Asymmetric hydrosilylation of styrenes catalyzed by palladium-MOP complexes: Ligand modification and mechanistic studies

Article abstract of DOI:10.1021/jo001614p

In the palladium-catalyzed asymmetric hydrosilylation of styrene (3a) with trichlorosilane, several chiral monophosphine ligands, (R)-2-diarylphosphino-1,1′-binaphthyls (2a-g), were examined for their enantioselectivity. The highest enantioselectivity was observed in the reaction with (R)-2-bis[3,5-bis(trifluoromethyl)phenyl]phosphino-1, 1′-binaphthyl (2g), which gave (S)-1-phenylethanol (5a) of 98% ee after oxidation of the hydrosilylation product, 1-phenyl-1-(trichlorosilyl)ethane (4a). The palladium complex of 2g also efficiently catalyzed the asymmetric hydrosilylation of substituted styrenes on the phenyl ring or at the β position to give the corresponding chiral benzylic alcohols of over 96% ee. Deuterium-labeling studies on the hydrosilylation of regiospecifically deuterated styrene revealed that β-hydrogen elimination from 1-phenylethyl(silyl)palladium intermediate is very fast compared with reductive elimination giving hydrosilylation product when ligand 2g is used. The reaction of o-allylstyrene (9) with trichlorosilane catalyzed by (R)-2g/Pd gave (1S,2R)-1-methyl-2-(trichlorosilylmethyl)indan (10) (91% ee) and (S)-1-(2-(propenyl)phenyl)-1-trichlorosilylethanes (11a and 11b) (95% ee). On the basis of their opposite configurations at the benzylic position, a rationale for the high enantioselectivity of ligand 2g is proposed.

Full text of DOI:10.1021/jo001614p

J . Org. Chem. 2001, 66, 1441-1449
1441
Asym m etr ic Hyd r osilyla tion of Styr en es Ca ta lyzed by
P a lla d iu m -MOP Com p lexes: Liga n d Mod ifica tion a n d
Mech a n istic Stu d ies
Tamio Hayashi,* Seiji Hirate, Kenji Kitayama, Hayato Tsuji, Akira Torii, and
Yasuhiro Uozumi†
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, J apan
thayashi@kuchem.kyoto-u.ac.jp
Received November 13, 2000
In the palladium-catalyzed asymmetric hydrosilylation of styrene (3a ) with trichlorosilane, several
chiral monophosphine ligands, (R)-2-diarylphosphino-1,1′-binaphthyls (2a -g), were examined for
their enantioselectivity. The highest enantioselectivity was observed in the reaction with (R)-2-
bis[3,5-bis(trifluoromethyl)phenyl]phosphino-1,1′-binaphthyl (2g), which gave (S)-1-phenylethanol
(5a ) of 98% ee after oxidation of the hydrosilylation product, 1-phenyl-1-(trichlorosilyl)ethane (4a ).
The palladium complex of 2g also efficiently catalyzed the asymmetric hydrosilylation of substituted
styrenes on the phenyl ring or at the â position to give the corresponding chiral benzylic alcohols
of over 96% ee. Deuterium-labeling studies on the hydrosilylation of regiospecifically deuterated
styrene revealed that â-hydrogen elimination from 1-phenylethyl(silyl)palladium intermediate is
very fast compared with reductive elimination giving hydrosilylation product when ligand 2g is
used. The reaction of o-allylstyrene (9) with trichlorosilane catalyzed by (R)-2g/Pd gave (1S,2R)-
1-methyl-2-(trichlorosilylmethyl)indan (10) (91% ee) and (S)-1-(2-(propenyl)phenyl)-1-trichlorosi-
lylethanes (11a and 11b) (95% ee). On the basis of their opposite configurations at the benzylic
position, a rationale for the high enantioselectivity of ligand 2g is proposed.
In tr od u ction
lylation of simple terminal alkenes such as 1-octene2,5
with trichlorosilane and that of cyclic alkenes such as
norbornene6 giving the corresponding secondary alkyl
alcohols of over 90% enantioselectivity. Recently, we
found that MeO-MOP is not as effective for the asym-
metric hydrosilylation of styrene derivatives as for that
of simple terminal alkenes or cyclic alkenes.7 We modified
the MOP ligands by replacement of the methoxy group
at the 2′-position by other substituents and found that
2-diphenylphosphino-1,1′-binaphthyl (H-MOP (2a )) is
much more enantioselective than MeO-MOP for the
reaction of styrene derivatives.8,9 However, unfortunately,
the enantioselectivity was still not high enough, espe-
cially for the styrene derivatives containing electron-
donating groups on the phenyl ring. Thus, for example,
hydrosilylation of 4-methylstyrene and 4-methoxystyrene
with trichlorosilane in the presence of palladium catalyst
coordinated with H-MOP gave 1-(4-methylphenyl)ethanol
of 89% ee and 1-(4-methoxyphenyl)ethanol of 61% ee,
respectively, while the reaction of styrene gave 1-phen-
ylethanol of 93% ee.8 We have further modified H-MOP
ligand on the diphenylphosphino group and found that
Catalytic asymmetric hydrosilylation of alkenes has
been recognized to be one of the most useful methods for
the asymmetric transformation of prochiral alkenes into
optically active alcohols.1 We have previously reported
the preparation of a series of enantiomerically pure
monophosphine ligands, whose chirality is due to 1,1′-
binaphthyl axial chirality,2,3 and their use as chiral
ligands for transition metal-catalyzed asymmetric reac-
tions4 including palladium-catalyzed asymmetric hy-
drosilylation of prochiral alkenes.5,6 A representative of
the axially chiral monophosphine ligands is 2-diphen-
ylphosphino-2′-methoxy-1,1′-binaphthyl (MeO-MOP (1)),
which has been demonstrated to be an effective chiral
ligand for the palladium-catalyzed asymmetric hydrosi-
* To whom correspondence should be addressed. Phone: +81-75-
753-3983. Fax: +81-75-753-3988.
† Present address: Institute for Molecular Science, Myodaiji, Oka-
zaki 444-8585, J apan.
(1) For a review: Brunner, H.; Nishiyama, H.; Itoh, K. In Catalytic
Asymmetric Synthesis; Ojima, I., Ed.; VCH: New York, 1993; p 303.
(2) Uozumi, Y.; Hayashi, T. J . Am. Chem. Soc. 1991, 113, 9887.
(3) (a) Uozumi, Y.; Tanahashi, A.; Lee, S.-Y.; Hayashi, T. J . Org.
Chem. 1993, 58, 1945. (b) Uozumi, Y.; Suzuki, N.; Ogiwara, A.;
Hayashi, T. Tetrahedron 1994, 50, 4293.
(4) (a) Matsumoto, Y.; Naito, M.; Uozumi, Y.; Hayashi, T. J . Chem.
Soc., Chem. Commun. 1993, 1468. (b) Hayashi, T.; Iwamura, H.; Naito,
M.; Matsumoto, Y.; Uozumi, Y.; Miki, M.; Yanagi, K. J . Am. Chem.
Soc. 1994, 116, 775. (c) Hayashi, T.; Iwamura, H.; Uozumi, Y.;
Matsumoto, Y. Ozawa, F. Synthesis 1994, 526. (d) Hayashi, T.;
Iwamura, H.; Uozumi, Y. Tetrahedron Lett. 1994, 35, 4813. (e) Hayashi,
T.; Kawatsura, M.; Iwamura, H.; Yamaura, Y.; Uozumi, Y. Chem.
Commun. 1996, 1767. (f) Hayashi, T.; Kawatsura, M.; Uozumi, Y.
Chem. Commun. 1997, 561.
(7) Uozumi, Y.; Kitayama, K.; Hayashi, T. Tetrahedron: Asymmetry
1993, 4, 2419.
(8) Kitayama, K.; Uozumi, Y.; Hayashi, T. J . Chem. Soc., Chem.
Commun. 1995, 1533.
(9) For the palladium-catalyzed asymmetric hydrosilylation of sty-
rene with other chiral ligands: (a) Yamamoto, K.; Kiso, Y.; Ito, R.;
Tamao, K.; Kumada, M. J . Organomet. Chem. 1981, 210, 9. (b)
Hayashi, T.; Tamao, K.; Katsuro, Y.; Nakae, I.; Kumada, M. Tetrahe-
dron Lett. 1980, 21, 1871. (c) Okada, T.; Morimoto, T.; Achiwa, K.
Chem. Lett. 1990, 999. (d) Marinetti, A. Tetrahedron Lett. 1994, 35,
5861. (e) Marinetti, A.; Ricard, L. Organometallics 1994, 13, 3956. (f)
Gladiali, S.; Pulacchini, S.; Fabbri, D.; Manassero, M.; Sansoni, M.
