Sixty years of staudinger reaction

Design and synthesis of a library of C8-substituted sulfamidoadenosines to probe bacterial permeability

Gram-negative bacteria pose a major challenge in antibiotic drug discovery because their cell envelope presents a permeability barrier that affords high intrinsic resistance to small-molecule drugs. The identification of correlations between chemical structure and Gram-negative permeability would thus enable development of predictive tools to facilitate antibiotic discovery. Toward this end, have advanced a library design paradigm in which various chemical scaffolds are functionalized at different regioisomeric positions using a uniform reagent set. This design enables decoupling of scaffold, regiochemistry, and substituent effects upon Gram-negative permeability of these molecules. Building upon our recent synthesis of a library of C2-substituted sulfamidoadenosines, we have now developed an efficient synthetic route to an analogous library of regioisomeric C8-substituted congeners. The C8 library samples a region of antibiotic-relevant chemical space that is similar to that addressed by the C2 library, but distinct from that sampled by a library of analogously substituted oxazolidinones. Selected molecules were tested for accumulation in Escherichia coli in a pilot analysis, setting the stage for full comparative evaluation of these libraries in the future.

Arene displacement, C-H activation and acetonitrile insertion reactions enabled by coordination of a functionalized iminophosphorane to a RuII-p-cymene scaffold

Reaction of a sterically demanding iminophosphorano-phosphine, Ph2PCH2Ph2PNAr* (here onwards referred to as PCPNAr*; Ar* = 2,6-dibenzhydryl-4-methylphenyl), (1) with [Ru(η6-p-cymene)Cl2]2 yielded three different types of complex, [RuCl2{(η6-p-cymene)(PCPNAr*)-κ1-P}] (2), [RuCl{(P(O)CPNAr*)(κ2-N,C)(C-η6-arene)}] (3) and [RuCl{(POCPNAr*)(κ2-N,C-o)(C-η6-arene)}] (4), depending on the reaction conditions via CH activation, tethered η6-arene coordination, ortho-metallation or PN bond cleavage/rearrangement reactions. Interestingly, a similar reaction in CH3CN in the presence of AgBF4 resulted in the insertion of CH3CN into the PN bond to form a novel metallacycle [Ru(NCMe)3{(PC2PN(CH3)CNAr*)-κ3-N,N,P}][BF4]2 (5) containing 4- and 5-membered rings via an aza-Wittig type reaction. Complex 4 showed very good catalytic activity in the transfer hydrogenation of carbonyl compounds.

Chemoselective Staudinger Reactivity of Bis(azido)phosphines Supported with a π-Donating Imidazolin-2-iminato Ligand

Synthesis and characterization of new P(III) and P(V) bis(azido)phosphines/phosphoranes supported by an N,N'-bis(2,6-diisopropylphenyl) imidazolin-2-iminato (IPrN) ligand and their reactivity with various secondary and tertiary phosphines result in the formation of chiral and/or asymmetric mono(phosphinimino)azidophosphines via the Staudinger reaction. The reaction of IPrNP(N3)2 (2) or IPrNP(S)(N3)2 (4S) with an excess of tertiary phosphine resulted in the chemoselective formation of IPrNP(N3)(NPMe3) (7) or IPrNP(S)N3(NPR3) (5R), respectively. The chemoselective Staudinger reactivity was also observed in reactions using a secondary phosphine (HPCy2) to produce IPrNP(S)N3[NP(H)Cy2] (6a), which exists in equilibrium with a tautomeric IPrNP(S)N3[N(H)PCy2] form (6b), as confirmed by 31P-31P nuclear Overhauser effect spectroscopy (NOESY). Density functional theory (DFT) calculations point to a combination of energetically unfavorable lowest unoccupied molecular orbitals (LUMOs) and the accumulation of increasing negative charge at the terminal azido-nitrogen upon a single azide-to-phosphinimine conversion that gave rise to the observed chemoselectivity.

Cyclic Sulfinamides

The literature on cyclic sulfinamides (put simply, sultims) published from 1989 to 2022 has been summarized and reviewed. The information is divided into two sections: the analysis of synthetic methods on the preparation of cyclic sulfinamides and the discussion of the chemical properties of cyclic sulfinamides focusing on their reactions and applications. The survey of the reaction conditions, provided in the most detailed way, and a critical view of the reaction mechanisms add an extra dimension to the text. The data presented will be useful to specialists in different areas, especially those who work in the field of synthetic organic and pharmaceutical chemistry.

