A novel P-chirogenic phosphine ligand, (S,S)-1,2-bis-[(ferrocenyl)methylphosphino]ethane: Synthesis and use in rhodium-catalyzed asymmetric hydrogenation and palladium-catalyzed asymmetric allylic alkylation

Article abstract of DOI:10.1016/S0957-4166(03)00439-7

A new P-chirogenic diphosphine ligand, (S,S)-1,2-bis[(ferrocenyl)methylphosphino]ethane, was prepared via phosphine-borane intermediates. The ligand was used in the rhodium-catalyzed asymmetric hydrogenation of dehydroamino acid derivatives (up to 77% ena

Full text of DOI:10.1016/S0957-4166(03)00439-7

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 14 (2003) 2171–2175
A novel P-chirogenic phosphine ligand,
(S,S)-1,2-bis-[(ferrocenyl)methylphosphino]ethane: synthesis and
use in rhodium-catalyzed asymmetric hydrogenation and
palladium-catalyzed asymmetric allylic alkylation
Nobuhiko Oohara,a Kosuke Katagirib and Tsuneo Imamotob,*
aResearch & Development Division, Nippon Chemical Co., Ltd., 9-11-1, Kameido, Koto-ku, Tokyo 136-8515, Japan
bDepartment of Chemistry, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
Received 19 April 2003; accepted 27 May 2003
Abstract—A new P-chirogenic diphosphine ligand, (S,S)-1,2-bis[(ferrocenyl)methylphosphino]ethane, was prepared via phos-
phine–borane intermediates. The ligand was used in the rhodium-catalyzed asymmetric hydrogenation of dehydroamino acid
derivatives (up to 77% enantioselectivity) and in the palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl
acetate (up to 95% enantioselectivity).
© 2003 Elsevier Ltd. All rights reserved.
Hundreds of optically active phosphine ligands contain-
ing a ferrocenyl moiety have been designed, synthe-
ferrocenyl group may result in the high catalytic
efficiency of the ligand compared with that of previ-
ously reported 1,2-bis(arylmethylphosphino)ethanes.
Herein we report the preparation of enantiomerically
pure 1,2-bis[(ferrocenyl)methylphosphino]ethane and its
use in rhodium-catalyzed asymmetric hydrogenation
and palladium-catalyzed asymmetric allylic alkylation.
sized, and used in
a variety of enantioselective
transition metal-catalyzed reactions.1 Most of the lig-
ands are planar chiral and/or possess chirality due to a
stereogenic carbon center, and have been proven to be
highly effective in many asymmetric catalyses. In con-
trast, relatively less attention has been paid to P-chiro-
genic phosphines bearing ferrocenyl groups despite
their potential utility as ligands in asymmetric reac-
tions.2 Previously, we prepared P-chirogenic bis(tri-
alkyl-phosphine), (S,S)-1,2-bis(alkylmethylphosphino)-
ethanes (BisP*), in which a bulky alkyl group and the
smallest alkyl group (methyl group) were bonded to
each phosphorus atom, and demonstrated that they
exhibited excellent asymmetric induction in rhodium
catalyzed hydrogenation.3 On the other hand, non-
racemic 1,2-bis(arylmethylphosphino)ethanes have been
prepared by other groups and their catalytic perfor-
mance in a few representative catalytic asymmetric
reactions evaluated.2c,4,5 To the best of our knowledge,
however, a similar ligand bearing a ferrocenyl group as
the aryl group has not yet been reported. We envi-
sioned that the steric and electronic effects of the
Previously, we reported that ethylene bridged P-chiro-
genic diphosphines are prepared via phosphine–borane
intermediates.3,6 This methodology and Evans et al.’s
(−)-sparteine assisted enantioselective deprotonation
procedure5 permitted the short-step preparation of
enantiomerically
pure
1,2-bis-[(ferrocenyl)methyl-
phosphino]ethane 1 from ferrocene (Scheme 1). The
mono-lithioferrocene, that was generated directly from
ferrocene using Guilanex and Kagan’s procedure,7 was
treated sequentially with phosphorus trichloride, methyl
magnesium bromide, and a borane–THF complex to
give ferrocenyl(dimethyl)phosphine–borane 2 in a 30–
40% yield. One of the enantiotopic methyl groups of 2
was selectively deprotonated with a (−)-sparteine/sec-
BuLi complex5 and the resulting carbanion subjected to
oxidative dimerization by treatment with copper(II)
chloride to give the diphosphine–borane crude product
3. Recrystallization of the product from hot toluene
afforded an enantiomerically pure compound in 25–
35% yield based on 2. Compound 3 was subjected to
* Corresponding author. Fax: +81-43-290-2791; e-mail: imamoto@
faculty.chiba-u.jp
0957-4166/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0957-4166(03)00439-7

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N. Oohara et al. / Tetrahedron: Asymmetry 14 (2003) 2171–2175
The pure ligand was obtained as orange plates by
recrystallization from methanol. Surprisingly, this lig-
and was quite stable in air: it remained unchanged on
exposure to air at least for one month. The molecular
structure of 1 was determined not only from spectro-
scopic data but also by single-crystal X-ray analysis.