Tetrahedron: Asymmetry 1998, 9, 391. (g) Pioda, G.; Togni, A. Tetra-
hedron: Asymmetry 1998, 9, 3903.
(5) Uozumi, Y.; Kitayama, K.; Hayashi, T.; Yanagi, K.; Fukuyo, E.
Bull. Chem. Soc. J pn. 1995, 68, 713.
(6) (a) Uozumi, Y.; Lee, S.-Y.; Hayashi, T.; Tetrahedron Lett. 1992,
33, 7185. (b) Uozumi, Y.; Hayashi, T.; Tetrahedron Lett. 1993, 34, 2335.
10.1021/jo001614p CCC: $20.00 © 2001 American Chemical Society
Published on Web 02/01/2001

1442 J . Org. Chem., Vol. 66, No. 4, 2001
Hayashi et al.
Ta ble 1. Asym m etr ic Hyd r osilyla tion of Styr en e (3a )
w ith Tr ich lor osila n e Ca ta lyzed by P a lla d iu m Com p lexes
of (R)-H-MOP a n d Its Der iva tives 2a -ga
Sch em e 1
T
(°C)
time yieldb (%)
% eec
entry
ligand (Ar)
C6H5 (2a )
4-MeOC6H4 (2b)
4-CF3C6H4 (2c)
3-CF3C6H4 (2d )
3,5-Me2C6H3 (2e)
3,5-Cl2C6H3 (2f)
3,5-(CF3)2C6H3 (2g)
(h)
of 4a
(confign)d
1
2
3
4
5
6
7e
8
0
0
0
0
0
0
0
12
24
11
15
16
20
1
100
89
92
81
95
89
93
85
93 (S)
92 (S)
93 (S)
95 (S)
92 (S)
94 (S)
97 (S)
98 (S)
3,5-(CF3)2C6H3 (2g) -20
24
a
The hydrosilylation was carried out without solvent unless
otherwise noted. The catalyst was generated in situ by mixing
[PdCl(π-C3H5)]2 and a chiral phosphine ligand 2. The initial ratio
of styrene/HSiCl3/Pd/P is 1:1.2:0.001:0.002. b Isolated yield by bulb-
to-bulb distillation. c Determined by HPLC analysis of (3,5-dinitro-
phenyl)carbamate ester of alcohol 5a with a chiral stationary
phase column (Sumichiral OA-4700, hexane/dichloroethane/etha-
d
nol ) 50:15:1). Determined by optical rotation of 5a . For entry
8, [R]22 -48.8 (c 1.61, dichloromethane). e In benzene (1.0 M
D
solution).
(Table 1). It was found that the enantioselectivity is not
strongly dependent on the electron-withdrawing or elec-
tron-donating characters of the para substituents, H-
MOP(p-OMe) (2b) and H-MOP(p-CF3) (2c), giving (S)-
5a of 92% ee (entry 2) and 93% ee (entry 3), respectively.
These values are almost the same as that observed with
unsubstituted H-MOP (2a ) (entry 1). On the other hand,
higher enantioselectivity (95% ee) was observed with
H-MOP(m-CF3) (2d ) (entry 4). On the basis of the higher
selectivity observed with the meta substitution, three
H-MOP ligands, H-MOP(m,m-2Me) (2e), H-MOP(m,m-
2Cl) (2f), and H-MOP(m,m-2CF3) (2g), were also pre-
pared, all of which are disubstituted at the meta,meta
positions. Of the three ligands, bis-trifluoromethylated
ligand 2g was found to be the most effective ligand, giving
(S)-5a of 97% ee (entry 7). In addition to the high
enantioselectivity, the reaction with 2g is much faster
than that with other ligands. The reaction in the presence
of the palladium/2g catalyst was so exothermic that the
reaction temperature is difficult to be kept at 0 °C under
the standard reaction conditions where no solvents were
used. The reaction diluted with benzene (1.0 M solution)
in the presence of 0.1 mol % of the palladium/2g catalyst
was completed in 1 h at 0 °C (entry 7). Higher enantio-
selectivity (98% ee) was observed in the reaction carried
out at -20 °C (entry 8). The 98% ee observed here is by
far the highest of the enantioselectivities reported for
asymmetric hydrosilylation of styrene.7-9
introduction of bis[3,5-bis(trifluoromethyl)phenyl]phos-
phino group greatly enhances both the enantioselectivity
and catalytic activity in the palladium-catalyzed asym-
metric hydrosilylation of styrene derivatives. Here, we
report the preparation of (R)-2-bis[3,5-bis(trifluorometh-
yl)phenyl]phosphino-1,1′-binaphthyl (2g), its use for the
hydrosilylation of styrene derivatives,10 and some mecha-
nistic aspects of the palladium-catalyzed asymmetric
hydrosilylation.
Resu lts a n d Discu ssion
We have previously modified the MOP ligands by
replacement of the methoxy group in MeO-MOP (1) by
some substituents including hydrogen and alkyl groups.3
In the present studies, H-MOP ligand (2a ) was modified
on the diphenylphosphino group by introduction of a
methoxy group or a trifluoromethyl group on the phenyl
ring, and these substituted H-MOP ligands were exam-
ined for their enantioselectivity in the palladium-
catalyzed asymmetric hydrosilylation of styrene (3a ) with
trichlorosilane (Scheme 1). The hydrosilylation was car-
ried out at 0 °C without solvent in the presence of 0.1
mol % of the palladium catalyst generated in situ by
mixing [PdCl(π-C3H5)]2 with 2 equiv (to palladium) of the
H-MOP ligand. The hydrosilylation product, 1-trichloro-
silyl-1-phenylethane (4a ), was oxidized into 1-phenyl-
ethanol (5a ) with hydrogen peroxide in the presence of
potassium fluoride, which is known to proceed with
retention of configuration at the stereogenic carbon
center.11 The enantiomeric purity of 5a was determined
by HPLC analysis with a chiral stationary phase column
The H-MOP ligands 2 that contain substituted dia-
rylphosphino groups at the 2-position on the 1,1′-binaph-
thyl skeleton were prepared starting from (R)-2-trifluoro-
methanesulfonyloxy-1,1′-binaphthyl (6)3 (Scheme 2).
Diarylphosphinyl groups were introduced at the 2-posi-
tion by the palladium-catalyzed cross-coupling type reac-
tion,2,3,12 and the phosphine oxide was reduced with
trichlorosilane and triethylamine according to the re-
ported procedures.3
(11) (a) Tamao, K.; Ishida, N.; Tanaka, T.; Kumada, M. Organome-
tallics 1983, 2, 1694. (b) Tamao, K.; Ishida, N. J . Organomet. Chem.
1984, 269, C37. (c) Tamao, K.; Nakajo, E.; Ito, Y. J . Org. Chem. 1987,
52, 4412. (d) Tamao, K. In Organosilicon and Bioorganosilicon
Chemistry; Sakurai, H., Ed.; Ellis Horwood: Chichester, 1985; p 231.
(12) Kurz, L.; Lee, G.; Morgans, D., J r.; Waldyke, M. J .; Wars, T.
Tetrahedron Lett. 1990, 31, 6321.
(10) Preliminary communication: Hayashi, T.; Hirate, S.; Kitayama,
K.; Tsuji, H.; Torii, A.; Uozumi, Y. Chem. Lett. 2000, 1272.

Asymmetric Hydrosilylation of Styrenes
J . Org. Chem., Vol. 66, No. 4, 2001 1443
Ta ble 2. Asym m etr ic Hyd r osilyla tion of Styr en es 3 w ith Tr ich lor osila n e Ca ta lyzed by P a lla d iu m -(R)-2ga
styrene ArCHdCHR 3
optical rotation value
entry
Ar
R
T (°C) time (h) yieldb (%) of 4
% eec (abs confign)d
of alcohol 5
1e
3a
3a
3b
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
Ph
Ph
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
0
1
24
10
1
93
85
83
92
91
90
88
93
92
90
95
90
89
81
85
87
97 (S) (93)
98 (S)
2f
-20
[R]22 -48.8 (c 1.61, CH2Cl2)
D
3
2-MeC6H4
2-MeC6H4
3-MeC6H4
4-MeC6H4
2-ClC6H4
3-ClC6H4
4-ClC6H4
3-BrC6H4
4-BrC6H4
4-MeOC6H4
3-NO2C6H4
H
0
0
97 (S)
[R]21 -48.1 (c 1.76, EtOH)
D
4f
96 (S)
97 (S)
95 (S) (89)
91 (S)
96 (S) (95)
98 (S) (94)
94 (S)
97 (S)
97 (S) (61)
98 (S)
5
0
0
4
[R]21 -36.5 (c 1.97, EtOH)
D
6
0.5
[R]21 -40.8 (c 1.54, EtOH)
D
7
0
15
4
4
[R]20 -48.0 (c 1.65, CHCl3)
D
8
0
[R]20 -41.0 (c 1.41, CHCl3)
D
9
0
[R]21 -48.5 (c 2.11, Et2O)
D
10f
11
12
13
14
15f
16f
0
6 days
[R]20 -32.2 (c 2.50, CHCl3)
D
-10
-10
0
15
20
[R]20 -35.1 (c 1.11, CHCl3)
D
[R]20 -41.0 (c 1.41, CHCl3)
D
6 days
[R]20 -36.6 (c 1.34, CHCl3)
D
0
0
20
48
30
16
98 (S) (89)
97
97 (S)
[R]20 -50.0 (c 1.23, CHCl3)
D
3m
3n
H
H
CH2OMe
[R]20 -35.8 (c 1.62, c-C5H10
)
D
CH2OCH2Ph
[R]20 -37.4 (c 1.23, CHCl3)
D
a
The hydrosilylation was carried out in toluene (1.0 M solution) unless otherwise noted. The catalyst was generated in situ by mixing
b
[PdCl(π-C3H5)]2 and ligand (R)-2g. The initial ratio of styrene/HSiCl3/Pd/P is 1:1.2:0.001:0.002. Isolated yield by bulb-to-bulb distillation.
