Synthesis of new terpene derivatives via ruthenium catalysis: Rearrangement of silylated enynes derived from terpenoids

Article abstract of DOI:10.1016/j.tet.2003.09.073

Enyne rearrangement of silylated modified terpenoids has been used as the key step for the synthesis of new terpenes and terpenoids. The catalytic system generated in situ from [RuCl₂(p-cymene]₂, 1,3-bis(mesityl)imidazolinium chlorid

Full text of DOI:10.1016/j.tet.2003.09.073

Tetrahedron 59 (2003) 9425–9432
Synthesis of new terpene derivatives via ruthenium catalysis:
rearrangement of silylated enynes derived from terpenoids
*
´ ˆ ˆ
Jerome Le Notre, Ana Acosta Martinez, Pierre H. Dixneuf and Christian Bruneau
´ ´
Institut de Chimie, UMR 6509, Organometalliques et Catalyse, Universite de Rennes 1 Campus de Beaulieu-35042 Rennes Cedex, France
Received 12 December 2002; revised 21 February 2003; accepted 16 September 2003
Abstract—Enyne rearrangement of silylated modified terpenoids has been used as the key step for the synthesis of new terpenes and
terpenoids. The catalytic system generated in situ from [RuCl2(p-cymene]2, 1,3-bis(mesityl)imidazolinium chloride and cesium carbonate is
able to perform the transformation of silylated 1,7-enynes into cyclic siloxanes. Selective cleavage of the silicon–carbon and silicon–oxygen
bonds by simple reactions has been performed to afford new terpenes and terpenoids by formal addition of a C5 unit.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
and bases7,15 and that this catalytic system could be used to
prepare spiro compounds bearing a five membered dihy-
drofuran ring from terpenoids containing a carbonyl
group.16
The intramolecular cyclic rearrangement of enynes rep-
resents a powerful tool for the formation of carbon–carbon
bond in synthetic organic chemistry.1–3 This catalytic
reaction using mostly ruthenium precursors tolerates a
large number of functionalities4 and allows the synthesis of
natural compounds or analogues.5 It has been shown that
alkylidene ruthenium catalysts6 or in situ generated catalytic
systems based on ruthenium species7 were able to transform
Si–O containing enynes into metathesis type silylated
vinylcycloalkenes. These vinylallylsilanes present a great
interest in synthesis due to the presence of the siloxane
group which react under selected conditions to provide
3-vinyltetrahydrofurans,8 allylic alcohols9 or allylic diols.6,10
The temporary introduction of the Si–O group makes
possible the easy modification of chemical structures which
would required multi-step organic transformations.
We now report the use of the same in situ prepared catalysts
to produce new terpenes and terpenoids by formal addition
of a C5 unit to natural compounds via sequential reactions
including a cyclic rearrangement of Si–O containing
enynes, as exemplified from menthone in Scheme 1.
We show that starting from the natural carbonyl-containing
terpenoids 1, the corresponding enynes 2 can easily be
synthesised in two steps by addition of lithium acetylide and
reaction of allyldimethylchlorosilane with the intermediate
propargylic alcohols. The cyclic rearrangement of the
silylated enynes 2 to give the corresponding cyclic
allylsilanes 3 occurs in the presence of the in situ generated
catalytic system based on the ruthenium dimer [RuCl2(p-
cymene)]2, 1,3-bis(mesityl)imidazolinium chloride and
cesium carbonate. Different selective transformations of
the siloxane function open the route to the novel terpenes 4
and 5 and terpenoids 6.
On the other hand, terpenes and terpenoids represent an
important class of natural products possessing interesting
organoleptic properties.11 Their simple chemical modifi-
cations via organic reactions12 or metal-catalysed reac-
tions13 such as hydrogenation,13c hydroformylation13d or
diene metathesis14 allow the formation of new molecules
with unprecedented properties in the field of flavours or
fragrances. We have recently reported that the intramole-
cular rearrangement of 1,6-enynes to produce five mem-
bered heterocyclic derivatives could efficiently be catalysed
by a simple three component system generated in situ from
[RuCl2(p-cymene]2, an imidazolium or imidazolinium salt
2. Results and discussion
Silylated enynes were prepared in two steps starting from
the natural terpenoids: (2)-menthone 7, (2)-carvone 8,
(þ)-pulegone 9, citral (cisþtrans) 10 and (2)-myrtenal 11,
and isolated in good yields. Treatment of acetylene in
tetrahydrofuran (2788C) by n-butyllithium gave the
corresponding monoacetylide as a white suspension.
Addition of the natural terpenoid bearing a ketone or an
aldehyde function led to the corresponding propargylic
Keywords: homogeneous catalysis; enyne rearrangement; ruthenium
catalyst; terpenoids; cyclic siloxanes.
*
Corresponding author. Tel.: þ33-2-23-23-62-83; fax: þ33-2-23-23-69-
39; e-mail: christian.bruneau@univ-rennes1.fr
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.09.073

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J. Le Notre et al. / Tetrahedron 59 (2003) 9425–9432
9426
Scheme 1. Retrosynthetic strategy.
alcohol which was obtained in very good yield (91–97%)
after quenching with an acidic aqueous solution. As
indicated by 13C NMR, there was no stereocontrol in this
addition and the two stereoisomers were formed in various
proportions depending on the initial carbonyl compound
and the precise reaction conditions. Subsequent treatment of
these propargylic alcohols with allylchlorodimethylsilane in
the presence of triethylamine and a catalytic amount of
4-dimethylaminopyridine at room temperature led to the
formation of the corresponding silylated 1,7-enynes 13–17
in good yields (74–94% based on the alcohol) (Scheme 2).
