Aerobic oxidative kinetic resolution of racemic alcohols with bidentate ligand-binding Ru(salen) complex as catalyst

Article abstract of DOI:10.1016/j.tet.2007.03.105

Chiral Ru(salen)(nitrosyl) complex 1 is a useful catalyst for asymmetric aerobic oxidation of alcohols under photo-irradiation. In?this study, it was found that addition of β-hydroxy ketone or 1,3-diketone had a significant influence on its asymmetric catalysis. For example, the addition of 1,3-bis(p-bromophenyl)propane-1,3-dione 9 improved the relative reaction ratio in kinetic resolution of simple racemic secondary alcohols up to 30, while the addition gave an adverse effect on desymmetrization of an acyclic meso-1,3-diol. This additive effect was considered to be attributable to the chelate formation of the β-hydroxy ketone or 1,3-diketone with a Ru(salen) complex.

Full text of DOI:10.1016/j.tet.2007.03.105

Tetrahedron 63 (2007) 6383–6387
Aerobic oxidative kinetic resolution of racemic alcohols with
bidentate ligand-binding Ru(salen) complex as catalyst
*
Yukie Nakamura, Hiromichi Egami, Kazuhiro Matsumoto, Tatsuya Uchida and Tsutomu Katsuki
Department of Chemistry, Faculty of Science, Graduate School, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
Received 12 January 2007; revised 3 March 2007; accepted 16 March 2007
Available online 21 March 2007
Abstract—Chiral Ru(salen)(nitrosyl) complex 1 is a useful catalyst for asymmetric aerobic oxidation of alcohols under photo-irradiation.
In this study, it was found that addition of b-hydroxy ketone or 1,3-diketone had a significant influence on its asymmetric catalysis. For
example, the addition of 1,3-bis(p-bromophenyl)propane-1,3-dione 9 improved the relative reaction ratio in kinetic resolution of simple ra-
cemic secondary alcohols up to 30, while the addition gave an adverse effect on desymmetrization of an acyclic meso-1,3-diol. This additive
effect was considered to be attributable to the chelate formation of the b-hydroxy ketone or 1,3-diketone with a Ru(salen) complex.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
OH
OH
O
1
(2 mol%), h
+
C H Cl, rt, air
Ph
6
5
Ph
Ph
Oxidation of alcohols is of tremendous importance for
organic synthesis and numerous methods have been devel-
oped. Although various oxidants have also been introduced,
most of them are unsatisfactory from the viewpoint of atom
economy and ecological sustainability, because their use
produces waste co-products. Of various oxidants, molecular
oxygen is the oxidant of choice, since the co-product is
k /k =11
91% ee (61% conversion)
S
R
OH
Ph
Ph
2
(2 mol%), h
OH
O
HO
CHCl , rt, air
3
Ph
Ph
8
8
1% ee, 82%
OH
1
water. Moreover, molecular oxygen in ambient air is
ubiquitous and abundant. Thus, aerobic oxidation has been
extensively studied but there is still a big room for improve-
ment in aerobic oxidation of alcohols. In particular, the
asymmetric version of aerobic oxidation is still immature
and only a few examples of asymmetric aerobic oxidation
OH 3 (2 mol%), h
OH
CHCl , rt, air
O
3
0% ee, 67%
2
have been reported to date. We for the first time achieved
aerobic oxidative kinetic resolution by using chiral (ON)-
(R)
R
R
NO
Ru
X
N
O
N
2
a
Ru(salen) complex 1 as the catalyst (Scheme 1). Subse-
quently, (ON)Ru(salen) complexes (2 and 3) bearing axial
methyl groups at the cyclohexane moiety were found to serve
O
Ar Ar
(
R)
as efficient catalysts for oxidativedesymmetrization of meso-
1
3
,4-primary diols. The following aspects of the reactions are
unique: the oxidation is promoted by irradiation of visible
light under ambient condition in the absence of any auxiliary
activator such as a base or mediator. On the other hand,
oxidative kinetic resolution has been well effected by using
a Pd/sparteine/base system. Recently, efficient oxidative
kinetic resolution of racemic a-hydroxy esters using molec-
1
: R=H, Ar=Ph, X=Cl
2: R=Me, Ar=Ph, X=Cl
: R=Me, Ar=4-PhC H , X=OH
3
6
4
2
d–h
Scheme 1. Ru(salen) complexes used as catalyst for aerobic asymmetric
oxidation.
ular oxygen under atmospheric pressure has been achieved
by using a vanadium–Schiff base complex as catalyst.
