Synthesis and application of bulky phosphoramidites: Highly effective monophosphorus ligands for asymmetric hydrosilylation of styrenes

Article abstract of DOI:10.1039/b909334f

A series of bulky monodentate phosphoramidite ligands were synthesized from chiral 3,3′-diaryl substituted BINOL derivatives and achiral or dendritic amines in good yields. Asymmetric hydrosilylation of styrenes with trichlorosilane in the presence of palladium complexes of these bulky ligands gave chiral silanes in high yields with excellent activity and productivity. Oxidation of these chiral silanes with hydrogen peroxide gave the corresponding chiral secondary alcohols in up to 96% ee.

Full text of DOI:10.1039/b909334f

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthesis and application of bulky phosphoramidites: highly effective
monophosphorus ligands for asymmetric hydrosilylation of styrenes†
Feng Zhang and Qing-Hua Fan*
Received 12th May 2009, Accepted 21st July 2009
First published as an Advance Article on the web 20th August 2009
DOI: 10.1039/b909334f
A series of bulky monodentate phosphoramidite ligands were synthesized from chiral 3,3¢-diaryl
substituted BINOL derivatives and achiral or dendritic amines in good yields. Asymmetric
hydrosilylation of styrenes with trichlorosilane in the presence of palladium complexes of these bulky
ligands gave chiral silanes in high yields with excellent activity and productivity. Oxidation of these
chiral silanes with hydrogen peroxide gave the corresponding chiral secondary alcohols in up to 96% ee.
materials and good stability.6 In 2002, Johannsen and co-workers
Introduction
firstly applied chiral phosphoramidite 2 to the Pd-catalyzed
The asymmetric catalytic functionalization of alkenes has been
asymmetric reaction of styrenes, which afforded the chiral alcohols
upon oxidation in up to 99% ee.3a Subsequently, Zhou et al.
recognized as one of the most powerful tools for the construc-
tion of chiral units.1 In particular, the Pd-catalyzed asymmetric
hydrosilylation of alkenes with trichlorosilane is one important
example of hydrometallation reactions that display excellent
developed a novel class of chiral monophosphoramidite ligand
containing a 1,1¢-spirobiindane scaffold7 and demonstrated that
these ligands were highly efficient for the Pd-catalyzed asymmetric
regioselectivities and enantioselectivities for a variety of aryl-
hydrosilylation of styrenes affording high yields with excellent
and alkyl-substituted terminal olefins.2–4 The resulting chiral
organosilanes can be converted into chiral alcohols via a Tamao
oxidation with complete retention of configuration at the carbon
center.5 In this hydrosilylation reaction, a monophosphane–
palladium combination has proven to be a necessary requirement
for achieving high catalytic activity and enantioselectivity.2a Thus
far, a number of chiral monophosphorus ligands have been
developed for such reactions.1–4 However, only a few of them
have displayed high efficiency with respect to both reactivity
and enantioselectivity. Among them, the most efficient ligands
include Hayashi’s MOP ligands2 (such as ligand 1 shown in Fig. 1)
based on an axially chiral biaryl scaffold and Johannsen’s MOPF
ligands4a,4b based on a planar chiral ferrocene scaffold. Therefore,
it is still desirable to develop highly effective and easily available
chiral monophosphorus ligands for Pd-catalyzed hydrosilylation.
enantioselectivities (up to 99.1% ee).3b It was noted that the
chiral side chains in these ligands played a dominant role in
enantioselection in this reaction. In contrast, much lower reactivity
and enantioselectivity were observed with similar ligands lacking
the additional chirality on the side chain.3
Recently, we reported a series of chiral dendritic phospho-
ramidites by attaching dendritic wedges on the nitrogen atom.8
It was found that these ligands exhibited unprecedented en-
hancement of enantioselectivity in the Rh-catalyzed asymmetric
hydrogenation of olefins. As indicated by the reaction mechanism,
Pd intermediates bearing only one phosphorus ligand have proven
to be the real catalytically active species.2a,2c It is thus reasonable to
expect that our sterically demanding dendritic phosphoramidites
without additional chiral elements in the side chain will be effective
in this reaction. In addition, most recently, de Vries et al. reported
that an iridium(I) complex containing a single phosphoramidite
ligand could induce an efficient asymmetric hydrogenation.9 It
demonstrated that the steric properties of the substituents in
the 3,3¢-positions of the chiral diol backbone played a very
important role in achieving high reactivity and enantioselectivity.
