Asymmetric hydrosilylation of styrenes by use of new chiral phosphoramidites

Article abstract of DOI:10.1055/s-2008-1032199

New chiral phosphoramidites were synthesized from chiral unsymmetrical amines and BINOL in good yields. Enantioselective hydrosilylation of styrenes with trichlorosilane in the presence of palladium complexes of these ligands provided chiral silanes in medium to high yields. Oxidation of these chiral silanes with hydrogen peroxide gave the corresponding chiral secondary alcohols in up to 97% ee. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1032199

PAPER
925
Asymmetric Hydrosilylation of Styrenes by Use of New Chiral
Phosphoramidites
Asymmetric
H
ydro
i
silylat
nses heng Li,* Jianan Song, Dongcheng Xu, Lichun Kong
Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry, Zhejiang Normal University,
Jinhua 321004, P. R. of China
Fax +86(579)82282610; E-mail: sky33@zjnu.cn
Received 18 September 2007; revised 4 December 2007
Ph
Abstract: New chiral phosphoramidites were synthesized from
Ph
O
chiral unsymmetrical amines and BINOL in good yields. Enantiose-
lective hydrosilylation of styrenes with trichlorosilane in the pres-
ence of palladium complexes of these ligands provided chiral
silanes in medium to high yields. Oxidation of these chiral silanes
with hydrogen peroxide gave the corresponding chiral secondary al-
cohols in up to 97% ee.
O
O
N
P
P
N
O
Ph
Ph
1
2
Key words: hydrosilylation, phosphoramidites, asymmetric syn-
thesis, chiral secondary alcohols, palladium
Figure 1
tested in the reaction. Herein, we wish to report the results
of the palladium-catalyzed hydrosilylation of styrenes.
Catalytic asymmetric functionalization of alkenes has
been recognized to be one of the most useful methods for
the transformation of prochiral alkenes into optically ac-
tive units.1 Asymmetric palladium-catalyzed hydrosilyla-
tion of olefins with trichlorosilane affords chiral alcohols
upon Tamao–Fleming stereospecific oxidation.2 The very
low catalyst loading and stereospecific oxidation make
the hydrosilylation of olefins an outstanding method for
the synthesis of chiral alcohols. Bisphosphine ligands
have shown excellent enantioselectivity in some asym-
metric transition-metal catalysis, but unsatisfactory re-
sults have been reported when these ligands are used in
palladium-catalyzed asymmetric hydrosilylation.1 As in-
dicated by the reaction mechanism, the catalytic process
requires a free coordination site on the metal. Thus,
monodentate ligands are essential if high reactivities and
enantioselectivities are to be obtained.
Chiral aminonaphthols 3 (Scheme 1) were easily
synthesized8,9a and transformed into different amino-
containing compounds, which were versatile ligands and
have been successfully applied in asymmetric synthesis,
such as the addition of diethylzinc or alkenylzinc to alde-
hydes,9 phenyl transfer reactions,10 allylic alkylations,11
and optical resolution as chiral auxiliary by the diaste-
reomer method.12 The unsymmetrical secondary amines 3
could be conveniently transformed into phosphoramidites
7 in good yields by reaction with axially chiral BINOL
(Scheme 1). Alkylation of the hydroxy group of naphthols
3a, 3c, and 3d with methyl or ethyl iodide in acetone after
protection of the amino group with benzyl chloroformate
in dichloromethane provided 5a–d in quantitative total
yields (Scheme 1). Hydrogenolysis of carbamates 5a–d
with 5% palladium on carbon in alcohol offered free sec-
ondary amines 6a–d in good yields (Scheme 1). The free
amines reacted with phosphorus trichloride and chiral
BINOL to provide chiral phosphoramidites 7a–d in 32–
74% yield after flash chromatography.
According to literature reports of monophosphine ligands,
only axially chiral MOP [2-(diarylphosphino)-2¢-meth-
oxy-1,1¢-binaphthyl]3 and planar chiral MOPF (aryl-
monophosphinoferrocene)4 have shown excellent
catalytic activities in the hydrosilylation of olefins. Re-
cently, phosphoramidites 15 and 26 (Figure 1) have been
successfully developed for the hydrosilylation of styrenes.
These phosphoramidites consist of chiral symmetrical
amines and diols. However, phosphoramidites derived
from unsymmetrical amines are scarcely used in the hy-
drosilylation of olefins.7 To develop new catalysts and
evaluate the effect of the structure of the amine on hydro-
silylation, several new phosphoramidites with chiral un-
symmetrical amines were prepared conveniently and
Asymmetric hydrosilylation of styrene (8a) with trichlo-
rosilane was carried out in the presence of 1 mol% catalyst
obtained in situ by the mixing of [Pd(h3-C3H5)Cl]2 (0.50
mol% of this dimer) and chiral phosphoramidites 7a–d at
room temperature (Scheme 2, Table 1). The results
showed that the reactivity and enantioselectivity of the hy-
drosilylation strongly depended on the configuration of
the ligands (Table 1, entries 1–6 versus 7–11). Ligands
with (R,R,R)-configuration had poor catalytic activity and
led to low enantioselectivity (Table 1, entries 1–6). High-
er catalyst loading could improve yields and enantioselec-
tivities (Table 1, entries 3–7). For example, silane 9a (cf.
