Intermolecular Hydroalkoxylation and Hydrocarboxylation of 2-Azadienes with High Efficiency

Serviano, Juan M I; Phipps, Erik J T; Holland, Patrick L.

doi:10.1021/acs.joc.2c02534

Cited by 7 publications

(6 citation statements)

References 50 publications

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“…On the basis of literature reports ,,,− and our own observations, we envision the plausible mechanistic pathway (Figure B). The reaction is initiated by the first anodic event that involves the oxidation of Co(II) catalyst 3 to concurrently form Co(III)-hydride 22 upon rapid reaction with silane 4 .…”

Section: Resultsmentioning

confidence: 73%

Electrocatalytic Access to Azetidines via Intramolecular Allylic Hydroamination: Scrutinizing Key Oxidation Steps through Electrochemical Kinetic Analysis

et al. 2023

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Azetidines are prominent structural scaffolds in bioactive molecules, medicinal chemistry, and ligand design for transition metals. However, state-of-the-art methods cannot be applied to intramolecular hydroamination of allylic amine derivatives despite their underlying potential as one of the most prevalent synthetic precursors to azetidines. Herein, we report an electrocatalytic method for intramolecular hydroamination of allylic sulfonamides to access azetidines for the first time. The merger of cobalt catalysis and electricity enables the regioselective generation of key carbocationic intermediates, which could directly undergo intramolecular C–N bond formation. The mechanistic investigations including electrochemical kinetic analysis suggest that either the catalyst regeneration by nucleophilic cyclization or the second electrochemical oxidation to access the carbocationic intermediate is involved in the rate-determining step (RDS) of our electrochemical protocol and highlight the ability of electrochemistry in providing ideal means to mediate catalyst oxidation.

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Section: Resultsmentioning

confidence: 73%

Electrocatalytic Access to Azetidines via Intramolecular Allylic Hydroamination: Scrutinizing Key Oxidation Steps through Electrochemical Kinetic Analysis

et al. 2023

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“…Despite the initial progress in the domain of radical coupling strategies enabled by 2-azaallyl anions as SEDs, there is still a broad scope for further development in terms of applying newer nonstabilized ketimines as substrates, application of more clean and efficient energy sources (photocatalytic and electrocatalytic) as catalytic conditions. Similarly, the relatively recent discovery of transition-metal-catalyzed, [57,59] photoredoxcatalyzed, [59][60] and electro-catalyzed [61] CÀ H activation to generate 2-azaallyl radical species finally provides a more diverse protocol for these intriguing reactive species. In summary, the development of sustainable technologies to achieve more types of functionalization reactions using 2-azaallyl anions as SEDs and coupling partners still has a promising future.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, cobalt‐catalyzed HAT and oxidation for intermolecular hydroalkoxylation and hydrocarboxylation of 2‐azadienes [57] and transition‐metal‐free catalyzed α‐difluoroalkylation of benzyl amines with trifluoromethylarenes [58] have been reported. These protocols demonstrate excellent chemoselectivity and provide green and operationally simple approaches to afford a variety of functionalized products in good yields.…”

Section: C−x Bond Formationmentioning

confidence: 99%

Recent Advances in Radical Coupling Strategies Enabled by 2‐Azaallyl Anions as Super‐Electron‐Donors

Zou.,

Wang,

Ying

2024

Adv Synth Catal

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Abstract. Due to amine derivatives widely existing in numerous clinical medicines and bioactive compounds, their synthesis has received considerable attention over the past few decades. Traditional methods for the synthesis of amine derivatives largely relied on the reduction of nitroarenes, amides, hydrazines, nitriles, and azides. Recently, the discovery of 2‐azaallyl anions as super‐electron‐donors (SEDs) has opened up new possibilities for the construction of diverse carbon−carbon and carbon−heteroatom bonds through radical coupling strategies. This breakthrough highlights the potential of generating 2‐azaallyl radicals as versatile intermediates in organic synthesis. Then, hydrolysis of the coupling product can easily separate the corresponding amine derivatives. Thus, tremendous attention has been paid to the C–H functionalization of 2‐azaallyls as an alternative strategy for the synthesis of amine derivatives. Herein, we comprehensively summarize the recent progress in radical coupling strategies enabled by 2‐azaallyl anions as SEDs. Their proposed mechanistic pathways, advantages, and limitations are also discussed in detail.

