Three-membered Ring Research Articles

Iron-Catalyzed Ortho C-H Homoallylation of Aromatic Ketones with Methylenecyclopropanes.

We report here a C-H homoallylation reaction of aromatic ketones with methylenecyclopropanes (MCPs) only using a catalytic amount of Fe(PMe3)4. A variety of aromatic ketones and MCPs are applicable to the reaction to form ortho-homoallylated aromatic ketones selectively via regioselective scission of the three-membered rings. The homoallylated products are amenable to further elaborations, providing functionalized 1,2-dihydronaphthalenes.

Isolable Phospha- and Arsaalumenes.

The combination of (AlCp*)4, a source of monomeric :AlCp* at elevated temperatures, with DipTerPnPMe3 (Pn = P, As), so-called pnicta-Wittig reagents, at 80 °C cleanly gives the pnictaalumenes DipTerPnAlCp* with polarized Pn-Al double bonds and intramolecular stabilization through interactions of Al with a flanking aryl group of the terphenyl substituent on Pn. In contrast, using MesTerPPMe3, the reaction with 2 equiv of :AlCp3t or :AlCp* afforded the three-membered 2π-aromatic ring systems MesTerP(AlCpx)2 (x = 3t, *).

Protic Ionic Liquid as Reagent, Catalyst, and Solvent: 1-Methylimidazolium Thiocyanate.

We propose a new concept of the triple role of protic ionic liquids with nucleophilic anions: a) a regenerable solvent, b) a Brønsted acid inducing diverse transformations via general acid catalysis, and c) a source of a nucleophile. The efficiency of this strategy was demonstrated using thiocyanate‐based protic ionic liquids for the ring‐opening of donor‐acceptor cyclopropanes. A wide variety of activated cyclopropanes were found to react with 1‐methylimidazolium thiocyanate under mild metal‐free conditions via unusual nitrogen attack of the ambident thiocyanate ion on the electrophilic center of the three‐membered ring affording pyrrolidine‐2‐thiones bearing donor and acceptor substituents at the C(5) and C(3) atoms, respectively, in a single time‐efficient step. The ability of 1‐methylimidazolium thiocyanate to serve as a triplex reagent was exemplarily illustrated by (4+2)‐annulation with 1‐acyl‐2‐(2‐hydroxyphenyl)cyclopropane, epoxide ring‐opening and other organic transformations.

Detonation properties and impact sensitivities of trinitromethane derivatives of three-membered heterocyclic ring compounds

We have carried out the design and theoretical investigation of a series of trinitromethane derivatives of three-membered heterocyclic ring compounds – aziridine, 1H-azirine, diaziridine, 1H-diazirine, triaziridine, 1H-triazirene, oxaziridine, oxadiaziridine, dioxaziridine, oxirane, and dioxirane – in search for new high energy density materials (HEDM). We have estimated the properties relevant to HEDMs of the proposed molecules using Density Functional Theory (B3LYP/aug-cc-pVDZ). The results show that most of the molecules have a high value of solid-phase heat of formation, crystal density, detonation velocity and pressure with satisfying values for impact sensitivities. We have identified some of these molecules, 1-(triinitromethyl)diaziridine, 2-(trinitromethyl)-1-nitro-1H-azirine, and (2-(trinitromethyl)-3-nitrooxirane) are potential candidates of energetic molecules among the 60 molecules we investigated. As most of them are having a high positive oxygen balance, they can be recommended for use as oxidisers in solid propellants.

Modification of soda-lime silicate glass under corona poling in air and nitrogen atmosphere

Modifications of a soda-lime silicate glass under thermal poling in corona discharge (CDP) in air and in dry nitrogen is studied with micro Raman technique to evaluate the possibility of glass structuration using poling in nitrogen. It is shown that CDP in dry nitrogen, contrary to CDP in atmospheric air, increases the concentration of silicon-oxygen tetrahedra bound into three-member rings in the subsurface region of the glass. The formation of the three-member rings is accompanied by the release of molecular oxygen.

Azide Radical Initiated Ring Opening of Cyclopropenes Leading to Alkenyl Nitriles and Polycyclic Aromatic Compounds.

