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Abstract

Department of ChemistryRecently, irradiation of visible light photoredox catalyst has been widely used to drive transformation of organic molecules though the highly desirable processes. Absorption of visible light induces the long-lived excited-triplet state of the photocatalyst. The returning from this excited state to the bench state of the catalyst leads single-electron-transfer (SET), transforming the reacting substrates into radical intermediates. The radical cation/anion intermediates show their reactivity which is basically differentiated from those of electronically ground state of molecules. Multicomponent reaction (MCR) serves as a powerful tool, employing three or more simple building blocks to produce complex molecular frameworks in a single step. Given its advantages of rapid access to structural complexity, MCR has been adopted as a valuable means for the discovery of bioactive compounds. As such, photoredox catalysis has been explored in the context of MCR. However, the limited examples are mostly based on radical-polar crossover mechanisms, in which the process is in operation for initial coupling of two reactants, while a third component is incorporated via a polar process. Although this approach is useful, quenching of radical processes by redox catalysts entailing the involvement of polar processes poses limitations in the scope of coupling partners. To the best of our knowledge, MCR with three consecutive bond formation based on radical processes via visible-light photoredox catalysis has not been reported. Due to their utilities, significant efforts have been made to develop efficient synthetic methods for quinolines. However, the conventional methods rely on condensation under harsh conditions and more recent developments are limited to transitional metal-catalyzed and iodine-mediated synthesis. Here, a successful development of a new tandem radical cyclization based on visible-light photoredox catalysis enables the efficient formation of quinolines based on consecutive radical processes.ope