Electronic and steric effects of ligands as control elements for rhodium-catalyzed asymmetric hydrogenation

Article abstract of DOI:10.1016/j.tetasy.2004.04.023

Chiral diphosphine ligands analogous to bdpp have been synthesized and tested in order to study the effect of the electronic nature of the ligands in Rh-catalyzed asymmetric hydrogenation of some prochiral olefins. The results are compared with those obtained with the analogous unsubstituted ligand (bdpp). The rhodium-catalyzed asymmetric hydrogenation of olefins was influenced by ligand-based electronic effects, as well as substrate based ones. Excellent ee's (up to 98.3%) have been obtained in the rhodium-catalyzed hydrogenation of (Z)-α-acetamidocinnamic acids and esters.

Full text of DOI:10.1016/j.tetasy.2004.04.023

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 1673–1676
Electronic and steric effects of ligands as control elements for
rhodium-catalyzed asymmetric hydrogenation
q
a
a
b
c
a,
*
ꢀ
Zsanett Herseczki, Ildik oꢀ Gergely, Csaba Heged u€ s, Aron Sz o€ ll o} sy and J oꢀ zsef Bakos
a
Department of Organic Chemistry, University of Veszpr ꢀe m, Hungary
b
Research Group for Petrochemistry, Hungarian Academy of Science, H-8201 Veszpr ꢀe m, PO Box 158, Hungary
Department of General and Analytical Chemistry, Technical University of Budapest, H-1521 Budapest, Hungary
c
Received 4 February 2004; revised 16 April 2004; accepted 19 April 2004
Abstract—Chiral diphosphine ligands analogous to bdpp have been synthesized and tested in order to study the effect of the
electronic nature of the ligands in Rh-catalyzed asymmetric hydrogenation of some prochiral olefins. The results are compared with
those obtained with the analogous unsubstituted ligand (bdpp). The rhodium-catalyzed asymmetric hydrogenation of olefins was
influenced by ligand-based electronic effects, as well as substrate based ones. Excellent ee’s (up to 98.3%) have been obtained in the
rhodium-catalyzed hydrogenation of (Z)-a-acetamidocinnamic acids and esters.
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
contain stereogenic centres on the backbone as well as
on the terminal groups.
10
Asymmetric hydrogenation using soluble rhodium cata-
lysts constitutes a key synthetic step in many industrial
processes. The precise control of molecular chirality
We and others have recently reported that the perfor-
mance of enantioselective catalysts can be boosted by
appropriate electronic tuning of the chiral ligand.
Electronic and steric effects in the rhodium diphosphinite
catalyzed asymmetric hydrogenation were investigated.
A series of electronically and sterically modified (S)-BI-
2
1;11;12
plays an increasing role in chemistry, life science and
material science. High activity, selectivity and stability,
readily accessible ligands and enzyme-like stereocontrol
are among the characteristic features of an ideal catalyst
2
for practical asymmetric synthesis.
NOL and (S)-H -BINOL ligands was synthesized and
8
the effects on the catalytic performance were studied.
In asymmetric catalysis bidentate phosphine ligands
have been found to give excellent control in a number of
catalytic asymmetric reactions. Chiral ligands based on
a 2,4-pentane-2,4-diyl skeleton have found widespread
application in asymmetric synthesis. The most well-
known derivatives of this type are (2S,4S)-2,4-
Phosphinite basicity was varied by using p-CH O,
3
3 3 3 2 3 2
p-CH , p-H, p-CF , 3,5-(CH ) , 3,5-(CF ) substituents
1
on the diphenylphosphine moieties. In the hydrogena-
tion of dimethyl itaconate and methyl (Z)-a-acetamido-
cinnamate, an increase in enantioselectivity and activity
was observed with increasing phosphinite basicity. Thus,
the electronic tuning of the ligands offered a unique
chance to improve the selectivity of such reactions.
Herein, we report the first results concerning the elec-
tronic tuning of (S,S)-bdpp ligand. Targets were chosen
both to probe the electronic effects of the ligands and the
substrate.
