Relative Reactivity Research Articles

Analysis of Photochemical Characteristics and Sensitivity of Atmospheric Ozone in Nanjing in Summer

Tropospheric ozone (O3) is mainly produced through a series of photochemical reactions of nitrogen oxides (NOx) and volatile organic compounds (VOCs). The reaction process presents complex non-linear relationships. In this work, datasets of atmospheric ozone and volatile organic compounds (VOCs) observed during the summer of 2018 in Nanjing were used. Combining with the framework for 0-D atmospheric model-master chemical mechanism (F0AM-MCM), the characteristics of photochemical reactions for ozone (O3) formation in Nanjing during the O3 episode days and non-episode days were investigated. The results showed that φ(O3) and φ(TVOCs) in the O3 episode days were 47.8×10-9 and 49.0×10-9, respectively, exceeding those in the non-episode days by factors of 1.8 and 1.6. Furthermore, F0AM, the empirical kinetic modeling approach (EKMA), and relative incremental reactivity (RIR) were utilized for the calculation of ozone chemical sensitivity. It was found that O3 formation in Nanjing was attributed to both VOCs and NOx limitation. In addition, the modeled ·OH and HO2 concentrations in the O3 episode days were 1.3 and 1.8 times higher than those in the non-episode days. The higher formation and loss rates of ·OH and HO2 were also found during O3 episode days. These findings reflected that the enhancements of atmospheric oxidation capacity resulted in increased production rates of O3, providing an explanation for the enhancements of O3 concentrations in Nanjing during the O3 episode days. The findings also improved the understanding of the O3 photochemical characteristics over Nanjing in the summer during the O3 episode days.

The effect of the unsaturation degree on the gas-phase autoignition of methyl oleate and methyl linoleate: Experimental and modeling study

As the product of transesterification between various oils and alcohols, biodiesel exhibits characteristics of renewability and a wide range of raw materials. The ignition delay times (IDTs) of methyl oleate (MEOLE) and methyl linoleate (MLINO), the primary constituents of biodiesels, were measured in a heated rapid compression machine (RCM) to investigate the impact of CC double bond on the reactivity and autoignition characteristics. The experiment was conducted under two pressures of 8 bar and 10 bar at an equivalence ratio of 0.3–0.8 and a temperature range of 800–1000 K. The qualitative investigation unveiled the influence of compressed pressure, equivalence ratio, and oxygen mole fraction on the IDT of MEOLE and MLINO under varying compressed temperatures. Besides, a comparison of the IDTs for two fuels with different unsaturation degrees under identical conditions revealed that MEOLE exhibited greater reactivity at low temperatures compared to MLINO, while the increase in unsaturation degree can moderate and enhance reactivity at high temperatures. Moreover, three kinetic models in the literature were validated against the newly measured IDTs. The results indicate that the detailed lumped kinetic model exhibits better predictive capacity compared to other models, but it still underestimates the reactivity of MEOLE and MLINO within the investigated temperature range. Subsequently, the detailed kinetic model was optimized based on sensitivity analysis, resulting in excellent agreement between the predicted values of the optimized model and experimental data. Furthermore, accurate predictions were made regarding the relative reactivity changes of MEOLE and MLINO with temperature. Finally, different types of experimental data in the literature were employed to validate the optimized model, yielding satisfactory results.

Composition and Reactivity of Volatile Organic Compounds and the Implications for Ozone Formation in the North China Plain

