SIMPLE CHIRAL CU(II) COMPLEX AS AN EFFECTIVE PHASE-TRANSFER CATALYST
945
Louis, MO) or Fluka (Buchs, Switzerland) and used as received. Solvents
were distilled according to known procedures.
in vacuo. The chiral Schiff base ligand 3 crystallized out as vivid yellow
needles after addition of little hexane (0.82 g, 97%), Rf = 0.43 (5:5
EtOAc/Hexane), mp = 176 °C, [α]2D5 = -57 (c = 1, EtOH); 1H NMR δ
(ppm): 3.73-3.81 (m, 2H, CH2), 3.88 (t, J = 7.5 and 12 Hz, 1H, C*H), 5.00
(s, 1H, CH2OH), 6.75 (s, 0.5H), 6.78 (s, 0.5H), 7.11-7.28 (m, 2H),
7.3-7.39 (m, 3H), 7.41-7.49 (m, 2H), 7.55-7.58 (m, 1H), 7.70 (m, 0.5H),
7.73 (m, 0.5H), 7.78 (m, 0.5H), 7.81 (m, 0.5H), 8.68 (s, 1H), 10.2 (sb,
1H, Nap-OH); 13C NMR δ (ppm): 65.9 (CH2OH), 69.9 (C*H),
120.4 (C8), 125.3 (C4’), 126.5 (C6), 126.8 (C3), 127.0 (C7), 127.1 (C6’),
127.2 (C2’), 128.1 (C5), 128.7 (C3’), 128.8 (C5’), 128.9 (C4), 129.1 (C9),
129.2 (C10), 134.7 (C1’), 138.5 (C1) , 162.2 (COH), 171.3 (C=N); IR
(KBr): 3435, 3239, 2860, 1626, 1493, 1274 cm-1; MS (EI) 291(M+), 170,
143; Anal. Calcd for C19H17NO2: C, 78.33; H, 5.88; N, 4.81. Found: C,
78.40; H, 5.81; N, 4.79.
Syntheses
Naphthalen-1-yl(phenyl)methanimine 1. In a 25-ml two-necked flask
equipped with a dropping funnel and reflux condenser fitted with a
calcium chloride drying tube, were introduced magnesium turnings
(0.21 g, 8.9 mmol), anhydrous THF (4 ml) and 0.2 g of 1-
bromonaphthalen. When the reaction started, a moderate reflux began
which was maintained by slow addition under vigorous stirring of a solu-
tion of the remaining amounts of 1-bromonaphthalen (total of 1.79 g,
8.7 mmol) in THF (8 ml). The resulting brown solution was heated under
reflux for 2 h, after which time it was cooled and a solution of benzonitrile
(0.85 g, 8.3 mmol, 0.95 eq) in THF (8 ml) was added. The dark solution
was then heated to reflux for 4 h. The stirred mixture was cooled to room
temperature before addition of absolute methanol (3 ml) and the stirring
continued for 30 min. The solvents were removed in vacuo and the resid-
ual brown oil taken in ethyl acetate (30 ml). The solid which separated
was collected by filtration and the filtrate concentrated to dryness in
vacuo. Column chromatography on silica gel afforded pure
[(+)-R-1-(2-hydroxy-1-phenylethylimino)methyl-2-naphthol]2CuCl2.
H2O 4. To a solution of the chiral ligand (0.7 g, 2.4 mmol) in methanol
(12 ml) was added CuCl2.2H2O (0.38 g, 2.4 mmol) and the mixture stirred
at room temperature overnight. Evaporation of the solvent under reduced
pressure led to a dark green solid which was washed with ether and dried
25
methylenimine
1 as orange oil (1.78 g, 93%), Rf = 0.22 (0.5:9.5
in the desiccator over P2O5 (1.85 g, 97%), mp = 190°C (decomp.), [α]D
=
EtOAc/Hexane); 1H NMR δ (ppm): 7.22-7.42 (m, 3H), 7.43-7.6 (m,
4.5H), 7.70 (m, 0.5H), 7.75-7.79 (m, 2H, H2’, H6’), 7.89 (m, 0.5H), 7.91-
7.99 (m, 1.5H)(H2, H8), 9.01 (s, 1H, NH); 13C NMR δ (ppm): 126.7
(C3’), 127.0 (C5’), 128.1 (C5), 128.4 (C7), 128.5 (C6), 128.6 (C3), 128.9
(C6’), 129.2 (C2’), 129.6 (C2), 130.4 (C8), 130.5 (C4), 130.6 (C4’), 131.3
(C9), 133.2 (C10), 133.5 (C1’), 133.6 (C1) , 178.2 (C=N); IR (KBr): 3057,
1659, 1282, 1257, 1150 cm-1; MS (EI) 231 (M+), 154; ESI-HRMS:
m/z = 231.1048 (M+); C17H13N requires 231.1050.
