Furanoside diphosphinites as suitable ligands for the asymmetric catalytic hydrogenation of prochiral olefins

Article abstract of DOI:10.1016/j.tetasy.2004.05.047

Diphosphinite ligands, derived from inexpensive D-(+)-xylose, were tested in the rhodium- and iridium-catalyzed asymmetric hydrogenation of prochiral olefins. Our results show that the enantiomeric excesses are strongly dependent on the absolute configura

Full text of DOI:10.1016/j.tetasy.2004.05.047

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 2247–2251
Furanoside diphosphinites as suitable ligands for the asymmetric
catalytic hydrogenation of prochiral olefins
*
*
ꢀ
Eugeni Guimet, Montserrat Dieguez, Aurora Ruiz and Carmen Claver
Departament de Quꢀımica Fꢀısica i Inorgꢁanica, Universitat Rovira i Virgili, Pl. Imperial Tꢁarraco 1, 43005 Tarragona, Spain
Received 2 April 2004; accepted 3 May2004
Available online 10 July2004
Abstract—Diphosphinite ligands, derived from inexpensive
D
-(þ)-xylose, were tested in the rhodium- and iridium-catalyzed
asymmetric hydrogenation of prochiral olefins. Our results show that the enantiomeric excesses are strongly dependent on the
absolute configuration of the C-3 stereocenter of the carbohydrate backbone and on the metal source. Enantiomeric excesses of up
to 78% with moderate to high activities were obtained under very mild reactions conditions with the catalytic systems
[Rh(cod)(2)]BF4 and [Ir(cod)(1)]BF4.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
Following our interest in carbohydrates as an inexpen-
sive and highlymodular chiral source for preparing
ligands,8 and encouraged bythe success of the carbo-
hydrate diphosphinite ligands and the excellent results
obtained with the previouslymentioned furanoside
ligands, we have designed their diphosphinite 1 and 2
counterparts (Fig. 1).
The increasing demand for enantiomericallypure
pharmaceuticals, agrochemicals, flavors and other fine
chemicals has advanced the field of asymmetric catalytic
technologies.1 Asymmetric hydrogenation utilizing
molecular hydrogen to reduce prochiral olefins has
become one of the most efficient asymmetric catalytic
methods for constructing chiral compounds.1 Over
manyeyars the scope of this reaction has gradually
extended in terms of reactant structure and catalyst
efficiency.2 Manychiral ligands, mainlyP- and N-con-
taining ligands with either C2- or C1-symmetry, have
been successfullyapplied. Diphosphines have played a
dominant role among the P-ligands. However, diphos-
Ph
Ph
Ph
Ph
Ph
Ph
P
P
P
5
O
O
O
O
3
O
1
4
2
O
O
O
O
Ph
Ph
O
P
1
2
phinites, to a lesser extent, have also demonstrated their
1;2
potential utilityin asymmetric hydrogenation.
One of
Figure 1. Diphosphinite ligands 1–2.
the most successful families of diphosphinites are
derived from carbohydrates.3 Despite the earlysuccess
of carbohydrate phosphinite ligands in hydrogenation,
reports on their use are rare.3a;b;d;4 Recently, a new class
of diphosphine,5 phosphine–phosphite,6 and diphosph-
Herein we report the synthesis of these diphosphinite
ligands 1 and 2, their Rh(I) and Ir(I) complexes and
their use in the Rh and Ir-catalyzed enantioselective
hydrogenation of prochiral olefins. We have investigated
the influence of the stereogenic carbon atom C-3, since
ligands 1 and 2 are epimeric at C-3.
ite7 sugar ligands, derived from
D
-(þ)-xylose and -(þ)-
D
glucose, with furanoside backbones have successfully
been applied in the Rh-catalyzed asymmetric hydroge-
nation of several olefins.
