Addition of ester enolates to N-alkyl-2-fluoropyridinium salts: Total synthesis of (±)-20-deoxycamptothecin and (+)-camptothecin

Journal of Organic Chemistry

Volumn 67, Issue 21, 2002, Pages 7465-7474

  Bennasar, M Lluïsa ^a   Zulaica, Ester ^a   Juan, Cecília ^a   Alonso, Yolanda ^a   Bosch, Joan ^a  

^a UNIVERSITY OF BARCELONA   (Spain)

Author keywords

[No Author keywords available]

Indexed keywords

CHEMOSELECTIVE REDUCTION;

DERIVATIVES; DESULFURIZATION; HYDROLYSIS; ORGANIC ACIDS; OXIDATION; REDUCTION;

ESTERS;

20 DEOXYCAMPTOTHECIN; CAMPTOTHECIN; DIPYRONE; ESTER DERIVATIVE; HYDROXYBUTYRIC ACID; LACTONE DERIVATIVE; N (QUINOLYLMETHYL) 2 FLUOROPYRIDINIUM TRIFLATE; PYRIDINIUM DERIVATIVE; UNCLASSIFIED DRUG;

ARTICLE; CHEMICAL ANALYSIS; CHEMICAL REACTION; CHEMICAL STRUCTURE; CYCLIZATION; DESULFURIZATION; DRUG SYNTHESIS; HYDROLYSIS;

ANTINEOPLASTIC AGENTS, PHYTOGENIC; CAMPTOTHECIN; ESTERS; INDICATORS AND REAGENTS; MODELS, MOLECULAR; MOLECULAR CONFORMATION; PYRIDINIUM COMPOUNDS; STEREOISOMERISM;

EID: 0037131240     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo026173j     Document Type: Article

References (73)

