Reaction Mode Research Articles

Redox‐Tunable Ring Expansion Enabled By A Single‐Component Electrophilic Nitrogen Atom Synthon

Controllable installation of a single nitrogen atom is central to many major goals in skeletal editing, with progress often gated by the availability of an appropriate N‐atom source. Here we introduce a novel reagent, termed DNIBX, based on dibenzoazabicycloheptadiene (dbabh), which allows the electrophilic installation of dbabh to organic substrates. When indanone β‐ketoesters are aminated by DNIBX, the resulting products undergo divergent ring expansions depending on the mode of activation, producing heterocycles in differing oxidation states under thermal and photochemical conditions. The mechanism of each transformation is discussed, and the different reactivity modes of the indanone‐dbabh adducts are compared to other nitrogenous precursors.

Redox‐Tunable Ring Expansion Enabled By A Single‐Component Electrophilic Nitrogen Atom Synthon

Controllable installation of a single nitrogen atom is central to many major goals in skeletal editing, with progress often gated by the availability of an appropriate N‐atom source. Here we introduce a novel reagent, termed DNIBX, based on dibenzoazabicycloheptadiene (dbabh), which allows the electrophilic installation of dbabh to organic substrates. When indanone β‐ketoesters are aminated by DNIBX, the resulting products undergo divergent ring expansions depending on the mode of activation, producing heterocycles in differing oxidation states under thermal and photochemical conditions. The mechanism of each transformation is discussed, and the different reactivity modes of the indanone‐dbabh adducts are compared to other nitrogenous precursors.

Experimental Insights into the Formation, Reactivity, and Crosstalk of Thionitrite (SNO−) and Perthionitrite (SSNO−)

AbstractHydrogen sulfide (H2S) and nitric oxide (NO) are important gaseous biological signaling molecules that are involved in complex cellular pathways. A number of physiological processes require both H2S and NO, which has led to the proposal that different H2S/NO⋅ crosstalk species, including thionitrite (SNO−) and perthionitrite (SSNO−), are responsible for this observed codependence. Despite the importance of these S/N hybrid species, the reported properties and characterization, as well as the fundamental pathways of formation and subsequent reactivity, remain poorly understood. Herein we report new experimental insights into the fundamental reaction chemistry of pathways to form SNO− and SSNO−, including mechanisms for proton‐mediated interconversion. In addition, we demonstrate new modes of reactivity with other sulfur‐containing potential crosstalk species, including carbonyl sulfide (COS).

Semiconductor WO3 thin films deposited by pulsed reactive magnetron sputtering

A pulsed reactive magnetron sputtering system with a tungsten target and a gas mixture of argon and oxygen was investigated as a source for the deposition of semiconductor WO3 thin films on soda lime glass substrates and on the glass with transparent conductive SnO2:F (FTO) electrode. The reactive sputtering process was performed in HiPIMS mode with low pulse repetition frequency fp ≈ 50–100 Hz and short pulse duration in HiPIMS discharge Ton = 100 μs. The second mode investigated was the mid-frequency (MF) magnetron discharge with pulse frequency fp = 40 kHz and pulse length Ton = 15 μs. The plasma parameters were investigated for both HiPIMS and MF modes using the planar RF probe operating at the frequency fprobe = 350 kHz and the grid QCM with biased collector electrode. Ion density ni and tail electron temperature (Te) were determined in both pulsed reactive magnetron sputtering discharge modes with time resolution. The maximum value ni ≈ 5 · 1017 m−3 was found in the reactive HiPIMS mode, and the maximum value ni ≈ 7 · 1016 m−3 was found in the reactive MF (40 kHz) mode. The degree of ionization of sputtered particles in reactive HiPIMS was determined for different values of (QO2) and was found to be in the range of ri ≈ 0.1–0.3. The deposition rate determined by QCM in reactive HiPIMS was practically independent on (QO2), but in the case of reactive MF, the measured deposition rate decreased significantly with increasing (QO2). The WO3 films deposited in both modes have a predominantly monoclinic crystal structure. The light and dark conductivity and the light/dark conductivity ratio (Ld) were measured under dark conditions and UV light illumination. At higher (QO2), the maximum value of Ld ≈ 300 was found for MF deposited WO3 and the maximum value of Ld ≈ 30 was found for HiPIMS deposited WO3. The photoelectrochemical measurement of WO3 deposited on FTO electrodes confirmed the n-type conductivity, and these films functioned as photoanodes in photoelectrochemical cells. MF deposited WO3 films systematically exhibited slightly higher photocurrents than HiPIMS deposited WO3. It was shown that these optimum photocurrents for HiPIMS and MF were found at QO2 ≈ 80 sccm and could not be improved by further increasing of (QO2).

