slower. We speculate that the longer
C±Si bonds21 and the reduced ability for silicon to stabilise
Table 1.

8312
J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
an axial methyl group, may be ruled out. In the cyclisation
of the trans-isomer 27 the conformational possibilities are
more clearly de®ned and the silabicycle 36 was predicted.
These predictions were con®rmed experimentally with 88
and 48% yields of adducts 35 and 36 being obtained under
the standard conditions.
Figure 1.
1
trans-product 31 being visible in the H NMR spectrum
(500 MHz) of the crude material [d 4.01 (ca. tt, Jˆ5.9,
2.6 Hz CHOH)]. Similar trends were observed for the a-iso-
propyl (16) and a-benzyl (17) precursors which both
cyclised with high cis-stereoselectivity (32, 21:1 and 33,
.98:,2, respectively). Finally, the b-phenyl precursor 21
also cyclised successfully, the isopropyl substituents not
markedly affecting the reaction rate, and, as with b-methyl
substrate 9, only the trans-product 34 was observed. In each
case stereochemical assignment was possible either by
coupling constant analysis of the CHOH resonance or of
the allylic CH2 resonances which typically showed small
(Jˆ,6 Hz) vicinal couplings indicating an axial hydroxyl
group in adducts 29 and 31±34.
Conclusions
We have developed the silicon tethered Type II ene cycli-
sation to the point where we have reliable methods for the
preparation of precursors bearing substitution at either or
both the linking carbon atoms and have shown that the
ene cyclisations follow a predictable stereochemical course.
With this methodology in hand we are in a position to
address synthetic applications and will report on the
development of this chemistry in due course.
Experimental
General
These stereochemical results may be rationalised by a
transition state model in which both isomers are obtained
through distorted chair conformations, the favoured confor-
mation having the alkyl substituent equatorially disposed.
The less favoured transition state conformer could be either
chair-like with axial alkyl substituents23,24 or the alkyl
substituents could remain in equatorial sites but the C±CO
and Si±Cv bonds could rotate by approximately 1808 with
respect to the favoured conformer to give a boat-like confor-
mation.26 These possibilities are sketched in Fig. 2.
1H and 13C NMR spectra were recorded on Varian Gemini
200, Bruker AC 200, or Bruker AM 500 spectrometers with
1H assignments being made on the basis of a combination of
chemical shift, coupling constant, COSY, and NOE data as
appropriate; 13C assignments were supported by DEPT
experiments. Coupling constants (J) are quoted to the
nearest 0.1 Hz. Infrared spectra were recorded on either
Perkin±Elmer 1750 or Perkin±Elmer Paragon 1000 FT
spectrometers as thin ®lms unless stated otherwise. Mass
spectra were recorded on VG Micromass ZAB 1F, Masslab
20±250, VG Platform, or VG TRIO-1 spectrometers.
Accurate mass data were obtained by the EPSRC National
Mass Spectrometry Service Centre. All solvents and
commercially available reagents were dried and puri®ed
according to standard procedures. `Petrol' refers to the
fraction of light petroleum ether boiling in the range
30±408C. Bromoacetals 1±3 were prepared essentially
according to the method of Ayers11a but with the inclusion
of dicinnamalacetone as an indicator;11b Diels±Alder
Applying these considerations to the ene cyclisation of the
more complex precursors 26 and 27 led to the expectation
that the cis-isomer 26 should cyclise to give silabicycle 35
through a conformation in which the cyclohexenyl methyl
substituent is pseudo-equatorial in a favourable half-chair
conformation with the forming ring adopting a chair-like
arrangement (Scheme 6). A boat-like arrangement would
be required in order to form the hydroxyl epimer if the
alternative half-chair cyclohexene conformation, having
Figure 2.
Scheme 6. Reagents: MeAlCl2, CH2Cl2 (allylic methyl group in products omitted for clarity).

J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
8313
adducts 22 and 23 were prepared by the method of
Stork17a and Sieburth.17b All experiments involving air-
sensitive reagents were performed under an argon
atmosphere.
vacuo and the resulting oil carried onto the next step crude.
An analytical sample was obtained by column chroma-
tography (44:1 petrol:ether) to yield acetal 5 as a colourless
oil. Rf 0.61 (3:1 petrol:ether); Accurate mass: Found
185.1362, C10H21OSi (MH12MeOH) requires 185.13616;
1,1-Dimethoxy-4,4,5-trimethyl-4-silahex-5-ene (4). To a
warmed (35±408C) suspension of Mg turnings (51 mg,
2.09 mmol) in THF (0.4 cm3) was added dropwise a
solution of bromoacetal 111 (0.3 cm3, 2.2 mmol) in THF
(3 cm3) and the mixture stirred for 1.75 h. To a cooled
(2788C) solution of t-butyllithium (2.7 cm3 of a 1.7 M solu-
tion in pentane, 4.60 mmol) in THF (4 cm3) was added
dropwise 2-bromopropene (0.21 cm3, 2.3 mmol). After 1 h
chlorodimethyl(dimethylamino)silane (0.34 cm3, 2.2 mmol)
was added and the mixture stirred for 5 min at 2788C then
at rt for 15 min. Acetyl chloride (0.16 cm3, 2.2 mmol) was
added dropwise and the mixture stirred for 1 h. The
previously prepared Grignard reagent was added to the
cooled (08C) alkenylsilane mixture and stirred for 5 min at
08C then at 35±408C for 15 h. The mixture was added to a
mixture of water (20 cm3) and ether (5 cm3) then 1 M hydro-
chloric acid was added dropwise until the emulsions had
dispersed (ca. 0.5 cm3). The aqueous layer was separated,
extracted with ether (3£8 cm3) and the combined organic
portions were washed with brine (15 cm3), dried (mag-
nesium sulphate) and concentrated in vacuo. The resulting
oil (which could also be carried onto the next step crude)
was puri®ed by column chromatography (34:1 petrol:ether)
to yield acetal 4 as a colourless oil (218 mg, 52%). Rf
0.55 (3:1 petrol:ether); Accurate mass: Found 171.1205,
n
max/cm21 2955s, 2911s, 1449m, 1249m, 1122s, 1107s,
1079s, 1059s, 920m, 834s; dH (500 MHz; CDCl3) 0.10
and 0.11 (2£3H, 2£s, SiMe2), 0.42 (1H, dd, Jˆ15.0,
10.6 Hz) and 0.90 (1H, dd, Jˆ15.0, 7.5 Hz, SiCH2), 0.92
(3H, d, Jˆ6.8 Hz, MeCH), 1.82±1.88 (1H, m, MeCH), 1.83
(3H, t, Jˆ1.4 Hz, MeCv), 3.34 and 3.35 (2£3H, 2£s,
HC(OMe)2), 3.90 (1H, d, Jˆ6.1 Hz, HC(OMe)2), 5.26
(1H, dq, Jˆ3.3, 1.4 Hz) and 5.57 (1H, dq, Jˆ3.3, 1.4 Hz,
vCH2); dC (125 MHz; CDCl3) 23.0, 22.8, 16.9, 17.2,
22.5, 32.3, 54.1, 54.2, 110.4, 125.0, 147.5; m/z (CI) 185
(MH12MeOH, 10%), 169 (5), 153 (5), 143 (5), 106 (25),
89 (30), 75 (100).
1,1-Dimethoxy-3,4,4,5-tetramethyl-4-silahex-5-ene (6).
To a cooled (2788C) solution of t-butyllithium (1.3 cm3
of a 1.7 M solution in pentane, 2.26 mmol) in THF
(3 cm3) was added dropwise 2-bromopropene (0.1 cm3,
1.13 mmol). After 1 h chlorodimethyl(dimethylamino)si-
lane (0.17 cm3, 1.08 mmol) was added and the mixture stir-
red for 5 min at 2788C and at rt for 25 min. Acetyl chloride
(77 mL, 1.08 mmol) was added dropwise and the mixture
stirred for 1.25 h. To a suspension of powdered Mg (87 mg,
3.56 mmol) in THF (1 cm3) at rt was added dropwise 1,2-
dibromoethane (28 mL, 0.32 mmol) and the mixture stirred
for 50 min. A solution of acetal 3 (0.5 cm3, 3.24 mmol) in
THF (2 cm3) was added dropwise and the mixture stirred for
2.5 h after which time the chlorosilane solution was added
by cannula to the Grignard solution at rt then stirred for
15 h. The reaction mixture was added to a mixture of 1 M
hydrochloric acid (15 cm3) and ether (10 cm3), extracted
with ether (3£10 cm3) and the combined organic portions
washed with brine (20 cm3), dried (magnesium sulphate)
and concentrated in vacuo. The resulting oil was puri®ed
by column chromatography (39:1 petrol:ether) to yield ace-
tal 6 as a colourless oil (69 mg, 30%). Rf 0.46 (3:1 petrol:
ether); Accurate mass: Found 185.1362, C10H21OSi (MH12
MeOH) requires 185.13616; nmax/cm21 2952s, 1450m,
1376m, 1250m, 1196m, 1124s, 1079m, 1055s, 961m,
921m, 834s, 816s, 770m; dH (500 MHz; CDCl3) 0.06 (6H,
s, SiMe2), 0.89±0.94 (1H, m, MeCH), 0.97 (3H, d, Jˆ
6.9 Hz, MeCH), 1.32 (1H, ddd, Jˆ14.3, 10.8, 4.1 Hz) and
1.74±1.79 (1H, ddd, Jˆ14.3, 7.7, 3.3 Hz, CH2), 1.82 (3H, t,
Jˆ1.5 Hz, MeCv), 3.29 and 3.33 (2£3H, 2£s, HC(OMe)2),
4.50 (1H, dd, Jˆ7.7, 4.1 Hz, HC(OMe)2), 5.26 (1H, dq,
Jˆ3.3, 1.5 Hz) and 5.62 (1H, dq, Jˆ3.3, 1.5 Hz, vCH2);
dC (125 MHz; CDCl3) 25.9, 25.7, 13.7, 14.1, 23.0, 34.0,
51.6, 53.3, 103.4, 126.0, 145.8; m/z (CI) 202
(MNH14 2MeOH, 5%), 185 (40), 169 (15), 153 (15), 143
(30), 125 (10), 106 (35), 95 (15), 89 (50), 86 (20), 81
(20), 75 (100).
