Stereoselective synthesis of optically active disilanes and selective functionalization by the cleavage of silicon-naphthyl bonds with bromine

Article abstract of DOI:10.1021/jo049398y

Optically active disilanes with one chiral silicon center, (R)-1,2-dimethyl-1-(naphth-1-yl)-1,2,2-triphenyldisilane and (R)-1,2,2 -trimethyl-2-(4-methoxynaphth-1-yl)-1-(naphth-1-yl)-1-phenyldisilane, were obtained by the reaction of (S)-methyl(naphth-1-yl

Full text of DOI:10.1021/jo049398y

Ster eoselective Syn th esis of Op tica lly Active Disila n es a n d
Selective F u n ction a liza tion by th e Clea va ge of Silicon -Na p h th yl
Bon d s w ith Br om in e
Keigo Suzuki, Yusuke Kawakami,* Devadasan Velmurugan,† and Takashi Yamane‡
Graduate School of Materials Science, J apan Advanced Institute of Science & Technology [J AIST],
Asahidai 1-1, Tatsunokuchi, Ishikawa 923-1292, J apan, Department of Crystallography & Biophysics,
University of Madras Guindy Campus, Chennai 600 025 India, and Department of Biotechnology, School
of Engineering, Nagoya University, Furo-cho, Chikusa Nagoya 464-8603, J apan
kawakami@jaist.ac.jp
Received April 11, 2004
Optically active disilanes with one chiral silicon center, (R)-1,2-dimethyl-1-(naphth-1-yl)-1,2,2-
triphenyldisilane and (R)-1,2,2-trimethyl-2-(4-methoxynaphth-1-yl)-1-(naphth-1-yl)-1-phenyldisilane,
were obtained by the reaction of (S)-methyl(naphth-1-yl)phenylchlorosilane (>99% ee) with
methyldiphenylsilyllithium or by the reaction of methyldiphenylchlorosilane with optically active
(S)-methyl(naphth-1-yl)phenylsilyllithium and by the reaction of (S)-methyl(naphth-1-yl)phenyl-
chlorosilane (>99% ee) with dimethyl(4-methoxynaphth-1-yl)silyllithium. Under the optimized
conditions, the reactions proceeded with almost complete inversion for the cholorosilanes and
retention for the silyl anions. Optically active disilanes with two chiral centers, (1R,2R)-1,2-dimethyl-
1,2-di(naphth-1-yl)-1,2-diphenyldisilane and (1S,2S)-1,2-di(4-methoxynaphth-1-yl)-1,2-dimethyl-1,2-
diphenyldisilane, were obtained in high optical purity by the reactions of corresponding optically
active halogenosilanes (Cl or F) with optically active silyllithiums. The silicon-silicon bond and
the silicon-naphthyl bond of (R)-1,1,2-trimethyl-1,2-di(naphth-1-yl)-2-phenyldisilane and (1R,2R)-
1,2-dimethyl-1,2-di(naphth-1-yl)-1,2-diphenyldisilane were cleaved without selectivity on bromi-
nation. The silicon-(4-methoxynaphth-1-yl) bond of (R)-1,2,2-trimethyl-2-(4-methoxynaphth-1-yl)-
1-(naphth-1-yl)-1-phenyldisilane was regiospecifically cleaved, followed by the stereoselective
cleavage of the remaining chiral silicon-naphthyl bond (94% inversion). Although the silicon-(4-
methoxynaphth-1-yl) bonds of (1S,2S)-1,2-di(4-methoxynaphth-1-yl)-1,2-dimethyl-1,2-diphenyld-
isilane (>99% ee) were regioselectively cleaved without silicon-silicon bond scission, remarkable
racemization could not be avoided during the one-pot reaction.
In tr od u ction
related phenomena. Thus, control of conformation of
these polymers is of particular interest to develop many
important applications of the polymers, which is one of
the most challenging tasks.
Functionalized disilanes1 are useful precursors to
polymers composed of the regular alternating arrange-
ment of a disilanylene and a π-electron system (poly-
(disilanylene-π-conjugated systems))2 and also linear
silicon-silicon catenative structures (oligo-3 and polysi-
lanes4 including dendrimers5), which are of considerable
interest because of their unique electrooptical properties
due to the σ-σ conjugation and σ conjugation along the
polymer chain. The electronic structure of these polymers
is easily changed by the change of σ-π and σ conjugation
caused by the conformational change of the mobile
backbone and reflects in the thermochromism6 and
(2) (a) Ishikawa, M.; Matsusaki, K.; Naka, T.; Yokono, H. J . Polym.
Sci. Polym. Lett. Ed. 1984, 22, 669. (b) Ohshita, J .; Matsuguchi A.;
Furumori, K.; Hong, R.; Ishikawa, M.; Yamanaka, T.; Koike, T.; Shioya,
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* To whom correspondence should be addressed. Fax: +81-761-51-
1635.
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Stu¨ger, H. J . Organomet. Chem. 1993, 458. 1. (c) Yatabe, T.; Shimo-
mura, M.; Kaito, A. Chem. Lett. 1996, 551. (d) Obata, K.; Kabuto, C.;
Kira, M. J . Am. Chem. Soc. 1997, 119, 11345. (e) Yatabe, T.; Kaito,
A.; Tanabe, Y. Chem. Lett. 1997, 799. (f) Obata, K.; Kira, M.
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† University of Madras Guindy Campus.
‡ Nagoya University.
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10.1021/jo049398y CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/02/2004
J . Org. Chem. 2004, 69, 5383-5389
5383

Suzuki et al.
SCHEME 1
The conformation of a polymer is principally controlled
by its stereoregularity and optical activity. Optically
active functionalized disilanes with one chiral center or
two chiral centers with C2 symmetry will act as key
intermediates to synthesize stereoregular and/or optically
active silicon-silicon bond-containing polymers, as re-
ported in the case of polysiloxane,7 and the resulting
polymers are expected to exhibit novel unique properties
different from those without controlled stereoregularity.
To realize such systems, it is essential to develop a
selective functionalization of the optically active disilanes
without cleavage of the silicon-silicon bond.
