New methodology for the synthesis of fluorinated aromatics

Abstract

This thesis is concerned with new methodology for the introduction of fluorine atoms, and trifluoromethyl groups into aromatic systems and the following approaches have been adopted: (i) The possibility of selective cleavage of the aryl-silicon bond of aryltrimethylsilanes by elemental fluorine to give the corresponding fluorinated aromatic compound was explored, and competing silicon and hydrogen substitution was observed. The affect of temperature and solvent upon this process was investigated. (ii) Attempts to modify the reactivity of dilute elemental fluorine (10% fluorine/nitrogen) towards aromatic systems at low reaction temperatures were made by the addition of pyridine and substituted pyridines. The effectiveness of this methodology was limited by the reactivity of the pyridine systems towards elemental fluorine.(Hi) The potential electrophilic fluorinating agents N-fluoro-2,3- bis(2H hexafluoropropyl) pyrrolidine and N-fluorosuccinimide have been synthesised by the direct fluorination of the corresponding N-trimethyl- silyl compounds.(iv) The cycloaddition reactions of hexafluorobut-2-yne with furan and 2-substituted furans have been employed to synthesise a series of benzenoid and heteroaromatic compounds containing two trifluoromethyl groups in high yield.(v) The synthesis of trifluoromethylpyridines by the cycloaddition of 3,3,3-trifluoropropene with oxazoles has also been investigated.