Theoretical Mechanistic Investigation of the Dynamic Kinetic Resolution of N-Protected Amino Acid Esters using Phase-Transfer Catalysts.

A detailed theoretical mechanistic investigation on the dynamic kinetic resolution of N-protected amino acid esters using phase-transfer catalysts is described. Semiautomatic exhaustive conformation search of transition state (TS)-like structures were carried out using the ConFinder program and the pseudo-TS conformational search (PTSCS) method. This conformational search method successfully provided reasonable TS structures for determining the stereoselectivity in the asymmetric base hydrolysis of hexafluoroisopropyl (HFIP) esters as well as the racemization mechanism.

Enantioselective Protonation of Enol Esters with Bifunctional Phosphonium/Thiourea Catalysts.

Bifunctional phosphonium/thioureas derived from tert-leucine behaved as highly selective catalysts for enantioselective protonation of enol esters, providing α-chiral ketones in yields of up to 99% with high enantioselectivities (up to 98.5:1.5 er).