Stereoselective polycyclisations of allyl and enyne silanes: Evidence for bicyclo[3.2.0]hept-1(7)ene structure

Article abstract of DOI:10.1016/S0022-328X(01)01393-6

The intramolecular copper(I)-catalyzed [2 + 2]-photocycloaddition of diphenyldiallysilane (1) (or tetraallylsilane (4)) led to sila-3-bicyclo[3.2.0]heptane (3) (or to spiro analogous 6) in the cis (or cis-cis) configuration whereas the α,ω-diiodide (2) obtained by cyclozirconation of 1 (or from the homologous tetraiodide 5) followed by addition of n-BuLi, produced the sila-3-bicyclo[3.2.0]heptane (3) (or to the spiro analogous 6) in the trans (or trans-trans configuration). The same cyclozirconation reaction, starting from the hetero enyne 7, selectively led to the highly strained silacyclobutene moiety 15 which represents the first stable hetero bicyclo[3.2.0]hept-1(7)ene skeleton, hypothetical intermediate in methathesis reactions.

Full text of DOI:10.1016/S0022-328X(01)01393-6

Journal of Organometallic Chemistry 643–644 (2002) 324–330
www.elsevier.com/locate/jorganchem
Stereoselective polycyclisations of allyl and enyne silanes: evidence
for a bicyclo[3.2.0]hept-1(7)ene structure
Gabriel Oba, Georges Moreira, Georges Manuel, Max Koenig *
Laboratoire d’He´te´rochimie Fondamentale et Applique´e, UMR CNRS no. 5069, Uni6ersite´ Paul-Sabatier, 118 route de Narbonne,
31062 Toulouse, Cedex 04, France
Received 13 July 2001; accepted 18 October 2001
Dedicated to Professor F. Mathey on occasion of his 60th birthday
Abstract
The intramolecular copper(I)-catalyzed [2+2]-photocycloaddition of diphenyldiallylsilane (1) (or tetraallylsilane (4)) led to
sila-3-bicyclo[3.2.0]heptane (3) (or to spiro analogous 6) in the cis (or cis–cis) configuration whereas the a,v-diiodide (2) obtained
by cyclozirconation of 1 (or from the homologous tetraiodide 5) followed by addition of n-BuLi, produced the sila-3-bicy-
clo[3.2.0]heptane (3) (or to the spiro analogous 6) in the trans (or trans–trans configuration). The same cyclozirconation reaction,
starting from the hetero enyne 7, selectively led to the highly strained silacyclobutene moiety 15 which represents the first stable
hetero bicyclo[3.2.0]hept-1(7)ene skeleton, hypothetical intermediate in metathesis reactions. © 2002 Published by Elsevier Science
B.V.
Keywords: Photocycloaddition; Cyclo and spirozirconation; Allyl silanes; Enyne silanes; Sila-3-bicyclo[3.2.0]heptanes; Bicyclo[3.2.0]hept-1(7) ene;
Metathesis reactions
1. Introduction
led to trans heterocyclopentanes only. By a similar
process, the formation of a trans–trans isomer was
induced by the spirozirconation of tetrallyl silane and
germane (Td) [5].
We applied such reactions to prepare silabicy-
clo[3.2.0]heptanes 3 and 6 in trans and trans–trans
configurations (A) (Fig. 1). The synthesis of the corre-
sponding cis isomer (B) was selectively obtained by
photocycloaddition.
On the other hand, the catalytic reaction on 1,6-eny-
nes has already provided a valuable approach to cyclic
1,3- and 1,4-dienes. In particular, the mechanism of a
palladium-catalyzed intramolecular carbometallation
proposed by Trost et al. [6], for the production of the
unexpected skeletally rearranged product, invokes the
intermediacy of a bicyclo[3.2.0]hept-1(7)-ene (E). Such
cyclobutene moiety was postulated as an intermediate
Intramolecular carbometalations offer an exciting
opportunity to form rings under mild conditions. In
particular, metal-promoted bicyclisations of 1,6-dienes
and 1,6-enynes are synthetically attractive and fruitfully
methodologies [1].
