Cationic rearrangements controlled by the presence of a silyl group

Article abstract of DOI:10.1016/S0022-328X(03)00548-5

1,1-Disilylcarbinols having two alkyl groups on the adjacent carbon atom react with thionyl chloride in sulfur dioxide to give the product in which one of the alkyl groups has migrated towards the two silyl groups, and one of the silyl groups has been removed from the resultant cation. The reaction is seen in ring-expansion, as in the conversion of cyclohexylbis[dimethyl(phenyl)silyl]carbinol (7) into 1-dimethyl(phenyl) silylcycloheptene (11), and in open chains, as in the conversion of 1,1-bis[dimethyl(phenyl)silyl]-2-methylpropanol (26) into (E)- and (Z)-2-dimethyl(phenyl)silylbut-2-ene (27). Phenyldimethylsilyllithium reacts with pinacolone to give the α-silyl carbinol (44), which rearranges in the same way to give 2,3-dimethylbut-2-ene (46), effectively achieving a pinacolone-to-pinacol rearrangement.

Full text of DOI:10.1016/S0022-328X(03)00548-5

Journal of Organometallic Chemistry 686 (2003) 84Á93
/
www.elsevier.com/locate/jorganchem
Cationic rearrangements controlled by the presence of a silyl group
Alain Che´nede´ a, Ian Fleming a,*, Roger Salmon b, Mark C. West a
a Department of Chemistry, Lensfield Road, Cambridge CB2 1EW, UK
b Syngenta, Jealott’s Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK
Received 27 March 2003; received in revised form 27 May 2003; accepted 27 May 2003
Abstract
1,1-Disilylcarbinols having two alkyl groups on the adjacent carbon atom react with thionyl chloride in sulfur dioxide to give the
product in which one of the alkyl groups has migrated towards the two silyl groups, and one of the silyl groups has been removed
from the resultant cation. The reaction is seen in ring-expansion, as in the conversion of cyclohexylbis[dimethyl(phenyl)silyl]carbinol
(7) into 1-dimethyl(phenyl)silylcycloheptene (11), and in open chains, as in the conversion of 1,1-bis[dimethyl(phenyl)silyl]-2-
methylpropanol (26) into (E)- and (Z)-2-dimethyl(phenyl)silylbut-2-ene (27). Phenyldimethylsilyllithium reacts with pinacolone to
give the a-silyl carbinol (44), which rearranges in the same way to give 2,3-dimethylbut-2-ene (46), effectively achieving a
pinacolone-to-pinacol rearrangement.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Wagner-Meerwein; Vinylsilane; Allylsilane; 1,1-Disilylcarbinol; a-Silyl carbocation; b-Silyl carbocation
1. Introduction
groups R move towards the silyl group in order to create
a cation 5 stabilised by the b-effect.
We described some years ago how a strategically
placed silyl group could be used to control the outcome
of cationic rearrangements of g-silyl alcohols in the
Migration of hydride [2] and other groups [3] towards
an a-silyl cation or its equivalent has been seen
occasionally by others, and we suspected that it was
involved in the pathway by which a terminal vinylsilane
with only one silyl group was produced as a byproduct
when we dehydrated alcohols of the type 4 in which one
or both of the R groups was a hydrogen atom [4]. A
carbene pathway has been suggested for the purely
thermal reaction of this type [5], but in our work we
usually used thionyl chloride in pyridine, at room
temperature or below, which makes that pathway
unlikely. The present work was undertaken to see if
we could make rearrangement the major pathway when
both R groups were alkyl.
general sense illustrated as 10
that work, the silyl group caused the substituent R to
2 in order to create a
/
20/3 in Scheme 1 [1]. In
move away from the silyl group 10
/
cation stabilised by the b-silicon effect. The outcome
was also controlled, because the silyl group was the
preferred electrofugal group 20/3, determining the site
of the double bond. Using this device, we showed that
the cationic rearrangements of phosphonyl, phenylthio,
hydride, aryl and alkyl groups could be controlled. In
this article, we describe how two silyl groups placed on
the carbinol carbon can control cationic rearrangements
in the general sense 40
/
50/6, in which alkyl or aryl
2. Results and discussion
* Corresponding author. Tel.: ꢀ
33-6362.
E-mail address: if10000@cam.ac.uk (I. Fleming).
/
44-1223-33-6372; fax: ꢀ44-1223-
/
We studied most carefully the reaction of the disilyl
alcohol 7, prepared from cyclohexylcarbonyl chloride
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00548-5

A. Che´nede´ et al. / Journal of Organometallic Chemistry 686 (2003) 84Á
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85
groups. There cannot have been much of it present, but
we cannot be completely sure that it was absent, since it
would not have any distinctive protons with which to
1
characterise it in the H-NMR spectra of the mixtures
we obtained, and we were unable to make an authentic
sample to make identification easier.
