UV/visible light-promoted external photocatalyst-free transformations: A Decade's Journey of N-heterocycles and their functionalisation

Abstract

Heterocycles continue to captivate the attention of scientists owing to their distinctive structures that have resulted in numerous practical uses across various fields, including organic chemistry, pharmaceuticals, and materials science. They have been recognized as the fundamental framework of a variety of compounds that hold significance in both biological and industrial applications. In the realm of organic synthesis, activation of small molecules through visible light-promoted reactions becomes easier in the presence of a photocatalyst; however, complex reaction conditions are required to achieve the target product. Recently, researchers have devoted significant amount of effort to designing and developing photoactive scaffolds that inherently absorb light and undergo cyclization or functionalization reactions. To comprehend all the findings related to photocatalyst-free activation in a single platform, a review is necessary to guide new researchers to solve critical problems in the field. In this context, herein, we provide a comprehensive analysis of the construction of N-containing heterocyclic compounds and their functionalization without the use of external photocatalysts, under UV/visible light exposure in different conditions. Furthermore, various scopes, limitations and mechanistic investigations on research findings published since 2015 are discussed.