+79 (c = 0.6, EtOH); IR (KBr): 1626, 1540, 1458, 1426, 1310, 1253, 1182,
1169, 1143, 1098, 1040, 940, 863, 740, 571, 528, 430 cm-1; MS (EI) 388
(M+), 346, 246, 172; Anal. Calcd for C38H34Cl2Cu2N2O5: C, 57.29; H, 4.30;
N, 3.52. Found: C, 58.88; H, 4.01; N, 3.90.
Phase-Transfer α-Benzylation of Substrate 2
Liquid/liquid system. To a solution of 2a (0.2 g, 0.58 mmol) in dichlo-
romethane (2 ml) was added a solution of the chiral ammonium salt 6
(24.3 mg, 0.058 mmol) or 7 (35 mg, 0.058 mmol) and benzyl bromide
(0.49 g, 2.9 mmol, 5 eq) in dichloromethane (4 ml), and under stirring,
50% aqueous NaOH (2.4 ml) was added. The mixture was then vigorously
stirred at room temperature until the reaction was complete (TLC, 0.5:9.5
EtOAc/Hexane). Ether (6 ml) was added and the organic layer was
washed with water and dried over MgSO4. Evaporation of the solvents
and purification of the residual oil by column chromatography (0.5:9.5
EtOAc/Hexane) gave Schiff base 5a as yellow oil.
Tert-butyl-2-(naphthalen-1-yl(phenyl)methyleneamino)acetate
2a. Methylenimine 1 (1.7 g, 7.3 mmol) and tert-butylglycinate hydro-
chloride (1.35 g, 8.1 mmol) were dissolved in 1,2-dichloroethane (15 ml)
and the resulting solution heated to reflux for 72 h. Then the crude prod-
uct was subjected to column chromatography over silica gel using (0.1:9.9
EtOAc/Hexane) to purify and separate the geometric stereoisomers.
Data for imine E-2a: orange oil, (0.5 g, 20%), Rf = 0.41 (0.5:9.5
EtOAc/Hexane); 1H NMR δ (ppm): 0.87-0.91 (m, 1.5H), 0.92-0.96 (m,
1.5H)(CH3), 1.26-1.43 (m, 6H)(2CH3), 3.16 (s, 2H, CH2), 7.25-7.30 (m,
1.5H), 7.31-7.35 (m, 1.5H)(H3, H7, H5’), 7.37-7.41 (m, 1H, H3’),
7.42-7.48 (m, 1H, H4’), 7.49-7.53 (m, 1H, H5), 7.53-7.55 (m, 1H, H6),
7.56-7.60 (m, 1H, H4), 7.66-7.69 (m, 1H, H6’), 7.69-7.73 (m, 1H, H2’),
7.92-7.95 (m, 1H, H2), 7.95-8.02 (m, 1H, H8); 13C NMR δ (ppm): 28.83
(CH3), 68.1 (CH2), 77.3 (C-CH3), 126.5 (C5, C3’), 127.1 (C5’), 128.4 (C3,
C6), 128.7 (C4), 128.8 (C7), 128.9 (C2), 129 (C8), 130.1 (C2’, C6’), 130.9
(C4’), 131.3 (C9), 132.4 (C10), 133.4 (C1’), 138.6 (C1), 167.8 (C=O),
170.8 (C=N); IR (KBr): 2976, 1749, 1626, 1448, 1152 cm-1; MS (EI) 345
(M+), 291, 245; ESI- HRMS: m/z = 345.1732 (M+); C23H23NO2 requires
345.1729.
Data for imine Z-2a: white solid, (1.01 g, 40%), mp = 99-101 °C, Rf = 0.32
(0.5:9.5 EtOAc/Hexane); 1H NMR δ (ppm): 1.16-1.58 (m, 9H, 3CH3),
3.85-4.13 (dd, J = 13.5 and 16.2 Hz, 2H, CH2), 7.18-7.31 (m, 3H, H3, H4,
H5), 7.33-7.44 (m, 2H, H6, H4’), 7.5-7.61 (m, 3H, H7, H3’, H5’), 7.66-7.75
(m, 2H, H2’, H6’), 7.88-8.01 (m, 2H, H2, H8); 13C NMR δ (ppm): 28.0
(CH3), 55.9 (CH2), 81.1 (C-CH3), 125.3 (C3’, C5’), 126.5 (C5, C7), 127.1
(C6), 128.2 (C3), 128.6 (C2’, C6’), 128.7 (C2), 129.1 (C8), 130.1 (C9),
130.4 (C4), 130.9 (C4’), 133.4 (C10), 133.9 (C1’), 138.7 (C1),, 169.5
(C=O), 171.3 (C=N); IR (KBr): 2976, 1749, 1626, 1448, 1152 cm-1; MS
(EI) 345 (M+), 290, 246; Anal. Calcd for C23H23NO2: C, 79.97; H, 6.71;
N, 4.05. Found: C, 79.92; H, 6.74; N, 4.01.
