Published on Web 10/20/2010
1,4-Addition of Lithium Diisopropylamide to Unsaturated Esters: Role of Rate-Limiting Deaggregation, Autocatalysis, Lithium Chloride Catalysis, and Other Mixed Aggregation Effects Yun Ma, Alexander C. Hoepker, Lekha Gupta, Marc F. Faggin, and David B. Collum* Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell UniVersity, Ithaca, New York 14853-1301 Received July 2, 2010; E-mail:
[email protected] Abstract: 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