"Click Chemistry": An Emerging Tool for Developing a New Class of Structural Motifs against Various Neurodegenerative Disorders

Click chemistry is a set of easy, atom-economical reactions that are often utilized to combine two desired chemical entities. Click chemistry accelerates lead identification and optimization, reduces the complexity of chemical synthesis, and delivers extremely high yields without undesirable byproducts. The most well-known click chemistry reaction is the 1,3-dipolar cycloaddition of azides and alkynes to form 1,2,3-triazoles. The resulting 1,2,3-triazoles can serve as both bioisosteres and linkers, leading to an increase in their use in the field of drug discovery. The current Review focuses on the use of click chemistry to identify new molecules for treating neurodegenerative diseases and in other areas such as peptide targeting and the quantification of biomolecules.

Frustrated Lewis Pair Chelation in the p-Block

Frustrated Lewis pairs (FLPs) have been the subject of considerable study since the field's inception. While much of the research into FLPs has centered around small molecule activation for diverse stoichiometric and catalytic transformations, intramolecular FLPs also show promise as chelating ligands. The cooperative action of Lewis basic and acidic moieties enables intramolecular FLPs to stabilize low oxidation state centers and (consequently) reactive molecular fragments through a donor-acceptor approach, making them an attractive ligand class in main group element chemistry. This review outlines the state of FLP chelation to date throughout the p-block, encompassing primarily groups 13-16.

Chemodivergent Staudinger Reactions of Secondary Phosphine Oxides and Application to the Total Synthesis of LL-D05139β Potassium Salt

Unprecedented Staudinger reaction modes of secondary phosphine oxides (SPO) and organic azides are herein disclosed. By the application of various additives, selective nitrogen atom exclusion from the azide group has been achieved. Chlorotrimethylsilane mediates a stereoretentive Staudinger reaction with a 2-N exclusion which provides a valuable method for the synthesis of phosphinic amides and can be considered complementary to the stereoinvertive Atherton-Todd reaction. Alternatively, a 1-N exclusion pathway is promoted by acetic acid to provide the corresponding diazo compound. The effectiveness of this protocol has been further demonstrated by the total synthesis of the diazo-containing natural product LL-D05139β, which was prepared as a potassium salt for the first time in 6 steps and 26.5 % overall yield.

Reactions of main group compounds with azides forming organic nitrogen-containing species

Since the seminal discovery of phenyl azide by Grieß in 1864, a variety of organic azides (R-N3) have been developed and extensively studied. The amenability of azides to a number of reactions has expanded their utility as building blocks not only in organic synthesis but also in bioorthogonal chemistry and materials science. Over the decades, it has been demonstrated that the reactions of main group compounds with azides lead to diverse N-containing main group molecules. In view of the pronounced progress in this area, this review summarizes the reactions of main group compounds with azides, emphatically introducing their reaction patterns and mechanisms. The reactions of forming inorganic nitrogen species are not included in this review.

Strategies for the Preparation of Phosphorus Janus Dendrimers and Their Properties

Dendrimers, being highly branched monodispersed macromolecules, predominantly exhibit identical terminal functionalities within their structural framework. Nonetheless, there are instances where the presence of two distinct surface functionalities becomes advantageous for the fulfilment of specific properties. To achieve this objective, one approach involves implementing Janus dendrimers, consisting of two dendrimeric wedges terminated by dissimilar functionalities. The prevalent method for creating these structures involves the synthesis of dendrons that possess a core functionality that complements that of a second dendron, facilitating their coupling to generate the desired dendrimers. In this comprehensive review, various techniques employed in the fabrication of phosphorus-based Janus dendrimers are elucidated, displaying the different coupling methodologies employed between the two units. The advantages of phosphorus dendrimers over classic dendrimers will be shown, as the presence of at least one phosphorus atom in each generation allows for the easy monitoring of reactions and the confirmation of purity through a simple technique such as ³¹P NMR, as these structures typically exhibit easily interpretable patterns.