In the literature, zirconocene promoted stereoselec-
tive cyclisation of 1,6-dienes led to cis–trans disubsti-
tuted cyclopentanes with a predominant trans isomer
[2].
Our previous results, starting from heterodienes,
confirmed that the selectivity depends on several
parameters [3] as the relative size of the substituents
or/and the nature of the heteroelement. In the case of
the corresponding diallyl phosphine boranes [4], we
noted the absence of selectivity of the zirconocycliza-
tion. All symmetrical (C2n) diallyl silanes and germanes
* Corresponding author. Tel.: +33-5-61556298; fax: +33-5-
61558204.
E-mail address: koenig@chimie.ups-tlse.fr (M. Koenig).
Fig. 1. Bicyclo[3.2.0]heptane and heptane isomers.
0022-328X/02/$ - see front matter © 2002 Published by Elsevier Science B.V.
PII: S0022-328X(01)01393-6

G. Oba et al. / Journal of Organometallic Chemistry 643–644 (2002) 324–330
325
derivative 6 (Scheme 2). The photocyclometalation pro-
duces the racemic (SRSR/SRSR) spirocyclic silane 6
cis–cis.
Nakanishi et al. [14] have shown that the irradiation
of 1 and 4, in presence of 1,4-dicyanonaphtalene in
benzene, afforded the intramolecular [2p+2p] photocy-
cloadducts in good yields via (1,4-DCNꢀC6H6ꢀSi com-
pound) triplexes. However, no information about the
streochemistry was given.
On the other hand, the cyclozirconation of 1 was also
stereoselective and the successive addition of I2 and
n-BuLi [15,16] on the metal complex leads to the corre-
sponding bicyclic silane 3 in the trans configuration
(Scheme 1). By the same process, the spirozirconation
of 4 produces the racemic 6 trans–trans (RRRR/SSSS)
(Scheme 2). In this case, the possible 6 meso (RRSS/
SSRR) was not observed. The 6 trans–trans configura-
tion was recently confirmed by an X-ray structural
determination of the corresponding spirocyclic te-
trabromide analogous to 5 [5].
Scheme 1.
The cis–trans isomerism was easily characterized by
13C-NMR. The high symmetry (C2 axis) of the trans–
trans isomers involves an equivalence of the C2/C5,
C3/C4 and C2/C6 carbons while these carbons in the
cis–cis isomerism are diastereotopic [17]. Furthermore,
the chemical shifts of the C3 and C4 stereogenic carbons
are quite different: 38.2Bl13CB39.1 in the cis
configuration and 47.0Bl13CB47.3 in the trans
configuration.
Scheme 2.
2.2. Enyne silane cyclisation
in transition metal-catalyzed [2+2]-cycloaddition.
However, unlike cyclobutenes (C) [7], (D) [8] and (F)
[9], this intermediate (E), structurally equivalent to the
trans cycloheptene [10], was not yet isolated.
The metal-promoted bicyclisation reaction of enynes
is also of particular interest, since desired products
would readily allow further regioselective transforma-
tions. This reaction was extensively studied by several
authors [18,19]. Negishi et al., by cyclozirconation of
1,6-enynes, followed by treatment with I2 and addition
of n-BuLi, synthesized cleanly the 8-(trimethylsi-
lyl)bicyclo[4.2.0]oct-1(8)-ene (F) in 70% yield [9]. The
same method failed to prepare the corresponding bicy-
clo[3.2.0] (E).
2. Results and discussion
2.1. Allyl silanes cyclisation
We investigated two different stereoselective cyclisa-
tions, in order to prepare sila bicyclic compounds in cis
and trans configurations.
The enyne 7 was prepared by the successive addition
of 3-bromo-1-trimethylsilyl-1-propyne and allyl magne-
sium bromide on diphenyldichlorosilane (Scheme 3).
