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Biomimetic oxidation of primary amines to carboxylic acids has been developed where the copper-containing amine oxidase (CuAO)-like o-NQ-catalyzed aerobic oxidation was combined with the aldehyde dehydrogenase (ALDH)-like TBHP-mediated imine oxidation protocol. Notably, the current tandem oxidation strategy provides a new mechanistic insight into the imine intermediate and the seemingly simple TBHP-mediated oxidation pathways of imines. The developed metal-free amine oxidation protocol allows the use of molecular oxygen and TBHP, safe forms of oxidant that may appeal to the industrial application.

A photocatalyst-free visible-light-induced selenofunctionalization of alkenes has been developed using a variety of nucleophiles. The homolytic scission of diselenides under visible-light conditions coupled with the aerobic selenol oxidation to diselenides allowed the successful implementation of three-component selenofunctionalization under visible-light irradiation in open-air conditions. The mechanistic studies revealed the critical role of oxygen content in a reaction medium, where the electron transfer process from the carbon-based radicals to either molecular oxygen or selenyl radicals was controlled.

A biomimetic alcohol dehydrogenase (ADH)-like oxidation protocol was developed using an

The generation of aminium radical cation species from N-nitrosoamines is disclosed for the first time through visible-light excitation at 453 nm. The developed visible-light-promoted photoaddition reaction of N-nitrosoamines to alkenes was combined with the o-NQ-catalyzed aerobic oxidation protocol of amines to telescope the direct handling of harmful N-nitroso compounds, where the desired α-amino oxime derivatives were obtained in a one-pot tandem N-nitrosation and photoaddition sequence.

The interplay between copper catalysts and molecular oxygen provides the opportunity to control the promiscuous catalytic behaviors in aerobic Csp3–H bond oxidations without using stoichiometric amounts of oxidants. This mini-review aims to cover the Cu-catalyzed aerobic benzylic and α-carbonyl Csp3–H oxidations and that of the carbon next to an amine group in the past five years. The development of tandem multicomponent reactions employing aerobic Csp3–H bond oxidations will be discussed to highlight the controlled catalyst behaviors and the catalyst interactions between multiple reaction components.

The nitroso group served as a traceless directing group for the C–H functionalization of N-alkylanilines, ultimately removed after functioning either as an internal oxidant or under subsequent redu...

A catalytic asymmetric desymmetrization of cyclohexadienones was accomplished via Van Leusen pyrrole synthesis in the presence of a chiral silver catalyst. The ready access to chiral-fused pyrrole derivatives is attributed to the identification of a suitable isocyanomethyl sulfone surrogate, NasMIC. The current Ag(I)-chiral phosphino-carboamide ligand system can be extended to the kinetic resolution of racemic cyclohexadienones, capitalizing on the differentiated reactivity of chiral quaternary complexes from AgSbF

A direct cross-coupling between sodium sulfinates and 2H-indazoles has been developed under electrochemical conditions. The utilization of a graphite anode and platinum cathode in an undivided cell with a constant current of 7 mA allowed the concurrent oxidations of sulfinates and 2H-indazoles to sulfonyl radical and radical cationic 2H-indazoles, facilitating the direct radical-radical coupling strategy to 3-sulfonylated 2H-indazole derivatives. The transition-metal- and redox-reagent-free synthetic approach should serve as a valuable synthetic tool to achieve heteroaromatic compounds.

The photoredox chloroacylation of alkenes has been developed as a substitute for the Friedel-Crafts acylation of alkenes to β-chloroketones. The direct generation of acyl radical species from acid chlorides under the photoredox conditions allows the formation of β-chloroketones without dehydrochlorination with the help of KHCO3. The synthetic utility of the current method is demonstrated in the one-pot synthesis of dihydroisoxazole, dihydropyrazole, and dihydropyrimidine-2-thione in 1 mmol scale.

A facile access to fused pyrimidin-4(3H)-one derivatives has been established by using the metal-free ortho-naphthoquinone-catalyzed aerobic cross-coupling reactions of amines. The utilization of two readily available amines allowed a direct coupling strategy to quinazolinone natural product, bouchardatine, as well as sildenafil (Viagra™) in a highly convergent manner.