1. For compilations on this subject, see: (a) Bennasar, M.-L.; Lavilla, R.; Alvarez, M.; Bosch, J. Heterocycles 1988, 27, 789. (b) Comins, D. L.; Joseph, S. P. In Comprehensive Heterocyclic Chemistry II; Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds; Pergamon: London, UK, 1996; Vol. 5, pp 70-78. (c) Comins, D. L.; Joseph, S. P. In Advances in Nitrogen Heterocycles; Moody, C. J., Ed.; JAI Press: London, UK, 1996; Vol. 2, pp 251-294.
2. For compilations on this subject, see: (a) Bennasar, M.-L.; Lavilla, R.; Alvarez, M.; Bosch, J. Heterocycles 1988, 27, 789. (b) Comins, D. L.; Joseph, S. P. In Comprehensive Heterocyclic Chemistry II; Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds; Pergamon: London, UK, 1996; Vol. 5, pp 70-78. (c) Comins, D. L.; Joseph, S. P. In Advances in Nitrogen Heterocycles; Moody, C. J., Ed.; JAI Press: London, UK, 1996; Vol. 2, pp 251-294.
3. For compilations on this subject, see: (a) Bennasar, M.-L.; Lavilla, R.; Alvarez, M.; Bosch, J. Heterocycles 1988, 27, 789. (b) Comins, D. L.; Joseph, S. P. In Comprehensive Heterocyclic Chemistry II; Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds; Pergamon: London, UK, 1996; Vol. 5, pp 70-78. (c) Comins, D. L.; Joseph, S. P. In Advances in Nitrogen Heterocycles; Moody, C. J., Ed.; JAI Press: London, UK, 1996; Vol. 2, pp 251-294.
4. For the pioneering use of this reactivity pattern for the construction of indoloquinolizidine alkaloids, see: Wenkert, E. Pure Appl. Chem. 1981, 53, 1271-1276. (b) Wenkert, E.; Angell, E. C.; Drexler, J.; Moeller, P. D. R.; Pyrek, J. S.; Shi, Y.-J.; Sultana, M.; Vankar, Y. D. J. Org. Chem. 1986, 51, 2995-3000.
5. For the pioneering use of this reactivity pattern for the construction of indoloquinolizidine alkaloids, see: Wenkert, E. Pure Appl. Chem. 1981, 53, 1271-1276. (b) Wenkert, E.; Angell, E. C.; Drexler, J.; Moeller, P. D. R.; Pyrek, J. S.; Shi, Y.-J.; Sultana, M.; Vankar, Y. D. J. Org. Chem. 1986, 51, 2995-3000.
6. For a review, see: Bosch, J.; Bennasar, M.-L. Synlett 1995, 587-596.
7. For reviews on the rich chemistry of dihydropyridines, see: (a) Eisner, U.; Kuthan, J. Chem. Rev. 1972, 72, 1-42. (b) Stout, D.; Meyers, A. I. Chem. Rev. 1982, 82, 223-243. (c) Sausins, A.; Duburs, G. Heterocycles 1988, 27, 291-314. (d) Lavilla, R. J. Chem. Soc., Perkin Trans. 1 2002, 1141-1156.
8. For reviews on the rich chemistry of dihydropyridines, see: (a) Eisner, U.; Kuthan, J. Chem. Rev. 1972, 72, 1-42. (b) Stout, D.; Meyers, A. I. Chem. Rev. 1982, 82, 223-243. (c) Sausins, A.; Duburs, G. Heterocycles 1988, 27, 291-314. (d) Lavilla, R. J. Chem. Soc., Perkin Trans. 1 2002, 1141-1156.
9. For reviews on the rich chemistry of dihydropyridines, see: (a) Eisner, U.; Kuthan, J. Chem. Rev. 1972, 72, 1-42. (b) Stout, D.; Meyers, A. I. Chem. Rev. 1982, 82, 223-243. (c) Sausins, A.; Duburs, G. Heterocycles 1988, 27, 291-314. (d) Lavilla, R. J. Chem. Soc., Perkin Trans. 1 2002, 1141-1156.
10. For reviews on the rich chemistry of dihydropyridines, see: (a) Eisner, U.; Kuthan, J. Chem. Rev. 1972, 72, 1-42. (b) Stout, D.; Meyers, A. I. Chem. Rev. 1982, 82, 223-243. (c) Sausins, A.; Duburs, G. Heterocycles 1988, 27, 291-314. (d) Lavilla, R. J. Chem. Soc., Perkin Trans. 1 2002, 1141-1156.
