Divalent samarium triflate mediated stereoselective pinacol coupling of planar chiral phosphanyl and phosphoryl ferrocenecarbaldehyde

Article abstract of DOI:10.1002/ejoc.200801138

The pinacol coupling reaction of (Rp)-2-diphenylphosphanyl ferrocenecarbaldehyde (1) was smoothly mediated by divalent samarium triflate to give (R,R)-diol 2a predominantly, whereas the use of samarium(II) iodide resulted in low selectivity as described in the previous literature. In contrast, the coupling reaction of (Rp)-2-diphenylphosphoryl ferrocenecarbaldehyde (3) with Sm(OTf)₂ gave the (S,S)-diol as the major isomer, which was the opposite stereochemistry of that obtained in the reaction with 1. The rhodium complexes of diphosphanes 2a were good catalysts for the asymmetric hydrogenation of α-acetamidocinnamic acid, and the product was obtained quantitatively with up to 92 % ee.

Full text of DOI:10.1002/ejoc.200801138

FULL PAPER
DOI: 10.1002/ejoc.200801138
Divalent Samarium Triflate Mediated Stereoselective Pinacol Coupling of
Planar Chiral Phosphanyl and Phosphoryl Ferrocenecarbaldehyde
[a]
[a]
[a]
[a]
Shin-ichi Fukuzawa,* Ichiro Oura, Kenta Shimizu, Minoru Kato, and
Ken-ichi Ogata[
a]
Keywords: Samarium / Sandwich complexes / Radical reactions / Phosphanes / P ligands
The pinacol coupling reaction of (Rp)-2-diphenylphosphanyl
ferrocenecarbaldehyde (1) was smoothly mediated by di-
valent samarium triflate to give (R,R)-diol 2a predominantly,
whereas the use of samarium(II) iodide resulted in low selec-
tivity as described in the previous literature. In contrast, the
major isomer, which was the opposite stereochemistry of that
obtained in the reaction with 1. The rhodium complexes of
diphosphanes 2a were good catalysts for the asymmetric hy-
drogenation of α-acetamidocinnamic acid, and the product
was obtained quantitatively with up to 92%ee.
coupling reaction of (Rp)-2-diphenylphosphoryl ferrocene- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
carbaldehyde (3) with Sm(OTf)
2
gave the (S,S)-diol as the
Germany, 2009)
Introduction
previously reported highly diastereoselective pinacol coup-
ling reactions of chiral ortho-oxazoline-substituted ferro-
Thousands of ferrocenyl phosphane ligands, which are
useful tools for metal-catalyzed asymmetric reactions, have
been designed.
phanes are expected to be efficient ligands for metal-com-
plex-catalyzed asymmetric synthesis. The bifep [2,2ЈЈ-bis(di-
phenylphosphanyl)1,1Ј-bisferrocene][ ligand was first pre-
pared by Sawamura and Ito as an analogue of well-estab-
lished binap and related biaryl diphosphanes[ by optical
resolution of its racemate. Weissensteiner et al. and Wid-
halm et al. reported an alternative synthetic method of
cenecarbaldehyde by divalent samarium triflate [Sm-
[9]
(
OTf)2]. We attempted to prepare a single isomer of diol
[
1]
C -symmetrical bisferrocenyl diphos-
[10]
2
diphosphane by Sm(OTf) selectively.
In this paper we
report our results of the pinacol coupling reaction of (Rp)-
(Scheme 1) together with the results for ortho-phosphoryl
2
1
2]
derivative 3 and the benchmark rhodium-catalyzed asym-
[11]
metric hydrogenation.
3]
bifep without optical resolution, and applied it to metal-
complex-catalyzed asymmetric reactions.[
4–5]
Bisferrocenyl
methane diphosphane homologues, which are more readily
accessible than bifep,[
6–7]
have been applied to the rhodium-
complex-catalyzed asymmetric hydrogenation of alkenes
and ketones. In these asymmetric reactions, bifep and its Scheme 1. Pinacol coupling reaction of 1 with divalent samarium
reagents.
homologues have provided moderate-to-good enantio-
selectivities.
