Asymmetric transfer hydrogenation of aromatic ketones catalyzed by new chiral C2-symmetric bis(sulfonyl) tetraaza ligands complexed with [Ru(η6-p-cymene)Cl2]2 in water

Article abstract of DOI:10.1007/s10562-014-1254-0

In this report, a new series of C2-symmetric bis(sulfonyl) tetraaza ligands were synthesized from (1S,2S)-1,2-diarylethylenediamine analogues and tested in the asymmetric transfer hydrogenation (ATH) of aromatic ketones by complexing with [Ru(η⁶-p-cymene)Cl₂]₂ employing sodium formate as hydrogen source in neat water. A moderate to excellent conversion (～99.8 %) and overall satisfying enantioselectivity (～92.8 %) were obtained with varied electronic and steric effects of the substituents on ligands and substrates.

Full text of DOI:10.1007/s10562-014-1254-0

Catal Lett
DOI 10.1007/s10562-014-1254-0
Asymmetric Transfer Hydrogenation of Aromatic Ketones
Catalyzed by New Chiral C2-Symmetric Bis(sulfonyl) tetraaza
Ligands Complexed with [Ru(g6-p-cymene)Cl2]2 in Water
•
•
•
Xungao Liu Tian Zhang Yingying Hu
Liang Shen
Received: 3 January 2014 / Accepted: 2 April 2014
Ó Springer Science+Business Media New York 2014
Abstract In this report, a new series of C2-symmetric
bis(sulfonyl) tetraaza ligands were synthesized from
(1S,2S)-1,2-diarylethylenediamine analogues and tested in
the asymmetric transfer hydrogenation (ATH) of aromatic
ketones by complexing with [Ru(g6-p-cymene)Cl2]2
employing sodium formate as hydrogen source in neat
water. A moderate to excellent conversion (*99.8 %) and
overall satisfying enantioselectivity (*92.8 %) were
obtained with varied electronic and steric effects of the
substituents on ligands and substrates.
optimize the conversion and stereoselectivity of the cata-
lytic system.
The previous study in our group has provided a useful
insight for the design of efficient C2-symmetric chiral
tetraaza ligands (Fig. 1) [22]. Inspired by these results, we
aimed to explore the electronic and steric effects on the
catalytic activity of ligands by developing a new set of
bis(sulfonyl) tetraaza ligands derived from (1S,2S)-di-
phenylethylenediamine complexed with [Ru(g6-p-
cymene)Cl2]2 and used in the ATH of acetophenone and
propiophenone as well as their analogues in water with
sodium formate as the hydrogen source [23–25]. In this
work, we report on the preparation of five C2-symmetric
chiral bis(sulfonyl) tetraaza ligands, 3a–3e, which are used
in the Ru-catalyzed asymmetric transfer hydrogenation of
aromatic ketones, giving the corresponding optically active
secondary alcohols in moderate to excellent conversion
together with favorable enantioselectivity.
Keywords Bis(sulfonyl) tetraaza ꢀ Asymmetric transfer
hydrogenation ꢀ Ruthenium ꢀ Ketones ꢀ HCOONa
1 Introduction
Asymmetric transfer hydrogenation (ATH) is a typical and
effective method to obtain chiral secondary aromatic
alcohols, which are essential intermediates in synthesizing
physiological active pharmaceuticals under its safe and
mild reaction condition. Noyori et al. [1–4] have achieved
high enantioselectivity up to 90 % with Ru–TsDPEN
complexes in the reduction of ketones and imines for the
first time since the transition-metal catalyzed ATH was
reported in 1970s [5]. Since then, lots of efforts have been
put into this field using monotosylated 1,2-ethylenediamine
[6–12], amino alcohols [13–15], tetraaza [16–21], e.g.
