Search

Chiral aziridines are important motifs in natural products and biologically significant compounds, as well as one of the most valuable and versatile building blocks for the construction of diverse chiral functionalized amines. Because of the importance of chiral aziridines, various novel transition‐metal‐based catalytic systems and synthetic strategies have been established to investigate the highly effective and enantioselective aziridination process. This review outlined the recent significant advances made in the transition‐metal catalyzed enantioselective aziridination reactions, as well as the challenges and potential of the field at the current stage. [ABSTRACT FROM AUTHOR]

Copper(I)-catalyzed (4+3)-cycloaddition of 4-indolylcarbinols with aziridines has been accomplished to furnish azepinoindoles. The chirality transfer, substrate scope, functional group tolerance, natural product modification and tandem C–C/C–N bond formation are the important practical features. [ABSTRACT FROM AUTHOR]

This perspective discusses bibliography data that has been published since 2018 on the synthesis of oxazolidinones by reacting corresponding aziridines with CO2. The versatility and viability of various procedures have been analyzed by considering the variety of tested substrates as well as experimental conditions and catalytic systems used. Collected data highlights that the reaction can be effectively promoted by several homogeneous and heterogeneous catalytic systems that have been optimized in order to conjugate the process sustainability and productivity with convenient procedural costs. [ABSTRACT FROM AUTHOR]

The carbon‐carbon bond in three‐membered ring of 2,3‐diaryl aziridines was reductively cleaved to give the corresponding dibenzylamine derivatives by electrocyclic ring opening of N‐Li or N‐Na aziridines followed by reduction of the 2‐azaallyl anion formed with sodium borohydride in ethanol. Hydrocyanation of the 2‐azaallyl anion with trimethylsilyl cyanide gave a secondary amine bearing a cyano group at the benzylic position. The effects of substituents on the electrocyclic ring opening of N‐Li aziridines were also clarified. [ABSTRACT FROM AUTHOR]

Molecules containing three‐membered heterocycles, including oxiranes (epoxides), thiiranes (episulfides) and aziridines, are considered privileged structures as they serve as key precursors or intermediates for the synthesis of a varied range of organic compounds, such as natural products, mimetics and pharmaceuticals. The principal advantage of this type of heterocycles is their reactivity towards the nucleophilic ring‐opening, which usually occurs in a regioselective manner, resulting in the formation of 1,2‐disubstituted products. When attached to a chiral scaffold, such as a carbohydrate molecule, the ring‐opening process is usually highly diastereoselective. Therefore, these compounds have been extensively employed in the field of carbohydrates for the synthesis of enantiomerically pure modified sugars that are useful as glycobiology tools. This review presents an overview of the recent methodologies developed for the construction of epoxide, thiirane, and aziridine rings from common or modified sugars. Due to their structural similarity to carbohydrates, three‐membered heterocyclic derivatives of cyclitols and carbasugars have been included. All these compounds, and their ring‐opening derivatives have shown to be crucial in the synthesis of glycomimetics, which display diverse biological activities. These include enzyme inhibition, binding to lectin receptors, and more recently, the use as probes for the diagnosis and monitoring of diseases. [ABSTRACT FROM AUTHOR]

An efficient chalcogenative annulation strategy for constructing functionalized saturated N-heterocycles from unactivated alkenes with dichalcogenides under electrochemical conditions has been presented. This protocol is applicable to mono-, di- or tri-substituted alkenes, providing a straightforward pathway to aziridines, azetidines, pyrrolidines, and piperidines with high regioselectivity. Moreover, the strategy is qualified to realize the oxychalcogenation of alkenes as well. [ABSTRACT FROM AUTHOR]

The development of greener methods for the preparation of three‐membered rings has increased in the last decade, not only due to their biological activity but also to the ring strain of those heterocycles that make them useful precursors of more complex molecules. In this work, the visible‐light‐promoted synthesis and ring‐opening of aziridines and epoxides, reported in the last five years, were reviewed. Both homogeneous and heterogeneous catalysts were discussed and, in addition, the plausible mechanism pathways were highlighted. [ABSTRACT FROM AUTHOR]

We describe the first total syntheses of tabernanthine and ibogaline. Entry to these iboga alkaloid natural products is enabled by a thermal coupling of indoles and aziridines to furnish the requisite nosyl tryptamine starting materials. This route features a Friedel‐Crafts type alkylation to form the key indole‐isoquinuclidine C−C bond. Finally, a regio‐ and diastereoselective hydroboration‐oxidation enables C−N bond formation to close the isoquinuclidine ring system and deliver tabernanthine and ibogaline in 10 and 14 % yield respectively. Both syntheses were completed in eight steps. [ABSTRACT FROM AUTHOR]