C9H19OSi (MH12MeOH) requires 171.12051; nmax
/
cm21 2947s, 2829s, 1449w, 1249m, 1162m, 1125s,
1064s, 920m, 839s, 773m; dH (500 MHz; CDCl3) 0.75
(6H, s, SiMe2), 0.59±0.62 (2H, m, SiCH2), 1.54±1.59
(2H, m, CH2), 1.81 (3H, t, Jˆ1.5 Hz, MeCv), 3.31
(6H, s, HC(OMe)2), 4.28 (1H, t, Jˆ5.7 Hz,
HC(OMe)2), 5.25 (1H, dq, Jˆ3.3, 1.5 Hz) and 5.58
(1H, dq, Jˆ3.3, 1.5 Hz, vCH2); dC (125 MHz; CDCl3)
24.1, 8.9, 22.5, 26.7, 52.7, 106.3, 125.3, 146.6; m/z (CI)
171 (MH12MeOH, 15%), 156 (5), 129 (10), 106 (20), 89
(30), 75 (100).
1,1-Dimethoxy-2,4,4,5-tetramethyl-4-silahex-5-ene (5).
To a cooled (2788C) solution of t-butyllithium (6.3 cm3
of a 1.7 M solution in pentane, 10.7 mmol) in THF
(9 cm3) was added dropwise 2-bromopropene (0.48 cm3,
5.33 mmol).
After
1 h
chlorodimethyl(dimethyl-
amino)silane (0.78 cm3, 5.07 mmol) was added and the
mixture stirred for 5 min at 2788C and at rt for 30 min.
Acetyl chloride (0.36 cm3, 5.07 mmol) was added dropwise
and the mixture stirred for 1 h. To a suspension of powdered
Mg (1.6 g, 66 mmol) in THF (8 cm3) at rt was added drop-
wise 1,2-dibromoethane (0.57 cm3, 6.6 mmol) and the
mixture stirred for 30 min. A solution of bromoacetal 2
(4.3 g, 21.8 mmol) in THF (5 cm3) was added dropwise
and the mixture stirred for 1 h after which time the
chlorosilane solution was added by cannula to the Grignard
solution at rt. The mixture was stirred at rt for 2 h and at 35±
408C for 15 h. The mixture was added to a mixture of 1 M
hydrochloric acid (50 cm3) and ether (15 cm3), separated
and the aqueous layer extracted with ether (3£20 cm3).
The combined organic portions were washed with brine
(20 cm3), dried (magnesium sulphate) and concentrated in
4,4,5-Trimethyl-4-silahex-5-enal (7). A mixture of crude
acetal 4 (1.13 g, 5.59 mmol), isopropanol (1 cm3), water
(5 cm3) and PTSA (105 mg, 0.55 mmol) in THF (12 cm3)
was heated at re¯ux for 1.5 h. The reaction mixture was
added to a mixture of water (10 cm3), saturated sodium
hydrogen carbonate solution (10 cm3) and ether (10 cm3)
and the separated aqueous layer was extracted with ether

8314
J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
(3£10 cm3). The combined organic portions were washed
with brine (10 cm3), dried (magnesium sulphate) and
concentrated in vacuo. The resulting oil was puri®ed by
column chromatography (39:1 petrol:ether) to yield
aldehyde 7 as a colourless oil (410 mg, 47% based on
Mg). Rf 0.49 (3:1 petrol:ether); Accurate mass: Found
m/z (CI) 171 (MH1, 90%), 155 (35), 148 (50), 129 (100),
116 (55), 99 (35), 95 (75), 91 (65), 85 (65), 74 (45), 58 (25).
1-(Bromomethyl)dimethylsilyloxy-3-methylbut-2-ene (10).
To a cooled (08C) solution of DMAP (61 mg, 0.5 mmol),
triethylamine (1.3 cm3, 9 mmol), and (bromomethyl)chloro-
dimethylsilane (1.2 cm3, 9 mmol) in DCM (12 cm3) was
added dropwise 3-methyl-2-butenol (1.0 cm3, 10 mmol).
The mixture was allowed to warm up to rt then stirred for
18 h. The solvent was removed in vacuo and the resultant
paste triturated with petrol (4£10 cm3) then the combined
extracts were ®ltered through Celitew. The solvent was
removed in vacuo and the residual oil puri®ed by distillation
(Kugelrohr, bath temperature 508C, 2 mm Hg) to give silane
10 as a colourless oil (1.69 g, 80%). Rf 0.71 (1:1 petrol:
ether); Accurate mass: Found 254.0576, C8H21BrNOSi
(MNH14 ) requires 254.05762; nmax/cm21 2970m, 2933m,
1676w, 1447w, 1382w, 1254m, 1120m, 1067s, 838s; dH
(500 MHz; CDCl3) 0.28 (6H, s, SiMe2), 1.67 and 1.74
(2£3H, 2£s, Me2Cv), 2.49 (2H, s, CH2Br), 4.21 (2H, d,
Jˆ6.9 Hz, CH2O), 5.33 (1H, ca. tsept, Jˆ6.9, 1.4 Hz,
vCH); dC (125 MHz; CDCl3) 23.1, 16.1, 17.9, 25.8,
60.1, 123.3, 135.5; m/z (CI) 256 (M(81Br)NH41, 5%), 254
(M(79Br)NH14 , 5), 223 (32), 221 (30), 170 (19), 168 (17), 92
(21), 86 (100), 69 (11).
174.1314, C8H20NOSi (MNH14 ) requires 174.13141; nmax
/
cm21 3048w, 2955m, 2901m, 2811m, 2716w, 1726s,
1449m, 1413m, 1251m, 1178m, 1035w, 938m, 923m,
880m, 838s, 690w, 675w, 624w; dH (500 MHz; CDCl3)
0.10 (6H, s, SiMe2), 0.83±0.87 (2H, m, SiCH2), 1.81 (3H,
t, Jˆ1.5 Hz, MeCv), 2.35±2.39 (2H, m, CH2), 5.26 (1H,
dq, Jˆ3.1, 1.5 Hz) and 5.62 (1H, dq, Jˆ3.1, 1.5 Hz, vCH2),
9.75 (1H, t, Jˆ1.8 Hz, CHO); dC (125 MHz; CDCl3) 24.2,
6.2, 22.4, 38.3, 125.9, 145.8, 202.9; m/z (CI) 174 (MNH14 ,
15%), 157 (MH1, 10), 141 (55), 115 (100), 99 (25), 90 (25),
76 (40), 74 (40), 73 (35), 59 (25).
2,4,4,5-Tetramethyl-4-silahex-5-enal (8). A mixture of
crude acetal 5 (1.1 g, 5.09 mmol) and 1 M hydrochloric
acid (7.6 cm3) in acetone (10 cm3) was stirred at rt for 2 h.
The reaction mixture was added to saturated sodium hydro-
gen carbonate solution (40 cm3) and extracted with ether
(3£20 cm3). The combined organic portions were washed
with brine (25 cm3), dried (magnesium sulphate) and
concentrated in vacuo. The resulting oil was puri®ed by
column chromatography (49:1 petrol:ether) to yield
aldehyde 8 as a colourless oil (260 mg, 30% from chloro-
dimethyl(dimethylamino)silane). Rf 0.61 (3:1 petrol:ether);
Accurate mass: Found 171.1205, C9H19OSi (MH1) requires
171.12051; nmax/cm21 2958s, 1727s, 1450m, 1257m,
1058m, 923m, 836s; dH (500 MHz; CDCl3) 0.13 (6H, s,
SiMe2), 0.57 (1H, dd, Jˆ14.9, 8.9 Hz) and 1.06 (1H, dd,
Jˆ14.9, 5.4 Hz, SiCH2), 1.11 (3H, d, Jˆ7.0 Hz, MeCH),
1.82 (3H, t, Jˆ1.5 Hz, MeCv), 2.35±2.40 (1H, m,
MeCH), 5.28 (1H, dq, Jˆ3.3, 1.5 Hz) and 5.61 (1H, dq,
Jˆ3.3, 1.5 Hz, vCH2), 9.55 (1H, d, Jˆ1.8 Hz, CHO); dC
(125 MHz; CDCl3) 23.1, 15.6, 16.1, 22.4, 42.5, 125.9,
146.3, 204.7; m/z (CI) 188 (MNH14 , 10%), 171 (MH1,
15), 155 (30), 129 (100), 116 (20), 99 (15), 95 (20), 91
(20), 74 (30), 58 (30).
(E)-1-(Bromomethyl)dimethylsilyloxy-3-phenylprop-2-
ene (11).1b To a cooled (08C) solution of DMAP (61 mg,
0.5 mmol), triethylamine (1.3 cm3, 9 mmol), and (bromo-
methyl)chlorodimethylsilane (1.3 cm3, 9 mmol) in DCM
(12 cm3) was added dropwise a solution of cinnamyl alcohol
(1.34 g, 10 mmol) in DCM (2 cm3). The mixture was
allowed to warm to rt and stirred for 18 h. The solvent
was removed in vacuo and the resultant paste triturated
with petrol (4£10 cm3). The extracts were combined and
®ltered through Celitew then concentrated in vacuo and
the residual oil distilled (Kugelrohr, bath temperature
1708C, 2 mm Hg) to give silyl ether 111b as a colourless
oil (2.21 g, 86%). Rf 0.69 (1:1 petrol:ether); nmax/cm21
3083w, 3060m, 3027m, 2961m, 2936m, 2859m, 1599w,
1495m, 1450m, 1380m, 1255s, 1116s, 1059s, 966s, 840s,
733s, 692s; dH (200 MHz; CDCl3) 0.32 (6H, s, Me2Si), 2.52
(2H, s, CH2Br), 4.40 (2H, dd, Jˆ5.5 Hz, 1.5 Hz, CH2O).
6.29 (1H, dt, Jˆ16.0, 5.5 Hz, PhCHvCH), 6.60 (1H, dt,
Jˆ16.0, 1.5 Hz, PhCHvCH), 7.24±7.41 (5H, m, Ph); m/z
(CI) 286 (3%), 284 (3), 134 (26), 117 (100).
