Search

Olefin hydrogenation is one of the most important transformations in organic synthesis. Electrochemical transition metal‐catalyzed hydrogenation is an attractive approach to replace the dangerous hydrogen gas with electrons and protons. However, this reaction poses major challenges due to rapid hydrogen evolution reaction (HER) of metal‐hydride species that outcompetes alkene hydrogenation step, and facile deposition of the metal catalyst at the electrode that stalls reaction. Here we report an economical and efficient strategy to achieve high selectivity for hydrogenation reactivity over the well‐established HER. Using an inexpensive and bench‐stable nickel salt as the catalyst, this mild reaction features outstanding substrate generality and functional group compatibility, and distinct chemoselectivity. In addition, hydrodebromination of alkyl and aryl bromides could be realized using the same reaction system with a different ligand, and high chemoselectivity between hydrogenation and hydrodebromination could be achieved through ligand selection. The practicability of our method has been demonstrated by the success of large‐scale synthesis using catalytic amount of electrolyte and a minimal amount of solvent. Cyclic voltammetry and kinetic studies were performed, which support a NiII/0 catalytic cycle and the pre‐coordination of the substrate to the nickel center. [ABSTRACT FROM AUTHOR]

Olefin hydrogenation is one of the most important transformations in organic synthesis. Electrochemical transition metal‐catalyzed hydrogenation is an attractive approach to replace the dangerous hydrogen gas with electrons and protons. However, this reaction poses major challenges due to rapid hydrogen evolution reaction (HER) of metal‐hydride species that outcompetes alkene hydrogenation step, and facile deposition of the metal catalyst at the electrode that stalls reaction. Here we report an economical and efficient strategy to achieve high selectivity for hydrogenation reactivity over the well‐established HER. Using an inexpensive and bench‐stable nickel salt as the catalyst, this mild reaction features outstanding substrate generality and functional group compatibility, and distinct chemoselectivity. In addition, hydrodebromination of alkyl and aryl bromides could be realized using the same reaction system with a different ligand, and high chemoselectivity between hydrogenation and hydrodebromination could be achieved through ligand selection. The practicability of our method has been demonstrated by the success of large‐scale synthesis using catalytic amount of electrolyte and a minimal amount of solvent. Cyclic voltammetry and kinetic studies were performed, which support a NiII/0 catalytic cycle and the pre‐coordination of the substrate to the nickel center. [ABSTRACT FROM AUTHOR]

We report the development of an electrocatalytic protocol for the chlorophosphinoylation of simple alkenes. Driven by electricity and mediated by a Mn catalyst, the heterodifunctionalization reaction takes place with high efficiency and regioselectivity. Cyclic voltammetry data are consistent with a mechanistic scenario based on anodically coupled electrolysis in which the generation of two distinct radical intermediates occur simultaneously on the anode and are both mediated by the Mn catalyst. [ABSTRACT FROM AUTHOR]

We report a Mn-catalyzed electrochemical dichlori-nation of alkenes with MgCl2 as the chlorine source. This method provides operationally simple, sustainable, and efficient access to a variety of vicinally dichlorinated compounds. In particular, alkenes with oxidatively labile functional groups, such as alcohols, aldehydes, sulfides, and amines, were transformed into the desired vicinal dichlorides with high chemoselectivity. Mechanistic data are consistent with metal-mediated Cl atom transfer as the predominant pathway enabling dual C-Cl bond formation and contradict an alternative pathway involving electrochemical evolution of chlorine gas followed by Cl[sub 2]-mediated electrophilic dichlorination. [ABSTRACT FROM AUTHOR]

The first efficientand highly enantioselective Michael addition–protonationreaction of malononitriles to α-substituted vinyl ketones hasbeen developed by using a chiral primary amine as the organocatalyst.With a Hantzsch ester as the hydride source, an enantioselective tandemreduction, Michael addition–protonation reaction of benzylidenemalononitrilehas also been achieved with good yields and high enantioselectivities. [ABSTRACT FROM AUTHOR]

The exceptional versatility of carboxylic acids has been extensively exploited in organic synthesis across several decades. There has been a recent upsurge of radical decarboxylative transformations. The process can be initiated under mild conditions, and the resultant radicals have orthogonal reactivities to closed‐shell species, thus providing immense opportunities for streamlining novel reactions. The use of free carboxylic acids is the most desirable owing to its high atom and step economy. Aiming to demonstrate the attractiveness of the strategy and to inspire chemists to tackle existing challenges, this review outlines the recent advances on radical decarboxylative functionalization of free carboxylic acids. [ABSTRACT FROM AUTHOR]

