A General Method to Access Underexplored Ylideneamino Sulfates as Interrupted Beckmann-Type Rearrangement Intermediates.

The Beckmann rearrangement of ketoximes to their corresponding amides, using a Brønsted acid-mediated fragmentation and migration sequence, has found wide-spread industrial application. We postulated that the development of a methodology to access ylideneamino sulfates using tributylsulfoammonium betaine (TBSAB) would afford isolable Beckmann-type intermediates and competent partners for subsequent rearrangement cascades. The ylideneamino sulfates generated, isolated as their tributylammonium salts, are sufficiently activated to undergo Beckmann rearrangement without additional reagent activation. The generation of sulfuric acid in situ from the ylideneamino sulfate giving rise to a routine Beckmann rearrangement and additional amide bond cleavage to the corresponding aniline was detrimental to reaction success. The screening of bases revealed inexpensive sodium bicarbonate to be an effective additive to prevent classic Brønsted acid-mediated fragmentation and achieve optimal conversions of up to 99%.

Synthesis of Long-Chain Polyamides via Main-Chain Modification of Polyethyleneketones.

Long-chain polyamides (polyethyleneamides) were prepared from polyethylenes bearing in-chain carbonyl groups (polyethyleneketones) by the oxime formation and successive Beckmann rearrangement. (Diethylamino)sulfur trifluoride (DAST) was utilized as a promoter, which allowed mild conversion of the oxime group in spite of low solubility of the polymers. The polyethyleneamide exhibited different tensile property compared to a commercial HDPE.

Acetylcholinesterase Inhibitory Activity of Modified Lupane, Oleanane, and Ursane A-seco-Triterpenoids.

A series of new lupane, ursane, and oleanane type triterpenic A-seco-derivatives containing bromo-, azido-, alkyne-, 1H-tetrazol-5-yl-, 5-methyloxazol-2-yl-, N-(4-(4-methylpiperazin-1-yl)but-2-yn-1-yl), and a carbonyl group at C2, C24, C28, C30 positions has been synthesized. The bioactivity was evaluated by Ellman's method, and the results showed that most of the compounds displayed moderate acetylcholinesterase inhibitory activities in vitro. Among them, A-seco-derivatives of 28-oxo-allobetuline and betulinic acid with bromo- and azido-groups exhibited the most potent inhibitory activity against AChE. Extra experiments showed methyl 2-cyano-3,4-seco-dibromo- and 2-cyano-3,4-seco-diazido-derivatives of betulinic acid as mixed-type inhibitors, with Ki values as low as Ki =0.18 µM and Ki =0.21 µM, respectively.

A Novel Unified Framework for Energy-Based Spectrum Sensing Analysis in the Presence of Fading.

This paper studies the performance of the energy-based sensing procedure in the presence of multipath fading and shadowing effects in terms of its average probability of detection (APD), average receiver operating characteristic (AROC) and the area under the AROC curve (AUC). A new generalization for the class of the fading channel moment generating functions (MGFs) (i.e., factorized power type (FPT) MGF) was proposed and applied for the construction of the unified framework for the analytical treatment of the formulated problem. The contiguity of the proposed model with the existing classical ones (Rayleigh, Nakagami-m, Hoyt, η-µ, κ-µ shadowed and Mixture-Gamma) was demonstrated. Within the assumed MGF representation, the novel closed-form solutions and computationally efficient approximation for APD and AUC are derived. The obtained general expressions were then applied for derivation of the new results for the recent generalized fading channel models: Fluctuating Beckmann and Beaulieu-Xie shadowed. For each of the models, high-SNR asymptotic expressions were obtained. Lastly, numeric simulation was performed to verify the correctness of the derived results, to establish the dependencies of the sensing performance quality from the channel parameters and to identify the specific ranges of their asymptotic behavior.

Diversity-Oriented Synthesis Catalyzed by Diethylaminosulfur-Trifluoride-Preparation of New Antitumor Ecdysteroid Derivatives.

Fluorine represents a privileged building block in pharmaceutical chemistry. Diethylaminosulfur-trifluoride (DAST) is a reagent commonly used for replacement of alcoholic hydroxyl groups with fluorine and is also known to catalyze water elimination and cyclic Beckmann-rearrangement type reactions. In this work we aimed to use DAST for diversity-oriented semisynthetic transformation of natural products bearing multiple hydroxyl groups to prepare new bioactive compounds. Four ecdysteroids, including a new constituent of Cyanotis arachnoidea, were selected as starting materials for DAST-catalyzed transformations. The newly prepared compounds represented combinations of various structural changes DAST was known to catalyze, and a unique cyclopropane ring closure that was found for the first time. Several compounds demonstrated in vitro antitumor properties. A new 17-N-acetylecdysteroid (13) exerted potent antiproliferative activity and no cytotoxicity on drug susceptible and multi-drug resistant mouse T-cell lymphoma cells. Further, compound 13 acted in significant synergism with doxorubicin without detectable direct ABCB1 inhibition. Our results demonstrate that DAST is a versatile tool for diversity-oriented synthesis to expand chemical space towards new bioactive compounds.