3,4,4,5-Tetramethyl-4-silahex-5-enal (9). A mixture of
pure acetal 6 (34 mg, 0.16 mmol) and 1 M hydrochloric
acid (0.24 cm3) in acetone (1 cm3) was stirred at rt for
2.5 h. The mixture was added to saturated sodium hydrogen
carbonate solution (10 cm3) and extracted with ether
(3£5 cm3). The combined organic portions were washed
with brine (10 cm3), dried (magnesium sulphate) and
concentrated in vacuo. The resulting oil was puri®ed by
column chromatography (44:1 petrol:ether) to yield
aldehyde 9 as a colourless oil (24 mg, 89%). Rf 0.45 (3:1
petrol:ether); Accurate mass: Found 171.1205, C9H19OSi
(MH1) requires 171.12051; nmax/cm21 3049w, 2957s,
2710m, 1728s, 1451m, 1412w, 1254s, 1059m, 938m,
924m, 835s, 817s, 775m, 688w; dH (500 MHz; CDCl3)
0.08 and 0.09 (2£3H, 2£s, SiMe2), 0.98 (3H, d, Jˆ7.4 Hz,
MeCH), 1.34±1.42 (1H, m, MeCH), 1.82 (3H, t, Jˆ1.5 Hz,
MeCv), 2.16 (1H, ddd, Jˆ16.3, 10.9, 3.3 Hz) and 2.44 (1H,
ddd, Jˆ16.3, 3.6, 1.1 Hz, CH2), 5.27 (1H, dq, Jˆ3.2,
1.5 Hz) and 5.65 (1H, dq, Jˆ3.2, 1.5 Hz, vCH2), 9.73
(1H, dd, Jˆ3.3, 1.1 Hz, CHO); dC (125 MHz; CDCl3)
25.9, 25.7, 12.7, 14.5, 22.9, 46.0, 126.7, 145.0, 203.0;
1,1-Dimethyl-4-isopropyl-2-oxa-1-silacyclopentane (12).
To a solution of silyl allyl ether 10 (1.19 g, 5 mmol) and
AIBN (82 mg, 0.5 mmol) in degassed ether (120 cm3)
heated at re¯ux was added a solution of tributyltin hydride
(2.0 cm3, 7.5 mmol) and AIBN (82 mg, 0.5 mmol) in ether
(18 cm3) over a period of 48 h (syringe pump). Heating was
maintained for a further 2 h then the ether was removed by
distillation at atmospheric pressure. The residue was
distilled (Kugelrohr, bath temperature 1508C, 220 mm Hg)
to give an oil (560 mg, 71%) consisting of the hydrolytically
labile oxasilacyclopentane 12 and the direct reduction
product, 3-methyl-1-(trimethylsilyloxy)but-2-ene, in
a
ratio of 6.6:1. Data for 12: dH (200 MHz; CDCl3) 0.18
and 0.24 (2£3H, 2£s, SiMe2), 0.36 (1H, dd, Jˆ14.0,
11.5 Hz) and 0.90±1.05 (1H, m, CH2Si), 0.88 and 0.95
(2£3H, 2£d, Jˆ6.5 Hz, Me2C), 1.42 (1H, apparent oct,

J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
8315
Jˆ6.5 Hz, Me2CH), 1.66±1.89 (1H, m, PriCH), 3.36 (1H,
dd, Jˆ10.0, 8.5 Hz) and 4.08 (1H, dd, Jˆ10.0, 6.5 Hz,
CH2O); m/z (CI) 159 (MH1, 100%), 141 (32).
(magnesium sulphate) and the solvent removed in vacuo.
Puri®cation by column chromatography (9:1 petrol:ether)
afforded the alcohol 15 as a colourless oil (148 mg, 39%
based on silyl ether 11). Rf 0.44 (1:1 petrol:ether); Accurate
mass: found 266.1944, C15H28NOSi (MNH14 ) requires
266.19401; nmax/cm21 3350s, 3085m, 3047m, 3027m,
2952s, 1604m, 1496s, 1453s, 1248s, 1051s, 1030s, 920s,
835s, 787s, 700s; dH (500 MHz; CDCl3) 0.13 and 0.14
(2£3H, 2£s, Me2Si), 0.68 (1H, dd, Jˆ14.9, 6.5 Hz) and
0.74 (1H, dd, Jˆ14.9, 7.2 Hz, CH2Si), 1.38 (1H, br s,
OH), 1.83 (3H, t, Jˆ1.4 Hz, MeCv), 1.95±1.98 (1H, m,
BnCH), 2.64 (1H, dd, Jˆ13.5, 6.3 Hz) and 2.70 (1H, dd,
Jˆ13.5, 8.0 Hz, PhCH2), 3.46±3.48 (2H, m, CH2OH), 5.31
(1H, dq, Jˆ3.2, 1.4 Hz) and 5.62 (1H, dq, Jˆ3.2, 1.4 Hz,
vCH2), 7.19±7.23 (3H, m) and 7.28±7.32 (2H, m, Ph); dC
(125 MHz; CDCl3) 23.1, 22.9, 16.5, 22.5, 39.2, 40.6, 66.8,
125.4, 125.9, 128.3, 129.2, 140.7, 147.3; m/z (CI) 266
(MNH14 , 100%), 207 (58), 189 (28), 116 (57), 91 (69), 74 (42).
5-Hydroxymethyl-2,3,3,6-tetramethyl-3-silahept-1-ene
(14). To a cooled (2788C) solution of t-butyllithium
(4.8 cm3 of a 1.7 M solution in pentane, 8.16 mmol) in
THF (6.5 cm3) was added dropwise 2-bromopropene
(0.36 cm3, 4.1 mmol) and the mixture was stirred for 1 h.
A solution of impure oxasilacyclopentane 12 (308 mg,
1.95 mmol) in THF (3 cm3) was added dropwise; the
mixture was stirred for 3 h at 2788C then allowed to
warm up to rt and stirred for a further 2.5 h. Water
(20 cm3) was added and the product extracted with ether
(3£20 cm3). The combined organic portions were washed
with brine (20 cm3) then dried (magnesium sulphate) and
the solvent removed in vacuo. The yellow oil was puri®ed
by column chromatography (8:1 petrol:ether) to afford the
alcohol 14 as a colourless oil (190 mg, 61% based on the
purity of 12). Rf 0.47 (1:1 petrol:ether); Accurate mass:
Found 159.1202, C8H19OSi (MH12propene) requires
159.12051; Found: C, 65.64; H, 12.51; C11H24OSi requires
C, 65.93; H, 12.07%; nmax/cm21 3334m, 3048m, 2956s,
1466m, 1447m, 1386m, 1368m, 1248s, 1045s, 920s, 836s;
dH (500 MHz; CDCl3) 0.10 and 0.11 (2£3H, 2£s, SiMe2),
0.43 (1H, dd, Jˆ15.0, 9.3 Hz) and 0.60 (1H, dd, Jˆ15.0,
4.1 Hz, CH2Si), 0.85 and 0.88 (2£3H, 2£d, Jˆ6.9 Hz,
Me2C), 1.34 (1H, br s, OH), 1.51±1.57 (1H, m, PriCH),
1.83 (3H, t, Jˆ1.5 Hz, MeCv), 1.85 (1H, septd, Jˆ6.9,
4.0 Hz, Me2CH), 3.47 (1H, dd, Jˆ10.9, 4 Hz) and 3.50
(1H, dd, Jˆ10.9, 4.9 Hz, CH2OH), 5.27 (1H, dq, Jˆ3.3,
1.5 Hz) and 5.59 (1H, dq, Jˆ3.3, 1.5 Hz, vCH2); dC
(125 MHz; CDCl3) 23.2, 23.0, 12.0, 17.9, 19.7, 22.6,
29.2, 42.6, 65.4, 125.3, 147.5; m/z (CI) 218 (MNH14 , 9%),
201 (MH1, 9), 185 (15), 176 (11), 159 (100), 141 (15), 118
(54), 101 (56), 99 (60), 92 (72), 75 (86), 59 (31).
5-Formyl-2,3,3,6-tetramethyl-3-silahept-1-ene (16). To a
Ê
cooled mixture of alcohol 14 (290 mg, 1.45 mmol) and 4 A
molecular sieves (1.45 g) in DCM (7 cm3) was added PDC
(817 mg, 2.17 mmol). The mixture was allowed to warm to
rt and stirring continued for 16 h. After dilution with ether
(15 cm3) the mixture was ®ltered through Celitew, washing
through with ether (2£20 cm3), and the ®ltrate concentrated
in vacuo. Puri®cation by column chromatography (8:1
petrol:ether) afforded the aldehyde 16 as a colourless oil
(213 mg, 74%). Rf 0.71 (1:1 petrol:ether); Accurate mass:
Found 199.1518, C11H23OSi (MH1) requires 199.15181;
n
max/cm21 3049w, 2960s, 2875m, 1727s, 1464w, 1370w,
1250m, 922m, 838s; dH (500 MHz; CDCl3) 0.07 and 0.08
(2£3H, 2£s, Me2Si), 0.65 (1H, dd, Jˆ14.9, 3.1 Hz) and 0.96
(1H, dd, Jˆ14.9, 10.1 Hz, CH2Si), 0.92 and 0.96 (2£3H,
2£d, Jˆ6.8 Hz, Me2C), 1.81 (3H, t, Jˆ1.5 Hz, MeCv),
2.00 (1H, septd, Jˆ6.8, 5.0 Hz, Me2CH), 2.22 (1H, apparent
ddt, Jˆ10.1, 5.0, 3.1 Hz, CHCHO), 5.25 (1H, dq, Jˆ3.2,
1.5 Hz) and 5.59 (1H, dq, Jˆ3.2, 1.5 Hz, vCH2), 9.60 (1H,
d, Jˆ3.1 Hz, CHO); dC (125 MHz; CDCl3) 23.5, 23.2, 9.7,
19.0, 19.8, 22.4, 30.2, 53.9, 125.8, 146.4, 205.2; m/z (CI)
216 (MNH14 , 100%), 199 (MH1, 17), 198 (23), 183 (80),
157 (100), 141 (21), 116 (78), 99 (94), 91 (41), 74 (46), 59
(28).
