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The enantioselective benzylic oxidation to synthesize chiral benzyl alcohols from alkylarenes poses a challenge. This study introduces a one-pot, two-step C–H bond hydroxylation process that integrates HRP-catalyzed oxidation and carbonyl reductase-catalyzed reduction for the enantiocomplementary synthesis of benzyl alcohols (up to 77% yield and 99% ee). This mild and operationally simple process provides an alternative approach to enantioselective benzylic hydroxylation. [ABSTRACT FROM AUTHOR]

Adding HClO4 to [(BnTPEN)MnIII–OO]+ in MeOH generates a short-lived MnIII–OOH species, which converts to a putative MnV＝O species. The potent MnV＝O species in MeCN oxidizes the pendant phenyl ring of the ligand in an intramolecular fashion. The addition of benzene causes the formation of (BnTPEN)MnIII-phenolate. These findings suggest that high valent Mn species have the potential to catalyze challenging aromatic hydroxylation reactions. [ABSTRACT FROM AUTHOR]

Metal oxoclusters constitute a dynamic and expanding domain of research with versatile applications in catalysis, materials science, medicine, and beyond. Particular attention has been given to their potential utility due to their distinctive properties. The incorporation of ionic liquid (IL) environments into metal oxocluster (MOC) systems offers numerous advantages, including higher stability, tunable coordination to metal sites, and the capability to dissolve diverse substrates for catalytic applications. Although IL-stabilized MOCs (IL--MOCs) are still in the developmental phase, their potential to revolutionize catalysis is substantial. As research progresses, IL--MOCs will likely play an increasingly important role in catalysis. This perspective article focuses on the preparation methods of IL--MOCs, how the MOCs are stabilized/regulated by ILs or even PIL (polymeric ILs), as well as their catalytic applications, including oxidation, epoxidation, oxidative desulfurization, biomass oxidation, hydroxylation of benzene, acid catalysis, CO2 activation and utilization, carbonylation, hydrogenation/hydrolysis, electrochemistry, etc. IL--MOCs have played a crucial role in the development of sustainable chemistry in the light of the potential opportunities and challenges. The unique advantages make IL--MOCs outstanding candidates for industrial catalysts. [ABSTRACT FROM AUTHOR]

Adherent bubbles at electrodes are generally treated as reaction penalties. Herein, in situ hydroxylation of indium tin oxide surfaces can be easily achieved by applying a constant potential of +1.0 V in the presence of bubbles. Its successful hydroxylation is further demonstrated by preparing a ferrocene-terminated film, which is confirmed by cyclic voltammetry and X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

The development of photocatalysts that are effective in different organic processes is a topic of great interest to researchers in materials chemistry. Herein, we report the design and synthesis of a new covalent triazine framework (CTF) built by acid-catalyzed trimerization of 4,4′-(benzo[b]benzo[4,5]thieno[2,3-d]thiophene-2,7-diyl)dibenzonitrile activated by microwaves that generates a new organic polymer, DPhBTBT-CTF. This CTF exhibits visible-light absorption due to the electron-donating BTBT units and the extended π-conjugated framework with the electron-acceptor triazine node and proves to be an efficient and versatile metal-free heterogeneous photocatalyst for different organic processes such as selective oxidations of both sulfides and benzyl alcohols to sulfoxides and benzaldehydes, respectively or the oxidative bromination of electron rich aromatic compounds. Moreover, two different proof of concept reactions were tested: the Diels–Alder cycloaddition and the hydroxylation of boronic acids. Heterogeneity studies confirmed that this photocatalyst can be recycled without significant loss of selectivity, and also some mechanistic tests suggested the preferred oxidation pathway. [ABSTRACT FROM AUTHOR]

Reported herein is an efficient and eco-friendly peri-selective monohydroxylation of naphthalene monoimides (NMIs) to access 4-hydroxy NMIs, which possess multidisciplinary applications. The key aspect of this method is the utilization of cobalt(II)-catalysis via a single electron transfer mechanism to achieve site-selective C(sp2)-hydroxylation. Transformation of the hydroxyl group into pseudohalides reveals its applications towards cross-coupling reactions. [ABSTRACT FROM AUTHOR]

It is a major challenge to perform one-pot hydroxylation of benzene to phenol under mild conditions, which replaces the environmentally harmful cumene method. Thus, finding highly efficient heterogeneous catalysts that can be recycled is extremely significant. Herein, a (POM)-based hybrid compound {[FeII(pyim)2(C2H5O)][FeII(pyim)2(H2O)][PMo V2 Mo VI9 V IV3 O42]}·H2O (pyim = 2-(2-pyridyl)benzimidazole) (Fe2-PMo11V3) was successfully prepared by hydrothermal synthesis using typical Keggin POMs, iron ions and pyim ligands. Single-crystal diffraction shows that the Fe-pyim unit in Fe2-PMo11V3 forms a stable double-supported skeleton by Fe–O bonding to the polyacid anion. Remarkably, due to the introduction of vanadium, Fe2-PMo11V3 forms a divanadium-capped conformation. Benzene oxidation experiments indicated that Fe2-PMo11V3 can catalyze the benzene hydroxylation reaction to phenol in a mixed solution of acetonitrile and acetic acid containing H2O2 at 60 °C, affording a phenol yield of about 16.2% and a selectivity of about 94%. [ABSTRACT FROM AUTHOR]

