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A visible-light-induced multicomponent reaction of vinyl sulfoxonium ylide, thiol, and diazo ester to generate tertiary sulfide is described. The present diastereoselective gem -difunctionalization of the diazo ester can be achieved under mild conditions, as it does not require any additives, catalysts, or transition metals and is tolerant of air and moisture. Due to more nucleophilicity, vinyl sulfoxonium ylide undergoes S–H insertion with thiols to generate an allyl sulfide intermediate. Simultaneously, diazo ester undergoes photolysis to generate a carbene intermediate. Subsequently, the coupling of carbene and allyl sulfide intermediates generates sulfonium ylide, which undergoes Doyle–Kirmse rearrangement to generate tertiary sulfide scaffolds. [ABSTRACT FROM AUTHOR]

Through 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. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Allenes, served as highly sought‐after building blocks, are an indispensable component of synthetic chemistry. Their utility in modulating the chemical, physical, and pharmaceutical properties of organic compounds make allenes a desirable choice in various applications. Here, we report a facile method for the atom‐economical synthesis of propargyl allenylamines via an underdeveloped [2,3]‐sigmatropic rearrangement. Our strategy employs easily accessible propargylamines as starting materials, which are first converted into propargyl ammonium salts, followed by a base‐promoted [2,3]‐sigmatropic rearrangement. This one‐pot, two‐step reaction proceeds in the absence of transition metals, displays a very broad scope, and does not require the introduction of the electron‐withdrawing group into the starting materials. [ABSTRACT FROM AUTHOR]

A novel gold (I)‐catalyzed synthetic strategy has been achieved for an efficient construction of indenylidene derivatives from substituted 1,6‐diynes. This reaction describes the unique reactivity of gold catalysis in facilitating the intramolecular [3,3]‐sigmatropic rearrangement, 5‐exo dig cyclization followed by 1,5‐migration of acryl group, resulting in the formation of substituted indenylidenes. Various substituted indenylidenes were successfully synthesized with up to 92 % yields. In this protocol, two new C−C bonds were sequentially formed atom economically in one pot. [ABSTRACT FROM AUTHOR]

A series of substituted ferrocenyl boron derivatives was synthesized. The oxidation of the ferrocenyl unit resulted in a significant increase of the boron‐centered Lewis acidity. The neutral and cationic Lewis acids were characterized by NMR spectroscopy, crystal structure analysis and by computational methods. The new Lewis acids were then applied in the Meinwald rearrangement of epoxides, predominantly furnishing aldehydes as the kinetic products. [ABSTRACT FROM AUTHOR]

We here reported a highly stereoselective method for the synthesis of polysubstituted conjugated dienes from α‐aryl α‐diazo alkynyl ketones and pyrazole‐substituted unsymmetric aminals under mild conditions, which was promoted by photo‐irridation and involved with 1,6‐dipolar intermediate and quadruple sigmatropic rearrangements, was successfully developed. In this transformation, the cleavage of four bonds and the recombination of five bonds were implemented in one operational step. This protocol provided a modular tool for constructing dienes from amines, pyrazoles and α‐alkynyl‐α‐diazoketones in one‐pot manner. The results of mechanistic investigation indicated that the plausible reaction path underwent the 1,6‐sigmatropic rearrangement instead of the 1,5‐sigmatropic rearrangement. [ABSTRACT FROM AUTHOR]

This article discusses the use of photocatalysis in [2,3]-sigmatropic rearrangement reactions of diazo compounds. Metal catalysts are commonly used to access the carbene fragment necessary for these reactions, but visible-light-mediated transformations have gained interest for their green and sustainable synthesis potential. The authors explore the use of heavy atoms and organosulfur compounds as catalysts in these reactions, and optimize the conditions using ruthenium catalysts. The photocatalytic rearrangement reactions are found to be efficient and yield moderate to high yields of the desired products. [Extracted from the article]

Mining of two multiproduct sesterterpene synthases from Lentzea atacamensis resulted in the identification of the synthases for lentzeadiene (LaLDS) and atacamatriene (LaATS). The main product of LaLDS (lentzeadiene) is a new compound, while one of the side products (lentzeatetraene) is the enantiomer of brassitetraene B and the other side product (sestermobaraene F) is known from a surprisingly distantly related sesterterpene synthase. LaATS produces six new compounds, one of which is the enantiomer of the known sesterterpene Bm1. Notably, for both enzymes the products cannot all be explained from one and the same starting conformation of geranylfarnesyl diphosphate, demonstrating the requirement of conformational flexibility of the substrate in the enzymes' active sites. For lentzeadiene an intriguing thermal [1,5]‐sigmatropic rearrangement was discovered, reminiscent of the biosynthesis of vitamin D3. All enzyme reactions and the [1,5]‐sigmatropic rearrangement were investigated through isotopic labeling experiments and DFT calculations. The results also emphasize the importance of conformational changes during terpene cyclizations. [ABSTRACT FROM AUTHOR]

