Novel chiral bisoxazoline ligands with a bipyridinyl backbone: Preparation and interesting complexation behavior

Article abstract of DOI:10.1016/j.tetlet.2011.03.102

Novel C₂-symmetric chiral bisoxazoline ligands with a bipyridinyl backbone were prepared with ease from 3,3′-dicarbomethoxy-2, 2′-bipyridine and enantiomerically pure 2-amino alcohols via a corresponding amide as intermediate. Interestingly, when these ligands were coordinated with Pd(II) and Cu(I), different complexation behaviors were found.

Full text of DOI:10.1016/j.tetlet.2011.03.102

Tetrahedron Letters 52 (2011) 2844–2848
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Novel chiral bisoxazoline ligands with a bipyridinyl backbone: preparation
and interesting complexation behavior
⇑
Feng Jiang , Zhengxing Wu, Guoqiang Yang, Fang Xie, Wanbin Zhang
School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel C2-symmetric chiral bisoxazoline ligands with a bipyridinyl backbone were prepared with ease
from 3,30-dicarbomethoxy-2,20-bipyridine and enantiomerically pure 2-amino alcohols via a correspond-
ing amide as intermediate. Interestingly, when these ligands were coordinated with Pd(II) and Cu(I), dif-
ferent complexation behaviors were found.
Received 22 January 2011
Revised 14 March 2011
Accepted 22 March 2011
Available online 30 March 2011
Ó 2011 Elsevier Ltd. All rights reserved.
The design and development of effective chiral ligands have
played a significant role in the advancement of asymmetric catal-
ysis and have attracted a great deal of attention from both academ-
ics and industry. Thousands of ligands with various chiral elements
have been developed and applied in many catalytic asymmetric
reactions to produce enantiomerically pure compounds.1 Among
them, chiral pyridinyl-oxazoline compound is one type of impor-
tant ligand, which was first prepared by Brunner and co-workers
from readily available amino acids.2 Afterward, these ligands have
been found to have widespread use in metal-catalyzed asymmetric
reactions, such as cyclopropanation,3 Friedel–Crafts alkylation,4
hydrosilylation,5 aza-Wacker-type cyclization6, and so on,7 and
extensive efforts have been devoted to the preparation of their effi-
cient structural derivatives.
Most of the earlier pyridinyl-oxazoline ligands possess only the
central chirality element in the oxazoline moiety. Within the coor-
dination plane composed of two nitrogen atoms of the pyridine
ring and the oxazoline ring and a metal ion, the planes of pyridine
and oxazoline rings were involved, and the asymmetric induction
is controlled only by the central chirality element in the oxazoline
ring.2–7 Axial chiral oxazoline ligands possess not only the central
chirality element in the oxazoline moiety, but also an additional
chirality element in the backbone.8,9 Owing to the introduction of
the chiral backbone, there is a possibility that the asymmetric
induction by these ligands can be effectively controlled by a com-
bination of the chirality elements in the oxazoline moiety and the
backbone. Numbers of C2-symmetric chiral oxazoline with an axi-
ally chiral biaryl backbone have been successfully employed as chi-
ral ligands.8 However, these axis-fixed ligands require
inconvenient diastereomeric separation in their synthetic process,
and generally, only one of the diastereomers works effectively in
catalytic asymmetric reactions due to the configurational match-
ing-mismatching effect. Our group has developed a series of axis-
unfixed chiral oxazoline ligands based on our chelation-induced
concept, which could afford only one of the two possible diastereo-
meric metal complexes during the coordinating process and
showed excellent enantioselectivities in several asymmetric catal-
yses.9 Herein we introduce a new type of chiral bisoxazoline ligand
1 bearing an axis-unfixed bipyridine backbone and report their
preparation and interesting complexation behaviors (Fig. 1).
