Investigations into the selective oxidation of vicinal diols to α-hydroxy ketones with the NaBrO3/NaHSO3 reagent: pH dependence, stoichiometry, substrates and origin of selectivity

The NaBrO₃/NaHSO₃ reagent is one of the few oxidizing agents that chemoselectively oxidizes vicinal diols to α-hydroxy ketones with little overoxidation to the corresponding vicinal-dione or dicarboxylic acid. Oxidation reactions performed with this reagent showed strong pH dependence. cis-Vicinal diols reacted faster than trans-vicinal diols to the α-hydroxy ketone product. Hydroxy functional groups at axial ring positions were more readily oxidized than equatorial hydroxy groups. The application of the NaBrO₃/NaHSO₃ reagent for the chemoselective oxidation of vicinal diols was limited to simple systems and failed with more complex monosaccharide compounds probably due to acid catalyzed dehydrogenation reactions. Despite the simple reaction set-up and good selectivity towards the α-hydroxy ketone product, the actual oxidation reaction mechanism is highly complex and postulated to involve at least six different equilibria with a plethora of bromine containing species. A possible oxidation reaction mechanism is discussed.     

Asymmetric electrochemical oxidation of 1,2-diols, aminoalcohols, and aminoaldehydes in the presence of chiral copper catalyst

Asymmetric oxidation of 1,2-diols, aminoalcohols, and aminoaldehydes in the presence of copper(II) triflate and (R,R)-Ph-BOX was accomplished by electrochemical method using Br⁻ as a mediator. This oxidation was applicable to kinetic resolution of racemic cis-cycloalkane-1,2-diols, aminoalcohols, and aminoaldehydes to afford optically active compounds with good to high enantioselectivity.     

Methyltrioxorhenium catalyzed oxidation of 1,2-diols to 1,2-diketones using hydrogen peroxide as oxidant

A variety of 1,2-diols were oxidized selectively to the corresponding 1,2-diketones by the dropwise addition of 30% aqueous hydrogen peroxide using methyltrioxorhenium as catalyst.     

Stepwise oxidation of 1,2-diols resulting from molecular oxygen activation by copper

The oxidation of 1,2-diols through copper promoted activation of molecular oxygen was studied. The influence of the substituents and experimental conditions is discussed, and examples of catalytic applications are reported.     

Asymmetric oxidation of 1,2-diols using N-bromosuccinimide in the presence of chiral copper catalyst

Asymmetric oxidation of 1,2-diols using N-bromosuccinimide (NBS) in the presence of copper(II) triflate and (R,R)-Ph-BOX has been exploited. This oxidation was applicable to asymmetric desymmetrization of meso-hydrobenzoin and kinetic resolution of dl-hydrobenzoin and racemic-cycloalkane-cis-1,2-diols to afford optically active α-ketoalcohols with good to high enantiomeric excess.     

Kinetic resolution of d,l-1,2-diols catalyzed by amine-phosphinite bifunctional organocatalysis derived from quinidine

Racemic C₂-symmetric 1,2-diols were kinetically resolved by the acylation reaction catalyzed by the phosphinite derivative of quinidine to afford the corresponding monoacylated product with good to high enantioselectivities.     

A novel method of synthesis of 1,2-diketones from 1,2-diols using N-bromosuccinimide

A simple and convenient procedure is reported for the synthesis of benzils and aliphatic 1,2-diketones of cyclic and open chain compounds from corresponding hydrobenzoins and 1,2-diols by refluxing with N-bromosuccinimide in carbon tetrachloride in presence or absence of pyridine.     

Regioselective ring-opening reactions of 1,2-epoxides with thiols and arylselenols directly promoted by [Bmim]BF4

Regioselective ring-opening reactions of 1,2-epoxides with ArSH and ArSeH promoted by ionic liquid [Bmim]BF₄ were investigated. A variety of β-hydroxy selenides and β-hydroxy sulfides were obtained in excellent yields (81-99%) with good regioselectivities using a mild, simple and environmentally benign procedure.     

Reaction of C3 and C4 ketoses with alkenals and alkenones in water

Treatment of 1,3-dihydroxyacetone and acrolein with aqueous KOH gave a tetrahydrofuran derivative, 1,4-dihydroxy-3,7-dioxabicyclo[3.3.0]octane, in 80% yield. Similarly, 6-alkyl substituted 1,4-dihydroxy-3,7-dioxabicyclo[3.3.0]octanes were obtained by reaction of 1,3-dihydroxyacetone with various α,β-unsaturated aldehydes. In the cases of long chain alkenals, the reaction was effectively accelerated in the presence of organic co-solvent. On the other hand, the corresponding tricyclic products were synthesized by reaction of 1,3-dihydroxyacetone with cyclic enones, such as 2-cyclopentenone and 2-cyclohexenone. This method was successfully applied to the reaction of a tetrulose in the absence of any protecting groups.     

Alkane oxidation by the H2O2-NaVO3-H2SO4 system in acetonitrile and water

A simple system is described, which oxidizes saturated hydrocarbons either in acetonitrile or (less efficiently) in water. The system consists of 50% aqueous hydrogen peroxide as an oxidant, sodium metavanadate, NaVO₃, as a catalyst and sulfuric (or oxalic) acid as a co-catalyst. The reactions were carried out at 20-50 °C. In the oxidation of cyclohexane in acetonitrile, the highest yield (37% based on cyclohexane) and turnover number (TON=1700) were attained after 3 h at 50 °C. The corresponding parameters were 16% and 1090 for n-heptane oxidation under the same conditions. The oxidation of higher alkanes, RH, in acetonitrile gives almost exclusively the corresponding alkyl hydroperoxides, ROOH. Light alkanes (n-butane, propane, ethane, and methane) have been also oxygenated by the system under consideration. The highest TON (200) was attained for ethane and the highest yield (19%) was obtained in the case of n-butane. The selectivity parameters measured for the oxidation of linear and branched alkanes are low, the reaction with cis- and trans-1,2-dimethylcyclohexanes is not stereoselective. These facts lead us to conclude that the oxidation occurs with the formation of hydroxyl radicals in the crucial step.     

