Fluorocarbonyl groups

In all these reactions, HCl acceptors, such as pyridine (3) or triethylamine 110), are used. In this respect fluorocarbonylsulfenyl chloride behaves quite extraordinarily 48) witii alcohols it reacts at the fluorocarbonyl group with formation of alkoxycarbonylsulfenyl chlorides. 

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]. 

According to studies on the reactivity of hexafluoroacetone, these carbonyl groups are very reactive to radicals. There are two possibilities for the addition of R radicals to fluorocarbonyl groups ... 

Nitro compounds are oxidized at carbon bonded to nitro group 2-nuoronitro compounds and silyl mtronates are converted to 2-fluorocarbonyl compounds by ceric ammonium salt [7l (equation 73)... 

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] ... 

The interaction of Si(NCO), or MejSi(NCO) with COF occurs in an autoclave at 200-283 C the NCO group is substituted and fluorocarbonyl isocyanates are formed according to [771a] ... 

Conformations about two bonds must be considered for fluorocarbonyl trifluoromethanesulfonate, FC(0)0S02CF3.33 There are two different arrangements of the FC(O) groups relative to the CF3 group, trans [67(8%)] and gauche, with the CSOC dihedral angle 72(6)°. In both of these the C=0 bond is orientated synperiplanar with respect to the OS single bond. This distribution... 

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. 

The system CFs COF + M+F 5 CF, CFsO M+(M = Li—Cs inclusive) has been subjected to radiotracer investigation. (Comparison between the CFs-COF-Cs F and (CFa)jCO-Cs F systems (see Table 1) indicates that only the fluorocarbonyl F atom exchanges readily under the conditions used and, at 50—150 °C, the degree of F exchange between CFj-CO F and Group I fluorides varies in the order Cs > Rb > K > Na > Li (see Table 2). These results are in keeping with preparative experience. ... 

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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