Aerobic Benzylic C(sp3)-H Bond Oxygenations Catalyzed by NBS under Visible Light Irradiation

An efficient photocatalytic oxidation of benzylic C(sp3)-H bonds to ketones, esters, and amides has been developed using NBS as a metal-free photocatalyst and O2 as an oxidant. A variety of synthetically and biologically valuable compounds are assembled in moderate to excellent yields. The synthetic utility of this approach has been demonstrated by gram-scale experiments. A possible free radical mechanism was proposed to rationalize the reaction procedure.

Iodine-Promoted Controlled and Selective Oxidation of (Aryl)(Heteroaryl)Methanes

The development of direct and controlled oxidation of C_(sp3)-H bonds is of great importance. Herein, an iodine-catalyzed controlled oxidation of (aryl)(heteroaryl)methanes to (aryl)(heteroaryl)methanols is disclosed under metal-free reaction conditions. A catalytic system comprised of iodine/silyl chloride with HI as an additive in the presence of dimethyl sulfoxide selectively oxidizes the C_(sp3)-H bonds without being overoxidized to corresponding ketones. Therapeutically important aryl heteroaryl methanol derivatives were obtained in good yields. The preliminary mechanistic investigation proves that the primary source of oxygen is DMSO.

Recent Advances in Organoselenium Catalysis

Abstract:

: Organoselenium chemistry has developed as an important tool in the field of synthetic and medicinal chemistry. Various organoselenium reagents have been developed and used successfully to achieve different organic transformations such as the selenocyclizations, oxyselenenylations and selenoxide eliminations etc. Additionally, the potential of organoselenium reagents is not limited their use as stoichiometric reagents but they have successfully used as organocatalyst in number of synthetic transformations. Various organic and inorganic oxidants have been identified as terminal oxidants to regenerate the active catalytic specie. In this review article, the recent progress of organoselenium reagents in catalysis is being highlighted along with their asymmetric variants.

Efficient and eco-friendly oxidative cleavage C–C bonds of 1,2-diols to ketones: electrochemistry vs thermochemistry

Two efficient methods for the oxidative cleavage C–C single bonds of vicinal tertiary diols by electrochemical and thermochemical strategies have been independently developed. The corresponding ketone products are smoothly assembled...

Electrochemical Enabled Cascade Phosphorylation of N-H/O-H/S-H Bonds with P-H Compounds: An Efficient Access to P(O)-X Bonds

An electrochemical three component cascade phosphorylation reaction of various heteroatoms-containing nucleophiles including carbazoles, indoles, phenols, alcohols, and thiols with Ph₂ PH has been established. Electricity is used as the "traceless" oxidant and water and air are utilized as the "green" oxygen source. All kinds of structurally diverse organophosphorus compounds with P(O)-N/P(O)-O/P(O)-S bonds are assembled in moderate to excellent yields (three categories of phosphorylation products, 50 examples, up to 97 % yield). A tentative free radical course is put forward to rationalize the reaction procedure.

SELENIUM AS A VERSATILE REAGENT IN ORGANIC SYNTHESIS: MORE THAN ALLYLIC OXIDATION

For many years since its discovery, Selenium has played the role of a bad boy who became a hero in organic transformations. Selenium dioxide, for instance, is one of the most remembered reagents in allylic oxidations, having been applied in the synthesis of several naturally occurring products. The main goal of this review is to show the recent advances in the use of classical and new selenium reagents in organic synthesis. As demonstrated through around 60 references discussed in this study, selenium can go even forward as a versatile reagent. We bring a collection of selenium reagents and their transformations that are still hidden from most synthetic organic chemists.

Synergetic catalysis of Se and Cu allowing diethoxylation of halomethylene ketones using O2 as the mild oxidant

Catalyzed by PhSe(O)OH/Cu(OAc)₂, sp³-C–H alkylation of bromomethylene ketones produced useful α-carbonyl acetals under mild conditions. Bromo-containing substrates could release HBr during the reaction, avoiding the use of acidic additives.

Electrochemical Oxidative Dehydrogenative Phosphorylation of N-Heterocycles with P(O)-H Compounds in Imidazolium-Based Ionic Liquid

We report a direct and green electrochemical oxidative cross-dehydrogenative coupling reaction of N-heterocycles with hydrogen phosphoryl compounds under external oxidant-free conditions. Various phosphorylation products of substituted carbazoles and indoles are assembled in modest to excellent yields. A hydrogen release process is preliminarily demonstrated and H₂ is the sole byproduct. An imidazolium based ionic liquid is selected as the optimal electrolyte.

Metal-free oxidative C(sp3)–H functionalization: a facile route to quinoline formaldehydes from methyl-azaheteroarenes

A facile protocol for the synthesis of quinoline formaldehydes via direct oxidative C–H bonds functionalization of methyl-azaheteroarenes in the presence of I2–DMSO has been described. This method is metal-free and easy to operate. This reaction provided a convenient route for the preparation of a range of important quinoline formaldehydes.