2
i
Oxidative desymmetrization of meso-1,3-diols is a use-
ful method for synthesizing b-hydroxy ketones that are
a sub-unit seen in various natural products such as aceto-
genins. Sigman and co-workers have reported that
*
Corresponding author. Fax: +81 92 642 2607; e-mail: katsuscc@mbox.nc.
kyushu-u.ac.jp
0
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.03.105

6384
Y. Nakamura et al. / Tetrahedron 63 (2007) 6383–6387
desymmetrization of meso-1,3-diols can be effected with
good enantioselectivity by using the Pd/sparteine/base/mo-
preferentially in the second step. We next examined the
oxidative kinetic resolution of the racemic 5, and it was
observed that the enantiomer corresponding to the minor
isomer of the oxidative desymmetrization was oxidized pref-
2
d,f
lecular oxygen system.
Our recent study indicated that
complex 1 is not the best catalyst for oxidative desymmetri-
3
c
zation of meso-diols. However, we expected that desym-
metrization of meso-1,3-diols using complex 1 as catalyst
would give the corresponding b-hydroxy ketones with
high enantiomeric excess, if the minor enantiomer of the
resultant b-hydroxy ketones is consumed in preference to
erentially. However, the relative reaction ratio (k ) also di-
rel
minished, as the reaction proceeded. On the other hand,
alteration in krel and enantioselectivity has not been observed
in both oxidative kinetic resolution of simple racemic
2
a
secondary alcohols and oxidative desymmetrization of
meso-1,4-diols, in which the products are mono-dentate
4
3
the major isomer in the second oxidation (Scheme 2).
Contrary to our expectation, the desymmetrization gave
a disappointing result, but it led us to a new oxidation
system. In this paper, we describe improvement of a
Ru(salen) catalyst based on the unexpected result and
aerobic oxidative kinetic resolution of racemic secondary
alcohols with the improved catalyst.
ketones and lactols, respectively. Thus, the decrease of the
stereoselectivity observed in the present desymmetrization
and kinetic resolution was considered to be attributable not
only to a slow exchange of the hydroxy ketone but also to
the bidentate nature of the products. Since both desymmetri-
zation of 4 and kinetic resolution of racemic 5 produced bi-
dentate 1,3-diketone 6, we examined kinetic resolution of
racemic 5 using 1 pre-treated with 6, as catalyst. Although
both 1 and the pre-treated 1 showed the same sense of enan-
tiomer differentiation, the oxidation with the pre-treated 1
was ca. twice as fast as that with 1. Moreover, the krel value
in the reaction using the pre-treated 1 as the catalyst scarcely
changed, while the value was much smaller than that ob-
served with 1 at the early stage of the kinetic resolution.
This result suggested that, in the kinetic resolution of 5, com-
plex 1 gradually changed to a new catalyst that might be
equal to the pre-treated 1. We also examined a consecutive
oxidation of 1,3-di(p-bromophenyl)propane-1,3-diol 7 and
major
R
R
slow
KR
fast
R
R
OH O
R
R
desymmetrization
OH OH
O
O
R
R
slow
O
fast
OH
minor
Scheme 2. An expected reaction pathway of aerobic oxidation of meso-1,3-
diols: meso-trick strategy.
4
in one pot (Scheme 4). At first, 7 was oxidized under the
standard condition for 40 h to give a mixture containing 7
61%), hydroxy ketone 8 [32% (43% ee)], and diketone 9
2
. Results and discussion
(
We examined oxidative desymmetrization of meso-1,3-di-
phenylpropane-1,3-diol 4 using 2 mol % of 1 in anticipation
of the so-called ‘meso-trick’. Contrary to our expectation,
the enantiomeric excess of the resultant b-hydroxy ketone
(7%), followed by the addition of 4 to the reaction mixture.
