Lithium Salts of Conformationally Constrained and Restricted Chiral Allylic α-Sulfonyl Carbanions − A Joint Study of their Structures, Dynamics, and Stereoselectivities
作者:Hans-Joachim Gais、Markus van Gumpel、Marcel Schleusner、Gerhard Raabe、Jan Runsink、Cornelia Vermeeren
DOI:10.1002/1099-0690(200111)2001:22<4275::aid-ejoc4275>3.0.co;2-1
日期:2001.11
isomerization and approached kinetic quenching, while those with MeI and allyl iodide were slower, approaching the Curtin−Hammett limit and preferentially giving the exo sulfones. Deprotonation-deuteration experiments of the 7-oxa-sulfone endo-11 showed that the corresponding 7-oxa-substituted carbanion salts endo-6 and exo-6 not only can be generated at low temperatures but may also, despite their tendency to
1H、13C、6Li 和 6Li,1H HOESY 研究了手性双环烯丙基 α-磺酰基碳负离子 3-5 锂盐的结构,每个碳负离子都具有降冰片烷骨架和 S 原子上的叔丁基核磁共振光谱、冷冻和 X 射线晶体结构分析。由于它们相对较高的内-外异构化障碍,3-5 的 Cα-S 内和外非对映异构体可以通过 NMR 光谱在 -30°C 至 -50°C 下在 [D8]THF 中观察到。如 1H,1H HOESY 实验所示,在这些条件下,内型非对映异构体是优选的平衡物质。碳负离子盐 3 的内-外异构化势垒为 ΔG#270 = 13.1±0.1 kcal/mol 和 12.6±0.1 kcal/mol,而 7-二苯甲基取代的碳负离子盐 5 的势垒为 ΔG#288 = 13.5±0.1 kcal/ mol 和 13.3±0.1 kcal/mol。在-100°C 至-108°C 下,5 在 THF 中的低温镜检和