M. Ciclosi et al. / Tetrahedron: Asymmetry 15 (2004) 1937–1943
1941
C
H, 7.76; N, 6.43.
13
H
17NO
2
: C, 71.21; H, 7.81; N, 6.39. Found: C, 71.17;
C, 70.57; H, 6.51; N, 4.11. Found: C, 70.54; H, 6.47; N,
4.15.
0
0
0
3
.5. Ethyl (E)-4-p-methoxybenzylamino-2-butenoate 1d
3.7. (4R,1 R)-4-Benzenesulfonylmethyl-3-(1 -phenyl-
ethyl)-1,3-oxazolidin-2-one 2b and its (4S,1 R)-isomer 3b
16
According to the literature method, the title com-
pound was obtained in 60% yield. Yellow oil. IR
Following the same procedure as for 2a and 3a, but
starting from the hydroxysulfone 1b (1.0 g; 5 mmol),
pure isolated compounds 2b and 3b were obtained in
76% overall yield and 70:30 dr MS (EI): m=z 345 (M ),
330, 204, 141, 105, 91, 77.
ꢂ1
CHCl ): 3344, 1708 cm ; H NMR: 1.28 (t, 3H,
3
1
(
J ¼ 7:2), 1.62 (br s, 1H, NH), 3.40 (dd, 2H, J ¼ 1:8,
þ
J ¼ 5:5), 3.73 (s, 2H), 3.79 (s, 3H), 4.19 (q, 2H, J ¼ 7:2),
6
7
.00 (dt, 1H, J ¼ 1:8, J ¼ 15:8), 6.86 (d, 2ArH, J ¼ 8:7),
.00 (dt, 1H, J ¼ 5:5, J ¼ 15:8), 7.23 (d, 2ArH, J ¼ 8:7);
C NMR: 14.6, 49.8, 53.1, 55.6, 60.7, 114.2, 122.0,
13
0
0
1
29.7, 132.4, 147.2, 159.2, 166.8; MS (EI): m=z 250
3.7.1. (4R,1 R)-Benzenesulfonylmethyl-3-(1 -phenylethyl)-
1,3-oxazolidin-2-one 2b. White solid, mp: 55-57 °C. H
þ
1
(M +1), 235, 234, 121, 113. Anal. Calcd for C H NO :
C, 67.45; H, 7.68; N, 5.62. Found: C, 67.41; H, 7.65; N,
5
14
19
3
NMR: 1.53 (d, 3H, J ¼ 7:2), 2.52 (dd, 1H, J ¼ 1:3,
.58.
J ¼ 14:1), 2.81 (dd, 1H, J ¼ 10:2, J ¼ 14:1), 4.21–4.49
(
m, 3H), 5.16 (q, 1H, J ¼ 7:2), 7.21–7.41 (m, 5ArH),
13
7.52–7.65 (m, 2ArH), 7.66–7.75 (m, 3ArH); C NMR:
16.5, 48.9, 52.1, 58.0, 68.4, 127.7, 128.2, 128.9, 129.5,
0
0
3.6. Benzyl (4S,1 R)-[3-(1 -phenylethyl)-1,3-oxazolidin-2-
on-4-yl]acetate 2a and benzyl (4R,1 R)-[3-(1 -phenyl-
ethyl)-1,3-oxazolidin-2-on-4-yl]acetate 3a
0
0
130.0, 134.9, 139.2, 140.3, 157.9; ½aꢃ ¼ ꢂ67:1 (c 0.5,
D
3 4
CH OH). Anal. calcd for C18H19NO S: C, 62.59; H,
5.54; N, 4.06. Found: C, 62.55; H, 5.49; N, 4.02.
To a solution containing the hydroxy ester 1a (1.0 g;
5
mmol) and DBU (0.2 mL) in acetonitrile (50 mL) (R)-
0 0
(4S,1 R)-4-Benzenesulfonylmethyl-3-(1 -phenyl-
ethyl)-1,3-oxazolidin-2-one 3b. White solid, mp: 66-
phenylethylisocyanate (0.74 g; 5 mmol) was added at
room temperature and subsequently the mixture was
stirred at 40 °C for 2 h. After cooling, the solvent was
removed under reduced pressure, the residue was dis-
solved in ethyl acetate (150 mL) and the organic layer
3.7.2.
1
68 °C. H NMR: 1.57 (d, 3H, J ¼ 7:2), 3.29 (dd, 1H,
J ¼ 9:8, J ¼ 14:0), 3.37 (dd, 1H, J ¼ 3:3, J ¼ 14:0),
3.73–3.85 (m, 1H), 4.28–4.38 (m, 2H), 5.11 (q, 1H,
J ¼ 7:2), 7.12–7.21 (m, 3ArH), 7.24–7.32 (m, 3ArH),
was washed with 0.1 M HCl (50 mL) and then with H O
2
13
(
100 mL). After drying over Na
2
SO
4
, the solvent was
7.51–7.62 (m, 2ArH), 7.66–7.78 (m, 2ArH); C NMR:
19.1, 50.2, 53.5, 59.1, 68.0, 127.4, 127.6, 128.2, 128.8,
128.9, 129.3, 129.4, 130.2, 134.9, 138.6, 139.0, 157.9;
½aꢃ ¼ þ21:8 (c 0.5, CH OH). Anal. Calcd for
removed under reduced pressure and the residue was
purified by silica gel chromatography (cyclohexane–
ethyl acetate 70:30) to give pure isolated 2a and 3a in
D
3
þ
7
3
8% overall yield and 85:15 dr MS (EI): m=z 340 (M ),
25, 235, 191, 105, 91, 77.
