From Carbohydrates to the Discovery of Pronounced Heteroatomic Effects on Anionically Accelerated [3,3]-Sigmatropic Rearrangements
✍ Scribed by Leo Paquette; Qingbei Zeng; Hui-Ling Wang; Tzenge-Lien Shih
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 394 KB
- Volume
- 2000
- Category
- Article
- ISSN
- 1434-193X
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✦ Synopsis
The (Z)-(iodovinyl)oxetane 12 was prepared from d-glucose and the acyclic analog 18 was obtained from d-mannitol. Following the generation of their lithium derivatives by halogen-metal exchange, coupling to the enantiopure vinylsubstituted norbornanones 20, 23, and 29 proceeded exclusively via endo attack to deliver the targeted exo-carbinols. The anionic oxy-Cope rearrangements of 21 and 24 were seen to differ appreciably in rate. While the sulfur derivative 24 experiences [3,3] sigmatropy with a half-life of less than a minute at -78 °C, its oxygen analogue 21 proved unreactive below -20 °C under entirely comparable conditions. This phenomenon is critically examined in a synthetic context in- [a