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Relevant academic research and scientific papers

N-Rich 2D Heptazine Covalent Organic Frameworks as Efficient Metal-Free Photocatalysts

Heptazine serves as the solely repetitive unit of graphitic carbon nitride (g-C3N4), which represents a progressive metal-free photocatalyst. However, synthesizing high-quality 2D heptazine-based covalent organic frameworks (COFs) remains a formidable challenge, probably due to the scarcity of suitable and ample reactive heptazine-based building blocks. Herein, we designed and synthesized a 4-(methylene diacetate)phenyl-substituted heptazine monomer (HEP-OAc) by oxidation of tris(4-tolyl)heptazine. Accordingly, two highly ordered N-rich COFs (HEP-TAPT-COF and HEP-TAPB-COF) were readily prepared by the direct condensation of HEP-OAc with two C3-symmetric aromatic amines under solvothermal conditions. In comparison to the pristine g-C3N4, HEP-TAPT-COF exhibited greatly enhanced photocatalytic performance for benzylic C–H oxidation and selective sulfoxidation under mild conditions. This work provides meaningful insights into developing highly crystalline N-rich COFs with better photocatalytic capacities.

Oxidaition of cyclic benzylic ethers by an electronically tuned nitroxyl radical

The reactivity of an electronically tuned nitroxyl radical catalyst for the oxidation of cyclic benzylic ethers has been investigated. The oxidation of phthalan resulted in oxidative cleavage of the saturated ring to give an aromatic dialdehyde. Additionally, oxidation of isochromans afforded isochromanones, which are often seen in natural products, in a rapid manner.

Iridium-Catalyzed Enantioselective Hydrogenation of Oxocarbenium Ions: A Case of Ionic Hydrogenation

Ionic hydrogenation has not been extensively explored, but is advantageous for challenging substrates such as unsaturated intermediates. Reported here is an iridium-catalyzed hydrogenation of oxocarbenium ions to afford chiral isochromans with high enantioselectivities. A variety of functionalities are compatible with this catalytic system. In the presence of a catalytic amount of the Br?nsted acid HCl, an α-chloroether is generated in situ and subsequentially reduced. Kinetic studies suggest first-order kinetics in the substrate and half-order kinetics in the catalyst. A positive nonlinear effect, together with the half kinetic order, revealed a dimerization of the catalyst. Possible reaction pathways based on the monomeric iridium catalyst were proposed and DFT computational studies revealed an ionic hydrogenation pathway. Chloride abstraction and the cleavage of dihydrogen occur in the same step.

Flavin Nitroalkane Oxidase Mimics Compatibility with NOx/TEMPO Catalysis: Aerobic Oxidization of Alcohols, Diols, and Ethers

Biomimetic flavin organocatalysts oxidize nitromethane to formaldehyde and NOx - providing a relatively nontoxic, noncaustic, and inexpensive source for catalytic NO2 for aerobic TEMPO oxidations of alcohols, diols, and ethers. Alcohols were oxidized to aldehydes or ketones, cyclic ethers to esters, and terminal diols to lactones. In situ trapping of NOx and formaldehyde suggest an oxidative Nef process reminiscent of flavoprotein nitroalkane oxidase reactivity, which is achieved by relatively stable 1,10-bridged flavins. The metal-free flavin/NOx/TEMPO catalytic cycles are uniquely compatible, especially compared to other Nef and NOx-generating processes, and reveal selectivity over flavin-catalyzed sulfoxide formation. Aliphatic ethers were oxidized by this method, as demonstrated by the conversion of (-)-ambroxide to (+)-sclareolide.

Thiyl radical promoted iron-catalyzed-selective oxidation of benzylic sp3 C-H bonds with molecular oxygen

A ligand-free iron-catalyzed method for the oxygenation of benzylic sp3 C-H bonds by molecular oxygen (1 atm) using a thiyl radical as a cocatalyst has been developed. This transformation provides a facile access to amides, esters and ketones from readily accessible corresponding amines, ethers and alkanes. It features high regioselectivity, mild oxidative conditions and excellent functional group compatibility, providing good opportunities to the site-selective functionalization of complex molecules. Preliminary mechanistic studies suggest that this reaction may not undergo a benzylic cation intermediate pathway and the carbonyl oxygen atom in the products may be derived from molecular oxygen.

Ligand-Free, Copper-Catalyzed Aerobic Benzylic sp 3 C-H Oxygenation

A ligand-free and operationally simple copper-catalyzed aerobic benzylic sp 3 C-H oxygenation was developed. The addition of tert -butyl hydroperoxide, either in a catalytic or stoichiometric amount, was key for activating stable C-H bonds under mild conditions to furnish the corresponding ketones or esters in moderate to excellent yield.

Catalytic oxidation synthesis method of isochroman-4-one compounds

The invention discloses a catalytic oxidation synthesis method of isochroman-4-one compounds. The method comprises following steps: isochroman compounds, Fe(NO3)3.9H2O and fluorine-containinginorganic salt are added to an acetonitrile solvent and react at the temperature of 75-85 DEG C for 4-10 h under the condition of normal-pressure oxygen, and the isochroman-4-one compounds are obtained; a quantity ratio of the isochroman-4-one compounds as reaction substrates, Fe(NO3)3.9H2O and theinorganic salt is 100:(8-15):(15-30); after the complete reaction, the isochroman-4-one compounds can be obtained through conventionalcolumn chromatographic separationand purification. The method is simple and safe to operate and has the main beneficial effects as follows: A), clean oxygen is utilized as an oxidizing agent, so that the environmental cost is greatly reduced; B), Fe(NO3)3.9H2O is taken as a catalyst, and the cost is low.

Organocatalytic Aerobic Oxidation of Benzylic sp3 C-H Bonds of Ethers and Alkylarenes Promoted by a Recyclable TEMPO Catalyst

An entirely metal-free catalyst system consisting of an easily prepared recyclable new TEMPO derived sulfonic salt catalyst, and mineral acids (NaNO2 and HCl) has been developed for selective aerobic oxidation of structurally diverse benzylic sp3 C-H bonds of ethers and alkylarenes. The mild reaction conditions allow for the generation of synthetically and biologically valued isochromanones and xanthones from readily accessible alkyl aromatic precursors in good yields.

Dehydrogenative α-oxygenation of ethers with an iron catalyst

Selective α-oxidation of ethers under aerobic conditions is a long-pursued transformation; however, a green and efficient catalytic version of this reaction remains challenging. Herein, we report a new family of iron catalysts capable of promoting chemoselective α-oxidation of a range of ethers with excellent mass balance and high turnover numbers under 1 atm of O2 with no need for any additives. Unlike metalloenzymes and related biomimetics, the catalyst produces H2 as the only byproduct. Mechanistic investigations provide evidence for an unexpected two-step reaction pathway, which involves dehydrogenative incorporation of O2 into the ether to give a peroxobisether intermediate followed by cleavage of the peroxy bond to form two ester molecules, releasing stoichiometric H2 gas in each step. The operational simplicity and environmental friendliness of this methodology affords a useful alternative for performing oxidation, while the unique ability of the catalyst in oxygenating a substrate via dehydrogenation points to a new direction for understanding metalloenzymes and designing new biomimetic catalysts.

Enzymatic Baeyer-Villiger oxidation of Benzo-Fused ketones: Formation of regiocomplementary lactones

Baeyer-Villiger monooxygenases (BVMOs) are enzymes that are known to catalyse the Baeyer-Villiger oxidation of ketones in aqueous media using O2 as oxidant. Herein, we describe the oxidation of a set of diverse benzo-fused ketones by three different BVMOs