The slow reaction of adamantane with nitronium tetrafluoroborate at room temperature in purified, nitrilefree nitromethane or in nitroethane gives 1-nitroadamantane in 66% and 74% isolated yield, respectively. Similar reaction of diamantane gives 62% 1 -and 5% 4-nitrodiamantane. Initial reaction upon aqueous workup gives 1 -adamantanol with 1 -fluoroadamantane, 3-fluoro-1 -adamantanol, and adamantanone as byproducts. Upon prolonged reaction 1 -nitroadamantane is formed in good yield. The experimental data are in accord with intermediate formation of the 1-adamantyl cation (by hydride abstraction or cleavage of initially formed 1-nitroadamantane) followed by reaction with HNO2 or NO2-formed in the reaction, giving 1-adamantyl nitrite, which then undergoes cleavage-rearrangement to give 1-nitroadamantane. A small kinetic hydrogen isotope effect of & /& = 1.2-1.3 is indicative of a nonlinear highly unsymmetrical transition state in the rate-determining step of the reaction.
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