As an extension of our research and inspired by de Vries’s work,
we report here the synthesis and application of a new kind of
bulky phosphoramidite ligand (such as 3 in Fig. 1) based on a
1,1-binaphthyl backbone with substituents in the 3,3¢-positions
and/or dendritic wedges attached on the nitrogen atom of the
ligand for the Pd-catalyzed asymmetric hydrosilylation reaction
of styrenes.
Fig. 1 Binaphthol-based monophosphane and phosphoramidite ligands.
Monodentate chiral phosphoramidite ligands have recently
attracted considerable attention because of their excellent perfor-
mance, relatively simple synthesis from readily available building
Beijing National Laboratory for Molecular Sciences, CAS Key Labo-
ratory of Molecular Recognition and Function, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100190, P. R. China. E-mail:
fanqh@iccas.ac.cn
† Electronic supplementary information (ESI) available: Selected charac-
terization data of bulky chiral monodentate phosphoramidite ligands and
palladium complexes. See DOI: 10.1039/b909334f
Results and discussion
Firstly, a series of 1,1¢-binaphthol derivatives (S)-4 were syn-
thesized according to the published methods.10 The resulting
diols were refluxed with trichlorophosphine in the presence of a
catalytic amount of N-methyl-2-pyrrolidinone (NMP)11, followed
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by reaction with a dendritic secondary amine8 or dibenzylamine at
50 ◦C, providing the desired phosphoramidites 3a–3k in 46–86%
yields (Scheme 1). All these chiral ligands were well characterized
by 1H, 13C and 31P NMR spectroscopy as well as MALDI-TOF or
high-resolution mass spectrometry. All the results were consistent
with the compounds synthesized. The target ligands obtained with
this method possess modular properties, thus allowing fine-tuning
of their steric and electronic characteristics.
Table 1 The Pd-catalyzed asymmetric hydrosilylation of styrene: steric
effect and ligand screeninga
Entry Ligand 3/Pd Temp./◦C Conv. to 6a (%)b
Ee of 7a (%)c
1
2
3
4
5
6
7
8
9
10
11d
12d
13
14
15
16
17
18
3a
3a
3b
3b
3c
3c
3d
3d
3e
3e
3f
2
1
2
1
2
1
2
1
2
1
2
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
-20
-20
-20
-20
-20
-20
20
46
16
11 (R)
4 (R)
Racemic
5 (S)
30
>95
>95
>95
>95
>95
>95
>95
>95
>95
>95
43 (R)
36 (R)
38 (S)
8 (R)
88 (S)
86 (S)
76 (S)
85 (S)
92 (S)
82 (S)
94 (96)e (S)
80 (S)
82 (S)
96 (S)
3f
3f
3g
3h
3i
50 (>95)e
>95
>95
>95
3j
3k
a The reactions were conducted with 5a : HSiCl3 : [PdCl(h -C3H5)]2 : 3 =
1 : 1.2 : 0.00125 : 0.0025, solvent free, 8 h. b Conversion determined
by 1H NMR spectroscopy. c Ee values determined by GC analysis with
chiral column, and absolute configuration determined by optical rotation.
d Reaction time is 6 h. e Data in brackets were obtained upon prolonged
reaction time (16 h).
3
Scheme 1 Synthesis of bulky binaphthol-based chiral phosphoramidites.
With these ligands in hand, we first investigated the steric effect
on catalytic properties by choosing the asymmetric hydrosilylation
of styrene 5a as the standard reaction. The reaction was carried
out without additional organic solvents at 0 ◦C in the presence of
(L : Pd) ratio was reduced to 1 : 1, both ligands 3e and 3f exhibited
similar high enantioselectivities (entries 10 and 12).
Given the excellent performance of the catalyst with 3f, we
intended to further explore the influence of the aryl substituents
on the reactivity and enantioselectivity in the asymmetric hy-
drosilylation of 5a. As compared to 3f, ligand 3g bearing
2-naphthyl substituents showed lower enantioselectivity (entry 13
vs. entry 14). However, further increasing the bulkiness of the
aryl substituents (ligand 3h) led to high enantioselectivity, albeit
with reduced reactivity (entry 15). A comparison of selectivity
between ligand 3i and 3d revealed that the steric properties of the
substituents did play an important role in selectivity (entry 16 vs.
entry 8). In addition, the electronic effect of the substituents was
also observed. Ligand 3j with electron-deficient aryl substituents
gave lower enantioselectivity (entry 17). In contrast, an electron-
rich aryl substituent (3k) was beneficial for the enantioselectivity
(entry 18). Therefore, ligand 3k was found to be the best choice of
ligand for this asymmetric hydrosilylation reaction in terms of the
reactivity and enantioselectivity.
