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An improved synthetic procedure for the intramolecular ketene [2+2] cycloaddition was developed for the preparation of 1‐heteroatom‐substituted bicyclo[2.1.1]hexan‐5‐ones. It was found that the use of the Mukaiyama reagent (2‐chloro‐N‐methyl‐pyridinium iodide) was key to efficiently generate the α‐heteroatom substituted homoallyl ketene intermediate for the cycloaddition reaction. The synthetic utility of the resulting bicyclic ketone was demonstrated through the preparation of a saturated variant of vortioxetine. [ABSTRACT FROM AUTHOR]

The present review is a comprehensive update of the synthesis of monocyclic β-lactams via cycloaddition reactions. According to the IUPAC definition of cycloaddition, both elementary and stepwise processes (formal cycloadditions) have been considered. The years 2019–2022 are covered by the cited literature. The focus of the review is on synthetic aspects with emphasis on the structural scope, reaction conditions, mechanistic aspects, and selectivity results. Selected significant data related to biological activities and synthetic applications are also highlighted.

The present review is a comprehensive update of the synthesis of monocyclic β-lactams via cycloaddition reactions. According to the IUPAC definition of cycloaddition, both elementary and stepwise processes (formal cycloadditions) have been considered. The years 2019–2022 are covered by the cited literature. The focus of the review is on synthetic aspects with emphasis on the structural scope, reaction conditions, mechanistic aspects, and selectivity results. Selected significant data related to biological activities and synthetic applications are also highlighted. [ABSTRACT FROM AUTHOR]

A formal atom transfer radical [3+2] annulation (ATRAn) reaction between different homoallyl radical precursors and 1,1‐diborylethene was developed. It provides a rapid access to polysubstituted cyclopentanes containing a gem‐diboronic ester moiety. The synthetic utility of theses uniquely functionalized 5‐membered rings is highlighted by their easy conversion to attractive borylated building blocks such as 1‐borylated bicyclo[3.1.0]hexanes. The ATRAn reaction was extended to homopropagylic radicals giving access to unique allylic gem‐diboronic esters that could be used in allylboration of aldehydes. Furthermore, this work highlights that 1,1‐diborylethene represents a synthetic equivalent to ketene, a so far elusive radical trap due to its daunting reactivity. [ABSTRACT FROM AUTHOR]

Copper salts, which are widely applied in chemical processes, are highly toxic for aquatic life with devastating and long‐lasting effects. The most sustainable measure to prevent negative impact on surface water bodies is the elimination of copper from chemical processes. In Grignard reactions, acyl chlorides are widely used in combination with copper(I) chloride to introduce acyl substituents to aromatic compounds. We demonstrate that carboxylic acid anhydrides are a competent and highly selective alternative to acyl chlorides when used in the absence of copper(I) catalysts. An integrated value stream cycle allows for recycling of the carboxylate salt byproducts by reaction with ketene, thereby reducing the waste output to almost zero. This proposed process can therefore contribute to minimizing both chemical waste and heavy metal input into water bodies. [ABSTRACT FROM AUTHOR]

The ring‐expansion of arylthiiranes and phenoxyacetyl chloride was performed in the presence of triethylamine and provided a novel strategy for the synthesis of 4,5‐dihydrobenzo[d]thiepin‐2(1H)‐ones, benzo[d]‐ϵ‐thiolactones, directly without catalysts or additives. Its linear free energy analysis was conducted on the basis of competitive experiments. The results indicate that both reaction constants are close to zero (0.14 for σm and 0.20 for σp), supporting the proposed sulfur‐shifted ene mechanism. The current reaction features atom and step‐economic one‐pot characteristic via a tandem sequence of in situ ketene generation, sulfur‐shifted ene reaction, and aromatization. [ABSTRACT FROM AUTHOR]

C1 coupling reactions over zeolite catalysts are central to sustainable chemical production strategies. However, questions persist regarding the involvement of CO in ketene formation, and the impact of this elusive oxygenate intermediate on reactivity patterns. Using operando photoelectron photoion coincidence spectroscopy (PEPICO), we investigate the role of CO in methyl chloride conversion to hydrocarbons (MCTH), a prospective process for methane valorization with a reaction network akin to methanol to hydrocarbons (MTH) but without oxygenate intermediates. Our findings reveal the transformative role of CO in MCTH at the low pressures, inducing ketene formation in MCTH and boosting olefin production, confirming the Koch carbonylation step in the initial stages of C1 coupling. We uncover pressure‐dependent product distributions driven by CO‐induced ketene formation, and its subsequent desorption from the zeolite surface, which is enhanced at low pressure. Inspired by the above results, extension of the co‐feeding approach to CH3OH as another simple oxygenate showcases the additional potential for improved catalyst stability in MCTH at ambient pressure. [ABSTRACT FROM AUTHOR]

The reactivity of the complex [(dpp-bian)GaNa(DME)2] (1) (dpp-bian = 1,2-bis[(2,6-di-isopropylphenyl)imino]acenaphthene) towards isocyanates, benzophenone, diphenylketene, and 1,2-dibenzylidenehydrazine has been studied. Treatment of 1 with isocyanates led to derivatives of imidoformamide [(dpp-bian)Ga{C(=NPh)2}2–NPh][Na(DME)3] (2), biuret [(dpp-bian)Ga(NCy)2(CO)2NCy][Na(DME)] (3), or carbamic acids [(dpp-bian)GaN(Cy)C(O)O]2[Na(THF)(Et2O)] (4), [(dpp-bian)GaC(=NCy)N(Cy)C(O)O][Na(Py)3] (5). Treatment of 1 with 2 equiv. of Ph2CO resulted in gallium pinacolate [(dpp-bian)GaO(CPh2)2O][Na(Py)2] (9), while the reaction of 1 with 2 equiv. Ph2CCO gave divinyl ether derivative [(dpp-bian)Ga{C(=CPh2)O}2][Na(DME)3] (10). Complex 1 treated with 2 equiv. 1,2-dibenzylidenehydrazine underwent [1+2+2] cycloaddition to give C–C coupling product [(dpp-bian)Ga{N(NCHPh)}2(CHPh)2][Na(DME)3] (11). When complex 1 was sequentially treated with 1 equiv. of 1,2-dibenzylidenehydrazine and 1 equiv. of pyridine or pyridine-d5; it gave [1+2+2] cycloaddition product [(dpp-bian)GaN(NCHPh)C(Ph)CN][Na(DME)3] (12). Compounds 2–12 were characterized by NMR and IR spectroscopy, and their molecular structures were established by single-crystal X-ray diffraction analysis.