After being stirred for another 1 h, the mixture was worked
up and the ee of 5 was determined to be ꢀ33% ee. On the
other hand, the oxidation of 4 using the 1 pre-treated with
diketone 6 showed 48% ee at 8% conversion. This result
meant that the resultant b-hydroxy ketone also affected
the stereochemistry of the oxidative desymmetrization. If the
coordination of bidentate product(s) is responsible for the
unusual stereochemistry observed in the oxidative desym-
metrization of 4 as described above, the oxidative desym-
metrization of meso-indan-1,3-diol 10 that gives the
corresponding mono-dentate b-hydroxy ketone 11 and di-
ketone 12 was considered to show the stereochemistry as
5
the reaction was much slower than the oxidation of simple
diminished over the reaction time (Scheme 3). In addition,
2
a
secondary alcohols. These results seemed explicable,
given that the hydroxy ketone yielded in the first step
remains coordinated to the ruthenium ion and the major
enantiomer can be oxidized to the 1,3-diketone
Ph
Ph
OH OH
4
Ph
Ph Ph
+
Ph
1
(2 mol%), air
h , CHCl , rt
OH
5
O
O
O
3
a
6
1
(2 mol%) + 7
conversion ( 20 h) = 9.6%: 67% ee (1 : 0.2)
conversion ( 64 h) = 12%: 50% ee (1 : 0.2)
conversion (160 h)= 20%: 25% ee (1 : 0.3)
h , CHCl3
rt, air, 40 h
Ph
Ph
Ph
Ph
Ph
Ph Ph
+
Ph
Ph
Ph
Ph
Ph
Ph Ph
+
Ph
OH OH
1
(2 mol%), air
OH
O
O
O
6
OH
O
5
hν, CHCl , rt
OH
5
O
O
O
4
3
a
racemic 5
6
-33% ee
conversion (8 h)= 17%, 19% ee, apparent krel= 33
conversion (24 h)= 42%, 58% ee, apparent krel= 16
conversion (75 h)= 65%, 93% ee, apparent krel= 9
conversion ( 4 h)= 22%, 22% ee, apparent krel= 7.3
Ph 1
Ph Ph
+
(2 mol%) + 6
h , CHCl3, rt, air
OH OH
4
OH
5
O
O
O
6
b
48% ee
b
conversion (26 h)= 49%, 62% ee, apparent krel= 7.8
a)
R
R R
OH OH
7
R R
R
The ee of 5 was determined by HPLC analysis using
Daicel Chiralcel OD-H .
The reaction was carried out with 1 pre-treated with 6.
R= p-BrC6H4
OH
O
O
O
b)
8
9
Scheme 3. Oxidative desymmetrization of 4 and kinetic resolution of
racemic 5 using 1 or the pre-treated 1.
Scheme 4. Consecutive oxidation of 7 and 4 using 1 as catalyst, and oxida-
tive kinetic resolution of 4 using the pre-treated 1 as catalyst.

Y. Nakamura et al. / Tetrahedron 63 (2007) 6383–6387
6385
OH
OH
OH
O
OH
1 (2 mol%), h
OH
O
+
1
(2 mol%)
CHCl , rt, air
Ph
3
Ph
Ph
+
h , CHCl , rt, air
Additive (5 mol%)
3
O
O
10
11
12
Table 1. Aerobic oxidative KR of racemic 1-phenylethanol 13
conversion = 43%, 71% ee, 11:12 = 1:0.13
conversion = 69%, 77% ee, 11:12 = 1:0.19
a
b
Entry Additive Time (h) Conv. (%)
ee (%)
k
rel
c
1
2
3
4
5
6
7
8
9
1
—
6
(S)-5
(S)-5
(R)-5
(R)-5
9
14
15
7
10
8
14
5
13
12
10
12
10
41
62
37
59
28
53
61
60
62
62
50
97
53
93
34
80
98
95
97
97
11 (ꢁ1)
Scheme 5. Oxidative desymmetrization of meso-indan-1,3-diol 10.
15 (ꢁ1)
33 (ꢁ1)
14 (ꢁ1)
21 (ꢁ1)
d
d
exhibited in Scheme 2. Indeed, the ee of the resultant 11
increased as the reaction proceeded: 71% ee at 43% conver-
sion (11:12¼1:0.13) and 77% ee at 69% conversion
d
d
14.5 (ꢁ1)
19 (ꢁ1)
16 (ꢁ1)
15 (ꢁ1)
15 (ꢁ1)
(
11:12¼1:0.19) (Scheme 5).
