Mechanisms of cascade reactions in the syntheses of camptothecin-family alkaloids: intramolecular [4+ + 2] reactions of n-arylimidates and alkynes

Organic Letters

Volumn 11, Issue 22, 2009, Pages 5302-5305

  Liang, Yong ^a   Jiang, Xing ^a   Yu, Zhi Xiang ^a  

^a PEKING UNIVERSITY   (China)

Author keywords

[No Author keywords available]

Indexed keywords

ALKYNE; CAMPTOTHECIN; IMIDOESTER;

ARTICLE; CHEMICAL MODEL; CHEMICAL STRUCTURE; CHEMISTRY; COMPUTER SIMULATION; CYCLIZATION; STEREOISOMERISM; SYNTHESIS; X RAY CRYSTALLOGRAPHY;

ALKYNES; CAMPTOTHECIN; COMPUTER SIMULATION; CRYSTALLOGRAPHY, X-RAY; CYCLIZATION; IMIDOESTERS; MODELS, CHEMICAL; MODELS, MOLECULAR; MOLECULAR STRUCTURE; STEREOISOMERISM;

EID: 70749107888     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol902260a     Document Type: Article

References (34)

1. Thomas, C. T.; Rahier, N. J.; Hecht, S. M. Bioorg. Med. Chem. 2004, 12, 1585.
2. 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.
3. For a review, see; Du, W. Tetrahedron 2003, 59, 8649.
4. For selected recent examples, see; (a) Servais, A.; Azzouz, M.; Lopes, D.; Courillon, C.; Malacria, M. Angew. Chem., Int. Ed. 2007, 46, 576.
5. (b) Chavan, S. P.; Pathak, A. B.; Kalkote, U. R. Synlett 2007, 2635.
6. (c) Liu, G.-S.; Dong, Q.-L.; Yao, Y.-S.; Yao, Z.-J. Org. Lett. 2008, 10, 5393.
7. (d) Pin, F.; Comesse, S.; Sanselme, M.; Daich, A. J. Org. Chem. 2008, 73, 1975.
8. (e) Ju, Y.; Liu, F.; Li, C. Org. Lett. 2009, 11, 3582.
9. (a) Fortunak, J. M. D.; Mastrocola, A. R.; Mellinger, M.; Sisti, N. J.; Wood, J. L.; Zhuang, Z.-P. Tetrahedron Lett. 1996, 37, 5679.
10. (b) 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.
11. (a) Zhou, H.-B.; Liu, G.-S.; Yao, Z.-J. Org. Lett. 2007, 9, 2003.
12. (b) Zhou, H.-B.; Liu, G.-S.; Yao, Z.-J. J. Org. Chem. 2007, 72, 6270.
13. (a) Hendrickson, J. B.; Schwartzman, S. M. Tetrahedron Lett. 1975, 16, 277.
14. (b) Hendrickson, J. B.; Hussoin, M. S. J. Org. Chem. 1989, 54, 1144.
15. (c) You, S.-L.; Razavi, H.; Kelly, J. W. Angew. Chem., Int. Ed. 2003, 42, 83.
16. Zhou, H.-B. Thesis Dissertation, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 2007.
17. Frisch, M. J.; Gaussian 03, revision C. 02; Gaussian, Inc.; Wallingford, CT, 2004. For details, see the Supporting Information.
18. (a) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. J. Comput. Chem. 2003, 24, 669.
19. (b) Takano, Y.; Houk, K. N. J. Chem. Theory Comput. 2005, 1, 70.
20. For a recent review, see; Kouznetsov, V. V. Tetrahedron 2009, 65, 2721.
21. Beck, K.; Hoffman, P.; Hünig, S. Chem.-Eur. J. 1997, 3, 1588.
22. + + 2] reactions between the N-protonated azadiene and olefins, see; Ding, Y.-Q.; Fang, D.-C J. Org. Chem. 2003, 68, 4382.
23. +] reactions of iminium cations, see; Domingo, L. R. J. Org. Chem. 2001, 66, 3211.
24. (c) Iafe, R. G.; Houk, K. N. J. Org. Chem. 2008, 73, 2679.
25. (d) Domingo, L. R.; Sáez, J. A. Org. Biomol. Chem. 2009, 7, 3576.
26. Stepwise mechanisms can be ruled out by calculations. For details, see the Supporting Information. For theoretical studies on stepwise Diels-Alder reactions, see; (a) Domingo, L. R.; Oliva, M.; Andrés, J. J. Org. Chem. 2001, 66, 6151.
27. (b) Wakayama, H.; Sakai, S. J. Phys. Chem. A 2007, 111, 13575.
28. (a) Gonzalez, C.; Schlegel, H. B. J. Chem. Phys. 1989, 90, 2154.
29. (b) Gonzalez, C.; Schlegel, H. B. J. Phys. Chem. 1990, 94, 5523.
30. After many attempts, the nucleophilic substitution transition state for the generation of 18 could not be located. Nevertheless, this step is expected to be facile with a low activation free energy because the similar amide activation by Hendrickson reagent can smoothly occur at 0 °C for 10 min (for details, see ref 7c).
31. For detailed analysis using the FMO theory, see Table 1 and the Supporting Information.
32. For comparison, the aza-Diels-Alder reaction involving neutral precursor 25 was also computed, whose activation free energy was 35.3 kcal/mol (eq 2), 11.7 kcal/mol higher than that in the reaction involving cationic precursor 22.
33. Houk, K. N. Acc Chem. Res. 1975, 8, 361.
34. For DFT studies on inverse electron-demand Diels-Alder reactions, see; Yu, Z.-X.; Dang, Q.; Wu, Y.-D. J. Org. Chem. 2005, 70, 998, and references therein.