Piperazines constitute an important structural feature of many pharmaceuticals. For the discovery of new drugs, the ability to modify the lead compound's structure is crucial. Herein, we provide an efficient method for the synthesis of chiral 2,3,5-trisubstituted piperazine structures. Our route enables the synthesis of several novel chiral aryl aziridinyl ketones that could be converted into aziridine-fused bicyclic imines. The reduction of these imines and the nucleophilic ring-opening reaction of the aziridine ring allowed us to synthesize highly functionalized piperazine derivatives. [ABSTRACT FROM AUTHOR]

β‐Phenethylamines are widely represented in biologically and pharmacologically active organic small molecules. Here, we introduce N‐pyridinium aziridines as latent dual electrophiles for the synthesis of β‐phenethylamines. Bromide‐promoted ring opening generates β‐halopyridinium amines. Selective Ni‐catalyzed C−C cross‐coupling between organozinc nucleophiles and the benzylic C−Br electrophile affords a diverse family of β‐functionalized phenethylaminopyridinium salts, and coupling is stereoconvergent in the presence of chiral ligands. Subsequent Ni‐catalyzed reductive N−N bond activation within the β‐functionalized phenethylaminopyridinium salts furnishes the products of formal olefin carboamination. Other reductive N−N cleavage reactions are demonstrated to provide access to free primary amines, alkylated amines, heterocycles, and products derived from N‐centered radical chemistry. The developed reaction sequence can be implemented in the context of complex molecules and natural product derivatives. Together, the described results provide a general and modular synthesis of β‐phenethylamines and significantly expand the utility of N‐pyridinium aziridines as linchpins in chemical synthesis. [ABSTRACT FROM AUTHOR]

β‐Phenethylamines are widely represented in biologically and pharmacologically active organic small molecules. Here, we introduce N‐pyridinium aziridines as latent dual electrophiles for the synthesis of β‐phenethylamines. Bromide‐promoted ring opening generates β‐halopyridinium amines. Selective Ni‐catalyzed C−C cross‐coupling between organozinc nucleophiles and the benzylic C−Br electrophile affords a diverse family of β‐functionalized phenethylaminopyridinium salts, and coupling is stereoconvergent in the presence of chiral ligands. Subsequent Ni‐catalyzed reductive N−N bond activation within the β‐functionalized phenethylaminopyridinium salts furnishes the products of formal olefin carboamination. Other reductive N−N cleavage reactions are demonstrated to provide access to free primary amines, alkylated amines, heterocycles, and products derived from N‐centered radical chemistry. The developed reaction sequence can be implemented in the context of complex molecules and natural product derivatives. Together, the described results provide a general and modular synthesis of β‐phenethylamines and significantly expand the utility of N‐pyridinium aziridines as linchpins in chemical synthesis. [ABSTRACT FROM AUTHOR]

A general and atom-efficient synthesis of quinoline-C2-substituted β-hydroxyarylethylamino derivatives was achieved by copper-catalyzed [3+3]-cycloaddition reaction of N -oxide with N -Ts aziridines. Notably, temperature has a huge impact on this transformation as evidenced by the fact that, at 80 °C, exclusively the [3+3] cycloadduct was isolated whereas, at elevated temperature (140 °C), it has been converted into the aminated product with good yield. Notably, there is no byproduct in the overall process. The use of base-free conditions, excellent site selectivity, and good functional group tolerance are the important features of the process. [ABSTRACT FROM AUTHOR]

Elevated concentrations of CO2 in the atmosphere pose significant challenges, notably contributing to the greenhouse effect. CO2 as an abundant C1 resource converting into high-value oxazolidinones is a promising avenue for effective carbon fixation. Herein, a highly stable binuclear cerium–organic framework, [Ce2(DCTP)2(DMA)2(OAc)2]n (1), has been successfully designed and synthesized, which maintains the intact three-dimensional framework after immersing in solutions with pH ranging from 1 to 12 and various common solvents for 24 hours, respectively. Explorations on CO2 conversion indicate that compound 1 exhibits remarkable catalytic efficiency in the cycloaddition reaction of CO2 with aziridines to form oxazolidinones under relatively low CO2 pressure. 1 can be easily regenerated five times without a significant decrease in yield. Mechanistic experiments show that the high catalytic activity of 1 is attributed to the stable three-dimensional framework, high Lewis acidity, and ample cerium active sites. Notably, 1 is a rare lanthanide metal–organic framework-based (Ln-MOF-based) catalyst for the cycloaddition of CO2 with aziridines under mild pressure. [ABSTRACT FROM AUTHOR]

The asymmetric [3+2] cycloaddition of azomethine ylides generated from the corresponding imino ester-to-trans-β-nitrostyrene catalysis by chiral aziridine-containing phosphines and phosphine oxides is described. Of the sixteen stereoisomers that could be formed as a result of the title reaction, three were formed, two of which were obtained in an enantiomerically enriched or pure form, and one in a racemic form. One of the products underwent epimerization under basic reaction conditions. [ABSTRACT FROM AUTHOR]

A new strategy for the synthesis of 3‐substituted phthalides has been developed via a Lewis acid‐catalyzed intramolecular ring opening of aziridines with esters. Broad substrate scope, good yields and mild conditions made the cyclization reaction very suitable for the rapid construction of libraries of 3‐substituted phthalide compounds. [ABSTRACT FROM AUTHOR]