Kagan et al. prepared C -symmetrical bisferrocenyl diol
2
diphosphanes by pinacol coupling reactions of planar chiral
ortho-phosphanyl ferrocenecarbaldehyde by samarium(II)
Results and Discussion
iodide and showed that they are efficient ligands for the
(
Rp)-2-Diphenylphosphanyl ferrocenecarbaldehyde (1)
rhodium-catalyzed asymmetric hydrogenation of α-acet-
amidocinnamic acid.[ Although readily prepared by a sim-
ple procedure, the diol diphosphane was obtained as a mix-
ture of three diastereomers with fairly low selectivity. We
was prepared starting from the optically active ferrocenyl
sulfoxide according to the literature, and it was used to
verify the SmI -induced pinacol coupling reaction of Ka-
gan and Uemura.
8]
[7]
2
[8]
[11]
Table 1 summarizes the pinacol
coupling reaction together with reference results. The prod-
uct was a mixture of three diol diphosphane diastereomers,
[
a] Department of Applied Chemistry, Institute of Science and
Engineering, Chuo University,
1
-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
(R,R)-2a, (S,S)-2b, and (R,S)-2c. The isomeric ratio was de-
Fax: +81-3-3817-1895
termined by 1H NMR spectroscopic integration of al-
E-mail: orgsynth@kc.chuo-u.ac.jp
coholic methine protons and/or Cp ring protons of the
crude product, (R,R)-2a/(S,S)-2b/(R,S)-2c, 32:16:52
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
716
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 716–720

Divalent Samarium Triflate Mediated Stereoselective Pinacol Coupling
(Table 1, Entry 5). The isomers could be separated by flash
column chromatography. In the previous two studies, the
Sp isomer of 1 was used, so the present three diastereomers
2a–c are enantiomers of the previous diol diphosphanes. In
experiments performed by Kagan and Uemura, the iso-
meric ratios were ent-2a/ent-2b/ent-2c, 30:40:30 (r.t.) and
[
8,12]
52:24:24 (0 °C), respectively (Table 1, Entries 1 and 3).
Our results are different, but the stereochemical outcome is
similar in that the selectivity was fairly low. We next carried
out the pinacol coupling of 1 by using divalent samarium
triflate, which was prepared by the reduction of Sm(OTf)3
with sBuLi at 0 °C in THF. The reaction was complete in
Scheme 2. Pinacol coupling reaction of 3 with divalent samarium
reagents.
5
min as seen by the decolorization of the initial deep pur-
1
ple color. H NMR spectroscopic analysis revealed that the
selectivity for (R,R)-2a was remarkably enhanced with a ra-
tio of (R,R)-2a/(S,S)-2b/(R,S)-2c, 79:8:13, 2a = 58%de
(Table 1, Entry 7). The structure of major product (R,R)-2a
was confirmed by X-ray crystallographic analysis. This
higher diastereoselectivity was reproducible and was almost
the same at room temperature (Table 1, Entry 6) and at
0
°C. Kagan et al. improve their diastereoselectivity by low-
ering the reaction temperature from room temperature to
[
8]
–
25 °C in the SmI -mediated reaction (Table 1, Entry 2),
2
but Uemura et al. reported that no reaction occurs at
[
12]
–
78 °C. Therefore, the control of stereochemistry by tem-
perature has limitations with SmI , whereas Sm(OTf) -me-
2
2
diated reactions can achieve high diastereoselectivity at
either room temperature or at 0 °C.
Figure 1. Molecular structure of 4b (ORTEP plot). Selected bond
lengths [Å]: P1–O1 1.49, P2–O4 1.48, C18–C19 1.55, O2–C18 1.40,
O3–C19 1.40. Selected bond angles [°]: O1–P1–C13 113.0, O4–P2–
C24 114.7, O2–C18–C17 115.3, O2–C18–C19 112.3, O3–C19–C20
Table 1. Pinacol coupling of (Rp)-1 with divalent samarium rea-
[
a]
gents.