The corresponding six membered rings 18–20, 22 were
isolated in 76, 68, 62, 65% yield, respectively, after
distillation under vacuum rather than flash chromatography
to avoid degradation of the products on silica gel. Under
similar conditions, the conversion of the silylated enyne 16
arising from citral was very slow (26%) and the use of
5 mol% of [RuCl2(p-cymene]2, a higher temperature
reaction (1208C) or a longer reaction time did not improve
the formation of the cyclic product. Moreover, the high
structural similarity of the starting enyne 16 and the cyclic
siloxane 21 did not allow their separation by chromato-
graphy or distillation. The cyclic compound 21 was yet
observed by GC–MS.
Starting from the enynes 13–17, the cyclic rearrangement
was performed by using the in situ generated ruthenium
catalytic system recently developed in the laboratory,7,15,16
which is based on commercially available and air stable
materials. Indeed, the in situ generated catalytic system was
prepared from the dimer [RuCl2(p-cymene]2, 1,3-bis(mesi-
tyl)imidazolinium chloride and cesium carbonate in the
molar ratio 1:2:4. The cyclisation of the silylated 1,7-enynes
13–15, 17 was achieved within 16 h at 808C in toluene by
using 1.25–2.5 mol% of the ruthenium complex (Scheme 3).
In addition to their conjugated diene structure, which has
already been used to perform [2þ4] cycloaddition reac-
tions,7 the cyclic siloxane compounds present interesting
properties due to the specific reactivity of the Si–O-allyl
group to afford desilylated products.
For instance, under Tamao oxidative conditions,17 cyclic
allylsiloxanes are known to give allylic diols.6,10 Applied to
Scheme 2. Synthesis of the silylated enynes 13–17. Reagents and conditions: (i) acetylene, n-BuLi, THF, 2788C to rt then H2O; (ii) allylchlorodimethylsilane,
DMAP, Et3N, CH2Cl2, rt.

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J. Le Notre et al. / Tetrahedron 59 (2003) 9425–9432
9427
Scheme 3. Enyne cycloisomerisation.
the cyclic siloxanes that we have obtained from natural
terpenoids, this reaction can lead to the higher class of
terpenoids containing two additional allylic alcohol func-
tionalities. Thus, the cyclic allylsilanes 18 and 22 were
oxidized with an excess of hydrogen peroxide in a THF/
MeOH mixture in the presence of potassium fluoride and
potassium hydrogen carbonate at 408C for 24 h (Scheme 4)
and the diols 23 and 24 were isolated in 68 and 82% yield,
respectively. These three step transformations of 7 and 11
into new terpenoids with formal addition of a C5 unit
represent a modifications which would be difficult to
perform in a simple manner.
took place to form the trienes 25 and 26, which are
representatives of a new class of nonnatural terpenes
bearing a highly unsaturated C5H6 group connected to the
terpene structure through its central carbon atom via an
alkylidene double bond.
The hydrolysis/hydrogenation of 18 and 22 with palladium
on charcoal under an atmosphere of hydrogen was
investigated and led to desilylated compounds. The
treatment of the cyclic siloxane 18 with 10 wt% of Pd/C
under an atmosphere of hydrogen at room temperature in
dichloromethane afforded the compound 27 in a moderated
yield (52%). The overall reaction leads to formal hydro-
genation of the terminal double bonds of 25 (Scheme 6).
Under the same conditions, the cyclic siloxane 22 led to the
very volatile saturated product 28 isolated in only 43%
yield. These new terpenes 27 and 28 correspond to the
partially or completely hydrogenated analogs of compounds
25 and 26, respectively.
The cyclic siloxanes 18 and 22 were reacted in CH2Cl2 at
2788C with an excess of tetrabutylammonium fluoride in
solution in THF. After one night stirring at room
temperature, the polyenes 25 and 26 were isolated in 70
and 63% yield, respectively (Scheme 5). Under these
conditions desilylation and complete selective dehydration
Scheme 4. Oxidative cleavage with hydrogen peroxide. Reagents and
conditions: (i) KF, KHCO3, H2O2, THF/MeOH, 408C, 24 h.
Scheme 5. Cleavage of the siloxane function by fluorine anion. Reagents
and conditions: (i) NBu4F 1.0 M in THF, CH2Cl2, 2788C to rt, 16 h.

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J. Le Notre et al. / Tetrahedron 59 (2003) 9425–9432
9428
and after 30 min at 2788C, (2)-menthone 7 (1.0 g,
6.7 mmol) were slowly added. After 1 h stirring at 2788C
the reaction mixture was treated with 1N HCl to give, after
column chromatography on silica gel (eluent: heptane/
diethyl ether, 15:1), the propargylic alcohol (1.2 g, 97%).
Subsequently, this alcohol (1.2 g, 6.5 mmol) was treated
with allylchlorodimethylsilane (1.1 mL, 7.2 mmol), DMAP
(80 mg, 0.65 mmol) and triethylamine (1.3 g, 13.0 mmol) at
room temperature in dry dichloromethane (20 mL) for 16 h.
The column was eluted with a heptane/diethyl ether (30:1)
mixture to give the silylated enyne 13 (1.45 g, 80%) as a
1
colourless oil. H NMR (200 MHz, CDCl3): d 0.16–0.23
(m, 6H, Si(CH3)2), 0.78–1.01 (m, 9H, 3£CH3), 1.10–1.41
(m, 4H, CH(CH3)CH2CH2), 1.60–1.73 (m, 5H, SiCH2-
CHvCH2, CH(CH3)CH2C(quat.)), 1.90–1.99 (dm, 1H,
3JHH¼13.8 Hz, CHCH(CH3)2), 2.11–2.28 (m, 1H,
CHCH(CH3)2), 2.49 (s, 1H, CuCH), 4.80–4.90 (m, 2H,
SiCH2CHvCH2), 5.70–5.92 (m, 1H, SiCH2CHvCH2).
