Oxygen‐Involved Oxidative Deacetylation of α‐Substituted β‐Acetyl Amides – Synthesis of α‐Keto Amides

α‐Substituted β‐acetyl amides could undergo C C bond cleavage to form α‐keto amides when treated with copper(II) chloride (CuCl₂) and boron trifluoride diethyl etherate (BF₃⋅OEt₂) under an oxygen atmosphere. The yield can be increased by the addition of tert‐butyl hydroperoxide which alone can also effect the reaction. The reaction provides a new protocol for the synthesis of α‐keto amides.

     

Iron‐Catalyzed Oxidative Cleavage of Olefins and Alkynes to Carboxylic Acids with Aqueous tert‐Butyl Hydroperoxide

A new method for the oxidation of aromatic olefins and alkynes has been developed using inexpensive iron(III) chloride hexahydrate (FeCl₃⋅6 H₂O, 5 mol%) catalyst in combination with commercially available aqueous 70% tert‐butyl hydroperoxide (TBHP) as oxidant. The present system works well for aromatic alkenes and alkynes with both electron‐donating and electron‐withdrawing substituents being tolerated. The protocol is free from chromatographic purification and the carboxylic acids are obtained in high yields by simple filtration.     

Vanadium‐Catalyzed Selective Oxidation of Alcohols to Aldehydes and Ketones with tert‐Butyl Hydroperoxide

The oxidation of alcohols to aldehydes and ketones has been described using silica‐supported vanadium(IV ) oxide (V/SiO₂, 1 ) in the presence of tert‐butyl hydroperoxide in tert‐butyl alcohol at ambient temperature with quantitative yields. The procedure is simple, efficient and environmentally benign.     

Copper‐Catalyzed Cycloaddition between Secondary Phosphine Oxides and Alkynes: Synthesis of Benzophosphole Oxides

Benzophosphole derivatives have attracted significant attention as promising organic optoelectronic materials. We have successfully developed a copper (2 mol%)/tert‐butyl hydroperoxide (2 equiv.) catalyst system for reaction of readily available secondary phosphine oxides and alkynes in acetonitrile at 60 °C under air, which provides a rapid access to a structurally diverse array of benzophosphole oxides in moderate to good yields within 30 min. The method can be easily used for a large‐scale preparation. Preliminary mechanistic studies revealed that the addition of a phosphoryl radical onto a triple bond followed by cyclization on the phenyl moiety of the secondary phosphine oxide might occur to form the benzophosphole oxide.

     

A Practical Procedure for Reduction of Primary,Secondary and Tertiary Amides to Amines

A mild and general procedure for reduction of primary, secondary, and tertiary amides using catalytic triruthenium dodecacarbonyl and 1,1,3,3‐tetramethyldisiloxane as reductant is described. The reaction is tolerant of numerous functional groups, and the amine products can often be isolated by direct crystallization as hydrochloride salts. The catalyst and silane are commercially available, air stable, and inexpensive, making the procedure accessible for both laboratory and large‐scale applications.     

Synthesis of Pyrazolo[1,2‐a]cinnolines via a Rhodium‐Catalyzed Oxidative Coupling Approach

An efficient synthetic strategy for the unique class of pyrazolo[1,2‐a]cinnolines was developed through a rhodium‐catalyzed oxidative coupling of N‐aryl‐1H‐pyrazol‐5(4H)‐ones with internal alkynes. This protocol features use of the pyrazolone function in the substrate as an intrinsic directing group, hexafluoroisopropyl alcohol (HFIP) as the solvent, and mild reaction conditions as well as a wide substrate scope.

     

Oxidative Coupling of Alkenes with Aldehydes and Hydroperoxides: One‐Pot Synthesis of 2,3‐Epoxy Ketones

A new transition metal‐free oxidative coupling of unactivated terminal alkenes with aldehydes and hydroperoxides in the presence of 10 mol% potassium tert‐butanolate (t‐BuOK) is described thereby realizing trifunctionalization of alkenes toward 2,3‐epoxy ketones. This method is applicable to a wide range of aldehydes, including aryl and alkyl aldehydes, with excellent functional group tolerance, and provides for the one‐step assembly of 2,3‐epoxy ketones.

     

Formation of Tertiary Amides and Dihydrogen by Dehydrogenative Coupling of Primary Alcohols with Secondary Amines Catalyzed by Ruthenium Bipyridine‐Based Pincer Complexes

Dehydrogenative coupling of primary alcohols with secondary amines to form tertiary amides and dihydrogen (H₂) is efficiently catalyzed by bipyridyl‐based ruthenium pincer complexes (0.2–1 mol%) under neutral conditions (in case of the dearomatized complexes), or with added catalytic amount of base. The reaction is sensitive to steric hindrance; in the case of amidation of bulky secondary amines a less sterically hindered complex is more efficient. Selective acylation of primary amines in the presence of secondary amines was also demonstrated.

