Superacidic and HUSY-zeolite activation of 1,3-indandione: reactions with benzene and cyclohexane

1,3-Indandione (1) readily condenses with benzene and undergoes selective ionic hydrogenation with cyclohexane when activated by superacids, such as CF₃SO₃H, AlCl₃ and AlBr₃ to give 3,3-diphenyl-1-indanone (4) and 1-indanone (7), respectively. Combination of these reactions in ‘one-pot’ yields 3-phenyl-1-indanone (5). In addition, similar reactions have been carried out using the regenerable solid acid, HUSY-zeolite, providing an effective excess of acidic sites. The mechanism of these reactions, with potential involvement of superelectrophilic dicationic intermediates, is discussed.