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Unlike cyclopropanes, the analogous B2C species (diboriranes) tend to adopt non‐classical Hückel‐aromatic structures with bridging moieties R between the boron atoms. The coordination of the thus generated cyclic 2e− π‐system to transition metals is completely unexplored. We here report that complexation of non‐classical diboriranes cyclo‐μ‐RB2Dur2CPh (R=H, SnMe3; Dur=2,3,5,6‐tetramethylphenyl) to Fe(CO)3 fragments allows for the carbonylative ring expansion of the B2C ring to either four‐ or five‐membered rings depending on the nature of the BRB 3‐center‐2‐electron bond (3c2e): The H‐bridged diborirane (R=H) initially reacts with Fe2(CO)9 to the allylic π‐complex with an agostic BH/Fe interaction. Subsequent formal hydroboration of CO from excess Fe2(CO)9 results in the side‐on ring expansion under formation of a five‐membered B2C2O ring, coordinated to the Fe(CO)3 moiety. In contrast, in case of the stannyl‐bridged diborirane (R=SnMe3) under the same conditions, CO is added end‐on to the B−B bond with the carbon terminus formally inserting into the B2Sn 3c2e‐bond. The two carbonylative ring expansion products can also be described as nido and closo clusters, respectively, according to the Wade‐Mingos rules. [ABSTRACT FROM AUTHOR]

Breaking aromaticity by inserting additional atoms within the skeleton of heteroaromatic rings has gained significant attention over the years. As part of the emerging concept of 'skeletal editing', this short review retraces the recent progress made on dearomative enlargement reactions of both five- and six-membered heterocycles. 1 Introduction 2 Dearomative Enlargement of Five-Membered Rings 2.1 Pyrroles, Furans, Thiophenes and Their Fused Analogues 2.2 Pyrazoles, Isoxazoles, Isothiazoles and Their Fused Analogues 3 Dearomative Enlargement of Six-Membered Rings 4 Conclusion and Perspectives [ABSTRACT FROM AUTHOR]

Herein we report the development of an oxidative amination process for the streamlined synthesis of pyridones from cyclopentenones. Cyclopentenone building blocks can undergo in situ silyl enol ether formation, followed by the introduction of a nitrogen atom into the carbon skeleton with successive aromatisation to yield pyridones. The reaction sequence is operationally simple, rapid, and carried out in one pot. The reaction proceeds under mild conditions, exhibits broad functional group tolerance, complete regioselectivity, and is well scalable. The developed method provides facile access to the synthesis of 15N‐labelled targets, industrially relevant pyridone products and their derivatives in a fast and efficient way. [ABSTRACT FROM AUTHOR]

Synthetic options for conversion of indeno[2,1‐c]fluorene‐5,8‐diones into larger polyaromatic compounds with extended π‐conjugated systems were explored. The crucial two‐fold transformation of the five‐membered ketone moieties of indeno[2,1‐c]fluorene‐5,8‐diones was based either on a one‐carbon homologation or on a ring‐expansion reaction which eventually enabled syntheses of compounds possessing substituted tribenzo[a,e,l]indeno[1,2,3‐hi]acephenanthrylenes and [5]helicenes scaffolds. The former was prepared by using a reaction sequence based on Ramirez olefination, intramolecular Heck reaction, and intermolecular Suzuki‐Miyaura cross‐coupling, whereas the latter utilized a sequence comprising Büchner−Curtius−Schlotterbeck reaction and intermolecular Suzuki‐Miyaura cross‐coupling. Scholl reaction of selected [5]helicenes yielded planarized polyaromatic compounds with the tribenzo[a,e,l]indeno[1,2,3‐hi]acephenanthrylene scaffold. Where possible, structures of products were confirmed by X‐ray diffraction analyses. Photophysical properties were determined as well. [ABSTRACT FROM AUTHOR]

Functionalized isocyanide chemistry represents an important research area in organic synthesis. A structurally unique 2‐isocyanophenyl propargylic ester has been designed to incorporate the reactivity of isocyanide and propargylic ester functionalities. Thus, the reaction of 2‐isocyanophenyl propargylic ester and 2‐aminoaromatic aldimine facilitates the synthesis of a wide range of polycyclic benzo[b] indolo [3,2‐h][1,6] naphthyridine derivatives. Furthermore, reaction with 2‐hydroxyaromatic aldimine enables the divergent synthesis of both the aforementioned scaffolds and structurally distinct diazabenzo [f] naphtho[2,3,4‐ij] azulenes featuring a [7‐6‐5] core skeleton. Experimental results and DFT calculations suggest that these transformations likely proceed by the in situ generation of a strained cyclopropenimine species followed by [3+2] cycloaddition. Next, switchable nucleophilic attack/ring expansion/aromatization and nucleophilic addition/ring expansion/elimination account for the observed selectivity. [ABSTRACT FROM AUTHOR]

