Alternative modes of decomposition of allylic selenoxides diastereoisomeric at selenium. Preparation of Δ5,7- and 5β-hydroxy-Δ6-steroiods.
✍ Scribed by W.G. Salmond; M.A. Barta; A.M. Cain; M.C. Sobala
- Publisher
- Elsevier Science
- Year
- 1977
- Tongue
- French
- Weight
- 233 KB
- Volume
- 18
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
Selenoxides containing B-hydrogena are well known to decompose readily to yield olefins' (Scheme I). Allylic selenoxides normally undergo a 2,3-sigmatropic rearrangement very rapidly at low temperature to yield an allylic alcohol after solvolysis of the intermediate selenate ester2 (Scheme II); in some rare cases3'4 a competitive syn-elimination may occur. Such an example is shown in Scheme III where the ratio of the products of rearrangement and elimination was 85:15. This departure from the norm was rationalized4 in terms of enhanced elimination by the phenyl substituent and retardation of the sigmatropic shift by the y-substituents. In such sterically