The ORTEP drawing of 1 in Figure 2 indicated an
(S,S)-configuration at the phosphorus atoms in agree-
ment with retention of the configuration occurring at
the phosphorus atom in the deboranation step.9 The
catalytic efficiency of ligand 1 was tested first in the
rhodium catalyzed asymmetric hydrogenation of some
dihydroamino acid derivatives. The catalyst precursor
was generated in situ by mixing ligand 1 with
[RhCl(cod)]2 in methanol, and the hydrogenation was
carried out in the same solvent. The results are summa-
rized in Table 1.10 The reaction proceeded slowly at
room temperature and required a higher temperature
(50°C) for completion within a short time. The
observed enantioselectivity was moderate to good, and
was higher than that observed by the use of 1,2-bis-
(methylphenylphosphino)ethane (e.g. 22% enantioselec-
tivity for a-(N-benzoylamino)cinnamic acid).4 It is
noteworthy that the reactions of b,b-disubstituted
derivatives gave rise to higher enantioselectivity than
those of b-monosubstituted derivatives. In all the cases,
(R)-configuration products were obtained. These stereo-
chemical outcomes are consistent with the prediction
based on our reformulated quadrant rule11 since the
ferrocenyl group is bulkier than the methyl group.
Scheme 1.
single-crystal X-ray analysis to confirm its molecular
structure and to determine the absolute configurations
at the phosphorus atoms using the Flack parameter
method. The ORTEP drawing of 3 in Figure 1 indi-
cated an (S,S)-configuration at the chiral phosphorus
atoms. The configuration is consistent with the stereo-
chemistry that was predicted based on previously
reported results.5,3 Compound 3 was heated with a
large excess of pyrrolidine at 65°C for 90 min to furnish
the desired ligand 1 without any loss of enantiomeric
purity.8
Figure 2. An ORTEP drawing of 1.
Figure 1. An ORTEP drawing of 3.
Table 1. Asymmetric hydrogenation of dehydroamino acid derivatives by rhodium complexes coordinated with 3
Entry
R1
R2
R3
Temp. (°C)
Atm.
Time (h)
Yield (%)a
Ee (%)b (config.)c
1
2
3
4
5
6
7
H
H
H
H
H
Me
Ph
Ph
Ph
Ph
H
Me
Me
Me
H
Me
Me
Me
rt
2
2
6
2
2
6
6
1
1
1
1
1
3
3
56
>99
>99
>99
>99
>99
>99
35 (R)
52 (R)
46 (R)
28 (R)
45 (R)
66 (R)
77 (R)
50
50
50
50
50
50
Me
-(CH2)4-
a Determined by GC or HPLC.
b The ee% values were determined by HPLC using Daicel Chiralcel OJ or chiral capillary GC using Chrompack’s Chiral-
L-Val Column (25 m).
The acids were converted to the corresponding methyl esters by the reactions with diazomethane.
c Absolute configurations were confirmed by comparison of chiral HPLC or GC elution orders with those reported in the literature.

