Rearrangement Reactions Research Articles

Mechanism, thermochemistry, and kinetics of formation of PhC(O)H and HOPhC(O)H during unimolecular decomposition of P-PhC(O2•)HPhOH.

Bisphenols are one of the main components of bio-oil, produced during the pyrolysis of lignin-containing biomass. Synthetic bisphenols are used in polycarbonate plastics, epoxy resins, and thermal papers. Their mechanism of oxidation is important for the determination of the fire safety of these materials and the possibility of using them as additives in fuels for the decrease and description of ignition delays, as well as for the determination of their health risk assessment in medicine. One representative of bisphenols is p-benzylphenol (p-PhCH2PhOH), which is formed during the fast pyrolysis of lignine-containing biomass. Its thermochemistry of oxidation has been partially studied previously. It is shown that the reaction of chain oxidation of p-PhCH2PhOH is thermochemically favorable at low temperatures. However, these studies consider only two pathways of this reaction: (1) the chain oxidation of RH by RO2• and (2) the tautomerization of R'HO2• to R'O2H with following production of R'O• and OH radicals. At the same time, the reactions of intramolecular rearrangement of RO2•, produced PhC(O)H and •PhOH or HOPhC(O)H and •Ph, are not reported but can be an important part of its oxidation mechanism. The five DFT (M06-2X (i = 1), B3LYP (i = 2), wB97XD (i = 3), M08HX (i = 4), MN15 (i = 5)) approaches with 6-311 + + G(d,p) basis set are used for the determination of standard enthalpies of atomization (ΔraH°(Xi)) of considered compounds (molecules, radicals, and transition states). These values of ΔraH°(Xi) are corrected using the empirical linear calibration dependencies, reported previously. The different calibration dependencies are used for the hydrocarbons (including the aromatics and simple oxygenated derivatives) and for the peroxides. The corrected values of ΔraH°(Xi, CORR) are used according to Hess's law for the determination of ΔfH°(Xi, CORR). The most consistent values of ΔfH°(X, MEAN) are derived from the coordination of the values of ΔfH°(Xi,CORR) using the intersection of their values of standard deviations (3SDi). These values of ΔfH°(X, MEAN), as well as the B3LYP values of S°(X), which are accounting the frequencies correction and internal rotations, as well as their temperature dependencies, are used for the determination of thermochemistry of considered reactions and of the calculation, within transition state theory (TST), of the values of high pressure limits of the rate constant. The values of H°(Xi), S°(Xi), and G°(Xi) are calculated using the Gaussian 16w program. The considered mechanism is prepared using ISIS/Draw package. The temperature dependencies of thermochemical properties and the values of rate constants are determined using the ChemRate program (v.1.5). The optimized structures are visualized using the Chemcraft package.

Recent Advances in Synthetic Strategies of Piperazine & its Analogs Via Rearrangement Reactions: A Review

Abstract: In the six-membered heterocyclic compound piperazine, two nitrogen atoms are positioned within the ring at 1 and 4 positions. Numerous studies have shown that piperazine has the potential to be a useful pharmacophore in many harmful pharmacological conditions such as microbiocidal, antiinflammatory, anticancer, antioxidant, etc. In this present review, we highlighted the synthetic protocols for piperazine and its analogs, as well as the synthetic protocol for piperazine via rearrangement reaction, which have been adopted in recent years. The study also involved a listing of several patents (granted), which comprised important work on piperazine and its derivatives. Among all the methods, the most commonly adopted synthetic methods included the synthesis of piperazine analogs by dizacope, hydrolytic, mumm, multi-component, ugi-smiles, [2+3]-stevens, aza-Wittig, Curtius, Schmidt rearrangement reactions, etc. These synthetic protocols have also been compared based on different reaction conditions, feasibility, and economy to help the researchers in designing their work.

