Anionic halocuprate(II) complexes as catalysts for the oxaziridine-mediated aminohydroxylation of olefins

Eco-Friendly Homo- and Cross-Etherification of Benzyl Alcohols Catalyzed by Iron(II/III) Chloride in Propylene Carbonate as a Green and Recyclable Solvent

A new catalytic approach toward the symmetrical and nonsymmetrical etherification of benzyl alcohols was developed. The symmetrical etherification reaction was carried out in the presence of FeCl3·6H2O (5 mol %) as the catalyst and propylene carbonate as a green and recyclable solvent and led to the corresponding symmetrical ethers in 53 to 91% yields. The nonsymmetrical etherification of benzylic alcohols was achieved by using FeCl2·4H2O (10 mol %) in the presence of a pyridine bis-thiazoline ligand (12 mol %) and allowed for high selectivity and in 52 to 89% yields. These methods take advantage of eco-friendly conditions.

Emerging Trends in Copper-Promoted Radical-Involved C-O Bond Formations

The C-O bond is ubiquitous in biologically active molecules, pharmaceutical agents, and functional materials, thereby making it an important functional group. Consequently, the development of C-O bond-forming reactions using catalytic strategies has become an increasingly important research topic in organic synthesis because more conventional methods involving strong base and acid have many limitations. In contrast to the ionic-pathway-based methods, copper-promoted radical-mediated C-O bond formation is experiencing a surge in research interest owing to a renaissance in free-radical chemistry and photoredox catalysis. This Perspective highlights and appraises state-of-the-art techniques in this burgeoning research field. The contents are organized according to the different reaction types and working models.

Regiodivergent Electrophotocatalytic Aminooxygenation of Aryl Olefins

A method for the regiodivergent aminooxygenation of aryl olefins under electrophotocatalytic conditions is described. The procedure employs a trisaminocyclopropenium (TAC) ion catalyst with visible light irradiation under a controlled electrochemical potential to convert aryl olefins to the corresponding oxazolines with high chemo- and diastereoselectivity. With the judicious choice between two inexpensive and abundant reagents, namely water and urethane, either 2-amino-1-ol or 1-amino-2-ol derivatives could be prepared from the same substrate. This method is amenable to multigram synthesis of the oxazoline products with low catalyst loadings.

Chiral Hypervalent Iodine Catalysis Enables an Unusual Regiodivergent Intermolecular Olefin Aminooxygenation

A novel iodide-catalyzed intermolecular aminooxygenation strategy is described here. Amide is used as the O- and N- source to probe for regiocontrol strategies. Notably, simple additives can be selectively introduced to achieve regiodivergent oxyamination processes for electronically activated alkenes while being regio-complementary for unactivated alkenes. Our preliminary data demonstrates that this regiocontrol strategy based on nucleophile can also be applied in asymmetric processes using chiral hypervalent iodine catalysis.

Organoiodine-Catalyzed Enantioselective Intermolecular Oxyamination of Alkenes

Metal-free, catalytic enantioselective intermolecular oxyamination of alkenes is realized by use of organoiodine(I/III) chemistry. The protocol is applicable toward aryl- and alkyl-substituted alkenes with high enantioselectivity and electronically controlled regioselectivity. The oxyaminated products can be easily deprotected in one step to reveal free amino alcohols in high yields without loss of enantioselectivity. A key to our success is the discovery of a virtually unexplored chemical entity, N-(fluorosulfonyl)carbamate, as a bifunctional N,O-nucleophile.

Beyond osmium: progress in 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes

Olefin 1,2-difunctionalization has emerged as a popular strategy within modern synthetic chemistry for the synthesis of vicinal amino alcohols and derivatives. The advantage of this approach is the single-step simplicity for rapid diversification, feedstock nature of the olefin starting materials, and the possible modularity of the components. Although there is a vast number of possible iterations of 1,2-olefin difunctionalization, 1,2-amino oxygenation is of particular interest due to the prevalence of both oxygen and nitrogen within pharmaceuticals, natural products, agrochemicals, and synthetic ligands. The Sharpless amino hydroxylation provided seminal results in this field and displayed the value in achieving methods of this nature. However, a vast number of new and novel methods have emerged in recent decades. This review provides a comprehensive review of modern advances in accomplishing 1,2-amino oxygenation of alkenes, 1,3-dienes, alkynes, and allenes that move beyond osmium to a range of other transition metals and more modern strategies such as electrochemical, photochemical, and biochemical reactivity.

Enantioselective, Aerobic Copper-Catalyzed Intramolecular Carboamination and Carboetherification of Unactivated Alkenes

Reduction of waste is an important goal of modern organic synthesis. We report herein oxidase reactivity for enantioselective intramolecular copper-catalyzed alkene carboamination and carboetherification reactions where previously used stoichiometric MnO2 has been replaced with oxygen. This substitution was risky as the reaction mechanism is thought to involve C-C bond formation via addition of alkyl carbon radicals to arenes. Such intermediates are also susceptible to C-O bond formation via O2 addition. Control of absolute stereochemistry under aerobic conditions was also uncertain. The oxidative cyclization efficiencies appear to track with the ease of the radical addition to the arenes.

