Catalytic Alkylation of 2-Aryl-2-oxazoline-4-carboxylic Acid Esters Using Cyclopeptoids; Newly Designed Phase-Transfer Catalysts

Abstract

Nonionic, chiral macrocyclic peptoids are efficient phase-transfer catalysts in the C-4 enantioselective alkylation of 2-[4-(trifluoromethyl)phenyl]-2-oxazoline-4-carboxylic acid esters. Screening of the structural features of cyclic peptoids, namely the ring size, symmetry elements­, number of proline residues, and substituents on the side chains, showed that the alternated <i>N</i>-(4-methoxybenzyl)glycine/<sc>l</sc>-proline cyclohexapeptoid is the optimal catalyst (good yields and up to 75% ee) for the stereocontrolled construction of α-alkylated serine <i>tert</i>-butyl esters.