Advances in the chemistry of oxaziridines

Carbene reactive metabolite explains the hepatotoxicity of the hot flashes drug fezolinetant: A DFT investigation

Fezolinetant, the first-in-class hot flashes drug, was flagged in September 2024 by US-FDA for liver injury. It is alarming that an FDA-approved drug shows liver toxicity within a year. Fezolinetant's metabolic pathways and metabolites are not disclosed in the FDA label, clinical trial, or other literature reports. This creates a gap in understanding the mechanisms of metabolism and toxicity. In this manuscript, we have investigated novel metabolic pathways that generate reactive metabolites and rationalize hepatotoxicity. Quantum chemical calculations were performed to assess the reactivity of various sites using B3LYP/CC-PVTZ level of theory and H2O2 as the model oxidant. A combination of reaction free-energy (ΔG°) ≤ kBT = 18.5 kcal/mol and docking-based site of metabolism (SOM) to Heme-Fe distance (DAFe ≤ 6 ± 1.95 Å) criterion was used to assess metabolism feasibilities. Metabolic reactions and sites were considered potential only if both reactivity and accessibility criteria were met. A novel pathway involving Me oxidation at the thiadiazole ring to acid leading to reactive Fezo-carbene metabolite is most feasible (ΔG° and DAFe: 11 kcal/mol and 6.84 Å). Other feasible pathways include radical formation at the triazolopiperazine ring forming the Fezo-pip-dehydro metabolite (12 kcal/mol and 7.96 Å). The epoxidation, N-oxidation, and S-oxidation of the fluorophenyl, triazolopiperazine, and thiadiazole ring cleavage have minor contributions. Global and local electrophilicity analysis also confirms the higher reactivity potential of Fezo-carbene (ω = 2.77 eV) metabolite. Differences in local electrophilicity (Δωc+) further confirm the higher reactivity of the thiadiazole, fluorophenyl, and triazolopiperazine ring in Fezo-carbene, Fezo-epoxy, and Fezo-pip-dehydro metabolites respectively. Reactions with model nucleophiles (MeOH, H2O, MeNH2, and MeSH) show that Fezo-carbene is likely to form thiol adducts. In summary, these results give vital insights into the metabolic mechanisms of fezolinetant's hepatotoxicity and are likely to be useful for the design of less-toxic analogues.

The study of the photochemical behavior of 5-aryl-2,3-dihydropyrazine 1,4-dioxides

For the first time, the photochemical behavior of aryl-substituted 2,3-dihydropyrazine 1,4-dioxides was investigated. A common feature of all observed photoprocesses is the conversion of nitrone moieties into an oxaziridine ring to give substituted bi- or polycyclic systems. It was shown that the direction of the reaction depends on the irradiation wavelength and the employed solvent. For instance, the use of 365 nm UV light leads to the cyclization of both nitrone moieties. In contrast, visible-light irradiation (450 nm) allows one to regiospecifically utilize an aldonitrone unit to form 7-oxa-1,4-diazabicyclo[4.1.0]hept-4-ene 4-oxide derivatives. Generally, the oxaziridine ring possesses high reactivity and can be transformed in situ by various reagents. The molecular and crystal structures of the representatives of both bicyclic systems were solved for the first time with X-ray diffraction analysis.

Decarboxylative Aminomethylation of Indole-3-carboxylic Acids via Strain Release-Driven Ring Opening of 1,2-Oxazetidines

A copper-catalyzed decarboxylative aminomethylation of indole-3-carboxylic acids with 1,2-oxazetidines has been developed, enabling the rapid synthesis of structurally diverse 3-aminomethylindoles in good to excellent yields. Remarkably, an unprecedented decarboxylative aminomethylation/cyclization cascade was further achieved by a combination of copper and iron salts to construct complex γ-carbolines with high efficiency. It is worth noting that one of the obtained products proved to be a good dual-emissive luminogen, exhibiting both aggregation-caused quenching and aggregation-induced emission.