In this article, we report an unambiguous determina-
tion of the absolute configuration of the products formed
upon reaction of achiral chlorosilane with optically active
silyllithium, or of optically active chlorosilane with
achiral silyllithium by using X-ray analysis. We also
report the synthesis of optically active functionalized
disilanes and regio- and stereoselective functionalization
of optically active disilanes by bromination.
Silyllithiums8 are useful reagents for the formation of
silicon-silicon bonds. Although a great number of ster-
eochemical studies have been carried out on substitution
reactions at the chiral silicon center of optically active
halogenosilanes with carbanions (alkyl- and aryllithi-
um),9 stereochemistry with silyl anions has received only
little attention, probably because of the limitation of
synthetically versatile methods to obtain optically active
organosilylmetals.10 Recently, we reported a successful
preparation of configurationally stable naphthyl-substi-
tuted optically active silyllithium,11 which is a powerful
starting material to introduce a chiral silicon center to
silicon-silicon bonds, and the spectral feature of optically
active naphthyl-substituted disilanes having one or two
chiral centers thus obtained was described.12 We also
reported the synthesis of both optically pure stereoiso-
mers of chiral disilanes with one chiral center from a
single antipode of the fluorosilane enantiomer as the
starting material.13
Resu lts a n d Discu ssion
We reported the synthesis and configurational stability
of optically active methyl(naphth-1-yl)phenylsilyllithium
3 in THF at -78 °C prepared by tin-lithium exchange
reaction of optically active methyl(naphth-1-yl)phenyl-
silylstannane derived from (S)-methyl(naphth-1-yl)-
phenylchlorosilane, (S)-2 (<99% ee),14 with methyllithium
in THF at -78 °C.11
The absolute configuration of 3 was determined to be
the (S)-form by the X-ray crystallographic analysis of the
product (R,R)-1,2-dimethyl-1,2-di(naphth-1-yl)-1,2-di-
phenyldisilane (R,R)-4,12(b) obtained by the reaction of 3
with (S)-2 assuming inversion and retention stereochem-
istry of chiral silicon centers of the chlorosilane (S)-2 and
silyllithium (S)-3 in the formation of Si-Sn and Si-Si
bonds, respectively, and retention of the chiral silicon
center in the cleavage of the Si-Sn bond (Scheme 1).
Although these seem reasonable assumptions,10a some
contamination of stereoisomers of 4 formed in the syn-
thesis of (S)-3 and present in the reaction system made
the conclusion a little obscure.
To exclude such uncertainty, the stereochemistry of the
reaction of (S)-2 (>99% ee) with an achiral methyldi-
phenylsilyllithium (product is 5a ) and that of an achiral
methyldiphenylchlorosilane with optically active silyl-
lithium 3 (90% ee) (product is 5b) were investigated
(Scheme 2).
Compound 5 was characterized as 1,2-dimethyl-1-
(naphth-1-yl)-1,2,2-triphenyldisilane, and the configura-
tion of 5a and 5b was proven to be the same by HPLC
on an optically active stationary phase. The absolute
configuration was determined as the (R)-form by X-ray
analysis (see Figure 1 in Supporting Information).
The enantiomeric excess (ee) of 5a is 99% and that of
5b is 90% by HPLC, respectively. This clearly indicates
the complete inversion of the chlorosilane and retention
of the silyllithium at chiral silicon centers in the substi-
(4) For reviews, see: (a) Miller, R. D.; Michl, J . Chem. Rev. 1989,
89, 1359. (b) J ones, R. G.; Ando, W.; Chojnowski, J . Silicon-Containing
Polymers; Kluwer Academic Publishers: Norwell, MA, 2000; Section
3. (c) Michl, J .; West, R. Acc. Chem. Res. 2000, 33, 821. (d) Fujiki, M.
Macromol. Rapid Commun. 2001, 22, 539. (e) Fujiki, M.; Koe, J . R.;
Terao, K.; Sato, T.; Teramoto, A.; Watanabe, J . Polym. J . 2003, 35,
297.
(5) (a) Lambert, J . B.; Pflug, J . L.; Stern, C. L. Angew. Chem., Int.
Ed. Engl. 1995, 34, 98. (b) Suzuki, H.; Kimata, Y.; Satoh, S.; Kuriyama,
A. Chem. Lett. 1995, 293. (c) Sekiguchi, A.; Nanjo, M.; Kabuto, C.;
Sakurai, H. J . Am. Chem. Soc. 1995, 117, 4195.
(6) Bukalov, S. S.; Leites, L. A.; West, R. Macromolecules 2001, 34,
6003 and references therein.
(7) (a) Oishi, M.; Kawakami, Y. Macromolecules 2000, 33, 1960. (b)
Oishi, M.; Moon, J .-Y.; J anvikul, W.; Kawakami, Y. Polym. Int. 2001,
50, 135.
(8) For recent reviews on silyl anion, see: (a) Kawachi, A.; Tamao,
K. Adv. Orgnomet. Chem. 1995, 38, 1. (b) Lickiss, P. D.; Smith, C. M.
Coord. Chem. Rev. 1995, 145, 75. (c) Sekiguchi, A.; Lee, V. Y.; Nanjo,
M. Coord. Chem. Rev. 2000, 210, 11. (d) Belzner, J .; Dehnert, U. In
The Chemistry of Organic Silicon Compounds; Apeloig, Y., Rappoport,
Z., Eds.; J ohn Wiley & Sons: Chichester, 1998; Vol. 2, Chapter 14, p
779.
(9) For the excellent reviews on reaction mechanism of the nucleo-
philic substitution reaction at silicon, see: (a) Corriu, R. J . P.; Guerin,
C.; Moreau, J . J . E. Dynamic Stereochemistry at Silicon. In The
Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z.,
Eds., Wiley: Chichester, U.K., 1989; Vol. 1, Chapter 4, p 305. (b) Brook,
M. A. Silicon in Organic, Organometallic, and Polymer Chemistry;
Wiley: New York, 2000; Part 1,
p 115. (c) Sommer, L. H. In
Stereochemistry, Mechanism and Silicon; McGraw-Hill: New York,
1965.
(10) (a) Sommer, L. H.; Mason, R. J . Am. Chem. Soc. 1965, 87, 1619.