The aromatic Cope rearrangement is an elusive transformation that has been the subject of a limited number of investigations compared to those seemingly close analogues, namely the Cope and aromatic Claisen rearrangement. Herein we report our investigations inspired by moderate success observed in the course of pioneering works. By careful experimental and theoretical investigations, we demonstrate that key substitutions on 1,5‐hexadiene scaffold allow fruitful transformations. Especially, efficient functionalisation of the heteroaromatic rings results from the aromatic Cope rearrangement, while highly stereoselective interrupted aromatic Cope rearrangements highlight the formation of chiral compounds through a dearomative process. [ABSTRACT FROM AUTHOR]

Indoles are important heterocycles in pharmaceuticals and agrochemicals, and their atom‐economical synthesis is needed. Herein, we describe the synthesis of indoles using sigmatropic rearrangements. The N‐allylaniline was oxidized by environmentally benign hydrogen peroxide, and spontaneous [2,3]‐Meisenheimer rearrangement gave N‐allyloxyaniline. Subsequent treatment with a ruthenium catalyst afforded N‐vinyloxyaniline, which underwent [3,3]‐sigmatropic rearrangement to give indoles, expelling water as the only byproduct. The whole sequence is free of quantitative salt byproducts, thereby avoiding aqueous work up and cutting off the inorganic waste. [ABSTRACT FROM AUTHOR]

Under microwave (MW) irradiation at 150 °C in toluene and in the presence of nucleophiles (DMAP, triphenylphosphine and tetrahydrothiophene) 1‐substituted 1‐ethynyl‐2‐vinyldi‐ and tetrahydroisoquinolines undergo [3,3]‐sigmatropic rearrangement providing pyrrolo[2,1‐b][3]benzazepines in good yields. The replacement of toluene with acetonitrile directs the rearrangement towards the formation of 7,11b‐dihydro‐6H‐pyrido[2,1‐a]isoquinolines. [ABSTRACT FROM AUTHOR]

An in‐depth computational study reveals the intriguing mechanism of the recently reported isomerization of hydroxamic acids into para‐aminophenols catalyzed by phenylselenyl bromide under mild conditions. The computations not only align with the reported experimental data, effectively explaining observed phenomena such as para‐selectivity but also shed light on crucial aspects of the reaction mechanism that establish limitations on the scope of the studied rearrangement. Additionally, a joint theoretical/experimental study was performed to examine the potency of the phenylsulfenyl bromide to mediate the reaction under the same conditions. [ABSTRACT FROM AUTHOR]

The hapalindole‐type metabolites have garnered significant interest due to their diverse biological activities and unique chemical structures. Recently, the biosynthesis of this family of indole alkaloids has been uncovered and shown to involve a rare biocatalytic Cope rearrangement. Previously, we demonstrated cis‐indole isonitrile C‐3 normal geranylation using FamD2. Thus, we sought to explore further the reaction potential with this substrate and dimethylallyl pyrophosphate (DMAPP) using prenyltransferases and cyclases from the hapalindole biosynthetic pathways. Here, we report a new compound derived from an unexpected biosynthetic Cope rearrangement, which expands further the scope of metabolites generated from cyanobacterial Stig cyclases. [ABSTRACT FROM AUTHOR]

The accomplishment of self‐healing polybutadienes (PB) is decisive for multitude of aerospace applications. We here present the first‐time report on a self‐healing PB derived from a blend of allyloxy end functionalized PB elicited through intramolecular thermally activated sigmatropic Claisen rearrangement coupled with stratified hydrogen bonding for use in polymer bonded explosives (PBX). Heteronuclear Single Quantum Correlation (HSQC), Heteronuclear Multiple Bond Coherence (HMBC), Total Correlation Spectroscopy (TOCSY) and Fourier Transform Infrared spectroscopy (FTIR) Spectroscopy were utilized to confirm the mechanistic aspects of the rearrangement for the proposed application. The mechanism of self‐healing is further elucidated using density functional theory (DFT) computations and confirmed through Raman spectroscopy. The biphasic polymer network architecture is disclosed through two glass transitions at −54 °C and 15–25 °C, as confirmed by Dynamic Mechanical Analysis (DMA) and Atomic Force Microscopy (AFM). The polymer exhibited healing efficiency of 85 % suitable for adhesive or coating applications. Self‐healing in bonding formulations of insensitive polymer bonded explosives was also expedited which exhibited a healing efficiency of 49–54 %. [ABSTRACT FROM AUTHOR]

This article explores the field of organosulfur chemistry and its applications in various industries. The authors specifically discuss their research on aryne chemistry and its interaction with organosulfur compounds. They detail their efforts in developing synthetic methodologies using sulfonium zwitterions and the unique reactivities of the resulting S(IV) intermediates. The article highlights their recent achievements in sigmatropic rearrangement, ring-opening reactions of cyclic sulfides, and selective arylation of thio-oxindoles. The authors aim to advance zwitterion chemistry and expand its applications through selectivity control and diversity-oriented synthesis. [Extracted from the article]

