Lithium Enolates in the Enantioselective Construction of Tetrasubstituted Carbon Centers with Chiral Lithium Amides as Noncovalent Stereodirecting Auxiliaries
作者:Kai Yu、Ping Lu、Jeffrey J. Jackson、Thuy-Ai D. Nguyen、Joseph Alvarado、Craig E. Stivala、Yun Ma、Kyle A. Mack、Trevor W. Hayton、David B. Collum、Armen Zakarian
DOI:10.1021/jacs.6b11673
日期:2017.1.11
Lithium enolates derivedfrom carboxylic acids are ubiquitous intermediates in organic synthesis. Asymmetric transformations with these intermediates, a central goal of organic synthesis, are typically carried out with covalently attached chiral auxiliaries. An alternative approach is to utilize chiral reagents that form discrete, well-defined aggregates with lithium enolates, providing a chiral environment
Chemo- and Enantioselective Pd/B Hybrid Catalysis for the Construction of Acyclic Quaternary Carbons: Migratory Allylation of <i>O</i>-Allyl Esters to α-<i>C</i>-Allyl Carboxylic Acids
We describe herein the asymmetric synthesis of α-allyl carboxylic acids containing an α-quaternarystereocenter by a chiral hybrid catalyst system comprising palladium and boron complexes. The reaction proceeded through palladium-catalyzed ionization of α,α-disubstituted O-allyl esters for the generation of chiral π-allyl palladium complex as an electrophile, boron-catalyzed enolization of the carboxylate