Angewandte
Chemie
[3] A related reaction has been used in the synthesis of [5]helicenes
that provides precedent for this hypothesis; see: a) D. C.
Harrowven, M. I. T. Nunn, D. R. Fenwick, Tetrahedron Lett.
2002, 43, 3189 – 3191; b) D. C. Harrowven, M. I. T. Nunn, D. R.
Fenwick, Tetrahedron Lett. 2002, 43, 7345 – 7347.
[4] The mechanism of rearomatization has been the subject of much
discussion; for some leading references, see: a) D. C. Har-
rowven, B. J. Sutton, S. Coulton, Tetrahedron 2002, 58, 3387 –
3400; b) A. L. J. Beckwith, V. W. Bowry, W. R. Bowman, E.
Mann, J. Parr, J. M. D. Storey, Angew. Chem. 2004, 116, 97 – 100;
Angew. Chem. Int. Ed. 2004, 43, 95 – 98.
[5] a) G. W. Yeager, D. N. Schissel, Synthesis 1991, 63 – 68; b) O.
Dann, J. Ruff, H.-P. Wolff, H. Griessmeier, Liebigs Ann. Chem.
1984, 409 – 425; c) G. M. Keserꢀe, Z. Dienes, M. Nogradi, M.
Kajtar-Peredy, J. Org. Chem. 1993, 58, 6725 – 6728.
[6] a) D. E. Ames, A. Opalko, Tetrahedron 1984, 40, 1919 – 1926;
b) T. Harayama, H. Yasuda, Heterocycles 1997, 61 – 64;
c) A. V. R. Rao, T. K. Chakraborty, S. P. Joshi, Tetrahedron
Lett. 1992, 33, 4045 – 4048; d) G. Bringmann, D. Menche, J.
Muehlbacher, M. Reichert, N. Saito, S. S. Pfeiffer, B. H. Lip-
shutz, Org. Lett. 2002, 4, 2833 – 2836.
[7] T. Eicher, S. Fey, W. Puhl, E. Bꢀchel, A. Speicher, Eur. J. Org.
Chem. 1998, 877 – 888.
[8] K. J. Edgar, S. N. Falling, J. Org. Chem. 1990, 55, 5287 – 5291.
[9] For a related macrocyclization reaction leading to bazzanin A
tetramethyl ether, see: A. Speicher, J. Kolz, R. P. Sambanje,
Synthesis 2002, 2503 – 2512.
[10] Riccardin C was first isolated from the liverwort Reboulia
hemisphaerica, see: a) Y. Asakawa, R. Matsuda, Phytochemistry
1982, 21, 2143 – 2144; b) Y. Asakawa, M. Toyota, Z. Taira, T.
Takemoto, M. Kido, J. Org. Chem. 1983, 48, 2164 – 2167; it
displays in vitro cytotoxicity against nasal epidermoid carcinoma
cells and weak inhibitory activity against HIV-1 reverse tran-
scriptase, see: c) T. Yoshida, T. Hashimoto, S. Takaoka, Y. Kan,
M. Tori, Y. Asakawa, J. M. Pezzuto, T. Pengsuparp, G. A.
Cordell, Tetrahedron 1996, 52, 14487 – 14500.
[11] For previous total syntheses of riccardin C, see: a) A. Gottsegen,
M. Nogradi, B. Vermes, M. Kajtar-Peredy, E. Bihatsi-Karsai, J.
Chem. Soc. Perkin Trans. 1 1990, 315 – 320; b) A. Gottsegen, M.
Nogradi, B. Vermes, M. Kajtar-Peredy, E. Bihatsi-Karsai,
Tetrahedron Lett. 1988, 29, 5039 – 5040, and reference [6].
[12] D. C. Harrowven, B. J. Sutton, S. Coulton, Org. Biomol. Chem.
2003, 1, 4047 – 4057.
[13] C. Chatgilialoglu, Organosilanes in Radical Chemistry, Wiley,
Chichester, UK, 2003.
Scheme 4. Total synthesis of cavicularin (1) and riccardin C (20).
Ts =p-toluenesulfonyl, TTMSS=tris(trimethylsilyl)silane, AIBN=azo-
bis(isobutyronitrile).
Keywords: arenes · macrocycles · radical reactions ·
.
ring contraction · total synthesis
[1] M. Toyota, T. Yoshida, Y. Kan, S. Takaoka, Y. Asakawa,
Tetrahedron Lett. 1996, 37, 4745 – 4748.
[2] D. C. Harrowven, M. I. T. Nunn, D. R. Fenwick, Tetrahedron
Lett. 2002, 43, 3185 – 3187.
Angew. Chem. Int. Ed. 2005, 44, 3899 –3901
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3901