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4.4.1. Synthesis of N,O ligand 3a. The above procedure
was followed using 2-methylpyridne and chiral ketone
1a. After work-up, it gave 2.8 g (80%) of 3a; mp
121–122°C; [h]D25=−41.8 (c 0.53, CHCl3); 1H NMR
(CDCl3): l 1.16 (s, 3H), 1.37 (s, 3H), 1.47 (s, 3H), 1.50
(s, 3H), 3.07 (d, 2H, J=13.6 Hz), 4.05–4.21 (m, 5H),
4.36 (d, 1H, J=9.6 Hz), 7.20 (s, 1H), 7.28 (t, 1H,
J=7.2 Hz), 7.66 (s, 1H), 8.48 (d, 1H, J=3.2 Hz); 13C
NMR (CDCl3): l 25.50, 25.55, 25.77, 26.29, 41.03,
60.22, 71.31, 71.91, 72.30, 75.55, 106.77, 108.72, 111.85,
121.62, 124.93, 136.99, 147.27, 158.17; HRMS (ESI)
calcd for C18H25NO6 (M++1): 352.1682, found:
352.1624.
1b. After work-up, it gave 3.8 g (79%) 4b; mp 122–
123°C; [h]2D5=+35.6 (c 0.53, CHCl3); 1H NMR
(CDCl3): l 0.99–1.01 (m, 3H), 1.31–1.43 (m, 7H),
1.56–1.81 (m, 10H), 3.17 (d, 1H, J=14.0 Hz), 3.46 (d,
1H, J=14.0 Hz), 4.10–4.21 (m, 4H), 4.28 (d, 1H,
J=5.6 Hz), 4.49 (d, 1H, J=9.6 Hz), 7.38 (d, 1H,
J=8.4 Hz), 7.49 (t, 1H, J=7.6 Hz), 7.67 (t, 1H, J=
7.8 Hz), 7.79 (d, 1H, J=8.0 Hz), 7.98 (d, 1H, J=8.4
Hz); 13C NMR (CDCl3): l 23.37, 23.42, 23.72, 23.85,
24.89, 24.98, 34.57, 35.17, 35.73, 42.32, 60.68, 70.71,
71.55, 72.50, 75.34, 106.46, 109.19, 112.60, 123.12,
125.87, 126.72, 127.37, 128.47, 129.45, 136.29, 146.84,
159.52; HRMS (ESI) calcd for C28H35NO6 (M++1):
482.2464, found: 482.2464.
4.4.2. Synthesis of N,O ligand 3b. The above procedure
was followed using 2-methylpyridne and chiral ketone
1b. After work-up, it gave 3.3 g (77%) of 3b; mp
94–95°C; [h]2D5=−40.2 (c 0.58, CHCl3); 1H NMR
(CDCl3): l 1.19–1.79 (m, 20H), 3.00 (dd, 2H, J1=13.6
Hz, J2=13.6 Hz), 4.08–4.24 (m, 1H), 4.43 (d, 1H,
J=9.6 Hz), 5.43 (s, 1H), 7.15–7.18 (m, 1H), 7.26 (t, 1H,
J=6.6 Hz), 7.61–7.64 (m, 1H), 8.48 (d, 1H, J=4.4 Hz);
13C NMR (CDCl3): l 22.58, 23.52, 23.77, 23.88, 25.02,
31.52, 34.68, 35.12, 35.35, 35.71, 42.25, 60.55, 70.72,
71.66, 72.11, 74.89, 106.38, 109.18, 112.68, 121.41,
124.78, 136.49, 148.10, 158.52; HRMS (ESI) calcd for
C24H33NO6 (M++1): 432.2308, found: 432.2377.
4.5. Synthesis of bipyridines 5a–b
To a solution of NiCl2·6H2O (6 mmol) in degassed
DMF (30 mL), triphenylphosphine (24 mmol) was
added at 70°C under N2 to give a blue solution. Zinc
powder (13 mmol) was then added and the resulting
mixture was stirred for 1 h, which resulted in the
formation of a dark brown mixture. Compound 7 (5
mmol) in degassed DMF was added slowly and the
mixture was stirred for another 3 h. When the mixture
was cooled to room temperature, the 5% aqueous NH3
(50 mL) was added. The layers were separated, and
the aqueous layer was extracted with CH2Cl2 (3×50
mL). The combined organic layers were washed with
water. Dried over Na2SO4 and removal of the solvent
under reduced pressure gave a pale yellow solid, which
was purified by silica gel column chromatography
(20:1 to 4:1 CH2Cl2: ethylacetate) to give a white solid.
4.4.3. Synthesis of N,O ligand 3c. The above procedure
was followed using compound 8 and chiral ketone 1b.