Background: In this review, we summarize current scientific knowledge on psychoactive cannabinoids synthesized from cannabidiol (CBD) and sold in the semi-legal market established in response to the passage of the US Agriculture Improvement Act of 2018, commonly known as the 2018 Farm Bill. The discussion focuses on recent developments that suggest this unregulated market may be fertile ground for a potential health crisis. Summary: Current research into CBD-derived cannabinoids is mainly limited to Δ8-tetrahydrocannabinol (Δ8-THC) products, with some recent publications beginning to explore O-acetyl-THC, a term describing the acetate ester of Δ8-THC or Δ9-THC, and its potential pulmonary toxicity. We advance the discussion on the CBD-derived cannabinoid market, shedding light on the introduction and associated dangers of novel cannabinoids, likely produced via fully synthetic routes using sidechain variants of CBD, with purportedly greater agonist activity at the human cannabinoid receptor 1 (as a source of euphorigenic activity) than Δ9-THC. We discuss the expanded incorporation of the acetate ester motif into other THC analogues. We also discuss the lack of regulatory oversight for the production of CBD-derived cannabinoids and the unlabeled presence of under-researched cannabinoids formed as reaction side products in the CBD-derived cannabinoid products being sold. Accordingly, we suggest approaches to monitoring the CBD-derived cannabinoid market and investigating the pharmacology of the cannabinoids being consumed. Finally, important epidemiological findings are discussed and future directions for research are suggested to call investigators to this critically understudied field. Key Messages: The CBD-derived cannabinoid market is growing internationally, and the market has diversified to include potent synthetic cannabinoids. The products sold on this unregulated market are under-researched despite growing availability and consumer interest. Ernest investigation of the pharmacology of these novel cannabinoids and the contents of CBD-derived cannabinoid products is critical for monitoring this potential source of another vaping-related epidemic.

The reactivity of the complex [(dpp-bian)GaNa(DME)2] (1) (dpp-bian = 1,2-bis[(2,6-di-isopropylphenyl)imino]acenaphthene) towards isocyanates, benzophenone, diphenylketene, and 1,2-dibenzylidenehydrazine has been studied. Treatment of 1 with isocyanates led to derivatives of imidoformamide [(dpp-bian)Ga{C(=NPh)2}2–NPh][Na(DME)3] (2), biuret [(dpp-bian)Ga(NCy)2(CO)2NCy][Na(DME)] (3), or carbamic acids [(dpp-bian)GaN(Cy)C(O)O]2[Na(THF)(Et2O)] (4), [(dpp-bian)GaC(=NCy)N(Cy)C(O)O][Na(Py)3] (5). Treatment of 1 with 2 equiv. of Ph2CO resulted in gallium pinacolate [(dpp-bian)GaO(CPh2)2O][Na(Py)2] (9), while the reaction of 1 with 2 equiv. Ph2CCO gave divinyl ether derivative [(dpp-bian)Ga{C(=CPh2)O}2][Na(DME)3] (10). Complex 1 treated with 2 equiv. 1,2-dibenzylidenehydrazine underwent [1+2+2] cycloaddition to give C–C coupling product [(dpp-bian)Ga{N(NCHPh)}2(CHPh)2][Na(DME)3] (11). When complex 1 was sequentially treated with 1 equiv. of 1,2-dibenzylidenehydrazine and 1 equiv. of pyridine or pyridine-d5; it gave [1+2+2] cycloaddition product [(dpp-bian)GaN(NCHPh)C(Ph)CN][Na(DME)3] (12). Compounds 2–12 were characterized by NMR and IR spectroscopy, and their molecular structures were established by single-crystal X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive analysis of nickel–phosphine complexes, specifically Ni(PH3)2(OCCH2), Ni(PH3)2(H2CCO), Ni(PH3)2(H2CCCH2), Ni(PH3)2(NNCH2), and Ni(PH3)2( η 1 -H2CNN). Utilizing ETS-NOCV analysis, we explored orbital energy decomposition and the Hirshfeld charges of the ligands, providing insights into the electronic structures and donor–acceptor interactions within these complexes. The interactions in the ketene and allene complexes exhibit similar deformation densities and NOCV orbital shapes to those calculated for Ni(PH3)2(NNCH2), indicating consistent interaction characteristics across these complexes. The total interaction energy for all η 2 complexes is observed to be over 60 kcal/mol, slightly exceeding that of the analogous carbon dioxide complex reported earlier. Furthermore, the study highlights the stronger back-donation as compared to donor interactions across all η 2 complexes. This is further corroborated by Hirshfeld analysis, revealing the charge distribution dynamics within the ligand fragments. The research offers new perspectives on the electron distribution and interaction energies in nickel–phosphine complexes, contributing to a deeper understanding of their catalytic and reactive behaviors. [ABSTRACT FROM AUTHOR]

Background: In this review, we summarize current scientific knowledge on psychoactive cannabinoids synthesized from cannabidiol (CBD) and sold in the semi-legal market established in response to the passage of the US Agriculture Improvement Act of 2018, commonly known as the 2018 Farm Bill. The discussion focuses on recent developments that suggest this unregulated market may be fertile ground for a potential health crisis. Summary: Current research into CBD-derived cannabinoids is mainly limited to Δ8-tetrahydrocannabinol (Δ8-THC) products, with some recent publications beginning to explore O-acetyl-THC, a term describing the acetate ester of Δ8-THC or Δ9-THC, and its potential pulmonary toxicity. We advance the discussion on the CBD-derived cannabinoid market, shedding light on the introduction and associated dangers of novel cannabinoids, likely produced via fully synthetic routes using sidechain variants of CBD, with purportedly greater agonist activity at the human cannabinoid receptor 1 (as a source of euphorigenic activity) than Δ9-THC. We discuss the expanded incorporation of the acetate ester motif into other THC analogues. We also discuss the lack of regulatory oversight for the production of CBD-derived cannabinoids and the unlabeled presence of under-researched cannabinoids formed as reaction side products in the CBD-derived cannabinoid products being sold. Accordingly, we suggest approaches to monitoring the CBD-derived cannabinoid market and investigating the pharmacology of the cannabinoids being consumed. Finally, important epidemiological findings are discussed and future directions for research are suggested to call investigators to this critically understudied field. Key Messages: The CBD-derived cannabinoid market is growing internationally, and the market has diversified to include potent synthetic cannabinoids. The products sold on this unregulated market are under-researched despite growing availability and consumer interest. Ernest investigation of the pharmacology of these novel cannabinoids and the contents of CBD-derived cannabinoid products is critical for monitoring this potential source of another vaping-related epidemic. [ABSTRACT FROM AUTHOR]