Azide-Free Synthesis of N-Alkyliminophosphoranes from Phosphines and Hydroxylamine Derivatives

A broadly applicable and efficient method for the synthesis of N-alkyliminophosphoranes from phosphines that does not use potentially hazardous alkyl azides is reported. Under iron catalysis, a hydroxylamine-derived triflic acid salt oxidizes phosphines to a wide range of iminophosphorane triflic acid salts. Diphosphines afford phosphine-iminophosphoranes that can serve as ligands in transition metal complexes. The developed method can be employed in the synthesis of mixed diiminophosphoranes and in a traceless Staudinger ligation.

Mesoionic N-Heterocyclic Imines as Super Nucleophiles in Catalytic Couplings of Amides with CO2

An extended class of stable mesoionic N-heterocyclic imines (mNHIs), containing a highly polarized exocyclic imine moiety, were synthesized. The calculated proton affinities (PA) and experimentally determined Tolman electronic parameters (TEPs) reveal that these synthesized mNHIs have the highest basicity and donor ability among NHIs reported so far. The superior nucleophilicity of newly designed mNHIs was utilized in devising a strategy to incorporate CO₂ as a bridging unit under reductive conditions to couple inert primary amides. This strategy was further extended to hetero-couplings between amide and amine using CO₂ . These hitherto unknown catalytic transformations were introduced in the diversification of various biologically active drug molecules under metal-free conditions. The underlying mechanism was explored by performing a series of control experiments, characterizing key intermediates using spectroscopic and crystallographic techniques.

Enantioselective Synthesis of Quaternary Oxindoles: Desymmetrizing Staudinger-Aza-Wittig Reaction Enabled by a Bespoke HypPhos Oxide Catalyst

This paper describes a catalytic asymmetric Staudinger-aza-Wittig reaction of (o-azidoaryl)malonates, allowing access to chiral quaternary oxindoles through phosphine oxide catalysis. We designed a novel HypPhos oxide catalyst to enable the desymmetrizing Staudinger-aza-Wittig reaction through the PIII/PV═O redox cycle in the presence of a silane reductant and an IrI-based Lewis acid. The reaction occurs under mild conditions, with good functional group tolerance, a wide substrate scope, and excellent enantioselectivity. Density functional theory revealed that the enantioselectivity in the desymmetrizing reaction arose from the cooperative effects of the IrI species and the HypPhos catalyst. The utility of this methodology is demonstrated by the (formal) syntheses of seven alkaloid targets: (-)-gliocladin C, (-)-coerulescine, (-)-horsfiline, (+)-deoxyeseroline, (+)-esermethole, (+)-physostigmine, and (+)-physovenine.

Ortho-Phosphinoarenesulfonamide-Mediated Staudinger Reduction of Aryl and Alkyl Azides

Conventional Staudinger reductions of organic azides are sluggish with aryl or bulky aliphatic azides. In addition, Staudinger reduction usually requires a large excess of water to promote the decomposition of the aza-ylide intermediate into phosphine oxide and amine products. To overcome the challenges above, we designed a novel triaryl phosphine reagent 2c with an ortho-SO₂NH₂ substituent. Herein, we report that such phosphine reagents are able to mediate the Staudinger reduction of both aryl and alkyl azides in either anhydrous or wet solvents. Good to excellent yields were obtained in all cases (even at a diluted concentration of 0.01 M). The formation of B-TAP, a cyclic aza-ylide, instead of phosphine oxide, eliminates the requirement of water in the Staudinger reduction. In addition, computational studies disclose that the intramolecular protonation of the aza-ylide by the ortho-SO₂NH₂ group is kinetically favorable and responsible for the acceleration of Staudinger reduction of the aryl azides.

Reactions of Mesityl Azide with Ferrocene-Based N-Heterocyclic Germylenes, Stannylenes and Plumbylenes, Including PPh2 -Functionalised Congeners

The reactivity of ferrocene-based N-heterocyclic tetrylenes [{Fe(η5 -C5 H4 -NSitBuMe2 )2 }E] (E=Ge, Sn, Pb) towards mesityl azide (MesN3 ) is compared with that of PPh2 -functionalised congeners exhibiting two possible reaction sites, namely the EII and PIII atom. For E=Ge and Sn the reaction occurs at the EII atom, leading to the formation of N2 and an EIV =NMes unit. The germanimines are sufficiently stable for isolation. The stannanimines furnish follow-up products, either by [2+3] cycloaddition with MesN3 or, in the PPh2 -substituted case, by NMes transfer from the SnIV to the PIII atom. Whereas [{Fe(η5 -C5 H4 -NSitBuMe2 )2 }Pb] and other diaminoplumbylenes studied are inert even under forcing conditions, the PPh2 -substituted congener forms an addition product with MesN3 , thus showing a behaviour similar to that of frustrated Lewis pairs. The germylenes of this study afford copper(I) complexes with CuCl, including the first structurally characterised linear dicoordinate halogenido complex [CuX(L)] with a heavier tetrylene ligand L.

