A-Ketoximes

A ketoxime tosylate 1 can be converted into an a-amino ketone 2 via the Neber rearrangement by treatment with a base—e.g. using an ethoxide or pyridine. Substituent R is usually aryl, but may as well be alkyl or H substituent R can be alkyl or aryl, but not H. 

The reaction that normally occurs on treatment of a ketoxime with a Lewis or proton acid is the Beckmann rearrangement (18-17) fragmentations are considered side reactions, often called abnormal or second-order Beckmann rearrangements. Obviously, the substrates mentioned are much more susceptible to fragmentation than are ordinary ketoximes, since in each case an unshared pair is available to assist in removal of the group cleaving from the carbon. However, fragmentation is a side reaction even with ordinary ketoximes and, in cases where a particularly stable carbocation can be cleaved, may be the main reaction. ... 

In 1994, the scope of this p-hydroxy sulfoximine ligand was extended to the borane reduction of ketimine derivatives by these workers. The corresponding chiral amines were formed with enantioselectivities of up to 72% ee, as shown in Scheme 10.57. It was found that the A -substituent of the ketimine had a major influence on the asymmetric induction, with a ketoxime thioether (SPh) being the most successful substrate. 

A modification of this method, related to the Beckmann rearrangement, entails treatment of a ketoxime with one equivalent of CDI, then four to five equivalents of a reactive halide such as allyl bromide or methyl iodide (R3X) under reflux in acetonitrile for 0.5-1.5 h. Quatemization of the imidazole ring effectively promotes the reaction by increasing the electron-withdrawing effect. The target amides then are obtained by hydrolysis. High yields, neutral conditions, and a very simple procedure make this modification of the synthesis of amides by azolides a very useful alternative. 1243... 

Fischer formula, 4 697 a-Ketoxime, reduction, 2 572 Kettle soap making, 22 723, 736-737 Kettle-type reboilers, 79 510 Kevlar, 70 211, 212 79 742 20 79, 399 TD resins in, 22 589 Kevlar fibers, 73 373-376 26 760 Kew laboratories, 77 248—249 Key-and-lock principle, 7 574 Keyword-in-context (KWIC) index, 78 239 KF alumina, 5 337 Kharasch process, 79 114 Kidney, citric acid in, 6 632t Kidney Disease Outcome Quality Initiative (K/DOQI), 26 823 Kidney failure, 26 813 Kidney function, normal, 26 813 Kielselguhr 22 402... 

Beckmann rearrangement org chem An intramolecular change of a ketoxime into its isomeric amide when treated with phosphorus pentachloride. bek-man re-g ranj-mont ... 

The ammonia leach leaves the iron as an insoluble residue that is removed by filtration. The filtrate is contacted with a ketoxime reagent (e.g., LIX84I, Cognis) to extract the nickel [14]. 

We will look at three pairs of syn and anti aldoxime isomers, 9A and 9B, corresponding to R = CH3 (acetaldoxime), R = CH2CI (chloroacetaldoxime) and R = CgH5 (benzal-doxime). We will also consider the two isomeric forms lOA and lOB of acetophenone oxime, a ketoxime in which R = CH3 and R" = CeHs. 

In Table 2 are listed the hydroxylamines, oximes and hydroxamic acids for which we have determined the gas phase structures. We tried to select a representative group in each category. There are two types of oximes, as indicated, aldoximes and ketoximes. Due to restricted rotation around the C=N double bond, these can exist in two isomeric forms (except when R = H for an aldoxime and R = R" for a ketoxime). We have investigated both isomers in nearly every instance. For aldoximes, they are generally labeled syn when the H and OH are on the same side of the double bond and anti when on opposite sides. Note that the ketoximes in Table 2 contain one pair of isomers in which the >C=NOH group is not bonded to two carbons instead one bond is to a chlorine. One of these isomers wiU be of interest in Section B.D in the context of hydrogen bonding vi lone pair—lone pair repulsion. 

Oximes are a class of chemical compounds with general formula R R C=N0H, where R is an organic side chain and R may be either hydrogen, forming an aldoxime, or another organic residue, forming a ketoxime (Chart 1). 

Tundo and colleagues reported the synthesis of 4-oxazolin-2-one 110 by [3,3]-sigmatropic rearrangement of an enehydroxylamine derivative 109 resulting from the reaction of a ketoxime with dimethyl carbonate at high temperatures and in basic medium (equation 33). 

Sheradsky has found that the hydroxyl function of a ketoxime such as acetophenone oxime can be made to react with DMAD when the reaction is carried out in methanol with a basic catalyst, to give mixture of the fumarate and maleate isomers (164) in the ratio 2 1. This mixture on heating undergoes a hetero-Cope rearrangement followed by cyclization and dehydration to give dimethyl 5-phenylpyrrole-2,3-dicarboxylate (168) (Scheme 25). Similarly, Heindel and Chun have reported that vinyl ether adducts (171), obtained by the condensation of arylamide oximes with DMAD, get thermally converted into oxa-diazolines (172) or imidazolinones (174), depending on the reaction conditions. A similar reaction occurs with aromatic amidoxime-methyl propiolate adducts to give imidazoles (170) (Scheme 26). 1,2,4-Dioxazoles have been reported to be formed in the reaction of hydrox-amic acids with DMAD. - ... 