3
bis(diphenylphosphino)pentane (S,S)-bdpp, sulfonated
4
derivatives, aryl-derivatives 4-CH
5
3
-, 4-CF
(2S,4S)-pentane-2,4-diyl-bis(5H-di-
3 3
-, 3,5-CH -,
3
benzo-[b]phosphindole) [(S,S)-bdbpp], tetra-p-amino-
,5-CF -bdpp,
3
6
7
8
2 4
functionalized [(S,S)-bdpp-(pNMe ) ], 3-benzyl-bdpp,
(2S,4S)-2-(dibenzophospholyl)-4-(diphenylphosphino)pen-
tane or different diphosphite diastereomers, which
9
2. Results and discussion
q
First part of the series see Ref. 1.
Corresponding author. Tel.: +36-88-422022; fax: +36-88-427492;
e-mail: bakos@almos.vein.hu
3
*
Having a reliable synthetic route for bpdp in hand, the
structurally similar analogues were obtained from
0
957-4166/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.04.023

1674
Z. Herseczki et al. / Tetrahedron: Asymmetry 15 (2004) 1673–1676
3
;6
1
. TsCl
. LiPAr2
THF, 273K
phines. The complete enantioselectivity and diastereo-
selectivity of the double substitution is supported by the
(
S,S )-TA-MRNi
2
OH OH
OH OH
PAr2 PAr2
31
1
presence of only one singlet in the P{ H} NMR
spectrum of the product.
3
8
73 K, THF
0-100 bar H2
O
O
The ionic catalysts [Rh(NBD)(S,S)(P )]PF 4 were pre-
2
6
pared by the reaction of phosphines with [Rh(NBD)
Cl ] in methanol followed by the addition of the corre-
sponding sodium salt of the anion. For all diphosphine
ligands, the formation of the [(diphosphines)Rh(NBD)]
2
(R,R)-TA-MRNi
1
2
. TsCl
. LiPAr2
THF, 273K
2
14
PAr2 PAr2
OH OH
1
6
PF complexes with square planar geometry was evi-
31
denced by the appearance of a doublet in the P NMR
spectra. The results show that itaconic acid and di-
methyl itaconate containing electron-withdrawing
groups show a better performance with less electron-rich
phosphines in the order of 1a > 1b > 1c > 1d (Table 1).
Enantioselectivities range from 63.1% with 1a to 8.4%
with 1d. It was noted that the enantioselectivity of the
catalyst was sensitive to the solvent used. Higher ee
values of 3a and 3b were achieved in aprotic and/or less
polar solvents. In contrast, hydrogen pressure had a
slight effect on the enantioselectivity, but a profound
effect on the reaction rate. The ee of 70.8 % (entry 7) was
Ar:
OMe
c
OMe
a
b
d
Scheme 1. General synthesis of ligands (TA ¼ tartaric acid, MRNi
2
modified Raney Ni).
i
ii
iii
iv
v
ArNH2
ArBr
PAr3
LiPAr2
obtained at 1 bar of H
entry 1) at 20 bar.
2
, but the value decreases to 63.1%
(
Scheme 2. Reagents and conditions: (i) NaNO , HBr, 0 °C; (ii) CuBr,
°C and then 120–140 °C; (iii) Mg, Et
°C; (v) Li, THF, room temperature.
2
5
2
3 2
O, 20–30 °C; (iv) PCl , Et O,
To assess the advantages of using an electron-rich ligand
with a broader range of olefins, we investigated the
hydrogenation of (Z)-amidoacrylic acids and esters 2c–f,
which have more electron-rich double bonds (Scheme 4).
In these cases the enantioselectivities were distinctly
higher. When the aryl groups on the phosphorus of the
phosphine ligand, which had phenyl groups replaced
0
i
ii
iii
H(O)P(OEt)2
H(O)PAr2
HPAr2
LiPAr2
Scheme 3. Reagents and conditions: (i) ArMgBr, THF, 0 °C; (ii)
HSiCl , Et
N, xylol, rt, then 100 °C and then reflux; (iii) BuLi, hexane,
60 °C.