Scheme 2) was obtained in 16 and 47% yields (26% ee in
the latter case) in the presence of 0.25 and 0.5 mol% of
palladium/(R,R,R)-7a, respectively, after 48 hours at
SYNTHESIS 2008, No. 6, pp 0925–0931
x
x
.
x
x
.2
0
0
8
Advanced online publication: 28.02.2008
DOI: 10.1055/s-2008-1032199; Art ID: F16807SS
© Georg Thieme Verlag Stuttgart · New York

926
X. Li et al.
PAPER
R
R
R
O
O
NH
OH
N
O
N
O
a
b
OH
OR1
3a,c,d
4a,c,d
5a–d
R
(R,R,R)-7a R = H, R1 = Me
(S,R,R)-7a R = H, R1 = Me
(R,R,R)-7b R = H, R1 = Et
(S,R,R)-7b R = H, R1 = Et
(R,R,R)-7c R = Me, R1 = Me
(S,R,R)-7c R = Me, R1 = Me
(R,R,R)-7d R = Cl, R1 = Me
(S,R,R)-7d R = Cl, R1 = Me
OR1
O
O
NH
c
d
P
N
OR1
R
6a–d
7a–d
Scheme 1 Synthesis of phosphoramidites 9a–d. Reagents and conditions: (a) BnOCOCl, CH2Cl2, Et3N, 0 °C to r.t.; (b) MeI or EtI, acetone,
reflux; (c) 5% Pd/C, H2, EtOH; (d) n-BuLi, –78 °C, then PCl3, –78 to 0 °C, (R)-BINOL or (S)-BINOL, Et3N, 0 °C to r.t.
OH
*
SiCl3
*
Pd-L (0.25 mol%)
HSiCl3
H2O2
KF, KHCO3
R
R
R
8a–g
10a–g
9a–g
8a R = H
8e R = p-F
8f R = p-Me
8g R = p-MeO
8b R = o-Cl
8c R = m-Cl
8d R = p-Cl
8h
8i
Scheme 2 Hydrosilylation of styrenes 8a–g by use of chiral monophosphoramidite ligands
room temperature (Table 1, entries 1 and 2). However, the tiomeric excesses (73–97%) (Table 2). The electronic
yield and the enantiomeric excess of the silane were dra- properties of the styrene derivatives had a significant ef-
matically improved to 93 and 32% when 1 mol% of palla- fect on the rate of the hydrosilylation. Electron-withdraw-
dium was loaded (Table 1, entry 3). The hydrosilylation ing groups on the benzene ring resulted in a decrease in
of 8a with (R,R,R)-7b–d as ligands provided modest enan- the reaction rate (Table 2, entries 2–7). Hydrosilylation of
tiomeric excesses (24–33%) and high yields (87–93%) m-chlorostyrene (8c) needed a longer reaction time than
under the same conditions (Table 1, entries 4–6). In com- was needed for other acyclic styrene derivatives (Table 2,
parison, ligands with the (S,R,R)-configuration, derived entry 3). The position of the substituent on the benzene
from (S)-BINOL and (R,R)-6, were found to be the ring had a minor effect on the enantioselectivity, with the
ligands of choice and afforded products in high yields and product of o-chlorostyrene (8b) obtained in better enan-
good enantioselectivities (Table 1, entries 7–11). For ex- tioselectivity than that of m- and p-chlorostyrene (8c,d)
ample, (S)-9a was obtained in 94% yield and 90% ee in (Table 2, entries 2–4). Hydrosilylation of p-methoxysty-
the presence of 0.25 mol% palladium and 0.5 mol% rene (8g) followed by oxidation led to the formation of the
(S,R,R)-7d in 36 hours (Table 1, entry 11). The higher cat- alcohol with the best enantioselectivity (Table 2, entry 7).
alytic activity and enantioselectivity suggested that
(S,R,R)-ligands were matched configurations in the hy-
drosilylation.
The cycloalkenes indene (8h) and 1,2-dihydronaphtha-
lene (8i) were also examined as substrates in the reaction
(Scheme 2, Table 2). Hydrosilylation of indene (8h) in the
A variety of styrene derivatives 8 were tested as substrates presence of 0.25 mol% palladium provided product 9h in
for the hydrosilylation catalyzed by the chiral palladium 92% yield and 92% ee (Table 2, entry 8). 1,2-Dihy-
complex of (S,R,R)-7d (Scheme 2, Table 2). Most of the dronaphthalene (8i) underwent hydrosilylation at a very
substituted styrenes 8 reacted completely with trichlorosi- slow reaction rate, even at 2 mol% catalyst loading
lane at room temperature, and provided the corresponding (Table 2, entry 9), and product 9i was obtained in 65%
products in good to high yields (65–96%) and good enan- yield and in 73% ee after oxidation to 10i.
Synthesis 2008, No. 6, 925–931 © Thieme Stuttgart · New York

PAPER
Asymmetric Hydrosilylation of Styrenes
927
Table 1 Palladium-Catalyzed Hydrosilylation of Styrene (8a) in the
Presence of Chiral Monophosphoramidite Ligands 7a–da
Table 2 Asymmetric Hydrosilylation of Aromatic Alkenes Cata-
lyzed by [Pd(h3-C3H5)Cl]2/(S,R,R)-7da
Entry
1d
Ligand 7
Time (h)
48
Yieldb (%)
eec (%)
Entry
Substrate 8
Time (h)
36
Yieldb (%)
eec (%)
92 (S)
93 (S)
84 (S)
85 (S)
89 (S)
73 (S)
97 (S)
92 (S)
73 (S)
e
(R,R,R)-7a
(R,R,R)-7a
(R,R,R)-7a
(R,R,R)-7b
(R,R,R)-7c
(R,R,R)-7d
(S,R,R)-7a
(S,R,R)-7a
(S,R,R)-7b
(S,R,R)-7c
(S,R,R)-7d
16
47
93
92
90
87
94
95
95
93
94
–
1d
2
8a
8b
8c
8d
8e
8f
96
76
71
81
68
90
93
92
65
2f
48
26 (R)
32 (R)
30 (R)
33 (R)
24 (R)
83 (S)
79 (S)
64 (S)
84 (S)
90 (S)
96
3g
24
3
108
96
4g
24
4
5g
24
5
96
6g
24
6
36
7g
12
7
8g
8h
8i
36
8d
36
8
36
9d
36
9e
120
10d
11d
36
a Reagents and conditions: 8 (1 equiv), HSiCl3 (2 equiv), [Pd(h3-
C3H5)Cl]2 (0.125 mol%), (S,R,R)-7d (0.5 mol%), no solvent, r.t.
b Isolated yields of silanes 9 after distillation.
