Enantioselective intermolecular free radical conjugate additions. Application of a pyrazole template

Tetrahedron Letters

Volumn 38, Issue 34, 1997, Pages 5955-5958

  Sibi, Mukund P ^a   Shay, John J ^a   Ji, Jianguo ^a  

^a NORTH DAKOTA STATE UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

PYRAZOLE DERIVATIVE;

ARTICLE; CHIRALITY; DRUG SYNTHESIS; IN VITRO STUDY; METHODOLOGY; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY; REACTION ANALYSIS; STEREOCHEMISTRY;

EID: 0030873409     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(97)01353-1     Document Type: Article

References (31)

1. (a) Catalytic Asymmetric Synthesis, Ojima, I. Ed., VCH, Weinheim, 1993.
2. (b) Noyori, R. Asymmetric Catalysis in Organic Synthesis, Wiley, New York, 1994.
3. Evans, D. A.; Murry, J. A.; von Matt, P.; Norcross, R. D.; Miller, S. J. Angew. Chem. Int. Ed. Engl. 1995, 34, 798.
4. Gothelf, K. V.; Hazell, R. A.; Jørgensen, K. A. J. Org. Chem. 1996, 61, 346.
5. (a) Wu, J. H.; Radinov, R.; Porter, N. A. J. Am. Chem. Soc. 1995, 117, 11029.
6. (b) Wu, J. H.; Zhang, G.; Porter, N. A. Tetrahedron Lett. 1997, 38, 2067.
7. Fahl, A-R.; Renaud, P. Tetrahedron Lett. 1997, 38, 2661.
8. Sibi, M. P.; Ji, J.; Wu, J. H.; Gürtler, S.; Porter, N. A. J. Am. Chem. Soc. 1996, 118, 9200.
9. For a general discussion see: Curran, D. P.; Porter, N. A.; Giese, B. Stereochemistry of Radical Reactions, VCH, Weinheim, 1995.
10. For other examples of enantioselective radical reactions see: (a) Urabe, H.; Yamashita, K.; Suzuki, K.; Kobayashi, K.; Sato, F. J. Org. Chem. 1995, 60, 3576.
11. (b) Murakata, M.; Tsutsui, H.; Hoshino, O. J. Chem. Soc., Chem. Commun. 1995, 481.
12. (c) Nanni, D.; Curran, D. P. Tetrahedron: Asymmetry 1996, 7, 2417.
13. (d) Haque, M. B.; Roberts, B. P. Tetrahedron Lett. 1996, 37, 9123.
14. (e) Blumenstein, M.; Schwarzkopf, K.; Metzger, J. O. Angew. Chem., Int. Ed. Engl. 1997, 36, 235.
15. (f) Braslau, R.; Burrill, L. C. II; Mahal, L. K.; Wedeking, T. Angew. Chem., Int. Ed. Engl. 1997, 36, 237.
16. (g) Nishida, M.; Hayashi, H.; Nishida, A.; Kamahara, N. Chem. Commun. 1996, 579.
17. (a) For the use of 2 see: Reetz, M. T. Acc. Chem. Res. 1993, 26, 462.
18. (b) For the use of 3 see: Jensen, K. B.; Gothelf, K. V.; Hazell, R. G.; Jørgensen, K. A. J. Org. Chem. 1997, 62, 2471.
19. 2) see: Ref. 7a. For a discussion on the chelation of Weinreb amides 4 (X=N) with Lewis acids see: Figueras, S.; Martin, R.; Romea, P.; Urpi, F.; Vilarrasa, J. Tetrahedron Lett. 1997, 38, 1633.
20. Kashima, C.; Takahashi, K.; Fukuchi, I.; Fukusaka, K. Heterocycles 1997, 44, 289 and references cited therein.
21. Sibi, M. P.; Jasperse, C. P.; Ji, J. J. Am. Chem. Soc. 1995, 117, 10779.
22. For the preparation of 6 and 7 see: Besida, J.; Brown, R. F. C.; Colamanet, S.; Leach, D. N. Aust. J. Chem. 1982, 35, 1373. 3,5-Diphenylpyrazole was also evaluated as a template. The reactions were complex and chemical yields were low.
23. Bisoxazolines were the only class of ligands examined in this study since they had shown the best characteristics in our earlier work (ref. 5). For a review on the use of bisoxazolines see: Pfaltz, A. Acc. Chem. Res. 1993, 26, 339.
24. We have recently shown that box ligands (specially 10d) provide excellent enantioselectivity in conjugate radical additions: Sibi, M. P.; Ji, J. J. Org. Chem. 1997, 62, 3800.
25. All new compounds showed spectral (IR, NMR) and analytical characteristics consistent with their structure.
26. A variety of other box ligands were also screened with limited success.
27. Typically, <1% of ethyl radical (from triethylborane) addition product was observed.
28. Lardicci, L.; Salvadori, P.; Caporusso, A. M.; Menicagli, R.; Belgodere, E. Gazz. Chim. Ital. 1972, 102, 64.
29. 2 and ligand 10d. See ref. 13.
30. Kashima, C.; Takahashi, K.; Fukusaka, K. J. Heterocyclic Chem. 1995, 32, 1775.
31. D = -49.66 (7.0 benzene), Lardicci, L.; Menicagli, R.; Salvadori, P. Gazz. Chim. Ital. 1968, 98, 738.