To reduce the likelihood of isocyanate-induced toxicity, some commercial companies that manufacture and use isocyanates in coating systems mask the electrophilic character of this functional group by converting it into a ketoxime derivative, as represented by 10. 

S. Blechert, Helv. Chim, Acta, 1985, 68, 1835 for a similar pyrrole-forming process by addition of a ketoxime to acetylenedicarboxylate, see T. Sheradsky, Tetrahedron Lett., 1970, 25. 

The reaction is performed as follows KOH powder is dispersed in a ketoxime solution in DMSO. The dispersion thus obtained is quickly heated and a dihaloethane is added. The mixture is stirred for another half an hour at the same temperature, and then it is poured on ice and the... 

The addition of ZnBi 2 to die tandem 1,3-azaprotio cyclotransfer-cycloaddition of a ketoxime with divinyl ketone results in rate enhancement and the exclusive formation of l-aza-7-oxabicyclo[3.2.1]octan-3-ones.79 The 1,3-dipolar cycloaddition of 1-aza-l-cyclooctene 1-oxide with alkenes produces the corresponding isoxazolidines in high yields with a minimum of polymeric material.80 The cycloaddition of thiophene-2 -carbaldehyde oxime with acetonitrile and methyl acrylate produces the 1,3-dipolar adduct, substituted isoxazolidines, and not the previously reported 4 + 2-adducts.81 Density functional theory and semi-empirical methods have been used to investigate the 3 + 2-cycloaddition of azoxides with alkenes to produce 1,2,3-oxadiazolidines.82 The 3 + 2-cycloaddition of a-nitrosostyrenes (62) with 1,3-diazabuta-l,3-dienes (63) and imines produces functionalized cyclic nitrones (64) regioselectively (Scheme 22).83... 

Aminoacetonitrile (83) can be condensed with a-ketoximes such as 82 using a stoichiometric amount of FeCl3 (Scheme 8.35). The reaction presumably proceeds with initial imine formation (intermediate 85) followed by tautomerization to give ketenimine 86 and ring closure to 2-aminopyrazine N-oxide 87, which can be isolated. In a one-pot protocol this product 87 can be further reduced with Pd/C/H2 to give aminopyrazine 84 (80% over two steps) [105]. 

A new synthesis of isoxazoles is by successive treatment of a ketoxime with butyllithi-um, the ester of a carboxylic acid and sulfuric acid, e.g. 1 -> 2 (94S989). Hitrovinyl oximes 3 (R1, R3 = alkyl or aryl) undergo oxidative cyclization to isoxazoles 4 by the action of DDQ or iodine/potassium iodide (94JHC861). Flash-vacuum pyrolysis of the 1,3-dipolar cycloadduct 5 of acrylonitrile oxide to norbornadiene results in a retro-Diels-Alder reaction to give cyclopentadiene and 3-vinylisoxazole 6 (94CC2661). 

Although Raney nickel will induce the rearrangement of an aldoxime to the amide, it will not effect the reaction with a ketoxime. This type of rearrangement has been effected with reduced copper with which... 

Oxygenation of the dianion of a ketoxime - by MoOPH (c/. Section 2.3.2.1.2) provides a-l droxy ketones after hydrolysis, albeit in relatively low yield. The equivalent process for hydrazcmes was unsuc-essful, although it appears that this was a problem associated with manipulation of the products rather than an intrinsic failure of reaction. Indeed subsequent work with hydrazone anions has shown that the process is viable. 

Various trisubstituted imidazoles (xix) have been synthesized in good yields by Shaabani et al. [19] via the condensation of 1,2-diketone or a-hydroxyketone or a-ketoxime with various aromatic aldehydes and ammonium acetate using a solid acid catalysis. 

Reduction of a ketoxime is a very useful procedure for introducing a primary amine. Many reducing agents will perform this reduction, including borane, lithium aluminum hydride, and... 

Heating of secondary carboxylic acid amides with HMPA gives rise to formation of A(-substituted V JV -dimethylamidines (310 Scheme 48). - In this procedure the secondary amide can be replaced by a ketoxime in which at least one substituent has to be an aromatic one. Similar methods were de-... 

Various other procedures have been developed for the synthesis of ct-diazo ketones and, although less popular in modem organic chemistry, may occasionally be valuable for the preparation of specific compounds. These routes include the oxidation of a-ketoximes with chloramine, the oxidation of a-ketohydrazones with yellow mercury(II) oxide or manganese dioxide, the hydroxide ion assisted decomposition of tosylhydrazones, and the diazotization of a-amino ketones. 

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