Deoximation reactions

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

R = aryl alkyl R = H, aryl, alkyl Scheme 8.15. MW-assisted deoximation reactions. 

Oximes are converted to the corresponding carbonyl compound when treated with NCS in CCI4 at room temperature in excellent yields. The workup of these deoximation reactions is especially simple with the removal of insoluble succinimide and concentration of the solvent to afford the product carbonyl compound in high purity. For example, 4-methoxyacetophenone oxime was readily converted to the corresponding ketone in 4 h at room temperature (eq 27). 4... 

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>. 

The first step involves the above considered a, 3-C,C-coupling reaction of two different AN molecules the second step, selective deoximation of the 3-nitro oximes obtained the third step, selective reduction of the carbonyl group. 

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

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... 

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... 

Deoximation.1 This reaction can be effected with this combination of reagents and a phase-transfer catalyst at room temperature in yields generally >90%. The actual reagent is believed to be nitrosyl chloride, NOC1. 

The approach has found further applications in cleavage of benzyl esters, dethioacetalization, deoximation, and desilylation reactions [34],... 

Sitosterol (24-ethylcholesterol) is degraded to desmosterol (A -cholesterol) in the silkworm Bombyx mori, through the (245,285)-epoxide. The stereochemical features of the isomeric 24,28-epoxides and the derived 24,28-glycols have been worked out by a combination of physical and chemical methods. a,/8-Epoxyoximes give trans-a-alkyl-/8-hydroxy-ketones by reaction with lithium dialkylcup-rate and deoximation, a procedure with potentialities for alkylation in steroid chemistry. ... 

Deoximation. The transformation is carried out in aqueous MeCN at reflux. Friedel-Crafts alkylations. Alkenes and ethers are used as electrophiles in the reaction catalyzed by MofCO). Allyl acetates and alcohols are also suitable substrates. ... 

Deoximation.9 Oximes are converted into aldehydes and ketones in yields of 70-95 % when treated with TTN in methanol at room temperature. The reaction is complete within a few minutes. The precipitated thallium(I) nitrate is removed, the filtrate shaken with dilute sulfuric acid, and the aldehyde or ketone extracted with ether or chloroform. The process is formulated as shown. One limitation is that the method... 

T pe of reaction deprotection Reaction condition solvent-free Keywords oxime, deoximation, ammonium K-10, microwave irradiation, aldehyde, ketone... 

Conversion of ketoximes into ketones. Corey and Richman1 have reported a new procedure for regeneration of ketones from their oximes. The oxime is first converted into the O-acetate by treatment with acetic anhydride at 20° this derivative is then reductively deoximated by treatment with > 2 molar equivalents of chromous acetate in 9 1 THF-water at 25-65°. The reaction presumably involves reductive fission of the oxime N—O linkage to give an imine which is then rapidly hydrolyzed. Yields are in the range 75-85%. It is noteworthy that the reaction occurs more readily with acetoximes of conjugated ketones than with those of nonconjugated ketones and that the reaction occurs readily with acetoximes of hindered ketones such as camphor. 

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>. 

Neutral solutions of gold(in) bromide catalyse transoximations at ambient temperature the reaction is so mild that a-stereocentres are unepimerized, and most functional or protecting groups are unaffected, and reactions such as Beckmann or dehydration do not occur. Free gold(in) is essential, as the formation of gold nanoparticles (so useful for other chemistries) inactivates the metal. For deoximation, a protocol with diacetyl provides a cheap oxime acceptor. ... 

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). 

A route to hept-2-ulosonic acid derivatives is available by way of the reaction of 2,3 4,5-di-0-isopropylidene-L-arabinose and 2,4 3,5-di-0-ethylidene-L-xylose with ethyl nitrosoacetate. ° Isomerization of the intermediate nitroso derivatives with alcoholic sodium nitrite yielded the corresponding oximes, which can be deoximated with lead tetra-acetate in acetic acid. 3-Deoxy-D-manno-oct-2-ulosonic acid 5-(dihydrogen phosphate) and its D-gluco analogue have been obtained by base-catalysed condensation of o-arabinose 2-phosphate (obtained by way of phosphorylation of benzyl 3,4-0-isopropylidene-P-D-arabinopyrano-side) with oxalacetic and separation of the isomers by ion-exchange chromato-graphy. ... 

Considerable effort has gone into the synthesis of aminoacid glycosides mainly because of their significance in glycopeptide chemistry. Reaction of the dimer of tri-Q-acetyl-2-deoxy-2-nitroso-a-D-glucopyranosyl chloride with methyl M substituted-L-serinate (and L-threoninate and L-tyrosinate) gave mixed anomers of the oximes (9), and their deacylated products on deoximation, reduction and reacetylation afforded the corresponding q-d-... 

Decrease in the reaction temperature to 100 C and lower leads to deceleration of pyrrolization in comparison with rates of side processes, the most probable of which are prototropic isomerization of the bond in the initial ketoxime and partial deoximation. At 100°C (5 h), along with oxime of A -chloesten-3-one (isomer of A -cholesten-3-one), only traces of N-vinylpyrrolocholestene are detected in the reaction mixture OH NMR). When the temperature is raised above 120°C, a considerable amount of resin is formed that complicates isolation of the target pyrroles. 

To avoid the undesirable deoximation, the reaction (120°C, 1 h) with dicesium salt of progesterone dioxime, prepared from dilithium derivative and cesium fluoride (CsF) has been carried out [217]. In this case, only dipyrrole derivative of progesterone (8% yield) is formed, whereas deoximation product is not detected. This can be explained by lower (trace) content of water necessary for deoximation in this system. 

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