Cycloadditions of allylsilanes, Part 12. Regio- and stereoselective transformations of silylbicyclo [n.3.0]alkanes

Article abstract of DOI:10.1055/s-1999-3684

Lewis acid promoted [3+2] cycloaddition of 1-acetylcycloalkenes and allylsilanes provides the silylbicyclo[n.3.0]-alkanes 4 and 5. The sequence of regioselective Baeyer-Villiger oxidation and elimination of acetic acid affords the 3-silylbicyclo[3.3.0]oct-1(5)-enes 8a and 9a and the 8- (triphenylsilyl)bicyclo[4.3.0]non-1(6)-ene (8b). Epoxidation and catalytic hydrogenation of these olefins proceeds with complete stereoselectivity anti relative to the silyl substituent. Ozonolysis of 8b leads to 3- (triphenylsilyl)cyclononane- 1,5-dione (15).

Full text of DOI:10.1055/s-1999-3684

PAPER
145
Cycloadditions of Allylsilanes, Part 12.1 Regio- and Stereoselective
Transformations of Silylbicyclo[n.3.0]alkanes
Hans-Joachim Knšlker,* Norbert Foitzik, Christoph Gabler, Regina Graf
Institut fŸr Organische Chemie, UniversitŠt Karlsruhe, Richard-WillstŠtter-Allee, D-76131 Karlsruhe, Germany
Fax: + 49(721)698529; E-mail: knoe@ochhades.chemie.uni-karlsruhe.de
Received 27 April 1998; revised 15 June 1998
further synthetic transformations of the silylbicyc-
lo[n.3.0]alkanes which are initiated by chemoselective
oxidation of the angular acetyl group via a BaeyerÐVil-
liger reaction. In this oxidation the silyl group is preserved
and utilized as a stereodirecting group in subsequent reac-
tions. Cycloaddition of the 1-acetylcycloalkenes 1 with
the allylsilanes 2 and 3 provides the triphenylsilyl deriva-
tives 4 and the triisopropylsilyl derivatives 5 of the bicyc-
lo[3.3.0]octane a, bicyclo[4.3.0]nonane (hydrindane) b,
and bicyclo[5.3.0]decane (hydroazulene) c, which repre-
sent important natural product frameworks found in many
sesquiterpenes. The triphenylsilyl group was selected be-
cause it is easily transformed into a hydroxy group by a
one-pot protodesilylation/FlemingÐTamao oxidation se-
Abstract: Lewis acid promoted [3+2] cycloaddition of 1-acetylcy-
cloalkenes and allylsilanes provides the silylbicyclo[n.3.0]-alkanes
4 and 5. The sequence of regioselective BaeyerÐVilliger oxidation
and elimination of acetic acid affords the 3-silylbicyclo[3.3.0]oct-
1(5)-enes 8a and 9a and the 8-(triphenylsilyl)bicyclo[4.3.0]non-
1(6)-ene (8b). Epoxidation and catalytic hydrogenation of these
olefins proceeds with complete stereoselectivity anti relative to the
silyl substituent. Ozonolysis of 8b leads to 3-(triphenylsilyl)cy-
clononane-1,5-dione (15).
Key words: allylsilanes, [3+2] cycloadditions, BaeyerÐVilliger ox-
idation, molecular modelling, diastereoselective epoxidation
A few years ago the Lewis acid promoted [3+2] cycload-
dition of allylsilanes and electron-deficient olefins was
described as a side reaction of the HosomiÐSakurai reac-
tion.2 It was found that allylsilanes containing bulky
substituents at the silicon atom, especially allyl-triisopro-
pylsilane, follow almost exclusively the course of the cy-
cloaddition reaction.3 Subsequently this reaction was
developed to a useful synthetic method for the stereo-
selective construction of cyclopentanes.4Ð6 Depending on
the substrate and the reaction temperature a selective
[2+2] cycloaddition of allylsilanes and electron-deficient
olefins leading to silylmethylcyclobutanes was also ob-
served.7 Moreover, several related Lewis acid promoted
cycloadditions of allylsilanes providing heterocyclic ring
systems were reported.8
A broad range of angularly acetyl-substituted silylbicyc-
lo[n.3.0]alkanes is stereoselectively available by Lewis
acid promoted [3+2] cycloaddition of allylsilanes and 1-
acetylcycloalkenes.4 The chemo-, regio-, and stereoselec-
tive functionalization of these products directed toward
potential applications to the synthesis of biologically ac-
tive terpenes is currently under active investigation. One
problem was the selective oxidative cleavage of the car-
bonÐsilicon bond containing a bulky silyl group by modi-
fications of the classical FlemingÐTamao oxidation.9
Recently this transformation was achieved for cycload-
ducts of allylsilanes containing the methyldiphenylsilyl,10
triphenylsilyl,10 dimethyltritylsilyl,11 diisopropylsilyl,1
and tert-butyldiphenylsilyl groups.1 Using these modifi-
cations of the FlemingÐTamao oxidation the silylbicyc-
lo[n.3.0]alkanes can be conveniently transformed to the
corresponding hydroxybicyclo[n.3.0]alkanes with reten-
tion of configuration by oxidative cleavage of the sterical-
ly hindered carbonÐsilicon bond.1,10 We now describe
Scheme 1
Table 1 Synthesis of the Cycloadducts 4 and 5 and Results of their
Transformations to the Olefins 8 and 9
R
a, Yield (%)
b, Yield (%) c, Yield (%)
n = 1
anti/syn
n = 2
n = 3
4
6
8
5
7
9
Ph
Ph
Ph
i-Pr
i-Pr
i-Pr
254b
81
1:0
1:0
–
3:1
3:1
–
514b
87
344b
0
87
96
–
714b
93
864b
23
684b
0
45
–
–
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146
H.-J. Knšlker et al.
