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Olefin metathesis, which is well established in the petrochemical industry, is also emerging as a green technology in the manufacture of pharmaceutical and specialty chemicals. Arylbenzofurans are of interest for potential medicinal applications. In this paper we report on the synthesis of various 2-aryl- and 3-arylbenzo[ b ]furans with natural substitution patterns from readily available starting materials in a strategy that applies ring-closing metathesis with the Grubbs second generation catalyst as key step. [ABSTRACT FROM AUTHOR]

The present article presents a personal account on the synthesis of heterocycles by the combination of regioselective Pd-catalyzed cross-coupling reactions of polyhalogenated heterocycles, i.e., Suzuki–Miyaura and Sonogashira reactions, with alkyne-carbonyl-metathesis (ACM) reactions. The products, which show interesting optical, electronic or medicinal properties, are not readily available by other methods. [ABSTRACT FROM AUTHOR]

The carbonyl‐alkyne metathesis reaction is a powerful method for the synthesis of α,β‐unsaturated carbonyls. We now report on the development of a halogen‐bond catalyzed protocol for both the intra‐ and intermolecular reaction. Our studies revealed that methanol is a highly efficient solvent and that a very broad range of functional groups are tolerated under the reaction conditions. Mechanistic studies support the proposed halogen‐bond interaction. Furthermore, the halogen‐bond protocol is compared with other available catalytic systems for these reactions. [ABSTRACT FROM AUTHOR]

This manuscript describes a new strategy for prodrug synthesis in which a relatively inert ether group is introduced at an early stage in a synthetic sequence and functionalized in the final step to introduce a prodrug‐activating group through a chemoselective process. Boryl allyloxy (BAO) ether groups are synthesized through several metal‐mediated processes to form entities that are readily cleaved under oxidative conditions commonly found in cancer cells. The high cleavage propensity of the BAO group allows for ether cleavage, making these compounds substantially more hydrolytically stable in comparison to acyl‐linked prodrugs while retaining the ability to release alcohols. We report the preparation of prodrug analogues of the natural products camptothecin and pederin from acetal precursors that serve as protecting groups in their synthetic sequences. The BAO acetal groups cleave in the presence of hydrogen peroxide to release the cytotoxic agents. The pederin‐based prodrug shows dramatically greater cytotoxicity than negative controls and outstanding selectivity and potency toward cancer cell lines in comparison to non‐cancerous cell lines. This late‐stage functionalization approach to prodrug synthesis should be applicable to numerous systems that can be accessed through chemoselective processes. [ABSTRACT FROM AUTHOR]

A highly efficient, convenient and ecofriendly approach to access highly functionalized 2H‐chromenes via intramolecular aldehyde alkyne metathesis reaction was established starting from readily accessible alkyne‐tethered 2‐((3‐phenylprop‐2‐yn‐1‐yl) oxy)benzaldehydes and catalyzed by silica sulfuric acid (SiO2‐OSO3H, SSA) coupled with microwave irradiation. This reaction was well tolerated for various substituents including different functional groups and furnished the desired highly functionalized 2H‐chromene derivatives in good to excellent yields in a very short time. A systematic study of the conventional heating approach and microwave irradiation was performed to demonstrate the advantages of the microwave‐assisted condition in terms of high yield and shorter reaction time. [ABSTRACT FROM AUTHOR]

Ring‐opening metathesis polymerization (ROMP) is an effective method for synthesizing functional polymers, but since the technique typically relies on high ring strain cyclic olefins, the most common monomers are norbornene derivatives. The reliance on one class of monomer limits the obtainable properties of ROMP polymers. In this work, we investigate new bicyclic monomers synthesized via epoxidation of commercial dienes. DFT estimates of these monomers’ ring strains suggests a significant increase in strain for cyclic olefins containing allylic epoxides. We found that the eight‐membered (3,4‐COO) and five‐membered (CPO) cyclic olefins were particularly effective for ROMP. CPO was of especially intriguing due to its excellent polymerizability when compared to the limited reactivity of other five‐membered rings. Unlike polynorbornenes, the resulting polymers of both monomers displayed glass transition temperatures well below room temperature. Interestingly, poly(3,4‐COO) showed both high stereo‐ and regioregularity while poly(CPO) showed little regularity. Both polymers could be readily modified via post‐polymerization ring‐opening of the reactive allylic epoxides. With a high epoxide density in poly(CPO), CPO is an exciting new ROMP monomer that is easily synthesized, can be polymerized to high conversion at room temperature, and may be facilely modified to yield a wide range of functional materials. [ABSTRACT FROM AUTHOR]

We report the synthesis and full characterization of the copper dinitrogen complex [(η1‐N2)Cu{Al(ORF)4}] 2 (RF=C(CF3)3) prepared by a cascade metathesis reaction of Ag[Al(ORF)4] with CuI‐excess in iso‐perfluorohexane (i‐pfh) under N2 atmosphere. Title compound 2 features an extraordinarily high N2 stretching frequency at 2313/2314 cm−1 (IR/Raman) and was characterized by single‐crystal and powder X‐ray diffractometry. Quantum chemical charge displacement analysis based on natural orbitals of chemical valence (CD‐NOCV) indicates that the copper‐dinitrogen interaction is still governed by weak π‐backdonation, but is significantly reduced compared to all literature‐known transition metal dinitrogen complexes. [ABSTRACT FROM AUTHOR]

