Kinetics‐Based Approach to Developing Electrocatalytic Variants of Slow Oxidations: Application to Hydride Abstraction‐Initiated Cyclization Reactions

Lawrence, Jean-Marc I A; Floreancig, Paul E.

doi:10.1002/chem.202200335

Cited by 3 publications

(4 citation statements)

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“…The reaction of trisubstituted alkene 5 to yield 6 (Entry 2) was faster than the oxidation of 1, as expected based on the enhanced capability of a trisubstituted alkene to stabilize a cation in comparison to a disubstituted alkene, and the transformation was similarly clean. Notably, this reaction can be conducted on 1 mmol scale to give an 82 % yield and is suitable for electrocatalytic oxidation, [13] showing that these processes can be conducted with substoichiometric quantities of oxidant. The conversion of 7 to 8 (Entry 3) demonstrated that alkene geometry can be conserved in these processes, which is a distinct advantage over the oxidation of vinyl carbamates whereby stereoselectivity for trisubstituted alkene products through hydride abstraction from a methine group in a branched substrate would not be expected.…”

Section: Resultsmentioning

confidence: 99%

Nitrogen Heterocycle Synthesis through Hydride Abstraction of Acyclic Carbamates and Related Species: Scope, Mechanism, Stereoselectivity, and Product Conformation Studies

Miller,

Damodaran,

Floreancig

2023

Chemistry A European J

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Acyliminium ions and related species are potent electrophiles that can be quite valuable in the synthesis of nitrogen‐containing molecules. This manuscript describes a protocol to form these intermediates through hydride abstractions of easily accessible allylic carbamates, amides, and sulfonamides that avoids the reversibility that is possible in classical condensation‐based routes. These intermediates are used in the preparation of a range of nitrogen‐containing heterocycles, and in many cases high levels of sterocontrol are observed. Specifically areas of investigation include the impact of chemical structure on oxidation efficiency, the geometry of the intermediate iminium ions, the impact of a substrate stereocenter on stereocontrol, and an examination of transition state geometry.

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Section: Resultsmentioning

confidence: 99%

Nitrogen Heterocycle Synthesis through Hydride Abstraction of Acyclic Carbamates and Related Species: Scope, Mechanism, Stereoselectivity, and Product Conformation Studies

Miller,

Damodaran,

Floreancig

2023

Chemistry A European J

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“…Oxocarbenium ions 162 derived from allylic or benzylic ethers 161 can easily be trapped with nucleophiles other than water without fragmentation (Scheme c). With water as the nucleophile, a hemiacetal is formed, which can fragment to an alcohol and aldehyde (see above) or can be oxidized to an ester. , Other nucleophiles used in the oxoammonium salt-mediated oxidative α-functionalization of benzylic ethers to give products of type 163 are 1,3-dicarbonyl compounds, enols derived from aldehydes, enol acetates, alcohols, and allyl silanes …”

Section: Oxidation Reactionsmentioning

confidence: 99%

“…With water as the nucleophile, a hemiacetal is formed, which can fragment to an alcohol and aldehyde (see above) or can be oxidized to an ester. 1030,1031 Other nucleophiles used in the oxoammonium salt-mediated oxidative α-functionalization of benzylic ethers to give products of type 163 are 1,3-dicarbonyl compounds, 1032 enols derived from aldehydes, 1033 enol acetates, alcohols, 1034 and allyl silanes. 1035 4.7.3.…”

Section: Oxidations Of C Nucleophilesmentioning

confidence: 99%

Organic Synthesis Using Nitroxides

Leifert

Studer

2023

Chem. Rev.

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Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R 1 R 2 N−O • . The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R 1 and R 2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R 1 R 2 N�O + ) or reduced to anions (R 1 R 2 N−O − ), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C−O bonds, allowing for the thermal generation of C radicals through reversible C−O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.

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“…The low concentration of hydroxylamine leads to significant increases in potential when the reaction is conducted under constant current conditions, creating the possibility for substrate and product decomposition through single electron oxidation pathways. These problems were addressed by Lawrence, 180 who showed that constant potential conditions are desirable for these transformations where the potential is substantially higher than the oxidation potential of the hydroxylamine but lower than the oxidation potential of the substrate. Additionally, trifluoroethanol (TFE) is the optimal additive to ensure that the kinetics of oxidant regeneration are suitable for conducting the transformations in a reasonable time frame (Scheme 66).…”

Section: Oxoammonium Ionsmentioning

confidence: 99%