Entry
SmX
2
T [°C]
Yield [%]
2a/2b/2c[b]
115.6, O3–C19–C18 112.4.
[
[
[
c]
c]
e]
[d]
1
2
3
4
5
6
7
SmI
SmI
SmI
SmI
SmI
Sm(OTf)
Sm(OTf)
2
25
–25
0
25
0
25
0
80
–
41
90
90
Ͼ99
Ͼ99
30:40:30
[d]
2
25:65:10
Although the detailed mechanism is not yet clear, the
transition-state model discussed in the previous reaction of
[d]
2
2
2
52:24:24
17:19:64
32:16:52
79:10:11
79:8:13
ortho-substituted ferrocenecarbaldehyde may also explain
[
9,12]
2
the stereochemistry of the reaction of 1 (Scheme 3).
The
2
carbonyl oxygen atom is oriented away from the ortho phos-
II
[
a] 1 (0.5 mmol), SmX (1.2 mmol), THF (5 mL). [b] Determined phane group by steric effects and Sm attacks the carbonyl
2
1
[
8
]
by H NMR spectroscopy. [c] Ref. [d] When (Sp)-1 was used, the
group from the exo side to form the corresponding exo ke-
tyl radical intermediate. The sterically demanding triflate
isomeric ratio was ent-2a/ent-2b/ent-2c. [e] Ref.[
12]
We next examined the pinacol coupling reaction of (Rp)- group prevents diastereomerization, and the predominant
-diphenylphosphoryl ferrocenecarbaldehyde 3 with SmI2 exo ketyl radicals could couple with each other at the less-
2
and Sm(OTf) in THF at 0 °C for 0.5–1 h (Scheme 2). It is hindered re face to give (R,R)-diol 2a. In contrast, in the
2
1
interesting that the analysis of the crude product by H reaction of 3, the phosphoryl oxygen atom can coordinate
NMR spectroscopy showed the presence of (S,S)-pinacol 4b to the samarium atom and the endo ketyl radical is favored,
[
13]
predominantly (70–71%de) with both SmI and Sm(OTf) ; which then self-couples to form (S,S)-diol 4b.
2
2
for SmI2 4a/4b/4c, 4:86:10 and for Sm(OTf)2 4a/4b/4c,
:85:10. Combined pinacols 4a–c were obtained quantita- were checked by the benchmark rhodium-catalyzed asym-
tively and are separable by flash silica gel column metric hydrogenation of α-acetamidocinnamic acid (5)
The catalytic activities of diol diphosphanes 2a and 2b
5
[
14]
chromatography. The structure of main product (S,S)-4b (Scheme 4).
The reaction was carried out by using
was confirmed by X-ray crystallographic analysis, and its 0.01 mol and 0.02 mol equivalents of [Rh(cod)Cl] and the
2
X-ray structure is shown in Figure 1. Reduction of the ligand to 5, respectively, in MeOH at room temperature un-
[
5]
phosphoryl group in 4b afforded diphosphane 2b, which der 10 atm of hydrogen. The enantiomeric excess and abso-
was a minor product in the reaction of 1 with Sm(OTf)2. lute configuration of product 6 were determined by HPLC
Thus, either diastereomer 2a or 2b can be obtained selec- analysis after methyl esterification. The results are shown
tively by the pinacol coupling reaction of 1 or 3 with in Table 2. The complex of 2a catalyzed the hydrogenation
Sm(OTf)2.
smoothly to give (S)-6 quantitatively with high enantio-
Eur. J. Org. Chem. 2009, 716–720
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
717

S.-i. Fukuzawa, I. Oura, K. Shimizu, M. Kato, K.-i. Ogata
FULL PAPER
Conclusions
Sm(OTf) -mediated pinacol coupling reactions of ortho-
2
phosphanyl and phosphoryl-substituted ferrocenecarbal-
dehyde with high diastereoselection was achieved and C2-
symmetric (R,R)- or (S,S)-diol diphosphanes were obtained
selectively from each aldehyde. It was revealed that the
(R,R)-diol diphosphane worked more efficiently in the rho-
dium-catalyzed asymmetric hydrogenation of α-acet-
amidocinnamic acid.