36
c The ee values of alcohols 10 were determined by GC (Chiralsil-Dex
CB column). Absolute configurations were determined by compari-
son of specific rotations with literature data.13,
a Reagents and conditions: 8a (1 equiv), HSiCl3 (2 equiv), [Pd(h3-
C3H5)Cl]2 (0.125–0.50 mol%), ligand 7 (0.02 equiv), no solvent, r.t.
b Isolated yield of silane 9a after distillation.
d The reaction was carried out at 0 °C.
c The ee value of alcohol 10a was determined by GC (Chiralsil-Dex
CB column). Absolute configurations were determined by compari-
son of specific rotations with literature data.13,
e [Pd(h3-C3H5)Cl]2 (1 mol%) was used.
d [Pd(h3-C3H5)Cl]2 (0.125 mol%) was used.
layer was separated and the aqueous layer was extracted with
CH2Cl2 (2 × 10 mL). The combined organic phase was washed with
H2O (15 mL) and dried (Na2SO4). After removal of the solvent un-
der reduced pressure, the residue was recrystallized (EtOAc–hex-
ane) to afford a white solid.
e The ee value was not determined.
f [Pd(h3-C3H5)Cl]2 (0.25 mol%) was used.
g [Pd(h3-C3H5)Cl]2 (0.50 mol%) was used.
In summary, a series of new chiral phosphoramidite
ligands were prepared in high yields from unsymmetrical
amines and BINOL. The ligands with (S,R,R)-configura-
Benzyl [(R)-(2-Hydroxynaphthalen-1-yl)(phenyl)methyl][(R)-1-
phenylethyl]carbamate [(R,R)-4a]
Yield: 100%; mp 124–126 °C; [a]D20 –164.4 (c 1.0, CHCl3).
tion were effective for the palladium-catalyzed enantio- IR (KBr): 3405, 3029, 1665 cm–1.
1H NMR (400 MHz, CDCl3): d = 9.00 (s, 1 H), 7.59 (d, J = 8.0 Hz,
2 H), 7.37–6.98 (m, 16 H), 6.73–6.71 (m, 3 H), 6.52 (s, 1 H), 5.21
(q, J = 6.8, 13.6 Hz, 1 H), 5.19 (s, 1 H), 1.82 (d, J = 6.8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 157.8, 154.2, 138.6, 135.8, 133.1,
130.3, 128.8, 128.7, 128.5, 128.4, 128.3, 128.2, 127.4, 127.3, 127.1,
126.9, 126.7, 126.3, 122.4, 121.3, 120.3, 114.3, 68.2, 58.0, 57.1,
18.1.
selective hydrosilylation of styrene derivatives. The
resulting silanes were oxidized to provide secondary alco-
hols in medium to high yields (up to 96% yield) and good
enantiomeric excesses (up to 97% ee). The results showed
that the enantioselectivities obtained with ligands with un-
symmetrical amines were inferior to those obtained with
symmetrical amines. Further adjustments of structure and
applications of the ligands in other asymmetric syntheses Anal. Calcd for C33H29NO3: C, 81.29; H, 5.99; N, 2.87. Found: C,
81.18; H, 5.90; N, 2.89.
are currently under investigation.
Benzyl [(R)-(2-Hydroxynaphthalen-1-yl)(p-tolyl)methyl][(R)-1-
Elemental analyses were performed on a Carlo Erba 1110 analyzer.
The 1H NMR, 13C NMR, and 31P NMR spectra were recorded on a
Bruker Avance 400 spectrometer with TMS as internal reference or
85% H3PO4 as external reference. The ee values were determined
by HPLC on a Chiralcel OD-H column or by GC on a Chiralsil-Dex
CB column. IR spectra were determined on a Nicolet-670 FT spec-
trophotometer. All reactions were carried out in dry glassware un-
der N2.
phenylethyl]carbamate [(R,R)-4c]
Yield: 99%; mp 160–162 °C; [a]D20 –261.8 (c 2.0, CHCl3).
IR (KBr): 3448, 3030, 1639 cm–1.
1H NMR (400 MHz, CDCl3): d = 9.06 (s, 1 H), 7.58 (d, J = 8.0 Hz,
2 H), 7.36–6.97 (m, 15 H), 6.71–6.69 (m, 3 H), 6.45 (s, 1 H), 5.20
(q, J = 6.8, 13.6 Hz, 1 H), 5.19 (s, 1 H), 2.31 (s, 3 H), 1.82 (d, J = 6.8
Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 157.8, 154.2, 139.0, 137.0, 135.9,
135.4, 135.1, 130.3, 129.5, 128.7, 128.5, 128.4, 128.3, 128.2, 127.3,
127.2, 126.9, 126.7, 126.3, 121.3, 120.3, 114.5, 68.2, 60.4, 57.0,
21.1, 14.2.
Benzyl Carbamates 4a,c,d; General Procedure
Benzyl chloroformate (2.6 g, 15 mmol) in CH2Cl2 (10 mL) was add-
ed to a mixture of the appropriate chiral aminonaphthol 3 (10 mmol)
and Et3N (3.1 g, 30 mmol) in CH2Cl2 (30 mL) at 0 °C. After the
mixture had stirred at r.t. overnight, H2O was added. The organic
Anal. Calcd for C34H31NO3: C, 81.41; H, 6.23; N, 2.79. Found: C,
81.35; H, 6.21; N, 2.89.