We record in Table 1 the yields of the products under
the various conditions that we tried for these three
reagents. The major products in almost every case were
the skeletally rearranged vinylsilane 11 and the product
of hydride shift, the exocyclic vinylsilane 13. The ratio of
skeletally rearranged to unrearranged product was
affected by solvent polarity, with skeletal rearrangement
encouraged in the more polar solvents, as shown by
Scheme 1.
with an excess of phenyldimethylsilyllithium [6]. We
tried a wide range of the reagents commonly used for the
dehydration of alcohols, but a surprising number of
them, including such obvious candidates as methane-
sulfonyl chloride, Burgess’s reagent and Martin’s sulfur-
ane, had no effect, and the alcohol 7 was recovered
unchanged under all conditions mild enough to isolate
any recognisable products. The most promising excep-
tions were thionyl chloride, thionyl diimidazole, and
phosphorus oxychloride. These reagents can be expected
to encourage the formation of the cation 8, which may
or may not be a discrete intermediate, and hence the
formation of either of the rearranged cations 9 from
ring-expansion or 10 from hydride shift. The chloride
ion released from the thionyl chloride can be expected to
remove selectively the silyl group from these cations,
leading to such products as 11 and 13, and the nitrogen-
based counterion released from thionyl diimidazole can
be expected to remove selectively a proton, leading to
such alkenes as 12 and 14. Another possible product
would follow from the loss of the ring proton in the
cation 8 (or the exocyclic proton in the cation 10),
leading to an exocyclic alkene with two silyl groups
entries 1Á7. To our surprise, the expectation that the
/
absence of a halide counterion would lead to more
proton loss was not fulfilled: the products in entry 8 are
the same as those in entry 4, and in much the same ratio.
The deliberate addition of halide ion to the imidazole-
containing reaction in entry 9 merely changed the ratio
in favour of the exocyclic vinylsilane 13. Phosphorus
oxychloride in pyridine (entry 11) needed a much higher
temperature to induce elimination, and the surprising
product, in low yield, but which we saw otherwise only
in even smaller amounts, was the allyldisilane 14.
Because all the reactions in entries 1Á10 gave mixtures
/
of at least two products, we were inclined at this stage to
think that the reaction had very limited potential in
organic synthesis. Furthermore, the total yield was
rarely outside the 40Á60% range, and we were unable
/
to find the lost mass, indicating perhaps that both silyl
groups had been removed to some extent. The break-
through came when we discovered that reactions carried
out in sulfur dioxide as the solvent (entries 12Á
/14),
attached. Although we saw each of the alkenes 11Á14,
/
we found none of the exocyclic alkene with two silyl
although still not giving a high yield, were cleanly in
Table 1
Yields of alkenes 11Á14 from the 1,1-dislylcarbinol 7 (Scheme 2)
/
Entry
Reagents and conditions
11
Yield (%)
12
Yield (%)
13
Yield (%)
14
Yield (%)
1
SOCl2, Py, MeCN, r.t.
SOCl2, Py, CH2Cl2, r.t.
SOCl2, CDCl3, r.t.
33
32
37
15
9
-
-
-
-
-
-
-
-
-
5
-
-
-
-
5
18
13
25
37
30
52
38
50
31
-
-
-
2
3
-
4
SOCl2, Py, THF, r.t.
SOCl2, Py, Et2O, r.t.
SOCl2, Py, toluene, r.t.
SOCl2, Py, CCl4, r.t.
SOIm2, THF, r.t.
-
5
-
6
8
-
7
8
-
8
21
17
10
-
-
9
SOIm2, LiCl, THF, r.t.
SOIm2, Et2O, r.t.
-
10
11
12
13
14
-
POCl3, Py, 110 8C
20
-
POCl3, Py, SO2, 10 8C
SOCl2, Py, SO2, 10 8C
SOIm2, Py, SO2, 10 8C
50
70
68
-
-
-
-
-
1
Determined by integration of characteristic signals in the H-NMR spectra using an internal standard (CH2I2) added in weighed amounts to the
crude product. Yields of 1% or less are entered as a hyphen.

86
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/
favour of the more interesting product, the skeletally
rearranged vinylsilane 11.
stabilised than a cyclopropyl cation. The only problem,
in this otherwise clean ring-expansion, was the forma-
tion of a little of the butadiene 25, which might be the
result of electrocyclic ring-opening of the major product,
the cyclobutene 24, or it might be a product from the
homoallyl isomer of the cyclopropylmethyl cation.
In the open-chain substrates in Scheme 4, it is perhaps
noteworthy that the phenyl group migrates rather than
the methyl in the alcohol 34, as usual for cationic
rearrangements, but the methyl group migrates rather
than the isopropyl in the alcohol 31, which is not the
usual pattern. It seems likely that the migration of the
larger group towards the relatively hindered cationic
centre carrying two silyl groups may be inhibited.
Some of the products in Scheme 4 can be E- or Z-
isomers, and in each case the major product was the E-
isomer. The loss of the silyl group is almost certainly
irreversible, and the products are unlikely to be able to
equilibrate under these reaction conditions, suggesting
that the E:Z ratio is kinetically controlled. On the
whole, the proportion of E-isomer was greater in those
reactions carried out in the less polar solvents, indicating
that the first-formed conformations of the rearranged
cations may not reflect the relative energies of the
transition structures. If an a-silyl cation is formed in
the first step from the alcohol 26, it will have a
conformation 38, from which a methyl group can
migrate suprafacially in the usual way to give a cation
39. Although it is probably not a discrete intermediate,
it is a useful simplification to think of it as such. This
cation can change its conformation to increase the b-
silicon effect by rotation about the central bond, clock-
wise to give the cation 40 or anticlockwise to give the
cation 41. The former is the lower-energy pathway, since
the left hand silyl group has to eclipse briefly only the
hydrogen atom, whereas in the latter the right hand silyl
group has to eclipse briefly the methyl group. The cation
40 has the conformation suitable for giving the vinylsi-
lane E-27. In sulfur dioxide, the cations can be expected
to live longer, and so the ratio of the isomeric cations 40
and 41 can change more nearly to reflect their thermo-
dynamic energies. In this way the proportion of the
kinetically less-favoured cation 41 may build up, and
hence account for the formation of mote of the
vinylsilane Z-27 in this and other polar solvents. It is
We also carried out a reaction on the bistrimethylsilyl
analogue of the disilylcarbinol 7 using thionyl chloride
and pyridine in sulfur dioxide, and obtained a 65% yield
of 1-trimethylsilylcycloheptene, analogous to the vinyl-
silane 11. Using other substrates, we found mixtures of
products in most solvents, similar to the results in entries
1Á
/
10 in Table 1, but predominantly one in sulfur
14. Selections
dioxide, similar to the results in entries 12Á
/
[7] of our results for candidates for ring-expansion are
shown in Scheme 3, and for candidates for open-chain
rearrangements in Scheme 4. Although not all of our
results are illustrated, we saw the same trends in both
sets as we had seen in the reactions in Scheme 2: hydride
shift was the major pathway in the less polar solvents,
alkyl shift was the major pathway in the more polar
solvents, and almost the only pathway in sulfur dioxide.