Chemical Modifications on the αvβ6 Integrin Targeting A20FMDV2 Peptide: A Review

Integrin proteins have received a significant increase in attention in recent scientific endeavors. The current trend uses the pre-established knowledge that the arginyl-glycyl-aspartic acid (RGD) structural motif present in the A20FMDV2 peptide is highly selective for the integrin class αvβ6 which is overexpressed in many cancer types. This review will provide an extensive overview of the existing literature research to date to the best of our knowledge, highlighting significant improvements and drawbacks of structure-activity relationships (SAR) work undertaken, aiding future research to identify established SAR for an informed design of future A20FMDV2 mimetic inhibitors. Herein, the review aims to collate the existing structural chemical modifications present on A20FMDV2 in the literature to highlight key structural analogues that display more potent biological activity.

Catalyst-Controlled [3 + 2] Annulation of Allenes with N-Monosubstituted Hydroxylamines for Regioselective Synthesis of Two Types of Isomeric Isoxazolidines

Catalyst-controlled regioselective [3 + 2] cascade annulation of allenes with N-monosubstituted hydroxylamines for precise construction of two types of isoxazolidine regiomers has been developed. The Ce(OTf)3 and MgCl2 can guide the nitrogen and oxygen atoms of N-hydroxyarylamides to both ends of the consecutive double bond of allenes, respectively, to afford two kinds of isomeric products. Notably and remarkably, the consecutive double bond of allenes served as a C3 synthon.

Enantioselective Synthesis of Sulfinamidines via Asymmetric Nitrogen Transfer from N-H Oxaziridines to Sulfenamides

Sulfinamidines are promising aza-SIV chiral building blocks in asymmetric synthesis and drug discovery. However, no report has documented their enantioselective synthesis. Here we present an enantioselective synthesis of sulfinamidines via electrophilic amination of sulfenamides using an enantiopure N-H oxaziridine. The resulting enantiomerically enriched primary sulfinamidines are configurationally stable at 90 °C in solution and show remarkable stability against organic acids and bases under non-aqueous conditions. We also demonstrate a one-pot, three-component, enantioselective synthesis of sulfinamides using N-H oxaziridine reagents.

Exploring Protein Bioconjugation: A Redox-Based Strategy for Tryptophan Targeting

Amino acid bioconjugation technology has emerged as a pivotal tool for linking small-molecule fragments with proteins, antibodies, and even cells. The study in Nature by Chang and Toste introduces a redox-based strategy for tryptophan bioconjugation, employing N-sulfonyloxaziridines as oxidative cyclization reagents, demonstrating high efficiency comparable to traditional click reactions. Meanwhile, this tool provides feasible methods for investigating the mechanisms underlying functional tryptophan-related biochemical processes, paving the way for protein function exploration, activity-based proteomics for functional amino acid identification and characterization, and even the design of covalent inhibitors.

Brønsted Acid-Catalyzed Cascade Ring-Opening/Cyclization of 3-Ethoxy Cyclobutanones to Access 2,8-Dioxabicyclo[3.3.1]nonane Derivatives

A cascade ring opening of 3-ethoxy cyclobutanones followed by a double cyclization strategy has been developed via Brønsted acid catalysis. A range of 2,8-dioxabicyclo[3.3.1]nonanes are obtained from various substituted naphthols in a one-pot and open flux manner. Additionally, a 15-membered macrocycle has been synthesized by ring closing metathesis as a synthetic application.

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.

Deoxygenation of Oxiranes by λ3 σ3 -Phosphorus Reagents: A Computational, Mechanistic, and Stereochemical Study

The deoxygenation of parent and substituted oxiranes by λ3 σ3 -phosphorus reagents has been explored in detail, therefore unveiling mechanistic aspects as well as regio- and stereochemical consequences. Attack to a ring C atom is almost always preferred over one-step deoxygenation by direct P-to-O attack. In most cases a carbene transfer occurs as first step, leading to a phosphorane and a carbonyl unit that thereafter react in the usual Wittig fashion via the corresponding λ5 σ5 -1,2-oxaphosphetane intermediate. Betaines rarely constitute true minima after the first C-attack to oxiranes, at least in the gas-phase. Use of the heavier derivatives AsMe3 and SbMe3 as oxirane deoxygenating reagents was also mechanistically studied. The thermodynamic tendency of λ3 σ3 -phosphorus reagents to act as oxygen (O-attack) or carbene acceptors (C-attack) was theoretically studied by means of the thermodynamic oxygen-transfer potential (TOP) and the newly defined thermodynamic carbene-transfer potential (TCP) parameters, that were explored in a wider context together with many other acceptor centres.

