Syntheses and Enantiomeric Resolution of Chiral Anthracene-Acetylene Cyclic Oligomers

Abstract

We studied structures and stereochemistry of two types of chiral anthracene-acetylene cyclic oligomers, which were synthesized by Sonogashira and Eglington couplings. The first structure is cyclic tetramers 1, where an 1,5-anthracene or naphthalene unit is connected by three 1,8- and 9,10-anthracene units. These compounds took C2 symmetric structures, and enantiomers of 1b and 1c were successfully resolved by chiral HPLC. The barrier to enantiomerization of 1b was determined to be 114 kJ/mol. The second structure is macrocyclic compound 2 with six anthracene units, which has unique D2 symmetric figure-eight structure. Enantiomers of 2 were also resolved by chiral HPLC, and underwent no racemization at 90 degrees C. These high barriers to racemization are discussed on the basis of the molecular rigidity and steric effects.