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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]

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]

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]

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]

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.

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]

α‐Trifluoromethyl azocanes are accessible from 2‐(trifluoropropan‐2‐ol) piperidines by metal‐free ring‐expansion involving a bicyclic azetidinium intermediate. The opening of the azetidinium intermediate was achieved by various nucleophiles (amines, alcoholates, carboxylates, phosphonates, halides and pseudo‐halides) with an excellent regio‐ diastereo‐ and enantioselectivity and in good yields. The relative configuration of the piperidines and azocanes were assigned and the deprotected azocanes offer opportunities for further derivatization. [ABSTRACT FROM AUTHOR]

A facile route to polysubstituted 2-pyrones from readily available 2-acylcyclopropane-1-aryl-1-carboxylates mediated by TfOH is reported. The strongly donating 1-aryl group is important for directing the C–C bond cleavage of the donor-acceptor cyclopropane ring, which then leads to the formation of the 2-pyrone ring through lactonization. [ABSTRACT FROM AUTHOR]

A metal‐free approach for the synthesis of seven‐membered heterocycles (chromane, thiochromane) or rings fused with heterocycles (furan, indole, pyrrole, and thiophene) is described. The salient feature of the strategy is based on the ring expansion of methylenic heterocycles mediated by the iodine(III) reagent HTIB (PhI(OH)OTs) in aqueous acetonitrile. [ABSTRACT FROM AUTHOR]

We herein report an efficient and systematic synthesis of 1‐pyrrolines from cyclobutyl azides under thermal and neutral conditions. The reaction proceeded without any additional reagents, and nitrogen was generated as the sole by‐product. Furthermore, the generated 1‐pyrrolines could be continuously transformed into pyrroles, N‐Boc‐amines, and oxaziridines in an one‐pot manner. [ABSTRACT FROM AUTHOR]

Vinyl aziridines are versatile starting materials toward ring-expansion transformations. Such processes are widely used to give various medium or larger N-heterocycles of synthetic interest. This letter describes a copper-catalyzed ring expansion of vinyl aziridines to 3-pyrrolines by using a Cu(I) salt [(CuOTf)2 ·toluene or Cu(MeCN)4 ·PF6 ]. In particular, this transformation occurs under mild conditions (THF, rt). [ABSTRACT FROM AUTHOR]

The title compounds were synthesized from readily available quinolone and coumarin derivatives by a cascade reaction (12 examples, 90–98% yield). The cascade comprised a [2+2] photocycloaddition which occurred upon sensitized irradiation at λ = 420 nm (or direct UV irradiation at λ = 366 nm) and a subsequent acid-catalyzed ring-opening reaction. A variety of substituents are compatible with the conditions and a 3-alkyl group in the coumarin (or quinolone) is crucial to achieve a high chemoselectivity. Key to the success of the ring opening is the formation of a 4,5,5a-trihydrocyclobuta-2 H -furan containing a strained bridgehead double bond which stems from the allenyl group tethered to the 4-position of the starting materials. [ABSTRACT FROM AUTHOR]

A new pathway for the ring expansion reaction of antiaromatic boroles with organic azides is reported. While the reaction usually leads to 1,2‐azaborinines, it was diverted to the formation of a 1,2,3‐diazaborinine by changing the electronic characteristics of the reagents. The isolable azo‐azaborinine intermediate initially formed from the reaction of 1‐(2,3,4,5‐tetraphenylborolyl)ferrocene with 4‐azido‐N,N‐dimethylaniline gradually decomposed to a 1,2,3‐diazaborinine and benzonitrile. Both the spectroscopic properties and the reactivity of the heteroaromatic compound show analogies to pyridine, to which it is isoelectronic. Density functional theory (DFT) calculations provided insight into the mechanism of this unusual transformation. Nitrile & error: A new pathway for the ring expansion reaction of boroles with organic azides is presented, leading to a 1,2,3‐diazaborinine instead of the expected 1,2‐azaborinine. Mechanistic DFT calculations provided insight into the mechanism of formation of the BN2C3 heterocycle, and spectroscopic and reactivity studies demonstrated the analogies of the 1,2,3‐diazaborinine to pyridine. [ABSTRACT FROM AUTHOR]