Next, we focused on the examination of reaction parameters,
and the results are collected in Table 2. The effect of the L : Pd
ratio was first investigated. Generally, a L : Pd ratio of 2 : 1 was
applied in most of the reported catalytic systems.2–4 In our cases, it
was interesting to note that higher enantioselectivity was observed
upon changing the L : Pd ratio from 2 : 1 to 1 : 1 (entries 11 and
12 in Table 1, and entries 1 and 2 in Table 2). When the L : Pd
ratio was further reduced to 0.5 : 1, complete conversion could
be achieved but with much lower enantioselectivity together with
the appearance of Pd black (entry 3). In contrast, the complex
3
0.25 mol% catalyst generated in situ by the mixing of [PdCl(h -
C3H5)]2 and the chiral phosphoramidite at room temperature. As
shown in Table 1, in the cases with a ligand : Pd ratio of 2 : 1, it
was found that both the reactivities and enantioselectivities were
strongly dependent on the substituents in the 3,3¢-positions of
the binaphthyl backbone as well as the dendritic wedges on the
nitrogen atom of the ligand. As expected, the most simple ligand 3a
afforded low conversion (20%) in 8 h. The oxidation of the resulting
silane 6a under Tamao conditions provided alcohol 7a in only 11%
ee with an (R) configuration (entry 1).3a Surprisingly, the dendritic
ligand 3b bearing sterically demanding substituents on the nitro-
gen atom provided even lower conversion and racemic product
(entry 3). Introducing methyl groups into the 3,3¢-positions of 3b
to afford ligand 3c enhanced the reactivity significantly (entry 5).
It was interesting to note that ligand 3d with only the methyl
substituents resulted in moderate enantioselectivity, but with
opposite configuration as compared to 3c (entry 7 vs. entry 5).
When we replaced the methyl groups with bulky phenyl groups,
to our delight, much higher enantioselectivities and reactivities
were achieved (entries 9 and 11). Unlike ligands 3c and 3d, both
3e and 3f gave the chiral alcohols with the same configuration
upon oxidation. Furthermore, the dendritic ligand 3e exhibited
better enantioselectivity than ligand 3f (88% vs. 76% ee, entries
9 and 11), indicating the synergistic effect of the combination of
aryl substituents in the 3,3¢-positions and dendritic wedges on the
nitrogen atom of the ligand. However, when the ligand : palladium
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Table 2 The Pd-catalyzed asymmetric hydrosilylation of styrene using
phosphoramidite 3k: reaction conditions optimizationa
Table 3 Catalytic asymmetric hydrosilylation of styrene derivatives cat-
alyzed by Pd–3ka
Entry
3k/Pd
Sub./cat.
Temp./◦C
Time
Ee of 7a (%)b
1
2
3
2
1
0.5
4
1
1
1
1
1
400
400
400
400
400
400
400
1000
1000
1000
5000
10 000
-20
-20
-20
-20
-20
-20
-20
r.t.
0
8 h
8 h
8 h
8 h
8 h
8 h
8 h
20 min
20 min
8 h
12 h
72 h
93
96
78
c
Entry Substrate (Ar, R)
Temp./◦C Time/h Ee of 7 (%)b
4
—
5d
6e
7f
8
87
93
94
77
92
93
90
81
1
2
3
4
5
6
7
8
9
5a (Ar = C6H5; R = H)
-20
-20
-20
8
16
16
16
16
16
16
24
16
24
96 (S)
80 (S)
93 (S)
89 (S)
89 (S)
90 (S)
91 (S)
87 (S)
87 (S)
94 (S)
5b (Ar = 2-Me-C6H4; R = H)
5c (Ar = 4-Me-C6H4; R = H)
9
5d (Ar = 4-OMe-C6H4; R = H) -20
10
11
12
1
1
1
-20
0
0
5e (Ar = 4-Br-C6H4; R = H)
5f (Ar = 3-Br-C6H4; R = H)
5g (Ar = 4-Cl-C6H4; R = H)
-20
-20
-20
5h (Ar = 4-CF3-C6H4; R = H) r.t.