The current traditional phenol production process has many shortcomings, and the efficient and clean photocatalytic one-step oxidation to phenol is gradually attracting attention. Heteropolyacids (PMo10V2) with high-density Lewis acid active sites and excellent photoelectron transfer ability are ideal choices for catalytic reactions. In this study, a copper-modified isolated dimeric hybrid nanocluster, [Cu(pyim)2]2[Cu(pyim)2(P2Mo VI20 Mo V2 V IV4 O82)]2·(H2O) (pyim = [2-(pyridin-2-yl)imidazole]), was synthesized by a convenient hydrothermal method. The structural analysis demonstrated that the compound was composed of metal–organic complexes containing pyim ligands, Keggin-type heteropolyacids, and transition metal copper ions. Remarkably, this not only solves the difficulty that the heteropolymeric acid cannot be recovered by dissolving in the solvent but also introduces the copper atom as a second active center. The catalyst exhibited a benzene conversion of 15.6% and a selectivity of 85.2% in a mixed solution of acetonitrile and acetic acid under optimal reaction conditions. After four catalytic cycles, the PXRD pattern proved that the catalyst was still stable. This study provides a good idea for photocatalytic reactions and other environmental applications. [ABSTRACT FROM AUTHOR]

Efficiently devising a strategy to synthesize titanium silicate-1 (TS-1) zeolite crystals with desired particle size and enriched framework titanium content for improved catalytic oxidation properties could be challenging. This study explores the incorporation of polyvinyl alcohol (PVA) and ammonium bicarbonate (NH4HCO3) as additives to decrease the particle size and increase the framework titanium content of TS-1, respectively. Powder X-ray diffraction (XRD), UV-vis absorption spectra, nitrogen adsorption–desorption, Fourier transform infrared (FT-IR) spectra, field-emission scanning electron microscopy (FESEM), and inductively coupled plasma (ICP) were used to characterize the TS-1 catalysts. The experimental results indicated that in the presence of NH4HCO3 and PVA (TS-1-S), the particle size and Si/Ti molar ratio of TS-1 were determined to be 170 nm and 43.55, respectively. Furthermore, the catalytic activity of the prepared catalysts in regard to the phenol hydroxylation with H2O2 has been evaluated. The TS-1-S sample showed a conversion of 29.52%, while the conversion of the conventional sample was 23.08%. This improvement can be attributed to the synergistic impact of reduced particle size and enriched framework titanium content. [ABSTRACT FROM AUTHOR]

Peroxygenase from Agrocybe aegerita catalyses the selective hydroxylation of tertiary C–H bonds, whereby tertiary alcohols, diols, ketols, etc., were obtained in good to high regioselectivity and turnover numbers. This method can also be expanded for late-stage functionalization of drug molecules, which represents a streamlined synthetic method to give access to useful compounds. [ABSTRACT FROM AUTHOR]

Herein, we have demonstrated Lewis acid Fe(III)-assisted hydroxylation of ZIF-67 to form FexCo-layered double hydroxide (LDH) nanosheets. The catalyst Fe0.4Co-LDH produced an excellent water oxidation activity to reach a current density of 20 mA cm−2 at only 190 mV overpotential, superior to that of hydrothermally synthesized LDH with a similar composition. [ABSTRACT FROM AUTHOR]

The enhanced mechanochemical reactivity of potassium hydroxide (KOH) in the presence of 18-crown-6 ether is supported by potassium complexation under milling and has been demonstrated in the Henry reaction and SNAr hydroxylation: in both cases, the desired product is formed within 10 minutes, but requires the presence of the crown ether. [ABSTRACT FROM AUTHOR]

Two new tetradentate N4 ligands (LN4), LN4 = Me2,Me2PyzTACN (1-(2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl)-4,7-dimethyl-1,4,7-triazacyclononane) and Me2,MeImTACN (1-((1-methyl-1H-imidazol-1-yl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane) have been synthesized and their corresponding Fe(II) complexes [FeII(Me2,Me2PyzTACN)(CF3SO3)2], 1Pz, and [FeII(Me2,MeImTACN)(CF3SO3)2], 1Im, have been prepared and characterized. Complexes 1Pz and 1Im catalyse the hydroxylation of C–H bonds of alkanes with excellent efficiencies, using hydrogen peroxide as oxidant. The high H/D kinetic isotope effect values for C–H hydroxylation, large normalized tertiary/secondary C–H (C3/C2) bond selectivities in adamantane oxidation, and high degrees of stereoretention in the oxidation of cis-1,2-dimethylcyclohexane are indicative of metal-based oxidation processes. The complexes also catalyse the oxidation of cyclooctene to form its corresponding epoxide and syn-diol. For 1Pz the epoxide is the main product, while for the analogous complex 1Im the syn-diol predominates. The active oxidant is proposed to be an [(LN4)FeV(O)(OH)]2+ species (2Pz, LN4 = Me2,Me2PyzTACN and 2Im, LN4 = Me2,MeImTACN) which may exist in two tautomeric forms related by a proton shift between the oxo and hydroxo ligands. Isotope labelling experiments show that the oxygen atom in the hydroxylated products originates from both water and hydrogen peroxide, and labelling experiments involving oxygen atom transfer to sterically bulky substrates provide indirect information on the steric influence exerted by the two ligands in the relative reactivities of the two hypervalent iron tautomers. Based on these labelling studies, the steric influence exerted by each of the ligands towards the relative reactivity of the oxo ligands of the corresponding pair of Fe(V)(O)(OH) tautomers can be derived. Furthermore, this steric influence can be gauged relative to related complexes/ligands. [ABSTRACT FROM AUTHOR]