2-Benzyl-4,4,5-trimethyl-4-silahex-5-en-1-ol (15). To a
solution of silyl ether 11 (1.0 g, 3.51 mmol) and AIBN
(29 mg, 0.18 mmol) in degassed benzene (65 cm3) heated
at re¯ux was added a solution of tributyltin hydride
(1.42 cm3, 5.26 mmol) and AIBN (29 mg, 0.18 mmol) in
benzene (5 cm3) over 2 h (syringe pump). Heating was
maintained for a further 2.5 h then the solvent was removed
in vacuo to give a pale brown oil that was distilled (Kugel-
rohr, bath temperature 1508C, 20 mm Hg) to give the hydro-
lytically labile oxasilacyclopentane 13 as a colourless oil
(1.16 g, impure) that was used directly in the next reaction.
dH (200 MHz; CDCl3) 0.16 and 0.25 (2£3H, 2£s, Me2Si),
0.47 (1H, dd, Jˆ14.5, 10.2 Hz, CHHSi; second CHHSi
proton obscured by tin residues), 2.25±2.42 (1H, m,
BnCH), 2.57 (1H, dd, Jˆ13.3, 7.5 Hz) and 2.70 (1H, dd,
Jˆ13.3, 7.0 Hz, PhCH2), 3.46 (1H, apparent t, Jˆ9.3 Hz)
and 3.95 (1H, dd, Jˆ9.3, 6.0 Hz, CH2O), 7.12±7.37 (5H, m,
Ph). 2-Bromopropene (0.45 cm3, 5.09 mmol) was added
dropwise to a cooled (2788C) solution of t-butyllithium
(6 cm3 of a 1.7 M solution in pentane, 10.2 mmol) in THF
(8 cm3) and the mixture was stirred for 1 h. A solution of the
impure oxasilacyclopentane 13 (500 mg) in THF (1 cm3)
was added dropwise and the mixture allowed to warm to
rt over 16 h. Water (20 cm3) was added and the product
extracted with ether (3£20 cm3). The combined organic
portions were washed with brine (25 cm3) then dried
2-Benzyl-4,4,5-trimethyl-4-silahex-5-enal (17). To
cooled (08C) mixture of alcohol 15 (178 mg, 0.72 mmol)
a
3
and 4 A molecular sieves (720 mg) in DCM (5 cm ) was
Ê
added PDC (403 mg, 1.07 mmol); the mixture was allowed
to warm to rt then stirring was continued for 16 h. Ether
(10 cm3) was added, the mixture ®ltered through Celitew,
washing through with ether (2£10 cm3), and the combined
®ltrate concentrated in vacuo to give a brown-orange oil.
Puri®cation by column chromatography afforded aldehyde
17 as a colourless oil (128 mg, 72%). Rf 0.66 (1:1 petrol:
ether); Accurate mass: Found 264.1784, C15H26NOSi
(MNH14 ) requires 264.17836; nmax/cm21 3029m, 2954s,
2716m, 1728s, 1604m, 1497m, 1455s, 1413m, 1250s,
938m, 923m, 836s, 746m, 700s; dH (500 MHz; CDCl3)
0.12 (6H, s, Me2Si), 0.73 (1H, dd, Jˆ14.9, 5.7 Hz) and
0.99 (1H, dd, Jˆ14.9, 7.7 Hz, CH2Si), 1.79 (3H, t, Jˆ
1.5 Hz, MeCv), 2.70 (1H, ca. dddd, Jˆ7.7, 6.2, 5.7,
2.5 Hz, CHCHO), 2.73 (1H, dd, Jˆ13.2, 6.2 Hz) and 2.99
(1H, dd, Jˆ13.2, 7.7 Hz, PhCH2), 5.27 (1H, dq, Jˆ3.0,

8316
J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
1.5 Hz) and 5.63 (1H, dq, Jˆ3.0, 1.5 Hz, vCH2), 7.17 (2H,
ca. dt, Jˆ7.3, 1.4 Hz), 7.22 (1H, tt, Jˆ7.3, 1.4 Hz) and 7.30
(2H, ca. tt, Jˆ7.3, 1.4 Hz, Ph), 9.62 (1H, d, Jˆ2.5 Hz,
CHO); dC (125 MHz; CDCl3) 23.3, 23.1, 13.7, 22.3,
38.1, 49.6, 126.1, 126.4, 128.5, 129.0, 138.8, 146.1, 203.9;
m/z (CI) 264 (MNH14 , 100%), 247 (MH1, 11), 231 (34), 205
(46), 155 (13), 116 (22), 99 (24), 91 (85), 73 (22), 59 (12).
(9:1 petrol:ether) gave the alcohol 20 as a colourless oil
(402 mg, 66%). Rf 0.39 (1:1 petrol:ether); Found: C,
74.50; H, 10.88; C18H30OSi requires C, 74.42; H, 10.41%;
n
max/cm21 3306s, 3025m, 2944s, 1599s, 1492s, 1458s,
1389m, 1247m, 1144m, 1032s, 922m, 883m, 803m, 775m,
759m; dH (500 MHz; CDCl3) 0.99±1.09 (13H, m) and 1.17
(1H, sept, Jˆ7.3 Hz, Pri2Si), 1.32 (1H, br s, OH), 1.82 (3H,
t, Jˆ1.3 Hz, MeCv), 2.03±2.15 (2H, m, PhCHCH2), 2.55
(1H, dd, Jˆ12.2, 3.1 Hz, PhCH), 3.42 (1H, apparent dt,
Jˆ10.4, 7.4 Hz) and 3.55 (1H, ddd, Jˆ10.4, 7.3, 4.5 Hz,
CH2OH), 5.29 (1H, dq, Jˆ3.1, 1.3 Hz) and 5.79 (1H, dq,
Jˆ3.1, 1.3 Hz, vCH2), 7.10 (1H, tt, Jˆ7.2, 1.5 Hz), 7.16
(2H, ca. dt, Jˆ7.2, 1.5 Hz), and 7.23 (2H, tt, Jˆ7.2, 1.5 Hz,
Ph); dC (125 MHz; CDCl3) 10.7, 11.2, 18.2, 18.5, 18.6, 28.7,
24.7, 28.8, 33.5, 62.2, 124.8, 128.1, 128.5, 128.9, 142.3,
142.8; m/z(CI) 308 (MNH14 , 100%), 291 (MH1, 6), 264
(7), 249 (10), 247 (11), 172 (12), 146 (12), 130 (11), 118
(34), 91 (10).
(E)-1-Diisopropylsilyloxy-3-phenylprop-2-ene (18).15
A
mixture of DMAP (18 mg, 0.15 mmol), triethylamine
(63 ml, 0.45 mmol) and cinnamyl alcohol (50 mg,
0.37 mmol) in hexane (2 cm3) was stirred at rt for 10 min
then chlorodiisopropylsilane (83 ml, 0.48 mmol) was added
dropwise. The mixture was stirred for 4.5 h then ®ltered
through Celitew, the ®ltrate being concentrated in vacuo to
give an oil that was puri®ed by column chromatography
(99:1 petrol:ether). Hydrosilane 1815 was obtained as a
colourless oil (82 mg, 89%). Rf 0.71 (1:1 petrol:ether);
n
max/cm21 3028m, 2944s, 2865s, 2094s, 1496m, 1463s,
1382m, 1244m, 1126s, 1059s, 1001s, 964s, 881s, 832s,
731s, 691s; dH (500 MHz; CDCl3) 0.93±1.34 (14H, m,
Pri2Si), 4.30 (1H, s, folded SiH), 4.48 (2H, dd, Jˆ5.3,
1.6 Hz, CH2O), 6.35 (1H, dt, Jˆ15.8, 5.3 Hz, PhCHvCH),
6.67 (1H, dt, Jˆ15.8, 1.6 Hz, PhCHvCH), 7.27 (1H, ca. tt,
Jˆ7.3, 1.4 Hz), 7.36 (2H, ca. tt, Jˆ7.3, 1.4 Hz), 7.43 (2H,
ca. dt, Jˆ7.3, 1.4 Hz, Ph); dC (125 MHz; CDCl3) 12.5, 17.3,
17.4, 66.2, 126.4, 127.4, 128.5, 130.0, 137.0; m/z (CI) 249
(MH1, 11%), 222 (32), 205 (36), 117 (100), 115 (21), 91
(15).
4,4-Diisopropyl-5-methyl-3-phenyl-4-silahex-5-enal (21).
To a cooled (08C) mixture of alcohol 20 (100 mg,
0.34 mmol) and 4 A molecular sieves (344 mg) in DCM
Ê
(2 cm3) was added PDC (194 mg, 0.52 mmol). The mixture
was allowed to warm to rt then stirred for 4 h. Ether
(10 cm3) was added, the mixture ®ltered through Celitew,
washing through with ether (4£10 cm3), and the combined
®ltrates were concentrated in vacuo to give an orange oil.
Puri®cation by column chromatography (40:1 petrol:ether)
afforded aldehyde 21 as a colourless oil (63 mg, 64%). Rf
0.67 (1:1 petrol:ether); Accurate mass: Found 306.2253,
1,1-Diisopropyl-2-oxa-5-phenyl-1-silacyclopentane (19).
To a mixture of Wilkinson's catalyst (5.5 mg, 0.2 mol%)
C18H32NOSi (MNH14 ) requires 306.22530; max/cm21
n
3428w, 3026m, 2946s, 2868s, 2717m, 1728s, 1600s,
1494s, 1451s, 1384s, 1371m, 1247m, 1188m, 1079m,
1018s, 924s, 883s, 776m, 701s; dH (500 MHz; CDCl3)
0.98, 1.05, 1.07 and 1.13 (4£3H, 4£d, Jˆ7.0 Hz), 1.03±
1.12 (1H, m) and 1.17 (1H, septd, Jˆ7.0 Hz, 1.0, Pri2Si),
1.80 (3H, t, Jˆ1.4 Hz, MeCv), 2.72 (1H, d, Jˆ12.7 Hz,
PhCH), 3.04 (1H, td, Jˆ12.7, 2.6 Hz) and 3.09 (1H, d,
Jˆ12.7 Hz, CH2CHO), 5.31 (1H, dq, Jˆ3.0, 1.4 Hz) and
5.83 (1H, dq, Jˆ3.0, 1.4 Hz, vCH2), 7.11 (1H, tt, Jˆ7.3,
1.6 Hz), 7.18 (2H, ca. dt, Jˆ7.3, 1.6 Hz) and 7.23 (2H, tt,
Jˆ7.3, 1.6 Hz, Ph), 9.60 (1H, d, Jˆ2.6 Hz, CHO); dC
(125 MHz; CDCl3) 10.5, 11.0, 18.1, 18.4 (2), 18.6, 24.5,
26.0, 44.5, 125.2, 128.2, 128.3, 129.5, 141.5, 141.7, 202.7;
m/z (CI) 306 (MNH14 , 100%), 289 (MH1, 4), 271 (3), 262
(6), 245 (24).
