Reactions on a 1,2-Dicarbonyl Moiety of a Fullerene Skeleton.

A 1,2-dicarbonyl moiety on a cage-opened fullerene skeleton is one of suitable building blocks for the further derivatization. Herein, we discuss the chemical transformation of a 1,2-dicarbonyl compound into β-oxo-phosphorus ylide, acid anhydride, and α-methylene carbonyl derivatives. Despite possessing a sterically small methylene unit in the last one, the release of an encapsulated water molecule was significantly supressed whereas the β-oxo-phosphorus ylide bearing three bulky p-tolyl groups on the P-atom enabled the faster insertion/release dynamics, implying the flexibility of the phosphonium substituent. The replacement of the carbonyl group with phosphorus ylide and methylene units largely varied electrochemical properties of the fullerene skeleton, likely arising from the anionic charge delocalized over the entire molecule and removal of an electron-withdrawable carbonyl group, respectively.