We report herein a radical-mediated amination of cyclopropenes. The transformation proceeds through a cleavage of the three-membered ring after the addition of an azide radical on the strained double bond and leads to tetrasubstituted alkenyl nitrile derivatives upon loss of N2 . With 1,2-diaryl substituted cyclopropenes, this methodology could be extended to a one-pot synthesis of highly functionalized polycyclic aromatic compounds (PACs). This transformation allows the synthesis of nitrile-substituted alkenes and aromatic compounds from rapidly accessed cyclopropenes using only commercially available reagents.

Three-membered cyclic digermylenes stabilised by an N-heterocyclic carbene

Treatment of potassium salts of silole dianions with donor stabilised germanium dichlorides gave the anticipated silagermafulvenylidenes R2Si = Ge(Do) (R2Si = 1-silacyclopentadiendiyl, Do = N-heterocyclic carbene (NHC)) only as transient intermediates in a side reaction. They were detected by NMR spectroscopy and, in one case, the formal dimer, 2,4-disila-1λ3,3λ3-digermetane, was isolated. The main products of these reactions are sila-bis-λ3-germiranes, i.e. directly interconnected digermylenes that are part of a three-membered ring. The structural data, supported by the results of density functional calculations confirm the digermylene nature of these products with a long inner cyclic Ge–Ge bond that decreases the inherent high ring strain in silagermiranes.

Planar Tetracoordinated Silicon (ptSi): Room-Temperature Stable Compounds Containing Anti-van't Hoff/Le Bel Silicon.

While a variety of compounds containing planar tetracoordinated carbon (ptC), the so-called anti-van't Hoff/Le Bel carbon, are known experimentally, stable systems containing planar tetracoordinated silicon (ptSi) are barely known. As part of our studies on the application of stereoelectronically well-defined transition-metal fragments to stabilize silicon in unprecedented bonding modes, we report herein the synthesis and full characterization of a series of thermally stable complexes of the general formula [Tp'(CO)2MSiC(R1)C(R2)M(CO)2Tp'] (M = Mo, W; R1 = R2 = Me or R1 = H, R2 = SiMe3, Ph; Tp' = κ3-N,N',N″-hydridotris(3,5-dimethylpyrazolyl)borate), which incorporate a ptSi atom in addition to two ptC atoms. The complexes were obtained by reacting the metallasilylidyne complexes [Tp'(CO)2M≡Si-M(CO)2(PMe3)Tp'] with alkynes R1C≡CR2 and were comprehensively analyzed by experimental studies and quantum chemical calculations. The analyses revealed that the ptSi atom is embedded in a tricyclic trapezoidal core featuring one internal SiC2 and two outer M-Si-C three-membered rings, which are fused via two Si-C bonds. The structural peculiarities evoked by the presence of an anti-van't Hoff/Le Bel ptSi center, such as the short M-Si bonds, a nearly linear M-Si-M spine, long M-C bonds, and the presence of two planar tetracoordinated carbon atoms were elucidated by a detailed analysis of the electronic structure, suggesting that one factor for the stabilization of the ptSi geometry is the aromaticity of the central SiC2 ring having two delocalized π electrons. Remarkably, the results further indicate the existence of both anti-van't Hoff/Le Bel carbon and silicon centers next to each other in the isolated complexes.

Water-soluble manganese porphyrins as good catalysts for cipro- and levofloxacin degradation: Solvent effect, degradation products and DFT insights

Synthetic manganese porphyrins (MnPs), in the presence of oxidants, were employed for the degradation of fluoroquinolone antibiotics. Ciprofloxacin (CIP) and levofloxacin (LEV) degradation by iodosylbenzene, iodobenzene diacetate, H2O2 and meta-chloroperbenzoic acid using water-soluble MnP catalysts yielded thirteen and nine products, respectively, seven of which have been proposed for the first time. The MnP catalysts have demonstrated the ability to degrade these antibiotics to a high degree (up to 100% degradation). The structures of the degradation products were proposed based on mass spectrometry analysis, and density functional theory calculations could confirm how the substituent moieties attached to the basic chemical structure of the fluoroquinolones influence the degradation reactions. CIP has been shown to be a more reactive substrate towards the porphyrinic catalysts tested because of its three-membered ring. However, the catalysts could almost completely degrade LEV, highlighting the ability of these porphyrins to act as catalysts to degrade environmental pollutants.

