Mixed trifluoroacetyl

A very convenient synthetic procedure for nitration involves the mixing of a nitrate salt with trifluoroacetic anhydride. This presumably generates trifluoroacetyl nitrate. 

The trifluoroacetyl group, which is extremely labile towards hydrolysis, may be readily removed under mild conditions from carbohydrate mixed-esters. Thus, treatment of an acetone solution of methyl... 

A closely related method does not require conversion of enantiomers to diastereomers but relies on the fact that (in principle, at least) enantiomers have different nmr spectra in a chiral solvent, or when mixed with a chiral molecule (in which case transient diastereomeric species may form). In such cases the peaks may be separated enough to permit the proportions of enantiomers to be determined from their intensities.145 Another variation, which gives better results in many cases, is to use an achiral solvent but with the addition of a chiral lanthanide shift reagent such as tris[3-trifluoroacetyl-d-camphorato]europium-(III).146 Lanthanide shift reagents have the property of spreading nmr peaks of compounds with which they can form coordination compounds, e.g., alcohols, carbonyl compounds, amines, etc. Chiral lanthanide shift reagents shift the peaks of the two enantiomers of many such compounds to different extents. 

Nitration of 1-arylpyrroles with acetyl nitrate and 1-arylpyrroles and l-(2-ethoxycarbonylbenzyl)pyrrole with trifluoroacetyl nitrate gave 2- and 3-nitro products. The latter were further nitrated with mixed nitric and sulfuric acids.37... 

This mixed anhydride, in combination with a base such as 2,6-di-f-butyl-4-methylpyridine, is a potent reagent for trifluoroacetylation. The reaction of 1 with anthracene results in formation of the 9-trifluoroacetyl derivative (81% yield). Cyclohexanone reacts with 1 to form the enol trilluoroacetate (72% ield). The reaction of trityl chloride and 1 leads to trityl triflate. ... 

Although the 2,3-dimethyl and 3,4-dimethyl ethers of L-rhamnose were known, the 2,4-dimethyl ether had not been synthesized prior to its preparation through a trifluoroacetyl intermediate. - The synthesis started from methyl 2,3-0-isopropylidene-a-L-rhamnopyranoside this was methylated and the acetal group removed, to give methyl 4-0-methyl-a-L-rhamnopyranoside (6). Conversion to the 2,3-bis(trifluoroacetate) (7) was readily achieved with trifluoroacetic anhydride in the presence of sodium trifluoroacetate. As expected, the trifluoroacetate (7) was completely de-acylated by treatment with alcohol, regenerating (6) this process was complete after 25 min. at room temperature. The procedure for selective de-esterification was based on the observation that, if excess carbon tetrachloride (6 vol.) is present, very little methanolysis occurs. By use of a mixed methanol-carbon tetrachloride solvent (65 35 vol./vol.), the meth-... 

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. "... 

Anhydrides may also be employed instead of an acid chloride. The mixed anhydride of acetic and formic acid reacts with 1-iV-morpholinocyclohexene to give 2-hydro-xymethylenecyclohexanone . Acylation of isobutyraldehyde enamines with trichloroacetic anhydride in tetrahydrofuran at room temperature gives the a-trichloromethyl-j5-trichloroacetyl adduct . This occurs by initial ) -acylation to give the acyl iminium trichloroacetate, followed by decarboxylation and nucleophilic addition of the tri-chloromethyl anion to the iminium group. Trifluoroacetic anhydride under the same conditions just gave the -trifluoroacetyl derivative . 

Folic and homofolic acid analogues with the glutamic acid moiety replaced by glycine and DL-alanine were described [72] as part of a larger series consisting mainly of compounds with dicarboxylic acid side-chains (vide infra). A -Acetyl-A - trifluoroacetylpteroic acid andfV -acetyl-V°-trifluoroacetyl-homopteroic acid was each activated with isobutyl chloroformate, the mixed anhydride was condensed with ethyl glycinate or ethyl DL-alaninate, and all... 

The derivatives used for GLC are indicated by methyl, acetyl, TFA (trifluoroacetyl) and TMS (trimethylsilyl) at the head of the list of compounds separated. All available hydroxyl groups are assumed to be substituted except in the case of partial or mixed derivatives where the positions of substitution are given under the appropriate monosaccharide. 

An efficient and eco-friendly procedure for the small-scale acylation of forocene with carboxylic acids is based on the in situ production of the mixed carboxylic-trifluoroacetyl anhydride [76]. The reaction is simply performed by adsorbing ferrocene on the surface of activated alumina (preheated at 150°C for 3 h) and adding a mixture of carboxylic acid and trifluoroacetic anhydride at room temperature for a selected time. Products are recovaed in 55-98% yield simply by elution with diethyl ether. 

---