PAPER
quence with tetrabutylammonium fluoride/hydrogen per-
oxide recently developed in our laboratories.10 On the
other hand, the triisopropylsilyl derivatives are obtained
in high yields.
Titanium(IV) chloride promoted [3+2] cycloaddition of
the 1-acetylcycloalkenes 1 and either allyltriphenylsilane
2 or allyltriisopropylsilane 3 using our previously report-
ed optimized reaction conditions provided the (triphenyl-
silyl)bicyclo[n.3.0]alkanes 4 and the (triisopropyl)-
silylbicyclo[n.3.0]alkanes 5 (Scheme 1, Table 1).4 By this
procedure the bicyclo[3.3.0]octane 4a, the bicyclo-
[4.3.0]nonanes 4b and 5b, and the bicyclo[5.3.0]decanes
4c and 5c were obtained stereoselectively as the anti dia-
stereoisomers, the bicyclo[3.3.0]octane 5a was isolated as
a 3:1 mixture of the anti and the syn diastereoisomer (anti
and syn denote the position of the silyl relative to the
acetyl group).4 We envisaged a functionalization of the
angular position of the silylbicyclo[n.3.0]alkanes 4 and 5
by a regioselective BaeyerÐVilliger oxidation, which is
known to occur with retention of configuration at the mi-
grating carbon atom.12 The triphenylsilyl-substituted bi-
cyclo[3.3.0]octane 4a and bicyclo[4.3.0]nonane 4b were
readily transformed to the corresponding acetoxy deriva-
tives 6a and 6b by treatment with m-chloroperoxybenzoic
acid (MCPBA) in dichloromethane for 5 days at reflux.
However, the homologous bicyclo[5.3.0]decane 4c did
not undergo BaeyerÐVilliger oxidation to 6c. Neither un-
der buffered basic (sodium hydrogen carbonate) or acidic
(p-toluenesulfonic acid) reaction conditions with MCPBA
nor using trifluoroperoxyacetic acid the formation of an
acetoxy derivative was observed. The failure of the
BaeyerÐVilliger oxidation of 4c was tentatively explained
by the increased steric hindrance of the angular acetyl
group caused by the annulated conformationally more
flexible seven-membered ring. This attempted rational-
ization is supported by molecular model inspections
(compare also the molecular structures of 4a, 4b, and 4c
in the crystal4b). The 1-acetoxy-3-(triphenylsilyl)bicyc-
lo[3.3.0]octane (6a) and the 1-acetoxy-9-(triphenylsi-
lyl)bicyclo[4.3.0]nonane (6b) were converted into the
symmetrical bicyclic olefins 8a and 8b in excellent yields
by tetrafluoroboric acid promoted elimination of acetic
acid in tetrahydrofuran at reflux (Scheme 1, Table 1). The
simple two-step sequence of BaeyerÐVilliger oxidation
and elimination opened up the way for the functionaliza-
tion of both bridgehead carbon atoms of the cycloadducts
4a and 4b.
Scheme 2
We performed an extensive 13C NMR spectroscopic in-
vestigation of the silylbicyclo[n.3.0]alkanes resulting
from Lewis acid promoted [3+2] cycloaddition of 1-ace-
tylcycloalkenes and allylsilanes. The chemical shift of the
signal for the CH α to the silyl group at the five-mem-
bered ring proved to be dependent on the ring size of the
additional annulated ring, the substituents at the silicon at-
om, and the relative stereochemistry at this carbon atom
(anti or syn arrangement of the silyl group relative to the
acetyl group).4 Thus, for the triisopropylsilyl derivatives
in the bicyclo[3.3.0]octane series a stereochemical assign-
ment is possible by comparison of the characteristic 13C
NMR data with those of the corresponding triphenylsilyl
derivatives. An X-ray analysis unequivocally confirmed
the anti stereochemistry for 4a and consequently also for
the acetoxy derivative 6a.4b Based on the comparison of
the chemical shifts of the signals for the αSi-CH group
(C3) the major diastereoisomers of 5a and 7a were as-
signed to have anti stereochemistry (Table 2). A high field
shift is observed for the corresponding signals of the syn
diastereoisomers.