Visible-Light-Driven Multicomponent Diamination and Oxyamination of Alkene

Herein, we describe an effective method for the synthesis of 2-alkoxyamides and 1,2-diamines through visible-light-mediated difunctionalization of alkenes. N-Aminopyridinium salts were employed as appropriate precursors to generate key amidyl radical intermediates via a photoinduced single-electron transfer (SET) process. The amidyl radicals would react with alkenes, followed by oxidation and nucleophilic addition. Excellent functional group tolerance and good yields demonstrate the synthetic potential of this transformation.

Chemical technology principles for selective bioconjugation of proteins and antibodies

Proteins are multifunctional large organic compounds that constitute an essential component of a living system. Hence, control over their bioconjugation impacts science at the chemistry-biology-medicine interface. A chemical toolbox for their precision engineering can boost healthcare and open a gateway for directed or precision therapeutics. Such a chemical toolbox remained elusive for a long time due to the complexity presented by the large pool of functional groups. The precise single-site modification of a protein requires a method to address a combination of selectivity attributes. This review focuses on guiding principles that can segregate them to simplify the task for a chemical method. Such a disintegration systematically employs a multi-step chemical transformation to deconvolute the selectivity challenges. It constitutes a disintegrate (DIN) theory that offers additional control parameters for tuning precision in protein bioconjugation. This review outlines the selectivity hurdles faced by chemical methods. It elaborates on the developments in the perspective of DIN theory to demonstrate simultaneous regulation of reactivity, chemoselectivity, site-selectivity, modularity, residue specificity, and protein specificity. It discusses the progress of such methods to construct protein and antibody conjugates for biologics, including antibody-fluorophore and antibody-drug conjugates (AFCs and ADCs). It also briefs how this knowledge can assist in developing small molecule-based covalent inhibitors. In the process, it highlights an opportunity for hypothesis-driven routes to accelerate discoveries of selective methods and establish new targetome in the precision engineering of proteins and antibodies.

Convergent synthesis of thiodiazole dioxides from simple ketones and amines through an unusual nitrogen-migration mechanism

We report the modular preparation of dihydro-1,2,5-thiodiazole dioxide heterocycles starting from methyl ketones and primary amines. This one-pot, three-component coupling employs 2,3-dimethylimidazole-1-sulfonyl azide triflate as a coupling reagent and oxidant. The transformation is scalable and various ketones and amines can be used, yielding thiodiazole dioxide products in up to 89% yield. In addition, 15N- and 13C-labeling studies suggest a mechanism involving a 1,2-nitrogen migration. Together with the mechanistic studies, DFT calculations provide insight into the reaction pathway and set the stage for further exploration of the mechanistic nuances of reactions that use sulfamoyl azides. In combination with the demonstrated modularity of the approach reported herein, the derivatization of the thiodiazole dioxide products highlights the potential of this methodology to rapidly access diverse chemical structures.

Synthesis of Indoles Using the Electrophilic Potential of Diazirines

The electrophilic potential of diazirines has been utilized to obtain N-substituted diaziridines that are directly hydrolyzed to produce monosubstituted hydrazines. The hydrazines can undergo the Fisher process with enolizable carbonyls to yield multiple indole derivatives in moderate to high yields. The N-metalated diaziridine intermediates can undergo isomerization prior to electrophilic substitution, to form N,N-disubstituted hydrazones. The latter react with enolizable carbonyls to produce N-protected indole derivatives in a single step. This protocol was used to efficiently synthesize indomethacin, an anti-inflammatory drug.

Chemistry of Gold(III) with a Pyridine-Oxaziridine Ligand: Competition between C-O and N-O bond Activation

The oxaziridine derivative 2-t-butyl-3-(2-pyridinyl)oxaziridine reacted with Na[AuCl4 ].2H2 O to give, after recrystallization from a solvent mixture containing methanol, a mixture of gold(III) complexes which were characterized crystallographically as the amide complex [AuCl2 {κ2 -N,N'-2-C5 H4 NC(=O)N(t-Bu)] and the aldolate complex [AuCl2 {κ2 -N,O-2-C5 H4 NCH(OMe)O)]. It is suggested that these products arise after initial O-N or C-N bond cleavage respectively of the strained oxaziridine ring, after coordination to the gold(III) center. Monitoring of reactions by NMR spectroscopy showed that O-N bond cleavage of the oxaziridine ring was favoured in the presence of a protic solvent.

