Oxime acetates ketones

Interestingly, treatment of a-nitrostilbene in water-ethyl acetate mixture by the cation-radical of A,A -dioctyl-4,4 -bipyridinium (the octylviologen cation radical) leads to the formation of products derived from the nitro group reduction. No dimerization is observed (Tomioka et al. 1986). Water is responsible for the fixation of transferred electron within the nitro group. Further reactions result in the formation of the corresponding oxime and ketone as shown in Scheme 2.10. 

Oximes of ketones undergo rearrangement (the Beckmann rearrangement) to amides under the influence of a variety of acidic reagents (e.g. sulphuric acid, hydrogen fluoride, acetic anhydride, phosphorus pentachloride, thionyl chloride, etc.). The process is illustrated by the conversion of benzophenone oxime to benzanilide in the presence of phosphorus pentachloride. 

On successive treatment with trimethyloxonium tetrafluoroborate, triethylamine and aqueous acid, oxime acetate 83 prepared from cyclohexanone oxime and Ac20 yields a-acetoxy ketone 87 (Scheme 7). A similar result is obtained with other symmetric ketones including 4-heptanone, deoxybenzoin and dibenzyl ketone. 87 can also be formed by the reaction of cyclohexanone and O-acetyl-Af-methylhydroxylamine hydrochloride upon hydrolysis. If the reaction time is prolonged prior to hydrolysis, ketoamide 89 is isolated as the main product. The key step of the reaction is the [l,3]-acetoxy shift of 7V-acetoxyenamine 85 to the a-acetoxyimine 86. The formation of 89 provides support for the intermediacy of acetoxyimine 86 in the reaction sequence. The evidence available suggests that the [l,3]-acetoxy migration proceeds via a Claisen-type rearrangement (Scheme 7)78. 

Deoximiation Oximes, oximic ethers, or oxime 0-acetates can be converted into the corresponding ketones by reaction with Fe,(CO)9 in CH,OH at 60°. This reaction proceeds particularly readily and in good yield with oxime acetates. 

Hydroxylamine converts a 16a-bromoandrostan-17-one (216) cleanly into the 17-oxime (217) of the 16a-hydroxy-ketone,""" closely paralleling the action of hydrazine."" Reduction of the oxime-acetate (218) with diborane gave the 17/8-acetamido- 16a -acetoxy-derivative (219)."""... 

The same srategy has been developed with (bromomethyl)aryl ketones, which, before reacting with triethyl phosphite, are converted into oxime acetates or oxime ethers. A subsequent Michaelis-Arbuzov reaction leads to protected diethyl 2-aryl-2-oxoethylphosphonates in excellent yields (67-99%). - "... 

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). 

Oxime acetates or benzoates afford their parent ketones on triplet-sensitised photolysis, or the amides (lactams) by direct photo-isomerisation. Both products probably result from further reactions of an intermediate oxaziran (Scheme 31),... 

More complex monosaccharides such as daunosamine and fucose are assembled using a similar strategy (Scheme 31).- - Cyclocondensation of diene (104) with acetaldehyde (9f) using the lanthanide catalyst Eu(hfc)3 gives the syn cycloadduct (105). Treatment of (105) with TFA followed by oxymercuration [Hg(OAc)2-NaCNBH4] and reductive amination of the oxime acetate (derived from the ketone) gives daunosamine (108). Fucose (107) is prepared from compound (106) by reduction of the ketone and treatment of the glycal with MCPBA in methanol. 

Chromous acetate Ketones from oxime acetates 192. C6H5-C-C2H5... 

Since hydroxylamine is usually available only in the form of its salts, e.g., the hydrochloride or sulphate, the aqueous solution of these salts is treated with sodium acetate or hydroxide to liberate the base before treatment with the aldehyde or ketone. Most oximes are weakly amphoteric in character, and may dissolve in aqueous sodium hydroxide as the sodium salt, from which they can be liberated by the addition of a weak acid, e.g., acetic acid. 

Place 80 g, of hydroxylamine sulphate (or 68-5 g. of the hydrochloride), 25 g. of hydrated sodium acetate, and 100 ml. of water in a 500 ml. flask fitted with a stirrer and a reflux water-condenser, and heat the stirred solution to 55-60°. Run in 35 g (42 nil,) of -hexyl methyl ketone, and continue the heating and vigorous stirring for ij hours. (The mixture can conveniently be set aside overnight after this stage.) Extract the oily oxime from the cold mixture twice with ether. Wash the united ethereal extract once with a small quantity of water, and dry it with sodium sulphate. Then distil off the ether from the filtered extract, preferably using a distillation flask of type shown in Fig. 41 (p. 65) and of ca, 50 ml, capacity, the extract being run in as fast as the ether distils, and then fractionally distil the oxime at water-pump pressure. Collect the liquid ketoxime, b.p. 110-111713 mm. Yield, 30-32 g. 

Aldehydes and ketones may frequently be identified by their semicarbazones, obtained by direct condensation with semicarbazide (or amino-urea), NH,NHCONH a compound which is a monacidic base and usually available as its monohydrochloride, NHjCONHNH, HCl. Semicarbazones are particularly useful for identification of con jounds (such as acetophenone) of which the oxime is too soluble to be readily isolated and the phenylhydrazone is unstable moreover, the high nitrogen content of semicarbazones enables very small quantities to be accurately analysed and so identified. The general conditions for the formation of semicarbazones are very similar to those for oximes and phenylhydrazones (pp. 93, 229) the free base must of course be liberated from its salts by the addition of sodium acetate. 

Oximes. The method given for semicarbazones (see 2) may be employed use 1 g. of hydroxylamine hydrochloride, 2 g. of crystallised sodium acetate and 0 5 g. of the aldehyde or ketone. It is usually advisable to warm on a water bath for 10 minutes. 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty 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-cataly2ed 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. 

Dimethyl ketals and enol ethers are stable to the conditions of oxime formation (hydroxylamine acetate or hydroxylamine hydrochloride-pyridine). Thioketals and hemithioketals are cleaved to the parent ketones by cadmium carbonate and mercuric chloride. Desulfurization of thioketals with Raney nickel leads to the corresponding methylene compounds, while thioenol ethers give the corresponding olefin. In contrast, desulfurization of hemithioketals regenerates the parent ketone. ... 

In order to establish the primary character of farnesol, farnesenic acid was prepared from farnesal oxime and the corresponding nitrile. Saponification of the farnesene-nitrile with caustic soda solution yields farnesenic acid and acetic acid, and also a ketone which was identified as a dihydropsewdoionone. The semi-carbazone melts between 95° and 96°. The dihydropmtdoionone from farnesene nitrile proved to be... 

Diazonium salts react with oximes to give aryl oximes, which are easily hydrolyzed to aldehydes (R = H) or ketones." A copper sulfate-sodium sulfite catalyst is essential. In most cases higher yields (40-60%) are obtained when the reaction is used for aldehydes than for ketones. In another method for achieving the conversion ArNj —> ArCOR, diazonium salts are treated with R4Sn and CO with palladium acetate as catalyst. In a different kind of reaction, silyl enol ethers of aryl ketones, Ar C(OSiMe3)=CHR, react with sohd diazonium fluoroborates, ArNj BF4, to give ketones, ArCHRCOAr. " This is, in effect, an arylation of the aryl ketone. 

---