PCC-mediated novel oxidation reactions of homobenzylic and homoallylic alcohols

A new PCC-mediated carboncarbon bond cleavage reaction during oxidation of homobenzylic alcohols leading to the formation of benzylic carbonyl compounds has been observed. Homobenzylic alcohols with no benzylic substitution (R¹=H) gave benzylic aldehydes without further oxidation, while those with benzylic substitution (R¹=Me, Et, Ar) gave benzylic ketones. In contrast, homoallylic alcohols gave products arising from double bond migration, cis- to trans-olefin isomerization and/or allylic oxidation.     

FeCl3-catalyzed Ritter reaction. Synthesis of amides

A safe and inexpensive synthesis of amides, from benzylic alcohols and nitriles and from t-butyl acetate and nitriles, using a Ritter reaction catalyzed by FeCl₃·6H₂O is described.     

Combination of CuBr2 and multi-functional ligand bearing a bidentate nitrogen unit,a phenol group and a TEMPO moiety as catalyst for the aerobic oxidation of primary alcohols

A novel ligand (L) bearing a bidentate nitrogen ligand unit, a phenol group and a TEMPO moiety has been synthesized. The ligand has been used as a catalyst precursor for the copper-catalyzed aerobic oxidation of alcohols to aldehydes, in the presence of K₂CO₃. The complex obtained in-situ from the ligand with copper(II) bromide (CuBr₂) in a 2:1 acetonitrile/water mixture, selectively catalyzes the aerobic oxidation of primary benzylic and allylic alcohols to their corresponding aldehydes, and no over-oxidation products are detected.     

Aerobic oxidation of secondary alcohols in water with ABNO/tert-butyl nitrite/KPF6 catalytic system

A green and efficient transition-metal free ABNO/tert-butyl nitrite/KPF₆-catalyzed aerobic oxidation of secondary alcohols in water has been achieved. Under the optimal reaction conditions, a number of secondary aliphatic alcohols and secondary benzylic alcohols can be converted to their corresponding ketones in excellent yields (up to 99%).     

Cu(OTf)2-catalyzed arylmethylation of terminal alkynes with benzylic alcohols under ligand-, base-, and additive-free reaction conditions

An effective, convenient, and mild coupling reaction of benzylic alcohols with terminal alkynes has been developed. As an effective Lewis acid, Cu(OTf)₂-catalyzed arylmethylation of terminal alkynes with benzylic alcohols generated the corresponding products in BrCH₂CH₂Br with good yields in the absence of ligand, base, and additive.     

Solvent-free oxidation of alcohols by t-butyl hydroperoxide catalyzed by water-soluble copper complex

The catalytic system composed of CuCl₂ and 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC), was found to be highly efficient for the selective oxidation of secondary benzylic, allylic and propargylic alcohols to the corresponding ketones, with aqueous t-butyl hydroperoxide under phase-transfer catalysis conditions. The catalytic system is stable and can be recycled and reused several times without loss of activity.     

A remarkable effect of ionic liquids in transition-metal-free aerobic oxidation of benzylic alcohols

The transition-metal-free aerobic oxidation of benzylic alcohols is uniquely accelerated by a 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF₆)/PhCF₃ biphasic system and Cs₂CO₃ to afford the corresponding ketones in good yields. The reaction system is also applicable to an oxidative cross-esterification of primary benzyl alcohols with a higher aliphatic alcohol.     

Synthesis,structural characterization and alcohol oxidation activity of a new mononuclear manganese(II) complex

A manganese(II) complex of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) has been synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, IR, and UV–Vis spectroscopic techniques. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted by this catalyst using oxone (2KHSO₅·KHSO₄·K₂SO₄) as an oxidant under biphasic reaction conditions (CH₂Cl₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature. Easy preparation, mild reaction conditions, high yields of the products, short reaction times, no further oxidation to the corresponding carboxylic acids, high selectivity and inexpensive reagents make this catalytic system a useful oxidation method for aliphatic and benzylic alcohols.     

Efficient oxidation of alcohols with tert-butyl hydroperoxide catalyzed by Mo(CO)6 supported on multiwall carbon nanotubes

Efficient oxidation of alcohols with tert-butyl hydroperoxide catalyzed by Mo(CO)₆ supported on multiwall carbon nanotubes modified with 4-aminopyridine is reported. The effect of various parameters such as catalyst amount, solvent and oxidant was studied. The catalyst, [Mo(CO)₅@APy-MWCNT], showed high activity not only in the oxidation of benzylic and linear alcohols but also in the oxidation of secondary alcohols. The catalyst can be reused several times without significant loss of its activity.     

