Ketones trifluoromethanesulfonic acid

Trifluoromethanesulfonic acid is miscible in all proportions with water and is soluble in many polar organic solvents such as dimethylformamide, dimethyl sulfoxide, and acetonitrile. In addition, it is soluble in alcohols, ketones, ethers, and esters, but these generally are not suitably inert solvents. The acid reacts with ethyl ether to give a colorless, Hquid oxonium complex, which on further heating gives the ethyl ester and ethylene. Reaction with ethanol gives the ester, but in addition dehydration and ether formation occurs. 

Friedel-Crafts acylation using nittiles (other than HCN) and HCI is an extension of the Gattermann reaction, and is called the Houben-Hoesch reaction (120—122). These reactions give ketones and are usually appHcable to only activated aromatics, such as phenols and phenoHc ethers. The protonated nittile, ie, the nitrilium ion, acts as the electrophilic species in these reactions. Nonactivated ben2ene can also be acylated with the nittiles under superacidic conditions 95% trifluoromethanesulfonic acid containing 5% SbF (Hg > —18) (119). A dicationic diprotonated nittile intermediate was suggested for these reactions, based on the fact that the reactions do not proceed under less acidic conditions. The significance of dicationic superelectrophiles in Friedel-Crafts reactions has been discussed (123,124). 

A novel and versatile method for preparing polymer-supported reactive dienes was recently developed by Smith [26]. PS-DES (polystyrene diethyl-silane) resin 28 treated with trifluoromethanesulfonic acid was converted to a polymer-supported silyl triflate 29 and then functionalized with enolizable a,jS-unsaturated aldehydes and ketones to form silyloxydienes 30 and 31 (Scheme 4.4). These reactive dienes were then trapped with dienophiles and the Diels Alder adducts were electrophilically cleaved with a solution of TFA. 

Vinyl trifluoromethanesulfonates (triflates) are a new class of compounds, unknown before 1969, that have been used most extensively in solvolytic studies to generate vinyl cations.2,3,812 Three methods have been used to prepare these sulfonic esters. The first, involving the preparation and decomposition of acyltriazines,4 requires several steps to prepare the acyltriazines and is limited to the preparation of fully substituted vinyl triflates. The second method involves the electrophilic addition of trifluoromethanesulfonic acid to acetylenes5,8,15 and, consequently, is not applicable to the preparation of trisubstituted vinyl triflates and certain cyclic vinyl triflates. However, this second procedure is relatively simple and often gives purer products in higher yield than the subsequently discussed reaction with ketones. Table I lists vinyl triflates that have been prepared by this procedure. ... 

Pyrazinyl ketones can be protected as the acetal by treatment with alkanediol in the presence of trifluoromethanesulfonic acid <1999JA8783> or 8-amino-l,3,6-pyrenetrisulfonic acid (APTS) <2005JOC2616>. 

Imines of acyclic and C10- to C15-membered carbocyclic ketones are prepared under the conditions described for cyclohexanone imines using trifluoromethanesulfonic acid or trifluoroacetic acid as additional catalyst. The reaction often takes several days in refluxing benzene or toluene9. 

Oxidation. This reagent is prepared by reaction of CAN with K2C03 (2 equiv.) to form Ce(C03)2, which is then treated with trifluoromethanesulfonic acid (4 equiv.). This oxidant is effective for oxidation of benzylic alcohols to aldehydes (72-92% yield), and of alkylarenes to aldehydes or ketones (65-70% yield). 

The method is particularly well-suited to the fluorination of dithioketals of aromatic ketones (Table 12). To achieve reasonable yields with dithioketals of aliphatic or alicyclic ketones, the addition of trifluoromethanesulfonic acid or hydrogen fluoride/pyridine is required. In general, dithiane derivatives give better yields than dithiolane derivatives. 

The most important method for the preparation of aryl ketones is known as Friedel-Crafts acylation. The reaction is of wide scope. Reagents other than acyl halides can be used," including carboxylic acids," anhydrides, and ketenes. Oxalyl chloride has been used to give diaryl 1,2-diketones." Carboxylic esters usually give alkylation as the predominant product (see 11-11)." A-Carbamoyl p-lactams reacted with naphthalene in the presence of trifluoromethanesulfonic acid to give the keto-amide." ... 