In Scheme 3, the cyclobutyldisilylcarbinol 20 was
anomalous in giving in sulfur dioxide some of the
product 22 of hydride shift, although the product of
ring-expansion 21 was still the major product. Consis-
tent with this result, the same reaction in dichloro-
methane gave a higher proportion than usual of the
product of hydride shift 22. The case of hydride shift in
this case may be a consequence of the unusual stability
of cyclobutyl cations. In contrast, the corresponding
cyclopropyldisilylcarbinol 23 gave no product from
hydride shift in any solvent, presumably because a
cyclopropylmethyl cation is intrinsically much better
Scheme 2.

A. Che´nede´ et al. / Journal of Organometallic Chemistry 686 (2003) 84Á
/93
87
Scheme 3.
part of this argument that a silyl group, with its long Cꢀ
/
Martin’s sulfurane to give the vinylsilane 13, but with
thionyl chloride in sulfur dioxide the major product, too
volatile to measure the yield, appeared to be the product
of hydride shift, the exocyclic alkene 43. Had ring-
expansion and silyl loss taken place the product would
have been cycloheptene, but there were no signals in the
1H-NMR spectrum of the crude product to indicate that
this had been formed. More interesting was the a-
silylcarbinol 44 derived from pinacolone in 69% yield. It
Si bond, is not as big a steric encumbrance as its actual
size might lead one to think, making it less obvious
which of the two cations 40 or 41 is the lower in energy.
We also investigated briefly the possibility that one
silyl group might still encourage migration towards it
(Scheme 5). The a-silylcarbinol 42, derived from the
reaction of cyclohexanecarboxaldehyde and phenyldi-
methylsilyllithium, underwent simple dehydration with
Scheme 4.

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/
3. Experimental
3.1. General
Infrared spectra were recorded on a PerkinÁElmer
/
FT-IR 1600 spectrometer, using sodium chloride plates.
NMR spectra were recorded on a Bruker Avance DPX
250 or a Bruker Ultrashield 400. Chemical shifts were
measured relative to chloroform (1H d 7.25, 13C d 77.0).
13C-NMR spectra taken using the APT protocol are
Scheme 5.
labelled ꢀ
for methane and methyl carbons. Flash column
chromatography was carried out using Merck Kieselgel
60 (230Á400 mesh). Thin layer chromatography was
performed using plates coated with Kieselgel 60 PF254
Ether and THF were distilled from lithium aluminium
hydride immediately before use. Toluene, hexane, di-
chloromethane and acetonitrile were distilled from
calcium hydride.
/
for quaternary and methylene carbons, and
ꢁ
/
/
.
underwent simple dehydration to give the vinylsilane 45
with most reagents, but underwent relatively clean
rearrangement with thionyl chloride in sulfur dioxide
to give 2,3-dimethylbut-2-ene 46 in 23% yield when
isolated as its dibromide. Since this alkene can be
dihydroxylated to give pinacol [8], this reaction provides
a pathway for a pinacolone-to-pinacol transformation,
but more work is needed to raise the yield before it can
be said to compete with the standard retro-pinacol
rearrangement of pinacolyl alcohols to tetraalkylethy-
lenes [9].
3.2. Synthesis of the 1,1-disilyl alcohols
Typically, the acid chloride (10 mmol) in toluene (5
cm3) was added dropwise over 3 min to dimethyl(phe-
nyl)silyllithium [20] (1 mol dmꢁ3 solution in THF, 22
cm3, 22 mmol) and toluene (20 cm3) under nitrogen with
vigorous stirring and cooling in a dry-ice acetone bath.
An alternative reaction of the general type 470
/
48, in
which a substituent migrates from the silyl group to the
neighbouring electrophilic carbon, is a much better
known pathway, but was not detectable in any of the
work described here. This type of rearrangement is more
often than not either a unimolecular, diotropic, and
often gas-phase reaction [10], or one promoted by a
nucleophilic ‘push’ from a fluoride ion [11], an alkoxide
ion [12,13] or a powerful nucleophile already coordi-
nated to the silyl group [14]. It is relatively rarely seen
when it is initiated by electrophilic ‘pull’ from a well-
developed carbocation [15], as in the work described
here. With respect to the extent to which a cation a to a
silyl group is stabilised, the consensus appears, both
computationally [16] and experimentally [17], to be that
a trialkylsilyl group is effectively more stabilising than a
hydrogen atom, but less stabilising than a methyl group.
