Oxygen Nucleophiles Research Articles

Polyhydroxylated Nanosized Graphite as Multifunctional Building Block for Polyurethanes.

Polyurethane nanocomposites were prepared with a nanosized high surface area graphite (HSAG) functionalized on its edges with hydroxyl groups as a building block. Edge functionalization of HSAG was obtained through reaction with KOH. The addition of OH groups was demonstrated by means of infrared (FTIR) and thermogravimetric analysis (TGA), and the Boehm titration allowed estimation of a level of about 5.0 mmolOH/gHSAG. Results from wide-angle X-ray diffraction (WAXD) and Raman spectroscopy suggested that functionalization of the graphene layers occurred on the edges. The evaluation of the Hansen solubility parameters of G-OH revealed a substantial increase of δP and δH parameters with respect to HSAG. In line with these findings, homogeneous and stable dispersions of G-OH in a polyol were obtained. PU were prepared by mixing a dispersion of G-OH in cis-1,4-butenediol with hexamethylene diisocyanate. A model reaction between catechol, 1,4-butanediol, and hexamethylene diisocyanate demonstrated the reactivity of hydroxylated aromatic rings with isocyanate groups. PU-based G-OH, characterized with WAXD and differential scanning calorimetry (DSC), revealed lower Tg, higher Tc, Tm, and crystallinity than PU without G-OH. These results could be due to the higher flexibility of the polymer chains, likely a consequence of the dilution of the urethane bonds by the carbon substrate. Hence, G-OH allowed the preparation of PU with a larger temperature range between Tg and Tm, with potential positive impact on material applications. The model reaction between butylisocyanate and 1-butanol revealed that HSAG and G-OH promote efficient formation of the urethane bond, even in the absence of a catalyst. The effect of high surface area carbon on the nucleophilic oxygen attack to the isocyanate group can be hypothesized. The results here reported lead us to comment that a reactive nanosized sp2 carbon allotrope, such as G-OH, can be used as a multifunctional building block of PU. Indeed, G-OH is a comonomer of PU, a promoter of the polymerization reaction, and can definitely act as reinforcing filler by tuning its amount in the final nanocomposite leading to highly versatile materials. The larger temperature range between Tg and Tm, together with the presence of G-OH acting as a reinforcing agent, could allow the production of piezoresistive sensing, shape-memory PU with good mechanical features.

Palladium-catalyzed base- and solvent-controlled chemoselective allylation of amino acids with allylic carbonates

The utilization of readily available amino acids, which is not only an oxygen nucleophile but also a nitrogen nucleophile, in palladium-catalyzed allylic substitution is realized under mild conditions. The chemoselectivity and multiple allylation are controlled by adjusting the reaction conditions. This represents the first example of this convenient access to valuable N,O-diallylated amino acids. Under the title conditions, a range of amino acids (α-, β-, γ-) and dipeptides can be readily converted in to the corresponding allylic products with excellent yields (67 examples, up to 99% yield) as well as good functional group tolerance.

Rh-Catalyzed Regio- and Enantioselective Allylic Phosphinylation.

Transition-metal-catalyzed branched and enantioselective allylic substitution of monosubstituted precursors with carbon, nitrogen, oxygen, sulfur, and fluoride nucleophiles has been well-established. However, such a selective carbon-phosphorus bond formation has not been realized probably due to the catalyst deactivation by the strong coordinating nature of phosphinylating reagents. Herein, we report a Rh-catalyzed highly regio- and enantioselective synthesis of allylic phosphine oxides in the presence of a chiral bisoxazoline-phosphine ligand. The application of α-hydroxylalkylphosphine oxides to keep the low concentration of the secondary phosphine oxides is essential for the high yields. The addition of diphenyl phosphoric acid was found to not only activate allylic alcohols but also accelerate the carbon-phosphorus bond formation.

