[3+2] Cycloaddition Reaction of Cyclopropyl Ketones with Alkynes Catalyzed by Nickel/Dimethylaluminum Chloride

Tamaki, Takashi; Ohashi, Masato; Ogoshi, Sensuke

doi:10.1002/ange.201106174

Cited by 24 publications

(16 citation statements)

References 50 publications

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“…13 Reductive ring openings of the analogous cyclopropanecarboxyl esters and amides have only been achieved by employing excess SmI 2 activated by H 2 O, where care must be taken to avoid over-reduction to the alcohol. 156 Reductive ring openings of cyclopropyl ketones have enabled many valuable transformations including mono 157 and di-functionalizations, 152,153,[158][159][160][161][162][163][164] so we anticipate that further development of these ester and amide ring opening protocols will enable more complex transformations.…”

Section: Scheme 2 Additional Reductive Transformationsmentioning

confidence: 99%

CdS Quantum Dots as Potent Photoreductants for Organic Chemistry Enabled by Auger Recombination

Widness

Enny

McFarlane-Connelly

et al. 2022

Preprint

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Strong reducing agents (< -2.0 V vs SCE) enable a wide array of useful organic chemistry, but suffer from a variety of limitations. Stoichiometric metallic reductants such as alkali metals and SmI2 are commonly employed for these reactions, however considerations including expense, ease of use, safety, and waste generation limit the practicality of these methods. Recent approaches utilizing energy from multiple photons or electron-primed photoredox catalysis have accessed reduction potentials equivalent to Li0 and shown how this enables selective transformations of aryl chlorides via aryl radicals. However, in some cases low stability of catalytic intermediates can limit turnover numbers. Herein we report the ability of CdS nanocrystal quantum dots (QDs) to function as strong photoreductants and present evidence that a highly reducing electron is generated from two consecutive photoexcitations of CdS QDs with intermediate reductive quenching. Mechanistic experiments suggest that Auger recombination, a photophysical phenomenon known to occur in photoexcited anionic QDs, generates transient thermally excited electrons to enable the observed reductions. Using blue LEDs and sacrificial amine reductants, aryl chlorides and phosphate esters with reduction potentials up to -3.4 V vs. SCE are photo-reductively cleaved to afford hydrodefunctionalized or functionalized products. In contrast to small molecule catalysts, the QDs are stable under these conditions and turnover numbers up to 47500 have been achieved. These conditions can also effect other challenging reductions, such as tosylate protecting group removal from amines, debenzylation of alcohols, and reductive ring-opening of cyclopropanecarboxylic acid derivatives.

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Section: Scheme 2 Additional Reductive Transformationsmentioning

confidence: 99%

CdS Quantum Dots as Potent Photoreductants for Organic Chemistry Enabled by Auger Recombination

Widness

Enny

McFarlane-Connelly

et al. 2022

Preprint

View full text Add to dashboard Cite

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“…Early in reaction development we recognized that the ligands that promote concerted nickel(0) oxidative addition of cyclopropyl ketones, such as monodentate phosphines and Nheterocyclic carbenes, form metallacyclic intermediates that are unreactive for Negishi crosscoupling reactions (6)(7)(8)(9)(10). On the other hand, while it is known that bi-and tridentate N-donor ligands promote cross-coupling reactions with alkyl halides to form C(sp 2 )-C(sp 3 ) and C(sp 3 )-C(sp 3 ) bonds (21)(22)(23)(24)(25), these ligands have not been reported for C-C bond activation reactions.…”

Section: Main Textmentioning

confidence: 99%

Ligand-Metal Cooperation Enables C–C Activation Cross-Coupling Reactivity of Cyclopropyl Ketones

Gilbert

Trenerry

Longley

et al. 2021

Preprint

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Activation of C-C bonds has the potential to revolutionize how molecules are made by altering the carbon skeleton and enabling new synthetic routes. Stereodefined cyclopropyl ketones have become readily available and would be an ideal source of linear 3-carbon fragments, but this reactivity is unknown. In this study we show how a new type of C-C activation catalyst, that relies upon a different, metalloradical mechanism, can enable new subsequent reactivity: the crosscoupling of cyclopropyl ketones with organozinc reagents and chlorotrimethylsilane to form 1,3difunctionalized, ring-opened products. A mixture of experiment and theory sheds light on how cooperation between the redox-active ligand and the nickel catalyst enables the C-C bond activation step, suggesting how this approach could be applied in other systems.One-Sentence Summary: A new C-C activation mechanism unlocks new subsequent reactivity and a new approach to using cyclopropyl ketones in synthesis.

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“…This strategy has enabled the discovery of many new reactions, such as ring expansions with π components, but broadening the reactivity of the metallacyclic intermediates derived from cyclopropane oxidative addition remains an outstanding challenge (4,5). For example, while nickel-catalyzed "cut-and-sew" reactions of cyclopropyl ketones with alkenes and alkynes has transformed how cyclopentanes are synthesized (6)(7)(8)(9), difunctionalization to acyclic products has been elusive (Fig. 1A) (10).…”

Section: Main Textmentioning

confidence: 99%

Section: Main Textmentioning

confidence: 99%

Ligand-Metal Cooperation Enables C–C Activation Cross-Coupling Reactivity of Cyclopropyl Ketones

Gilbert

Trenerry

Longley

et al. 2021

Preprint

View full text Add to dashboard Cite

Activation of C–C bonds has the potential to revolutionize how molecules are made by altering the carbon skeleton and enabling new synthetic routes. Stereodefined cyclopropyl ketones have become readily available and would be an ideal source of linear 3-carbon fragments, but this reactivity is unknown. In this study we show how a new type of C–C activation catalyst, that relies upon a different, metalloradical mechanism, can enable new subsequent reactivity: the cross- coupling of cyclopropyl ketones with organozinc reagents and chlorotrimethylsilane to form 1,3- difunctionalized, ring-opened products. A mixture of experiment and theory sheds light on how cooperation between the redox-active ligand and the nickel catalyst enables the C–C bond activation step, suggesting how this approach could be applied in other systems.

show abstract

[3+2] Cycloaddition Reaction of Cyclopropyl Ketones with Alkynes Catalyzed by Nickel/Dimethylaluminum Chloride

Cited by 24 publications

References 50 publications

CdS Quantum Dots as Potent Photoreductants for Organic Chemistry Enabled by Auger Recombination

CdS Quantum Dots as Potent Photoreductants for Organic Chemistry Enabled by Auger Recombination

Ligand-Metal Cooperation Enables C–C Activation Cross-Coupling Reactivity of Cyclopropyl Ketones

Ligand-Metal Cooperation Enables C–C Activation Cross-Coupling Reactivity of Cyclopropyl Ketones

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