Chemistry of novel fluorinated alkenes

Abstract

The work described in this thesis is concerned with three areas relating to nueleophilic reactions of novel-polyfluorinated alkenes-. a) Very highly strained fluorinated epoxides have been synthesised from bicyclic internal alkenes using Ca(OCl)(_2). These molecules display an almost unprecedented therira.1 and chemical stability. b) Aromatic bifunctional nucleophiles have been reacted with a variety of perfluorinated alkenes and cycloalkenes to give high yielding heterocyclic compounds. These are discussed within a mechanistic framework which my rationalise the product structures. c) Additions of fluoride ion from CsF and TAS-F to fluorinated alkenes in a suitable solvent are shown to yield long-lived fluorocarbanions. N.m.r. observations indicate the systems are whollyin the form of the respective anions and are essentially static on then.m.r. timescale. Competition experiments for a deficiency of CsF are available and can render useful infornmtion on F(^-) affinities. The (^13) and (^19)F n.m.r. spectra of the anions display unusual chemical shift and coupling constant phenomena. The n.m.r. spectra are unchanged over a wide temperature range but at a distinct threshold temperature line broadening occurs. This is indicative of the onset of F exchange on the n.m.r. timescale, is specific to the M(^+)C(^-) system and. therefore, is a guide to the carbanion stabilities. High yielding trapping reactions with simple electrophiles are described but, in some cases F(^-) donation from the carbanion is preferred. This competing reaction is found for particular electrophiles and above the threshold exchange temperature as determined by n.m.r.