3
and 4 A molecular sieves (61 mg) in THF (4.5 cm ) at rt
Ê
was added dropwise a solution of hydrosilane 18 (630 mg,
2.54 mmol) in THF (2 cm3) and the mixture brought to
re¯ux. Heating was continued for 3.5 h then the THF was
removed in vacuo to give a brown oily residue (641 mg)
containing oxasilacyclopentane 19 which was suf®ciently
pure to be used directly in the next reaction. Rf 0.50 and
0.62 (1:1 petrol:etherÐhydrolysis); nmax/cm21 2943s,
2866s, 1601m, 1464s, 1384w, 1245w, 1055s, 1032s,
999m, 883s, 825s, 786s, 698s; dH (200 MHz; CDCl3) 0.75
and 0.79 (2£3H, 2£d, Jˆ6.5 Hz) and 0.85±1.28 (8H, m,
Pri2Si), 2.24±2.40 (2H, m, PhCHCH2), 2.79 (1H, dd, Jˆ
10.5, 8.5 Hz, PhCH), 3.90 (1H, apparent dt, Jˆ9.5,
6.0 Hz) and 4.25 (1H, apparent dt, Jˆ6.0, 3.0 Hz, CH2O),
7.08±7.32 (5H, m, Ph); dC (50.3 MHz; CDCl3) 12.1, 12.4,
16.7, 16.9, 17.4, 17.6, 30.1, 32.2, 67.2, 124.6, 126.8, 128.5,
142.6; m/z (CI) 266 (MNH41, 6%), 249 (MH1, 98), 248 (47),
222 (83), 205 (100), 177 (28), 117 (83), 91 (37).
(1SR, 2SR, 5RS)-2-Hydroxymethyl-5-methyl-1-[dimethyl-
(propen-2-yl)silyl]cyclohex-3-ene (24) and (1RS, 2SR,
5RS)-2-hydroxymethyl-5-methyl-1-[dimethyl(propen-2-
yl)silyl]cyclohex-3-ene (25). A solution of the dimethyl-
(vinyl)silyl ether of sorbyl alcohol17 (275 mg, 1.51 mmol)
in benzene (20 cm3) was heated at 1708C (sealed tube) for
13 h. The solution was cooled and concentrated in vacuo
and the resulting oil dissolved in THF (5 cm3). To a cooled
(2788C) solution of t-butyllithium (4.7 cm3 of a 1.6 M solu-
tion in pentane, 7.52 mmol) in THF (6.5 cm3) was added
dropwise 2-bromopropene (0.34 cm3, 3.79 mmol). After
1.5 h the THF solution of the Diels±Alder adduct was
added by cannula and the mixture was allowed to warm
up to 08C then stirred for 6 h at 08C and at rt for 12 h. The
mixture was added to a mixture of water (25 cm3) and 1 M
hydrochloric acid (5 cm3) and extracted with ether
4,4-Diisopropyl-5-methyl-3-phenyl-4-silahex-5-en-1-ol
(20). 2-Bromopropene (0.39 cm3, 4.43 mmol) was added
dropwise to a cooled (2788C) solution of t-butyllithium
(5.9 cm3 of a 1.5 M solution in pentane, 8.85 mmol) in
THF (7 cm3) and the mixture was stirred for 1 h. A solution
of the crude oxasilacyclopentane 19 (524 mg, 2.11 mmol) in
THF (2 cm3) was added dropwise then the mixture was
allowed to warm to rt and stirred for 18 h. Water (20 cm3)
was added and the product extracted with ether (3£20 cm3).
The combined organic extracts were washed with brine
(25 cm3), dried (magnesium sulphate) and the solvent
removed in vacuo. Puri®cation by column chromatography

J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
8317
(3£5 cm3). The combined organic portions were washed
with brine (20 cm3), dried (magnesium sulphate) and
concentrated in vacuo and the resulting oil puri®ed by
column chromatography (14:1 petrol:ether) to yield
alcohols 24 (135 mg, 40%) and 25 (91 mg, 27%). Data for
24: Rf 0.53 (1:1 petrol:ether); Accurate mass: Found
3.00 (1H, br m, CHCHO), 5.29 (1H, dq, Jˆ3.0, 1.5 Hz) and
5.66 (1H, dq, Jˆ3.0, 1.5 Hz, vCH2), 5.58 (1H, ddd, Jˆ9.9,
5.2, 2.6 Hz, vCHCHMe), 5.89 (1H, d, Jˆ9.9 Hz,
vCHCHCHO), 9.62 (1H, d, Jˆ 3.3 Hz, CHO); dC
(125 MHz; CDCl3) 24.6, 24.5, 21.4, 22.7, 22.9, 29.5,
31.9, 49.9, 122.1, 126.8, 138.9, 145.4, 201.5; m/z (CI) 240
(MNH14 , 100%), 223 (MH1, 15), 207 (20), 181 (65), 147
(25), 116 (20), 107 (60), 73 (35), 59 (20).
242.1940, C13H28NOSi (MNH14 ) requires 242.19401; nmax
/
cm21 3340m, 3048m, 3015m, 2954s, 2909s, 2870s, 1648w,
1456m, 1370m, 1250s, 1126w, 1035s, 1003m, 938m, 921s,
860s, 833s, 819s, 783s, 762m, 732s, 689m, 674m; dH
(500 MHz; CDCl3) 0.16 and 0.18 (2£3H, 2£s, SiMe2),
1.00 (3H, d, Jˆ7.1 Hz, MeCH), 1.15±1.25 (2H, m, CHSi
and ring-CHH), 1.68 (1H, br s, OH), 1.72 (1H, dd, Jˆ10.4,
4.8 Hz, ring-CHH), 1.88 (3H, br s, MeCv), 2.14±2.19 (1H,
br m, MeCH), 2.37±2.39 (1H, br m, CHCH2OH), 3.57 (1H,
dt, Jˆ10.5, 5.5 Hz) and 3.71 (1H, dt, Jˆ10.5, 5.5 Hz,
CH2OH), 5.34 (1H, dq, Jˆ3.0, 1.5 Hz) and 5.66 (1H, dq,
Jˆ3.0, 1.5 Hz, vCH2), 5.74 (1H, dd, Jˆ10.2, 1.2 Hz,
vCHCHMe), 5.80 (1H, ddd, Jˆ10.2, 4.7, 2.4 Hz,
vCHCHCH2OH); dC (125 MHz; CDCl3) 24.5, 24.3,
21.7, 23.0 24.0, 29.3, 32.4, 38.1, 65.5, 125.9, 128.5, 136.2,
146.9; m/z (CI) 242 (MNH14 , 75%), 209 (10), 200 (20), 183
(70), 165 (15), 116 (30), 108 (80), 99 (50), 93 (80), 75 (100),
59 (30). Data for 25: Rf 0.47 (1:1 petrol:ether); Accurate
mass: Found 242.1940, C13H28NOSi (MNH14 ) requires
242.19401; nmax/cm21 3320s, 3048m, 3012m, 2954s,
2928s, 2870s, 1456s, 1410m, 1370m, 1248s, 1055s,
1026s, 1002m, 938m, 920s, 855s, 834s, 814s, 776s, 726s,
696m; dH (500 MHz; CDCl3) 0.13 (6H, s, SiMe2), 0.99 (3H,
d, Jˆ7.0 Hz, MeCH), 1.23 (1H, dt, Jˆ6.0, 4.5 Hz, CHSi),
1.45 (1H, ddd, Jˆ13.3, 8.1, 4.5 Hz, ring-CHH), 1.71 (1H, s,
OH), 1.73 (1H, dd, Jˆ13.3, 6.0 Hz, ring-CHH), 1.88 (3H, t,
Jˆ1.3 Hz, MeCv), 2.16±2.20 (1H, br m, MeCH), 2.25±
2.27 (1H, br m, CHCH2OH), 3.56 (2H, `d'Ðonly inner
peaks resolved, Jˆ5.9 Hz, CH2OH), 5.31 (1H, dq, Jˆ3.2,
1.3 Hz) and 5.64 (1H, dq, Jˆ3.2, 1.3 Hz, vCH2), 5.63 (1H,
ddd, Jˆ10.1, 3.7, 2.2 Hz, vCHCHMe), 5.75 (1H, dt,
Jˆ10.1, 2.2 Hz, vCHCHCH2OH); dC (125 MHz; CDCl3)
24.5, 24.2, 18.5, 21.4, 22.9, 28.9, 29.4, 38.2, 66.5, 125.8,
127.7, 136.2, 146.6; m/z (CI) 242 (MNH14 , 20%), 207 (10),
200 (10), 193 (20), 183 (55), 165 (10), 148 (10), 134 (10),
118 (20), 116 (100), 107 (25), 99 (95), 93 (40), 91 (30), 75
(50), 73 (70), 59 (25).
(1RS,2SR,5RS)-2-Formyl-5-methyl-1-[dimethyl(propen-
2-yl)silyl]cyclohex-3-ene (27). To a cooled (08C) solution
of alcohol 25 (81 mg, 0.36 mmol) in DCM (3 cm3) was
Ê
added powdered 4 A molecular sieves (0.27 g) and PDC
(0.21 g, 0.54 mmol) and the mixture was allowed to warm
up to rt over 14 h. Petrol:ether (10 cm3, 3:1) was added to
the mixture that was then ®ltered through a pad of silica,
washed through with petrol:ether (100 cm3, 3:1) and the
®ltrate concentrated in vacuo. The resulting oil was puri®ed
by column chromatography (90:1!15:1 petrol:ether) to
yield aldehyde 27 as a colourless oil (47 mg, 59%). Rf
0.61 (3:1 petrol:ether); Accurate mass: Found 240.1784,
C13H26NOSi (MNH14 ) requires 240.17836; nmax/cm21
3018w, 2957s, 2872m, 1725s, 1454w, 1370w, 1251m,
1164w, 1019w, 922m, 835m, 816s, 779m, 737w; dH
(500 MHz; CDCl3) 0.14 and 0.15 (2£3H, 2£s, SiMe2),
1.03 (3H, d, Jˆ7.1 Hz, MeCH), 1.43 (1H, ddd, Jˆ13.1,
7.4, 4.4 Hz, ring-CHH), 1.62 (1H, dt, Jˆ7.0, 4.4 Hz,
CHSi), 1.75 (1H, ddd, Jˆ13.1, 7, 5.7 Hz, ring-CHH), 1.86
(3H, t, Jˆ1.4 Hz, MeCv), 2.21±2.27 (1H, m, MeCH), 2.92
(1H, dq, Jˆ4.4, 2.5 Hz, CHCHO), 5.32 (1H, dq, Jˆ3.1,
1.4 Hz) and 5.68 (1H, dq, Jˆ3.1, 1.4 Hz, vCH2), 5.64
(1H, ddd, Jˆ10.0, 4.1, 2.5 Hz, vCHCHMe), 5.93 (1H, dt,
Jˆ10.0, 2.5 Hz, vCHCHCHO), 9.54 (1H, d, Jˆ2.5 Hz,
CHO); dC (125 MHz; CDCl3) 24.2, 24.8, 16.4, 21.0,
22.8, 28.5, 29.2, 49.4, 120.8, 126.7, 138.3, 145.4, 201.5;
m/z (CI) 240 (MNH14 , 45%), 223 (MH1, 15), 205 (15),
193 (15), 181 (35), 147 (25), 116 (65), 107 (100), 99 (50),
91 (25), 73 (30), 59 (10).
