Groundwork for a rational synthesis of C60: cyclodehydrogenation of a C60H30 polyarene.

A C60H30 polycyclic aromatic hydrocarbon (PAH) that incorporates all 60 carbon atoms and 75 of the 90 carbon-carbon bonds required to form the fullerene C60 has been synthesized in nine steps by conventional laboratory methods. Laser irradiation of this C60H30 PAH at 337 nanometers induces hydrogen loss and the formation of C60, as detected by mass spectrometry. A specifically labeled [13C3]C60H30 retains all three 13C atoms during the cage formation process. A structurally related C48H24 PAH that lacks the three peripheral benzene rings cannot be transformed into C60, whereas the next higher homolog, a C80H40 PAH, degrades to the C60H30 PAH, which then loses hydrogen to give [60]fullerene. These control experiments verify that the C60 is formed by a molecular transformation directly from the C60H30 PAH and not by fragmentation and recombination in the gas phase.