Ring-opened Products Research Articles

Activation of diverse carbon-heteroatom and carbon-carbon bonds via palladium(II)-catalysed β-X elimination.

Chemists' ability to synthesize structurally complex, high-value organic molecules from simple starting materials is limited by methods to selectively activate and functionalize strong alkyl C(sp3) covalent bonds. Recent activity has focused on the activation of abundant C-O, C-N and C-C bonds via a mechanistic paradigm of oxidative addition of a low-valent, electron-rich transition metal. This approach typically employs nickel(0), rhodium(I), ruthenium(0) and iron catalysts under conditions finely tuned for specific, electronically activated substrates, sometimes assisted by chelating functional groups or ring strain. By adopting a redox-neutral strategy involving palladium(II)-catalysed C-H activation followed by β-heteroatom/carbon elimination, we describe here a catalytic method to activate alkyl C(sp3)-oxygen, nitrogen, carbon, fluorine and sulfur bonds with high regioselectivity. Directed hydrofunctionalization of the resultant palladium(II)-bound alkene leads to formal functional group metathesis. The method is applied to amino acid upgrading with complete regioselectivity and moderate to high retention of enantiomeric excess. Low-strain heterocycles undergo strong-bond activation and substitution, giving ring-opened products.

H-Atom-Forming Reaction Pathways in the Pyrolysis of Furan, 2-Methylfuran, and 2,5-Dimethylfuran: A Shock-Tube and Modeling Study.

The methyl-substituted furan derivatives 2-methylfuran (2-MF) and 2,5-dimethylfuran (2,5-DMF) are often discussed as alternative fuels. Despite the large number of mechanistic studies on the pyrolysis and oxidation of 2-MF, 2,5-DMF, and unsubstituted furan (F), detailed kinetic investigations of the initial reaction steps are scarce. In this work, we report on shock-tube studies with detection of hydrogen atoms by atom resonance absorption spectroscopy to investigate the thermal decomposition of F, 2-MF, and 2,5-DMF. Hydrogen atom concentration-time profiles were recorded behind reflected shock waves at temperatures between 1200 and 1900 K and pressures between 0.7 and 1.6 bar with Ar as the bath gas. The recorded profiles were compared with results from kinetic simulations performed on the basis of a joint F/2-MF/2,5-DMF oxidation mechanism recently published. Kinetic parameters for a small number of reactions with high sensitivities for the formation and consumption of H atoms were adapted by taking values from other references to improve the agreement of the experimentally determined and simulated concentration-time profiles. In this way, an adequate description of the H atom concentration-time profiles for all three furan derivatives with the joint mechanism could be achieved. On the basis of this adapted mechanism, the formation pathways of H atoms in the pyrolysis of all three furan derivatives were identified and analyzed. It turned out that the formation of H atoms in the case of 2-MF and 2,5-DMF is governed by a competition between H split-off from the methyl group(s) of the reactant molecule as well as from the primary ring-opening product. In the case of F, only decomposition steps of the ring-opening product are relevant. The adapted mechanism is given in machine-readable form for modeling purposes, and the alterations made are discussed.

Formation and Evolution of aqSOA from Aqueous-Phase Reactions of Phenolic Carbonyls: Comparison between Ammonium Sulfate and Ammonium Nitrate Solutions.

We investigate the effects of sulfate and nitrate on the formation and evolution of secondary organic aerosol formed in the aqueous phase (aqSOA) from photooxidation of two phenolic carbonyls emitted from wood burning. AqSOA was formed efficiently from the photooxidation of both syringaldehyde (C9H10O4) and acetosyringone (C10H12O4) in ammonium sulfate and ammonium nitrate solutions, with mass yields ranging from 30% to 120%. Positive matrix factorization on the organic mass spectra acquired by an Aerosol Mass Spectrometer revealed a combination of functionalization, oligomerization, and fragmentation processes in the chemical evolution of aqSOA. Functionalization and oligomerization dominated in the first 4 h of reaction, with phenolic oligomers and their derivatives significantly contributing to aqSOA formation;andoxidation of the first-generation products led to an abundance of oxygenated ring-opening products. Degradation rates of syringaldehyde and acetosyringone in nitrate solutions were 1.5 and 3.5 times faster than rates in sulfate solutions, and aqSOA yields in nitrate experiments are twice as high as in sulfate experiments. Nitrate likely promoted the reactions because it is a photolytic source of OH radicals, while sulfate is not, highlighting the importance of aerosol-phase nitrate in the formation of aqSOA by facilitating the photooxidation of organic precursors.

