Trifluoroacetics ester

Lcad(rV) trifluoroacetate is a strong electrophilic and oxidizing reagent It IS a valuable reagent for the hydroxylatton of aromatic compounds [5S, 59] Lead(IV) trifluoroacetate also reacts with silylated benzenes with the exclusive formation of the corresponding trifluoroacetate esters [59] (equation 28)... 

Trifluoroacetyl)benzotriazole, THF, rt, 85-100% yield. This reagent can be used to prepare trifluoroacetate esters. 

Fig. 6 CDI-catalyzed synthesis of cellulose trifluoroacetate esters, from reference [23]...

Trifluoroacetylbenzotriazole,[125a] which is easily prepared from benzotriazole and trifluoroacetic anhydride, is a very expedient trifluoroacetylating agent. Because of its stability the solid product can be stored in the covered bottle for several weeks without decomposition. By reaction with alcohols the trifluoroacetate esters were obtained in high yields ... 

The resultant spectrum is clearly very different from the alcohol, as the trifluoroacetic ester function is far more deshielding with respect to the alpha proton than is the -OH group. A downfield shift of > 1 ppm can be seen. This clearly distinguishes the alcohol from the analogous chloro compound which would of course give no reaction. 

Secondary Alkyl Alcohols. Treatment of secondary alkyl alcohols with tri-fluoroacetic acid and organosilicon hydrides results only in the formation of the trifluoroacetate esters no reduction is reported to occur.1,2 Reduction of secondary alkyl alcohols does take place when very strong Lewis acids such as boron trifluoride126 129 or aluminum chloride136,146 are used. For example, treatment of a dichlo-romethane solution of 2-adamantanol and triethy lsilane (1.3 equivalents) with boron trifluoride gas at room temperature for 15 minutes gives upon workup a 98% yield of the hydrocarbon adamantane along with fluorotriethylsilane (Eq. 10).129... 

The tertiary alcohol m,m,/ra ,v-perhydro-9h-phcnalcnol (7) is converted stereospecifically and in high yield (92%) to /ran.v,/ran.v,/ran.v-pcrhydrophcnalcnc (10) when treated with either triethylsilane or triphenylsilane and trifluoroacetic acid in dichloromethane (Eq. 15). Studies indicate that the reaction path follows the cation rearrangement 8 9 and that the trans trifluoroacetate ester related to... 

Cyclopropylcarbinols. Treatment of cyclopropylcarbinols 15 (R = Ph, C-C3H5) with trifluoroacetic acid in dichloromethane leads to the rapid formation of ring-opened 4-substituted 3-butenyl-l-trifluoroacetate esters 16 (Eq. 20).130 Cyclopropylcarbinyl trifluoroacetates are not formed. Ring opening is facilitated by phenyl substituents. Addition of organosilicon hydrides to the reaction mixture favors the formation of cyclopropylmethanes 17 and suppresses the formation of the ring-opened esters.130... 

The triethylsilane/trifluoroacetic acid reagent system reduces alkenes to alkanes in poor to excellent yields depending largely on the ability of the alkene to form carbocations upon protonation. Under these conditions the more substituted olefins are reduced in better yields and styrene double bonds are reduced in high yields.127,202,207,221-228 The reduction of 1,2-dimethylcyclohexene with this reagent gives a mixture of cis- and trans- 1,2-dimethylcyclohexane.229 The formation of the trifluoroacetate esters is a side reaction.205,230... 

When trifluoroacetic acid is used as the source of protons, it is known that rapid formation of trifluoroacetate esters precedes reduction to hydrocarbons.134,204 206 Use of acetic acid in place of trifluoroacetic acid, for example, would be expected to fail to produce good conversion to reduced product because of the combination of decreased acidity and increased nucleophilicity of acetic acid relative to... 

Treatment of progesterone with trifluoroacetic acid and triethylsilane in dichloromethane followed by saponification of the mixture of the trifluoroacetate ester intermediates of 5-/3-pregnane-3a,20/3-diol and 5-j6-pregnane-3a,20a-diol and Jones oxidation yields 5-/3-pregnanedione in 65% yield (Eq. 81).238... 

One study of the Et3SiH/TFA reduction of acid anhydrides reports the formation of one equivalent each of the alcohol and the trifluoroacetate ester of the acid (Eq. 139).287... 

Another potential mechanistic complication is capture of the intermediate carbenium ion by the conjugate base of the acid. When CF3C02H is used as the acid, this would lead to trifluoroacetate esters. Kursanov et al. showed that, under the reaction conditions for ionic hydrogenations, trifluoroacetate esters can be converted to the hydrocarbon product (Eq. (3)). 

The intermediacy of the trifluoroacetate ester does not undermine the efficacy of the overall hydrogenation reaction, since the ionizing solvent CF3C02H converts the ester back to the carbenium ion under the reaction conditions, resulting in its ultimate conversion to the hydrogenation product. 

A mixture of anhydrous lithium nitrate and trifluoroacetic anhydride in acetonitrile in the presence of sodium carbonate has been used to convert alcohols to nitrate esters for a range of peptide, carbohydrate and steroid substrates. Yields are good to high but products need puritication to remove trifluoroacetate ester impurities, which can be signiflcant in the absence of the carbonate. A similar system used for the nitration of electron-rich aromatic heterocycles employs trifluoroacetic anhydride with ammonium or potassium nitrate. ... 

Oxalate and trifluoroacetate esters are reactive compounds, which are hydrolyzed in aqueous acid at rates which are not a great deal faster than the rates in neutral solution. Moffat and Hunt170, for example, studied the hydrolysis of a series of alkyl trifluoroacetates in 70% acetone-water, and found that the... 

Alcohol Procedure Carbonyl (%) Trifluoroacetate ester (%) Methylthiomethyl ether (%)... 

Shulgin, A.T., Separation and analysis of methylated phenols as their trifluoroacetate ester derivatives, Anal. Chem., 36, 920, 1964. 

A solution of methanesulfonylhydrazide (0.0303 mole) in tetrahydrofuran (70 ml, 30 ml for rinsing) was added with stirring to a solution of (2a,5a,17a)-2-(diethoxymethyl)-17-[(trifluororacetyl)oxy]pregn-20-yn-3-one (0.025 mole) in tetrahydrofuran (190 ml). The mixture was allowed to stand for 3 days at room temperature, heated under reflux for 4 h and evaporated. The residue was purified by crystallization and recrystallization from methanol, affording (5a,17a)-l,-(methylsulfonyl)-l H-pregn-20-yno[3,2-c]pyrazol-17-ol trifluoroacetate (ester), 69% yield, MP 166°-168°C. 

Finally, acetate ester (43) and trifluoroacetate ester can be reduced with silane in the presence of peroxide under sealed conditions (eq. 7.20) [46, 47]. 

Selective hydrolysis of the highly labile trifluoroacetate ester was then easily achieved by adjusting the pH of the reaction mixture to 6.5 with aqueous so-dium carbonate to give the diol monoacetate 92j6 in 87% yield. 

---