Part of the apparent ‘stabilisation,’ in solvolysis studies
at least, may be steric destabilisation of the starting
materials [18], but, in any case, the effect is much less
than b-stabilisation by a silyl group [19]. It seems likely
from this evidence that the cation 8 is an intermediate.
After 0.5Á1 h, the solution was poured into hexane (100
/
cm3) and aqueous ammonium chloride solution, the
organic layer separated, washed with hydrochloric acid
(3 mol dmꢁ3, 30 cm3) and with brine (30 cm3), dried
(MgSO4), and evaporated under reduced pressure. The
residue was chromatographed (SiO2, hexaneÁEt2O) to
/
give the 1,1-disilyl alcohols. In some cases the product
was distilled (kugelrohr). The synthesis by this method
and the characterisation of the alcohols 7 (94%), 15
(87%), 20 (72%), 26 (87%), 31 (62%), 34 (63%) and 36
(76%) have been described earlier [6,13].
The TMS analogue of structure 11 was prepared by
the method of Kuwajima [21]. The major product of its
rearrangement, 1-trimethylsilylcycloheptene, is also
known [22].
3.3. 3,3-Dimethyl-2-dimethyl(phenyl)silylbutan-2-ol
(44)
Pinacolone (2.8 g, 20 mmol) was added at ꢁ
/
78 8C to
dimethyl(phenyl)silyllithium(1.08 mol dmꢁ3 in THF, 25

A. Che´nede´ et al. / Journal of Organometallic Chemistry 686 (2003) 84Á
/93
89
cm3, 27 mmol) and toluene 20 cm3 via syringe, and the
3.4.3. Method C
mixture kept at ꢁ
/
78 8C for 1 h. The mixture was added
Thionyl chloride (0.15 cm3, 4 mmol) was added to a
stirred solution of the silylalcohol (1 mmol) and pyridine
(2 mmol) in sulfur dioxide (3 cm3 distilled from P2O5
to hydrochloric acid (3 mol dmꢁ3, 20 cm3). Hexane (250
cm3) was added to the mixture, the organic layer was
separated and washed with brine (30 cm3) and dried
(MgSO4). The solvents were removed under reduced
pressure and the residue chromatographed (SiO2,
into the flask containing the alcohol) at ꢁ10 8C under
nitrogen, and then allowed to warm to r.t. After 1 h, the
brown residue was either: (a) diluted with water (5 cm3),
/
hexaneÁ
mg, 69%); Rf (hexaneÁ
cmꢁ1 3330 (OH), 2953 (Cꢀ
and SiMe) and 1110 (SiPh); dH (400 MHz; CDCl3) 7.64
7.35 (3H, m, Ph), 1.34 (1H, br s, OH),
/
Et2O, 25:1) giving the alcohol as an oil (326
Et2O, 94:6) 0.22; nmax (film)
H), 1427 (Ph), 1248 (br, OH
extracted with pentane (2ꢂ
/
20 cm3), the extract washed
10 cm3) and
/
with hydrochloric acid (3 mol dmꢁ3, 2ꢂ
/
/
with brine (10 cm3), dried (MgSO4) and evaporated
under reduced pressure, or (b) diluted with pentane (5
cm3) and stirred for 2 min then passed through a silica
pad (ca. 4 cm3) and eluted with pentane (20 cm3); the
solvent was then evaporated off under reduced pressure.
The following compounds were isolated by one or
more of these methods, or by minor variations of them.
(2H, m, Ph), 7.37Á
/
1.21 (3H, s, Me), 0.89 (9H, s, But), 0.47 (3H, s,
SiMeAMeB) and 0.46 (3H, s, SiMeAMeB; dC(100 MHz;
CDCl3) 139.1 (i-Ph), 134.5 (o-Ph), 128.8 (p-Ph), 127.6
(m-Ph), 72.5 (CO), 38.5 (CMe3), 26.4 (CMe3), 21.8 (Me),
ꢁ
/
1.7 (SiMe) and ꢁ
[M1]), 235 (5, [Mꢀ
H]) and 221 (6, [Mꢀ
(Found: [Mꢀ
Na1], 259.1490. C14H24OSi requires [Mꢀ
/
2.1 (SiMe); m/z (EI) 236 (1%,
/
/Me]); (ESI)
3.4.4. 1-Dimethyl(phenyl)silylcycloheptene (11)
Rf-(hexane) 0.50; nmax(film) cmꢁ1 2919 (Cꢀ
/
H), 1616
Me) and 1112
(SiPh); dH(400 MHz; CDCl3) 7.57 (2H, m, Ph), 7.41Á
CH), 2.22 (2H,
/
/
Na], 259.1494). The known alcohol 42 (86%) was
prepared similarly [23].
(Cꢁ
/
C), 1446 (Ph), 1427 (Ph), 1246 (Siꢀ
/
/
7.35 (3H, m, Ph), 6.33 (1H, t, J 6.0, CSiꢁ
/
m, allylic CH2), 2.18 (2H, m, allylic CH2), 1.80 (2H, m,
CH2), 1.51 (2H, m, CH2), 1.42 (2H, m, CH2) and 0.36
3.4. General procedures for the rearrangement reactions
(6H, s, SiMe2); dC(100 MHz; CDC13) 143.8ꢁ
143.5ꢀ (SiC ꢁCH), 138.9ꢀ (i-Ph), 134.0ꢁ
128.7ꢁ (p-Ph), 127.6ꢁ (m-Ph), 33.0ꢀ (CH2), 30.7ꢀ
(CH2). 27.4ꢀ (CH2), 26.8ꢀ (CH2) and 3.4ꢁ
/
(Cꢁ
/
CH),
Many procedures were tried, but the following were
the most informative and are representative. For asses-
sing the yields, a measured quantity of diiodomethane
was added to a known weight of the crude product, and
/
/
/
/
(o-Ph),
/
/
/
/
/
/
ꢁ
/
/
(SiMe2); m/z (EI) 230.1 (58%, [M]), 215.1 (47%, [Mꢀ
/
1
Me]) and 135.1 (100%, SiMe2Ph) (Found: [M4],
230.1491, C15H22Si requires 230.1491). An alternative
synthesis to confirm this structure was carried out in
96% yield using dimethyl(phenyl)silyllithium and cyclo-
heptanone, followed by dehydration using Method A.
