Synthesis of 3,4‐Fused Tricyclic Indoles Using 3‐Alkylidene Indolines as Versatile Precursors.

In this personal account, our recent studies of novel synthetic methods of 3,4‐fused tricyclic indole derivatives using 3‐alkylidene indoline derivatives as versatile precursors are discussed. Two types of cascade reactions producing 3,4‐fused tricyclic 3‐alkylidene indolines were developed based on a palladium‐catalyzed intramolecular Heck insertion to an allene‐allylic amination cascade and a platinum‐catalyzed intramolecular Friedel‐Crafts type C−H coupling‐allylic amination cascade. Furthermore, three types of 3,4‐fused tricyclic indoles were accessible from a single 3‐alkylidene indoline precursor via acid‐promoted olefin isomerization or oxidative treatments. The application of the developed methods to the synthesis of natural products bearing a 3,4‐fused tricyclic indole skeleton, (−)‐aurantioclavine, fargesine, and synthetic studies of dragmacidin E are also highlighted. Our recent studies of novel synthetic methods of 3,4‐fused tricyclic indoles using 3‐alkylidene indoline derivatives as versatile precursors are discussed. Two types of cascade cyclizations producing 3,4‐fused tricyclic 3‐alkylidene indolines were developed using palladium catalysis and platinum catalysis. These compounds could be efficiently converted into the tricyclic indole derivatives. The developed reactions were successfully applied to the synthesis of related indole alkaloids. [ABSTRACT FROM AUTHOR]