Pagodane structure

FIGURE 17. Three isomers of Si2oH20 having the [10]prismane, pagodane, and dodecahedrane structures. Reprinted with permission from References 10. Copyright 1995 American Chemical Society... 

For pagodane-related carbon skeletons 4C/3e radical cations with tight and extended geometries could be established by spectroscopy (predominately EPR) and quantum chemical calculations at the DFT level of theory. Such structures resemble frozen stages of cycloadditions/cycloreversions on the hyper energy surface of the hole-catalyzed cyclobutane formation. 

Scheme 4.17 presents a couple of other strange-looking cationic species which were discovered in studies in a related field. In connection with the problem of dodecahedrane synthesis via the isomerization of pagodane 34 (cf. data in Schemes 4.10 and 4.11), Olah s and Prinzbach s groups engaged in studies of the behavior of pagodane derivatives under superacid conditions. Their hope was to force the cationic isomerization of 34 to 3. Despite all attempts, this route was unworkable. As a reward for these apparently futile efforts they were able to observe the unexpected formation of a very stable cationic species, the pagodane dication 55 (Scheme 4.17). The pattern of its NMR spectra combined with the nature of its quenching adduct 56, and the theoretical analysis of possible alternatives, enabled the authors to ascribe to this dication the unprecedented four-center/two-electron delocalized bis-homoaromatic structure.

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