especially bis(sulfonyl) tetraaza ligands [18–21] to
2 Experimental
All ATH reactions were carried out under nitrogen atmo-
sphere using oven-dried glassware in oil bath. Acetophe-
none and dichloromethane were distilled according to
standard methods. (1R, 2R)-1,2-bis-(2-hydroxyphenyl)-
1,2-diaminoethane and 1,3-benzenedisulfonyl chloride
were purchased from Sigma-Aldrich (Steinem, Germany)
and TCI (Shanghai, China), respectively. 40-nitrobenzal-
dehyde, 40-trifluoromethylbenzaldehyde and 20-methyl-
oxybenzaldehyde were obtained from J&K chemicals
(Shanghai, China). [Ru(g6-p-cymene) Cl2]2 was from Alfa
X. Liu ꢀ T. Zhang ꢀ Y. Hu ꢀ L. Shen (&)
College of Material Chemistry and Chemical Engineering,
Hangzhou Normal University, Hangzhou 310036, People’s
Republic of China
1
Aesar (Ward Hill, Massachusetts, UK). The H NMR and
13C NMR spectra were recorded on a 500 MHz Bruker
spectrometer. Chiral GC analysis was carried out using
e-mail: shenchem@hotmail.com
123

X. Liu et al.
Fig. 1 The chiral tetraaza
ligands in the previous study of
our group (Ts = tosyl)
NH
HN
HN
HN
HN
NH
NH
Ts
NH
Ts
Ts
Ts
HN
HN
NH
NH
HN
HN
NH
Ts
NH
Ts
Ts
Ts
Ts
Ts
N
N
NH
NH
HN
NH
HN
HN
Ts
Ts
Ts
Ts
N
N
H
OC
H
3CO
3
NH
HN
H
3CO
H
OC
3
Agilent GC 7890A with CP-Chiralsil-Dex-CB Chiral col-
umn (Santa Clara, CA, USA). Mass spectra were measured
with Agilent (Santa Clara, CA, USA) 5979 spectrometer.
LC–MS was measured with Agilent (Santa Clara, CA, USA)
Infinity 1290 LC and 6530 Accurate-Mass Q-TOF MS.
for 2 h. The mixture was stirred under room temperature for
another 12 h. The solvent was removed under reduced pres-
sure. The mixed solid was dissolved in dichloromethane
(20 mL) and filtered, and then dichloromethane was removed
under reduced pressure. Repeat the procedure of dissolving
and filtering for 3 times until affording a yellow solution.
Finally the solvent was removed under reduced pressure to
obtain 3a as light yellow powder (0.875 g, 96 % yield). [a]2D0:
2.1 Preparation of the C2-Symmetric Bis(sulfonyl)
1
tetraaza Ligands 3–3e
?88.4° (c 0.1, CHCl3). H NMR (500 MHz, DMSO-d6): d
(ppm) 3.375 (6H, br singlet, NH), 3.993 (2H, d, J = 7.5 Hz,
NH–CH), 4.318 (2H, d, J = 7.5 Hz, NH–CH), 6.869–6.920
(10H, m, CH ofphenyl), 7.081–7.090 (10H, m, CH ofphenyl),
7.192 (1H, m, CH of –SO2–phenyl), 7.290 (2H, dd,
J = 1.5 Hz, 8.0 Hz, CH of –SO2–phenyl), 7.696(1H, singlet,
CH of –SO2–phenyl). 13C NMR (125 MHz, DMSO-d6): d
(ppm) 60.219(CHNH), 64.227(CHNH), 124.713, 127.310,
127.824, 127.984, 128.092, 128.138, 128.289, 128.577,
129.494, 138.412, 140.724, 140.087, 141.092. EI-MS:
[M ? H]?: 633.
2.1.1 Preparation of (S,S,S,S)-N,N-bis(1,2-
diphenylethylenediamino)-1,3-benzenedisulfonyl
amine (3a) (Scheme 1)
A solution of (1S,2S)-1,2-diphenylethylenediamine (3 mmol,
0.637 g) in dichloromethane (30 mL) was mixed with tri-
ethylamine (0.5 mL, 2.8 mmol). The mixture was cooled to
0 °C and 1,3-benzenedisulfonyl chloride (0.275 g, 1 mmol)
dissolved in dichloromethane (10 mL) was added dropwise
123

Asymmetric Transfer Hydrogenation of Aromatic Ketones Catalyzed
O2S
NH
SO2
HN
ClO2S
SO2Cl
NH2
NH2
triethleneaminey,
CH2Cl2
NH2
H2N
3a
Scheme 1 Preparation of (S, S, S, S)-N,N-bis(1,2-diphenylethylenediamino)-1,3-benzenedisulfonyl amine (3a)
H
O
Ar
Ar
NH2
ClO2S
SO2Cl
NH2
NH2
1. ArCHO
O2S
NH
SO2
HN
Ar
Ar
Ar
Ar
.