3
3
)
H
R
CO R"
CO R"
2
H2
2
H
Cat., CH OH
R'
3
R
R'
reaction of the corresponding lithium diarylphosphide
13
2
3
with (2S,4S)-pentanediol ditosylate (Scheme 1). The
route for the preparation of diphenylphosphide and
bis(3,5-dimethylphenyl)phosphide is shown in Scheme 2
a. R = H,
b. R = H,
c. R = C
d. R = C
e. R = 4-CH
f. R = 4- CH
R’ = CH
R’ = CH
R’ = NHCOCH
R’ = NHCOCH
R’ = NHCOCH
, R’ = NHCOCH
2
CO
CO
2
CH
H, R” = H
2
3
, R” = CH
3
2
6
H
5
,
,
3
,
R” = H
for bis(4-methoxyphenyl)phosphide and
bis(3,5-di-
6
H
5
3
,
,
R” = CH
3
methyl-4-methoxyphenyl)phosphide in Scheme 3. Both
nucleophilic attacks occurred with complete inversion at
the stereogenic centres to give new homochiral diphos-
3
O-C
O-C
6
H
6
H
4
,
4
3
R” = H
R” = CH
3
3
3
,
Scheme 4. Asymmetric catalytic hydrogenation.
a
Table 1. Enantioselective Rh-catalyzed hydrogenation of 2a and 2b
b
Entry
Substrate
Catalyst
Solvent
t (min)
p(H
2
) (bar)
Conv. (%)
Ee (%)
1
2
3
4
5
6
7
8
9
2a
2a
2a
2a
2a
2a
2a
2b
2b
4a
4b
4c
4d
4a
4a
4a
4a
4a
CH
CH
CH
CH
CH
3
3
3
3
2
OH
OH
OH
OH
5
5
20
20
20
20
20
20
1
100
100
95.4
76.6
100
100
34.1
100
100
63.1 (R)
49.4 (R)
32.8 (R)
8.4 (R)
22
45
15
40
10
2
Cl
2
71.1 (R)
73.1 (R)
70.8 (R)
20.8 (R)
48.5 (R)
THF
CH
CH
3
OH
OH
3
20
20
THF
25
a
Reaction conditions: 23 °C; substrate/Rh ratio 500; catalyst preparation see text.
b
The enantiomeric excess of the product was determined by GC analysis of the distilled product [Hewlett–Packard HP 4890 gas chromatograph,
split/spitless injector, b-DEX 225, 30 m, internal diameter 0.25 mm, film thickness 0.25 lm, carrier gas: 100 kPa nitrogen, FID detector; the retention
times of the enantiomers are 33.3 min (S), 36.9 min (R)]. Absolute configuration was determined by comparison with the known sign of the specific
rotation.

Z. Herseczki et al. / Tetrahedron: Asymmetry 15 (2004) 1673–1676
1675
a
Table 2. Enantioselective Rh-catalyzed hydrogenation of (Z)-a-acetamidocinnamic acids and esters 2c–f
Entry
Substrate
Catalyst
Solvent
S/C
t (min)
Conv. (%)
Ee (%)
1
2
3
4
5
6
7
8
9
2c
2c
2c
2c
2c
2d
2d
2e
2e
2f
4a
4b
4b
4c
4d
4a
4b
4b
4b
4b
CH
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
3
OH
OH
OH
OH
OH
OH
OH
50
50
8
2
100
100
100
100
100
100
100
100
100
100
94.4 (R)
97.2 (R)
96.9 (R)
82.2 (R)
96.5 (R)
78.0 (R)
90.8 (R)
93.3 (R)
98.3 (R)
91.3 (R)
200
50
3
2
50
5
100
200
100
100
50
3
2
THF
8
CH
CH
3
3
OH
OH
2
11
10
a
Reaction conditions: 15 °C; p(H
2
)¼1 bar; other experimental conditions see footnotes under Table 1. The enantiomeric excess was determined on
CP-CHIRASIL-L-VAL column [25 m, internal diameter 0.25 mm, film thickness 0.12 lm, carrier gas: 100 kPa nitrogen, FID detector; the retention
times of the enantiomers are 32.5 min (R), 34.2 min (S)].
with aryl groups with electron-donating groups, the
enantioselectivity and the activity of catalyst were
enhanced (Table 2).
lytic system in the case of itaconic acid and (Z)-a-
acetamidocinnamic acids reveals an opposite trend,
implying that there is a change in the mechanism.
Comparison of the effect of the asymmetric induction by
1
a–d, suggested that the electronic effect is one of the key
Acknowledgements
elements that controls enantioselectivity. The electronic
nature of the para-substituents on the phosphines and
substrates has a significant effect not only on the
enantioselectivity but also on the activity of the catalysts.
Support from the Hungarian National Science Foun-
dation (OTKA T 032004 and T 046825) is gratefully
acknowledged. One of us, I.G. is grateful for the fel-
lowships to Gedeon Richter Ltd. We thank Mr. B ꢀe la
Edes for skillful assistance in the synthetic and catalytic
experiments.