The strasseriolide macrolides show promising in vitro and in vivo activities against P. falciparum and T. cruzi, the parasites causing malaria and Chagas disease, respectively. However, the as yet poor understanding of structure/activity relationships and the fact that one family member proved systemically toxic for unknown reasons render a more detailed assessment of these potential lead compounds difficult. To help overcome these issues, a collective total synthesis was devised. The key steps consisted of a ring closing alkyne metathesis (RCAM) reaction to forge a common macrocyclic intermediate followed by a hydroxy‐directed ruthenium catalyzed trans‐hydrostannation of the propargyl alcohol site thus formed. The resulting alkenyltin derivative served as the central node of the synthesis blueprint, which could be elaborated into the natural products themselves as well as into a set of non‐natural analogues according to the concept of diverted total synthesis. The recorded biological data confirmed the potency of the compounds and showed the lack of any noticeable cytotoxicity. The "northern" allylic alcohol subunit was recognized as an integral part of the pharmacophore, yet it provides opportunities for chemical modification. [ABSTRACT FROM AUTHOR]

We report here the preparation and characterization of new well‐defined silica‐supported Ti imido complexes that present an L‐ligand variation in a structure of currently the most active oxo/imido heterometathesis catalyst (≡SiO)Ti(=NtBu)(Me2Pyr)(py)2 (1s), where py is replaced with stronger electron‐donating 4‐(N,N‐dimethylamino)pyridine (2s) or bidentate 2,2′‐bipyridine (3s). The materials were characterized with elemental and mass balance analyses and IR and solid‐state NMR that confirmed the selective formation of surface Ti species with terminal imido ligand. Evaluation of the catalytic oxo/imido heterometathesis activity of the obtained materials demonstrated that L‐ligands have a pronounced influence on the catalytic performance. In particular, the replacement of pyridine with stronger donating ligands resulted in a significant drop of activity. The catalytic results are discussed in view of the reaction mechanism and implications for further catalyst development. [ABSTRACT FROM AUTHOR]

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We present evidence for iconicity as the motivation for two patterns of morphophonological alternation in Nigerian Pidgin, also known as Naijá. To express an ‘unconventional positive’ in all varieties of Naijá, some nouns with the tone melodies H-L and L-H surface with the tone melodies L-H and H-L, respectively. In addition to unconventional positive, the Wafi variety of Naijá also expresses ‘unconventional negative.’ In this case, the first syllable of bisyllabic nouns (analogously, the first foot of four-syllable nouns) is transposed with the second syllable. However, in onsetful monosyllabic nouns, the initial consonant is deleted to express an unconventional negative. We account for the metatheses and truncation using transderivational faithfulness constraints and other independent constraints. Expressing the notion of unconventionality by changing the prosaic linear order of phonological elements in a word is a kind of form-meaning resemblance. Similarly, the association of (unconventional) negative with a reduction in a string of segments is another pattern of iconicity. This suggests that crossmodal depiction of sensory imagery, in addition to articulatory and auditory factors, can motivate morphophonological patterns. The morphophonological metatheses and truncation in Naijá contribute to the typology of morphophonological alternations with iconicity as their motivation. Most importantly, these patterns run counter to the claim that pidgins and creoles have simplified morphophonology.

Continuing our investigation of catalytic oxo/imido heterometathesis as novel water‐free method for C=N bond construction, we report here the application of classical transition metal oxides dispersed on silica (MOx/SiO2, M=V, Mo, W) as cheap, robust and readily available alternative to the catalysts prepared via Surface Organometallic Chemistry (SOMC). The oxide materials demonstrated activity in heterometathetical imidation of ketones, WO3/SiO2 being the most efficient. We also describe a new well‐defined supported W imido complex (≡SiO)W(=NMes)2(Me2Pyr) (Mes=2,4,6‐Me3C6H2, Me2Pyr=2,5‐dimethylpyrrolyl) and characterize it with SOMC protocols, which allowed us to identify the position of W on the oxo/imido heterometathesis activity scale (Mo

A unified approach to access the naturally occurring cyclic tetrapeptide JM‐47 and some of its structural variants from a common macrocyclic scaffold has been developed. The key reactions involved a difficult macrocyclization to access the scaffold, and its late‐stage diversification by cross‐metathesis to access the natural product as well as analogues. The synthesis proceeded in good overall yield and high stereochemical integrity. It also confirms the structure and configuration assigned to JM‐47. [ABSTRACT FROM AUTHOR]

In this study, the production of propylene from 2-butene and 1-butene via the metathesis process was investigated and simulated. The effects of operational parameters, including reactor temperature, residence time, and 1-butene/2-butene molar ratio, on reactor performance were examined, and statistical models were developed. The design of experiment (DoE) was performed using the response surface methodology (RSM)-central composite design (CCD) approach for efficient experimentation and model development as well as optimization. The study's findings indicate a high conversion rate for 2-butene. By statistically analyzing the obtained data and performing analysis of variance (ANOVA), the influential parameters and their degree of importance were determined. Sensitivity analysis was conducted based on the developed models. Finally, using these models and desirability function as a powerful optimization algorithm, optimal conditions for the process were obtained. The results of the optimization showed that the maximum propylene molar fraction (32.5 %) was obtained at a temperature of 508.4 °C, a residence time of 20.7 s, and a 1-butene/2-butene molar ratio of 0.1.

