Dienyl, allylic dications

Benzene-derived dienyl, allylic dications 239 Fluorenyl dications 240... 

It was also of interest to generate the related symmetric primary benzylic trication. However, the ionization of the 2,4,6-tris(chloromethyl)mesitylene (112) in excess SbF5/S02ClF at -78°C gave apparently only the dienylic allylic dication Lewis acid-base complex (113). The unionized chloromethyl carbon displayed a relatively deshielded NMR absorption, 35.3, indicative of a weak Lewis acid-base interaction. The terminal methylene carbons of the dienylic system showed a 8 C of 197.7 and the terminal carbons of the allylic system displayed a 8 C of 194.8, quite similar to that of the previously described dienylic allylic dications, 107 and 108. 

The dications display NMR spectra, which are very similar to those of allylic carbocations. The terminal carbons of the dienylic and the allylic systems of the carbodications 107 and 108 show between 192 and 198, characteristic of the typical allylic carbocations. The IGLO-calculated chemical shifts closely match with those of the experimentally observed values for these carbodications. 

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