Synthesis, structures, and properties of helically fused anthraquinones with unusually close carbonyl–carbonyl contacts

Kozue Morioka, Kan Wakamatsu, Eiji Tsurumaki, Shinji Toyota

Electron-deficient aromatic ketones consisting of three fused anthraq uinone units I [R = H, 2,4,6-Me3C6H2, 4-OC8H17C6H4] were synthesized by oxidation of the corresp onding fused anthracenes. X-ray anal. revealed that these compounds had nonplanar helical structures with unusual contacts, C=O···C=O 2.467 S, between the inner carbonyl groups. The role of n···π* interactions in the short contacts was evaluated using a noncovalent interaction plot and natural bond orbital anal. The dynamic process involving helical inversion was observed by the variable temperature 1H NMR measurement of a derivative with 2,4,6-trimethylphenyl groups, and the barrier was estimated to be 77 kJ mol-1. DFT calculations indicated that the helical inversion proceeded via a multistep mechanism. The characteristic spectroscopic and electrochem. data due to the electron-deficient anthraquinone units and the sterically congested carbonyl groups are discussed with the aid of DFT calculations

Chem. Eur. J.

28

1

e202103694

10.1002/chem.202103694