Arene Oxides Research Articles

Stereoselective Synthesis of meso- and l,l-Diaminopimelic Acids from Enone-Derived α-Amino Acids.

The stereoselective synthesis of meso-diaminopimelic acid (meso-DAP), the key cross-linking amino acid of the peptidoglycan cell wall layer in Gram-negative bacteria, and its biological precursor, l,l-DAP, is described. The key step involved stereoselective reduction of a common enone-derived amino acid by substrate- or reagent-based control. Overman rearrangement of the resulting allylic alcohols, concurrent alkene hydrogenation and trichloroacetamide reduction, and subsequent ruthenium-catalyzed arene oxidation completed the synthesis of each stereoisomer. The synthetic utility of this approach was demonstrated with the efficient preparation of an l,l-DAP-derived dipeptide.

Proteogenomic Characterization of Pseudomonas veronii SM-20 Growing on Phenanthrene as Only Carbon and Energy Source.

In this study, we conducted an extensive investigation of the biodegradation capabilities and stress response of the newly isolated strain Pseudomonas veronii SM-20 in order, to assess its potential for bioremediation of sites contaminated with polycyclic aromatic hydrocarbons (PAHs). Initially, phenotype microarray technology demonstrated the strain's proficiency in utilizing various carbon sources and its resistance to certain stressors. Genomic analysis has identified numerous genes involved in aromatic hydrocarbon metabolism. Biodegradation assay analyzed the depletion of phenanthrene (PHE) when it was added as a sole carbon and energy source. We found that P. veronii strain SM-20 degraded approximately 25% of PHE over a 30-day period, starting with an initial concentration of 600 µg/mL, while being utilized for growth. The degradation process involved PHE oxidation to an unstable arene oxide and 9,10-phenanthrenequinone, followed by ring-cleavage. Comparative proteomics provided a comprehensive understanding of how the entire proteome responded to PHE exposure, revealing the strain's adaptation in terms of aromatic metabolism, surface properties, and defense mechanism. In conclusion, our findings shed light on the promising attributes of P. veronii SM-20 and offer valuable insights for the use of P. veronii species in environmental restoration efforts targeting PAH-impacted sites.

Highly Anti-Markovnikov Selective Oxidative Arene Alkenylation Using Ir(I) Catalyst Precursors and Cu(II) Carboxylates.

The Ir(I) complex [Ir(μ-Cl)(coe)2]2 (coe = cis-cyclooctene) is a catalyst precursor for benzene alkenylation using Cu(II) carboxylate salts. Using [Ir(μ-Cl)(coe)2]2, propenylbenzenes are formed from the reaction of benzene, propylene, and CuX2 (X = acetate, pivalate, or 2-ethylhexanoate). The Ir-catalyzed reactions selectively produce anti-Markovnikov products, trans-β-methylstyrene, cis-β-methylstyrene, and allylbenzene, along with minor amounts of the Markovnikov product, α-methylstyrene. The selectivity for the anti-Markovnikov products changed as the reaction progressed. For example, in a reaction that uses 240 equiv of Cu(OHex)2 (related to Ir), the selectivity for the anti-Markovnikov products increases from 18:1 at 3 h to 42:1 at 42 h with 30 psig of propylene at 150 °C. Studies of product stability have revealed that the increase in the selectivity for anti-Markovnikov products is not the result of an isomerization process or the selective decomposition of specific products. Rather, the change in selectivity correlates with the ratio of Cu(II) to Cu(I) in the solution, which decreases as the reaction progresses. We propose that the identity of the active catalyst changes as Cu(I) is accumulated, resulting in the formation of an active catalyst that is more selective for anti-Markovnikov products. Using a 4:1 Cu(I)/Cu(II) ratio at the start of the reaction, a 65(3):1 anti-Markovnikov/Markovnikov ratio is observed.

Retraction: Aqueous aerobic oxidation of alkyl arenes and alcohols catalyzed by copper(II) phthalocyanine supported on three-dimensional nitrogen-doped graphene at room temperature.

Retraction of 'Aqueous aerobic oxidation of alkyl arenes and alcohols catalyzed by copper(II) phthalocyanine supported on three-dimensional nitrogen-doped graphene at room temperature' by Mojtaba Mahyari et al., Chem. Commun., 2014, 50, 7855-7857, https://doi.org/10.1039/C4CC01406E.

