Development of a new building block for the synthesis of silicon-based drugs and odorants: Alternative synthesis of the retinoid agonist disila-bexarotene

Article abstract of DOI:10.1021/om700570f

With 4,4,5,5-tetramethyl-2-(3,5,5,8,8-pentamethyl-5,8-disila-5,6,7,8- tetrahydro-2-naphthyl)-1,3,2-dioxaborolane (5) a new building block for the synthesis of biologically active 5,8-disila-5,6,7,8-tetrahydronaphthalene derivatives has been made available. The high synthetic potential of 5 has been demonstrated by the development of a new synthesis of the retinoid agonist disila-bexarotene (1).

Full text of DOI:10.1021/om700570f

Organometallics 2007, 26, 4835-4838
4835
Notes
Development of a New Building Block for the Synthesis of
Silicon-Based Drugs and Odorants: Alternative Synthesis of the
Retinoid Agonist Disila-bexarotene
Matthias W. Bu¨ttner, Jennifer B. Na¨tscher, Christian Burschka, and Reinhold Tacke*
UniVersita¨t Wu¨rzburg, Institut fu¨r Anorganische Chemie, Am Hubland, D-97074 Wu¨rzburg, Germany
ReceiVed June 12, 2007
Summary: With 4,4,5,5-tetramethyl-2-(3,5,5,8,8-pentamethyl-5,8-
disila-5,6,7,8-tetrahydro-2-naphthyl)-1,3,2-dioxaborolane (5) a
new building block for the synthesis of biologically actiVe 5,8-
disila-5,6,7,8-tetrahydronaphthalene deriVatiVes has been made
aVailable. The high synthetic potential of 5 has been demon-
strated by the deVelopment of a new synthesis of the retinoid
agonist disila-bexarotene (1).
Introduction
Disila-substitution of the 5,6,7,8-tetrahydronaphthalene skel-
eton (f5,8-disila-5,6,7,8-tetrahydronaphthalene) has been dem-
onstrated to be a very useful approach for the development of
novel silicon-based drugs and odorants.1 The retinoid agonists
disila-bexarotene1d (1) and disila-TTNPB1h (2), the musky
odorant disila-versalide1f (3), and the ambergris odorant disila-
okoumal1g (4) are examples of this principle.
The synthesis of such compounds is not trivial. The 5,8-disila-
5,6,7,8-tetrahydronaphthalene skeleton can be built up by using
[2+2+2] cycloadditions of the silicon-containing diyne 1,2-
bis(ethynyldimethylsilyl)ethane and appropriately functionalized
monoynes in the presence of CpCo(CO)2 or Co2(CO)8. However,
in all cases studied so far the yields were very poor, and the
workup and product isolation were difficult and tedious.1
Recently, we have reported on a new catalytic system (CoI2/
Zn in acetonitrile) for such [2+2+2] cycloadditions that can
overcome these problems.2 Using this particular method, we
have succeeded in preparing a novel and versatile building block,
the 2-(5,8-disila-5,6,7,8-tetrahydro-2-naphthyl)-1,3,2-dioxaboro-
lane 5, that can be used for the synthesis of various biologically
active 5,8-disila-5,6,7,8-tetrahydronaphthalene derivatives. This
approach has been applied to an alternative synthesis of disila-
bexarotene (1) and to the synthesis of the 5,8-disila-5,6,7,8-
tetrahydronaphth-2-ol 6, which can also serve as a precursor in
the synthesis of related biologically active silicon compounds.
We report here on the syntheses and crystal structure analyses
of 5 and 6 and a new synthesis of disila-bexarotene (1).