Thefirst effective exampleof asymmetric conjugate addition–protonation reactions of thiolsto α-substituted vinyl ketones by chiral primary amine catalysisis reported. A simple chiral primary–tertiary diamine catalystderived from l-phenylalanine was found to promote the sulfa-Michaeladdition–protonation reactions with good to excellent enantioselectivity. [ABSTRACT FROM AUTHOR]

Enantioselective protonation with a catalytic enamine intermediate represents a challenging, yet fundamentally important process for the synthesis of α-chiral carbonyls. We describe herein chiral primary-amine-catalyzed conjugate additions of indoles to both α-substituted acroleins and vinyl ketones. These reactions feature enamine protonation as the stereogenic step. A simple primary-tertiary vicinal diamine 1 with trifluoromethanesulfonic acid (TfOH) was found to enable both of the reactions of acroleins and vinyl ketones with good activity and high enantioselectivity. Detailed mechanistic studies reveal that these reactions are rate-limiting in iminium formation and they all involve a uniform H2O/acid-bridged proton transfer in the stereogenic steps but divergent stereocontrol modes for the protonation stereoselectivity. For the reactions of α-branched acroleins, facial selections on H2O-bridged protonation determine the enantioselectivity, which is enhanced by an OH⋅⋅⋅π interaction with indole as uncovered by DFT calculations. On the other hand, the stereoselectivity of the reactions with vinyl ketones is controlled according to the Curtin-Hammett principle in the CC bond-formation step, which precedes a highly stereospecific enamine protonation. [ABSTRACT FROM AUTHOR]

We report an efficient and sustainable electrocatalytic approach for azidoesterification of alkenes. The reaction proceeds by electrochemical iron‐catalyzed oxidation of commercially available carbazates to produce alkoxycarbonyl radicals. Upon addition across alkenes, the generated transient carbon‐centered radicals get trapped by azido metal complexes to furnish the alkene difunctionalization products. This mild, operationally simple protocol transforms a wide variety of alkenes into the corresponding β‐azido esters in good to excellent yields, thereby providing a practical access to β‐amino acid derivatives from simple and readily available starting materials. [ABSTRACT FROM AUTHOR]

Asymmetric catalysis with benzyne remains elusive because of the highly fleeting and nonpolar nature of benzyne intermediates. Reported herein is an electrochemical approach for the oxidative generation of benzynes (cyclohexyne) and its successful merging with chiral primary aminocatalysis, formulating the first catalytic asymmetric enamine–benzyne (cyclohexyne) coupling reaction. Cobalt acetate was identified to stabilize the in situ generated arynes and facilitate its coupling with an enamine. This catalytic enamine‐benzyne protocol provides a concise method for the construction of diverse α‐aryl (α‐cyclohexenyl) quaternary carbon stereogenic centers with good stereoselectivities. [ABSTRACT FROM AUTHOR]

Asymmetric catalysis with benzyne remains elusive because of the highly fleeting and nonpolar nature of benzyne intermediates. Reported herein is an electrochemical approach for the oxidative generation of benzynes (cyclohexyne) and its successful merging with chiral primary aminocatalysis, formulating the first catalytic asymmetric enamine–benzyne (cyclohexyne) coupling reaction. Cobalt acetate was identified to stabilize the in situ generated arynes and facilitate its coupling with an enamine. This catalytic enamine‐benzyne protocol provides a concise method for the construction of diverse α‐aryl (α‐cyclohexenyl) quaternary carbon stereogenic centers with good stereoselectivities. [ABSTRACT FROM AUTHOR]

An abstract of the article "Chiral primary amine catalyzed asymmetric tandem reduction-Michael addition-protonation reaction between alkylidene Meldrum's acid and α-substituted vinyl ketones," by N. Fu and colleagues is presented.

Review: 74 refs. [ABSTRACT FROM AUTHOR]

The catalytic system is efficiently applied to the Michael addition-protonation reaction of malonitriles to α-substituted vinyl ketones as well as the tandem reduction, Michael addition-protonation reaction sequence of benzylidenemalonitriles in the presence of Hantzsch ester to α-substituted vinyl ketones. [ABSTRACT FROM AUTHOR]

The article presents chemical equations for the article "Asymmetric Sulfa-Michael Addition to α-Substituted Vinyl Ketones Catalyzed by Chiral Primary Amine" by L. Zhang and others published in "Organic Letters" in 2014.