The first palladium‐catalyzed allylation of isocyanoacetates with vinyl aziridines has been developed. The reaction conditions were suitable for a variety of α‐aryl isocyanoacetates as well as N‐substituted vinyl aziridines, affording the corresponding allylation products in moderate to high yields (up to 98 %) along with excellent stereoselectivity and regioselectivity. Transformations of the allylation products into trans‐4,5‐dehydrolysine analogues and a highly functionalized proline ester derivative were further demonstrated, and a preliminary asymmetric version of the reaction has also been evaluated. [ABSTRACT FROM AUTHOR]

In previous works, we demonstrated that tertiary 3‐chloropiperidines are potent chemotherapeutics, alkylating the DNA through the formation of bicyclic aziridinium ions. Herein, we report the synthesis of novel secondary 3‐chloropiperidine analogues. The synthesis incorporates a new procedure to monochlorinate unsaturated primary amines utilizing N‐chlorosuccinimide, while carefully monitoring the temperature to prevent dichlorination. Furthermore, we successfully isolated highly strained bicyclic aziridines by treating the secondary 3‐chloropiperidines with a sufficient amount of base. We conclude this work with a DNA cleavage assay as a proof of principle, comparing our previously known substrates to the novel compounds. In this, the secondary 3‐chloropiperidine as well as the isolated bicyclic aziridine, proved to be more effective than their tertiary counterpart. [ABSTRACT FROM AUTHOR]

The chiral aziridine-containing vicinal iminophenol tridentate ligands (named salazins) are a class of readily prepared chiral ligands from enantiopure aziridines and salicylaldehydes. Their scandium and yttrium triflate complexes show excellent reactivity and enantioselectivities in the catalytic asymmetric aldol condensation of electron-deficient aromatic aldehydes and ketones, including acetone and cycloalkanones. The stereoselectivity is rationalized to the strong π–stacking interaction between aromatic aldehydes and the vicinal iminophenol group in the chiral ligands. [ABSTRACT FROM AUTHOR]

The oxirane and aziridine rings are valuable building blocks in modern synthetic chemistry and catalytic asymmetric ring opening reactions of these three membered ring systems have emerged as a powerful chemical tool for the synthesis of natural products and biologically active compounds. In this context, the regioselective ring‐opening of structurally or electronically unbiased epoxides and aziridines is challenging. Recently, metal‐catalyzed substrate directed strategies have successfully applied in the regio‐ and enantioselective ring opening of functionalized epoxy alcohols by the Yamamoto group. Subsequently, our group realized the ring opening reactions of functionalized 2,3‐aziridinyl alcohols with the dinuclear zinc complex. These enantioselective nucleophilic ring opening reactions of functionalized epoxy alcohols and aziridinyl alcohols allow for the facile synthesis of amino alcohol derivatives and the introduction of new concepts in catalysis. [ABSTRACT FROM AUTHOR]

We report an approach to the diastereoselective synthesis of 1,2‐disubstituted heterocyclic aziridines. A Brønsted acid‐catalyzed conjugate addition of anilines to trisubstituted heterocyclic chloroalkenes provides an intermediate 1,2‐chloroamine. Diastereocontrol was found to vary significantly with solvent selection, with computational modelling confirming selective, spontaneous fragmentation in the presence of trace acids, proceeding through a pseudo‐cyclic, protonated intermediate and transition state. These chloroamines can then be converted to the aziridine by treatment with LiHMDS with high stereochemical fidelity. This solvent‐induced stereochemical enrichment thereby enables an efficient route to rare cis‐aziridines with high dr. The scope, limitations, and mechanistic origins of selectivity are also presented. [ABSTRACT FROM AUTHOR]

Under the catalysis of a Cu(I) or Ag(I) salt with a chiral diphosphine ligand, the enantioselective nucleophilic ring opening of racemic 2‐styrenylaziridines via kinetic resolution or dynamic kinetic asymmetric transformation (DyKAT) and of meso aziridines via desymmetrization with alcohols was realized. The reaction provided a range of chiral vicinal amino ether derivatives in 47%‐98% yields and with 50%–98% ee. The reaction could be extended to aliphatic carboxylic acids as nucleophiles. The synthetic utility was demonstrated in a four‐step formal synthesis of a diastereomer of the antirythmetic agent vernakalant. [ABSTRACT FROM AUTHOR]

