Ru(III)-catalyzed oxidation of homopropargyl alcohols in ionic liquid: an efficient and green route to 1,2-allenic ketones

An efficient and environmentally benign synthesis of 1,2-allenic ketones via RuCl₃-catalyzed oxidation of homopropargyl alcohols in ionic liquid with tert-butyl hydroperoxide (TBHP) as the oxidant was reported for the first time. With its reasonable efficiency and green nature, this oxidation provides a novel alternative route to 1,2-allenic ketones.     

Mild propargylic oxidation using a diacetoxyiodobenzene/tert-butyl hydroperoxide protocol

A mild propargylic oxidation of alkynes is reported using a diacetoxyiodobenzene/tert-butyl hydroperoxide (DIB/TBHP) protocol. The reactions proceed smoothly at 0 °C and a number of α,β-unsaturated alkynoic ketones are obtained.     

Transition metal free one pot synthesis of aryl carboxylic acids via dehomologative oxidation of styrenes

Iodine/NaOH-catalyzed one-pot dehomologative oxidation of styrenes to aryl carboxylic acids has been reported. A wide range of carboxylic acids are obtained using iodine (I₂) as a catalyst, tert-butyl hydroperoxide (TBHP) as an oxidant and sodium hydroxide (NaOH) as a base. This reliable conversion involves dehomologation of styrene to aromatic aldehyde which on subsequent oxidation affords aryl carboxylic acid. This protocol was used for gram-scale synthesis as it is free from chromatographic purification. This is the first report for the oxidative transformation of styrenes into aryl carboxylic acids under transition metal-free conditions.     

Copper-Catalyzed CH Oxidation/Cross-Coupling of α-Amino Carbonyl Compounds

Keeping options open: The new and mild title reaction involving indoles selectively furnishes 1 and 2 with the aid of tert-butyl hydroperoxide (TBHP). The method represents the first example of a copper-catalyzed α?arylation of α-amino carbonyl substrates leading to α-aryl α-imino and α-aryl α-oxo carbonyl compounds using a C?H oxidation strategy.     

Catalytic reactivity of Cr/SiO2 in the liquid phase oxidation of cyclohexanol by tert-butyl hydroperoxide

Silica supported chromium is a heterogeneous, active and selective catalyst for the liquid phase oxidation of cyclohexanol by tert-butyl hydroperoxide (TBHP) in the presence or absence of oxygen. It is also active for the decomposition of TBHP. The reactivity at 70ºC and atmospheric pressure is higher than over other catalysts and the cyclohexanone selectivity is 100%.     

Rh-Catalyzed Oxidation of Anthracenes with tert-Butyl Hydroperoxide. Kinetic Aspects

The polar effects of substituents on reactivity in oxidation of 2-substituted anthracenes with tert-butyl hydroperoxide (TBHP)/Rh(PPh₃)₃Cl have been investigated and compared with those obtained with TBHP/VO(acac)₂ and chromic acid. The anthracene reactivities obtained from competition experiments are correlated with Hammett's σ_p-constants. The P-values are -2.60 for chromic acid and 0.72 for TBHP/VO(acac)₂. A poor correlation with p = ?0.17 (r = 0.756) was obtained for TBHP/Rh (PPh₃)₃Cl. It is concluded that the Rh-catalyzed reaction does not consist in electrophilic oxygen transfer to the anthracene.     

Facile synthesis of Ti-TUD-1 for catalytic oxidative desulfurization of model sulfur compounds

A facile synthesis route for Ti-TUD-1 at room temperature employing silatrane and titanium glycolate as Si and Ti sources (2?C8 mol%), respectively, over a triethanolamine template is proposed. XRD, N₂ adsorption?Cdesorption isotherms, and TEM analysis confirmed disordered mesoporous structures with high surface area (715?C824 m²/g). According to the UV?Cvisible spectroscopy of the calcined materials, titanium species of ca. 2.7 mol% Ti loading were present mostly in tetrahedral coordination for a sample prepared with 4 mol% Ti in the substrate mixture. Ti-TUD-1 showed catalytic activity in cyclohexene epoxidation, which depended on the amount of tetrahedrally coordinated Ti species. The hydrophilic nature of the surface of Ti-TUD-1 was confirmed by the effect of oxidant such that tert-butyl hydroperoxide (TBHP, 5?C6 M in decane) was superior to other oxidants in water (cyclohexene conversion: TBHP in decane 36.5% vs. TBHP in water 30.6%). Ti-TUD-1 was more active in oxidative desulfurization (ODS) reaction than Ti-MCM-41 at the same Ti loading; the former produced 4,6-dimethyldibenzothiophene (4,6-DMDBT) conversion near 100% after reacting for 15 min, whereas Ti-MCM-41 produced final conversion of 4,6-DMDBT of 89% after reacting for 180 min. ODS over Ti-TUD-1 was influenced both by electron density and steric hindrance in model sulfur compounds. Partially polymerized Ti sites seemed to also contribute to the reaction.     

