Acyl oximes

Oximes unsaturated synthesis, 1, 462 Oxindole, 3-acyl-oximes... 

In contrast, oxime ethers and esters are usually stable in solution but the E/Z isomerization can be induced by acids " or by irradiation ". Recently, Narasaka and colleagues"" "" studied the equilibration-isomerization of (E)-O-acyl oximes 239 in the presence of an acid in a nucleophilic solvent (equation 71). Isomerization probably proceeds via protonation of the oxime nitrogen followed by addition-elimination of a nucleophilic solvent until the equilibrium of E and Z isomers is achieved. The isomerization of the more labile 0-acyloximes occurs either by an Sjv2 substitution at the oxime nitrogen with acids and/or by acyl exchange through the formation of a mixed anhydride and the free oxime. 

Durch Umsetzung mit Nitroso-Verbindungen (z. B. Nitrosylchlorid, Nitrosobenzol) erhalt man aus l-Alkylamino-l-alkylthio-3-oxo-l-alkenen 5-Acyl-4-alkylthio-imidazole2SS. Mit Nitrosylchlorid verlauft die Reaktion iiber die entsprechenden a-Acyl-oxime als Zwischenpro-dukte, die isoliert und in einem getrennten Schritt cyclisiert werden konnen. 

Auch O-Acyl-oxime lassen sich zu den entsprechenden primaren Aminen reduzieren. Da hierbei jedoch nicht nur der Oxim-Teil des Molekiils sondern auch der Acyl-Teil reduziert wird, benotigt die Reduktion z. B. bei Verwendung von Diboran die doppelte Menge an Hydrid wie bei der Reduktion von 0-Alkyl-oximen4. 

The second arm of the scheme involves first a reaction of the (3-beta ketoester (7-1) with nitrous acid. The first product from nitrosation on the activated carbon spontaneously rearranges to afford oxime (7-2). Treatment with acetyl chloride then affords the (9-acylated oxime (7-3). Condensation of that compound with the imino ether from propionitrile leads to the formation of the imidazole (7-4). 

Another important consideration was the fact that the absorption maxima of oxime acrylate monomers could be tuned to the desired wavelength by the selection of desired ketone or aldehyde chromophore from whence the oxime was originally synthesized. In our design, UV photocrosslinking followed dye-sensitized visible polymerization which formed a soft gel. It is very important to be able to choose the absorption window for the crosslinking reaction to prevent interfering absorption, if any, from the residual dye initiator. Acyl oximes as part of the backbone of a photodegrading polymer chain have been studied by Smets [217],... 

Transition metal hydroxyoxime complexes have been reviewed very recently.2507 Their use in both analytical chemistry and extraction metallurgy is well known. The square planar structure of the bis chelate complex NiL (347) with the deprotonated 2-hydroxybenzaldoxime (HL) is typical of this series of nickel complexes.2508 Their bis adducts, NiLJ, with bases such as py, substituted pyridines and cyclomethyleneimines, are six-coordinate.2509 The acyl oxime (H2L) complexes are similar to the aforementioned complexes being either square planar bis chelates Ni(HL)2 (348) or octahedral bis adducts, Ni(HL)2B2.2507 When the acyl oxime acts as a dibasic ligand L, the corresponding (NiL) complexes are insoluble and involve extensive polymerization. 

A further type of linker, especially designed for facile nucleophilic cleavage, is the oxime linker. Oximes of resin-bound ketones or aldehydes can be acylated to yield O-acyl oximes, which are readily cleaved by a variety of nucleophiles (Table 3.14). A widely used support of this type is p-nitrobenzophenone oxime resin (Kaiser oxime... 

A number of formal ATRC of O-acylated oximes (review [328]) catalyzed by... 

A reductive acylation of oximes was developed621. Acylated oximes in the presence of excess acetic anhydride in dimethylformamide are readily reduced to imines using... 

In an analogous manner, the generation of alkyl radicals in benzene solution by the O-acyl oxime method results in the formation of alkylbenzenes with moderate to good yields for simple acids (equation 55). Use of pyridine as solvent leads to the formation of alkylpyridines as mixtures of ortho, meta and para isomers in which the para isomer predominates. The 0-acyI benzophenone oxime chemistry can also be applied to aryl acids in benzene or pyridine, resulting in the formation of mixed biaryls. A closely related method involves photolysis of mixed anhydrides of arenecarboxylic acids with the hydrox-amic acid A -hydroxy-Z-pyridone in benzene solution (equation 56). 

Benzylalkohol 4-Nitro- IV/ld, 165/ 175 (COOH - CH2OH), 378 (aus O-Acyl-oxim) Vl/lb, 210f. 

Table 12 Reduction of O-Alkyl, O-Aryl and O-Acyl Oximes to O-Substituted Hydroxylamines... 

The reduction of 0-acyl oximes to 0-acylhydroxylamines also is accomplished under mild conditions with pyridine-BHs/HCl, NaBHsCN/HCl, and NaBHsCN/AcOH in a similar fashion as with other oxime derivatives. In addition, BH3 (1 equiv.) and the combination of EtsSiH/TFA also effects efficient reduction. With the former reagent, rearrangement to N-acylhydroxylamines has been observed (equation 3). Representative examples of 0-acyl oxime reductions are presented in Table 12. The related derivatives nitrones are also reduced by LAH, or NaBHsCN/H to hydroxylamines (equation 4).202... 

---