Electrosynthetic access to unsymmetrical oxaza[8]helicenes with high chiral stability and strong circularly polarized luminescence (CPL).

Abstract

Heterohelicenes are compelling chiral π-conjugated scaffolds for optoelectronic and chiral-photonic technologies because their helical frameworks and doped heteroatoms endow them with various photophysical, chiroptical, and electronic merits. However, unsymmetrical heterohelicenes remain rare, as their synthesis is often hindered by chemoselectivity and regioselective control. Here, we exploit the differential redox potentials of two coupling partners as a key player to achieve a chemo- and regioselective electrosynthetic access to a new family of unsymmetrical oxaza[8]helicenes. A controlled anodic sequence enables selective oxidative hetero-coupling followed by dehydrative cyclization, furnishing the extended [8]helical scaffold efficiently under mild, oxidant-free conditions. Structural analyses show retained aromaticity, increased helical distortion, and higher configurational stability (≈38 kcal/mol) relative to their oxaza[7]helicene analogues (<25 kcal/mol). After chiral HPLC separation, the enantiomers display mirror-image CD and strong solution CPL, with |g _lum | up to 2.6 × 10^-3 and fluorescence brightness up to 30.75 M^-1 cm^-1.