Results and Discussion
Compounds 1, 5, and 6 were synthesized according to Scheme
1. Disila-bexarotene (1) was prepared in a multistep synthesis,
starting from the 1,3,2-dioxaborolane 7. Thus, treatment of 7
with propyn-1-yllithium provided the 2-alkynyl-1,3,2-diox-
aborolane 8 (89% yield),3 which was allowed to react with the
silicon-containing diyne 9 in the presence of CoI2/Zn to afford
the 2-(5,8-disila-5,6,7,8-tetrahydro-2-naphthyl)-1,3,2-dioxaboro-
lane 5 in 48% yield (in this context, see also ref 4). Compound
5 was then treated with the triflate 10,5 in the presence of
(PPh3)2PdCl2,6 to provide the disila-bexarotene precursor 11
(86% yield), which upon treatment with potassium hydroxide
in methanol/water and subsequent acidification with hydrochlo-
* To whom correspondence should be addressed. Phone: +49-931-888-
5250. Fax: +49-931-888-4609. E-mail: r.tacke@mail.uni-wuerzburg.de.
(1) (a) Montana, J. G.; Fleming, I.; Tacke, R.; Daiss, J. (Inventors)
(Amedis Pharmaceuticals Ltd.) PCT Int. Pat. Appl. WO 2004/045625 A1,
June 3, 2004. (b) Montana, J. G.; Showell, G. A.; Fleming, I.; Tacke, R.;
Daiss, J. (Inventors) (Amedis Pharmaceuticals Ltd.) PCT Int. Pat. Appl.
WO 2004/048390 A1, June 10, 2004. (c) Montana, J. G.; Showell, G. A.;
Tacke, R. (Inventors) (Amedis Pharmaceuticals Ltd.) PCT Int. Pat. Appl.
WO 2004/048391 A1, June 10, 2004. (d) Daiss, J. O.; Burschka, C.; Mills,
J. S.; Montana, J. G.; Showell, G. A.; Fleming, I.; Gaudon, C.; Ivanova,
D.; Gronemeyer, H.; Tacke, R. Organometallics 2005, 24, 3192-3199. (e)
Miller, D. J.; Showell, G. A.; Conroy, R.; Daiss, J.; Tacke, R.; Tebbe, D.
(Inventors) (Amedis Pharmaceuticals Ltd.) PCT Int. Pat. Appl. WO 2005/
005443 A1, January 20, 2005. (f) Bu¨ttner, M. W.; Penka, M.; Doszczak,
L.; Kraft, P.; Tacke, R. Organometallics 2007, 26, 1295-1298. (g) Bu¨ttner,
M. W.; Burschka, C.; Junold, K.; Kraft, P.; Tacke, R. ChemBioChem 2007,
in press. (h) Bu¨ttner, M. W.; Burschka, C.; Daiss, J. O.; Ivanova, D.; Rochel,
N.; Kammerer, S.; Peluso-Iltis, C.; Bindler, A.; Gaudon, C.; Germain, P.;
Moras, D.; Gronemeyer, H.; Tacke, R. ChemBioChem 2007, in press.
(2) Doszczak, L.; Fey, P.; Tacke, R. Synlett 2007, 5, 753-756.
(3) Compound 8 has already been reported in the literature, but to the
best of our knowledge, a detailed procedure for its synthesis is missing.
Concerning the NMR and physical data of 8, see also: Hansen, E. C.; Lee,
D. J. Am. Chem. Soc. 2005, 127, 3252-3253 (Supporting Information).
(4) Gandon, V.; Leca, D.; Aechtner T.; Vollhardt, K. P. C.; Malacria,
M.; Aubert, C. Org. Lett. 2004, 6, 3405-3407.
(5) Qing, F.-L.; Fan, J.; Sun, H.-B.; Yue, X.-J. J. Chem. Soc., Perkin
Trans. 1 1997, 3053-3057.
(6) (a) Chemler, S. R.; Trauner, D.; Danishefsky, S. J. Angew. Chem.
2001, 113, 4676-4701; Angew. Chem., Int. Ed. 2001, 40, 4544-4568. (b)
Occhiato, E. G.; Trabocchi, A.; Guarna, A. J. Org. Chem. 2001, 66, 2459-
2465.
10.1021/om700570f CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/16/2007

4836 Organometallics, Vol. 26, No. 19, 2007
Notes
Scheme 1
Table 1. Crystal Data and Experimental Parameters for the
Crystal Structure Analyses of 5 and 6
ric acid afforded disila-bexarotene (1) in 96% yield. Compound
6 was prepared in 62% yield by treatment of 5 with hydrogen
peroxide in the presence of sodium hydroxide and water.
Compounds 1, 5, 6, and 11 were isolated as colorless
crystalline solids, whereas 8 was obtained as a colorless liquid.
The identities of these compounds were established by elemental
analyses (C, H) and NMR studies (1H, 11B, 13C, 29Si), and 5
and 6 were additionally characterized by crystal structure
analyses. The crystal data and experimental parameters used
for these studies are given in Table 1. The molecular structures
of 5 and 6 are depicted in Figures 1 and 2 (for further details
concerning the crystal structure analyses, see the Supporting
Information).
