Ketones trifluoroacetic anhydride

In an alternate synthesis of the intermediate ketone, the benzylic halide, 69, is used to alkylate sodium phenoxide. Cyclization of the acid (70) obtained on hydrolysis of the ester by means of trifluoroacetic anhydride again gives 67... 

Several alternative procedures have been developed in which other reagents replace carbon monoxide as the migration terminus.11 The most generally applicable of these methods involves the use of cyanide ion and trifluoroacetic anhydride (TFAA). In this reaction the borane initially forms an adduct with cyanide ion. The migration is induced by N-acylation of the cyano group by TFAA. Oxidation and hydrolysis then give a ketone. 

In method B, iV-trifluoroacetylimidazole and carboxylic acids are the acylating reagents. This method is also thought to proceed via a carboxylic trifluoroacetic anhydride. This second system is a very convenient reagent for obtaining aromatic ketones because of the use of free carboxylic acids [97]... 

Nitration of the potassium enolates of cycloalkanones with pentyl nitrate81 or nitration of silyl enol ethers with nitronium tetrafluoroborate82 provides a method for the preparation of cyclic a-nitro ketones. Trifluoroacetyl nitrate generated from trifluoroacetic anhydride and ammonium nitrate is a mild and effective nitrating reagent for enol acetates (Eq. 2.41).83... 

Under Dakin-West reaction conditions (trifluoroacetic anhydride-MeCN/80 °C/5 h), At-methoxycarbonylproline (128 R = Me) yielded Af-methoxycarbonyl-4-trifluoro-acetyl-2,3-dihydropyrrole (129 R = Me) and none of the expected Dakin-West product, the trifluoromethyl ketone (127). A possible mechanism proposed by the authors involves initial formation of a mesoionic l,3-oxazolium-5-olate (130 R = Me), but the pathway to the iV-methoxycarbonyl-2,3-dihydropyrrole (131 R = Me) and thence the final product (129 R = Me) was unexplained. ... 

Rate constants and Arrhenius parameters for the reaction of Et3Si radicals with various carbonyl compounds are available. Some data are collected in Table 5.2 [49]. The ease of addition of EtsSi radicals was found to decrease in the order 1,4-benzoquinone > cyclic diaryl ketones, benzaldehyde, benzil, perfluoro propionic anhydride > benzophenone alkyl aryl ketone, alkyl aldehyde > oxalate > benzoate, trifluoroacetate, anhydride > cyclic dialkyl ketone > acyclic dialkyl ketone > formate > acetate [49,50]. This order of reactivity was rationalized in terms of bond energy differences, stabilization of the radical formed, polar effects, and steric factors. Thus, a phenyl or acyl group adjacent to the carbonyl will stabilize the radical adduct whereas a perfluoroalkyl or acyloxy group next to the carbonyl moiety will enhance the contribution given by the canonical structure with a charge separation to the transition state (Equation 5.24). 

Synthesis of quinolines by nucleophilic substitution of nitrogen atom in oxime derivatives was described by Narasaka and coworkers. /3-Aryl ketone oximes 297 in the presence of trifluoroacetic anhydride and 4-chloranil afforded quinolines 298 in 72-82% yield (equation 128). However, interaction of oxime 299 with 48% HBr at 105 °C proceeded with elimination of hydroxyimino group and gave 2,3-dimethoxynaphtho[l,2-fc]quinolizinium bromide (300) in 45% yield (equation 129). ... 

Subsequent steps involve introduction of a thexyl group and then the second ketone substituent. Finally, the ketone is formed by the cyanide-trifluoroacetic anhydride method. 

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... 

Methods of acylating pyrrole similar to the present one have been reported using oxalyl chloride,5 trifluoroacetic anhydride,6 carbamic acid chloride,7 and trichloroacetyl chloride.8 In the last preparation, it was necessary to separate the product from highly colored by-products by alumina chromatography. Pyrrol-2-yl trichloromethyl ketone has also been prepared by the interaction of pyrrolylmagnesium halide and trichloroacetyl chloride.9... 

Representatives of this new type of meso-ionic system (502) have been prepared by cyclodehydration of the acid derivatives 503 using trifluoroacetic anhydride. For example, the acid 503, R = p.ClCgH4, gave the red crystalline meso-ionic l,3-oxathiol-5-one (502, R =p.Cl.CgH4, R = CF3.CO) which is readily hydrolysed to the ketone (504, R = j3.Cl.CgH4). The trifluoroacetyl group in the 4-position appears to be essential for the stability of the meso-ionic system (502). 