(b) Colomer, E.; Corriu, R. J . P. J . Chem. Soc., Chem. Commun. 1976,
176. (c) Colomer, E.; Corriu, R. J . P. J . Organomet. Chem. 1977, 133.
159. (d) Stromann, C.; Ho¨rnig, J .; Auer, D. Chem. Commun. 2002, 766.
(11) Omote, M.; Tokita, T.; Shimizu, Y.; Imae, I.; Shirakawa, E.;
Kawakami, Y. J . Organomet. Chem. 2000, 611, 20.
(12) (a) Oh, H. S.; Imae, I.; Kawakami, Y. Chirality 2003, 15, 231.
(b) Oh, H. S.; Imae, I.; Kawakami, Y.; Raj, S. S.; Tamane, T. J .
Organomet. Chem. 2003, 685, 35.
(14) (a) Sommer. L. H.; Frye, C. L.; Parker, G. A.; Michael, K. W. J .
Am. Chem. Soc. 1964, 20, 3271. (b) Sommer, L. H. Angew. Chem., Int.
Ed. Engl. 1962, 1, 143. (c) Ashida, T.; Pepinsky, R.; Okaya, Y. Acta
Crystallogr. 1963, 16, A48. (d) Okaya, Y. Ashida, T. Acta Crystallogr.
1996, 20, 461.
(13) Suzuki, K.; Kawakami, Y. Organometallics 2003, 22, 2367.
5384 J . Org. Chem., Vol. 69, No. 16, 2004

Optically Active Disilanes
SCHEME 2
SCHEME 3
TABLE 1. Nu cleop h ilic Su bstitu tion Rea ction of
Op tica lly Active Ha logen osila n es 2X w ith Ach ir a l
Silyllith iu m u n d er Va r iou s Con d ition s
tution reactions, the same as the inversion stereochem-
istry of chlorosilane by alkyllithium.9c
To use thus produced optically active disilanes as
starting materials for further synthesis of stereoregular
polymers containing a disilane constitutional unit, stereo-
selective functionalization of the disilane is needed. One
of the typical ways to functionalize oraganosilicon com-
pounds is to introduce Br, Cl, and CF3SO3 (TfO) by the
electrophilic cleavage reaction of the silicon-aromatic
bonds. Unfortunately, when optically active (R)-1,2,2-
trimethyl-1,2-di(naphth-1-yl)-1-phenyldisilane or (1R,2R)-
1,2-dimethyl-1,2-di(naphth-1-yl)-1,2-diphenyldisilane (1R,
2R)-4 was treated with bromine, indiscriminate cleavage
of silicon-naphthyl and silicon-silicon bonds15 occurred.
This result is similar to that by Sommer.16 Selectivity of
the cleavage of the silicon-naphthyl bond over the
silicon-silicon bond must be given. Cleavage by TfOH
gave completely racemized products at room tempera-
ture.
Kumada17 and Stolberg18 reported that the cleavage
of a silicon-silicon bond having an electron-withdrawing
substituent by halogen was remarkably slow. If we could
selectively cleave the silicon-naphthyl bond by bromine
by enhancing the reactivity of the silicon-naphthyl bond,
we should be able to suppress the following cleavage of
the silicon-silicon bond by the effect of the introduced
bromo group on the silicon atom. Meanwhile, we reported
that stereoselectivity (92% inversion, 84.5% optical purity
of the product)19 of the cleavage of the silicon-naphthyl
bond of (R)-(+)-[(+)-menthoxy]methyl(naphth-1-yl)-
phenylsilane by bromine in CHCl3 at -64 °C can be
improved (96% inversion, 91.3% optical purity of the
product)20 by the introduction of methoxy group at
4-position of naphthyl group.
entry
X
temp (°C) solvent yield (%)b stereoselectivity (%)c
1
2
3
4
5
6
7
8
Cl
rt
rt
rt
-78
-78
-78
rt
rt
rt
-78
-78
-78
rt
THF
Et2O
pentane
THF
Et2O
pentane
THF
Et2O
pentane
THF
Et2O
pentane
THF
Et2O
pentane
THF
Et2O
52
46
40
44
49
45
40
48
35
38
39
37
37
39
39
44
40
36
racemization
77 (inversion)
79 (inversion)
89 (inversion)
96 (inversion)
99 (inversion)
racemization
racemization
72 (inversion)
racemization
89 (inversion)
90 (inversion)
80 (retention)
84 (retention)
81 (retention)
93 (inversion)
93 (inversion)
97 (inversion)
Br
F
9
10
11
12
13
14
15
16
17
18
rt
rt
-78
-78
-78
pentane
a
Solution of 2X in each solvent (0.2 M, 2.5 mL) was added to
b
the achiral silyllithium in THF (0.12 M, 5 mL). Based on the
achiral silyllithium. c Absolute configuration of 6 was determined
by HPLC using a Daicel OD column.
chlorosilane with (S)-3 (94% ee) in THF at -78 °C, by
adding a THF solution of the chlorosilane to (S)-3, gave
(R)-1,2,2-trimethyl-2-(4-methoxynaphth-1-yl)-1-(naphth-
1-yl)-1-phenyldisilane (R)-6 with 93% ee in 49% yield as
a highly viscous colorless oil, indicating that the reaction
proceeded in >99% retention of the silyl anion center
(Scheme 3).
The reactions of (S)-chloro-, (S)-bromo-, or (R)-fluoro-
[methyl(naphth-1-yl)phenyl]silane (2x; X ) Cl, Br, F,
>99% ee)14 with 1,1-dimethyl(4-methoxynaphth-1-yl)-
silyllithium prepared in the same manner as for (S)-3
were also carried out (Table 1).
To synthesize optically active disilane with one chiral
center, a methoxy group was introduced into dimethyl-
(naphth-1-yl)chlorosilane or dimethyl(naphth-1-yl)silyl-
lithium. Reaction of dimethyl(4-methoxynaphth-1-yl)-
It was found that racemization of (S)-2x (X ) Cl and
Br) could be suppressed by decreasing the polarity of the
solvent of (S)-2x or by lowering the reaction temperature.
