(m, 1H, C4H), 4.00 (m, 1H, C5H2, both diastereomers); 2im: d
NCH3), 3.31 (m, 1H, C4H), 4.66 (d, 1H, C5H, 3JHH = 6.86), 5.53
(s, 1H, C2H). Pyridyl and phenyl peaks could not be assigned
unambiguously to the diastereomers. They are: d 7.27 (m, Ph),
7.40 (pd, py), 7.44 (d, 1H, 3JHH = 8.85), 7.58 (d, py, 3JHH = 7.19),
2
3
2.77 (dd, 1H, CH2Ph, JHH = 13.69, JHH = 7.12), 3.13 (dd, 1H,
CH2Ph, 2JHH = 13.69, 3JHH = 7.12), 3.51 (pt, 1H, C5H2), 3.75 (m,
1H, C4H), 3.93 (pt, 1H C5H2), 4.75 (br s, 1H, OH), 8.12 (s, 1H,
2
3
3
=
HC N). Pyridyl and phenyl proton peaks could not be assigned
7.70 (m, py), 8.55 (d, py, JHH = 4.86), 8.61 (d, py, JHH = 4.80).
to either 2im or 2ox. They are: d 7.27 (m), 7.42 (m), 7.70 (m), 7.88 (d,
13C{ H} NMR: major diastereomer only: d 14.4, 35.8, 69.3, 87.2,
1
1
3JHH = 7.84), 8.59 (t, 3JHH = 4.83), 8.62 (d, 3JHH = 5.23). 13C{ H}
99.7, 122.0, 123.9, 126.9, 128.3, 128.6, 137.2, 140.2, 148.9, 159.7.
NMR (2ox/im, some quaternary carbon atoms were not observed):
d 39.1, 40.2, 59.4, 61.1, 65.9, 71.0, 71.2, 74.3, 91.9, 93.0, 121.9,
122.4, 122.9, 123.9, 124.2, 125.1, 126.5, 126.8, 128.6, 128.9, 129.0,
129.4, 129.8, 136.8, 137.0, 137.1, 138.5, 138.6, 139.0, 149.7, 149.8,
163.0. MS: calc. (found): m/z 240.30 (241.13).
MS: calc. (found): m/z 254.33 (253.82).
Variable-temperature NMR spectroscopic study of 1ox/im
Four independ◦ent sets of NMR data were collected at r.t, 0,
−20 and −40 C using approximately 5.2 × 10−3 M solutions
of 1ox/im in CDCl3. The sample was allowed to equilibrate for
2 min at each temperature before acquisition was begun, and
a delay of 6 s (equivalent to 5 × T1, as determined by spin-
inversion recovery experiments) was used between each pulse.
The equilibrium constant, K, was determined by the ratio of
imine to oxazolidine isomers, which was calculated by dividing
the integration for the imine C2 proton (∼d 8.3) by the sum of the
integrations of the oxazolidine C2 protons (∼d 5.4). The resulting
van’t Hoff plot (Fig. S1, ESI†) gave DH◦ = 8 1 kJ mol−1 and
DS◦ = 15 5 J mol−1 K−1.
(4R)-4-Isopropyl-2-(pyridin-2-yl)oxazolidine (3ox) and (R,E)-
3-methyl-2-(pyridin-2-ylmethyleneamino)butan-1-ol (3im). Using
the same procedure as for the synthesis of 1ox/im, the reaction
of (R)-valinol (0.320 g, 3.14 mmol) and 2-pyridinecarbaldehyde
(0.300 g, 2.80 mmol) over 2.5 h gave 0.57 g (95%) of a dark yellow
1
1
oil. H and 13C{ H} NMR data were identical to those reported
for 1ox/im, as expected.
(4R)-4-Benzyl-2-(pyridin-2-yl)oxazolidine (4ox) and (R,E)-3-
phenyl-2-(pyridin-2-ylmethyleneamino)propan-1-ol (4im). Using
the same procedure as for the synthesis of 1ox/im, the reaction of (R)-
phenylalaninol (1.00 g, 6.62 mmol) and 2-pyridinecarbaldehyde
(0.709 g, 6.62 mmol) in C6H6 (40 mL) over 2 h gave 1.50 g (95%)
Procedures for the synthesis of metal complexes
1
of a dark yellow oil. 1H and 13C{ H} NMR data were the same as
PdCl2(1ox-jN,jNꢀ) (7ox) and PdCl2(1im-jN,jNꢀ) (7im). The
ligand 1ox/im (0.10 g, 0.50 mmol) and trans-PdCl2(PhCN)2 (0.20 g,
0.50 mmol) were combined with CH2Cl2 (50 mL) in a round-
bottomed flask fitted with a condenser and heated to reflux for
2 h. The solution was concentrated by rotatory evaporation and
the product was precipitated by the addition of Et2O (30 mL).
The yellow solid was washed with Et2O (3 × 50 mL) and dried
those reported for 2ox/im
.
(4S,5R)-3,4-Dimethyl-5-phenyl-2-(pyridin-2-yl)oxazolidine (5ox).
