Carbon-fluorine bond forming reactions

Carbon - Fluorine Bond Forming Reactions C-F bond 1... 

SCHEME 1.9 Examples of a palladium-catalyzed carbon-fluorine bond-forming reaction [21]. 

The principal advantage to this method is that the heat evolved for each carbon—fluorine bond formed, 192.5 kj/mol (46 kcal/mol), is much less than that obtained in direct fluorination, 435.3 kJ/mol (104 kcal/mol). The reaction yields are therefore much higher and less carbon—carbon bond scisson occurs. Only two metal fluorides are of practical use, Agp2 and GoF. ... 

Nakamura, Y, Takeuchi, S. and Ohgo, Y. (2(X)3) Enantioselective carbon xffbon bond forming reactions using fluorous chiral catalysts. J. Fluorine Chem., 120,121-9. 

Organocatalytic asymmetric carbon-halogen bond-forming reactions have been combined with other catalytic asymmetric reactions in a single flask to effect cascade reactions. Quintard and Alexakis [78] developed a cascade reaction in which a Cu-catalyzed conjugate addition to an a,p-unsaturated aldehyde was followed by an enamine-catalyzed a-fluorination or chlorination. 

Organic fluorine compounds were first prepared in the latter part of the nineteenth century. Pioneer work by the Belgian chemist, F. Swarts, led to observations that antimony(Ill) fluoride reacts with organic compounds having activated carbon—chlorine bonds to form the corresponding carbon—fluorine bonds. Preparation of fluorinated compounds was faciUtated by fluorinations with antimony(Ill) fluoride containing antimony(V) haUdes as a reaction catalyst. 

The extension of an array to include, for example, a halodifluoromethyl ketone sets the stage for a second carbon-carbon bond forming reaction via a di-fluoroenolate or synthetic equivalent (Eq. 123). Despite the obvious power of this approach for the assembly of more complex molecules around a C-2 fluorinated unit, there are relatively few examples in the literature. 

It is frequently overlooked that, following fluorination, some of these systems, e.g. Selectfluor , are extremely acidic and may, consequently, ionise the carbon-fluorine bond just formed, leading to a carbocation and subsequent reaction with the solvent (see Section IIIA) [65]. 

Carbon monofluoride of lower stoichiometry has been normally prepared by the reaction of elemental fluorine with graphite at temperatures in the range 400-600°. It is interesting to observe that graphite does not begin to react with a fluorine atmosphere until 400°, while all carbon compounds containing double bonds will burn in fluorine under identical conditions. Examination of the thermodynamics of fluorine addition to normal double bonds reveals that this reaction is exothermic by approximately 68 kcal/ mol of carbon fluoride bonds formed. 

Electrophilic fluorination is the process by which fluorine is delivered to an electron-donating reactant, such as an alkene, aromatic ring or carbanion, by a formal positive-fluorine reagent to form a carbon-fluorine covalent bond. These reactions are fast and have proven extremely valuable for some important fluorine-18-labelled radiopharmaceuticals. Over the years several reviews on electrophilic fluorination were written. The reader is encouraged to seek out these works for greater detail on the subject [7,68-70]. 

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