A new approach for the synthesis of highly functionalized tetrahydrocyclohepta[ b]indoles through [5 + 2] cycloaddition was developed. Two carbon-carbon bonds were formed by the simple addition of an indium catalyst, which acted as both a π-Lewis acid and σ-Lewis acid to activate the alkyne and unsaturated ester, respectively. The reaction could be applied to various substrates and proceeded regio- and diastereoselectively in all cases.

A new approach to cycloocta[b]indole through formal [5+3] cycloaddition was developed. This methodology was realized by using an indole derivative as a C5 unit and a cyclopropane derivative as a C3 unit. These two units have both donor and acceptor properties. Two carbon–carbon bonds were formed stepwise by the successive addition of a Lewis acidic catalyst and a Brønsted base. The reaction could be performed as a one‐pot process. Optically active cycloocta[b]indole was also synthesized by using this methodology with a chiral cyclopropane as a C3 substrate.