Diastereoselective Formation of Quaternary Stereocenters in Imidazole N-Oxide Cycloaddition with Fluoroalkenes

Imidazole N-oxides are attractive starting materials for the preparation of complex molecules containing an imidazole ring. Dipolar cycloaddition between 1,1-difluoroalkenes and imidazole N-oxides bearing a chiral auxiliary performed in the presence of oxygen or nitrogen nucleophiles was found to provide access to esters and amides bearing a 2-azaheteroaryl substituent at the α position of the imidazole ring as mixtures of diastereomers that, in most cases, are readily separable. This three-component reaction introduces a new tertiary or quaternary all-carbon stereocenter into the heterocyclic ring at a position originally occupied by hydrogen. Importantly, products containing a trifluoromethyl group attached to this stereocenter are readily available as well.

Access to β-Lactams via Iron-Catalyzed Olefin Oxyamidation Enabled by the π-Accepting Phthalocyanine Ligand.

Herein, we report the development of an iron-catalyzed olefin oxyamidation by utilizing tethered dioxazolones as the nitrenoid precursor to produce valuable β-lactam scaffolds. Mechanistic studies revealed that a relatively strong π-accepting ability of the phthalocyanine ligand is critical in generating the key triplet iron-imidyl radical intermediate to enable the 4-exo-trig-lactamization with the incorporation of oxygen nucleophiles in high diastereoselectivity. This cyclization approach was readily extended to the highly efficient γ-lactam synthesis (TON > 300).

Unconventional mechanism and selectivity of the Pd-catalyzed C\u2013H bond lactonization in aromatic carboxylic acid

The search for more effective and highly selective C–H bond oxidation of accessible hydrocarbons and biomolecules is a greatly attractive research mission. The elucidating of mechanism and controlling factors will, undoubtedly, help to broaden scope of these synthetic protocols, and enable discovery of more efficient, environmentally benign, and highly practical new C–H oxidation reactions. Here, we reveal the stepwise intramolecular SN2 nucleophilic substitution mechanism with the rate-limiting C–O bond formation step for the Pd(II)-catalyzed C(sp3)–H lactonization in aromatic 2,6-dimethylbenzoic acid. We show that for this reaction, the direct C–O reductive elimination from both Pd(II) and Pd(IV) (oxidized by O2 oxidant) intermediates is unfavorable. Critical factors controlling the outcome of this reaction are the presence of the η3-(π-benzylic)–Pd and K+–O(carboxylic) interactions. The controlling factors of the benzylic vs ortho site-selectivity of this reaction are the: (a) difference in the strains of the generated lactone rings; (b) difference in the strengths of the η3-(π-benzylic)–Pd and η2-(π-phenyl)–Pd interactions, and (c) more pronounced electrostatic interaction between the nucleophilic oxygen and K+ cation in the ortho-C–H activation transition state. The presented data indicate the utmost importance of base, substrate, and ligand in the selective C(sp3)–H bond lactonization in the presence of C(sp2)–H.

Chiral Sulfide/Phosphoric Acid Cocatalyzed Enantioselective Intermolecular Oxysulfenylation of Alkenes with Phenol and Alcohol O -Nucleophiles

Chiral Sulfide/Phosphoric Acid Cocatalyzed Enantioselective Intermolecular Oxysulfenylation of Alkenes with Phenol and Alcohol <i>O</i> -Nucleophiles

Oxy- and aminoselenation of alkenes utilizing an isolable selenenyl iodide

Application of an isolable selenenyl iodide BpqSeI (Bpq denotes 5',5'''-bis(2,6-diisopropylphenyl)-2,6,2'''',6''''-tetra-isopropyl-1,1':3',1'':3'',1''':3''',1''''-quinquephenyl-2''-yl) to selenofunctionalization of alkenes with external oxygen or nitrogen nucleophiles was investigated. In the presence of N-iodosuccinimide as an additive, alcohols, a carboxylic acid, or aromatic amines were smoothly introduced to alkenes to give the corresponding β-oxy or β-amino selenides in moderate to high yields.

