A Transition-Metal-Free Homogeneous TEMPO-Based Catalyst: Aerobic Oxidation of Alcohols in Aqueous Media

Laeini, Mohammad Sadegh; Shaabani, Ahmad

doi:10.1002/slct.201701428

Cited by 9 publications

(4 citation statements)

References 38 publications

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“…It is remarkable to note that solasodine (3, Figure 2) after oxidation using that catalytic system yields carbonyl derivative only without any collateral reaction in the NH functionality. The probable mechanism for this oxidation process is similar to the pathway earlier described in the literature and depicted in Figure 3 [34,[48][49][50][51]]. It appears that the role of the hypervalent iodine compound (BAIB) is to regenerate the TEMPO-4-N-acetoxyamine in the catalytic cycle.…”

Section: Resultssupporting

confidence: 64%

Eco-Sustainable Catalytic System for Green Oxidation of Spirostanic Alcohols Using Hypervalent Iodine (III) Tempo-4-n-Acetoxyamine System

Sigüenza¹,

Villavicencio²,

Canchingre³

et al. 2022

Green Chemistry - New Perspectives

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The oxidation of the 3β-hydroxy group in the steroidal substrates obtained from naturally occurring sources, i.e., solanaceae steroidal sapogenins, is an important process in the preparation of ecdysteroid analogs. The need for selective green oxidation methodologies for steroidal alcohols (spirostenols, diosgenine, and derivatives) avoid the use of toxic Cr (VI) derivatives, without the isomerization of the double bond at 5,6 position and also without the oxidative cleavage of the spirocetal moiety is of great methodological significance. Herein, we report the oxidation of spirostanic steroidal alcohols to their carbonyl analogs using hypervalent iodine (III)/TEMPO-4-N-acetoxyamine system. The present method is simple, eco-sustainable, efficient, and high-yielding process for the oxidative transformation of secondary steroidal alcohols without any over-oxidation, isomerization of the double bond, or oxidative cleavage of spirocetalic fragment in different substrates. Therefore, this method does not involve toxic heavy metals and is expected to have wide utility in the oxidation process of these compounds.

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Section: Resultssupporting

confidence: 64%

Eco-Sustainable Catalytic System for Green Oxidation of Spirostanic Alcohols Using Hypervalent Iodine (III) Tempo-4-n-Acetoxyamine System

Sigüenza¹,

Villavicencio²,

Canchingre³

et al. 2022

Green Chemistry - New Perspectives

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“…In fact, TEMPO-based and nitroxyl radical-based transition-metal-free systems have already been reported. However, the reaction needed several co-catalysts, high temperature, and corrosive solvents. − …”

mentioning

confidence: 99%

Metal-Free Catalyst for Visible-Light-Induced Oxidation of Unactivated Alcohols Using Air/Oxygen as an Oxidant

et al. 2018

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9-Fluorenone acts as a metal-free and additive-free photocatalyst for the selective oxidation of primary and secondary alcohols under visible light. With this photocatalyst, a plethora of alcohols such as aliphatic, heteroaromatic, aromatic, and alicyclic compounds has been converted to the corresponding carbonyl compounds using air/oxygen as an oxidant. In addition to these, several steroids have been oxidized to the corresponding carbonyl compounds. Detailed mechanistic studies have also been achieved to determine the role of the oxidant and the photocatalyst for this oxidation.

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“…Guided by this valuable process, various other protocols have been developed, which also allow the transformation to be performed at room temperature at atmospheric pressure (Table ). − …”

Section: Oxidation Reactionsmentioning

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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A Transition-Metal-Free Homogeneous TEMPO-Based Catalyst: Aerobic Oxidation of Alcohols in Aqueous Media

Cited by 9 publications

References 38 publications

Eco-Sustainable Catalytic System for Green Oxidation of Spirostanic Alcohols Using Hypervalent Iodine (III) Tempo-4-n-Acetoxyamine System

Eco-Sustainable Catalytic System for Green Oxidation of Spirostanic Alcohols Using Hypervalent Iodine (III) Tempo-4-n-Acetoxyamine System

Metal-Free Catalyst for Visible-Light-Induced Oxidation of Unactivated Alcohols Using Air/Oxygen as an Oxidant

Organic Synthesis Using Nitroxides

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