Experimental Section
General: The H and 13C NMR spectra were recorded with a Var-
1
ian Mercury 300 NMR (300 MHz) spectrometer as solutions in
CDCl
3
. The chemical shifts are reported in δ units downfield from
Si. The optical rotations were deter-
the internal reference, Me
4
mined with a JASCO DIP-370 instrument. The HPLC analyses
were carried out with a Hitachi L-7100 apparatus equipped with a
UV detector by using chiral columns (Chiralcel OD-H, AS-H, OB).
Column chromatography was performed by using a Yamazen
YFLC-254 and a Michael Miller column equipped with a UV de-
tector by using Merck Silica Gel 60. Preparative TLC was con-
ducted with the use of a 20ϫ20 cm glass sheet coated with a 2 mm
Scheme 3. Proposed nonchelation and chelation mechanism for the
pinacol coupling reaction.
thick layer of Merck Kieselgel 60 PF254
.
selectivity (92%ee; Table 2, Entry 1), whereas the complex
of 2b gave low enantioselectivity (49%ee; Table 2, Entry 2).
We also examined the selectivity and reactivity of the reac-
tion by using ent-2a,b and the results were consistent with
those obtained with 2a,b (Table 2, Entries 3 and 5). These
Crystallography: The diffraction data were collected at room tem-
perature with a Rigaku AFC7R four-circle automated dif-
fractometer with graphite monochromated Mo-K radiation and
α
the ω-2θ scan technique to a maximum 2θ value of 50 or 55°. The
structure solution and refinements were carried out by using the
results were different from those of Kagan’s rhodium-cata- teXsan and Crystal Structure crystallographic software packages.
lyzed asymmetric hydrogenation of 5 by using ent-2a,b; ent- The positions of the non-hydrogen atoms were determined by Pat-
2
a and ent-2b give the product in 40% yield with 85%ee terson methods (DIRDIF PATTY) or direct methods (SIR92) and
expanded by using Fourier techniques (DIRDIF94 or 99). The car-
and 100% yield with 89%ee, respectively (Table 2, Entries 4
and 6). Ligand 2a, which is obtained as the major prod-
[
15]
2 2
bon atoms of the solvating CH Cl molecules were refined iso-
tropically.
CCDC-697469 [for (R,Rp;R,Rp)-2a] and -697470 [for (S,Rp;S,Rp)-
b] contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
uct of the pinacol coupling of 1 by Sm(OTf) , was a more
2
efficient ligand in our studies.
4
Crystallographic
data_request/cif.
Data
Centre
via
www.ccdc.cam.ac.uk/
General Procedure for the Sm(OTf)
Reaction of 1: Under a nitrogen atmosphere, Sm(OTf)
.2 mmol) was placed in a 50-mL Schlenk tube and equipped with
2
-Mediated Pinacol Coupling
3
(0.72 g,
1
a septum inlet. The tube was heated at 180 °C in vacuo for 2 h.
After the tube was cooled to room temperature, a magnetic stirring
bar was placed in the flask, which was flushed with nitrogen. THF
Scheme 4. Asymmetric hydrogenation of 5 by using rhodium/2a,b
complexes.