Stereoselectivity with chlorosilane was higher than that
with bromosilane, and (R)-6 with 99% ee could be
obtained in 45% yield for a pentane solution of (S)-2Cl
(entry 6). Fluorosilane (R)-2F generally gave higher
stereoselectivity at both room temperature and -78 °C
(entries 13-18). The fact that the same configuration of
6 was derived from (S)-2x (X ) Cl and Br) and (R)-2F at
(15) (a) Gilman, H.; Ingham, R. K.; Smith, A. G. J . Org. Chem. 1953,
18, 1743. (b) Kumada, M.; Shiina, K.; Yamaguchi, M. Kogyo Kagaku
Zasshi 1954, 57, 230.
(16) Sommer, L. H.; Posbrough. K. T. J . Am. Chem. Soc. 1969, 91,
7067.
(17) Takeda, A.; Kumada, M.; Karama, K. Nippon Kagaku Zasshi
1957, 78, 999.
(18) (a) Stolberg, U. G. Chem. Ber. 1963, 96, 2798. (b) Stolberg, U.
G. Angew. Chem. 1963, 75, 206.
(19) Kawakami, Y.; Takahashi, T.; Yada, Y.; Imae, I. Polym. J . 1998,
30, 1001.
(20) Oishi, M.; Kawakami, Y. Org. Lett. 1999, 1, 549.
J . Org. Chem, Vol. 69, No. 16, 2004 5385

Suzuki et al.
SCHEME 4
SCHEME 5. Regio- a n d Ster eoselective Clea va ge
of Silicon -Na p h th yl Bon d s of (R)-6 by Br om in e
room temperature and the opposite configuration of 6
arose from (R)-2F at -78 °C, evidenced by HPLC,
indicates that the reaction of fluorosilane with the
silyllithium proceeded with inversion of configuration of
the chiral halogen silicon center at -78 °C and retention
of configuration at room temperature.13
To get optically active functionalized disilane having
two chiral centers (C2-symmetric structure), we at-
tempted to introduce a methoxy group into the optically
active halogenosilane component. However, optically
active (4-methoxynaphth-1-yl)-substituted chlorosilane is
not easily accessible because of the cleavage of the
silicon-(4-methoxynaphth-1-yl) bond in the chlorination
step of (S)-methyl(4-methoxynaphth-1-yl)phenylsilane
((S); >99% ee) by chlorine gas. (R)-Fluoro(4-methoxy-
naphth-1-yl)methylphenylsilane (R)-7 (>99% ee), ob-
tained from (S)-(-)-[(-)-menthoxy](4-methoxynaphth-1-
yl)methylphenylsilane (>99% ee)20 with boron trifluoride/
ether complex (BF3‚Et2O) in toluene at 50 °C for 7 days,
was used to synthesize optically active (R)-(4-methox-
ynaphth-1-yl)methylphenylsilyllithium (R)-8 (96% ee)21
by conversion to (S)-(4-methoxynaphth-1-yl)methyl-
phenylsilylstannane (96% ee)22 followed by the tin-
lithium exchange reaction with methyllithium (Scheme
4).
The reaction between (R)-7 (>99% ee) and (R)-8 (96%
ee) could give optically pure disilane with a methoxy-
naphthyl group on both silicon atoms, (S,S)-1,2-di(4-
methoxynaphth-1-yl)-1,2-dimethyl-1,2-diphenyldisilane
(S,S)-9 ((S,S); > 99% ee), after purification by recrystal-
lization from pentane at 0 °C to remove meso-9 as a
solid.23
Functionalization of methoxynaphthyl-substituted di-
silane by bromine was studied. Contrary to the indis-
criminate cleavage seen for (R)-1,2,2-trimethyl-1,2-di-
(naphth-1-yl)-1-phenyldisilane and (1R,2R)-4, the optically
active 1,2-di(naphth-1-yl)-substituted disilanes, the reac-
tion of (R)-6, having one methoxynaphthyl group, with 2
equiv of bromine in CHCl3 at -64 °C gave (R)-1,2-
dibromo-1,2,2-trimethyl-1-phenyldisilane (R)-11 as the
major product, evidenced by HPLC as the reduced
hydorosilane14(a) 1,2,2-trimethyl-1-phenyldisialne 1224 by
LiAlH4 (Scheme 5).
Stepwise addition of 1 equiv of bromine to 6 gave
2-bromo-1,2,2-trimethyl-1-(naphth-1-yl)-1-phenyldisi-
lane 10 as the only product by the selective cleavage of
the silicon-methoxynaphthyl bond. Addition of another
1 equiv of bromine to 10 gave 11 as the major product.
Electrophilic attack on the naphthyl group by bromo
cation was preferentially enhanced over the attack on the
silicon-silicon bond by the introduction of methoxy group
as electron-donating substituent at the 4-position of the
naphthyl group. The attack of bromo anion on the silicon
atom linked to the methoxynaphthyl group20,25 led to the
selective elimination of the methoxynaphthyl group from
6 to give 10 by the first 1 equiv of bromine. Once
monobromodisilane 10 was produced, the electron-
withdrawing bromo group introduced on one silicon atom
of the disilane suppressed the cleavage of the silicon-
silicon bond, and the remaining silicon-naphthyl bond
was selectively cleaved to give 11. The regioselective
cleavage reaction of the silicon-naphthyl bonds of (R)-6
((R); 95% ee) afforded (R)-11 in 68% yield with 84% ee
(21) Configuration of 8 (96% ee) was stable at -78 °C for at least 3
h. Absolute configuration of 8 was determined as (R)-form after
hydrolysis to hydrosilane (retention) by the comparison of its HPLC
with (R)-(4-methoxynaphth-1-yl)methylphenylsialne prepared by the
reduction of (S)-(-)-[(-)-menthoxy](4-methoxynaphth-1-yl)methylsial-
ne with LiAlH4 (retention).14a The fact indicated the inversion stere-
ochemistry of fluorosilane (R)-7 with stanyllithium in THF.
(22) Optically pure (R)-MeONpMePhSiSnMe3 (96% ee) was obtained
as a colorless viscous oil by the reaction of (R)-7 (>99% ee) with Me3-
SnLi in THF and recrystallization from pentane at -78 °C to remove
rac-MeONpMePhSiSnMe3. Although stereochemistry crossover from
inversion to retention of configuration in the substitution reaction of
optically active fluorosilane with achiral silyllithium was observed by
changing temperature, solvents, and additives,13 stereochemistry of
the reaction of (R)-7 with the stanyllithium was not affected by these
factors and proceeded with 85% inversion of configuration.
