Oxime oxygen

Piperidine derivatives 161 and 164 could be cyclized to hexahydropyridooxadiazines 162, 165 via a dehydrogenation process by six oxidation equivalents of Hg(n)-EDTA. However, in both reactions, side products were also formed. From 161, piperidone derivative 163 was obtained, whereas starting from the amide 164, pyridopyrimidine 166 was isolated via cyclization by the amide nitrogen instead of oxime oxygen (Scheme 21) <1999ZNB632>. 

Analysis of intermolecular interactions in the crystal structures of oxime molecules has been used to answer that question. In all available complex structures with one central metal ion we found no coordinative bonds from the oxime oxygen to the metal, but exclusively coordination between the nitrogen atom and the metal ion (data were retrieved from the Cambridge Crystallographic Database [14]). In a comprehensive study Bohm et al. investigated complexes of oxazoles, methoxypyridines, and oxime ethers with water [15]. On the basis of interaction energies obtained... 

The introduction of an electron-withdrawing group such as acetyl at the oxime oxygen will decrease the intramolecular electron transfer reaction from the nitrogen lone pair and will enhance the aza-di-jr-methane rearrangement134-138 (equation 78). 

In oximes 305 with a nucleophile anti to the oxime oxygen atom, the cyclization is endo and a nitrogen heterocycle 306 is formed. These cyclizations are extremely useful in natural product syntheses. 

In the solid state, the metal atoms in bis(salicylaIdoximato)copper(II) show two additional contacts with the oxime oxygens of adjacent molecules, resulting in a distorted octahedral structure. However, the axial Cu—O distance (2.66 A) is much longer than the metal—ligand distances in the square-planar array (Cu—O, 1.92 A and Cu—N, 1.94 A).154 Studies by ESR of copper(II) extracts of the commercial reagent SME 529 (14 R = Me, R = C9H)9) have shown that the copper complex exists as a square-planar species in hydrocarbon solutions, but that five-coordinate adducts are formed in the presence of ammonia or pyridine.155... 

An intramolecular example (Scheme 147) has chloride being displaced by oxime oxygen generating the bicyclic products 764 <2003JHC303>. 

Similarly to derivatives phenylhydrazone, 1,4-dilithio oximes also react with an achiral ester to give a heterocyclic isoxazole ring102 (equation 33). When two of the a-carbons on an oxime of a ketone are able to undergo deprotonation, the question of the deprotonation site arises. It was found that the regioselectivity in the electrophilic reaction of 1,4-dilithioketoxime salts is especially high and the electrophile reacts with the carbon syn to the oximic oxygen. Kofron and Yeh proved that this is the case by... 

In the reaction of the lithium salt of 62 with acetone after a short lithiation time of 30 min, a 10% or 25% E Z mixture of 63 was obtained together with the addition product 64 in 65% yield (equation 42)65. The formation of only one addition product, and the quick disappearance of the -isomer, are due to a fast deprotonation process the -isomer compared with the Z-isomer, and the high rate of equilibration between the lithium compounds that greatly favors the syn anion, which reacts with acetone to give 64. These results point out that the formation of the syn lithium compounds is favored in oxime ethers for kinetic as well as for thermodynamic reasons. The kinetic preference, according to Ensley and Lohr65, is due to coordination between the lithium amide and the oxime oxygen. 

The oxime must have the structure Al. since ring closure takes place in the presence of base to give C by a nucleophilic substitution reaction. In the other isomer, the oxime oxygen atom would be too... 

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