The diethylzinc–<scp>L</scp>‐α‐amino acid systems as catalysts for the asymmetric‐selection polymerization of propylene oxide

Abstract

Abstract The binary systems consisting of equimolar amounts of diethylzinc and L ‐α‐amino acids were found to be effective as catalysts for the asymmetric‐selection polymerization of propylene oxides. Various L ‐α‐amino acids were compared, in order to investigate the influence of the spatial character of the asymmetric center of catalysts on their efficiencies for asymmetric selection. It was found that all the L ‐α‐amino acids investigated allow ( – )‐propylene oxide to polymerize preferentially over the (+) enantiomer, irrespective of the sign of their specific rotations, [α] D . For each amino acid the [α] D value of recovered monomer was proportional to –1n (1 – x ), where x is the extent of polymerization. The proportionality factor, which may be regarded as a measure of the relative asymmetric‐selection efficiencies of catalysts, was found to parallel the bulkiness of the alkyl group attached to the asymmetric carbon atom of the amino acids used.