Lithium enolates constitute one of he most important classes of reactive intermediate in organic synthesis. The pharmaceutical industry uses these reagents frequently and on very large scales. In this proposal we describe efforts to understand the underlying chemistry of the most important reactions of lithium enolates. With methods to establish solution structures that dominated the first funding period largely developed, structural studies will be more targeted in support of mechanistic studies. In the most general sense, we will examine how solvation and aggregation influence reactivity. The mechanistic investigations will focus on specific classes of reaction-case studies-that include: (1) aza-aldol condensations;(2) O-silylations;(3) alkylations;(4) acylations;(5) [2,3]- and [3,3]-sigmatropic rearrangements;and (6) nucleophilic aromatic substitutions (SNAr). A uniquely integrated approach based on a combination of NMR spectroscopy, solution kinetics, and computational chemistry will develop an understanding of the mechanistic principles and how to control reactivity and selectivity. By bringing synthetic organic, physical organic, analytical, and computational chemistry together under one roof, we reveal the consequences of solvation and aggregation with an unprecedented clarity.
Project Narrative Lithium enolates are reactive intermediates used by other academic and pharmaceutical process chemistry laboratories on a daily basis around the globe. Our mechanistic studies described herein are designed to understand and improve their efficacy. The project originated from collaboration with Sanofi-Aventis to develop anti-asthmatics. The proposed funding period includes a collaboration with Amgen as part of their program to synthesize treatments for colorectal cancer.
|Ma, Yun; Mack, Kyle A; Liang, Jun et al. (2016) Mixed Aggregates of the Dilithiated Koga Tetraamine: NMR Spectroscopic and Computational Studies. Angew Chem Int Ed Engl 55:10093-7|
|Tallmadge, Evan H; Jermaks, Janis; Collum, David B (2016) Structure-Reactivity Relationships in Lithiated Evans Enolates: Influence of Aggregation and Solvation on the Stereochemistry and Mechanism of Aldol Additions. J Am Chem Soc 138:345-55|
|Jin, Kyoung Joo; Collum, David B (2015) Solid-State and Solution Structures of Glycinimine-Derived Lithium Enolates. J Am Chem Soc 137:14446-55|
|Tallmadge, Evan H; Collum, David B (2015) Evans Enolates: Solution Structures of Lithiated Oxazolidinone-Derived Enolates. J Am Chem Soc 137:13087-95|
|Han, Yifeng; Ma, Yun; Keresztes, Ivan et al. (2014) Preferential geminal bis-silylation of 3,4-benzothiophane is caused by the dominance of electron withdrawal by R3Si over steric shielding effects. Org Lett 16:4678-9|
|Tomasevich, Laura L; Collum, David B (2014) Method of continuous variation: characterization of alkali metal enolates using Â¹H and Â¹â¹F NMR spectroscopies. J Am Chem Soc 136:9710-8|
|Bruneau, Angela M; Liou, Lara; Collum, David B (2014) Solution structures of lithium amino alkoxides used in highly enantioselective 1,2-additions. J Am Chem Soc 136:2885-91|
|Renny, Joseph S; Tomasevich, Laura L; Tallmadge, Evan H et al. (2013) Method of continuous variations: applications of job plots to the study of molecular associations in organometallic chemistry. Angew Chem Int Ed Engl 52:11998-2013|
|Ma, Yun; Stivala, Craig E; Wright, Ashley M et al. (2013) Enediolate-dilithium amide mixed aggregates in the enantioselective alkylation of arylacetic acids: structural studies and a stereochemical model. J Am Chem Soc 135:16853-64|
|Tomasevich, Laura L; Collum, David B (2013) Structure determination using the method of continuous variation: lithium phenolates solvated by protic and dipolar aprotic ligands. J Org Chem 78:7498-507|
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