(
5 mL) was added by syringe through the rubber septum, and the
Table 2. Asymmetric hydrogenation of 5 by using rhodium/diol di-
mixture was stirred at room temperature for 1 h. Then, a solution
of sBuLi (1.0  in cyclohexane, 1.2 mL, 1.2 mmol) was injected
slowly into the suspension at 0 °C. The solution was warmed to
room temperature over a period of 0.5 h during which time a purple
solution of the divalent samarium triflate was obtained. To the re-
sulting THF solution of Sm(OTf) was added 1 (199 mg, 0.5 mmol)
2
at 0 °C. The deep purple color of the solution faded in 5 min, and
the solution was stirred for an additional 30 min. The solution was
quenched with saturated NH Cl, and the aqueous phase was ex-
[
a]
phos complexes.
Entry
L
Conv. [%]
ee [%][b]
Config.
1
2
3
2a
Ͼ99
92
Ͼ99
40
90
100
93
49
80
85
40
89
S
S
R
R
R
R
2b
ent-2a
ent-2a
ent-2b
ent-2b
[
c]
c]
4
5
6
[
4
tracted with ethyl acetate. The combined organic extract was
[
a] 5 (1 mmol), Rh (0.010 mol), L (0.011 mol), MeOH (2 mL),
room temp., 24 h, H (10 atm). [b] The %ee were determined by
HPLC (Chiralcel AD-H) after esterification with MeOH/SOCl
4
washed with brine and dried (MgSO ). Evaporation of the solvent
2
1
2
.
left a pale-yellow residue, and H NMR measurements of the crude
product revealed the presence of three diol diphosphane dia-
[
8]
[c] Data from Ref.
718
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 716–720

Divalent Samarium Triflate Mediated Stereoselective Pinacol Coupling
stereomers. (R,R)-Isomer 2a was produced as the major product.
The diastereomers were isolated by flash column chromatography
on silica gel (hexane/ethyl acetate, 4:1 to 2:1).
3.82 (s, 2 H), 4.23 (s, 10 H, Cp), 4.33 (dd, J = 2.5, 4.9 Hz, 2 H),
4.65 (s, 2 H), 4.75 (d, J = 4.0 Hz, 2 H), 5.21 (d, J = 4.0 Hz, 2 H),
7.2–7.8 (m, 20 H) ppm. C NMR (75 MHz, CDCl ): δ = 68.5 (d,
3
1
3
J = 115.2 Hz), 69.6, 70.0 (d, J = 12.0 Hz), 71.4 (Cp), 72.3 (d, J =
15.6 Hz), 73.0 (d, J = 9.6 Hz), 97.2 (d, J = 9.6 Hz), 128.0 (d, J =
(
R,Rp;R,Rp)-2a: Yield: 155 mg, 78%. Brown solid, m.p. 94–95 °C.
25
1
D 3 3
[α] = +310 (c = 0.41, CHCl ). H NMR (300 MHz, CDCl ): δ =
1
2.0 Hz), 128.2 (d, J = 12.0 Hz), 131.3 (d, J = 10.8 Hz), 131.6 (d,
1
2
.73 (br. s, 2 H), 3.66 (s, 2 H), 3.76 (s, 10 H, Cp), 4.24 (t, J =
.3 Hz, 2 H), 4.36 (s, 2 H), 4.53 (s, 2 H, CHO), 7.3–7.5 (m, 20 H)
3
1
J = 9.6 Hz), 132.7, 133.6, 134.0, 134.9 ppm. P NMR (121.5 MHz,
CDCl ): δ = 32.7 (s) ppm. C46 (830.44): calcd. C 66.53,
H 4.85; found C 66.61, H 4.52.
13
3
2 4 2
H40Fe O P
ppm. C NMR (75 MHz, CDCl
3
): δ = 69.1, 69.2, 69.6 (Cp), 71.7,
2.0, 74.7(C-O), 93.9 (C-P), 128.0, 128.8, 133.1 (d, J = 10 Hz),
33.3 (d, J = 10 Hz), 134.9 (d, J = 10.5 Hz), 135.1 (d, J = 10.5 Hz),
40.1 ppm. 31P NMR (121.5 MHz, CDCl
): δ = –26.4 (s) ppm.
798.1171; found 798.1178.