4-Hydroxy-2-pyrones are of interest as potential biorenewable molecules for a sustainable transition from biomass feedstock to valuable chemical products. This review focuses on the methodologies for the synthesis of 4-hydroxy-2-pyrones published over the last 20 years. These pyrones as polyketides are widespread in Nature and possess versatile bioactivity that makes them an attractive target for synthesis and modification. Biosynthetic paths of the pyrones are actively developed and used as biotechnological approaches for the construction of natural and unnatural polysubstituted 4-hydroxy-2-pyrones. The major synthetical methods are biomimetic and are based on the cyclization of tricarbonyl compounds. Novel chemical methods of de novo synthesis based on alkyne cyclizations using transition metal complexes and ketene transformations allow for straightforward access to 4-hydroxy-2-pyrones and have been applied for the construction of natural products. Possible directions for further pyrone ring modification are discussed. [ABSTRACT FROM AUTHOR]

Meldrum's acid mediated ketene chemistry (MAMKC) is applied to synthesis of poly(ester amide)s in this work. An MA-functionalized phenolic amide compound (MA_PhOH-Am) is synthesized from the reaction between a MA-functionalized amine and 3,4-dihydrocoumarine (DHC, a biomass-based chemical) through amine-lactone addition reaction. Polymerization of MA_PhOH-Am results in the corresponding poly(ester amide) (P(Es-Am)), through MA thermolysis reaction (generating the corresponding ketene groups) and ketene-phenol addition reaction. Both MA_PhOH-Am and P(Es-Am) have been characterized with spectral methods and thermal analysis. P(Es-Am) has an inherent viscosity of 0.49 dL g-1, a molecular weight of 76,500 Da, a glass transition temperature of 145°C (tand peak in dynamic mechanical analysis), a thermal stability of about 320°C, and a storage modulus at 50°C of 1.0 GPa. In the stress-strain measurement, P(Es-Am) exhibits a Young's modulus, a tensile strength, and an elongation at break of 10.6 ± 0.7 GPa, 165 ± 40 MPa, and 1.83 ± 0.41%, respectively. An effective approach for the synthesis of high-performance poly(ester amide)s has been demonstrated. [ABSTRACT FROM AUTHOR]

Design, Synthese und Anwendung von Benzolbioisosteren haben in den letzten 20 Jahren viel Aufmerksamkeit erfahren. In jüngster Zeit haben sich Bicyclo[2.1.1]hexane als äußerst attraktive Bioisostere für ortho‐ und meta‐substituierte Benzole erwiesen. In diesem Artikel beschreiben wir eine milde, skalierbare und übergangsmetallfreie Methode zur Herstellung von hochsubstituierten Bicyclo[2.1.1]hexanen über eine Lewis‐Säure‐katalysierte (3+2)‐Cycloaddition von Bicyclo[1.1.0]butanketonen mit disubstituierten Ketenen. Die Reaktion zeigt eine hohe Toleranz gegenüber funktionellen Gruppen, wie die erfolgreiche Herstellung verschiedener 3‐Alkyl‐3‐Aryl‐ sowie 3,3‐Bisalkyl‐Bicyclo[2.1.1]hexan‐2‐onen belegt (26 Beispiele, bis zu 89 % Ausbeute). Die Folgechemie an der exozyklischen Ketonfunktion wird ebenfalls demonstriert. [ABSTRACT FROM AUTHOR]

Diketene (4-methylideneoxetan-2-one) is a precursor to the formation of either two molecules of ketene, or allene and CO2 using pyrolysis techniques. It is not known experimentally which of these pathways is followed, or indeed if both are, during the dissociation process. We use computational methods to show that the formation of ketene has a lower barrier than formation of allene and CO2 under standard conditions (by 12 kJ/mol). According to CCSD(T)/CBS, CBS-QB3 and M06-2X/cc-pVTZ calculations the formation of allene and CO2 is favoured thermodynamically under standard conditions of temperature and pressure; however, kinetically the formation of ketene is favoured from transition state theory calculations at standard and elevated temperatures. [ABSTRACT FROM AUTHOR]

Under an atmosphere of carbon monoxide (CO), a (phosphino)diazomethyl anion salt [[P]‐CN2][K(18‐C‐6)(THF)] (1) ([P]=[(CH2)(NDipp)]2P; 18‐C‐6=18‐crown‐6; Dipp=2,6‐diisopropylphenyl) undergoes a facile N2/CO exchange reaction giving the (phosphino)ketenyl anion salt [[P]‐CCO][K(18‐C‐6)] (2). Oxidation of 2 with elemental Se affords the (selenophosphoryl)ketenyl anion salt [P](Se)‐CCO][K(18‐C‐6)] (3). These ketenyl anions feature a strongly bent geometry at the P‐bound carbon and this carbon atom is highly nucleophilic. The electronic structure of the ketenyl anion [[P]‐CCO]− of 2 is examined by theoretical studies. Reactivity investigations demonstrate 2 as a versatile synthon for derivatives of ketene, enolate, acrylate and acrylimidate moieties. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive analysis of nickel–phosphine complexes, specifically Ni(PH3)2(OCCH2), Ni(PH3)2(H2CCO), Ni(PH3)2(H2CCCH2), Ni(PH3)2(NNCH2), and Ni(PH3)2(η1-H2CNN). Utilizing ETS-NOCV analysis, we explored orbital energy decomposition and the Hirshfeld charges of the ligands, providing insights into the electronic structures and donor–acceptor interactions within these complexes. The interactions in the ketene and allene complexes exhibit similar deformation densities and NOCV orbital shapes to those calculated for Ni(PH3)2(NNCH2), indicating consistent interaction characteristics across these complexes. The total interaction energy for all η2 complexes is observed to be over 60 kcal/mol, slightly exceeding that of the analogous carbon dioxide complex reported earlier. Furthermore, the study highlights the stronger back-donation as compared to donor interactions across all η2 complexes. This is further corroborated by Hirshfeld analysis, revealing the charge distribution dynamics within the ligand fragments. The research offers new perspectives on the electron distribution and interaction energies in nickel–phosphine complexes, contributing to a deeper understanding of their catalytic and reactive behaviors.

