Acyloximes

Acyloximes hydrolysis and cyclization Cationic micelles inhibit hydrolysis but not cyclization Soto etal., 1981... 

Silanes in the presence of trifluoroacetic acid reduce O-acyloximes 84 into O-acylhy-droxylamines 85 (equation 58) ... 

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. 

Photopolymerizable acyloxime ester initiators, (III), were prepared by Sasaki et al. (3) and used to produce color film. 

O-Acyloxime thioxanthone photoinitiators, (IV), have been prepared and are discussed (3). 

Copolymers of 2,3-butanedione-2-< -methacryloyl-oxime with MMA [poly (BOMA-co-MMA)], containing different amounts (7-30 mol%) of side-chain O-acyloxime moieties, have also been used [75] as macro-initiators for the photochemical grafting of styrene and acrylamide in benzene and dioxane solution, respectively,... 

Polymeric systems based on side-chain acyloxime moieties and prepared by copolymerization of 1,2-diphenyl-l,2-ethanedione-2-0-acryloyloxime with men-thyl acrylate [poly(BMOA-co-MtA)], have been used as photoinitiators in the UV curing, under nitrogen, of the HDDA/BA equimolar mixture and their activity compared with that of the corresponding low-molecular-weight structural model compound 1,2-diphenyl-l,2-ethanedione-2-0-acetyloxime (BMOAc) [61,84]. 

Photoinitiator concentration 0.5 mol% of O-acyloxime moiety in the HDDA/BA mixture. Irradiation conditions see Table 2 Determined by microwave dielectrometry Induction period Half-time of the process... 

The induction period values for the curing process of the HDDA/BA mixture in the presence of either polymeric or low-molecular-weight photoinitiators based on benzoin methyl ether moieties are found to be quite similar (Table 21) and one order of magnitude shorter than those reported for the systems based on 0-acyloxime moieties (Table 15). 

Benzotriazolyl esters of A-(alkoxycarbonyl)-A-methyl amino acids have greatly diminished reactivity relative to those of unmethylated residues,however the succinimido esters react sufficiently to be of practical use.l A variant of esters of substituted hydroxylamines that can be used to generate amide and peptide bonds is the acyloxime resin.P A new type of active ester has been developed based on the reaction of acids with substituted pyrazolinones, the products being 1-phenylpyrazolinone enol esters 83 (Scheme 24).t More than a dozen of these esters of Fmoc-valine have been characterized. They are about as reactive as esters 63, are self indicating, and show promise for the future. 

Similar results were obtained through the acylation of Grignard reagents with O-acyloximes (Scheme 23), although a higher degree of metal to substrate interaction is possible in this case. The extent to which the species drawn in Scheme 23 actually participates in the reaction is unknown. ... 

A second example relates to an eosin linked to an (9-acyloxime (10.62) where radicals are generated according to a complex mechanism [218]. 

Ph3P.Br2. Polymer-bound Ph2P.Br2 functions are also effective intermediaries in esterifications. 6 Virtually quantitative yields of esters are realised by coupling alcoholates with O-acyloximes... 

Sakuraji, M. Yoshida, H. Kinoshita, K. Utena, K. Tokumam, and M. Yoshiro, Structure reactivity relationships in triplet sensitized photolysis of aromatic ketone O acyloximes, Tetrahedron Lett. 20, 1529 (1978). 

The kinetics of acid hydrolysis of the p-methoxybenzaldehyde-O-acyloximes (7) in SDS micelles modified by BuOH has also been fitted to the PIE model [86]. The substrates differ only in their hydrophobicities, and while the acetyl derivative partitions between water and micelles, the octanoyl derivative is wholly micelle-bound. The simple PIE model fits rate data in dilute HCl [Eq. (6)], but it underpredicts observed rate constants in more concentrated acid. This increased rate was analyzed in terms of a model that does not involve a constant value of a but allows concentrations of reactive and inert ions, and Na" ", in the micellar pseudophase to increase, following Langmuir isotherms [106]. This model was reasonably satisfactory except at high 1-butanol concentration. Alternatively, the rate data in more concentrated acid can be fitted in terms of Eq. (12). 

Acylaminoalcohols Acyl formimidates N-Acyliminoesters Acylisocyanates Acyloximes... 

The second approach, by Menichincheri and her associates, used the oxime 2.2.5, prepared from baccatin III, as their key intermediate (45). Acylation with protected side chain gave an unstable acyloxime which... 

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