Silenes as novel synthetic reagents: Identification of a practical method for silene generation and trapping

Article abstract of DOI:10.1039/b404166f

The elucidation of a robust and reliable sequence for the generation of highly reactive transient silenes from simple aldehydes is described. The key step involves a silyl-modified Peterson olefination which critically depends on the presence of a sub-sto

Full text of DOI:10.1039/b404166f

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A R T I C L E
Silenes as novel synthetic reagents: identification of a practical
method for silene generation and trapping
Malcolm B. Berry,b Russell J. Griffiths,a Mahesh J. Sanganee,b Patrick G. Steel*a and
Daniel K. Whelligana
a
Department of Chemistry, University of Durham, Science Laboratories, South Road, Durham,
UK DH1 3LE. E-mail: p.g.steel@durham.ac.uk
Synthetic Chemistry, GlaxoSmithKline, Gunnels Wood Road, Stevenage, Herts.,
b
UK SG1 2NY
Received 22nd March 2004, Accepted 22nd June 2004
First published as an Advance Article on the web 28th July 2004
The elucidation of a robust and reliable sequence for the generation of highly reactive transient silenes from simple
aldehydes is described. The key step involves a silyl-modified Peterson olefination which critically depends on the
presence of a sub-stoichiometric amount of soluble lithium salts (LiBr).
diphenylsilylmethanol.7 This report was subsequently shown to
Introduction
be erroneous8 and the first synthesis was not realised until 1967,
when Gusel’nikov and Flowers unambiguously demonstrated the
transient existence of silenes in the pyrolysis of dimethylsilacy-
clobutane.9 Since then, reflecting the growing interest in their
chemistry, a large number of methods have been developed for the
generation of silenes. However, many of these are not suitable for
general preparative purposes as they require reagents or conditions
that are incompatible with many functional groups. In this paper
we describe our attempts to develop robust and versatile methods
for the selective generation of silenes. In particular we report our
mechanistic findings on the modified Peterson olefination strategy
to provide a convenient method for low temperature silene genera-
tion.10 In the accompanying paper (see ref. 38) we describe how
this approach can be employed to provide a novel method for the
functionalisation of simple butadienes.
Owing to their high reactivity, and in most cases, transient existence
silenes –compoundscontainingasilicon–carbondoublebond – have
been the object of considerable interest.1–6 Much of this effort has
been focused on structural and bonding aspects with a particular
emphasis on the preparation of stable isolable silenes. In many cases,
evidence for the formation of silenes is obtained from the isolation of
adducts from reaction with a large variety of functionality including
alcohols, alkenes and carbonyl compounds, Fig. 1.
Results and discussion
Our initial approach to the application of silenes as new synthetic
reagents was based on the thermolysis of acylpolysilanes first re-
ported by Brook et al.11 The requisite acylsilanes 2 were prepared by
condensation of the Gilman reagent, (Me3Si)3SiLi·3THF,12,13 gener-
ated in situ from (Me3Si)4Si 1 and MeLi, with the appropriate acid
chloride, Scheme 2.14,15 Subsequently, heating a degassed toluene
solution of the acylpolysilane and a two-fold excess of the diene 3 in
a sealed glass tube at 180 °C for 4 h afforded the [4 + 2] silacycload-
ducts 5 in good yields, Table 1, and moderate selectivities favouring
the endo silene R substituent.10a
Fig. 1 Typical reactions of silenes.
However, despite this broad repertoire of chemistry there has
been little effort to exploit the unique reactivity of these species in
organic synthesis. With this objective in mind, we have initiated a
programme to explore this aspect of silene chemistry with a par-
ticular emphasis on cycloaddition chemistry coupled with recently
developed silicon oxidation methods to provide a novel strategy for
the functionalisation of dienes, Scheme 1.
Synthetic approaches to silenes date to 1912 when Schlenk and
Renning first claimed an approach through the dehydration of
Scheme 2 Reagents and conditions: i. MeLi, THF, 18 h, rt then RCOCl
(52–94%); ii. diene 3, PhMe, 180 °C (20–91%).
Scheme 1
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 4
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2
2 3 8 1

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Table 1 Yields of trisilanes 5 obtained through thermolysis of acyl-
polysilanes 2 in the presence of dienes 3
Silene
Diene
4a
4b
4c
4d
4e
4f
b
3x
3y
3z
64%
(2:1)
91%
80%
(3:2)
68%
(2.5:1)
n.a.
46%
(4:1)
85%
(4:1)
n.a.
(80%)a
(2:1)
n.a.
46%
(4:1)
n.a.
—
70%
(6:1)
n.a.
(3:1)
61%c
n.a.
n.a.
a Decomposed upon purification – GC yield. b Inseparable mixture with
competing ene product. c Ca. 1:1 mixture of regioisomers.
Scheme 4 Reagents and conditions: i. h, cyclohexane 10 45%, 11a 5%,
11b 100%; ii. 1,3-pentadiene, THF, 70 °C, 5ax or 1,3-pentadiene, THF, rt,
12b 70%; iii. cyclohexadiene, THF, rt, 13b 69%.
However, despite several literature precedents,16–18 we were
unable to achieve the desired oxidative fragmentation of the trisi-
lanes 5. Based on the work of Fleming et al., we recognised that
incorporation of a silyl aryl group into the silene precursor would
facilitate the oxidative fragmentation.19 Consequently we prepared
the corresponding bis-phenylacyldisilane 8 as outlined in Scheme 3.
Disappointingly, all attempts to carry out the thermolysis with this
substrate failed affording only a polymeric residue.20 At this point,
although providing an efficient means for silene generation we
recognised that this thermal approach had a number of other limita-
tions, namely the use of sealed tube technologies and the moderate
diastereoselectivities.
adducts 12 and 13 in good yields, albeit as inseparable 1:1 mixtures
of diastereoisomers. Having established that these dimers can repre-
sent a convenient source of silenes we then attempted to extend the
scope of this approach. However, photolysis of the corresponding
phenyl analogue 9a afforded the desired dimer in only 5% yield
whilst the alkyl-substituted acylsilanes 9c and 9d underwent com-
plete decomposition. Whilst these problems could potentially be
circumvented by more precise control of the photolysis conditions
the low diastereoselectivity and difficulties in carrying out Flem-
ing–Tamao oxidations of the cycloadducts caused us to abandon
this approach and explore alternative silene generation strategies.
Attracted by the pioneering studies by Oehme and his co-work-
ers, we turned to the silyl-modified Peterson reaction in which
elimination of R3SiO− from a disilanyl alkoxide 16 drives the
generation of the transient silene.22–28 This key intermediate can
be generated in a number of ways, Scheme 5, and we opted to use
the two-stage process via the hydroxypolysilane 15 (path C) since
this would avoid potential problems of competing enolisation and
electron transfer reactions that have been reported with the alterna-
tive pathways.29,30
Scheme 3 Reagents and conditions: i. Mg, TMSCl, HMPA, THF (53%);
ii. MeLi, THF, 18 h, rt then RCOCl (54%); iii. diene, PhMe, 180 °C.
Attempts to enhance the selectivity through the use of various
silyl Lewis acids did not provide a viable solution,21 so we turned to
alternative strategies which avoided the high temperatures required
in the simple thermolysis. In his early work towards stable silenes,
Brook and co-workers demonstrated that silenes can exist in equi-
librium with their corresponding head-to-head dimers.14 Based on
this we speculated that these dimers might provide a convenient
lower temperature source of silenes for our studies. Interestingly,
to the best of our knowledge, no examples have been reported of
the reaction of such silene dimers with dienes. Preliminary studies
using acylpolysilane 2a involved generation of the silene dimer
10a through photolytic activation using a 1 kW mercury arc lamp
in 45% yield, Scheme 4. Dissolution of 10a in THF in the presence
of E-1,3-pentadiene and heating at reflux for 2 h afforded a mixture
of the desired cycloadduct 5ax and unreacted dimer. Importantly,
the diastereoselectivity was slightly enhanced (3:1) as compared
to the original sealed tube thermolysis protocol. Encouraged by this
we then prepared the Si-phenyl-substituted acylpolysilanes 9a–d.
The phenyl 9a and tert-butyl 9b derivatives could be generated by
a method analogous to that described above whilst the alkyl ana-
logues 9c and 9d required a two-step procedure proceeding via the
silyl alcohols 14 (vide infra) to circumvent problems of enolisation
of the initially formed acylsilanes.
Scheme 5
Consequently, silicon–metal exchange of phenyltristrimethyl-
silylsilane 17 with MeLi in THF for 18 h at room temperature
afforded the corresponding silyllithium reagent. Following sol-
vent exchange to Et2O, transmetallation with MgBr2 afforded the
desired silyl Grignard reagent 18. More conveniently, using the
elegant chemistry developed by Marschner, we found that we could
generate 18 by treatment of the silane with KOtBu at room tempera-
ture for 2 h prior to transmetallation with MgBr2 in diethyl ether.31
Subsequent addition of the aldehyde at −78 °C then afforded the
desired alcohol 14 albeit with only moderate levels of conversion
(ca. 50%), Scheme 6.
Amajor by-product in this process was the ester 19 which we pro-
pose was formed by a Tischenko-type process triggered by addition
of the initially formed alkoxide to unreacted aldehyde, Scheme 7.32
Evidence to support this came from a simple crossover experiment
in which the isopropyl-substituted alkoxide 21 was generated by
Photolysis of acylsilane 9b using a 125 W medium pressure mer-
cury lamp in a cooled jacketed reactor afforded the desired head-to
head dimer 11b in excellent yield. Interestingly, it proved necessary
to use a dilute (0.5 M) solution of CuSO4 as the coolant to obtain
efficient yields. We speculate that this acts as a crude filter of higher
energy wavelengths which promote decomposition of the dimer or
intermediate silene. Simply stirring this dimer in THF in the pres-
ence of cyclohexadiene and pentadiene afford the desired [4 + 2]
2 3 8 2
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2

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silacycle 29 could be isolated in 50–63% yield accompanied by a
number of minor components including the silanes 30 and 31 (vide
infra), Scheme 8. However, since attempts to reproduce and opti-
mise this observation gave extremely inconsistent results, we under-
took a detailed analysis of the process. The proposed mechanism for
the generation of the silene involved generation of the alkoxide, mi-
gration of a trimethylsilyl group and then elimination of TMSOLi.25
This suggested that almost any strong base would be sufficient to
promote this reaction and we therefore screened a number of alter-
native conditions, Table 2. Entries 1–3 highlight the unreliability
of MeLi for silene generation although, ironically, no other base
led to generation of silacycle 29, which implies that no other base
gave silene. Entries 4–7 show that the reaction proceeds through the
1,3-Si–O TMS migration with nBuLi and NaH but the resulting silyl
anion does not eliminate Me3SiO− to give silene, hence silanes 30/
31 are produced on work-up. Entry 7 shows that the migration can
be forced to completion by the use of higher temperatures. Entries
8–10 involve bases which are too weak to sufficiently deprotonate
the silyl alcohol 14a, which is believed to have a high pKa due to
electron donation by the electropositive silyl group.
Scheme 6 Reagents and conditions: iA. MeLi, THF, rt 18 h; iB. KOtBu,
THF, 2 h; ii. MgBr2, Et2O; iii. RCHO, Et2O, −78 °C; a CH(CH3) 52%,
b C3H7 74%, c Me 49%, d CH(CH3)C2H5 58%, e C(CH3)3 37%, f c-C6H11
38%, g Ph 63%.
treatment of 14a with MeMgBr and then combined with benzalde-
hyde. GCMS analysis of the reaction mixture revealed formation
of both the cross ester 25 and benzyl alcohol 26 together with trace
amounts of the acylsilane 24, presumably formed by an alternative
hydride transfer process 27.
Whilst the KOtBu method tended to afford greater quantities of
the ester it was found that this could be minimised by the use of 1.1
equivalents of the aldehyde. This optimised procedure afforded the
desired alcohol in yields ranging from 37 to 63% with the major
by-product being the silane 20 corresponding to protonation of the
silyl metallic reagent. Enolisation of the aldehyde was ruled out as
a major factor in this process as a study of the reaction with pivalde-
hyde revealed a similar, if unoptimised, product profile. Our current
hypothesis is that there may be a ligand exchange process occurring
involving the alkoxide and silyl Grignard reagent to produce the
mixed organometallic species 28 which is unreactive with respect
to aldehydes.33 Attempts to enhance the conversion (yield) through
a screen of various other metal counter ions (including Ce, Yb, Cu
and Zn) and additives (TMEDA, DMPU, etc.) were not productive
and further detailed studies of this transformation are in progress.
With the silyl alcohols readily available we then turned to study
the key silene generation step. Oehme had reported that deproton-
ation with MeLi in the presence of a diene at −78 °C afforded the
silene as detected by the [4 + 2] cycloadduct formed with 2,3-di-
methylbutadiene.26 In our hands, using alcohol 14a as the silene
precursor and E-1,3-pentadiene as the silenophile, no reaction
occurred until the mixture was warmed to ca. −30 °C, when the
Scheme 8
The use of TBAF and Me3SiOK in entries 11 and 12 were tests of
an alternative mechanistic hypothesis involving nucleophilic attack
at a TMS group of silyl alcohol 14a and elimination of hydroxide
to produce the silene, Scheme 9.34 However, in neither case was
Scheme 7
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2
2 3 8 3