It was reported that chiral bisoxazoline ligands with a biphenyl
backbone could be prepared with 2,20-biphenyldicarboxylic acid
dichloride.9a–c Therefore, we thought the chiral 2,20-bis(oxazoli-
nyl)pyridines ligands 1 could be prepared from 2,20-bipyridinyl-
3,30-dicarboxylic acid with the same method. However, only a trace
product was obtained. Fortunately, we obtained our ligands using
2,20-bipyridinyl-3,30-dicarboxylate as the starting material
(Scheme 1). Thus, a mixture of 2,20-bipyridinyl-3,30-dicarboxylate
2 and aminoalcohol (3 equiv) was heated at 160 °C for 16 h to give
the crude hydroxylethylamide 3. The intermediate 3 was dissolved
in dicholoromethane and to this solution SOCl2 (5 equiv) was
slowly added at 0 °C. After refluxing for 2 h, the reaction mixture
was evaporated in vacuo to give crude chloroethylamide 4. The
crude 4 was dissolved in methanol and to this solution sodium
hydroxide (3 equiv) was slowly added. After refluxing for 6 h, li-
gands 1a–d were afforded in overall yields from 32% to 61%.10
It has been pointed out that enantiomerically stable biaryls re-
quire at least three ortho-substituents to avoid the racemization
due to the rotation around the internal bond of the biaryls.11 As
R
N
O
N
N
O
N
R
⇑
Corresponding author. Tel./fax: +86 21 5474 3265.
E-mail address: wanbin@sjtu.edu.cn (W. Zhang).
1
On leave from Ningbo University.
Figure 1. The structure of the ligands 1.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.03.102

F. Jiang et al. / Tetrahedron Letters 52 (2011) 2844–2848
2845
R
N
N
O
OH
OH
COOCH3
H2N
NH
a
H3COOC
HN
OH
N
N
R
O
N
R
2
3
R
R
N
O
R
N
O
Cl
b
NH
c
HN
N
Cl
O
O
N
N
R
4
1
1a
1b
: R=i-Pr, : R=Ph
1c: R=Bn, 1d: R=t-Bu
Scheme 1. Reagents and conditions: (a) 160 °C; (b) SOCl2, CH2Cl2, reflux; (c) NaOH, MeOH, reflux (32–61%, overall yields).
same as the bisoxazoline ligands with biphenyl backbone,9 the li-
gand 1 has only two ortho-substituents on the bipyridinyl back-
bone. So, two diastereomers, (S, aS, S)-1 and (S, aR, S)-1, should
be present in equilibrium in solution due to the rotation around
the internal bond of the bipyridinyl backbone (Scheme 2). How-
ever, the two diastereomers of all the ligands were not observed
by 1H NMR determination in CDCl3 and CD3OD even at ꢀ60 °C. This
result showed that for this type of ligand, the activation barrier to
axial torsion is very small and the interconversion between the two
diastereomers is very fast.
R
R
R
M
N
N
N
N
M
O
O
O
N
N
N
N
N
O
O
O
N
N
N
R
R
R
M
M
5
6
7
Figure 2. The possible complexes of ligands 1 with metal ions.
Different from the bisoxazoline ligands with biphenyl back-
bone, there may be two kinds of complexation behaviors when
these ligands coordinate with different metal ions. The first one
is that these ligands form pyridine-oxazoline-coordinated mono-
or di-metal complexes 5 or 6 upon complexation with 1 or 2 equiv
of metal ion (Fig. 2). The second one is that these ligands afford
only one type of bisoxazoline-coordinated complex 7 upon com-
plexation with 1 equiv of metal ion and the two pyridine rings
do not coordinate to the metal ion (Fig. 2). The complexes 7 could
produce a maximal or minimal dihedral angle because only lone
pair electrons of the nitrogen atoms of the pyridine rings could af-
fect the rotation around the internal bond of the bipyridine. So
these ligands could match more reactions than that with a biphe-
nyl backbone. However, as same as the oxazoline ligands with
biphenyl backbone,9 either of the two different complexation
behaviors of these ligands may afford two diastereomer com-
plexes, and one may form in greater preference to the other due
to the difference in steric hindrance between them. If the ratio of
the two diastereomer complexes is large enough, it may be possi-
ble to utilize the complex as a chiral catalyst in asymmetric
reactions.