11. (a) Bennasar, M.-L.; Vidal, B.; Bosch, J. J. Org. Chem. 1995, 60, 4280-4286.
12. (b) Bennasar, M.-L.; Vidal, B.; Bosch, J. J. Org. Chem. 1997, 62, 3597-3609.
13. (c) Bennasar, M.-L.; Vidal, B.; Kumar, R.; Lázaro, A.; Bosch, J. Eur. J. Org. Chem. 2000, 3919-3925.
14. (a) Bennasar, M.-L.; Alvarez, M.; Lavilla, R.; Zulaica, E.; Bosch, J. J. Org. Chem. 1990, 55, 1156-1168.
15. (b) Bennasar, M.-L.; Zulaica, E.; Jiménez, J.-M.; Bosch, J. J. Org. Chem. 1993, 58, 7756-7767.
16. (c) Bennasar, M.-L.; Zulaica, E.; Ramírez, A.; Bosch, J. J. Org. Chem. 1996, 61, 1239-1251.
17. (d) Bennasar, M.-L.; Zulaica, E.; Ramírez, A.; Bosch, J. Tetrahedron 1999, 55, 3117-3128.
18. (e) Bennasar, M.-L.; Zulaica, E.; Alonso, Y.; Vidal, B.; Vázquez, J.-T.; Bosch, J. Tetrahedron: Asymmetry 2002, 13, 95-106.
19. (a) Bennasar, M.-L.; Vidal. B.; Bosch, J. J. Am. Chem. Soc. 1993, 115, 5340-5341.
20. (b) Bennasar, M.-L.; Vidal. B.; Bosch, J. J. Chem. Soc., Chem. Commun. 1995, 125-126.
21. Bennasar, M.-L.; Jiménez, J.-M.; Vidal, B.; Sufi, B. A.; Bosch, J. J. Org. Chem. 1999, 64, 9605-9612.
22. For the hydrolysis of the C-F bond in 2-fluoropyridines, see: (a) Rocca, P.; Cochennec, C.; Marsais, F.; Thomas-dit-Dumont, L.; Mallet, M.; Godard, A.; Quéguiner, G. J. Org. Chem. 1993, 58, 7832-7838. (b) Comins, D. L.; Saha, J. K. Tetrahedron Lett. 1995, 36, 7995-7998.
23. For the hydrolysis of the C-F bond in 2-fluoropyridines, see: (a) Rocca, P.; Cochennec, C.; Marsais, F.; Thomas-dit-Dumont, L.; Mallet, M.; Godard, A.; Quéguiner, G. J. Org. Chem. 1993, 58, 7832-7838. (b) Comins, D. L.; Saha, J. K. Tetrahedron Lett. 1995, 36, 7995-7998.
24. For N-acyliminium chemistry on enamides, see: Hiemstra, H.; Speckamp, W. N. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford, UK, 1991; Vol. 2, pp 1047-1082.
25. For the chemistry of lactam-derived vinyl triflates, see: (a) Foti, C. J.; Comins, D. L. J. Org. Chem. 1995, 60, 2656-2657. (b) Luker, T.; Hiemstra, H.; Speckamp, W. N. J. Org. Chem. 1997, 62, 8131-8140. (c) Occhiato, E.; Trabocchi, A.; Guarna, A. J. Org. Chem. 2001, 66, 2459-2465.
26. For the chemistry of lactam-derived vinyl triflates, see: (a) Foti, C. J.; Comins, D. L. J. Org. Chem. 1995, 60, 2656-2657. (b) Luker, T.; Hiemstra, H.; Speckamp, W. N. J. Org. Chem. 1997, 62, 8131-8140. (c) Occhiato, E.; Trabocchi, A.; Guarna, A. J. Org. Chem. 2001, 66, 2459-2465.
27. For the chemistry of lactam-derived vinyl triflates, see: (a) Foti, C. J.; Comins, D. L. J. Org. Chem. 1995, 60, 2656-2657. (b) Luker, T.; Hiemstra, H.; Speckamp, W. N. J. Org. Chem. 1997, 62, 8131-8140. (c) Occhiato, E.; Trabocchi, A.; Guarna, A. J. Org. Chem. 2001, 66, 2459-2465.
28. For a preliminary communication of this part of the work, see: Bennasar, M.-L.; Juan, C.; Bosch, J. Chem. Commun. 2000, 2459-2460.
29. (a) Katritzky, A. R.; Zhang, S.; Kurz, T.; Wang, M.; Steel, P. J. Org. Lett. 2001, 3, 2807-2809 and references therein. See also:
30. (b) Raussou, S.; Gosmini, R.; Mangeney, P.; Alexakis, A.; Commerçon, M. Tetrahedron Lett. 1994, 35, 5433-5436.
31. (c) Yamada, S.; Misono, T.; Ichikawa, M.; Morita, C. Tetrahedron 2001, 57, 8939-8949.
32. (d) Rudler, H.; Denise, B.; Parlier, A.; Daran, J.-C. Chem. Commun. 2002, 940-941.
33. Bennasar, M.-L.; Zulaica, E.; Juan, C.; Llauger, L.; Bosch, J. Tetrahedron Lett. 1999, 40, 3961-3964.