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Table 2
Table 3
Molar % by NMRa
Molar % by NMRa
Entry
Base
Temp./°C
Time/h
14a
30
29
Entry
Base
Additive (mol%)
Method
14a
30
33b
1
2
3
4
5
6
7
8
9
MeLib
MeLid
MeLie
nBuLi
NaH
2NaH
2NaH
LiH
−78 to −30
−78 to −30
−78 to −30
−78 to −30
−78 to RT
−78 to −30
−78 to reflux
−78 to −30
−78 to reflux
−78 to −30
−78 to −30
−78 to −20
22
18
20
18
39
87
7
18
41
18
18
21
0
83
72
52
69
18
0
95
95
100
100
93
9
17
8
48
31
82
100
5
5
0
0
7
91c
0
20
0
0
0
0
0
0
0
1
2
3
4
5
6
7
8
9
nBuLi
NaHc
nBuLi
nBuLid
nBuLi
nBuLi
nBuLi
nBuLi
nBuLi
nBuLi
None
—
B
A
A
A
A
A
B
B
B
52
12
71
100
86
90
60
7
48
88
29
0
14
10
40
17
21
14
0
0
0
0
0
LiCl (220%)
LiCl (60%)
LiBr (70%)
LiBr (100%)
LiBr (30%)
LiBr (6%)
LiBr (100%)
LiBr (10%)
LiI 100%c
0
0
76e
72
80f
2LiH
7
6
10
11
12
LiOH
TBAF
Me3SiOK
10
0
0
aAnalysis of crude reaction mixture following work-up – see Experimental
section. b Identified as [4 + 2] cycloadduct 29. c 2 equiv. d 1.7 equiv. e 50%
isolated yield. f 36% isolated yield.
a Ratio of products detected in the crude NMR spectrum for the reaction
with each base. b Batch X ≤ 6 mol% LiBr. c Isolated yield 52%. d Batch Y.
e Batch Z.
A thorough investigation into the addition of lithium salts to the
reaction mixture of silyl alcohol 14a, 1,3-pentadiene and base was
then undertaken and these results are summarised in Table 3. The
salts were added either prior to the addition of base (Method A)
or after complete conversion to silylmetallic 38 (Method B). Ad-
dition of LiCl even in large excesses did not lead to any products
arising from a silene being detected (entries 2, 3). This suggested
that elimination of Me3SiOLi had not occurred, which could be at-
tributed to the insolubility of LiCl. Attempts to simulate successful
reactions using MeLi by the addition of LiBr prior to base were
also unsuccessful (entries 4–7). Finally, it was discovered that low
temperature addition of LiBr, after complete conversion of silyl
alcohol 14a to silyllithium 38 by treatment with nBuLi at rt for 3 h,
afforded silene (entry 8) and that the LiBr could be used in sub-stoi-
chiometric quantities (entry 9). Similar experiments with LiI were
also successful but this reagent was harder to dry, due to its lower
temperature of sublimation, and ultimately produced lower overall
yields (entry 10).
the silene generated. Speculating that a better leaving group than
hydroxide was required, attempts were made to convert the alcohol
into the tosylate and mesylate. Although these reactions failed due
to the steric congestion around the silyl alcohol 14a, the correspond-
ing trifluoroacetate was prepared. However, reaction of this with
MeLi re-generated silyl alcohol 14a, due to nucleophilic attack at
the ester, and treatment with TBAF yielded a complex mixture of
products, none of which could be ascribed to silene generation.
Scheme 9
We rationalise these observations using the mechanistic scheme
shown below, Scheme 11. Treatment of the silyl alcohol with BuLi
generates the alkoxide 37. A 1,3-Si–O silyl migration then occurs
over 3 h at rt to produce the silyl anion 38 which undergoes elimi-
nation promoted by a catalytic amount of LiBr.36 In the absence of
soluble Li salts no elimination occurs, whilst in the presence of a
high initial concentration of Li ions the initial silyl migration is hin-
dered by coordination/aggregation resulting in low conversions.
At this stage suspecting that additive(s) within the commercial
samples of ethereal MeLi used were aiding the generation of the
silene we looked in more detail at the MeLi solutions that had been
used. Although described as ‘low chloride’, these are reported to
n
contain varying amounts of LiBr (≤6%). In contrast, the BuLi
used was a solution in hexane and free from additional lithium salts
which was consistent with our inability to generate silenes with this
base. A search of the literature revealed that Oehme and co-workers
had found the presence of LiBr to have an effect on the rate of silene
generation;35 formation of silene 36, by treatment of silyl alcohol
34 with a Grignard reagent, normally proceeded extremely slowly,
but in the presence of LiBr, the reaction was complete within a few
hours, Scheme 10. Unfortunately, Oehme’s group did not offer an
explanation for this observation.
Scheme 10
Scheme 11
2 3 8 4
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2

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With a reliable protocol in hand we were able to extend our stud-
ies to a range of different silenes and dienes (silenophiles), Fig. 2.
In all cases the reactions were carried out by treating the mixture
of silyl alcohol, diene in Et2O with BuLi at room temperature until
complete migration of the trimethylsilyl group had occurred as
monitored by analysis of an aliquot (GC/TLC). Cooling to −78 °C,
addition of a freshly dried sample of LiBr in Et2O and allowing the
reaction to warm to −30 °C overnight afforded, after simple aqueous
work-up and chromatography, the desired silacycles, accompanied
by small and varying amounts of competing ene, [2 + 2] and silene
dimers. However, with dienes lacking a terminal methyl group,
2,3-dimethylbutadiene and isoprene, more significant amounts of
ene product were isolated (ca. 12%). In all cases involving non-
symmetrical dienes good regioselectivity was observed, being
consistent with simple FMO theory placing the largest coefficient
of the silene LUMO on silicon. Morever, good diastereoselectivity
was observed suggesting that silene generation had occurred with
a high degree of selectivity.37 The only difference between this
method and those using MeLi that were successful is that the latter
affords slightly higher, albeit less reproducible, selectivities (see
Experimental section). We speculate that, when successful, the use
of MeLi solutions affords a slower elimination of Me3SiOLi, limit-
ing the transient concentration of silene present and thus minimising
the possibility for the alternative pathways. Limitations appeared in
that more hindered dienes, e.g. cyclohexadiene, do not undergo the
reaction competitively with silene dimerisation, whilst attempts to
carry out the reaction with 1,6-bismethoxyhexa-2,4-diene failed to
proceed beyond the silyl migration stage.
Still et al. (W. C. Still, M. Kahn and A. Mitra, J. Org. Chem., 1978,
43, 2923) using 200–400 mesh silica gel. Yields refer to isolated
yields of products of greater than 95% purity as determined by 1H
and 13C NMR spectroscopy or elemental analysis (Durham Univer-
sity Microanalytical Laboratory).
Melting points were determined using Gallenkamp melting point
apparatus and are uncorrected. Infrared spectra were recorded as thin
films between KBr plates (liquids) or as compression-formed discs
made using KBr (solids) on a Perkin-Elmer FT-IR 1600 spectrome-
ter. Unless otherwise stated 1H NMR spectra were recorded in CDCl3
on Varian Mercury 200, Bruker AM-250, Varian Unity-300, Varian
VXR-400 or Varian Inova-500 spectrometers and are reported as fol-
lows: chemical shift  (ppm) [number of protons, multiplicity, cou-
pling constant J (Hz), assignment]. Residual protic solvent CHCl3
(H = 7.26 ppm) was used as the internal reference. 13C NMR spectra
were recorded at 63 MHz, 101 MHz or 126 MHz on Bruker AM-
250, Varian VXR-400 or Varian Inova-500 instruments, respectively,
using the central resonance of CDCl3 (c = 77.0 ppm) as the internal
reference. 29Si NMR spectra were recorded at 99 MHz on a Varian
Inova-500 spectrometer. 19F NMR spectra were recorded at 376 MHz
or 282 MHz on Varian VXR-400 or Varian Unity-300 spectrometers,
respectively. All chemical shifts are quoted in parts per million rela-
tive to tetramethylsilane (H = 0.00 ppm) and coupling constants are
given in Hertz to the nearest 0.3 Hz. All 13C spectra were proton de-
coupled. Assignment of spectra was carried out using DEPT, COSY,
HSQC and NOESY experiments. Low-resolution mass spectra (EI
or CI) were obtained on a Micromass Autospec Mass Spectrom-
eter. Gas chromatography–mass spectra (GCMS, EI or CI) were
taken using a Hewlett Packard 5890 Series II gas chromatograph,
equipped with a 25 m 5% diphenyl-/95% dimethyl-polysiloxane col-
umn and flame ionisation detection, connected to a VG Trio-1000
mass spectrometer. Electrospray mass spectra (ES) were obtained on
a Micromass LCT Mass Spectrometer. High-resolution mass spectra
were performed by the EPSRC service at the University of Swansea
or on a Micromass Autospec Mass Spectrometer in Durham.
General procedure for the formation of acyltris(trimethylsilyl)-
silanes (ref. 11)
Methyllithium (1.6 M solution in ether) was added to a solution
of tetrakis(trimethylsilyl)silane (0.23 M, 1 equiv.) in THF. After
approximately 18 h, 1H NMR showed the complete disappearance
of the signal for tetrakis(trimethylsilyl)silane and the appearance at
0.32 ppm of the signal for tris(trimethylsilyl)silyllithium.The yellow
solution was then cooled to −78 °C and added dropwise via cannula
to a cooled (−78 °C) solution of acyl chloride (0.46 M, 2 equiv.) in
THF over a 2 h period. After stirring for 4 h at −78 °C, dilute HCl
(3 M, 100 ml) was added. The organic layer was separated, and the
aqueous layer extracted with diethyl ether. The combined organic
layers were dried over MgSO4. The mixture was then filtered, and
the solvents removed via rotary evaporation. Flash column chroma-
tography yielded the pure acyltris(trimethylsilyl)silane.
Fig. 2 [4 + 2] Silacycloadducts generated via the modified Peterson reac-
tion: a ratio of isomeric [4 + 2] cycloadducts (major isomer only shown – see
ref. 39); b accompanied by ca. 12% ene product; c mixture of regioisomers.
Benzoyltris(trimethylsilyl)silane 2a.11 (77% yield) vmax (thin
film) 3062, 2949, 2893, 2360, 2341, 1737, 1607, 1593, 1575, 1445,
1399, 1308, 1245, 1200, 1167 cm−1; H (200 MHz) 7.7–7.3 (5H,
m, Ar–H), 0.25 (27H, s, Si(CH3)3); C (126 MHz) 234.26, 144.09,
133.35, 128.48, 127.52, 1.26; MS (EI) m/z 352 (M+, 1%), 279 [M+ −
Si(CH3)3, 5%], 135 (14), 73 (100).
In conclusion, we have developed a reliable method for the gen-
eration of simple alkyl- and aryl-silenes from aldehydes. These can
be trapped in situ by alkylbutadienes to afford silacyles in moderate
yields and good selectivities. These represent useful building blocks
for the generation of diols and lactones and this is described in detail
in the following paper.38
4-Methoxybenzoyltris(trimethylsilyl)silane 2b.39 (62%). vmax
(thin film) 3004, 2953, 2895, 2839, 2360, 2341, 1691, 1608, 1586,
1569, 1505, 1463, 1552, 1399, 1307, 1259, 1209, 1159 cm−1; H
(400 MHz) 7.73 (2H, d, J = 8.7 Hz, Ar–H), 6.92 (2H, d, J = 8.7 Hz,
Ar–H), 3.67 (3H, s, OCH3), 0.25 (27H, Si(CH3)3); C (126 MHz)
232.98, 163.16, 137.61, 129.97, 113.28, 55.42, 1.528; MS (EI) m/z
383 (MH+, 4%), 367 (M+ − CH3, 15%), 311 (MH+ − SiMe3, 17%),
279 (40), 221 (12), 209 (41) 152 (100), 147 (61), 135 (100), 92 (40),
73 (100); MS (CI) m/z 383 (MH+, 6%), 209 (19), 170 (17), 152 (27),
137 (32), 90 (42).
Experimental
All air- and/or moisture-sensitive reactions were carried out under
an argon atmosphere. Solvents were purified following established
protocols. Petrol refers to petroleum spirit, boiling point in the
40–60 °C range. Ether refers to diethyl ether. Commercially avail-
able reagents were used as received unless otherwise stated. Flash
column chromatography was performed according to the method of
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2
2 3 8 5