Isomerization Metathesis (ISOMET) reaction is an emerging tool for "open loop" chemical recycling of polyethylene to propylene. Novel, latent N‐Alkyl substituted Cyclic(Alkyl)(Amino)Carbene (CAAC)–ruthenium catalysts (5a‐Ru, 3b‐Ru – 6c‐Ru) are developed rendering "inverted" chemical structure while showing enhanced ISOMET activity in combination with (RuHCl)(CO)(PPh3)3 (RuH) double bond isomerization co‐catalyst. Systematic investigations reveal that the steric hindrance of the substituents on nitrogen and carbon atom adjacent to carbene moiety in the CAAC ligand have significantly improved the catalytic activity and robustness. In contrast to the NHC‐Ru and CAAC‐Ru catalyst systems known so far, these systems show higher isomerization metathesis (ISOMET) activity (TON: 7400) on the model compound 1‐octadecene at as low as 3.0 bar optimized pressure, using technical grade (3.0) ethylene. The propylene content formed in the gas phase can reach up to 20% by volume. [ABSTRACT FROM AUTHOR]

The given text is a scientific research article that explores the synthesis and characterization of various compounds using different reactions and starting materials. The compounds synthesized include isoxazolines, pyrazolines, isoxazolidines, cinnamyl- and indenyl-linked moieties, and 2-phosphorylated 2,5-dihydrofurans. The document provides detailed information on the reaction conditions, yields, physical properties, and spectroscopic data of the synthesized compounds. The information presented can be useful for researchers studying the synthesis and characterization of these compounds. [Extracted from the article]

The tetracyanamidometallates Li4[T(CN2)4] with T=Si, Ge were prepared by solid‐state metathesis (SSM) reactions between TI4 and Li2(CN2). The new compounds Li4[T(CN2)4] are obtained as crystalline phases in high yields and represent the most basic examples of the family of tetracyanamidometallates. The formation of these compounds, via SiI4 and Li2(CN2), is analyzed by means of differential scanning calorimetry (DSC). The [Si(CN2)4]4− ion in the structure of Li4[Si(CN2)4] can be considered an analogue to the [SiO4]4− ion in Li4SiO4. The crystal structures of Li4[T(CN2)4] were solved and refined isotypically on the basis of single‐crystal X‐ray diffraction data in the space group C2/c, and further characterized by infrared and solid‐state NMR techniques. [ABSTRACT FROM AUTHOR]

Diversity‐oriented synthesis of some novel functionalized azaheterocyclic β‐amino esters with multiple chiral centers from 1,3‐cyclooctadiene‐based β‐amino acids through a stereocontrolled synthetic route has been accomplished. The strategy was based on the creation of some novel unsaturated N‐protected cyclic β‐amino esters from 1,3‐cyclooctadiene. Products were subjected to ring‐opening metathesis (ROM) followed by selective ring‐closing metathesis (RCM). A comparative investigation on the selectivity, regarding the catalysts, yields, conversions, and substrate directing effect on ring‐rearrangement metathesis (RRM) transformation has been accomplished. Importantly, the procedure used in this synthetic process does not affect the configuration of the chiral centers. The pathway takes place across conservation of the configurations of the stereocenters; therefore, the architectural skeleton of the starting cyclooctene‐based β‐amino acids predetermined the structure of the new azaheterocyclic systems. [ABSTRACT FROM AUTHOR]

The current study investigates the representational status of [Ch] sequences in Sevillian Spanish. Like many Spanish varieties, Sevillian debuccalizes coda /s/ to [h] (/sC/ → [hC]). Unlike other varieties, Sevillian is undergoing a change whereby [hC] sequences are variably realized as [Ch] sequences. I argue that surface (phonetic) [Ch] sequences are metathesized versions of underlying /sC/ clusters, and have not phonologized into a new series of aspirated stops. Evidence supporting the /sC/ cluster analysis comes from a perception study in which Sevillians reconstruct /s/ on the word preceding [Ch] sequences. Listeners of other dialects do not attribute [h] in [Ch] sequences to a preceding /s/. I present a brief cross-dialectal analysis corresponding to the participant groups' different behavior in the perception experiment, in which the dialects share underlying representations but map them differently to surface forms. I also discuss reasons the aspirated stop analysis may be implausible, from both a learning and analytical perspective. The findings have broader implications for our understanding of the mapping between underlying and surface forms, segments, and the connection between dialect variation and perception. [ABSTRACT FROM AUTHOR]

The germylone dimNHCGe (5, dimNHC=diimino N‐heterocyclic carbene) undergoes a [2+2] cycloaddition with isocyanates RNCO (R=4‐tolyl or 3,5‐xylyl) to furnish novel alkyl carboxamido germylenes 7 (R=4‐tolyl) and 8 (R=3,5‐xylyl), featuring a C−C bond between the former carbene carbon and the isocyanate moiety. Heating a mixture of 8 with 4‐tolyl isocyanate to 100 °C results in isocyanate metathesis, demonstrating reversible C−C bond formation on the reduced germanium compound. DFT calculations suggest that this process occurs via the reductive dissociation of isocyanate from 8 that regenerates the parent Ge(0) compound 5. [ABSTRACT FROM AUTHOR]

