Step‐Wise Synthesis of Fullerenones Through Fullerene‐Mixed Peroxide Chemistry: Open‐Cage [60]Fullerenes With up to Six Carbonyl Groups on the Rim of the 18‐Membered Orifice

The previously reported open‐cage fullerene derivative C 60 (O) 2 (OO t Bu) 4 with two carbonyl groups was converted into an orifice‐expanded new compound with four carbonyl groups, two of which reacted with one water molecule to form hydrated hemiketals. Further orifice expansion and reduction led to the open‐cage derivative C 60 (O) 5 (OH) 4 with six carbonyl groups, one of which readily reacts with a water molecule to form a hydrated carbonyl group on the 18‐membered orifice. An analogous open‐cage derivative C 60 (O) 5 (OH) 2 Cl 2 was also obtained with five carbonyl groups and a dichloromethylene moiety. Selective cleavage of the tert‐butylperoxo groups plays a key role in the cage‐opening processes.