Figure 3. The complexation of ligands 1a with CuBr.
Then complexation behaviors of these ligands with different
metal ions were investigated. At first, the complexation of ligand
1a with Cu(I) in CDCl3 was examined (Fig. 3, from top to bottom,
the proportions of CuBr and 1a are 0:1.0, 0.3:1.0, 0.5:1.0, 0.7:1.0,
and 1.0:1.0). Upon treating 1a with different portions of CuBr in
CDCl3, most of the proton signals of the ligand shifted gradually
to downfield in proportion to the amount of CuBr, indicating the
rapid equilibrium between the free ligand and the ligand-CuBr
complex on the NMR time-scale. However, when more than
1 equiv of CuBr was added, further downfield shift of the proton
signals was not observed. This result showed the formation of a
1:1 N,N-chelating complex 8a in solution, of which the coordina-
tion plane is composed of two nitrogen atoms of the two oxazoline
rings and a Cu(I) ion. Ligands 1b–1d showed a similar complexa-
tion behavior to that of 1a toward CuBr to afford 8b–8d, respec-
tively.12 When changing CuBr to CuOTfꢁ0.5C6H6 and CuCl, similar
complexation behaviors were observed.13
Since a metal ion has its own peculiar atomic radius and coor-
dination structure, the complexation behavior of ligand 1a with
Pd(II) in CD2Cl2 was also examined. It was found that the complex-
ation behavior of 1a toward Pd(II) was quite different from that to-
ward Cu(I) (Fig. 4, from top to bottom, the proportions of
R
R
O
N
N
O
N
N
N
N
N
N
O
O
R
R
(S,aS,S)-1
Scheme 2. The equilibrium of the two diasteromers of the ligands.
(S,aR,S)-1

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F. Jiang et al. / Tetrahedron Letters 52 (2011) 2844–2848
Figure 4. The complexation of ligands 1a with PdCl2(CH3CN)2.
PdCl2(MeCN)2 and the ligand are 0:1.0, 0.5:1.0, 1.0:1.0, 1.5:1.0, and
2.0:1.0). Upon the addition of 0.5 equiv of PdCl2(MeCN)2 to 1a dis-
solved in CD2Cl2, the 1H NMR spectrum showed complicated sig-
nals due to a mixture of resultant substance along with 1a.
When an additional 0.5 equiv of PdCl2(MeCN)2 was added, only
one set of signals was observed in the 1H NMR spectrum. This com-
plex was assigned as 9a, of which the coordination plane is com-
posed of two nitrogen atoms of the pyridine ring and the
oxazoline ring and a Pd(II) ion. When an additional 0.5 equiv of
PdCl2(MeCN)2 was added, the 1H NMR spectrum showed compli-
cated signals due to another mixture of resultant substance along
with 9a. When 0.5 equiv of PdCl2(MeCN)2 was added again, only
one set of signals was observed in the 1H NMR spectrum, which
was assigned as a C2-symmertic dimetal complex 10a. Further
addition of PdCl2(MeCN)2 did not affect the 1H NMR spectrum
and the complex deposited quickly. Ligand 1d bearing t-Bu on
the oxazoline ring showed a similar complexation behavior to that
of 1a toward PdCl2(MeCN)2 to afford 9d and 10d, respectively. But
ligand 1b and 1c only afforded 9b and 9c, respectively, and when
additional 0.5 equiv of PdCl2(MeCN)2 was added, the 1H NMR spec-
trum showed no change albeit with some deposition. When
0.5 equiv of PdCl2(MeCN)2 was added again, further deposition
was found and the 1H NMR spectrum of the solution showed that
the proton signals of 9b and 9c disappeared, showing that all the
ligands formed insoluble dimetal complexes 10b and 10c, respec-
tively.14 When changing the Cl anion to acetate, similar complexa-
tion behavior was observed.15
Figure 5. The CD spectra of the complexes 8a and 9a.