It is well known that a metallosalen complex adopts a cis-b
0
16
5
,6
configuration, on chelation of a bidentate ligand. More-
over, recent studies by us and others have revealed that
cis-b metallosalen complexes show unique asymmetric ca-
a
Determined by GLC analysis using optically active column (SPELCO
BETA-DEX-325).
Determined by HPLC analysis using chiral stationary phase column
b
6
talysis. In particular, cis-b metallosalen complexes bearing
the same salen ligand as complex 1 showed high enantio-
selectivity in the oxidation of simple sulfides and ketones.
From the above described results, we expected that complex
(
The reaction was carried out in chlorobenzene (Ref. 2a).
Both the enantiomeric excesses of (R)- and (S)-5s are 97.5% ee.
Daicel Chiralcel OB-H; hexane/iPrOH¼49:1).
c
7
d
1
pre-treated with a suitable bidentate ligand might serve as
O
O
an efficient catalyst for oxidative kinetic resolution of sim-
ple racemic alcohols. Thus, we examined the kinetic resolu-
tion of racemic 1-phenylethanol 13 using 1 pre-treated with
a 1,3-diketone or a b-hydroxy ketone, as catalyst (Table 1).
The krel value of the kinetic resolution using complex 1 is 11
9: R=p-BrC6H4 15: R=2-Naphtyl
4: R=p-ClC6H4 16: R=t-Bu
1
R
R
8
intramolecular hydrogen-atom transfer and subsequently
dissociates the resultant carbonyl compound (Scheme 7).
Further coordination of substrate alcohol to the sterically
crowded ruthenium complex (A) is unlikely and, moreover,
the coordination giving (C) formally violates the 18-electron
2
a
(entry 1). The krel was enhanced to 15 by using the com-
plex 1 pre-treated with 1,3-diketones 6, without reducing
9
the reaction rate (entry 2). Although the kinetic resolution
2
a
11
using 1 as catalyst was well effected in chlorobenzene, it
was found that kinetic resolution using the pre-treated 1
was better performed in chloroform. Consequently, the
following reactions were performed in chloroform. Pre-
treatment with (S)- or (R)-5 resulted in further enhancement
of the krel values to 33 or 21 at the early stages of the reac-
tions, respectively (entries 3–6). However, both the values
diminished to 14, as the reactions proceeded. Therefore,
we examined the pre-treatment with various 1,3-diketones
and the best value of 19 was attained when 1,3-bis(p-bromo-
phenyl)propane-1,3-dione 9 was added (entry 7). It should
be noted that the reduction of krel values was not observed
during the reactions, when 1 was pre-treated with a 1,3-di-
ketone.
rule. Although the participation of a trans- or cis-b species
D (Fig. 1), in which the bidentate ligand partially dissociates,
cannot be completely ruled out, it is also considered unlikely
by the present experimental results (cf. Schemes 3 and 5).
However, further study is required to conclude the mecha-
nism of the present oxidation.
In conclusion, we have disclosed that addition of an acyclic
b-hydroxy ketone or 1,3-diketone to Ru(salen) complexes
changed their catalytic performance for asymmetric aerobic
OH
OH
O
1
(2 mol%), h
+
CHCl3, rt, air
R
R
R
diketone 9 (5 mol%)
Oxidative kinetic resolution of various racemic secondary
alcohols was also examined with complex 1 pre-treated
with 9 and the improvement (up to 30) of the krel values
was observed (Table 2).
Table 2. Aerobic oxidative KR of simple racemic secondary alcohol in the
presence of diketone 9
a
b
Entry Substrate R]
Time (h) Conv. (%) ee (%) krel
c
1
2
3
4
5
PhC^C
(E)-PhCH]CH 18
17 10
58
54
57
54
41
99
82
95
90
30 (ꢁ2) [20]
14 (ꢁ1) [11]
23 (ꢁ1)
c
9
9
9
Our recent kinetic study on the aerobic oxidation of alcohols
with a Ru(salen) complex under irradiation disclosed that
oxidation of mono-ols includes three steps, a single electron
transfer (SET), an intramolecular hydrogen-atom transfer
d
d
e
4-ClC
4-BrC
PhCH
6
H
4
19
20
21 11
6
H
4
22 (ꢁ1)
2
55
15 (ꢁ1) [11]
a
b
c
d
e
Determined by GLC analysis using optically active column (SPELCO
BETA-DEX-325).
