Deoximation

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

Scheme 6.10 Deoximation of carbonyl compounds by silica-supported ammonium persulfate.

Scheme 6.11 Deoximation of ketoximes with silica-supported periodate.

A facile deoximation procedure with sodium periodate impregnated on moist silica (Scheme 6.11) has also been introduced that is applicable exclusively to ketoximes [50], Aldehydes have been regenerated from the corresponding bisulfites (85-98%) on KSF clay surface [51]. 

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. 

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... 

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... 

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

Deoximation.2 A new prostaglandin synthesis is based on the ability of the O-methyloxime 2, when complexed with BF3, to react with the mixed cyanocuprate formed from 3, and then with 4 to give the prostanoid 5 in 75% yield. 

Conversion of 5 to PGE2 (6) requires Lindlar reduction, saponification to the acid group, desilylation (HF), and deoximation. Usual methods for the last step are ineffective, but deoximation was achieved with the solid Ti reagent (1) in 73% yield. 

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

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

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

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.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. 

Acylated 2-oxoglycosyl bromides of type II may efficiently be generated from hydroxyglycal esters by either of two ways, i. e. a high-yield, three-step procedure involving hydroxylaminolysis (29), deoximation (30), and photo-bromination (31), or, alternately, by a one-step process, simply consisting of exposure of hydroxyglycal ester I, in dichloromethane solution, to NBS or... 

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