2. Results and discussion
2.1. Synthesis of the chiral diphosphinite ligands
Ligands 1 and 2 were synthesized very efficiently in one
step from the corresponding alcohols 39 and 4,10 which
* Corresponding authors. Tel.: +34-977559572; fax: +34-977559563;
e-mail addresses: dieguez@quimica.urv.es; aruiz@quimica.urv.es
0957-4166/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.05.047

2248
E. Guimet et al. / Tetrahedron: Asymmetry 15 (2004) 2247–2251
HO
O
OH
PPh2Cl
1
2
O
O
Py / DMAP
a)
b)
O
O
3
D-(+)-xylose
HO
O
PPh2Cl
Py / DMAP
HO
4
Scheme 1. Synthesis of ligands 1–2. (a) Ref. 9; (b) Ref. 9.
were easilyprepared on a large scale from inexpensive
D
mation from 1H–1H COSY, 13C–1H, and 31P–1H
correlation measurements.
-(þ)-xylose (Scheme 1). The synthesis of ligand 1 was
adapted from a previouslypublished procedure (see
Section 4).3a The reaction of 3 and 4 with 2 equiv of
chlorodiphenylphosphine in dry THF, under nitrogen
and in the presence of pyridine and 4-(dimethylamino)-
pyridine (DMAP) provided the corresponding ligands in
85% and 68% yields, respectively.
1
For complexes 5, 6, and 8 the variable temperature H
and 13C NMR measurements indicated the presence of
one isomer with an overall C1-symmetry in solution.
However, for complex 7 several isomers were detected.
Onlytwo of these (denoted as a and b), in a ratio of 2:1,
have been fullycharacterized. These different isomers
maybe attributed to the different conformers of the
eight-membered chelate ring.11
All the ligands were stable during purification on neutral
alumina under an atmosphere of argon and theywere
1
isolated as pale yellow oils. The H, 31P, and 13C NMR
spectra were as expected for these C1 ligands (see Section
4). The spectral assignments were based on information
from 13C–1H and 31P–1H correlation measurements.
Over the whole temperature range explored (from 40 to
1
À80 ꢁC), the H and 13C NMR of complexes 5, 6, and 8
showed four signals for the olefinic protons and four
signals for the olefinic carbon atoms of the coordinated
cyclooctadiene, as expected for a C1-symmetrical com-
plex. For each isomer of complex 7, onlytwo broad
signals for the olefinic protons and one broad signal for
the olefinic carbon atoms were observed. This is prob-
ablydue to an overlap of the broad signals. The signals
from the diphosphinite ligands produced the expected
1H and 13C NMR pattern for the xylo- and ribo-furan-
oside nucleus (Table 1, Scheme 2).
2.2. Synthesis of rhodium and iridium complexes
The reaction of the corresponding chiral diphosphinite
ligands 1 and 2 with [M(cod)2]BF4 (M ¼ Rh, Ir) in di-
chloromethane solution proceeded with the displace-
ment of one molecule of the 1,5-cyclooctadiene ligand to
afford the cationic complexes [M(cod)(P–P)]BF4 5–8
(Scheme 2). All attempts to isolate these complexes were
unsuccessful.
The 31P NMR spectra (see Section 4) of the rhodium
complexes 5 and 6 showed two signals split into clearly
resolved double doublets due to the 31P, 103Rh and 31P,
31P coupling. The iridium complexes 7 and 8 showed two
doublets due to the 31P, 31P coupling. When the tem-
1
The complexes were characterized in solution using H,
13C, and 31P NMR spectroscopy. The spectral assign-
ments (selected data in Table 1) were based on infor-
Ph
Ph
Ph
P
Ph
P
O
M
O
O
Ph2P
PPh2
M
+
BF4
BF4
cod
+
O
5
O
2
O
1
O
4
O
O
3
O
1
2
M
Diphosphinite
5
6
7
8
Rh
1
2
1
2
Rh
Ir
Ir
Scheme 2. Synthesis of rhodium and iridium complexes 5–8.

