Approaches to open fullerenes:: A 1,2,3,4,5,6-hexaadduct of C60

Complete saturation of a single six-membered ring on fullerene C-60 has been achieved. The critical step in this first synthesis of a fully characterized 1,2,3,4,5,6-hexaadduct consisted of a remarkable double 5-exo-trig addition of alkoxyl radicals promoted by lead tetraacetate. Two possible opening pathways ([2+2+2] retrocycloadditions) for the newly synthesized compound were explored using quantum mechanical calculations. We found that the oxa bridges in the hexaadduct prevent ring opening through the retro[ 2+2+2] mechanism due to the high activation barrier and endothermicity of the reaction.