Copper-Catalyzed Intramolecular Amination of C(sp3)-H Bond of Secondary Amines to Access Azacycles

Recent synthetic strategies for N-arylation of pyrrolidines: a potential template for biologically active molecules

The chemistry of nitrogen-containing heterocyclic compounds has been a multifaceted area of research for an extended period due to their varied therapeutic and biological significance. N-Aryl pyrrolidine formed by condensation of aryl group with nitrogen atom of pyrrolidine is present in a wide array of compounds. Various significant activities shown by N-arylated pyrrolidine include anti-Alzheimer, antihypoxic, anticancer, plant activator, analgesic effect, and hepatitis C inhibitor. This review summarizes different synthetic approaches, e.g., transition-metal catalyzed and transition-metal-free synthesis, decarboxylation reaction, reductive amination, nucleophilic cyclization, Ullmann-Goldberg amidation, Buchwald-Hartwig reaction, Chan-Evans-Lam coupling, addition to benzyne, multistep reaction, green synthesis, rearrangement reaction, and multicomponent reaction, to afford the derivatives of N-aryl pyrrolidine. It encompasses synthetic strategies documented from 2015 to 2023.

Tandem Synthesis of Polysubstituted Pyrroles via Cu(I)-Catalyzed Cyclization of Ketene N,S-Acetals with β-Ketodinitriles

A new approach to multifunctionalized pyrroles has been explored by the tandem cyclization of α-oxoketene-N,S-acetals with β-ketodinitriles using Cu(MeCN)4BF4 and Ag2CO3 in toluene under reflux conditions. The reaction involves C-C/C-N bond creation, and is assumed to proceed via enamine formation, intramolecular cyclization, and rearrangement. The potential of the methodology has also been demonstrated for a gram-scale reaction as well as for some useful organic transformations. The reaction offers a practical pathway to achieve polysubstituted pyrroles with broad substrate scope and good functional group tolerance.

Copper-Catalyzed, Intramolecular Amination of Unactivated C(sp3)-H Bonds through Radical Relay

Although copper-catalyzed amination of activated C(sp3)-H bonds through radical relay has been developed, amination of unactivated C(sp3)-H bonds is rare. Herein, copper-catalyzed intramolecular amination of remote unactivated C(sp3)-H bonds is reported. The reaction is conducted in a mild and effective manner with moderate to good yields, demonstrating broad tolerance toward various functional groups and exhibiting complete regio- and chemoselectivities. This innovation supplies novel synthetic pathways for the construction of saturated nitrogenated heterocycles.

Metal-organic frameworks for organic transformations by photocatalysis and photothermal catalysis

Organic transformation by light-driven catalysis, especially, photocatalysis and photothermal catalysis, denoted as photo(thermal) catalysis, is an efficient, green, and economical route to produce value-added compounds. In recent years, owing to their diverse structure types, tunable pore sizes, and abundant active sites, metal-organic framework (MOF)-based photo(thermal) catalysis has attracted broad interest in organic transformations. In this review, we provide a comprehensive and systematic overview of MOF-based photo(thermal) catalysis for organic transformations. First, the general mechanisms, unique advantages, and strategies to improve the performance of MOFs in photo(thermal) catalysis are discussed. Then, outstanding examples of organic transformations over MOF-based photo(thermal) catalysis are introduced according to the reaction type. In addition, several representative advanced characterization techniques used for revealing the charge reaction kinetics and reaction intermediates of MOF-based organic transformations by photo(thermal) catalysis are presented. Finally, the prospects and challenges in this field are proposed. This review aims to inspire the rational design and development of MOF-based materials with improved performance in organic transformations by photocatalysis and photothermal catalysis.

Reductive Transamination of Pyridinium Salts to N-Aryl Piperidines

Saturated N-heterocycles are found in numerous bioactive natural products and are prevalent in pharmaceuticals and agrochemicals. While there are many methods for their synthesis, each has its limitations, such as scope and functional group tolerance. Herein, we describe a rhodium-catalyzed transfer hydrogenation of pyridinium salts to access N-(hetero)aryl piperidines. The reaction proceeds via a reductive transamination process, involving the initial formation of a dihydropyridine intermediate via reduction of the pyridinium ion with HCOOH, which is intercepted by water and then hydrolyzed. Subsequent reductive amination with an exogenous (hetero)aryl amine affords an N-(hetero)aryl piperidine. This reductive transamination method thus allows for access of N-(hetero)aryl piperidines from readily available pyridine derivatives, expanding the toolbox of dearomatization and skeletal editing.

Photoredox Catalyzed Synthesis of gem-Difluoroalkenes and Monofluorinated Cyclooctenes via 1,5-HAT Process

gem-Difluoroalkenes and monofluorinated cycloalkenes have emerged as basic structural units in a variety of bioactive molecules and natural products. Thus, developing straightforward and efficient methods for synthesizing fluorinated alkene compounds is of considerable significance. Herein, we disclose a visible-light-induced defluorination of 2-trifluoromethyl-1-alkene via a 1,5-HAT process using N-alkoxyphtalimides as both radical precursor and potential nucleophile. The mild and stepwise reaction leads to a variety of structurally diverse gem-difluoroalkenes and monofluorinated cyclooctenes with high efficiency, respectively.

Iodine-Mediated δ-Amination of sp3 C-H Bonds

We present a direct δ-amination reaction of sp3 C-H bonds, employing molecular iodine (I2) as the sole oxidant under transition-metal-free conditions. This remote C-H functionalization approach is operationally simple and provides facile, efficient access to pyrrolidines and related heterocyclic derivatives from readily accessible substrates.

