For more than 70 years, nitrogen-centered radicals have been recognized as potent synthetic intermediates. This review is a survey designed for use by chemists engaged in target-oriented synthesis. This review summarizes the recent paradigm shift in access to and application of N-centered radicals enabled by visible-light photocatalysis. This shift broadens and streamlines approaches to many small molecules because visible-light photocatalysis conditions are mild. Explicit attention is paid to innovative advances in N-X bonds as radical precursors, where X = Cl, N, S, O, and H. For clarity, key mechanistic data is noted, where available. Synthetic applications and limitations are summarized to illuminate the tremendous utility of photocatalytically generated nitrogen-centered radicals.

Strategies to Generate Nitrogen-centered Radicals That May Rely on Photoredox Catalysis: Development in Reaction Methodology and Applications in Organic Synthesis.

Amide Bond Formation Strategies: Latest Advances on a Dateless Transformation

Visible light promoted cross-dehydrogenative coupling: a decade update

The catalytic aminocarbonylation of (hetero)aryl halides is widely applied in the synthesis of amides but relies heavily on the use of precious metal catalysis. Herein, we report an aminocarbonylation of (hetero)aryl halides using a simple cobalt catalyst under visible light irradiation. The reaction extends to the use of (hetero)aryl chlorides and is successful with a broad range of amine nucleophiles. Mechanistic investigations are consistent with a reaction proceeding via intermolecular charge transfer involving a donor–acceptor complex of the substrate and cobaltate catalyst.

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Cobalt-catalyzed aminocarbonylation of (hetero)aryl halides promoted by visible light.

Controlled Relay Process to Access N-Centered Radicals for Catalyst-free Amidation of Aldehydes under Visible Light

Cross-Dehydrogenating Coupling of Aldehydes with Amines/R-OTBS Ethers by Visible-Light Photoredox Catalysis: Synthesis of Amides, Esters, and Ureas.

α-Arylation of ketones with electron rich arenes via sp2(C)–H has been achieved by the reaction of α-phenylselanylketones using organic photoredox catalysis. The reaction proceeds via an α-methylene ketone radical generated by sp3(C)–SePh activation. The developed method has been found to have broad substrate scope and is free from the use of pre-functionalized aromatics.

Pramod Kumar Sahani

Papers

Cross-Dehydrogenating Coupling of Aldehydes with Amines/R-OTBS Ethers by Visible-Light Photoredox Catalysis: Synthesis of Amides, Esters, and Ureas.

Transition-metal-free photoredox intermolecular α-arylation of ketones