Analysis and Radiometric Calibration for Backscatter Intensity of Hyperspectral LiDAR Caused by Incident Angle Effect.

Hyperspectral LiDAR (HSL) is a new remote sensing detection method with high spatial and spectral information detection ability. In the process of laser scanning, the laser echo intensity is affected by many factors. Therefore, it is necessary to calibrate the backscatter intensity data of HSL. Laser incidence angle is one of the important factors that affect the backscatter intensity of the target. This paper studied the radiometric calibration method of incidence angle effect for HSL. The reflectance of natural surfaces can be simulated as a combination of specular reflection and diffuse reflection. The linear combination of the Lambertian model and Beckmann model provides a comprehensive theory that can be applied to various surface conditions, from glossy to rough surfaces. Therefore, an adaptive threshold radiometric calibration method (Lambertian-Beckmann model) is proposed to solve the problem caused by the incident angle effect. The relationship between backscatter intensity and incident angle of HSL is studied by combining theory with experiments, and the model successfully quantifies the difference between diffuse and specular reflectance coefficients. Compared with the Lambertian model, the proposed model has higher calibration accuracy, and the average improvement rate to the samples in this study was 22.67%. Compared with the results before calibration with the incidence angle of less than 70°, the average improvement rate of the Lambertian-Beckmann model was 62.26%. Moreover, we also found that the green leaves have an obvious specular reflection effect near 650-720 nm, which might be related to the inner microstructure of chlorophyll. The Lambertian-Beckmann model was more helpful to the calibration of leaves in the visible wavelength range. This is a meaningful and a breakthrough exploration for HSL.

Sulfuryl Fluoride Mediated Synthesis of Amides and Amidines from Ketoximes via Beckmann Rearrangement.

A metal-free and redox-neutral method for Beckmann rearrangement employing inexpensive and readily available SO2 F2 gas is described. The reported transformation proceeds at ambient temperature and is compatible with a wide range of sterically and electronically diverse aromatic, heteroaromatic, aliphatic and lignin-like oximes providing amides in good to excellent yields. The reaction proceeds through the formation of an imidoyl fluoride intermediate that can also be used for the synthesis of amidines.

Integrated Theoretical and Empirical Studies for Probing Substrate-Framework Interactions in Hierarchical Catalysts.

Soft templating with siliceous surfactant is an established protocol for the synthesis of hierarchically porous silicoaluminophosphates (HP SAPOs) with improved mass transport properties. Motivated by the enhanced performance of HP SAPOs in the Beckmann rearrangement of cyclohexanone oxime to the nylon 6 precursor ϵ-caprolactam, an integrated theoretical and empirical study was carried out to investigate the catalytic potential of the siliceous mesopore network. Inelastic neutron scattering (INS) studies, in particular, provided unique insight into the substrate-framework interactions in HP (Si)AlPOs and allowed reactive species to be studied independent of the catalyst matrix. The spectroscopic (INS, FTIR spectroscopy, MAS NMR spectroscopy) and computational analyses revealed that in the organosilane-templated SAPO, the interconnectivity of micro- and mesopores permits cooperativity between their respective silanol and Brønsted acid sites that facilitates the protonation of cyclohexanone oxime in a physical mixture at ambient temperature.

Visible Light-Promoted Beckmann Rearrangements: Separating Sequential Photochemical and Thermal Phenomena in a Continuous Flow Reactor.

The Beckmann rearrangement of oximes to amides typically requires strong acids or highly reactive, hazardous electrophiles and/or elevated temperatures to proceed. A very attractive alternative is the in situ generation of Vilsmeier-Haack reagents, by means of photoredox catalysis, as promoters for the thermal Beckmann rearrangement. Investigation of the reaction parameters for this light-induced method using a one-pot strategy has shown that the reaction is limited by the different temperatures required for each of the two sequential steps. Using a continuous flow reactor, the photochemical and thermal processes have been separated by integrating a flow photoreactor unit at low temperature for the electrophile generation with a second reactor unit, at high temperature, where the rearrangement takes place. This strategy has enabled excellent conversions and yields for a diverse set of oximes, minimizing the formation of side products obtained with the original one-pot method.

ß-Thujone and Its Derivatives Modify the Probing Behavior of the Peach Potato Aphid.

