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

Perfluoro-3,4-dimethylhex-3-en-2-one 1 has been shown to react with nucleop hiles both at the double bond and at the carbonyl group depending on the ty pe of nucleophilic centre and also on the steric requirements of the attack ing reagent. In many cases the first formed product undergoes further react ions either with the original nucleophile or by intramolecular processes. T hus, reaction of 1 with primary amines afforded azetines 3 and 4 in the cas es of ethylamine and cyclohexylamine and a mixture of the azetine 5 and a k etenimine 6 from tert-butylamine. The ketenimine 6 either on standing at ro om temperature or more quickly on heating cyclised quantitatively to the az etine 5 found in the original reaction. Reaction of the enone with secondar y amines took a different course; the products from reaction with diethylam ine were an unsaturated amide 8 and N,N-diethyltrifluoroethanamide 7, and p iperidine afforded not only an unsaturated amide 11 and the corresponding e thanamide 10 but also a piperidyl ketone 12. This intermediate is postulate d to be the archetype of the first formed product for all the reactions rep orted. Reaction with dimethylamine yielded a different product, a disubstit uted unsaturated ketone 9, but none of the corresponding amides as seen wit h other secondary amines. The reaction with hydrazine afforded a substitute d pyrazolidine 2. When the enone was treated either with triethylamine or w ith fluoride ion cyclisation to yield a perfluorotetramethyldihydrofuran 13 occurred. Reaction with sodium methoxide or sodium phenoxide yielded the c orresponding bis-ethers 14, 15, whilst reaction with sodium hypochlorite ga ve a hydrogen containing epoxide 16, postulated to arise from a haloform ty pe reaction from the first formed epoxide. Finally, reaction with methylmag nesium iodide gave a dimethyl substituted derivative 17. A mechanistic rati onale based on a series of addition-elimination reactions with or without s ubsequent cyclisation is proposed to explain these reactions.