(23) The stereoisomer ratio of 9 was found to be (S,S):(S,R):(R,R) )
72:28:0 by 1H NMR and HPLC based on the inversion and retention
stereochemistry of the chiral silicon centers of attacked fluorosilane
and attacking silyllithium at -78 °C, respectively. Stereoselectivity
in this reaction was low, probably because the stereoisomer 9 was
produced by the reaction between remaining optically active silylstan-
nane and produced (R)-8.
(24) (a) Corey, J . Y.; Zhu, X.-H.; Bedard, T. C.; Lange, L. D.
Organometallics 1991, 10, 924. (b) Corey, J . Y.; Zhu, X.-H. Organo-
metallics 1992, 11, 672. (c) Corey, J . Y.; Kraichely, D. M.; Huhmann,
J . L.; Braddock-Wilking, J .; Lindeberg, A. Organometallics 1995, 14,
2704. (d) Rosenberg, L.; Davis, C. W.; Yao, J . J . Am. Chem. Soc. 2001,
123, 5120.
(25) Eaborn, C.; Steward, O. W. Proc. Chem. Soc. 1963, 59.
5386 J . Org. Chem., Vol. 69, No. 16, 2004

Optically Active Disilanes
TABLE 2. F u n ction a liza tion of (R)-6 by Va r iou s
active silyllithium was elucidated as inversion and reten-
tion for attacked and attacking chiral silicon, respectively,
by X-ray crystallographic analysis. Optically active bis-
(naphth-1-yl)-substituted disilanes having one or two
chiral silicon centers were successfully synthesized by the
substitution reactions from the combination of optically
active halogenosilanes and silyllithiums. Stepwise cleav-
age of the silicon-naphthyl bonds of the disilaneby
bromine proceeded regio- and stereoselectively for the
disilane with a 4-methoxy group on one naphthyl group
by the suppression of the cleavage of the silicon-silicon
bond. Although regioselectivity could be controlled, the
stereochemistry of the cleavage of bis(4-methoxynaphth-
1-yl)-substituted disilane could not be controlled.
Electr op h ilic Rea gen ts
electrophilic temp % ee
% ee
(R)-12
stereoselectivity
(%)a
entry
reagent
(°C) (R)-6
1
2
3
4
5
6
Br2
ICl
IBr
-64
-64
-64
-64
0
95
96
92
99
78
99
84
77
64
racemic
racemic
94 (inversion)
90 (inversion)
85 (inversion)
racemization
racemization
TfOH
TfOH
b
Cl2
0
a
The absolute configuration of 12 was determined by HPLC
b
Exp er im en ta l Section
using a Daicel OD column. This reaction was carried out in CCl4.
(R)-1,2-Dim et h yl-1-(n a p h t h -1-yl)-1,2,2-t r ip h en yld isi-
la n e (R)-5 fr om MeP h 2SiLi a n d (S)-2. Methyldiphenylsi-
lyllithium was prepared by adding methyldiphenylchlorosilane
(0.7 g, 3 mmol) dropwise to a lithium dispersion (0.1 g, 15
mmol) in dry THF (6 mL). The solution was stirred at room
temperature for 2 h and filtered in an argon atmosphere. To
this solution was added dropwise during 10 min at -78 °C
(S)-methyl(naphth-1-yl)phenylchlorosilane (S)-2Cl in pentane
(6 mL), prepared by the chlorination of (R)-methyl(naphth-1-
yl)phenylsilane (0.745 g, 3 mmol, >99% ee) in CCl4 (6 mL) with
chlorine gas at 0 °C, and following removal of the solvent and
excess chlorine gas the mixture was stirred at the temperature
for 30 min. The resulting solution was poured into 1 N HCl
solution, extracted with Et2O, and dried over anhydrous
MgSO4. Evaporation of the solvent gave a solid as crude
product. The crude product was purified by column chroma-
tography on silica gel with hexane/ethyl acetate (40/1) as
eluent (Rf ) 0.29) to give (R)-5 as a colorless solid (0.18 g, 14%
yield). The enantiomeric excess of (R)-5 was determined as 99%
ee by HPLC analysis: (R)-(+)-5 retention time (tR) ) 28.2 min;
(S)-(-)-5 tR ) 31.3 min. Recrystallization of (R)-5 (> 99% ee)
with pentane at room temperature afforded (R)-5 as a crystal
SCHEME 6
estimated by HPLC after reduction with LiAlH4. Thus,
the stereochemistry of the cleavage reaction of the
silicon-naphthyl bond by bromine is evaluated as a 94%
inversion process (Table 2, entry 1).
Other electrophilic reagents were also investigated as
summarized in Table 2. Iodine monochloride and bromine
monochloride could give the product under the same
condition, but the stereoselectivity was lower than that
by bromine. Trific acid gave the racemic products under
the same or even milder condition. Chlorine gas afforded
a mixture of products through the indiscriminate cleav-
age reaction of the silicon-silicon and silicon-naphthyl
bonds.
Functionalization of optical pure 9 ((S,S); > 99% ee)
with 2 equiv bromine under the same reaction condition
of 6 gave only the desired 1,2-dimethyl-1,2-diphenyldisi-
lane 13 after the reduction with LiAlH4 (Scheme 6).