Piperidine Derivatives: Recent Advances in Synthesis and Pharmacological Applications

Piperidines are among the most important synthetic fragments for designing drugs and play a significant role in the pharmaceutical industry. Their derivatives are present in more than twenty classes of pharmaceuticals, as well as alkaloids. The current review summarizes recent scientific literature on intra- and intermolecular reactions leading to the formation of various piperidine derivatives: substituted piperidines, spiropiperidines, condensed piperidines, and piperidinones. Moreover, the pharmaceutical applications of synthetic and natural piperidines were covered, as well as the latest scientific advances in the discovery and biological evaluation of potential drugs containing piperidine moiety. This review is designed to help both novice researchers taking their first steps in this field and experienced scientists looking for suitable substrates for the synthesis of biologically active piperidines.

Progress in copper-catalysed/mediated intramolecular dehydrogenative coupling

Transition metal-catalysed C-H functionalization reactions are one of the most efficient synthetic methodologies to construct carbon-carbon and carbon-heteroatom bonds. The initial developments in the field were largely dominated by expensive transition metal catalysts. However, in the past decade, the focus of the catalyst shifted to first-row transition metals and copper catalysis contributed significantly. Abundant, cost-effective, and less toxic copper catalysts are an ideal green alternative to palladium and similar metals. The intramolecular dehydrogenative coupling itself developed as a prominent area of focus as the strategy straightaway affords complex polycyclic scaffolds in one pot. Regioselective activation of inert C-H bonds were made possible with copper catalysts and interestingly, oxygen served as the terminal oxidant in most of the cases. In the present review the focus is on the intramolecular dehydrogenative coupling reactions between carbon-hydrogen and heteroatom-hydrogen bonds to afford carbon-carbon and carbon-hetero atom bonds, catalysed/mediated by copper salts. Though the intermolecular dehydrogenative coupling reactions of copper have already been reviewed more than once, to the best of our knowledge this is the first comprehensive account of copper-based intramolecular dehydrogenative coupling.

Copper-catalyzed aerobic benzylic C(sp3)-H lactonization of 2-alkylbenzamides via N-centered radicals

Herein, we describe the copper-catalyzed aerobic C(sp³)-H functionalization of 2-alkylbenzamides for the synthesis of benzolactones. This reaction proceeds via 1,5-hydrogen atom transfer of N-centered radicals directly generated by N-H bond cleavage and does not require the synthesis of pre-functionalized N-centered radical precursors or the use of strong stoichiometric oxidants.

Gold-Catalyzed Hydroarylation Reactions: A Comprehensive Overview

The hydroarylation of alkynes, alkene, and, allene is a cost-effective and efficient way to incorporate unsaturated moieties into aromatic substrates. This review focuses on gold-catalyzed hydroarylation, which produces aromatic alkenes,...

Copper-Catalyzed Fluoroamide-Directed Remote Benzylic C-H Olefination: Facile Access to Internal Alkenes

A general, site-selective copper-catalyzed fluoroamide-directed remote benzylic C-H olefination of N-fluoroamides with terminal alkenes for producing internal alkenes is disclosed. This protocol proceeds via a hybrid Cu-radical mechanism, which synergistically...

Intermolecular 1,2-Difunctionalization of Alkenes Enabled by Fluoroamide-Directed Remote Benzyl C(sp3)-H Functionalization

A copper-catalyzed remote benzylic C-H functionalization strategy enabling 1,2-difunctionalization of alkenes with 2-methylbenzeneamides and nucleophiles, including alcohols, indoles, pyrroles, and the intrinsic amino groups, is reported, which is characterized by its redox-neutral conditions, exquisite site-selectivity, broad substrate scope, and wide utilizations of late-stage modifying bioactive molecules. This reaction proceeds through nitrogen-centered radical generation, hydrogen atom transfer, benzylic radical addition across the alkenes, single-electron oxidation, and carbocation electrophilic course cascades. While using external nucleophiles manipulates three-component alkene alkylalkoxylation and alkyl-heteroarylation with 2-methylbenzeneamides to access dialkyl ethers, 3-alkylindoles, and 3-alkylpyrroles, omitting the external nucleophiles results in two-component alkylamidation ([5+2] annulation) of alkenes with 2-methylbenzeneamides to benzo-[f][1,2]thiazepine 1,1-dioxides.

Asymmetric Synthesis of Enantiopure Pyrrolidines by C(sp3 )-H Amination of Hydrocarbons

The asymmetric synthesis of enantiopure pyrrolidines is reported via a streamlined strategy relying on two sequential C-H functionalizations of simple hydrocarbons. The first step is a regio- and stereoselective catalytic nitrene C-H insertion. Then, a subsequent diastereoselective cyclization involving a 1,5-hydrogen atom transfer (HAT) from a N-centered radical leads to the formation of pyrrolidines that can then be converted to their free NH-derivatives.

I2/NaH2PO2-mediated deoxyamination of cyclic ethers for the synthesis of N-aryl-substituted azacycles

We have developed a protocol for efficient synthesis of N-aryl-substituted azacycles from aryl amines and cyclic ethers using I2/NaH2PO2 as the mediator.

Organocatalytic electrochemical amination of benzylic C–H bonds

An organocatalytic site-selective electrochemical method for the benzylic C–H amination of alkylarenes with azoles through hydrogen evolution has been developed.