Stable carbocations. Part X. Generation, observation, and reactions of ferrocenyl-stabilised cyclopropylalkylium and related ions

Abstract

In trifluoroacetic acid solutions, 1-ferrocenyl-1-cyclopropylalkylium ions are stable and show no tendency towards rearrangement. When these solutions are quenched with aqueous sodium carbonate, mixtures of products are formed including those of cyclopropyl ring opening. In the same acid solvent, 4-ferrocenylbut-3-en-1-ols undergo protonation giving 1-ferrocenyl-4-hydroxyalkylium ions which are slowly converted into their O-trifluoroacetyl derivatives. On deprotonation, the former ions give 2-ferrocenyltetrahydrofurans; the latter afford mainly the trifluoroacetates of the starting ferrocenylbutenols. Hydrolysis of these esters in acetate-buffered aqueous acetone gives alcohols without rearrangement.