Asymmetric epoxidation of olefins catalyzed by chiral iminium salts generated in situ from amines and aldehydes

Organic Letters

Volumn 3, Issue 16, 2001, Pages 2587-2590

  Wong, Man Kin ^a   Ho, Lai Mei ^a   Zheng, Yan Song ^a   Ho, Chun Yu ^a   Yang, Dan ^a  

^a UNIVERSITY OF HONG KONG   (Hong Kong)

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EID: 0000652906     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol016260i     Document Type: Article

References (18)

1. For reviews on asymmetric epoxidation of allylic alcohols, see: (a) Johnson, R. A.; Sharpless, K. B. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.; VCH: New York, 1993; Chapter 4.1.
2. (b) Katsuki, T. In Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. 2, p 621. For a recent review on asymmetric epoxidation of unfunctionalized olefins, see:
3. (c) Jacobsen, E. N.; Wu, M. H. In Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. 2, p 649.
4. (a) Lusinchi, X.; Hanquet, G. Tetrahedron 1997, 53, 13727.
5. (b) Hanquet, G.; Lusinchi, X.; Milliet, P. Tetrahedron Lett. 1988, 29, 3941.
6. (a) Bohe, L.; Hanquet, G.; Lusinchi, M.; Lusinchi, X. Tetrahedron Lett. 1993, 34, 7271.
7. (b) Bohe, L.; Lusinchi, M.; Lusinchi, X. Tetrahedron 1999, 55, 141.
8. Aggarwal, V. K.; Wang, M. F. J. Chem. Soc., Chem. Commun. 1996, 191.
9. (a) Page, P. C. B.; Rassias, G. A.; Bethell, D.; Schilling, M. B. J. Org. Chem. 1998, 63, 2774.
10. (b) Page, P. C. B.; Rassias, G. A.; Barros, D, Bethell, D.; Schilling, M. B. J. Chem. Soc., Perkin Trans. 1 2000, 19, 3325.
11. (a) Armstrong, A.; Ahmed, G.; Garnett, I.; Goacolou, K. Synlett 1997, 1075.
12. (b) Armstrong, A.; Ahmed, G.; Garnett, I.; Goacolou, K.; Wailes, J. S. Tetrahedron 1999, 55, 2341.
13. Minakata, S.; Takemiya, A.; Nakamura, K.; Ryu, I.; Komatsu, M. Synlett 2000, 12, 1810.
14. 4, filtered, and concentrated under reduced pressure. The residue was purified by flash column chromatography to provide trans-stilbene epoxide (18.4 mg, 99% yield based on 95% conversion) as a white solid. The enantioselectivity of the epoxide was determined to be 30% by chiral HPLC (Chiralcel OD column).
15. While our work was ongoing, Aggarwal and co-workers reported that amines could be used as catalysts for epoxidation with Oxone as the primary oxidant, and the reaction conditions were quite similar to ours; see: Adamo, M. F. A.; Aggarwal, V. K.; Sage, M. A. J. Am. Chem. Soc. 2000, 122, 8317.
16. Control experiments were performed in the absence of aldehyde for epoxidation reactions in Table 3, and it was found that less than 5% conversion of olefins were observed for olefins 12-15 within the indicated reaction time. However, for olefins 16-18, up to 48% conversion of styrene 16 and 25% conversion of olefins 17 and 18 were observed in 8 h. The origin of these amine promoted epoxidation reactions is under investigation.
17. Job, D. Ann. Chim. (Paris) 1928, 9, 113.
18. 2 symmetric amine 5 and an aliphatic aldehyde may provide two diastereomeric oxaziridinium salts (with opposite configurations of the oxaziridinium ring), which may afford epoxides of different configurations and enantioselectivities. Without knowledge on the reactivities and relative ratio of the two diastereomeric oxaziridinium salts, it is difficult to draw a clear conclusion for the transition state geometry and the origin of asymmetric induction. For recent theoretical calculations favoring a spiro transition state for epoxidation by oxaziridinium salts, see: Washington, I.; Houk, K. N. J. Am. Chem. Soc. 2000, 122, 2948.