Enantioselective Oxidation of Secondary Alcohols Using a Chiral Nitroxyl (<i>N</i>-Oxoammonium salt) Catalyst

Rychnovsky, S. D.; McLernon, and Terri L.; Rajapakse, Hemaka A.

doi:10.1021/jo9522320

Cited by 101 publications

(58 citation statements)

References 20 publications

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“…Selectivity (S) values of up to 7 were achieved for reactions of 1-aryl ethanol derivatives under Anelli conditions. [92] Electrooxidative kinetic resolution of secondary alcohols with 23 afforded S values of up to 20 under optimized conditions (Scheme 14). [93] Enantioselective electrocatalytic oxidation was also reported for a TEMPO-modified graphite felt electrode in the presence of (À)-sparteine.…”

Section: Kinetic Resolution Of Alcoholsmentioning

confidence: 99%

Nitroxides: Applications in Synthesis and in Polymer Chemistry

2011

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This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures.

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Section: Kinetic Resolution Of Alcoholsmentioning

confidence: 99%

Nitroxides: Applications in Synthesis and in Polymer Chemistry

2011

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“…It is suggested that the s value for any given case be measured at more than one concentration. 89,90 Some authors have given s values along with ee and conversion values, and some have not.…”

Section: Two-electron Secondarymentioning

confidence: 99%

“…85 Reactions with the chiral binaphthyl derivative 9 have been more successful. 90 Treatment of racemic 1-phenylethanol with sodium hypochlorite/potassium bromide as the secondary oxidant, in the presence of catalytic amounts of nitroxide 9, results in the S-isomer of the phenylethanol being preferentially oxidized with s values of 5-7. The values are measured at two conversions, (Eqs.…”

Section: Two-electron Secondarymentioning

confidence: 99%

Oxoammonium‐ and Nitroxide‐Catalyzed Oxidations of Alcohols

2009

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The discovery in 1959 of stable nitroxide‐based free radicals such as the prototypical 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) led to their use as electron spin resonance (ESR) spin labels in chemistry, biomedicine, and materials science. These nitroxides are prepared by the oxidation of secondary amines that contain no hydrogen atoms on the alpha‐carbons. The unique redox properties of nitroxides enable their use as oxidants in organic synthesis. The varied preparation and uses of oxoammonium salts as stoichiometric oxidants for alcohols are one subject of this review. Oxoammonium ions as oxidants for alcohols have a number of advantages, for example, the method is heavy‐metal free and some of the reactions can be performed in water or aqueous mixtures. A few side reactions are associated with these oxidations. The most serious is the fast reaction of the oxoammonium ion with free amines The several ways these oxidation reactions can be carried out are discussed in detail. They are: Oxidations using stoichimetric quantities of preformed oxoammonium salts carried out in either acidic, neutral, or basic conditions; reactions in which stoichiometric quantities of oxoammonium salts are generated in situ by disproportionation of a nitroxide in the presence of a strong acid; nitroxide‐catalyzed oxidations using a secondary oxidant; efficient nitroxide‐catalyzed oxidations of primary alcohols to carboxylic acids; and oxidations of primary alcohols or hemiacetals that can lead to lactones.

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“…In the present paper, the catalytic activity of the novel nitroxides was demonstrated, proving their ability to cycle between radical and hydroxylamine oxidation states. Since these compounds are chiral, it is especially attractive to consider potential applications in asymmetric catalysis 25,26,55 and as probes for biological studies. Indeed, multiple applications in catalysis, biology and medicine may be foreseen; however, this is beyond the scope of the present communication and will form the basis of further reports.…”

Section: Discussionmentioning

confidence: 99%

Design concept for α-hydrogen-substituted nitroxides

et al. 2015

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Stable nitroxides (nitroxyl radicals) have many essential and unique applications in chemistry, biology and medicine. However, the factors influencing their stability are still under investigation, and this hinders the design and development of new nitroxides. Nitroxides with tertiary alkyl groups are generally stable but obviously highly encumbered. In contrast, a-hydrogen-substituted nitroxides are generally inherently unstable and rapidly decompose. Herein, a novel, concept for the design of stable cyclic a-hydrogen nitroxides is described, and a proof-of-concept in the form of the facile synthesis and characterization of two diverse series of stable a-hydrogen nitroxides is presented. The stability of these unique a-hydrogen nitroxides is attributed to a combination of steric and stereoelectronic effects by which disproportionation is kinetically precluded. These stabilizing effects are achieved by the use of a nitroxide co-planar substituent in the g-position of the backbone of the nitroxide. This premise is supported by a computational study, which provides insight into the disproportionation pathways of a-hydrogen nitroxides.

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Enantioselective Oxidation of Secondary Alcohols Using a Chiral Nitroxyl (N-Oxoammonium salt) Catalyst

Cited by 101 publications

References 20 publications

Nitroxides: Applications in Synthesis and in Polymer Chemistry

Nitroxides: Applications in Synthesis and in Polymer Chemistry

Oxoammonium‐ and Nitroxide‐Catalyzed Oxidations of Alcohols

Design concept for α-hydrogen-substituted nitroxides

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