Photocycloaddition of Cyclic 1,3-Diones to C60

Irradiation of cyclic 1,3-diones (1a and 2a) with C60 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, 1H NMR, 13C NMR, and 3He NMR spectroscopy. These fullerene adducts presumably are formed after initial [2 + 2] photocycloaddition, followed by either intermolecular oxidation of the cyclobutyl intermediates (58) by 1O2 to form 3 or intramolecular oxidation of the appended group by the triplet fullerene moiety of 58 to form 4.