Selenium-catalyzed oxidation of alkenes: insight into the mechanisms and developing trend

Recent progresses of the selenium-catalyzed oxidation of alkenes are summarized at the mechanism level. It may be beneficial for designing novel selenium-containing catalysts and alkene oxidation protocols for the next phase of studies.

Switchable Synthesis of Aryl Sulfones and Sulfoxides through Solvent-Promoted Oxidation of Sulfides with O2/Air

A practical and switchable method for the synthesis of aryl sulfones and sulfoxides via sulfide oxidation was developed. The chemoselectivities of products were simply controlled by reaction temperature using O₂/air as the terminal oxidant and oxygen source. The broad substrate scope, easy realization of gram-scale production, and the simplification of a sulfide oxidation system render the strategy attractive and valuable.

Trash to Treasure: Eco-Friendly and Practical Synthesis of Amides by Nitriles Hydrolysis in WEPPA

The hydration of nitriles to amides in a water extract of pomelo peel ash (WEPPA) was realized with moderate to excellent yields without using external transition metals, bases or organic solvents. This reaction features a broad substrate scope, wide functional group tolerance, prominent chemoselectivity, and good reusability. Notably, a magnification experiment in this bio-based solvent at 100 mmol further demonstrated its practicability.

Organotellurium catalysis-enabled utilization of molecular oxygen as oxidant for oxidative deoximation reactions under solvent-free conditions

Catalyzed by commercially available (PhTe)₂, molecular oxygen could be utilized as the mild, cheap and safe oxidant for oxidative deoximation reactions under solvent-free conditions. As the first report on organotellurium-catalyzed deoximation reaction, this work not only provides an efficient deoximation method, but also discloses new features of tellurium catalyst different from those of the organoselenium catalysts.

Catalytic Aerobic Oxidation of C(sp3 )-H Bonds

Oxidation reactions are a key technology to transform hydrocarbons from petroleum feedstock into chemicals of a higher oxidation state, allowing further chemical transformations. These bulk-scale oxidation processes usually employ molecular oxygen as the terminal oxidant as at this scale it is typically the only economically viable oxidant. The produced commodity chemicals possess limited functionality and usually show a high degree of symmetry thereby avoiding selectivity issues. In sharp contrast, in the production of fine chemicals preference is still given to classical oxidants. Considering the strive for greener production processes, the use of O₂ , the most abundant and greenest oxidant, is a logical choice. Given the rich functionality and complexity of fine chemicals, achieving regio/chemoselectivity is a major challenge. This review presents an overview of the most important catalytic systems recently described for aerobic oxidation, and the current insight in their reaction mechanism.

Recent progress in selenium-catalyzed organic reactions

Selenium-based catalysts, including organo- and inorganoselenium ones, in organic synthesis in the recent decade are reviewed.

Organoselenium small molecules as catalysts for the oxidative functionalization of organic molecules

This perspective highlights the critical analysis of the challenges, in the past decade, which led to the development of organoselenium compounds and their use as versatile catalysts in organic synthesis towards the oxidation of olefins and C–H bonds. Furthermore, the emphasis here differs from previous reviews of the field by classifying the various types of catalyses and the diverse strategies.

Selenium reagents as catalysts

Organoselenium chemistry has become an important tool in synthetic and medicinal chemistry.

B2pin2-catalyzed oxidative cleavage of a CC double bond with molecular oxygen

B₂pin₂-catalyzed oxidative cleavage of the CC double bond of an olefin with molecular oxygen as the oxidant and oxygen source has been developed.

Recent Advances in Homogeneous Metal-Catalyzed Aerobic C–H Oxidation of Benzylic Compounds

Csp3–H oxidation of benzylic methylene compounds is an established strategy for the synthesis of aromatic ketones, esters, and amides. The need for more sustainable oxidizers has encouraged researchers to explore the use of molecular oxygen. In particular, homogeneous metal-catalyzed aerobic oxidation of benzylic methylenes has attracted much attention. This account summarizes the development of this oxidative strategy in the last two decades, examining key factors such as reaction yields, substrate:catalyst ratio, substrate scope, selectivity over other oxidation byproducts, and reaction conditions including solvents and temperature. Finally, several mechanistic proposals to explain the observed results will be discussed.

Fabrication of Se/C using carbohydrates as biomass starting materials: an efficient catalyst for regiospecific epoxidation of β-ionone with ultrahigh turnover numbers

Fabrication of Se/C catalyst from glucose as the biomass starting materials was reported for the first time, affording an efficient and regiospecific epoxidation of β-ionone.

One pot preparation of α-dithioacetal/α-diselenoacetal amides via a dual-C–S/C–Se bond formation and C–C bond cleavage cascade of 3-oxo-butanamides

A new and practical approach to α-dithioacetal/α-diselenoacetal amides has been developed.