1,5‐X insertions of alkylidene carbenes are powerful methods to construct five‐membered carbocycles and heterocycles, but the mechanisms of these 1,5‐X insertions of alkylidene carbenes remain unclear (concerted or stepwise?). Here we disclose different mechanisms of 1,5‐X insertions of free alkylidene carbenes based on DFT calculations. Except for the 1,5 S−H insertion, all 1,5‐X insertions proceed through stepwise processes via forming ylide intermediates. However, subsequent 1,2 rearrangements of ylides occur through different mechanisms. The formal 1,5 O−H/N−H insertion except S−H insertion happens through deprotonation rather than insertion reaction, while other pathways including nucleophilic substitution, 2,3‐sigmatropic rearrangement, and homolysis of O−C bond are invoked in various 1,5 O−C insertions. The competition between 1,5‐X insertions and other side reactions (such as 1,2 migration, dealkylation) has been discussed to answer why the target insertion products were not obtained in some cases. [ABSTRACT FROM AUTHOR]

The [2,3]- and [1,2]-sigmatropic rearrangement reactions between pyridotriazoles and sulfides catalyzed by rhodium(II) were investigated. The utilization of pyridotriazoles as the carbene precursors in this kind of reaction efficiently constructed the C(sp3)-S and C(sp3)-Se bond with broad substrate scope and great functional group tolerance. [ABSTRACT FROM AUTHOR]

Acetylene terminated polymers are gaining interest due to the need for easily processable thermally stable networks. The Metal Organic Frameworks (MOFs)—aluminum fumarate (Al_FA_A) and copper fumarate (Cu_FA_A) MOFs were synthesized and blended with bispropargyl ether (bis (4-propargyloxyphenyl) sulfone—SPE). The (SPE + 1% MOFs) blends were characterized and thermally polymerized to give P(SPE + MOFs). The synthesized materials were characterized using FTIR, DSC, TG and TG-FTIR. The addition of both MOFs decreased the enthalpy of fusion and enthalpy of curing by 60%. The addition of copper MOF to SPE drastically reduced the temperature at which the thermal curing was maximum (300 °C to 252 °C). The 2-H chromenes were formed from bispropargyl ethers by Claisen-type sigmatropic rearrangement. Compared to pure SPE, the polymers resulting from hybrid systems show a slower thermal degradation rate. The sulfone as a swivel group in SPE and the involvement of fumarate π-bonds of MOFs during polymerization make the material more versatile. The investigation concluded that these novel inorganic–organic hybrid blends may be a good start for low-temperature curable sufficiently thermally stable matrix resin systems having a wide scope of applicability in the field of filler-reinforced composites. [ABSTRACT FROM AUTHOR]

A mixture of a nucleophilic substitution product and its isomeric azide resulting from [3,3]-sigmatropic rearrangement was obtained as a result of the reaction of hindered bromides of the adamantane series with sodium azide. Epoxidation reactions of allylic azides of the adamantane series were investigated. The reduction of the syntesized trans-2-(adamantan-1-yl)-3-(azidomethyl)oxirane with lithium alumohydride gave (S*)-(adamantan-1-yl)[(S*)-aziridin-2-yl]methanol. Under heating with HCl, the latter underwent aziridine ring opening to form (1S*,2R*)-1-(adamantan-1-yl)-3-chloro-1-hydroxypropan-2-aminium chloride. [ABSTRACT FROM AUTHOR]

The review briefly describes the synthetic potential of acetylenic and allenic carbanion adducts with isothiocyanates and azatriene systems based thereon as precursors to fundamental aza- and thiaheterocycles, namely pyrroles, 2,3-dihydropyridines, pyridines, quinolines, 3H-azepines, 4,5-dihydro-3H-azepines, 2-azabi-cyclo[3.2.0]hept-2-enes, thietanes, thiophenes, thiophen-2(5H)-imines, 1,3-thiazoles, 4,5-dihydro-1,3-thiazoles, and other heterocyclic structures with rare and/or difficultly introducible functional and pharmacophoric substituents. [ABSTRACT FROM AUTHOR]

An exceptional level of control over the direction of the (2,3)‐sigmatropic rearrangement between N‐oxides and alkoxylamine is achieved by simply changing the solvent in which they are dissolved. Protic solvents like water, methanol and hexafluoroisopropanol favour the N‐oxide form, while other solvents like acetone, acetonitrile and benzene favour the alkoxylamine. The reaction temperature and nature of the substituents on the alkene affect the rate of rearrangement. A N‐oxide fragment was attached to two fluorescent molecules and acted as an on/off switch for their fluorescence. The conversion of alkoxylamines into the corresponding N‐oxides has not previously been described and is here termed the 'Reverse Meisenheimer Rearrangement'. [ABSTRACT FROM AUTHOR]

