Catalytic, Enantioselective Syn-Oxyamination of Alkenes

Organoselenium-Catalyzed Enantioselective Synthesis of 2-Oxazolidinones from Alkenes

An operationally simple method for generating enantioenriched 2-oxazolidinones from N-Boc amines and mono- or trans-disubstituted alkenes via chiral organoselenium catalysis is described. Critical to the success of the transformation was the inclusion of triisopropylsilyl chloride (TIPSCl), likely because it sequestered fluoride generated by the oxidant (N-fluorocollidinium tetrafluoroborate) throughout the reaction and suppressed side reactivity. The scope of both the amine and alkene substrates was explored, generating a variety of 2-oxazolidinones in modest to high yields with high enantioselectivities.

Hypervalent iodine-catalyzed amide and alkene coupling enabled by lithium salt activation

Hypervalent iodine catalysis has been widely utilized in olefin functionalization reactions. Intermolecularly, the regioselective addition of two distinct nucleophiles across the olefin is a challenging process in hypervalent iodine catalysis. We introduce here a unique strategy using simple lithium salts for hypervalent iodine catalyst activation. The activated hypervalent iodine catalyst allows the intermolecular coupling of soft nucleophiles such as amides onto electronically activated olefins with high regioselectivity.

Intermolecular Aza-Wacker Coupling of Alkenes with Azoles by Photo-Aerobic Selenium-π-Acid Multicatalysis

Herein, the intermolecular, photoaerobic aza-Wacker coupling of azoles with alkenes by means of dual and ternary selenium-π-acid multicatalysis is presented. The title method permits an expedited avenue toward a broad scope of N-allylated azoles and representative azinones under mild conditions with broad functional group tolerance, as is showcased in more than 60 examples including late-stage drug derivatizations. From a regiochemical perspective, the protocol is complementary to cognate photoredox catalytic olefin aminations, as they typically proceed through either allylic hydrogen atom abstraction or single electron oxidation of the alkene substrate. These methods predominantly result in C-N bond formations at the allylic periphery of the alkene or the less substituted position of the former π-bond (i.e., anti-Markovnikov selectivity). The current process, however, operates through a radical-polar crossover mechanism, which solely affects the selenium catalyst, thus allowing the alkene to be converted strictly through an ionic two-electron transfer regime under Markovnikov control. In addition, it is shown that the corresponding N-vinyl azoles can also be accessed by sequential or one-pot treatment of the allylic azoles with base, thus emphasizing the exquisite utility of this method.

Catalytic 1,1-diazidation of alkenes

Compared to well-developed catalytic 1,2-diazidation of alkenes to produce vicinal diazides, the corresponding catalytic 1,1-diazidation of alkenes to yield geminal diazides has not been realized. Here we report an efficient approach for catalytic 1,1-diazidation of alkenes by redox-active selenium catalysis. Under mild conditions, electron-rich aryl alkenes with Z or E or Z/E mixed configuration can undergo migratory 1,1-diazidation to give a series of functionalized monoalkyl or dialkyl geminal diazides that are difficult to access by other methods. The method is also effective for the construction of polydiazides. The formed diazides are relatively safe by TGA-DSC analysis and impact sensitivity tests, and can be easily converted into various valuable molecules. In addition, interesting reactivity that geminal diazides give valuable molecules via the geminal diazidomethyl moiety as a formal leaving group in the presence of Lewis acid is disclosed. Mechanistic studies revealed that a selenenylation-deselenenylation followed by 1,2-aryl migration process is involved in the reactions, which provides a basis for the design of new reactions.

Asymmetric Synthesis with Organoselenium Compounds - The Past Twelve Years

The discovery and synthetic applications of novel organoselenium compounds and their reactions proceeded rapidly during the past fifty years and such processes are now carried out routinely in many laboratories. At the same time, the growing demand for new enantioselective processes provided new challenges. The convergence of selenium chemistry and asymmetric synthesis led to key developments in the 1970s, although the majority of early work was based on stoichiometric processes. More recently, greater emphasis has been placed on greener catalytic variations, along with the discovery of novel reactions and a deeper understanding of their mechanisms. The present review covers the literature in this field from 2010 to early 2023 and encompasses asymmetric reactions mediated by chiral selenium-based reagents, auxiliaries, and especially, catalysts. Protocols based on achiral selenium compounds in conjunction with other species of chiral catalysts, as well as reactions that are controlled by chiral substrates, are also included.