Recent updates and future perspectives in aziridine synthesis and reactivity

In this review, selected recent advances in the preparation and reactivity of aziridines using modern synthetic approaches are highlighted, while comparing these new strategies with more classical approaches. This critical analysis is designed to help identify current gaps in the field and is showcasing new and exciting opportunities to move the chemistry of aziridines forward in the future.

Asymmetric imino-acylation of alkenes enabled by HAT-photo/nickel cocatalysis

By merging nickel-mediated facially selective aza-Heck cyclization and radical acyl C-H activation promoted by tetrabutylammonium decatungstate (TBADT) as a hydrogen atom transfer (HAT) photocatalyst, we accomplish an asymmetric imino-acylation of oxime ester-tethered alkenes with readily available aldehydes as the acyl source, enabling the synthesis of highly enantioenriched pyrrolines bearing an acyl-substituted stereogenic center under mild conditions. Preliminary mechanistic studies support a Ni(i)/Ni(ii)/Ni(iii) catalytic sequence involving the intramolecular migratory insertion of a tethered olefinic unit into the Ni(iii)-N bond as the enantiodiscriminating step.

Fluorine-Assisted Rearrangement of Geminal Azidofluorides to Imidoyl Fluorides

Organoazide rearrangement constitutes versatile synthetic strategies but typically requires an extremely strong acid and/or a high reaction temperature. Our group recently discovered the remarkable accelerating effect of the geminal fluorine substituent that enables the facile rearrangement of azides into imidoyl fluorides without the aid of acid under much milder reaction conditions. The role of geminal fluorine was elucidated by both experimental and computational investigations. This new reactivity led to the development of a practical one-step tandem preparative method for potentially useful and bench-stable imidoyl fluorides from a wide range of structurally diverse geminal chlorofluorides. Our additional efforts to expand the reaction scope regarding the migrating group, halogen, and carbonyl function are described, and the synthetic utility of the imidoyl fluoride products was demonstrated in hopes of promoting the use of this under-appreciated functional group in the synthetic organic community.

Asymmetric Rubottom-Type Oxidation Catalyzed by Chiral Calcium Phosphates

A highly efficient catalytic asymmetric Rubottom-type oxidation is described. Using meta-chloroperbenzoic acid (m-CPBA) as the oxidant and chiral calcium phosphate as the catalyst, the facile transformation enables direct hydroxylation of N-Boc oxindoles and β-ketoesters in high yields (up to 99 %) and in a highly enantioenriched fashion (up to >99 % ee). The application of the established method was demonstrated by the synthesis of a pharmaceutically important 3-hydroxyoxindole with excellent enantiocontrol.

The quest for unligated oxaphosphiranes with phosphorus in different coordination numbers

After more than 160 years of oxirane (epoxide) chemistry, the first derivative of a phosphorus analogue, namely oxaphosphirane, has been synthesized. Reactions with borane sulfane, a peroxy compound and elemental sulfur, as well as tetra-chloro-ortho-benzoquinone (TOB) reveal a significant destabilization upon increasing the coordination number at phosphorus from σ³ to σ⁴, thus somehow supporting previous reports on such fleeting species. Theoretical studies provide insight into ring strain energy, ring/ring interconversion and the oxidation pathways.

Merging Two Strained Carbocycles: Lewis Acid Catalyzed Remote Site-Selective Friedel-Crafts Alkylation of in Situ Generated β-Naphthol

Lewis acid catalyzed tandem activation of the two smallest carbocycles, 3-ethoxy cyclobutanones, and donor-acceptor cyclopropanes has been demonstrated. The diphenyl-substituted 3-ethoxy cyclobutanone rearranges itself by intramolecular cyclization for the in situ generation of 1-phenyl 2-naphthol, which further undergoes remote site-selective Friedel-Crafts alkylation with donor-acceptor cyclopropane to synthesize a series of γ-naphthyl butyric acid derivatives. Further control experiments for mechanistic investigations and synthetic applications have also been carried out.