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928
X. Li et al.
PAPER
Benzyl [(R)-(4-Chlorophenyl)(2-hydroxynaphthalen-1-yl)meth-
yl][(R)-1-phenylethyl]carbamate [(R,R)-4d]
13C NMR (100 MHz, CDCl3): d = 156.8, 138.7, 135.1, 134.1, 131.1,
129.5, 128.7, 128.2, 128.1, 128.0, 127.6, 127.2, 126.9, 126.1, 125.7,
125.6, 124.2, 123.4, 113.8, 66.9, 58.4, 55.9, 21.0, 20.1.
Yield: 99.5%; mp 144–146 °C; [a]D20 –249.8 (c 2.8, CHCl3).
IR (KBr): 3350, 3064, 1640, 1279 cm–1.
Anal. Calcd for C35H33NO3: C, 81.52; H, 6.45; N, 2.72. Found: C,
81.40; H, 6.35; N, 2.75.
1H NMR (400 MHz, CDCl3): d = 9.21 (s, 1 H), 7.59 (d, J = 8.0 Hz,
2 H), 7.35–6.99 (m, 15 H), 6.71–6.70 (m, 3 H), 6.35 (s, 1 H), 5.26
(q, J = 6.8, 13.6 Hz, 1 H), 5.19 (s, 2 H), 1.79 (d, J = 6.8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 157.9, 154.2, 138.6, 137.2, 135.7,
130.0, 132.9, 130.5, 128.8, 128.7, 128.6, 128.6, 128.6, 128.4, 128.4,
128.3, 128.3, 127.4, 127.2, 127.0, 126.4, 122.5, 121.0, 120.4, 113.8,
68.5, 57.5, 57.2, 17.9.
Benzyl [(R)-(4-Chlorophenyl)(2-methoxynaphthalen-
1-yl)methyl][(R)-1-phenylethyl]carbamate [(R,R)-5d]
Yield: 99.5%; mp 50–52 °C; [a]D20 118.1 (c 2.1, CHCl3).
IR (KBr): 3030, 2934, 1685 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.80–7.41 (m, 3 H), 7.37–7.04 (m,
12 H), 6.89–6.72 (m, 5 H), 5.14 (d, J = 12.0 Hz, 1 H), 5.01 (d,
J = 12.0 Hz, 1 H), 4.58 (q, J = 6.8, 13.6 Hz, 1 H), 3.54 (s, 3 H), 1.87
(d, J = 6.8 Hz, 3 H).
Anal. Calcd for C33H28ClNO3: C, 75.92; H, 5.41; N, 2.68. Found: C,
75.81; H, 5.24; N, 2.88.
Benzyl Carbamates 5; General Procedure
13C NMR (100 MHz, CDCl3): d = 156.7, 143.2, 133.9, 131.5, 131.2,
129.4, 128.8, 128.3, 128.2, 128.1, 128.0, 127.8, 127.3, 127.0, 126.0,
125.7, 123.7, 123.6, 113.7, 67.1, 58.3, 55.8, 22.8, 20.0.
A mixture of 4 (5 mmol), K2CO3 (1.4 g, 10 mmol), and MeI or EtI
(7.5 mmol) in acetone (20 mL) was refluxed until TLC indicated
that 4 had been consumed. H2O was added to the mixture. The or-
ganic layer was separated, and the aqueous layer was extracted with
CH2Cl2 (2 × 10 mL). The combined organic phase was washed with
H2O (10 mL) and dried (Na2SO4). After removal of the solvent un-
der reduced pressure, the sufficiently pure products 5 were obtained
in quantitative yields.
Anal. Calcd for C34H30ClNO3: C, 76.18; H, 5.64; N, 2.61. Found: C,
76.25; H, 5.60; N, 2.64.
(R)-N-[(R)-(2-Methoxynaphthalen-1-yl)(phenyl)methyl]-1-phe-
nylethanamines 6; General Procedure
A mixture of 5 (4 mmol) in EtOH (15 mL) was hydrogenated in the
presence of 5% Pd/C (0.15 g) under standard conditions. When the
sum of theoretical H2 was consumed, the hydrogenation was ceased.
After removal of the solvent under reduced pressure, the residue
was purified by column chromatography to afford a white solid.
Benzyl [(R)-(2-Methoxynaphthalen-1-yl)(phenyl)methyl][(R)-1-
phenylethyl]carbamate [(R,R)-5a]
Yield: 99.5%; [a]D20 100.6 (c 2.0, CHCl3).
IR (KBr): 3058, 2939, 1694 cm–1.
(R)-N-[(R)-(2-Methoxynaphthalen-1-yl)(phenyl)methyl]-1-phe-
nylethanamine [(R,R)-6a]
1H NMR (400 MHz, CDCl3): d = 7.69–7.62 (m, 4 H), 7.37–7.06 (m,
12 H), 6.85–6.72 (m, 5 H), 5.17 (d, J = 12.0 Hz, 1 H), 5.01 (d,
J = 12.0 Hz, 1 H), 4.61 (q, J = 6.8, 13.6 Hz, 1 H), 4.57 (s, 1 H), 3.48
(s, 3 H), 1.91 (d, J = 6.8 Hz, 3 H).
Yield: 89%; mp 104–106 °C; [a]D20 61.8 (c 1.2, CHCl3).
IR (KBr): 3442, 3056, 2969 cm–1.
13C NMR (100 MHz, CDCl3): d = 156.8, 143.6, 134.2, 131.2, 129.5,
128.7, 128.6, 128.5, 128.4, 128.3, 128.2, 127.9, 127.6, 127.3, 127.2,
127.0, 126.1, 125.8, 125.7, 125.6, 124.0, 123.4, 113.9, 67.0, 58.7,
55.8, 46.2, 20.2.
