Fig. 1
This work was supported by a Korea Research Foundation
Grant funded by the Korean Government (MOEHRD) (KRF-
2005-005-J11901 and KRF-2005-070-C00073).
Scheme 3 Reagents and conditions: i, LiAlH4, THF, 230 uC, 30 min; ii,
OsO4, NMO, t-BuOH–THF–H2O (8 : 6 : 3), 25 uC, 12 h, then NaIO4,
25 uC, 12 h; iii, PPh3CH3Br, NaHMDS, 0 uC, 2 h; iv, PCC, celite, CH2Cl2,
25 uC, 3 h.
Notes and references
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3 T. Hartmann and L. Witte, Alkaloids: Chemical and Biological
Perspectives, Pergamon, Oxford, UK, 1995. See also: D. J. Robins,
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6 D. M. Hodgson, T. D. Avery, A. C. Donohue and T. Bruckl, J. Org.
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7 Catalytic asymmetric reaction: (a) E. J. Corey and T. P. Loh,
Tetrahedron Lett., 1993, 34, 3979; (b) I. Yamamoto and K. Narasaka,
Chem. Lett., 1995, 1129; (c) D. A. Evans and D. M. Barnes, Tetrahedron
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A. Iyobe and T. Koizumi, J. Chem. Soc., Chem. Commun., 1986, 771; (e)
J. M. Fraile, J. I. Garcia, D. Gracia, J. A. Mayoral and E. Pires, J. Org.
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Scheme 4 Reagents and conditions: i, CsOH, t-BuOH, 25 uC, 12 h, then
10% citric acid, pH 5 4–5, TMSCHN2, MeOH, 25 uC, 5 min; ii, I2, PPh3,
THF, imidazole, 25 uC, 1 h; iii, BH3?THF, THF, 0 uC, 3 h then, H2O2,
0.15 N NaOH, 0 uC, 1 h; iv, Zn, CH3COOH, 25 uC, 6 h; v, PCC, celite,
CH2Cl2, 25 uC, 3 h; vi, 2-methyl-2-butene, 1 M NaClO2, 1 M NaH2PO4,
t-BuOH–THF–H2O (4 : 4 : 1), 25 uC, 3 h, then 2 N NaOH, 25 uC, 6 h.
aldehyde 13 in 84% yield over the two steps. Finally, Pinnick
oxidation15 and basic hydrolysis of aldehyde 13 were efficiently
carried out to release (+)-cis-nemorensic acid 1 (Scheme 4).
Spectral data for the synthetic acid were in accord with those of the
natural isolate.1a,6 Comparison of the optical rotation determined
the absolute stereochemistry to be as shown in 1 [a]D 5 +47
(EtOH, c 0.50) [lit.1a,c [a]D 5 +49 ¡ 4 (EtOH, c 0.76)]. As we
predicted, the mechanistic model of the cationic oxazaborolidium
catalyst 5 was supported (Fig. 1).9
In conclusion, we have achieved an asymmetric synthesis of (+)-
cis-nemorensic acid 1 from 2,5-dimethylfuran. We are now
applying this strategy to the preparation of other substituted
tetrahydrofurans.
12 A. R. Bressette and L. C. Glover, IV, Synlett, 2004, 4, 0738.
13 T. Tsunoda, T. Nishii, M. Yoshizuka, C. Yamasaki, T. Suzuki and
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14 C. Zhi and Q. Y. Chen, J. Chem. Soc., Perkin Trans. 1, 1996, 1741.
15 L. E. Overman and D. V. Paone, J. Am. Chem. Soc., 2001, 123, 9465.
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