Design and Synthesis of a Doubly Functionalized Core Structure of a Glycosylphosphatidylinositol Anchor Containing Photoreactive and Clickable Functional Groups

A bifunctional derivative of the core structure of glycosylphosphatidylinositol (GPI) anchors having a clickable alkynyl group and a photoreactive diazirine group attached to the GPI glucosamine and lipid moieties, respectively, was synthesized from myo-inositol, d-glucosamine, and (R)-1,2-O-acetonized glycerol. The target molecule should be useful for the investigation of GPI-interacting components in the cell membrane that play a key role in the signal transduction and other biological functions of GPI-anchored proteins.

Synthesis of a New Chelating Iminophosphorane Derivative (Phosphazene) for U(VI) Recovery

A new synthetic chelating N–hydroxy–N–trioctyl iminophosphorane (HTIP) was prepared through the reaction of trioctylphosphine oxide (TOPO) with N–hydroxylamine hydrochloride in the presence of a Lewis acid (AlCl₃). Specifications for the HTIP chelating ligand were successfully determined using many analytical techniques, ¹³C–NMR, ¹H–NMR, FTIR, EDX, and GC–MS analyses, which assured a reasonable synthesis of the HTIP ligand. The ability of HTIP to retain U(VI) ions was investigated. The optimum experimental factors, pH value, experimental time, initial U(VI) ion concentration, HTIP dosage, ambient temperature, and eluents, were attained with solvent extraction techniques. The utmost retention capacity of HTIP/CHCl₃ was 247.5 mg/g; it was achieved at pH = 3.0, 25 °C, with 30 min of shaking and 0.99 × 10⁻³ mol/L. From the stoichiometric calculations, approximately 1.5 hydrogen atoms are released during the extraction at pH 3.0, and 4.0 moles of HTIP ligand were responsible for chelation of one mole of uranyl ions. According to kinetic studies, the pseudo–first order model accurately predicted the kinetics of U(VI) extraction by HTIP ligand with a retention power of 245.47 mg/g. The thermodynamic parameters ΔS°, ΔH°, and ΔG° were also calculated; the extraction process was predicted as an exothermic, spontaneous, and advantageous extraction at low temperatures. As the temperature increased, the value of ∆G° increased. The elution of uranium ions from the loaded HTIP/CHCl₃ was achieved using 2.0 mol of H₂SO₄ with a 99.0% efficiency rate. Finally, the extended variables were used to obtain a uranium concentrate (Na₂U₂O₇, Y.C) with a uranium grade of 69.93% and purity of 93.24%.

Phenolic 3° Phosphine Oxides as a Class of Metal-Free Catalysts for the Activation of C–O Bonds in Aliphatic Alcohols: Direct Synthesis of Catalyst Candidates, and Kinetic Studies

It was recently reported that a (2-hydroxybenzyl)phosphine oxide (2-HOBPO) can serve as a phosphorus-centered catalyst for the stereo-invertive coupling of aliphatic alcohols and acidic pronucleophiles (akin to a Mitsunobu reaction, but without additional reagents). Herein, we report an improved synthesis, which provides direct access to systematically varied 2-HOBPOs in a single step from commercially available precursors (salicylaldehydes and secondary phosphines). The efficiency and generality of the synthetic method enabled limited structure–activity relationship (SAR) studies, from which it was determined that substituents on both the phenolic and phosphine oxide portions can exert significant influence on the turnover frequency (TOF) of each catalyst. Importantly, for all catalytically active 2-HOBPOs examined, the molecularity of catalyst in the rate law of the alcohol coupling was determined to be <1. Thus, for high catalyst loadings, differences in catalytic activity between 2-HOBPOs appear to be dominated by differences in catalytic auto-inhibition, while for low catalyst loadings, differences are attributed to inherent differences in the energetic span of the catalytic cycle, ignoring off-cycle species, in good agreement with density functional theory (DFT) modeling at the ωB97X-D/6-311G(d,p) level.

