Catalytic aza-Wittig Reaction of Acid Anhydride for the Synthesis of 4H-Benzo[d][1,3]oxazin-4-ones and 4-Benzylidene-2-aryloxazol-5(4H)-ones

Acid-Promoted Cyclization of α-Azidobenzyl Ketones through C═N Bond Formation: Synthesis of 6-Substituted Quinoline Derivatives

An acid-promoted cyclization of α-azidobenzyl ketones has been developed for the synthesis of 6-substituted quinoline derivatives. A variety of synthetically useful 6-OTf or -OMs quinoline derivatives were obtained in moderate to good yields. The reaction proceeds via C═N bond formation without organophosphine, providing convenient access to structurally interesting and synthetically important 6-substituted quinoline derivatives in moderate to good yields. A mechanistic perspective that is different from the traditional intramolecular Schmidt reaction has been proposed.

(3+2) Annulation of 4-Acetoxy Allenoate with Aldimine Enabled by AgF-Assisted P(III)/P(V) Catalysis

A phosphine-catalyzed (3+2) annulation of 4-acetoxy allenoate and aldimine with the assistance of AgF is described. The success of this reaction hinges on the metathesis between the enolate-phosphonium zwitterion and AgF, leading to a key intermediate comprising of silver enolate and a fluorophosphorane P(V)-moiety. The former is able to undergo a Mannich reaction with aldimine, whereas the latter initiates a cascade sequence of AcO-elimination/aza-addition, thus furnishing the P(III)/P(V) catalysis. By taking advantage of the silver enolate, a preliminary attempt at an asymmetric variant was conducted with the combination of an achiral phosphine catalyst and a chiral bis(oxazolinyl)pyridine ligand (PyBox), giving moderate enantioselectivity.

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.

Transition Metal Catalysis Controlled by Hydrogen Bonding in the Second Coordination Sphere

Transition metal catalysis is of utmost importance for the development of sustainable processes in academia and industry. The activity and selectivity of metal complexes are typically the result of the interplay between ligand and metal properties. As the ligand can be chemically altered, a large research focus has been on ligand development. More recently, it has been recognized that further control over activity and selectivity can be achieved by using the "second coordination sphere", which can be seen as the region beyond the direct coordination sphere of the metal center. Hydrogen bonds appear to be very useful interactions in this context as they typically have sufficient strength and directionality to exert control of the second coordination sphere, yet hydrogen bonds are typically very dynamic, allowing fast turnover. In this review we have highlighted several key features of hydrogen bonding interactions and have summarized the use of hydrogen bonding to program the second coordination sphere. Such control can be achieved by bridging two ligands that are coordinated to a metal center to effectively lead to supramolecular bidentate ligands. In addition, hydrogen bonding can be used to preorganize a substrate that is coordinated to the metal center. Both strategies lead to catalysts with superior properties in a variety of metal catalyzed transformations, including (asymmetric) hydrogenation, hydroformylation, C-H activation, oxidation, radical-type transformations, and photochemical reactions.

Multicomponent synthesis of substituted pyridines via a catalytic intermolecular aza-Wittig/Diels–Alder sequence

A three-component synthesis of polysubstituted pyridines, based upon the Diels–Alder reactions of 2-azadienes formed by a novel redox-neutral catalytic intermolecular aza-Wittig reaction.

Synthesis and Discovery of Schiff Base Bearing Furopyrimidinone for Selective Recognition of Zn2+ and its Applications in Cell Imaging and Detection of Cu2

A simplefuro [2,3-d]pyrimidinone-based Schiff base FPS was synthesized via aza-Wittig reaction and structure elucidation was carried out by spectroscopic studies FT-IR, 1H NMR, and 13C NMR and mass spectrometry. FPS showed weak fluorescence emission in methanol and the selectivity of FPS to different metal ions (Mn²⁺, Ca²⁺, Fe²⁺, Fe³⁺, Mg²⁺, Al³⁺, Ba²⁺, Ag⁺, Co²⁺, Na⁺, K⁺, Cu²⁺, Zn²⁺, Pb²⁺, Bi³⁺) were studied by absorption and fluorescence titration. The results show that FPS has selective fluorescence sensing behavior for Zn²⁺ ions and the limit of detection (LOD) was calculated to be 1.19 × 10^–8 mol/L. Moreover, FPS-Zn²⁺ acts as a metal based highly selective and sensitive new chemosensor for Cu²⁺ ions and the LOD was calculated to be 2.25 × 10^–7 mol/L. In accordance with the results and theoretical calculations, we suspected that the binding mechanisms of FPS to Zn²⁺ and Cu²⁺ were assigned to be the cooperative interaction of Zn²⁺(Cu²⁺)-N.

