O. Poupardin et al. / Tetrahedron Letters 42 (2001) 1523–1526
1525
described using a mixture of K2CO3–CaCO3: CaCO3
being as an efficient scavenger of the liberated fluoride
anion.14
K.; Komatsu, K.; Hara, H.; Hoshino, O. Chem. Pharm.
Bull. 1995, 43, 1325–1335; (c) Inoue, T.; Sazaki, T.;
Takayanagi, H.; Harigaya, Y.; Hoshino, O.; Hara, H.;
Inaba, T. J. Org. Chem. 1996, 61, 3936–3937; (d) Boger,
These conditions were applied to the synthesis of the
14-membered ring of RA-IV. Treatment of a 0.01 M
solution of the dipeptide 13 with K2CO3–CaCO3 (4
D. L.; Zhou, J. ibid 1996, 61, 3938–3939; (e) Boger, D. L.;
Borzilleri, R. M.; Nukui, S. Biorg. Med. Chem. Lett. 1996,
6, 1089–1092; (f) Bigot, A.; Tran Huu Dau, M. E.; Zhu,
J. J. Org. Chem. 1999, 64, 6283–6296 and references cited
therein.
,
equiv./5 equiv.) in the presence of 3 A molecular sieves
in DMSO for 1 h at room temperature afforded the
desired macrocyle 6.15 After preparative thin layer chro-
matography, (8S,9S,12S)-6 was isolated in 10% yield as
an inseparable mixture of atropoisomers.
5. Boger, D. L.; Patane, M. A.; Zhou, J. J. Am. Chem. Soc.
1994, 116, 8544–8556.
6. (a) Rao, A. V. R.; Gurjar, M. K.; Reddy, L.; Rao, A. S.
Chem. Rev. 1995, 95, 2135–2167; (b) Burgess, K.; Lim, D.;
Martinez, C. I. Angew. Chem., Int. Ed. Engl. 1996, 35,
1077–1078; (c) Zhu, J. Synlett 1997, 133–144.
7. (a) Greck, C.; Geneˆt, J. P. Synlett 1997, 741–748; (b) Geneˆt,
J. P.; Greck, C.; Lavergne, D. In Modern Amination
Methods; Ricci, A., Ed.; Wiley: VCH: New York, 2000; pp.
65–102.
8. We thank Dr. J. Zhu for the gift of N-Boc (S)-4-fluoro-3-
nitrophenylalanine. For synthesis, see: Vergne, C.; Bois-
Choussy, M.; Ouazzani, J.; Beugelmans, R.; Zhu, J.
Tetrahedron: Asymmetry 1997, 8, 391–398 and references
cited therein.
In conclusion, an efficient synthesis of the dipeptide
unit 13 has been developed. In spite of the low macro-
cyclisation yield, this synthesis represents the first
approach via an intramolecular SNAr to a 14-mem-
bered ring system including a b-hydroxytyrosine 6,
which is the direct precursor of the cycloisodityrosine
unit of RA-IV.
Acknowledgements
9. (a) Geneˆt, J. P.; Pinel, C.; Ratovelomanana-Vidal, V.;
Mallart, S.; Pfister, X; Bischoff, L.; Cano de Andrade, C.;
Lafitte, J. A. Tetrahedron: Asymmetry 1994, 675–690; (b)
Geneˆt, J. P.; Ratovelomanana-Vidal, V.; Cano de
Andrade, C.; Pfister, X.; Guerreiro, P.; Lenoir, J. Y.
Tetrahedron Lett. 1995, 36, 4801–4804.
10. For the obtention of b-ketoesters, see: Clay, R. J.; Collom,
T. A.; Karriek, G. L.; Wemple, J. Synthesis 1993, 290–292.
11. The asymmetric hydrogenation of b-ketoesters in the
presence of the Ru(II) catalyst bearing atropoisomeric
ligands proceeds in a predictable sense, as shown below:
We thank Glaxo-Wellcome France for a grant to O.P.
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