Direct C-H transformation via iron catalysis.

Transition-Metal-Catalyzed C−S, C−Se, and C−Te Bond Formation via Cross-Coupling and Atom-Economic Addition Reactions

Visible-light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross-coupling reactions, α-amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible-light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible-light-absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo- or metal catalysis.

Visible-Light Photocatalysis: Does It Make a Difference in Organic Synthesis?

This critical review examines transition metal-catalyzed decarboxylative couplings that have emerged within recent years as a powerful strategy to form carbon–carbon or carbon–heteroatom bonds starting from carboxylic acids. In these reactions, C–C bonds to carboxylate groups are cleaved, and in their place, new carbon–carbon bonds are formed. Decarboxylative cross-couplings constitute advantageous alternatives to traditional cross-coupling or addition reactions involving preformed organometallic reagents. Decarboxylative reaction variants are also known for Heck reactions, direct arylation processes, and carbon–heteroatom bond forming reactions.

Decarboxylative coupling reactions: a modern strategy for C–C-bond formation

A review. Transition metal catalyzed decarboxylative allylations, benzylations, and interceptive allylations are reviewed.

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Transition Metal-Catalyzed Decarboxylative Allylation and Benzylation Reactions

Allylic esters of nitrobenzene acetic acids undergo facile palladium-catalyzed decarboxylative coupling. Both mono- and dinitroarene substrates give high yields of the coupled products. Moreover, the rates of the reactions suggest that decarboxylation is rate-limiting and substrates that sterically disfavor attainment of the reactive conformation for decarboxylation are not viable. Finally, reduction of the product nitroarenes to the corresponding anilines provides access to a variety of heterocycles including quinolines and dihydroquinolones.

Palladium-Catalyzed Decarboxylative sp3−sp3 Coupling of Nitrobenzene Acetic Esters

Allylic esters of heteroaromatic alkanes undergo facile palladium-catalyzed decarboxylative coupling. The resulting C−C bond is formed with high diastereoselectivity and high regioselectivity for coupling at the more substituted allyl terminus. It is proposed that this unusual combination of selectivities results from a tandem allylation/aza-Cope rearrangement sequence. After allylation, decarboxylative dearomatization produces an intermediate for the aza-Cope rearrangement. The subsequent aza-Cope rearrangement occurs under mild conditions because it is driven by rearomatization.

Regio- and diastereoselective decarboxylative coupling of heteroaromatic alkanes.

A wide variety of aldehydes, ketones, and lactols undergo redox amination when allowed to react with 3-pyrroline in the presence of a mild Bronsted acid catalyst This reaction utilizes the inherent reducing power of 3-pyrroline to perform the equivalent of a reductive amination to form alkyl pyrroles In doing so, the reaction avoids stoichiometric reducing agents that are typically associated with reductive aminations Moreover, the redox amination protocol allows access to alkyl pyrroles that cannot be made via standard reductive amination

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Shelli R. Waetzig

Papers

Palladium-Catalyzed Decarboxylative sp3−sp3 Coupling of Nitrobenzene Acetic Esters

Regio- and diastereoselective decarboxylative coupling of heteroaromatic alkanes.

Formation of N-alkylpyrroles via intermolecular redox amination.

A Versatile Hexadiene Synthesis by Decarboxylative sp3–sp3 Coupling/Cope Rearrangement

Palladium(II)-Catalyzed Cyclization of Unsaturated Hydroperoxides for the Synthesis of 1,2-Dioxanes