Role of Enaminonitriles in Heterocyclic Synthesis: Synthesis of Some New Aminothiazole Derivatives against Prostate Carcinoma

Among sulfur- and nitrogen-containing heterocyclic compounds, the aminothiazole scaffold is one of the most unique architectures in drug development, since it comprises a variety of biological effects. Furthermore, numerous aminothiazole-based compounds have been widely used as medical drugs to treat a range of illnesses, resulting in a slew of new inventions. The synthetic procedures employed to get new aminothiazole derivatives from enaminonitrile acrylamide derivative 2, which was previously used as a key step in the synthesis of pyrazole, isoxazole, and pyrimidine derivatives, are innovative (4, 6 and 8). In addition, enaminonitrile 2 showed chemical activity toward some N-nucleophiles such as heterocyclic amines for synthesis triazolo, imidazo and pyrazolo pyrimidine derivatives (10, 12, and 14). Enaminonitrile precursor 2 was cyclocondensed with various carbon and oxygen nucleophiles to provide some complex polyfunctionally substituted fused 2-pyridone and chromenone derivatives with a thiazoyl sulfonamido moiety (16, 18, 20, and 24). The anticancer efficacy of all novel aminothiazoles was tested in vitro against human prostate carcinoma (PC3) utilizing normal prostate epithelial cell line (PNT2) as control cells. The most powerful derivatives against prostate cancer cell lines were determined to be 14 and 16, which had no impact on normal cells. Compound 20 on the other hand, has just mediocre anticancer properties.

An isotopic strategy to investigate the role of water vapor in the oxidation of 1,2-dichloroethane over the Ru/WO3 or Ru/TiO2 catalyst

Electron paramagnetic resonance, in situ diffuse reflection infrared Fourier transform spectroscopy, and temperature-programmed techniques by means of the isotopic trace strategies were used to investigate the effects of water vapor on oxygen species, reaction pathways, byproducts distributions, and accumulation of the chlorine and carbon species on the catalyst surface for 1,2-dichloroethane oxidation over Ru/WO3 or Ru/TiO2 catalyst. The introduction of water vapor produced the OOH species that were converted into more active oxygen (O2– and O−) species. The mulliken population analysis indicates that βC and αC in VC are bonded with H and nucleophilic oxygen of −OH in sequence, respectively, which proved that water directly promoted the transformation of vinyl chloride to CH3COOH. Besides, water could be partially adsorbed at the hydroxyl groups on the Ru/WO3 sample surface, which were provided the adsorption sites for 1,2-dichloroethane molecules. However, the severe competitive adsorption on the surface of Ru/TiO2 resulted in insufficient oxygen adsorption to supplement the oxygen vacancy.

Boosting Toluene Combustion by Tuning Electronic Metal-Support Interactions in In Situ Grown Pt@Co3O4 Catalysts.

Electronic metal-support interaction (EMSI) has attracted great attention in volatile organic compound (VOC) abatement. Herein, Pt@Co3O4 catalysts were prepared via a metal-organic framework (MOF) in situ growth approach to boost toluene degradation. The partial electron transfer from Co3O4 to Pt species was induced by the EMSI effect to generate the electron-rich Pt and Co3+ species. The electrophilic O2 molecules could be activated by picking up the electrons from electron-rich Pt species to form nucleophilic oxygen species, which is conducive to attack C-H bonds in toluene. The redox ability and surface oxygen species activity of catalysts were improved due to strong EMSI. As expected, the excellent toluene activity was achieved, meanwhile exhibiting satisfactory water resistance and long-term stability for toluene combustion. In situ diffuse reflectance infrared Fourier transform spectroscopy results elucidated that surface lattice oxygen species should deeply participate in toluene degradation, which could be efficiently replenished by gaseous oxygen. This work may provide a new idea for exploring the relationship between the electron transfer effect and efficient catalytic performance of VOCs.

Iodine-Mediated Fluorination of Alkenes with an HF Reagent: Regioselective Synthesis of 2-Fluoroalkyl Iodides.

Fluorination reaction of alkenes with iodine and HF·pyridine complex (pyr·9HF) was performed under mild conditions in the presence of K2S2O8 or Na2S2O8 as an oxidant. Aliphatic and aromatic alkenes underwent iodofluorination to give the iodofluorinated products with high regioselectivity. The substitution reactions of the iodofluorinated product by nitrogen, sulfur, and oxygen nucleophiles indicated further applications as a building block for synthesis of 2-fluoroalkyl-substituted compounds.