Fe(II) complexes with pentadentate ligands, including N-heterocyclic carbene moieties, were prepared and electrostatically attached onto the perfluorinated surface of a mesoporous aluminosilicate. The heterogeneous catalysts were applied to the catalytic oxidation of cyclohexane and cyclohexene using H2O2 as an oxidant in CH3CN, demonstrating high performance and selectivity in alkane hydroxylation and cyclohexene epoxidation. [ABSTRACT FROM AUTHOR]

The reaction of (NMe4)2[NiII(LPh)(OAc)] (1[OAc], LPh = 2,2′,2′′-nitrilo-tris-(N-phenylacetamide); OAc = acetate) with 3-chloroperoxybenzoic acid (m-CPBA) resulted in the formation of a self-hydroxylated NiIII-phenolate complex, 2, where one of the phenyl groups of LPh underwent hydroxylation. 2 was characterised by UV-Vis, EPR, and XAS spectroscopies and ESI-MS. 2 decayed to yield a previously characterised NiII-phenolate complex, 3. We postulate that self-hydroxylation was mediated by a formally NiIV＝O oxidant, formed from the reaction of 1[OAc] with m-CPBA, which undergoes electrophilic aromatic substitution to yield 2. This is supported by an analysis of the kinetic and thermodynamic properties of the reaction of 1[OAc] with m-CPBA. Addition of exogenous hydrocarbon substrates intercepted the self-hydroxylation process, producing hydroxylated products, providing further support for the formally NiIV＝O entity. This study demonstrates that the reaction between NiII salts and m-CPBA can lead to potent metal-based oxidants, in contrast to recent studies demonstrating carboxyl radical is a radical free-chain reaction initiator in NiII/m-CPBA hydrocarbon oxidation catalysis. [ABSTRACT FROM AUTHOR]

Cu(II) complexes supported by tetradentate amido-quinoline acyclic ligands (L1 & L2) have been synthesized, characterized, and employed as catalysts for aromatic C–H hydroxylation using H2O2 as an oxidant in the absence of an external base with a high selectivity of around 90% for phenols via the non-radical pathway (TON ≥720). The KIE value, various spectroscopic studies and DFT calculation supported the involvement of Cu(II)–OOH species. [ABSTRACT FROM AUTHOR]

Triphenylamine-based donor–acceptor conjugated microporous polymers, namely PTPA-AQ and PTPA-AM, were synthesized for the first time via Suzuki–Miyaura coupling of tris(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-amine as a donor with 2,6-dibromoanthracene-9,10-dione and 2,2′-(2,6-dibromoanthracene-9,10-diylidene)dimalononitrile acceptors for efficient visible-light driven oxidative hydroxylation of various phenylboronic acids. The dimalononitrile derivative having greater acceptor ability showed tunable photophysical properties of PTPA-AM (lower band gap of 1.47 eV and better exciton separation efficiency) as well as porosity (lower Brunauer–Emmett–Teller (BET) surface area of 43 m2 g−1). PTPA-AQ having higher BET surface area (400 m2 g−1), suitable HOMO–LUMO positions and an optimal band gap (1.94 eV) showed better photocatalytic activity for the hydroxylation with yields up to 96%. [ABSTRACT FROM AUTHOR]

We describe an ecofriendly two-step synthesis of glycoamphiphiles, capable of hierarchical self-assembly into supramolecular hydrogels, consisting of Knoevenagel condensation of barbituric acid derivatives with biobased carbohydrates (glucose and maltose) and selective H2O2-mediated oxidative hydroxylation of barbiturates in water. By modifying the molecular design of glycostructures and the hydrophilic/hydrophobic balance, various glyco-nanostructures (ribbons, tapes, vesicles, helices, fibers) have been created via supramolecular self-assembly. In addition, we found that a water-soluble glycoamphiphile underwent sol-to-gel phase transition upon the addition of α-glucosidase as a result of the hydrolysis of the non-reducing-end glucose in the maltose moiety. [ABSTRACT FROM AUTHOR]

A concise synthesis of the tetrahydropyranyl side chain of verucopeptin, an antitumor antibiotic cyclodepsipeptide efficacious against MDR cancers in vivo, is achieved using 12 steps in the longest linear sequence and 21 total steps, in which Julia–Kocienski olefination for the segments coupling, asymmetric hydroxylation as well as stereoselective synthesis of stable tetrahydropyran ring from a D -isoascorbic acid derivative are key steps. This convergent synthetic strategy enables the structural modification and mechanism study of verucopeptin for its clinical applications. [ABSTRACT FROM AUTHOR]