Keywords: [2,3]-Wittig rearrangement; -hydroxycarboxylic acids; chiral lithium amide; enantioselectivity; rearrangement EN [2,3]-Wittig rearrangement -hydroxycarboxylic acids chiral lithium amide enantioselectivity rearrangement 1727 1731 5 08/18/23 20230901 NES 230901 Graph -Hydroxycarboxylic acids are essential and versatile compounds. In this classical [2,3]-sigmatropic rearrangement reaction, a new carbon-carbon bond can be formed at the -position of an electron-withdrawing group (i.e., CO SB 2 sb H) to obtain -hydroxycarboxylic acids from prochiral -allyloxycarboxylic acids in a single operation. Although, as pioneering works, their methods achieved asymmetric [2,3]-Wittig rearrangement of -propargyloxycarboxylic acids in moderate enantioselectivity, the potential of a versatile -allyloxycarboxylic acids remained unclear. [Extracted from the article]

Dynamic covalent chemistry (DCC) has, in recent years, provided valuable tools to synthesize molecular architectures of increasing complexity. We have also taken advantage of imine DCC chemistry to prepare TPMA‐based supramolecular cages for molecular recognition applications. However, the versatility of this approach has as a major drawback the intrinsic hydrolytic lability of imines, which hampers some applications. We present herein a synthetic strategy that combines the advantages of a thermodynamic‐driven formation of a supramolecular structure using imine chemistry, together with the possibility to synthetize chiral hydrolytically stable structures through a [3,3]‐sigmatropic rearrangement. A preliminary mechanistic analysis of this one‐pot synthesis and the scope of the reaction are also discussed. [ABSTRACT FROM AUTHOR]

We propose a data sampling scheme for high-dimensional neural network potentials that can predict energies along the reaction pathway calculated using the hybrid density functional theory. We observed that a data sampling scheme that combined partial geometry optimization of intermediate structures with random displacement of atoms successfully predicted the energies along the reaction path with respect to five chemical reactions: Claisen rearrangement, Diels–Alder reaction, [1,5]-sigmatropic hydrogen shift, concerted hydrogen transfer in the water hexamer, and Cornforth rearrangement. [ABSTRACT FROM AUTHOR]

The asymmetric total synthesis of two sesquiterpenoids, (−)‐HM‐3 and (−)‐HM‐4, isolated from a phytopathogenic fungus, has been developed using a gold‐catalyzed [3,3]‐sigmatropic rearrangement of sulfonium as key step. During this transformation, an excellent chirality transfer was observed between the chiral sulfoxide substrate and the newly formed quaternary stereogenic center with 96 % enantiomeric excess. The implementation of this efficient methodology allowed us to isolate the two natural products in only 7–8 chemical steps with overall yields reaching 12–16 %. [ABSTRACT FROM AUTHOR]

Claisen and Cope rearrangements are [3,3]-sigmatropic rearrangements thermally activated that occur through six-membered transition states. Although extensively investigated for decades, little is known about the magnetochemistry of these rearrangements. In view of this, we carried out an investigation based on chemical-computational models through methods based on Density Functional Theory, QTAIM, Multicenter Bond Order, NCI, GIAO, and GIMIC. We demonstrated that CCR mechanisms are concerted in which the 6-membered cyclic transition states present high aromaticity character. The molar and anisotropic susceptibility, NICS(1), and NICSzz signals were verified to have a good correlation with J (nA T−1). However, these indices demonstrated insufficient to evaluate the magnitudes of aromaticity in these transition states. Among the magnetic and topological descriptors applied in this work, the magnetically induced current density (J) proved, this to be an excellent strategy for theoretically estimative of the aromaticity of the transition states involved in the investigated rearrangements. Among the rearrangements with chair conformation, it was noted that the higher aromaticity is associated with the less favoured kinetics. For chair conformations, Claisen rearrangement (TS2) presents J = 8.63 nA T−1 and Cope (TS4) presents J = 10.43 nA T−1. However, the following order of aromaticity TS4 > TS2 > TS3 > TS1, with high paramagnetic currents in the boat conformations reducing the total current in the ring, suggests that it is not possible to establish a direct correlation between aromaticity and the kinetics of the Cope and Claisen rearrangements, since the most stable transition estate geometries are not necessarily the most aromatic. [ABSTRACT FROM AUTHOR]

1,3,2‐diazaphospholene hydrides (DAP−H) enable smooth conjugate reduction of polarized double bonds. The transiently formed phosphorus‐enolate provides a potential platform for reductive α‐functionalizations. In this respect, asymmetric C‐heteroatom bond forming processes are synthetically appealing but remain elusive. We report a 1,3,2‐diazaphospholene‐catalyzed three‐step cascade reaction of N‐sulfinyl acrylamides comprised of conjugate reduction, [2,3]‐sigmatropic aza‐Mislow‐Evans rearrangement and subsequent S−O bond cleavage. The obtained enantio‐enriched α‐hydroxy amides are formed in good yields and excellent enantiospecificity. The stereo‐defined P‐bound N,O‐ketene aminal ensures an excellent transfer of chirality from the sulfur stereocenter to α‐carbon. The transformation operates under mild conditions at ambient temperature. Moreover, DAP−H is a competent reductant for the cleavage of formed sulfenate ester, eliminating the extra step in traditional Mislow‐Evans processes. [ABSTRACT FROM AUTHOR]

