Fluorinating agents nucleophilic

In principle, two mechanisms involving either one or two-electron transfer from the aromatic substrate to fluorine may occur and, in practice, the mechanism of fluorination of any given aromatic molecule probably lies between these two extremes. The distinction between electron transfer (Path A, Fig. 55) and SN2-type processes (Path B, Fig. 55) in reactions between various electrophilic fluorinating agents and nucleophiles has been addressed by Differding [144, 145] but these principles can also be applied to reactions involving elemental fluorine. 

Kinetics of the transformations of the N-F class of fluorinating agents in water, acetonitrile, alcohols, and aqueous solutions of alkali metal hydroxides have been studied.159 Other kinetic studies include die reactions of triphenylphosphine with 3-methoxy- or 3-acctoxy-4,4,5,5-tetrasubstitutcd-1,2-dioxolanes,160 the reactions of 2-amino-5-chlorobenzophenone witii HC1 in MeOH-H20 (die aspect of nucleophilic aliphatic substitution lies in certain products arising from attack of AH2 on CH3OH there are six products in all, and rate constants are evaluated for die formation of each of them),161 and the hydrolysis of derivatives of diazidophenyhnethane.162... 

Albanese, D. Landini, D. Penso, M. Hydrated TBAF as a powerful nucleophilic fluorinating agent./. Org Chem. 1998, 63, 9587-9589. 

Current understanding of the reaction suggests that an unprecedented mechanism is operating. Unlike in classical Lewis acid catalysed reactions [28], the metal complex does not activate the carbonyl moiety but is understood to enhance the degree of enolisation and thus create the necessary nucleophilic enol structure for reaction with the fluorinating agent [29]. 

Many metal fluorides beside KF have been tried as nucleophilic fluorinating agents but only a few succeeded in establishing themselves as such. We will briefly survey here fluorides of silver, mercury, cesium and antimony. 

The actual chemical nature of the support material may be and often is of direct importance to its usefulness as a support material.15 Silicas can react with small nucleophiles such as F-, OH- and CN. Thus, silica-supported fluorides are inactive, both as nucleophilic fluorinating agents and as bases. Similarly, silicas are not effective support materials for cyanides due to the formation of strong Si-CN bonds. For different reasons, an acidic clay would not be a suitable support for cyanides, due to the possible formation of toxic HCN. Charcoal is the most effective support material for stabilising Cu(I), probably due to its aromatic character.16 For many chemisorbed supported reagent catalysts, silicas are preferred since they give relatively strong surface bonds. However, Si-O-C bonds are hydrolytically vunerable and direct Si-C bonds are preferred.17... 

In a previous study on the use of fluoroxytrifluoromethane (CF3 OF) as an electrophilic fluorinating agent, it was suggested that fluoroxy-compounds as a class might be disposed to undergo nucleophilic attack at fluorine. This hypothesis... 

Applications in Fluorination. lodofluorinated compounds are obtained using the so-called three-component reaction [a substrate, an electrophile (NIS), and a nucleophile (fluorination agent)] from alkenes or alkynes in a regio- and stereoselective way (eq 13).3 -32... 

As a postscript to this story, we may add that, as a nucleophilic fluorinating agent, [i8F]-TBAFjyjj has been found to be significantly superior to cryptand-activated K F, which is the standard source in positron-emission tomography (PET). 

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