The value observed in the absence of diketone 9 was taken from Ref. 3a
and is shown in parentheses.
(
oxygen atom of the ligand, and ligand exchange (Scheme
HAT) from the a-carbon of the alkoxide to the phenolic
3
c
6
with a b-hydroxy ketone or a 1,3-diketone under irradiation
). The present results suggested that pre-treatment of 1
Determined by HPLC analysis using chiral stationary phase column
(Daicel Chiralcel OD-H; hexane/iPrOH¼19:1).
1
0
gives an addition product A. It is known that metal alkox-
ide makes a hydrogen-bond with alcohol, and it is likely that
the irradiation of A in the presence of alcohol gives a cation
radical species (B) carrying the alcohol, which undergoes an
Determined by HPLC analysis using chiral stationary phase column
(Daicel Chiralcel OB-H; hexane/iPrOH¼24:1).
Determined by HPLC analysis using chiral stationary phase column
(Daicel Chiralpak IA; hexane/iPrOH¼99:1).

6386
Y. Nakamura et al. / Tetrahedron 63 (2007) 6383–6387
R
H
R
R
R
R'
OH
R'
R'
R'
H
H
[
HAT]
O
O
O
N
IIIN
N
IIIN
N
N
N
N
Ru
Ru
RuIII
RuIII
O
O
O
O
• O2- H2O2
O
O
O
O
O
O
Cl
Cl
X
X
RR'CHOH
O
cis- -D
trans-D
•
O2-
h
O2
X= COCH , CH(OH)CH
R
3
3
[SET]
R'
Figure 1. Non-chelated cation radical species.
R
H
R'
OH
RuIII
[ligand exchange]
obtained with a SHIMADZU FTIR-8400 instrument. Opti-
cal rotations were measured with a JASCO P-1020 polari-
meter. Column chromatography was conducted on silica
gel 60N (spherical, neutral), 63–210 mm, available from
Kanto Chemical Co., Inc. Preparative thin-layer chromato-
graphy was performed on 0.5 mmꢂ20 cmꢂ20 cm E. Merck
silica gel plate (60 F-254). Conversions of alcohols were
determined by GLC analysis using SHIMADZU GC-1700
and GC-17A with chiral capillary column chiral SUPELCO
BET-DEX 325. Enantiomeric excesses were determined by
HPLC analysis using SHIMADZU LC-10AT-VP with an
appropriate optically active column, as described in the
footnotes to the corresponding tables. Ru(salen) complex
NO
Ru
Cl
N
O
N
h
N
N
O
RR'CHOH
O
O
Cl
(
R)
H
H
N
NO
Ru
O Cl O
Ph Ph
N
(
R)
1
1
3
1
3
(
, rac-secondary alcohols, (3R)- and (3S)-1,3-diphenyl-
-hydroxypropan-1-one 5, and 1,3-diketone derivatives
6, 9, and 14–16) were prepared according to the literature
Scheme 6. The mechanism of the oxidation of alcohols using 1 as catalyst.
The salen ligand is omitted for clarity, except for their donor atoms.
14
15
procedures. All the reagents and the solvents were carefully
dried immediately before use.