The desired product, after purification with Chroma-
totron, was isolated in moderate yield (38%) because of
the unavoidable formation of two symmetrical silanes:
the diyne 8 and the corresponding diallylsilane 1. An
excess of zirconocene precursor was added at low tem-
perature to the enyne 7. The bicyclic intermediate 9,
characterized by NMR, was quenched by various
electrophiles.
We carried out the intramolecular copper(I)-cata-
lyzed [2+2]-photocycloaddition of the di- and tetraal-
lyl silanes 1 and 4, using the method first described by
Evers [11] and extensively investigated by Salomon [12].
The irradiation at 254 nm for 37 h of a THF solution
of diphenyldiallylsilane (1) in presence of one equiva-
lent of CuOTf, leads selectively to the sila-3-bicy-
clo[3.2.0]heptane (3) in cis configuration [13] (Scheme
1). The same stereoselectivity was observed in the for-
mation of the four stereogenic centers of the spiro
The protonation at 0 °C by a solution of HCl (0.1
M) led to a mixture of silacyclopentenes 10−10§,

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G. Oba et al. / Journal of Organometallic Chemistry 643–644 (2002) 324–330
Scheme 3.
Scheme 4.
obtained in form of colorless oil after purification with
Chromatotron. The presence of four different isomers
10, 10%, 10¦ and 10§, detected by NMR, is a conse-
quence of the lability of the double bond in acidic
media (Scheme 4).
The addition of a slight excess of bromine in CCl4
solution, at −78 °C, after hydrolysis by H2SO4 (10%)
led to Z/E isomers 11 and 11% (Scheme 5).
When the same intermediate 9 was treated by I2 and
hydrolyzed by aqueous NH4Cl, the diiodo derivative 12
was selectively isolated in form of Z isomer (Scheme 5).
This assigned structure was confirmed by a subsequent
cyclisation.
In order to extend cyclometallation reactions to the
dienynes, we synthesized the dienyne 13 by addition of
the Grignard reagent BrMgCH2CꢁCSiMe3 on dichloro-
diallylsilane (Scheme 6).
The cyclozirconation of 13, carried out by the usual
method and followed by addition of bromine, was
effective. The spiranic tetrabromides 14–14% decom-
posed on silica but were characterized by mass spectra
and 13C-NMR.
Using the Negishi method, by treatment of 12 in the
Z form with one equivalent of n-BuLi in ether at
−78 °C, we prepared 15 in 82% yield (Scheme 7). This
strained cyclobutene represents the first stable bicy-
clo[3.2.0]hept-1(7)ene skeleton (E). The bicyclisation
was confirmed by 13C-NMR. The important deshielding
of quaternary C3 and C6 (l=168.2 and 138.8, respec-
tively) is in good agreement with the bicyclo[3.2.0]hept-
1(7)ene skeleton (E). The stable cyclobutene (F)
presents similar values for the corresponding sp2 car-
bons [9].
metal catalyzed olefin metathesis might proceed by a
[2+2]-cycloaddition followed by cycloreversion was
proved incorrect. Nevertheless, the intriguing prospect
for transition metal-catalyzed [2+2] cycloaddition re-
mains [6]. Various attempts to stabilize the correspond-
ing cylobutene (E) by substitution [9] or complexation
[6] failed. Yet, few examples of (E) structures exist in
some polycyclic derivatives [20–23]. Recently, Blum et
al. [24] described a novel PtCl4 catalyzed cycloarrange-
ment of 1,6-enyne and suggested that the primary cycli-
sation product was the bicyclo[3.2.0]heptene (E). But,
in the absence of oxygen, the authors observed a poly-
merisation of this intermediate. To underline the steric
strain, Trost [25] performed molecular mechanics calcu-
lations. Three cyclobutenes (E) were studied indicating
that the high steric strain was dependent on the substi-
tution pattern. The calculated energies (between 58 and
64 kcal mol−1) confirmed the high steric strain of these
models.