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4-Trifluoromethylbenzoyltris(trimethylsilyl)silane 2c. (94%)
vmax (thin film) 3063, 2956, 2896, 1933, 1800, 1730, 1619, 1605,
1580, 1505, 1405, 1327, 1249 cm−1; H (200 MHz) 7.80 (2H, d,
J = 8.4 Hz)−7.72 (2H, d, J = 8.4 Hz), 0.23 (27H, s, 3 × Si(CH3)3; C
(126MHz)236.50,145.88,133.28(q,2JC–F = 32.7Hz,C–CF3),127.02,
125.11 (q, JC–F = 3.8 Hz, C–C–CF3), 123.34 (q, JC–F = 272.9 Hz,
CF3), 1.20; F (235 MHz) −63.28; MS (EI) m/z 405 (M+–CH3), 281
(60), 207 (36), 190 (35), 173 (62), 147 (66), 73 (100).
column chromatography, gave the Diels–Alder adduct as a mixture
of regio- and/or diastereo-isomers.
1,1-Bistrimethylsilyl-2-phenyl-2-(trimethylsilyloxy)-4-
methylsilacyclohex-4-ene 5azA; and 1,1-bistrimethylsilyl-2-
phenyl-2-(trimethylsilyloxy)-5-methylsilacyclohex-4-ene 5azB.
Reaction of benzoyltris(trimethylsilyl)silane with isoprene gave
the title compounds as a mixture of regioisomers (1:1) (61%). Mp
113–114 °C. vmax (CHCl3) 3019, 2955, 2894, 1597, 1488, 1443,
1400, 1248 cm−1; H 7.45–6.90 (5H, m, Ar–H), 6.75–5.65 [0.5H, m,
4-H, (B)], 5.45–5.35 [0.5H, m, 5-H,(A)], 2.95–2.50 (2H, m, 3-H2),
1.79 [1.5H, s, 5-(CHd3) (B)], 1.70 [1.5H, s, 4-(CH3) (A)], 1.65–1.15
(2H, m, 6-H2), 0.11 [4.5H, s, Si(CH3)3], 0.02 [4.5H, s, Si(CH3)3],
0.01 [4.5H, s, Si(CH3)3], −0.08 [4.5H, s, Si(CH3)3], −0.18 [4.5H, s,
Si(CH3)3], −0.25 [4.5H, s, Si(CH3)3]; C (63 MHz) 149.89, 135.41,
134.25, 127.79, 125.32, 125.07, 124.59, 121.60, 46.27, 40.50,
30.87, 27.60, 25.30, 13.80, 7.90, 2.89, 0.07, −0.49; m/z (CI) 421
(MH+, 2%), 348 (18), 331 (67), 90 (64), 73 (100); HRMS (CI):
Found MH+, 421.2235; C21H40Si4O requires M, 421.2234.
3
1
2,4-(Dimethoxy)benzoyltris(trimethylsilyl)silane 2d. (35%).
vmax (thin film) 2955, 2893, 2837, 2361, 2340, 1606, 1497, 1464,
1439, 1412, 1307, 1284, 1258, 1245, 1159 cm−1; H (250 MHz)
7.20–7.10 (1H, m, Ar), 6.5–6.3 (2H, m, Ar), 3.83 (3H, s, –OCH3),
3.78 (3H, s, –OCH3), 0.19 (27H, s, –Si(Si(CH3)3)); C (63 MHz)
237.81, 162.43, 157.35, 131.38, 129.92, 103.59, 98.56, 56.51, 1.27;
MS (EI) m/z 413 (MH+, 15%), 398 (MH+ − CH3, 15%), 339 [M+ −
Si(CH3)3, 11%], 309 (31), 281 (24), 239 (36), 191 (60), 165 (100),
149 (63), 131 (58), 73 (100).
Acetyltris(trimethylsilyl)silane 2e.11 (76%) vmax (CHCl3)
3019, 2959, 2867, 2360, 2340, 1740, 1626, 1251, 1225 cm−1; H
(200 MHz) 2.29 (3H, s, –CH3), 0.24 (27H, s, –SiCH3); C (50 MHz)
244.03, 42.11, 1.00.
1,1-Bistrimethylsilyl-2-phenyl-2-(trimethylsilyloxy)-3-
methyl-silacyclohex-4-ene 5ax. Reaction of benzoyltris(tri-
methylsilyl)silane with E-1,3-pentadiene gave the title compound
as a mixture of diastereoisomers [64%, 2:1 endo(Ph):exo(Ph)]. Mp
173–174 °C; vmax (CHCl3) 3155, 2998, 2953, 2895, 1793, 1639,
1599, 1471, 1389, 1251 cm−1; H (250 MHz) 7.32–7.03 (5H, m,
Ar–H), 5.93–5.85 (1H, m, 4-H), 5.56–5.43 (1H, m, 5-H), 3.20–3.10
(0.33H, m, 3-H exo), 3.10–2.95 (0.67H, 3-H endo) 1.80–1.23 (2H,
m, 6-H2), 1.04 (1H, d, J = 7.4 Hz, CH3 exo), 0.95 (2H, d, J = 7.2 Hz,
CH3 endo), 0.18 [6H, s, OSi(CH3)3 endo], 0.17 [6H, s, Si(CH3)3
endo], 0.07 [3H, s, OSi(CH3)3 exo], 0.03 [3H, s, Si(CH3)3 exo], −0.02
[6H, s, Si(CH3)3 endo], −0.32 [3H, s, –Si(CH3)3 exo]; C (50 MHz)
148.10, 146.00, 136.98, 134.44, 127.95, 127.65, 126.61, 125.89,
125.37, 125.00, 80.98, 79.11, 43.17, 40.19, 16.57, 16.19, 9.21, 8.44,
3.76, 3.50, 0.71, 0.24, −0.97; m/z (EI) 420 (M+, 3%), 405 (M+ − CH3,
1%), 347 (M+ − SiMe3, 37%), 205 (41), 199 (61), 73 (100).
Trimethylacetyltris(trimethylsilyl)silane 2f.11 (52%). Mp
181–182 °C decomp. vmax (CHCl3) 3020, 2963, 2896, 1709, 1619,
1522, 1247, 1225 cm−1; H (250 MHz) 1.02 [s, 9H, C(O)C(CH3)3],
0.23 {s, 27H, 3 × [Si(CH3)3]}; C (63 MHz) 248.5, 49.5, 24.7, 1.61;
MS (EI) m/z 317 (M+ − CH3, 16%), 275 [M+ − C(CH3)3, 5%], 259
[M+ − Si(CH3)3, 22%], 205 (11), 191 (10), 173 (100), 159 (19), 147
(55), 131 (31), 117 (21), 73 (100); (CI) m/z 317 (M+ − CH3, 13%),
191 (9), 90 (13).
Benzoyldiphenyltrimethylsilylsilane 8. Prepared in an identi-
cal fashion starting from diphenylbis(trimethylsilyl)silane (3.02 g,
9.21 mmol) to give the title compound as a colourless oil (1.79 g,
54%). vmax (thin film) 3067, 3050, 2955, 2894, 1608, 1574, 1428,
1246, 1207, 839 cm−1; H (300 MHz) 7.80–7.30 (15H, m, Ar–H),
0.22 [9H, s, Si(CH3)3]; C (50 MHz) 232.76, 142.22, 135.81, 134.11,
129.40, 128.33, 128.19, 128.10, 127.74, −1.21; m/z (EI) 360 (M+, 5%),
345 (M+ − Me, 22%), 287 (M+ − SiMe3, 25%), 105 (67), 73 (100).
1,1-Bistrimethylsilyl-2-(4-methoxyphenyl)-2-(trimethyl-
silyloxy)-3-methyl-silacyclohex-4-ene 5bx. Reaction of 4-
methoxybenzoyltris(trimethylsilyl)silane with E-1,3-pentadiene
gave the title compound as a mixture of diastereoisomers [80%,
3:2 endo(Ar):exo(Ar)].
Benzoylbis(trimethylsilyl)phenylsilane 9a. Prepared in an
identical fashion starting from phenyltris(trimethylsilyl)silane
(5.16 g, 15.94 mmol) to give the title compound as a yellow oil
(2.75 g, 50%). vmax (thin film) 3066, 2953, 2893 1739, 1720, 1700,
1605, 1573, 1400, 1314, 1247, 1202, 1171, 1110, 1065, 838 cm−1;
H (300 MHz) 7.75–7.30 (10H, m, Ar–H), 0.23 [18H, s, Si(CH3)3];
C (100 MHz) 235.39, 142.65, 135.77, 134.91, 132.60, 128.52,
128.37, 128.26, 128.17, 0.42; m/z (ES+) 357 (M + 1, 20%), 279
(M − Ph, 100%).
vmax (thin film) 2997, 2951, 2894, 2833, 1608, 1508, 1463, 1441,
1391, 1291, 1250, 1179, 1068, 836 cm−1; H (400 MHz) 7.30–7.18
(2H, m, Ar–H), 6.90–6.75 (2H, m, Ar–H), 6.0–5.85 (1H, m, 4-H),
5.6–5.4 (1H, m, 5-H), 3.81 (1.2H, s, –OMe, exo), 3.80 (1.8H, s,
–OMe, endo), 3.20–3.10, (0.4H, m, 3-H exo), 3.10–3.00 (0.6H,
m, 3-H endo), 1.85–1.2 (2H, m, 6-H2), 1.08 (1.2H, d, J = 7.2 Hz,
3-CH3 exo), 0.97 (1.8H, d, J = 7.2 Hz, 3-CH3 endo), 0.20 [5.4H,
s, OSi(CH3)3 endo], 0.18 [5.4H, s, Si(CH3)3 endo], 0.08 [3.6H, s,
OSi(CH3)3 exo], 0.04 [3.6H, s, Si(CH3)3 exo], −0.07 [3.6H, Si(CH3)3
exo], −0.25 [5.4H, Si(CH3)3 endo]; C (63 MHz) 157.20, 157.17,
140.46, 138.39, 136.91, 134.46, 126.79, 126.63, 126.53, 125.88,
113.23, 113.00, 80.44, 78.82, 55.25, 55.22, 43.18, 40.31, 16.53,
16.13, 9.15, 8.50, 3.63, 3.40, 0.61, 0.23, 0.15, −0.03, −0.88; m/z
(EI) 450 (M+, 7%), 435 (M+ − CH3, 9%), 377 [M+ − Si(CH3)3, 12%],
275 (100), 147 (24), 73 (84).
Trimethylacetylbis(trimethylsilyl)phenylsilane 9b.14 Pre-
pared in an identical fashion using phenyltris(trimethylsilyl)silane
(14.85 g, 45.83 mmol) and trimethylacetyl chloride to give the title
compound as a colourless oil (12.57 g, 82%). vmax (thin film) 3069,
2957, 2897, 2868, 1729, 1703, 1619, 1475, 1428, 1361, 1246, 1063,
943, 837 cm−1; H (200 MHz) 7.64–7.30 (5H, m, Ar–H), 0.95 [9H, s,
–C(CH3)3], 0.25 [18H, s, Si(CH3)3]; C (125 MHz) 249.55, 136.87,
135.38, 128.76, 128.10, 50.27, 25.01, 0.33; m/z (EI) 279 [M+ −
C(CH3)3, 25%], 265 [M+ − Si(CH3)3, 3%], 251 [M+ − C(O)tBu,
100%], 209 (26), 193 (32), 177 (22), 73 (67).
1,1-Bistrimethylsilyl-2-(2,4-bismethoxyphenyl)-2-(tri-
methylsilyloxy)-3-methyl-silacyclohex-4-ene 5dx. Reaction of
2,4-bis(methoxy)benzoyltris(trimethylsilyl)silane 2d with E-1,3-
pentadiene gave the title [4 + 2] adduct as a mixture of diastereo-
isomers (ca. 80%, ca. 1:1 endo:exo) (1H NMR) along with several
inseparable components; m/z (CI) 481 (MH+, 100%), 408 [MH+ −
Si(CH3)3, 4%], 392 [MH+ − OSi(CH3)3, 31%].
General procedure for the thermolysis of acyltris(trimethyl-
silyl)silanes in the presence of dienes.
A solution of the acylpolysilane (0.28 M) and diene (2 equiv.) in
benzene or toluene was placed in a Carius tube, and thoroughly
degassed using the freeze–pump–thaw technique (minimum 3
cycles). The tube was then sealed, and heated at 180 °C for 4 h.
Removal of the solvent by rotary evaporation, followed by flash
1-Bistrimethylsilyl-2-(4-trifluoromethyl)phenyl-2-trimethyl-
silyloxy-3-methylsilacyclohex-4-ene 5cx. Reaction of 4-trifluor
omethylbenzoyltris(trimethylsilyl)silane 2c with E-1,3-pentadiene
gave the title compound as a mixture of diastereoisomers (46%,
2 3 8 6
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2