ꢀ
Phosphines with electron-donating substituents (Table
2
, entries 2–5 and 7) gave higher catalytic activities than
that of the unsubstituted bdpp (entries 1 and 6).
Somewhat surprisingly, 4c gave a low enantioselectivity,
which we cannot explain at present. Comparison of
substrates 2c and 2e, 2d and 2f is particularly revealing
as the structural difference between these two com-
pounds is minimal meaning that the electronic effect of
the methoxy group can be clearly identified.
References and notes
ꢀ
1
2
. Gergely, I.; Heged u€ s, C.; Sz o€ ll o} sy, A.; Monsees, A.;
Riermeier, T.; Bakos, J. Tetrahedron Lett. 2003, 44,
9
025.
. (a) Noyori, R. Asymmetric Catalysis in Organic Synthesis;
Wiley: New York, 1994; (b) Catalytic Asymmetric Syn-
thesis; Ojima, I., Ed.; VCH: New York, 1999; (c)
Comprehensive Asymmetric Catalysis; Jacobsen, E. N.,
Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; (d)
Handbook of Enantioselective Catalysis; Brunner, H.,
Zettlmeier, W., Eds.; VCH: New York, 1993.
Substrates with electron-donating para-methoxy sub-
stituents, 2e and 2f gave 98.3%, and 91.3% ee, respec-
tively. The unsubstituted substrates, 2c and 2d gave
96.9% and 90.8% ee, respectively. The special ‘3,5-di-
alkyl meta effect’ has been well demonstrated.
15
3
. (a) MacNeil, P. A.; Roberts, N. K.; Bosnich, B. J. Am.
Chem. Soc 1981, 103, 2273; (b) Bakos, J.; T oꢀ th, I.; Heil, B.;
Mark oꢀ , L. J. Organomet. Chem. 1985, 279, 23.
These results suggest that the strong electron-donating
ability of the para-methoxy group of substrates as well
as the electron-donating aryl groups of ligands promotes
the rate of oxidative addition of hydrogen to rhodium
and changes the reactivity pattern of the major and
minor diastereomeric substrates complexes by increasing
the electron density on the central Rh atom, thereby
4
. Amrani, Y.; Lecomte, L.; Sinou, D.; Bakos, J.; T oꢀ th, I.;
Heil, B. Organometallics 1989, 8, 542.
5. Hu, W.; Pai, C. C.; Chen, C. C.; Xue, G.; Chan, A. S. C.
Tetrahedron: Asymmetry 1998, 9, 3241.
6
7
8
9
. T oꢀ th, I.; Elseiver, C. J.; de Vries, J. G.; Bakos, J.; Smeets,
W. J. J.; Spek, A. J. Organomet. Chem. 1997, 540, 15.
. T oꢀ th, I.; Guo, I.; Hanson, B. E. Organometallics 1993, 12,
848.
. Bianchini, C.; Barbaro, P.; Scapacci, G.; Zanobini, F.
Organometallics 2000, 19, 2450.
12a
affecting the relative rate of oxidative additions.
3. Conclusion
ꢀ
. Heged u€ s, C.; Madar ꢀa sz, J.; Guly ꢀa s, H.; Sz o€ ll o} sy, A.;
Bakos, J. Tetrahedron: Asymmetry 2001, 20, 2867.
In summary, we have employed electronic effects as a
control element for enantioselectivity while the elec-
tronically modified ligands and substrates produced
an improvement in the activity and selectivity in the
hydrogenation of (Z)-a-acetamidocinnamic acids.
Remarkably, a comparison of the effect of ligand basi-
city on asymmetric induction and activity of the cata-
1
0. (a) Szalontai, G.; Bakos, J.; T oꢀ th, I.; Heil, B. Magn.
Reson. Chem. 1987, 25, 761; (b) Cser e´ pi-Sz u} cs, S.; Bakos,
J. J. Chem. Soc., Chem. Commun. 1997, 635; (c) Babin, J.
E.; Whiteker, G. T. W. O. U.S. Patent 911 518, 1992 (to
Union Carbide Corp.); (d) Buisman, G. J. H.; Kamer, P.
