Oximes aromatic

Despite the numerous entries in Table 2, there are few entries that correspond to trustworthy species. More precisely, there are but two derived from contemporary, well-characterized measurements, where contemporary means the primary data were reported since the mid-20 century. These are for pyridine-2-carboxaldoxime and salicylaldoxime. The formal solid phase reaction 24 is but 5 kJmol endothermic. 

This near-thermoneutrality gives confidence in both values of the oxime enthalpies of formation, the salicylaldoxime some 50 years old and the pyridine-2-carboxaldoxime within a year from when the chapter was submitted. Consider now the formal solid phase reaction 25 involving the some decades older pyrrole-2-carbaldoxime.  

As written, the reaction is endothermic by ca 30 kJmoD. Pyrrole and pyridine are both 6-71 nitrogen-containing heterocycles. However, the former is electron-rich while the latter is electron-deficient and so conjugative stabilization mechanisms are different for the two species. Furthermore, the former can form one more hydrogen bond per molecule than the latter, a feature that may account for pyrrole-2-carboxaldehyde being a solid while pyridine-2-carboxaldehyde is a liquid. We wonder if either difference accounts for the profound lack of thermoneutrality for the above reaction. 

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 

Although the existence of syn and awf/-isomers of monooximes with the structure R C(=N0H)R has long been known, there are surprisingly few studies that address the question of the difference in their enthalpies of formation. Reference 6 reports values for two isomeric acetaldoximes, a high melting solid and a low melting liquid as always, no primary reference is available. The respective condensed phase enthalpies of formation of the two isomers are —77.9 and —81.6 kJmoD, respectively. 

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Imines are easily reduced and rarely accumulate (62,83). Hydroxylamines are reduced relatively slowly and can be obtained in good yield platinum in acidic media appears to be the preferred system (6,27,54,58,65). Best yields are obtained from oximes of aliphatic carbonyls aromatic oximes give amines. 

Soufiaoui reported that arylnitrile oxides 10 can be generated under microwaves not only from aromatic oxime chlorides, such as 174, by the action of alumina (Method A) but also from aryloximes, such as 176, by the addition of a chlorination agent, N-chlorosuccinimide (NCS), supported on alumina (Method B) (Scheme 9.54) [29a]. Both methods afforded identical cydoadducts in similar yields - when indene was used as the dipolarophile the yield was 86%. In the absence of alumina, method B fails (reagents are less reactive and decompose) and method A does not yield any cydoadduct but a dimer of the dipole. 

The aromatic oximes usually give secondary amines from rearrangement, sometimes as side products and sometimes as main products. 

The Ponzio reaction provides a useful route to gem-dinitro compounds and involves treating oximes with a solution of nitrogen dioxide or its dimer in diethyl ether or a chlorinated solvent. The Ponzio reaction works best for aromatic oximes where the synthesis of many substituted aryldinitromethanes have been reported. Compound (56), an isomer of TNT, is formed from the reaction of dinitrogen tetroxide with the oxime of benzaldehyde (55) followed by mononitration of the aromatic ring with mixed acid. Yields are usually much lower for aliphatic aldoximes and ketoximes. " The parent carbonyl compound of the oxime is usually the major by-product in these reactions. 

Preparative scale reduction of oximes at a mercury or lead cathode in acid solution has been used in the conversion of the carbonyl function to amine. Originally, 30-50% sulphuric acid was used as solvent [195] but ethanol with dilute hydrochloric acid is usually satisfactory. Aliphatic and aromatic oximes give amines in 64-86% yields [196]. Aromatic ketoximes are also reducible in alkaline solution and acetophenone oxime has been converted to 1-phenylethylamine in a tri-potassium orthophosphate solution [197], The reduction of oximes in acid solution is tolerant of many other substituents as indicated by a number of examples [198, 199, 200. Phenylglyoxa monoxime in acid solution is however reduced at both the carbonyl and the oxime centres by sodium amalgam to yield 2-amino-1-phenylethanol [201]... 