This compound has been reported previously by Jin et al.,
1
but neither synthetic nor 13C{ H} NMR data were given.6 In
addition, these workers observed only one of the possible two
1
diastereomers, while we invariably saw both. The H NMR data
1
in vacuo. Yield: 0.19 g (99%). H NMR: 7ox major diastereomer:
for our major diastereomer are nearly identical to those of the
single diastereomer they observe. Using the same procedure as for
the synthesis of 1ox/im, the reaction of (1R,2S)-ephedrine (0.50 g,
3.0 mmol) and 2-pyridinecarbaldehyde (0.32 g, 3.0 mmol) over 3 h
gave 0.78 g (99%) of an orange oil. 1H NMR: major diastereomer:
d 0.78 (d, 3H, C4H(CH3), 3JHH = 6.44), 2.31 (s, 3H, NCH3), 3.03
(m, 1H, C4H), 4.83 (s, 1H, C2H), 5.19 (d, 1H, C5H, 3JHH = 8.13);
minor diastereomer: d 0.73 (d, 3H, C4H(CH3), 3JHH = 6.71), 2.34
(s, 3H, NCH3), 3.71 (m, 1H, C4H), 5.41 (s, 1H, C2H), 5.62 (d,
d 0.87 (d, 3H, CH(CH3)2,3JHH = 6.76), 0.93 (d, 3H, CH(CH3)2,
3JHH = 7.03), 2.34 (m, 1H, CH(CH3)2), 3.57 (m, 1H, C4H, obscures
that of minor diastereomer), 3.79 (m, 2H, C5H2), 6.07 (d, 1H, C2H,
3
3JHH = 5.63), 6.75 (pt, 1H, NH), 7.55 (d, 1H, py, JHH = 7.83),
7.63 (pt, 1H, py), 8.16 (pt, 1H, py), 8.76 (d, 1H, py, 3JHH = 7.17);
minor diastereomer: d 0.77 (d, 3H, CH(CH3)2, 3JHH = 7.32), 0.83
3
(d, 3H, CH(CH3)2, JHH = 7.26), 2.56 (m, 1H, CH(CH3)2), 3.80
(m, 2H, C5H2), 6.05 (d, 1H, C2H, 3JHH = 7.55), 6.89 (m, 1H, NH),
3
3
1H, C5H, JHH = 5.33). Pyridyl and phenyl proton peaks could
7.50 (d, 1H, py, JHH = 7.53), 7.76 (m, 1H, py), 8.64 (d, 1H, py,
3
3JHH = 6.82), 9.20 (d, 1H, py, JHH = 9.17); 7im: d 0.76 (d, 1H,
not be assigned unambiguously to the diastereomers. They are: d
7.27 (m, Ph), 7.35 (m, Ph), 7.47 (pd, py), 7.64 (d, py, 3JHH = 7.85),
3
3
CH(CH3)2, JHH = 6.92), 0.82 (d, 1H, CH(CH3)2, JHH = 7.18),
2.34 (m, 1H, CH(CH3)2), 3.57 (m, 1H, C4H), 3.79 (m, 2H, C5H2),
5.04 (br s, 1H, OH), 7.85 (m, 1H, py), 8.34 (pt, 1H, py), 8.54 (s, 1H,
3
3
7.77 (m, py), 8.60 (d, py, JHH = 5.70), 8.64 (d, py, JHH = 5.62).
13C{ H} NMR (both diastereomers, two quaternary carbon atoms
1
2
3
3
=
HC N), 8.64 (d, 1H, py, JHH = 5.33), 8.98 (d, 1H, py, JHH
=
not seen): d 9.3, 15.1, 33.7, 36.3, 61.8, 64.5, 83.0, 83.1, 95.7, 99.0,
121.9, 122.4, 123.6, 124.0, 126.5, 127.5, 127.9, 128.2, 128.3, 137.0,
137.2, 139.9, 149.1, 149.3, 158.3. MS: calc. (found): m/z 254.33
(253.82).
6.30); 13C{ H} NMR (7ox/im, quaternary carbon atoms not seen): d
16.3, 21.0, 28.1, 28.2, 49.3, 66.4, 66.5, 79.3, 79.6, 80.0, 94.5, 125.2,
126.6, 129.1, 141.4, 142.0, 149.2, 150.6, 162.5. Anal. Calc. for
C11H16N2Cl2OPd: C, 35.75; H, 4.36; N, 7.58%. Found: C, 36.26;
H, 4.27; N, 7.72%. Crystals of 7ox suitable for X-ray diffraction
analysis were grown from a concentrated CH2Cl2 solution by slow
diffusion of Et2O.
1
(4R,5R)-3,4-Dimethyl-5-phenyl-2-(pyridin-2-yl)oxazolidine (6ox).
Using the same procedure as for the synthesis of 1ox/im, the
reaction of (1R,2R)-pseudoephedrine (0.50 g, 3.0 mmol) and 2-
pyridinecarbaldehyde (0.32 g, 3.0 mmol) over 2 h gave 0.77 g
1
(99%) of a yellow oil. H NMR: major diastereomer: d 1.18 (d,
PdCl2(2ox-jN,jNꢀ) (8ox) and PdCl2(2im-jN,jNꢀ) (8im). Using
the same procedure as for the synthesis of 7ox/im, the reaction
of 2ox/im (0.52 g, 2.17 mmol) and trans-PdCl2(PhCN)2 (0.83 g,
3
3H, C4H(CH3), JHH = 6.45), 2.30 (s, 3H, NCH3), 2.54 (m, 1H,
3
C4H), 4.77 (d, 1H, C5H, JHH = 8.79), 5.07 (s, 1H, C2H); minor
diastereomer: d 0.92 (d, 3H, C4H(CH3), 3JHH = 6.19), 2.31 (s, 3H,
4676 | Dalton Trans., 2006, 4672–4678
2.2 mmol) over 5 h gave 0.50 g (55%) of an orange solid. H
1
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The Royal Society of Chemistry 2006
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