The Effect of Intramolecular Proton Transfer on the Mechanism of NO Reduction to N2O by a Copper Complex: A DFT Study.

DFT calculations were performed to explore the mechanism underlying the reduction of NO to N2O by a CuI complex. A nitrosyl complex reacts with another NO molecule and the CuI complex, leading to the formation of a dicopper-hyponitrite complex (Cu2N2O2). The first steps follow a common pathway until the formation of the intermediate [CuII-N2O2]+, after which the reaction pathway diverges into three Cu2N2O2 species: κ2-N,N', κ2-O,O', and κ3-N,O,O'. These species yield different products along their respective reaction pathways. In the case of the κ2-N,N' and κ3-N,O,O' species, the subsequent steps involve a methanol-mediated proton transfer and N-O bond cleavage, resulting in the generation of N2O and [CuII-OH]+. Conversely, for the κ2-O,O' species, two proton transfers occur without N-O bond cleavage, leading to the formation of H2N2O2 and [CuII]2+. H2N2O2 spontaneously converts into N2O and H2O. These computational results elucidate how the coordination mode of hyponitrite influences reactivity and provide insights into NO reduction via proton transfer. Notably, switching of the N2O2 coordination mode to metal ions from N to O was not required, offering insights for more efficient NO reduction strategies in the future.

Theoretical Perspective on the Sensing Mechanism of a Pyrazinium‐Based Fluorescent Probe Towards 2,4,6‐Trinitrophenol

ABSTRACTRapid detection of chemical explosives plays a critical role in national security and public safety. An in‐depth study of the sensing mechanism is particularly urgent for the development of highly efficient, sensitive, and selective chemical sensors for the precise detection of chemical explosives. Density functional theory (DFT) and time‐dependent DFT approaches were used in this work to examine the sensing mechanism of a novel fluorescent probe 1‐benzyl‐3,5‐di (thiophen‐2‐yl)pyrazin‐1‐ium bromide (BTPyz) for the detection of 2,4,6‐trinitrophenol (TNP). A comprehensive theoretical exploration was carried out, and a different interaction mode between the probe and TNP from that in the original experiment was proposed. The π–π stacking was established to be the recognition interaction between BTPyz and TNP anion, and the active site was determined from the three potential sizes according to the Gibbs free energy analysis results. The rationality of the reaction mode and the π–π stacking product between the BTPyz and TNP (BTN) was further confirmed by the fluorescence properties (absorption and emission spectra). According to the findings of frontier molecular orbitals (FMOs), photoinduced electron transfer (PET) is the intrinsic mechanism through which TNP quenches the probe's fluorescence.

Asymmetric Synthesis of Dialkyl Carbinols by Ni-Catalyzed Reductive-Oxidative Relay of Distinct Alkenes.

