Chemistry of anthracene-acetylene oligomers. XVII. Synthesis, structure, and dynamic behavior of 1,8-anthrylene pentamers and hexamers with acetylene linkers

Three types of cyclic oligomers consisting of five or six 1,8-anthrylene units with acetylene linkers were synthesized by macrocyclization of the corresponding acyclic precursors with coupling reactions. DFT calculations at the M05/3-21G level revealed that the pentamers had a relatively rigid structure with strained alkyne carbons. Meanwhile, out of several possible conformers the hexamers preferred to take parallelogram-prism structures due to transannular π···π interactions, and conformational interconversions via rotation about the acetylene axes took place rapidly at room temperature. NMR spectra and electronic spectra are discussed on the basis of molecular structures. The enantiomers of the chiral hexamer with one diacetylene linker were resolved by chiral HPLC, and showed optical activity.