Chiral Frustrated Lewis Pairs Catalyzed Highly Enantioselective Hydrosilylations of Ketones

Article abstract of DOI:10.1002/cjoc.201900121

A highly enantioselective Piers-type hydrosilylation of simple ketones was successfully realized using a chiral frustrated Lewis pair of tri-tert-butylphosphine and chiral diene-derived borane as catalyst. A wide range of optically active secondary alcohols were furnished in 80%—99% yields with 81%—97% ee's under mild reaction conditions.

Full text of DOI:10.1002/cjoc.201900121

Accepted Article
Title: Chiral Frustrated Lewis Pairs Catalyzed Highly Enantioselective
Hydrosilylations of Ketones
Authors: Xiaoqin Liu, Qiaotian Wang, Caifang Han, Xiangqing Feng,* and Haifeng
Du*
This manuscript has been accepted and appears as an Accepted Article online.
This work may now be cited as: Chin. J. Chem. 2019, 37, 10.1002/cjoc.201900121.
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published online in Early View: http://dx.doi.org/10.1002/cjoc.201900121.
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Chiral Frustrated Lewis Pairs Catalyzed Highly Enantioselective
Hydrosilylations of Ketones
Xiaoqin Liu,a,b Qiaotian Wang,a,b Caifang Han,a,b Xiangqing Feng,*,a,b and Haifeng Du*,a,b
a
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, CAS Research/Ed
Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
b
School of Chemical Science, University of Chinese Academy of Sciences, Beijing 100049, China
*E-mail: fxq@iccas.ac.cn; haifengdu@iccas.ac.cn
Cite this paper: Chin. J. Chem. 2019, 37, XXX—XXX. DOI: 10.1002/cjoc.201900XXX
ucation Center for
Summary of main observation and conclusion A highly enantioselective Piers-type hydrosilylation of simple ketones was successfully realized using a
chiral frustrated Lewis pair of tri-tert-butylphosphine and chiral diene-derived borane as catalyst. A wide range of
furnished in 80−99% yields with 81−97% ee’s under mild reaction conditions.
Background and Originality Content
preliminary results on this subject.
Optical active secondary alcohols are indispensable as chiral
auxiliaries and building blocks in the synthetic and pharmaceutical
Scheme
hydrosilylation of ketones
1
Representative examples for asymmetric Piers
optically active secondary alcohols were
[
1]
chemistry. The catalytic asymmetric hydrogenation of ketones is
undoubtedly the most efficient and straightforward approach for
[2]
their synthesis. Alternatively, the asymmetric hydrosilylation
also represents a fundamental methodology, and a variety of
transition-metal and metal-free catalytic systems have already
[
3]
been well established. Among them, metal-free Piers-type
hydrosilylation has attracted intensive synthetic and mechanistic
interest since the seminal work reported in 1996, in which Lewis
-type
[
4]
acids activated silanes instead of substrates. Some significant
[
5]
advances have been achieved in the past two decades. However,
[
6]
the asymmetric Piers-type hydrosilylation still remains sluggish.
Several chiral boranes were developed as catalysts for the
asymmetric hydrosilylation of imines, unfortunately, few of them
[
7]
can give high enantioselectivities. For simple ketone substrates,
Oestreich and co-workers reported a binaphthyl-based chiral
2 2
borane catalyzed asymmetric hydrosilylation with Ph SiH to give
[
8]
up to 99% ee in 2016 (Scheme 1). Despite this advance, the Results and Discussion
development of highly effective chiral catalysts is still in great
We initially examined the asymmetric hydrosilylation of
acetophenone (1a) with Ph SiH (5a) using chiral diene 3a (2.5
mol %) and Piers’ borane HB(C (5 mol %) without phosphine
Lewis base (Scheme 2). The reaction was carried out in toluene at
0 °C for 4 h and followed by silyl group deprotection with TBAF
to afford 1-phenylethanol (2a) in a quantitative conversion but
demand.
The chemistry of frustrated Lewis pairs (FLPs) has witnessed a
very rapid growth and become an extremely important frontier of
2
2
6 5 2
F )
[
9,10]
synthetic chemistry.
