Imidoyl fluorides cyclic, perfluorinated

The presence of highly electrophilic C=N bond defines the reactivity of this class of compounds. Similar to other perfluorinated imidoyl fluorides, cyclic analogues are sensitive to the action of nucleophiles. For example, compounds 81 and 124 react with metal fluoride anion in polar solvents with the formation of the salt 125, which can react with a strong electrophiles (Fig. 9.38). 

The reaction of perfluorinated cyclic amines with strong Lewis acids, such as SbFs or aluminum chlorofluoride (ACF), at elevated temperature results in rapid cleavage of amine, leading to the formation of cyclic perfluorinated imidoyl fluorides (Fig. 9.23). In contrast to AICI3 reactions, this process is catalytic. The outcome of the reaction depends on the structure of amine. For example, the reaction of A-alkyl piperidines or morpholines leads to the elimination of perfluoroalkane... 

The mechanism of the reductive defluorination of perfluorinated N F amines may involve a relatively low laying LUMO of N—F bond. The injection of an electron on this orbital leads to the formation of radical anion D, which can further lose fluoride anion, forming radical E. The reduction of E to azaanion F followed by second fluoride anion elimination may lead to the corresponding cyclic imidoyl fluoride as a result of reductive defluorination (Scheme 9.1). 

Several methods are available for the preparation of perfluorinated cyclic imidoyl fluorides. For example, reductive defluorination of cyclic A-fluoro compounds... 

Fig. 9.26) by ferrocene or PPh3 was used for the preparation of imidoyl fluorides 81,83, and 91. The cleavage of perfluorinated tertiary amines under the action of SbFs (see Fig. 9.23) is another convenient method for the synthesis of cyclic imines, such as 81-83. 

It is noteworthy, that in contrast to noncyclic perfluorinated imidoyl fluorides RfN = CFR f, cyclic imines 124 and 81 undergo the dimerization upon treatment with fluoride anion (Fig. 9.40). 

FIGURE 9.40 Dimerization of cyclic perfluorinated imidoyl fluorides. 

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