NOE
no NOE
H
H
H
N
Pd
N
N
Pd
N
Ox
Ox
N
O
H
N
O
(S,aR,S)-9d
(S,aS,S)-9d
not found
Then the circular dichroism (CD) spectra of the complexes 8a
and 9a were measured in CH3OH solution (Fig. 5). The cotton ef-
fects demonstrated that the induction of axial chirality occurred
when the ligand was coordinated to the CuBr or PdCl2(MeCN)2.16
The absolute configuration of the complex 9d was assigned to
(S, aR, S)-9d by the NOESY experiment, because the NOE was ob-
served between the methyl protons of oxazolinyl tertiary butyl
and 6-proton of the pyridinyl group, and no obvious NOE was ob-
served between the methyl protons of the oxazolinyl tertiary butyl
and 4-proton of the pyridinyl group (Fig. 6). As for the absolute
Figure 6. The two diasteromers of the complex 9d.
configuration of the complex 10d, we reasoned that it should be
(S, aR, S)-10d because the torsion direction is the same as 9d.
However, for the complex 8d, no obvious NOEs were observed
between the methyl protons of the oxazolinyl tertiary butyl and
other protons, regardless of 6-proton of the pyridinyl group or 4-
proton of the pyridinyl group. Because the complexation behavior
of ligands 1 with Cu(I) is the same as that of bisoxazolines ligands
with biphenyl backbone,9a–c we reasoned that the absolute config-

F. Jiang et al. / Tetrahedron Letters 52 (2011) 2844–2848
2847
7. Selected papers see: (a) Lundgren, S.; Lutsenko, S.; Jönsson, C.; Moberg, C. Org.
Lett. 2003, 5, 3663–3665; (b) Bisai, A.; Singh, V. K. Org. Lett. 2006, 8, 2405–2408;
(c) Yoo, K. S.; Park, C. P.; Yoon, C. H.; Sakaguchi, S.; O’Neill, J.; Jung, K. W. Org.
Lett. 2007, 9, 3933–3935; (d) Yi, C. S.; Kwon, K.-H.; Lee, D. W. Org. Lett. 2009, 11,
1567–1569.
8. For a review see: (a) McManus, H. A.; Guiry, P. J. Chem. Rev. 2004, 104, 4151–
4202; Selected papers see: (b) Gant, T. G.; Noe, M. C.; Corey, E. J. Tetrahedron
Lett. 1995, 36, 8745–8748; (c) Uozumi, Y.; Kyota, H.; Kishi, E.; Kitayama, K.;
Hayashi, T. Tetrahedron: Asymmetry 1996, 7, 1603–1606; (d) Andrus, M. B.;
Asgari, D.; Sclafani, J. A. J. Org. Chem. 1997, 62, 9365–9368; (e) Rippert, A. J. Helv.
Chim. Acta 1998, 81, 676–687; (f) Imai, Y.; Zhang, W.; Kida, T.; Nakatsuji, Y.;
Ikeda, I. Synlett 1999, 1319–1321.
t-Bu
O
N
N
O
t-Bu
N
N
N
Cu
N
N
Cu
N
O
O
t-Bu
t-Bu
Br
Br
(S,aS,S)-8d
(S,aR,S)-8d
Figure 7. The two diasteromers of the complex 8d.
9. (a) Imai, Y.; Zhang, W.; Kida, T.; Nakatsuji, Y.; Ikeda, I. Tetrahedron Lett. 1997,
38, 2681–2684; (b) Imai, Y.; Zhang, W.; Kida, T.; Nakatsuji, Y.; Ikeda, I. J. Org.
Chem. 2000, 65, 3326–3333; (c) Zhang, W.; Xie, F.; Matsuo, S.; Imahori, Y.; Kida,
T.; Nakatsuji, Y.; Ikeda, I. Tetrahedron: Asymmetry 2006, 17, 767–777; (d) Zhang,
W.; Xie, F.; Yoshinaga, H.; Kida, T.; Nakatsuji, Y.; Ikeda, I. Synlett 2006, 1185–
1189; (e) Wang, F.; Zhang, Y. J.; Yang, G.; Zhang, W. Tetrahedron Lett. 2007, 48,
4179–4182; (f) Tian, F.; Yao, D.; Liu, Y.; Xie, F.; Zhang, W. Adv. Synth. Catal.