     

A Practical Way to Prepare Isobutyronitrile Amides through Reactions between Carboxylic Acids and Azobisisobutyronitrile

A practical and efficient synthesis of N‐isobutyronitrile amides has been achieved through the direct condensation of carboxylic acid and azobisisobutyronitrile (AIBN). Carboxylic acids bearing variously substituted phenyl rings and cinnamic or phenylpropiolic acids were employed to furnish both tertiary and secondary isobutyronitrile amides in moderate to high yields. A radical pathway was proposed. The methodology presented here requires no catalysts and additives, and represents the first practical approach to a variety of valuable amides containing the isobutyronitrile structural unit.

     

Pd‐Catalyzed ortho‐Selective Oxidative Coupling of Halogenated Acetanilides with Acrylates

Coupling of different halogenated acetanilides with acrylates using Pd‐catalyzed ortho‐selective C H bond activation is reported. The yields of coupled products are low to high depending on the substrate. In general, arenes with electron‐rich substituents like methoxy and methyl groups gave higher yields of the coupled products. The presence of the halogen substituent did not interfere with the activation process under these conditions     

Surface Praseodymium Species on MgO: Characterization and Activity for Oxidative Coupling of Methane

On pulsing CH₄ over MgO containing various amounts of praseodymium oxide (PrO_x) at 1023 K, the CH₄ conversion decreased with increasing pulse number, and both the initial activity and selectivity to C₂ products (corresponding to the first pulse) decreased with increasing PrO_x content. Characterization by XRD, SEM-EDX and XPS showed calcined materials to contain well-dispersed PrO_x (x = 1·83–2) at low Pr concentrations, but only crystalline PrO_1·83 at high (10 wt%) Pr concentration. A PrO_1·83 phase was present at all Pr concentrations after the He treatment at 1023 K, and PrO_1·83, PrO_1·75 and PrO_1·5 after reaction. © 1997 SCI     

Combined Single-pass Conversion of Methane Via Oxidative Coupling and Dehydro-aromatization

A single-pass process with the combination of oxidative coupling (OCM) and dehydro-aromatization (MDA) for the direct conversion of methane is carried out. With the assistance of the OCM reaction over the SrO–La₂O₃/CaO catalyst loaded on top of the catalyst bed, the duration of the dehydro-aromatization reaction catalyzed by a 6Mo/HMCM-49 catalyst shows a significant improvement, and. the initial deactivation rate constant of the overall process revealed about 1.5×10⁻⁶ s⁻¹. Up to 72 h on stream, the yield of aromatics was still maintained at 5.0% with a methane conversion of 9.6%, which is obviously higher than that reported for the conventional MDA process with single catalyst. Upon the TPR results, this wonderful enhancement would be attributed to an in-situ formation of CO₂ and H₂O through the OCM reaction, which serves as a scavenger for actively removing the coke formed during the MDA reaction via a reverse Boudouard reaction and the water gas reaction as well.     

甲烷氧化偶联制C2烃催化剂及催化反应机理研究进展

综述了甲烧氧化偶联制乙烷、乙烯催化剂及催化机理研究概况。重点介绍1989年以来对碱及碱土金属化合物、烯土氧化物、复合氧化物等各类催化剂的研究进展。对目前催化剂上甲烷活化途径、甲基自由基在反应过程中的作用机理、不同氧化物种及表面酸、碱位与催化性能的关系等方面的研究抉况及不同观点也作了简介。     

Oxidative coupling of aromatic thiols to corresponding disulfides using magnetic particle-supported sulfonic acid catalyst and hydrogen peroxide under mild conditions

A green and efficient method for chemoselective oxidation of aromatic thiols to the corresponding disulfides is reported using a recoverable supported iron oxide nanoparticle (γ-Fe₂O₃–SO₃H) catalyst in the presence H₂O₂ as the oxidant and methanol as the solvent at room temperature. This reaction is operationally simple with an easy work-up, utilizes mild reaction conditions, is high-yielding, clean, and exhibits high selectivity toward aromatic disulfides with no side reactions. The supported iron oxide nanoparticles can be easily recovered using an external magnet from the reaction mixture and reused several times. Reaction progress was monitored by potentiometric titration.     

tert‐Butyl Hydroperoxide and Tetrabutylammonium Iodide‐Promoted Free Radical Cyclization of α‐Imino‐N‐arylamides and α‐Azido‐N‐arylamides

