Octahedrane cage in one step

When irradiated with ultraviolet light, the two benzene units of a diazacyclophane have been found to dimerize, forming a (CH)₁₂ framework known as an octahedrane in one step, as shown (J. Am. Chem. Soc., DOI: 10.1021/ja067350r). Although octahedrane itself was prepared more than a decade ago through a multistep synthesis, this is the first time that this carbon cage has been formed photochemically, according to a team led by Hideki Okamoto of Okayama University, in Japan. The researchers found that the analogous carbon-bridged cyclophane is "almost photochemically inert" and does not undergo this dimerization. The nitrogen-containing bridges seem to be key to the diazacyclophane's reactivity: They hold the benzene rings closer together, and the through-bond coupling between the -orbitals of the benzene rings and the bridge C-N -bonds probably make the rings interact more significantly in the excited state, the researchers explain.