Visible-Light-Promoted Manganese-Catalyzed Atom Transfer Radical Cyclization of Unactivated Alkyl Iodides.

An expedient visible-light-promoted atom transfer radical cyclization (ATRC) reaction of unactivated alkyl iodides facilitated by earth-abundant and inexpensive manganese catalysis is described. The practical protocol shows a broad substrate scope and good functional-group tolerance, allowing for the preparation of synthetically valuable alkenyl iodides and diquinanes under simple and mild reaction conditions. Notably, the method provides a net redox-neutral strategy for ATRC reactions that avoids classic hydrogen atom transfer mechanism.

Visible-Light-Mediated Aerobic Oxidation of Organoboron Compounds Using in Situ Generated Hydrogen Peroxide.

A simple and general visible-light-mediated oxidation of organoboron compounds has been developed with rose bengal as the photocatalyst, substoichiometric Et3N as the electron donor, as well as air as the oxidant. This mild and metal-free protocol shows a broad substrate scope and provides a wide range of aliphatic alcohols and phenols in moderate to excellent yields. Notably, the robustness of this method is demonstrated on the stereospecific aerobic oxidation of organoboron compounds.

Visible-Light-Initiated, Photocatalyst-Free Decarboxylative Coupling of Carboxylic Acids with N-Heterocycles.

A general and efficient protocol for direct C-H alkylation and acylation of N-heterocycles, using readily accessible carboxylic acids as radical precursors under visible-light irradiation without a photocatalyst and an additional acid additive, has been developed. This protocol provides expedient access to substituted N-heterocycles under mild and metal-free conditions. Mechanistic experiments indicate that this reaction proceeds through a visible-light-initiated radical chain propagation mechanism.

Mild and efficient synthesis of indoles and isoquinolones via a nickel-catalyzed Larock-type heteroannulation reaction.

A simple and efficient approach for the preparation of substituted indoles and isoquinolones via a nickel-catalyzed Larock-type heteroannulation reaction is reported. This transformation employed air-stable and inexpensive Ni(dppp)Cl2 as a precatalyst and Et3N as a mild base. Moreover, the reaction occurs efficiently under mild conditions, and a wide range of substituted indoles and isoquinolones bearing various functional groups are obtained in moderate to excellent yields.

Eosin Y-catalyzed, visible-light-promoted carbophosphinylation of allylic alcohols via a radical neophyl rearrangement.

A visible-light-promoted phosphinylation of allylic alcohols with concomitant 1,2-aryl migration is described. This transformation proceeds smoothly under metal-free and mild conditions by using an inexpensive organic dye, eosin Y, as the photocatalyst, affording various ß-aryl-γ-ketophosphine oxides in moderate to good yields. Mechanistic studies suggested that the 1,2-aryl migration proceeded through a radical (neophyl) rearrangement.

Recent Advances in the Synthesis of ß-Functionalized Ketones by Radical-Mediated 1,2-Rearrangement of Allylic Alcohols.

ß-Functionalized ketones are a highly important and valuable class of compounds that have gained increasing attention from organic chemists due to their intensive uses as versatile synthetic intermediates and building blocks in complex molecule assembly and natural product synthesis. Accordingly, there is continuing interest in the development of new approaches for the synthesis of ß-functionalized ketones. In recent years, radical-mediated 1,2-rearrangement reactions of allylic alcohols, which proceed through cationic (semipinacol) rearrangements or radical (neophyl) rearrangements, have presented an attractive and powerful strategy to access various diversely ß-functionalized ketones. Interestingly, this strategy allows for the direct installation of a variety of valuable functional groups at the ß-position of cyclic and acyclic ketones by employing different radical precursors. However, a review focusing on the preparation of ß-functionalized ketones by radical-mediated 1,2-rearrangement reactions of allylic alcohols has not been summarized to date. This Minireview highlights recent progress made in this highly active and interesting research area, and the corresponding mechanisms will also be discussed.

α-Quaternary Mannich Bases through Copper-Catalyzed Amination-Induced 1,2-Rearrangement of Allylic Alcohols.

A novel copper-catalyzed amination-induced 1,2-rearrangement reaction of allylic alcohols has been developed under simple and mild conditions. The commercially available N-fluorobenzenesulfonimide (NFSI) is employed as an amination reagent. In this transformation, not only alkyl, but also aryl substituents can efficiently undergo 1,2-carbon atom migration, thereby providing an efficient and powerful route to prepare a wide range of α-quaternary Mannich bases. The reaction features a broad substrate scope, operational simplicity, and excellent practicality.