Chloroperoxidase from Caldariomyces fumago catalyzes the selective oxidation of furfuryl alcohols in an Achmatowicz‐type ring expansion. In combination with glucose oxidase as oxygen‐activating biocatalyst, a purely enzymatic, aerobic protocol for the synthesis of 6‐hydroxypyranone building blocks is obtained. Thanks to an only modest stereochemical bias of the oxygenating heme protein, optically active alcohols of either configuration are converted without a significant mismatch opening up opportunities for enantioselective multienzymatic cascades. Balancing the oxidase‐driven aerobic activation, extended enzyme half‐lives and productive conversion of poorly soluble and slowly reacting substrates can be achieved with high yields of the six‐membered O‐heterocycles. [ABSTRACT FROM AUTHOR]

Abstract: Described herein is the first intermolecular σ‐bond exchange reaction between the C−C bond of cyclopropenones and C−Si bond of (benzo)silacyclobutanes and it proceeds smoothly by treatment with either 1 mol % of a palladium or 2 mol % of a nickel catalyst. This reaction constitutes an unprecedented route for the synthesis of various sila(benzo)suberones. And it is also the first example of a σ‐bond exchange reaction involving cyclopropenones. [ABSTRACT FROM AUTHOR]

The endocyclic ring expansion of N-heterocyclic carbene (NHC) rings by transition metal (group 12) and main group (group 13-16) element hydrides has been investigated in a computational study. In addition to previously reported insertion reactivity with Si, B, Be and Zn, similar reactivity is predicted to be feasible for heavier group 13 elements (Al, Ga, In, Tl), with the reaction barriers for Al-Tl calculated to be lower than for boron. Insertion is not expected with group 15-16 element hydrides, as the initial adduct formation is thermodynamically unfavorable. The reaction pathway with group 12 hydrides is calculated to be more favorable with two NHCs rather than a single NHC (analogous to Be), however hydride ring insertion with metal dihydrides is not feasible, but rather a reduced NHC is thermodynamically favored. For group 14, ring-insertion reactivity is predicted to be feasible with the heavier dihydrides. Trends in reactivity of element hydrides may be related to the protic or hydridic character of the element hydrides. [ABSTRACT FROM AUTHOR]

Electronic and steric factors have been investigated in the thermal ring expansion of boroles with organic azides, a reaction that provides access to highly arylated 1,2-azaborinines, BN analogues of benzene. Reactions of a variety of boroles and organic azides demonstrate that the synthetic method is quite general in furnishing 1,2-azaborinines, but the respective reaction rates reveal a strong dependence on the substituents on the two reactants. The products have been characterized by UV/Vis, electrochemical, NMR, and X-ray diffraction methods, clarifying their constitutions and highlighting substituent effects on the electronic structure of the 1,2-azaborinines. Furthermore, analysis of several possible mechanistic pathways for 1,2-azaborinine formation, as studied by DFT, revealed that a two-step mechanism involving azide-borole adduct formation and nitrene insertion is favored. [ABSTRACT FROM AUTHOR]

The ring expansion and skeletal rearrangement of two types of propargyl alcohol substituted aziridines with or without cycloalkane moieties was induced by a ruthenium cyclopentadienyl phosphine complex. In the simple aziridine system with no cycloalkane, the unique cycloisomerization process altered the absolute connectivity of the two-carbon unit in the three-membered ring to give organometallic products with substituted pyridine or dihydropyridine ligands. For the aziridine on a cyclohexyl ring, the cycloisomerization process was controlled by an interchange process between vinylidene and allenylidene species, thus creating a better relative configuration of the aziridinyl and the alkynyl units. This determines the stereochemistry of the metal carbene products of the octahydroindole derivatives. The structures of five products were determined by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

Simple benzo-fused nitrogen heterocycles (indolines, tetrahydroquinolines, and their homologues) undergo migratory ring expansion through deprotonation of their benzylic urea derivatives with lithium diisopropylamide (LDA) in the presence of N,N′-dimethylpropylideneurea (DMPU). The products of the reactions are benzodiazepines, benzodiazocines, and their homologues, with ring sizes of 8-12. The reactions tolerate a range of substituent patterns and types, and may exhibit enantiospecificity or diastereoselectivity. Considerable complexity is rapidly generated in an efficient synthesis of these otherwise difficult-to-obtain medium-ring nitrogen heterocycles. [ABSTRACT FROM AUTHOR]

Described are the first examples of intermolecular electrophilic additions of epoxides to alkenes, which proceed through a classic cationic mechanism initiated by epoxide C-O bond cleavage. Treatment of styrene oxides and either styrenes or dienes with a variety of Lewis-acidic triflate salts generates tetrahydrofurans as products of [3+2] cycloaddition in moderate to good yields (up to 71 %). Careful choice of catalyst and reaction conditions favors the desired intermolecular reaction over epoxide degradation without requiring additional reagents or additives. The reaction proceeds diastereoselectively and provides only one regioisomer of the product. Additional highlights include inexpensive precursors, mild conditions, short reaction times, low catalyst loading, and scalability. [ABSTRACT FROM AUTHOR]