A low-cost manganese-catalyzed oxidant-free selective C–H acylation of indole with ketene is reported. This protocol features mild reaction conditions and good functional group tolerance. The yield is from middle to excellent. The acylation products can be further converted to diverse useful compounds. Mechanism study reveals the acylation transformation possibly undergoes a cyclomanganated complex species as reactive intermediate.

In this study, polystyrene was functionalized with Meldrum's acid toward the introduction of the ketenes (CCO) system to its backbone for producing a dramatically reactive intermediate. Meldrum's acid, as a ketene source, was reacted by poly(styrene‐co‐p‐chloromethyl styrene) through a simple nucleophilic reaction to synthesize poly(styrene‐co‐styryl Meldrum's acid). Then, the pendant Meldrum's acid under thermal treatment converted to ketene intermediate resulting in highly reactive polystyrenes derivatives, which rapidly reacted by nucleophilic reagents to afford ultimate organic building blocks. The polystyrene derivatives were characterized using elemental analysis, FT‐IR, high‐resolution solid‐state NMR, thermogravimetric analysis (TGA), and differential thermogravimetric analysis (DTG). To clarify the evolutionary mechanisms of polystyrene products, density functional theory (DFT) method B3LYP with the 6–311++G(2d,p) basis set was used. We studied the preparation of polystyrene model compounds through Meldrum's acid thermolysis and nucleophilic substitution. The kinetic and thermodynamic parameters in all reactions and the structural and electronic properties of all molecules were calculated. These data exhibited that based on Gibbs Free energy values, the structure of syndiotactic polystyrene is more stable than that of isotactic polystyrene. Furthermore, it was found that the presence of an electron donor or acceptor substituent on the polystyrene structure affects the electronic bandgap. [ABSTRACT FROM AUTHOR]

The manuscript describes a synthetic route for the formation of 5‐(methylisoindole‐1,3‐dione) pyrimidinones by [4+2] cycloaddition reactions of functionalized 1,3‐diazabuta‐1,3‐dienes with 2‐(3‐Oxo‐allyl)‐isoindole‐1,3‐dione generated in situ from phthaloylalanine and tosyl chloride using triethylamine as a base. The functionalized 5‐(methylisoindole‐1,3‐dione) pyrimidinones were further explored in the deprotection of amines to afford a variety of 5‐methylamino pyrimidinones. The synthesis of such functionalized pyrimidinones is significant as they have a wide range of pharmacological profiles and are valuable as organic synthons. Mechanistic insights are also proposed for the given synthetic methodology. [ABSTRACT FROM AUTHOR]

Phenyl acetate (CH 3 COOC 6 H 5 , PA) shares a similar aryl acetate group with vitamin E acetate, which is thought to be responsible for producing pulmonary toxic ketene in e-cigarettes. Hence, PA is reported to be a model compound of vitamin E acetate in producing ketene. To better understand the pyrolysis chemistry of vitamin E acetate, pyrolysis of PA in a jet-stirred reactor was investigated by using synchrotron vacuum ultraviolet photoionization mass spectrometry at atmospheric pressure and at temperature range of 700 – 1025 K. Several key products such as acetylene, ethylene, carbon monoxide, formaldehyde, carbon dioxide, vinyl acetylene, 1,3-butadiene, 1,3-cyclopentadiene, benzene, phenol, etc., and especially, ketene, were identified and measured. By extending the phenyl formate pyrolysis model, a detailed PA pyrolysis model containing 735 species and 3365 reactions was constructed and validated against the current experimental results of PA pyrolysis. Rate of production analysis and sensitivity analysis show that the main reaction pathways of PA pyrolysis are the unimolecular decomposition forming phenol and ketene, followed by the C–CH 3 bond cleavage forming phenoxycarbonyl and methyl. The corresponding products of these two reactions and of the subsequent reactions, including phenol, ketene and carbon monoxide, etc., are demonstrated to be the key products in PA pyrolysis. Toxic aromatic compounds, such as benzene, toluene and ethylbenzene, etc., also have relatively high mole fractions in PA pyrolysis. [ABSTRACT FROM AUTHOR]

Ketene (CH 2 CO) mechanism is a building block for developing combustion kinetic models of practical fuels. To revisit the combustion chemistry related to ketene, oxidation experiments of butane-2,3‑dione (diacetyl, CH 3 COCOCH 3), considered as an effective precursor of CH 2 CO, are conducted in a jet-stirred reactor (JSR) at 10 bar and temperatures ranging from 650 to 1160 K. Identification and quantification of intermediates are achieved by Fourier transform infrared spectrometry, gas chromatography, and mass spectrometry. A kinetic model of diacetyl is constructed based on recent theoretical and modeling studies on diacetyl and ketene, which has been validated against the present data and experimental data of diacetyl and CH 2 CO in literature. Generally, the present model can adequately predict most of them, and better predict the methyl-related intermediates under wide pyrolysis and combustion conditions than previous models. Based on modeling analyses, the unimolecular decomposition reaction of diacetyl is the dominant reaction pathway for fuel consumption under different equivalence ratio conditions, especially at high temperatures. Under lean conditions, both the H-atom abstraction reactions by methyl (i.e. CH 3 COCOCH 3 + CH 3 = CH 4 + CH 2 CO + CH 3 CO, R3) and by OH (i.e. CH 3 COCOCH 3 + OH = H 2 O + CH 2 CO + CH 3 CO, R5) are important for diacetyl consumption, while under rich conditions R5 becomes negligible. As the most important intermediates in diacetyl oxidation, the main consumption pathways of CH 2 CO and CH 3 are dependent on the equivalence ratio conditions. Under lean conditions, CH 2 CO mainly reacts with OH to produce CH 2 OH and CO (i.e. CH 2 CO + OH = CH 2 OH + CO, R10), while methyl reacts with HO 2 to produce CH 3 O and OH (i.e. CH 3 + HO 2 = CH 3 O + OH, R20). In contrast, under rich conditions, the addition-elimination reaction between CH 2 CO and H becomes competitive with R10, while the CH 3 self-combination producing C 2 H 6 plays a more important role than the CH 3 oxidation pathway R20. Sensitivity analysis of CH 2 CO shows that not only the reactions of CH 2 CO, but also those of CH 3 are sensitive to CH 2 CO formation. This is because CH 3 related reactions influence the distribution of radical pool, which determines the oxidation reactivity of the reaction system. [ABSTRACT FROM AUTHOR]