Chiral Pentacarboxycyclopentadiene-Based Brønsted Acid-Catalyzed Enantioselective Desymmetrization of Meso-Epoxides by 2-Mercaptobenzothiazoles.

Enantioselective desymmetrization of meso-epoxides by 2-mercaptobenzothiazoles was realized by using the pentacarboxycyclopentadiene-based chiral Brønsted acid in combination of N-isopropylaniline as amine additive to give up to 90.5:9.5 er of the ring opening products.

Electrochemical behaviour of 9-methylcaffeinium iodide and in situ electrochemical synthesis of hymeniacidin

9-Methylcaffeinium iodide, a bio-based salt obtained by reaction of caffeine with methyl iodide, is an imidazolium salt. The electrochemical behaviour of 9-methylcaffeinium iodide was studied by means of cyclic voltammetry, differential pulse voltammetry and electrolysis. Its behaviour revealed to be very similar to that of common imidazolium salts. In fact, its cathodic reduction yielded the corresponding N-heterocyclic carbene, which was evidenced by its reaction products with dioxygen and with sulfur, although in low amounts. In fact, this electrogenerated carbene was very unstable and prone to add water, yielding a ring opening product (hymeniacidin) in high yield. Hymeniacidin is a natural product from the marine sponge Hymeniacidon sp. The voltammetric behaviour of isolated hymeniacidin confirmed the in situ formation of this ring opening product, by comparison of the voltammetric peak potentials of starting caffeinium salt and hymeniacidin. This study allowed to determine that hymeniacidin derives from NHC, and not by hydrolysis of the caffeinium salt.

Thiophilic ring opening reactions of 3,3-bis(trifluoromethyl)-5-alkoxy-1,2-dithiolanes under action of nucleophiles

The reaction of 3,3-bis(trifluoromethyl)-5-alkoxy-1,2-dithiolanes (RO= OEt or OBu-n) proceeds through thiophilic attack of BuLi leading to the formation of ring-opened product BuSCH(OR)CH2C(CF3)2SLi, which can be converted into the corresponding thiols or sulfides by the reaction with H+ or alkyl halide. Interaction of 3,3-bis(trifluoromethyl)-5-n-butoxy-1,2-dithiolane with CF3Si(CH3)3 resulted in unusual reaction leading to the formation of CF3SCH(OBu)CH2C(CF3)=CF2 (7). The treatment of 7 with CsF in the presence pentafluoropyridine led to equimolar mixture of 2-n-butoxy-1,1-bis(trifluoromethyl)cyclopropane and 4-(trifluoromethylthio)tetrafluoropyridine (as a result of interception of liberated in this process CF3S- anion by pentafluoropyridine).

Oxidation of steroid estrogens by peroxymonosulfate (PMS) and effect of bromide and chloride ions: Kinetics, products, and modeling

Recently, in situ chemical oxidation (ISCO) using peroxymonosulfate (PMS) for environmental decontamination has received increasing interest. In this study, oxidation kinetics and products of four steroid estrogens (i.e., estrone, 17β-estradiol, estriol, and 17α-ethinylestradiol) by PMS under various conditions were investigated. PMS could fairly degrade steroid estrogens over the pH range of 7–10, and the degradation rate increased with the increase of solution pH. This pH-dependence was well described by parallel reactions between individual acid-base species of steroid estrogens (E and E−) and PMS (HSO5− and SO52−), where specific second-order rate constants for E− with HSO5− and SO52− were in the range of 2.11–5.58 M−1s−1 and 0.77–1.25 M−1s−1, respectively. Identification of oxidation products by liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometer showed that PMS readily oxidized the phenolic group of steroid estrogens, leading to the generation of hydroxylated and ring-opening products. The presence of bromide and chloride ions (Br− and Cl−) at environmentally relevant levels could greatly accelerate the degradation of steroid estrogens by PMS with the formation of halogenated aromatic products. This effect was quantitatively estimated by a kinetic model, where the formation of free bromine and chorine and their rapid electrophilic substitution with steroid estrogens were taken into consideration. Eco-toxicity of transformation products of 17α-ethinylestradiol by PMS treatment in the absence and presence of bromide and chloride was estimated by quantitative structure–activity relationship analysis using ECOSAR. These findings advance the understanding of ISCO using PMS.

