V-Trifluoroacetylation

A sensitive method for primary amines is shown in reaction 2, leading to the corresponding 7V-benzenesulfonyl-/V-trifluoroacetyl derivatives. These can be determined by GC-ECD using SE-30 columns LOD 1-5 pg, which is about 200 times more sensitive than GC-FID. The method was applied for determination of phenethylamine (33) in urine110. This analysis was performed also by LLE into n-pentane, derivatization to the benzenesulfonamide and GC-FPD using a capillary column recoveries of aliphatic primary amines in urine were 91-107%, RSD 0.2-4.5%111,112. Amines in environmental waters and sediments were determined after LLE with dichloromethane, derivatization with benzenesulfonyl chloride and GC-SIM-MS LOD 0.02-2 pg/L of water and 0.5-50 ng/g of sediment113. 

A new synthetic method of benzofuran was reported (equation 39). The [3,31-sigma-tropic rearrangement of Af-trifluoroacetyl enehydroxylamines 136 obtained in situ by acylation of oxime ethers 135 in the presence of trifluoroacetic anhydride lead to the synthesis of cyclic or acyclic dihydrobenzofurans 138. The effects of base and temperature on the reaction products were studied. A similar pathway to that of Fisher indolization was proposed. The acylimine formed by the [3,3]-sigmatropic rearrangement of the V-trifluoroacetyl enehydroxylamine 136 gave the dihydrobenzofuran 137 by an intramolecular cyclization or the benzofuran 138 after elimination. 

A recent procedure which utilizes the pivaloyl derivative of o-bromoaniline as one of the fragments is also a type llac approach. The compound is converted to its dilithio derivative at -78 °C. Reaction with a-halo ketones then affords indole hydrates by N-alkylation and reaction of the o-lithiated position with the carbonyl group dehydration subsequently yields indoles (equation 108) (81TL1475). The (V-trifluoroacetyl and N-t-butoxycarbonyl derivatives of o-bromoaniline exhibit similar reactivity. 

Recently Barton et al. (98) reported extremely selective high-yield reactions at —78°C in CFCl3 between fluorine and adamantane and substituted adamantanes. 1-Fluoroadamantane is produced in 84% yield from adamantane, and 3-fluoro-/V-trifluoroacetyl adamantane is produced from /V-trifluoro-acetyladamantane in 83% yield (98). In addition, Barton, Hesse and coworkers reported regioselective reactions of a number of steroids with yields ranging from 25 to 75% (99). Some of the selectivity in the steroids is rather remarkable and is thought to result from electrophyllic reactions that are strongly influenced by polar substituents on the molecules and by solvents (98,99) p. 73. Although the yields are very impressive in these reports, no information is provided on the conversion or the scale. 

In an alternative route employing fewer overall steps, Borbas and Lipt k119 synthesized the trisaccharide hapten as a 4-aminophenyl glycoside protected as the (V-trifluoroacetyl derivative 13 for potential conjugation to protein.108 Ethyl 1-thio-a-L-rhamnopyranoside as the 2,3-O-diphenylmethylene acetal 23 was the precursor for both rhamnosyl residues. Condensation of 23 with glycosyl bromide 24 with silver triflate as promoter, followed by O-deacetylation and O-benzyliden-... 

Scheme 8.23 Sammakia s chiral alcohol-catalyzed KR of a-acetoxy- and a-(/V-trifluoroacetyl) amino acid-N-acyloxazolidinethiones [195, 196].

For GC, the two most useful chiral reagents are /V-trifluoroacetyl-L-prolyl chloride (TCP) and menthyl chloroformate (MCF). TCP is used for the resolution of amines and MCF for alcohols. At best the reagents are 99% optically pure, but they can be as little as 90% pure. 

Preparation of R-(+)-3-/V-trifluoroacetyl-2,3-dihydro-7-methyl-1 H-pyrrolo-[1,2- a]-benzimidazole... 

The resolution of optically active compounds by gas chromatography with chiral phases is a well-established procedure, and the separation of iV-perfluoro-acetylated amino acid ester enantiomers in 1967 was the first successful application of enantioselective gas-liquid chromatography [59] Ammo acids have been resolved as their /V-trifluoroacetyl esters on chiral diamide phases such as N-lauroyl-L-valine terr-butylamidc or 7V-docosanoyl-L-valme /ert-butylamide [40,41,... 

L-Proline, /V-trifluoroacetyl-, 56,125 L-PROLYLGLYCYLGLYCINE, A-CARBO-BENZOXY-3-1IYDROXY-, ETHYL ESTER, 56, 88... 

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... 

Abbreviations ABS, acrylonitrile-butadiene-styrene terpolymer PB, polybutadiene PC, polycarbonate PS, polystyrene PET, poly(ethylene terephthalate) PBT, poly(butylene terephthalate) SBR, styrene-butadiene rubber TEA, V-trifluoroacetylated polyamides PMMA, poly(methyl methacrylate) SAN, poly(styrene-acrylonitrile) SBS, poly(styrene-butadiene-styrene) PVA, poly(vinyl acetate) PVB, poly(vinyl butyral) PVC, poly(vinyl chloride) PDMS, poly(dimethyl siloxane) PE, polyethylene EVA, poly(ethylene-vinyl acetate) UHMWPE, ultra high molecular weight polyethylene PP, polypropylene. 

Reagent used to prepare V-trifluoroacetyl derivs. of amino acids etc. Bp 148-149°. 

McCoy et al. [133] have shown that it is possible to carry out V-trifluoroacetylation in polyaniline. In this reaction polyaniline displays a continuum of states of nucleophilicity determined by the degree of oxidation of the polymer. It is interesting to note that the V-trifuluoroacetyl moiety can be hydrolysed to obtain original polyaniline. These aspects may prove important for the fabrication of certain devices. 

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