Enhanced ozone (O3) pollution has emerged as a pressing environmental concern in China, particularly for densely populated megacities and major city clusters. However, volatile organic compounds (VOCs), the key precursors to O3 formation, have not been routinely measured. In this study, we characterize the spatial and temporal patterns of VOCs and examine the role of VOCs in O3 production in five cities (Dongying (DY), Rizhao (RZ), Yantai (YT), Weihai (WH), and Jinan (JN)) in the North China Plain (NCP) for two sampling periods (June and December) in 2021 through continuous field observations. Among various VOC categories, alkanes accounted for the largest proportion of VOCs in the cities. For VOCs, chemical reactivities, aromatic hydrocarbons, and alkenes were dominant contributors to O3 formation potential (OFP). Unlike inland regions, the contribution to OFP from OVOCs increased greatly at high O3 concentrations in coastal regions (especially YT). Model simulations during the O3 episode show that the net O3 production rates were 27.87, 10.24, and 10.37 ppbv/h in DY, RZ, and JN. The pathway of HO2 + NO contributed the most to O3 production in JN and RZ, while RO2 + NO was the largest contributor to O3 production in DY. The relative incremental reactivity (RIR) revealed that O3 formation in DY was the transitional regime, while it was markedly the VOC-limited regime in JN and RZ. The O3 production response is influenced by NOx concentration and has a clear daily variation pattern (the sensitivity is greater from 15:00 to 17:00). The most efficiencies in O3 reduction could be achieved by reducing NOx when the NOx concentration is low (less than 20 ppbv in this study). This study reveals the importance of ambient VOCs in O3 production over the NCP and demonstrates that a better grasp of VOC sources and profiles is critical for in-depth O3 regulation in the NCP.

Photochemical Mechanism and Control Strategy Optimization for Summertime Ozone Pollution in Yining City

To explore the formation mechanism of the ozone （O3） and emission reduction strategy in a northwestern city， an extensive field campaign was conducted in summertime in 2021 in Yining City， in which the 0-D box model incorporating the latest explicit chemical mechanism （MCMv3.3.1） was applied for the first time to quantify the O3-NOx-VOCs sensitivity and formulate a precise O3 control strategy in this city. The results showed that： ① the three indicators ［i.e.， O3 formation potential （OFP）， ·OH reaction rate （k·OH）， and relative incremental reactivity （RIR）］ jointly indicated that alkenes， oxygenated volatile organic compounds （OVOCs）， and aromatics were the highest contributors among anthropogenic volatile organic compounds （AVOC） to O3 formation， and the contribution of biogenic volatile organic compounds （BVOC） also could not be ignored. Additionally， the results based on RIR calculation implied that that the acetaldehyde， ethylene， and propylene were the most sensitive individual VOCs species in Yining City. ② The in-situ photochemical O3 variations were primarily influenced by the local photochemical production and export process horizontally to downwind areas or vertically to the upper layer， and the reaction pathways of HO2·+ NO and ·OH + NO2 contributed the most to the gross Ox photochemical production （60%） and photochemical destruction production （53%）， respectively. Hence， the reduction in local emissions for O3 precursors was more essential to alleviate O3 pollution in this city. ③ The outcome based on RIR（NOx） / RIR（AVOC） and EKMA jointly suggested that the photochemical regime in this city can be considered a transitional regime that was also nearly a VOCs-limited regime. Detailed mechanism modeling based on multiple scenarios further suggested that the NOx and VOCs synergic emission reduction strategies was helpful to alleviate O3 pollution. These results are useful to provide policy-related guidance for other cities facing similar O3 pollution in northwest China.

Self-Assembled FeIII-TAML-Based Magnetic Nanostructures for Rapid and Sustainable Destruction of Bisphenol A.

This study focused on constructing iron(III)-tetraamidomacrocyclic ligand (FeIII-TAML)-based magnetic nanostructures via a surfactant-assisted self-assembly (SAS) method to enhance the reactivity and recoverability of FeIII-TAML activators, which have been widely employed to degrade various organic contaminants. We have fabricated FeIII-TAML-based magnetic nanomaterials (FeIII-TAML/CTAB@Fe3O4, CTAB refers to cetyltrimethylammonium bromide) by adding a mixed solution of FeIII-TAML and NH3·H2O into another mixture containing CTAB, FeCl2 and FeCl3 solutions. The as-prepared FeIII-TAML/CTAB@Fe3O4 nanocomposite showed relative reactivity compared with free FeIII-TAML as indicated by decomposition of bisphenol A (BPA). Moreover, our results demonstrated that the FeIII-TAML/CTAB@Fe3O4 composite can be separated directly from reaction solutions by magnet adsorption and reused for at least four times. Therefore, the efficiency and recyclability of self-assembled FeIII-TAML/CTAB@Fe3O4 nanostructures will enable the application of FeIII-TAML-based materials with a lowered expense for environmental implication.