In summary, with compound 5 a new building block for the
synthesis of biologically active 5,8-disila-5,6,7,8-tetrahydronaph-
thalene derivatives has been made available. The high synthetic
potential of 5 has been demonstrated by the development of a
new synthesis of the retinoid agonist disila-bexarotene (1), which
is much more advantageous compared to the original synthesis
5
6
empirical formula
formula mass, g mol-1
collection T, K
λ(Mo KR), Å
cryst syst
space group (No.)
a, Å
C19H33BO2Si2
360.44
C13H22OSi2
250.49
193(2)
173(2)
0.71073
0.71073
triclinic
P1h (2)
monoclinic
P21/c (14)
15.5982(19)
13.2100(15)
11.1157(12)
90
9.2211(18)
10.489(2)
16.445(3)
92.22(3)
102.27(3)
100.55(3)
1522.9(5)
4
b, Å
c, Å
R, deg
â, deg
108.847(12)
90
γ, deg
V, Å3
2167.6(4)
4
Z
D(calcd), g cm-3
µ, mm-1
1.104
1.093
0.172
0.214
F(000)
784
544
cryst dimens, mm
2θ range, deg
index ranges
0.5 × 0.5 × 0.4
6.16-55.90
-20 e h e 20,
-17 e k e 17,
-14 e l e 14
24 408
0.3 × 0.3 × 0.1
4.54-56.00
-12 e h e 12,
-13 e k e 13,
-21 e l e 21
22 192
no. of collected reflns
no. of indep reflns
Rint
5141
6771
0.0695
0.0400
no. of reflns used
no. of params
5141
226
1.038
6771
301
1.027
Sa
weight params a/bb
R1c [I > 2σ(I)]
wR2d (all data)
max./min. residual electron
density, e Å-3
0.0510/0.7449
0.0498
0.1072
+0.344/-0.195
0.0564/0.5354
0.0413
0.1132
+0.546/-0.587
2
2
a S ) {∑[w(Fo - Fc )2]/(n - p)}0.5; n ) no. of reflections; p ) no. of
parameters. w-1 ) σ2(Fo ) + (aP)2 + bP, with P ) [max(Fo ,0) + 2Fc ]/
b
2
2
2
3. R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo )2]}0.5
.
c
d
2
2
2
Figure 2. Molecular structures of the two crystallographically
independent molecules in the crystal of 6 (probability level of
displacement ellipsoids 50%).
Figure 1. Molecular structure of 5 in the crystal (probability level
of displacement ellipsoids 50%).

Notes
Organometallics, Vol. 26, No. 19, 2007 4837
reported in the literature.1d As shown with the synthesis of 6,
compound 5 may additionally serve as a building block for the
synthesis of biologically active 5,8-disila-5,6,7,8-tetrahydronaph-
thalene derivatives with OR (R ) organyl) substituents at the
carbon atom C-2.
NMR (C6D6): δ -1.5 (2 C, SiCH3), -1.3 (2 C, SiCH3), 8.0
(SiCH2C), 8.2 (SiCH2C), 22.8 (CCH3), 24.9 (4 C, C(CH3)2), 83.3
(2 C, C(CH3)2), 135.3 (C-1, Naph), 141.2 (C-3, Naph), 142.0 (C-
4, Naph), 144.8 (C-4a, Naph), 149.2 (C-8a, Naph), BC not detected.
29Si NMR (C6D6): δ -7.1, -7.4. 11B NMR (C6D6): δ 31.3. Anal.
Calcd for C19H33BO2Si2: C, 63.31; H, 9.23. Found: C, 63.2; H,
9.1.
Experimental Section
Preparation of 3,5,5,8,8-Pentamethyl-5,8-disila-5,6,7,8-tet-
rahydronaphth-2-ol (6). A 30% solution of hydrogen peroxide in
water (D, 1.11 g cm-1; 1.14 mL, 11.2 mmol of H2O2) was added
dropwise over a period of 3 min to a stirred mixture of 5 (400 mg,
1.11 mmol), sodium hydroxide (1.25 g, 31.3 mmol), water (13 mL),
and THF (16 mL). The reaction mixture was stirred for 15 min at
20 °C, and diethyl ether (24 mL) and water (24 mL) were added.