1H NMR (400 MHz, CDCl3): d = 7.81 (d, J = 8.8 Hz, 2 H), 7.38 (d,
J = 7.6 Hz, 2 H), 7.34–7.11 (m, 13 H), 5.60 (s, 1 H), 3.67 (s, 3 H),
3.57 (q, J = 6.4, 12.8 Hz, 1 H), 2.87 (s, 1 H), 1.24 (d, J = 6.0 Hz, 3
H).
Anal. Calcd for C34H31NO3: C, 81.41; H, 6.23; N, 2.79. Found: C,
81.38; H, 6.20; N, 2.83.
13C NMR (100 MHz, CDCl3): d = 155.6, 129.2, 128.6, 128.3, 128.2,
127.8, 127.7, 127.3, 127.2, 126.8, 126.7, 126.4, 125.8, 123.5, 114.2,
56.3, 55.8, 25.8.
Benzyl [(R)-(2-Ethoxynaphthalen-1-yl)(phenyl)methyl][(R)-1-
phenylethyl]carbamate [(R,R)-5b]
Anal. Calcd for C26H25NO: C, 84.98; H, 6.86; N, 3.81. Found: C,
84.90; H, 6.78; N, 3.83.
Yield: 100%; [a]D20 107.7 (c 2.0, CHCl3).
IR (KBr): 3058, 2939, 1695 cm–1.
(R)-N-[(R)-(2-Ethoxynaphthalen-1-yl)(phenyl)methyl]-1-phe-
nylethanamine [(R,R)-6b]
1H NMR (400 MHz, CDCl3): d = 9.00 (s, 1 H), 7.76–7.71 (m, 4 H),
7.25–7.06 (m, 12 H), 6.87–6.70 (m, 5 H), 5.16 (d, J = 12.0 Hz, 1 H),
5.02 (d, J = 12.0 Hz, 1 H), 4.68 (q, J = 6.8, 13.6 Hz, 1 H), 3.98 (m,
1 H), 3.52 (q, J = 6.8, 13.6 Hz, 1 H), 1.92 (d, J = 6.8 Hz, 3 H), 0.86
(t, J = 7.2 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 156.2, 143.6, 134.5, 131.2, 129.3,
128.7, 128.3, 128.0, 128.2, 127.9, 127.6, 127.2, 127.1, 126.2, 125.6,
125.5, 123.8, 123.4, 119.5, 114.2, 67.1, 64.3, 58.7, 55.6, 19.8, 14.3.
Yield: 86%; mp 116–118 °C; [a]D20 52.1 (c 2.0, CHCl3).
IR (KBr): 3448, 2963, 1594 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.79 (d, J = 12.8 Hz, 2 H), 7.58 (d,
J = 7.6 Hz, 2 H), 7.42–7.11 (m, 13 H), 5.61 (s, 1 H), 4.13–4.09 (m,
1 H), 3.78–3.74 (m, 1 H), 3.60 (q, J = 6.0, 12.0 Hz, 1 H), 2.88 (s, 1
H), 1.26 (d, J = 6.0 Hz, 3 H), 0.86 (t, J = 7.2 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 154.9, 129.2, 129.0, 128.6, 128.3,
128.2, 127.7, 127.2, 126.9, 126.8, 126.7, 125.5, 123.5, 114.8, 64.7,
55.7, 29.7, 25.9, 14.8.
Anal. Calcd for C35H33NO3: C, 81.52; H, 6.45; N, 2.72. Found: C,
81.50; H, 6.40; N, 2.75.
Anal. Calcd for C27H27NO: C, 85.00; H, 7.13; N, 3.67. Found: C,
84.87; H, 7.10; N, 3.71.
Benzyl [(R)-(2-Methoxynaphthalen-1-yl)(p-tolyl)methyl][(R)-1-
phenylethyl]carbamate [(R,R)-5c]
Yield: 99.5%; mp 124–126 °C; [a]D20 109.8 (c 3.0, CHCl3).
(R)-N-[(R)-(2-Methoxynaphthalen-1-yl)(p-tolyl)methyl]-1-phe-
nylethanamine [(R,R)-6c]
IR (KBr): 3448, 3030, 1639, 1273 cm–1.
Yield: 84%; mp 101–103 °C; [a]D20 34.5 (c 2.0, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.76–7.70 (m, 4 H), 7.39–7.07 (m,
11 H), 6.86–6.72 (m, 5 H), 5.17 (d, J = 12.0 Hz, 1 H), 4.99 (d,
J = 12.4 Hz, 1 H), 4.61 (q, J = 6.8, 13.6 Hz, 1 H), 3.53 (s, 1 H), 2.32
(s, 1 H), 1.89 (d, J = 6.8 Hz, 3 H).
IR (KBr): 3448, 3067, 2956, 1512 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.83–7.81 (m, 2 H), 7.79–7.74 (m,
1 H), 7.34–7.22 (m, 10 H), 7.02 (d, J = 8.0 Hz, 2 H), 5.56 (s, 1 H),
Synthesis 2008, No. 6, 925–931 © Thieme Stuttgart · New York

PAPER
Asymmetric Hydrosilylation of Styrenes
929
3.69 (s, 3 H), 3.52 (q, J = 6.4, 12.8 Hz, 1 H), 2.92 (s, 1 H), 2.26 (s,
3 H), 1.24 (d, J = 6.0 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 155.6, 146.4, 141.9, 135.2, 129.1,
128.6, 128.5, 128.2, 127.2, 126.8, 126.7, 126.4, 125.6, 123.4, 114.3,
56.4, 55.8, 25.8, 21.0.
13C NMR (100 MHz, CDCl3): d = 155.7, 155.6, 151.2, 150.5, 150.1,
150.4, 149.5, 132.8, 132.4, 131.2, 130.1, 130.0, 129.3, 129.2, 128.3,
128.2, 128.0, 127.5, 127.2, 127.1, 126.3, 126.1, 125.9, 125.8, 124.6,
126.5, 125.9, 125.8, 125.7, 125.6, 124.5, 124.3, 122.8, 122.6, 122.5,
122.4, 121.5, 120.9, 120.8, 113.7, 55.5, 53.9, 53.8, 18.9.