Crystals suitable for X-ray analysis were obtained by recrystalli-
zation from hexane/CH Cl
S,Rp;S,Rp)-2b: Yield: 20 mg, 10%. Brown solid, m.p. 210–211 °C.
7
1
1
(
(
S,Rp;S,Rp)-4b: Yield: 176 mg, 85%. Brown solid, m.p. Ͼ300 °C
3
25
1
decomp.). [α]
): δ = 3.46 (s, 2 H), 3.79 (d, J = 9.1 Hz, 2 H), 3.89 (s, 2 H),
.06 (s, 10 H, Cp), 5.92 (d, J = 9.4 Hz, 2 H, CHO), 7.5–7.6 (m, 16
D 3
= +247 (c = 0.17, CHCl ). H NMR (300 MHz,
2 2 2
HRMS (ESI): calcd. for C46H40Fe O P
CDCl
4
3
2
2
.
13
3
H), 7.8–7.9 (m, 4 H) ppm. C NMR (75 MHz, CDCl ): δ = 69.4
(
(d, J = 67.1 Hz), 69.9 (d, J = 34.8 Hz), 70.4, 73.0 (d, J = 15.6 Hz),
74.0 (d, J = 10.8 Hz), 74.8, 95.1 (d, J = 10.9 Hz), 128.2 (d, J =
12.0 Hz), 128.3 (d, J = 12.0 Hz), 131.6 (d, J = 9.7 Hz), 131.7 (d, J
2
5
1
[α]
D
= +320 (c = 0.5, CHCl
3 3
). H NMR (300 MHz, CDCl ): δ =
2
2
.63 (br. s, 2 H), 3.80 (s, 2 H), 4.10 (s, 10 H), 4.24 (t, J = 2.3 Hz,
3
1
H), 4.40 (s, 2 H), 4.84 (d, J = 6.2 Hz, 2 H, CHO), 7.3–7.4 (m, 16 = 9.6 Hz), 132.2, 133.1, 133.8, 134.7 ppm. P NMR (121.5 MHz,
13
H), 7.5–7.6 (m, 4 H) ppm. C NMR (75 MHz, CDCl
3
): δ = 69.4,
9.8 (Cp), 71.1 (d, J = 3.8 Hz), 71.3 (d, J = 3.2 Hz), 73.0 (d, J =
.3 Hz), 75.3 (d, J = 8.9 Hz, C-O), 94.4 (d, J = 22.5 Hz, C-P), X-ray analysis were obtained by recrystallization from hexane/
CDCl3):
δ
=
30.2 (s) ppm. HRMS (ESI): calcd. for
+
6
6
1
2
C H Fe O P Na 853.0967; found 853.0963. Crystals suitable for
4
6
40
2
4 2
28.1, 128.2, 128.3, 129.1, 132.7 (d, J = 18.9 Hz), 134.9 (d, J =
2 2
CH Cl .
0.9 Hz), 137.1 (d, J = 8.2 Hz), 139.9 (d, J = 9.5 Hz), 140.1 ppm.
3
1
(R,Rp;S,Rp)-4c: Yield: 21 mg, 9.6%. Brown solid, m.p. Ͼ300 °C
P NMR (121.5 MHz, CDCl
calcd. for C46 798.1171; found 798.1200.
