Oximes, acid catalyzed ketones

Lewis acid catalyzed reaction of oximes 172 (equation 113) with divinyl ketone (173) provided l-aza-7-oxabicyclo[3.2.1]octan-4-ones 174 through a sequential Michael addition and [3 + 2] cycloaddition. The reaction occurred with complete stereoselectivity giving the same product with both cis- and frawi-oximes . 

The acid catalyzed conversion of oximes over different acidic solids in "dry media under soft conditions gives as major products the amide (Beckmann rearrangement) and the ketone (hydrolysis). The... 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availability of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-catalyzed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

One of the best known reactions of 1-azirines is the acid/catalyzed hydrolysis to aminoketones. Since the Neber reaction also accomplishes this same synthetic end, this reaction may appear to have little practical value. This is not the situation because with the Neber reaction there is no control over the aminoketone that will be obtained from a given ketone. For example, when oxime (127) derived from benzyl methyl ketone (126) is subjected to the Neber reaction aminoketone 128 is obtained.59 The amino function is substituted for the most acidic a-hydrogen. The isomeric aminoketone (132) that could not be prepared by the Neber reaction can be formed by the hydrolysis of 1-azirine (131). The synthesis of this 1-azirine has been accomplished from allyl benzene (129) through vinyl azide (130) using iodine azide.22... 

In the nitrosation of ethyl isopropyl ketone (Preparation 2-4), acetyl chloride is used as a catalyst. While aqueous hydrochloric acid has also been used to catalyze this reaction, anhydrous hydrogen chloride or acetyl chloride evidently is more effective as far as the yield is concerned. To be noted here is that the greater yield is that of the true nitroso compound. However, the secondary carbon atom of the ethyl group is converted into an oxime on nitrosation. 

Palladium-catalyzed cyclization of the oxime derivative 47 provided a good yield of the pyrrole 48 (Equation 9) <1999CL45>. Similar reactions have been observed in connection with cyclization studies of related ketone trimethylhydrazonium salts <2005H(65)273>. Photochemical radical cyclization of 7,5-unsaturated ketone oximes has been reported to produce 1-pyrrolines <2005TL2373>. Similar 0-acetyloximes may also be annulated to 1-pyrrolines by treatment with acetic acid in the presence of 1,4-cyclohexadiene and naphthalene-l,5-diol, possibly proceeding via a radical mechanism <2002CL144>. 

Reduction of oximes to ketones. Ketoximes can be converted to ketones by hydrogenation catalyzed by Raney nickel (deactivated with acetone) in THF/CH,OH/H,0 or in CHiOH/H,0 containing boric acid to facilitate hydrolysis of the intermediate imine... 

Ketones having an a-methylene group, that is, —CH2 bound to the carbonyl group, can react with nitrous acid, nitrite esters, or nitrosyl chloride to form nitroso compounds and oximes. These reactions are catalyzed by acids or bases. 

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