Enantioenriched unsymmetric dialkyl carbinol derivatives are of importance in natural products, bioactive molecules, and functional organic materials. However, the catalytic asymmetric synthesis of dialkyl carbinol derivatives remains challenging due to the similar steric and electronic properties of two alkyl substituents. Herein, an unprecedented synthesis of chiral dialkyl carbinol ester derivatives from Ni-catalyzed reductive-oxidative relay cross-coupling of two alkenes is developed for the first time. The reaction features the use of enol esters and unactivated alkenes as two different alkyl equivalents to undergo head-to-tail and enantioselective alkyl-alkyl cross-coupling. The reaction undergoes two-electron reduction and single electron oxidation in the presence of both reductants and oxidants. The use of an allyl bromide as single electron acceptor is crucial for the success of this non-trivial asymmetric cross-coupling, providing a new reaction mode for asymmetric alkyl-alkyl bond-forming event in the absence of stoichiometric alkyl electrophiles.

Gold-Catalyzed Cope Rearrangements

Over decades, Cope rearrangements have attracted significant research interest in the field of synthetic organic chemistry relying on their ability to undergo stereoselective structural reorganization. Despite substantial progress, the development of this field remained confined to the use of parent 1,5-hexadienes. Against the backdrop of classical Cope reaction, we reported the utilization of unconventional 1,6-heptadienes to develop the arylative Cope rearrangement by harnessing the interplay between the π-activation and cross-coupling reactivity mode of gold complexes. Several mechanistic investigations such as 31P NMR study, HRMS analysis, cross-over experiment, control experiments were performed to support the proposed cyclization-induced [3,3]-rearrangement mechanism in arylative Cope reaction.

Recent Progress on Organic Electron Donors (OEDs) Enabled Radical Reactions

Over the past few decades, organic transformations facilitated by small organic molecules have witnessed considerable advancements. Small organic molecules have been widely applied to the construction of various skeletons. However, reduction as one of the fundamental reactions is generally initiated by metal‐containing reducing agents, although the initial progress of organic electron donors (OEDs) enabled reductive cleavage of some chemical bonds had been achieved in 1990s. Due to their structural diversity and tunability, OEDs can overcome the limitations of metal‐based reducing agents, such as low selectivity and poor functional group tolerance as well as the environmental problems caused by substantial inorganic waste after reactions. Building on a brief historical overview of OED research, this review focuses on the rencent advancements of the OEDs promoted radical reactions. It covers the reduction of C‐X (X =C, O, N etc.) single bonds, radical cyclization, intermolecular radical addition to unsaturated bonds, radical coupling, functionalization of aromatics, and C‐H bond activation. Additionally, the mechanistic insights of the typical reactions are highlighted for well understanding of the reaction mode involving OEDs.

Effect of Reactive Magnetron Sputtering Modes (DCMS, HIPIMS, and DC + HIPIMS) on the Properties of Copper Oxide Films

Effect of Reactive Magnetron Sputtering Modes (DCMS, HIPIMS, and DC + HIPIMS) on the Properties of Copper Oxide Films

Oxenoid reactivity enabled by targeted photoactivation of periodate.

The chemistry of low-valent intermediates continues to inspire new modes of reactivity across synthetic chemistry. But while the generation and reactivity of both carbenes and nitrenes are well-established, difficulties in accessing oxene, their oxygen-based congener, has severely hampered its application in synthesis. Here, we report a conceptually novel approach to oxene generation through the violet-light photolysis of tetrabutylammonium periodate. By revealing an unexpected geometric change upon periodate photoexcitation that facilitates intersystem crossing, we have exploited the near-barrierless dissociation of triplet periodate into oxene. Under these operationally simple conditions, we have demonstrated the epoxidation of a wide range of substituted olefins, revealing unprecedented functional group compatibility. By overcoming the historic challenges associated with employing oxene as an intermediate in organic chemistry, we believe that this platform will inspire the development of new reactive oxygen-based methodologies across industry and academia.