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4:1 endo:exo). Mp 98–100 °C; vmax (KBr disc) 2998, 2955, 2895,
1614, 1408, 1329, 1243, 1161, 1119, 1079, 1069, 835 cm−1; H
(250 MHz) 7.60–7.20 (4H, m, Ar–H), 6.00–5.80 (1H, m, 4-H),
5.50–5.20 (1H, m, 5-H), 3.20–3.10 (0.2H, m, 3-H exo), 3.10–3.00
(0.8H, m, 3-H endo), 1.80–1.30 (2H, m, 6-H2), 1.03 (0.6H, d,
J = 7.4 Hz, 3-CH3 exo), 0.97 (2.4H, d, J = 7.2 Hz, 3-CH3 endo),
0.22 [7.2H, s, OSi(CH3)3 endo], 0.20 [7.2H, s, Si(CH3)3 endo], 0.12
[1.8H, s, Si(CH3)3 exo], 0.08 [1.8H, s, OSi(CH3)3 exo], −0.30 [7.2H,
s, Si(CH3)3 endo], −0.01 [1.2H, s, Si(CH3)3 exo]; 19F (235 MHz)
−62.52; m/z (EI) 487 (M+ − H, 2%), 415 [M+ − Si(SiMe3)3, 17%],
312 (30), 262 (37), 147 (28), 73 (100). Repeated flash column
chromatography (eluting petrol) gave the endo diastereoisomer as
a single isomer. H (300 MHz) 7.51 (2H, d, J = 8.4 Hz, Ar–H), 7.46
(2H, d, J = 8.4 Hz, Ar–H), 5.95 (1H, m, 4-H), 5.58 (1H, m, 5-H),
3.10 (1H, m, 3-H), 1.40 (2H, m, 6-H2), 0.98 (3H, d, J = 7.4 Hz, 3-
CH3), 0.22 [9H, s, OSi(CH3)3], 0.20 [9H, s, Si(CH3)3], −0.30 [9H, s,
Si(CH3)3]; C (75 MHz) 150.59, 136.82, 127.06 (q, 2JC–F = 31.95 Hz
s, Si(CH3)3 exo], −0.16 [6.48H, Si(CH3)3 endo], −0.26 [6.48H, s,
Si(CH3)3 endo], −0.27 [2.52H, s, Si(CH3)3 exo]; C (50 MHz)
157.86, 140.18, 138.86, 133.52, 132.21, 131.34, 130.97, 129.73,
129.50, 113.16, 112.98, 87.50, 86.45, 55.31, 55.25, 51.85, 50.89,
45.30, 44.58, 34.22, 33.4, 30.96, 2.55, 2.46, 0.94, 0.14, −0.13,
−0.37; m/z (EI) 448 (M+, 1%), 209 (20), 73 (100); HRMS (EI):
Found M+, 448.2113; C22H40O2Si4 requires M, 448.2105.
2,2-Bistrimethylsilyl-3-[4′-(trifluoromethyl)phenyl]-3-tri-
methylsilyloxy-2-silabicyclo[2.2.1]hept-5-ene 5cy. Reaction of
4-trifluoromethylbenzoyltris(trimethylsilyl)silane 2c with cyclopen-
tadiene gave the title compound as a mixture of diastereoisomers
(85%, 4:1 endo:exo). vmax 3062, 2955, 2896, 1926, 1794, 1614,
1445, 1406, 1326, 1250, 1168 cm−1; H (250 MHz) 7.51 (1.6H, d,
J = 8.2 Hz, Ar–H endo), 7.40 (1.6H, d, J = 8.2 Hz, Ar–H endo),
7.35 (0.4H, d, J = 8.2 Hz, Ar–H exo), 7.27 (0.4H, d, J = 8.2 Hz,
Ar–H exo), 6.30 (0.2H, dd, J = 8.3, 3.6 Hz, 5-H exo), 6.15 (0.8H,
dd, J = 8.3, 3.6 Hz, 5-H endo), 5.94 (0.2H, dd, J = 8.3, 3.2 Hz, 6-H
exo), 5.79 (0.8H, dd, J = 8.3, 3.2 Hz, 6-H endo), 3.31 (0.2H, m, 4-
H exo), 3.05 (0.8H, m, 4-H endo), 2.35 (2H, m, 7-H2), 2.05 (0.8H,
m, 6-H endo), 2.01 (0.2H, m, 1-H exo), 0.32 [7.2H, s, –OSi(CH3)3
endo], 0.14 [1.8H, s, OSi(CH3)3 exo], −0.07 [1.8H, s, Si(CH3)3 exo],
−0.16 [7.2H, s, Si(CH3)3 endo], −0.30 [9H, s, Si(CH3)3]; C (63 MHz)
152.85, 151.14, 141.03, 139.39, 129.54 (q, J = 32.4 Hz, C–CF3 exo),
128.20 (q, J = 32.4 Hz, C–CF3 endo), 125.80(q, J = 3.6 Hz, C–C–CF3
exo) 124.72 (q, J = 3.7 Hz, C–C–CF3 endo), 124.24 (q, J = 272.3 Hz,
CF3 endo) 123.80 (q, J = 272.4 Hz, CF3 exo), 86.82, 84.51, 51.53,
50.93, 45.62, 44.79, 34.21, 30.95, 2.5, 2.14, 0.86, 0.03, −0.36, −0.61;
19F (235 MHz) −62.69; m/z (CI, NH3) 487 (MH+, 2%), 466 (MH+ −
F, 3%), 405 (24), 397 (30), 203 (57), 147 (20), 90 (58), 73 (100).
3
F3C–C), 126.02, 125.32, 124.60 (q, JC–F = 3.75 Hz, F3C–C–CH),
1
124.49 (q, JC–F = 269.93 Hz, CF3), 122.69, 119.10, 79.09, 42.97,
16.52, 8.26, 3.45, 0.66, −1.10.
2-Methyl-1-bistrimethylsilyl-2-trimethylsilyloxy-3-methyl-
silacyclohex-4-ene 5ex. Reaction of acetyltris(trimethylsilyl)-
silane 4e with E-1,3-pentadiene gave the title compound as a
mixture of diastereoisomers (ca. 21%, 2:1 endo:exo), along
with other inseparable components. H (200 MHz) 5.80–5.20 (2H,
m, CH), 2.60–2.50 (0.33H, m, 3-H exo), 2.26–2.20 (0.67H, m,
3-H endo), 1.70–1.10 (2H, m, 6-H2), 1.53 (1H, s, 2-CH3 exo), 1.34
(2H, s, 2-CH3 endo), 1.09 (1H, d, J = 6.8 Hz, 3-CH3 exo), 1.00
(2H, d, J = 7.2 Hz, 3-CH3 endo), 0.16–0.13 [5 × 9H, s, Si(CH3)3];
C (100 MHz) 135.00, 125.78, 45.62, 43.48, 30.70, 23.34, 16.48,
14.92, 8.86, 7.98, 3.54, 0.38, 0.23; m/z (EI) 285 [M+ − Si(CH3)3,
7%], 207 (61), 183 (29),147 (72), 133 (58), 73 (100).
2,2-Bistrimethylsilyl-3-tert-butyl-3-trimethylsilyloxy-2-sila-
bicyclo[2.2.1]hept-5-ene 5fy. Reaction of trimethylacetyltris(tri-
methylsilyl)silane 2f with cyclopentadiene gave the title compound
as a mixture of diastereoisomers (70%, 6:1 endo:exo).
2,2-Bis(trimethylsilyl)-3-phenyl-3-trimethylsilyloxy-2-
silabicyclo[2.2.1]hept-5-ene 5ay. Reaction of benzoyltris(tri-
methylsilyl)silane 2a with cyclopentadiene gave the title compound
as a mixture of diastereoisomers (0.433 g, 68%, 3:1 endo:exo).
Mp 88–89 °C; vmax (CHCl3) 3050, 2948, 2878, 1599, 1500, 1250,
1169, 1041, 1021, 838 cm−1; H (400 MHz) 7.40–7.05 (5H, m,
Ar–H), 6.32 (0.25H, dd, J = 5.4, 3.3 Hz, 5-H exo), 6.11 (0.75H,
dd, J = 5.4, 3.3 Hz, 5-H endo), 5.86 (0.25H, dd, J = 5.4, 3.3 Hz,
6-H exo), 5.77 (0.75H, dd, J = 5.4, 3.3 Hz, 6-H endo), 3.40 (0.25H,
m, 4-H, exo), 3.30 (0.75H, m, 4-H, endo), 2.45 (0.25H, m, 7-HH
exo), 2.35 (1.75H, m, 7-H2 endo and 7-HH exo), 2.02 (0.75H, m,
1-H endo), 1.95 (0.25H, m, 1-H exo), 0.28 [6.75H, s, OSi(CH3)3
endo], 0.21 [2.25H, s, OSi(CH3)3 exo], −0.16 [2.25H, s, Si(CH3)3
exo], −0.18 [6.75H, s, Si(CH3)3 endo], −0.28 [6.75H, s, Si(CH3)3
endo], −0.29 [2.25H, s, Si(CH3)3 exo]; C (100 MHz) 148.11,
146.46, 140.37, 139.07, 129.89, 129.51, 127.84, 127.75, 126.10,
125.66, 87.07, 84.45, 51.54, 50.66, 45.44, 44.56, 34.15, 30.86, 2.44,
0.89, 0.06, −0.33, −0.59; m/z (EI) 418 (M+, 2%), 403 (M+ − CH3,
1%), 345 (M+ − SiMe3, 16%), 337 (50), 147 (42), 135 (21), 117
(21), 73 (100).
vmax (thin film) 3051, 2945, 2887, 1621, 1500, 1212, 1153, 1042,
1021, 822 cm−1; H (250 MHz) 6.31 (0.14H, dd, J = 5.3, 3.2 Hz,
5-H), 6.09 (0.86H, dd, J = 5.4, 3.2 Hz, 5-H), 5.90 (0.14H, dd,
J = 5.3, 3.2 Hz, 6-H), 5.65 (0.86H, dd, J = 5.4, 3.2 Hz, 6-H), 2.89
(0.14H, m, 4-H), 2.77 (0.86H, m, 4-H), 2.35–2.18 (2H, m, 7-Hd2);
2.90–2.80 (1H, m, 3-H), 1.06 [1.26H, s, C(CH3)3], 0.99 [7.74H,
s, C(CH3)3], 0.22 [7.74H, Si(CH3)3], 0.21 [1.26H, Si(CH3)3], 0.19
[1.26H, Si(CH3)3], 0.17 [7.74H, Si(CH3)3], 0.15 [7.74H, Si(CH3)3],
0.14 [1.26H, Si(CH3)3]; C (100 MHz) 138.77, 129.36, 100.14,
52.12, 47.69, 38.43, 31.24, 30.42, 4.68, 2.08, 1.53; m/z (EI) 400
(M+, 1%), 385 (M+ − CH3, 1%), 73 (100).
2,2-Diphenyl-1,1,1,3,3,3-hexamethyltrisilane 7.40 A mixture
of chlorotrimethylsilane (14.96 g, 137.2 mmol) and dichloro-
diphenylsilane (17.36 g, 68.62 mmol) was added to a stirred suspen-
sion of magnesium turnings in THF/HMPA (1:1, 100 ml), so as to
maintain a gentle reflux. The mixture was then heated to reflux for
a further 12 h. Saturated NH4Cl solution (100 ml) was then carefully
added. The organic layer was separated, and the aqueous layer ex-
tracted with ether (3 × 40 ml). The combined organic extracts were
dried over MgSO4, filtered and concentrated. Distillation gave the
title compound as a colourless oil (11.90 g, 53%). Bp 140 °C/1 mbar
(lit.40 147–148 °C/2 mbar). vmax (thin film) 3021, 2948, 2885, 1420,
1216, 1201, 1196, 914, 842 cm−1; H (300 MHz) 7.55–7.28 (10H,
m, Ar–H), 0.19 [18H, s, Si(CH3)3]; C (75 MHz) 135.93, 133.97,
128.12, 127.81, −0.50; m/z (EI) 328 (M+, 33%), 313 (M − CH3,
10%), 255 [M − Si(CH3)3, 100%].
2,2-Bis(trimethylsilyl)-3-[4′-methoxyphenyl]-3-trimethyl-
silyloxy-2-silabicyclo[2.2.1]hept-5-ene 5by. Reaction of 4-
methoxybenzoyltris(trimethylsilyl)silane 2b with cyclopentadiene
gave the title compound as a mixture of diastereoisomers (68%,
5:2 endo:exo). vmax (thin film) 3048, 2953, 2894, 1608, 1509,
1249, 1177, 1042, 1021, 838 cm−1; H (200 MHz) 7.21 (0.56H, d,
J = 7.6 Hz,Ar–H exo), 7.17 (1.44H, d, J = 7.6 Hz,Ar–H endo), 6.81
(0.56H, d, J = 7.6 Hz, Ar–H exo), 6.75 (1.44H, d, J = 7.6 Hz, Ar–H
endo) 6.40–6.30 (0.28H, dd, J = 5.4, 3.0 Hz, 5-H exo), 6.20–6.10
(0.72H, dd, J = 5.4, 3.0 Hz, 5-H endo), 5.95–5.85 (0.28H, dd,
J = 5.4, 3.0 Hz, 6-H exo), 5.85–5.75 (0.72H, dd, J = 5.4, 3.0 Hz,
6-H endo), 3.87 (0.84H, s, –OCH3 exo), 3.85 (2.16H, s, –OCH3
endo), 3.37 (0.28H, m, 4-H exo), 3.25 (0.72H, m, 4-H endo), 2.40
(0.28H, m, 7-HH exo), 2.35 (1.72H, m, 7-H2 endo and 7-HH exo),
1.98 (0.72H, m, 1-H endo), 1.90 (0.28H, m, 1-H exo), 0.26 [6.48H,
s, –OSi(CH3)3 endo], 0.16 [2.52H, s, OSi(CH3)3 exo], −0.14 [2.52H,
3,4-Diphenyl-3,4-bis(trimethylsilyloxy)-1,1,2,2-tetrakis-
(trimethylsilyl)-1,2-disilacyclobutane10a.11 Asolutionofbenzoyl-
tris(trimethylsilyl)silane (0.49 g, 1.38 mmol) in cyclohexane (50 ml)
was irradiated for approx. 2 h using a 1 kW mercury lamp. Con-
centration gave the crude product. Flash column chromatography
(eluting: petrol) gave the title compound as a white crystalline solid
(0.21 g, 43%); mp 148 °C (lit.11 149–150 °C). vmax (KBr disc) 3050,
2956, 2893, 1597, 1489, 1442, 1402, 1250 cm−1; H (200 MHz)
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2
2 3 8 7