3
a The reactions were conducted with 5a : HSiCl3 : [PdCl(h -C3H5)]2 : 3k =
1 : 1.2 : 0.00125 : 0.0025, solvent free. b Complete conversions were obtained
in all cases; ee values were determined by GC analysis with chiral column.
c No reaction determined by 1H NMR spectroscopy. d Pd(acac)2 as metal
precursor. e CH2Cl2 as solvent. f 4 equiv of HSiCl3 to styrene.
5i (Ar = 3-CF3-C6H4; R = H) -20
10
5j (Ar = C6H5; R = Me)
r.t.
a The reactions were conducted with 5 : HSiCl3 : [PdCl(h -C3H5)]2 : 3k =
1 : 1.2 : 0.00125 : 0.0025, solvent free. b Complete conversions were obtained
in all cases; ee values were determined by GC analysis with chiral column.
3
obtained from a L : Pd ratio of 4 : 1 was found to be an inactive
catalyst (entry 4). Although similar L : Pd ratio effects were
reported by Johannsen and co-workers for the same reaction,
they found that the reaction became more problematic when
approaching a L : Pd ratio of 1 : 1 or less than 1 : 1.4b
different peaks at 159.4, 144.6 and 117.0 ppm were presented.
These results suggest that introducing aryl groups into the 3,3¢-
positions of the binaphthyl backbone of the ligand can influence
the coordination mode of palladium with the phosphoramidite.
The ability to provide a vacant coordination site for the olefin
substrate during the catalytic reaction by the bulky ligand 3f might
be responsible for its excellent catalytic performance. However,
further study is still required to confirm if the catalyst precursor
contains only one 3f ligand per Pd ion.9,12
To further demonstrate the efficacy of the bulky ligands, we
decided to investigate the applications of the Pd complex of
3k in the asymmetric hydrosilylation of a variety of styrene
derivatives (Table 3). In general, most of the substituted styrenes
were efficiently hydrosilylated with good enantioselectivities and
conversions within 16 h at -20 ◦C. The hydrosilylation of a
2-substituted styrene derivative resulted in the lowest enantios-
electivity (entry 2). High enantioselectivities were observed for
all the 3- and 4-substituted substrates (entries 3–9). It was
noted that the positioning of the electron-withdrawing CF3
group on the aromatic ring showed significant effect on the
reactivity. The hydrosilylation of 4-trifluoromethylstyrene 5h could
be completed at room temperature in 24 h, while the reaction
with 3-trifluoromethylstyrene 5i proceeded fast at -20 ◦C. In
addition, b-methyl-substituted styrene 5j is another exception,
with a prolonged reaction time at room temperature (entry 10).
In addition to the L : Pd ratio, other parameters such as metal
precursor, solvent, reaction temperature and substrate/catalyst
(S/C) ratio were also studied. It was found that catalyst prepared
from the neutral complex [Pd(acac)2] was less selective than
that from [PdCl(C3H5)]2 under otherwise identical conditions
(entry 5). When the reaction was carried out in CH2Cl2, slightly
low enantioselectivity was observed (entry 6). Similar results
with excess amount of HSiCl3 were observed (entry 7). Notably,
this reaction was found to be highly sensitive to the reaction
temperature. The asymmetric hydrosilylation of 5a proceeded very
fast at room temperature, but rather low enantioselectivity was
observed (entry 8). Most importantly, excellent reactivity and
enantioselectivity were achieved at low temperature even under
much lower catalyst loading (entries 2, 9 and 10), affording a
TOF number of at least 3000 h-1. When the S/C ratio was further
increased to 10 000, the reaction still proceeded smoothly to give
complete conversion to the product upon prolonged reaction time,
but at the expense of reduced enantioselectivity (entry 12). This
result clearly demonstrated that the catalyst obtained from the
bulky phosphoramidite 3k with a L : Pd ratio of 1 : 1 was highly
stable.
To understand the high efficiency of the bulky ligand, we
then investigated the coordination of the phosphoramidite with
palladium precursors by using 31P NMR spectroscopy. It was
Conclusions
3
found that the addition of one equivalent of 3f to [PdCl(h -C3H5)]2
In summary, we have developed a new type of bulky mon-
odentate phosphoramidite ligand prepared from chiral 3,3¢-diaryl
substituted BINOL derivatives and achiral or dendritic amines.
