An electrochemically driven nickel-catalyzed enantioselective reductive cross-coupling of aryl aziridines with alkenyl bromides has been developed, affording enantioenriched β-aryl homoallylic amines with excellent E-selectivity. This electroreductive strategy proceeds in the absence of heterogeneous metal reductants and sacrificial anodes by employing constant current electrolysis in an undivided cell with triethylamine as a terminal reductant. The reaction features mild conditions, remarkable stereocontrol, broad substrate scope, and excellent functional group compatibility, which was illustrated by the late-stage functionalization of bioactive molecules. Mechanistic studies indicate that this transformation conforms with a stereoconvergent mechanism in which the aziridine is activated through a nucleophilic halide ring-opening process.

https://pubs.acs.org/doi/pdf/10.1021/jacs.2c12869

Nickel-Catalyzed Enantioselective Electrochemical Reductive Cross-Coupling of Aryl Aziridines with Alkenyl Bromides

Herein, an electroreductive carboxylation of organic carbon-halogen bonds (X = Br and Cl) promoted by catalytic amounts of naphthalene as an organic mediator is reported. This transformation proceeds smoothly under mild conditions with a broad substrate scope of 59 examples, affording the valuable and versatile carboxylic acids in moderate to excellent yields without the need of costly transition metal, wasted stoichiometric metal reductants, or sacrificial anodes. Further late-stage carboxylation of natural product and drug derivatives demonstrate its synthetic utility. Mechanistic studies confirmed the activation of carbon-halogen bonds via single-electron transfer and the key role of naphthalene in this reaction.

Metal-Free Electrochemical Carboxylation of Organic Halides in the Presence of Catalytic Amounts of an Organomediator.

Merging electrochemistry with asymmetric catalysis promises to provide an environmentally friendly and efficient strategy for the construction of nonracemic chiral molecules. However, in practice, significant challenges arise from the instability or incompatibility of the chiral catalysts under the electrochemical conditions at the interface of electrode and solution. Herein, we report a catalytic asymmetric indirect electrolysis employing the combination of a redox mediator and a chiral-at-rhodium Lewis acid, which achieves a previously elusive enantioselective nucleophilic α-C(sp3)-H alkenylation of ketones. Specifically, 2-acyl imidazoles react with potassium alkenyl trifluoroborates in high yields (up to 94%) and with exceptional enantioselectivities (27 examples with ≥99% ee) without the need for any additional stoichiometric oxidants (overall 40 examples). The new indirect electrosynthesis can be scaled to gram quantities and was applied to the straightforward synthesis of intermediates of the natural product cryptophycin A and a cathepsin K inhibitor.

Electrochemical Enantioselective Nucleophilic α-C(sp3)-H Alkenylation of 2-Acyl Imidazoles.

Herein, an efficient and facile approach to valuable β -hydroxy acid derivatives from readily available aryl epoxides and CO 2 with high chemo- and regioselectivity under mild and sustainable electrochemical conditions is described. This approach showed broad substrate scope and good functional-group compatibility. In addition to aryl epoxides, four- to six-membered aryl cyclic ethers could all be tolerated in the reaction to provide synthetically useful hydroxy acids with high efficiency. Further late-stage carboxylation of complex molecules and drug derivatives demonstrated its potential application in the pharmaceutical industry. Mechanistic studies disclosed possible reaction pathways.

Electrocarboxylation of Aryl Epoxides with CO2 for the Facile and Selective Synthesis of β-Hydroxy Acids.

Abstract Electrochemical asymmetric catalysis has emerged as a sustainable and promising approach to the production of chiral compounds and the utilization of both the anode and cathode as working electrodes would provide a unique approach for organic synthesis. However, precise matching of the rate and electric potential of anodic oxidation and cathodic reduction make such idealized electrolysis difficult to achieve. Herein, asymmetric cross-coupling between α-chloroesters and aryl bromides is probed as a model reaction, wherein alkyl radicals are generated from the α-chloroesters through a sequential oxidative electron transfer process at the anode, while the nickel catalyst is reduced to a lower oxidation state at the cathode. Radical clock studies, cyclic voltammetry analysis, and electron paramagnetic resonance experiments support the synergistic involvement of anodic and cathodic redox events. This electrolytic method provides an alternative avenue for asymmetric catalysis that could find significant utility in organic synthesis. 

