Department of Chemistry and Chemical Biology Baker Laboratory, Cornell University , Ithaca, New York 14853-1301, United States.
J Am Chem Soc. 2017 Jan 25;139(3):1233-1244. doi: 10.1021/jacs.6b11354. Epub 2017 Jan 12.
Lithium hexamethyldisilazide (LiHMDS)-mediated enolization of (+)-4-benzyl-3-propionyl-2-oxazolidinone in THF-hydrocarbon mixtures shows unusual sensitivity to the choice of hydrocarbon cosolvent (hexane versus toluene) and to isotopic labeling. Four mechanisms corresponding to monosolvated monomers, trisolvated dimers, octasolvated monomers, and octasolvated dimers were identified. Even under conditions in which the LiHMDS monomer was the dominant observable form, dimer-based metalation was significant. The mechanism-dependent isotope and cosolvent effects are discussed in the context of ground-state stabilization and transition-state tunneling.
六甲基二硅叠氮化锂（LiHMDS）介导的（+）-4-苄基-3-丙酰基-2-恶唑烷酮在 THF-碳氢混合物中的烯醇化对碳氢混合溶剂（己烷与甲苯）和同位素标记的选择表现出异常的敏感性。鉴定出了四种相应的机理，分别为单溶剂化单体、三溶剂化二聚体、八溶剂化单体和八溶剂化二聚体。即使在 LiHMDS 单体是主要可观察形式的条件下，基于二聚体的金属化作用也很显著。讨论了基于机理的同位素和混合溶剂效应，涉及到基态稳定化和过渡态隧穿。
