Irradiation of cyclic 1,3-diones (1a and 2a) with C-60 in benzene leads to formation of two fused furanylfullerenes, one achiral (3) and the other chiral (4), as opposed to the expected De Mayo cyclooctane-1,3-dione addition product. The same products are obtained when 1,3-diones are replaced with trimethylsilyl-protected diones (1b and 2b). The adduct structures were characterized by MS (ESI and MALDI), IR, UV, H-1 NMR, C-13 NMR, and He-3 NMR spectroscopy. These fullerene adducts presumably are formed after initial [2 + 2] photocycloaddition, followed by either intermolecular oxidation of the cyclobutyl intermediates (5-8) by O-1(2) to form 3 or intramolecular oxidation of the appended group by the triplet fullerene moiety of 5-8 to form 4.