Synthesis and cytotoxicity of novel dispiro derivatives of 5-arylidenoxazolones, potential inhibitors of p53—MDM2 protein-protein interaction

Regioselective synthesis of new dispiro indolinones combining both an indolinone and an oxazolone fragment in their structure comprised the 1,3-dipolar cycloaddition of azomethine ylides, generated in situ from isatin and sarcosine, at 2-aryl-5-arylmethylidene-substituted 1,3-oxazol-5(4H)-ones. When ortho and para halogen atoms were present in the aromatic substituents of the starting oxazolones, complex mixtures containing large amounts of oxazoline ring opening products and their dispiro derivatives were formed. The cytotoxicity of compounds was tested by MTT on LNCaP, PC3, HCT116, MCF7, A549, HEK, and VA13 cell lines. The compound possessing the best cytotoxicity revealed the IC50 = 1.08±0.96 μM towards the p53- expressing LNCaP cells and lower activity (IC50 = 3.21±1.45 μM) towards the non-expressing p53 protein PC3 cells, however, it has proved inactive towards the HCT cells, both expressing (HCТ+/+) and non-expressing (HCT–/–) p53.

Dual acidic titania carbocatalyst for cascade reaction of sugar to etherified fuel additives

An inexpensive carbocatalyst containing Brønsted acidic sulfonic acid group and Lewis acidic Ti4+ is found to be effective for cascade conversion of C6 sugar to 5-ethoxymethylfurfural (EMF) via sequential dehydration, and etherification reactions. HMF and fructose conversions at mild conditions achieved 91% and 64% EMF yields, respectively. The results indicate that the two acid sites interplay synergistically for high EMF yield and minimal ring-opened product ethyl levulinate (EL), another promising biofuel additive. Etherification of 2,5-bis(hydroxymethyl)furan (BHMF) with alcohols of varying carbon lengths formed alkoxymethylfurans (AMF) with high yields. The catalyst retained good activity upon recycling. The nature and strength of the acid sites are elucidated.

Decalin ring opening on Pt-Ru/SiO2 catalysts

Pt-Ru/SiO2 bimetallic catalysts were studied in the reaction of decalin ring opening. For comparison, a monometallic Ru/SiO2 catalyst was also tested. The main products of ring opening are isomeric alkylcyclohexanes C9. Isomeric alkylcyclohexanes C10 are formed to a lesser extent, while the linear paraffin C10 is not observed. The lowest temperature of the process was found for the monometallic Ru-containing catalyst which affords an 80% decalin conversion already at 250 °C. The introduction of platinum significantly increases the value of the temperature affording the 50% decalin conversion, T50. The method of preparation of bimetallic Pt- and Ru-containing catalysts (Pt after Ru (Pt@Ru), Ru after Pt (Ru@Pt) or simultaneous introduction (Pt + Ru)) affects the activity of the catalysts in the decalin ring opening reaction. The activity of bimetallic catalysts follows the order: Pt@Ru > Ru@Pt > Pt + Ru. The XRD and EXAFS studies and the results of catalytic experiments have shown that the bimetallic catalyst Pt@Ru in which the metals are in the form of segregated or isolated phases is maximally close in the properties to the monometallic catalyst.

Acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with alcohols.

The acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicylic alkene using alcohol nucleophiles were investigated. Although this acid-catalyzed ring-opening reaction did not cleave the cyclopropane unit as planned, this represent the first examples of ring-openings of cyclopropanated 3-aza-2-oxabicyclo[2.2.1]alkenes that lead to the cleavage of the C–O bond instead of the N–O bond. Different acid catalysts were tested and it was found that pyridinium toluenesulfonate in methanol gave the best yields in the ring-opening reactions. The scope of the reaction was successfully expanded to include primary, secondary, and tertiary alcohol nucleophiles. Through X-ray crystallography, the stereochemistry of the product was determined which confirmed an SN2-like mechanism to form the ring-opened product.

Magnetically Bistable Nitrenes: Matrix Isolation of Furoylnitrenes in Both Singlet and Triplet States and Triplet 3-Furylnitrene

Two simple acylnitrenes, 2-furoylnitrene (2) and 3-furoylnitrene (6), were generated through 266 nm laser photolysis of the corresponding azides. Both are magnetically bistable in cryogenic matrices, as evidenced by the direct observation of the closed-shell singlet state with IR spectroscopy in solid Ne, Ar, Kr, Xe, and N2 matrices (3-40 K) and the triplet state in toluene (10 K) with EPR spectroscopy (32: |D/hc| = 1.48 cm-1 and |E/hc| = 0.029 cm-1; 36: |D/hc| = 1.39 cm-1 and |E/hc|c = 0.039 cm-1). Subsequent visible-light and UV laser irradiations led to the formation of furyl isocyanates (3 and 7) and ring-opening product 3-cyanoacrolein (9-E and 9-Z), respectively, in which the elusive 3-furylnitrene (38) was also identified by IR and EPR spectroscopy (|D/hc| = 1.12 cm-1 and |E/hc| = 0.005 cm-1).

Development of micro-mesoporous materials with lamellar structure as the support of NiW catalysts

An original approach for preparing hybrid support ZSM-5/MCM-41 is presented. Three types of ZSM-5/MCM-41(X) (X – thermostating time; 0, 6, 16 h) materials were synthesized with the different thermostating time of the mesoporous structure. The adopted preparation strategy was based on the effective synergy of sulfided particles and porous structure of the support. The NiW/ZSM-5/MCM-41(6; 16) catalysts demonstrated high activity in naphthalene hydrogenation under mild conditions, the ring-opening products selectivity was 32–36%. The deep aromatics saturation in light cycle oil (LCO) was observed over NiW/ZSM-5/MCM-41(16) catalyst at the following conditions: 5.0 MPa pressure, 2.0 h−1 LHSV, 300 l/l H2 -to-LCO volume ratio, and temperature of 360–380 °C.

Effect of H2S on the mechanisms of naphthene ring opening and isomerization over Ir/NaY: A comparative study of decalin, perhydroindan and butylcyclohexane hydroconversions

Selective ring opening is an important hydrotreating process for gas oil upgrading. In this work, we have used an Ir/NaY bifunctional catalyst -highly efficient in sulfur-free conditions- as a reference system to assess the effect of H2S impurity concentration (0–1 %) on the kinetics and mechanisms of naphthene conversion under high hydrogen pressure (5 MPa). Three model naphthenic molecules (decalin, perhydroindan and butylcyclohexane) were compared to evaluate the influence of the ring size (C5 vs C6) and number (1 vs 2). The numerous reaction products were identified, quantified and classified by using two-dimensional gas chromatography (GC × GC). In the absence of sulfur, it is confirmed that C5 rings are opened faster than C6 rings, and that single-ring naphthenes are converted faster than double-ring naphthenes. The presence of H2S, even at concentrations as low as 30 ppm, drastically and irreversibly changes the dominant catalytic function (from metallic to acidic), mechanism (from dicarbene-mediated to carbocation rearrangement) and family of products (from ring-opening products to skeletal-isomerization products). Together with experiments at variable reactant conversion, these results allow us to propose mechanistic reaction schemes for the three naphthenes under similar conditions, both for sulfur-free and sulfur-rich atmospheres.

Nitroisoxazolones Showing Diverse Chemical Behavior: A Use ful Building Block for Polyfunctionalized Systems.

