1- Acylimidazoles reactions with

The functional micellized surfactant contained both imidazole and hydroxyethyl groups and the final products of reaction with p-nitrophenyl alkanoates are acyl derivatives of the hydroxyethyl group. However, these O-acylated products were formed from an acylimidazole intermediate which... 

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). 

When (253) reacts with phosgene the 1-acyl chloride product (254) can react with amines to give amides (79LA1756X while in a further transfer reaction with ketones the compounds (255) and (256) are produced (Scheme 146) (80H(14)97). Acylation of aromatic hydrocarbons using 1-acylimidazoles in the presence of trifluoracetic acid gives high yields provided that the aryl compounds are electron rich, e.g. p-dimethoxybenzene, thiophene, anisole <80BCJ1638). 

Now the seven-membered ring must be built up. Here an azole-based reagent, CDI, carbonyl di-imidazole proves invaluable. Reaction with 232 gives the acylimidazole 233 and this acylates the potassium enolate of nitromethane in good yield to give 234 and hence, by reduction, the diamine 235. The /V-benzyl group can now be removed and the synthesis of the seven-membered ring is completed with the one-carbon electrophile HC(OEt)3. 

Acylimidazoles also give carboxylic anhydrides on reaction with carboxylic acids.972... 

Activation of Carboxylic Acids Synthesis of Acyl Imidazoles. iV,AA-Carbonyldiimidazole (1) converts carboxylic acids into the corresponding acylimidazoles (2) (eq 1). The method can be applied to a wide range of aliphatic, aromatic, and heterocyclic carboxylic acids, including some examples (such as formic acid and vitamin A acid) where acid chloride formation is difficult. The reactivity of (2) is similar to that of acid chlorides, but the former have the advantage that they are generally crystalline and easily handled. Isolation of (2) is sirr5>le, but often unnecessary further reaction with nucleophiles is usually performed in the same reaction vessel. Conversion of (2) into acid chlorides (via reaction with HCl), hydrazides, hydroxamic acids, and peroxy esters have all been described. Preparation of the more irr5)ortant carboxylic acid derivatives is described below. 

Aldehydes and Ketones from Carboxylic Acids. Reduction of the derived acylimidazole (2) with Lithium Aluminum Hydride achieves conversion of an aliphatic or aromatic carboxylic acid to an aldehyde (eq 6). DiisobutyUduminum Hydride has also been used, allowing preparation of a-acylamino aldehydes fromiV-protected amino acids. Similarly, reaction of... 

Electroreduction of styrenes or alkyl methacrylates in the presence of aliphatic acid anhydrides or N-acylimidazoles with zinc anode brought about novel one-pot vicinal double C-acylation to afford the corresponding 1,4-diketones in good to high yields. This is an example of cross-coupling reaction with no use of halogenated compounds. 

Reactions with 1-acylimidazoles Ketones from 1-acylimidazoles... 

The synthetic utility of a-trimethylsilyl ester enolates has been extended by an investigation of their behaviour with acylating agents. In theory, three products are possible, and while ethyl acetate and acetamide proved inert and acetyl chloride gave a complex mixture, reaction with acylimidazoles led smoothly to the formation of jS-ketoesters in 70—94 % yield. 

Mixed carbonic anhydrides, acyl guanidine, N-acylimidazoles, N-acyl-N -methylimidazolium chloride and acyl phosphates are other agents that have been used to esterify starch in water [65-76]. Starch esters containing carboxylic acid group have been prepared by reaction with cyclic dibasic anhydrides [65]. 

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]... 

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]... 

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

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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