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7.70–7.58 (5H, m, Ar–H), 7.40–7.20 (5H, m, Ar–H), 0.41 [18H, s,
OSi(CH3)3], 0.07 [18H, s, Si(CH3)3], −0.26 [18H, s, Si(CH3)3]; C
(63 MHz) 158.28, 144.92, 132.74, 127.08, 98.69, 3.53, 3.07, 2.89;
m/z (CI, NH3) 592 (12%), 356 (12), 353 (monomer MH+, 11), 221
(44), 148 (65), 90 (90), 73 (100).
tration followed by flash column chromatography (eluting: petrol)
gave the title compound (a 1:1 mixture of diastereoisomers) as a
colourless oil (1.74 g, 70%). vmax (thin film) 3066, 2953, 1478, 1427,
1359, 1258, 1247, 1127, 1104, 967, 887 836 cm−1; H (300 MHz)
7.65–7.30 (5H, m, Ar–H), 6.90–5.30 (2H, m, 4-H, 5-H), 3.3–3.0,
(1H, m, 3-H), 1.70 (3H, bd J = 6.7 Hz, 3-CH3), 1.55–1.22 (2H, m, 6-
H2), 1.04, [4.5H, s, C(CH3)3], 0.98 [4.5H, s, C(CH3)3], 0.11 [4.5H, s,
OSi(CH3)3], 0.06 [4.5H, s, OSi(CH3)3], −0.24 [4.5H, s, SiSi(CH3)3],
−0.30 [4.5H, s, SiSi(CH3)3]; C (100 MHz) 138.95, 135.08, 134.574,
134.07, 128.41, 128.13, 127.58, 127.48, 124.32, 122.90, 96.17,
92.50, 53.72, 45.16, 38.00, 37.30, 28.20, 28.00 (broad), 18.03,
17.56, 11.53, 10.71, 2.80, 2.31, −0.95, −1.50; m/z (EI) 404 (M+,
1%), 389 (M − CH3, 1%), 347 (M − tBu, 5%), 331 (M − SiMe3, 5%),
263 (58), 209 (89), 193 (100); HRMS (EI): Found M+, 404.2397;
C22H40OSi3 requires M, 404.2387.
General procedure for oxidation of silyl alcohols to acylsilanes
as applied to:
2-Methylpropanoylbis(trimethylsilyl)phenylsilane 9c. Di-
methyl sulfoxide (1.20 g, 15.33 mmol) was added to a stirred solution
of oxalyl chloride (1.17 g, 9.20 mmol) in DCM at −78 °C, and the re-
sultant solution stirred at this temperature for 10 min. The solution of
silyl alcohol 14a (1.99 g, 6.14 mmol) in dichloromethane was added
dropwise, and the reaction was stirred at −78 °C for a further 20 min.
Triethylamine (4.26 ml, 30.7 mmol) was then added, and the reaction
was allowed to attain ambient temperature. The reaction mixture was
then diluted with ether (50 ml) and washed with dilute hydrochloric
acid (2 × 15 ml) and saturated NaHCO3 solution (15 ml). After back
extraction of the aqueous washings with ether (20 ml), the combined
organic layers were dried over MgSO4, filtered and concentrated.
Flash column chromatography (eluting: 5% ether:petrol) gave the
title compound as a colourless oil (1.98 g, 93%). vmax (thin film)
3067, 2962, 2894, 2870, 1728, 1627, 1465, 1427, 1400, 1377, 1245,
1095, 971, 836 cm−1; H (200 MHz) 7.60–7.30 (5H, m, Ar–H), 2.95
(1H, septet, J = 6.8 Hz, 2-H), 0.89 (6H, d, J = 6.8 Hz, CH3), 0.24
[18H, s, Si(CH3)3]; C (50 MHz) 249.94, 136.16, 135.61, 128.69,
128.17, 46.77, 16.51, 0.13; m/z (CI, NH3) 323 (MH+, 23%), 307 (M −
CH3, 8%), 249 (M − SiMe3, 22%), 209 (37), 193 (63), 135 (100).
3-(tert-Butyl)-2-phenyl-2-trimethylsilyl-3-trimethylsilyloxy-
2-silabicyclo[2.2.2]oct-5-ene 13b. Silene dimer 11b (5.08 g,
7.56 mmol) and cyclohexa-1,3-diene (2.42 g, 30.26 mmol) were
dissolved in THF (40 ml). The solution was stirred for 18 h. Con-
centration followed by flash column chromatography (eluting: pet-
rol) gave the title compound (a 1:1 mixture of diastereoisomers) as
a colourless solid (4.37 g, 69%), mp 114–115 °C. Found: C, 65.92;
H, 9.67; required for C23H40OSi3 C, 66.28; H, 9.67%; vmax (KBr disc)
3069, 3045, 2982, 2950, 2861, 1476, 1426, 1390, 1261, 1247, 1103,
965, 836 cm−1; H (500 MHz) 7.60–7.30 (5H, m, Ar–H), 6.20–6.18
(0.5H, m, 5-H), 6.16–6.14 (0.5H, m, 5-H), 6.10–6.02 (0.5H, m,
6-H), 3.25 (0.5H, m, 4-H), 2.85 (0.5H, m, 4-H) 2.42 (0.5H, m, 1-H),
2.40 (0.5H, m. 1-H), 2.02 (1H, m, 7-HH and 8-HH), 1.90 (1H, m,
7-HH and 8-HH), 1.75 (1H, m, 7-HH and 8-HH), 1.65 (1H, m, 7-
HH and 8-HH), 1.08 [4.5H, s, C(CH3)3], 1.06 [4.5H, s, C(CH3)3],
−0.02 [4.5H, s, OSi(CH3)3], 0.11 [4.5H, s, OSi(CH3)3], −0.18 [4.5H,
s, SiSi(CH3)3], −0.19 [4.5H, s, SiSi(CH3)3]; C (125 MHz) 138.20,
136.10, 132.42, 129.21, 128.03, 122.00, 121.63, 96.80, 90.22,
44.00, 42.10, 39.21, 30.11, 26.95, 21.00, 19.80, 9.80, 3.11, −0.08,
−0.20; m/z (EI) 416 (M+, 2%), 401 (M − CH3, 5%), 343 (M − SiMe3,
15%), 327 (M − OSiMe3, 10%), 73 (100).
Butanoylbis(trimethylsilyl)phenylsilane 9d. Obtained from
silyl alcohol 14b following the procedure described for 9c as a
colourless oil (0.50 g, 95%). Found: C, 59.30; H, 9.36; Calc. for
C16H30OSi3 C, 59.56; H, 9.37%; vmax (thin film) 3068, 3051, 2958,
2894, 1631, 1427, 1399, 1246, 1095, 837 cm−1; H (400 MHz)
7.60–7.30 (5H, m, Ar–H), 2.58 (2H, t, J = 7.2 Hz, 2-H2), 1.51 (2H,
tq, 3-H2), 0.83 (3H, t, J = 7.2 Hz, 4-H3), 0.24 [18H, s, Si(CH3)3]; C
(100 MHz) 246.67, 136.04, 133.46, 128.64, 128.13, 54.22, 15.78,
13.84, 0.24; m/z (CI, NH3) 323 (MH+, 11%).
General procedures for the preparation of silyl alcohols as
applied to:
3,4-Diphenyl-3,4-bis(trimethylsilyloxy)-1,2-bis(trimethyl-
silyl)-1,2-diphenyl-1,2-disilacyclobutane 11a. A solution of
benzoylphenylbis(trimethylsilyl)silane 9a (1.00 g, 2.80 mmol) was
dissolved in cyclohexane (150 ml). This solution was then degassed
by the passage of a steady flow of nitrogen for 30 min. The mixture
was then irradiated for 45 min in a cooled jacketed reactor (Photo-
chemical Reactors Ltd) using a 125 W medium pressure mercury
lamp and a solution of CuSO4 as the coolant solution. Flash column
chromatography (eluting: hexane) gave the title compound as a
white solid, (0.04 g, 5%); mp 165–166 °C decomp. Found: C, 62.75;
H, 7.73; C38H56O2Si6 requires C, 63.98; H, 7.91%; vmax (KBr disc)
3052, 2957, 2894, 1596, 1488, 1442, 1427, 1249, 1042 cm−1; H
(300 MHz) 7.80–7.20 (20H, m, Ar–H), −0.01 [18H, s, OSi(CH3)3],
−0.54 [18H, s, SiSi(CH3)3]; C (75 MHz) 144.51, 137.33, 136.51,
131.24, 128.19, 127.41, 127.15, 126.72, 95.68, 3.22, 0.39; m/z (EI)
712 (M+, 1%), 639 (M+ − TMS, 2%), 356 (monomer M+, 100%).
1,1,1,3,3,3-Hexamethyl-2-phenyl-2-(1′-hydroxy-2′-methyl-
propyl)trisilane 14a.
Method A. Methyllithium (1.6 M solution in ether, 21 ml,
33 mmol) was added to a stirred solution of phenyltris(trimethyl-
silyl)silane 17 (10.15 g, 31.3 mmol) in THF (56 ml) at 0 °C. This
was allowed to warm to RT and stirred for 17 h to produce a dark red
solution of the silyl anion. The THF was evaporated directly using
a vacuum manifold and ether (50 + 6 ml) was added. The result-
ing solution was added via cannula to a suspension of magnesium
bromide diethyl etherate (11.33 g, 43.9 mmol) in ether (56 ml).
After becoming a homogeneous solution, the reaction mixture
was stirred for 1 h and was then cooled to −78 °C. Freshly distilled
isobutyraldehyde (4.3 ml, 47 mmol) was added dropwise. The reac-
tion was then stirred for 19 h. Saturated ammonium chloride solu-
tion (100 ml) was added and the mixture allowed to reach RT. The
aqueous layer was separated and extracted with ether (3 × 100 ml).
The combined organic layers were dried over MgSO4, filtered,
concentrated and dried in vacuo. Flash column chromatography,
gradient elution (petroleum ether; petroleum ether/ether [29:1];
[19:1]; [12:1]; ether) gave a mixture of the starting material phenyl-
tris(trimethylsilyl)silane [PhSi(SiMe3)3] 17 and bis(trimethylsilyl)-
phenylsilane [PhSi(H)(SiMe3)2] 20 (0.79 g, 10 and 8%, respectively,
calculated from NMR); Rf (petroleum ether/ether [9:1]) 0.89; H for
20 (300 MHz) 7.46–7.40 (2H, m, Ar–H), 7.28–7.23 (3H, m, Ar–H),
3.74 (1H, s, Si–H), 0.22 [18H, s, Si(Si(CH3)3)2] followed by the title
compound 14a as a colourless oil (6.76 g, 67%).
3,4-Bis(tert-butyl)-3,4-bis(trimethylsilyloxy)-1,2-bis-
(trimethylsilyl)-1,2-diphenyl-1,2-disilacyclobutane 11b.14
Pre-
pared from trimethylacetylphenylbis(trimethylsilyl)silane 9b (9.31 g,
27.7 mmol) following an identical procedure as described for 11a.
(9.15 g, 98%), mp 98–100 °C decomp. vmax (CHCl3) 3017, 2957, 2897,
1703, 1614, 1479, 1427, 1362, 1253, 1206, 1060, 931, 841 cm−1; H
(300 MHz) 7.70–7.25 (10H, m, Ar–H), 1.20 [18H, bs, C(CH3)3],
10.28 [18H, s, OSi(CH3)3], 0.13 [18H, s, SiSi(CH3)3]; C (63 MHz)
137.72, 137.05, 127.74, 126.94, 108.82, 38.90, 26.93, 5.96, 0.70.
2-(tert-Butyl)-3-methyl-1-phenyl-1-trimethylsilyl-2-(tri-
methylsilyloxy)silacyclohex-4-ene 12b. Silene dimer 11b (2.07 g,
3.08 mmol) and E-1,3-pentadiene (0.82 g, 12.40 mmol) were dis-
solved in THF (10 ml). The solution was stirred for 18 h. Concen-
Method B. Dry phenyltris(trimethylsilyl)silane 17 (4.82 g,
14.88 mmol) and potassium tert-butoxide (1.72 g, 15.33 mmol)
were combined under Ar. THF (27 ml) was added and the resulting
2 3 8 8
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2