The BaeyerÐVilliger oxidation of the bicyc-
lo[4.3.0]nonane 5b required more drastic reaction condi-
tions (MCPBA, CHCl3, reflux) and afforded the acetoxy
We next investigated the same sequence for the triiso-
propylsilyl derivatives 5aÐc. The BaeyerÐVilliger oxida-
tion of the 3:1 mixture of the anti and syn diastereo-
isomers of 5a by treatment with MCPBA in dichlo-
romethane for 22 hours at reflux afforded a 3:1 mixture of
the corresponding acetoxy derivatives anti-7a and syn-7a
in high yield (Scheme 2, Table 1). Tetrafluoroboric acid
promoted elimination of acetic acid transformed both
diastereoisomers of 7a to the symmetrical 3-(triisopropyl-
silyl)-bicyclo[3.3.0]oct-1(5)-ene (9a).
Table 2 Chemical Shift of the α-Silyl Carbon Atom (C3) in the 13
NMR Spectrum (100 MHz, CDCl3) for Various Silylbi-
cyclo[3.3.0]octane Derivatives
C
R = Ph
δ (C3)
R = i-Pr
δ (C3)
4a
6a
8a
11
25.23 (anti)
24.42 (anti)
26.07
5a
7a
9a
12
24.94 (anti) 21.14 (syn)
23.76 (anti) 21.27 (syn)
25.16
25.65
24.56
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Cycloaddition of Allylsilanes, Part 12
147
derivative 7b in only 23% yield along with 31% of start-
ing material. As described above for the triphenylsilyl de-
rivative 4c, the triisopropylsilyl derivative 5c did not
undergo BaeyerÐVilliger oxidation using MCPBA and
trifluoroperoxyacetic acid. Obviously, BaeyerÐVilliger
oxidation of bicyclo[5.3.0]nonanes containing an acetyl
group in the angular position can not be achieved by the
applied conditions.
The BaeyerÐVilliger oxidation of the 1-acetylbicyc-
lo[n.3.0]alkanes followed by cleavage of the resulting
acetic acid ester enables the introduction of an angular hy-
droxy group. Saponification of the acetoxy derivative 6b
by treatment with potassium hydroxide in ethanol/dichlo-
romethane (5:1) at reflux for 2 days provided the 1-hy-
droxybicyclo[4.3.0]nonane 10 in only 57% yield. The low
yield is explained by the rather harsh reaction conditions
which are required for tert-alkyl esters. However, removal
of the acetyl group by reduction of 6b using lithium alu-
minum hydride in tetrahydrofuran at room temperature
for 30 minutes afforded the carbinol 10 in 89% yield
(Scheme 3).
Figure 1 Calculated structure and bond lengths of 8b determined by
molecular mechanics13 (SCHAKAL representation).14
Scheme 3
The olefins 8 and 9 were considered as good starting ma-
terials for further transformations at both bridgehead car-
bon atoms simultaneously. Because of the rigid
conformation of the bicyclo[3.3.0]octene and bicyc-
lo[4.3.0]nonene frameworks and the steric hindrance ex-
Figure 2 Space filling model of 8b (HyperChem program).13
place anti relative to the silyl substituent. The same mode
of stereoselectivity was expected for reactions of the ole-
fins 8a and 9a.
hibited by the silyl moiety
a high degree of
stereoselectivity was expected for reactions at the central
double bond. The bulky triphenylsilyl and triisopropylsi- Epoxidation of the triphenylsilyl-substituted bicyclo-
lyl substituents were expected to function as stereodirect- [3.3.0]octene 8a with MCPBA in dichloromethane at
ing groups which enforce an approach of reagents from room temperature proceeded in 10 minutes and provided
the face opposite to silicon (anti selectivity). This predic- stereoselectively the (triphenylsilyl)oxapropellane 11 in
tion for the stereoselectivity of subsequent reactions at the 94% yield (Scheme 4). The same reaction with the triiso-
central double bond derived support from molecular mod- propylsilyl-substituted bicyclo[3.3.0]octene 9a required
elling studies. The minimum energy conformation of the 45 minutes and afforded the epoxide 12 in only 64% yield.
triphenylsilyl-substituted bicyclo[4.3.0]nonene 8b was
Epoxidation of the triphenylsilylbicyclo[4.3.0]nonene 8b
by reaction with MCPBA for 10 minutes at room temper-
ature provided quantitatively the (triphenylsilyl)oxa-
propellane 13 (Scheme 4). Catalytic hydrogenation of the
calculated using the HyperChem program.13 The structure
of the olefin 8b as determined by molecular mechanics
calculations (MM+) is presented in Figure 1.14 The bond
lengths for the triphenylsilyl moiety of 8b calculated by
olefin 8b with platinum dioxide in acetic acid under a hy-
molecular mechanics are in good agreement with those
drogen atmosphere at room temperature afforded almost
obtained by the X-ray crystal structure analysis of 4b.4b
quantitatively the bicyclo[4.3.0]nonane 14. The epoxida-
The space filling model of 8b generated based on the mo-
tions of the bicyclic olefins 8 and 9a to the epoxides 11,
lecular mechanics result shows that one face of the sym-
12, and 13 and the catalytic hydrogenation of 8b to 14 pro-
ceeded with complete stereoselectivity. The relative stere-
metrical olefin is shielded by the bulky triphenylsilyl
group (Figure 2). Thus, based on steric arguments an at-
ochemistry of these products was assigned based on the
tack of reagents at the central double bond should take
steric considerations described above.
