Preparation and Isolation of Three Isomeric C70 Isoxazolines: Strong Deshielding in the Polar Region of C70

The C[sub 70] fullerene reacts with acetonitrile oxide and with 4-methoxybenzonitrile oxide to form a mixture of three isomeric monoadducts in addition to small amounts of di- and triadducts. The three isomeric monoadducts were separated and were found to result from 1,3-dipolar addition to 6-6 ring fusions of C[sub 70] at the 1,9 position and at the 7,8 position. The 1,9 addition occurs in two different modes, while addition at the 7,8 positions results in an unseparated D,L pair of isomers. Proton NMR indicates that the fullerene moiety is strongly deshielding and that the deshielding is stronger over the poles of the fullerene than over the sides. 74 refs., 5 figs.