2010, 352, 1841–1845; (g) Liu, Y. Y. G.; Yao, D.; Tian, F.; Zhang, W. Sci. China.
Chem. 2011, 54, 87–94; (h) Yao, D.; Tian, F.; Zhang, W. Chin. J. Org. Chem. 2011,
31, in press.
uration of the complex 8d should be (S, aS, S)-8d (Fig. 7). This com-
plex has a trigonal planar coordination structure, in which the two
planes of the oxazoline rings are inclined to the N-Cu(I)-N coordi-
nation plane by the introduction of the bipyridinyl backbone in the
molecule. For (S, aR, S)-8d, the two substituents on the oxazoline
rings are almost in the coordination plane, while for (S, aS, S)-8d,
the two substituents are perpendicular to the plane in opposite
directions and almost out of plane. Therefore, the steric repulsion
between the substituents on the oxazoline rings and the Br coordi-
nated to the Cu(I) in (S, aS, S)-8d is much smaller than that in (S, aR,
S)-8d, resulting the formation of (S, aS, S)-8d other than (S, aR, S)-
8d.
In summary, novel C2-symmertic chiral bisoxazoline ligands
with a bipyridinyl backbone were prepared with ease, and the
complexation behaviors of these ligands toward Pd(II) and Cu(I)
were studied. It was found that these ligands afforded pyridine-
oxazoline-coordinated mono- or di-metal complexes upon com-
plexation with PdCl2(MeCN)2. The axial chirality of these com-
plexes was assigned as aR. However, upon complexation with
CuBr, these ligands afforded only one type of bisoxazoline-coordi-
nated complexes, the axial chirality of which was assigned as aS.
Further study on the application of these ligands to asymmetric
reactions is in progress in our laboratory.
10. Characterization data of the ligand 1a: 1H NMR (400 MHz, CDCl3): d 8.70 (dd,
J = 2.0 Hz, 4.8 Hz, 2H), 8.24 (dd, J = 2.0 Hz, 8.0 Hz, 2H), 7.36 (dd, J = 4.8 Hz,
8.0 Hz, 2H), 4.15–4.11 (m, 2H), 3.87–3.79 (m, 4H), 1.64–1.59 (m, 2H), 0.78 (t,
J = 6.0 Hz, 12H); 13C NMR (100 MHz, CDCl3): d 161.8, 158.4, 150.4, 137.4, 123.6,
122.6, 73.1, 70.6, 33.0, 18.9, 18.5; HR-MS calcd for C22H26N4O2, 378.2056,
found 378.2059. Characterization data of the ligand 1b: 1H NMR (400 MHz,
CDCl3): d 8.75 (s, 2H), 8.36–8.32 (m, 2H), 7.42–7.35 (m, 2H), 7.32–7.22 (m, 6H),
7.20–7.16 (m, 4H), 5.24 (dd, J = 8.4 Hz, 9.6 Hz, 2H), 4.54 (dd, J = 8.4 Hz, 9.6 Hz,
2H), 3.96 (t, J = 8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3): d 163.8, 150.7, 142.3,
138.0, 128.8, 127.7, 126.9, 122.9, 122.8, 75.3, 70.4; HR-MS calcd for
C
28H22N4O2, 446.1743, found 446.1735. Characterization data of the ligand 1c:
1H NMR (400 MHz, CDCl3):
d
8.73 (dd, J = 2.0 Hz, 5.0 Hz, 2H), 8.23 (dd,
J = 2.0 Hz, 8.0 Hz, 2H), 7.37 (dd, J = 5.0 Hz, 8.0 Hz, 2H), 7.29–7.23 (m, 4H), 7.22–
7.17 (m, 2H), 7.13–7.10 (m, 4H), 4.42–4.34 (m, 2H), 4.08 (t, J = 8.8 Hz, 2H), 3.87
(dd, J = 7.4 Hz, 8.0 Hz, 2H), 3.02–2.95 (m, 2H), 2.59–2.52 (m, 2H); 13C NMR
(100 MHz, CDCl3): d 162.7, 158.1, 150.7, 138.2, 137.6, 129.4, 128.7, 126.6,
123.8, 122.7, 72.3, 68.3, 41.6; HR-MS calcd for C30H26N4O2, 474.2056, found
474.2059. Characterization data of the ligand 1d: 1H NMR (400 MHz, CDCl3): d
8.69 (dd, J = 2.0 Hz, 4.8 Hz, 2H), 8.25 (dd, J = 2.0 Hz, 8.0 Hz, 2H), 7.35 (dd,
J = 4.8 Hz, 8.0 Hz, 2H), 4.11–4.05 (m, 2H), 3.92–3.78 (m, 4H), 0.72 (s, 18H); 13
C
NMR (100 MHz, CDCl3): d 161.4, 158.7, 150.3, 137.3, 123.4, 122.5, 76.7, 68.7,
33.9, 26.0; HR-MS calcd for C24H30N4O2, 406.2369, found 406.2372.