A series of optically pure aziridine phosphines and their corresponding phosphine oxides were synthesized through established chemical methodologies. The compounds were systematically investigated for their biological properties. Notably, all synthesized compounds demonstrated moderate antibacterial activity only against the reference strain of Staphylococcus aureus. However, compounds 5 and 7 exhibited noteworthy cell viability inhibition of human cervical epithelioid carcinoma HeLa cells and endometrial adenocarcinoma Ishikawa cells. Further studies of these compounds revealed additional biological effects, including disruption of the cell membrane in high concentrations, cell cycle arrest in the S phase, and the induction of reactive oxygen species (ROS). Comparative analysis of the two classes of chiral organophosphorus derivatives of aziridines indicated that chiral phosphine oxides displayed significantly higher biological activity. Consequently, these findings suggest that chiral phosphine oxides may be potential candidates for the development of anticancer drugs. In light of the significant interest in preparations whose structure is based on a three-membered aziridine ring in terms of potential anticancer therapy, this research fits into the current research trend and should constitute a valuable addition to the current state of knowledge and the existing library of aziridine derivatives with anticancer properties. [ABSTRACT FROM AUTHOR]

The coupling of diaziridines with donor–acceptor aziridines (DAAs) has been achieved using Zn-catalysis to furnish imidazopyrazole-4,4-dicarboxylates via [1,4]-hydride shift. The use of Zn-catalysis, [1,4]-hydride shift, natural product modification and a late-stage molecular docking study are important practical features. [ABSTRACT FROM AUTHOR]

Chiral cyclopentadienyl‐rhodium(III) CpxRh(III) catalysis has been demonstrated to be competent for catalyzing highly enantioselective aziridination of challenging unactivated terminal alkenes and nitrene sources. The chiral CpxRh(III) catalysis system exhibited outstanding catalytic performance and wide functional group tolerance, yielding synthetically important and highly valuable chiral aziridines with good to excellent yields and enantioselectivities (up to 99 % yield, 93 % ee). This protocol presents a novel and effective strategy for synthesizing enantioenriched aziridines from simple alkenes. Various transformations were performed on the aziridine products, illustrating the versatility and synthetic potential of this protocol for constructing highly functionalized compounds. [ABSTRACT FROM AUTHOR]

This manuscript describes the development of alkyne addition to the aziridine moiety of aziridinoquinoxalines using dual Ir(III)/Cu(I) catalytic system under green light‐emitting diode (LED) photolysis (λmax=525 nm). This mild method features high levels of chemo‐ and regioselectivity and was used to generate 30 highly functionalized substituted dihydroquinoxalines in 36–98 % yield. This transformation was also carried asymmetrically using phthalazinamine‐based chiral ligand to provide 9 chiral addition products in 96 : 4 to 86 : 14 e.r. The experimental and quantum chemical explorations of this reaction suggest a mechanism that involves Ir(III)‐catalyzed triplet energy transfer followed by a ring‐opening reaction ultimately leading to the formation of azomethine ylide intermediates. These azomethine intermediates undergo sequential protonation/copper(I) acetylide addition to provide the products. [ABSTRACT FROM AUTHOR]

Azetidines, being four‐membered N‐heterocycles, possess significant potential in contemporary medicinal chemistry owing to their favorable pharmacokinetic properties. Regrettably, the incorporation of functionalized azetidines into pharmaceutical lead structures has been impeded by the absence of efficient synthetic methods for their synthesis. In this study, a Rh‐catalyzed one‐carbon ring expansion of aziridines with vinyl‐N‐triftosylhydrazones is presented, which facilitates the synthesis of high value‐added 2‐alkenyl azetidine products. This research represents the first example of ring expansion of aziridines enabled by vinyl carbenes. Additionally, a one‐pot two‐step protocol, initiated from cinnamaldehyde, was successfully achieved, offering a step‐economical and facile approach for the synthesis of these compounds. The pivotal aspect of this successful transformation lies in the in situ formation of an alkenyl aziridinium ylide intermediate. Experimental investigations, coupled with computational studies, suggest that a diradical pathway is involved in the reaction mechanism. [ABSTRACT FROM AUTHOR]

Chiral cyclopentadienyl‐rhodium(III) CpxRh(III) catalysis has been demonstrated to be competent for catalyzing highly enantioselective aziridination of challenging unactivated terminal alkenes and nitrene sources. The chiral CpxRh(III) catalysis system exhibited outstanding catalytic performance and wide functional group tolerance, yielding synthetically important and highly valuable chiral aziridines with good to excellent yields and enantioselectivities (up to 99 % yield, 93 % ee). This protocol presents a novel and effective strategy for synthesizing enantioenriched aziridines from simple alkenes. Various transformations were performed on the aziridine products, illustrating the versatility and synthetic potential of this protocol for constructing highly functionalized compounds. [ABSTRACT FROM AUTHOR]

This manuscript describes the development of alkyne addition to the aziridine moiety of aziridinoquinoxalines using dual Ir(III)/Cu(I) catalytic system under green light‐emitting diode (LED) photolysis (λmax=525 nm). This mild method features high levels of chemo‐ and regioselectivity and was used to generate 30 highly functionalized substituted dihydroquinoxalines in 36–98 % yield. This transformation was also carried asymmetrically using phthalazinamine‐based chiral ligand to provide 9 chiral addition products in 96 : 4 to 86 : 14 e.r. The experimental and quantum chemical explorations of this reaction suggest a mechanism that involves Ir(III)‐catalyzed triplet energy transfer followed by a ring‐opening reaction ultimately leading to the formation of azomethine ylide intermediates. These azomethine intermediates undergo sequential protonation/copper(I) acetylide addition to provide the products. [ABSTRACT FROM AUTHOR]

