Gitonic dication intermediates

The different chemistry of the dications 99 and 101 seems to reflect the superelectrophilic nature of the gitonic dication. It has also been shown that simple peptides may be multiply protonated in acids like FSOsH-SbFs, generally being protonated at the terminal amino group, the carboxyl group, and at the peptide bonds. In a study of the chemistiy of /V-tosylated phenylalanine derivatives, the diprotonated intermediate (103) was proposed in a reaction with superacid CF3SO3H (eq 33).42... 

Related classes of gitonic superelectrophiles are the previously mentioned protoacetyl dications and activated acyl cationic electrophiles. The acyl cations themselves have been extensively studied by theoretical and experimental methods,22 as they are intermediates in many Friedel-Crafts reactions. Several types of acyl cations have been directly observed by spectroscopic methods and even were characterized by X-ray crystal structure analysis. Acyl cations are relative weak electrophiles as they are effectively stabilized by resonance. They are capable of reacting with aromatics such as benzene and activated arenes, but do not generally react with weaker nucleophiles such as deactivated arenes or saturated alkanes. 

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