/pdf/paired-electrolysis-enabled-nickel-catalyzed-tml23rjl.pdf

Paired electrolysis-enabled nickel-catalyzed enantioselective reductive cross-coupling between α-chloroesters and aryl bromides

An electrochemical asymmetric coupling of secondary acyclic amines with ketones via a Shono-type oxidation has been described, affording the corresponding amino acid derivatives with good to excellent diastereoselectivity and enantioselectivity. The addition of an N-oxyl radical as a redox mediator could selectively oxidize the substrate rather than the product, although their oxidation potential difference is subtle (about 13 mV). This electrochemical transformation proceeds in the absence of stoichiometric additives, including metals, oxidants, and electrolytes, which gives it good functional group compatibility. Mechanistic studies suggest that proton-mediated racemization of the product is prevented by the reduction of protons at the cathode.

TEMPO-Enabled Electrochemical Enantioselective Oxidative Coupling of Secondary Acyclic Amines with Ketones.

The selective difluoromethylene insertion into a C-Cu bond is a challenging task and is currently limited to either a single CF2 insertion into CuCF3 or double CF2 insertions into CuC6F5 (or (Z)-CF3CF = CFCu). Achieving both selective single and double CF2 insertions into the same C-Cu bond is even more difficult. Herein, highly controllable single and double CF2 insertions into CuCF2H species with a TMSCF2Br reagent have been described, affording two previously unknown fluoroalkylcopper species "Cu(CF2)nCF2H" (n = 1 and 2) independently under different reaction conditions. This work represents the first example of both single and double CF2 insertions into the same C-Cu bond in a highly selective manner. The synthetic value of the obtained "Cu(CF2)nCF2H" (n = 1 and 2) species is demonstrated by their reactions with aryl iodides, halogenation agents, and cinnamyl chloride, which enables the direct transfer of HCF2CF2 and HCF2CF2CF2 moieties into organic molecules. The key to controllable fluorocarbon chain elongation from C1 to C2 and from C1 to C3 is presumably attributed to the different reactivities of "Cu(CF2)nCF2H" species (n = 0, 1, 2 and 3) and the loading of the TMSCF2Br reagent.

Controllable Single and Double Difluoromethylene Insertions into C-Cu Bonds: Copper-Mediated Tetrafluoroethylation and Hexafluoropropylation of Aryl Iodides with TMSCF2H and TMSCF2Br.

Synthesis of fluoroalkenes via Julia and Julia-Kocienski olefination reactions

Copper-mediated pentafluoroethylation of organoboronates and terminal alkynes with TMSCF3.

The transition-metal-catalyzed carbonylation reaction is a useful approach for ketone synthesis. But it is often problematic to use exogenous carbonyl reagents, such as the gaseous carbon monoxide. In this manuscript, we report a novel palladium-catalyzed coupling reaction of gem -difluoroalkenes and aryl boronic acids that yields bioactive indane-type ketones with an all-carbon α-quaternary center. Characterization and stoichiometric reactions of the key intermediates RCF 2 Pd II support a water-induced defluorination and cross-coupling cascade mechanism. The vinyl difluoromethylene motif serves as an in-situ carbonyl precursor which is unprecedented in the transition-metal-catalyzed coupling reactions. It is expected to raise broad research interest from the perspectives of ketone synthesis, fluoroalkene functionalization, and rational design of new synthetic protocols based on the unique reactivity of difluoroalkyl palladium(II) species.

Palladium-Catalyzed Defluorinative Coupling of Difluoroalkenes and Aryl Boronic Acids for Ketone Synthesis.

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Papers

TEMPO-Enabled Electrochemical Enantioselective Oxidative Coupling of Secondary Acyclic Amines with Ketones.

Controllable Single and Double Difluoromethylene Insertions into C-Cu Bonds: Copper-Mediated Tetrafluoroethylation and Hexafluoropropylation of Aryl Iodides with TMSCF2H and TMSCF2Br.

Synthesis of fluoroalkenes via Julia and Julia-Kocienski olefination reactions

Copper-mediated pentafluoroethylation of organoboronates and terminal alkynes with TMSCF3.

Palladium-Catalyzed Defluorinative Coupling of Difluoroalkenes and Aryl Boronic Acids for Ketone Synthesis.