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148
H.-J. Knšlker et al.
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1-Acetoxy-8-(triphenylsilyl)bicyclo[4.3.0]nonane (6b)
A solution of 4b (1.00 g, 2.35 mmol) in anhyd CH2Cl2 (50 mL) was
added to MCPBA (1.72 g, content: 70%; 6.98 mmol of MCPBA)
and NaHCO3 (198 mg, 2.36 mmol). The mixture was stirred at re-
flux. Further MCPBA was added after 24 h (470 mg, content: 70%;
1.91 mmol of MCPBA) and 48 h (1.00 g, content: 70%; 4.06 mmol
of MCPBA). After a reaction time of 5 d at reflux the cold mixture
was stirred over solid NaHCO3 and then poured into aq NaHCO3
(50 mL). The aqueous layer was extracted with CH2Cl2 (3 × 50 mL)
and the combined organic layers were dried (MgSO4). The solvent
was evaporated in vacuo and the residue subjected to flash chroma-
tography (silica gel, hexane/Et2O 7:1). Recrystallization from Et2O
at Ð20¡C afforded 6b as colorless crystals; yield: 905 mg (87%); mp
87Ð89¡C (Et2O).
IR (KBr): ν = 1720 cmÐ1 (C=O)
1H NMR (400 MHz, CDCl3): δ = 0.59 (m, 1H), 1.02 (m, 1H), 1.14
(m, 2H), 1.30 (m, 2H), 1.44Ð1.58 (m, 2H), 1.80 (ddd, J = 13.6, 9.0,
4.2 Hz, 1H), 2.00 (dd, J = 13.8, 10.7 Hz, 1H), 2.03 (s, 3H), 2.17 (m,
2H), 2.34 (quint, J = 9.4 Hz, 1H), 2.52 (dd, J = 13.8, 9.6 Hz, 1H),
7.41 (m, 9H), 7.60 (m, 6H).
13C NMR and DEPT (100 MHz, CDCl3): δ = 17.95 (CH), 22.48
(CH3), 22.61 (CH2), 23.07 (CH2), 27.97 (CH2), 30.39 (CH2), 31.31
(CH2), 35.77 (CH2), 44.73 (CH), 91.56 (C), 127.83 (6 CH), 129.47
(3 CH), 134.62 (3 C), 136.04 (6 CH), 170.70 (C=O).
MS (100¡C): m/z (%) = 381 (M+ Ð OAc, 4), 332 (30), 330 (28), 327
(11), 259 (49), 214 (11), 199 (15), 86 (69), 84 (100), 81 (21), 79
(10), 59 (5).
Scheme 4
Cleavage of the central double bond of the bicyc-
lo[4.3.0]nonene 8b by ozonolysis15 afforded 3-(triphenyl-
silyl)cyclononane-1,5-dione (15) and shows the potential
of the bicyclic olefins as synthetic precursors for function-
alized medium-sized ring compounds.
1-Acetoxy-3-(triisopropylsilyl)bicyclo[3.3.0]octane (7a)
MCPBA (1.20 g, content: 70%; 4.87 mmol of MCPBA) was added
to a solution of 5a (mixture of diastereoisomers, anti/syn 3:1,
500 mg, 1.62 mmol) in CH2Cl2 (20 mL). The mixture was stirred at
reflux for 22 h. After cooling to r.t. the solution was poured into aq
NaHCO3 (20 mL) and the layers were separated. The aqueous layer
was extracted with CH2Cl2 (3 × 20 mL), the combined organic lay-
ers were dried (MgSO4), and the solvent was evaporated in vacuo.
Flash chromatography (silica, gel, hexane/Et2O 15:1) of the residue
provided 7a as a mixture of diastereoisomers (anti/syn 3:1) as a col-
orless oil; yield: 490 mg (93%).
All reactions were carried out using anhydrous and degassed sol-
vents under an inert gas atmosphere. MCPBA from Acros Chimica
(art. 25.579.68, peracid content: 70%) was used. Flash chromatog-
raphy: Baker or Merck silica gel (0.03Ð0.06 mm). Mps: BŸchi 535.
IR spectra: PerkinÐElmer 1710, Bruker IFS-88. H NMR and 13C
1
NMR spectra: Bruker AM-400; internal standard: the signal of the
deuterated solvent; coupling constants J in Hz. MS: Finnigan MAT-
312 and MAT-90; ionization potential: 70 eV.
IR (film): ν = 1736 cmÐ1 (C=O).
1H NMR (400 MHz, CDCl3): δ = 0.83Ð0.89 (m, 1H), 1.06 (m, 21H),
1.13Ð1.37 (m, 4H), 1.41Ð1.61 (m, 3H), 1.65Ð1.85 (m, 2H), 1.98 (s)
and 1.99 (s, Σ 3H), 2.10Ð2.21 (m, 1H), 2.43Ð2.52 (m, 1H).