Thujone is a natural biologically active monoterpene ketone component of essential oils of numerous plants. The aim of the study was to evaluate the effect of ß-thujone and ß-thujone derivatives bisulfite adduct, lactone, oxime, and lactam application on behavior of Myzus persicae (Sulz.) (Hemiptera: Aphididae) during probing and settling. The choice and no-choice tests (aphid settling and Electrical Penetration Graph (EPG), respectively) revealed that stereochemistry of thujone was important for biological activity (ß-thujone caused changes in aphid behavior while α-thujone did not) and that cyclopentane ring modifications and functional groups addition gave derivatives that possessed stronger and more durable deterrent effects. The most effective modification was the incorporation of a lactam moiety into the ß-thujone molecule. Application of ß-thujone lactam limited aphid settling for at least 24 h, caused restlessness in aphids and a delay or failure in reaching phloem phase by M. persicae. ß-Thujone lactam can be considered a deterrent of medium potency with activity expressed at preingestive phase of aphid probing. Other compounds did not restrain aphid stylet penetration in non-phloem tissues but slightly limited sap ingestion (lactone, oxime), and restrained aphid settling for a period of less than 24 h (ß-Thujone, bisulphite adduct, lactone).

Beckmann Rearrangement of Ketoxime Catalyzed by N-methyl-imidazolium Hydrosulfate.

Beckmann rearrangement of ketoxime catalyzed by acidic ionic liquid-N-methyl-imidazolium hydrosulfate was studied. Rearrangement of benzophenone oxime gave the desirable product with 45% yield at 90 °C. When co-catalyst P2O5 was added, the yield could be improved to 91%. The catalyst could be reused three cycles with the same efficiency. Finally, reactions of other ketoximes were also investigated.

Mesoporous Silica Scaffolds as Precursor to Drive the Formation of Hierarchical SAPO-34 with Tunable Acid Properties.

Using a distinctive bottom-up approach, a hierarchical silicoaluminophosphate, SAPO-34, has been synthesized using cetyl trimethylammonium bromide (CTAB) encapsulated within ordered mesoporous silica (MCM-41) that serves as both the silicon source and mesoporogen. The structural and textural properties of the hierarchical SAPO-34 were contrasted against its microporous analogue, and the nature, strength, and accessibility of the Brønsted acid sites were studied using a range of physicochemical characterization tools; notably probe-based FTIR and solid-state magic angle spinning (SS MAS) NMR spectroscopies. Whilst CO was used to study the acid properties of hierarchical SAPO-34, bulkier molecular probes (including pyridine, 2,4,6-trimethylpyridine and 2,6-di-tert-butylpyridine) allowed particular insight into the enhanced accessibility of the acid sites. The activity of the hierarchical SAPO-34 catalyst was evaluated in the industrially-relevant, acid-catalyzed Beckmann rearrangement of cyclohexanone oxime to ϵ-caprolactam, under vapor-phase conditions. These catalytic investigations revealed a significant enhancement in the yield of ϵ-caprolactam using our hierarchical SAPO-34 catalyst compared to SAPO-34, MCM-41, or a mechanical mixture of these two phases. The results highlight the merits of our design strategy for facilitating enhanced mass transfer, whilst retaining favorable acid site characteristics.

On the Reaction of Carbonyl Diphosphonic Acid with Hydroxylamine and O-alkylhydroxylamines: Unexpected Degradation of P-C-P Bridge.

Derivatives of methylenediphosphonic acid possess wide spectra of biological activities and are used in enzymology as research tools as well as in practical medicine. Carbonyl diphosphonic acid is a promising starting building block for synthesis of functionally substituted methylenediphosphonates. Investigation of the interaction of carbonyl diphosphonic acid with hydroxylamine clearly demonstrates that it is impossible to isolate oxime within the pH range 2-12, while only cyanophosphonic and phosphoric acids are the products of the fast proceeding Beckmann-like fragmentation. In the case of O-alkylhydroxylamines, corresponding alcohols are found in the reaction mixtures in addition to cyanophosphonic and phosphoric acids. Therefore, two residues of phosphonic acid being attached to a carbonyl group provide new properties to this carbonyl group, making its oximes very unstable. This principally differs carbonyl diphosphonic acid from structurally related phosphonoglyoxalic acid and other α-ketophosphonates.

The Molecular Design of Active Sites in Nanoporous Materials for Sustainable Catalysis.

At the forefront of global development, the chemical industry is being confronted by a growing demand for products and services, but also the need to provide these in a manner that is sustainable in the long-term. In facing this challenge, the industry is being revolutionised by advances in catalysis that allow chemical transformations to be performed in a more efficient and economical manner. To this end, molecular design, facilitated by detailed theoretical and empirical studies, has played a pivotal role in creating highly-active and selective heterogeneous catalysts. In this review, the industrially-relevant Beckmann rearrangement is presented as an exemplar of how judicious characterisation and ab initio experiments can be used to understand and optimise nanoporous materials for sustainable catalysis.