A combination of CuCl and DM-SEGPHOS catalyst system has allowed the development of highly enantioselective and diastereoselective conjugate addition of bis(pinacolato)diboron to α-alkylidene-γ-lactams. The key structural feature of conjugate acceptors, α-alkylidene-γ-lactams, was identified as the carbamate group such as N-Boc and N-Cbz, where the typical low reactivity and stereoselectivity issues associated with α,β-unsaturated lactams as conjugate acceptors were resolved.

Two distinctive transition-metal-promoted aerobic oxidation protocols have been developed for the synthesis of isoquinolones from 2-vinylbenzaldehydes and aniline derivatives. Thus, the one-pot tandem reaction sequence of imine formation, thermal 6π-electrocyclization, followed by either Cu(OAc)2-mediated or Pd(OAc)2-catalyzed aerobic oxidation protocol allowed the ready access to isoquinolone derivatives. The control experiments revealed that the 1,2-dihydroisoquinoline intermediates from the 6π-electrocyclization of 1-azatrienes were aerobically oxidized to isoquinolones in the presence of either Cu(OAc)2 or Pd(OAc)2 catalyst.

The synthesis of isoxazoles has been achieved in a continuous flow system composed of two reaction units: the Friedel-Crafts acylation of alkynes and the azide conjugate addition to the resulting β-chlorovinyl ketones followed by a photochemical-thermal reaction sequence. The salient feature of the current flow system includes the safe handling of potentially explosive organic azide species as well as the rapid conversion of batch reactions into flow conditions with the integration of multiple reactor units.

The on-board tilting mirror calibration mechanism has a mechanical driving part that helps to achieve the main functional modes of deployment and stow when calibrating a spaceborne imaging sensor. In general, it is necessary to consider a holding and release device in the mechanism design, to secure the structural safety of the mechanical driving part in severe launch environments. However, in the present study, we proposed a novel design strategy based on mass balancing, to guarantee mechanical safety on the driving part of the tilt mirror mechanism, although the implementation of the holding and release mechanism was not considered in the design. The effectiveness of the proposed design was experimentally verified via launch vibration and life cycle tests. The test results demonstrated that the mechanism fulfills all the required functions, and the design approach proposed in this study is effective for ensuring mechanical safety on the driving part of the tilting mirror mechanism in severe launch vibration environments.

Oxidation potential-guided electrochemical radical-radical cross-coupling reactions between N-heteroarenes and sodium sulfinates have been established. Thus, simple cyclic voltammetry measurement of substrates predicts the likelihood of successful radical-radical coupling reactions, allowing the simple and direct synthetic access to 3-sulfonylated imidazopyridines and indolizines. The developed electrochemical radical-radical cross-coupling reactions to sulfonylated N-heteroarenes boast the green synthetic nature of the reactions that are oxidant- and metal-free.

ortho-Naphthoquinone-based organocatalysts have been identified as versatile aerobic oxidation catalysts. Primary amines were readily cross-coupled with primary nitroalkanes via deaminative pathway...

A convenient visible-light photoredox catalysis has been developed for the synthesis of thioesters from two readily available starting materials: acid chlorides and sodium sulfinates. The facile generation of acyl radical species under the visible light photoredox conditions allows the formation of thiyl radical species from sodium sulfinates via multiple single electron transfer reactions, where the final acyl radical-thiyl radical coupling has been accomplished. The direct radical-radical coupling strategy offers a mild and controlled photochemical approach to important synthetic building blocks such as thioesters.

The Friedel–Crafts acylation of alkynes stereoselectively provides (Z)-β-chlorovinyl ketones, whereas the AlCl3-promoted reaction yields a mixture of stereoisomeric β-chlorovinyl ketones. To develop the (E)-selective synthesis of β-chlorovinyl ketones, a flow chemistry approach was devised for the Friedel–Crafts acylation of alkynes that defies the facile (E) → (Z) isomerization under the AlCl3-promoted reaction conditions. Compared to batch reactions, the flow chemistry approach provides a fast, clean, high yielding, and stereoselective synthetic route to (E)-β-chlorovinyl ketones.

