Novel fluorinated cyclic dienes and their chemistry

Abstract

The work described in this thesis is concerned with three areas which are synthesis, nucleophilic reactions, and cycloaddition reactions of novel fluorinated cyclic dienes.1 Sodium amalgam has been investigated as an electromimetic medium to reduce various fluorinated alkenes. It has been found that this can act as a single electron transfer reagent and defluorinate a series of cyclic alkenes to yield their corresponding dienes in good yield and conversion. Tetrakis(dimethylamino) ethylene (TDAE) has also been found to be a suitable reagent. The chemistry of these dienes, in particular (A) and (B), is then discussed. A number of reactions with nucleophiles has been studied employing novel dienes (A) and (B). Basically vinylic fluorine has been replaced to yield a range of mono- or di-substituted products. Reactions of fluoride ion sources with (A) and (B) have been studied. Addition of fluoride ion sources to these dienes in a solvent forms their carbanionic intermediates. That of (A) is very unstable and reacts further with (A) to give its oligomers. However it can lead to the observable carbanion by reaction of the precursor of (A) with TDAE. On the other hand, the carbanionic ivintermediate of (B) is very stable, being observed by (^19)F-NMR. These carbanions have been characterised by various methods. 3 Numerous cycloaddition reactions have been attempted. Dienes (A) and(B) did not undergo Diels-Alder reaction as diene because of their extremely electron-deficient double bonds and their specific conformations. Diene (A) has reacted as a dienophile with hydrocarbon dienes to yield the corresponding cycloadducts. Addition of an excess of diazomethane to dienes (A) and (B) has given rise to 1,3-dipole cycloaddition reactions forming their corresponding diadducts, which have been identified as Δ(^2)-dihydropyrazole derivatives.