The possible reasons of the relative stability of 15
would be due to the presence of diphenylsilane and
trimethylsilyl groups in a and b positions relative to the
intracyclic double bond [26].
This molecule 15 represents the first example of the
hypothetical intermediate of the intramolecular enyne
metathesis reaction. The suggestion that the transition-
Scheme 5.

G. Oba et al. / Journal of Organometallic Chemistry 643–644 (2002) 324–330
327
Scheme 6.
3.2. Compound 2 trans
To a solution of dichlorozirconocene (Cp2ZrCl2)
(0.87 g, 3 mmol) in 10 ml of THF at −78 °C was
added n-BuLi 1.6 M (3.8 ml, 6 mmol). After stirring (1
h), the diphenyldiallylsilane (1) (0.60 g, 3.0 mmol) in 5
ml THF was added at −78 °C. The solution was
stirred for 12 h at room temperature (r.t.). Then 1.9 g
(2.5 equivalents, 7.5 mmol) of I2 were added at −
78 °C.The reaction was quenched with H2SO4 (10%).
After extraction with ether, the reaction mixture was
washed with aq. NaHCO3, dried over MgSO4 and
filtered. Removal of the solvents followed by purifica-
tion with Chromatotron (C6H14) gave 2 trans (69%
yield) as white powder (m.p.: 116–118 °C).
Scheme 7.
In conclusion, it appears that the photocycloaddition
and the cyclozirconation are two complementary meth-
ods to obtain pure cis or pure trans bicyclic (or spi-
ranic) compounds starting from the same allylic
derivative. In the case of enyne, the cyclozirconation,
carried out with moderate yield, allow us to obtain the
high strained cyclobutene 15. This structure (E) was
often postulated as an intermediate in metathesis
reactions.
1H-NMR (250 MHz, CDCl3): l=1.2–1.6 (m, 6H,
CH2Si, CH), 3.3–3.6 (m, 4H, CH2I); 7.2–7.6 (m, 10H,
arom.). 13C-NMR (62.89 MHz, CDCl3) (J.mod): l=
17.2 (s, CH2I), 19.3 (s, CH2Si), 44.9 (s, CH), 135.4 (s,
ipso) MS (EI): m/z=391 [M−I]+ (100%). Anal. Calc.
3. Experimental
C
for C18H20I2Si: C, 41.69, H, 3.96. Found: C, 42.27; H,
4.01%.
3.1. General procedure
3.3. Compound 3 trans
All manipulations, except chromatography on silica
gel with Chromatotron® apparatus, were carried under
an argon atmosphere. Tetrahydrofuran, Et2O and
C6H14 were distilled from sodium–benzophenone solu-
tion and stored under Ar. All NMR spectra were
recorded at 25 °C on Bruker AC 80 and 250 MHz in
n-BuLi (one equivalent, 1.7 ml, 2.7 mmol) was slowly
added at −78 °C to 2 trans (one equivalent 1.4 g, 2.7
mmol) in 15 ml of ether. The mixture was then allowed
to warm to r.t. After hydrolysis with 50 ml of NH4Claq,
the product extracted by ether, dried by MgSO4 and
filtrated, was purified with Chromatotron (C6H14) and
obtained as colorless oil in 45% yield.
1
CDCl3. The H and 13C chemical shifts are referenced
relative to Me4Si. Coupling constants are given in
Hertz. Mass spectra were obtained on a Ribermag
R1010 under electron impact (EI) or chemical ioniza-
tion (DCI conditions) with CH4 or NH3. Low-resolu-
tion mass spectra were determined by GC–MS using
Hewlett–Packard 5890 series II gas chromatograph
equipped with a HP/MS 5989A mass selective detector.
M.p. were determined in evacuated capillaries with a
Buchi–Tottoli apparatus. IR spectra were recorded on
Perkin–Elmer 1600 Series FTIR. Elemental analyses
were performed by the Microanalytical Laboratory of
the Ecole Nationale Supe´rieure de Chimie de Toulouse.