31P NMR (161.9 MHz, CDCl3): d = 146.0.
Anal. Calcd for C27H27NO: C, 85.00; H, 7.13; N, 3.67. Found: C,
84.90; H, 7.10; N, 3.69.
Anal. Calcd for C46H36NO3P: C, 81.04; H, 5.32; N, 2.05. Found: C,
81.01; H, 5.30; N, 2.12.
(R)-N-[(R)-(4-Chlorophenyl)(2-methoxynaphthalen-1-yl)meth-
yl]-1-phenylethanamine [(R,R)-6d]
[(R)-1,1¢-Dinaphthyl-2,2¢-diyl] [(R)-(2-Ethoxynaphthalen-1-
yl)(phenyl)methyl][(R)-1-phenylethyl]phosphoramidite
[(R,R,R)-7b]
Yield: 85%; mp 100–102.5 °C; [a]D20 38.7 (c 2.3, CHCl3).
IR (KBr): 3449, 3022, 2946, 1511 cm–1.
Yield: 69%; mp 158–160 °C; [a]D20 –48.8 (c 0.5, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.85–7.81 (m, 2 H), 7.58–7.56 (m,
1 H), 7.31–7.24 (m, 10 H), 7.14 (d, J = 8.0 Hz, 2 H), 5.50 (s, 1 H),
3.69 (s, 3 H), 3.55 (q, J = 6.4, 12.8 Hz, 1 H), 2.82 (s, 1 H), 1.23 (d,
J = 6.0 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 155.5, 146.1, 143.7, 131.4, 129.4,
128.7, 128.3, 128.2, 128.1, 127.8, 127.2, 126.9, 126.6, 123.5, 114.3,
56.3, 55.8, 25.9.
IR (KBr): 3056, 2932, 1592, 1462 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.93 (d, J = 8.8 Hz, 1 H), 7.87 (d,
J = 8.0 Hz, 1 H), 7.76 (d, J = 7.6 Hz, 1 H), 7.66–7.02 (m, 19 H),
6.92–6.83 (m, 3 H), 6.70–6.67 (m, 3 H), 6.47–6.42 (m, 1 H), 4.79
(q, J = 6.8, 13.6 Hz, 1 H), 4.03–3.96 (m, 1 H), 3.89–3.75 (m, 1 H),
1.57 (d, J = 6.8 Hz, 3 H), 1.26 (t, J = 6.8, 13.6 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 151.3, 151.2, 150.0, 140.7, 131.2,
131.1, 130.7, 130.3, 130.1, 129.6, 129.3, 129.0, 128.6, 128.4, 128.3,
128.2, 128.1, 127.9, 127.6, 127.3, 127.2, 127.1, 126.9, 126.5, 126.1,
125.8, 125.6, 124.5, 124.3, 124.2, 124.1, 122.9, 122.7, 122.3, 121.5,
113.5, 63.7, 53.9, 31.5, 22.6, 14.9.
Anal. Calcd for C26H24ClNO: C, 77.70; H, 6.02; N, 3.48. Found: C,
77.65; H, 6.00; N, 3.51.
[(R)-1,1¢-Dinaphthyl-2,2¢-diyl] [(R)-(2-Methoxynaphthalen-1-
yl)(phenyl)methyl][(R)-1-phenylethyl]phosphoramidites 7a–d;
General Procedure
31P NMR (161.9 MHz, CDCl3): d = 152.1.
A 2.0 M soln of n-BuLi in hexane (1.1 mL, 2.2 mmol) was added to
a mixture of the appropriate 6 (2 mmol) in anhyd THF (40 mL) at
–78 °C. After the mixture had stirred at –78 °C for 30 min, PCl3
(0.27 g, 2 mmol) in anhyd THF (1 mL) was added. The temperature
of the suspension was slowly allowed to reach 0 °C, and the mixture
was stirred at 0 °C for 3 h. Et3N (10 mmol) was added to the mixture
at 0 °C, followed by (R)- or (S)-BINOL (0.57 g, 2 mmol) in anhyd
THF (30 mL). The resulting mixture was stirred at r.t. for 12 h. After
removal of the solvent under reduced pressure, the residue was pu-
rified by flash column chromatography to afford a white solid.
Anal. Calcd for C47H38NO3P: C, 81.13; H, 5.50; N, 2.01. Found: C,
81.08; H, 5.50; N, 2.18.
[(S)-1,1¢-Dinaphthyl-2,2¢-diyl] [(R)-(2-Ethoxynaphthalen-1-
yl)(phenyl)methyl][(R)-1-phenylethyl]phosphoramidite
[(S,R,R)-7b]
Yield: 65%; mp 228–230 °C; [a]D20 –174.4 (c 0.5, CHCl3).
IR (KBr): 3030, 2932, 1591, 1462 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.87–7.85 (m, 4 H), 7.74–7.58 (m,
4 H), 7.37–7.20 (m, 15 H), 6.97–6.93 (m, 3 H), 6.80–6.77 (m, 1 H),
6.47–6.43 (m, 1 H), 4.96 (q, J = 6.8, 13.6 Hz, 1 H), 3.87–3.85 (m, 1
H), 3.70–3.67 (m, 1 H), 1.67 (d, J = 6.8 Hz, 3 H), 0.87 (t, J = 6.8 Hz,
3 H).
13C NMR (100 MHz, CDCl3): d = 151.2, 151.0, 150.0, 140.5, 131.1,
130.8, 130.6, 130.1, 129.8, 129.4, 129.2, 129.1, 128.8, 128.6, 128.4,
128.3, 128.2, 127.9, 127.8, 127.2, 127.1, 126.8, 126.6, 126.5, 126.0,
125.2, 124.8, 124.5, 124.4, 124.3, 122.8, 122.3, 121.8, 121.2, 113.0,
63.5, 53.7, 31.6, 22.4, 18.9.