Chiral FLPs also proved to be effective
6
[
11]
catalysts for the asymmetric Piers-type hydrosilylation.
For
example, Klankermayer and co-workers developed a chiral FLP of
camphor-derived borane and phosphine for the hydrosilylation of
[
11c]
with only 5% ee.
Phosphines 4a-d were next employed as the
Lewis base component of chiral FLPs catalysts for this reaction.
Triphenylphosphine (4a) and tri-n-butylphosphine (4b) gave very
low ee’s. Tricyclohexylphosphine (4c) and tri-tert-butylphosphine
[
11c]
acetophenone with Ph
Recently, our group realized an asymmetric hydrosilylation of
,2-dicarbonyl compounds with Ph MeSiH using an FLP of chiral
2
MeSiH to afford a 37% ee (Scheme 1).
1
2
(
4d) could give 78% and 89% ee, respectively. Silanes 5b-d were
further evaluated for this asymmetric hydrosilylation, much lower
ee’s were obtained than that with Ph SiH (5a) (Table 1, entries 1
diyne-derived alkenylborane and tricyclohexylphosphine to
furnish the corresponding products in high yields with up to 99%
ee.
2
2
[11d]
When acetophenone was employed, 42% ee was obtained
vs 2-4). Chiral dienes 3b−f derived boron Lewis acids were
investigated subsequently, and all reactions proceeded smoothly
to afford 1-phenylethanol (2a) in quantitative conversions with
(Scheme 1), which provides a chance to solve the challenging
asymmetric Piers-type hydrosilylation of simple ketones with
chiral FLPs.
6
7-82% ee’s (Table 1, entries 5-9). When chiral diyne 6-derived
As our general interest in the FLP catalysis, we have developed
a variety of chiral boron Lewis acids in situ via the hydroboration
alkenylborane was used, 75% ee was obtained (Table 1, entry 10).
Scheme 2 Initial study on asymmetric hydrosilylation of acetophenone
[
12]
of chiral dienes with HB(C
6
F
5
)
2
, which were highly effective for
[
10h-j,13]
the asymmetric hydrogenation.
Due to the easy availability
of these chiral FLPs catalysts, we wish to contribute our efforts on
their further application in the asymmetric Piers-type
hydrosilylation of simple ketones. Herein, we report our
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Table 2 Optimization of reaction conditions a
1
. chiral diene 3a (2.5 mol %)
HB(C6F5)2 (5 mol %)
phosphine 4 (5 mol %)
O
OH
Me
1. chiral diene 3a (2.5 mol %)
HB(C6F5)2 (5 mol %)
Ph
Me
Ph
O
OH
Me
Ph2SiH2 (5a) (1.5 equiv)
toluene, 60 °C, 4 h
. TBAF, rt, 0.5 h
tBu P (4d) (5 mol %), Ph SiH (5a)
3
2
2
1a
2a
Ph
Me
solvent, 4 h
Ph
2
>
99% conv
1a
2. TBAF, rt, 0.5 h
2a
entry 5a (equiv) solvent
temp (°C) conv (%)b ee (%)c
Ar
without 4: -5% ee
Ph3P (4a): 9% ee
nBu3P (4b): 2% ee
1
2
3
4
5
6
7
8
9
1
1
1.5
1.2
2.0
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
toluene
toluene
toluene
n-hexane
60
60
60
60
60
60
60
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
89
88
87
89
30
89
78
68
88
92
70
91
93
Cy3P (4c): 78% ee
Ar
tBu3P (4d): 89% ee
t
Ar = 3,5- BuC6H3
CH
2
Cl
2
3a
p-xylene
o-xylene
Table 1 Evaluation of silanes and catalystsa
cyclohexane 60
Ar
Ar
Ar
F-benzene
toluene
toluene
toluene
toluene
60
50
30
50
50
3
3
3
3
3
b: Ar = 3-OMeC6H4
t
c: Ar = 4-BuC6H4
0
1
i
d: Ar = 2-OPr-5-OMeC6H3
e: Ar = 3,5-F2C6H3
12d
3e
f: Ar = 2-MeC6H4
Ar
t
6: Ar = 3,5- Bu2C6H3
1
entry
diene
3a
3a
3a
3a
3b
3c
silane
conv (%)b
>99
83
ee (%)c
89
a
All reactions were carried out with 1a (0.10 mmol), chiral diene 3a
t
1
2
3
4
5
6
7
8
9
Ph
Ph
2
SiH
MeSiH (5b)
SiH (5c)
(5d)
2
(5a)
(0.0025 mmol), HB(C
6
F )
5 2
(0.005 mmol), Bu
3
P (0.005 mmol), and Ph
2
SiH
2
b
1
c
2
66
in solvent (1.0 mL, 0.1 M) for 4 h. Determined by crude H NMR. The ee
was determined by chiral HPLC. d With 0.2 M. e With 0.5 M.