c Determined by HPLC analysis of (3,5-dinitrophenyl)carbamate esters of alcohols 5 with a chiral stationary-phase column(Sumichiral
d
OA-4700 or 4100). The values shown in parentheses are enantiomeric purities of 5 obtained with H-MOP (2a ). Determined by
measurement of the optical rotation of alcohol 5. e In benzene (1.0 M solution). f The reaction was carried out without solvent.
Sch em e 2a
Sch em e 3
a
Key: (a) HP(O)Ar2, Pd(OAc)2, dppb, i-Pr2NEt, DMSO, 100 °C,
24 h; (b) HSiCl3, Et3N, PhMe, reflux, 15 h.
The high efficiency of (R)-H-MOP(m,m-2CF3) (2g) was
also observed in the asymmetric hydrosilylation of sty-
rene derivatives substituted on the phenyl ring 3b-k and
â-alkyl-substituted styrenes 3l-n (Scheme 3). The results
are summarized in Table 2 which also includes some data
obtained with H-MOP (2a ) ligand for comparison. The
regioselectivity in forming benzylic silanes was always
perfect, as is usually observed in the palladium-catalyzed
hydrosilylation of styrene derivatives.8,9 The enantio-
selectivity is generally very high with H-MOP(m,m-2CF3)
(2g) irrespective of the electron-withdrawing or electron-
donating characters of the substituents on the phenyl,
ranging between 94% and 98% ee, mostly over 96% ee,
except for one example (entry 7). Styrenes substituted
with methyl (3b-3d ), chloro (3f,3g), bromo (3h ,3i), meth-
oxy (3j), or nitro groups (3k ) successfully underwent the
asymmetric hydrosilylation to give the corresponding
benzylic alcohols of high enantiomeric purity (entries
1-13). Although the difference in enantioselectivity
between unsubstituted H-MOP (2a ) and H-MOP(m,m-
2CF3) (2g) is not very large for the styrenes substituted
with chloride on the phenyl (entries 8 and 9), the
enantioselectivity was greatly improved for the styrenes
substituted with electron-donating groups, methyl and
methoxy (entries 6 and 12). The asymmetric hydrosilyl-
ation of â-alkyl-substituted styrenes, â-methylstyrene (3l)
and cinnamyl ethers (3m , 3n ) was also successful with
the (R)-2g ligand to give the corresponding benzylic
alcohols of over 97% ee (entries 14-16). All the benzylic
alcohols 5a -n obtained here with (R)-2g have the (S)
configuration, indicating that the addition of hydrosilane
to styrenes always took place on R-si face of the styrene
double bond irrespective of the substitution patterns on
styrene.
Hydrosilylation of styrene with trichlorosilane cata-
lyzed by palladium complexes coordinated with a tertiary
phosphine ligand has been shown13 to proceed through
the catalytic cycle proposed by Chalk and Harrod,14 which
involves hydropalladation of an olefin on hydrido(silyl)-
(olefin)palladium B generating alkyl(silyl)palladium spe-
cies C and reductive elimination of the alkyl and silyl
fragments from C forming a hydrosilylation product.
Generally, intermediates B and C are in equilibrium by
the reversible processes, hydropalladation (olefin inser-
(13) Uozumi, Y.; Tsuji, H.; Hayashi, T. J . Org. Chem. 1998, 63, 6137.
(14) (a) Chalk, A. J .; Harrod, J . F. J . Am. Chem. Soc. 1965, 87, 16.
(b) Harrod, J . F.; Chalk, A. J . J . Am. Chem. Soc. 1965, 87, 1133.

1444 J . Org. Chem., Vol. 66, No. 4, 2001
Hayashi et al.
Ta ble 3. Asym m etr ic Hyd r osilyla tion of
Deu ter iu m -La beled Styr en es 3a -r-d 1 a n d 3a -â,â-d 2 w ith
Tr ich lor osila n e Ca ta lyzed by P a lla d iu m Com p lexes of
(R)-2a a n d (R)-2ga
Sch em e 4
time yield (%)b D atom %c at % eed
entry styrene ligand (h)
of 4a
R and â in 8 (confign)
1
2
3
3a -R-d1 (R)-2g
3a -â,â-d2 (R)-2g
1
1
94
89
99
>99, <1
<1, 40
<1, 140
97 (S)
97 (S)
94 (S)
3a -â,â-d2 (R)-2a 36
a
The hydrosilylation was carried out at 0 °C with 20 equiv of
trichlorosilane in the presence of 0.1 mol % of the palladium
catalyst generated in situ by mixing [PdCl(π-C3H5)]2 and a chiral
b
phosphine ligand. The ratio of Pd/P is 1:2. Determined by GC
and NMR analyses. c Determined by 1H and 2H NMR analyses of
acetate 8 which was obtained by the oxidation of 2a followed by
acetylation. Integration of R and â hydrogens relative to acetyl
methyl three hydrogens was used. One deuterium atom is de-
Sch em e 5
d
scribed as 100. Determined by HPLC analysis of (3,5-dinitro-
phenyl)carbamate ester of alcohol 5a with a chiral stationary
phase column (Sumichiral OA-4700, hexane/dichloroethane/etha-
nol ) 50:15:1).
Sch em e 6
tion to hydridopalladium) and â-hydrogen elimination
(Scheme 4). We studied the palladium-catalyzed hydro-
silylation of regiospecifically deuterated styrenes (Scheme
5), which gave us significant information on the regio-
selectivity in forming 1-phenylethylpalladium intermedi-
ate and the relative rates of hydropalladation, â-hydrogen
elimination, and reductive elimination in the catalytic
cycle.
Hydrosilylation of 3a -R-d1 (PhCDdCH2) with a large
excess (20 equiv) of trichlorosilane in the presence of 0.1
mol % of the palladium-2g catalyst gave a quantitative
yield of (S)-1-phenyl-1-trichlorosilylethane (4a ) (97% ee)
where all deuterium remained at the original R-position
(entry 1 in Table 3). The deuterium content was deter-
mined by 1H and 2H NMR analyses of 1-phenylethyl
acetate (8) obtained by the oxidation of 4a followed by
acetylation of the resulting alcohol 5a . The retention of
all the deuterium in the styrene indicates that the
hydrosilylation does not involve 2-phenylethylpalladium
intermediate D in the catalytic cycle (Scheme 6). The
reason 2-phenylethylsilane is not produced in the present
hydrosilylation is not that the reductive elimination from
D is slow compared with â-hydrogen elimination from D
but that hydropalladation takes place regiospecifically in
forming 1-phenylethylpalladium intermediate C. It has
been proposed that the preferential fromation of C is
ascribed to the contribution of a π-benzylpalladium
species C′.9a,g
tion product 4a . Thus, abstraction of â-deuterium from
1-phenyl-2,2-dideuterioethylpalladium C1 forms silyl-
(deuterio)palladium B2 where styrene lost one of the two
deuterium atoms on the â-position. Substitution of deu-
teriosilane with hydrosilane followed by hydropalladation
of â-d1-styrene on B2′ and reductive elimination from C2
gives the hydrosilylation product containing only one
deuterium atom. Further â-deuterium elimination from
C2 results in formation of the hydrosilylation product
with no deuteriums by way of B3.