Azetidines, being four‐membered N‐heterocycles, possess significant potential in contemporary medicinal chemistry owing to their favorable pharmacokinetic properties. Regrettably, the incorporation of functionalized azetidines into pharmaceutical lead structures has been impeded by the absence of efficient synthetic methods for their synthesis. In this study, a Rh‐catalyzed one‐carbon ring expansion of aziridines with vinyl‐N‐triftosylhydrazones is presented, which facilitates the synthesis of high value‐added 2‐alkenyl azetidine products. This research represents the first example of ring expansion of aziridines enabled by vinyl carbenes. Additionally, a one‐pot two‐step protocol, initiated from cinnamaldehyde, was successfully achieved, offering a step‐economical and facile approach for the synthesis of these compounds. The pivotal aspect of this successful transformation lies in the in situ formation of an alkenyl aziridinium ylide intermediate. Experimental investigations, coupled with computational studies, suggest that a diradical pathway is involved in the reaction mechanism. [ABSTRACT FROM AUTHOR]

A vicinal diamine motif can be found in numerous natural compounds and pharmaceuticals, making it an important synthetic target. Herein, we report a telescoped synthesis of vicinal diamines under continuous flow conditions. This approach involves the electrochemical aziridination of alkenes with primary amines, followed by the strain-release driven ring-opening using various nitrogen nucleophiles. The efficacy of the developed method was demonstrated through the synthesis of diverse symmetrically and non-symmetrically substituted vicinal diamines, as well as vicinal amino azides, which can be further hydrogenated to diamines in flow. Additionally, O-centered nucleophiles were employed for the ring-opening of aziridines in our telescoped synthesis, yielding vicinal amino ethers and alcohol. This process offers a streamlined and efficient pathway for the direct synthesis of valuable products from readily available starting materials, bypassing the isolation of unstable aziridine intermediates. [ABSTRACT FROM AUTHOR]

Isothiourea is an important class of sulfur-containing molecules showing unique catalytic and biological activities. As such, polyisothiourea is envisioned to be an interesting type of polymer that potentially exhibits a number of interesting properties. However, there is no access to synthesizing well-defined polyisothiourea, and currently isothiourea-containing polymers are mainly prepared by immobilizing onto other polymer's side chain. Herein, we report the first facile synthesis of polyisothioureas via alternating copolymerization of aziridines and isothiocayanates. Mediated by the catalytic system of phosphazene superbases/alcohol, a broad scope of aziridines and isothiocayanates could be transformed into polyisothioureas with adjustable substitutions (11 examples). The structures of obtained polyisothioureas were fully characterized with 1H-NMR, 13C-NMR, and 1H-13C HMBC NMR. Moreover, the polyisothioureas show tunable thermal properties depending on substitutions on the isothiourea linkages. The novel structure of these polyisothioureas will enable a powerful platform for the discovery of next-generation functional plastics. [ABSTRACT FROM AUTHOR]

The development of innovative methods for the construction of heterocycles is an important topic in synthetic and medicinal chemistry. Ring expansion strategies, involving the cyclization of strained aza rings, have been well developed in the synthesis of diverse heterocyclic compounds. This microreview summarizes recent advances in the ring expansion reactions of aziridines, oxetanes, and azetidines to access a series of functionalized 2-oxazolines, which are versatile structural motifs in drugs and bioactive molecules. [ABSTRACT FROM AUTHOR]

The bulk radical polymerization of bis(aziridine) with molten elemental sulfur resulted in brittle, cross‐linked polymers. However, when the bis(aziridine) was treated with elemental sulfur in the presence of an organobase, the ring‐opening reaction of aziridine with oligosulfide anions occurred, leading to the formation of linear polymers by step‐growth polymerization. These newly synthesized polymers possess repeating units containing a sulfonamide or amide functional moiety and oligosulfide bonds with an average sulfur segment of about two. A small molecular model reaction confirmed the nucleophilic addition reaction of elemental sulfur to aziridine. It was verified that S−S dynamic bond exchange takes place in the presence of an organic base within the linear chains. The mixture of the synthesized polysulfides with pyridine exhibits exceptional adhesive properties when applied to steel, and aluminum substrates. Notably, these prepared adhesives displayed good reusability due to the dynamic S−S exchange and complete recyclability due to their solution processability. This elemental sulfur‐involved polymerization approach represents an innovative method for the synthesis of advanced sulfur‐containing polymers, demonstrating the potential for various applications in adhesives and beyond. [ABSTRACT FROM AUTHOR]