3 + 2] Cycloaddition of nitrile oxides to dichloropropenes and 1,3‐dichlorobut‐2‐ene: A regioselectivity issue

AbstractThe reaction of nitrile oxides with 2,3‐dichloroprop‐1‐ene, 1,3‐dichloroprop‐1‐ene, and 1,3‐dichlorobut‐2‐ene leads to 5‐(chloromethyl)isoxazoles, 4‐(chloromethyl)isoxazoles, or to mixtures of both regioisomers. The direction of cycloaddition and reactivity of substrate is determined by the steric hindrance at the terminal carbon atom of the alkene double bond. It has been found that the isomeric products of cycloaddition of nitrile oxides to 1,3‐dichloropropene have significantly different dehydrochlorination capabilities. The experimental data on the regioselectivity of cycloaddition and the relative reactivity of substrates are in agreement with the results of quantum chemical calculations.

Comparative analysis for the impacts of VOC subgroups and atmospheric oxidation capacity on O3 based on different observation-based methods at a suburban site in the North China Plain

The persistent O3 pollution in the Beijing-Tianjin-Hebei (BTH) region remains unresolved, largely due to limited comprehension of O3-precursor relationship and photochemistry drivers. In this work, intraday O3 sensitivity evolution from VOC-limited (volatile organic compound) regime in the forenoon to transition regime in the late afternoon was inferred by relative incremental reactivity (RIR) in summer 2019 at Xianghe, a suburban site in BTH region, suggesting that VOC-focused control policy could combine with stringent afternoon NOx control. Then detailed impacts of VOC subgroups on O3 formation were further comprehensively quantified by parametric OH reactivity (KOH), O3 formation potential (OFP), as well as RIR weighted value and O3 formation path tracing (OFPT) approach based on photochemical box model. O3 episode days corresponded to stronger O3 formation, depicted by higher KOH (10.4 s−1), OFP (331.7 μg m−3), RIR weighted value (1.2), and F(O3)-OFPT (15.5 ppbv h−1). High proportions of isoprene and OVOCs (oxygenated VOCs) to the total KOH and the OFPT method were demonstrated whereas results of OFP and RIR-weighted presented extra great impacts of aromatics on O3 formation. The OFPT approach captured the process that has already happened and included final O3 response to the original VOC, thus reliable for replicating VOC impacts. The comparison results of the four methods showed similarities when utilizing KOH and OFPT methods, which reveals that the potential applicability of simple KOH for contingency VOC control and more complex OFPT method for detailed VOC- and source-oriented control during policy-making. To investigate propulsion of VOC-involved O3 photochemistry, atmospheric oxidation capacity (AOC) was quantified by two atmospheric oxidation indexes (AOI). Both AOIp_G (7.0 × 107 molec cm−3 s−1, potential AOC calculated by oxidation reaction rates) and AOIe_G (8.5 μmol m−3, estimated AOC given redox electron transfer for oxidation products) were stronger on O3 episode days, indicating that AOC promoted the radical cycling initiated from VOC oxidation and subsequent O3 production. Result-oriented AOIe_G reasonably characterized actual AOC inferred by good linear correlation between AOIe_G and O3 concentrations compared to process-oriented AOIp_G. Therefore, with continuous NOx abatement, AOIe_G should be considered to represent actual AOC, also O3-inducing ability.

