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Lithiated Oppolzer Enolates: Solution Structures, Mechanism of Alkylation, and Origin of Stereoselectivity
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2022-12-19 , DOI: 10.1021/jacs.2c09341 Nathan M Lui 1 , Samantha N MacMillan 1 , David B Collum 1
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2022-12-19 , DOI: 10.1021/jacs.2c09341 Nathan M Lui 1 , Samantha N MacMillan 1 , David B Collum 1
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Camphorsultam-based lithium enolates referred to colloquially as Oppolzer enolates are examined spectroscopically, crystallographically, kinetically, and computationally to ascertain the mechanism of alkylation and the origin of the stereoselectivity. Solvent- and substrate-dependent structures include tetramers for alkyl-substituted enolates in toluene, unsymmetric dimers for aryl-substituted enolates in toluene, substrate-independent symmetric dimers in THF and THF/toluene mixtures, HMPA-bridged trisolvated dimers at low HMPA concentrations, and disolvated monomers for the aryl-substituted enolates at elevated HMPA concentrations. Extensive analyses of the stereochemistry of aggregation are included. Rate studies for reaction with allyl bromide implicate an HMPA-solvated ion pair with a +Li(HMPA)4 counterion. Dependencies on toluene and THF are attributed to exclusively secondary-shell (medium) effects. Aided by density functional theory (DFT) computations, a stereochemical model is presented in which neither chelates nor the lithium gegenion serves roles. The stereoselectivity stems from the chirality within the sultam ring and not the camphor skeletal core.
中文翻译：
锂化 Oppolzer 烯醇化物：溶液结构、烷基化机制和立体选择性的起源
基于樟脑磺胺的锂烯醇化物通俗地称为 Oppolzer 烯醇化物，通过光谱学、结晶学、动力学和计算方法进行检查，以确定烷基化机制和立体选择性的起源。溶剂和底物依赖性结构包括甲苯中烷基取代的烯醇化物的四聚体、甲苯中芳基取代的烯醇化物的不对称二聚体、THF 和 THF/甲苯混合物中的底物非依赖性对称二聚体、低 HMPA 浓度下的 HMPA 桥接三溶剂化二聚体，和在升高的 HMPA 浓度下芳基取代的烯醇化物的溶解单体。包括对聚合立体化学的广泛分析。与烯丙基溴反应的速率研究表明 HMPA 溶剂化离子对与+ Li(HMPA)4抗衡离子。对甲苯和 THF 的依赖完全归因于二级壳层（介质）效应。在密度泛函理论 (DFT) 计算的帮助下，提出了一种立体化学模型，其中螯合物和锂反离子均不发挥作用。立体选择性源于苏丹环内的手性，而不是樟脑骨架核心。
更新日期：2022-12-19
中文翻译：
锂化 Oppolzer 烯醇化物：溶液结构、烷基化机制和立体选择性的起源
基于樟脑磺胺的锂烯醇化物通俗地称为 Oppolzer 烯醇化物，通过光谱学、结晶学、动力学和计算方法进行检查，以确定烷基化机制和立体选择性的起源。溶剂和底物依赖性结构包括甲苯中烷基取代的烯醇化物的四聚体、甲苯中芳基取代的烯醇化物的不对称二聚体、THF 和 THF/甲苯混合物中的底物非依赖性对称二聚体、低 HMPA 浓度下的 HMPA 桥接三溶剂化二聚体，和在升高的 HMPA 浓度下芳基取代的烯醇化物的溶解单体。包括对聚合立体化学的广泛分析。与烯丙基溴反应的速率研究表明 HMPA 溶剂化离子对与+ Li(HMPA)4抗衡离子。对甲苯和 THF 的依赖完全归因于二级壳层（介质）效应。在密度泛函理论 (DFT) 计算的帮助下，提出了一种立体化学模型，其中螯合物和锂反离子均不发挥作用。立体选择性源于苏丹环内的手性，而不是樟脑骨架核心。
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