The bulk radical polymerization of bis(aziridine) with molten elemental sulfur resulted in brittle, cross‐linked polymers. However, when the bis(aziridine) was treated with elemental sulfur in the presence of an organobase, the ring‐opening reaction of aziridine with oligosulfide anions occurred, leading to the formation of linear polymers by step‐growth polymerization. These newly synthesized polymers possess repeating units containing a sulfonamide or amide functional moiety and oligosulfide bonds with an average sulfur segment of about two. A small molecular model reaction confirmed the nucleophilic addition reaction of elemental sulfur to aziridine. It was verified that S−S dynamic bond exchange takes place in the presence of an organic base within the linear chains. The mixture of the synthesized polysulfides with pyridine exhibits exceptional adhesive properties when applied to steel, and aluminum substrates. Notably, these prepared adhesives displayed good reusability due to the dynamic S−S exchange and complete recyclability due to their solution processability. This elemental sulfur‐involved polymerization approach represents an innovative method for the synthesis of advanced sulfur‐containing polymers, demonstrating the potential for various applications in adhesives and beyond. [ABSTRACT FROM AUTHOR]

The BF3⋅OEt2‐catalyzed reaction of azulene with N‐protected aziridines represents a general, efficient (up to 91% yield) and regioselective approach to phenethylamine‐azulene conjugates. Stereochemical studies and DFT calculations lend support to a concerted SN2‐type mechanism governing the ring‐opening of the aziridine. [ABSTRACT FROM AUTHOR]

Commercially available poly(lactic acid) exhibits poor hydrolytic stability, which makes it impossible for use in durable applications. Therefore, a novel hydrolysis inhibitor based on an aziridine derivative as well as a novel stabilizer composition, containing an aziridine derivative and an acid scavenger, were investigated to improve the hydrolytic stability. To evaluate the stabilizing effect, the melt volume rate (MVR) and molecular weight were monitored during an accelerated hydrolytic aging in water at elevated temperatures. Temperatures were selected according to the glass transition temperature (~60 °C) of PLA. It was shown that the novel hydrolysis inhibitor as well as the novel stabilizer composition exhibited excellent performance during hydrolytic aging, exceeding commercially available alternatives, e.g., polymeric carbodiimides. A molecular weight analysis resulted in a molecular weight decrease of only 10% during approximately 850 h and up to 20% after 1200 h of hydrolytic aging, whereas poly(lactic acid) stabilized with a commercial polycarbodiimide revealed comparable molecular weight reductions after only 300 h. Furthermore, the stabilization mechanism of the aziridine derivative alone, as well as in the synergistic combination with the acid scavenger (calcium hydrotalcite), was investigated using nuclear magnetic resonance (NMR) spectroscopy. In addition to an improved hydrolytic stability, the thermal properties were also enhanced compared to polymeric carbodiimides. [ABSTRACT FROM AUTHOR]

A sequential one‐pot direct strategy for the synthesis of 2‐hydroxy‐2‐substituted‐2H‐benzo[b][1,4]oxazin‐3(4H)‐ones is developed under ambient conditions with moderate to good yields (up to 75 %) by regioselective ring‐opening of spiro‐epoxy/aziridine oxindoles with 50 % aq. H2O2 followed by rearrangement reaction in presence of amberlyst‐15 catalyst. Further, sequential reaction with aldehydes/ketones and carbonyldiimidazole (CDI) gave spiro[benzo[b][1,4]oxazine‐2,4′‐[1,3]dioxolan]‐3(4H)‐ones and spiro[benzo[b][1,4]oxazine‐2,4′‐[1,3]dioxolane]‐2′,3(4H)‐diones, respectively. [ABSTRACT FROM AUTHOR]

An in situ generated photoactive copper(I)‐complex‐catalyzed aziridination reaction of cyclic N‐sulfonyl imines with α‐aryl‐substituted vinyl azides irradiated by blue‐LEDs light is reported for the first time. This novel SET process represents a mild, sustainable, and pragmatic method for accessing synthetically resourceful sulfamidate‐fused aziridines in acceptable chemical yields with excellent diastereoselectivities. Delightedly, pharmacologically attractive benzo[f][1,2,3]oxathiazepine dioxides and fused isoxazoline frameworks were achieved through our newly developed metal‐free based ring‐expansion techniques, highlighting the synthetic value of accessed aziridines. Finally, the possible mechanism for [2+1] aza‐cyclization was presented based on the conduction of a series of control experiments. [ABSTRACT FROM AUTHOR]

N‐Trifluoromethylated organics may be applied in drug design, agrochemical synthesis, and materials science, among other areas. Yet, despite recent advances in the synthesis of aliphatic, cyclic and heterocyclic N‐trifluoromethyl compounds, no strategy based on trifluoromethyl nitrene has hitherto been explored. Here we describe the formation of triplet trifluoromethyl nitrene from azidotrifluoromethane, a stable and safe‐to‐use precursor, by visible light photocatalysis. The addition of CF3N to alkenes via biradical intermediates afforded previously unknown aziridines substituted with trifluoromethyl group on the nitrogen atom. The obtained aziridines were converted into either N‐trifluoromethylimidazolines, via formal [3+2] cycloaddition with nitriles, mediated by a Lewis acid, or into N‐trifluoromethylaldimines, via ring opening and aryl group migration mediated by a strong Brønsted acid. Our findings open new opportunities for the development of novel classes of N‐CF3 compounds with possible applications in the life sciences. [ABSTRACT FROM AUTHOR]

