Bronsted Acid-Catalyzed Intramolecular Hydroarylation of β-Benzylstyrenes

Using triphenylmethylium tetrakis(pentafluorophenyl)borate as a convenient Bronsted acid precatalyst, beta-(alpha,alpha-dimethylbenzyl)styrenes are shown to cyclize efficiently to afford a variety of new indanes that possess a benzylic quaternary center. The geminal dimethyl-containing quaternary center is proposed to be necessary to arm the substrate for cyclization through steric biasing.