Building Cyclic Planar Chirality via Intermolecular [2+2] Photocycloaddition

Abstract

Planar–chiral compounds have garnered significant interest due to their unique stereochemical features and promising applications in asymmetric catalysis, materials science, and molecular recognition. To date, only a few representative classes have been discovered and synthesized, including planar-chiral cyclophanes, ferrocenes, and macrocyclic hosts such as pillararenes and calixarenes. The construction of novel planar-chiral architectures therefore continues to pose a formidable challenge. Herein, we present a simple but highly effective approach for constructing a new form of planar chirality through the formation of three-dimensional double-layered cyclic molecular architectures. Photocycloaddition of C=C double bonds embedded within benzo[b]thiophene 1,1-dioxide affords trans Z-type (Trans-1) and cis-∏-type (Cis-Rac-1) dimers. While Trans-1 is achiral owing to its central symmetry, Cis-Rac-1 adopts a distinctive bisplanar geometry that gives rise to an unprecedented type of planar chirality. The enantiomers of Cis-Rac-1 are successfully resolved via chiral high-performance liquid chromatography. Circular dichroism spectroscopy and single-crystal X-ray diffraction unequivocally confirm the planar–chiral nature of these enantiomers. Moreover, both experimental and computational results show that the planar chirality is highly stable, with a racemization barrier exceeding 35 kcal/mol. These findings establish a general and straightforward strategy for construction of planar chirality, opening new avenues for the design of planar–chiral functional materials.