Carboxylic acid esters trifluoroacetates

Addition of halogen fluorosulfates XOS02F (X=C1, Br, I) to fluoroolefins is considered an electrophilic reaction [8]. However, the question of whether this process is concerted or the reaction proceeds via an independent carbocationic intermediate (Eqs. 2 and 3) is still open. Formation of carboxylic acid esters as byproducts in the reaction of HFP with C10S02F, which was carried out in trifluoroacetic or heptafluorobutyric acids as solvents, could not be a solid proof of conjugate addition, since formation of esters may be a result of addition of C10C(0)Rf to olefin. These materials are known to be formed in the reaction of ClOS02F with fluorinated carboxylic acids, even at low temperature [99]. 

In mixed trifluoroacetic anhydrides, the strong electron-withdrawing tri-fluoroacetyl group polarizes the bonds to the anhydride oxygen in such a way that it tends to split to acylium cation and trifluoroacetate anion [/0/. Generally, the products of the reaction of hydroxy compounds with acyl trifluoroacetates are esters of carboxylic acids and trifluoroacetic acid, because the acyl carbonyl is better fit for a nucleophilic attack than the carbonyl next to the trifluoromethyl group [707]. 

A convenient one-step transformation of primary and secondary amines into the corresponding unprotected guanidines using 4-benzyl-3,5-dimethyl-l/f-pyrazole-l-carboxamidine 90 and its polymer-bound variant were described <06S461>. 1,3-Dipolar cycloaddition of polymer-bound alkynes to azomethine imines generated in situ from N-aminopyridine iodides followed by aromatization of the cycloadducts gave polymer-bound pyrazolopyridines that were released from the resin as carboxylic acids with trifluoroacetic acid or as methyl esters with sodium methoxide <06JCO344>. 

Treatment of a carboxylic acid with trifluoroacetic anhydride leads to an unsym-metiical anhydride that rapidly reacts with alcohol to give an ester ... 

Formation of exocyclic iminium ions can be achieved under special circumstances where a functionality other than hydrogen is lost during the elimination step. One version of this technique takes advantage of the fact that carboxylic acid esters are readily hydrolyzed to the parent acids during iV-oxide formation with hydrogen peroxide. Thus, on sequential treatment of the A/-oxide (19) with hydrogen peroxide, trifluoroacetic acid and potassium cyanide the exocyclic, rather than the endocyclic, aminonitrile (20) is produced in 48% yield (equation 9). ... 

Protection of carboxylic acids. Esters are prepared using DCC-DMAP, and they are cleaved on contact with 1% trifluoroacetic acid in CH2CI2 at room temperature for a short time. The deblocking conditions do not affect r-butyl esters and t-Boc amines. 

Renaud RN, Champagne PJ (1975) Electrochemical oxidation of trifluoroacetic acid in an organic substrate. III. In the presence of substituted malonic acid half esters and unsaturated carboxylic acid esters. Can JChem 53 529-534... 

Various 2-isoxazolines were synthesized from resin-bound nitrile oxide (Scheme 11.35) or alkene (Scheme 11.36). ° Oxidative treatment of aldoximes with bleach generated nitrile oxides that reacted with various alkenes. The ester-linked products were cleaved from the Wang resin as carboxylic acids using trifluoroacetic acid. Cycloaddition of terminal alkenes... 

Besides acetates and benzoates many other types of carboxylic acid esters can be formed, such as chloroacetates, trifluoroacetates, pivalates, carbonates, and thiocarbonates, by reaction with chloroacetic anhydride, trifluoroacetic anhydride, pivaloyl chloride (2,2-dimethyl propanoyl chloride), phosgene or methylchloro-formate, and carbon disulfide or carbonyl sulfide, respectively. Each of the ester derivatives imparts specific chemical properties to the carbohydrates so they can be used selectively in synthetic schemes. It was found that the sulfonic acid esters... 

Activated Esters. Mixed anhydrides may be prepared by reaction of carboxylic acids with trifluoroacetic anhydride. The method has been used widely as a means of activating carboxyl groups to nucleophilic attack. The method has also been highly useful in Friedel-Crafts acylation of arenes (eqs 1 and 2). Sulfonic acids are also activated to nucleophilic attack substituted sulfones result. Intramolecular Friedel-Crafts reactions are also facilitated, but only for formation of six-membered rings. ... 

The change of mechanism with tertiary alkyl esters is valuable in synthetic methodology because it permits certain esters to be hydrolyzed very selectively. The usual situation involves the use of t-butyl esters, which can be cleaved to carboxylic acids by action of acids such as p-toluenesulfonic acid or trifluoroacetic acid under anhydrous conditions where other esters are stable. 

Studies on Trifluoroacetic Acid. Part I. Trifluoroacetic Anhydride as a Promotor of Ester Formation between Hydroxy-Compounds and Carboxylic Acids, E. J. Bourne, M. Stacey, J. C. Tatlow, and J. M. Tedder, J. Chem. Soc., (1949) 2976-2979. 

So do anhydrides and many compounds that enolize easily (e.g., malonic ester and aliphatic nitro compounds). The mechanism is usually regarded as proceeding through the enol as in 12-4. If chlorosulfuric acid (CISO2OH) is used as a catalyst, carboxylic acids can be ot-iodinated, as well as chlorinated or brominated. N-Bromosuccinimide in a mixture of sulfuric acid-trifluoroacetic acid can mono-brominate simple carboxylic acids. ... 

In the case of phosphoryl chloride, the primary products were 4-chloro-quinoline-3-carboxylates. As the quinoline-3-esters were very insoluble, the reaction products were hydrolyzed to quinoline-3-carboxylic acids, and the isomeric ratios were determined by H-NMR in trifluoroacetic acid. Thermal cyclization in Dowtherm A resulted mainly in formation of the 7-substituted isomer. In the case of chloro derivatives (250), only traces of 5-isomer could be detected. [Earlier, others observed and reported the formation of a small amount of the 5-isomer too (e.g., 46JA1204 47JA374]. 

The hydrolysis of diethyl N-(3-alkoxycarbonyl-2-thienyl)aminomethy-lenemalonates (1439, R = Me, Et) by potassium hydroxide in ethanol yielded diethyl Af-(3-carboxy-2-thienyl)aminomethylenemalonates (1439, R = H) [75GEP2435025, 75JAP(K)77393]. The treatment of the /erf-butyl esters 1439, R = rBu, R1 = R2 = H, Me, (CH2)4] with formic acid or trifluoroacetic acid at room temperature also afforded the carboxylic acid derivatives [1439, R = H, R = R2 = H, Me, (CH2)4] [75JAP(K)77394]. 

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