2 H2O
triethyleneamine,
NH2
CH2Cl2
NH2
H2N
OH
(1S, 2S)- 2
(1R, 2R)- 1
(S, S, S, S)- 3
OCH3
3b Ar=
3d Ar=
3e Ar=
3c Ar=
CF3
OCH3
NO2
Scheme 2 Preparation of (S, S, S, S)-N,N-bis(1,2-diarylethylenediamino)-1,3-benzenedisulfonyl amine (3b–3e)
2.1.2 Preparation of (S,S,S,S)-N,N-bis(1,2-bis (40-
phenyl), 7.300 (1H, d, J = 1.5 Hz, CH of –SO2–phenyl),
7.316 (1H, d, J = 2.0 Hz, CH of –SO2–phenyl), 7.655 (1H,
s, CH of –SO2–phenyl). 13C NMR (125 MHz, DMSO-d6):
d (ppm) 55.214(OCH3), 55.321(OCH3), 59.853(CHNH),
64.256(CHNH), 113.405, 113.576, 124.821, 128.908,
129.063, 129.400, 131.002, 133.251, 142.007, 158.251,
158.556. HR-ESI–MS: [M ? H]?: 747.2480.
3c (0.852 g, 65 % yield) as yellow powder. [a]2D0: ?125°
(c 0.1, CHCl3). 1H NMR (500 MHz, CDCl3): d (ppm) 3.421
(6H, s, OCH3), 3.553 (6H, s, OCH3), 4.811 (2H, s, NH–CH),
5.100 (2H, s, NH–CH), 6.275 (2H, d, J = 8.0 Hz, CH of
phenyl), 6.415 (2H, d, J = 7.5 Hz, CH of phenyl),
6.714–6.797 (7H, m, CH of phenyl), 6.929 (2H, t,
J = 7.5 Hz, 8.0 Hz, CH of phenyl and –SO2–phenyl), 7.118
(2H, td, J = 1.0 Hz, 8.0 Hz, CH of phenyl), 7.197 (2H, dd,
J = 1.5 Hz, 8.0 Hz, CH of phenyl), 7.296 (2H, s, CH of
–SO2–phenyl), 7.434 (1H, s, CH of –SO2–phenyl). 13C NMR
methyloxybenzene) ethylenediamino)-1,3-
benzenedisulfonyl amine (3b–3e) (Scheme 2)
(1S,2S)-2 was prepared according to the literature proce-
dure [26–31]. A solution of (1S,2S)-2 (3 mmol) in
dichloromethane (30 mL) was mixed with excess triethyl-
amine (1.5 mL). The mixture was cooled to 0 °C and a
solution of 1, 3-benzenedisulfonyl chloride (0.275 g,
1 mmol) in dichloromethane (10 mL) was added dropwise
over 2 h. After the addition, the mixture was warmed to
room temperature and stirred for 12 h. The resulting
reaction mixture was washed with hydrochloric acid (2 M,
4 9 5 mL). The dichloromethane layer was dried over
anhydrous MgSO4, filtered, and the solvent was removed
under reduced pressure to obtain 3b–3e.
3b (0.817 g, 62 % yield) as bright yellow powder. [a]2D0:
1
-109° (c 0.1, CHCl3). H NMR (500 MHz, DMSO-d6): d
(125 MHz,
CDCl3):
d
(ppm)
45.784(CHNH),
(ppm) 3.580 (s, 6H, OCH3), 3.648 (s, 6H, OCH3), 3.991
(2H, d, J = 8.0 Hz, NH–CH), 4.283 (2H, d, J = 8.0 Hz,
NH–CH), 6.441 (4H, d, J = 8.5 Hz, CH of phenyl), 6.659
(4H, d, J = 9.0 Hz, CH of phenyl), 6.761 (4H, d,
J = 8.5 Hz, CH of phenyl), 7.014 (4H, d, J = 9.0 Hz,
CH of phenyl), 7.057 (1H, t, J = 8.0 Hz, CH of –SO2–
46.066(CHNH), 55.387(OCH3), 55.936(OCH3), 110.240,
111.316, 119.896, 120.326, 129.118, 129.359, 129.581,
130.457, 140.824, 155.838, 156.858. HR-ESI-MS:
747.2480.
