Synthesis of Stable Derivatives of C₆₂:  The First Nonclassical Fullerene Incorporating a Four-Membered Ring

A rational synthetic approach to the first four-membered ring-containing derivatives of C₆₂ is reported. They were synthesized by an inverse electron demand Diels−Alder reaction of 3,6-diaryl-1,2,4,5-tetrazines with C₆₀ in o-dichlorobenzene, followed by visible light irradiation at reflux. The structure of these nonclassical fullerenes derivatives was determined by X-ray single-crystal diffraction.