R,Rp;S,Rp)-2c: Yield: 22 mg, 11%. Brown solid, m.p. 189–190 °C
3
): δ = –23.8 (s) ppm. HRMS (ESI):
2
5
1
(
decomp.). [α]
D
= +111 (c = 0.17, CHCl
3
). H NMR (300 MHz,
2 2 2
H40Fe O P
CDCl
3
): δ = 3.70 (s, 1 H), 3.89 (s, 1 H), 4.00 (d, J = 8.9 Hz, 1 H),
(
4
1
4
.23 (s, 5 H), 4.24 (s, 5 H), 4.00 (s, 1 H), 4.29 (dd, J = 2.9, 5.2 Hz,
25
1
D 3 3
[α] = +287 (c = 0.17, CHCl ). H NMR (300 MHz, CDCl ): δ =
H), 4.35 (d, J = 9.0 Hz, 1 H), 4.43 (dd, J = 2.3, 4.5 Hz, 1 H),
.63 (s, 1 H), 5.03 (s, 1 H), 6.04 (s, 1 H), 6.64 (d, J = 11.3 Hz, 1
3
3
2
7
.78 (t, J = 5.0 Hz, 1 H), 3.80 (s, 5 H), 3.86 (s, 1 H), 3.88 (s, 1 H),
.90 (s, 5 H), 4.00 (s, 1 H), 4.18 (t, J = 2.5 Hz, 1 H), 4.20 (t, J =
.5 Hz, 1 H, CHO), 4.76 (m, 1 H, CHO), 7.3–7.4 (m, 16 H), 7.5–
1
3
H), 7.3–7.8 (m, 20 H) ppm. C NMR (75 MHz, CDCl
3
): δ = 68.3–
6
1
9
1
3
8
9.8 (several Cp signals), 70.0 70.3, 72.7, 72.9, 73.0, 73.2 (d, J =
13
3
.6 (m, 4 H) ppm. C NMR (75 MHz, CDCl ): δ = 68.3–69.8
5.5 Hz), 73.9 (d, J = 10.8 Hz), 75.5 (d, J = 10.8 Hz), 97.1 (d, J =
.6 Hz), 97.7 (d, J = 10.2 Hz), 127.7–131.9 (several Ph signals),
(
several Cp signals), 71.1 72.0, 73.0 (d, J = 10.1 Hz), 73.5, 76.0 (C-
O), 92.4 (d, J = 21.5 Hz), 95.5 (d, J = 23.7 Hz, C-P), 127.7–128.3
several Ph signals), 128.9, 129.1, 132.5 (d, J = 17.5 Hz), 133.4 (d,
J = 19.5 Hz), 134.6 (d, J = 21.3 Hz), 135.2 (d, J = 21.3 Hz), 137.0
3
1
3
32.8, 133.1, 133.2, 134.2 ppm. P NMR (121.5 MHz, CDCl ): δ =
(
+
3.9 (s), 35.1 (s) ppm. HRMS (ESI): calcd. for C46
53.0967; found 853.0947.
2 4 2
H40Fe O P Na
(
(
–
d, J = 9.3 Hz), 137.3 (d, J = 5.1 Hz), 139.6 (d, J = 10.2 Hz), 139.8
3
1
d, J = 4.3 Hz) ppm. P NMR (121.5 MHz, CDCl
26.4 (s) ppm. HRMS (ESI): calcd. for C46
found 798.1180.
Rp)-3: To a methanol solution (5 mL) of 1 (1.12 g, 2.8 mmol) was (8.0 mg, 2 mol-%) in MeOH (4 mL), and the mixture was stirred
3
): δ = –22.8 (s),
[
Rh(cod)Cl]
α-Acetamidocinnamic Acid (5): In a 20-mL Schlenk tube containing
a stirring bar was dissolved [Rh(cod)Cl] (4.9 mg, 2 mol-%) and 2a
2
/2a-Complex Catalyzed Asymmetric Hydrogenation of
H40Fe O P 798.1171;
2 2 2
2
(
added H
of the oxidation reaction was monitored by TLC, and after 5 h
aqueous Na was added to the solution. Methanol was evapo-
rated in vacuo, and the residue was diluted with CH Cl . The solu-
tion was dried by MgSO and filtered. The solvent was evaporated
2
O
2
(30%, 0.5 mL) at room temperature. The completion
under a nitrogen atmosphere at room temperature. After 30 min,
the in situ formed catalyst solution was transferred to stainless au-
toclave containing α-acetamidocinnamic acid (5; 102 mg,
0.5 mmol) by using a cannula. The autoclave was purged three
times with hydrogen, and placed under hydrogen pressure (10 atm).