Synthesis of Fluoro-, Monofluoromethyl-, Difluoromethyl-, and Trifluoromethyl-Substituted Three-Membered Rings.

This Minireview describes recent advances toward the synthesis of fluoro-, monofluoromethyl-, difluoromethyl-, and trifluoromethyl-substituted three-membered rings such as cyclopropanes, aziridines, epoxides, episulfides, cyclopropenes, and 2 H-azirines. The main synthetic methodologies since 2016 for cyclopropanes and since 2010 for the other three-membered rings are reported.

Immunomodulatory Constituents of Conocephalum conicum (Snake Liverwort) and the Relationship of Isolepidozenes to Germacranes and Humulanes.

Structural elucidation of three new sesquiterpenoids, namely, (1Z,4E)-lepidoza-1(10),4-dien-14-ol (1), rel-(1(10)Z,4S,5E,7R)-germacra-1(10),6 diene-11,14-diol (2), and rel-(1(10)Z,4S,5E,7R)-humula-1(10),5-diene-7,14-diol (3), isolated from the liverwort Conocephalum conicum, was accomplished by a combination of extensive NMR experiments, 1H NMR simulation, and other means. Additionally, the change of the identity of bicyclogermacren-14-al, previously reported as a C. conicum constituent, to isolepidozen-14-al is proposed. Compounds 2 and 3 appear to be related to 1 via hydration involving a shared intermediate, a substituted cyclopropylmethyl cation, formed by a highly regio- and stereoselective protonation of 1, followed by a stereospecific fission of the three-membered ring. In other words, an isolepidozene derivative might be a branchpoint to humulanes and germacranes; this transformation could be of, up to now, unknown, biosynthetic and/or synthetic relevance. Multivariate statistical analysis of the compositional data of C. conicum extract constituents was used to probe the hypothesized biochemical relations. The immunomodulatory effect of 1-3 and conocephalenol (4) was evaluated in an in vitro model on both nonstimulated and mitogen-stimulated rat splenocytes. The compounds displayed varying degrees of cytotoxicity to nonstimulated splenocytes, whereas 2 and 3 were found to exert immunosuppressive effects on concanavalin A-stimulated splenocytes while not being cytotoxic at the same concentrations.

Cover Feature: Attempts to Synthesize a Thiirane, Selenirane, and Thiirene by Dealkylation of Chalcogeniranium and Thiirenium Salts (Chem. Eur. J. 2/2021)

The Apollonian spirit of art and knowledge flows over the ancient house on Delos. However, even these forces cannot bridge the difference in reactivity: Thiiranium ions [Ad2SCH2CH2SiMe3]+ are fragmented by the fluoride ion to form thiirane Ad2S, Me3SiF, and C2H4 through attack on Si. In the case of seleniranium ions [Ad2SeCH2CH2SiMe3]+, the attack of the fluoride ion takes place on the Se and the three-membered ring is cleaved. Reaction products are the alkene Ad=Ad and the unstable selenenyl fluoride Me3SiCH2CH2SeF, but no selenirane Ad2Se are formed. We thank Harald Hirsch, Potsdam, for his help with the picture design. More information can be found in the Full Paper by H. Poleschner and K. Seppelt on page 649.

Attempts to Synthesize a Thiirane, Selenirane, and Thiirene by Dealkylation of Chalcogeniranium and Thiirenium Salts.

Thiiranium salts [Ad2SR]+X− (5, 8, 9, 11, 12; X−=Tf2N− (Tf=CF3SO2), SbCl6 −) and seleniranium salts [Ad2SeR]+X− (14, 16, 17, 23–25; X−=Tf2N−, BF4 −, CHB11Cl11 −, SbCl6 −) are synthesized from strained alkene bis(adamantylidene) (1). The disulfides and the diselenides (Me3SiCH2CH2E)2 (4, 13), (tBuMe2SiCH2CH2E)2 (7, 22), and (NCCH2CH2E)2 (10, 15; E=S, Se) have been used. The thiirenium salts [tBu2C2SR]+X− (34) and [Ad2C2SR]+X− (35, 36) are prepared from the bis‐tert‐butylacetylene (2) and bis‐adamantyl‐acetylene (3) with R=Me3SiCH2CH2 and tBuMe2SiCH2CH2. Attempts to cleave off the groups Me3SiCH2CH2, tBuMe2SiCH2CH2, and NCCH2CH2 resulted in thiiranes 27, 30. No selenirane Ad2Se (33) is formed from seleniranium salts, instead cleavage to the alkene (1) and diselenide (13, 15) occurs. The thiirenium salt [Ad2C2SCH2CH2SiMe3]+Tf2N− (35) does not yield the thiirene Ad2C2S (37), the three‐membered ring is cleaved, forming the alkyne (3) and disulfide (4). All compounds are characterized by ESI mass spectra, NMR spectra, and by quantum chemical calculations. Crystal structures of the salts 8, 12, 25, 17, 26, 36 and the thiiranes 27, 30 are presented.