Irradiations were carried out using as light source a
Rayonet photochemical reactor.
1H-NMR (250 MHz, CDCl3): l=0.9–1.8 (m, 8H,
CH2Si, CH2), 2.0–2.1 (m, 2H, CH), 7.4–7.7 (m, 10H,
arom.). 13C-NMR (62.89 MHz, CDCl3) (J.mod): l=
19.0 (s, CH2Si), 29.9 (s, CH2), 47.3 (s, CH), 137.1 (s,
Cipso). MS (DCI–NH3): m/z=282 [M, NH4]+ (100%).
Anal. Calc. for C18H20Si: C, 81.8, H, 7.6. Found: C,
80.7; H, 7.8%.
3.4. Compound 3 cis
In a quartz vessel, 0.05 equivalent (0.024 g, 0.05
mmol) of CuOTf was added to one equivalent (0.30 g,

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G. Oba et al. / Journal of Organometallic Chemistry 643–644 (2002) 324–330
1.14 mmol) of 1 in 3 ml of ether. The mixture was
irradiated at 254 nm for 37 h. After removal of the
solvent, the product was purified with Chromatotron
(hexane) and obtained as colorless oil in 44% yield.
1H-NMR (250 MHz, CDCl3): l=1.0–2.7 (m, 8H,
CH2Si, CH2), 2.7–3.2 (m, 2H,CH), 7.2–7.8 (m, 10H,
arom.). 13C-NMR (62.89 MHz, CDCl3) (J.mod): l=
18.6 (s, CH2Si), 27.7 (s, CH2), 39.1 (s, CH), 136.9 (s,
1H-NMR (80 MHz, CDCl3): l=0.3–2.1 (m, 20H,
CH2Si, CH2, CH). 13C-NMR (62.89 MHz, CDCl3)
(J.mod): l=18.7 (s, CH2Si), 19.7 (s, CH2Si), 27.1 (s,
CH2), 28.3 (s, CH2), 38.2 (s, CH), 38.9 (s, CH).
3.8. Compound 7
3-Bromo-1-trimethylsilyl-1-propyne (10 g, 1.1 equiva-
lents, 5.3×10−2 mol) in 10 ml of ether are added to
4.9 g of Mg (4.5 equivalents, 1.07×10−1 mol) in 10 ml
of ether. After addition of 80 ml of ether and 4 h
stirring at r.t., the supernatant was introduced, at 0 °C,
to a solution of Ph2SiCl2 (one equivalent, 4.76×10−2
mol) in 10 ml of ether. The solution was stirred 12 h at
r.t. (solution I). Separately, a solution of allyl MgBr
(solution II) was prepared by addition of 6.3 ml of allyl
bromide (1.1 equivalents, 5.2×10−2 mol) on 2.7 g of
Mg (two equivalents, 0.12 mol) in ether. After 1 h
refluxing, the supernatant was added to solution I.
After 12 h refluxing, the solution was hydrolyzed
(NH4Cl). The product, extracted with ether, dried with
MgSO4, and concentrated, was purified with Chroma-
totron (C6H14–CH2Cl2=90/10) and obtained as color-
less oil in 38% yield.
C
ipso), 137.1 (s, Cipso) MS (DCI–NH3): m/z=282 [M,
NH4]+ (100%). Anal. Calc. for C18H20Si: C, 81.8, H,
7.6. Found: C, 80.7; H, 7.7%.
3.5. Compound 5 trans–trans
To a solution of Cp2ZrCl2 (2.68 g, 9.4 mmol) in 10
ml of THF at −78 °C was added n-BuLi 1.6 M (5.95
ml, 9.4 mmol). After 1 h stirring, the tetraallylsilane (4)
(0.9 g, 4.7 mmol) in 5 ml THF was added at −78 °C.
