Asymmetric Phase-Transfer Catalysis

The asymmetric alkylation of protected amino acids by benzyl and allyl halides using asymmetric phase-transfer-catalysis (PTC) has received much attention in the past decade.  The groups of Corey (J Am Chem Soc, 1998, 120, 13000; 1997, 119 12414) and Lygo (Tetrahedron Lett, 1999, 40, 8671, 1325, 1389; 1997, 38, 8595) have used anthracene derived salts of cinchona alkaloids rather than the original benzyl salts used by O’Donnell and others, giving increased ee's.  A Korean group (Jew S-S et al, Org Lett, 2002, 4, 4245) has now found that ortho fluorine substituents on the benzyl groups can increase the ee.