The effects of Nano-Fe2O3 on the mechanical, physical and microstructure of cementitious composites

In this study, properties of cement composites and mortars were investigated in presence of Nano-Fe2O3 as their modifier. Cement composites were synthesized using the sol-gel method with tetraethylammonium orthosilicate as the complex legend. Subsequently, Nano-Fe2O3 was added at 2, 4, and 6 wt% dosages to the cement composite, while for mortars 2, 3 and 4 wt% of Nano-Fe2O3 dosages were used. FTIR and XRD tests were conducted to analyze the phase composition, molecular, and microstructure of cement composites, additionally, the effects of adding Nano-Fe2O3 on compressive and flexural strengths of mortars were investigated. The results indicated a change in the phase composition of the molecular-structure of cement composites, leading to stronger bonds in silicate network with more ordered arrangement in the presence of nanoparticles. The formation of three-membered silicate rings was also evident in composite samples containing higher amounts of Nano-Fe2O3 (i.e. 4 and 6 wt%). The microstructure analysis revealed that samples with Nano-Fe2O3 had a denser structure with a smaller pore size in comparison with control samples. The mechanical performance of mortar samples were enhanced with the incorporation of Nano-Fe2O3, where 3 wt% dosage was identified as the optimum.

Multifunctional Near-Infrared Fluorescent Probes with Different Ring-Structure Trigger Groups for Cell Health Monitoring and In Vivo Esterase Activity Detection.

A series of multifunctional ratiometric near-infrared fluorescent probes (CYOH-3, CYOH-4, CYOH-5, and CYOH-6) for esterase detection are designed by gradually changing the deflection of the plane twist in the molecule. These probes are composed of different ring-structure trigger groups (from three-membered ring to six-membered ring) and the same luminescent group CYOH. These probes show maximum absorption at ∼585 nm and a fluorescence emission peak at ∼655 ± 5 nm. In the presence of esterase, the probes were hydrolyzed to expose the fluorophore CYOH (λabs = 690 nm, λem = 710 ± 5 nm), thus exhibiting ratiometric near-infrared fluorescence. The probe CYOH-6 has lower plane deflection angle and better ratiometric (R = I710±5nm/I657±4nm) fluorescence properties than probes CYOH-3, CYOH-4, and CYOH-5. CYOH-6 (six-membered ring) has been successfully used to target esterase in mitochondria and distinguish between dead cells (esterase inactivation) and live cells. In addition, CYOH-6 has been well used for monitoring of esterase activity in zebrafish and mice, which proves that these probes have good prospects for clinical biomedical applications.

Adaptive σ-Aromaticity in an Unsaturated Three-Membered Ring.

Based on Hückel's and Baird's rules, species are aromatic either in the lowest singlet state (S0 ) or the lowest triplet state (T1 ) only. Thus, species with adaptive aromaticity (with aromaticity in both the S0 and T1 states) is particularly rare. On the other hand, σ-aromaticity in the T1 state has been underdeveloped, let alone adaptive σ-aromaticity. Herein, via various aromaticity indices including NICS, ACID and EDDB, we demonstrate adaptive σ-aromaticity in an unsaturated three-membered ring, which is a traditional area dominated by π-aromaticity. The origin of adaptive σ-aromaticity could be attributed to the excitation mode of the T1 state formed from out-of-plane π molecular orbital to the π* orbitals. Thus the σ-aromaticity of the three-membered ring in the S0 state could hold in the T1 state. Our findings extendthe concept of adaptive σ-aromaticity into three-membered rings and could be useful to further develop the concept of both σ-aromaticity and adaptive aromaticity.