Degradation kinetics of sugars (glucose and xylose), amino acids (proline and aspartic acid) and their binary mixtures in subcritical water: Effect of Maillard reaction

A systematic kinetic study was conducted in subcritical water medium in the temperature range from 150 to 200 °C for pure glucose, xylose, proline and aspartic acid as well as binary mixtures of sugars + amino acids to understand the reaction kinetics and interactions among biomass components and to discern the influence of Maillard reaction (MR) on the overall reaction kinetics.The main degradation products identified for glucose and xylose were the respective dehydration products, hydroxymethyl furfural and furfural, yielding an increasing solid residue with temperature (15.9 wt% at 200 °C) with an augmented heating value. The degradation of sugars and amino acids in binary systems was faster compared to pure compounds due to MR and the production of dehydration products was delayed when considering total sugar conversion. Higher relative reactivity in MR was observed for xylose over glucose showing also higher antioxidant activity.

Functional correlates of a novel 8-factor model of PTSD in U.S. military veterans: Results from the National Health and Resilience in Veterans Study

Emerging evidence indicates that more nuanced models of posttraumatic stress disorder (PTSD) may better capture the condition's symptom structure. Recent theoretical and empirical work suggest that an 8-factor model of PTSD with separate internally- (e.g. flashbacks) and externally- (e.g. trauma-cue related physiological reactivity) generated intrusive symptom clusters may advance understanding of PTSD and its treatment and course. However, the model's functional and clinical significance still requires evaluation. To this end, we analyzed data from the National Health and Resilience in Veterans Study, a nationally representative sample of 3847 trauma-exposed U.S. military veterans. Multivariable regressions were performed to assess the relationship between the 8 PTSD symptom clusters, assessed using the PTSD Checklist for DSM-5, and clinical and functional measures. Results revealed that externally-generated intrusions were associated with higher odds of current depression and anxiety and worse mental, cognitive, and psychosocial functioning. Anhedonia (e.g., loss of interest in enjoyable activities) symptoms were associated with all the correlates tested, while negative affect (e.g., having strong negative feelings such as fear) symptoms were associated with all measures except depression. Avoidance symptoms were associated with lower odds of current anxiety while externalizing behavior symptoms were linked to higher odds of suicidal ideation. Anxious arousal symptoms were associated with lower odds of suicidal ideation but higher odds of PTSD-related impairment/distress, while dysphoric arousal symptoms were associated with higher odds of current depression, PTSD-related impairment/distress and worse mental and cognitive functioning. Results suggest that a more nuanced 8-factor model of PTSD symptoms may help inform understanding of the clinical and functional correlates of this multi-faceted disorder.

Anaerobic photocyclization of ortho‐dialkylamino substituted stiff‐stilbenes

AbstractThe photocyclization of diarylethenes toward polycyclic aromatic hydrocarbons and analogs has been well‐documented. However, stiff‐stilbene was reported to be inactive, and examples of photocyclization‐induced deamination remain unknown. Here, we report that ortho‐(N,N‐dimethylamino)‐stiff‐stilbene (1a) undergoes efficient photocyclization‐induced deamination, forming the dicyclopenta‐fused phenanthrene (DCPP) with good yield (65%) under anaerobic conditions. The relative reactivities of stiff‐stilbenes with different o‐amino substituents (1b–1g) or with an o‐methoxy (1h) group, and those of o‐(N,N‐dimethylamino)stilbenes (2a and 2aMe), provide insights into the substituent and structural effects.

Mercury binding to proteins disclosed by ESI MS experiments: The case of three organomercurials