The organic layer was separated, the aqueous layer was extracted
with diethyl ether (4 × 25 mL), and the organic extracts were
combined and dried over anhydrous sodium sulfate. The solvent
was removed under reduced pressure, and the residue was dried in
vacuo (0.001 mbar, 20 °C, 2 h) to give a yellow oil, which was
crystallized from n-hexane (3 mL; crystallization at -20 °C over
a period of 8 days), followed by recrystallization from n-hexane,
to afford 6 in 62% yield as a colorless crystalline solid (173 mg,
691 µmol); mp 138-139 °C. 1H NMR (CD2Cl2): δ 0.186 (s, 6 H,
SiCH3), 0.190 (s, 6 H, SiCH3), 0.96 (s, 4 H, SiCH2C), 2.22-2.25
(m, 3 H, CCH3), 4.6 (br s, 1 H, OH), 6.86-6.89 (m, 1 H, H-1,
Naph), 7.22-7.24 (m, 1 H, H-4, Naph). 13C NMR (CD2Cl2): δ
-1.5 (2 C, SiCH3), -1.3 (2 C, SiCH3), 7.5 (SiCH2C), 7.7 (SiCH2C),
15.6 (CCH3), 119.6 (C-1, Naph), 124.1 (C-3, Naph), 136.7 (C-4,
Naph), 136.9 (C-4a, Naph), 145.2 (C-8a, Naph), 154.0 (C-2, Naph).
29Si NMR (CD2Cl2): δ -6.9, -7.5. Anal. Calcd for C13H22OSi2:
C, 62.34; H, 8.85. Found: C, 62.2; H, 8.6.
General Procedures. All syntheses were carried out under dry
nitrogen. The organic solvents used were dried and purified
according to standard procedures and stored under dry nitrogen.
Melting points were determined with a Bu¨chi Melting Point B-540
1
apparatus using samples in sealed glass capillaries. The H, 11B,
13C, and 29Si NMR spectra were recorded at 23 °C on a Bruker
DRX-300 NMR spectrometer (1H, 300.1 MHz; 11B, 96.3 MHz;
13C, 75.5 MHz; 29Si, 59.6 MHz). C6D6 or CD2Cl2 was used as
the solvent. Chemical shifts were determined relative to internal
C6HD5 (1H, δ 7.28; C6D6), internal C6D6 (13C, δ 128.0; C6D6),
internal CHDCl2 (1H, δ 5.32; CD2Cl2), internal CD2Cl2 (13C, δ 53.8;
CD2Cl2), external TMS (29Si, δ 0; C6D6, CD2Cl2), or external BF3‚
OEt2 (11B, δ 0; C6D6). Assignment of the 1H NMR data was
supported by 1H,1H gradient-selected COSY, 13C,1H gradient-
selected HMQC and gradient-selected HMBC, and 29Si,1H gradient-
2
selected HMQC experiments (optimized for JSiH ) 7 Hz).
Assignment of the 13C NMR data was supported by DEPT 135
2
and the aforementioned 13C,1H correlation experiments. The JHH
coupling constant reported for the CdCH2 group of 11 represents
an absolute value.
Preparation of 4-[1-(3,5,5,8,8-Pentamethyl-5,8-disila-5,6,7,8-
tetrahydro-2-naphthyl)ethenyl]benzoic Acid (Disila-bexarotene,
1). This compound was synthesized from 11 according to ref 1d
(96% yield).
Preparation of 4,4,5,5-Tetramethyl-2-propyloxy-1,3,2-dioxa-
borolane (7). This compound was synthesized according to
ref 7.
Preparation of 4,4,5,5-Tetramethyl-2-(3,5,5,8,8-pentamethyl-
5,8-disila-5,6,7,8-tetrahydro-2-naphthyl)-1,3,2-dioxaborolane (5).