1-Acetoxy-3-(triphenylsilyl)bicyclo[3.3.0]octane (6a)
NaHCO3 (1.23 g, 14.6 mmol) and MCPBA (1.80 g, content 70%;
7.30 mmol of MCPBA) were added in small portions over a period
of 2 d to a refluxing solution of 4a (1.00 g, 2.44 mmol) in CH2Cl2
(40 mL). After a reaction time of 5 d the cold mixture was quenched
with aq NaHCO3 (40 mL). The layers were separated and the aque-
ous layer was extracted with CH2Cl2 (3 × 40 mL). The combined or-
ganic layers were dried (MgSO4) and the solvent was evaporated in
vacuo. The residue was subjected to flash chromatography (silica
gel, hexane/Et2O 7:1) to provide 6a as colorless crystals, yield:
840 mg (81%); mp 85Ð86¡C.
13C NMR and DEPT (100 MHz, CDCl3):
anti-7a: δ = 11.38 (3 CH), 19.18 (6 CH3), 22.19 (CH3), 23.76 (CH),
25.30 (CH2), 30.42 (CH2), 37.22 (CH2), 38.66 (CH2), 42.19 (CH2),
51.90 (CH), 100.32 (C), 170.83 (C=O).
syn-7a: δ = 11.38 (3 CH), 19.18 (6 CH3), 21.27 (CH), 22.19 (CH3),
26.07 (CH2), 33.63 (CH2), 33.89 (CH2), 39.36 (CH2), 41.91 (CH2),
50.59 (CH), 99.73 (C), 170.83 (C=O).
MS (30¡C): m/z (%) = 324 (M+, 0.3), 264 (1), 221 (3), 173 (100),
IR (KBr): ν = 1723 cmÐ1 (C=O)
131 (4).
1H NMR (400 MHz, CDCl3): δ = 1.07Ð1.26 (m, 4H), 1.51 (dt, J =
2.8, 14.0 Hz, 1H), 1.60 (m, 1H), 1.74 (m, 2H), 2.02 (s, 3H), 2.13 (m,
1H), 2.28 (m, 1H), 2.61 (m, 2H), 7.34Ð7.42 (m, 9H), 7.53 (m, 6H).
HRMS: calcd for C19H36O2Si (M+): 324.2485. Found: 324.2493.
1-Acetoxy-8-(triisopropylsilyl)bicyclo[4.3.0]nonane (7b)
13C NMR and DEPT (100 MHz, CDCl3): δ = 22.25 (CH3), 24.42
(CH), 25.09 (CH2), 30.32 (CH2), 36.40 (CH2), 38.40 (CH2), 41.44
(CH2), 51.78 (CH), 100.49 (C), 127.83 (6 CH), 129.43 (3 CH),
134.40 (3 C), 135.94 (6 CH), 170.82 (C=O).
MS (150¡C): m/z (%) = 366 (M+ Ð HOAc, 13), 259 (100), 241 (56),
199 (8), 181 (11).
A solution of 5b (394 mg, 1.22 mmol) in CHCl3 (15 mL) was added
to MCPBA (956 mg, content: 70%; 3.88 mmol of MCPBA) and
NaHCO3 (493 mg, 5.87 mmol). The mixture was stirred at reflux for
4 d, the cold mixture was quenched by addition of sat. aq NaHCO3
(15 mL), and the layers were separated. The aqueous layer was ex-
tracted with CHCl3 (3 × 15 mL), the combined organic layers were
dried (MgSO4), and the solvent was evaporated in vacuo. Flash
chromatography (silica gel, pentane/Et2O 60:1) of the residue af-
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PAPER
Cycloaddition of Allylsilanes, Part 12
149
forded 7b as the less polar fraction (light yellow oil, yield: 95 mg,
23%) and the starting material 5b as the more polar fraction (yield:
122 mg, 31%).
13C NMR and DEPT (100 MHz, CDCl3): δ = 11.34 (3 CH), 19.25
(6 CH3), 25.16 (CH), 28.81 (CH2), 29.33 (2 CH2), 32.33 (2 CH2),
146.67 (2 C).
IR (film): ν = 1733 cmÐ1 (C=O).
MS (25¡C): m/z (%) = 264 (M+, 13), 221 (100), 179 (9), 115 (8),
105 (11), 87 (10), 73 (15), 59 (22).
HRMS: calcd for C17H32Si (M+): 264.2273. Found: 264.2260.
1H NMR (400 MHz, CDCl3): δ = 1.07 (m, 21H), 1.33 (m, 4H),
1.44Ð1.52 (m, 3H), 1.68 (m, 1H), 1.85Ð2.00 (m, 3H), 1.98 (s, 3H),
2.10 (m, 2H), 2.29 (dd, J = 14.0, 8.5 Hz, 1H).