The preparation and characterization of six rare earth 2‐methyl‐3‐furoate (2m3fur) complexes are detailed in this study. Analysis through single‐crystal X‐ray diffraction, as well as powder XRD, reveals that all six compounds belong to one of two structural groups: {[RE2(2m3fur)6(EtOH)] ⋅ H2O}n (RE=La, Ce, Pr) and [RE3(2m3fur)9]n (RE=Y, Er, Yb). These structural groups feature carboxylate coordinated linear polymers. The former complexes have two distinct metal centers, one ten coordinate and one nine, with lattice water participating in a hydrogen bond with coordinated ethanol. The latter structures, involving erbium, ytterbium, and yttrium, have three unique metal centers: two eight coordinate, and one seven‐coordinated. In corrosion inhibition tests on mild steel in 0.01 M NaCl solution, the maximum efficiency was observed with [Y3(2m3fur)9]n at 59 %, which is less effective than yttrium 3‐furoate (90 % efficiency). The results suggest that the steric effect of the methyl group adversely affects corrosion inhibition. [ABSTRACT FROM AUTHOR]

Biobased composite films have been prepared by solvent cast and hot press methods using saturated aliphatic polyester (expressed as HP1) with different loading (i.e., 1 and 3 wt %) of CNF, citrus fiber, and dextrin. HP1 was prepared by acyclic diene metathesis (ADMET) polymerization of biobased α,ω-dienes of bis(undec-10-enoate) with isosorbide (M1) using a RuCl2(IMesH2)(CH-2–OiPr–C6H4) (HG2, IMesH2 = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) catalyst and subsequent tandem hydrogenation (H2 2.0 MPa, 50 °C, 12 h). The appearance (morphology, transmittance, haze), the thermal properties (including degree of crystallinity by DSC thermograms), and the tensile properties of the fabricated films were evaluated to explore effect of the additives. The prepared composite films by solvent cast and hot press methods were transparent and showed enhancement of tensile strength. The citrus fiber, upcycled product made from the waste residue of squeezed citrus juice and oil, among the other additives showed the highest tensile strength and toughness values irrespective of the molecular weight of the employed polyester or the used fabrication method. [ABSTRACT FROM AUTHOR]

[Display omitted] Well-defined silica-supported Ti imido complex (SiO)Ti(NBut)(Me 2 Pyr)(Py) 2 (Me 2 Pyr = 2,5-dimethyl- pyrrolyl) catalyzes condensation of N -sulfinylanilines into sulfurdiimines via the oxo/imido heterometathesis providing a convenient synthetic route to functionalized sulfurdiimines. [ABSTRACT FROM AUTHOR]

The beauty of one‐pot cascade reaction lies in the efficient disconnection and construction of several bonds in a single reaction flask, without the isolation of any intermediates. Herein, we report the first photoinduced thermally promoted cascade reactions of readily available aromatic ketones and aromatic gem‐difluoroalkenes for the synthesis of phenanthrenes which possess potential utility in drug design and materials science. The reaction combines carbonyl‐olefin metathesis (cascade photoinduced [2+2] cyclization and thermally controlled retro [2+2] cyclization) and dehydrogenative cyclization (cascade photoinduced conrotatory 6π electrocyclization and collidine‐promoted dehydrogenative aromatization) together in one pot. The oxidant‐free, acid‐free and metal‐free reaction shows broad substrate scope and wide functional group tolerance. [ABSTRACT FROM AUTHOR]

Macrocycles with bent π‐conjugation motif are extremely rare in nature and synthetically daunting and anticancer haouamines and spirohexenolides were representative of such rare natural products with synthetically challenging bent π‐conjugation within a macrocycle. While the total synthesis of haouamines has been elegantly achieved, spirohexenolides remains an unmet synthetic challenge due to the highly strained bent 1,3,5‐triene conjugation within C15 macrocycle. Inspired by the chemical synthesis of cycloparaphenylenes (CPPs) and haouamines, herein we devise a synthetic strategy to overcome the highly strained bent 1,3,5‐triene conjugation within the macrocycle and achieve the first, asymmetric total synthesis of spirohexenolides A (>20 mg) and B (>50 mg). Our synthesis features strategic design of ring‐closing metathesis (RCM) macrocyclization followed by double dehydration to achieve the C15 macrocycle with the deformed nonplanar 1,3,5‐triene conjugation. In addition, we have developed a new enantioselective construction of highly functionalized spirotetronate fragment (northeast moiety) through RCM and Ireland–Claisen rearrangement. Our in vitro bioassay studies reveal that both spirohexenolides are cytotoxic against a panel of human cancer cells with IC50 1.2–13.3 μM and spirohexenolide A is consistently more potent (up to 3 times) than spirohexenolide B, suggesting the importance of alcohol for their bioactivity and for medicinal chemistry development. [ABSTRACT FROM AUTHOR]

Atropisomers – separable conformers that arise from restricted single‐bond rotation – are frequently encountered in medicinal chemistry. However, preparing such compounds with the desired configuration can be challenging. Herein, we present a biocatalytic strategy for achieving atroposelective synthesis relying on artificial metalloenzymes (ArMs). Based on the biotin‐streptavidin technology, we constructed ruthenium‐bearing ArMs capable of producing atropisomeric binaphthalene compounds through ring‐closing metathesis in aqueous media. Further, we show that atroposelectivity can be fine‐tuned by engineering two close‐lying amino acid residues within the streptavidin host protein. The resulting ArMs promote product formation with enantiomeric ratios of up to 81 : 19, while small‐molecule catalysts for atroposelective metathesis under aqueous reaction conditions are yet unknown. This study represents the first demonstration that stereoselective metathesis can be achieved by an artificial metalloenzyme. [ABSTRACT FROM AUTHOR]