Sigmatropic rearrangement provides a versatile strategy to site-selectively reorganize carbon-skeleton with high atom- and step-economy. Herein, we disclose a Mn(I)-catalyzed sigmatropic rearrangement of β, γ-unsaturated alcohols via C-C σ bond activation. A variety of α-aryl-allylic alcohols and α-aryl-propargyl alcohols could undergo in-situ 1,2- or 1,3- sigmatropic rearrangements to allow for converting to complex structural arylethyl- and arylvinyl- carbonyl compounds under a simple catalytic system. More importantly, this catalysis model can be further applied to assemble macrocyclic ketones through bimolecular [2n + 4] coupling-cyclization and monomolecular [n + 1] ring-extension. The presented skeleton rearrangement would be a useful tool complementary to the traditional molecular rearrangement. Molecular rearrangements are ubiquitous in modern synthetic chemistry, providing a powerful strategy to arrive at complex structures in an atom- and step-economic process. Here, the authors disclose a Mn(I)- catalyzed sigmatropic rearrangement of β, γ-unsaturated alcohols via C-C σ-bond activation to site-selectively reorganize carbon skeletons. [ABSTRACT FROM AUTHOR]

The Sc(III)-catalyzed [2,3]-sigmatropic rearrangement of sulfonium ylides derived from azoalkenes has been established. Owing to the absence of a carbenoid intermediate, this protocol represents the first non-carbenoid variant of the Doyle–Kirmse reaction. Under mild conditions, a variety of tertiary thioethers have been readily prepared in good to excellent yields. [ABSTRACT FROM AUTHOR]

A computational study of the aza-Cope rearrangement leading to angularly substituted 1-azabicyclic ring systems is presented. The calculations estimate the probability of the proton transfer between reaction intermediates and protic solvents, explain the experimentally observed reaction selectivity, and suggest new potentially more efficient systems for further in vitro and in silico investigations. [ABSTRACT FROM AUTHOR]

The reaction of the oxygen‐bridged frustrated Lewis pairs (FLPs) tBu2P−O−Si(C2F5)3 (1) and tBu2P−O−AlBis2 (2) with azobenzene, promoted by UV irradiation, led to a selective complexation of the cis‐isomer. The addition product of 2 is stable, while the adduct of 1 isomerizes in solution in an ortho‐benzidine‐like [3,3]‐rearrangement by cleavage of the N−N bond, saturation of the nitrogen atoms with hydrogen atoms and formation of a new bond between two phenyl ortho‐carbon atoms. Similar rearrangements take place with different para‐substituted azobenzenes (R=Me, OMe, Cl) and di(2‐naphthyl)diazene, while ortho‐methylated azo compounds do not form adducts with 1. All adducts were characterized by multinuclear NMR spectroscopy and elemental analyses and the mechanism of the rearrangement was explored by quantum‐chemical calculations. [ABSTRACT FROM AUTHOR]

Covering: 2009 to 2021 Biosynthetically, most of the syntheses of triterpenes follow the cascade cyclization and rearrangement of the acyclic precursors viz., squalene (S) and 2,3-oxidosqualene (OS), which lead to the very well known tetra- and pentacyclic triterpene skeletons. Aside from these, numerous other triterpenoid molecules are also reported from various natural sources and their structures are derived from "S" and "OS" via some unusual cyclization operations which are different from the usual tetra- and pentacyclic frameworks. Numerous compelling advances have been made and reported in the identification of these unusual cyclized mono-, di-, tri- and tetracyclic triterpenes between 2009 and 2021. Besides a dramatic increase in the newly isolated uncommon cyclized triterpenoids, substantial progress in the (bio)-synthesis of these triterpenes has been published along with significant progress in their biological effects. In this review, 180 new unusual cyclized triterpenoids together with their demonstrated biogenetic pathways, syntheses and biological effects will be categorized and discussed. [ABSTRACT FROM AUTHOR]

Previous publications in this series on the history of the development of the Woodward–Hoffmann rules revealed why Woodward and Hoffmann were prime candidates to solve the pericyclic no‐mechanism problem. This publication explains why it was the collaborative team of R. B. Woodward and Roald Hoffmann who did solve this mechanistic problem in a series of five communications in the Journal of the American Chemical Society in 1965. That is, the reasons why Woodward and Hoffmann were the perfect team, and why their individual capabilities, experiences, and qualities provided the perfect synergy are described. In part, this was the right time and the right place for them both, but the synergies were fundamental, intrinsic and idiosyncratic as a collaborative pair. Their orbital symmetry rules provided the mechanism of all concerted pericyclic reactions including electrocyclizations, cycloadditions, and sigmatropic rearrangements. Why it was 1965 and not earlier is also discussed. [ABSTRACT FROM AUTHOR]