Hydrothermal Carbon Enriched with Oxygenated Groups from Biomass Glucose as an Efficient Carbocatalyst.

Metal-free carbocatalysts enriched with specific oxygenated groups with different morphology and size were synthesized from glucose by hydrothermal carbonization, in which cheap and widely available biomass could be converted into functionalized carbon using an environmentally benign process. The hydroxy- and carbonyl-enriched hydrothermal carbon (HTC) could be used in nitrobenzene reduction, and higher conversion was obtained on the sphere morphology with smaller size. In the Beckmann rearrangement of cyclohexanone oxime, carboxyl-enriched HTC exhibited superior performance compared with conventional solid acid (such as HY and HZSM-5), on which the strong acid sites and weak Lewis acid sites lead to high selectivity for the side product. Although the intrinsic acidity of carbon is weak, the carboxyl-enriched carbon was used in weak Brønsted acid-catalyzed reactions, such as the Beckmann rearrangement.

Synthesis of a tricyclic lactam via Beckmann rearrangement and ring-rearrangement metathesis as key steps.

A tricyclic lactam is reported in a four step synthesis sequence via Beckmann rearrangement and ring-rearrangement metathesis as key steps. Here, we used a simple starting material such as dicyclopentadiene.

Sustainable Beckmann Rearrangement using Bead-Milling Technology: The Route to Paracetamol.

To address the growing demand for more sustainable and greener chemistry, mechanochemical methodologies are emerging as key players. However, to date there has been little data highlighting the benefits of these rising mechanochemical technologies with regard to process scale-up activities or implementation in commercial production scale. Herein, we report the first application of bead-mill technology (Dyno®-mill) for the sustainable mechanochemical synthesis of Acetaminophen, known under the brand name Paracetamol. Using the Beckmann rearrangement, the optimized solvent-free methodology delivered a final product on a scale of several tens of grams. In comparison to current production solvent-based process, the proposed process achieves a higher yield while also allowing the removal of solvents in the chemical reaction, hereby reducing one of the extensive drivers to waste generation. The mechanochemical approach was compared to solvent-based process using a combination of green metrics and EcoScale score. The mechanochemical synthesis of paracetamol scores the highest for all the metrics over currently used solution-based processes.

Amine-free approach toward N-toluenesulfonyl amidine construction: a phosphite-mediated Beckmann-like coupling of oximes and p-toluenesulfonyl azide.

Atom hopping: A chlorophosphite-mediated Beckmann ligation of oximes and p-toluenesulfonyl azide gives access to N-sulfonyl phosphoramidines in good to excellent yields. The reaction proceeds under exceptionally mild conditions and constitutes a bioorthogonal approach toward amidines by avoiding the use of amines and transition-metal catalysts. dmp-ol=3,3-dimethylpropanediol.

Approaches to α-amino acids via rearrangement to electron-deficient nitrogen: Beckmann and Hofmann rearrangements of appropriate carboxyl-protected substrates.

The titled approaches were effected with various 2-substituted benzoylacetic acid oximes 3 (Beckmann) and 2-substituted malonamic acids 9 (Hofmann), their carboxyl groups being masked as a 2,4,10-trioxaadamantane unit (an orthoacetate). The oxime mesylates have been rearranged with basic Al(2)O(3) in refluxing CHCl(3), and the malonamic acids with phenyliodoso acetate and KOH/MeOH. Both routes are characterized by excellent overall yields. Structure confirmation of final products was conducted with X-ray diffraction in selected cases. The final N-benzoyl and N-(methoxycarbonyl) products are α-amino acids with both carboxyl and amino protection; hence, they are of great interest in peptide synthesis.

Recent Advances in the Development of Catalytic Methods that Construct Medium-ring Lactams, Partially Saturated Benzazepines and their Derivatives.

Recent catalytic methods to construct medium-sized lactams and partially saturated benzazepines and their derivatives are surveyed. The review is divided into the following sections: 1 Introduction 2 Non-Transition Metal Catalyzed Reactions 2.1 Beckmann Rearrangement 2.2 Non-Beckmann Rearrangement Reactions 2.3 Multi-component reactions 3 Transition Metal-Catalyzed Reactions 3.1 Au-catalyzed reactions to access medium-sized N-heterocycles 3.2 Reactions involving a metal η3-complex catalytic intermediate 3.3 Transition metal-catalyzed reactions of strained cycloalkanes 4 Conclusions.