Preparation of an enantioenriched product from achiral or racemic starting materials, such that one enantiomer predominates, is enantioselective synthesis. The stereochemical bias may come from a chiral catalyst, a chiral reagent, or a chiral auxiliary that is later removed; the defining outcome is unequal formation of the two mirror-image products. Catalytic enantioselective construction of quaternary carbon stereocenters is a stringent instance in which the new stereogenic carbon bears four non-hydrogen substituents [1]. Related methods create all-carbon quaternary stereogenic centers in acyclic frameworks, where conformational flexibility makes facial discrimination more demanding [2]. Phase-transfer catalysis of alkylation of achiral Schiff-base glycine esters produces enantioenriched α-amino acids and exemplifies reagent- or catalyst-controlled enantioselective C–C bond formation at a prochiral enolate [3]. The concept names the synthetic objective and its stereochemical result, whereas enantioselective catalysis names the catalytic means. Resolution of a racemate is not enantioselective synthesis of that racemate’s constituents, because the stereocenters already exist before separation.
- enantioselective synthesis
- asymmetric synthesis
- quaternary stereocenters
- chiral products
Asymmetric Synthesis and Catalysis • Organic Chemistry • Chemistry • Physical Sciences
References
- Kyle W. Quasdorf; Larry E. Overman; Catalytic enantioselective synthesis of quaternary carbon stereocentres. Nature 2014, 516, 181-191, 10.1038/nature14007.
- Jaya Prakash Das; Ilan Marek; Enantioselective synthesis of all-carbon quaternary stereogenic centers in acyclic systems. Chem. Commun. 2011, 47, 4593-4623, 10.1039/c0cc05222a.
- Martin J. O'Donnell; The Enantioselective Synthesis of α-Amino Acids by Phase-Transfer Catalysis with Achiral Schiff Base Esters. Acc. Chem. Res. 2004, 37, 506-517, 10.1021/ar0300625.