13C NMR (50 MHz, CDCl3): d 20.93, 20.76, 17.9, 21.9,
23.4, 25.9, 26.3, 30.3, 34.7, 52.2, 53.8, 73.5, 76.0, 86.7,
113.3, 134.7. MS (EI): m/z (%) 278 ([M]þ, ,1), 237 (18),
181 (10), 137 (10), 127 (11), 95 (15), 81 (48), 75 (100), 69
(19), 59 (28), 55 (23), 43 (21), 41 (30), 28 (34). Found: C,
73.52; H, 10.81. Calcd for C17H30SiO: C, 73.31; H, 10.86.
Scheme 6. Cleavage of the siloxane function by hydrogenation. Reagents
and conditions: (i) Pd/C, H2 (1 atm), CH2Cl2, rt, 16 h.
3. Conclusion
We have shown that the synthesis of new nonnatural
terpenes and terpenoids was possible from natural terpe-
noids by using, as the key step, the formation of cyclic
siloxanes via a catalytic enyne rearrangement. This
selective catalytic transformation represents another
example of the usefulness of this cyclisation reaction with
atom economy. The easily available catalytic system
generated in situ from [RuCl2(p-cymene]2 as a ruthenium
source, 1,3-bis(mesityl)imidazolinium chloride and cesium
carbonate was used to carry out the cycloisomerisation of
silylated 1,7-enynes. The specific reactivity of cyclic allylic
siloxane makes possible the preparation of new terpenic
diols via controlled oxidation with hydrogen peroxide and
new terpenes via desilylation under neutral conditions with
a fluoride salt or under reducing conditions with hydrogen in
the presence of a catalytic amount of palladium on charcoal.
4.2.2. Allyl-(1-ethynyl-5(S)-isopropenyl-2-methylcyclo-
hex-2-enyloxy)dimethylsilane (14). Acetylene (430 mL,
19.1 mmol) and 15 mL of dry tetrahydrofuran were cooled
down to 2788C then n-butyllithium (3.6 mL, 5.7 mmol) and
after 30 min at 2788C, (2)-carvone 8 (726 mg, 4.8 mmol)
were slowly added. After 1 h stirring at 2788C the reaction
mixture was treated with 1N HCl to give, after column
chromatography on silica gel (eluent: heptane/diethyl ether,
10:1), the propargylic alcohol (790 mg, 94%). Sub-
sequently, this alcohol (790 mg, 4.5 mmol) was treated
with allylchlorodimethylsilane (0.75 mL, 5.0 mmol),
DMAP (55 mg, 0.45 mmol) and triethylamine (0.90 g,
8.9 mmol) at room temperature in dry dichloromethane
(15 mL) for 16 h. The column was eluted with a heptane/
diethyl ether (30:1) mixture to give the silylated enyne 14
(1.07 g, 87%) as a colourless oil. 1H NMR (200 MHz,
CDCl3): d 0.19–0.25 (m, 6H, Si(CH3)2), 1.68–1.71 (m,
6H, CHvC(CH3), H2CvC(CH3)), 1.75–1.78 (m, 2H,
SiCH2CHvCH2), 1.83–2.00 (m, 2H, CH(isopropenyl)
CH2C(quat.)), 2.05–2.27 (m, 2H, CvCHCH2CH), 2.54 (s,
1H, CuCH), 2.45–2.61 (m, 1H, CH2CH(isopropenyl)CH2),
4.71–4.74 (m, 2H, C(CH3)vCH2), 4.82–4.93 (m, 2H,
SiCH2CHvCH2), 5.40–5.46 (m, 1H, CH2CHvC(CH3)),
5.75–6.01 (m, 1H, SiCH2CHvCH2). 13C NMR (50 MHz,
CDCl3): d 20.4, 20.3, 17.5, 20.4, 26.0, 30.8, 39.3, 44.5,
71.1, 73.5, 86.9, 109.1, 113.4, 123.4, 134.2, 137.0, 148.1.
MS (EI): m/z (%) 274 ([M]þ, ,1), 233 (21), 173 (17), 77
(12), 76 (10), 75 (100), 59 (17), 41 (10). Found: C, 74.48; H,
9.43. Calcd for C17H26SiO: C, 74.39; H, 9.55.
4. Experimental
4.1. General experimental procedures
All experiments except the hydrogenation reactions were
carried out in Schlenk tubes under an inert atmosphere of
nitrogen. The solvents were dried and distilled prior to use.
1H and 13C NMR were recorded with a Bruker AC 200 MHz
spectrometer and GC–MS were performed with a CE
Instrument GC 8000 Top (capillary column OV1,
25 m£0.35 mm, 0.1–0.15 mm) chromatograph linked to a
Automass II Finnigan MAT (70 eV) apparatus. The HRMS
analyses were carried out with a Varian MAT311
spectrometer.