Nitride‐Bridged Mo‐Fe‐S Double‐Cubanes: Syntheses, Redox Behaviors and Comparison with their W Analogs

The FeMo cofactor (FeMoco) of the Mo‐dependent nitrogenase was identified as a Mo‐Fe‐S cluster incorporating a 2p atom in the core. The edge‐bridged double‐cubane (EBDC, [M2Fe6(µ3‐S)6(µ4‐S)2]z (M = Mo/V; z denotes charge)) clusters were demonstrated to undergo rearrangement reactions to generate the apex‐fused double‐cubane clusters ([M2Fe6(μ2‐S)2(μ3‐S)6(μ6‐S)]z) as mimics of the PN‐clusters. The introduction of 2p atoms into the core of EBDC clusters will furnish the possibility of mimicking the FeMoco structure through rearrangement. In this work, an EBDC Mo‐Fe‐S cluster with core nitrides, namely [(Tp*)2Mo2Fe6(μ4‐N)2S6Cl4]2− (Tp* = tris(3,5‐dimethyl‐1‐pyrazolyl)hydroborate), has been synthesized. Subsequent terminal ligand substitution has produced a series of EBDC clusters with isostructural cores. Further studies of the series of nitride‐containing EBDC clusters are focused on their structures and redox properties, as well as comparisons with their W analogs. The results indicate that the core structures of these clusters are affected by distinct hetero‐metal centers and different terminal ligands to a limited extent, but the redox behavior and redox potentials of these clusters differ significantly. This work provides us with a viable method for regulating the properties of the nitride‐containing EBDC clusters, which may be enlightening for further studies of the rearrangement reactions towards mimicking the FeMoco structure.

Introducing Regioselectivity in Rearrangement Reactions through a Discovery Experiment Using an Improved Schmidt-Type Reaction

Introducing Regioselectivity in Rearrangement Reactions through a Discovery Experiment Using an Improved Schmidt-Type Reaction

An unprecedented synthesis of axially chiral biaryls by rearrangement and aromatization of carbocations with central-to-axial conversion of chirality

An unprecedented synthesis of axially chiral biaryls by rearrangement and aromatization of carbocations with central-to-axial conversion of chirality

Visible-Light-Photocatalyzed Self-Cyclopropanation Reactions of Dibenzoylmethanes for the Synthesis of Cyclopropanes.

A new self-cyclopropanation of 1,3-diphenylpropane-1,3-dione, leading to tetrasubstituted cyclopropane containing three contiguous stereogenic centers with high stereoselectivity, has been achieved through violet-light-emitting diode-irradiated photocatalysis, featuring both cycloaddition and a distinctive rearrangement. Diverging from conventional cyclopropanation pathways, this reaction yields a tetrasubstituted cyclopropane through unprecedented rearrangement and cascade reactions.

Studying the Intrinsic Reactivity of Chromanes by Gas-Phase Infrared Spectroscopy.

Tandem mass spectrometry is routinely used for the structural analysis of organic molecules, but many fragmentation reactions are not well understood. Because several potential structures can correspond to a measured mass, the assignment of product ions is ambiguous using mass spectrometry alone. Here, we combine mass spectrometry with high-resolution gas-phase infrared spectroscopy and computational chemistry tools to identify product ion structures and derive collision-induced fragmentation mechanisms of the chromane derivatives Trolox and Methyltrolox. We find that protonated Trolox and Methyltrolox fragment identically via dehydration and decarbonylation, while deprotonated ions display substantially diverging reactivities. For deprotonated Methyltrolox, we observe unusual radical fragmentation reactions and suggest a [1,2]-Wittig rearrangement involving aryl migration in the gas phase. Overall, the combined experimental and theoretical approach presented here revealed complex proton dynamics and intramolecular rearrangement reactions, which expand our understanding on structure-reactivity relationships of isolated molecules in different protonation states.

Correlation Study between Multi-Scale Structure and In Vitro Digestibility of Starch Modified by Temperature Difference.

Physical techniques are widely applied in the food industry due to their positive impact on food quality and the environment. Temperature differences can effectively modify starch, but the resulting changes in starch structure and quality remain unclear. In this study, the corn starch was processed with high temperature, low temperature, and temperature difference (TD), including high temperature before low temperature (H-L) and low temperature before high temperature (L-H). The results showed that high temperature induced the umbilicus to concave inward shape and sharply decreased the amylose content, while low temperature increased the surface micropores and reduced the A-chain. TD reduced the fluorescence intensity and increased the clearness of the growth ring. TD elevated the relative crystallinity (RC), short-range order, A/B1 chains, hydrolysis parameters, and resistant starch (RS), and reduced amylose content, B2/B3 chains, and viscosity. Moreover, the corn starches treated by H-L had lower amylose content and higher RC, 1047/1022, A-chain, and RS than those treated by L-H. Overall, high temperature degraded the amylose and low temperature destroyed the amylopectin. During the TD, H-L can accelerate the starch molecular rearrangement more than the opposite temperature treatment order. These results will help produce novel starches for better food applications.