The products were identical (1H-NMR, TLC).
the H-NMR spectrum taken before any chromatogra-
phy. For the isolation of the various products, the
residue was chromatographed (SiO2, hexane or pen-
tane).
3.4.1. Method A
Thionyl chloride (0.15 cm3, 4 mmol) was added to a
stirred solution of the silylalcohol (1 mmol) and pyridine
(2 mmol) in dichloromethane (3 cm3) at 0 8C under
nitrogen and then allowed to warm to room temperature
(r.t.). After 1 h, the brown solution was diluted with
ether (15 cm3), washed with hydrochloric acid (3 mol
3.4.5. 3,3-Bis[dimethyl(phenyl)silyl]cycloheptene (12)
dH(400 MHz; CDCl3) 5.81 (1H, d, J 12.9, Si2CCH ꢁ
/
CH), 5.68 (1H, dt, J 12.9 and 5.1, Si2CCHꢀ
/
CH), 0.25
(3H, s, SiMeAMeB) and 0.15 (3H, s, SiMeAMeB).
dmꢁ3, 2ꢂ
/
10 cm3) and with brine (10 cm3), dried
3.4.6. Dimethyl(phenyl)silylmethylenecyclohexane (13)
(MgSO4) and evaporated under reduced pressure.
Rf (hexane) 0.44; nmax(film) cmꢁ1 2918 (Cꢀ
/
H), 1451
Me); dH(400 MHz; CDCl3) 7.58 (2H, m,
7.37 (3H, m, Ph), 5.30 (1H, s, CꢁCHSi) 2.03
(2H, br s, allylic CH2), 1.85 (2H, br s, allylic CH2), 1.71
(2H, br s, CH2), 1.62Á1.55 (4H, m, CH2) and 0.36 (s,
SiMe2); dC(100 MHz; CDC13) 140.4 (C ꢁCSi), 134.7 (i-
Ph), 133.6 (o-Ph), 128.8 (p-Ph), 127.6 (m-Ph), 119.8 (Cꢀ
CHSi), 31.2 (CH2), 27.4 (CH2), 26.3 (CH2), 23.3 (CH2),
21.7 (CH2) and ꢁ2.6 (SiMe2.). An alternative synthesis
(Ph), 1253 (Siꢀ
/
Ph), 7.42Á
/
/
3.4.2. Method B
Thionyl chloride (0.15 cm3, 4 mmol) was added to a
stirred slurry of imidazole (0.544 g, 8 mmol) in THF (6
cm3) at 0 8C under nitrogen and after 10 min the
supernatant filtered into a solution of the silylalcohol
(1 mmol) in THF (1 cm3) at 0 8C. After 2 h the solution
was diluted with hexane (100 cm3) and washed with
hydrochloric acid (3 mol dmꢁ3, 30 cm3) and with brine
(10 cm3), dried (MgSO4) and evaporated under reduced
pressure.
/
/
/
/
to confirm the structure of this known compound [24]
was carried out in 51% yield by dehydration of the
alcohol 42 using Martin’s sulfurane [25]. The products
were identical (1H-NMR, TLC).

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A. Che´nede´ et al. / Journal of Organometallic Chemistry 686 (2003) 84Á93
/
3.4.7. Cyclohexenylbis[dimethyl(phenyl)silyl]methane
(14)
3.4.11. Cyclopentenylbisdimethyl(phenyl)silylmethane
(19)
Rf (hexane) 0.35; nmax(film) cmꢁ1 2900 (Cꢀ
/
H), 1635
Me) and 1110 (SiPh);
dH(400 MHz; CDCl3) 7.45 (4H, m, Ph), 7.32Á7.27
(6H, m, Ph), 5.23 (1H, m, CH ꢁC), 1.97 (2H, m, allylic
CH2), 1.47 (2H, m, allylic CH2), 1.35Á1.30 (4H, m,
Rf (hexane) 0.50; nmax(film) cmꢁ1 2900 (Cꢀ
/
H), 1635
Me) and 1110 (SiPh);
dH(250 MHz; CDCl3) 7.55 (4H, m, Ph), 7.42Á7.32
(6H, m, Ph), 5.27 (1H, s, CH ꢁC), 2.38 (2H, m, allylic
(Cꢁ
/
C), 1448 (Ph), 1248 (Siꢀ
/
(Cꢁ
/
C), 1448 (Ph), 1248 (Siꢀ
/
/
/
/
/
/
CH2), 1.95 (2H, m, allylic CH2), 1.67 (2H, septet, J 7.5,
CH2), 1.35 (1H, s, CHSi2), 0.33 (6H, s, SiAMeAMeB)
and 0.31 (6H, s, SiMeAMeB); dC(100 MHz; CDCl3)
CH2), 0.98 (1H, s, CHSi2), 0.24 (6H, s, SiMeAMeB) and
0.22 (6H, s, SiMeAMeB); dC(100 MHz; CDCl3) 140.0 (i-
Ph), 136.1 (C ꢁ
/
CH), 133.8 (o-Ph), 128.7 (p-Ph), 127.3
142.7ꢀ
128.6ꢁ
40.6ꢀ
/
(C ꢁ
(p-Ph), 127.6ꢁ
(CH2), 33.4ꢀ (CH2), 23.6ꢀ
/
CH), 140.1ꢀ
(m-Ph), 122.2ꢁ
(CH2), 22.3ꢁ
(SiMeA-
/
(i-Ph), 133.9ꢁ
/
(o-Ph),
(m-Ph), 120.3 (Cꢁ
/
CH), 33.8 (CH2), 27.7 (CHSi2), 25.5
1.7 (SiMeAMeB);
/
/
/
(Cꢁ
/CH),
(CH2), 23.0 (CH2), 22.0 (CH2) and ꢁ
/
/
/
/
/
m/z (EI) (Found: [Mꢀ], 364.2040, C23H32Si2 requires
364.2043).