Divergent Photosensitizer Controlled Reactions of 4‐Hydroxycoumarins and Unactivated Olefins: Hydroarylation and Subsequent [2+2] Cycloaddition

AbstractHerein, we report a photoinduced approach for hydroarylation of unactivated olefins using 4‐hydroxycoumarins as the arylating reagent. Key to the success of this reaction is the conversion of nucleophilic 4‐hydroxycoumarins into electrophilic carbon radicals via photocatalytic arene oxidation, which not only circumvents the polarity‐mismatch issue encountered under ionic conditions but also accommodates a broad substrate scope and inhibits side reactions that were previously observed. Moreover, divergent reactivity was achieved by changing the photocatalyst, enabling a subsequent [2+2] cycloaddition to deliver cyclobutane‐fused pentacyclic products that are otherwise challenging to access in high yields and with high diastereoselectivity. Mechanistic studies have elucidated the mechanism of the reactions and the origin of the divergent reactivity.

Divergent Photosensitizer Controlled Reactions of 4-Hydroxycoumarins and Unactivated Olefins: Hydroarylation and Subsequent [2 + 2] Cycloaddition.

Herein, we report a photoinduced approach for hydroarylation of unactivated olefins using 4-hydroxycoumarins as the arylating reagent. Key to the success of this reaction is the conversion of nucleophilic 4-hydroxycoumarins into electrophilic carbon radicals via photocatalytic arene oxidation, which not only circumvents the polarity-mismatch issue encountered under ionic conditions but also accommodates a broad substrate scope and inhibits side reactions that were previously observed. Moreover, divergent reactivity was achieved by changing the photocatalyst, enabling a subsequent [2+2] cycloaddition to deliver cyclobutane-fused pentacyclic products that are otherwise challenging to access in high yields and with high diastereoselectivity. Mechanistic studies have elucidated the mechanism of the reactions and the origin of the divergent reactivity.

Exploring the bioremediation capability of petroleum-contaminated soils for enhanced environmental sustainability and minimization of ecotoxicological concerns.

The bioremediation of soils contaminated with petroleum hydrocarbons (PHCs) has emerged as a promising approach, with its effectiveness contingent upon various types of PHCs, i.e., crude oil, diesel, gasoline, and other petroleum products. Strategies like genetically modified microorganisms, nanotechnology, and bioaugmentation hold potential for enhancing remediation of polycyclic aromatic hydrocarbon (PAH) contamination. The effectiveness of bioremediation relies on factors such as metabolite toxicity, microbial competition, and environmental conditions. Aerobic degradation involves enzymatic oxidative reactions, while bacterial anaerobic degradation employs reductive reactions with alternative electron acceptors. Algae employ monooxygenase and dioxygenase enzymes, breaking down PAHs through biodegradation and bioaccumulation, yielding hydroxylated and dihydroxylated intermediates. Fungi contribute via mycoremediation, using co-metabolism and monooxygenase enzymes to produce CO2 and oxidized products. Ligninolytic fungi transform PAHs into water-soluble compounds, while non-ligninolytic fungi oxidize PAHs into arene oxides and phenols. Certain fungi produce biosurfactants enhancing degradation of less soluble, high molecular-weight PAHs. Successful bioremediation offers sustainable solutions to mitigate petroleum spills and environmental impacts. Monitoring and assessing strategy effectiveness are vital for optimizing biodegradation in petroleum-contaminated soils. This review presents insights and challenges in bioremediation, focusing on arable land safety and ecotoxicological concerns.

Non-Noble Metal Aromatic Oxidation Catalysis: From Metalloenzymes to Synthetic Complexes

The development of selective aromatic oxidation catalysts based on non-noble metals has emerged over the last decades, mainly due to the importance of phenol products as intermediates for the generation of pharmaceuticals or functional polymers. In nature, metalloenzymes can perform a wide variety of oxidative processes using molecular oxygen, including arene oxidations. However, the implementation of such enzymes in the chemical industry remains challenging. In this context, chemists have tried to mimic nature and design synthetic non-noble metal catalysts inspired by these enzymes. This review aims at providing a general overview of aromatic oxidation reactions catalyzed by metalloenzymes as well as synthetic first-row transition-metal complexes as homogeneous catalysts. The enzymes and complexes discussed in this review have been classified based on the transition-metal ion present in their active site, i.e., iron, copper, nickel, and manganese. The main points of discussion focus on enzyme structure and function, catalyst design, mechanisms of operation in terms of oxidant activation and substrate oxidation, and substrate scope.

