Selective Allylic Oxidation Research Articles

SiO2 supported Ce–Co mixed oxide catalyzed selective allylic oxidation of cyclohexene

CeO2–Co3O4/SiO2 catalyst exhibited superior catalytic activity compared to pure oxides for cyclohexene oxidation with 94% conversion and 90% of selectivity towards allylic products.

Enhanced PMS/O2 activation by self-crosslinked amine-gluteraldehyde/chitosan-Cu biocomposites for efficient degradation of HEPES as biological pollutants and selective allylic oxidation of cyclohexene

Optimization and mechanism elucidation of the catalytic degradation of HEPES and selective aerobic oxidation of cyclohexene by Cu@cross-linked magnetic chitosan.

Highly Dispersed MnOx Nanoparticles on Shape-Controlled SiO2 Spheres for Ecofriendly Selective Allylic Oxidation of Cyclohexene

Shape-controlled metal nanomaterials are considered as a unique class of catalysts because of their synergistic size- and shape-dependent catalytic properties. This work reports the synthesis of a novel size- and shape-controlled catalyst, consisting of highly dispersed MnOx nanoparticles (average particle size of 4.5 nm) on shape-controlled SiO2 nanospheres (250–300 nm) for selective cyclohexene oxidation using air as the oxidant under solvent- and base-free conditions. The MnOx/SiO2 catalyst exhibited an excellent cyclohexene conversion (~ 92%) with a high selectivity (~ 96%) to the allylic products (2-cyclohexene-ol and 2-cyclohexene-one) under mild conditions, outperforming various SiO2 supported CoOx, FeOx, and CuOx catalysts. The better performance of shape-controlled MnOx/SiO2 nanocatalyst is due to high redox nature of Mn, uniform dispersion of smaller sized MnOx nanoparticles, and synergetic interaction between MnOx and SiO2 spheres, as evidenced by XPS and TEM studies. Further, the MnOx/SiO2 catalyst could be reused at least 5 times for selective cyclohexene oxidation with a negligible loss in its catalytic performance, indicating the excellent stability of shape-controlled metal nanocatalysts in organic synthesis under economically viable and mild conditions. Shape-controlled MnOx/SiO2 nanocatalyst shows an excellent catalytic activity and a high selectivity to allylic products in the oxidation of cyclohexene under mild conditions

Selective Allylic Oxidation of Terpenic Olefins Using Co-Ag Supported on SiO2 as a Novel, Efficient, and Recyclable Catalyst

Co-Ag supported on the SiO2 catalyst was synthesized by the sol-gel method and characterized using XRD, FT-IR, TG-DTG, BET, CV, and SEM/EDX analysis. The catalytic performance of the resulting catalyst was examined by the oxidation of mono and sesquiterpenic olefins using hydrogen peroxide and tert-butyl peroxide as oxidant agents. Various parameters such as catalyst amount, temperature, and solvents have been studied. The Co-Ag supported on the SiO2 catalyst showed a high activity, selectivity, and recyclability for the selected oxidation reaction.

Selective aerobic allylic oxidation of α-pinene catalyzed by metalloporphyrins in the absence of solvents and additives

Selective aerobic oxidation of α-pinene to high-value products is a major challenge in chemistry. Metalloporphyrins are proved to be selective catalysts for aerobic oxidation of simple hydrocarbons. Herein, we extend this method to more complex substrates using metallodeuteroporphyrins as model catalysts. It was found that the oxidation occurs mainly on the C=C and allylic C–H bonds of α-pinene influenced by the reaction temperature, reaction time, catalyst concentration, and oxygen flow rate. Allylic C–H oxidation products are obtained with a maximum selectivity value of 78.4% using the following reaction conditions: 105°C, 7 h, 5 ppm, and 60 mL/min. The influence of the metal nuclei of the metallodeuteroporphyrins on this reaction is also investigated. It was found that metallodeuteroporphyrins with Fe3+ as the metal nucleus exhibit the highest catalytic activity.