C. J.; van Leeuwen, P. W. N. M. Tetrahedron: Asymmetry
1993, 4, 1625; (e) Buisman, G. J. H.; Martin, M. E.; Vos,

1676
Z. Herseczki et al. / Tetrahedron: Asymmetry 15 (2004) 1673–1676
1
3
1
E. J.; Klootwijk, A.; Kamer, P. C. J.; van Leeuwen, P. W.
N. M. Tetrahedron: Asymmetry 1995, 7, 719.
4H; diast. C
o
), C{ H} NMR (125.76 MHz, CDCl
3
):
), 16.86 (s, diast.
), 16.88 (s, diast. ArCH ), 28.24 (dd,
J(P,C) ¼ 8.5 Hz, CH), 37.10 (t,
J(P,C) ¼ 19.4 Hz, CH ), 60.18 (s, diast. OCH ), 60.21 (s,
diast. ArOCH ),
overlapped by the signal of
), 134.45 (d,
), 134.61 (d, J(P,C) ¼ 18.2 Hz,
), 158.00 (s, diast. COCH ), 158.05 (s, diast.
).
2
d ¼ 16:44 (d, J(P,C) ¼ 16.9 Hz, CH
3
1
1. The electronic effects on rhodium enantioselective olefin
hydrogenation with C symmetric phosphines: (a) Mor-
imoto, T.; Chiba, M.; Achiwa, K. Tetrahedron Lett. 1989,
0, 735; Morimoto, T.; Chiba, M.; Achiwa, K. Chem.
ArCH
3
3
1
3
2
J(P,C) ¼ 12.1,
2
2
3
3
3
3
), 131.05 (d, J(P,C) ¼ 4.8 Hz, diast. C
m
1
Pharm. Bull. 1992, 40, 2894; (b) Morimoto, T.; Nakajima,
N.; Achiwa, K. Tetrahedron: Asymmetry 1995, 6, 23; (c)
Mashima, K.; Kusano, K.; Sato, N.; Matsumura, Y.;
Nozaki, K.; Kumobayashi, H.; Sayo, N.; Hori, Y.;
Ishizaki, K.; Akutagawa, S.; Takaya, H. J. Org. Chem.
131.09 (d, J(P,C) ¼ 2.4 Hz, C
i
3
C
m
), 131.11 (d, J(P,C) ¼ 6.1 Hz, diast. C
m
2
2
J(P,C) ¼ 18.2 Hz, diast. C
diast. C
COCH
o
o
3
3
1994, 59, 3064; (d) Schmid, R.; Broger, E. A.; Cereghetti,
M.; Crameri, Y.; Foricher, J.; Lalonde, M.; Muller, R. K.;
Scalone, M.; Schoettel, G.; Zutter, U. Pure Appl. Chem.
14. [Rh(NBD){(2S,4S)-2,4-bis[di(3,5-dimethylphenyl)phos-
3
1
1
phino]pentane}]PF
(121.49 MHz, CDCl
6
4b: Yield: 76%;
): d ¼ 24:48 (d, J(Rh,P) ¼
P{ H} NMR
1
3
1
1
1
996, 68, 131.
2. Substantial electronic effects on rhodium enantioselective
olefin hydrogenation with C symmetric phosphinites have
148.5 Hz), ꢁ145.53 (septet, J(F,P) ¼ 712.8 Hz);
H
3
1
NMR (500.13 MHz, CDCl
3
): d ¼ 1:16 (dd, J(P,H) ¼
3
1
13.2 Hz, J(H,H) ¼ 6.9 Hz, 6H; CH
3
), 1.65 (br s, 2H; H
1
3
3
been described before. See: (a) RajanBabu, T. V.; Ayers,
T. A.; Casalnuovo, A. L. J. Am. Chem. Soc. 1994, 116,
H
10), 1.91 (tt, J(P,H) ¼ 20.7, J(H,H) ¼ 6.3 Hz, 2H; CH
2.34 (s, 12H; diast. ArCH ), 2.42 (s, 12H; diast. ArCH
2.76 (m, 2H; CH), 3.96 (m, 2H; H , H
), 7.04 (s, 4H; H
Rh: C 59.19%, H 6.09 %.
2
),
),
4
,
3
3
4101; (b) RajanBabu, T. V.; Radetich, B.; You, K. K.;
2
5
), 4.35 (m, 2H; H
Ayers, T. A.; Casalnuovo, A. L.; Calabrese, J. C. J. Org.