Photocatalytic direct oxygen-isotopic labelings of carbonyls in ketones and aldehydes with oxygen-isotopic waters

Oxygen-isotopic labelings play important roles in identifying and understanding chemical and biological processes. Direct C=O to C=18O or C=17O conversion in a single step leading to labeled compounds can alleviate synthetic burdens without the need for resynthesis. Here we describe a photocatalytic oxygen-isotopic labeling protocol that can efficiently and selectively install 18O and 17O on carbonyls of ketones and aldehydes via oxygen isotope exchange with oxygen-isotopic waters (H218O or H217O) as the sources of oxygen isotopes, in which light and oxygen-enabled sodium alkanesulfinates catalyzed this process. This strategy was extended to the in-situ formed ketones from the photocatalytic aerobic oxidation of alkyl arenes and secondary alcohols. Furthermore, reduction of the oxygen-isotopically labeled aldehydes with NaBH4 provided the corresponding oxygen-isotopically labeled primary alcohols. We believe that the oxygen-isotopically labeling method will be widely used in chemistry, biology and medicine fields.

Kemampuan Bacillus sp. Sebagai Bioremediasi Bahan Pencemar

The presence of heavy metal sources in inappropriate places can contaminate the surrounding soil, so that it will interfere with human and animal health if they enter the food chain. The purpose of writing this review is to determine the ability of Bacillus in bioremediation of pollutants and to determine the enzymes in Bacillus that are able to remediate pollutants. Monooxygenase enzymes and dioxygenase enzymes produced by bacteria can open carbon bonds in aromatic rings and produce primary alcohols. Dioxygenase enzymes produced by bacteria reduce PAHs and form cis-dihydrodiol. This compound is then dehydrogenated to form dihydroxy-PAH which is a substrate for the ring-opening enzyme. Through the addition of one oxygen molecule, the monooxygenase enzyme can also reduce PAH and form arene oxide, then these molecules will be used by bacteria as a source of nutrition. Bacillus bacteria are able to remediate various kinds of pollutants. These bacteria are able to reduce these pollutants because they have hydrocarbon enzymes that will break down harmful chemical compounds in pollutants into simpler compounds that can be used as energy sources.

Mechanistic Investigations into Amination of Unactivated Arenes via Cation Radical Accelerated Nucleophilic Aromatic Substitution.

A mechanistic investigation into the amination of electron-neutral and electron-rich arenes using organic photoredox catalysis is presented. Kinetic and computational data support rate-limiting nucleophilic addition into an arene cation radical using both azole and primary amine nucleophiles. This finding is consistent with both fluoride and alkoxide nucleofuges, supporting a unified mechanistic picture using cation radical accelerated nucleophilic aromatic substitution (CRA-SNAr). Electrochemistry and time-resolved fluorescence spectroscopy confirm the key role solvents play in enabling selective arene oxidation in the presence of amines. The synthetic limitations of xanthylium salts are elucidated via photophysical studies. An alternative catalyst scaffold with improved turnover numbers is presented.

Rational Design of First-Row Transition Metal Complexes as the Catalysts for Oxidation of Arenes: A Homogeneous Approach

Rational Design of First-Row Transition Metal Complexes as the Catalysts for Oxidation of Arenes: A Homogeneous Approach

Direct Synthesis of Fluorescent Oxazolo-phenoxazines by Copper-Catalyzed/Hypervalent Iodine(III)-Mediated Dimerization/Cyclization of 2-Benzylamino-phenols

A dimerization/cyclization reaction of 2-benzylamino-phenols for the direct synthesis of the oxazolo-phenoxazine skeleton is reported. The reaction occurs under copper catalysis in the presence of hypervalent iodine(III), giving selectively the 5H-oxazolo[4,5-b]phenoxazine compounds. The cascade process, which allows the conversion of the substrates into the tetracyclic products, involves three C-H functionalization steps. Initial oxidation of electron-rich arenes by the hypervalent iodine is essential for the dimerization of substrates, whereas the formation of the five-membered rings is promoted by the copper species. 1-Benzyl-2-phenyl-6-(aryl-benzyl)amino-benzimidazoles are regioselectively obtained using N,N'-dibenzyl-phenylenediamines as starting substrates. The fluorescence emission properties of these classes of products have been evaluated.