4,4-Dimethyl-3-methylene-4-silacyclohexanol (28). To a
cooled (2788C) solution of aldehyde
7 (326 mg,
2.09 mmol) in DCM (7 cm3) was added dropwise methyl-
aluminium dichloride (3.1 cm3 of a 1 M solution in hexane,
3.1 mmol). After 6 h saturated sodium hydrogen carbonate
solution (3 cm3) was added dropwise and the mixture was
allowed to warm up to rt then added to a mixture of ether
(10 cm3), saturated sodium hydrogen carbonate solution
(5 cm3), water (5 cm3) and saturated potassium sodium
tartrate solution (5 cm3, which dissolved the white precipi-
tate on shaking). The separated aqueous layer was extracted
with ether (3£10 cm3) and the combined organic portions
washed with brine (20 cm3), dried (magnesium sulphate)
and concentrated in vacuo. The resulting oil was puri®ed
by column chromatography (5:1 petrol:ether) to yield the
silacycle 28 as a colourless oil (258 mg, 80%). Rf 0.32 (1:1
petrol:ether); Accurate mass: Found 174.1314, C8H20NOSi
(MNH14 ) requires 174.13141; nmax/cm21 3350s, 2953s,
2916s, 1438m, 1411m, 1249s, 1037s, 924m, 874m, 839s,
821s, 781s, 721m, 689m, 644m; dH (500 MHz; CDCl3) 0.12
and 0.13 (2£3H, 2£s, SiMe2), 0.57 (1H, ddd, Jˆ14.7, 10.1,
4.4 Hz) and 0.82 (1H, ddd, Jˆ14.7, 8.4, 4.2 Hz, SiCH2),
1.64 (1H, br s, OH), 1.82 (1H, dtd, Jˆ18.1, 8.4, 4.4 Hz)
and 1.96±2.02 (1H, m, CH2), 2.42 (1H, dd, Jˆ13.3,
(1SR,2SR,5RS)-2-Formyl-5-methyl-1-[dimethyl(propen-
2-yl)silyl]cyclohex-3-ene (26). To a cooled (08C) solution
of alcohol 24 (125 mg, 0.56 mmol) in DCM (4 cm3) was
Ê
added powdered 4 A molecular sieves (0.42 g) and PDC
(0.32 g, 0.84 mmol) and the mixture was allowed to warm
up to rt over 14 h. Petrol:ether (10 cm3, 3:1) was added to
the mixture that was then ®ltered through a pad of silica,
washed through with petrol:ether (100 cm3, 3:1), and the
®ltrate concentrated in vacuo. The resulting oil was puri®ed
by column chromatography (150:1!10:1 petrol:ether) to
yield aldehyde 26 as a colourless oil (73 mg, 59%). Rf
0.60 (3:1 petrol:ether); Accurate mass: Found 240.1784,
C13H26NOSi (MNH14 ) requires 240.17836;
n
max/cm21
3017m, 2956s, 2854s, 2719m, 1716s, 1455m, 1370w,
1251s, 1191w, 1126w, 1069w, 922m, 819s, 785s, 730m,
691m; dH (500 MHz; CDCl3) 0.14 and 0.15 (2£3H, 2£s,
SiMe2), 1.02 (3H, d, Jˆ7.1 Hz, MeCH), 1.23±1.30 (2H,
m) and 1.79±1.82 (1H, m, CHSi and ring-CH2), 1.84 (3H,
t, Jˆ1.5 Hz, MeCv), 2.20±2.22 (1H, br m, MeCH), 2.99±

8318
J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
8.4 Hz) and 2.64 (1H, ddd, Jˆ13.3, 3, 1.3 Hz, CH2Cv),
3.72 (1H, tt, Jˆ8.4, 3 Hz, CHOH), 5.28 (1H, d, Jˆ3.4 Hz)
and 5.57 (1H, dd, Jˆ3.4, 1.3 Hz, vCH2); dC (125 MHz;
CDCl3) 24.6, 24.2, 10.0, 32.0, 47.3, 71.9, 124.5, 148.1;
m/z (CI) 174 (MNH14 , 75%), 158 (20), 157 (MH1, 10),
156 (45), 141 (80), 139 (80), 123 (15), 115 (30), 91 (70),
74 (100).
carbonate solution (5 cm3), water (5 cm3) and saturated
potassium sodium tartrate solution (5 cm3, which dissolved
the white precipitate on shaking). The separated aqueous
layer was extracted with ether (3£5 cm3) and the combined
organic portions washed with brine (15 cm3), dried (mag-
nesium sulphate) and concentrated in vacuo. The resulting
oil was puri®ed by column chromatography (44:1!3:1
petrol:ether) to yield silacycle 31 as a colourless oil
(40 mg, 69%). Rf 0.34 (1:1 petrol:ether); Accurate mass:
Found 188.1471, C9H22NOSi (MNH14 ) requires
(cis)-5-Methylene-2,4,4-trimethyl-4-silacyclohexanol (29)
and (trans)-5-methylene-2,4,4-trimethyl-4-silacyclohexa-
nol (30). To a cooled (2788C) solution of aldehyde 8
(91 mg, 0.53 mmol) in DCM (2.5 cm3) was added dropwise
methylaluminium dichloride (0.91 cm3 of a 1 M solution in
hexane, 0.91 mmol). After 3 h water (2 cm3) was added
dropwise and the mixture allowed to warm up to rt then
added to a mixture of ether (10 cm3), saturated sodium
hydrogen carbonate solution (5 cm3) and saturated potas-
sium sodium tartrate solution (6 cm3, which dissolved the
white precipitate on shaking). The separated aqueous layer
was extracted with ether (3£8 cm3) and the combined
organic portions washed with brine (15 cm3), dried (mag-
nesium sulphate) and concentrated in vacuo. The resulting
oil was puri®ed by column chromatography (3:1 petrol:
ether) to yield a mixture of silacycles 29 and 30 in a ratio
of 13:1 (cis:trans) as a colourless oil (73 mg, 80%). Separa-
tion of the isomers was possible by further chromatography
(19:1 petrol:ether). Data for 29: Rf 0.51 (1:1 petrol:ether);
Accurate mass: Found 188.1471, C9H22NOSi (MNH14 )
requires 188.14706; nmax/cm21 3429m, 2955s, 2903s,
1452m, 1434m, 1411m, 1250s, 1184w, 1145w, 1024m,
984m, 921m, 874m, 844s, 802s, 758w, 659m; dH
(500 MHz; CDCl3) 0.11 and 0.15 (2£3H, 2£s, SiMe2),
0.56±0.63 (2H, m, SiCH2), 1.09 (3H, d, Jˆ6.8 Hz,
MeCH), 1.28 (1H, br s, OH), 1.90 (1H, dqdd, Jˆ14.0, 6.8,
2.6, 1.9 Hz, MeCH), 2.56 (1H, dd, Jˆ14.0, 4.4 Hz) and 2.61
(1H, dq, Jˆ14.0, 2.3 Hz, CH2Cv), 3.77 (1H, ddd, Jˆ4.4,
2.3, 1.9 Hz, CHOH), 5.37 (1H, dd, Jˆ3.1, 2.3 Hz) and 5.61
(1H, dd, Jˆ3.1, 2.3 Hz, vCH2); dC (125 MHz; CDCl3)
24.2, 23.9, 17.4, 23.2, 35.1, 45.6, 73.7, 126.0, 146.8; m/z
(CI) 188 (MNH14 , 75%), 171 (MH1, 10), 170 (15), 155 (70),
153 (100), 137 (10), 129 (30), 91 (40), 74 (65), 60 (15). Data
for 30: Rf 0.43 (1:1 petrol:ether); Accurate mass: Found
188.14706;
n
max/cm21 3353s, 2951s, 2905s, 2865s,
1457m, 1377m, 1353m, 1250s, 1195m, 1035s, 991m,
959m, 922s, 839s, 814s, 776s, 694s, 617m; dH (500 MHz;
CDCl3) 0.04 and 0.15 (2£3H, 2£s, SiMe2), 0.96 (3H, d,
Jˆ7.1 Hz, MeCH), 1.01±1.07 (1H, m, MeCH), 1.55 (1H,
br s, OH), 1.61 (1H, ddd, Jˆ13.8, 11.1, 2.2 Hz) and 1.97
(1H, dddd, Jˆ13.8, 5.9, 4.7, 1.6 Hz, CH2), 2.46 (1H, dd,
Jˆ13.6, 5.9 Hz) and 2.60 (1H, br dq, Jˆ13.6, 1.6 Hz,
CH2Cv), 4.01 (1H, ca. tt, Jˆ5.9, 2.6 Hz, CHOH), 5.34
(1H, d, Jˆ3.0 Hz) and 5.61 (1H, dt, Jˆ3.0, 1.2 Hz,
vCH2); dC (125 MHz; CDCl3) 28.7, 26.8, 13.6, 14.4,
39.5, 45.1, 67.9, 124.6, 146.3; m/z (CI) 188 (MNH14 , 5%),
171 (MH1, 5), 170 (20), 153 (100), 137 (25), 109 (15), 95
(15), 91 (30), 74 (55), 59 (30).
(cis)-4,4-Dimethyl-5-methylene-2-(2-propyl)-4-silacyclo-
hexanol (32). To a cooled (2788C) solution of aldehyde 16
(50 mg, 0.25 mmol) in DCM (1.5 cm3) was added dropwise
methylaluminium dichloride (0.53 cm3 of a 1 M solution in
hexane, 0.53 mmol) and the mixture stirred for 6 h. Water
(1 cm3) was added and the mixture was allowed to warm to
rt whereupon more water (10 cm3) was added and the
product was extracted with ether (3£10 cm3). The combined
extracts were washed with brine (20 cm3) then dried
(magnesium sulphate) and the solvent removed in vacuo.