C
18
H
19NO
5
S: C, 62.59; H, 5.54; N, 4.06. Found: C,
62.55; H, 5.51; N, 4.09.
0
0
0
0
3
2
1
1
3
.6.1. Benzyl (4S,1 R)-[3-(1 -phenylethyl)-1,3-oxazolidin-
-on-4-yl] acetate 2a. Colourless oil. IR (CHCl ): 1750,
3.8. Ethyl (5S,1 R)-[3-benzyl-1-(1 -phenylethyl)imidazoli-
din-2-on-5-yl]acetate 2c and its (5R,1 R)-isomer 3c
0
3
ꢂ1
1
744 cm ; H NMR: 1.68 (d, 3H, J ¼ 7:3), 2.12 (dd,
H, J ¼ 9:0, J ¼ 16:9), 2.38 (dd, 1H, J ¼ 4:5, J ¼ 16:9),
.97 (dd, 1H, J ¼ 5:2, J ¼ 8:8), 4.14–4.28 (m, 1H), 4.46
Following the same procedure as for 2a and 3a but
starting from the amino ester 1c (1.0 g; 5.0 mmol), a
mixture of compounds 2c and 3c very difficult to sepa-
rate was obtained in 74% overall yield and 80:20 dr,
(
dd, 1H, J ¼ 8:5, J ¼ 8:8), 5.02 (s, 2H), 5.15 (q, 1H,
13
J ¼ 7:3), 7.21–7.42 (m, 10ArH); C NMR: 16.7, 38.8,
1
13
5
1
0.8, 52.0, 67.3, 68.5, 127.5, 128.5, 128.9, 129.0, 129.1,
29.2, 135.6, 141.2, 157.3, 170.3; ½aꢃ ¼ þ78:5 (c 1,
which gave however definite patterns in H and
þ
C
NMR spectra. MS (EI): m=z 366 (M ), 351, 260, 155,
D
: C, 70.57; H, 6.51;
CHCl
3
). Anal. Calcd for C20
H
22NO
N, 4.11. Found: C, 70.53; H, 6.55; N, 4.07.
4
105, 91. Anal. Calcd for C22
N, 7.64. Found: C, 72.14; H, 7.11; N, 7.60.
26 2 3
H N O : C, 72.11; H, 7.15;
0
0
0
0
3
2
1
1
3
.6.2. Benzyl (4R,1 R)-[3-(1 -phenylethyl)-1,3-oxazolidin-
-on-4-yl] acetate 3a. Colourless oil. IR (CHCl ): 1751,
3.8.1. Ethyl (5S,1 R)-[3-benzyl-1-(1 -phenylethyl)-imidaz-
olidin-2-on-5-yl]acetate 2c. Colourless oil. IR (CHCl ):
3
3
ꢂ1
1
ꢂ1
1
744 cm ; H NMR: 1.65 (d, 3H, J ¼ 7:3), 2.57 (dd,
H, J ¼ 9:8, J ¼ 16:6), 2.78 (dd, 1H, J ¼ 3:7, J ¼ 16:6),
.74–3.88 (m, 1H), 4.16 (dd, 1H, J ¼ 5:1, J ¼ 9:0), 4.36
1744, 1657 cm . H NMR: 1.13 (t, 3H, J ¼ 7:1), 1.66
(d, 3H, J ¼ 7:2), 1.97 (dd, 1H, J ¼ 9:6, J ¼ 16:2), 2.14
(dd, 1H, J ¼ 4:0, J ¼ 16:2), 2.84 (dd, 1H, J ¼ 6:3,
J ¼ 9:0), 3.42 (dd, 1H, J ¼ 8:8, J ¼ 9:0), 3.97 (q, 2H,
J ¼ 7:1), 3.94–3.06 (m, 1H), 4.41 (ABq, 2H, J ¼ 14:9),
(
dd, 1H, J ¼ 8:8, J ¼ 9:0), 5.07 (s, 2H), 5.14 (q, 1H,
13
J ¼ 7:3), 7.24–7.43 (m, 10ArH); C NMR: 19.1, 39.6,
13
5
1
½
1.5, 53.3, 67.4, 68.4, 127.5, 127.7, 128.5, 128.6, 128.7,
28.9, 129.1, 129.2, 129.4, 135.6, 139.4, 158.4, 170.1;
5.25 (q, 1H, J ¼ 7:2), 7.18–7.42 (m, 10ArH); C NMR:
14.4, 16.3, 19.4, 39.4, 48.5, 49.3, 51.0, 60.9, 127.6, 127.7,
127.8, 128.5, 128.8, 129.0, 137.6, 142.8, 160.9, 170.8.
aꢃ ¼ þ69:4 (c 1, CHCl
3 4
). Anal. Calcd for C20H22NO :
D