The cross-reaction kinetics of acetone/ketene (CH 3 COCH 3 /CH 2 CO) + amino (NH 2) radicals are first theoretically reported for a wide range of conditions (T = 300–2500 K and P = 0.1–100 atm) in this work. The high-level electronic structure method CCSD(T)/cc-pV n Z(n = T, Q)//B3LYP-D3BJ/6–311++G(d,p) is used to explore the potential energy profiles on which the temperature- and pressure-dependence kinetic behaviors of the title reactions are characterized using the Rice-Ramsperger-Kassel-Marcus/Master Equation (RRKM/ME) theory. Corrections of the one-dimensional hindered rotor approximation and asymmetric Eckart tunneling effect are also included in the rate constant calculations. Furthermore, this work delves into the competitive relationships among the H-abstraction, NH 2 addition and addition-dissociation reaction pathways. For CH 3 COCH 3 + NH 2 , the H-abstraction reaction of CH 3 COCH 3 is highly favored over the addition-dissociation reaction and other isomerization channels. For CH 2 CO + NH 2 , the reaction channel of addition-dissociation to form CH 2 NH 2 + CO under low temperature conditions is more advantageous, while the H-abstraction reaction plays a dominant role under combustion conditions (T ≥ 1000 K). To reveal the impact of the studied reaction kinetics on model predictions, the rate constants of dominant reaction channels calculated in this work are incorporated into a kinetic model for the auto-ignition, oxidation and pyrolysis of CH 3 COCH 3 /NH 3 mixtures. The simulated results show that the effect of the updated rate constants on ignition delay time is mainly at low temperatures and the promotion effect of CH 3 COCH 3 addition on the ignition of NH 3 presents a nonlinear enhancement. The updated rate constants can also accelerate the consumption of CH 3 COCH 3 and CH 2 CO formation, while also influence the concentration distributions of other significant species (e.g., NH 3 , CO). Therefore, the cross-reaction kinetics of CH 3 COCH 3 /CH 2 CO + NH 2 are critical in controlling the fuel consumption, important intermediate formation and ignition delay time of CH 3 COCH 3 /NH 3 mixtures. • The potential energy profiles and reaction kinetics of CH 3 COCH 3 /CH 2 CO + NH 2 were explored. • Developed a novel kinetic model for CH 3 COCH 3 /NH 3 mixtures. • Assessed the impact of kinetic calculation results on the overall kinetic model. [ABSTRACT FROM AUTHOR]

Alkyl 2-diazo-3-oxoalkanoates generate alkoxycarbonylketenes, which undergo an electrophilic ring expansion with aziridines to afford alkyl 2-(oxazolin-2-yl)alkanoates in good to excellent yields under microwave heating. The method is a convenient and clean reaction without any activators and catalysts and can be also applied in the synthesis of 2-(oxazolin-2-yl)alkanamides and 1-(oxazolin-2-yl)alkylphosphonates.

Concise synthesis of eight-membered lactones, a kind of medium-sized heterocycles widespread in many bioactive natural products, is highly significant. However, it still remains a challenge due to unfavorable entropic factor and transannular interaction. Herein, we disclose an enantioselective synthesis of eight-membered lactones through a Pd-catalyzed asymmetric (6 +2) dipolar annulation of vinyl oxetanes and α-diazo ketones (20 examples, up to 93% yield and 95:5 er). This reaction features simple operation, mild conditions and good enantiocontrol, especially the challenging chiral all-carbon quaternary stereocenter. A newly developed chiral hybrid P,S ligand and the in-situ photo-generation of ketene dipolarophiles are crucial to this success. [ABSTRACT FROM AUTHOR]

Introduction: In the wake of continued consumer demand despite increasing regulatory scrutiny, there is a need to develop systematic methods for identifying the harm profile of new psychoactive substances derived from hemp. Tetrahydrocannabinol-O (THC-O)-acetate, colloquially known as THCO, is the acetate ester of the principal psychoactive compound in cannabis. The heating of THCO can create ketene gas, which is harmful to the lungs. Materials and Methods: The research team used a multidisciplinary, iterative process to develop a survey to incorporate consumers' perspectives of semisynthetic cannabinoids. The survey was then distributed across the social media platform Reddit to learn about delivery device preferences and associated use styles when consuming THCO. Results: Most participants (74.9%) vaped THCO and one-quarter of participants (24.3%) dabbed THCO and tended to report higher temperatures for dabbing than vaping THCO. A small portion (12.0%) of participants reported concerns regarding ketene risk. Conclusion: As there are multiple variables associated with the formation of ketene, and consumer responses indicate temperatures use that might enable ketene formation, more research is needed to understand the risk profile of hemp-derived substances like THCO. Further studies are needed to understand the how various routes of administration and delivery devices used with THCO may exacerbate the risk of ketene formation and other potential harms.

