Recent Developments in Photo-Catalyzed/Promoted Synthesis of Indoles and Their Functionalization: Reactions and Mechanisms

The use of clean and renewable light sources is increasingly common in organic synthesis due to its safety, practicality and economy. Recently, photoredox catalysis has shown great application values in organic transformations because of its advantages of environmentally friendly and abundant resources. Indoles and their derivatives (indolines, oxindoles and isatins) are the core skeletons of some important organic compounds and widely-present in various natural products and pharmaceuticals with different biological activities. Therefore, the research on the synthesis and modification of indoles is particularly important for chemists and pharmacologists. This review summarizes the effects of photocatalysis on indole synthesis and modification in recent decades. These transformations are accomplished by using metal photocatalysts (i. e., Ir, Ru, Ni, Cu, Fe, Au, Rh, TiO2, etc.) or non-metallic photocatalysts (i. e., Rose Bengal, Eosin Y, quinones, naphthols, N-heterocyclic carbenes, carbazoles, pyrylium salts, etc.), or without the need of photocatalysts. The detailed mechanisms of these photo-catalyzed/promoted organic reactions are also highlighted deeply. And we hope this review will be helpful to researchers interested in this promising field of photocatalyzed transformations.

Automated summary

This review discusses the significant role of photoredox catalysis in the synthesis and modification of indoles. It highlights the use of metal and non-metal photocatalysts, as well as reactions that do not require a photocatalyst. The detailed mechanisms of photo-catalyzed organic reactions are also deeply analyzed in the review.