The hydrosilylation of 3a -â,â-d2 (PhCHdCD2) brought
about a considerable loss of the deuterium atoms, demon-
strating that the 1-phenylethylpalladium intermediate
C undergoes â-hydrogen elimination to some extent
before the reductive elimination giving the hydrosilyla-
It is significant that the amount of loss of deuterium
is dependent on the phosphine ligand used. In this
hydrosilylation, 20 equiv (to PhCHdCD2) of hydrosilane
HSiCl3 was used. It follows that the ratio of deuterium

Asymmetric Hydrosilylation of Styrenes
J . Org. Chem., Vol. 66, No. 4, 2001 1445
Sch em e 7
to hydrogen, which possibly participates in the hydro-
(deuterio)palladation and â-hydrogen (deuterium) elimi-
nation, is 2:20. Assuming that the reductive elimination
takes place after complete deuterium-hydrogen scram-
bling, the deuterium content of the hydrosilylation
product starting from PhCHdCD2 is calculated to be 27%
(3 × 2/(2 + 20)). The 40% deuterium observed in 4a with
ligand 2g (entry 2 in Table 3) is close to this value,
indicating that the â-hydrogen elimination is very fast
compared with the reductive elimination. In the reaction
catalyzed by palladium-2g complex, which is the most
enantioselective catalyst, the reductive elimination takes
place after very fast equilibration between B and C. On
the other hand, the â-hydrogen elimination is not so fast
in the reaction with less enantioselective ligand 2a , 140%
(originally 200%) of deuterium remaining at the original
â-position (entry 3). The much faster rate of â-hydrogen
elimination than reductive elimination observed with
ligand 2g is related to the higher enantioselectivity of
2g (vide infra). Studies on the relationship between the
deuterium scrambling and enantioselectivity have been
reported in nickel-catalyzed hydrocyanation of a styrene
derivative, but less deuterium scrambling was observed
with a catalyst of higher enantioselectivity in their
system.15
Reaction of o-allylstyrene (9) with trichlorosilane cata-
lyzed by palladium complexes coordinated with 2a and
2g gave us further insight into the mechanism of the
present asymmetric hydrosilylation.16 The reaction of 9
in the presence of 0.3 mol % of the palladium-2g catalyst
at -20 °C for 120 h gave 74% yield of the hydrosilylation
product, which consists of trans-1-methyl-2-(trichloro-
silylmethyl)indan (10), 1-(2-(2-propenyl)phenyl)-1-tri-
chlorosilylethane (11a ), and 1-(2-((E)-1-propenyl)phenyl)-
1-trichlorosilylethane (11b) in a ratio of 47:42:11 (Scheme
7). Compounds 11a and 11b are the hydrosilylation
products on the styrene double bond, isomerization of the
2-propenyl group into 1-propenyl being accompanied
under the reaction conditions. The indan derivative 10
is formed by insertion of the 2-propenyl group into the
palladium-carbon bond formed by the hydropalladation
of styrene double bond.13 It should be noted that 10 was
not produced at all in the hydrosilylation catalyzed by a
palladium complex of 2a under otherwise the same
reaction conditions, only 11 being produced.
The enantiomeric purities of hydrosilylation products
10, 11a , and 11b obtained with ligand 2g were deter-
mined to be 91%, 95%, and 95% ee, respectively, by GLC
analysis using a chiral stationary phase column (Cyclo-
dex â236M) of their trimethylsilyl derivatives prepared
by treatment of the trichlorosilanes with an excess of
methylmagnesium bromide. The absolute configurations
were assigned by correlation with known compounds,
1-methylindan17 (14) and 3-methylphthalide18 (15). Thus,
trichlorosilyl group in 10 was converted into hydroxy
group by the hydrogen peroxide oxidation to give trans-
1-methyl-2-(hydroxymethyl)indan (12). The primary al-
cohol was oxidized into aldehyde, and deformylation with
Sch em e 8
a stoichiometric amount of RhCl(PPh3)3 gave (S)-(-)-14.
Oxidation of a mixture of isomers 11a and 11b into
alcohols 13a and 13b followed by isomerization of olefinic
double bond by treatment of the mixture of alcohols with
PdCl2(MeCN)2 gave isomerically pure 1-(2-((E)-1-pro-
penyl)phenyl)ethanol (13b). Ozonolysis of the double
bond followed by oxidation of the resulting lactol gave
lactone, (S)-(-)-15. Thus, the hydrosilylation products 10
and 11 were determined to have the absolute configura-
tion of (1S,2R) and (S), respectively. The (S) configuration
of 11 shows that it is formed by reductive elimination
from (S)-alkylpalladium intermediate (S)-E, which is
generated by hydropalladation of styrene double bond on
its si face (Scheme 8). The enantioface selection is the
same as that observed for the asymmetric hydrosilylation
of styrene derivatives 3 including ortho-substituted
styrenes 3b and 3e with (R)-2g ligand. Rather surpris-
ingly, the cyclization product (1S,2R)-10 is formed through
(R)-alkylpalladium intermediate (R)-E, which is deduced
by the (1S) configuration of 10. Thus, the products 10
and 11 were formed from different diastereoisomeric
intermediates coordinated with (R)-2g ligand. Consider-
(15) Casalnuovo, L. A.; RajanBabu, T. V.; Ayers, T. A.; Warren, T.
H. J . Am. Chem. Soc. 1994, 116, 9869.
(16) We have reported nonasymmetric version of the palladium-
catalyzed hydrosilylation of o-allylstyrene (ref 13).
(17) Hansen, H.-J .; Sliwka, H.-R.; Hug, W. Helv. Chim. Acta 1979,
62, 1120.
(18) (a) Nagai, U.; Shishido, T.; Chiba, R.; Mitsuhashi, H. Tetrahe-
dron 1965, 21, 1701. (b) Brown, H. C.; Wetherill, R. B. Tetrahedron
Lett. 1996, 37, 2205.

1446 J . Org. Chem., Vol. 66, No. 4, 2001
Hayashi et al.
recorded on J EOL J NM-AL400 spectorometer (400 MHz for
1H NMR) or J EOL J NM LA500 spectrometer (500 MHz for
1H, 125 MHz for 13C and 202 MHz for 31P). Chemical shifts
are reported in δ ppm referenced to an internal SiMe4 standard
for 1H NMR, and to an external 85% H3PO4 standard for 31P
NMR. Residual chloroform (δ 77.0 for 13C) was used as internal
reference for 13C NMR. 1H, 13C, and 31P NMR spectra were
recorded in CDCl3 at 25 °C unless otherwise noted.
Sch em e 9
Ma ter ia ls. (R)-2-(Trifluoromethanesulfonyloxy)-1,1′-binaph-
thyl (6) was prepared from (R)-(+)-2-hydroxy-1,1′-binaphthyl19
by treatment with trifluoromethanesulfonic anhydride and
pyridine in 1,2-dichloroethane according to the reported
procedures.3 Deuterated styrenes, 3a -R-d1 and 3a -â,â-d2,20
[PdCl(π-C3H5)]2,21 and o-allylstyrene22 (9) were prepared ac-
cording to the reported procedures.
P r ep a r a tion of H-MOP Liga n d s (R)-2a -g. (R)-2-Diphen-
ylphosphino-1,1′-binaphthyl (2a ) was prepared by the pal-
ladium-catalyzed diphenylphosphinylation3,12 of (R)-2-(trifluoro-
methanesulfonyloxy)-1,1′-binaphthyl (6) with diphenylphosphine
oxides followed by reduction of the resulting phosphine oxide
(R)-7a with trichlorosilane and triethylamine according to the
reported procedures.3 In a similar manner, other H-MOP
Ligands (R)-2b-g were prepared by use of the corresponding
diarylphosphine oxides. A typical procedure shown below is
for the preparation of (R)-2-bis(3,5-bis(trifluoromethyl)phenyl)-
phosphino-1,1′-binaphthyl (2g).
ing that the â-hydrogen elimination from alkylpalladium
intermediate is fast compared to reductive elimination
in the reaction with 2g which was observed in the
hydrosilylation of 3a -â,â-d2, two diastereomeric alkyl-
palladium intermediates (S)-E and (R)-E must be in a
fast equilibration by way of π-olefin complexes. It is likely
that one of the diastereomeric intermediates, that is (S)-
E, is much more reactive than the other diastereomer
(R)-E toward the reductive elimination giving 11 while
(R)-E does not undergo the reductive elimination but
undergoes insertion of the 2-propenyl double bond into
the palladium-carbon bond giving cyclization product 10.
As mentioned above, the hydrosilylation of o-allylstyrene
(9) by use of ligand 2a does not give any cyclization
product 10. It is in good agreement with the relatively
fast reductive elimination observed with ligand 2a in the
reaction of 3a -â,â-d2.