A comparative mechanistic study of Cu-catalyzed oxidative coupling reactions with N-phenyltetrahydroisoquinoline

A comparative mechanistic study of Cu-catalyzed oxidative coupling reactions of N-phenyltetrahydroisoquinoline with different nucleophiles was conducted. Two previously reported combinations of catalyst and oxidant were studied, CuCl(2)·2H(2)O/O(2) and CuBr/tert-butyl hydroperoxide (TBHP). On the basis of a synthetic study with different nucleophiles, the electrophilicity of the intermediate iminium ion was estimated and differences between the two methods were revealed. The key intermediate in the aerobic method is shown to be an iminium ion, formed through oxidation by copper(II), which can react with any nucleophile of sufficient reactivity. The role of oxygen is the reoxidation of the reduced catalyst. In the CuBr/TBHP system, an α-amino peroxide is proposed as a true intermediate within the catalytic cycle, formed from the amine and TBHP by a Cu-catalyzed radical reaction pathway and acting as a precursor to the iminium ion intermediate.     

Oxidative transformation of azides to aryl nitriles using DIB/TBHP: scope and mechanistic insights

Bis(tert-butylperoxy)iodobenzene, generated in situ by the reaction between diacetoxyl iodobenzene (DIB) and tert-butyl hydroperoxide (TBHP), was used in the oxidative transformation of primary azides to nitriles, and secondary azides to ketones.     

A silica gel-supported ruthenium complex of 1,4,7-trimethyl-1,4,7-triazacyclononane as recyclable catalyst for chemoselective oxidation of alcohols and alkenes by tert-butyl hydroperoxide

A silica gel-immobilized [(Me(3)tacn)Ru(III)(CF(3)COO)(2)(H(2)O)]CF(3)CO(2) complex (1-SiO(2), Me(3)tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) was prepared by simple impregnation, and the catalyst was characterized by powdered X-ray diffraction, nitrogen adsorption/desorption, Raman, and diffuse reflectance UV-vis spectroscopies. The supported Ru catalyst can effect facile oxidation of alcohols by tert-butyl hydroperoxide (TBHP). Primary and secondary benzyl, allylic, and propargylic alcohols were transformed to their corresponding aldehydes and ketones in excellent yields; no oxidation of the C=C and Ctbd1;C bonds was observed for the allylic and propargylic alcohol oxidations. Likewise alkene epoxidation by TBHP can be achieved by 1-SiO(2); cycloalkenes such as norbornene and cyclooctene were oxidized to their exo-epoxides exclusively in excellent yields (>95%). The 1-SiO(2) catalyst can be recycled and reused for consecutive alcohol and alkene oxidations without significant loss of catalytic activity and selectivity; over 9000 turnovers have been attained for the oxidation of 1-phenyl-1-propanol to 1-phenyl-1-propanone. 4-Substituted phenols were oxidized by the "1 + TBHP" protocol to give exclusively ruthenium-catecholate complexes, which were characterized by UV-vis and ESI-MS spectroscopies. No (tert-butyldioxy)cyclohexadienone and other radical coupling/overoxidation products were produced using the "1 + TBHP" protocol. The formation of ruthenium-catecholate is proposed to proceed via ortho-hydroxylation of phenol.     

Oxidation of secondary amines catalyzed by dirhodium caprolactamate

The dirhodium caprolactamate [Rh(2)(cap)(4)] catalyzed oxidation of secondary amines to imines by tert-butyl hydroperoxide (TBHP) occurs with high chemo- and regioselectivity.     

Chemoselective alkane oxidation by superoxo-vanadium(V) in vanadosilicate molecular sieves

Electron paramagnetic resonance (EPR) spectroscopy of reactive superoxo-vanadium(V) species in vanadosilicate molecular sieves (microporous VS-1 and mesoporous V-MCM-41) generated on contact with H2O2, tert-butyl hydroperoxide (TBHP), or (H2+O2) is reported for the first time. By suitable choice of the silicate structure, solvent, and oxidant, we could control the vanadium-(O2-*) bond (i.e., the V-O bond) covalency, the mode of O-O cleavage (in the superoxo species), and, therefore, chemoselectivity in the oxidation of n-hexane: Oxidation by TBHP over V-MCM-41, for example, yielded 27.2% of (n-hexanol+n-hexanal+n-hexanoic acid), among the highest chemoselectivities for oxidation of the terminal -CH3 in a linear paraffin reported to date. Over these vanadosilicates, oxidation of the primary C-H bond occurs only via a homolytic O-O bond cleavage; the secondary C-H bond oxidations may proceed via both the homo- and heterolytic O-O cleavage mechanisms.     

Preparation,characterization and catalytic activity of a nano-Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene,cyclohexene, and benzyl alcohol

This paper reports the preparation of a nano-Co(II)-catalyst (NCC) by anchoring of Co ions on immobilized bipyridylketone over the nano-sized SiO₂/Al₂O₃ mixed oxides. The nano-Co(II)-catalyst has been characterized by elemental analysis, BET, FT-IR, DR UV–vis and SEM. The catalytic activity of the catalyst towards the oxidation of ethylbenzene, cyclohexene, and benzylalcohol to different chemically and pharmaceutically important products were evaluated with tert-butyl hydroperoxide (TBHP) in the absence of solvent. Under optimized conditions, the nano-catalyst proved highly selective towards the acetophenone, 2-cyclohexene-1-one and benzaldehyde as reaction products, with excellent conversion rates.     