We describe the facile synthesis of [(Me3Si)2CH]2E=PMes* (E=Ge, Sn) from the reaction of the tetrylenes with the phospha‐Wittig reagent, Me3P−PMes*. Their reactivity towards a range of substrates with protic and hydridic E−H bonds (E=N, O, Si) is described. In addition to hydroelementation reactions of the E=P bonds, we show that these compounds, particularly [(Me3Si)2CH]2Sn=PMes*, also act as base‐stabilized phosphinidenes, allowing phosphinidene transfer to other nucleophiles. [ABSTRACT FROM AUTHOR]

In this account our aim was to give an insight into the application of metathesis protocols (ROM, RCM, RCEYM, CM, RRM) for the synthesis of various azaheterocyclic frameworks. Due to the high biological potential and importance in peptide chemistry and drug design of β‐amino acids our intention is to give a highlight on the synthetic procedures and transformation of these class of compounds with the above‐mentioned metathesis strategies with emphasis on selectivity, stereocontrol, substrate‐directing effect or functional group tolerance. [ABSTRACT FROM AUTHOR]

Abstract Isomerization Metathesis (ISOMET) reaction is an emerging tool for “open loop” chemical recycling of polyethylene to propylene. Novel, latent N‐Alkyl substituted Cyclic(Alkyl)(Amino)Carbene (CAAC)–ruthenium catalysts (5a‐Ru, 3b‐Ru – 6c‐Ru) are developed rendering “inverted” chemical structure while showing enhanced ISOMET activity in combination with (RuHCl)(CO)(PPh3)3 (RuH) double bond isomerization co‐catalyst. Systematic investigations reveal that the steric hindrance of the substituents on nitrogen and carbon atom adjacent to carbene moiety in the CAAC ligand have significantly improved the catalytic activity and robustness. In contrast to the NHC‐Ru and CAAC‐Ru catalyst systems known so far, these systems show higher isomerization metathesis (ISOMET) activity (TON: 7400) on the model compound 1‐octadecene at as low as 3.0 bar optimized pressure, using technical grade (3.0) ethylene. The propylene content formed in the gas phase can reach up to 20% by volume.

Covalent organic frameworks (COFs) offer vast structural and chemical diversity enabling a wide and growing range of applications. While COFs are well-established as heterogeneous catalysts, so far, their high and ordered porosity has scarcely been utilized to its full potential when it comes to spatially confined reactions in COF pores to alter the outcome of reactions. Here, we present a highly porous and crystalline, large-pore COF as catalytic support in α,ω-diene ring-closing metathesis reactions, leading to increased macrocyclization selectivity. COF pore-wall modification by immobilization of a Grubbs-Hoveyda-type catalyst via a mild silylation reaction provides a molecularly precise heterogeneous olefin metathesis catalyst. An increased macro(mono)cyclization (MMC) selectivity over oligomerization (O) for the heterogeneous COF-catalyst (MMC:O=1.35) of up to 51 % compared to the homogeneous catalyst (MMC:O=0.90) was observed along with a substrate-size dependency in selectivity, pointing to diffusion limitations induced by the pore confinement.

Terminal aluminium and gallium imides of the type K[(NON)M(NR)], bearing heteroatom substituents at R, have been synthesised via reactions of anionic aluminium(I) and gallium(I) reagents with silyl and boryl azides (NON=4,5‐bis(2,6‐diisopropyl‐anilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethyl‐xanthene). These systems vary significantly in their lability in solution: the N(SiiPr3) and N(Boryl) complexes are very labile, on account of the high basicity at nitrogen. Phenylsilylimido derivatives provide greater stabilization through the π‐acceptor capabilities of the SiR3 group. K[(NON)AlN(SitBuPh2)] offers a workable compromise between stability and solubility, and has been completely characterized by spectroscopic, analytical and crystallographic methods. The silylimide species examined feature minimal π‐bonding between the imide ligand and aluminium/gallium, with the HOMO and HOMO‐1 orbitals effectively comprising orthogonal lone pairs centred at N. Reactivity‐wise, both aluminium and gallium silylimides can act as viable sources of nitride, [N]3−, with systems derived from either metal reacting with CO to afford cyanide complexes. By contrast, only the gallium system K[(NON)Ga{N(SiPh3)}] is capable of effecting a similar transformation with N2O to yield azide, N3−, via formal oxide/nitride metathesis. The aluminium systems instead generate RN3 via transfer of the imide fragment [RN]2−. [ABSTRACT FROM AUTHOR]

The use of template molecules as chemical scaffolds that significantly influence the course of the reaction has recently been intensively studied. Peptide nucleic acids (PNA) are molecules that mimic natural nucleic acids. They are a promising matrix in such reactions because they possess high affinity and specificity in their interactions. The manner of PNA interaction is predictable based on sequence complementarity. Recently, we report the visible light-induced metathesis reaction in peptides containing a diselenide bond. Herein, we present an efficient and straightforward method of the visible light-driven diselenide-based metathesis of peptide–nucleic acid conjugates. Compared to a similar photochemical transformation in peptides, a significant increase in the metathesis efficiency was obtained due to the template effect. [ABSTRACT FROM AUTHOR]

