Nucleophilic reactions, fluorinated

Nucleophilic Reactions. The strong electronegativity of fluorine results in the facile reaction of perfluoroepoxides with nucleophiles. These reactions comprise the majority of the reported reactions of this class of compounds. Nucleophilic attack on the epoxide ring takes place at the more highly substituted carbon atom to give ring-opened products. Fluorinated alkoxides are intermediates in these reactions and are in equiUbrium with fluoride ion and a perfluorocarbonyl compound. The process is illustrated by the reaction of methanol and HFPO to form methyl 2,3,3,3-tetrafluoro-2-methoxypropanoate (eq. 4). 

N-fluorine displacement, 7, 272 1-Azetine, 2-alkoxy-nucleophilic reactions, 7, 271 1-Azetine, 2-aryl-mass spectrometry, 7, 268 nucleophilic reactions, 7, 271 1-Azetine, 2-chIoro-nucleophilic reactions, 7, 271... 

As has been exemplified in this chapter, fluorinations with fluorine-18 can be classified into two categories (1) the nucleophilic reactions, which usually involve no-carrier-added [ F]fluoride of high-specific radioactivity as its Kf FIF-K complex and include substitutions in the aliphatic and the /lomoaromatic series and (2) the electrophilic reactions, which mainly use moderately low-specific radioactivity molecular [ F]fluorine, or other reagents prepared from it, such as acetyl [ F] hypofluorite, and include addition across double bonds, reactions with carbanions and especially fluorodehydrogenation and fluorodemetallation reactions. 

Chambers RD, Vaughan JFS (1995) Nucleophilic Reactions of Fluorinated Alkenes. 192 1-38 Chambron J-C, Dietrich-Buchecker Ch, Sauvage J-P (1993) From Classical Chirality to Topologically Chiral Catenands and Knots. 165 131-162. 

Furthermore, the halofluorination method can also be modified to prepare vicinal difluorides by a one-pot two-step reaction. Halofluorination followed by nucleophilic halogen-fluorine exchange is carried out simply by adding silver(I) fluoride to a solution of the initially formed a-fluoro-/J-haloalkanes, effecting the exchange in situ202 203 (Table 12). 

Fluorinated -alkenes and -cycloalkenes have a special relationship with their hydrocarbon analogues, usually exhibiting a chemistry that is complementary. For example, the fluorinated systems are frequently susceptible to nucleophilic attack, in some cases dramatically so, and therefore reactions of nucleophiles with fluorinated alkenes often reveal unique new chemistry. This chapter covers electrochemical reduction, principles governing orientation and reactivity of fluorinated alkenes towards nucleophiles, fluoride ion as a nucleophile and the mirror-image relationship of this chemistry with that of proton-induced reactions, reactions with nitrogen-, oxygen-, carbon- centred nucleophiles etc., and, finally, chemistry of some oligomers of fluorinated -alkenes and -cycloalkenes. 

Ishikawa N (1979) The first regular meeting of soviet-japanese fluorine chemists. Nucleophilic reactions of hexafluoropropene oligomers, Tokyo, p 125 and references contained... 

The data for competition between formation of (19) and (20) in aliphatic systems are more limited, but they are only partly accounted for by the carbanionic theory. Attack on chlorotrifluoroethylene, for example, is nucleophile-dependent fluorine from the CF2 group is replaced on reaction with PhMgBr (Tarrant and Warner, 1954), PhLi (Dixon, 1956) and LiNBu2 (Yakubovich et al., 1966), while Re(CO) ... 

Because of the presence of nitrogen in the aromatic ring, electrons in pyridine are distributed in such a way that their density is higher in positions 3 and 5 (the P-positions). In these positions, electrophilic substitutions such as halogenation, nitration, and sulfonation take place. On the contrary, positions 2, 4, and 6 (a- and y-positions, respectively) have lower electron density and are therefore centers for nucleophilic displacements such as hydrolysis or Chichibabin reaction. In the case of 3,5-dichlorotrifluoropyridine, hydroxide anion of potassium hydroxide attacks the a- and y-positions because, in addition to the effect of the pyridine nitrogen, fluorine atoms in these position facilitate nucleophilic reaction by decreasing the electron density at the carbon atoms to which they are bonded. In a rate-determining step, hydroxyl becomes attached to the carbon atoms linked to fluorine and converts the aromatic compound into a nonaromatic Meisenheimer complex (see Surprise 67). To restore the aromaticity, fluoride ion is ejected in a fast step, and hydroxy pyridines I and J are obtained as the products [58],... 

In aromatic systems, oxazolines can have three different functions (Fig. 4). Firstly, they can be used as protecting groups for carboxylic acids. Secondly, they activate even electron-rich aromatic systems for nucleophilic substitution. Fluorine or alkoxy groups in the ortho position can be substituted by strong nucleophiles such as Grignard reagents. Thirdly, when biaryl compounds with axial chirality are synthesized in these reactions, oxazolines can induce the formation of only one atropisomer with excellent selectivity. These three qualities were all used in the synthesis of 20, a precursor of the natural product isochizandrine [10]. 

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