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 N-(4-methoxybenzyl)glycine/l-proline cyclohexapeptoid is the optimal catalyst (good yields and up to 75% ee) for
the stereocontrolled construction of α-alkylated serine tert-butyl esters.
Key words
organocatalysis - asymmetric catalysis - phase-transfer catalysis - peptidomimetics
- cyclopeptoids - α,α-dialkyl-α-amino acid