154554-67-3Relevant academic research and scientific papers
Absolute Rate Constants for the Reactions of Some Carbon-Centered Radicals with 2,2,6,6-Tetramethylpiperidine-N-oxyl
Chateauneuf, J.,Lusztyk, J.,Ingold, K. U.
, p. 1629 - 1632 (1988)
A time-resolved, laser flash photolysis study of the reaction of a variety of carbon-centered radicals with Tempo (2,2,6,6-tetramethylpiperidine-N-oxyl) at room temperature is reported.Some of the radicals examined and the corresponding measured rate constants (M-1 s-1) are CH3(CH2)7CH2-radical, 1.2 * 109; (CH3)3C-radical, 7.6 * 108; C6H5CH2-radical, 4.9 * 108; C6H5C(CH3)2-radical, 1.2 * 108; (C6H5)2CCH3-radical, 4.6 * 107.Arrhenius parameters have also been determined for the n-nonyl and benzyl radicals.
Synthesis of N-alkoxy amines via catalytic oxidation of hydrocarbons
Kirner, Hans-J.,Schwarzenbach, Franz,Van Der Schaaf, Paul A.,Hafner, Andreas,Rast, Valerie,Frey, Markus,Nesvadba, Peter,Rist, Guenther
, p. 554 - 560 (2004)
Sterically hindered N-alkoxy amines 3 are synthesized in good yields by coupling nitroxides 2 with hydrocarbyl radicals generated in situ by t-BuOOH hydrogen abstraction from hydrocarbons. The reaction is catalyzed by copper halides as well as by onium iodides.
On-demand acid-gated fluorescence switch-on in photo-generated nanospheres
Barner, Leonie,Barner-Kowollik, Christopher,Cavalli, Federica,Delafresnaye, Laura,Feist, Florian,Hooker, Jordan P.
, p. 4986 - 4989 (2020)
Herein, we introduce a fast, additive-free, ambient temperature photochemical approach - utilising the novel Diels-Alder cycloaddition of a photo-activeortho-methylbenzaldehyde (oMBA) with a terminal alkyne - for preparing functional acid-sensitive proflu
Phosphite mediated asymmetric N to C migration for the synthesis of chiral heterocycles from primary amines
Alam, Md Nirshad,Bera, Asish,Dash, Soumya Ranjan,Maity, Pradip,Rani, Soniya,Vanka, Kumar
, p. 8996 - 9003 (2021)
A phosphite mediated stereoretentive C-H alkylation ofN-alkylpyridinium salts derived from chiral primary amines was achieved. The reaction proceeds through the activation of theN-alkylpyridinium salt substrate with a nucleophilic phosphite catalyst, followed by a base mediated [1,2]aza-Wittig rearrangement and subsequent catalyst dissociation for an overall N to C-2 alkyl migration. The scope and degree of stereoretention were studied, and both experimental and theoretical investigations were performed to support an unprecedentedaza-Wittig rearrangement-rearomatization sequence. A catalytic enantioselective version starting with racemic starting material and chiral phosphite catalyst was also established following our understanding of the stereoretentive process. This method provides efficient access to tertiary and quaternary stereogenic centers in pyridine systems, which are prevalent in drugs, bioactive natural products, chiral ligands, and catalysts.
Selective electrochemical generation of benzylic radicals enabled by ferrocene-based electron-transfer mediators
Lennox, Alastair J.J.,Nutting, Jordan E.,Stahl, Shannon S.
, p. 356 - 361 (2018)
The generation and intermolecular functionalisation of carbon-centred radicals has broad potential synthetic utility. Herein, we show that benzylic radicals may be generated electrochemically from benzylboronate derivatives at low electrode potentials (ca. -0.3 V vs. Cp2Fe0/+) via single electron oxidation. Use of a catalytic quantity of a ferrocene-based electron-transfer mediator is crucial to achieve successful radical functionalisation and avoid undesirable side reactions arising from direct electrochemical oxidation or from the use of stoichiometric ferrocenium-based oxidants.
