Solution Structures of Lithium Amino Alkoxides Used in Highly Enantioselective 1,2-Additions

Abstract

Lithium ephedrates and norcarane-derived lithium amino alkoxides used to effect highly enantioselective 1,2-additions on large scales have been characterized in toluene and tetrahydrofuran. The method of continuous variations in conjunction with 6Li NMR spectroscopy reveals that the lithium amino alkoxides are tetrameric. In each case, low-temperature 6Li NMR spectra show stereoisomerically pure homoaggregates displaying resonances consistent with an S4-symmetric cubic core rather than the alternative D2d core. These assignments are supported by density functional theory computations and conform to X–ray crystal structures. Slow aggregate exchanges are discussed in the context of amino alkoxides as chiral auxiliaries.

Solid-State and Solution Structures of Glycinimine-Derived Lithium Enolates

“…11 However, enolates 1a or 3a with excess [ 6 Li, 15 N]LiHMDS in neat toluene afford—in addition to the homoaggregates discussed below—two 6 Li doublets consistent with substructure 13 likely derive from ladder 14 . 12,13 …”

Transition‐Metal‐Free Heterobiaryl Synthesis via Aryne Coupling

“…The previous investigation evaluating the effect of ligands clearly underlined influences of such compounds on the reactivity of organolithiums. [44] In this context, "salt effects" have attracted significant interest in recent years, leading to comprehensive spectroscopic and theoretical investigations, [71][72][73][74][75][76][77][78][79][80][81] more specifically in organolithium chemistry where the effects of lithium halides are commonly encountered. [82][83][84][85][86][87][88][89][90][91][92][93][94][95] Lithium salts are undoubtedly among the most widely studied salts, being ubiquitous in a large number of lithiation reactions -either because they are generated in the reaction, or because they are involuntarily brought by a contaminated commercial source.…”

My maize and blue brick road to physical organic chemistry in materials

“…1 ). We recruited physics graduate student Gil Toombes to help us fit the data using an iterative parametric method and what emerged was a beautiful story [ 3 – 5 ] (and method) that is still being used to determine the aggregation state of lithium enolates [ 6 – 9 ] and alkoxides [ 10 – 13 ]. From Dave, I learned a tremendous amount about being a scientist.…”