N. Oohara et al. / Tetrahedron: Asymmetry 14 (2003) 2171–2175
2173
Next, we focused our attention on the enantioselectivity
of ligand 1 in palladium-catalyzed asymmetric allylic
alkylation.12 Experiments using 1,3-diphenyl-2-propenyl
acetate and dimethyl malonate with various solvents
and conventional base/additive conditions (Table 2,
entries 1–5) revealed that the reaction proceeded
smoothly in THF at room temperature to give the
substitution product in an almost quantitative yield
with 95% ee (entry 5). Other nucleophiles also reacted
under similar conditions to give the corresponding
products with high enantioselectivity (entries 6–9). The
number of reaction runs is limited; however, we believe
that this ligand may exhibit high catalytic efficiency in
other asymmetric allylic alkylation reactions.
High-resolution mass spectra were obtained on a JMS-
DX303 mass spectrometer (JEOL). FT-IR spectra were
obtained on an FT/IR-430 spectrometer (JASCO).
Melting points were determined with MP-V500
(Yanako) or FP-62 (Mettler). Specific rotation was
measured on SEPA-300 polarimeter (HORIBA). TLC
was performed on glass plates pre-coated with silica gel
60 F-254 (0.2 mm) from Merck.
1.2. Preparation of ferrocenyldimethylphosphine–borane
2
t-BuLi (56 mL, 1.43 M, 80 mmol) was added dropwise
to a solution of ferrocene (14.88 g, 80 mmol) in THF
(40 mL) and hexane (40 mL) at 0°C. After stirring for
1 h, the mixture was added to a solution of phosphorus
trichloride (10.99 g, 80 mmol) in THF (160 mL) at
−78°C through a cannula over a period of 30 min under
argon. The mixture was stirred at the same temperature
for 1 h, and then gradually raised to 0°C. Methyl
magnesium bromide (200 mL, 0.93 M THF solution,
192 mmol) was added to the solution, and the mixture
warmed to 50°C. After stirring for 1 h, the mixture was
cooled to 0°C, and a borane–THF complex (87 mL,
1.03 M THF solution, 90 mmol) added. The reaction
mixture was carefully poured into a mixture of ice-
water containing HCl. The organic layer was separated,
and the aqueous layer extracted with ethyl acetate. The
combined organic extracts were sequentially washed
with 1 M HCl, water and brine, dried over Na2SO4,
and concentrated in vacuo. Unreacted ferrocene and
volatiles were removed in vacuo at 100°C under vac-
uum (0.1 torr), and the residue recrystallized from ethyl
acetate/hexane to afford practically pure product (7.9 g,
38%). Orange needles: mp 105–106°C; 1H NMR
(CDCl3) l 0.75 (br q, JHB=95.6 Hz, 3H), 1.49 (d,
2JHP=10.4 Hz, 6H), 4.29 (s, 5H), 4.41 (s, 2H), 4.44 (s,
2H); 13C NMR l 14.03 (d, JCP=20.0 Hz), 69.49 (s),
We have prepared a new P-chirogenic diphosphine
ligand,
(S,S)-1,2-bis[(ferrocenyl)methylphosphino]-
ethane. The ligand is a solid crystal that is stable in air
and can be easily handled without special precautions.
The ligand gave moderate to good enantioselectivity of
up to 77% in the rhodium-catalyzed asymmetric hydro-
genation and high enantioselectivity of up to 95% in the
palladium-catalyzed asymmetric allylic alkylation of
1,3-diphenyl-2-propenyl acetate.
1. Experimental
1.1. General
All reactions were carried out under argon atmosphere.
All pieces of glassware were dried in an oven before
use. Solvents were treated prior to use according to the
1
standard method. H, 13C, and 31P NMR spectra were
recorded on a JMN-LA300 spectrometer (JEOL).
Chemical shifts were referenced to solvent peaks or
internal TMS (1H, 13C), or external 85% H3PO4 (31P).
