New chiral auxiliaries for highly stereoselective asymmetric methoxyselenenylations

Organic Letters

Volumn 2, Issue 19, 2000, Pages 3007-3009

  Back, Thomas G ^a   Moussa, Ziad ^a  

^a UNIVERSITY OF CALGARY   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000073992     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol000187z     Document Type: Article

References (36)

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2. (b) Topics in Current Chemistry: Organoselenium Chemistry; Wirth, T., Ed.; Springer-Verlag: Berlin, 2000; Vol. 208.
3. For a recent review, see: Wirth, T. Tetrahedron 1999, 55, 1-28.
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6. (c) Back, T. G. In The Chemistry of Organic Selenium and Tellurium Compounds; Patai, S., Ed.; Wiley: Chichester, 1987; Vol. 2, Chapter 3.
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8. (e) Schmid, G. H.; Garratt, D. G. In The Chemistry of Double-bonded Functional Groups. Supplement A, Part 2; Patai S., Ed.; Wiley: New York, 1977; Chapter 9.
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10. For asymmetric electrophilic reactions of 1b-1d and 2b-2d, see: (a) Back, T. G.; Dyck, B. P.; Nan, S. Tetrahedron 1999, 55, 3191-3208.
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15. For a review of asymmetric oxyselenenylations, see: (a) Fujita, K. In Reviews on Heleroatom Chemistry; Oae, S., Ed.; MYU, Tokyo, 1997; Vol. 16, pp 101-117. For examples of other chiral auxiliaries used in oxyselenenylations, see:
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30. 2Se: 417.2146. Found: 417.2124.
31. It has been pointed out (see refs 7a and 7i) that the stereochemistry of oxyselenenylations of symmetrically cis-disubstituted alkenes is fixed in the second step, where ring opening of the seleniranium intermediate occurs, rather than in the initial addition of the electrophile to the alkene. This is in contrast to unsymmetrical or frans-disubstituted alkenes, where the stereochemistry is set in the first step and may account for the poorer diastereoselectivities generally observed with ns-alkenes. The reason for the particular effectiveness of 3d with cis-alkenes is not known.
32. For a theoretical analysis of some asymmetric oxyselenenylations where an Se-coordinating substituent is present in the chiral auxiliary, see: Wang, X.; Houk, K. N.; Spichty, M.; Wirth, T. J. Am. Chem. Soc. 1999, 121, 8567-8576.
33. (a) Coordination via the oxime nitrogen is less likely because it - would require isomerization to the more crowded E-oxime in order to render the nitrogen atom's nonbonding electrons accessible to the selenium atom. Moreover, coordination through nitrogen instead of through the oxime oxygen would involve a more strained four-instead of five-membered ring,
34. 77Se NMR spectra of diselenides 3a and 4a are very similar to that of 1a (δ 377.3, 375.3, and 375.2 ppm relative to dimethyl selenide, respectively), suggesting that coordination effects are not significant in the parent diselenides 3a and 4a. However, the X-ray structure of 4a reveals relatively short interatomic distances of 2.95 and 2.97 Å between the oxime O and Se atoms of the two camphorseleno moieties. Thus, O - Se coordination should be possible in species where the selenium atom assumes a more strongly positive character.
35. Clive, D. L. J.; Chittattu, G. J.; Farina, V.; Kiel, W. A.; Menchen, S. M.; Russell, C. G.; Singh, A.; Wong, C. K.; Curtis, N. J. J. Am. Chem. Soc. 1980, 102, 4438-4447.
36. Authentic (R)-5 was obtained from (R)-1-phenylethanol by treatment with NaH and iodomethane.