11. (a) Mayers, A. I.; Himmelsbach, R. J. J. Am. Chem. Soc. 1985, 107, 682–685; (b)
Rawson, D.; Meyers, A. I. J. Chem. Soc., Chem. Commun. 1992, 494–496; (c)
Meyers, A. I.; Meier, A.; Rawson, D. Tetrahedron Lett. 1992, 33, 853–856.
12. Characterization data of the complex 8a: 1H NMR (400 MHz, CDCl3): d 8.68–8.61
(m, 2H), 8.04 (d, J = 8.0 Hz, 2H), 7.45–7.38 (m, 2H), 4.58–4.52 (m, 2H), 4.40–
4.33 (m, 2H), 4.30–4.22 (m, 2H), 1.71–1.61 (m, 2H), 0.60 (d, J = 8.0 Hz, 6H),
0.51(d, J = 8.0 Hz, 6H); HR-MS calcd for C22H26CuN4O2 ([MꢀBr]+), 441.1352,
found 441.1351. Characterization data of the complex 8b: 1H NMR (400 MHz,
CDCl3): d 8.65 (br s, 2H), 7.97 (d, J = 8.0 Hz, 2H), 7.34 (br s, 2H), 7.20–7.10 (m,
6H), 6.96–6.91 (m, 4H), 5.54–5.41 (m, 2H), 4.90–4.82 (m, 2H), 4.64–4.57 (m,
2H); HR-MS calcd for C28H22CuN4O2 ([MꢀBr]+), 509.1039, found 509.1048.
Characterization data of the complex 8c: 1H NMR (400 MHz, CDCl3): d 8.73 (br s,
2H), 8.04 (d, J = 8.0 Hz, 2H), 7.45(br s, 2H), 7.26–7.15 (m, 6H), 7.09–7.05 (m,
4H), 4.62(br s, 2H), 4.52–4.36 (m, 4H), 2.86–2.75 (m, 2H), 2.06–1.92 (m, 2H);
Acknowledgments
This work was supported by the National Nature Science Foun-
dation of China (No. 20772081), Science and Technology Commis-
sion of Shanghai Municipality (No. 09JC1407800) and Nippon
Chemical Industrial Co., Ltd. We thank Professor T. Imamoto and
Dr. M. Sugiya for the helpful discussion and Instrumental Analysis
Center of Shanghai Jiao Tong University for HR-MS analysis.
References and notes
HR-MS calcd for
C
30H26CuN4O2 ([MꢀBr]+), 537.1352, found 537.1364.
Characterization data of the complex 8d: 1H NMR (400 MHz, CDCl3): d 8.65 (br
s, 2H), 8.11 (d, J = 8.0 Hz, 2H), 7.43(br s, 2H), 4.54–4.44 (m, 4H), 4.32–4.25 (m,
2H), 0.64 (s, 18H); HR-MS calcd for C24H30CuN4O2 ([MꢀBr]+), 469.1665, found
469.1672.
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5126.