3d (0.826 g, 59 % yield) as brownish red powder. [a]2D0:
-107° (c 0.1, CHCl3). 1H NMR (500 MHz, CDCl3):
123

X. Liu et al.
d (ppm) 4.197 (4H, s, NH–CH), 6.815 (1H, t, J = 7.5 Hz,
CH of –SO2–phenyl), 6.940 (1H, d, J = 8.0 Hz, CH of
–SO2–phenyl), 6.978 (1H, d, J = 7.5 Hz, CH of –SO2–
phenyl), 7.209 (1H, t, J = 7.0 Hz, 8.0 Hz, CH of –SO2–
phenyl), 7.418 (8H, d, J = 8.5 Hz, CH of phenyl), 8.135
(8H, d, J = 8.5 Hz, CH of phenyl). 13C NMR (125 MHz,
DMSO-d6): d (ppm) 45.996(CHNH), 82.891, 89.176,
123.765, 123.853, 123.896, 124.168, 128.896, 128.925,
129.392, 129.664. HR-ESI-MS: [M ? H]?: 807.1454.
3e (1.056 g, 70 % yield) as pinkish purple solid. [a]2D0:
degassed water (2 mL) and stirred at 40 °C for 1 h, subse-
quently, anhydrous sodium formate (10 mmol, 0.6801 g) and
the substrate (1.0 mmol) were added. At 60 °C the mixture
was heated for another 11 h. The suspension was extracted
with dichloromethane (3 9 5 mL). The oganic layers were
combined, dried over anhydrous MgSO4, filtered and con-
centrated under reduced pressure, and then passed through a
short silicagel column. The enantiomeric excess (ee) was
measured by Chiral GC analysis along with the conversion.
1
-95.6° (c 0.1, CHCl3). H NMR (500 MHz, CDCl3): d
(ppm) 4.204 (2H, d, J = 4.5 Hz, NH–CH), 4.490 (2H, d,
J = 5.0 Hz, NH–CH), 6.818 (1H, t, J = 7.5 Hz, 8.0 Hz,
CH of –SO2–phenyl), 7.299 (4H, d, J = 8.0 Hz, CH of
phenyl), 7.357 (4H, d, J = 8.0 Hz, CH of phenyl), 7.382
(4H, d, J = 8.5 Hz, CH of phenyl), 7.450 (4H, d,
J = 8.5 Hz, CH of phenyl), 7.546 (3H, d, J = 8.0 Hz,
CH of –SO2–phenyl), 7.951 (1H, s, CH of –SO2–phenyl).
13C NMR (125 MHz, CDCl3): d (ppm) 61.598(CHNH),
62.706(CHNH), 125.286(CF3), 125.545(CF3), 126.664
(CF3), 126.920(CF3), 127.275, 129.419, 129.527, 129.919,
130.172, 140.816, 142.535, 144.575, 146.998. HR-ESI-
MS: [M ? H]?: 899.1587.
3 Results and Discussion
To investigate the electronic and steric effects of ligands,
we prepared five bis(sulfonyl) tetraaza ligands with dif-
ferent substituents as indicated in Schemes 1 and 2, using
the ATH of acetophenone to be a model reaction. The
corresponding results are listed in Table 1. The ligands 3b,
carrying an electron donating group on the phenyl in para-
position, displayed lower catalytic conversion (85.3 %) and
enantioselectivity (82.6 % (S)-enantiomer) comparing to
3a (entries 2 and 4). The ligands bearing an electron
withdrawing group may have a complicated impact on the
ligands’ activities. As described in Table 1, the reduction
under 3e proceeded smoothly giving a conversion of
98.3 % better than that of 3a (86.0 %) at 40 °C (entries 1
and 7). The case of entry 2 only displayed a slight loss of
enantioselectivity about 2.6 % comparing to 3a (90.0 %)
2.2 General Procedure of ATH in Water
The complex-precursor [Ru(g6-p-cymene)Cl2]2 (0.005 mmol,
3.1 mg) and the ligands 3a–3e (0.011 mmol) were mixed in
