Diprotonated species, electrophilic reactivities

Among the reported distonic superelectrophiles, a significant number of ammonium-carboxonium dications and related species have been studied. It has been shown that these electrophiles show enhanced reactivities compared with monocationic carboxonium ions. For example, 4-piperidone (172) is diprotonated in superacidic CF3SO3H to give the distonic superelectrophile (173), which condenses with benzene in high yield (eq 59).56 In contrast, cyclohexanone forms the monocationic carboxonium (174) ion, but ion 174 is not sufficiently electrophilic to react with benzene (eq 60). 

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