Recent Progress in Synthesis and Application of Chiral Organoselenium Compounds

Chiral organoselenium compounds have shown an important role as intermediates in many areas, such as drug discovery, organic catalysis, and nanomaterials. A lot of different methods have been developed to synthesize chiral compounds which contain selenium, because they have interesting properties and can be used in real life. Over the last few decades, a lot of progress has been made in synthesizing chiral organoselenium compounds. This work gives an overview of the progress made in creating new ways to synthesize chiral organoselenium compounds by categorizing them into groups based on the reactions they undergo. In addition, the use of chiral organoselenium compounds is also discussed.

Catalytic Enantioselective Aminative Difunctionalization of Alkenes

Enantioselective difunctionalization of alkenes offers a straightforward means for the rapid construction of enantioenriched complex molecules. Despite the tremendous efforts devoted to this field, enantioselective aminative difunctionalization remains a challenge, particularly through an electrophilic addition fashion. Herein, we report an unprecedented approach for the enantioselective aminative difunctionalization of alkenes via copper-catalyzed electrophilic addition with external azo compounds as nitrogen sources. A series of valuable cyclic hydrazine derivatives via either [3 + 2] cycloaddition or intramolecular cyclization have been achieved in high chemo-, regio-, enantio-, and diastereoselectivities. In this transformation, a wide range of functional groups, such as carboxylic acid, hydroxy, amide, sulfonamide, and aryl groups, could serve as nucleophiles. Importantly, a new cyano oxazoline chiral ligand was found to play a crucial role in the control of enantioselectivity.

Synthesis of aminoalcohols from substituted alkenes via tungstenooxaziridine catalysis

Herein we report the WO2Dipic(H2O) promoted oxyamination of alkenes using sulfonamides as the quantitative source of N. The reaction works for activated and unactivated alkenes in high yields, diastereoselectivities, and stereospecificity. A catalytic cycle involving the formation of tungstenooxaziridine complex 1 as the active catalyst and hydrolysis of tungstenooxazolidine intermediate A as the rate-determining-step has been proposed. Initial kinetic and competition experiments provide evidence for the proposed mechanism.

CuI-Catalyzed Radical Reaction of Benzimidates to Form Valuable 4,5-Dihydrooxazoles through Regioselective Aerobic Oxidative Cross-Coupling

A straightforward Cu(I)-catalyzed oxidative cross-coupled organic transformation has been developed under mild conditions for the construction of functionalized 4,5-dihydrooxazoles through a four-bond-forming regiocontrolled C-C/C-N/C-O coupling strategy emerging benzimidates, paraformaldehyde, and 1,3-diketo analogues using eco-friendly O2 as the sole oxidant. The fundamental features of these designed approaches involve operational simplicity, selectivity, generality, and a broad substrate scope with high yields under the same reaction conditions.

Mechanochemical synthesis of organoselenium compounds

We disclose herein a strategy for the rapid synthesis of versatile organoselenium compounds under mild conditions. In this work, magnesium-based selenium nucleophiles are formed in situ from easily available organic halides, magnesium metal, and elemental selenium via mechanical stimulation. This process occurs under liquid-assisted grinding (LAG) conditions, requires no complicated pre-activation procedures, and operates broadly across a diverse range of aryl, heteroaryl, and alkyl substrates. In this work, symmetrical diselenides are efficiently obtained after work-up in the air, while one-pot nucleophilic addition reactions with various electrophiles allow the comprehensive synthesis of unsymmetrical monoselenides with high functional group tolerance. Notably, the method is applied to regioselective selenylation reactions of diiodoarenes and polyaromatic aryl halides that are difficult to operate via solution approaches. Besides selenium, elemental sulfur and tellurium are also competent in this process, which showcases the potential of the methodology for the facile synthesis of organochalcogen compounds.

Asymmetric Photoaerobic Lactonization and Aza-Wacker Cyclization of Alkenes Enabled by Ternary Selenium-Sulfur Multicatalysis

An adaptable, sulfur-accelerated photoaerobic selenium-π-acid ternary catalyst system for the enantioselective allylic redox functionalization of simple, nondirecting alkenes is reported. In contrast to related photoredox catalytic methods, which largely depend on olefinic substrates with heteroatomic directing groups to unfold high degrees of stereoinduction, the current protocol relies on chiral, spirocyclic selenium-π-acids that covalently bind to the alkene moiety. The performance of this ternary catalytic method is demonstrated in the asymmetric, photoaerobic lactonization and cycloamination of enoic acids and unsaturated sulfonamides, respectively, leading to an averaged enantiomeric ratio (er) of 92:8. Notably, this protocol provides for the first time an asymmetric, catalytic entryway to pharmaceutically relevant 3-pyrroline motifs, which was used as a platform to access a 3,4-dihydroxyproline derivative in only seven steps with a 92:8 er.