13C NMR and DEPT (100 MHz, CDCl3): δ = 11.16 (3 CH), 18.36
(CH), 19.26 (6 CH3), 22.40 (CH3), 22.61 (CH2), 23.03 (CH2), 28.65
(CH2), 31.47 (CH2), 32.24 (CH2), 37.04 (CH2), 45.24 (CH), 91.01
(C), 170.62 (C=O).
MS (70¡C): m/z (%) = 278 (M+ Ð HOAc, 5), 235 (18), 172 (100),
157 (3).
1-Hydroxy-8-(triphenylsilyl)bicyclo[4.3.0]nonane (10)
By Reduction of 6b with LiAlH4
A solution of 6b (150 mg, 0.340 mmol) in THF (5 mL) was added
slowly to a stirred suspension of LiAlH4 (13 mg, 0.343 mmol) in
THF (5 mL). After 30 min at r.t. the mixture was quenched by ad-
dition of ice (20 g) and 1 M HCl (0.4 mL). The aqueous layer was
extracted with Et2O (3 × 20 mL) and the combined organic layers
were dried (MgSO4). Evaporation of the solvent in vacuo and flash
chromatography (silica gel, hexane/Et2O 2:1) of the residue afford-
ed the carbinol 10 as a colorless oil; yield: 120 mg (89%).
3-(Triphenylsilyl)bicyclo[3.3.0]oct-1(5)-ene (8a)
54% HBF4 in Et2O (0.22 mL, 140 mg, 1.60 mmol of acid) was added
to a solution of 6a (200 mg, 0.469 mmol) in THF (10 mL). The mix-
ture was heated at reflux for 20 h and then quenched by addition of aq
NaHCO3 (6 mL). The layers were separated, the aqueous layer was
extracted with Et2O (3 × 10 mL), and the combined organic layers
were dried (MgSO4). Removing of the solvent in vacuo and flash
chromatography (silica gel, hexane/Et2O 10:1) of the residue provid-
ed 8a as colorless crystals; yield: 150 mg (87%); mp 92Ð93¡C.
IR (drift): ν = 3371 cmÐ1 (OÐH).
1H NMR (400 MHz, CDCl3): δ = 0.17 (m, 1H), 1.04 (m, 2H), 1.22
(m, 2H), 1.45 (m, 3H), 1.65Ð1.84 (m, 4H), 1.94 (m, 1H), 2.42Ð2.50
(m, 1H), 2.60 (tt, J = 11.3, 8.4 Hz, 1H), 7.36Ð7.45 (m, 9H), 7.65 (m,
6H).
13C NMR and DEPT (100 MHz, CDCl3): δ = 17.62 (CH), 23.30
(CH2), 24.53 (CH2), 30.12 (CH2), 32.54 (CH2), 35.54 (CH2), 38.17
(CH2), 46.97 (CH), 81.52 (C), 127.78 (6 CH), 129.40 (3 CH),
134.87 (3 C), 136.04 (6 CH).
MS (105¡C): m/z (%) = 398 (M+, 0.4), 276 (15), 259 (100), 199
(14), 181 (8), 122 (13).
1H NMR (400 MHz, CDCl3): δ = 2.04 (m, 2H), 2.12 (m, 2H), 2.19
(m, 2H), 2.43 (m, 2H), 2.57 (m, 2H), 2.85 (tt, J = 9.9, 7.6 Hz, 1H),
7.32Ð7.42 (m, 9H), 7.53 (m, 6H).
13C NMR and DEPT (100 MHz, CDCl3): δ = 26.07 (CH), 28.65
(CH2), 29.13 (2 CH2), 32.34 (2 CH2), 127.75 (6 CH), 129.26 (3 CH),
135.24 (3 C), 135.85 (6 CH), 146.49 (2 C).
HRMS: calcd for C27H30OSi (M+): 398.2066. Found: 398.2076.
MS (90¡C): m/z (%) = 366 (M+, 2), 288 (40), 259 (100), 183 (7),
181 (10).
By Saponification of 6b with KOH
HRMS: calcd for C26H26Si (M+): 366.1804. Found: 366.1818.
KOH (28 mg, 0.5 mmol) was added to a solution of 6b (200 mg,
0.454 mmol) in EtOH (5 mL)/CH2Cl2 (1 mL) and then heated at re-
flux for 24 h. Additional KOH (28 mg, 0.5 mmol) was added and
the mixture was heated at reflux for further 24 h. The cold mixture
was poured into water (10 mL) and the aqueous layer was extracted
with Et2O (3 × 10 mL). The combined organic layers were dried
(MgSO4) and the solvent was removed in vacuo. Flash chromatog-
raphy (silica gel, hexane/Et2O 2:1) of the residue provided the alco-
hol 10 as a colorless oil; yield: 103 mg (57%), spectral data, see
above.
8-(Triphenylsilyl)bicyclo[4.3.0]non-1(6)-ene (8b)
54% HBF4 in Et2O (72 µL, 46 mg, 0.523 mmol of acid) was added
to a solution of 6b (200 mg, 0.454 mmol) in THF (10 mL) and the
mixture was heated at reflux for 3 h. After cooling to r.t. the mixture
was quenched by addition of aq NaHCO3 (10 mL). The aqueous
layer was extracted with Et2O (3 × 10 mL), the combined organic
layers were dried (MgSO4), and the solvent was removed in vacuo.