4-Functionalized isoxazolin-5-ones (isoxazolones) have attracted much attentions as precursors of functionalized building blocks because the multiple functionalities. These structural features facilitate the construction of large compound libraries that is important for development of new functional materials. However, the systematic review article dealing with nitroisoxazolone has not been published although they exhibit different reactivity from other functionalized isoxazolones. This review describes the interesting behavior of the nitroisoxazolone motif and its application to the synthesis of polyfunctionalized compounds. Peer-reviewed research literatures describing the chemistry of nitroisoxazolones were collected, and each paper was appraised using standard criteria. inclusion/exclusion criteria. The papers were analyzed, and divided according to the reaction patterns. This review consists of two parts. In the former part, the chemistry of pyridinium salt of nitroisoxazolone is described, and in the latter part, chemistry of methylnitroisoxazolone is introduced. Sixty-eight papers were included in this review. Twelve papers deal with pyridinium salt or its ring-opened product, cyano-aci-nitroacetate. Nine papers mention the chemistry of methylnitroisoxazolones and derived nitroenamines and nitrile oxide. With regard to each chemistry, reaction mechanism and reactivity are discussed with citing related literatures. The findings of this review confirm the importance of nitroisoxazolones in synthetic chemistry for polyfunctionalized compounds, which are not readily available by alternative methods. This review will provide useful information and synthetic tools for many chemists studying synthetic chemistry and medicinal chemistry.

Experimental and theoretical study of oxidative stability of alkylated furans used as gasoline blend components

Alkylated furans such as 2,5-dimethylfuran and 2-methylfuran can be produced from biomass and have very attractive properties for use as spark-ignition fuel blendstocks. Their high octane numbers, relatively high energy density, low water solubility, and minimal effect on gasoline blend volatility are potentially significant advantages over alcohol-based fuels. However, prior studies have reported poor oxidative stability for furanic compound-gasoline blends, as well as the potential for the formation of dangerous organic peroxides. We show that alkylated furans have very low oxidative stability compared to conventional gasoline. Upon oxidation they form highly polar ring-opening products that can react with the starting furanic compound to form dimers, trimers, and higher polymers with intact furan rings. Dimers of the starting furan compounds were also observed. These gasoline-insoluble gums can be problematic for fuel storage or in vehicle fuel systems. Evaporation to dryness under ambient conditions also produced gum with similar composition. Gums produced via evaporation were found to contain peroxides; however, whether these pose a threat of shock initiated explosion has not been determined. We also propose a density functional theory-based analysis of possible reaction pathways, showing that OH radicals can form by reaction of the alkyl group and that addition of OH radicals to the furan ring is energetically favored and leads to ring opening products. Antioxidant additives can be effective at limiting the oxidation reaction in gasoline, but require much higher concentrations than are commonly used in commercial gasolines.

Tetrel, Chalcogen, and Charge-Assisted Hydrogen Bonds in 2-((2-Carboxy-1-(substituted)-2-hydroxyethyl)thio) Pyridin-1-ium Chlorides

Reaction of 2-chloro-2-(diethoxymethyl)-3-substitutedoxirane or 1-chloro-1-(substituted) -3,3-diethoxypropan-2-one with pyridine-2-thiol in EtOH at 25 °C yields 3-(diethoxymethyl)-3-hydroxy-2-substituted-2,3-dihydrothiazolo[3,2-a]pyridin-4-ium chlorides, which subsequently, in MeCN at 85°C, transforms into ring-opening products, 2-((2-carboxy-1-(substituted) -2-hydroxyethyl)thio)pyridin-1-ium chlorides. The tetrel (C···O) and chalcogen (S···O) bonds are found in the structures of 5 and 6, respectively. Compound 6 is also present in halogen bonding with a short O···Cl distance (3.067 Å). Both molecules are stabilized in crystal by tetrel, chalcogen, and multiple charge-assisted hydrogen bonds.