Chem. 1999, 64, 3429, and references cited therein.
3. (2S,4S)-2,4-Bis[di(3,5-dimethylphenyl)phosphino]pentane
H
H
7
), 4.87 (m, 2H; H
). Anal. Calcd for C44
3
, H
6
p
), 7.20 (s, 8H;
o
54 6 3
H F P
1
Found: C 59.02, H 6.10.
[Rh(NBD){(2S,4S)-2,4-bis[Di(4-methoxyphenyl)phos-
2
0
1
b: Yield: 38%; mp 132–134 °C; ½aꢀ ¼ ꢁ105:0 (c 3.0,
D
). P{ H} NMR (202.46 MHz, CDCl
3
1
1
31
1
CHCl
s),
3
3
): d ¼ ꢁ0:13
6
phino]pentane}] PF 4c: Yield: 34%; P{ H} NMR
1
1
(
H
NMR (500.13 MHz, CDCl
3
): d ¼ 0:97 (dd,
), 1.37
), 2.24 (s,
), 2.26 (s, 12H; diast. ArCH ), 2.44
(121.49 MHz, CDCl
ꢁ145.40 (septet,
3
): d ¼ 23:93 (d, J(Rh,P) ¼ 151.5 Hz),
3
3
1
1
J(P,H) ¼ 15.0 Hz, J(H,H) ¼ 7.0 Hz, 6H; CH
3
J(F,P) ¼ 712.8 Hz);
H
NMR
3
3
3
(
1
(
C
quint., J(P,H) ꢂ J(H,H) ꢂ 7.2 Hz, 2H; CH
2
(300.15 MHz, CDCl
3
): d ¼ 1:08 (dd, J(P,H) ¼ 13.1 Hz,
3
2H; diast. ArCH
3
3
J(H,H) ¼ 6.9 Hz, 6H; CH
3
), 1.58 (brs, 2H; H
(tt, J(P,H) ¼ 20.0, J(H,H) ¼ 6.9 Hz, 2H; CH
2H; CH), 3.87 (s, 6H; diast. ArOCH ), 3.88 (s, 6H; diast.
ArOCH ), 3.97 (m, 2H; H , H ), 4.33 (m, 2H; H , H ),
4.79 (m, 2H; H , H
), 7.04 (d, J(H,H) ¼ 8.0 Hz, 4H; diast.
), 7.07 (d, J(H,H) ¼ 8.0 Hz, 4H; diast. H ), 7.32 (m,
4H; diast. H ), 7.67 (m, 4H; diast. H ). Anal. Calcd for
Rh: C 52.87%, H 5.10%. Found: C 52.79, H
1
1
,H ), 1.73
0
2
3
3
3
sept., J(P,H) ꢂ J(H,H) ꢂ 7.0 Hz, 2H; CH), 6.91 (s, 4H;
2
), 2.66 (m,
3
13
1
p
), 7.04 (d, J(P,H) ¼ 7.6 Hz, 8H; C
o
2
). C{ H} NMR
): d ¼ 15:93 (d, J (P,C) ¼ 16.5 Hz,
3
(75.46 MHz, CDCl
CH
2
3
3
2
5
4
7
3
3
), 21.31 (s, diast. ArCH
1
3
), 21.32 (s, diast. ArCH
3
),
3
6
3
3
7.11 (dd, J(P,C) ¼ 11.5, J(P,C) ¼ 9.9 Hz, CH), 36.70 (t,
H
m
m
2
J(P,C) ¼ 18.7 Hz, CH
2
), 130.46 (s, diast. C
p
), 130.51 (s,
), 131.30 (d, J(P,C) ¼ 19.2 Hz, diast. C ), 131.41
136.42 (d,
), 137.05 (d, J(P,C) ¼13.7 Hz,
).
o
o
2
diast. C
d,
p
o
40 46 6 4 3
C H F O P
2
(
J(P,C) ¼ 19.2 Hz,
diast.
C
o
),
4.85.