Herein, we report a novel and efficient method for the synthesis of new class of 5‐oxo‐5,6‐dihydro‐[1,2,3]triazolo[1,5‐c]quinazoline derivatives by copper‐catalyzed reaction of α, β‐unsaturated keto/ester methyleneindolinone with sodium azide at room temperature via an azide‐alkene cyclization and ring expansion rearrangement. This method is applicable to a variety of α, β‐unsaturated keto/ester methyleneindolinone and displayed wide functional group tolerance. [ABSTRACT FROM AUTHOR]

This paper outlines a novel strategy for the preparation of seven-membered-ring lactams from simple nitroarenes. The approach is based on a photochemical dearomative ring expansion starting with the conversion of the nitro group into a singlet nitrene. This process is mediated by blue light, occurs at room temperature and overall enables the insertion of the nitro N -atom into the benzenoid framework. This step transforms the aromatic starting material into a seven-membered ring azepine that, following hydrogenation and hydrolysis, is converted into the desired caprolactams in just three steps. [ABSTRACT FROM AUTHOR]

Attempts to carry out intramolecular annulation of 9,10‐diarylbenzo[h]quinolines and 9,10‐di(hetero)arylphenanthrenes to aromatics with expanded π‐conjugated systems by using different methods are described. The starting compounds (9,10‐diarylbenzo[h]quinolines and 9,10‐di(hetero)arylphenanthrenes) were prepared by C−C bond activation in 1‐azabiphenylene or biphenylene followed by insertion of internal alkynes. Interestingly, unlike in purely carbon‐based aromatics, the course of the annulation turned out to be highly dependent on the structure of maternal compounds. In a handful of cases were obtained the expected or desired products. In others, unexpected rearrangements of the basic molecular frameworks were observed. [ABSTRACT FROM AUTHOR]

The ring‐expansion of arylthiiranes and phenoxyacetyl chloride was performed in the presence of triethylamine and provided a novel strategy for the synthesis of 4,5‐dihydrobenzo[d]thiepin‐2(1H)‐ones, benzo[d]‐ϵ‐thiolactones, directly without catalysts or additives. Its linear free energy analysis was conducted on the basis of competitive experiments. The results indicate that both reaction constants are close to zero (0.14 for σm and 0.20 for σp), supporting the proposed sulfur‐shifted ene mechanism. The current reaction features atom and step‐economic one‐pot characteristic via a tandem sequence of in situ ketene generation, sulfur‐shifted ene reaction, and aromatization. [ABSTRACT FROM AUTHOR]

This document provides information on the synthesis and characterization of various thiochromeno[2,3-c]pyrrole derivatives. The compounds were synthesized using specific reactions and their structures were confirmed using spectroscopic techniques. Crystallographic analysis was also performed on one of the compounds. The document includes detailed information on the synthesis, characterization, and analysis of each compound. [Extracted from the article]

This article explores the synthesis of medium-sized lactones, which are important structural components in natural products and pharmaceuticals. The authors provide examples of specific lactones and their biological activities. They then discuss their own research on synthesizing benzannulated lactams and lactones using a specific starting material and different reaction conditions. The article includes a table summarizing their experimental results, demonstrating the formation of various lactones. The authors conclude by discussing the implications and potential applications of their findings. The study was supported by Evonik Industries, and the authors express gratitude to individuals who assisted in the laboratory. [Extracted from the article]

This article explores the stabilization of carbenium ions and their role in bond reorganizations, with a specific focus on the β-silicon effect. It discusses the generation of cyclopropyl-stabilized silylium ions and their reactivity in bond reorganization processes, including various rearrangements involving vinylcyclopropanes. The article provides insights into the mechanisms and outcomes of these reactions and discusses their potential applications in the synthesis of silicon-containing compounds. The authors also investigate different variations of substituents and nucleophilic coupling partners, highlighting the importance of careful reaction conditions in obtaining specific products. [Extracted from the article]

A simple one-pot method for the synthesis of 2-substituted quinolin-4(1H)-ones from synthetically accessible 2-(2-aryl(alkyl)- 3-oxoindolin-2-yl)-2-phenylacetonitriles was developed. [ABSTRACT FROM AUTHOR]