Sigmatropic rearrangement reactions are of prime interest in the construction of small complex molecules and find widespread application in drug discovery and natural product synthesis. Herein, we report on the application of aryl/aryl diazoalkanes in rhodium-catalyzed sigmatropic rearrangement reactions of allyl sulfides. Overall, a broad variety of different allyl sulfides and different aryl/aryl diazoalkanes were compatible and the desired products were obtained in high yield. Detailed studies on aryl/aryl diazoalkanes are still underrepresented in organic synthesis. Herein, we report on rhodium-catalyzed [2,3]-sigmatropic rearrangement reactions of such diazoalkanes to further broaden the applicability of aryl/aryl diazoalkanes for the construction of densely functionalized small molecules. [ABSTRACT FROM AUTHOR]

The Sommelet–Hauser rearrangement of X-benzylic onium ylides (X = heteroatom) is an interesting transformation in organic synthesis. This rearrangement proceeds via dearomative [2,3]-sigmatropic rearrangement, followed by aromatization to form a carbon(sp2)–carbon(sp3) bond. Few advances were made in studies performed around 2000 on this rearrangement because of several competitive side reactions and structural limitations. However, studies performed in the last 15 years on the rearrangement have remarkably expanded the substrate scope and synthetic applications. In this review, the utility of the Sommelet–Hauser rearrangement and recent advances for the generation of onium ylides are described. 1 Introduction 2 Base-Induced Rearrangement 3 Transition-Metal-Catalyzed Rearrangement 4 Light-Mediated Rearrangement 5 Aryne-Induced Rearrangement 6 Conclusions and Outlook [ABSTRACT FROM AUTHOR]

A dinaphthoylmethyl‐substituted bullvalene derivative is presented that exhibits excimer fluorescence. It is demonstrated that the fluxional bullvalene core supports the excimer formation of the aroyl substituents, thus offering the opportunity to monitor externally induced structural changes by fluorescence spectroscopy, as exemplarily shown by fluorimetric analysis of host‐guest interactions of the diaroylbullvalene with metal cations, which lead to significant changes of the excimer emission. During the synthesis of the bullvalenes, it was discovered coincidentally that the corresponding triplet‐sensitized photoreaction also yielded three unknown lumibullvalene isomers. The NMR‐spectroscopic analysis of this reaction revealed a sequence and combination of different di‐ and tri‐π‐methane rearrangements and sigmatropic rearrangements. More importantly, the static lumibullvalenes proved useful as reference compounds for the evaluation of the emission properties of the fluxional bullvalenes. [ABSTRACT FROM AUTHOR]

Both aryne 1,4‐disubstitution and 1,2,4‐trifunctionalization were accomplished from tertiary amines bearing a penta‐2,4‐dien‐1‐yl moiety. These transformations could directly incorporate a C−N and a C−C bond para to each other on an aryne intermediate via a sequential nucleophilic addition and [5,5]‐sigmatropic rearrangement. When arynes bearing 3‐tethered electrophiles were employed, a cascade regioselective nucleophilic addition, intramolecular cyclization, and remote diastereoselective [5,5]‐sigmatropic rearrangement process was observed. Our density functional theory (DFT) calculations revealed that hydrogen‐bonding interactions between two C−H hydrogens on the penta‐2,4‐dien‐1‐yl chain and the oxygen anion generated upon N‐nucleophilic annulation reaction in the [5,5]‐sigmatropic rearrangement step is responsible for the remote diastereoselective control in this reaction system. [ABSTRACT FROM AUTHOR]

A series of novel 4-(aryl)-benzo[4,5]imidazo[1,2-a]pyrimidine-3-carbonitriles were obtained through the Povarov (aza-Diels–Alder) and oxidation reactions, starting from benzimidazole-2-arylimines. Based on the literature data and X-ray diffraction analysis, it was discovered that during the Povarov reaction, [1,3] sigmatropic rearrangement leading to dihydrobenzimidazo[1,2-a]pyrimidines took place. The structures of all the obtained compounds were confirmed based on the data from 1H- and 13C-NMR spectroscopy, IR spectroscopy, and elemental analysis. For all the obtained compounds, their photophysical properties were studied. In all the cases, a positive emission solvatochromism with Stokes shifts from 120 to 180 nm was recorded. Aggregation-Induced Emission (AIE) has been illustrated for compound 6c using different water fractions (fw) in THF. The compounds 6c and 6f demonstrated changes in emission maxima or/and intensities after mechanical stimulation. [ABSTRACT FROM AUTHOR]