Oxidant-dependent selective oxidation of alcohols utilizing multinuclear copper-triethanolamine complexes

Multinuclear Cu(II)-triethanolamine complexes were employed as catalysts for the selective oxidation of primary and secondary alcohols using tert-butylhydroperoxide (TBHP) and O₂/2,2′,6,6′-tetramethylpiperidinyl-1-oxyl (TEMPO) system, respectively. The catalytic performances, especially in terms of selectivities, were oxidant-dependent in forming the corresponding carbonyl compounds as the major products. Excellent selectivities and moderate to good yields were obtained for the transformation of secondary alcohols to ketones in the case of TBHP and also for the conversion of benzylic primary alcohols to aldehydes in the case of O₂/TEMPO system.     

Cu(II) 2-quinoxalinol salen catalyzed oxidation of propargylic,benzylic, and allylic alcohols using tert-butyl hydroperoxide in aqueous solutions

The synthesis of carbonyl compounds by oxidation of alcohols is a key reaction in organic synthesis. Such oxidations are typically conducted using catalysts featuring toxic metals and hazardous organic solvents. Considering green and sustainable chemistry, a copper(II) complex of sulfonated 2-quinoxalinol salen (sulfosalqu) has been characterized as an efficient catalyst for the selective oxidation of propargylic, benzylic, and allylic alcohols to the corresponding carbonyl compounds in water when in combination with the oxidant tert-butyl hydroperoxide. The reactions proceed under mild conditions (70 °C in water) to produce yields up to 99% with only 1 mol % of catalyst loading. This reaction constitutes of a rare example of propargylic alcohol oxidation in water, and it makes this process greener by eliminating the use of hazardous organic solvents. Excellent selectivity was achieved with this catalytic protocol for the oxidation of propargylic, benzylic, and allylic alcohols over aliphatic alcohols. The alcohol oxidation is thought to go through a radical pathway.     

Facile synthesis of α, β-unsaturated esters through a one-pot copper-catalyzed aerobic oxidation-Wittig reaction

An efficient one-pot synthesis of α, β-unsaturated esters through the aerobic oxidation – Wittig tandem reaction of alcohols and phosphorous ylide is developed. This new method operates under mild reaction conditions, and uses CuI/TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) as co-catalyst and air (O₂) as the oxidant. It tolerates a wide range of functionalized benzylic alcohol and aliphatic alcohols.     

Metal-free one-pot oxidative conversion of benzylic alcohols and benzylic halides into aromatic amides with molecular iodine in aq ammonia, and hydrogen peroxide

Various primary alcohols, particularly benzylic alcohols, could be converted into the corresponding aromatic amides in good yields in a one-pot manner by treatment with molecular iodine in aq. NH₃, followed by reaction with ∼30% aq H₂O₂. Similarly, various benzylic halides could be also converted into the corresponding aromatic amides in good yields in a one-pot manner by treatment with molecular iodine in aq NH₃, followed by reaction with ∼30% aq H₂O₂. The present reactions involve the metal-free one-pot oxidative conversion of benzylic alcohols and benzylic halides into the corresponding aromatic amides, respectively.     

Efficient Swern oxidation and Corey–Kim oxidation with ion-supported methyl sulfoxides and methyl sulfides

The Swern oxidation of various benzylic and allylic alcohols, primary alcohols, and secondary alcohols with two ion-supported methyl sulfoxides A-1 (C₆) and B-1 (C₁₀), and oxalyl chloride in the presence of triethylamine in dichloromethane, followed by simple diethyl ether extraction of the reaction mixture, gave the corresponding aldehydes and ketones, respectively, in good yields with high purity. Similarly, the Corey–Kim oxidation of various benzylic and allylic alcohols, primary alcohols, and secondary alcohols with two ion-supported methyl sulfides A-2 (C₆) and B-2 (C₁₀), and N-chlorosuccinimide in the presence of triethylamine in dichloromethane, followed by simple diethyl ether extraction of the reaction mixture, furnished the corresponding aldehydes and ketones, respectively, in good yields with high purity. Both reactions did not produce any unpleasant odor at all. In the Swern oxidation, ion-supported methyl sulfides were recovered in high yields and could be re-oxidized to produce ion-supported methyl sulfoxides A-1 (C₆) and B-1 (C₁₀), for reuse in the same oxidation. In the Corey–Kim oxidation, ion-supported methyl sulfides A-2 (C₆) and B-2 (C₁₀) were recovered in high yields and could be also reused for the same oxidation.     

