Carboxonium-vinyl dication

There have been two reports involving gitonic superelectrophiles composed of carboxonium ions and vinylic carbocations in a 1,3-relationship. In the reaction of 3-phenylpropynoic acid (65) with benzene in superacid the novel carboxonium-vinyl dication 66 is generated, followed by reaction with benzene and then cyclization (eq 22).26a Likewise, the unsaturated amide (67) gives the cyclization product in high yields (70-97%) in very strong acids (polyphosphoric acid, CF3SO3H, Nation SAC-13, or HUSY eq 23).30... 

The carboxonium-vinylic dication (68) is considered the key intermediate leading to the cyclization product. The analogous vinylic dications (69-71) have also been generated in superacid.31 Each of the species exhibits high electrophilic reactivity. 

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