Cyclobishelicenes: Shape-Persistent Figure-Eight Aromatic Molecules with Promising Chiroptical Properties
Résumé
Cyclobis[n]helicenes (n = 3 or 5) are chiral D2-sym- metric p-conjugated macrocycles with stable lemniscular, or figure-eight, shapes. The conformational analysis of five dif- ferent cyclobis[n]helicenes revealed that these molecules can only exist as their lemniscular conformers with high barriers to enantiomerization (> 200 kJ/mol). The enantiomers of a cyclobis[5]helicene were resolved by HPLC and their un- usual chiroptical properties were attributed to the inherent chirality of their macrocyclic figure-eight.