Photocycloaddition of Cyclic 1,3-Diones to C<sub>60</sub>

Irradiation of cyclic 1,3-diones (<b>1a</b> and <b>2a</b>) with C<sub>60</sub> in benzene leads to formation of two fused furanylfullerenes, one achiral (<b>3</b>) and the other chiral (<b>4</b>), 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 (<b>1b</b> and <b>2b</b>). The adduct structures were characterized by MS (ESI and MALDI), IR, UV, <sup>1</sup>H NMR, <sup>13</sup>C NMR, and <sup>3</sup>He NMR spectroscopy. These fullerene adducts presumably are formed after initial [2 + 2] photocycloaddition, followed by either <i>intermolecular</i> oxidation of the cyclobutyl intermediates (<b>5</b>−<b>8</b>) by <sup>1</sup>O<sub>2</sub> to form <b>3</b> or <i>intramolecular</i> oxidation of the appended group by the triplet fullerene moiety of <b>5</b>−<b>8</b> to form <b>4</b>.