Solution interactions of three organomercury compounds, i.e., methylmercury chloride, thimerosal and phenylmercury acetate, with a group of biochemically relevant proteins, namely cytochrome c (Cyt c), ribonuclease A (RNase A), carbonic anhydrase I (hCA I), superoxide dismutase (SOD), and serum albumin (HSA), were investigated using an established ESI MS approach. Temporal analysis of sample aliquots provided insight into the binding kinetics, while comparative analysis of the obtained mass spectra disclosed adduct formation of each mercurial with the tested proteins and the relative abundance of the species. The three organomercurials bind, exclusively and tightly, to free cysteine residues as no binding was observed in the case of proteins lacking such groups. hCA I, SOD and HSA formed distinct mercury adducts, preserving the Hg bound alkyl/aryl ligands; yet, the three organomercurials displayed significant differences in reactivity in relation to their chemical structure. The investigation was then extended to analyze the reactions with the C-terminal dodecapeptide of the enzyme human thioredoxin reductase, which contains a characteristic selenol-thiol moiety: tight Hg binding was observed. Notably, this peptide was able to remove effectively and completely the alkyl/aryl ligands of the three tested organomercurials; this behavior may be relevant to the detoxification mechanism of organomercurials in mammals. Finally, a competition experiment was carried out to establish whether protein bound mercury centers may be displaced by other competing metals. Interestingly, and quite unexpectedly, we observed that a protein bound mercury fragment may be partially displaced from its coordination site in hCA I by the medicinal gold compound auranofin.

Aryl diazonium salts and benzene derivatives bearing two electron-donor substituents: chemical and mechanistic behaviours.

The reaction between benzene derivatives 1-4 and p-substituted benzenediazonium tetrafluoroborates 5a-c provided novel azo-coupling products in high yields under mild conditions. The monitoring of the reaction progress using 1H-NMR provided mechanistic information on both the relative reactivity of the reagents and the possibility to detect novel reaction intermediates.

Aberrant Mannosylated and Highly Fucosylated Glycoepitopes of Prostatic Acid Phosphatase as Potential Ligands for Dendritic-Cell Specific ICAM-Grabbing Nonintegrin (DC-SIGN) in Human Seminal Plasma-A Step towards Explaining Idiopathic Infertility.

Semen prostatic acid phosphatase (PAP) has been proposed as an endogenous ligand for dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN), which plays a critical immuno-modulating role in maintaining homeostasis in the female reproductive tracts. In the current study, we assumed that semen PAP bears a set of fucosylated and mannosylated glycans, which may mediate the efficient binding of PAP to DC-SIGN. To investigate this hypothesis, we developed ELISA assays using Galanthus nivalis and Lotus tetragonolobus lectins capable of binding mannose-containing glycans or LewisX and LewisY motifs, respectively. In our assay with Galanthus nivalis, we detected that the relative reactivity of PAP mannose-presenting glycans in the normozoospermic idiopathic group was significantly higher than in the asthenozoospermic, oligozoospermic and oligoasthenozoospermic groups. Simultaneously, we observed slight differences in the relative reactivities of PAP glycans with Lotus tetragonolobus lectin among groups of patients with abnormal semen parameters. Subsequently, we examined whether DC-SIGN interacts with seminal plasma PAP glycans, and we detected a significantly higher relative reactivity in the normozoospermic group compared to the oligozoospermic group. Finally, we concluded that the significantly aberrant abundance of mannosylated functional groups of PAP among patients with semen disorders can suggest that PAP may thereby be engaged in modulating the immune response and promoting a tolerogenic response to male antigens in the female reproductive system.

EXPLORING THE WITHIN-PERSON RELATIONSHIP BETWEEN DAILY DISCRIMINATION AND DAILY STRESS REACTIVITY

Abstract Experiencing discrimination has been associated with a variety of negative impacts such as poorer health and well-being. Some research has shown that those who experienced discrimination at an initial timepoint were more likely to have poorer health and well-being outcomes 20 years later through the mediating role of threat appraisals and stress reactivity. Research has demonstrated a link between experiencing discrimination and affective reactions to everyday stressful experiences, however, these associations have only been studied at the between-person level. For the current study, we examined the within-person relationship in daily stress reactivity in relation to experiencing discrimination on a daily basis over the course of 20 years. Participants (n = 1,315) completed waves 1 to 3 of the Midlife in the United States (MIDUS) survey with each wave about 10 years apart in which participants were asked to self-report their daily discrimination. Participants also completed the National Study of Daily Experiences (NSDE) which was a daily diary design over 8 consecutive days asking about their daily stress reactivity. Results found that during timepoints when people experienced greater than their average level of discrimination, they also reacted more negatively to daily stressful events (b = .002, 95% CI [0.001, 0.002]). These results are particularly striking because they show that within-person changes in reported discrimination are related to changes in affective responses to daily stressors. These findings suggest that experiencing discrimination is related to greater reactivity to daily stressors, which may lead to worse physical and mental health over time.