Table 1 A comparison of Ru(II)–Ligand 3a–3e catalysts for the asymmetric transfer hydrogenation of acetophenone by sodium formate in water
O
OH
∗
[Ru(p-cymene)Cl2]2, ligands 3a-3e
S/C 100:1, HCOONa ,H2O
Entry
Ligand
Conversion (%)a
ee (%)a,b
Configurationa
1c
2
3c
3a
3a
3b
3b
3c
3d
3e
3e
86.0
99.8
78.8
85.3
72.4
22.0
98.3
99.8
92.8
90.0
91.7
82.6
78.4
42.3
81.5
87.4
S
S
S
S
S
R
S
S
4
5
6
7c
8
Reaction conditions: Catalyst: 1.1 9 10-5 mol; HCOONa: 1.0 9 10-2 mol; substrate: 1.0 9 10-3 mol; water: 2 cm3; temperature 60 °C;
reaction time 11 h; nitrogen protection
a
Determined by chiral GC (CP-Chiralsil-Dex-CB Chiral column)
b
Enantiomeric excess
c
Reaction temperature 40 °C
123

Asymmetric Transfer Hydrogenation of Aromatic Ketones Catalyzed
Fig. 2 The proposed six-
membered metal-ligand-
substrate transition state (TS)
Ar
Ar
Ar
Ar
H
H
O
O
H
H
N
N
N
N
C
C
H
H
R
Ru
Ru
S
O2
R
S
O2
Ar
Ar
Table 2 A comparison of Ru(II)–Ligand 3a–3e catalysts for the asymmetric transfer hydrogenation of aromatic ketones by HCOONa in water
O
OH
∗
R
R
[Ru(p-cymene)Cl ] , ligands 3a-3e
2 2
S/C 100:1, HCOONa, H O
2
X
X
(X=Cl, NO2, OCH3; R= CH3, Cl, CH2Cl, N(CH3)2)
Entry
Ligand
Substrate
Conversion (%) (the reduction by-product)
ee (%)a,b
Configurationa
1
3a
3b
3c
3d
3e
3a
3b
3c
3d
3e
3a
3b
3e
3a
3b
3a
3b
3c
3d
3e
3a
3b
3e
3a
3a
40-chloroacetophenone
40-chloroacetophenone
40-chloroacetophenone
40-chloroacetophenone
40-chloroacetophenone
20-chloroacetophenone
20-chloroacetophenone
20-chloroacetophenone
20-chloroacetophenone
20-chloroacetophenone
40-nitroacetophenone
40-nitroacetophenone
40-nitroacetophenone
40-methyloxyacetophenone
40-methyloxyacetophenone
2-chloroacetophenone
2-chloroacetophenone
2-chloroacetophenone
2-chloroacetophenone
2-chloroacetophenone
Propionphenone
99.8
80.4
68.5
79.6
44.2
72.3
87.8
75.6
86.3
48.5
84.5
79.4
73.2
79.2
91.5
86.4
91.0
87.7
82.6
60.8
87.7
85.2
79.4
80.2
90.4 (85.2)
–
S
S
S
R
S
S
S
S
R
S
S
S
S
S
S
S
S
S
R
S
S
S
S
S
–
2
95.9
3
78.5
4
19.0
5
99.7
6
99.7
7
94.7
8
76.9
9
36.5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
95.6
78.2
86.4
67.5
52.4
48.6
56.2 (9.8)
51.9 (6.7)
52.0 (20.5)
65.8 (9.8)
57.2 (13.9)
55.6
Propionphenone
51.8
Propionphenone
96.2
3-chloropropionphenone
3-N,N-dimethylpionphenone
33.8 (52.6)
-(99.5)
Reaction conditions: Catalyst: 1.1 9 10-5 mol; HCOONa: 1.0 9 10-2 mol; substrate: 1.0 9 10-3 mol; water: 2 cm3; temperature 60 °C;
reaction time 11 h; nitrogen protection
a
Determined by chiral GC (CP-Chiralsil-Dex-CB Chiral column)
b
Enantiomeric excess
123

X. Liu et al.
(Entry 8). It is suggested that the electron donating effect
depress the stability of the six-membered metal-ligand-
substrate transition state (TS, Fig. 2) [19, 20, 32, 33]. The
double metal complex in TS is confirmed by the elemental
analysis of the isolated Ru(II) complex with 3a when
mixing 1:1 ratio of Ru to ligand 3a in water at 60 °C.