Fe(II)-phthalocyanine supported on chitosan aerogel as a catalyst for oxidation of alcohols and alkyl arenes

Manipulation of materials is considered as one of the eminent strategies to create desirable catalysts. In this regard, increasing surface area and decreasing dimensions of catalysts have been widely employed on account of effectiveness of these methods. Herein, aerogel form of chitosan as a sustainable, and high aspect ratio compound is employed as a green support for the catalytic purposes. Chitosan aerogel was modified with Fe(II)-phthalocyanine to produce a heterogeneous catalyst for oxidation reactions. The synthesized catalyst promoted the oxidation reactions of alcohols and alkyl arenes to the corresponding aldehydes and ketones using H2O2 as an oxidant in 24 h. The reactions for aliphatic and aromatic alcohols gave turnover numbers of 106–109 at 80 °C and 106–117 at room temperature, respectively. The oxidations of alkyl arenes were carried out with turnover numbers laying in the range of 106–117 at 100 °C. The low toxicity, inexpensive nature, and recycling possibility of the catalyst accompanied by the reaction mild conditions, clean oxidant, and excellent yields offer chitosan aerogel modified with Fe(II)-phthalocyanine as a promising catalyst for oxidation reactions.

Photoactivated Osmium Arene Anticancer Complexes

Half-sandwich Os-arene complexes exhibit promising anticancer activity, but their photochemistry has hardly been explored. To exploit the photocytotoxicity and photochemistry of Os-arenes, O,O-chelated complexes [Os(η6-p-cymene)(Curc)Cl] (OsCUR-1, Curc = curcumin) and [Os(η6-biphenyl)(Curc)Cl] (OsCUR-2), and N,N-chelated complexes [Os(η6-biphenyl)(dpq)I]PF6 (OsDPQ-2, dpq = pyrazino[2,3-f][1,10]phenanthroline) and [Os(η6-biphenyl)(bpy)I]PF6 (OsBPY-2, bpy = 2,2'-bipyridine), have been investigated. The Os-arene curcumin complexes showed remarkable photocytotoxicity toward a range of cancer cell lines (blue light IC50: 2.6-5.8 μM, photocytotoxicity index PI = 23-34), especially toward cisplatin-resistant cancer cells, but were nontoxic to normal cells. They localized mainly in mitochondria in the dark but translocated to the nucleus upon photoirradiation, generating DNA and mitochondrial damage, which might contribute toward overcoming cisplatin resistance. Mitochondrial damage, apoptosis, ROS generation, DNA damage, angiogenesis inhibition, and colony formation were observed when A549 lung cancer cells were treated with OsCUR-2. The photochemistry of these Os-arene complexes was investigated by a combination of NMR, HPLC-MS, high energy resolution fluorescence detected (HERFD), X-ray adsorption near edge structure (XANES) spectroscopy, total fluorescence yield (TFY) XANES spectra, and theoretical computation. Selective photodissociation of the arene ligand and oxidation of Os(II) to Os(III) occurred under blue light or UVA excitation. This new approach to the design of novel Os-arene complexes as phototherapeutic agents suggests that the novel curcumin complex OsCUR-2, in particular, is a potential candidate for further development as a photosensitizer for anticancer photoactivated chemotherapy (PACT).

Steric effect of NHC ligands in Pd(II)–NHC-catalyzed non-directed C–H acetoxylation of simple arenes

Although there has been a lot of progress in oxidative arene C–H functionalization reactions catalyzed by Pd(II/IV) system, the non-directed, site-selective functionalization of arene molecules is still challenging. It has been established that ligands play a pivotal role in controlling rate- as well as selectivity-determining step in a catalytic cycle involving well-defined metal-ligand bonding. N-heterocyclic carbene (NHC) ligands have had a tremendous contribution in the recent extraordinary success of achieving high reactivity and excellent selectivity in many catalytic processes including cross-coupling and olefin-metathesis reactions. However, the immense potential of these NHC ligands in improving site-selectivity of non-directed catalytic C–H functionalization reactions of simple arenes is yet to be realized, where overriding the electronic bias on deciding selectivity is a burdensome task. The presented work demonstrated an initiative step in this regard. Herein, a series of well-defined discrete [Pd(NHCR′R)(py)I2] complexes with systematically varied degree of spatial congestion at the Pd centre, exerted through the R and R’ substituents on the NHC ligand, were explored in controlling the activity as well as the site-selectivity of non-directed acetoxylation of representative monosubstituted and disubstituted simple arenes (such as toluene, iodobenzene and bromobenzene, naphthalene and 1,2-dichlorobenzene). The resulting best yields were found to be 75% for toluene and 65% for bromobenzene with [Pd(NHCMePh)(py)I2], 75% for iodobenzene and 79% for naphthalene with [Pd(NHCMeMe)(py)I2], and 41% for 1,2-dichlorobenzene with [Pd(NHCCyCy)(py)I2]. Most importantly, with increasing the bulkiness of the NHC ligand in the complexes, the selectivity of the distal C-acetoxylated products in comparison to the proximal ones, was enhanced to a great extent in all cases. Considering the vast library of NHC ligands, this study underscores the future opportunity to develop more strategies to improve the activity and the crucial site-selectivity of C–H functionalization reactions in simple as well as complex organic molecules.