A proposed total synthesis of a clerodane-type diterpenoid Scaparin C

A theoretically feasible synthetic route for Scaparin C, a clerodane-type diterpenoid new-ly discovered in nature is depicted. A Diels-Alder reaction followed by oxidative cleavage of the olefin generates a 1,3,6-tricarbonyl compound as the substrate. Based on the rela-tive reactivities of the three carbonyl groups, the primary aldehyde group is protected as the acetal. It is expected that the right aldol and alkylation reactions take place for the remaining carbonyl groups, collaboratively giving a bi-fused ring system which is the most important constituent of Scaparin C. After deprotection, the primary aldehyde group is connected with the 3-bromofuran through a Friedel-Crafts reaction. Finally, reactions including sequential reduction of the carbonyl groups, selective protection, acylation and oxidation of the alcohols can preserve the diol and the ketone groups needed, intramolec-ularly forming the cyclic acetal and epoxidation of alkene with the m-CPBA completing the synthesis.

A machine learning approach for predicting the reactivity power of hypervalent iodine compounds

The knowledge of chemical reactivity of substrates is a prerequisite to accurately design a chemical reaction; however, it has been a challenging task due to the slow trial-and-error experimental approaches and the high computational cost associated with in silico investigations. Artificial intelligence techniques could serve as an alternative to efficiently determine the relative reactivity of chemical entities. In the context of this research, we propose an artificial neural network model to predict the bond dissociation energies of hypervalent iodine reagents. An open-source cheminformatics package, namely, Mordred, was employed for calculating various 1D, 2D and topological descriptors. The approach utilizes a dataset of more than 1000 hypervalent iodine reagents, and the bond dissociation energies can be predicted with a remarkable accuracy, as suggested by an R2 score of 0.97 and a mean absolute error of 1.96 kcal/mol. Owing to the low cost and high efficiency, this machine learning approach can provide an alternative to the theoretical/experimental approaches to rationally design a chemical reaction and without having to go through the hassle of high-throughput experimentation to reach the desired reaction outcome. In an effort to make the model interpretable, a feature importance algorithm was applied, which identified descriptors contributing most to the development of the model. Features describing electronegativity and polarizability are some of the important contributors to the model’s training.

Vinyl-Addition Homopolymeization of Norbornenes with Bromoalkyl Groups.

Vinyl-addition polynorbornenes are of great interest as versatile templates for the targeted design of polymer materials with desired properties. These polymers possess rigid and saturated backbones, which provide them with high thermal and chemical stability as well as high glass transition temperatures. Vinyl-addition polymers from norbornenes with bromoalkyl groups are widely used as precursors of anion exchange membranes; however, high-molecular-weight homopolymers from such monomers are often difficult to prepare. Herein, we report the systematic study of vinyl-addition polymerization of norbornenes with various bromoalkyl groups on Pd-catalysts bearing N-heterocyclic carbene ligands ((NHC)Pd-systems). Norbornenes with different lengths of hydrocarbon linker (one, two, and four CH2 groups) between the bicyclic norbornene moiety and the bromine atom were used as model monomers, while single- and three-component (NHC)Pd-systems were applied as catalysts. In vinyl-addition polymerization, the reactivity of the investigated monomers varied substantially. The relative reactivity of these monomers was assessed in copolymerization experiments, which showed that the closer the bromine is to the norbornene double-bond, the lower the monomer's reactivity. The most reactive monomer was the norbornene derivative with the largest substituent (with the longest linker). Tuning the catalyst's nature and the conditions of polymerization, we succeeded in synthesizing high-molecular-weight homopolymers from norbornenes with bromoalkyl groups (Mn up to 1.4 × 106). The basic physico-chemical properties of the prepared polymers were studied and considered together with the results of vinyl-addition polymerization.