The solution was stirred for 12 h at r.t. Then 5.9 g (five
equivalents, 23.4 mmol) of I2 in 24 ml of THF were
added at −78 °C. The reaction was quenched with
H2SO4 (10%). After extraction with ether, the reaction
mixture, neutralized with NH4Claq was dried over
MgSO4 and filtered. After crystallisation in C6H14–
CH2Cl2 (98/2) 5 trans–trans was obtained as white
powder in 64% yield (m.p.: 144–145 °C).
1H-NMR (80 MHz, CDCl3): l=0.1 (s, 9H, SiMe3),
2.2–2.3 (m, 4H, CH2Si, 4.8–5.1 (m, 2H, H2Cꢂ), 5.7–6.1
(m, 1H, CH), 7.4–7.8 (m, 10H, H arom.). 13C-NMR
(62.89 MHz, CDCl3): l=0.1 (s, SiMe3), 5.2 (s,
SiCH2ꢀCHꢂ), 20.1 (s, SiCH2ꢀCꢁCꢀ), 85.2 (s, SiꢀCꢁCꢀ),
104.4 (s, SiꢀCꢁCꢀ), 115.1 (s, H2Cꢂ), 133.8 (s, Cipso),
127.8–135.1 (CH arom.).
1H-NMR (80 MHz, CDCl3): l=0.5–1.5 (m, 12H,
CH2Si, CH), 3.1–3.5 (m, 8H, CH2I). 13C-NMR (62.89
MHz, CDCl3) (J.mod): l=16.9 (s, CH2I), 19.1 (s,
CH2Si), 44.6 (s, CH) MS (EI): m/z=573 [M−I]+
(100%). Anal. Calc. for C12H20I4Si: C, 20.58, H, 2.86.
Found: C, 20.65; H, 2.94%.
3.9. Compound 10
3.6. Compound 6 trans–trans
To a solution of Cp2ZrCl2 (0.84 g, 2.9×10−3 mol) in
10 ml of THF at −78 °C was added n-BuLi 1.6 M
(3.6 ml, 6.5×10−3 mol). After 1 h stirring, the enyne 7
(1.8×10−3 mol) in 10 ml of THF was added. The
reaction was stirred 12 h at r.t., leading to the bicyclo
intermediate 9. The solution of 9 was quenched by HCl
(0.1 M) at 0 °C. After stirring 30 min at r.t., the
product 10, extracted, dried and purified with Chroma-
totron (C6H14) was isolated in form of colorless oil
(28% yield).
n-BuLi (two equivalents, 3.4 ml, 5.4 mmol) was
slowly added at −78 °C to 5 trans–trans (one equiva-
lent, 1.9 g, 2.7 mmol) in 15 ml of ether. The mixture
was then allowed to warm to r.t. After hydrolysis with
NH4Claq, the product, extracted by ether, dried by
MgSO4 and filtrated, was purified with Chromatotron
(C6H14) and obtained as colorless oil in 40% yield.
1H-NMR (80 MHz, CDCl3): l=1.4–1.7 (m, 16H,
CH2), 1.8 (m, 4H, CH). 13C-NMR (62.89 MHz, CDCl3)
(J.mod): l=19.7 (s, CH2Si), 30.0 (s, CH2), 47.0 (s,
CH).
1H-NMR (80 MHz, CDCl3): l= −0.07, 0.11, 0.12,
0.21, (s, 9H, SiMe3), 0.9–2.4 (m, 8H, CH2SiMe3,
CH2Si, CH, CH3), 5.4–5.9 (m, 1H, Ph2SiCHꢂ or
ꢂCHSiMe3), 7.4–7.6 (m, 10H, H arom.).
