Hemi-Labile Ligands in Organolithium Chemistry: Rate Studies of the LDA-Mediated α- and β-Metalations of Epoxides
Hemi-Labile Ligands in Organolithium Chemistry: Rate Studies of the LDA-Mediated α- and β-Metalations of Epoxides
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有机锂化学中的半不稳定配体：LDA 介导的环氧化物 α- 和 β- 金属化的速率研究
DOI：
10.1021/ja992166
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发表时间：
1999
影响因子：
15
通讯作者：
D. Collum
中科院分区：
文献类型：
--
作者：
Antonio Ramírez and;D. Collum
描述了二异丙基氨基锂（LDA）介导的环氧化物的α-和β-消除。LDA/n-BuOMe混合物和LDA/MeOCH 2CH 2NMe 2（LDA/3）混合物之间的比较揭示了被“半不稳定”氨基醚3溶剂化的LDA二聚体赋予显著的速率加速，改变基于单体和二聚体的金属化的相对功效，并影响α-和β-金属化之间的分配。LDA/n-BuOMe和LDA/3对外消旋氧化物的α-消除仅通过具有过渡结构[（R2 NLi）2（环氧化物）（配体）] π的基于二聚体的途径进行。LDA/n-BuOMe和LDA/3对四甲基环氧乙烷的β-消除仅通过具有过渡结构[（R2 NLi）（环氧化物）（配体）] π的基于单体的途径进行。顺式环辛烯环氧化物与LDA/3反应，得到两种产物：（1）由α-金属化和二聚体过渡结构[（R2 NLi）2（环氧）（配体）]取代得到的双环辛醇;（2）由单体过渡结构和二聚体过渡结构[（R2 NLi）2（环氧）（配体）]取代得到的2-环辛烯-1-醇。
Lithium diisopropylamide (LDA)-mediated α- and β-eliminations of epoxides are described. A comparison between LDA/n-BuOMe mixtures and LDA/MeOCH2CH2NMe2 (LDA/3) mixtures reveals that the LDA dimer solvated by the “hemi-labile” amino ether 3 imparts dramatic rate accelerations, alters relative efficacies of monomer- and dimer-based metalations, and influences the partitioning between α- and β-metalation. The α-elimination of exo-norbornene oxide by LDA/n-BuOMe and LDA/3 proceeds exclusively via a dimer-based pathway with a transition structure, [(R2NLi)2(epoxide)(ligand)]⧧. The β-elimination of tetramethylethylene oxide by LDA/n-BuOMe and LDA/3 proceeds exclusively via a monomer-based pathway with a transition structure, [(R2NLi)(epoxide)(ligand)]⧧. cis-Cyclooctene epoxide reacts with LDA/3 to give two products: (1) a bicyclooctanol derived from an α-metalation and a dimer-based transition structure, [(R2NLi)2(epoxide)(ligand)]⧧, and (2) 2-cycloocten-1-ol derived from both a monomer-based transition struc...