Recent Advances in the Use of Diorganyl Diselenides as Versatile Catalysts

The importance of organoselenium compounds has been increasing in synthetic chemistry. These reagents are well-known as electrophiles and nucleophiles in many organic transformations, and in recent years, their functionality as catalysts has also been largely explored. The interest in organoselenium-based catalysts is due to their high efficacy, mild reaction conditions, strong functional compatibility, and great selectivity. Allied to organoselenium catalysts, the use of inorganic and organic oxidants that act by regenerating the catalytic species for the reaction pathway is common. Here, we provide a comprehensive review of the last five years of organic transformations promoted by diorganyl diselenide as a selenium-based catalyst. This report is divided into four sections: (1) cyclisation reactions, (2) addition reactions and oxidative functionalisation, (3) oxidation and reduction reactions, and (4) reactions involving phosphorus-containing starting materials.

Asymmetric Synthesis of β-Aminoboronates via Copper-Catalyzed Reductive Coupling of Vinyl Boronates with Imines

We report a copper-catalyzed asymmetric reductive coupling of vinyl boronates with imines, which directly access enantiomerically enriched β-aminoalkylboronates. Stereoselective addition of the in situ generated chiral α-borylalkyl copper to N-phosphinoyl imines provided target products in good yields with high diastereo- and enantioselectivity. Vinyl boronate with methylated acenaphthoquinone as a boron ligand was essential to efficiently spawn asymmetric products, and organic transformations of the boron moiety, along with the easily removable N-protecting group, proved their synthetic utility.

Catalytic Amide Activation with Thermally Stable Molybdenum(VI) Dioxide Complexes

Oxazolines and thiazolines are important constituents of bioactive natural products and pharmaceuticals. Here, we report the development of an effective and practical method of oxazoline and thiazoline formation, which can facilitate the synthesis of natural products, chiral ligands, and pharmaceutical intermediates. This method capitalized on a Mo(VI) dioxide catalyst stabilized by substituted picolinic acid ligands, which is tolerant to many functional groups that would otherwise be sensitive to highly electrophilic alternative reagents.

Regiospecific Alkene Aminofunctionalization via an Electrogenerated Dielectrophile

Modular strategies to rapidly increase molecular complexity have proven immensely synthetically valuable. In principle, transformation of an alkene into a dielectrophile presents an opportunity to deliver two unique nucleophiles across an alkene. Unfortunately, the selectivity profiles of known dielectrophiles have largely precluded this deceptively simple synthetic approach. Herein, we demonstrate that dicationic adducts generated through electrolysis of alkenes and thianthrene possess a unique selectivity profile relative to more conventional dielectrophiles. Specifically, these species undergo a single and perfectly regioselective substitution reaction with phthalimide salts. This observation unlocks an appealing new platform for aminofunctionalization reactions. As an illustrative example, we implement this new reactivity paradigm to address a longstanding synthetic challenge: alkene diamination with two distinct nitrogen nucleophiles. Studies into the mechanism of this process reveal a key alkenyl thianthrenium salt intermediate that controls the exquisite regioselectivity of the process and highlight the importance of proton sources in controlling the reactivity of alkenyl sulfonium salt electrophiles.

A Facile Synthesis of 2-Oxazolines via Dehydrative Cyclization Promoted by Triflic Acid

2-oxazolines are common moieties in numerous natural products, pharmaceuticals, and functional copolymers. Current methods for synthesizing 2-oxazolines mainly rely on stoichiometric dehydration agents or catalytic dehydration promoted by specific catalysts. These conditions either generate stoichiometric amounts of waste or require forcing azeotropic reflux conditions. As such, a practical and robust method that promotes dehydrative cyclization while generating no byproducts would be attractive to oxazoline production. Herein, we report a triflic acid (TfOH)-promoted dehydrative cyclization of N-(2-hydroxyethyl)amides for synthesizing 2-oxazolines. This reaction tolerates various functional groups and generates water as the only byproduct. This method affords oxazoline with inversion of α-hydroxyl stereochemistry, suggesting that alcohol is activated as a leaving group under these conditions. Furthermore, the one-pot synthesis protocol of 2-oxazolines directly from carboxylic acids and amino alcohols is also provided.

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.

Enantioselective Selenol-ene Using Rh-Hydride Catalysis

This study showcases the first enantioselective hydroselenation of styrenes. Organoselenium building blocks are accessed with selectivity for the branched isomer. Through a Rh-hydride pathway, C-Se bonds can be forged with excellent regio- and enantiocontrol.