E. Guimet et al. / Tetrahedron: Asymmetry 15 (2004) 2247–2251
Table 1. Selected NMR spectroscopic data for complexes 5–8a
2249
cod
Diphosphinite
5
CH2
CH@
1
2
3
4
50
CH3
CMe2
1H
5
2.31 (m)
2.43 (m)
2.57 (m)
4.62 (m), 4.70 (m)
4.84 (m), 4.99 (m)
5.88 (d)b
4.29 (d)b
4.48 (d)c
4.36 (m)
4.70 (dd)d 4.45 (dd)d 1.22 (s)
1.37 (s)
––
––
6
2.39 (br)
2.58 (br)
4.45 (m), 4.67 (m)
4.76 (m), 4.95 (m)
5.72 (d)e
5.73 (d)f
5.77 (d)h
5.36 (d)j
4.60 (t)e
4.40 (d)f
4.38 (d)h
4.38 (t)j
4.44 (m)
4.03 (d)g
3.99 (d)i
4.17 (m)
3.68 (m)
4.19 (m)
4.21 (m)
4.08 (m)
3.96 (m)
3.80 (m)
3.90 (m)
3.98 (m)
4.08 (m)
3.68 (m)
3.57 (m)
3.85 (m)
1.36 (s)
1.23 (s)
––
––
––
––
7a
7b
8
2.05 (br)
5.24 (br), 5.47 (br)
1.16 (s)
1.29 (s)
2.05 (br)
5.24 (br), 5.47 (br)
1.14 (s)
1.26 (s)
1.26 (br)
1.44 (br)
5.23 (m), 5.24 (m)
5.25 (m), 5.47 (m)
1.24 (s)
1.27 (s)
13C
5
29.7 (br)
28.1 (br)
103.6 (dd)k, 105.4 (dd)l 105.1
105.6 (dd)k, 105.9 (dd)l
84.8 (d)m
78.7 (d)o
85.6
81.1 (d)n
79.8 (d)p
75.4
78.2 (m)
74.4 (br)
76.0
67.2 (br)
68.2 (m)
60.3 (br)
60.3 (br)
72.3 (d)s
67.2 (br)
68.2 (m)
60.3 (br)
60.3 (br)
72.3 (d)s
26.5
27.0
112.8
113.1
111.5
111.6
113.8
6
31.6, 31.5
29.4, 29.3
100.9 (m), 103.5 (m)
104.9 (m), 106.6 (m)
103.9
105.2
104.7
104.4
26.9
26.8
7a
7b
8
30.4 (br)
105.4 (br)
24.6
25.8
30.4 (br)
105.4 (br)
85.8
79.9
75.7
24.5
25.6
26.8 (m)
27.1 (m)
104.2 (m), 104.3 (m)
104.3 (m), 104.5 (m)
78.9 (d)q
77.8 (d)r
79.0 (m)
27.03
27.08
a Chemical shifts in ppm, coupling constants in Hz; room temperature except for complexes 7a and b (at À20 ꢁC); 1H and 13C NMR in CD2Cl2.
Abbreviations: s, singlet; m, multiplet; d, doublet; t, triplet; dd, double doublet; br, broad.
3J ¼ 3:9.
b
c
3J ¼ 3:2.
d
3J ¼ 3:2, 2J ¼ 10:9.
e
3J ¼ 3:5.
f
3J ¼ 3:9.
g
3J ¼ 2:8.
h
3J ¼ 3:6.
i
3J ¼ 2:8.
j
3J ¼ 3:6.
k
1J ¼ 9:7, 2J ¼ 6:6.
l
1J ¼ 9:5, 2J ¼ 6:5.
m
3J ¼ 3:6.
n
2J ¼ 7:2.
o
3J ¼ 3:6.
p
2J ¼ 4:2.
q
3J ¼ 2:2.
r
2J ¼ 6:7.
s
3J ¼ 5:3. 1H NMR and 13C NMR data for the Ph part appears at d 7.1–7.8 ppm and d 127–136, respectively.
perature was lowered, none of the rhodium or iridium
complexes showed anysplitting, which confirms that
onlyone isomer is present for complexes 5, 6, and 8. In
the case of complex 7, it suggests that the presence of
onlyone doublet for the two isomers is probablycaused
byan accidental isocronicity.
olefins 9–11 under mild reaction conditions (1 bar of
H2). The selected results are shown in Table 2. The
catalysts were prepared in situ by adding the corre-
sponding diphosphinite ligands to the catalyst precursor
[M(cod)2]BF4 (M ¼ Rh, Ir).