34. For the addition of these nucleophiles to N-alkylpyridinium salts followed by acid-induced cyclization on the indole nucleus, see: Spitzner, D.; Zaubitzer, T.; Shi, Y. J.; Wenkert, E. J. Org. Chem. 1988, 53, 2274-2278. See also ref 2b.
35. Alkylation of 2-halopyridines with alkyl halides and tosylates is a difficult process: (a) Dobbs, A. P.; Jones, K.; Veal, K. T. Tetrahedron Lett. 1997, 38, 5383-5386. (b) Vega, J. A.; Vaquero, J. J.; Alvarez-Builla, J.; Ezquerra, J.; Hamdouchi, C. Tetrahedron 1999, 55, 2317-2326.
36. Alkylation of 2-halopyridines with alkyl halides and tosylates is a difficult process: (a) Dobbs, A. P.; Jones, K.; Veal, K. T. Tetrahedron Lett. 1997, 38, 5383-5386. (b) Vega, J. A.; Vaquero, J. J.; Alvarez-Builla, J.; Ezquerra, J.; Hamdouchi, C. Tetrahedron 1999, 55, 2317-2326.
37. Hutchinson, C. R. Tetrahedron 1981, 37, 1047-1065.
38. Wall, M. E.; Wani, M. C.; Cook, C. E.; Palmer, K. H.; McPhail, A. T.; Sim, G. A. J. Am. Chem. Soc. 1966, 88, 3888-3890.
39. Fan, Y.; Weinstein, J. N.; Kohn, K. W.; Shi, L. M.; Pommier, Y. J. Med. Chem. 1998, 41, 2216-2226 and references therein.
40. For synthetic references up to 1992, see: (a) Cai, J. C.; Hutchinson In Indoles, The Monoterpenoid Indole Alkaloids; Saxton, J. E., Ed. In The Chemistry of Heterocyclic Compounds; Weissberger, A., Taylor, E. C., Eds.; Wiley: New York, 1983; Vol. 25, Part 4, pp 753-781. (b) Wall, M. E.; Wani, M. C. In Monoterpenoid Indole Alkaloids; Saxton, J. E., Ed. In The Chemistry of Heterocyclic Compounds; Taylor, E. C., Ed.; Wiley: Chichester, UK, 1994; Vol. 25, Supplement to Part 4, pp 689-713.
41. For synthetic references up to 1992, see: (a) Cai, J. C.; Hutchinson In Indoles, The Monoterpenoid Indole Alkaloids; Saxton, J. E., Ed. In The Chemistry of Heterocyclic Compounds; Weissberger, A., Taylor, E. C., Eds.; Wiley: New York, 1983; Vol. 25, Part 4, pp 753-781. (b) Wall, M. E.; Wani, M. C. In Monoterpenoid Indole Alkaloids; Saxton, J. E., Ed. In The Chemistry of Heterocyclic Compounds; Taylor, E. C., Ed.; Wiley: Chichester, UK, 1994; Vol. 25, Supplement to Part 4, pp 689-713.
42. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
43. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
44. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
45. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
46. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
47. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
48. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
49. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
50. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
51. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
52. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
53. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
54. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
55. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
