Superacidic Activation of Quinoline and Isoquinoline; Their Reactions with Cyclohexane and Benzene¹

Quinoline (1) and isoquinoline (2), upon activation by strong acids, lead to intermediate N,C-diprotonated dications, which are involved in reactions with weak nucleophiles. Thus, 1 and 2 undergo selective ionic hydrogenation with cyclohexane in CF3SO3H−SbF5, HBr−AlBr3−CH2Br2, or HCl−AlCl3−CH2Cl2 acid systems to give their 5,6,7,8-tetrahydro derivatives. They also readily condense with benzene in the presence of HBr−AlBr3 or HCl−AlCl3 to provide 5,6,7,8-tetrahydro-5,7-diphenylquinoline (10) and 5,6,7,8-tetrahydro-6,8-diphenylisoquinoline (12), respectively.