PhMe
2
94
62
2
Et SiH
2
>99
>99
>99
>99
>99
>99
>99
62
Scheme 3 Asymmetric Piers-type hydrosilylation of ketones
5a
5a
5a
5a
5a
5a
67
79
1
. chiral diene 3a (2.5 mol %)
HB(C6F5)2 (5 mol %)
tBu3P (4d) (5 mol %)
3d
3e
3f
82
O
OH
74
Ar
R
F
Ar
R
Ph2SiH2 (5a) (1.2 equiv)
toluene (0.5 M), 50 °C, 4 h
. TBAF, rt, 0.5 h
OH Cl
OH
Me Me
1
2
67
2
1
0
6
75
a
All reactions were carried out with acetophenone (1a) (0.10 mmol),
(0.005 mmol), phosphine 4d
0.005 mmol), and silane 5 (0.15 mmol) in toluene (1.0 mL) at 60 °C for 4 h.
OH
Me
Br OH
Me OH
Me
chiral diene 3 (0.0025 mmol), HB(C
6
F
5 2
)
Me
(
b
1
c
Determined by crude H NMR. The ee was determined by chiral HPLC.
2a
2b
2c
2d
2e
88% (93% ee) 80% (94% ee) 87% (94% ee) 98% (93% ee) 94% (94% ee)
The reaction conditions were optimized to further improve
OH
Me
OH
Me
OH
Me
OH
Me
OH
Me
the enantioselectivity. As shown in Table 2, the loading amount of
Ph SiH (5a) varied from 1.2 to 2.0 equivalents gave very similar
2
2
results (entries 1-3). Solvents were found to have little impact on
the reactivity, but influence the enantioselectivity largely (entries
2
f
2g
2h
2i
2j
F
Cl
Br
Me
OMe
4
-9), and toluene proved to be the optimal one. Lowering the
temperature from 60 °C to 50 °C led a little higher ee (entries 1 vs
0). But further lowering to 30 °C resulted in an obvious loss of
99% (81% ee) 93% (81% ee) 91% (87% ee) 94% (94% ee) 95% (96% ee)
OH
Me
Cl
OH
Me
Br
OH
Me
Me
OH
Me
Et
OH
Me
1
enantioselectivity (entry 11). When the reaction concentration
was increased from to 0.1 M to 0.2 and 0.5 M, 91% and 93% ee’s
were obtained, respectively (entries 12 and 13).
F
2
k
2l
2m
2n
2o
9
8% (97% ee) 95% (88% ee) 87% (94% ee) 94% (97% ee) 97% (88% ee)
Under the optimal conditions, a wide range of ketones 1a-A
were subjected to the asymmetric hydrosilylation. As shown in
Scheme 3, all reactions proceeded well to furnish the desired
secondary alcohols 2a-A in 80−99% yields with 81−97% ee’s.