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“…A variety of silanes have been used in oxidative MHAT catalysis, including PhSiH 3 , PhMeSiH 2 , Et 2 SiH 2 , and (Me 2 SiH) 2 O. − The oxidant is usually an N -fluoro-2,4,6-trimethylpyridinium ( N -fluorocollidinium) salt, but some methodologies utilize other oxidants such as N -fluorobenzenesulfonimide (NFSI), peroxybenzoates, or iodine(III) reagents. ,− Oxidative MHAT catalysis most often employs intramolecular nucleophiles, which are typically neutral O- and N-donor Lewis bases. These intramolecular reactions can afford epoxides, aziridines, lactones, lactams, ethers, pyrrolidines, and even benzocyclic compounds. ,,− Intermolecular reactions can add greater diversity to the products, and a few examples have been reported with alcohols, secondary amines, triazoles, or benzoic acids serving as the nucleophilic coupling partners. ,,,− Many solvents and functional groups are compatible with the reaction, and oxidative MHAT catalysis seldom requires temperatures above 25 °C, making it quite facile.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Alkene Hydrofunctionalization by Oxidative Cobalt(salen) Catalyzed Hydrogen Atom Transfer

Wilson,

Holland

2024

J. Am. Chem. Soc.

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Oxidative MHAT hydrofunctionalization of alkenes provides a mild cobalt-catalyzed route to forming C−N and C−O bonds. Here, we characterize relevant salen-supported cobalt complexes and their reactions with alkenes, silanes, oxidant, and solvent. These stoichiometric investigations are complemented by kinetic studies of the catalytic reaction and catalyst speciation. We describe the solution characterization of an elusive cobalt(III) fluoride complex, which surprisingly is not the species that reacts with silane under catalytic conditions; rather, a cobalt(III) aquo complex is more active. Accordingly, the addition of water (0.15 M) speeds the catalytic reaction, and kinetic studies show that water addition enables catalytic product formation in 2 h at −50 °C in acetone. Under these conditions, cobalt(III) resting states can be observed by UV−vis spectrophotometry, including a cobalt(III)-alkyl complex. It comes from a transient cobalt(III) hydride complex that is formed in the turnover-limiting step of the catalytic cycle. This hydride readily degrades but not to H 2 ; it releases H + through a bimetallic pathway that explains the [Co] 2 dependence of the off-cycle reaction. In contrast, the rate of the catalytic reaction follows the power law k obs [Co] 1 [silane] 1 . Because of the different [Co] dependence of the catalytic reaction and the degradation reaction, lower catalyst loading improves the yield of the catalytic reaction by reducing the relative rate of unproductive silane/oxidant consumption. These studies illuminate mechanistic details of oxidative MHAT hydrofunctionalization of alkenes and lay the groundwork for understanding other catalytic reactions mediated by cobalt hydride and cobalt alkyl complexes.

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Intermolecular Hydroalkoxylation and Hydrocarboxylation of 2-Azadienes with High Efficiency

Cited by 7 publications

References 50 publications

Electrocatalytic Access to Azetidines via Intramolecular Allylic Hydroamination: Scrutinizing Key Oxidation Steps through Electrochemical Kinetic Analysis

Electrocatalytic Access to Azetidines via Intramolecular Allylic Hydroamination: Scrutinizing Key Oxidation Steps through Electrochemical Kinetic Analysis

Recent Advances in Radical Coupling Strategies Enabled by 2‐Azaallyl Anions as Super‐Electron‐Donors

Mechanism of Alkene Hydrofunctionalization by Oxidative Cobalt(salen) Catalyzed Hydrogen Atom Transfer

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