Oxyamination of Unactivated Alkenes with Electron-Rich Amines and Acids via a Catalytic Triiodide Intermediate

An aerobic catalytic oxidation process is described for the olefin oxyamination using acids and primary amines as the sources of O and N. Our mechanistic findings point to the formation of triiodide as a critical catalytic intermediate to account for the tolerance of electron-rich nucleophiles. This dual iodide and copper catalytic system is suitable for a formal [5+1] annulation process to access valuable lactam structures and highlighted by the synthesis of the pharmaceutical Zamifenacin.

Copper-Catalyzed 1,2-Amino Oxygenation of 1,3-Dienes: A Chemo-, Regio-, and Site-Selective Three-Component Reaction with O-Acylhydroxylamines and Carboxylic Acids

A three-component reaction for 1,2-amino oxygenation of 1,3-dienes has been achieved using O-acyl hydroxylamines and carboxylic acids. The reaction occurs through copper-catalyzed amination of olefins followed by nucleophilic addition of carboxylic acids, offering high levels of chemo-, regio-, and site-selectivity. The method is effective for both terminal and internal 1,3-dienes, including those bearing multiple, unsymmetrical substituents. The amino oxygenation conditions also exhibited remarkable selectivity toward 1,3-dienes over alkenes, good tolerance of sensitive functional groups, and reliable scalability.

Oxidative sulfamidation as a route to N-heterocycles and unsaturated sulfonamides

Oxidative sulfamidation is a promising approach to the synthesis of numerous organic compounds, including N-heterocycles or unsaturated species having the sulfonamide group, which is a key structural motif of synthetic antimicrobial drugs. The formed products can undergo further reactions leading to a wide variety of functionalized sulfonamides. This review summarizes the current state of knowledge on the oxidative reactions of sulfonamides and their derivatives with unsaturated and CH-active compounds with an emphasis on dienes as substrates. This produces a diverse range of compounds possessing sulfonamide function and capable of further functionalization.

Intermolecular alkene difunctionalizations for the synthesis of saturated heterocycles

Saturated heterocycles are important structural motifs in a range of pharmaceuticals and agrochemicals. As a result of their importance, syntheses of these molecules have been extensively investigated. Despite the progress in this area, the most adopted strategies are still often characterized with inefficiency or relying on functionalizations with specialized precursors and pre-existing cores. This review highlights a dynamic synthetic strategy for the direct synthesis of saturated heterocycles from intermolecular alkene difunctionalizations. These coupling processes are highly modular, and therefore, offer perhaps the most convenient means to prepare diverse heterocyclic structures in compound libraries for bioactivity evoluations.

Trinuclear copper(ii) bromide complex [C3H5N3Br]2n[Cu3Br8]n. Structure, magnetic properties and DFT calculations

Halidocuprates(ii) show unusual magnetic properties and a high degree of structural flexibility.

Recent Advances in the Catalytic Asymmetric Reactions of Oxaziridines

Oxaziridines have emerged as powerful and elegant oxygen- and nitrogen-transfer agents for a broad array of nucleophiles, due to the remarkably high and tunable reactivities. However, the asymmetric catalysis involving oxaziridines is still in its infancy. Herein, this review aims to examine recent advances in the catalytic asymmetric transformations of oxaziridines, including oxidation, amination, cycloaddition and deracemization.

Iridium catalyzed fragmentation/cyclization of N-butynyl 4,4-dimethylisoxazolidine-3,5-diones: a unique access to multiply substituted pyrroles

A novel protocol for the synthesis of multiply substituted pyrroles has been developed through the iridium catalyzed fragmentation/cyclization of N-butynyl 4,4-dimethylisoxazolidine-3,5-diones in hot ethanol.

Sterically Demanding Oxidative Amidation of α-Substituted Malononitriles with Amines Using O2

An efficient amidation method between readily available 1,1‐dicyanoalkanes and either chiral or nonchiral amines was realized simply with molecular oxygen and a carbonate base. This oxidative protocol can be applied to both sterically and electronically challenging substrates in a highly chemoselective, practical, and rapid manner. The use of cyclopropyl and thioether substrates support the radical formation of α‐peroxy malononitrile species, which can cyclize to dioxiranes that can monooxygenate malononitrile α‐carbanions to afford activated acyl cyanides capable of reacting with amine nucleophiles.

