Synthesis of a C70 Fragment Buckybowl C28H14 from a C60 Fragment Sumanene

A C70 fragment (1) (C28H14) was synthesized by conversion of a C60 fragment sumanene, via ring expansion and annulation in 3 steps, the key step being the Wagner–Meerwein rearrangement of a five-membered ring to a six-membered one. Both theoretical and experimental investigations exhibited the shallower bowl structure of 1, resulting in the lower bowl inversion barrier than sumanene. It was also revealed that the indenopyrene skeleton largely contributed to the physical properties of 1.