The synthesis of valuable organic compounds is a novel possibility for the application of physical plasma. As model reactants 2,5-dihydroxybenzoic acid derivatives were used and the resulting reactions investigated in detail. The formation of methoxylated and hydroxylated products as well as dimers (biaryls) was mediated by physical plasma in aqueous solution at atmospheric pressure and room temperature. Additionally, nitrated or nitrosated products were assumed. The direct (reactant is part of the liquid which is plasma-treated) and indirect (liquid is treated by plasma and afterwards reactant is added) plasma treatment resulted in a partly different product pattern, but both reaction concepts are suitable for the synthesis of organic compounds. The influence of operating parameters such as duration of plasma treatment, volume of the liquid, or concentration of reactants was varied to study the reaction course in order to increase product yields. Nitrite, nitrate, hydrogen peroxide, a decreased pH-value and an increased temperature was determined for the plasma-treated liquid. Consequently, the reactions with the 2,5-dihydroxybenzoic acid derivatives were pursued in the presence of these compounds at acidic pH-value and 50 °C. As result, nitrite, a low pH-value (pH = 2.2) and an elevated temperature were at least in part responsible for the formation of the products. The advantages of plasma-mediated synthesis are discussed in detail. The environmentally friendly reaction conditions without the need for catalysts or buffer components recommend physical plasma as novel mean in green chemistry. [ABSTRACT FROM AUTHOR]

The selective hydroxylation of steroids through chemical synthesis is a complex reaction with a high environmental impact. The use of photoautotrophic microorganisms expressing heterologous monooxygenases could overcome this problem by fueling the reaction with electrons and O2 derived from the light-dependent oxidation of water, occurring during photosynthesis. Here, the light-driven selective hydroxylation of testosterone into 15β-hydroxytestosterone was achieved using whole-cells of the unicellular cyanobacterium Synechocystis sp. PCC 6803 expressing the heterologous CYP450 monooxygenase, CYP110D1. Additionally, the reaction conditions including cell density, aeration, and substrate concentration were optimized, leading to a maximum specific activity of 1 U gCDW−1. This value is about 2-fold higher than the one achieved using the model heterotrophic bacterium, E. coli, in which was necessary to express not only CYP110D1 but also its electron partners, and to use glucose as a sacrificial electron donor. Altogether, the results obtained here demonstrate the higher efficiency and sustainability (94% atom economy) of testosterone hydroxylation using our engineered Synechocystis chassis, compared to biocatalysis with heterotrophic microorganisms or chemical synthesis. [ABSTRACT FROM AUTHOR]

Hierarchical TS-1 materials were synthesized using hydrothermal synthesis and a post modification technique through desilication. They were evaluated for hydroxylation of anisole to produce industrially important chemicals, o-methoxyphenol (OMP) and p-methoxyphenol (PMP). The detailed characterization of the prepared catalysts, such as morphology, structure, nature of Ti and surface area were obtained by SEM, HR-TEM, XRD, UV-VIS spectroscopy and the BET technique. The effects of various operational parameters such as substrate/H2O2 molar ratio, reaction temperature, catalyst concentration and solvent effect on the hydroxylation of anisole have been studied in detail. The microporous TS-1 catalyst showed 32% anisole conversion with 34% selectivity to PMP, while the micro/mesoporous DTS-1 catalyst showed enhanced activity for anisole hydroxylation, i.e. 54% conversion with 55% selectivity towards PMP. The increased framework Ti and improved accessibility of the active sites located in the channels of DTS-1, which permit the mass transfer of reactants, transition states and products from the mesopores of DTS-1, were responsible for the enhanced catalytic activity and selectivity towards p-methoxyphenol. [ABSTRACT FROM AUTHOR]

Second near-infrared (NIR-II) laser-mediated photothermal therapy and sonothermal therapy using low-intensity focused ultrasound exposure for tumors have attracted increasing attention owing to their ability to penetrate deep tissues and provide noninvasive ablation with high therapeutic efficacy. However, their applications were limited by the shortness of optimal NIR-II photothermal agents and sonothermal agents. In this study, we discovered that the edge-selectively hydroxylated graphene nanosheets (EHG NSs) with excellent water dispersibility and an "intact conjugated plane" were not only an outstanding NIR-II photothermal agent but also an effective sonothermal agent for tumor therapy. EHG NSs were incorporated into an injectable adhesive thermosensitive hydrogel with a characteristic sol-gel phase transition behavior. EHG NSs endowed the injectable hydrogel with an exceptional photothermal effect under the laser irradiation (1064 nm, 1.0 W cm -2 ) as well as an effective sonothermal effect under ultrasonic exposure (3.0 MHz, 2.1 W cm -2 ), effectively killing tumor cells in vitro and inhibiting tumor growth after intratumoral injection. Especially, the NIR-II photothermal therapy based on the hybrid hydrogel completely ablated the primary tumors and effectively activated systemic anti-tumor immune responses benefiting from the protein adsorption capacity of the injectable hydrogel, significantly inhibiting the growth of the distal tumors. Collectively, EHG nanosheets loaded in the injectable hydrogel will be a promising "all-rounder" for noninvasive deep penetrating thermotherapy and a potent platform that integrates various therapies.

