Chiral spherical aromatic amides: one-step synthesis and their stereochemical/chiroptical properties

Macrocyclic aromatic amides 2, in which the meta-positions of all four benzene rings are linked by tertiary amide bonds, were successfully synthesized by a one-step condensation reaction of two monomers using dichlorotriphenylphosphorane or triphenylphosphine/hexachloroethane (dehydration-condensation reagents for carboxy and amino groups), or LiHMDS (aminolysis for esters) as coupling reagents. Single crystal X-ray analyses of the N-methyl and N-ethyl derivatives were performed and revealed that each compound adopted a spherical structure with chirality because of the fixed axis rotation and combined polarity of the amide bonds. Enantiomers of each spherical macrocycle were separated by chiral column chromatography and showed mirror-imaged CD spectra to each other.