The first set of experiments, was the rhodium-catalyzed
hydrogenation of methyl N-acetamidoacrylate 9 to
scope the potential of ligands 1 and 2 (Table 2). The
2.3. Asymmetric hydrogenation
Diphosphinite ligands 1 and 2 were tested in the Rh- and
Ir-catalyzed asymmetric hydrogenation of prochiral
reaction proceeded smoothlyat 1 bar of H at room
2
temperature in CH2Cl2. The use of ligand 1 afforded

2250
E. Guimet et al. / Tetrahedron: Asymmetry 15 (2004) 2247–2251
Table 2. Asymmetric hydrogenation of prochiral substrates 9–11 with
[M(cod)]BF4/1–2, M ¼ Rh, Ira
3. Conclusions
Diphosphinite ligands, prepared in a few steps from the
readilyavailable
R'
R
9
R'
H2 (1 bar)
[M]
D
-(þ)-xylose, were tested in the rho-
dium- and iridium-catalyzed asymmetric hydrogenation
of prochiral olefins. Our results show that enantiomeric
excesses depend stronglyon the absolute configuration
of the C-3 stereocenter of the carbohydrate backbone
and on the metal source. Enantiomeric excesses of up to
78% with moderate to high activities were obtained
under verymild reactions conditions with the catalytic
systems [Rh(cod)(2)]BF4 and [Ir(cod)(1)]BF4.
COOCH3
R
COOCH3
*
R=NHCOCH3; R'=H
10 R=NHCOCH3; R'=Ph
11 R=CH2COOCH3; R'==H
b
EntryM/L
Substrate
% Conv
(t/min) % Eec
1
Rh/1
Rh/2
Ir/1
9
9
100 (15)
8 (R)
2
100 (10)
100 (25)
76 (45)
76 (R)
78 (R)
15 (R)
10 (R)
35 (R)
20 (R)
10 (R)
9 (S)
3
9
Further research into more selective catalysts and other
types of hydrogenation reactions is now in progress to
exploit the fact that these sugar ligands can be modified
so easily.
4
Ir/2
9
5
Rh/1
Rh/2
Ir/1
10
10
10
10
11
11
11
11
9
100 (10)
100 (10)
100 (25)
100 (45)
100 (50)
99 (25)
6
7
8
Ir/2
9
Rh/1
Rh/2
Ir/1
10
11
12
13d
15 (R)
3 (R)
4. Experimental
2 (300)
100 (1680)
96 (45)
Ir/2
Rh/2
24 (S)
81 (R)
4.1. General comments
a [M(cod)2]BF4 ¼ 0.01 mmol.
Ligand/M ¼ 2.
Substrate/M ¼ 100.
All syntheses were performed using standard Schlenk
techniques under argon atmosphere. Solvents were
purified bystandard procedures. Compounds 3 and 4
CH2Cl2 ¼ 6 mL. PH2 ¼ 1 bar. T ¼ 25 ꢁC.
b % Conversion measured byGC.
c % Enantiomeric excess measured byGC using a Permabond
Chirasil-Val column for substrates 9 and 10 and a Chiraldex-G-TA
L-
9;10
were prepared bypreviouslydescribed methods.
All
other reagents were used as commerciallyavailable. 1H,
13C{1H} and 31P{1H} NMR spectra were recorded on a
Varian Gemini 400 MHz spectrometer. Chemical shifts
are relative to SiMe4 (1H and 13C) as internal standard
or H3PO4 (31P) as external standard. All assignments in
for substrate 11.
d T ¼ À25 ꢁC.
quantitative yields of hydrogenation product with 8% ee
(entry1). The use of the epimeric ligand 2, whose con-
figuration of carbon atom C-3 is opposite, had a positive
effect on activity(Table 2, entry2) and an extremely
positive effect on enantioselectivity(76% ee).
1
NMR spectra were determined by H–1H, 13C–1H, and
31P–1H spectra. The reaction under 1 atm of H2 was
performed in a previouslydescribed hydrogen vacuum
line.12 Gas chromatographyanalyses were performed in
a Hewlett–Packard Model 5890A instrument. Enantio-
meric excesses (ee) were measured using a fused silica
Interestingly, when the [Ir(cod)2]BF4 was used as cata-
lyst precursor, the best activity and enantioselectivity
(78% ee) was obtained with ligand 1 (entry3 vs 4).
capillarycolumn 25 m  0.25 mm Permabond
L-Chira-
sil-Val for the determination of ee for substrates 9 and
10, and in Chiraldex-G-TA (30 m  0.25 mm) for sub-
strate 11.