The discovery and development of new synthetic methods exploiting earth-abundant-element-based catalysts is an important goal in contemporary synthetic organic chemistry, which faces increasingly stringent requirements of sustainability. In this work, we disclose alumina-mediated propargylic C–H activation inducing a challenging transformation of readily available alkynes into a valuable 1,3-diene moiety under unprecedentedly mild conditions. Combining DFT-investigation and synthetic observations, we demonstrate that partial hydroxylation of alumina's surface might play an essential role in this process. [ABSTRACT FROM AUTHOR]

The structural properties of the (WOx)n phase dispersed on TiO2 (P25, anatase) at surface densities of 0.5–4.5 W nm−2 (i.e. up to approximately a monolayer) were explored by using in situ Raman and FTIR spectroscopy, in situ Raman/18O exchange and Raman spectroscopy in static equilibrium at temperatures of 175–430 °C. Deciphering the temperature and coverage dependence of the spectral features under oxidative dehydration conditions showed that (i) the (WOx)n dispersed phase is heterogeneous at 430 °C consisting of two distinct mono-oxo species: Species-I with C3v-like O＝W(–O–)3 configuration (W＝O mode at 1009–1014 cm−1) and Species-II with C4v-like O＝W(–O–)4 configuration (W＝O mode at 1003–1009 cm−1); (ii) the O＝W(–O–)3 site is formed with first order of priority and its formation ceases after the complete consumption of the most basic hydroxyls that are titrated first, hence is abundant at low coverage (<1.5 W nm−2); (iii) the O＝W(–O–)4 site prevails over the O＝W(–O–)3 site at medium to high coverage (≥2 W nm−2) and partially occurs in associated (polymerized) coverages above 2 W nm−2; (iv) lowering the temperature in the 430 → 250 → 175 °C sequence does not affect the structural and vibrational properties of O＝W(–O–)3 but leads to the gradual transformation of the O＝W(–O–)4 site to a di-oxo (O＝)2W(–O–)3 site (with a symmetric stretching mode at ∼985 cm−1) and the partial association of adjacent O＝W(–O–)4 units. All temperature-dependent structural/configurational transformations are fully reversible in the 430–175 °C range and are interpreted at the molecular level by a mechanism involving water molecules retained at the surface that act in a reversible temperature-dependent mediative manner resulting in hydroxylation (upon cooling, e.g. to 250 °C) and dehydroxylation (upon heating, e.g. to 430 °C). The Raman spectra obtained for the hydroxyl region confirm the successive hydroxylation/dehydroxylation steps during temperature cycles (e.g. 430 → 250 → 430 °C). One can tune the speciation of the dispersed (WOx)n phase under dehydrated conditions by appropriate control of temperature and coverage. [ABSTRACT FROM AUTHOR]

An unprecedented metal-free and catalyst-free synthesis of benzo[c]chromeno[4,3,2-gh]phenanthridine derivatives, a class of 1,6-diheterophenalenoid heterocycle, is reported for the first time. The oxidative cross-coupling reaction for the remote cyclization is achieved through the in situ generated o-quinone methide intermediate followed by an electrocyclic ring closure reaction. The aromatization of the cyclohexane ring is achieved by sequential H shift, hydroxylation, and elimination reaction. DMSO-assisted concomitant cyclization and aromatization reactions are also disclosed for the first time. [ABSTRACT FROM AUTHOR]

The late stage photochemical hydroxylation of biaryl sulfonium salts was enabled with a TEMPO derivative as a simple oxygen source, in metal free conditions. The scope and mechanism of this exceptionally simple synthetic method, which constructs important arylated phenols from aromatic C–H bonds, are herein discussed. [ABSTRACT FROM AUTHOR]

Simple use of KOH allows the direct F to OH exchange of aromatic and heteroaromatic substrates under mechanochemical conditions. The reaction is performed in the absence of solvent with potassium hydroxide as OH source. As a result, this approach is both more atom economical and environmentally friendly than previously described methods for this transformation. [ABSTRACT FROM AUTHOR]

Direct hydroxylation of benzene with a high selectivity and durability for phenol production is still a challenge. Herein, a reusable VxOy/AC(cit)-DBD catalyst was synthesized using a facile and environmentally benign method in which a mixture of citric acid, NH4VO3 and activated carbon (AC) was treated using dielectric barrier discharge (DBD) at room temperature and under an N2 atmosphere. Compared with VxOy/AC-DBD, which is prepared without citric acid, more vanadium species were exposed on the surface of VxOy/AC(cit)-DBD. The residues of citric acid formed by DBD treatment can stabilize the vanadium species on the surface of AC by restraining the leaching of vanadium from the catalyst during the reaction. Moreover, the addition of citric acid increased the ratio of V4+/V5+ and benzene adsorption on the catalyst surface, which are favorable for the hydroxylation of benzene. Additionally, the resulting vanadium particles are smaller (less than 10 nm) and amorphous owing to the inhibiting effect of citric acid residues on particle growth and the low temperature characteristics of DBD treatment. Under the optimized reaction conditions, VxOy/AC(cit)-DBD showed a good stability and recyclability in the hydroxylation of benzene and achieved a benzene conversion of 21.5% and phenol selectivity of 99.1%. [ABSTRACT FROM AUTHOR]

