Butyl trifluoroacetate

Trifluoroacetic acid removes tert-butyl-based protectors by the S vl mechanism, with the cation being trapped by the trifluoroacetate anion however, the tert-butyl trifluoroacetate produced is an alkylating agent, and the acid is not strong enough to protonate the side chains of methionine, tryptophan, and cysteine, so these are acceptors of tert-butyl. A scavenger is required to prevent their alkylation. Anisole... 

The acidic cleavage of the Boc group is most probably proceeded by the protonation of the carbamate carbonyl with subsequent elimination of isobutene, either by an open or, more likely, by a cyclic transition state. Protonation leads to the liberated anoine or the annmonium salt, respectively (Scheme 35). The byproduct isobutene is either protonated to give the stable carbenium ion, or generates the tcrt-butyl trifluoroacetate, both of which act as terf-butylating agents, especially, when nucleophilic amino acid side chains are present in the molecule (vide infra). 

Pentafliioro-2-(pcntafluoroethyl)-2-(trifluoromethyl)butyl Trifluoroacetate (8) Typical Procedure 229... 

Electrophilic substitution of aromatic nuclei in tyrosine and tryptophan side chains has frequently been reported in connection with acidolytic removal of blocking groups. C-Benzylation and tert.butylation of the tyrosine side chain and N-alkylation of the indole nucleus in tryptophan are often attributed to the alkyl cations generated in the reaction. This common side reaction is caused, however, mainly by the alkylating agents formed in the process, such as benzyl bromide or tert.butyl trifluoroacetate. The same is true for the S-alkylation of the methionine side chain. Conversion of the thioether to a sulfonium salt can... 

QHsF302]- CF3C02(CH2)3CH2 Reaction of TBO with butyl trifluoroacetate/ DTBP EPR/ 250 2H(a) 2.13 2H(jS) 2.60 84Basl... 

The reaction of ethylene with 82 leads to formation of the ethylplatinum complex with a trifluoroacetate ligand 84 and 2-butyl trifluoroacetate. Conversion of ethylene into a mixture of as- and frans-Z-hutcnc is promoted by 82. 

Figure 3.1 Fluorine-19 NMR spectra of several HFA adducts. From left HFA (free), butyl trifluoroacetate, trifluoroacetic acid, HFA dimethyl glyoxime, HFA (benzyl alcohol), HFA (methanol), HFA (ethanol), HFA (isopropanol), HFA ( er -butanol) and HFA H2O. The numbers on top are Hz downfield from CgFg lock. Reprinted with...

The quantative aspect of hydroxyl determination is illustrated in Table 3.4 for the analysis of hydroxyl in some polymeric materials. In most cases, the fluorine resonance from -butyl trifluoroacetate (at 7463 Hz in Figure 3.1) was used as internal standard to calibrate the spectral integral. From the data shown in Table 3.4 it seems that the adduct formation is quantitative for primary and secondary hydroxyls. The reaction normally requires less than 20 minutes at room temperature. However, as with the chemical acylation methods, tertiary hydroxyl was found to react only partially, and the reaction for ter -butanol required about 24 hours to reach equilibrium. The method can be used for the determination of hydroxyl groups in polymers of unknown structure. 

Methyl-2-butyl trifluoroacetate Product of normal Markovnikov addition... 

Methyl -2-butyl trifluoroacetate Product resulting from carbocation rearrangement... 

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