One-Pot Synthesis of Cycloocta[b]indole Through Formal [5+3] Cycloaddition Using Donor-Acceptor Cyclopropanes

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 Bronsted 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.