Synthesis of 2-Aryl- and 2-Vinylpyrrolidines via Copper-Catalyzed Coupling of Styrenes and Dienes with Potassium β-Aminoethyl Trifluoroborates

2-Arylpyrrolidines occur frequently in bioactive compounds, and thus, methods to access them from readily available reagents are valuable. We report a copper-catalyzed intermolecular carboamination of vinylarenes with potassium N-carbamoyl-β-aminoethyltrifluoroborates. The reaction occurs with terminal, 1,2-disubstituted, and 1,1-disubstituted vinylarenes bearing a number of functional groups. 1,3-Dienes are also good substrates, and their reactions give 2-vinylpyrrolidines. Radical clock mechanistic experiments are consistent with the presence of carbon radical intermediates and do not support participation of carbocations.

Spin-Selective Generation of Triplet Nitrenes: Olefin Aziridination through Visible-Light Photosensitization of Azidoformates

Azidoformates are interesting potential nitrene precursors, but their direct photochemical activation can result in competitive formation of aziridination and allylic amination products. Herein, we show that visible-light-activated transition-metal complexes can be triplet sensitizers that selectively produce aziridines through the spin-selective photogeneration of triplet nitrenes from azidoformates. This approach enables the aziridination of a wide range of alkenes and the formal oxyamination of enol ethers using the alkene as the limiting reagent. Preparative-scale aziridinations can be easily achieved under continuous-flow conditions.

Copper-catalyzed oxidative carbon–heteroatom bond formation: a recent update

This review updates recent advances in Cu-catalyzed (anaerobic) oxidative carbon–heteroatom bond formation on sp³- and sp²-C–H bonds as well as alkenes, classified according to the types of stoichiometric oxidants.

Copper-catalyzed oxyamination of electron-deficient alkenes with N-acyloxyamines

An intermolecular version of copper-catalyzed oxyamination of electron-deficient alkenes by making use of N-acyloxyamines as both amino and oxygen donors was developed.

A Simple Primary Amine Catalyst for Enantioselective α-Hydroxylations and α-Fluorinations of Branched Aldehydes

A new primary amine catalyst for the asymmetric α-hydroxylation and α-fluorination of α-branched aldehydes is described. The products of the title transformations are generated in excellent yields with high enantioselectivities. Both processes can be performed within short reaction times and on gram scale. The similarity in results obtained in both reactions, combined with computational evidence, implies a common basis for stereoinduction and the possibility of a general catalytic mechanism for α-functionalizations. Promising initial results in α-amination and α-chlorination reactions support this hypothesis.

mCPBA-mediated metal-free intramolecular aminohydroxylation and dioxygenation of unfunctionalized olefins

We report a mild and metal-free process to prepare a variety of 2-hydroxymethylpyrrolidine and oxolanimine compounds.

Cu(ii)-catalyzed enantioselective oxygen atom transfer from oxaziridine to oxindole derivatives with chiral phenanthroline

In the presence of a Cu(ii) complex of chiral, N,N,O-tridentate phenanthroline ligand (S)-2, asymmetric oxygen atom transfer of oxindole (3) using Davis’ oxaziridine (4) occurred to give the corresponding 3-aryl-3-hydroxy-2-oxindole derivatives (1) with excellent enantioselectivity.

Nef reaction with molecular oxygen in the absence of metal additives, and mechanistic insights

A Nef reaction has been developed that is conducted under mildly basic conditions with molecular oxygen as an oxidant, without the need for metal additives. Whereas nitroalkanes are converted into ketones in good yield, nitroalkenes are transformed into α,β-unsaturated ketones in one-pot by double-bond isomerization followed by the oxygen-mediated Nef reaction. The reaction protocol is both mild and general, and tolerates acid- and base-labile functionality or protecting groups. When oxygen-saturated solvents are employed, the reaction completes within 20 min. Mechanistically, the addition of nitronate ion and molecular oxygen is proposed to proceed initially through a single-electron transfer event, as indicated by radical clock experiments. This ultimately generates a putative 1,1-dioxirane, which reacts further with another nitronate ion to generate the ketone. Involvement of a 1,1-dioxirane is supported by intramolecular trapping experiments with sulfide at the γ-position of the nitro-moiety.

Catalytic asymmetric oxidation of N-sulfonyl imines with hydrogen peroxide-trichloroacetonitrile system

An efficient and highly enantioselective Payne-type oxidation of N-sulfonyl imines is developed. The reaction exhibits broad substrate generality and unique chemoselectivity based on the combined use of hydrogen peroxide and trichloroacetonitrile under the catalysis of P-spiro chiral triaminoiminophosphorane.

Copper-catalyzed oxaziridine-mediated oxidation of C-H bonds

The highly regio- and chemoselective oxidation of activated C-H bonds has been observed via copper-catalyzed reactions of oxaziridines. The oxidation proceeded with a variety of substrates, primarily comprising allylic and benzylic examples, as well as one example of an otherwise unactivated tertiary C-H bond. The mechanism of the reaction is proposed to involve single-electron transfer to the oxaziridines to generate a copper-bound radical anion, followed by hydrogen atom abstraction and collapse to products, with regeneration of the catalyst by a final single-electron transfer event. The involvement of allylic radical intermediates was supported by a radical-trapping experiment with TEMPO.