(R)-2-Bis(3,5-b is(t r iflu or om et h yl)p h en yl)p h osp h in o-
1,1′-bin a p h th yl (2g). To a mixture of (R)-2-(trifluoromethane-
sulfonyloxy)-1,1′-binaphthyl (6) (365 mg, 0.908 mmol), bis(3,5-
bis(trifluoromethyl)phenyl)phosphine oxide (879 mg, 1.85 mmol),
palladium diacetate (104 mg, 0.464 mmol), and 1,4-bis-
(diphenylphosphino)butane (dppb, 195 mg, 0.458 mmol) were
added dimethyl sulfoxide (4.2 mL) and N,N-diisopropylethyl-
amine (0.80 mL), and the mixture was heated with stirring at
100 °C for 2.5 h. After being cooled to 50 °C, the mixture was
concentrated under reduced pressure (0.1-0.2 mmHg). The
residue was diluted with ethyl acetate, and the solution was
washed with water (three times), dried over anhydrous
magnesium sulfate, and concentrated under reduced pressure.
The residue was chromatographed on silica gel (hexane/ethyl
acetate )1/1) to give 497 mg (75% yield) of (R)-2-bis(3,5-bis-
Con clu sion
We have demonstrated that the (R)-H-MOP(m,m-2CF3)
(2g) ligand shows the highest enantioselectivity in the
asymmetric hydrosilylation of styrene derivatives, and
the difference between ligands 2a and 2g is that the
â-hydrogen elimination from alkylpalladium intermedi-
ate is fast compared to reductive elimination in the
reaction with 2g and the â-hydrogen elimination is not
so fast with 2a . The higher enantioselectivity of 2g is
attributable to the fast â-hydrogen elimination from
alkylpalladium intermediates coordinated with 2g and
highly selective reductive elimination from one of the
diastereomeric intermediates (Scheme 9). The enantio-
face selectivity of styrene on coordination to the pal-
ladium bearing 2g ligand is probably not so high as to
give hydrosilylation product 4 of over 96% ee. The
catalytic cycle involves both of the diastereomeric alkyl-
palladium intermediates (S)-C and (R)-C in a certain
ratio, which are in a fast equilibrium by â-hydrogen
elimination and hydropalladation processes. Reductive
elimination takes place selectively from (S)-C to give
hydrosilylation product (S)-4, and (R)-C, which is much
less reactive toward reductive elimination, undergoes
â-hydrogen elimination to turn back to (S)-C resulting
in the formation of (S)-4. Questions why bistrifluoro-
methylated H-MOP ligand 2g causes the fast â-hydrogen
elimination resulting in high enantioselectivity and
which characteristics of 2g are responsible for it, elec-
tronic or steric, remain to be answered. We are currently
trying to disclose the structure of palladium complexes
coordinated with the H-MOP ligands.
(trifluoromethyl)phenyl)phosphinyl-1,1′-binaphthyl (7g) as white
1
powder. (R)-7g: [R]20 +24.3 (c 1.15, CHCl3); H NMR δ 6.88
D
(d, J ) 8.6 Hz, 1), 7.1-7.4 (m, 5H), 7.5-7.8 (m, 8H), 7.8-8.1
(m, 3H), 8.21 (d, J ) 10.9 Hz, 2H); 13C{1H} NMR δ 122.4 (q,
J C-F ) 273 Hz, CF3), 122.7 (q, J C-F ) 273 Hz, CF3), 124.4-
145.9; 31P{1H} NMR δ 22.6 (s). Anal. Calcd for C36H19OF12P:
C, 59.50; H, 2.64. Found: C, 59.77; H, 2.91.
To a mixture of (R)-7g (253 mg, 0.348 mmol) and triethyl-
amine (1.20 mL, 8.6 mmol) in toluene (6.0 mL) was added
trichlorosilane (0.40 mL, 4.0 mmol) at 0 °C. The reaction
mixture was stirred at 100 °C for 5 days. After being cooled to
room temperature, the mixture was diluted with ether and a
small amount of saturated aqueous sodium bicarbonate was
added. The resulting suspension was filtered through Celite.
The filtrate was dried over anhydrous magnesium sulfate and
concentrated under reduced pressure. Chromatography on
silica gel (hexane/ethyl acetate ) 10/1) gave (178 mg, 72%
yield) of (R)-2g as white powder: [R]20 -22.2 (c 0.77, CHCl3);
D
1H NMR δ 6.90 (d, J ) 8.3 Hz, 1H), 7.12 (t, J ) 8.3 Hz, 1H),
7.2-7.6 (m, 8H), 7.63 (d, J ) 5.9 Hz, 2H), 7.70 (s, 1H), 7.9-
8.0 (m, 6H); 13C{1H} NMR δ 122.9 (q, J C-F ) 273 Hz, CF3),
123.0 (q, J C-F ) 273 Hz, CF3), 122.9-146.7; 31P{1H} NMR δ
-11.2 (s). Anal. Calcd for C36H19F12P: C, 60.84; H, 2.70.
Found: C, 60.86; H, 2.92.
(19) (a) Sasaki, H.; Irie, R.; Katsuki, T. Synlett 1993, 3000. (b)
Tamai, Y.; Nakano, T.; Koike, S.; Kawahara, K.; Miyano, S. Chem. Lett.
1989, 1135. (c) Meyers, A. I.; Lutomski, K. A. J . Am. Chem. Soc. 1982,
104, 879.
(20) Schubert, W. M.; Lamm, B. J . Am. Chem. Soc. 1966, 88, 120.
(21) Auburn, P. R.; Mackenzie, P. B.; Bosnich, B.J . Am. Chem. Soc.
1985, 107, 2033.
Exp er im en ta l Section
Gen er a l Meth od s. All manipulations were carried out
under a nitrogen atmosphere. Nitrogen gas was dried by
passage through P2O5 (Merck, SICAPENT). NMR spectra were
(22) (a) Garratt, P. J .; Vollhardt, K. P. C. Synthesis 1971, 423. (b)
Bestmann, H. J .; Kratzer, O. Chem. Ber. 1963, 96, 1899.

Asymmetric Hydrosilylation of Styrenes
J . Org. Chem., Vol. 66, No. 4, 2001 1447
1
For phosphine oxides 7b-f and phosphines 2b-f, spectral
and analytical data are shown below:
analysis and H NMR study of the reaction mixture indicated
that 1-phenyl-1-(trichlorosilyl)ethane (4a ) was formed quan-
titatively. The crude mixture was purified by bulb-to-bulb
distillation under reduced pressure to give 520 mg (100% yield)
of 1-phenyl-1-(trichlorosilyl)ethane (4a ).
(R)-2-Bis(4-m eth oxyp h en yl)p h osp h in yl-1,1′-bin a p h th -
yl (7b): 61% yield; [R]20 -54.3 (c 1.00, CHCl3); 1H NMR δ
D
3.68 (s, 3H), 3.73 (s, 3H), 6.49 (d, J ) 6.9 Hz, 2H), 6.56 (d, J
) 6.9 Hz, 2H), 6.84 (d, J ) 8.4 Hz 1H), 7.0-7.7 (m, 13H), 7.93
(d, J ) 8.3 Hz, 1H), 7.99 (d, J ) 7.8 Hz, 2H); 13C{1H} NMR δ
54.37, 55.49, 112.52, 113.59, 123.1-134.8, 143.39, 161.21; 31P-
{1H} NMR δ 28.9 (s). Anal. Calcd for C34H27O3P: C, 79.36; H,
5.29. Found: C, 79.16; H, 5.57.
The results obtained for the asymmetric hydrosilylation of
styrenes 3a -n are summarized in Tables 1 and 2. 1H NMR
data for the hydrosilylation products are shown below:
1-P h en yl-1-(tr ich lor osilyl)eth a n e (4a ): H NMR δ 1.64
(d, J ) 7.6 Hz, 3H), 2.89 (q, J ) 7.6 Hz, 1H), 7.20-7.38 (m,
5H).
1-(2-Met h ylp h en yl)-1-(t r ich lor osilyl)et h a n e (4b ): 1H
NMR δ 1.60 (d, J ) 7.3 Hz, 3H), 2.36 (s, 3H), 3.16 (q, J ) 7.3
Hz, 1H), 7.05-7.33 (m, 4H).
1
(R)-2-Bis(4-tr iflu or om eth ylp h en yl)p h osp h in yl-1,1′-bi-
n a p h th yl (7c): 65% yield; [R]20D -3.8 (c 1.01, CHCl3); 1H NMR
δ 6.91 (d, J ) 8.3 Hz, 1H), 7.06 (d, J ) 6.4 Hz, 2H), 7.12 (dd,
J ) 6.9, 8.3 Hz, 1H), 7.20 (d, J ) 8.3 Hz, 1H), 7.2-7.8 (m,
14H), 7.95 (d, J ) 8.3 Hz, 1H), 8.01 (d, J ) 8.8 Hz, 1H); 13C-
{1H} NMR δ 122.1-136.9, 144.59, 171.01; 31P{1H} NMR δ 26.2
(s). Anal. Calcd for C34H21F6OP: C, 69.16; H, 3.58. Found: C,
69.46; H, 3.79.