Table 2. Asymmetric allylic alkylation catalyzed by palladium complexes coordinated with 3
Entrya
Nu
Solvent
Temp. (°C)
Time (h)
Yield (%)b
Ee (%)c, (config.)d
1
2
3
4
5
6
CH(COOMe)2
CH(COOMe)2
CH(COOMe)2
CH(COOMe)2
CH(COOMe)2
CH(COOtBu)2
CH(COMe)2
CH3CN
DMF
CH2Cl2
Toluene
THF
THF
THF
THF
THF
rt
rt
rt
rt
rt
rt
40
40
40
24
24
5
3
1
4
10
4
44
55
99
99
99
99
99
99
98
29 (S)
95 (S)
94 (S)
95 (S)
95 (S)
93 (S)
94 (S)
92 (R)
94 (R)
7e
8e,f
9e,f
AcNC(COOMe)2
AcNC(COOEt)2
3
a 1 mmol% catalyst and 1 mL/mmol of solvents were used, unless otherwise stated.
b Isolated yields.
c The ee% values were determined by HPLC using Daicel Chiralcel AD-H.
d Determined by HPLC elution order.
e 2 mol% catalyst and high reaction temperature was required for rapid completion of the reaction.
f 3 mL/mol solvent was needed for the solubility of Nu-H.

2174
N. Oohara et al. / Tetrahedron: Asymmetry 14 (2003) 2171–2175
2
3
70.75 (d, JCP=10.6 Hz), 71.28 (d, JCP=7.47 Hz); 31P
NMR (1H decoupled, CDCl3) l 0.25 (br q, JPB=59.5
Hz); IR (KBr) 3078, 2920, 2377, 1421, 1287, 1072, 819
cm−1; HRMS calcd for C12H18BPFe (M+) 260.0589,
found 260.0591.
mounted on a glass needle. All measurements were
conducted on a Rigaku RAXIS-II Imaging Plate dif-
fractometer with graphite monochromated Mo Ka
,
radiation (u=0.71070 A) at −100°C. Cell constants and
an orientation matrix for data collection corresponded
to a primitive orthorhombic cell. The data were col-
lected at a temperature of −100 1°C to a maximum 2q
value of 49.9°. A total of 126.00° oscillation images
were collected, each being exposed for 8.0 min. Crystal
data: C24H34B2P2Fe2, Mw=517.79, orthorhombic, space
1.3. Preparation of (S,S)-1,2-bis[boranato(ferrocenyl)-
methylphosphino]ethane 3
s-BuLi (34 mL, 0.99 M, 33 mmol) was added to a
solution of (−)-sparteine (7.73 g, 33 mmol) in Et2O (65
mL) at −78°C. After stirring for 30 min, ferro-
cenyl(dimethyl)phosphine–borane (3.9 g, 15 mmol) in
toluene (20 mL) was slowly added to the solution and
the mixture kept at the same temperature for 5 h.
Copper(II) chloride (3.09 g, 23 mmol) was added in one
portion with vigorous stirring. The cooling bath was
removed and the mixture warmed to rt over 2 h. The
stirring was then continued for another 15 h before
quenching the reaction with aqueous NH3 (25%, 45
mL). Most of the organic solvent was removed on an
evaporator, and the residue was vigorously stirred with
aqueous NH3 (25%, 45 mL) and chloroform (100 mL).
The organic layer was separated and the aqueous layer
extracted with chloroform. The combined organic lay-
ers were washed with 5% aqueous NH3, 2 M HCl, and
brine, and dried over Na2SO4. Purification by flash
column chromatography on silica gel using chloroform
as the eluent, followed by recrystallization from chloro-
form/hexane, afforded the desired (S,S) coupling
product (1.7 g) that contained a small amount (ca. 2%)
of meso-isomer (HPLC analysis: Daicel Chiralpak AD-
H, 2-PrOH:hexane:AcOH=5:95:0.05, 1 mL/min, (R,R)
t1=17.0 min, (S,S) t2=18.5 min, meso t3=20.4 min)..
Further recrystallization from hot toluene (ca. 60 mL)
furnished enatiomerically pure 3 (1.3 g, 33%). Orange
,
,
group P212121 (c19), a=14.24(1) A, b=15.27(2) A,
3
,
,
c=11.41(3) A, V=2481(7) A , Z=4, Dcalcd=1.386 g/
cm3, F(000)=1080.00, v (Mo Ka)=13.06 cm−1. The
structure was solved by direct methods and expanded
using Fourier techniques. The non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were
included but not refined. The final cycle of full matrix
least-squares refinement was based on 867 observed
reflections (I >2.00|(I), 2q <49.92) and 271 variable
parameters and converged (largest parameter shift was
0.05 times its esd) with unweighted and weighted agree-
ment factors of: R=0.071, Rw=0.067. The absolute
configuration was determined by the Flack parameter
method, value=0.054865 (0.182087).