Ortho-substituted acetophenones 2b-e were effective substrates
to afford high levels of reactivity and enantioselectivity. Both
electron-rich and -deficient substituents at the meta or para
positions 2f-u were also well tolerated. Asymmetric
hydrosilylations of α- and β-acetonaphthone (1v and 1w) gave the
desired products 2v and 2w in high yields with 89% ee. Ketones
OH OH
OH
OH
Me
Me
Me
Me
Me
nBu
Ph
F3CO
Me
2
p
2q
2r
2s
9
8% (84% ee)
97% (90% ee)
97% (83% ee)
90% (86% ee)
OH
OH
Me
OH
Me
OH
Me
Me
Me
2
t
2u
2v
2w
Me
8
5% (94% ee)
97% (88% ee)
91% (89% ee)
96% (89% ee)
2x-z bearing other alkyl groups instead of methyl were also
suitable substrates to give up to 97% ee. Moreover, an
asymmetric hydrosilylation of 2-acetylbenzothiophene (1A)
furnish alcohol 2A in 96% yield with 81% ee.
OH
Et
OH
OH
OH
Ph
Me
S
2
x
2y
2z
2A
97% (97% ee)
99% (86% ee)
93% (87% ee)
96% (81% ee)
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Conclusions
Determined Chemo- and Enantioselectivities in Asymmetric
Hydrogenation of Multi-Functionalized Ketones. Coord. Chem. Rev.
In summary, with the use a frustrated Lewis pair of chiral
diene-derived borane and tri-tert-butylphosphine as catalyst,
asymmetric Piers-type hydrosilylations of simple ketones were
realized under a mild condition. A wide range of optically alcohols
were furnished in 80−99% yields and 81−97% ee’s. Further efforts
on searching for more effective chiral FLP catalysts and their
application in other reactions are underway in our laboratory.
2
018, 355, 39–53.
For leading reviews, see: (a) Riant, O.; Mostefaï, N.; Courmarcel, J.
Recent Advances in the Asymmetric Hydrosilylation of Ketones,
Imines and Electrophilic Double Bonds. Synthesis 2004, 18,
2943-2958. (b) Gibson, S. E.; Rudd, M. The Role of Secondary
Interactions in the Asymmetric Palladium-Catalysed Hydrosilylation
of Olefins with Monophosphane Ligands. Adv. Synth. Catal. 2007,
3
49, 781-795. (c) Díez-González, S.; Nolan, S. P. Copper, Silver, and
Gold Complexes in Hydrosilylation Reactions. Acc. Chem. Res. 2008,
1, 349-358. (d) Guizzetti, S.; Benaglia, M. Trichlorosilane-Mediated
Stereoselective Reduction of C=N Bonds. Eur. J. Org. Chem. 2010,
010, 5529-5541. (e) Jones, S.; Warner, C. J. A. Trichlorosilane
Mediated Asymmetric Reductions of the C=N Bond. Org. Biomol.
Chem. 2012, 10, 2189-2200.
Parks, D. J.; Piers, W. E. Tris(pentafluorophenyl)boron-Catalyzed
Hydrosilylation of Aromatic Aldehydes, Ketones, and Esters. J. Am.
Chem. Soc. 1996, 118, 9440-9441.
Experimental
4
Representative procedure for the FLP-catalyzed asymmetric
hydrosilylation of ketones: To a glass sealed tube (15 mL) in a
2
6 5 2
nitrogen atmosphere glovebox, Piers’ borane HB(C F ) (0.0086 g,
0
.025 mmol), chiral diene 3a (0.0085 g, 0.0125 mmol), and dry
toluene (1.0 mL) were added. The mixture was stirred at room
temperature for 5 min before addition of tri-tert-butylphosphine
(
(
4d) (0.0506 g, 10 wt. % in pentane, 0.025 mmol), diphenyl silane
5a) (0.1106 g, 0.6 mmol), and ketone 1a (0.5 mmol) sequentially.
For selected examples, see: (a) Blackwell, J. M.; Sonmor, E. R.;
The reaction mixture was stirred at 50 °C for 4 h. After being
cooled to room temperature, tetra-n-butylammonium fluoride
Scoccitti, T.; Piers, W. E. B(C
F
6 5
3
) -Catalyzed Hydrosilylation of Imines
via Silyliminium Intermediates. Org. Lett. 2000, 2, 3921-3923. (b)
(
1.0 mL, 1.0 M, in THF) was added. The mixture was further
stirred at room temperature for 30 min. The resulting mixture
was directly poured onto silica gel and purified by flash
Mohr,
J.;
Durmaz,
M.;
Irran,
E.;
Oestreich,
M.