Diborane in THF has been successfully used for reduction of aliphatic and aromatic oximes to hydroxylamines. Reported yields are highly variable although the low... 

Enantioselective reduction of ketoxime ethers with chiral boron hydrides produces chiral 0-alkylhydroxylamines with variable ee. Reduction of oxime ethers of type 94 (equation 65) with norephedrine-derived oxazoborolidine 95 proceeds with very high ee. However, an analogous reduction of acyclic aromatic oximes with chiral oxab-orazolidines produced a mixture of amine and hydroxylamine . 

Mahadevan reviewed research up to 1973, with respect to the pathways of oxime metabolism in plants, and evaluated a series of aliphatic and aromatic oximes that are precursors for the biosynthesis of plant secondary metabolites (as opposed to basic metabolism products that are essential for cell survival), such as cyanogenic glycosides, glucosinolates and certain phytohormones . Some of these oximes are shown below. 

Bovine aldose reductase Inhibited by ahphatic, cychc and aromatic oximes, using benzyl alcohol as substrate 123... 

In contrast to the plethora of reactions between DIB and -containing compounds, BTI has so far limited applications. Among them, its reactivity with oximes is of interest, because several products are formed, depending on the substrate [36]. Aromatic oximes were converted directly into ketones in good yield, whereas aliphatic ketoximes gave isolable intermediates, i.e. 1-nitroso-l-trifluoroacetoxy-alkanes. 

Aromatic oximes, for example, can be converted back to carbonyl compounds with only 2 equiv. of PDC in 1 h at rotmi temperature. PDC will also cleave enol ethers. ... 

Electrochemical reduction of aromatic oximes in DMF containing phenol as proton donor results in amines analogous to the reduction in aqueous acidic solvent [61]. 

Leclerc, G., Mann, A., Wermuth, C. G., Bieth, N., Schwartz, J. Synthesis and (3-adrenergic blocking activity of a novel class of aromatic oxime ethers. J. Med. Chem. 1977, 20, 1657-1662. 

In contrast to this imide-based synthesis, amides of the type RC(0)NH2 are decarbonylated to primary amines (RNH2) with chlorine in the presence of base. This process, often called the Hofmann reaction, involves an intermediate isocyanate (R-N = C = 0) (Fieser and Fieser, 1961 Sandler and Karo, 1983). Aromatic oximes, lacking an a-hydrogen, react with chlorine to form intermediates that are converted to nitrile Af-oxides with base. (Nitrile N-oxides are highly reactive species.)... 

One of the classical methods for the synthesis of pyrazines involves dimerization of an a-amino carbonyl compound and subsequent aromatization. Oximes have often been used as the latent functionality to generate the amine by a variety of reductive processes. 3-Oxo-2-oximinobutanoic esters or the amides (146), which are formed by nitrosation of acetoacetic acid derivatives, are reduced by catalytic hydrogenation <82CPB3424, 91JHC1731> or titanium(III)-induced reduction <88H(27)il23> to give the tetrasubstituted pyrazines (147) (Equation (17)). 

Recently, Increasing interest has been given to the photochemical behavior of carbon-nitrogen double bond. Imlnoradlcals were generated by the photolysis of aromatic oxime esters In benzene (37). These authors confirmed the N-0 bond cleavage proposed for the photolysis of O-acylated Imlnoketones. 

Aliphatic and aromatic oximes (such as LIX63 and LIX65N), quinolines (for instance, KELEX 100), polyols (e.g. phenyl glycol)... 

Soon afterward, the 3-hydroxylation of enones was published by Melchiorre and co-workers [70]. The authors obtained 1,3-hydroxy ketones with moderate yields and good stereoselectivities using aromatic oximes as the oxygen nucleophile. The use of a catalytic primary amine salt in which both the cation and the anion are chiral was found to be crucial. 

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