Puri®cation by column chromatography (30:1 petrol:ether)
gave the silacycle 32 as a colourless oil (42 mg, 84%). Rf
0.39 (3:1 petrol:ether); Accurate mass: Found 216.1789,
C11H26NOSi (MNH14 ) requires 216.17836;
n
max/cm21
3469m, 3041m, 2956s, 2899s, 2872s, 1475m, 1432m,
1384m, 1250s, 1144m, 1030m, 923m, 843s, 765s, 664m;
dH (500 MHz; CDCl3) 0.10 and 0.17 (2£3H, 2£s, Me2Si),
0.51 (1H, apparent t, Jˆ14.0 Hz) and 0.75 (1H, dd, Jˆ14.0,
3.4 Hz, CH2Si), 0.94 and 0.97 (2£3H, 2£d, Jˆ6.7 Hz,
Me2C), 1.22 (1H, d, Jˆ7.7 Hz, OH), 1.35 (1H, dddd,
Jˆ14.0, 6.7, 3.4, 1.1 Hz, PriCH), 1.65 (1H, apparent oct,
Jˆ6.7 Hz, Me2CH), 2.53±2.60 (2H, m, CH2CHOH), 4.11
(1H, br s, CHOH), 5.38 (1H, d, Jˆ2.9 Hz) and 5.60 (1H, ca.
t, Jˆ2.9 Hz, vCH2); dC (125 MHz; CDCl3) 24.3, 23.9,
12.0, 20.6, 21.2, 33.1, 46.3, 46.6, 70.4, 126.0, 147.5; m/z
(CI) 216 (MNH14 , 64%), 183 (100), 181 (86), 157 (46), 155
(64), 141 (73), 137 (48), 127 (73), 113 (61), 99 (64), 92 (95).
188.1471, C9H22NOSi (MNH14 ) requires 188.14706; nmax
/
cm21 3371s, 2955s, 2903s, 2876s, 1442m, 1412w, 1252m,
1093m, 1075m, 1029m, 923w, 819m, 784m, 842m; dH
(200 MHz; CDCl3) 0.12 and 0.14 (2£3H, 2£s, SiMe2),
0.36 (1H, dd, Jˆ14.6, 11.7 Hz) and 0.85 (1H, dd, Jˆ14.6,
3.7 Hz, SiCH2), 1.13 (3H, d, Jˆ6.5 Hz, MeCH), 1.56 (1H, br
s, OH), 1.71±1.81 (1H, m, MeCH), 2.41 (1H, ddt, Jˆ13.2,
10.1, 1.9 Hz) and 2.68 (1H, dd Jˆ13.2, 3.7 Hz, CH2Cv),
3.16 (1H, td, Jˆ10.1, 3.7 Hz, CHOH), 5.24 (1H, dd, Jˆ3.3,
1.5 Hz) and 5.57 (1H, ca. t, Jˆ2.6 Hz, vCH2); m/z (CI) 188
(MNH14 , 25%), 171 (MH1, 10), 170 (30), 155 (60), 153
(100), 137 (10), 129 (20), 113 (10), 100 (10), 91 (40), 74
(65), 60 (15).
(cis)-2-Benzyl-4,4-dimethyl-5-methylene-4-silacyclohexa-
nol (33). To a cooled (2788C) solution of aldehyde 17
(252 mg, 1.02 mmol) in DCM (6 cm3) was added dropwise
methylaluminium dichloride (1.53 cm3 of a 1 M solution in
hexane, 1.53 mmol) and the mixture stirred for 7 h. Water
(5 cm3) was added, the mixture was allowed to warm to rt,
more water (30 cm3) was added and the product extracted
with ether (3£30 cm3). The combined organic extracts were
dried (magnesium sulphate) and the solvent removed in
(trans)-3-Methylene-4,4,5-trimethyl-4-silacyclohexanol
(31). To a cooled (2788C) solution of aldehyde 9 (58 mg,
0.34 mmol) in DCM (1.5 cm3) was added dropwise methyl-
aluminium dichloride (0.51 cm3 of a 1 M solution in hexane,
0.51 mmol). After 3 h water (2 cm3) was added dropwise
and the mixture allowed to warm up to rt then added to a
mixture of ether (5 cm3), saturated sodium hydrogen
vacuo.
Puri®cation
by
column
chromatography

J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
8319
(30:1!18:1 petrol:ether) gave silacycle 33 as a colourless
oil (199 mg, 79%). Rf 0.26 (3:1 petrol:ether); Accurate
mass: Found 229.1413, C15H21Si (MH12H2O) requires
229.14125; nmax/cm21 3566m, 3466s, 3027s, 2951s,
2909s, 1602m, 1496s, 1454s, 1435m, 1410s, 1249s,
1165s, 1074s, 1031m, 993m, 930s, 844s, 798s, 779s, 740s,
700s, 663s; dH (500 MHz; CDCl3) 0.10 and 0.18 (2£3H,
2£s, Me2Si), 0.62 (1H, dd, Jˆ14.6, 12.3 Hz) and 0.67
(1H, dd, Jˆ14.6, 4.6 Hz, CH2Si), 1.38 (1H, br s, OH),
1.98 (1H, dtdd, Jˆ12.3, 7.5, 4.6, 1.4 Hz, BnCH), 2.54
(1H, dd, Jˆ14.1, 4.4 Hz) and 2.59 (1H, dd, Jˆ14.1,
2.1 Hz, CH2CHOH), 2.64 (1H, dd, Jˆ13.3, 7.5 Hz) and
2.87 (1H, dd, Jˆ13.3, 7.5 Hz, PhCH2), 3.86 (1H, br s,
CHOH), 5.41 (1H, dd, Jˆ3.1, 1.1 Hz) and 5.64 (1H, ca. t,
Jˆ2.6, vCH2), 7.20±7.23 (3H, m) and 7.31 (2H, ca. t,
Jˆ7.5 Hz, Ph); dC (125 MHz; CDCl3) 24.4, 24.0, 15.3,
42.3, 43.6, 45.7, 70.7, 125.7, 126.2, 128.2, 129.3, 141.1,
146.9; m/z (CI) 264 (MNH41, 9%), 248 (15), 246 (24), 231
(46), 229 (97), 228 (46), 156 (23), 139 (72), 91 (100), 74
(86), 59 (61).
less oil (60 mg, 88%). Rf 0.60 (1:1 petrol:ether); Accurate
mass: Found 240.1784, C13H26NOSi (MNH14 ) requires
240.17836; nmax/cm21 3566m, 3480m, 3005m, 2953s,
2919s, 2868s, 1456m, 1436m, 1386m, 1304m, 1246s,
1172m, 1126w, 1068m, 1036m, 1006m, 942m, 922m,
864s, 827s, 800s, 783s, 768s, 722w, 676m, 643m, 607s;
dH (500 MHz; CDCl3) 0.16 and 0.22 (2£3H, 2£s, SiMe2),
1.00 (3H, d, Jˆ7.1 Hz, MeCH), 1.20 (1H, ddd, Jˆ14.4, 5.0,
2.9 Hz, CHSi), 1.39 (1H, td, Jˆ14.4, 10.5 Hz) and 1.64 (1H,
ddd, Jˆ14.4, 5.9, 2.9 Hz, CH2), 1.58 (1H, br d, Jˆ2.1, OH),
2.14±2.19 (1H, m, MeCH), 2.42 (1H, td, Jˆ5.0, 2.5 Hz,
CHCHOH), 2.64 (1H, br d, Jˆ14.2 Hz) and 2.73 (1H, dd,
Jˆ14.2, 4.1 Hz, CH2Cv), 3.95 (1H, br s, CHOH), 5.41 (1H,
apparent dd, Jˆ3.1, 2.0 Hz) and 5.71 (1H, apparent dd,
Jˆ3.1, 2.7 Hz, vCH2), 5.68 (1H, ddd, Jˆ10.1, 5.0,
2.5 Hz, vCHCHMe), 5.91 (1H, br d, Jˆ10.1 Hz,
vCHCHCHOH); dC (125 MHz; CDCl3) 26.7, 22.9,
21.7, 22.5, 30.6, 31.1, 39.8, 43.6, 71.8, 125.6, 128.9,
137.9, 145.6; m/z (CI) 240 (MNH14 , 15%), 223 (MH1, 5),
205 (35), 146 (20), 127 (100), 113 (20), 107 (30), 94 (35), 91
(30), 75 (75), 74 (50), 59 (10).
(trans)-4,4-Diisopropyl-5-methylene-3-phenyl-4-silacyclo-
hexanol (34). To a cooled (2788C) solution of aldehyde 21
(63 mg, 0.22 mmol) in DCM (1.5 cm3) was added dropwise
methylaluminium dichloride (0.33 cm3 of a 1 M solution in
hexane, 0.33 mmol) and the mixture was stirred for 7 h.
Water (3 cm3) was added, the mixture warmed to rt, and
more water (10 cm3) added. The product was extracted
into ether (3£15 cm3) and the combined extracts were
washed with brine (20 cm3) then dried (magnesium
sulphate) and concentrated in vacuo. The oil was puri®ed
by column chromatography (9:1 petrol:ether) to afford sila-
cycle 34 (48 mg, 76%) as a white solid. Rf 0.35 (1:1 petro-
l:ether); mp 61±628C; Accurate mass: Found 306.2253,
(1RS,5SR,6SR,9RS)-5-Hydroxy-3-methylene-2,2,9-tri-
methyl-2-silabicyclo[4.4.0]dec-7-ene (36). To a cooled
(2788C) solution of aldehyde 27 (40 mg, 0.18 mmol) in
DCM (3 cm3) was added dropwise methylaluminium
dichloride (0.27 cm3 of a 1 M solution in hexane,
0.27 mmol). After 7 h water (5 cm3) and ether (5 cm3)
were added and the mixture was stirred vigorously and
allowed to warm up to rt. The mixture was added to water
(5 cm3), extracted with ether (38 cm3) and the combined
organic portions were washed with brine (10 cm3), dried
(magnesium sulphate) and concentrated in vacuo. The
resulting oil was puri®ed by column chromatography
(20:1!10:1 petrol:ether) to yield silabicycle 36 as a colour-
less oil (19 mg, 48%). Rf 0.24 (3:1 petrol:ether); Accurate
mass: Found 240.1784, C13H26NOSi (MNH14 ) requires
240.17836; nmax/cm21 3447m, 3042m, 3008s, 2955s,
2903s, 2868s, 1456m, 1432m, 1394m, 1368m, 1247s,
1196m, 1161m, 1126w, 1091m, 1075m, 1055m, 1043m,
1021m, 1003m, 924s, 852s, 834s, 822s, 785s, 759s, 704s,
667m, 642m, 616s; dH (500 MHz; CDCl3) 0.19 and 0.22
(2£3H, 2£s, SiMe2), 1.04 (3H, d, Jˆ7.1 Hz, MeCH), 1.10
(1H, ddd Jˆ13.6, 12.2, 2.2 Hz, CHSi), 1.43 (1H, d,
Jˆ5.5 Hz, OH), 1.53 (1H, br d, Jˆ13.6 Hz) and 1.75 (1H,
td, Jˆ13.6, 6 Hz, CH2), 2.24±2.28 (1H, m, MeCH), 2.31
(1H, br d, Jˆ12.2 Hz, CHCHOH), 2.64 (1H, dd, Jˆ14.3,
3.8 Hz) and 2.67 (1H, dq, Jˆ14.3, 2.4, CH2Cv), 4.01±4.02
(1H, br s, Jˆ2.2 Hz, CHOH), 5.42 (1H, apparent dd, Jˆ3.0,
1.6 Hz) and 5.67 (1H, apparent d, Jˆ3.0 Hz, vCH2), 5.65
(1H, dt, Jˆ10.0, 1.5 Hz, vCHCHCHOH), 5.82 (1H, br d,
Jˆ10.0 Hz, vCHCHMe); dC (125 MHz; CDCl3) 27.3,
26.9, 15.4, 21.0, 28.2, 29.2, 43.6, 45.0, 73.0, 125.7,
130.9, 135.7, 147.2; m/z (CI) 240 (MNH14 , 80%), 222
(10), 207 (15), 206 (20), 205 (100), 189 (10), 180 (10),
146 (25), 127 (30), 107 (20), 92 (20), 91 (35), 75 (90), 74
(60), 59 (10).
