Benzannulated Double Aza[9]helicenes: Synthesis, Structures, and (Chir)optical Properties

Abstract

AbstractA benzannulated double aza[9]helicene 1 was successfully synthesized via a one‐pot oxidative fusion reaction. 1 was derivatized to N‐alkylated double aza[9]helicene 1‐Et and 1‐Bu, whose structures were determined by X‐ray diffraction analysis. 1‐Et and 1‐Bu exhibited red‐shifted absorption and fluorescence spectra compared to single aza[9]helicene. The double aza[9]helicenes were expected to have two different conformers. Consistent with solid‐state structure, the chiral‐isomer was estimated to be more stable by 16 kcal/mol relative to meso‐isomer. Indeed, enantiomers of 1‐Et and 1‐Bu were optically resolved by HPLC and showed mirror‐imaged CD and CPL spectra with the CPL brightness up to 19.2 M−1cm−1 for 1‐Bu.