Ar
O
Ru
O
h
OH
N
O
IIIN
1
3.2. General procedure for kinetic resolution of rac-sec-
ondary alcohols using Ru(salen) complex 1 pre-treated
with 1,3-bis(p-bromophenyl)propane-1,3-dione 9
O
O
Ar
Ar
Ar
A
R
hν, O2
O
Ru(salen) complex 1 (2.0 mg, 2.0 mmol) and diketone 9
(1.9 mg, 5.0 mmol) were dissolved in 1.0 mL of CHCl and
H2O2
R'
RR'CHOH
O2-
3
•
stirred over 1 h under photo-irradiation with a halogen
lamp. To this solution was added rac-secondary alcohol
Ar
(0.1 mmol) and bicyclohexyl (19 ml, 0.10 mmol) as an inter-
Ar
O
nal standard for GLC analysis. An aliquot (80 ml) of this
solution was taken out of the flask as a zero point and passed
through a pad of silica gel (hexane/ethyl acetate¼8:2). The
filtrate was submitted to GLC analysis to adjust the molar
ratio. The remnant solution was stirred at room temperature
under irradiation in air and aliquots (100 mL) of the solution
were then periodically taken via a syringe. After passing
through a pad silica gel, the samples were then analyzed
using a GC and HPLC equipped with a chiral column to
determine the conversion of alcohol and the enantiomeric
excesses of the unreacted alcohols, respectively. The krel
was then calculated according to Kagan’s equation.
R
H
N
O
O
Ru
O
N
IIIN
R'
IIIN
H
Ru
O
O
O
Ar
O
O
Ar
H
OH
R'
C
B
R
Scheme 7. Proposed mechanism for the oxidation of alcohols using 1 in the
presence of a bidentate ligand. The salen ligand is omitted for clarity, except
for their donor atoms.
oxidation of alcohols and the addition showed a significant
positive effect on oxidative kinetic resolution of simple race-
mic secondary alcohols using complex 1 as catalyst. The
present study will open a new entry to further improvement
of catalytic performances of Ru(salen) complexes.
1
2
3.2.1. (R)-1-Phenylethanol (13). Colorless oil; con-
version¼47%, 71% ee; [a] +35.9 (c 0.367, CHCl ) [lit.
2
1
16
D
3
2
3
[
a] +48.6 (c 1.0, CH Cl ), (R)-configuration, 96% ee];
D 2 2
1
H NMR (CDCl ): d 7.38–7.24 (m, 5H), 4.95–4.87 (m,
3
3. Experimental
1H), 1.50 (d, 3H, J¼6.4 Hz).
3
.1. General
3.2.2. (2R,3E)-4-Phenylbut-3-en-2-ol (17). Colorless solid;
conversion¼57%, 87% ee; [a] +26.0 (c 0.267, CHCl3)
2
1
D
1
13
17
20
H and C NMR spectra were recorded at 400 MHz on
a JEOL JNM-AL 400 instrument. All signals were expressed
as parts per million down field from tetramethylsilane used
[lit. [a] +31.4 (c 1.38, CHCl ), (R)-configuration, 98%
D 3
1
ee]; H NMR (CDCl ): d 7.43–7.16 (m, 5H), 6.57 (d, 1H,
3
J¼15.9 Hz), 6.26 (dd, 1H, J¼6.6, 15.9), 4.55–4.45 (m,
as an internal standard (d value in CDCl ). IR spectra were
3
1H), 1.38 (d, 3H, J¼6.4 Hz).

Y. Nakamura et al. / Tetrahedron 63 (2007) 6383–6387
6387
3
.2.3. (R)-4-Phenylbut-3-yn-2-ol (18). Colorless oil;
D. R.; Pugsley, J. S.; Sigman, M. S. J. Org. Chem. 2003, 68,
4600–4603; (g) Mandal, S. K.; Sigman, M. S. J. Org. Chem.
2003, 68, 7535–7537; (h) Bagdanoff, J. T.; Stoltz, B. M.
Angew. Chem., Int. Ed. 2004, 43, 353–357; (i) Radosevich,
A. T.; Musich, C.; Toste, F. D. J. Am. Chem. Soc. 2005, 127,
1090–1091.
. (a) Shimizu, H.; Nakata, K.; Katsuki, T. Chem. Lett. 2002, 31,
1080–1081; (b) Shimizu, H.; Katsuki, T. Chem. Lett. 2003, 32,
480–481; (c) Shimizu, H.; Onitsuka, S.; Egami, H.; Katsuki, T.
J. Am. Chem. Soc. 2005, 127, 5396–5413.
4. For the meso-trick strategy, see: Schreiber, S. L.; Schreiber,
T. S.; Smith, D. B. J. Am. Chem. Soc. 1987, 109, 1525–1529.
. Metallosalen complex can adopt two cis-configurations, cis-a
and cis-b; however, the cis-a isomer is in general much less
stable than the cis-b isomer.
