Unexpected Formation of Pyrazoline-Fused Metallofullerenes from the Multicomponent Cascade Reaction of Sc₃N@I_h‑C₈₀ with Tetrazines, Water, and Oxygen

The multicomponent cascade reaction of Sc₃N@I_h-C₈₀ with 3,6-di­(pyridin-2-yl)-1,2,4,5-tetrazines, water, and oxygen unexpectedly affords the pyrazoline-fused Sc₃N@I_h-C₈₀ derivatives. The obtained endohedral metallofullerene derivatives have been characterized by various spectral means, and their structures have been unambiguously established by single-crystal X-ray crystallography. A possible reaction mechanism via a complicated sequence of Diels–Alder reaction, retro Diels–Alder reaction, hydration, rearrangement, and dehydrogenation processes is proposed for the formation of pyrazoline-fused metallofullerenes.