Mixed Aggregates of an Alkyl Lithium Reagent and a Chiral Lithium Amide Derived from N‑Ethyl‑O‑triisopropylsilyl Valinol

The crystal structure of a mixed aggregate containing lithiated (S)-N-ethyl-3-methyl-1-(triisopropylsilyloxy)­butan-2-amine derived from (S)-valinol and cyclopentyllithium is determined by X-ray diffraction. The mixed aggregate adopts a ladder structure in the solid state. The ladder-type mixed aggregate is also the major species in a toluene-d8 solution containing an approximately 1:1 molar ratio of the lithiated chiral amide to cyclopentyllithium. A variety of NMR experiments including diffusion-ordered NMR spectroscopy (DOSY) with diffusion coefficient-formula (D-FW) weight correlation analyses and other one- and two-dimensional NMR techniques allowed us to characterize the complex in solution. Solution state structures of the mixed aggregates of n-butyl, sec-butyllithium, isopropyllithium with lithiated (S)-N-ethyl-3-methyl-1-(triisopropylsilyloxy)­butan-2-amine are also reported. Identical dimeric, ladder-type, mixed aggregates are the major species at a stoichiometric ratio of 1:1 lithium chiral amide to alkyllithium in toluene-d8 solution for all of the different alkyllithium reagents.

本研究通过X射线衍射解析了由(S)-缬氨醇与环戊基锂衍生得到的锂化(S)-N-乙基-3-甲基-1-(三异丙基硅氧基)丁-2-胺混合聚集体的晶体结构。该混合聚集体在固态下呈现梯状结构。当锂化手性酰胺与环戊基锂的摩尔比约为1:1时，该梯状混合聚集体同样是氘代甲苯-d8（toluene-d8）溶液中的主要存在物种。本研究通过多种核磁共振实验手段——包括结合扩散系数-式量（D-FW）相关性分析的扩散排序核磁共振谱（diffusion-ordered NMR spectroscopy，DOSY）以及其他一维、二维核磁共振技术——对溶液中的该复合物进行了表征。本文还报道了正丁基锂、仲丁基锂、异丙基锂分别与锂化(S)-N-乙基-3-甲基-1-(三异丙基硅氧基)丁-2-胺形成的混合聚集体的溶液态结构。对于所有不同的烷基锂试剂，当手性酰胺锂与烷基锂的化学计量比为1:1时，氘代甲苯-d8溶液中的主要存在物种均为相同的二聚体梯状混合聚集体。