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solution stirred for 2 h after which time it had become bright red. The
THF was evaporated directly using a vacuum manifold and ether
(20 + 7 ml) was added. The resulting solution was added via can-
nula to a suspension of magnesium bromide diethyl etherate (5.00 g,
19.3 mmol) in ether (27 ml). The reaction mixture was stirred for
1 h and was then cooled to −78 °C. Freshly distilled isobutyral-
dehyde (1.49 ml, 16.37 mmol) was added and the mixture stirred
for 17 h. Saturated ammonium chloride solution (50 ml) was added
and the mixture allowed to reach RT. The aqueous layer was sepa-
rated and extracted with ether (3 × 50 ml). The combined organic
layers were dried over MgSO4, filtered, concentrated and dried in
vacuo. Flash column chromatography, gradient elution (petroleum
ether; petroleum ether/ether [39:1]; [29:1]) gave a mixture of the
starting material phenyltris(trimethylsilyl)silane [PhSi(SiMe3)3] 17
and bis(trimethylsilyl)phenylsilane [PhSi(H)(SiMe3)2] 20 (1.09 g, 2
and 26%, respectively, NMR) followed by the title compound 14a
as a colourless oil (2.50 g, 52%); Rf (petroleum ether/ether [9:1])
0.57; max (thin film) 3590 and 3480 (broad, O–H), 3070, 3054,
2955, 2900, 2820, 1468, 1430, 1245 (Si–C), 1100, 988, 835 cm−1;
H (300 MHz) 7.54–7.45 (2H, m, Ar–H), 7.30–7.28 (3H, m, Ar–H),
3.79 (1H, d, J = 6.9 Hz, CHOH), 1.96 [1H, octet, J = 6.9 Hz,
CH(Me)2], 0.99 and 0.88 [3H, d, J = 6.9 Hz, CH(CH3)2], 0.24
and 0.20 [9H, s, Si(CH3)3]; C (63 MHz) 136.44 (Ar), 135.60 (Ar),
128.04 (Ar), 127.83 (Ar), 72.39 (Si–CH), 34.63 [CH(Me)2], 21.18
and 19.88 [CH(CH3)2], 0.50 [Si(CH3)3], 0.32 [Si(CH3)3]; m/z (CI)
128.23 (Ar), 127.99 (Ar), 61.52 (Si–CH), 22.79 (CH3–COH),
0.31 [Si(CH3)3], 0.01 [Si(CH3)3]; m/z (ES+) 319 (M + Na+, 100%);
+
HRMS (ES+): Found MNH4 , 314.1786; C14H32NOSi3 requires
MNH4, 314.1792.
1,1,1,3,3,3-Hexamethyl-2-phenyl-2-(1′-hydroxy-2′-methyl-
butyl)trisilane 14d. Reaction with 2-methylbutyraldehyde fol-
lowing method B afforded the title compound as a mixture of
diastereoisomers (5:2, 58%); Rf (petroleum ether/ether [9:1]) 0.61;
max (thin film) 3594 and 3472 (broad, O–H), 3067, 2959, 2893,
2875, 1461, 1427, 1245, 1093, 835 cm−1; H (300 MHz) (* signals
for minor diastereoisomer) 7.56–7.51 (2H, m, Ar–H), 7.32–7.29
(3H, m, Ar–H), 4.01 (0.86H, d, J = 5.0 Hz, 1′-H), 3.89 (0.4H, d,
J = 5.0 Hz, 1′-H*), 1.79–1.63 (1.14H, m, 2-H, 2-H* and 3-HH*),
1.43 (0.86H, m, 3-HH), 1.30–1.11 (1H, m, 3-HH and 3-HH*), 0.95
(2.58H, d, J = 7.0 Hz, 2′-CH3), 0.88 (2.58H, t, J = 7.5 Hz, 4′-H3),
0.86 (0.42H, t, J = 7.0 Hz, 4′-H3*), 0.86 (0.42H, d, J = 7.0 Hz, 2′-
CH3*), 0.24 [1.26H, s, Si(CH3)3*], 0.23 [7.74H, s, Si(CH3)3], 0.22
[7.74H, s, Si(CH3)3], 0.21 [1.26H, s, Si(CH3)3*]; C (100 MHz)
136.56 (ipso-Ar*), 136.40 (ipso-Ar), 135.75 (Ar), 135.60 (Ar*),
128.07 (Ar and Ar*), 127.87 (Ar*), 127.84 (Ar), 71.44 (Si–CH*),
70.10 (Si–CH), 41.00 (2-C and 2-C*), 27.42 (3-C), 25.94 (3-
C*), 17.17 (5-C*), 16.49 (5-C), 11.97 (4-C), 11.16 (4-C*), 0.50
[Si(CH3)3*], 0.36 [Si(CH3)3], 0.27 [Si(CH3)3], 0.23 [Si(CH3)3*];
+
m/z (CI) 356 (M + NH4 , 50%), 338 (M + NH4+ − OH2, 90%), 268
+
+
342 (M + NH4 , 100%), 324 (M+, 90%), 307 (M+ − OH, 68%).
(42); HRMS (CI): Found MNH4 , 356.2266; C17H38NOSi3 requires
MNH4, 356.2261.
1-(1′,1′,1′,3′,3′,3′-Hexamethyl-2′-phenyl-trisilan-2′-yl)-2-
methylpropyl-2″-methylpropanoate 19. Ester 19a was sometimes
obtained as a by-product of the above reaction and could be isolated
as a pure sample by repeated chromatography. Rf (petroleum ether/
ether [9:1]) 0.61; max (thin film) 3070, 3050, 2963, 2894, 1730
(CO), 1469, 1427, 1385, 1246, 1187, 1153, 1095, 837 cm−1; H
(300 MHz) 7.50–7.46 (2H, m, Ar–H), 7.30–7.25 (3H, m, Ar–H),
5.38 (1H, d, J = 7.0 Hz, 1-H), 2.49 (1H, septet, J = 6.9 Hz, Me2CH–
CO), 2.05 (1H, octet, J = 7.0 Hz, 2-H), 1.15 [3H, d, J = 6.9 Hz,
CO–CH(CH3)2], 1.07 [3H, d, J = 6.9 Hz, CO–CH(CH3)2], 0.87
(3H, d, J = 7.0 Hz, 3-H3], 0.84 (3H, J = 7.0 Hz, 3–H3), 0.22 [18H,
s, Si(Si(CH3)3)2]; C (63 MHz) 176.74 (CO), 135.71 (Ar), 135.55
(Ar), 128.07 (Ar), 127.72 (Ar), 72.49 (Si–CH), 34.45 [CH(Me)2],
33.51 [CH(Me)2], 21.19, 20.09, 19.62 [CH(CH3)2], 18.69
[CH(CH3)2], 0.28 [9H, s, Si(CH3)3], 0.10 [9H, s, Si(CH3)3]; m/z
(CI) 379 (M+ − Me, 8%), 321 (M+ − SiMe3, 30%), 265 (M+ − Me −
iPrCO − iPr, 100%), 251 ([PhSi(SiMe3)2]+, 32%); HRMS (CI) Found
1,1,1,3,3,3-Hexamethyl-2-phenyl-2-(1′-hydroxy-2′,2′-
dimethylpropyl)trisilane 14e. Reaction with trimethylacetal-
dehyde following method B afforded the title compound (37%);
Rf (petroleum ether/ether [9:1]) 0.66; max (thin film) 3477 (broad,
O–H), 3067, 3050, 2951, 2896, 2867, 2813, 1476, 1463, 1427, 1393,
1363, 1245, 1093, 975, 835, 699, 689 cm−1; H (300 MHz) 7.55–7.52
(2H, m, Ar–H), 7.30–7.27 (3H, m, Ar–H), 3.83 (1H, d, J = 6.0 Hz,
CHOH), 1.30 (1H, d, J = 6.0 Hz, O–H), 0.92 [9H, s, C(CH3)3], 0.30
[9H, s, Si(CH3)3], 0.21 [9H, s, Si(CH3)3]; C (101 MHz) 137.03 (ipso-
Ar), 136.06 (meta-Ar), 128.14 (para-Ar), 127.85 (ortho-Ar), 77.19
(CHOH), 36.64 [C(CH3)3], 28.05 [C(CH3)3], 1.02 [Si(CH3)3], 0.43
[Si(CH3)3]; m/z (CI) 356 (M + NH4+, 15%), 338 (M+, 7%), 321 (M+ −
OH, 100%), 268 (12), 250 (14), 233 (20), 208 (30), 191 (44).
1,1,1,3,3,3-Hexamethyl-2-phenyl-2-(1′-hydroxy-1′-
cyclohexylmethyl)trisilane 14f. Reaction with cyclohexane-
carboxaldehyde following method A afforded the title compound
(38%); Rf (petroleum ether/ether [9:1]) 0.56; max (thin film) 3591
and 3473 (broad, O–H), 3066, 3049, 2925, 2896, 2851, 1448, 1427,
1245, 835 cm−1; H (400 MHz) 7.53–7.50 (2H, m, Ar–H), 7.30–7.29
(3H, m, Ar–H), 3.86 (1H, d, J = 7.2 Hz, Si–C–H), 1.99–0.98 [11H,
m, (CH2)5CH], 0.24 [9H, s, Si(CH3)3], 0.21 [9H, s, Si(CH3)3]; C
(100 MHz) 136.57 (ipso-Ar), 135.52 (Ar), 128.00 (Ar), 127.84
(Ar), 71.63 (Si–CH), 44.64 (2-C), 31.35 [–(CH2)5–], 30.44
[–(CH2)5–], 26.42 [–(CH2)5–], 26.30 [–(CH2)5–], 26.17 [–(CH2)5–],
0.43 [Si(CH3)3], 0.18 [Si(CH3)3]; m/z (CI) 365 (M + H+, 2%), 349
(M+ − Me, 60%), 291 (M+ − SiMe3, 41%), 274 (29), 259 (71), 251
+
MNH4 , 412.2525; C20H42NO2Si3 requires MNH4, 412.2523.
1,1,1,3,3,3-Hexamethyl-2-phenyl-2-(1′-hydroxybutyl)-
trisilane 14b. Obtained from butanal in 74% yield following
method A or 36% yield following method B; Rf (petroleum
ether/ether [9:1]) 0.41). Found: C, 59.24; H, 10.00; required for
C16H32OSi3: C, 59.19; H, 9.93%. max (thin film) 3582 and 3463
(broad, O–H), 3066, 3050, 2955, 2894, 1427, 1245, 1095, 835,
699 cm−1; H (400 MHz) 7.53–7.50 (2H, m, Ar–H), 7.34–7.31 (3H,
m, Ar–H), 4.09 (1H, dd, J = 11.0 Hz, 2.5, Si–C–H), 1.82–1.57 (3H,
m, 3′-HH and 2′-H2), 1.37 (1H, m, 3′-HH), 0.94 (3H, t, J = 7.0 Hz,
4′-H3), 0.23 [9H, s, Si(CH3)3], 0.22 [9H, s, Si(CH3)3]; C (100 MHz)
135.65 (meta-Ar), 135.37 (ipso-Ar), 128.18 (para-Ar), 127.95
(ortho-Ar), 65.39 (1′-C), 38.80 (2′-C), 20.44 (3′-C), 13.78 (4′-C),
0.28 [Si(CH3)3], 0.14 [Si(CH3)3]; m/z (CI) 342 (M + NH4+, 100%),
325 (M + H+, 91%), 308 (M + H+ − OH, 72%), 247 (34), 237 (45),
209 (16), 194 (16), 152 (28), 135 (20); HRMS (CI): Found MNH4+,
342.2099; C16H36NOSi3 requires MNH4, 342.2103.
+
[PhSi(SiMe3)3 , 54%], 215 (34), 200 (35), 195 (53), 190 (46), 177
(35), 135 (71); HRMS (ES+): Found MNa+, 387.1982; C19H36NaOSi3
requires MNa, 387.1972.
1,1,1,3,3,3-Hexamethyl-2-phenyl-2-(1′-hydroxy-1′-phenyl-
methyl)trisilane 14g. Reaction with benzaldehyde (1.15 ml,
11.29 mmol) following method B afforded the title compound as
a yellow crystalline solid (2.41 g, 63%); Rf (petroleum ether/ether
[9:1]) 0.56; mp 61–62 °C; max (KBr disc) 3538, 3428 (broad, O–H),
3066, 3050, 3024, 2946, 2890, 1594, 1488, 1447, 1426, 1398, 1243,
1189, 1093, 1004, 840, 763, 734, 699 cm−1; H (300 MHz) 7.47 (2H,
m, Ar–H), 7.27 (2H, m, Ar–H), 7.16 (3H, m, Ar–H), 7.07 (3H, m,
Ar–H), 5.11 (1H, s, CHOH), 0.06 [9H, s, Si(CH3)3], 0.02 [9H, s,
Si(CH3)3]; C (126 MHz) 145.50 (ipso-C–Ar), 136.21 (meta-Si–Ar),
135.15 (ipso-Si–Ar), 128.49 (para-Si–Ar), 128.23 (ortho- or meta-
C–Ar), 127.93 (ortho-Si–Ar), 125.98 (para-C–Ar), 125.08 (ortho-
1,1,1,3,3,3-Hexamethyl-2-phenyl-2-(1′-hydroxyethyl)-
trisilane 14c. Reaction with acetaldehyde following method A aff-
orded the title compound (49%); Rf (petroleum ether/ether [9:1])
0.19; max (thin film) 3441 (broad, O–H), 3067, 2950, 2893, 1427,
1245, 1049, 1068, 1029, 835 cm−1; H (500 MHz) 7.54–7.52 (2H, m,
Ar–H), 7.33–7.32 (3H, m, Ar–H), 4.24 (1H, q, J = 7.5 Hz, CHOH),
1.49 (3H, d, J = 7.5 Hz, CH3–COH), 0.25 [9H, s, Si(CH3)3], 0.21
[9H, s, Si(CH3)3]; C (126 MHz) 135.64 (Ar), 135.18 (ipso-Ar),
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2
2 3 8 9