Isatins have been widely used in the preparation of a variety of heterocyclic compounds, where the skeletal editing of isatins has shown significant advantages for the construction of diverse heterocycles. This review highlights the progress made in the last decade (2013−2023) in the skeletal editing of the isatin scaffold. A series of ring expansion reactions for the construction of quinoline skeleton, quinolone skeleton, polycyclic quinazoline skeleton, medium‐sized ring skeleton, as well as a series of ring opening reactions for the generation of 2‐(azoly)aniline skeleton by the cleavage of C−C bond and C−N bond are highlighted. It is hoped that this review will provide some understanding of the chemical transformations of isatins and contribute to the further realization of its molecular diversity. [ABSTRACT FROM AUTHOR]

The one-carbon ring expansion of benzocyclobutenones is an efficient methodology for the assembly of cyclic ketones. However, hazardous reagents or noble metal catalysts are frequently required. Herein, we disclose a copper-catalyzed intermolecular formal [4 + 1] annulation of 1,5-diynes with benzocyclobutenones, allowing the practical and atom-economical construction of diverse pyrryl 1-indanones in generally good yields under mild reaction conditions. This reaction represents an important advancement in the ring expansion of benzocyclobutenones via vinyl cation pathway.

Cyclic β,β‐difluoro‐carbonyl compounds have a venerable history as drug discovery leads, but limitations in the synthesis arsenal continue to impede chemical space exploration. This challenge is particularly acute in the arena of fluorinated medium rings where installing the difluoromethylene unit subtly alters the ring conformation by expanding the internal angle (∠C−CF2−C>∠C−CH2−C): this provides a handle to modulate physicochemistry (e.g. pKa). To reconcile this disparity, a highly modular ring expansion has been devised that leverages simple α,β‐unsaturated esters and amides, and processes them to one‐carbon homologated rings with concomitant geminal difluorination (6 to 10 membered rings, up to 95 % yield). This process is a rare example of the formal difluorination of an internal alkene and is enabled by sequential I(III)‐enabled O‐activation. Validation of enantioselective catalysis in the generation of unprecedented medium ring scaffolds is reported (up to 93 : 7 e.r.) together with X‐ray structural analyses and product derivatization. [ABSTRACT FROM AUTHOR]

The reaction of the amine‐stabilized alane (NMe3) ⋅ AlH31 with the backbone‐saturated N‐heterocyclic carbene (NHC) SIDipp (SIDipp=1,3‐bis‐{2,6‐di‐iso‐propyl‐phenyl}‐imidazolidin‐2‐ylidene) at 0 °C yielded the NHC alane adduct (SIDipp) ⋅ AlH32. Reaction at elevated temperatures or prolonged reaction at room temperature gave the product of a ring expansion reaction (RER) of the NHC, (NMe3) ⋅ AlH(RER‐SIDippH2) 3 ⋅ (NMe3). Subsequent reaction of the latter with sterically less hindered NHCs (IMeMe {=1,3,4,5‐tetramethyl‐imidazolin‐2‐ylidene}, IiPrMe {=1,3‐di‐iso‐propyl‐4,5‐dimethyl‐imidazolin‐2‐ylidene}, and IiPr {=1,3‐di‐iso‐propyl‐imidazolin‐2‐ylidene}) afforded the NHC‐stabilized RER‐products (NHC) ⋅ AlH(RER‐SIDippH2) 3 ⋅ (NHC) (NHC=IMeMe, IiPrMe, IiPr), while no reaction was observed with the sterically more demanding NHCs IDipp (=1,3‐bis‐{2,6‐di‐iso‐propyl‐phenyl}‐imidazolin‐2‐ylidene), SIDipp and ItBu (=1,3‐di‐tert‐butyl‐imidazolin‐2‐ylidene). The compounds 3 ⋅ (NHC) were also obtained starting from (SIDipp) ⋅ AlH32 and NHC at room temperature. Heating solutions of (SIDipp) ⋅ AlH32 without additional base to 95 °C resulted in decarbonization of the NHC and substitution of the carbene carbon atom with aluminum hydride under loss of ethene. Subsequent dimerization afforded cis‐[AlH{μ‐N(Dipp)CH2CH2N(Dipp)}]24_dimer. Heating solutions of the NHC‐ligated aluminum alkyls (SIDipp) ⋅ AlR32R (R=Me, Et) to 145 °C instead led to complete scission of the NHC backbone with evolution of ethene and isolation of the dialkylaluminium(III) amidinates {DippNC(R)NDipp}AlR25R (R=Me, Et). [ABSTRACT FROM AUTHOR]