We present here two new methods based on rearrangement reactions to obtain novel 2-substituted 3-hydroxy-4-oxo-1,4-dihydroquinolines, an important family of heterocycles with potential applications. Alkyl 3-hydroxy-4-oxo-1,4-dihydroquinoline-2-carboxylates were obtained by alkoxide promoted rearrangement of alkyl isatinacetates. A second synthetic route involves the alkoxide promoted reaction of both isatin and N -methylisatin, with alkylating agents having acidic methylenes. This reaction leads to the formation of spiroepoxyoxindoles via Darzens’ condensation. When phenacyl bromides are used, the initially obtained benzoyl substituted spiroepoxyoxindoles were smoothly transformed into the corresponding 2-benzoyl-3-hydroxy-4-quinolinones with good to excellent yields. [ABSTRACT FROM AUTHOR]

A new metal-free, ring-expansion reaction of six-membered N-sulfonylimines with unstable diazomethanes, generated in situ from the N-tosylhydrazones, has been developed. This reaction delivers valuable seven-membered enesulfonamides by a Tiffeneau-Demjanov rearrangement and intramolecular proton transfer tautomerization process. Moreover, this ring-expansion reaction can be carried out in a one-pot fashion and scaled up to the gram scale by using aryl aldehydes, without the need to isolate the N-tosylhydrazone. [ABSTRACT FROM AUTHOR]

A mild and efficient gold-catalyzed oxidative ring-expansion of a series of alkynyl heterocycles using pyridine-N-oxide as the oxidant has been developed, which affords highly valuable six- or seven-membered heterocycles with wide functional group toleration. The reaction consists of a regioselective oxidation and a chemoselective migration of an endocyclic carbon-heteroatom bond (favored over C-H migration) with the order of migratory aptitude for carbon-heteroatom bonds being C-S>C-N>C-O. In the absence of an oxidant, polycyclic products are readily constructed through a ring-expansion/ Nazarov cyclization reaction sequence. [ABSTRACT FROM AUTHOR]

The rhodium(II)-catalyzed denitrogenative coupling of N-alkylsulfonyl 1,2,3-triazoles with 1,3,5-trioxane led to nine-membered-ringed trioxazonines in moderate-togood yields. 1,3,5-Trioxane, acting as an oxygen nucleophile, reacted with the a-aza-vinylcarbene intermediate, giving rise to ylide formation, which was probably the key step in the reaction. Triazoles that contained aryl substituents with various electronic and steric features on the C4 carbon atom were well-tolerated. The synthesis of trioxazonine derivatives was achieved through a one-pot, two-step procedure from 1-mesylazide and a terminal alkyne by combining CuI-catalyzed 1,3-dipolar cycloaddition and rhodium-catalyzed transformations. [ABSTRACT FROM AUTHOR]

Access to novel imine-substituted 1,2-azaborinines, as well as highly arylated boracyclohexa-3,5-dienes has been developed by ring expansion of boroles with diazoalkanes with varying degrees of steric bulk. The formation of a diazoalkane intermediate is also discussed for the reaction of ortho-brominated p-tolyl-azide with 1,2,3,4,5-pentaphenylborole. Structural details as well as UV/Vis spectroscopic and cyclic voltammetric data are provided. These boron-containing heterocycles have the potential to serve as building blocks for boron-containing materials. [ABSTRACT FROM AUTHOR]

A one pot synthesis of 1 H-benzo[g]indoles, tetrahydrobenzo[h]quinolines, and naphtho[1,2-b]azepines from 2-alkynyl benzaldehydes and cyclic amino acids is reported. The salient feature of the strategy involves formation of three new bonds (one CN and two CC bonds) by a metal-free decarboxylation/cyclization/one-carbon ring expansion sequence in one pot. [ABSTRACT FROM AUTHOR]

Herein, we present the results of our investigations on the effect of ortho substitution of aryl azides on the ring-expansion reaction of boroles, five-membered unsaturated boron heterocycles. These studies led to the isolation of the first 1,2-azaborinine-substituted azo dyes, which are bright yellow solids. One of the derivatives, ( E)-2-mesityl-1-(mesityldiazenyl)-3,4,5,6-tetraphenyl-1,2-azaborinine, was found to be unstable in solution and to transform through a Jacobsen-like reaction into an indazole and 1-hydro-1,2-azaborinine. DFT calculations were performed to shed light on possible mechanisms to rationalize the unexpected azo-azaborinine formation and to draw conclusions about the role played by the ortho substituents in the reaction. [ABSTRACT FROM AUTHOR]