Phosphinoindenyl and phosphazidoindenyl complexes of lanthanum and samarium: synthesis, characterisation, and hydroamination catalysis

The phosphinoindenyl rare-earth metal complexes [1-(Ph2P)-η5-C9H6]2LnIIIN(SiMe3)2, Ln = La (1-La), Sm (1-Sm), were prepared by heating two equivalents of 1-(Ph2P)C9H7 with LnIII[N(SiMe3)2]3 in toluene at 100 °C. The treatment of 1-La with one equivalent of benzonitrile gave (PhCN)[1-(Ph2P)-η5-C9H6]2LaIIIN(SiMe3)2, 2, while no adduct was formed in case of the samarium derivative 1-Sm. The reaction of 1-La and 1-Sm with two equivalents of benzyl azide yielded the (phosphazido)indenyl complexes {1-[BnN3-κN(Ph2)P]-η5-C9H6}{1-[BnN3-κ2N,N'(Ph2)P]C9H6}LnIIIN(SiMe3)2, Ln = La (3-La), Sm (3-Sm), respectively. The five complexes catalyse the intramolecular hydroamination/cyclisation of 2,2-diphenylpent-4-ene-1-amine using 2% catalyst loading. All compounds were characterised by NMR and UV-Vis spectroscopy, single-crystal X-ray diffraction, and elemental analysis and DFT calculations were performed for 3-La.

Structural and Thermal Characterization of Halogenated Azidopyridines: Under-Reported Synthons for Medicinal Chemistry

Owing to their participation in Click reactions, bifunctional azides are valuable intermediates in the preparation of medicines and biochemical tool compounds. Despite the privileged nature of pyridines among pharmaceutical scaffolds, reports of the synthesis and characterization of azidopyridines bearing a halogen substituent for further elaboration are almost completely unknown in the literature. As azidopyridines carry nearly equal numbers of nitrogen and carbon atoms, we hypothesized that safety concerns limited the application of these useful bifunctional building blocks in medicinal and biological chemistry. To address this concern, we prepared and characterized nine azidopyridines bearing a single fluorine, chlorine, or bromine atom. All were examined by differential scanning calorimetry (DSC), in which they demonstrated exotherms of 228-326 kJ/mol and onset temperatures between 119 and 135 °C. Selected azidopyridines were advanced to mechanical stress testing, in which impact sensitivity was noted for one regioisomer of C5H3FN4. The utility of these versatile intermediates was demonstrated through their use in a variety of Click reactions and the diversification of the halogen handles.

Reductive Alkylation of Azides and Nitroarenes with Alcohols: A Selective Route to Mono- and Dialkylated Amines

Herein, we demonstrated an efficient protocol for reductive alkylation of azides/nitro compounds via a borrowing hydrogen (BH) method. By following this protocol, selective mono- and dialkylated amines were obtained under mild and solvent-free conditions. A series of control experiments and deuterium-labeling experiments were performed to understand this catalytic process. Mechanistic studies suggested that the Ir(III)-H was the active intermediate in this reaction. KIE study revealed that the breaking of the C-H bond of alcohol might be the rate-limiting step. Notably, this solvent-free strategy disclosed a high TON of around 5600. Based on kinetic studies and control experiments, a metal-ligand cooperative mechanism was proposed.

Electrophilic Aminating Agents in Total Synthesis

Classical amination methods involve the reaction of a nitrogen nucleophile with an electrophilic carbon center; however, in recent years, umpoled strategies have gained traction where the nitrogen source acts as an electrophile. A wide range of electrophilic aminating agents are now available, and these underpin a range of powerful C-N bond-forming processes. In this Review, we highlight the strategic use of electrophilic aminating agents in total synthesis.

Iron-Catalyzed Asymmetric Decarboxylative Azidation

The first iron-catalyzed asymmetric azidation of benzylic peresters has been reported with trimethylsilyl azide (TMSN₃) as the azido source. Hydrocarbon radicals that lack of strong interactions were capable to be enantioselectively azidated. The reaction features good functional group tolerance, high yields, and mild conditions. The chiral benzylic azides can further be used in click reaction, phosphoramidation, and reductive amination, which demonstrate the synthetic values of this reaction.

