Oximes tetraacetate

An unactivated methyl group can be functionalized by the cyclopalladation of oximes. The equatorial methyl of geminal methyls in steroids or hexapyr-anosides is selectively aceto.xylated by the reaction of the palladation complex 523 of the 3-oxime with lead tetraacetate[467,468]. 

Benzisoxazole N-oxides have recently been synthesized from 2-hydroxypropio-phenone oxime and lead tetraacetate (equation 63) (80CC421). 

The mixed hydrazones (667), prepared from diacetyl monobenzoyl hydrazone and arylhydrazines, undergo oxidative cyclization to 2-aryl-jV-benzoyl-4,5-dimethyl-l,2,3-triazol-l-ylimines (668) in 32-76% yield upon treatment with lead tetraacetate in acetonitrile (Scheme 132) <92JOC2252>. The cychzation of bishydrazones to 1,2,3-triazoles can also occur in acidic or basic media. For instance, the tetrahydrobenzo[ /]triazol-4-one (669) is prepared by the base-catalyzed cyclization of the corresponding a-hydrazono oxime (Equation (53)) <85HCA1748>. 3-Methyl-1,2-cyclohexanedione reacts... 

The cadmium complexes were also investigated potentiometrically. Using this method, the complexes of cadmium with asparagine [128], taurine [129], A -(6-ami-no-3-methyl-5-nitroso-4-oxo-3,4-dihydro-pyrimidin-2-yl)glycine [130], succinate and malate [131], acetate at different temperatures [132], pyridine oxime ligands [133], 2-hydroxypropene-l,3-diamine-Af,Af,Af, A -tetraacetic acid [134] were studied. The stoichiometry and stability constants of these complexes were determined. 

Lead tetraacetate oxidation of the oxime (64) in glacial acetic acid at room temperature gives the yellow crystalline derivative (65) in good yield (Equation (3)) <76JHC793,76MI714-01,77MI 714-01). 

Heating o-nitrosophenols with hydroxylamine is reported to give furazans, naphtho[l,2-c]furazan (95) being formed from both l-nitroso-2-naphthol and 2-nitroso-l-naphthol, presumably by oximation of the tautomeric o-naphthoquinone monooximes and subsequent dehydration. Compound (95) has also been prepared by oxidation, using alkaline ferri-cyanide or hypochlorite, of l-amino-2-nitroso- and 2-amino-l-nitroso-naphthalene. This latter approach is suitable for heterocyclic fused furazans thus 4,6-diamino-5-nitrosopyrimidine is converted into the furazanopyrimidine (96) by oxidation with lead tetraacetate (71JOC3211). In a similar reaction alkaline hypochlorite oxidizes o-nitrosoacetaniiide to benzofurazan in quantitative yield. 

Direct dehydrogenation of oximes is also possible, particularly for sterically hindered nitrile oxides. The most successful oxidizing agents are alkaline hypobromite and NBS in the presence of base, the latter being valuable when basic groups are present. Lead tetraacetate and alkaline hypochlorite have also been employed, but the yields are lower. The formation of furoxans from the reaction of alkoximes with nitrogen oxides is believed to proceed via the corresponding nitrolic acids. 

The oxime 157 (R = CH=NOH), quantitatively obtained as a mixture of the syn- and ////-isomers from the meso-/ra/w-formylvinylporphyrin 157 (R = CHO), was reacted with lead tetraacetate in the presence of Et3N to give the macrocycle with a condensed oxazocine 158, as the result of oxidative cyclization as a single isomer relative to the exo-ethylidene bond (Equation 10) <2003CHE388>. 

Lead tetraacetate oxidizes oximes to various products. For exanqrle, the oxime of cyclohexanone gives a-acetoxynitrosocyclohexane in 35% yield.Aldoximes react with lead tetraacetate to give nitrile oxides which then yield acetyl hydroxamates 1 reaction with acetic acid. ... 

In a related reaction, primary aromatic amines have been oxidized to azo compounds by a variety of oxidizing agents, among them Mn02, lead tetraacetate, O2 and a base, barium permanganate, and sodium perborate in acetic acid. tert-Butyl hydroperoxide has been used to oxidize certain primary amines to azoxy compounds. " Aromatic hydroxylamines (Ar—NH—OH) are easily oxidized to nitroso compounds (Ar—N=0), most commonly by acid dichromate. Oximes of... 

Oximes react with lead tetraacetate (one-half equivalent) in acetic acid at 70° (1 hr.) to give the corresponding carbonyl compound in 60-90% yield. The reaction can even be applied to unsaturated oximes if an equivalent amount of anhydrous... 

The sequence can be applied to unsymmetrical ketones. The isomeric oxime acetates of 2-methylcyclohexanone (7) and (8), lead to mixtures of stereoisomeric acetoxy ketones (9) and (10) in 41-51% yield. Less than 1% of the tertiary acetate (11) is obtained. This result contrasts with acetoxylation of the ketone with lead tetraacetate which gives a substantial amount of the tertiary acetate as well as (9) and (10). 

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