Promotion mechanism of CuMn2O4 modification with NaOH on toluene oxidation: Boosting the ring-opening of benzoate

To elucidate the mechanism of the promotion effect of CuMn2O4 catalyst modification with NaOH on toluene oxidation, NaOH-modified CuMn2O4 catalysts with similar physical structures and chemical properties were fabricated through a mild impregnation strategy. The results showed that the NaOH species had a remarkable promotion effect on the CuMn2O4 catalytic performance without lattice oxygen activity improvement. The 2NaOH/CuMn2O4 showed the best catalytic activity with the T90 (the temperature corresponding to 90% conversion) of 188 °C, which was 20 °C lower than that of the unmodified CuMn2O4. In situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFT)S study revealed that carbonate and benzoate were the main intermediates over CuMn2O4, and the NaOH introduction inhibited carbonate formation and accelerated the degradation of the benzoate aromatic ring. The H2O present in the reaction system could be dissociated into hydroxyl groups under the action of NaOH to form a hydroxyl-rich environment, which boosted the ring-opening of benzoate. In addition, the toluene adsorption experiments confirmed that the nucleophilic lattice oxygen species broke the activated aromatic ring, and the toluene oxidation followed the Mars–vanKrevelen mechanism. In this study, the mechanism of the promotion effect of catalyst modification with NaOH on toluene oxidation was revealed, which is of great significance for the design of high-efficiency toluene degradation catalysts.

Controlling the Gold(I)-Catalyzed 1,5-Allenene Reaction: Construction of Fused Rings with Excellent Diastereoselectivity.

In the present study, the gold(I)-catalyzed reaction of 1,5-allenenes was controlled in such a way that instead of a [2 + 3] cycloaddition, a 5-exo-cyclization with the formation of a carbocation occurred. The latter could be trapped with both oxygen and carbon nucleophiles. In the investigated system, fused tricyclic frameworks with three contiguous stereocenters with excellent chemo- and diastereoselectivity in up to 95% yield were obtained.

Photoinduced Copper‐Catalyzed Asymmetric Three‐Component Coupling of 1,3‐Dienes: An Alternative to Kharasch–Sosnovsky Reaction

AbstractKharasch–Sosnovsky reaction is one of the most powerful methods for allylic oxidation of alkenes. However, the inherent radical mechanism and use of peroxides as both oxidants and oxygen nucleophiles render dearth of universal catalytic systems for highly enantioselective variants and limited scope. Herein, an alternative to the asymmetric Kharasch–Sosnovsky reaction that utilized a chiral copper catalyst and purple‐LED irradiation to enable the three‐component coupling of 1,3‐dienes, oxime esters, and carboxylic acids is reported. This protocol features mild conditions, remarkable scope and functional group tolerance as evidenced by &gt;80 examples and utility in the late‐stage modification of pharmaceuticals and natural products. Detailed mechanistic studies provide evidences for the radical‐based reaction pathway.

Photoinduced Copper-Catalyzed Asymmetric Three-Component Coupling of 1,3-Dienes: An Alternative to Kharasch-Sosnovsky Reaction.

Kharasch-Sosnovsky reaction is one of the most powerful methods for allylic oxidation of alkenes. However, the inherent radical mechanism and use of peroxides as both oxidants and oxygen nucleophiles render dearth of universal catalytic systems for highly enantioselective variants and limited scope. Herein, an alternative to the asymmetric Kharasch-Sosnovsky reaction that utilized a chiral copper catalyst and purple-LED irradiation to enable the three-component coupling of 1,3-dienes, oxime esters, and carboxylic acids is reported. This protocol features mild conditions, remarkable scope and functional group tolerance as evidenced by >80 examples and utility in the late-stage modification of pharmaceuticals and natural products. Detailed mechanistic studies provide evidences for the radical-based reaction pathway.