Activation of O-Electrophiles via Structural and Solvent Effects: SN2@O Reaction of Cyclic Diacyl Peroxides with Enol Acetates

The reactions of O-electrophiles, such as organic peroxides, with carbon nucleophiles are an umpolung alternative to the common approaches to C-O bond formation. Nucleophilic substitution at the oxygen atom of cyclic diacyl peroxides by enol acetates with the following deacylation leads to α-acyloxyketones with an appended carboxylic acid in 28-87% yields. The effect of fluorinated alcohols on the oxidative functionalization of enol acetates by cyclic diacyl peroxides was studied experimentally and computationally. Computational analysis reveals that the key step proceeds as a direct substitution nucleophilic bimolecular (S_N2) reaction at oxygen (S_N2@O). CF₃CH₂OH has a dual role in assisting in both steps of the reaction cascade: it lowers the energy of the S_N2@O activation step by hydrogen bonding to a remote carbonyl and promotes the deacylation of the cationic intermediate.

Ring Strain Energies of Three-Membered Homoatomic Inorganic Rings El3 and Diheterotetreliranes El2Tt (Tt = C, Si, Ge): Accurate versus Additive Approaches

Accurate ring strain energies (RSEs) for three-membered symmetric inorganic rings El₃ and organic dihetero-monocycles El₂C and their silicon El₂Si and germanium El₂Ge analogues have been computed for group 14–16 “El” heteroatoms using appropriate homodesmotic reactions and calculated at the DLPNO-CCSD-(T)/def2-TZVPP//B3LYP-D4/def2-TZVP(ecp) level. Rings containing triels and Sn/Pb heteroatoms are studied as exceptions to the RSE calculation as they either do not constitute genuine rings or cannot use the general homodesmotic reaction scheme due to uncompensated interactions. Some remarkable concepts already related to the RSE such as aromaticity or strain relaxation by increasing the s-character in the lone pair (LP) of the group 15–16 elements are analyzed extensively. An appealing alternative procedure for the rapid estimation of RSEs using additive rules, based on contributions of ring atoms or endocyclic bonds, is disclosed.

Accurate ring strain energies (RSEs) are calculated for saturated three-membered homoatomic inorganic rings El₃ and diheterotetreliranes El₂Tt (Tt = C, Si, Ge). Aromaticity, lone-pair-induced strain relaxation for the group 15−16 elements, and bond stiffness are extensively discussed as main factors affecting the RSE. An attractive alternative procedure for fast estimation of the RSE using additive rules is proposed.

Copper-Catalyzed Nitrogen Atom Transfer to Isoquinolines via C-N Triple Bond Cleavage and Three-Component Cyclization

A copper(I)-catalyzed tandem reaction of 2-bromoaryl ketones, terminal alkynes, and CH₃CN is developed, which combines N atom transfer and three-component [3 + 2 + 1] cyclization, and efficiently produces densely functionalized isoquinolines in a facile, highly selective, and general manner. In the reaction, the formation of aromatic C-N bonds along with the complete C-N triple bond cleavage is first realized; Cu(III)-acetylide species might serve as the intermediates, which allow highly selective 6-endo-dig cyclization.

Advances of Sulfenate Anions in Catalytic Asymmetric Synthesis of Sulfoxides

In recent years, sulfenate anions as key intermediates in enantioselective synthesis have attracted considerable attention. Typically, development of novel synthetic methods to generate sulfenate anions allows for the preparation of various enantiopure sulfoxides, which are prevalently used as auxiliaries, ligands, organocatalysts, and biologically active compounds. This review presents the in situ preparation methods and the recent applications of sulfenate anions in catalytic asymmetric synthesis of chiral sulfoxides.

Copper-Nitrene-Catalyzed Desymmetric Oxaziridination/1,2-Alkyl Rearrangement of 1,3-Diketones toward Bicyclic Lactams

Although copper-nitrene has been extensively studied as a versatile active species in various transformations, asymmetric reactions involving copper-nitrene have been limited to the aziridination of olefins. Herein, we report the novel copper-nitrene-catalyzed desymmetric oxaziridination reaction of cyclic diketones with alkyl azides and the subsequent rearrangement of the resulting highly active intermediate, which produces a synthetically challenging chiral bicyclic lactam containing a quaternary carbon center. This procedure not only enriches the copper-nitrene-catalyzed asymmetric reactions, but also provides an alternative strategy to address the inherent challenges of catalytic asymmetric Schmidt reactions. This unique reaction could inspire the investigation of novel copper-nitrene-catalyzed asymmetric transformations and their reaction mechanisms.