Improved Synthesis of the Antitubercular Agent SQ109

We present here an improved procedure for the preparation of the promising antitubercular drug SQ109 that is currently in phase Ib/III of clinical trials against Mycobacterium tuberculosis. We investigated and tested the literature synthetic procedure that enables the development of structure–activity relationships and report the observed inconsistencies as well as presenting improvements or novelties for the more efficient preparation of SQ109. Most significantly we applied a novel reduction step of the aminoamide precursor using Me3SiCl­/LiAlH4 under mild conditions. These findings are important for research groups investigating the efficacy of this drug and analogues in academia and industry.

Total Synthesis of (-)-Picrinine, (-)-Scholarisine C, and (+)-5-β-Methoxyaspidophylline

The first asymmetric total synthesis of three picrinine-type akuammiline alkaloids, (-)-picrinine, (-)-scholarisine C, and (+)-5-β-methoxyaspidophylline, has been accomplished. The synthesis features an efficient acid-promoted oxo-bridge ring-opening and further carbonyl O-cyclization to assemble the furoindoline scaffold, an unusual Dauben-Michno oxidation to construct the requisite α,β-unsaturated aldehyde functionality, and a nickel-mediated reductive Heck reaction to forge the [3.3.1]-azabicyclic core.

Phosphorus-Containing Superbases: Recent Progress in the Chemistry of Electron-Abundant Phosphines and Phosphazenes

The renaissance of Brønsted superbases is primarily based on their pronounced capacity for a large variety of chemical transformations under mild reaction conditions. Four major set screws are available for the selective tuning of the basicity: the nature of the basic center (N, P, …), the degree of electron donation by substituents to the central atom, the possibility of charge delocalization, and the energy gain by hydrogen bonding. Within the past decades, a plethora of neutral electron-rich phosphine and phosphazene bases have appeared in the literature. Their outstanding properties and advantages over inorganic or charged bases have now made them indispensable as auxiliary bases in deprotonation processes. Herein, an update of the chemistry of basic phosphines and phosphazenes is given. In addition, due to widespread interest, their use in catalysis or as ligands in coordination chemistry is highlighted.

Hermann Staudinger – Organic chemist and pioneer of macromolecules

To commemorate the centenary of the birth of modern polymer science, a review of the life and accomplishments of Hermann Staudinger is given within the framework of the first half of the twentieth century. Staudinger is remembered for his discovery of ketenes and the Staudinger reaction, but his greatest contribution to chemistry was in developing the concept of macromolecules, for which he received the Nobel Prize in 1953.

Ethanol: Unlocking an Abundant Renewable C2 -Feedstock for Catalytic Enantioselective C-C Coupling

With annual production at >85 million tons/year, ethanol is the world's largest-volume renewable small molecule carbon source, yet its use as a C2 -feedstock in enantioselective C-C coupling is unknown. Here, the first catalytic enantioselective C-C couplings of ethanol are demonstrated in reactions with structurally complex, nitrogen-rich allylic acetates incorporating the top 10 N-heterocycles found in FDA-approved drugs.

An original pronucleotide strategy for the simultaneous delivery of two bioactive drugs

The synthesis and in vitro anti-HIV activity of a novel series of phosphoramidate pronucleotides including a S-pivaloyl-2-thioethyl (tBuSATE) group as biolabile phosphate protecting group are reported. Such constructs, obtained through different phosphorus chemistries, are characterized by the association of two different anti-HIV nucleoside analogues linked to the phosphorus atom respectively by the sugar residue and the exocyclic amino function of the nucleobase. In vitro, comparative anti-HIV evaluation demonstrates that such original prodrugs are able to allow the efficient intracellular combination release of a 5'-mononucleotide as well as another nucleoside analogue. In human T4-lymphoblastoid cells, the pronucleotide 1 shows remarkable antiviral activity with an EC₅₀ in the nanomolar range (0.6 ηM) and without additional cytotoxicity. In addition, these two pronucleotide models exhibit higher selectivity index than the equimolar mixture of their constitutive nucleoside analogues opening the way to further studies with regard to the current use of drug combinations.

