Rate Profiling the Impact of Remote Functional Groups on the Redox-Relay Heck Reaction

Urea Ligand-Promoted Chainwalking Heteroannulation for the Synthesis of 6- and 7-membered Azaheterocycles

Typical approaches to heterocycle construction require significant changes in synthetic strategy even for a change as minor as increasing the ring size. The ability to access multiple heterocyclic scaffolds through a common synthetic approach, simply through trivial modification of one reaction component, would enable facile access to diverse libraries of structural analogues of core scaffolds. Here, we show that urea-derived ligands effectively promote Pd-mediated chainwalking processes to enable remote heteroannulation for the rapid construction of six- and seven-membered azaheterocycles under essentially identical reaction conditions. This method demonstrates good functional group tolerance and effectively engages sterically hindered substrates. In addition, this reaction is applicable to target-oriented synthesis, demonstrated through the formal synthesis of antimalarial alkaloid galipinine.

Ni(ii)-Catalyzed intermolecular selective Heck-type arylation of unactivated alkenes with arylboronic acids

This work: directing group-assisted Ni(ii)-catalyzed intermolecular Heck arylation of unactivated alkenes.

Chain-walking reactions of transition metals for remote C-H bond functionalization of olefinic substrates

Past several decades have witnessed the great evolution of inert C-H bond functionalization reactions as an emerging technique for synthesizing drug molecules, agrochemicals, and functional materials with intricate three-dimensional architectures. Although most activation of "unreactive" C-H bonds was accomplished by exploiting the power of transition metal catalysts, the distant and selective activation of unreactive C-H bonds in an undirected fashion remains one of the critical challenges to this rapidly growing field of organic chemistry. In this context, to meet all these concerns, much more attractive and challenging transition metal catalytic transformations have begun to blossom in recent years with the aid of the chain-walking process. The chain-walking strategy is one of the state-of-the-art techniques in organic synthesis to functionalize the unreactive C-H bonds by allowing the movement of a metal complex along the hydrocarbon chain of the substrate to recognize preferable bond-forming sites. The essential advantage of this strategy is that the bonds are formed only at the places where the catalyst selects for the specific C-H bonds to be cleaved, which not only avoids tedious synthetic procedures for prefunctionalization and the emission of undesirable wastes but also inspires chemists to plan novel synthetic strategies in a completely different manner. Consequently, various C-H bond functionalization reactions have been reported in recent years, employing the vast opportunity provided by this growing field mainly for the acyclic olefinic systems with flexible alkyl chains. Thus, chain-walking reactions allow the reactivity of the reaction centers within the substrates that cannot be realized via the classical mode of reactivity of the substrates. Applying this approach, inexpensive feedstock materials and simple hydrocarbons as an isomeric mixture can be converted to a single isomeric product in a regioconvergent scenario. Simultaneously, the site-selectivity of these reactions can also be switched using a regiodivergent strategy via appropriate tuning of ligands or a slight modification of reaction conditions. Herein, we have provided a comprehensive overview of the chain-walking reactions involving a variety of catalytic systems ranging from the first-row transition metal catalysts to the third-row transition metal catalysts for C-H activation in a concise fashion with the hope for further developments in this area through the appropriate application of the chain-walking reactions.

Palladium-Catalyzed γ,γ'-Diarylation of Free Alkenyl Amines

The direct difunctionalization of alkenes is an effective way to construct multiple C-C bonds in one-pot using a single functional group. The regioselective dicarbofunctionalization of alkenes is therefore an important area of research to rapidly obtain complex organic molecules. Herein, we report a palladium-catalyzed γ,γ'-diarylation of free alkenyl amines through interrupted chain walking for the synthesis of Z-selective alkenyl amines. Notably, while 1,3-dicarbofunctionalization of allyl groups is well precedented, the present disclosure allows 1,3-dicarbofunctionalization of highly substituted allylamines to give highly Z-selective trisubsubstituted olefin products. This cascade reaction operates via an unprotected amine-directed Mizoroki-Heck (MH) pathway featuring a β-hydride elimination to selectively chain walk to furnish a new terminal olefin which then generates the cis-selective alkenyl amines around the sterically crowded allyl moiety. This operationally simple protocol is applicable to a variety of cyclic, branched, and linear secondary and tertiary alkenylamines, and has a broad substrate scope with regard to the arene coupling partner as well. Mechanistic studies have been performed to help elucidate the mechanism, including the presence of a likely unproductive side C-H activation pathway.