Efficient degradation of tetrabromobisphenol A via electrochemical sequential reduction-oxidation: Degradation efficiency, intermediates, and pathway

Tetrabromobisphenol A (TBBPA), a toxic persistent pollutant, should be effectively removed from the environment. In this study, an electrochemical sequential reduction-oxidation system was proposed by controlling reaction atmosphere with Pd-Fe nanoparticles modified Ni foam (Pd-Fe/Ni) electrode as cathode for TBBPA degradation. To obtain an efficient Pd-Fe/Ni electrode for TBBPA degradation, various factors, like Pd loading, Fe2+ adding amounts, were examined. The Pd-Fe/Ni electrode exhibited higher TBBPA conversion and debromination than the counterparts, due to the synergism of Fe0 and electrochemical reduction. Similar TBBPA conversions and debromination ratios were observed for the cases of sparging N2 only and sparging N2 followed by air, which were higher than those of aeration. Reductive debromination occurred while first bubbling N2, forming tri-BBPA, di-BBPA, mono-BBPA and BPA; and these intermediates were likely to be further oxidized by OH generated from H2O2 together with Pd-Fe/Ni electrode under aeration. Reductive and oxidative intermediates (including aromatic ring-opened product) were identified by HPLC and UPLC-QTOF-MS. Based on the intermediates, the possible TBBPA degradation mechanism and pathway were proposed. This study demonstrates that sequential reduction-oxidation process tuned by N2 and air bubbling was favored for TBBPA degradation, thus, it should be a promising process for HOCs degradation.

Acid-Induced Reactions of 1,2-Oxaphosphetane Complexes

Selective P–O bond activation of 1,2-oxaphosphetane complexes [(OC)5W(P{CH(SiMe3)2}CH2CRR′O)] (R/R′ = H/H (1a), H/CH3 (1b), H/CF3 (1c), CF3/CF3 (1d)) was achieved using different Bronsted acids. In case of acids with nucleophilic anions, such as HCl and HBF4·OEt2, the corresponding halophosphane complexes [(OC)5W(XP{CH(SiMe3)2}CH2CRR′OH] (X = Cl (2a–c), F (3c,d)) resulted as ring-opened products; 2b could be closed again with tBuLi/12-crown-4. In contrast, trifluoromethanesulfonic acid could be used to initiate either a ring-opening hydrolysis with a subsequent cleavage of the P–M bond to yield PH(O){CH(SiMe3)2}{CH2C(CF3)2OH} (7) or, in the presence of nitriles, a ring expansion yielding [(OC)5W(P{CH(SiMe3)2}CH2CH2OCR═N)] (R = CH3 (5a), Ph (5b), C(CH3)3 (5c)). P–O bond cleavage in 1a was achieved using the Lewis acidic catechol(chloro)borane to give [(OC)5W(P{CH(SiMe3)2}CH2CH(CH3)OBcat}Cl)] (8; cat = catechol).

Mechanism insights into the oxidative degradation of decabromodiphenyl ethane by potassium permanganate in acidic conditions

The KMnO4 degradation of decabromodiphenyl ethane (DBDPE), an additive in brominated flame retardants (BFRs), was investigated in a sulfuric acid system. The degradation tests showed that DBDPE reacted completely with KMnO4 in sulfuric acid, and a removal rate of 99.71% seems realistic. Many products were detected by liquid chromatography-quadrupole-time-of-flight-mass spectrometry (LC-Q-TOF-MS) analysis and gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) analysis. The degradation initially forms 1,2-bis(perbromophenyl)ethane-1,2-dione (P1), pentabromophenol (P2), 2-(perbromophenyl)ethanol (P3) and pentabromobenzoic acid (P28), and the subsequent transformation of these primary intermediates generates ring-opening, five-membered ring and six-membered heterocycle products over time. Two main reaction pathways involving the direct oxidation of the C–C bond of the ethyl group and the cleavage of the C–C bond between ethyl carbon and the adjacent carbon were proposed, and were further confirmed by point charges analyses and Wiberg bond order calculations. Furthermore, the toxicity of DBDPE and its degradation products were evaluated using the ECOSAR program. DBDPE was found to be a toxic substance that could cause great damage to three kinds of organisms in different trophic levels, while all the transformation products were less toxic than parent compound.