4.2.3. Allyl-(1-ethynyl-2-isopropylidene-5(R)-methyl-
cyclohexyloxy)-dimethylsilane (15). Acetylene (345 mL,
15.4 mmol) and 15 mL of dry tetrahydrofuran were cooled
down to 2788C then n-butyllithium (2.3 mL, 3.7 mmol) and
after 30 min at 2788C, (þ)-pulegone 9 (469 mg, 3.1 mmol)
were slowly added. After 1 h stirring at 2788C the reaction
mixture was treated with 1N HCl to give, after column
chromatography on silica gel (eluent: heptane/diethyl ether,
4.2. Preparation of silylated enynes
4.2.1. Allyl-(1-ethynyl-2(S)-isopropyl-5(R)-methylcyclo-
hexyloxy)-dimethylsilane (13). Acetylene (450 mL,
20.1 mmol) and 15 mL of dry tetrahydrofuran were cooled
down to 2788C, then n-butyllithium (5.0 mL, 8.1 mmol)

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J. Le Notre et al. / Tetrahedron 59 (2003) 9425–9432
9429
15:1), the propargylic alcohol (500 mg, 91%). Sub-
sequently, this alcohol (500 mg, 2.8 mmol) was treated
with allylchlorodimethylsilane (0.47 mL, 3.1 mmol),
DMAP (34 mg, 0.31 mmol) and triethylamine (568 mg,
5.6 mmol) at room temperature in dry dichloromethane
(15 mL) for 16 h. The column was eluted with a heptane/
diethyl ether (30:1) mixture to give the silylated enyne 15
(1.25 g, 12.3 mmol) at room temperature in dry dichloro-
methane (20 mL) for 16 h. The column was eluted with a
heptane/diethyl ether (30:1) mixture to give the silylated
enyne 17 (1.37 g, 81%) as a colourless oil. 1H NMR
(200 MHz, CDCl3): d 0.10–0.15 (m, 6H, Si(CH3)2), 0.78–
0.82 (m, 3H, CH3), 1.11–1.18 (m, 1H, C(CH3)2CH(CH2)
CH2), 1.21–1.28 (m, 3H, CH3), 1.52–1.70 (m, 2H,
SiCH2CHvCH2), 2.01–2.12 (m, 1H, C(CH3)2CH(CH2)
CvCH), 2.22–2.45 (m, 5H, CuCH, CH2, CH2), 4.69–4.73
(m, 1H, CH(O-silyl)(CuCH)), 4.81–4.93 (m, 2H,
SiCH2CHvCH2), 5.51–5.59 (m, 1H, CvCHCH2), 5.68–
5.90 (m, 1H, SiCH2CHvCH2). 13C NMR (50 MHz,
CDCl3): d 22.1, 22.0, 21.0/21.1, 24.7/24.8, 26.0/26.1,
31.0/31.1, 31.6/31.7, 37.9/38.0, 40.7/40.8, 42.5/42.6, 68.4/
68.5, 72.7/72.8, 83.2, 113.3/113.8, 118.4/118.7, 133.9/
134.4, 146.3/146.4. MS (EI): m/z (%) 274 ([M]þ, ,1),
189 (10), 115 (12), 83 (10), 77 (14), 75 (100), 59 (13), 43
(12), 41 (13), 32 (15), 28 (69). Found: C, 74.51; H, 9.48.
Calcd for C17H26SiO: C, 74.39; H, 9.55.
1
(570 mg, 74%) as a colourless oil. H NMR (200 MHz,
CDCl3): d 0.22–0.26 (m, 6H, Si(CH3)2), 0.91 (d, 3H,
J¼6.5 Hz, CH(CH3)), 1.43 (t, 2H, J¼11.2 Hz, CH(CH3)-
CH2C(quat.)), 1.70 (s, 3H, CvC(CH3)2), 1.58–1.79 (m,
3H, SiCH2CHvCH2, CH(CH3)), 2.00 (s, 3H, CvC(CH3)2),
1.90–2.20 (m, 4H, CH(CH3)CH2CH2), 2.59 (s, 1H,
CuCH), 4.80–4.94 (m, 2H, SiCH2CHvCH2), 5.68–5.94
(m, 1H, SiCH2CHvCH2). 13C NMR (50 MHz, CDCl3): d
0.0, 21.7, 22.0, 23.7, 26.3, 27.6, 29.4, 33.8, 51.7, 73.5, 77.3,
87.6, 113.4, 126.0, 132.0, 134.5. MS (EI): m/z (%) 276
([M]þ, 1.2), 235 (28), 105 (18), 91 (23), 83 (13), 79 (10), 77
(18), 75 (100), 59 (22), 41 (15), 28 (30). Found: C, 74.05; H,
10.11. Calcd for C17H28SiO: C, 73.85; H, 10.21.
4.3. General procedure for the preparation of cyclic
siloxanes
4.2.4. Allyl-(1-ethynyl-3,7-dimethyl-octa-2,6-dienyloxy)-
dimethylsilane (16). Acetylene (450 mL, 20.1 mmol) and
15 mL of dry tetrahydrofuran were cooled down to 2788C
then n-butyllithium (5.0 mL, 8.1 mmol) and after 30 min at
2788C, citral 10 (1.02 g, 6.7 mmol) were slowly added.