Strategies to Enhance the Stability of Non‐Fullerene Acceptor‐Based Organic Solar Cells

AbstractThrough comprehensive density functional theory calculations, the photodegradation mechanisms, including cis–trans isomerization, electrocyclization, and sigmatropic rearrangement reactions are investigated in indacenodithieno [3,2‐b] thiophene (IT)‐based non‐fullerene acceptors (NFAs). Various functional group substitutions on the core (fluorine, ethyl, and cyano groups) and end groups (fluorine) of NFA are introduced to elucidate the influence of chemical modifications on photodegradation pathways. The findings reveal that the core substitution can effectively suppress electrocyclization and 1,5‐sigmatropic shift reactions, which are major contributors to photodegradation. Furthermore, the electronic, excited‐state, and charge transport properties of pristine and degraded products are studied to gain insights into the impact of degradation on photovoltaic parameters. The results suggest that photodegradation leads to the formation of shallow energy trap states, hindering charge transport and increasing charge recombination, ultimately affecting the power conversion efficiency of organic solar cells (OSCs). The study not only provides a comprehensive understanding of photodegradation mechanisms but also offers valuable molecular design strategies to enhance the stability of NFAs for future large‐scale applications of OSCs. By establishing a clear connection between the chemical structure and photostability of NFA, this research represents a pivotal contribution to the field of organic electronics and sustainable energy technologies.

Unified chemical synthesis of cephalotaxus diterpenoids: A biosynthetic reversed strategy

In this work, we present the details of the first unified chemical synthesis of cephalotaxus diterpenoids with three distinct carbon skeleton structures. Drawing on our previous synthesis of cephalotane-type C18 dinorditerpenoid and inspired by the proposed biosynthetic synthesis pathway, we formulated a biosynthetic reversed chemical synthetic strategy. This strategy facilitated the conversion of C18 dinorditerpenoid into troponoid-type C19 norditerpenoid and intact cephalotane-type C20 diterpenoid through pivotal one-carbon introduction and ring expansion reactions. In the synthesis of troponoid-type C19 norditerpenoid, we utilized TMSCHN2 as one-carbon unit and meticulously examined the selective regulatory effect of halogen substituents in ring expansion and rearrangement reactions. This endeavor culminated in the successful synthesis of natural product molecules within this subclass, notably including cephinoid H and fortalpinoid C, marking the first chemical total synthesis in this line of research. In the investigation of intact cephalotane-type C20 diterpenoid synthesis, while adhering to the overall synthesis strategy, we initially pursued a ring expansion before carbon introduction approach, which proved unsuccessful. Subsequently, we explored a synthetic route of introducing carbon first and then expanding the ring, leading to a successful outcome and resulting in the first chemical total synthesis of the representative molecule cephanolide E within this subclass. Various challenges such as establishing crucial quaternary carbon stereocenters, selecting appropriate one-carbon units, and controlling ring expansion reactions were effectively addressed throughout this process. Moreover, enantioselective synthesis of natural products within this family was achieved through the development of asymmetric Michael reactions.

Polysulfides for presulfiding of hydrogenation catalysts: synthesis, mechanism and applications

Presulfiding agents are widely used in oil refining and chemical industry, how to produce safe and efficient presulfiding agent by more environmentally friendly synthesis process are still problems to be solved. In this study, the organic polysulfide FSA-55 was synthesized by a practical one-pot process using isobutene and sulfur as raw materials and organic amine as a catalysts. The product components were analyzed and the possible catalytic reaction pathways in the thermal conversion of sulfides were elucidated. The amine catalysts showed a catalytic activities in inducing the ring opening of the cyclic molecular structure of sulfur at high temperature, thereby releasing the reactive sulfur radicals, which react with unsaturated double bonds through addition reactions. Different molecular structures of polysulfide were generated through molecular rearrangement and cyclization reactions. The suitability of the product as a presulfiding agent was investigated by analyzing the thermal properties and studying the presulfiding effect on hydrogenation catalysts. The polysulfide has a wide decomposition temperature range (100–260 °C), which can effectively avoid the occurrence of concentrated exothermic phenomena during presulfiding of hydrogenation catalysts. The presulfiding degree of the catalysts can reach 58.32%, which shows the great potential of oil processing as a presulfiding agent.

Discovery of an Azabicyclo[2.1.1]hexane Piperazinium Salt and Its Application in Medicinal Chemistry via a Rearrangement.

