Chemistry of Anthracene-Acetylene Oligomers XV. Synthesis, Structures, and Dynamic Behavior of Chiral Anthrylene Ethynylene Cyclic Tetramers and Related Derivatives and Resolution of Enantiomers

A cyclic arylene-ethynylene tetramer with a 1,5-anthrylene unit and a cramp moiety consisting of three anthrylene units and its derivatives with a 1,4-phenylene, 1,5-naphthylene, or 2,6 di-t-butyl-1,5-naphthylene unit were synthesized by macrocyclization with Sonogashira coupling. Except for the 1,4-phenylene compound, these cyclic compounds take the chiral C-2 structure with parallel orientation of the two arylene units, as revealed by X-ray analysis and DFT calculation at the M05/3-21G level. The enantiomers of 1,5-anthrylene and 2,6 di-t-butyl-1,5-naphthylene compounds were resolved by chiral HPLC and their rotational barriers were determined to be 114 and >146 kJ mol(-1), respectively, by classical kinetics. These high barriers are in contrast to the facile racemization or topomerization in the other compounds. These kinetic data of the rotation of arylene units about the acetylene axes are discussed in terms of steric hindrance based on molecular structures. The electronic spectra of the cyclic compounds and the chiroptical properties of the resolved samples were also measured.