Tris(5,6,7,8-tetrafluoronaphthalen-2-yl)
Borane,
a
Partially
chromatography on silica gel using
a
mixture 10/1 of
Fluorinated Boron Lewis Acid with Fluorination Distal to the Boron
Atom. Organometallics 2014, 33, 1108-1111. (c) Rubin, M.; Schwier,
pentane/ether to afford compound 2a as a colorless oil (0.0546 g,
2
5
20
8
+
8% yield, 93% ee). [α]
42.92 (c 1.04, CHCl ) (96% ee for R-isomer)] ; H NMR (400
, ppm) δ 7.40-7.22 (m, 4H), 7.22-7.14 (m, 1H), 4.80 (q,
D
= +44.9 (c 1.26, CHCl
3
), [lit.: [α]
D
=
T.; Gevorgyan, V. Highly Efficient B(C
6
F ) -Catalyzed Hydrosilylation
5
3
[
14]
1
3
of Olefins. J. Org. Chem. 2002, 67, 1936-1940. (d) Simonneau, A.;
Oestreich, M. 3-Silylated Cyclohexa-1,4-dienes as Precursors for
MHz, CDCl
J = 6.4 Hz, 1H), 1.97 (brs, 1H), 1.41 (d, J = 6.4 Hz, 3H); C NMR
100 MHz, CDCl , ppm) δ 146.0, 128.7, 127.6, 125.6, 70.6, 25.3.
3
1
3
Gaseous
Hydrosilylation of Alkenes. Angew. Chem., Int. Ed. 2013, 52,
1905-11907. (e) Pérez, M.; Hounjet, L. J.; Caputo, C. B.; Dobrovetsky,
Hydrosilanes:
The
B(C
6
F
5 3
) -Catalyzed
Transfer
(
3
1
R.; Stephan, D. W. Olefin Isomerization and Hydrosilylation Catalysis
by Lewis Acidic Organofluorophosphonium Salts. J. Am. Chem. Soc.
Supporting Information
2013, 135, 18308-18310.
Characterization of products, and data for the determination
of enantiomeric excesses along with the NMR spectra are
included. The supporting information for this article is available
on the WWW under https://doi.org/10.1002/cjoc.2018xxxxx.
Oestreich, M.; Hermeke, J.; Mohr, J. A Unified Survey of Si–H and H–
H Bond Activation Catalyzed by Electron-Deficient Boranes. Chem.
Soc. Rev. 2015, 44, 2202-2220.
(a) Mewald, M.; Oestreich, M. Illuminating the Mechanism of the
Borane-Catalyzed Hydrosilylation of Imines with Both an Axially
Chiral Borane and Silane. Chem. Eur. J. 2012, 18, 14079-14084. (c)
Hermeke, J.; Mewald, M.; Oestreich, M. Experimental Analysis of the
Catalytic Cycle of the Borane-Promoted Imine Reduction with
Hydrosilanes: Spectroscopic Detection of Unexpected Intermediates
Acknowledgement
We are grateful for generous financial support from the
National Natural Science Foundation of China (21572231,
21521002, and 21825108).
and
7537-17546. (d) Zhu, X.; Du, H. A Chiral Borane Catalyzed
Asymmetric Hydrosilylation of Imines. Org. Biomol. Chem. 2015, 13,
013-1016.
a Refined Mechanism. J. Am. Chem. Soc. 2013, 135,
1
References
1
(a) Noyori, R. Asymmetric Catalysis in Organic Synthesis, Wiley: New
Süsse, L.; Hermeke, J.; Oestreich, M. The Asymmetric Piers
Hydrosilylation. J. Am. Chem. Soc. 2016, 138, 6940−6943.
Welch, G. C.; San Juan, R. R.; Masuda, J. D.; Stephan, D. W. Reversible,
Metal-Free Hydrogen Activation. Science 2006, 314, 1124-1126.
