Alcohol groups trifluoroacetic anhydride

Several laboratories have reported that Swern oxidation of alcohols can be accompanied of a-chlorination of keto or (1-keto ester groups. Undesired electrophilic chlorination can be avoided by use of oxalyl chloride (1.05 equiv.) and DMSO (2.5 equiv.) in stoichiometric amounts or by use of acetic anhydride or trifluoroacetic anhydride in place of oxalyl chloride.1... 

A very useful group of procedures for oxidation of alcohols to ketones have been developed which involve DMSO and any one of several electrophilic reagents, such as dicyclohexylcarbodiimide, acetic anhydride, trifluoroacetic anhydride, oxalyl chloride, or... 

Thus, in line with earlier observation, the use of dimethylsulfoxide and trifluoroacetic anhydride led, by preferential oxidation of the secondary alcohol, to the hemiketal ( )-tazettine (400). On the other hand, application of the Dess-Martin method furnished, by selective oxidation of the primary alcohol group, ( )-11-epipretazettine (412) (also known as ( )-6a-epipretazettine), in 73% yield, previously converted into ( )-tazettine [100]. 

Although the a-hydrogen atoms in alcohols are very reactive, those of ethers and particularly esters are substantially more sluggish toward oxidation than those of alcohols. Thus, the overoxidation of primary and secondary alcohols may be prevented by protection of the newly formed hydroxy group by in-situ acylation with trifluoroacetic anhydride [23], Preparatively most significant, the C-H bonds adjacent to carbonyl (ketone, aldehyde, ester, and amide) and cyano groups are inert towards DMD and even TFD oxidation. 

Below room temperature, two alkyl groups are transferred and oxidation gives ketones. If an excess of trifluoroacetic anhydride and higher temperatures are used then the third alkyl group can be induced to migrate and oxidation leads to tertiary alcohols (figure B3.5). 

Although many oxidizing reagents remove the chromium tricarbonyl group, benzylic alcohols can be oxidized to benzaldehydes using dimethyl sulfoxide with acetic anhydride, trifluoroacetic anhydride, or sulfurtrioxide with minimal decomplexation. Asymmetric oxidation of aUcylthio-substituted complexes can be achieved using titanium tetraisopropoxide and an optically active tartrate ester (Scheme 108). Dimethyloxirane can also be used to oxidize sulfides to sulfoxides. 

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-... 

This group has recently reported the CAB-promoted additions of 2-butenylstan-nanes to branched and chiral aldehydes [88]. The reactions were optimized using cyclohexanecarboxaldehyde and ( )-85 in the presence of the CAB catalyst and trifluoroacetic anhydride. Under optimized conditions, the reaction affords a 92/8 mixture ot syn/anti homoallylic alcohols in 71% yield and the syn diastereomer is obtained in 93% ee. 

Corey s group subsequently developed a novel and more efficient conversion of racemic 5-HPETE to racemic LTA4 methyl ester. It was found that allylic hydroperoxides undergo a remarkable intramolecular rearrangement upon treatment with trifluoroacetic anhydride to produce epoxy alcohols in high yields. Standard transformations then effected the conversion of this intermediate to racemic LTA4 methyl ester. 

A recent study has further proven the applicability of gas-phase reactions to functional groups at the monolayer surface. Alcohol terminal groups were quantitatively converted to trifluoroacetates by exposure to the vapours of trifluoroacetic anhydride (equation 7). Reaction with perfluoropropionic and perfluorobutyric anhydrides proceeded similarly, but with ca 80% yield (XPS). Very high contact angles (>120°) of perfluoro-terminated layers proved the formation of esters333. 

Three methods that were used to measure the chemical changes associated with oxidative degradation of polymeric materials are presented. The first method is based on the nuclear activation of lsO in an elastomer that was thermally aged in an, 802 atmosphere. Second, the alcohol groups in a thermally aged elastomer were derivatized with trifluoroacetic anhydride and their concentration measured via 19F NMR spectroscopy. Finally, a respirometer was used to directly measure the oxidative rates of a polyurethane foam as a function of aging temperature. The measurement of the oxidation rates enabled acceleration factors for oxidative degradation of these materials to be calculated. 

Analysis of the lactic acid is performed after esterification of the alcohol group with trifluoroacetic anhydride. 

While this method is applicable to symmetrical alcohols or ketones, formation of unsymmetrical ketones is difficult unless selective transfer of the alkyl groups can be achieved. Thexylborane provides a solution since it can react sequentially with two different alkenes to generate an unsymmetrical trialkylborane. Reaction of thexylborane with cyclopentene and then arylalkene 172, for example, gave 173. Subsequent reaction with sodium cyanide gave the unsymmetrical ate complex ( 74) and this generated unsymmetrical ketone 175 upon treatment with trifluoroacetic anhydride followed by oxidation. 20b... 

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