TOPOLOGICALLY SPHERICAL MOLECULES - EFFICIENT SYNTHESIS OF C16-HEXAQUINACENE AND ITS LACK OF NEUTRAL HOMO-AROMATIC CHARACTER

The feasibility of gaining access to C16-hexaquinacene in eight steps from the domino Diels-Alder adduct S was explored. With lithium hydride and methyllithium, this diacid was transformed to the diacetyl derivative 6 whose methyl groups were σ bonded by formation of the dienolate at low temperature and oxidative coupling with Cu(II). Selenium dioxide oxidation of the resulting 1,4-cyclohexanedione ring in 9 gave the pivotal trienedione 10. When irradiated, 10 underwent efficient π2S + π2s closure to the caged diketone 12, a molecule ideally constructed stereoelectronically for ready cleavage of both of its 1,4-dicarbonyl systems. This transformation, which was achieved with zinc in hot acetic acid, produced 14 which was in turn converted to the title compound in three conventional steps. The electronic and structural properties of 4 are summarized, and a brief outline of preliminary reactions is given. © 1979, American Chemical Society. All rights reserved.