Lithium Diisopropylamide-Mediated Reactions of Imines, Unsaturated Esters, Epoxides, and Aryl Carbamates: Influence of Hexamethylphosphoramide and Ethereal Cosolvents on Reaction Mechanisms
作者:Yun Ma、David B. Collum
DOI:10.1021/ja074554e
日期:2007.11.28
Several reactions mediated by lithium diisopropylamide (LDA) with added hexamethylphosphoramide (HMPA) are described. The N-isopropylimine of cyclohexanone lithiates via an ensemble of monomer-based pathways. Conjugate addition of LDA/HMPA to an unsaturated ester proceeds via di- and tetra-HMPA-solvated dimers. Deprotonation of norbornene epoxide by LDA/HMPA proceeds via an intermediate metalated epoxide
Structure and reactivity of lithium diisopropylamide (LDA) in hydrocarbon solutions. Formation of unsolvated ketone, ester, and carboxamide enolates
作者:Yong Joo Kim、Max P. Bernstein、Angela S. Galiano Roth、Floyd E. Romesberg、Paul G. Williard、David J. Fuller、Aidan T. Harrison、David B. Collum
DOI:10.1021/jo00014a019
日期:1991.7
Enolization of ketones, tert-butyl esters, and carboxamides by solvent-free lithium diisopropylamide (LDA) in hexane or toluene are described. Enolates are isolated as spectroscopically pure, white (often crystalline) solids. Solubilities of the enolates in hexane range from highly soluble to completely insoluble. Enolizations of aldehydes, methyl esters, and acetone afford complex mixtures. Analysis of [Li-6]LDA and [Li-6, N-15]LDA in hexane by Li-6 and N-15 NMR spectroscopy show evidence of an equilibrium mixture of at least three cyclic oligomers.