Dynamic motion often controls selectivity in reactions featuring two consecutive potential‐energy transition states. Here we report density functional theory (DFT)‐based direct dynamics trajectories and machine learning classification analysis for cyclopentadienone dimerization and a N2 extrusion reaction leading to semibullvalene. These reactions have consecutive transition states, and there is dynamic selectivity that determines which of two possible C‐C bonds is formed after the first transition state. For cyclopentadienone dimerization with a bispericyclic first transition state, machine learning analysis using transition‐state based features provided >90% trajectory classification accuracy, but only using AdaBoost and random forest algorithms. Many other relatively sophisticated machine learning algorithms showed poor accuracy despite the obvious motion responsible for selectivity. Feature importance analysis confirmed that the sigmatropic rearrangement vibrational motion in the bispericyclic transition state provides prediction of which of the second C‐C bonds is dynamically formed. For the reaction leading to semibullvalene, machine learning analysis provides solid accuracy for classifying trajectories and predicting which C‐C bond is formed and which C‐C bond is broken immediately after N2 ejection. Like the cyclopentadienone dimerization reaction, machine learning feature importance analysis showed that the sigmatropic rearrangement vibrational motion in the N2 extrusion transition state determines which C‐C bond is formed and which is broken. Surprisingly, machine learning struggles to predict which trajectories undergo a subsequent [3,3] sigmatropic rearrangement process, which isomerizes equivalent forms of semibullvalene. [ABSTRACT FROM AUTHOR]

The reaction of N-(2-methylpropenyl)pyrrolidine with 3-vinylchromones containing non-acidic electron-withdrawing groups (ester, nitrile) was studied. The conditions, that make it possible to manage the side [1,5] sigmatropic rearrangement, were found. As a result, new derivatives of 4,4a-dihydroxanthone containing ester and nitrile groups were obtained. [ABSTRACT FROM AUTHOR]

In the absence of transition-metal catalysts and additional oxidants, arylhydroxylamines can undergo an unconventional O -sulfinylation/[2,3]-sigmatropic rearrangement/rearomatization cascade with trifluoromethylsulfinyl chloride to rapidly and efficiently synthesize versatile ortho -sulfonylated aromatic amines. This Synpacts article describes the discovery, further study, and practical application of the rearrangement reactions in arylhydroxylamine compounds and highlights our recent advances in this area. 1 Introduction 2 Discovery of a New Reaction 3 O -Sulfinylation of Arylhydroxylamines Followed by [2,3]-σ Rearrangement 4 Conclusion [ABSTRACT FROM AUTHOR]

We disclose a practical and efficient strategy for the expedient synthesis of 2,3‐dihydroquinazolin‐4‐(1H)‐one derivatives by one carbon insertion into cyclic N−N bond. Spontaneous manipulations with operationally simple procedures furnishing pharmaceutically useful compounds are key features of the developed protocol. Mechanistic studies reveal that the predicted intramolecular rearrangement occurs via consecutive ring‐opening and cyclization sequences. A gram‐scale reaction and synthetic transformation of products to quinazolinone derivatives have also been demonstrated during the course of the study. [ABSTRACT FROM AUTHOR]

The Overman rearrangement is a very useful C–N bond forming reaction described for the first time in 1974. This transformation allows a chirality transfer with an excellent predictible induction, starting from a configurationally pure allylic alcohol, yielding in only one step an amide moiety, via a [3,3]-sigmatropic rearrangement of an intermediate imidate. A recent valuable extension was developed by Chida and co-workers on orthoamide structures starting from allylic vicinal diols, avoiding time consuming protections. However, this attractive modified approach suffers generally from elevated temperatures, long reaction times and sometimes disappointing yields. To bridge this gap, we have carried out a combined experimental and theoretical study with the aim of elucidating the structures and the reactivities of these orthoamides. In order to rationalize the experimental results, it was first fundamental to identify the actual reactive species. The reactivity of these orthoamides was then investigated. Theoretical calculations using density functional theory (wB97X-D/Def2TZVP method) were then performed in the gas phase at 453 K to characterize the relevant chemical species (conformers of orthoamide diastereoisomers, prereactive complexes, and transition states structures) and to estimate the free energies of activation. The role of temperature has also been taken into consideration at 298 K and 373 K in comparison with 453 K. A major contribution of the theoretical part of this study has been to show that the reactivity of orthoamides in the Overman rearrangement crucially depends on diastereoisomers present in the reaction media. Molecular simulation has allowed us to clarify the reasons behind the temperature requirements and the reaction time, tentatively helping chemists to understand their troubles in orthoamide Overman rearrangement. [ABSTRACT FROM AUTHOR]

Polymers are ubiquitous materials that have driven technological innovation since the middle of the 20th century. As such, the logic that guides polymer synthesis merit considerable attention. Thus far, this logic has often been 'forward-synthetic', which constrains the accessible structures of polymer materials. In this article, we emphasize the benefits of 'retrosynthetic' logic and posit that the development of skeletal rearrangements of polymer backbones is central to the realization of this logic. To illustrate this point, we discuss two recent examples from our laboratory – Brook and Ireland–Claisen rearrangements of polymer backbones – and contextualize them in prior reports of sigmatropic rearrangements and skeletal rearrangements of polymers. We envision that further development of skeletal rearrangements of polymers will enable advances in not only the chemistry of such rearrangements and the logic of polymer synthesis, but also polymer re- and upcycling. [ABSTRACT FROM AUTHOR]

