Synthesis and asymmetric polymerization of chiral maleimides bearing an aza crown ether

Abstract

Chiral N-substituted maleimide derivatives bearing L-phenylalanine- or L-leucine-introduced aza crown ether ((S)-A15C5PAMI, (S)-A15C5LMI) were synthesized from maleic anhydride, corresponding amino acids and aza crown ether, and polymerized with an organometal/chiral ligand. The number-average-molecular weights and the specific optical rotations of the polymers were 700–5600 and −105.8° to −38.3°, respectively. The specific optical rotations of all polymers tended to a positive direction, compared with model compounds ((S)-A15C5PASI ([α]435=−218.1°), (S)-A15C5LSI ([α]435=−215.1°)). Asymmetric inductions in the main chains of the polymers were investigated by the measurements of specific optical rotation, circular dichroism. Asymmetric anionic homopolymerizations of (S)-(–)-N-maleoyl-L-leucine-aza-15-crown-5 ((S)-A15C5LMI) and (S)-(–)-N-maleoyl-L-phenylalanine-aza-15-crown-5 ((S)-A15C5PAMI) were carried out with chiral anionic initiator consisting of organometal and chiral ligand to obtain optically active polymers. Chiroptical properties and structures of the polymers obtained were analyzed by circular dichroism, ultraviolet, nuclear magnetic resonance and gel permeation chromatography measurements. The additional effects of (R)-cyclohexylethylamine (to the obtained poly((S)-A15C5LMI) were investigated.