After 1 h stirring at 2788C the reaction mixture was treated
with 1N HCl to give, after column chromatography on silica
gel (eluent: heptane/diethyl ether, 15:1), the propargylic
alcohol (1.09 g, 91%). Subsequently, this alcohol (1.09 g,
6.1 mmol) was treated with allylchlorodimethylsilane
(1.0 mL, 6.7 mmol), DMAP (75 mg, 0.61 mmol) and
triethylamine (1.24 g, 12.2 mmol) at room temperature in
dry dichloromethane (25 mL) for 16 h. The column was
eluted with a heptane/diethyl ether (30:1) mixture to give
the silylated enyne 16 (1.59 g, 94%) as a colourless oil. 1H
NMR (200 MHz, CDCl3): d 0.15–0.18 (m, 6H, Si(CH3)2),
1.50–1.73 (m, 11H, 3£CH3, SiCH2CHvCH2), 1.96–2.15
(m, 4H, 2£CH2), 2.43 (d, 1H, J¼2.2 Hz, CuCH), 4.79–
4.94 (m, 2H, SiCH2CHvCH2), 5.02–5.11 (m, 2H,
CHvC(CH3)2, CH(O)(CuCH)CHvC(CH3)CH2), 5.30–
5.37 (m, 1H, CH(O)(CuCH)CHvC(CH3)CH2), 5.64–5.99
(m, 1H, SiCH2CHvCH2). 13C NMR (50 MHz, CDCl3): d
21.9, 21.6, 16.4/17.5, 23.0, 24.7, 25.5, 26.0, 32.1, 39.0,
59.1/59.5, 72.0/72.1, 84.4/84.7, 113.2/113.6, 123.5/123.6,
125.0/125.1, 131.5/131.9, 133.6, 137.9/138.2. MS (EI): m/z
(%) 276 ([M]þ, ,1), 145 (15), 117 (13), 105(15), 91 (46),
83(11), 77 (22), 76 (24), 75 (85), 69(95), 61 (16), 59 (29), 45
(19), 43 (16), 41 (100), 39 (24), 28 (21). Found: C, 73.97; H,
10.18. Calcd for C17H28SiO: C, 73.85; H, 10.21.
[RuCl2(p-cymene)]2 (0.5–1.25 mmol%), 1,3-bis(mesityl)
imidazolinium chloride and cesium carbonate (molar ratio:
1:2:4) were dissolved in toluene (5 mL per mmol of enyne)
and the mixture was stirred for 5 min at room temperature.
The enyne (13–17) was added to the orange–red solution
and the mixture was stired at 808C until GC–MS analysis
indicated the complete conversion into the cyclic product.
The solvent was then removed and the crude mixture was
dissolved in heptane, filtered and evaporated to dryness. For
reaction times and purification procedures, see below.
4.3.1. 7(S)-Isopropyl-2,2,10(R)-trimethyl-5-vinyl-1-oxa-
2-silaspiro[5.5]undec-4-ene (18). By using 46.2 mg
(7.5£1022 mmol, 2.5 mol%) of [RuCl2(p-cymene)]2,
51.8 mg (0.15 mmol, 5 mol%) of 1,3-bis(mesityl)imidazo-
linium chloride and 98.4 mg (0.30 mmol, 10 mol%) of
cesium carbonate in 15 mL of toluene, the total conversion of
the enyne 13 (840 mg, 3.02 mmol) was observed after 16 h at
808C. After a distillation under vacuum, the cyclic compound
18 (640 mg, 76%) was obtained as a colourless oil. 1H NMR
(200 MHz, CDCl3): d 0.10–0.16 (m, 6H, Si(CH3)2), 0.78–
0.94 (m, 9H, 3£CH3), 1.12–1.42 (m, 4H, CH(CH3)CH2CH2),
1.50–1.79 (m, 5H, SiCH2CHvC(vinyl), CH(CH3)CH2C
(quat.)), 1.87–2.00 (m, 1H, CHCH(CH3)2), 2.27–2.30 (m,
1H, CHCH(CH3)2), 4.80 (dd, 1H, J¼10.5, 2.3 Hz, cis
CHvCH2), 5.10 (dd, 1H, J¼16.6, 2.3 Hz, trans CHvCH2),
5.94(tm, 1H, J¼5.9 Hz, SiCH2CHvC(vinyl)), 6.49–6.66(m,
1H, CHvCH2). 13C NMR (50 MHz, CDCl3): d 21.1, 13.6,
19.0, 22.9, 24.5, 27.2, 30.2, 35.1, 51.9, 56.0, 80.7, 113.2,124.0,
142.0, 146.4. MS (EI): m/z (%) 278 ([M]þ, 3), 193 (26), 166
(13), 75 (100), 32 (20), 28 (27). HRMS (EI): 278.2060;
C17H30SiO requires 278.2066. Found: C, 73.25; H, 10.95.
Calcd for C17H30SiO: C, 73.31; H, 10.86.
4.2.5. Allyl-[1-(6,6-dimethyl-bicyclo[3.1.1]hep-2-en-2-
yl)-prop-2-ynyloxy]-dimethylsilane
(17).
Acetylene
(450 mL, 20.1 mmol) and 15 mL of dry tetrahydrofuran
were cooled down to 2788C then n-butyllithium (4.8 mL,
7.6 mmol) and after 30 min at 2788C, (2)-myrtenal 11
(0.95 g, 6.4 mmol) were slowly added. After 1 h stirring at
2788C the reaction mixture was treated with 1N HCl to
give, after column chromatography on silica gel (eluent:
heptane/diethyl ether, 15:1), the propargylic alcohol (1.09 g,
97%). Subsequently, this alcohol (1.09 g, 6.2 mmol) was
4.3.2. 10(S)-Isopropenyl-2,2,7-trimethyl-5-vinyl-1-oxa-2-
silaspiro[5.5]undeca-4,7-diene (19). By using 14.0 mg
(2.3£1022 mmol, 1.25 mol%) of [RuCl2(p-cymene)]2,
15.6 mg (4.6£1022 mmol, 2.5 mol%) of 1,3-bis(mesityl)
imidazolinium chloride and 29.7 mg (0.09 mmol, 5 mol%)
of cesium carbonate in 8 mL of toluene, the total conversion
treated
6.8 mmol), DMAP (76 mg, 0.62 mmol) and triethylamine
with
allylchlorodimethylsilane
(1.03 mL,

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J. Le Notre et al. / Tetrahedron 59 (2003) 9425–9432
9430
of the enyne 14 (500 mg, 1.82 mmol) was observed after
16 h at 808C. After a distillation under vacuum, the cyclic
compound 19 (340 mg, 68%) was obtained as a colourless
oil. 1H NMR (200 MHz, CDCl3): d 0.17–0.22 (m, 6H,
total conversion of the enyne 17 (1.0 g, 3.65 mmol) was
observed after 16 h at 808C. After a distillation under
vacuum, the cyclic compound 22 (651 mg, 65%) was
obtained as a colourless oil. 1H NMR (200 MHz, CDCl3): d
0.04–0.15 (m, 6H, Si(CH3)2), 0.72–0.77 (m, 3H, CH3),
1.08–1.14 (m, 1H, C(CH3)2CH(CH2)CH2), 1.18–1.24 (m,
3H, CH3), 1.38–1.43 (m, 2H, SiCH2CHvCH2), 1.99–2.05
(m, 1H, C(CH3)2CH(CH2)CvCH), 2.11–2.25 (m, 2H,
CH2), 2.30–2.40 (m, 2H, CH2), 4.80–5.03 (m, 3H, trans
CHvCH2, CH(O-silyl), SiCH2CHvC(vinyl)), 5.35 (m,
1H, cis CHvCH2), 6.02–6.08 (m, 1H, CvCHCH2), 6.13–
6.27 (m, 1H, CHvCH2). 13C NMR (50 MHz, CDCl3): d
0.5, 0.8, 13.6/13.7, 21.2/21.5, 26.3, 31.2/31.3, 31.7/31.8,
37.9, 40.6/40.7, 43.0/43.1, 75.1/75.6, 110.7/110.9, 118.9/
119.1, 127.9/128.1, 138.1/138.2, 147.4, 148.1. MS (EI): m/z
(%) 274 ([M]þ, ,1), 91 (13), 77 (12), 75 (100), 69 (59), 41
(30), 32 (17), 28 (85). HRMS (EI): 274.1750; C17H26SiO
requires 274.1753. Found: C, 74.24; H, 9.52. Calcd for
C17H26SiO: C, 74.39; H, 9.55.