Flash chromatography (pentane/Et2O 7:1) of the residue afforded
8b as colorless crystals; yield: 166 mg (96%); mp 89Ð90¡C.
1H NMR (400 MHz, CDCl3): δ = 1.57 (m, 4H), 1.76Ð1.99 (m, 4H),
2.38 (tt, J = 10.1, 7.4 Hz, 1H), 2.53 (m, 2H), 2.71 (m, 2H), 7.35Ð
7.44 (m, 9H), 7.58 (m, 6H).
13C NMR and DEPT (100 MHz, CDCl3): δ = 18.55 (CH), 23.12 (2
CH2), 25.75 (2 CH2), 39.26 (2 CH2), 127.76 (6 CH), 129.26 (3 CH),
134.51 (2 C), 135.36 (3 C), 135.89 (6 CH).
MS (25¡C): m/z (%) = 380 (M+, 3), 303 (16), 302 (57), 260 (27),
259 (100), 224 (5), 183 (22), 182 (10), 181 (15), 120 (11).
HRMS: calcd for C27H28Si (M+): 380.1960. Found: 380.1947.
3-(Triphenylsilyl)-9-oxatricyclo[3.3.1.01,5]nonane (11)
A solution of MCPBA (34 mg, content 70%; 0.138 mmol of
MCPBA) in CH2Cl2 (2 mL) was added to a stirred solution of the
bicyclooctene 8a (50 mg, 0.136 mmol) in CH2Cl2 (1 mL). After a
reaction time of 10 min at r.t. the mixture was quenched by the ad-
dition of aq NaHCO3 (10 mL) and the layers were separated. The
aqueous layer was extracted with CH2Cl2 (3 × 10 mL) and the com-
bined organic layers were dried (MgSO4). Evaporation of the sol-
vent provides 11 as colorless crystals; yield: 49 mg (94%); mp
118¡C.
1H NMR (400 MHz, CDCl3): δ = 1.47 (m, 2H), 1.69 (dd, J = 13.8,
11.1 Hz, 2H), 1.89 (m, 4H), 2.19 (dd, J = 13.8, 7.6 Hz, 2H), 2.60 (tt,
J = 11.1, 7.6 Hz, 1H), 7.35Ð7.45 (m, 9H), 7.54 (m, 6H).
13C NMR and DEPT (100 MHz, CDCl3): δ = 25.65 (CH), 27.52 (2
CH2), 27.84 (CH2), 30.60 (2 CH2), 77.34 (2 C), 127.90 (6 CH),
129.51 (3 CH), 134.45 (3 C), 135.88 (6 CH).
MS (44¡C): m/z (%) = 382 (M+, 4), 278 (90), 259 (100), 201 (78),
199 (38), 181 (14), 154 (50), 149 (36), 123 (10), 111 (16), 109 (12),
97 (25), 95 (17), 85 (20), 83 (32), 81 (14), 71 (25), 69 (25), 57 (39).
3-(Triisopropylsilyl)bicyclo[3.3.0]oct-1(5)-ene (9a)
54% HBF4 in Et2O (0.4 mL, 255 mg, 2.90 mmol of acid) was added
to a solution of 7a (242 mg, 0.746 mmol) in THF (15 mL). The mix-
ture was heated at reflux for 5 d. The mixture was poured into aq
NaHCO3 (20 mL) and the aqueous layer was extracted with Et2O (3
× 20 mL). The combined organic layers were dried (MgSO4) and
the solvent was evaporated. The residue was subjected twice to
flash chromatography (silica gel, 1. pentane/Et2O 20:1; 2. pentane)
to afford 9a as a colorless oil; yield: 89 mg (45%).
HRMS: calcd for C26H26OSi (M+): 382.1753. Found: 382.1777.
1H NMR (400 MHz, CDCl3): δ = 1.03Ð1.18 (m, 21H), 2.12Ð2.36
(m, 11H).
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150
H.-J. Knšlker et al.
PAPER
3-(Triisopropylsilyl)-9-oxatricyclo[3.3.1.01,5]nonane (12)
A solution of 9a (110 mg, 0.416 mmol) in CH2Cl2 (8 mL) was added
to MCPBA (124 mg, content: 70%; 0.503 mmol of MCPBA). After
stirring for 45 min at r.t. the mixture was poured into aq NaHCO3
(10 mL). The aqueous layer was extracted with CH2Cl2 (3 ×
10 mL), the combined organic layers were dried (MgSO4), and the
solvent was evaporated. Flash chromatography (silica gel, pentane/
Et2O 20:1) of the residue provided 12 as a colorless oil; yield: 75 mg
(64%).
1H NMR (400 MHz, CDCl3): δ = 1.04 (m, 21H), 1.52 (m, 2H), 1.64
(m, 2H), 1.80 (m, 1H), 1.85Ð1.98 (m, 6H).
