Acknowledgements
We thank the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie for financial support of our project.
We are grateful to the BASF AG, Ludwigshafen, for a generous
gift of pentacarbonyliron.
References
1 Part 34 of transition metal complexes in organic synthesis. Part 33:
H.-J. Knölker and C. Hofmann, Tetrahedron Lett., 1996, 37, 7947.
2 (a) K. Sakano, K. Ishimaru and S. Nakamura, J. Antibiot., 1980, 33,
683; (b) K. Sakano and S. Nakamura, J. Antibiot., 1980, 33, 961;
(c) M. Kaneda, K. Sakano, S. Nakamura, Y. Kushi and Y. Iitaka,
Heterocycles, 1981, 15, 993; (d) K. Yamasaki, M. Kaneda,
K. Watanabe, Y. Ueki, K. Ishimaru, S. Nakamura, R. Nomi,
N. Yoshida and T. Nakajima, J. Antibiot., 1983, 36, 522; (e)
S. Kondo, M. Katayama and S. Marumo, J. Antibiot., 1986, 39, 727;
( f ) T. Naid, T. Kitahara, M. Kaneda and S. Nakamura, J. Antibiot.,
1987, 40, 157; (g) M. Kaneda, T. Naid, T. Kitahara and S. Naka-
mura, J. Antibiot., 1988, 41, 602; (h) D. J. Hook, J. J. Yacobucci,
S. O’Connor, M. Lee, E. Kerns, B. Krishnan, J. Matson and
G. Hesler, J. Antibiot., 1990, 43, 1347.
3 U. Pindur, Chimia, 1990, 44, 406; J. Bergman and B. Pelcman, Pure
Appl. Chem., 1990, 62, 1967; D. P. Chakraborty, in The Alkaloids,
ed. A. Brossi, Academic Press, New York, 1993, vol. 44, p. 257;
C. J. Moody, Synlett, 1994, 681.
4 H.-J. Knölker, in Organic Synthesis via Organometallics, ed. K. H.
Dötz and R. W. Hoffmann, Vieweg, Braunschweig, 1991, p. 119;
H.-J. Knölker, Synlett, 1992, 371; H.-J. Knölker, in Advances in
Nitrogen Heterocycles, ed. C. J. Moody, JAI Press, Greenwich, CT,
1995, vol. 1, p. 173.
Scheme 3
the desired 6-methoxy isomer 9b. The tricarbonyliron-
complexed 4b,8a-dihydrocarbazol-3-ones are useful synthetic
precursors for 3-hydroxy-9H-carbazole alkaloids.11 Thus,
demetallation of the complexes 9a and 9b using trimethylamine
N-oxide12 afforded the 3-hydroxycarbazole derivatives 10a and
10b, which after O-methylation gave 4-deoxycarbazomycin C 3
and carbazomycin D 2.‡
Carbazomycin C 1 was obtained via the iron-mediated
arylamine cyclization. Electrophilic substitution of the ami-
nophenol 5c by 4 afforded the complex 6c which was trans-
formed into the acetate 6d (Scheme 2). Oxidative cyclization of
6d using very active manganese dioxide8 to give the carbazole
12 followed by saponification of the ester provided carbazomy-
cin C 1 (Scheme 4).§
5 A. J. Birch, L. F. Kelly and D. J. Thompson, J. Chem. Soc., Perkin
Trans. 1, 1981, 1006.
6 H.-J. Knölker, M. Bauermeister, J.-B. Pannek, D. Bläser and
R. Boese, Tetrahedron, 1993, 49, 841.
7 H.-J. Knölker and M. Bauermeister, Helv. Chim. Acta, 1993, 76,
2500.
8 A. J. Fatiadi, Synthesis, 1976, 65.
9 H.-J. Knölker, F. Budei, J.-B. Pannek and G. Schlechtingen, Synlett,
1996, 587.
Scheme 4 Reagents and conditions: i, very active MnO2, CH2Cl2,
25 ЊC; ii, NaOH, H2O, reflux
10 A. J. Birch, K. B. Chamberlain, M. A. Haas and D. J. Thompson,
J. Chem. Soc., Perkin Trans. 1, 1973, 1882; A. J. Pearson, Acc. Chem.
Res., 1980, 13, 463; A. J. Pearson, Metallo-organic Chemistry, Wiley,
Chichester, 1985, ch. 8.
11 H.-J. Knölker, M. Bauermeister, J.-B. Pannek and M. Wolpert,
Synthesis, 1995, 397.
‡ This synthesis affords carbazomycin D 2 in 5 steps and 23% overall
yield based on 4 as pale yellow needles, mp 125 ЊC (from cyclohexane)
(lit.,2f mp 129.5–130 ЊC, colourless needles from hexane–
1
dichloromethane). All spectral data (UV, IR, H and 13C NMR, MS)
12 Y. Shvo and E. Hazum, J. Chem. Soc., Chem. Commun., 1974, 336;
H.-J. Knölker, J. Prakt. Chem., 1996, 338, 190.
are in full agreement with those reported for the natural product.
§ Carbazomycin C 1 was obtained in 4 steps and 25% overall yield
based on 4 as colourless crystals, mp 190–191 ЊC (from hexane–ethyl
acetate) (lit.,2f mp 198–198.5 ЊC, pale yellow prisms from hexane–ethyl
Paper 6/08351J
Received 12th December 1996
Accepted 18th December 1996
1
acetate). All spectral data (UV, IR, H and 13C NMR, MS) are in full
agreement with those reported for the natural product.
350
J. Chem. Soc., Perkin Trans. 1, 1997