Si(CH3)2),
1.19–1.32
(m,
6H,
CHvC(CH3),
H2CvC(CH3)), 1.51–1.59 (m, 2H, SiCH2CHvC(vinyl)),
1.68–1.71 (m, 2H, CH(isopropenyl)CH2C(quat.)), 1.92–
2.43 (m, 3H, CvCHCH2CH, CH2CH(isopropenyl)CH2),
4.58–4.92 (m, 4H, C(CH3)vCH2, CHvCH2) 5.25–5.40
(m, 1H, SiCH2CHvC(vinyl)), 5.51–5.64 (m, 1H,
CH2CHvC(CH3)), 6.08–6.28 (m, 1H, CHvCH2). 13C
NMR (50 MHz, CDCl3): d 20.1, 13.6, 18.0, 20.4, 30.8,
38.9, 44.9, 68.7, 108.7, 112.2, 122.5, 125.1, 137.4, 139.2,
149.2, 149.5. MS (EI): m/z (%) 274 ([M]þ, 11), 231 (14),
189 (25), 159 (14), 143 (11), 115 (39), 91 (22), 77 (25), 75
(100), 59 (26), 41 (25). HRMS (EI): 274.1749; C17H26SiO
requires 274.1753. Found: C, 74.26; H, 9.60. Calcd for
C17H26SiO: C, 74.39; H, 9.55.
4.3.3. 7-Isopropylidene-2,2,10(R)-trimethyl-5-vinyl-1-
oxa-2-silaspiro[5.5]undec-4-ene (20). By using 31.6 mg
(5.2£1022 mmol, 2.5 mol%) of [RuCl2(p-cymene)]2,
35.4 mg (0.103 mmol, 5 mol%) of 1,3-bis(mesityl)imida-
zolinium chloride and 67.3 mg (0.207 mmol, 10 mol%) of
cesium carbonate in 10 mL of toluene, the total conversion
of the enyne 15 (570 mg, 2.07 mmol) was observed after
16 h at 808C. After a distillation under vacuum, the cyclic
compound 20 (350 mg, 62%) was obtained as a colourless
oil. 1H NMR (200 MHz, CDCl3): d 0.20–0.25 (m, 6H,
Si(CH3)2), 0.90 (d, 3H, J¼6.1 Hz, CH(CH3)), 1.43–1.50
(m, 2H, CH(CH3)CH2C(quat.)), 1.72 (s, 3H, CvC(CH3)2),
1.58–1.84 (m, 3H, SiCH2CHvCH2, CH(CH3)), 1.98 (s,
3H, CvC(CH3)2), 1.95–2.22 (m, 4H, CH(CH3)CH2CH2),
4.72 (dd, 1H, J¼10.5, 2.1 Hz, cis CHvCH2), 5.19 (dd, 1H,
J¼17.0, 2.1 Hz, trans CHvCH2), 6.02–6.09 (m, 1H,
SiCH2CHvC(vinyl)), 6.14–6.31 (m, 1H, CHvCH2)). 13C
NMR (50 MHz, CDCl3): d 0.6, 13.3, 22.0/22.4, 23.4, 25.8,
26.6, 30.4, 47.7, 79.3, 111.9, 121.0, 130.2, 133.2, 139.5,
148.1. MS (EI): m/z (%) 276 ([M]þ, 7), 261 (12), 219 (12),
187 (22), 179 (14), 131 (18), 91 (27), 77 (19), 75 (100), 59
(12), 41 (14). HRMS (EI): 276.1906; C17H28SiO requires
276.1909. Found: C, 73.75; H, 10.23. Calcd for C17H28SiO:
C, 73.85; H, 10.21.
4.4. Preparation of the diols 23 and 24
4.4.1. 1-(3-Hydroxy-1-vinylpropenyl)-2(S)-isopropyl-
5(R)-methylcyclohexanol
(23).
