Oxidative deoximation

Oxidative deoximation/ Ketoximes revert to ketones by reaction with H,0, in an alkaline medium (75 95° yield, five examples). 

The kinetics of oxidative deoximation of aldo- and keto-oximes by 2,2/-bipyridinium chlorochromate (back to the parent carbonyl compounds) have been studied in DMSO, where the reaction is found to be first order in both oxime and oxidant.89 The aldoximes proved more reactive, and rates correlated well with the Pavelich-Taft dual substituent equation. Following extension of the study to hindered cases, and to 18 other solvents (analysed by Taft and Swain multi-parametrics), a cyclic intermediate is proposed for the rate-determining step. The same reaction order behaviour is found using the pyridinium version, and again electronic, steric, and solvent effects were examined.90... 

A variety of metal ion oxidants has been applied27-35 and different types of mechanisms postulated for these oxidative deoximation reactions. 

Deoximation. Jones reagent and chromic anhydride-pyridine (3,55-56 4, 96) have been added to the known reagents for oxidative deoximation. The former reagent was used in acetic acid rather than acetone for solubihty reasons. Periodic acid also can be used, but it sometimes gives rise to iodinated products. ... 

Oxidative deoximation. Aldehydes and ketones can be recovered from the oxime derivative by treatment with pyridinium chlorochromate (2 equiv.) in CH2CI2 (12-24 hours, 25°). Addition of sodium acetate inhibits epimerization in the case of a-methyl ketones. Yields range from 30 to 85%. ... 

Oxidative deoximation of aldo- and keto-oximes by tetraethylammonium chlorochro-mate in DMSO is first-order in oxime and oxidant, and the kinetic study was extended to 19 organic solvents. Similar kinetic behaviour was found for imidazolium fiuorochromate in the case of acetaldoxime, the same solvent survey was performed. Pyridinium fluorochromate as oxidant was also studied in DMSO. ... 

The kinetics of oxidative deoximation (in AcOH) ofiV-methyl-2,6-diphenyl piperidin-4-one oximes by acid dichromate and of 3,5-dimethyl-2,6-diaryl piperidin-4-one oximes by pyridinium chlorochromate have been detennined and are found to be consistent with polar mechanisms, first order in each reactant and subject to acid catalysis. 

The oxidation of aromatic aldoximes with ceric ammonium nitrate produces nitrile oxides which undergo subsequent cycloaddition to nitriles to produce 1,2,4-oxadiazoles (Equation 47) <1997PJC1093>. The anodic oxidation of aromatic aldoximes in the presence of acetonitrile has been reported to give low yields of either 3-aryl-5-methyl-1,2,4-oxadiazoles (2-25%) or 3,5-bis-aryl-l,2,4-oxadiazoles (6-28%), although the synthetic utility of this route is limited by competitive deoximation to the carbonyl being the major reaction pathway <1997MI3509>. 

Deoximation (8, 427). Oximes can be oxidatively cleaved by PCC alone, but a long reaction time is necessary. Cleavage occurs within minutes at 0-10° when 30% H2.02 is added. Yields are generally 65-85%. The actual oxidant may be pyridinium oxodiperoxychlorochromate (1).1... 

Oxidative cleavage of oximes.2 PDC is recommended for regeneration of ketones and aromatic aldehydes from the oximes (80-100% conversion). The rate of deoximation is increased by addition of 3A molecular sieves, but the yield of the carbonyl compound is lowered. 

Deoximation. Oximes are converted into the corresponding carbonyl compounds by oxidation with this reagent in CHoCh at room temperature. Yields range from 50-... 

Chaudhari, S. S., Akamanchi, K. G. A mild, chemoselective, oxidative method for deoximation using Dess-Martin periodinane. Synthesis 1999, 760-764. 

An oxidizing agent prepared from CrOj in water containing NH Cl at 40° followed by addition of alumina (cf. reagent on silica gel ) retains its power when kept in the air for several months. Deoximation under nonaqueous conditions is accomplished with dimethylammonium chlorochromate adsorbed on alumina. ... 

Deoximation. Regeneration of carbonyl compounds by oxidation with the supported reagent is aided by microwave irradiation. 

Deoximation To the numerous procedures for recovery of carbonyl compounds from oximes is added one involving oxidation with TSNCI2 in aqueous MeCN. 

Some polyfunctional isoxazolines of generic structure 44 were obtained in 78-91% yields by treatment of aryl aldoximes 42 with Baylis-Hillman adducts 43 in the presence of diacetoxy iodobenzene (DIB). The reaction is completely diastereoselective and involves the formation of nitrile oxides from aldoximes followed by 1,3-DC with the activated alkenes. Under the same conditions, ketoximes afforded only deoximation products <04TL7347>. 

Deoximation. - A method for the regeneration of carbonyl compounds from oximes calls for oxidation with the Dess-Martin periodinane. 

Deoximation. Oxidation with NaBOj in HOAc provides another method for the cleavage of oximes. 

The rates of deoximation of oximes using cetyltrimethylammonium dichromate in the presence of acetic acid and a cationic surfactant is sensitive to the concentrations of aU four substances substituent effects are also reported. The oxidant preferentially oxidizes oxime over hydroxyl groups. 

Karami, B., Montazerozohori, M. and Habibi, M. H. 2006. Tungstate sulfuric acid (TSA) A novel and efficient heterogeneous system for rapid deoximation solid acidic reagent for the oxidation of thiols to disulfides and oxidative demasking of 1,3-dithianes. Phosphorous Sulfur Silicon Relat. Elem. 181(12) 2825-2831. 

An interesting stoichiometric oxidative cleavage reaction of an oxime with a palladium dioxygen complex has been observed [160]. The palladium dioxygen complex, [Pd(PPh3)2(02)] has been shown to rapidly deoximate a variety of ketoximes in benzene at 25 °C. The yield of ketone formed was 98%. A l -dipolar cycloaddition of the dioxygen complex to the ketoxime was proposed, equation (119). 

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