Superacid-catalyzed preparation of aryl-substituted piperidines via dicationic electrophiles

The electrophilic chemistry of 1,2,3,6-tetrahydropyridines has been studied in the Bronsted superacid, CF3SO3H (triflic acid). The 1,2,3,6-tetrahydropyridines react with arenes to give aryl-substituted piperidines. It is proposed that the reactions occur through dicationic electrophilic intermediates. Depending upon substituents, either 1,4-dications or 1,3-dications are formed. The dicationic intermediates react with moderately deactivated arenes, such as o-dichlorobenzene.