H2O2
(6.6 mL,
64.7 mmol) was added to a solution of the cyclic siloxane
18 (0.45 g, 1.6 mmol), KF (0.47 g, 8.1 mmol) and KHCO3
(0.38 g, 3.7 mmol) in 15 mL of THF and 15 mL of
methanol. After 24 h at 408C, the reaction mixture was
extracted with diethyl ether (3£10 mL) and the diol 23
(264 mg, 68%) was isolated as a colourless oil after flash
chromatography on silica gel with diethyl ether as eluent. 1H
NMR (200 MHz, CDCl3): d 0.74 (d, 3H, J¼6.9 Hz, CH3),
0.82 (d, 3H, J¼6.9 Hz, CH(CH3)2), 0.91 (d, 3H, J¼7.0 Hz,
CH(CH3)2), 1.20–1.50 (m, 6H, CHCH2CH2CHCH2), 1.60–
2.00 (m, 3H, C(OH)CH2CHCH3, CHCH(CH3)2,
CHCH(CH3)2), 4.58–4.65 (m, 2H, CvCHCH2OH), 5.05
(dd, 1H, J¼10.7, 2.0 Hz, cis CHvCH2), 5.42 (dd, 1H,
J¼16.1, 2.0 Hz, trans CHvCH2), 5.90–5.93 (m, 1H,
CvCHCH2OH), 6.36–6.50 (m, 1H, CHvCH2). 13C
NMR (50 MHz, CDCl3): d 18.4, 23.3, 23.9, 26.2, 29.8,
34.9, 49.8, 53.0, 72.8, 76.0, 115.9, 122.8, 132.0, 144.7. MS
(EI): m/z (%) 238 ([M]þ, ,1), 220 (19), 136 (15), 135 (100),
107 (19), 93 (11), 91 (26), 79 (41), 77 (26), 69 (20), 67 (14),
65 (17), 55 (40), 53 (14), 43 (27), 41 (64), 39 (27). Found: C,
75.28; H, 10.52. Calcd for C15H26O2: C, 75.58; H, 10.99.
4.3.4. 6-(2,6-Dimethyl-hepta-1,5-dienyl)-2,2-dimethyl-5-
vinyl-3,6-dihydro-2H-[1,2]oxasi-line (21). By using
23.2 mg(3.8£1022 mmol, 2.5 mol%)of[RuCl2(p-cymene)]2,
26.0 mg (7.6£1022 mmol, 5 mol%) of 1,3-bis(mesityl)imi-
dazolinium chloride and 49.5 mg (0.15 mmol, 10 mol%) of
cesium carbonate in 7.5 mL of toluene, 26% of conversion
of the enyne 16 (420 mg, 1.5 mmol) was observed after 48 h
at 808C. The cyclic compound 21 was not separated from
the starting enyne but observed in GC–MS. MS (EI): m/z
(%) 276 ([M]þ, 5), 171 (21), 125 (12), 123 (34), 91 (16), 77
(28), 75 (75), 69(28), 43 (31), 41 (100), 39 (12)). Found: C,
73.79; H, 10.29. Calcd for C17H28SiO: C, 73.85; H, 10.21.
4.4.2. 1-(6,6-Dimethylbicyclo[3.1.1]hept-2-en-2-yl)-2-
vinylbut-2-ene-1,4-diol (24). H2O2 (2.7 mL, 29.1 mmol)
was added to a solution of the cyclic siloxane 22 (0.20 g,
0.73 mmol), KF (0.21 g, 3.6 mmol) and KHCO3 (0.17 g,
2.3 mmol) in 7 mL of THF and 7 mL of methanol. After
24 h at 408C, the reaction mixture was treated as described
above to give the diol 24 (139 mg, 82%) as a colourless oil,
after flash chromatography on silica gel with diethyl ether as
1
eluent. H NMR (200 MHz, CDCl3): d 0.79 (s, 3H, CH3),
1.07–1.15 (m, 1H, C(CH3)2CH(CH2)CH2), 1.23 (s, 3H,
CH3), 2.04–2.17 (m, 1H, C(CH3)2CH(CH2)CvCH), 2.23–
2.47 (m, 4H, CH2, CH2), 2.80 (broad s, 2H, 2£OH), 4.19–
4.38 (m, 2H, CvCHCH2OH), 4.90–5.07 (m, 2H, CH(OH),
cis CHvCH2), 5.25–5.37 (m, 1H, trans CHvCH2), 5.49–
5.57 (m, 1H, CH(OH)CvCHCH2), 5.90 (t, 1H, J¼6.8 Hz,
CHvCH2OH), 6.19–6.32 (m, 1H, CHvCH2). 13C NMR
(50 MHz, CDCl3): d 21.1/21.2, 26.1, 31.2, 31.7, 37.8/37.9,
4.3.5. 6-(6,6-Dimethyl-bicyclo[3.1.1]hept-2-en-2-yl)-2,2-
dimethyl-5-vinyl-3,6-dihydro-2H-[1,2]oxasiline (22). By
using 55.8 mg (9.1£1022 mmol, 2.5 mol%) of [RuCl2(p-
cymene)]2, 62.5 mg (0.182 mmol, 5 mol%) of 1,3-bis(mesi-
tyl)imidazolinium chloride and 118.9 mg (0.365 mmol,
10 mol%) of cesium carbonate in 18 mL of toluene, the

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J. Le Notre et al. / Tetrahedron 59 (2003) 9425–9432
9431
40.7/40.8, 43.0/43.1, 58.6/58.9, 71.3/71.6, 114.2/114.5,
117.7/118.2, 130.6/130.7, 137.2/137.3, 140.1/140.3, 147.4/
147.8. MS (EI): m/z (%) 234 ([M]þ, 4), 219 (14), 193 (16),
169 (21), 155 (20), 129 (18), 103 (21), 91 (14), 77 (32), 75
(100), 59 (20), 43 (12), 41 (30). Found: C, 76.38; H, 9.40.
Calcd for C15H22O2: C, 76.88; H, 9.46.
1.29 (m, 4H, CH2CH2), 1.40–1.48 (m, 2H, CH(CH3)2,
CH(CH3)), 1.59–1.80 (m, 6H, CH2CvC(CH2CH3)2),
1.88–1.98 (m, 1H, CHCH(CH3)2. 13C NMR (50 MHz,
CDCl3): d 13.5/13.8, 20.8, 23.8/23.9, 27.0, 27.3, 27.4, 29.8,
35.3, 42.0, 47.1, 140.9, 146.1. MS (EI): m/z (%) 208 ([M]þ,
12), 165 (61), 123 (33), 109 (74), 95 (100), 93 (18), 81 (56),
79 (28), 69 (26), 67 (47), 55 (52), 53 (17), 43 (33), 41 (64),
39 (11). Found: C, 86.36; H, 13.49. Calcd for C15H28: C,
86.46; H, 13.54.