13. Characterization data of the complex of ligand 1c with CuOTfꢁ0.5C6H6: 1H NMR
(400 MHz, CDCl3): d 8.76 (br s, 2H), 8.24 (br s, 2H), 7.42–7.00 (m, 12H), 4.40 (br
s, 2H), 4.00 (br s, 2H), 3.81 (br s, 2H), 2.97 (br s, 2H), 2.52 (br s, 2H); HR-MS
calcd for
C
30H26CuN4O2 ([MꢀOTf]+), 537.1352, found, 537.1356.
Characterization data of the complex of ligand 1c with CuCl: 1H NMR (400 MHz,
CDCl3): d 8.75 (br s, 2H), 8.06 (br s, 2H), 7.48–7.00 (m, 12H), 4.70–4.30 (m, 6H),
2.79 (br s, 2H), 2.05 (br s, 2H); HR-MS calcd for C30H26CuN4O2 ([MꢀCl]+),
537.1352, found, 537.1351.
14. Characterization data of the complex 9a: 1H NMR (400 MHz, CD2Cl2): d 9.19 (dd,
J = 6.0 Hz, 4.0 Hz, 1H), 8.87 (dd, J = 6.0 Hz, 4.0 Hz, 1H), 8.43 (dd, J = 8.0 Hz,
6.0 Hz, 1H), 8.29 (dd, J = 8.0 Hz, 6.0 Hz, 1H), 7.63–7.71 (m, 2H), 4.66–4.76 (m,
2H), 4.38–4.43 (m, 1H), 4.12–4.18 (m, 1H), 3.79–3.82 (m, 1H), 3.54–3.59 (m,
1H), 2.39–2.44 (m, 1H), 1.65–1.73 (m, 1H), 0.87 (d, J = 7.2 Hz, 3H), 0.84 (d,
J = 7.2 Hz, 6H), 0.58 (d, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CD2Cl2): d 164.8,
160.0, 156.8, 153.9, 153.3, 152.6, 141.3, 137.7, 129.4, 125.8, 124.7, 122.0, 73.3,
72.0, 71.6, 70.1, 32.6, 30.8, 18.7, 18.3, 17.8, 15.6; HR-MS calcd for
C24H29ClN5O2Pd
([MꢀCl+CH3CN]+),
560.1045,
found
560.1081.
Characterization data of the complex 9b: 1H NMR (400 MHz, CD2Cl2): d 8.91
(dd, J = 6.0 Hz, 4.0 Hz, 1H), 8.57 (dd, J = 6.0 Hz, 4.0 Hz, 1H), 8.47 (dd, J = 8.0 Hz,
6.0 Hz, 1H), 8.35 (dd, J = 8.0 Hz, 6.0 Hz, 1H), 7.70 (dd, J = 8.0 Hz, 4.0 Hz, 1H),
7.45–7.26 (m, 9H), 7.03–6.99 (m, 2H), 5.71–5.65 (m, 1H), 5.19–5.09 (m, 2H),
4.71–4.65 (m, 1H), 4.57–4.51 (m, 1H), 3.69–3.63 (m, 1H); 13C NMR (100 MHz,
CD2Cl2): d 164.5, 162.0, 155.9, 154.1, 153.3, 152.8, 141.7, 141.3, 138.7, 137.8,

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F. Jiang et al. / Tetrahedron Letters 52 (2011) 2844–2848
129.6, 129.3, 129.1, 129.0, 128.7, 128.0, 127.1, 126.9, 126.8, 125.6, 124.9, 121.7,
137.9, 129.0, 125.8, 124.6, 122.1, 76.9, 73.9, 72.3, 69.9, 34.0, 33.7, 25.8, 25.7;
HR-MS calcd for C26H33ClN5O2Pd ([MꢀCl+CH3CN]+), 588.1358, found 588.1382.
