A new reaction of fullerenes: [2+2]-photocycloaddition of enones

We now report functionalization of C[sub 60] by [2 + 2] photocycloaddition of cyclic enones, allowing the simple preparation of a large new class of C[sub 60] derivatives. This is another application of a classic photochemical reaction which is widely used synthetically. The mechanistic features also are of considerable interest. We have shown (a) that the new technique of electrospray ionization mass spectrometry (ESI-MS) is a uniquely suitable tool for studying the reactions of fullerenes, (b) that a variety of functionally substituted derivatives of C[sub 60] can be prepared by [2 + 2] photocycloaddition to cyclic enones, and (c) that these adducts arise by the stepwise addition of enone triplets to the fullerenes. 29 refs., 1 fig.