4.5. Preparation of the polyenes 25 and 26
4.5.1. 1(S)-Isopropyl-4(R)-methyl-2-(1-vinylprop-2-eny-
lidene)cyclohexane (25). n-Bu4NF (1.65 mL, 1.65 mmol)
was added at 2788C to a solution of the cyclic siloxane 18
(153 mg, 0.55 mmol) in 5 mL of THF and 5 mL of CH2Cl2.
After 16 h at room temperature and purification by flash
chromatography with heptane as eluent, the polyene 25
4.6.2. 2-(2-Ethylbutyl)-6,6-dimethylbicyclo[3.1.1]hep-
tane (28). Cyclic siloxane 22 (150 mg, 0.55 mmol) was
added to Pd/C (15 mg, 10 wt%) in 5 mL of dichloro-
methane. After removal of the nitrogen atmosphere by
hydrogen, the reaction mixture was stirred 16 h at room
temperature under 1 atm of hydrogen. After filtration on
celite and purification of the crude product by chromatog-
raphy over silica gel with heptane, the terpene 28 (49 mg,
1
(79 mg, 70%) was obtained as a colourless oil. H NMR
(200 MHz, CDCl3): d 0.76 (d, 3H, J¼6.7 Hz, CH3), 0.92
and 0.94 (2£d, 6H, J¼7.2 Hz, CH(CH3)2), 1.15–1.32 (m,
4H, CHCH2CH2CHCH2), 1.53–1.87 (m, 2H, CH(CH3),
CHCH(CH3)2), 1.96–2.21 (m, 2H, CHC(vC)CH2), 2.44–
2.58 (m, 1H, CHC(vC)CH2), 5.08–5.25 (m, 4H,
2£(CHvCH2)), 6.42–6.69 (m, 2H, 2£(CHvCH2)). 13C
NMR (50 MHz, CDCl3): d 18.1, 20.8, 23.7, 27.1, 29.7, 30.5,
32.4, 45.1, 116.1, 116.8, 132.9, 134.3, 134.5, 140.8. MS
(EI): m/z (%) 204 ([M]þ, 19), 161 (40), 133 (20), 119 (32),
117 (12), 107 (18), 105 (83), 93 (48), 91 (100), 83 (18), 81
(65), 79 (51), 77 (40), 69 (28), 67 (36), 55 (37), 41 (43), 39
(18). Found: C, 88.26; H, 11.72. Calcd for C15H24: C, 88.16;
H, 11.84.
1
43%) was isolated as a colourless oil. H NMR (200 MHz,
CDCl3): d 0.80–1.09 (m, 22H, 4£CH3, 5£CH2), 1.05–1.14
(m, 1H, C(CH3)2CH(CH2)CH2), 1.26–1.44 (m, 5H,
CHCH2CHCHCH2CHEt2). 13C NMR (50 MHz, CDCl3): d
10.2/10.5, 19.5, 21.0/21.4, 26.2, 28.5, 28.8, 31.0/31.1, 31.6,
37.8, 39.9, 44.0, 46.8. MS (EI): m/z (%) 208 ([Mþ1]þ, 7),
165 (26), 119 (26), 91 (100), 89 (29), 75 (73), 73 (16), 61
(22), 59 (49), 43 (15), 41 (22).). Found: C, 86.41; H, 13.52.
Calcd for C15H28: C, 86.46; H, 13.54.
Acknowledgements
4.5.2. 6,6-Dimethyl-2-(2-vinylbuta-1,3-dienyl)-bicy-
clo[3.1.1]hept-2-ene (26). n-Bu4NF (1.65 mL, 1.65 mmol)
was added at 2788C to a solution of the cyclic siloxane 22
(150 mg, 0.55 mmol) in 5 mL of THF and 5 mL of CH2Cl2.
After 16 h at room temperature and purification by flash
chromatography with heptane as eluent, the polyene 26
´
The authors are grateful to the Region Bretagne for a grant
to J. L. N. and to the European ERASMUS Programme for a
grant to A. A. M. from the University of Burgos.
1
(69 mg, 63%) was obtained as a colourless oil. H NMR
(200 MHz, CDCl3): d 0.88 (s, 3H, CH3), 1.14–1.27 (m, 1H,
C(CH3)2CH(CH2)CH2), 1.30 (s, 3H, CH3), 2.03–2.13 (m,
1H, C(CH3)2CH(CH2)CvCH), 2.37–2.45 (m, 4H, CH2,
CH2), 5.06–5.42 (m, 4H, (2£CHvCH2)), 5.63–5.69 (m,
1H, CHCvCHCH2), 5.96–6.01 (m, 1H, CHvC(vinyl)2),
6.35–6.49 (m, 1H, CHvCH2), 6.58–6.72 (m, 1H,
CHvCH2). 13C NMR (50 MHz, CDCl3): d 21.1, 26.2,
31.5, 32.2, 37.7, 40.2, 46.3, 114.6, 116.7, 126.3, 131.0,
135.4, 138.1, 144.3, 146.8. MS (EI): m/z (%) 200 ([M]þ,
25), 157 (19), 130 (68), 128 (24), 116 (30), 103 (11), 91
(100), 79 (12), 77 (30), 65 (15), 53 (21), 51 (14), 41 (44), 39
(30). Found: C, 88.19; H, 11.78. Calcd for C15H24: C, 88.16;
H, 11.84.
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