N‐Trifluoromethylated organics may be applied in drug design, agrochemical synthesis, and materials science, among other areas. Yet, despite recent advances in the synthesis of aliphatic, cyclic and heterocyclic N‐trifluoromethyl compounds, no strategy based on trifluoromethyl nitrene has hitherto been explored. Here we describe the formation of triplet trifluoromethyl nitrene from azidotrifluoromethane, a stable and safe‐to‐use precursor, by visible light photocatalysis. The addition of CF3N to alkenes via biradical intermediates afforded previously unknown aziridines substituted with trifluoromethyl group on the nitrogen atom. The obtained aziridines were converted into either N‐trifluoromethylimidazolines, via formal [3+2] cycloaddition with nitriles, mediated by a Lewis acid, or into N‐trifluoromethylaldimines, via ring opening and aryl group migration mediated by a strong Brønsted acid. Our findings open new opportunities for the development of novel classes of N‐CF3 compounds with possible applications in the life sciences. [ABSTRACT FROM AUTHOR]

Transition metal-catalyzed asymmetric nitrene transfer is a powerful method to generate enantioenriched amines found in natural products and bioactive molecules. A highly chemo- and enantioselective intramolecular silver-catalysed aziridination of 2,2,2-trichloroethoxysulfonyl (Tces)-protected carbamimidates gives [4.1.0]-bicyclic aziridines in good yields and up to 99% ee. [ABSTRACT FROM AUTHOR]

Azomethine ylides are typically in situ generated synthons for making N‐heterocycles through cycloaddition reactions. But an offbeat aspect about them is the isomeric nature of aldiminium‐based azomethine ylides and (alkyl/aryl)(amino)carbenes, interconvertible by a formal 1,3‐H+ transfer. Herein, two thermally robust azomethine ylides with a N‐appended picolyl sidearm are isolated, which cyclize to pyaziridines at 80 °C but unprecedentedly result N−picoCAAC‐CuCl (CAAC=cyclic(alkyl)(amino)carbene) complexes when heated with CuCl at merely 60 °C. The pendant Npy, as revealed by computational analysis, plays a crucial role in this unusual 1,3‐H+ shift using a deprotonation‐protonation sequence, as well as in placing the CuCl at the carbenic site in tandem. The softer nature of Cu(I) is also critical. Chelating CAACs are rare and one with a N‐tethered additional donor is priorly unknown. Both N‐picoCAAC and pyaziridine are bidentate chelators giving highly active cationic Rh(I) catalysts for hydrosilylating unactivated olefins by Et3SiH. Notably, the pyaziridine‐Rh(I) is superior than the N‐picoCAAC‐Rh(I) catalyst. [ABSTRACT FROM AUTHOR]

Azomethine ylides are typically in situ generated synthons for making N‐heterocycles through cycloaddition reactions. But an offbeat aspect about them is the isomeric nature of aldiminium‐based azomethine ylides and (alkyl/aryl)(amino)carbenes, interconvertible by a formal 1,3‐H+ transfer. Herein, two thermally robust azomethine ylides with a N‐appended picolyl sidearm are isolated, which cyclize to pyaziridines at 80 °C but unprecedentedly result N−picoCAAC‐CuCl (CAAC=cyclic(alkyl)(amino)carbene) complexes when heated with CuCl at merely 60 °C. The pendant Npy, as revealed by computational analysis, plays a crucial role in this unusual 1,3‐H+ shift using a deprotonation‐protonation sequence, as well as in placing the CuCl at the carbenic site in tandem. The softer nature of Cu(I) is also critical. Chelating CAACs are rare and one with a N‐tethered additional donor is priorly unknown. Both N‐picoCAAC and pyaziridine are bidentate chelators giving highly active cationic Rh(I) catalysts for hydrosilylating unactivated olefins by Et3SiH. Notably, the pyaziridine‐Rh(I) is superior than the N‐picoCAAC‐Rh(I) catalyst. [ABSTRACT FROM AUTHOR]

An available method for a synthesis of N-substituted (E)-2-(diphenylphosphoryl)aziridines with high yields by the reaction of (1,2-dibromoethyl)(diphenyl)phosphine oxide with a number of primary amines, in particular, methyl-, ethyl-, isopropyl-, tert-butyl-, cyclohexyl- and benzylamines at room temperature in the presence of sodium hydroxide, has been developed. The antibacterial activity of the synthesized compounds was evaluated. [ABSTRACT FROM AUTHOR]