Correction for 'Recent advances in the copper-catalyzed aerobic C

The generation of aminium radical cation species from

The nitroso group served as a traceless directing group for the C-H functionalization of

A direct cross-coupling between sodium sulfinates and 2

An ortho-naphthoquinone-catalyzed oxidative deamination reaction has been developed where the molecular oxygen and water serve as the sole oxidant and nucleophile. The current aerobic deamination reaction proceeds via the ketimine formation between ortho-naphthoquinones and amines followed by the prototropic rearrangement and hydrolysis by water, representing a biomimetic oxidative deamination of amine species in the human body by the liver and kidneys. The compatibility of ortho-naphthoquinone organocatalysts with molecular oxygen and water opens up a new biomimetic catalyst system that can function as versatile deaminases for a variety of amine-containing molecules such as amino acids and DNA nuclear bases.

A rhodium-catalyzed decarbonylative aerobic oxidation of cyclic α-diketones has been developed for the first time, where the regioselective formations of α-pyrones and isocoumarins have been achieved. The current decarbonylative aerobic oxidation pathway proceeds via the C-C bond cleavage followed by a C-O bond formation, representing a biomimetic oxidation approach to unsaturated six-membered cyclic lactones. The unique ability of rhodium catalysts to induce the decarbonylative aerobic oxidation opens up a new synthetic toolbox that utilizes the "regioselective single carbon" extrusion strategy.

A palladium-catalyzed intermolecular hydroamination of vinylarene derivatives using anilines has been developed for the first time under aerobic conditions, where the regioselective formation of N-arylketimines is accomplished. The current aerobic oxidative hydroamination pathway of anilines is distinct from that of palladium-catalyzed hydroamination reactions that proceed to give sec-arylethylamine and arylethylamine derivatives, identifying a longstanding missing reaction pathway, Wacker-type amination, to N-arylketimines using anilines. The ready availability of both starting materials, vinylarenes and anilines, offers an attractive and facile synthetic route to N-arylketimines in good to excellent yields.

The one-pot sulfenylation of (E)-β-chlorovinyl ketones was investigated under soft α-vinyl enolization conditions. Modulating the nature of nucleophilic species using a “hard” base the regioselective formation of α,γ-dithio-allenyl ketones has been achieved, where the thermodynamic control was mimicked by the presence of Et3N·HCl. The sulfenylated products, α,γ-dithio-allenyl and α,α-dithio-propargyl ketones, smoothly underwent cycloisomerization to 3,4-dimercaptofurans via a novel 1,2-sulfur migration in excellent yields.

The direct regioselective synthesis of highly functionalized pyrroles with two different electron-withdrawing groups has been developed using an angle strain-induced 1,2-shift of an electron-withdrawing group in 2H-pyrroles. The preferential migration aptitude of an electron-withdrawing group over alkyl and aryl groups is believed to be the result of the orbital overlap between the internal alkene and the electron-withdrawing group. The newly developed regioselective synthesis of pyrroles features a wide substrate scope, simple reaction set-up, and high yields (60–82%), capturing the essence of alkyne-isocyanide “click” reactions.

Recently, an annular-stepwise-diverging-tube (ASDT) was developed to investigate the length-scale effects on the flame propagation velocity (FPV), and the overall FPV of a specific fuel was described as a continuous surface in the physical domain of the concentration-length-velocity. In this study, the ASDT burner was improved in three aspects. First, all flame images taken during the experiment were analyzed to improve the experimental resolution and reliability. Second, an appropriate condition for the flow rate reduction was determined. Third, the thickness of the step-unit was reduced from 10 mm to 3 mm. Precise FPV values depending on the length-scale could be obtained using a compact ASDT burner.

A tandem aerobic oxidation protocol has been developed for the facile synthesis of indole-3-carboxylates. Two readily available starting materials, anilines and benzylamines, were efficiently cross-coupled under the o-naphthoquinone-catalyzed aerobic oxidation conditions to the corresponding 2-arylmethyleneaminophenylacetates that in turn smoothly underwent the Cu(II)-catalyzed intramolecular Mannich reaction. The resulting indoline derivatives were aerobically oxidized to indole-3-carboxylates, providing a ready access to indole derivatives from two simple amine derivatives.