13C NMR and DEPT (100 MHz, CDCl3): δ = 11.34 (3 CH), 19.17
(6 CH3), 24.56 (CH), 27.75 (2 CH2), 27.85 (CH2), 30.63 (2 CH2),
77.29 (2 C).
3-(Triphenylsilyl)cyclononane-1,5-dione (15)
A stream of ozone/oxygen was passed through a solution of 8b
(100 mg, 0.263 mmol) in CH2Cl2 (10 mL) at Ð78¡C until the blue
color of the solution persisted. After purging with N2 the mixture
was warmed to r.t. and poured slowly into a suspension of zinc pow-
der (500 mg, 7.65 mmol) in 50% HOAc (15 mL). This mixture was
heated at reflux for 1 h, the layers were separated, and the aqueous
layer was extracted with Et2O (3 × 20 mL). The combined organic
layers were neutralized by washing with aq NaHCO3 (20 mL) and
the layers were separated. The organic layer was dried (MgSO4) and
the solvent was evaporated in vacuo. Flash chromatography (silica
gel, hexane/EtOAc 2:1) of the residue provided the dione 15 as a
light yellow oil, yield: 50 mg (46%).
IR (drift): ν = 1703 cmÐ1 (C=O).
1H NMR (400 MHz, CDCl3): δ = 1.64Ð1.90 (m, 4H), 1.92Ð2.08 (m,
1H), 2.14Ð2.74 (m, 7H), 2.78Ð2.87 (m, 1H), 7.31Ð7.48 (m, 9H),
7.53Ð7.67 (m, 6H).
13C NMR and DEPT (100 MHz, CDCl3): δ = 19.88 (CH), 23.84 (2
CH2), 40.90 (2 CH2), 43.36 (2 CH2), 128.21 (6 CH), 129.94 (3 CH),
132.79 (3 C), 136.01 (6 CH), 215.33 (2 C=O).
MS (20¡C): m/z (%) = 412 (M+, 0.3), 335 (48), 259 (100), 199 (7),
181 (10).
HRMS: calcd for C27H28O2Si (M+): 412.1859. Found: 412.1865.
MS (20¡C): m/z (%) = 280 (M+, 4), 237 (100), 121 (12), 103 (14),
75 (16), 61 (12), 59 (17).
HRMS: calcd for C17H32OSi (M+): 280.2222. Found: 280.2210.
8-(Triphenylsilyl)-10-oxatricyclo[4.3.1.01,6]decane (13)
A solution of 8b (200 mg, 0.525 mmol) in CH2Cl2 (5 mL) was add-
ed slowly at 0¡C to a vigorously stirred solution of MCPBA
(130 mg, content: 70%; 0.527 mmol of MCPBA) in CH2Cl2 (5 mL).
After warming to r.t. the mixture was stirred for 10 min. The mix-
ture was poured into aq NaHCO3 (10 mL) and the layers were sep-
arated. The aqueous layer was extracted with CH2Cl2 (3 × 10 mL),
the combined organic layers were dried (MgSO4), and the solvent
was evaporated in vacuo to afford 13 as colorless crystals; yield:
208 mg (100%); mp 125¡C.
Acknowledgement
This work was supported by the Deutsche Forschungsgemein-
schaft (Gerhard-Hess award) and the Fonds der Chemischen Indu-
strie.
1H NMR (400 MHz, CDCl3): δ = 1.23 (m, 2H), 1.47 (m, 2H), 1.66
(dd, J = 13.6, 11.4 Hz, 2H), 1.67Ð1.72 (m, 2H), 1.96Ð2.10 (m, 3H),
2.31 (dd, J = 13.6, 7.6 Hz, 2H), 7.38Ð7.47 (m, 9H), 7.59 (m, 6H).
13C NMR and DEPT (100 MHz, CDCl3): δ = 17.13 (CH), 20.30 (2
CH2), 26.49 (2 CH2), 35.02 (2 CH2), 67.15 (2 C), 127.93 (6 CH),
129.51 (3 CH), 134.61 (3 C), 135.94 (6 CH).
MS (70¡C): m/z (%) = 396 (M+, 3), 278 (26), 277 (10), 276 (40),
260 (17), 259 (82), 201 (27), 199 (100), 181 (14), 154 (17), 122
(14), 69 (13), 57 (16).
References
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8-(Triphenylsilyl)bicyclo[4.3.0]nonane (14)
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7.65 (m, 6H).
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13C NMR and DEPT (100 MHz, CDCl3): δ = 20.99 (CH), 23.76 (2
CH2), 28.12 (2 CH2), 32.73 (2 CH2), 40.09 (2 CH), 127.77 (6 CH),
129.32 (3 CH), 135.40 (3 C), 136.15 (6 CH).
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201 (27), 183 (35).
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HRMS: calcd for C27H30Si (M+): 382.2117. Found: 382.2162.
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PAPER
Cycloaddition of Allylsilanes, Part 12
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Synthesis 1999, No. 1, 145–151 ISSN 0039-7881 © Thieme Stuttgart · New York