13C-NMR (62.9 MHz, CDCl3): l= −1.7, −1.0,
−0.7, −0.3 (s, SiMe3), 19.9, 20.7, 21.1, 21.6, 21.7, 22.1
(s, Ph2SiCH2), 21.5, 21.6, 22.8, 23.6 (CH3), 26.3, 26.9
(CH2SiMe3), 42.6, 42.8, 43.1 (s, CH), 114.4, 114.9 (s,
Cq), 120.1 (s, ꢂCHSiMe3), 128, (s, Ph2SiCHꢂ), 128.5 (s,
Ph2SiCHꢂ), 127, 135 (CH arom.), 165 (s, Cq). MS
(DCI–NH3): m/z=354 [M, NH4]+ (100%), 337 [MH]+
(18%). IR: w (cm−1)=3069, 2059, 1593, 1564, 1248,
854, 734.
3.7. Compound 6 cis–cis
In the same experimental conditions as 3 cis, 0.05
equivalent (0.024 g, 0.05 mmol) of CuOTf was added to
one equivalent (0.218 g, 1.14 mmol) of 4 in 3 ml of
ether. The mixture was irradiated at 254 nm for 08:30
h. After removal of the solvent, the product was
purified with Chromatotron (C6H14) and obtained as
colorless oil in 40% yield.

G. Oba et al. / Journal of Organometallic Chemistry 643–644 (2002) 324–330
329
3.10. Compound 11
Mg (2.5 g ) (six equivalents, 1.02×10−1 mol) in ether
(10 ml). After adition of 80 ml of ether and stirring (4
h) at r.t., the supernatant was added, at 0 °C, to a
solution of dichlorodiallylsilane (one equivalent, 1.7×
10−2 mol) in 10 ml of ether. After addition, the solu-
tion was allowed to warm to r.t., stirred for 12 h and
hydrolyzed with 100 ml of distilled water. The product
extracted with ether, dried with MgSO4 and concen-
trated, was obtained as an orange oil in 95% yield
without purification.
Br2 (0.22 ml, 2.35 equivalents, 4.2 mmol) in CCl4 (8
ml) were added at −78 °C on the intermediate 9 (1.8
mmol). The solution was allowed to warm to r.t. (12 h).
After hydrolysis by H2SO4 (10%) and stirring (30 min),
the organic phase was extracted with ether, washed
with K2CO3aq and dried with MgSO4. The solution was
concentrated under reduced pressure and the residue,
purified with Chromatotron (C6H14–CH2Cl2=98/2),
was obtained as a yellow oil in 41% yield.
1H-NMR (80 MHz, CDCl3): l=0.1 (s, 18H, SiMe3),
1.7–1.8 (m, 8H, CH2Si), 4.8–5.1 (m, 4H, H2Cꢂ), 5.7–
6.1 (m, 2H, CH).
1H-NMR (250 MHz, CDCl3): l=0.23 (s, 9H, SiMe3)
(isomer I); 0.25 (s, 9H, SiMe3) (isomer II); 1.55–1.57
(Part AB of ABX, JAB=15 Hz, JAX=4 Hz, JBX=7
2
3
3
2
Hz, 2H, CH2Si), 2.00–2.44 (Part A%B% of A%B%X, JAB
=
3.13. Compound 14
4
4
15 Hz, JBX=1.5 Hz, JAX=0 (2H, CH2Si) (isomer I),
2
2.00–2.45 (A¦B¦ system), JAB=16.5 Hz, 2H, CH2Si)
After the cyclozirconation reaction (carried out by
the usual method as for compound 9) 0.65 ml of Br2
(4.2 equivalents, 12.6×10−3 mol) in 15 ml of CCl4
were added at −78 °C on 1.8 mmol of the intermedi-
ate. The solution was allowed to warm to r.t. for 12 h.
After hydrolysis by H2SO4 (10%) and stirring (30 min),
the organic phase was extracted with ether, washed
with K2CO3aq and dried with MgSO4. The product
decomposes on silica but the solution of the crude
product indicates the presence of tetrabromide spirosi-
lane 14.