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or meta-C–Ar), 69.70 (CHOH), 0.15 [Si(CH3)3], 0.01 [Si(CH3)3];
(Ar), 127.66 (Ar), 123.56 (5-C), 38.21 (2-C), 32.77 (3-C), 30.02
(2′-C), 23.56 (7-C), 22.99 (1′-C), 22.45 (1′-C), 9.74 (6-C), −0.55
+
m/z (CI) 376 (M + NH4 , 8%), 358 (M+, 100%), 341 (M+ − OH,
i
33%), 281 (31).
[CH3)3]; m/z (EI) 302 (M+, 7%), 259 (M+ − Pr, 4%), 229 (M+ −
SiMe3, 56%), 218 (27), 203 (47), 185 (11), 173 (29), 161 (100),
145 (31), 135 (82), 121 (69); HRMS (EI): Found M+, 302.1889;
C18H30Si2 requires M, 302.1886.
Trifluoroacetic acid 1-(1′,1′,1′,3′,3′,3′-hexamethyl-2′-phenyl-
trisilan-2′-yl)-2-methyl-propyl ester 32. A mixture of silyl alco-
hol 14a (0.28 g, 0.85 mmol) and triethylamine (0.18 ml, 1.28 mmol)
in dry DCM (16 ml) was cooled to −10 °C. Trifluoroacetic anhy-
dride (0.14 ml, 0.98 mmol) was added dropwise. The solution
was warmed to RT and stirred for 17 h. Water (15 ml) was then
added. The aqueous layer was separated and extracted with DCM
(3 × 15 ml). The combined organic extracts were dried over MgSO4,
filtered, concentrated and dried in vacuo. Filtration through a pad
of silica (hexane) gave the title compound as a clear oil (0.26 g,
73%); Rf (hexane/ether [9:1]) 0.99; max (thin film) 2963, 2896,
1777 (CO), 1428, 1369, 1248, 1216, 1154, 1095, 837, 743, 735,
699 cm−1; H (200 MHz) 7.50–7.45 (2H, m, Ar–H), 7.32–7.28 (3H,
m, Ar–H), 5.49 (1H, d, J = 6.8 Hz, CHOCOCF3), 2.15 [1H, octet,
J = 6.8 Hz, CH(Me)2], 0.90 and 0.86 (3H, d, J = 6.8 Hz, CH(CH3)2],
0.25 and 0.20 [9H, s, Si(CH3)3]; C (63 MHz) 157.75 (q, J = 41.2 Hz,
CO), 135.56 (Ar), 134.35 (Ar), 128.61 (Ar), 128.04 (Ar), 114.86
(q, J = 286.7 Hz, CF3), 79.67 (Si–CH), 33.42 [CH(Me)2], 20.88 and
19.74 [CH(CH3)2], 0.16 [Si(CH3)3], 0.10 [Si(CH3)3]; F (188 MHz)
1-Phenyl-1-trimethylsilyl-2-(prop-2′-yl)-4,5-dimethyl-
silacyclohex-4-ene 41, and 1-phenyl-1-isobutyl-2,2,2-trimethyl-
1-(3-methyl-2-methylene-but-3-enyl)-disilane 49. Reaction of
14a with 2,3-dimethylbutadiene according to method A gave the
title compounds as a mixture in a ratio of 41:49 ([83:8]:7), (45%)
and according to method B in a ratio of 41:49 ([73:15]:12), (48%)
(ratio of product peak integrals by GC); Rf (petroleum ether) 0.70;
max (thin film) 3067, 3049, 2953, 2925, 2866, 1464, 1443, 1430,
1390, 1246, 1121, 1108, 853, 838, 732, 706 cm−1; 41: H (200 MHz)
7.48–7.47 (2H, m, Ar–H), 7.30–7.29 (3H, m, Ar–H), 2.23 (1H, dd,
J = 15.0, 5.0 Hz, 3a-H), 1.98 (1H, dd, J = 15.0, 11.0 Hz, 3b-H),
1.83 [1H, m, CH(CH3)2], 1.74 (3H, s, 8-H3), 1.69 (3H, s, 7-H3),
1.58 (2H, s, 6-H2), 1.09 (1H, ddd, J = 11.0, 8.5, 5.0 Hz, 2-H), 0.99
[3H, d, J = 7.0 Hz, CH(CH3)2], 0.98 [3H, d, J = 7.0 Hz, CH(CH3)2],
0.11 [18H, s, Si(Si(CH3)3)2]; C (126 MHz) 139.51 (ipso-Ar), 134.52
(Ar), 128.68 (4 or 5-C), 128.26 (Ar), 127.66 (Ar), 125.33 (4- or
5-C), 35.33 (3-C), 34.47 (2-C), 30.30 (2′-C), 24.89 (1′-C), 22.61
(8-C), 22.20 (1′-C), 20.74 (7-C), 18.92 (6-C), −0.33 [Si(Si(CH3)3)2];
m/z (GCMS, CI) 317 (M + H+, 100%), 316 (M+, 65%), 315 (M+ −
H, 15%), 303 (25), 301 (M+ − Me, 60%), 273 (M+ − iPr, 1%), 243
(M+ − SiMe3, 79%), 245 (13), 239 (M+ − Ph, 23%), 187 (24),
161 (21), 135 (17); 49: H (200 MHz) (discernable peaks only)
5.08 (1H, s, CH2), 5.06 (1H, s, CH2), 4.98 (1H, s, CH2) and
4.86 (1H, s, CH2); m/z (GCMS, EI) 316 (M+, 13%), 259 [M+ −
(CH3)2CHCH2, 9%], 245 (10), 243 (M+ − SiMe3, 9%), 235 [M+ −
CH3CH(CH2)CH(CH2)CH2, 8%], 187 (72), 180 (55), 179 (100), 177
(22), 159 (20), 145 (29), 135 (84), 121 (40).
+
−74.85 (3 F, s, CF3); m/z (CI) 438 (M + NH4 , 100%), 342 (3), 324
(M + H+ − CF3CO, 10%); HRMS (ES+): Found MNH4+ 438.1927;
C18H34F3NO2Si3 requires MNH4, 438.1928.
General protocols for silene generation and trapping as
applied to:
1-Phenyl-1-trimethylsilyl-2-(prop-2′-yl)-3-methylsilacyclo-
hex-4-ene 29.
Method A. Methyllithium (1.6 M solution in ether, 13.0 ml,
20.9 mmol) was added to a stirred solution of silyl alcohol 14a
(6.76 g, 20.9 mmol) and 1,3-pentadiene (mixture of endo- and
trans-isomers, 12.5 ml, 125.2 mmol) in ether (300 ml) at −78 °C.
The mixture was allowed to warm to −30 °C and stirred for 22 h,
then to 0 °C and stirred for 8 h. Saturated ammonium chloride solu-
tion (200 ml) was added and the mixture allowed to reach RT. The
aqueous layer was separated and extracted with ether (3 × 200 ml).
The combined organic layers were dried over MgSO4, filtered,
concentrated and dried in vacuo. Flash column chromatography
(hexane) gave the title compound as a mixture of diastereoisomers
as a colourless oil (3.25 g, 52%).
1-Phenyl-1-trimethylsilyl-2-(prop-2′-yl)-5-methyl-
silacyclohex-4-ene
silyl-2-(prop-2′-yl)-4-methylsilacyclohex-4-ene
42a,
1-phenyl-1-trimethyl-
42b, and
1-phenyl-1-isobutyl-2,2,2-trimethyl-1-(2-methylene-but-3-
enyl)-disilane 50. Reaction of 14a with isoprene according to
method A gave the title compounds as a mixture in a ratio of
42a:42b:50 ([84:11]:5), (27%) and according to method B in a
ratio of 42a:42b:50 ([72:16]:12) (41%) (ratio of product peak in-
tegrals by GC); max (thin film) 2954, 2927, 2893, 2869, 1462, 1445,
1427, 1244, 1101, 855, 833, 733, 719, 699 cm−1. 42a: H (500 MHz)
7.51–7.49 (2H, m, meta-Ar–H), 7.32–7.31 (3H, m, ortho- and para-
Ar–H), 5.48 (1H, m, 4-H), 2.34 (1H, dt, J = 15.5, 6.5 Hz, 3-HH),
1.96 (1H, m, 3-HH), 1.87 [1H, m, CH(CH3)2], 1.78 (3H, s, 7-H3),
1.53 (2H, m, 6-H2), 1.14 (1H, m, 2-H), 0.96 [3H, d, J = 6.5 Hz,
CH(CH3)2], 0.94 [3H, d, J = 6.5 Hz, CH(CH3)2], 0.18 [9H, s,
Si(CH3)3]; C (126 MHz) 134.45 (meta-Ar), 128.34 (para-Ar),
127.71 (ortho-Ar), 123.80 (4-C), 32.34 (2-C), 30.27 (2′-C), 27.75
(3-C), 27.62 (7-C), 24.51 (1′-C), 21.90 (1′-C), 16.38 (6-C), −0.37
[Si(CH3)3]; m/z (GCMS, CI) 303 (M + H+, 39%), 302 (M+, 96%),
288 (M + H+ − Me, 31%), 287 (M+ − Me, 100%), 245 (16), 233 (10),
231 (18), 230 (M + H+ − SiMe3, 29%), 229 (M+ − SiMe3, 86%), 225
(35), 217 (13), 193 (14), 179 (14), 173 (23), 169 (13), 167 (11), 161
(48), 155 (24), 152 (16), 135 (49); HRMS (EI): Found M+, 302.1882;
C18H30Si2 requires M, 302.1886). 42b: H (500 MHz) (discernable
peak) 5.61 (1H, m, 5-H); m/z (GCMS, CI) 303 (M + H+, 24%), 302
(M+, 93%), 288 (M + H+ − Me, 31%), 287 (M+ − Me, 100%), 245
(17), 233 (11), 231 (20), 230 (M + H+ − SiMe3, 33%), 229 (M+ −
SiMe3, 94%), 225 (29), 217 (13), 193 (21), 179 (31), 173 (31), 169
(13), 167 (14), 161 (62), 155 (24), 152 (20), 145 (10), 135 (49). 50:
H (500 MHz) (discernable peaks) 6.35 (1H, dd, J = 16.5 Hz, 10.5,
4-H), 5.11 (1H, d, J = 16.5 Hz, 5-HZ), 5.01 (1H, d, J = 10.5 Hz,
5-HE), 4.94 (1H, s, 6-HH), 4.81 (1H, s, 6-HH); m/z (GCMS, CI)
302 (M+, 13%), 287 (M+ − Me, 10%), 247 (14), 246 (24), 245 (M+ −
Method B. n-Butyllithium (1.6 M solution in hexane, 0.58 ml,
0.92 mmol) was added to a stirred solution of silyl alcohol 14a
(0.29 g, 0.88 mmol) and 1,3-pentadiene (mixture of cis- and
trans-isomers, 0.53 ml, 5.28 mmol) in dry ether (10 ml) at RT.
The mixture was stirred for 2 h after which time TLC showed
complete consumption of starting material. The solution was
cooled to −20 °C and an anhydrous suspension of LiBr in ether
(1.75 M, 0.5 ml, 0.88 mmol) was added and seen to go into solu-
tion. The mixture was stirred at −20 °C for 19.5 h after which time
saturated ammonium chloride solution (10 ml) was added and the
mixture allowed to reach RT. The aqueous layer was separated and
extracted with ether (3 × 10 ml). The combined organic layers were
dried over MgSO4, filtered, concentrated and dried in vacuo. Flash
column chromatography (petroleum ether) gave the title compound
as a colourless oil (0.133 g, 50%) as a mixture of diastereoisomers
in a ratio of 83:9:8 (ratio of product peak integrals by GC); Rf
(hexane) 0.71; max (thin film) 3067, 2997, 2958, 2872, 1461, 1396,
1246, 1108, 855, 838, 736, 702 cm−1; NMR data for major isomer:
H (200 MHz) 7.51–7.48 (2H, m, Ar–H), 7.31–7.28 (3H, m, Ar–H),
5.82 (1H, dtd, J = 10.5, 5.2, 1.8 Hz, 5-H), 5.54 (1H, ddt, J = 10.5,
4.4, 1.8 Hz, 4-H), 2.36 (1H, m, 3-H), 2.10 [1H, septet d, J = 6.8,
3.3 Hz, CH(CH3)2], 1.68 (1H, ddt, J = 17.2, 5.2, 1.8 Hz, 6-HH), 1.47
(1H, ddt, J = 17.2, 5.2, 1.8 Hz, 6-HH), 1.20 (1H, dd, J = 6.5, 3.3 Hz,
2-H), 1.03 [3H, d, J = 6.8 Hz, CH(CH3)2], 0.93 (3H, d, J = 7.2 Hz,
7-H3), 0.88 [3H, d, J = 6.8 Hz, CH(CH3)2], 0.14 [9H, s, Si(CH3)3];
C (126 MHz) 139.36 (ipso-Ar), 137.41 (4-C), 134.48 (Ar), 128.19
i
CH2 Pr, 50%), 235 [M+–CH2C(CH2)CHCH2, 23%], 231 (31),
179 (100), 173 (13), 169 (15), 135 (26), 105 (12).
2 3 9 0
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2

