Oximes deoximation

Keywords oxime, deoximation, ammonium chlorochromate, montmorillonite K-10, microwave irradiation, aldehyde, ketone... 

Oximes have been used as protecting groups for carbonyl compounds owing to their hydrolytic stability. Consequently, the development of newer deoximation reagents... 

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. 

The resulting radicals R efficiently alkylate BENAs (495) at the (3-C atom to give silyl derivatives of oximes (496) in good yields. The latter readily undergo deoximation in the presence of 1 M hydrochloric acid to give the corresponding carbonyl compounds (494). Thus, a convenient procedure was developed for the synthesis of carbonyl compounds (494) from secondary AN (493) through the intermediate terminal BENA (495) (527). 

The remaining aromatic oximes are primarily a collection of hydroxyl- and methyl-substituted acetophenones and benzaldehydes. Thwarting a comprehensive analysis is a lack of data for the corresponding carbonyl compounds or even deoximated compounds. A comparison of the benzaldoximes with benzaldehydes would be interesting, except there... 

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... 

Demetallation 1,3-Propanedithiol, 261 Deoximation (see Hydrolysis of oximes to carbonyls)... 

Keywords oxime, hydrazone, deoximation, ammonium persulfate-silica gel, microwave irradiation, ketone, aldehyde... 

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. 

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

Deoximation. Regeneration of carbonyl compounds from oximes by refluxing with Mn(OAc)j in benzene is quite efficient (11 examples, 86-96%). ... 

Reductive cleavage of oximes.1 Vanadium(II) chloride in THF is a convenient reagent for deoximation (75-90% yield). 

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... 

The Cj p3-O bond of 2-tert-butoxy-furan and -thiophene is cleaved catalytically by BiCl3 or Bi(OTf)3 to produce 2(5H)-furanone and -thiophenone, respectively [254]. The selective hydrolysis of aryl esters is catalyzed by bismufh(III) mandelate in DMSO [255]. In the presence of 50 mol% Bi(NO3)3-5H2O, 10 mol% Cu(OAc)2, and Montmorillonite KIO ketoximes undergo facile deoximation in acetone-H2O [256]. Under microwave irradiation the BiCls-promoted hydrolytic cleavage of the C=N bond of dimethylhydrazines, tosylhydrazines, semicarbazones, and oximes proceeds in wet THF (Scheme 14.120) [257-259]. 

Microwave irradiation of ketoxirnes on wet silica-supported NaBiOj produces the original ketones within a few minutes [270]. The deoximation of allylic and benzylic oximes can also be achieved by use of Zn(BiO3)2 [271]. 

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. 

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

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

Hydrolysis of oximes and amides. While deoximation is accomplished by heating an oxime or O-benzyloxime with CuCh 2H2O in MeCN, hydrolysis of amides is carried out in the presence of aqueous glyoxal. 

Deoximation. The conversion seems to be limited to allylic and benzylic oximes. 

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

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%. ... 

A variety of ketoximes 291, easily prepared from the corresponding ketones, undergo the Beckmann rearrangement upon treatment with 2,4,6-trichloro[l,3,5]triazine in A,A-dimethylformamide at room temperature in excellent yields (Equation 47). This method can be applied successfully on a large scale and no deoximation of the oximes to carbonyl compounds occurs. This procedure can be applied also to aldoximes for the preparation of the corresponding nitriles <2002JOC6272>. 

Also, in a closely related study, a similar sol-gd synthetic pathvray was used to prepare silica gel supported ionic liquid deoximation catalysts from carboxylic acid-functionalized ionic liquids [85]. Here various aryl and alkyl oximes were converted into the corresponding 0x0 compounds with high conversions (up to 94%) and excellent selectivity (>99%) in aqueous acetone at room-temperature by coproduction of 2-propanone oxime. TONs of up to 200 h obtained with the SILC were about four times higher than the TONs obtained using pure ionic liquids as catalysts. 

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... 

Ketoximes generally react with HTIB to afford the corresponding ketones as deoximation products [481]. However, the treatment of oximes of o-allyloxyacetophenones 396 with HTIB gives tricyclic products 397... 

Oximes play an important role as protecting groups due to their hydrolytic stability. Their frequent use has provided incratives far the develqnnent of newo deoximation reagents such as pyridinium chlorochromate, Raney nickel, triethylammonium chlorochromate, pyridinium chlorochromate-H202, nitrogen tetroxide, trimethylsilyl chlorochromate, H2O2 over titanium silicalite-1, Dowex-SO, dimethyl dioxirane, zirconium sulfophenyl phosphonate, AT-haloamides, and bismuth dil( ide (22). 

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. ... 

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