Iodine (17.0 mg, 134 µmol) was added to a stirred suspension of
zinc (40.0 mg, 612 µmol) in acetonitrile (10 mL), and the mixture
was heated for 1 min until the yellow color disappeared. Compound
8 (1.66 g, 10.0 mmol) and a 0.1 M solution of cobalt(II) iodide in
acetonitrile (1.25 mL, 125 µmol of CoI2) were added sequentially,
each in a single portion, and after warming of the resulting mixture
to 50 °C, compound 9 (972 mg, 5.00 mmol) was added within 5
min. The reaction mixture was stirred for 15 min at 50 °C and
then for 30 min at 20 °C. After addition of sodium carbonate (100
mg, 943 µmol), the resulting mixture was applied to the top of a
pad of silica gel in a glass frit (frit dimensions, 5 × 6 cm; silica
gel (63-200 µm, 60 g), and the product was washed out of the
residue with diethyl ether/n-hexane (4:1 (v/v), 100 mL). The wash
solutions were combined, the solvent was removed under reduced
pressure, triethylamine (1 mL) was added to the residue, and the
resulting mixture was purified by column chromatography on silica
gel (column dimensions, 35 × 3 cm; silica gel (32-63 µm), 180
g; eluent, n-hexane/ethyl acetate (96:4 (v/v))). The relevant fractions
(GC control) were combined, activated carbon (150 mg) was added,
and the suspension was heated under reflux for 30 min. The hot
mixture was applied to the top of a pad of silica gel in a glass frit
(frit dimensions, 5 × 6 cm; silica gel (63-200 µm), 60 g), and the
product was washed out of the residue with n-hexane/ethyl acetate
(96:4 (v/v), 150 mL). The total volume of the solution was reduced
in vacuo to 2 mL, and the product crystallized from this mixture
(crystallization at 20 °C over a period of 2 h). The product was
then recrystallized from n-pentane (5 mL; crystallization at 20 °C
over a period of 24 h) to afford 5 in 48% yield as a colorless
crystalline solid (865 mg, 2.40 mmol); mp 133-134 °C. 1H NMR
(C6D6): δ 0.36 (s, 6 H, SiCH3), 0.38 (s, 6 H, SiCH3), 1.13 (s, 4 H,
SiCH2C), 1.23 (s, 12 H, C(CH3)2), 2.87-2.89 (m, 3 H, CCH3),
7.57-7.61 (m, 1 H, H-4, Naph (Naph ) 5,5,8,8-tetramethyl-5,8-
Preparation of 4,4,5,5-Tetramethyl-2-prop-1-ynyl-1,3,2-di-
oxaborolane (8). A 2.5 M solution of n-butyllithium in hexanes
(80 mL, 200 mmol of n-BuLi) was added dropwise at -75 °C
within 30 min to a stirred solution of propyne (9.05 g, 226 mmol)
in diethyl ether (250 mL), and the resulting suspension was stirred
for 1.5 h at -75 °C. A solution of 7 (37.2 g, 200 mmol) in diethyl
ether (150 mL) was added dropwise to the reaction mixture within
1 h, and the suspension was then allowed to warm to 20 °C within
4 h and was stirred for 16 h. A 2.0 M solution of hydrogen chloride
in diethyl ether (100 mL, 200 mmol of HCl) was added dropwise
to the stirred reaction mixture at 0 °C within 45 min, and the
resulting mixture was then stirred for 30 min at 0 °C and for a
further 1.5 h at 20 °C. The precipitate was filtered off and washed
with n-hexane (2 × 50 mL), the organic solutions were combined,
and the solvent was removed under reduced pressure. The resulting
residue was purified by fractional distillation to give 8 in 89% yield
as a colorless liquid (29.6 g, 178 mmol); bp 66-68 °C/5 mbar. 1H
NMR (C6D6): δ 1.12 (s, 12 H, C(CH3)2), 1.51 (s, 3 H, CCH3). 13
C
NMR (C6D6): δ 4.0 (CCH3), 24.6 (C(CH3)2), 82.5 (C(CH3)2),
BC not detected. 11B NMR (C6D6): δ 23.5. Anal. Calcd for
C9H15BO2: C, 65.11; H, 9.11. Found: C, 64.8; H, 9.3.
Preparation of 1,2-Bis(ethynyldimethylsilyl)ethane (9). This
compound was synthesized according to ref 1d.
Preparation of Methyl 4-[1-(Trifluoromethylsulfonyloxy)-
ethenyl]benzoate (10). This compound was synthesized according
to ref 5.
