Fluorinated reactive intermediates

Systematics and Surprises in Bond Energies of Fluorinated Reactive Intermediates... 

A/-Chloro fatty acid amides have been synthesized from the direct halogenation of the amide in boiling water (28). They are useful as reactive intermediates for further synthesis. Fluorination has also been reported by treating the fatty amide with fluorine-containing acid reagents at 200 °C to reach a fluorinated amide with less reactivity toward fluorocarbon polymers (29). 

Diazocines are isolated, as byproducts, in another photochemical reaction which starts from fluorinated pyridazines. On irradiation of 6 a Dewar diazabenzene derivative is formed, via an electrocyclic ring closure, which looses a fluorinated nitrile to give the azacyclobutadiene system 7. This reactive intermediate then leads vide supra) to the 1,5-diazocine 8.50... 

It might be pertinent to consider the basis of the extremely facile isomerization in anhydrous HF or pyridinium poly(hydrogen fluoride). HF is an extremely strong proton donor, but it is also a potent fluorinating agent. It is highly probable that the postulated cationic intermediates in these isomerizations are fluori-nated and serve as reactive intermediates in the same way as the fructofuranosyl... 

Irradiation of 1,2,4-oxadiazoles 205 bearing fluorinated substituents in the 3- or 5-positions in the presence of an amine delivered the corresponding 1,2,4-triazoles 206a-e and 207a-e via a photochemical rearrangement. Several other competing reactions served to divert some of the reactive intermediates and, hence, yields of the fluorinated triazoles were modest (Equation 64 and Table 44) <2005H(65)387>. 

P. A. G. O Hare. The Nuts and Bolts and Results of Fluorine Bomb Calorimetry. In Energetics of Stable Molecules and Reactive Intermediates M. E. Minas da Piedade, Ed. NATO ASI Series C, Kluwer Dordrecht, 1999 55-75. 

Organo-fluorine compounds have a diverse, often unanticiptated chemistry. The chemical behavior of fluorinated species is much more comprehensible if the effects of fluorination on reactivity are rationalized. It is the effect of fluorine on reactive intermediates that in turn governs the outcome of reactions. The principal properties of fluorine which have the most profound influence on bonding and, therefore, reactivity are the pronounced electronegativity of fluorine1 and its associated low polarizability,2 the availability of three nonbonded electron pairs, and the excellent overlap that is possible between the 2s and 2p orbitals of fluorine and those of carbon.3... 

Organofluorine Chemistry Fluorinated Alkenes and Reactive Intermediates (Topics in Current Chemistry, Vol. 192) Chambers, R. D.. Ed. Springer Berlin. 1997. 

Fluorinated carbocations play an important role as intermediates in electrophilic reactions of fluoroolefins and other unsaturated compounds. For example, F-allyl cation 1 was proposed as a reactive intermediate in reactions of HFP with fluoroolefins catalyzed by Lewis acids [7]. The difference in stability of the corresponding allylic cations was suggested as the explanation for regio-specific electrophilic conjugated addition to CF2=CC1CF=CF2 [11]. Allylic polyfluorinated carbocations were proposed as intermediates in the reactions of terminal allenes with HF [53] and BF3 [54], ring-opening reactions of cyclopropanes [55], Carbocations are also an important part of the classic mechanism of electrophilic addition to olefins (see Eq. 2). This section deals with the questions of existence and stability of poly- and perfluorinated carbocations. 

Deprotonation of A-fluoropyridinium fluorides, e.g., 363, generated in situ by reaction of pyridines with fluorine gas, undergoes reaction with isonitriles to give 2-picolinamides 365 in moderate to good yields, the carbene 364 being the reactive intermediate <2005TL2279>. 

Usually, high oxidation states of metals are stabilized most effectively when in combination with the most electronegative atoms, fluorine and oxygen. Rather surprisingly, no FeIV or higher oxidation state compounds with fluorine are known. Indeed rather few stable or well-defined higher oxidation state iron compounds are known. Despite this, there can be no doubt about the importance of such compounds. We have already encountered the FeIV and Fev states in reactive intermediates in the reactions of several metalloproteins and of several synthetic porphyrin complexes. 

With CF3C=CCF3 or olefins with an internal double bond such as cis- or fraras-F-2-pentene, F-cyclobutene, or l,2-dichloro-l,2-difluoro-ethylene, or with a geminally disubstituted olefin such as 1,1-dichloro-2,2-difluoroethylene, only fully fluorinated products were obtained, likely through a nucleophilic fluorination mechanism. This fact, plus the necessity for a Lewis acid catalyst for addition to proceed, is evidence for an electrophilic addition mechanism. Others have suggested polar addition of BF3 to the olefin with RfBF2 as a reactive intermediate (294). 

R.D. Chambers (ed.), Organofluorine Chemistry. Fluorinated Alkenes and Reactive Intermediates, Springer-Verlag, Berlin, 1997. 

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