Reactions of tetrafluoroethene oligomers. Part 15. Reactions of perfluoro-3,4-dimethylhex-3-en-2-one; a highly reactive α,β-unsaturated ketone

Abstract

Perfluoro-3,4-dimethylhex-3-en-2-one 1 has been shown to react with nucleophiles both at the double bond and at the carbonyl group depending on the type of nucleophilic centre and also on the steric requirements of the attacking reagent. In many cases the first formed product undergoes further reactions either with the original nucleophile or by intramolecular processes. Thus, reaction of 1 with primary amines afforded azetines 3 and 4 in the cases of ethylamine and cyclohexylamine and a mixture of the azetine 5 and a ketenimine 6 from tert-butylamine. The ketenimine 6 either on standing at room temperature or more quickly on heating cyclised quantitatively to the azetine 5 found in the original reaction. Reaction of the enone with secondary amines took a different course; the products from reaction with diethylamine were an unsaturated amide 8 and N,N-diethyltrifluoroethanamide 7, and piperidine afforded not only an unsaturated amide 11 and the corresponding ethanamide 10 but also a piperidyl ketone 12. This intermediate is postulated to be the archetype of the first formed product for all the reactions reported. Reaction with dimethylamine yielded a different product, a disubstituted unsaturated ketone 9, but none of the corresponding amides as seen with other secondary amines. The reaction with hydrazine afforded a substituted pyrazolidine 2. When the enone was treated either with triethylamine or with fluoride ion cyclisation to yield a perfluorotetramethyldihydrofuran 13 occurred. Reaction with sodium methoxide or sodium phenoxide yielded the corresponding bis-ethers 14, 15, whilst reaction with sodium hypochlorite gave a hydrogen containing epoxide 16, postulated to arise from a haloform type reaction from the first formed epoxide. Finally, reaction with methylmagnesium iodide gave a dimethyl substituted derivative 17. A mechanistic rationale based on a series of addition–elimination reactions with or without subsequent cyclisation is proposed to explain these reactions.