Photocycloaddition of Cyclic 1,3-Diones to C60

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, 1 H NMR, 13 C NMR, and 3 He 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 1 O 2 to form 3 or intramolecular oxidation of the appended group by the triplet fullerene moiety of 5 − 8 to form 4 .