Electrocatalytic Oxyesterification of Hydrocarbons by Tetravalent Lead

The selective catalytic oxidative monofunctionalization of gaseous alkanes found in natural gas and commodity chemicals such as benzene and cyclohexane is an important objective in the field of carbon–hydrogen bond activation. Past research has demonstrated the possibility of stoichiometric oxyesterification of such substrates using lead(IV) trifluoroacetate (PbIV(TFA)4) as oxidant, which is driven by the high 2-electron redox potential of lead(IV). However, this redox potential then precludes reoxidation of lead(II) by a convenient oxidant such as O2, nullifying an effective catalytic cycle. In order to utilize renewable energy resources as alternatives to high-temperature thermocatalysis, we demonstrate the room-temperature electrocatalytic oxyesterification of alkanes and benzene with PbIV(TFA)4 as catalysts. At 1.67 V versus SHE, alkanes and benzene yielded the corresponding trifluoroacetate esters at room temperature; typically, good yields and high faradaic efficiencies were observed. High intrinsic turnover frequencies were obtained, for example, of >1000 min–1 for the oxyesterification of ethane at 30 bar. An analysis of the possible mechanistic pathways based on previously investigated stochiometric reactions, cyclic voltammetry measurements, kinetic isotope effects, and model compounds led to the conclusion that catalysis involves lead-mediated proton-coupled electron transfer of alkanes at and to the anode, followed by reductive elimination through an SN2 reaction to yield the alkyl-TFA products. Similarly, lead-mediated electron transfer from benzene at and to the anode leads to phenyl-TFA. Cyclic voltammetry also shows the viability of in situ reoxidation of Pb(II) species. The synthesis results obtained as well as the mechanistic insight are important advances towards the realization of selective alkane and arene oxidation reactions.

Synthesis of new Zn (II) complexes for photo decomposition of organic dye pollutants, industrial wastewater and photo-oxidation of methyl arenes under visible-light

Synthesis of new Schiff’s base Zn-complexes for photo-oxidation of methyl arenes and xylenes are reported under visible light irradiation conditions. All the synthesized new ligands and Zn-complexes are thoroughly characterized with various spectral analyses and confirmed as 1:1 ratio of Zn and ligand with distorted octahedral structure. The bandgap energies of the ligands are higher than its Zn-complexes. These synthesized new Zn(II) complexes are used for the photo-fragmentation of organic dye pollutants, photodegradation of food industrial wastewater and oxidation of methyl arenes which are converted into its respective aldehydes with moderate yields under visible light irradiation. The photooxidation reaction dependency on the intensity of the visible light was also studied. With the increase in the dosage of photocatalyst, the methyl groups are oxidized to get aldehydes and mono acid products, which are also identified from LC-MS data. Finally, [Zn(PPMHT)Cl] is with better efficiency than [Zn(PTHMT)Cl] and [Zn(MIMHPT)Cl] for oxidation of methyl arenes is reported under visible-light-driven conditions.

Metal-free photocatalytic C(sp3)–H bond activation

Over nearly two decades, visible-light catalysis has emerged as a method for activating C–H bonds. Such reactions typically involve photoinduced electron transfer between the photocatalyst and substrate. Recently, König reported that the highly oxidizing photoredox catalyst 2,4,6,-triphenylpyrylium tetrafluoroborate could facilitate the oxidation of methyl arenes to cyanoarenes through C(sp3)–H bond activation. The substrate scope was demonstrated to extend to alcohols, aldehydes, and oximes as well.

Ozone-Mediated Amine Oxidation and Beyond: A Solvent-Free, Flow-Chemistry Approach.

Ozone is a powerful oxidant, most commonly used for oxidation of alkenes to carbonyls. The synthetic utility of other ozone-mediated reactions is hindered by its high reactivity and propensity to overoxidize organic molecules, including most solvents. This challenge can largely be mitigated by adsorbing both substrate and ozone onto silica gel, providing a solvent-free oxidation method. In this manuscript, a flow-based packed bed reactor approach is described that provides exceptional control of reaction temperature and time to achieve improved control and chemoselectivity over this challenging transformation. A powerful method to oxidize primary amines into nitroalkanes is achieved. Examples of pyridine, C-H bond, and arene oxidations are also demonstrated, confirming the system is generalizable to diverse ozone-mediated processes.