J. Wang et al. / Tetrahedron: Asymmetry 18 (2007) 1115–1123
1121
NHCH), 4.78 (1H, d, J = 3.4 Hz, CHOH), 6.70 (2H, d,
J = 6 Hz, ArH), 6.58 (2H, d, J = 6 Hz, ArH), 7.25 (5H,
m, ArH). 13C NMR (126 MHz, CDCl3):
14.1
4.6. General procedure for the formation of oxazolidines 4
and 12
d
(OCH2CH3), 55.7 (OCH3), 60.6 (CHNH), 73.5 (CHCO),
61.9 (OCH2CH3), 114.8 (NHAr–C ortho), 115.5 (NHAr–
C meta), 127.6 (Ar–C ortho), 128.4 (Ar–C meta), 136.1
(Ar–C–NH), 140.5 (Ar–C–CH), 152.5 (Ar–C–OCH3),
172.3 (CO); EI-MS, m/z: M+: 315, 211 (Mꢀ103)+, 103
(Mꢀ211)+, 77, 89. HRMS: calcd for C18O4NH21 (M+):
315.14706; found: 315.14686.
Phosphorus pentoxide (568 mg, 2 mmol, calculated with
P4O10, MW = 284) was added to dry dimethylsulfoxide
(3 mL) and ultrasonicated for 10 min. Compound 3 or 11
(1 mmol) in dimethylsulfoxide (2 mL) was then added
and the resulting mixture was stirred at room temperature
until TLC indicated complete conversion (24 h). The reac-
tion mixture was quenched with cooled saturated sodium
bicarbonate solution (20 mL) followed by a small amount
of water. The mixture was extracted with ethyl acetate
(3 · 30 mL). The combined organic layers were washed
with water (3 · 40 mL) to remove unreacted dimethyl-
sulfoxide, then washed with brine, dried over magnesium
sulfate, filtered, concentrated, and separated by flash chro-
matography on silica gel and then crystallized from hexane
and ethyl acetate to give colorless crystals.
4.5.3. anti-( )-Ethyl 3-(4-chlorophenylamino)-2-hydroxy-3-
phenylpropanoate 3c. Yellow crystals, 93% yield; mp: 96–
96.5 ꢁC; IR (CHCl3) cmax/cmꢀ1: 3473, 3400, 3029, 2981,
2932, 1936, 1600, 1453, 1245, 1210, 1095, 1024, 816, 720,
700; 1H NMR (500 MHz, CDCl3): d 1.25 (3H, t,
J = 6.7 Hz, CH3), 2.92 (1H, d, J = 7.3 Hz, NH), 4.15
(3H, m, J = 7.3 Hz, CH2 and OH), 4.63 (1H, d, J =
3.7 Hz, NHCH), 4.78 (1H, d, J = 3.7 Hz, CHOH), 6.51
(2H, d, J = 8.6 Hz, ArH), 6.70 (2H, d, J = 8.6 Hz, ArH),
7.25 (5H, m, ArH). 13C NMR (126 MHz, CDCl3): d 14.1
(OCH2CH3), 59.6 (CHNH), 62.1 (OCH2CH3), 73.4
(CHCO), 115.0 (NHAr–C ortho), 122.6 (NHAr–C para),
127.4 (Ar–C ortho), 128.5 (Ar–C meta), 129.0 (NHAr–C
meta), 136.6 (Ar–C–CH), 144.7 (Ar–C–NH), 171.8 (CO);
HRMS: calcd for C17H18ClO3N (M+): 319.09649; found:
319.09753.
4.6.1. cis-( )-Ethyl 3-(4-methoxyphenyl)-4-phenyl-1,3-oxaz-
olidine-5-carboxylate 4b. Yellow crystals, 85% yield; mp:
78–78.5 ꢁC; IR (CHCl3) cmax/cmꢀ1: 2980, 2930, 2836,
1746, 1514, 1244, 1200, 1038; 1H NMR (500 MHz, CDCl3):
d 0.94 (3H, t, J = 7.3 Hz, CH3), 3.88 (2H, dd, J = 7.3 Hz,
CH2), 3.74 (3H, s, OCH3), 5.59 (1H, d, J = 1.9 Hz,
NCHO), 5.01 (1H, d, J = 1.9 Hz, NCHO), 4.94 (1H, d,
J = 7.3 Hz, NCH), 4.90 (1H, d, J = 7.3 Hz, COH), 6.74
(2H, d, J = 6.9 Hz, ArH), 6.42 (2H, d, J = 6.9 Hz, ArH),
7.29 (5H, m, ArH); 13C NMR (126 MHz, CDCl3): d 13.7
(OCH2CH3), 55.7 (OCH3), 61.0 (OCH2CH3), 64.4
(NCHC), 83.4 (NCH2O), 81.7 (OCHC), 115.0 (NAr–C
ortho), 114.1 (NAr–C meta), 152.5 (NAr–C para), 127.6
(Ar–C para), 128.4 (Ar–C meta), 128.2 (Ar–C ortho),
138.8 (Ar–C–CH), 168.1 (CO); GC–MS (SPB-5 column)-
MS. RT = 10.65 minute. EI-MS, m/z: M+ 327, 73, 77,
86, 91,105, 118, 122. HRMS: calcd for C19O4NH21 (M+):
327.14706; found: 327.14743.