These bulky ligands were successfully applied in the Pd-catalyzed
asymmetric hydrosilylation of styrenes, providing the chiral silanes
with excellent activity and productivity, which are much higher
than those obtained from all the reported phosphoramidite
ligands and most of the other monodentate phosphorus ligands.2–5
Oxidation of these chiral silanes with hydrogen peroxide gave
the corresponding chiral secondary alcohols in good to high
led to the complete disappearance of the 31P NMR signal of the
free ligand at 141.4 ppm and the appearance of a single peak at
143.2 ppm. If another equivalent of 3f was added, the peak at
143.2 ppm was retained and another peak at 141.5 ppm appeared,
which was temporarily assigned to the excess free ligand. In
contrast, the complex obtained from the less sterically bulky ligand
3a provided much different 31P NMR spectra. In the case of a 3a :
Pd ratio of 1 : 1, two peaks at 145.3 and 144.6 ppm were observed.
When the L : Pd ratio changed from 1 : 1 to 2 : 1, completely
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enantioselectivities (up to 96% ee). These bulky ligands are
modular, allowing fine-tuning of their steric and electronic char-
acteristics, and further applications to other asymmetric reactions
are under way in our laboratory.
4.49 (s, 8H), 4.81 (s, 16H), 5.93 (d, J = 1.8 Hz, 4H), 6.15 (s, 2H),
6.42 (d, J = 2.0 Hz, 4H), 6.48 (d, J = 2.0 Hz, 8H), 6.94 (t, J =
7.3 Hz, 1H), 7.15–7.453 (m, 51H), 7.61 (d, J = 7.6 Hz, 2H), 7.77
(d, J = 7.3 Hz, 2H), 7.86 (d, J = 8.5 Hz, 2H), 7.91 (s, 1H), 7.99 (s,
1H). 13C NMR (75 MHz, CDCl3): d = 50.8, 51.0, 70.0, 70.1, 100.8,
101.8, 106.7, 107.8, 124.3, 125.2, 125.5, 126.3, 127.0, 127.2, 127.3,
127.7, 127.8, 128.1, 128.2, 128.4, 128.7, 130.3, 130.3, 131.1, 131.4,
132.5, 132.7, 134.4, 135.1, 137.0, 137.3, 137.9, 138.2, 139.4, 141.3,
141.3, 147.3, 147.3, 159.5, 160.2. 31P NMR (122 MHz, CDCl3): d =
143.6. MS (MALDI-TOF): m/z for C130H106O14NP: calcd 1937.2.
found 1934.7.
Experimental
General
Unless otherwise noted, all experiments were carried out under
an inert atmosphere of dry nitrogen by using standard Schlenk-
1
type techniques, or performed in a nitrogen-filled glovebox. H
3f. 51% yield; [a]D = +312.7 (c 0.1, CH2Cl2). 1H NMR
20
NMR, 13C NMR and 31P NMR spectra were recorded on a Bruker
Model Avance DMX 300 or 400 Spectrometer (1H 300 MHz,
13C 75 MHz and 31P 121 MHz, respectively). Chemical shifts
(d) are given in ppm and are referenced to residual solvent or
TMS peaks (1H and 13C NMR), or to an external standard (85%
H3PO4, 31P NMR). MALDI-TOF mass spectra were obtained
on a BIFLEX III instrument with a-cyano-4-hydroxycinnamic
acid (CCA) as the matrix. High resolution mass spectra [HRMS
(ESI)] were obtained on a Bruker Moder Apex-Qe-FTMS. Optical
rotations were measured with PerkinElmer 341 polarimeter. All
enantiomeric excess values were obtained from GC analysis with
a Chrompack CHIR-L-VAL column. All solvents were dried using
standard published methods, and were distilled under a nitrogen
atmosphere before use. All other chemicals were used as received
from Aldrich or Acros without further purification. Chiral 1,1-
binaphthol derivatives 410 and chiral dendritic ligands 3b–3c8 were
synthesized according to the published methods.
