New methods for selective fluorination
New methods have been developed for the selective introduction of fluorine into benzenoid aromatic compounds involving the cleavage of aryl-metal bonds by various ‘electrophilic’ fluorinating agents. Cleavage of aryl-metal bonds has been achieved using trifluoromethyl hypofluorite (CF(_3)OF), caesium fluoroxysulphate (CsSO(_4)F) and elemental fluorine and, by the nature of the process, is regiospecific. Attempts have been made to extend this method to the introduction of fluorine into imidazole bases with some success. This approach has involved the synthesis of trialkylstannyl derivatives of several benzene derivatives and trimethylstannyl derivatives of 1,2-dimethylimidazole and N-methylimidazole. Prior to our attempts at selective introduction of fluorine into the sugar ring of 5-amino-l-(β-D-ribofuranosyl) imidazole-4-carboxamide (AICAR) a series of protection and selective deprotection reactions on the nucleoside were carried out and trifluoromethane sulphonate ester derivatives of the protected nucleoside were synthesized. Fluoride ion displacement of the trifluoromethane sulphonate group to give a fluorosugar has been attempted.