Kinetics and mechanism of KBrO3 oxidation of D(+) xylose in acidic medium

KBr₃ oxidation of xylose, in presence of H₂SO₄, follows first order kinetics in [KBrO₃] and [xylose], and second order in [H₂SO₄]. The acid-catalyzed reaction gives aldonic acid as product. A mechanism consistent with temperature, solvent, higher acidity and salt effects has been proposed. Thermodynamic constants have been calculated.

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KBrO₃ H₂SO₄ [KBrO₃] [] [H₂SO₄]. - . , , , . .

     

Structure elucidation of 21,22-dihydroxyonnamides A1-A4 from the marine sponge Theonella swinhoei: an empirical rule to assign the relative stereochemistry of linear 1,5-diols

A polar cytotoxic fraction of the marine sponge Theonella swinhoei was analyzed to be a mixture of four isomeric compounds, 21,22-dihydroxyonnamides A₁, A₂, A₃, and A₄. They were separated after conversion to the isopropyridene derivatives. The structures of the 21S,22S- and 21R,22R-isomers were determined by comparison of their spectral data with those prepared from onnamide A by asymmetric dihydroxylation. During the analysis of NMR data of these derivatives, an empirical rule was implied to assign the relative stereochemistry of linear 1,5-diol. This rule was applied to assign the stereochemistry of the remaining congeners.     

Fe3O4 nanoparticles/ethyl acetoacetate system for the efficient catalytic oxidation of aldehydes to carboxylic acids

A new methodology for the oxidation of aldehydes promoted by commercially available Fe₃O₄ nanoparticles (Fe₃O₄ NPs) activated by ethyl acetoacetate was developed. The use of ethyl acetoacetate as additive was crucial to achieve high reactivities. All reactions were realized under solvent free conditions, using air or tBuOOH as oxidants. Finally, the separation and reuse of the magnetically recoverable nanoparticles make this methodology very practical, simple and economical.     

Applications involving oxidation with KBrO3: Potentiometric determination of some inorganic white and yellow pigments

Rapid potentiometric methods were given for determination of some sulfide and chromate pigments in pure as well as adulterated samples. The methods are based on oxidation of S^2? or Cr³⁺ with known excess of KBrOs³ to the corresponding (S ↓) or Cr^6?. Oxidation of trivalent chromium proceeds only toward completion in presence of a catalyst such as Co²⁺. Sulfide oxidation needs gradual liberation of H₂S—which can be achieved by dropwise additions of the acid—together with the presence of excessive amount of water, in order to obtain accurate results excess oxidant was subsequently reduced with SO₂ to produce Br^? that can be titrated against Hg(I). The potential breaks are quite sharp for accurate determination of the equivalent points.     

SnCl4-promoted rearrangement of 2,3-epoxy alcohol derivatives: stereochemical control of the reaction

The SnCl₄-promoted rearrangement of 2,2,3,3-tetrasubstituted-2,3-epoxy-1-alcohol derivatives proceeded in a regio- and stereo-controlled manner to selectively give two types of rearranged products from a single isomer by changing the protecting group of the alcohol.     

Synthesis of cyclopentenyl and cyclohexenyl ketones via [3 + 2] and [4 + 2] annulations of 1,2-allenic ketones简

In this paper, an efficient synthesis of cyclopentenyl ketones and cyclohexenyl ketones through tertiary phosphine catalyzed [3 ＋ 2] and [4 ＋ 2] annulations of 1,2-allenic ketones with activated alkenes has been developed. Compared with published synthetic methods on cyclopentenyl ketones and cyclohexenyl ketones, the protocols developed in this paper have the advantages such as readily available starting materials, mild reaction conditions and high efficiency.     

Regioselective oxidation of N-alkylpyrrolidines to pyrrolidin-5-ones by RuCl3/NaIO4

RuCl₃/NaIO₄ under EtOAc/H₂O biphasic conditions, selectively oxidizes the Nα-endo-methylene group of pyrrolidine derivatives, without affecting the exo-methylene group adjacent to the N-heteroatom.     

A mild and efficient procedure for the oxidation of epoxides and aziridines using cerium(IV) ammonium nitrate and NBS

The CAN and NBS combination has been used for the first time for the synthesis of versatile α-hydroxy ketones and α-amino ketones from oxiranes/aziridines, respectively, in excellent yields. This method is a direct, one-pot, synthesis under mild conditions using acetonitrile-water (9:1) as solvent.     

Recyclable silica-supported iodoarene-RuCl3 bifunctional catalysts for oxidation of alcohols and alkylarenes

Novel, efficient, and recyclable bifunctional catalysts bearing SiO₂-supported RuCl₃ and iodoarene moieties were developed and used for environmentally benign oxidation of alcohols or alkylarenes at the benzylic position. These reactions in the presence of oxone as stoichiometric oxidant afforded the corresponding carbonyl compounds in high yields under mild conditions and convenient work-up. Furthermore, these SiO₂-supported bifunctional catalysts can be recovered by simple filtration and directly reused.