Weak base-promoted selective rearrangement of oxaziridines to amides via visible-light photoredox catalysis

The selective rearrangement of oxaziridines to amides via a single electron transfer (SET) pathway is unexplored. In this study, we present a weak base-promoted selective rearrangement of oxaziridines to amides via visible-light photoredox catalysis. The developed method shows excellent functional group tolerance with a broad substrate scope and good to excellent yields. Furthermore, control experiments and density functional theory (DFT) calculations are performed to gain insight into the reactivity and selectivity.

Relieving the stress together: annulation of two different strained rings towards the formation of biologically significant heterocyclic scaffolds

Small carbo- and heterocycles have become versatile building blocks owing to their intrinsic ring strain and ease of synthesis. However, the traditional approaches of heterocycle synthesis involved the combination of one strained-carbocycle or heterocycle with one unsaturated molecule. On the contrary, there is an exciting possibility of combining two different strained rings to furnish varieties of heterocycles, where one of the strained rings can act as a valuable alternative to the unsaturated molecule. These strategies are also useful to access multi-functionalized rings. Despite these distinctive synthetic benefits, this chemistry has not drawn considerable attention of the community. In this minireview, we explicitly choose this topic to reveal the unexplored possibilities with these different strained rings. This minireview provides comprehensive details with the mechanistic rationale about the reactivity of these pairs of small rings when they are allowed to react together in the presence of different Lewis acids. Subsequently, it will also open a new avenue for heterocycle synthesis.

New Trends in Diaziridine Formation and Transformation (a Review)

This review focuses on diaziridine, a high strained three-membered heterocycle with two nitrogen atoms that plays an important role as one of the most important precursors of diazirine photoaffinity probes, as well as their formation and transformation. Recent research trends can be grouped into three categories, based on whether they have examined non-substituted, N-monosubstituted, or N,N-disubstituted diaziridines. The discussion expands on the conventional methods for recent applications, the current spread of studies, and the unconventional synthesis approaches arising over the last decade of publications.

Competitive Reactivity of SO2 and NO2 with N-Heterocyclic Carbene: A Mechanistic Study

Recent DFT based molecular engineering to obtain stable oxathiirane S-oxide derivatives evokes the recommencement of the use of carbenes for the sequestering of SO₂, which has been kept separate so far. Carbene is one of the key chemicals for the sequestering of various premier greenhouse gases like CO₂, CO, N₂O, etc. In this respect, a comparative study of the reactivity of carbenes with variant greenhouse gases is highly demanding. The present investigation is engrossed in the comparative reactivity of SO₂ and NO₂ with carbenes. All three selected carbenes are highly susceptible to SO₂ and NO₂. Through an immaculate mechanistic study, we are able to corroborate that the end product of the carbene-SO₂ reaction is an adduct which has a preferable structure having a six-membered ring with hydrogen bonding instead of ketone and SO with higher thermodynamic stability than the corresponding oxathiirane S-oxide derivative. Carbene reacts with NO₂ to form a stable carbene N, N-dioxide derivative which forms vibrationally excited oxaziridine N-oxide which rapidly dissociates to form a ketone derivative. The formation of carbene S, S-dioxide and carbene N, N-dioxide is a barrierless process. The dissociation of oxaziridene N-oxide is also a barrierless process.

Decarboxylative Amination: Diazirines as Single and Double Electrophilic Nitrogen Transfer Reagents

The ubiquity of nitrogen-containing small molecules in medicine necessitates the continued search for improved methods for C-N bond formation. Electrophilic amination often requires a disparate toolkit of reagents whose selection depends on the specific structure and functionality of the substrate to be aminated. Further, many of these reagents are challenging to handle, engage in undesired side reactions, and function only within a narrow scope. Here we report the use of diazirines as practical reagents for the decarboxylative amination of simple and complex redox-active esters. The diaziridines thus produced are readily diversifiable to amines, hydrazines, and nitrogen-containing heterocycles in one step. The reaction has also been applied in fluorous phase synthesis with a perfluorinated diazirine.

