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K. W. Lee et al.
LETTER
(18) (a) Vabeno, J.; Brisander, M.; Lejon, T.; Luthman, K. J. Org.
Chem. 2002, 67, 9186. (b) Chakravarty, P. K.; de Laszlo, S.
E.; Sarnella, C. S.; Springer, J. P.; Schuda, P. F. Tetrahedron
Lett. 1989, 30, 415. (c) Steuer, S.; Podlech, J. Org. Lett.
1999, 1, 481. (d) Brewer, M.; Rich, D. H. Org. Lett. 2001, 3,
945. (e) Pegorier, L.; Larcheveque, M. Tetrahedron Lett.
1995, 36, 2753. (f) Kang, S. H.; Ryu, D. H. Bioorg. Med.
Chem. Lett. 1995, 5, 2959.
J = 17.5, 8.7 Hz), 2.98 (1 H, dd, J = 13.3, 6.9 Hz), 2.90 (1 H,
dd, J = 13.3, 8.7 Hz), 2.48 (dd, 2 H, J = 9.7, 7.4 Hz), 2.16–
2.03 (2 H, m); 13C NMR (CDCl3,125 MHz): d = 177.2,
156.7, 137.1, 136.4, 129.4, 128.8, 128.6, 128.2, 128.0,
126.9, 79.9, 54.9, 39.3, 28.7, 24.1; MS: m/z = 340 [M + H].
(26) Casado-Bellver, F. J.; Gonzalez-Rosende, M. E.; Asensio,
A.; Jorda-Gregori, J. M.; Alvarez-Sorolla, A.; Sepulveda-
Arques, J.; Orena, M.; Galeazzi, R. J. Chem. Soc., Perkin
Trans. 1 2002, 1650.
(19) Ene-acid 3a is available in multi-kg quantities (Z/E
selectivity, 24:1; 83% ee); see ref. 20.
(27) Amino-ester side-product (Figure 1): 1H NMR (CDCl3,
400 MHz): d = 7.34–7.28 (5 H, m), 3.57 (3 H, s), 3.51 (1 H,
m), 3.24 (1 H, dd, J = 13.6, 5.6 Hz), 2.95 (1 H, dd, J = 13.6,
8.8 Hz), 2.32 (2 H, m), 1.95–1.69 (4 H, m); MS: m/z = 222
[M + H].
(20) Lee, K. W.; Hwang, S. Y.; Kim, C. R.; Nam, D. H.; Chang,
J. H.; Choi, B. S.; Choi, H.-w.; Lee, K. K.; So, B.; Cho, S.
W.; Shin, H. Org. Process Res. Dev. 2003, 7, 839.
(21) Cooper, M. S.; Heaney, H.; Newbold, A. J.; Sanderson, W.
R. Synlett 1990, 533.
(22) Preparation of 4a: To a stirred mixture of 3b (660 mg, 1.87
mmol), urea hydrogen peroxide (790 mg, 8.40 mmol), and
Na2HPO4 (1.12 g, 7.89 mmol) in CH2Cl2 (10 mL) was added
(CF3CO)2O (784 mg, 3.73 mmol) at 0 °C. The mixture was
allowed to warm to r.t. and stirred for 4 h. The reaction
mixture was washed with a sat. aq solution of NaHCO3, a 5%
solution of NaHSO3, and finally H2O. The separated organic
layer was concentrated and MTBE (15 mL) was added to the
residue. The mixture was stirred for 5 h. The solid formed
was filtered and washed with MTBE (2 mL). The cake was
dried over a stream of nitrogen to give 4a (615 mg, 86.1%)
as a white solid; 4a tR 31.4 min, ent-4a tR 40.8 min
(Chiralpak® AD-H; 35 °C; 10% i-PrOH–hexane; 1 mL/min;
250 nm); ee of isolated 4a ≥99.9%, while the ee of the filtrate
was 50%, which reflects highly selective recrystallization.
1H NMR (CDCl3, 400 MHz): d = 7.38–7.18 (10 H, m), 5.12
(1 H, d, J = 12.4 Hz), 5.09 (1 H, d, J = 12.4 Hz), 4.95 (1 H,
br), 3.71 (1 H, m), 3.67 (3 H, s), 3.32 (1 H, m), 3.07 (1 H, m),
3.01 (1 H, dd, J = 8.0, 4.4 Hz), 2.85 (1 H, dd, J = 13.2, 8.0
Hz), 2.38 (1 H, dd, J = 16.8, 7.6 Hz), 2.03 (1 H, dd, J = 17.2,
4.8 Hz); 13C NMR (CDCl3, 125 MHz): d = 170.8, 155.8,
136.6, 136.5, 129.6, 128.7, 128.6, 128.2, 128.1, 127.0, 67.0,
57.6, 53.6, 52.0, 51.8, 39.5, 33.3.
O
H2N
OMe
Figure 1
(28) Lactam side-product (Figure 2): 1H NMR (CDCl3, 400
MHz): d = 7.35–7.17 (5 H, m), 5.65 (1 H, br), 3.61 (1 H, m),
2.88 (1 H, dd, J = 13.6, 5.2 Hz), 2.62 (1 H, dd, J = 13.6, 9.2
Hz), 2.43–2.29 (2 H, m), 1.94 (2 H, m), 1.68 (1 H, m), 1.47
(1 H, m); MS: m/z = 190 [M + H] .
HN
O
Figure 2
(23) Ibuka, T.; Habashita, H.; Otaka, A.; Fujii, N. J. Org. Chem.
1991, 56, 4370.
(24) Brown, H. C.; Brown, C. A. J. Am. Chem. Soc. 1963, 85,
1003.
(25) Benzyl (1S)-1-[(2¢S)-5¢-oxotetrahydrofuran-2¢-yl]-2-
phenylethylcarbamate (6): [a]D25 = –9.6 (CHCl3, c 1); 1H
NMR (CDCl3, 500 MHz): d = 7.34–7.25 (10 H, m), 5.09 (1
H, d, J = 12.4 Hz), 5.05 (1 H, d, J = 12.4 Hz), 4.87 (d, 1 H,
J = 10.0Hz), 4.48 (1 H, t, J = 7.8 Hz), 4.07 (dd, 1 H,
(29) Benzyl (1S)-1-[(2¢R)-5¢-oxotetrahydrofuran-2¢-yl]-2-
phenylethylcarbamate (10): [a]D25 = –8.6 (CHCl3, c 0.02);
1H NMR (CDCl3, 400 MHz): d = 7.37–7.18 (10 H, m), 5.04
(2 H, s), 4.66 (1 H, br), 4.40 (1 H, m), 4.05 (1 H, m), 3.03 (1
H, dd, J = 14.4, 4.4 Hz), 2.90 (1 H, m), 2.52 (2 H, m), 2.25
(1 H, m), 2.11 (1 H, m); 13C NMR (CDCl3, 100 MHz): d =
176.6, 165.9, 136.1, 132.7, 129.5, 128.8, 128.6, 128.3,
128.0, 127.0, 80.4, 60.4, 50.0, 30.9, 28.2, 24.7; MS: m/z =
340 [M + H] .
Synlett 2005, No. 20, 3136–3138 © Thieme Stuttgart · New York