However the electron withdrawing effect favors the for-
mation of hydrogen bonds in TS via increasing the nucle-
ophilicity of ligands to Ru(II). The electron effects on
activity are in accord with Noyori’s theoretical calculations
[32]. Moreover, by building a more crowded space around
the chiral center in the ligands, both steric hindrance and
electron donating effect on the ortho-position (ligand 3c,
entry 5) exerted a more negative influence on conversion
(72.4 %) and enantionselectivity (78.4 %, (S)-enantiomer).
When (S,S,S,S)-tetraaza ligand and p-cymene were used as
ancillaries, two (R)-configured Ru(II) centers were
obtained, in which two parts of the C2 symmetric ligand
were bound to metals independently. The transfer hydro-
genation via this (R)-configured TS with S conformation of
carbonyl carbon atom, resulting perhaps from the attractive
CH/p interaction between p-cymene ligand of the Ru-
complex and the aryl substituent in the substrate, afforded
(S)-enantiomer.
3-chloropropionphenone gave much lower yield but more
replacement by-product (propionphenone, 13.5 %) and the
reduction by-product (1-phenylpropanol, 52.6 %). It seems
that the nucleophilicity of the R group on substrates enables
the ketones to block the ligands to coordinate with the metal
center. In order to prove what was hypothesized, we tried the
3-N,N-dimethylpionphenone as a substrate. We failed to get
the expected alcohol but all propionphenone with its reduc-
tion outcome (1-phenylpropanol), which was in agreement
with the results in Wills’ and Qu’s experiments [34, 35].
4 Conclusions
Herein we report a new series of C2-symmetric bis(sulfo-
nyl) tetraaza ligands. By complexing with Ru(g6-p-
cymene)Cl2]2, the ligands exhibited good catalytic activi-
ties in the asymmetric transfer hydrogenation of aromatic
ketones employing sodium formate as the hydrogen source
in neat water at a modest temperature under insert gas
protection. A moderate to excellent conversions and overall
satisfying enantioselectivities of the chiral secondary
alcohols were obtained under ligand 3a and 3e. The
experiment results reveal that the electron donating effect
and steric effect corrode the reactivity of the ligands but the
electron withdrawing effect enhances the reactivity via
consolidating the sixed-membered transition state. How-
ever, given the applicability of the catalytic system, the
conditions for a wider range of aromatic ketones are still in
a further performance optimization.
Surprisingly, when nitro was imported in para-position
(3d), the yield of the expected 1-phenethylalcohol fallen to
22.0 % and a reversion of enantioselectivity was observed.
This was out of what we expected as only (S)-enantiomer
being the predominant product in the previous reactions.
The same reversion was caught in other substrates such as
entries 4, 9 and 19 exhibited in Table 2. It is speculated
that the delocalized p-bond of nitro causes this distinctness
of enantioselectivity and conversion by dragging the
hydrogen attached upon the prochiral carbon.
Acknowledgments We express our gratitude to the Public Benefit
Project of Zhejiang Science and Technology Department for financial
Support through Project No. 2012C21098 and the National Natural
Science Foundation of China (21101048).
Furthermore, the ATH of different aromatic ketones
(substrates) was explored under the same conditions as
previous. The effect of electron withdrawing had a positive
impact on the ATH over the electron donating groups on
substrates as shown in entries 2, 7, 12 and 15 in Table 2. It
may be attributed to the electron withdrawing effect which
giving more stable hydrogen bonds consisting in TS. Com-