Highly Stable Univalent Copper of a Cu@Al/SBA-15 Nanocomposite Catalyzes the Synthesis of Fluorescent Aminobenzotriazoles Derivatives

With the development of green chemistry, it is still a challenge to maintain the unstable valence state of the metal in heterogeneous catalysts and realize new catalytic synthesis methods. In this paper, it is reported that an univalent copper nanocomposite (Cu@Al/SBA-15) can efficiently catalyze the formation of novel amino-containing benzotriazoles with great fluorescence properties in a new synthetic strategy. Subsequently, its application is further verified by an acylation reaction to produce a series of novel benzotriazoles derivatives with high yield. It is worth noting that the Cu@Al/SBA-15 nanocomposites not only enable the reaction completed with high yield in a short time, but can also be recycled many times without a significant reduction in activity, and the leaching of copper and aluminum species in reaction system is negligible. Finally, the detailed and feasible reaction mechanism is also provided.

Pd-Catalyzed Carbonylative Synthesis of 4H-Benzo[d][1,3]Oxazin-4-Ones Using Benzene-1,3,5-Triyl Triformate as the CO Source

A facile synthesis of 4H-benzo[d][1,3]oxazin-4-one derivatives by Pd-catalyzed carbonylative cross-coupling between N-(ortho-bromoaryl)amides and benzene-1,3,5-triyl triformate (TFBen) was developed. This procedure does not require the toxic and flammable gas CO as the carbonyl source and tolerates a wide scope of functional groups. Remarkably, 4H-benzo[d][1,3]oxazin-4-ones incorporated to natural products and drugs can be constructed by this method.

Four-Component Synthesis of Polysubstituted Pyrazin-2(1H)-ones through a Ugi/Staudinger/Aza-Wittig/Isomerization Sequence

A new efficient synthesis of polysubstituted pyrazin-2(1H)-ones via the sequential Ugi/Staudinger/aza-Wittig/isomerization reaction has been developed. The four-component Ugi reactions of arylglyoxals 1, primary amines 2, α-azidovinyl acids 3, and isocyanides 4 produced the azides 5, which were treated with triphenylphosphine to give pyrazin-2(1H)-ones 6 in good yields through domino Staudinger/aza-Wittig/isomerization reactions.

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?

Mild synthesis of isoxazoline derivatives via an efficient [4 + 1] annulation reaction of transient nitrosoalkenes and sulfur ylides

An efficient [4 + 1] annulation between α-bromooximes and sulfur ylides via in situ generation of nitrosoalkenes under mild basic reaction conditions has been developed, providing an expeditious and scalable approach to synthesize biologically interesting isoxazoline derivatives with good to excellent yields.

Visible-light-driven photocyclization reaction: photocatalyst-free mediated intramolecular N–N coupling for the synthesis of 2H-indazole-3-carboxamides from aryl azides

A visible-light-driven photocyclization reaction of aryl azides to access 2H-indazole-3-carboxamides in moderate to excellent yields has been realized efficiently under photocatalyst-free and external additive-free conditions.

The synthesis and structure of an amazing and stable carbonized material Cu-PC@OFM and its catalytic applications in water with mechanism explorations

An amazing and stable carbonized octahedral frame material Cu-PC@OFM was synthesized and characterized through HRTEM, SEM, XRD, XPS, and Raman spectroscopy and nitrogen adsorption/desorption analysis.

Synthesis of diaryl sulfides based on copper-doped OMS-2

We describe a practical protocol for efficiently preparing diaryl sulfide compounds using Cu–OMS-2 as the catalyst. Cu–OMS-2 originates from manganese oxide octahedral molecular sieves modified with copper ions and catalyzes the C–S coupling reaction of substituted thiophenols and aryl halides. This protocol has the advantages of environmental friendliness, simple operation, high yields, good tolerance of functional groups, and the Cu–OMS-2 catalytic material can be recycled several times.

Development of a novel thymidylate synthase (TS) inhibitor capable of up-regulating P53 expression and inhibiting angiogenesis in NSCLC

Introduction

The development of a new type of Thymidylate synthase (TS) inhibitor that could inhibit cancer cells' proliferation and anti-angiogenesis is of great significance for cancer's clinical treatment.

Objectives

Our research hopes to develop a TS inhibitor that is more effective than the current first-line clinical treatment of pemetrexed (PTX) and provide a new reference for the clinical treatment of non-small cell lung cancer (NSCLC).

Methods

We obtained a series of novel TS inhibitors by chemical synthesis. Moreover, TS assay and molecular docking to verify the target compound's inhibitory mode. Use MTT assay, colony-forming assay, flow cytometry, and western blot to verify the compound's inhibitory effect on cancer cell proliferation and its mechanism; and explore the compound’s effect on angiogenesis in vitro and in vivo. Further, explore the hit compound's anti-cancer ability through the xenograft tumor model and the orthotopic cancer murine model.

