Enantioselective homologation of helical architectures from fluorenones to phenanthrenones with enhanced circular dichroism.

The development of efficient synthetic methods to access optically pure helical chiral molecules is a central challenge in organic chemistry due to their unique photophysical properties and potential applications in chiral photonic devices. Conventional strategies often struggle to simultaneously install multiple chiral elements with high fidelity and are typically limited to synthesizing a single scaffold at a time. Here we show that a chiral Sc(III)-catalyzed ring-expansion of racemic helical fluorenones with α-diazo esters, enables the simultaneous synthesis of both optically enriched helical fluorenones and one-carbon-inserted helical phenanthrenones with high diastereo- and enantioselectivity. This process achieves simultaneous kinetic resolution and homologation, but also intriguing regioselectivity at the cases of un-symmetric ketones. Furthermore, the synthesized helical compounds exhibit significant chiroptical activity, with their circularly polarized absorption dissymmetry factors (gabs) showing a strong dependence on the position and steric nature of aryl substituents, and some derivatives also display circularly polarized luminescence (CPL).