Acid Is Key to the Radical-Trapping Antioxidant Activity of Nitroxides
Haidasz, Evan A.,Meng, Derek,Amorati, Riccardo,Baschieri, Andrea,Ingold, Keith U.,Valgimigli, Luca,Pratt, Derek A.
, p. 5290 - 5298 (2016)
Persistent dialkylnitroxides (e.g., 2,2,6,6-tetramethylpiperidin-1-oxyl, TEMPO) play a central role in the activity of hindered amine light stabilizers (HALS)-additives that inhibit the (photo)oxidative degradation of consumer and industrial products. The accepted mechanism of HALS comprises a catalytic cycle involving the rapid combination of a nitroxide with an alkyl radical to yield an alkoxyamine that subsequently reacts with a peroxyl radical to eventually re-form the nitroxide. Herein, we offer evidence in favor of an alternative reaction mechanism involving the acid-catalyzed reaction of a nitroxide with a peroxyl radical to yield an oxoammonium ion followed by electron transfer from an alkyl radical to the oxoammonium ion to re-form the nitroxide. In preliminary work, we showed that TEMPO reacts with peroxyl radicals at diffusion-controlled rates in the presence of acids. Now, we show that TEMPO can be regenerated from its oxoammonium ion by reaction with alkyl radicals. We have determined that this reaction, which has been proposed to be a key step in TEMPO-catalyzed synthetic transformations, occurs with k ～ 1-3 × 1010 M-1 s-1, thereby enabling it to compete with O2 for alkyl radicals. The addition of weak acids facilitates this reaction, whereas the addition of strong acids slows it by enabling back electron transfer. The chemistry is shown to occur in hydrocarbon autoxidations at elevated temperatures without added acid due to the in situ formation of carboxylic acids, accounting for the long-known catalytic radical-trapping antioxidant activity of TEMPO that prompted the development of HALS.
Electrochemical and Electrostatic Cleavage of Alkoxyamines
Zhang, Long,Laborda, Eduardo,Darwish, Nadim,Noble, Benjamin B.,Tyrell, Jason H.,Pluczyk, Sandra,Le Brun, Anton P.,Wallace, Gordon G.,Gonzalez, Joaquin,Coote, Michelle L.,Ciampi, Simone
, p. 766 - 774 (2018)
Alkoxyamines are heat-labile molecules, widely used as an in situ source of nitroxides in polymer and materials sciences. Here we show that the one-electron oxidation of an alkoxyamine leads to a cation radical intermediate that even at room temperature rapidly fragments, releasing a nitroxide and carbocation. Digital simulations of experimental voltammetry and current-time transients suggest that the unimolecular decomposition which yields the "unmasked" nitroxide (TEMPO) is exceedingly rapid and irreversible. High-level quantum computations indicate that the collapse of the alkoxyamine cation radical is likely to yield a neutral nitroxide radical and a secondary phenylethyl cation. However, this fragmentation is predicted to be slow and energetically very unfavorable. To attain qualitative agreement between the experimental kinetics and computational modeling for this fragmentation step, the explicit electrostatic environment within the double layer must be accounted for. Single-molecule break-junction experiments in a scanning tunneling microscope using solvent of low dielectric (STM-BJ technique) corroborate the role played by electrostatic forces on the lysis of the alkoxyamine C-ON bond. This work highlights the electrostatic aspects played by charged species in a chemical step that follows an electrochemical reaction, defines the magnitude of this catalytic effect by looking at an independent electrical technique in non-electrolyte systems (STM-BJ), and suggests a redox on/off switch to guide the cleavage of alkoxyamines at an electrified interface.
D0Metal-Catalyzed Alkyl-Alkyl Cross-Coupling Enabled by a Redox-Active Ligand
Belli, Roman G.,Joannou, Matthew V.,Roberts, Courtney C.,Tafuri, Victoria C.
