From carbohydrates to the discovery of prounced heteroatomic effects on anionically accelerated [3,3]-sigmatropic rearrangements

doi:10.1002/1099-0690(200006)2000:12<2187::AID-EJOC2187>3.0.CO;2-2

淡江大學機構典藏 > 理學院 > 化學學系暨研究所 > 期刊論文 > Item 987654321/61605

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题名:	From carbohydrates to the discovery of prounced heteroatomic effects on anionically accelerated [3,3]-sigmatropic rearrangements
作者:	Paquette, L.A.
贡献者:	淡江大學化學學系
日期:	2000-06
上传时间:	2011-10-15 23:21:03 (UTC+8)
摘要:	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 vinyl-substituted 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 involving 26 and 30, where the heavily functionalized acyclic side chain involved previously is supplanted by an oxetane assembly. In the sulfur example, isomerization occurs very rapidly as before with 100% transfer of chirality. The kinetic response of vinyl ether 26 now proved to be entirely comparable. However, the pathway followed in this instance was intramolecular nucleophilic attack by the “naked” alkoxide at the less substituted C−O bond of the oxetane with ring cleavage and formation of alcohol 28. The global findings provide a glimpse of the subtle way in which [3,3]-sigmatropic transpositions can be modulated by heteroatomic substitution.
關聯:	European journal of organic chemistry 2000(12), pp.2187-2194
DOI:	10.1002/1099-0690(200006)2000:12<2187::AID-EJOC2187>3.0.CO;2-2
显示于类别:	[化學學系暨研究所] 期刊論文

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