1-Acylimidazole

Ac-Imidazole, PtCl2(C2H4), 23°, 0.5-144 h, 51-87% yield. Platinum(II) acts as a template to catalyze the acetylation of the pyridinyl alcohol, C5H4N(CH2) CH20H. Normally acylimidazoles are not very reactive acy-lating agents with alcohols. 

Acylimidazoles and related amides in which the nitrogen atom is part of an aromatic ring hydrolyze much more rapidly than other amides. A major factor is the decreased resonance stabilization of the carbonyl group, which is opposed by the delocalization of the nitrogen lone pair as part of the aromatic sextet. 

Acyclic dienes, 433 Acylation, Friedel-Crafts, 329 A-Acylimidazoles, 78 Acyloxyphosphonium salts, 79 Adamantane, 354... 

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

Steric distortion by phenyl rings in the 4 and 5 positions of Af-acylimidazoles further gave rise to enhanced rates of hydrolysis proceeding in a concerted manner.[17]... 

The diimidazolide is very hygroscopic.[24] In analogy to CDI it is also called phenoxyphosphoryldiimidazole. Just like CDI, it reacts with carboxylic acids to give the corresponding JV-acylimidazoles. 

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

For the aminolysis of TV-acylimidazoles in dry tetrahydrofuran a bimolecular reaction is suggested. The rate constant for conversion of AT-acetylimidazole with an ammonia-saturated solution in tetrahydrofuran at 25 °C was found to be 0.01 min-1, with t1/2 = 69.3 min.[3]... 

It is interesting that one observes exclusive TV-acylation of ethanolamine even when the molar ratio of polymer-bound acylimidazole to amine is 1 2. 

Chemical modifications of proteins (enzymes) by reacting them with iV-acylimidazoles are a way of studying active sites. By this means the amino acid residues (e.g., tyrosine, lysine, histidine) essential for catalytic activity are established on the basis of acylation with the azolides and deacylation with other appropriate reagents (e.g., hydroxylamine). 

The reaction of iV-acylimidazole with dimethyl acetylenedicarboxylate in acetonitrile at 25 °C provided (2-imidazolyl)maleates and, as by-product, dimethyl(imidazol-l-yl)-fumarate tl57]... 

Organo copper and lithium enolates of cyclic ketones, lactones, and lactams or acyclic ketones are converted with acylimidazoles or imidazole-N-carboxylates into the corresponding / -diketones or / -ketoesters ... 

Electron-rich aromatic compounds such as durene, p-dimethoxybenzene, mesitylene, anisole, thiophene, and fluorene can be benzoylated or acetylated by the corresponding Af-acylimidazole in trifluoroacetic acid to give the corresponding benzophenone or acetophenone derivative in good yield (Method A). As the actual acylating agent, a mixed anhydride of trifluoroacetic acid and benzoic acid has been proposed 1973... 

Acylimidazoles and 1-acyl-3,5-dimethylpyrazoles reacted with phenols and phenol ethers in the presence of AICI3 and at higher temperatures (110-120 °C) to give ketones in moderate yield.1"1... 

Sulfoxides and sulfones are acylated in the a-position by aroyl- or acylimidazoles in the presence of methyllithium as base [100]... 

In the reaction of 1,3-dithiane oxide anions with iV-acylimidazoles the optimum procedure involved a sodium hexamethyldisilazide/butyllithium mixture as base [101]... 

A-Acylimidazoles are easily reduced to the corresponding aldehydes with LiAlH4 in THF or ether as solvent.[1] Thus, aliphatic, conjugated aliphatic, aromatic, conjugated aromatic, and heteroaromatic aldehydes can all be obtained in this way in moderate to high yields. 

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,... 

Acylimidazoles in the presence of benzophenone lead to oxetanes on irradiation with a medium-pressure mercury lamp [8]... 

Irradiation of 1-acyl-1,2,4-triazoles, contrary to A-acylimidazoles affords no photo-Fries products, but instead forms aldehydes and other products via the corresponding acyl radicals.t9]... 

Figure 3.12 CDI reacts with carboxylate groups to form an active acylimidazole intermediate. In the presence of an amine nucleophile, amide bond formation can take place with release of imidazole.

Having seen that the excess acidity method works for second-order as well as for first-order acid-catalyzed processes, it is of interest to see whether it extends to reactions that are not acid catalyzed. The hydrolysis of acylimidazoles, equation (68), takes place in aqueous acids the substrate is protonated on the ring nitrogen in the pH range, and in acid media the reaction rate constants decrease steadily with increasing acidity.251,253... 

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