Lifetimes of Simple Ketocarbenes

Toscano, John P.; Platz, Matthew S.; Nikolaev, V. A.

doi:10.1021/ja00121a032

Cited by 55 publications

(53 citation statements)

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“…In this way the production of α‐ketocarbene intermediates from α‐diazoketone could be realised. Consequently, the formation of these reaction intermediates can be confirmed either spectroscopically,14–16 or chemically from their characteristic reactions, like the Z ‐conformation specific17, 18 Wolff rearrangement, which involves a stereospecific 1,2‐carbon shift leading to the formation of ketene 11. Accordingly, we illustrate the first successful electrochemical Wolff rearrangement of α‐diazoketone, facilitating fine tuning of the electrode potential (Ag n 0 ) with the redox potential of α‐diazoketone, ultimately leading to the formation of the rearranged product in excellent yield.…”

Section: Methodsmentioning

confidence: 99%

“…The in situ UV‐visible spectrum (see Supporting Information Part 7) recorded by applying an anodic bias (0.5 V vs Ag/AgCl), using a Ag n electrode, to a solution of α‐diazoketone 1 a in an electrolyte solution of 0.1 M tetrabutylammoniumtetrafluoroborate in dichloromethane containing pyridine as the nucleophilic probe, exhibits the presence of a strong absorption band around λ =418 nm, indicating the involvement of either α‐ketocarbene intermediate 6 or ketene 7 . However, it is difficult to pinpoint the species due to close proximity of bands arising from α‐ketocarbene–pyridine ylide14–16 and ketene–pyridine ylide 29…”

Section: Methodsmentioning

confidence: 99%

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Silver Nanocluster Redox‐Couple‐Promoted Nonclassical Electron Transfer: An Efficient Electrochemical Wolff Rearrangement of α‐Diazoketones

Sudrik

Chaki

Chavan

et al. 2006

Chemistry A European J

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In this work we report the unique electrocatalytic role of benzoic acid protected silver nanoclusters (Ag(n), mean core diameter 2.5 nm) in the Wolff rearrangement (Scheme 1) of alpha-diazoketones. More specifically, the presence of a Ag(n) (0)/Ag(n) (+) redox couple facilitates a nonclassical electron-transfer process, involving chemical reaction(s) interposed between two electron-transfer steps occurring in opposite directions. Consequently, the net electron transfer between the electron mediator (Ag(n)) and alpha-diazoketone is zero. In-situ UV-visible studies using pyridine as a nucleophilic probe indicate the participation of alpha-ketocarbene/ketene as important reaction intermediates. Controlled potential coulometry of alpha-diazoketones using Ag(n) as the anode results in the formation of Wolff rearranged carboxylic acids in excellent yield, without sacrificing the electrocatalyst.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Silver Nanocluster Redox‐Couple‐Promoted Nonclassical Electron Transfer: An Efficient Electrochemical Wolff Rearrangement of α‐Diazoketones

Sudrik

Chaki

Chavan

et al. 2006

Chemistry A European J

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“…The ''ylide probe technique'', introduced by Platz and Jackson, [165] was applied to ethoxycarbonyl carbene, [166] bis(methoxycarbonyl)carbene (157), [167] and thio analogues, [68c] focusing on carbene lifetimes and intermolecular reactions. LFP of diazo ketones 182 (R ϭ H, Me, iPr, tBu) in the presence of pyridine or acetone showed that the yields of the presumed ylides decrease with increasing bulk of R. [168] Toscano suggested that scavengeable carbonyl carbenes 183 arise from s-E-182 whereas excited s-Z-182 produces ketene 185 by a concerted route (Scheme 28). A point of concern is that the products absorbing at ഠ 450 nm might be ketene-derived zwitterions 186 rather than Scheme 28.…”

Section: Laser Flash Photolysis (Lfp)mentioning

confidence: 99%

100 Years of the Wolff Rearrangement

2002

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The conversion of α‐diazo ketones into ketenes, and products derived therefrom, was discovered by Wolff in 1902. Major applications of the Wolff rearrangement, such as the Arndt−Eistert reaction (homologation of carboxylic acids) and the ring contraction of cyclic ketones, have been with us for some while. Nevertheless, substantial progress has been made recently. The reaction mechanism has been explored by means of matrix isolation, time‐resolved spectroscopy, and computation. Full retention of configuration of the migrating group has been established by using enantioselective chromatography. The Arndt−Eistert reaction has witnessed a renaissance in the field of natural products, in particular β‐amino acids and β‐peptides. Ring‐contracting Wolff rearrangements and ketene cycloadditions have been applied in syntheses of increasingly complex, biologically active target molecules. These accomplishments, as well as unsolved problems, are addressed in the present review. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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“…One such process involves photoconversion of a diazirine to a carbene, a highly-reactive diradical carbon center generated by irradiation at~310-350 nm [21], a less damaging wavelength for protein states. Carbenes have short lifetimes, on the order of tens of nanoseconds [22], and could permit fast-sampling of an equilibrated protein state. The products of the reaction involve insertions that can generate mass shifts based on the choice of reagent [23].…”

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confidence: 99%

Amino Acid Insertion Frequencies Arising from Photoproducts Generated Using Aliphatic Diazirines

Ziemianowicz

Bomgarden

Etienne

et al. 2017

J. Am. Soc. Mass Spectrom.

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Abstract. Mapping proteins with chemical reagents and mass spectrometry can generate a measure of accessible surface area, which in turn can be used to support the modeling and refinement of protein structures. Photolytically generated carbenes are a promising class of reagent for this purpose. Substituent effects appear to influence surface mapping properties, allowing for a useful measure of design control. However, to use carbene labeling data in a quantitative manner for modeling activities, we require a better understanding of their inherent amino acid reactivity, so that incorporation data can be normalized. The current study presents an analysis of the amino acid insertion frequency of aliphatic carbenes generated by the photolysis of three different diazirines: 3,3'-azibutyl-1-ammonium, 3,3'-azibutan-1-ol, and 4,4'-azipentan-1-oate. Leveraging an improved photolysis system for single-shot labeling of sub-microliter frozen samples, we used EThCD to localize insertion products in a large population of labeled peptides. Counting statistics were drawn from data-dependent LC-MS 2 experiments and used to estimate the frequencies of insertion as a function of amino acid. We observed labeling of all 20 amino acids over a remarkably narrow range of insertion frequencies. However, the nature of the substituent could influence relative insertion frequencies, within a general preference for larger polar amino acids. We confirm a large (6-fold) increase in labeling yield when carbenes were photogenerated in the solid phase (77 K) relative to the liquid phase (293 K), and we suggest that carbene labeling should always be conducted in the frozen state to avoid information loss in surface mapping experiments.

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Lifetimes of Simple Ketocarbenes

Cited by 55 publications

References 1 publication

Silver Nanocluster Redox‐Couple‐Promoted Nonclassical Electron Transfer: An Efficient Electrochemical Wolff Rearrangement of α‐Diazoketones

Silver Nanocluster Redox‐Couple‐Promoted Nonclassical Electron Transfer: An Efficient Electrochemical Wolff Rearrangement of α‐Diazoketones

100 Years of the Wolff Rearrangement

Amino Acid Insertion Frequencies Arising from Photoproducts Generated Using Aliphatic Diazirines

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