Correlation Study of the Spin-Orbit State-Resolved Scattering of Al(2P) in Oxidation Reaction and Nonreactive Collision.

Spin-orbit coupling plays an important role in chemical reactivity, especially in reactions that require the change of electron spin states. However, it is difficult to measure and analyze the reaction dynamics between spin-orbit splitting states, particularly for splitting states with a small energy difference. In this study, we find that nonreactive scattering of spin-orbit splitting states can provide complementary information that is overlooked in chemical reaction studies. Here, the oxidation reactivities of spin-orbit Al(2P1/2,3/2) states with small energy difference of 112 cm-1 are clearly distinguished in the high rotational AlO(v = 0 and 1, N) products at low collision energy of 507 cm-1 using a laser ablation crossed-beam and time-sliced ion velocity mapping technique, in conjunction with state-selected nonreactive scattering studies. For both the AlO(v = 0 and 1) channels, the spin-orbit relative reactivity σ3/2/σ1/2 increases with the increase of rotational level N of AlO products. However, for AlO(v = 0), the reactivity of the Al(2P3/2) excited state is consistently lower than that of the Al(2P1/2) ground state, whereas for AlO(v = 1), the reactivity of Al(2P3/2) is higher than that of Al(2P1/2) at a higher rotational state. The relative reactivity of spin-orbit split Al(2P) states at different scattering angles shows a more pronounced enhancement of forward scattering relative to side and backward scattering for Al(2P3/2) when a higher rotationally excited AlO is produced. Nonreactive scattering studies of Al(2P) suggest that the Al(2P3/2) state is deexcited to the ground Al(2P1/2) state at the sideways and backward scattering directions, and the deexcitation is supposed to reduce the reactivity of the excited Al(2P3/2) at the corresponding direction.

Condensation reactions of dialkoxy-2-phenylchroman-4-ones with 1,2-diamines: A method for the preparation of chromenoquinoxalines

Reactions of dialkoxy-2-phenylchroman-4-ones (2,3-diethoxy-3-hydroxy-2-phenylchroman-4-one (1) and 2,3-dimethoxy-3-hydroxy-2-phenylchroman-4-one (2)) with various phenylenediamines in refluxing chloroform led to quinoxaline ring formation to produce racemic mixtures of chromenoquinoxaline molecules in good to moderate yields (3–10). The proposed mechanism involves the hemiacetals (1 and 2) rearranging upon heating to form a reactive dione intermediate that subsequently reacts with phenylenediamine derivatives to produce the title compounds. Reactions of 1 and 2 with asymmetric phenylenediamines led to mixtures of two regioisomers, for which the major products were dictated by the relative reactivity of the nucleophilic amine and the electrophilic carbonyl groups. The chromenoquinoxaline products were characterized by 1H, 13C, 19F (when necessary), nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry, melting point determination, and in some cases (compounds 6–10) single crystal X-ray diffraction studies. Herein, the synthesis, characterization, and reactivity of this new class of molecules are discussed.

Unraveling the promoter effect and the roles of counterion exchange in glycosylation reaction.

The stereoselectivity of glycosidic bond formation continues to pose a noteworthy hurdle in synthesizing carbohydrates, primarily due to the simultaneous occurrence of SN1 and SN2 processes during the glycosylation reaction. Here, we applied an in-depth analysis of the glycosylation mechanism by using low-temperature nuclear magnetic resonance and statistical approaches. A pathway driven by counterion exchanges and reaction byproducts was first discovered to outline the stereocontributions of intermediates. Moreover, the relative reactivity values, acceptor nucleophilic constants, and Hammett substituent constants (σ values) provided a general index to indicate the mechanistic pathways. These results could allow building block tailoring and reaction condition optimization in carbohydrate synthesis to be greatly facilitated and simplified.