After work-up, it gave 2.7 g (53%) 3c; mp 121–122°C;
[h]2D5=+93.4 (c 0.51, CHCl3); 1H NMR (CDCl3): l
1.36–1.74 (m, 20H), 2.58 (d, 1H, J=13.6 Hz), 3.07 (d,
1H, J=14.0 Hz), 3.69–3.78 (m, 1H), 3.98 (d, 1H,
J=14.0 Hz), 1.13–4.18 (m, 3H), 4.33 (d, 1H, J=8.4
Hz), 7.21 (t, 1H, J=13.2 Hz), 7.38–7.47 (m, 3H), 7.58
(d, 1H, J=7.6 Hz), 7.69 (t, 1H, J=7.6 Hz), 7.87 (d, 2H,
J=7.2 Hz); 13C NMR (CDCl3): l 22.50, 23.41, 23.51,
23.65, 23.77, 24.91, 34.66, 35.08, 35.31, 35.69, 41.21,
59.69, 60.64, 70.69, 71.49, 72.31, 75.31, 106.45, 109.16,
112.52, 118.24, 123.01, 126.68, 128.55, 129.02, 137.67,
155.48, 158.41; HRMS (ESI) calcd for C30H37NO6 (M+
+1): 508.2621, found: 508.2615.
4.5.1. Synthesis of bipyridine 5a. The above procedure
was followed using the compound 7a. After work-up, it
gave 0.92 g (55%) 5a; mp 203–204°C; [h]2D5=−200.6 (c
0.30, CHCl3); 1H NMR (CDCl3): l 1.10 (s, 6H), 1.36 (s,
6H), 1.49 (s, 6H), 1.64 (s, 6H), 3.72 (d, 2H, J=9.6 Hz),
4.05 (d, 2H, J=9.6 Hz), 4.40 (t, 6H, J=11.6 Hz), 5.04
(d, 2H, J=5.6 Hz), 5.30 (s, 2H), 7.81 (d, 2H, J=8.0
Hz), 7.93 (t, 2H, J=8.0 Hz), 8.38 (d, 2H, J=7.6 Hz);
13C NMR (CDCl3): l 25.65, 25.76, 25.81, 26.22, 59.91,
71.42, 72.25, 73.78, 75.73, 106.61, 109.42, 112.80,
120.35, 123.07, 137.55, 152.91, 157.05; HRMS (ESI)
calcd for C34H44N2O12 (M++1): 673.2894, found:
673.2889.
4.4.4. Synthesis of N,O ligand 4a. The above procedure
was followed using 2-methylquinoline and chiral ketone
1a. After work-up, it gave 3.3 g (83%) of 4a; mp
127–128°C; [h]D25=+36.5 (c 0.66, CHCl3); 1H NMR
(CDCl3): l 1.09 (s, 3H), 1.33 (s, 3H), 1.48 (s, 3H), 1.51
(s, 3H), 3.15 (d, 1H, J=14.4 Hz), 3.27 (d, 1H, J=14.4
Hz), 4.09–4.23 (m, 5H), 4.43 (d, 1H, J=9.6 Hz), 6.84
(br, 1H), 7.35 (d, 1H, J=9.2 Hz), 7.49 (t, 1H, J=7.2
Hz), 7.67 (t, 1H, J=7.4 Hz), 7.78 (d, 1H, J=8.0 Hz),
7.97 (d, 1H, J=8.3 Hz), 8.09 (d, 1H, J=8.2 Hz); 13C
NMR (CDCl3): l 25.50, 25.71, 26.24, 41.33, 60.28,
71.30, 71.85, 72.58, 76.04, 106.82, 108.68, 111.68,
122.84, 125.83, 126.55, 127.40, 128.19, 129.46, 136.95,
146.38, 159.42; HRMS (ESI) calcd for C22H27NO6 (M+
+1): 402.1838, found: 402.1857.
4.5.2. Synthesis of bipyridine 5b. The above procedure
was followed using the compound 7b. After work-up,
it gave 1.1 g (52%) 5b; mp 168–169°C; [h]2D5=−171.2
1
(c 0.59, CHCl3); H NMR (CDCl3): l 1.24–1.77 (m,
40H), 3.69 (d, 2H, J=9.6 Hz), 4.06 (d, 2H, J=9.2
Hz), 4.37 (d, 6H, J=10.4 Hz), 5.03 (d, 2H, J=5.6
Hz), 5.36 (br, 2H), 7.81 (d, 2H, J=8.0 Hz), 7.90 (t,
2H, J=8.0 Hz), 8.35 (d, 2H, J=7.6 Hz); 13C NMR
(CDCl3): l 23.85, 23.94, 24.09, 24.90, 25.14, 26.86,
34.66, 35.06, 35.32, 35.88, 60.13, 70.96, 71.96, 73.65,
75.25, 106.29, 110.04, 113.59, 120.28, 123.03, 137.39,
152.97, 157.34; HRMS (ESI) calcd for C46H60N2O12
(M++1): 833.4146, found: 833.4121.
4.4.5. Synthesis of N,O ligand 4b. The above procedure
was followed using 2-methylquinoline and chiral ketone