Herein we report the discovery of an azabicyclo[2.1.1]hexane piperazinium methanesulfonate salt from an unexpected rearrangement reaction in the preparation of ligand-directed degraders (LDDs). This bench-stable compound was found to be a versatile electrophile in a ring-opening reaction with various types of nucleophiles. Its utility as a versatile medicinal chemistry building block is further demonstrated in the synthesis of an LDD compound targeting degradation of the androgen receptor.

An Ultra-Conductive and Patternable 40nm-Thick Polymer Film for Reliable Emotion Recognition.

Understanding psychology is an important task in modern society which helps predict human behavior and provide feedback accordingly. Monitoring of weak psychological and emotional changes requires bioelectronic devices to be stretchable and compliant for unobtrusive and high-fidelity signal acquisition. Thin conductive polymer film is regarded as an ideal interface; however, it is very challenging to simultaneously balance mechanical robustness and opto-electrical property. Here, a 40nm-thick film based on photolithographic double-network conductive polymer mediated by graphene layer is reported, which concurrently enables stretchability, conductivity, and conformability. Photolithographic polymer and graphene endow the film photopatternability, enhance stress dissipation capability, as well as improve opto-electrical conductivity (4458 S cm-1@>90% transparency) through molecular rearrangement by π-π interaction, electrostatic interaction, and hydrogen bonding. The film is further applied onto corrugated facial skin, the subtle electromyogram is monitored, and machine learning algorithm is performed to understand complex emotions, indicating the outstanding ability for stretchable and compliant bioelectronics.

Photochromic luminescence of organic crystals arising from subtle molecular rearrangement

Photoluminescence (PL) colour-changing materials in response to photostimulus play an increasingly significant role in intelligent applications for their programmability. Nevertheless, current research mainly focuses on photochemical processes, with less attention to PL transformation through uniform aggregation mode adjustment. Here we show photochromic luminescence in organic crystals (e.g. dimethyl terephthalate) with PL varying from dark blue to purple, then to bright orange-red, and finally to red. This change is attributed to the emergence of clusters with red emission, which is barely achieved in single-benzene-based structures, thanks to the subtle molecular rearrangements prompted by light. Crucial to this process are the through-space electron interactions among molecules and moderate short contacts between ester groups. The irradiated crystals exhibit reversible PL transformation upon sufficient relaxation, showing promising applications in information storage and smart optoelectronic devices. This research contributes to the development of smart photochromic luminescent materials with significant PL colour transformations through molecular rearrangement.

Astroblastoma With a Novel YAP1::BEND2 Fusion: A Case Report.

In the most recent fifth edition of the World Health Organization Classification of Tumors of the Central Nervous System, astroblastoma has been defined by molecular rearrangements involving the MN1 gene, with common partners being BEND2 or CXXC5 . Accordingly, this tumor entity is now known as "astroblastoma, MN1 -altered." However, gliomas with EWSR1::BEND2 fusions, devoid of MN1 fusion alterations, have recently been shown to exhibit astroblastoma-like histomorphologic features and reside in a distinct epigenetic subgroup based on DNA methylation studies similar to high-grade neuroepithelial tumor with MN1 alteration, which includes astroblastoma, MN1 altered tumors. This new epigenetically distinct subtype of astroblastoma containing EWSR1::BEND2 fusions lacks the required MN1 alteration and, thus, does not satisfy the current molecular classification of these lesions. Here, we describe a case of glioma with histologic features and DNA methylation profiling consistent with astroblastoma with a novel YAP1: : BEND2 fusion. This case and others further expand the molecular findings observable in astroblastoma-like tumors outside the constraints of MN1 alteration. Such cases of astroblastoma with EWSR1::BEND2 and YAP1::BEND2 fusions challenge the current molecular classification of astroblastoma based solely on an MN1 alteration.

An Overview of the Synthesis of 3,4-Fused Pyrrolocoumarins of Biological Interest.

3,4-Fused pyrrolocoumarins, synthetically prepared or naturally occurring, possess interesting biological properties. In this review, the synthetic strategies for the synthesis of the title compounds are presented along with their biological activities. Two routes are followed for that synthesis. In one, the pyrrole ring is formed from coumarin derivatives, such as aminocoumarins or other coumarins. In the other approach, the pyranone moiety is built from an existing pyrrole derivative or through the simultaneous formation of coumarin and pyrrole frameworks. The above syntheses are achieved via 1,3-dipolar cycloaddition reactions, Michael reaction, aza-Claisen rearrangement reactions, multi-component reactions (MCR), as well as metal-catalyzed reactions. Pyrrolocoumarins present cytotoxic, antifungal, antibacterial, α-glucosidase inhibition, antioxidant, lipoxygenase (LOX) inhibition, and fluorescent activities, as well as benzodiazepine receptor ability.