Herein, we present a unified chemical synthesis of three subgroups of cephalotaxus diterpenoids. Key to the success lies in adopting a synthetic strategy that is inspired by biosynthesis but is opposite in nature. By employing selective one‐carbon introduction and ring expansion operations, we have successfully converted cephalotane‐type C18 dinorditerpenoids (using cephanolide B as a starting material) into troponoid‐type C19 norditerpenoids and intact cephalotane‐type C20 diterpenoids. This synthetic approach has enabled us to synthesize cephinoid H, 13‐oxo‐cephinoid H, 7‐oxo‐cephinoid H, fortalpinoid C, 7‐epi‐fortalpinoid C, cephanolide E, and 13‐epi‐cephanolide E. Furthermore, through the development of an intermolecular asymmetric Michael reaction between β‐oxo esters and β‐substituted enones, we have achieved the enantioselective synthesis of advanced intermediates within our synthetic sequence, thus formally realizing the asymmetric total synthesis of the cephalotaxus diterpenoids family. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: A mild and practical method for synthesizing fluorinated quinoline derivatives, which have a wide range of applications in pharmaceuticals, materials, and organic synthesis, was described through C—F bond insertion into indoles using CHBr2F. The simple conditions, readily availability of CHBr2F, as well as the versatility of the transformations make this strategy very powerful in synthesizing 3‐fluoroquinoline and 3‐fluoroquinolone. The mechanistic studies reveal that bromofluorocarbene generated in‐situ under basic condition was the key intermediate. [ABSTRACT FROM AUTHOR]

Skeleton editing has rapidly advanced as a synthetic methodology in recent years, significantly streamlining the synthesis process and gaining widespread acceptance in drug synthesis and development. This field encompasses diverse ring reactions, many of which exhibit immense potential in skeleton editing, facilitating the generation of novel ring skeletons. Notably, reactions that involve the cleavage of two distinct rings followed by the reformation of new rings through ring insertion play a pivotal role in the construction of novel ring skeletons. This article aims to compile and systematize this category of reactions, emphasizing the two primary reaction types and offering a thorough exploration of their associated complexities and challenges. Our endeavor is to furnish readers with comprehensive reaction strategies, igniting research interest and injecting fresh impetus into the advancement of this domain. [ABSTRACT FROM AUTHOR]

Ring expansion of 4-[(2R)-1-[(1R)-1-phenylethyl]aziridin-2-yl]butyl tosylate obtained from tosylation of 4-[(2R)-1-[(1R)-1-phenylethyl]aziridin-2-yl]butan-1-ol via formation of 1-azabicyclo[4.1.0]heptane tosylate gives substituted piperidine. The ring openings of azabicycloheptane tosylate with acetate nucleophiles proceeded in highly regio- and stereoselective manner with release of the ring-strain of the three-membered aziridine ring through the breakage of either C-N bond. This ring expansion streategy of aziridine provides a short route for asymmetric synthesis of biologically active natural alkaloid such as (R)-pipecolic acid. [ABSTRACT FROM AUTHOR]

Herein, we successfully inhibited the preferential homodimerization and C−Si/Si−H bond cross‐exchange of benzosilacyclobutenes and monohydro‐silacyclobutanes and achieved the first highly selective C−Si/C−Si bond cross‐exchange reaction by deliberately tuning the Ni‐catalytic system, which constitutes a powerful and atom‐economical ring expansion method for preparing medium‐sized cyclic compounds bearing two silicon atoms at the ring junction, which are otherwise inaccessible. The DFT calculation explicitly elucidated the pivotal role of Si−H bond at silacyclobutanes and the high ring strain of two substrates in realizing the two C−Si bonds cleavage and reformation in the catalytic cycle. [ABSTRACT FROM AUTHOR]

Azetidines, being four‐membered N‐heterocycles, possess significant potential in contemporary medicinal chemistry owing to their favorable pharmacokinetic properties. Regrettably, the incorporation of functionalized azetidines into pharmaceutical lead structures has been impeded by the absence of efficient synthetic methods for their synthesis. In this study, a Rh‐catalyzed one‐carbon ring expansion of aziridines with vinyl‐N‐triftosylhydrazones is presented, which facilitates the synthesis of high value‐added 2‐alkenyl azetidine products. This research represents the first example of ring expansion of aziridines enabled by vinyl carbenes. Additionally, a one‐pot two‐step protocol, initiated from cinnamaldehyde, was successfully achieved, offering a step‐economical and facile approach for the synthesis of these compounds. The pivotal aspect of this successful transformation lies in the in situ formation of an alkenyl aziridinium ylide intermediate. Experimental investigations, coupled with computational studies, suggest that a diradical pathway is involved in the reaction mechanism. [ABSTRACT FROM AUTHOR]

