Synthesis of Nitrogen-Doped Aza-Helicenes with Chiral Optical Properties.

Aza-helicenes are one of the most important series of heterohelicenes; herein, a series of novel aza-helicenes ( 5H , 6H , 6S , and 8S ) were prepared via Bischler-Napieralski cyclization, and the interconversion dynamic process of these aza-helicenes was revealed using density functional theory calculations. The novel nitrogen-doped [6]helicene ( 6H ) possesses a very high interconversion energy barrier of 36.0 kcal/mol. Two enantiomers of 6H were successfully resolved by high-performance liquid chromatography and showed desired chiral optical properties. 6H with chiral optical activity and lone electrons can be a potential candidate for chiral switches, which was demonstrated using the UV and circular dichroism spectra obtained upon titration with an acid and a base.