This cleavage reaction is also regiospecific for the
silicon-methoxynaphthyl bond over the silicon-silicon
bond. However, remarkable racemization in this reaction
was observed even with 1 equiv of bromine. Contrary to
the cleavage of (R)-6 by bromine, where stepwise reaction
seemd to occur and good stereoselectivity was attained,
the cleavage of (S,S)-9 may proceed under the influence
of two equivalent oxygen atoms on each naphthyl group
complexing with bromo cation, and the stereoselection
has been changed. Further improvement of the stereo-
chemistry is still needed by studying the reaction condi-
tions to obtain stereospecificity, for instance, the synthe-
sis starting from (1S,2S)-1-(4-methoxynaphth-1-yl)-2-
(naphth-1-yl)-1,2-dimethyl-1,2-diphenyldisilane, which is
considered to proceed in a stepwise manner.
suitable for X-ray analysis. Mp 115 °C. [R]24 ) +15.23 (c )
D
1
1.05, cyclohexane). H NMR δ 0.68 (s, 3H, -SiPh2CH3), 0.797
(s, 3H, -SiNpPhCH3), 7.07-7.103 (m, 1H, aromatic), 7.21-
7.24 (m, 6H, aromatic), 7.27-7.39 (m, 11H, aromatic), 7.68-
7.71 (m, 2H, aromatic), 7.81 (d, J ) 8.2 Hz, 1H, aromatic),
7.85 (d, J ) 8.2 Hz, 1H, aromatic). 13C NMR δ -3.61, -2.54,
125.13, 125.38, 125.40, 127.78 (overlapped), 127.81, 128.74,
128.79, 128.89, 128.90, 129.35, 130.12, 133.44, 134.69, 135.10,
135.26, 135.30, 136.13, 136.69, 136.71, 137.14, 137.32. 29Si
NMR δ -21.15, -22.26. Anal. Calcd for C30H28Si2: C, 81.02;
H, 6.35. Found: C, 81.00; H, 6.49.
(R)-5 fr om MeP h 2SiCl a n d (S)-3. (R)-Methyl(naphth-1-
yl)phenylsilyltrimethylstannane (0.19 g, 0.5 mmol, 90% ee) in
THF (2.5 mL) was added to a solution of methyllithium (0.6
mL as 1.04 M Et2O solution, 0.64 mmol) in THF (1.25 mL) at
-78 °C during 10 min, and the mixture was stirred for 20 min.
To the resulting solution of (S)-3 was added methyldiphenyl-
chlorosilane (0.12 g, 0.52 mmol) in THF (2.5 mL) during 10
min. The reaction mixture was stirred at -78 °C for 30 min,
and the resulting mixture was poured into 1 N HCl, extracted
with Et2O, and dried over anhydrous MgSO4. Similar workup
and purification as the procedure above gave (R)-5 (0.072 g,
32% yield, 90% ee) as a colorless solid. The compound gave
reasonable analytical data.
(R)-1,2,2-Tr im eth yl-2-(4-m eth oxyn aph th -1-yl)-1-(n aph th -
1-yl)-1-p h en yld isila n e (R)-6 fr om MeONp Me2SiCl a n d
(S)-3. To a solution of (S)-3, prepared from (R)-methyl(1-
naphthyl)phenylsilyltrimethylstannane (0.4 g, 0.98 mmol, 93%
ee) in THF (20 mL), was added dimethyl(4-methoxynaphth-
1-yl)chlorosilane (0.76 g, 3.0 mmol) in THF (20 mL). The
resulting solution was poured into a 1 N HCl solution,
Con clu sion
The stereochemistry of the nucleophilic substitution
reaction of optically active halogenosilane by optically
J . Org. Chem, Vol. 69, No. 16, 2004 5387

Suzuki et al.
extracted with Et2O, dried over anhydrous MgSO4, and puri-
fied by silica gel column chromatography with hexane/toluene
Racemic (4-methoxynaphth-1-yl)methylphenylsilylstananne
was prepared in the same way.
) 10:1- 10:2 to give 0.22 g (49%) of a highly viscous oil. [R
D
(S,S)-1,2-Dim et h yl-1,2-d i(4-m et h oxyn a p h t h -1-yl)-1,2-
diph en yldisialn e (S,S)-9. To (R)-8 from (S)-(4-methoxynaphth-
1-yl)methylphenylsilylstananne (1.3 g, 2.95 mmol, 96% ee) was
slowly added (R)-7 (0.87 g, 2.95 mmol, >99% ee) in THF (15
mL) at -78 °C, and the reaction system was stirred for 30
min at the temperature. Decomposition with 1 N HCl, extrac-
tion with Et2O, concentration, and addition of hexane led to
the precipitation of meso-9 as a colorless solid at 0 °C. The
crude product from the solution was purified by column
chromatography (hexane/ethyl acetate ) 40/1, Rf ) 0.22) to
give (S,S)-9 (0.70 g, 43%, (S,S); >99% ee) as a colorless solid.
25
]
) +13.99 (c ) 1.0, cyclohexane). 1H NMR δ 0.51 (s, 3H,
NpOMeSiMe), 0.59 (s, 3H, NpOMeSiMe), 0.74 (s, 3H, NpSiMe),
4.00 (s, 3H, NpOMe), 6.76-6.77 (d, J ) 7.8 Hz, 1H), 6.99-
7.02 (m, 1H), 7.13-7.16 (m, 1H), 7.27-7.45 (m, 8H), 7.56-
7.57 (d, J ) 7.8 Hz, 1H), 7.59-7.61 (m, 2H), 7.80-7.83 (t, J )
7.8 Hz, 3H), and 8.22-8.24 (d, J ) 8.2 Hz, 1H). 13C NMR δ
-2.32, -1.04, -0.96, 55.38, 103.44, 122.22, 124.66, 125.20
(overlapped), 125.32, 125.63, 127.81, 128.42, 128.62 (over-
lapped), 128.70, 129.26, 129.81, 133.35, 133.81, 134.42, 135.08,
135.29, 135.40, 137.19, 137.97, 138.03, 156.68. 29Si NMR δ
-20.85 (overlapped). Anal. Calcd for C30H30OSi2: C, 77.87;
6.53. Found: C, 77.23; H, 6.66.
[R ]27 ) -9.689 (c ) 1.01, cyclohexane). (S, S)-(-)-9 tR ) 100
D
min, (R, R)-(+)-9 tR ) 146 min. 1H NMR δ 0.79 (s, 6H,
(-SiCH3)2), 3.98 (s, 6H, (-NpOCH3)2), 6.67 (d, J ) 7.8 Hz, 2H,
aromatic), 7.02-7.05 (m, 2H, aromatic), 7.17-7.24 (m, 4H,
aromatic), 7.30-7.36 (m, 6H, aromatic), 7.47 (s, 2H, aromatic).