A versatile asymmetric synthesis of bicyclic pyrazolidinones through alkaloid‐catalyzed formal [3+2]‐ and [3+2+2]‐cycloadditions of ketenes with azomethine imines is described. The methodology was found to be tolerant of ketene and a variety of monosubstituted ketenes (R=alkyl, OAc). The products were formed in good to excellent yields (71–99 % for 24 examples, 39 examples in all), with good to excellent diastereoselectivity in many cases (dr 3 : 1 to 27 : 1 for 22 examples), and with excellent enantioselectivity for most examples (≥93 % ee for 34 products). In the case of most disubstituted ketenes, the reaction proceeded through a [3+2+2]‐cycloaddition to form structurally interesting bicyclic pyrazolo‐oxadiazepinediones with moderate diastereoselectivity (dr up to 3.7 : 1) and as racemic mixtures (3 examples). The method represents the first unambiguous example of an enantioselective reaction between ketenes and a 1,3‐dipole. [ABSTRACT FROM AUTHOR]

Photochemical reactions of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores like a 5,6 dibenzoyl moiety and bulky electron-deficient substituents like phenyl or isopropenyl at the bridgehead position were analyzed for the first time in different solvents and upon irradiation with different wavelengths. In all cases, a regioselective photoinduced 1,5-phenyl migration leading to vinyl ketenes from the more congested site of the molecule to the less congested one has been observed. The ketenes were exceptionally stable both in air and solution. Its stability studies in acetonitrile through time-dependent UV absorption spectra revealed that it remained almost unchanged at least for a couple of weeks.

• Acidic catalyst can reduce the side effects and increase the reaction rate. • The catalyst with 1.5% volume fraction has the best catalytic effect. • The suitable reaction temperature of acetone esterification reaction is 45 °C–55 °C. • The macro reaction kinetics equation was obtained with the conditions of temperature. • Two-step elementary reaction rate was calculated by means of quantum chemistry. Isopropenyl acetate, an important chemical raw material intermediate, has an extremely wide range of applications in chemicals, materials and medicine. In this paper, acetone and ketene are used as raw materials to synthesize isopropenyl acetate under acidic conditions. The process conditions were studied through experiments with one variable, and the effects of the catalyst activity and dosage, the reaction time and the reaction temperature on the yield of isopropenyl acetate were investigated. The optimal reaction conditions were obtained, and macroscopic kinetic equations of esterification reaction was obtained by fitting the experimental data. The mechanism of the reaction was studied by quantum chemistry. The results of experimental and theoretical research can provide theoretical guidance for further expanding experiment and industrial quantitative production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reaction mechanism established for ketene formation from acetic acid. • Identification of a reaction intermediate by combining surface sensitive techniques. • Reaction intermediate structure: ketene bonded via all C and O atoms to the Cu 2 O surface. • Theoretical confirmation of a local surface reorganization in the vicinity of the adsorbate. Ketene, a versatile reagent in production of fine and specialty chemicals, is produced from acetic acid. We investigate the synthesis of ketene from acetic acid over the (3,0;1,1) surface of Cu 2 O(1 0 0) through analysis of the adsorption and desorption characteristics of formic and acetic acids. The results allow us to establish a reaction mechanism for ketene formation. Observations from x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy, and temperature programmed desorption (TPD), supported by a comparison with formic acid results, suggest that acetic acid reacts with Cu 2 O through deprotonation to form acetate species coordinated to copper sites and hydroxylation of nearby surface oxygen sites. For formic acid the decomposition of adsorbed formate species results in desorption of CO 2 and CO while, for acetic acid, high yields of ketene are observed at temperature >500 K. Modeling by density functional theory (DFT) confirms the strong interaction of acetic acid with the (3,0;1,1) surface and the spontaneous dissociation into adsorbed acetate and hydrogen atom species, the latter forming an OH-group. In an identified reaction intermediate ketene binds via all C and O atoms to Cu surface sites, in agreement with interpretations from XPS. In the vicinity of the adsorbate the surface experiences a local reorganization into a c(2 × 2) reconstruction. The total computed energy barrier for ketene formation is 1.81 eV in good agreement with the 1.74 eV obtained from TPD analysis. Our experimental observations and mechanistic DFT studies suggests that Cu 2 O can operate as an efficient catalyst for the green generation of ketene from acetic acid. [ABSTRACT FROM AUTHOR]

Die ersten Beispiele für Lewis‐Basen‐Addukte des Stammboraphosphaketens H2B‐PCO und ihre cyclischen Dimere wurden hergestellt. Eines dieser Addukte zeigt unter milden Bedingungen eine Decarbonylierung und anschließende Insertion des Phosphinidens in die B‐C‐Bindung eines Borols, was in der Bildung sehr seltener Beispiele für 1,2‐Phosphaborinine, B,P‐Isostere von Benzol, resultiert. Die starken Donoreigenschaften dieser 1,2‐Phosphaborinine wurden durch die Synthese ihrer π‐Komplexe mit Metallen der Gruppe 6 bestätigt. [ABSTRACT FROM AUTHOR]

Bibenzyl natural products, such as the amorfrutins, contain a heavily substituted aromatic core and display a diverse range of biological activities (anti-tumor, anti-diabetic, antimicrobial, and antibiotic). In this study, we report unified syntheses of amorfrutin A to D either through total or formal synthesis by employing a dual biomimetic strategy of polyketide aromatization followed by remote terpene functionalization. The key core structures were synthesized from β-keto dioxinone esters through a magnesium(II) mediated regioselective C-acylation, palladium catalyzed decarboxylative allylic rearrangement, and dehydrative cyclization. [ABSTRACT FROM AUTHOR]

Intramolecular [2+2] cycloaddition of ene–ketenes gives either fused‐ring (via normal [2+2] cycloaddition) or bridged‐ring (via cross‐[2+2] cycloaddition) cyclobutanones. For example, terminal ene–ketenes give the fused‐ring cycloadducts, whereas dimethyl‐substituted ene–ketenes furnish bridged‐ring cycloadducts. For monomethyl‐substituted ene–ketenes, both [2+2] cycloadducts are generated. However, there are no systematic theoretical studies on such regiochemistry in the literature. Herein, we report our DFT study on the mechanism and regioselectivity of these intramolecular [2+2] cycloadditions. DFT calculations reveal that both normal and cross‐[2+2] cycloadditions are concerted processes. The normal [2+2] cycloaddition transition state is forming an internal carbocation while the cross‐[2+2] cycloaddition transition state is generating an external carbocation (see Scheme 1 of the paper). On the basis of the relative stability of these carbocations, which is affected by both the tether and the substituent(s) on the alkene, a regiochemistry prediction model is proposed to understand and predict the reaction outcome. [ABSTRACT FROM AUTHOR]