Solid/liquid system. Catalyst 4 (46 mg, 0.058 mmol) was added to a
suspension of imine 2a (0.2 g, 0.58 mmol) or 2b (0.17 g, 0.58 mmol),
benzyl bromide 0.49 g, 2.9 mmol, 5 eq) and dried solid KOH (0.32 g,
5.8 mmol, 10 eq) in dichloromethane (6 ml). After 72 h of vigorous stirring
at room temperature, ether (5 ml) was added, the solid removed by filtra-
tion, and the filtrate washed with water and dried over MgSO4. Evapora-
tion of the solvents and purification of the residual oil by column
chromatography (0.5:9.5 EtOAc/Hexane) afforded Schiff base 5 as a
yellow oil.
Data for imine E-5a: (0.12 g, 48%), Rf = 0.37 (0.5:9.5 EtOAc/Hexane),
[α]D25 = -21.5 (c = 1, CHCl3); 1H NMR δ (ppm): 0.85-0.99 (m, 1.25H),
1.23-1.38 (m, 5.25H), 1.4-1.49 (m, 2.5H), 3.18-3.29 (m, 2H), 3.86-3.98 (m,
0.5H), 4.21-4.28 (m, 0.5H), 6.98-7.07 (m, 1.5H), 7.09-7.14 (m, 0.75), 7.17-
7.25 (m, 2H), 7.26-7.35 (m, 2H), 7.36-7.44 (m, 2H), 7.45-7.49 (m, 1.25H),
7.5-7.58 (m, 2H), 7.6-7.8 (m, 2.5H), 7.81-7.91 (m, 2H), 7.95-8.12 (m, 1H);
13C NMR δ (ppm): 27.9 (CH3), 28.0 (CH3), 28.9 (CH3), 38.7 CH2), 68.2
(C*H), 81.1 (C-CH3), 124.9 (C4”), 125.2 (C2”), 125.3 (C6”), 125.5 (C3”),
125.6 (C5”), 125.9 (C3’), 126.2 (C5’), 126.3 (C5), 126.5 (C7), 128.0 (C6),
128.1 (C3), 128.2 (C2’), 128.3 (C6’), 128.4 (C2), 128.5 (C8), 128.6 (C4),
129.7 (C4’), 130.2 (C9), 131.1 (C10), 133.0 (C1”), 138.5 (C1’), 139.8
(C1), 166.1 (C=O), 169.0 (C=N); IR (KBr) 3054, 3022, 2963, 2926, 1724,
1617, 1449, 1260, 1153 cm-1; MS (EI) 435 (M+), 380, 246, 153; ESI- HRMS:
m/z = 435.2196 (M+); C30H29NO2 requires: m/z = 435.2198.
Preparation of Catalyst 4
(–)-(R)-1-((2-hydroxy-1- phenylethylimino)methyl)naphthalen-2-ol
Data for imine Z-5a: (0.12 g, 50%), Rf = 0.37 (0.5:9.5 EtOAc/Hexane),
[α]2D5 = +23 (c = 1, CHCl3); 1H NMR δ (ppm): 1.33-1.42 (m, 9H), 3.23-3.24
(d, J = 8.1 Hz, 2H), 5.86-7.89 (d, J = 9.9 Hz, 1H), 7.12-7.53 (m, 11H), 7.6-
7.68 (m, 3.5H), 7.8-7.94 (m, 2.5H); 13C NMR δ (ppm): 27.9 (CH3), 28.0
(CH3), 28.9 (CH3), 38.7 (CH2), 68.0 (C*H), 81.2 (C-CH3), 124.0 (C4"),
124.8 (C2"), 124.9 (C6"), 125.2 (C3"), 125.5 (C5"), 125.8 (C3’), 126.1
(C5’), 126.2 (C5), 126.3 (C7), 127.0 (C6), 127.5 (C3), 128.0 (C2’), 128.1
3.
A suspension consisted of 2-hydroxy-1-naphthaldehyde (0.5 g,
2.9 mmol), (R)-phenylglycinol (0.4 g, 2.9 mmol, 1 eq), and anhydrous
MgSO4 (0.48 g) in dichloromethane (7 ml) was stirred at room tempera-
ture overnight for complete reaction. The yellow solid that precipitated
was dissolved by addition of ethanol (5 ml). The resulting suspension
was filtered to remove MgSO4, and the filtrate concentrated to dryness
Chirality DOI 10.1002/chir