7.66 (d, 2H, J ) 8.7 Hz, aromatic), 7.67 (d, 2H, J ) 7.8 Hz,
aromatic), 8.25 (d, J ) 8.2 Hz, 2H, aromatic). 13C NMR δ
-2.399 (SiCH3, S, S), 55.37, 103.400, 122.28, 124.74, 125.45,
125.84, 125.92, 127.71, 128.61, 128.98, 135.27, 137.15, 137.84,
138.13, 157.04. 29Si NMR δ -20.29. Anal. Calcd for C36H34O2-
Si2: C, 77.93; H, 6.18. Found: C, 77.44; H, 6.20.
(R)-6 fr om MeONp Me2SiLi a n d 2X (X ) Cl, Br , (S)-for m ;
X ) F , (R)-for m ). To (4-methoxynaphth-1-yl)dimethysilyl-
lithium, prepared from dimethyl(4-methoxynaphth-1-yl)silyl-
trimethylstannane (0.19 g, 0.5 mmol) and methyllithium (0.6
mL as 1.04 M Et2O solution, 0.62 mmol) in THF at -78 °C
was slowly added 2X (0.5 mmol, X ) Cl, Br, F, >99% ee) in
pentane (2.5 mL) at the designated temperature during 30
min, and the mixture was stirred for 60 min. Similar workup
as above gave the product, which gave reasonable analytical
data.
Addition of hexane (10 mL) to diastereo-9 from rac-(4-
methoxynaphth-1-yl)methylphenylsilylstananne (0.62 g, 1.41
mmol) and rac-7 (0.42 g, 1.42 mmol) at room temperature led
to the precipitation of meso-9 as a white solid (0.25 g, 0.45
mmol, 32%). Further addition of hexane (10 mL) to the residue
at 0 °C gave dl-9 as colorless solid (0.14 g, 0.26 mmol, 18%).
meso-9: 1H NMR δ 0.83 (s, 6H, (-SiCH3)2), 3.98 (s, 6H,
(-NpOCH3)2), 6.70 (d, J ) 7.8 Hz, 2H, aromatic), 7.05-7.09
(m, 2H, aromatic), 7.17-7.20 (m, 4H, aromatic), 7.28-7.37 (m,
6H, aromatic), 7.47 (s, 2H, aromatic), 7.69 (d, 2H, J ) 7.8 Hz,
aromatic), 7.71 (d, 2H, J ) 8.2 Hz, aromatic), 8.29 (d, J ) 8.2
Hz, 2H, aromatic). 13C NMR δ -2.002 (SiCH3, meso), 55.37,
103.42, 122.299, 124.73, 125.202, 125.859, 125.91, 127.62,
128.56, 129.04, 135.19, 137.103, 137.93, 138.16, 157.06. 29Si
NMR δ -20.55. Anal. Calcd for C36H34O2Si2: C, 77.93; H, 6.18.
Found: C, 77.51; H, 6.20. dl-9: Analytical data are basically
the same as those for (S,S)-9.
(R )-F lu or o(4-m e t h oxyn a p h t h -1-yl)m e t h ylp h e n ylsi-
la n e (R)-7. To a solution of (S)-(-)-[(-)-menthoxy](4-methox-
ynaphth-1yl)methylphenylsilane (>99% ee)20 (11.7 g, 27 mmol,
>99% de) in toluene (60 mL) was added freshly distilled BF3‚
Et2O (7.8 g, 55 mmol) at room temperature, and the mixture
was heated at 50 °C for 7 days. After the removal the solvent
and excess BF3‚Et2O under reduced pressure, the residue was
distilled (0.18 Torr, 130-140 °C) to give the mixture of (-)-
menthol and 7. Recrystallization of the mixture from pentane
at -78 °C gave 7 as a colorless crystal. Further recrystalliza-
tion of 7 in pentane at 0 °C for several times gave 1.16 g (>99%
ee, 13%) and 1.84 g (80% ee, 25%) of 7 as colorless crystal.
The absolute configuration was determined as the (R)-form
by the comparison of its HPLC profile with (S)- and (R)-fluoro-
(naphth-1-yl)methylphenylsilane.14a (S)-(+)-7 tR ) 90.0 min;
(R)-(-)-7 tR ) 107 min. [R ]27D ) 12.25 (c ) 0.97, cyclohexane).
1H NMR δ 0.85 (d, J ) 7.4 Hz, 3H, -SiCH3), 4.03 (s, 3H,
-NpOCH3), 6.85 (d, J ) 7.8 Hz, 1H, aromatic), 7.36-7.40 (m,
2H, aromatic), 7.42-7.50 (m, 3H, aromatic), 7.61-7.65 (m, 2H,
aromatic), 7.72 (d, J ) 7.8 Hz, 1H, aromatic), 7.94-7.98 (m,
1H, aromatic), 8.32-8.35 (m, 1H, aromatic). 13C NMR δ -1.25
(d, J ) 17.3 Hz), 55.48, 103.15, 122.62, 123.18 (d, J ) 15.4
Hz), 125.17, 125.72, 126.92, 127.83, 128.04, 130.44, 134.00,
135.35 (d, J ) 17.3 Hz), 135.74 (d, J ) 3.8 Hz), 137.72. 29Si
NMR δ 10.47 (d, J ) 280.0 Hz). Anal. Calcd for C18H17OSiF:
C, 72.94; H, 5.78. Found: C, 72.77; H, 5.824.
Clea va ge of (R)-6 by Br om in e a n d Su ccessive Red u c-
tion to (R)-1,2,2-Tr im eth yl-1-p h en yld isila n e (R)-12. Bro-
mine (1.0 mL, 0.49 M CHCl3 solution) was added dropwise to
(R)-6 (0.234 g, 0.5 mmol, (R); 95% ee) in CHCl3 (5 mL) for 10
min, and the mixture was stirred at -64 °C for 60 min.