Benzo‐fused nitrogen heterocycles are common features of bioactive molecules, and the enantioselective synthesis of their substituted analogues is an important goal. In this paper we demonstrate a practical and mechanistically intriguing approach to the enantioselective synthesis of 1‐arylbenzazepines and their analogues. The reaction sequence starts with an asymmetric migratory ring expansion of indoline, tetrahydroquinoline, or tetrahydrobenzazepine ureas on treatment with a chiral lithium amide base. Treatment of the ring‐expanded ureas with acid triggers a two‐atom ring contraction—an 'azatropic shift' in which one urea nitrogen displaces the other—with almost complete retention of stereochemistry. Aminolysis of the urea products provides enantioenriched 1‐aryl‐tetrahydrobenzazepine derivatives and their congeners, including an analogue of an intermediate in the synthesis of the drug solifenacin. Deuteration, in situ IR, and DFT studies provide evidence for the mechanisms of the reaction steps. [ABSTRACT FROM AUTHOR]

2H‐arizines are important three‐membered heterocycles in organic chemistry. Recently, many advances in the synthesis and functionalization of 2H‐arizines have been reported. Neber rearrangement, isomerization of isoxazole, oxidation of enamine, C−H bond activation, decomposition of vinyl azide, functionalization of alkyne, and multi‐step synthesis have been developed for the efficient assembly of 2H‐azirines. As versatile and highly strained three‐membered unsaturated heterocycles, 2H‐azirines can be used as distinctive building blocks towards significant functional groups, and have attracted extensive attention for the fabrication of numerous heterocycles. Recent studies have focused on [3+n] ring‐expansion reactions, nucleophilic addition of C=N double bond or continuous nucleophilic addition followed by cyclization, ring‐opening of 2H‐azirines to acyclic compounds, and substitution of sp3‐C−H of 2H‐azirines. One of the most critical challenges is seeking for a selective opening of the specific three bonds of the strained azirine circle, some of what can be achieved on the basis of metal catalyst, photocatalysis, or combination of metal catalyst and photocatalysis. In this review, recent advances involving the synthesis and reactivity of 2H‐arizines accompanied with challenges and breakthroughs are summarized. The review mainly covers the period from 2019 to 2023. [ABSTRACT FROM AUTHOR]

The nitrogen‐heteroatom single bonds of 1,2‐azoles and isoxazolines underwent methylene insertion in the presence of CH2I2 (6 equiv.) and diethylzinc (3 equiv.) to produce a wide variety of the ring‐expanded six‐membered heterocycles. Density functional theory calculations suggest that the methylene insertion proceeds via cleavage of nitrogen‐heteroatom single bonds followed by ring closure. [ABSTRACT FROM AUTHOR]

Thanks to an unprecedented gem‐dialkyl substituent effect, an efficient synthesis of tetrahydro oxepine derivatives is achieved by ring expansion of vinyl oxetanes using acceptor(−acceptor) diazo reagents under Cu(II)‐catalysis. A large scope of 2‐vinyl oxetanes and either diazo mono or diester reagents give access to a series of functionalized oxepines. [ABSTRACT FROM AUTHOR]

A ring‐expansion process for the biomass derivative Cyrene obtained from levoglucosenone has been developed using gem‐dihalocyclopropanes as intermediates. The process involves conversion of Cyrene to an enamine, reaction with an in situ generated dihalocarbene, and then ring‐opening. Competition between endocyclic and exocyclic olefinic products was switchable using solvent and temperature, and ring‐expanded alkenyl halides were obtained in 50–64 % yield from Cyrene. Under extended heating, dehalogenation occurred giving homologated levoglucosenone in 25 % overall yield from Cyrene in 3 steps. [ABSTRACT FROM AUTHOR]

Macrocyclic and medium‐sized ring ketones, lactones and lactams can all be made from common acryloyl imide starting materials through divergent, one‐pot cascade ring‐expansion reactions. Following either conjugate addition with an amine or nitromethane, or osmium(VIII)‐catalysed dihydoxylation, rearrangement through a four‐atom ring expansion takes place spontaneously to form the ring expanded products. A second ring expansion can also be performed following a second iteration of imide formation and alkene functionalisation/ring expansion. In the dihydroxylation series, three‐ or four‐atom ring expansion can be performed selectively, depending on whether the reaction is under kinetic or thermodynamic control. [ABSTRACT FROM AUTHOR]

