O-Trifluoroacetylation

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,... 

Takeuchi and co-workers showed that the ratio of N- to C-substitution on the apparent intermediate 75a by a series of aromatics in arene/TFA mixtures was sensitive to the structure of the precursor to 75a (phenyl azide, N-phenylhydroxylamine or O-trifluoroacetyl-N-phenylhydroxylamine) even though the decomposition rates of these precursors were unaffected by the identity of the arene. This result is consistent with the characterization of 75a from N3 and Br trapping studies as a short-lived intermediate that will usually react through ion pair or preassociation processes that may be leaving-group dependent. ... 

Fig. 13. Enantiomeric separations of monohalohydrocarbons on a 2,6-0-dipentyl-3-O-trifluoroacetyl-y-cyclodextrin coated capillary column (10 m, 0.25...

Dipropionyl peroxide, 2436 Dipropyl peroxydicarbonate, 3030 Peroxodisulfuryl difluoride, 4322 Phthaloyl peroxide, 2895 Potassium benzenesulfonylperoxosulfate, 2250 Potassium O—O-benzoylmonoperoxosulfate, 2680 O-Trifluoroacetyl-S -fluoroformyl thioperoxide, 1047 See PEROXIDES, PEROXYCARBONATE ESTERS... 

A possible application of the blocking effect of trifluoroacetyl groups, making use of the difference in reactivity of the i (-(trifluoroacetyl) and O-(trifluoroacetyl) groups toward hydrolytic attack, would be for conversion of a hexosamine into its tetra-O-acetyl derivative containing the free amino group. The procedure for this synthesis would require the conversion of the hexosamine to its pentakis(trifluoroacetate), the selective removal of the O-(trifluoroacetyl) groups with dry methanol, followed by... 

In addition to glycosyl acetates, 1-O-trifluoroacetyl [79] and 1-O-p-nitrobenzoyl esters [68], trichloroacetimidates [2], methyl glycosides [80-83], furanose glycosyl acetates [48] and ketose acetates [84] have been successfully modified in this manner. With respect to the use of -0-p-nitrobenzoyl esters, extended olefins [85,86], substituted olefins [87] and allenes [88] were incorporated onto sugar scaffolds. 

These conclusions were drawn from the X-ray structures of some of the hydrox-ylated prolines and related N-acetyl methyl ester derivatives [39,40] as well as from the thermodynamic parameters obtained by NMR conformational analysis of the model compounds Ac-Pro -OMe, with Pro corresponding to 1-4 [15,21,32], and Ac-Phe-Pro -NHMe, with Pro being 1-5 (Tables 11.1 and 11.2) [41], While O-acetylation or O-trifluoroacetylation of the 4-hydroxyproline increases the inductive effects [40], and thus stabilizes the O-exo pucker and trans-conformation of aminoacyl-Hyp bonds, unfavorable steric interactions reduce these effects in terms of triple-helix induction and stability [40]. In addition, Table 11.2 reports the thermodynamic parameters of (3R,4S)-Dhp (6) which displays a similar behavior... 

Analysis of methyl o-Trifluoroacetyl lactate type derivatives)... 

The derivative corresponds to the octakis (2,6 di O pentyl-3-O trifluoroacetyl) -y-cyclodextrine... 

The analytical conditions are identical to those described in Figure 3. Figure 7 represents the separation of the enantiomers of the isobutyl ester of lactic acid (O trifluoroacetyl derivative). 

When trifluoroacetic anhydride was used for the Pummerer rearrangement of phenylboronate ester 465, the 1-O-trifluoroacetyl derivative 469 was formed rapidly and could be used in situ for further reactions. The 1-O-trifluoroacetyl group could be replaced by bromide which, in turn, was exploited for glycoside synthesis. 

O-Trifluoroacetylation (cf. Synth. Meth. 34, 719). A soln. of phenol and 0.5 eqs. 2,6-di- er/-butyl-4-methylpyridine in carbon tetrachloride treated with 1 eq. trifluoro-... 

Jiang B, Si YG (2002) Zn(II)-mediated alkynylation-cyclization of o-trifluoroacetyl anilines one-pot synthesis of 4-trifluoromethyl-substituted quinoline derivatives. J Org Chem 67 9449-9451... 

The proline-catalyzed Friedlander reaction has been used for the synthesis of 2-substituted 4-trifluoromethyl quinolines 110 (Scheme 54) [82], Compounds 110 have also been obtained through the Zn(II)-mediated alkynylation-cycUzation of o-trifluoroacetyl anilines (Scheme 54) [83],... 

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