1-(3-Met h ylp h en yl)-1-(t r ich lor osilyl)et h a n e (4c): 1H
NMR δ 1.60 (d, J ) 7.4 Hz, 3H), 2.35 (s, 3H), 2.85 (q, J ) 7.4
Hz, 1H), 7.0-7.1 (m, 3H), 7.21 (t, J ) 7.8 Hz, 1H).
1-(4-Met h ylp h en yl)-1-(t r ich lor osilyl)et h a n e (4d ): 1H
NMR δ 1.60 (d, J ) 7.6 Hz, 3H), 2.33 (s, 3H), 2.85 (q, J ) 7.6
Hz, 1H), 7.13 (s, 4H).
1-(2-Ch lor oph en yl)-1-(tr ich lor osilyl)eth an e (4e): 1H NMR
δ 1.60 (d, J ) 7.6 Hz, 3H), 3.62 (q, J ) 7.6 Hz, 1H), 7.14-7.46
(m, 4H).
1-(3-Ch lor oph en yl)-1-(tr ich lor osilyl)eth an e (4f): 1H NMR
δ 1.61 (d, J ) 7.6 Hz, 3H), 2.87 (q, J ) 7.6 Hz, 1H), 7.09-7.30
(m, 4H).
(R)-2-Bis(3-tr iflu or om eth ylp h en yl)p h osp h in yl-1,1′-bi-
n a p h th yl (7d ): 79% yield; [R]20 +8.98 (c 1.00, CHCl3); 1H
D
NMR δ 6.87 (d, J ) 8.9 Hz, 2H), 7.1-7.8 (m, 15H), 7.9-8.0
(m, 4H); 31P{1H} NMR δ 25.5 (s). Anal. Calcd for C34H21OF6P:
C, 69.14; H,3.59. Found: C, 68.89; H, 3.36.
(R)-2-Bis(3,5-d im eth ylp h en yl)p h osp h in yl-1,1′-bin a p h -
1
th yl (7e): 97% yield; [R]20 -12.1 (c 1.01, CHCl3); H NMR δ
D
1.90 (s, 6H), 2.08 (s, 6H), 6.47 (s, 1H), 6.7-7.6 (m, 15H), 7.8-
7.9 (m, 3H); 13C{1H} NMR δ 20.52, 21.14, 21.77, 123.8-133.3,
134.44, 134.54, 136.62, 136.71, 137.13, 137.26, 143.85; 31P{1H}
NMR δ 28.5 (s). Anal. Calcd for C36H31OP: C, 84.68; H, 6.12.
Found: C, 84.41; H, 6.47.
1-(4-Ch lor op h en yl)-1-(t r ich lor osilyl)et h a n e (4g): 1H
NMR δ 1.60 (d, J ) 7.6 Hz, 3H), 2.87 (q, J ) 7.6 Hz, 1H), 7.17
(d, J ) 8.6 Hz, 2H), 7.30 (d, J ) 8.6 Hz, 2H).
1-(3-Br om op h en yl)-1-(t r ich lor osilyl)et h a n e (4h ): 1H
NMR δ 1.60 (d, J ) 7.3 Hz, 3H), 2.85 (q, J ) 7.3 Hz, 1H),
7.16-7.22 (m, 2H), 7.38-7.41 (m, 2H).
(R)-2-Bis(3,5-d ich lor op h en yl)p h osp h in yl-1,1′-bin a p h -
1
th yl (7f): 64% yield; [R]20 +26.5 (c 0.45, CHCl3); H NMR δ
D
6.84 (s, 2H), 6.90 (d, J ) 8.6 Hz, 1H), 6.95 (dd, J ) 2.0, 12.2
Hz, 1H), 7.2-7.8 (m, 13H), 7.98 (d, J ) 8.3 Hz, 1H), 8.04 (dd,
J ) 2.6, 8.6 Hz, 1H); 31P{1H}NMR δ 23.8 (s). Anal. Calcd for
1-(4-Br om oph en yl)-1-(tr ich lor osilyl)eth an e (4i): 1H NMR
δ 1.60 (d, J ) 7.4 Hz, 3H), 2.86 (q, J ) 7.4 Hz, 1H), 7.11 (d, J
) 8.6 Hz, 2H), 7.45 (d, J ) 8.6 Hz, 2H).
C
32H19Cl4PO: C, 65.09; H, 3.25. Found: C, 64.84; H, 3.16.
(R)-2-Bis(4-m eth oxyp h en yl)p h osp h in o-1,1′-bin a p h th -
1-(4-Meth oxyp h en yl)-1-(tr ich lor osilyl)eth a n e (4j): 1H
NMR δ 1.59 (d, J ) 7.6 Hz, 3H), 2.84 (q, J ) 7.6 Hz, 1H), 3.80
(s, 3H), 6.87 (d, J ) 8.6 Hz, 2H), 7.16 (d, J ) 8.6 Hz, 2H).
1-(3-Nitr oph en yl)-1-(tr ich lor osilyl)eth an e (4k): 1H NMR
δ 1.68 (d, J ) 7.4 Hz, 3H), 3.04 (q, J ) 7.4 Hz, 1H), 7.52 (t, J
) 8.3 Hz, 1H), 7.59 (d, J ) 7.9 Hz, 1H), 8.10-8.15 (m, 2H).
1-P h en yl-1-(tr ich lor osilyl)p r op a n e (4l): 1H NMR δ 0.93
(t, J ) 7.3 Hz, 3H), 1.89-2.29 (m, 2H), 2.62 (dd, J ) 11.6, 4.0
Hz, 1H), 7.14-7.43 (m, 5H).
yl (2b); 91% yield; [R]20 -91.2 (c 1.00, CHCl3); 1H NMR δ
D
3.72 (s, 3H), 3.77 (s, 3H), 6.72 (d, J ) 7.9 Hz, 2H), 6.82 (d, J
) 8.3 Hz, 2H), 7.01 (d, J ) 6.8 Hz, 1H), 7.03 (d, J ) 7.4 Hz,
1H), 7.1-7.4 (m, 13H), 7.84 (t, J ) 8.8 Hz, 2H), 7.89 (dd, J )
7.3, 7.9 Hz, 2H); 13C{1H} NMR δ 55.13, 55.16 (OMe), 113.92,
123.9-137.4, 144.36, 159.87; 31P{1H} NMR δ -16.3(s). Anal.
Calcd for C34H27O2P: C, 81.91; H, 5.46. Found: C, 81.64; H,
5.70.
(R)-2-Bis(4-t r iflu or om et h ylp h en yl)p h osp h in o-1,1′-b i-
1-P h en yl-3-m eth oxy-1-(tr ich lor osilyl)p r op a n e (4m ): 1H
NMR δ 2.05-2.22 (m, 1H), 2.29-2.46 (m, 1H), 3.00 (dd, J )
11.9, 3.6 Hz, 1H), 3.13-3.23 (m, 1H), 3.25 (s, 3H), 3.33-3.43
(m, 1H), 7.16-7.43 (m, 5H).
1-P h en yl-3-ben zyloxy-1-(tr ich lor osilyl)p r op a n e (4n ):
1H NMR δ 2.09-2.24 (m, 1H), 2.36-2.52 (m, 1H), 3.05 (dd, J
) 11.9, 3.7 Hz, 1H), 3.22-3.35 (m, 1H), 3.44-3.55 (m, 1H),
4.34 (d, J ) 11.9 Hz, 1H), 4.43 (d, J ) 11.9 Hz, 1H), 7.14-
7.46 (m, 10H).
Oxid a tion of Hyd r osilyla tion P r od u cts 4a -n . Typ ica l
P r oced u r e. To a suspension of potassium fluoride (690 mg,
11.9 mmol) and potassium bicarbonate (1.76 g, 17.6 mmol) in
100 mL of THF/MeOH (1/1) was added 1-phenyl-1-(trichloro-
silyl)ethane (4a ) (460 mg, 1.90 mmol). To the suspension was
added 2.0 mL of 30% hydrogen peroxide at ambient temper-
ature, and the reaction mixture was vigorously stirred for 11
h. To the reaction mixture was added 10 mL of saturated
Na2S2O3 solution, and then the entire mixture was stirred for
1 h. The mixture was filtered through a Celite plug, and the
filter cake was rinsed with ether. The filtrate was concentrated
in vacuo, and the resulting residue was extracted with ether.
After the residue was dried over anhydrous magnesium
sulfate, the solvent was removed in vacuo and the resulting
crude mixture was chromatographed on silica gel (hexane/ethyl
acetate ) 5/1) to give 225 mg (97% yield) of 1-phenylethanol
(5a ):
n a p h t h yl (2c): 80% yield; [R]20 -69.9 (c 1.00, CHCl3); 1H
D
NMR δ 6.97 (d, J ) 8.6 Hz, 1H), 7.0-7.5 (m, 16H), 7.8-7.9
(m, 4H); 13C{1H} NMR δ 122.9-133.8, 136.9, 142.3, 146.1; 31P-
{1H} NMR δ -13.3(s). Anal. Calcd for C34H21F6P: C, 71.08;
H, 3.68. Found: C, 70.87; H, 3.95.