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1-Phenyl-1-trimethylsilyl-2-(prop-2′-yl)-3,4-dimethyl-
silacyclohex-4-ene 43. Reaction of 14a with trans-3-methyl-1,3-
pentadiene according to method B gave the title compound as a
mixture of isomers in a ratio of 86:9:4:1 (38%) (ratio of product
peak integrals by GC); Rf (petroleum ether) 0.75 as a mixture of
four isomers in a ratio of % (ratio of product peak integrals by GC);
max (thin film) 2955, 2926, 2891, 2869, 1427, 1382, 1243, 1099,
1057, 1027, 854, 833, 699 cm−1. NMR data for the major isomer:
H (500 MHz) 7.51–7.49 (2H, m, meta-Ar–H), 7.33–7.29 (3H, m,
ortho- and para-Ar–H), 5.56 (1H, ddd, J = 7.5, 4.0, 1.5 Hz, 5-H),
2.24 (1H, qd, J = 7.0, 2.5 Hz, 3-H), 2.00 [1H, m, CH(CH3)2], 1.72
(3H, s, 8-H3), 1.71 (1H, m, 6-HH), 1.55 (1H, dd, J = 15.5, 7.5 Hz,
6-HH), 1.24 (1H, dd, J = 5.0, 2.5 Hz, 2-H), 1.03 [3H, d, J = 7.0 Hz,
CH(CH3)2], 0.93 [3H, d, J = 7.0 Hz, CH(CH3)2], 0.92 (3H, d,
J = 7.0 Hz, 7-H3), 0.09 [9H, s, Si(CH3)3]; C (101 MHz) 142.52 (5-
C or ipso-Ar), 140.16 (5-C or ipso-Ar), 134.17 (Ar), 128.06 (Ar),
127.64 (Ar), 118.76 (Ar), 39.08 (2-C), 37.66 (3-C), 31.70 (2′-C),
24.95 (8-C), 24.06 (1′-C), 22.42 (7-C), 21.88 (1′-C), 9.32 (6-C),
−0.72 [Si(CH3)3]; m/z (GCMS, EI) 316 (M+, 7%), 243 (M+ − SiMe3,
65%), 217 (10), 215 (12), 187 (47), 161 (100), 135 (38), 121 (40),
110 (22), 105 (PhSi+, 29%); HRMS (EI): Found M+, 316.2039;
C19H32Si2 requires M, 316.2037.
data for the major isomer: H (400 MHz) 7.51–7.49 (2H, m, Ar–H),
7.34–7.31 (3H, m, Ar–H), 5.83 (1H, ddt, J = 10.5, 5.0, 2.0 Hz, 5-H),
5.51 (1H, ddt, J = 10.5, 4.0, 2.0 Hz, 4-H), 2.25 (1H, m, 3-H), 1.65
(1H, ddt, J = 17.5, 5.0, 2.0 Hz, 6-HH), 1.64–1.50 (3H, m, 6-HH and
1′-H2), 1.48–1.27 (3H, m, 2-H and 2′-H2), 1.03 (3H, d, J = 7.0 Hz,
7-H3), 0.86 (3H, t, J = 7.5 Hz, 3′-H3), 0.17 [9H, s, Si(CH3)3]; C
(126 MHz) 136.95 (4-C), 134.50 (ipso-Ar), 134.43 (meta-Ar),
128.36 (para-Ar), 127.70 (ortho-Ar), 124.07 (5-C), 35.93 (3-C),
34.19 (6-C), 30.04 (1′-C), 23.44 (2′-C), 22.26 (7-C), 14.49 (3′-C),
9.87 (2-C), −0.57 [Si(CH3)3]; m/z (GCMS, EI) 302 (M+, 18%), 287
(M+ − Me, 6%), 229 (M+ − SiMe3, 80%), 218 (67), 203 (88), 201
(58), 187 (68), 177 (65), 175 (54), 173 (100), 163 (37), 161 (58),
159 (71), 145 (83), 135 (98), 121 (95).
3-Methyl-2-(2′-dimethylethyl)-1-phenyl-1-(trimethylsilyl)-
silacyclohex-4-ene 47. Reaction of 14e with 1,3-pentadiene
according to method B gave the title compound as a mixture of
diastereoisomers in a ratio of 85:5:5:5 (35%) (ratio of product
peak integrals by GC); Rf (petroleum ether) 0.65; max (thin film)
3067, 3049, 2995, 2954, 2897, 2867, 1465, 1427, 1393, 1364,
1245, 1099, 853, 835, 737, 711, 699 cm−1; NMR data for the major
isomer: H (500 MHz) 7.53–7.52 (2H, m, Ar–H), 7.33–7.29 (3H,
m, Ar–H), 5.85 (1H, m, 5-H), 5.74 (1H, dd, J = 10.0 Hz, 7.0, 4-H),
2.53 (1H, pent, J = 7.0 Hz, 3-H), 1.75 (1H, dd, J = 16.5 Hz, 2.0, 6-
HH), 1.50 (1H, dd, J = 16.5 Hz, 6.0, 6-HH), 1.24 (1H, s, 2-H), 1.02
[s, C(CH3)3], 0.89 (3H, d, J = 7.0 Hz, 7-H3), 0.14 [9H, s, Si(CH3)3];
C (126 MHz) 140.40 (ipso-Ar), 136.88 (4-C), 134.49 (meta-Ar),
127.92 (para-Ar), 127.60 (ortho-Ar), 123.83 (5-C), 45.77 (2-C),
34.50 [C(CH3)3], 32.65 (3-C), 30.65 [C(CH3)3], 24.55 (7-C), 9.35
(6-C), −0.41 [Si(CH3)3]; m/z (GCMS, EI) 316 (M+, 20%), 301 (M+ −
Me, 7%), 259 (21), 247 (26), 243 (M+ − SiMe3, 83%), 218 (57), 203
(79), 175 (100).
1-Phenyl-1-trimethylsilyl-2-(prop-2′-yl)-3,5-dimethylsilacy-
clohex-4-ene 44. Reaction of 14a with 2-methyl-1,3-pentadiene
according to method A gave the title compounds as a mixture of
isomers in a ratio of 94:5:1 (9%) and according to method B in
a ratio of 80:14:4:2 (44%) (ratio of product peak integrals by
GC); Rf (petroleum ether) 0.77; max (thin film) 2956, 2928, 2900,
2868, 1427, 1244, 1101, 855, 833, 725, 697 cm−1; NMR data for the
major isomer: H (400 MHz) 7.51–7.49 (2H, m, Ar–H), 7.33–7.30
(3H, m, Ar–H), 5.32 (1H, m, 4-H), 2.33 (1H, m, 3-H), 2.10 [1H, m,
CH(CH3)2], 1.82 (3H, s, 8-H3), 1.64 (1H, d, J = 16.8 Hz, 6-HH),
1.43 (1H, d, J = 16.8 Hz, 6-HH), 1.14 (1H, ddd, J = 6.4, 3.2, 0.8 Hz,
2-H), 1.03 [3H, d, J = 6.8 Hz, CH(CH3)2], 0.95 (3H, d, J = 6.8 Hz,
7-H3), 0.89 [3H, d, J = 6.8 Hz, CH(CH3)2], 0.16 [9H, s, Si(CH3)3];
C (101 MHz) 139.71 (5-C), 135.20 (ipso-Ar), 134.40 (Ar), 131.17
(4-C), 128.15 (Ar), 127.62 (Ar), 38.38 (2-C), 33.05 (3-C), 29.64
(2′-C), 28.27 (8-C), 23.56 (7-C), 22.81 [1′-C (×2)], 15.05 (6-C),
0.44 [Si(CH3)3]; m/z (GCMS, EI) 316 (M+, 43%), 301 (M+ − Me,
3-Methyl-1,2-diphenyl-1-(trimethylsilyl)silacyclohex-4-ene
48. Reaction of 14g with 1,3-pentadiene according to method B
gave the title compounds as a mixture of diastereoisomers in a
ratio of 74:20:6 (45%) (ratio of product peak integrals by GC);
Rf (petroleum ether) 0.40; max (thin film) 3065, 3019, 2998, 2951,
2920, 2890, 2868, 1597, 1490, 1449, 1427, 1243, 1102, 857, 834,
783, 735, 699 cm−1; NMR data for the major isomer: H (500 MHz)
7.33–7.27 (5H, m, Ar–H), 7.17–7.12 (3H, m, Ar–H), 6.02 (1H, dtd,
J = 10.5, 5.5, 2.5 Hz, 5-H), 5.68 (1H, ddt, J = 10.5, 3.0, 2.0 Hz,
4-H), 2.88 (1H, m, 3-H), 2.46 (1H, d, J = 9.5 Hz, 2-H), 1.89
(1H, ddt, J = 17.0, 5.0, 2.0 Hz, 6-HH), 1.69 (1H, ddt, J = 17.0,
5.5, 2.0 Hz, 6-HH), 1.01 (3H, d, J = 7.0 Hz, 7-H3), −0.02 [9H, s,
Si(CH3)3]; C (126 MHz) 144.53 (ipso-Ar), 136.62 (4-C), 134.45
(Ar), 134.00 (Ar), 128.52 (Ar), 128.34 (Ar), 128.09 (Ar), 127.59
(Ar), 124.62 (Ar), 124.58 (5-C), 40.90 (2-C), 36.22 (3-C), 22.02 (7-
C), 9.57 (6-C), −1.29 [Si(CH3)3]; m/z (GCMS, EI) 336 (M+, 36%),
321 (M+ − Me, 10%), 268 (93), 253 (100), 235 (42), 221 (57), 207
(49), 203 (76), 197 (44), 185 (67), 183 (78), 177 (61), 175 (73),
159 (54), 145 (70), 135 (91); HRMS (EI): Found M+, 336.1726;
C21H28Si2 requires M, 336.1730.
i
4%), 273 (M+ − Pr, 3%), 259 (6), 245 (27), 243 (M+ − SiMe3,
93%), 232 (17), 219 (56), 217 (45), 201 (86), 187 (87), 161 (100),
135 (79), 121 (81), 109 (84); HRMS (EI): Found M+, 316.2038;
C19H32Si2 requires M, 316.2043.
2,3-Dimethyl-1-phenyl-1-(trimethylsilyl)silacyclohex-4-ene
45. Reaction of 14c with 1,3-pentadiene according to method B
gave the title compound as mixture of diastereoisomers in a ratio
of 89:7:4 (28%) (ratio of product peak integrals by GC); Rf (pe-
troleum ether) 0.58; max (thin film) 2998, 2951, 2867, 1427, 1243,
1102, 855, 833, 698 cm−1. NMR data for the major isomer: H
(500 MHz) 7.52–7.49 (2H, m, Ar–H), 7.35–7.32 (3H, m, Ar–H),
5.82 (1H, m, 5-H), 5.48 (1H, dm, J = 10.5 Hz, 4-H), 2.13 (1H, m,
3-H), 1.68 (1H, ddd, J = 18.0, 5.0, 2.0 Hz, 6-HH), 1.52 (1H, ddd,
J = 18.0, 5.5, 2.0 Hz, 6-HH), 1.20 (3H, d, J = 7.5 Hz, 7-H3), 1.08
(3H, d, J = 7.0 Hz, 8-H3), 1.05 (1H, m, 2-H), 0.16 [9H, s, Si(CH3)3];
C (126 MHz) 137.90 (ipso-Ar), 137.03 (4-C), 134.44 (meta-Ar),
128.53 (para-Ar), 127.76 (ortho-Ar), 124.12 (5-C), 38.00 (3-C),
23.87 (2-C), 21.35 (8-C), 15.97 (7-C), 9.70 (6-C), −0.50 [Si(CH3)3];
m/z (GCMS, EI) 274 (M+, 42%), 259 (M+ − Me, 30%), 245 (7), 231
(12), 218 (56), 203 (91), 200 (M+ − H − SiMe3, 95%), 191 (73), 179
(48), 177 (51), 175 (57), 173 (56), 163 (46), 158 (78); HRMS (EI):
Found M+, 274.1567; C16H26Si2 requires M, 274.1568.
Acknowledgements
We thank the EPSRC and GlaxoSmithKline for financial sup-
port of this work (CASE award to D. K. W.); The EPSRC Mass
Spectrometry Service for accurate mass determinations, Dr A. M.
Kenwright for assistance with NMR experiments and Dr M. Jones
for mass spectra.
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O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2
2 3 9 1

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2 3 9 2
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 8 1 – 2 3 9 2