Readily prepared cis - β -( α ’, α ’-dimethyl)-4’-methindolylstyrenes undergo Brønsted acid-catalyzed intramolecular hydroarylation to afford a variety of 3-aryl-5,5-dimethyl-1,3,4,5-tetrahydrobenzo[ cd ]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 cis substrates; all trans -configured substrates that we evaluated failed to cyclize efficiently.

Readily prepared cis-β-(α',α'-dimethyl)-4'-methindolylstyrenes undergo acid-catalyzed intramolecular hydroindolation to afford tetrahydrobenzo[ cd]indoles. Our experimental and computational investigations suggest that dispersive interactions between the indole and styrene preorganize substrates such that 6-membered ring formation is preferred, apparently via concerted protonation and C-C bond formation. When dispersion is attenuated (by a substituent or heteroatom), regioselectivity erodes and competing oligomerization predominates for cis substrates. Similarly, all trans-configured substrates that we evaluated failed to cyclize efficiently.