The electrochemical cleavage of protecting groups

Montenegro, M.I.

doi:10.1016/0013-4686(86)87027-x

Cited by 36 publications

(16 citation statements)

References 33 publications

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“…93 In our initial examination of this reaction, several p-toluenesulfonamides were reductively cleaved to afford the free amines in 62-88% yield. Arylamine 9a and melatonin-derived 9b were completely deprotected within 24 hours, while alkylamines 9c and 9d were slower and required 72 h, presumably due to their more-negative reduction potentials (E red ~ -2.4 V vs. SCE for N-tosyl alkylamines), 144 or higher propensity for back-electron transfer before fragmentation. Notably, sulfonyl-protected phenols have been reductively deprotected using CuInS 2 /ZnS QDs as a photocatalyst, 50 however only electron-poor sulfonyl groups with reduction potentials lessnegative than the employed QDs were cleaved under these conditions, in contrast to this study with CdS QDs.…”

Section: Kinetic Dependence On Light Intensity Kinetic Studies Of The...mentioning

confidence: 99%

“…Debenzylation is commonly accomplished through Pd-catalyzed hydrogenation. However, in situations where hydrogenolysis is incompatible with other substrate functionalities, it may also be accomplished by strong stoichiometric reductants [145][146][147][148] , electroreduction (E red = -3.1 V vs. SCE) 144 , or the combination of an organic reductant and UV light. 149 This approach allows clean deprotection to proceed under visible light irradiation with amine terminal reductants.…”

Section: Scheme 2 Additional Reductive Transformationsmentioning

confidence: 99%

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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: Kinetic Dependence On Light Intensity Kinetic Studies Of The...mentioning

confidence: 99%

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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“…AACC experienced recently a tremendous development as an efficient, selective, but also mild and functional-group-tolerant coupling chemistry. [37,38] While electrochemically addressable protection groups are known for a variety of functional groups, [39][40][41][42][43][44][45] there are no suitable masking groups for alkynes reported so far to the best of our knowledge. [37,38] While electrochemically addressable protection groups are known for a variety of functional groups, [39][40][41][42][43][44][45] there are no suitable masking groups for alkynes reported so far to the best of our knowledge.…”

Section: Introductionmentioning

confidence: 99%

“…[35,36] Its integration in a novel constructive surface built-up concept would be ideal as it proved to be useful for the further functionalization of surfaces exposing alkyne groups with azide derivatives. [37,38] While electrochemically addressable protection groups are known for a variety of functional groups, [39][40][41][42][43][44][45] there are no suitable masking groups for alkynes reported so far to the best of our knowledge. We became thus interested in electrochemically triggerable protection groups for alkynes as individually addressable electrodes would facilitate a siteselective molecular assembly for the reasons given above.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical Multiplexing: Control over Surface Functionalization by Combining a Redox‐Sensitive Alkyne Protection Group with “Click”‐Chemistry

Hellstern

Gantenbein

Puebla‐Hellmann

et al. 2019

Adv Materials Inter

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and molecular electronics, [11,12] over medical diagnostic devices [13][14][15] to applications tuning macroscopic and/or environmental features like, e.g., the wettability [16][17][18] or the biocompatibility [19][20][21] of material surfaces. In most cases, a bifunctional molecule, combining an anchor group attaching the molecular compound to the surface with an exposed subunit representing the active moiety with tailored physiochemical properties is used to tune the surface's terminal appearance. While such approaches are successfully applied for entire objects and surfaces of considerable dimensions and macroscopic separations, there are limitations as soon as spatial patterns of varying surface functionalities and microscopic separations are desired or a spatially constrained surface-access including buried microfluidic chips has to be overcome. For example, conventional wet chemical surface functionalization procedures are spatially limited to the size of the droplet deposited (and its subsequent surface interaction) and methods depositing the molecules from gas-phase in vacuum require advanced masking strategies. Challenging are devices with a variety of molecular features to be created in a parallel process and in a locally controlled manner, like, e.g., multidimensional sensing platforms where a multitude of nearby molecular receptors are screening analytes in parallel. Or microfluidic chips with constrained access to functional sites as the channels are locally enclosed and inaccessible for droplet deposition. Of great interest are devices analyzing molecular binding events electronically, due to their miniaturization potential and the analyte-selective binding without the requirement of labels. In such devices, each electrode is electrically addressable in a separated manner as they were contacted individually. Such a preexisting electrical wiring scheme is a unique feature for an immobilization strategy able to distinguish between the applied electrical potentials of each electrode and a common electrolyte. The electrochemical release of thiol-based self-assembled monolayers (SAMs) on gold electrodes has been reported. [22] This allows the disintegration of existing SAMs. The subsequent decoration of the liberated electrode with an alternative thiol-molecule, however, is handicapped by scrambling with the remaining SAMs. Electrochemical triggered constructive build-up of molecular Local functionalization of surfaces is a current technological challenge. An electrochemically addressable alkyne protection group is presented enabling the site-selective liberation of alkynes exclusively on electrified electrodes. This controlled deprotection is based on a mendione chromophore which becomes a strong enough nucleophile upon reduction to intramolecularly attack the trialkylsilane alkyne protection group. The site-selective liberation of the alkyne is demonstrated by immobilizing the protected alkyne precursor on a transparent TiO 2 electrode and subsequently immobilizing red and blue azide dyes by azide-alky...

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“…The electrochemical cleavage method [1][2][3][4][5][6] has been an excellent alternative to chemical methods for the removal of reducible protecting groups from amine and alcohol functionalities in polyfunctional molecules. Unfortunately, many commonly used protecting groups reduce only at very negative potentials (above -2 V vs. SCE), resulting in other difficulties which diminish selectivity.…”

Section: Introductionmentioning

confidence: 99%

The Cathodic Cleavage of the Nitrobenzoyl Group from Protected Aliphatic Amines in N,N-Dimethylformamide

Jorge¹,

Campos²,

Stradiotto³

1999

J. Braz. Chem. Soc.

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A redução eletroquímica de aminas alifáticas protegidas pelo grupo 4-e 3-nitrobenzoila em N,N-dimetilformamida foi estudada. Os compostos são reduzidos em duas etapas catódicas. A primeira em aproximadamente -1 V vs. ECS ocorre com a formação de radicais ânions relativamente estáveis, envolvendo a transferência de um elétron. A redução ao diânion ocorre no intervalo de -1,5 e -2,0 V vs. ECS por um processo ECE, conduzindo à clivagem da ligação CN com rendimentos acima de 50%.The electrochemical reduction of aliphatic amines protected by the 4-and 3-nitrobenzoyl group in N,N-dimethylformamide was reported. The compounds are reduced in two cathodic steps. The first one at about -1 V vs. SCE occurs with the formation of the rather stable anion radicals, involving one electron transfer . The reduction to dianion occurs at potentials between -1.5 and -2.0 V vs. SCE by an ECE process and leads to cleavage of the CN bond in yields above 50%. FAPESP helped in meeting the publication costs of this article Figure 3. Cyclic voltammograms of N-N-butyl-4-nitrobenzamide 10 mmol dm -3 . (---) before, (-) after electrolysis. Potential scan rate 0.10 V s -1 . (I) -1.25 V vs. SCE; (II) -2.07 V vs. SCE.

show abstract

The electrochemical cleavage of protecting groups

Cited by 36 publications

References 33 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

Electrochemical Multiplexing: Control over Surface Functionalization by Combining a Redox‐Sensitive Alkyne Protection Group with “Click”‐Chemistry

The Cathodic Cleavage of the Nitrobenzoyl Group from Protected Aliphatic Amines in N,N-Dimethylformamide

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