Preparation of Methyl 4-[1-(3,5,5,8,8-Pentamethyl-5,8-disila-
5,6,7,8-tetrahydro-2-naphthyl)ethenyl]benzoate (11). (Ph3P)2PdCl2
(48.6 mg, 69.2 µmol), 5 (600 mg, 1.66 mmol), and a 2 M solution
of sodium carbonate in water (4.80 mL, 9.60 mmol of Na2CO3)
were added one after another to a stirred solution of 10 (430 mg,
1.39 mmol) in THF (16 mL). The mixture was stirred for 2 h at 20
°C, while its color changed from colorless to red. Additional 10
disila-5,6,7,8-tetrahydro-2-naphthyl)), 8.58 (s, 1 H, H-1, Naph). 13
C

4838 Organometallics, Vol. 26, No. 19, 2007
Notes
(200 mg, 645 µmol) was added, and the reaction mixture was stirred
for 3 h at 20 °C. Water (20 mL) was added, the aqueous layer was
separated and extracted with diethyl ether (3 × 20 mL), and the
combined organic solutions were dried over anhydrous sodium
sulfate. The solvent was removed under reduced pressure, and the
residue was dried in vacuo (0.001 mbar, 20 °C, 1 h) and then
purified by column chromatography on silica gel (column dimen-
sions, 70 × 5 cm; silica gel (32-63 µm), 400 g; eluent, n-hexane/
ethyl acetate (97:3 (v/v))). The relevant fractions (GC control) were
combined, and the solvent was removed under reduced pressure.
The residue was redissolved in boiling n-hexane (2 mL), and the
product was crystallized (slow cooling to 0 °C and crystallization
at this temperature over a period of 2 h) to afford 11 in 86% yield
as a colorless crystalline solid (560 mg, 1.42 mmol); mp 129-130
transferred to the cold nitrogen gas stream of the diffractometer
(Stoe IPDS; graphite-monochromated Mo KR radiation (λ )
0.71073 Å)). The structures were solved by direct methods.8 All
non-hydrogen atoms were refined anisotropically.9 A riding model
was employed in the refinement of the CH hydrogen atoms. The
OH hydrogen atoms were localized in difference Fourier syntheses
and refined freely.
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Centre as supplementary publication
nos. CCDC-653122 (5) and CCDC-653123 (6). Copies of the data
can be obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: (+44)1223/336033; e-
mail: depositqccdc.cam.ac.uk).
1
°C. H NMR (CD2Cl2): δ 0.22 (s, 6 H, SiCH3), 0.25 (s, 6 H,
Supporting Information Available: Tables of atomic coordi-
nates and equivalent isotropic displacement parameters, anisotropic
displacement parameters, experimental details of the X-ray dif-
fraction studies, and bond lengths and angles for 5 and 6. This
material is available free of charge via the Internet at http://pubs.acs.
org.
SiCH3), 1.04 (s, 4 H, SiCH2C), 1.98-2.00 (m, 3 H, CCH3), 3.88
2
(s, 3 H, C(O)OCH3), 5.31 (d, JHH ) 1.2 Hz, 1 H, CdCHAHX),
2
5.87 (d, JHH ) 1.2 Hz, 1 H, CdCHAHX), 7.30-7.38 (m, 4 H,
H-3/H-5, Phe (Phe ) 1-(methoxycarbonyl)phenyl), H-1/H-4, Naph),
7.92-7.97 (m, 2 H, H-2/H-6, Phe). 13C NMR (CD2Cl2): δ -1.42
(2 C, SiCH3), -1.40 (2 C, SiCH3), 7.86 (SiCH2C), 7.89 (SiCH2C),
20.2 (CCH3), 52.3 (C(O)OCH3), 117.2 (CdCH2), 126.8 (C-3/C-5,
Phe), 129.6 (C-1, Phe), 129.9 (C-2/C-6, Phe), 135.1 (C-1, Naph),
135.7 (C-4, Naph), 136.0 (C-3, Naph), 141.1 (C-2, Naph), 143.3
(C-4a, Naph), 145.4 (C-4, Phe), 145.7 (C-8a, Naph), 149.4 (Cd
CH2), 167.0 (C(O)OCH3). 29Si NMR (CD2Cl2): δ -7.1, -7.0. Anal.
Calcd for C23H30O2Si2: C, 70.00; H, 7.66. Found: C, 70.0; H, 7.5.
Crystal Structure Analyses. The crystals were mounted in inert
oil (perfluoroalkyl ether, ABCR) on a glass fiber and then
OM700570F
(7) Andersen, M. W.; Hildebrandt, B.; Ko¨ster, G.; Hoffman, R. W. Chem.
Ber. 1989, 122, 1777-1782.
(8) (a) Sheldrick, G. M. SHELXS-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997. (b) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46,
467-473.
(9) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.