Tricyclic dibenzoxepines and dibenzazepines are important therapeutic agents for the pharmaceutical industry and academic research. However, their syntheses are generally rather tedious, requiring several steps that involve a Wagner-Meerwein-type rearrangement under harsh conditions. Herein, we present the first copper(I)-catalyzed oxidative CH bond functionalization and ring expansion with TMSCHN2 to yield these important derivatives in a facile and straightforward way. [ABSTRACT FROM AUTHOR]

Three regioisomeric thieno[c]azocine derivatives were prepared in six steps from bromothiophene carboxylic acids. The reaction sequence started with an esterification with isopropyl alcohol. The resulting esters were submitted to a Heck reaction with tert-butyl acrylate followed by catalytic hydrogenation. Subsequent Dieckmann condensation gave cyclopentathiophenes with a cyclic β-oxo ester motif, which were α-alkylated with phenacyl bromide to furnish 1,4-diketones. The latter were converted in the key step, a bismuth-catalyzed ring transformation with methylamine, yielding the racemic eightmembered ring lactams, that is, tetrahydrothieno[2,3-c]-, [3,2-c]-, and -[3,4-c]azocine derivatives in overall yields of 25%, 16% and 12%, respectively. [ABSTRACT FROM AUTHOR]

In this work, for the first time, a cationic polymer containing pendant pyridinium groups was synthesized via post-functionalization of the polymeric backbone based on a calix[4]resorcinarene, and characterized by AFM, TEM, analytical CHN, TGA, and DTG techniques. The functionalized polymer is conveniently loaded with desired anions, thereby providing novel and recyclable polymer-supported reagents for achieving synthetic goals. The thermal stability of this cationic polymer (up to 250 °C by TGA) allows thermally demanding ring transformation and expansion of 2,4,6-triarylthiopyrylium salts on its side chains and polymeric backbone without decomposition and leaching of active species in the reaction media. This green method furnished a straightforward route for the synthesis of valuable 2,4,6-triarylpyridines, along with novel 2,5,7-triaryl-1,3-thiazepine derivatives, which are widely present as motifs in an assortment of biologically active molecules. [ABSTRACT FROM AUTHOR]

Rearrangements of nitrile-stabilized ammonium ylides are useful reactions for the construction of alkylamines, nitrogen heterocycles, or carbonyl compounds. In spite of their attractive synthetic potential, they are much less frequently used than rearrangements of ammonium ylides either carrying charge-stabilizing carbonyl groups or being devoid of additional stabilization of the negative charge. This review focuses on different classes of rearrangements of nitrile-stabilized ammonium ylides as well as their application in synthetic organic chemistry. 1 Introduction 2 [1,2]-Stevens Rearrangements 3 [2,3]-Sommelet-Hauser Rearrangement 4 [2,3]-Stevens Rearrangements 5 Competitive [1,2]-, [2,3]-, and [1,4]-Rearrangements 6 [1,4]-Rearrangements Involving Ring Expansion 7 Summary [ABSTRACT FROM AUTHOR]

1-[(1 R)-(1-Phenylethyl)]-1-azoniabicyclo[3.1.0]hexane tosylate was generated as a stable bicyclic aziridinium salt from the corresponding 2-(3-hydroxypropyl)aziridine upon reaction with p-toluenesulfonyl anhydride. This bicyclic aziridinium ion was then treated with various nucleophiles including halides, azide, acetate, and cyanide in CH3CN to afford either piperidines or pyrrolidines through regio- and stereoselective ring opening, mediated by the characteristics of the applied nucleophile. On the basis of DFT calculations, ring-opening reactions under thermodynamic control yield piperidines, whereas reactions under kinetic control can yield both piperidines and pyrrolidines depending on the activation energies for both pathways. [ABSTRACT FROM AUTHOR]