The reactions of α-substituted vinyl aldehydes are a summary of previous results and are not shown. [ABSTRACT FROM AUTHOR]

Electrochemistry offers a sustainable platform for discovering reactions involving single‐electron transfer (SET) that generates highly reactive and synthetically versatile radical species. Compared with photochemistry similarly specializing in SET which requires expensive photocatalysts, electrochemistry employs low‐cost electricity to drive the electron flow. Paired electrolysis makes use of both half‐reactions, thus obviating the need for sacrificial reactions and maximizing the atom and energy economy. In convergent paired electrolysis, anodic oxidation and cathodic reduction occur simultaneously to generate two intermediates, which are then coupled to furnish the product. It represents a distinctive approach to challenging redox‐neutral reactions. However, the gap between the two electrodes makes it hard for a reactive intermediate to come across the other coupling partner. This concept article summarizes recent state‐of‐the‐art advances on radical‐based convergent paired electrolysis, which adopted different strategies to overcome the difficulty. [ABSTRACT FROM AUTHOR]

In contrast to the rapid growth of electrophotocatalysis in recent years, enantioselective catalytic reactions powered by this unique methodology remain rare. In this work, we report an electrophotochemical metal‐catalyzed protocol for direct asymmetric decarboxylative cyanation of aliphatic carboxylic acids. The synergistic merging of electrophotochemical cerium catalysis and asymmetric electrochemical copper catalysis permits mild reaction conditions for the formation and utilization of the key carbon centered radicals by combining the power of light and electrical energy. Electrophotochemical cerium catalysis enables radical decarboxylation to produce alkyl radicals, which could be effectively intercepted by asymmetric electrochemical copper catalysis for the construction of C−CN bonds in a highly stereoselective fashion. This environmentally benign method smoothly converts a diverse array of arylacetic acids into the corresponding alkyl nitriles in good yields and enantioselectivities without using chemical oxidants or pre‐functionalization of the acid substrates and can be readily scaled up. [ABSTRACT FROM AUTHOR]

An electrophotochemical dual metal‐catalyzed protocol for decarboxylative arylation of simple aliphatic carboxylic acids with aryl halides is reported. The relative stabilities of catalytically active metal complexes simultaneously generated at anode and cathode are the key design elements for the success of this convergent paired electrolysis. This new electrophotocatalytic method is mild, robust, and most importantly, capable of accommodating simple primary aliphatic acids including acetic acid – ubiquitous and variegated structural motifs yet remain oddly challenging substrates – directly as native functional groups for decarboxylative C(sp2)−C(sp3) bond formation. [ABSTRACT FROM AUTHOR]

Electroorganic synthesis has recently become a rapidly blossoming research area within the organic synthesis community. It should be noted that electrochemical reaction is always a balanced reaction system with two half‐cell reactions‐oxidation and reduction. Most electrochemical strategies, however, typically focus on one of the two sides for the desired transformations. Paired electrolysis has two desirable half reactions running simultaneously, thus maximizing the overall margin of atom and energy economy. Meanwhile, the spatial separation between oxidation and reduction is the essential feature of electrochemistry, offering unique opportunities for the development of redox‐neutral reactions that would otherwise be challenging to accomplish in a conventional reaction flask setting. This review discusses the most recent illustrative examples of paired electrolysis with special emphasis on sequential and convergent processes. [ABSTRACT FROM AUTHOR]

Abstract: The stereoselective synthesis of chlorotrifluoromethylated pyrrolidines was achieved using anodically coupled electrolysis, an electrochemical process that combines two parallel oxidative events in a convergent and productive manner. The bench‐stable and commercially available solids CF3SO2Na and MgCl2 were used as the functional group sources to generate CF3. and Cl., respectively, via electrochemical oxidation, and the subsequent reaction of these radicals with the 1,6‐enyne substrate was controlled with an earth‐abundant Mn catalyst. In particular, the introduction of a chelating ligand allowed for the ene–yne cyclization to take place with high stereochemical control over the geometry of the alkene group in the pyrrolidine product. [ABSTRACT FROM AUTHOR]