Results

A series of N-(3-(5-phenyl-1,3,4-oxadiazole-2-yl) phenyl)-2,4-dihydroxypyrimidine-5-sulfamide derivatives were synthesized as TS inhibitors for the first time. All target compounds significantly inhibited hTS enzyme activity and demonstrated significant antitumor activity against five cancer cell lines. Notably, 7f had a high selectivity index (SI) and unique inhibitory effects on eight NSCLC cells. In-depth research indicated that 7f could induce apoptosis by the mitochondrial pathway in A549 and PC-9 cells through the upregulation of wild-type P53 protein expression. Additionally, 7f was shown to inhibit angiogenesis in vitro and in vivo. In vivo studies, compared to PTX, 7f significantly inhibited tumor growth in A549 cell xenografts and had a higher therapeutic index (TGI). Moreover, 7f could prolong the survival of the orthotopic lung cancer murine model more effectively than PTX.

Conclusion

The anti-angiogenic effect of 7f provides a new reference for the development of TS inhibitors and the clinical treatment of NSCLC.

Recyclable Heterogeneous Palladium-Catalyzed Cyclocarbonylation of 2-Iodoanilines with Acyl Chlorides in the Biomass-Derived Solvent 2-Methyltetrahydrofuran

A highly efficient, green palladium-catalyzed cyclocarbonylation of 2-iodoanilines with acyl chlorides has been developed that proceeds smoothly in a biomass-derived solvent 2-methyltetrahydrofuran with N,N-diisopropylethylamine as base at 100 °C under 20 bar of carbon monoxide using an 2-aminoethylamino-modified MCM-41-anchored palladium acetate complex [2N-MCM-41-Pd(OAc)₂] as a heterogeneous catalyst, yielding a wide variety of 2-substituted 4H-3,1-benzoxazin-4-one derivatives in good to excellent yields. This supported palladium catalyst could be facilely obtained by a two-step procedure from easily available starting materials and readily recovered via a simple filtration process and recycled at least 8 times without any apparent decrease in catalytic efficiency. The developed methodology not only avoids the use of toxic solvents such as tetrahydrofuran and dimethylformamide but also solves the basic problem of expensive palladium catalyst recovery and reuse and prevents effectively palladium contamination of the desired product.

Let's Make White Phosphorus Obsolete

Industrial and laboratory methods for incorporating phosphorus atoms into molecules within the framework of Green Chemistry are in their infancy. Current practice requires large inputs of energy, involves toxic intermediates, and generates substantial waste. Furthermore, a negligible fraction of phosphorus-containing waste is recycled which in turn contributes to negative environmental impacts, such as eutrophication. Methods that begin to address some of these drawbacks are reviewed, and some key opportunities to be realized by pursuing organophosphorus chemistry under the principles of Green Chemistry are highlighted. Methods used by nature, or in the chemistry of other elements such as silicon, are discussed as model processes for the future of phosphorus in chemical synthesis.

An Improved PIII/PV═O-Catalyzed Reductive C-N Coupling of Nitroaromatics and Boronic Acids by Mechanistic Differentiation of Rate- and Product-Determining Steps

Experimental, spectroscopic, and computational studies are reported that provide an evidence-based mechanistic description of an intermolecular reductive C–N coupling of nitroarenes and arylboronic acids catalyzed by a redox-active main-group catalyst (1,2,2,3,4,4-hexamethylphosphetane P-oxide, i.e., 1·[O]). The central observations include the following: (1) catalytic reduction of 1·[O] to P^III phosphetane 1 is kinetically fast under conditions of catalysis; (2) phosphetane 1 represents the catalytic resting state as observed by ³¹P NMR spectroscopy; (3) there are no long-lived nitroarene partial-reduction intermediates observable by ¹⁵N NMR spectroscopy; (4) the reaction is sensitive to solvent dielectric, performing best in moderately polar solvents (viz. cyclopentylmethyl ether); and (5) the reaction is largely insensitive with respect to common hydrosilane reductants. On the basis of the foregoing studies, new modified catalytic conditions are described that expand the reaction scope and provide for mild temperatures (T ≥ 60 °C), low catalyst loadings (≥2 mol%), and innocuous terminal reductants (polymethylhydrosiloxane). DFT calculations define a two-stage deoxygenation sequence for the reductive C–N coupling. The initial deoxygenation involves a rate-determining step that consists of a (3+1) cheletropic addition between the nitroarene substrate and phosphetane 1; energy decomposition techniques highlight the biphilic character of the phosphetane in this step. Although kinetically invisible, the second deoxygenation stage is implicated as the critical C–N product-forming event, in which a postulated oxazaphosphirane intermediate is diverted from arylnitrene dissociation toward heterolytic ring opening with the arylboronic acid; the resulting dipolar intermediate evolves by antiperiplanar 1,2-migration of the organoboron residue to nitrogen, resulting in displacement of 1·[O] and formation of the target C–N coupling product upon in situ hydrolysis. The method thus described constitutes a mechanistically well-defined and operationally robust main-group complement to the current workhorse transition-metal-based methods for catalytic intermolecular C–N coupling.