Oxenoid reactivity enabled by targeted photoactivation of periodate

The chemistry of low‐valent intermediates continues to inspire new modes of reactivity across synthetic chemistry. But while the generation and reactivity of both carbenes and nitrenes are well‐established, difficulties in accessing oxene, their oxygen‐based congener, has severely hampered its application in synthesis. Here, we report a conceptually novel approach to oxene generation through the violet‐light photolysis of tetrabutylammonium periodate. By revealing an unexpected geometric change upon periodate photoexcitation that facilitates intersystem crossing, we have exploited the near‐barrierless dissociation of triplet periodate into oxene. Under these operationally simple conditions, we have demonstrated the epoxidation of a wide range of substituted olefins, revealing unprecedented functional group compatibility. By overcoming the historic challenges associated with employing oxene as an intermediate in organic chemistry, we believe that this platform will inspire the development of new reactive oxygen‐based methodologies across industry and academia.

Formation and Mechano-Chemical Properties of Chromium Fluorides Originated from the Deposition of Carbon-Chromium Nanocomposite Coatings in the Reactive Atmosphere (Ar + CF4) during Magnetron Sputtering

The literature analysis did not indicate any studies on fluorination tests of carbon nanocomposite coatings doped with transition metals in a form of nanocrystalline metal carbide in amorphous carbon matrix (nc-MeC/a-C). As a model coating to investigate the effect of fluorination in a tetrafluoromethane (CF4) atmosphere, a nanocomposite carbon coating doped with chromium-forming nanocrystals of chromium carbides in a-C matrix (nc-CrC/a-C) produced by magnetron sputtering from graphite targets and using a Pulse-DC type medium frequency power supply was chosen. After the deposition of the gradient chromium carbonitride (CrCN) adhesive sublayer, the fluorination of the main coating was conducted in a reactive mode in an (Ar + CF4) atmosphere at various CF4 content. It was observed that the presence of CF4 in the atmosphere resulted in a reduced amount of chromium carbides formed in favor of chromium fluorides. Thus far, this is an observation that seems unnoticed by the carbon coatings researchers. Fluorine was assumed to bond much more readily to carbon than to chromium, due to the stability of tetrafluoromethane (CF4). The opposite seems to be true. The mechanical properties (nano-hardness and Young’s modulus) and tribological properties in the ‘pin-on-disc’ friction pair are presented, along with the analysis of bonds occurring between chromium, carbon, and fluorine by means of X-ray photoelectron spectroscopy (XPS).

Hydrodeoxygenation of Glycerol to Propene Over Molybdenum and Niobium Phosphate Catalysts

AbstractIn single‐step conversion of glycerol to propene, the intricate catalytic pathways with molybdenum and niobium catalysts remain elusive. While these catalysts can effectively accelerate the hydrogenolytic cleavage of the glycerol CO bonds, resulting in a high selectivity to propene, the routes have not been thoroughly studied. This study explores the reaction routes and the role hydrogen plays in determining the product distribution. The hydrodeoxygenation (HDO) of glycerol was investigated using various glycerol purities in both batch and continuous reaction modes. Remarkably, Mo(PO4)x and Nb(PO4)x demonstrated catalytic performance with raw glycerol, indicating that impurities had no detrimental effect on the catalyst's activity. In batch mode, a propene selectivity of 53% was achieved over Mo(PO4)x as the catalyst, highlighting the catalyst's stability under these conditions. In continuous operation, the highest product selectivity to propene (12%) was observed at low temperatures (573 K), while more C2 to C6 alkanes were formed at increased temperatures (623 and 673 K). Whereas a hydrogen atmosphere promotes formation of 2‐propenol, as primary precursor to propene, an inert atmosphere leads to increased formation of propanal and dissociation products. Our work has elucidated new routes to upcycle biorenewable glycerol to propene over Mo(PO4)x and Nb(PO4)x catalysts.

