[60]Fullerene-Fused ζ-Lactones: Synthesis and Further Transformations

Novel and challenging [60]fullerene (C₆₀)-fused ζ-lactones, containing an eight-membered ring, have been successfully synthesized via palladium-catalyzed annulations of C₆₀ with 2-arylbenzoic acids. This approach employs a carboxyl-directed C-H activation strategy to facilitate lactone formation. The formed ζ-lactones undergo an unprecedented deoxygenative skeletal rearrangement in the presence of triflic anhydride to generate C₆₀-fluorenone conjugates. The assigned structures were confirmed by single-crystal X-ray diffraction. The C₆₀-fused ζ-lactones can be further electrochemically transformed into 1,2-hydrofullerenes. In addition, a representative ζ-lactone was efficiently employed as the third component in organic solar cells, resulting in an improvement in device performance.