1.6. Preparation of (S,S)-1,2-bis[(ferrocenyl)methyl-
phosphino]ethane 1
A solution of 3 (104 mg, 0.2 mmol) in pyrrolidine (3
mL) was stirred at 65°C under argon. After 90 min,
pyrrolidine was removed in vacuo, and the residue
passed through a column of basic alumina using
degassed toluene. The eluent was evaporated in vacuo
to leave 77 mg of practically pure ligand 3 (78% yield).
Further purification by recrystallization from methanol
afforded orange plates: mp 133–134°C. 1H NMR
(CDCl3) l 1.19–1.20 (m, 6H), 1.40–1.50 (m, 4H), 4.06–
4.09 (m, 2H), 4.07 (s, 10H), 4.05–4.08 (m, 2H), 4.19–
4.23 (m, 4H); 13C NMR l 11.38–11.54 (m), 22.77 (br),
68.70 (s), 68.8–69.0 (m), 69.83 (s), 70.10–70.18 (m),
72.68–72.99 (m); 31P NMR (1H decoupled, CDCl3) l
−35.87 (s); IR (KBr) 3080, 2920, 1420, 1285, 1023, 817
cm−1; HRMS calcd for C24H28P2Fe2 (M+) 490.0365,
found 490.0397.
1
needles: mp 238°C (dec.); H NMR (CDCl3) l 0.65 (br
q, JHB=114.8 Hz, 6H), 1.50–1.54 (m, 6H), 1.65–1.93
(m, 4H), 4.23 (br s, 12H), 4.43 (br s, 6H); 13C NMR l
11.03 (d, JCP=39.7 Hz), 22.50 (d, JCP=34.7 Hz), 69.57
(s), 69.92 (m), 71.5–71.8 (m), 72.2–72.4 (m); 31P NMR
(1H decoupled, CDCl3) l 8.5–11.5 (m); IR (KBr) 3096,
2920, 2371, 1417, 1298, 1066, 823 cm−1; HRMS calcd
for C24H34B2P2Fe2 (M+) 518.1031, found 518.1052; [h]2D5
−53.0 (c 0.52, CHCl3).
1.7. Crystal data of (S,S)-1,2-bis[(ferrocenyl)methyl-
phosphino]ethane 1
1.4. meso-1,2-Bis[(Ferrocenyl)methylphosphino]ethane
1
Orange needles: mp 228°C (dec.); H NMR (CDCl3) l
An orange plate crystal of C24H28P2Fe2 having approx-
imate dimensions of 0.60×0.40×0.10 nm was mounted
on a glass needle. All measurements were conducted on
a Rigaku RAXIS-II Imaging Plate diffractometer with
graphite monochromated Mo Ka radiation (u=0.71070
0.05–1.25 (br q, 6H), 1.45–1.55 (m, 6H), 1.65–1.82 (m,
4H), 4.22–4.28 (m, 2H), 4.28–4.32 (br s, 10H), 4.42–
4.48 (br s, 6H); 13C NMR l 10.65 (d, JCP=40.3 Hz),
22.77 (d, JCP=33.5 Hz), 69.61 (s), 71.5–71.8 (m), 72.5–
72.7 (m); 31P NMR (1H decoupled, CDCl3) l 13.8–16.2
(m); IR (KBr) 3097, 2915, 2380, 1417, 1293, 1067, 821
cm−1; HRMS calcd for C24H34B2P2Fe2 (M+) 518.1031,
found 518.1018.
