Trifluoroacetyl groups

Trifluoroacetamides are more stable toward nucleophiles than the corresponding esters and are easily formed from trifluoroacetic anhydride and the amine. The trifluoroacetyl group (Tfac) is slowly cleaved by aqueous or methanolic HQ, NH, or Ba(OH)2 solutions as well as by NaBHj in methanol (M.L. Wolfrom, 1967). 

The need for pyrazoles substituted with the trifluoroacetyl group led to the reaction of ethoxyvinyl ether with trifluoroacetic anhydride, yielding 4-ethoxy-l,l,l-trifluoro-3-buten-2-one (38) this further reacted with aldehyde / fZ-butyUiydrazones, and after cyclization at room temperature under mildly acidic conditions the pyrazoles were obtained in satisfactory yields (eq. 7). Further treatment with H2SO4 removed the tert-huty group, thus providing an opportunity for further derivatization at N. ... 

AcOH, HBr, 10°, 10 min, 70% yield. Phthaloyl or trifluoroacetyl groups on amino acids are stable to these conditions benzyloxycarbonyl (Cbz) or /-butoxycarbonyl (BOC) groups are cleaved. 

In sugar chemistry, the trifluoroacetyl group became an imponant tool for different synthetic purposes [12, 13] Many sophisticated and effective acylating... 

The hydrogeh atom bound to the amide nitrogen in 15 is rather acidic and it can be easily removed as a proton in the presence of some competent base. Naturally, such an event would afford a delocalized anion, a nucleophilic species, which could attack the proximal epoxide at position 16 in an intramolecular fashion to give the desired azabicyclo[3.2.1]octanol framework. In the event, when a solution of 15 in benzene is treated with sodium hydride at 100 °C, the processes just outlined do in fact take place and intermediate 14 is obtained after hydrolytic cleavage of the trifluoroacetyl group with potassium hydroxide. The formation of azabi-cyclo[3.2.1]octanol 14 in an overall yield of 43% from enone 16 underscores the efficiency of Overman s route to this heavily functionalized bicycle. 

Neu5Ac2en 4, a micromolar inhibitor of influenza virus sialidase 4 x 10 M (A/N2)] (Holzer et al. 1993), was first identified as a very good inhibitor in the late 1960s (Meindl and Tuppy 1969). A series of C-5 modified Neu5Ac2en derivatives provided the first improved in vitro inhibitors compared with the parent compound 4. The replacement of the C-5 A-acetyl moiety with a A-trifluoroacetyl group resulted in the most potent inhibitor of this series, 2-deoxy-2,3-didehydro-A-trifluoroacetylneuraminic acid 10 [A] 8 x 10 M (A/Nl)] (Meindl et al. 1974). While these C-5 modified compounds were also very effective in cell culture assays (Palese et al. 1974a Palese and Compans 1976), none, including the parent... 

Entry 5 in Scheme 11.4 is a step in the synthesis of the anticancer drug tamoxifen. Explain why the 2-phenylbutanoyl group is introduced in preference to a trifluoroacetyl group. 

Kenna, J.G. et al., Metabolic basis for a drug hypersensitivity Antibodies in sera from patients with halothane hepatitis recognize liver neoantigens that contain the trifluoroacetyl group derived from halothane, J. Pharmacol. Exptl. Therap., 245, 1103, 1988. 

A study was made of the effects of derivatization on the 13C analysis of amino acid enantiomers. Conventional isotope ratio MS and GC-isotope ratio MS were used. The latter method requires volatilization of the analytes, which was accomplished by introducing O-isopropyl and A-trifluoroacetyl groups, causing a change in the 13C analysis of the original analytes. It was proposed to use a set of known standards for such analyses, which are applied in geological studies68. 

Because of the strong electron-withdrawing effect of the trifluoromethyl group, trifluoroacetamides are subject to hydrolysis under mild conditions. This has permitted trifluoroacetyl groups to be used as amino-protecting groups in some situations. 

Representatives of this new type of meso-ionic system (502) have been prepared by cyclodehydration of the acid derivatives 503 using trifluoroacetic anhydride. For example, the acid 503, R = p.ClCgH4, gave the red crystalline meso-ionic l,3-oxathiol-5-one (502, R =p.Cl.CgH4, R = CF3.CO) which is readily hydrolysed to the ketone (504, R = j3.Cl.CgH4). The trifluoroacetyl group in the 4-position appears to be essential for the stability of the meso-ionic system (502). 

In 1992, Legros and Fiaud found palladium-catalyzed benzyiic alkylation of naphthylmethyl and 1-naphthylethyl esters 103 with sodium dimethyl malonate 104 in dimethylformamide (DMF) to give the corresponding benzyiic alkylated products 105 in high yields (Equation (41)). " When trifluoroacetyl group is used as a leaving group of the ester partner, catalytic alkylation proceeds quite smoothly even at room temperature. In this reaction system, no reaction occurs with benzyiic acetates. 

Replacement of an O-acetyl group by an O-trifluoroacetyl group greatly increases the volatility of the sugar derivative, and this behavior was first utilized by Vilkas and associates,224 who studied the separation of pentoses, hexoses, aminoglycoses, methyl glycosides,... 

Heck cyclization with concomitant deprotection of the trifluoroacetyl group to form the indoleacetic methyl ester 68. Compound 68 was hydrolyzed and then treated with PCI5 followed by dimethylamine to give the amide 69, which was reduced with LiAlHi to afford almotriptan (5). 

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... 

The first of these inherent difficulties is that even a moderately reactive metallate such as CpFe(CO)2 can displace fluoride ion by means of a nucleophilic attack on the ligated trifluoroacetyl group. This reaction presumably results in an unstable bimetallic species which decomposes under the reaction conditions (17). Thus, in some instances, the yield of the desired trifluoroacyl substrate is inevitably low, often less than 10%. 

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