Metal-free oxoammonium salt-mediated C(sp<sup>3</sup>)–H oxidative Ugi-azide multicomponent reaction

Lohmann, Niklas; Milovanović, Vesna; Piekarski, Dariusz G.; Mancheño, Olga Garcı́a

doi:10.1039/d2ob00101b

Cited by 6 publications

(4 citation statements)

References 87 publications

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“…However, this report does not provide clear understanding of the mechanism of 1,5-dipolar cyclisation. 18 Overall, based on our computational study and supported by Leroy's report, an adequate representation of the 1,5-electrocyclization towards the 1,5-DS-T ring formation is shown in Scheme 6 (bottom).…”

Section: Resultssupporting

confidence: 70%

Ultrasound-assisted diastereoselective green synthesis of spiro-fused-γ-lactams functionalized with an amide bond heterocyclic bioisostere via the Ugi azide/domino process coupled strategy

Calderón-Rangel,

Rentería-Gómez,

Cruz-Jiménez

et al. 2024

Org. Biomol. Chem.

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Section: Resultssupporting

confidence: 70%

Ultrasound-assisted diastereoselective green synthesis of spiro-fused-γ-lactams functionalized with an amide bond heterocyclic bioisostere via the Ugi azide/domino process coupled strategy

Calderón-Rangel,

Rentería-Gómez,

Cruz-Jiménez

et al. 2024

Org. Biomol. Chem.

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“…Tetrahydroisoquinolines have been successfully used as substrates in oxidative α-functionalization, mostly applying oxoammonium salts as stoichiometric oxidants (Scheme ). − In the first step, an iminium ion is generated via hydride transfer to an oxoammonium salt (TEMPO + BF 4 – or Bobbitt’s salt). This iminium ion is trapped in the second step with various nucleophiles.…”

Section: Oxidation Reactionsmentioning

confidence: 99%

“…A very elegant approach was presented by the group of García Mancheño using diazomethane derivatives as nucleophiles, leading to a ring expansion to obtain valuable 3-benzazepines (Scheme f) . With sodium azide in combination with various isonitriles, tetrazoles are formed (Scheme i) . Of note, oxidative Ugi azide , or Ugi three-component , reactions were already performed on other N -alkyl amines.…”

Section: Oxidation Reactionsmentioning

confidence: 99%

“…667 With sodium azide in combination with various isonitriles, tetrazoles are formed (Scheme 26i). 670 Of note, oxidative Ugi azide 677,678 or Ugi three-component 677,679 reactions were already performed on other N-alkyl amines. The α oxidation of N-protected tetrahydroisoquinolines was realized using an electrochemical approach with water as the nucleophile to give the corresponding hemiaminals, which are finally oxidized to the amides (Scheme 26j).…”

Section: Physical Properties and Reactivitymentioning

confidence: 99%

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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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Harnessing Oxoammonium Salts for Oxidations in Organic Synthesis and Catalysis: Origins and Applications

Wang,

Wen,

Liu

et al. 2024

Eur J Org Chem

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The oxoammonium cation has been identified as the true oxidant intermediate in many aerobic oxidations promoted by long‐lived nitroxide radicals. Various oxoammonium salts have been synthesized and utilized to perform these oxidation reactions. In addition to alcohol dehydrogenation and oxidative coupling reactions, new types of reactions involving oxoammonium salts have recently been reported. This concept aims to discuss these oxidations from the perspective of reaction mechanisms, with a focus on progress made since 2019. Beyond the electron transfer route for synthesizing oxoammonium salts, four types of reaction mechanisms are included.

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Metal-free oxoammonium salt-mediated C(sp³)–H oxidative Ugi-azide multicomponent reaction

Abstract: In this work, an efficient oxidative C(sp3)–H Ugi-azide multicomponent reaction of cyclic benzylic amines to the corresponding α-tetrazolo compounds using a TEMPO salt as mild hydride abstractor-type oxidant is reported....

Cited by 6 publications

References 87 publications

Ultrasound-assisted diastereoselective green synthesis of spiro-fused-γ-lactams functionalized with an amide bond heterocyclic bioisostere via the Ugi azide/domino process coupled strategy

Ultrasound-assisted diastereoselective green synthesis of spiro-fused-γ-lactams functionalized with an amide bond heterocyclic bioisostere via the Ugi azide/domino process coupled strategy

Organic Synthesis Using Nitroxides

Harnessing Oxoammonium Salts for Oxidations in Organic Synthesis and Catalysis: Origins and Applications

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Metal-free oxoammonium salt-mediated C(sp3)–H oxidative Ugi-azide multicomponent reaction

Abstract: In this work, an efficient oxidative C(sp3)–H Ugi-azide multicomponent reaction of cyclic benzylic amines to the corresponding α-tetrazolo compounds using a TEMPO salt as mild hydride abstractor-type oxidant is reported....

Cited by 6 publications

References 87 publications

Ultrasound-assisted diastereoselective green synthesis of spiro-fused-γ-lactams functionalized with an amide bond heterocyclic bioisostere via the Ugi azide/domino process coupled strategy

Ultrasound-assisted diastereoselective green synthesis of spiro-fused-γ-lactams functionalized with an amide bond heterocyclic bioisostere via the Ugi azide/domino process coupled strategy

Organic Synthesis Using Nitroxides

Harnessing Oxoammonium Salts for Oxidations in Organic Synthesis and Catalysis: Origins and Applications

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Product

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Metal-free oxoammonium salt-mediated C(sp³)–H oxidative Ugi-azide multicomponent reaction