Heart of gold: enabling ligands for oxidative addition of haloorganics in Au(I)/Au(III) catalysed cross-coupling reactions.

The field of Au-catalysis has been an area rich with new discoveries due to the unique properties of the lustrous element. In the past decade, developments in Au(I)/Au(III) cross-coupling methodology have been made possible with the use of external oxidants that facilitate the challenging oxidation of Au(I) to Au(III) in a stable and catalytically competent fashion. Until recently, Au-chemistry was not known to undergo catalytic transformations that feature oxidative addition of haloarenes like those that were made famous by transition metals such as Pd and Ni.

Harnessing Radical Chemistry via Electrochemical Transition Metal Catalysis.

The merger of transition metal catalysis and electroorganic synthesis has recently emerged as a versatile platform for the development of highly enabling radical reactions in a sustainable fashion. Electrochemistry provides access to highly reactive radical species under extremely mild reaction conditions from abundant native functionalities. Transition metal catalysts can be used as redox-active electrocatalysts to shuttle electrons, chiral information to organic substrates, and the reactive intermediates in the electrolytic systems.

Formal Bromine Atom Transfer Radical Addition of Nonactivated Bromoalkanes Using Photoredox Gold Catalysis.

Organic transformations mediated by photoredox catalysis have been at the forefront of reaction discovery. Recently, it has been demonstrated that binuclear Au(I) bisphosphine complexes, such as [Au(μ-dppm)]X, are capable of mediating electron transfer to nonactivated bromoalkanes for the generation of a variety of alkyl radicals. The transfer reactions of bromine, derived from nonactivated bromoalkanes, are largely unknown.

Recent Advances in Titanium Radical Redox Catalysis.

New catalytic strategies that leverage single-electron redox events have provided chemists with useful tools for solving synthetic problems. In this context, Ti offers opportunities that are complementary to late transition metals for reaction discovery. Following foundational work on epoxide reductive functionalization, recent methodological advances have significantly expanded the repertoire of Ti radical chemistry.

Bimetallic Radical Redox-Relay Catalysis for the Isomerization of Epoxides to Allylic Alcohols.

Organic radicals are generally short-lived intermediates with exceptionally high reactivity. Strategically, achieving synthetically useful transformations mediated by organic radicals requires both efficient initiation and selective termination events. Here, we report a new catalytic strategy, namely, bimetallic radical redox-relay, in the regio- and stereoselective rearrangement of epoxides to allylic alcohols.

Hydrogen Atom Transfer Reactions via Photoredox Catalyzed Chlorine Atom Generation.

The selective functionalization of chemically inert C-H bonds remains to be fully realized in achieving organic transformations that are redox-neutral, waste-limiting, and atom-economical. The catalytic generation of chlorine atoms from chloride ions is one of the most challenging redox processes, where the requirement of harsh and oxidizing reaction conditions renders it seldom utilized in synthetic applications. We report the mild, controlled, and catalytic generation of chlorine atoms as a new opportunity for access to a wide variety of hydrogen atom transfer (HAT) reactions owing to the high stability of HCl.

Transformations of Isonitriles with Bromoalkanes Using Photoredox Gold Catalysis.

Isonitriles have excellent electronic compatibility to react with free radicals. Recently, photoredox catalysis has emerged as a powerful tool for the construction of C-C bonds with few protocols for alkylative heterocycle synthesis through isonitrile addition. Herein, we describe the photocatalytic generation of alkyl radicals from unactivated bromoalkanes as part of an efficient cross-coupling strategy for the diversification of isonitriles using a dimeric gold(I) photoredox catalyst, [Au(dppm)]Cl.

Homocoupling of Iodoarenes and Bromoalkanes Using Photoredox Gold Catalysis: A Light Enabled Au(III) Reductive Elimination.

The formation of homocoupled alkane byproducts have been identified in the reduction of bromoalkanes via photoredox gold catalysis with dimeric Au(I) complexes. This prompted further investigation into the mechanism of formation of these byproducts and the diversity of C-X bonds amenable to this transformation. Examples were found when considering bromoalkanes while a wide variety of iodoarenes underwent this process in good to excellent yields.

Indole Functionalization via Photoredox Gold Catalysis.

The use of photoredox catalyst [Au2(dppm)2]Cl2 to initiate free-radical cyclizations onto indoles is reported. Excitation of the dimeric Au(I) photocatalyst for the reduction of unactivated bromoalkanes and bromoarenes is used for the generation of carbon-centered radicals. Previous to this work, reduction processes leading to indole functionalization utilizing photoredox catalysts were limited to activated benzylic or α-carbonyl-positioned bromoalkanes.

Light-enabled synthesis of anhydrides and amides.

Recently, we have demonstrated that the photogeneration of Vilsmeier-Haack reagents is possible using only dimethylformamide (DMF) and tetrabromomethane (CBr4) in the bromination of alcohols. Extending these findings to carboxylic acid substrates has produced a mild and facile approach to the in situ formation of symmetric anhydrides, which were conveniently converted to amide derivatives in a one-pot process. The efficient protocols discussed herein are marked by use of UVA LEDs (365 nm), which have reduced the reaction times and come with a low setup cost.