These results clearlyshow that the enantiomeric excesses
depend stronglyon the absolute configuration of the C-3
stereocenter of the carbohydrate backbone and on the
metal source. Therefore, enantioselectivities and activi-
ties were best using the catalytic systems
[Rh(cod)(2)]BF4 and [Ir(cod)(1)]BF4.
4.2. Synthesis of the chiral diphosphinite ligands
4.2.1.
isopropylidene-a-
3,5-Dideoxy-3,5-bis(diphenylphosphinite)-1,2-O-
-xylofuranose 1. A solution of 25 lL
D
In general, the hydrogenation of substrates 10 and 11
(Table 2, entries 5–12) follows the same trend as for 9.
However, the enantiomeric excesses substantiallyde-
creased. The use of different solvents (THF, acetone,
methanol) or an increase of hydrogen pressure to 5 bar
(data not shown) did not significantlyimprove the cat-
alyst performance (activity and enantioselectivity).
(0.11 mmol) of chlorodiphenylphosphine in 2 mL of
THF was slowlyadded at 0 ꢁC to a solution of 10 mg
(0.05 mmol) of 3 and 6.47 mg (0.05 mmol) of DMAP in
2 mL of pyridine. The reaction mixture was stirred
overnight at room temperature. Diethyl ether was then
added and the pyridine salts were removed by filtration.
The residue was purified byflash chromatography
(eluent: toluene/NEt3 100/1, Rf 0.8) to produce 0.025 g
(85%) of a pale yellow oil. Anal. Calcd for C32H32O5P2:
C, 68.81; H, 5.77. Found: C, 68.78; H, 5.78. 31P{1H}
Lowering the temperature to À25 ꢁC resulted in an
increase of the enantioselectivity(entry2 vs 13).
1
NMR (CDCl3), d: 115.4 (s, P–C3), 117.4 (s, P–C5). H
It is interesting that these diphosphinite ligands showed
a much higher degree of enantioselectivityand higher
reaction rates than their diphosphite analogues under
similar reaction conditions.5a
NMR (CDCl3), d: 1.27 (s, 3H, CH3), 1.44 (s, 3H, CH3),
4.09 (m, 1H, H-5), 3.10 (m, 1H, H-50), 4.38 (m, 1H, H-4),
3
4.42 (m, 1H, H-3), 4.60 (dd, 1H, H-2, J2-P ¼ 1:6 Hz,

E. Guimet et al. / Tetrahedron: Asymmetry 15 (2004) 2247–2251
2251
3J2–3 ¼ 3:6 Hz), 5.93 (d, 1H, H-1, 3J1–2 ¼ 3:6 Hz), 7.2–7.5
Acknowledgements
(m, 20H, Ph). 13C NMR (CDCl3), d: 26.6 (CH3), 27.1
2
ꢀ
We thank the Spanish Ministerio de Educacion, Cultura
yDeporte for their financial support (BQU2001-0656).
(CH3), 67.3 (d, C-5, J5-P ¼ 18:3 Hz), 80.4 (t, C-4,
3J4-P ¼ 6:8 Hz,
3J4-P ¼ 6:8 Hz),
82.1
(d,
C-3,
2J3-P ¼ 19:0 Hz), 83.9 (d, C-2,3J2-P ¼ 6:0 Hz), 105.3 (C-
1), 112.3 (CMe2), 128–132 (Ph).
References and notes
4.2.2.
isopropylidene-a-
3,5-Dideoxy-3,5-bis(diphenylphosphinite)-1,2-O-
-ribofuranose 2. Treatment of
1. See, for example: (a) Noyori, R. Asymmetric Catalysis in
Organic Synthesis; Wiley: New York, 1994; (b) Ojima, I.
Catalytic Asymmetric Synthesis; Wiley: New York, 2000;
(c) Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H. Compre-
hensive Asymmetric Catalysis; Springer: Berlin, 1999.
2. Tang, W.; Zhang, X. Chem. Rev. 2003, 103, 3029.
3. (a) Jackson, R.; Thompson, D. J. J. Organomet. Chem.
1978, 159, C29; (b) Selke, R.; Pracejus, H. J. Mol. Catal.
1986, 37, 213; (c) Selke, R.; Schwarze, M.; Baudisch, H.;
Grassert, I.; Michalik, M.; Oehme, G.; Stoll, N.; Costi-
sella, B. J. Mol. Catal. 1993, 84, 223; (d) RajanBabu, T.
