Highly fluorinated heterocycles. Part XIII. Fluorination of 1-methylpyrrole and some reactions of derived compounds

Abstract

1-Methylpyrrole has been fluorinated over potassium tetrafluorocobaltate(III) and cobalt(III) fluoride to yield octafluoro-1-methylpyrrolidine (I), octafluoro-1-fluoromethylpyrrolidine (II), 3H-heptafluoro-1-methylpyrrolidine (III), 3H,4H-hexafluoro-1-methylpyrrolidine (IV), 3H-heptafluoro-1-fluoromethylpyrrolidine (V), and 3H,4H-hexafluoro-1-fluoromethylpyrrolidine (VI). The proportions obtained depend on the temperature and the fluorinating agent. Refluorination of (I) over CoF₃ yielded perfluoro-1-methylpyrrolidine (VII), 1-difluoromethyloctafluoropyrrolidine (VIII), and (II). Dehydrofluorination of (III) yielded hexafluoro-1-methyl-Δ³-pyrroline (IX), which reacted with cyclopentadiene to yield an endo-exo mixture of 2,6-difluoro-4-methyl-4-azatricyclo[5.2.1.0^2,6]dec-8-ene-3,5-dione (X) and in an attempted reaction with perfluorocyclohexa-1,3-diene gave 3,4-difluoro-1-methyl-Δ³-pyrroline-2,5-dione (XI). Reactions of (I) and (IV) with concentrated sulphuric acid gave the corresponding diones by hydrolysis of the α-CF₂ groups. Treatment of (VI) with aluminium chloride in methylene chloride gave 1-chloromethyl-3H,4H-hexafluoropyrrolidine and reaction of (II) with sodium ethoxide gave 1-ethoxymethyloctafluoropyrrolidine.