(300 MHz, CDCl3): d = 3.22 (AB system, J = 7.58 Hz, 1H),
3.26 (AB system, J = 7.58 Hz, 1H), 3.74 (AB system, J = 8.57 Hz,
1H), 3.78 (AB system, J = 8.57 Hz, 1H), 6.63 (d, J = 6.4 Hz, 4H),
6.97–7.04 (m, 6H), 7.25–7.32 (m, 2H), 7.38–7.54 (m, 10H), 7.75
(dd, J1 = 7.6 Hz, J2 = 0.7 Hz, 2H), 7.81 (dd, J1 = 7.9 Hz, J2 =
0.8 Hz, 2H), 7.91 (d, J = 8.0 Hz, 1H), 7.98 (d, J = 7.9 Hz, 2H), 8.05
(s, 1H). 13C NMR (75 MHz, CDCl3): d = 49.4, 49.7, 124.1, 125.3,
125.6, 126.4, 126.5, 126.9, 127.4, 127.4, 127.9, 128.0, 128.3, 128.3,
128.5, 128.7, 128.8, 130.5, 130.7, 130.9, 131.1, 131.6, 132.7, 134.8,
135.6, 137.8, 137.8, 138.4, 138.7, 147.3, 147.6, 147.7. 31P NMR
(122 MHz, CDCl3): d = 141.4. HRMS (ESI) for C46H34O2NP,
[M + H]+: calcd. 664.24054, found 664.24086.
3g. 47% yield; [a]D = +128.0 (c 0.1, CH2Cl2). 1H NMR
20
(300 MHz, CDCl3): d = 3.12 (AB system, J = 8.00 Hz, 1H),
3.16 (AB system, J = 8.00 Hz, 1H), 3.74 (AB system, J = 8.59 Hz,
1H), 3.78 (AB system, J = 8.59 Hz, 1H), 6.48 (d, J = 7.5 Hz,
4H), 6.64 (t, J = 7.5 Hz, 4H), 6.87 (t, J = 7.3 Hz, 2H), 7.29–
7.35 (m, 2H), 7.40–7.50 (m, 4H), 7.52–7.58 (m, 4H), 7.89–8.04
General procedure for the preparation of chiral bulky
phosphoramidite ligands 3d–3k
(m, 10H), 8.08 (s, 1H), 8.18 (s, 1H), 8.23 (s, 1H), 8.26 (s, 1H). 13
C
NMR (75 MHz, CDCl3): d = 48.7, 48.9, 123.9, 125.1, 125.4, 126.2,
126.3, 126.3, 126.6, 127.1, 127.4, 127.8, 127.8, 127.9, 128.2, 128.4,
128.4, 128.6, 128.7, 128.7, 128.8, 129.2, 130.8, 131.1, 131.4, 132.5,
132.7, 132.8, 132.9, 133.0, 133.5, 133.8, 134.5, 135.7, 136.0, 137.0,
137.0, 147.1, 147.4, 147.5. 31P NMR (122 MHz, CDCl3): d = 141.3.
HRMS (ESI) for C54H38O2NP, [M + H]+: calcd. 764.27184, found
764.27158.
Under a nitrogen atmosphere, a drop of NMP was added to a
warm solution (60 ◦C) of (S)-4 and trichlorophosphine (10 mL).
After refluxing for 5 h, azeotropic distillation of the residue with
anhydrous toluene (5 mL) gave the intermediate chlorophosphite
in quantitative yield.11 Then, to a solution of dibenzylamine
or dendritic amine (0.35 mmol) and Et3N (0.1 mL, 0.7 mmol)
in THF (10 mL) at 0 ◦C was added dropwise a solution of
the above chlorophosphite (0.35 mmol) in THF (20 mL). The
3h. 67% yield; [a]D = +63.4 (c 0.2, CH2Cl2). 1H NMR
20
◦
resulting mixture was stirred at 50 C overnight. The precipitate
(300 MHz, CDCl3): d = 2.93–3.05 (m, 2H), 3.54 (AB system,
J = 8.89 Hz, 1H), 3.58 (AB system, J = 8.89 Hz, 1H), 5.97 (d,
J = 7.4 Hz, 1H), 6.02 (d, J = 7.5 Hz, 2H), 6.12 (d, J = 7.5 Hz,
1H), 6.30 (t, J = 7.6 Hz, 1H), 6.38 (t, J = 7.6 Hz, 3H), 6.68 (quart,
J = 7.2 Hz, 2H), 7.42–8.16 (m, 24H), 8.75–8.89 (m, 4H). 13C NMR
(75 MHz, CDCl3): d = 48.8, 49.1, 122.6, 122.7, 122.9, 125.1, 125.5,
126.3, 126.4, 126.5, 126.7, 126.9, 127.0, 127.4, 127.6, 127.9, 128.4,
128.6, 128.6, 129.0, 130.3, 130.8, 131.5, 131.6, 133.1, 134.3, 136.9,
136.9, 148.2, 148.4, 148.6. 31P NMR (122 MHz, CDCl3): d = 141.0.