The metathesis of ethylene with 2‐butenes to propene is an established large‐scale process. However, the fundamentals behind in situ transformation of supported WOx, MoOx, or ReOx species into catalytically active metal‐carbenes and the intrinsic activity of the latter as well as the role of metathesis‐inactive cocatalysts are still unsolved. This is detrimental for catalyst development and process optimization. In this study, we provide the required essentials derived from steady‐state isotopic transient kinetic analysis. For the first time, the steady‐state concentration, the lifetime, and the intrinsic reactivity of metal carbenes were determined. The obtained results can be directly used for the design and the preparation of metathesis‐active catalysts and cocatalysts, thereby opening up possibilities for optimizing propene productivity. [ABSTRACT FROM AUTHOR]

A facile and efficient synthesis of 3‐spiro cycloalkene fused 7‐aza‐2‐indalones from 3,3′‐di‐ or N,3,3′‐tri‐ allyl/homoallyl/pentenyl 7‐aza‐2‐indalones via ring‐closing metathesis (RCM) using Grubbs‐II catalyst has been achieved. The scope of the reaction has been demonstrated by synthesizing spiro products of various ring sizes (n=5, 7, and 18), utilizing 2‐indalone/7‐azaindalone and various alkenylation agents such as allyl/homoallyl/pentenyl bromides as substrates. In addition to usual RCM products, a cross metathesis (CM) product was observed when the substrate was N,3,3′‐triallylated derivative from 2‐indalone. Notably, a macrocyclic, 18‐membered bis‐spirodiene of N‐methyl‐7‐azaindalone was observed by means of intermolecular ring‐closing metathesis (RCM‐RCM). Also, Structures of a few representative spiro‐annulated products were evidenced with single crystal XRD analysis. Furthermore, a plausible mechanism for the products is discussed. [ABSTRACT FROM AUTHOR]

Herein, we report the 16‐ and 19‐membered macrocycles which are closely resembles structurally musk like compounds such as "muscone". These macrocycles were prepared starting from 12‐membered cyclododecanone and 15‐membered cyclopentadecanone ring systems respectively. Like muscone, these compounds have a methyl and keto groups embedded within the macrocyclic ring system. The key reactions include, ring‐closing metathesis (RCM) and Tebbe olefination which are highly efficient and easy to perform. This strategy is very useful in the formation of macrocyclic systems. [ABSTRACT FROM AUTHOR]

The vastness of the scale of the plastic waste problem will require a variety of strategies and technologies to move toward sustainable and circular materials. One of these strategies to address the challenge of persistent fossil‐based plastics is new catalytic processes that are being developed to convert recalcitrant waste such as polyethylene to produce propylene, which can be an important precursor of high‐performance polymers that can be designed to biodegrade or to degrade on demand. Remarkably, this process also enables the production of biodegradable polymers using renewable raw materials. In this Perspective, current catalyst systems and strategies that enable the catalytic degradation of polyethylene to propylene are presented. In addition, concepts for using "green" propylene as a raw material to produce compostable polymers is also discussed. [ABSTRACT FROM AUTHOR]

Metallacyclobutanes are intermediates in several catalytic cycles such as olefin metathesis and cyclopropanation. Furthermore, nickel is attracting attention as a versatile, earth‐abundant metal in developing new homogeneous catalytic transformations. In this context, the current literature on nickelacyclobutanes and their role in catalysis is reviewed. First, catalytic reactions involving a (putative) nickelacyclobutane intermediate are discussed, including cyclopropanations and various transformations of methylenecyclopropane. Second, studies of the stoichiometric reactivity of nickelacyclobutanes relying on their direct observation or even isolation are detailed. In particular, the relationship between the structure of nickelacyclobutanes and their reactivity is highlighted. Finally, future prospects for the development of new catalytic transformations relying on nickelacyclobutane intermediates are briefly outlined. [ABSTRACT FROM AUTHOR]

Discontinuous agreement in Semitic verbal paradigms—that is, the exponence of agreement with a single argument distributed over more than one affix—presents a prima facie challenge to postsyntactic theories which assume a one-to-one mapping between syntactic terminals and morphophonological loci of exponence. The standard response has been to enrich the capacity of Vocabulary Insertion in these languages by making insertion responsible for the quantity of exponents, their relative positions, and their phonological makeup. An alternative view which presupposes a modular postsyntax assigns operational autonomy to rules responsible for feature splitting, displacement, and exponence. I argue that the latter approach is empirically superior on the basis of a novel set of allomorphic alternations from Semitic which demonstrate that feature splitting, i.e. Fission, and displacement feed, and hence cannot be equated with, Vocabulary Insertion. The result is that the inventory of postsyntactic operations must include at least the following three operations: Fission, Metathesis, and Vocabulary Insertion. [ABSTRACT FROM AUTHOR]

As the first known example of ring‐opening cross metathesis (ROCM) of polyfluorinated strained cyclobutenes, ROCM of 3,3,4,4‐tetrafluorocyclobutene with electronically rich alkenes, catalyzed by Grubbs or Hoveyda‐Grubbs 2nd generation precatalysts, gave a small library of non‐symmetrical isolated dienes bearing a tetrafluoroethylene spacer between the double bonds. 1‐Butoxy‐3,3,4,4‐tetrafluorohexa‐1,5‐diene thus formed underwent subsequent regioselective cross metathesis (CM) with a series of styrenes, catalyzed by Hoveyda‐Grubbs 2nd generation precatalyst, leading to non‐symmetrically substituted dienes. 6,6‐Dibutoxy‐3,3,4,4‐tetrafluorohex‐1‐ene, formed by regioselective butoxylation of 1‐butoxy‐3,3,4,4‐tetrafluorohexa‐1,5‐diene, was dihydroxylated and cyclized to the corresponding 3,3,4,4‐tetrafluorohexopyranose. [ABSTRACT FROM AUTHOR]

