Trifluoroacetic anhydride acylating agent

The active acylating agent may be the protonated mixed anhydride, or, alternatively, the anhydride m dissociate to the acylium and trifluoroacetate ions ... 

Mixed anhydrides with trifluoroacetic acid are particularly reactive acylating agents.48 For example, Entry 5 in Scheme 11.4 shows the use of a mixed anhydride in the course of synthesis of the anticancer agent tamoxifen. 

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... 

When carboxylic acids are treated with trifluoroacetic anhydride, mixed anhydrides (acyl trifluoroacetates) are formed. These compounds are useful acylating agents. What is the product of the reaction of an alcohol with acyl trifluoroacetate ... 

On the other hand, 9-benzyl-2-(tritluoromethyl)hypoxanthinc (18) is prepared by acylation of 5-amino-l-benzylimidazole-4-carboxamide with trifluoroacetic anhydride and subsequent heating of the intermediate. A number of dehydration agents fail to effect this ring closure. ... 

The rate of acetylation of 0-(hydrox3Tnethyl)cellulose (and other hydroxy compounds) by mixtures of carboxylic acids and their anhydrides has been found to increase greatly in the presence of trifluoroacetic acid. The acceleration is very much less with mono- and tri-chloroacetic acids, presumably because they form unsymmetrical anhydrides which are less effective acylating agents than acyl trifluoroacetates. The exceptional acylating power of the latter anhydrides is shown by their use in the synthesis of alkyl aryl ketones from polyalkylbenzenes, phenyl ethers, furan, and thiophene under mild conditions. The principle has been extended to include acids... 

The fact that, in the reaction formulated above, anisole yields the acetyl and not the trifluoroacetyl derivative means that the mixed anhydride is a more reactive acylating agent than trifluoroacetic anhydride. However, the pure anhydride alone is capable of effecting acylation. It reacts with azulene (blue) in carbon tetrachloride without catalyst at room temperature to give 1-trifluoroacetylazulene (red) in high yield. "... 

Acylations with carboxylic acids and anhydrides have been carried out with sulfuric acid as both solvent and catalyst, the reactive acylating agents from acyl halides probably being haloacyloxonium ions. Trifluoroacetic anhydride offers a rather milder reagent for reactions of carboxylic acids, with mixed anhydrides being likely intermediates. However, polyphosphoric acid remains the most widely used dehydrating agent for acylations by carboxylic acids. 

Trifluoroacetic anhydride obtained by action of P203 on the acid is widely used in organic chemistry as an acylating agent in presence of acid. 

Carboxylic acids react with trifluoroacetic anhydride to give reactive acylating agents that are especially useful for the acylation of hindered alcohols and phenols ... 

The eonversion of 34 to 35 aeeording to Cohen and eo-workers was speculated to go through a mechanism that involved a triacylated species as the requisite intermediate. The facility of the reaction with trifluoroacetic anhydride was due to its high reactivity as an acylating agent and/or the high electrophilic reactivity of the trifluoroacetyl carbonyl group. 

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