Catalytic Enantioselective Synthesis of Planar-Chiral Cyclophanes via a Chiral Octahedral Cobalt(III)-Templated C–H Macrocyclization

The catalytic enantioselective synthesis of planar-chiral cyclophanes is a formidable challenge due to the entropic and stereoelectronic constraints inherent in macrocyclization. Herein, we report a strategy that employs a cobalt(II) precatalyst with a chiral salicyloxazoline (Salox) ligand to direct the assembly of these architectures. This approach relies on a precise coordination assembly mediated by a chiral Salox-cobalt(III) complex, which templates linear precursors into cyclization-competent chiral conformations, mitigating the entropic penalty and ensuring exclusive facial selectivity. A range of 12- to 24-membered planar-chiral cyclophanes are obtained in good yields (up to 94%) with excellent enantioselectivities (93 to >99% ee) through enantioselective intramolecular C-H macrocyclization. This method also provides direct access to a novel class of crown ethers featuring planar-chiral cyclophane architectures, which serve as effective templates for the diastereoselective synthesis of mechanically planar-chiral rotaxanes. Furthermore, the representative fluorogenic cyclophanes exhibit strong circularly polarized luminescence, showcasing their potential for chiral photonic materials.