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We report a short synthetic approach to various tricyclic systems that are present in several diquinane‐based natural products starting with a readily available exo‐dicyclopentadiene‐1‐one. To this end, we have successfully assembled a fused 5/5/7‐tricyclic enone via ring‐rearrangement metathesis as a key step. The strategy has been further extended to synthesize the 1,3‐dihydroxy and then 1‐keto‐3‐hydroxy derivatives by utilizing regio‐ and stereoselective epoxidation and ring‐rearrangement metathesis reactions as key steps. All these target compounds are found to be present in diquinane‐based natural products such as longeracinphyllins A, himalenine D and daphnipaxianine A, etc. Moreover, the newly synthesized tricyclic compounds matches the exact ring‐junction stereochemistry (5/5‐exo) of these natural products. Hence, the synthetic studies disclosed here may be useful in the synthesis of biologically significant natural products and in the drug design. The newly synthesized molecules were characterized by NMR and HRMS data. Some of these structures were confirmed by a single crystal X‐ray diffraction studies. [ABSTRACT FROM AUTHOR]

3,3′,5,5′-Tetra-tert-butyl-2′-sulfanyl[1,1′-biphenyl]-2-ol (H2[tBu4OS]) was prepared in 24 % yield overall from the analogous biphenol using standard techniques. Addition of H2[tBu4OS] to Mo(NAr)(CHCMe2Ph)(2,5-dimethylpyrrolide)2 led to formation of Mo(NAr)(CHCMe2Ph)[tBu4OS], which was trapped with PMe3 to give Mo(NAr)(CHCMe2Ph)[tBu4OS](PMe3) (1(PMe3)). An X-ray crystallographic study of 1(PMe3) revealed that two structurally distinct square pyramidal molecules are present in which the alkylidene ligand occupies the apical position in each. Both 1(PMe3)A and 1(PMe3)B are disordered. Mo(NAd)(CHCMe2Ph)(tBu4OS)(PMe3) (2(PMe3); Ad=1-adamantyl) and W(NAr)(CHCMe2Ph)(tBu4OS)(PMe3) (3(PMe3)) were prepared using analogous approaches. 1(PMe3) reacts with ethylene (1 atm) in benzene within 45 minutes to give an ethylene complex Mo(NAr)(tBu4OS)(C2H4) (4) that is isolable and relatively stable toward loss of ethylene below 60 °C. An X-ray study shows that the bond distances and angles for the ethylene ligand in 4 are like those found for bisalkoxide ethylene complexes of the same general type. Complex 1(PMe3) in the presence of one equivalent of B(C6F5)3 catalyzes the homocoupling of 1-decene, allyltrimethylsilane, and allylboronic acid pinacol ester at ambient temperature. 1(PMe3), 2(PMe3), and 3(PMe3) all catalyze the ROMP of rac-endo,exo-5,6-dicarbomethoxynorbornene (rac-DCMNBE) in the presence of B(C6F5)3, but the polyDCMNBE that is formed has a random structure.

In the course of this work, fl uorinated catalysts MoO3 /Al2 O3 -F for the olefi ns metathesis have been synthesized. The materials have been characterized by various physicochemical methods and tested in the propylene metathesis reaction. It has been shown that the support fl uorination leads to partial replacement of surface hydroxyl groups by F, which is accompanied by an increase in the strength of both Lewis acid sites and residual bridging OH groups. Increasing the fl uorine content on γ-Al2O3 up to 3 wt. % leads to an increase in the conversion of propylene in the metathesis reaction by 1.5 times (WHSV = 1.1 h-1, Т = 100 °С, р = 9 atm.) with a selectivity of more than 95%. However, when the reaction is carried out at atmospheric pressure, fl uorinated samples show lower activity than unpromoted ones. The results of this work show that the support acidity plays an important role in propylene metathesis. The proposed method of catalyst modifi cation opens up new possibilities for improving classical metathesis catalysts.

Herein, a short synthetic approach to linearly fused tricyclic enone 1 and cis‐anti‐cis type hydroxy‐triquinane 2 has been described in an efficient manner by employing tandem‐metathesis as a key step. The triquinane‐based enone 1 is prepared by a Babler–Dauben oxidation of hydroxy‐triquinane 2, which is assembled by following a three‐step sequence involving a regio‐ and stereoselective allylation, vinyl Grignard addition, and tandem‐metathesis. Our strategy relies on exo‐tricyclic ketone, which is derived from readily available exo‐dicyclopentadiene‐1‐one. The newly synthesized molecules were identified and characterized by nuclear magnetic resonance spectroscopy (NMR), and high‐resolution mass spectrometry (HRMS) data. It is worth mentioning that tricyclic enone 1 is present as a core unit of many naturally occurring polyquinanes, particularly xeromphalinone family members. Hence, our approach may be useful in the synthesis of such bioactive molecules. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Two‐electron reduction of [N2NBn]TiIVCl2 (3) gave a highly reactive [N2N]TiII species, which underwent C—O bond activation of THF (tetrahydrofuran) to generate [N2NBn]TiIV[O(CH2)4] (4) through oxidative addition. The resulted TiIV–Csp3 bond in oxametallacyclohexane was tantamount to the elaborately‐designed Ti‐alkyl complexes, competent to activate intramolecular Csp2–H bond, forming ortho‐cyclometalated complex [N2NCH2C6H4]TiIV(OnBu) (5). Key intermediates were isolated and fully characterized by X‐ray crystallography. Mechanistic studies revealed that the oxidative addition of C—O bond took place at TiII‐center via a radical intermediate, while a Csp2–H bond activation proceeded by σ‐bond metathesis with a kitelike four‐centered TiIV‐transition state. [ABSTRACT FROM AUTHOR]