Expression, purification, properties, and substrate specificity analysis of Aspergillus niger GZUF36 lipase in Escherichia coli

The extracellular Aspergillus niger GZUF36 lipase (EXANL1) has broad applicability such as synthesis of functional lipids. The wild-type strain is unstable, and the culture time is long. Studies on the selectivity of substrates for EXANL1 are not available. Therefore, this study aimed to express, purify, characterize and analyze the substrate specificity of EAXNL1. The results showed that EXANL1 was stable in the presence of 40 % (v/v) dimethyl sulfoxide, glycerol, toluene, and n-hexane. The relative activity was 104 %, 88 %, 81 %, and 76 %. The residual enzyme activity of EXANL1 was more than 85 % in surfactants with a low concentration. EXANL1 exhibited a high conversion rate (79 %) for p-nitrophenyl palmitate. The molecular docking of p-nitrophenyl palmitate into the active site of EXANL1 indicated that the preference for this fatty acid chain length might be due to the formation of hydrogen bonds. The distance between the carbonyl carbon atom of p-nitrophenyl palmitate and the nucleophilic oxygen atom of serine 162 was 2.91 Å. Both experiments revealed that EXANL1 exhibited higher specificity for p-nitrophenyl palmitate. These results indicated that EXANL1 could be a promising tool in organic synthesis and detergent industry. The molecular docking provided a basis for the explanation on the substrate selectivity of EXANL1.

Introducing A New Class of Sulfonyl Fluoride Hubs via Radical Chloro-Fluorosulfonylation of Alkynes.

Sulfonyl fluorides have widespread applications in many important fields, including ligation chemistry, chemical biology, and drug discovery. Therefore, new methods to increase the synthetic efficiency and expand the available structures of sulfonyl fluorides are highly in demand. Here, we introduce a new and powerful class of sulfonyl fluoride hubs, β-chloro alkenylsulfonyl fluorides (BCASF), which can be constructed via radical chloro-fluorosulfonyl difunctionalization of alkynes under photoredox conditions. BCASF molecules exhibit versatile reactivities and well undergo a series of transformations at the chloride site while keeping the sulfonyl fluoride group intact, including reduction, Suzuki coupling, Sonogashira coupling, as well as nucleophilic substitution with various nitrogen, oxygen, and sulfur nucleophiles. By using BCASF as a synthetic hub, a wide range of sulfonyl fluorides becomes readily accessible, such as cis alkenylsulfonyl fluorides, dienylsulfonyl fluorides, and ynenylsulfonyl fluorides, which are challenging or even not possible to synthesize before with the known methods. Moreover, further application of BCASF to the late-stage modification of peptides and drugs is also demonstrated.

Introducing A New Class of Sulfonyl Fluoride Hubs via Radical Chloro‐Fluorosulfonylation of Alkynes

AbstractSulfonyl fluorides have widespread applications in many important fields, including ligation chemistry, chemical biology, and drug discovery. Therefore, new methods to increase the synthetic efficiency and expand the available structures of sulfonyl fluorides are highly in demand. Here, we introduce a new and powerful class of sulfonyl fluoride hubs, β‐chloro alkenylsulfonyl fluorides (BCASF), which can be constructed via radical chloro‐fluorosulfonyl difunctionalization of alkynes under photoredox conditions. BCASF molecules exhibit versatile reactivities and well undergo a series of transformations at the chloride site while keeping the sulfonyl fluoride group intact, including reduction, Suzuki coupling, Sonogashira coupling, as well as nucleophilic substitution with various nitrogen, oxygen, and sulfur nucleophiles. By using BCASF as a synthetic hub, a wide range of sulfonyl fluorides becomes readily accessible, such as cis alkenylsulfonyl fluorides, dienylsulfonyl fluorides, and ynenylsulfonyl fluorides, which are challenging or even not possible to synthesize before with the known methods. Moreover, further application of BCASF to the late‐stage modification of peptides and drugs is also demonstrated.

Molecular Electrostatic Potential and Noncovalent Interactions in Derivatives of Group 8 Elements

AbstractThis communication reports experimental and theoretical evidences of σ‐hole interactions in adducts between nitrogen or oxygen nucleophiles and tetroxides of osmium or other group 8 elements. Cocrystals between pyridine or pyridine N‐oxide derivatives and osmium tetroxide are characterized through various techniques and rationalized as σ‐hole interactions using DFT calculations and several other computational tools. We propose the term “osme bond” (OmB, Om=Fe, Ru, Os, (Hs)) for naming the noncovalent interactions wherein group 8 elements have the role of the electrophile. The word osme is the transcription of ὀσμή, the ancient Greek word for smell that was used to name the heaviest group 8 element in relation to the smoky odor of its tetroxide.