A ring enlargement reaction with methylamine gave new pyrido[2,3- c]-, pyrido[3,4- c]- and pyrido[3,2- c]azocanone derivatives from cyclic β-oxo esters with a cyclopentapyridine skeleton and a 1,4-diketone moiety. The starting materials for this ring transformation were either prepared from halogenopyridine carboxylates by Heck reaction and subsequent hydrogenation, or (halogenomethyl)pyridine carboxylates were submitted to SN reaction with diethyl malonate. Both routes were completed by Dieckmann condensation to build the cyclic β-oxo ester structure and alkylation with phenacylbromide to install the 1,4-diketone motif. [ABSTRACT FROM AUTHOR]

trans-2-Aroyl-3-arylcyclopropane-1,1-dicarboxylates upon treatment with aluminium(III) chloride (AlCl3) underwent ring-opening, fragmentation, recombination and lactonization to give highly substituted 2-pyrones. Alternatively, when treated with titanium(IV) chloride (TiCl4), the cyclopropane diesters underwent a Nazarov cyclization to afford 1-indanones with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

The PPh3-catalyzed ring-expansion reaction of sulfamate-derived cyclic imines with acetylenedicarboxylates has been developed. The reaction works quite efficiently under very mild conditions to afford benzo[ g][1,2,3]oxathiazocine-4,5-dicarboxylate 2,2-dioxide derivatives in high yields. [ABSTRACT FROM AUTHOR]

A formal [3+2] cycloaddition between aziridines and alkenes to give the corresponding pyrrolidines was successfully carried out in the presence of a cationic manganese porphyrin catalyst. The use of the porphyrin catalyst allowed, for the first time, styrene derivatives to react with aziridines. [ABSTRACT FROM AUTHOR]

One ring to bring them all: 4,5‐Spirocycles derived from 3‐oxetanone and β‐heteroatom‐substituted amino compounds undergo a Lewis acid mediated reaction cascade to form saturated nitrogen heterocycles. The unique reactivity of 3‐oxetanone facilitates access to biologically important morpholines, piperazines, and thiomorpholines with an otherwise difficult‐to‐access substitution pattern from readily available starting materials. [ABSTRACT FROM AUTHOR]

In the last decade, chemists have increasingly focused on the development of new and more efficient methods for the catalytic conversion of carbon dioxide into value-added organic molecules. Homogeneous catalysis has proved to be a key technology for the conversion of carbon dioxide under particularly mild reaction conditions that meet the increasing societal demands for sustainable chemical processing. In this account article, we focus on the most effective routes developed for ring expansion-addition reaction of carbon dioxide to epoxides mediated by either metal catalysts or organocatalyst systems to give cyclic organic carbonates. [ABSTRACT FROM AUTHOR]

The direct combination of the desymmetrization of Nheterocyclic meso-diols using lipase from Mucor miehei as biocatalyst and subsequent ring expansion of the optically active products by activation of the remaining hydroxy group gives rise to functionalized nonsymmetrical piperidines in a highly enantio- and diastereoselective manner. [ABSTRACT FROM AUTHOR]

A five-step procedure for the synthesis of cis-1-tosyl-2-tosyloxymethyl-3-(trifluoromethyl)aziridine was developed, starting from 1-ethoxy-2,2,2-trifluoroethanol, involving imination, aziridination, ester reduction, hydrogenation, and N-, O-ditosylation steps. Further synthetic elaborations revealed a remarkable difference in the reactivity of cis-1-tosyl-2-tosyloxymethyl-3-(trifluoromethyl)aziridine with respect to aromatic sulfur and oxygen nucleophiles, thus enabling the selective deployment of this versatile substrate as a building block for the synthesis of functionalized aziridines, azetidines, and benzo-fused dithianes, oxathianes, dioxanes, and (thio)morpholines. [ABSTRACT FROM AUTHOR]

Synthetic studies on a 17ß-hydroxysteroid dehydrogenase type 3 (17ß-HSD3) inhibitor are described. The unsymmetrical dibenzazocine skeleton was constructed by a regiocontrolled ring-expansion reaction of a cyclic oxime with DIBAL-H. [ABSTRACT FROM AUTHOR]

Deprotonated 1,2-diazetines react with various ketones containing an acidic CH to yield pyridazine derivatives. The reaction allows the synthesis of dihydropyridazines containing a cycloamidine substructure via a sequence of ring-opening and recyclization. In this case, the in situ generated anion of 1,2-diazetines acts as a base as well as a chelator. The structures of the novel synthesized derivatives were confirmed by X-ray structural analysis and multidimensional NMR experiments. [ABSTRACT FROM AUTHOR]

Abstract: Treatment of substituted 1,3-oxathiolanes with ethyl (triethylsilyl)diazoacetate in the presence of a copper catalyst effects one-carbon ring expansion to the corresponding 3-triethylsilyl-1,4-oxathiane-3-carboxylates. Subsequent desilylation can be brought about by treatment with tetrabutylammonium fluoride. [Copyright &y& Elsevier]