56. For more recent syntheses of camptothecin, see: (a) Shen, W.; Coburn, G. A.; Bornmann, W. G.; Danishefsky, S. J. J. Org. Chem. 1993, 58, 611-617. (b) Rama Rao, A. V.; Yadav, J. S.; Valluri, M. Tetrahedron Lett. 1994, 35, 3613-3616. (c) Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994, 59, 6142-6143. (d) Comins, D. L.; Hong, H.; Saha, J. K.; Jianhua, G. J. Org. Chem. 1994, 59, 5120-5121. (e) Comins, D. L.; Hoang, H.; Jianhua, G. Tetrahedron Lett. 1994, 35, 5331-5334. (f) Jew, S.; Ok, K.; Kim, H.; Kim, M. G.; Kim, J. M.; Hah, J. M.; Cho, Y. Tetrahedron: Asymmetry 1995, 6, 1245-1248. (g) Fortunak, J. M. D.; Kitteringham, J.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5683-5686. (h) Murata, N.; Sugihara, T.; Kondo, Y.; Sakamoto, T. Synlett 1997, 298-300.(i) Ciufolini, M. A.; Roschangar, F. Tetrahedron 1997, 53, 11049-11060. (j) Chavan, S. P.; Venkatraman, M. S. Tetrahedron Lett. 1998, 39, 6745-6748. (k) Josien, H.; Ko, S.-B.; Bom, D.; Curran, D. P. Chem. Eur. J. 1998, 4, 67-83. (l) Tagami, K.; Nakazawa, N.; Sano, S.; Nagao, Y. Heterocycles 2000, 53, 771-775. (m) Brown, R. T.; Jianli, L.; Santos, C. A. M. Tetrahedron Lett. 2000, 41, 859-862. (n) Comins, D. L.; Nolan, J. M. Org. Lett. 2001, 3, 4255-4257. (o) Yabu, K.; Masumoto, S.; Kanai, M.; Curran, D. P.; Shibasaki, M. Tetrahedron Lett. 2002, 43, 2923-2926.
57. For a recent review on the ortho-metalation of pyridines and quinolines, see: Mongin, F.; Quéguiner, G. Tetrahedron 2001, 57, 4059-4090.
58. Chatgilialoglu, C. Acc. Chem. Res. 1992, 25, 188-194.
59. For the radical arylation of 2-pyridones, see: (a) Nadin, R.; Harrison, T. Tetrahedron Lett. 1999, 40, 4073-4076. (b) Orito, K.; Satoh, Y.; Nishizawa, H.; Harada, R.; Tokuda, M. Org. Lett. 2000, 2, 2535-2537. (c) See also ref 21e.
60. For the radical arylation of 2-pyridones, see: (a) Nadin, R.; Harrison, T. Tetrahedron Lett. 1999, 40, 4073-4076. (b) Orito, K.; Satoh, Y.; Nishizawa, H.; Harada, R.; Tokuda, M. Org. Lett. 2000, 2, 2535-2537. (c) See also ref 21e.
61. For the radical arylation of 2-pyridones, see: (a) Nadin, R.; Harrison, T. Tetrahedron Lett. 1999, 40, 4073-4076. (b) Orito, K.; Satoh, Y.; Nishizawa, H.; Harada, R.; Tokuda, M. Org. Lett. 2000, 2, 2535-2537. (c) See also ref 21e.
62. (a) Winterfeldt, E.; Korth, T.; Pike, D.; Boch, M. Angew. Chem., Int. Ed. 1972, 11, 289-290.
63. (b) Krohn, K.; Winterfeldt, E. Chem. Ber. 1975, 108, 3030-3042.
64. For the use of chiral nucleophiles toward N-alkyl-3-acylpyridinium salts, see: (a) Amann, R.; Arnold, K.; Spitzner, D.; Majer, Z.; Snatzke, G. Liebigs Ann. 1996, 349-355. (b) See also ref 6e.
65. For the use of chiral nucleophiles toward N-alkyl-3-acylpyridinium salts, see: (a) Amann, R.; Arnold, K.; Spitzner, D.; Majer, Z.; Snatzke, G. Liebigs Ann. 1996, 349-355. (b) See also ref 6e.
66. Krohn, K.; Hamann, I. Liebigs Ann. 1988, 949-953.
67. For the development of this concept ("self-reproduction of chirality"), see: Seebach, D.; Naef, R.; Calderari, G. Tetrahedron 1984, 40, 1313-1324.
68. For similar transformations on tetracyclic DE substructures of camptothecin, see refs 21c and 21k.
69. Güngör, T.; Marsais, F.; Queguiner, G. J. Organomet. Chem. 1981, 215, 139-150.
70. (a) Ashimori, A.; Ono, T.; Uchida, T.; Ohtaki, Y.; Fukaya, C.; Watanabe, M.; Yokoyama, K. Chem. Pharm. Bull. 1990, 38, 2446-2458.
71. (b) Mallet, M. J. Organomet. Chem. 1991, 406, 49-56.
72. Comins, D. L.; Baevsky, M. F.; Hong, H. J. Am. Chem. Soc. 1992, 114, 10971-10972.
73. Mori, K.; Sasaki, M.; Tamada, S.; Suguro, T.; Masuda, S. Tetrahedron 1979, 35, 1601-1605.