V.; Ayers, T. A.; Casalnuovo, A. L. J. Am. Chem. Soc.
1994, 116, 4101; (e) RajanBabu, T. V.; Ayers, T. A.;
Halliday, G. A.; You, K. K.; Calabrese, J. C. J. Org.
Chem. 1997, 62, 6012; (f) Ayers, T. A.; RajanBabu, T. V.
US Patent 5,510,507, 1996; (g) Yonehara, K.; Hashizume,
T.; Ohe, K.; Uemura, S. Bull. Chem. Soc. Jpn. 1998, 71,
1967; (h) Yonehara, K.; Ohe, K.; Uemura, S. J. Org.
Chem. 1999, 64, 9381; (i) Yonehara, K.; Hashizume, T.;
Mori, K.; Ohe, K.; Uemura, S. J. Org. Chem. 1999, 64,
5593; (j) Shin, S.; RajanBabu, T. V. Org. Lett. 1999, 1,
1229; (k) Chen, Y.; Li, X.; Tong, S.; Choi, M. C. K.;
Chan, A. S. C. Tetrahedron Lett. 1999, 40, 957.
D
4
(0.05 mmol) with chlorodiphenylphosphine (25 lL,
0.11 mmol) as described for compound 1 afforded
diphosphinite 2, which was purified byflash chroma-
tography(eluent: toluene/NEt 3 100/1, Rf 0.7) to produce
0.019 g (68%) of a pale yellow oil. Anal. Calcd for
C3220H32O5P2: C, 68.81; H, 5.77. Found: C, 68.83; H, 5.76.
½aꢀ ¼ þ60 (c, 2.0, CHCl3) 31P{1H} NMR (CDCl3), d:
D
118.39 (s, P–C3), 118.42 (s, P–C5). 1H NMR (CDCl3), d:
1.30 (s, 3H, CH3), 1.53 (s, 3H, CH3), 4.14 (m, 1H, H-5),
3.98 (m, 1H, H-50), 4.23 (m, 1H, H-3), 4.26 (m, 1H, H-4),
3
3
4.52 (t, 1H, H-2, J2-P ¼ 3:6 Hz, J2–1 ¼ 3:6 Hz), 5.42 (d,
1H, H-1, J1–2 ¼ 3:6 Hz), 7.2–7.8 (m, 20H, Ph). 13C
3
NMR (CDCl3), d: 26.5 (CH3), 26.6 (CH3), 67.6 (d, C-5,
2J5-P ¼ 19:1 Hz), 76.9 (d, C-3, J3-P ¼ 19:0 Hz), 78.1 (d,
2
3
3
C-2, J2-P ¼ 3:1 Hz), 78.9 (t, C-4, J4-P ¼ 6:8 Hz,
3J4-P ¼ 6:8 Hz), 103.6 (C-1), 112.8 (CMe2), 127–132 (Ph).
4.3. Synthesis of rhodium and iridium complexes
4. (a) Yamashita, M.; Hiramatsu, K.; Yamada, M.; Suzuki,
N.; Inokawa, S. Bull. Chem. Soc. Jpn. 1982, 55, 2917; (b)
Yamashita, M.; Naoi, M.; Imoto, H.; Oshikawa, T. Bull.
Chem. Soc. Jpn. 1989, 62, 942; (c) Yamashita, M.;
Kobayashi, M.; Sigiura, M.; Tsunekawa, K.; Oshikawa,
T.; Inokawa, S.; Yamamoto, H. Bull. Chem. Soc. Jpn.
1986, 59, 175.
4.3.1. General procedure. Diphosphinite ligand
(0.11 mmol) was added to a solution of [M(cod)2]BF4
(0.1 mmol M ¼ Rh, Ir) in 2 mL of dichloromethane.
After stirring for 30 min, the desired products were ob-
1
tained and characterized in solution. H and 13C NMR
details are reported in Table 1.
ꢁ
5. (a) Pamies, O.; Net, G.; Ruiz, A.; Claver, C. Eur. J. Inorg.