For leading reviews, see: (a) Kenward, A. L.; Piers, W. E. Heterolytic
York, 1994. (b) Morris, R. H. Handbook of Homogeneous
Hydrogenation; de Vries, J. G.; Elsevier, C. J., Eds.; Wiley-VCH:
Weinheim, Germany, 2007; Volume 1, pp. 45–70, Chapter 3.
For leading reviews on asymmetric hydrogenations, see: (a) Noyori,
R.; Ohkuma, T. Asymmetric Catalysis by Architectural and Functional
Molecular Engineering: Practical Chemo- and Stereoselective
Hydrogenation of Ketones. Angew. Chem., Int. Ed. 2001, 40, 40-73. (b)
He, Y. M.; Fan, Q. H. Phosphine-Free Chiral Metal Catalysts for Highly
Effective Asymmetric Catalytic Hydrogenation. Org. Biomol. Chem.
H
(
2
Activation by Nonmetals. Angew. Chem., Int. Ed. 2008, 47, 38-41.
b) Stephan, D. W.; Erker, G. Frustrated Lewis Pairs: Metal-Free
Hydrogen Activation and More. Angew. Chem., Int. Ed. 2010, 49,
6-76. (c) Soos, T. Design of Frustrated Lewis Pair Catalysts for
Metal-Free and Selective Hydrogenation. Pure Appl. Chem. 2011, 83,
67-675. (d) Paradies, J. Metal-Free Hydrogenation of Unsaturated
Hydrocarbons Employing Molecular Hydrogen. Angew. Chem., Int. Ed.
014, 53, 3552-3557. (e) Stephan, D. W. Frustrated Lewis Pairs: From
4
́
2010, 8, 2497–2504. (c) Yoshimura, M.; Tanaka, S.; Kitamura, M.
6
Recent Topics in Catalytic Asymmetric Hydrogenation of Ketones.
Tetrahedron Lett. 2014, 55, 3635–3640. (d) Li, Y. Y.; Yu, S. L.; Shen, W.
Y.; Gao, J. X. Iron-, Cobalt-, and Nickel-Catalyzed Asymmetric Transfer
Hydrogenation and Asymmetric Hydrogenation of Ketones. Acc.
Chem. Res. 2015, 48, 2587−2598. (e) Xie, J. H.; Bao, D. H.; Zhou, Q. L.
Recent Advances in the Development of Chiral Metal Catalysts for
the Asymmetric Hydrogenation of Ketones. Synthesis 2015, 47,
2
Concept to Catalysis. Acc. Chem. Res. 2015, 48, 306-316. (f) Stephan,
D. W.; Erker, G. Frustrated Lewis Pair Chemistry: Development and
Perspectives. Angew. Chem., Int. Ed. 2015, 54, 6400-6441. (g) Shi, L.;
Zhou, Y.-G. Enantioselective Metal-Free Hydrogenation Catalyzed by
Chiral Frustrated Lewis Pairs. ChemCatChem 2015, 7, 54-56. (h) Liu,
460-471. (f) Xie, X. M.; Lu, B.; Li, M. F.; Zhang, Z. G. Coordination
This article is protected by copyright. All rights reserved.

Y.; Du, H. Frustrated Lewis Pair Catalyzed Asymmetric Hydrogenation.
HuaxueXuebao 2014, 72, 771-777. (i) Feng, X.; Du, H. Metal-Free
Asymmetric Hydrogenation and Hydrosilylation Catalyzed by
Frustrated Lewis Pairs. Tetrahedron Lett. 2014, 55, 6959-6964. (g)
Meng, W.; Feng, X.; Du, H. Frustrated Lewis Pairs Catalyzed
Asymmetric Metal-Free Hydrogenations and Hydrosilylations. Acc.
Chem. Res. 2017, 51, 191-201.
Metal-Free Asymmetric Hydrogenation of Imines. J. Am. Chem. Soc.
2013, 135, 6810-6813. (b) Wei, S.; Du, H. A Highly Enantioselective
Hydrogenation of Silyl Enol Ethers Catalyzed by Chiral Frustrated
Lewis Pairs. J. Am. Chem. Soc. 2014, 136, 12261-12264. (c) Zhang, Z.;
Du, H. A Highly cis-Selective and Enantioselective Metal-Free
Hydrogenation of 2,3-Disubstituted Quinoxalines. Angew. Chem., Int.