HRMS (ESI) for C62H42O2NP, [M + H]+: calcd. 864.30314, found
864.30467.
of Et3NHCl was filtered over a pad of celite. After the solvent
was removed under reduced pressure, the residue was purified by
flash column chromatography to give the product 3 as a white
foam.
3d. 67% yield; [a]D = +255.2 (c 0.2, CH2Cl2). 1H NMR
20
(300 MHz, CDCl3): d = 2.08 (s, 3H), 2.69 (s, 3H), 3.50 (t, J =
12.5 Hz, 2H), 4.21 (AB system, J = 7.9 Hz, 1H), 4.25 (AB system,
J = 7.9 Hz, 1H), 7.04–7.13 (m, 2H), 7.17–7.33 (m, 14H), 7.58
(s, 1H), 7.68 (d, J = 8.0 Hz, 1H), 7.80 (d, J = 8.0 Hz, 2H). 13C
NMR (75 MHz, CDCl3): d = 17.4, 17.7, 48.1, 48.4, 122.1, 124.1,
124.2, 124.4, 124.8, 124.9, 125.1, 127.0, 127.0, 127.2, 127.3, 127.5,
128.3, 129.1, 129.4, 129.7, 130.2, 130.5, 131.3, 131.4, 131.7, 137.5,
148.4, 149.0, 149.1. 31P NMR (122 MHz, CDCl3): d = 139.8.
HRMS (ESI) for C36H30O2NP, [M + H]+: calcd. 540.20924, found
540.20894.
3i. 78% yield; [a]D = -74.4 (c 0.5, CH2Cl2). 1H NMR
20
(300 MHz, CDCl3): d = 3.50–3.55 (m, 2H), 4.17 (AB system,
J = 8.00 Hz, 1H), 4.20 (AB system, J = 8.00 Hz, 1H), 5.73 (s, 1H),
6.31 (s, 1H), 6.66–6.69 (m, 2H), 7.05 (d, J = 7.9 Hz, 2H), 7.13–
7.47 (m, 34H), 7.65 (d, J = 8.1 Hz, 1H), 7.74 (d, J = 8.1 Hz, 1H).
13C NMR (75 MHz, CDCl3): d = 51.1, 52.2, 123.0, 124.8, 126.0,
126.1, 126.6, 126.6, 127.1, 127.3, 128.5, 128.6, 128.6, 128.9, 129.0,
3e. 58% yield; [a]D = +139.0 (c 0.1, CH2Cl2). 1H NMR
20
(300 MHz, CDCl3): d = 3.21–3.33 (m, 2H), 3.29–3.32 (m, 2H),
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129.1, 129.5, 130.0, 130.4, 130.4, 130.5, 131.0, 132.2, 135.8, 136.7,
138.0, 143.2, 143.3, 143.6, 144.4, 148.3, 148.8, 148.9. 31P NMR
(122 MHz, CDCl3): d = 141.8. HRMS (ESI) for C60H46O2NP,
[M + H]+: calcd. 844.33444, found 844.33416.
acetate, 90 : 10), affording the chiral alcohol 7a (76 mg, 99%) with
96% ee (S).
Acknowledgements
3j. 45% yield; [a]D = +125.7 (c 0.2, CH2Cl2). 1H NMR
20
We are grateful for the financial support from the National Natural
Science Foundation of China (20532010 and 20772128), MOST
under grant No. 2010CB833305 and Chinese Academy of Sciences.
(300 MHz, CDCl3): d = 3.16 (AB system, J = 9.24 Hz, 1H),
3.20 (AB system, J = 9.24 Hz, 1H), 3.77 (AB system, J = 8.93 Hz,
1H), 3.81 (AB system, J = 8.93 Hz, 1H), 6.66 (d, J = 7.0 Hz, 4H),
7.02–7.14 (m, 6H), 7.35–7.42 (m, 4H), 7.42–7.49 (m, 1H), 7.51–
7.58 (m, 1H), 7.89 (s, 1H), 7.96–7.99 (m, 3H), 8.05 (d, J = 8.2 Hz,
1H), 8.13 (s, 3H), 8.30 (s, 2H). 13C NMR (75 MHz, CDCl3): d =
48.3, 48.6, 121.4, 121.7, 123.8, 125.2, 125.7, 126.0, 126.9, 127.0,
127.2, 128.2, 128.6, 128.7, 130.0, 130.3, 130.5, 131.1, 131.2, 131.4,
131.5, 131.7, 131.9, 132.9, 133.1, 136.2, 136.3, 140.0, 140.2, 146.0,
146.3, 146.4. 31P NMR (122 MHz, CDCl3): d = 142.2. HRMS
(ESI) for C50H30O2F12NP, [M + H]+: calcd. 936.19008, found
936.18996.