,
A) at 15°C. Cell constants and an orientation matrix
for data collection corresponded to primitive
a
orthorhombic cell. The data were collected at a temper-
ature of 15 1°C to a maximum 2q value of 50.1°. A
total of 196.00° oscillation images were collected, each
being exposed for 4.0 min. Crystal data:13 C24H28P2Fe2,
Mw=490.13, orthorhombic, space group P212121
1.5. Crystal data of (S,S)-1,2-bis[boranato(ferrocenyl)-
methylphosphino]ethane 313
,
,
,
(c19), a=13.888(8) A, b=10.698(2) A, c=15.12(1) A,
3
V=2245(2) A , Z=4, Dcalcd=1.449 g/cm3, F(000)=
,
An orange plate crystal of C24H34B2P2Fe2 having
approximate dimensions of 0.40×0.20×0.10 nm was
1080.00, v (Mo Ka)=14.40 cm−1. The structure was

N. Oohara et al. / Tetrahedron: Asymmetry 14 (2003) 2171–2175
2175
solved by direct methods and expanded using Fourier
techniques. The non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were included but not
refined. The final cycle of full matrix least-squares
refinement was based on 2915 observed reflections (I
>2.00|(I), 2q <50.14) and 253 variable parameters and
converged (the largest parameter shift was 0.08 times its
esd) with unweighted and weighted agreement factors
of: R=0.057, Rw=0.070.
(g) Richards, C. J.; Locke, A. J. Tetrahedron: Asymmetry
1998, 9, 2377.
2. (a) Nettekoven, U.; Widhalm, M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M. Tetrahedron: Asymmetry 1997, 8,
3185; (b) Brown, J. M.; Laing, J. C. P. J. Organometal.
Chem. 1997, 529, 435; (c) Maienza, F.; Wo¨rle, M.; Stef-
fanut, P.; Mezzetti, A. Organometallics 1999, 18, 1041; (d)
Tsuruta, H.; Imamoto, T. Tetrahedron: Asymmetry 1999,
10, 877; (e) Maienza, F.; Spindler, F.; Thommen, M.;
Pugin, B.; Malan, C.; Mezzetti, A. J. Org. Chem. 2002,
67, 5239.
3. (a) Imamoto, T.; Watanabe, J.; Wada, Y.; Masuda, H.;
Yamada, H.; Tsuruta, H.; Matsukawa, S.; Yamaguchi,
K. J. Am. Chem. Soc. 1998, 120, 1635; (b) Imamoto, T.
Pure Appl. Chem. 2001, 73, 373; (c) Gridnev, I. D.;
Yamanoi, Y.; Higashi, N.; Tsuruta, H.; Yasutake, M.;
Imamoto, T. Adv. Synth. Catal. 2001, 343, 118.
4. Horner, L.; Simons, G. Z. Naturforsch. 1984, 396, 512.
5. Evans and his co-workers reported many enantiomeri-
cally pure borane adducts of 1,2-bis(arylmethylphos-
phino)ethanes. See: Muci, A. R.; Campos, K. R.; Evans,
D. A. J. Am. Chem. Soc. 1995, 117, 9075.
1.8. General procedure for rhodium-catalyzed asymmet-
ric hydrogenation of dehydroamino acid derivatives
Ligand 1 (5.8 mg, 0.012 mmol) was added to a solution
of [RhCl(cod)]2 (1.2 mg, 0.005 mmol) in MeOH (5 mL).
After stirring for 10 min, the catalyst solution was
transferred by syringe to a 50 mL pressure tight glass
vessel containing dihydroamino acid derivative (1
mmol). The vessel was immersed in a dry ice–ethanol
bath, evacuated and filled with hydrogen gas to a
predefined pressure. After four vacuum/H2 cycles, the
vessel was closed and the cooling bath removed. The
solution was magnetically stirred at ambient tempera-
ture until no further hydrogen uptake was observed.
6. (a) Imamoto, T.; Kusumoto, T.; Suzuki, N.; Sato, K. J.
Am. Chem. Soc. 1985, 107, 5301; (b) Imamoto, T.;
Oshiki, T.; Onozawa, T.; Kusumoto, T.; Sato, K. J. Am.
Chem. Soc. 1990, 112, 5244; (c) Imamoto, T. Pure Appl.
Chem. 1993, 65, 655.