Formation of (R)-1,2-dibromo-1,1,2-trimethyl-2-phenyldisilane
was evidenced as (R)-1,1,2-trimethyl-2-phenyldisilane (R)-1224
after the reduction with LiAlH4 (0.04 g, 1.1 mmol) in Et2O (5
mL) at 0 °C. The crude products, after the solution was
filtrated and concentrated, were separated by preparative
HPLC with hexane to afford (R)-6 (0.061 g, 68%, 84% ee). (R)-
1
(S)-(4-Meth oxyn a p h th -1-yl)m eth ylp h en ylsilyltr im eth -
ylsta n a n n e. This compound was synthesized similarly to (4-
methoxynaphth-1-yl)dimethylsilylstannnane from (R)-7 (1.0 g,
3.4 mmol, >99%ee). After evaporation of volatile materials,
hexane was added, and the mixture was vigorously stirred at
0 °C to make rac-silylstannane precipitate as a colorless
powder. After hexane was removed, the residue was purified
by column chromatography over silica gel with hexane/ethyl
acetate (80/1) as eluent (Rf ) 0.38) to give (S)-7 as a viscous
(-)-12 tR ) 13.05 min, (S)-(+)-12 tR ) 14.32 min. H NMR δ
0.20, 0.22 (two d, 6H, HSiMe2, J SiHCH ) 4.5 Hz), 0.47 (d, 3H,
PhHSiMe, J SiHCH ) 4.6 Hz), 3.87 (d septet, 1H, Me2SiH, J SiHCH
) 4.5 Hz, J SiHSiH ) 2.2 Hz), 4.32 (dq, 1H, MePhSiH, J SiHCH
)
4.6 Hz, J SiHSiH ) 2.2 Hz), 7.21-7.72 (m, 5H, aromatic). 13C
NMR δ -7.47, -6.13, 127.73, 127.81, 128.70, 134.60. EI-MS
(m/e) 180 (M+), 165 ([M - CH3]+), 135 ([M - 3CH3]+), 121
([MePhSi]+).
Clea va ge of (S,S)-9 by Br om in e. (S,S)-9 (0.277 g, 0.5
mmol, (S,S); >99% ee) at -64 °C for 20 min was similarly
treated with bromine (2.2 mL, 0.46 M CHCl3 solution). The
product was identified as reduced product, 1,2-dimethyl-1,2-
diphenyldisilane. 1H NMR δ 0.43 (d, 6H, SiMe, J CHSiH ) 4.7
Hz), 4.41 (q, 2H, SiH, J ) 4.7 Hz), 7.20-7.70 (m, 10H,
aromatic). 13C NMR δ -7.65, -7.44, 127.94, 128.98, 134.73,
134.85. EI-MS (m/e) 242 (M+), 197 ([M - 3CH3]+), 121
([MePhSi]+), 105 ([SiPh]+).
colorless oil (0.92 g, 62%, (S); >96.4% ee). [R ]27 ) -28.13 (c
D
) 1.21, cyclohexane). (R)-(+) tR ) 28.2 min, (S)-(-) tR ) 31.3
min. 1H NMR δ 0.089 (s, 9H, -Sn(CH3)3), 0.849 (s, 3H,
-SiCH3), 4.02 (s, 3H, -NpOCH3), 6.82 (d, J ) 7.8 Hz, 1H,
aromatic), 7.295-7.49 (m, 7H, aromatic), 7.579 (d, J ) 7.8 Hz,
1H, aromatic), 7.81 (d, 1H, J ) 8.2 Hz, aromatic), 8.316 (d, J
) 7.8 Hz, 1H, aromatic). 13C NMR δ -10.84, -1.49, 55.15,
103.26, 122.37, 124.69, 125.41, 125.55, 126.01, 127.703, 127.949,
128.48, 134.46, 135.16, 137.62, 138.519, 156.91. 29Si NMR δ
X-r a y Str u ctu r e Deter m in a tion of (R)-5. A single crystal
was obtained by recrystallization from hexane. Measurement
was made by Rigaku RAXIS-RAPID Imaging Plate, T ) 296
-7.19. Anal. Calcd for
Found: C, 57.11; H, 5.97.
C21H26OSiSn: C, 57.17; H, 5.94.
5388 J . Org. Chem., Vol. 69, No. 16, 2004

Optically Active Disilanes
K. The structure was solved by direct methods (SIR92)26 and
expanded using Fourier techniques (DIRDIF99):27 4630 reflec-
tions measured with 2θ in the range 6.3-143.5, 4606 unique
reflections; 3218 with I > 3σ(I); refinement by full matrix least-
squares methods; anisotropic thermal parameters for all non-H
atoms in the final cycles; H atoms were refined on a riding
model in their ideal geometric positions; Flack parameter
-0.00(3); R ) 0.034, and wR ) 0.037. All calculations were
performed using the CrystalStructure28,29 crystallographic
software package.
a ) 10.015(2), b ) 14.070(2), c ) 17.975(3) Å, V ) 2532.8(7)
Å3, orthorhombic, space group P212121 (No. 19), Z ) 4, µ(Cu
KR) ) 13.67 cm-1, λ ) 1.54187 Å.
Ad d it ion a l Cr yst a llogr a p h ic Da t a . CCDC 233409
contains supplementary crystallographic data for this
paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif,
by
emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, U.K.; fax +44 1223 336033.
Cr yst a llogr a p h ic Da t a for (R)-5. (R)-1,2-dimethyl-2-
(naphth-1-yl)-1,1,2-triphenyldisilane: C30H28Si2, M ) 444.72,
Su p p or tin g In for m a tion Ava ila ble: Crystal data, struc-
ture solution and refinement, atomic coordinates, bond lengths
and angles, anisotropic thermal parameters for (R)-5, and an
X-ray crystallographic file in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
(26) Altomare, A., Cascarano, G., Giacovazzo, C., Guagliardi, A.,
Burla, M., Polidori, G., and Camalli, M. J . Appl. Crystallogr. 1994,
27, 435.
(27) Beurskens, P. T., Admiraal, G., Beurskens, G., Bosman, W. P.,
de Gelder, R., Israel, R.; Smits, J . M. M. The DIRDIF-99 Program
System, Technical Report of the Crystallography Laboratory; Univer-
sity of Nijmegen: The Netherlands 1999.
J O049398Y
(28) CrystalStructure 3.6.0, Crystal Structure Analysis Package;
Rigaku and Rigaku/MSC (2000-2004), 9009 New Trails Dr., The
Woodlands, TX 77381.
(29) CRYSTALS, Issue 10; Watkin, D. J ., Prout, C. K. Carruthers,
J . R., Betteridge, P. W.; Chemical Crystallography Laboratory: Oxford,
U.K., 1996.
J . Org. Chem, Vol. 69, No. 16, 2004 5389