Copper/Nitroxyl-Catalyzed Synthesis of Pyrroles by Oxidative Coupling of Diols and Primary Amines at Room Temperature

Fu, Weiru; Zhu, Lina; Tan, Shangzhi; Zhao, Zhengjia; Yu, Xiangzhu; Wang, Lianyue

doi:10.1021/acs.joc.2c01646

Cited by 5 publications

(3 citation statements)

References 50 publications

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“…Due to the high importance of this oxidation process, other nitroxides, − ligands, and tetranuclear and dinuclear copper complexes were tested. Protocols for the selective oxidation of amino alcohols, selective oxidation of a serine in peptides, a nitrile synthesis by oxidation in the presence of aqueous ammonia, , a pyrrole synthesis starting from 1,4-diols and an amine, and a flow process for the alcohol oxidation were developed. Also, oxidative rearrangement of tertiary allylic alcohols with copper was investigated with O 2 as the terminal oxidant …”

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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Section: Oxidation Reactionsmentioning

confidence: 99%

Organic Synthesis Using Nitroxides

Leifert

Studer

2023

Chem. Rev.

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“…Recently, based on the Paal−Knorr reaction, we developed a Cu/ABNO catalyst system for the oxidative coupling of amine and 2,5-hexanediol to prepare N-substituted pyrrole. 12 Generally, amines can be obtained by reduction of nitro compounds, so the one-pot synthesis of pyrrole from nitro compound hydrogenation and Paal−Knorr condensation is considered to have attractive stepeconomic advantages. 13 At present, there are few reports on Paal−Knorr condensation after the reduction of nitro compounds.…”

Section: Introductionmentioning

confidence: 99%

“…Among them, the Paal–Knorr synthesis of pyrrole from primary amines with 1,4-diketones is a reliable transformation. Recently, based on the Paal–Knorr reaction, we developed a Cu/ABNO catalyst system for the oxidative coupling of amine and 2,5-hexanediol to prepare N -substituted pyrrole . Generally, amines can be obtained by reduction of nitro compounds, so the one-pot synthesis of pyrrole from nitro compound hydrogenation and Paal–Knorr condensation is considered to have attractive step-economic advantages …”

Section: Introductionmentioning

confidence: 99%

Metal-Free Nitrogen-Doped Mesoporous Carbons for the Mild and Selective Synthesis of Pyrroles from Nitroarenes via Cascade Reaction

Yu,

Miao,

Huo

et al. 2024

ACS Appl. Mater. Interfaces

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The cascade synthesis of pyrroles from nitroarenes is an attractive alternative strategy. However, metal catalysts and relatively high temperatures cover the existing reported catalytic systems for this strategy. The development of nonmetallic heterogeneous catalytic systems for the one-pot synthesis of pyrrole from nitroarenes under mild conditions is both worthwhile and challenging. Herein, we describe an exceptionally efficient method for the synthesis of N-substituted pyrroles by the reductive coupling of nitroarenes and diketones over heterogeneous metal-free catalysts under mild conditions. Nonmetallic NC-X catalysts with high activity were prepared from the pyrolysis of well-defined ligands via simple sacrificing hard template methods. Hydrazine hydrate, formic acid, and molecular hydrogen can all be used as reducing agents in the hydrogenation/Paal−Knorr reaction sequence to efficiently synthesize various N-substituted pyrroles, including drugs and bioactive molecules. The catalytic system was featured with good tolerance to sensitive functional groups and no side reactions such as dehalogenation and aromatics hydrogenation. Hammett correlation studies have shown that the electron-donating substituents are beneficial for the onepot synthesis of N-substituted pyrroles. The results established that the outstanding performance of the catalyst is mainly attributed to the contribution of graphitic N in the catalyst as well as the promotion effect of the mesoporous structure on the reaction.

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Five-membered ring systems: pyrroles and benzo analogs

Lopchuk

2023

Progress in Heterocyclic Chemistry

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Copper/Nitroxyl-Catalyzed Synthesis of Pyrroles by Oxidative Coupling of Diols and Primary Amines at Room Temperature

Cited by 5 publications

References 50 publications

Organic Synthesis Using Nitroxides

Organic Synthesis Using Nitroxides

Metal-Free Nitrogen-Doped Mesoporous Carbons for the Mild and Selective Synthesis of Pyrroles from Nitroarenes via Cascade Reaction

Five-membered ring systems: pyrroles and benzo analogs

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