Interception of Alkynyl Tetracoordinate Borons with Sulfur Electrophiles beyond the Zweifel Pathway

Zweifel reaction is a powerful strategy to construct olefins from alkenyl tetracoordinate borons in organoboron chemistry, however, it usually only involves one functional group migration and then undergoes an elimination process affording alkenes or alkynes exclusively. Herein, we disclose several intriguing interception of alkynyl tetracoordinate borons with sulfur electrophiles. Wherein, the substituted benzothiophenes are accessed by consecutive 1,2‐migrations and intramolecular electrophilic substitution, meanwhile, the challenging and elusive five/four‐membered boracycles are easily assembled, and an approach to alkenyl sulfides with good stereoselectivity was developed as well. Moreover, by adding readily available deuterium sources, the tetrasubstituted deuterated alkenyl sulfides with high deuteration rates are constructed. These protocols not only improve atom economy by prohibiting the elimination of Zweifel intermediate, but also enriches the reaction modes of alkynyl tetracoordinate borons achieving versatile value‐added sulfur‐containing molecules. Mechanistic investigations illustrate that dichlorosulfoxide (SOCl2) and dialkylaminosulfur trifluoride‐type reagents (DAST‐type) as surfur sources could promote dual 1,2‐aryl migration of alkynyl tetracoordinate borons, which are distinct from traditional Zweifel reaction, and the regulation of steric hindrance could also make four‐membered boracycles and alkenyl sulfides feasible. And these transformations feature novel reaction modes and unusual reaction mechanisms with valuable products in high efficiency.

Interception of Alkynyl Tetracoordinate Borons with Sulfur Electrophiles beyond the Zweifel Pathway.

Zweifel reaction is a powerful strategy to construct olefins from alkenyl tetracoordinate borons in organoboron chemistry, however, it usually only involves one functional group migration and then undergoes an elimination process affording alkenes or alkynes exclusively. Herein, we disclose several intriguing interception of alkynyl tetracoordinate borons with sulfur electrophiles. Wherein, the substituted benzothiophenes are accessed by consecutive 1,2-migrations and intramolecular electrophilic substitution, meanwhile, the challenging and elusive five/four-membered boracycles are easily assembled, and an approach to alkenyl sulfides with good stereoselectivity was developed as well. Moreover, by adding readily available deuterium sources, the tetrasubstituted deuterated alkenyl sulfides with high deuteration rates are constructed. These protocols not only improve atom economy by prohibiting the elimination of Zweifel intermediate, but also enriches the reaction modes of alkynyl tetracoordinate borons achieving versatile value-added sulfur-containing molecules. Mechanistic investigations illustrate that dichlorosulfoxide (SOCl2) and dialkylaminosulfur trifluoride-type reagents (DAST-type) as surfur sources could promote dual 1,2-aryl migration of alkynyl tetracoordinate borons, which are distinct from traditional Zweifel reaction, and the regulation of steric hindrance could also make four-membered boracycles and alkenyl sulfides feasible. And these transformations feature novel reaction modes and unusual reaction mechanisms with valuable products in high efficiency.

Electrochemical conversion of CO2 via C−X bond formation: recent progress and perspective

With the depletion of traditional energy sources and growing environmental concerns, it is becoming increasingly urgent to develop green, low-emission renewable energy technologies to replace fossil fuel-driven methods that emit carbon dioxide (CO2). Currently, the electrochemical production of high-value-added chemicals and fuels from CO2 has aroused great interest from scientists. However, to make full use of CO2 for the preparation of chemicals, it is necessary to expand the range of electrosynthesis methods, in particular by expanding reaction pathways through the reaction of CO2 with different substrates. In general, CO2 can form new covalent bonds with substrate molecules through the formation of C−X bonds, including C−H, C−C, C−N, C−O, and C−S bonds, which would expand the range of possible products by diversifying the reaction pathway. In this review, we focus on the research progress in electrochemical conversion of CO2 through C−X bond formation. We start by examining fundamentals of the reactions and summarizing the reaction modes. Next, we discuss the electrosynthesis of C−X bonds (C−H, C−C, C−N, C−O, C−S) using CO2 and different substrate molecules. Finally, (i) strategies for the design and activity optimization of catalyst materials and (ii) the future development of forming five types of bonds from CO2 and small molecules are discussed, along with an outlook on their future research prospects.