The oxidizing system of tert‐butyl hydroperoxide (TBHP) and tetrabutylammonium iodide (TBAI) is capable of generating α‐(arylaminocarbonyl)iminyl radicals from ethyl 2‐(N‐arylcarbamoyl)‐2‐iminoacetates. These iminyl radicals preferably undergo intramolecular ipso attack on the benzene ring to give azaspirocyclohexadienyl radicals, which are readily captured by molecular oxygen under an oxygen atmosphere to yield azaspirocyclohexadienones. In the absence of oxygen, the reaction affords quinoxalin‐2‐one products. This oxidizing system is also effective to convert α‐aryl‐α‐azido‐N‐arylamides to the corresponding iminyl radicals under basic conditions (sodium tert‐butoxide, t‐BuONa), and the subsequent cyclization of these iminyl radicals results in the formation of azaspirocyclohexadienone products in high yields under an oxygen atmosphere. Plausible mechanisms are proposed to rationalize the experimental results, and factors influencing the reactions are discussed.

     

A General and Practical Palladium‐Catalyzed Direct α‐Arylation of Amides with Aryl Halides

An efficient system for the direct catalytic intermolecular α‐arylation of acetamide derivatives with aryl bromides and chlorides is presented. The palladium catalyst is supported by Kwong’s indole‐based phosphine ligand and provides monoarylated amides in up to 95% yield. Excellent chemoselectivities (>10:1) in the mono‐ and diarylation with aryl bromides were achieved by careful selection of bases, solvents, and stoichiometry. Under the coupling conditions, the weakly acidic α‐protons of amides (pK_a up to 35) were reversibly depotonated by lithium tert‐butoxide (LiO‐t‐Bu), sodium tert‐butoxide (NaO‐t‐Bu) or sodium bis(trimethylsilyl)amide [NaN(SiMe₃)₂].

     

Tuning the Selectivity of Heterogeneous Catalysts: A Trimetallic Approach to Reductive Coupling of Chloroarenes in Water

Reductive homocoupling of chlorobenzenes to the respective biphenyls affords high yields (93–95%), in the presence of catalytic PEG‐400 and 0.4 mol % of a recycleable, heterogeneous trimetallic catalyst (4% Pd, 1% Pt, and 5% Bi on carbon). The competing reduction process is minimized. The catalytic cycle is completed using hydrogen gas, or formate + water or zinc + water mixtures, which generate dihydrogen in situ. Primary kinetic data and some process parameters are studied. The roles of the Pd, Pt, and Bi, different reducing agents, and the phase‐transfer agent are discussed. The reaction mechanism is proposed to depend on the relative concentration of hydride species in the immediate vicinity of the palladium metal.     

Ruthenium Pincer‐Catalyzed Cross‐Dehydrogenative Coupling of Primary Alcohols with Secondary Alcohols under Neutral Conditions

Cross‐dehydrogenative coupling of primary alcohols with secondary alcohols to obtain mixed esters with the liberation of molecular hydrogen is achieved in high yield and good selectivity under neutral conditions, using a bipyridyl‐based PNN ruthenium(II) pincer catalyst.     

A Practical Procedure for Iron‐Catalyzed Cross‐Coupling Reactions of Sterically Hindered Aryl‐Grignard Reagents with Primary Alkyl Halides

Although iron‐catalyzed cross‐coupling reactions of arylmagnesium halides with alkyl halides are well established and proceed effectively under a variety of experimental conditions, they often find limitations when working with sterically hindered aryl‐Grignard reagents. Outlined in this paper is a practical solution that allows this gap in coverage to be filled. Specifically, it is shown that bis(diethylphosphino)ethane (depe) crafts an effective coordination environment about Fe(+2). This commercially available ligand is slim enough not to interfere with the loading of the iron center even by ortho,ortho‐disubstituted arylmagnesium halides, yet capable of preventing premature reductive coupling of the resulting organoiron species, which seem to be hardly basic either. The reaction is compatible with various polar functional groups as well as with substrates containing β‐heteroatom substituents. Moreover, the procedure even allows encumbered neopentylic electrophiles to be arylated with donors as bulky as mesitylmagnesium bromide, whereas secondary alkyl halides tend to eliminate.

     

Oxidative Coupling of Enamines and Disulfides via Tetrabutylammonium Iodide/tert‐Butyl Hydroperoxide‐Mediated Intermolecular Oxidative C(sp2)?S Bond Formation Under Transition Metal‐Free Conditions

The reaction of enamine compounds with disulfides in the presence of tert‐butyl hydroperoxide and a catalytic amount of tetrabutylammonium iodide conveniently afforded a variety of α‐thioenamine compounds through the intermolecular oxidative C(sp²) S coupling. Incorporating both of the sulfide moieties in the disulfides into the final products under oxidative conditions, this novel approach exhibits the feature of atom efficiency. A radical mechanistic pathway for the reaction process has been proposed.