Direct catalytic hydroxylation of benzene under mild reaction conditions proceeded efficiently in the presence of a monocationic μ-nitrido-bridged iron phthalocyanine dimer with 16 peripheral methyl groups in an acetonitrile solution with excess H2O2. Mechanistic studies suggested that the reaction was catalyzed by a high-valent iron–oxo species generated in situ. Moreover, the peripheral methyl groups of the catalyst were presumed to have enhanced the production rate of the iron–oxo species. [ABSTRACT FROM AUTHOR]

DFT and ab initio DLPNO-CCSD(T) calculations predict a stable S = 2 six-coordinate FeIV=O species with cucurbit[5]uril (CB[5]) as a ligand ([(CB[5])FeIV=O(H2O)]2+(1)). The strong oxidising capability of 1 far exceeds even that of metalloenzymes such as sMMOs in activating inert substrates such as methane, setting the stage for a new generation of biomimetic catalysts. [ABSTRACT FROM AUTHOR]

para-Selective hydroxylation of alkyl aryl ethers is established, which proceeds with a ruthenium(II) catalyst, hypervalent iodine(III) and trifluoroacetic anhydride via a radical mechanism. This protocol tolerates a wide scope of substrates and provides a facile and efficient method for preparing clinical drugs monobenzone and pramocaine on a gram scale. [ABSTRACT FROM AUTHOR]

Steroids are an important family of bioactive compounds. Steroid drugs are renowned for their multifaceted pharmacological activities and are the second-largest category in the global pharmaceutical market. Recent developments in biocatalysis and biosynthesis have led to the increased use of enzymes to enhance the selectivity, efficiency, and sustainability for diverse modifications of steroids. This review discusses the advancements achieved over the past five years in the enzymatic modifications of steroid scaffolds, focusing on enzymatic hydroxylation, reduction, dehydrogenation, cascade reactions, and other modifications for future research on the synthesis of novel steroid compounds and related drugs, and new therapeutic possibilities.

The introduction of the 2-pyridylsulfenyl directing group to o-carboranes allowed either B(3)–Ir or B(4)–Ir bond formation using a steric effect strategy. Moreover, the reactivity of the B(4)–Rh o-carborane complexes with small molecules was probed by reactions with N-bromosuccinimide, N-iodosuccinimide and O2. Rhodium-mediated B(4)-hydroxylation and B(4)-halogenation which are seldom reported have been achieved under practical and mild conditions. [ABSTRACT FROM AUTHOR]

In this work, a series of CuZnFeAl-LDH catalysts for phenol oxidation to dihydroxybenzene have been prepared through a co-precipitation method. Versatile characterization studies are applied to reveal electron transfer from oxygen vacancies to Cu2+ on the LDH surface. The resulting Cu+ benefits the formation of hydroxyl radicals to promote the catalytic activity. Besides, through inverse gas chromatography (IGC), the acid–base hydrotalcite surface can be quantitatively determined. Both the oxygen vacancies and acid–base ratio (Ka/Kb) abide by a volcano-like tendency with the addition of copper content, which is consistent with the catalysis result. Among all these catalysts, 15/CuZnFeAl-LDH presents the optimal conversion (66.9%), selectivity (71.3%), and stable recyclability under mild conditions (60 °C, 1.0 MPa), respectively, and is environmentally-friendly and energy efficient. The high efficiency of this catalyst is mainly attributed to the synergistic effect between Cu+ and oxygen vacancies promoted by Ka/Kb. [ABSTRACT FROM AUTHOR]

A formal hydroxylation/cyclization of cyclopropanemethanols with DMSO is described, which involves isomerization and cyclization under Tf2O catalysis. This reaction undergoes ring-opening of the cyclopropane moiety to generate homoallylic alcohols, which react with DMSO to produce 3-benzylidenetetrahydrofurans. With various substituted groups on cyclopropanemethanols the reactions proceed smoothly and the desired 3-benzylidenetetrahydrofurans are obtained in moderate to good yields. [ABSTRACT FROM AUTHOR]

The use of ZnO as a photocatalyst for organics degradation has been reported in the literature, but a divergence of results suggests that surface groups play a critical role in its photoactivity. In this paper, we describe the influence of annealing time on the photoactivity of ZnO particles by analyzing their behavior against molecules with typically high surface adsorption, i.e., methylene blue and rhodamine B. ZnO prepared through the chemical precipitation route at room temperature has been calcined at mild temperatures to gradually eliminate surface –OH groups. Although the increase in annealing time had promoted the crystallite size to increase through the elimination of Zn(OH)2, the particle growth reduced the specific surface area and surface hydroxylation, both of which are critical features concerning photocatalysis. The probing of the main degradation mechanisms evinced that the generation of OH* radicals is the only relevant process for oxidation, which is closely related to the nature of –OH groups. After the complete ZnO crystallization, a balance of morphology, surface area, exposed surface, and surface hydroxylation is necessary to obtain the most efficient materials. [ABSTRACT FROM AUTHOR]