1.9. General procedure for palladium-catalyzed asym-
metric allylic alkylation of rac-1,3-diphenyl-2-propenyl
acetate
7. Guilaneux, D.; Kagan, H. B. J. Org. Chem. 1995, 60,
2502.
To a 10 mL flask containing a magnetic stirrer bar was
added rac-1,3-diphenyl-2-propenyl acetate (252 mg, 1
mmol), solvent (1 mL), malonate derivative (2 mmol),
N,O-bis(trimethylsilyl)acetamide (470 mL, 2 mmol) and
K2CO3 (14 mg, 0.1 mmol) in this order under argon. To
this solution was added [Pd(p-C3H5)Cl]2 (1.8 mg, 0.005
mmol), and ligand 1 (5.8 mg, 0.012 mmol) in one
portion. The mixture was stirred at ambient tempera-
ture with occasional monitoring by TLC. The reaction
mixture was diluted with the minimum amount of ethyl
acetate and purified by flash chromatography on silica
gel (ethyl acetate/hexane=1/7) to give the pure
product.
8. No epimerization under these conditions was confirmed
by HPLC analysis of the phosphine–borane adduct which
was obtained by the reaction of crude product 1 with
borane–THF.
9. (a) Imamoto, T; Kusumoto, T.; Suzuki, N.; Sato, K. J.
Am. Chem. Soc. 1985, 107, 5301; (b) Imamoto, T.;
Oshiki, T.; Onozawa, T.; Kusumoto, T.; Sato, K. J. Am.
Chem. Soc. 1990, 112, 5244.
10. Use of cationic rhodium complex [Rh(nbd)2]+BF4 or
−
−
[Rh(cod)2]+BF4 instead of [RhCl(cod)]2 resulted in slug-
gish reaction providing very low enantioselectivity.
11. (a) Gridnev, I. D.; Higashi, N.; Asakura, K.; Imamoto,
T. J. Am. Chem. Soc. 2000, 122, 7183; (b) Cre´py, K. V.
L.; Imamoto, T. Adv. Synth. Catal. 2003, 345, 79.
12. For representative reviews, see: (a) Trost, C. G.;
Howarth, J.; Williams, J. M. J. Tetrahedron: Asymmetry
1992, 3, 1089; (b) Hayashi, T. In Catalytic Asymmetric
Synthesis; Ojima, I., Ed.; Wiley-VCH: New York, 1993;
pp. 325–365; (c) Trost, B. M.; van Vranken, D. L. Chem.
Rev. 1996, 96, 395; (d) Trost, B. M.; Lee, C. in Catalytic
Asymmetric Synthesis, 2nd ed.; Ojima, I., Ed.; Wiley-
VCH: New York, 2000; pp. 593–649; (e) Pflatz, A.;
Lautens, M. In Comprehensive Asymmetric Catalysis II;
Jacobsen, E. N.; Pflatz, A.; Yamamoto, H., Eds;
Springer: Berlin, pp. 833–884.
Acknowledgements
This work was supported in part by a Grant-in-Aid for
Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
References
1. For representative reviews and accounts, see: (a) Hayashi,
T.; Kumada, M., Acc. Chem. Res. 1982, 15, 395; (b)
Hayashi, T. Pure Appl. Chem. 1988, 60, 7; (c) Sawamura,
M.; Ito, Y. Chem. Rev. 1992, 92, 857; (d) Hayashi, T.
Ferrocenes; Togni, A.; Hayashi, T., Eds.; Wiley-VCH:
Weinheim, 1995; pp. 105–142; (e) Togni, A. Angew.
Chem. Int. Ed. Engl. 1996, 35, 1475; (f) Kagan, H. B.;
Riant, O. Advance in Asymmetric Synthesis; Hassner, A.,
Ed.; JAI Press Inc.: Greenwich, CT, 1997; 2, pp. 189–235;
13. CCDC 212697 for compound 3 and CCDC 212698 for
compound 1 contains the supplementary crystallographic
data for this paper. These data can be obtained free of
charge
via
http://www.ccdc.cam.ac.uk/conts/
retrieving.html (or from The Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ,
UK;
fax:
(+44)
1223-336-033;
or
e-mail:
deposit@ccdc.cam.ac.uk).