960197-75-5Relevant academic research and scientific papers
1,4-addition of lithium diisopropylamide to unsaturated esters: Role of rate-limiting deaggregation, autocatalysis, lithium chloride catalysis, and other mixed aggregation effects
Ma, Yun,Hoepker, Alexander C.,Gupta, Lekha,Faggin, Marc F.,Collum, David B.
, p. 15610 - 15623 (2010)
Lithium diisopropylamide (LDA) in tetrahydrofuran at -78 °C undergoes 1,4-addition to an unsaturated ester via a rate-limiting deaggregation of LDA dimer followed by a post-rate-limiting reaction with the substrate. Muted autocatalysis is traced to a lithium enolate-mediated deaggregation of the LDA dimer and the intervention of LDA-lithium enolate mixed aggregates displaying higher reactivities than LDA. Striking accelerations are elicited by 1.0 mol % LiCl. Rate and mechanistic studies have revealed that the uncatalyzed and catalyzed pathways funnel through a common monosolvated-monomer-based intermediate. Four distinct classes of mixed aggregation effects are discussed.
Lithium diisopropylamide-mediated reactions of imines, unsaturated esters, epoxides, and aryl carbamates: Influence of hexamethylphosphoramide and ethereal cosolvents on reaction mechanisms
Ma, Yun,Collum, David B.
, p. 14818 - 14825 (2008/09/17)
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 diand tetra-HMPA-solvated dimers. Deprotonation of norbornene epoxide by LDA/HMPA proceeds via an intermediate metalated epoxide as a mixed dimer with LDA. Ortholithiation of an aryl carbamate proceeds via a mono-HMPA-solvated monomer-based pathway. Dependencies on THF and other ethereal cosolvents suggest that secondary-shell solvation effects are important in some instances. The origins of the inordinate mechanistic complexity are discussed.
