A-fluorocarbonyl compound

Chlorinated oxiranes can be treated with silver(I) tetrafluoroborate to yield the corresponding a-fluorocarbonyl compounds as major products and the isomeric a-chlorocarbonyl compounds as minor products.74... 

Thallium(I) fluoride is, furthermore, used for the conversion of acyl chlorides to acyl fluorides6 and the preparation of a-fluorocarbonyl compounds.7,8... 

Many fluorinations by electropositive fluorine reagents produce a-fluoro carbonyl compounds as the final result An extensive review exists on the preparation of a-fluorocarbonyl compounds [10]. Also, electropositive reagents are used, widely in the preparation ofISF-labeled radioactive materials required in positron emission tomography for biomedical research Excellent reviews are available on fluonne-18 labeling [11, 12]. 

Aziridines behave similarly to epoxides and were used for making aliphatic and steroidal fluoroamines (equations 12 and 13)25, the latter via trans diaxial opening26. Azirines were also treated with HF Py producing a,a -difluoroamines or a-fluorocarbonyl compounds depending on the reaction solvent (equation 14)27. 

Another stereoelectronic effect induced by electronegative substituents is the "Anh-Eisenstein effect [44] (Scheme 4.17) which can be of particular importance to the stereochemical outcome of enzymatic reactions involving fluorinated substrates [45]. In a-fluorocarbonyl compounds nucleophilic attack of the carbonyl group occurs preferentially anti to the fluorine substituent [46]. The resulting, unusually high stereospecificity, e.g. in some enzymatic reactions of fluorinated substrates [45], cannot be explained by the slightly different steric demands of hydrogen and fluorine alone. 

S. Rozen and R. Filler, a-Fluorocarbonyl Compounds and Related Chemistry, Tetrahedron, 1985, 4J, 1111. 

Monofluorination of Enolates. /V Fluorosultam (1) has been successfully used to prepare a-fluorocarbonyl compounds by electrophilic fluorination starting, for example, from disubstituted enolates derived from ketones, esters, and -dicarbonyl compounds (eqs 13). The related /V-fluorosulfonamide reagents ... 

Fluorination of Enolates and Silyl Enol Ethers. iV-fluoro-Af-(phenylsulfonyl)henzenesulfonamide (1) can be used successfully to prepare a-fluorocarbonyl compounds starting from esters, ketones, or 8-dicarbonyl precursors by electrophilic fluorination of the corresponding enolates (eqs 1-3) or silyl enol ethers (eq 4). Diastereoselective fluorination of enolates with 1 has recently been reported. ... 

Obviously, CsF is a better source for nucleophilic fluorine than any other metal fluoride and, indeed, it is used to attack fluorocarbonyl compounds on route to make hypofluorites... 

Group 1 metal fluorides have been employed as column packings for the determination of COF2 (and other fluorocarbonyl compounds) in mixtures with tetrafluoroethene [967]. By using a column composed of CsF supported upon CaFj, the tetrafluoroethene is not chemisorbed and is eluted rapidly. The fluorocarbonyl compounds (CF3)jC=0 (b.pt. -28 C), CF3C(0)F (b.pt. -59 C), and COF (b.pt. -84.6 C), however, are eluted in reverse order of boiling temperatures, so that carbonyl difluoride is eluted last [967]. The chemisorption arises from the reversible chemical process [1692] ... 

On the other hand, in -fluoroalkyl groups (with one uncompensated C-F dipole moment) fluorination usually reduces lipophilicity. Another important instance of fluorine substitution reducing lipophilicity is in compounds with a-fluorocarbonyl groups. In these fluorination can increase the electrophilicity of the carbonyl carbon atom to such an extent that the formation of stable, polar hydrates occurs this again reduces the lipophilicity significantly (Scheme 4.13). In a-fluorocar-boxylic acids and fluorinated phenols the lipophilicity is also reduced by the increased ionization constant which results from the negative inductive —la) effect of fluorine [16]. 

Unsaturated halogenated compounds with a central C = C or C = C bond undergo cleavage on oxidation in the middle of the molecule and form two carboxylic acids without loss of a carbon atom. The reaction mechanism of the oxidation of internal fluoroalkenes by potassium permanganate includes hydroxylation of the C = C bond in 2 by permanganate, accompanied by dehydrofluorination of the geminal fluoroalkane-1,2-diol 3 and formation of an intermediate fluorocarbonyl compound 4 oxidative cleavage of the C-C bond in 4 leads to the final products 5.1... 

Nitrosyl fluoride also catalyses the addition of chlorine monofluoride (and of fluorine) across G=0 bonds in fluorocarbonyl compounds, the reaction apparently proceeding via initial formation of a-fluoro-nitrites. Apparently, no reaction occurs between carbon dioxide and chlorine monofiuoride in the presence of caesium fluoride in the temperature range -78 to 80 G [c/. CO3 + 2F °S GF COF), (100%)], but thionyl... 

Triaminopyrimidin-6(l/0-one 39 reacts with a range of fluorocarbonyls to give fluoropterins (Scheme 6). The fluoropterins are even more insoluble than the parent compounds and are also stable to nucleophiles and bases in dilute aqueous solution <96113017 >. 

N-Formylsaccharin 102, an easily accessible crystalline compound, has been employed as an efficient CO source in Pd-catalyzed fluorocarbonyl-ation of aryl halides 103 to afford the corresponding acyl fluorides 104 (13OL5370). Reagent KF is expected to serve as a dual role not only as a nucleophile for Pd-catalyzed carbonylation but also as an activator for CO generation from 102. The reactions use a near-stoichiometric amount of the CO source (1.2 eq) and tolerate diverse functional groups. The acyl fluorides 104 can be readily transformed into various carboxylic acid derivatives such as carboxylic acid, esters, thioesters, and amides in a one-pot procedure. 

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