A tandem three-component reaction has been developed for the synthesis of spirocyclic 2-indolinylformamidines through a cooperative action of palladium and copper catalysts. The Pd-catalyzed benzylation of α-isocyano lactams with 2-bromobenzyl bromides allows efficient formation of α-substituted α-isocyano lactams. A subsequent in situ Cu-catalyzed amine addition to the isocyanide moiety provides amidine intermediates that readily undergo intramolecular N-arylation via the cooperative action of Pd/Cu catalysis, allowing a facile chiral resolution of the spirocyclic 2-indolines.

A tandem synthetic route to a diverse array of cyclic compounds has been developed from Friedel-Crafts acylation of alkynes followed by the microwave irradiation of β-chlorovinyl ketone intermediates. The stereoisomeric β-chlorovinyl ketone intermediates smoothly underwent a thermal α-vinyl enolization and ring expansion to vinyl and carbocyclic furans as well as cyclopetene derivatives in good to excellent yields without the need for any catalysts.

Correction for ‘Recent advances in the copper-catalyzed aerobic Csp3–H oxidation strategy’ by Hun Young Kim et al., Org. Biomol. Chem., 2021, DOI: 10.1039/d1ob00081k.

A modular aerobic oxidation of amines to imines has been achieved using an ortho-naphthoquinone (o-NQ) catalyst. The cooperative catalyst system of o-NQ and Cu(OAc)2 enabled the formation of homocoupled imines from benzylamines, while the presence of TFA helped the formation of cross-coupled imines in excellent yields. The current mild aerobic oxidation protocol could also be applied to the oxidation of secondary amines to imines or ketimines with the help of cocatalyst, Ag2CO3, with excellent yields.

Enantiodivergent catalyst systems were developed using metals with different ionic radii and a multifunctional brucine diol (BD) ligand. The catalytic use of purported 1:1 Cu-BD complexes in the 1,3-dipolar cycloaddition of azomethine ylides with chalcones resulted in the selective formation of endo-pyrrolidines in 87–96% ees with an absolute stereochemical outcome of (2R,3S,4R,5S). In contrast, an opposite absolute stereochemical outcome was observed by using the catalysts derived from Ag(I) salts and BD. The demonstration of enantiodivergent approaches to a broad class of substrates/reaction types underlines their synthetic value in asymmetric synthesis.

A direct acyl radical addition to 2 H-indazoles has been achieved for the first time, where the less-aromatic quinonoid 2 H-indazoles readily accepted radical species to the C-3 position. Motivated by the lack of direct acylation strategy for 2 H-indazoles, the current method utilizes the radical acceptability of 2 H-indazoles, discovering an ambient temperature reaction to provide facile access to a diverse array of 3-acyl-2 H-indazoles with three points of structural diversification in 25%-83% yields.

A highly selective and practical asymmetric Ag(I) catalyst system has been developed for the [3 + 2] cycloaddition reactions between isocyanoacetates and cyclopentenediones. The current Ag(I) catalyst system tolerates moisture and air and readily utilizes class III solvents such as EtOAc and acetone. The development of on demand generation of an active chiral catalyst in the presence of isocyanides paves a way to the efficient asymmetric preparation of bicyclic pyrrolidines with four stereogenic centers, including two quaternary centers in 80–97% ee.

The direct conjugate addition reactions of imino esters to β-chlorovinyl ketones have been accomplished in the presence of a substoichiometric amount of hard base, LiHMDS. An in situ generated species from the conjugate addition reaction readily acted as autocatalyst to convert the imino esters to its corresponding enolates. By utilizing a sequence of conjugate addition/elimination/lactonization followed by either reduction or reaction with amines, the novel one-pot syntheses of highly functionalized pyranone and pyrrole derivatives were accomplished in good to excellent yields.

A mechanism-driven enantiodivergent approach to chiral 1,1′-bi-2-naphthols via catalytic asymmetric oxidative coupling of 2-naphthol derivatives is described for the first time. By utilizing 2-naphthol derivatives with low oxidation potential, the substrates were activated by either chiral mononuclear or dinuclear vanadium(V) catalyst to promote distinctively different asymmetric reaction pathways: single versus dual substrate activation mechanisms.