Highly selective allylic oxidation of cyclohexene to 2-cyclohexen-1-one under mild conditions over vanadyl-porphyrin implanted onto the amino-functionalized SBA-15

Abstract A new metalloporphyrin containing mesoporous framework briefly named VOTMCPP@N-SBA was prepared via a simple anchoring of vanadyl-porphyrin through (3- aminopropyl)-triethoxysilane as a linker to SBA-15, and its performance for cyclohexene oxidation by hydrogen peroxide as oxidant was investigated under ambient conditions in different solvents. The characterization techniques such as FTIR, UV–Vis, XPS, XRD, TGA, BET, FE-SEM, and HRTEM confirm the incorporation of vanadyl-porphyrin in the pores of the mesoporous SBA-15 framework. The prepared catalyst has shown high catalytic activity and stability (5 runs) in the oxidation of cyclohexene at room temperature when 2-cyclohexen-1-one was obtained as the principal product with a considerable selectivity.

Computational Mechanism Study on Allylic Oxidation of cis-Internal Alkenes: Insight into the Lewis Acid-Assisted Brønsted Acid (LBA) Catalysis in Heteroene Reactions.

The catalytic allylic C-H oxidation of alkenes plays an important role in the field of medicine chemistry. Recently, Tambar et al. improved this transformation via a heteroene reaction with the assistance of a Lewis acid-assisted chiral Brønsted acid (LBA) and achieved a selective allylic oxidation of inactivated cis-internal alkenes to versatile oxidation products. By means of density functional theory (DFT) calculations, we provided a detailed investigation on the mechanism of the heteroene reaction and successfully located a new catalytic process, which is able to explain the experimental observations very well. Four different reactive pathways (pathways A, B, C, and D) for the LBA-catalyzed heteroene reaction have been designed. We found pathway D, which undergoes a protonation process for the activation of enophile benzenesulfonyl sulfurimide, has the lowest overall free energy barrier. Pathway E was put forward to lead to a minor enantiomer. The theoretical enantiomeric ratio calculated via their energy difference is consistent with the experimental report. For the heteroene reaction, we proposed a new reaction mechanism, which can assist in related transformations and the design of new LBA catalysts.

Selective allylic oxidation of cyclohexene over a novel nanostructured CeO2–Sm2O3/SiO2 catalyst

Selective allylic oxidation of cyclohexene was investigated over nanostructured CeO2/SiO2 and CeO2–Sm2O3/SiO2 catalysts synthesized by a feasible deposition precipitation method. The CeO2–Sm2O3/SiO2 catalyst showed excellent catalytic efficiency with ~89 % cyclohexene conversion and ~90 % selectivity for allylic products (i.e., 2-cyclohexen-1-ol and 2-cyclohexene-1-one), while only ~50 and ~35 % cyclohexene conversion was observed, respectively, over CeO2/SiO2 and CeO2 catalysts. Systematic characterization of the designed catalysts was undertaken to correlate their catalytic activity with the physicochemical properties using X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) surface area measurements, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and NH3-temperature programmed desorption (TPD) techniques. The results revealed that doping of Sm3+ into the ceria lattice and simultaneous dispersion of resultant Ce–Sm mixed oxides on the silica surface led to improved structural, acidic, and catalytic properties. The better catalytic efficiency of CeO2–Sm2O3/SiO2 was due to high specific surface area, more structural defects, and high concentration of strong acid sites, stimulated by synergistic interaction between various oxides in the catalyst. The cyclohexene conversion and selectivity for allylic products depended on the reaction temperature, nature of solvent, molar ratio of cyclohexene to oxidant, and reaction time. Possible reaction pathways are proposed for selective allylic oxidation of cyclohexene towards 2-cyclohexen-1-ol and 2-cyclohexene-1-one products. SiO2-supported CeO2–Sm2O3 nanocatalyst exhibited outstanding catalytic performance with superior selectivity for allylic products in liquid-phase selective oxidation of cyclohexene under mild reaction conditions.