The mechanism of the reaction of ketene with hydroxyl radical has been studied by ab initio CCSD(T)-F12/cc-pVQZ-F12//B3LYP/6-311G(d,p) calculations of the potential energy surface. Temperature- and pressure-dependent reaction rate constants have been computed using the RRKM-Master Equation and transition state theory methods in the temperature range of 300–3000 K and in the pressure range of 0.01–100 atm. Three main channels have been analyzed: through direct abstraction of H atoms or starting with OH addition to the terminal carbon and to the central carbon atoms. Major products identified agree with the recent theoretical studies, however, significant difference was found with the rate constants derived by Xu et al. [13] and Cavallotti et al. [11]. To investigate the impact of the choice of reactions between CH 2 CO and OH radicals on the predicted burning velocities of the flames sensitive to ketene chemistry, namely diacetyl and acetic acid flames, a detailed kinetic mechanism was updated with pertinent reactions suggested in the literature. Then the rate constants of four most important product channels of reaction CH 2 CO + OH forming HCCO + H 2 O, CH 2 OH + CO, CH 3 + CO 2 and CH 2 COOH from the present and from the recent theoretical studies were tested. Good agreement with the burning velocities of diacetyl + air flames was found for the present model, while the expressions from the literature underestimate them. On the contrary, any combination of the rate constants of reactions between ketene and hydroxyl radical overpredicts burning velocities of acetic acid + air flames, which strongly indicates that the kinetic model of acetic acid is most probably incomplete and requires consideration of additional reactions. [ABSTRACT FROM AUTHOR]

A combined analytical, theoretical, and experimental study has shown that the vaping of vitamin E acetate has the potential to produce exceptionally toxic ketene gas, which may be a contributing factor to the upsurge in pulmonary injuries associated with using e-cigarette/vaping products. Additionally, the pyrolysis of vitamin E acetate also produces carcinogen alkenes and benzene for which the negative longterm medical effects are well recognized. As temperatures reached in vaping devices can be equivalent to a laboratory pyrolysis apparatus, the potential for unexpected chemistries to take place on individual components within a vape mixture is high. Educational programs to informof the danger are nowrequired, as public perception has grown that vaping is not harmful. [ABSTRACT FROM AUTHOR]

The Staudinger cycloaddition reaction represents an efficient way to readily afford β‐lactams from ketenes and imines in an asynchronous [2+2] process. Herein, a computational evaluation of the scope of the Staudinger cycloaddition reactions was undertaken by using simplified molecular models. The results pointed out that the kinetics and thermodynamics of the reaction are independent of the substituents of the imine and are essentially determined by the steric and electronic nature of the substituents of the α‐position of the ketene, being the latter the one that exerts a more dominant effect on the global feasibility of the reaction. [ABSTRACT FROM AUTHOR]

The [AgL2]ClO4 complex, where L is ketene S,S-dithioacetal type ligand, is synthesized and characterized using elemental analysis, different spectroscopic techniques (FTIR and NMR) and single crystal X-ray diffraction (SC-XRD). The Ag-atom is coordinated by two oxygen and two sulfur atoms of both bidentate ligands resulting in a distorted square planar environment augmented by two weak contacts with two oxygen atoms from the perchlorate anion. The H⋯H (42.0%), O⋯H (29.7%), C⋯H (10.8%) and S⋯H (11.7%) intermolecular contacts were quantified using Hirshfeld analysis. The PBEPBE and WB97XD methods are the best to predict the Ag–S and Ag–O(L) distances. Natural bond orbital (NBO) analysis showed that each ligand (L) transferred 0.1507 e (exp. 0.1715 e) to Ag-atom while the perchlorate anion lost 0.1748 e (exp. 0.1481 e) to silver {0.5227 e (exp. 0.5088 e)}. The structure aspects of the newly synthesized square planar [AgL2]ClO4 complex, where L is ketene S,S-dithioacetal ligand, were analyzed using different spectroscopic techniques (FT-IR, NMR) and X-ray single crystal structure combined with DFT calculations. [ABSTRACT FROM AUTHOR]

Unprecedented phosphine‐catalyzed [4+1] cycloadditions of allenyl imides have been discovered using various N‐based substrates including methyl ketimines, enamines, and a primary amine. These transformations provide a one‐pot access to cyclopentenoyl enamines and imines, or (chiral) γ‐lactams through two geminal C−C bond or two C−N bond formations, respectively. Several P‐based key intermediates including a 1,4‐(bis)electrophilic α,β‐unsaturated ketenyl phosphonium species have been detected by 31P NMR and HRMS analyses, which shed light on the postulated catalytic cycle. The synthetic utility of this new chemistry has been demonstrated through a gram‐scaling up of the catalytic reaction as well as regioselective hydrogenation and double condensation to form cyclopentanoyl enamines and fused pyrazole building blocks, respectively. [ABSTRACT FROM AUTHOR]

A series of natural product inspired piperidines spiro‐fused with resorcylic, chromenic and chromanic amides were prepared from a general derivative of a N‐Boc‐4‐oxo‐4H‐spiro[benzo[d][1,3]dioxinone‐2,4‐piperidine], which was prepared through biomimetic aromatization of a β,δ‐diketo dioxinone, in turn synthesized from N‐Boc‐4‐piperidone and geraniol using ketene coupling reagents. [ABSTRACT FROM AUTHOR]

As ketene is a crucial intermediate for the high-temperature combustion of oxygenated hydrocarbons in general, an in-depth understanding of its chemistry is a fundamental requirement for the kinetic modeling of bio-based fuels. To gain a profound insight into the decomposition of ketene and subsequent reaction pathways high level ab initio methods were used. DSD-PBEP86/cc-pVTZ level of theory was applied for the geometries and frequencies, while single-point energies were determined at the CCSDT-1a level of theory extrapolated to the basis set limit. The reaction rate parameters for 38 reactions involved in the ketene chemistry including C1 to C4 species like acetylene, ethylene, propyne and allene were computed. For a total of 16 species, the thermochemistry were updated. The calculated rate parameters and the two new species cyclopropenone and 1,4-dioxo-1,3-butadiene were used to update the AramcoMech 3.0 base mechanism, which was then validated against speciation measurements during ketene pyrolysis. A reaction pathway analysis was performed to find the most prominent reactions at the investigated conditions and to discuss the simulation results. A significant improvement in the model's prediction capability was found when applying the newly calculated reaction rate parameter and thermochemical data. [ABSTRACT FROM AUTHOR]