(–)-Galiellalactone is a secondary fungal metabolite. It was found from dead wood in Chile and first isolated from ascomycetes Galiella rufa (strain A75-86) and A111-95. It has unique architecture. This molecule consists of [5,5,6]-fused tricyclic ring system. The α,β-unsaturated lactone ring present in (–)-galiellalactone acts as Michael acceptor. It has four stereocenters. The tertiary stereocenter has the angular hydroxyl group, which is very important for its bioactivity. This fungal metabolite shows different bioactivities like anti-tumor, anti-inflammatory, anti-HIV, and anti-cancer activities. The unique structural feature along with its excellent bioactivities encouraged us to write this review article. This review comprises the different synthetic approaches with the beauty and uniqueness of various reactions like intramolecular Diels–Alder reaction and Metathesis. Herein, we have discussed the syntheses for the molecule (–)-galiellalactone and its stereoisomers available to date. [ABSTRACT FROM AUTHOR]

Olefin metathesis catalysts like AquaMet are vulnerable to different decomposition pathways under biologically relevant conditions. Currently, stabilizing strategies are focused on approaches with limited relevance for application under biologically relevant conditions. Initial attempts to stabilise AquaMet by encapsulation within a supramolecular metallocage showed that the nitrate counterions of the cage improve the activity of the catalyst. We show that the chloride ligands of AquaMet can be replaced with nitrates by simple anion‐exchange. Catalytic studies into metathesis of a diallyl substrate showed that the presence of nitrate generates higher yields of the ring‐closed product compared to AquaMet alone, under aqueous and biological conditions. Kinetic studies support that the nitrate‐containing catalyst both initiates faster and performs catalysis at a much faster rate than AquaMet, while the rate of catalyst deactivation was similar. This new strategy of kinetic protection of a transition metal catalyst may have future applications for other catalytic reactions applied in vivo. [ABSTRACT FROM AUTHOR]

The reactions of a terminal aluminium imide with a range of oxygen‐containing substrates have been probed with a view to developing its use as a novel main group transfer agent for the [NR]2− fragment. We demonstrate transfer of the imide moiety to [N2], [CO] and [Ph(H)C] units driven thermodynamically by Al−O bond formation. N2O reacts rapidly to generate the organoazide DippN3 (Dipp=2,6‐iPr2C6H3), while CO2 (under dilute reaction conditions) yields the corresponding isocyanate, DippNCO. Mechanistic studies, using both experimental and quantum chemical techniques, identify a carbamate complex K2[(NON)Al‐{κ2−(N,O)−N(Dipp)CO2}]2 (formed via [2+2] cycloaddition) as an intermediate in the formation of DippNCO, and also in an alternative reaction leading to the generation of the amino−dicarboxylate complex K2[(NON)Al{κ2−(O,O′)−(O2C)2N‐(Dipp)}] (via the take‐up of a second equivalent of CO2). In the case of benzaldehyde, a similar [2+2] cycloaddition process generates the metallacyclic hemi‐aminal complex, Kn[(NON)Al{κ2−(N,O)−(N(Dipp)C(Ph)(H)O}]n. Extrusion of the imine, PhC(H)NDipp, via cyclo‐reversion is disfavoured thermally, due to the high energy of the putative aluminium oxide co‐product, K2[(NON)Al(O)]2. However, addition of CO2 allows the imine to be released, driven by the formation of the thermodynamically more stable aluminium carbonate co‐product, K2[(NON)Al(κ2−(O,O′)−CO3)]2. [ABSTRACT FROM AUTHOR]

Chemical reactivity plays a major role in understanding several aspects of selectivity. Therefore, in this account, we present a plethora of reactions that demonstrate our efforts in exploiting interesting cases of selectivity over the past three decades. Among them, chemoselectivity, regioselectivity and stereoselectivity are discussed. Strain, steric factors, and separation of the reacting functionalities are revealed as prominent features in generating selectivity. 1 Introduction 2 Chemoselectivity 3 Regioselectivity 4 Diastereoselectivity 5 Substrate-Based Selectivity 6 Reagent-Based Selectivity 7 Steric-Volume-Induced Selectivity 8 Role of Temperature and Reaction Time in Achieving Selectivity 9 Role of the Catalyst in Observing Selectivity 10 Separation as a Parameter for Selectivity 11 p K a (Acidity of the Active Methylene Component) 12 Sequence as a Tool for Selectivity 13 Strain of the Ring System 14 Examples of Miscellaneous Selectivity 15 Conclusions [ABSTRACT FROM AUTHOR]