[Rh(NBD){(2S,4S)-2,4-bis[di(3,5-dimethyl-4-methoxy-
1
1
J(P,C) ¼ 12.6 Hz, diast. C
i
3
31
1
diast. C
i
), 137.51 (d, J(P,C) ¼ 7.7 Hz, C
m
phenyl)phosphino]pentane}]PF
NMR (121.49 MHz, CDCl
6
4d: Yield: 48%; P{ H}
1
(
2S,4S)-2,4-Bis[di(4-methoxyphenyl)phosphino]pentane 1c:
3
1
): d ¼ 22:92 (d, J(Rh,P) ¼
3
1
1
1
Yield: 48%;
P{ H} NMR (202.46 MHz, CDCl
3:92 (s), H NMR (300.15 MHz, CDCl
): d ¼ 0.93 (dd,
), 1.31
), 2.39
3
): d ¼
150.0 Hz), ꢁ145.59 (septet, J(F,P) ¼ 712.8 Hz); H NMR
1
3
ꢁ
3
(300.15 MHz, CDCl
3
): d ¼ 1:10 (dd, J(P,H) ¼ 13.5 Hz,
3
3
3
J(P,H) ¼ 15.6 Hz, J(H,H) ¼ 6.9 Hz, 6H; CH
3
J(H,H) ¼ 6.9 Hz, 6H; CH
3
), 1.61 (br s, 2H; H
(tt, J(P,H) ¼ 20.9, J(H,H) ¼ 6.6 Hz, 2H; CH
12H; diast. ArCH ), 2.33 (s, 12H; diast. ArCH
2H; CH), 3.77 (s, 6H; diast. ArOCH ), 3.80 (s, 6H; diast.
ArOCH ), 3.93 (m, 2H; H , H ), 4.34 (m, 2H; H , H ),
4.83 (m, 2H; H , H
), 7.04 (d, J(P,H) ¼ 4.4 Hz, 2H; diast.
), 7.06 (d, J(P,H) ¼ 4.4 Hz, 2H; diast. H ), 7.14 (d,
), 7.16 (d, J(P,H) ¼ 5.1 Hz,
). Anal. Calcd for C48 Rh: C
56.92%, H 6.17%. Found: C 56.55, H 5.98.
1
H
10), 1.84
), 2.23 (s,
3
), 2.65 (m,
3
3
3
3
(
(
6
8
(
quint., J(P,H) ꢂ J (H,H) ꢂ 7.2 Hz, 2H; CH
2
2
2
3
sept., J(P,H) ꢂ J (H,H) ꢂ 6.9 Hz, 2H; CH), 3.75 (s,
3
H; diast. ArOCH
H; C ), 7.35 (m, 8H; C
2S,4S)-2,4-Bis[di(3,5-dimethyl-4-methoxyphenyl)phosphino]-
3
), 3.77 (s, 6H; diast. ArOCH
3
), 6.80 (m,
3
o
m
).
3
2
5
4
7
3
3
6
2
0
3
pentane 1d: Yield: 46%; mp 142–145 °C; ½aꢀ ¼ ꢁ83:5 (c
H
o
o
D
P{ H} NMR (202.46 MHz, CDCl
3
1
1
3
3
4
.0, CHCl
3
).
3
):
J(P,H) ¼ 5.1 Hz, 2H; diast. H
o
1
d ¼ ꢁ3:02 (s), H NMR (300.15 MHz, CDCl
3
): d ¼ 0:95
dd, J(P,H) ¼ 15.6 Hz, J(H,H) ¼ 6.8 Hz, 6H; CH ), 1.32
), 2.20 (s,
), 2.21 (s, 12H; diast. ArCH ), 2.42
sept., J(P,H) ꢂ J(H,H) ꢂ 6.5 Hz, 2H; CH), 3.67 (s, 6H;
diast. ArOCH ), 3.69 (s, 6H; diast. ArOCH ), 7.07 (d,
), 7.09 (d, J(P,H) ¼ 5.4 Hz,
2H; diast. H
o
62 6 4 3
H F O P
3
3
(
(
1
3
3
3
quint., J (P,H) ꢂ J(H,H) ꢂ 6.9 Hz, 2H; CH
2
15. (a) Guo, R.; Au-Yeng, T. T.-L.; Wu, J.; Choi, M. C. K.;
Chan, A. S. C. Tetrahedron: Asymmetry 2002, 13, 2519; (b)
Traubesinger, G.; Albinati, A.; Feiken, E.; Kunz, R. W.;
Pregosin, P. S.; Tschoerner, M. J. Am. Chem. Soc. 1997,
119, 6315.
2H; diast. ArCH
3
3
2
3
(
3
3
3
3
J(P,H) ¼ 5.4 Hz, 4H; diast. C
o