PHENACENES - A FAMILY OF GRAPHITE RIBBONS .2. SYNTHESES OF SOME [7]PHENACENES AND AN [11]PHENACENE BY STILBENE-LIKE PHOTOCYCLIZATIONS

It is proposed that members of the family of polycyclic aromatic compo unds with an extended phenanthrene-like structural motif be designated as [n]phenacenes, where n is the number of fused benzene rings. [n]Ph enacene molecules are related to layers of graphite in the way that ri bbons are related to sheets. In order to investigate the properties of [n]phenacenes as materials, methods for the syntheses of these molecu les have been developed that involve Wittig reactions and stilbene-lik e photocyclizations for the construction of carbon-carbon bonds. The s olubilities of the unsubstituted [n]phenacene molecules decrease drama tically with increasing n; [7]phenacene, the largest known example, me lts with decomposition at 565 degrees C and is essentially intractable for chemical investigation owing to its extreme insolubility. This so lubility problem was solved by incorporating alkyl substituents. 2,13- Di-n-pentyl[7]phenacene, 2,13-di-tert-butyl[7]phenacene, and 15,18-di- n-pentyl[7]phenacene (mp 325, 290, and 235 degrees C, respectively) we re synthesized and found to be moderately soluble compounds. As a firs t step in the exploration of the chemistry of larger phenacenes, 2,17, 21,24-tetra-n-pentyl[11]phenacene was synthesized.