Deoxygenation of nitrosoarene by N-heterocyclic carbene (NHC): an elusive Breslow-type intermediate bridging carbene and nitrene

N-Heterocyclic carbene (NHC) activates and deoxygenates nitrosoarene (ArNO) to afford arylnitrene (ArN), thereby portraying a fundamental route connecting two 6e- species. A combination of spectroscopic and computational studies suggests that the interaction of ArNO with NHC affords a transient 2,2'-diamino imine-N-oxide as a key intermediate in ArNO deoxygenation.

Synergistic Ammonium (Hypo)Iodite/Imine Catalysis for the Asymmetric α-Hydroxylation of β-Ketoesters

The synergistic use of chiral bifunctional ammonium iodide catalysts in combination with simple catalytically relevant aldimines allows for an unprecedented asymmetric α-hydroxylation reaction of β-ketoesters using H2O2. The reaction proceeds via in situ formation of a hypervalent iodine species, which then reacts with the used aldimine to generate an activated electrophilic oxygen transfer reagent.

Straightforward Approach toward Multifunctionalized Aziridines via Catalyst-Free Three-Component Reactions of α-Diazoesters, Nitrosoarenes, and Alkynes

A straightforward, catalyst-free atom- and step-economical approach for the synthesis of multisubstituted 1-arylaziridine-2-carboxylates via one-pot three-component reactions of α-diazoesters, nitrosoarenes, and alkynes has been described. This method could provide facile access to a variety of multifunctionalized aziridines in up to 91% yields under mild reaction conditions and features the catalyst-free strategy and use of cheap and readily accessible starting materials.

Gas Phase Identification of the Elusive N-Hydroxyoxaziridine (c-H2CON(OH)): A Chiral Molecule

The hitherto elusive N-hydroxyoxaziridine molecule (c-H₂CON(OH)), a chiral, high energy isomer of nitromethane (CH₃NO₂) and one of the simplest representatives of an oxaziridine, is detected in the gas phase. Electronic structure calculations propose an impending synthesis eventually via addition of carbene (CH₂) to the nitrogen-oxygen double bond of nitrous acid (HONO). The oxaziridine ring demonstrates an unusual kinetic stability toward ring opening compared to the isoeletronic cyclopropane (C₃H₆) counterpart. This system defines a fundamental benchmark to explore the formation and stability of racemic derivatives of strained oxaziridines (c-H₂CONH) and changes our perception how we think about fundamental decomposition and isomerization mechanisms in (model compounds of) energetic materials.

Cobalt-catalyzed regioselective hydrohydrazination of epoxides

Using an air-stable cobalt catalyst [Cp*Co(1,2-Ph2PC6H4S)(NCMe)]BF4 (1, Cp* = Me5C5-), we have achieved catalytic regioselective hydrohydrazination of epoxides to 1,1-hydrazinoalcohols in an atom-economical manner. The catalysis involves a cobalt-hydrazine intermediate, in which the NH2 group of the hydrazine binds to the metal center, inhibiting its nucleophilic reactivity and allowing the NH group to participate in the regioselective hydrohydrazination.

Gas phase identification of the elusive oxaziridine (cyclo-H2CONH) – an optically active molecule

First detection of the chiral oxaziridine (cyclo-H₂CONH) molecule.

Expanding the Toolbox of Chemoselective Modifications of Protein-Like Polymers at Methionine Residues

Selective modifications at methionyl residues in proteins have attracted particular attention in recent years. Previously described methods to chemoselectively modify the methionine side chain in elastin-like polypeptides (ELPs) involved nucleophilic addition using alkyl halides or epoxides yielding a sulfonium group with a positive charge strongly affecting ELPs' physicochemical properties, in particular their thermal responsiveness. We herein explored the recently reported ReACT method (Redox-Activated Chemical Tagging) based on the use of oxaziridine derivatives, yielding an uncharged sulfimide as an alternative route for chemoselective modifications of methionine-containing ELPs in aqueous medium. The different synthetic strategies are herein compared in order to provide a furnished toolbox for further biorthogonal postmodifications of any protein polymers.