C18H32NOSi (MNH14 ) requires 306.22530;
n
max/cm21
3254s, 3024w, 2945s, 2866s, 1599m, 1496m, 1464m,
1448m, 1313m, 1219m, 1087m, 1040m, 928m, 854m,
769s, 700s, 662s; dH (500 MHz; CDCl3) 0.76, 1.03 and
1.04 (3£3H, 3£d, Jˆ7.2 Hz), 1.10 (1H, ca. sept, Jˆ
7.2 Hz), and 1.16±1.24 (4H, m, Pri2Si), 1.58 (1H, br s,
OH), 2.28±2.31 (2H, m, PhCHCH2), 2.60 (1H, dd, Jˆ
14.6, 4.6 Hz) and 2.71 (1H, dq, Jˆ14.6, 2.5 Hz, CH2Cv),
2.87 (1H, ca. t, Jˆ9.0 Hz, PhCH), 4.27 (1H, br s, CHOH),
5.48 (1H, t, Jˆ2.5 Hz) and 5.81 (1H, t, Jˆ2.5 Hz, vCH2),
7.12 (1H, tt, Jˆ7.3, 1.4 Hz), 7.19 (2H, ca. dt, Jˆ7.3, 1.4 Hz)
and 7.26 (2H, tt, Jˆ7.3, 1.4 Hz, Ph); dC (125 MHz; CDCl3)
9.5, 9.7, 17.5, 17.6, 18.2, 19.3, 25.3, 38.1, 47.2, 68.3, 124.6,
127.7, 128.2, 128.3, 142.6, 144.4; m/z (CI) 306 (MNH14 ,
100%), 288 (9), 271 (30), 262 (10), 245 (24), 91 (11).
(1SR,5SR,6SR,9RS)-5-Hydroxy-3-methylene-2,2,9-tri-
methyl-2-silabicyclo[4.4.0]dec-7-ene (35). To a cooled
(2788C) solution of aldehyde 26 (68 mg, 0.31 mmol) in
DCM (5 cm3) was added dropwise methylaluminium
dichloride (0.46 cm3 of a 1 M solution in hexane,
0.46 mmol). After 6 h water (5 cm3) and ether (5 cm3)
were added and the mixture was stirred vigorously and
allowed to warm up to rt. The mixture was added to water
(5 cm3), extracted with ether (3£8 cm3) and the combined
organic portions were washed with brine (10 cm3), dried
(magnesium sulphate) and concentrated in vacuo. The
resulting oil was puri®ed by column chromatography
(20:1!10:1 petrol:ether) to yield silabicycle 35 as a colour-
Acknowledgements
We are very grateful to P®zer Central Research and the
EPSRC for a CASE Award (G. O'C.) and to the University

8320
J. Robertson et al. / Tetrahedron 56 (2000) 8309±8320
Chem. 1976, 54, 473±481. (b) Stowell, J. C.; Keith, D. R.; King,
B. T. Org. Synth. Col. Vol. VII 1990, 59±63.
of Oxford for funding (T. S.). The EPSRC Mass Spectro-
metry Service Centre is also acknowledged for exact mass
measurements. We also thank Dr John Brown at the Dyson
Perrins Laboratory for helpful discussions.
12. This modi®cation is necessary in order to obtain acceptable
conversions with less reactive organometallic nucleophiles.
13. (a) Yamamoto, Y.; Takeda, Y.; Akiba, K.-Y. Tetrahedron Lett.
1989, 30, 725±728. (b) Murakami, M.; Oike, H.; Sugawara, M.;
Suginome, M.; Ito, Y. Tetrahedron 1993, 49, 3933±3946. (c)
Murakami, M.; Suginome, M.; Fujimoto, K.; Nakamura, H.;
Andersson, P. G.; Ito, Y. J. Am. Chem. Soc. 1993, 115, 6487±6498.
14. (a) Corriu, R.; Guerin, C. J. Organomet. Chem. 1980, 195,
261±274. (b) Corriu, R. J. P.; Kpoton, A.; Barrau, J.; Satge, J.
J. Organomet. Chem. 1976, 114, 21±33.
References
1. (a) Stork, G.; Kahn, M. J. Am. Chem. Soc. 1985, 107, 500±501.
(b) Nishiyama, H.; Kitajima, T.; Matsumoto, M.; Itoh, K. J. Org.
Chem. 1984, 49, 2298±2300.
2. (a) Tamao, K.; Tanaka, T.; Nakajima, T.; Sumiya, R.; Arai, H.;
Ito, Y. Tetrahedron Lett. 1986, 27, 3377±3380. (b) Tamao, K.;
Nakajima, T.; Sumiya, R.; Arai, H.; Higuchi, N.; Ito, Y. J. Am.
Chem. Soc. 1986, 108, 6090±6093.
15. Bergens, S. H.; Noheda, P.; Whelan, J.; Bosnich, B. J. Am.
Chem. Soc. 1992, 114, 2121±2128.
16. Anwar, S.; Davis, A. P. Proc. R. Ir. Acad. B 1989, 89, 71±78.
17. (a) Stork, G.; Chan, T.-Y.; Breault, G. A. J. Am. Chem. Soc.
1992, 114, 7578±7579. (b) Sieburth, S. McN.; Fensterbank, L.
J. Org. Chem. 1992, 57, 5279±5281.
3. (a) Tamao, K.; Kakui, T.; Akita, M.; Iwahara, T.; Kanatani, R.;
Yoshida, J.; Kumada, M. Tetrahedron 1983, 39, 983±990. (b)
Fleming, I.; Henning, R.; Plaut, H. J. Chem. Soc., Chem. Commun.
1984, 29±31.
18. Snider, B. B.; Rodini, D. J.; Kirk, T. C.; Cordova, R. J. Am.
Chem. Soc. 1982, 104, 555±563.
4. (a) Bols, M.; Skrydstrup, T. Chem. Rev. 1995, 95, 1253±1277.
(b) Fensterbank, L.; Malacria, M.; Sieburth, S. McN. Synthesis
1997, 813±854. (c) Fleming, I.; Barbero, A.; Walter, D. Chem.
Rev. 1997, 97, 2063±2192. (d) Gauthier, D. R., Jr.; Zandi, K. S.;
Shea, K. J. Tetrahedron 1998, 54, 2289±2338.
19. (a) Karras, M.; Snider, B. B. J. Am. Chem. Soc. 1980, 102,
7951±7953. (b) Snider, B. B.; Karras, M.; Price, R. T.; Rodini, D. J.
J. Org. Chem. 1982, 47, 4538±4545.
20. Andersen, N. H.; Hadley, S. W.; Kelly, J. D.; Bacon, E. R.
5. Dubac, J.; Laporterie, A. Chem. Rev. 1987, 87, 319±334.
6. Snider, B. B. In Comprehensive Organic Synthesis, Trost, B. M.,
Fleming, I. Eds.; Pergamon: Oxford, 1991; Vol. 2, pp 527±561.
7. Oppolzer, W.; Snieckus, V. Angew. Chem., Int. Ed. Engl. 1978,
17, 476±486.
J. Org. Chem. 1985, 50, 4144±4151.
Ê
Ê
21. Bond lengths: C±C, 1.54 A; C±Si, 1.89 A.
22. (a) Wierschke, S. G.; Chandrasekhar, J.; Jorgensen, W. L.
J. Am. Chem. Soc. 1985, 107, 1496±1500. (b) Lambert, J. B.
Tetrahedron 1990, 46, 2677±2689.
8. (a) Robertson, J.; O'Connor, G.; Middleton, D. S. Tetrahedron
Lett. 1996, 37, 3411±3414. (b) Robertson, J.; Middleton, D. S.;
O'Connor, G.; Sardharwala, T. Tetrahedron Lett. 1998, 39, 669±
672.
23. Marshall, J. A.; Andersen, M. W. J. Org. Chem. 1992, 57,
5851±5856.
24. Johnston, M. I.; Kwass, J. A.; Beal, R. B.; Snider, B. B. J. Org.
Chem. 1987, 52, 5419±5424.
9. Stork, G.; Keitz, P. F. Tetrahedron Lett. 1989, 30, 6981±6984.
10. Prepared using the halogen±metal exchange method of
Seebach: (a) Seebach, D.; Neumann, H. Chem. Ber. 1974, 107,
847±853. (b) Neumann, H.; Seebach, D. Tetrahedron Lett. 1976,
4839±4842.
25. Eliel, E. L.; Wilen, S. H.; Mander, L. N. Stereochemistry of
Organic Compounds; Wiley: New York, 1994; pp 696±697.
26. Braddock, D. C; Hii, K. K.; Brown, J. M. Angew. Chem., Int.
Ed. Engl. 1998, 37, 1720±1723.
11. (a) Ayer, W. A.; Dawe, R.; Eisner, R. A.; Furuichi, K. Can. J.