(CHSi2), ꢁ
/
2.9ꢁ
/
(SiMeAMeB) and ꢁ
/
3.0ꢁ
/
MeB); m/z (EI) (Found0: [Mꢀ], 350.1900, C22H30Si2
requires 350.1886).
3.4.12. 1-Dimethyl(phenyl)silylcyclopentene (21) [26]
3.4.8. 1-Dimethyl(phenyl)silylcyclohexene (16)
Rf (hexane) 0.40; nmax(film) cmꢁ1 2910 (Cꢀ
/
H), 1610
Me) and 1110 (SiPh);
dH(400 MHz; CDC13) 7.56 (2H, m, Ph), 7.38Á7.35 (3H,
m, Ph), 5.35 (1H, sept, J 2.5, CꢁCH), 2.81 (2H, m,
Rf (hexane) 0.46; nmax(film) cmꢁ1 2920 (Cꢀ
/
H), 2849
Me) and
1111 (SiPh); dH(400 MHz; CDCl3) 7.54 (2H, m, Ph),
7.40Á7.36 (3H, m, Ph), 6.17 (1H, m, CꢁCH), 2.11 (2H,
m, allylic CH2), 2.07 (2H, m, allylic CH2), 1.70Á1.62
(4H, m, CH2) and 0.37 (6H, s, SiMe2); dC(100 MHz;
CDCl3) 138.8 (C ꢁCH), 137.9 (CꢁCH), 136.7 (i-Ph),
133.9 (o-Ph), 128.7 (p-Ph), 127.6 (m-Ph), 26.8 (CH2),
26.8 (CH2), 22.9 (CH2), 22.4 (CH2) and ꢁ3.6 (SiMe2).
(Cꢁ
/
C), 1431 (SiPh), 1250 (Siꢀ
/
(Cꢀ
/
H), 1618 (Cꢁ
/
C), 1429 (SiPh), 1243 (Siꢀ
/
/
/
/
/
allylic CH2), 2.68 (2H, m, allylic CH2), 1.95 (2H, qn, J
6.5, CH2) and 0.35 (6H, s, SiMe2); dC(100 MHz; CDCl3)
/
139.9 (C ꢁ
127.7 (m-Ph), 116.7 (Cꢁ
(allylic CH2), 16.4 (CH2) and ꢁ
/
CH), 138.8 (i-Ph), 133.8 (o-Ph), 128.9 (p-Ph),
CH), 35.6 (allylic CH2), 33.6
1.6 (SiMe2).
/
/
/
/
/
An alternative synthesis to confirm the structure of this
known compound [26] was carried out in 92% yield
using dimethyl(phenyl)silyllithium and cyclohexanone,
followed by dehydration using Method A. The products
were identical (1H-NMR, TLC).
3.4.13. Dimethyl(phenyl)silylmethylenecychbutane (22)
[24]
Rf (hexane) 0.47; nmax(film) cmꢁ1 2953 (Cꢀ
/
H), 2840
C), 1589 (Ph), 1448 (SiPh), 1250
Me) and 1110 (SiPh); dH(250 MHz; CDCl3) 7.52
(2H, m, Ph), 7.39Á7.33 (3H, m, Ph), 6.08 (1H, s, CH ꢁ
C), 2.45Á2.35 (4H, m, allylic CH2), 1.84 (2H, quintet, J
7.5, CH2) and 0.36 (6H, s, SiMe2); dC(100 MHz; CDCl3)
142.6 (CꢁCH), 142.4 (C ꢁCH), 138.8 (i-Ph), 133.7 (o-
Ph), 128.8 (p-Ph), 127.7 (m-Ph), 36.0 (allylic CH2), 35.0
(allylic CH2), 24.1 (CH2) and ꢁ3.0 (SiMe2).
(Cꢀ
/
H), 1649 (w, Cꢁ
/
(Siꢀ
/
/
/
/
3.4.9. 3,3-Bis[dimethyl(phenyl)silyl]cyclohexene (17)
dH(400 MHz; CDCl3) 5.91 (1H, dd, J 10.0 and 2.5,
/
/
Si2CCH ꢁ
/
CH), 5.78 (1H, dt, J 10.0 and 4.8, Si2CCHꢁ
/
CH),1.8 2H, m, CHꢁ
/
CHCH2), 0.31 (6H, s, SiAMeA-
/
MeB) and 0.21 (6H, s, SiMeAMen) with COSY connec-
tions between the signals at d5.91 and d5.78, and of
both of these with the signal at d1.8.