(isomer II), 3.38 (ft, 2JHH=3JHH=9.5 Hz, 1H,
2
3
CHHBr), 3.61 (dd, JHH=9.5Hz, JHH=4.5 Hz, 1H,
CHHBr), 3.9–4.1 (m, 1H, CH), 7.3–7.7 (10H, H
arom.). 13C-NMR (62.9 MHz, CDCl3): l=0.6 (s,
SiMe3) (isomer I), 0.8 (s, SiMe3). (isomer II); 15.5 (s,
C5), 21.8 (s, C2) (isomer I or II); 22.1 (s, C2) (isomer I
or II); 38.5 (s, C7); 49.1 (s, C4), 124.1 (s, C6), 133.6 (s,
Cipso), 128–134 (CH arom.), 153.9 (s, C3) (isomer I or
II), 154.7 (s, C3) (isomer I or II). MS (DCI–NH3):
m/z=512 [M, NH4]+, 432 [M−Br, NH4]+. Anal.
Calc. for C21H26Br2Si2: C, 51.01, H, 5.26. Found: C,
51.34; H, 5.84%.
13C-NMR (62.9 MHz, CDCl3): l=0.7 (s, SiMe3),
17.1 (s, C5), 22.0 (s, C2), 40.4 (s, C7), 47.7 (s, C4), 120.0
(s, C6), 154.1 (s, C3). MS (DCI–NH3): m/z=670 [M,
NH4]+, 653 [MH]+.
3.11. Compound 12
In the same conditions as before, 1.1 g of I2 (2.5
equivalents, 4.5 mmol) in 6 ml of THF were added to 9
(1.8. mmol) at −78 °C. The solution was allowed to
warm to r.t. for 12 h and stirred for 96 h. The reaction
mixture was hydrolyzed with NH4Cl solution, extracted
with ether, dried, concentrated and purified with Chro-
matotron (C6H14–CH2Cl2=90/10). Compound 12 was
obtained as a yellow oil in low yield (14%).
3.14. Compound 15
n-BuLi (0.16 ml, one equivalent, 2.55×10−4 mol)
were added at −78 °C, to (0.15 g, one equivalent,
2.55×10−4 mol) 12 in ether (3 ml). The solution was
allowed to warm to r.t. (1 h). After hydrolysis, the
organic phase was extracted with ether, dried with
MgSO4 and concentrated. The product, obtained as
colorless oil (82% yield), is stable, with or without
solvent, at r.t. But during purification with Chroma-
totron apparatus, a slight decomposition was observed.
1H-NMR (80 MHz, CDCl3): l=0.2 (s, 9H, SiMe3),
0.8–3.2 (m, 7H, CH2Si, CH2, CH), 7.1–7.8 (m, 10H, H
arom.). 13C-NMR (50.3 MHz, C6D6): l= −1.2 (s,
SiMe3), 17.9 (s, C5), 20.2 (s, C2), 38.6 (s, C7), 44.5 (s,
C4), 128–135 (CH arom), 138.8 (s, C6), 168.3 (s, C3).
MS (EI): m/z=334 [M+].
1H-NMR (250 MHz, CDCl3): l=0.3 (s, 9H, SiMe3),
2
3
1.59, 1.61 (Part AB of ABX, JAB=10.1 Hz, JAX=5.8
3
Hz, JBX=2.9 Hz, 2H, CH2Si), 2.1–2.5 (AB system,
2JAB=11.5 Hz, CH2Si), 3.1 (ft, JHH=3JHH=9.5 Hz,
2
2
3
1H, CHHI), 3.46 (dd, JHH=9.5 Hz, JHH=4.0 Hz,
1H, CHHI), 3.8–3.9 (m, 1H, CH), 7.4–7.7 (10 H, H
arom.). 13C-NMR (62.9 MHz, CDCl3): l=1.9 (s,
SiMe3), 13.1 (s, C7), 17.6 (s, C5), 22.0 (s, C2), 56.5 (s,
C4), 109.5 (s, C6), 127–134 (CH arom.), 160.1 (s, C3).
MS (DCI–NH3): m/z=606 [M, NH4]+ (100%); 589
[MH]+.
References
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