Fluoro-tagged osmium and iridium nanoparticles in oxidation reactions

Osmium and iridium metal nanoparticles were supported on a fluorous organic-inorganic hybrid material prepared by the sol-gel process. Moreover, we also found that the thermolysis of the Ir₄(CO)₁₂ cluster in simply diphenylether also gave Ir(0) nanoparticles. All the materials were studied as catalysts in oxidation processes. Fluoro-tagged iridium nanoparticles were particularly active in aerobic oxidation processes, whereby the catalytic activity could be greatly enhanced through a simple pre-activation procedure. With this material, benzylic alcohols could be oxidized under O₂ balloon in the absence of a basic additive; the oxidative stopped selectively to the corresponding benzaldehyde. Promisingly, the same reaction conditions were used in a benzylic CH oxidation of xanthene.     

Selective aerobic oxidation of allylic and benzylic alcohols catalyzed by N-hydroxyindole and copper(I) chloride

In the presence of copper(I) chloride, tert-butyl 1-hydroxy-2-methyl-6-trifluoromethyl-1H-indole-3-carboxylate acted as a catalyst for the chemoselective aerobic oxidation of allylic and benzylic alcohols. A variety of primary and secondary allylic and benzylic alcohols were oxidized into the corresponding α,β-unsaturated carbonyl compounds in good yields without affecting non-allylic alcohols.     

Synthesis,characterization and crystal structure of a manganese(III) Schiff base complex and investigation of its catalytic activity in the oxidation of benzylic alcohols

A new Mn(III) Schiff base complex was prepared by the reaction of 6,6′-diethoxy-2,2′-[2,2-dimethylpropane-1,3-diylbis(nitrilomethylidyne)]diphenol with Mn(OAc)₂·4H₂O. The complex was characterized by physicochemical and spectroscopic methods. Also, its molecular structure was determined by single-crystal X-ray diffraction. The complex was used as a catalyst for the efficient oxidation of benzylic alcohols with tetrabutylammonium periodate. Various reaction parameters were optimized for the reaction of benzyl alcohol.     

Efficient synthesis of carbonyl compounds: oxidation of azides and alcohols catalyzed by vanadium pentoxide in water using tert-butylhydroperoxide

Catalytic amount of vanadium reagent with tert-butylhydroperoxide as the oxidant was found to be an excellent oxidizing agent in aqueous medium. Vanadium pentoxide with aq tert-butylhydroperoxide readily oxidizes primary benzylic azides to the corresponding acids and secondary benzylic azides to the corresponding ketones in excellent yields. Further, vanadium pentoxide and aq tert-butylhydroperoxide combination turned out to be an effective catalyst for the oxidation of alcohols. Using vanadium pentoxide and aq tert-butylhydroperoxide primary alcohols were oxidized to the corresponding acids, whereas secondary alcohols underwent a smooth transformation to furnish corresponding ketones in excellent yields. All the oxidations are performed in water.     

A mild and efficient method for the oxidation of benzylic alcohols by two-phase electrolysis

Electrochemical oxidation of benzylic and substituted benzylic alcohols by two-phase electrolysis yields the corresponding aldehydes as products. The reaction was carried out in a single compartment cell with platinum electrodes at room temperature in chloroform using an aqueous sodium bromide solution (25%) containing a catalytic amount of HBr. The two-phase electrolysis resulted in high yields (74-96%) of benzaldehyde from primary alcohols and secondary alcohols were oxidized to the corresponding ketone but only in low yields under these conditions.     

Iodine/DMSO promoted oxidation of benzylic Csp3–H bonds to diketones – A mechanistic investigation

This article describes a mechanistic investigation into the I₂/DMSO mediated benzylic C_sp³–H oxidation of an α-methylene ketone. The electron paramagnetic resonance (EPR) spectrum centred at g = 2.0011 supports the involvement of iodine and benzylic radicals, as the α-iodinated compound 2-iodo-1,2-diphenylethanone was isolated as a key reactive intermediate. The oxidation reaction relies, primarily, on DMSO as a source of oxygen in benzil, proven by the reaction of benzyl phenyl ketone with diphenyl sulfoxide (DPSO).