An unprecedented Pd‐catalyzed fluorinative bifunctionalization of aziridines and azetidines was successfully developed via regioselective C−C and C−F bond cleavage of gem‐difluorocyclopropanes, leading to various β,β′‐bisfluorinated amines and β,γ‐bisfluorinated amines. This reaction was achieved by incorporating a 2‐fluorinated allyl group and a fluorine atom scissored from gem‐difluorocyclopropane in 100 % atom economy for the first time. The mechanistic investigations indicated that the reaction underwent amine attacking 2‐fluorinated allyl palladium complex to generate η2‐coordinated N‐allyl aziridine followed by fluoride ligand transfer affording the final β‐ and γ‐fluorinated amines. [ABSTRACT FROM AUTHOR]

An unprecedented Pd‐catalyzed fluorinative bifunctionalization of aziridines and azetidines was successfully developed via regioselective C−C and C−F bond cleavage of gem‐difluorocyclopropanes, leading to various β,β′‐bisfluorinated amines and β,γ‐bisfluorinated amines. This reaction was achieved by incorporating a 2‐fluorinated allyl group and a fluorine atom scissored from gem‐difluorocyclopropane in 100 % atom economy for the first time. The mechanistic investigations indicated that the reaction underwent amine attacking 2‐fluorinated allyl palladium complex to generate η2‐coordinated N‐allyl aziridine followed by fluoride ligand transfer affording the final β‐ and γ‐fluorinated amines. [ABSTRACT FROM AUTHOR]

Aziridines derived from bioactive molecules may have unique pharmacological activities, making them useful in pharmacology (e.g. mitomycin C). Furthermore, the substitution of the epoxide moiety in epothilone B with aziridine, an analog of epoxides, yielded a pronounced enhancement in its anticancer efficacy. Thus, there is interest in developing novel synthetic technologies to produce aziridines from bioactive molecules. However, known methods usually require metal catalysts, stoichiometric oxidants and/or pre-functionalized amination reagents, causing difficulty in application. A practical approach without a metal catalyst and extra-oxidant for the aziridination of bioactive molecules is in demand, yet challenging. Herein, we report an electro-oxidative flow protocol that accomplishes an oxidant-free aziridination of natural products. This process is achieved by an oxidative sulfonamide/alkene cross-coupling, in which sulfonamide and alkene undergo simultaneous oxidation or alkene is oxidized preferentially. Further anticancer treatments in cell lines have demonstrated the pharmacological activities of these aziridines, supporting the potential of this method for drug discovery. [ABSTRACT FROM AUTHOR]

Application of a binary Ga‐based catalyst system for the coupling of CO2 and aziridines to form oxazolidinones is presented. It has been possible to optimize the catalyst system for the selective formation of a single regioisomer, in excellent yield, under relatively mild reaction conditions. The optimized catalyst system has been successfully applied to a range of substituted aziridines derived from styrene oxide. It has been observed that aziridines bearing two aromatic substituents result in piperazine formation through an unexpected dimerization reaction. These piperazine products can be selectively formed in the absence of CO2 or are favored at lower reaction temperatures. A detailed DFT study into the reaction mechanism for the formation of both products has been carried out and an unusual ligand assistance in the case of oxazolidinone synthesis has been identified. More specifically, this ligand interaction promotes the initial ring‐opening of the aziridine and this work presents the first fully elucidated mechanism involving this intermediate. [ABSTRACT FROM AUTHOR]

Carbon dioxide is a cheap, easily available, and practically inexhaustible source of synthetic carbon (C1-synthon). Among various transformations of CO2, the synthesis of cyclic carbonates from epoxides and cyclic carbamates from aziridines can be referred to as priority areas in the development of contemporary chemical synthesis and catalysis. Cyclic carbonates found wide application in modern industry (electrolytes, solvents, reagents, polymers) and their use and production will be constantly increased. The development of effective catalytic processes that would allow the synthesis of carbonates under mild conditions (atmospheric pressure of CO2 or lower, temperature 25°C) and low loads of durable and affordable catalysts is at the forefront of research. In the present review we analyze the existing directions of research on the catalytic systems based earth-abundant metals Al3+, Fe2+(3+), and Zn2+ for the synthesis of cyclic carbonates from epoxides and cyclic carbamates from aziridines. [ABSTRACT FROM AUTHOR]

Keywords: photocatalysis; Barbier reaction; aziridines; azetidines; C-N bond cleavage EN photocatalysis Barbier reaction aziridines azetidines C-N bond cleavage 1385 1390 6 07/11/23 20230725 NES 230725 Graph C-C bond-formation processes are an essential class of reactions for the construction of the skeletons of organic compounds. Photocatalysis, Barbier reaction, aziridines, azetidines, C-N bond cleavage After the reduction, the radical-anion intermediate B I b smoothly undergoes C-N bond cleavage to deliver the benzyl radical intermediate B II b . [72] Here, we report a visible-light photocatalytic Barbier-type reaction of aziridines and azetidines with nonactivated aldehydes through reductive cleavage of C-N bonds [75] (Scheme 1 C). [Extracted from the article]