Oxyfunctionalization of Non-Natural Target by Dioxiranes. Efficient Oxidation of Buckminsterfullerene C60 with Methyl(trifluoromethyl)dioxirane

By employing methyl(trifluoromethyl)dioxirane (Ib), the stepwise oxyfunctionalization of C-60 can be carried out with high conversions (>90%) under mild conditions (0 degrees C); the products have been compared with those produced by the oxidation of C-60 with m-chloroperoxybenzoic acid. Along with the previously characterized oxide C60O, a wider set of higher oxidation products is obtained by using Ib; among these, regioisomeric dioxides C60O2 are isolated in good overall yield (40%). One of the dioxides is predominant (yield 23%), corresponding to a C-8-symmetry dioxide previously well characterized and presenting the epoxide functionalities in close proximity over the 6:6 ring junctions. The oxidation with dioxirane 1b also produces sufficient quantities of trioxides, so that mixtures of C60O3 regioisomers can be isolated. The main trioxide fraction was found amenable to spectroscopic characterization; the C-13 NMR spectra indicates that the sample consists of two possible regioisomers, one having C-8, and the other C-2 symmetry. In both, the three epoxide rings are assembled over 6:6 ring junctions and in close proximity to each other; this shows that, in the ensuing sequential O-transfers from the dioxirane to the fullerene framework, the 6:6 carbon-carbon double bonds adjacent to an existing epoxide functionality are more easily oxidized. The whole of the spectroscopic data indicate that the fullerene core remains intact and no rupture of the cage occurs following oxidation at the trioxide level.