Reactions of 5‐SIDipp ⋅ BH3 (5‐SIDipp=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene) (1) with diphenyldiselenide provide access to 5‐SIDipp–boryl mono‐ (5‐SIDipp ⋅ BH2SePh) (2) and bis‐selenide (5‐SIDipp ⋅ BH(SePh)2) (3). The facile cleavage of the B−Se bond makes 2 a neutral source of selenium nucleophiles in substitutions reactions with benzyl bromides, and provide access to the corresponding selenoethers. The direct transformations of one of the C(sp2)−F bonds of C5F5N and C6F5CF3 to C−Se bonds have also been achieved by the use of 2 without employing transition‐metal catalysts. While it was previously established that C6F6 could undergo complete defluoroselenation under harsh conditions, we successfully achieved partial defluorination of C6F6 by employing 2 as a mild selenide transfer reagent. During the formation of C−Se bonds through the cleavage of C−F bonds, the potential by‐product NHC ⋅ BH2F undergoes ring expansion of the NHC, leading to the formation of the six‐membered diaazafluoroborinane (7). [ABSTRACT FROM AUTHOR]

3‐Fluorinated quinolines and pyridines are prevalent pharmacophores, yet their synthesis is often challenging. Herein, we demonstrate that dibromofluoromethane as bromofluorocarbene source enables the one‐carbon ring expansion of readily available indoles and pyrroles to structurally diverse 3‐fluorinated quinolines and pyridines. This straightforward protocol requires only a short reaction time of ten minutes and can be performed under air atmosphere. Preliminary investigations reveal that this strategy can also be applied to the synthesis of other valuable azines by using different 1,1‐dibromoalkanes as bromocarbene sources. [ABSTRACT FROM AUTHOR]

This article discusses the total synthesis of complanadine A, a Lycopodium alkaloid with potential applications in the treatment of neurological disorders and pain management. The authors describe their novel pyrrole-to-pyridine molecular editing strategy, which enables the efficient synthesis of complanadine A. They outline the retrosynthetic analysis and the key steps involved in the synthesis, including the use of cross-coupling and C-H arylation reactions. The authors also highlight the challenges and optimizations encountered during the synthesis process. The document provides a detailed account of a chemical reaction and the resulting compounds, including information about reaction conditions, purification methods, and characterization data. It is intended for researchers in the field of organic chemistry. [Extracted from the article]

We herein report an efficient synthetic method for preparing [6‐7‐6]‐icetexane derivatives. This approach employs our previously designed copper‐catalyzed intramolecular cyclization of enyne‐aryl carbonyl substrates to generate a [6‐6‐6]‐tricyclic abietane framework and a subsequent ring expansion protocol for the [6‐7‐6] scaffold. By synergizing these protocols, we established a highly efficient pathway for synthesizing icetexane compounds from readily available enyne‐aryl starting materials, exhibiting remarkable versatility in accommodating various functional groups while delivering consistently high yields. [ABSTRACT FROM AUTHOR]

Abstract The nitrogen‐heteroatom single bonds of 1,2‐azoles and isoxazolines underwent methylene insertion in the presence of CH2I2 (6 equiv.) and diethylzinc (3 equiv.) to produce a wide variety of the ring‐expanded six‐membered heterocycles. Density functional theory calculations suggest that the methylene insertion proceeds via cleavage of nitrogen‐heteroatom single bonds followed by ring closure.

A series of imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazines was synthesized via a cascade sequence of hydrolysis and skeletal rearrangement of imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazin-7(8H)-ylidene)acetic acid esters in methanol upon treatment with excess KOH. Imidazo[4,5-e]thiazolo[3,2-b][1,2,4]triazin-6(7H)-ylidene)acetic acid esters are also suitable substrates for the reaction. In this case hydrolysis and thiazole ring expansion were accompanied with the change of the thiazolotriazine junction type from thiazolo[3,2-b][1,2,4]triazine to thiazino[2,3-c][1,2,4]triazine.

