Lithium Diisopropylamide-Mediated Reactions of Imines, Unsaturated Esters, Epoxides, and Aryl Carbamates: Influence of Hexamethylphosphoramide and Ethereal Cosolvents on Reaction Mechanisms
作者:Yun Ma、David B. Collum
DOI:10.1021/ja074554e
日期:2007.11.28
Several reactions mediated by lithium diisopropylamide (LDA) with added hexamethylphosphoramide (HMPA) are described. The N-isopropylimine of cyclohexanone lithiates via an ensemble of monomer-based pathways. Conjugate addition of LDA/HMPA to an unsaturated ester proceeds via di- and tetra-HMPA-solvated dimers. Deprotonation of norbornene epoxide by LDA/HMPA proceeds via an intermediate metalated epoxide
描述了由二异丙基氨基锂 (LDA) 与添加的六甲基磷酰胺 (HMPA) 介导的几种反应。环己酮的 N-异丙亚胺通过一系列基于单体的途径锂化。LDA/HMPA 与不饱和酯的共轭加成通过二和四 HMPA 溶剂化二聚体进行。LDA/HMPA 对降冰片烯环氧化物的去质子化通过中间金属化环氧化物作为与 LDA 的混合二聚体进行。芳基氨基甲酸酯的正锂化通过基于单 HMPA 溶剂化单体的途径进行。对 THF 和其他醚类助溶剂的依赖性表明,在某些情况下,二级壳溶剂化效应很重要。讨论了过度机械复杂性的起源。