Late-stage direct functionalization of the C–H bond is synthetically desirable. Metalloenzymes having metal-oxo active sites are well known to selectively catalyze hydroxylation and halogenation reactions with high efficiency. This review highlights the recent developments in the field of direct C–H halogenation and pseudohalogenation reactions catalyzed by the functional models of metalloenzymes. [ABSTRACT FROM AUTHOR]

The efficient conversion of aryl halides to phenols under mild reaction conditions remains a great challenge. Here we demonstrate that a facile and efficient hydroxylation reaction of aryl halides with water could be accomplished through a merger of a heterogeneous organic semiconductor graphitic carbon nitride (g-C3N4) photocatalyst and a homogeneous nickel(II) bipyridine organometallic catalyst under visible-light irradiation at room temperature. The protocol is tolerant to a wide range of substituted aryl halides, resulting in various phenol products with excellent conversion and selectivity. It is worth noting that the OH group of the resulting phenols originating from water increased the environmental friendliness of the reaction. It is worth noting that among all the previously reported catalysts (even including thermal catalysts with harsh reaction conditions), our Nidabpy/g-C3N4 dual catalytic system demonstrated the highest catalytic activity reported in the shortest reaction time. This remarkable catalytic performance was attributed to the strong interaction between the Nidabpy complex and g-C3N4, which decreased the transfer distance of photogenerated electrons transferring to Ni(II), accelerating the catalytic cycle. Furthermore, g-C3N4 was easily recovered from the reaction mixture and reused five times, showing the good potential of green hydroxylation reactions for large-scale industrial application. [ABSTRACT FROM AUTHOR]

Copper(I) complexes [Cu(L1–7)2](ClO4) (1–7) of bidentate ligands (L1–L7) have been synthesized via spontaneous reduction and characterized as catalysts for aromatic C–H activation using H2O2 as the oxidant. The single crystal X-ray structure of 1 exhibited a distorted tetrahedral geometry. All the copper(I) complexes catalyzed direct hydroxylation of benzene to form phenol with good selectivity up to 98%. The determined kinetic isotope effect (KIE) values, 1.69–1.71, support the involvement of a radical type mechanism. The isotope-labeling experiments using H218O2 showed 92% incorporation of 18O into phenol and confirm that H2O2 is the key oxygen supplier. Overall, the catalytic efficiencies of the complexes are strongly influenced by the electronic and steric factor of the ligand, which is fine-tuned by the ligand architecture. The benzene hydroxylation reaction possibly proceeded via a radical mechanism, which was confirmed by the addition of radical scavengers (TEMPO) to the catalytic reaction that showed a reduction in phenol formation. [ABSTRACT FROM AUTHOR]

Hydroxyl compounds serve as key building blocks in the preparation of biologically active natural products and drugs. Traditionally, hydroxylation of the aromatic ring is achieved using stoichiometric amounts of oxidants, which leads to low atom-economy, undesired by-products, potential explosion risk and environmental pollution. Recently, electrosynthesis has attracted increasing attention as it employs clean electrical energy to promote redox reactions avoiding the use of oxidants. However, due to the poor mass and heat transfers of batch cells, low productivity and selectivity limit its further application. Herein, we develop a catalyst-, oxidant-, acidic solvent- and quaternary ammonium salt-free electrochemical para-selective hydroxylation of N-arylamides at room temperature in batch and continuous-flow. This proposal features excellent position control and water, air and functional group tolerance. Also, it is easy to scale up with higher productivity and selectivity using a flow electrolysis cell. [ABSTRACT FROM AUTHOR]

The soluble hydrogenase from Ralstonia eutropha provides an atom efficient regeneration system for reduced flavin cofactors using H2 as an electron source. We demonstrated this system for highly selective ene-reductase-catalyzed C＝C-double bond reductions and monooxygenase-catalyzed epoxidation. Reactions were expanded to aerobic conditions to supply H2O2 for peroxygenase-catalyzed hydroxylations. [ABSTRACT FROM AUTHOR]

Tris(oxazolynylmethyl)amine TOAR (where R denotes the substituent groups on the fourth position of the oxazoline rings) complexes of nickel(II) have been synthesized as catalyst precursors for alkane oxidation with meta-chloroperoxybenzoic acid (m-CPBA). The molecular structures of acetato, nitrato, meta-chlorobenzoato and chlorido complexes with TOAMe2 have been determined using X-ray crystallography. The bulkiness of the substituent groups R affects the coordination environment of the nickel(II) centers, as has been demonstrated by comparison of the molecular structures of chlorido complexes with TOAMe2 and TOAtBu. The nickel(II)-acetato complex with TOAMe2 is an efficient catalyst precursor compared with the tris(pyridylmethyl)amine (TPA) analogue. Oxazolynyl donors' strong σ-electron donating ability will enhance the catalytic activity. Catalytic reaction rates and substrate oxidizing position selectivity are controlled by the structural properties of the R of TOAR. Reaction of the acetato complex with TOAMe2 and m-CPBA yields the corresponding acylperoxido species, which can be detected using spectroscopy. Kinetic studies of the decay process of the acylperoxido species suggest that the acylperoxido species is a precursor of an active species for alkane oxidation. [ABSTRACT FROM AUTHOR]