[Display omitted] • Better stabilization of reaction intermediates in 8MR leads to higher activity. • Stronger interaction between ethylene and 8MR results in higher C 2 selectivity. • 12MR would facilitate the further methylation of CH 3 CH 2 CO+ to isopropyl. The origin of high ethylene selectivity in ketene conversion with the HMOR catalyst is revealed using ab initio molecular dynamics simulations, and the microenvironment of catalyst pores of 8-member ring (8MR) and 12MR are found to be playing a crucial role. The higher activity of ketene conversion in 8MR than that in 12MR is because the 8MR side pocket pore microenvironment has a better stabilization effect on reaction intermediates. In addition, the free energy barrier of methylation of ethylene is higher than that of ketene in 8MR, which is due to the stronger interaction between hydrogen in ethylene and the framework of 8MR side pocket, resulting in relatively high C 2 selectivity in 8MR. Similarly, the microenvironment of 12MR would facilitate the further methylation of CH 3 CH 2 CO+ to isopropyl, decreasing the selectivity of ethylene. These results strengthen the importance of understanding microenvironment of HMOR catalyst in improving ethylene selectivity from ketene conversion. [ABSTRACT FROM AUTHOR]

The reaction of 3-oxopropanenitriles with phenyl isothiocyanate in DMF containing KOH afforded the corresponding potassium salts. The latter salts were converted into ketene N,S-acetals upon acidification with hydrogen chloride. The reaction of the ketene N,S-acetals with 2-bromo-1-[5-methyl-1-(p-tolyl)-1H-1,2,3-triazol-4-yl]ethan-1-one or 3-(2-bromoacetyl)-2H-chromen-2-one gave novel thiophenes in good yields. Treatment of the ketene N,S-acetals with hydrazonyl halides afforded 1,3,4-thiadiazoles in good yields. The stereochemistry of the synthesized compounds was studied. [ABSTRACT FROM AUTHOR]

Diesters are important synthetic tools for many biologically active compounds. There are only few methods known for the synthesis of diesters, however the known methods have their own limitations such as substrate scope and drastic reactions conditions. Carbonylation of diazo compounds using Co2(CO)8 as a carbonyl source and generating ketene finds many useful applications in synthetic chemistry. In this regard, we have utilized the methodology to synthesize diesters via nucleophilic addition of alcohol to the ketene generated from diazo compounds using Co2(CO)8 as a carbonyl source and catalyst, under mild reaction conditions. Both aliphatic and aromatic alcohols with electron withdrawing and donating substituents are well tolerated giving rise to a large number of biologically active diesters in good yield, which is further characterized by standard analytical and spectroscopic techniques. [ABSTRACT FROM AUTHOR]

Ketene is an important combustion intermediate, but due to its high reactivity, it has been difficult to validate the corresponding kinetic sub-mechanisms with direct experimental measurements. It is shown here the possibility to refine the ketene combustion model through relevant experimental and modeling analyses of diacetyl [2,3-butadione, (CH 3 CO) 2 ] combustion. The consumption of diacetyl leads to abundant ketene under high-temperature oxidation conditions. From the aspect of the hierarchical structure of a kinetic mechanism, the ketene sub-mechanism acts as a part of a secondary mechanism in the kinetic scheme exploring diacetyl combustion. Therefore, this strategy to understand the kinetics of ketene through studying the combustion chemistry of diacetyl should be based on a good understanding of the diacetyl combustion kinetics. To this end, we investigated the flame chemistry of diacetyl through experimental, modeling, and theoretical approaches. Flame-sampling molecular-beam mass spectrometry with single-photon ionization was employed to measure the detailed chemical structure of a premixed diacetyl flame stabilized at the pressure of 18.0 Torr and the equivalence ratio of 1.2. The quantitative speciation measurements were essential in identifying important reactions in the fuel sub-mechanism, and the corresponding rate coefficients were obtained through high-level theoretical calculations. A kinetic model was proposed, which showed satisfactory performances in predicting the measured flame structure. With the diacetyl flame chemistry better understood, global sensitivity analyses were carried out to suggest conditions for future experiments potentially facilitating the development of ketene sub-mechanisms. [ABSTRACT FROM AUTHOR]

Gold‐catalyzed oxidations of alkynes by N‐oxides offer direct access to reactive α‐oxo gold carbene intermediates from benign and readily available alkynes instead of hazardous diazo carbonyl compounds. Despite various versatile synthetic methods developed based on this strategy, one of the hallmarks of α‐oxo carbene/carbenoid chemistry, that is, the Wolff rearrangement, has not been realized in this context. This study discloses the first examples that show the Wolff rearrangement can be readily realized by α‐oxo gold carbenes oxidatively generated from TBS‐terminated alkynes (TBS=tert‐butyldimethylsilyl). The thus‐generated silylketenes can be either isolated pure or subsequently trapped by various internal or external nucleophiles in one pot to afford α‐silylated carboxylic acids, their derivatives, or TBS‐substituted allenes. [ABSTRACT FROM AUTHOR]

The functionalization is known as a structural modification procedure of fullerenes and carbon nanotubes. This method improves the chemical and physical properties, such as reactivity and solubility. This paper intends to theoretically describe the possibility of functionalization of C20 fullerene with the simplest ketene CH2CO. In the first step, two possible [2+2] and [4+2] cycloaddition reactions between C20 and ketene are considered and simulated theoretically. The results show that the [2+2] reaction is favorable both thermodynamically and kinetically. Also, the IRC analysis of transition states indicates that the reaction takes place via a step-wise mechanism in which a zwitterionic intermediate is generated in a rate-determining step. The solvation effect study based on the CPCM model reveals that by changing the reaction medium from nonpolar to polar, the reaction rate is increased. The NBO analysis and the calculation of global electron density transfer (GEDT) indicate that the reaction involves polar transition states. The calculations of the thermodynamic and kinetic parameters of the [2+2] cycloaddition reaction of bowl C20 with ketene show that this reaction is unfavorable. [ABSTRACT FROM AUTHOR]