Trifluoromethyl group ketone

A large variety of newer poly(ether imide)s has been described. Included among these are perfluorinated polymers (96), poly(ester ether imide)s (97), poly(ether imide)s derived from A/,Ar-diamino-l,4,5,8-naphthalenetetracarboxyHcbisimide (98), and poly(arylene ether imide ketone)s (99). In addition, many other heterocyHc groups have been introduced into polyether systems, eg, poly(pyrazole ether)s (100) and poly(aryl ether phenylquinoxaLine)s (101) poly(aryl ether oxazole)s with trifluoromethyl groups (102) and polyethers with other heterolinkages, eg, poly(arylether azine)s (103). 

Four-membered heterocycles are easily formed via [2-I-2] cycloaddition reac tions [65] These cycloaddmon reactions normally represent multistep processes with dipolar or biradical intermediates The fact that heterocumulenes, like isocyanates, react with electron-deficient C=X systems is well-known [116] Via this route, (1 lactones are formed on addition of ketene derivatives to hexafluoroacetone [117, 118] The presence of a trifluoromethyl group adjacent to the C=N bond in quinoxalines, 1,4-benzoxazin-2-ones, l,2,4-triazm-5-ones, and l,2,4-tnazin-3,5-diones accelerates [2-I-2] photocycloaddition processes with ketenes and allenes [106] to yield the corresponding azetidine derivatives Starting from olefins, fluonnaied oxetanes are formed thermally and photochemically [119, 120] The reaction of 5//-l,2-azaphospholes with fluonnated ketones leads to [2-i-2j cycloadducts [121] (equation 27)... 

Although the sulfur trifluoride compounds are generally useful as selective agents for conversion of carbonyl and carboxyl groups to difluoromethylene and trifluoromethyl groups, variations in reaction conditions are often necessary.7 Thus the reaction of aromatic ketones requires heating at 150°. Since the reaction with aliphatic aldehydes and ketones is exothermic, it is advan-... 

The preparation of (128) (Scheme 34) highlights the use of the trifluoromethyl group to increase the dipolarophilicity of a ketone. This activating effect of electron withdrawing groups is also taken advantage of in the preparation of 3-carbonyl substituted 1,2,4-trioxolanes (131) via the ozonolysis of a vinyl ethers in the presence of a 1,2-dicarbonyl compound (Scheme 36) <9iJOC659l>. 

Similar transformations using a,P-unsaturated ketones activated with a trifluoromethyl group also proved to be highly efficient (e.g., 4 5 <99SL756>, 6- 7 <99TL2541>) for the... 

Reconversion of the ketonic carbonyl group into a diazo group sets the stage for intramolecular carbenoid addition to an alkene [276]. A recent paper described syntheses of 2-C-trifluoromethyl 3-deoxypentoses [277] from ethyl trifluoropyru-vate other approaches to heterocycles containing trifluoromethyl groups were reviewed recently and will therefore not be discussed further here [278]. 

Perfluoro ketones and perfluoro a-diketones, with a trifluoromethyl group in the -position to the carbonyl, cyclize in the presence of antimony(V) fluoride to give furan derivatives, as reviewed by Krcspan and Petrov.4 Perfluoro(4-methylpentan-2-one) (1) rearranges to per-fluoro(2,4-dimethyltetrahydrofuran) (2) in 84% yield, when heated in the presence of anti-mony(V) fluoride.5... 

The mechanism for the cyclization of these perfluoro ketones, proposed by German and coworkers5 and discussed in the review by Krcspan and Petrov.4 involves initial activation of the carbonyl with antimony V) fluoride and a 1.4-fluorine shift from the /1-trifluoromethyl group. The resultant difluoromethylene carbocation then cyclizes with the carbonyl oxygen to give the tetrahydrofuran. 

Peptidyl fluoromethyl ketones are widely used as fairly potent inhibitors for a variety of proteases, including serine, cysteine, and aspartyl proteases. Unlike other halomethyl ketones (Section 15.1.3), fluoromethyl ketones are reversible transition-state mimics. The electron-withdrawing fluorine(s) next to the carbonyl group enhances the electrophilicity of the a-fluoroalkyl ketone functionality, thereby making the carbonyl more susceptible to nucleophilic attack. a-Fluoroalkyl ketones are good mimics of peptide bonds due to the small size of the fluorine and the stability of C F bonds. There are three general classes of peptidyl fluoromethyl ketones fluoromethyl ketones (irreversible inhibitors of cysteine proteases), difluoromethyl ketones (reversible inhibitors of both serine and aspartyl proteases), and trifluoromethyl/perfluoroalkyl ketones, which typically exist in hydrated forms and are excellent inhibitors of both serine and cysteine proteasesJ1 ... 

Reactions of unsaturated ketones 62 containing a strong a electron-withdrawing trifluoromethyl group with urea and its analogues 28, 60 and 61 usually stop at the stage of the formation of hydroxytetrahydropyrimidines 63 [69] (Scheme 3.19). 

Nagai, T. Nishioka, G. Koyama, M. Ando, A. Miki, T. Kumadaki, I. Reactions of trifluoromethyl ketones. IX. Investigation of the steric effect of a trifluoromethyl group based on the stereochemistry on the dehydration of trifluoromethyl homoallyl alcohols./. Fluorine Chem. 1992, 57, 229-237. 

On the basis of differences in electronegativity, tlie C - Si bond possesses 12% ionic character. Silicon is the positive end and carbon is the negative end of the dipole. Trimethyl(trifliioro-methyl)silane is thus a reagent for introducing the trifluoromethyl group into carbonyl compounds (aldehydes, ketones, enoncs). ... 

The trifluorinated a./ -unsaturatcd ketone 43 can be prepared by two different methods and behaves like a Michael addition acceptor in reaction with nucleophilic species.1 Is reaction with an enamine gives an annulation product 44. This sequence constitutes a method to build up a ring bearing a trifluoromethyl group. 

Enantioselective Reduction of a,p-Enones. Oxazaborolidine catalyst Ic was also found to be a superior catalyst compared to la and lb for the reducdon of a,p-unsaturated ketone derivatives (eq 5). It is interesdng to note that the presence of a bulky substituent at the p-posidon is mandatory for high enandocon-trol. This reaction has been used as a key step in the synthesis of atractyligenin. This catalyst has also been used to reduce a,p-unsaturated ketones bearing a trifluoromethyl group in 87% ee. ... 

Imines 1110 derived from trifluoromethyl aryl ketones and orT o-phenylenediamines 1109 undergo intramolecular cyclization to afford 2-arylbenzimidazoles 1111. The reaction is carried out under basic conditions and the CF3 group serves as a leaving group (Scheme 268) <1999TL4119>. 

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