Palladium-catalyzed direct ortho-acylation through an oxidative coupling of 2-arylbenzothiazoles with benzylic alcohols

An efficient protocol was developed for Pd-catalyzed direct C–H bond acylation by cross-dehydrogenative-coupling of arylbenzothiazoles and benzylic alcohols using tert-butyl hydroperoxide (TBHP) as the oxidant. The acylation reactions exhibit good reactivities and excellent regioselectivity.     

An Efficient Preparation of 2,6-Di-t-Butyl-1,4-Benzoquinone

A convenient and high yielding preparation of 2,6-di-t-butyl-1,4-benzoquinone from the iron-catalyzed oxidation of 2,4,6-tri-t-butylphenol with t-butyl hydroperoxide (TBHP) under acidic conditions is reported.     

Mechanistic Studies on the Roles of the Oxidant and Hydrogen Bonding in Determining the Selectivity in Alkene Oxidation in the Presence of Molybdenum Catalysts

When the molybdenum oxo(peroxo) acetylide complex [CpMo(O? O)(O)C?CPh] is used as a catalyst for the oxidation of olefins, completely different product selectivity is obtained depending on the oxidant employed. When tert‐butyl hydroperoxide (TBHP, 5.5 M ) in dodecane is used as the oxidant for the oxidation of cyclohexene, cyclohexene oxide is formed with high selectivity. However, when H₂O₂ is used as the oxidant, the corresponding cis‐1,2‐diol is formed as the major product. Calculations performed by using density functional theory revealed the nature of the different competing mechanisms operating during the catalysis process and also provided an insight into the influence of the oxidant and hydrogen bonding on the catalysis process. The mechanistic investigations can therefore serve as a guide in the design of molybdenum‐based catalysts for the oxidation of olefins.     

Catalytic and electrocatalytic oxidation of aniline to nitrobenzene over vanadium silicate molecular sieves: VS-1 usingt-butyl hydroperoxide (TBHP) as oxidant

A comparison of the results of catalytic and electrocatalytic oxidation of aniline using VS-1 in the presence of H₂O₂ and TBHP indicates remarkable differences in conversion and selectivity. VS-1 catalyzes the oxidation of aniline selectively to nitrobenzene (73%) in the presence oft-butyl hydroperoxide (TBHP), while azoxybenzene (95.2%) is formed selectively when H₂O₂ is used. Cyclic voltammetric studies show a three-step oxidation of aniline to nitrobenzene in H₂O₂ but in the presence of TBHP only one step is observed. Electrocatalytic oxidation of aniline to nitrobenzene occurs at a potential 700 mV less than that corresponding to H₂O₂ as oxidant along with a selectivity of 91.8%. The enhancement of electrocatalytic rate is attributed to the stabilization of electron deficient transition state.     

Formation of 3-acyloxy-γ-butyrolactones from 4-pentenols in vanadium-catalyzed oxidations

O-Acyl derivatives of 3-hydroxy-γ-butyrolactone are formed in up to 20% yield as by-products from 1-alkyl- and 1-phenyl-substituted 4-pentenols and tert-butyl hydroperoxide (TBHP) in vanadium-catalyzed synthesis of (tetrahydrofuran-2-yl)-methanols. The lactones are secondary products formed from (tetrahydrofuran-2-yl)-methanols via hydrogen atom abstraction in positions 4 and 5, as derived from experiments starting from deuterium-labeled alkenols. Stereocenters at tetrahydrofuran carbon 2 and the proximate hydroxyl carbon of the alkanol side chain retain configuration in the course of oxidative tetrahydrofuran conversion. In an atmosphere of nitrogen or argon, no γ-butyrolactone formation occurs, pointing to dioxygen as terminal oxidant for the secondary oxidation. Adding cyclohexa-1,4-diene or γ-terpinene to a solution of a 4-pentenol, TBHP, and a vanadium catalyst exposed to air inhibits formation of γ-butyrolactones. A third approach to prevent γ-butyrolactones from being formed in oxidative 4-pentenol cyclization uses cis-2,6-bis-(methanol)-piperidine instead of N-salicylidene-ortho-aminophenol as tridentate auxiliary for the vanadium catalyst.     

Metal-free oxidation of secondary benzylic alcohols using aqueous TBHP

We report a simple, yet efficient metal-free oxidation of secondary benzylic alcohols in the presence of t-butyl hydroperoxide (70% TBHP) with high yields of up to 98%. This type of reaction can be carried out using a wide variety of substrates, requires no other organic solvent, and proves to be tolerant toward a variety of different functional groups.     

Selective Oxidation of Benzyl Alcohols to Aldehydes with a Salophen Copper(II) Complex and tert-Butyl Hydroperoxide at Room Temperature

An efficient and selective oxidation of benzyl alcohols has been developed using a salophen copper(II) complex as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant in the presence of base. Moderate to excellent yields of the corresponding benzaldehydes were obtained at room temperature without the carboxylic acids being formed.