[(R)-1,1¢-Dinaphthyl-2,2¢-diyl] [(R)-(2-Methoxynaphthalen-1-
yl)(phenyl)methyl][(R)-1-phenylethyl]phosphoramidite
[(R,R,R)-7a)]
Yield: 67%; mp 187–189 °C; [a]D20 –54.5 (c 1.0, CHCl3).
IR (KBr): 3054, 1954, 1462 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.91 (d, J = 8.8 Hz, 1 H), 7.86 (d,
J = 8.0 Hz, 1 H), 7.75 (d, J = 8.0 Hz, 1 H), 7.68–7.05 (m, 22 H),
6.70–6.67 (m, 3 H), 6.28 (s, 1 H), 4.76 (q, J = 8.0, 16.0 Hz, 1 H),
3.76 (s, 3 H), 1.72 (d, J = 6.8 Hz, 3 H).
31P NMR (161.9 MHz, CDCl3): d = 146.2.
13C NMR (100 MHz, CDCl3): d = 155.7, 151.4, 151.2, 142.2, 140.6,
140.5, 132.4, 131.2, 130.3, 130.1, 129.6, 129.3, 128.9, 128.5, 128.3,
128.2, 128.0, 127.9, 127.8, 127.3, 127.1, 126.9, 126.7, 126.5, 125.9,
125.8, 125.7, 125.6, 124.5, 124.3, 124.1, 122.8, 122.5, 122.4, 121.6,
120.9, 120.8, 112.9, 55.7, 53.8, 53.7, 18.9.
Anal. Calcd for C47H38NO3P: C, 81.13; H, 5.50; N, 2.01. Found: C,
81.07; H, 5.48; N, 2.11.
[(R)-1,1¢-Dinaphthyl-2,2¢-diyl] [(R)-(2-Methoxynaphthalen-1-
yl)(p-tolyl)methyl][(R)-1-phenylethyl]phosphoramidite
[(R,R,R)-7c]
31P NMR (161.9 MHz, CDCl3): d = 151.5.
Yield: 71%; mp 227–229.5 °C; [a]D20 –70.0 (c 1.0, CHCl3).
Anal. Calcd for C46H36NO3P: C, 81.04; H, 5.32; N, 2.05. Found: C,
81.00; H, 5.30; N, 2.10.
IR (KBr): 3054, 1954, 1462 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.94–7.64 (m, 8 H), 7.43–7.03 (m,
16 H), 6.64–6.62 (m, 3 H), 6.23 (s, 1 H), 4.73 (q, J = 6.8, 13.6 Hz,
1 H), 3.94 (s, 3 H), 2.20 (s, 3 H), 1.74 (d, J = 6.8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 155.8, 151.6, 140.5, 136.5, 134.3,
132.9, 132.8, 131.4, 131.3, 131.1, 130.9, 130.3, 130.0, 129.5, 129.4,
128.8, 128.7, 128.4, 128.3, 128.2, 128.0, 127.9, 127.3, 127.1, 127.0,
126.9, 126.4, 126.2, 126.1, 125.8, 125.7, 125.2, 125.0, 124.6, 124.3,
124.1, 122.8, 122.5, 121.9, 113.2, 55.3, 53.5, 21.2, 18.6.
[(S)-1,1¢-Dinaphthyl-2,2¢-diyl] [(R)-(2-Methoxynaphthalen-1-
yl)(phenyl)methyl][(R)-1-phenylethyl]phosphoramidite
[(S,R,R)-7a]
Yield: 70%; mp 262–264 °C; [a]D20 170 (c 0.6, CHCl3).
IR (KBr): 3054, 1953, 1461 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.89–7.84 (m, 5 H), 7.57–7.41 (m,
5 H), 7.39–7.10 (m, 13 H), 6.88–6.85 (m, 4 H), 6.48 (s, 1 H), 4.90
(q, J = 8.0, 16.0 Hz, 1 H), 3.55 (s, 3 H), 1.56 (d, J = 6.8 Hz, 3 H).
31P NMR (161.9 MHz, CDCl3): d = 151.5.
Synthesis 2008, No. 6, 925–931 © Thieme Stuttgart · New York

930
X. Li et al.
PAPER
Anal. Calcd for C47H38NO3P: C, 81.13; H, 5.50; N, 2.01. Found: C,
81.10; H, 5.35; N, 2.14.
ligand 7 (0.025 mmol), and the appropriate styrene 8 (5 mmol). Af-
ter the mixture had stirred at r.t. for 20 min, HSiCl3 (1 mL, 10 mmol)
was added at 0 °C. The reaction mixture was stirred at r.t. for 36–
120 h. The product was purified by distillation to provide pure si-
lanes 9 (cf. Table 2).
[(S)-1,1¢-Dinaphthyl-2,2¢-diyl] [(R)-(2-Methoxynaphthalen-1-
yl)(p-tolyl)methyl][(R)-1-phenylethyl]phosphoramidite
[(S,R,R)-7c]
Yield: 74%; mp 263–265 °C; [a]D20 138.6 (c 0.6, CHCl3).
Oxidation of Silanes 9; General Procedure
H2O2 (2 mL, 30%) was added to a suspension of the appropriate si-
lane 9 (1 mmol), KF (0.5 g, 8.6 mmol), and KHCO3 (1 g, 10 mmol)
in MeOH (25 mL) and THF (25 mL). The mixture was stirred for
16 h before being quenched with sat. Na2S2O3 (4 mL). After the
mixture had stirred for an additional 1 h, the solvent was removed
under reduced pressure. The residue was extracted with Et2O
(2 × 15 mL), and the combined organic phases were dried
(Na2SO4), filtered, and concentrated under vacuum. The crude
products were purified by flash column chromatography (silica gel)
(cf. Table 2).