3.4.14. 1-Dimethyl(phenyl)silylcyclobutene (24)
Rf (hexane) 0.5; nmax(film) cmꢁ1 2918 (Cꢀ
H), 1607w
(CꢁC), 1428 (Ph), 1249 (SiꢁMe) and 1111 (SiPh);
dH(400 MHz; CDCl3) 7.52 (2H, m, Ph), 7.36Á7.32
(3H, m, Ph), 6.56 (1H, t, J 1.0, CꢁCH), 2.69 (2H,
ddd, J 3.5, 3.1 and 1.0, CH2CHꢀ) and 2.57 (2H, dd, J
3.5 and 3.0, CH2CSiꢀ); dC(100 MHz; CDCl3) 153.5ꢀ
(CSiꢁCH), 149.8ꢁ (CꢁCH), 138.2ꢀ (i-Ph), 129.2ꢁ
(m-Ph), 127.9ꢁ (o-Ph), 127.7ꢁ (p-Ph), 32.4ꢀ (CH2)
and 32.2ꢀ
(CH2); m/z (EI) (Found: [Mꢀ], 188.1012,
/
/
/
/
3.4.10. Dimethyl(phenyl)silylmethylenecyclopentane
/
(18) [24]
/
Rf (hexane) 0.55; nmax(film) cmꢁ1 2900 (Cꢀ
/
H), 1635
Me) and 1110 (SiPh);
dH(250 MHz; CDCl3) 7.52 (2H, m, Ph), 7.39Á7.32
(3H, m, Ph), 6.07 (1H, septet, J 2.0, CH ꢁC), 2.12Á
1.96 (4H, m, allylic CH2), 1.66Á1.52 (4H, m, CH2) and
0.31 (6H, s, SiMe2); dC(100 MH2; CDCl3) 138.9ꢀ (C ꢁ
CH), 137.9ꢁ (CꢁCH), 136.7ꢀ (i-Ph), 134.0ꢁ (o-Ph),
128.7ꢁ (p-Ph), 127.7ꢁ (m-Ph), 26.9ꢀ (CH2), 26.8ꢀ
/
/
(Cꢁ
/
C), 1448 (Ph), 1248 (Siꢀ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
C12H16Si requires 188.1021).
/
/
/
/
/
/
3.4.15. 2-Dimethyl(phenyl)silylbuta-l,3-diene (25)
This known [27] diene was only present in small
amounts. It could not be completely separated, but was
identified in the mixture from HMBC and MQC
correlations: dH(400 MHz; CDCl3) 7.53 (2H, m, Ph),
/
/
/
/
(CH2), 22.9ꢀ
/
(CH2), 22.4ꢀ
/
(CH2), and
(SiMe2); m/z (E1) (Found: [Mꢀ], 216.1336, C14H20Si
requires 216.1334).
ꢁ
/
3.6ꢁ
/

A. Che´nede´ et al. / Journal of Organometallic Chemistry 686 (2003) 84Á
/93
91
7.35Á
CH ꢁCH2), 5.88 (1H, d, J 3.0, CSiꢁ
d, J 3.0, CSiꢁCHAHB), 5.10 (1H, d, J 17.5, CHꢁ
CHEHZ), 4.99 (1H, d, J 11.0, CHꢁCHEHZ) and 0.32
(6H, s, SiMe2); dC (100 MHz; CDCl3) 149.8 (CHꢁCH2),
130.4 (CSiꢁCH2), 116.7 (CHꢁCH2) and 0.8 (SiMe2).
/
7.32 (3H, m, Ph), 6.46 (1H, dd, J 17.5 and 11.0,
(3H, d, J 1,5, Cꢁ
/
CCH3), 0.80 (6H, d, J 7.0, CMe2) and
/
/CHAHB), 5.50 (1H,
0.37 (3H, s, SiMe2).
/
/
/
3.4.23. E-1-Dimethyl(phenyl)silyl-1-phenyl-propene (E-
35)
dH(400 MHz; CDCl3) 7.62 (2H, m, Ph), 7.40Á
(8H, m, Ph), 6.37 (1H, q, J 7.0, CꢁCH), 1.78 (3H, d, J
7.0, Me) and 0.36 (6H, s, SiMe2).
/
/
/
/7.30
/
3.4.16. E-2-Dimethyl(phenyl)silylbut-2-ene (E-27)
[28,29]
3.4.24. Z-1-[Dimethyl(phenyl)silyl]-1-phenyl-propene
(Z-35)
dH(400 MHz; CDCl3) 7.69 (2H, m, Ph), 7.47Á
(3H, m, Ph), 6.04 (1H, qq, J 6.5 and 1.5, CꢁCH), 1.83
(1H, d, J 6.5, CH3CHꢀC), 1.80 (1H, s, CHꢁCCH3) and
0.35 (6H, s, SiMe2); nOe 6.04Á7.68, 7.45, 1.83 and 0.35,
no effect to 1.80.
/
7.43
/
dH(400 MHz; CDCl3) 7.52 (2H, m, Ph), 7.35Á
(8H, m, Ph), 6.14 (1H, q, J 7.0, CꢁCH), 1.59 (3H, d, J
7.0, Me) and 0.43 (6H, s, SiMe2).