An Unconventional trans - exo -Selective Cyclization of Alkyne-Tethered Cyclohexadienones Initiated by Rhodium(III)-Catalyzed C–H Activation via Insertion Relay

Different from the established trans-endo-selective cyclization of alkyne-tethered electrophiles that involve an E/Z isomerization process, herein, the authors present a novel strategy to allow tra...

Synthetically Important Ring-Opening Acylations of Alkoxybenzenes

AbstractCyclic ketones, anhydrides, lactams and lactones are a particular class of molecules that are often used in synthesis, wherein their electrophilic properties are leveraged to enable facile Friedel–Crafts ring openings through nucleophilic attack at the carbonyl sp2 centre. The use of electron-rich alkoxybenzenes as nucleophiles has also become important since the discovery of the Friedel–Crafts reaction. As a result, various isomeric alkoxybenzenes are used for preparing starting materials in target-oriented syntheses. This review covers the instances of different alkoxybenzenes that are used as nucleophiles in ring-opening acylations with carbonyl-containing cyclic electrophiles, for the construction of important building blocks for multistep transformations. This review summarizes the ring-opening functionalization of three- to seven-membered molecular rings with alkoxybenzenes in a Friedel–Crafts fashion. Sometimes the rings need subtle or considerable activation by the help of Lewis acid(s), followed by nucleophilic attack. This review is aimed to be a summary of the important acylations of electron-rich alkoxybenzenes by nucleophilic ring-opening of cyclic molecules. The works cited employ a wide range of conditions and differently substituted substrates for target-oriented syntheses.1 Introduction and Scope2 Arenes for Acylative Ring Opening2.1 Three-Membered Rings: Ring Opening of Oxirane-2,3-dione2.2 Four-Membered Rings2.2.1 Ring Opening of Cyclobutanones2.2.2 Ring Opening of β-Lactams2.2.3 Ring Opening of β-Lactone2.3 Five-Membered Rings2.3.1 Ring Opening of Phthalimides2.3.2 Ring Opening of γ-Lactones2.3.3 Ring Opening of Anhydrides2.4 Six-Membered Rings2.5 Seven-Membered Rings3 Conclusion

Intramolecular Motions in 1,2,3-Triethyldiaziridine: A Quantum Chemistry Study

The potential energy surface of a 1,2,3-triethyldiaziridine molecule is studied with quantum chemical calculations at the B3LYP/cc-pVTZ and MP2/cc-pVTZ levels of theory. A relationship between the energy of a molecular system and the rotation of ethyl groups is considered. It is found that there are 12 configurations that differ slightly in energy, due to different rotation angles of ethyl groups relative to a three-membered ring. The barriers between the minima on the potential energy surface are relatively low. The structural characteristics of different configurations are obtained.

Theoretical kinetics analysis for ȮH radical addition to 1,3-butadiene and application to model prediction

The kinetics of the 1,3-butadiene + ȮH reactions and its impact on combustion kinetic model predictions have been investigated in this work. Geometries and vibrational frequencies for all stationary points were determined at the BH&HLYP/6–311++G(d,p) level of theory, accounting explicitly for the degeneration of torsional motions into hindered rotors. Electronic energies for all stationary points on the related potential energy surface were calculated at the ROCCSD(T)/CBS and G4 levels of theory. Hydroxyl radical addition to the 1,3-butadiene terminal carbon forming allylic hydroxyl radical is the dominant addition entrance channel, while CH2CHCHO+ĊH3 and allyl radical + formaldehyde are the main bimolecular products. A three-membered ring intermediate (IT7) is found to be important in merging pathways originated from terminal and central addition reactions. Pressure and temperature dependent rate constants for ȮH radical addition to 1,3-butadiene are determined integrating the Master Equation on the investigated potential energy surface. Variational transition state theory was used to determine rate constants for the terminal and central addition entrance channels, finding a good agreement with previous experimental measurements. Hydrogen atom abstraction reactions by ȮH radicals from 1,3-butadiene have also been investigated in this work. Rate constants of the important reactions and thermochemistry data for key species calculated in this work were incorporated into AramcoMech3.0 to investigate their influence on the prediction of the reactivity active during 1,3-butadiene oxidation.