Synthesis, Chiral Resolution, and Optical Properties of 2,18‐Dihydoxy‐5,10,15‐trioxa[9]helicene.

Herein, we report a simple and efficient approach to synthesize a functionalized 2,18‐dimethoxy‐5,10,15‐trioxa[9]helicene. It was synthesized from simple phenol building blocks using two subsequent reactions namely oxidative coupling and dehydrative cyclization or palladium mediated cyclization. The molecular integrity of the helical core was determined by single‐crystal X‐ray diffraction and NMR techniques. Its crystal structure showed the spontaneous resolution which was attributed to the conglomerate formation of the same helical isomer via C−H⋅⋅⋅O and π⋅⋅⋅π or H⋅⋅⋅π interactions. Then, it was converted to racemic 2,18‐dihydoxy‐5,10,15‐trioxa[9]helicene. Enantiomers were separated on preparative HPLC with high optical purity (>99 % ee). Based on electronic circular dichroism, the absolute configurations of dextrorotary and levorotatory antipodes were assigned as P and M, respectively. We also studied the absorption, emission and chiroptical behavior of these helical compounds in the solution state. [ABSTRACT FROM AUTHOR]