Selective allylic oxidation of cyclohexene catalyzed by nanostructured Ce-Sm-Si materials

The oxidation of cyclohexene was studied using nanostructured CeO2, CeO2/SiO2, CeO2-Sm2O3, and CeO2-Sm2O3/SiO2 catalysts. The CeO2-Sm2O3/SiO2 catalyst shows ~96% cyclohexene conversion and ~91% selectivity to allylic products, namely, 2-cyclohexen-1-one (~53%) and 2-cyclohexen-1-ol (~38%) owing to favorable redox (oxygen vacancies) and acid sites stimulated by synergistic interactions of dopant (Sm) and support (SiO2) with CeO2. In contrast, only ~40, ~55, and ~78% of cyclohexene conversions were observed, respectively, over CeO2, CeO2/SiO2, and CeO2-Sm2O3 catalysts. With the increase of reaction time, temperature, and molar ratio of cyclohexene/oxidant, the conversion of cyclohexene and the selectivity of 2-cyclohexen-1-one are increased considerably.

Catalytic allylic oxidation of internal alkenes to a multifunctional chiral building block.

The stereoselective oxidation of hydrocarbons represents one of the most significant advances in synthetic chemistry over the last fifty years1–3. Inspired by nature, chemists have developed enantioselective dihydroxylations, epoxidations, and other oxidations of unsaturated hydrocarbons. More recently, the catalytic enantioselective allylic C–H oxidation of alkenes has emerged as a powerful chemical strategy, streamlining the production of pharmaceuticals, natural products, fine chemicals and other functional materials4–7. Allylic functionalization provides a direct path to chiral synthons with a newly formed stereocenter from petrochemical feedstocks while preserving the olefin functionality as a handle for further elaboration. Various metal-based catalysts have been discovered for the enantioselective allylic C–H oxidation of simple alkenes with cyclic or terminal double bonds8–16. However, a general and selective allylic oxidation remains elusive with the more common internal alkenes. Here, we report the enantioselective, regioselective, and E/Z selective allylic oxidation of unactivated internal alkenes via a catalytic asymmetric hetero-ene reaction with a chalcogen-based oxidant. This method represents the first example of selectively converting unsymmetrical internal alkenes into allylic functionalized products with high stereoselectivity and regioselectivity. Stereospecific transformations of the multifunctional allylic oxidation products highlight the potential for rapidly converting internal alkenes into a broad range of enantioenriched structures that can be utilized in the synthesis of complex target molecules.

Highly selective allylic oxidation of cyclohexene over molybdenum-doped manganese oxide catalysts

A facile synthesis of molybdenum-doped manganese oxides was achieved by a single step reflux method. The catalytic activity of molybdenum-doped manganese oxides for the oxidation of cyclohexene was investigated under solvent-free conditions. Various techniques such as X-ray diffraction, transmission electron microscopy, hydrogen temperature-programmed reduction, thermogravimetric analysis and diffuse reflectance infrared Fourier transform spectroscopy of adsorbed pyridine were employed to indentify the features of catalysts as prepared. The characterization results indicate that Mo dopants were successfully incorporated into the crystal structure of manganese oxide and the concentration of Mo dopant had an influence on redox properties as well as the Lewis acid sites of Mo dopant catalysts. Furthermore, 1.0 mol%Mo-MnO2 catalyst exhibited highest total yield (32.4%) and almost 100% selectivity towards allylic oxidation products, which could be attributed to its relative lower redox properties and the highest Lewis acidity. These results thereby provide an insight of catalyst design in selective catalytic oxidation of cyclohexene.

A novel route for preparation of Mn-containing hollow framework TS-1, and its selective allylic oxidation of cyclohexene

TS-1 (MTS-1) was prepared via simple recrystallization of TS-1 in the presence of TPAOH and manganese(iii)–acetylacetonate, and its catalytic performance was tested for aerobic oxidation of cyclohexene without solvents.

Selective Allylic Oxidation of Cyclohexene Catalyzed by Nitrogen-Doped Carbon Nanotubes

Carbon nanotubes (CNTs) and nitrogen-doped CNTs (NCNTs) were systematically investigated as metal-free catalysts in the selective allylic oxidation of cyclohexene using molecular oxygen as oxidant ...

