Organocatalyzed Asymmetric Synthesis of Indole-Fused Polycycles

The present review summarizes the developments of asymmetric organocatalytic strategies toward the construction of indole-fused carbocyclic as well as heterocyclic frameworks during the time span from 2016 till date. It has been found that cycloaddition reactions of the indole derivatives with other reacting partners are prevalent in this research area which signifies that the reported strategies are based on asymmetric derivatization of the indole rings to frame-fused polycycles. Due to their high abundance in naturally occurring compounds that are advantageous to biological systems, synthetic approaches toward fused polycycles with indole cores have drawn considerable focus to organic chemists. Apart from their wide distribution in several natural sources, a large numbers of marketed drugs contain indole cores as well. This article is a comprehensive documentary of the asymmetric synthesis of such polyheterocyclic through different organocatalytic processes over the past decade. Activation mode of covalent and non-covalently interacting organocatalysts and their influences on asymmetric induction have been elaborated as well. The mechanistic rationale with special emphasis on stereoinduction under the catalytic activation has been explained.