The acylation of alkenes with trifluoroacetic anhydride having only weak elec-trophilicity was reported to give a,p-unsaturated ketones in 19-49% yields.117 118 The reaction requires the use of the Me2S—BF3 complex as catalyst and takes place only with alkenes that readily form stable carbocations. Alkenes were also electrolyzed in CH2C12 solution of Et4NCl as the electrolyte at —5 to — 10°C in the... 

Optically active 4-alkoxycarbonyl-3-hydroxycyclohexanones (formed in highly enantio- and diastereoselective organocatalytic asymmetric domino Michael aldol reaction of / -keto esters and a,/ -unsaturated ketones) are transformed into corresponding chiral oxepanones under the action of urea-hydrogen peroxide and trifluoroacetic anhydride <2004AGE1272>. 

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. 

Trifluoromethyl derivatives of thiochromone are also available from thiosalicylic acid by conversion to alkyl 2-mercaptophenyl ketones followed by a Baker-Venkataraman reaction with trifluoroacetic anhydride in triethyl-amine (Scheme 205) <2005PS(180)1315>. 

The synthetic scheme often applied for the preparation of 3-aryl-3-(trifluoromethyl)-3//-diazirine nowadays is shown in Scheme 5a [60]. It starts by lithiation of an aryl bromide (38), which subsequently reacts with /V-ftrifluoroacetyl)piperidine 39 (easily prepared from trifluoroacetic anhydride and piperidine) under the formation of trifluoroacetophenone 40. Next, the ketone is converted into the corresponding oxime 41, after which the hydroxyl group is converted into its tosylate (42). Reaction with liquid ammonia (usually under pressure) allows the installment of the diaziridine group (43). Subsequent oxidation with iodine finally results in the diazirine (44). This five-step reaction sequence is especially compatible with acid-labile protective groups, which are often used to protect and/or install functionalities at the R position. 

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). 

The presence of amino substituents in the 2- or 5-position activates the oxazole ring (4-aminooxazoles are unknown). Thus 2-amino-3-aryloxazoles yield the derivatives (127 X = Cl or Br) on halogenation, and nitration of 2-dimethylamino-4-phenyloxazole afforded 2-dimethylamino-5-nitro-4-(4-nitrophenyl)oxazole, the sole example of direct nitration of the oxazole ring. 5-Dialkylamino-2-phenyloxazoles react with trifluoroacetic anhydride to form the ketones (128) and they couple with arene diazonium fluoroborates the products (129) readily rearrange to 1,2,4-triazoles (130) in DMSO solution. 

The first simple 5(2/f)-oxazolones were the trifluoromethyl derivatives obtained by treating a-amino acids with trifluoroacetic anhydride (equation 156). A general synthesis of 2,2-disubstituted 5(2/f)-oxazolones is the condensation of a- (hydroxylamino) acids with ketones (equation 157) (80S55). The dehydrogenation of 2,2-bis(trifluoromethyl)-5-oxazolidinones affords bis(trifluoromethyl) derivatives (equation 158) (79LA1547). 

Cyclic hydroboration of ( + )-limonene with thexylborane yields the pure borabicyclic compound (138), which is oxidized to the diol (32 X = OH) or protonol-ysed with acetic acid to yield pure (—)-carvomenthol (32 X = H) after the usual oxidation.227 The treatment of dialkylcyanothexylborates with trifluoroacetic anhydride followed by oxidation as a route to ketones has been used with ( + )-limonene to give the two bridged-ring ketones (139).228... 

Unsaturated ketones are known to react with dichloromethyl phenyl sulfoxide to give adducts which produced fully substituted furans in high yields after treatment with trifluoroacetic anhydride and Nal, as illustrated in the following scheme. Trisubstituted... 

Cyanotrialkylborates (11), which can Iw readily prej red and are stable, are of interest due to their synthetic applicability in organic synthesis. Although no detail introduction of the reactions is n here, a brief account is presented. Cyanotrialkylborates react smoothly with 1 equivalent of trifluoroacetic anhydride (TFAA) at —78 °C and then at room temperature. Oxidation of the intermediates with hydrogen peroxide under basic conditions gives the corresponding symmetrical ketones in excellent yields The reaction is considered to proceed via the reaction path, as indicated in Eq. 23. Unsymmetrical ketones can also be obtained... 

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