Synthesis of Versatile Aryliodine Synthons by Aryliodonium Rearrangement Reactions

AbstractThe excellent reactivity of diaryliodonium salts has primarily been attributed to the efficient departure of the iodoarene unit, facilitating a variety of arylation reactions. However, one equivalent of iodoarene as a side‐product is a chemical waste in these reactions, which was criticized by chemists for hindering its popularity. Recently, the development of synthetic methodology that preserve the aryl iodine moiety received increasing attention. Oxidative rearrangement reactions involving aryliodonium reagents have significantly addressed the atom‐economic issue, thereby broadening the reaction scope. The resulting intricate aryliodine products are viewed as valuable synthons for the synthesis of natural products, pharmaceutical intermediates and other fine chemicals.

Difluorocarbene-induced [1,2]- and [2,3]-Stevens rearrangement of tertiary amines

The [1,2]- and [2,3]-Stevens rearrangements are one of the most fascinating chemical bond reorganization strategies in organic chemistry, and they have been demonstrated in a wide range of applications, representing a fundamental reaction tactic for the synthesis of nitrogen compounds in chemical community. However, their applicabilities are limited by the scarcity of efficient, general, and straightforward methods for generating ammonium ylides. Herein, we report a general difluorocarbene-induced tertiary amine-involved [1,2]- and [2,3]-Stevens rearrangements stemmed from in situ generated difluoromethyl ammonium ylides, which allows for the rearrangements of versatile tertiary amines bearing either allyl, benzyl, or propargyl groups, resulting in the corresponding products in one reaction under the same reaction conditions with a general way. Broad substrate scope, simple operation, mild reaction conditions and late-stage modification of natural products highlight the advantages of this strategy, meanwhile, this general rearrangement reaction is believed to bring opportunities for the transformations of nitrogen ylides and the assembly of valuable tertiary amines and amino acids. This will further enrich the reaction repertoire of difluorocarbene species, facilitate the development of reactions involving difluoromethyl ammonium salts, and provide an avenue for the development of this type of rearrangement reactions.

The efficient synthesis of Pregabalin with impurity control using a continuous flow system

This article developed a microreactor system for the continuous synthesis of Pregabalin. Due to the exceptional heat transfer and mixing capabilities exhibited by the system at the microscale, the Hofmann rearrangement reaction, traditionally requiring multiple sequential steps in batch reactors, can now be efficiently achieved in a consolidated single-step microreactor process. The reaction was executed at a comparatively elevated temperature range of 40–50 °C, and took 5–6 min to achieve the yield of over 90 %, which was a significant improvement compared to the conventional batch reactor method, requiring 7–8 h with a yield of 83 %. The microreactor system utilized its excellent mass and heat transfer performance to reduce the level of the key impurity to below 0.15 % at higher reaction temperatures, meeting the quality requirements for pharmaceutical production. Through experimental research, we determined the effects of reaction conditions like concentration, temperature, and residence time on the reaction rate, as well as key trace impurities.

Coupled cluster method tailored with quantum computing

Introducing an active space approximation is inevitable for the quantum computations of chemical systems. However, this approximation ignores the electron correlations related to nonactive orbitals. Here, we propose a computational method for correcting quantum computing results using a well-established classical theory called coupled cluster theory. Our approach efficiently extracts the quantum state from a quantum device by computational basis tomography. The extracted expansion coefficients of the quantum state are embedded into the coupled cluster ansatz within the framework of the tailored coupled cluster method. We demonstrate the performance of our method by verifying the potential energy curves of LiH, H2O, and N2 with a correlation-energy correction scheme. Our method demonstrates reasonable potential energy curves even when the standard coupled cluster fails. The sufficient numbers of measurements for tomography were also investigated. Furthermore, this method successfully estimated the activation energy of the Cope rearrangement reaction of 1,5-hexadiene together with perturbative triples correction. These demonstrations suggest that our approach has the potential for practical quantum chemical calculations using quantum computers. Published by the American Physical Society 2024