/7.25
/
/
/
/
3.4.25. E-1-Dimethyl(phenyl)silylpropene (E-37) [30]
dH(400 MHz; CDCl3) 7.52 (2H, m, Ph), 7.35Á7.33
(3H, m, Ph), 6.12 (1H, dq, 18.5 and 6.0, CHꢁCHMe),
CHMe), 1.84 (3H, dd,
3.4.17. Z-2-Dimethyl(phenyl)silylbut-2-ene (Z-27)
[29]
/
/
dH(400 MHz; CDCl3) 7.62 (2H, m, Ph), 7.46Á
(3H, m, Ph), 6.33 (1H, qq, J 7.0 and 1.5, CꢁCH), 1.94
(3H, dq, J 1.5 and 1.5, CHꢁCCH3), 1.73 (3H, dq, J 7.0
C) and 0.54 (6H, s, SiMe2); nOe 6.33Á
/
7.43
5.78 (1H, dq, 18.5 and 1.5, CH ꢁ
/
/
6.0 and 1.5, allylic Me) and 0.30 (6H, s, SiMe2).
/
and 1.5, CH3CHꢁ
/
/
3.4.26. Z-1-Dimethyl(phenyl)silylpropene (Z-37) [30]
1.94 and 1.73, no effect to 7.62, 7.45 or 0.54.
dH(400 MHz; CDCl3) 7.57 (2H, m, Ph), 7.39Á
(3H, m, Ph), 6.54 (1H, dq, 14.0 and 7.0, CHꢁCHMe),
CHMe), 1.84 (3H, dd,
/7.31
/
3.4.18. 3,3-Bisdimethyl(phenyl)silylbutene (28)
5.67 (1H, dq, 14.0 and 1.5, CH ꢁ
/
dH(400 MHz; CDCl3) 6.41 (1H, dd, J 17.0 and 10.5,
CH2ꢁCH), 5.16 (1H, dd, J 10.5 and 1.5, CHEHZꢁCH),
4.76 (1H, dd, J 17.0 and 1.5, CHEHZꢁCH), 1.32 (3H, s,
7.0 and 1.5, allylic Me) and 0.39 (6H, s, SiMe2).
/
/
/
3.4.27. Methylenecyclohexane (43) [31]
Rf (pentane) 0.80; dH(400 MHz; CDCl3) 4.62 (2H, s,
CH3), 0.32 (6H, s, SiMeAMeB) and 0.28 (6H, s,
SiMeAMeB).
Cꢁ
/
CH2), 2.15 (4H, m, allylic CH2), 1.59Á
/
1.55 (6H, m,
3ꢂ
/
CH2); COSY correlations 4.62Á
/
2.15, 2.15Á
/1.55;
3.4.19. 1-Dimethyl(phenyl)silyl-2-methylpropene (29)
identical (1H-NMR) with an authentic sample.
dH(400 MHz; CDCl3) 5.56 (1H, br s, Cꢁ/CHSi), 2.07
(3H, d, J 1.0, Me), 1.91 (3H, br s, Me) and 0.53 (6H, s,
SiMe2).
3.5. 2,3-Dibromo-2,3-dimethylbutane
The alcohol 44 (0.55 g, 2.3 mmol) was dehydrated
using Method C. The residue was diluted with heptane
3.4.20. 3,3-Bisdimethyl(phenyl)silyl-2-methylpropene
(30)
(30 cm3), washed with hydrochloric acid (3 mol dmꢁ3
,
20 cm3) and saturated sodium hydrogencarbonate solu-
tion (20 cm3), and dried (MgSO4). The mixture was
carefully concentrated using a fractionating column, and
the residue cooled to 0 8C. Bromine (0.5 cm3, 10 mmol)
was added. After 5 min the solution was washed with
dH(400 MHz; CDCl3) 4.89 (1H, m, CH2ꢁ
/
C), 4.69
(1H, m, CH2ꢁC, 1.65 (3H, br s, CH3), 1.45 (1H, s,
/
CHSi2), 0.44 (6H, s, SiMeAMeB) and 0.42 (6H, s,
SiMeAMeB).
saturated sodium thiosulfate solution (5ꢂ
50 cm3) and
/
3.4.21. E-4-Methyl-2-dimethyl(phenyl)silylpent-2-ene
(E-32)
dH(400 MHz; CDCl3) 5.86 (1H, dq, J 10.5 and 1.5,
brine (20 cm3), dried (MgSO4), and solvent removed
under reduced pressure to give the dibromide (0.15 g,
Cꢁ
/
CH), 2.34 (1H, d septet, J 10.5 and 6.5, CHMe2),
23%) as needles m.p. 175Á
[32] 177 8C, mixed m.p. 176Á
/
177 8C (from hexane) (Ref.
1.77 (3H, d, J 6.5, Cꢁ
/CCH3), 0.80 (6H, d, J 6.5, CMe2)
/
177 8C).
and 0.37 (3H, s, SiMe2), with configuration assigned by
comparison with the chemical shift values for 2-
dimethyl(phenyl)silylbut-2-ene, (E-27).
Acknowledgements
3.4.22. Z-4-Methyl-2-dimethyl(phenyl)silylpent-2-ene
(Z-32)
dH(400 MHz; CDCl3) 5.63 (1H, dq, J 9.0 and 1.5, Cꢁ
CH), 2.71 (1H, d septet, J 9.0 and 7.0, CHMe2), 1.65
We thank Synthelabo (as it then was) for a fellowship
(AC), the EPSRC and Zeneca Agrochemicals (as it then
was) for a CASE award (MCW), and Dr A. Gelormini
for some preliminary results (Scheme 5).
/

92
A. Che´nede´ et al. / Journal of Organometallic Chemistry 686 (2003) 84Á93
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