15. Characterization data of the complex of ligand 1c with Pd(OAc)2: 1H NMR
(400 MHz, CD2Cl2): d 9.20 (dd, J = 6.0 Hz, 4.0 Hz, 1H), 8.81(dd, J = 6.0 Hz, 4.0 Hz,
1H), 8.35 (dd, J = 8.0 Hz, 6.0 Hz, 1H), 8.25 (dd, J = 8.0 Hz, 6.0 Hz, 1H), 7.68–7.64
(m, 1H), 7.60–7.55 (m, 1H), 7.32–7.24 (m, 6H), 7.19–7.15 (m, 2H), 7.10–7.07
(m, 2H), 4.63–4.58 (m, 1H), 4.45–4.25 (m, 2H), 4.18–4.13 (m, 1H), 3.80–3.75
(m, 1H), 3.60–3.54 (m, 1H), 2.98–2.92 (m, 1H), 2.78–2.72 (m, 1H), 2.64–2.55
(m, 2H), 1.88 (s, 3H), 1.77 (s, 3H); 13C NMR (100 MHz, CD2Cl2): d 177.5, 177.4,
165.9, 161.1, 157.2, 153.7, 153.0, 152.2, 140.9, 138.0, 137.9, 135.7, 129.6, 129.4,
129.3, 129.0, 128.6, 127.3, 126.7, 125.5, 124.4, 122.2, 74.1, 73.2, 68.5, 66.3,
41.3, 40.2, 22.8, 22.7; HR-MS calcd for C32H29N4O4Pd ([MꢀAcO]+), 639.1224,
found 639.1326.
77.3, 76.3, 70.6, 68.8; HR-MS calcd for C30H25ClN5O2Pd ([MꢀCl+CH3CN]+),
628.0732, found 628.0769. Characterization data of the complex 9c: 1H NMR
(400 MHz, CD2Cl2): d 9.02 (dd, J = 6.0 Hz, 4.0 Hz, 1H), 8.76 (dd, J = 6.0 Hz,
4.0 Hz, 1H), 8.40 (dd, J = 8.0 Hz, 6.0 Hz, 1H), 8.22 (dd, J = 8.0 Hz, 6.0 Hz, 1H),
7.64–7.58 (m, 2H), 7.32–7.26 (m, 6H), 7.17–7.13 (m, 2H), 7.12–7.08 (m, 2H),
5.08–5.04 (m, 1H), 4.75–4.69 (m, 1H), 4.45–4.40 (m, 1H), 4.32–4.25 (m, 1H),
4.20–4.14 (m, 1H), 3.61–3.54 (m, 2H), 2.95–2.88 (m, 1H), 2.79–2.65 (m, 2H);
13C NMR (100 MHz, CD2Cl2): d 165.2, 160.8, 156.6, 154.2, 153.1, 152.5, 141.1,
137.9, 137.8, 135.5, 129.6, 129.5, 129.3, 129.1, 128.6, 127.4, 126.7, 125.8, 124.5,
121.7, 74.7, 73.1, 68.5, 65.8, 41.1, 40.4; HR-MS calcd for C32H29ClN5O2Pd
([MꢀCl+CH3CN]+), 656.1045, found 656.1064. Characterization data of the
complex 9d: 1H NMR (400 MHz, CD2Cl2): d 9.17 (dd, J = 6.0 Hz, 4.0 Hz, 1H), 8.85
(dd, J = 6.0 Hz, 4.0 Hz, 1H), 8.45 (dd, J = 8.0 Hz, 6.0 Hz, 1H), 8.33 (dd, J = 8.0 Hz,
6.0 Hz, 1H), 7.73–7.66 (m, 2H), 4.75–4.69 (m, 1H), 4.55–4.45 (m, 2H), 4.10–4.05
(m, 1H), 3.78–3.72 (m, 1H), 3.70–3.64 (m, 1H), 0.95 (s, 9H), 0.79 (s, 9H); 13C
NMR (100 MHz, CD2Cl2): d 165.5, 159.8, 157.3, 153.8, 153.7, 152.7, 141.2,
16. Wang, F. Synthesis of Novel Oxazoline Ligands with a Biphenyl Backbone and
Their Applications in Asymmetric Catalysis; Doctoral Dissertation of Shanghai
Jiao Tong University, 2007.