2
2
conversion¼54%, 94% ee; [a] +34.8 (c 0.40, CHCl3)
D
1
8
21
[
lit. [a] 36.68 (c 0.81, CHCl ), (R)-configuration,
D 3
1
>
7
99% ee]; H NMR (CDCl ): d 7.46–7.40 (m, 2H), 7.34–
3
.29 (m, 3H), 4.76 (quintet, 1H, J¼6.6 Hz), 1.56 (d, 3H,
J¼6.6 Hz).
3
3
.2.4. (R)-1-(p-Bromophenyl)ethanol (19). Colorless oil;
2
2
conversion¼59%, 98% ee; [a] +39.8 (c 0.375, CHCl3)
D
1
9
25
D
[
lit. [a] ꢀ37.9 (c 1.13, CHCl ), (S)-configuration, >99%
3
1
ee]; H NMR (CDCl ): d 7.47 (d, 2H, J¼8.8 Hz), 7.25 (d,
3
2
H, J¼8.8 Hz), 4.92–4.83 (m, 1H), 1.47 (d, 3H, J¼6.4 Hz).
.2.5. (R)-1-(p-Chlorophenyl)ethanol (20). Colorless oil;
5
3
2
1
conversion¼61%, 99% ee; [a] +47.6 (c 0.125, CHCl3)
D
2
0
20
D
[
ee]; H NMR (CDCl ): d 7.38–7.19 (m, 4H), 4.93–4.85
lit. [a] ꢀ48.8 (c 3.13, CHCl ), (S)-configuration, 99%
6. Katsuki, T. Chem. Soc. Rev. 2004, 33, 437–444.
3
1
7. (a) Saito, B.; Katsuki, T. Tetrahedron Lett. 2001, 42, 3873–
3876; (b) Watanabe, A.; Uchida, T.; Irie, R.; Katsuki, T.
Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 5737–5742.
8. Various 1,3-diketones are known to chelate with metallosalen
complexes to afford the corresponding cis-b isomers: (a)
Calligaris, M.; Manzini, G.; Nardin, G.; Randaccio, L.
J. Chem. Soc., Dalton Trans. 1972, 543–547; (b) Nakamura,
M.; Okawa, H.; Inazu, T.; Kida, S. Bull. Chem. Soc. Jpn.
1982, 55, 2400–2403.
3
(
m, 1H), 1.48 (d, 3H, J¼6.6 Hz).
3
.2.6. (R)-3-Phenyl-propan-2-ol (21). Colorless oil; con-
2
2
version¼46%, 65% ee; [a] ꢀ24.3 (c 0.292, CHCl )
D
3
2
1
15
[
lit. [a] +39.7 (c 0.515, CHCl ), (S)-configuration,
D 3
1
>
4
99.9% ee]; H NMR (CDCl ): d 7.35–7.19 (m, 5H),
3
.08–3.98 (m, 1H), 2.80 (dd, 1H, J¼4.7, 13.6 Hz), 2.69
(
dd, 1H, J¼8.2, 13.6 Hz), 1.26 (d, 3H, J¼6.1).
9
. The values of krel were calculated based on Kagan’s equation:
Balavoine, G.; Moradpour, A.; Kagan, H. B. J. Am. Chem.
Soc. 1974, 96, 5152–5158.
Acknowledgements
1
0. In the course of our study, Mezzetti et al. recently reported that
Ru(II)(PNNP) can make complexes with 1,3-dicarbonyl com-
pounds: Althaus, M.; Bonaccorsi, C.; Mezzetti, A.; Santoro, F.
Organometallics 2006, 25, 3108–3110.
Financial support (Specially Promoted Research 18002011)
from a Grant-in-Aid for Scientific Research from the Minis-
try of Education, Science, and Culture, Japan is gratefully
acknowledged. H.E. and K.M. are grateful for the JSPS
Research Fellowships for Young Scientists.
11. Sauve, A.; Groves, J. T. J. Am. Chem. Soc. 2002, 124, 4770–
4778.
1
2. A part of this study was reported in the 86th Annual Meeting of
the Chemical Society of Japan, March 2006, Abstracts, Vol. 2,
p 1106 (3 J1-45).
References and notes
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