(R)-2-Bis(3-t r iflu or om et h ylp h en yl)p h osp h in o-1,1′-b i-
n a p h th yl (2d ): 93% yield; [R]20 -53.6 (c 1.10, CHCl3); 1H
D
NMR δ 7.04 (d, J ) 8.3 Hz, 1H), 7.1-7.6 (m, 16H), 7.92 (d, J
) 8.6 Hz, 3H), 7.96 (d, J ) 8.6 Hz, 1H); 31P{1H} NMR δ -12.66
(s). Anal. Calcd for C34H21F6P: C, 71.06; H, 3.69. Found: C,
70.84; H, 3.68.
(R)-2-Bis(3,5-d im et h ylp h en yl)p h osp h in o-1,1′-b in a p h -
1
th yl (2e): 90% yield; [R]20 -52.7 (c 1.01, CHCl3); H NMR δ
D
2.13 (s, 6H), 2.21 (s, 6H), 6.71 (d, J ) 7.8 Hz, 2H), 6.78 (s,
1H), 6.86 (d, J ) 7.8 Hz, 2H), 6.91 (s, 1H), 7.1-7.4 (m, 9H),
7.8-7.9 (m, 4H); 13C{1H} NMR δ 21.19, 21.31, 124.9-137.6,
144.72, 144.94; 31P{1H} NMR δ -12.7 (s). Anal. Calcd for
C
36H31P: C, 87.42; H, 6.32. Found: C, 87.14; H, 6.31.
(R)-2-Bis(3,5-d ich lor op h en yl)p h osp h in o-1,1′-b in a p h -
1
th yl (2f): 74% yield; [R]20 -38.3 (c 0.88, CHCl3); H NMR δ
D
6.86 (dd, J ) 2.0, 6.9 Hz, 2H), 7.04 (d, J ) 6.6 Hz, 2H), 7.2-
7.6 (m, 11H), 7.9-8.0 (m, 4H); 31P{1H} NMR δ -10.4 (s). Anal.
Calcd for C32H19Cl4P: C, 66.90; H, 3.34. Found: C, 66.82; H,
3.61.
Asym m etr ic Hyd r osilyla tion of Styr en es. Typ ica l P r o-
ced u r e. To a mixture of [PdCl(η3-C3H5)]2 (0.37 mg, 2.0 µmol
Pd), (R)-H-MOP (2a ) (1.77 mg, 4.0 µmol), and styrene (3a )
(2144 mg, 2.05 mmol) was added trichlorosilane (0.25 mL, 2.5
mmol) at 0 °C. The mixture was stirred at 0 °C for 12 h. GC
Specific rotations of alcohols 5a -n obtained by the asym-
metric hydrosilylation are shown in Table 2. The reported
specific rotation values for the alcohols 5a -l are as follows.

1448 J . Org. Chem., Vol. 66, No. 4, 2001
Hayashi et al.
(S)-5a :23 [R]22 -52.5 (c 1.3, dichloromethane). (S)-5b of 95%
compounds, (S)-(-)-1-methylindan17 (14) and (S)-(-)-3-meth-
ylphthalide18 (15), which are shown below.
D
ee:24 [R]20 -58.6 (c 0.0665, ethanol). (S)-5c:25 [R]25 -39.8 (c
D
D
0.944, ethanol). (R)-5d of 94% ee:26 [R]20 +51.6 (c 1.0,
Oxid a tion of 10 a n d 11. To a suspension of potassium
fluoride (3.83 g, 63.6 mmol) and potassium bicarbonate (9.92
g, 95.4 mmol) in 400 mL of THF/MeOH (1/1) was added a
mixture of 10 and 11 (2.98 g, 10.6 mmol) which contained 10
(85% ee) and 11 (83% ee) in a ratio of 55:45. To the suspension
was added 12.5 mL of 30% hydrogen peroxide at ambient
temperature, and the reaction mixture was vigorously stirred
for 10 h. To the reaction mixture was added 50 mL of saturated
Na2S2O3 solution and then entire mixture was stirred for 1 h.
The mixture was filtered through a Celite plug, and the filter
cake was rinsed with ether. The filtrate was concentrated in
vacuo and the resulting residue was extracted with ether. After
drying over anhydrous magnesium sulfate, the solvent was
removed in vacuo and the resulting crude mixture was
chromatographed on silica gel (hexane/ethyl acetate ) 5/1) to
give 646 mg of 1-methyl-2-(hydroxymethyl)indan13 (12) (68%)
and 748 mg of a mixture of 1-(2-(2-propenyl)phenyl)ethanol13
(13a ) 1-(2-((E)-1-propenyl)phenyl)ethanol13 (13b) (96%) as
D
chloroform). (R)-5e of 72% ee:26 [R]20D +22.4 (c 1.1, chloroform).
(R)-5f of 85% ee:26 [R]20 +36.7 (c 1.0, chloroform). (R)-5g:27
D
[R]D +49.9 (c 2.0, Et2O). (S)-5h :25 [R]26 -28.6 (c 1.78,
21
D
ethanol). (S)-5i of 96% ee:24 [R]D -37.5 (c 0.0666, chloroform).
(R)-5j of 89% ee:26 [R]20 +47.2 (c 1.0, chloroform). (S)-5k of
D
45% ee:28 [R]27 -17.2 (c 2.03, methanol). (S)-5l:29 [R]D -45.45
D
(c 5.15, chloroform).
The absolute configuration of 5n was assigned to be (S)-(-)
by 1H and 19F NMR studies of its (R)-MTPA ester.30 Major
1
isomer: 19F NMR (CDCl3, reference ) CF3COOH) δ 6.31; H
NMR δ 2.08 (-CH2CH2O-), 2.28 (-CH2CH2O-), 4.47 (-OCH2-
Ph). Minor isomer: 19F NMR (CDCl3, reference ) CF3COOH)
δ 6.49; 1H NMR δ 2.05 (-CH2CH2O-), 2.25 (-CH2CH2O-),
4.41 (-OCH2Ph).
P a lla d iu m -Ca ta lyzed Asym m etr ic Hyd r osilyla tion of
Deu ter a ted Styr en es (3a -r-d 1 a n d 3a -â,â-d 2). The reaction
conditions and results are summarized in Table 3. The reaction
was carried out with 20 equiv (to styrene) of trichlorosilane.
After oxidation of the hydrosilylation product, 1-phenylethanol
was converted into acetate ester 8 by treatment with acetic
anhydride and triethylamine. The deuterium and hydrogen
colorless oil. 12 (85% ee): [R]20 -28.0 (c 1.12, CHCl3). A
D
mixture of 13a and 13b: (83% ee) [R]20D -48.1 (c 1.40, CHCl3).
(S)-(-)-1-Meth ylin d a n (14). To a suspension of pyridinium
chlorochromate (PCC) (2.16 g, 10.0 mmol) and powdered 4A
molecular sieves (1.62 g) in dichloromethane (15 mL) was
added a solution of 1-methyl-2-(hydroxymethyl)indan (12) (81%
ee) in dichloromethane (5 mL) at room temperature. The
reaction mixture was stirred at room temperature for 1 h,
diluted with ether, and filtered through a Celite plug. The filter
cake was rinsed with dichloromethane. The combined filtrates
were concentrated in vacuo and the residue was chromato-
graphed on silica gel (hexane/ethyl acetate ) 5:1) to give
(1S,2R)-1-methyl-2-formylindan as colorless oil (253 mg, 1.58
mmol, 81%): 1H NMR δ 1.41 (d, J ) 6.8 Hz, 3H), 2.87 (dddd,
J ) 2.4, 7.3, 8.3, 8.3 Hz, 1H), 3.15 (dd, J ) 8.3, 16.1 Hz, 1H),
3.21 (dd, J ) 8.3, 16.1 Hz, 1H), 3.53 (dq, J ) 7.3, 6.8 Hz, 1H),
7.13-7.36 (m, 4H), 9.83 (d, J ) 2.4 Hz, 1H).