Ligand-Free Ru-Catalyzed Direct sp3 C-H Alkylation of Fluorene Using Alcohols

The sp³ C-H alkylation of 9H-fluorene using alcohol and a Ru catalyst via the borrowing hydrogen concept has been described. This reaction was catalyzed by the [Ru(p-cymene)Cl₂]₂ complex (3 mol %) and exhibited a broad reaction scope with different alcohols, allowing primary and secondary alcohols to be employed as nonhazardous and greener alkylating agents with the formation of environmentally benign water as a byproduct. A variety of 9H-fluorene underwent selective and exclusive mono-C9-alkylation with primary alcohols in good to excellent isolated yield (26 examples, 50-92% yield), whereas this reaction with secondary alcohols in the absence of any external oxidants furnished the tetrasubstituted alkene as the major product. Furthermore, a base-mediated C-H hydroxylation of the synthesized 9H-fluorene derivatives afforded 9H-hydroxy-functionalized quaternary fluorene derivatives in excellent yield.

One-pot synthesis of N-confused porphyrin-dipyrrin conjugates and their optical properties

A conjugated N-confused porphyrin-dipyrrin system NCP-IN-X (X = H, Br, Cl, OMe, COOEt) has been reported via N-Confused tetraphenylporphyrin (NCTPP) as a π-enlarged pyrrole and substituted trimethylindole subunits in 75-82% yields by one pot. All the NCP-INs show red-shifted absorption and emission in the NIR range compared with NCTPP in a series nonpolar and polar solvents. Interesting, relative higher emission in DMF can be observed. The structures of dipyrrin-NCP conjugates are characterized by ¹H-NMR and high resolution mass spectrum (HR-MS). Four frontier molecular orbital and simulated stick absorption spectra are calculated by DFT and TD-DFT calculation which is in good agreement with the experiments.

A practical chlorination of tert-butyl esters with PCl3 generating acid chlorides

For the first time, using PCl3, a range of tert-butyl esters is chlorinated successfully, allowing access of both aromatic acid chlorides and aliphatic acid chlorides in good yields. The method features simple reaction conditions and wide substrate scope. Various tert-butyl esters including aryl esters, alkenyl esters, and alkyl esters were tolerated well in the reaction. A plausible mechanism is proposed.

Convergent Synthesis of Polysubstituted Furans via Catalytic Phosphine Mediated Multicomponent Reactions

Tri- or tetrasubstituted furans have been prepared from terminal activated olefins and acyl chlorides or anhydrides by a multicomponental convergent synthesis mode. Instead of stoichiometric nBu₃P, only catalytic nBu₃P or nBu₃P=O is needed to furnish the furans in modest to excellent yields with a good functional group tolerance under the aid of reducing agent silane. This synthetic method features a silane-driven catalytic intramolecular Wittig reaction as a key annulation step and represents the first successful application of catalytic Wittig reaction in multicomponent cascade reaction.

Retracted: Synthesis of 2-Arylisoindoline Derivatives Catalyzed by Reusable 1,2,4-Triazole Iridium on Mesoporous Silica through a Cascade Borrowing Hydrogen Strategy

Covalent attachment of a 1,2,4-triazole iridium complex to mesoporous MCM-41 generated a heterogeneous catalyst that was found to be effective in the synthesis of 2-aryl isoindolines, quinolines, cyclic amines, and symmetrical secondary amines through a cascade borrowing hydrogen strategy. Interestingly, the supported heterogeneous iridium catalyst prepared from the 1,2,4-triazole iridium complex and mesoporous MCM-41 exhibited high catalytic activity in the preparation of 2-aryl isoindoline derivatives and symmetrical secondary amines. The catalyst system is highly recyclable for at least five times. Besides the important effect of the triazole, iridium sites grafted on siliceous supports can act as multifunctional catalytic centers and thus greatly enhance the catalytic activity of the catalysts. Furthermore, mechanistic experiments revealed that the reaction is initiated by an initial alcohol dehydrogenation and promoted by an iridium hydride intermediate. Importantly, the direct detection of a diagnostic iridium hydride signal confirmed that the synthesis of 2-aryl isoindolines occurs by a borrowing hydrogen process. This work provides an efficient example of isoindolines synthesis through a borrowing hydrogen strategy.