The exhaustive hydroboration of triquinacene ( 8) and C16-hexaquinacene (1) has been investigated and the pair of isomeric exo3 4-triols separated in both cases. Whereas 8 reacts with diborane to give 37% of the C^-symmetric product 10, 1 affords an amount of 3a (28%) closer to the statistical value of 25%. Because difficulties were encountered in the oxidation of 3a, the utility of triketone 4 as a possible precursor of dodecahedrane was not examined further. A four-step conversion of C16-hexaquinacenedione (26a) to monoketone 29 was developed.However, this compound was exceptionally susceptible to base-promoted enolization and therefore proved unreactive to homologation reagents designed to give the cyclopentenone 31. The chemical reactivity of 26a toward phosphonate reagents was investigated, and a number of homologated derivatives, e.g., 41, 45, and 47, were prepared. However, all attempts to accomplish transannular bond formation with compounds derived from these intermediates were unsuccessful. The diamines 62a and 63a also could not be bridged.C16-Hexaquinacene (1), a beautifully symmetric triene of highly convex topology, has played a pivotal role in the advancement of our understanding of neutral homoaromatic character.2 A second point of interest in this molecule is the relationship it bears to the pentagonal dodecahedrane (2).3,4 With its hexaquinane nature5 and ! 2
The conformationally rigid a-diketones 4-7 have been synthesized and their photoelectron (PE), absorption, and emission spectra recorded. Assignment of the first bands in the PE spectra is based upon correlation with related molecules and substantiated by MIND0/3 results. The first band (T; -n+) in the electronic spectra of 4-6 shows a hypsochromic shift through the series. This finding is explained in terms of interaction involving the T ; orbital of the CzOz fragment and the T orbital of the olefinic moiety in 4 and 5. This interpretation is supported by CNDO/S calculations.
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