paring the ATH of 2-chloroacetophenone and propionphe-
none with acetophenone under the same ligands (such as
entries 20 and 23 in Table 2, together with entry 8 in
Table 1), we found that a methyl or chlorine atom on a-
position of carbonyl group discouraged the performance of
ATH. This revealed that the bulkier around the carbonyl, the
lower stability of the TS. Notably, in entries 16–20, the
ATH of 2-chloroacetophenone had furnished acetophe-
none as a substitution by-product (9.8–20.5 %). But we
didn’t trace the reduction by-product (1-phenylalcohol),
indicating the priority of ATH to the side reaction of
chlorine atom replacement. In entry 24, the ATH of
References
1. Noyori R, Hashiguchi S (1997) Acc Chem Res 30:97–102
2. Noyori R, Yamakawa M, Hashiguchi S (2001) J Org Chem
66:7931–7944
3. Yamakawa M, Ito H, Noyori R (2000) J Am Chem Soc
122:1466–1478
4. Hashiguchi S, Fujii A, Takehara J, Ikariya T, Noyori R (1995) J
Am Chem Soc 117:7562–7563
5. Wang C, Wu XF, Xiao JL (2008) Chem Asian J 3:1750–1770
6. Hannedouche J, Clarkson GJ, Wills M (2004) J Am Chem Soc
126:986–987
7. Cheung FK, Hayes AM, Hannedouche J, Yim ASY, Wills M
(2005) J Org Chem 70:3188–3197
8. Hayes AM, Morris DJ, Clarkson GJ, Wills M (2005) J Am Chem
Soc 127:7318–7319
9. Morris DJ, Hayes AM, Wills
71:7035–7044
10. Cheung FK, Graharn MA, Minissi F, Wills M (2007) Organo-
metallics 26:5346–5351
M (2006) J Org Chem
123

Asymmetric Transfer Hydrogenation of Aromatic Ketones Catalyzed
11. Cheung FK, Lin CX, Minissi F, Criville AL, Graharn MA, Fox
DJ, Wills M (2007) Org Lett 9:4659–4662
24. Ma YP, Liu H, Chen L, Cui X, Zhu J, Deng JG (2003) Org Lett
5:2103–2106
12. Cortez NA, Aguirre G, Parra-Hake M, Somanathan R, Arita AJ,
Cooksy AL, de Parrodi CA, Huelgas G (2010) Synth Commun
41:73–84
25. Wu XF, Li XG, Hems W, King F, Xiao JL (2004) Org Biomol
Chem 2:1818–1821
26. Kim H, Nguyen Y, Yen PHC, Chagal L, Lough AJ, Kim BM,
Chin J (2008) J Am Chem Soc 130:12184–12191
27. Kim H, Staikova M, Lough AJ, Chin J (2009) Org Lett
11:157–160
13. Baratta W, Benedetti F, Zotto AD, Fanfoni L, Felluga F, Mag-
nolia S, Putignano E, Rigo
29:3563–3570
P (2010) Organometallics
14. Reetz MT, Li X (2006) J Am Chem Soc 128:1044–1045
15. Ahlford K, Adolfsson H (2011) Catal Commun 12:1118–1121
16. Charles MM, Schwarz I (2000) Tetrahedron Lett 41:8999–9003
28. Lee DN, Kim H, Mui L, Myung SW, Chin J, Kim HJ (2009) J
Org Chem 74:3330–3334
29. Cartigny D, Puntener K, Ayad T, Scalone M, Ratovelomanana-
Vidal V (2010) Org Lett 12:3788–3791
30. Tang YF, Xiang J, Cun LF, Wang YQ, Zhu J, Liao J, Deng JG
(2010) Tetrahedron Asymmetry 21:1900–1905
31. Wang L, Zhou Q, Qu C, Wang QW, Cun LF, Zhu J, Deng JG
(2013) Tetrahedron 69:6500–6506
17. Ranocchiari M, Mezzetti
28:1286–1288
A
(2009) Organometallics
18. Sterk D, Stephan MS, Mohar B (2004) Tetrahedron Lett
45:535–537
´
19. Cortez NA, Rodrıguez-Apodaca R, Aguirre G, Parra-Hake M,
Cole T, Somanathan R (2006) Tetrahedron Lett 47:8515–8518
20. Cortez NA, Aguirre G, Parra-Hake M, Somanathan R (2009)
Tetrahedron Lett 50:2228–2231
32. Yamakawa M, Ito H, Noyori R (2000) J Am Chem Soc
122:1466–1478
33. Soni R, Cheung FK, Clarkson GC, Martins JED, Grahamb MA,
Wills M (2011) Org Biomol Chem 9:3290–3294
34. Kenny JA, Palmer MJ, Smith ARC, Walsgrove T, Wills M (1999)
Synlett 10:1615–1617
´
´
21. Montalvo-Gonzalez R, Chavez D, Aguirre G, Parra-Hake M,
Somanathan R (2010) J Braz Chem Soc 21:431–435
22. Hong YL, Tan HJ, Qiu J, Shen L (2012) Synth React Inorg Met-
Org Nano-Met Chem 42:502–506
35. Zhao JF, Dou HJ, Zhou YH, Qu JP (2011) Chem J Chin Uni-
versities 32:2331–2334
23. Rhyoo HY, Park HJ, Chung YK (2001) Chem Commun
2064–2065
123