Dispersion-Controlled Regioselective Acid-Catalyzed Intramolecular Hydroarylation of cis-Methindolylstyrenes to Access Tetrahydrobenzo[cd]indoles

Readily prepared <i>cis</i>-<i>β</i>-(<i>α</i>’,<i>α</i>’-dimethyl)-4’-methindolylstyrenes undergo Brønsted acid-catalyzed intramolecular hydroarylation to afford a variety of 3-aryl-5,5-dimethyl-1,3,4,5-tetrahydrobenzo[<i>cd</i>]indoles. Our experimental and computational investigations suggest that dispersive interactions between the indole and styrene preorganize substrates such that 6-membered ring formation occurs via a concerted hydroarylation step. When dispersability is attenuated (by a substituent or heteroatom), regioselectivity erodes and competing oligomerization predominates for <i>cis</i> substrates; all <i>trans</i>-configured substrates that we evaluated failed to cyclize efficiently.