Diastereo- and Enantioselective Ruthenium-Catalyzed C-C Coupling of 1-Arylpropynes and Alcohols: Alkynes as Chiral Allylmetal Precursors in Carbonyl anti-(α-Aryl)allylation

Highly tractable 1-aryl-1-propynes, which are readily accessible via Sonogashira coupling, serve as chiral allylmetal pronucleophiles in ruthenium-JOSIPHOS-catalyzed anti-diastereo- and enantioselective aldehyde (α-aryl)allylations with primary aliphatic or benzylic alcohol proelectrophiles. This method enables convergent construction of homoallylic sec-phenethyl alcohols bearing tertiary benzylic stereocenters. Both steric and electronic features of aryl sulfonic acid additives were shown to contribute to the efficiency with which a more selective and productive iodide-bound ruthenium catalyst is formed. As corroborated by isotopic labeling studies, a dual catalytic process is operative in which alkyne-to-allene isomerization is followed by allene-carbonyl reductive coupling via hydrogen auto-transfer. Crossover of ruthenium hydrides emanating from these two discrete catalytic events is observed. The utility of this method is illustrated by conversion of selected reaction products to the corresponding phenethylamines and the first total syntheses of the neolignan natural products (-)-crataegusanoids A-D.

Main Group Redox Catalysis of Organopnictogens: Vertical Periodic Trends and Emerging Opportunities in Group 15

A growing number of organopnictogen redox catalytic methods have emerged-especially within the past 10 years-that leverage the plentiful reversible two-electron redox chemistry within Group 15. The goal of this Perspective is to provide readers the context to understand the dramatic developments in organopnictogen catalysis over the past decade with an eye toward future development. An exposition of the fundamental differences in the atomic structure and bonding of the pnictogens, and thus the molecular electronic structure of organopnictogen compounds, is presented to establish the backdrop against which organopnictogen redox reactivity-and ultimately catalysis-is framed. A deep appreciation of these underlying periodic principles informs an understanding of the differing modes of organopnictogen redox catalysis and evokes the key challenges to the field moving forward. We close by addressing forward-looking directions likely to animate this area in the years to come. What new catalytic manifolds can be developed through creative catalyst and reaction design that take advantage of the intrinsic redox reactivity of the pnictogens to drive new discoveries in catalysis?

A metastable RuIII azido complex with metallo-Staudinger reactivity

The metastable purple [(Py5Me2)RuIII(N3)]2+ ion reacts with PPh3 at room temperature to form the phosphinimine complex [(Py5Me2)RuII(N(H)PPh3)]2+ and free [H2NPPh3]+ in a combined 23% conversion. Mechanistic studies suggest that this is the first metallo-Staudinger reaction of a late transition metal that bypasses the nitrido mechanism and instead utilizes a Ru-N[double bond, length as m-dash]N[double bond, length as m-dash]N-PPh3 phosphazide intermediate.

π-Extended Coumarins Derived with Nonhydrolyzable Iminophosphoranes as Two-Photon-Excited Fluorophores

Novel coumarin-iminophosphorane (IPP) fluorophores that have stable resonance contributions from aza-ylides were formed by using the nonhydrolysis Staudinger reaction. The N═P formation reaction kinetics obey the conventional Staudinger reaction. The absorption and emission profiles of the coumarin-IPP derivatives can be fine-tuned: an electron-donating group at PPh₃ enhances absorption and fluorescence, whereas an electron-withdrawing group at C-3 drives absorption and emission peaks toward blue-light wavelengths. Two-photon adsorption, accompanied by anti-Stokes fluorescence, is achieved under near-infrared femtosecond laser excitation.

Modular Approach to the Functionalization of Polymersomes

Functionalizing polymersomes remains a challenge due to the limitation in reaction conditions applicable to the chemistry on the surface, hindering their application for selective targeting. In order to overcome this limitation, functionalization can be introduced right before the self-assembly. Here, we have synthesized a library (32 examples) of PEG-b-PS and PEG-b-PDLLA with various functional groups derived from the amine-functionalized polymers, leading to functionally active polymersomes. We show that polymersome formation is possible via the general method with all functionalized groups and that these handles are present on the surface and are able to undergo reactions. Additionally, this methodology provides a general synthetic tool to tailor the functional group of the polymersome right before self-assembly, without limitation on the reaction conditions.