References
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Synthesis, Wiley, New York, 1994, p. 124; (b) H. Nishiyama, K. Itoh,
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M. Johannsen, Chem. Commun., 1999, 2517; (b) H. L. Pedersen and
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Asymmetry, 1998, 9, 3903.
3k. 78% yield; [a]D = +224 (c 0.1, CH2Cl2). 1H NMR
20
(300 MHz, CDCl3): d = 3.25 (AB system, J = 7.89 Hz, 1H),
3.30 (AB system, J = 7.89 Hz, 1H), 3.82 (AB system, J = 8.64 Hz,
1H), 3.82 (AB system, J = 8.64 Hz, 1H), 3.90 (s, 3H), 3.92 (s,
3H), 6.68 (dd, J1 = 7.6 Hz, J2 = 1.5 Hz, 4H), 7.00–7.06 (m, 10H),
7.21–7.44 (m, 6H), 7.72 (t, J = 9.0 Hz, 4H), 7.88 (d, J = 8.2 Hz,
1H), 7.92–7.96 (m, 2H), 8.02 (s, 1H). 13C NMR (75 MHz, CDCl3):
d = 48.8, 49.1, 55.3, 55.4, 113.5, 113.9, 123.7, 124.9, 125.2, 125.8,
125.9, 126.6, 127.0, 127.9, 128.1, 128.4, 130.0, 130.0, 130.4, 130.7,
130.9, 131.1, 131.3, 131.4, 131.4, 132.1, 134.1, 134.8, 137.4, 137.4,
147.0, 147.3, 147.4, 159.2. 31P NMR (122 MHz, CDCl3): d = 140.6.
HRMS (ESI) for C48H38O2NP, [M + H]+: calcd. 724.26167, found
724.26153.
General procedure for the asymmetric hydrosilylation of alkenes
A dried Schlenk tube containing a stirring bar was charged
with allylpalladium chloride dimer (1.5 mg, 0.0041 mmol), the
corresponding phosphoramidite ligand 3 (0.0082 mmol) and
styrene 5a (341 mg, 3.28 mmol). After 20 min stirring at room
temperature, trichlorosilane (0.66 mL, 6.56 mmol) was added at
-20 ◦C. Conversion of the resulting silane was determined by 1H
NMR spectroscopy. The product was purified by distillation to
yield 705 mg (90%) of 6a.
5 For a comprehensive review on oxidation of the carbon–silicon bond,
see: G. R. Jones and Y. Landais, Tetrahedron, 1996, 52, 7599.
6 (a) I. V. Komarov and A. Borner, Angew. Chem., Int. Ed., 2001, 40,
1197; (b) T. Jerphagnon, J. L. Renaud and C. Bruneau, Tetrahedron:
Asymmetry, 2004, 15, 2101; (c) J. G. de Vries and L. Lefort, Chem.–
Eur. J., 2006, 12, 4722; (d) M. T. Reetz, Angew. Chem., Int. Ed., 2008,
47, 2556; (e) L. Eberhardt, D. Armspach, J. Harrowfield and D. Matt,
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E. P. Schudde, J. van Esch, A. H. M. de Vries, J. G. de Vries and B. L.
Feringa, J. Am. Chem. Soc., 2000, 122, 11539; (g) A. G. Hu, Y. Fu, J. H.
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7 J. H. Xie and Q. L. Zhou, Acc. Chem. Res., 2008, 41, 581.
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General procedure for the oxidation of silanes
The silane 6a (177 mg, 0.741 mmol), KF (258 mg, 4.446 mmol),
KHCO3 (445 mg, 4.446 mmol), MeOH (15 mL) and THF (15 mL)
were transferred to a 50 mL flask. H2O2 (0.89 mL, 30%) was added,
and the mixture was stirred for 16 h before quenching with 4 mL
saturated Na2S2O3 solution. After stirring for an additional 1 h,
the reaction mixture was extracted with Et2O (3 ¥ 30 mL), and
the combined organic phases were dried over MgSO4, filtered
and concentrated in a vacuum. The crude residue was purified
by flash column chromatography on silica gel (pentane–ethyl
4474 | Org. Biomol. Chem., 2009, 7, 4470–4474
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The Royal Society of Chemistry 2009
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