IR (KBr): 3056, 1953, 1461 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.90–7.64 (m, 9 H), 7.55–7.14 (m,
14 H), 7.13–7.12 (m, 2 H), 7.00–6.84 (m, 3 H), 6.53–6.51 (m, 1 H),
4.83 (q, J = 6.8, 13.6 Hz, 1 H), 3.64 (s, 3 H), 2.32 (s, 3 H), 1.60 (d,
J = 6.8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 155.6, 150.5, 149.8, 148.5, 147.5,
147.0, 139.6, 136.1, 134.3, 132.8, 132.7, 131.4, 131.1, 130.8, 130.3,
130.0, 129.8, 129.3, 128.7, 128.4, 128.3, 128.2, 128.1, 127.3, 127.1,
127.0, 126.9, 126.8, 126.2, 126.1, 125.8, 125.9, 125.8, 125.1, 124.9,
124.6, 124.3, 122.8, 122.4, 121.7, 113.4, 55.5, 52.2, 21.1, 19.4.
31P NMR (161.9 MHz, CDCl3): d = 145.9.
Acknowledgment
Anal. Calcd for C47H38NO3P: C, 81.13; H, 5.50; N, 2.01. Found: C,
81.11; H, 5.39; N, 2.10.
This work was supported by the Natural Science Foundation of
Zhejiang Province (Y405013). Dr. Xiaoxia Wang is thanked for the
useful discussion.
[(R)-1,1¢-Dinaphthyl-2,2¢-diyl] [(R)-(4-Chlorophenyl)(2-meth-
oxynaphthalen-1-yl)methyl][(R)-1-phenylethyl]phosphoramid-
ite [(R,R,R)-7d]
References
Yield: 32%; mp 222–225 °C; [a]D20 –36.1 (c 1.0, CHCl3).
(1) (a) Itoh, K. Catalytic Asymmetric Synthesis, 2nd ed.; Wiley-
VCH: New York, 2000. (b) Gibson, S. E.; Rudd, M. Adv.
Synth. Catal. 2007, 349, 781.
IR (KBr): 3053, 1954, 1461 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.98–7.95 (m, 2 H), 7.90–7.67 (m,
5 H), 7.44–7.05 (m, 17 H), 6.72–6.70 (m, 3 H), 6.20 (s, 1 H), 4.77
(q, J = 6.0, 12.0 Hz, 1 H), 3.77 (s, 3 H), 1.74 (d, J = 6.4 Hz, 3 H).
(2) Tamao, K.; Ishida, N.; Tanaka, T.; Kumada, M.
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13C NMR (100 MHz, CDCl3): d = 156.3, 151.6, 142.3, 140.5, 140.3,
136.8, 132.8, 132.4, 131.4, 130.5, 130.3, 130.0, 129.5, 129.3, 129.0,
128.3, 128.1, 128.0, 127.1, 126.9, 126.7, 126.1, 126.1, 125.9, 125.8,
124.7, 124.6, 124.5, 124.2, 124.1, 122.9, 122.8, 122.7, 122.5, 122.4,
113.6, 56.9, 55.3, 29.7.
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31P NMR (161.9 MHz, CDCl3): d = 150.9.
Anal. Calcd for C46H35ClNO3P: C, 77.14; H, 4.93; N, 1.96. Found:
C, 77.10; H, 4.90; N, 2.04.
[(S)-1,1¢-Dinaphthyl-2,2¢-diyl] [(R)-(4-Chlorophenyl)(2-meth-
oxynaphthalen-1-yl)methyl][(R)-1-phenylethyl]phosphoramid-
ite [(S,R,R)-7d]
Yield: 48%; mp 265–268 °C; [a]D20 173.6 (c 0.7, CHCl3).
(4) (a) Pedersen, H. L.; Johannsen, M. Chem. Commun. 1999,
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IR (KBr): 3055, 1956, 1461 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.88–7.85 (m, 4 H), 7.67–7.52 (m,
5 H), 7.35–7.11 (m, 15 H), 6.91–6.85 (m, 4 H), 6.47 (s, 1 H), 4.89
(q, J = 6.0, 12.0 Hz, 1 H), 3.55 (s, 3 H), 1.55 (d, J = 6.4 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 155.7, 150.6, 150.4, 149.7, 140.5,
136.8, 132.9, 132.8, 132.7, 131.3, 130.4, 130.3, 130.1, 129.4, 129.3,
128.9, 128.4, 128.2, 128.1, 127.6, 127.2, 127.1, 126.9, 126.4, 126.3,
126.2, 125.9, 125.8, 124.7, 124.6, 124.5, 124.4, 124.3, 122.9, 122.7,
122.6, 122.5, 121.8, 113.7, 56.8, 55.5, 22.7.
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L.; Johannsen, M. J. Am. Chem. Soc. 2002, 124, 4558.
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Tissot-Croset, K.; Corminboeuf, C.; Ditrich, K. Chem. Eur.
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31P NMR (161.9 MHz, CDCl3): d = 146.0.
Anal. Calcd for C46H35ClNO3P: C, 77.14; H, 4.93; N, 1.96. Found:
C, 77.11; H, 4.92; N, 2.07.
Asymmetric Hydrosilylation of Styrenes 8; General Procedure
A dried Schlenk flask containing a stirrer bar was charged with
[Pd(h3-C3H5)Cl]2 (2.3 mg, 0.0063 mmol), the phosphoramidite
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Synthesis 2008, No. 6, 925–931 © Thieme Stuttgart · New York

PAPER
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Asymmetric Hydrosilylation of Styrenes
931
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Synthesis 2008, No. 6, 925–931 © Thieme Stuttgart · New York