2
content was determined by 1H and H NMR analyses of acetate
8. (R)-8 (entry 1 in Table 3, 3a -R-d1 and 2g): 1H NMR (C6D6)
δ 1.33 (s, 3.0H), 1.64 (s, 3.0H, CH3C(O)), 7.03-7.26 (m, 5H);
2H NMR (CHCl3/CDCl3) δ 5.88 (br s). (R)-8 (entry 2 in Table
3, 3a -â,â-d2 and 2g): 1H NMR (C6D6) δ 1.33 (d, J ) 6.6 Hz,
2.6H), 1.64 (s, 3.0H, CH3C(O)), 5.94 (q, J ) 6.6 Hz, 1.0H), 7.03-
7.26 (m, 5H); 2H NMR (CHCl3/CDCl3) δ 1.53 (br s). (R)-8 (entry
3 in Table 3, 3a -â,â-d2 and 2a ): 1H NMR (C6D6) δ 1.28-1.35
(m, 1.6H), 1.64 (s, 3.0H, CH3C(O)), 5.90-5.97 (m, 1.0H), 7.03-
2
7.26 (m, 5H); H NMR (CHCl3/CDCl3) δ 1.52 (br s).
P a lla d iu m -Ca ta lyzed Asym m etr ic Hyd r osilyla tion of
o-Allylstyr en e (9). To a mixture of [PdCl(η3-C3H5)]2 (0.69 mg,
1.9 µmol), (R)-2-bis(3,5-bis(trifluoromethyl)phenyl)phosphino-
1,1′-binaphthyl (2g) (5.3 mg, 3.8 µmol), and o-allylstyrene (9)
(174 mg, 1.2 mmol) was added trichlorosilane (165 mg, 1.2
mmol) at -78 °C, and the reaction mixture was stirred at -20
°C for 120 h. The reaction progress was monitored by GLC
To a solution of RhCl(PPh3)3 (1.48 g, 1.60 mmol) in aceto-
nitrile (15 mL) was added a solution of (1S,2R)-1-methyl-2-
formylindan (253 mg, 1.58 mmol) in acetonitrile (10 mL) at
room temperature. The reaction mixture was refluxed for 26
h, cooled to ambient temperature, and filtered. The filtrate was
extracted with pentane (three times). The pentane phase was
separated and concentrated. The residue was chromato-
graphed on silica gel (pentane) to give 14 as colorless oil. The
oil was distilled by bulb-to-bulb distillation (32 mmHg, 120
1
analysis. GLC and H NMR study on the whole crude mixture
indicated that the ratio of 1-methyl-2-(trichlorosilylmethyl)-
indan (10)/1-(2-(2-propenyl)phenyl)-1-trichlorosilylethane (11a)/
1-(2-((E)-1-propenyl)phenyl)-1-trichlorosilylethane (11b) was
47/42/11. The mixture was distilled (bulb-to-bulb) under
reduced pressure to give 249 mg (74% yield) of the mixture of
10, 11a , and 11b. The mixture was treated with an excess of
methylmagnesium bromide in ether according to the reported
procedures13 to give a mixture of 1-methyl-2-(trimethylsilyl-
methyl)indan (10′), 1-(2-(2-propenyl)phenyl)-1-trimethylsilyl-
ethane (11a ′), and 1-(2-((E)-1-propenyl)phenyl)-1-trimethyl-
silylethane (11b′) as colorless oil. The mixture was analyzed
by GLC using a chiral stationary phase column (Cyclodex
â236M) to determine their enantiomeric purities, 10′, 11a ′, and
11b′ being 91% ee, 95% ee and 95% ee, respectively. Their
absolute configuration was assigned by correlation with known
°C) to give pure 14 (86.0 mg, 0.651 mmol, 41%): [R]20 -8.05
D
(c 1.47, benzene) (lit.17 for (R)-(+) [R]20 +10.0 (c 0.014,
D
benzene)); 1H NMR δ 1.29 (d, J ) 6.8 Hz, 3H), 1.60 (dddd, J )
8.3, 8.3, 8.8, 12.2 Hz, 1H), 2.30 (dddd, J ) 3.9, 7.8, 8.3, 12.2
Hz, 1H), 2.83 (ddd, J ) 8.3, 8.3, 16.6 Hz, 1H), 2.91 (ddd, J )
3.9, 8.3, 16.6 Hz, 1H), 3.18 (ddq, J ) 7.8, 8.8, 6.8 Hz, 1H),
7.12-7.25 (m, 4H).
(S)-1-(2-((E)-1-P r op en yl)p h en yl)eth a n ol (13b). To a so-
lution of PdCl2(CH3CN)2 (25.9 mg, 10.0 mmol) in benzene (4
mL) was added a mixture of 1-(2-(2-propenyl)phenyl)ethanol
(13a ) 1-(2-((E)-1-propenyl)phenyl)ethanol (13b) (324 mg, 2.00
mmol) (13a /13b ) 4/1) at room temperature. The reaction
mixture was refluxed for 5 min and concentrated in vacuo.
The residue was chromatographed on silica gel (hexane/ethyl
acetate ) 10/1 to 5/1) to give isomerically pure 13b (265 mg,
1.64 mmol, 82%): 1H NMR δ 1.48 (d, J ) 6.3 Hz, 3H), 1.77 (br
s, 1H), 1.91 (dd, J ) 1.5, 6.8 Hz, 3H), 5.22 (q, J ) 6.3 Hz, 1H),
6.08 (dq, J ) 15.6, 6.8 Hz, 1H), 6.69 (dd, J ) 1.5, 15.6 Hz,
1H), 7.14-7.57 (m, 4H).
(S)-(-)-3-Meth ylp h th a lid e (15). To a solution of 13b (80.0
mg, 0.493 mmol) in dichloromethane (5 mL) was bubbled O3
at -78 °C for 1 h. Excess ozone was purged from the solution
with nitrogen (5 min). To the reaction mixture were added zinc
powder (200 mg) and acetic acid (0.4 mL) at the same
temperature, and the mixture was allowed to warm to 0 °C.
After being stirred for 2 h under nitrogen atmosphere, the
reaction mixture was filtered and washed with dichloro-
methane. The combined filtrates were washed with saturated
sodium bicarbonate, water, and brine (once each). The organic
(23) Nagai, U.; Shishido, T.; Chiba, R.; Mitsuhashi, H. Tetrahedron
1965, 21, 1701.
(24) Carter, M. B.; Schiøtt, B.; Gutie´rrez, A.; Buchwald, S. L. J . Am.
Chem. Soc. 1994, 116, 11667.
(25) Nakamura, K.; Matsuda, T. J . Org. Chem. 1998, 63, 8957.
(26) Hayashi, T.; Matsumoto, Y.; Ito, Y. Tetrahedron: Asymmetry
1991, 2, 601.
(27) Ishizaki, T.; Miura, H.; Nohira, H. Nippon Kagaku Kaishi 1980,
1381.
(28) Naemura, K.; Murata, M.; Tanaka, R.; Yano, M.; Hirose, K.;
Tobe, Y. Tetrahedron: Asymmetry 1996, 7, 3285.
(29) (a) Brown, H. C.; Chandrasekharn, J .; Ramachandran, P. V. J .
Am. Chem. Soc. 1988, 110, 1539. (b) Pickard, R. H.; Kenyon, J . J . Chem.
Soc. 1914, 105, 1115.
(30) (a) Sullivan, G. R.; Dale, J . A.; Mosher, H. S. J . Org. Chem.
1973, 38, 2143. (b) Takano, S.; Takahashi, M.; Yanase, M.; Sekiguchi,
Y.; Iwabuchi, Y.; Ogasawara, K. Chem. Lett. 1988, 1827. (c) Ohtani,
I.; Kusumi, T.; Kashman, Y.; Kakisawa, H. J . Am. Soc. Chem. 1991,
113, 4092.

Asymmetric Hydrosilylation of Styrenes
J . Org. Chem., Vol. 66, No. 4, 2001 1449
phase was dried over anhydrous sodium sulfate and concen-
trated in vacuo. The crude lactol (60.8 mg) obtained was
subjected to the oxidation without further purification.
To a suspension of PCC (437 mg, 2.03 mmol) and powdered
4A molecular sieves (600 mg) in dichloromethane (2 mL) was
added a solution of crude lactol in dichloromethane (2 mL) at
room temperature. The reaction mixture was stirred at room
temperature for 1.5 h, diluted with ether, and filtered through
a Celite plug, and the filter cake was rinsed with dichloro-
methane. The combined filtrates were concentrated in vacuo
and the residue was chromatographed on silica gel (hexane/
ethyl acetate ) 5/1) to give 15 as colorless oil (26.0 mg, two
steps, 36%): [R]22 -25.6 (c 0.675, MeOH) (lit.18 for 97% ee of
D
(S)-(-) [R]22 -27.85 (c 1.3, MeOH)); H NMR δ 1.65 (d, J )
1
D
6.8 Hz, 3H), 5.57 (q, J ) 6.8 Hz, 1H), 7.44-7.91 (m, 4H).
Ack n ow led gm en t. This work was supported by
“Research for the Future” Program, the J apan Society
for the Promotion of Science and a Grant-in-Aid for
Scientific Research, the Ministry of Education, J apan.
J O001614P