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40.1.1.4.1.5.5 Variation 5: Hofmann–Löffler–Freytag Rearrangement

DOI: 10.1055/sos-SD-040-00241

Purchase, R.; Sainsbury, M.Science of Synthesis, (200940392.

Other rearrangements included within the same general classification may not involve aromatic amines and, in an example of the HofmannLöfflerFreytag rearrangement N-chloro-N-methylbutylamine (136, R1=Me; R2=H; n=1) when heated with sulfuric acid rearranges to 4-chloro-N-methylbutylamine (137, R1=Me; R2=H; n=1); however, this product then undergoes cyclodehydrochlorination to afford N-methylpyrrolidine (138, R1=Me; R2=H; n=1) (Scheme 40).[‌152‌‌154‌] Other N-halogenated primary alkylamines (136, R1=R2=alkyl) undergo similar rearrangements and, if the alkyl chain is long enough, eventually give the corresponding pyrrolidines or piperidines. The mechanism of these reactions may involve radicals, the key step being an internal hydrogen atom abstraction.[‌155‌]

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