Chem. 2000, 2011; (b) Dieguez, M.; Pamies, O.; Ruiz, A.;
ꢀ
ꢁ
• [Rh(cod)(1)]BF4 5. 31P NMR (CD2Cl2), d: 128.37 (dd,
ꢀ
Castillon, S.; Claver, C. Tetrahedron: Asymmetry 2000, 11,
4701.
2
1JP–Rh ¼ 172:4 Hz, JP–P ¼ 25:9 Hz, P–C5), 132.09
1
2
(dd, JP–Rh ¼ 175:3 Hz, JP–P ¼ 25:9 Hz, P-C3).
ꢁ
ꢀ
6. (a) Pamies, O.; Dieguez, M.; Net, G.; Ruiz, A.; Claver, C.
ꢁ
• [Rh(cod)(2)]BF4 6. 31P NMR (CD2Cl2), d: 126.56 (dd,
ꢀ
Chem. Commun. 2000, 2383; (b) Pamies, O.; Dieguez, M.;
Net, G.; Ruiz, A.; Claver, C. J. Org. Chem. 2001, 66, 8364.
1JP–Rh ¼ 177:7 Hz, JP–P ¼ 20:2 Hz, P–C3), 127.66
2
1
2
ꢀ
7. (a) Dieguez, M.; Ruiz, A.; Claver, C. J. Org. Chem. 2002,
67, 3796; (b) Dieguez, M.; Ruiz, A.; Claver, C. Dalton
(dd, JP–Rh ¼ 177:7 Hz, JP–P ¼ 20:2 Hz, P–C5).
• [Ir(cod)(1)]BF4 7. 31P NMR (CD2Cl2), d: 110.72 (d,
ꢀ
2JP–P ¼ 27:4 Hz, P–C3), 113.98 (d, JP–P ¼ 27:4 Hz,
2
Trans. 2003, 2957.
8. (a) Penne, J. S. In Chiral Auxiliaries and Ligands in
Asymmetric Synthesis; John Wileyand Sons: New York,
1995; (b) Hanessian, S. In Total Synthesis of Natural
Products: The ‘‘Chiron’’ Approach; Pergamon: London,
1983; Vol. 3.
P–C5).
• [Ir(cod)(1)]BF4 8. 31P NMR (CD2Cl2), d: 117.70 (d,
2JP–P ¼ 13:3 Hz, P–C5), 118.34 (d, JP–P ¼ 13:3 Hz,
2
P–C3).
9. (a) Kartha, K. P. R. Tetrahedron Lett. 1986, 27, 3415; (b)
Vogel, A. I. In Vogel’s Textbook of Practical Organic
Chemistry, 5th ed.; Longman: New York, 1994.
10. (a) Levene, P. A.; Raymond, A. L. J. Biol. Chem. 1933,
102, 317; (b) Hollenberg, D. H.; Klein, D. H.; Fox, J. J.
Carbohydr. Res. 1978, 67, 491; (c) Ritzmann, G.; Klein, R.
S.; Hollenberg, D. H.; Fox, J. J. Carbohydr. Res. 1975, 39,
227; (d) Tsutsumi, H.; Kawai, Y.; Ishido, Y. Carbohydr.
Res. 1979, 73, 293.
4.4. Asymmetric hydrogenation reactions
In a typical experiment, a Schlenk tube was filled with a
dichloromethane solution (6 mL) of substrate (1 mmol),
[M(cod)2]BF4 (4.95 mg, 0.01 mmol) and ligand
(0.011 mmol). This was then purged three times with H2
and vacuum. The reaction mixture was then shaken
under H2 (1 bar) at room temperature. To remove the
catalyst, the solution was placed on a short silica gel
column and eluted with CH2Cl2. Conversion and
enantiomeric excesses were determined bygas chroma-
tography.
ꢁ
ꢀ
11. (a) Pamies, O.; Dieguez, M.; Net, G.; Ruiz, A.; Claver, C.
Organometallics 2000, 19, 1488; (b) Dieguez, M.; Pamies,
ꢀ
ꢁ
O.; Ruiz, A.; Claver J. Organomet. Chem. 2001, 629, 77.
ꢀ
12. Cativiela, C.; Fernandez, J.; Mayoral, J. A.; Melendez, E.;
Uson, R.; Oro, L. A.; Fernandez, M. J. J. Mol. Catal.
ꢀ
ꢀ
1992, 16, 19.