Bifunctional sulfilimines enable synthesis of multiple N-heterocycles from alkenes

Intramolecular cyclization of nitrogen-containing molecules onto pendant alkenes is an efficient strategy for the construction of N-heterocycles, which are of paramount importance in, for example, pharmaceuticals and materials. Similar intermolecular cyclization reactions, however, are scarcer for nitrogen building blocks, including N-centred radicals, and divergent and modular versions are not established. Here we report the use of sulfilimines as bifunctional N-radical precursors for cyclization reactions with alkenes to produce N-unprotected heterocycles in a single step through photoredox catalysis. Structurally diverse sulfilimines can be synthesized in a single step, and subsequently engage with alkenes to afford synthetically valuable five-, six- and seven-membered heterocycles. The broad and diverse scope is achievable by a radical-polar crossover annulation enabled by the bifunctional character of the reagents, which distinguishes itself from all other N-centred-radical-based reactions. The modular synthesis of the sulfilimines allows for larger structural diversity of N-heterocycle products than is currently achievable with other single cyclization methods.

Electrochemical Organoselenium-Catalyzed Intermolecular Hydroazolylation of Alkenes with Low Catalyst Loadings

The organoselenium-catalyzed amination of alkenes is a promising way to construct functionalized amines. However, the use of chemical oxidants and the unavoidable formation of allylic amine or enamine are the two main limitations of these methodologies. Against this background, we herein report an electro-selenocatalytic regime for the hydroazolylation of alkenes with azoles under external oxidant-free conditions with low catalyst loadings. Moreover, this protocol enables the generation of amines without vinyl substituents.

Diselenide–yne chemistry for selenium-containing linear polymer modification

Selenium-containing brush polymers with diverse functional segments were easily prepared through diselenide–yne chemistry.

Layered Double Hydroxides as Reusable Catalysts for Cyclocondensation of Amidines and Aminoalcohols: Access to Multi-functionalized Oxazolines

An efficient catalytic protocol based on reusable MgAl-layered double hydroxides has been developed for the synthesis of multi-functionalized oxazolines via the cyclocondensation of amidines and aminoalcohols. The developed method has a broad substrate scope and excellent functional group tolerance and uses a reusable catalyst. The catalyst can be conveniently recycled by filtration and reused for at least five times without obvious deactivation. Additionally, the selective ortho C-H silylation of oxazolines was performed using Ru(II) as the catalyst and triethyl silane as the silylating reagent, which proved to be a convenient and practical method for the synthesis of versatile organosilyl-functionalized oxazolines with advantageous biological and physical properties.

Phosphorus-Based Organocatalysis for the Dehydrative Cyclization of N-(2-Hydroxyethyl)amides into 2-Oxazolines

A metal-free, biomimetic catalytic protocol for the cyclization of N-(2-hydroxyethyl)amides to the corresponding 2-oxazolines (4,5-dihydrooxazoles), promoted by the 1,3,5,2,4,6-triazatriphosphorine (TAP)-derived organocatalyst tris(o-phenylenedioxy)cyclotriphosphazene (TAP-1) has been developed. This approach requires less precatalyst compared to the reported relevant systems, with respect to the phosphorus atom (the maximum turnover number (TON) ∼ 30), and exhibits a broader substrate scope and higher functional-group tolerance, providing the functionalized 2-oxazolines with retention of the configuration at the C(4) stereogenic center of the 2-oxazolines. Widely accessible β-amino alcohols can be used in this approach, and the cyclization of N-(2-hydroxyethyl)amides provides the desired 2-oxazolines in up to 99% yield. The mechanism of the reaction was studied by monitoring the reaction using spectral and analytical methods, whereby an ¹⁸O-labeling experiment furnished valuable insights. The initial step involves a stoichiometric reaction between the substrate and TAP-1, which leads to the in situ generation of the catalyst, a catechol cyclic phosphate, as well as to a pyrocatechol phosphate and two possible active intermediates. The dehydrative cyclization was also successfully conducted on the gram scale.

Visible light bromide catalysis for oxazoline, pyrrolidine, and dihydrooxazine syntheses via Csp3-H functionalizations

A catalytic benzylic C_sp³-H functionalization protocol is described here. This visible light-mediated process is centered on the utilization of a bromide catalyst and oxidant to generate a nitrogen (N)-centered radical for a site-selective hydrogen atom transfer (HAT) process. This strategy enabled the unconventional syntheses of a number of N-heterocycles dependent on the amide identity. We also discovered a nucleophilicity-dependent kinetic resolution for stereochemical differentiation of C_sp³-H bonds that enabled the stereoselective synthesis of cis- and trans-oxazolines.