The oxidative cleavage of epoxides with hydrogen peroxide gives vicinal hydroxy hydroperoxides [178]. With dimethyl sulfoxide in the presence of trifluoromethanesulfonic acid and diisopropylethylamine, epoxides are converted into a-hydroxy ketones [1014], and with periodic acid, dicarbonyl compounds are formed [761] (equations 343 and 344). 

Hydroxylamine sulfonic acid, hydroxylamine and catalytic amounts of trifluoromethanesulfonic acid, or 0-mesitylenesulfonylhydroxylamine converts ketones directly to the lactams under mild conditions (reflux in formic acid). 

More tractable and potentially useful polyether ketones, incorporating phenylene-carborane-phenylene units, and with properties suitable for high temperature applications, have been prepared by acylation reactions (using trifluoromethanesulfonic acid as both medium and catalyst) between appropriate dicarboxylic acids and phenoxyphenylcarboranes. For example, the polyetherketone 20 (Scheme 3.6), derived from bis(4-phenoxyphenyl)-para-carborane and biphenyl-4,4 -dicarboxylic acid, is essentially amorphous on isolation from trifluoromethanesulfonic acid, but crystallizes when heated above its glass transition temperature (267°C) before hnally melting at about 390 0... 

It is assumed that this reaction proceeds via the cationoid intermediates 251 and 252 which are analogous to those described by Zielinski (equations 48 and 50). The same type of nitrilium intermediates 258 and 259 are assumed to be formed by protonation of vinyl chlorides 255 by trifluoromethanesulfonic acid in the nitrile as a solvent (equation 71)86,133 highly reactive vinyl cations 262 and 263 are generated from the vinyl triflates 261, obtained from corresponding ketones. These cations react... 

Condensation of ketones with two mole equivalents of a nitrile in the presence of trifluoromethanesulfonic acid anhydride is a nsefnl method for the production of a limited range of pyrimidines, where the substituents at C-2 and C-4 are identical. ... 

The combination of triethylsilane and trifluoromethanesulfonic acid reduces aryl ketones to the methylene derivative61 (equation 53). 

In a complementary approach for preparing a-ketotriflates Varma and Kumar used the combination of iodobenzene diacetate and trifluoromethanesulfonic acid to prepare p-oxobis[trifluoromethanesulfonato(phenyl)iodme] 207 in situ. This reagent cleanly converted aromatic a-methyl ketones to the corresponding a-ketotriflates 204, which reacted with nitriles to afford 2-alkyl-5-aryloxazoles 206 in variable yield (Scheme 1.58). Mechanistically, the authors proposed the same... 

High-molecular-weight poly(ketone)s and poly(ketone sulfone)s can be prepared by reacting dicarboxylic acids with aromatic compounds in the presence of trifluoromethanesulfonic acid and phosphorus pentoxide for water binding. 

Poly(aryl ether ketone) Cone, sulfuric acid, trifluoromethanesulfonic acid, diphenyl sulfone, sulfolane Alcohol, ether, methylene chloride... 

One of the significant differences between hydrocarbon ionomers and perfluoro-sulfonic acid polymers is add groups. The pKa value of benzenesulfonic acid (PhSOsH) is 2.5 and that of trifluoromethanesulfonic acid (CF3SO3H) is —13. The pKa value was estimated to be ca. 1 for sulfonated polyether ketone and ca. —6 for Nafion membranes [78]. Therefore, the effective proton concentration and proton mobility should be lower in the hydrocarbon ionomer membranes. Without appropriate molecular design such as multiblock copolymer and sulfonic acid clusters as mentioned above, hydrocarbon ionomer membranes lack well-developed ionic channels due to less pronounced hydrophilic and hydrophobic phase separation, which causes the lower proton conductivity at low humidity. 

As described in Sect. 2.1.2, the a-functi(Mialization (tosylation, triflation) of ketones with hypervalent iodine, followed by nucleophilic attack by diverse nucleophiles in an intramolecular fashion offers a convenient entry to various heterocycles [6]. Such a transformation can also be realized in an intermolecular fashion. Along these lines, Togo and coworkers [97] reported an elegant one-pot synthesis of 2,4,5-trisubstituted oxazoles 142 from alkyl aryl ketones 140 and nitriles 141 via an iodoarene-catalyzed oxidation reaction (Scheme 35). In this reaction sequence, reactive aryliodonium species were generated in situ by the reaction of aryl iodide with mCPBA and trifluoromethanesulfonic acid (TfOH). Afterwards, aryliodOTiium species reacted with alkyl aryl ketone to form a fi-keto aryliodonium species. 

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