Ed. 2015, 54, 623-636. (d) Ren, X.; Li, G.; Wei, S.; Du, H. Facile
Development of Chiral Alkenylboranes from Chiral Diynes for
Asymmetric Hydrogenation of Silyl Enol Ethers. Org. Lett. 2015, 17,
990-993. (e) Li, S.; Li, G.; Meng, W.; Du, H. A Frustrated Lewis Pair
Catalyzed Asymmetric Transfer Hydrogenation of Imines Using
Ammonia Borane. J. Am. Chem. Soc. 2016, 138, 12956-12962. (f) Liu,
X.; Liu, T.; Meng, W.; Du, H. Asymmetric Hydrogenations of Imines
with Chiral Alkene-Derived Boron Lewis Acids. Org. Biomol. Chem.
2018, 16, 8686-8689.
(a) Rendler, S.; Oestreich, M. Conclusive Evidence for an S
N
2-Si
Mechanism in the B(C -Catalyzed Hydrosilylation of Carbonyl
6
F
)
5 3
Compounds: Implications for the Related Hydrogenation. Angew.
Chem., Int. Ed. 2008, 47, 5997–6000. (b) Hog, D. T.; Oestreich, M.
B(C
6
F ) -Catalyzed Reduction of Ketones and Imines Using
5
3
Silicon-Stereogenic Silanes: Stereoinduction by Single-Point Binding.
Eur. J. Org. Chem. 2009, 5047–5056. (c) Chen, D.; Leich, V.; Pan, F.;
Klankermayer, J. Enantioselective Hydrosilylation with Chiral
Frustrated Lewis Pairs. Chem. Eur. J. 2012, 18, 5184–5187. (d) Ren, X.;
Du, H. Chiral Frustrated Lewis Pairs Catalyzed Highly Enantioselective
Hydrosilylations of 1,2-Dicarbonyl Compounds. J. Am. Chem. Soc.
Sokeirik, Y. S.; Mori, H.; Omote, M.; Sato, K.; Tarui, A.; Kumadaki, I.;
Ando, A. Synthesis of a Fluorous Ligand and its Application for
Asymmetric Addition of Dimethylzinc to Aldehydes. Org. Lett. 2007, 9,
1927-1929.
2
(
016, 138, 810−813.
a) Parks, D. J.; Spence, R. E. von. H.; Piers, W. E.
Bis(pentafluorophenyl)borane: Synthesis, Properties, and
(
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Manuscript revised: XXXX, 2019
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Hydroboration Chemistry of a Highly Electrophilic Borane Reagent.
Angew. Chem., Int. Ed. Engl. 1995, 34, 809-811. (b) Parks, D. J.; Piers,
W. E.; Yap, G. P. A. Synthesis, Properties, and Hydroboration Activity
of the Highly Electrophilic Borane Bis(pentafluorophenyl)borane,
HB(C
6
5
F )
2
. Organometallics 1998, 17, 5492-5503.
(a) Liu, Y.; Du, H. Chiral Dienes as “Ligands” for Borane-Catalyzed
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Entry for the Table of Contents
Page No.
Chiral Frustrated Lewis Pairs Catalyzed Highly
Enantioselective Hydrosilylations of Ketones
Ar
Ar
chiral diene (2.5 mol %)
HB(C F ) (5 mol %)
6
5 2
OH
O
t
Bu P (5 mol %)
3
Ar
0-99% yields
1-97% ee's
R
Ar
R
Ph SiH
2
2
8
8
27 examples
t
Ar = 3,5-( Bu) C H
6 3
2
Asymmetric hydrosilylations of simple ketones were realized by using a frustrated Lewis of chiral
t
diene-derived borane and Bu
high yields with up to 97% ee.
3
P as catalyst. A variety of optically active alcohols were obtained in
Xiaoqin Liu,a,b Qiaotian Wang, Caifang Han,
a,b
a,b
,
a,b
,a,b
Xiangqing Feng,* and Haifeng Du*
This article is protected by copyright. All rights reserved.