, p. 3094 - 3099 (2022/03/15)
Alkyl-alkyl cross-coupling through well-defined mechanisms that allow for controlled oxidative addition, prevent β-hydride elimination, and tolerate hindered electrophiles is still challenging. Described herein is a redox-active ligand-enabled alkyl-alkyl cross-coupling using a d0 metal. This tris(amido) ScIII complex as well as the oxidized variant have been thoroughly characterized (NMR, X-ray, EPR, CV, UV-vis, DFT). Insight into the likely radical nature of the mechanism is disclosed. Additionally, a substrate scope that includes functional groups incompatible with late-transition-metal catalysis and both coupling partners bearing β-hydrogens is reported.
Enantioconvergent Cu-Catalyzed Radical C-N Coupling of Racemic Secondary Alkyl Halides to Access α-Chiral Primary Amines
Cheng, Jiang-Tao,Dong, Xiao-Yang,Gu, Qiang-Shuai,Li, Zhong-Liang,Liu, Juan,Liu, Xin-Yuan,Luan, Cheng,Wang, Fu-Li,Wang, Li-Lei,Yang, Ning-Yuan,Zhang, Yu-Feng
supporting information, p. 15413 - 15419 (2021/09/30)
α-Chiral alkyl primary amines are virtually universal synthetic precursors for all other α-chiral N-containing compounds ubiquitous in biological, pharmaceutical, and material sciences. The enantioselective amination of common alkyl halides with ammonia is appealing for potential rapid access to α-chiral primary amines, but has hitherto remained rare due to the multifaceted difficulties in using ammonia and the underdeveloped C(sp3)-N coupling. Here we demonstrate sulfoximines as excellent ammonia surrogates for enantioconvergent radical C-N coupling with diverse racemic secondary alkyl halides (>60 examples) by copper catalysis under mild thermal conditions. The reaction efficiently provides highly enantioenrichedN-alkyl sulfoximines (up to 99% yield and >99% ee) featuring secondary benzyl, propargyl, α-carbonyl alkyl, and α-cyano alkyl stereocenters. In addition, we have converted the masked α-chiral primary amines thus obtained to various synthetic building blocks, ligands, and drugs possessing α-chiral N-functionalities, such as carbamate, carboxylamide, secondary and tertiary amine, and oxazoline, with commonly seen α-substitution patterns. These results shine light on the potential of enantioconvergent radical cross-coupling as a general chiral carbon-heteroatom formation strategy.
The effect of viscosity on the coupling and hydrogen-abstraction reaction between transient and persistent radicals
Li, Xiaopei,Kato, Tatsuhisa,Nakamura, Yasuyuki,Yamago, Shigeru
, p. 966 - 972 (2021/04/29)
The effect of viscosity on the radical termination reaction between a transient radical and a persistent radical undergoing a coupling reaction (Coup) or hydrogen abstraction (Abst) was examined. In a non-viscous solvent, such as benzene (bulk viscosity bulk 99% Coup/Abst selectivity, but Coup/Abst decreased as the viscosity increased (89/11 in PEG400 at 25 °C [bulk = 84 mPa s]). While bulk viscosity is a good parameter to predict the Coup/Abst selectivity in each solvent, microviscosity is the more general parameter. Poly(methyl methacrylate) (PMMA)-end radicals had a more significant viscosity effect than polystyrene (PSt)-end radicals, and the Coup/Abst ratio of the former dropped to 50/50 in highly viscous media (bulk = 3980 mPa s), while the latter maintained high Coup/ Abst selectivity (84/16). These results, together with the low thermal stability of dormant PMMA-TEMPO species compared with that of PSt-TEMPO species, are attributed to the limitation of the nitroxide-mediated radical polymerization of MMA. While both organotellurium and bromine compounds were used as precursors of radicals, the former was superior to the latter for the clean generation of radical species.