Synthetic methodologies based on cycle expansion reactions have proven to be highly effective in delivering valuable medium‐sized cycles and macrocycles. A primary method of ring expansion relies on intramolecular transamidation reactions. These reactions typically employ N‐aminoalkyl and N‐aminoacyl derivatives of lactams and their analogues as starting materials, yielding a diverse spectrum of unique nitrogen‐containing heterocycles. This Review aims to provide a comprehensive analysis of the research outcomes related to intramolecular transamidation reactions that lead to cycle expansion. This will offer the reader a perspective on the potential applications of such reactions in generating novel and intriguing types of heterocyclic systems. [ABSTRACT FROM AUTHOR]

This review summarizes achievements in the synthesis of 1,2-disubstituted adamantane derivatives by the construction of the tricyclic framework either by total synthesis or by ring expansion/contraction reactions of corresponding adamantane homologues. It is intended to complement reviews focusing on the preparation of 1,2-disubstituted derivatives by C–H functionalization methods. [ABSTRACT FROM AUTHOR]

The dearomative spirocyclisation of benzisoxazoles through a radical chain mechanism is described. Densely functionalised spirocycles were prepared in high yields by reacting benzisoxazole‐tethered ynones with aryl thiols in 1,2‐dichloroethane (DCE) at 60 °C. The identification of stabilising three‐electron interactions was key to the development of this new radical cascade reaction. The obtained spirocyclic products were converted into other spirocyclic scaffolds through a two‐step hydrogenolysis‐cyclisation sequence. [ABSTRACT FROM AUTHOR]

A synthetic strategy involving a Simmons‐Smith cyclopropanation, followed by an acid‐catalyzed pinacol rearrangement, was developed to transform α‐hydroxy silyl enol ethers into 1‐substituted bicyclo[2.1.1]hexan‐5‐ones. These bicyclic ketones underwent further synthetic manipulations to generate various 1,5‐disubstituted bicyclo[2.1.1]hexanes, which could serve as potential bioisosteres of ortho‐substituted arenes. [ABSTRACT FROM AUTHOR]

For the insertion of amino acid derivatives, the Fmoc protecting group strategy was used (SuRE method B), with both - and -amino acids again being compatible ( B 25 b , B 31 b - B 34 b ). Using this method, I N i -acylation of B 21 b using the more stable Fmoc-protected amino acid chloride B 22 b proceeded well (based on full consumption of B 21 b by TLC analysis) to form imide B 23 b (Scheme 3). It is clear that lactam B 21 b undergoes I N i -acylation less readily than lactam B 8 b , and in previous work we have found Cbz-protected amino acid chlorides to be less stable than the analogous Fmoc derivatives. Keywords: macrocycles; medium-sized rings; ring expansion; natural product analogues; lactams; lactones; solomonamides EN macrocycles medium-sized rings ring expansion natural product analogues lactams lactones solomonamides 1694 1698 5 08/18/23 20230901 NES 230901 Graph Solomonamides A and B were first isolated in 2011 by Zampella and coworkers from the marine sponge I Theonella swinhoei i . [Extracted from the article]

Skeleton editing has rapidly advanced as a synthetic methodology in recent years, significantly streamlining the synthesis process and gaining widespread acceptance in drug synthesis and development. This field encompasses diverse ring reactions, many of which exhibit immense potential in skeleton editing, facilitating the generation of novel ring skeletons. Notably, reactions that involve the cleavage of two distinct rings followed by the reformation of new rings through ring insertion play a pivotal role in the construction of novel ring skeletons. This article aims to compile and systematize this category of reactions, emphasizing the two primary reaction types and offering a thorough exploration of their associated complexities and challenges. Our endeavor is to furnish readers with comprehensive reaction strategies, igniting research interest and injecting fresh impetus into the advancement of this domain.

A photoredox‐mediated radical amidation ring‐expansion sequence that enables the generation of all‐carbon quaternary centers bearing a protected aminomethyl substituent is described. The methodology can be applied to both styrene and unactivated alkene substrates generating structurally diverse sp3‐rich amine derivatives in a concise manner. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: A general and efficient strategy for the synthesis of γ‐lactams has been reported. The hydroxylamines form Lossen rearrangement products of electron‐deficient group migration with base and then undergo [3+2] cycloaddition reaction with vinyl cyclopropane, which could be performed with broad substrate scope, excellent functional group tolerance and high efficiency to produce the desired products. It also allowed further modification to other derivatives of these γ‐lactams. [ABSTRACT FROM AUTHOR]