The mixture was stirred at room temperature for 24 h under an
atmosphere of hydrogen (10 atm). The solvent was removed under
2 2 3
S O
2
2
4
in vacuo, and the crude product was purified by flash column
chromatography on silica gel (ethyl acetate). Yield: 0.75 g,
2
5
1
.8 mmol, 64%. Brown solid, m.p. 176–177 °C. [α]
D
= –512 (c =
2
reduced pressure, and the residue was treated with MeOH/SOCl .
1
0.31, CHCl ). H NMR (300 MHz, CDCl
3
3
): δ = 4.17 (s, 1 H), 4.34 The inorganic part was removed by short column chromatography
(
s, 5 H), 4.71 (s, 1 H), 4.36 (s, 2 H), 5.17 (s, 1 H, CHO), 7.3–7.5 on silica gel to give almost pure product. The enantiomeric excess
13
(
m, 10 H, Cp), 10.3 (s, 1 H, CH = O) ppm. C NMR (75 MHz, (92%ee, S) of the crude product was determined by HPLC [Chi-
–
1
CDCl
3
): δ = 69.5, 71.2, 74.3 (d, J = 10.7 Hz), 75.8, 78.6 (d, J =
ralpack AD-H; 25 cm; hexane/iPrOH, 90:10; 0.8 mLmin ; t
= 14.7 min, t (S) = 18.7 min]. The pure methyl ester of 6 was
10.5 Hz), 133.1 (d, J = 7.6 Hz), 133.3 (d, J = 7.6 Hz), 131.7, obtained by flash column chromatography on silica gel. Yield:
R
(R)
1
=
4.0 Hz), 82.4 (d, J = 10.1 Hz), 128.2 (d, J = 10.5 Hz), 128.3 (d, J
R
31
1
131.8, 133.2 (d, J = 17.7 Hz), 134.8, 194.2 ppm. P NMR
3
91 mg, 4.4 mmol, 88%. H NMR (300 MHz, CDCl ): δ = 1.97 (s,
(
121.5 MHz, CDCl
3
): δ = 27.6 (s) ppm. C23
H19FeO
2
P (414.21): 3 H), 3.07 (dd, J = 5.9, 13.8 Hz, 1 H), 3.14 (dd, J = 5.8, 13.8 Hz,
1 H), 3.71 (s, 3 H), 4.87 (ddd, J = 5.8, 5.9, 7.8 Hz, 1 H), 6.11 (d, J
calcd. C 66.69, H 4.62; found C 66.63, H 4.64.
1
3
=
7.8 Hz, 1 H), 7.1–7.3 (m, 5 H) ppm. C NMR (75 MHz, CDCl
δ = 22.9, 37.7, 52.2, 53.0, 127.0, 128.5, 129.1, 135.8, 169.6,
72.1 ppm.
3
):
Pinacol Coupling Reaction with 3: The reaction of 3 with Sm-
OTf) and SmI was carried out with a similar procedure to that
of 1.
R,Rp;R,Rp)-4a: Yield: 10 mg, 5%. Brown solid, m.p. 184–185 °C.
(
2
2
1
(
Supporting Information (see footnote on the first page of this arti-
2
5
1
1
13
[α]
D
= +66.4 (c = 0.41, CHCl
3
). H NMR (300 MHz, CDCl
3
): δ =
cle): H and C NMR spectra of 1, 2a–c, 3, and 4a–c.
Eur. J. Org. Chem. 2009, 716–720
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
719

S.-i. Fukuzawa, I. Oura, K. Shimizu, M. Kato, K.-i. Ogata
FULL PAPER
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Acknowledgments
This study was financially supported by a Chuo University Grant
for Special Research.
[10] Pinacol coupling reaction of formylphosphaferrocene by SmI
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[
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Received: November 17, 2008
Published Online: December 29, 2008
720
www.eurjoc.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 716–720