Andrew A. Lindley

Relative reactivities of isomeric perfluoroalkenes

Abstract We have already reported on some reactions of perfluoro-3,4-dimethyl-3-hexene (1) with O-nucleophiles and the products are derived from attack on both (1) and its isomer (2), which are apparently in equilibrium in solution and in the presence of fluoride ion [1].

Reactions involving fluoride ion. Part 22. Dimerisation of perfluoro-2,3-dimethylbutadiene and related reactions

Reaction of perfluoro-2,3-dimethylbutadiene (1) with caesium fluoride gives two dimers, the ratios being very temperature-dependent. The structures of the dimers and mechanism of formation are proposed. A corresponding reaction but in the presence of bromine provides a good route to perfluoro-2,3-dimethylbut-2-ene. Further fluorination of the dimers of (1) occurs over cobalt trifluoride and the product may be rationalised on the basis of an intermediate radical cation.

Reactions involving fluoride ion. Part 20. Competition between isomerization and nucleophilic attack on a perfluoroalkene

Reaction of perfluoro-3,4-dimethylhex-3-ene (1) with amine gives products which arise from nucleophilic attack directly on (1) but also products derived from attack on isomers of (1), i.e. perfluoro-3,4-dimethylhex-2-ene (2) and perfluoro-3-methylene-4-methylhexane (3), promoted by fluoride ion which is generated during reaction. The products obtained depend critically on the steric requirements of the attacking amine, e.g. Et2NH gives products arising exclusively from attack on isomer (3).

Reactions involving fluoride ion. Part 16. Nucleophilic attack on a perfluorotetra-alkylethylene and a synthesis of perfluorotetramethylfuran

Reaction of perfluoro-3,4-dimethylhex-3-ene (1) with oxygen nucleophiles gives products arising from attack on (1) as well as products arising from attack on the isomer, perfluoro-3,4-dimethylhex-2-ene (4). A novel cyclisation and defluorination is described for the reaction of (1) with MeOH and Et3N, giving perfluorotetramethylfuran. Reactions of (1) with difunctional nucleophiles give cyclic products and oxidation of (1) with KMnO4 in acetone yields a diol. An unusual intramolecular nucleophilic displacement of fluoride from a perfluoroalkyl group is reported.

Perfluorinated derivatives of furan via novel cyclisation reactions of perfluoro-olefins

Perfluorotetramethylfuran (7) is obtained in a cyclisation reaction of the perfluoro-olefin (1) using triethylamine and methanol, the process involving a novel defluorination; a cyclisation is described which clearly involves the rare displacement of fluoride ion from a saturated position in a perfluoroalkyl group.

Reactions involving fluoride ion. Part 29. Reactions of perfluoro-2,3-dimethylbuta-1,3-diene

Reactions of perfluoro-2,3-dimethylbutadiene (1) with methanol, phenol, and sodium methoxide yield products arising from substitution; with methanol a 1,2-addition product is also observed. Reactions of (1) with enolate anions derived from ethyl acetoacetate and acetylacetone yield pyran derivatives, and an oxepine. The diene (1) undergoes free radical addition with methanol, and cycloaddition with diazomethane. Except under strongly nucleophilic conditions, reactions occur at only one of the double bonds of the diene (1) and, on the basis of this and u.v. spectral data, the diene (1) is considered to be conjugated, contrary to other conclusions.

Reactions involving fluoride ion. Part 27. Reactions of perfluoro-3,4-dimethylhex-3-ene with carbon nucleophiles

Reaction of methyl- and ethyl-lithium with perfluoro-3,4-dimethylhex-3-ene (1) gives products arising from nucleophilic attack with allylic displacement of fluorine from both CF3 and CF2 positions. Phenylmagnesium bromide gives biphenyl via a process which appears to involve one-electron transfer to (1). Enolate anions undergo substitution in (1) with concomitant cyclisation to give fluorinated pyran derivatives.

Reactions involving fluoride ion. Part 23. Thermolytic defluorination of perfluoroalkenes in the synthesis of fluorinated dienes and cyclobutenes

Passage of perfluoro-3,4-dimethylhex-3-ene over iron or platinum at elevated temperatures leads to defluorination and fragmentation, giving fluorinated dienes, e.g. perfluoro-2,3-dimethylbutadiene (over Pt) and perfluoro-3,4-dimethylhexa-2,4-diene (over Fe), together with other products. Similar reactions occur with other fluorinated alkenes and the variation between fragmentation and defluorination is rationalised on the basis of the metal used, etc. The fluoride induced reaction between perfluoropropene and perfluorobut-2-ene gives perfluoro-2,3-dimethylpent-2-ene.

Syntheses and reactions of some fluorinated dienes, cyclobutenes and furans

Abstract There are many reports 1 of the pyrolysis of fluorinated organic compounds, including the defluorination of cyclic fluorocarbons over iron to give aromatic compounds. Extending this technique we have investigated the flow pyrolysis of some readily accessible unsaturated fluorocarbons, such as I, II, and III, and found these to be synthetically useful routes to fluorinated dienes, cyclobutenes, and furans. Pyrolyses were carried out using a nitrogen flow over platinum, iron or caesium fluoride heated at 430–700°. The various products can all be rationalized in terms of intermediate allylic radicals, and the solid substrate influences which allylic radicals are formed. We are also investigating the chemistry of those now accessible compounds, such as IV, V, and VI, and some of the preliminary results are described. For example the fluoride ion induced dimerisation of IV gave two major products VII and VIII via a particular interesting mechanism.

Synthesis of fluorinated dienes and cyclobutenes

Pyrolysis of some fluorinated alkenes over platinum or iron, gives good yields of dienes and fluorinated furan derivatives.