N-Acylimidazoles

Esterification of 5 -nucleoside derivatives with N-(aminoacyl)-imidazoles yields 2 - and 3 -(aminoacyl) derivatives and proceeds with apparently little selectivity169,170 this is not surprising in view of the facile, base-catalyzed, ester migration that may occur in 2 (3 )-esters of the D-ribofuranose system (see Section VII,1). 

Differentiation between the secondary hydroxyl groups in methyl 4,6-O-benzylidene-a-D-glucopyranoside was observed on reaction with methyl benzoate-sodium methoxide at 200° for 45 minutes the 2- and 3-esters and the 2,3-diester were formed176 in the molar ratios of 55 23 10. 

Direct esterification of D-glucose by heating with 50% acetic acid at 100° was reported to yield 26-30% of the 6-acetate after chromatography on cellulose, together with unchanged starting-material and 

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Table 1—2. Relative rates for aminolysis and neutral hydrolysis of N-acylimidazoles [ 10-3 M solutions, 25 °C].[14]...

Table 3-1. Monoesters prepared from carboxylic acids and alcohols or phenols using AyV -carbonyldiimid-azole (CDI), N-acylimidazole (RCOIm), or AyV -sulfinyldiimidazole (ImSOIm).

Photochemical treatment of an N-acylimidazole results in a 1,2-shift (N-C migration) of the acyl group to give a mixture of 2- and 5-acylimidazoles (photo-Fries products) [1],[2]... 

Conformational factors in the photolysis of N-acylimidazoles leading to Norrish type II products or cyclobutanols have been discussed in reference [7]. 7V-Acylimidazoles have been irradiated in tetrahydrofuran using a low-pressure mercury lamp (quartz well,... 

Mechanisms of Hydrolysis of N-Acylimidazoles and N-Acyl-benzimidazoles, Ace. Chem. Res. 26, 325 (1993). 

T.H. Fife, Kinetic and Mechanistic Effects of Ease of C-N-hond Breaking in Amide Hydrolysis, The Mechanisms of Hydrolysis of N-Acylimidazoles and N-Acyl-benzimidazoles, Acc. Chem. Res. 26, 325 (1993). 

N-acylimidazoles may be prepared269-271, and because of their relevance to enzyme chemistry (via histidine272) they have been the subject of much... 

Unsaturated ketones.9 Allyltris(diethylamino)titanium (1) reacts with N-acylimidazoles (2) to give almost exclusively (3,7-unsaturated ketones (equation I). A similar reaction is observed with the crotyltris(diethylamino)titanium 3 (equation... 

Methyl esters may be prepared by reaction of the aromatic carboxylic acid with diazomethane (cf. Section 4.2.25, p. 433) or, more conveniently, by reaction with a boron trifluoride-methanol reagent. The latter procedure is illustrated by the preparation of methyl m-chlorobenzoate and dimethyl terephthalate (Expt 6.164). t-Butyl esters may be prepared by conversion of the acid into an N-acylimidazole by reaction with N,N -carbonyldiimidazole, followed by reaction with t-butyl alcohol in the presence of DBU62 (Expt 6.165). 

Analogous to the N-acylimidazoles, in which the enhanced reactivity of the acyl group towards nucleophiles is favoured by inclusion of the amide-nitrogen lone electron pair in the/ -system of the heterocycle, nucleophilic attack on the trityl part of the N-trityla-zoles also should be a facile process (11). 

Peracids can also be prepared from reaction of hydrogen peroxide with acyl halides, anhydrides, amides, dialkyl phosphates, N-acylimidazoles, aromatic aldehydes, lipase catalysis and esters (Figure 2.38).100-107... 

Tetraacetylethylenediamine (TAED) and pentaacetylglucose (PAG) are employed as bleach pre-cursors of peracetic acid this allows the bleach to occur at a temperature lower than when hydrogen peroxide is used. Perhydro-lysis of the sulfonated aromatic ester, shown in Figure 2.38, gives superb bleach performance on textiles, probably due to the surface active properties of the compound. The acyl dialkyphosphates and the N-acylimidazoles are also effective peracetic acid precursors at low temperature. 

The concentration of N-acylimidazole in the reacting solution is high enough for a detection by UV spectrophotometric measurement [ 5, 29]. 

As mentioned earlier (Section IV,B,l,a) N-acylimidazoles, although resistant to quaternization by virtue of the electron-withdrawing nature of the acyl group, can be methylated by reagents such as methyl fluorosulfo-nate and trimethyloxonium fluoroborate. ... 

N-Acylimidazoles (azolides) have continued to provide a synthetic source of acid derivatives,and the various olysis reactions of these compounds have been studied. " The reactions of acetyl-imidazolium ions with amines have been found to depend largely on amine basic) The thermal decarboxylation of JV-alkoxycarbonylimid-... 

There was a continuous increase in the second order rate constant (k at) from 20- to 100-fold at pH 9.15 through the Sn series. The nearly equivalent catalytic efficiencies of the copolymer and homopolymer grafts suggest that the major hydro-phobic interaction involved the N-acylimidazole intermediate. However, throughout this series, the copolymers were still better catalysts than the homopolymer. 

The imidazole-catalyzed isomerization of penicillin into penidllenic acids probably involves initial nucleophilic attack of imidazole on penicillin. Imidazole-catalyzed N-acylimidazole hydrolysis was used by Charton in obtaining a values (see Section III,I). 

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