4.5.4. (2R,3S)-(+)-Methyl 3-(4-methoxyphenylamino)-2-
hydroxy-3-phenylpropanoate 11b. Yellow crystals, 90%
25
yield; ½aꢁD ¼ þ10:3 (c 0.99, CH2Cl2); >99% ee; mp: 76–
77 ꢁC; IR (CHCl3) cmax/cmꢀ1: 3285, 2979, 2936, 2471,
1
1737, 1511, 1258, 1217, 1028, 701; H NMR (400 MHz,
CDCl3): d 3.69 (3H, s, CH3), 3.74 (3H, s, OCH3), 4.47
(1H, d, J = 2.4 Hz, NHCH), 4.84 (1H, d, J = 2.4 Hz,
CHOH), 6.50 (2H, d, J = 8.8 Hz, ArH), 6.63 (2H, d,
J = 8.8 Hz, ArH), 7.25–7.36 (5H, m, ArH). 13C NMR
(126 MHz, CDCl3): d 52.3 (OCH3), 55.7 (OCH3), 60.0
(CHNH), 74.7 (CHCO), 114.7 (NHAr–C ortho), 115.4
(NHAr–C meta), 127.0 (Ar–C ortho), 128.6 (Ar–C meta),
136.1 (Ar–C–NH), 140.4 (Ar–C–CH), 152.3 (Ar–C–
OCH3), 173.3 (CO); HRMS: calcd for C17O4NH19 (M+):
301.13141; found: 301.13142.
4.6.2. cis-( )-Ethyl 3-(4-chlorophenyl)-4-phenyl-1,3-oxazol-
idine-5-carboxylate 4c. Colorless crystals, 90% yield; mp:
105–105.5 ꢁC; IR (CHCl3) cmax/cmꢀ1: 2982, 2902, 2836,
1760, 1744, 1599, 1493, 1469, 1341, 1201, 1097, 1041,
1
809, 737, 699, 504; H NMR (500 MHz, CDCl3): d 0.90
(3H, t, J = 7.1 Hz, CH3), 3.70 (1H, m, J = 3.6 Hz, CH2),
3.86 (1H, m, J = 3.6 Hz, CH2), 4.92 (1H, d, J = 7.8 Hz,
OCH), 4.96 (1H, d, J = 7.8 Hz, NCH), 5.04 (1H, d,
J = 1.8 Hz, NCHO), 5.56 (1H, d, J = 1.8 Hz, NCHO),
6.35 (2H, d, J = 8.7 Hz, ArH), 6.74 (2H, d, J = 8.7 Hz,
ArH), 7.29 (5H, m, ArH); 13C NMR (126 MHz, CDCl3):
d 13.7 (OCH2CH3), 61.2 (OCH2CH3), 63.6 (NCHC), 82.6
(NCH2O), 81.6 (OCHC), 113.8 (NAr–C ortho), 123.1
(Ar–C para), 127.5 (Ar–C meta), 128.6 (Ar–C ortho),
129.2 (NAr–C meta), 137.1 (Ar–C–CH), 142.5 (NAr–C
para), 167.6 (CO); HRMS: calcd for C18O3NClH18 (M+):
331.09829; found: 331.09753.
4.5.5.
(2R,3S)-(+)-Methyl
3-(4-chlorophenylamino)-2-
hydroxy-3-phenylpropanoate 11c. Colorless crystals, 92%
25
yield; ½aꢁD ¼ þ7:9 (c 1.36, CH2Cl2); >99% ee; mp: 89–
89.5 ꢁC; IR (CHCl3) cmax/cmꢀ1: 3473, 3400, 3029, 2981,
2932, 1936, 1600, 1453, 1245, 1210, 1095, 1024, 816, 720,
700; 1H NMR (400 MHz, CDCl3): d 3.6 (3H, s, CH3),
3.14 (1H, OH), 4.49 (1H, d, J = 2.0 Hz, NHCH), 4.79
(1H, d, J = 2.0 Hz, CHOH), 6.45 (2H, d, J = 8.6 Hz,
ArH), 7.05 (2H, d, J = 8.6 Hz, ArH), 7.24–7.33 (5H, m,
ArH). 13C NMR (126 MHz, CDCl3): d 53.1 (OCH3), 59.0
(CHNH), 74.5 (CHCOH), 115.0 (NHAr–C ortho), 122.6
(NHAr–C para), 127.8 (Ar–C ortho), 128.7 (Ar–C meta),
129.0 (NHAr–C meta), 138.8 (Ar–C–CH), 144.7 (Ar–C–
NH), 173.2 (CO); HRMS: calcd for C16H16ClO3N (M+):
305.08187; found: 305.08065.
4.6.3. (4S,5R)-(+)-Methyl 3-(4-methoxyphenyl)-4-phenyl-1,3-
oxazolidine-5-carboxylate 4–12b. Colorless crystals, 86%
25
yield; ½aꢁD ¼ þ48:7 (c 1.02, CH2Cl2); >99% ee; mp:
90–90.5 ꢁC; IR (CHCl3) cmax/cmꢀ1: 2982, 2902, 2836,
1760, 1744, 1599, 1493, 1469, 1341, 1201, 1097, 1041,
1
809, 737, 699, 504; H NMR (500 MHz, CDCl3): d 3.68