An electrochemical oxidative regio- and stereo-selective thio(seleno)cyanation of enamides has been developed to access (E)-β-thio(seleno)cyanated enamide compounds under environmentally-benign conditions without metal and exogenous oxidant in an undivided cell. The protocol features good reaction efficiency and functional group tolerance, providing a sustainable pathway for the thio(seleno)cyanation of enamides. The practicabilities of this protocol were further demonstrated by intramolecular cross-coupling reactions to prepare six- and seven-membered heterocycles by varying the position of halide substituents. Mechanistic investigation reveals that the reaction may proceed via [1,5]-H sigmatropic rearrangement to achieve exclusive E stereoselectivity. [ABSTRACT FROM AUTHOR]

Copper-catalyzed reactions of N-Boc-gramine with diazo compounds have been studied. In the case of ethyl diazoacetate, an indoline derivative with an exocyclic double bond is formed due to a [2,3]-sigmatropic rearrangement. The reaction of N-Boc-gramine with CF3-substituted diazo compounds, viz., diazocarboxylate and diazophosphonate, proceeds via a [1,2]-sigmatropic rearrangement with the formation of new derivatives of tryptophan and its P analogue. [ABSTRACT FROM AUTHOR]

New-to-Nature biocatalysis has emerged as a promising tool in organic synthesis thanks to progress in protein engineering. Notably, hemeproteins have been evolved into robust catalysts for carbene and nitrene transfers and related sigmatropic rearrangements. In this work, we report the first example of a [2,3]-sigmatropic Sommelet-Hauser rearrangement initiated by a carbene transfer of the sperm whale myoglobin mutant L29S,H64V,V68F that was previously reported to catalyze the mechanistically similar [2,3]-sigmatropic Doyle-Kirmse rearrangement. This repurposed heme enzyme catalyzes the Sommelet-Hauser rearrangement between ethyl diazoacetate and benzyl thioethers bearing strong electron-withdrawing substituents with good yields and enantiomeric excess. Optimized catalytic conditions in the absence of any reductant led to an increased asymmetric induction with up to 59% enantiomeric excess. This myoglobin mutant is therefore one of the few catalysts for the asymmetric Sommelet-Hauser rearrangement. This work broadens the scope of abiological reactions catalyzed by iron-carbene transferases with a new example of asymmetric sigmatropic rearrangement. We report the first example of a biocatalytic [2,3]-sigmatropic rearrangement initiated by a carbene transfer. A sperm whale myoglobin mutant catalyzes the reaction between ethyl diazoacetate and benzyl thioethers bearing strong electron-withdrawing substituents with good yields and up to 59% enantiomeric excess. [Display omitted] • A myoglobin carbene transferase catalyzes a Sommelet-Hauser rearrangement. • Benzyl thioethers bearing strong electron-withdrawing substituents are substrates. • No reductant is needed to initiate the iron-carbene formation with ethyl diazoacetate. [ABSTRACT FROM AUTHOR]

The heating of O‐furfuryl S‐methyl xanthate in p‐xylene solvent that is known from the literature to yield in parallel S‐furfuryl S‐methyl dithiocarbonate and furfuryl methyl sulfide via the thione‐to‐thiol rearrangement and carbon oxysulfide extrusion, respectively, have been studied theoretically. The CBS‐QB3 energies in conjugation with the solvation model density and B3LYP/6‐311G(2d,d,p) monodeterminantal wave functions have been used to investigate the kinetics of the parallel reaction by means of canonical transition state theory and molecular mechanism of the thione‐to‐thiol rearrangement by means of topological approaches. According to the supplied kinetic data the considered reactions are assisted strongly by the solvent molecules implying implicit solvent model cannot account properly the effect of solvent media. The cross topological analysis of the thione‐to‐thiol rearrangement via [1,3]‐sigmatropic rearrangement revealed that the electron density flow along the reaction is not concerted and the sequence of catastrophes can be summarized as 4‐EF†C‐0. In simple chemical term, chemical events through the reaction are heterolytic breaking of C−O bond, formation of pseudoradical center on the C atom, and creation of a new chemical C−S bond via the C‐to‐S coupling of pseudoradical centers, respectively. [ABSTRACT FROM AUTHOR]

The stereospecific sigmatropic [1,5] carbon shift of C3 ammonium enolates is discovered. According to mechanistic, kinetic and computational experiments, this new rearrangement proceeds via the catalytic generation of a transient C3 ammonium enolate by intramolecular aza‐Michael addition. This intermediate rapidly undergoes [1,5] sigmatropic carbon migration to furnish the respective tetrahydroquinoline‐4‐ones with excellent diastereoselectivities of d.r. >99 : 1 and in 61–98 % yield. [ABSTRACT FROM AUTHOR]