We demonstrate that arylchlorodiazirines serve as photo‐activated halocarbene precursors for the selective one‐carbon ring expansion of N‐substituted pyrroles and indoles to the corresponding pyridinium and quinolinium salts. Preliminary investigations indicate that the same strategy also enables the conversion of N‐substituted pyrazoles to pyrimidinium salts. The N‐substituent of the substrate plays an essential role in: (1) increasing substrate scope by preventing product degradation, (2) enhancing yields by suppressing co‐product inhibition, and (3) activating the azinium products towards subsequent synthetic manipulations. This latter point is illustrated by subjecting the quinolinium salts to four complementary partial reductions, which provide concise access to ring‐expanded products with different degrees of increased C(sp3) character. Thermal analysis of the diazirines by differential scanning calorimetry (DSC) provides detailed insight into their energetic properties, and highlights the safety benefits of photolyzing—rather than thermolyzing—these reagents. [ABSTRACT FROM AUTHOR]

Two acyclic acylaluminums and one cyclic acylaluminum dimer were synthesized by reaction of the recently reported Al‐anion with acyl chloride. The reaction of the acylaluminums with TMSOTf and DMAP gave a ring‐expanded iminium‐substituted aluminate and a 2‐C−H cleaved product. In the reaction of acylaluminums toward C=O and C=N bonds, acyclic acylaluminums reacted as an acyl nucleophile, while the cycilc dimer showed no reactivity. Amide‐bond forming ligation using acyclic acylaluminums and hydroxylamines was further demonstrated. Throughout the study, acyclic acylaluminums exhibited higher reactivity than that of the cyclic dimer. [ABSTRACT FROM AUTHOR]

The crude product was purified by PLC (40% EtOAc in hexane) to afford compound B 26 b [yield: 10.7 mg (25%); pale-yellow solid] and compound B 27 b . [13] Methylation of compound B 11a b was performed using MeI in the presence of K SB 2 sb CO SB 3 sb or NaH in THF as a solvent to introduce a methyl carbon at the I endo i - or I exo i -secondary amide of the lactam moiety, as shown in Table 1. The percentage inhibition was calculated using the following equation: % Inhibition = {[(Vc - Vb) - (Vi - Vb)] / (Vc - Vb)} × 100 where Vc is the enzymatic reaction rate of the control (absence of a test compound, negative control), Vb is the enzymatic reaction rate of the blank (absence of enzyme) and Vi is the enzymatic reaction rate of the test compound. Keywords: Clausena alkaloids; -clausenamides; balasubramides; benzo[ d ]azocinones; eight-membered lactams; ring expansion EN Clausena alkaloids -clausenamides balasubramides benzo[ d ]azocinones eight-membered lactams ring expansion 2241 2252 12 07/03/23 20230718 NES 230718 Plants in the genus I Clausena i (Rutaceae family) have been used as traditional medicinal herbs in the tropical and subtropical parts of Asia, particularly in China, India and Thailand. [Extracted from the article]

Comprehensive Summary: The utilization of cyclobutanones as the synthon in transition metal catalysis has been made great success. Because C(carbonyl)−C bond of cyclobutanones can be cleaved through strain release. Despite those advancements, the main catalysts in literature are Rh catalysts or Ni catalysts and the reaction with C—H bond is still underdeveloped. Herein, we realized the first palladium‐catalyzed skeletal reorganization of cyclobutanones involving successive cleavage of C(carbonyl)−C bonds and C—H bond cleavage, which constitutes an rapid access to diverse indanones. In contrast to the previous Rh‐catalytic system, the Pd‐catalytic system herein involves different mechanism and features several advantages: 1) no need of directing group to facilitate the C(carbonyl)−C bond cleavage; 2) much milder reaction condition and 3) simplified work‐up. [ABSTRACT FROM AUTHOR]

Simultaneous electrochemical ring contraction and expansion reactions remain unexplored to date. Herein, the reductive electrosynthesis of heterocycle‐fused fulleroids from fullerotetrahydropyridazines and electrophiles in the presence of a trace amount of oxygen has been achieved with concurrent ring contraction and ring expansion. When trifluoroacetic acid and alkyl bromides are employed as electrophiles, heterocycle‐fused fulleroids with a 1,1,2,6‐configuration are regioselectively formed. In contrast, heterocycle‐fused fulleroids with a 1,1,4,6‐configuration are regioselectively produced as two separable stereoisomers if phthaloyl chloride is used as the electrophile. The reaction proceeds through multiple steps of electroreduction, heterocycle ring‐opening, oxygen oxidation, heterocycle contraction, fullerene cage expansion, and nucleophilic addition. The structures of these fulleroids have been determined by spectroscopic data and single‐crystal X‐ray diffraction analyses. The observed high regioselectivities have been rationalized by theoretical calculations. Representative fulleroids have been applied in organic solar cells as the third component and exhibit good performance. [ABSTRACT FROM AUTHOR]