ChemInform Abstract: Co(acac)2‐Catalyzed Allylic and Benzylic Oxidation by tert‐Butyl Hydroperoxide.

AbstractThe conditions render possible the selective allylic and benzylic oxidation of a variety of substrates.

An improved and efficient synthesis for IPL576,092 and its analogues

An improved and efficient preparation of IPL576,092 was developed. The synthetic route involves selective allylic oxidation of ∆5-sterols and subsequent hydroboration–oxidation as the key steps. In addition, two analogues were readily synthesized from commercially available steroidal compounds in two steps in the same way.

Synthesis of (−)‐3‐Carene‐2,5‐dione via Allylic Oxidation of (+)‐3‐Carene

AbstractActivated carbon‐supported CuCl2 (CuCl2/AC) is a heterogeneous catalyst for the liquid‐phase selective allylic oxidation of (+)‐3‐carene with tert‐butyl hydroperoxide (TBHP) and O2 to produce (−)‐3‐carene‐2,5‐dione. The possible reaction mechanism and the effects of different factors on the allylic oxidation were investigated. The optimal conditions are as follows: reaction temperature, 45 °C; molar ratio of CuCl2 to (+)‐3‐carene, 1%; volume ratio of (+)‐3‐carene to TBHP, 1:3; and reaction time, 12 h. Under the optimal conditions, the conversion of (+)‐3‐carene reached 100%, whereas the selectivity for (−)‐3‐carene‐2,5‐dione reached 78%. The CuCl2/AC catalyst was characterized via X‐ray diffraction, and the chemical structure of the target compound was identified via infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, mass spectrometry, and optical analysis.

Visible‐Light‐Induced Metal‐Free Allylic Oxidation Utilizing a Coupled Photocatalytic System of g‐C3N4 and N‐Hydroxy Compounds

AbstractGraphitic carbon nitride (g‐C3N4) and N‐hydroxy compounds can function as a non‐metal photocatalytic system to activate O2 for the selective allylic oxidation under mild conditions, avoiding the employment of any metal derivative or organic oxidizing agents. Interestingly, the novel photocatalytic system affords a remarkably high selectivity towards the formation of aldehydes, especially in the oxidation of toluene. By combining the unique nature of g‐C3N4 (surface basicity, semiconductor features, high stability) and the remarkable catalytic oxidation reactivity of nitroxyl radicals, this photocatalytic system opens up a mild and efficent access for CH bond activation.

Selective Allylic oxidation of Cyclohexene by a Magnetically Recoverable Cobalt Oxide Catalyst

In this work, we prepared a new magnetically recoverable CoO catalyst through the deposition of the catalytic active metal nanoparticles of 2–3 nm on silica-coated magnetite nanoparticles to facilitate the solid separation from liquid media. The catalyst was fully characterized and presented interesting properties in the oxidation of cyclohexene, as for example, selectivity to the allylic oxidation product. It was also observed that CoO is the most active species when compared to Co2+, Co3O4 and Fe3O4 in the catalytic conditions studied.

Heterogeneous Selective Oxidation of Alkenes to α,β‐ Unsaturated Ketones over Coordination Polymer MIL‐101

AbstractThe mesoporous metal‐organic framework MIL‐101 is an efficient heterogeneous catalyst for the selective allylic oxidation of alkenes with tert‐butyl hydroperoxide. The selectivity towards α,β‐unsaturated ketones reaches 86–93%. The temperature of the catalyst activation strongly affects the ketone yield. MIL‐101 is stable to chromium leaching, behaves as a true heterogeneous catalyst, can be easily recovered by filtration, and can be reused several times without loss of the catalytic performance.

Enantioselective Synthesis of (+)-Cephalostatin 1

This Article describes an enantioselective synthesis of cephalostatin 1. Key steps of this synthesis are a unique methyl group selective allylic oxidation, directed C-H hydroxylation of a sterol at C12, Au(I)-catalyzed 5-endo-dig cyclization, and a kinetic spiroketalization.