Computational Study on Flavin-Catalyzed Aerobic Dioxygenation of Alkenyl Thioesters: Decomposition of Anionic Peroxides.

Flavin-dependent catalysts are widely applied to aerobic monooxygenation/oxidation reactions. In contrast, flavin-catalyzed aerobic dioxygenation reactions exhibit higher atomic economy but are less reported, not to mention the relevant mechanistic studies. Herein, a density functional theory study on flavin-catalyzed aerobic epoxidation-oxygenolysis of alkenyl thioesters was performed for the first time. Different from the previous mechanistic proposal, a pathway featuring two catalytic stages, monoanionic flavin-C(4a)-peroxide/oxide intermediates, and a reverse reaction sequence (epoxidation goes prior to oxygenolysis) was revealed. In comparison, the pathways involving dianionic flavin catalysts, monoanionic flavin-N(5)-(hydro)peroxide/C(10a)-peroxide, or neutral flavin-C(4a)-hydroperoxide/hydroxide/N(5)-oxide, and the pathways where oxygenolysis goes prior to epoxidation are less favored. Epoxidation goes through intramolecular substitution of the O-O bond of anionic flavin-C(4a)-peroxide by β-carbon, while the resulting flavin-C(4a)-oxide accomplishes the oxygenolysis. Furthermore, two other reaction modes, i.e., concerted O-O cleavage/1,2-shift of α-substituents and dyotropic rearrangement were discovered for the decomposition of other anionic peroxides, and preliminary rules were summarized for understanding the chemoselectivity for this process. This study sheds light on the different reaction features of numerous flavin-dioxygen derivatives, providing deeper insights into flavin-catalyzed dioxygenation reactions, and is expected to inspire experimental design based on unconventional anionic peroxides.

Manganese-Catalyzed Cycloalkene Ring Expansion Synthesis of Azaheterocycles.

Herein, a Mn catalytic protocol has been developed for the cycloalkene ring expansion synthesis of azaheterocycles, allowing broad-substrate-scope access to pyridine and isoquinoline derivatives. The initial monoaddition of an azidyl radical to alkene and further as-generated C-radical addition to O2, followed by intramolecular rearrangement and aromatization, showcase a distinct Mn-catalyzed radical reactivity mode. The reaction features a short reaction time and a broad substrate scope, with applications demonstrated in complex structure elaboration and gram-scale vismodegib synthesis.

A new intelligent scheduler to improve reactive OpenFlow communication in SDN-based IoT data streams

The significant adoption of the Internet of Things (IoT) has increased the challenges in providing adequate IoT infrastructures meeting essential requirements, such as dynamicity networks and low latency. In this context, the Software-Defined Networking (SDN) paradigm and the OpenFlow protocol provide new possibilities for IoT networks. Based on the global view of network elements enabled by the Controller, SDN allows the programmability and control of the infrastructure according to the actual demands of applications. The OpenFlow protocol defines the exchange of messages between controllers and switches, enabling communication and network control. OpenFlow implements three operation modes: proactive, reactive, and hybrid. Due to the dynamic characteristic of the IoT data stream, the reactive mode is mainly used and indicated for IoT environments. As the OpenFlow controller installs rules dynamically, there is no need to know the network’s sources, destinations, and paths in advance. Although reactive mode introduces dynamicity, it can generate additional delay due to switch-controller communication. This delay increases the response time of the IoT data stream. We propose an SDN-IoT scheduler based on Deep Neural Networks (DNN) to predict the time between data stream changes from IoT devices and install rules in advance, suppressing the existing delay in reactive mode. The proposal automatically uses previous data from the IoT data stream to calculate the time of the following communication from IoT devices. Our results indicate that predicting IoT data stream changes and installing OpenFlow rules in advance reduced about 51% of communications response time.