M. M. M. Santos et al. / Tetrahedron Letters 45 (2004) 2347–2349
2349
275–281; For a recent application of this strategy culmi-
nating in a successful synthesis of K252a, see: (b)
Kobayashi, Y.; Fujimoto, T.; Fukuyama, T. J. Am. Chem.
Soc. 1999, 121, 6501–6502.
2980, 1708 cmꢀ1 1H NMR d (CDCl3): 9.08 (1H, br s,
;
exchangeable with D2O), 8.15 (1H, d, J ¼ 8:2 Hz), 7.65
(1H, d, J ¼ 7:8 Hz), 7.58 (1H, d, J ¼ 7:6 Hz), 7.42 (1H, d,
J ¼ 8:0Hz), 7.36 (1H, t, J ¼ 7:5 Hz), 7.28 (1H, t,
J ¼ 7:5 Hz), 7.23 (1H, t, J ¼ 7:7 Hz), 7.14 (1H, t,
J ¼ 7:3 Hz), 6.90(1H, s), 6.80(1H, s), 1.53 (9H, s) ppm.
Found: C, 75.81; H, 5.91; N, 8.57 (C21H20N2O2 requires C,
75.88; H, 6.06; N, 8.43).
5. (a) Omura, S.; Iwai, Y.; Hirano, A.; Nakagawa, A.;
Awaya, J.; Tsuchiya, H.; Takahashi, Y.; Masuma, R. J.
Antibiot. 1977, 30, 275–282; (b) Furusaki, A.; Hashiba, N.;
Matsumoto, T. Chem. Commun. 1978, 800–801.
6. Kase, H.; Iwahashi, K.; Matsuda, Y. J. Antibiot. 1986, 39,
1059–1065.
11. Hamilakis, S.; Kontonassios, D.; Sandris, C. J. Hetero-
cycl. Chem. 1996, 33, 825–829.
7. Nakanishi, S.; Matsuda, Y.; Iwahashi, K.; Kase, H. J.
Antibiot. 1986, 39, 1066–1071.
12. Beletskaya, I. P. J. Organometal. Chem. 1983, 250, 551–
564.
8. Williams, D. E.; Bernan, V. S.; Ritacco, F. V.; Maiese,
W. M.; Greenstein, M.; Andersen, R. J. Tetrahedron Lett.
1999, 40, 7171–7174.
9. Bergman, J.; Koch, E.; Pelcman, B. Tetrahedron 1995, 51,
5631–5642.
10. A suspension of 1,10-carbonyl-2,20-bi-indole (1.5 g,
5.81 mmol, 1.0equiv) and 18-crown-6 ether (205.0mg), in
benzene (13 mL), under argon atmosphere was stirred at rt
(10min) after which time potassium tert-butoxide
(814.0mg, 7.25 mmol, 1.2 equiv), was introduced. On
completion of the reaction (45 min, TLC control) aq
acetic acid (25 mL; 1 M) and water were added and the
resulting mixture extracted with ether. The residue
obtained on evaporation of the dried organic phase was
chromatographed to give 7a (1.6 g; 84%) as a colourless
solid, mp 137–138 °C (ether/n-hexane); IR (KBr): 3377,
13. Han, X.; Stoltz, B.; Corey, E. J. Am. Chem. Soc. 1999,
121, 7600–7605.
14. Siro, J. G.; Martin, J.; Garcia-Navio, J. L.; Remuinan,
M. J.; Vaquero, J. J. Synlett 1998, 147–148.
15. It is to be noted that the trienes 9b and 9c are also valid
progenitors of the glycosidic indolocarbazole alkaloids.
16. Mild basic aqueous hydrolysis of 10a liberated stauro-
sporinone (2, R ¼ R1 ¼ R2 ¼ H) identical with an authentic
sample17 thereby confirming the presence of the aglycone
common to the alkaloids mentioned above.
^
17. Gaudencio, S. P.; Santos, M. M. M.; Lobo, A. M.;
Prabhakar, S. Tetrahedron Lett. 2003, 44, 2577–2578.
18. For the preparation of N6-methyl, N12-MeOCO-stauro-
sporinone via IMDA reaction with inverse electronic
demand, see: Nomak, R.; Snyder, J. K. Tetrahedron Lett.
2001, 42, 7929–7933.