Liquid-phase hydroxylation of benzene to phenol using Schiff base complexes anchored on a mesoporous organosilica support was investigated in various solvents when molecular oxygen was utilized as a green oxidant. The mesoporous organosilica support was prepared through the condensation of tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES) in different ratios, and then Schiff base complexes were anchored on it. Various aromatic heterocycles such as imidazole, 1-methyl imidazole, pyridine, and some pyridine derivatives were used as a proximal axial ligand, and their role in the reactivity of the catalyst was investigated experimentally and theoretically. Impressive promotion of the reactivity of the catalyst was the result of this coordination. Although all the synthesized catalysts showed catalytic reactivity, the vanadyl complex showed higher activity. The results show that SiO2-Pro-Sal-VO was extremely stable concerning leaching of the vanadyl group and rendered excellent recyclability in the hydroxylation of benzene to phenol with a yield of 11.3% and selectivity of >95%. The activity of the other catalysts was as follows: SiO2-Pro-Sal-Co > SiO2-Pro-Sal-Cu > SiO2-Pro-Sal-Fe > SiO2-Pro-Sal-Zn > SiO2-Pro-Sal-Mn. [ABSTRACT FROM AUTHOR]

Hyoscyamine 6β-hydroxylase (H6H) is a bifunctional non-heme 2-oxoglutarate/Fe2+-dependent dioxygenase that catalyzes the two final steps in the biosynthesis of scopolamine. Based on high resolution crystal structures of H6H from Datura metel, detailed information on substrate binding was obtained that provided insights into the onset of the enzymatic process. In particular, the role of two prominent residues was revealed – Glu-116 that interacts with the tertiary amine located on the hyoscyamine tropane moiety and Tyr-326 that forms CH–π hydrogen bonds with the hyoscyamine phenyl ring. The structures were used as the basis for QM/MM calculations that provided an explanation for the regioselectivity of the hydroxylation reaction on the hyoscyamine tropane moiety (C6 vs. C7) and quantified contributions of active site residues to respective barrier heights. [ABSTRACT FROM AUTHOR]

DNA base repair mechanisms of alkylated DNA bases is an important reaction in chemical biology and particularly in the human body. It is typically catalyzed by an α-ketoglutarate-dependent nonheme iron dioxygenase named the AlkB repair enzyme. In this work we report a detailed computational study into the structure and reactivity of AlkB repair enzymes with alkylated DNA bases. In particular, we investigate the aliphatic hydroxylation and C＝C epoxidation mechanisms of alkylated DNA bases by a high-valent iron(IV)–oxo intermediate. Our computational studies use quantum mechanics/molecular mechanics methods on full enzymatic structures as well as cluster models on active site systems. The work shows that the iron(IV)–oxo species is rapidly formed after dioxygen binding to an iron(II) center and passes a bicyclic ring structure as intermediate. Subsequent cluster models explore the mechanism of substrate hydroxylation and epoxidation of alkylated DNA bases. The work shows low energy barriers for substrate activation and consequently energetically feasible pathways are predicted. Overall, the work shows that a high-valent iron(IV)–oxo species can efficiently dealkylate alkylated DNA bases and return them into their original form. [ABSTRACT FROM AUTHOR]

Lipid oxidation plays a major role in biochemical processes and nutrition. Structural changes during oxidation can lead to alterations of lipid functions. Rancidification and production of secondary lipid messengers are well-known examples for the impact of oxidation on lipid function. Especially lipids with a high degree of unsaturation are prone to oxidize. In order to investigate structural changes of lipids upon oxidation, we here introduce a photochemical Paternò–Büchi functionalization workflow and subsequent mass spectrometric analysis for analysis of unsaturated, oxidized lipids. Results for hydroxylated fatty acids and triglycerides containing isolated and conjugated C＝C bonds will be presented making use of 3-acetylpyridine as a photochemically active compound. Photochemical derivatization is performed in nano-electrospray emitter tips in 30 s resulting in the formation of oxetanes without inducing light-triggered oxidation of analytes. Collisional-activation of photoproducts facilitates selective cleavage of oxetane moieties. Resulting fragment ions not only allow the determination of C＝C bond locations for isolated and conjugated C＝C bonds but also restrict the site of oxidation. By registering the mass shift in some fragment ions of +15.99 Da due to hydroxylation, the oxidized sections of lipids can be identified. In order to demonstrate its analytical robustness, the method is applied to determine the structural impact of non-selective ambient oxidation on fatty acids, triglycerides and complex triglyceride mixtures obtained from Sacha inchi oil. [ABSTRACT FROM AUTHOR]

Copper mediated C(sp2)–H amination and hydroxylation of arylphosphinic acid are accomplished by adopting phosphinamide as the directing group. This method is distinguished by its wide substrate scope and excellent functional group tolerance, thus allowing for the rapid preparation of organophosphorus compounds in organic synthesis. [ABSTRACT FROM AUTHOR]

Pyrenediones (PYDs) are efficient photocatalysts for three oxygenation reactions: epoxidation of electron deficient olefins, oxidative hydroxylation of organoborons, and oxidation of sulfides via in situ generation of H2O2 under visible light irradiation, using oxygen as a terminal oxidant and IPA as a solvent and a hydrogen donor. [ABSTRACT FROM AUTHOR]